United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
rreiimmary
Environmental
Assessment of
F.PA GOO 7 /8 204
Octobei 19/8
on
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide range of energy-related environ-
mental issues.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/7-78-204
October 1978
PRELIMINARY ENVIRONMENTAL ASSESSMENT
OF BIOMASS CONVERSION
TO SYNTHETIC FUELS
by
S. T. DiNovo, W. E. Ballantyne, L. M. Curran,
W. C. Baytos, K. M. Duke, B. W. Cornaby,
M. C. Matthews, R. A. Ewing, and B. W. Vlgon
Battelle Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
Contract No, 68-02-1323
Project Officer
Thomas J. Powers
Energy Systems Environmental Control Division
Industrial Environmental Research Laboratory
Cincinnati, Ohio 45268
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Industrial Environmental Research
Laboratory, U. S. Environmental Protection Agency, and approved for publica-
tion. Approval does not signify that the contents necessarily reflect the
views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
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FOREWORD
When energy and material resources are extracted, processed, converted,
and used, the related pollutional impacts on our environment and even on our
health often require that new and increasingly more efficient pollution con-
trol methods be used. The Industrial Environmental Research Laboratory -
Cincinnati (lERL-Ci) assists in developing and demonstrating new and improved
methodologies that will meet these needs both efficiently and economically.
A preliminary assessment of biomass conversion to synthetic fuels has
been made. This study was conducted to provide a preliminary evaluation of
biomass production and conversion technologies, and their associated environ-
mental consequences. The magnitude of the U.S. biomass resources is reviewed
relative to environmental aspects of this potential source of energy. The
research users will find the data base of this report an adequate starting
point for further investigations into biomass utilization. It is indicated
that biomass has the potential for making significant contributions to energy
needs on a regionalized basis. Further information on biomass energy
resources can be obtained from the IERL-Cincinnati Fuels Technology Branch.
David G. Stephan
Director
Industrial Environmental Research Laboratory
Cincinnati
111
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ABSTRACT
This study was conducted to provide a preliminary evaluation of biomass
production and conversion technologies, and their associated environmental
consequences. Biomass, as used in this study, refers to materials which are
either directly or indirectly the result of plant cultivation. Since a sub-
stantial portion of the organic fraction of urban and industrial wastes are
the "indirect" result of plant growth (that is, plant materials, especially
fibers which have already been utilized in some fashion), they are considered
biomass as well.
Five categories of biomass production were considered in detail;
agricultural and forestry wastes, aquaculture (aquatic plant species which
may be cultivated for energy production), silviculture (intense cultivation
of tree species), energy crops (special crops adaptable to intense cultiva-
tion for the production of energy), and urban and industrial wastes. It was
found that agricultural and forestry wastes, and urban and industrial wastes
are the two categories with the nearest term potential for significant con-
tribution to energy production in localized situations. The remaining cate-
gories represent potentially high yield biomass sources, in which varying
degrees of technological innovation will be required for full development.
The conversion processes which were considered were classified as
thermochemical and biochemical technology. Primary thermochemical processes
which were reviewed in detail were direct conversion (including combustion),
pyrolysis, and acid hydrolysis. Less developed technologies, in particular,
hydrogenation and naval stores processes, were also briefly analyzed.
Primary biochemical processes considered in detail included anaerobic diges-
tion and enzymatic hydrolysis. Secondary processes (that is, processes
which convert products from primary processes to useful fuels), were also
evaluated and included methanol and other Fisher-Tropsch-type products from
synthesis gas, ethanol production from sugar solutions, and several minor
process systems.
Six regionalized scenarios (brief studies of commercial scale plants
processing appropriate regionalized feedstock) were prepared as part of this
work. A seventh scenario, directed at a mobile facility was also prepared.
Most processes under development use heterogeneous solid waste as a
feedstock. The emission and effluents from processes when operated on solid
waste are believed to pose more severe control requirements than operating
the same processes on other biomass feedstock. The environmental and socio-
economic effects of locating large conversion plants in rural environments
need to be studied.
iv
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This report was submitted in fulfillment of Contract No. EPA 68-02-1323
by Battelle Columbus Laboratories under the sponsorship of the U.S. Environ-
mental Protection Agency. This report covers the period February 12, 1976 to
September 21, 1976.
v
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CONTENTS
Foreword iii
Abstract ..... iv
Figures viii
Tables xii
1. Technical Summary 1
Introduction i
Biomass Sources ..... i
Conversion Processes . 4
Environmental Assessment 6
Energy Potential of Biomass g
References to Section 1 13
2. Introduction 15
3. Conclusions 17
General 17
Biomass Sources 17
Conversion Processes 18
Environmental Assessment 19
4. Recommendations ..... 20
Environmental Recommendations 20
Recommendations for Production/Conversion
Technology Development 21
5. Biomass Sources 22
Overview 22
Potential Biomass Sources 22
Agricultural and Forestry Residues ... 22
Aquacultural Production 45
Energy Crops 53
Silvicultural Production 56
Industrial and Urban Wastes 67
6. Conversion Processes . 74
Preprocessing of the Selected Biomass Feedstocks .... 74
Primary Thermochemical Conversion Processes 94
Primary Biochemical Conversion Process .. 169
Secondary Conversion Processes 185
Product Storage and Transportation 199
Development of Regional Scenarios of Biomass
Conversion Plots 202
7. Environmental Assessment ... 253
Objectives of Preliminary Environmental Assessment . . . 253
Impact Associated with Growth and Procurement of
Feedstock/Source Materials 253
vii
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CONTENTS - (Continued)
Impacts Associated with Biomass Conversion to
Fuel/Energy ...................... 287
Environmental Review of Scenarios ............
8. Current Government Agency Effort in the Biomass
Production/Conversion Field .................
References .... .......................... 327
vlii
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FIGURES
Number Page
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Comparison of production and biomass estimates of Spartina
alterniflora and Spartina patens along a south to north
An overview of urban waste stream in the United States
for 1973
The application of forces in size-reduction operations ....
Available energy of refuse as a function of moisture
A C-E steam generating unit with spreader stoker for
48
69
75
76
78
80
81
82
82
84
86
90
96
99
99
100
102
104
106
IX
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FIGURES - (Continued)
Number
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
CFU-400 pilot plant
Schematic of Battelle-Pacific Northwest gasification process .
Carborundum Environmental Systems, Incorporated - Torrax
Schematic of West Virginia University pyrolysis process . . .
Flow chart for forest products laboratory process for
Conceptual acid hydrolysis plant based on municipal
Simplified flowsheet for the Albany pilot plant
Reactions occurring during anaerobic digestion
Block diagram of the biogas process
Mass balance summary for a 1000 ton/day biogas plant
Material balance for waste digestion process .
Page
107
111
113
124
129
131
133
137
139
140
146
148
150
156
159
161
165
170
172
174
176
177
178
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FIGURES - (Continued)
Number Page
43 A conceptualized lignin structure 182
44 Conversion of cellulose to glucose 183
45 Flowsheet of enzymatic hydrolysis ..... 184
46 Typical high pressure methanol process 186
47 Vulcan methyl fuel process 187
48 Low pressure methanol process (based on ICI process) 189
49 Product distribution from conversion of methanol 194
50 Gasoline fraction after alkylation 194
51 The Anflow reactor 197
52 Pictorial presentation of regions 205
53 Process flow schematic of wood waste pyrolysis system .... 212
54 Low pressure methanol process based on ICI process 213
55 Process flow schematic of hydrolysis - fermentation process . 223
56 Flowsheet of two-stage anaerobic digestion process 228
57 Process flow schematic of gas turboelectric generating
system 237
58 Flowsheet of single-stage anaerobic digestion plant 239
59 Process flow schematic for municipal solid waste to
stream conversion process 246
60 Schematic of mobile agricultural residue incinerator system . 250
61 Effects of clearcutting on hydrology and materials cycling . . 263
62 Relationship between soil erodibility and physical-
chemical composition 267
63 Treatment continuum and expected range of treatment using
anaerobic digestion for gas production and recycling residue . 273
64 Global production of organic matter .... 275
XI
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FIGURES - (Continued)
Number
65 Occurrence of kelps in quantities sufficient for
66
67
68
69
70
Distribution of organic matter produced by marine seaweeds
Seasonal variations in temperature in salt marshes near
Diurnal variations in pH of the surface of the sediments
Mass balance summary for a 1600 ton/day biogas plant
Diagram structure for DOE Fuels from Biomass Branch
276
276
281
281
298
315
Xll
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TABLES
Number Page
1 Energy Supply Estimate for Biomass (1973) 11
2 Estimate of Annual Energy Usage for the City of
Columbus, Ohio 12
3 Unused Wood Waste Available in the United States, 1970 .... 25
4 Uses of Wood and Bark Residues Produced by Primary Wood
Processing Plants in the United States, 1970 27
5 Chemical Analyses of Wood and Bark of Various Tree
Species Types 28
6 Cellulose Contents of Various Wood Species 29
7 Densities and Heating Values of Wood and Bark of
Various Species 30
8 Energy Consumption for Collecting, Field Processing, and
Transporting Logging Residues to a 50-MWe Electric Plant
Requiring 370,000 Metric Tons (410,000 Tons) Per Year .... 33
9 Wastes Generated by Major Farm Animals in the United
States, 1971 36
10 Growth in Numbers of Large Beef Feedlots in the U.S.
from 1962 to 1970 37
11 Chemical Composition of Fresh Manure from Beef Cattle .... 38
12 Yields, Production, and Distributions of Residues from
Selected Crop Species 42
13 Chemical Parameters of Selected Crop Residues 43
14 Chemical Composition of Harvested and Field-Dried
Bagasse and Rice Straw 44
15 Aquatic Plant Productivity in Major World Habitats 46
16 Biomass Production for Four Species of Marsh Plants 47
xiii
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TABLES - (Continued)
Number —*-
17 Elemental Compositions of Selected Marsh Plants 4-7
18 Chemical Composition of Water Hyacinth
19 Composition of the Giant California Kelp 52
20 Geographic Locations and Areas of Sugarcane Cultivation
in the United States • 5^
21 Composition of Sugarcane
22 Geographic Locations and Areas of Sugar Beet Cultivation
in the United States ..................... 56
23 Tree Species Considered for Silvicultural Production ..... 58
24 Above Ground Biomass Yields of Selected Tree Species ..... 60
25 Energy Consumed in an Intensively Managed Tree Crop
Energy Plantation ...................... 66
26 Average Percent Composition of Municipal Solid Waste ..... 68
27 Categories of Organic Waste with Their Patterns of Generation
and Collection in the United States for 1971 ......... 70
28 Net Solid Waste (Wet Weight) by Major Categories in the
United States for 1971 and 1973 ............... 71
29 Projections for Solid Waste Generation, Recovery, and
Disposal in the United States ................ 73
30 Current Size Reduction Equipment and Potential Applications
to Municipal Solid Waste ........ . .......... 77
31 Comparison of Wet and Dry Shredding Methods in Relation
to Preprocessing of Waste Biomass Feedstock ......... 89
32 Milling Costs ........................ 92
33 Composition and Cellulase Digestion of Various Woods
Before and After S02 Treatment ................ 93
34 Chemical Composition of Harvested and Field-Dried
Bagasse ........................... 95
35 Chemical Analyses of Wood and Bark of Various Tree Species
Types ............................ 97
xiv
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TABLES - (Continued)
Number page
36 Overall Boiler Efficiency as a Function of Wood
Moisture Content .......................
37 Wood Firing Methods for Different Size Categories for
Boilers Sold Between 1965 and 1975 .............. 101
38 Summary of Selected Direct-Fired Refuse to Energy
Combustion Processes ..................... 108
39 Summary of Major Supplementary Fired Refuse to Energy
Conversion Processes ............. . ....... 109
40 Reactor Type Characteristics ................. 116
41 Influence of Temperature on Pyrolysis Products ........ 117
42 Composition of Pyrolysis Gas ......... . ....... 117
43 Products from Pyrolysis of Newspaper ............. 119
44 Pyrolysis of Dried Refuse at 900 C .............. 120
45 Pyrolysis and Partial Oxidation Classifications ....... 121
46 Typical Products of Pyrolysis ................ 125
47 Average Yields of Pyrolysis Products from Douglas Fir Bark,
Rice Hulls, Grass Straw, and Cow Manure ........... 126
48 Typical Properties of No. 6 Fuel Oil and Pyrolytic Oil .... 127
49 Purox System Product Gas Analysis .............. 134
50 Purox System Residue Analysis ................ 135
51 Analysis of Carbon Char Residue ............... 142
52 Quality of Ferrous Metal Recovered from Pyrolysis Residue . . 144
53 Analysis of Glassy Aggregate Recovered from
Pyrolysis Residue ...................... 144
54 Bovine Waste Pyrolyzed at 900 C .......... ..... 149
55 Typical Yields of Products from the Pyrolysis of
Cattle Manure ........................ 151
xv
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Number
TABLES - (Continued)
Page
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
Typical Composition of Product Gas from the Pyrolysis
Stack Gas Analyses, PPM by Volume Corrected to 12 Percent
C02
Typical Hydrolysis Yields • *
Typical Experimental Results of Hydrogasification of
Typical Experimental Results of Hydrogasification of
Solid Waste on a Free-Fail Reactor
Typical Distillation Yields from 1.8 Metric Tons
(2 Tons) of Hardwood
Products Obtained from Kellogg and Arge Units of
Material Balance for Acetone-Butanol Fermentation ......
States Contained in Various Regions Defined for Study ....
Summary of Waste to Energy Processes for the Six Scenarios . .
Summary of Forest Residue to Methyl Fuel Process .
Material Balance for Wood Waste Pyrolysis Process
Chemical Analysis of Bark and Bark Ash
Spectrographic Analysis of Hogged Fuel Ash
153
153
157
157
162
163
167
168
182
190
192
192
196
198
204
208
210
214
217
218
XVI
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TABLES - (Continued)
Number Page
77 Summary of Bagasse and Forest Residue to Ethanol Process . . . 221
78 Material Balance for Hydrolysis - Fermentation Process .... 224
79 Summary of Kelp and Urban Waste to SNG Process 229
80 Material Balance of Two-Stage Anaerobic Digestion 231
81 Summary of Conversion of Wood and Corn Residue to
Electricity Process 234
82 Material Balance for Gas Turboelectric Generation Process . . 238
83 Summary of Waste Feedstocks for Anaerobic Digestion Plant . . 240
84 Material Balance for Single-Stage Anaerobic Digestion Plant . 242
85 Summary of Municipal Solid Waste to Steam Process 244
86 Material Balance for Conversion of Urban Refuse to Heat . . . 247
87 Fuel Characteristic of Corn Stover 251
88 Heat Balance on Corn Residue Incinerator - Dryer System . . . 252
89 Estimate of Material Removal Due to Clear Cutting and
Residue Collection Compared to Instantaneous Pool Size .... 256
90 Correlation Between Forest Soil Parameters and
Infiltration Rate 257
91 Cover Factors for Woodland Used in the Universal
Soil Loss Equation 259
92 Changes in Acreage of Slash Created and Slash Treatment on
Forests of the Pacific Northwest Region 261
93 Amounts of Major Nutrients Removed by Corn Residue
Collection for Use as a Fuel Source 265
94 Range of Observed Values in Concentration and Area
Yield for Various Land Uses 269
95 Characteristics of Seepage from Stacked Dairy Cattle
Manure and Bedding 270
96 Airborne Pollutant Emission Factors - Transport/Harvesting . . 278
xv 11
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Number
TABLES - (Continued)
Page
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
Characteristics and Distribution of Typical Municipal
Effect of Compost and Nitrogen Addition on Physical and
Chemical Characteristics of Soil at Muscle Shoals
Particulate and Gaseous Emission Factors for Direct
Combustion of Biomass Compared with Coal Combustion
Concentration of Some Trace Materials in Incinerator Fly Ash .
Elemental Content of 42 Day-Old Compost at Johnson City . . .
Stimulatory and Inhibitory Concentrations of Metals and
Operating Parameters for Mesophilic Anaerobic Digestor
Physical and Chemical Characteristics of Refuse and
Effluent Quality and Solids Reduction at the Optimum Refuse
Digestion Temperatures and a Detention Time and Loading
Rate of 12 Days and 0.14 Lb vs/CF-Day, Respectively
Scenario 1: Environmental Summary, Pyrolysis of Wood ....
Scenario 2: Environmental Summary for Acid Hydrolysis
of Bagasse/Forest Residues
Scenario 3: Environmental Summary for Anaerobic
Digestion of Kelp/MSW
285
285
286
288
289
289
292
293
295
295
300
300
301
301
304
305
306
114 Scenario 4: Environmental Summary for Turboelectric Peaking
Electrical Generator with Fluidized Bed Using Energy
Crop/Corn Residue 307
xviii
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TABLES - (Continued)
Number
115 Scenario 5: Environmental Summary for Anaerobic Digestion
of Animal Waste/Wheat Straw 308
116 Scenario 6: Environmental Summary for Direct Conversion to
Steam in a Waterwall Incinerator 309
117 Agricultural Residue Projects 314
118 Terrestrial Biomass Production and Conversion Projects .... 316
119 Marine Biomass Production and Conversion Projects 316
120 Research/Development Projects 317
121 Summary of Projects Underway by DOE's Urban Waste
Technology Branch 321
xix
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SECTION 1
TECHNICAL SUMMARY
INTRODUCTION
The diverse nature of this study, requiring data from several
different disciplines, suggests the need for a technology-directed summary
which is more definitive than that which is usually provided in an executive
summary. This section is directed toward that need.
Sections 5, 6, and 7 are summarized in discrete sections. These are
followed by a synthesis of this data to produce an evaluation of the energy
potential of biomass and conversion technology. This estimate is supple-
mented by discussions of other relevant factors in an attempt to place
biomass conversion in its proper perspective.
BIOMASS SOURCES
Approximately 50 million metric tons (55 million tons) of forest
residue, on a moisture- and ash-free basis, were produced in 1971. This
residue was generated predominantly in the Pacific and the southern regions.
There are also other high density pockets throughout the United States.
Typical dry-basis heating values for those residues range from 4450-5200
kcal/kg (8000-9400 Btu/lb). Primary technological problems to be overcome
in utilizing these wastes are related to development of efficient systems
and equipment to collect residue materials. Once efficient systems have
been developed, it is likely that the value placed on these materials by
building product industries will represent strong competition with its
use for fuel.
Approximately 180 million metric tons (200 million tons) of animal
manure were produced in 1971. Beef manure production was more than an order
of magnitude larger than the next largest source (swine). Cattle manure
is produced in two distinguishably different agricultural systems: feedlot
and dairy operation. Cattle concentrations on feedlots are high, with the
tendency towards the largest sizes (e.g., greater than 8000 head) becoming
more pronounced. Fresh manure has a moisture content of approximately" 85
percent and a dry heating value of 3450 kcal/kg (6200 Btu/lb). Most feedlot
operations are in the West and Southwest. Dairy operations are concentrated
in the upper Midwest. Manure from feedlots tends to be drier than that from
dairy operations.
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While the logistics of collection does not appear to be a technological
problem in most situations (50-80 percent of all farm animals are confined),
effective use of unconverted residual from likely conversion systems
(anaerobic digestion system, for example) will require attention.
Crop residues are the single largest current source of biomass feed-
stock available for conversion to fuel. Approximately 350 million metric
tons (390 million tons) on an ash- and moisture-free basis, were produced
in 1971. The residues from corn, soybeans, wheat, grain sorghum, sugar
cane, and sugar beet production, in that order, are the largest sources.
Crop residues are concentrated in the Midwest and South. Moisture contents
range from 50 to 85 percent when freshly cut but fall to 9 to 15 percent
when allowed to sun-dry in the field. A typical heating value for most
grain crops is 3600 kcal/kg (6500 Btu/lb); dried bagasse may reach 4400
kcal/kg (8000 Btu/lb), primarily because of its higher cellulose content.
Exploitation of crop residues will require development of equipment which
simultaneously harvests both crop and residue. A major constraint to
utilizing these biomass sources is their seasonality.
Kelp, freshwater algae, water hyacinths, and marsh grasses are
classified in the aquaculture biomass category. Giant kelp, the most
discussed aquatic biomass feedstock, is limited in its natural habitat to
the lower Pacific coast. Various freshwater algae are indigenous to all
regions. Water hyacinths occur primarily in the South and are a freshwater
species. The northern extreme of their range is limited by their suscepti-
bility to frost. Marsh grasses are also widespread. The current harvested
productivity of marsh grasses is meaningless, since they are not presently
cultivated on a large scale.
Kelp can be produced, in suitable locations, with yields as high as 170
metric tons per hectare per year (75 tons/acre/year) (dry basis). However,
approximately 45 percent of the dry materials are ash, predominantly salts.
When harvested, kelp has a moisture content of about 88 percent.
Water hyacinths yield approximately 25 metric tons per hectare per
year, dry basis, as an annual average. The fresh moisture content is
reported as 94 percent.
Because of the intrinsic value in their natural habitat and their
limited range, marsh grasses are not considered a significant potential
source of biomass feedstock.
No data on heat content of aquaculture materials were found. However,
on a dry basis, it is conservatively estimated to be on the order of 3300
kcal/kg (6000 Btu/lb), except possibly for kelp which might have a lower
value because of its high ash content.
Development of kelp as a significant biomass source will require
development of a complete cultivation technology. Harvesting might be
accomplished by techniques presently used on a limited scale in the
commercial kelp recovery industry. However, high value chemicals are
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recovered in these operations. Water hyacinths should be more easily
cultivated and harvested.*" However, their limited range represents a major
constraint.
Sugar cane and sugar beets were the energy crops considered in this
study. The major states where sugar cane is presently cultivated include:
Florida, Louisiana, Texas, and Hawaii. The states with the largest current
production of sugar beets are California, Minnesota, Idaho, Colorado, and
North Dakota. Approximately 290,000 hectares (740,000 acres) of sugar cane
and 600,000 hectares (1,500,000 acres) of sugar beets are in cultivation;
however, development of these species for biomass conversion would require
substantial increases in these acreages as well as development of new
varieties. Yields for sugar cane are estimated to be from 30 to 35 metric
ton per hectare (13-16 ton/acre), dry basis, for current varieties, using
conventional management techniques; sugar beet yields are estimated to be
10 metric tons per acre per year, dry basis. Fresh moisture content for
sugar cane is about 70 percent; for sugar beets, approximately 85 percent.
As noted earlier, the expected heating value for sugar cane is 4400 kcal/kg
(8000 Btu/lb); a value for sugar beets was not located.
In order for sugar cane to become a significant biomass source, the
area under cultivation must be extended. Likewise, new higher-total-yield
varieties and more productive techniques need to be developed. Exploita-
tion of sugar beets will require control of Nematode infestation.
Hardwood species (the generic rather than common term) are the most
likely source of silviculture for energy production. Poplars and cotton-
woods are the species with widest distribution. Although optimum annualized
growth rate for a single species will be regionalized, each region where
silviculture might reasonably be practical has species which can be adapted.
Alders, which have the ability to fix nitrogen, might be particularly good
species for combined energy production/reclamation activities. Yields
between 2-20 metric tons per hectare per year (0.9-9 tons/acre/year), dry
basis, are common for trees.
The moisture content of wood is typically 40-50 percent. Heating
values between 4500-5000 kcal/kg (8100-9000 Btu/lb), including all tree
parts, are common.
Cultivation and management of forests is, of course, well established.
However, their use for energy conversion will require significant innova-
tion. In particular, the practice of coppicing (e.g., forcing growth from
stumps), multiple harvesting of each plant, and development of a silage-
type harvester will probably be required.
As was noted earlier, strong competition for feedstock from existing
wood-based industries is anticipated.
Urban and industrial wastes are produced throughout the country and,
obviously, concentrated in urban centers. Approximately 270 million metric
tons per year (300 million tons per year) wet basis were produced in 1973.
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Approximately 66 million metric tons per year (73 million tons per year),
dry basis, are "organic" and could be converted to energy. These
organics typically have heating values on the order of 7000 Btu/lb on a
moisture- and ash-free basis.
Collection of these residues presently is accomplished by integrated,
highly complex systems of private and public organizations. However, these
wastes are the most concentrated large source of biomass and, likewise,
the most readily utilizable for energy production.
Major problems to be overcome relate to institutional, health, and
environmental considerations.
CONVERSION PROCESSES
There exist established techniques in wood processing, food processing,
pulp and paper and urban waste industries for preparing diverse biomass
materials to suitable conditions of size, organic concentration, and
moisture content. Details are contained in the body of this report.
Direct conversion of biomass to steam and/or electricity is the most
highly developed conversion technology. Experience using wood, bagasse,
and urban waste can be cited. Thermal efficiencies range from 55 to 80
percent. Equipment and process design will be a strong function of feed-
stock characteristics and preparation. A major limitation is the stora-
bility of these energy crops utilizing existing technology.
Pyrolysis can produce intermediate to high heating value gas streams,
liquids, and chars. While a great many systems have been proposed, only
10-12 are under active development, including a mobile processing facility.
Feedstocks have included municipal/industrial solid waste, agricultural
and forestry wastes (wood, crop residue, livestock manure), and energy
crops. Two systems have reached near-commercial levels of development.
Vertical and horizontal shaft, rotary kiln, and fluidized-bed reactors
have been utilized. Direct and indirect heating methods exist. The major
variables affecting product yields and compositions are temperature,
residence time, and feed conditions. Moisture content is a particularly
important feed condition. Thermal efficiencies in the range of 50-75
percent are common.
Acid hydrolysis of cellulose (wood) to produce sugar solution for
fermentation was practiced commercially before World War II. The advent
of cheap petroleum brought about the demise of commercial production.
Dilute and concentrated acid processes were commercialized. All previous
practice was in the batch mode. In even the most advanced technology of
the earlier time, 2 hours residence time was required. Besides long res-
idence times, useless by-product formation tended to be a problem.
Recently, renewed interest in the process has arisen. At a small laboratory
scale, residence times on the order of 20 seconds and sugar yields on the
order of 53 percent have been achieved.
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Two hydrogenation technologies are under development: one produces a
liquid while the other makes an intermediate grade (4500 kcal/cubic meter)
gas. Close similarities to fossil fuel (especially coal) conversion
processes are evident. Integrated pilot-scale demonstrations and, ulti-
mately, modular-size demonstrations will be required before more than a
tentative assessment of the value of the technologies can be made.
The naval stores industry dates to the early 1600's but has been in
steady decline since the turn of the century. Many of the products produced
are saturated and unsaturated hydrocarbons (e.g., terpenes). Renewal of the
industry has an aesthetic appeal, because its processes yield long-chained
hydrocarbons directly. However, evaluation of this potential will require
an effort beyond that expended in this study.
Anaerobic digestion, as a technology, is over 100 years old and began
as a sewage treatment practice. Extention to municipal solid waste has
begun during the past 10 years. Two process configurations, high rate,
single-stage and two-stage fermentations, have received attention. Two
optimum process temperatures, mesophilic (~35 C) and thermophilic (~55 C)
are utilized.
Calculations of thermal efficiencies based on published material
balances yield about 50 percent.
An anaerobic digestion demonstration plant using municipal solid
waste is presently under development and is being supported by ERDA. Two
plants based on animal manure have also been proposed and are believed to
be under development.
Enzymatic hydrolysis to produce sugar solution has been under develop-
ment for about 15 years. The technology, which operates at modest process
condition and without the by-product formation present in acid hydrolysis
system, is still at an early stage of development. Long residence times
appear to be the major stumbling block.
Biochemical production of hydrogen is still poorly developed; its
commercial potential is unknown.
A number of secondary conversion processes, i.e., processes which
convert the products from other technologies to useful fuels (ethanol from
sugar solutions, methanol from pyrolysis gas), have been considered. Most
of these processes are commercially available. Examples include:
methanol, ammonia, hydrocarbon, and higher alcohol production from synthesis
gas and ethanol fermentation. In most of these cases, the major effort
required is adapting them to developing technologies. In a few cases,
notably C»-C,- production from synthesis gas and gasoline from methanol,
basic process development and/or demonstration will be required.
Product storage and distribution will, by and large, require use of
existing technology. However, since many of these products will be used
in situations where their intrinsic dangers are not well understood (for
-------
example, in municipal departments and rural, agricultural environments), a
sense of caution reinforced with intensive training will be required. This
is particularly true of methanol, where distribution in existing consumer
fuel delivery system, could pose significant danger to the public at large.
Six regionalized scenarios, involving production and conversion
technologies, were developed as part of these studies. The purpose was
to demonstrate a recommended analysis technique and propose initial
direction, rather than definitely assess technological and environmental
effects which would occur. It is possible, however, to begin to appreciate
the scale of development required for implementation of these technologies
and to preliminarily suggest approximate levels of streams requiring
disposition. The interested reader is referred to Sections 6 and 7 for
details.
ENVIRONMENTAL ASSESSMENT
A preliminary assessment of the environmental consequences of biomass
production and conversion was prepared.
Development of forestry residue and/or silviculture as a biomass
source is expected to raise environmental issues in the areas of land use,
physical and chemical alteration of the environment, and ecological effects.
Land use considerations are expected to focus on other valuable uses of the
land (and its tree crop) as well as the more aesthetic aspects related to
removing logging wastes. Physical and chemical alterations, in particular,
those associated with increased erosion and nutrient release, are expected
to be critical questions. Assuming erosion and nutrient release effects
occur in at least modest amounts, the secondary effects on the aquatic
population and diversity will have to be considered. The small amount of
data which were accumulated are reviewed in the text.
The environmental assessment for agricultural crop residues and energy
crops were developed as a single unit. Qualitatively, these effects are
similar to those noted above. However, questions relating to productivity
and nutrient release are of overwhelming importance for these biomass
sources, as substantial reduction of soil productivity could adversely
affect human and/or animal food production. A thorough analysis of these
effects will be necessary.
The concept of recovering energy from animal manures and returning the
residue (at least from anaerobic digestion processes) to the land, appears
to have generally favorable environmental effects. The major concern will
be application rate and assurance of sites for use of the residue. When
actual systems are installed, close monitoring of surface and subsurface
waters will be advisable to assure these systems are not adversely affected.
The environmental effects of large-scale aqvjaculture are speculative.
At near shore sites, favorable effects related to increasing species diver-
sity are accrued. Unfavorable effects relate to sea-floor coverage by
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detritus and introduction of species into new regions. Deep-ocean farming
appears to circumvent most objections. However, the state of development
is so early that even preliminary analysis will require a more substantial
effort.
Harvesting of marsh plants does not appear to be acceptable on a
large scale, from an environmental point of view.
The environmental effect of municipal waste "production" was given
only nominal consideration due to the multiplicity of studies of this waste.
Generally favorable effects are believed to accrue from properly managed
systems. Heavy metal concentration and disposition is the major area for
concern.
The process stream requiring closest monitoring in direct conversion
systems will be the stack. Particulate will be important, as may be gas-
phase metallic fume and organic "hydrocarbon" concentrations, especially
in process systems where municipal solid waste is burned. Proper ash
disposal will also be required. For biomass originating from crops,
returning the nutrient to the soils from which they were removed may be
possible. Ashes emanating from direct conversion systems based on municipal
solid waste and marine crops (e.g., kelp) may require special disposition.
Air emissions from pyrolysis processes will be low compared with
direct conversion systems because the products are generally combusted off-
site. However, the sum total will not be grossly different. Combustion
conditions in pyrolysis systems are more uniform and product gas clean-up
requirements are not as extensive as in direct conversion systems.
The pyrolytic oils which are prepared will likely produce higher NO
emissions than comparable hydrocarbon analogs, because of the inherently
higher nitrogen content of the feedstock. However, sulfur emissions will
be lower on a comparable basis. Waste water parameters from pyrolysis
conversion systems are expected to be well within conventional sewage
treatment practice.
Because of its origin in sewage treatment technology, much is known
about the qualitative aspects of waste streams leaving anaerobic digestion
systems. Disposition of the digester broth (fermentation media) will be of
prime concern. These concerns will be magnified during upset conditions if
the digester contents must be released. With most biomass feedstocks,
disposal to the soil will be acceptable if properly managed.
If the product gas is upgraded to pipeline quality, emissions of
hydrogen sulfide from the acid gas removal system are expected. If these
must be controlled, the technology should be within the range of conven-
tional practice.
Emissions and effluent stream characteristics from other conversion
technologies were not developed as part of this study.
-------
Crude quantification of the several process systems at commercial
production scale are given at the end of Section 7. These should be
considered highly tentative and in need of expansion. In particular,
the environmental effects associated with production should be added and
the process emissions greatly strengthened.
ERDA currently provides the major thrust in biomass conversion
technology development. This effort was preceded by that at NSF. Besides
EPA, other agencies with identified missions in this technology include
NSF, USDA, NASA, and HUD.
ENERGY POTENTIAL OF BIOMASS
Having discussed in detail the availability of biomass sources,
conversion systems for these sources, and their environmental implication,
it is appropriate to provide an estimate of the significance of these
technologies in relation to the total energy supply picture. Such estimates
always should be treated with a healthy skepticism but must be made in order
to provide insight to the decision-maker on relative support work appro-
priate for these technologies, given the limited resources available. In
preparing the estimates for biomass, the following strategy has been adopted.
A conservative estimate, on a relatively current basis, was made for
the total quantity of feedstock available from each source category. Using
a typical heating value for each category, the gross amount of energy
available in the category was then calculated. This approximates the total
energy pool currently available and is probably the data in the analysis
with the highest confidence factor. Next, an estimate was made of the
amount that might be collected for conversion. The assumption here is that
a concentrated but not all-out effort is made to assemble the various
sources. These values should be treated as highly uncertain and represent
little more than educated guesses. The product of these estimates and
those of the energy pool provides an estimate of energy available at the
biomass plant sites for conversion to synthetic fuels. Next, a typical
thermal conversion efficiency is estimated for each source category, with
the value chosen primarily based on whether thermochemical or biochemical
processes would be the predominant choice for conversion. The confidence
level on these data is higher than that for availability but still not
beyond one significant figure. The product of these numbers is the net
energy that might be available for consumption. These results are shown
in Table 1.
To allow other investigators to adjust the basis as is necessary for
their use, the following supplemental data taken from the text is provided.
The estimates of municipal and industrial organic waste available were
derived from Smith^1''. The data were published in 1976 but represent
inventories for the year 1973. The categories used included the paper,
wood, food, and yard components of solid waste.
Agricultural and forest wastes were used directly from Anderson
The data were published in 1972 and were for the year 1971.
8
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Silviculture was estimated in the following manner. EPA^ ^ has
estimated that 4.4 million acres of strip-mined land are presently in need
of reclamation. This is increasing at approximately 200,000 acres per
year, and about 50 percent of the total is associated with coal mining.
It was assumed that about one-half the 4.4 million acres might be available
for silviculture use and that a sustained annual yield of approximately 3
tons/acre/year could be reasonably expected on these low productivity lands.
Obviously, there are other marginal lands which might be used for silvi-
culture. However, their availability on a long-term basis is questionable.
The basis for energy crop estimates is current production figures for
sugar cane and sugar beets. There are presently about 291,000 hectares
(740,000 acres) of sugar cane under cultivation in the United States. There
are land areas available for expansion, and different species might be used
to increase total biomass yields. However, there are also other demands for
the product, so that only the yield from current cultivation was used, and
a net value of 14 dry tons per acre was estimated. It should be noted
that the most likely energy use for these crops may be in the context of
current production facilities, e.g., in boiler. Sugar beet production was
treated similarly but represented a much smaller quantity. Marsh grasses
were assumed to be insignificant.
Aquaculture's contribution was estimated based on the 100,000-acre
kelp demonstration plant being utilized. Since this technology is in an
early stage of development, it is believed to represent the most signifi-
cant source of error in the estimation.
The data contained in Table 1 indicate that an estimated gross total
of 10 Quads of energy might be available from the biomass sources
considered, that possibly 4 Quads might be available for conversion, and
that slightly less than 3 Quads might be available in produced fuels. Since
these estimates are based on current availability, they are best compared
to the present energy demand which is on the order of 70 Quads. These
values would then represent approximately 15 percent, 6 percent, and 4
percent, respectively, of the current energy demand. This is not completely
valid, of course, because the energy expended by the processes and equip-
ment to collect and convert this energy are not available. However, the
estimated gross energy pool is likely to generally follow the population
(and total energy demand growth) during the coming development years, and
the gross pool is the basis for subsequent calculations as have been
described. Consequently, it is estimated that, given the multitudinous
counter-balancing effects which will occur between now and the turn of the
century, approximately 4 percent of the energy demand in the year 2000
might be met by biomass sources. If the total demand is on the order of
150 Quads as some have estimated, this might amount to 6 Quads. Further-
more, if significant inroads are made in energy conservation and solar
heating and cooling technologies, it might be a considerably more signifi-
cant source of storable, transportable fuels.
The calculated energy potential can be compared with the ERDA objective
for Fuels and Biomass(137 keeping in mind that the ERDA estimate does not
-------
include solid waste. The calculations described above are certainly
substantially less rigorous than those prepared by ERDA and were done com-
pletely independently. The good agreement (ERDA's objective was 2-5 Quads
before the year 2000) is probably fortuitous. The relative magnitudes
developed in this estimate, however, should be approximately correct.
While these calculations are informative, to base value judgments
solely on their relative magnitude is to miss much of the significance of
the biomass effort. To put the problem in perspective, consider the
magnitude of a Quad of energy, namely 1015 Btu. An order-of-magnitude
estimate of the energy utilization of a modest-size city (Columbus, Ohio)
was prepared to provide this insight. The local newspaper^) prepares a
weekly accounting of the natural gas and electricity usage for Franklin
County, which approximately represents the Columbus area and includes a
population on the order of 1 million people. The electricity demand was
converted to fuel by using a heating rate of 10,000 Btu/kwh, a typical
value for a relatively modern power boiler. This was supplemented by data
from the Ohio Public Utilities Commission^15) which provided estimates of
the liquid fuel consumption for Franklin County (approximately 12.5 million
barrels per year). These data allowed the estimate contained in Table 2
to be prepared.
It is clear from these calculations that several plants producing on
the order of 0.1 Quads would have a significant impact on the energy
consumption of a city the size of Columbus, a fairly large city by mid-
western standards. Using the data developed in Table 1 for crop wastes,
this would require on the order of 40,000 metric tons/day, wet basis, or
probably 4 large plants, to produce 20 percent of Columbus' current energy
demand.
This analysis suggests another characteristic of biomass utilization
which is important. By far, the largest source of biomass available is
agricultural and forestry wastes (see Table 1). These residues predominantly
occur in the nation's broad midlands. This area also is characterized by a
number of medium- to large-sized cities (50,000 to 1,000,000) and a
tremendous number of smaller communities. These smaller communities charac-
teristically service agricultural areas and are often near terminal points
on energy distribution systems. They are difficult and expensive to
service, both in monetary and energy terms. Consequently, it would seem
to make good sense to use the local resources (energy crops and agricultural
and forestry residues) to provide for local energy needs.
In order to visualize a third consideration, attention must be
refocused on Table 1. The last category (aquaculture), on the basis of
current projections, represents a minimal impact. Yet, if each of the
other categories are considered in relation to expanding the energy supply
available, an upper limit is quickly reached. For example, even with much
higher recovery rates and greater than expected population growth, it is
hard to visualize more than 1-2 quads available from solid waste. Like-
wise, assuming new total biomass crop species and development of organized
efficient collection system, to expect more than about 10 quads from
10
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TABLE 1. ENERGY SUPPLY ESTIMATE FOR BIOMASS (1973)
Feedstock
Urban and Industrial
Wastes
Agricultural and
Forest Wastes
Silviculture
Energy Crop
Aquaculture
Feedstock
Urban and Industrial
Wastes
Agricultural and
Forest Wastes
Silviculture
Energy Crop
Aquaculture
Estimated Gross Availability
Typical Million Metric Tons/Year
Component (moisture and ash-free)
Municipal Solid 66<4>
Forest and Crop 445^
Residue
(corn silage)
Manures (cattle) 200 ^*
Alder 8
Sugar Cane 15
Kelp 2
TABLE 1. (Continued)
Typical
Net Energy Thermal Net
Recoverable Before Conversion Energy
.. Conversion (quads) Efficiency Recoverable
0.4 0.7 0.3
1.9 0.8 1.5
1.7 0.4 0.7
0.2 0.7 0.1
0.3 0.7 0.2
<0.1 0.4 <0.1
Potential
Estimated Heating Energy percent
Value Available Assumed
Btu/lb (MAF) (quads) Recoverable
(5)*
7000V ' 1.0 40
6500 (6)* 6.4 30
6300^7'8'9)* 2.8 60
8700 0.2 SO
/ii 12)*
8000X ' ' 0.3 90
6000** < 0.1 90
* Numbers in raised parentheses
denote references which are
given on page 13.
** Assiimnl-inn
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TABLE 2. ESTIMATE OF ANNUAL ENERGY USAGE
FOR THE CITY OF COLUMBUS, OHIO
Category
Natural Gas
Electricity
Liquid Fuel 'a'
Total
Energy Use,
Quad
0.37
0.09
0.04
0.50
Percentage
of Total
72
18
8
100
^Includes gasoline, distillate, residual, kerosene,
and liquefied petroleum gases.
agricultural production of all types would be unrealistic, considering
other nonfuel demands for these materials which are likely. The single
exception to this agreement is aquaculture. The potential is staggering,
far beyond the estimates provided in Table 1. The problems that must be
resolved to exploit these resources are multitudinous, very difficult,
and will likely require decades of concentrated effort. Yet the fact
remains that, given a significant commitment, the problems can be resolved,
and it is the only biomass source without a clear upper bound on its
availability.
Finally, various experts have estimated the total reserves of fossil
fuel. Some have suggested that several hundred years are available when
coal is included. A quite interesting case is made by Huebler(16) , who has
projected, based on world energy demands since 1850, that if the history of
worldwide energy growth rate is maintained, all fossil fuel reserves will
be depleted before the middle of the next century. Given the energy demand
likely from developing countries, such an assumption does not appear overly
conservative. While the relative merits of the various energy demand
estimates can be argued unendingly, two facts remain. The first is that,
within the foreseeable future, fossil fuel reserves will be exhausted.
Secondly, as they are depleted, they will become more and more dear for a
variety of uses. The conclusion is inescapable: biomass conversion will
eventually be implemented. The only question is when. While direct~solar
and fusion application may supply large quantities of future energy needs
it is unlikely that the need for gaseous and liquid fuels will disappear
completely or even decrease significantly from their current levels. It
seems that the wiser choice is to begin now while we have a substantial
lead on the problem and can devise solutions which minimize environmental
and sociological effects rather than delay to a time when fossil energy
reserves more closely approach exhaustion.
12
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REFERENCES TO SECTION 1
1. Smith, F. A. 1976. Quantity and Composition of Post-Consumer Solid
Waste: Material Flow Estimates for 1973 and Baseline Future
Projects. Waste Age 7:2, 6-10.
2. Anderson, L. L. Energy Potential from Organic Wastes: A Review of
the Quantities and Sources. U.S. Dept. of Interior, Bureau of Mines
Information Circular 8549, Washington, B.C. 16 pages. 1972.
3. EPA, 1974. Surface Mining of Coal, EPA Report No. 670/2-74-093.
4. Klass, D. L. 1976. Wastes and Biomass as Energy Resources: An
Overview, pp. 21-58. In Symposium Papers Clean Fuels. Orlando,
Florida. January 27-30, 1976. Institute of Gas Technology.
5. Jackson, Frederick. Energy from Solid Waste. Noyes Data Corporation,
Park Ridge, New Jersey, 1974, Chapter 1.
6. Szego, G. C. and C. C. Kemp. Energy Plantations. Chapter 3 in New
Resources from the Sun. Proceedings of the 34th Annual Conference of
the Chemurgic Council, Washington, B.C., November 1-2, 1973. Various
paging.
7. Wells, D. M., G. A. Whetstone, and R. M. Sweazy. Manure, How it
Works. Paper Presented at the American National Cattlemen's
Association/Environmental Protection Agency Action Conference,
August 28-29, 1973, Benver, Colorado. 1973.
8. Coe, W. B. and M. Turk. Processing Animal Waste by Anaerobic
Fermentation, pp. 29-37 in Symposium: Processing Agricultural and
Municipal Wastes. G. E. Inglett (ed.), Avi Publishing Company,
Westport, Conn. 221 pages. 1973.
9. Halligan, J. E., K. L. Herzog, H. W. Parker, and R. M. Sweazy.
Conversion of Cattle Feedlot Wastes to Ammonia Synthesis Gas.
Environmental Protection Technology Series EPA 660/2-74-090,
United States EPA, Corvallis, Oregon. 46 pages. 1974.
10. Hall, E. H., et al. Comparison of Fossil and Wood Fuels. Final
Report from Battelle's Columbus Laboratories to the Environmental
Protection Agency. Contract No. 68-02-1323, March, 1976.
13
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11. Alich, J. A., Jr., and R. E. Inman. Effective Utilization of Solar
Energy to Produce Clean Fuel. Report to National Science Foundation,
NSF/RANN/SE/GI 38723/FR/74/2, Stanford Research Institute, Menlo
Park, California. 161 pages. 1974.
12. Klass, D. L. A Perpetual Methane Economy - Is it Possible? Chemtech
4:161-168. 1974.
13. ERDA, 1976. A National Plan for Energy Research, Development and
Demonstration; Creating Energy Choices for the Future, Volume 2:
Program Implementation.
14. The Columbus Dispatch, February 8, 1976, p. K-l, and July 25, 1976,
p. K-l.
15. Personal communication, Mr. Jim Shaffer, Public Utilities Commission
of Ohio (September 2, 1976).
16. Huebler, J. 1975. Energy Overview, a paper given at Clean Fuels from
Coal, Symposium II (June 23-27, 1975).
14
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SECTION 2
INTRODUCTION
During the past decade in the United States, an awareness has developed
that the highly specialized industrial and agricultural production that are
this country's trademark are producing vast quantities of "waste" along with
their primary products. During the late 1960's and early 1970's, there was
a substantial effort, in both the public and private sectors, to develop
technologies that could "dispose" of these materials in a manner less detri-
mental to the environment. As this effort matured, greater emphasis began to
be placed on management systems and process technology that recovered usable
material and/or energy from these wastes. The initial impetus for this
waste recovery was to mitigate the rather substantial increased costs associ-
ated with improved disposal methods. As the energy shortfall from tradi-
tional fossil fuels became more apparent, this interest again shifted focus,
and many of these systems began to be viewed for their energy capacities.
Finally, it became apparent that many of these systems could be utilized to
process other "feedstocks," which were not wastes per se but rather crops
that were specifically cultivated for their energy conversion and chemical
feedstock value. This whole field--including waste, as well as terrestrial
and aquatic crop production--is now generally defined as Biomass Conversion
Technology.
The foregoing discussion implies several features about this technology.
First, with the possible exception of urban wastes, most of these materials
are sparsely distributed relative to other established and developing energy
sources such as coal, petroleum, uranium, etc. From this fact, it is con-
cluded that an important factor dictating the economic use of these sources
will be the efficiency with which they can be collected, concentrated,
stored, and used.
Another important characteristic of most of these materials is their
high initial moisture content. This characteristic places a substantial
efficiency burden on many of the thermochemical conversion processes (e.g.,
those systems, including combustion methods, that substantially raise
processing temperature to produce a desired chemical change) where a sub-
stantial portion of the energy content must be used to evaporate contained
water. Consequently, the alternative approaches, which have been termed
biochemical conversion processes (e.g., those systems which bring about
desired chemical changes by the direct or indirect action of biological
agents), appear at first glance, to possess distinct economic and source
control advantages. The early stage of development of these technologies
and the characteristically long storage times required for conversion to fuel
products tend to offset these advantages. Furthermore, in some cases,
15
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downstream product purification often requires a water-fuel separation,
partially negating the advantages achieved in the actual conversion step.
In terms of fuels, the most desirable feature of biomass as feedstock is
its carbonaceous content. For most biomass materials, this can be inter-
preted as cellulosic content. Biomass sources also generally exhibit several
additional favorable characteristics. Among the most significant, for
sources other than urban waste and most ocean-grown aquatic crops, is the low
ash and sulfur content that they exhibit. As a consequence, concentration of
environmentally undesirable components, notably sulfur and heavy metals, is
usually quite low.
The objective in undertaking this study was to develop a "preliminary
environmental assessment of biomass conversion to synthetic fuels." The size
of this report may suggest to some that it represents a more definitive docu-
ment that in fact is the case. While the report contains large quantities of
data and extensive analyses were undertaken, a conclusion that the work is
beyond a preliminary stage would be erroneous. The scope of this report did
not permit economic analyses, thereby limiting the conclusions regarding
possible biomass sources, process technologies, and environmental controls
to technical feasibility factors rather than economic feasibility factors.
A review of the technical summary, conclusions, and recommendations confirms
the substantial need for additional data and more in-depth analyses of
important systems.
This report has been organized to present a review of the currently
relevant technologies. To this end, the first two chapters deal with biomass
sources and biomass conversion processes, respectively. These chapters have
been developed in detail. The field of biomass technology is both broad and
rapidly expanding. Consequently, the development of numerous crop species as
potential feedstocks as well as new process configurations are anticipated.
Using the technological basis for commercialization of these technolo-
gies, it is then possible to begin to make preliminary estimates of the
environmental consequences of biomass source development and process oper-
ations. However, this provides an incomplete basis as it overlooks
environmental factors associated with feedstock and product collection,
storage, and distribution, and certain socio-economic factors related to
establishing large production facilities in previously agricultural and
undeveloped settings. To analyze these factors, a series of scenarios was
developed. The most prominent sources and processes were visualized in the
context of a large production facility. For the purposes of this study, it
was not necessary to develop these scenarios in great detail. However
characterizations that have been developed should be useful in preparing more
comprehensive descriptions that might be required at a later date.
Finally, it was deemed important to assess the current plans of
governmental agencies with relevant interest in biomass-energy technological
developments. The breadth of the technology made it difficult to be assured
that all programs had been reviewed, and as a practical matter, there prob-
bly were some oversights. However, the discussion included in this report
should provide a worthwhile benchmark as of mid-1976 pointing to the expected
direction of future development of biomass resources.
16
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SECTION 3
CONCLUSIONS
The following conclusions highlight the more salient points identified
during the course of this study on biomass resource development.
GENERAL
1. Biomass sources might reasonably be developed to satisfy 3 to 8 percent
of the projected energy demand in the United States by the turn of the
century.
2. In developing technology, emphasis should be placed on meshing biomass
sources with localized energy needs. The biomass production/conversion
process scenarios developed in this report provide an analytical tech-
nique that might be used in making the required judgments, and developing
a basis for assessing environmental consequences.
3. Because of the limited resources likely to be available in developing
these technologies, it is imperative that the activities of various
agencies be well coordinated.
4. Since biomass to energy conversion technology is in an early stage of
development, an excellent opportunity exists to assure that process
technology and environmental protection develop simultaneously.
5. This preliminary study focused on the technological aspects of biomass
production and conversion, and associated environmental effects. Addi-
tional data on the economics of production and of its attendant environ-
mental protection is needed.
BIOMASS SOURCES
1. It is anticipated that the various biomass sources will be integrated
into the synthetic fuels production industry within different time
frames. The various biomass sources when ranked from nearest to longest
term entry to such industry, are expected to follow the development order
given below:
• Urban and industrial waste
• Agriculture and forestry wastes
• Silviculture
17
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• Energy crops
• Aquaculture
2. The potential amount of energy that is available from these biomass
sources is significant. A conservative estimate of both energy pool and
the net fuel potential which might reasonably be expected from these
biomass sources is presented in Table 1. It is emphasized that these
projections must be considered tentative.
3. It is apparent from the studies undertaken in this work that the avail-
ability of each of the biomass sources will vary by section of the
country. It is possible to regionalize the country in a manner that per-
mits identification of discrete biomass sources. Battelle's attempt at
defining these regions and identifying some of the major biomass sources
for each region are summarized in Tables 71 and 72 respectively.
4. The technology and economics of harvesting, collecting, storing and
transporting large volumes of crop related materials to central locations
have been poorly defined to date. Additional data is needed in this
area. A more pragmatic technology development choice might be to reduce
the size of operations to decrease the transportation distance, while
concentrating on making localized areas independent of energy importa-
tion. Data on this option needs to be developed as well.
5. While economics were not addressed explicitly in these studies, it is
anticipated that successful development of biomass resources will elicit
strong competition from other industries, notably food, fiber and
chemical manufacturers.
6. The major technological problem areas anticipated in relation to biomass
sources can be generalized to (1) difficulties in raw materials storage,
(2) crop seasonality, and (3) the energetics and logistics of harvesting
and transportation.
CONVERSION PROCESSES
1. The development of biomass conversion processes, in many cases, has been
initiated by earlier work in solid waste recovery activities .
2. Direct conversion systems are well developed and can (and probably will)
be applied on a commercial basis to many biomass sources.
3. A host of pyrolysis conversion systems are under private and public
development. Because of the versatility of the products, continued
development should be encouraged.
4. Anaerobic digestion processes for methane production are receiving con-
siderable attention, and do not appear to need additional concentrated
support. However, most emphasis is on single-stage systems. Redirec-
tion of some of the effort towards multi-stage systems would seem
appropriate.
18
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5. Several new or revived technologies need more detailed study. These
include hydrogenation, acid and enzymatic hydrolysis, naval stores
processes, and fermentations not directed at methane. Feedstocks which
should be emphasized include urban and agricultural/forestry wastes.
6. Ethanol fermentation is a well developed technology. However, histori-
cally, processes have been batch-operated. It is difficult to visualize
processes directed at fuel production operated in batch modes. While
difficulties in continuous fermentation are well known, process develop-
ment along these lines appear necessary. These have been initiated, and
should continue to be supported.
ENVIRONMENTAL ASSESSMENT
1. For all agricultural and forestry-derived biomass feedstocks, the over-
whelming concerns relate to effects on land productivity and displacement
when crops and crop residues are removed.
2. For processes operating on materials other than industrial waste and salt
saturated aquatic crops, redispersal of process residuals to the land may
be environmentally and technically sound. This area needs to be explored
in more detail than was possible in this report.
3. For the most part, environmental control technology being developed for
solid waste conversion processes should be applicable to other biomass
feedstock, and is expected to represent typical case applications for
biomass controls. Metal fume and heavy metal particulate removal and
nitrogen oxide control from pyrolytic and hydrogenated liquids are the
air pollution problems of most concern. Treatment of wastewater from
processes such as anaerobic digestion and acid/enzymatic hydrolysis are
significant water-related problem areas.
4. One disturbing fact which has arisen is the noted respiratory disease
potential which occurs when bagasse is stored (see p. 45). Controlled
storage methods need to be documented.
5. While only briefly addressed in this study, environmental and socio-
economic implications of locating large conversion plants in rural
environments is a research area which needs attention.
6. Various global environmental concerns (for example, monoculture effects
on ecological diversity and secondary productivity, changes induced by
large plantations on solar reflectivity, wind currents, and other such
variables) were beyond the scope of this study, but do need to be
addressed before large scale implementation is undertaken. The near-
term needs appear to be (1) definition of the problems and (2) collection
of indicative data.
19
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SECTION 4
RECOMMENDATIONS
This study reviews both production/conversion technological and
environmental aspects of biomass production and its subsequent conversion to
energy or fuel. The primary objective was to develop a preliminary environ-
mental assessment and identify areas where environmentally related research
is needed. Additional impressions however, evolved with regard to the needs
of technology development. Since it is hoped that this report will be
useful to a wide spectrum of readers interested in the various aspects of
technological development, recommendations also have been included in this
area as well. These recommendations are presented with the purpose of
furthering the development of the state of conversion technology.
ENVIRONMENTAL RECOMMENDATIONS
1. A study, complementary to that described herein, needs to be undertaken
with emphasis directed at specific economic aspects: (1) detailed
development of cultivation, harvesting, transportation, and storage, and
their associated costs, (2) first order approximation of the costs for
production/conversion technology, and (3) first-order approximation of
the costs of environmental controls. These data need to be assessed in
an expansion of the scenario concept presented in this report, leading
to a more quantified projection of the environmental and sociological
implications, and associated costs.
2. A most pressing need identified is to undertake studies directed at
quantifying the effect on land productivity and related variables of
wholesale removal of biomass from the land. It is anticipated that the
mitigating management practices can be developed. However, their
development should precede, or, at the most, coincide with technology
development in the production/conversion field.
3. As noted in the conclusions, storage of bagasse has been identified as a
source of an agent which causes respiratory ailments. A detailed study
should be undertaken identifying the limits of viability of the agents,
related organisms that might cause similar ailments, the viability of
the agents on major biomass crops that have been detailed in this report,
and possible control measures.
4. Return of certain process residuals to the land may prove to be an
environmentally and technologically sound practice. Studies directed at
characterizing process residuals (such as insecticides, herbicides, etc.)
20
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from the major conversion processes, when operated on crop-derived
biomass, need to be undertaken.
The potential global effects of widespread biomass development could have
important environmental and sociological effects. Studies need to be
undertaken to address these effects. Objective definition of the nature
of the problems, their potential effects, possible mitigating circum-
stances, and filling certain data gaps needs more research.
The possibilities of using nitrogen-fixing tree species for strip-mined
reclamation, while producing a fuel-conversion crop warrants detailed
investigation. The brief consideration given in this study suggests
the environmental and potential energy recovery benefits greatly over-
whelm unfavorable factors. However, clearer definition is required of
the scope and implication of such activities before they are undertaken
on a large scale.
RECOMMENDATIONS FOR PRODUCTION/CONVERSION
TECHNOLOGY DEVELOPMENT
1. Harvesting and transportation technology will be crucial in biomass
energy production activities. A study of the technological options
including raw materials storage should be undertaken for each biomass
category.
2. A study of localized (10-50 management) production/conversion alterna-
tives is needed to provide a clearer comparison of the cost/benefit
options to large scale developments.
3. Several of the less developed technologies need to be explored in more
detail than was possible in this report. These studies should be sub-
stantiated with experimental data.
4. An experimental study of two-stage anaerobic digestion should be under-
taken to provide data for a large-scale design and economic analysis.
21
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SECTION 5
BIOMASS SOURCES
OVERVIEW
Most of the energy used in the U.S. comes from coal, oil, and natural
gas. These are fossil fuels—energy-rich molecules resulting from photo-
synthesis in past geologic eras. As reserves of fossil fuels have been
depleted in recent years, much interest in alternative energy sources has
developed. Naturally some of that interest has focused on the photosynthetic
process and the energy-rich organic material-biomass that results. The pur-
pose of this chapter is to review the biomass sources potentially available
for conversion into easily used, easily stored, clean burning fuels.
POTENTIAL BIOMASS SOURCES
There are many biomass sources. Two major categories are (1) energy
crops and (2) wastes and residues. The former category includes vegetation,
both terrestrial and aquatic, cultivated and managed expressly for the pur-
pose of conversion into fuel. These energy plantations include aquaculture
using kelp and other species, terrestrial energy crops such as sugar beets,
and silviculture using productive species of trees. In addition to the
possibility of growing and managing crops for energy, there is a large quan-
tity of energy-rich organic wastes and residue from forestry, agricultural,
and urban and municipal activities. This biomass source is of interest in
that it may be possible not only to extract the previously unutilized energy
but also reduce the costly treatment required to properly "dispose" or
recycle some of these wastes.
This chapter will examine these potential biomass sources. The charac-
teristics of the more productive species and the cultivation and harvesting
techniques necessary for their growth will be discussed. Problems and limita-
tions in their use as a fuel source will be examined. Finally, future trends
for the use of these sources will be presented.
AGRICULTURAL AND FORESTRY RESIDUES
Initial Screening
Solid wastes from agricultural and forestry residues have been esti-
mated to make up 73 percent of all organic wastes, including municipal and
industrial wastes, generated annually in the United States.U) The largest
22
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quantities of agricultural residues are in the form of portions of crops—
stalks, leaves, vines, straw, stubble—that are left on the field after
harvesting, and animal manure. The volume of forestry residues generated
annually is considerably smaller than that of agricultural residues and con-
sists of wood wastes remaining on the forest floor after timber removals,
or accumulating at sawmills, pulpmills, and other wood processing industries.
Anderson(1) has calculated the quantities of organic solids ("organic
solids" refers to the moisture- and ash-free fractions of the wastes) gener-
ated from various sources in the United States in 1971. He has also calcu-
lated conservative estimates of the proportions of these volumes which are
in some way readily available at centralized locations; 4.5 million metric
tons of forestry residues, 20.5 million metric tons of crop wastes, and
23.6 million metric tons of animal manures.
When a particular type of biomass waste happens to be available at
centralized locations, it is more valuable as a potential feedstock for con-
version to synthetic fuel since less energy needs to be expended in procur-
ing it. For example, forestry residues are easy to collect from wood
processing plants, as are manures from animals being raised in confined
conditions. Residues from most agricultural crops are generally not avail-
able in large quantities at centralized locations, since after harvest
operations they are not collected and therefore end up being uniformly dis-
tributed over fields covering many hectares. However, exceptions exist for
a small percentage of the total crop residue volume. Bagasse and beet pulp
accumulated at sugar mills, chaff from wheat at cereal grain mills, and
other wastes from canning and food processing plants are typical examples.
Agricultural and forestry residues possess several unique advantages
over other potential biomass energy feedstocks. In the first place, they
are generated from the same large contiguous areas of land that are used to
grow food or fiber so that it is not necessary to set aside land expressly
for the purpose of producing them (as in the case of a biomass plantation).
Also, many types of agricultural and forestry wastes are characterized
by large percentages of carbon, moderately high heating values, and low
sulfur content. They contain virtually no extraneous non-combustible mate-
rials such as glass, ceramics, or metal as would be found in urban refuse.
Some forms of residue are produced in such large quantities that they become
disposal and pollution problems. Manure is a disposal problem when the
supply exceeds the demand for its use as a fertilizer. Clearly, the utili-
zation of these wastes for synthetic fuel production would help solve the
disposal problems while simultaneously creating a new source of energy.
Many forestry and agricultural wastes are presently being directly
recycled back into the land, so that they are not really considered wastes.
Forestry residues may remain on the forest floor to decompose and return
nutrients to the soil, while creating niches and habitats for many types of
wildlife. Manure has always been utilized as a fertilizer although a
limit exists as to the amount in which it can safely be applied to crop
soils. Grain and vegetable stalks are left for farm animals to graze upon
and are eventually plowed down into the soil where they serve as soil
conditioners. It should be considered that the above-ground portions of
23
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crop residues could probably be collected for energy purposes since the roots
still remain to provide the soil with organic matter.
In recent years, crop harvesting methods have become increasingly
mechanized so that as much residue as possible stays in the field instead
of being unnecessarily transported to food processing facilities. Con-
sequently, the total residue volume from some crop species is left in the
field widely distributed over expansive areas. This means that more energy
will be required to collect these residues, unless technological developments
create a harvesting machine that can separate the food and the residue while
harvesting them both simultaneously.
The three broad types of residues that show the most potential for con-
version to energy are forestry residues, animal manures, and crop residues.
Among the crop species, the ones that produce the largest volumes of residue
per unit area are the grains, oilseeds, and sugar crops.
Forest Residues
Yields, Distributions, and Characteristics—
Forestry residues are wood wastes from two different sources, logging
and milling. Logging residues or slash are the portions of trees which
remain on the forest floor after logging operations have taken place in an
area. They consist of tops of trunks, branches and leaves, and stumps.
Residue may also result from stand improvement, when cull trees, rough and
rotten or dead trees, undersize trees, and noncommercial species are removed
from a woodlot or timber stand, and from thinning performed on growing stock.
Milling or processing residues consist of slabs, shavings, trimmings, saw-
dust, bark, and log cores resulting from all processing operations occurring
in primary and secondary manufacturing plants—especially sawmills, pulpmills,
and veneer and plywood plants.
It is estimated(1) that about one-third of the volume of wood harvested
in the United States each year is unused. Estimates of actual tons wasted
vary considerably in the literature. The data in Table 3 are given for both
logging and milling wastes for each of nine regions in the coterminous
United States.(2)
Logging residues which are not collected at the same time as the har-
vested timber are almost always left on the ground unless disposed of by
some means, usually by burning. Their lack of utilization is due to the
energy expenditure that would be required in making a special effort to
collect them, since they are composed of irregular shapes and sizes of
material widely distributed over all types of terrain. New chippers have
made it possible to utilize much more of this logging residue at the time
of the primary harvest. However, Table 3 indicates that logging residues
exist in large quantities in some regions in the country—notably in the
South and in the Pacific states, where logging operations are extensive.
For instance, one studyO) found that an average of 20 cubic meters (70
cubic feet) or about 14 metric tons (15 tons), of residue per acre remained
on sites in Alabama where clearcutting has been completed. Residues are
even more concentrated in the Douglas-fir region in Washington and Oregon,
24
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TABLE 3. UNUSED WOOD WASTE AVAILABLE IN THE UNITED STATES, 1970
(a)
Logging Residues
Region
New England
(Me., Vt., N.H., Mass.,
Conn., R.I.)
Middle Atlantic
(N.Y., Pa., N.J.)
West North Central
10° metric tons
10.4
6.7
6.5
(106 tons)
(11.5)
( 7.4)
( 7.2)
Unused Primary and Secondary
Milling Residues
106 metric tons
2.6
1.6
1.6
(106
( 2
( 1
< 1
tons)
.9)
.8)
.8)
(N. Dak., S. Dak., Nebr.,
Kans., Minn., Iowa, Mo.)
East North Central
(Mich., Wis., Ind., 111.,
Ohio)
South Atlantic
(Md., Del., Va., W. Va.,
N.C., S.C., Ga., Fla.)
East South Central
(Ky., Term., Ala., Miss.)
West South Central
(Tex., Okla., Ark., La.)
Mountain
(Idaho, Mont., Wyo., Utah,
Nev., Colo., N. Mex., Ariz.)
Pacific
(Wash., Oreg., Calif.)
14.6
57.7
35.6
34.8
17.1
74.7
258.0
(16.2)
(63.6)
(39.2)
(38.0)
(18.9)
(82.4)
(284.4)
3.7
14.4
8.9
8.6
4.3
18,7
64.5
( 4.1)
(15.9)
( 9.8)
( 9.5)
( 4.7)
(20.6)
(71.1)
(a) Reference (2), p. 210.
-------
where they constitute over 50 percent of all logging residues in the Pacific
coast states including Alaska.(4) This is collaborated by other studies(5)
which report that residues in the Douglas-fir region exist in ranges of 90
to 508 metric tons per hectare (40 to 227 tons per acre) after clearcutting
has taken place in an area.
For various reasons amounts of logging residues have increased along
with improved timber productivity in some areas. This may be a consequence
of the increasingly mechanized harvesting procedures which have come into
usage in the last decade and the decline in the practice of collecting
scrap wood for fuel. In the Western states, in particular, residues
appear to be accumulating in many areas.
Milling residues are a much more easily available source of material
for potential energy uses than are logging residues because they are con-
centrated at processing plants instead of being scattered over wide areas.
However, the sharply increasing demand for wood products in recent years has
resulted in the creation of new products which utilize milling residues that
formerly were wasted. In 1962, about half of all milling residues in the
United States were wasted, but by 1970 this had decreased to about a
quarter. (6) Particle board is a relatively new product which can be manu-
factured from residues, and it has found wide acceptance for use in many
items where plywood, for example, was formerly required. Pulp for paper
can also be produced from many types of milling residues as long as they
are debarked.
Table 4 shows percentages of current uses for milling residues sepa-
rately for wood and bark. Almost 70 percent of bark residues are unused,
which is much larger than the 26 percent of unused wood residue. Bark com-
prises around two-thirds to three-quarters of all milling residues that
are ultimately wasted.(7,8) BV contrast, bark makes up only about 10 to 15
percent of felled timber and logging residues. More stringent air pollution
regulations which limit the disposal of bark by burning have provided incen-
tives to find new uses and products from bark. Some new products which have
evolved are bark mulches, compressed fireplace logs, hardboard, and live-
stock bedding; bark is also used in the manufacture of charcoal and in
smelting alloys. However, no single use has yet been found for bark to
match the large quantities which are generated each year. One of its major
drawbacks is that its chemical structure precludes its use in many pulp
products, including paper.
Table 4 shows that a substantial proportion, 19 percent, of milling
residues are already being used as fuel. In 1972, as much as 37 percent
of the energy requirements of the pulp and paper industry were met through
combustion of bark and pulp liquors.(*) Primary manufacturing industries,
in general, are in a position to turn their own readily-available wastes
into energy. Also, mills provide residues for use as fuel to several local
electric-generating plants in the Pacific northwest. Although most of these
plants are old and infrequently-operated facilities, one steam-electric plant
in Eugene, Oregon, operated by the Eugene Water and Electric Board has been
modernized and presently generates electricity eight months a vear exclusive-
ly through the combustion of hogged wood and bark! (9) This plant is probably
26
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TABLE 4. USES OF WOOD AND BARK RESIDUES PRODUCED BY
PRIMARY WOOD PROCESSING PLANTS IN THE
UNITED STATES, 1970(a)
Item Percent
Uses of wood residues
Pulp 47
Fuel 19
Other products (particle board, etc.) 8
Unused 26
100
Uses of bark residues
Industrial fuel and charcoal 23
Domestic fuel 4
Fiber products 1
Miscellaneous products and uses 3
Unused (burned or dumped) 69
100
(a) Reference (6), pp. 33-34.
the exception, though it illustrates that a small proportion of milling
residues are already being used as a fuel source for generating electricity.
Table 5 shows the results of chemical analyses of wood and bark from
several tree species. Table 6 shows alpha-cellulose contents of the wood
from a number of tree species. Alpha-cellulose is defined as lignin-free
cellulose insoluble in 17.5 percent sodium hydroxide and in essence con-
sisting of long chains of glucose molecules with beta-oxygen linkage
between carbon atoms 1 and 4.(10) The alpha-cellulose contents and also the
carbon contents do not vary much among tree species. Wood in general con-
sists of 90 to 95 percent of all types of cellulose and 5 to 10 percent of
volatiles, resins, fatty acids, minerals and other matter.(2) Wood cellulose
has a heating value of 4610 kcal/kg (8,300 Btu/lb) dry weight, whereas the
resins have a heating value of 9388 kCal/kg (16,900 Btu/lb). It is these
resins which mainly account for the differences in the heating values of
different species of wood. Thus, many softwoods which contain larger
amounts of resinous material have somewhat higher heating values than do hard-
woods (see also Table 5).
Water content has an extremely strong influence on the heating value of
wood regardless of the tree species. Water has no caloric value, so the
27
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TABLE 5. CHEMICAL ANALYSES OF WOOD AND BARK OF VARIOUS TREE SPECIES TYPES
00
Wood and Bark
Analyses
(dry basis), % by wt
Proximate
Volatile matter
Fixed carbon
Ash
Ultimate
Hydrogen
Carbon
Sulfur
Nitrogen
Oxygen
Ash
Heating value, kcal/kg
(Btu/lb)
Ash Analyses, % by wt
Si02
Fe203
Ti02
A1203
Mn304
CaO
MgO
Na20
K20
so3
Cl
P2o5
"Southern
Pine" Bark (a)
66.0
33.4
0.6
5.5
56.5
0.0
0.4
37.0
0.6
4940
(8900)
19.0
1.0
*
21.0
*
27.0
5.0
3.0
9.0
6.0
4.0
Pine
Bark
72.9
24.2
2.9
5.6
53.4
0.1
0.1
37.9
2.9
5020
(9030)
39.0
3.0
0.2
14.0
Trace
25.5
6.5
1.3
6.0
0.3
Trace
*
Oak(b>
Bark
76.0
18.7
5.3
5.4
49.7
0.1
0.2
39.3
5.3
4650
(8370)
11.1
3.3
0.1
0.1
Trace
64.5
1.2
8.9
0.2
2.0
Trace
*
Spruce 'b'
Bark
69.6
26.6
3.8
5.7
51.8
0.1
0.2
38.4
3.8
4860
(8740)
32.0
6.4
0.8
11.0
1.5
25.3
4.1
8.0
2.4
2.1
Trace
*
Redwood (b)
Bark
72.6
27.0
0.4
5.1
51.9
0.1
0.1
42.4
0.4
4640
(8350)
14.3
3.5
0.3
4.0
0.1
6.0
6.6
18.0
10.6
7.4
18.4
*
Redwood (b)
82.5
17.3
0.2
5.9
53.5
0
0.1
40.3
0.2
5120
(9220)
PineO>)
79.4
20.1
0.5
6.3
51.8
0
0.1
41.3
0.5
5070
(9130)
(a) Reference (12), pp. 36-37.
(b) Reference (2), p. 60.
* Analyses not included in the given reference.
-------
water content in wood is negatively correlated with the caloric value of the
green wood.
Water contents for green woods and densities for green and oven-dry
woods are given in Table 7 for several wood species. Harvested wood can also
vary in moisture content depending on how it is treated or stored. The water
content of freshly-cut wood can be reduced from 50 percent to 25 percent in
about a year simply by air-drying.(2) in fact, logging slash lying in the
summer sun in western states dries to a 10 percent water content in only 2
to 3 weeks.(13) On the other hand, wood exposed to rain or humid conditions
will increase in water content to values of 70 to 80 percent or more.
TABLE 6. CELLULOSE CONTENTS OF VARIOUS WOOD SPECIES
Alpha-Cellulose Content
Species (7o of Oven-Dry Extractive-Free Wood)
Red maple 44
Southern red oak 44
Quaking aspen 53
Paper birch 41
Balsam fir 45
Black spruce 46
Douglas-fir 48
Jack pine 42
Loblolly pine 47
Western hemlock 45
Western redcedar 48
White spruce 45
(a) Reference (10), p. 30.
29
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TABLE 7. DENSITIES AND HEATING VALUES OF WOOD AND BARK OF VARIOUS SPECIES
U)
o
Species
Douglas-fir, wood'3/
bark
Western hemlock, wood^a'
bark
Ponderosa pine, wood^a^
bark
White fir, wood'a^
Western red cedar, wood'3'
Lodgepole pine, wood' '
Red alder, wood^ '
Oregon white oak, wood' '
Southern pine species, wood^c'
Vermont forest residues (average
representing expected species
mixture) (^'
Oven-Dry Weight
kg/m3 (lb/ft3)
449
432
417
464
369
336
369
321
385
369
593
—
481
(28)
(27)
(26)
(29)
(23)
(21)
(23)
(20)
(24)
(23)
(37)
—
(30)
Green
kg/m3
609
609
801
817
705
385
753
—
—
—
—
—
865
Weight
(lb/ft3)
(38)
(38)
(50)
(51)
(44)
(24)
(47)
—
—
—
—
—
(54)
Moisture
Content-Wet
Basis (percent)
26
29
48
43
48
12
51
—
—
—
—
50
45
Heating
of Dry
kcal/kg
4950
5450
4650
5200
5050
5050
4550
5400
4800
4450
4500
4950
4700
Value
Weight
(Btu/lb)
(8,900)
(9,800)
(8,400)
(9,400)
(9,100)
(9,100)
(8,200)
(9,700)
(8,600)
(8,000)
(8,110)
(8,900)
(8,500)
(a) Reference (9), p. 13.
(b) Reference (11), p. 30.
(c) Reference (12), p. 36.
(d) Reference (2), p. 9.
13.
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Collection and Handling Methods—
Methods of collecting logging residues will probably have to be tailored
to particular regions in the country if they are to be carried out on a con-
tinual basis and if they are to be profitable in the long run. Tree species,
terrain, and primary harvesting methods used in a given region will be among
the factors to determine which methods of collecting residues will be most
productive and least expensive in a given area.
Several facts seem to be universally true with respect to collection
methods. The first is that collecting residues can be much cheaper if as
much is done as possible in conjunction with the primary commercial cut.
For instance, in southern forests in particular, whole trees can be pulled
with four-wheel drive skidders to landing operations before the tops are
removed; then the tops and branches can be mechanically chipped and blown
into a van. The chips will contain a mixture of wood and bark, making them
unsuitable for many pulp products but not detracting from their value as a
fuel source. Other forms of logging residues, such as non-commercial trees
and defective boles, can often be brought to a central location using the
same logging system that was designed for primary harvesting.
Another major consideration is that the minimum size requirement for
the materials to be collected has a strong influence on the costs incurred
per unit area. For example, the final yield per acre will be increased if
all wood greater than 4 feet in length and 4 inches in diameter is to be
collected in an area compared to the yield obtained if only those pieces
greater than 8 feet in length and 8 inches in diameter are collected.(9)
However, the costs incurred in yarding, loading, and transporting the
smaller size materials will be substantially higher. A 1974 study("' cites
this cost as $l,960/ha ($793/acre) for the 8' x 8" minimum size material,
as opposed to $3,066/ha ($l,241/acre) for the 4' x 4" minimum size material.
This difference exists because primary harvesting equipment is not designed
to handle small irregularly-shaped matter in an efficient way. Therefore,
the collection costs will have to be weighed against the gains in residue
volume in deciding what minimum size is acceptable.
In some western forests, a practice called yarding unutilized materials
(Y.U.M.) has been initiated. This was brought about largely in response to
pressure put upon lumber companies resulting from negative public reactions
to the unsightly appearance of slash lying in large clearcut areas. Y.U.M.
methods consist of bringing logging residues to centralized sites near roads
so they can be deposited into relatively neat piles. This is carried out
immediately after primary harvesting has removed the larger pieces of
timber from the area. Y.U.M. practice has several advantages whether or not
the piled-up residue is utilized for fuel or any other purpose. Aside from
the esthetic standpoint, the isolation of the residue from the surrounding
forest makes it more difficult for an outbreak of fire or pests to spread
to the healthy standing timber. Presently, most Y.U.M. piles are simply
burned under supervision or left to stand indefinitely. However, this
method for spatially concentrating forest residues has a clear potential
for making more material readily available for the production of energy.
31
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Relatively little data are available to determine actual energy expendi-
tures entailed in collecting and transporting residues. In a study by
Battelle(2) these values were calculated in terras of Btu's expended to
supply a 50-MWe electric plant with wood fuel over a period of a year
(Table 8). It was estimated that this plant would consume a total input of
410,000 tons of wood per year. The energy expenditures required to collect,
field process (chip), and truck-transport green wood in Vermont were given
as 39,000 kcal/metric ton, 92,000 kcal/metric ton, and 300 kcal/metric
ton-km (140,000 Btu/ton, 330,000 Btu/ton, and 1730 Btu/ton-mile), respec-
tively. The energy expended per ton of wood for all three activities would
then be a total of O.,16x 106 kcal/metric ton (0.57 x 106 Btu/ton), assuming
that the average transportation distance would be 65 km (40 miles). In the
southern forest region, typical hauling distances to the nearest processing
plant are reported to be less than or equal to 24 km (15 miles) for 50 per-
cent of the available residue volume, and less than or equal to 48 km
(30 miles) for 90 percent of the residue volume.(3)
Once the fuel is delivered to the plant, additional energy must be used
if the wood is to be dried in a short time period. Presses can be used for
this purpose, although energy costs can be cut by incorporating a design to
utilize wasted hot air from boiler flue gas. Storage of wood chips over a
length of time should not pose any substantial problems as long as they have
been dried enough to prevent fungi from developing, and as long as they are
stored in an area safe from fire hazards. Very small, dry wood particles
like sawdust should not be stored indefinitely unless very thorough pre-
cautionary measures are taken to prevent spontaneous combustion.
Since wood has a relatively high heating value by itself and a certain
amount of energy is always lost in conversion processes, it appears that an
efficient use of wood energy can result when power plants directly utilize
hogged wood fuel collected from local sources. Hogging is a hammer-milling
process which renders the wood suitable for direct clean burning. There
appears to be economic potential in the operation of steam/electric plants
which can obtain wood from nearby mills or logging operations. However,
the problem of obtaining the necessary volumes of residue impose an upper
limit on the generating capacity of such an electric facility. One rough
estimate is that about 1 ton (metric or English) of bone-dry, or 2 tons of
wet, wood is required per hour to produce one megawatt-hour of electricity.^
Because of this factor, some authors(9) conclude that an optimal generating
capacity for an electric plant using hogged wood fuel would be 50 Mw. Below
this size, scale economy is lost, and above this size, the quantities of
residue necessary might not be available on a continual basis. The pre-
viously mentioned electric plant in Eugene, Oregon, has a generating capacity
of 32 Mw. One conversion process that might extend the generating capacity
up to 75 Mw is a gasification process using direct heating to produce low
kcal fuel from residue volumes of 100-1,000 tons per day. Battelle^2) has
determined that collection and other problems might put an absolute size
limit of 200-250 Mwe on any single wood-fueled plant. Therefore, a generat-
ing plant with wood as its sole fuel might be ideally suited for providing
electric power to small remote communities.
32
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TABLE 8. ENERGY CONSUMPTION FOR COLLECTING, FIELD PROCESSING, AND TRANSPORTING
LOGGING RESIDUES TO A 50-MWe ELECTRIC PLANT REQUIRING
370,000 METRIC TONS (410,000 TONS) PER
Activity
Annual Energy Consumption
kcal x 106 (Btu x 106)
Collecting residues from forest
372,000 metric tons x 39,000 kcal/metric ton
(410,000 tons x 140,000 Btu/ton)
Field Processing with chipper
372,000 metric tons x 92,000 kcal/metric ton
(410,000 tons x 330,000 Btu/ton)
Transporting by truck*
372,000 metric tons x 97 km x 300 kcal/metric ton-km
(410,000 tons x 60 miles x 1730 Btu/ton-mile)
Total
Energy expended per metric ton (ton)
for all activities
14,500 ( 57,400)
34,200 (135,300)
10,800 ( 42,600)
59,500 (235,300)
0.16 (0.57)
(a) Reference (2), p. 119.
* Using an average distance of 40 miles one way, equivalent to a weighted value of
97 km (60 miles) per round trip (64 km or 40 miles empty).
-------
Wood processing industries are in a better position to utilize wood
residues more efficiently when the energy content of the residues can be
converted to steam energy instead of to electrical energy. The pulp and
paper industry, for example, uses about 14 million kcal/metric ton (50
million Btu/ton) of paper produced. About 80 percent of this demand is
required in the form of process steam for the pulping and paper-making
operations.(9) Since under typical boiler conditions 1 kwh of thermal
energy yields only 1/3 kwh of electrical energy, the energy value of wood
is more effectively realized when direct conversion to steam is acceptable.
Projections of Current Trends and Recommendations—
Projections of current trends indicate that forest residue quantities
will continue to increase along with increases in timber production. How-
ever, demand for timber products will also increase. Stephens and HeichelO-0)
estimate that the total timber demand for the year 2000 will be 0.57 billion
cubic meters (20.3 billion cubic feet) whereas the anticipated growth of
timber at the 1970 level of management will be 0.55 billion cubic meters
(19.6 billion cubic feet). Grantham et al.W estimate that the demands
for domestic wood by the year 2000 will show an increase of 0.21 x 10" m3
(7.4 x 109 ft3) over present consumption; 0.14 x 109 m3 (4.9 x 109 ft3) of
this increase is expected to be supplied by logging residues and .05 x 109 m3
(1.8 x 109 ft3) by milling residues. In short, the use of forestry residues
for fuel will be in strong competition with the use of residues for wood,
fiber, and chemical products. Even less waste will be accumulated at mills
as new ways of utilizing mill residues are found, and as present utilization
for such items as pulp and particleboard increases.
One response to the demand for more wood products will be an actual
increase in timber volume. Stephens and Heichel(lO) believe that timber
production could actually be doubled through better, more intensive manage-
ment, and that the Pacific forests in particular show the most potential
for increased productivity. The southern region is also of extreme impor-
tance due to its large area of production.
It is very probable that, if new methods and equipment are developed
for collecting logging residues, at least some of the material collected
will be reclaimed for use in wood products since its value in commodities
may be greater than its energy value. Therefore, new technology may be
required to fulfill both types of needs. For instance, systems may be
developed which will concentrate logging residues at a roadside and then
separate them into two categories depending on their subsequent use New
equipment will be needed to deal with small, irregular pieces and perhaps
to sort them into size classes, debark larger pieces suitable for pulp
chip the smaller branches as well as larger cull trees usable only for'fuel
and so on. Bark is still one form of residue which can be readily collected
from processing mills and for which there is presently not much demand
As an example of future yields production of southern pine bark is expected
to reach 9 million metric tons (10 million tons) a year by the year 2000 (12)
Bark wastes can clearly be utilized for fuel immediately without prior '
technological advancements.
34
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In summary, wood is a valuable energy source because of its high Btu
content and its clean-burning fuel properties. However, most of the resi-
dues easily obtainable from processing plants are probably utilizable for
other higher value products, and residues from logging operations are so
scattered over large areas that a major investment of energy is required to
collect them. If the gathering of logging residues is to be economically
profitable, it will require major improvements in harvesting systems (e.g.,
to coordinate residue collection with primary removal operations) and techno-
logical developments to make present equipment more adaptable. Some motiva-
tion to effect these changes may already be provided by certain problems
not related to the search for new fuels. For example, logging slash in the
West, in particular, is a serious fire hazard during dry months as well as a
breeding site for pests and diseases. Also, slash has to be removed in
areas of short-rotation forestry if a plot of ground is being prepared for
new plantings.
A more complete utilization of forest residues for both wood products
and fuel is necessary. This will undoubtedly require a more intensive and
far-sighted level of management in all phases of forestry.
Animal Manures
Yields, Distributions, and Characteristics—
Animal manures are being produced at the rate of 1.4-1.8 billion
metric tons (1.5-2.0 billion tons) per year in the United States,(1) making
them one of the largest sources of organic waste. Their value as a potential
energy feedstock owes to their availability in large quantities which are
continually being generated in centralized locations, and to the fact that
they are often the source of solid waste disposal and water pollution prob-
lems. If fuel production from animal wastes could be made economically
profitable, farmers would be motivated to provide conversion plants for
animal wastes. The potential for added income from the fuel produced, con-
trolled fertilizer production, and the advantage of having a dependable means
for disposing of the non-recycleable wastes present opportunities for exten-
sive environmental control.
Table 9 presents estimated quantities of solid organic wastes produced
by the four major farm animals in the United States in 1971. Organic solid
wastes are defined as moisture- and ash-free waste materials, and the values
were calculated on the bases of expected percentages of these solids in the
total weight of wastes excreted from each type of animal. From Table 9 it is
to be noted that organic solids from cattle wastes make up the great majority
(88 percent) of that from all major farm animals.
About 50 to 80 percent of all farm animals are in confined conditions/ '
This is especially true of cattle, since they are either dairy cattle resid-
ing in intensively-organized milk producing operations, or beef cattle which
are being raised in increasingly large feedlots in the southwestern and
southern plain states. Table 10 shows the numbers of feedlots of various
size ranges in the United States in 1962 and 1970. The largest feedlots
(8,000 or more head/lot)are the fastest-growing lots, and there is also a
dramatic increase in the absolute numbers of these feedlots.
35
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TABLE 9. WASTES GENERATED BY MAJOR FARM ANIMALS IN THE UNITED STATES, 1971^
00
Animals
Cattle
Hogs
Sheep
Poultry
Numbers of Animals
in U.S. (Thousands)
114,568
67,540
19,560
1,116,680
Amounts of Solid Organic Waste Generated*
Metric Tons (Tons) x 10 /
Kg (Lbs)/Each Animal/Day All Animals/Year
3.72
0.41
0.21
0.02
(8.20 )
(0.91 )
(0.46 )
( .047)
156
10.2
1.49
8.65
176.4
(172 )
( 11.3 )
( 1.64)
( 9.54)
(194.5 )
(a) Reference (1), p. 5.
* Moisture- and ash-free.
-------
TABLE 10. GROWTH IN NUMBERS OF LARGE BEEF FEEDLOTS
IN THE U.S. FROM 1962 TO 1970<»
Total No. of Cattle in
-------
TABLE 11. CHEMICAL COMPOSITION OF FRESH MANURE
FROM BEEF CATTLE
•&.
Constituent
Water
Dry Solids
Volatile Solids
Ash
Carbon
Nitrogen- organic
Phosphorus
Potassium
Calcium
Magnesium
Sodium
Sulfur
Iron
Percent of Wet Weight
85.0
15.0
11.9
3.1
7.5
.32
.06
.15
.15
.06
.15
.05
.06
* PH = 7.3
Density of dry manure = 0.96 kg/1 (60 lbs/ft3)
i
Heating value of dry manure = 3429 kcal/kg
(6173 Btu/lb)
(a) Reference (17), p. 5; Reference (18), p. 31;
Reference (19), p. 19, Reference 14, p. 119.'
38
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The biochemical process involved is aerobic or anaerobic, often by default
depending on the dissolved oxygen concentration in the pond. The solids
settle to the bottom and can eventually be pumped out. In some cases the
liquid can then be used to directly irrigate cropland through use of large
sprinklers or sprayers.
In other dairy operations, the solid disposal system is employed.
Cows are bedded with straw, sawdust or mulch. The manure, which becomes
mixed with and partially absorbed by the bedding, is removed daily and
stacked to dry for a few months before hauling. This is an example of one
solid disposal system utilized by smaller operations. Other types of solid
disposal are used extensively on the large beef feedlots in the southwestern
United States. Manure excreted on the open ground dries very quickly and
odor is minimal as long as the weather is dry. Then it can be scooped into
mounds where aerobic composting processes take place rapidly—in the hot
dry conditions the mounds smolder and smoke from the heat of the composting
reactions. Several times a year it is loaded into trucks with front-end
loaders and hauled to farmers for use as fertilizer. Large feedlots are
also required to have lagoons which can accommodate runoff that takes place
during the wetter winter months.
In the Greeley, Colorado, feedlot area, grain farmers sometimes
receive an allotment of manure for use as fertilizer in relation to the
amount of grain they sell the feeders, and the farmers do their own hauling.
In Texas, Arizona, and California, manure is handled by contractors who
invest in the large equipment necessary to haul and transport the manure,
sell it to the farmers, and spread it on the field. However, in the areas
surrounding the large feedlots in these latter three states, the supply has
been exceeding the demand in recent years, so the excess manure remains
stockpiled on the feedlots. Overfertilization of crops and soil salinity
problems result when manure is over-applied to croplands. Consequently,
none of the contractors in these areas have been netting profits from their
manure-handling systems in recent years, though exact data on costs incurred
for loading and transportation of manure are not presently available. A
recycle system should address salinity removal benefits as well as environ-
mental control of the balanced application of land use chemicals and con-
ditions .
Projections of Current Trends and Recommendations—
Various experimenters using cattle manure in anaerobic digesters have
reported that volumes of .30-.55 cubic meters of "biogas" can be produced
from each kilogram (5-9 cubic feet from each pound) of volatile solids
present in the input material, and an average of 60 percent of this gas is
me thane. C1**20) At least three firms in the United States have announced
plans for the construction of pilot plants to produce methane by anaerobic
digestion of livestock manures. These will be located in Lubbock, Texas
(operated by Ecological Research Associates, Inc.); Optima, Oklahoma
(Calorific Anaerobic Processes, Inc.); and Greeley, Colorado (BioGas of
Colorado, Inc.). The production capabilities of each of these conversion
processes will be 18 x 106 m3 (650 x 106 ft3), 18 x 106 m3 (650 x 106 ft3),
and 24 x 106 m3 (840 x 106 ft3) of synthetic natural gas per year,
39
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respectively^21) The Ecological Research Associates are the originators
of the HYMETH, or high-quality methane generating process. Their proposed
Texas pilot plant will utilize 8.5-17.0 metric tons (9.5-18.5 tons) of
cattle waste from a nearby feedlot in order to determine optimal operating
characteristics of the process.C22) In addition, the Biomass Energy
Institute of Canada started operating a pilot plant in 1971 which produces
methane from manure obtained from swine barns maintained by the University
of Manitoba.
Much technological work remains to be completed with regard to the
conditions necessary for stable, optimal methane production from anaerobic
digesters. If successful processes are developed, systems for collecting
the manure for the digestors will probably have to be improved also. The
solid disposal systems so widely used in large feedlots in the southwest,
in particular, may have to be modified considerably if they are to provide
feedstock for large-scale methane production. This is because their present
handling methods consist of letting the manure become dried and biochemically
degraded before collecting it, whereas fresh manure which still contains
high levels of volatile solids is a much more productive source of methane.
One experiment with dairy manure showed that digestors produced 2.3 times
as much gas using fresh manure containing its original moisture as using
aged manure.(23) Therefore, collection of feedlot manure for methane pro-
duction may be required on a more frequent basis than is currently being
employed. This will entail greater expenditures of energy for collection
and hauling since fresh manure has a greater weight due to the high moisture
content. These added costs will have to be measured against the benefits
of increased methane production.
In the liquid disposal systems presently used in this country, methane
is constantly being generated from the natural anaerobic processes taking
place in the holding ponds and lagoons incorporated into the systems. So
far, however, this methane is simply escaping into the surrounding environ-
ment because it has not appeared economical to invest in the equipment
necessary for collecting it.
Projections of current trends(^ indicate that by 1980 the annual
production of solid organic wastes from cattle in the United States will be
213 million metric tons (235 million tons) . This waste will be generated
in increasingly concentrated locations because the largest feedlots are
now the fastest-growing feedlots, and even dairies with around a thousand
head are common. These various factors all demonstrate the enormous
potential of livestock manures towards synthetic fuel production.
The use of manure residuals as a fertilizer may increase as the costs
of chemical nitrogenous fertilizers (which require fossil fuel energy in
their manufacture) continue to rise. It is fortunate that the use of
manure for fuel production need not compete with its use as fertilizer
The anaerobic processes which produce methane are such that after coro^
pletion, a large fraction of the original weight of the manure is left
in the form of humus-like residues and liquors that are rich in nitrogen (16>
In other words, the nitrogen value of the manure, while low, remains intact,
and could be recycled after processing.
40
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Crop Residues
Yields, Distributions, and Characteristics—
Crop residues are produced in tremendous volumes each year in the United
States, mostly becoming available after the harvest season in the fall. It
is estimated that the total production is about 350 million metric tons
(390 million tons) of organic solids (moisture- and ash-free solids) each
year.d) Grain and oilseed crops, particularly corn, wheat, and soybeans,
are responsible for a large proportion of this production because they are
grown on millions of acres and because their biomass yields per unit area
are also large. Sugar crops like sugarcane and sugar beets are only grown on
a small fraction of the United States cropland but they are capable of pro-
ducing exceptionally large yields of residue per unit area. Table 12
summarizes these yields for six selected crop species.
Grain and oilseed crops generate residues in the form of leaves and
stalks distributed uniformly over the field from which the grain or seeds
were harvested. Residues like these which remain on the fields account for
94 percent of the organic solids produced annually by crop residues. The
remaining 6 percent are from wastes available at centralized locations such
as sugar refineries, mills, canneries, and other food processing plants.
Residues from sugar crops, namely bagasse from sugarcane and pulp from
sugar beets, fall into this latter category because the entire canestalk
or beet must be transported to the sugar mill after it is harvested in
order to extract the sugar. In the case of corn or soybeans grown for
silage, no substantial volumes of residue are produced because there the
entire stalk is harvested and cut up to be used for animal consumption.
The most common practice for processing residual crop materials, like
cornstalks left on harvested fields, is to plow them back down into the
soil before the next planting season. This organic material, essential in
crop rotation systems, is an important soil conditioner because it improves
the air- and water-holding capacity of the soil and it reduces wind and
water erosion. Hay, straw, and leaves are also used as food or bedding for
farm livestock. Sugar beet pulp is processed and sold as an animal
nutrient supplement. Sugarcane bagasse has shown limited use in the manu-
facture of fiberboard and acoustical wall-board, and in some areas it is
burned to fuel the boilers of the sugar refineries where it originates.
Corn cobs are used to manufacture chemicals or are ground into abrasive
particles for polishing or blasting.
Table 13 presents water, ash, carbon, and sulfur contents of various
crop components. The carbon contents given correspond to ultimate chemical
analysis results, though they should not be construed as precise values
because they were calculated from nutritional data. Cellulose contents in
herbaceous plant stalks can generally range anywhere from 25 to 60 percent,
with alpha-cellulose contents ranging from 15 to 40 percent;(26' however,
the carbon contents of the crops shown in Table 13 fall into the more con-
sistent range of 33 to 42 percent. Heating values for dried stalks of
corn, wheat, and many other crop species are on the order of 3600 kCal/kg
(6,500 Btu/lb).^27) Dried bagasse has a larger heating value of about
4400 kCal/kg (8,000 Btu/lb), close to that of wood. Table 14 gives chemical
41
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TABLE 12. YIELDS, PRODUCTION, AND DISTRIBUTIONS OF RESIDUES
FROM SELECTED CROP SPECIES (a)
Residue Yield
Crop Residue (metric tons/ha) (a>°-
Wheat
(straw, stubble)
Corn for grain
(leaves and stalks)
.p. Sorghum for grain
f1-3 (leaves and stalks)
Soybeans for beans
(leaves and stalks)
Sugarcane for sugar
(bagasse)
Sugar beets
(pulp)
3 - 3.5
6-10
6-7
4.5 - 5
20 - 25
8-15
Millions of Hectares
> Harvested (1974) (b)
26.5
26.4
5.6
21.2
0.3
0.5
Total Residue
Production (millions
of metric tons)
80 - 93
158 - 264
34 - 39
95 - 106
6 - 7.5
4 - 7.5
Percent of Total U.S.
Food Production by Top
Five States (b) (1974)
50.2 (Kans., N. Dak., Okla., Wash.,
Mont.)
62.5 (Iowa, 111., Ind., Nebr., Minn.)
88.3 (Tex., Kans., Nebr., Okla., Mo.)
55.6 (111., Iowa, Ind., Mo., Ark.)
100.0 (Hawaii, Fla., La., Tex.)
62.2 (Calif., Colo., Minn., Idaho,
N. Dak.)
(a) Reference (10), p. 32.
(b) Reference (24), pp. 1-130.
One hectare =2.471 acres
One metric ton = 1.102 tons
One metric ton/hectare = 0.446 tons/acre
-------
TABU: 13. CHEMICAL PARAMETERS OF SELECTED CROP RESIDUES^
OJ
Water-%
Crop Residue wet weight
Wheat straw
Corn cobs
Corn stalks and leaves
Sorghum stalks and leaves
Soybean hay
Sugarcane bagasse
Sugar beet leaves
Sugar beet pulp
12.2
9.6
15.6*
66.4**
9.7*
67.0**
8.9*
77.3**
8.5*
50.0**
84.1**
88.7
Ash-%
dry weight
7.2
1.8
7.3
8.6
7.3
3.1
20.6
4.7
Cellulose-%
dry weight
43.6
35.5
33.4
20.5
35.8
48.6
10.7
30.1
Carbon-%
dry weight
39.3
41.8
38.8
37.9
39.7
40.9
32.9
39.9
Sulfur-%
dry weight
0.18
0.47
0.17
—
—
—
0.57
* Sun-dried after harvesting
** Fresh
(a) Reference (25), pp. 104-105.
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TABLE 14. CHEMICAL COMPOSITION OF HARVESTED AND
FIELD-DRIED BAGASSE AND RICE STRAW
Composition
Proximate (%)
Moisture
Volatile
Fixed carbon
Ash
Ultimate (%)
Moisture
Hydrogen
Carbon
Nitrogen/oxygen
Sulfur
Ash
Heating value
kcal/kg
(Btu/lb)
Bagasse as
Harvested ^a^
52.0
40.2
6.1
1.7
52.0
2.8
23.4
20.1
Trace
1.7
2,200
(4,000)
CHt
Bagasse
Field-Dried(a>b)
15.0
71.2
10.8
3.0
15.0
5.0
41.4
35.6
Trace
3.0
3,930-4,590
(7,080-8,260)
Rice
Straw
7.4
5.1
33.6
37.3
0.1
16.5
3,370
(6,080)
Bulk density, stacked ''"'
(lbs/ft3)
(a) Reference (28),
(b) Reference (29),
(c) Reference (30),
(d) Reference (31),
p. 98.
p. 164.
p. 97.
p. 68.
200.4
(12.5)
192.4
(12.0)
analyses in more detail for bagasse and straw.
Collection and Handling Methods —
Crops grown for grain or seed are presently harvested through highly
^
from 18
to 87 per-
Data are not available regarding the enerev that wn,,i A x ^ ,
specifically to collect this material. Thus fS therlh^ b%"qulred 4
incentive for anyone to actually do this. However III r T ec°n°mic
in the nutritional value of corn stalks for ' reCent interest
£lras Kave started
44
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harvest the grain and the residue simultaneously, while grinding and com-
pressing the stover into a van separate from the one containing the grain.
This type of equipment would have obvious potential application towards
collecting residues for conversion to synthetic fuel as well as for food,
because it would eliminate the need to make an additional expedition over
the field for the express purpose of collecting the residues.
Table 13 indicates the extent to which crop parts become dried by the
sun while lying in the field. However, plant material is still very perish-
able even after dehydration. Present methods for handling the large
quantities of bagasse that accumulate at sugar mills in the United States,
consist of treating the bagasse with fungicides and forming it into bales
which are piled outdoors. The piles are covered to keep out rainwater and
are specially constructed to permit ventilation and drying. However, the
effect of deterioration of the bagasse by weather conditions and micro-
organisms produces a dust that is capable of causing a peculiar respiratory
disorder when inhaled. Similar types of problems would probably place
limitations upon the lengths of time and the quantities in which any species
of crop residues could be stored.
Projections of Current Trends and Recommendations—
Agricultural production has substantially increased over the past two
decades, not because marginal land has been converted into cropland but
because new hybrids and improved agricultural technology have increased
the yields per acre for many crop species. As the food productivity from
crops increases, so do residue volumes. Combines that collect food and
residues simultaneously will be essential if the utilization of residues
as an energy source is to be made economically feasible. Such combines
are being developed, but their development was motivated by the increasing
costs of livestock feed. Fertilizer costs are also increasing, so the
potential use of crop residues for fuel will have to compete with their
use for feed and green manure.
Still, the total crop residue volume produced annually is so large
that there may be a sufficient supply for all these purposes. Storage
problems and its limited seasonal availability may be the factors which
utlimately place the heaviest restrictions upon the use of crop residues
for energy production. Feasibility may depend on a biomass conversion
process which (1) can be implemented on a local level so that farmers do
not have to transport bulky residue volumes long distances, and (2)
operates quickly enough so that entire fields of residue can be converted
to fuel soon after collecting and drying. This would eliminate residue
storage problems and the fuel produced would be simpler to store until it
could be supplied to meet local energy needs.
AQUACULTURAL PRODUCTION
Initial Screening
The productivity of plant biomass is higher in aquatic systems than in
terrestrial systems. Thus, particular attention needs to be placed on
45
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biomass sources from both freshwater and saltwater media. Lelth's(33) review
of energy fixation of the major vegetations units of the world shows the
following trends:
TABLE 15. AQUATIC PLANT PRODUCTIVITY IN MAJOR WORLD HABITATS
Mean-kg (dry)/
Habitat m2/yr (Ib/ft2/yr) Range
Marine
open ocean 0.13 (0.03) 0.002 - 0.4 (0.0004-0.08)
continental shelf 0.36 (0.07) 0.2 - 0.6 (0.04-0.12)
algal beds and reefs 0.6 (0.12) 0.5 - 4.0 (0.10-0.82)
estuaries 1.8 (0.37) 0.002 - 4.0 (0.0004-0.82)
Freshwater
swamps and marsh
land and stream
2.0 (0.41)
0.5 (0.10)
0.8
0.1
- 4.0 (0.16-0.82)
- 1.5 (0.02-0.31)
The most productive zones are estuaries, swamps, and marshes. In addition
to these natural production systems, managed aquatic systems whose produc-
tivity is high includes the culture of algae and kelp.
This characterization focuses on three, kinds of biomass sources.
Natural production sources will include marsh plants, especially highly
productive salt marsh species. The other two biomass sources are from
managed systems of algal culture, including kelp and water hyacinth.
Marsh Plants
Distributions and Yields—
Marshlands or wetlands border the coastlines and river margins of the
United States. Extensive wetlands occur in Florida, Louisiana, and Georgia.
For example, 1,520,000 hectares (3,750,000 acres) of coastal marshes are
found in Louisiana^) ; the saline, brackish and freshwater marshes extend
80-97 km (50-60 miles) inland in certain parishes. There are smaller
marshes in the northeast, northwest, and Great Lakes region.
Primary production of marshes is high when compared to production in
terrestrial communities.UiJ Four of about 25 species of plants exhibit
high production:^<» smooth cord grass (Spartina alternlflora) . common reed
(Phragmites communis), bulrush (Scirpus spp.), and cattail (Typha spp )
A profile of their highest observed production and locales are~ihown in*
Table 16. These totals range from 19 to 64 metric tons dry weight
46
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TABLE 16. BIOMASS PRODUCTION FOR FOUR
SPECIES OF MARSH PLANTS
Species
Above Ground Production
kg (dry)/m2/yr (Ib/ft2/yr) Locale
Source
Spartina alterriiflora 2.000-2.300 (0.410-0.471) Georgia Odum(35)
Long Island Harper(39)
Germany
Phragmites communis 2.695
Scirpus lacustris 6.400
Typha latifolia and
T. angustifolia 1.905
(0.552)
(1.311)
(0.390)
New Jersey Jervis
(41)
biomass/hectare/year (8.5-28.5 tons/acre/yr).
Production of these species generally decreases from south to north.
Figure 1 shows this general trend. This means that higher yields will be
found in California, Florida, the Gulf states and Georgia than states
further north.
Elemental compositions of these marsh plants(36) are provided in
Table 17. Percent carbon averages about 44, percent nitrogen (N) about 2,
and phosphorus (P) <1. Carbon-to-nitrogen ratios are 20-30 and a little
below the range (30-40) for terrestrial plants.(37) Variations in percent
N and P reflect nutrient availability in the environment.
TABLE 17. ELEMENTAL COMPOSITIONS OF
SELECTED MARSH PLANTS
Percent
Species C
Spartina alterniflora 43.0
Phragmites communis
Scirpus lacustris
Typha latifolia and 44.9
T, angustifolia
Percent
N
1.6
1.8
-
2.1
Percent
P
0.3
0.1
-
0.2
C:N
(atomic)
26.9
-
-
21.4
The values are averages of individually reported studies; the number of
studies ranges from 1 to 13 for a given cell of information.
Studies of energy flow reveal that Spartina sp. in Georgia accounts for
2/3 to 3/4 of the plant production in the marshes.(38) In this and three
47
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3500
3000
E 2500
o
o
E
.5 2000
CO
„*• 1500
'e
-J?
c
£ 1000
500
D Spjar^ina a[ternjfjorg Production
© SgcirtirKJ olternijiqra Biomass
^T Spjartina pqten_s Production
• Spirting patens Biomass
D
•(r
Georgia North Virginia Delaware New New York
Carolina Jersey
Location of Marsh
Figure 1. Comparison of production and biomass estimates
of Spartina alterniflora and Spartina patens
along a south to north gradient in Atlantic
coast marshes.(36)
48
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other marshes, efficiency of conversion of incident radiation to biomass is
less than 1 percent. However, the large amounts of biomass produced com-
pensates for the seemingly inefficient energy conversion.
Current uses of these marsh plants reflect their role in ecological
systems rather than their direct consumption as human food or fuel per se.
Wetland vegetation buffers the mainland from erosion by storms and tides.
The decomposing marsh plants form the basis for many of the nearshore
foodwebs, including shellfish and shrimp. Also, the marsh plants provide
food and cover for many species of waterfowl, furbearers, and nurseries for
many marine organisms.
Cultivation, Harvest, and Storage—
Planting and cultivation practices are well developed, particularly for
Spartina alterniflora.(42) Machines to harvest seeds, prepare soil and trans-
planting are used if the substrate is firm. Experiments have shown that
single stems should be spaced 2.3 cm (0.9 inch) apart. The best months for
transplanting are in the spring, although it may be done during other sea-
sons. Seeding can be done at the rate of 100 seed/m . (11 seeds/ft2)
After two growing seasons, artificially propagated marshes are little
different from long-established natural marshes. Addition of nitrogen and
phosphorus fertilizers can increase growth.
The life form of the four species of marsh plants is a slender stalk
of relatively soft tissue from 0.6-1.2 m (2-4 ft) tall. Stands of marsh
plants number 700-1000 shoots/m2 (65-93/ft2)(43) and are essentially mono
cultures. For example, cordgrass grows as a single species community in
salinity ranges beyond the physiological ranges of most plants.
There is an annual die-back each year in the fall and winter, but since
the plants are perennials new shoots grow from root stock each spring in
temperate zones. Fungi attacks the decomposing plants. The presence of
water also accelerates physical deterioration.
There are no known studies on energy costs of harvesting marsh plants.
Indeed, harvest methods are not well developed. Cattle grazing and mowing
of pump-out pastures are practiced, however.
Projections of Current Trends and Recommendations—
Harvest methods for marsh plants are not well developed. One of the
major engineering obstacles of harvesting marsh plants is the manufacture
of marsh buggies or hover craft that minimize compaction damage to the soft,
mucky soils of marshes.
The wetland vegetation, particularly salt marshes, represents an
extensive, good biomass source from an environment in which only these
particular plants can grow. Future use of marsh plants for fuels must be
tempered by the realization of the ecological value of intact, natural wet-
lands and the laws and regulations that control their development. Because
of the limited range of the species on the natural aesthetic appeal of
wetlands, it does not appear a good prospect for major fuel conversion
effort.
49
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Water Hyacinth
Distributions and yields—
Water hyacinth (Eichhornia crassipes) grows in subtropical and tropical
regions of the world. Thus, in the United States it is concentrated in the
southeast, particularly in the area of the lower Mississippi River and its
distributaries.(44) The plant is considered a weed since it grows rapidly
and chokes many navigational canals.
The productivity of water hyacinth is not well established for typical
growing conditions. Maximum production occurs in the period March through
October and attains standing crops of about 25 metric tons/hectare (dry
wt).(44) Projected values for productivity are about 150 metric tons/
hectare/year.(45) This projection assumes optimum growth conditions.
Actual productivity under natural conditions would be much less than this
projection.
Boyd and Blackburn reported that percent dry matter for water
hyacinth averages about 6, while cellulose is about 23 percent dry weight.
They also show that proximate composition of water hyacinth varies by
season. Parra and Mortenstine(47) reported that environmental conditions
also cause the composition to vary from place to place. Mean chemical
compositions from 19 locales in Florida are shown in Table 18. Note that
carbon is about 1/3 the dry weight biomass.
The most important limiting factor is temperature. The plant is highly
susceptible to frost and exposure to temperatures above 34 C. Water
hyacinth does not grow in water whose salinity is greater than 15 percent
of seawater. Also, dissolved oxygen and pH (3-10 range) affect growth.
Water hyacinths have little or no commercial use at present. Indeed,
considerable effort is spent on their eradication. However, there are
several proposed uses, e.g., compost, cattle feed, and living filters in
sewage treatment.
Cultivation, Harvest,and Storage—
Propagation by man is generally not deliberate. The plant reproduces
two ways. About 50 seeds per capsule are deposited on the hyacinth mat or
sink to the bottom of the waterway where they germinate. Rhizomes produce
vegetatively, doubling in approximately 2 weeks.(44)
Harvest procedures are not well developed. Presumably, large suction
devices could slurp up hyacinth mats. To assure continued propagation via
rhizomes, an underwater cutting device may be another must. Barges could be
mounted with harvesting devices including drying kilns.
Storage must consider the water content which is about 95 percent. It
would be necessary to dry the plants to reduce the problems of decomposition.
Projections of Current Trends and Recommendations—
Attitudes toward water hyacinth as a noxious water weed can be altered.
The plant can be used as a biomass source for fuels. Since water hyacinth
50
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TABLE 18. CHEMICAL COMPOSITION OF WATER
HYACINTH
Element
Aluminum
Calcium
Carbon
Chromium
Copper
Iron
Magnesium
Manganese
Nitrogen
Phosphorus
Potassium
Sodium
Zinc
Ash
C/N ratio
Chemical
Composition
(% dry wt)
0.3
1.7
34.9
<.01
<.01
0.4
0.6
0,01
1.6
0.3
3.8
0.6
<0.01
19.2
23.3
uptakes many elements, the plant is also a candidate for living filters in
sewage lagoons.
Seaweed and Freshwater Algal Culture
Distribution and Yields—
Freshwater algae grows in waterbodies throughout the country. Marine
algae is found in coastal environments. Algal productivity tends to be
higher in more southern latitudes.(48)
Most of the research in algal productivity has been in mass culturing
experiments. Yields reach 169 metric tons (dry weight biomass)/hectare/year
(75 tons/acre/yr).(49>
Algal yields in freshwater exceed those of marine environments.
Goldman, Ryther, and Williams(48) indicate that yields 10-20 g (dry wt
51
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7 2
biomass)/m /day (0.002-0.004 Ib/ft /day) have been reported for freshwater
algae in Europe. On an extrapolated basis this is the equivalent of
36.5-72.5 metric tons/ha/year (16.2-32.3 tons/acre/yr). The same authors
review that 5-12 g (dry weight biomass) (0.01-0.03 Ib) has been attained
in marine mass cultures. This equates to about 18 metric tons/hectare/yr
(8.2 tons/acre/yr) for the lower value assuming sustained yields are
possible.
Detailed chemical compositions for freshwater algae have not been
located. Algae is well known for its high protein content. Table 19 shows
composition for the giant California kelp, Macrocystis pyrifera.(50) xhe
kelp is about 88 percent water.
Cultivation, Harvest, and Storage—
Turnover rate of new fronds is about 6 months. Propagation can be
achieved by experimental manipulations.
Rafts of rope networks serve as substrate for kelp plants in some
experimental facilities in southern California waters. The raft covers
about 3 hectares (7.4 acres) and is anchored 9 meters (30 ft) below the
ocean surface. Once successful, ocean energy farms could be much larger.
The common red seaweed, Eucheuma isiforme, is being grown experimentally
as a source of chemical colloids. Harvesting methods at the present are by
hand in natural populations and occur at the rate of 4,000 metric tons per
year (4408 tons).(52) Marine farms could support about 1,100 plants/hectare.
Each hectare could yield 300-500 wet metric tons of harvested
organic matter/year.(50) ^he cultures would do best in upwelling areas.
Harvest and storage regimes are being worked out. '
TABLE 19. COMPOSITION OF THE GIANT
CALIFORNIA KELP
Percent of
Component Dry Weight
Ash (45)
KC1 29
NaCl 7
Na2S04 4
Ca, Mg 4
Volatile Solids (55)
Carbohydrates <64
Proteins and Fats Ca. 10
52
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Projections of Current Trends and Recommendations—
Mariculture as a biomass source for fuels merits consideration. In
principle, the high productivity and vast cultivation area potential would
seem ideal. However, the embryotic level of cultivation and certain engi-
neering developments as well as unusual susceptibility to adverse weather
conditions, suggest this biomass source will be one of the last developed.
The literature on aquaculture is vast. A closer look at this litera-
ture is needed before projections can be made. One of the problems with
small body sizes is the reduced volumes of material for handling. Another
is the energy subsidy needed to maintain the growth in the log phase.
Dykyjova^52' has shown that emergent marsh plants (see Marsh Plants) are
more productive than cultures of uni-cellular algae under similar climatic
conditions. However, algae can be grown in conditions not conducive to
growth of marsh plants. Szetella, Krascella, and Blecher(53) detail many
other aspects of mariculture farming and fuel production.
ENERGY CROPS
Initial Screening
Energy crops are those crops grown especially for their potential as
sources of energy. Some of the important criteria for recognizing a good
energy crop include the following:
• High net ecological productivity
• Easy cultivation of large acreages
• Sound genetic stock for resistance to disease and pests.
Several crops meet these criteria. They include sugarcane and sugar beets.
Sugarcane
Distributions and Yields—
Sugarcane (Saccharum afficinarum) is grown in Florida, Louisiana, Texas,
Hawaii, and Puerto Rico. The approximate areas are provided in Table 20.
In Florida sugarcane is being grown in three counties peripheral to Lake
Okeechobe.(54) South central Louisiana is the principal growing area in
Louisiana, with small acreages in central Louisiana.(55) Four of the
Hawaiian Islands have sugarcane; almost one-half of the cultivation occurs
on the Island of Hawaii.
Yields of cane are expressed in various ways. Generally, only the
above-ground portion actually utilized for sugar production is considered.
When yields are given as total biomass, the sugar producing stalks constitute
about 70 percent and the tops, root system, and soil approximately 30 per-
cent. Yield is also a function of geographical location and cultural
practices. For example, the ratoon system produces 4 harvests in 5 years.
In Florida and Louisiana yields average 105 metric tons biomass/hectare
(wet weight) (47 tons/acre). Wet weight yields range from 155 to 185 metric
tons/hectare (69-83 tons/acre) for certain varieties. Experimental
53
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TABLE 20. GEOGRAPHIC LOCATIONS AND AREAS OF SUGARCANE
CULTIVATION IN THE UNITED STATES(24)
Location
Florida
Louisiana
Texas
Hawaii
Puerto Rico
Area
Hectares
107,000
130,000
14,000
40,000
53,000
Acres
272,000
331,000
35,700
101,000
132,000
varieties and conditions have produced even higher yields. Assuming 30
percent dry matter, then average dry weight yield is about 30-35 metric
tons/hectare/year (13-16 tons/acre/yr).
Chemical composition of sugarcane is shown in Table 21. Note that
water content is about 70 percent. Ash content for sun-cured sugarcane
(aerial part) is about 4 percent.
Ecological limitations on sugarcane production are temperature and
availability of soil moisture. Sugarcane is susceptible to freezing.
Soil temperature must attain 21C (70 F) to start the growing season.
Sugarcane needs adequate rainfall. Also, pests such as rats, sugarcane
borer, and certain weeds are problems. Management limitations include
milling facilities and planting methods. It is thought that sugarcane pro-
duction could be improved by harvesting annually in Florida and other main-
land states.
Current uses of sugarcane are principally for the production of cane
sugar. Of course, some of the land is devoted to seed production.
Bagasse and other cane residues are used for soil amendments, papermaking,
bedding for animals, and wallboard.(56)
TABLE 21. COMPOSITION OF SUGARCANE
Mean
Percent of
Component Wet Weight
Dry Matter 24-27
Fiber n_16
Soluble Solids 10-16
54
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Cultivation, Harvest, and Storage —
Nearly all phases of sugarcane farming are mechanized. Several experi-
mental stations research new varieties; the practice and development of sugar-
cane farming is an active area.
Fields in Hawaii are planted and harvested continuously. In Florida
and Louisiana the ratoon system is used; this harvest system depends on
growth from root stocks for 5 years with 4 harvests. Experimental work
should show that, by reducing the distance between row spacing or by
broadcast planting, production of biomass can be greatly increased.
After harvesting in the field, sugarcane can be attacked by fungi.
Usually the cane is processed rapidly enough that deterioration is not a
problem.
Projections of Current Trends and Recommendations —
There is essentially no more land into which to expand sugarcane pro-
duction in Hawaii, so expansion in the United States will be limited to the
south southern regions of the continental U.S. Sugarcane has been reintro-
duced into Texas in the last few years and its area there is expected to
increase. Presumably, sugarcane could be grown in other southern states.
Sugarcane is one of the most productive crops in the world. Genetic
and breeding programs could accelerate the identification of varieties
whose biomass yields are even greater. Different management practices can
also improve the yield.
Sugar Beets
Distribution and Yields —
Sugar beets have been grown in the western and midwestern United States
for many years. Not only has sugar and beet pulp for cattle been processed
from the root, but ;ifter harvest the leaves or tops have been grazed by
cattle and ensiled for animal feed. Although sugar beets are cultivated
in 17 states, about 81 percent are grown in 8 states; Table 22 shows the
hectarage for
Productivity of sugar beets expressed as metric tons (wet weight)/
hectare/year ranges from 25 to 61 (11-27 tons/acre/yr) . '"' The following
highest average yields for the period 1973-75 are: Washington; 58 metric
tons/hectare/yr (26 tons/acre/yr), and California; 57 metric tons/hectare/yr
(25 tons/acre/yr).'57) In general, an average annual yield of about 43
metric tons is considered a good crop. Assuming dry weight to be 20 percent
of wet weight and tops to be about 15 percent of total plant biomass, the
average productivity of the sugar beet is about 10 metric tons (dry weight)/
hectare/year (4 tons/acre/yr). Since about 614,000 hectares (1,520,000 acres)
were in beet cultivation in 1975, there were about 21,000,000 metric tons
(23,000,000 tons) of sugar beets produced in that year.
Biological and management limitations to sugar beet production ar.
-------
needed as a fertilizer.C59) Nematodes are the major pest and crop rotation
is a must to regulate this worm. In certain areas of the west, sugar beet
production has ceased because of high nematode infestations.
Sugar beets are utilized as a major source of raw sugar in the United
States. Pulp from the roots is used as a food additive for cattle produc-
tion. Tops are used for feed to animals.
Cultivation, Harvest, and Storage—
Sugar beet technology is well advanced. Most all phases of sugar
beet production and processing are mechanized. Pest management systems
have been developed. Harvesting machines have gone through several genera-
tions of design.
TABLE 22. GEOGRAPHIC LOCATIONS AND AREAS OF SUGAR
BEET CULTIVATION IN THE UNITED STATES
Area
Locale Hectares Acres
California
Minnesota
Idaho
Colorado
North Dakota
Nebraska
Michigan
Washington
132,000
79,000
64,000
63,000
53,000
39,000
37,000
33,000
326,168
195,206
158,142
155,671
130,961
96,368
91,426
81,542
Projections of Current Trends and Recommendations—
Demand for sugar will probably increase and thus areas of cultivated
sugar beets will also increase. Sugar beets can be grown in many parts of
the country where they are not currently being cultivated. The technolo-
gies of sugar beet production, processing, harvesting and storage are welJ
advanced. The recycle of waste products is so extensive that little, if
any, energy could be recovered from this resource.
SILVICULTURAL PRODUCTION
Initial Screening
A literature survey was initiated to select those tree species which
appeared to have potential for biomass production on a large scale. The
criteria for selection of these species were high productivity (rapid
56
-------
growth), ease of establishment, vigorous regeneration, and wide geographical
distributions covering large areas of the U.S. capable of supporting trees.
A list of the tree species evaluated is given in Table 23.
Potential Silvicultural Species
The species of trees initially selected as having greatest potential
for commercial production of biomass are all hardwoods (Table 24). These
species are rapid growing, are easily planted and sprout vigorously from
stumps and are generally pioneer or subclimax successional species.
Several of the species (e.g., sycamore) are grown commercially in planta-
tions and data are readily available on production, but some (e.g., tree of
heaven) have not been studied extensively and information is sparse.
Distributions, Yields, and Characteristics—
The tree species under consideration (Table 24) for which data are
available have similar chemical characteristics. Oven dry weight is
approximately 50 to 60 percent of wet weight, ash content is 1 to 2 percent
of dry weight and cellulose content is approximately 35 to 40 percent
except for Eucalyptus which may be 8 to 10 percent higher.(28) Energy con-
tent for trees (including foliage, branches and bole) ranges 4500-5000
kcal/kg (8100-9000 Btu/lb). Above ground biomass yields of selected tree
species are presented in Table 24.
Poplars (Populus spp.) and cottonwoods have the widest distributions
of the trees selected. Eastern cottonwood is (P_. deltoides) found in
eastern North America from Quebec and southern Ontario west to North Dakota,
south to southern Texas and northern Florida; it is absent in the higher
elevations. Best growth occurs in alluvial bottomlands of the Mississippi
River and its tributaries from Missouri to Louisiana. Black cottonwood
(P_. trichocarpa) is found in the Pacific Northwest forests from southeast
Alaska to the mountains in southern California; its range extends eastward
to Montana, central Idaho and northern Utah and Nevada. The largest trees
are found in moist areas at low elevations. Cottonwoods exhibit rapid
growth of up to 2.5 cm (1 in.) and 1.5-2.4 m (5-8 ft) in diameter and
height, respectively, per year.(65) They sprout vigorously from stumps and
are thus good for coppicing, e.g., regeneration from stumps. Cottonwoods
are intolerant of shade and require moist soil.(°"' Other poplar species
which may be good prospects for intensive management are Lombardy poplar
(P_. nigra var. italica) , an introduction from Europe and used extensively
for windbreaks and as ornamentals, and poplar hybrids. Lombardy poplars
have been planted extensively in the western U.S. and do not appear to
require as moist conditions as cottonwoods. Various hybrids are being
experimentally developed to obtain fast growing and hardy trees.
Sycamore (Platamis occidentalis) is another rapid-growing tree common
in the eastern U.S. It is found east of the Great Plains, south to Texas
and Georgia, and north to the Great Lakes and New England. It is limited
in the north by cold temperatures and in the west by insufficient moisture.
In natural stands, its growth is exceeded only by cottonwoods and sometimes
a few pines, soft maple and black willow.(65) Sycamore is easy to estab-^
lish in plantations and sprouts quickly from stumps after coppicingo It is
57
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TABLE 23. TREE SPECIES CONSIDERED FOR
SILVICULTURAL PRODUCTION
Common Name
Scientific Name
(a\
Alder, Europeanv '
Alder, red(a)
Ash, white
Basswood
Birch, gray
Birch, river
Cherry, pin
Cottonwood, eastern
Cottonwood, black
Eucalypts^
Fir, Balsam
Fir, Douglas
Fir, white
Larch, western
Locust, black
Maple, bigleaf
Maple, red
Maple, silver'
Mountain-ash
Oak, black
Oak, live
Oak, red
Pine, loblolly
Pine, longleaf
Pine, slash
Pine, white, eastern
Pine, white, western
Poplar, hybrid^'
(a)
.(a)
Alnus glutinosa
Alnus rubra
Fraxinus americana
Tilia spp.
Betula populifolia
Betula nigra
Prunus pennsylvanica
Populus deltoides
Populus trichocarpa
Eucalyptus spp.
Abies balsamae
Pseudotsuga menziesii
Abies concolor
Larix occidentalis
Robinia pseudoacacia
Acer macrophylum
Acer rubrum
Acer saccharanium
Sorbus americana
Querqus velutina
Querqus virginiana
Quertme rubra
Pinus taeda
Pinus palustris
Pinus elliottii
Pinus strobus
Pinus monticola
Populus
58
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TABLE 23. (continued)
Common Name
Scientific Name
(a.)
Poplar, Lombardyv '
Redcedar, western
Sassafras
Spruce, blue
Spruce, Sitka
Sweetgum
Sycamore
(a)
Tree of heaven (Ailanthus)
Yellow poplar (Tuliptree)^
(a)
Populus nigra
var. italica
Thuja plicata
Sassafras albidum
Picea pungens
Picea sitchensis
Liquidambar styraciflua
Platanus occidentalia
Ailanthus altissima
Liriodendron tulipifera
(a) Tree species deemed as having highest potential for silvicultural
production of biomass, based on ease of establishment, growth
rate, regeneration and distribution.
59
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TABLE 24. ABOVE GROUND BIOMASS YIELDS OF SELECTED TREE SPECIES
Name
Eastern cottonwood
Black cottonwood
Hybrid poplars
Sycamore
Red alder
Eucalyptus spp.
Yellow poplar forest
Temperate deciduous forest
Location
Louisiana
Washington
Washington
Pennsylvania
Georgia
Oregon
Washington
Washington;
British Columbia
California
Growth
Seedling
—
Seedling
Coppice
Seedling
Coppice
Seedling
Coppice
Seedling
— —
Seedling
Seedling
Seedling
Yield (dry wt.)
Mt/ha/yr
(ton/ac/yr)
3.8-12.1
(1.6-5.4)
10.1
(4.5)
9.2
(4.1)
2.2-13.4
(1.0-6.0)
9.0
(4)
17.9
(8)
0.4-37.0
(0.2-16.5)
6.7-9.0
(3.0-4.0)
13.2-22.2
(5.9-9.9)
22.4
(10)
4.5-56.0
(20-25.0)
34.5-62.0
(15.4-27.7)
24.1
(10.8)
12.0
(5.4)
Source
60
28
60
60
28
28
61
62
28
60
28
63
64
* Forest includes trees and understory.
-------
very shade intolerant and requires the use of herbicides for seedlings to
survive. Seedling growth is rapid, up to 1.5 m (5 ft) the season after
planting. tbl.> Moist soil is required for optimum growth.
Red alder (Alnus rubra) is a very rapid growing tree found along the
Pacific coast from southeast Alaska to southern California. It is usually
within 160 km (99 mi) of the coast and below 760 m (2500 ft) elevation.
Best growth is below 460 m (1500 ft). Red alder requires humid to superhumid
conditions with at least 635 mm (25 in) of precipitation annually(65). con_
sequently its range is quite limited by its habitat requirements. It'is
very intolerant of shade(66) and easily damaged by fire. Stands are some-
times defoliated by tent caterpillars. (67) Re(j aider is one of the most
important timber trees in the Northwest.(°5' Alders are a pioneer species
and are important in the ecosystem for their ability to fix nitrogen and
thus increase the soil fertility. Because of this ability, alders are
often planted in disturbed areas and are able to survive where other species
cannot. During a 20-year rotation, red alder may increase soil fertility
by the addition of nearly 165 metric tons per hectare (74 tons per acre) of
nitrogen. (62) European alder (A_. glutinosa) has been planted on strip-mined
lands. Yields on strip-mined lands will be reduced by the low soil fertility
and will be affected by the available soil moisture, but site protection
and improvement would result along with the production of wood fiber.(68)
Eucalyptus spp. are among the fastest growing trees in the world. They
are natives of Australia and New Zealand but have been introduced into many
parts of the world. They are currently grown in California and Hawaii.
Eucalyptus robusta is the most abundant hardwood in Hawaii.(""' .E. globulus
is one of the more common species in California. Eucalypts are very fire
sensitive and may be susceptible to frost. It is pest resistant and sprouts
profusely from stumps, lending itself to short rotations. Eucalypts pro-
duce dense wood, have a high cellulose content and low water content (about
40 to 45 percent) . _E. globulus grows best in well-drained soils with ample
moisture but is tolerant of poor shallow soils. Seedlings of E^. globulus
may reach 18.3 m (60 ft) in nine years.(28) Sources of detailed information
on eucalypts grown in the U.S. have not been identified.
Yellow poplar (= tuliptree, Liriodendron tulipifera) is a rapid growing
tree of the eastern U.S. It is found west to Michigan, south to central
Florida, and north to southern New England. It requires moist, well-drained
soils and is intolerant of shade. Annual diameter growth may be 0.8 cm
(1/3 in.).(65) Seedlings are difficult to transplant, but stumps sprout
vigorously. Because this species is usually considered together with other
hardwoods, specific information is not readily available.
Soft maples, particularly silver maple (Acer saccharinum), are rapid
growing trees. Silver maple is found in the eastern U.S. west to Minnesota,
south to Florida and Louisiana. It is absent in the higher elevations and
along the Atlantic coast. It is a bottomland species, requiring good soil
moisture. Stumps sprout vigorously and stems may grow 1,3 cm (0.5 in.)
in diameter annually.(65^ It is not tolerant of shade/66' Specific infor-
mation on growth rates is lacking as it is generally classified with other
forest species.
61
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The tree of heaven (Ailanthus altissitna) is a very rapid growing species
introduced from Eastern Asia. It is used as an ornamental but has escaped
and become naturalized in the eastern U.S/67) It is a very hardy species,
growing well in hard packed soils.(66) It sprouts vigorously from stumps
and may grow as much as 2.5 cm (1 in.) a day. It has been reported to grow
3.6 m (12 ft) in a season.(67^ The flowers have a very noxious odor.
Because it is not considered of commercial importance as a tree and is
planted as an ornamental, data on growth, yield, and air pollution charac-
teristics are very sparse.
Cultivation, Harvest, and Storage
It is widely held(28,60,70) that intensive management practices, such
as those currently used in agriculture to produce large amounts of food and
fiber, can be applied to various tree species to produce large amounts of
biomass for conversion into energy. Such management practices for energy
plantations are still in the initial stages of development and definitive
silviculture techniques for the tree species likely to be used for planta-
tions have not been established. However, based on experience with inten-
sively cultivated agricultural species and research with tree species such
as sycamore, a generalized management scheme, including cultivation, harvest-
ing, and storage techniques, can be envisioned for energy plantations using
the hardwood species having potential as an energy crop.
Cultivation techniques begin with the selection and preparation of the
energy plantation site. As with any crop, the best sites are those with
relatively flat, fertile land and good moisture availability.^ ' Energy
plantations will have to compete with agricultural and other uses (sub-
developments, urban expansion, etc.) of this land. The decision governing
land use will be strongly influenced by the economics of the various
competing uses. Marginal lands represent another kind of site that have
potential for energy plantations. These lands include those that have been
surface mined, those with infertile soils and steep slopes, and others
with deficiencies that make them unsuited to agriculture. Energy planta-
tions on such land will be less productive than those with better soil,
slope, and moisture conditions. At the same time, tree crops on these
lands will often result in considerably higher productivity than would be
realized under natural, unmanaged conditions and will offer potential for
reclamation and improvement of these marginal lands.
Upon selection of the site for the energy plantation, the land must be
prepared for planting. This involves clearing and tilling, followed by
treatment with herbicide and fertilizer.(28,61) Herbicide treatment will
reduce competition by weeds for valuable nutrients. The fertilizer will
augment the natural soil nutrients and act to increase productivity. The
ratio of nitrogen, phosphorous, and potash will vary according to soil
characteristics and species to be planted.
The prepared land will be planted with the tree species of choice.
Most plantings will involve the use of seedlings reared in a nursery. The
spacing of the seedlings is important. The seedlings must be placed close
enough to result in a dense stand of trees that intercepts most of the
incident sunlight and grows rapidly to provide a large amount of biomass per
62
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hectare. Too close spacing results in competition among seedlings for light
and nutrients and reduced growth and productivity. Experiments with seed-
ling spacing have indicated that 1x4 (seedlings in each row spaced 1 foot
[0.3 meters] apart; rows are 4 feet [1.2 meters] apart) or 2 x 4 are most
productive for energy crops.(28) Trees for energy can be spaced considerably
closer than trees for timber. Some experimental work done with vegetative
propagation results in considerably less effort and cost than seedling
transplants of sycamore.(61) Stems of sycamore from 0.3 to 1.2 meters
(1-4 feet) long were placed horizontally in furrows and covered with 8 to
15 cm (0.3-0.5 feet) of soil. The buds on the buried stems produced new
plants. Because most of the hardwood species considered for energy planta-
tions can reproduce from coppice or root stalk (the alders), only a single
planting will be necessary to produce multiple short rotation crops.
Cultivation practices after the planting of the tree crop may include
treatment with pesticides and fertilizer and irrigation. The frequency and
kind of application will depend on the location of the plantation and the
species grown. In most cases, one application of herbicide during the first
year of growth will be sufficient for weed control. The shading by the
dense canopy in later years will act to reduce weeds. Insecticides and
fungicides will likely be needed periodically throughout the rotation
period. Application of pesticides of all types after the first year of
growth will probably have to be done by aircraft. The dense stands will
prevent the effective use of ground-based application techniques.(")
Irrigation may be necessary since most of the tree species do require
significant quantities of moisture for high productivity. Irrigation may
be particularly needed for plantations on marginal soils or where natural
precipitation is low or out of synchrony with the growing season.
Fertilization will be needed if high yields are to be obtained. The
amounts and kinds of fertilizer will depend on the natural fertility and
other important characteristics of the soil and the tree species that
is being grown. In addition to nitrogen, phosphorus, and potassium normally
required, other additives, such as lime in acid soils (especially on surface
mined lands), may be required to achieve high growth rates. Commercially
available fertilizers as well as sewage are likely sources of these nutrients.
The treatment of land with liquid sewage merits special consideration in
areas where it is readily available—primarily near large urban centers.(70)
Sewage is nutrient rich and the spreading of this material on land as an
ameliorant rather than discharging it to a river or lake shows much promise
in reducing the costs of fertilizing as well as the costs for further
sewage treatment and disposal.
It is envisioned that all of the aspects of cultivation, from the
initial preparation of the site through water, fertilizer, and pesticide
application will be highly mechanized and that labor requirements would be
comparatively small.
Harvesting procedures for tree plantations are based on a short rota-
tion time of 2 to 6 years.(28.60»7°) The fastest growing species (Eucalyptus
and alder) may be cropped every 2 years on good sites. Slower growing
63
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species and plantations on poor quality sites should be harvested at longer
intervals, up to 6 years. The timing of the harvest during the year will
depend on several factors. The above ground portions of the trees can be
taken at any season without endangering the regenerative ability of the
stumps or roots.(60) However, cropping in mid summer (August) may result
in frost damage to the new buds in the fall of the year and consequently
slow the growth rate of the succeeding crop. Another influencing factor is
the operating schedule of the processing plant. In most cases, it is
advantageous to convert the biomass to energy relatively soon after harvest
to eliminate the need for costly storage facilities and prevent potential
degradation of the crop by pests and other causes. Ideally, the harvest
should be at a time that will permit processing quickly. In cases where
several different kinds of biomass are processed by a single facility, the
timing of the harvest should coincide as much as possible with the time when
the facility can best process the material. Short-term storage may be
required in many cases. A third factor influencing the time of harvest is
the overall objectives of the energy plantation. If energy yield is the
only objective, harvesting the energy rich foliage, as well as the stems
and boles, during the early fall may be best. If management objectives
include reclamation of marginal or disturbed lands or a reduction of
intensity of fertilization, then harvesting after leaf fall would be
desirable. The leaves would be permitted to fall to the soil where decom-
position would replace some of the nutrients taken up by tree growth and
reduce the amount of fertilizer needed to maintain high growth rates.
Dormant season harvesting would also reduce the net yield of the energy crop.
In terms of timing of the harvest, the energy plantation would be
designed to have a staggered rotation sequence so that a fraction of the
crop would be available for harvest each year. For 2- to 6-year short
rotation crops, one-half to one-sixth of the total crop would be ready for
harvest each year. This will even out the material available for the
processing facility.
As with cultivation, harvesting will be highly mechanized. A silage-
type harvester taking all the above ground material would be used.(28) The
harvested material would be fed to a chipper where it would be reduced to
small chips. This material would be transported by truck to a nearby drying
area where it would be air dried for several days. Additional equipment
would be required to turn the wood chips periodically to insure complete
air drying. In very humid climates a more rigorous drying procedure using
indirect heat sources may be necessary.
Storage is the final consideration in the management of tree biomass
for energy conversion. Because the availability of tree biomass and the
feedstock demands of the conversion facility are not likely to be well
synchronized, storage of the feedstock at least for short periods of time
(a few months) will likely be required. Of the possible biomass sources,
tree biomass is among those better suited for storage. Chipped wood stored
in large piles is relatively resistant to pest and chemical degradation.
The interior of these piles should be nearly anaerobic and cellulose and
related compounds comprising wood are not easily or quickly decomposed.
Storage areas may be located on the energy plantation or at the conversion
64
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plant. If considerable distance separates the two, storage at the conver-
sion facility may be most desirable insuring a supply of biomass feedstock
whenever it is needed.
The ultimate factor determining if energy plantations using trees will
be competitive with other uses of the land (agriculture, recreation, urban
development) is economics. While economic analysis is beyond the scope of
this program, it is possible to at least estimate the energy costs asso-
ciated with the silviculture practices. Dollar costs can then be assigned
to the energy costs. However, inflation, changing supplies and demands,
and shifting local, state, national, and societal needs make dollar costs
virtually impossible to fix, especially for a new, untried energy source
such as biomass. Thus, the analysis presented here will be limited to
energy costs in kcal per hectare-yr.
Table 25 summarizes the energy consumption estimates for an intensively
managed 4-year short rotation energy plantation (data modified slightly
from Alich and Inman).(2°) it indicates that for every kcal consumed in
farming or production of farm equipment and materials, more than 5 kcal can
be harvested in the tree crop. Rose'™) reported ratios of 1:6.48 to
1:8.44 but assumed somewhat more biomass production per hectare.
It must be emphasized that these energy estimates are generalized
figures which would be produced per hectare-year. Tree plantations, while
less productive than some of the grasses, can produce considerable energy
for long periods of time. Only a thorough economic analysis can determine
if such plantations can compete with other uses of the land.
Projections of Current Trends and Recommendations
The use of tree plantations as a renewable energy resource constitutes
a new and competitive use of land in the U.S. The prime competitors are
agriculture, silviculture for sawtimber and pulp, and urban development.
At present, economics likely place energy crops at a disadvantage with these
other uses. However, as nonrenewable fossil fuel reserves are depleted and
demands for energy continue to grow, renewable sources of energy will be-
come a more important and competitive use of high quality, fertile land.
Recent trends in land use in the U.S. have shown a drop in the amount
of land in intensive agriculture^71^ and silviculture.t60' This reduction
is likely the result of two causes: (1) the use of land for other develop-
ments, especially urban and suburban expansion, and (2) the cessation of
these intensive activities on marginal lands of low productivity. These
trends are likely to continue in the near future. The human population in
the U.S. will continue to grow requiring more living space. New develop-
ments in intensive cultivation techniques as well as new, highly productive
varieties of trees and other crops will continue to improve the productivity
per hectare on fertile land and make marginal land even more unsuitable for
intensive cultivation (it is uneconomical to use intensive, expensive
farming methods on land whose best yields can only be a small fraction of
those having more fertile soils).
65
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TABLE 25. ENERGY CONSUMED IN AN INTENSIVELY MANAGED
TREE CROP ENERGY PLANTATION
Management Operation
Farming operations
Field tasks
Irrigation
Miscellaneous
Farm chemicals manufacture
Farm machinery manufacture
Seed production
Total energy consumption
Total energy yield (11.2
metric tons at 3.4 x
106 kcal/ton)
Energy balance
Energy input : energy output
kcal/ha-yr
Consumed
750,072
1,222,025
31,741
6,977,852
255,485
27,712
9,264,887
46,500,000
37,235,113
1:5.0
Btu/acre-yr
Consumed
1,204,655
1,962,636
50,978
11,206,793
410,322
44,507
14,879,890
74,681,416
59,801,526
1:5.0
(28)
Source: Alich and Inman. ' Data modified slightly and converted to
metric units.
66
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These patterns in land use reveal that marginal lands offer immediate
opportunities for the development of energy crops. Of all the energy crops,
trees have the most potential for efficient productivity on such lands.
While trees are less productive than many other energy crops, they also
require less intensive management and can provide good, if not outstanding,
yields on moderate energy, labor, and capital inputs. In addition, tree
species, especially nitrogen fixers such as the alders, can assist under
proper management techniques to reclaim marginal lands by enriching the soil
and reducing erosion as well as provide an energy crop.(°8' For surface
mined lands where reclamation is desirable or required, a shift in manage-
ment objectives and the species used for reclamation could result in the
establishment of energy plantations with little additional research, labor,
machinery, and capital.
In the future, as demands for renewable energy sources increase, large
energy plantations (~ 40,000 hectares) (2°) wm become feasible. In the
warmer climates of the U.S., the prime energy crops will be sugarcane and
other species. Smaller amounts of land will be planted in trees to augment
production during the cool months of the year. In cooler temperate and
northern climates, trees may take a more important role in energy planta-
tions. Many of the techniques now used in food and fiber crops will need
to be utilized for tree species if tree productivity is to be maximized.
Highly productive and disease, draught, and pest resistant varieties and
hybrids will need to be developed, as will efficient planting, cultivation,
harvest, and storage techniques. With the development of appropriate tree
varieties and corresponding management techniques, energy plantations
using trees will be a competitive alternative use of both marginal and
fertile lands of the U.S.
INDUSTRIAL AND URBAN WASTES
Screening of Materials
Sources of industrial and urban solid wastes number in the hundreds,
and include food and kindred product industries, slaughtering of animals,
textile mills, chemical plants, rubber and plastic products, explosives, and
insecticides, and even waste treatment plants. The multiplicity of sources
and the nature of the wastes have resulted in various differing estimates
of the national industrial and urban waste flow. These estimates are based
on the inclusion and/or exclusion of various materials, and on the use of
information at various points in time; often the assumptions are not clearly
shown with the estimates. However, the estimates vary in minor ways rather
than by orders of magnitude. Another important consideration, not always
possible to evaluate in the data, revolves on the inability to distinguish
organic and inorganic materials. Information from various perspectives
will be provided because of the complexity of obtaining and interpreting
data on industrial and urban wastes.
Because of the multiplicity of studies of solid and industrial wastes,
the post and current commitment of EPA and others to this biomass source,^
and the broader objectives of this study, a decision was made early in this
67
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work to de-emphasize this category.
It should not be implied that this decision suggests this source as
unimportant; rather, it is a recognition of the existence of an already
comprehensive body of knowledge, in this area, and the need to begin develop-
ing a complimentary data base in other biomass sources.
Kinds of Materials
The majority of the organic portion of solid waste mix is associated
with paper, food, and yard materials (Table 26). Inorganic composition
includes glass, metals, and plastics. The ratio of organic to inorganic
municipal wastes seems to be about 4 to 1 according to Niessen and
Chansky.(72)
TABLE 26. AVERAGE PERCENT COMPOSITION OF MUNICIPAL
SOLID WASTED
Organic
Material
Paper
Food waste
Yard waste
Leather, rubber
Wood
Textiles
Total
Percent
35.8
18.7
20.4
1.4
2.3
1.9
80.5
Inorganic
Material
Glass
Metal
Plastics
Dirt
Total
Percent
8.4
8.2
1.3
1.6
19.5
Distribution and Quantities
Figure 2 provides an overview of the urban waste stream in the United
States for 1973.(73) Note that over one-half of the 273 x 106 metric
tons/yr (300 x 10" tons/yr) is being used or is usable in processing plants.
Of 145 x 10" metric tons/yr (160 x 10^ tons/yr) of municipal solid waste,
about 118 x 106 metric tons/yr (130 x 106 tons/yr) could be diverted to
processing systems. The other 27 x 10^ metric tons/yr (30 x 10^ tons/yr) is
currently being incinerated (some for generation of electricity) and being
placed in landfills or dumped in some other way. The flow—not suitable
for processing plants—contains fly ash, junk autos, appliances, rocks, and
similar materials.
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Total urban refuse
generated annually -
273 (300)
145y(16°)
128 (140)
MSW of type suitable
for processing plants
127 (140) household,
18 (20) commercial)
27 (30)
118 (130)
Municipal refuse
now going to
dumps. Could be
diverted to raw
refuse processing
systems
Other urban refuse contains
73 (80) commercial
27 (30) fly ash
2 (2) junk autos
3 (3) tires
2 (2) appliances
21 (23) miscellaneous rubble,
light industrial waste,
trees, rocks, other
Operating
municipal
incinerators
6.8 ,(7.5)
Incineration
residues, presently
going to dumps.
Could be diverted
to residue plants
128 (140)
Disposed in part to
to dumps, by
abandonment, or
disposal at origin,
litter, other
Figure 2. An overview of the urban waste stream
in the United States for 1973.(73)
[Units are 106 metric tons/year
(106 tons/year)]
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The quantitative flow of organic wastes from industrial and urban
sources was estimated as being 213 x 10^ metric tons/yr (235 x 10^ tons/yr)
in 1971.(74) xhe estimates include four categories of organic wastes:
urban refuse (117 x 10^ metric tons/yr); industrial wastes (40 x 10^ metric
tons); miscellaneous organic wastes (45 x 10° metric tons/yr); and munici-
pal sewage solids (11 x 10^ metric tons/yr). Table 2'7 shows these amounts
and further indicates that a larger proportion of urban refuse is being
collected than other categories. Thus, industrial wastes, miscellaneous
organic wastes, and municipal sewage solids are a potential target for
collection.
TABLE 27. CATEGORIES OF ORGANIC WASTE WITH THEIR
PATTERNS OF GENERATION AND COLLECTION^'4'
IN THE UNITED STATES FOR 1971
Portion
_ Status _ Collected
Category Generated * Collected * (%)
Primary
Urban refuse 117 (129) 64 (71.0) 55
Industrial wastes 40 (44) 4.7 (5.2) 12
Miscellaneous ^ 4>5 1Q
organic wastes
Secondary
11 (12) 1.4 (1.5) 13
Totals 213 (235) 75.0 (82.7)
\ t
Units are 10 metric tons/yr (10 tons/yr).
Net solid wastes for 1971 and 1973 averaged about 118,000,000 metric
tons/yr (130,000,000 tons) (Table 28). (75) Combined paper and food wastes
represent about 55.5 x 106 metric tons/yr (61.1 x 106 tons/yr) (1971) and
(60. 4 x 1066tons/yr) (19p) of the total 113.2 x 106 (124.8 x 106) and
122.3 x 10 (134.8 x 10 ) , respectively. Paper and food wastes in 1973 rep-
resent 49 percent of the total net weight of these types of urban/industrial
waste (Table 28). Paper wastes increased about 13 percent between the two
years; thus, paper represents a growing organic source of waste.
Recent studies of the residential-commercial components of municipal
solid waste equated to 1.5 Kg (3.3 Ibs) per capita per day in 1971. (75)
The estimates for 1976 are 1.6 Kg (3.6 Ib) per capita per day. (75)
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TABLE 28. NET SOLID WASTE (WET WEIGHT) BY MAJOR
CATEGORIES IN THE UNITED STATES FOR
1971 AND 1973(75>
Material Composition
1971'
1973'
Growth. 1971-1973
Percent
Weight* Change
Paper
Glass
Metal
Plastics
Rubber & Leather
Textiles
Wood
Subtotal: Non-food
products
Food Waste
Subtotal: Product
waste
Yard Waste
Miscellaneous Inorganics
Total Material
35.5 (39.1)
10.9 (12.0)
10.7 (11.8)
3.8 (4.2)
3.0 (3.3)
1.6 (1.8)
4.2 (4.6)
69.8 (76.9)
20.0 (22.0)
89.7 (98.9)
21.9 (24.1)
1.6 (1.8)
113.2 (124.8)
40.1 (44.2)
12.0 (13.2)
11.3 (12.5)
4.5 (5.0)
3.3 (3.6)
1.7 (1.9)
4.5 (4.9)
77.5 (85.4)
20.3 (22.4)
97.8 (107.8)
22.7 (25.0)
1.7 (1.9)
122.3 (134.8)
4.6 (5.1)
1.1 (1.2)
0.6 (0.7)
0.7 (0.8)
0.3 (0.3)
0.1 (0.1)
0.3 (0.3)
7.7 (8.5)
0.4 (0.4)
8.1 (8.9)
0.8 (0.9)
0.1 (0.1)
9.1 (10.0)
13.0
10.0
5.9
19.0
9.0
5.5
6.5
11.1
1.8
9.0
3.7
5.6
8.0
*Units are 106 metric tons/yr (106 tons/yr).
Of course, the larger the population of a city, the larger the solid
waste stream. Indeed, the amount of municipal solid waste from the
residential-commercial sector of any city could be estimated by multiplying
the per capita rate by the population. This approach would be useful for
a national perspective. Regional and certainly smaller geographical units
(counties) will require more specific information for planning purposes.
At least three toxic materials are important in urban waste: metals,
pathogens, and disease vectors. Metals include tin, lead, sulfur, iron,
zinc, and mercury. Pathogens include viruses, bacteria, cestodes, and
dipteran larvae. Direct and indirect vector transmission of disease is
possible via rats, fleas, sick animals, and pests that feed on or live in
garbage and refuse.
71
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One of the major limitations is the dispersed nature of the wastes.
It is often not profitable to collect the material. Also, the material is
often of diverse composition and must be processed and/or separated before
usable fractions are available. Separation of inorganics from organics
can present a technological problem.
The technology of using urban wastes is sophisticated in many places.
Recycling plants and production systems that generate electricity by
burning municipal wastes are growing in number. A third use category is
landfills. Many studies of waste-to-energy projects exist; one list is
found in a paper by
Collection and Handling
The volume of solid waste has required increasingly organized collec-
tion, handling, and management systems. Collection and handling procedures
are well established, especially in large cities. Some of the many approach-
es are provided in such documents as follows: Decision-makers Guide to
Solid Waste Management ( 76 ) > Decision-makers Workbook: Resource Recovery
from Solid Waste^77) , Mineral Resources and the Environment.''-^) In brief,
while many challenges exist on the management of solid wastes, substantial
progress is occurring.
Projections of Current Trends and Recommendations
Projections estimate that net waste disposal will slightly increase
over the next few decades (Table 29).^ Resource recovery will improve,
but expected gross discards will probably exceed the percentage improve-
ment in recycling technology. It seems that solid waste will be in suffi-
cient quantities to challenge the development of technology to utilize its
energy.
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TABLE 29. PROJECTIONS FOR SOLID WASTE GENERATION,
RECOVERY AND DISPOSAL IN THE UNITED
STATES
_ Estimated _ _ Projected _
1971* 1973* 1980* 1985* 1990*
Total: Gross
Discards 121 (133) 131 (144) 159 (175) 182 (201) 204 (225)
Less: Resource 7 (8) 8 (9) 17 (19) 32 (35) 53 (58)
Recovery
Equals: Net Waste 113 (125) 123 (135) 142 (156) 151 (166) 152 (167)
Disposal available
for landfill,
energy use, other
challenges
*Units are 10" metric tons/yr (10® tons/yr),
Ref: Resource Recovery Division, Office of Solid Waste Management Programs,
U.S. EPA, revised December, 1974. Projections for 1980 to 1990 based
in part on contract work by Midwest Research Institute. Baseline
Forecasts of Resource Recovery, 1972 to 1990. Final Report Revised,
March, 1975.
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SECTION 6
CONVERSION PROCESSES
Section 5 has been directed at characterizing the different materials
which constitute biomass feedstocks. This section will be directed at
describing the various processes which might be used to convert these feed-
stocks into usable energy forms.
These processes have been categorized as primary thermochemical, primary
biochemical, and secondary conversion systems. The primary thermochemical
processes have been defined as those which utilize elevated temperature to
directly convert biomass materials into energy forms or intermediate
products. Combustion is considered in this class. Primary biochemical
processes use microbiological species or their biochemical agents to convert
feedstocks to fuel products or intermediates. Secondary processes are
defined as those which convert intermediate products from primary processes
into fuel products. Ethanol fermentation of glucose is a member of this
class.
The processes and the important variations of the more significant
processes will be described. Important process variables and their approxi-
mate levels will be presented, as well as schematic flow sheets when avail-
able. For more highly developed processes, equipment descriptions are
provided.
Apart from this information, approximate calculations were prepared
describing "scenarios". These "scenarios" represent first-order approxima-
tions of commercial plants and were made based on a brief analysis of the
primary biomass feedstocks available within defined regions and an assessment
of the most likely conversion system which might be used for these feed-
stocks. These calculations should be broadened and made more explicit in
later work.
PREPROCESSING OF THE SELECTED BIOMASS FEEDSTOCKS
Preprocessing in this study refers to all steps involved in preparing
the biomass feedstock into an acceptable form for energy recovery. These
steps include harvesting and/or collecting, size reducing, sorting, blending,
and hauling of the raw material from the point of origin to the energy con-
version plant. Each biomass feedstock requires unique preprocessing steps.
For example, agricultural and forest product wastes are shredded while in
the field, after the primary product is recovered. Biomass products derived
from aquaculture and silviculture practice might be shredded at the time of
74
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harvesting. Urban wastes, in an idealized example are first collected then
delivered to a transfer station, weighed, shredded, separated into organic
and non-organic fractions before processing for further size reduction and
separation. This section will be limited to size reduction practices, and
separation and drying techniques, since harvesting and transportation'of
biomass were briefly covered in Section 5.
Advantages for Size Reduction
Many advantages are derived when biomass feedstock is preprocessed.
Some of the most readily identifiable advantages obtained from shredded
biomass are:
1. Increased density while reducing volume up to 70%^ '
2. A uniform mix blended from a heterogeneous feedstock
3. Controlled moisture, odor and dust
4. Eased mechanical assist
Principles Involved in Size Reduction Equipment
Size reduction requires mechanical energy. There are three types of
mechanical forces associated with biomass material size reduction. These
three forces are tension, compression and shear. Usually, all three are
interrelated when biomass material is mechanically shredded. Tension forces
on a body tend to pull it apart; compression forces are the opposite--
squeezing and crushing the body. Shearing is the act of cutting and usually
is accompanied with the other two forces. The relationship of these three
basic forces is illustrated in Figure 3. (79' These forces are usually
Tension -vmterrelated
forces
Compression
Shear
Figure 3. The application of forces
in size-reduction operations.
75
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combined in the various types of size reduction equipment. As an illustra-
tion of the variety of size reduction equipment currently available, the
basic types and the potential for processing urban wastes are listed in
Table 30. (79)
Primary Shredders
The most common and versatile piece of equipment used in industry for
initial size reduction is the hammermill. It has been accepted by industry
as the standard. For example, in the forest products industry, the hammer-
mill is used for shredding wood bark and waste wood. Agricultural fibers,
as wheat straw, hay, corn stalks are chopped in hammermill equipment.^
Installations vary in capacity; the sugar cane industry has machines capable
of processing 250 tons of waste cane per hour. However installations of
50 to 100 tons per hour are more common in the forest products industry.
Hammermills--
The hammermill is composed of five essential parts; a rotor with fly
wheels, hammers attached to the rotor, a stationary anvil, the housing, and
the grate bars. The chopping (or shredding) action of product occurs when
the rotor turns at high speeds, striking the product and forcing it against the
stationary anvil. The final product discharges through the openings in the
grate bars. The housing, or main frame, supports the rotor and hammers and
the stationary parts of the mill.
Numerous variations in the basic design are common; there are swing
hammer and rigid hammer types; vertical and horizontal mills, each of which
has certain advantages depending upon the feedstock source. Depending upon
the position of the rotor, the hammermills are classified as either vertical
or horizontal. Both types are being successfully operated, although more
horizontal mills are available by manufacturers.^° ' However, the function
and the basic operating principles remain the same. The essential parts of
the hammermill are shown in Figure 4.v'9)
load*1
Grate
bars
Shredder teeth
Shredder
teeth
Figure 4. Hammermill principles.
76
-------
TABLE 30. CURRENT SIZE REDUCTION EQUIPMENT AND POTENTIAL APPLICATIONS
TO MUNICIPAL SOLID WASTE^79>
Basic Types
Variations
Potential Application to Municipal Solid Waste
Crushers
Cage disintegrators
Shears
Shredders, cutters,
and chippers
Rasp mills and drum
pulverizers
Disk mills
Wet pulpers
Hammermills
Impact
Jaw, roll, and
gyrating
Multi-cage or
single-cage
Multi-blade
or single blade
Pierce-and-tear
type
Cutting type
Single or multiple
disk
Single or multiple
disk
Direct application as a form of hammermill.
As a primary or parallel operation on brittle or
friable material.
As a parallel operation on brittle or friable material.
As a primary operation on wood or ductile materials.
Direct as hammermill with meshing shredding members,
or parallel operation on paper and boxboard.
Parallel on yard waste, paper, boxboard, wood, or
plastics.
Direct on moistened municipal solid waste; also as
bulky item sorter for parallel line operations.
Parallel operation on certain municipal solid waste
fractions for special recovery treatment.
Second operation on pulpable material.
Direct application or in tandem with other types.
-------
The two basic differences are diagrammed in Figure i.
(81) suggests a comprehensive check-list to aid in the
for processing biomass feedstocks. Advan-
SG J_cC t J_ OH. O J- oii i CVAU. -Liij^ ^-^t i -i • 1 J
tages cited for the vertical shaft hammermill include.
1. A discharge conveyor is often not required.
2. Requirements for concrete foundations are reduced.
3 The total required building enclosure height is reduced
because the machine discharges shredded material from the side
instead of from the bottom as is the case with horizontal
shaft shredders.
4 Electric power requirements are reduced due to design effi-
ciency? While this advantage is not reflected in the shredder
cost, it will be realized in the total system expense.
5 The shredder is much less subject to damage because difficult-
to-shred items will pass through the machine and/or be
rejected.
6 A more even distribution of wear and significantly lower
hammer wear rates are possible because input material is
gradually reduced in particle size as it passes from input
to output, and one force is spread over the entire rotor area.
SJ;:>INPUT CONV
"* 7
VERTICAL SHAFT HAWERMILL
HORIZONTAL SHA-T HAMMERMILL
Figure 5. Vertical and horizontal shaft hammermills.
78
-------
However, there are possible disadvantages associated with the vertical
shaft mill and these should be mentioned. Replacement of the lower bearings
is a major repair item, requiring considerable down time. Replacement and/
or resurfacing of the lower hammers is difficult, since the space at the
lower end is restricted due to the housing shape.
Other Types of Size Reduction Equipment
After the product is processed in the primary shredder, a secondary
size reduction is often needed. Primary shredding reduces the product to
approximately 6 inches. A second shredding operation will reduce the product
to about 2 inches, with some smaller particles. The conversion process and
the feedstock will dictate the need for further size reduction. Equipment
for secondary reduction stages are available and are classified into five
basic types. These types are hydraulic action pulpers, knife cutters, rasp,
revolving drum pulverizer, and hammermills.
Knife Cutters, Choppers--
Knife cutters are particularly useful if only one type of waste feed-
stock is fed to them. The knife cutters are commonly found in the wood
product industry. The familiar yard waste chippers is an example of the
knife cutter. The knife cutter is best suited on feedstock which has a
fibrous structure. The efficiency of the machines is dependent upon the
sharpness of the knives blades, and knife maintenance tends to be an expen-
sive factor. For field harvesting of aquatic plants, (either hyacinth or
kelp), the shear-bar forage chopper appears applicable. It has been used
successfully in hyacinth harvesting, and has been noted to cut cleanly and
uniformly, producing particles of one inch length. This chopper, when modi-
fied, can chop 50 to 60 tons of water hyacinths per hour. The energy
required by this one machine is 0.46 HPhr/ton.(82)
Rasps —
The rasp mill has the capability of accepting a variety of feedstock,
including urban refuse. The rasp mills are huge cylindrical machines, some
with diameters of 20 feet. This machine is common in European composting
installation, with one installation of this design in the United States
(Johnson City, Tennessee). The machine processes feedstock to smaller size
(2 inches) by rotating massive cutting arms over rasping pins which forces
product through discharge holes in a bottom plate. This machine is useful
as a secondary size reducing machine. Units with 100 HP are capable of
processing approximately 15 tons per hour.('"'
Wet-Pulpers--
The wet-pulper, a common piece of size reducing equipment originally
developed for the paper making industry, is currently used for preprocessing
urban refuse. The wet-pulper is part of the "Hydraposal System" of the EPA's
Franklin, Ohio demonstration project. The purpose of this project j^ to
recover resources from urban wastes using a wet processing system.
Essentially, the wet-pulper is a large tube-like container (up to
12 feet diameter) with high speed cutting blades in the bottom. The wet-
pulper can be visually compared to a huge kitchen garbage disposal unit.
79
-------
The refuse, mixed with excess water, is shredded into a pumpable slurry.
The solids content is low, averaging 2%. Fibrous feedstocks are best suited
for this type of preprocessing equipment. If mixed refuse is a feedstock,
then a pregrinding and a presorting operation is required. Figure 6 is a
cutaway view of the Franklin hydropulper. (<"/
A second variation of wet pulping is a combined system. In this
separation system as applied to urban waste, the refuse is shredded to a
particle size of 3 to 6 inches. From this stream, the tin cans are removed
magnetically before being conveyed to the hydropulper. Excess recycle water
is mixed with the refuse and pulping commences. The effluent from the hydro-
pulper is fed to a liquid cyclone where the stream is split. The underflow,
which contains the heavier solids as aluminum, glass and small ferrous
metals, is sent to a recovery unit, while the overflow is sent to a series
of screens and filters for the recovery of the organic constituents. The
organics, mostly cellulose fibers, are then sent to a digester or to a paper
processing plant, dependent upon the type of recovery desired. Figure 7 is
a schematic diagram of the wet-separation process.
Disk Mill--
Disk mills are massive, stationary machines specifically designed for
producing either fine grains or refined pulp. This machine is commonly found
in the paper making and food processing industries. The feedstock to be
processed by this machine is restricted to a material with uniform size,
usually less than 2 inches. This restriction is due to the small sized
opening port for product entry. The product to be processed is fed into the
center of two high speed rotating disks, where the product is torn to small
bits. Fin?l product size is regulated by adjustment of the distance between
the disc(°^' (Figure 8). Disk mills, with power requirements of up to
4000 hp can be commonly found in large paper mills.(79)
Figure 6. Cut-away view of wet-pulper.
80
-------
WATER
•'
RECEIVING
SHREDDER
MAGNETIC
SE PARATOR
FINE SCREEN
HYDROPULPER
FINES TO
DISPOSAL
CYCLONES
NONFERROUS,
GLASS <*—
DEWATERING
TO MIXING
TANK
Figure 7. Schematic diagram of wet
separation system.
81
-------
— CLEARANCE
INPUT
Figure 8. Disk mill schematic.
Pulpable feedstock, as derived from agricultural, silvicultural or
forest product wastes could be processed in this type of machinery, since
the primary shredding has been done in the field usually at the time of
harvest.
Drum Pulverizers—
Drum pulverizers, or rotating drum mills are popular size reducing
machines found in European waste processing plants. The drum pulverizer is
similar in operation to that of the rasp mill and accept a variety of feed-
stock material. The operation is slow, and size reduction is accomplished by
the tumbling action of the feedstock material inside of the rotating drum
(10 feet diameter). Increased grinding action of the feedstock material is
accomplished by the addition of internal baffles in the drum, and/or station-
ary central blades. Final size of the feedstock material is regulated by the
diameter of the perforations in the rotating drum wall (Figure 9)
Input
^j?. Rejects
^Perforated inner drum:
circular .octagon or hexagon
II rpm
Figure 9. Drum pulverizers.
82
-------
Separation Techniques as Applied
to Municipal Wastes
Essentially, there are three general classifications for separating
the organic from the non-organic fractions found in municipal wastes. These
are, (1) manually hand-sorting the refuse off a moving belt, (2) grinding the
as-received refuse, followed by a magnetic separation and air classification,
and (3) grinding the as-received refuse in a wet-pulper followed by separa-
tion with various screens, cyclones and magnets.
Hand Sorting--
Hand sorting of refuse is now obsolete and would not apply to any large
scale separation plant. Some of the factors cited are unfavorable economics,
incomplete separation and human indifference. The prices received for the
recovered materials do not match the wages required to recover them. While
separation would be limited to only the larger items; most of the organics
are packed tightly with the inorganic matter. The two plants operating a
hand sorting operation in Montreal and Houston have found that the plants
cannot operate economically and have ceased operation.
An automated plant, in which human judgments are replaced by electronic
sensors coupled to a minicomputer, is operating experimentally at
Massachusetts Institute of Technology. (°5) in this plant, the large pieces
of refuse are examined by the sensors, then categorized by a minicomputer.
Subsequently, once the item is categorized, it is switched to an appropriate
bin for baling.
A third type of sorting operation which is incorporated in some
communities is that of segregating the refuse at the source, i.e., the home.
In this method, the public as well as municipal workers, are educated to
segregate their solid wastes into four categories - garbage, metal cans,
bottles, and newspapers. With this system, separate collections are needed,
thereby increasing collection cost. However, the ease of further
processing is also increased.
Magnetic Separation and Air Classif ication--
In the case of non- segregated compacted municipal trash which has
been shredded at a central size reduction plant, separation of the metallics
is achieved with the use of magnetic belts and air classification methods.
The shredded trash which has been reduced to less than 6 inches particle size
is conveyed through a magnetic field. The magnetic field may be either
permanent or electro-magnetic. In this system, the tin cans are easily
recovered. The use of magnetic belts for separation (Figure 10) is a well
established method, as there are several companies specializing in the
manufacture of this equipment.
After the magnetic items have been removed from the trash, the next
step in the separation process is air classification. In this method, the
trash is separated in different density gradients. The shredded trash is
fed into an air current in which the trash is fluidized. The lighter frac-
tions, such as paper and plastics, are carried out of the unit, while the
heavier materials, such as rocks, glass and aluminum cans drop to the bottom.
83
-------
SUSPENDED-TYPE PERMANENT MAGNETIC SEPARATOR
PULLEY-TYPE PERMANENT MAGNETIC SEPARATOR
Figure 10. Two types of magnetic separators.
84
-------
The National Center for Resource Recovery, Bureau of Mines, and the Columbus,
Ohio's Solid Waste Transfer Stations all use separation systems based upon
these techniques. Diagrams of the various types of air classifiers currently
in use are shown in Figure 11.
Screens--
Air classified-shredded municipal trash contains dirt and other non-
organics, which are usually concentrated in the minus 0.5 inch particle size
range. This fraction, if not removed, contaminates the shredded trash when
used in energy or fiber recovery processes. Furthermore, the dirt adds
unnecessary ash. Thus the removal is often important. A method of removing
this fraction can be accomplished by screening. Several screening techniques
are available, such as flat-bed vibratory and the inclined, cylindrical,
rotating screens. A study comparing the two techniques is described in a
report by the University of California, Berkeley.C86) This study demonstrated
a 96% removal of the minus 0.5 inch particle size range in a rotating
cylindrical inclined rotating screen. As a comparison, a flat-bed vibratory
screen removed 72% of the minus 0.5 inch particle size fraction from the
same feedstock (air classified, municipal trash). No noticeable effects on
screening efficiency were observed when the moisture content was varied
between 20 to 30%.
Wet Separation Methods--
There are several processes based upon the use of water for separating
the organic portions found in municipal trash. The Black-Clawson system in
Franklin, Ohio is the first of its kind, and therefore it is referenced in
the literature frequently. Another system which combines hand sorting and
water floatation technique is the Tracy system.
In the Black-Clawson method, segregated urban wastes (with large trash
items as tires, stuffed chairs, refrigerators excluded) are shredded in a
hydrapulper described in earlier paragraphs. Excess water is mixed with the
urban wastes, and shredded to a slurry. This slurry is further refined to
remove the inorganics, such as glass, dirt and metals through a series of wet
cyclones, hydrascreens, and filter presses. The final recovered organic
product is a cellulose fiber suitable for use in construction paper, such as
asphalt roofing shingles. For an energy recovery process, the cellulose
could be suitable for a biological digester, such as an anaerobic methane
gas producer.
The Tracy separation system represents a different concept in wet
separation systems. First, the refuse is hand sorted; large items like
bundled newspaper, automobile tires, etc., are removed for salvage. The
semi-selected trash is then pushed into the trough so that a float and sink
separation is made. The float portion, which contain the organics, is
skimmed and fed to choppers, then screened and finally pumped to an anaerobic
digester for stabilization. The sink portion, which is mostly inorganics, is
removed by dragline, and magnetically separated for the iron constituents.
The non-magnetic material is then hand-picked before final disposal.^
85
-------
KEY
I SHREDDED REFUSE IN
2 AIR IN
3 LIGHT FRACTION OUT
4 HEAVY FRACTION OUT
VANE/ROTATIONAL AIR CLASSIFIER
OPTIONAL /
AIR LOCK
FEEDER
A IS
HEAVY FRACTION
ZIG-ZAG AIR CLASSIFIER
OPTIONAL
AIRLOCK FEEDER
CONVEYOR
fl, ' '..'-- .»*.', 7-LIGHT
* I »
HEAVY MIX MOSTLY
FRACTION LIGHT
HORIZONTAL AIR CLASSIFIER
*From catalogs and information furnished by Eriez
Magnetics Company, Erie, Pennsylvania 16512.
Figure 11. Various types of air classifiers,
-------
LIGHT FRACTION
HEAVY FRACTION
oo
--a
VERTICAL AIR CLASSIFIER
SHREDDED
MSW
•5-
LIGHT
FRACTION
CROSS FLOW AIR CLASSIFIER
HEAVY
FRACTION
AIR LIGHT AIR
FRACTION
HEAVY FRACTION
SORTEX AIR CLASSIFIER
IMPULSE TYPE AIK CLASSIFIER
Figure 11. (continued)
-------
Comparison of Wet and Dry Shredding Processes--
The question which arises when preprocessing methods for size reduction
and separators are considered is which would be the preferred method - wet
or dry shredding. The answer to the question will depend upon many factors.
Two of the more important are the type of energy conversion/recovery process
considered and the physical characteristics of the biomass feedstock avail-
able. Obviously, if the energy/recovery process is either thermochemical
or the feedstock is a dry material, then a dry shredding process would be
selected. Conversely, if the energy/recovery process is biological, as an
anaerobic fermentation, and the feedstock source is a wet material, then a
wet shredding process would probably be the method of choice.
Many studies have been concerned with processing of municipal wastes,
either for resource or energy recovery. Both wet and dry processes which
include shredding and separation have been considered. Black-Clawson Company
is pursuing the wet-pulping and separation method, while the U.S. Bureau of
Mines and the National Center for Resource Recovery are investigating the
dry processing method. Both methods show a high degree of success. '°7 ^ A
general comparison of the wet and dry preprocessing methods is presented in
Table 31.
Drying of Biomass Feedstock for Thermo-Chemical Process
The net available energy value from a fuel, in this case the biomass
feedstock, is affected by the moisture and ash content. Both moisture and
ash dilute the available energy when the biomass is delivered to a thermo-
chemical process. The ideal solid fuel is one with zero moisture and ash.
Air classified municipal refuse averages 25 to 30% moisture and 25% ash.
Vaporization of the moisture in a fuel consumes a portion of the available
energy. A 30% increase in the available heating value is obtained when a
fuel with a 30% moisture content is reduced to zero moisture content. The
relationship of available energy and moisture content for a refuse derived
fuel (RDF) is shown in Figure 12.
Removal of all of the moisture currently is impractical. This is due to
two factors, the reduced drying rate at lower biomass moistures contents, and
the hydroscopic nature of many biomass materials. For example, dry newsprint
placed in a 50% relative humidity environment equilibrates at 8% moisture.
There are many manufacturers who specialize in the construction of
drying equipment. Types of dryers which are available are categorized as -
air, fluid bed, rotary, spray, conveyor, flash, drum and vacuum and are
offered by more than 85 companies.
It should be noted in passing, that the heat required for drying also
represents an energy demand. In thermochemical processes (e.g., those most
likely to require drier feedstocks), the heat is generated in and transfers
from process feedstock. Heat transfer rates are usually quite high. Con-
versely, drying in separate preprocessing equipment will usually require at
least two, and possibly several, additional steps. For example, combustion
of a portion of the feedstock, transfer of the heat to a gas stream, and then
drying of the remaining feedstock. Generally, the overall thermal efficiency
88
-------
TABLE 31. COMPARISON OF WET AND DRY SHREDDING METHODS IN RELATION
TO PREPROCESSING OF WASTE BIOMASS FEEDSTOCK
Wet Preprocessing
Dry Preprocessing
Feedstock
Characteristics
Primary shredding required
Fibrous material, as cellulose
shred faster; Hydrogen bonds are
loosened in water.
Primary shredding required
Feedstock can be variable
00
Final
Product
Process Energy
(Heat of Friction)
Moisture content not critical
Slurry, TL solids content
Dewatering equipment is required
to increase solids concentration
Recovered in slurry, which can be
useful if digestion conversion
process is used.
Low moisture feedstock shreds
faster, but increases machine
wear due to the abrasive nature
of the feedstock
Particle size adjustable, depen-
dent upon moisture contents and
grate openings
Final moisture can be adjusted
to desired concentration
Reduces moisture content of
product
-------
9000
8000
7000
6000
5000
•4COO
B
&
3000
2000
1000
•1000
2092
1860
1627
i 139* „
r s
i 1162 S1
i I
i I
i 930 ST
r ^
i s
! 232
"20
breakeven point •
40 "" 60
Moisture content of fuel, weight f. •.
-100-
I
-232
Figure 12. Available energy of refuse as a
function of moisture content,
considered as a binary system.
90
-------
will be lower 'than in-process drying. Consequently, only when economics ™
dictate, or when a supplemental heat source is available fg ITsTehlat
or solar-aided techniques, will the drying add to the thermal efficiency^
the system. J
Pretreatment of Cellulose-Containing;
Products to Increase Enzymatic and
Microbiological Conversion Processes
Perhaps the one most important step in the waste-to-energy conversion
process which uses cellulose-containing products is that of pretreatment.
The pretreatment step is the most energy-consuming step and also is often
a significant single cost factor in the economic evaluation of enzymatic and
microbiological method for energy recovery.
Cellulose is one of the most abundant natural occurring energy resources
and, for our purposes, occurs in two forms, the pure form obtained from
plant life and waste. The wastes occur as a residue from forest product and
the agricultural industries, as a fraction of urban refuse, and in cattle
manures.
Some of the synonyms used for cellulose after pretreatment are crude
cellulose, complex carbohydrate, holocellulose, carbohydrate fraction in
extracted wood, alpha cellulose, lignin-free cellulose, hemicellulose and
simple or mixed polysaccharides. As a convention, alpha celluloses are
referred to as those celluloses derived from woody plants, while the terms,
crude or holocellulose, are derived from agricultural crops.
Each of these cellulose-containing products derived from any of these
sources, requires unique pretreatment procedures specific for that product.
Thus, there is no single uniform pretreatment method applicable to the
general form of cellulose-containing products. A general discussion of
various pretreatments available follows.
Pretreatment Methods--
The literature reveals a wide variety of chemical and physical means for
modifying the complex chemical structure of the cellulose containing products.
The purpose for modifying the chemical structure is to enhance the subsequent
biological conversion to other useful products; untreated cellulose is resis-
tant to biological attack. Chemical treatment causes the cellulose to swell,
thereby weakening the chemical bonds, while physical treatment reduces the
size and thus increases the surface area and the bulk density.
Chemical Treatment--
Alkaline chemicals, as sodium hydroxide and ammonia, have been success-
fully used for more than 50 years for cellulose utilization. Some of the
first studies were designed to increase the nutritional value of straw for
animal feed, and at one time sawdust, when conventional fodders were not
available. In this method, straw is presoaked in a 1.5 percent solution of
sodium hydroxide for at least 24 hours. The disadvantage of this method is
that the solubilized hemicellulose is lost when the straw was washed^ for the
purpose of removing excess sodium hydroxide. A variation of this original
91
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method was developed in which the straw was treated with a 20 percent sodium
hydroxide solution, allowed to stand for a period of time, then neutralized
with either silage or acetic acid. In another variation of this method, rice
straw and sugar cane bagasse is treated with a 4 percent solution of sodium
hydroxide and heated to 100 C. This pretreatment almost doubled the bacterial
conversion of carbohydrate.(89)
Another variation of the alkali treatment method is the substitution of
ammonia or ammonium hydroxide for sodium hydroxide. The advantage of substi-
tuting ammonia is that the nitrogen values are increased, and this adds
nutrient value to the straw when used as either an animal feed or in a fermen-
tation system. Another variation of the ammonia method is the application of
heat and pressure of up to 70 psi.
Physical Pretreatment--
Physical treatment methods require the use of mechanical energy and the
typical equipment available are hammer, ball and fluid energy mills. The
purpose is to obtain micron-sized particles, sometimes less than 50 microns.
The advantage of having small particles in an enzymatic or bacterial reactor
is that the enzymatic activity is increased proportionately to the available
surface active area. Milling history also effects the reactivity of the
particle size - such items as the time and temperature profile while milling
could change the crystallinity of the cellulose. These contributing factors
are currently being investigated.
The major disadvantage of physically obtaining micron-sized particles
is the high costs. Milling costs (1975) are listed by particle size in
Table 32.T90;)
TABLE 32. MILLING COSTS
Mesh Power Cost Maintenance Overhead Cost Total Cost
Size Inch Micron Ib/hphr $/ton $/ton $/ton c/lbm
40
80
100
200
270
.0165
.007
.0059
.0029
.0021
420
117
149
74
53
16
5
4
1
.55
< $2.00
4.00
5.00
20.00
36.45
$1.40
4.40
6.50
24.00
45.00
$ .20
.40
.50
1.00
1.40
.18
.40
.60
2.25
4.14
92
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Delignification--
An active area of research is the field of altering the lignin-cellulose
bonds of woody plant cells. The lignin-cellulose bond is very resistant to
enzymatic and bacterial attack. A few of the methods currently being investi-
gated are (1) treating the wood residues with active chemical gases as
chlorine dioxide or sulfur dioxide, and (2) direct fungal inoculation of wood
residues in the holding area.
In the chlorine dioxide conversion method, the gas is passed directly
into a bed of dried wood residue. The treated product was evaluated in
enzymatic tests and marked improvements in digestibility were observed.
However, later economic studies show that this method is expensive; one
estimate was stated to be around $200/ton of product processed for chemicals
alone.
In the sulfur dioxide treatment method, the gas is reacted with sawdust
in a pressure vessel at 120 C and 30 psi for either 2 or 3 hours, dependent
upon the sawdust being hardwood or softwood. After the reaction, the sawdust
was neutralized with sodium hydroxide (although ammonium hydroxide would add
nutrient value). The reacted sawdust was then evaluated in enzymatic digestion
studies. The analytical results of the various wood species treated with
sulfur dioxide are shown in Table 33.
TABLE 33. COMPOSITION AND CELLULASE DIGESTION OF VARIOUS
WOODS BEFORE AND AFTER S02 TREATMENT
Species
Lignin
7
/o
Before After
Carbohydrate
7
/o
Before
After
Digestibility
Before After
Quaking aspen 20 7
Yellow birch 23 9
Sweetgum 20 5
Red oak 26 8
Douglas-fir 30 24
Ponderosa pine 31 19
Alfalfa 17
70
66
66
62
65
59
51
71
67
64
60
63
58
9
4
2
1
0
0
25
63
65
67
60
46
50
93
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PRIMARY THERMOCHEMICAL CONVERSION PROCESSES
Direct Thermoconversion to Power
The most thermally efficient method of converting biomass to energy is
by direct combustion for the generation of heat or steam. This method of
solid waste treatment is the most expeditious means of minimizing the volumi-
nous quantities of waste and refuse and is the most developed of the waste-
to-energy processes. The most common application of biomass (municipal,
industrial, agricultural, forest wastes, etc.) for direct energy production
is as a direct boiler feed or a supplemental boiler feed for the production
of steam either for on-site use or for the subsequent generation of electri-
city. Another application currently being explored is incineration of the
waste to produce a combustion gas for directly powering a turbine-driven
electric generator. Each of the direct-fired applications of waste biomass
is examined in more detail in the following sections.
Direct Boiler Feed--
The use of biomass as a direct boiler feed for the generation of heat or
steam has been widely practiced in the United States. Bagasse is commonly
burned at sugar cane processing plants to provide process steam; tree bark
and pulping liquors are combusted to supply steam for pulp and paper processing
plants; wood chips, sawdust, and tree bark are used as primary fuel at plywood
plants, particleboard plants, furniture plants, and sawmills; industrial and
mining wastes are finding increased application as a raw feed for the genera-
tion of process steam and steam-generated electrical energy. More recently,
some manufacturing facilities, not directly related to the use or processing
of wood or other organic fuels, e.g., textile mills, are constructing wood-
burning steam boilers.'" ' Although other types of agricultural wastes have
also been utilized on an experimental or limited basis for direct or supple-
mentary fuel for boilers, e.g., peanut shells and livestock manure, most of
the direct-fired applications of biomass waste in the United States utilize
wood*-y ' or bagasse, with some use of municipal/industrial solid waste. Since
the technology employed to recover energy from the less conventional waste
feeds would be similar to that used for wood, bagasse or municipal/industrial
solid waste, only the technologies applicable for handling the latter three
wastes will be addressed in detail.
Bagasse--Bagasse is the refuse generated from the milling of sugar cane.
It is comprised primarily of matted cellulose fibers and fine particles. A
typical analysis of bagasse is shown in Table 34. Bagasse generally contains
about 50 percent moisture and has a net heat content of about 2200 kcal/kg
(4000 Btu/lb).
Bagasse is commonly burned at the sugar cane processing facility to
augment the energy requirements for process steam production. The early
incinerators were Dutch ovens. These were followed by the Cook furnace, a
variation of the Dutch oven utilizing a refractory horseshoe-shaped hearth
with air-admitting tuyeres located around the curved side wall.(§3) xhis
design, however, was plagued by high maintenance costs and was replaced by
the Ward furnace.(94' The Ward furnace consists of individual refractory
cells into which the bagasse is fed with approximately 85 percent of stoichio-
metric air. Initial combustion takes place in the cells and the remaining
94
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TABLE 34. CHEMICAL COMPOSITION OF HARVESTED AND
FIELD-DRIED BAGASSE (92>
Composition
Bagasse as
Harvested
Bagasse
Field-Dried
Proximate (%)
Moisture 52.0
Volatile 40.2
Fixed carbon 6.1
Ash 1.7
Ultimate (%)
Moisture 52.0
Hydrogen 2.8
Carbon 23.4
Hitrogen/oxygen 20.1
Sulfur Trace
Ash 1*.7
Heating value
kcal/kg 2200
(Btu/lb) (4,000)
Bulk density, stacked
r—
kg/m
(d)
(lbs/ft3)
15.0
71.2
10.8
3.0
15.0
5.0
41.4
35.6
Trace
3.0
3930-4590
(7,080-8,260)
200.4
(12.5)
combustion occurs in a secondary chamber or
reach as high as 65 percent.
will not perform
percent.
excess P
required from
ciency by 15 to 20 percent. W*> The stoker
well with a moisture content in the bagasse feed in
Wood_Refuse--The largest single use for wooc 1 is ; fjr
43 percent of the world's wood is consumed "fuel.
States, for the direct firing of boilers wood ranks next
major fossil fuels, coal, oil, and natural gas.
95
-------
FIGURE 13. A C-E STEAM GENERATING UNIT WITH
SPREADER STOKER FOR BAGASSE FIRING
(92)
Typical compositions of various types of wood and bark and the resulting
ash composition when burned are shown in Table 35. The moisture content has
the most significant effect on the heating value of the wood and may vary
considerably. Otherwise, the wood has a reasonably uniform composition and
has heating values ranging from 4640 kcal/kg (8350 Btu/lb) to 5120 kcal/kg
(9220 Btu/lb).
To maintain combustion, the moisture content of the wood generally must
be kept below 60 percent. As the moisture content increases to 70 to 80
percent, the wood no longer has sufficient heat content to support its own
combustion and becomes useless waste.(96) The wood can be dried, however,
to a combustible state by a variety of means: (1) presses can be used to
squeeze the excess moisture out of the wood and can potentially reduce the
moisture down to 55 to 66 percent(97). (2) air drying can effectively reduce
moisture content of freshly cut wood from 50 percent down to 25 percent in
about a year (9°); and (3) hot air, using heat from boiler flue gas, can be
used to partially dry the wood.
Heat losses in the burning of wood consist mainly of those due to
moisture in the stack gas and the sensible heat of the stack gas after
96
-------
TABLE 35. CHEMICAL ANALYSES OF WOOD AND BARK OF VARIOUS TREE SPECIES TYPES
(92)
VO
Wood and Bark
Analysed
(dry basis), 7. by wt
Proximate
Volatile matter
Fixed carbon
Ash
Ultimate
Hydrogen
Carbon
Sulfur
Nitrogen
Oxygen
Ash
Heating value, kcal/kg
(Btu/lb)
Ash Analyses, 7» by wt
Si02
Fe203
Ti02
A12°3
Mn304
CaO
MgO
Na20
K20
so3
Cl
T>_ft_
"Southern
Pine" Bark
66.0
33.4
0.6
5.5
56.5
0.0
0.4
37.0
0.6
4943
<8900)
19.0
1.0
*
21.0
*
27.0
5.0
3.0
9.0
6.0
i.O
Pine
Bark
72.9
24.2
2.9
5.6
53.4
0.1
0.1
37.9
2.9
5016
(9030)
39.0
3.0
0.2
14.0
Trace
25.5
6.5
1.3
6.0
0.3
Trace
*
Oak
Bark
76.0
18.7
5.3
5.4
49.7
0.1
0.2
39.3
5.3
4649
(8370)
11.1
3.3
0.1
0.1
Trace
64.5
1.2
8.9
0.2
2.0
Trace
*
Spruce
Bark
69.6
26.6
3.8
5.7
51.8
0.1
0.2
38.4
3.8
4855
(8740)
32.0
6.4
0.8
11.0
1.5
25.3
4.1
8.0
2.4
2.1
Trace
*
Redwood
Bark
72.6
27.0
0.4
5.1
51.9
O.I
0.1
42.4
0.4
4638
(8350)
14.3
3.5
0.3
4.0
O.I
6.0
6.6
18.0
10.6
7.4
18.4
*
Redwood
82.5
17.3
0.2
5.9
53.5
0
0.1
40.3
0.2
5121
(9220)
Pine
79.4
20.1
0.5
6.3
51.8
0
0.1
41.3
0.5
5071
(9130)
-------
combustion. Other losses consist of radiation and miscellaneous heat losses
from the boiler and carbon loss in the ash. The various heat losses in a
wood-burning boiler are identified in Table 36. The loss in boiler efficiency
as a function of the moisture content of the wood is illustrated in Figure 14.
This loss is largely attributable to the latent heat of vaporization of the
water vapor in the stack gas. The loss of energy as a result of the sensible
heat of the stack gases is determined by the volume and temperature of the
stack gas. A high percentage of excess air and high stack gas temperature
will result in a reduced overall efficiency. Some of the sensible heat may
be captured by the use of heat recovery equipment such as combustion air
preheater and economizers or feed water heaters, and modifications in the type
of furnace can reduce the excess air requirements.
Wood waste is commonly burned in three types of equipment, pile, thin-
bed, and suspension furnaces. Prior to 1940, the Dutch oven was the most
common type of boiler used; see Figure 15. The wood is fed into the top of
the oven where it collects on a pile on the water-cooled grate. Combustion
air is fed through the sides of the cell and grate causing the wood to be
gasified and combusted. The hot gases are fed into a secondary boiler section
where they are combusted further. The Dutch oven partially gasifies or
TABLE 36. OVERALL BOILER EFFICIENCY AS A FUNCTION
OF WOOD MOISTURE CONTENT (92)
Percent Lost
Heat Loss Factors
5% Moisture 25% Moisture 50% Moisture
Heat loss to dry stack gases
Heat loss to moisture in fuel
Heat loss from formation of mois-
ture from hydrogen in the
9
0.5
7-8
9
4
7-8
9
13
7-8
Heat loss from incomplete
combustion W)
Heat loss from radiation and
unaccounted for
• 4
"T
A
*T
» A
> *f
21.5 23 34
Corresponding boiler Efficiency 78.5 75 66
(a) Based on 40% excess air, 400 - 500 F stack gas temperature.
(b) Based on stack gas temperature of 400 - 500 F.
(c) Based on Douglas fir bark fuel.
(d) Assumed.
98
-------
30
Q>
20
(A
in
Q
D
0>
I
» 10
"6
m
Stack gas
temperature.
0 25 50 75
Moisture, percent (wet basis)
Figure 14. Boiler heat loss versus wood moisture content.(95)
TO STACK
FUEL IN
Figure 15. Boiler with a Dutch-oven furnace.
99
(95)
-------
distills the wood and, therefore, can tolerate higher moisture contents than
direct combustion. This method is not extensively employed in wood-fired
boiler units today.
Most modern applications of wood firing utilize the thin bed type of
furnace with a stoker. The most common of these is the spreader stoker
shown in Figure 16. This fact is illustrated in Table 37, a summary of the
percentages of boiler sales for various boiler configurations in five
different size categories from 1965 through 1975. In stoker-fired arrangement
hog fuel or wood chips are introduced well above the grate permitting the
smaller particles to dry out and burn in suspension while the remainder of the
fuel continues in flight to the grate where the combustion is completed.
Various types of grates are utilized in stoker furnaces. In smaller size
boilers (less than 100,000 Ib of steam per hour), stationary or intermittent
dumping grates are common. For larger boilers, traveling grates or self-
cleaning grates are generally used. A boiler equipped with a traveling grate
is shown in Figure 16.
A A
Figure 16. Wood-fired spreader stoker.
(95)
100
-------
TABLE 37. WOOD FIRING METHODS FOR DIFFERENT SIZE CATEGORIES
FOR BOILERS SOLD BETWEEN 1965 AND 1975(92)
Firing
Methods
Spreader
Stoker
Underfeed
Stoker
Overfeed
Stoker
Suspension
Other
-
10-16
50.0
0
0
0
50.0
•
Capacity
16-100
1 — —
34.6
1.9
34.0
0
29.5
—
x 10-3 Ibs
100-250
—...i—
72.5
0
20.0
2.5
5.0
—
steam/hr
250-500
100.0
0
0
0
0
•
Over 500
•
66.7%
0
0
11.1%
22.2 %
Heat release rates on spreader stoker type operations commonly approach
1,000,000 Btu per hour per square foot of grate area with 35 to 70 excess air
and 400 F air temperature. (98) Generally, about 80 percent of the combustion
air is supplied through the grate and 10 to 20 percent is injected over the
grate to stimulate turbulence and mixing in the combustion gases inducing
rapid combustion and reduction of smoke emissions.(95) Spreader stoker type
boilers can handle wood up to about 55 percent moisture.(") Moisture
contents above 45 percent, however, decrease the combustion rate rapidly.(100)
Under these conditions furnace temperature must be maintained above 750 to
1000 F to maintain stable combustion conditions.("°'
The thin fuel bed and rapid burning rates of the spreader stoker result
in its being very sensitive to changes in boiler load. Control over boiler
feed rates and air supply is necessary to maintain stable combustion condi-
tions. A variation in the thin bed type furnace, the inclined type grate
shown in Figure 17, however, characteristically has a deeper fuel bed than a
spreader stoker. This large fuel inventory on the grate itself results in
its being much less sensitive to load changes.
In all types of stoker applications, care must be taken to prevent over-
heating of the grate in localized areas. Often, the fuel becomes unevenly
distributed across the surface of the grate resulting in irregularities in
air flow. Overheating occurs in those areas where the air flow is restricted
and may cause grate damage. Many times grates are water-cooled to alleviate
this problem. Careful control of fuel size is also an important factor in
preventing grate overheating by lessening the wide variation in fuel density
on the grate. Minimizing the amount of slack or material under 1/4-inch
101
-------
APPROXIMATE CONTOUR r
OF WOOD REFUSE
BED
WATER COOLED
INCLINED GRATE
SF.PARATELY
CONTROLLED
OVERFIRE
AIR SUPPLY
Figure 17. Wood-fired inclined grate.
(95)
102
-------
diameter that enters in the fuel is most important. Usually fuel sizes nf
less than about 1-1/4 to 2 inches with a maximum of 40 percent slack «e
specified for stoker applications.(101) percent slack are
Suspension firing of wood is similar to pulverized coal firing For
successful suspension firing, the wood should be dried and reduced to as
small a size as possible with a minimum of 50 percent of the wood particles
smaller than a 1/4 inch. (101) Suspension firing results in a simpler, less
expensive boiler than stoker firing, but requires more extensive hogging It
is recommended that an auxiliary fossil fuel, such as oil, natural gas, or
pulverized coal, be fired in suspension along with the wood.(101) Normally,
wood firing in suspension burning units should not exceed 40 to 50 percent
of the total heat input to the boiler, the rest being carried by the auxiliary
fossil fuel. A typical suspension fired wood boiler normally has a small
dumping type grate installed at the base of the unit to handle excess wood
ash or chips which may fall to the bottom without burning.
Urban and municipal solid waste—The solid waste disposal problem and
the energy shortage have focussed attention on the utilization of solid urban
and municipal waste as a direct boiler feed. Direct incineration is capable
of reducing the volume and weight of refuse by as much as 92 percent and
80 percent, respectively, and the heat generated can be used to produce steam
for heating and cooling or for generating electricity. The residue formed by
the thermal reduction process is inert and may be landfilled or in some cases
utilized as a construction material.
The recovery of waste heat in conjunction with the incineration of
municipal refuse was initially tried on water-wall boilers in Europe, parti-
cularly in Germany, on combined municipal incinerator steam power generating
stations. This was followed in the United States by both direct and combined
refuse fired boilers. The first direct-fired water-wall solid waste incinera-
tor was installed at the U.S. Naval Station in Norfolk, Virginia, in 1966.(102)
This was followed by other larger installations in Chicago, Harrisburg,
Nashville, Saugus, and several other cities.
The quantity of heat or energy that a biomass waste feed will produce
when burned is a function of its moisture content, ash content, and degree
of heterogeniety. A lower moisture and ash content in the waste will result
in a higher heating value. A highly heterogeneous waste, containing a
significant percentage of ash and inorganic noncombustibles, will have a
lower heating value than a waste with a high organic content. The limits of
these physical parameters as related to self-sustained combustion of refuse
is illustrated in Figure 18, a three-coordinate chart showing the range of
refuse that can be burned without auxiliary fuel. (-w^> The typically higher
moisture contents and percentage of noncombustibles in the municipal solid
waste limit their average heating value to about 4000 to 6000 Btu/lb, U^^
and the heterogenieties and ash content result in a furnace and boiler effi-
ciency of 65 percent as opposed to efficiencies in excess of 80 percent
obtained with coal, oil, or gas.(103)
Two general combustor designs are used to recover energy from refuse.
The first design employs a conventional refractory furnace followed by a
103
-------
o
•o
Percent Combustible
Figure 18. Composition limits for self-burning of refuse.U°3)
-------
waste heat boiler. The second and more recent design utilizes a water-wall
furnace; see Figure 19. The wall consists of closely spaced vertical water
tubes, each connected to the neighboring tube by welded steel fins. A moving
grate at the base of the furnace evenly distributes, mixes, and conveys the
burning refuse through the combustion chamber. The furnace is generally
followed by a main heat exchanger, superheater, and an economizer. The
water-wall furnace offers improved heat transfer efficiency over the refrac-
tory furnace and permits operation at lower percentages of excess air (150 as
opposed to 300 percent). (102) T^g features result in more effective utili-
zation of the waste feed and the generation of smaller volumes of combustion
gases and subsequently smaller gas handling equipment. The disadvantages of
the water-wall furnace is the slightly higher associated capital and operating
costs.
Typical waste incineration furnaces are capable of accommodating a wide
variety of heterogeneous waste feeds, e.g., commercial, residential, and
industrial and two of the major problems with the combustion of solid munici-
pal waste, the nonuniformities in composition and size and air pollution,
have been largely obviated by the utilization of agitated stokers and stack
gas cleanup equipment.
The boiler designs for various water-wall incinerator systems are funda-
mentally similar to each other and detailed information on one direct-fired
installation, the Chicago Northwest incinerator, is provided below. Informa-
tion on some of the other installations is presented in Table 38. (^03)
The largest waste-to-heat installation in the United States is the
Chicago Northwest Incinerator. The system was developed by the Ovitron
Corporation and has been in operation since March, 1971. The 1450 metric
tons per day (1600 TPD) plant consists of four 363 metric tons per day (400
TPD) incinerators producing a total of 440,000 Ib/hr of steam and 77 metric
tons per day (85 TPD) of metals.(103,105)
Shredded municipal solid waste, separated from the ferrous metals, is
fed directly to the incinerator feed hopper (see Figure 20). From the feed
hopper, the waste is introduced to the stoker by a hydraulic ram feeder. The
reverse-reciprocating stoker is specifically designed for burning municipal
refuse. The stoker is inclined and equipped with reverse-acting grate bars
that push the refuse back up the inclined slope, creating a mixing and
tumbling action. This action, coupled with the flow of air through the grate
bars, ensures effective burnout of the waste.
The ash and residue are pushed off the grate into a quench tank from
where it is hydraulically pushed up an incline slope and allowed to drain.
This quenching and drying arrangement produces a residue with less than 15
percent moisture and also provides a water seal preventing the infiltration
of air into the furnace.
To help dry and ignite the raw feed, the hot combustion gases are
directed over the incoming refuse. The gases are then passed through the
boiler section and economizer and introduced to an electrostatic precipitator
for removal of particulates prior to discharge to the stack.
105
-------
Figure 19. One form of water-walled incineration.
(92)
106
-------
Figure 20. Chicago northwest incinerator.
(103)
-------
TABLE 38. SUMMARY OF SELECTED DIRECT-FIRED REFUSE
TO ENERGY COMBUSTION PROCESSES(103)
LOCATION
Montreal
Canada
Chicago
Korthwest
f ncinerator
Harrisburg
Penn.
Nashville
Tennessee
Saugus
Mans .
DATE
OF
START
UP
1971
1972
1972
Late
1974
1975
STOKER
Jon Roll
Martin
Martin
Von Roll
Von Roll
CAPACITY
METRIC TPD
TPD
4x272
4x300
4x363
4x400
2x326
2x360
2x326
2x360
4x272
4x300
PARTICLE
SEPARATION
TECHNIQUE
Electro-
static
Precipi-
tator
Electro-
Static
Precipi-
tator
Electro-
Static
Precipi-
tator
Wet
Scrubbers
Dry
Cyclone
Electro-
Static
Free ip i-
tator
STEAM
FLOW RATE
kg/hr x 10-3
Ib/hr x 10~ 3
45
100
200
440
63
138
99
218
102
225
OUTPUT
~TEHP~
°C
Op
260
500
204
400
232
460
185
SAT
365
SAT
427
800
PRESSURE
kg/m2 x 10~6
Psig
1.55
225
1.7
250
1.7
250
1.03
150
4.3
USAGE
Heating
&
Auxiliary
Power
Limited
Auxiliary
Power
Auxiliary
Collant,
Steam
Power
COMMENTS
10-15Z of
input - ash
d scrap metal
Recovered
Magnetic
Metals
$16.5
Million
The boiler, approximately 12 meters (40 feet) in height, is constructed
of membrane water-walled tubes with extruded fins. The refractory surface
is limited to 4.6 meters (15 feet) above the grate to prevent corrosion of
the water walls when burning plastics. The boiler is designed with five
passes, providing for a maximum amount of heat recovery. Each pass is pro-
vided with a hopper to collect fly ash which is automatically returned to the
ash discharger where it is mixed with the other plant residue and trucked to
a landfill site.
There is no present market for the steam, and that not utilized in plant
to drive turbines for pump and blower operation is condensed in air-cooled
exchangers.
Supplemental Boiler Feed--
The use of refuse as a supplemental boiler feed has been more widely
practiced in Europe than in the United States. Large size installations in
Munich and Stuttgart, Germany, and Zurich, Switzerland, have been on stream
since the 1960's. The only major on-stream facility in the United States
utilizing refuse as a supplemental fuel is in St. Louis, Missouri, at Union
Electric's Meremac Plant.(!03) other projects, proposed or under development,
are listed in Table 39 along with a summary of some of the larger on-stream
installations.
108
-------
TABLE 39. WORLDWIDE INSTALLATIONS OF REFUSE-FIRED BOILERS
(105)
1. ENERGY RECOVERY PROCESSES
No.
1
2
3
4
5
6
7
8
9
10
Nome
American
Thermogen
Chicago N.W.
Incinerator
Montreal Incinerator
Issy-les-Moulineaux
Munich North
Incinerator
Munich Power
Station
Zurich 11 Incinerator
Basel II Incinerator
Osaka Plant
Itogo Plant
Principal
Producl(i)
Steam
Steam
Steam
Steam
Electricity
Electricity
Electricity
Steam
Electricity
Electricity
Electricity
Steam
Other
Products
Frit
Fe Me lali
Metal
Steam
Steam
Capacity
(Tons/Day)
1,650
(Proposed)
1,600
1,200
1,500
1,056
960
520
600
400
450
Capital
Costs
($Aon/Day)
11,800
14,400
12,500
15,300
15,400
NA
NA
NA
NA
NA
Operating
Coils
(S/Ton)
4.42
NA
7.00
7.70
13.96
NA
NA
NA
NA
NA
Revenue
(VTon)
3.01
NA
3.50
2.88
1.96
NA
NA
NA
NA
NA
Net Costs
(JAon)
3.41
NA
3.50
4.82
12.00
NA
NA
NA
NA
NA
Development Stahit
Pilot plant
Plonf completed Morch 1971
Plont completed Februory 1970
Plont completed 1965
Plant completed 1967
Plant completed 1971
Plant completed 1969
Plant completed 1969
Plant completed 1966
Plant completed 1968
-------
St. Louis supplemental fuel- -The incoming municipal and industrial refuse
is initially screened for the removal of large bulky items such as appliances,
furniture, or tires and processed through a shredder or air classifier and a
magnetic separator. The refuse, free of ferrous metals and shredded to a
particle size of less than 2.5 cm (1 inch), is conveyed by pneumatic feeders
into the two furnaces.
The 125 mw rated furnaces were originally fired with natural gas but were
modified to burn refuse and coal. The refuse burning ports were installed in
the corners of the furnaces, between the two middle coal burners. The milled
refuse is burned in suspension, in the same flame pattern as the pulverized
coal or gas, and as the furnace has no grates, the unburned particles fall to
the bottom of the ash hopper (Figure 21).
At full load, the refuse is fed at a rate equivalent to 10 percent of the
heating value of the coals or about 540 metric tons of refuse per day (600 TPD).
Based on average heat value of 2700 kcal/kg (5000 Btu/lb) for the refuse,
approximately one ton of coal is conserved for every two tons of refuse burned.
The manufacturer of the boiler cited several reasons for the low percentage
of refuse fired, among them being the corrosive potential of refuse, lack of
homogeneity in refuse, moisture content of refuse, decreased fly ash resisti-
vity, and the logistical and institutional constraints of reliably moving and
processing large amounts of refuse.
In addition to the steam generated from the burning of the refuse, credit
is also claimed for the ferrous metals recovered during the preprocessing step
and the fly ash collected in the electrostatic precipitators . The coal bottom
ash, previously used by the Missouri State Highway Department for snow-covered
roads, is now unacceptable for application to the roads due to the presence
of unburned wood, metal and other materials resulting from the burning of
refuse.
The test operation on the two boilers was hampered by technical
problems with feeding and conveying the refuse and did not operate at the
full anticipated load of 540 metric tons per day (600 TPD) of refuse. The
concept was, however, regarded by Union Electric management to be successful
enough to warrant an expansion of the project to handle essentially all of
the refuse generated in the St. Louis metropolitan region (2.2 to 2.7 million
metric tons annually (2.5 to 3 million TPY)) and burn it in the Meremac and
Labadie power plants . (106)
Little information was available on the environmental impact of burning
the refuse coal combination except that S02 emissions are somewhat less and
the particulate discharges are almost three times that experienced with pure
Direct Thermo Conversion to Electricity--
A process has been developed by the Combustion Power Company of Menlo
Park, California, in which refuse is incinerated in a modular fluidized bed
combustor and the hot gases passed through a gas turbine electric generating
system. The process has been demonstrated on an EPA-sponsored 63.5 metric
tons/day (70 tons/day) pilot plant using municipal waste as feed.
110
-------
INITIAL
SOPCRHEATER
ECONOMIZ
ERS
Figure 21. Meramec unit no. 1. Union Electric Company.
Ill
-------
The incoming refuse is shredded and air classified into heavy and light
materials; see Figure 22. The light materials reportedly account for
about 83 percent of the feed stream and consist of the light combustible
with about 15 percent inert materials such as metal foil or sand. (103) The
heavy material, consisting of the metals and inert material with about 25
percent combustible, is further separated to recover the ferrous and aluminum
metals.
The light refuse material is pneumatically fed into the fluidized-bed
combustor constructed of carbon steel lined with refractory brick and ceramic
fiber insulation. In the combustor, the refuse contacts suspended sand
particles which serve as a heat transfer medium to quickly heat the incoming
refuse to the ignition temperature of 810 to 1000 C (1500-1800 F). To improve
the electrical energy recovery the combustion reaction is conducted at a
pressure of 3.5 atmospheres (37 psig); higher pressures, of 8.7 atmospheres
(130 psig), have been recommended for a prototype installation. (103)
The exhaust stream from the fluid bed contains particles of sand, ash,
particulates, and a small fraction of molten aluminum. The cleanup stage is
very critical for the correct operation of the turbine electric generator.
To prevent erosion of the turbine blades the minimum particle size entering
the turbine should be considerably less than 5 microns. The initial separation
is done in a large cyclone separator to remove the larger particles. The
second and third cyclone separators are designed to remove smaller particles
and ash.
The gases exiting the third cyclone separator are directed into the two-
stage turbine-compressor and electric power generator. The gas expanding in
the first turbine drives a compressor which provides the pressurized air for
the fluidized bed combustor. The second turbine generates approximately 1 mw
of electrical power.
This system is a relatively unique concept in waste-to-energy conversion.
The front end processing system and electrical generating concept can recover
marketable materials and produce saleable electricity.
The system, however, has been hampered with solids separation problems.
The cyclone separators have proven to be inadequate for removing all of the
small molten aluminum particles, resulting in deposits of aluminum oxide on
the downstream turbine blades. A granular filter has been installed in an
effort to alleviate this problem; the success of the new filter is not known
as yet. The heterogeneous refuse fuel is also regarded as being a potential
problem as it may interfere with the fluid nature of the bed. If proper
velocities and temperatures are not maintained, large "chunks" may be formed,
possibly resulting in a plugged bed.
The idea of generating electrical power on site is highly cost intensive
and requires a balanced operation between two unrelated operations - disposal
of refuse and the generation of electric power. The concept has yet to be
satisfactorily proven, even on the pilot plant scale.
112
-------
SOLID WASTE PROCESSING
Shredded Waste
Storage
Generator
Exhaust Ducts
Turbine
Bag House
Filter
CONTROL ROOM
2nd Separator
Air Inlet
Figure 22. CPU-400 pilot plant.
-------
Pyrolysis
Introduction--
Pyrolysis has been defined as the physical and chemical decomposition of
organic matter brought about by the action of heat in an oxygen-free or low-
oxygen atmosphere.(108) This method of thermal decomposition has also been
referred to as partial oxidation or destructive distillation depending on the
method by which heat is supplied and the nature of the organic feed; in this
report, all of these processes are regarded as pyrolysis.
In recent years, there has been an increasing interest in applying
pyrolysis to solid organic wastes (biomass) principally to: (1) reduce the
volume of wastes requiring disposal in an environmentally suitable manner;
and, (2) to transform the organic waste into an alternate, easily usable
energy form. As a result, several systems have been developed utilizing
pyrolysis as one reaction in a multistep process, the entire process being
typically referred to as "pyrolysis".
Development Status--
Pyrolysis has been applied to a wide variety of biomass waste. Some of
the wastes on which experimental or more advanced pyrolysis evaluations have
been conducted are as follows.
Municipal/industrial solid waste
Wood waste
Agricultural waste
Livestock waste
Tires and rubber
Energy crops
Sewage
Most of the research on pyrolysis has been directed toward processing munici-
pal solid waste. These processes are not well developed as yet; at present,
there are only about 10-12 different systems in various stages of develop-
ment. (108,109) of these, 2 commercial size systems are onstream and 2 more
are under construction; the remaining systems are either in the pilot plant
or bench scale stages.
Chemical Reactions and Product Distribution--
Pyrolysis involves a complex process of simultaneous and consecutive
endothermic chemical reactions. In pyrolysis, the heat causes the organic
material to break down into smaller, simpler organic compounds yielding carbon
monoxide, hydrogen, carbon dioxide, methane, and various hydrocarbons. Two
of the principal reactions that occur during pyrolysis are described below.
C + H20 + heat —• H2 + CO
C + C02 + heat —» 2CO
The reactive portion of the solid waste is composed primarily of cellulosic
material. The decomposition of this material occurs in a temperature range
of 180 C (360 F) to 1600 C (3000 F) (HO) producing a mixture of solid, liquid,
114
-------
and gaseous fuels, the compositions and proportions depending on the operating
conditions Some of the fuels are of sufficient quality that they may be
blended with or substituted for conventional fossil fuels; others are of lower
quality and are amenable to on-site use for the production of steam or elec-
™ity\J;yPiC^ h!ating values for the by-products are 900 to 5400 kcal/m3
(100 to 600 Btu/scf) for gases, 5600 to 6200 kcal/kg (10,000 - 11 000 Btu/lb)
for solid char, and 3400 to 5000 kcal/kg (6000 - 9000 Btu/lb) for'liquids.
Reactor Types--
Primarily three basic reactor types have been used for pyrolysis reac-
tions: shaft, rotary kiln, and fluidized-bed. The shaft reactor may be
either horizontal or vertical and is the simplest of the three reactor types;
it is also the least capital intensive. In the horizontal type, the solid
waste is continuously fed into the reactor on a conveyor system (mechanical,
molten bed, etc.) where it is pyrolyzed to the solid, liquid, and gaseous
products. In the vertical reactor, the solid waste is fed into the top and
settles under its own weight. The produced gases diffuse up through the
reactor and discharge out the top. The solid waste is typically fed by screw
conveyors, rotary devices, and rams. The vessels are either lined with a
refractory material or metal capable of withstanding the high reaction temper-
ature, 180 - 1650 C (360 - 3000 F).
The rotary kiln consists of a metal rotary cylinder installed on
bearings and inclined slightly to the horizontal. The feed waste is intro-
duced into the upper end of the kiln and by rotation and gravity progresses
to the lower end where it is discharged. The metal cylinder is usually
lined with refractory brick. The rotation of the reactor provides mixing
advantages over the shaft reactor but makes sealing of the feed and discharge
ports a problem.
In the fluidized-bed reactor, the solid waste is introduced into a vessel
and is contacted by solid particles (e.g., sand) suspended by an upward
flowing gas stream. The solid particles, which may be heated in the same
vessel or an external vessel, provide the heat of pyrolysis. The fluidized-
bed reactor offers improved heat transfer and temperature control over the
other reactor types but suffers from erosion, entrainment of solid particles,
and gas velocity control.
Heating Methods--
There are 2 distinct methods of providing heat for the endothermic
pyrolysis reaction, direct and indirect. In this study, the direct method is
defined as the partial combustion of the waste and/or supplementary fuel
within the pyrolysis reactor to provide the heat of reaction. In direct
heating the combustion reaction consumes oxygen and generates C02 and 1^0
which dilute the product gas resulting in a reduced heating value. The use
of air as a source of oxygen further dilutes the gas with the large amounts
of N2 and when burned can cause potential environmental problems as a result
of NOX formation.
In the indirect method, the pyrolysis zone is separated from the heat
source. The separation may be accomplished by the use of a heat conduction
barrier (wall) or a separate heat transfer medium (e.g., sand, char, molten
115
-------
bed). For solid waste pyrolysis applications the barrier or wall is not as
attractive as the separate heat transfer medium due to corrosion problems and
the larger heat resistances of the refractory linings and slag coatings. The
separate heat transfer medium, however, suffers from solids transfer and
separation problems. In summary, indirect methods generate a less diluted
gaseous by-product but are generally less efficient than direct methods.
The general characteristics and methods of heating used by the different
reactor types are listed in Table 40.
Process Variables--
The major parameters affecting the product yields and composition are the
temperature, residence time/heating rate, and waste feed conditions. (HI) At
low reaction temperatures, the products are heavier in molecular weight, the
ratio of gases and liquids to solids is relatively low, and the gases that are
generated contain higher molecular weight molecules. As the reaction tempera-
ture increases, more cracking occurs forming more lighter weight gases richer
in hydrogen. This trend is illustrated in Table 41. The gaseous product mix
obtained from the pyrolysis of municipal solid waste from which glass and
metal components had been previously removed is shown in Table 41. The
composition of the pyrolysis gas is shown in Table 42.
TABLE 40. REACTOR TYPE CHARACTERISTICS
Indirect Heating
Wall Transfer Circ. Medium
Direct Heating High High
Type of Operational Heating Operational Heating Operational Heating
Reactor Simplicity Rate Simplicity Rate Simplicity Rate
Vertical Shaft + + - - +
Horizontal Shaft NONE NONE ... +
Rotary Kiln + + - - +
Fluidized Bed - + NONE NONE - +
Note: 1. A plus (+) entry indicates a virtue while a minus (-) entry indicates
a detriment.
2. A NONE entry indicates that no process development has been reported
in that category.
3. No entry implies neither a virtue nor a detriment.
116
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TABLE 41. INFLUENCE OF TEMPERATURE ON PYROLYSIS PRODUCTS (H2)
Products, wt percent
Temperature Pyroligneous
C Gases Acids & Tars Char
500
650
800
900
750
900
12.3
18.6
23.7
24.4
23.7
39.5
61.1
59.2
59.7
58.7
57.1
48.0
24.7
21.8
17.2
17.7
11.5
7.7
Mass
Balance
percent
98.1
99.6
100.6
100.7
92.3
95.2
Gases Produced per .454 kilograms
(1 Ib) of Combustibles
m3(cu ft)
0.05 (1.9)
0.08 (2.78)
0.10 (3.62)
0.09 (3.39)
0.14 (4.84)
0.25 (8.90)
kcal/m3
(Btu/cu ft)
2700 (300)
3380 (376)
3100 (344)
3160 (351)
4170 (463)
4020 (447)
kcal/kg
(Btu/lb)
320 (570)
580 (1045)
690 (1245)
660 (1190)
1500 (2700)
2220 (3990)
(a) At 1 atmosphere and 21 C.
TABLE 42. COMPOSITION OF PYROLYSIS GAS(112)
Gas Produced, percent
Constituent
Hydrogen
Methane
Carbon monoxide
Carbon dioxide
Ethy lene
Ethane
500 C
5.56
12.4
33.5
44.8
0.45
3.03
650 C
16.6
15.9
30.5
31.8
2.18
3.06
800 C
28.6
13.7
34.1
20.6
2.24
0.77
900 C
32.5
10.5
35.3
18.3
2.43
1.07
750 C
30.9
22.6
15.6
18.4
7.56
2.05
900 C
51.9
12.7
18.2
11.4
0.14
0.14
117
-------
The residence time and rate of heating also affect the yields of gas,
liquid, and char. Table 43 shows the products obtained from the pyrolysis of
newspaper at various heating rates. (*•") As can be seen, the char and gas
yields increased with a decreased heating rate and the yield of organic liquid
showed a general increase with heating rate.
Some pyrolysis reactors have been designed to accommodate specific waste
feed conditions while others are more flexible and operate with a variety of
waste fuel conditions. The flexibility of a process is usually determined by
the reactor type, operating conditions, and inorganic product utilization
considerations. The more selective processes will usually require preprocess-
ing of some form or another, e.g., shredding, drying, separation, etc. Pre-
processing, however, is generally desirable regardless of whether the process
requires it.
One feed condition that can influence the yield of the various products
is the moisture content. A study was conducted by the Bureau of Mines on the
effects of moisture content in solid municipal waste on the product yields and
composition.(113) it was discovered that the presence or absence of moisture
in the feed can significantly alter the product distribution. At the pyroly-
sis temperatures, the water-gas-shift, the steam-carbon, and the steam-hydro-
carbon reactions all proceed rapidly.
H20 + CO - C02 + H2
H20 + C -> CO + H2
H20 + CH4 -» CO + 3H2
Large quantities of moisture will shift the equilibrium of the above reactions
to the right. This trend is illustrated in Table 44, a summary of experi-
mental results on refuse pyrolyzed at 900 C (1620 F).(H3)
Description of Processes--
Table 45 presents a summary of the more significant pyrolysis processes
highlighting some of the major design and operating classifications. An "x"
entry indicates that the process qualifies for the specific classification,
no entry means that the process does not qualify for the classification,
and an "N.A." means that the information is not available. Each of the
tabulated processes is addressed in more detail in the following discussions.
Vertical Shaft Reactors--
Five vertical shaft reactor processes were selected for examination.
Garrett process--The Garrett Research and Development Company (recently
merged into its parent company, Occidental Petroleum Corporation) has modified
a coal conversion process to convert municipal refuse and other wastes into
synthetic fuel oil for possible use as a substitute for No. 6 fuel oil. The
process has been tested on a 3.6 metric tons per day (4 tons per day) pilot
plant over an 18-month period and construction has been completed on a
180 metric tons per day (200 tons per day) EPA-funded demonstration plant in
San Diego. (HO)
118
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TABLE 43. PRODUCTS FROM PYROLYSIS OF NEWSPAPER
(112)
Constituents
Gas
Water
Organic liquids
Char
Ash
Minutes
to 800C — > I
36.3
24.1
19.1
19.1
1.43
6
27.1
27.4
25.6
18.6
1.43
10
24.8
27.4
25.7
20.7
1.43
Yields,
21
23.5
28.2
26.2
20.6
1.43
wt percent
30
24.3
27.9
24.5
21.9
1.43
40
24.1
27.1
24.8
22.5
1.43
60
25.3
33.2
12.0
28.1
1.43
60
29.6
30.7
9.93
28.1
1.43
71
31.1
28.3
10.7
28.5
1.43
Kcal(Btu) in gas
per .454 kg
(1 Ib) newspaper
500
350
300
275
300
275
325
425
400
(2,000) (1,400) (1,200) (1,100) (1,200) (1,100) (1,300) (1,700) (1,600)
-------
TABLE 44. PYROLYSIS OF DRIED REFUSE AT 900 C
(113)
Characteristic
High Moisture
Refuse
Low Moisture
Refuse
Moisture in feed, wt percent
Yields per 0.9 MT (1 Ton) of
feed
Gas, cu meters (SCF)
Oil, liters (gal)
Ammonium sulfate, kg (lb)
Aqueous, liters (gal)
43.3
496 (17,741)
1.8 (0.5)
11.2 (25.1)
427 (114)
7.3
517 (18,470)
61.2 (16.2)
16.9 (37.5)
127 (34.1)
Gas Composition, vol percent
CO
C? and heavier
3
Heating value, kcal/m
(Btu/cu ft)
Heat available million kcal/MT
(million Btu/T)
Feed
Gas
(a)
v
11.4
18.1
51.9
12.7
5-9
4040 (447)
2.21 (9.65)
1.81 (7.93)
9-1
23.0
37.8
24.4
5.7
4910 (545)
4.06 (17.78)
2.30 (10.07)
(a) Metric ton.
120
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TABLE 45. PYROLYSIS AND PARTIAL OXIDATION CLASSIFICATIONS
Process
Name
Garrett
Battelle
TORRAX
Union Carbide
Purox
Georgia Tech
Barber- Co Iman
Monsanto
Land Card
DEVCO
West Virginia
Process
Type
Pyrolysis
Partial
oxida-
tion
Partial
oxida-
tion
Partial
oxida-
tion
Partial
oxida-
tion
Pyrolysis
Partial
oxida-
tion
Partial
oxida-
tion
Pyrolysis
Feed Characteristics
Size Separa-
Feed Types Raw Reduction tion Drying
MSW, sewage XXX
agricultural
and feed lot
wastes, tires
MSW.* X
MSW
MSW XX
Agricultural & X X
forest wastes
MSW X X
MSW, sewage X
waste,
tires
MSW X X
MSW XXX
Method
of
Heating
Indirect
Direct
Direct
Direct
Direct
Indirect
Direct
Direct
Indirect
Reactor
Vertical
shaft
Vertical
fixed
bed
Vertical
fixed
bed
Vertical
fixed
bed
Vertical
shaft
Horizontal
shaft
Horizontal
rotary
kiln
Horizontal
rotary
kiln
Fluidized
bed
Maximum
Reactor
Temperature
"C (°F)
482 (900)
1090(2000)
1650(3000)
1650(3000)
400-500
(750-930)
650
(1200)
1090(2000)
540(1000)
815(1500)
Reactor
Pressure
(Atm
Absolute)
1
1
1
1
1
1
1
1
* Municipal solid waste
-------
TABLE 45. (Continued)
Supple-
mental
Process Fuel
Name Required
Garrett
Battelle
TORRAX X
Union Carbide
Purox
Georgia Tech
Barber- Co Iman
Monsanto X
Land Card
DEVCO X
West Virginia
Product
Solid
kcal/kg
(Btu/lb)
5000
(9000)
6100-7200
(11,000-13,000)
3800
(7000)
5,500
(10,000)
Distribution
Liquid Gas
kcal/kg kcal/tnj
(Btu/lb) (Bttt/scf)
5,500 4500-5400
(10,000) (500-600)
900-1800
(100-200)
1000
(110)
3150
(350)
4500-5400
(500-700)
1080
(120)
N.A.
3600
(400)
Pilot Plant
Metric Tons Per
(Ton Per Day)
3.6(4)
1.8(2)
67 (75)
4.5(5)
23 (25)
0.7(.75)
32 (35)
6.3(7)
< 1 (1)
Status
Commercial
Day Metric Tons Per Day
(Ton Per Day)
180 (200)
Under construction
180 (200)
Operating
900 (1000)
Operating
1350 (1500)
Under construction
Other Resource
Recovery Options
Glass, ferrous
metals, aluminum
None
None
Ferrous metals
None
Ferrous metals
Ferrous metals,
glass
Metals
-------
,. ! P^CfS 1S schematically depicted in Figure 23. Incoming refuse is
first shredded to a particle size of 2 inches or less. An air classifier then
separates the light, organic fraction from the heavy', inorganic fraction. The
organic fraction is dried in a rotary drier to above 3 percent moisture
screened to reduce the inorganic content to less than 4 percent, and further
shredded to about 28 mesh size. The ferrous metals are magnetically reclaimed
from the heavy inorganic fraction and sand-sized, mixed-color glass of 99-7
percent purity is recovered from the remaining inorganics.
The organic material is fed to the base of the vertical shaft pyrolysis
reactor where it is mixed with burning char (indirect heating). Both materials
are conveyed into the reactor by the spent combustion gases from the drying
combustor. In the reactor, the finely shredded organic waste and the hot char
suspension rise upward and mix under turbulent flow conditions. At an opera-
ting temperature of 480 C (900 F), the organic material flash pyrolyzes into
oil, gas,char, and water products. The entire suspension flows out of the top
of the reactor into a cyclone separator, where the char is removed. A venturi
quench system, operating with recovered oil, quickly cools the rich effluent
product gas stream from 480 C (900 F) before extensive thermal cracking of the
liquid constituents occurs. The outlet gas is cooled further to about 43 C
(110 F) in a packed-bed scrubber before recycling to the combustor. The oil
product separates from the cooling water and is withdrawn from the bottom of
the scrubber.
Research was conducted on the pilot plant using a municipal solid waste
feed; the product yields are shown in Table 46. (1]-4)
The product gas, which accounts for about 27 weight percent of the
products, is not intended for market sale and is consumed by the system to
provide process heat. The comparatively rich gas has a heating value of
4500 to 5400 kcal/m3 (500 to 600 Btu/scf). Based on pyrolyzing the municipal
refuse, the gas is reported to have the following composition.
Component Volume Percent
H2 16.7
CH4 15-4
CO
17.9
C02 23.1
Co hydrocarbons 22.2
Cn-C7 hydrocarbons 4.7
Gas obtained from various agricultural products, however, is higher in
C02 and lower in caloric value. Typical values range from 40 mole percent
COo and 2250 kcal/m3 (250 Btu/scf) for rice hulls to 28 mole percent C02 and
3000 kcal/m3 (330 Btu/scf) for grass straw. Table 47 shows the representative
product yields obtained from laboratory experiments on other waste feeds.
123
-------
RAW REFUSE FROM
PACKER TRUCKS
MINUS 200
MESH TO
LANDFILL
PRODUCT "OARBOIL"
TO UTILITY
STREAM
NO.
1
>
4
t
1
7
t
t
10
RAW REFUSE FEED
LIGHT FRACTION FROM DRYER
FEED TO SECONDARY SHREDDER
SCREENED GLASS FROM
LIGHT FRACTION
FEIO TO PYROLYSIS REACTOR
PYROLYSIS PRODUCTS TO
OILS * OASES TO SEPARATOR
COLUMN
CHAR FROM PYROLYSIS
PRODUCTS
PYWJLYSIS GASES TO REACTOR
COMPONENT
RAW REFUSE
LIGHT FRACTION
LIGHT FRACTION
OLASS. CERAMICS. ETC.
LIGHT FRACTION
CHAR
OASES
OILS
GASES
CHAR
OASES
TONS/
DAY
1000
778
754
21
764
•0
434
240
434
•0
167
TOTAL
TONS/
DAY
1000
778
764
21
784
764
•74
to
167
TONS/
HflPER
TRAIN
* 1 A 2
STREAM
NO.
11
13
14
18
ie
PRODUCT PYROLYSI3 OIL
CLASSIFIER
FERROUS METALS FROM
MAGNETIC SEPARATOR
NONFERROUS MATERIALS TO
LANDfILL
SCREENED CLASS, CERAMICS
TO ROD MILL
PRODUCT GLASS FROM
rLOTATION CELLS
FRACTION
COMPONENT
OILS
HEAVY FRACTION
FERROUS METALS
NONFERROUS MATERIALS
GLASS. CERAMICS. ETC.
0 LASS PRODUCT
WATER
TONS/
DAY
240
226
70
«
100
•2
277
TOTAL
TONS/
DAY
240
22ft
70
«
too
13
277
TONS/
HRPEH
TRAIN
•1 FROW END SYSTEM THROUOH SECONDARY SHREDDER OKRATE 10 HOURS/DAY,
I DAYS/WEEK. TWO TRAINS REQUIRED.
'< rYROLYSIS SECTION WOULD OfERATE U HOURUDAY, 7 DAYS/WEEK.
LAROEST MODULE SIZE NOT RELEASED BY OARRETT.
Figure 23. Flow schematic of Garrett pyrolysis process.
124
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TABLE 46. TYPICAL PRODUCTS OF
Char fraction (20 wt percent), heating value 5000 kcal/kg (9000 Btu/lb)
48.8(b> Carbon
3.9 Hydrogen
1.1 Nitrogen
0.3 Sulfur
31.8 Ash
0-2 Chlorine
13 . 9 Oxygen (by difference)
Oil fraction (40 wt percent), heating value 5800 kcal/kg (10,500 Btu/lb)
C -I C r1^ v"krt«
57.5
7.6
0.9
0.1
0.2
0.3
33.4
Carbon
Hydrogen
Nitrogen
Sulfur
Ash
Chlorine
Oxygen (by difference)
3
Gas fraction (27 wt percent), heating value 5000 kcal/m (550 Btu/scf)
„ -, fn\ T.Tnf-QT"
O.l(c)
42.0
27-0
10.5
<0.1
5.9
4.5
8.9
Water fraction (13 wt percent)
Contains
Water
Carbon monoxide
Carbon dioxide
Hydrogen
Methyl chloride
Methane
Ethane
C^~C7 hydrocarbons
Acetaldehyde
Acetone
Formic acid
Furfural
Methanol
Methylfurfural
Ehenol
Etc.
(a) Shredded municipal refuse with about 90 percent ofQ^inorganics
Shredded municipa re""V"^™ awson Company of Middletown,
removed was supplied by the Black ClawsP ' pyrolyzed
was supplied by the BiacK ^j.awoun ««...r—_, ...
Product yields are based upon oven-dried feed, pyrolyzed at
^.j^rMij- hvdroaenation.
Ohio. Product yieias are ua.o^^. ~t— _.-_
about 500 C at atmospheric pressure without hydrogenation
(b) In units of wt percent
(c) In units of mole percent
125
-------
TABLE 47 AVERAGE YIELDS OF PYROLYSIS PRODUCTS FROM
DOUGLAS FIR BARK, RICE HULLS, GRASS STRAW,
AND COW MANURE (114)
Material
Douglas fir bark
Rice hulls
Grass straw
Cow manure
Weight percentage of dry
Oil Char Gas
35-50 50-25 5-15
40 35 10
50 20 15
30 45 15
feed
Water
10
15
5
10
The char accounts for about 20 weight percent of the products from
municipal waste pyrolysis and has a heating value of about 5000 kcal/kg
(9000 Btu/lb). A representative analysis of the char, based on pyrolyzing
municipal waste, is presented as follows.
Component Weight Percent
Carbon 48.8
Hydrogen 3.9
Nitrogen 1.1
Sulfur 0.3
Ash 31.8
Chlorine 0.2
Oxygen (by difference) 13.9
Approximately 2/3 of the produced char is burned as fuel for process heat.
No marketable value has been assigned to the remainder of the char except
perhaps as a solid fuel.
The liquid fuel obtained from the solid municipal waste pyrolysis
reaction accounts for about 40 weight percent of the products. It is a
complex, highly oxygenated organic fluid, lower in both carbon and hydrogen
than No. 6 fuel oil (see Table 48). The heat value of the pyrolysis oil is
about 5800 kcal/kg (10,500 Btu/lb) as compared to 10,000 kcal/kg (18,200 Btu/
Ib) for typical No. 6 fuel oil. The fuel oil is also more viscous than No.
6 fuel oil and at temperatures above 93 C (200 F) is thermally unstable
and will undergo changes which further increase its viscosity. The fuel oil
is also slightly acidic and will corrode mild steel at 93 C (200 F). Proper
blending of the pyrolysis fuel with No. 6 fuel oil, however, is reported to
result in a thermally stable, noncorrosive mixture which may be successfully
126
-------
TABLE 48. TYPICAL PROPERTIES OF NO. 6 FUEL OIL
AND PYROLYTIC OIL
Property
No. 6 oil
Pyrolytic oil
Carbon (wt percent)
Hydrogen (wt percent)
Sulfur (wt percent)
Chlorine (wt percent)
Ash (wt percent)
Nitrogen (wt percent)
Oxygen (wt percent)
kcal/kg (Btu/lb)
Specific gravity
Pour point C (F)
Flash point C (F)
Viscosity (SSU at 88 C)
Pumping temperature C (F)
Atomization temperature C (F)
85.7
10.5
0.5-3.5
<0.5
)
}2.0
10,000 (18,200)
0.98
18-29 (65-85)
66 (150)
90-250
46 (115)
104 (220)
57.5
7.6
0.1-0.3
0.3
0.2-0.4
0.9
33.4
5,800 (10,500)
1.30
32 (90)
56 (133)
1000
71 (160)
115 (240)
burned in utility boilers with properly designed fuels handling and automi-
zation systems.
Based on the pilot plant results, the Garrett Process will produce
approximately 1 bbl of oil, 64 kg (140 Ib) of magnetic metals, 55 kg (120 Ib)
of glass, 73 kg (160 Ib) of char, and 146 kg (320 Ib) of landfill material
from 0.9 metric ton (1 ton) of municipal solid waste.
As can be seen from Table 46, the produced water accounts for about
13 percent of the products. The water contains alcohol and other oxygenated
hydrocarbons and has a high BOD. It was stipulated, however, that the water
would present no disposal problem provided secondary sewage facilities are
available.<114>
Other pyrolysis tests have been conducted on cow manure. The oxygen
content of the oil was lower and the average caloric value was about 560 kcal/
kg (1000 Btu/lb) higher than oil from municipal waste. However, in view of
the restrictions being placed on NOX emissions, the high nitrogen content of
the oil (5-7 weight percent) was believed to make it an unattractive boiler
feed.(114)
The various advantages and disadvantages cited for the Garrett Process
are listed below.
127
-------
Advantages Disadvantages
• Production of low sulfur • Corrosive and unstable nature
fuel oil possibly adaptable of fuel oil
to utility boilers
• Relatively extensive
• Process adaptable to a preprocessing of waste
variety of waste feeds feed required
• No auxiliary fuel required • Large-scale tests of oil
in boilers not yet started
• Recovery of other resources,
aluminum, glass and ferrous • Low net thermal efficiency
metals about 45 percent (109)
Battelle pyrolysis process—Battelle-Northwest developed a pyrolysis
process in which solid waste is progressively dried, pyrolyzed, and finally
oxidized by an air/steam mixture to produce a low Btu fuel gas. The process
was evaluated on municipal waste and wood chips in the e,arly 1970's on a
3 to 5 ton per day pilot plant at Richland, Washington. '•LJ-->^
The system utilized a vertical shaft reactor (Figure 24) into the top of
which is dumped shredded solid refuse or waste. Air and steam are injected
into the combustion zone at the bottom of the reactor. The hot combustion
gases rising up through the descending waste provide the heat for hydrogen
production and drying and generate a low Btu fuel gas. The fuel gas, based
on the pyrolysis of MSW, has a heating value of 900 to 1800 kcal/m3 (100 to
200 Btu/scf), or about 80 percent of the energy charged to the system. A
typical analysis of the gas is shown below. (H5)
Component Mole Percent (dry basis)
H2 21.6
CO 21.0
CH4 1.8
C2H5 0.15
C2H4 0.27
02 trace
N2 43.3
C02 11.8
100.0
The slagged wastes tapped from the reactor bottom are quenched and
disposed of in a landfill.
128
-------
SOLID WASTE
DRYING AND
PREHEAT ZONE
PYROLYSIS ZONE
CHAR GASIFICATION ZONE
ASH ZONE
ROTARY GRATE
ASH RECEIVER
AIRLOCK ASH
DISCHARGE
AIRLOCK FEEDER
4—PRODUCT GASES
21% Hj.21% CO. 1.8% CH«,
43% N2. 12%C02;
172BTU/FT3;
PLUS TARS
100°C
200°C
700°C
800 °C
1000°C
AIR-STEAM
'lOO°C~500°C
Figure 24. Schematic of Battelle-Pacific Northwest gasification
process
129
-------
Two advantages cited for the process are its versatility and apparent
ability to process unsegregated refuse and its high thermal efficiency. The
major disadvantage is the production of a low Btu, nonstorable fuel gas.
Torrax process—The Torrax pyrolysis process was developed by Carborundum
Environmental Systems, Inc., and was demonstrated from 1969 through the early
1970's on a 68 metric tons per day (75 tons per day) pilot plant in Erie County,
New York. The process burns natural gas for preheating air to 1100 C (2000 F)
to help induce pyrolysis and achieve the high slagging temperature in the com-
bustion zone. Although designed to convert energy from refuse to steam, the
process can also be altered to produce a low-Btu fuel gas. Andco-Torrax is the
present process developer; they have constructed several units for European
operation.
A simplified schematic of the process is shown in Figure 25. Unsorted
refuse is periodically charged without pretreatment into the top of the
vertical shaft reactor. Air, preheated to 1090 C (2000 F) by passing through
a natural gas or oil-fired blast superheater, is introduced into the bottom
of the reactor. Natural gas heat requirements average about 250,000 kcal/
metric ton (1 million Btu/ton) of municipal waste. The air provides the oxygen
and heat to maintain the temperature at the base of the reactor at 2600 -
3000 F. As the refuse slowly descends in the reactor, the hot gases permeating
up through the refuse decompose the more readily combustible materials to form
the pyrolysis gas. The gas leaves the gasifier at a temperature of 480 -
540 C (900 - 1000 F) and passes into an ignitor where it is. combusted to
produce steam. The gas has a heat value ranging between 910 and 1350 kcal/nr
(110 and 150 Btu/scf) and a composition typical to that shown below. The
supplier estimates that an energy content of 57,300 kcal/metric ton (7.6
million Btu/ton) of MSW feed can be recovered from the fuel gas.(109)
Component Mole Percent (dry basis)
Carbon dioxide 9.9
Nitrogen 64.5
Oxygen 5.0
Carbon monoxide 9.5
Hydrogen 10.8
Methane 1.4
Ethane 0.2
Propane 0.13
The molten slag produced in the reactor ignitor is tapped and fritted
to produce a glassy aggregate. No marketable value was assigned to the
aggregate.
Union^Carbide Purox process--The Linde Division of the Union Carbide
Corporation has developed a slagging temperature pyrolysis system (Purox
System) which utilizes oxygen for the combustion of pyrolysis char to produce
a fuel gas for off-site use. The original pilot plant work was conducted on
a 4.5 metric tons per day (5 tons per day) reactor in Tarrytown, New York,
130
-------
SOLIDS
SEPARATOR
BYPRODUCT FUEL GAS TO |
INDUSTRIALPROCESSES
OR UTILITY BOILER
SECONDARY
COMBUSTION
BYPRODUCT STEAM TO
INDUSTRIAL PROCESSES
STEAM SYSTEM
Figure 25. Carborundum Environmental Systems, Incorporated - Torrax process.
-------
and a full-scale 180 metric tons per day (200 tons per day) demonstration
plant, funded by Union Carbide, has been operating since April, 1974, in
South Charleston, West Virginia.
Figure 26 depicts the flow diagram of the Purox Process. The waste feed
is initially shredded to nominal 15 cm x 15 cm (6 in. x 6 in.) size particles
after which the ferrous metals are removed in a magnetic separator. The
remaining feedstock, consisting primarily of organic wastes and gas, is fed
by a ram feeder into the side of the vertical shaft furnace. Oxygen, at a
rate of approximately 0.18 metric ton (0.2 ton) per ton of solid waste, is
injected into the base of the solid waste column where it reacts with the char
(the solid residue remaining after the pyrolysis of the waste). The 1650 C
(3000 F) bed temperature is sufficient to melt or slag the inorganic residue
(metal and glass) which continuously drains into a water quench tank where it
coalesces to form a hard, granular material. Essentially all of the drying,
pyrolysis, and combustion of the waste occurs in the lower 0.9 meter (3 feet)
of the reactor where the temperature ranges from 1650 C (3000 F) at the base
of the reactor to 120 C (240 F) at the 0.9 meter (3 foot) level. (HO)
The hot combustion gases rising up through the descending solid waste
provide the heat for pyrolysis and drying. The gas exhausting from the shaft
furnace contains some water vapor and oil mist and minor undesirable compo-
nents. These components are removed by a gas cleanup train consisting of a
water scrubber and an electrostatic precipitator. The removed materials
are disposed of by recirculating to the furnace.
The use of oxygen, rather than air, for promoting the combustion yields
a more concentrated gas fuel with a heating value of about 3200 kcal/m^
(350 Btu/scf). A constituent analysis of the gas resulting from the pyrolysis
of municipal solid waste is presented in Table 49. (H6) xhe gas is essen-
tially free of sulfur and has combustion characteristics similar to natural
gas; for this reason, it is suggested that the gas either be substituted for
natural gas in modified gas boilers or upgraded to pipeline quality and sold
as natural gas. Due to the high hydrogen and carbon monoxide content, Union
Carbide also suggests that the gas may be useful for synthesis of ammonia,
methanol, or oxygenated organic chemicals. (H6)
The major limitation on the use of the gas is the extra cost of compress-
ing it for storage and shipment. Three times more energy will be required to
compress the pyrolysis gas than to compress natural gas. As a result, Union
Carbide suggests that the market for the pyrolysis gas not be more than 1
or 2 miles from the producing facility. (H°)
The slagged reactor bottoms are comprised primarily of glass and alumi-
num. Table 50 presents an analysis of the residue. (H6) xhe residue is
claimed to be useful as a construction aggregate.
The only waste stream is the water condensed from the product gas at a
rate of about 80 gallons per ton of refuse. The stream, which is high in BOD,
may be reduced to acceptable limits (200 to 300 BOD) by existing technology
before discharge to a municipal sewer.
132
-------
SHAFT FURNACE
REFUSE
• FEEDER (A.}
SLAG CONVEYOR
PRSSUCT
> TO WA.5TeV.WCR
TRCATMtNT
Figure 26. Union Carbide Purox process
-------
TABLE 49. PUROX SYSTEM PRODUCT GAS ANALYSIS
(116)
Component
H2
CO
co2
CH4
C2H2
C2H4
C2Hfi
C3H6
C3H8
C
C5
C6H6
C7H8
Ct
H2S
/"ITT f\TJ
\j£i— \j n.
Organic Vapors (a)
o
Heating Value, Dry Basis, kcal/mj
Higher
Lower
Volume
Typical
24
40
25
5.6
0.7
2.1
0.3
0.3
0.2
0.5
0.4
0.3
0.1
0.2
0.05
0.1
0.15
(Btu/scf)
3330 (370)
3100 (345)
Percent - Dry Basis
Range
21-31
38-42
20-26
4-7
0.4-1.1
1-3
0.2-0.4
0.2-0.4
0.1-0.3
0.3-0.6
0.2-0.5
0.2-0.5
0.05-0.15
0.1-0.7
0.02-0.06
0.5-0.15
0.05-0.3
2700-2100 (300-390)
2520-3240 (280-360)
(a) Higher alcohols, aldehydes, ketones, and organic acids.
134
-------
Component
TABLE 50. PUROX SYSTEM RESIDUE ANALYSIS(116)
Weight Percent, Expressed as Oxide
Silicon
Aluminum
Calcium
Sodium
Iron
Magnesium
Potassium
Other
Component
Silicon
Copper
Carbon
Miscellaneous
Iron
Slag Fraction - 97 Percent of Total
Typical
59.7
10.5
10.3
8.0
6.2
2.2
1.0
2.1
Metal Fraction - 3 Percent of Total
Weight Percent
0.25-4
0.2-2.2
< 1
< 1
balance
Residue
Range
57-62
9-13
9-12
7-10
1-8
1-4
Residue
135
-------
The process will produce approximately 770 kg (1700 Ib) of wet gas (30
percent water), 90 kg (200 Ib) of oil and tar, and 135 kg (300 Ib) of slag
from 0.9 metric ton (1 ton) of municipal solid waste and 0.18 metric ton
(0.2 ton) of oxygen.(109)
The process has been operated on municipal and commercial refuse and is
compatible with the full range of materials normally experienced in domestic
and commercial refuse. A thermal efficiency of 75 percent can be obtained
with municipal solid waste provided the refuse moisture content is less than
45 percent and the refuse heating value exceeds 1950 kcal/kg (3500 Btu/lb).(116)
Some of the advantages and disadvantages cited for the Purox Process are
listed below.
Advantages
Low nitrogen content of gas
(minimal NOX pollution)
Relatively high heating
value of gas. Application
in existing power plant
Large size demonstration
project underway
Ferrous metals are
reclaimed
Disadvantages
• No reclamation of glass and
aluminum
• Fuel gas not compatible
with natural gas
distribution network
• Storage of fuel not
possible
• Requires high energy
oxygen generating plant
• Energy consumption of
oxygen generating facility,
approximately 1/3 of gross
reclaimed energy
Georgia Tech pyrolysis system—The Georgia Institute of Technology has
developed a mobile, low temperature vertical shaft pyrolysis system. Most of
the work has been done using agricultural or wood wastes, although limited
testing has been done with municipal refuse. The primary objective of the
process is to convert wet biomass waste into a low sulfur, char-oil fuel for
use as a substitute for coal.
A flow schematic of the mobile process is presented in Figure 27. (117)
The wet feed is continuously shredded and dried and introduced to the reactor,
where at 400 to 500 C (750 to 930 F) the feed pyrolyzes to a wet gas and char.
The use of low temperatures reduces the insulation requirements and mechanical
and material design problems and favors the production of large amounts of char
and small amounts of gas.
The wet gas exits the reactor and passes through a cyclone where particu-
lates are removed and through a condenser where the liquid fraction is
separated. Some of the gas is incinerated to provide the heat for drying the
136
-------
LO
Wet Sawdust
Vent to
Atmosphere
Fine Dry
Sawdust
Hot Water
Cold Water
I! lower
r-»... Cooling
Ql.lKI I. Ill
Kan
H- 1
[Hill
Condenser |
"/-• '|Mut_ Gati.
- (Waste
I Particles
m Gas
Charcoal
Hot Gas
By Pass to Atmosphere
Filter
T
1
Engine &
Generatoi
Electrical
Power
to the
Syatem
Blower
Oil
Mixer
Finished Product—
Charcoal and Oil Mixed
Figure 27. Mobile pyrolysis unit process flow diagram.
-------
feed, and the remainder is directed through a turbine electric generator to
provide electrical power for the system. The char is withdrawn from the
reactor and mixed with the condensed oil to form the product fuel.
When the feed contains little inert material, as in agricultural or wood
wastes, the produced char has a high heating value [6100 - 7200 kcal/kg
(11,000 - 13,000 Btu/lb)] and a low ash content. The use of municipal solid
waste as a feed material, however, is expected to introduce more inert
ingredients into the char and reduce its attractiveness as a fuel. (HO)
No information was available on the thermal efficiency of the process.
Horizontal Shaft--
One horizontal shaft reactor process, the Barber-Colman Process, was
examined in this study.
The Barber-Colman process—The Barber-Colman process utilizes indirect
heating by the use of a molten lead heat transfer media in a horizontal shaft
reactor. The process has been demonstrated on a 700 kg/day (1500 Ib/day)
pilot plant.
Figure 28 is a schematic flow diagram of the process. O The refuse
is initially fed to a metal detector where the larger pieces of metal (15 cm
or greater) are removed. The remaining material is shredded to about 5 cm
(2 in.) and fed to the reactor via an air lock. In the reactor, the refuse
floats on the molten lead surface where it is pyrolyzed at a temperature of
about 650 C (1200 F) producing a gas with a heating value of 450 - 5400 kcal/m^
(500 - 700 Btu/scf). The lead is circulated in the reactor via a gas lift
pump operating on the produced pyrolysis gas and heated from the top by
radiant tube burners. About one-fourth of the produced gas is consumed in the
gas lift system; the remainder would be available for sale. The system has
an overall efficiency of about 66 percent.
Some material dissolves and settles in the lead and at prescribed inter-
vals a portion of the lead bath is withdrawn and reclaimed by the addition of
new lead.
Rotary Kiln Reactors--
Two rotary kiln reactor processes, the Monsanto and Devco processes,
were examined in this study.
Monsanto Landgard process-- In the Monsanto Landgard process (Figure 29),
mixed municipal solid waste is pyrolyzed with supplemental fuel in a horizon-
tal reactor to form a solid residue and a low energy gas 1100 kcal/m3 (120
Btu/scf).
Development of the system began in 1969 on a 0.27 metric ton per day
(0.3 ton per day) pilot plant in Dayton, Ohio. The pilot plant was followed
by a 32 metric ton per day (35 ton per day) prototype plant in St. Louis
County, Missouri. Data from the prototypes were used to design a 910 metric
tons per day (1000 tons per day) facility which began start-up in Baltimore,
Maryland, in Spring of 1975.
138
-------
REFUSE
PREPARATION
HEAT BOILER
LOCK
EXHAUST
GAS
GAS
FURNACE
QUENCH SCRUBBER EXHAUSTER ~~METER
\ WS(
1—*-CHAR
LIQUOR
TOGAS
QUENCH
DISCHARGE
COOLING-
AUGER
CHAR
STORAGE
DRAW FROM
QUENCH S SCRUBBER
SETTLING BASIN
CIRCULATING
PUMP
TO "AIR-LIFT" PUMP-
SAMFLE
TO
ANALYSIS
Figure 28. Barber-Colman pyrolysis system flowsheet.
139
-------
CLEAN Alii TO
AIMOSJ>ME«£
HATER
OUEHCHIHO
FUEL
GLASSY
AGGREGATE
mow
Figure 29. Monsanto "Landgard" process. (119)
140
-------
The Landgard process will accept any typical residential or commercial
solid waste and sewage sludge; industrial wastes, however, are excluded
After removing oversize items, the waste stream is shredded into particles
about 4 inches in diameter. The shredded refuse is fed by a hydraulic ram
into the elevated end of a tilted, horizontal rotary kiln pyrolysis reactor
A portion of the solid waste is combusted using 40 percent of the air theore-
tically required for complete combustion. The remainder of the required heat
is supplied by an oil burner, located at the discharge end of the kiln. The
pyrolysis gases, formed by the heat of combustion, move countercurrent to the
waste and exit the kiln at the feed end. The temperature of the burning
refuse is maintained below 1100 C (2000 F) to prevent slagging of the residue;
the temperature of the exit gas is approximately 650 C (1200 F) . The
produced pyrolysis gas is a low energy fuel with a heating value, based on
MSW, of about 1100 kcal/m3 (120 Btu/scf) and a composition typical of that
shown below. (H8)
Component
Nitrogen
Carbon dioxide
Carbon monoxide
Hydrogen
Methane
Ethylene
Oxygen
The pyrolytic gases, exiting the kiln, are directed into an afterburner
(gas purifier) where they are combusted with additional air at about 760 C
(1400 F). Modular waste heat boilers (heat exchangers) are utilized to
recover approximately 91,000 Kg (200,000 Ib) of steam per hour. After exiting
the boilers, the gases are directed through a wet scrubber, a demister, and
an induced draft fan, and vented to the stack.
The hot residue is discharged from the kiln into a water-filled quench
tank and on to a flotation separator where the light carbon char is separated
from the heavy material. The heavy material is further classified into
ferrous metals and glass residue in a magnetic separator.
The residue carbon char consists of about 50 percent carbon (dry weight
basis) with the remainder consisting of mostly glass and ash. An analysis of
the char is presented in Table 51.
Approximately 72 metric tons per day (80 tons per day) of char residue,
64 metric tons per day (70 tons per day) of ferrous metal, and 154 metric
tons per day (170 tons per day) of glassy aggregate are recovered from the
910 metric tons per day (1000 tons per day) pyrolysis facility when processing
typical municipal solid waste.(118> At present, the char is disposed of in
141
Percent by Volume, dry basis
-------
TABLE 51. ANALYSIS OF CARBON CHAR RESIDUE
Component
Carbon
Ash and glass
Volatiles
Sulfur
Analysis, dry basis
50.0%
45.8%
4.0%
0.2%
Analysis of water-extractable fraction
Sodium
Calcium
Copper
Magnesium
Potassium
Boron
Strontium
Iron
Molybdenum
Silicon
Phosphorus
Chromium
Lead
Tin
Vanadium
Zinc
Aluminum
Cadmium
Manganese
Silver
Titanium
over 30%
0.1-1.0%
0.03-0.3%
0.03-0.3%
0.03-0.3%
0.01-0.1%
0.001-0.1%
0.001%*
0.001%*
0.001%*
25 ppm*
10 ppm*
10 ppm*
10 ppm*
5 ppm*
5 ppm*
1 ppm*
1 ppm*
1 ppm*
1 ppm*
1 ppm*
'a'Bulk density, 325-811 kg per cubic meter
Moisture content, 50% by weight
Heating value, dry basis, 7,000 Btu per pound
Less than figure shown.
142
-------
a landfill, although it has been suggested that the char may have application
as a soil conditioner when mixed with sewage sludge. The iron waste streak
is reasonably free of contaminants (Table 52) and has been recommended f^
metainfreee TabfeMf T .found^- • The glassy aggregate is relatively
metal free (Table 53) and is recommended for use in road construction in
asphalt paving mixtures . (Ho)
The various advantages and disadvantages cited for the process are
listed below.
Advantages Disadvantages
• 910 metric tons per day • Produces low-Btu gas fuel,
(1000 tons per day) commercial primarily applicable for
size plant has been built (though on-site generation of steam
initial operations have been
beset with difficulties) • Storage of gas not possible
• Reclaims glass and ferrous • Facility must be located in
metals close proximity to steam
consumer
• Requires supplemental fuel
• Disposal of solid residue
is still a problem
Devco—Devco Management, Inc., has developed a rotary kiln pyrolysis
process that is basically similar to the Monsanto Landgard process. The
most notable differences in the Devco System are the lower kiln operating
temperatures 540 C (1000 F) and the absence of shredding. Devco uses a
proprietary "selective pulverizer" which breaks up the low tensile strength
items in a low energy process. (HO)
Tests have been conducted on a 6.4 metric tons per day (7 tons per day)
pilot plant in Queens, New York, and a larger municipal solid waste pyrolysis
unit, 136 metric tons per day (150 tons per day), is currently under
construction in Brooklyn, New York.
As with the Monsanto process, the low Btu pyrolysis gas is combusted to
produce saturated steam in a heat exchanger. The burned char product is
claimed to have a heating value of 10,000 Btu/lb and produce less than 10
percent ash when burned.
Fluidized Bed Reactors--
The only fluidized bed pyrolysis process that has received significant
attention in the literature is the West Virginia process.
West Virginia process — The West Virginia University fluidized bed reactor
has been studied on an experimental scale on a 15-inch diameter vessel for the
Pyrolysis of municipal solid waste. Based on the results of the experiments,
the process was revised and theoretically scaled up and evaluated as a 910
143
-------
TABLE 52. QUALITY OF FERROUS METAL. RECOVERED
FROM PYROLYSIS RESIDUE (US') (a)
Component
Percent
Component
Percent
Iron
Tin
Carbon
Copper
Nickel
Lead
Manganese
Silicon
Chromium
98.850
.153
.150
.150
.140
.088
.048
.045
.035
Antimony
Sulfur
Phosphorus
Cobalt
Molybdenum
Titanium
Vanadium
Aluminum
Other
.020*
.016
.015
.010*
.010*
.010*
.010*
.001*
.249
(a\
v ''Bulkdensity, 576.5 kg per cubic meter
Iron, 98.857o by weight
Contaminants, 1.15% by weight
*Less than percent shown.
TABLE 53. ANALYSIS OF GLASSY AGGREGATE RECOVERED
FROM PYROLYSIS RESIDUE OJ.8}
Bulk density
2432 kg per cubic meter
Component
Glass
Rock and miscellaneous
Ferrous metal
Nonferrous metal
Carbon
Percent
65
28
3
2
2
144
-------
metric tons per day (1000 tons per day) plant by the Stanford Research Insti-
tute. _The process as conceptually designed, produces a rich fuel gas by
utilizing two fluidized beds and indirectly heating the solid wastes to avoid
dilution of the fuel gas by air or oxygen. (119) A simple schematic is shown
in Figure 30.
The solid waste is initially shredded, classified to remove noncombusti-
bles, and dried prior to introduction into the gasifier. In the gasifier
the shredded organic waste is contacted by hot sand at 815 C (1500 F) in a
fluidized bed. The gases formed by the pyrolysis reaction in the oxygen-free
atmosphere exit the gasifier and enter a cyclone separator where the entrained
char is removed. The cleaned gas is relatively rich, with a heating value
of about 3600 kcal/nr5 (400 Btu/scf); based on the pyrolysis of municipal
waste the gas has the following composition.
Component Percent by Volume (dry basis)
H2 44.5
C02 15.8
CO 24.7
CH4 7.0
C2H2 5.0
C2H4 1.5
C2H6 0.6
C3Hg 0.9
100.0
The sand withdrawn from the gasifier is fed to the combustor where it is
heated to about 950 C (1750 F) by burning the char collected by the cyclone
separator and the liquids recovered from the pyrolysis gas. The heated sand
is then recycled to the gasifier to heat and pyrolyze the solid waste feed.
A side stream of sand and ash is removed from both the gasifier and
combustor and screened to separate the sand from the waste ash.
The advantages and disadvantages for the process are cited below.
Advantages Disadvantages
• Pyrolysis gas is relatively • The two vessel process
rich and may be upgraded to has not yet been experi-
natural gas pipeline quality mentally proven on waste
• Pyrolysis gas fuel cannot
be stored
• Process suffers from problems
characteristic to fluidized
bed reactors, i.e., entrainment
and separation of particles
145
-------
PRODUCT
FUEL GAS
COMBUSTION
(SHREDDED,
CLASSIFIED
AND DRIED)
(TO SALE)
COMBUSTION
EFFLUENT GAS
(TO REFUSE DRYER)
GAS CLEANUP
AND STACK)
ASH AND
AGGLOMERATES
(TO SALE OR
LANDFILL)
Figure 30. Schematic of West Virginia University pyrolysis process.(119)
-------
Other Applications of Pyrolysis for Biomass--
Additional small-scale (bench-scale or small pilot plant) research has
been conducted on the pyrolysis of other wastes, livestock waste municipal
sewage, rubber tires, and automobile batteries to name a few. Ascription
of some of the results of specific experiments is detailed below.
Cattle manure--Due to the relatively large volumes generated daily and
the high organic content, the pyrolysis of cattle manure has received consi-
derable attention. Several papers have been published on the pyrolysis of
cattle manure and some experimental work (bench scale) was performed,
primarily in the early 1970' s. The results of two experimental research
studies are presented herein; one study was conducted by the United States
Bureau of Mines (USBM) (113) ; the other study was supported by the EPA.
The Bureau of Mines study was performed in a small, closed batch reactor
(Figure 31). The dried cattle manure was introduced to the reactor and pyro-
lyzed at 900 C (1650 F) to produce a gas, oil, and char product. An analysis
of the yields and compositions of the products is shown in Table 54. The gas
showed to be mainly a mixture of CO, C02, H2, and CH^. The light oil was
predominantly aromatic, with about 87 percent benzene, toluene, and xylene.
The char residue was about 50 percent ash and had a heating value of 4050
kcal/kg (7290 Btu/lb).
This study addressed the technological feasibility of pyrolyzing cattle
manure; no recommendations or statements were mad,e as to the commercial
feasibility of such a process.
The EPA-funded study utilized a tubular reactor to pyrolyze the cattle
manure. Helium scavanger gas was passed through the reactor to carry off
the produced gases (Figure 32). Operating temperatures were at 400 to 500 C
(750 to 930 F) . The typical pyrolysis product yields and a gas analysis are
shown in Tables 55 and 56.
Based on the results of the experiments, the process was scaled up and
evaluated on an economic basis. The evaluation concluded that, with predrying
the manure, the low energy recovery efficiency (20-30 percent) does not make
the process competitive with simple incineration when used to produce energy
fuels. The process was also plagued by environmental liabilities. The light
oils had a pestiferous odor and there was fear that the manure pyrolysates
would be carcinogenic, although no studies were conducted to substantiate
this belief.
Rubber tires- -In 1969, the Firestone Rubber and Tire Company and the
USBM investigated the feasibility of applying the pyrolysis technique to
used automobile tires in the USBM 3.5 cubic foot batch reactor; a process
flow schematic is presented in Figure 31, the same as used for manure.
Experiments were conducted at temperatures ranging from 140 C to 900 C
with residence times of 7 to 14 hours. (!2l) The experiments at low tempera-
tures resulted in high yields of oil and small quantities of gas.^ The
inverse was true for the high temperature experiments. Typical yields of
the pyrolysis products are shown as follows . (121)
147
-------
LEGEND
.p-
oo
/ Thermocouple
2 Electric furnace
5 Retort
4 Tor trap
5 Tubular condenser
6 Electrostatic preciplfotor
7 Ammonia scrubber
8 Acid pump
Steam
9 Corbon dioxide ond Hj
IO Caustic pump
// Large wet-test meter
12 Drying tube
13 Light oil condenser
14 Small wet-test meter
15 Gas sample holder
scrubber
— 1
1
5
1
Water
out
Water
in
V*
EK
• /
6
T
;ctr
r\
«•
odes
X
k»-
rt
6
T
1
Excess gas
is flared
Sample cock for
HgS and NH3 tests
To Btu and
sp gr recorders
Heating elements
Figure 31. Bureau of Mines experimental pyrolysis apparatus.
-------
TABLE 54. BOVINE WASTE PYROLYZED AT 900
Ultimate analysis of feed wt percent*
C
H
0
N
S
Ash
Yields
Gas
Oil
Aqueous
(NH4)2S04
Residue
Gas composition, vol percent
co2
CO
H2
CH4
r+
C2
Analysis of residue, wt percent
C
H
0
N
S
41.2
5.7
33.3
2.3
0.3
17.2
Wt percent of feed
38.5
5.8
15.9
0.15 (NH3)
36.3
24.5
18.0
27.5
22.7
7.3
49.4
0.4
0.4
1.1
0.3
Per .9 MT (1 ton) of feed
390m3 (13,940 cu ft)
49 liters (13.0 gal)
143 liters (38.3 gal)
30 kg (65.8 Ib)
330 kg (726 Ib)
Ash
Heating values
Feed, kcal/kg (Btu/lb)
Gas, kcal/m3 (Btu/scf)
Residue, kcal/kg (Btu/lb)
48.4
3950 (7,110)
4050 (450)
4050 (7,290)
* Dried to 3.6 percent moisture.
-------
1U6E CHAR
COUPLING PACKING
Ol
O
2nd TRAP - 78*C TRAP
WET TEST METER
Figure 32. Experimental pyrolysis apparatus
(120)
-------
TABLE 55. TYPICAL YIELDS OF PRODUCTS FROM THE
PYROLYSIS OF CATTLE MANURE (120)
Compound
JWt percent
.(a)
Water
Volatile
Tar
Noncondensible
Char
24
1
2
32
41
100
(a) Raw feed dried to 7 percent moisture.
TABLE 56. TYPICAL COMPOSITION OF PRODUCT GAS FROM
THE PYROLYSIS OF CATTLE MANUREU2°)
Compound
Mole percent (dry basis)
N2
°2
CO
co
C2H6
8.6
10.9
16
38.9
12.9
0.3
1.8
151
-------
Light Heavy
Temperature C Residue Oil Oil Gas Total
500 42.0 4.2 45.2 5.0 96.7
900 52.3 6.5 14.5 20.8 97.3
Based on these data, it was estimated that 0.9 metric ton (1 ton) of
pyrolyzed tires would produce the following.
Gas - 320 m3 (11,460 ft3)
Oil - 194 liters (51.5 gallons)
Residue - 474 kg (1,046 Ib)
The product gas contained over 50 percent hydrogen and had a heating value of
6300 kcal/m3 (700 Btu/scf ) . The residue contained mostly carbon with about
10 percent ash and had a heating value of 7500 kcal/kg (13,500 Btu/lb).
Raw sewage- - The USBM---- also conducted pyrolysis experiments using
sewage sludge as feed. The raw sewage sludge was initially dried to 23.5
percent moisture and pyrolyzed at 500 to 900 C. The yields and some of the
product analyses are shown in Table 57.
Environmental Aspects--
The two most significant environmental impacts of the pyrolysis systems
are (1) the reduction in landfill or disposal requirements of the wastes,
particularly municipal waste; and (2) the reduction in fossil fuel require-
ments corresponding to the energy content of the produced fuel. Pyrolysis
is also regarded as being more environmentally appealing than incineration
as a method for waste- to- energy conversion due to the lower air requirements
and reduced total volumes of flue gas (and associated pollutants) per ton of
fuel.
There is very little "hard" information available on the integrity of the
effluent streams from pyrolysis processes. And there is similarly limited
information on whether or not pyrolysis does present a significantly lower
environmental impact than does incineration. Table 58 presents a calculated
comparison of emissions from various thermal processes . (112) j^ was stated
that the results in Columns 1 and 2 are not strictly comparable, as different
waste streams were used and could have varied widely in composition. The
significant aspect is the lower S02 and NOX emissions generated from thermal
processing of municipal waste as opposed to burning coal or fuel oil.
A prediction of the quality of the effluents from the Monsanto Landgard
facility in Baltimore, Maryland, generally concurs with the data in Table
58. ' °' The particulates were expected to be less than 0.03 grains per cubic
foot, and the S02 and NOX emissions will be less than 100 ppm and 50 ppm,
respectively.
Hydrolysis - Acid-Based
Cellulosic bearing materials can be hydrolyzed in the presence of an
acid to form glucose.
152
-------
TABLE 57. PYROLYSIS OF RAW SEWAGE
(500-900 C)
(113)
Yields per 0.9 metric ton (1 ton) fuel:
3
Gas, m (scf)
Light oil, liters (gallons)
Tar, liters (gallons)
Ammonium sulfate, kg (lb)
Aqueons, liters (gallons)
Residue, kg (lb)
254 (9100)
21 (5.6)
87 (23.2)
18 (40.2)
242 (64.1)
262 (576)
Heating value of gas, kcal/m (Btu/scf) 6615 (735)
TABLE 58. STACK GAS ANALYSES, PPM BY
CORRECTED TO 12 PERCENT CO
Municipal Waste
Sulfur dioxide
Nitrogen oxides
Hydrocarbons
Chloride
Particulates,
Pyrolysis
130
55
9
20
0.03
Incineration
100
80
17
440
0.04
Other Fuels
Natural
Gas
0.3
170
-
-
0.01
No. 6
Fuel Oil
500
450
6
-
0.02
Coal
3,500
360
12
-
1
gr/scf
153
-------
C6H10°5 + H2° - C6H12°6
The generated glucose may then be used for a variety of purposes, one of which
is a feedstock for the fermentation to ethyl alcohol.
Yeast
C6H12°6 ' 2C2H5OH + 2C02
Although cellulosic materials such as corncobs, cottonseed hulls, peanut shells,
and bagasse have been proposed as potential feedstock for the hydrolysis-
fermentation sequence, only wood pulp and wood waste feeds have been proven
on a commercial scale. The waste disposal problem and the energy crisis
have engendered interest in utilizing municipal waste as a feedstock; however,
the scope of work has been limited to bench-scale experimentation and evalua-
tion.
Two fundamentally different acid-based processes have been utilized for
the production of sugar from wood: (1) dissolving the cellulosic material in
a concentrated-acid, followed by dilution and distillation, and (2) hydrolysis
in a dilute-acid solution at elevated temperatures and pressures followed by
separation of the acid and sugar.
The concentrated-acid process was applied on a commercial basis on a
300 metric ton per day plant in Regensburg, Germany, during World War II.
The process, referred to as the Bergins process, was based on an earlier
patent by Willstathter.(122) Chipped wood feed was dissolved in a 42-45
percent solution of HC1, followed by washing to remove the acid from the
residue and distillation to recover the acid. The remaining hydrolyzate
was spray-dried and used in the production of yeast fodder. The concentrated-
acid process produced a comparatively pure sugar product but required large
quantities of highly-corrosive reagent acid.
The dilute-acid process received its first industrial trial at the
beginning of this century. The process was first applied in a plant at
Georgetown, South Carolina, then at one in Fullertown, Louisiana. These
plants manufactured about 19,000 to 26,000 liters (5,000 to 7,000 gallons)
per day of alcohol from sawdust. Single-staged batch reactors were used in
which the sawdust feeds was hydrolyzed in the presence of a dilute sulfuric
acid catalyst. The low-yields, approximately 7 liters of 100 percent alcohol
per 100 kg of southern pine sawdust (20 gal/ton), and a decrease in the price
of blackstrap molasses resulted in the closing of both plants within 2 years
after World War II.(123)
The major drawback to the single-stage batch process is that the rate of
sugar production and destruction are almost equal. As a result, the yields
from the batch-wise process as practiced are only about one-third of the
theoretical yield. To improve the efficiency of the dilute-acid process,
Scholler developed a process in which dilute acid is injected into the top
of the hydrolysis vessel and withdrawn through a screen in the bottom. In
this manner, sugar production and extraction proceed simultaneously with the
sugar being withdrawn and immediately cooled to stop the destruction reaction.
The hydrolysis-extraction operation was accomplished by alternately percolating
154
-------
0.6 percent sulfunc acid through the wood feed and injecting steam into the
top of the reactor to press the solution out the bottom. This process
produced a 3_percent sugar solution with a 60 to 70 percent recovery effi-
ciency Typical yields were 21 liters per 100 kg of wood (61 gallons per
ton . The process was applied on a commercial scale in Germany and Switzerland
during World War II; the plants are no longer operative.
In 1943, the War Production Board recommended a study of the Scholler
process by the U.S. Forest Products Laboratory. A pilot-plant facility was
constructed based on a modification of the Scholler process, and the Vulcan
Copper and Supply Company was requested to operate the plant and conduct the
design of a commercial scale plant. The commercial plant was subsequently
constructed in Springfield, Oregon, in 1944 with a design throughput of 201
metric tons per day (221 TPD) of sawmill waste for a production of 41,600
liters (11,000 gallons) of 190 proof alcohol.(122) The actual production
rate, however, fell far short of the design rate and in total approximately
189,000 liters (50,000 gallons) of ethyl alcohol were produced before the plant
was surrendered to the Reconstruction Finance Corporation in 1947.
The pilot-plant operations begun at Marquette, Michigan, were transfered
to Madison, Wisconsin, where a process referred to as the Madison Wood-Sugar
Process was developed. This process involved percolating dilute sulfuric
acid through a reactor charged with wood. The process required shorter resi-
dence times than the Scholler process (2.5 hours as opposed to 16 hours), less
heat input, and higher alcohol yields. (122) jn the process, chipped wood
waste (chips, sawdust, and slabs) with up to 25 percent bark was loaded into
large reactors (Figure 33). Steam was passed through the bed of chips to heat
them to approximately 150 C. Dilute acid, with an initial concentration of
approximately 2 percent was introduced into the reactor until the average
acid concentration reached 0.6 percent at which time the feed acid concentra-
tion was decreased to 0.6 percent. After a short initial holding period
(20 minutes), continuous injection of the dilute acid and withdrawal of the
sugar product was begun during which the temperature of the inlet acid stream
was increased to 185 C. The run was continued at the 185 C temperature for
about 2 hours. At the end of the percolation, after draining the charge, the
liquor was emptied from the reactor.
The sugar solution removed from the bottom of the reactor was flashed from
20 atm pressure to cool it to 30 C and stop the associated destructive
reactions.(124) The solution was neutralized with lime and filtered to
produce a filtrate containing 5 percent reducing sugar which was concentrated
to a 50 percent molasses product; sugar yields ranged from 45 to 55 percent.
Approximately 58 kg (130 Ib) of sulfuric acid and 45 kg (100 lb) of lime
were required per 0.9 metric ton (ton) of hydrolyzed bark-free wood wasted **'
Additional tests were run on the pilot plant to evaluate the feasibility
of a hydrolysis-fermentation operation. Some of the results, showing the
volumes of reducing sugar and produced alcohol per metric ton of wood feed are
given in Table 59. (125) other by-products of the hydrolysis reaction were
(1) liquor, constituting the bulk of the insoluble residue, (2) methanol,
discharged with the flash stream from the hydrolyzer, (3) acetic acid, in
solution with the hydrolyzate and in steam from the hydrolyzer, (4) furfural,
155
-------
Ol
Figure 33. Flow chart for forest products laboratory process for producing molasses from wood.
-------
TABLE 59. TYPICAL HYDROLYSIS YIELDS
(125)
Ln
Type of
Wood
Spruce Chips
Douglas Fir Chips
Pine Chips
Fir Chips
Redwood Chips
Turpentine Spent Chips
Oak Saw Dust
Maple Slabs
Total Wt. of
Wt. of Dry Sugar Solution
Wood (kg)
147
178
159
193
163
230
246
186
(kg)
1,434
1,693
1,480
2,000
1,704
1,760
2,154
2,000
Reducing Sugar Yield of 95%
Concentration Alcohol
(%)
5.3
5.0
5.0
5.5
4.0
4.2
5.0
4.7
(liter/metric ton)
210
227
210
219
168
151
147
151
TABLE 60. ADDITIONAL HYDROLYSIS BY-PRODUCTS (124>126)
Item
Quality (wt. percent per metric
ton of dry wood waste feed)
Lignin
Methanol
Acetic Acid
Furfural
Nonfermentable Sugars
25-30
0.5-1.5
1.5-5.0
0.1-1.0
5.0
-------
resulting from the decomposition during hydrolysis and discharged with the
flash steam, (5) nonfermentable sugars in the hydrolyzate solution, and (6)
uronic acid and other sugar decomposition products. The representative
quantities of most of these by-products are given in Table 60. (12q-, 126)
Madison Pilot-Plant produced several hundred tons of wood-sugar and a larger
plant, based on an adaptation of the process, was operated by the Tennessee
Valley Authority for a short time following World War II. (127)
None of the above processes survived the post-World War II era. The
world demand for yeasts was easily met by cane and beet molasses, sulfite
liquor, whey and fruit products,(127) and the cost for generating ethanol
could not compete with ethanol derived from petroleum feedstock. As mentioned,
however, the recent increase in the cost of petroleum-based chemicals and the
waste disposal problem have rekindled interest in acid hydrolysis of cellulo-
sic bearing wastes (wood waste, refuse, etc.) as an economically feasible
method for the production of reducing sugars for subsequent fermentation to
ethanol. Current research has been limited to laboratory bench-scale studies,
some of which have been conducted at Dartmouth College. Hydrolysis decomposi-
tion rate data were utilized in the design of a mini-size reactor for hydro-
lyzing municipal refuse to sugar. A 1/4-inch diameter continuous plug flow
reactor was used to model the hydrolysis yields as a function of the tempera-
ture and residence times. Sugar yields from refuse reached 53 percent with
residence times of 20 seconds and operating temperatures of 230 C. The feed
slurry was, however, very dilute (1 percent) and resulted in low glucose
product concentrations (0.3 to 0.5 percent). Based on these results a full
scale plant processing 225 metric tons per day (250 TPD) of municipal refuse
was conceptualized.(128)
The conceptual process involves pretreatment by the Black Clawson "Hydro-
sposal" process followed by hydrolysis in a tubular flow reactor with recycle,
a neutralizer, and an evaporator to concentrate the sugar product (Figure 34).
Hydrogenation
Hydrogenation of biomass, or other organic bearing materials, involves
reacting hydrogen (generally contained in a synthesis gas) with the organic
substance under elevated temperatures and pressures. The produced synthetic
gaseous or liquid fuel generally has a higher heating value than fuels custo-
marily obtainable via other processes, e.g., pyrolysis.
The use of hydrogenation has been more extensively evaluated for the
production of synthetic gases from coal and as yet has found only limited
application for biomass waste. Two processes that have been demonstrated
in part, for converting biomass waste into synthetic fuels, are the Battelle
hydrogasification process and the Pittsburgh Energy Research Center's (for-
merly U.S. Bureau of Mines) COSTEAM process.
Battelle Hydrogasification Process--
Battelle's Columbus Laboratories have recently developed a process utili-
zing a hydrogasifier to convert solid waste into a rich synthesis gas amenable
to upgrading to pipeline quality. The hydrogasification unit has been demon-
strated on a 0.18 metric ton per day pilot plant (0.2 TPD), and an 1800 metric
ton per day (2000 TPD) large-scale facility has been conceptualized for
processing municipal solid waste. .._„
-------
VD
FRETREATED FEED
Y SLURRY HEATER
STEAM
GENERATION
550 psi
1 GOO CF
SCREW
FEEDER
REC.
MOYNO. ,
3LEED
TO DISPOSAL
WATER TO
LIMEST. SLURRY TANK
FLASH
REACTOR
psi
LIMESTONE.
•••> i
12 «
P2 psi
"ni
CENTRIFUGE
EVAPORATORS ( LTV, FF)
CONDENSER
Sra* r -
VA i
Q)
rrrFPf.
rlTr
ACID STORAGE
LIMESTONE
FEEDER
\' V
NEUT-
RALIZ-
ES
J
CENTRIFU6S
TO
DISPOSAL
Figure 34. Conceptual acid hydrolysis plant based on municipal solid waste.
-------
A schematic flow diagram of the conceptualized process is shown in
Figure 35. The shredded (unseparated) municipal waste is fed from the feed
hopper through the pressurized lock hoppers (17 atm.) and into the top of
the hydrogasification reactor. The waste fuel is charged to a free-fall or
moving-bed reactor where it countercurrently contacts 1100 C (2000 F) synthe-
sis gas stream composed predominantly of hydrogen. The synthesis gas heats
the waste to approximately 550 C (1000 F), converting it to a medium grade
[about 4500 kcal/cubic meter (400 Btu/cubic foot)] syngas which exits the
top of the reactor.
The unreacted solids pass through the bottom of the reactor into a
stripping zone where injected steam entrains the organic char, separating it
from the heavier inert (metal and glass) portion. The inert solids are
quenched to- generate supplemental steam and processed to recover ferrous
metals and glass. The separated char is transported to the oxygen-fed water-
gas shift reactor where it is combusted and converted into the hydrogen-rich
synthesis gas. Any ash residue is withdrawn from the bottom of the gasifier
and disposed of by any appropriate means.
Tests were conducted in the hydrogasifier in both the free-fall and
moving-bed mode using a mixture of 25 weight percent raw potatoes and 75
weight percent paper. Typical results and operating conditions from a run
made on the moving-bed are given in Table 61. Typical results made with the
solid waste in free-fall are given in Table 62. These tests were conducted
with a pure hydrogen feed gas rather than a synthesis gas, and heat was
supplied indirectly through the reactor wall. Major advantages cited for
the process are as follows.
(1) It permits the use of unseparated waste feed and postpones the
separation and recovery of inert materials until after the hydro-
gasification step. This concept is believed to enable easier
separation of the organic from the inert material due to the
increased density differences.
(2) It produces a raw product gas amenable to purification and
methanation by existing technology.
The major disadvantages are the more complicated and interdependent
reactor systems and the early stage of development. The system should be
easily amenable to processing other biomass feedstocks.
COSTEAM--
DOE's Pittsburgh Energy Research Center (formerly U.S. Bureau of Mines)
developed a process for converting solid organic wastes (paper, wood, manure,
etc.) into a useful fuel oil by heating the solid to about 300 C under carbon
monoxide and a steam pressure (100-300 atm) and in the presence of a sodium
carbonate catalyst, water and recycle oil.(129) Bench-scale tests were
conducted in a 500-ml autoclave, and limited continuous flow experiments
were performed on a 0.45 kg/hr reactor using a variety of waste feeds. Based
on the results, & 2.1 metric ton per day pilot plant was designed to process
carbonaceous wastes. The plant, currently in operation in Albany, Oregon,
under DOE sponsorship, is designed to convert waste wood into liquid fuel.
160
-------
hFeed
oppers
hoppers
High methane
product gas
Hydrogasificr feed
gas distributor
Char plus metal
and glass
Organic Char/Metal-Glass
Separation Zone
V
^•—Moving -bed or free-fall hydrogasif
Hof synthesis gas to hydrogasifier
^>:rr "" '
Entrained char
gasifier
Steam
injection/'^
Drawing Not To Scale
I'l
t
•
O O 0
« . o •
Metal
and glass
Saturated
steam
Ash discharge
Quench lank: For rne'al and glass. Generates
steam at 250 paig from sensible
heot in rnetal and glass
(§J Removal of metal and glass as a water slurry
Figure 35. Conceptual solid waste gasifier system.
161
-------
TABLE 61. TYPICAL EXPERIMENTAL RESULTS OF HYDROGASIFICATION
OF SOLID WASTE IN A MOVING BED REACTOR
Solid Waste Feed Rate
Hydrogen Feed Rate
Pressure
Temperature
Approximate Solid Waste
Residence Time
Carbonaceous Char Yield
Oil Yield
Water Yield
Product Gas Yield
Product Gas Composition
(volume percent^ dry basis)
C,H, = 0.50
o b
N2 - 0.74
100.00
3.95 kg (8.69 Ib) (dry basis)
4.72 kg (10.4 Ib) (as fed basis)
per hour
2.8 cu m, 100 scf, per hour
18 atm
840 C (1550 F)
21 minutes
0.154 kg/kg waste as fed
0.008 kg/kg waste as fed
0.400 kg/kg waste (dry basis)
0.86 cu m/kg dry waste
(14.0 std cu ft/lb dry waste)
H2
CH4
CO
CO-
2
C2H6
= 32.42
= 27.34 ;
= 24.20
= 13.30
1.50
162
-------
TABLE 62. TYPICAL EXPERIMENTAL RESULTS OF HYDROGASIFICATION
OF SOLID WASTE IN A FREE-FALL REACTOR
Solid Waste Feed Rate
Hydrogen Feed Rate
Pressure
Reactor Temperature
Approximate Solid Waste
Residence Time
Carbonaceous Char Yield
Oil Yield
Water Yield
Product Gas Yield
Product Gas Composition
(volume percent, dry basis)
H2
CH4 =
CO
co2 =
C2H6 -
C2H4 =
C6H6 =
N0 -
61.1
12.9
17.4
4.6
1.5
0.1
0.6
1.8
100.0
6.2 kg (13.5 Ib) as fed,
4.8 kg (10.5 Ib) as dry,
per hour
2.8 cu m, 98 scf per hour
(18 atm)
870 C (1600 F)
1 second
0.271 kg/kg waste as fed
not measured (less than 170)
0.247 kg/kg of dry waste
1.05 cu m/kg dry waste
(16.3 std cu ft/lb dry waste)
163
-------
A process flow schematic of the plant is provided in Figure 36. The
waste wood chips will be initially dried and shredded to a -50 mesh particle
size and slurried with the recycle product oil. A catalyst solution, consist-
ing of sodium carbonate in water, will be blended with the wood-oil feed
slurry. The resulting mixture will be preheated to about 230 C and introduced
into one of two lock hoppers, operating in alternate sequence, where the
mixture will be pressurized to 100 to 275 atm with carbon monoxide. The
slurry will be fed continuously to the reactor, where at 230-400 C and under
steam pressure, it will contact a gaseous mixture of CO and H^. The liquid
product will flow from the bottom of the reactor where it will be cooled and
depressurized. An oil centrifuge will separate the oil from the water. The
water will be collected in a sludge drum for disposal, and the oil will be
filtered and pumped to the recycle storage tank from where it will be with-
drawn either as product or recycle oil. Gases from the reactor bottoms flash
tank will be cooled to condense the heavier ends and flared. The reactor
off-gases will also be cooled to capture any condensate and flared. Conden-
sate from both gas streams will be disposed of and any char collected in the
bottom of the reactor will be withdrawn and disposed.
The oil yields are sensitive to operating pressures, temperatures,
reactor residence times, and feed type and are not clearly defined. Bench-
scale studies indicate, however, that oil yields can exceed 30-40 weight
percent of the raw wood feed. The oil product is highly oxygenated, contain-
ing in excess of 4 percent oxygen, has a viscosity in excess of 50 centistokes,
and, depending on the oxygen content, will have a heating value in the range
of 5600 to 9400kcal/kg (10,000 to 17,000 Btu/lb).(130,131) The oil is
reportedly very low in sulfur.(129)
The condensates from the reactor off-gas, reactor product flash tank,
wood chip dryer and preheater, and the process water from the centrifuge
constitute the liquid waste streams. Little is known about the environ-
mental integrity of these streams, and they may require treatment prior to
discharging into the municipal sewage system.
The gaseous waste streams are all flared and are not expected to present
a pollution problem. This conclusion should be substantiated, however, by
monitoring the composition of the gas streams.
Naval Stores Industry
The naval stores industry involves the production of turpentine, rosin,
pine oils, rosin oils, pine-pitches and tars from coniferous trees, specifi-
cally southern long leaf and slash pine. The industry dates back to the
early 1600's when the products were used principally in the manufacture of
wooden ships. The use of steel ships, however, forced the naval stores
industry to explore new markets for their products, and today the major uses
are centered in the retail sales, chemical and pharmaceutical, and paper and
paper sizing industries.
Naval stores industry may be subcategorized into three separate subin-
dustries depending on the method of harvesting and product production; they
are (1) gum naval stores, (2) wood naval stores, and (3) sulfate pulping.
164
-------
FEED PREPARATION
SODIUM CARBONATE
SOLUTION
RECYCLE
OIL
PRODUCT
OIL
PREHEATER
CO + H,
TANKS
REACTOR
FLARE
-------
Gum Naval Stores--
The gum naval stores are produced from the crude gum (oleoresin) collected
from chipped or wounded slash and southern long leaf pines. The gum contains
principally turpentine and resin in proportions and with a composition typical
of that shown in Table 63. The gum is collected every 1 to 2 weeks and
transferred to a central plant where it is steam-distilled, either batch-wise
or continuously to produce a variety of products, turpentine, wood rosin, and
tar.
The wounding and harvesting of the tree represents the oldest and most
labor-intensive method of extracting the oleoresin feedstock. The use of
chemical treatments (such as paraquot solutions) applied to the surface of
the tree near the wound have increased the production of resin; however, the
characteristically low pay scale and unappealing working conditions have
encouraged a migration of the labor force away from this industry. At
present, the gum naval stores represent the least productive of the three
naval stores industries and in the foreseeable future cannot be regarded as
particularly viable sources of fuel.
Wood Naval Stores--
The wood naval stores industry uses the stumps and other resinous waste
wood from cut-over pine forest. The wood is sometimes allowed to age for a
few years to permit the non-resinous parts to rot away after which time it is
hogged and shredded and introduced into the steam-heated extraction vessel.
A petroleum-base solvent (so selected for its ease of separation from turpen-
tine) contacts the wood chips and extracts the rosin and terpene oils. The
hot extract is drained off and fractionally distilled to recover the solvent,
rosin, and terpene oils.
The chips are steamed once more to recover any residual solvent and are
used as fuel or marketed as feedstock for particle board. From 0.9 metric ton
(1 ton) of wood, about 180 kg (400 Ib) of rosin, 30 liters (8 gallons) of
turpentine, 13 liters (3.5 gallons) of pine oil, and 5.6 liters (1-5 gallons)
of monoacylic hydrocarbons are produced.
The wood naval stores industry represents the second largest of the tree
industries in terms of total turpentine and rosin production. One of the
major products of this industry is pine oil which is not found in gum.
Sulfate Pulping Industry--
The off-gases and liquid residue from the sulfate (or kraft) pulping
process are now the principal sources of turpentine and a major source of
rosin (as tall oil rosin). This method for naval stores production is the
most recent and was not practiced on a commercial scale until after World
War I.(132)
The relief gases from the digesters for sulfate pulp contain turpentine
and pine oil. When the gases are condensed, the crude oil in quantities of
8 to 40 liters per metric ton (2 to 10 gallons/ton) floats to the top. The
oil contains 50 to 60 percent turpentine and 10 to 20 percent pine oil which
are separated by fractional distillation. The resulting turpentine contains
offensive mercaptans which are removed by a hypochlorite solution of ethylene
diamine.
166
-------
TABLE 63. THE COMPOSITION OF OLEORESIN
Commercial Per Cent
Fraction of of
Per Cent of Per Cent of
Compound in Compound in
Commercial in
Oieoresin Oieoresin Compound
Turpentine 20 a-Pinene
p-Pinene
Low-Boiling Matter
High-Boiling Matter
Rosin 80 Levopimaric Acid
Neoabietic Acid
Abietic Acid*
Dextropimaric
Isodextropimaric
Dehydroabietic Acid*
orDihydroabietic
Resenes
Fraction
60
35
0.07
5
32
18
18
7
7
4
4
10 .
Oieoresin
12
7
0.01
1
26
14
14
6
6
3
3
8
*There remains some doubt as to the presence of these compounds as primary
constituents of oleoresin. See Simonsen, F. L., The Terpenes. Volume III,
University Press, Cambridge, 1947, pp. 375-458.
The tall oil or liquid rosin is obtained upon acidification of the
digestor liquor. The tall oil soap is skimmed from the top of the liquor
and fractionated to produce turpentine, pitch, fatty acids, and rosins.
Product Application as a Fuel--
Most of the naval stores products, tall oil, pitch, and pine oils are
combustible but are viscous liquids and, as is, are not amenable for use in
commercial liquid-fueled boilers or combustors. The turpentine has a heating
value about 8000 kal/kg (15,000 Btu/lb) and could be considered as a possible
supplemental fuel. The turpentine could probably be best suited as a boiler
fuel rather than as an automotive fuel due to its volatilizing characteristics.
If the turpentine were hydro-cracked into smaller, hydrogenated molecules, it
167
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might serve as a suitable feedstock to a refinery; this would be an extremely
cost intensive method, however, to manufacture gasoline. In view of the
market value of turpentine as a solvent and chemical feedstock, its availabi-
lity and its high cost per Btu, it cannot be regarded as a likely candidate
for a supplementary fuel without major technological breakthroughs and complete
modernization of the industry. Paraquot stimulation, as noted earlier, has
increased naval stores products in growing trees substantially. Comparable
process technology improvements will also be required. Finally, competition
with pulp and paper and wood products industries for feedstock is a likely
source of economic difficulties.
Charcoal Production
Charcoal is commonly manufactured by low temperature distillation, or
pyrolysis, of hard wood wastes. The distillation of hard wood has been
practiced for decades, originally as a method for producing acetic acid,
acetone, and methanol (wood alcohol). The details of the manufacturing
process are technologically well known and are not presented in detail in
this study. Predried wood waste (sawdust, chips, etc.) is continuously fed
into the reactor or kiln. At a temperature of about 400 C (750 F) and in an
oxygen-deficient atmosphere, the wood is pyrolyzed to a rich gas and charcoal
solid is continuously withdrawn from the reactor. The product gas is cooled
to condense recoverable acids, alcohols, and tars. The charcoal product,
accounting for about 25 percent of the dry wood feed, is either sold as is
for a reducing agent or a purifying medium, or briquetted primarily for use
as a recreational fuel. Typical yields from the distillation of 1.8 metric
tons (2 tons) of raw hard wood are presented in Table 64. C1-33) As a recrea-
tional fuel, charcoal is attractive for its non-smoking properties and its
high heating value, 7200 - 7700kcal/kg (13,000 to 14,000 Btu/lb).
TABLE 64. TYPICAL DISTILLATION YIELDS FROM 1.8 METRIC
TONS (2 TONS) OF HARDWOOoC133)
Item Percent Yield
Charcoal 25.2
Crude Methanol 1.9
Autic acid or equivalent 2.9
Tar, oil 5.0
Gas 18.3
Water, etc. 46.7
100.0
168
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The use of other cellulosic materials as a feedstock for the manufacture
of charcoal has been investigated in recent years, and bagasse, peanut shells,
agricultural wastes, and soft wood waste have all been utilized as feedstock
in pilot-scale evaluations.(134,135) ^ resultg Qf ^ evaluatlons indicate
that these types of biomass waste are suitable charcoal feedstocks and produce
a charcoal with a heating value of 6100-7200 kal/kg (11,000-13,000 Btu/lb).(135)
No information was available on environmentally related problems with the
waste streams generated from the charcoal manufacturing process. The entire
process involves drying, pyrolysis, condensation, separation and combustion
and should be expected to produce generically the same solid (ash and residue
charcoal), liquid (condensed water and organic chemicals), and gases (pyroly-
sis, drying and combustion gas) as a pyrolysis process operating with wood
feed.
PRIMARY BIOCHEMICAL CONVERSION PROCESS
Methane Production by Anaerobic Digestion
Anaerobic digestion is a biological process by which bacteria converts
organic material to gaseous products in the absence of oxygen. It has been
used as a method of waste treatment for over 100 years. Anaerobic digestion
is used primarily for liquid waste treatment and more recently has been applied
to disposal of urban refuse. The conversion of wastes into an energy source
has been a recent adaptation of the process.
If the complexity of the biochemical reactions is ignored, anaerobic
digestion is a simple process. It occurs at lower rates and temperatures
than thermochemical processes and therefore is less energy intensive. Anaero-
bic digestion is usually considered to occur in three steps. In the first
step, complex organics are hydrolyzed to simpler organics. These compounds
are then converted to volatile fatty acids, carbon dioxide, hydrogen, and the
cell mass of acid-forming bacteria. In the last step, methane-forming bacteria
convert the simple acids formed in the second step to methane, carbon dioxide,
and methanogenic organisms. The rate limiting step in this process is the
slow growth rate of the methane-forming bacteria.
Microbiology--
Although all biomass feedstocks contain the major substrates necessary
for the growth of the general microbial population, the amounts and types of
substrates vary with the composition of each feedstock. Therefore, different
feedstocks support the growth of different types of bacteria.
The nonmethanogenic bacteria are a widely diverse group of anaerobic and
facultative bacteria. Obligate anaerobic bacteria appear to be mainly respon-
sible for acid production. A review of the counts and isolations of the
highly specialized group of methanogenic bacteria is given by Hobson, et al.(136)
An outline of the basic reactions involved in anaerobic digestion is
shown in Figure 37.
169
-------
Proteins nonprotein N Carbohydrates
Lipids
A<
Salts Waxes,
Hydrocarbon
efts, plastics,
etc.
Amino acids -* Ammonia
Simple sugars
Bacterial cells
Glycerol
/ plus
long chain acids
Hydropenation
cgradation (?)
Volatile fatty acids, H2, COj
(which?) ^NN lactic,
>A.succinic, *••'
\ethanol (?)
CH« CO,
SO«NO,
SH NH,
Bacteria, buffering
of medium
A "liquefaction"
B "mcthanogenesis"
Bacteria, salts
indigestible residues
Figure 37. Reactions occurring during anaerobic digestion.
170
-------
represented oy the following reactions.
C6H12°6 - ^ 2CH3COCOOH + 2H2
2 CH3COCOOH + 2H20 — +> 2 CH^OOH + 2H + 2CO
2 CH3COOH -- p» 2CH + 2CO
C6H12°6 —** 3CH4 + 3C°2
Critical Variables--
The critical variables involved in the maintenance of a proper environ-
ment are (1) temperature, (2) anaerobic conditions, (3) nutrients, (4) pH, and
(5) absence of toxic materials.
Two optimum temperature levels have been established for anaerobic
processes: mesophilic (30 C to 37.5 C) and thermophilic (49 C to 60 C).
Operation of a digester in the thermophilic range results in increased rates
of reaction, lower retention time, and a smaller required volume. Currently,
most sewage sludge digesters operate at the mesophilic level because heat
requirements to maintain the thermophilic temperature level are high. Since
more methane can be produced at the higher temperature, this increased produc-
tion must be weighed against the energy requirements. There has also been
speculation that digesters are more unstable at thermophilic temperatures. (•'•37)
While anaerobic digestion can occur in the pH range of 6.6 to 7-6, the
optimum pH is from 7.0 to 7.2. Below pH 6.2, the acidic conditions become
toxic to the methane forming bacteria. An increase in the volatile fatty
acids produced by the acid-forming bacteria can inhibit the methane production
because of the reduced pH.
Non-anaerobic or aerobic conditions in the digester cause instability
and, in time, complete failure. (138)
The raw material must be free of toxic substances. High concentrations
of salts, ammonia, sulfides, heavy metals, or other toxic organics may cause
instability or complete failure of the digester.
One-Stage Digester--
A conventional single-stage digester employs one tank for all phases of
digestion. The feed is introduced either periodically or continuously and
mixed with the digester contents. The effluent, which contains microorganisms,
residual feed, and intermediate products is withdrawn at the same rate.
171
-------
As the retention time is reduced, larger quantities of bacteria are
removed. The limiting retention time occurs when more of the bacteria are
removed from the tank than are reproduced. The limiting retention time is
usually three to five days. For increased reliability and practical control,
retention times of ten to thirty days are normally used.
Gas is produced continuously from the digestion tank. The gas is pro-
cessed to remove acid gases (chiefly CC>2 and t^S), dried, and compressed to
standard pipeline pressure.
The effluent from the digester is dewatered and the separated water is
either recycled or sent to a sewage treatment plant. The residual sludge
represents a disposal problem. Typically the sludge is disposed of by land-
fill, lagooning or incineration. The suitability of the residue as a ferti-
lizer varies with the quantity of nitrogen, phosphorus, and other chemicals
present in the cake. Their presence depends on the type of raw material
used in the feed.
Two-Stage Digester--
One variation of anaerobic digestion is the two-stage digester. A typi-
cal system is illustrated in Figure 38. In this system the acidogenic reaction
can be separated from the methanogenic reaction. The separate reactors are
operated in series.
The separation of the two stages could be done on a large scale only by
differing the retention times of the two tanks. Using an easily digestible
material as the feedstock to the first digester shortens the required retention
time in the first stage. A longer retention time in the second stage allows
the methanogenic bacteria to grow on the effluent from the first stage.
Feed
Gas
Gas
Effluents
Solids Recycle
Waste Solids Recycle
Solids
Waste SoUds
Figure 38. Two-stage anaerobic digestion.
172
-------
f J£!!n!dVttf if8 f a "W°;Sta8e system are CD the increased concentration
of methane and therefore higher Btu content of the gas, (2) the capability
of maintaining the optimum environmental conditions for each stage (3) reduc-
tion in reactor volume, and (4) increased stability of the reactors. (139)
The major disadvantages of a 2-stage system are the increased operating
costs over a single-stage system due to heating requirements(139) and probably
higher investment costs. Data are also sparse on operating characteristics
of these systems, and the data which do exist are at laboratory scale.
High Rate Digester--
The high rate digester is a single-stage system with recycle of bacteria
to increase the efficiency of the system. An example of bacterial cell
recycle is an activated sludge system. This method is applicable to dilute
wastes at high flow rates. Mechanical separation of the active bacteria from
the partially degraded solids increases the time for the reattachment of the
bacteria to the solids upon return to the digester. Therefore, a recycle sys-
tem is not suitable for wastes of high solids content which are not readily
degradable, because the required high solids concentration in the reactor will
probably make mixing power requirements prohibitive.
Feed Materials--
Anaerobic digestion is applicable to a variety of feed materials which
can be characterized by the following factors: (1) method and cost of collec-
tion; (2) methane yield from digestion; and (3) sludge characteristics.
Raw sewage and sewage sludge—Sewage sludge is the concentrated waste
obtained after various sewage treatment steps and typically contains 3 to 6
percent solids. The composition of the gas produced from digestion of sewage
is 65 to 70 percent methane, 25 to 30 percent carbon dioxide, and small
quantities of hydrogen, nitrogen, and other gases. Total gas production
ranges between 0.5 and 0.75 cu m per kg (8 and 12 cu ft per pound) of volatile
solids.
Refuse--The composition of urban refuse has been analyzed in numerous
studies. Gas production of a typical sample is approximately 0.4 cu meters
per kg (6 cu ft per pound) of volatile solids with methane composing 50 to
60 percent of the gas. Gas production depends primarily on the quantity and
form of cellulose present in the refuse. Refuse is deficient in the necessary
nutrients which must be supplied to the system either by mixing with sludge
or other nutritious raw material.
The Biogas Process, developed by IGT, is a continuous anaerobic digestion
system designed to process municipal refuse and sewage sludge. The process
is in the pre-pilot plant stage of development. Large-scale units (over 900
metric tons/day) have been designed, but not built by the Institute of Gas Technology.
The unit operations involved in the process are particle-size reduction,
separation of the inorganics, biological gasification, and gas cleaning.
Figure 39 is a block diagram of the Biogas Process.
173
-------
h
PROCESSES OPERATED 5 CAYS PER WEEK. 8 HOURS PER DAY
4-
PROCESSES OPERATED CONTINUOUSLY
MUNICIPAL
REFUSE
•P-
METALS,
GLASS.AND
INORGANICS
TO MATERIAL
RECOVERY
Figure 39. Block diagram of the biogas process.
(140)
-------
The incoming refuse is shredded to 6-inch nominal size before magnetic
and air separation of the ferrous and non-ferrous metal scrap. Additional
shredding of the organic fraction is necessary to reduce the partial size for
efficient digestion. The shredded refuse is stored and measured quantities
are withdrawn for further shredding to minus 20 mesh. The material is blended
with sewage sludge, separated from heavier particles which are washed and fed
to a holding tank.
The refuse-sludge mixture is pumped to heated (approximately 35 C)
digestion tanks which are mixed. Detention times of approximately 12 days
are anticipated. Raw gas from the digesters is processed to remove acid
gases which are sent to a sulfur recovery plant. The product gas is dried
and compressed for pipeline distribution. 0-40)
A material balance of the process for a nominal plant size of 900 metric
ton/day (1000 t/d) is detailed in Figure 40. Approximately 39 percent of the
solids are gasified, 31 percent are disposed of as sludge, and 1 percent are
removed in the liquid effluent. The BOD concentration of the liquid stream
is approximately 500 mg/1. The remaining 29 percent of the entering solids
are recovered as saleable scrap metal or glass.
The Dynatech anaerobic digestion process was developed to process
municipal refuse and sewage sludge. The design of the system is similar to
the design described for the Biogas Process. Preliminary designs and cost
estimates of a pilot plant (1.5 metric tons/day) and a commercial- scale plant
(900 metric tons/day) have been completed.
A material balance of the system based on 900 metric tons/day is calcu-
lated in Figure 41. (142)
Based on laboratory work done by John T. Pfeffer of the University of
Illinois, a thermophilic anaerobic digestion system was developed. The
digester temperature is 60 C. The preprocessing system design is similar to
the previously described refuse digesting systems. (144) A conceptual flow-
sheet is diagrammed in Figure 42.
Agricultural wastes- -Animal waste (including pig, cattle, poultry, and
sheep wastes) and other farm wastes such as corn cobs, straw, grasses, and
vegetable wastes have been investigated as sources of high Btu-gas from
anaerobic treatment processes. These investigations have been limited to
laboratory experiments from which a number of large-scale plants have been
conceptualized. (145,146,147) The major deterrent to large-scale plants is
the economic restrictions of collection and transportation of farm wastes.
Feed lots provide a large quantity of concentrated waste material which
is relatively easy to collect. Approximately 0.3 cu m per kg (5 cu ft of
gas per pound) of volatile solids is produced. Methane content is about
50 percent. Different types of animals produce manures which vary in the
amount of energy content. The more thoroughly the animal digests its own
food, the less energy available for methane generation by anaerobic digestion.
175
-------
995 Tons/day
(CONTINUOUS)
56.9% VS
CELLULOSICS — 454.8
GARBAGE 138.3
METALLICS 135.8
GLASS 165.3
PLASTICS 20.8
RUBBER,
LEATHER 10.6
TEXTILES 18.7
DIRT, ROCKS,
ASH 30.7
OTHER - 19._9
994.9
PRIMARY SLUDGE
147.7 (58.5% VS)
ACTIVATED SLUDGE
49.2 (63.0% VS)
AIR FOR COMBUSTION
530.0
CAUSTIC
(5.11
SOUR GASES
297.0
106 SCF/day)
EXCESS PIPELINE GAS
125.3
(6 x 104 SCF/day)
CONSUMER
BIOGAS™ PROCESS
INTERNAL OPERATIONS
WEIGHING & TIPPING
2-STAGE COARSE SHREDDING
DRY AND WET SEPARATIONS
FIBERIZING
STORAGE
BLENDING
BIOGASIFICATION
0.6
REJECTS FROM MAGNETIC
SEPARATION
GAS SWEETENING
GAS DEHYDRATION
SULFUR RECOVERY (?)
GAS COMPRESSION
I
FURTHER
TREATMENT
LIQUID STREAM
(2.9 MGD)
VOLATILE ACIDS - 2.4
OTHER SOLUBLES - 10.6
COMBUSTION
GASES - 567.0
347.9 STABILIZED
SOLIDS (48.2% VS)
REJECTS FROM AIR-
GRAVITY SEPARATION
T
TO MARKET
CELLULOSICS - 4.6
GARBAGE 2.2
METALLICS — 43.0
CUSS 162.3
OTHER 54.0
266.1
GRITS
(MATERIALS
' RECOVERY
TO LAN.D APPLICATION
(ALL FIGURES ARE IN TONS/DAY UNLESS INDICATED OTHERWISE)
B-34-4 95
Figure 40.- Mass balance summary for a 1000 ton/day biogas plant.
-------
Material Balance for Waste Digestion Process
Mass Units in Tons Basis: I Day
31
n
^ hMGVE
Ferrous 61. 2
Non-ferrous 1. 2
Total 62.4
~~~--
3. 8 x 10° cu ft <*« „
GAS SCRUBBER
fi
3. 8 x 10
Glass = 67. 5
Ash = 25.0
Total 92. 5
'TIC TROUUEL
IATOR ' SCREEN
RESOURCE
RECOVERY
• cu ft cog „
AIR *"*
SHREDDFR STCRAKF
CLASSir/CR j TA
- t /
/ /
/ /
/ /
/
Solids = 18G.4
Water = 435. 0
DIGESTER Total 621_ 4
OAS
CAKE
TO CISFOSAL
HG
DIGESTER DEWATERINr;
WATER
water = 2446. 6
TO RECYCLE water =
614. 9
TO TREATMENT FL.'-HT
^~-— ~-___^ ' / SLUDGE
^^~~-~ -^.Fced Classifier From
Waste Re.iect Shredder Solids = 37.5
Organics (except plastic) = 500. u 'tt>.
Metals = 80.0 16.
Glass
Plastics
Ash
Moisture
90.0 19.
30.0 15.
50.0 21.
250.0 37.
Water = 899.6
0 424. 8
8 0. 8 Total S37. 1
1 3.4
0 15.0
2 3.7
5 212.4
Total
1000.0
184.6
660.1
Figure 41. Material balance for waste digestion process.
-------
SHREDDER
waste t) C)
FEEDER
Chemical
feed
MAGNETIC
SEPARATOR
Reclaimed^***
ferrous scrap
BLENDER-SCRUBBER
»
ID
CONVEYOR
Heavy fraction
AIR
CLASSIFIER
To landfill
221J
BLOWER
To other
recovery units
Light fraction
Offgas
Slurry
DIGESTER
(60°C; 5-d detention)
Slurry
HS"
To other
energy-
conversion
units
GAS
SEPARATOR
~CH^
CO,
Figure 42. Thermophilic anaerobic digestion system.^ '
Laboratory experiments have shown that manures must be collected and
digested immediately after excretion to prevent destruction of the volatile
solids.
Residual digester solids have potential value as a fertilizer or feed
material.
Algae--Few actual results have been obtained on the digestion of algae,
but methane yields are expected to be in the same range as grass clippings,
or approximately 0.4 cu m per kg (7.0 cu ft per pound) volatile solids of
70 percent methane gas. One possible combination of feed materials which has
been suggested is the growing of algae in ponds fed by sewage, which acts
both as a nutrient source and digestible material. Residual material from the
digester would have good nutrient value and would be suitable as a fertilizer
supplement.
Anaerobic Process Concept Comparison--
It is clear from the work of many investigators that the primary con-
straint which must be overcome to commercialize anaerobic digestion in a
significant sense is the high capital cost associated with long digester
residence times for cellulose feedstock. Process developers have taken two
routes to achieve this objective: high-rate, single-stage systems with feed
pretreatment and solids recycle; and two-stage systems with interstage solid
recycle. Both concepts have a common problem. Developers are designing
their systems at very high solids concentrations in the reactors. In the
small-scale digesters where process development is proceeding, maintenance
of these concentration levels is not difficult and is not particularly
178
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consumptive of mixing power. However, experience in the pulp and paper and
municipal solid waste industries suggest that power requirements for large-
diameter vessels at concentration levels of six percent and greater scale
very unfavorably. It appears that most developers have sized their mixing
power requirements for large systems based on either sewage sludge digestion
practice (a considerably different solid than that which predominates with
the majority of biomass feedstocks) or as a direct function of vessel diameter.
The above-noted industrial practice at high solids concentrations suggests
that the diameter raised to the second or third power is more appropriate.
If this industrial practice noted proves transferable, digesters being
designed on the simpler bases will prove to be grossly underpowered and fail
at design conditions. Alternatively, they may be run at reduced feedstock
throughout and lower solids concentration, with very serious consequences
relevant to net energy production.
The high-rate, single-stage digestion systems are attractive because of
their inherent simplicity. Likewise, they are only a first-order extension
of existing technology. However, because the methanogenic and acidogenic
cultures are mixed, the product gas contains only about 50 percent methane.
Removal of approximately one-half of the stream in an acid gas removal system
may be economically prohibitive.
Secondarily, some research is proceeding, using caustic soda as a pre-
treatment agent, to allow more rapid solubilization of the cellulose in the
feedstock. From strictly process considerations, this is advantageous.
However, it must be recognized that the ultimate sink for the spent sodium
ion is the process water effluent, where it appears as total dissolved solids
(TDS). It can be removed from this stream with only the greatest difficulty,
in essence, requiring desalination technology. Furthermore, for certain
feedstocks, notably manures and kelp with high salt contents, the use of
caustic with its associated TDS load may be impractical.
The alternative is a more radical departure from the state-of-the-art,
the two-stage system. It is beyond question more complex, and the inter-
relation of the two stages is only poorly understood. In fact, there are
notable experts who claim the system is inoperative because the entire process
requires synergetics activity between acidogenic and methanogenic species.
However, this latter point is based on too literal an interpretation of the
two-stage concept. While the first stage is likely to be almost completely
acidogenic, with C02 concentration in the range 90-95 volume percent, the
second stage will likely contain both methanogenic and acidogenic organisms,
with the acidogenic at considerably lower concentration than in single-stage
systems.
The convincing argument to show that a second-stage fermentation is
plausible is simply waste treatment practices in the distilling and pickling
industries, where organic acid wastes abound. In the case of the two-stage
digestion system based on cellulosic biomass, it is necessary to maintain
the "methanogenic" culture at levels which insure the acid content in the
digester is below that toxic to methanogenic species. High concentrations
of active micro-organisms are much simpler to maintain in the second stage ^
of a two-stage system as compared to single-stage systems, because the "solids
179
-------
are not diluted by unreacted biomass, and consequently the higher active
concentrations translate into higher volumetric reaction rates.
The two-stage system offers an additional advantage; that is, it effec-
tively performs a gas phase separation. There does not appear to be signifi-
cantly different total gas production between one- and two-stage systems,
based on the meager data available. (139) However, the portion of the total
produced in first stage is almost totally C02- Consequently, the second
stage produces higher methane gas concentration (on the order of 80 volume
percent), with the commensurate reduction in acid gas removal requirements.
This reduction may amount to as much as 60 percent or more.
While two-stage systems offer several potential advantages, it must
be emphasized that the level of development is very much limited, and
undoubtedly, additional problems remain to be uncovered. However, it would
seem the potential deserves research support.
Enzymatic Hydrolysis
Cellulose is becoming increasingly recognized as an important potential
resource. Cellulosic substrates are used in energy production of materials,
protein, and essential chemicals. The advantages in the use of enzymes to
hydrolyze cellulose instead of acid are: (1) the enzyme is specific for cellu-
lose and does not react with impurities which may be present in the waste;
(2) hydrolysis occurs under moderate conditions--therefore, corrosion-resistant
vessels are not required, and the products do not decompose under high temper-
atures; and (3) the glucose product is relatively pure and of a constant
composition.(14-8)
The greatest drawback in the development of a process to convert cellu-
lose to glucose is the slow rate of hydrolysis of untreated substrates.
Therefore, increases in yields from enzyme hydrolysis are important in that
they can reduce the need for extensive pretreatment.
Cellulose is a polymeric insoluble substance. The physical structure
consists of chains which can be interacting or completely non-interacting.
Reactivity depends on the degree of interaction of the cellulose chains. Loose
chains or free ends are more reactive than highly ordered crystalline
cellulose. Most substances contain some reactive free chains, some crystalline
cellulose, and a spectrum of partially crystalline cellulose, and so exhibit
limited hydrolysis. (^9)
Although many fungi and bacteria degrade cellulose, the enzyme system
produced by Trichoderma viride has been examined most extensively as a source
of cellulase enzymes. Cellulase is a complex of enzymes and enzyme-like fac-
tors which hydrolyze cellulose. Total hydrolysis is prevented if a complete
enzyme system is not present. (^°> 150)
The moisture content of cellulosic materials must be above a critical
level before microbial decomposition begins. For wood, the critical level is
the fiber saturation point, usually 24 to 32 percent. Ten percent moisture
is adequate for decomposition of cotton. Moisture creates greater accessibi-
180
-------
t0 the substrate by swelling the cellu-
Some metals and metallic salts such as mercury, silver, copper, chromium,
and zmc salts contained in the ash of cellulosic materials are in general
inhibitory to microbial degradation. On the other hand, manganese, magnesium,
cobalt and calcium in the presence of phosphate are stimulatory.
Organic substances, such as ethanol, methanol, ether, and benzene, are
present as extraneous materials in cellulosic sources. Some materials promote
growth and others, such as soluble carbohydrates, provide substrates for
rapid growth of cellulytic microorganisms. Toxic substances, particularly
phenols, inhibit growth of microorganisms. Materials which are deposited in
the capillary structure reduce the accessibility of the cellulose to the
enzymes. Lack of sufficient nitrogen and phosphorus in most cellulose sources
reduces the microbial activity .
The physical association of lignin with partially crystalline cellulose
prevents degradation by most enzymes and microorganisms. Lignin is a complex
aromatic polymer of high molecular weight (Figure 43) which is degraded natu-
rally by enzymes of white-rot fungi. Lignin-degrading enzymes used in conjunc-
tion with celluloses represent a possible means of conversion of lignocellu-
losics. This system is being studied as part of a cooperative program by the
U.S. Forest Products Laboratory and the University of Wisconsin. (151,152)
An enzymatic hydrolysis process is being developed at the U.S. Army
Natick Laboratories in Natick, Massachusetts. A functional schematic diagram
of the process is pictured in Figure 44. A bench-scale integrated laboratory
facility has been set up to investigate the process. The equipment is designed
to study batch, s emi- continuous , and continuous processes. The reaction vessel
is 250 liters (66 gallons) and has a capacity between 454 and 1800 kg of
cellulose per month (1000 to 4000 Ibs per month).
The rate of hydrolysis of a number of cellulose sources is illustrated
in Table 65. The rate is slow for crystalline cellulose materials such as
cotton or bagasse; however, pretreatment increases the reactivity signifi-
cantly. Fibers obtained from the Black Clawson hydrapulping process are
good sources for hydrolysis, especially after milling. (148)
Wilke has proposed several conceptualized process schemes for enzymatic
hydrolysis of cellulose. A flow sheet of a process is shown in Figure 45.
Wilke has also made preliminary cost estimates of the system.
Several areas of uncertainty occur in an economic evaluation of enzymatic
hydrolysis. It is difficult to determine the value of the waste cellulose
material, which includes both the cost of acquisition and preparation. Second,
the quantities of enzymes which can be produced by fermentation and recovered
for recycle by filtration of the effluent are also uncertain. The rate of
cellulose conversion in a continuous system represents the most significant
unresolved process uncertainty. This must be answered to determine the cost
of disposal of the unconverted fraction. Without this information, reliable
assessments of enzymatic hydrolysis of cellulose for comparison with other
181
-------
(152)
Figure 43. A conceptualized lignin structure.
TABLE 65. ENZYMATIC HYDROLYSIS OF VARIOUS CELLULOSE SOURCES
Substrate
Cotton - Fibrous
Cotton - Milled
Bagaase
Bagaase - Milled
Black Clawson Hydrapulped Fibers
Black Clawson Fibers - Milled
Air Classified Municipal Refuse
Air Classified Refuse - Milled
7c Saccharif ication
1 hr
1
14
1
14
5
13
7
13
4 hr
2
26
3
29
11
28
16
31
24 hr
6
49
6
42
32
53
25
43
48 hr
10
55
6
48
36
56
30
57
182
-------
TRiCHODERMA
ViRlDE
MUTANT
pH 4.8
50 °C
CELLULOSE
_. 30%
ENZYME
0.1%
REACTOR
«_JL.
— -
SE
E
>
f^
)
i
t
fc r-i — - —
1
RECY
1 ENZ^i
AND
UNRE
CELL
i
=-.- ~ _ -
r
FILTER
I FERMENTATION
PRODUCT
/
\
SINGLE
CELL
PROTEIN
ALCOHOL
Figure 44. Conversion of cellulose to glucose
183
(148)
-------
AdsOf ption train
Waste pcper
685 T/day
5 sloqe counter cyrrent mixer-filters
339 T/doy
Superphosphate 9.75T
/doy, proflo oil I.625T
/day, woter 7.426* I05
GPO -—
6 s'oqe counler current mixer filter
Spent solids
416-44 T/doy
to reboiler (urnccer
Q power/steom
generation
Reducing sugars
33T/day
1.424 x I05 GPD
Hydrolyzer
82 % conversion
50°C,4.8 pH
average residence
lime 40 ^rs
Precipitated
moke up enzyme
4133 Its/day
Figure 45. Flowsheet of enzymatic hydrolysis.(153)
methods of treatment cannot be made.(153) Therefore, although enzymatic
hydrolysis may prove at some future date to be the more economic hydrolysis
method, the scenarios developed in this report will rely on the better
established acid hydrolysis process systems.
Biochemical Generation of Hydrogen
It has been demonstrated that a few biological systems produce hydrogen
by the direct photolysis of water. The photosynthetic process in some green
plants and bacteria can be altered by limiting the quantities of carbon
dioxide and oxygen available to the plant to induce hydrogen production.
The enzyme system is very sensitive to oxygen, which inhibits the evolution
of hydrogen.
Laboratory experiments carried out with Anabaena cylindrica, a blue-green
alga, have produced both hydrogen and oxygen from water and light. The
reaction is inhibited by nitrogen but insensitive to carbon monoxide. (154)
The conversion efficiencies of a system of this type are very low. Although,
theoretically, ten percent conversion of solar energy can be achieved by
photosynthesis, the conversion efficiency with hydrogen production is much
lower. Instead of allowing the evolution of hydrogen and oxygen, Calvin(155)
184
-------
has proposed a photoelectrochemical cell which uses the electrons formed in
the reactions to generate a current. This synthetic system would be a means
of converting solar energy directly to electricity.
These systems are in the very early stages of development and do not,
at this time, represent practical alternate energy sources.
SECONDARY CONVERSION PROCESSES
This section examines the various processes that could potentially be
utilized to convert the gas or liquid products generated from primary biomass
conversion process into more selective specific fuels or chemicals.
Gas Based Conversion Processes
Methanol Production--
Methanol has been demonstrated as being a satisfactory fuel substitute
for applications in automobiles, boilers and gas turbine generators.(156)
The advantages cited for methanol over conventional petroleum fuels are the
reduced environmental implications associated with its use.
Natural gas is currently the major feedstock for methanol production.
Methane is initially processed through a steam reformer to yield CO and E^
which are subjected to a water-gas reaction to establish the correct molar
relationship of approximately 2 to 1. The synthesis gas produced from some
pyrolysis processes, however, is rich in CO and H2 and could potentially serve
as a feedstock to a conventional methanol production process. The details of
the production of methanol from synthesis gas are established technology and
are only highlighted in this report.
The commercial methanol processes may be categorized into two classifi-
cations: (1) high pressure (> 100 atm) and (2) low pressure (< 100 atm).
High pressure methanol processing—Most of the earlier methanol produc-
tion was obtained from the high pressure processing scheme. Silver or copper
catalysts are utilized to generate methanol at a pressure of 300 atm and a
temperature of 300 C (Figure 46). The conversion of carbon monoxide is low
(12-15 percent) and is limited by the characteristics of the catalyst. More-
over, the process is not selective in producing methanol but produces higher
alcohols, methyl ethers, and methyl acetate. However, when viewing the
resulting methanol as a fuel, the presence of higher alcohols are not objec-
tionable as they increase the heat of combustion. The presence of higher
alcohols may also minimize problems associated with phase separation in
methanol-gasoline-water systems. With emphasis on the production of a methyl
fuel mixture, the Vulcan Manufacturing Company has conceptualized a high
pressure process employing longer residence times in the converter and subse-
quently higher conversions of carbon monoxide; see Figure 47. Vulcan claims
this concept produces a methyl product richer in higher alcohols and more
suitable as a fuel.(157^
185
-------
SYNTHESIS GAS
oo
ON
Purified Dry Gas
fc02, H23
Reactor Feed
•(
b
£
a
§
2
3
y
Stcaia
Spent
-------
REFORMER
HEAT RECOVERY FEED & RECYCLE COMPRESSOR CONVERTER
K.P. STEAM
SYNTHESIS GAS
oo
BFW PREHEATING
H.P. STEAM GENERATION
H.P. STEAM SUPERHEATING
C02
(OPTIONAL)
VENTS AS FUEL f
LETDOWH EXCHANGER &
HIGHER ALCOHOLS COLUMN RECTIFYING COLUMN DRUM SEPARATOR CONDENSER
Figure 47. Vulcan methyl fuel process.
(157)
-------
Low pressure methanol processing--A major breakthrough in methanol syn-
thesis occurred in the early 1960's when it was discovered that high methanol
yields could be obtained at low operating pressures of 50 to 100 atm using a
fixed-bed copper-zinc-chromium catalyst. The decrease in pressure resulted
in substantially reduced capital, operating and maintenance costs, and, since
the mid-1960's, essentially all new methanol plants have been of the low-
pressure type.
The low-pressure methanol catalyst has a high selectivity and produces
99-85 percent pure methanol, thus reducing the purification costs. The
catalyst is, however, sensitive to sulfur poisoning and limits the concentra-
tion of H2S in the feed stream to 0.5 ppm. Moreover, unlike the catalyst in
the high pressure process, the low pressure catalyst cannot be regenerated.
A schematic flow diagram, based on the Imperial Chemical Industries, Ltd.,
(ICI) low-pressure process is shown in Figure 48. (158) After compression to
about 50 atm, the synthesis gas is directed through an absorption sequence for
the removal of t^S and other sulfur compounds. The gas is then sent to a
series of guard chambers which hydrogenate the unsaturated compounds, remove
any remaining traces of I^S and chlorine compounds. This sequence of guard
chambers protects the water-shift and methanol catalyst from contamination.
In the next step, the water-gas shift reactor employs an iron oxide-
chromium oxide type catalyst to convert carbon monoxide and steam to carbon
dioxide and hydrogen. The objective is to adjust the hydrogen to carbon
monoxide ratio to that desired for the methanol synthesis. The normal temper-
ature range for this reaction is 380-510 C (650-850 F) .
Following the water-gas shift reaction, a second absorption train removes
excess CC>2 to reduce the load on the methanol reactor and other downstream
equipment. The purified gas enters the methanol reactor where at 50 atm and
250 C (480 F) the carbon monoxide and hydrogen are reacted over a catalyst to
form methanol. The product is subsequently purified in a devolatilization
column and dewatering column and distilled to separate it from the higher
alcohols. For use strictly as a fuel, the increased heating value of the
heavier alcohols would augment the combustion characteristics of the product
alcohol and the final distillation step could be eliminated in favor of
forming a methyl fuel blend.
Higher Alcohols--
An alternative to the standard low pressure (50 atm) methanol process is
to operate with a less selective catalyst at a higher pressure (~ 100 atm)
with the objective of producing a lower purity methanol at a higher yield
and heating value. As operating temperature and pressure of the methanol
reactor are increased, by-product formation (namely, methyl ether, methyl
acetate, ethanol, and higher alcohols) tends to increase as a result of the
non-selectivity. These by-products have higher heating values than methanol
and would not only increase the heat of combustion, but as stated earlier,
would improve the solubility of methanol in gasoline. Although the moderate
pressure processes are currently being marketed and, for natural gas feed-
stock, show a cost savings in overall plant production, the emphasis is not
on by-product formation but rather higher methanol yields. There is, in fact,
188
-------
2
SYNTHESIS
GAS
DSY GAS
COV.?RESSOS
PURIFIED
SYKTHESIS
i CO
V
SULFUR
H2S CONVERTER
STEAM
HIGH TEMP.
(McCW
°2
SYNTHESIS
GAS
H2 + CO
i
L. RECYCLE
fS-~~ -v^
H20 AND
SAS SHIFT co?
PURIFICATION REACTORS REMOVAL
REMOVAL
PURIFICATION TRAIN FOR SYNTHESIS GAS PREPARATION
PURGE TO FUEL
METHAWL REACTOR
VOLATkES
TO PROCESS
HEAT
INDUSTRIAL
METHANOL
V
CRUDE WATER AND
KETHANOL HEAVY ENDS
METHANOL SYNTHESIS
K
I » HIGHER
* ALCOHOLS
METHYL FUEL
Figure 48. Low pressure methanol process (based on ICI process).(158)
-------
very little published regarding intentional increases of by-product yield in
methane 1 manufacture.
Ammonia Production- -
Ammonia is not consumed as a fuel; in fact, the largest markets for ammo-
nia are in the manufacture of fertilizers and explosives. However, natural
gas fuel, which is in increasingly short supply, is used as the hydrogen
source for the manufacture of ammonia.
N2 + 3H2 -» 2NH3
The use of a gaseous substitute, derived from a biomass-to-energy conversion
process, as a feedstock for ammonia production would contribute toward
reducing the demand for natural gas. The synthesis gas, from either a
pyrolysis or hydrogasification reaction, already contains some hydrogen and
significant quantities of CO. The process for converting CO and H2 synthesis
gas to ammonia would be essentially the same as the process utilizing methane
as the feed, with the exception of the reformer. This concept was examined
by the city of Seattle in a study designed to determine the feasibility of
converting municipal solid waste into ammonia. (-J-Dy; The details of the
process are well known and are not examined in detail in this study.
Co-Cr Hydrocarbons--
Battelle's Columbus Laboratories has developed a series of catalysts
which convert synthesis gas to light hydrocarbons (C2-C5) in a Fischer- Tropsch
process. (160> Synthesis of the light hydrocarbons can be represented by the
following reactions.
(2n + 1)H2 + nCO =
(n 4- 1)H2 + 2nCO = CnH2n+2 + nC02
Conversions between 21 to 55 percent per pass of carbon monoxide have
been achieved. The hydrocarbon product formed has a composition similar to
that listed in Table 6&.
TABLE 66. LIGHT HYDROCARBON PRODUCT COMPOSITION
Volume Percent
Ethane
Propane
Methane
Water
Total
190
-------
The product gases can be used as a synthetic natural gas (SNG) which
would have an increased heating value over normal methane. Separation of
ethane from the product gases could yield a source of substitute petro-
chemical feedstock.
The process is in the laboratory development stage and represents a
possible future use for synthesis gas produced from several processes such
as pyrolysis or gasification.
Higher Hydrocarbons (Fischer-Tropsch Synthesis)--
The Fischer-Tropsch synthesis is basically the catalytic conversion of
a mixture of carbon monoxide and hydrogen to a mixture of hydrocarbons and
various oxygenated organic compounds. The nature and quantities of products
are dependent on the catalysts and operating conditions used during the
reaction.
The Fischer-Tropsch synthesis process was developed in Germany in the
early twenties. Several large-scale plants were erected before the war and
became a reliable source of fuel and chemical feedstocks. Several large
plants were erected in Japan and demonstration plants were built in England
and the U.S. A plant completed in Brownsville, Texas, in 1950 was designed
to convert 2.5 million cubic meters per day (90,000,000 cubic ft/day) of
natural gas to synthesis gas for the production of 326,000 metric tons per
year (360,000 ton/yr) of gasoline and other liquid fuels, and 36,000 metric
tons per year (40,000 ton/yr) of chemical products. Many technical diffi-
culties were experienced, primarily in the synthesis sections, and economic
considerations dictated shutdown decommissioning of the plant. (161)
The only operating plant at the present time is located at Sasolburg,
South Africa, and has a capacity of 113,000 metric tons per year (125,000
ton/yr) of primary products. In the Fischer-Tropsch process as presently
practiced at the Sasol-I plant, synthesis gas is produced from coal; the
gas is purified to remove sulfur compounds which would poison the catalysts;
and the mixture of carbon monoxide and hydrogen is fed into the catalytic
reactors. The recovered products are separated by solvent extraction and
fractional distillation techniques.
The most significant problem associated with large-scale operation is
the method of dissipation of heat from the reactors to avoid inactivation
of the catalyst. The heat is generated by the hignly exothermic reactions.
The optimum temperature ranges for nickel and cobalt catalysts are 170 to
205 C and 200 to 325 C for iron. Several methods and various designs of
reaction vessels have been used to achieve this heat removal. Originally,
water under pressure was used as the cooling medium. A fluidized-bed cataly-
tic reactor is used at the Sasol plant. Experiments have been carried out
with oil circulation, slurry, and hot-gas recycle. (162) xhe Sasol-I plant
uses both the fixed-bed (iron-cobalt catalyst) Arge reactor and the fluidized-
bed (promoted iron catalyst) M. W. Kellogg reactor. The product distributions
for the two processes, as seen in Table 67, are quite different. A breakdown
of the C5+ fractions are listed in Table 68.(163)
191
-------
TABLE 67. PRODUCTS OBTAINED FROM KELLOGG AND ARGE
UNITS OF SASOL-I PLANT(163)
Distribution, percent
Product Kellogg Arge
Methane 13 . 1 7.8
Ethylene 4.4 0.6
Ethane 5.8 2.6
Propylene 12.8 3.9
Propane 3.4 2.2
Butylene 10.0 2.5
Butanes 3.2 2.4
05 and above 39.0 75.7
Non-acid chemicals 7.3 2.3
Acids 1.0
TOTAL 100 . 0 100 . 0
TABLE 68. COMPOSITION OF THE C5+ FRACTIONS (163)
Distribution, percent
Kellogg Arge
Product C5-C10 CU-C18 C5-C10
Paraffins 13 15 45
Olefins 70 60 50
Aromatics 5 15 0
Alcohols 655
Carbonyl Compounds 6 5 Trace
TOTAL 100 100 100
C11"C18
55
40
0
5
Trace
100
192
-------
A second plant, Sasol-II, was announced in 1974 and is scheduled to go
onstream ih 1979-1981. The Ralph M. Parsons Co. was awarded a three-year
ERDA contract in 1974 which will include preliminary design work on a Fischer-
Tropsch synthesis plant in connection with a coal-oil-gas refinery.
Liquid-Based Conversions
Methanol to Gasoline--
Methanol itself is a potential motor fuel or fuel additive that can be
made from synthesis gas by existing technology. However, several problems are
involved with using methanol directly as a fuel additive. A catalytic process
has been demonstrated by Mobil Oil Corp. which converts methanol to hydrocar-
bons and water by the following reaction.
xCH3OH -* (CH2)X + xH20
The hydrocarbons are predominantly in the gasoline boiling range (C^ to C^Q)
with Research Octane Numbers of 90 to 100. The catalyst used in the reaction
is a shape-selective zeolite. A typical product composition is illustrated
in Figure 49.
About 757o of the products are in the C$+ fraction. Part of the n-butane
fraction is included in the gasoline fraction, and C3 and C^. gases,, olefins,
and isobutane can be converted by alkylation to increase the gasoline yield
to 907o of the product (Figure 50). Currently, both fixed-bed and fluid-bed
bench-scale reactors are operating. Mobil has a contract with ERDA (DOE) to design
a pilot plant of 100 bbl per day capacity. (177)
Secondary Biochemical Processes
The Fermentation of Sugar Solutions to Ethanol--
Ethanol may be produced from any fermentable sugar by yeasts under
suitable conditions. There are many available sources of fermentable sugars
which can be classified into three areas.
(1) Saccharine materials - such as molasses, sugar cane,
and fruit juices.
(2) Starch materials - such as grains, for example, oats,
barley, rice, and wheat; and potatoes.
(3) Cellulosic materials - wood, waste sulfite liquor.
The operating conditions of the fermentation process and the product
yields depend on the nature of the starting material and the microorganisms
used in the process. The characteristics of a good yeast culture are (1)
tolerance to high temperatures; (2) tolerance to high alcoholic, sugar,
and non-sugar solids concentrations and (3) the ability to ferment rapidly. (164)
Process description of molasses fermentation--In the United States,
molasses and grain are the principal raw materials used in ethanol fermenta-
tion. Strains of Saccharomyces cerevisiae are commonly used in molasses
fermentation. Cultures are propagated in two stages: (1) small 150-ml
flasks, and (2) 6-liter flasks which directly seed the initial fermentors.
193
-------
Total Hydrocarbons
Yield
Based
on (CH2)
Charged,
% wt.
Figure 49.
90-
80-
70-
60-
50-
An
30-
20-
10-
0 -
Produc
100 -
90-
80-
70 -
60-
50-
40 -
30-
20-
10-
n -
t distrib
C3
C4
C5
C6
C7
A6 ' A9+
(aromatics)
ution from conversion of methanol
C4
c5 - c6
c7 - c9+
A6 " A9+
(aromatics)
Figure 50. Gasoline fraction after alkylation.
194
-------
The molasses is diluted with water to a sugar concentration of 14 to 18
percent and pumped to the fermentors. Inoculum which is 2 to 4 percent
volume active yeast is added to the fermentor. The pH is adjusted between
4.0 and 5.0 with sulfuric acid. Small quantities of ammonium salts may be
added to increase the rate and efficiency of fermentation.
Initial temperatures are usually between 21 and 27 C. Water sprays,
internal cooling coils, or external coolers to remove heat formed by the
exothermic reaction cool the mash during fermentation. Theoretically, 144 k
cal per kilogram of sugar (260 Btu/lb) are liberated during the following
reaction.
C6H12°6 "* 2C2H5OH
Government regulations allow four days for a cycle, but usually 36 to
50 hours are used for fermentation. The effluent from the fermentors is called
a beer and is distilled in a beer still. The overhead vapors from the still
which contain alcohol, waster, and aldehydes, are condensed and passed through
a second column. Aldehydes are removed as overhead vapors and condensed.
The effluent is pumped to a recycling column. Ninety-five percent alcohol is
taken off the top of the column.
The higher boiling (90 to 150 C) fusel oils are removed further down
the column and sold as impure amyl alcohol. The fraction is a mixture of
isopropyl, isobutyl, isoamyl, and amyl alcohols. Water is discharged from
the bottom of the rectifying column.
The principal waste stream in the process is the residue discharged from
the bottom of the beer still. The stillage contains 7 to 10 percent solids
and has a very high B.O.D. (18,000 to 22,000 ppm). A typical composition of
stillage is listed in Table 69-
Residues from molasses fermentations have been used as animal feed and
fertilizer. Another method of disposing of a portion of the stillage is to
use it as a substance on which to grow yeast aerobically. The yeast is then
mixed with molasses and fermentation proceeds anaerobically.(166)
The Melie process--In the fermentation of molasses, the conversion of
sugar averages about 95 percent of the theoretical amount. Part of the
remaining 5 percent is converted to cell mass and is, therefore, not available
for alcohol fermentation. The Melle process is designed to partially reduce
this loss by centrifuging out the yeast after fermentation and recycling the
yeast to the next fermentor. The problem of bacterial contamination is
avoided by washing the centrifuged yeast with large volumes of water and
reducing the pH for several hours in the presence of CC^.
The process has been applied in distilleries in foreign countries and
in sulfite liquor plants in the U.S.(I65)
Fermentation of wood sugar — Sugars produced from dilute acid hydrolysis
are difficult to ferment by conventional methods. Wood-sugar fermentation
was first carried out during World War I in the U.S. at plants in Georgetown,
195
-------
TABLE 69. COMPOSITION OF STILLAGE
(165)
Component
Mineral matter
Sugars
Proteins
Volatile acids
Gums
Combined lactic acid
Other combined organic acids
Glycerol
Wax, phenolics, lignins, etc.
Wt. % (dry basis)
28.5 -
10.0 -
8.0 -
1.0 -
20.0 -
4.0 -
1.0 -
5.0 -
22.0 -
29.0
12.0
10.
2.0
22.0
7.0
2.0
6.0
12.0
South Carolina, and Fullerton, Louisiana. The fermentations were started by
adding wood-sugar to molasses and continued for 96 hours.
Toxic substances present in wood sugars are derived from four potential
sources: (1) carbohydrate decomposition, (2) lignin decomposition; (3) extra-
neous materials present in wood; and (4) metal ions from corrosion of equip-
ment. Operations which are successful in reducing the toxicity are: (1)
steam distillation; (2) acclimation of yeast; (3) tin treatment; (4) adsorp-
tion; (5) pH adjustment; (6) high temperatures; and (7) sulfide precipitation.
One advantage which exists in the fermentation of wood hydrolyzates is that
they are so inhibitory there is virtually no problem with contamination.
A Springfield, Oregon, plant was designed to produce 40,500 liters
(10,700 gal) of alcohol and to operate with continuous fermentations. Because
the wood-sugar was not produced at full capacity nor at a steady rate, the
plant was operated on a batch basis with recycling of the yeast. Some type
of yeast recycling system is required in wood sugar fermentation to operate
economically.
In this plant, the hydrolyzate was prepared for fermentation by neutrali-
zation with calcium hydroxide under 40 psi steam pressure. The neutralized
liquor was filtered, cooled, and filtered a second time. Yeast was added
immediately after the second filtration. The yeast used at the plant was
Saccharomyces cerevisiae, although strains of Torulosis were also tested.
196
-------
The maximum number of times for yeast recycle was not determined. The
fermentation time for one percent yeast varied between 16 and 40 hours; most
were complete in 24 hours. At the Springfield plant, 78 percent of the
sugar was fermentable. The theoretical yield was 51.9 percent of alcohol
and the actual yields varied between 44 and 48.5 percent. Thus, the fermen-
tation efficiencies varied between 75 and 86 percent. C-67)
The Anflow process--Union Carbide has developed an upflow packed column
which acts as a continuous biological reactor. Several products could be
produced from the fermentation process depending on the starting materials
and microorganisms attached to the packing. Examples are (1) methane from
sewage sludge; (2) lactic acid from whey; (3) methanol from sewage; and (4)
ethanol from grains or other materials.
The process is in the laboratory experimental stage of development and
the size of reactors varies between 1.5 inches in diameter and 2 feet in
length to 5.5 inches in diameter and 5 feet in length. A simple schematic
diagram of the reactor is given in Figure 51.
The greatest problem associated with the reactor is the difficulty in
the attachment of microorganisms to the packing. However, flow-through rates
are greatly increased compared to other fermentation processes.
In a large-scale unit, capital costs could be substantially reduced due
creased retention timi
tional fermentation processes.
to the decreased retention times and possible increased stability over conven-
(168,169,170,171,172)
The Fermentation of Sugar Solutions to Butanol/Acetone--
Pasteur was the first investigator to show butanol was a direct product
of fermentation. During World War I, the demand for synthetic rubber and
explosives stimulated the development of a commercial process for the fermen-
tation of acetone. Butanol was formed as a by-product but later became the
more desired end product when it was used in lacquers in the automotive
industry. Fermentation plants were built in England, Canada, the U.S., and
Gas Product Out
." • *
***.*•:
* ' i
.'.•
•:'::•
* * • *»
• * * • .
t
;.
•.':
•
^*
;.-.
»
•••••• ;
• *^ • 1
••;:-. .--•
•-'•N'-'-.
•.*."•'"••
.**«*••
t
-» Liquid Product Out
Packing
Fuel In
Figure 51. The Anflow reactor,
197
-------
India. Butanol and acetone are now derived synthetically from petrochemicals
because of the high costs of raw materials for fermentation.(1/3)
The microorganisms used in the fermentation process differ with the
starting material. Clostridum acetobutylicum are used to ferment starches,
and almost all species of the genus Clostridrium are used to ferment saccharin
materials.
The optimum temperature for fermentation is 39.5 C (87 F). The initial
pH is 5.5 to 6.5. The product yields based on 100 kg of raw material (black-
strap molasses) are listed in Table 70. (175)
The stillage has a solids content of 2.4 g per 100 ml and has a high
concentration of riboflavin. The stillage can be distilled to a syrup which
is evaporated and dried. The recovered material was used as a vitamin supple-
ment for foodstuffs.(174)
Experiments were conducted in 1947 on the fermentation of wood sugars.
It was found that sugar solutions produced under either very mild or very
extreme conditions were difficult to ferment. (175)
The Fermentation of Sugar Solutions to Other Products--
The fermentation in which isopropanol and butanol are produced as end
products are related to the butanol-acetone and ethanol-acetone fermentations.
Several closely related organisms have the ability to produce isopropanol.
Clostridium butylicum are the best known.
TABLE 70. MATERIAL BALANCE FOR ACETONE-
BUTANOL FERMENTATION C175)
Starting materials Kg
Total solids 81.5
Sugars 57.0
Protein 3.1
Ash 6.2
Yields
Butanol 11.5
Acetone 4.9
Ethyl alcohol 0.5
Carbon dioxide 32.1
Hydrogen 0.8
Dry Feed 28.6
198
-------
Several, commercial plants were constructed in Formosa in 1943-44 which
produced butanol, isopropanol, and acetone.
Raw materials used in the plants were sugar cane, sugar syrup, and
blackstrap molasses. The final product composition varied with the nature
of the raw materials and operating conditions during fermentation. The
products were formed in the ranges of 53 to 65 percent butanol, 19 to 44
percent isopropanol, and 1 to 24 percent actone. The products were separated
by continuous distillation.
Wood sugars were investigated by Sjolasder, Langlykke, and Peterson in
1938 as a source of butanol and isopropanol. The wood hydrolyzates were
treated with calcium carbonate to increase the pH, filtered, treated with
lime to precipitate iron and copper, and filtered a second time. As a
result, more isopropanol was produced from wood sugars than from glucose.
A second experiment showed the increased isopropanol production was due to
the acetic acid present in the solution.(176)
PRODUCT STORAGE AND TRANSPORTATION
The objective of the technologies reviewed in this report is to produce
fuels of commercial significance. A review of the products involved will
reveal that many are commercial commodities already utilized in utility, fuels,
or chemical industries. Because this is the case, good engineering practice
has been developed for most and need not be reviewed in detail in this
report. There are several good reference handbooks available which give
excellent perspective to the range of considerations needed in design.
180)
The purpose of this section of the report, then, is to briefly highlight
special functional requirements. It is particularly important to do this in
the context of the likely environments where the technologies will be imple-
mented (for example, rural agricultural communities and municipal waste
handling facilities), and to flag those areas which should be investigated
in more detail in later work.
Direct Conversion Systems
The major product from these systems will be steam and/or electricity.
Storage of these products at the current level of technological development,
for more than transient periods, is economically impractical. Consequently,
the major consideration is distribution.
Electrical power distribution equipment is dangerous for untrained staff,
but the common fare of electric utility companies. Likewise, many municipali-
ties have departments dedicated to power production. Since any electrical
production facility will likely involve a utility as the customer, it would
seem logical to use their expertise at and beyond the point of electricity
production.
199
-------
Steam distribution is well established, and competent designs are well
within the capabilities of most architect and engineering firms. The major
hazard is high temperature, a hazard familiar to essentially all commercial
establishments.
Pyrolysis Systems
These systems may produce gases, liquids, or chars. Gaseous systems
will generally produce low to medium Btu product streams, which are unlikely
to be stored for long periods. It is probable in some situations that the
gas will be combusted or chemically converted at sites located several miles
from the production facility. Two components in the typical product gases
need to receive special consideration: hydrogen and carbon monoxide.
Even without the presence of hydrogen, the gas should be regarded with
caution due to its explosive and asphyxiation qualities. The presence of
hydrogen, a highly explosive and inherently diffusive agent, serves to
reinforce the need for transport by tank car. This will likely require use
of special code enclosures for electrical connections and equipment in some
instances, and careful monitoring of all piping connection, most importantly
where high pressure transmission of the gases are involved. High pressure
hydrogen leaks have reportedly self-ignited in some instances and could
constitute fire and possibly explosive hazards.
Carbon monoxide is, of course, a highly toxic agent. However, house-
keeping practices established for hydrogen, as noted above, should minimize
the likelihood of escape.
Liquid streams produced in pyrolysis systems are expected to have roughly
comparable characteristics with their petroleum counterparts. Spills and
leakage will have to be controlled to the same level as required for the
petroleum and petrochemical industry. Human exposure limitations are expected
to be similar to hydrocarbons with approximately the same characteristics,
but this is a speculation and needs to be confirmed.
Storage equipment is likely to be similar to that used for petroleum
products, except for the noted tendency of these liquids to "polymerize" and
become more viscous. Heating and agitation may be required. However,
heating reportedly increases polymerization rates. If suitable inhibitors
can be found, then long-term storage may not be a significant problem; if not,
only short-term storage may be possible.
Char storage does not present any new technological problem. It is
possible that some chars may spontaneously combust, as will coal under certain
conditions. Also, care will have to be taken to collect and treat run-off
from open storage piles, as these may contain appreciable concentrations
of toxic substances, notably heavy metals.
Hydrogenation Systems
The products and associated problems with these systems are expected to
be categorically similar to those noted in the previous section.
200
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Acid Hydrolysis Systems
The product from this system will be a sugar-rich aqueous stream. In
most instances, this will likely be converted on-site to secondary products,
probably ethanol.
Storage does not represent substantial problems as it is well established
in the current sugar industry, as well as in earlier plant practice (see the
report section on Acid Hydrolysis). One consideration which may be important,
especially for long-term storage, is prevention of microbiological contamina-
tion. Contamination could cause two types of problems. Obviously, inadver-
tent culturing of some glucose-using microorganisms could result in loss of
product in storage. Equally as important, unnoticed contamination could
create downstream process problems in subsequent fermentation steps.
Anaerobic Digestion Systems
The handling and storage of methane, the major product of this technology,
is well established in the natural gas industry. On-site storage of signifi-
cant quantities of this product is unlikely, because of unfavorable density
characteristics.
However, compression and transmission to a main natural gas trunk pipe-
line is anticipated to be required in most installations. Since transmission
pressures are often 1000 psig, or greater, care will have to be exercised
in operating this equipment. Thorough training of operating staff in the
safety features associated with these functions will be necessary.
Enzymatic Hydrolysis Systems
The same considerations noted under the section on acid hydrolysis
systems hold here as well. However, because this conversion process is not
likely to sterilize the product, contamination potential will be increased
substantially, and storage time requirement may need to be more restrictive.
Methanol Production Systems
These systems will require special consideration. While there is consi-
derable established practice in the chemical industry for handling methanol,
use of this highly toxic material in fuel distribution systems will present
a host of new problems. Control of spills will be essential. Spills and
pipeline leakage in transport could adversely affect both humans and animals
in contact, as well as crop lands. In an agricultural setting, this may be
particularly significant to conventional heterogeneous farming systems. The
tendency of methanol and methanol mixtures to pick up water may adversely
affect product quality and require special storage constraints. The health
and safety implications of methanol storage and distribution needs to be
studied thoroughly, before large-scale implementation of the technology is
undertaken.
These comments hold for methyl fuel products as well.
201
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Light and Mid-range Hydrocarbons
Storage and transportation of these products are common practice in the
petroleum and petrochemical industry. While safety and health requirements
are extensive, they are well established.
Ethanol Fermentation System
Storage and transportation of the industrial ethanol are also well
known in the chemical industry. Design of storage and transportation equip-
ment does not represent technological difficulties; however, IRS regulation
relative to production and distribution of ethanol must be considered. While
there is not the degree of concern as with spills, it is conceivable that
continued exposure of personnel in enclosed spaces might adversely affect
operative decision making.
Other Fermentation Systems
The comments noted above generally hold for other fermentation products
as well.
DEVELOPMENT OF REGIONAL SCENARIOS OF
BIOMASS CONVERSION PLOTS
Introduction
The previous sections have been directed at characterizing the individual
biomass sources and energy conversion technologies. The applicability of any
of the conversion technologies, however, for transforming biomass waste into
a usable form of energy for a particular region depends upon two major factors:
(1) the availability of suitable quantities of biomass feedstock for a
reasonable size conversion facility, and (2) the applicability of the conver-
sion process to the specific type of biomass feedstock and the marketability
of the conversion product in that region.
The resultant regional environmental impact of such a system must address
the implications of an integrated biomass production/collection and conversion
system in total and will understandably vary with different regions and
conversion technologies. To this end, a series of six scenarios have been
prepared to superficially examine the environmental implications of different
conversion technologies applicable to different geographical areas of the
United States. The engineering and environmental analyses of each region
are not comprehensive in nature as such developments are beyond the scope of
this report. The analyses are, however, sufficiently detailed to identify
generically the environmental and social consequences of such ventures.
Rationale for Scenario Source/
Conversion Process Selection
Characteristically, the availability of most biomass sources is highly
regionalized. Likewise, a review of the chemical and physical properties of
202
-------
the materials shows that there exists inherent characteristics which make
individual biomass sources more amenable to one broad classification of
conversion process, in contrast to a second class. Consequently, the
strategy was adopted that regional sources and their "natural" conversion
process counterparts would be utilized wherever possible. Over this criteria
was superimposed the necessity of trying to depict most of the relevant
conversion technology, as well as a specialized scenario directed at develop-
ment of a mobile facility.
Consideration of region selection was limited to the continental United
States. Likewise, broad areas of the western region which are particularly
arid were excluded from serious consideration because their development would
imply importation of tremendous quantities of fresh water, a project of such
monumental environmental significance that it would overwhelm any factors
related to the various source/conversion process development. While consi-
deration of such an undertaking is not beyond consideration from the context
of biomass source development, dealing with it in a competent fashion is
beyond the scope of this study.
Four regions, only partially homogeneous in nature, were defined for use
in this study. These were the Northeastern, Southern, Midwestern, and West
Coast regions. The states included in these regions are listed in Table 71
and shown graphically in Figure 52. Review of these regions will show that
the definition adopted here will not correspond to normal geopolitical classi-
fication. Likewise, the distinction between regions is necessarily arbitrary
in some cases because change from the characteristics of one region are
continuous rather than abrupt events.
The Northeastern region consists of the New England and upper eastern
seaboard states down to Virginia. These states are highly populated; large
forest tracts exist in portions of New England as well as several other states,
Some agriculture exists, but tonnage quantities are much smaller than other
regions. An ocean coastline as well as prodigious quantities of fresh water
exist. However, the climate is temperate so that mariculture yield would be
lower than in southern and western regions. Likewise, major ports and the
commensurate commercial traffic also tend to mitigate against development of
ocean-based aquatic systems. While the freshwater systems are large, their
dedication to industrial use makes fresh water aquaculture unlikely, as does
the high cost of land. Energy farming crops are obviously of only passing
consideration.
Consequently, the major biomass sources of interest in this region are
urban waste, silviculture, and forest residue. Since these materials all
have fairly low moisture content and relative high net Btu content, a thermo-
chemical conversion system in the region appears to be indicated.
The Southern region is characterized as highly productive of biomass.
The warmer climate generally extends growing seasons and increases annual
yields. Energy-farming crops (sugar cane, various grasses) may become
attractive in this region, as might silviculture. The existing commitment
to pulp and forest products tends to reinforce this latter biomass category,
but this industry's existence also represents a highly competitive use for
203
-------
TABLE 71. STATES CONTAINED IN VARIOUS REGIONS
DEFINED FOR STUDY
Northeast Region
Connecticut
Delaware
Maine
Maryland
Massachusetts
New Hampshire
New Jersey
New York
Pennsylvania
Rhode Island
Vermont
Virginia
West Virginia
Alabama
Arkansas
Florida
Georgia
Louisiana
Southern Region
Mississippi
North Carolina
South Carolina
Tennessee
Texas (partial)
Midwest Region
Illinois
Indiana
Iowa
Kansas
Kentucky
Michigan
Minnesota
Missouri
Montana (partial)
Nebraska
North Dakota
Ohio
Oklahoma
South Dakota
Texas (partial)
Wisconsin
Wyoming (partial)
West Coast Region
California
Oregon
Washington
204
-------
j Mortheast Region
| Southern Region
I Midwest Region
West Coast Region
Figure 52.
Pictorial presentation of regions,
-------
the resource. Agriculture production exists at appreciable levels, but not
nearly on a scale with the Midwestern region. Likewise, animal husbandry is
widespread with especially high concentrations in Florida. However, absolute
totals are dwarfed by Midwestern concentrations. An extensive coastline
along with semi-tropical weather conditions would appear to make aquaculture
a viable option, and kelp production has been proposed. The lack of specific
experiments related to this thesis as well as the danger from hurricanes in
the region tend to balance their positive attributes. Urban population is
relatively sparse, especially in comparison to portions in the Midwest,
the East and West.
These considerations, especially the generally high productivity of the
region, have been the basis for choosing a multiple feedstock plant. The
plant will be based on cellulose conversion and will process a combination of
silviculture (slash pine) or an energy crop residue (bagasse) as feedstock.
The Midwestern region is the largest in terms of area and is the region
most highly dedicated to high-volume agriculture. Obviously, agricultural
residue including both crop and animal wastes are available in large quanti-
ties. Some forestry exists, especially along boundaries with other regions.
Large urban centers are distributed throughout the region so that urban and
industrial waste inventories are substantial. Marine agriculture is, of
course, out of the question. However, fresh water systems, especially in the
Great Lakes section, remain a possibility. Tropical energy crops (e.g.,
sugar cane) are possible only in very limited sections; however, grasses
would appear viable, although their use would no doubt be limited to marginal
lands.
One special consideration is the existence of much of the U.S. coal
reserves in the region. This is of interest because strip-mined lands are
excellent candidates for combined reclamation/energy production. Both
grasses and certain tree species are candidates.
Two scenarios have been defined for this region. One is based on combined
crop and manure wastes and the other on silviculture products grown on strip-
mined lands.
The final region is that of the West Coast. This region is characterized
by some of the most productive land in the United States. It is also some of
the most expensive land, and its commitment is almost totally for direct
human consumption. Consequently, its use for energy crops would appear
unlikely.
Several large urban population centers exist in the region, as does a
very significant forest products industry. The coast is a natural site for
kelp, the major aquaculture crop presently being considered. Fresh water is
limited; however, wastewater from metropolitan centers could conceivably
be the source of a fresh water aquatic crop.
Given this diversity of potential feedstocks, the choice of feedstocks
for the two scenarios in the West Coast region is reduced to accommodating
choices not previously made. Primarily for this reason, a scenario based on
urban waste and one on combined kelp and urban waste were chosen
206
-------
Finally, the special case of a mobile conversion plant, with multiple
feedstock capabilities, was considered in order to provide insight into the
other end of the process plant size spectrum.
Process Selection for Region-Based Feedstock
In this section, biomass waste-to-energy conversion systems were selected
and examined in each of the four regions. The intention was, where possible,
to match the characteristics of energy needs with the resources and appropriate
conversion processes for the region. For example, the scenario developed for
the Northeast, where there is an abundance of relatively dry urban and forest
wastes, is to produce material, which might be used as a supplemental auto-
mobile fuel and for peaking electrical power. An attempt was made in the
selection of the conversion processes to include representative processes
from both the thermochemical and biochemical areas.
The criteria used in the selection of each process included not only the
state of development of the process but (1) the applicability of the process
to the specific biomass feed as dictated by the physical characteristics of
the feed and the operational constraints that the feeds impose on the process,
and (2) the marketability of the energy or conversion product in the specific
region.
For each region, the physical characteristics, the methods of harvesting,
the seasonal influences, and the geographical distribution of the waste
feedstock were examined. Within these constraints, a reasonable determination
of the plant capacity was made and an appropriate plant site selected. A
brief description was developed for each selected process along with a genera-
lized process flow schematic, a material balance, and estimates of the size
of the major process equipment were also prepared.(a' A summary of the
salient features of each of the processes for the six scenarios is presented
in Table 72.
Scenario No. 1 (Northeast)--
In this six-state region (Maine, New Hampshire, Vermont, Connecticut,
Massachusetts, and Rhode Island), approximately 10.4 million metric tons of
forest residue is made available each year from logging operations. The
heaviest concentration of forest residue lies in the three-state region of
Maine, Vermont, and New Hampshire where 8.4 million metric tons are discarded
annually. It is in this region that a waste-to-energy conversion plant would
be most appropriately located.
Several energy conversion processes are applicable for treating the
forest wastes, direct-fired boiler feed, hydrolysis with fermentation to
ethanol, pyrolysis to a fuel gas with subsequent combustion, or pyrolysis to
a synthesis gas for the manufacture of a fuel substitute, e.g., methane or
methanol. Of these processes, direct boiler feed is the most commonly employed
(a) The material balances should not be construed as being rigorous determi-
nation as sufficient experimental or analytical data were usually not
available and conversion factors and yields were based solely on engi-
neering judgment.
207
-------
TABLE 72. SUMMARY OF WASTE TO ENERGY PROCESSES FOR THE SIX SCENARIOS
Type
of
Scenario Waste
Type
of
Process
Size
of
Process
(metric tons /day)
Product
Produced
No. 1 (Northeast -
Maine, New Hampshire
and Vermont)
No. 2 (South -
Louisiana)
Forest residue Pyrolysis followed 5,000 Methyl fuel
by methanol pro-
duction
33% bagasse, Acid hydrolysis 3,000 957. .ethanol
67% pine slash with fermentation
No. 3 (West Coast)
50% kelp
50%, urban refuse
Anaerobic diges- 10,000
tion, 2-stage
SNG
No. 4- (Midwest -
Ohio)
So. 5 (Midwest -
Kansas)
No. 6 (West Coast
Urban Center)
80% European
alder, 20% corn
residue
4% feedlot waste
96% wheat straw
Urban refuse
Gas turbine 350
electric generator
Anaerobic digss- 10,000
tion, 1-stage
Direct boiler 5,000
feed
Electricity
SNG
Low pressure
steam
Scenario
No. 1 ('."crtheast -
I-'.air.e, Sew Hampshire
ar.d Vermont)
So. 2 (South -
Louisiana)
Quantity of
Product
Produced
(metric tons/day)
790
204
Product
Uses
Automobile and
boiler fuel
Petrochemical
feedstock
Waste
Streams
Pyrolyzer ash,
condensed water
Calcium sulfate
sludge, still and
rectifying bottoms
Major
Pollutants
High COD in
condensed
water
Sulfate,
high BOD
No. 3
Coast)
No. 4.(Midwest -
Ohio)
705
16.5 mw (per
8 hour day)
Utility gas
Electrical
peaking power
Digester sludge,
brine off gas
brine liquid waste
Bottom ash and
flue gas
High BOD
5 (Midwest -
.Vo. 6 (West Coast
Urban Center)
1.73jsl06
m /day
16,800
Utility gas
Industrial steam
or municipal
heating & cooling
Column bottoms
digester sludge
Bottom ash and
flue gas
High 300
208
-------
wood waste-to-energy conversion process, and wood-fueled boilers are commer-
cially available in a wide range of sizes. The process, however, has limited
application and is site-specific, i.e., the generated steam must be consumed
on-site rather than in the energy-intensive urban centers of the East.
Hydrolysis of wood waste has been technologically demonstrated on a
commercial scale and is regarded as a viable candidate process. The hydro-
lysis reaction is conducted in a water medium, however, and the relatively
low moisture content of the forest residues, as opposed to the residue wastes
in other regions suggests that a combustion or pyrolytic thermal conversion
process, rather than a water-intensive hydrolysis process, would more effec-
tively capitalize on the physical characteristics of the raw forest waste.
The pyrolysis of the wood waste to produce a fuel gas suffers from the
site-specific constraints characteristic with the direct boiler feed process.
The fuel gas cannot be stored and would not be suitable for incorporation
into the natural gas distribution network.
A pyrolysis process with conversion to a secondary fuel would permit
the fuel to be utilized in regions not in close proximity to the pyrolysis
plant. Some of the secondary fuels that could be manufactured from the
pyrolysis synthesis gas are methane, C2~C^ hydrocarbons, and methanol (or
methyl fuel). Of these, methanol was selected as the most appropriate fuel
for the Northeast region due to its versatility, applicability as an automo-
bile fuel substitute, and the ease with which it can be transported and
stored.
Of the dozen or so existing pyrolysis processes, the Union Carbide Purox
Process was regarded as the most suitable choice for producing a synthesis
gas from the wood waste. The process has been demonstrated on a commercial
scale and produces a gas high in H2 and CO with little nitrogen or inert
impurities. Of the two major methanol production process schemes, low pressure
and high pressure, the low pressure process was chosen because of its charac-
teristically lower capital cost and milder operating conditions. A detailed
explanation of the rationale for these two selections is presented in a
draft Battelle report to the Environmental Protection Agency on methanol
production from non-coal sources, (lo-*-)
Process description--Some of the salient features of the feedstock and
the conversion process are presented in Table 73. Figures 53 and 54(158) are
schematic flow diagrams of the pyrolysis and methanol processes and Table 74
presents a material balance of the overall process.
The pyrolysis facility will consist of a single 1000-ton-per-day oxygen-
generating plant, sixteen 315-metric-ton-per-day pyrolysis reactors (4 meters
in diameter by 13 meters high), a gas cleanup module, and a 2500-cubic-meter-
per-day wastewater treatment plant. Raw wood chips will be fed from the
storage pile via conveyor belt into the individual feed hoppers (Stream No. 1).
A ram feeder will introduce the wood fed into the top of the reactor where hot
combustion gases, rising up through the wood chips, will dry and pyrolyze the
wood to a gaseous product. Pure oxygen (Stream No. 2), fed into the combustion
zone, will provide the environment for combustion of the wood. Approxi-
209
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TABLE 73. SUMMARY OF FOREST RESIDUE TO METHYL FUEL PROCESS
(Northeast Region)
Waste Feedstock
Characteristics of Waste:
Type of waste - forest residue (tops of trunks, branches, and
stumps)
Moisture content - 45 percent
Ash content - 3 percent
Heating value - 2600 kcal/kg (4675 Btu/lb)
Bulk density (green) - 800 kg/cu. m. (54 Ib/cu. ft.)
Method of Harvesting Waste:
The forest residue from logging operations or from stand improve-
ment and thinning operations will be collected on site, chipped, loaded
into a truck and transported to the centrally located energy conversion
plant.
Geographic Aspects of Waste:
Location of waste sources - the forest residues will be harvested
from the commerical forest regions of Maine, Vermont and New Hampshire.
Geographical density-of waste - based on a total, for the three
state region, of 8.4 x 10 metric tons per year of sustained harvest of
forest residue and, 16.9, 5.0 and 4.4 million acres of commercial forest
residue is estimated to be 0.32 metric tons per acre per year. Based on
the total area of three states, and the fraction of area devoted to
commerical forestry (80 percent), the overall effective harvestable yield
is approximately 0.26 metric tons per acre per year.
Energjy Conversion Plant
Type of Plant:
Purox pyrolysis followed by a low pressure methanol or methyl fuel
process
210
-------
TABLE 73. (continued)
Product:
Methanol or methyl fuel
Size:
5000 metric tons per day (chipped forest residue)
Geographical Location:
Centrally located in the three state region, preferably near the
Maine-New Hampshire border.
Based on a 90 percent plant load factor and an effective harvest-
able forest waste density of 0.26 metric tons/acre, sufficient feed-
stock should be available, on a continuous year-round basis, within a
radius of 55 miles from the central plant.
Storage Facilities:
Area will be provided for 7 days of open storage. The volume
occupied by the 35,000 metric tons of wood chips is approximately
41,000 cu. m. (1.4 million cu. ft.). This volume would constitute a
mound approximately 5 meters high by 90 meters on a side (15 ft. high
by 300 ft on a side).
211
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WET PYROLYSIS GAS
STREAM (3)
RECYCLED SCRUBBING
WATER
ELECTROSTATIC
PRECIPITATOR
CHIPPED WOOD
STORAGE PILE
SLAG
3-PHASE
SEPARATOR
BOTTOMS TIT QUENCH TANK
(6)
YY
DRY PRODUCT GAS
STREAM (4)
TO
METHANOL
PLANT
CONDENSER
Y
ORGANIC LIQUIDS
AND WATER
CONDENSED WATER
TO WASTE TREATMENT
Figure 53. Process flow schematic of wood waste pyrolysis system.
-------
SYNTHESIS
GAS
DSY GAS
(4)
SULFUR
CONVERTER
STEAM
HIGH
TEKP.
H)
^-^ ^-^ K20 AND
H,S GAS SHIFT co?
PURIFICATION RECTORS REMOVAL
COMPRESSOR
PURIFICATION TRAIN FOR SYNTHESIS GAS PREPARATION
'PURIFIED
SYNTHESIS
GAS
°2
SYNTHESIS
^ttt
H2 + CO
i
_ RECYCLED
S*"^ ^
PURGI TO TUEL
WETHANOL REACTOR
VOLATKES
TO
(8)
—,»-
INOUSTRTAL
KZTKAWl
CRUDE WATER AND . N
METHANOL HEAVY ENDS '(7) ALCCHOLS
HETHANOL SYNTHESIS *'™L FUEL liLENO
Figure 54. Low pressure methanol process based on ICI process.
(158)
-------
TABLE 74. MATERIAL BALANCE FOR WOOD WASTE PYROLYSIS PROCESS
Basis: 5000 metric tons of chipped wood waste
Stream
Stream (1) Chipped Wood Waste
Organic cellulosic compounds
Water
Ash
Sulfur
Nitrogen
Total
Stream (2) Oxygen
Assumed pure
Stream (3) Wet Gas
H
C(3
CO
CH4
C,H,
H,S
N2
H.O
Oils
Other water solubles
Total
Stream (4) Dry Gas
H2
CO
CO,
CHA
C2 4
FLS
2*n
H^O
Total
Weight Percent
51.7
45.0
3.0
0.1
0.2
100.0
Volume Percent
11.15
19.1
11.9
2.7
1.5
0.02
0.08
53.5
—
—
100.0
22.3
38.2
23.9
5.4
3.0
0.04
0.16
7.0
100.0
Metric Ton
2585
2250
150
5
10
5000
1000
59
1320
1390
112
72
1
1
2600
250
50
5855
59
1320
1390
112
72
1
1
170
3125
214
-------
TABLE 74. (continued)
Stream Weight Percent Metric Ton
Stream (5) Condensed Water
Water 98.0 2430
Other water solubles 2.0 50
Total 100.0 2480
Stream (6) Slag
Predominantly Ash 145
Stream (7) Methyl Fuel Blend
Methanol 94.0 742
High alcohols 2.0 16
Water 4.0 32
Total 100.0 790
Stream (8) Purified Methanol
Methanol 99.9 738
Higher alcohols 0.1 1
Total 100.0 739
Stream (9) Higher Alcohols
Methanol 8.0 4
Higher alcohols 30.0 15
Water 64.0 32,
Total 102.0 51
215
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mately 230 standard cubic meters (9200 scf) of pyrolysis gas (Stream No- 3)
will exit each reactor per minute. The gas will be manifolded into a common
line and pass through a gas cleanup system consisting of a wet scrubber, an
electrostatic precipitator, and a condenser. Approximately 3120 metric tons
per day (3530)tpd) of the dry synthesis gas (Stream No. 4) will be produced.
The product synthesis gas, with a composition typical of that shown in
Table 74, will be directed to the methanol facility where it will be compressed
to about 50 atm. and passed through an absorption sequence for the removal of
H2S and other sulfur compounds. The gas will then be sent to a series of guard
chambers which hydrogenate the unsaturated compounds and remove any remaining
traces of I^S and chlorine compounds. This sequence of guard chambers protects
the water-shift and methanol catalyst from contamination.
The next step, the water-gas shift reactor will employ an iron oxide-
chromium oxide type catalyst to convert the carbon monoxide and steam to
carbon dioxide and hydrogen. The objective is to adjust the hydrogen to
carbon monoxide ratio to that desired for the methanol synthesis. The normal
temperature range for this reaction is 380-510 C (650-850 F).
Following the water-gas shift reaction, another absorbing train will
remove excess C02 to reduce the load on the methanol reactor and other down-
stream equipment. The purified gas will enter the methanol reactor where, at
50 atm and 250 C (480 F), the carbon monoxide and hydrogen will react over
a catalyst to form methanol. The product will be subsequently purified in a
devolatilization column and dewatering column and distilled to separate it
from the higher alcohols. For use strictly as a fuel, the higher heating value
of the heavier alcohols would augment the combustion characteristics of the
product alcohol and the final distillation step could be eliminated in favor
of forming a methyl fuel blend (Stream No. 7). From the 5,000 metric tons
per day of forest residue feed, approximately 790 metric tons of methyl fuel
or 739 metric tons of purified methanol (Stream No. 8) and 51 metric tons of
heavier alcohols (Stream No. 9) would be produced per day.
Environmental aspects--In the pyrolysis process, approximately 150 metric
tons per day of wood ash (Stream No. 6) will be withdrawn as slag from the
reactor bottom. The slag will be quenched, separated from the water, and
transported to a landfill for disposal. An analysis of ash residue obtained
from the burning of various types of wood bark is presented in Table 75 and
an analysis of boiler ash from an approximately 70 percent bark-30 percent
wood fuel burned in a Eugene, Oregon, power plant is presented in Table 76.
As expected, the major components are inert silicon (silica) and aluminum
(alumina) oxides). Because of the similarities of the elemental analysis of
wood, regardless of species or location (as noted in Table 75), the ash
composition from wood combusted in Vermont or Maine should be similar to the
analysis in Tables 75 and 76. The wood ash can be generically characterized
as a relative inert powdery solid with a minor fraction of sodium, magnesium,
and potassium along with the trace amounts of heavy metals.
Approximately 2500 cubic meters per day (670,000 gpd) of water and water
solubles (Stream No. 5) will be condensed from the product gas. The water
will be high in BOD and COD and will require secondary treatment prior to
216
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TABLE 75. CHEMICAL ANALYSIS OF BARK AND BARIC AStt(182)
Analyses
(dry basis), % by wt
Proximate
Volatile matter
Fixed carbon
Ash
Ultimate
Hydrogen
Carbon
Sulfur
Nitrogen
Oxygen
Ash
Heating value, Btu/lb
Ash Analyses, % by wt
Si00
L
Fe2°3
Ti02
M2°3
Mn3°4
CaO
MgO
Na2°
K20
S03
Cl
Pine
72.9
24.2
2.9
5.6
53.4
0.1
0.1
37.9
2.9
9030
39.0
3.0
0.2
14.0
Trace
25.5
6.5
1.3
6.0
0.3
Trace
Oak
76.0
18.7
5.3
5.4
49.7
0.1
0.2
39.3
5.3
8370
11.1
3.3
0.1
0.1
Trace
64.5
1.2
8.9
0.2
2.0
Trace
Spruce
69.6
26.6
3.8
5.7
51.8
0.1
0.2
38.4
3.8
8740
32.0
6.4
0.8
11.0
1.5
25.3
4.1
8.0
2.4
2.1
Trace
Redwood
72.6
27.0
0.4
5.1
51.9
0.1
0.1
42.4
0.4
8350
14.3
3.5
0.3
4.0
0.1
6.0
6.6
18.0
10.6
7.4
18.4
217
-------
TABLE 76. SPECTROGRAPHIC ANALYSIS OF
HOGGED FUEL ASH<182)
Components
Silicon (Si)
Aluminum (Al )
Calcium (Ca)
Sodium (Na)
Magnesium (Mg)
Potassium (K)
Titanium (Ti)
Manganese (Mn)
Zirconium (Zr)
Lead (Pb)
Barium (Ba)
Strontium (Sr)
Boron (B)
Chromium (Cr)
Vanadium (V)
Copper (Cu)
Nickel (Ni)
Mercury (Hg)
Radioactivity
Concentration
19.6
3.6
2.9
2.1
0.8
0.3
0.1
0.016
0.006
0.003
0.010
0.002
0.003
Less than
Less than
Less than
Less than
Nil
Nil
, percent
0.001
0.001
0.001
0.001
218
-------
discharging into a sewage system. All oils and participates collected in the
gas cleanup system will be combined and recycled to the reactor.
The discharge streams from the methanol process are (1) the purge stream
following the methanol reactor controlling the buildup of hydrocarbon compounds,
particularly methane and ethane, (2) the condensed water from the shift
reactor, (3) the effluent from the methanol devolatilizing column, and (4)
the bottoms from the dewatering column; these streams are described in more
detail below. The I^S stripped from the absorber in the stripping column
does not pose an environmental threat as it would be directed to a Glaus
plant for conversion to elemental sulfur.
The hydrocarbon purge stream regulates the quantity of methane and ethane
that builds up in the methanol recycle stream. Due to the relatively high
concentration of methane and ethane in the pyrolysis synthesis gas, the purge
gas constitutes a significant volume, about 4 percent of the raw waste feed.
This gas, however, is very rich in methane and ethane, has a high heating value
[about 9500 kcal/cu m (1050 Btu/cu ft)] and would be utilized as process fuel.
No information was available on the quantity of the shift reactor conden-
sate stream. The condensate is not, however, expected to be a significant
source of pollution as most of the soluble organics in the synthesis gas were
removed in the pyrolysis water scrubber.
The gaseous effluent from the methanol devolatilizing column is a small
stream, accounting for only 0.4 percent of the waste feed. The stream contains
volatile hydrocarbons, however, and would be burned with the purge gas as a
fuel.
The liquid dewatering bottoms contain heavy organic ends, soluble metha-
nol, water, and some higher alcohols. The heavy ends would likely be separated
from the water fraction and could be utilized as a fuel. The water fraction
would have a high COD and a high concentration of methanol and may require
treatment before discharge.
Scenario No. 2 (South)--
In the South, the state of Louisiana was selected as one of the regions
for the scenario study due to the availability of significant quantities of
bagasse and slash pine forest residue. Approximately 2.5 million metric tons
of bagasse and 8.5 million metric tons of forest residue are generated annually
in Louisiana.(183) ^ot all of these wastes are available as feedstock for
energy conversion, as a substantial portion (estimated to be 50 percent) of
the bagasse is used as a fuel or in the manufacture of particle board, (1°4)
Also, some of the forest residues are used for miscellaneous purposes, such
as in naval stores production. The wastes are in sufficient quantity, however,
to provide a year-round supply of raw feedstock to an energy conversion plant.
Both the bagasse and forest residue are high in cellulose (about 24
percent, wet basis) and water (about 50 percent). In view of these physical
characteristics and the burgeoning petrochemical demands of Louisiana and
Texas, the energy conversion process chosen as the most applicable for this
region is hydrolysis with subsequent fermentation to ethanol. Of the hydrolysis
219
-------
processes, acid-based hydrolysis was selected over enzymatic hydrolysis due
to the significantly shorter residence times associated with the acid-based
system and its more advanced stage of development. Although not demonstrated
on larger than a bench-scale apparatus, a continuous mode of operation was
chosen over the batch operation due to the shorter residence times and the
potential for higher theoretical sugar yields.v128)
Process description—A summary of major features of the waste feed and
the hydrolysis fermentation process is presented in Table 77.
All acid-based hydrolysis processing to date on the pilot plant or
commercial scale has been of the batch type. However, studies on the kinetics
of hydrolysis and subsequent destruction of the fermentable sugar molecule
ki k2
cellulose » fermentable sugar > decomposed sugar
reveal that the rate of hydrolysis and destruction are a function of the
reaction temperature, and that with increasing temperature the rate of hydro-
lysis increases faster than the rate of destruction.(128) jt was thus con-
cluded that high reaction temperatures and short residence times should result
in the highest theoretical sugar yields. The range of reaction times and lack
of reaction control, characteristic of batch-type operations, make the achieve-
ment of maximum theoretical sugar yields nearly impossible. To ensure closer
control of the operating conditions and subsequently the reaction kinetics, a
continuous isothermal plug flow hydrolysis reactor was proposed. (128) With
this reactor, hydrolysis and destruction during a rapid heat-up step could be
minimized, and when the desired reaction temperature is reached the reaction
could be carried out with maximum selectivity for the sugar. Based on bench-
scale, experimental work, a commercial size process was conceptualized for
hydrolyzing municipal refuse.(128) This process is described briefly in the
section on acid-based hydrolysis and is chosen as the model on which the
selected wood residue-bagasse hydrolysis-fermentation process is based.
A simplified process flow schematic is shown in Figure 55, and an overall
material balance is given in Table 78. The raw bagasse and wood chip mixture
will be initially pulverized to form a 50 percent water slurry by a process
similar to the Black Clawson "Hydrasposal" process. The slurry stream will be
diluted to a 7:1* liquid-to-solid ratio with water, and steam-heated to the
operating temperature of 230 C (459 F). Sufficient sulfuric acid will be
added to the slurry to make a 0.4 percent solution. The resulting slurry
will be introduced via a screw feeder into one of seven 5-meter long by 0.5-
meter in diameter (15 feet long by 2 feet in diameter) continuous-flow
hydrolysis reactors. Reactor residence time will be about 1.2 minutes. On
discharging from the reactors the product slurry will be cooled to 100 C by
flashing in a series of chambers, neutralized by limestone, filtered, and
cooled further to 40 C by the preparation water in countercurrent heat exchan-
gers.
* This ratio is an engineering judgement only and has not been substantiated
by experimental research.
220
-------
TABLE 77. SUMMARY OF BAGASSE AND FOREST RESIDUE TO ETHANOL PROCESS
(South Louisiana Region)
Waste Feedstock
Characteristic of Waste:
Type of waste - bagasse (33 percent) and slash pine forest
residue (67 percent)
Moisture content - bagasse, 50 percent; slash pine residue,
50 percent
Ash content - bagasse, 3.0 percent; slash pine residue, 0.5
percent (dry basis)
Cellulose content - bagasse, 24.3 percent; slash pine residue,
24.0 percent (wet basis)
Approximate bulk density - bagasse 200 kg/nP (13 Ib/cu ft);
slash pine residue, 600 kg/m3(40 Ib/cu ft)
Method of Harvesting:
The forest residue will be harvested as described for
Scenario No. 1. The bagasse residue is a by product of the
sugar cane processing plants and some is used as fuel and as a
raw material for fiberboard production. The remainder (assumed
to be about 50 percent) will be collected and transported to the
central energy conversion plant.
The sugar cane will be harvested seasonally, and since the
bagasse is more susceptible to deterioration and fungus attack
than the forest residue, during the harvest season the relative
proportion of bagasse feedstock will be increased.
Geographical Aspects of Waste:
Location of waste source - the bagasse is produced in the
southern sector of the state. The commercial forestlands lie
predominantly in the central and northern sectors of the state.
Geographical density of waste - the density of bagasse is
assumed to be 8 metric tons per acre. Based on a total of
316,000 acres devoted to the production of sugar contained within
a total estimated land area of 4 million acres, and assuming that
50 percent of the bagasse is not utilized as fuel or for fiberboard
production, the effective geographical density of bagasse is
estimated to be 0.3 metric tons/acre per year.
221
-------
TABLE 77. (continued)
As no information could be found on the average density of
forest residues for the Southern states, an effective density of
0.5 metric tons per acre year was chosen. This estimate was based
on the value of 0.32 metric tons per acre year calculated for the
northeast region adjusted to account for the comparatively higher
growth rates of wood in the South.
Energy Conversion Plant
Type of Plant:
Continuous acid hydrolysis with fermentation to ethanol.
Product:
Ethanol
Size:
3000 metric tons per day (2000 metric tons per day of forest
residue, 1000 metric tons per day of bagasse). Assuming a 55
percent of theoretical yield of sugar (glucose) and a 95 percent
fermentability, approximately 204 metric tons per day of 95 percent
ethanol will be produced.
Geographical Location:
In South Central Louisiana. Based on the estimated effective
geographical densities of 0.5 and 0.3 metric tons per acre for
the forest residue and bagasse respectively, and assuming a reason-
ably uniform distribution of the residue within the harvest region,
sufficient feedstock should be available to supply the plant with
3000 metric tons per day within a radius of about 80 miles from
the plant.
Storage Facilities:
Area will be provided for 3 days of open storage of wood chips
and 3 days of sheltered storage of bagasse. The wood chips will
constitute a mound 35 meters square (125 feet square) by 8 meters
high; the bagasse will require two covered, ventilated storage
facilities 6 meters high (21 feet) by 35 meters square (125 feet
square).
222
-------
CO
K>
UJ
FOREST RESIDUE
AND BAGASSE FEED (3) SULFURIC
«fS?w« 0) SLURRYING ACID FLASH
PREPARATION ^ & PUMPING HEATING CHAMBERS
"
957.
ALCOKOL
Figure 55. Process flow schematic of hydrolysis - fermentation process.
-------
TABLE 78. MATERIAL BALANCE FOR HYDROLYSIS - FERMENTATION PROCESS
Basis: 3000 metric tons per day raw forest residue and bagasse
Stream
Stream (1) Biomass Feed
Forest Residue (Slash Pine)
Cellulose
Water
Other organics
Total
Bagasse
Cellulose
Water
Other organics
Total
Stream (2) Water
Stream (3) Sulfuric Acid
98 percent
Stream (4) Reactor Feed
Cellulose
Water
Unhydrolyzables
Sulfuric acid
Total
Stream (5) Reactor Effluent
Fermentable sugar product
Water
Unhydrolyzables
Sulfuric acid
Unreacted cellulose
Decomposed sugar
Total
Weight Percent
24
50
26
100.0
24.3
50
25.7
100.0
6
87.1
6.5
0.4
100.0
3.3
87.1
6.5
0.4
1.4
1.3
100.0
Metric Ton
480
1000
520
2000
243
500
257
1000
9000
50
723
10,500
777
50
12,050
400
10,500
780
50
170
150
12.050
Stream (6) Limestone
CaCO_
52
224
-------
TABLE 78. (continued)
Stream Weight Percent Metric Ton
Stream (7) Sugar Product
Fermentable sugar 3.7 400
Water 94.9 10,400
Decomposed sugar 1.4 150
Total 100.0 10,950
Stream (8) Solution from Fermenter
Alcohol 1.8 194
Water 96.7 10,400
Other 1.5 150
Total 100.0 10,744
Stream (9) Alcohol Product
Alcohol 95 194
Water 5.0 10
Total 100.0 204
Based on a low cellulose content in the feedstock of 48 percent (dry
basis) and a sugar yield of 55 percent of theoretical yields, approximately
400 metric tons of 3.7 percent sugar slurry will be produced daily.
A flow chart of the fermentation process is also shown in Figure 55 and
the material balance is listed in Table 78. Industrial scale fermentation of
wood hydrolyzate was practiced approximately 30 years ago but only on batch-
type processes. However, the subsequent development of improved process
technology has resulted in the introduction of a continuous molasses fermen-
tation process. (128) jn vj[ew of the proven performance of this continuous
fermentation process, a similar process, based on wood hydrolyzate feed, is
believed to be technologically feasible and is selected as the model process
for this scenario.
The sugar product solution is pumped to the fermentor where the yeast
(approximately 1 percent by volume) is added. The solution is permitted to
ferment for 24 hours after which time the yeast is withdrawn from the fermented
sugar solution and recycled. The alcohol product is separated from solution
by distillation. The overhead vapors from the distillation column (beer still)
are condensed and conducted to the purifying column. Effluent liquor from
this column flows to the rectifying column where 95 percent alcohol is taken
off the top of the column and passed through a condenser. Fusel oils are
taken off near the bottom of the column and sold as impure amyl alcohol. The
bottom of the column discharges the water waste.
225
-------
Environmental aspects—Waste streams generated in the process are
discharged from three areas: the hydrolyzate filters, the fermentation
product beer still, and rectifying column.
The filter cake from the hydrolysis step is composed primarily of
unreacted cellulose, residual lignin (unhydrolyzables), the CaS04 resulting
from lime neutralization, and entrained water, product, and decomposed sugars.
Approximately 1150 metric tons/day of this material will require treatment.
The liquid portions will be high in BOD but will be easily treated by conven-
tional waste treatment scheme. The solid portion, high in lignin, might be
air dried and used to meet process demand for steam and/or electric power.
The two streams leaving the fermentation section of the plant are the
beer still and the rectifying column bottoms. The sum of these two streams
will be approximately 10,000 metric tons per day (11,000 ton/day). The beer
still bottoms will contain yeast particles not recaptured for recycle, as well
as sugars and mixed alcohol products. After filtration, the solids portion
remaining is often sold as cattle feed supplement in current industrial
practice. Since this scenario is located within reasonable shipping distance
of major feedlot operations, this market would seem to be readily available
to this hypothetical plant as well.
The recovery of the beer still bottoms will not grossly alter the volume
of wastewater to be treated. The BOD load will be high, but, again, it should
be very susceptible to conventional wastewater treatment techniques. Alter-
natively, an algae-growing process system might be considered. The recovered
algae from such a system would be high in protein and integratable with the
beer stills bottoms, in a cattle feed marketing strategy.
Scenario No. 3 (West Coast)--
The region of the West Coast (primarily southern California) represents
an area which could successfully combine ocean farming of kelp with refuse
from urban areas located near the coast, as feedstocks for an energy conver-
sion plant.
The high moisture content of the material indicates that a thermochemical
conversion process would be less efficient than a biochemical process. The
two primary biochemical processes that are considered as possible commercial
processes are hydrolysis-fermentation and anaerobic digestion. Due to the
non-uniform composition of urban refuse and the deleterious effect it would
have on fermentation yields, anaerobic digestion of the feedstock for
conversion to methane was selected as the more appropriate process.
Two-stage digestion was selected for evaluation in this scenario. The
partial pressure of methane in the gas collected from the second stage is
significantly greater than that collected from a single-stage system. This
may be due to the relatively high pH (7.5) which occurs in the second stage.
At this pH, the carbonic acid equilibria is shifted to the right, and more
C02 is present in the aqueous phase, as opposed to the gaseous phase. There-
fore, the partial pressure of C02 is reduced, and the partial pressure of CIU
is increased. The increased concentration of methane and the higher heating
value of the gas results in reduced operating costs for gas purification for
the two-stage system relative to a single-stage system.
226
-------
Process description—A schematic flow diagram of the process conceptua-
lized for Scenario 3 is presented in Figure 56. Relevant data used to con-
struct the scenario are summarized in Table 79; the associated material
balance is presented in Table 80.
The two types of feedstock, urban refuse and kelp, are collected and
transported to the plant site. Each of the feedstocks is pretreated separately
before entering the first-stage digester. Urban refuse is shredded, ferrous
metals are separated, the material is screened, air classified, and shredded
a second time. Ferrous metals, non-ferrous metals, and glass are recovered
during the preprocessing steps.
Kelp is pretreated with calcium ion and pressed to remove salt. Potassium
chloride, sodium carbonate, and sodium sulfate are extracted from the brine.
Sugar syrups are recovered from the juice in the pressing operation.
Pretreated refuse and kelp is mixed and pumped to the first-stage diges-
ter. The residence time in the first-stage is approximately 4 days. The
required volume of the digester is 69,000 cu m (2.44 x 10$ cu ft). Effluent
from the first stage ..is separated and the liquids are transferred to the
second stage. The required volume of the second stage digester is 172,500 cu
m (6.1 x 10^ cu ft). Gas is collected from the second-stage digester and
purified. Effluent from the second stage is separated and the solids are
combined with first-stage solids and recycled to the mixing tank.
Environmental aspects—The discharge streams from the process are (1)
liquid effluent from the digesters, (2) sludge from the digesters, (3) gas
from the first stage which primarily contains carbon dioxide, and possibly
(4) waste brine from the kelp pretreatment section. The liquid stream from
the digester effluent has a relatively high pH (greater than 7.0) and high
BOD and COD. The liquid requires secondary treatment before discharging to
the sewage system. Liquid waste from the brine processing operation can be
recycled to the kelp beds to provide nutrients. If recycling is not economic,
the waste brine will require secondary treatment. Although most of the solids
are recycled, 3362 metric tons per day are discharged as sludge from the
system to avoid buildup. The sludge can be used as a fertilizer or disposed
of by landfill.
Scenario No. 4 (Midwest) —
Ohio was selected as representative of the Midwest region because of the
large area of potentially reclaimable strip-mined land and the growing demand
for electric power. As discussed in the previous section on the selection of
regions, a viable method of reclaiming the strip-mined land and producing
an energy crop is by planting fast-growing, nitrogen-fixing trees, e.g.,
European alders. These trees may be cropped every 5 to 6 years and utilized
as a feedstock for an energy conversion process.
One energy conversion process with an application for this region is the
CPU-400 gas turbine electric generator. This system can utilize the cropped
wood and generate peak load electric power for the Ohio-Western Pennsylvania
region. The wood feed should be more suitable as a feedstock for the fluidized-
bed combustor than municipal solid waste, as the wood is free of aluminum and
227
-------
N3
N3
00
MAGNETIC
SHREDDER SEPARATOR
(14)
KELP
STORAGE
PRE-
TREATMENT PRESSING
(10)
(ID
LIQUID BRINE
TREATMENT PROCESSING
co2
I
|
, H20
1 f
SUGAR — _
CVT3TTDC
(15)
FIRS!
STAGf
:
:
SEPARATC
)RI r
^
SECOND
STAGE
» WATER
TREATMENT
*• SALT RECOVERY
LIQUID
WASTE
Figure 56. Flowsheet of two=-stage anaerobic digestion process.
-------
•TABLE 79. SUMMARY OF KELP AND URBAN WASTE TO SNG PROCESS
Waste Feedstock
Characteristics of Waste:
Urban Refuse
Kelp (before screening)
Moisture Content 87.5% 25%
Ash Content 5.2% 3% (after screening
and shredding)
Density 1009 kg/cu m 486 kg/cu m
(62.2 Ib/cu ft) (30 Ib/cu ft)
Cellulose Content 0.2% 46%
Volatile Solids 7.3 57%
Method of Harvesting Waste:
Kelp will be harvested with special boats which will be equipped
to cut off the tops of the fronds and transport the harvested material
to the processing plant. Kelp is currently harvested from natural beds
with boats of this type. Urban waste will be collected in the usual
manner and transported to the processing plant in trucks.
Geographic Aspects of Waste:
Seven hundred forty metric tons of kelp can be produced per
hectare of ocean area (330 tons/acre/year). Therefore, the area re-
quired to supply the plant with 5000 metric tons of kelp/day (assuming
330 days/yr) is 2230 hectares (5510 acres). It should be noted that
while 5000 tons/day is on a wet basis, this flow represents about
600 tons/day on a dry basis or approximately 14 percent of the solid
waste flow, dry basis.
Five thousand metric tons/day of urban refuse can be supplied from
an area with a moderately large population density. The city of
Los Angeles has a population density of approximately 23 persons/
hectare (9.5 persons/acre).(185) Assuming 0.5 kg of refuse is produced
per person per day, 4.3 x 105 hectares (1.1 x 10° acres) would be re-
quired to support the plant.
In more conventional terms, at 0.5 kg per person per day, a popu-
lation of about 10 million, or essentially the entire population of the
Los Angeles area would be required. On the basis of actual data,
Los Angeles city produces on the order of 4600 metric tons/day
(5000 tons/day),(I86) with the difference probably due to the
229
-------
TABLE 79. (continued)
industrial waste component. However, it is clear that a plant of^this
size would represent a major commitment from the second largest city in
the nation. Alternatively, the relative percentage of feedstock
supplied from the kelp could be increased.
Energy Conversion Plant
Type of Plant:
Two-stage anaerobic digestion
Major Product:
SNG
By-Products from Urban Waste Feed:
Ferrous, nonferrous metals, glass
c .,
By-Products from Kelp Feed:
Sugar, salts, fertilizer
Size:
10,000 metric tons per day, 507» kelp, 50% urban refuse
Based on a potential methane production of 0.3 cu m/kg (dry basis)
(5.5 scf/lb) of kelp and 0.4 cu m/kg (6 scf/lb) of urban refuse, the
plant will produce approximately 986,000 cu m of methane per day.
Geographical Location:
West Coast (southern California)
Storage Facilities:
One week's storage facilities for kelp would be available at the
plant site. This would require 35,000 cu m (1.2 x 106 cu ft) of
storage. Facilities for 1 week storage of urban refuse requires
72,000 cu m (2.5 x 106 cu ft).
230
-------
TABLE 80.
Stream
Stream 1
Stream 2
Stream 3
Stream 4
Stream 5
Stream 6
Stream 7
Stream 8
Stream 9
MATERIAL BALANCE OF TWO-STAGE ANAEROBIC
Composition
Urban Refuse
Moisture
Organics
Other
Total
Total
Total
Metals
Total
Glass, Ash
Total
Organics
Metals
Glass
Plastics
Ash
Moisture
Organics
Metals
Glass
Plastics
Ash
Moisture
DIGESTION
Metric Tons
1250
2500
1250
5000
5000
4688
312
4225.5
462.5
3302.5
375
84
95.5
75
106
187.5
923.0
2126
4
17
75
18.5
1062
3302.5
231
-------
TABLE 80. (continued)
Stream
Composition
Metric Tons
Stream 10
Stream 11
Stream 12
Stream 13
Stream 14
Stream 15
Stream 16
Stream 17
Total
Volatile Solids
Water
Ash
Total
Volatile. Solids
Water
Other
Total
Solids
Water
Total
Carbon Dioxide
Methane
Carbon Dioxide
Methane
Water
Solids
Water
Total
5000
340
4375
240
4955
2466
14437
354.5
17257.5
1466
9000
10466
cu m
296,000 cu m
(assume zero)
296,000 cu m
246,600 cu m
986,400 cu m
1,233,000 cu m
Metric Tons
3075
1000
2362
3362
232
-------
thus obviates one of the major problems plaguing the existing CPU-400 pilot
plant, that of aluminum oxide particulate removal.
Process description—The characteristics of the waste feeds and the energy
conversion process are summarized in Table 81. Figure 57 is a schematic flow
diagram of the electric generating facility and Table 82 gives a material
balance of the facility based on a daily biomass waste feed of 350 metric
tons. A detailed description of the CPU-400 gas electric generator is pro-
vided in Section 5 and is not addressed in this discussion. Basically, the
facility would consist of a fluidized-bed combustor, the cyclone separators,
a granular filter and two-stage turbine compressor and electrical generating
unit. The facility would operate at peak load periods (approximately 8 hours
per day) and during this period would generate approximately 16.5 MW of
electrical power.
Environmental aspects—The exhaust gases from the generator should be
low in SOX and NOX and particulates and should not require control equipment.
The other waste streams, the ash, and captured particulates would be disposed
of in a landfill.
Scenario No. 5 (Midwest) —
In the Midwest, the State of Kansas was selected as one of the regions
to be analyzed in this study because of the availability of large quantities
of agricultural wastes. Wheat crops are harvested twice a year in this area,
leaving wheat straw as a residue. Following collection and proper storage of
this material, it would be available as a potential feedstock to an energy
conversion process. Large numbers of feedlots exist in the same area, providing
sources of easily collectable manure which would be available as a supplemental
feedstock. Due to the relatively high moisture content and low cellulose
content of the potential feedstocks, a biochemical conversion process was
chosen to be evaluated in this study. Of the possible products which can be
produced from biochemical processes (methane, ethanol, butanol), methane was
chosen as a product because of the potentially large demand for grain drying
and the close proximity of major pipelines leading to the more populous East;
single-stage anaerobic digestion to produce methane was selected as the
conversion process.
Process description—Figure 58 is a simplified process schematic for the
single-stage anaerobic digestion process. Pertinent general information is
summarized in Table 83 while Table 84 presents a material balance. The
process is modified from the work of Singh. (145) Both feedstocks are removed
from storage, water is added to the mixture which is then pumped to the
digester. Some pretreatment, such as size reduction may be required for
wheat straw to increase the methane production. Assuming a retention time of
ten days, the required volume is 750,000 cu m (2 x 108 gal). The effluent
from the digester is filtered and the solids are either used as fertilizer or
landfill. Eighty percent of the liquid is recycled to the mixing tank. The
remaining 20 percent is sent to a water treatment plant. The BOD concentration
of this stream is approximately 500 rag/t.
Environmental aspects—Slurry from the digester is separated into two
streams by filtration. The filter cake contains 50% solids and has a high
concentration (500-1000 mgAO. The filter cake (3113 metric tons/day)
233
-------
TABLE 81. SUMMARY OF CONVERSION OF WOOD AND CORN RESIDUE
TO ELECTRICITY PROCESS
(Midwest Region - Ohio)
Waste Feedstock
Characteristics of Biomass Feed:
Type - European alder (80%); corn residue (20%)
Moisture content - Alder, 50 percent; corn, 50 percent
Ash content - Alder, 3 percent; corn, 2 percent
Sulfur content - Alder, 0.1 percent; corn, 0.17 percent
Approximate heating value - Alder, 2600 kcal/kg (4,675 Btu/lb);
corn, 2600 kcal/kg (4,675 Btu/lb)
Approximate bulk density (green) - chipped alder, 800 kg/cu m
(54 Ib/cu ft); corn, 400 kg/cu m
(27 Ib/cu ft)
Method of Harvesting:
The alders will be harvested on a 6-year staggered rotation
period on a year-round schedule. A silage-type harvester will crop
the trees and feed them to a chipper where they will be reduced to
chips. The wood chips will then be transported by truck to the
power generating plant for storage and subsequent use.
The corn residue will be harvested seasonally by a combine that
will collect both the grain and residue simultaneously. The residue
will be ground and compressed and loaded into a truck for transport
to the power generating plant.
Due to the lower bulk density of the corn residue as opposed
to wood chips and the susceptibility of corn residue to deteriora-
tion, during the corn harvesting seasons the relative proporation
of corn residue feedstock will likely be increased.
Geographical Aspects of the Waste:
Location of waste sources - as explained in the introduction
to this section, the European alders will be planted on the
reclaimed strip-mined land in Ohio. This region is centered
primarily in the eastern section of the State where approximately
121,500 hectares (300,000 acres) have been strip-mined.<187)
The corn fields are assumed to be scattered in the more agri-
culturally productive pockets of the region.
234
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TABLE 81. (continued)
Geographical density of waste - based on a 6-year rotation
period and a yield of 15 metric tons of alder wood per acre per
year, the average harvestable field density would be 2.5 metric
tons per acre per year. Assuming 20 percent of the surface area
in the selected region is suitable for strip mining and has been
reclaimed or is amenable to reclaiming, the effective geographical
density of the harvestable alder crop is 0.5 metric ton per acre
per year.
The average field density of the corn residue crop is assumed
to be 2.5 metric tons per acre per year. Assuming 10 percent
of the surface area in the selected region is utilized for corn
growth, the effective geographical density of the corn residue
is 0.25 metric ton per acre per year.
Energy Conversion Plant
Type of Plant:
Gas turbine electric generator (CPU-400)
Product:
Electricity for peak load demand
Size:
Three hundred fifty metric tons per day (an average annual balance
of 280 metric tons per day of wood chips and 70 metric tons per day of
corn residue) - equivalent to 5.5 MW of continuous power or 16.5 MW of
peak power based on a larger generator operating only during peak load
periods for 8 hours per day.
Geographical Location:
Centrally located in the strip-mining region of eastern Ohio.
Based on: (1) an effective geographical density for harvestable alder
of 0.5 metric tons per acre per year; and (2) 63 metric tons per 'day
of green wood waste or corn residue will generate approximately 1 MW-hr
of electrical energy,* sufficient feedstock should be available, on a
continuous year-round basis, within a radius of 25 miles from the
central plant.
235
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TABLE 81. (continued)
Storage Facilities:
Area will be provided for 3 days of open storage of wood chips and
corn residue. The 1,060 metric tons of waste will occupy a volume of
1,470 cu m (53,000 cu ft). This volume would represent a mound approxi-
mately 8 meters high by 13 meters on a side (27 ft high by 45 ft on a
side). Special consideration must be given to the corn residue; it is
more perishable than wood chips and might require a covered, ventilated
storage facility, e.g., a silo.
*This is an estimate based on the results of the pilot plant work on the
CTU-400 process at Menlo Park, California.(188)
236
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FLUIDIZED BED
COKBUSTOR
STORED WOOD CHIPS
AND CORN RESIDUE
OO
ASH
EXHAUST GAS
TO ATMOSPHERE
CYCLONE
SEPARATOR
GRANULAR
FILTER
COMPRESSOR
ELECTRIC
GENERATOR
FLUIDIZING AIR
TO COMBUSTOR
(2)
TO LANDFILL
(3)
Figure 57. Process flow schematic of. gas turboelectric generating system.
-------
TABLE 82. MATERIAL BALANCE FOR GAS TURBOELECTRIC GENERATION PROCESS
Basis: 350 Metric Tons Per Day Chipped Wood and Corn Residue Feed
Stream
Weight Percent Metric Ton
Stream (1) Biomass Feed)
Chipped European Alder
(280 metric tons per day)
Organic compounds
Water
Ash
Sulfur
Nitrogen
Total
Corn Residue
(70 metric tons per day)
Organic compounds
Water
Ash
Sulfur
Nitrogen
Total
Stream (2) Ash and Particulates
Predominantly oxides of
silica, calcium, and
aluminum
Stream (3) Exhaust Gases to Atmosphere
Predominantly water, carbon
dioxide, and nitrogen
100.0
47.6
50.0
2.0
0.17
0.2
100.0
130
140
10
280
33
35
1
70
-24
-5000
(a)
(a) Assumes 10 percent excess air.
238
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WHEAT STRAW
(1)
MANURE
(2)
MIXING
MAKEUP
WATER
OFFGAS
CH4
<6) ^ SOLIDS
DISPOSAL
WATER
TO
TREATMENT PLANT
Figure 58. Flowsheet of single-stage anaerobic digestion plant/145)
-------
TABLE 83. SUMMARY OF WASTE FEEDSTOCKS
FOR ANAEROBIC DIGESTION PLANT
Waste Feedstock
Characteristics of Waste:
Moisture Content
Ash Content
Density
Cellulose Content
Methane Production
Method of Harvesting:
Manure
Wheat Straw
85% (fresh)
3.1%
1005 kg/cu m
(62 Ib/cu ft)
177, (dry)
0.2 cu m/kg V.S.
(3.6 cu ft/lb V.S.)
12.2% (field dried)
7.27, (dry)
778 kg/cu m
(48 Ib/cu ft)
53.6%
0.4 cu m/kg V.S.
(7.0 cu ft/lb V.S.)
Wheat is harvested twice a year. The residue would be collected
and stored. Manure would be collected from feedlots on a daily or
weekly basis and would not require long storage periods.
Geographical Aspects:
Location - Kansas Manure
Availability - 22-27 kg/animal/day
(wet)
(48-60 Ib/animal/day)
6.4 x 106 animals
Wheat Straw
3.5 metric tons/hectare/yr
(1.5 tons/acre/yr)
4.7 x 106 hectare
(11.6 x 106 acres)
16.4 x 10° metric tons/yr (18 x 106 tons/yr) of wheat straw
are available. Based on 330 days per year, this represents 49,700
metric tons/day (54,500 tons/day)
r
The quantity of manure available on a yearly basis is 52 8 x 10*
metric tons/yr (58.2 x 10° tons/yr) or 160,000 metric tons/Hay
(176,000 tons/day). ^
240
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TABLE 83. (continued)
Energy Conversion Plant
Type of Plant:
Single-stage anaerobic digestion plant
Product:
Methane
Size:
10,000 metric tons/day (11,025 TPD)
Feed Rate:
Manure - 5000 metric tons/day (5513 TPD)
Wheat Straw - 5000 metric tons/day (5513 TPD)
Storage Requirements:
Manure - 7 day storage: 35,000 cu m (1.24 x 106 cu ft)
Wheat Straw - 6 month storage: 1 x 106 cu m (38 x 106 cu ft)
Digester Temperature:
35-37 C
241
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TABLE 84. MATERIAL BALANCE FOR SINGLE-STAGE
ANAEROBIC DIGESTION PROCESS
Basis: 10,000 metric tons/day (11,025 ton/day)
Stream
Composition
Metric Tons
Stream 1
Stream 2
Stream 3
Stream 4
Stream 5
Stream 6
Stream 7
Stream 8
Wheat Straw
Moisture
Volatile Solids
Ash
Total
Manure
Moisture
Volatile Solids
Ash
Total
Water Makeup
Water
Digester Off-Gas
Methane
Carbon Dioxide
Water
Total
Slurry
Solids
Water
Total
Solids Disposal
Solids
Water
Total
Water to Treatment Plant
Solids
Water
Total
Liquid Recycle
Solids
Water
Total
610
4,030
360
5,000
4,250
595
155
5,000
7,073
Cubic Meters
589 (822,000 CM/D)
1,097 (548,000 CM/D)
142
1,837
5,218
46,962
52,180
3,000
3,000
6,000
443
8,793
9,236
1,773
35,171
36,944
242
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can be disposed of either by landfill or combustion of the solids for heat
recovery. The filtrate contains 4.8% solids and 9,236 metric tons/day are
sent to the secondary treatment plant.
The quantity of water required for the process is 7,073 metric tons/day.
Scenario No. 6 (West-Urban Center)--
The municipal solid waste chosen as the biomass energy source for the
western urban center may be converted to utilizable energy by almost any of
the previously described thermochemical processes. Of the thermal processes,
direct combustion for the generation of steam was selected as one of the more
appropriate processes for this region. Direct incineration is the most ther-
mally efficient method of converting biomass to energy and is one of-the
most expeditious means of minimizing the huge quantities of municipal waste.
Moreover, steam has a significant potential market in an urban center for use
in industry or for municipal heating and cooling.
Process description—A summary of the waste characteristics and the
steam generating system is presented in Table 85. Figure 59 is a schematic
flow diagram of the heat recovery process and Table 86 gives an estimated
material balance based on 5000 metric tons of raw MSW feed.
The facility will consist of (1) a preprocessing unit which will shred
the refuse and separate ferrous metals; (2) the refuse storage facilities and
conveying system; (3) the heat recovery system, consisting of ten-500 metric-
ton-per-day capacity stoker-fired incinerators (similar to that described in
the section on urban and municipal solid waste under the heading "Primary
Thermochemical Conversion Processes"); (4) an ash collection and transfer
system; and, (5) a combustion gas manifolding and cleanup system consisting
of a single electrostatic precipitator.
The raw waste will first be shredded in a hammermill and passed through
a magnetic separator where the ferrous metals will be removed. The remaining
refuse consisting primarily of combustible organics, will be conveyed to the
storage facility from where it will be subsequently withdrawn and fed into
the incinerators. The combustion gases will pass through the boiler section
and economizer and will be manifolded into a single, common exhaust duct for
treatment by the electrostatic precipitator. The total gas flow from all
ten boilers will be approximately 1100 standard cu m per second (40,000 cfs).
Mobile Biomass-to-Energy Conversion Process
This section involves a preliminary feasibility analysis of a mobile
pyrolysis installation designed for remote or rural areas for converting on-
site, waste biomass directly to energy or into a utilizable fuel. To help
facilitate the conceptualization of the modular process, the following criteria
were established on which to base the determination of (1) the type of waste
feed, (2) the type of fuel produced, and (3) the specific type of conversion
technology.
(1) Simplicity - the process must be functionally simple and
.easy to operate, preferably by a single operator.
243
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TABLE 85. SUMMARY OF MUNICIPAL SOLID WASTE TO
STEAM PROCESS
Waste Feedstock
Characteristics of Waste:
Type of waste - municipal solid waste
Moisture content - 25 percent
Ash content - 14 percent
Sulfur content - 0.2 percent
Heating value - 2700 kcal/kg (5000 Btu/lb)
Bulk density (shredded) - 440 kg/cu m (30 Ib/cu ft)
Method of Harvesting:
The municipal waste will be collected daily, on a 5-day per week
basis, and transported by truck to conveniently located depots where it
will be unloaded and transported by rail to the energy conversion plant.
Energy Conversion Plant
Type of Plant:
A water-walled incinerator, similar to the Chicago Northwest
facility
Product:
7 x 105 kg/hr (15 x 105 Ib/hr) of 250 psig steam for industrial
processing and heating or municipal heating, cooling etc.
Size:
5000 metric tons per day (5600 TPD) of MSW feed.
244
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TABLE 85. (continued)
Geographical Location:
The plant will be located in close proximity to the industrial
or municipal market.
Storage Facilities:
Enclosed buildings will be provided for storing the shredded,
solid waste for up to 4 days. The volume occupied by 20,000 metric
tons of shredded municipal waste is approximately 41,000 cu m
(1.5 million cu ft). This quantity of waste will require five storage
buildings 6 meters high (20 ft) by 37 meters square (120 ft square).
245
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SHREDDER
MAGNETIC SEPARATOR
STORAGE
RAW MSW
V
FERROUS METALS
CLEAN COMBUSTION GASES
TO STOCK
ELECTROSTATIC PRECIPITATOR STOKER-FIRED BOILER
W
I FLY ASH
BOTTOM ASH
TO LANDFILL
Figure 59. Process flow schematic for municipal solid waste
to steam conversion process.
-------
TABLE 86. MATERIAL BALANCE FOR CONVERSION OF URBAN REFUSE TO HEAT
Basis: 5000 metric tons per day of municipal solid waste (MSW)
Stream (1) Raw MSW
Organics
Metals
Ferrous
Aluminum
Glass
Other Inorganics
Moisture
Weight Percent
52
Metric Tons
2600
600
50
350
50
1250
5000
Stream (2) Incinerator Feed
Organics
Metals
59
2600
Ferrous <1
Aluminum 1
Glass 8
Other Inorganics 2
Miscellaneous Solids 1
Moisture 28
100
Stream (3) Ferrous Metals
Stream (4) Ash, Residue and Fly Ash
Predominantly silica, Aluminum and
calcium oxide
Stream (5) Combustion Gas
Predominantly Carbon Monoxide and
Water
30
50
350
100
50
1250
4430
Metric Tons
570
Metric Tons
»580
Metric tons
95,000(a)
'Assumes 10 percent excess air
247
-------
(2) Maintenance and Operating Requirements - the maintenance
and operating requirements must be low.
(3) Preprocessing - a minimal amount of preprocessing of the
waste should be required.
(4) Applicability to Different Waste Feed Characteristics -
the process should be able to accommodate heterogeneous
wastes with varying water and cellulose contents.
(5) Mobility - the modular unit should be compact, light in
weight, and mobile.
(6) Environmental Aspects - the operation of the mobile unit
and the use of the produced fuel, if any, should introduce
minimal secondary environmental problems.
(7) Application - the mobile conversion system should produce
energy or a fuel directly utilizable at the remote site
with minimal modification requirements for existing
equipment.
(8) Practicality - maximum use of established equipment
technology and known energy demand should be made.
Consistent with the above criteria, several possible types and applica-
tions of mobile energy conversion processes can be eliminated. The biochemi-
cal processes (anaerobic digestion, fermentation, etc.) would not be appro-
priate due to the long residence times and prohibitively large vessel sizes.
The more involved primary thermochemical and all secondary processes (hydro-
genation, methanol production, etc.) would also be inappropriate as they are
too complex to be of practical application on a mobile trailer.
Three operations or processes that may be regarded as suitable candidates
are: (1) wood chippers, (2) fuel densifiers, and (3) grain dryers.
(1) Wood Chipper - this would be a mobile unit capable of mulching
forest residue into chips to facilitate easier handling and
transportation. These devices are commercially available
but must be classified as preprocessing methods as they rely
on another process for converting the wood chips to energy.
(2) Fuel Densifier - this would be a mobile pyrolysis unit that
would convert forest and agricultural residue into a solid
fuel with a higher heating value. This process has been
demonstrated by Georgia Tech (see the section on the Georgia
Tech pyrolysis system) for producing a fuel char on a mobile
unit installed on two flat-bed trailers. The merits of the
unit as a mobile energy conversion process are questionable,
however, as the produced char has limited application as a
fuel (not applicable to gas or oil-fired burners), and the
loss in net thermal efficiency in converting the wood to char
could likely offset the increased heating value of the char.
248
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(3) Agricultural Grain Dryer - this concept would burn crop
residue and utilize the hot, cleaned, combustion gases
to dry the harvested grain. The unit, as envisioned,
would be mounted on a flat-bed trailer and towed from
farm to farm where it converts the crop residue into heat
for drying the harvested grain. The crop residue would
serve as a cheap fuel substitute for natural gas, fuel oil,
or propane, which are currently used to supply the energy
for drying. Although practiced in large, stationary
2.5 to 5.0 million kcal/hr (10 to 20 million Btu/hr) dryers
located at central storage facilities (19°), no information
was available to suggest the existence of a mobile agri-
cultural residue fueled dryer for farm applications.
Of the above-mentioned energy-conversion alternatives, the system
regarded as the most appropriate in view of the eight assessment criteria is
the agricultural grain dryer. A more detailed discussion of such a system is
presented below.
Agricultural Grain Drying--
This system would be applicable to provide the thermal energy necessary
in drying most grain crops, corn, soybeans, oats, rice, etc. The thermal
calculations and engineering design for the mobile system are based on the
drying of field corn, as corn is not only produced in prodigious quantities
but usually requires more drying than most other grains (oats or soybeans)
and would thus impose a greater heat or energy load on a drying system. The
greater heat load would result in a conservative design estimate which would
likely prove adequate for drying most of the other less energy-demanding
grain crops.
The system would consist of a conveying mechanism, a feed hopper, a
mechanical grate incinerator, multiclone particulate collectors, an ash collec-
tor, and a combustion gas discharge duct adaptable to existing corn drying
units; a schematic of the system is shown in Figure 60- The corn residue
(stalks, leaves, and cob) harvested with the corn would be fed into the
incinerator where it would be combusted at about 650 C (1200 F) with air.
The hot combustion gas would be passed through the multiclone separators,
where the particulates would be removed, through the discharge duct, and into
the bottom of the corn dryer.
The fuel characteristics for corn stover are given in Table 87. Based
on a heating value of 2600 kcal/kg (4675 Btu/lb) for the corn residue, a 95
percent combustion efficiency, a 25 percent heat loss through the separators
and ductwork, a 25 percent net drying efficiency, and the assumption that
one kg of corn residue is harvested with each kilogram of shelled corn, a heat
balance (shown in Table 88) has been constructed. As can be seen, there is
sufficient heat value in the corn residue to dry the grain without the need
for supplemental fuel.
Several factors must be resolved before this concept can be regarded as
a viable waste-to-energy alternative, however. The thermal efficiency of the
entire system and the particulate removal efficiency of the multiclones must
249
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CROP
RESIDUE
HOPPER
FEEDER
FURNACE
MULTICLONES
VW
L
ASH DISCHARGE
EXHAUST GAS
. DUCT
DRYER
Figure 60. Schematic of mobile agricultural residue incinerator system.
-------
be determined. An overall energy balance must be performed with consideration
given to the incremental energy increase associated with combined harvesting
of the residue with the grain and the subsequent handling of the residue.
TABLE 87. FUEL CHARACTERISTIC OF CORN STOVER
Parameter
Water
Ash
Carbon
Sulfur
Remainder (predominantly
Weight
Percent
25
3.0
30
0.4
41.6
hydrogen, oxygen, and
nitrogen)
100.0
Heating value: 2600 kcal/kg (4675 Btu/lb)
(wet basis)
251
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TABLE 88. HEAT BALANCE ON CORN RESIDUE
INCINERATOR - DRYER SYSTEM
Basis: 1 kg of corn dried from 25 to 15 percent moisture
Heat In
., , , ., ../combustion efficiency,. _ , . .
(Heat value of corn residue) ( r^ ) - neat in
(2600 kcal/kg)(.95) = liZPJscal
Heat Losses
,„ . x / Percent heat lossN , . ,
(Heat in)( r^ ) = heat losses
(2470 kcal/kg)(.25) = 618 kcal/kg
Heat Available for Drying
/„ ... - , v/percent drying efficiency-. , . . n , ,
(Residual heat) (^ iQfi ' = available
(2470 kcal/kg - 618 kcal/kg)(.25) = 460 kcal/kg
Heat Required for Drying
-Difference in moisture content. .Latent heat of vapori-,. -Sensible heat-.
of undried and dried corn zation of water ^increases
(1.0 kg)(.10)(550 kcal/kg) + 1.0(0.5 kcal/kg-C)(50 C) = 80 kcal/kg
Net Heat Available
Heat available - heat required = (460 - 80) = 380 kcal/kg
252
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SECTION 7
ENVIRONMENTAL ASSESSMENT
OBJECTIVES OF PRELIMINARY ENVIRONMENTAL ASSESSMENT
The collection and processing of organic matter, together with the con-
version of these energy containing substrates, has potentially important
environmental impacts. These influences will almost certainly be felt at
the local and regional level but, if implemented on a large enough scale,
could become national or global issues. In many cases, the utilization of
biomass for energy must be considered as an environmentally sound alterna-
tive since present resource economics assign very low or negative market
values to these wastes. The disposal or recycling of the solid and liquid
residues from biomass conversion may also have beneficial aspects when
rising petrochemical fertilizer costs increase the attractiveness of these
options and land prices for disposal become prohibitive without volume
reduction of wastes.
Other biomass feed sources may be part of a complex natural feedback
system which provides a replenishment of mineral and organic material to
the production system. Unwarranted damages may be inflicted by the improper
management of these natural resources.
Little attention has been paid to a comprehensive analysis of the col-
lection and processing techniques for biomass synthetic fuels and the
associated effects on the environment. The areas impacted will range from
highly natural and unspoiled surroundings whose rhythms should not be up-
set to densely settled urban areas whose inhabitants justifiably lay claim
to clean air and water. Because of the early stage of development of these
technologies, information gathering on environmental effects can proceed
alongside research on engineering and process variables.
IMPACT ASSOCIATED WITH GROWTH AND PROCUREMENT
OF FEEDSTOCK/SOURCE MATERIALS
The range of materials which are amenable to collection and transfor-
mation spans the continuum from man generated to plant produced. Each of
the source regions presents a unique set of circumstances in terms of the
degree and nature of the disturbance. Careful management of the resources
contained in residues collected from agricultural and forested lands must
be practiced in order to maintain a continuing high level of productivity
while providing a useful source of energy. Conversely, conversion of
253
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animal manure and municipal wastes entails recognizing that the use of valu-
able energy resources should not eliminate the need to maintain closed
cycles of materials flow to the extent practicable.
Forestry Residues/Silviculture
Discussion of the environmental aspects of silviculture and forestry
residues as biomass sources can logically be treated as an entity. The
environmental effects of collecting and transporting these materials will
be subdivided into those associated with changing land use, alterations of
the physical/chemical environment, and alterations in the ecology of im-
pacted forest communities.
Land Use--
The potential land use impacts directly attributable to collection,
storage, and preprocessing of forest floor wood residues, mill wastes, and
other cellulosic fragments now considered unusable are linked with the
developing markets for these materials. Increasing acreage on which residue
collection is practiced is also related to" the trend toward more intensive
silviculture. An estimated two-thirds of the increase in the demand for
domestic wood by the year 2000 will be met by use of logging residues "'•'•).
Use of wood residues for new wood products will, therefore, compete, with
the use of residues for fuel.
Indications from the literature are that only a very small portion
(< 10 percent) of the total forested area in the U.S. is presently affected
by primary residue recovery activity. Primary residue recovery is defined
as an attempt to collect and utilize tree tops, small branches and leaves,
and stumps. The diffuse nature of this material has made its collection
unprofitable. However, the development of new methods of collection which
permit the efficient gathering of smaller, more irregular pieces will in-
crease the land impacts substantially. The practice of yarding unused
material (Y.U.M.) is a step in this direction. In addition, if the trend
toward outdoor recreation continues, negative public reaction to logging
slash in clear-cut areas will be magnified and logging concerns will be
forced to implement conservation practices on more acreage.
The land area needed for yard storage and drying facilities will in-
crease in direct proportion to the change in usable wood and wood wastes.
Actual assessment of the storage and drying needs will best be performed on
a regional basis taking into account:
• The daily supply requirements of the generating facility
• The degree of drying which produces optimal operating con-
ditions is related to energy conversion and plant emissions
• Whether gathering operations can proceed during the
winter months
• Constraints particular to the drying operation as for
example, the maximum dimensions of a drying pile and
the drying rate.
254
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Alterations in the Physical/Chemical Environment-
Forest systems generally consist of terrestrial, aquatic and atmospher-
ic components. Each of these is interrelated through the mixed physical
and chemical exchanges of materials and energy. If left undisturbed,
forests tend to reach an equilibrium which represents the most energet-
ically efficient use of available resources. Each of the components, soil,
water, and air, behaves in such a way as to maintain the balance.
Forest soil is classified into three zones or horizons which represent
stages in the recycling of vital elements:
1. L - Litter layer consisting of unaltered dead remains
of plants and animals.
2. F - Fermentation layer consisting of partly decomposed
organic matter. The structure of the plant debris is
generally well enough preserved to permit identification
of its source.
3. H - Humus layer consisting for the most part of well
decomposed, amorphous organic matter(192)t
Clearly, the impacts of removal of material from the forest floor will be
related to the rate and extent of removal and to the "characteristic pat-
terns of litter fall, humus accumulation, and decomposition occurring in
different forest types" (*-93) f Collection of residues leads to departures
from the steady-state nutrient and organic matter (OM) cycles typical of a
mature ecosystem. The magnitude and rate of the shift toward a smaller
nutrient and OM pool is determined by the fraction of new litter which is
removed. The percentage of vegetation removed will depend on the particular
harvesting practice adopted, e.g., whole tree versus chip collection. The
distribution of wood material among the various components of the forest
is shown in Table 89.
Loss of organic matter due to harvesting and residue collection occurs
in two ways. The primary harvesting effort removes about two-thirds of
the organic matter when all residue is collected. The amount of residue
generated by cutting operations is highly variable and dependent on tech-
nique and equipment employed. Various estimates place the quantity of
slash at between 15 and 227 metric tons per hectare (7 to 101 tons per
acre) (3,4,5) . During revegetation seasonal leaf and dead branch contri-
butions to forest floor litter loads are smaller than they had been in a
pre-harvest condition. Until this new growth is established, which may
require several years, the organic matter pool is not at a steady-state.
255
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TABLE 89. ESTIMATE OF MATERIAL REMOVAL DUE TO CLEAR CUTTING
AND RESIDUE COLLECTION COMPARED TO INSTANTANEOUS
POOL SIZE
Parameter Amount Percent of Total Vegetation
MT/ha
Total tree layer
Subterranean stems
163
15
69
6
and roots
Dead vegetation and 59 25
annual herb and shrub
layer
Total 237 100
(a) Content in each compartment was variable depending on season; oven-dry
weight basis
The quantitation of this loss is best performed by simulation modelling of
the ecosystem and is beyond the scope of this report.
The removal of organic matter and nutrients by slash harvesting is 20
to 50 percent of that due to bole and branch harvesting^94) m This quantity
may be important if short period rotation practices are utilized and in
fact is four to seven times the annual accumulation of litter reported for
white oak in Illinois^- "''. An extreme example of the detrimental effect
of the repeated removal of floor litter showed that in adjacent stands the
degradation in soil quality caused a 25 percent reduction in board foot
volume per acre when litter was removed *>"°'•
A number of other secondary changes in the physical-chemical systems
are induced by cutting and residue recovery. These include:
• Water holding capacity, evaporation, transplantation
and runoff
256
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• Soil loss
• Nutrient release rates
• Depth of aeration
• Reflectivity and heat flux.
Differences in infiltration capacity (and, by inference, in runoff) assoc-
iated with different soil properties have been measured by a number of
authors and are listed in Table 90 as simple linear correlation coef-
ficients. When these factors were combined, the highest multiple coef-
ficient was obtained with noncapillary porosity and organic matter in both
surface and subsoil (*-"'). The effect of removal of the top 7.5 cm of
forest floor organic matter in a Colorado pine stand was to decrease the
average infiltration rate by 40 percent which was highly significant sta-
tistically *• yy'. Reduced infiltration coupled with higher overland sheet
flow velocities caused severe sheet and rill erosion, increased loading of
nutrients to nearby waterways, and reduced dry weather soil moisture.
TABLE 90. CORRELATION BETWEEN FOREST SOIL PARAMETERS
AND INFILTRATION RATE
Parameter r
Noncapillary porosity, subsoil 0.54
Organic matter, surface 0.50
Clay content, subsoil -0.42
Organic matter, subsoil 0.40
Noncapillary porosity, surface 0.36
Total porosity, subsoil 0.36
Volume weight, subsoil -0.33
Aggregation, surface 0.30
Moisture equivalent, subsoil -0.30
Suspension, surface -0.29
Total porosity, surface 0.24
Silt + clay, subsoil -0.24
Volume weight, surface -0.24
257
-------
The influence of vegetal density on erosion rates can be best illus-
trated by pointing out that the material transport ability of moving water
varies as the velocity to the fifth power' ' so that erosive soil losses
may be substantially increased for small increments in water velocity.
The most comprehensive study located of particulate export from for-
ested ecosystems is that conducted on the Hubbard Brook System, New York,
by Borman et al^Ol). The findings were generally consistent with expec-
tations based on theoretical considerations. As stated in the results,
deforestation had a pronounced effect on the amount and size of particu-
late matter exported, the proportion of organic to inorganic material, and
the origin of organic matter.
In terms of erodibility, the mature forested ecosystem had an output
of 25.4 kg/ha (total particulate matter) versus 156.0 kg/ha for the clear-
cut plots (22.7 Ibs/acre versus 139.2 Ib/acre) . Short, intense rain
events were cited as being most responsible for the differences. In ad-
dition, the deforested systems tended to export a larger fraction of in-
organic materials. However, these relationships may be altered somewhat if
revegetation is allowed to proceed at the natural rate instead of being
suppressed as it was in this study. Finally, the major contribution to
organic material export differed for the two treatments. In the steady-
state, mature area, newly fallen litter was inconsequential as a source of
export of organic matter with the major supply derived from streambed
deposits. The opposite was true for the cut-over areas.
The implications of intensive silviculture and slash collection for
water quality relate to the increased transport of detached soil particles,
organic materials, and associated chemical species to nearby lakes and
streams. Most of the principal factors controlling changes in water
quality have been discussed previously. The yield of particulates, soil
material and organic debris is determined in part by the distance to water
and in part by topographic and hydrologic characteristics of an area. One
other consideration is the selection of logging and slash recovery systems.
Effects range from severe to superficial, depending on methods used and
degree of planning *• ' . Various methods have been developed to quantify
the loss of soil from various land parcels. Wooldridge(203) has used mean
water-stable aggregate size as a measure of erosion hazard. One of the
most widely used techniques for erosion estimation is the Universal Soil
Loss Equation developed by Wischmeier and Smith(204,205) an(j Wischmeier(206)
and widely used by the Soil Conservation Service of the USDA. It empiri-
cally predicts gross sediment transport from small watersheds as a function
of soil type, degree of vegetative cover, and topography. Table 91 pre-
sents cover factors for use of this equation. The accuracy of estimation
declines as the drainage basin area increases unless additional factors
are introduced. Generally, the higher the organic matter content, the
larger the aggregate, and the less erodible the soil(207). Increased los-
ses of nutrients and other elements as a result of forest floor and canopy
disturbance seem to be universal. Both surface and ground water are likely
to be affected. Increased levels of nitrates are a cause for concern where
258
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TABLE 91. COVER FACTORS FOR WOODLAND USED IN THE
UNIVERSAL SOIL LOSS EQUATION
Condition
Well stocked
Medium stocked
Poorly stocked
Tree Canopy-'
% of Area
100-75
75-40
40-20
Forest Litter^-
% of Area
100-90
90-75
70-40
c/
Undergrowth-
Managed— .
Unman aged-
Managed
Unmanaged
Managed
Unmanaged
Cover
Factor
0.001
0.003-0.011
0.002-0.004
0.01 -0.04
0.003-0.009
0.02 -0.09
a/ When tree canopy is less than 20% the area will be considered as grassland or
cropland for estimating soil loss.
b/ Forest litter is assumed to be at least 5 cm (2 in.) deep over the percent
ground surface area covered.
£/ Undergrowth is defined as shrubs, weeds, grasses, vines, etc., on the surface
area not protected by forest litter. Usually found under canopy openings.
&J Managed—grazing and fires are controlled; unmanaged—stands that are over-
grazed or subjected to repeated burning.
Reference: Wischmeier (208).
water is used for drinking purposes downstream or downgradient. Since un-
disturbed forest systems cycle nutrients vary efficiently, a disturbance
which creates additional runoff usually raises the primary productivity
of the aqueous system if nutritive factors were limiting.
Export of nutrients, as well as other elements, was monitored during
the Hubbard Brook investigation and reported in several articles.*-193,201,208)
Gosz, et al^ , determined that removal of elements by leaching was pro-
portional to the water-soluble organic content. Total nutrient loss was
determined to be a function of vegetation type, extent and nature of the
cut, slopes, and drainage patterns.
Deforestation had marked effects on loss of all elements measured with
the exception of sulfur. Elements were grouped according to the severity
of the increase in loss rates:
< 10 times
5-9 times
> 4 t ime s
N,P,K
Al,Ca,Fe
Gl,Si,Na.
It should be noted that the elements shown to suffer the greatest los-
ses are those required by plants in the largest amounts. The most immediate
response of the system was the increased solubility of nutrients. Because^
of the increased rate of organic matter decomposition and increased nitrifi-
cation, nitrogen was rapidly removed from the system. An estimated 1.5 to
2.5 times the annual uptake was lost as dissolved nitrogen mainly in the
259
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form of nitrates. The hydrogen ions from bacterial ly mediated nitrifi-
cation released nitrates according to the equation:
H+
The hydrogen ions tend to compete with and displace other cations, most
importantly calcium, from the exchange sites in the soil. Also, the ex-
cess proton activity acts to lower the soil solution pH affecting solubil-
ities of various elements. The general conclusion reached by the authors
was that while element cycling within the ecosystem is temporarily
"loosened", the natural equilibrium soon reasserts itself to minimize
adverse impacts.
Two other effects of canopy and residue removal should be mentioned
although their consequences can be minimized by proper management.
Research indicates that changes in percent canopy cover and the removal of
forest floor affect soil temperatures. Tourney and Neethling^09) state
that temperatures in the shade are as much as 17 C cooler than in sunny
areas where floor material (12.7 cm) is allowed to remain and 22 C cooler
than where both canopy and floor are removed. Higher soil temperatures
accelerate biological processes and may lead to stress on the decomposer
population.
Compaction of soil by harvesting/collecting equipment and reduced
infiltration caused by vegetation removal usually has pronounced effects
on the magnitude of flood flows. In a comparative study on forested and
deforested water sheds in Colorado, the beginning of the rise in the hydro-
graph was 12 days earlier, the dates of the flood crests were 3 days
earlier., and the crests averaged 69 percent higher in the deforested
basinU ;.
The air -related impacts of slash harvesting include the changes in
emission of hydrocarbons and oxides of nitrogen. Acceptance of the de-
finition of an atmospheric pollutant as a substance present in sufficient
quantities near enough to people, plants or animals to produce deleterious
effects demands the consideration of forest residue burning as a serious
pollutant. The area of slash created and the treatment merits mention,
although national data are not available (Table 92). Use of wood wastes
for fuel will partially alleviate the need for burn-over and the attendant
particulate and gaseous emissions. Offsetting this benefit to some degree
will be the increased emissions from internal combustion engines used in
slash recovery unless efforts are made to advance logging/harvesting
technology to the point where residues are collected simultaneously with
the primary harvest.
Ecological Impacts--
Removal of vegetation from the forest floor will cause changes
in most of the trophic levels associated with the decomposers. However,
the rate of decomposition is dependent on the mass and size distribu-
tion and the composition of decomposable litter. (2^) Nutrient
content varies with differences in tree species and is higher in the
foliage component. Foliage, twigs, and small branches are readily
260
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TABLE 92. CHANGES IN ACREAGE OF SLASH CREATED AND SLASH
TREATMENT ON FORESTS OF THE PACIFIC NORTHWEST
REGION (256)
Method 1963 ,n3 A 1972
-10 Acres-
Clearcut 57 63
Partial cut 284 549
Broadcast burn 45 26
Pile and burn 0 87
Receiving extra protection:
Clearcut 0 36
Partial cut 512 912
assimilated and contribute the major portion of microbial nutrients while
accounting for only a minor fraction of the total residue volume. Other
environmental niches which may be affected by residue and canopy removal
are those supplying forage and cover to small animals.
Transport of organic materials and sediments to streams causes changes
in productivity and species diversity. Depending on the previous water
quality history of the stream, higher suspended solids concentrations
(reduced light penetration) may decrease primary productivity or cause a
shift to more shade tolerant aquatic species with a resulting lower species
diversity index (SDI) . On the other hand, the enrichment potential of an
increased nutrient load may increase the net rate of carbon fixation,
associated with increased rooted aquatic plant and algae growth, while
still causing a reduced SDI due to the exclusion of less tolerant forms.
Increased BOD and sediment loads also cause stress on the fish and benthic
communities. Changes in peak storm flows and subsequent scouring effects
on stream banks and bottom may disturb spawning grounds and destroy niche
areas of bottom dwellers. In backwater pool areas, drops in dissolved^
oxygen levels due to organic decomposition may favor anaerobic fauna, if
low-flow conditions persist for long periods.
On the positive side, it has been claimed that large volumes of debris
depress forage production and increase the potential for fire and that some
type of treatment to reduce, but not eliminate, this volume would produce
desirable and beneficial ecological effects (212). High intensity fires
occur with heavy accumulations of fuel and are difficult to control^ '.
Quantity reduction, then, may offer a reduced hazard potential. Quantity
alone, however, does not indicate what fuel is available for^combustion.
Fuel availability depends on moisture content, size of material, and the
ratio of living to dead combustible material.
261
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Summary -- The literature on the inventory and estimation of environ-
mental impacts of silviculture and residue recovery for energy production
indicates a paucity of quantitative investigations. Where these have been
conducted, as in the case of the Hubbard Brook study, the experimental
treatment seems to be conceived of as a "worst case" situation. Since the
degree of ecosystem disturbance owing to harvesting, removing, and storage
of forest materials is a continuum which depends on many regional, site,
and engineering variables, it would seem appropriate to examine other
points along the continuum. In general, the transformations indicated by
Figure 61 should be examined in greater detail for their response to dif-
fering degrees of harvest/recovery activity. The manner in which the ter-
restrial, aquatic, atmospheric, and biological components interact and re-
spond to a severe perturbation is shown in Figure 61, excerpted from the
Hubbard Brook study. In general, the transformations are expected to be
qualitatively similar for all forest systems, but the magnitude of impact
will be contingent upon the degree of harvesting/recovery activity. Re-
ductions of organic matter in some regions may provide several benefits.
Research is needed to predict the amount of removal that can take place on
a continuous basis.
It should be emphasized further that many of the potentially adverse
impacts can be mitigated by utilization of available erosion control tech-
nology and engineering judgement. These measures might include stand
selection and harvesting techniques which minimize soil disturbance, de-
velopment of an adherence to specified guidelines, establishment of buffer
zones around environmentally or aesthetically sensitive areas and so forth.
Silviculture has also been tried successfully on marginal strip-mined land
in the hopes of restoring some degree of productivity. Thus the net impact
may be positive.
Agricultural Crop Residues/Energy Crops
Methods of collection and conversion of energy crops to fuels are
similar to those used in the conversion of agricultural residues. There-
fore, the environmental effects of the conversion of both biomass sources
will be discussed in this section. Since the basis for discussion pre-
supposes commitment to crop production, land use will not be discussed.
The ecological effects will be similar in many aspects to those discussed
in the section Forestry Residues/Silviculture and will not be repeated.
Alterations in the Physical/Chemical Environment—
Environmental responses to the collection and use of crop wastes and
harvesting of energy crops are qualitatively similar to those from forest
residue/silviculture. Keeping in mind that the time frame is much shorter
for crop residues and energy crops (1 year versus 2-15 years for intensive
short-rotation forestry), many of the highlights present in Section 3.1.1
are applicable.
The major alterations to be evaluated regarding intensified crop waste
collection or energy crop production are:
262
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TRANSPIRATION
REDUCED 100%
EVAPOTRANSPIRA-
TION. 0.3X
COMPLETE CUTTING
AND HERBICIDE
REPRESSION OF
NEW GROWTH
VELOCITY OF
STREAM DISCHARGE
UP IN SUMMER
RELEASE FROM INHIBITION
BY VEGETATION ?
MICROCLIMATE
WARMER, SOIL
MOISTURE HIGHER
IN SUMMER
BIOTIC REGULATION
OF EROSION AND
TRANSPORTATION
REDUCED
OUTPUT OF STREAM-
"-*JWATER. I.4X
MOSTLY IN SUMMER
ORGANIC MATTER
TURNOVER ACCELERATED
NITRIFICATION
INCREASED 2.5X->IOOX
IONS
ACIDIFICATION OF
CATION EXCHANGE
SITES.
I
CATIONS
CATIONS
ANIONS
CONCENTRATION OF
DISSOLVED INORGANIC
SUBSTANCES IN
STREAMWATER. 4.IX
OUTPUT OF
PARTICULATE
MATTER
4.3 X
NET OUTPUT-DISSOLVED
INORGANIC SUBSTANCES. I4.6X
pH OF STREAMWATER
5.1 DOWN TO 4.3
TO DOWNSTREAM ECOSYSTEM
Figure 61. Effects of clearcutting on hydrology and materials cycling.
(201)
263
-------
• Increased usage of inorganic or organic (animal
manure) fertilizers
• Changes in the amount of sediment transported by runoff
• Alterations in normal nutrient cycles
• Variations induced in soils-texture, organic matter,
water holding capacity, and mineral content.
The objective of soil management is the maintenance of near steady-
state conditions. Ideally, applications of fertilizers and mulch/organic
material should just match the deficits created by harvesting of the crop
because over-fertilization results in excessive nutrient runoff losses and
under-fertilization reduces yields. This statement is never totally true
in practice because of time-varying influences in nutrient availability and
crop needs. However, for present purposes the implications of the infor-
mation in Table 93, an assessment of nutrient removal when harvesting for
conversion, are that about 35-40 percent of the annual needs of the plant
crop would be removed each year in harvesting the stalks and leaves. This
imbalance would be correctable in a number of ways:
• Drawing on soil reserves to increase supply, e.g.,
increased solubility of phosphorus due to greater
concentration gradient
• Higher application rates of commercial fertilizers
• Use of supplemental fertilizers such as manure
and/or sludge.
Harvesting an energy crop such as sugar cane would, of course, remove
nearly 100 percent of the annual uptake.
Traditional soil management techniques preserve soil integrity through
additions of inorganic fertilizers, erosion reduction and plow-under of
crop residue. Recently, due to increased costs of fertilizers, many farms
have begun augmenting super phosphate and anhydrous ammonia treatments with
mulch derived from animal manure, secondary treated effluent or sludge.
The primary benefit of such practices (manure spreading or plow-down) is
the increased organic matter content carried over to the following growing
season, although some nutritional requirements of the crop may be satis-
fied in this manner. There have been some suggestions to utilize animal
manure and solid waste for energy production. Depending on the demand and
supply conditions, use of these materials as soil amendments may be
severely curtailed thus placing greater importance on soil conservation
practices and recycling of organic materials in stubble. Stubble left in
the field aids in erosion resistance by reducing the kinetic energy of rain-
drop impact, slowing the sheet velocity of overland flow, increasing tilth,
and improving soil agglomeration by increasing chemical and mechanical
binding.
A number of methodologies for estimating erosive soil loss and nutrient
transport have been developed ranging from highly generalized empirical
estimators such as the Universal Soil Loss Equation (USLE) to highly
sophisticated computer-based simulation models which incorporate detailed
264
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TABLE 93. AMOUNTS OF MAJOR NUTRIENTS REMOVED BY CORN RESIDUE
COLLECTION FOR USE AS A FUEL SOURCE (a)
Parameter
Annual Uptake
(kg/ha-yr)
Percent of Dry
Weight (mean)(c)
Amt. Removed
(kg/ha-yr)
Percent of Total
Annual Uptake
Removed(d)
p
N
K
Ca
Mg
32
168
158
-
-
0.15
0.91
0.74
0.32
0.24
11.3
68.4
55.6
24.1
18.0
35.3
40.7
35.2
-
-
(a)
(b)
(c)
Assumes 100 percent
Yield 120 bu/ac (297
Gerloff, G. C/214>.
residue collection
bu/ha). Keeney, D
efficiency.
. R., etal.<213>.
(d) Assuming 5600 Ib (2500 kg) residue per bushel (7.52 MT/ha for 297 bu/ha yield)<215)
Does not include below-ground portion of plant mass or nutrients.
-------
soil moisture accounting and chemical kinetic parameters. Because of the
diversity of agricultural management practices available, it would be futile
to generalize regarding the amount of change in soil or nutrient loss to be
expected with continuous removal of stubble. For example, on conventionally
tilled (continuous, row-planted) corn, average annual soil loss is increased
by approximately 24 percent if residue is removed. However, if a winter
cover crop is seeded and plowed under, soil loss is decreased by 5 percent,
even though residue is still removed. Also residue removal may be only
partial, that is, root material may be allowed to remain so that soil re-
tention ability is not completely lost.
Long-term continuous removals of residue and/or high yield production
would produce unacceptably high erosion rates under most slope and soil
conditions.
The USLE is:(208)
A = RKLSCP where
A = Average annual soil loss per unit area
R = Rainfall factor (accounts for both the duration and
intensity of a rain event by specifying the number of
erosive index units accumulated per year). The erosive
index unit is a measure of the erosive force of a
specified rainfall.
K = Soil erodibility factor
L = Slope length in feet
S = Degree of slope
C = Cropping management factor - permanent vegetation < grass
meadow - legumes - small grains - row crops - fallow =1.0
P = Cropping practice factor - contour tillage, strip-cropping,
etc.
The contribution of organic matter content, both directly and indirectly, to
the erodibility factor, K is shown in Figure 62. Besides the direct ef-
fects, low organic matter (PM) content produces tightly structured, low
permeability soils.
Water quality impacts under high productivity, poor management con-
ditions would be similar to those encountered under the "worst case" silvi-
culture/forest residue situation. Forest soils may have higher K values on
the average than soils suited for agriculture. If proper management is
neglected, heavy siltation and nutrient runoff will result. This will be
an especially severe problem on lands marginally suited for crop production.
Other water quality influences result from storage/drying of bagasse and
stubble. These areas must be protected from rainfall/runoff because of
the potential leaching and transport of BOD, nutrients, and solids to
streams and lakes. These pollutant sources are similar in some ways to
those generated from storage of animal wastes and may, in extreme cases,
need to be treated as such.
266
-------
fin«
2- fine granulor
3-mod or eoarje gronular
4-blocky, platy, or mos*i»«
SOIL STRUCTURE
PERMEABILITY
PERCENT SAND
0.10-2. Omm)
6- very slc.«
slow
4- slow to mod.
3- moderate
2-mod to ropid
1 - rapid
PROCEPUHE: With appropriate dot*, rnttr scale at left atid proceed to points representing
the soil's % sand (0.1C-2.0 m}, 1 organic ratter, structure, and permeability, Ijn that seojjencje.
Interpolate between plotted curves. The dotted line Illustrates procedure for a soil having;
s(+«.fs 65X, send 5X. OH 2-flI, structure 2, permeability 4. Solution: K • 0.31.
Figure 62. Relationship between soil credibility and physical-chemical composition.
-------
Atmospheric effects would include changes in reflectivity as a result
of longer periods of dark soil surface exposure and greater amounts of air-
borne dust due to wind erosion.
Summary--
The practice of removal of crop residues such as corn stalks
or the harvesting of energy crops has two major potential impacts - the
loss of nutrients and organic matter associated with continued withdrawals
of biomass and the increased erodibility of exposed soils, especially in
northern climes where spring snow melt-runoff occurs. Judging from previous
research on environmental effects associated with intensive agricultural
production, both of these limitations can be minimized. Methodologies for
minimizing erosion and nutrient loss will have to be utilized. These might
include terraces, contour cropping, fertilizer plow-down with controlled
application timing, and rotations which would permit only a limited number
of energy/residue crops. With good planning, adverse impacts should be at
or below those from traditional agriculture. Also, if a biochemical con-
version process, such as anaerobic fermentation, is utilized, much of the
original chemical content of the stubble remains and could be recycled back
to the land.
Animal Waste
Physical/Chemical Impacts--
Animal production facilities can be broadly classified as small,
individually-owned farms or large commercial operations. Animal waste col-
lection for biomass conversion is a more likely alternative on the large
feedlots for economic reasons. Therefore, the analysis will be largely
confined to these. Manure is presently stacked and allowed to ferment due
to a lack of utilization alternatives. In some instances, it is treated
further in anaerobic or aerobic lagoons to reduce pollutional loadings to
ponds and streams or is spread on agricultural land.
Land-spreading of raw or treated manure has both positive and negative
aspects. Application of manure at 33.6 MT/ha (15 T/ac) on continuously
cropped corn land decreased surface run-off by 16 to 24 percent(217). A
605 MT/ha (270 T/ac) loading rate with wet cattle manure reportedly increas-
ed the field moisture capacity 12 percent(217). Soil structure is also im-
proved by additions of manure. The potential pollution problems associated
with the handling and disposal alternatives for animal waste have been ad-
dressed in detail in the literature (Tables 94 and 95). Briefly, these in-
clude:
• Phosphorous and nitrogen loading to surface waters are
increased; especially when improper management practices
are adopted
• BOD loads are also often increased
• Odor problems sometimes create nuisances
• Nitrate contamination of ground water may occur
• Storage of large quantities of high moisture manure
induces vector production and may indirectly lead to
runoff of biocides used to control the pests.
268
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TABLE 94. RANGE OF OBSERVED VALUES IN CONCENTRATION AND
AREA YIELD FOR VARIOUS LAND USES^218)
1-0
Concentration (mg/1)
Source COD BOD NO,--N
Precipitation 9 16 12-13 0.14-1.1
Forested land - - 0.1-1.3
Range land - —
Agricultural 80 7 0.4
crop hind
Lund receiving — - —
manure
Irrigation tile drainage.
western United States
Surface flow — — 0.4-1.5
Subsurface - — 1.8-19
drainage
Crop land tile — — —
drainage
Urban land 85-110 12-160 -
drainage
Seepage from 25,900-31.500 10,300-13,800 -
stacked manure
Fccdlot runoff 3,100-41.000 1,000-11,000 10-23
Total N
1.2-1.3
0.3-1.8
-
9
—
0.6-2.2
2.1-19
10-25
3
1,800-2.350
920-2.100
Area yield rate (kg/ha/year)
Total P COD BOD
0.02-0.04 124 -
0.01-0.11 - —
-
0.02-1.7
_ _ _
0.2-0.4 - —
0.1-0.3 -
0.02-0.7 —
0.2-1.1 220-310 30-50
190-280 - —
290-360 7.200 1,560
NOj- N Total N
1.5-4.1 5.6-10
0.7-8.8 3-13
0.7
0.1-13
4-13
3-27
83 42-186
- 0.3-13
- 7-9
— —
- 100-1.600
Total P
0.05-0.06
0.03-0.9
0.08
0.06-2.9
0.8-2.9
1.0^.4
3-10
0.01-0.3
1.1-5.6
—
10-620
Surface area of interest
Total land area
Forest area
Range land
Active crop land
Crop or unused land
used for manure
disposal
Irrigated western soils
Irrigated western soils
Active crop land
requiring drainage
Urban land areas
Manure holding area
Confined, unenclosed
animal holding areas
" Data do nol reflect the extreme ranges caused by improper waste management or extreme storm conditions; the data represent the range of average values reported
in previous tables.
-------
/O 1 Q \
TABLE 95. CHARACTERISTICS OF SEEPAGE FROM STACKED DAIRY CATTLE MANURE AND BEDDINGV
-~J
o
Parameter
Total solids (7=)
Volatile solids (% TS)
Suspended solids (%)
BOD (mgAt)
COD (mgAt)
Total N (mgAt as N)
NH3-N (mg/-t)
Total P (mg/£ as P)
Potassium (mg/l as K)
Total precipitation (inches)
Seepage volume (gal/cow/day)
Average
2.8
55
0.35
13,800
31,500
2,350
1,600
280
4,700
Winter
Range
1.8-4.3
52-59
0.2-0.8
4,200-31,000
21,000-41,000
1,500-2,900
980-1,980
64-560
3,000-72,00
15.0
3.0
Average
2.3
53
0.24
10,300
25 , 900
1,800
1,330
190
3,900
Summer
Range
1.7-2.9
50-58
0.2-0.3
4,400-21,700
16,400-33,300
1,200-2,770
780-2,200
90-340
3,000-4,900
9.4
1.2
-------
The re-routing of manure to conversion facilities is only feasible if
these are located near the feedlot. In some cases this permits the re-
cycling of the spent materials back to nearby agricultural lands. The net
loss of the soil conditioners and plant nutrients depends on both the mode
of conversion and on the length of storage.
If thermochemical conversion processes such as incineration or mixed
refuse feed are chosen, then the options for recycling are limited. Chem-
ical analyses of the residue (char or ash) indicates adequate concentrations
of phosphorus and potassium, but less than trace amounts of nitrogen.
By itself this provides insufficient economic incentive or crop
value. However, if the char were mixed with a material high in organic
carbon, it might prove useful as a low-grade fertilizer.
On the other hand, the high moisture content favors the implementation
of a fermentation type conversion system. The fact that fresh manure pro-
duces much higher quantities of methane is also favorable from an environ-
mental standpoint for several reasons. First of all, the storage require-
ments may be reduced to some degree. Storage facilities presently employed
are less than ideal in many cases. Although the rate of oxygen demand for
animal manure is lower than that for secondary treated wastewater effluent,
the ultimate BOD is considerably higher by factors ranging from 5 to
167(219,220)f Immediate utilization and decomposition of manure in a
closed reactor would reduce the BOD problem but would not eliminate it be-
cause some liquid residue would still need to be treated. However, the
source would be centralized and it might be economically feasible to bio-
logically treat or apply the liquid waste stream to land (see the Section:
Impacts Associated with Growth and Procurement of Feedstock/Source Materials).
Anaerobic degradation produces a solid residue in which a large fraction of
the original weight is retained as a humus-like material ideal as a soil
amendment and a liquid by-product high in nitrogen(221)t
Small differences in crop yield and nutrient recoveries were noted by
Hensler et ai: with fresh, fermented, and anaerobically digested liquid
manure applied to corn fields. The diversion of animal manure to anaerobic
digestion plants may have advantages relative to two other aspects of manure
management, namely changes in soil chemistry and odor production as a result
of application of manure on land. In fact, one of the foremost problems in
land disposal of livestock wastes is odor emission(222,223). A wide variety
of compounds including volatile organic acids, mercaptans, sulfides, and
ammonia contribute to the problem and some or all could be controlled at a
central biomass conversion plant(224).
A study conducted by Hileman(225) demonstrated that changes in the
physical and chemical qualities of the soil resulted from subsurface.chicken
manure application.
• The soil pH increases as the equilibria between the
ammonia and soil pore water become established
271
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• The ammonium cation has a strong affinity for the
exchange sites on the soil clay/organic matter com-
plex, releasing Ca, Mg and K.
It was not stated whether these changes were persistent enough to
affect crop production. However, chicken manure conversion characteristics
are substantially different than those from cattle, as are inherent nutrient
content. Since chicken manure is not a major biomass source, it will not
be commented on further.
The anaerobic fermentation process alters the pH and converts ammonia
into bacterial protoplasm. Thus, the recycled residue is more stable than
the feedstock. If this material is then applied to land, the runoff pol-
lution potential with regard to BOD and nitrogen should be low, especially
when plowed-under. Nitrate pollution should also be reduced if the time
rate of release of nitrogen is lower in the digested material.
In many areas, it is necessary to observe a "resting" or nonapplication
period to avoid overloading the soil. The soil surface must be permitted
to drain periodically and the pore spaces permitted to fill with air.
This is important not only, for adequate root growth of crops but for the
use of the soil as disposal medium. Compaction impedes root growth, impairs
crop productivity, lowers the percolation capacity of the soil, and results
in more rapid soil saturation and water loss by runoff. The use of land as
a waste water disposal site is practical on a continuing basis only if the
application rate is less than the soil infiltration rate. Because the
volume of manure generated is often greater than the soil assimilative
capacity the tendency is to exceed appropriate levels. Production of
methane and recycling of the solid wastes offers the possibility of in-
creased soil loading rates with lower pollution potential.
Summary--
The expected environmental impacts from diversion of animal
manure to biomass conversion plants are essentially positive. The pol-
lutant runoff from manure left to lie in feedlots or applied improperly to
agricultural land has been identified as a serious concern, to the extent
that the U.S. EPA has promulgated effluent guidelines. The generation of
usable energy from this source apparently stabilizes the material, reduces
the possibility of adverse changes in soil chemistry or structure, mitigates
the malodors associated with on-site treatment, and should decrease the pro-
duction of flies and other pests since storage periods are shorter. The
anticipated benefits of using animal manure as a biomass source with regard
to environmental pollutants are indicated in Figure 63. A potential dis-
advantage is that the volume reduction due to digestion may increase the
concentrations of heavy metals, but no investigations to verify this could
be located.
Aquaculture
Intreduction--
In developing a discussion of aquaculture, two species have been
selected as representative of the class. Giant kelp has been proposed most
272
-------
[ Anaerobic Digested Residue .
l_ Odor Control [ BOD Removal and i Excess Nurient .
Solids Destruction Control
Untreated Highly
Waste Treated
Waste
Degree of Treatment
Figure 63. Treatment continuum and expected range of treatment using (218)
anaerobic digestion for gas production and recycling residue.
vigorously for marine systems, while water hyacinths have received consider-
able attention as a fresh water source for simultaneous sewage treatment and
energy production.
The oceans represent a vast potential resource above their ability to
produce high-quality protein for human consumption. Certain areas have
been proposed for transformation into oceanic biomass "farms" if defi-
ciencies in the nutrient levels are corrected and if precautions are taken
to protect the marine ecosystem. Giant kelp (Macrocystis) is one species of
plant proposed. Interactions may be classified as positive/synergistic,
neutral/non-existent, or negative/antagonistic. If the response of the
rest of the system are shown to be essentially negative, then some re-
thinking of the needs and goals of this biomass source seems in order.
Some of the same considerations apply to production of biomass from water
hyacinths in "closed" fresh water pond environments, albeit on a much re-
duced size and risk scale.
System Nutrient Requirements and Alterations
of the Physical/Chemical/Biological Environment—
The seeding, growth, and harvesting of kelp beds places demands
on assimilation and nutrient cycling mechanisms in the ocean. A feasi-
bility study of an ocean farming system in several variations has been _ _
conducted by Szetela, et al<226). They attempted to determine the nutrition
requirements for maximum growth under available light conditions. _ However,
some of the assumptions in the determination appear unreasonable in the
light of known aspects of phytoplankton physiology. In order to "Iculate
the availability of nutrients from dry weight measurements the assumptions
that there would be no competition for nutrients and that the kelp could
utilize 100 percent of the available nutrient were necessary. Both assump-
273
-------
tions seem to be gross simplifications of the complexities of nutrient
cycling in thermodynamically open systems. Although the density of phyto-
plankton in the ocean as a whole is very low, the areas suggested as good
places for mariculture are shallow (< 30 m) , well lit, and reasonably high
in naturally supplied nutrients. In other words, these areas not only are
attractive for kelp production, but also are conducive to the development
of other ecological communities. In fact, the western continental shelf
area is rated as moderate to high (25-50 mg/m3-yr) in terms of volumetric
productivity while the Gulf Coast is somewhat lower (10-25 mg/m3-yr) as
seen in Figure 64. The western continental shelf already supports a con-
siderable growth of Macrocystis, (Figure 65). This area however, appears
small relative to that expected for an ocean energy farm. No significant
beds occur off the southern Gulf coast.
The seeding and growth of kelp may alter productivity/nutrient pat-
terns in several ways:
• The kelp provides a substrate for the production of
epiphytic algae and bacteria. Nutrient estimates (in
terms of fertilization requirements) should be re-evaluated
considering this additional drain on the system.
• The addition of ammonia may stimulate growth of planktonic
algae because the assumption of non-competition seems un-
warranted by the results of research on algal physiology.
• The large increase in organic matter production may impact
on other ecosystem components because of the excretion of
external metabolites as dissolved organic matter (DOM)
(Figure 66). These metabolites may be directly used by
bacterial populations^^®) , multicellular algae'229) ^
and by some invertebrates.^30)
• The rain of organic detritus would likely increase in
intensity due to segments of stipes and blades breaking
off and sinking as a result of wave action. Depending on
ambient bottom conditions such as temperature, composition,
and currents, the sediment chemistry and benthic organisms
may be affected by the decomposition of this material.
• It has been suggested that 25 percent of the nutrient
requirements could be met by recycling the residue
from the digester (226) in a near-shore environment.
If this option proves attractive, the impact of this
fertilizer on other system components should be evalu-
ated. It may contain by-products toxic to certain
aquatic species or may chelate trace metals forming
soluble complexes which are harmful.
274
-------
170
IK)
NJ
-J
Ln
75
60
120 150
180
Figure 64. Global production of organic matter.
(226)
-------
Figure 65. Occurrence of kelps in quantities sufficient
for commercial harvesting.
Note: L = Laminaria, M = Macrocystis, E = Ecklonia.
The 20 C isotherms are for summer in the northern
and southern hemispheres, respectively. The
distribution of rockweeds (Fucales) is approxi-
mately the same as that of the kelps(227).
DOM
detritus
Figure 66. Distribution of organic matter produced by
marine seaweeds between different tropho-
dynamical flows. (DOM = Dissolved Organic
Matter).(228)
276
-------
• The introduction of kelp into new areas of ocean may
provide habitat for parasites and other undesirable
pests, but may also be suitable for desirable populations.
• The present areal productivity in marine systems is
insufficient to induce light-limitation in primary
productivity except over restricted areas (Figure 66).
The mats of blades are very dense and prevent
assimilative ratios much in excess of that observed
for a single layer because of shading(227). Studies
on the influence of shading effects on species diversity
were not located and may be negligible under most natural
marine conditions. However, the areal scope of the
harvesting program appears to justify some concern over
this point.
• Open ocean farms have been proposed, and may circumvent
many of the objections raised in the previous discussion,
directed mostly at coastal waters application. However
the technology of open ocean farming is embryotic in
development, and raises a host of new technological
problems. Environmental quantification of these should
probably await favorable technological economic develop-
ments .
Environmental Consequence of Harvesting Transport—
Water emissions for harvesting/transport of feedstock are believed to
be minimal on a routine basis, based on a comparison with transportation of
oil by tankers or barges. (231; ^e possibility of an accident does exist;
however, the probability of large spills of engine oil is low. Deck wash-
down and other maintenance would contribute minor amounts of pollutants.
Air emissions depend on the size and operations sequence chosen. The
emission factors for various chemical species are shown in Table 96. These
emissions are associated with internal combustion engines used to drive
harvesters and transporters. Compared to the emissions from commercial
fishing, shipping, and oil platforms, the incremental environmental costs
due to emissions from harvesters engaged in kelp production for biomass are
probably small.
Summary--
Ocean farming of kelp is an attractive concept for producing
low-Btu gas in that minimal impact on present resource use is expected.
Questions remain as to the availability of sufficient nutrients and sun-
light to provide the degree of growth necessary to make this biomass source
economically viable. Other issues pertaining to inter-species competition
and alterations in marine materials cycling have also been raised. Emis-
sions from harvesting and transport of the kelp appear minimal. Open ocean
farming, as opposed to near-shore production, may eliminate or at least
ameliorate these problems. In either case, the technology appears promising
enough to warrant further study.
277
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TABLE 96. AIRBORNE POLLUTANT EMISSION FACTORS - TRANSPORT/HARVESTING
Parameter
NO
X
ro
oo S02
CO
Particulates
Hydrocarbons
Emission
kg/Vessel-km
0.40
0.42
0.34
0.56
0.25
Factor
(lb/ Vessel-mi)
1.4
1.2
2.0
0.9
(a) Assuming 0.5 percent sulfur content.
-------
Marsh Harvesting
Physical/Chemical Impacts--
Marsh habitats are among the most productive and complex ecosystems
known. W) It is only within the past decade or so that the nutrient and
trophodynamic aspects of marshes have been elucidated. The physical/
chemical features of marshes which have been identified as possibly being
altered as a result of harvesting are the following:
• Wetland vegetation buffers the coast regions against
the erosive effects of wave, tidal, and wind action.
• The dense growth of plants commonly found in marshes
acts as a sedimentation barrier preventing excessive
siltation at the mouth of streams by creation of a
distributary network and provides mineral soil for
the marsh.
• The rate of water movement partially determines the
exchange of dissolved nutrients among the compart-
ments of the system.
• The soil temperature, pH, and radiation flux, are
affected by the degree of cover.
• The organic matter contained in the harvested plant
material may play a primary role in nutrient cycling.
The growth of marsh plants produces a network of root material and
rhizomes which act to prevent erosion in much the same manner as a cover
crop acts to prevent transport of soil particles from agricultural crop
land. Different plant types may offer differences in their ability to pre-
vent erosion. For example, a morphological study of growth by two marsh
dominants showed that Glyceria maxima produced short-lived, shallow rhizomes
while the Phragmites communis produced a persistent, deep seated rhi-
zomes' 233)^ jn gather case, the harvesting process would leave less
material above ground to resist erosion, but the root stock would still
provide a degree of protection. Some marsh soils are extremely fluid and
depend on the fibrous root material to prevent losses of soil material. In
these situations, harvesting may allow unfavorably high flows and result in
land loss. Willingham et al (234).suggested that disturbance of marsh vege-
tation in relation to gas pipelining activities would create severe adverse
impacts on the system.
The second, related point is that the development of a marsh at a
mouth of a stream often causes the flow to be diverted from the main channel.
Although most marshland is low-gradient, additional sedimentation is created
by the flow reduction in the distributary network. Mineral soil loading to
marsh soils is determined by the suspended load of the feeder stream and/or
the tides. Cutting of vegetation may have the effect of increasing the flow
rate and reducing th.e, amount of sediment deposited in the marsh proper.
In addition to controlling sedimentation, the flow rate influences the
exchange of dissolved substances between the marsh community and the water.
279
-------
When photosynthesis is proceeding at a maximum rate, plants which depend on
diffusion processes to supply a significant portion of nutrient needs can
become nutrient limited. The suggestion has been made that upper bound
values of productivity in intertidal marshes are observed which approximate
those estimated from consideration of CC>2 availability^ '. Thus, the ad-
vantages of a faster flowing system becomes obvious. For streamfed marshes
the differences may not be significant but the case is not clear for tidal
marshes. No specific studies were located which quantified the relation-
ship between flow and nutrient supply in greater detail. However, Odum(232)
stressed the importance of tidal action in maintaining a "subsidized"
fluctuating water level ecosystem. In general, the higher the tidal ampli-
tude the greater the production potential, provided that the ensuing cur-
rents are not too abrasive. The back and forth movement of water does the
work of removing wastes and transporting food and nutrients so that
organisms can maintain a sessile existence, which does not require expendi-
ture of much metabolic energy.
The investigation of Pomeroy(235) also demonstrated that the daytime
temperature of the sediments was influenced by insolation, shading by
Spartina alterniflora, the greenhouse effect, and evaporation of water from
the sediments. In winter the sediment temperature beneath dense strands of
Spartina was lower than in base areas. Surprisingly, in summer the sediment
temperature beneath dense growth was higher than that found for bare areas.
This was suggested to be the result of a combination of greenhouse effects
and reduced evaporation (see Figure 67).
It was also found that vegetal density influences the swings in pH
which normally accompany diurnal changes in photosynthesis (Figure 68).
However, the competing effects of increased pH due to high temperature
(lower CO™ solubility) and decreased pH (relative to an unshaded area) due
to reduced photosynthesis were not resolved. Hydrogen ion activity changes
in the bare areas were so marked that during the day the carbonate-bicar-
bonate equilibrium was shifted well to the right:
At pH 10, the concentration of carbonate ion, which is largely unavailable
as a carbon source for primary production, exceeds the concentration of bi-
carbonate by a factor of 2.5. The expected effects of harvesting would be
to exacerbate this condition.
The amount of radiation reaching the algal flora of the marsh sedi-
ments varied not only with the season and cloud cover but also with the
density of Spartina, the depth of water during the high tides, and the
turbidity of the water (related to flow regime)(235).
The harvesting of plant material from marsh systems would have much the
same impact as for harvesting of terrestrial agricultural residue, namely
the alteration of soil structure and ion availability for plants. It has
been suggested that the breakdown of organic material through decay pro-
cesses serves in a positive chemical way by contributing nutrients directly
and by adsorbing ions from the soil solution to be rendered available
280
-------
JAN. FEB. MAR. APRIL MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.
Figure 67. Seasonal variations in temperature in salt marshes near
Sapelo Island, Georgia.(235)
Note: Solid vertical bars: Observed daytime temperature
range of surface sediments under tall spartina.
Broken line: Water temperature at mouth of Duplin
River. Solid lines: Maximum and minimum air
temperature at Sapelo Island (monthly means for
1956-57).
pH •
Figure 68. Diurnal variations in pH of the surface of the sediments
of the salt marsh, south end of Sapelo Island.(235)
Note: Small open circles: Station in sparse, 0.3 meter
spartina well back in marsh. Large open circles:
Station in dense, 1-meter spartina on front of natural
levee. Black dots: Station on bare strand. All were
observed from first exposure by ebbing tide to covering
by flood tide.
281
-------
through ion exchange mechanisms'236)^ j£ this is true, then the leaching
of nutrient elements becomes more pronounced. Measurements of soil param-
eters indicate that a host of variables influence the mineral and nutrient
status of marsh soils (237), Among the most important are the degree of
saturation, and humus content and to a lesser extent plant type. A highly
consistent observation was that the more saturated the soil, the lower the
organic content. Similarly, nitrogen on a dry-weight basis was positively
correlated with humus content. The cation exchange capacity was also de-
pendent on humus content, being very high in peaty soils. Thus if harvest-
ing causes still lower humus levels, the productivity would further decline,
especially in the wetter environments.
A very critical environmental problem not mentioned previously is the
structural fragility of tidal marshes—only vehicles such as swamp buggies
equipped with high flotation tires can be used. It is not clear how
harvesting might be accomplished without destroying the vegetative mat at
the same time or over the course of several years. This factor alone, if
it cannot be resolved, may be enough to rule this out as a biomass source.
This compaction would essentially destroy the habitat, substantially
reducing its value as either a natural or exploited resource. Consequently,
successful development of harvesting equipment would appear essential before
serious consideration of other environmental factors or, certainly, serious
project development be undertaken.
Two factors mitigate the possible adverse impacts mentioned. The first
is that seasonal influences already are imposed on the system. An annual
die-back occurs in most growing areas during the fall and winter so that a
single harvesting effort at this time could maximize the use of wetlands
productivity for biomass fuel while minimizing the detrimental aspects.
Storage of harvested material could become a substantial incurred cost
under this alternative.
The second factor is that it may be possible to return the digested
residue to the land. The ramifications of such an action should be con-
sidered in greater detail.
Expected Ecological Consequences--
As mentioned previously, marsh/wetland habitats have been identified
as being ecologically complex. Indeed, the major impetus to their preser-
vation has been their value in providing unique environmental niches. These
areas have been documented numerous times as being critically important
resources for the protection and maintenance of large numbers of different
animal populations, including offshore fisheries.
No studies on the ecological aspects of marsh harvesting were located.
However, a study of coastal ecosystems, probably spanning the range of
those likely to be encountered in a harvesting effort, identified several
hundred species in more than 20 phyla. Because of the narrow range of
growth requirements of marsh plants, a high degree of sensitivity to modi-
282
-------
fications^of their habitat was noted<234). Other ecological cha fchat
might be induced through a harvesting program include removal of forage and
cover for small animals, alterations in species composition due to changes
in the physical/chemical environs, and differences in food webs. More de-
tailed evaluations of actual sites are needed; each area is likely to be
impacted differently and generalizations beyond those briefly stated above
would be unwarranted.
Summary--
The marsh community represents an extremely complex web of physical,
chemical, and ecological interactions which is just beginning to be under-
stood. What is known seems to justify the statement that marshes provide
important benefits for receiving bodies of water and protect valuable
ecological niches. Moreover, marshes are fragile and extreme caution is
warranted in utilizing these biomass sources.
Municipal Solid Waste (MSW)
Intreduction--
The present technology for dealing with municipal solid waste
emphasizes disposal mostly by landfilling rather than recycling. In
some applications, volume reduction is achieved through shredding and incin-
eration. In addition, ferrous metals recovery is practiced where economi-
cally feasible. Several alternatives aimed at the conversion of this waste
to usable energy have been suggested or are being examined on varying scales.
These may be classified as preparation of solid waste as a supplemental or
primary fuel for direct combustion; pyrolyzation to produce gas, oil, and
char; and anaerobic fermentation to yield methane and solid by-products.
The supplemental fuel and pyrolysis options are best discussed in the con-
text of environmental impacts of conversion processes (see - Impacts
Associated with Biomass Conversion to Fuel/Energy). The third alternative
is similar in some ways to another minor disposal method for solid waste
which has enjoyed a recent upsurge of interest, that is, the practice of
composting. This is important from an environmental viewpoint, because it
represents an alternative use for a biomass source, which may have positive
environmental significance.
Composting is a practice which stabilizes a waste material by the
action of thermophilic aerobic bacteria; the principal gaseous products are
C02 and water vapor. While the degradation processes and decomposition
gases are somewhat different from anaerobic fermentation, the solid residue
is expected to exhibit similarities in most physical and some of the
chemical characteristics. The results and implications of field experi-
ments carried out in this area as related to land application of anaerobic
fermentation residues will be compared with those now experienced with
landfilling, the most widely used and least costly method of disposal in
the U.S. No attempt will be made to comprehensively treat the environmental
implications of disposal/recycling of municipal solid waste. Several excel-
lent reviews of the state-of-the-art of the relevant technology and
characterization methods are available in the open literature.
283
-------
Characteristics of Raw and Composted Municipal Solid Waste--
Domestic refuse is composed or organic food wastes; paper and paper
products; wood; plastics, leather, and rubber materials; rags and textile
products; glass: metallics; inert stone, clay, and earthen products; and
yard wastes(238) ^
The type of refuse and percentage by volume and weight are listed in
Table 97. It can be seen that four of the eight categories would contribute
substantially to the BOD/COD and nitrogen content of leachate from a land-
filling operation. Furthermore, the wide range of degradation rates would
prevent rapid stabilization. Depending on pH, hydraulic conditions and
oxidation/reduction potential, metal species may also be mobilized to vary-
ing degrees. Table 98 lends credence to this interpretation. By compari-
son, a solid residue produced from municipal solid waste by composting con-
tained lower values of N and P and was high in organic content. The BOD of
leachate from treated plots was not determined in this study(240). it is
suggested that the leachate from anaerobically digested solid waste would
more closely resemble the "old" than the "new" leachate characteristics
(Table 98).
Incorporation of composted material over a two-year period effected a
statistically significant change in several physical and chemical soil
parameters (Table 99). Overall, the land application of carefully prepared,
composted solid waste seems to be beneficial, although the zinc increases
may be indicative of other heavy metal behavior.
Summary--
It appears the utilization of urban waste as fuel is a promising
alternative environmentally in that:
• The feedstock is already centralized and a reason-
ably efficient collection system exists,
• A reduction in volume by a factor of two to ten
is possible and desirable,
• Ferrous and non-ferrous metals and glass and
other ceramics may be recoverable,
• The solid residue from some processes may be
useful as a soil amendment to increase tilth and
water holding capacity, although supplements of
fertilizers may still be required for optimal
crop growth,
• The BOD content of the liquid waste stream from
biological processes can be reduced by conventional
treatment.
The drawbacks are that the question of heavy metal concentration in-
creases (in regard to digester operation and soil incorporation) has not
been fully determined and that the economics of transportation of the solid
by-product have not been worked out in detail. The former may not be
significant if the pH is maintained at or slightly above neutral.
284
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TABLE 97. CHARACTERISTICS AND DISTRIBUTION OF
TYPICAL MUNICIPAL SOLID WASTE(238)
Category of Refuse
Paper and Paper Products
Wood and Wood Products
Plastic, Leather, and Rubber
Products
Rags and Textile Products
Glass
Metallics
Stones, Sand, and other incrts
Garbage ( organ ics)
Percent by Weight
32.98
0.38
6.84
6.3h
16.06
10.74
0.26
26.38
Percent by Volume
62.61
0.15
9.06
5.10
5.31
9.12
0.07
8.58
TABLE 98. CHARACTERISTICS OF LEACHATE
AND WASTEWATER<239)
Constituent'1'
TSS
TDS
Conductivity
PH
COD
BOD.
TOC
Total P
Total N
Chloride
Calcium
Magnesium
Iron
Manganese
Zinc
Copper
I. each
Fresh
327
12.620
9,200
5.2
22.650
14,950
6,500
7.35
989
742
2,136
277
500
49
45
0.5
ale
Old
266
1.144
1,400
7.3
81.1
. —
70.0
4.96
7.51
197.4
254
81
1.5
—
0.16
0.1
Waste-
wntcr
200
—
700
8.0
500
200
200
10
40
50
50
30
0.1
0.1
—
—
Kalio
1.6
—
13
—
45
75
32
0.7
25
15
43
9
5.000
490
—
—
^Source: Characteristics of Percolate of Solid unit Haz-
ardous Waste Deposits.'
*A1I constituents reported as mg/1 except Conductivity,
which is reported as micromhos/cm. and pH, which is the
logarithm of the reciprocal or the hydrogen activity in
moles per liter.
285
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TABLE 99. EFFECT OF COMPOST AND NITROGEN ADDITION ON PHYSICAL AND CHEMICAL
CHARACTERISTICS OF SOIL AT MUSCLE SHOALS (24°)
2-year
total compost
application
metric tcns/ha
0
K> 0
00 U
ON
46
46
82
164
327
164
Annual
N rate
kg/ha
0
180
0
180
0
0
0
180
Moisture
holding capacity Soil
at 1/3 bar moisture
»
11.1 12.
11.
12.
11.
12.
13.0 13.
15.3 14.
13.
4
0
5
6
9
3
8
5
Bulk
density*
1.37 a
1.37 a
1.32 ab
1.30 be
1.27 cd
1.22 e
1.12 f
1.25 de
Unconf ined
compression
strength
kg /cm2
2.9 a
2.3 b
2.9 a
2.6 ab
2.6 ab
2.4 b
1.5 d
1.9 c
Organic
matter
%
1.58
1.47
1.81
1.99
1.96
2.66
4.22
2.58
Extractable
nutrients
pH
5.4
5.1
6.2
6.0
6.2
6.6
6.8
6.4
K
193
155
197
146
230
378
332
215
Ca
• kg /ha
1,653
1,472
2,341
2,285
2,610
3,349
3,920
3,181
Mg
181
156
199
193
206
224
234
189
Zn
7
6
29
35
38
91
490
86
*Values having the same letter in each column are not significantly different at the 95Z level.
-------
IMPACTS ASSOCIATED WITH BIOMASS
CONVERSION TO FUEL/ENERGY
The transformation of biomass feedstock to fuel/energy can be accomp-
lished in a number of ways, some direct and some indirect. The concomit-
ant production of solid, liquid, and gaseous waste streams is of concern
although a given process may not produce waste streams in all forms. It is
the purpose of this section to review the various generic classes of con-
version methodologies and to describe the residuals in a qualitative and
semi-quantitative manner. In some cases, information of interest is lack-
ing or incomplete. Such gaps will be bridged by drawing inferences from
available data on other technologies where feasible, or identified as areas
where research needs are indicated.
Direct Conversion
Energy conversion in the form of process heat or power production can
be accomplished by the biomass sources addressed in the preceding section
of this chapter. However, the difficulties in maintaining a stable com-
bustion zone for high moisture sources such as animal waste or kelp and/or
the cost of drying these to a suitable level will likely limit the appli-
cation of direct conversion to relatively "dry" sources such as municipal
solid waste (MSW) and air-dried wood/agricultural crop residue.
Emission factors for direct conversion are available for the burning
of an admixture of refuse and coal, the burning of refuse alone, and for
combustion of wood residue and bagasse. Table 100 lists the gaseous and
particulate emission factors for these four feedstocks and includes tra-
ditional coal combustion for comparison. It can be seen that biomass
sources appear favorable in terms of SOX and N0x emissions because of the
very low levels of these pollutants in the fuels. Particulate emission
levels are higher for the most part, but it is suspected that these would
be reduced if effort were expended to produce energy from these sources on
a greater scale. Carbon monoxide and hydrocarbon emission factors for wood
residues are probably higher because of the high lignin to cellulose ratio,
the higher moisture content when burned and the lower resultant flame
temperature. In addition, the particulates, especially from MSW, will con-
tain inorganic materials, including detectable amounts of free mercury and
beryllium, lead, zinc, cadmium, nickel and vanadium (see Tables 101 and 102)
These heavy metals and others, such as selenium, are potential health
hazards, whose overall effect at low exposure levels is poorly known at
present. Lead particulate inhalation may cause chronic intoxications;
soluble lead components are cumulative poisons. Particulate beryllium
produces pulmonary fibrosis. Cadmium oxide dust or fumes may cause pul-
monary edema or hemorrhage. Zinc inhalation may lead to "metal fume fever"
and damage to the respiratory tract.
287
-------
TABLE 100. PARTICULATE AND GASEOUS EMISSION FACTORS FOR DIRECT
COMBUSTION OF BIOMASS COMPARED WITH COAL COMBUSTION
Ni
00
00
Source
Parameter
Particulates
SO
X
NO
X
CO
HC
(a)
MSW
0.04-0.8
0.1
0.2
0.04
MSW .
+ Coal(b)
>0.04
0.4
0.3
0.04
Kg/106 Btu
Wood
Residue^
0.6
0.06
0.4
1.2
1.4
(d)
Bagasse
1.1
0
0.1
0.1
0.1
Coal(e)
0.04
0.5
0.3
.04
.02
(a) Hughes, et al.,(24l); Surprenant,(242)„ 10 kg particulates/ton refuse;
6000 Btu/lb heating value; second value refers to untreated refuse and
first value is 95% collection efficiency.
(b) 11,100 Btu/lb at 12 percent refuse content (wt/wt basis).
(c) Surprenant,(242). Assumes 6000 Btu/lb heating value.
(d) Surprenant, (242). Assumes 4600 Btu/lb heating value.
(e) Surprenant, (242). Assumes bituminous coal, stoker feed, 3% sulfur
content, 15% ash, 12,000 Btu/lb heating value.
-------
TABLE 101. CONCENTRATION OF SOME TRACE MATERIALS
IN INCINERATOR FLY ASH/241-)
Species
Be
Hg
Pb
Zn
Study 1
(amount)
Small or trace
Small or trace
Small or trace
Small or trace
Study 2
(percent)
0.001-0.01
0.01-0.1
1-10
TABLE 102. EMISSION FACTORS FOR MUNICIPAL INCINERATORS
Element
Be
Cd
Mn
Hg
Ni
V
Pb
Sample Conditions
Uncontrolled
ESP (a)
Uncontrolled
Wet scrubbe.d
Uncontrolled
ESP
Uncontrolled
Wet Scrubbed
Uncontrolled
Uncontrolled
_., Emission Factor
10~ kg/MT refuse burned
0.015
0.015
1.55
0.4
15.0
3.5
0.5
1.5
0.5
16.0
(a) Electrostatic precipitator.
289
-------
Fluidized-bed incineration will probably produce no more airborne
particulates than will normal incineration if both facilities are properly
managed^^ ^. In fact, the Combustion Power Company process in which com-
bustion gases are fed to a turbine to generate electricity requires extreme
cleanliness. Particles and metal vapors can cause erosion and other prob-
lems with turbine blades; thus, the process includes three stages of cyclone
separation for particle removal.
Fluidized-bed processes can usually be adjusted so as to absorb sulfur
dioxide into the bed. The low combustion temperatures in the bed are ex-
pected to reduce nitrogen oxide formation. This better thermal contact
should also reduce the quantities of unburned organic material, including
chlorinated and polynuclear hydrocarbons.
Combustion (incineration) processes in which refuse makes up a
small fraction of the total material fired will operate under the same
general conditions and produce the same general environmental effects as
coal-fired boilers.
Other volatile materials may escape combustion at low excess air values.
These may cause problems with eye irritation and odor but are not funda-
mentally hazardous. Formic, acetic, palmitic, stearic, and oleic acids;
methyl and ethyl acetate and ethyl stearate; formaldehyde and acetaldehyde,
hydrocarbons, and phenols have been found in incinerator stack gases.
Hydrogen chloride can be an undesirable product when chlorinated
hydrocarbons (such as those contained in PVC plastic films) are burned.
Proper incineration practice, including after-burning with additional fuel,
should reduce all of these to unnoticeable or negligible levels, although
this does not avoid the severe corrosion problems. Emissions of metals and
organics from feedstocks other than MSW are not well characterized.
Incineration may also produce liquid wastes, although the necessity
for water quenching may not exist for all plants. It has been estimated
that 5 to 50 liters (1 to 10 gallons) of quench water will be discharged
per ton of refuse treated(241)m Water required for other operations may
also be discharged. Cooling system and boiler blowdown/system cleaning
water is discharged intermittently. Ash handling may create a wastewater
stream other than that generated with the quench water.
Depending on the contact time and ambient conditions, the quench/ash
handling water may become highly caustic due to ash composition and contain
suspended and dissolved solids. This process stream will require neu-
tralization and sedimentation. Most heavy metals entrained in the bottom
ash should not be leached at alkaline pH values if contact times are short.
290
-------
BOD and COD may be high. Although most putrescible material will have
been destroyed, not all of the organic material, especially wood fiber is
burned Burning under conditions of excess air should prevent formation of
reduced metal salts. Wash water and other system water needs will contri-
bute organics such as oil and grease, detergents, algae and corrosion in-
hibitors, and so forth. The: incorporation of pre-treatment facilities
providing primary or secondary treatment internal to the conversion plant
may need to be considered.
Solid residuals amount to between 180 and 225 kg per ton of MSW, most
of which will likely find its way into a landfill. The composition of
this material is principally silicon, aluminum, calcium, and iron oxides but
may vary in the proportion of each depending on the characteristics of a
particular waste. Leachates from landfills may percolate to ground waters,
streams, and so forth. These leachates will have high hardness, but the
composition and quantity are too dependent upon local conditions for any
judgement of their ultimate environmental effect to be made without exten-
sive field work and analysis. The environmental impact analysis for an in-
dividual location must define the potential effects. Incineration should
mitigate common landfill problems such as high BOD and nitrates in leachate,
vector production, and disturbance of large tracts of land.
Solid residues from biomass sources other than MSW may also produce
highly mineralized leachates. The ash composition resulting from combustion
of wood/bark, animal waste, and agricultural residue is shown in Table 103.
The analyses indicate that other ash compositions are similar to those
generated by MSW so the above statements concerning the characteristics
and contamination potential from the leachate should be equally valid. It
has been suggested that the ash be returned to the soil as a fertilizer be-
cause it contains significant mineral and nutrient resources; however, the
question of heavy metal levels and behavior remains unanswered.
Table 104 lists the levels of several trace elements in MSW; others
are undoubtedly present.
Several of the feedstocks may require drying of the as-received sub-
staDceon an occasional or regular basis. (As-received refuse may have from
20 to 90 percent water; 30-35 percent is very common.) This drying and the
combustion of the material will release moisture to the environs of the
plant. Drying can produce noxious odors in the drying gas stream. Most of
this can be removed by passing the exit gas through a high-temperature
flame, 700 to 820 C (1300-1500 F). This requirement for an extra combustion
step and necessity for extra fuel could reduce the economic attractiveness
of the process that requires it. Use of exit air for primary or secondary
incinerator air source may partially relieve this constraint.
Handling, size reduction, and classification activities create dusts,
especially if the solid waste has been dried. The operator and designer
must take potential dusting into account so as to minimize its effects.
Vents or hoods over the equipment can lead the dusty air to a separate
filter system or to the main stack. Total particulate discharge will not
be measurably affected, and this impact can be controlled in the context
of total particulate discharge.
291
-------
TABLE 103. ASH ANALYSIS OF BIOMASS FEEDSTOCKS
N3
VD
NJ
Percent by Weight
Species
Si02
Fe2°3
Ti02
A12°3
Mn304
CaO
HgO
Na20
K20
so3
01
P2°5
Southern
Pine(a>
19.0
1.0
*
21.0
*
27.0
5.0
3.0
9.0
6.0
*
4.0
Pine
39.0
3.0
0.2
14.0
Tr.
25.5
6.5
1.3
5.0
0.3
Tr.
*
Oak
11.1
3.3
0.1
0.1
Tr.
64.5
1.2
8.9
0.2
2.0
Tr.
*
Spruce
BarkO)
32.0
6.4
0.8
11.0
1.5
25.3
4.1
8.0
2.4
2.1
Tr.
*
Corn
S talks (b'
*
0.3
*
ft
0.1
2.1
1.8
*
8.2
2.0
1.4
3.2
Cattle .
fc)
Manure
*e
5.5
*
*
*
6.8
3.2
13.0
11.6
4.0
*
8.8
MSW
50.0
7.9
0.9
11.4
A
12.2
1.3
8.8
1.6
1.5
*
1.4
(a) Abstracted from Table 5.
(b) Gerloff, G. C. unpublished data.
(c) Referred to 3.1 percent ash content and Table 11.
(d) Surprenant, (242).
(e) Asterisk indicates not reported.
-------
TABLE 104. TRACE ELEMENTS IN REFUSE ASH(242)
Species Mean Weight Percent
Sn02 0.05
CuO 0.32
ZnO 0.41
PbO 0.19
In any discussion of environmental effects, it should be noted that
most solid waste-disposal processes will require collection, with the
attendant noise and environmental effects of large truck transportation.
It the collection station, the noise of transfer operations and the odors
com ng from untreated material in storage will create loca l«ed prob ems
Size reduction, which is essential for some processes and desirable for any
materials recovery operation, is very noisy. Relatively small shredders
Pyro lysis
than those already existing.
Preliminary studies on the air emissions ™
pyrolytic oil produced by the Garrett proce s tends ^ ^ ^
reasoning <243>. In converting soll^ste to q cieangr than the
primary objectives is <=o produce a subBtance^t collected on emissions
original solid waste ^^J^n produced when the pyrolytic oil is
of sulfur dioxide and oxides of nitrogen p ^^ directly
burned. Concentrations of sulfur dioxide xn the flu 8 f^ 12Q_^
proportional to the sulfur content of the fueK y ^^ g ^ (having
293
-------
oxide production was somewhat higher for the pyrolytic oil than No. 6 oil.
Blends of No. 6 fuel oil and the pyrolytic oil produced an average of
420 ppm of oxides of nitrogen. Additional experimentation with various
firing methods is needed to determine the impact this fuel will have on
emissions of oxides of nitrogen. In order to assess fully the environ-
mental impact of this fuel, the San Diego Gas and Electric Company has
proposed a 21-month test program incorporating both laboratory and boiler
tests. Flue gas analysis will include particulates, oxides of nitrogen,
oxides of sulfur, hydrochloric acid, carbon monoxide, and visible emis-
sions ^243)^
The direct emissions from pyrolysis production processes should be
small. The product gases from each will be contained and can be scrubbed
to remove acid gases (I^S, CC^) and particulates. The entire gas output
of the Torrax and Union Carbide processes will be so treated. The Bailie
process produces separate streams of product and combustion gas. The latter
will be quite small in volume when compared to that from direct incinera-
tion processes. Only 10 to 15 percent of the combustibles will be directly
burned. The burning, in a fluidized-bed, should require little excess air,
produce only small quantities of nitrogen oxides, and have low unburned
hydrocarbon loads.
Ash loads from several of these processes will approximate those from
direct incineration. The fluidized-bed of the Bailie process will produce
about 50 percent more ash than the other processes. Thus, the landfill
requirement is larger and leachate loads may be slightly higher for it than
from the other processes.
A flow schematic described previously (Figure 23) on the Garrett pro-
cess makes quantitative and qualitative estimation of residual streams
possible. However, this analysis should be considered as representing only
a single feedstock and set of operating conditions. The materials balance
for a 1000 ton/day plant is shown in Table 105. Residuals generated in
water or gas treatment are not included nor is the additional water input
to the spray separator column.
Analyses of the gaseous fraction of pyrolysis products indicate high
concentrations of hydrocarbons (^ 20 volume percent) and carbon monoxide
(42 volume percent). However, the secondary combustion of the pyrolysis gas
for process heat will consume some of the hydrocarbons and other combusti-
bles. The gas burned in this step has a low heating value so that flame
temperatures are lower than in incineration. Estimated air emissions for
pyrolysis and incineration are compared to those from coal and oil in
Table 106.
The results in Columns 1 and 2 in Table 106 for municipal waste treat-
ment are not, of course, strictly comparable since different wastes were
used and could have varied quite widely in composition. The higher sulfur
dioxide level in the pyrolysis stack gas, as compared to the incineration
stack gas, is the result of two possible situations: (a) a higher sulfur
content in the waste or (b) the smaller stack gas volume. In any event, it
is obvious that municipal refuse contains much less sulfur than that in
294
-------
TABLE 105. MATERIALS BALANCE - GARRETT PROCESS
-------
No. 6 fuel oil or coal. The low nitrogen oxides in the pyrolysis stack
gas reflect the generally lower temperatures compared to those of com-
bustion processes. The unburned hydrocarbons are not significantly dif-
ferent, but the total emission from a pyrolysis system would be lower than
from the others because the volume of flue gas produced per ton of fuel is
lower. The lower chloride content in the pyrolysis gas probably reflects
a major difference in the waste composition, e.g., content of PVC plastic.
The particulate concentration from pyrolysis and incineration do not differ
significantly, but the total mass emission from a pyrolysis system would
be lower, again because of a smaller flue gas volume. Whether particulate,
hydrocarbon, and nitrogen oxide emission levels in actual operation are
lower for pyrolysis plants than for incineration plants is probably more
dependent upon individual differences in design and methods of operation
than upon process fundamentals(244)^
Pyrolysis processes such as Landgard, that produce steam as a prin-
cipal product, will have air emissions similar to those of the combustion
systems. Exit gas flows lie between those found in normal incineration
and those in combined burning with coal.
As noted earlier, the lower quantity of air required for pyrolysis/
gasification as compared to incineration should result in less entrainment
of particulate materials in the off-gases from the reactor. Since the off-
gas will be further reacted in a combustion process, any combustible particu-
lates, e.g., char or tar mists, will be re-exposed to oxidation conditions
during the combustion process. Other particulates like sand or grit can
generally be removed from the off-gas by a variety of means, and it is
likely that this will be done prior to the combustion of the gas.
One form of particulates is, however, of concern. It is known that
certain metals can be produced as a fine particle fume or smoke in a thermal
process. Among these are lead and zinc which are known to be toxic.
Another potential problem that may be encountered in pyrolysis/gasification
is related to the fact that certain metals can form gaseous and toxic
carbonyls by reaction with carbon monoxide, one of the gaseous products of
the process. There is no indication that such measurements or even total
metal emissions determinations have been carried out(245)<
During the pyrolysis step, water and organic compounds are formed and
distilled from the biomass material. While the resulting mix is somewhat
variable depending on the nature of the feed materials, the water fraction
has been shown to contain a variety of aldehydes, ketones, alcohols, phenol,
acids, etc.(-247'). It was stipulated that, although the BOD of such a
waste stream is high, the quantity of water is low relative to typical
municipal waste loads(246). Treatability is not expected to be a problem
if a conventional secondary sewage treatment plant (STP) is incorporated
into the design or is available nearby. System wash water and water used
in separators are also likely to contain significant amounts of water
soluble organics and should be treated. The BOD of these mixtures is
estimated to be in the range of 500-3000 mg/1. Generally, the BOD values
for municipal secondary influent are in the range of 150-250 mg/1(220)m
Thus, the imposition of the untreated waste load from a large pyrolysis
296
-------
plant on a municipal STP represents a high organic load, especially if dis-
charged as a slug flow. The small volume should be a mitigating factor as
dilution ratios will be high.
Most of the pyrolysis processes produce a solid char or ash which
contains the major portion of the metal content of the original feedstock
together with small amounts of nitrogen, sulfur, and chlorine. A portion
of the char may be used for heat (as is the case for the Garrett process).
The char material thus produced has been assigned little market values and,
unless a technological breakthrough occurs, is likely to be landfilled. A
small fraction of the inert solids produced by other pyrolysis schemes,
such as the Battelle or Torrax processes, can be utilized as a construction
aggregate; however, the main portion will probably be landfilled. Relative
to disposal of these materials, all of the pyrolysis technologies repre-
sent a reduction in volume and, at least, partial stabilization of the
solids. Some BOD/COD will remain; however, it should be well below
that of raw feed and the metals. Since it is concentrated into a
smaller volume, the metal content of the original material will be
amplified. Whether the pyrolysis conditions enhance the mobility of
metals has not been experimentally determined.
Anaerobic Digestion
The conversion of biomass to methane and carbon dioxide by the
action of obligate anaerobic bacteria produces, in addition to the pro-
duct gas, an aqueous slurry which is generally dewatered. Dewatering
may be passive as in sedimentation/flotation or active as with vacuum
or pressure filtration. The degree of dewatering will influence the
problems associated with the disposal/recycling of the solid cake.
Other operations involved are the following.
• Size reduction - shredding
• Removal of metals and chlorinated hydrocarbon plastics
• Addition of nutrient material (necessary if MSW is used
as feedstock)
• Gas scrubbing - removal of C02 and H S.
Several processes have been conceptualized; however, the Dynatech
system and the Biogas process have proceeded farthest towards com-
mercialization. The material balance for a nominal plant size of 1450
metric tons/day (1600 ton/day) using the Biogas process as shown in
Figure 69. The plant is expected to gasify 39 percent of the solids and
liquefy an additional 1 percent. Thirty-one percent are disposed/re-
cycled as sludge and the remaining 29 percent are recoverable secondary
products. It has been estimated that the production of each cubic meter
of methane (at standard conditions) from MSW removes 2.9 kg of COD/BOD
relative to the original raw waste(249)„
The atmospheric emissions are expected to be minimal with the pos-
sible exception of H S contained in the product gas and possibly the
refuse-sludge blending system, if used. An acid-gas scrubber will
probably be used to upgrade raw product gas to pipeline quality.
297
-------
995 Tons/day
(CONTINUOUS)
56.9% VS
CELLULOSICS — 454.8
GARBAGE 138.3
METALLICS 135.8
GLASS — 165.3
PLASTICS 20.8
RUBBER,
LEATHER 10.6
TEXTILES 18.7
DIRT, ROCKS,
ASH 30.7
OTHER 19.9
994.9
PRIMARY SLUDGE
147.7 (58.5% VS)
ACTIVATED SLUDGE
49.2 (63.0% VS)
00
AIR FOR COMBUSTION
530.0
CAUSTIC
0.6
(5.11
SOUR GASES
297.0
106 SCF/day)
t
EXCESS PIPELINE GAS
125.3
(6 x 104 SCF/day)
CONSUMER
BIOGAS™ PROCESS
INTERNAL OPERATIONS
WEIGHING & TIPPING
2-STAGE COARSE SHREDDING
DRY AND WET SEPARATIONS
FIBERIZING
STORAGE
BLENDING
BIOGASIFICATION
GAS SWEETENING
GAS DEHYDRATION
SULFUR RECOVERY (?)
GAS COMPRESSION
_^ FURTHER
TREATMENT
LIQUID STREAM
(2.9 MGD)
VOLATILE ACIDS - 2.4
OTHER SOLUBLES - 10.6
COMBUSTION
GASES - 567.0
347.9 STABILIZED
SOLIDS (48.2% VS)
REJECTS FROM MAGNETIC
SEPARATION
REJECTS FROM AIR-
GRAVITY SEPARATION
T
TO MARKET
CELLULOSICS - 4.6
GARBAGE 2.2
METALLICS --- 43.0
GLASS 162.3
OTHER 54.0
226.1
GRITS
kMATERIALS
"RECOVERY
TO LAND APPLICATION
(ALL FIGURES ARE IN TONS/DAY UNLESS INDICATED OTHERWISE)
B-34-495
Figure 69. Mass balance summary for a 1600 ton/day biogas plant«
(Reference: Ghosh and Klass, 248)
-------
Ancillary operations may generate noise and dust, but these ought
to be mainly local in impact and can be minimized.
The stripping column in this case will produce a gas stream rich in
CO and also containing essentially all the H S and related compounds
(odorants) produced by the digestor. For smaller systems, it is likely
this stream will be emitted (after burning) to the atmosphere. For very large
systems, it may be possible to install a Glaus plant for recovery of
sulfur content as elemental sulfur or sulfuric acid. The most likely
situation, however, is that the H2S will be controlled by oxidation to
SO 2 and reaction with lime. This scheme will produce a relatively small
sludge stream for disposal.
More difficult to handle may be the air quality problems encountered
during off-specification operations. These will probably be caused by
poisoning of the bacteria either by metals or acid. The "sour" partially
treated, reactor contents are vile-smelling, due to low-molecular weight,
volatile acids such as butyric and propionic. Its disposal by landfill
(the most likely alternative) would be perceived by people for several
miles downwind from a large plant and/or a disposal site, and would un-
doubtedly draw unfavorable reactions.
Water quality may be a problem for several reasons. The BOD of the
liquid stream is approximately 500 mg/1 and suspended solids may be
greater than 700 mg/1. Of itself this presents little difficulty since
standard BOD removals in secondary treatment are on the order of 80 per-
cent and SS removals approximately 90 percent. However, the maintenance
of slightly acidic pH conditions and long detention times may be conducive
to leaching of metals from the solids, if insufficient sulfide is present.
The actual metals content of the digestor supernatant is unknown.
Studies on the metal content of the solid residue could not be
located. In terms of total metal content, the values from a composting
process will give order-of-magnitude indications of concentrations (see
Table 107). Comparative studies of metal content in effluents from
digestion processes currently under development need to be made.
Solid residues may be landfilled with the attendant BOD/COD, ammonia,
solids, and metals control requirements. A second alternative is land-
spreading as a soil amendment if metals are immobilized.
The fact that anaerobic digestion is a microbiological process
does partially mitigate concern about heavy metal toxicity. As shown in
Table 108, prepared for mesophilic anaerobic digestion only, unsuccess-
ful operation would likely occur if the metal content in solution ex-
ceed greatly the moderately inhibitory values. However, the toxicity
of continuous land application over a long term with commensurate heavy
metal build-up remains an unanswered question.
Table 109 compares the physical and chemical characteristics of the
anaerobic digestor substrates. It can be seen that these are comple-
mentary in nature and that sewage sludge might be added for nutrients.
The effluent characteristics are listed in Table 110 as a function of
299
-------
TABLE 107. ELEMENTAL CONTENT OF 42 DAY-OLD
COMPOST AT JOHNSON CITY (249)
Percent dry weight
(average)
Element
Carbon
Nltrogon
Potassium
Sodium
Calcium
Phosphorus
Marjneaium
Iron
Aluminum
Copper
Manganeae
Nickel
/inc
Uoron
Mercury
Lead
Containing sludge
<3»-5%)
33.07
0.94
0.28
0.42
1.41
0.28
1.56
1.07
1.19
< 0.05
< 0.05
< 0.01
< 0.005
< 0.0005
not detected
not detected
Without sludge
32.89
0.91
0.33
0.41
1.91
0.22
1.92
1.10
1.15
< 0.03
< 0.05
< 0.01
< 0.005
< 0.0005
not detected
not detected
Range
(all samples)
26.23 - 37.53
0.85 - 1.07
0.25 - 0.40
0.36 - 0.51
0.75 - 3.11
0.20 - 0.34
0.83 - 2.52
0.55 - 1.68
0.32 - 2.67
TABLE 108. STIMULATORY AND INHIBITORY CONCENTRATIONS OF METALS
AND OPERATING PARAMETERS FOR MESOPHILIC ANAEROBIC
DIGESTOR PROCESSES USED IN SEWAGE SLUDGE TREATMENT
Parameter
Sodium, ppm
Potassium
Calcium
Magnesium
Ammonia Nitrogen
Sulfide
Temperature, C
pH
Volatile Acids
Alkalinity
Chromium (VI)
Copper
Nickel
Zinc
Stimulatory
100-200
200-400
100-200
75-150
50-200
30-35
6.8-7.4
50-5000
2000-3000
< 50
5-10
< 40
10
Moderately Strongly
Inhibitory Inhibitory
3500-5500 8000
2500-4500 12,000
2500-4500 8000
1000-1500 3000
1500-3000 3000
100-160 200
25 and 40
6.2 and 7.8
20,000
1000 and 5000
150-1000
2000-1000
350-1000
200-2000
Reference
Source
250
250
250
250
250
250
251
251
251
251
252
252
252
252
300
-------
TABLE 109. PHYSICAL AND CHEMICAL CHARACTERISTICS OF REFUSE
AND SEWAGE SLUDGE SUBSTRATES (253)
Parameter
Total Solids, wt %
Volatile Solids, wt %
Total Carbon, wt %
Total Nitrogen, wt %
Ammonia Nitrogen, wt %
Hydrogen, wt %
Ash, wt %
PH
Alkalinity, mg/i CaCO3
Heat Content (Dry Basis),
Btu/lb
Refuse
93.2-97.2
76. 1-84. 9
39.8-45.2
0.1-0.8
0.02-0.08
5. 58-5.67
14.6-15.2
7.20-7.30
173.7-202.0
6840-8120
Sewage Sludge
1.7-3.5
43.0-47. 5*
20.2*
1.9*
1.4*
2. 9*
61.1*
7.25-7.42
4120-4525
3520
Weight percent of dry sludge solids.
TABLE 110. EFFLUENT QUALITY AND SOLIDS REDUCTION AT THE
OPTIMUM REFUSE DIGESTION TEMPERATURES AND A
DETENTION TIME AND LOADING RATE OF 12 DAYS
AND 0.14 LB VS/CF-DAY, RESPECTIVELY (253)
Optimum Digestion
Temperatures. ° C
Effluent Volatile Acids, mg/£HAc
Effluent Soluble COD, mg//
Alkalinity, mg/4 CaCO3
pH
Ammonia Nitrogen, mg/jj N
Volatile Solids Reduction, %
35
135
904
3414
7.33
110
58.5
55
197*
1222
6188
7.10
680
69.1
Note: This concentration does not include unidentified volatile acids
which were detected but could not be measured separately.
Consequently, the actual volatile acid concentration would be
higher than that noted in ijiis table.
301
-------
operating temperature range. The ammonia nitrogen content is high and,
if discharged before being oxidized, could cause problems in a receiving
body of water. The second-stage BOD (e.g., the oxygen demand beyond
that reported in the BOD,- determination) is dominated by oxidation of
ammonia (NOD) and is probably responsible for the difference in BOD and
COD values.
A related fact in this regard is seen by comparing Table 110 with
Table 108. It was indicated in Table 108 that for mesophilic digestion
(~ 35 C), ammonia nitrogen might reasonably be expected to be in the
range of 50-200 ppm for optimum operation. The data in Table 110 con-
firms this assumption. However, thermophilic concentration exceeds this
value by more than a factor of three. This clearly demonstrates that
these two process conditions must be evaluated separately, both in terms
of the treatability of their output and the expected concentration of
heavy metal in effluent liquid and solid streams.
Certain of the digester feeds such as animal wastes are claimed to
produce a solid by-product with value as a fuel, soil conditioner, ferti-
lizer, and animal feed (254)p However, each cycle concentrates hazardous
materials and cannot eliminate residuals completely.
In summary, it seems apparent that insufficient data exist to com-
pletely characterize the residuals from anaerobic digestion of biomass
and other waste. Data which ought to be gathered include organic matter,
BOD, COD, bacteria and pathogen counts, pH, and sodium in both the
aqueous waste and solid residue. Leach tests on the solids under ex-
pected environmental conditions should provide data on contaminant
mobility potential.
Acid Hydrolysis
The breakdown of cellulosic wastes to fermentable sugars via acid
hydrolysis and the subsequent fermentation to ethanol produces both
solid and liquid by-products. These include lignin, which comprises
the major portion (60-70 percent) of the insoluble residue, plus methanol,
acetic acid, furfural, and non-fermentable sugars. The methanol and
acetic acid may prove recoverable if commercial-scale production is
achieved ^ ->~1-'. Uronic acid and other sugar decomposition products are
also discharged from the reactor and together with the furfural and non-
fermentable sugars represent a high BOD waste stream that would require
secondary aerobic biological treatment or perhaps could be land-treated.
The feedstock must be diluted in solids for reaction, so large volumes
of liquid will need to be treated and recycled to the feed and the
system or discharged.
Only one study was located which determined the BOD of the spent
liquor. Converse, et al,(256) measured the 5-day BOD of an unfiltered
liquor sample as 6,550 ppm and that of a filtered sample as 6,070 ppm.
The estimated quantity of effluent was 1,600 gallons per ton of material
hydrolyzed (based on a 250 ton/day capacity). An interesting point was
noted by these authors, who stated that the presence of ferrous and
302
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for L^nimaSS ^^ °n ^ Pr°CeSS variables and by-product marke,
for example the recovery of methanol. The dewatering of the lignin
nT.nn fYT11" Use as a solid ^el, since it has a high heating value
(10,500 Btu/lb). This would provide volume reduction. On the other
hand, carbonization or solvent extraction of the ligneous material may
provide new sources of compounds which are presently synthesized from
petroleum bases.
The technology of this conversion process has not yet proven suf-
ficiently attractive to warrant in-depth research. As a result, many of
the environmental impacts remain unquantified .
ENVIRONMENTAL REVIEW OF SCENARIOS
The regional scenarios developed earlier provide the rationale for
the tabular presentation of data on preliminary environmental impacts
of biomass collection and conversion. Because many of the systems have
not been studied beyond the bench or pilot-plant scale, the emissions
and effluent factors are of necessity extrapolations of available infor-
mation. Data for the tables are taken directly from the text, except in
those cases where a particular reference is noted. The express purpose
of the scenarios is not to provide final answers, but rather to suggest
a methodology and to point out problem areas where further investigation
is indicated.
In addition to the expected physical, chemical and ecological im-
pacts, a brief synopsis of the possible socio-economic consequences of
biomass is presented. Again, the purpose of the discussion is to point
the way for future research efforts.
Environmental Summaries of Scenarios
Capsule summaries of the salient environmental features of the six
scenarios developed in Section 6 are presented in Tables 111 through 116.
These were prepared to highlight these features and should not be con-
strued as more than an initial accounting of the environmental effects.
At some point in future, they should be expanded, with more detailed
site and plant data used to characterize the impacts.
Socio-Economic Aspects of Biomass
The implementation of large scale collection, treatment, processing
and conversion of biomass materials will alter existing social and
303
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TABLE 111. SCENARIO 1: ENVIRONMENTAL SUMMARY, PYROLYSIS OF WOOD
Pollutants
Quantity
Air Emissions
Particulates
Hydrocarbons, SO , NO
X X
Noise
Water Effluents
Organics
BOD/COD
Solid Residue
Metal Content
BOD/COD
0.6-1.2 kg/MT of wood wastes
(3,000-6,000 kg/day for
5,000 MT plant).
Small due to nature of source
and conversion process.
May be locally severe, e.g.,
near shredders, but most
activity will occur in remote
areas.
Should be negligible.
Estimated to be 500-3,000 mg/1
and plant to treat 2,600 MT/day
(~ 0.7 MGD) of wastewater.
This results in a needed treat-
ment capacity of 1,300-7,800 kg/
day or that required for a
population of 7,500-40,000.
Unknown but should be very low.
May be high in leachate (and
also may be contributed by the
material in storage, if not
covered properly or enclosed).
The quantity estimated to be
landfilled will occupy a volume
of 3,300-6,600 ft3/day based on
a bulk density of the ash between
50 and 100 Ib/ft3.
304
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TABLE 112, SCENARIO 2: ENVIRONMENTAL SUMMARY FOR ACID
HYDROLYSIS OF BAGASSE/FOREST RESIDUES
Pollutants
Quantity
Air Emissions Particulates
Hydrocarbons, SOX, NOX
Noise
Water Emissions BOD
Metals
Solid Residue
Nil
Unknown but expected to be
small due to nature of process.
Handling of feedstock may cause
dusting if partially dried
before processing.
Locally high, e.g., prepro-
cessing equipment, transporta-
tion.
6,000 mg/1; discharge of 4.8
MGD (based on 1,600 gal/ton
of feed). Resultant loading
is 109,000 kg BOD/day or a
population equivalent of 96,000.
Unknown; should be minimal.
If solid is landspread, the BOD,
suspended solids, and dissolved
materials may be spread over a
large enough area to eliminate
any difficulties. If, however,
the disposal is via landfill,
the residuals may need to be
monitored carefully.
305
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TABLE 113. SCENARIO 3: ENVIRONMENTAL SUMMARY FOR
ANAEROBIC DIGESTION OF KELP/MSW
Pollutants
Quantity
Air Emissions
Particulates, NO ,
S0x, HC X
Odor and Noise
Water Effluents
BOD
Insignificant due to process/
feed material.
Objectionable at times,
especially if "stuck"
reactor loads must be
disposed of.
Estimated volume of .7-.9 MGD
(3,000 MT/day) and concentra-
tion of 500 mg/1 produces a
loading of 1,500 kg/day
Suspended Solids
Solid Residue
3-4 MT/day
~ 3,100 MT/day spread as
fertilizer will require 155
ha/day at an application rate
of 20 MT/ha (~ 8 ton/ac).
Individual sites may have
run-off or ground water
contamination problems that
will have to be identified
by field analysis.
306
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TABLE 114. SCENARIO 4: ENVIRONMENTAL SUMMARY FOR TURBOELECTRIC PEAKING
ELECTRICAL GENERATOR WITH FLUIDIZED BED USING ENERGY
CROP/CORN RESIDUE
Pollutants
Quantity
Air Emissions
, HC
Particulates
Water Effluent
Solid Residue
Very low due to use of
fluidized-bed combustor.
Can be reduced to a level
equivalent to that experienced
with incineration. The small
plant capacity (3.6 x 109 Btu/
da) yields a particulate emis-
sion of less than 2,000 kg/da.
The only water requirements
are for cooling system make-up
and wash water and should
contribute minimal pollutants
for this size plant.
Leachate from spent bed
material will be high in
suspended and dissolved solids
and COD. However, the small
quantity of residue should be
a mitigating factor.
307
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TABLE 115. SCENARIO 5: ENVIRONMENTAL SUMMARY FOR ANAEROBIC
DIGESTION OF ANIMAL WASTE/WHEAT STRAW
Pollutant
Quantity
Air Emissions
(similar to those
in Scenario #3)
Water Effluents
(qualitatively
similar to those
in Scenario #3)
Particulates, NOX,
SOX, HC
Odor and Noise
BOD
Solid Residue
Insignificant due to process/
feed material. Dust may be a
problem on a local scale if
dried wheat straw is pre-
processed by shredding.
Objectionable at times,
especially if "stuck" reactor
loads are disposed of.
Estimated volume to be treated
daily is 24 MGD (9,240 MT/da)
at 500 mg/1 BOD. Calculated
loading is then 4,620 kg/da.
It is conceivable that this
waste stream could be land-
applied after treatment. It
should be free of most hazardous
material and could be pumped to
nearby fields. Storage periods
for feed should be minimized
to prevent run-off.
6,000 MT/da at 50 percent
moisture could be land-spread
as fertilizer. Careful manage-
ment and site selection should
minimize adverse effects of
leaching and maximize soil
amendment potential.
308
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TABLE 116. SCENARIO 6: ENVIRONMENTAL SUMMARY FOR DIRECT
CONVERSION TO STEAM IN A WATERWALL INCINERATOR
USING MSW
Pollutants
Quantity
Air Emissions
Particulates
NO-,
SOr
HC
Water Effluent BOD/COD
PH
Solid Residue
Dissolved Solids
Metals
BOD/COD
Metals
Based on 0.4 kg particulates
per ton refuse burned,(a)
emitted by the Chicago
incinerator, yields are
approximately 2,000 kg/day.
9,000 kg/day based on 3.53
Ib/ton of refuse^).
10,000 kg/day base
Ib/ton of refuse'
scrubber.
on 3.94
; no
4,000 kg/day based on 1.58
Ib/ton of refuse(b).
Wash water/cooling water will
contribute minor amounts of
these pollutants.
Leachate from ash handling
will exhibit pH values in the
range 10-12 due to ash
composition.
High due to leachable salts.
Should be negligible due to
high pH, but will be present
in trace amounts.
Some will be present due to
uncombusted material.
Analysis of MSW ash indicates
metals are present in the
range of 0.05-0.4 wt. percent.
However, the small volume of
waste and use of landfill
liners should minimize the
problem.
(a) Hughes, et al., 1974.
(b) Surprenant, et al., 1976.
309
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economic frameworks in the areas served. The analysis of the magnitude
of change is beyond the scope of this study. Hence, a brief description
of the type of social and economic pressures must suffice.
The two models to be treated are the rural small community type
and the urban center type. The parameters that appear to be important
are the employment picture, income distribution, alternative allocations
of resources, funding sources and public sentiment. The context of this
discussion is the regional scenario outlined previously. Projections of
expected specific trends for the future should be considered in a separate
investigation.
It is expected that, to be economically viable, the processing
facilities will have to be located near the growth and/or collection
areas. In the scenarios involving animal waste, crop residues, forest
residues, and perhaps energy crops, the plant will be a major industry
in an otherwise rural area. Judged in terms of available technology,
biomass conversion appears to be more labor intensive than fossil fuel
recovery. Thus, biomass facilities may provide additional jobs for
certain areas. Workers to fill these newly created positions may be
available locally where they may have been operating marginally productive
farms or small businesses. Alternatively or additionally, labor may be
imported from outside the region. The newly generated money flow may
induce secondary economic-growth in the form of expansion of existing
commercial and social services, but may also lead to changes in tax
structure required to construct new schools and other public buildings as
well as to foster continued public services. Depending on relative pay
scales, workers employed in these new positions may skew the income dis-
tribution of the community. The possibility of this fact should be
investigated.
In fact, the stable and often homogeneous areas likely to be im-
pacted upon by such development may prefer to forego the benefits al-
together. Public sentiment may determine that maintenance of the status
quo best represents local interests. This in itself may offer oppor-
tunities for friction since it is highly unlikely that a consensus will
be reached.
The other model type which is identifiable is the urban center. To
a limited degree these scenarios have already been implemented in the
form of incineration facilities for municipal solid waste. Since the col-
lection system is already developed, social and economic impacts will
differ only in degree rather than in type. Studies to isolate the particu-
lar groups affected should be conducted but, because of the heterogeneous
nature of urban populations, such socio-economic changes may prove minor.
Projected facilities are larger than any presently operating. Funding
sources and public sentiment regarding construction and operation of such
plants should be analyzed before large-scale development proceeds.
One scenario which is difficult to categorize as urban or rural is
the ocean farming of kelp. The harvesting and transport operation re-
quires significant manpower and capital inputs. As such, the supply and
310
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demand curves for other coastal industries, e.g., commercial fishing,
may be affected. The effects of this redistribution of resources and
income should be examined in detail. However, if market forces are
operating properly, economic efficiency should result.
The preceding outline can in no way substitute for a well researched
socio-economic investigation. Such a task could be based on the six
regional scenarios or could be defined in any other suitable fashion.
In either case, social and economic constraints may be just as important
as environmental considerations in the final choice of technology and
geographic area. Some consideration should also be given to the longer-
range implications of biomass conversion, when the scale of operations
may involve millions of acres of land and hundreds of thousands of people.
311
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SECTION 8
CURRENT GOVERNMENT AGENCY EFFORT IN THE
BIOMASS PRODUCTION/CONVERSION FIELD
Because of the multiple objectives and broad range of technologies
applicable to Biomass-to-Synthetic Fuels systems, government-sponsored
research and development is being undertaken by several agencies. Besides
the Environmental Protection Agency, other agencies known to be active in
the field include the Department of Energy (DOE) (formerly ERDA),
the National Science Foundation (NSF), the Department of Agriculture (USDA),
the National Aeronautical and Space Administration (NASA), the Department
of Defense (Army and Navy), and the Department of the Interior. State and
local governments (e.g., state agricultural departments and state environ-
mental protection agencies) are also sponsoring research; the level of effort,
however, is believed to be small. In addition to government sponsorship,
biomass-related research is also being funded by industrial groups engaged
in fuel production, utilization and distribution, notably the Electric Power
Research Institute (EPRI) and the American Gas Association (AGA). Finally,
several government agencies have more than one organizational element with
missions and expertise in biomass systems.
It is beyond the scope of this study to attempt to detail all of
the ongoing work relevant to Biomass-to-Synthetic Fuel technology. However,
in order to try to recommend areas of research that are technologically
relevant and complementary in nature to research projects supported by other
agencies, it is necessary to assimilate and categorize the major ongoing
efforts conducted by the most relevant agencies. It is believed that most
of this effort is concentrated in DOE. The following summary is based on
discussions with agency personnel responsible for the specific program areas.
Programs described are those which were underway in late 1976.
EPA - WASTE-TO-FUEL PROGRAM
Various offices and divisions within EPA have funded small-scale, pilot,
and demonstration programs in the waste-to-fuels areas. These programs span
the range of thermochemical and biochemical conversion processes and include
substantial efforts in combustion, pyrolysis, and anaerobic digestion activi-
ties.
Review of all these programs is beyond the scope of this report. The
interested reader is referred to a recent summary article by Huffman(257) for
a synopsis of recent efforts. More comprehensive documentation of EPA programs
in this area may be found in References (258) and (259).
312
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DOE - OFFICE; OF SOLAR, GEOTHERMAL
AND ADVANCED ENERGY SYSTEMS
The activities within this DOE office which are focused on biomass
T£ CTerSK10n t!chn0l°8y are -cl-ively within the Solar Energy
Three branches of this division conduct studies which are relevant
to some segment of this technology. These are the Fuels from Biomass Branch,
the Environmental and Resource Studies Branch, and the Agricultural and
Process Heat Branch.
The Fuels from Biomass Branch has primary responsibility for the
development of biomass production and conversion technology for all biomass
sources except urban and industrial waste. The overall objective of this
branch is to develop a unified program which will allow biomass energy sources
to be Developed at a level that meets or exceeds that projected in the ERDA
49(260) document.
The Environmental and Resource Studies Branch is charged with responsi-
bility for identifying the environmental consequences of technology develop-
ment in all solar energy fields. The technology developments of its sister
branch, Fuels from Biomass, are therefore consistent with the mission of this
branch.
The Agricultural and Process Heat Branch has responsibility for direct
use of solar energy for its thermal capacity. Its mission impinges on
biomass production/conversion technology only in the areas where it could be
used to dry grains and crops. For this reason, the activities of this branch
will not be discussed further.
Solar Energy Division, Fuels from
Biomass Branch (FFB)
The work being conducted by the Division of Solar Energy was initiated
when this organizational element was part of the National Science Foundation.
This initial thrust has continued and accelerated since FFB was incorporated
into DOE. As shown in Figure 70(261) , the Fuels from Biomass Program has
been organized into three program functions with technological thrust and one
support function. The time frame for the three programs extends to 1985 and
beyond.
For comparison with the definitions used in this report, the agricultural
residue projects are concerned with part of the biomass sources reviewed
under the heading Forest and Agricultural Waste. The projects on terrestrial
biomass incorporate the energy crop and silviculture as well as the forest
waste segment of the Forest and Agricultural Waste source. The marine
biomass project includes the ocean-based segment of aquaculture. However,
reviewing Tables 119 and 120 will show that DOE is also pursuing freshwater
biomass production as well.
The urban and solid waste source described earlier in the report is
outside the current mission of FFB. However, review of Table 120 will show
that some work initiated when this branch was part of NSF was based on a
313
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TABLE 117. AGRICULTURAL RESIDUE PROJECTS*
Program
Project Sub-Element
An Evaluation of the Use of Agricultural System Study
Residues as an Energy Feedstock
Feedlot Energy Reclamation Feedlot Experimental
Demonstration Facility
Methane Fermentation of Feedlot Wastes Feedlot Experimental
Facility
Technological and Economic Assessment of System Study
the Utilization of Rice Straw
Technological and Economic Assessment of System Study
Sugar Cane Production Residue
Technological and Economic Assessment of System Study
Methods for Direct Conversion of Agri-
cultural Residues to Usable Energy
* These are only projects being funded by the Fuels from Biomass
Branch of DOE's Solar Energy Division.
solid waste feedstock. Within DOE, major responsibility for this area now
resides with the Office of Energy Conservation.
Table 117, which categorizes current FFB projects which have emphasis
on agricultural residue, shows that a total of six projects are underway or
have been completed. Most projects can be categorized as system studies
although the Feedlot Energy Reclamation Demonstration (undertaken by Hamilton
Standard) and the Methane Fermentation of Feedlot Wastes (inter-agency agree-
ment with USDA) are actually related to the Feedlot Experiment Facility item
in the agricultural residue projects program.
Projects related to conversion of terrestrial biomass are reviewed in
Table 118. Four programs have been undertaken in this area, all identifiable
as system studies.
Three system studies, shown in Table 119, have been undertaken in the
marine biomass area.
314
-------
u>
I-1
Ln
PROGRAM ELEMENT
AGRICULTURAL RESIDUE PROJECTS
Crop Residue Pilot Plant
Feedlot Pilot Plant
Dairy Farm Animal Waste Pilot Plant
TERRESTRIAL BIOMASS PRODUCTION & CONVERSION PROJECTS
Intensive Agriculture Pilot Plant
Controlled Environment Agriculture Pilot Plant
Intensive Agriculture Demonstration
Wood Plantation Pilot Plant
Wood Plantation Demonstration
MARINE BIOMASS PRODUCTION & CONVERSION PROJECTS
System Studies
Marine Biomass Pilot Plant(s)
Marine Biomass Demonstration
RESEARCH DEVELOPMENT PROJECTS
Biomass Production Technology Projects
Conversion Technology Projects
FISCAL YEAR
75
76
^
77
78 79
P-
.
•__
,
,
'.
80
81
82
83
84
85
AFTER 85
Project Initiation
Begin Operation
Project Completion
Figure 70. Diagram structure for DOE Fuels from Biomass Branch
(261)
-------
TABLE 118. TERRESTRIAL BIOMASS PRODUCTION
AND CONVERSION PROJECTS*
Project
Program
Sub-Element
System study of energy concepts
based on sugarcane, sweet sorghum,
sugar beets, and corn
System study and program plan for
silviculture energy plantations
System study of fuels from grains
and grasses
Forest industry energy program
feasibility study
System study
System study
System study
System study
* These projects are only those funded by the Fuels
from Biomass Branch of the DOE Solar Energy
Division.
TABLE 119. MARINE BIOMASS PRODUCTION AND
CONVERSION PROJECTS*
Project
Program
Sub-Element
Evaluating ocean farming of seaweed
as sources of organics and energy
Ocean farming for kelp production
and harvesting
Marine pastures
System study
System study
System study
* These projects are only those funded by the Fuels from Biomass
Branch of DOE's Solar Energy Division.
316
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TABLE 120. RESEARCH/DEVELOPMENT PROJECTS 0
Project
Related
Program
Element
Project
Orientatic
Study to determine optimum
use of Albany, Oregon, pilot
plant for advancement of
processes for conversion of
cellulosic materials to
liquids or gases
Technological evaluation of
the waste-to-oil pilot plant
at Albany, Oregon
1. Terrestrial
Biomass
Conversion
Process
2. Terrestrial
Biomass
Pilot plant studies for pro- 3. Terrestrial
duction of sugars and ethanols Biomass
based on enzymatic hydrolysis
of cellulose
Large-scale cultivation of
filamentous blue algae in
solar bioconversion systems
Solar energy conversion with
hydrogen producing algae
6. Marine
Biomass
7. Marine
Biomass^ '
Bioconversion of agricultural 9. Agricultural
wastes for energy conservation Residue
and pollution control
Construction of wood waste-
to-oil facility
Cultivation of macroscopic
marine algae for energy
conversion, hydrocolloid
production and advanced waste
water treatment
Methane for farm energy
Utilization of woods as
chemical raw material
4.
Terrestrial
Biomass
8. Marine
Biomass
Conversion
Process
Conversion
Process
Production
Conversion
Process
Conversion
Process
Advanced
Process
Development
Production
10. Agricultural Conversion
Residue Process
5. Terrestrial Conversion
Biomass Process
317
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TABLE 120. (Continued)
Project
Biological conversion of
organic refuse to methane
Heat treatment of refuse for
increased anaerobic biode-
gradability
Related
Program
Element
11. Urban and
Industrial
Waste (c)
12 . Urban and
Industrial
Wastes
Orientation
Conversion
Process
Conversion
Process
Engineering evaluation of
program to recover fuel gas
from waste
Non-specific
Conversion
Process
Combustion of sulfur
compounds of sulfur-bearing
fuels
Non-specific
Conversion
Process
(a) These projects are only those funded by the Fuels from Biomass Branch of
DOE's Solar Energy Division.
(b) This program is a freshwater analog to marine studies and so logically fits
into the marine biomass element.
(c) These programs were initiated when the Fuels from Biomass Branch was part
of NSF and had pro.gram interests in this area.
Most of the projects sponsored to date by FFB have been categorized in
the research or development category. Reviewing Table 120 will show that
five of these projects have been in support of terrestrial biomass, two in
support of marine biomass, and two in support of agricultural residue
programs.
In addition, two have been related to solid waste sources of biomass,
and two were not specific in nature.
Reviewing these research and development projects in the context of their
project orientation, conversion processes are overwhelmingly favored over
biomass production and related research by an 11 to 2 margin. This emphasis
on conversion process development is not illogical since (1) in most cases,
the results of the system studies in the biomass area will be required to.
318
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identify plant species or waste systems on which work should concentrate,
and (2) most of the process development work would appear to be directed at
processes with broad application in terms of biomass source feedstocks.
Over the short term, the major effort within FFB will be to complete
the various system studies currently underway. These will be reviewed by
DOE to insure their conclusions are valid. These conclusions will then
provide the basis for integrated pilot plants associated with terrestrial and
agricultural residue biomass sources.
The system on aquaculture (an expansion from marine biomass projects)
will probably lag the completion of other biomass system studies. However,
some pilot-scale work will probably precede completion of the system study.
FFB anticipates that the conclusions reached in the various system
studies will provide the thrust for initiating work on critical collection,
storage, transportation,equipment, development problems. During the past
several years, FFB has supported work on single-farm energy conversion
systems, primarily through USDA. This thrust does not appear to be growing.
Solar Energy Division, Environmental and
Resource Studies Branch (ERSB)
This branch of DOE's Solar Energy Division is currently directing its
efforts toward determination of long-term social and environmental conse-
quences of solar energy development as projected in the ERDA 49 plan. Three
programs are currently underway that impinge on the biomass-to-synthetics
fuels technology.
One of the programs is preparing technology descriptions for each of
8 solar energy technologies, including biomass. These will then be evaluated
and the environmental problems associated with each will be identified.
These will likely include residuals, ambient impacts, social-economic impacts,
and similar data. This study will culminate in a development of detailed
environmental studies plan for each of the 8 technologies.
A second study is underway which is taking a very broad look at the
social and environmental implications of various solar energy scenarios using
the ERDA 49(260) as a data base. This study is designed to work from narrow
descriptions of various solar energy technologies and work outward until
social, political, economic, and environmental consequences of global
significance have been identified. The study will pose very fundamental
questions about whether it is possible on a long-term basis to develop a
distributed solar energy supply for use in the concentrated industrial
societies that are prevalent today.
A third study is underway which is primarily a support study for the
other two noted above. One task that has been initiated under this support
effort has been to try to quantify the relationship between the environmental
implications identified in the previously noted studies and the goals of the
National Environmental Policy Act. A second task has sought to evaluate the
sensitivity of conclusions made in the previous studies to various assump-
319
-------
tions or omissions. A third task, which will probably involve developing
a seminar to present the results of these earlier studies, is currently
being planned.
In the long-term plan this group is to assess the environmental and
social effects of each solar technology being developed as part of and in
concert with technological branches of the Solar Energy Division. Over
shorter term and in cooperation with the Fuels from Biomass Branch, it is
planned to initiate environmental studies of the planned pilot plants.
DOE - OFFICE OF ENERGY CONSERVATION
The Office of Energy Conservation of DOE has the general objective of
reducing consumption in the United States by reducing demand and by more
fully utilizing available energy sources. One energy source that is under-
utilized is wastes, and there are two branches within this office with
emphasis in this biomass source area. These branches are within two divisions:
the Buildings and Community Systems Division and the Industrial Energy
Conservation Division.
Building and Community Systems Division,
Urban Waste Technology Branch (UWTB)
This branch has become active in developing technology for waste
conversion. Table 121 has been constructed to place UWTB projects currently
being conducted within the definitions used in this report. There are seven
projects underway with thermochemical process orientation and eight projects
where the primary emphasis is on biochemical methods. Three studies of a
general support nature were identified. Within the thermochemical projects,
there is about equal distribution between pyrolysis and direct conversion
technologies. One project with a secondary process orientation was identified.
Within the biochemical technology area, there is a strong emphasis on
anaerobic digestion, with seven of the eight projects oriented in that direc-
tion. Anaerobic digestion is, of course, undoubtedly the biochemical process
nearest to commercialization. One project is directed at enzymatic hydrolysis
development.
The program emphasis within the group is anticipated to continue along
the lines of present program structure, with additional novel commercializa-
tion-oriented technologies receiving support as they are identified. In
terms of technology emphasis, additional work in combustion systems is
expected to be minor. Emphasis in this area will relate to boiler corrosion
and probably high pressure/temperature boiler design. Demonstration of a
pyrolysis process(es) is anticipated within a relatively short time frame.
Gaseous fuel cell and small system development are also likely to receive
support.
320
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TABLE 121. SUMMARY OF PROJECTS UNDERWAY BY DOE's URBAN WASTE TECHNOLOGY BRANCH
ho
Thermochemical
Description
Ammonia from Urban
Waste
Chemical Synthesis
Gas Production
European Waterwall
Incinerator
Assessment
Cofiring MSW in a
Cement Kiln
Waste Carbon Mon-
oxide as Natural
Gas Replacement
in Chemical Feed-
stocks
Hone Heating and
Cooling Utilizing
Wastes
Conversion of Cellu-
losic and Polymer
Wastes Co High
Systems
Technology
Pyrolysis
Pyrolysis
Direct
Conversion
Direct
Conversion
Secondary
Conversion
Process
Direct
Conversion
Pyrolysis
Bio-chemical Systems
Description
Advanced System Ex-
perimental Facility
Cellulosic Enzyme
Hydrolysis
Packed Bed
Anaerobic
Digestion
Enhanced Anaerobic
Digestion
Anaerobic Digestion
of Industrial
Wastes
High-rate Anaerobic
Digestion
Energy and Protein
Production from
Pulp Mill Wastes
Digestor Mixing
Tests
Technology
Anaerobic
Digestion
Enzyme
Hydrolysis
Anaerobic
Digestion
Anaerobic
Digestion
Anaerobic
Digestion
Anaerobic
Digestion
Anaerobic
Digestion
Anaerobic
Digestion
Support Studies
Description
Urban Waste Equipment
Test and Evaluation
Facility
Regional Waste
System Character-
ization
Development of a
Glass-Polymer Com-
posite Sewer Pipe
from Waste Glass
.
----
Technology
Pre-processing
General
Support
Not Fuel Con-
version
Related
- _ _ ~
Octane Gasoline
-------
Industrial Energy Conservation Division,
Materials Optimization Branch
This recently organized branch has responsibility for the industrial
waste utilization functions within the Office of Conservation. While
industrial waste utilization is an element of its overall responsibility,
primary program emphasis over the longer term will be toward optimizing
material flows and process trains to minimize total energy accumulation.
This will be accomplished by evaluating the elements of the processing train
from the extraction-harvesting stage to consumer distribution functions.
Bnplementative modifications may include the substitution of alternative
materials with lower energy use characteristics or modifications in the
processing train to decrease energy use. An adjacent program is the research,
evaluation and development to commercial scale of new engineering materials
as required for specific energy-related applications or as indicated to be
needed by the results of the materials optimization analysis.
As related to biomass, the industrial waste utilization opportunities
in the food and fiber industry are the most likely candidates for biomass
source materials. This branch will limit its interest to the waste available
at manufacturing sites, leaving to the Fuels from Biomass Branch the consi-
deration or production site waste utilization functions. Waste conversion
technology will apparently not receive major emphasis in this group, with
only very novel process systems being considered for support.
This branch also coordinates all modeling and systems analytic efforts
within the Division of Industrial Energy Conservation.
DOE - OFFICE OF ENVIRONMENT AND SAFETY
This office provides support to the DOE technology offices in the
areas of environmental control and containment requirements, and in health-
related topics. The programs of two divisions, Environmental Control Techno-
logy and Biomedical and Environmental Research, are expected to have impact
on biomass production/conversion technology.
DOE, Division of Biomedical
and Environmental Research
This division's current program impinges on biomass conversion technology
in only a single program. The division is supporting, in cooperation with
EPA, the Ames-Iowa combined firing project. The activities for DOE are being
carried out by DOE's Ames Laboratory. DOE's effort has included baseline
studies on the characterization of particle size throughout the process as
well as characterization of stack emission with respect to trace element
content of particulates, S02, NOX, and organics. There are also ongoing
studies on microbiological agents present in stored solid waste.
Immediate plans of this division are to develop a cooperative effort
with EPA on the environmental evaluation of the Pompano Beach anaerobic
digestion facility.
322
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DOEt Environmental Control
Technology Divisiojn.
r sL-ssy.23S?rt-
measurements of environmental emissions. The results of these
studies often take the form of recommendations of control technology develop-
ment which may be developed within (primarily, conversion process modifica-
tion) or outside the agency.
Given the mission of this division, their involvement in biomass-related
activities is anticipated to come primarily in support of technology-
development organizational elements.
UNITED STATES DEPARTMENT
OF AGRICULTURE
The USDA is clearly an agency with much expertise in the area of biomass
cultivation, species mutation, and agricultural/forestry management. Two
groups with USDA, the Fuels from Biomass Group and the Forestry Service,
presently have programs mobilized. There are probably other groups working
in the area that were not identified.
Fuels from Biomass Group, Beltsville
Agricultural Center
This group at USDA is conducting three projects', with funds provided by
NSF and FEA,. One of these studies is on bagasse utilization, a second
on anaerobic digestion of beef manure, and a third on utilization of rice
straw produced on a 450,000-500,000 acre farm in California.
All of these studies are directed at biomass conversion for the purposes
of making single farms less energy-dependent and approaching energy self-
sufficiency.
This group supports the concept that collection and harvesting technology
need to be emphasized early in biomass technology development in order for
complete system efficiency to be developed. Likewise, they feel an intensive
effort aimed at- improving species for total biomass and food production should
be emphasized.
lorest Service, Forestry Research
The USDA organization has an interest in biomass technology by virtue of
their general expertise in forest management. ERDA's Fuel from Biomass
program has funded work in two research areas. An effort is underway ^ to
simulate the harvesting and transport function involved in forest residue
use. Previously, a feasibility study was prepared on recovery of methanol,
ethanol, furfural, and similar compounds from wood products and residue. The
323
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latter work was funded from the Fuel from Biomass group while this was part
of NSF and in cooperation with FEA. In addition to ERDA-funded work, USDA
is currently conducting a study at Rhinelander, Wisconsin, on the extensive
cultivation of fast-growing hardwood which will sprout from stumps and can be
harvested every 6-7 years.
Expansion of the work currently underway is the anticipated course of
future work.
NATIONAL SCIENCE FOUNDATION
The utilization of biomass for both fuels and other purposes was
initiated within the National Science Foundation in its program on Research
Applied to National Needs (RANN). The Fuels from Biomass segment of this
effort was transferred to ERDA when ERDA was organized in 1975- However,
there remains an effort within the National Science Foundation on the use of
biomass as raw material for producing non-fuel commodities.
The RANN program is viewed as bridging the gap between basic and applied
science. Work on biomass conversion to other resources is primarily conducted
by the Advanced Energy and Resources Research and Technology Division (AERRT).
The primary resources of current interest are in foods, chemicals, and -ferti-
lizers. No work is currently underway in building materials; however, this
resource will also eventually be considered.
The structure of the program contains three elements. One of these is on
nonrenewable resources and is primarily directed at the mineral market and
consequently is of no interest in this study. A second element is directed
at resource systems and the work in this element is directed at determining
the interrelationship of social, technical, and economic inputs into general
resource systems. The renewable resources element has the purpose of devel-
oping biomass conversion/production technology and relating these developments
to the activities of other federal agencies. The program has three major
objectives: (1) to assess alternatives for effective use of biomass, (2) to
improve land productivity by evaluating and identifying alternative practices,
and (3) to increase the capability to produce protein from non-conventional
sources. Each of these objectives has associated with it a program sub-element.
Biomass utilization is one of these areas. Most of the emphasis has been
toward lignin-research, primarily because this is an area that has been
neglected by others. Both biological and chemical systems are of interest.
A second sub-element area is that of innovative resources. Biophotolysis
(in cooperation with a DOE effort) will be supported under this technology.
Also within this area is the research on the mechanism and utilization of
biological fixation of nitrogen. The third sub-element is that of photo-
synthesis research with the emphasis on improving biomass production. Projects
related to biomass utilization and supported by NSF/AERRT are:
• Bioconversion of lignocellulosics
• Conversion of lignocellulose by thermophylic actinomycetes micro-
organisms
• The isolation of lignin-degrading tropical microorganisms
324
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• Enzymatic transformation of lignin
• Enzymatic decomposition of lignin and cellobiose in relation to
hydrolysis of cellulose
• Pyrolytic conversion of cellulosic materials.
NATIONAL AERONAUTICS AND SPACE
ADMINISTRATION~~
There are at least two groups within NASA who are conducting or who
have conducted work related to biomass utilization. The Urban Systems Office
at NASA s Johnson Space Center has for several years been involved in the
Multiple Integrated Utility System (MIUS) program. This program sought to
develop housing systems, either at the individual or, more likely, at the
housing development level, which were completely independent of outside needs
for conventional utilities, including electricity, gas, sewage, urban waste
collection, etc. The basis for this work was NASA's manned spacecraft exper-
tise. At one point several years ago, studies were planned to develop both
pyrolysis and anaerobic digestion systems scaled down to these very small
levels. These studies were never executed, and NASA's involvement has been
steadily decreasing. As the work has approached demonstration scale, the
effort has been transferred to HUD and the National Bureau of Standards.
Their involvement is reviewed later in the report.
NASA'a National Space Technology Labs at Bay St. Louis, Mississippi, has
been developing technology for the use of water hyacinths (Eichhornia crassipes)
as a tertiary waste water treatment system. Part of the concept involves
converting the water hyacinth's plant tissue into anaerobic digestion gas,
animal feed, or fertilizer. Batch studies on anaerobic fermentation to
produce gas have been undertaken as have crop yield studies to ascertain
fertilizer value. Project personnel can see wide application as a tertiary
treatment technique in the tropical and semi-tropical climates. Several small
communities near the Bay St. Louis laboratory intend to install the system
and use the plant tissue for fertilizer after suitable composting. Disney
World in Florida is also apparently considering installing a treatment system
and developing an associated anaerobic system. Related research work has
been conducted on solar drying of the plant tissue and on animal feeding.
The plans for the project, which is entirely supported by NASA, are to continue
along current program lines for the immediate future.
HUD, OFFICE OF POLICY DEVELOPMENT AND
RESEARCH, DIVISION OF BUILDING TECHNOLOGY
This division of HUD, with the direct support of the Department of.
Commerce, National Bureau of Standard, is making an effort to demonstrate
the value of multiple integrated utility systems (MIUS) as a total package
for community growth. Their effort has taken the form of one demonstration
project (total energy supply only) which began operation in the second
quarter of 1976 and a second project which has just entered the design
phase.
325
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The first project, which has been implemented in a redevelopment area
of Jersey City, New Jersey, is directed at supplying the total energy require-
ment for 486 dwelling units as well as 250,000 square feet of commercial
property. The system was primarily designed to demonstrate reliability and
maintainability of these systems and operates unattended except for custodial
and emergency support. The complete instrumentation for monitoring demand
and modulating supply is in place and operational. Since only the demand
side is being- demonstrated, no use of solid and liquid wastes has been made.
This demonstration will be undertaken in a second project described below.
The second project has been initiated with a private developer in St.
Charles, Maryland, and is in the design phase. This system is designed to
supply the needs of the equivalent of 1,000 dwelling units, with a dwelling
unit rated at 8,000 square feet. Approximately 740 actual individual
dwelling units will be utilized, with the balance of the equivalency coming
from public/commercial installations such as schools, drug stores, churches,
gasoline stations, etc. However, in this system also, reliability has been
emphasized and only equipment which are articles of commerce will be utilized.
DOE's Building and Community Systems Division is supporting some research
work directed towards improvement of state-of-the-art of systems developed
for MIUS application. EPA», NASA, DOD, and other government agencies are
apparently members of an advisory panel to aid in MIUS development. A contin-
uing and expanded demonstration program is the likely future direction.
326
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250. McCartey, P., "Anaerobic Waste Treatment Fundamentals: Part III -
1964) er±alS and Their Control", Public Works, pp. 91-94 (November
251. Malina, J. F., "Anaerobic Waste Treatment", Process Design in Water
Engineering, University of Texas (1967).
252. Kugelman, I. J., and Chin, U. K., Ed. by Pohland, F. G., "Toxicity,
Synergism and Antagonism in Anaerobic Waste Treatment Processes",
Conference on Anaerobic Biological Treatment Processes, Advances in
Chemistry, Series 105, American Chemical Society, Washington, D.C.,
pp. 55-91 (1971).
253. Ghosh, S. and Klass, D. L., 1976, SNG from Refuse and Sewage Study by
the Biogas Process, Symposium Papers on Clean Fuels from Biomass,
Sewage, Urban Refuse, and Agricultural Wastes, Institute of Gas Tech-
nology.
254. Douglas, R. W. , 1976, Synthetic Natural Gas from Animal Waste by
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Sewage, Urban Refuse, and Agricultural Wastes, Institute of Gas
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255. Harris, E. E., 1949. Wood Saccharif icat ion iji Advances in Carbohydrate
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256. Converse, A. 0., Grethlein, H. E., Karandikar, S., and Kuhrtz, 1973.
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to Alcohol. EPA 670/2-73-11.
257. Huffman, G. L. , "Processes for the Conversion of Solid Wastes and Biomass
Fuels to Clean Energy Forms," A Conference on Capturing the Sun Through
Bio con version, March 10-12, 1976, Washington, D. C. , pp 454-484.
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and Demonstration Program. Solar Energy Division of ERDA.
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345
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
. REPORT NO.
EPA-600/7-78-204
3. RECIPIENT'S ACCESSION-NO.
TITLE AND SUBTITLE
PRELIMINARY ENVIRONMENTAL ASSESSMENT
OF BIOMASS CONVERSION TO SYNTHETIC FUELS
5 REPORT DATE
October 1978 issuing date
6. PERFORMING ORGANIZATION CODE
. AUTHOR(S)
S. T. DiNovo, W. E. Ballantyne, L. M. Curran,
W. C. Baytos, K. M. Duke, B. W. Cornaby, M. C. Matthews
R, a Kvrinr, ' xrt* P W ulfion J
8. PERFORMING ORGANIZATION REPORT NO
9, PERFORMING bti'GANrzATibN N'AME'AND'ADDRESS
Battelle Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
10. PROGRAM ELEMENT NO.
EHE 624
11. CONTRACT/GRANT NO.
68-02-1323
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Lab. - Cinn, OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Assessment, July-Dec. 1976
14. SPONSORING AGENCY CODE
EPA/600/12
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A preliminary evaluation of biomass production and conversion technologies,
and their associated environmental consequences. Five categories of biomass
production were considered in detail. Thermochemical and biochemical technology
were considered for conversion processes. Regionalized scenarios were prepared
utilizing commercial scale plants processing appropriate regionalized feedstock.
Most processes use heterogeneous solid waste as a feed stock which are believed
to pose more severe control requirements for emissions and effluents than other
biomass feedstocks. The environmental and socio-economic effects of locating
large conversion plants in rural environments need to be studied.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Biomass
Agricultural Wastes
Forestry
Aquaculture
Fuels
Agronomy
Industrial Wastes
Horticulture
Silviculture
Plant equipment
Organic properties
Chemical thermodynamics
Conversion techniques
Power sources
Agronomy and horticultur
Energy crops
2 ID
07A
07C
07D
10A
10B
02D
02F
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)'
UNCLASSIFIED
21. NO. OF PAGES
366
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
346
U. S. GOVERNMENT PRINTING OFFICE: 1978-657-060/1506 Region No. 5-||
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