EPA
United States
Environmental Protection
Agency
Office of
Research and
Development
Municipal Environmental Research
Laboratory
Cincinnati, Ohio 45268
EPA-600/7-78-047
March 1978
PRELIMINARY ENVIRONMENTAL
ASSESSMENT OF ENERGY
CONVERSION PROCESSES FOR
AGRICULTURAL AND FOREST
PRODUCT RESIDUES;
Volume I
Interagency
Energy-Environment
Research and Development
Program Report
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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-600/7-78-047
March 1978
PRELIMINARY ENVIRONMENTAL ASSESSMENT OF
ENERGY CONVERSION PROCESSES FOR
AGRICULTURAL AND FOREST PRODUCT RESIDUES
Volume I
by
Benjamin J. Gikis, F. Alan Ferguson, Jerry L. Jones, M.C.T. Kuo,
Clyde L. Witham, Shirley B. Radding, Jean S. Smith,
Constance T. Warmke, Katherine A. Miller,
John A. Alich, and Peter D. Stent
Stanford Research Institute
Menlo Park, California 94025
Contract No. 68-01-2940
Project Officer
John 0. Burckle
Solid and Hazardous Waste Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL 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 Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publication.
Approval does not signify that the contents necessarily reflect the views and
policies of the U.S. Environmental Protection Agency, nor does the mention
of trade names or commercial products constitute endorsement or recommendation
for use.
ii
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FOREWORD
The Environmental Protection Agency was created because of increasing
public and government concern about the dangers of pollution to the health
and welfare of the American people. Noxious air, foul water, and spoiled
land are tragic testimony to the deterioration of our natural environment.
The complexity of that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem solution
and it involves defining the problem, measuring its impact, and searching for
solutions. The Municipal Environmental Research Laboratory develops new and
improved technology and systems for the prevention, treatment, and management
of wastewater and solid and hazardous waste pollutant discharges from municipal
and community sources, for the preservation and treatment of public drinking
water supplies, and to minimize the adverse economic, social, health, and
aesthetic effects of pollution. This publication is one of the products of
that research; a most vital communication link between the researcher and the
user community.
With rapidly rising prices for energy, there has been increased interest
in obtaining energy from sources other than fossil fuels. The research con-
tained in this report investigated the environmental effects of selected
energy conversion processes for utilizing agricultural and forestry residues.
The conversion processes included direct combustion, co-firing with coal or
lignite, and pyrolysis to produce either gaseous or liquid products. The
results will be useful to decision-makers interested in developing future
energy sources and maintaining environmental quality.
Francis T. Mayo, Director
Municipal Environmental
Research Laboratory
iii
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ABSTRACT
I The goal of this project was to determine 1 in a preliminary study, j_the
environmental impacts of several types of conversion processes that could
produce energy or fuels from agricultural and forestry residues.[
^—1
1 Fifteen cases were chosen to be representative of the various combina-
tions~~"of agricultural residues and conversion processes available in various
geographic regions.] Technologies included gasification-pyrolysis (Purox),
liquefaction-pyrolysis (Tech-Air), combustion (direct firing both large and
small scale), co-combustion with coal (both large and small scale), and
anaerobic digestion.
Residues included in the study include manure and forestry, sugar cane
field, and field crop residues. Special attention is given to the pesticide
and herbicide residues and their ultimate fate in the conversion processes.
Material balances are developed for each case, and special effort is
given to include emissions from all sources—including harvesting, transpor-
tation, and feed preparation as well as from the conversion process itself.
The data generated are compared to expected emissions from coal combustion
and coal gasification processes on a net Btu basis to determine the relative
environmental impact of the alternatives.
Residue density maps were prepared and utilized in the selection of
sites with the highest geographic densities of residues.
This report was submitted in fulfillment of Contract No. 68-01-2940
by Stanford Research Institute International under the sponsorship of the
U.S. Environmental Protection Agency. This report covers the period
June 12, 1976, to April 30, 1977, when work was completed.
iv
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CONTENTS
Foreword
Abstract
Figures
Tables viii
Conversion Units xii
1. Introduction 1
2. Conclusions 2
3. Recommendations 6
4. Process and Site Selection Data 7
5. Residue Data 10
6. Pesticide Data 20
Pesticide usage 20
Pesticides and herbicides used on sugarcane in Florida .... 27
Pesticides used on cattle manure in Colorado 29
Pesticides and herbicides used on wheat in Colorado 32
Pesticide and heavy metal residue in chicken manure
in Arkansas 33
Pesticide used in forestry applications in the United States . 35
Pesticides and herbicides used on field crops 36
7. Collection and Transportation 38
Forestry residue 38
Sugarcane trash 39
Transportation of crop residue to power plants 41
Manure 41
8. Anaerobic Digestion 43
Locations 43
Process description 43
Environmental analysis 50
Potential process problems 53
9. Direct Firing of Residue 57
Introduction 57
Process description 57
Process feeds 57
Land disruption from conversion process 58
Direct combustion of forestry residue 59
Direct combustion of sugarcane residue 62
Cofiring with coal in a stoker-fired boiler 66
10. Large-Scale Cofiring with Coal 76
Cofiring of forestry wastes with coal 76
Cofiring of sugarcane field wastes with coal in
large utility boilers 76
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11. Pyrolysis Technology 78
Introduction 78
Processes 81
Process feeds 82
Tech-air with wood residue 85
Purox* with wood residue 102
Tech-air with rice and cotton wastes Ill
Purox* with rice waste 112
Purox* with barley and cotton waste 121
References 129
Appendices
A. Anaerobic digestion - supplemental data 132
B. Environmental analysis assumptions, calculations,
and data summary 151
C. Data comparison for bio-gas, CRAP, and SRI model cases .... 162
*Registered trademark
vi
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FIGURES
Number Page
1 Density of manure residue 12
2 Density of logging residue 14
3 Density of crop residue 16
4 Density of total residue 18
5 Pathways for the methane fermentation of complex wastes 44
6 Anaerobic process for manure digestion 46
7 Sample plot plan showing 32 digesting tanks 47
8 Energy production and consumption of anaerobic digestion process
using various agricultural wastes as digester feed 48
9 Simplified material balances 49
10 Material balance 51
11 Land requirements 54
12 Input water requirements 54
13 NO emissions 55
x
14 S02 emissions 55
15 Particulate emissions 56
16 Solid wastes 56
17 Direct firing of sugarcane trash 62
18 Cofiring with coal in a stoker-fired boiler 67
19 Georgia Tech pyrolysis process « 87
20 Purox* process 103
C-l CRAP system mass balance 162
C-2 Bio-Gas Inc. system mass balance 163
*Registered trademark
vii
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TABLES
Number Page
1 Environmental Impact 3
2 Sites and Processes 8
3 Conversion Technology 9
4 Physical Properties of Pesticides Applied to Cotton
and Barley in California 22
5 Physical Properties of Pesticides Applied to Cotton
in Mississippi 26
6 Sugarcane Pesticides 28
7 Pesticides Used for Fly Control in Cattle Feedlots 29
8 Mist Spray Calculation 31
9 Pesticides and Herbicides Applied to Wheat in Colorado 32
10 Fly Sprays and Application Rates 34
11 Forest Area Aerially Sprayed with Insecticides in the U.S 36
12 Estimated Emissions from Equipment Used to Transport
Cane Trash 41
13 Emission from Equipment Used to Transport Residue 42
14 Quantities of Waste Material Used in Anaerobic Digestion 45
15 Precipitation and Evaporation Rates 52
16 Sample Environmental Analysis Worksheet 52
17 Material Balance 60
18 Environmental Impacts of Direct Combustion of Logging
Residue, Humboldt County, California 61
viii
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Number Page
19 Material Balance for Sugarcane Trash Combustion 63
20 Environmental Impacts, Direct Combustion of Sugarcane Trash .... 64
21 Material Balance 72
22 Emissions 72
23 Energy Balance 73
24 Energy Consumption and Particulate Emission for Dryer 73
25 Material Balance Output 74
26 Land Usage for Crop Residue 75
27 Comparison of Air Emission 77
28 Pyrolysis and Gasification Reactions 79
29 Approximate Analysis of All Other Components 83
30 Assumed Analysis of Rice Hulls and Straw 83
31 Assumed Analyses of Barley Straw and Cotton Mixed Waste
Feed (Moisture Free Basis) 86
32 Tech-Air Pyrolysis Process Stream Flows 88
33 Fuel for Wood Drying 90
34 Diesel Engine Emissions 94
35 Analysis of Dryer Stack Effluents 95
36 Environmental Impacts of Tech-Air Pyrolysis of Wood Residue .... 96
37 Compounds Formed by Wood Carbonization 97
38 Compounds Reported to be Present in Hardwood Smoke 99
39 Comparison of Wood Residue and Refuse Composition 104
40 Purox® Product Gas Analysis (from Wood Residue Feed) 104
41 Disposition of Minor Constituents in Wood Residue Fed
to Purox® Process 105
ix
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Number Page
42 Environmental Impact of Purox® Pyrolysis of Wood Residue ..... 109
43 Estimated Disposition of Trace Elements in Wood Residues
Fed to Purox® System ...................... 110
44 Comparisons of Rice Waste and Refuse Composition ......... 112
45 Assumed Off gas Composition from Rice Waste Pyrolysis
via Purox® Process .......................
46 Purox® Process Stream Flows Using Rice Waste Feed ......... 114
47 Minor Elements Reported Present in Rice Hulls ........... 115
48 Sensible Heat Requirements .................... 116
49 Environmental Impacts of Purox® Pyrolysis of Rice Waste ...... 120
50 Comparisons of Barley/Cotton Waste and Refuse Compositions .... 121
51 Assumed Offgas Composition from Barley/Cotton Waste
Pyrolysis via Purox® Process .................. 122
52 Purox® Process Stream Flows Using Barley and Cotton
Waste as Feed .......................... 123
53 Environmental Impacts of Purox® Pyrolysis of Barley
and Cotton Waste ........................ 128
A-l Waste Characteristics ....................... 140
A-2 Summary of Assumptions for Determining f , G, and f , ....... 141
A-3 Material Balance for Fresh Cattle Manure as Digester
Feed with Liquid Recycling ................... 144
A-4 Material Balance for Five-Month-Old Cattle Manure as
Digester Feed with Liquid Recycling ............... 145
A-5 Material Balance for Fresh Manure and Wheat Residue as
Digester Feed with Liquid Recycling ............... 146
A-6 Material Balance for Chicken Manure as Digester Feed
Without Liquid Recycling .................... 147
A-7 Material Balance for Chicken Manure as Digester Feed
with Liquid Recycling ...................... 148
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Number Page
A-8 Sulfur and Nitrogen Emission per 106 Btu Net Supply
Production for Anaerobic Digestion Process 149
A-9 Sulfur and Nitrogen Emission Per Day for Anaerobic
Digestion Process 150
B-l Coal-Fired Power Plant Emissions to Air 151
B-2 Water Requirements for Coal-Fired Power Plant 152
B-3 Coal-Fired Power Plant System Emissions and Land Disturbance . . . 153
B-4 Coal Combustion for Electric Power Generation 154
B-5 Coal Gasification with Lurgi Technology 155
B-6 Water Requirements for Coal Gasification Using Lurgi
Technology 155
B-7 Lurgi Coal Gasification Plant Emissions and Land Disturbances . . . 156
B-8 Coal Gasification 157
B-9 Anaerobic Digestion 158
B-10 Anaerobic Digestion 159
B-ll Anaerobic Digestion 160
B-12 Anaerobic Digestion 161
C-l Comparison of Parameters Used by Bio-Gas, Inc. and
SRI for Cattle Manure 164
C-2 Comparison of Selected Parameters for Bio-Gas, Inc.,
CRAP, and SRI Model Cases 165
xi
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CONVERSION UNITS
Some English units that are still in common use are employed in this
report. The following table lists the factors to be used to convert English
units to metric.
Multiply
English unit
acres
acre-feet
barrel, oil
British thermal unit
By
conversion
0.405
1233.5
158.97
0.252
To obtain
metric unit
hectares
cubic meters
liters
kilogram-calories
British thermal unit/
pound
cubic feet/minute
cubic feet/second
cubic feet
cubic feet
cubic inches
degree Fahrenheit
feet
gallon
gallon/minut e
horsepower
inches
inches of mercury
pounds
million gallons/day
mile
pound/square inch
(gauge)
square feet
square inches
tons (short)
yard
0.555
0.028
1.7
0.028
28.32
16.39
0.555(°F -
0.3048
3.785
0.0631
0.7457
2.54
0.03342
0.454
3785
1.609
(0.06805 psig +
0.0929
6.452
0.907
0.9144
1)
a
kilogram calories/kilogram
cubic meters/minute
cubic meters/minute
cubic meters
liters
cubic centimeters
cegree Celsius
meters
liters
liters/second
kilowatts
centimeters
atmospheres
kilograms
cubic meters/day
kilometer
atmospheres (absolute)
square meters
square centimeters
metric tons (1000 kilograms)
meters
^Actual conversion, not a multiplier.
xii
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SECTION 1
INTRODUCTION
As a result of the energy crisis and the dwindling reserves of
conventional fossil fuels, much attention has been focused on the use of
waste materials and byproducts as sources of energy. Renewable resources
such as agricultural crop wastes, forestry wastes, and cattle manure are all
potential sources of energy and chemical feedstocks. To date, investigations
have considered the technical and economic problems — that is, how much
feedstock is available at what cost, and what are the costs and technical
problems associated with processing the waste? However, little attention has
been given to the environmental effects of using these agricultural reidues
as energy sources.
This study seeks to fill that need by assessing the environmental effects
of several energy conversion processes that use agricultural residue,
forestry residue, or manure as feedstocks. The conversion processes include
direct combustion, cofiring with coal or lignite (on both a large and small
scale), and pyrolysis to produce either gaseous or liquid products.
This study addresses waste availability and emissions from transportation,
pesticide and herbicide residue, and the conversion processes themselves.
The economics of the processes are not a main focus of this project, although
site locations and process selections were based on those combinations that
appear to have the most favorable economics. Conducting an environmental
assessment study of energy systems (including fuel extraction or production,
fuel preprocessing and transport, energy conversion, energy transport, and end
use) is difficult,however, without making a concurrent economic analysis.
This lack of an economic analysis is most severe in the energy conversion
portion. While one can compare the uncontrolled emission from the basic
processing units, the specific contaminant emissions per ton of material
processed or per unit of energy production can, almost without exception, be
controlled to comparable levels for all conversion processes. This control
is strictly a question of cost.
One approach to comparing conversion processes on a common basis is to
specify that emissions are compared for conversion plants producing an energy
product for $X/106 Btu and with capital investment costs ranging from $Y
to Z/106 Btu of daily capacity. Another approach is to specify the emission
levels and then to estimate the cost to achieve these levels. Neither
approach was within the scope of this project.
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SECTION 2
CONCLUSIONS
In this preliminary analysis, we have compared the relative environmental
effects of agricultural residue conversion systems with the most likely
alternative sources of energy — that is, gas- or oil-producing systems (such
as pyrolysis or anaerobic digestion) are compared with a gas-producing process,
namely, coal gasification. Direct combustion of residue is compared with
direct combustion of coal under favorable circumstances (mine-mouth power
plant burning low-sulfur coal). Cofiring is compared with the firing of
100% fossil fuel at the same location. Hence, crop residue cofired with
lignite in North Dakota is compared to the firing of lignite only at the
same location. This technique allows an assessment of the relative effects
of using the agricultural residues.
The format is similar to that of the Council on Environmental Quality
in that all effects are considered from resource extraction through the
conversion plant. Because the energy output from a coal conversion plant
and an agricultural residue processing plant differs, the results are compared
on the basis of units per million Btus produced. In calculating the net
energy produced from gas-producing processes, we have assumed that purchased
electric power is generated by coal-fired power plants with no transmission
losses and a plant thermal efficiency of 40%. In calculating the net outputs
a figure equal to the Btu equivalent of the fuel burned to produce the
'electric power is subtracted from the energy output of the coal gasification
and the residue processing systems. The pollutants generated in the production
of electric power for use at the gas-producing facilities are shown on the
emissions comparison tables, along with the emissions of the gas-producing
facilities.
The standard of comparison for a coal-fired power plant is a new mine-
mouth power plant burning 0.8% sulfur coal and using flue gas desulfurization
to reduce S02 emissions to 0.83 lb/10b Btu. The cofiring standard of
comparison uses locally available coal or lignite and does not use flue gas
desulfurization and particulate data presented for cases with and without
control measures.
The environmental impact data are summarized in Table 1. One important
point to note is that no wastewater need be discharged in areas with high net
evaporation rates. Purox® pyrolysis technology for Humboldt County,
California, and direct firing or cofiring processes to be located in Florida,
Alabama, Missouri, and Iowa may not be able to use evaporation ponds. In
all other cases, the wastewater is sent to evaporation ponds. This reflects
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TABLE 1. ENVIRONMENTAL IMPACT
Acres/
Case 10 /Btu/vr
Waste N- b
Water input water output ^
S02C
H2S
Air Emissions
Particulates CO
Hydrocarbons waete
Gas- and Oil-Producing Processes
Coal gasification - comparison case
(with environmental controls)
Anaerobic digestion
Cattle manure - Weld Co., Colorado
Cattle manure and wheat residue - Weld
Co. , Colorado
Chicken manure - Washington Co., Arkansas
Pyrolysis - Purox®
Wood - Humboldt Co., California
Rice - Cutter Co., California
Cotton and barley - Kern Co., California
Pyrolysis - Tech-Air
Wood - Humboldt Co., California
Cotton and rice - Bolivar Co., Mississippi
Coal combustion - comparison case,
mine-mouth power plant, low sulfur coal
Direct firing
Wood - Humboldt Co., California
Sugarcane residue - Hendry, Florida
Large scale
Wood and coal (25/75) - Green Co., Alabama
Coal only - Green Co., Alabama
Sugarcane and coal (25/75) - Hendry,
Florida
Coal only - Hendry, Florida
Small scale
Crops and lignite (25/75) - Tralll, N.D.
Lignite only - Traill, North Dakota
Crops and coal (25/75) - Marshall, Mo.
Coal only - Marshall, Missouri
Crops and coal (25/75) - Slbley, Iowa
Coal only - Siblcy, Iowa
0.014
0.25
0.113
0.116
<0.01
0.08
0.03
<0.01
N/A
0.085
0.001
0.011
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the anticipated planning of the process designs to avoid wastewater discharge
in excess of EPA standards. Actual wastewater generated by these processes
is quite low (a maximum of 8 gal/106 Btu output)*, which again reflects
proper process design to eliminate unnecessary wastewater discharge and to
achieve minimum water usage.
The data compare favorably with the coal combustion and coal gasification
standards of comparisons. In most cases, NOX emissions are lower in coal
combustion, and S02 emissions are lower when low-sulfur feedstock is used
exclusively. In cofiring, local coals are assumed as feedstocks and the
potential emission of SC>2 is quite high, thus requiring flue gas desulfur-
ization to meet environmental standards. Solid wastes are lower, and no
hard evidence is indicated of pesticide residue reentering the environment
in significant quantities. Since particulate emission tends to rise in
most cases of residue combustion, proper attention to particulate removal
must be given by the design engineers.
The following conclusions can be drawn from this study:
1. Organic pesticide residues found in crops are generally destroyed in
thermal processes, although some volatile compounds may be distilled
in the drying steps.
2. Pesticide residue is generally very low for crop and logging
residue.
3. Heavy metals (such as arsenic) are used in chickenfeed supplements
and cotton crops; these metals could present a serious process
and environmental problem.
4. Many sites in the United States have a high density of agricultural
residues making conversion processes more likely to be economically
feasible. However, economics generally prevent use of the technol-
ogies. In cases where a disposal cost is associated with a residue
(such as manure), the conversion processes may be economically
attractive.
5. Many highly carcinogenic compounds are found in pyrolysis oils,
such as the oil produced by the Tech-Air process.
6. Data are sparse on the combustion of agricultural residue in boilers;
no data exist on the cofiring of agricultural or forestry residue in
coal.
7. Some data indicate that removal of crop residue and forestry residue
(especially stumps) is detrimental to the soil condition and that
fertilizer is needed to replace the nutrients of the material removed.
Also, the removal of stumps in forests may increase erosion. However,
other data indicate that the removal of residue helps control rodents,
insects, and crop disease.
*
English measurements were the primary units of measure used during the
preparation of this study. For the convenience of the reader, a table
converting the units of measure to the metric system can be found
immediately preceding Section 1.
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8. The technologies discussed in this report are in various stages of
development. For instance, wood combustion has been practiced for
years; several wood-fired boilers are in operation. Conversion of
forestry residue may present some problems, however. Other
technologies, such as Purox®, have not yet been demonstrated on
agricultural residue.
9. It is difficult to accurately predict soil inclusion in agricultural
residues without specifying the harvesting technique as well as the
weather and soil condition at the time of harvest. Herbicide
residues in the soil which may be collected along with the
agricultural residues may present environmental problems resulting
from the collection and conversion processes.
10. In some combustion processes, the production of high-resistivity
fly ash could complicate the efficient operation of electrostatic
precipitators.
11. In general, it may be stated that solid waste disposal problems are
alleviated by the technologies being studied. However, because of
the differences in the basic processes and feedstocks considered
and used for residues, it is difficult to draw any firm conclusions
concerning the relative solid waste impacts.
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SECTION 3
RECOMMENDATIONS
Since this study is a preliminary assessment of environmental problems
associated with the use of agricultural residue, the main purpose is to
identify areas where potential environmental problems exist and where data
are needed. Recommendations for further work include a study of the process
economics and the specific environmental areas where data are lacking.
Specifically, in the areas of direct firing and cofiring of residue, data
are sparse. A complete emissions inventory on a specific proposed process
is needed, since the emissions may vary greatly from process to process,
even though the technologies are similar. Similarly, little data exist on
the nitrogen oxide emissions for these conversion processes. Particulate
emissions and control techniques are also difficult to estimate, as they
depend highly on the configuration and operating parameters of the combustion
processes.
Detailed studies are needed on the inclusion of herbicides and heavy
metals in agricultural residue and their end products in the processes.
Again, many variables are involved and a specific case must be evaluated
that includes specified collection, feed preparation, and conversion
technologies.
®
To date, the Purox process has not been demonstrated on agricultural
residue. Such a demonstration, with associated emissions data collection,
might be the most economical way to evaluate the process and collect the
required data.
Consideration should be given to the effect that removing residue from
the fields and forests has on the nutrient concentrations in the soil and
on erosion. Such a study is beyond the scope of this report.
Cofiring technology needs a study of the problems associated with feed
preparation and the handling of residue. Equipment design and operating
economics need to be determined and the overall effect on emissions must
be calculated.
As further specific technologies are proposed, they should be evaluated
in a preliminary manner. In this study, only a limited number of cases
could be considered.
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SECTION 4
PROCESS AND SITE SELECTION DATA
The specific processes and sites evaluated in this project were
selected at the outset of the project through discussions between Stanford
Research Institute (SRI) and the Environmental Protection Agency (EPA).
The six processes assigned by EPA included two pyrolysis processes (Purox®
and Tech-Air), anaerobic digestion, direct firing, large-scale cofiring, and
small-scale cofiring. After reviewing the waste inventory data, 15 cases
were selected. These cases represented at least two of each process, and a
total of 11 different locations. Table 2 shows the residue type and the
conversion technologies chosen. The numbers correspond to the specific
case numbers in Table 3. The process and site selection were based on
availability of large quantities of residue and on the suitability of the
specific process to handle the given feedstock. Those feedstocks (residue)
that are disposal problems or that are of little commercial value were given
high priority.
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TABLE 2. SITES AND PROCESSES
Case
No.
Location
Residue
Process
1 Humboldt County,
California
2 Humboldt County,
California
3 Humboldt County,
California
4 Green County,
Alabama
5 Weld County,
Colorado
6 Weld County,
Colorado
7 Washington County,
Arkansas
8 Sutter, Butte and
Colusa Counties,
California
9 Kern County,
California
10 Bolivar County,
Mississippi
11 Hendry and Palm
Beach, Florida
12 Hendry and Palm
Beach, Florida
13 Trail!, North
Dakota and
surrounding counties
14 Marshall, Missouri
and surrounding
counties
15 Sibley, Iowa and
surrounding counties
Forestry residue
Forestry residue
Forestry residue
Forestry residue
Cattle manure
Cattle manure mixed
with wheat residue
Chicken manure
Rice hulls and rice
straw
Cotton field waste,
cotton gin waste,
and barley straw
Cotton gin waste,
cotton field waste,
rice hulls, rice
straw
Sugarcane tops and
leaves
Sugarcane tops and
leaves
Barley, wheat and
sunflower residue
Wheat and field
corn waste
Field corn residue
Large-scale pyrolysis
(Purox®)
Small-scale pyrolysis
(Tech-Air)
Direct firing in
large utility boiler
Cofiring with coal in
large utility power
plant
Anaerobic digestion
Anaerobic digestion
Anaerobic digestion
Large-scale pyrolysis
(Purox®)
Large-scale pyrolysis
(Purox®)
Small-scale pyrolysis
(Tech-Air)
Direct combustion
Large-scale cofiring
with coal
Small-scale cofiring
with lignite in a
stoker-fired boiler
Small-scale cofiring
with coal in a stoker-
fired boiler
Small-scale cofiring
with coal in a stoker-
fired boiler
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TABLE 3. CONVERSION TECHNOLOGY
Residue
Forestry residue
Cattle manure
Cattle manure and wheat
Chicken manure
Cotton field and cotton
gin waste
Cotton field and cotton
gin waste plus barley
waste
Rice straw and rice hulls
Rice straw and hulls
plus cotton field plus
cotton gin waste
Sugarcane waste
Wheat, barley, sunflower
Wheat and field corn
Corn
Anaerobic
digestion
5
6
7
Large-scale
pyrolysis
(Purox®)
1
8
Small-scale
pyrolysis
(Tech-Air)
2
9
10
Direct
firing
3
11
Large-scale
cof iring
with coal
(St. Louis)
4
12
Small-scale
cofiring
with coal
(Battelle)
13
14
15
-------
SECTION 5
RESIDUE DATA
This section contains the residue density maps (Figures 1 through 4)
prepared from the computer printout of the data in volume 2. The four
residue categories presented are: crop residue, forestry (logging) residue,
livestock (manure) residue, and total residue. The basic data for this study
was taken from the National Science Foundation Data Bank of Agricultural
Residues (prepared by Stanford Research Institute under Grant No. AER74-18615
A03-NSF/RANN/SE/GI/18615/FR/76/3), which lists residue by state and county.
In this study, the data are grouped by agricultural regions within the
states. Each region is an area of similar agricultural activity having a
radius of approximately 50 miles. Generally, each region incorporates more
than one county.
The data represent only the available residue, those that are
realistically retrievable. Also, the data are corrected for moisture and
are presented on the basis of dry tons per year. The livestock (manure)
data are based entirely on confined feeding (feedlot). Logging residue
includes those residues left in the forest during logging operations as well
as mill residue at primary wood product plants (wood and bark). Crop
residue estimates are based on residue factors developed for each crop
(amount of residue per ton of product). These factors were applied to
production data during 1971-1973 to generate average annual quantities. Hay
and forage crops are specifically excluded.
The data are reported both as total dry tons by region and as a
density (dry tons per square mile). The crop residue, logging residue,
and total residue data are presented on the map as dry tons per square
mile. The manure data are presented slightly differently. Since the manure
is from a totally confined feeding operation (feedlots) the per-square-mile
approach is not meaningful. The more useful number is total dry tons per
year, and the numbers are presented in this way.
10
-------
This page intentionally left blank to permit the
maps in Figures 1 through 4 to be presented on
facing pages.
11
-------
NORTH DAKOTA
MANURE AVAILABLE RESIDUES
(Thousand dry tons per year)
1 1
50-249
I'ffiffi] 250-449
[iv;:^ 450+
j M1KINK
r^mi$jik
wtwMttwiMtf!
NE .
?M
iraW
24^
i»i'.
Hi
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12
-------
'TA
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V ...• -
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-;: -• ';:; \ S
1
«AS
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MICHIGAN
£. -NVtf**
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11 (-I
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Figure 1. Density of manure residue.
13
-------
LOGGING RESIDUES DENSITIES
(Dry tons per square mile)
I I <50
50-249
250-449
PSP 450+
14
-------
FUORIDV
Figure 2. Density of logging residue.
15
-------
W*-^m (
s
mm ••'•:-'
p|
;S
:/
S
CROP RESIDUES DENSITIES
(Dry tons per square mile)
< 50
~] 50-249
^ 250-449
:Sl 450+
16
-------
-------
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1
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OKLAHOMA
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TOTAL RESIDUES DENSITY
(Dry tons per square mile)
< 50
I 50-249
1 ' - •'
[',%£] 250-449
W$£\ 450+
TEXAS
V
\
\;
18
-------
Figure 4. Density of total residue.
19
-------
SECTION 6
PESTICIDE DATA
PESTICIDE USAGE
For each residue studied, data were collected and evaluated regarding
pesticide and herbicide usage and residual levels. In most cases, the
residual levels were quite low and are probably not significant to the
environment. This is especially true of forestry waste (since little
pesticide is used) and of crop waste (since tolerance levels on food crops
are quite stringent). Even cattle manure pesticide residues were quite low.
The main area of concern is with arsenical feed supplements in chicken
manure. Most of the arsenic in the feed is passed through the chicken and
is present in the manure pile. Since it is an inorganic heavy metal, it
passes through the anaerobic digestion process and is returned to the
environment.
The following paragraphs explain the pesticide usage data and the
assumptions made regarding pesticide residue in the agricultural residue
used as feedstocks in the conversion processes.
Rice (Sutter, Butte, and Colusa Counties, California)
Eight pesticides are used on rice in Sutter, Butte, and Colusa Counties,
California and can be expected to be found on the hulls and straw:
Furadan® MCPA
Ordram® Parathion
Propanil Sevin®
Toxaphene 2,4-D
Degradation of Propanil (1 to 3 days), Toxaphene (5 to 14 days), and
2,4-D (1 to 4 weeks) is fairly rapid and, since these pesticides are applied
2 to 3 months before harvesting, the amount remaining on the hulls and straw
should be extremely small. The products of degradation of these three
pesticides are not known.
Furadan® degrades at an intermediate rate. In soil, the concentration
is reduced 96% in 55 days. The degradation products are unknown.
MCPA, Ordram®, Parathion and Sevin® are all fairly stable pesticides.
The tolerances that should represent the maximum concentration of the
pesticide on the hull or straw are:
20
-------
Tolerance
(ppm)
MCPA 0.1
Ordram® 0.1
Parathion, mg/m3 0.05
Sevin® 100
Ordram® and Parathion, both liquids at room temperature, exhibit small
but significant vapor pressures at 120° to 200°C. These compounds (or in the
case of Parathion, an isomer) might be distilled from the pyrolysis furnace
and concentrated in the oil or water fractions. The allowed tolerances
for Ordram® and Parathion are low. If all the allowable residue were to
distill into the water, a maximum of 0.012 Ib/hr would be present. The
concentration in the condensate would be, at most, 0.8 ppm by weight.
MCPA and Sevin® have higher boiling points and would probably
decompose or react to form combustion products (H20, C02>• Other less
desirable combustion products could also be formed. For example, the active
ingredient in Sevin® is a carbamate which contains nitrogen. Midwest Research
Institute, in a study on pesticide incineration,1 found hydrogen cyanide
in the offgases from incineration of nitrogen-containing pesticides. The
active ingredient in Ordram® also contains nitrogen, so any decomposition
of Ordram® that occurs in the converter could also result in hydrogen
cyanide. If Sevin® and Ordram® were present at their tolerance levels and
all of the contained nitrogen were converted to hydrogen cyanide, 1.1 Ib/hr
of cyanide would be present in the product gas.
Ordram® and Parathion also contain sulfur, so decomposition of these
pesticides is likely to produce some volatile sulfur compounds, such as
hydrogen sulfide or sulfur dioxide. The quantitites of these materials
that could be produced would not be significant as air pollutants.
Other volatile decomposition products might also be formed but SRI
found no information as to what these products might be.
Cotton and Barley (Kern County, California)
The physical properties of the 20 pesticides applied to cotton and
barley in California are shown in Table 4. Of the 20 pesticides, 7 degrade
fairly rapidly in the field and are not likely to be found in any
significant amounts on the waste when it is ready to be processed. The
seven are:
Toxaphene Azodrin® Barban
2,4-D Di-Syston® Omite®
Methomyl
Superscript numbers refer to documents cited in text. For a complete list
of references, see the end of this report.
21
-------
TABLE 4. PHYSICAL PROPERTIES OF PESTICIDES APPLIED TO COTTON AND BARLEY IN CALIFORNIA
ho
NJ
Pesticide
Cacodylic
acid
Diuron
(Karmex®)
Nitralin
(Planarum)
Paraquat
Methomyl
Azodrin®
Demeton
Phorate
Melting
Physical point
state (°C)
Solid 200
Solid 158-159
Solid 151-152
Solid Not given
(applied as
solution)
Solid 78-78
Redbrown 53-55
solid
Light
brown
liquid
Clear
liquid
Boiling
point
(°C)
—
Decomposes @
180-190°C;
vp« 148xlO-5
@ 100°C
Decomposes
vigorously
@ 225°C;
vp 1.8xlO-8
,@ 25°C
Decomposes;
does not melt
or boil but
chars; non-
volatile
vp 1.6xlO-4
mmHg @ 40°C
vp 7xlO~7
mmHg @ 20°C
123-218°C
@ 1 mmHg
118-120°C
@ 0.8 mmHg
Solubility
Alcohol, H20
Acetone,
benzene,
cottonseed
oil; 42 ppm
in H20
Acetone, DSMC,
2-nitro-pr opane ,
benzene;
0 . 6 ppm in H20
H20; insoluble
in organics
H20, ethanol,
methanol
H20, acetone,
alcohol
Organic
solvents;
60 ppm in H20
Xylene, other
organics;
Degradation
Does not degrade on
plant
Degrades slowly
(1 year)
Degrades slowly;
sensitive to UV
Very stable;
sensitive to UV
Appears to degrade
in 7-14 days
Degrades in 1-2 wk
^^
Tolerance 1 ppm;
stable 2 yr
50 ppm in H20
-------
TABLE 4 (continued)
Ni
UJ
Pesticide
Kelthane®
Di-Syston®
Omite®
Treflan®
Def®
Sodium
chlorate
Toxaphene
Parathion
MCPA
2-4-D
Melting Boiling
Physical point point
state (°C) (°C)
Solid 77-78
Liquid — 62 °C
0.01 mmHg
Liquid
See Table 5
See Table 5
See Table 5
Solid 65-95
Liquid — 157-162
Solid 118-119
Solid 135-138
Solubility
Insoluble in
H20; soluble
in aromatic
aliphatic
solvents
Organic
solvents;
25 ppm in H20
Organic solvents;
insoluble in H20
—
—
—
—
Degradation
Appears stable
over 1 yr, but does
degrade considerably
Metabolizes to
sulphoxide and
sulphone
Loses activity in
about 3 wk
—
—
—
—
vp = vapor pressure
-------
Three other products — Treflan®, Diuron (Karmex®) and Nitralin
(Planquin) — are herbicides used to kill weeds. They would not be applied
directly to the weed and would probably not be present on the crop waste.
Paraquat, another herbicide, works by contact with the unwanted plant
rather than attacking the seed. Paraquat could be present in small
amounts on the crop waste. On heating however, Paraquat does not boil or
melt but chars, so if it were present on the crop residue, it would
decompose in the Pyrolysis converter.
The nine other pesticides are sprayed on the crops and degrade slowly,
so they are likely to be present on the waste that is to be processed. Two
of the nine, sodium chlorate and MCPA, would decompose in the converter into
generally harmless products. Not enough information was obtained on the
physical properties of Kelthane® to determine its end products in the
converter. However, it is known to degrade considerably in one year so
little is likely to be present even if it volatilizes and ends up in the
condensate.
Cacodylic acid is another pesticide whose end products in the reactor
are unknown. It is a stable solid having a melting point of 200°C. As an
organic arsenate, it could decompose into an inorganic arsenate and end up
as such primarily in the slag. The inorganic arsenates, however, have
finite vapor pressures so some (perhaps 1%) might report to the condensate.
Under the reducing conditions prevalent in parts of the converter, cacodylic
acid might be reduced to arsine, in which case the toxic arsine would
probably be found in the product gas.
The remaining five pesticides (Parathion, Methyl Parathion, Def®,
Phorate, and Demeton) are all relatively stable, have finite vapor pressures
below their decomposition temperatures, and are likely to report to the
condensate to some extent. The Parathion and methyl Parathion isomerize on
heating so the O.S. diethyl and O.S. dimethyl isomers would be the Parathion
products in the condensate.
The tolerance levels for the five pesticides are as follows:
Parts per million
Parathion 1
Methyl Parathion 0.75 (on cottonseed)
Def® 6 (on cottonseed hulls)
Phorate 0.1 (on straw)
Demeton 5 (on straw)
Since cotton waste generally does not end up on the food chain, no tolerances
are set for pesticides used on cotton stalks. Tolerances are set for the
concentration of the pesticides that can be present on the cottonseed and
the cottonseed hulls (as shown above) but this does little to establish
the concentration of the pesticide expected on the stalk. Consequently,
24
-------
it is almost impossible to estimate the quantity of these pesticides that
might be preseirt in the condensate.
Paraquat is the only pesticide that contains nitrogen in its structure
and that is likely to be present on the waste fed to the converter. Since
only small amounts of Paraquat are likely to be present on the waste, the
formation of hydrogen cyanide, which is distinctly possible from the
Pyrolysis processing of rice waste, does not appear a problem when the
waste is composed of cotton and barley.
Rice and Cotton (Bolivar County, Mississippi)
The pesticides used on rice in Mississippi are essentially the same as
those in California. Therefore, as far as the eight pesticides (below) are
concerned, their end products would be the same in the Tech-Air system as
in the Purox® system, except any volatile pesticide would be found in the
pyrolysis oil instead of in the condenser wastewater, as in the case in the
Purox® system.
The eight pesticides used on rice are:
Furadan® Propanil
MCPA Sevin®
Ordram® Toxaphene
Parathion 2,4-D
The following ten pesticides are used on cotton in Mississippi:
Caparol® Parathion
Cotoran® Sodium chlorate
Def® Toxaphene
DSMA or MSMA Treflan®
Endrin Folex®
Parathion and Toxaphene are also used on rice, so their end products
in the pyrolysis system would be the same if they came from rice.
(Toxaphene degrades rapidly, so it would not be present as such on cotton-
waste; its degradation products are not known. Parathion is stable and could
end up in the pyrolysis oil.)
Some of the physical properties of the eight other pesticides are given
in Table 5. Caparol® and Cotoran® degrade fairly rapidly (30 to 90 days)
and would normally be present in very minor amounts on the cottonplant at
anytime, even less so at harvest.
Treflan® is an herbicide used primarily prior to the emergence of the
cotton. If applied past emergence, it is laid along the side of the plant.
Except for abnormal situations, Treflan®should not be found on the cotton-
plant .
The remaining five pesticides are fairly stable in the field and are
likely to be present on the plant when it reaches the pyrolysis furnace.
25
-------
TABLE 5. PHYSICAL PROPERTIES OF PESTICIDES APPLIED
TO COTTON IN MISSISSIPPI
Pesticide
Caparol®
Melting
point
(°C)
118-120
Boiling
point
(°C)
vp 1x10- 6 mmHg
@ 20°C
Solubility
48 ppm in
H20; soluble
in organic
solvent
Degradation
Persists
1-3 mo in the
field; should
not be on
cotton plant
Cotoran®
163-164.5
Def®
Liquid
at room
temperature
vp 0.3 mmHg
@ 150°C
80 ppm in
H20; soluble
in ethonol,
aceton, and
isopropanol
Insoluble in
H20, soluble
in organic
solvents
Half-life:
60-75 days
Stable to heat
and acids
DSMA/MSMA 132-139
36% soluble
in H20
Endrin
Folex®
Sodium
chlorate
Treflan®
200
Liquid
at room
temperature
248
48-49
vp 2xlO
@ 25°C
~7
Decomposes
vp 0.18 mmHg
@ 96-97°C
Generally
insoluble
Soluble in
fl20 and
alcohols
Insoluble in
H20; soluble
in acetone
ethanol, and
xylene
Slowly
decomposes
at elevated
temperatures.
Could form
methyl arsine
under reducing
conditions.
Rearranges
when heated
over 200°C
Oxidizes
readily to
DEF
Decomposes on
heating
85-90% is lost
in 6-12 mos
in the field
26
-------
Three of the five, sodium chlorate, Endrin, and DSMA/MSMA, either rearrange
or decompose on heating. The product of rearrangement of Endrin is not
known but is presumably less toxic. Sodium chlorate decomposes to sodium
chloride and oxygen, so no problems are anticipated from this material.
DSMA/MSMA, however, forms a highly toxic methyl arsine at elevated temperatures
under reducing conditions. With a low solubility in water and a boiling point
of 2°C, any methyl arsine formed is likely to end up in the pipeline gas
product.
Def® and Folex® (the remaining pesticides), are defoliants normally
applied on the cottonplant when it is fully grown. Def® is a stable compound;
Folex® oxidizes readily to form Def® so it could be present in measurable
amounts in the pyrolysis oil, if any oil is produced.
PESTICIDES AND HERBICIDES USED ON SUGARCANE IN FLORIDA
Both pesticides and herbicides are used in sugarcane plantations.
Preemergence and postemergence herbicides are both used, but they are
directed onto the weeds and soil, and away from the cane stalks. The two
sources of herbicides in collected cane and cane trash are the overspray
that may fall onto the plant and the soil that may be included in the
collection process. While insecticides are directed onto the plant itself,
residues are minimized by proper timing of the application. Generally,
no sprays are applied within 30 days of harvest. Residues are quite low
and carefully controlled, since some of the bagasse is used as dairy
cattlefeed and the tolerance levels are quite low.
Sugarcane Insect Pests
The following insects cause damage to sugarcane:
Sugarcane borer Sharp-nozed grain leafhopper
Wireworms Spittlebug
Fall armyworm Gray sugarcane mealybug
Climbing cutworm Lesser cornstalk borer
Glassworm White grubs
Yellow sugarcane aphid Leafroller
West Indian sugarcane
delphacid
Pesticides
The pesticides presently used in Florida sugarcane fields are listed
in Table 6.
27
-------
TABLE 6. SUGARCANE PESTICIDES
Application
Trade name Chemical name and manufacturer rate
Azodrin® Dimethyl phosphate of 3-hydroxy-N- 3 to 4 Ib/acre
methyl-cis-cortonamide
(Shell Chemical Company)
Diazinon 0,o-diethyl o-(2-isopropyl-6-methyl- 2 to 4 Ib/acre
4-pyrimidinyl) phosphorothioate
(Ciba-Geigy Corporation)
Parathion 0,o-diethyl o-p-nitrophenyl 2 to 4 Ib/acre
phosphorothioate
(Monsanto and Stauffer)
Furadan® 2,3-dihydro-2,2-dimethyl-7- 2 to 4 Ib/acre
benzofuranyl methyl carbamate
(FMC Corporation)
Residue Concentration
Assuming four applications of each of the above pesticides at the
highest level indicated, a maximum of 64 Ib (4 x 4 x 4) would be applied
per acre. Since about 100 tons of cane plant are produced per acre, the
concentration would be <0.03% wt of pesticide residue. If we consider only
the pesticide that touches the plant (i.e., overspray), the maximum
concentration is less than 0.02% wt. Also, since one-third to one-half
of the pesticides are applied to the plantings and immature stalks, and no
pesticides are applied within 30 days of harvest, concentrations at harvest
are probably much less than 100 ppm. Estimated actual pesticide residues
in the collected cane and leafy trash are 1 to 10 ppm.
Herbicides for Weed Control
The main herbicides utilized in cane fields are AAtrex® (atrazine)
and dalapon.t Both compounds damage plants and care is taken to direct
sprays away from the sugarcane plants. Maximum application for preemergence
or postemergence control is 24 Ib/acre/yr.
Some soil is picked up with the cane and trash; therefore, an estimate
of the herbicide concentration in the collected trash is needed. We assume
Aatrex® = Atrazine, 2-chloro-4-ethylamino76-isopropylamino-S-triazine
(Ciba-Geigy).
Dalapon = Sodium salt of 2,2-dichloropropionic acid (several producers).
28
-------
that about 5% soil is collected in the harvest, that no washing or cleaning
of the cane occurs, and that any herbicides picked up remain with the cane
trash (i.e., the worst case). In fact, the dirt would probably be removed
by either a wet or dry screening before combustion.
Herbicide Soil Concentration
Assuming 24 Ib of herbicide is applied per acre (44,000 ft2) and no
degradation or runoff, the concentration is about 5.45x10-^ lb/ft2. If we
assume a uniform distribution of the herbicide in the top 6 inches of soil,
then the concentration is 1.09xlO~3 lb/ft3. Since the soil is a wet, heavy
muck, its density is over 100 lb/ft3. Therefore, the final herbicide
concentration in the soil is 1.09xlO~5 Ib/lb soil or around 11 ppm. Since
only 5% soil is collected with the can trash, the maximum herbicide
concentration (assuming no degradation or runoff) in the cane trash is less
than 0.5 ppm.
PESTICIDES USED ON CATTLE MANURE IN COLORADO
Cattle manure may contain pesticide residues from three sources:
feed-through fly control, flyspray control, and pesticide residue in the
feed. In this analysis, we assume the worst case (i.e., the maximum
concentration of pesticide residue in the manure). The hypothetical feedlot
is assumed to use both a feed-through and a mist spray to control flies.
Residue from the cattle feed is assumed negligible.
Sprays and Baits
Several pesticides (Table 7) can be used in spray or bait programs for
fly control. The sprays are generally directed onto the manure and are
TABLE 7. PESTICIDES USED FOR FLY CONTROL IN CATTLE FEEDLOTS
Pesticide Level (%) Application method
Rabon®, Ronnel - Feed-through
Dichlorvos 1 Mist spray
Dibrom® 1 Mist spray
Baytex® 1 Residual spray
Cygon® 1 Residual spray
Rabon® 1 to 2 Residual spray
Ravap® 1 to 2 Residual spray
Methoxychlor - Residual spray
Ronnel - Residual spray
Malathion - Residual spray
Trichlorfon (Dipterex®) - Residual spray
Diazinon - Residual spray
Ciodrin® - Residual spray
Dichlorvos 100 lb/5 miles of bunker Bait
29
-------
used 1 to 2 times per week during the fly season (about 4 months' duration)
Mist sprays are used for area-wide control, residual sprays are applied
to specific areas or directly onto the cattle.
Baits also may be used for fly control. Generally, the baits are
spread near the feeding troughs, and not broadcast over the manure. Very
little bait would probably be collected with the manure.
This analysis uses a mist spray program, utilizing both Dichlorvos
and Dibrom®.
Feed-Through
During the fly season, a feed-through may be used. This analysis
considers Rabon®to be fed. The residual Rabon® is excreted and would be
collected with the manure.
Discussion
During the maximum application period, when both sprays and feed-
throughs are used, the maximum concentration of pesticides in the manure
is less than 100 ppm as shown below:
Concentration
(ppm)
Sprays
Dibrom® 33
Dichlorvos 51
Feed-through
Rabon® -10
Total 94
This value (94 ppm) is the maximum that could be expected directly
after a combined spray and feed-through application. Since the pesticides
used are organophosphates and the concentration in the manure is low, no
detrimental effect is anticipated on the anaerobic bacteria or the process
equipment.
The analysis assumes that a fresh manure collection system is installed
and that no fly control program would be used, since the source of the
pesticide residues would be removed.
Also, assuming 5-month collection cycles, there are some periods with
no pesticide applications; thus, only a small percentage of the manure
would contain the high concentrations calculated here.
On a 5-month collection cycle, nearly all of the old pesticide residue
(those over 30 days old) have degraded. Thus, a realistic concentration
30
-------
for a 5-month collection cycle is the concentration produced during the last
30 days only. This would be about 20% of the maximum levels calculated in
Table 8, or 20 ppm or less.
TABLE 8. MIST SPRAY CALCULATION
Basis
2 applications per week
4-month fly season
32 total applications
Materials
Dichlorvos (Vapona®, DDVP):
6.25 oz, 44.5% Vapona® in 5 gal diluted spray per acre
Dibrom® (Naled®):
3 oz, 60% Dibrom® in 5 gal water spray per acre
Calculations
Active ingredients
Dichlorvos: 2.78 oz active ingredient/acre per application
Dibrom® : 1.8 oz active ingredient/acre per application
Total Dichlorvos: 32 applications x 2.78 oz = 89 oz or 5.5 Ib
active ingredient/acre
Total Dibrom® : 32 applications x 1.8 oz = 57.6 oz or 3.6 Ib
active ingredient/acre
There are two types of feedlots, surfaced and unsurfaced. On surfaced
feedlots, generally 150 sq ft is required per animal. On unsurfaced
feedlots, 400 sq ft per animal is required. An unsurfaced feedlot is
assumed as this results in a higher concentration of pesticide residue.
Defecation rate = 5.5 Ib dry matter per head per day; at 110 head
per acre, 605 Ib/acre-day
Assuming the maximum possible concentration:
Dichlorvos 5.5 Ib active ingredient/acre
Manure 108,900 Ib dry matter/acre per 120 days
Concentration 0.0051% wt or 51 ppm
Dibrom® 3.6 Ib active ingredient/acre
Manure 108,900 Ib/acre per 120 days
Concentration 0.0033% wt or 33 ppm
31
-------
PESTICIDES AND HERBICIDES USED ON WHEAT IN COLORADO
The wheat residue considered for anaerobic digestion is unlikely to
contain significant pesticide or herbicide levels. As the data in Table 9
show (except for the herbicide 2,4-D) only a small percentage of the acreage
is treated with pesticides or herbicides. The seed treatment insecticides
and fungicides are essentially lost to the soil and are not collected in the
wheat harvest. The other herbicides listed are applied at least 30 days
before harvest and do not appear on the harvested product above the tolerance
levels for human consumption. Therefore, the analysis considers the cattle
manure anaerobic digestion case with wheat residue added to contain less
pesticide/herbicide residue than the straight manure digestion.
TABLE 9. PESTICIDES AND HERBICIDES APPLIED TO WHEAT
IN COLORADO
Material
Planted
acreage
treated
(%)
Rate/
Active ingredient acre
Time of
Application
Herbicides
2,4-D 20.7
Bromoxynil 6.5
Barban 2.4
2,4-Dichlorophenoxyacetic acid 2. Ib May-June
3,5-Dibromo-4-hydroxybenzonitrile 0.5 Ib May-June
4-Chloro-2-butynyl-m- 0.75 Ib May-June
chlorocarbanilate
Insecticides
Endrin 1.4
Parathion 1.0
Hexachloroepoxyoctahydro-endo,
endo-dimethanonaphthalene
0,0-Diethyl-O-P-nitrophenyl
phosphorothioate
0.5 Ib July
0.5 Ib
Seed
treatments
(insecticides)
Heptachlor 4 . 3
Lindane 3 . 2
Fungicides
(limited to
see treat-
ments)
PMA 17 . 6
Captan 10.0
Terracoat® 7 . 5
L-205
Heptachlorotetrahydro-4-7
methano indene
Benzene hexachloride
Phenyl mercuric acetate
N- (Trichloromethylthio) -4-
cyclohexene
1, 2-dicarboximide
5-Ethoxy-3-trichloromethyl-l ,
2,4-thiodiazole
1 oz April
0.5 oz April
1 oz April
5 oz April
0.4 Ib April
32
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PESTICIDE AND HEAVY METAL RESIDUE IN CHICKEN MANURE IN ARKANSAS
Since detailed data are not avilable for Washington County, Arkansas,
a worst case is assumed, which includes arsinicals for therapeutic purposes
and growth promotion, a complete fly control program, and a chemical
pesticide control program for infestation of lice and mites. The data
derived are the theoretical upper limit of possible concentrations of the
specified compounds that might be found in the manure.
Feed Additives
Two principal compounds used are arsanilic acid and 3-nitro-4-
hydroxyphenylarsanic acid. These arsinicals are generally excreted unchanged
in chemical structure and with no evidence of conversion to inorganic forms
of arsenic. The maximum feed levels and concentrations in manure are shown
below:
Maximum Maximum
concentration concentration
in feed in manure*2
Compound (ppm) (ppm)
Arsanilic acid 100 87
3-nitro-4-hydroxyphenyl-arsanic acid 50 44
Based on 87% of the feed arsaenic excreted with the manure
Fly Control Programs
Some products used for fly control in the manure in poultry houses are:
Baytex®, Co-Ral®,* Cygon® * Diazinona®,* Dibrom®, Ronnel,* Malathion,
Pyrethrins, Rabon®, Sevin®, and DDVP. The type of spray and ratio for
widely recommended products are listed in Table 10.
In large operations where manure collection is most feasible, the manure
is removed from the houses at least every other day and stockpiled.
Therefore, a major source of pesticide residues in poultry manure would come
from the treatment of stockpiles. As manure dries, it becomes less of a
breeding site for flies.
As a sample calculation, we make the following assumptions:
• Manure density = 60 lb/ft3
• Manure production = 0.0062 ft3/bird/day
Can be sprayed under cages only.
33
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TABLE 10. FLY SPRAYS AND APPLICATION RATES
Material Rate Restrictions
Residual Spray
Cygon® 4E 8 oz/1500 ft2 Do not apply to birds or
Ronnel 24% EC with birds in house
Space Spray
DDVP 0.5% Not applicable
Dibrom® 37% EC
Ronnel 24% EC
Larvicides
Cygon® 4E 8 oz/1000 ft2 of Do not spray directly on
droppings poultry or feed
Rabon® 24% EC 26 oz/500 ft2 of
droppings
• Cygon® 4E at 8 oz/1000 ft2 of manure = 0.5 pt = 0.25 Ib of active
ingredient
• Assumed pile depth = 1 ft
The above calculations yield 25 Ib of active ingredient per 60,000 Ib
of manure.
Even if there were four applications to the manure before it dried,
and the pesticide did not degrade, the concentration would be negligible.
The same should be true for the other materials. The conclusion is that the
pesticide residue from fly control in poultry manure is negligible (less
than 5 ppm).
Ectoparasite Control
Among the mites that attack poultry are chicken mite, northern foul
mite, scaly-leg mite, depluming mite, and tropical fowl mite. Of the lice
that attack poultry, the body louse is the most common.
The recommended treatment is to dust the birds. As an example, 1 Ib
of 5% Sevin® dust will treat 100 birds. This amounts to 0.0005 Ib of active
ingredient per bird. Applications are not made more often than every
4 weeks. Assuming a growing period of 9 weeks for a broiler, the broiler
would not receive more than two applications. For a layer, who is productive
for approximately 18 to 24 months, she could get perhaps four treatments
per year in a 12-week period.
34
-------
In the worst case, the maximum concentration in the manure would be:
Wet manure per bird/day = 0.25 Ib
12 weeks = 84 days
Total manure = 21 Ib
4 applications @ 0.0005 = 0.002 Ib
Assume 20% falls off bird
onto manure = 0.0004 Ib
0.004 Ib active ingredient/21 Ib
manure = 0.0019% (19 ppm) concentration
Thus, pesticide residues in manure due to ectoparasite chemical control
are negligible.
Based on 430,000 tons/yr of chicken manure, the total quantity of
arsenic compounds used per year could be as high as 86,000 Ib/yr.
Total pesticide residue from fly, lice, and mite control amounts to
less than 25 ppm. This figure should be much lower, allowing for normal
degradation of these pesticides.
PESTICIDES USED IN FORESTRY APPLICATIONS IN THE UNITED STATED
Based on the forest pests involved and the amount of material used,
insecticide residue in forest residue for Humboldt County, California and
Green County, Alabama would be negligible. As a national average, less
than 1% of all forest acreage receives any insecticide treatment. In
addition, the two counties involved are not considered regions where insect
damage has had a high economic impact.
Zectran®, made by Dow Chemical Co., is the major insecticide used in
forests. It is effective against the Spruce budworm, Douglas Fir Tussock
moth, and gypsy moth, which are the three major species of forest insects
that are treated in the U.S. Zectran® has effectively replaced DDT, which
is no longer used, except under emergency permits; it is endorsed by the
U.S. Forest Service. The majority of the material is used in the Northwest.
No significant quantities of herbicides or fungicides are used in the
forests nor would be found in the forest residue. Table 11 shows the
materials used.
35
-------
TABLE 11. FOREST AREA AERIALLY SPRAYED WITH
INSECTICIDES IN THE U.S.a
Material
DDT
Carbaryl
(Sevin®)
Acres
treated
(000)
425
90
Active ingredient
Dichlorodiphenyltrichloroethane
1-Naphthyl methylcarbamate
Rate/acre
(lb)
1
1.0
Zectran® 470 4-(Dimethylamino-3,5-xylyl) 0.15
methylcarbamate
Trichlorofon
(Dylox®)
B.T. (Dipel®)
77
15
Dimethyl (2,2,2-trichloro)-!-
hydroxyethyl phosphonate
Live spores of Bacillus
Thuringiensis-Berliner
1.0
1 to 2
Source: Reference 2.
PESTICIDES AND HERBICIDES USED ON FIELD CROPS
Corn (Missouri and Iowa)
Herbicides used on corn in Missouri and Iowa are listed below, along
with EPA residue tolerances:
Tolerance
Herbicide (ppm)
Lasso® 0.02
AAtrex® 15
Atrazine 15
Lasso® II 0.02
2,4-D 20
Bladex® 0.05
Most of these herbicides are applied as preemergent materials; the
residual material at harvest is very low.
Insecticides used in both areas are Furadan and Counter; in Missouri,
Dyfonate®, Thimet®, and Dasanit® are also used. Tolerance levels are as
follows:
36
-------
Tolerance
Insecticide (ppm)
Counter® (Terbufos) 0.5
Dyfonate® N/A
Dasinit® 1
Furadan® (Carbofuran®) 25
Thimet® 0.5
Degradation rates appear relatively rapid for this group of insecticides
judging from the tolerance levels. Furadan® degrades from 25.4 to less than
1 microgram/cm2 in 55 days.
Sunflowers (North Dakota)
The only pesticides used on sunflowers in Traill, North Dakota are
the insecticides Endosulfan and methyl-Parathion. The residue tolerances
as set by EPA are 2 ppm on sunflower seeds for Endosulfan, and only 0.2 ppm
of methyl-Parathion. Neither material poses a problem at these levels.
Barley and Wheat (North Dakota)
Pesticides used on barley and wheat in North Dakota are listed below,
with residue tolerances as given by EPA:
Tolerance
(ppm)
Herbicides
2,4-D 20
MCPA 2
Barban 0.1
Insecticides
Malathion 135
Parathion 1
Wheat (Missouri)
The pesticides used on wheat in Marshall, Missouri include the herbicides
2,4-D and MCPA and the same seed treatments as for barley in Traill, North
Dakota. Toxaphene is the principal insecticide used. The residue tolerance
set by EPA is 5 ppm; the degradation rate is very rapid. The effectiveness
of the insecticide lasts only 5 to 14 days in the air.
37
-------
SECTION 7
COLLECTION AND TRANSPORTATION
FORESTRY RESIDUE
Collection
As in the case of most agricultural residue, the cost of collecting
logging residue is a major impediment to implementation. Conventional logging
practice involves felling the trees, trimming off the branches and tops, and
loading the trunks onto trucks for transportation to the lumber or pulp mill.
The branches and tops are removed because their bulk prevents safe stacking
of the logs on the trucks. Too, the branches would stick out beyond the
sides of the trucks, making highway transport impossible. Also, handling the
whole tree with branches is considerably more difficult than handling the
trunk alone.
Collection of the remaining "slash" has to date been uneconomical.
Because of the variable nature of the material and its random distribution,
collection is manually performed, although items such as stumps might be
mechanically removed. (Several stump-pulling machines are under development.)
Manual collection involves two options for transporting the residue to
the power plant: the residue is collected in bins and shipped directly to
the power plant; or more likely, a chipper is used to reduce the volume and
prepare the material for direct feeding to the boiler. A major problem is the
inclusion of dirt in the product.
Some items that are presently not logged, such as dead or diseased trees
or undesirable trees (wrong varieties, saplings, crooked or deformed trees),
could be cut and added to the pile.
Land Disruption from Collection
Very little land disruption is anticipated in collecting logging residue.
Since active logging is in progress at the site of residue collection, common
facilities (roads, etc.) can be shared. Less than 1 acre would be required
for the collection, field storage, chipping, and chip storage at a logging
site.
Air Emissions
There are four main sources of air emissions in the collecting and using
of logging residue:
38
-------
• Equipment used in the field for collecting and chipping
• Equipment used to transport chipped residue
• Equipment used during loading and unloading of chips
• Equipment used during combustion, plus the combustion process itself
Collecting and Chipping Equipment—
If portable chippers are used, the chipper is brought into the area of
recently felled trees, and the slash is fed into the chipper. Chippers can
process about 600 to 700 Ib wood/hp/day. A 3000-ton/day operation
(6,000,000 Ib divided by 600 Ib/hp), requires about 10,000 hp/day. If diesel
engines are used as power supplies for the chippers, about 1 gal of diesel
fuel is consumed per 20 hp/hr. In a 24 hr day, 417 hp/hr are required,
consuming about 20.8 gal of diesel fuel. The chipper engines produce
approximately 21 Ib/hr of hydrocarbons, plus NOX emission, and 42 Ib/hr of CO
emission.3
Loaders are not required since the chipper discharges directly into the
truck bed. Dust emissions are a concern, but could vary depending on the
precaution taken.
Transportation Equipment—
If the maximum one-way hauling distance is 50 miles and the average is
25 miles, the 3000-ton/day operation would use 75,000 ton-miles of trans-
portation per day. The hauling would be performed by large diesel truck/
trailer combinations. If a vehicle carries 40 tons per trip, 75 round trips
(3750 miles) would be driven per day. The emission factors used4 are 28.7
g/mile CO, 20.9 g/mile NOX, 1.3 g/mile particulates, 2.8 g/mile S02, and
4.6 g/mile hydrocarbons. Thus, the total emission from transportation
equipment is:
NOX 172 Ib/day or 7 Ib/hr
CO 237 Ib/day or 10 Ib/hr
HC 37 Ib/day or 1.5 Ib/hr
S02 23 Ib/day or 1.0 Ib/hr
Particulates 10.7 Ib/day or 0.4 Ib/hr
Equipment Used to Load and Unload Chips—
Large trucks would haul the chips to a storage area and unload them,
probably on a portable tilting platform with the chips discharging from the
rear of the truck. Minimum handling of the chips is needed once the dump is
completed. Actual emission from the dumping and handling equipment varies
widely, depending on the particle size, moisture content, and weather
conditions. If the chips are both damp and relatively large (a minimum of
1/2 inch x 1/2 inch), no serious particulate emissions are expected from the
handling equipment.
SUGARCANE TRASH
Harvesting
The use of leafy sugarcane trash as an energy source requires imporved
harvesting. To date, the economic benefit of using the trash as fuel has been
39
-------
more than offset by the cost of harvesting. Harvesting techniques vary from
plantation to plantation, but are generally classified as manual or mechanical.
In Florida, 75% of the cane is harvested manually; the remaining 25% is
harvested mechanically.
If the present high cost can be overcome and trash harvesting becomes
economically attractive, the trash and cane must be separated. In manual
harvesting, the trash and cane would probably be separated in the field as the
cane is cut. The cane would be hauled to the mill for sugar extraction, while
the trash would go directly to the boiler. Manual harvesting should present
less difficulties with dirt and rock inclusion than mechanical harvesting.
In mechanical harvesting, the trash can be separated from the cane at the
field or at the mill. If a field-cleaning technique is used, the harvester
would pick and cut up the entire stalk and separate the trash, probably by
air-classification. If field cleaning is not used, the entire stalk would be
transported to the mill, where a wet cleaning system would be used. The wet
trash would be dried before feeding into the boiler. Both techniques are
presently used in Hawaii.
A discussion of harvesting and separation techniques in Hawaii appears in
the literature.5 However, harvesting cost is the main roadblock to the use
of leafy trash and further study of the subject is needed. Basically, the
major problems with harvesting the trash are:
Cost
Soil inclusion
Separation of cane and trash
Sugar yield loss due to inclusion of trash in the milling operation
Mechanical harvesting techniques need to be perfected
Florida cane crop and soil characteristics are different than in
the Hawaiian fields and different equipment is needed
Transportation and Storage
Sugarcane trash and leaves are transported in the same way as sugarcane
is presently handled. The cane is loaded into wagons with a 4-ton capacity.
Four wagons are connected and pulled out of the field with 4-wheel-drive
tractors. At the roadside, the cane is dumped into trailers for highway
transport or into railcars for rail transport to the mill. Highway trailers
carry 20 tons per load.
If the average distance to a central plant is 25 miles (50 miles round-
trip) and the trash collected is 1,000,000 tons/yr, then 50,000 roundtrips
(2,500,000 miles) ars driven per year. The estimated emissions from equipment
used to transport cane trash are given in Table 12.
40
-------
TABLE 12. ESTIMATED EMISSIONS FROM EQUIPMENT USED TO TRANSPORT CANE TRASH
lb/106 Btu
g/mile x Miles = Total g/yr = Ib/yr
Particulate
Sulfur oxide
Carbon monoxide
Hydrocarbon
Nitrogen oxide
1.3
2.8
28.7
4.6
20.9
2.5xl06
2.5xl06
2.5xl06
2.5xl06
2.5xl06
3.25xl06
7xl06
71.75xl06
11. 5x10 6
52.25xl06
7,159
15,419
158,040
25,330
115,089
0.001
0.002
0.03
0.004
0.02
^Source: Reference 3
The emissions per unit energy (lb/106 Btu) assume IxlO6 ton/yr of cane
trash containing 50% moisture is burned to produce steam at a conservative net
heat output of 3000 Btu/lb wet trash. Thus, the heat output of 6xl012 Btu/yr
is assumed from IxlO6 tons/yr of cane trash.
TRANSPORTATION OF CROP RESIDUE TO POWER PLANTS
In all cases considered for use of crop residue, the following parameters
for transportation are used:
Distance: 25 miles (average, one way)
Vehicle: 20-ton capacity diesel truck trailer
Emission factors: from US EPA AP-42, "Compilation of Air Pollution
Emission Factors," Supplement 5, page 3.1.5-2, Table 3.1.5-1.
Table 13 shows the emissions from transportation equipment used to ship
residue from three sites: Traill, North Dakota; Marshall, Missouri; and
Sibley, Iowa.
MANURE
Since manure generation occurs at large confined feedlots, it is logical
to construct on-site anaerobic digestion facilities. Thus, no net increase
in collection costs, transportation costs, or emission levels would be noted
over the present system.
Details of transportation to, and feeding into, the digesters would vary
from location to location. In the cases presented here, the assumption is
that the pen-cleaning operation stacks the manure adjacent to the digester
where conveyors feed the digester. This operation is described in greater
detail in the following section.
41
-------
TABLE 13. EMISSION FROM EQUIPMENT USED TO TRANSPORT RESIDUE
Transported Energy Content
Tons/yr Dry (Btu/lb)
Traill,
N. Dakota
Marshall,
Missouri
Sibley,
Iowa
76,000
43,500
7,500
7,980
7,980
8,100
, Moisture
(%)
28
40
50
Energy
Content, Net Total
Wet Energy
(Btu/lb) (Btu/yr)
5,746
4,788
4,050
8.73xlOn
4.16xlOn
6xl010
Transportation Emissions
Traill,
N. Dakota
Marshall,
Missouri
Sibley,
Iowa
Particulates
S02
CO
Hydrocarbons
Particulates
S02
CO
Hydrocarbons
NO
X
Particulates
S02
CO
Hydrocarbons
NOV
A
g/mi
1.3
2.8
28.7
4.6
1.3
2.8
28.7
4.6
20.9
1.3
2.8
28.7
4.6
20.9
mi/yr
190,000
190,000
190,000
190,000
108,750
108,750
108,750
108,750
108,750
18,750
18,750
18,750
18,750
18,750
8/yr
247xl03
532xl03
5453xl03
874xl03
141xl03
304.5xl03
3121xl03
SOOxlO3
2273xl03
24,375
52,500
538,125
86,250
391,875
Ib/yr
544
1,172
12,000
1,925
312
671
6,874
1,101
5,006
54
116
1,185
190
863
lb/106 Btu
0.0006
0.0013
0.014
0.002
0.0007
0.0016
0.0165
0.0026
0.0120
0.0009
0.0019
0.020
0.003
0.014
42
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SECTION 8
ANAEROBIC DIGESTION
LOCATIONS
This section considers three cases for the application of anaerobic
digestion to the production of methane gas from agricultural residue. The
following residues and sites, selected from the National Waste Inventory,
offer the best potential for commercial application because of the large
quantities of wastes available and the applicability of anaerobic digestion
to the processing of those wastes.
The first case involves anaerobic digestion of cattle manure in Weld
County, Colorado, where approximately 400,000 tons of feedlot cattle manure
are generated each year. The second case, also in Weld County, considers
the use of approximately 200,000 tons of wheat residue per year as a supple-
ment to the cattle manure. The third case selected is Washington County,
Arkansas, where 430,000 tons of chicken manure are available per year.
PROCESS DESCRIPTION
The degradation of waste by anaerobic digestion requires a variety of
anaerobic and facultative bacteria. Complex materials such as cellulose
and protein are first hydrolyzed by extracellular enzymes. The smaller
organic molecules are then fermented by acid-forming bacteria to produce
simple organic acids such as acetic, propionic, and butyric acids. These
acids are then fermented by bacteria to produce methane and carbon dioxide.
Figure 5 illustrates the fermentation of complex wastes.
The quantities of waste material to be fed to the anaerobic bacteria
are listed in Table 14. Characteristics of the materials with respect to
contaminants such as pesticides are described in section 6.
Different collection cycles were chosen for cattle manure to show the
effect of natural manure digestion on the system gas yield. The solids
content of manure varied from 20% solids for fresh manure with urine to an
average of 50% solids for manure collected every 6 months.
Completely mixed digesters with no solids recycle (Figure 6) are
considered for fermentation of agricultural waste. The slurry feed is
prepared by mixing water with the waste solids, producing a solids
concentration of 7% for chicken manure, 10% for cattle manure, and 10%
for cattle manure and wheat residue. (Input water, if required, is pumped
43
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ACID FORMATION
OTHER
INTERMEDIATES
METHANE
FERMENTATION
Figure 5. Pathways for the methane fermentation of complex
wastes (source: reference 6).
from wells at 50°F.) Greater dilution of the chicken manure is necessary
because of the higher nitrogen content and the possible inhibitory effect of
ammonia on the process. The chicken manure with liquid recycling requires
continual removal of ammonia from the recycled liquid and the anaerobic
bacteria. The following discussion shows that liquid recycling may be very
important in terms of energy conservation.* Liquid recycling also conserves
water and reduces water pollution.
Because of evaporative cooling in the dewatering process, the temperature of
the recycled water has been assumed to be approximately 75°F (as opposed
to 50°F for makeup water).
44
-------
TABLE 14. QUANTITIES OF WASTE MATERIAL USED IN
ANAEROBIC DIGESTION
106 Ib/day
Case Location (Dry basis)
1A Weld County, Cattle manure (fresh) 2.20
Colorado
IB Weld County, Cattle manure (5-month 1.41
Colorado collection cycle)
2 Weld County, Cattle manure (fresh) and wheat 2.2 + 1.1
Colorado residue
3A Washington Chicken manure (without liquid 3.08
County, recycle)
Arkansas
3B Washington Chicken manure (with liquid 3.08
County, recycle
Arkansas
For this analysis, aboveground digesters were assumed in making heat
loss calculations. In commercial installations, in-ground vessels may be
installed for economic reasons.
The digestion tanks are assumed to be 110 ft in diameter and 35 to
40 ft deep. A sample plot plan (Figure 7) shows 32 digesters. The actual
number of digesters for the cases considered varies from 19 to 33. A
retention time of 20 days has been assumed for all cases. (An economic
optimization study might lead to a design with a lower retention time.) The
digesters are mixed by recirculating the product gas and heated by direct
firing of the product gas (625 Btu/scf or 65 volume % CH^) in boilers. Heat
losses are calculated assuming that the digester operating temperature is
maintained at 95°F with an average yearly ambient temperature of 50°F. The
tanks are insulated with 2 inches of foam insulation.
After gravity settling, the digested sludge solids are further dewatered
by vacuum filtration to produce a cake with 25% solids content.
The gross and net energy production figures are summarized in Figure 8.
Because of the relatively low gas yield for case 3A, it is excluded from
most comparisons. Simplified material balances are shown on Figure 9. (See
Appendix A for more details on the process and more complete mass and energy
balances.)
Note that the high input slurry heating requirements could possibly be
partially met by use of solar heaters but at a relatively high capital
investment cost.
45
-------
FRESH
MAKEU
AGRICULTURAL .
WASTE
J
P WATER
GROSS
PRODUCT!
, RAW SLUDGE
(10% SOLIDS)
NET PRODUCTION
— on .L oi_
ON
<
CONSUMPTIC
'
ANAEROBIC D|GESTEI
DIGESTION
(MIXED
REACTOR)
)N NH-,H,S
*3 Z
EXf
3 SLUDGE
4
NH3 AND H
CONTROLS
^UST GAS
LIDS
^ SEPARATION
CLEANED GAS
YSTEMS
WASTEWATER ^
RECYCLE WATER
CAKE (-25% SOLIDS)
Figure 6. Anaerobic process for manure digestion.
The potential air emission sources from the digestion operation include
the following:
1. Boilers for digester heating (S02, NOX)
2. Heavy equipment for hauling manure and product (S02,NOX)
3. Tank leakage (H2S, NH3)
4. Thickener (H2S, NH3)
5. Vacuum pump exhaust (H2S, NH3)
6. Manure storage piles (H2S, NH3)
7. Product storage (H2S, NH3)
In our analysis, source 2 is considered negligible; sources 3, 6, and 7
are not any higher than current losses from decomposition of manure in the
feedlots and have not been quantified; the thickener is covered to control
source 4, with offgases vented through the H2S and NH3 control system for
source 5. Source 1 is the only source quantified for the comparison of
anaerobic digestion with other gas-producing options.
The potential water emission sources include:
1. Manure storage area runoff water
2. Product area runoff water
3. Any water not recycled
46
-------
EFFLUENT SLURRY STORAGE
CENTRAL CONTROL BUILDING
NOTE: OPERATING BUILDINGS 1 TO 4 CONTAIN SLURRY PREPARATION EQUIPMENT,
BOILERS FOR DIGESTER HEATING, AND SLURRY DEWATERING EQUIPMENT.
Figure 7. Sample plot plan showing 32 digesting tanks.
47
-------
7.0
6.0
5.0
<
O
to
*0
CL
CO
O
U
a
z
<
O
O
Q
O
CC
Q.
O
DC
UJ
UJ
4.0
3.0
2.0
1.0
0.0
urn
HEATING REQUIREMENT
FOR INLET SLURRY
ENERGY FOR ELECTRIC
POWER PRODUCTION
FOR PLANT
HEAT LOSS FROM
DIGESTER SYSTEM
NET ENERGY
PRODUCED
1A
FRESH
CATTLE
MANURE
1B
5-MONTH
OLD
CATTLE
MANURE
2
FRESH
CATTLE
MANURE &
WHEAT
RESIDUE
3A
CHICKEN
MANURE
WITHOUT
LIQUID
RECYCLING
3B
CHICKEN
MANURE
WITH
LIQUID
RECYCLING
2.5
2.0
CO
CM
1.5 o
1.0
0.5
g
Q.
CO
O
u
Q
<
Q
O
IT
a.
O
CL
111
Z
Figure 8. Energy production and consumption of anaerobic digestion
process using various agricultural wastes as digester feed.
48
-------
MAKEUP WATER
AGRICULTURAL
WASTE
NET GAS PRODUCTION
GAS FOR
HEATING
f
ANAEROBIC DIGESTION
AND DEWATERING
SYSTEMS
LIQUID RECYCLING
SLUDGE
WASTEWATER
o
Agricultural wastes
Agricultural wastes
Solids
(Ib/d)
Water
(Ib/d)
O
Makeup
water
(Ib/d)
Sludge
Solids
(Ib/d)
Water
(Ib/d)
O
Water
recycled
(Ib/d)
©
Wastewater
(Ib/d)
Cas for
heating
(109 Btu/d) (
O
Net gas production
iO"* Btu/d)
Clli,
(10'- scf/d)
to.
(10b scf/d)
Cattle manure (fresh) 2.20xl06 O.SSxlO7 0 1.35xlOfc 0.41xl07 l.lOxlO7 u.A7xin7
0.74
5.03
Cattle manure (5-month 1.41xl06 0.14xl07 0.21xl07 i.lSxlO6 0.35xl07 0.92x10-' 0
collection cycle)
0.48
1.63
0.88
Cattle manure (fresh) 2.20xl06 0.89xl07 0 2.33xl06 0.70X107 2.08xl07 0.19xlO;
and wheat residue l.lOxlO6
1.12
4.93
5.14
2.77
Chicken manure (without 3.08xl06 0.31xl07 3.78xl07 -'.60X106 0.78xl07 n 3.31xl07
liquid recycling)
2.40
0.45
0.47
0.25-
Chicken manure (with 3.08xlOfj 0.31x10' 0.47xl07 2.60xlOr 0.78xin' 3.31xl07 (
liquid recycling
i.42
Figure 9. Simplified material balances.
1.43
1.49
0.80
-------
Manure and solid products are stored on sloped concrete storage areas;
the runoff is collected for slurry makeup water. It has been assumed that
the systems for cases IB and 3B can be designed without any liquid discharge
because an adequate system blowdown is achieved by disposing of a solids
cake containing 75% water from the vacuum filters. For cases 1A and 2, with
a fresh manure feed at 20% solids, wastewater streams are produced as
indicated in the material balances for the five cases shown in Figure 10
(based on 1 Ib of dry solids input for each case). Case 3A, without liquid
recycling also produces a relatively large wastewater stream, but this
alternative is not considered economically feasible by SRI, based on the
system energy balances.
Cases 1A, IB, and 2 are for a plant located in Weld County, Colorado.
As indicated from the data in Table 15, evaporation ponds may be used for
liquid disposal so that there would be no discharge to surface water. While
evaporation ponds could produce odor problems at certain times and be a source
of ammonia and I^S, photosynthetic organisms could oxidize the t^S and minimize
its release. This water effluent might be used to irrigate the land, but
dilution water may be required because of the high salt content.
This study has assumed that the entire solid residue can be sold or
disposed of free F.O.B. plant gate as a fertilizer product. This disposal
technique is planned for the proposed commercial installations. A credit
might be given for reducing the volume (and pollution potential) of solid
waste, but in this analysis we have assumed zero solid waste generated.
In our plant battery limits we did not include a gas-cleaning facility
to upgrade the gas to pipeline quality (dehydration and C02 and H2S removal).
For a discussion of the pesticide residues, see section 6 of this
report.
We have assumed that all heavy metals are precipitated as sulfides and
are contained in the solids cake from the dewatering operation. Nutrients
are entirely contained in the solids product, in either the liquid or solid
phases of that product for cases IB and 3B. For cases 1A and 2, where
wastewater is produced, some nutrients are discharged from the system to the
evaporation ponds.
ENVIRONMENTAL ANALYSIS
In the environmental analysis of agricultural residue conversion systems,
the gas-producing processes are compared with coal gasification (SNG); the
direct firing or cofiring cases are compared with electric power generation
in fossil fuel-fired power plants. The format, shown in Table 16, is similar
to that of the Council on Environmental Quality because impacts are considered
from the resource extraction through to the conversion plant. Because the
typical energy output quantities differ in a coal conversion plant and
agricultural residue processing plant, the comparison is based on common
units. We present the results as units per million of net Btu produced.
In calculating the net energy output for the gas-producing processes, we
50
-------
o
MAKEUP WATER GAS
r "
o
INPUT SOLIDS
AND WATER
-
•
A
T
'
'
SYSTEM
SYSTEM
\J RECYCLED WATER
L .
"I
SLUDGE
_l
WASTEWATER
Input
Dry solids
Case (lb/d)
1A
IB
2
3At
3B
*
Assumptions
Assumptions
1
1
1
1
1
for
for
solids Makeup
H20 H20
(lb/d) (lb/d)
4 0
1 1.511
2.7 0
1 12.285
1 1.532
percent solids in feed:
percent solids in produ
Output
Dry solids
(lb/d)
0.614
0.837
0.706
0.844
0.844
1A IB
20 50
ct: 25 25
solids
H20
(lb/d)
1.842
2.511
2.118
2.532
2.532
• 2 3A
27 50
25 25
Wastewater
(lb/d)
2.158
0
0.582
10.753
0
3B
50
25
No internal recycle liquid.
Figure 10. Material balance.
51
-------
TABLE 15. PRECIPITATION AND EVAPORATION RATES
Weld County,
Colorado
(in.)
Washington County,
Arkansas
(in.)
Average annual evaporation rate
from open water surfaces
Average annual precipitation
Average annual runoff
34 to 36
15
< 1
44 to 46
40 to 50
10 to 15
Western Texas and Oklahoma (where CRAP facility is planned) have average
annual evaporation rates from open surfaces of >60 inches and annual
precipitation rates of <25 inches.
TABLE 16. SAMPLE ENVIRONMENTAL ANALYSIS WORKSHEET
Impact
Onsite Transport to
Resource processing conversion Conversion
extraction or storage plant plant
Land
disruption
and use
Water
pollution
Input
Output
Ammonia
Phosphorous
Salts
Metals
Pesticides
Air pollution
NOX
SOX
H2S
Acres/
109 Btu/
day output
(gal/106 Btu)
(gal/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
Particulates (lb/106 Btu)
(lb/106 Btu)
Pesticides
Organisms
Solid waste
total
(lb/106 Btu)
52
-------
assume that purchased electric power is generated by coal-fired power plants
(CFPP) and that no loss in transmission occurs; a plant thermal efficiency
of 40% is assumed. The Btu equivalent of the fuel burned to produce the
electric power is subtracted from the energy output to calculate the net
output. The pollutants generated in the production of electric power for use
at the gas-production facilities are shown on the emissions comparison
graphs, along with the emissions from the gas production facilities. The
analysis for the digestion cases is based on a coal-fired power plant burning
0.8% sulfur coal with flue gas desulfurization to reduce 862 emissions to
0.83 Ib S02/106 Btu output.
The assumptions and data used for the analysis are summarized in
Appendix B. Resource requirements (land, water) and emissions are tabulated
for each process. The results of the analysis are illustrated in Figures 11
through 16.
POTENTIAL PROCESS PROBLEMS
The potential process problems for the anaerobic digestion processes
discussed in Appendix A include:
• Ammonia toxicity (may require recirculating gas treatment or
liquid recycle treatment in algae treatment lagoon)
H2S and NHs control for thickener and vacuum pump exhaust gases
(iron oxide or activated carbon bed, acid scrubbing)
53
-------
45
40
35
30
NOTE: LAND FOR ALGAL PONDS
NOT INCLUDED IN THE ANALYSIS.
m
i-
at
o
25
20 -
15
10 —
5 -
fl
LAND REQUIREMENT
FOR EVAPORATION POND
-------
FROM
CONVERSION
PLANT
2.5
2.0
2 1.5
CD
I-
LU
Z
"°
~ 1.0
0.5
0.1
FROM GENERATION OF
ELECTRIC POWER
un
SNG
CFPP
1A
Figure 13.
IB
NO
3B
emissions.
FROM GENERATION OF
ELECTRIC POWER
m
i-
LLI
Z
CD 1.0
FROM
CONVERSION
PLANT
0.1
77J
777
TTT.
SNG CFPP 1A 18 2
Figure 14. SC>2 emissions.
3B
55
-------
FROM GENERATION OF
ELECTRIC POWER
0.1
(O
o
1
0.01
FROM
CONVERSION
PLANT
J~L
SNG CFPP 1A
Figure 15.
1B 2
Particulate emissions.
3B
50
m
i-
UJ
Z
10
5
SNG CFPP 1A
Figure 16.
1B
3B
Solid wastes.
56
-------
SECTION 9
DIRECT FIRING OF RESIDUE
INTRODUCTION
Direct firing of many types of wood waste and sugarcane byproducts such
as bagasse is a well-established technology. Wood wastes such as sawdust,
bark, shavings, and hog fuel are increasingly being used in lumber mills and
paper mills as a source of energy. A substantial effort is being made in the
lumber industry to improve this technology so as to increase efficiency and
meet environmental control regulations. In the sugarcane industry, the
extracted cane, called bagasse, is burned in boilers to supply heat and
electrical power to the sugar mill. Sugar mills are generally energy self-
sufficient, although fuel oil is sometimes used as a backup fuel or for startup.
The two cases of direct firing technology discussed here use logging
residue and sugarcane trash as feedstocks. Logging residue is that residue
that, up to now, has been left in the forest. This residue includes tops,
limbs, stems, saplings, dead and rotting trees, undesirable trees, and possibly
even stumps and roots. Sugarcane trash is defined as the leaves, tops, and
field trash that are currently not desirable to collect. At present, this
trash is destroyed in a flashfire burn of the field the day before the harvest
of the cane.
PROCESS DESCRIPTION
Direct firing generally includes the following steps:
Harvesting or collecting of the material
Transportation to the plant
Feed preparation (cleaning, drying, size reduction, etc.)
Feeding to and combustion in a boiler
Heat recovery as steam used for process or building heat or for
electric power generators
• Cleanup of stack gas and disposal of ash residue
PROCESS FEEDS
Forestry Residue
Forestry residue is discussed in section 7 of this report. Basically,
wood waste is sulfur-free and lower in ash than coal. The waste is high in
57
-------
moisture, however, and the moisture content is highly variable. The following
elemental analysis has been assumed for this study:
Element Dry wt %
Carbon 49.6
Hydrogen 5.7
Oxygen 43.7
Nitrogen 0.2
Other 0.8
Moisture is assumed to be 50% wt (wet basis).
Sugarcane Residue
At present, sugarcane residue (leaves, tops, etc.) is burned in the field
before cane harvesting. To date, collection of this material has proved
uneconomical, since the energy value recovered does not offset the added cost
of collection. Sugarcane has the following elemental analysis (dry basis):
Reported range Value used
Element (% wt) (% wt)
Carbon 43 to 47
Hydrogen 5.4 to 6.6
Oxygen 45 to 49
Ash 1.5 to 3.0
100
The moisture content is highly variable, depending on the exact makeup of
the trash and the harvesting time, but we assume the moisture content to be
50% wt (wet basis).
LAND DISRUPTION FROM CONVERSION PROCESS
There are several options in the use of logging residue for direct
firing or cofiring technology. Two primary uses are steam or heat generation
in industrial plants (such as lumber drying or paper and pulp mills), or in
electric utility power plants. In either case, the net land disruption in
using logging residue, as opposed to alternative fuels, is mainly the storage
facility. Since both cases use a large combustion unit, the size and land
usage should be about the same.
If all 1,000,000 tons/yr of logging residue were collected, chipped, and
sent to a centrajrplant for direct combustion, an area equal to 30 days'
storage would be needed. If a pile 30 ft high contains 100,000 tons (assuming
a bulk density of 20 lb/ft3), the area required would be 330,000 sq ft, or
about 8 acres. Considering access area and operating room, about 14 acres
should be allowed.
Disposal of ash from a 3000 ton/day combustion plant requires about
0.2 acre/yr, or a total of 4 acres for a 20-yr project life.
58
-------
Total land disruption, therefore, is:
Acres
Collection 1
Storage 14
Ash disposal 4 (0.2 acre/yr)
Total 19
The 3000 ton/day plant (IxlO6 ton/yr) producing 4000 Btu/lb or
8,000,000 Btu/ton produces 8xl06xl06 = 8x10*2 Btu/yr, gross. Thus, 19 acres/
8,000xl09 Btu/yr = 0.0002 acre/109 Btu/yr. If a 30% efficiency is realized
in the combustion, then 0.0006 acre/109 Btu/yr is used.
DIRECT COMBUSTION OF FORESTRY RESIDUE
The forestry residue collected and chipped in the field is transported
to the point of use. (The collection, chipping and transportation are
discussed elsewhere.) The final steps in the process are grinding, drying,
and combustion. The first two steps may not be necessary, depending on the
size chip produced in the field and the moisture content.
Final Grinding, Drying, and Feeding
The chips are transported from the storage pile to the power plant.
A final reduction in size is probably needed to generate a sawdust-like
feedstock. This material may or may not need drying, but present thinking is
to use a dryer to increase the steam-generating capacity of the boilers. The
particulate emissions from the final grinding can be controlled by drawing
the particulate-laden air directly into the furnace.
Several types of dryers could be used, depending on the requirements of
the plant. The chips could be dried before final grinding or the fine
material could be dried in a fluid bed on a transport-type dryer. The
particulate emission is minimized if the larger chips are dried, but a higher
rate of drying is achieved if the fine feedstock is dried. This decision
must be made by the design engineers and appropriate steps taken to minimize
particulate emissions.
Material Balance
To simplify the calculations in Table 17, we assume that the as-received
wood is fed directly to the boiler. The total feed is 3000 tons/day or
125 tons/hr (250,000 Ib/hr). The wood is assumed to contain 8000 Btu/lb (dry
basis). Actually, several boilers would be operated in parallel to process
this amount of'feed. The units use 40% excess air and produce a total of
IxlO6 Ib of steam/hr at 600 psig and 900°F.
On this basis, 535xl06 Btu/hr are produced as high-pressure steam, while
465xl06 Btu/hr are lost to the stack gases. Based on reported data for wood
combustion, about 1250 Ib/hr each of CO and NOX are formed from the combustion;
with reasonable collection efficiency in a dry cyclone (80%), only 100 Ib/hr
59
-------
of particulates would be emitted. The solid waste from the boilers is mainly
ash, totaling about 400 Ib/hr.
TABLE 17. MATERIAL BALANCE
Flow
(103 Ib/hr)
Stream
1
Stream
2
Stream
3
Stream
4
Stream
5
Composition
Wood (50% moist)
Air
Steam (600 psig, 900°F)
Flue gas (400°F)
Ash
250
2238.4
365.8
2488.4
0.1
0.4
Elemental and component
balance
C 62
H
0
N
S
Ash
CO
C02
NOX
H20
S02
Btu
7.2
54.6
0.25
0
0.5
-
-
-
125
-
1x10 9
- -
235.0
884.2
- -
-
-
-
- -
365.8
- —
0 0.535xl09
-
67.1
884.2
-
0.1 0.4
1.25
227.3
1.25
189.8
0 —
0.465xl09
Emissions
Emissions are summarized in Table 18. The combustion process emits CO
and oxides of nitrogen. Proper design of the combustion chamber and proper
operation of the boiler minimize these emissions, but they still are present.
Sulfur dioxide emissions are quite low, the actual value depending on the
sulfur content of the wood waste used. In the wood waste used for this
material balance, no sulfur was reported. However, some wood contains amounts
of sulfur up to 0.1% wt (wet basis), which gives a S02 emission of about
0.25 Ib S02/106 Btu.
Particulates could be quite high if uncontrolled. Values as high as
8 to 10 Ib particulates/106 Btu are possible in uncontrolled systems burning
high concentrations of wet feed and bark.
Predrying of the feedstock greatly reduces the particulate emission from
the boiler, but may necessitate a particulate removal step at the dryer. Both
60
-------
TABLE 18. ENVIRONMENTAL IMPACTS OF DIRECT COMBUSTION
OF LOGGING RESIDUE, HUMBOLDT COUNTY, CALIFORNIA
Impact
Resource
extraction
Onsite
processing
or storage
Transport to
conversion
plant
Conversion
plant
Land
disruption
and use
Water
pollution
Input
Output
Wasteheat
Ammonia
Phosphorus
Salts
Metals
Pesticides
Air pollution
Acres/
109 Btu/
yr/output
(gal/106 Btu)
(gal/106 Btu)
(Btu/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
<0.001
<0.001
<0.001
175
0
NOX
sox
H2S
Particulates
Pesticides
Hydrocarbons
CO
Organisms
Solid waste
total
(lb/106
(lb/106
(lb/106
(lb/106
(lb/106
(lb/106
(lb/106
(lb/106
Btu)
Btu)
Btu)
Btu)
Btu)
Btu)
Btu)
Btu)
0
0
0
0
0
.02
.002
—
.002
_
.002
.007
-
-
0.
0.
0
<0.
0
0.
0.
0
0
01
002
001
003
02
0.
0
0.
0
-
0
0.
0
0.
7
1
25
7
baghouses and dry scrubbers show excellent efficiency in removing particulates
from wood waste fired boilers.7 Removal efficiencies for baghouses are 90%
and for dry scrubbers 87%, The baghouse requires a much lower pressure drop
(3 inches of water) compared to the dry scrubber (14 inches of water). Total
particulate matter at the outlet of these tests was between 0.033 and
0.061 grain/scf, or less than 0.1 Ib particulates/106 Btu output.
Therefore, while the potential particulate emissions are quite high, with
proper design, the actual emission should be well below the New Performance
Source Standards for coal-fired power plants (0.1 Ib particulates/106 Btu
input).
61
-------
DIRECT COMBUSTION OF SUGARCANE RESIDUE
Material Balance
Collected sugarcane trash is mixed with bagasse and fired in boilers at
the sugar mills, as shown in Figure 17. A material balance sheet is presented
in Table 19. This system makes better use of existing facilities than would
building a central power plant. Additional boilers and generating capacity
are added at each plant to accommodate the added feedstock.
FLUE GAS (400° F)
STEAM (600psi,900°F)
O
SUGARCANE TRASH
V
BOILER
AIR
ASH
Figure 17. Direct firing of sugarcane trash.
62
-------
TABLE 19. MATERIAL BALANCE FOR SUGARCANE TRASH COMBUSTION
(tons/day)
Sugarcane trash
Air
Flue gas
Ash
Steam
Btu
Elemental balance
C
H
0
N
S
Ash/particulate
H20
CO
C02
H20
S02
NOV
A
02
N2
Hydrocarbons
Stream Stream Stream
123
500
2016.5
556
3xl09 1.625xl09
112.5
15
117.5 423.5
1593
trace
5
250 556
250 556
423.5
1593
Stream
4
2515.5
0.5
1.375xl09
112.5
15
541
1593
7_
5.5*'*
250
/7
0.5a
412.5
385
0
XT
0.5a
121
1593
n
0.5a
Stream
5
5
5
Source: Reference 3.
Uncontrolled; with controls, approximately 0.5 ton/day.
As with forestry waste, there is the option of drying the feedstock. The
feed is chopped into small pieces, 2 inches (maximum) in diameter. Drying
generates some particulates, but firing the undried cane trash may produce an
equal amount. The real tradeoff is between the cost of a dryer and the cost
of a larger boiler. The dried feed generates more energy per pound and thus
requires a smaller boiler. However, the overall energy balance shows that the
water is removed somewhere and this heat of vaporization is lost.
This analysis assumes that no dryer is used and that the sugarcane trash
is fed as received. The emissions are summarized on Table 20. The main
pollutant potentially emitted is the particulate at a rate of 22 Ib/ton of feed
or about 3.5 lb/106 Btu. However, all Florida sugar mills are now being
equipped with wet scrubbers; present emissions from bagasse boilers are in the
range of 0.05 to 0.1 lb/106 Btu.
63
-------
TABLE 20. ENVIRONMENTAL IMPACTS, DIRECT COMBUSTION OF SUGARCANE TRASHa
Impact
Land
disruption
and use
Ons ite Transport to
processing conversion Conversion
or storage plant plant
Acres/
109 Btu/
yr output
0.011
Water
pollution
Input
Output
Wasteheat
Ammonia
Phosphorus
Salts
Metals
Pesticides
(gal/106 Btu)
(gal/106 Btu)
(Btu/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
Air
pollution
NOX (lb/106 Btu)
SOX (lb/106 Btu)
H2S (lb/106 Btu)
Particulates (lb/106 Btu)
Pesticides (lb/106 Btu)
Hydrocarbons (lb/106 Btu)
CO (lb/106 Btu)
Organisms
Solid waste
total
(lb/106 Btu)
0.62
0
0
6.77
(0.62)
0
0.62
0.62
6.6
a
Source: Reference 8.
Land Disruption - Conversion Process
The major impacts on land usage are the storage area for the cane trash
and the ash disposal area. The ash may be returned to the fields for its
fertilizer value (indeed, in the present field burning, that is exactly what
is done), but provision for interim storage of ash is made. Also, the cane
is harvested over about a 6-month period, and provision for storage must be
made for at least a 6 months' supply. If 1,000,000 tons/yr were collected,
the storage area should be able to contain a minimum of 500,000 tons. Two
options are available: (1) prepare the cane trash for combustion at the
time of harvest (i.e., grinding, drying, etc.) and store the resultant boiler
feed material in silos; (2) prepare the feed as needed and store the raw trash
-------
in large piles. The latter method is assumed as it uses a maximum amount of
land, even though there may be severe technical and operational problems
(rotting, moisture, rodents, etc.).
Assuming a bulk density of semicompacted leaves and trash to be 20 Ib/ft,
a storage area of 50,000,000 ft3 is required for 500,000 tons. If the material
can be stored in piles 20 ft high, 2,500,000 ft2 or 57 acres would be required.
Allowing another 10 acres for equipment access, a minimum of 67 acres is
required. Considering the heat content of 6xl012 Btu/yr, the land use factor
is 0.011 acre/109 Btu.
Collected and Fired Cane Trash Emissions Compared to Open Field Burning
To evaluate properly the environmental effects of collecting and firing
cane trash in a boiler, the alternative practice of flash burning in the field
must be considered. US EPA data9 show that the following emissions are
created when cane trash and weeds are burned in the field:
Composition Ib/acre
Particulate 225
Carbon monoxide 1500
Hydrocarbons 300
Nitrogen oxide 30
Based on 15 tons/acre, and 6xl06 Btu net heat per ton of trash, the
emis s ions are:
Composition lb/106 Btu
Particulate 2.5
Carbon monoxide 16.7
Hydrocarbons 3.3
Nitrogen oxide 0.3
In comparison, the total emissions from collecting, processing, and
combustion of sugarcane trash in a boiler are:
Composition lb/106 Btu
Particulate 0.62 (with controls)
Carbon monoxide 0.65
Hydrocarbons 0.624
Nitrogen oxide 0.64
Sulfur dioxide 0.002
Obviously, collection and boiler firing is both a more productive method
of disposal, yielding valuable energy, and environmentally more desirable.
Other items to consider that are beyond the scope of this report are:
• The possible pesticide emissions from field burning
• The positive effects of field burning on disease and rodent control
• The effects on product yield
• The overall economics
65
-------
COFIRING WITH COAL IN A STOKER-FIRED BOILER
The concept of using refuse and agricultural waste as a fuel is not new
in the United States, nor for that matter, in Europe. Studies have been made
to determine the practicality of using such materials as fuels for stoker-
fired boilers. Replacing part of the coal with agricultural waste appears
a viable concept, if the pollution factors are not greater or potentially
more harmful than that of coal alone, and if collection costs are reasonable.
(See Figure 18 for a flowchart of this process.)
At the three sites of this study, the crop residue comes from corn,
barley, wheat, and sunflower. This includes straw, chaff, and leaves.
Process Description
Stokers are designed to feed coal uniformly onto a grate within the
furnace and to remove ash residue. Most mechanical stokers can be classified
in three main groups:
• Overfeed: chain grate; traveling grate; vibrating and oscillating
grate
• Spreader
• Underfeed
Supplementing coal with agricultural waste involves the following
steps:
Harvesting or collecting the material
Transporting material to the plant
Preparing the feed (drying, size reduction, etc.)
Storing
Mixing with coal
Feeding to and combusting in the boiler
Recovering heat
Cleaning up of stack gas and disposal of ash residue
Collection
This study assumes that, in all cases, the wastes are harvested at the
same time as the food crop. The wastes are then separated from the food crop
and moved to the transportation unit.
Process Feeds
Barley—
Barley refuse is considered for use with lignite in the Traill, North
Dakota area, along with wheat and sunflower wastes. The mix is:
Waste Percent
Wheat 65
Barley 25
Sunflower 10
66
-------
REFUSE
1
COLLECTION
AIR WITH RESIDUE
H20
CLEAN
SLUDGE
POWER
RESIDUE* RESIDUE HEAT MOISTURE
CHOP
DRY
HEAT
S0x.
2, N0x, CO,
PARTICULATE N0
HC. H2S
TRACE
COMBUSTION
I
MIX
COAL
WASTE HEAT ASH PARTICULATE AIR RESIDUE
Figure 18. Cofiring with coal in a stoker-fired boiler.
67
-------
This mixture would supplement the lignite now used. Approximately
6,000,000 tons/yr of assorted crop waste are available; case studies were
prepared using 0, 25, and 50% waste-to-lignite ratios.
Barley straw is approximately 10 to 15% moisture and 5.5% ash. For this
study, the ultimate analysis of the material was assumed to be as follows:
Element Dry wt %
Carbon 43
Hydrogen 6
Nitrogen 0.5
Oxygen 5.5
The ash contains the following elements:
Element Dry wt %
Calcium 0.35
Chlorine 0.68
Iron 0.033
Magnesium 0.13
Manganese 0.0017
Phosphorus 0.10
Potassium 1.88
Sodium 0.14
Sulfur 0.17
Wheat—
Wheat waste is also considered for use with lignite in the Traill,
North Dakota area with barley and sunflower waste, and in the Marshall,
Missouri area with corn waste and corn. The mix considered is given under
barley. Approximately 6,000,000 tons/yr of assorted crop waste are available
in North Dakota; case studies were prepared using 0, 25, and 50% waste-to-
lignite ratios.
In the Marshall, Missouri area approximately 1,000,000 tons/yr of wheat
and field corn waste are available. Case studies were prepared using 0, 25,
and 50% waste-to-coal ratios. The wheat and corn mix considered was 50%
wheat and 50% corn.
Wheat waste is approximately 30% moisture and has about 4.3% ash.
The ultimate analysis of wheat waste was assumed to be as follows:
Element Dry wt %
Carbon 43.0
Hydrogen 4.2
Nitrogen 4.5
Oxygen 44.0
Ash 4.3
68
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The ash contains the following elements:
Element Dry wt %
Calcium 0.16
Chlorine 0.33
Copper trace
Iron 0.017
Magnesium 0.12
Manganese 0.006
Phosphorus 0.08
Potassium 0.67
Sodium 0.14
Sulfur 0.10
We assume that the waste is collected at the time of harvest and that the
waste is separated from the food crop mechanically before it is moved to the
transportation unit.
Sunflower—
Sunflower waste is considered for use with lignite, wheat, and barley in
the Traill, North Dakota area. The mix is:
Waste Percent
Wheat 65
Barley 25
Sunflower 10
Approximately 6,000,000 tons/yr of the assorted crop waste (barley,
wheat, sunflower) are available; case studies were prepared using 0, 25, and
50% waste-to-lignite ratios.
Sunflowers have 50% moisture and about 6% ash. The elemental analysis
used in this study was assumed to be as follows:
Element Dry wt %
Carbon 48.4
Hydrogen 7.0
Nitrogen 3.6
Oxygen 35.0
Ash 6.0
The ash contains the following elements:
Element Dry wt %
Calcium 1.72 - 2.2
Magnesium 0.09 - 0.64
Manganese 0.11
Phosphorus 0.20 - 0.56
Potassium 2.92 - 5.0
Sulfur 0.04
69
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Collection of the sunflower waste is assumed to be the same as barley
and wheat.
Corn—
Corn waste is considered for use in both the Marshall, Missouri and
Sibley, Iowa areas. In the Missouri region, there are available approximately
1,000,000 tons/yr of corn and wheat waste; in the Iowa area, approximately
4,500,000 tons/yr of corn are available. Case studies were prepared using
0, 25, and 50% corn waste-to-coal ratios.
Corn stalks and leaves are approximately 50% moisture and have about
4.5% ash.
The ultimate analysis of corn waste was assumed to be as follows:
Element Dry wt %
Carbon 43.5
Hydrogen 6.0
Nitrogen 1.5
Oxygen 44.5
Ash 4.5
The ash contains the following elements:
Element Dry wt%
Calcium 0.23
Potassium 0.92
Magnesium 0.18
Phosphorus 0.20
Iron 0.08
Silicon 1.17
Aluminum 0.11
Chlorine 0.14
Manganese 0.035
Sulfur 0.18
Coal and Lignite—
The coals used in this study were North Dakota lignite and Illinois No. 6
coal. For the purpose of this study, the following fuel mixes were used:
• Traill, North Dakota
Lignite
Refuse: wheat 65%, barley 25%, sunflower 10%
• Marshall, Missouri
Illinois No. 6 coal
Refuse: 50% wheat, 50% corn
• Sibley, Iowa
Illinois No. 6 coal
Refuse: 100% corn
70
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Lignite has a moisture content, after drying, of 11.4% and an ash content
of 9.6%. Illinois No. 6 coal has a moisture content, after air drying, of
8.4% and an ash content of 10.5%. The ultimate and ash analyses are as
follows:
Hydrogen
Carbon
Nitrogen
Oxygen
Sulfur
Illinois No. 6
coal
5.4
69.3
1.2
15.5
3.5
Ash analyses for lignite and coal are as follows;
Illinois No. 6
(total ash 10.5%)
North Dakota
lignite
5.1
57.9
0.8
25.8
1.2
Mercer lignite
(total ash 9.6%)
Si02
A1203
Fe203
Ti02
,7
,7
CaO
MgO
Na20
K20
S03
Material Balance
51.
15.
16.3
0.6
0.06
8.9
0.8
0.5
2.0
2.8
23.8
.5
,1
10.
10.
0.6
0.27
16.6
5.1
8.2
0.6
23.5
Tables 21 through 25 summarize the material balance and air emission at
the three sites; these are then compared with coal-only firing. As expected,
the sulfur emissions are lower due to the lower sulfur concentration in the
feedstocks. No data for NOX emissions were found, so no increased emissions
were considered. However, we do feel that the NOX emissions might be lower
due to the lower temperatures in the boiler. In all cases the CO concentra-
tions increased with increasing agricultural residue in the feed. This is
due mainly to the extra combustion required of drying feedstocks to give a
comparable output energy. Particulates also increase, due mainly to a low
collection efficiency on the residue dryer (80%) compared to the higher
efficiency of the particulate collection devices on the boiler (98%). In the
case of lignite firing in Traill, North Dakota, the total hydrocarbons
actually decrease with increasing agricultural residue in the feed. This is
due to the dilution effect of the residues. Agricultural residues emit less
hydrocarbons on combustion than does lignite. However, the reverse is true
in the case of Illinois No. 6 coal. The residues actually emit more hydro-
carbon than does coal.
71
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TABLE 21. MATERIAL BALANCE
(tons/day)
Site
Traill,
N. Dakota
Marshall,
Missouri
Sibley
Iowa
Feed
refuse
(%)
50
25
0
50
25
0
50
25
0
Coal
in
211
311
408
189
274
355
16.9
24.2
30.9
Refuse
in
242
119
—
426
207
-
43.4
20.7
-
SO/
out
6.7
9.5
12
14
20
25
1.3
1.7
2.2
Ash
out
28
34
39
31
34
37
2.8
3.0
3.2
Par-
ticu-
late
outa
9.8
11.8
13.7
16.9
20.7
24.2
1.8
2.0
2.1
CO
out
0.57
0.49
0.41
0.73
0.45
0.17
0.089
0.055
0.031
HC
out
0.14
0.17
0.20
0.092
0.072
0.053
0.030
0.022
0.015
NOX
out
1.2
1.2
1.2
5.3
5.3
5.3
0.23
0.23
0.23
Uncontrolled
TABLE 22. EMISSIONS
(lb/106 Btu)
Site
Traill,
N. Dakota
Marshall,
Missouri
Sibley,
Iowa
Feed
refuse
(%)
50
25
0
50
25
0
50
25
0
so2a
1.2
1.7
2.1
1.7
2.4
3.1
1.9
2.5
3.2
Particulate
0.37
0.34
0.32
0.45
0.42
0.39
0.56
0.49
0.41
NOX
1.4
1.4
1.4
4.3
4.3
4.3
2.2
2.2
2.2
CO
0.66
0.57
0.48
0.59
0.37
0.14
0.87
0.54
0.30
HC
0.16
0.20
0.23
0.075
0.059
0.043
0.29
0.21
0.15
Pesticides
0
0
0
0
0
0
0
0
0
S02 after 85% removal in S0£ scrubbers.
Particulate after 98% removal from boiler and 80% from dryer.
72
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TABLE 23. ENERGY BALANCE
Site
Traill,
N. Dakota
Marshall ,
Missouri
Sib ley,
Iowa
Power
output
(MW)
21
30
2.5
Input
(BtuxlO6/
hr)
224
320
26.7
Dry
Coal refuse
energy energy Refuse
(Btu/ (Btu/ moisture
lb) lb) (%)
6,590 7980 28
10,817 7980 40
10,377 8100 50
Coal/
refuse
mix
(%)
50/50
75/25
100/0
50/50
75/25
100/0
50/50
75/25
100/0
Coal
(ton/
day)
211
311
408
189
274
355
16.9
24.2
30.9
Wet
refuse
(ton/
day)
242
119
-
426
207
-
43.4
20.7
-
a
Assume full capacity operation at 32% thermal efficiency for power generator.
Dryer efficiency = 70%.
TABLE 24. ENERGY CONSUMPTION AND PARTICULATE EMISSION FOR DRYER
Site
Traill,
N. Dakota
Marshall,
Missouri
Sib ley,
Iowa
Coal/refuse
mix
(%)
50/50
75/25
50/50
75/25
50/50
75/25
Dryer
energy
(BtuxlO6)
8.1
3.5
20.3
9.8
2.6
1.2
Particulate out
(Ib/day)
After cyclone
242
119
426
207
43.4
20.7
Before cyclone
1210
595
2130
1035
217
104
^Cyclone assumed to remove 80% of the particulates.
73
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TABLE 25. MATERIAL BALANCE OUTPUT
(tons/day)
Site
Traill,
N. Dakota
Marshall,
Missouri
Sib ley,
Iowa
Coal/refuse
mix
(%)
50/50
Coal
Barley
Wheat
Sunflower
Total
75/25
Coal
Barley
Wheat
Sunflower
Total
100/0
Coal
50/50
Coal
Wheat
Corn
Total
75/25
Coal
Wheat
Corn
Total
100/0
Coal
50/50
Coal
Corn
Total
75/25
Coal
Corn
Total
100/0
Coal
S02 out
6.33
0.174
0.220
0
6.72
9.33
0.086
0.108
0
9.52
12.2
13.2
0.298
0.383
13.9
19.2
0.145
0.186
19.5
24.9
1.18
0.123
1.30
1.69
0.0373
1.73
2.16
Ash out
20.3
2.83
4.73
0.28
28.1
29.9
1.39
2.33
0.0032
33.6
39.2
19.8
6.41
4.79
31.0
28.8
3.12
2.33
34.3
37.3
1.77
0.977
2.75
2.54
0.466
3.01
3.24
74
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Land Disruption - Crop Residue
The major usage of land is for the storage of the crop waste. Since the
crop residue is collected annually during a short period of time, provision
is made for an entire year's volume. This analysis (Table 26) considers the
residue to be stored in 30-ft-high open piles. A bulk density of 20 lb/ft3
is assumed in the calculations. Actual practice may involve a feed preparation
step (grinding/drying) at the time of harvest with storage in large silos.
However, for purposes of estimating the maximum impact, the open piles are
considered here.
TABLE 26. LAND USAGE FOR CROP RESIDUE
Site
Traill,
N. Dakota
Mixture
coal/
residue
(%)
50/50
75/25
Storage
volume
required
(ft3;
8. 8x10 6
4. 4x10 6
Land for
20-ft-high_
piles
(acres)
10
5
Acres /
109 Btu
0.012
0.011
Marshall, 50/50 15.6x10* 17 0.013
Missouri 75/25 7.8xl06 8 0.013
Sibley, 50/50 1.6x10* 2 0.018
Iowa 75/25 O.SxlO6 1 0.019
75
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SECTION 10
LARGE-SCALE COFIRING WITH COAL
COFIRING OF FORESTRY WASTES WITH COAL
Forestry wastes can be cofired with coal in large suspension-fired
boilers. The wood must be finely divided and dry, but otherwise there is
little difference between direct firing and cofiring. The sulfur emissions
are reduced when the coal is mixed with wood in direct proportion to the
average sulfur content in each feed. Total particulate emissions could be
potentially much higher if proper control techniques are not employed. The
grinding and drying operations of the wood are the largest contributors to
the particulate emissions. NOX emissions may actually be lower due to
lower combustion temperatures, but more data are needed to support this
conclusion. The CO emission is probably slightly higher for cofiring due
primarily to the extra combustion required to dry the feedstocks.
COFIRING OF SUGARCANE FIELD WASTES WITH COAL IN LARGE UTILITY BOILERS
As with wood, it may be possible to fire sugarcane field waste (tops,
leaves, etc.) with coal in large utility boilers. The feed must be finely
divided and dried to be compatible with the coal in large suspension-fired
boilers. The sulfur emissions in the cofiring of sugarcane waste are reduced
in direct proportion to the average sulfur content of each feedstock. Both
the particulate emissions and the carbon monoxide emissions are expected to
be higher on a Btu output basis than for coal only. Drying and grinding
(plus the combustion characteristics of the sugarcane waste) increases the
potential particulate emissions. Drying, coupled with the lower Btu content
of the sugarcane waste, also increases the carbon monoxide emission per
106 Btu of energy output. Estimates of NOX emissions are difficult because
of a lack of good data. Lower flame temperatures tend to produce less NO ,
but some researchers have estimated higher than expected NOX from combustion
of wood in similar wastes.10 Because of the lack of good data, we are noting
the deficiency in data and assuming no change in the NOX emissions.
DATA
Table 27 summarizes the air emission data for the two cases considered
and compares the data with the case of coal-only firing. A feed rate of 25%
biomass residue and 75% coal is assumed. The location of the forestry residue
case is Greene County, Alabama at the Greene Power Station of Alabama Power
Company. The sugarcane residue case is based on a hypothetical coal-fired
power plant to be constructed in Southern Florida in the future (as oil
76
-------
availability decreases). In both cases, Kentucky No. 6 coal is assumed, and
the values of biomass collection, transportation, and feed preparation
reported for direct firing of the forestry and sugarcane residue are
incorporated in the data reported here. For simplicity, only the emissions
per 106 Btu output are calculated rather than a complete material balance for
any one specific case. This allows for calculation of any sized boiler or
power plant. Very little data are available, especially regarding the NOX
emissions. The SOX emissions are calculated directly from the average sulfur
content of the feedstocks. The CO, hydrocarbon, and particulate data are
taken from published USEPA data.9
TABLE 27. COMPARISON OF AIR EMISSION
(output, lb/106 Btu)
Uncontrolled
NOX
Coal, 100% 0.4 to 0.6
Coal, 75% 1.0 to 1.2
Wood, 25%
Coal, 75% 0.6 to 0.7
Sugarcane, 25%
S02a
5.7
4.3
4.3
Parti-
culate
8.18
10 to 14
7
S02b
1.1
0.86
0.86
Controlled
Parti-
Q
culate
0.16
0.3 to 0.4
0.2 to 0.4
CO HC
0.06 0.015
0.14 0.10
0.27 0.15 to 0.17
a.
'Based on 2.6% wt sulfur in coal
80% scrubber efficiency
?
'98% control on combustion, 80% on dryer
77
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SECTION 11
PYROLYSIS TECHNOLOGY
INTRODUCTION
In a study of this nature it is impossible to consider all, or even
the majority, of the developing pyrolysis technologies. This overview
presents a brief discussion of pyrolysis and describes the wide variety of
possible reactor designs. This should allow the reader to place in proper
perspective our analysis of the two processes selected (Purox® and Tech-Air).
Definitions
Before discussing pyrolysis, several definitions are in order. Pyrolysis
is defined here as a process that thermally decomposes carbonaceous material
in an atmosphere devoid of elemental oxygen. The products include gases,
organic liquids, and a carbon char. Terms such as destructive distillation,
thermal cracking, carbonization, and degasification have been used to describe
pyrolysis. To be a true pyrolysis process, heat generation must occur in
a vessel separate from the reactor, with indirect heat transfer through a
wall, via a recirculating heat transfer media (sand, char, molten metal),
or a hot flue gas produced by combustion of. a fuel using a stoichiometric
oxygen/fuel mixture. An important industrial example of pyrolysis is the
coking of coal in batch feed retorts for metallurgical uses.
Gasification processes involve pyrolysis as well as reactions between
the solid carbon char and gases such as C02 and H20. While a continuous
flow pyrolysis reactor may contain a drying zone as well as a pyrolysis zone,
a gasification reactor may also contain a char gasification zone (not
necessarily as separate zones) and a char combustion zone. Gasification
processes using combustion of char are autothermic in nature. The heat source
may be internal to the reactor (char combustion) or the char may be combusted
in a separate vessel with hot char or some other heat carrier recycled to
the reactor. Oxygen (perhaps air) and steam may be injected into a
gasification reactor; the reactions that occur are described in the following
paragraph.
Reactions
The composition and relative amounts of products produced in the
pyrolysis or gasification of solid wastes are extremely difficult to predict.
The reactions that occur are simplistically described in Table 28. The
temperatures at which various pyrolysis reactions occur may be roughly
divided into three ranges:
78
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TABLE 28. PYROLYSIS AND GASIFICATION REACTIONS
Pyrolysis of Solids arid Condensible Gases (Organic Liquids)
Carbonaceous
solids
Heat
High and moderate
molecular weight
organic liquids + Carbon
(tars, oils,
aromatics)
char
Low molecular
weight organic
liquids (some
oxygenated)
, ,
H2
. .
CO + C02 + NH3
+ H2S + COS + HCN
Organic
liquids
L°
liquids
Pyrolysis Gas Phase Equilibria
„ , Aromatic organic . °Y ™>ecu*r
Heat liquids weight organic + Gases + Char
liquids
+ H20f . + CO + 3 H2
CO
H20
, ,
Char Gasification
2H20
f .
»; C02 + H2
-»• C02 + 2H2
-> CO + H2
+ 2CO
Endothermic
Slightly exothermic
C + H20
C + C02
C + 2H2
Char Combustion for Gasification Heat Source
C + 02
C02
Endothermic
Exothermic
Exothermic
a.
'Because of this reaction methane yield decreases greatly as temperature
increases.
High energy consuming reactions.
3At atmospheric pressure, the equilibrium conversion to methane is quite
low and decreases as temperature rises from 1000°F to 1500°F. High
pressure operation is required to achieve significant degree of
hydrogenation of char or liquid products.
79
-------
<100°C Drying (free water evolved)
200 to 500°C Decomposition of high molecular weight compounds
such as cellulose, lignin, proteins, and fats to
relatively large quantities of organic liquids,
some gases, and char
500 to 1200°C Decomposition to permanent gases and char
The actual yield of products from carbonaceous solids is determined
by the following factors: the characteristics of the input material (C/H/0
ratios, type of organic structure, moisture content); the reaction conditions,
such as heating rate (which is a function of particle size, heat transfer
technique, temperature driving force); temperature levels; and residence
time in various temperature zones of the reactor (which determines the
extent of thermal cracking). Note that a pyrolysis process with concurrent
solids flow may involve gasification of a significant quantity of char via
reaction of water evolved from the drying zone of the reactor. In such a
case, the moisture content of the feed may be a significant factor in
determining char yield and gas yield.
Reactor Types
Only continuous flow reactors are considered in this discussion. To
describe a process reactor adequately one must specify:
• Relative direction of gas and solids flow (cocurrent or
countercurrent, also referred to as updraft or downdraft
for systems with down-flowing solids)
• Method of heat transfer (direct or indirect)
• Method of solids removal (slagging vs. nonslagging)
The major reactor types now being developed or used for pyrolysis and
gasification of solid wates include:
Vertical top feed shaft reactors
Vertical transport reactors
Multiple hearth reactors
Fluidized bed reactors
Rotary kiln reactors
Horizontal shaft reactors
By varying the relative direction of gas and solids flow, heat transfer
methods and solids removal, over a dozen distinctly different processes are
possible using the six types of reactors listed above.
Form of Energy Produced
Processes for pyrolysis or gasification of solid wastes may be
selected and designed to produce varying amounts of organic liquids, char,
80
-------
and gaseous products. The products may be directly fired in a combustion
chamber for steam production or processed for storage and subsequent use.
Removing condensible organics and water vapor from gases can, however, produce
a very significant water pollution problem. The higher the moisture content
of the feed to the reactor, the larger is the volume of the wastewater. One
of the processes to be evaluated in this study involved predrying, which is
one method to minimize the problem.
PROCESSES
Tech-Air Process
The Tech-Air process, originally developed at Georgia Tech's Engineering
Experiment Station, uses air to pyrolyze wastes in what might be described
as a vertical kiln. The waste organic feed enters the top of the kiln and
air is injected near the bottom to provide the partial combustion necessary
to release the energy for pyrolysis. The products include: solid char
(discharged from the bottom of the reactor); tars and liquids with varying
boiling points and molecular weights; water; and noncondensible organic
gases (hydrogen, carbon monoxide, carbon dioxide and nitrogen).
The Tech-Air process is used commercially to produce char and pyrolysis
oils from wood waste. The gases in this case are burned to provide heat
to dry the wood before it enters the kiln.
The process was also used to pyrolyze cotton gin waste in an early
pilot scale unit at Georgia Tech. However, operating problems were
encountered and, even though an extended run was achieved, the feed rates
were lower than expected, and little or no condensible liquids were obtained.
Other wastes were also run through the pilot scale unit but none of the
other wastes are being considered in this study.
(3)
Purox Process
The Purox® process differs from most other pyrolysis systems in three
respects. First, and most important, oxygen is used instead of air (or
indirect heating) to provide the partial combustion needed to supply the
energy for pyrolysis. Second, all, or nearly all, of the organic matter is
either oxidized or pyrolyzed into gaseous components (a medium Btu-eontent
gas); no solid organic or char remains. Third, production of a liquid
organic stream or oil is minimized or nearly eliminated; virtually the sole
product is a medium Btu-content gas.
The large Purox® process pilot plant at South Charleston, West Virginia,
has only been operated with municipal refuse as the feed. No experimental
evidence is available that shows the Purox® process will function on the
types of waste considered here. The Purox® converter appears to operate
best when about 20% of the feed is noncombustibles. The noncombustibles
form a melting bridge at the hearth zone, which tends to prevent unreacted
organic materials from falling into the slag quench water below the hearth.
Because of the low ash and negligible metals content of the waste feeds
81
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considered here, the converter configuration, particularly in and around the
high-temperature hearth zone, would probably have to be altered to prevent ex-
cessive loss of organics into the slag pit. (Another alternative might be to
mix the wood, cotton, or rice waste with municipal refuse to provide the higher
metal content in the feed. That alternative has not been considered here.)
SRI has assumed, and Union Carbide concurs, that the Purox® converter shape
can be changed so it can accommodate the waste feeds being studied.
PROCESS FEEDS
Wood Residue
Wood residue that can be fed to pyrolysis units includes bark, sawdust,
branches, other mill residue, and leaves or slash. With the exception of the
leaves, these wastes have a higher moisture content — sometimes as high as
70%, but more typically 50%. Ash content is low (1 to 3%) and the carbon-to-
oxygen ratio is higher than in agricultural residues, due to the high lignin
content of wood. Also, the residue is dense enough to make uniform in size
for easy handling. Except for the high moisture content, the chemical and
physical properties of wood make it easier to process in pyrolysis units than
some of the other agricultural wastes.
The elemental analysis of the wood waste assumed for this study is as
follows:
Element Dry wt %
Carbon 49.6
Hydrogen 5.7
Oxygen 43.7
Nitrogen 0.2
All other 0.8
As with all natural materials, the analysis of the material actually
being processed at any one time can vary over a sizeable range. For
example, the carbon content on the limited number of samples of wood residue
run by Georgia Tech ranged from 45 to 49%.
The feed is assumed to be 50% moisture.
An analysis of all other elements in the feed is provided by data10*11
in Table 29.
Rice Hulls and Straw
Rice hulls .and straw differ from wood waste in at least three important
respects. First, they tend to contain much less water, as shown in Table 30
(wood waste contains typically 50% moisture; rice waste contains 5 to 10%
moisture). Second, rice waste has a higher ash content, in some cases over
20% (see Table 30) whereas ash in wood typically runs 1 to 2%. Third, the
82
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TABLE 29. APPROXIMATE ANALYSIS OF ALL OTHER COMPONENTS^
Cations
Iron
Vanadium
Manganese
Potassium^
Zinc
Copper
Nickel
Chromium
Cobalt
Percent of
total feed
0.26
0.09
0.14
0.06
0.035
0.005
0.008
0.007
0.002
Anions
Chloride
Phosphate^
Sulfur
Percent of
total feed
0.14
0.06
0.005
a
Source: Reference 11.
Source: Reference 12.
TABLE 30. ASSUMED ANALYSIS OF RICE HULLS AND STRAW
Carbon
Hydrogen
Oxygen
Nitrogen
Sulfur
Ash
Moisture
Straw
(wt %)
38.5
5.7
39.8
0.5
-
15.5
7.6
Hulls
(wt %)
35.8
5.4
39.1
0.6
0.1
19.0
7.4
carbon-to-oxygen ratio in rice waste usually is less than 1, while the ratio
is greater than 1 in wood waste. The lower ratio means that the heat of
combustion is lower per pound of organic matter in rice waste than in wood.
This lower heat, coupled with the low bulk density of rice waste and its
tendency to agglomerate and bind rather, than flow, may present operational
problems in the pyrolysis units that are difficult to overcome.
As an indication of the variations in analysis that can be expected,
the ash content of rice hulls has been reported as low as 13.6% and as high
as 24.2%.
The waste rice hulls and rice straw available in California are:
Hulls
Straw
16,300 tons/yr
875,600 tons/yr
83
-------
The feed to the Purox® system is assumed to be 8,000 tons/yr of hulls
and 322,000 tons/yr of straw. So, the analysis of the rice waste feed to
the Purox Unit is as follows:
Element Wt %
Carbon 38.44
Hydrogen 5.69
Nitrogen 0.50
Oxygen 39.78
Ash 15.59
Moisture 7.60
The waste rice hulls and rice straws available in Mississippi are:
Hulls 9,000 tons
Straw 56,000 tons
While a 100-ton-per-day Tech-Air unit could be operated in Mississippi on
rice waste alone, considerable cotton gin trash and cotton field waste are
also available, so the assumed feed to a Tech-Air unit in Mississippi is a
mixture of all these wastes. The analysis of that mixture is provided as
part of the description of the cotton waste.
Cotton Waste
Cotton waste comes from ginning operations and from the field. The
waste generally has the same composition. The elemental composition assumed
for this waste is shown below:
Element Dry wt %
Carbon 47.3
Hydrogen 6.0
Nitrogen 1.6
Oxygen 39.0
Ash 6.1
Moisture 5.0
Cotton waste is slightly different from other wastes being considered
in that the moisture content is low and the carbon-to-oxygen ratio is high.
The mixed rice and cotton waste feed proposed for the Tech-Air process
would come frpm Bolivar County, Mississippi. The quantities available are
(in tons per year, dry wt.).
Cotton gin waste 12,000
Cotton field waste 32,000
Rice hulls 9,000
Rice straw 56,000
Total 109,000
84
-------
The elemental composition of a feed composed of these wastes in the same
proportions as generated — which SRI has assumed for this mixed feed case —
would be as shown below:
Element Dry wt (%)
Carbon 41.8
Hydrogen 5.8
Nitrogen 1.0
Oxygen 39.4
Ash 12.0
Total 100.0
Moisture content 6.5 ~
Barley Straw Waste
Barley straw and rice straw have similar compositions except that the
barley straw generally contains less inorganic matter, so the ash content
is lower:
Element Dry wt %
Carbon 43
Hydrogen 6
Nitrogen 0.5
Oxygen 45
Moisture content 7 to 10
About 185,000 tons a year of barley straw is available in Kern County,
California as a feed to a pyrolysis unit. This quantity (560 tons/day)
is too small to be feasible for operation of a Purox® process unit because
the units come in 350-ton/day modules and a single module is seldom
economic. However, another 110,000 tons of cotton field waste (80,000 tons
per year) and cotton gin trash (30,000 tons per year) is also generated in
Kern County. The combined waste would be sufficient to operate at least a
700-ton/day Purox® unit (two modules). Even this size operation is
marginal, at best.
Assuming that the Purox® plant processes 700 tons/day of such waste
330 days/year and that the proportion of waste fed is the same as the
proportions available, the estimated composition of the individual and mixed
wastes are as shown on Table 31.
TECH-AIR WITH WOOD RESIDUE
Mass Balance
The Tech-Air unit would be designed to process 200 tons/day of wood
waste containing 50% dry solids and 50% moisture, wastes such as bark,
chips, sawdust, etc. This rate is equivalent to 16,700 Ib of feed per hour
85
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TABLE 31. ASSUMED ANALYSES OF BARLEY STRAW AND COTTON
MIXED WASTE FEED (MOISTURE FREE BASIS)(WT %)
Element
Carbon
Hydrogen
Nitrogen
Oxygen
Ash
Total
Moisture
Barley
straw
43
6
0.5
45.0
5.5
100
10
Cotton gin and
field waste
47.3
6.0
1.6
39.0
6.1
100
5
Barley/cotton
mixed waste
44.6
6.0
0.9
42.8
5.7
100
7.5
(the hour of operation being the basis of mass and energy balances provided
in this section). The basic components of the feed are cellulose and lignin.
The elemental analysis of the dry solids is approximately as follows:
Element Wt %
Carbon
Oxygen
Hydrogen
Nitrogen
All other
100.0
The above elemental analysis was used in SRI calculations. Some
variations in the percentages shown above are common and expected.
The flowsheet for the Tech-Air process using wood residue feed is shown
in Figure 19. The weights of the major elements of each numbered flow on
Figure 19 are provided in Table 32.
To derive the stream flows in Table 32, SRI made a number of
assumptions required primarily because the data available in Georgia Tech's
report10 did not specifically provide the information needed to develop the
case considered.
The major piece of missing data was the quantity, composition, and heat
content of the flowstream SRI has chosen to call the tars or condensible
pyrolysis gas. SRI has assumed that such a stream or streams exist because
of the "carbon" lost in each run. Such carbon losses ranged from 2 lb/100 Ib
of feed up to nearly 14 lb/100 Ib of feed. Since the carbon loss cannot
very well be built up in the pyrolysis furnace, one must assume that either
carbon or organic materials are escaping without being accounted for.
86
-------
NOMINAL CAPACITY: 100 TONS/DAY
MOISTURE FREE
VENT GAS
1
WASTE STORAGE
(SAWDUST AND
RICE AND COTTON
WASTE)
DRYER AND
COMBUSTION
CHAMBER
FURNACE
u-
TO DRYER
TO DRYER
CONDENSER
Figure 19. Georgia Tech pyrolysis process.
Using the ultimate analyses provided for Run 15, it was possible to
devise a complete energy balance and the material balance for the Tech-Air
system. The latter is as recorded on Table 32. That material balance also
includes a mass balance for carbon, hydrogen, oxygen, and nitrogen.
To close the material balance, the following material must be accounted
for: 6.3 Ib of carbon, 0.7 Ib of hydrogen and 8.4 Ib of oxygen per 100 Ib
of dry feed. This material, if available (and SRI has assumed it is) can
provide sufficient extra energy when combined with the combustible gases
used for drying the feed to permit operation of the pyrolysis furnace with
about 0.2 to 0.3 Ib of air per pound of feed rather than the 0.5 Ib of air
per pound of feed that would be needed otherwise. (SRI used 0.22 Ib of
air per pound of feed, although this may be a slightly lower ratio than what
can actually be used.) The advantage of the lower air-to-feed ratio is that
a higher proportion of the feed becomes saleable fuel oil or char.
87
-------
TABLE 32. TECH-AIR PYROLYSIS PROCESS STREAM FLOWS
(Ib/hr)
Stream
Carbon
Hydrogen
Nitrogen
-------
The hourly flow of the minor elements in the feed and char as reported
by Georgia Tech (Run 15) are as follows:
Feed
Iron 22 55
Manganese 12 13
Vanadium 7 11
Potassium 5
Zinc 3 12
Nickel 1 3
Chromium <1 <1
Copper <1 <1
Cobalt <1 <1
Chloride 12 3
Phosphate 5
Sulfur <1 <1
With the possible exception of the chloride ion, all of the minor
elements appear to remain in the char. Even if the chlorides are all
volatilized, their concentration in the off gases would be very low (10 Ib/hr
or 67 ppm by weight in the dryer vent gas) .
The major products of pyrolysis, in pounds per hour, are:
Char 2757
Oil 1414
Gas (both tar or conden-
sible and noncondensible) 4662
Water 1813
SRI has assumed that by proper design and operation the water, part of
which might report in the oil fraction, could all end up as part of the
pyrolysis gases used to provide heat for drying the wet wood residue.
The water shown separately above would be an integral part of the
off gases, unless it were impossible to keep it out of the oil fraction.
In either case, the quantity of water shown, 1813 lb, came from:
Moisture in the feed and
pyrolysis air 457
Product of pyrolysis
reactions 1356
Total 1813 lb
89
-------
The water formed by the pyrolysis reaction was determined by assuming
a reasonable C/H/0 ratio for the organic component in both the oil fraction
and the tar or noncondensible gas fraction. With the above assumption and
the elemental analysis, the percent of water in each fraction was
calculated.
The above method of calculation is a departure from the method used by
Georgia Tech.11 (They assumed that all the oxygen in the oil/water mixture
was in the water and they ignored the missing hydrogen and oxygen, along
with the "lost" carbon. This, again, was on the assumption that the
missing hydrogen and oxygen had combined to form water, even though the
ratios of the missing hydrogen and oxygen indicate otherwise.) The oily
products of pyrolysis of wood are known to be oxygenated organics. Such oils
typically contain 35 wt % oxygen.
Using the SRI procedure for calculating the water has three effects on
the analysis: it increases the quantity of oil formed; it decreases the
unit heat content of the oil product; and it changes the energy balances
of the system, particularly those in and about the pyrolysis furnace.
According to SRI's method of calculation, 1414 Ib of oil product are
formed per hour, with a heat of combustion of 11,806 Btu/lb. Using the
Georgia Tech procedure, 1008 Ib of oil are produced, with a heat of
combustion of 16,300 Btu/lb.
The effect on energy balance of the alternative methods of calculation
is described in the next subsection (Energy Balance).
The stream unaccounted for in the Georgia Tech analysis11 has been
assumed by SRI to be added as part of the fuel for drying the wood prior
to pyrolysis. The analysis of that fuel is shown on Table 33.
As is shown by the energy balance, this fuel provides more than enough
heat on combustion to dry the wood from 50% moisture to 5% moisture or less.
TABLE 33. FUEL FOR WOOD DRYING
Component Lb Wt %
rv na
Ln^i). U
CO
H2
CHij
C2
C3
Cit
C02
N2
H20
Total
1294
825
29
119
58
24
10
903
1400
1813
6475
20.0
12.7
0.4
1.8
0.9
0.4
0.2
14.0
21.6
28.0
100.0
Tar or condensible gas
90
-------
Energy Balance
The energy balances in the system are important, not only to indicate
what percent of the energy in the original feed becomes available in the
products but to indicate the operability of various system units, such as
the pyrolysis furnace and the feed dryer.
The heats of combustion of the dried feed and char were measured with
a Parr bomb at 7968 and 11078 Btu/lb, respectively. The heats of combustion
of the noncondensible gases can be calculated and the heat of combustion of
the oil and condensible gas can be estimated from their molecular composition.
The overall energy balance in millions of Btu per hour of operation is
as follows:
Heat of 1Q6 Btu/hr
combustion Lb/hr ^n Out
Feed 7968 8630a 68.76
Char 11078 2757 30.27
Oil 11806^ 1414 16.67
Totals 58.76 46.94
The 7968 Btu heat of combustion was presumably determined
on a feed that contained 3.44% moisture:
8333
= 8630 Ib
u.yooo
Calculated value.
0.9656
b
Over 68% of the original energy is recovered as usable energy in the
two products. The energy consumed, 21.82 million Btu/hr, must be sufficient
to perform the pyrolysis and drying.
The pyrolysis reaction can be depicted by the following equation:
C17.217H23.66°11.40(S) + 0.66 0,, = C +
C402H404°115W + C2.20H3.80°2.20(g) + ^ C° + ^ C°2 +
0.72 H2 + 0.37 CH4 + 0.10 C^ + 0.03 C^g + 0.01 C^ + 3.77 H£0
The enthalpy AH of this reaction is an estimated -129.503 Kcal/g-mol, which
would provide 4.65 million BTU/hr of energy to the pyrolysis system. Put
91
-------
another way, the energy balance around the pyrolysis furnace based on this
reaction is as follows, in millions of Btu/hr:
106 Btu/hr
Heat of
combustion Lb/hr In Out
Feed 7,968 8,630 68.76
Char 11,078 2,757 30.27
Oil 11,790 1,414 16.67
Noncondensible gases 10.17
Tars or condensible gases 7.00
Totals 68.76 64.11
The difference between the energy in and out is 4.65 million Btu.
If all 4.65 million Btu are used to heat the pyrolysis products, they
would leave the pyrolysis furnace at about 1050°F. Even though this estimate
does not include any heat losses from the furnace itself, it indicates that
the air-to-feed ratio used is quite adequate to provide stable operation of
the furnace.
The sensible heat in the condensible and noncondensible gases, plus
the energy from their combustion (assuming the gases from the condenser
enter the combustion chamber at about 200°F), would provide the following
energy for drying the wet wood, in millions of Btu/hr.
106 Btu/hr
Heat of combustion
Noncondensible gases 10.17
Tars or condensible gases 7.00
Sensible heat Q.45
Total 17.62
There are 7895 Ib of water to be removed from the residue feed in the
dryer. The energy available is 2232 Btu/lb of water to be removed. Most
commercial dryers reduce the moisture in the wood to 5% or less with 1700
to 1800 Btu/lb of water. The energy available for drying is also more than
adequate for the purpose.
92
-------
Energy is also consumed in the process for:
• Loading the refuse into the system via fork lift or front-end
loader
• Conveyors, pumps, lifts, fans, etc., that are part of the
process equipment.
The loading operation (17,000 Ib/hr) assuming a Hyster Model 50 that
consumes 2.5 gal/hr for operation would require O.SlxlO6 Btu/hr.
The process energy could be supplied by a 100 kW power substation or a
self-contained 100 kW motor-generator burning 19 gal of diesel oil per hour
(140,000 Btu gal). The 200 kW requirement is based on the design in the RM
Parsons's report rather than using the 150 kW capacity originally suggested
by Tech-Air.
Overall, the process energy requirement is:
106 Btu/hr
Loading 0.30
Processing 1.95 to 2.66
3xl06
and the net energy available from the system is 47.2 - 3, or 44.2 million
Btu/hr or 44.2xl06/16,667 = 2,650 Btu/lb of wet feed.
Pollution and Hazards
The Tech-Air system using wood residue as feed is unique in that no
solid or liquid residue results. Little or no pesticide is used on the
woods under consideration (Humboldt County, California) so pesticide
residue is probably not significant.
Land Disruption—
Land use is minimal. An acre appears more than adequate for feed and
product storage and for siting of the three trailers that would hold the
process equipment. If the plant operates 300 days/yr (assuming 2 moves/
year) and provides char and oil with a net combined energy content of
318xl09 Btu/yr (24 hr/day, 300 days/yr, 44.2 million Btu/hr), the land
requirements are 0.003 acre/109 Btu/yr.
93
-------
Air Pollution--
There are three sources of air emissions from the process:
• Loader
• Motor-generator (if used)
• Offgases from the wood residue dryer
Measured emissions from similar diesel engines installed in the loader
and motor-generator are shown in Table 34.
TABLE 34. DIESEL ENGINE EMISSIONS
(grams per brake horsepower-hour)
Hydrocarbons + NOX Carbon monoxide Smoke
Motor-generator (280 hp)
Brake horsepower 160 11 5 <3%
Loader 68 hp
Brake horsepower 50 11 5 -3%
Table 35 provides the results of a stack emission test of the dryer
offgases. Based on these results, the emissions from the total system are
as follows (in pounds per hour):
Engines Total
Carbon monoxide 4.5 2.3 6.8
N0xa negl. 5.1 5.1
Particulates 0.06 negl. 0.06
Includes some hydrocarbons.
All other possible pollutants — such as ammonia, sulfur dioxide, hydrogen
sulfide — are considered present in negligible amounts.
The summary of known impacts is provided on Table 36. The process
also could .generate some unquantifiable pollutants. The most likely are
particulates (fugitive dust) from the handling of the residue and its
grinding prior to being fed to the pyrolysis furnace. Careful handling and
hooding are needed to keep this source from adding significantly to the
pollution levels. Improper handling of the char product could also
generate fugitive dust.
Overall, this process should be an extremely clean source of energy.
94
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TABLE 35. ANALYSIS OF DRYER STACK EFFLUENTS
A. COMPONENTS DETECTED
Component
Water
Oxygen
Nitrogen
Carbon dioxide
Carbon monoxide
Particulates
Composition
by volume
14%
9.0%
69%
7.7%
30 ppm
14 micro
gms/ft3
Test method
Liquid impinger
collection
GCTCa
GCTC
GCTC
Liquid impinger
collection
Mass rate of
pollutants
(Ib/min)
N/A
N/A
N/A
6.5xlO~2
9x10-^
Component
B. COMPONENTS TESTED FOR BUT NOT DETECTED
Threshold sensitivity
of tests-/
(ppm)
Test method
Hydrogen
Methane
Sulfur dioxide
Nitrogen dioxide
Ammonia
Hydrogen sulfide
0.0009
0.0009
0.4
0.04
0.09
0.009
GCTC
GCFIDC
MSA?
MSA0'
Odor
Odor
Gas chromatography — thermal conductivity detector
MSA — Mine Safety Appliance Co. Test Part No. 91229
Q
Gas chromatography — flame ionization detector
MSA — Mine Safety Appliance Co. Test Part No. 92623
SMSA — Mine Safety Appliance Co. Test Part No. 83099
f
These components would have to be present in concentration shown to be
detected; therefore, these results represent the maximum amounts of these
components which could be in the stack gas
%/A — not applicable
Source: Reference 11.
95
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TABLE 36. ENVIRONMENTAL IMPACTS OF TECH-AIR PYROLYSIS
OF WOOD RESIDUE
Impact
Land
disruption
and use
Onsite Transport to
Resource processing conversion Conversion
extraction or storage plant plant
Acres/
109 Btu/
yr/output
0.003
Water
pollution
Input
Output
Waste heat
Ammonia
Phosphorus
Salts
Metals
Pesticides
Air pollution
NOX
CO
sox
H2S
Particulates
Pesticides
Hydrocarbons
Organisms
Solid waste
total
(gal/106 Btu)
(gal/106 Btu)
(Btu/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
0.57
0
0
0
0
0
0
0.12
0.15
negl.
negl.
negl.
0
incl. in NO,
0
0
Hazardous Materials—
The products of pyrolysis are extremely diverse.
for lists of likely products.
See Tables 37 and 38
TABLE 37. COMPOUNDS FORMED BY WOOD CARBONIZATION0'
a
Carbon dioxide
Ammonia
Water
Formaldehyde
Formic acid
Source: Reference 13.
Methanol
Methylamine
Glyoxal
Acetaldehyde
Acetic acid
96
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TABLE 37 (continued)
Methyl formate
Glycolaldehyde
Glycolic acid
Ethyl alcohol
Dimethylamine
Acrylic acid
Acetone
Allyl alcohol
Propionaldehyde
Methyl acetate
Propionic acid
Isopropyl alcohol
Propyl alcohol
Methylal
Trimethylamine
Succinic anhydride
Furan
Crotonaldehyde
Biacetyl
3-Butenoic acid
Butyrolactone
Crotonic acid
Methacrylic acid
Methacrylic acid, polymer
2-Butanone
2-Buten-l-ol
Butyric acid
Isobutyric acid
Methyl propionate
Isobutyl alcohol
2-Furyl methyl ketone
Catechol
5-(Hydroxymethyl)-2-
furfuraldehyde
4-Methyl 2-furoic acid
Methyl 2-furoate
Maltol
Pyrocinchonic anhydride
Pyrogallol
2-Picolene
2-Methyl-2-cyclopenten-l-one
4-Methyl-2-cyclopenten-l-one
2,5-Dimethylfuran
l-(3 or 4) Cyclohexanedione
2-Hydroxy-3-Methyl-2-cyclo-
penten-1-one
-Methyl ethylacrolein
Cyclohexanone
3-Hexen-2-one
Mesityl oxide
l-Hydroxy-2-butanone acetate
2,3-Hexanedione
4-Methyl-2-pentenoic acid
Hydroxy-2-propanone propionate
Levoglucosan
Cyclohexanol
Tetrahydro-2-5-dimethylfuran
3-Hexanone
Butyl methyl ketone
2-Methyl-3-pentanone
Caproic acid
Isocaproic acid
-Methylvaleric acid
Methyl valerate
Toluene
o-Cresol
m-Cresol
p-Cresol
Guaiacol
l-Methoxy-2,3-dihydroxybenzene
5-Methyl pyrogallol
Lutidine
l-Methyl-2-cyclohexen-5-one
Propylfuran
2,3,5-Trimethylfuran
1-Heptyne
Cyclohexanecarboxaldehyde
Dimethylcyclopentanone
2-Ethyl-2,3-dihydro-5-methylfuran
5-Heptenoic acid
Butyrone
Enanthaldehyde
Methyl caproate
Enanthic acid
Heptane
Benzofuran
m-Xylene
o-Ethylphenol
2,3-Xylenol
2,4-Xylenol
3,5-Xylenol
Creosol
6-Methylguaiacol
2,6-Dimethoxyphenol
Methoxy-4-homocatechol
2,4-Dimethyl-4-cyclohexene-l-one
Methylcyclopentanone
3-Isopropyl-2-cyclopenten-l-one
97
-------
TABLE 37 (continued)
Trimethylcyclopentanone
3,5-Octanedione
Caprylic acid
Methyl enanthate
Dihydroxycaprylic acid
4-Vinylguaiacol
Cumene
P s eudo cutnene
3,5-Dimethylguaiacol
4-Ethylguaiacol
Homoveratrole
2,6-Dimethyoxy-4-Methylphenol
5-Propylpyrogallol
Isophorone
Amy1furan
2,4,4-Trimethylcyclohexanone
Cyclohexanepropionaldehyde
3,3,5-Trimethylcyclopentanone
Pelargonic acid
Naphthalene
Estragole
Eugenol
Isoeugenol
Cymene
Durene
Thymol
4-Propylguaiacol
2,6-Dimethoxy-4-ethylphenol
A5-propyl-monomethyl ether of
pyrogallol
Camphene
Limonene
Nopinene
Pinene
Sylvestrene
-Terpinene
Terpinolene
Camphor
Borneol
Cineole
Melene
Frenchyl alcohol
Isofrenchyl alcohol
-Terpineol
Capric acid
l,3,3-Trimethylbicyclo(2.2.2)
5-octen-2-one
5-Propyl-l,3-dimethoxy-2-
hydroxybenz ene
2,5-Difurfuryledine-1-cyclo-
pentanone
Cadinene
Pentadecane
Palmitic acid
Heptadecane
Chrysene
Retene
Oleic acid
Stearic acid
Octadecane
Nonadecane
Abietic acid
Pimaric acid
Arachidic acid
Eicosane
Heneicosane
Behenic acid
Docosane
Tricosane
Lignoceric acid
98
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TABLE 38. COMPOUNDS REPORTED TO BE PRESENT IN HARDWOOD SMOKEa
Acids
Phenols
Formic
Acetic
Propionic
Butyric
Aconitic ?
Tricarballylic ?
a-Ketoglutaric ?
Alcohols
Methane1
Ethanol
Carbonyls
Formaldehyde
Acetaldehyde
Acetone
Diacetyl
Furfural
Methyl Furfural
Hydrocarbons
3,4-Benzpyrene
1,2,5,6-Dibenzanthracene
20-Methylcholanthrene
Cresols
Creosol
Guaiacol
Guaiacol derivatives
4-Ethyl
4-Propyl
6-Methyl
6-Ethyl
6-Propyl
Pyrogallol ethers
1-0-Methyl
1,3-Dimethyl
1,3-Dimethyl Pyrogallol derivatives
5-Methyl
5-Ethyl
5-Propyl
l-O-Methyl-5-Methyl Pyrogallol
Veratrole
Xylenols
Others
Ammonia
Carbon dioxide
Resins
Water
Waxes
a
Source: Reference 13.
SRI's Chemical Environmental Group has identified (from the chemicals
listed in Table 37) 22 chemicals or chemical groups that are or might be
carcinogens or otherwise hazardous materials. These chemicals and the
reasons they are considered hazardous are listed below:
Dimethylamine
Butyrolactone
May form the potent carcinogen,
dimethylnitiosamine, under conditions
of nitrosation.
Structurally related to the known
carcinogen, beta-propiolactone. How-
ever, as a five-membered lactone,
butyrolactone is expected to be less
reactive as an alkylating agent and hence
less carcinogenic. No carcinogenic
effects have been observed in tests on
mice by oral, topical, or subintaneous
99
-------
Catechol
Pyrogallol
0-Cresol
M-Cresol
P-Cresol
Estragole
Limonene
• Pinene
Chrysene
• Oleic acid
administration and in rats by sub-
intraneous administration. Tumors were
produced in a single test in weanling
rats by oral administration but the
significance of these results is
questionable due to inadequate protocol.
Known to be a cocarcinogen due to its
ability to significantly enhance the
carcinogenicity of benzo[a]pyrene in
mouse skin.
Known to be a cocarcinogen due to its
ability to enhance the carcinogenicity
of benzo[a]pyrene in mouse skin.
Known to be tumor promoters because of
their ability to elicit skin tumors in
mice by repeated applications following
a single, subcarcinogenic dose of
7,12-dimethylbenz[a]anthracene.
Should be considered a suspected
carcinogen until proven otherwise by
adequate testing because of its
structural relationship to safrole, a
known carcinogen in mice and rats.
Known to have tumor promoting activity
in mouse skin.
Reported to have tumor-promoting
activity in mouse skin.
Has produced skin tumors in mice
following repeated topical applications.
Produced low incidence of local sarcomas
in mice following subcutaneous
administration. Is an initiator of
skin tumors in mice when followed by
promotion with croton oil. Hence,
chrysene should be considered a weak
carcinogen.
Reported to have tumor-promoting
activity in mouse skin.
100
-------
Octadecane
Eicosane
3,4 Benzpyrene
1,2,5,6 Dibenzanthracene
20-Methylcholanthrene
Cresols
Creosol
Xylenols
Known to be a cocarcinogen in mice by
its activity to enhance the rate of
induction of skin tumors by
benzo[a]pyrene. It is also a known
tumor-promoter in mice by its ability
to elicit skin tumors by repeated
topical applications following a
single, subcarcinogenic dose of
7,12 dimethylbenz[a]anthracene.
Same as for Octadecane.
Is both a local and systemic carcinogen
in all animals in which it has been
tested by several routes of administra-
tion including oral, topical, intra-
tracheal and inhalational, and
subcutaneous.
A local and systemic carcinogen in mice,
rats, guinea pigs, frogs, pigeons, and
chickens by different routes of
administration including oral, topical,
and subcutaneous.
A local and systemic carcinogen in
several species, including mice and
rats, by several routes of administration
including topical, subcutaneous,
intratracheal, and oral.
As cited previously (Table 37) cresols
are known tumor promoters.
One of the active constituents of
creosote. Wood creosote is a wood tar
phenol mixture which is an irritant
and probable tumor-promoter. Coal tar
creosote is an aromatic hydrocarbon
containing coal tar distillate which is
carcinogenic in animals by topical
application.
As cited above (Table 37) xylenols are
known tumor-promoters.
With this information in hand, we must consider the pyrolysis oil a
possible carcinogen and recommend that it be handled as such until data
are available on the pyrolysis oil itself. The carcinogenic nature of
several of the components of the pyrolysis products should prompt a study
of the various streams and emission from the plant to determine the extent
of the hazard.
101
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PUROX® WITH WOOD RESIDUE
Refuse, the only waste fed so far to the large pilot plant, not only
has a higher percentage of noncombustible (metal, glass, dirt) material, but
generally has a lower moisture content than undried wood waste. The major
effect of changing from refuse to wood, other than the converter configuration
changes already mentioned, is the higher oxygen-to-feed ratio required. The
extra oxygen is needed to increase the heat release in the converter in order
to evaporate the extra water present in the wood. (Less energy is needed
to melt the smaller amounts of inorganic residue in the wood, but this is
more than offset by the heat needed for the moisture evaporation).
The proposed location to process wood residue by the Purox® system is
somewhere in Humboldt County, California. The county is small enough and
the quantities of avilable wood residue large enough that the plant can
probably be located near lumber mills; no further purification, drying, or
major compression of the product gas would be necessary to prepare it for
pumping to plants that can use it.
Mass Balance
Purox® converters are designed to process 350 tons/day of refuse. For
wood residue, a system is envisioned with three converters that would
process 83,333 Ib/hr (1000 tons/day) of wood waste.
The flowsheet for the Purox® process using wood residue feed is provided
as Figure 20.
An examination of the elemental and basic composition of the wood residue
and refuse (Table 39) shows the big difference between the moisture and ash
content in the two feeds. However, the sum of moisture plus ash in wood,
50.4%, and in refuse, 45.0%, is not that different. Also, the carbon-to-
hydrogen ratio (and even the carbon-to-oxygen ratio) is about the same.
Based on this similarity, one can assume that the distribution of pyrolysis
products is about the same for wood residue as for refuse.
Table 40 shows the estimated analysis of the offgas before and after
it has passed through the condenser to remove most of the water and the
condensible organics.
Union Carbide, the developer of the Purox® process, has found that more
oxygen is needed (0.23 Ib/lb feed) to achieve the offgas composition shown
on Table 40 than is necessary for refuse (0.2 Ib/lb refuse). The oxygen-to-
feed ratio for wood residue was determined from an analysis of the energy
release and the energy requirements in the case of refuse feed as compared
to the case of wood residue feed.
The ratio actually required may be somehwat lower than the 0.23
indicated. The actual ratio used will be set so the temperature of the gases
leaving the converter will require some cooling (adiabatic) in the spray
condenser. SRI has assumed that the gases leaving the converter must have
102
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NOMINAL CAPACITY: 1,000 TONS/DAY
o
LO
WASTE
STORAGE
\
OXYGEN
PLANT
CONVERTER
O
SPRAY
CONDENSER
SOLID-LIQUID
SEPARATOR
ELECTROSTATIC
PRECIPITATOR
GAS-COOLED
CONDENSER
LIQUID
SEPARATOR
WASTE WATER
| TREATMENT |
. (OPTIONAL) |
I •
I , !
Figure 20. Purox® process.
-------
TABLE 39. COMPARISON OF WOOD RESIDUE AND REFUSE COMPOSITION
(wt %)
Wood residue Refuse
Carbon
Hydrogen
Nitrogen
Oxygen
Ash
Moisture
24.8
2.8
0.1
21.9
0.4
50.0
29.0
3.2
N/A
22.8
17.9
27.1
TABLE 40. PUROX® PRODUCT GAS ANALYSIS (FROM WOOD RESIDUE FEED)
Wt % Vol %
(wet product gas) (cool, noncondensibles)
CO
C02
H2
C2H2
C2H4
C3
Cit+
(COH2)N
20.9
24.4
0.7
1.3
0.2
0.8
0.1
0.4
1.5
0.1
40.5
30.1
18.8
4.4
0.5
1.6
0.2
0.4
1.2
0.2
Condensible 1.6
organic
N2
H20
TOTAL 100.0 99.9
2 million Btu/hr of heat removed in order to condition it for passage
through the electrostatic precipitator. The cooling is achieved by
evaporating just over 2000 Ib/hr of water in the spray condenser.
The extra oxygen used was distributed between the carbon monoxide and
carbon dioxide to use the carbon remaining after distributing the available
hydrogen among the hydrocarbons and water in the same proportions as it
was distributed among these products when refuse was the feed.
104
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Union Carbide has considered the ultimate fate of all other components
because these and many more minor elements are likely to be present in the
refuse. From their analyses of the slag and metal residue fractions and the
material condensed from the offgases, all other components are found entirely
in the slag residue with the following exceptions: chromium, copper,
manganese, nickel, zinc, sulfur, and chlorides.
Based on Union Carbide's analyses, the fate of the minor elements in
the wood residue is as shown in Table 41.
TABLE 41. DISPOSITION OF MINOR CONSTITUENTS IN WOOD RESIDUE
FED TO PUROX® PROCESS (Ib/hr)
Iron
Manganese
Vanadium
Potassium
Zinc
Nickel
Chromium
Copper
Cobalt
Chloride
Phosphate
Sulfur
Feed
108
58
38
25
15
3
3
2
<1
58
25
2
Slag
(or metal)
108
58
38
N.D.
14
3
3
<1
N.D.
25
Wastewater
N.D.*
0.08
—
N.D.
1.2
0.03
0.001
<0.0001
58
N.D.
Offgas
2
a.
N.D. = no data
Energy Balance
The energy balance about the converter in millions of Btu/hr of operation
is as follows:
Btu/lb
4126
a
106 Btu/hr
Feed
Gas
Organic in
wastewater
TOTAL
aThe heat of combustion (7968 Btu/lb) was calculated for a feed that
contained 3.44% moisture. A feed with 50% moisture should have the
heat of combustion shown.
In
343.83
343.83
Out
235.02
17.46
252.48
105
-------
Thus, 68% of the energy available in the feed, as measured by the heat of
combustion, is still available in the fuel gas product. The 91.35 million
Btu/hr consumed by the process (343.83 - 252.48) is used to perform the
pyrolysis which, in this case, includes drying the feed. The reaction
involved in providing the energy for pyrolysis and drying can be described
as follows:
C17.22H23.65°11.40 + 5'"°2 = 7'66 C0 + 5'69 C02 + 7'12H2 + 3'93H2°
+ f\ Q O ^TT |_ f\ ^ f\^ TT 1 f\ O f\fl TJ I 'f\ f\/, O TI
w • o j w£i • IT \j * A-\J\J & £1 A T^ \j • j ui«» ft a I ^r \j • WT\J ** n. ^
+ 0.08C + 0.226 C^ + 0.03COH2 + 0.37C2H,0(1)
The theoretical heat of the reaction (AH reactions -518.6 Kcal/g-mol)
would provide 93.35 million Btu/hr of energy, which is in fair agreement
with the 91.35 million Btu/hr, considering the number of assumptions
required to derive the figure.
Much of the 91.35 to 93.35 million Btu/hr is present in the gases
leaving the converter. If the gases leave the converter at 250°F, their
sensible heat content would be 56.99 106 Btu/hr, as shown in the following
tabulation:
H^f0 Sensible heat
Ib/hr Btu/lb 106 Btu/hr
H20 48,733.9 1,118.9 54.53
Other gases 52,268.2 41.5 2.17
Liquifier
Organic 1.640.9 175
TOTAL 102,643
Some additional heat would leave the converter in the hot slag. If we
assume the slag temperature is 2777°F, the sensible heat in the slag would
be 0.17 million Btu — (2777 - 77)*(0.2)t(315)*.
The heat loss in the converter then is around 34 to 36 106 Btu/hr. This
loss appears about the same as the heat loss when the feed is refuse instead
of moist wood.
*
Temperature difference, F
Specific heat of solid, Btu/lb
*Weight of slag, Ib
106
-------
Energy is also consumed in the processing of wood residue to:
• Operate the air separation plant
• Load the waste into the system
• Drive the various motors and fans required in the process itself
The air separation plant requires an estimated 300 kWh. If we assume
that 9400 Btu of fuel energy makes 1 kWh of electricity, the energy
requirement for air separation is 28.2 million Btu/hr.
The loading operation (83,330 Ib/hr), assuming two 120-hp loaders
that each consume 6 gal/hr of diesel fuel, requires 1.5 million Btu hr.
No definite value was found for the amount of energy required to drive
the converter and gas cleanup system. SRI has assumed that 20 kWh/ton for
this purpose, which is equivalent to 833 kWh/hr, or 7.8 million Btu/hr.
In summary, the process energy requirements are:
106 Btu/hr
Loading 1.5
Air separation 28.2
System operation 7.8
37.5
and the net energy available from the system is 235.02 - 37.5 or 197.5
million Btu/hr, which is equivalent to 197.5xl06/83,333 = 2,370 Btu/lb of
wet feed.
Pollution and Hazards
The Purox® system has one important waste stream — the wastewater
condensed from the converter offgas — and two minor streams — the slag
and cooling tower blowdown. The slag, which should be primarily metals or
metal silicates, should present no pollution or hazard problem. The blowdown
is also minor and should pose no problem. Since little or no pesticide is
used in the forests where the wood residue comes from, pesticide residue
should not be a problem.
Land Disruption—
A small amount of land, no more than 0.06 acre/yr, need be dedicated to
slag disposal. To accommodate the slag for the life of the plant, 1 acre
was set aside for slag disposal. Union Carbide has estimated that a
1000 ton/day plant requires about 9.5 acres, including space for a Unox
wastewater treatment system (estimated at 1.67 acres). SRI has assumed
9.5 acres is more than adequate for the plant, plus another 2 acres for
storage of a week's supply of wood residue. If the plant operates
107
-------
330 days/yr and provides gas with a net energy content of I,560xl09 Btu/yr
(24 hr/day, 330 days/yr, 197.5 million Btu hr), the land requirements are
0.008 acre/109 Btu/yr (9.5 + 2 + 1/1560). If the wastewater treatment system
is not included, land requirements reduce to 0.007 acre/109Btu/hr.
Air Emissions—
If the offgas is not dried and compressed and if electricity is the
source of energy used to operate the plant, the only sources of emissions
would be the exhaust gases from the loaders and fugitive particulate
emissions from moving dusty material to and from storage and into the process.
The amount of fugitive emissions depends on the method used and the care
exercised, so those emissions cannot be quantified.
The estimated emissions from the two loaders and the total system are
as follows:
Ib/hr
Carbon monoxide 2.7
Nitrogen oxide plus hydrocarbons 5.9
Large quantities (65,000 Ib/hr) of nitrogen and carbon dioxide will be
discharged from the air separation plant but neither are considered
pollutants.
The contaminants in the offgas that are eventually burned are one
indirect source, as are the emissions from the trucks used to deliver the
wood residue to the plant. Another indirect source is the emission from
power plants that supply the energy to operate the air separation plant,
the Purox® system itself and, if required, the associated wastewater
treatment system.
A summary of the direct environmental impact from the pyrolysis of
wood residue via the Purox® process is provided in Table 42.
Water Pollution—
The two possible sources of water pollution from the Purox system are
the water condensed from the gas and leachate from the slag dump. The
condensed water contains appreciable amounts of light organics, either
steam-distilled from the wood or produced during pyrolysis. These organics
are soluble in the condensed water and are too heavy to report to the gas
stream.
Data provided by Union Carbide indicates that the organics are
GI to Cij aliphatics compounds and low molecular weight aromatics such as
phenols, benezene, and furans. Unfortunately, the diversity of the
compounds and the large dilution in the water makes recovery impractical.
In addition to the organic compounds, metallic substances are present
in the wood and some are likely to be volatilized and end up in the
wastewater. Table 43 shows the pounds per hour of minor elements in the
108
-------
TABLE 42. ENVIRONMENTAL IMPACT OF PUROX® PYROLYSIS OF WOOD RESIDUE
Impact
Onsite Transport to
Resource processing conversion Conversion
extraction or storage plant plant
Land
disruption
and use
Water
pollution
Input
Output
Wasteheat
Ammonia
Phosphorus
Salts
Metals
Pesticides
Air pollution
NOX
SOX
H2S
Particulates
Pesticides
Hydrocarbons
Carbon
monoxide
Organisms
Solid waste
total
Acres/
109 Btu/
yr output
(gal/106 Btu)
(gal/106 Btu)
(gal/106 Btu)
(gal/106 Btu)
(gal/106 Btu)
(gal/106 Btu)
(gal/106 Btu)
(gal/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
0.008
1.25?
3.17b
0.29
N/A
0
negl.
0
negl.
0
negl.
0
0.03
0.01
0
1.6
a.
For adiabatic cooling only
Includes condensed moisture from feed
*
'Included with hydrocarbons
wood residue feed and an estimate of the quantity and concentration likely
to be in the slag and in the wastewater.
The chloride ion, if it reaches the 800+ mg/£ concentration in the
wastewater, could present a problem since the concentration would probably
not be reduced by secondary treatment and the drinking water standard for
the chloride ion is 250 mg/Jl.
The concentration of zinc, 31 mg/&, also exceeds the safe drinking
water standard of 5 mg/&. However, the zinc concentration could be reduced
109
-------
TABLE 43. ESTIMATED DISPOSITION OF TRACE ELEMENTS IN WOOD RESIDUES
FED TO PUROtf8 SYSTEM (Ib/hr)
Element
Iron ,
Chlorine
Zinc
Nickel
Manganese
Potassium
Vanadium
Chromium
Copper
Cobalt
Feed*
108.3
56.7
14.6
3.3
58.3
25.0
37.5
2.9
2.1
0.8
Slag*
NRC
14.2
13.0
3.2
58.3
NR
NR
2.9
2.1
NR
Waste-
water^
NR
42.5
1.6
0.1
0.01
NR
NR
0.002
0.0002
NR
Concentration in
wastewater
(mg/A)
__
815e
31
1.5
0.1
—
—
negligible
negligible
__
aData from Georgia Tech
Data from Union Carbide
NR means not reported
Based on statements made by Union Carbide — organic chloride reports to
wastewater and inorganic chloride reports to slag — and data from Georgia
Tech that shows 1/4 of chloride in wood ends up in the char.
SUnion Carbide reports maximum chloride concentrations of 20 ppm in the
condensate. Based on data from Georgia Tech, the wood residue contains
over 0.1% chloride ion and 2/3 of this reports to the gaseous phase.
Since very little, 1 ppm, is in the noncondensible gases, 2/3 must be in
the condensate. So, chloride ion concentration must be much higher than
reported in the Union Carbide tests.
during treatment to suitable levels. None of the other trace elements
appear to present a pollution hazard or problem in the concentrations
expected in the wastewater.
Leachate from the slag dump is another potential source of water
pollution. Union Carbide had perimeter tests performed on their slag and
some slag soil mixtures. Lead was the only element leached from the slag
that exceeded the 0.05 mg/£. limit set for drinking water. Since lead is
not reported as a trace element in wood residue (at least not in the residues
tested by Georgia Tech), ground water contamination from slag-pile leachate
appears to be no problem, at least as far as contaminating drinking water
is concerned. However, there should be some soluble potassium and phosphate
in the slag. Phosphate, in particular, can cause eutrophication if too
much is allowed to enter surface waters, especially lakes or bays. Most
soils absorb phosphates, so impoundment of any leachate should be sufficient
to prevent phosphate contamination of surface waters.
110
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-TECH-AIR WITH -RICE AND COTTON WASTES
The Tech-Air system should be able to process the mixed rice and cotton
waste and do so more simply and economically than it can process wood
waste. The moisture content of the rice hulls and straw (7 to 10%) appears
low enough that drying can be eliminated. Even though the rice and cotton
waste is less dense and probably does not flow as easily as the wood waste,
experience with cotton gin trash as feed to the system indicates that
mechanisms can be developed to make the waste move through the furnace
efficiently and effectively.
Mass Balance
Predicting a mass balance for the system using rice and cotton waste,
however, is another matter. Even though these wastes are composed of
cellulose and lignin (just as are wood wastes), SRI cannot, based on the
data available, estimate the weights or compositions of the products of
pyrolysis with any reasonable degree of certainty.
This uncertainty stems, in part, from the difficulty Georgia Tech had
trying to pyrolyze cotton gin trash. Even though the objective of that
pyrolysis was to produce an oil fraction, they were unable to do so. This
result is in marked contrast to the pyrolysis of wood, where the oil fraction
was 6 to 20% of the feed. Another reason for the uncertainty is the
differences between pulping of wood and rice. Rice straws are encased in
a hard, noncellulosic skin. Removal of this skin in pulping of straws
requires fairly drastic treatment with caustic. This skin could affect the
rate and products of pyrolysis. The different heat transfer characteristics
between the straw and wood could also affect the pyrolysis and the product
mix.
Energy Balance
Without a product distribution, an energy balance cannot be developed.
Pollution and Hazards
As far as SRI knows, there is no published analysis that indicates the
products formed when rice straws and hulls are pyrolyzed or distilled.
Land Disruption
Although minimal, the land use requirements are greater than for
pyrolysis of wood residue because the feed is harvested in the third and
fourth quarters of the year; up to 6 months' storage is needed.
Air Emission
The air emissions sources are the loader and motor-generator (if used).
The emissions from these units would be the same as in the case of processing
wood residue: 2.3 Ib/hr of carbon monoxide and 5.1 Ib/hr of NOX. Except
111
-------
for possible pesticide residue, other pollutants are probably present in
negligible amounts.
A summary of the environmental impacts cannot be provided as no data
on net energy output could be developed.
PUROX® WITH RICE WASTE
The low bulk densities of rice hulls, and particularly rice straw,
could cause problems in the Purox® converter unless changes are made. When
compressed, refuse has a density of 40 to 50 lb/ft3, which is probably twice
as dense as the rice waste can be made. The mass of refuse moves from its
own weight down the converter as the material at the bottom is melted or
volatilized. Rice waste may not be dense enough to cause this same downward
movement. Rice straw, because of its shape and density, is also more likely
to cause bridging than is refuse. The burning characteristics of the rice
waste may also be sufficiently different from refuse to cause problems.
Revisions in the Purox® converter may be necessary and considerable
experimentation may be required before the converter could operate
satisfactorily using rice waste as a feed.
Mass Balance
Sufficient rice hulls and straws are available in the test area
(Colusa, Sutter, and Butte Counties, California) to suggest a design of a
plant to process 1000 tons/day of waste (three 350-ton/day Purox® converters
in parallel) or 83,333 Ib/hr.
The block flow diagram of the Purox® process, provided earlier in
Figure 20, shows the processing of rice waste. The condensate, rather than
being sent to a wastewater treatment plant for further processing, is
distilled to recover the organics fraction.
The typical elemental analysis of ash and moisture content of the rice
waste is different from the typical contents in refuse, as shown in
Table 44.
TABLE 44. COMPARISONS OF RICE WASTE AND REFUSE COMPOSITION
(wt %)
Element
Carbon
Hydrogen
Nitrogen
Oxygen
Ash
Moisture
Rice hulls
and straw
35.5
5.3
0.5
36.7
14.4
7.6
Refuse
29.0
3.2
N.A.a
22.8
17.9
27.1
flNot available
112
-------
Not only is the moisture content and ash lower and the organic matter
(C + H + 0) higher in the rice waste, but the organic fraction of rice waste
contains more oxygen and hydrogen in relation to the carbon content than
does the refuse. The basic composition of the rice waste is obviously
different from the organic portion of refuse, so the products of decomposition
are very likely to differ. Without some experimental data on product gas
compositions, no reliable estimate can be made of the distribution of products
that can be expected.
There are, however, some limits on the product composition. Obviously,
the ash and moisture in the feed are products. Also, the composition of
the offgases must be such that the energy released in the converter is just
sufficient to: (1) heat the slag to its temperature of exit; (2) evaporate
both the moisture in the feed and the water formed by the reactions in the
converter; (3) heat the gases to their exit temperatures; and (4) provide
for heat losses in and around the converter.
Even with this constraint, carbon, hydrogen, and oxygen can be
distributed in many ways among the possible products. One such possible
distribution is shown in Table 45. To achieve this distribution, 0.22 Ib
of oxygen is required per pound of waste. The elemental compositions and
weights of each numbered flow on Figure 20 are shown in Table 46. (A
small amount of sulfur is shown on Table 46, some of which is present in
the offgases. The quantities are small and their form unknown (e.g., COS,
H2S, S02); they are not included in Table 45).
TABLE 45. ASSUMED OFFGAS COMPOSITION FROM RICE WASTE
PYROLYSIS VIA PUROX® PROCESS
Vol % of dry,
Ib/hr Wt % noncondensibles
Hydrogen
Carbon monoxide
Carbon dioxide
Methane (CHO
Acetylene (C2H2)
Ethylene (C^)
Ethane (C2H6)
C3
Cij+
Oxygenated organics
H20 from reaction
Water-soluble organics
Nitrogen
H20 (moisture in feed)
TOTAL
1,759.0
25,657.1
35,366.5
2,655.7
539.4
1,742.8
266.8
634.3
3,177.4
177.8
8,590.3
2,398.2
1,243.1
6,329.1
90,537.5
1.9
28.3
39.1
2.9
0.6
1.9
0.3
0.7
3.5
0.2
9.5
2.7
1.4
7.0
100
29.6
30.8
27.1
5.6
0.7
2.1
0.3
0.5
1.6
0.2
1.5
100
113
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TABLE 46. PUROX PROCESS STREAM FLOWS USING RICE WASTE FEED
(1000 tons/day or 83.333 Ib/hr)
Rice waste
Oxygen
Converter
of fgas
Slag
Spray water
Spray
stream
Refractory
organics
Wet offgas
Residue
solids
Cool offgas
Condenser
H20
Spray water
discharge
Wastewater
treatment
discharge
Recovered
organics
Nitrogen
Stream Carbon Hydrogen (and argon) Oxygen Sulfur Ash
1 29,596.43 4,383.83 387.33 30,634.45 1.54 12,000.28
2 855.81 18,350.52
3 29,596.43 3,429.36 1,243.14 41,349.18 1.54
4 12,000.28
5
6
7
8 29,596.43 3,429.36 1,243.14 41,349.18 1.54
9
10 28,288.34 3,211.34 1,243.14 40,477.12 1.54
11 1,308.09 218.02 872.06
12
13 n.a. n.a. n.a. n.a. —
14 n.a. n.a. n.a. n.a. —
Refractory
organic Water Total
6,329.14 83,333
19,206.33
9,750.5 14,919.40 100,289.55
12,000.28
20,000 20,000
9,750.5 17,967 27,717.5
9,750.5 9,750.5
16,952.4 92,572.05
n.a.a n.a.a
468.61 73,690.09
16,483.79 18,881.96
— n.a.
n.a.
Data not available; any solids, organic liquids, or water removed here would be recycled to stream.
-------
As mentioned earlier, the process condensate is expected to contain
nearly 13% (by weight) organics. This is much more concentrated than the
condensate from the processing of wood residue, which would contain about
3% organics. Actually, the quantity of organic present in the condensate is
about the same, but the amount of water in the wet gas from the converter
processing of rice waste is much smaller than in the processing of wood
residue. The condensate with a high concentration of organics could be
steam-stripped to remove the organic portion for sale or use. The exact
composition of the organic in the condensate is unknown, so the design of
a system for its removal from the condensate cannot be provided. However,
many of the organic compounds that could be present in the condenser should
be separable from the water.
No data were found on the minor elements in the rice waste. Some data
presented on Table 47 are available on a few of the minor constituents in
rice hulls.
Of the elements listed on Table 47, only manganese and zinc appear to
exhibit any volatility in the Purox® converter (see Mass Balance part of
Purox with Wood Residue section). Therefore, unless manganese and zinc or
chromium or nickel are present in much higher concentrations in rice straw
than in hulls, they should not cause handling or disposal problems.
TABLE 47. MINOR ELEMENTS REPORTED PRESENT IN RICE HULLS
Element Wt % in hull
Silicon
Potassium
Calcium
Sodium
Magnesium
Phosphorus
Iron
Copper
Manganese
Zinc
7.7 to
0.2 to
0.1 to
0.01 to
0.04
<0.04
<0.01
<0.006
<0.001
<0.001
8.5a
0.7
0.2
0.02
aBased on silica content of rice hull ash.
Energy Balance
The energy balance about the converter (in millions of Btus per hour
of operation) is as follows:
115
-------
Ib/hr
83,333
Heat of
combustion
(Btu/lb)
5,855
a
„ -
1()6 Btu/hr
Feed
Gas
Organic in
wastewater
TOTALS
aThis is the theoretical heat of combustion estimated from the elemental
composition of the rice wastes.
In
487.9
_
487.9
Out
425.7
25.6
451.3
Of the energy available in the feed, as measured by the heats of
combustion, 87% is still available in the fuel gas product. The 36.6 million
Btu/hr consumed in processing performs the pyrolysis, evaporates the water,
and heats the gases and the slag to their exit temperatures. It is much
less than the energy required for pyrolyzing wood or refuse because the
sensible heat in the water and slag leaving the converter is much less. If
the wet gases leave the converter at 250°F and the slag at 2700°F, the
sensible heat required would be as shown in Table 48.
The 10 million Btu/hr difference between the 36.6 million Btu/hr of
energy consumed and the 26.6 million Btu/hr lost as sensible heat in the
products is heat lost in and around the converter.
/a*
Energy is also consumed in processing of rice waste in the Puroxw
system to:
• Operate the air separation plant
• Load the waste into the system
TABLE 48. SENSIBLE HEAT REQUIREMENTS
Ib/hr
(Btu/lb)
Sensible heat
(106 Btu/hr)
Water
Other gases
Liquified organics
Slag
TOTALS
14,920
72,347
2,398
12,000
101,665
1,118.9
41.5
175
540a
16.69
3.00
0.42
6.48
26.59
aAIT270u
AH77
116
-------
• Drive the motors, fans, etc., required by the process itself
• Dry and compress the gas for pipelining
The air separation plant requires an estimated 2900 kW. The energy
requirement for air separation is 27.2 million Btu/hr (assuming the 9400 Btu
of fuel energy make 1 kWh of electricity).
The loading operation (83,300 Ib/hr) can be accomplished with two
120-hp loaders, each consuming 6 gal/hr of diesel oil. Loading would require
1.5 million Btu/hr.
Since no definite figures are available for the converter and gas
cleanup system energy requirements, SRI has assumed 20 kWh/ton for
this purpose, which is equivalent to 833 kW or 7.8 million Btu/hr.
Since it is unlikely that a customer for the gas could be found so
close that the gas could be piped directly to him, we assume that the gas
would be compressed and dried for pipelining to customers 5 to 6 miles away.
The compression to 50 psi for such pipelining would require 3420 kW
and the ethylene glycol stripping/reboiler unit would use 1.3% of the product
gas to drive the abosrbed water from the ethylene glycol. The total energy
required for compression (again assuming 9400 Btu/kWh) would be
32.15xl06 Btu/hr for compression and 4.63xl06 Btu/hr for drying.
The separation of some or most of the organic component from the
condensate before discharge also requires an expenditure of energy, if
undertaken. The amount of energy required can be estimated approximately.
The condensate leaving the condenser is at about 100°F. The condensate
must be reheated to its boiling point and the organics plus some water
boiled off. Most organics in the wastewater have heats of vaporization
around 150 Btu/lb. So the approximate energy expended per hour in separation
is as follows:
106 Btu/hr
Reheat 18,900 Ib condensate to 212°F 2.12
Vaporize 90% of organics with a reflux 0.64
(0.9)(2400)(150)(2) ratio of 1:1
Vaporize 5% of water with a reflux
(16,500)(0.05)(970)(2) ratio of 1:1
Loses @ 40% of heat utilized (0.4)(4.36)
TOTAL
This energy could be supplied by burning part of the product gas. If
this is done, the emissions would contain minor and probably harmless
amounts of emissions other than water and carbon dioxide.
117
-------
In summary, the process energy requirements are:
106 Btu/hr
Loading
Air separation
System operation
Compression, pipelining
Organics recovery
TOTAL 79.4
and the net energy available from the system is 425.7 - 79.4, or 346.3
million Btu/hr, which is equivalent to 346.3/83,333 = 4,156 Btu/lb of rice
waste feed.
Pollution and Hazards
Land Disruption—
More land is probably required on which to dispose of the slag from
rice waste processing than from wood residue. About 48,000 tons/yr of
slag or ash are produced, which requires about 13.8 acres/yr, assuming the
bulk density of the ash is 9 Ib/ft . (The bulk density of ash from rice
hulls is reported14 to be 6 to 12 Ib/ft3). The ash from a mixture of rice
straw and hulls probably has about the same density). A plant with a 15-yr
life needs just over 200 acres dedicated to slag disposal.
A number of uses have been proposed for rice hull ash. Among the
considered proposals are the use of the ash as a reinforcement for rubber
and as a substitute for part of the cement in concrete. The total
elimination of the slag dump is possible if either of these uses were to
develop.
The plant itself still requires about 9.5 acres. SRI has assumed that
the compression plant increases this requirement by 1/2 acre.
Rice waste storage also requires additional space. One hundred percent
of the rice hulls and straw are produced in the fourth quarter of the year.
While part of the rice straw might be left in the field in January and
February, by March the field must be prepared for the next season's crop.
So storage for about 7 months of rice wastes (190,000 tons) must be provided
if the plant is to operate continuously. Assuming a bulk density of
25 Ib/ft3, and a pile depth of 30 ft, another 12 acres would be required
for feed storage.
The plant would be designed to operate 330 days/yr and to provide gas
with a net energy content of 2743xl09 Btu/yr (24 hr/day, 330 days/yr,
346.3xl06 Btu/hr). The land requirements, assuming no use or better method
of disposal for the ash, would be 222 acres or 0.08 acre/109 Btu/yr. If the
ash can be used, the land requirement would be about 17 acres (feed = 12
acres, plant = 10 acres, product (ash) storage = 5 acres) or 0.01 acre/109
Btu/year.
118
-------
Air Emissions—
The loading requirement for and the emissions from rice waste and wood
residue are essentially the same: 6 Ib/hr of hydrocarbons and NO.., and
2 Ib/hr of carbon monoxide.
Since the product gases must be dried and compressed and the waste
stream separated into an organic-rich and a water-rich stream, additional
process energy must be provided, which also produced pollutant emissions.
The quantities of emissions depend on the fuels used to supply the
6.1 million Btu/hr for condensate stripping and 5.02 million Btu for drying
the ethylene glycol used as gas desicant. If No. 2 fuel oil (0.6% sulfur)
is used, the emissions would be
Component Ib/hr
Particulates 1.3
Sulfur dioxide 6.9
Carbon monoxide 0.3
Hydrocarbons 0.3
Nitrogen oxides 4.8
If the converter offgas is used as the fuel instead of diesel oil, the
emissions are much lower. Not all the emission data are available for such
a case, but the following provides some of the information:
/Rj
Emissions from Purox
gas combustion to
furnish process heat
Component (Ib/hr)
Particulates 0.03
Sulfur dioxide 0.08
Carbon monoxide n.a.a
Hydrocarbons n.a.a
Nitrogen oxides n.a.a
aAll emissions should be much less than from burning a
comparable amount of diesel fuel oil.
Water Pollution—
As with the leachate from wood residue slag dumps, leachate from the
rice waste slag dumps should not be a problem as long as the leachate is
impounded and not allowed to flow directly into surface waters.
The water from the condenser will still contain some organic even if
the majority of it is steam-stripped. By SRl's very preliminary
approximation, the condenser water discharge of some 16,000 Ib/hr (32 gpm)
still includes about 240 Ib of organics, probably mostly organic acids
(formic, acetic, propionic, etc.) that are not readily separable from the
water. Considering the small quantities involved and the need for water
119
-------
in the area where the rice wastes are generated, the most likely and effective
disposition would be to use the condensate water for irrigation. If the BOD
of the water is too high for it to be used directly for irrigation, it could
be stored first in a lined or impervious stabilization pond.
Table 49 provides a summary of the information available on the known
environmental impacts of pyrolyzing rice waste using the Purox® process.
TABLE 49. ENVIRONMENTAL IMPACTS OF PUROX® PYROLYSIS OF RICE WASTE
Impact
Land
disruption
and use
Water
pollution
Input
Output
Wasteheat
Ammonia
Phosphorus
Salts
Metals
Pesticides
Air pollution
NO
SO*
H2S
Particulates
Pesticides
Hydrocarbons
Carbon
monoxide
Organisms
Solid waste
total
Onsite
Resource processing
extraction or storage
Acres/
109 Btu/
yr output
(gal/106 Btu)
(gal/106 Btu)
(Btu/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
Transport to
conversion Conversion
plant plant
0.08
0.7a
5.4^
0.06
n.a.
0
negl.
0
3.5xlO~5C
j
0.014
0.02e
negl.
0.004
0
0.018/
0.01
0
34.7
For adiabatic cooling only.
Includes condensed moisture from feed.
Q
Maximum possible quantity.
Plus some NOX included with hydrocarbons.
Maximum quantity; could be as low as 8.7xlO~5 lb/106 Btu.
f
JIncludes some NOX.
120
-------
PUROX® WITH BARLEY AND COTTON WASTE
As indicated earlier, the quantities of these wastes available in Kern
County, California are only sufficient to sustain the operation of a
750 ton/day Purox® plant. Except for size, the basic plant would be the
same as the plant for processing rice waste. The basic flowsheet for that
plant is shown in Figure 20.
The low bulk density of the barley and cotton waste feed could cause
the same problems as was outlined for the case where rice wastes are used
as feed.
Mass Balance
The typical analysis of the barley and cotton waste is also different
than the typical analysis of refuse, as shown in Table 50.
TABLE 50. COMPARISONS OF BARLEY/COTTON WASTE AND REFUSE
COMPOSITIONS (Wt %)
Carbon
Hydrogen
Nitrogen
Oxygen
Ash
Moisture
Barley
cotton
41.2
5.6
0.8
39.6
5.3
7.5
Refuse
29.0
3.2
n.a.
22.8
17.9
27.1
As with other agricultural waste, both the ash and moisture content are
typically lower than in refuse. The barley and cotton waste also contains
more hydrogen and oxygen in relation to carbon than does the refuse. These
basic differences in composition mean again that no reliable estimate can
be made of the expected distribution of products.
One possible distribution of reaction products, which takes into
account the energy provided by the reaction and energy consumed through
heat losses, is shown in Table 51.
To achieve the composition shown, 0.21 Ib of oxygen is required per
pound of waste.
The estimated elemental compositions and weights (in Ib/hr) of each
numbered flow on Figure 20 are shown in Table 52. As shown, the process
condensate is expected to contain over 19% (by weight) organics. This is
even more concentrated than the condensate from the processing of rice
waste. A condensate with such a high organic content should be steam-
stripped to remove as much as possible of the organic portion to sell
121
-------
TABLE 51. ASSUMED OFFGAS COMPOSITION FROM BARLEY/COTTON WASTE
PYROLYSIS VIA PUROX® PROCESS
Volume %
(of dry
Ib/hr Wt % noncondensibles)
Hydrogen
Carbon monoxide
Carbon dioxide
Methane (CHi^)
Acetylene (C2H2)
Ethylene (02^)
Ethane (C3H6)
C3
C^+
Oxygenated organics
H20 (from reaction)
Water-soluble organics
Nitrogen
H20
TOTAL
1,298.9
19,431.3
27,726.2
2,424.6
492.5
1,591.2
243.5
579.1
2,901.0
162.4
3,722.2
2,189.5
872.0
4,375.0
68,009.4
1.9
28.6
40.8
3.6
0.7
2.3
0.4
0.8
4.3
0.2
5.5
3.2
1.3
6.4
100.0
28.2
30.1
27.4
6.6
0.8
2.5
0.4
0.6
1.9
0.2
1.3
100.0
(possibly as a solvent) or use. The composition of the organics in the
condensate is unknown; so, as with the condensate from the rice waste
pyrolysis, the exact system design for removing the organics cannot be
provided at this time. However, the probability is quite high that such a
system can be designed and operated successfully.
No significant data were found on the minor elements in the barley and
cotton waste. Calcium, magnesium, potassium, sodium and phosphate contents
of barley straw are reported,12 but these are present in very low
concentrations and would end up in the ash. They should be considered
neither toxic nor hazardous.
Energy Balance
The energy balance about the converter is as follows:
106 Btu/hr
Ib/hr Btu/lb In Out
Feed 58,333 6,721a 392.1
Gas 346.8
Organic in
wastewater 22.3
TOTAL 392.1 370.1
This is the theoretical heat of combustion estimated from the elemental
composition of barley/cotton waste.
122
-------
TABLE 52. PURO^ PROCESS STREAM FLOWS USING
BARLEY AND COTTON WASTE AS FEED
ISJ
Nitrogen Refractory
Stream Carbon Hydrogen (and argon) Oxygen Ash organic Water Total
Barley/
cotton
waste
Oxygen
Converter
offgas
Slag
Spray water
Spray
stream
Refractory
organic
Wet offgas
Residue
solids
Cool offgas
Condenser
water
Spray water
discharge
1 24,065.4 3,237.5 485.6
2 386.4
3 24,065.4 2,823.9 872.0
4
5
6
7
8 24,065.4 2,823.9 872.0
9
10 22,871.1 2,624.9 872.0
11 1,194.3 199.0
12
23,094.2 3,075.6 4,375 58,333.3
12,365.3 12,751.
32,150.9 7,632.4 8,097.2 75,641.
3,075.6 3,075.
13,500 13,500
7,632.4 12,138 19,770.
7,632.4 7,632.
32,150.9 9,459.2 69,371.
a a
n. a. n. a.
31,354.7 370.6 58,093.
796.2 9,088.6 11,278.
7
8
6
4
4
4
3
1
aData not available; any solids, organic liquids, or water removed here would be recycled to stream 6.
-------
Thus, 88% of the energy available in the feed, as measured by the heats
of combustion, is available in the fuel gas product. As in the other cases
the 22 million Btu/hr performs the pyrolysis, evaporates the water and heats
the bases and slag to their exit temperatures. The low moisture content
and the small quantity of ash are the reasons why the pyrolysis of barley
and cotton waste is so efficient (88%) because the sensible heat in the
water and slag is low.
If the wet gases leave the converter at 250°F and the slag at 2700°F,
the sensible heat required would be as shown in the following tabulation:
Lost sensible
AH77 heat
Ib/hr Btu/lb 106 Btu/hr
Water 8,097 1,118.9 9.06
Other gases 57,723 41.5 2.40
Liquified organics 2,189 175 0.38
Slag 3.076 540a 1.66
TOTAL 71,085 13.50
aAU2700
AH7?
Energy is also consumed to:
• Operate the air separation plant
• Load the waste into the system
• Drive the motors, fans, etc., required by the process itself
• Dry and compress the gas for pipelining
The air separation plant requires an estimated 200 kW. The energy
requirement for air separation is 18.8 million Btu/hr (9400 Btu/1 kWh
of electricity).
The loading operation (48,300 Ib/hr) can be accomplished with two
90-hp loaders that each consume 4 gal/hr of diesel oil. The loading
operation would require 1.1 million Btu/hr.
With no specific data on the energy requirements of the converter and
gas cleanup system, SRI has assumed 20 kWh/ton, which is equivalent to
583 kW or 5.5 million Btu/hr.
SRI has assumed, as in the rice waste -case, that the product gas must
be dried, compressed and pipelined to customers 5 to 6 miles away.
124
-------
The compression to 50 psi for pipelining would require about 2670 kW
and the ethylene glycol stripping/reboiler would use 1% of the produced
gas to drive the absorbed water from the ethylene glycol absorbant. (A
smaller percentage of product gas — 1.3% ~ is needed to drive the reboiler/
stripper than in the case of rice waste, because this gas has a higher Btu
content — 448 Btu/scf — than the gas produced from rice wastes — 342
Btu/scf). The total energy required for compression would be 25.10xl06 Btu/hr
for compression and 3.60xl06 Btu/hr for drying.
The fractionation of the separable organic components from the condensate
before discharge requires the following estimated amounts of energy (in
106 Btu/hr):
106 Btu/hr
Reheat condensate from 100°F to 212°F
(11278.1 lb/hr)(112°) = 1.26
Vaporize 90% of organics, with 1:1
reflux ratio (0.9)(2189.5)(150)(2) = 0.59
Vaporize 5% of water, with 1:1 reflux
ratio (0.05)(9088.6)(970)(2) = 0.88
Losses @ 40% of heat utilized
(0.4)(2.73) = 1.09
TOTAL 3.82
In summary, the process energy requirements are:
106 Btu/hr
Loading 1.1
Air separation 18.8
System operation 5.5
Compression, pipelining 28.7
Organics recovery 3.8
TOTAL 57.9
The net energy available from the system is 346.8 - 57.9 or 289
106Btu/hr, which is equivalent to 289/58,333 or 4954 Btu/lb of barley and
cotton waste feed.
Pollution and Hazards
Land Disruption—
About 12,000 tons/yr of slag or ash would be produced in processing
the 750 tons/day of barley (330 days/yr). If this ash has the same density
as ash from rice hulls, i.e., 9 lb/ft3, about 3.5 acres/yr would be needed
for disposal. A processing plant with a 15-yr life would need just over
50 acres dedicated to slag disposal.
125
-------
The composition of this ash or slag is not known, although it certainly
contains less silica than rice ash. Consequently, it probably could not be
used for rubber reinforcement or as a cement additive. Since it does contain
some phosphates and potash, it might be plowed back into the fields as a
low value fertilizer. However, extensive testing of the ash/fertilizer
concept would be required before the design of the plant without an area for
ash disposal could be contemplated.
The plant itself, having a capacity of 750 tons/day, instead of
1000 tons/day as in the case of rice waste, would probably only require
about 8 acres of land, including the land for the gas compression plant.
Storage of the waste prior to processing also requires additional space.
All barley is harvested in June, the residue becoming available in July and
August; all cotton is harvested in December, the residues becoming available
in January and February. Under these circumstances, about 200,000 tons of
waste may have to be stored at one time (in July or January).
Assuming a bulk density of 25 lb/ft3 and a pile depth of 30 ft, another
13 acres would be required for feed storage.
The plant would be designed to operate 330 days/yr, and provide gas
with a net energy content of 2289xl09 Btu/yr (24 hr/day, 330 days/yr,
289xl06 Btu/hr). The land requirements, assuming no use for the ash,
would be 71 acres (50 acres for ash, 8 acres for plant, and 13 acres for
feed) or 0.03 acre/109 Btu. If the ash can be used, the land requirement
could be reduced to 21 acres, or 0.01 acre/109 Btu.
Air Emissions—
The two major potential sources of air pollution in the Purox® process
operating on barley and cotton waste are: the exhausts from the loaders
used to transfer the feed from storage to the converter; the burners used
to provide heat to the condensate and heat to strip the water from the
ethylene glycol absorbant. (Fugitive dust from the loading operation could
also be a problem. To what extent this dust is a problem depends on the
system devised and cannot be established at this time).
Two loaders with 90-hp diesel engines would emit:
4.4 Ib/hr of NOX plus hydrocarbons
2.0 Ib/hr of carbon monoxide
The emissions from the condensate-stripper heaters depend on the fuel
used. If No. 2 fuel oil (0.6% sulfur) is used, the emissions would be:
Component Ib/hr
Particulates 0.9
Sulfur dioxide 4.6
Carbon monoxide 0.2
Hydrocarbons 0.2
Nitrogen oxide 3.2
126
-------
If converter offgas is used as the fuel instead of diesel oil, the
emissions would be much lower. Actual emission data are not available. The
particulate concentration in the offgas has been determined for the case
where refuse is the feed. The particulate concentration using barley and
cotton waste should be about the same. Based on that assumption, particulate
emissions would be about 0.02 Ib/hr. The emissions of all the other pollutants
should also be much lower than from burning the diesel fuel oil.
Water Pollution—
The leachate from the slag made by processing barley and cotton waste
should be very similar to leachate from rice waste slag. So, the leachate
from barley and cotton slag dumps should not present a problem as long as
the same precautions are exercised in preventing the leachate from entering
surface waters directly.
The other possible source of water pollutants, the steam-stripped
condensate, is again similar to the condensate from processing rice waste,
at least as far as the BOD demand of the condensate is concerned. However,
the pesticide content in the condensate is likely to be different.
Table 53 contains a summary of the known environmental impacts from
pyrolyzing barley and cotton waste using the Purox® process.
127
-------
TABLE 53. ENVIRONMENTAL IMPACTS OF PUROX® PYROLYSIS OF BARLEY
AND COTTON WASTE
Onsite Transport to
Resource processing conversion Conversion
Impact extraction or storage plant plant
Land
disruption
and use
Water
pollution
Input
Output
Wasteheat
Ammonia
Phosphorus
Salts
Metals
Pesticides
Air pollution
NOX
sox
H2S
Particulates
Pesticides
Hydrocarbons
Carbon
monoxide
Organisms
Solid waste
total
Acres/
109 Btu/
yr output
(gal/106 Btu)
(gal/106 Btu)
(Btu/106 Btu)
(Ib 106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
0.03
0.6a
3.6b
0.04
n.a.
0
negl.
0
n.a.
0.026
0.016C
negl.
0.003
0
0.001^
10.6
a
For adiabatic cooling only.
Includes condensed moisture from feed. Includes some hydrocarbons.
Q
'Maximum quantity.
I
Some hydrocarbon is included as part of NOX.
128
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APPENDIX A
ANAEROBIC DIGESTION - SUPPLEMENTAL DATA
INTRODUCTION
The information needed to evaluate the energy and pollution potentials of
the anaerobic digestion process includes a mathematical model of the process
and a raw material characterization of the agriculture waste. A mathematical
model is developed first to describe waste degradation, methane production,
and pollutant transport in the anaerobic process. Then, waste characteristics
(including volatile solids content, nutrients, and heavy metals) are obtained
from the literature. Tolerance levels for specific liquid phase constituents
are assumed to allow estimation of purge stream flow. Using waste character-
istics as input to the mathematical model, energy and pollution potentials
can then be evaluated.
MATHEMATICAL MODEL FOR THE ANAEROBIC DIGESTION PROCESS
Process Model
The process model assumes a completely mixed digester with no solids
recycled, as shown in Figure 6. The slurry feed to the digester is prepared
by mixing water with agricultural waste to produce a solids concentration of
10%. To minimize wastewater generation and to conserve water and heat, as
much water as possible is recirculated. The digested sludge solids that form
from gravity settling are further dewatered by vacuum filtration to produce
a cake with approximately 25% solids content.
Feed Slurry
Both biodegradable and refractory organics in the raw sludge can be
expressed in terms of COD as follows:
s° - a - fd)cx°
129
-------
where
S° = biodegradable COD in feed slurry (g/A)
a
S° = refractory COD in feed slurry (g/fc)
X° = total suspended solids in feed slurry (g/A)
G = ratio of COD to total suspended solids in feed slurry
f , = biodegradable fraction of organic solids in feed slurry (assumed
to be equivalent to biodegradable fraction of COD)
The total concentration of organic material in the feed slurry S- can
be expressed as the sum of S9 and S°, i.e.,
Total suspended solids in the feed slurry consist of inorganic, bio
degradable volatile, and refractory volatile suspended solids, i.e.,
t • *in+ Xd + Xr
VXt
Xd
where
X. = inorganic suspended solids in the feed slurry (g/A)
X, = biodegradable volatile suspended solids in the feed slurry
X = refractory volatile suspended solids in the feed slurry (g/fc)
f = fraction of total suspended solids that are volatile
Digested Slurry
A model has been developed15 to describe the rate of waste usage in a
biological reactor. According to this model, the concentration of
biodegradable organics in the digested slurry S,, can be expressed as:
130
-------
d 6 (Y k - b) - 1
where
k = maximum specific substrate utilization rate by bacteria
(g COD/g cells-day)
Kg = composite half-velocity coefficient for fatty acids (g/£ COD basis)
Ya = yield coefficient for the rate-limiting-step organisms involved in
the methane fermentation (g cells/g COD utilized)
b = microorganisms decay coefficient (day )
9c = digester solids detention time (day) = reactor detention time for
case with no solids recycle
The concentration of refractory organics in the slurry S remains the
same as that in the feed slurry, S°, i.e.,
S = S°
r r
The concentration of active organisms X in the digested slurry can
be expressed as:
Xa " 1 + b6
c
where Y is the yield coefficient for overall waste decomposition (g cells/
g COD utilized).
The concentration of refractory fraction of decayed organisms in the
digested slurry X can be written as:
X = 0.2bX 0
ar a c
where the constant, 0.2, represents the refractory portion of the bacterial
cells formed during cell decay.
The concentration of inorganic and refractory volatile suspended solids
in the digested slurry remains the same as those in the feed slurry, i.e.,
X. = X?
in in
X =X°
r r
131
-------
The concentration of organic material in the digested slurry ST consists
of three portions: the remaining biodegradable and refractory portions of the
original waste, S^ and Sr, plus the organic portion of the microorganisms.
To add these together, the microorganism concentration must be expressed in
COD units, rather than weight units, and so the conversion factor 1.42 is used:
ST = Sd + Sr + l'^\ + Xar}
The concentration of total suspended solids in the digested sludge Xt
can be expressed as the sum of five components:
X=X+X + X . + X + X,
t a ar in r d
Flow Rate and Digester Volume
Flow rate Q can be related to input rate of dry solids in agricultural
wastes W and concentration of suspended solids in the feed slurry X° as
follows :
W
0.0623X°
where 0.0623 is a conversion factor; Q is in ft3/day; W is in Ib/day; X
is in
Volume of digester V can be expressed as the product of flow rate Q
and solids detention time 9 :
c
V = Q6c
where V is in ft3; Q is in ft3/day; 9 is in days.
Gross Methane Production
In anaerobic digestion, gross methane production can be directly
correlated with COD reduction. According to McCarty6, a reduction of 1 gram
of COD is equivalent to the production of 0.35 liter of methane or 5.61 scf
Clfy/lb COD. Using this relationship,
M = 5.61Q(S° - SJ0.0623*
gross t T
where M is the gross rate of gas production in scf per day.
gross
Net Methane Production
To calculate net methane production, methane consumption for heating
must be known. Heat loss of a digester can be calculated from the product
0.0623 is a conversion factor for g/£ to lb/ft3-
132
-------
of heat transfer coefficient, temperature difference and surface area.
Assuming a cylindrical digester with a diameter of 110 ft and a depth of 35 ft
(volume = 0.338xl06 ft3), the heat loss per digester from wall, top, and
bottom can be calculated from the following relations:
q = U (T - T) (24) (12, 095)
s s a.
qt = Ut(T - Ta) (24) (9, 503)
qb = Ub(T - TS) (24) (9, 503)
where
q , q ,q, = heat loss from the sides, top, and bottom of each digester,
respectively (Btu/day)
U ,U ,U, = heat transfer coefficients for the sides, top, and bottom
of each digester, respectively (Btu/hr-ft^-day) assuming
2 inches foam insulation
T = temperature of digester, 95 °F
T = temperature of air (°F)
3.
T = temperature of soil (°F)
S
The total heat loss from a digester can be expressed as follows:
qloss
(qs + qt + Vlo. 338x10*)
where q, is in Btu/day and V is the total volume of all digesters required.
Heating requirement of a digester q
-------
For the case with recyling,
q. = (Q - Q - ) x 64 x 1 x (T - T°)
Md ^recycle
+Q . x 64 x 1 x (T - T .)
recycle recycle
where Qre , is the flow rate of recycle stream in ft3/day; Trecycle is
the temperature of recycle stream, chosen as 75°F based on the heat loss due
to water evaporation in the vacuum filter operation of dewatering process.
The methane consumption for both heat loss and digester heating can be
calculated by the following equation, assuming the fuel value of the methane
is 960 Btu/scf CH^, and the efficiency of methane utilization is 85%:
<«d + «loss>
consumption (960)(0.85)
where M .. is in the unit of scf/day.
consumption
Net methane production equals gross methane production minus methane
consumption:
M „ = M - M .
net gross consumption
where M , M , M are all in the unit of scf/day.
net gross consumption J
Nutrient Requirements
The quantity of the biological nutrients, nitrogen and phosphorus,
required by the microorganisms is directly proportional to their growth. The
daily nitrogen and phosphorus requirement can be calculated by the following
equations:*
N . . = 0.11X Q(0.0623)
required a
P . . = 0.02X Q(0.0623)
required a
where N . and P are both in the unit of Ib/day.
required required
Distribution of Nutrients, Heavy Metals, and Solids in Dewatering Process
Many particulate nitrogen and phosphorus compounds are converted to
soluble forms during anaerobic digestion.16'17 The distribution of nutrients
in digested sludge, settled sludge, and effluent has been reported.18
134
-------
The results are as follows:
Digested sludge Settled sludge Effluent
(Ib) (Ib) (Ib)
Nitrogen 14 (100%) 10.6 (76%) 3.4 (24%)
Phosphorus 8 (100%) 7.4 (93%) 0.6 (7%)
This study chose the following distribution coefficients for phosphorus
in the dewatering step for the case without liquid recycling. Total nitrogen
consists of soluble nitrogen (primarily NH^-N) and nitrogen in solids. Since
the concentration of soluble nitrogen is suspected to be nearly at the toxic
level, the solubilization of nitrogen in solids is considered and is assumed
to be in proportion to the biodegradation of organic solids. Heavy metals
in digested sludge are commonly precipitated as sulfides and exist in the solid
phase.19'20 The distribution of heavy metals has been studied.21 Based on
the results of that study, the following distribution coefficient for heavy
metals was chosen in dewatering for the case without liquid recycling:
Heavy Digested sludge Cake Wastewater
metals
\
Copper
Zinc
Manganese
Nickel
Cadmium
Mercury
100 70 30
The distribution for alkaline and earth alkaline metals is assumed to be
the same as heavy metals.
For the case with liquid recycling, the quantities of nutrients, heavy
metals, alkaline and earth alkaline metals in the dewatered solids are equal
to the quantities in the feed slurry.
In this study, solids separation efficiency for dewatering process is
assumed nearly 100%. The rate of solids output in cake can be expressed as
follows:
We . = 0.0623 x Q x X®
cake t
Numerical Values for Parameters in Process Model
The following data are used for heat loss and heating requirement
calculation:
U = U = 0.12 Btu/(ft2-hr-°F)
s b
U = 0.16 Btu/(ft2-hr-°F)
135
-------
T = T = T° = 50°F
a s
For mesophilic digestion (T = 35°C, or 95°F), a solids retention time
of 0C = 20 days was assumed, and the parameters for bacterial growth kinetics
were chosen as follows:
k = 6.67 g COD/(g cells-day)
K = 1.80 g COD/liter
Y = 0.20 g cells/g COD utilized
Y = O.OA g cells/g COD utilized
3.
b = 0.03 day'1
RAW MATERIAL CHARACTERIZATION
Detailed characteristics of agricultural wastes can be found in publica-
tions. 12'22'23 Table A-l summarizes characteristics for various agricultural
wastes considered in this study. Five cases of digester feed are considered:
(1) fresh cattle manure, (2) 5-month-old cattle manure, (3) fresh cattle
manure and wheat residue, (A) chicken manure without liquid recycling, and
(5) chicken manure with liquid recycling. In Table A-l, the values for
parameters f,, G and f are listed. Table A-2 explains the determination
of their values. v
MATERIAL AND ENERGY BALANCES
Energy and material balance calculations were carried out by using the
raw material characterization data (Table A-l) and the process model.
(Figure 8 showed energy production and consumption for various agriculture
wastes.) Tables A-3 through A-7 present results of the material balances.
Several points should be noted from analysis of these tables.
• The biodegradable fraction of volatile solids in cattle manure
influences energy production significantly. This can be seen by
comparing fresh manure and 5-month-old manure.
• Adding wheat residue to fresh manure does not increase net energy
production. However, adding wheat residue can reduce the ammonia
nitrogen concentration, which is only slightly below the assumed
toxicity level (3,000 ppm), when fresh manure is used.
• In chicken manure, the solids concentration in the feed slurry is
assumed to be 7% instead of 10%, as for cattle manure. This
selection keeps the ammonium nitrogen below the assumed toxicity
level.
136
-------
When chicken manure is processed without liquid recycling, net
energy production is negative, even though the ammonium nitrogen
concentration is below the toxicity level. When chicken manure
is processed with liquid recycling, but no nitrogen removal, the
ammonium nitrogen exceeds the toxicity level, even though net
energy production is positive. Therefore, the economic feasibility
of using chicken manure as digester feed remains questionable.
TABLE A-l. WASTE CHARACTERISTICS
Cattle
manure,
fresh
Cattle
manure,
5-mo
old
Wheat
residue
Fresh
cattle
manure
and
wheat
residue
Chicken
manure
Quantities01
Parameters
G
Nutrients
'2
Total N
Alkaline a
earth
metals
Na
K
Ca
Ma
2.20xl06
1.0
0.60
0.78
4.25x10^
0.71x10^
l.lSxlO1*
2.31x103
3.77xl03
5.63x103
3.74xl03
1.41xl06
0.9
0.31
0.67
3.54xl04
0
2.31x103
3.77xl03
5.63xl03
3.74x103
l.lOxlO6
1
0.1
0.93
_o
4.84x103
_c
4.68x103
_o
c
3.30xl06
0.43C
0.83C
4.25X101*
0.71X101*
1.63xl04
2.31x103
4.24xl03
5.63x103
3.74xl03
3.08xl06
0.86
0.26
0.77
1.85xl05
1.18x105
5.88x10^
1.17X101*
6.16x10^
9.86x10^
1.48x10^
Cu
Zn
13
99
13
99
o
_c
13
99
148
1.28xl03
aAll values are in the unit of Ib/day.
See Table A-2. 5.8 Ib dry solids/head (5-mo. cycle) = 0 64
9 Ib dry solids/head (fresh)
°Data are not found in literature and are believed to be negligible compared
to those of fresh cattle manure.
df = (1.1/3.3)(0.93) + (2.2/3.3)(0.78) = 0.83
v
f. = (1.1/3.3X0.1) + (2.2/3.3X0.6) = 0.43
137
-------
TABLE A-2. SUMMARY OF ASSUMPTIONS FOR DETERMINING f , G,^ AND f
v d
CATTLE MANURE: per 900 Ib (410 kg) steer (following based on data from
Reference 22)
Q
Quantity, fresh:
!43 Ib feces (20 kg)
17 Ib urine (8 kg)
9 Ib (4.1 kg) dry manure/day {1.5 Ib BOD5 (0.68 kg)
or J
7 Ib (3.2 kg) volatile solids/day (9 Ib COD (4.1 kg)
!2.0 Ib (0.91 kg) inorganics
2.8 Ib (1.3 kg) nondegradable org.
4.2 Ib (1.9 kg) degradable organic s
Volatile fraction of dry solids =0.78
Quantity, 5-month collection cycle:
{1.9 Ib (0.86 kg) inorganics
5.8 Ib (2.6 kg) dry manure/day )2'? Ib (1-2 kg) nondegradable org.
(l.2 Ib (0.55 kg) degradable organics
Volatile fraction of dry solids =0.67
Calculation of G;
Manure , fresh :
G = 9 Ib COD/ 9 Ib dry manure = 1
and 7 Ib organics/ 9 Ib dry manure
Therefore: 1.29 Ib COD/lb organic
Manure, 5-month
. , ~« ,,
collecion cycle: G = .i'*"1"8 ^
5.8 Ib dry manure Ib organics
= 0.91 Ib COD/lb dry manure
G = mass COD/mass dry solids
f, = fraction of organic solids that is degradable (assumed equal to
degradable fraction of COD)
CFresh manure (defined by SRI to be less than 1 month old)
138
-------
TABLE A-2 (continued)
CATTLE MANURE: (continued)
Calculation of f,,;
Q
Manure, fresh: - _ 4.2 Ib degradable organics n ,n
£ _ ~ _ -, . "~ U • OU
d 7 Ib organics
Manure, 5-month . _ ,,_/, j vi *
,, 1. , c 1.2 Ib/degradable organics A 01
collection cycle: f , = ' °, :— = 0.31
* d 3.9 Ib organics
WHEAT:
Calculation of G;
Assumed wheat composition:
Moisture 18 wt %
Ash 5.5 wt %
Volatile solids or organics 76.5 wt %
Volatile fraction of dry solids 0.93 (f )
v
76.5 Ib (CH20) 8 Ib COD
82 Ib dry straw solids X 7.5 Ib CH20
Calculation of f3 '
d
Digestible fraction of cellulose in wheat straw approximately = 25%.
(Reference 23)
Fraction of cellulose in wheat straw approximately = 40% on dry basis,
f. ~ 0.25 x 0.40 = 0.1.
a
CHICKEN MANURE: (per animal from Reference 12)
Quantity, fresh;
.066 Ib dry solids
0.25 Ib wet manure/day {0.051 Ib organics
.015 Ib inorganics
(0.
<0.
(0.
(0.057 Ib COD
0.051 Ib organics/day <
(0.015 Ib BOD
Volatile fraction of dry solids =0.77
139
-------
TABLE A-2 (continued)
CHICKEN MANURE: (continued)
Calculation of G:
= 0.057 Ib COD
0.066 Ib dry solids
Calculation of f,;
Q
f = 0.015 Ib BOD
d 0.057 Ib COD
140
-------
TABLE A-3. MATERIAL BALANCE FOR FRESH CATTLE MANURE AS DIGESTER FEED WITH LIQUID RECYCLING
(Ib/day)
Stream 1 Stream 2 Stream 3 Stream 4 Stream 5 Stream 6 Stream 7 Stream 8
Dry solids
Water
Nutrients
Total N
Soluble - N
Solids - N
Total P
Alkaline
earth
metals
Na
K
Ca
Mg
Heavy metals
Cu
Zn
Methane (scf/day)
2.20xl06
0.88xl07 0
4.25x10"
0.71x10"
3.54x10"
1.15x10"
2.31xl03
3.77x10"
5.63xl03
3.74xl03
13
99
2.20xl06 1.35xl06 1.35xl06
1.98xl07 1.98xl07 0.41xl07
7. 25x10"* 7.25x10" 2.97xl04
3.71X101* 5.39xl04 l.llxlO4
S.SAxlO1* 1.86X101* 1.86X101*
1.15x10"
2.31xl03
3. 77x10"
5.63xl03
3.74xl03
13
99
5.81xl06 1.15xl06 4.66xl06
Stream 9 Stream 10
0.47xl07 l.lOxlO7
1.28x10" 3.0x10"
1.28x10" 3.0x10"
-------
TABLE A-4. MATERIAL BALANCE FOR FIVE-MONTH-OLD CATTLE MANURE
AS DIGESTER FEED WITH LIQUID RECYCLING
(Ib/day)
Dry solids
Water
Nutrients
Total N
NH4-N
Solids - N
Total P
Alkaline
earth
metals
Na
K
Ca
Mg
Heavy metals
Cu
Zn
Methane (scf/day)
Stream 1 Stream 2 Stream 3 Stream 4 Stream 5
1.41xl06 l.AlxlO6
O.AlxlO7 0.21xl07 1.27xl07
3.54x10" 5. 01x10"
0 1.47x10"
3.54x10" 3.54x10"
1.15x10"
2.31xl03
3.77x10"
5.63xl03
3. 74x10 3
13
99
2.14xl06 0.74xl06
Stream 6 Stream 7 Stream 8 Stream 9 Stream 10
l.lSxlO6 l.lSxlO6
1.27xl07 0.35xl07 0
5.01x10" 3.54x10"
2.03x10" 0.56x10"
2.98x10" 2.98x10"
1.15x10"
2.31xl03
3.77x10"
5.65xl03
3.74xl03
13
99
1.40xl06
0.92xl07
1.47x10"
1.47x10"
-------
TABLE A-5. MATERIAL BALANCE FOR FRESH MANURE AND WHEAT RESIDUE
AS DIGESTER FEED WITH LIQUID RECYCLING
(Ib/day)
Stream 1 Stream 2 Stream 3 Stream 4 Stream 5 Stream 6 Stream 7 Stream 8
Dry solids
Water
Nutrients
Total N
Soluble - N
Solids - N
Total ?
Alkaline
earth
metals
Na
K
Ca
Mg
Heavy metals
Ca
Zn
Methane (scf/day)
3.30xl06
0.89xl07 0
4.25xl04
0.71X101*
3.54X104
1.63X101*
2. 31x10 3
4.24x10**
5.63xl03
3.74xl03
13
99
3.30xl06 2.33xl06 2.33xl06
2.97xl07 2.97xl07 0.70xl07
8.71X101* 8.71X101* 4.25x10**
5.17X101* 6.37xl04 l.SOxlO1*
3.54X101* 2.34xl04 2.34X101*
1.63X101*
2. 31x10 3
4.24x10'*
5.63xl03
3.74xl03
13
99
6.31xl06 1.63xl06 4.68xl06
Stream 9 Stream 10
0.19xl07 2.08xl07
0. 41x10"* 4.46X101*
0.41X101* 4. 46x10**
-------
TABLE A-6. MATERIAL BALANCE FOR CHICKEN MANURE AS DIGESTER FEED
WITHOUT LIQUID RECYCLING
(Ib/day)
Dry solids
Water
Nutrients
Total N
NHi,-N
Solids - N
Total P
Alkaline
earth
metals
Na
K
Ca
Mg
Heavy metals
Cu
Zn
Methane (scf/day)
Stream 1
3.08xl05
0.31xl07
1.85xl05
1.18xl05
0.67xl05
5.88x10**
1.17x10"
6.16x10"
9.86x10"
1.48x10"
148
1.28xl03
Stream 2 Stream 3 Stream 4
3.08xl06
3.78xl07 4.09xl07
1.85xl05
l.lSxlO5
0.67xl05
5.88x10"
1.17x10"
6.16x10"
9.86x10"
1.48x10"
148
1. 28x10 3
2.97x106
Stream 5 Stream 6 Stream 7
2.60xl06
4.09xl07
1.85xl05
1.31xl05
0.54xl05
5.88x10"
1.17x10"
6.16x10"
9.86x10"
1.48x10"
148
1.28xl03
3.04x106 -0.07x106
Stream 8
2.60xl06
0.78xl07
0. 79x10 5
0.25xl05
0.54xl05
5.47x10"
0.82x10"
4.31x10"
6.90x10"
1.04x10"
104
0. 90x10 3
Stream 9 Stream 10
3.31xl07 0
1.06xl05
1. 06x10 5
0.41x10"
0.35x10"
1.85x10"
2.96x10"
0.44x10"
44
0. 38x10 3
-------
Ul
TABLE A-7. MATERIAL BALANCE FOR CHICKEN MANURE
AS DIGESTER FEED WITH LIQUID RECYCLING
(Ib/day)
Dry solids
Water
Nutrirnts
Total N
NH4-N
Solids - N
Total F
Alkaline
earth
metals
Na
K
Ca
Mg
Heavy metals
Cu
Zn
Methane (scf/day)
Stream 1 Stream 2 Stream 3
3.08xl06 3.08xl06
0.31xl06 0.47xl07 4.09xl07
1.85xl05 7.41xl05
1.18xl05 6.74xl05
0.67xl05 0.67xl05
5.88x10"
1.17x10"
6.16x10"
9.86x10"
1.48x10"
148
1.28xl03
Stream 4 Stream 5 Stream 6 Stream 7 Stream 8 Stream 9 Stream 10
2.60xl06 2.60xl06
4.09xl07 0.78xl07 0
7.41xl05 1.85xl05
6.87xl05 1.31xl05
0.54xl05 0.54xl05
5.88x10"
1.17x10"
6.16x10"
9.86x10"
1.48x10"
]48
1.28xl03
2.97xl06 2.02xl06 0.95xl06
3.31xl07
5.56xl05
5.56xl05
-------
ENVIRONMENTAL CONSIDERATIONS
Sulfur and nitrogen emissions have been considered in this study due to
the combustion of produced gas for digestion system heating. For most
anaerobic digesters, 21* hydrogen sulfide is usually not above 100 grains/100 ft3
of gas, or, 205 Ib of sulfur /I, 000, 000 ft3 of methane produced. This emission
factor was used to estimate sulfur dioxide emissions from the boiler per day
and sulfur dioxide emissions per net million Btu produced for various cases
of agricultural waste.
Nitrogen oxides emissions from the boiler depend on the ammonia
concentration in the produced gas, which varies with the pH of the digestion
slurry. For a pH around 7.5, the NHs concentration in the gas is 2% of total
ammonium-nitrogen concentration. Using this factor and the ammonium-nitrogen
concentration in the digestion slurry, the digester gas ammonia concentrations
were estimated and the nitrogen oxides emissions from the boiler were
calculated.
Tables A-8 and A-9 present sulfur dioxide and nitrogen oxides emissions
per day and per net million Btu produced for various agricultural wastes.
TABLE A-8. SULFUR AND NITROGEN EMISSION PER 106 Btu
NET SUPPLY PRODUCTION FOR ANAEROBIC DIGESTION PROCESS
Sulfur emission Nitrogen emission
_ (Ib S/106 Btu) _ (Ib N/106 Btu)
Fresh cattle manure 0.054[0.108]a 0.049[0.161]Z>
Cattle manure •,
(5-month collection cycle) 0.11[0.22]a 0.057[0.187]P
Fresh cattle manure and ,
wheat residue 0.074[0.148]a 0.052[0.17ir
Chicken manure without
liquid recycling -
Chicken manure with ,
liquid recycling 0.45[0.90]a 0.57[1.87]
is Ib S02/106 Btu.
^Unit is Ib N02/106 Btu.
If the digester solids are separated by a vacuum filter, then an
laden gas stream would be emitted from the vacuum pump. This analysis
assumes that the exhaust gas from the vacuum pump is treated for E^S removal
by one of the following processes:
146
-------
• Scrubbing and subsequent liquid phase oxidation
• Air oxidation on a bed of activated carbon
• Air oxidation on a bed of iron oxide
In any of the above cases, the H2S emissions should be reduced to a very
low level. Ammonia removal would be achieved only by use of an acid-scrubbing
solution following the above devices.
H2S in the product gas would be removed before sales to a pipeline gas
company, but this has not been considered in this analysis. The gas burned
for digester heating is as received from the digesters and NOX and SOX emission
levels have been calculated and listed in Tables A-8 and A-9.
TABLE A-9. SULFUR AND NITROGEN EMISSION PER DAY
FOR ANAEROBIC DIGESTION PROCESS
Sulfur emission Nitrogen emission
(Ib S/day) (Ib N/day)
Fresh cattle manure 240 218
Cattle manure
(5-month collection cycle) 152 76
Fresh cattle manure and
wheat residue 334 235
Chicken manure without
liquid recycling 623 246
Chicken manure with
liquid recycling 414 517
147
-------
APPENDIX B
ENVIRONMENTAL ANALYSIS ASSUMPTIONS, CALCULATIONS,
AND DATA SUMMARY
TABLE B-l. COAL-FIRED POWER PLANT EMISSIONS TO AIR
(Power plant with low-sulfur coal and flue gas desulfurization)
Thermal efficiency -40%
Coal heating value 9000 Btu/lb
Coal sulfur content 0.81%
Plant heat rate 8500 Btu/kWh
Flue gas desulfurization 85% S02 removal
S02 emitted:
8500 Btu 0.01 lb S 2 lb S02 Q 15
kWh X lb coal X lb S X ' = 0.0028 lb S02
9000 Btu kWh
lb coal
0.0028 lb S02 = 0.83 lb S02b
°r 3414 Btu output 106 Btu output
Particulate collection efficiency 99.7%
Coal ash content 20%
Fly ash/bottom ash 4/1
Fly ash emitted:
8500 Btu 0.2 lb ash 0.8 lb fly ash 0.005 lb emitted
kWh lb coal lb ash lb fly ash = 4.5x10 lb
9000 Btu kWh
lb coal
or °-13 lb
106 Btu output
NO emitted (source): ^P.0* lb or in6 * lb
x _ _ kWh 10° Btu output
Some background information and data for the calculations contained in this
appendix were taken from References 25, 26, and 27.
•L
NSPS of 1.2 lb S02/106 Btu fired equivalent to approx 3 lb S02/106 Btu output
so that this example plant is far superior to one meeting NSPS.
148
-------
TABLE B-2. WATER REQUIREMENTS FOR COAL-FIRED POWER PLANT
POWER PLANT COOLING TOWERS:
Heat rate 8500 Btu/kWh
-3414
Total heat rejected 5086
Plant heat loss(12% of heat rate) -1017
Heat rejected by cooling tower 4069
4069 Btu/kWh = 4.1 Ib H20
1000 Btu/lb H20 kWh
1200 Ib H?0 144 gal
106 Btu output °r 106 Btu output
POWER PLANT SCRUBBERS:
Water with waste sludge and ash > 1 Ib H20/lb solids:
1 Ib H20 54 Ib solids = 54 Ib H?0 = 6.5 gal
Ib solids X 106 Btu output 105 Btu output 106 Btu output
Water evaporated in scrubber 763 Btu/kWh 0.76 Ib
(75% of plant heat loss for evaporative 1000 Btu/lb H20 = kWh
cooling of gas in scrubber):
222 Ib H?0 27 gal
105 Btu output °r 10b Btu output
Cooling tower -144 gal/106 Btu output
Scrubbers (evaporation) 27 gal/106 Btu output
(sludge) 7 gal/106 Btu output
Miscellaneous 22 gal/106 Btu output
Total 200 gal/106 Btu output
Wastewater - Assume water in cooling tower is concentrated five-fold in salt
content and that blowdown is used for scrubbers. Tower blowdown is about
46 gal/106 Btu output.
149
-------
TABLE B-3. COAL-FIRED POWER PLANT SYSTEM EMISSIONS
AND LAND DISTURBANCE
LAND
Mining land disruption 15.2 acres/109 Btu output/day
Coal cleaning land requirements 0.65 acre/109 Btu output/day
Conversion land requirements 15.3 acres/109 Btu output/day
WATER POLLUTION
Mining - silt runoff 0.25 lb/106 Btu output
Conversion - minimal - assume all blowdown from cooling towers and other
streams goes to evaporation ponds
SOLID WASTE (dry basis)
Mining Assume = 0 with all returned to mine
Conversion plant 54 lb/106 Btu output
(ash + FGD solids)
AIR POLLUTION
Coal cleaning 0.01 lb/106 Btu output
Conversion or power plant See Table B-l
150
-------
TABLE B-4. COAL COMBUSTION FOR ELECTRIC POWER GENERATION
Impact
Land
disruption
and use
Water
pollution
Input
Output*2
Ammonia
Phosphorus
Salts
Metals
Pesticides
Silt
Air pollution
NOX
sox
H2S
Particulates
Pesticides
Organisms
Solid waste
total
Resource
extraction
Acres/
109 Btu/
day output
(gal/106 Btu)
(gal/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
15.2
4 to 8
Neg.
0
0
0
0
0
0.25
Neg.
Neg.
Neg.
Neg.
0
0
0
Onsite
processing
or storage
0.65
0
0
0
0
0
0
0
0
0
0
0
0.01
0
0
0
Transport to
conversion
plant
Neg.
0
0
0
0
0
0
0
0
Neg.
Neg.
Neg.
Neg.
0
0
0
Conversion
plant
15.3
200
8
0
0
0
0
0
0
2.0
0.83
—
0.13
0
0
54
^Assume all wastewater goes to evaporation ponds with no discharge.
151
-------
TABLE B-5. COAL GASIFICATION WITH LURGI TECHNOLOGYa
Gas production ~250xl06 scf/day or 250xl09 Btu/day
9
Liquids production -50x10 Btu/day
Purchased electric power l.lSxlO6 kWh/day
Power plant input energy 9.8xl09 Btu/day
Net energy output ~290xl09 Btu/day
Total plant S02 emissions 30,000 Ib/day or 0.10 Ib S02
106 Btu output
Total plant NOX emissions 720 Ib/day or 0.0025 Ib
106 Btu output
Total plant particulate emissions 3600 Ib/day or 0.012 Ib
106 Btu output
Mining and hauling emissions
Particulate l.SxlO"4 lb/106 Btu output
S02 S.lxlO-4 lb/106 Btu output
NOV 4.2xlO~3 lb/106 Btu output
X
Proposed by Pacific Coal Gasification Company and Transwestern Coal
Gasification Company.
TABLE B-6. WATER REQUIREMENTS FOR COAL GASIFICATION
USING LURGI TECHNOLOGY
Assume 67% of heat load dissipated by air cooling.
Intake water - 5,100 gal/min (7.344xl06 gal/day)
or 25.3 gal/106 Btu output.
Water discharge to evaporation ponds or deep wells in western areas will be
S2xl06 gal/day or 6.9 gal/106 Btu output.
152
-------
TABLE B-7. LURGI COAL GASIFICATION PLANT EMISSIONS
AND LAND DISTURBANCES
LAND
Mining land disruption 1.9 acres/109 Btu/day
Coal cleaning and mining support 1.3 acres/109 Btu/day
Conversion plant 2 acres/109 Btu/day
WATER POLLUTION
Mining - silt runoff 0.25 lb/106 Btu output
Conversion See Table
SOLID WASTE
(Ash, water treatment solids, biological solids, FGD scrubber sludge,
boiler ash)
6,869 ton/day or 47 lb/106 Btu output
153
-------
TABLE B-8. COAL GASIFICATION^2
Impact
Land
disruption
and use
Onsite Transport to
Resource processing conversion Conversion
extraction or storage plant plant
Acres/
109 Btu/
day output 1.9 1.0 0.3
2.0
Water
pollution
Input
Output^1
Ammonia
Phosphorus
Salts
Metals
Pesticides
Silt
Air pollution
(no fugitive
emissions
included)
NOV
SO*
H2&
Particulates
Pesticides
Solid waste
total
(gal/106 Btu)
(gal/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
3 to 4
0
0
0
0
0
0
0.04
0
0
0
0
0
0
0
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
0.002
0.00015
0.00007
(lb/106 Btu) 0
0
0
0
0.04
0
0
0
0
0
0
0
0
0
0.003
0.0002
0.0001
0
25
<6.9
NA
NA
NA
NA
0.0025
0.10
0.012
47
Basis: 250 million scf/day of methane, Lurgi technology assuming North-
western New Mexico site as proposed by El Paso and WESCO.
Assume all wastewater goes to evaporation pond or deep well.
Noise: 85-90 dBA at gasification plant boundary 660 ft from accoustical
center; comparable levels for coal preparation plant; blasting noise
at mine and vehicle noise in mining areas and on haul roads.
154
-------
TABLE B-9. ANAEROBIC DIGESTION
(Case 1-A)
Impact
Land
disruption
and use
Water
pollution
Input
Output
Ammonia
Phosphorus
Salts
Metals
Pesticides
Air pollution
NOX
SOX
H2S
Particulates
Pesticides
Solid waste
total
Resource
extraction
Acres/
109 Btu/
day output
(gal/106 Btu)
(gal/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Onsite Transport to
processing conversion Conversion
or storage plant plant
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4.7
+
25 for
evap . pond
0
•7
b
0
0
0
0
0
0.16
0.18
Neg.
Neg.
0
Neg.
aBasis: Fresh cattle manure with liquid recycle.
All wastewater goes to evaporation pond.
155
-------
TABLE B-10. ANAEROBIC DIGESTION^
(Case 1-B)
Impact
Land
disruption
and use
Water
pollution
Input
Output
Ammonia
Phosphorus
Salts
Metals
Pesticides
Air pollution
NOV
A
sox
H2S
Particulates
Pesticides
Solid waste
total
Resource
extraction
Acres/
109 Btu/
day output
(gal/106 Btu)
(gal/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Onsite
processing
or storage
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Transport to
conversion Conversion
plant plant
0
0
0
0
0
0
0
0
0
0
0
0
0
0
15.6
187
0
0
0
0
0
0
0.187
0.22
Neg.
Neg.
0
Neg.
a.
Basis: Cattle manure collected on 5-month cycle with liquid recycle.
156
-------
TABLE B-ll.
ANAEROBIC DIGESTION'
(Case 2)
a
Impact
Land
disruption
and use
Onsite Transport to
Resource processing conversion Conversion
extraction or storage plant plant
Acres/ 0 0
109 Btu/
day output
0 7.3
34 for
Water
pollution
Input
Output
Ammonia
Phosphorus
Salts
Metals
Pesticides
Air pollution
NOX
SOX
H2S
Particulates
Pesticides
(gal/106 Btu) 0
(gal/106 Btu) 0
(lb/106 Btu) 0
(lb/106 Btu) 0
(lb/106 Btu) 0
(lb/106 Btu) 0
(lb/106 Btu) 0
(lb/106 Btu) 0
(lb/106 Btu) 0
(lb/106 Btu) 0
(lb/106 Btu) 0
(lb/106 Btu) 0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
evap . pond
0
0
0
0
0
0
0.171
0.148
Neg.
Neg.
0
Solid waste
total
(lb/106 Btu)
0
Neg.
a.
Basis: Fresh cattle manure and wheat residue with liquid recycle.
All wastewater goes to evaporation pond.
157
-------
TABLE B-12. ANAEROBIC DIGESTIO^
(Case 3-B)
Impact
Land
disruption
and use
Water
pollution
Input
Output
Ammonia
Phosphorus
Salts
Metals
Pesticides
Air pollution
NOX
sox
H2S
Particulates
Pesticides
Solid waste
total
Resource
extraction
Acres/
109 Btu/
day output
(gal/106 Btu)
(gal/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
(lb/106 Btu)
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Onsite
processing
or storage
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Transport to
conversion Conversion
plant plant
0
0
0
0
0
0
0
0
0
0
0
0
0
0
42.2
626
0
0
0
0
0
0
1.87
0.90
Neg.
Neg.
0
Neg.
Basis: Fresh chicken manure with liquid recycle.
158
-------
APPENDIX C
DATA COMPARISON FOR BIO-GAS, CRAP, AND SRI MODEL CASES
Makeup water
(77 gal/106 net Btu)
800,000 Ib solids
266.667 H^O
II
Fiber
recovery
1,066,667 Ib manure
(75% solids in manure)
(Age of manure feed will
vary from 1 to 6 months)
500,000 Ib
3,847,000 Ib
4,348,000 Ib
A 1.75x10£
T (net)
H20
slurry
'ciuCII lii 4870 Btu
BluCM4/U |bs solids digestec
^^ Solids
separation
I
(11.5% solids)
300,000 Ib solids
700,000 Ib H2O
1,000,000 Ib
(30% solids)
140,000 Ib solids
420,000 Ib H_O
560,000 Ib
(25% solids)
Water Balance
(No liquid discharge for this example)
With manure
Makeup water
266,667 Ib/day
853.333 Ib/day
1,120,000 Ib/day
Output
With fiber solids
With digested solids
700,000 Ib/day
420.000 Ib/day
1,120,000 Ib/day
Solids Disposition
Input 800,000 Ib/day ) 360,000 Ib/day digested or 45% of input with a net
Output 440,000 Ib/day > CHi, yield of about 1.753xl06 scf or 4870 Btu/lb
) solids digested
Note: It was indicated that an evaporative pond would be provided for storm
water runoff and any liquid purge stream. We assume purge stream
might be required if manure moisture content is higher than for the
case indicated in the example.
aSource: Personal communication with Mr. Chester Brooks of Oklahoma City,
Oklahoma representing CRAP in September 1976. (Informed that no
published information is available.)
Figure C-l. CRAP system mass balance.
a
159
-------
800 Ib H2O
1000 Ib solids
1000 Ib H2O
2000 Ib manure
3.1x10 Btu of methane (7750 Btu/lb solids digested)
(gross)
7200 Ib
Digestion
Solids
separation
a
(50% solids in manure
average)
Average age of manure
~ 3 months
(collected every 6 months)
Solids content in manure
varies from about 30 to 75%
depending on weather conditions.
Sources: References 28 and 29.
600 Ib solids
2400 Ib
(25% solids)
Figure C-2. Bio-Gas Inc. system mass balance.a
160
-------
TABLE C-l. COMPARISON OF PARAMETERS USED BY BIO-GAS, INC.
AND SRI FOR CATTLE MANURE
G
fd
f
V
Total N in manure
(dry basis)
Total N in digester
effluent (dry basis)
0 , days
Volatile solids loading
digester volume
(Ib vsa/ft3
Bio-Gas, Inc.
0.99
0.45 to 0.60
0.65
3.7%
2.8%
16.2
0.52xl06 Ib vsa
2.6xlOb ftd
0.20
SRI
Manure ,
fresh
1.0
0.67
0.78
1.9%
4.1%
20
1.72xl06 Ib vsa
7.0xlOb ftd
0.25
Manure, 5-month
collection
cycle
0.91
0.31
0.67
2.5%
3.3%
20
1.47xl06 Ib vsa
4.53xlOb ftd
0.32
a
vs = volatile solids
161
-------
TABLE C-2. COMPARISON OF SELECTED PARAMETERS FOR BIO-GAS,
INC., CRAP, AND SRI MODEL CASES
Feed solids
to digester, %
Solids content
in feed solids, %
Gas output /lb of
volatile solids
converted, expressed
in Btu/lb
Bio-Gas
8
50 average
(30 to 75 range)
7750 to 8800
(gross)
Coal-fired heaters
for digester
CRAP
11.5
75 (highest
solids content)
4870
(net)
SRI
7 to 10
20 to 50a
5682
(net)
6553*
(gross)
a
Solids content of fresh cattle manure and urine would be approximately
15%. For the case of "fresh manure," assume 20% solids (case 1-A).
For Case 1-B, assume an average manure solids content of 50%.
For Case 2, assume that the moisture content is 27% and for cases 3-A
and 3-B, 50%.
F
Case 1-A with fresh manure.
162
-------
REFERENCES
1. Ferguson, Thomas L., Fred J. Bergman, Gary R. Cooper, Raymond T. Li,
and Frank I. Honea. Determination of Incinerator Operating Conditions
Necessary for Safe Disposal of Pesticides. EPA/600/2-75/041, U.S.
Environmental Protection Agency, December 1975.
2. Pest Control: An Assessment of Present and Alternative Technologies,
Volume IV, Forest Pest Control. National Academy of Sciences, 1975.
3. Supplement No. 5 for Compilation of Air Pollutant Emission Factors.
AP-42, U.S. Environmental Protection Agency, Research Triangle Park,
North Carolina.
4. Supplement No. 6 for Compilation of Air Pollution Emission Factors.
AP-42, U.S. Environmental Protection Agency, Research Triangle Park,
North Carolina.
5. Biomass Energy for Hawaii. Institute for Energy Studies, Stanford
University, Stanford, California, February 1977.
6. McCarty, P. L. Anaerobic Waste Treatment Fundamentals. Public Works,
(9) 107, (10) 123, (11) 91, (12) 95, 1964.
7. Lehman, Marrien J. Air Pollution Abatement Applied to a Boiler Plant
Firing Saltwater Soaked Hogged Fuel. In: Wood Residue as an Energy
Source Proceedings. Forest Products Research Society, Madison,
Wisconsin, pp. 75-13.
8. Supplement No. 6 for Compilation of Air Pollution Emission Factors.
Appendix C, NEDS Source, Classification Codes and Emission Factor
Listing. AP-42, U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina.
9. Compilation of Air Pollution Emission Factors. AP-42, U.S. Environmental
Protection Agency, Research Triangle Park, North Carolina, p. 6.12.1.
10. Hall, E. H., C. M. Allen, D. A. Ball, J. E. Burch, H. N. Conkle,
W. T. Lawhon, T. J. Thomas, and G. R. Smithson, Jr. Comparison of Fossil
and Wood Fuels. EPA-600/2-76-056, U.S. Environmental Protection Agency,
Washington, D.C., March 1976.
11. Tatom, J. W., A. R. Colcord, J. A. Knight, and L. W. Elston. Clean
Fuels from Agricultural and Forestry Wastes. EPA-600/2-76-090, U.S.
Environmental Protection Agency, Washington, D.C., April 1976.
163
-------
12. Loehr, R. C. Agricultural Waste Management. Academic Press, N.Y.
13. Johnsen, V. The Chemical Composition of Hardwood Smoke. University
Microfilms International, Ann Arbor, Michigan. 1961.
14. Houston, David. Chemistry and Technology of Rice, Chapter 12. (In
press.)
15. McCarty, P. L. Anaerobic Processes. Presented at the Birmingham
Short Course on Design Aspects of Biological Treatment, International
Association of Water Pollution Research, Birmingham, England, September
1974.
16. McCarty, P. L. Phosphorus and Nitrogen Removal by Biological Systems.
Presented at University of California, Berkeley, 2nd Annual Sanitary
Engineering Research Laboratory Workshop, June 1970.
17. Shapiro, J., G. V. Levin, and Z. G. Humberto. Anoxically Induced
Release of Phosphate in Waste Water Treatment. JWPCF, 39(11): 1810,
1967.
18. Dalton, F. E., J. E. Stein, and B. T. Lynam. Land Reclamation — A
Complete Solution of the Sludge and Solids Disposal Problem. JWPCF,
40(5): 789, 1968.
19. Lawrence, A. W. and P. L. McCarty. The Role of Sulfide in Preventing
Heavy Metal Toxicity in Anaerobic Treatment. JWPCF, 37(3): 392, 1965.
20. Masselli, J. W., N. W. Masselli, and M. G. Burford. Sulfide Saturation
for Better Digester Performance. JWPCF, 39(8): 1369, 1967.
21. Chen, K. Y., C. S. Young, T. K. Jan, and N. Rohatgi. Trace Metals in
Wastewater Effluent. JWPCF, 46(12): 2663, 1974.
22. Schmid, L. A. Feedlot Wastes to Useful Energy — Fact or Fiction?
ASCE, JEED, EE5, p. 787, Oct. 1975.
23. Callihan, C. D. and C. E. Dunlap. Construction of a Chemical-Microbial
Pilot Plant for Production of Single-Cell Protein from Cellulosic
Wastes. USEPA Report SW-24c, 1971.
24. Norris, H. E. Scrubbing Sewage Gas. Water Works and Sewerage, 90(2):
61, 1943.
25. Energy and the Environment — Electric Power, Publication of the
Council on Environmental Quality, Washington, D.C. August 1973.
26. Stanford Research Institute, Private Multi-Client Reports. 1975, 1976.
164
-------
27. Detailed Environmental Analysis Concerning a Proposed Coal Gasification
Plant for Transwestern Coal Gasification Company, Pacific Coal
Gasification Company, Western Gasification Company. Battelle, Columbus
Laboratories, Columbus, Ohio. February 1973.
28. Burford, J. L., Jr. and F. T. Varani. Energy Potential through Bio-
Conversion of Agricultural Wastes. FCRC 651-366-075, Bio-Gas of
Colorado, Inc., Loveland, Colorado, September 1976.
29. Varani, F. T. and J. L. Burford, Jr. Economic Consideration and Energy
Potential of Agricultural Wastes. Presented at 171st National Meeting,
American Chemical Society, Division of Fuel Chemistry, New York, April
1976.
165
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-78-047
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
PRELIMINARY ENVIRONMENTAL ASSESSMENT OF ENERGY
CONVERSION PROCESSES FOR AGRICULTURAL AND FOREST
PRODUCT RESIDUES; Volume I
5. REPORT DATE
March 1978 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Benjamin J. Gikis, et al.
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Stanford Research Institute
333 Ravenswood Avenue
Menlo Park, California 94025
10. PROGRAM ELEMENT NO.
EHE624
11. CONTRACT/GRANT NO.
68-01-2940
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory—Gin. ,OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Volume II consists of computer printout data which is not published.
Project Officer: John 0. Burckle (513) 684-4491
16. ABSTRACT
A preliminary assessment was made of the environmental impacts of several types of
conversion processes for producing energy or fuels from agricultural and forestry
residues. Fifteen examples were selected to represent various combinations of
agricultural residues and conversion processes available in various geographic regions.
The conversion processes included gasification-pyrolysis (Purox), liquefaction-pyrolysi
(Tech-Air), combustion (direct firing, both large and small scale), co-combustion with
coal, and anaerobic digestion. Residues included animal manure, forestry, and field
crops, including sugar cane. Special attention was given to pesticide and herbicide
residues in conversion processes. Pesticide residues were found to be generally low
in crops and logging wastes and were generally destroyed during thermal processes.
While many areas in the United States have high densities of agricultural residues,
economic considerations appear to rule out the use of available technologies for
obtaining energy from these sources at the present time.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Held/Group
Pesticides
Residues
Contaminants
Solid waste
Energy conversion
Processes
97F
18. DISTRIBUTION STATEMENT
19. SECURITY CLASS (This Report)
Unclassified
Not restricted
21. NO. OF PAGES
178
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
166
•&U.S. GOVERNMENT PRINTING OFFICE: 1978-757-140/6806 Region No. 5-11
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