EPA-600/2-76-056
March 1976
Environmental Protection Technology Series
COMPARISON OF FOSSi AN&
FUELS
ftssearch Laboratory
of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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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 five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental degradation from point and non-point sources of pollution. This
work provides the new or improved technology required for the control and
treatment of pollution sources to meet environmental quality standards.
EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the
views and policy of the Agency, nor does mention of trade
names or commercial products constitute endorsement or
recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-76-056
March 1976
COMPARISON OF FOSSIL AND WOOD FUELS
E. H. Hall, C. M. Allen,
D. A. Ball, J. E. Burch, H. N. Conkle,
W. T. Lawhon, T. J. Thomas, and 6. R. Smlthson, Jr.
Battelle-Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
Contract No. 68-02-1323, Task 33
ROAP No. AAK-01A
Program Element No. EHB-527
EPA Project Officer: James D. Kllgroe
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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ABSTRACT
A preliminary assessment was conducted of the use of wood as a
fuel for a commercial electric power plant as compared with the use of
clean fossil fuels, or fossil fuels with suitable pollution control tech-
nology. In the context of this study, wood fuel'is to be derived from
forest surplus, i.e., the tops and branches of trees,cut for commercial
purposes, and the cull or noncommercial trees, and from waste from forest
products industries. Wood was compared with alternative fuels with respect
to boiler technology, pollutant emissions, control technology, energy
balance, environmental-ecological impact, and cost. The general conclusions
are as follows:
• The use of forest surplus and waste wood is
technically feasible .
• Pollutant emissions are controllable.
• Net energy balances are favorable.
• The preliminary estimated cost is competitive.
• With proper forest management) there is potentially
a net benefit to the ecology of Vermont's forest ecosystems .
• Wood is a renewable resource.
• Therefore, a demonstration to advance the concept
toward commercial application is recommended.
In view of the fact that wood is a competitive fuel, a cursory
study was made which showed the concept to be applicable to other regions
of the country for incremental electric power generation capacity.
ii
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TABLE OF CONTENTS
Page
CONCLUSIONS 1
INTRODUCTION 2
Background 2
Objectives . 4
Approach 4
Evaluation of Equivalent Fuel Costs 5
Basic Assumptions 9
SUMMARY OF FINDINGS „ 10
Overview 10
Specific Conclusions 12
Boiler Technology 12
Pollutant Emissions and Control Technology 12
Energy Balances 13
Cost Comparison 13
Environmental-Ecological Impacts 14
Applicability of the Concept to Other Regions 15
Use of the Milton Plant for Demonstration 16
SUMMARY OF BOILER TECHNOLOGY 18
Basic Boiler Types 20
Effect of Fuel Characteristics on Boiler Design 22
Coal as a Fuel . • « 24
Wood as a Fuel 38
Existing Wood-Burning Boilers 49
References ,>,,..<,.>o°°»<>°°°°°<'°<><><><>°°<>e 57
iii
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TABLE OF CONTENTS (Continued)
Page
POLLUTANT EMISSIONS AND CONTROL TECHNOLOGY 59
Gaseous and Particulate Boiler Emissions . . • "
Particulate Collection Efficiency 62
Factors Affecting Particulate Emissions 62
Effectiveness and Costs of Particulate Control
Equipment Currently Employed for Wood-Fired Boilers 64
Collectors in Series 65
Shave Off System 65
Multitube Collector and Scrubber in Series 68
Relative Performance and Cost of Alternative
Particulate Removal Equipment 68
Emission of Potentially Hazardous Organic Compounds 76
Carcinogenic Compounds 77
Photochemically Active Compounds 78
Solid Residues From Burning Wood 79
Residue Characterization 79
Disposal Problems or By-Product Uses 81
Emission Control Technology for Fossil-Fuel Boilers 82
Nitrogen Oxides 82
Sulfur Dioxide 84
Particulates 86
Comparison of Wood and Fossil-Fuel Emissions 88
Summary 95
Air Pollution Emissions 95
iv
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TABLE OF CONTENTS (Continued)
Page
Boiler Residue 97
Conclusions 97
References 99
ENERGY BALANCE ANALYSIS 102
Introduction , 102
Basic Data and Sources of Information 102
Pennsylvania Bituminous Coal 102
Physical Cleaning of Pennsylvania Bituminous Coal . . . 105
Stack Gas Scrubbing 106
Low Sulfur Oil 106
Transportation, Truck, Rail, and Pipeline 106
Green Wood Chip 107
Annual Energy Consumption for Selected Paths 109
Summary and Conclusions 122
References 124
COMPARATIVE COST ANALYSIS 126
Cost of Wood as Fuel 126
Availability of Wood as Fuel 126
Wood Fuel Procurement Costs 130
Cost of Harvesting Wood Fuel 130
Chipping Costs 134
Transportation Costs 135
Replacement of Soil Nourishment 135
Power Plant Costs Using Wood Fuel ...... 139
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TABLE OF CONTENTS (Continued)
Page
141
Summary of Wood Fuel Costs ...............
141
Costs of Various Coal Fuels ........ . .........
141
Low Sulfur Coal ....................
1 LU
Physically Cleaned Coal
High Sulfur Coal with Stack Gas Cleaning
Dual System - Green Wood Plus Cleaned Coal
Comparison of Various Solid Fuel Costs
Sensitivity of Power Generation Costs to Changes in Costs of
Various Inputs .......................
Effect of Changing Fuel Costs .............
Effect of Changing Transportation Costs ........ 154
Effect of Changing Costs of Pollution Control ..... 158
Effect of Changing Plant Size ............. 158
References ......................... 161
ENVIRONMENTAL-ECOLOGICAL IMPACTS OF WOOD FUEL USE ........ 163
Silvicultural Practices: Nutrient Budget .......... 163
Nutrient Removal .................... 163
Nutrient Input ..................... 169
Rotation Period .................... 171
Conclusions ................ . ..... 173
Stream Water Quality Impacts of Timber Harvesting ...... 175
Impacts and Mitigating Measures ........... . 175
Policy Implications in Vermont ............. 185
Conclusion .......................
Soil Erosion ........................
vi
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TABLE OF CONTENTS (Continued)
Page
Effects on Wildlife 193
Aesthetics 196
Summary 199
Recommendations „ 201
References 202
APPLICABILITY OF HASTE, WOOD FUEL CONCEPT TO OTHER,
PLANT^CAPACITIES., AND REGIONS OF THE COUNTRY 206
Applicability to Other Plant Capacities 206
Applicability to Other Regions 207
Forest Biomass Waste 207
Regional Fuel Requirements 208
Necessary Conditions for Fuel Wood Utilization 208
Conclusions 213
References 214
EVALUATION OF THE USE OF THE MILTON PLANT
IN THE PROPOSED DEMONSTRATION . 215
Air Quality and Stack Height Consideration 216
APPENDIX A. REPORT FROM A. E. STILSON, ASSOCIATES ON CONVERSION
OF THE MILTON PLANT TO BURN WOOD CHIPS
vii
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LIST OF TABLES
Table 1. Summary Comparisons of Alternative Fuels
Table 2. Progressive Stages of Transformation of _-
Vegetal Matter into Coal . • • *•>
39
Table 3. Analyses of Wood and Wood Ash
Table 4. Overall Boiler Efficiency as a Function of .«
Wood Moisture Content
Table 5. Total Boiler Sales in Each Capacity Category from 1965
Through 1973 ., 3U
Table 6. Wood Burning Boiler Sales in Each Capacity Range
from 1965 Through 1973 50
Table 7. Wood Firing Methods For Different Size Categories
for Boilers Sold Between 1965 and 1975. 51
Table 8. Comparative Chemical Analysis of Wood, and Bark,
Coal, and Oil 60
Table 9. Emission Factors for Wood and Bark Combustion
in Boilers with No Reinjection 61
Table 10. Distribution by Particle Size of Average Collection
Efficiencies for Various Particulate Control Equipment . 69
Table 11. Calculated Wood Ash Collection Efficiencies for
Various Control Equipment 71
Table 12. Particulate Control Costs for a 50) MWe
Coal or Wood Fired Power Plant 75
Table 13. Spectrographic Analysis of Hogged Fuel Ash 80
Table 14. Summary of "Source-to-Power" Unit Air Emissions
for Coal, Oil, and Wood Fuel Systems 90
Table 15. Summary of "Source-to-Power" Air Emissions for
.for Coal, Oil, and Wood Fuel Systems 92
Table 16. Emission Ranking of Alternative Fuel Paths 94
Table 17. Energy Consumption for Path 1, Wyoming
Low-Sulfur Coal
viii
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LIST OF TABLES (Continued)
Page
Table 18. Energy Consumption for Path 2, Pennsylvania
Bituminous Coal - Deep Mined and Physically Cleaned . . 112
Table 19. Energy Consumption for Path 3, Pennsylvania Bituminous
Coal, Deep Mined, Burned With Stack Gas Cleaning .... 113
Table 20. Energy Consumption for Path 4, Pennsylvania Bituminous
Coal, Surface Mined and Physically Cleaned 114
Table 21. Energy Consumption for Path 5, Pennsylvania Bituminous
Coal, Surface Mined, Burned with Stack Gas Cleaning. . . 115
Table 22. Energy Consumption for Path 6, Caribbean Residual
Fuel-Tanker to New York/Boston . 116
Table 23. Energy Consumption for Path 7, Domestic Crude Oil-
Refined and Desulfurized 117
Table 24. Energy Consumption for Path 8, Green Waste Wood -
Chip and Truck 119
Table 25. Energy Consumption for Path 9, Waste Wood Chips
Dried at the Power Plant . 120
Table 26. Energy Consumption for Path 10, Combined Pennsylvania
Bituminous - Green Wood Chip Firing 121
Table 27. Summary of Annual Energy Consumptions for Ten
Fueling Paths 123
Table 28. Forest Lands in Five Counties in Central Vermont .... 127
label 29. Potential Availability of Green Wood Fuel from
Five Vermont Counties on a Sustained-Harvest Basis . . . 128
Table 30. Financial Data, 1970, Lumber and Wood Products,
for New England and Vermont 132
Table 31. Financial Data, 1970 and 1972, Logging Camps and
Logging Contractors, for New England and Vermont .... 133
Table 32. Cost of Nutrients Removed by Multiple Harvest
in Vermont's Forest Lands 138
Table 33. Estimated Costs of Burning Various Fuels
in a 50-MW Power Plant - 1980. 140
ix
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LIST OF TABLES (Continued)
Table 34. The Cost of Wood As a Fuel to Generate
Electricity in Vermont - 1980
Table 35. The Cost of Low-Sulfur Coal from Wyoming to Generate
Electricity in Vermont - 1980 . . . . •
Table 36. The Cost of Using Cleaned Pennsylvania Bituminous
Coal to Generate Electricity in Vermont - 1980
Table 37. The Cost of Using High-Sulfur Pennsylvania Bituminous
Coal to Generate Electricity in Vermont - 1980 ..... 151
Table 38. The Cost of Using Green Wood and Physically Cleaned
Coal Interchangeably to Generate Electricity in
Vermont - 1980 ..... .— . . .- . ........... 153
Table 39. The estimated Costs of Using Various Fuels to
Generate Electricity in Vermont - 1980 .........
Table 40. Sensitivity of Power-Generation Costs to Fuel Costs
50 MW Power Plant, Central Vermont - 1980 ....... 156
Table -41... Sensitivity of Power-Generation Costs to Transportation
Costs 50 MW Power Plant, Central Vermont - 1980 .... 157
Table 42. Sensitivity of Power-Generation Costs to Pollution-
Control Costs 50 MW Power Plant, Central Vermont - 1980. 159
Table 43. Sensitivity of Power-Generation Costs to Plant Size
50 MW Power Plant, Central Vermont - 1980 ....... 160
Table 44. Distribution of Tree Biomass and Nutrients in a
16-year-old Loblolly Pine Plantation in the North
Carolina Piedmont .................... 164
Table 45. Nutrient Removal - Above Ground Trees Only ....... 166
Table 46. Comparison of Two Harvesting Techniques in Finland ... 167
Table 47. Effect of Harvest Method on Biomass and Nutrients
from a 16-year-old Loblolly Pine Plantation ....... 168
Table 48. Estimated Nutrient Losses Accompanying Silvicultural
Practices Routinely Applied on the Fernow Experimental
Forest, Parson, W. Va .................. 170
Table ^9. Gross Nutrient Budget for the Harvest Site ....... 172
Table 50. Replenishment of Soil Nutrients in a
North Carolina Hardwood Forest ............. 174
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LIST OF TABLES (Continued)
Page
Table 51. Summary of Studies of the Effect of Logging on^
Erosion and Sedimentation in the United States 192
Table 52. Comparison of Conventional Fuel Usage Versus Quanity
of Potentially Available Waste Wood Fuel, by Region. . . 210
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LIST OF FIGURES
Figure .1. Equivalent Value of Coal and Wood at .
5, 25, and 50 Percent Moisture < . . . • 6
Figure 2. Equivalent Value of Oil and Wood at
5, 25, and 50 Percent Moisture 7
Figure 3. Water-tube Boiler of Small tubes connected at
one end to a reservoir, John Stevens, 1803. . . . . • 19
Figure 4. Water-tube Boiler with Tubes Connecting Water
Chamber below and Steam Chamber above, John
Cox Stevens, 1805 19
Figure 5. Firetube Boiler 21
Figure 6. Pulverized Coal Fired Boiler ...... 27
Figure 7. Ball and Race Type Coal Pulvetizer. 28
Figure 8. Cyclone Furnace 30
Figure 9. Cyclone Burner 32
Figure 10. Traveling Grate Stoker 33
Figure 11. Vibrating Grate Stoker . 34
Figure 12. Spreader Stoker 35
Figure 13. Underfeed Stoker 37
Figure 14. Boiler Heat Loss Versus Wood Moisture Content .... 41
Figure 15. Boiler With a Dutch-Oven Furnace 43
Figure 16. Wood Fired Spreader Stoker 45
Figure 17 Pneumatic Wood Feeder for Spreader Stoker Boiler. . . 45
Figure 18. Wood Fired Inclined Grate . 47
Figure 19. Cumulative Wood Burning Boiler Capacities in
Various Capacity Ranges Sold from 1965 Through
1975 (ABMA DATA). 52
xii
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LIST OF FIGURES (Continued)
Figure 20. Size Distribution of Wood and Coal Fly Ash 63
Figure 21. Annualized Cost of Operation of Dry Centrifugal
Collectors 66
Figure 22. Installed Cost of Dry Centrifugal Collectors 66
Figure 23. Secondary Shave Off System for Additional Particulate
Removal 67
Figure 24. Annualized Cost of Operation of Wet Collectors. .... 72
Figure 25. Installed Cost of Wet Collectors 72
Figure 26. Annualized Cost of Operation of High-Voltage
Electrostatic Precipitatdrs .............. 73
Figure 27. Installed Cost of High-Voltage
Electrostatic Frecipitators . . 73
Figure 28. Annualized Cost of Operation of Fabric Filters 74
Figure 29. Installed Cost of Fabric Filters. ...... 74
Figure 30. Fuel Paths for Public Utility Electric Power in
Central Vermont ......... 103
Figure 31. Steais-Electric Utilities' Fuel Consumption
Trends, Coal, Oil and Gas, by Regions ......... 209
Figure 32. Steam-Electric Utilities' Fuel Cost Trends, Coals
Oil and Gas, by Regions 212
Figure 33. Ground Level Concentration as a Function of
Downwind Distance, Wind Speed, and Stability 220
Figure 34. Ground Level Concentration as a Function of
Exhaust Velocity V and Terrain Height H ....... 226
xlii
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ACKNOWLEDGMENTS
The authors wish to acknowledge the contributions of the many
representatives of industry who supplied information regarding various
aspects of this study.
Dr. Robert D. Burkett, of the Battelle-Columbus staff, authored
portions of the section on Environmental-Ecological Impacts. His name
was inadvertently omitted from the list of authors which appears on the
title page.
A subcontractor, Alden E. Stilson and Associates, Columbus,
Ohio, performed the evaluation of the modifications to the Milton Plant
required to burn wood. The work of John D. Hummel, who directed Stilson s
efforts, is gratefully acknowledged.
Mr. James Kilgroe, the EPA Task Officer, and Mr. G. Ray Smithson,
Jr., the Battelle-Columbus Program Manager, provided sound and helpful
direction to the program.
xiv
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CONVERSION OF UNITS
Some English units which 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 units.
Multiply
English Unit
by
Conversion
To Obtain
Metric Unit
acres
acre-feet
barrel, oil
British Thermal Unit
British Thermal Unit/pound
cubic feet/minute
cubic feet/second
cubic feet
cubic feet
cubic inches
degree Fahrenheit
feet
gallon
gallon/minute
horsepower
inches
inches of mercury
pounds
million galIons/day
mile [
pound/square irich (gauge)
square feet
square inches
tons (short)
yard
0.405 hectares
1233.5 cubic meters
158.97 liters
0.252 kilogram-calories
0.555 kilogram calories/kilogram
0.028 cubic meters/minute
1.7 cubic meters/minute
0.028 cubic meters
28.32 liters
16.39 cubic centimeters
0.555(°F-32)(a) degree Centigrade
0.3048 meters
3.785 liters
0.0631 liters/second
0.7457 kilowatts
2.54 centimeters
0.03342 atmospheres
0.454 kilograms
3785 cubic meters/day
1.609 kilometer
(0.06805 psig+1)(a) atmospheres (absolute)
0.0929 square meters
6.452 square centimeters
0.907 metric tons (1000 kilograms)
0.9144 meters
(a) Actual conversion, not a multiplier.
xv
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CONCLUSIONS
The use of forest surplus and waste wood as a fuel for an electric
power generating station is technically feasible. Between 1965 and March of
1975, 230 boilers with the capacity to burn wood as the primary fuel or as
an alternative fuel were sold in the United States„
The use of waste wood to fuel boilers is an environmentally
acceptable method of power generation,, Control technology for the collection
of particulates is available. Total air emissions for wood-fueled systems
are significantly less than acceptable alternative fuels such as physically-
cleaned coal or low-sulfur Western coal,,
Energy consumptions for recovery or procurement, for processing,
and for transportation of fuel are lower for green wood than for all other
alternatives except low-sulfur Western coal and imported oil.
The estimated cost of wood chips is competitive with the cost of
all alternative fuels. The estimated cost of electricity for a wood-fueled
plant is less than the costs estimated for electricity generated by the use
of alternative fuels. These costs are based on preliminary analysis only.
With sound forest management practice, the use of forest surplus
as fuel can be of benefit to the overall forest ecosystem. The effect of
nutrient removal through surplus wood harvest is not completely known at
this time. Available data are site specific and are difficult to project
to other sites.
The concept of using surplus wood as fuel appears to be applicable
to other regions of the country as well. Conservative estimates of surplus
and waste forest biomass show an availability equal to 77 to 103 percent of
the combined oil and gas consumption by utilities in the South Atlantic,
Mountain, and Pacific regions„
There are no apparent reasons why the Milton Plant cannot be
adapted to burn wood chips„ However, the physical arrangement of the boilers
is not preferred for burning such fuel* The deficiencies and countermeasures
which may overcome them are discussed in the report.
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INTRODUCTION
Background
The Green Mountain Power Corporation (GMPC) of Burlington, Vermont,
is planning the addition of 50 MW of electric power generation capacity to
their system. In view of the sharply higher costs of fossil fuels, the
company is evaluating the feasibility of fueling the new plant with wood.
The GMPC concept is to utilize forest surplus and the residuals from the
forest products industries as the source of the wood fuel. This concept is
distinctly different from the energy plantation concept, in which selected
species are grown for the sole purpose of converting the resulting biomass
to energy. The GMPC plan includes four principal sources of surplus or
waste wood.
(1) Commercial timber harvest. In conjunction with a
commercial timber cut, the tops, branches, and leaves
removed from merchantable logs would be chipped, blown
into a van, and transported to the power plant. During
the same operation, the noncommercial trees would be
cut and the entire tree chipped.
(2) Stand improvement cutting. Removal of culls from a tim-
ber stand improves the growing conditions for the remain-
ing commercial stock in the same way that weeding is
beneficial to a vegetable garden. Nevertheless, the
practice is underutilized in Vermont, largely because of
short-term economic considerations. A market for wood
chips obtained from a stand improvement cut should provide
wood lot owners an incentive to employ this beneficial
forest management practice.
(3) Ecological cutting. Selected cutting on State and Federal
forest lands designed to improve wildlife conditions could
be an additional source of surplus wood. Again, a market
for wood chips would allow government forest managers to
expand the use of this technique beyond existing budgetary
limitations.
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(4) Forest products industries waste. The waste from sawmills
and other forest products industries could be used to
supplement other sources of wood as fuel for a power plant.
The practice would benefit those industries by providing
an outlet for otherwise waste material.
Burning wood under a boiler is not a new concept. There were
230 boilers with capability to burn wood, either as the primary fuel or
as an alternate fuel, sold in this country between 1965 and March 1975.
The technology is available and vendors are able to supply equipment
designed to burn wood. Preliminary analysis by GMPC personnel showed that
the quantity of surplus wood in Vermont greatly exceeds the requirements
for a 50-MW plant. The major uncertainties in the concept lie in the lo-
gistics and the economics of the procurement of woodchips for fuel. In
order to obtain better understanding in these areas of uncertainty, GMPC
has submitted a proposal to the United States Environmental Protection
Agency requesting funds to conduct a demonstration program. GMPC proposes
to modify an existing 4 MW power plant located at Milton, Vermont, to receive
and burn wood fuel and to operate this plant for a period of two years.
During this time the critical factors in establishing a steady supply of
wood fuel will be investigated by letting various types of contracts
for wood chips. Other important elements of the proposed demonstration
include evaluation of the burning characteristics of wood fuel, measurement
of emissions, investigation of the ecological consequences of the proposed
wood procurement techniques, and definition of proper forest management
practices with respect to wood fuel procurement which will assure maximum
benefit to Vermont's forest lands.
As an element in the evaluation of this proposal, the EPA awarded
a contract to Battelle'.s Columbus Laboratories to conduct an independent
assessment of the concept of using forest surplus and wood waste as a
boiler fuel.
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Objectives
The objectives of the study were as fol.lows:
« To evaluate wood as a fuel for a 50-MW power plant
in Central Vermont as compared with alternative fuels,
which included: low-sulfur coal, physically cleaned
coal, high-sulfur coal burned with stack gas scrubbing,
and low sulfur fuel oil.
• To make a cursory study of the applicability of the con-
cept to other areas of the country and to other sized
power plants. ,
• To survey the Milton plant and assess the modifications
required to satisfactorily receive and fire wood fuel,
and to estimate the costs for all wood-handling, boiler-firing,
and pollution-control modifications.
After an initial visit to the Milton site, concern about the stack height
prompted the addition of a further objective, namely:
• To make a preliminary evaluation of the probable impact
of burning wood at the Milton plant on the air quality
in this vicinity; and, to estimate the usefulness of
increasing the height of the stack.
Approach
The evaluation of the use of wood as a power-plant fuel as
compared with alternative fuels was addressed with respect to five areas:
• Boiler technology
0 Pollutant emissions and control technology
• Energy requirements
• Environmental-Ecological impact of wood procurement
• Comparative costs.
The methodology employed and the results obtained in each of these areas
are described in separate chapters of this report.
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Evaluation of Equivalent Fuel Costs
It is instructive to consider, at the outset, the monetary value.
of wood as a fuel as compared with alternative fuels. The value of wood
depends upon its heating value and its moisture content. These properties
vary widely. Although numbers may be assumed and equivalent values deter-
mined, it is important to know the sensitivity of the equivalent value to
changes in heating value and moisture content. Such information is pre-
sented in Figure 1 for comparing the value of wood as a fuel for steam
production with the cost of coal, and Figure 2 for comparing wood with the
cost of residual oil.* Equivalent values are shown for two different
heating values of djry wood; 8,500 Btu/dry pound, a medium value; and
7,000 Btu/dry pound, a relatively low value. The sensitivity of the
equivalent value of wood to changes in moisture content also is displayed
in Figures 1 and 2. Values for moisture content (wet basis) of 5 percent,
25 percent, and 50 percent were chosen. The presence of moisture affects
the equivalent value of wood in two ways. The moisture adds to the weight
of the wood which results in a proportionate decrease in the heating value
"as received", as shown in the following tabulation:
Moisture Content
Percent (wet basis) Heating Value. Btu/lb
Medium Low
0 (bone dry) 8,500 7,000
5 8,075 6,650
25 6,375 5,250
50 4,250 3,500
The second impact of moisture in the wood arises from the fact that part
of the energy released as the wood burns is expended in vaporizing the
water contained in the wood. This energy is lost and, as a result, the
These comparisons assume a value equivalency which is only a function
of the fuel heating value and boiler efficiency. The relative costs
of firing coal, oil, and wood are not included in these comparisons.
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25%
moisture
Basis: 1115 Btu/lb steam
Coal-13,100 Btu/lb-82% effici
5% moisture-6650-8075 Btu/!b-78.5% eff.
25% moisture-5250-6375 Btu/lb-75% eff.
50% moisture-3500-4250 Btu/lb-66% eff
10 15 20 25
Equivalent Value-$/Ton Wood
FIGURE 1. EQUIVALENT VALUE OF COAL AND WOOD
AT 5, 25, AND 50 PERCENT MOISTURE
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Basis:lll5Btu/lbsteam
Oil-149,750 Btu/gal-84% efficiency
5% moisture-6650-8075Btu/lb-78.5% eff
25% moisture-5250-6375 Btu/lb-75% eff.
50% moisture-3500-4250 Btu/lb-66% eff.
25%
moisture
10 15 20 25
Equivalent Value- $/Ton Wood
FIGURE 2. EQUIVALENT VALUE OF OIL AND WOOD
AT 59 25, AND 50 PERCENT MOISTURE
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efficiency of the boiler is decreased. The efficiency penalty as a
function of moisture content is discussed on page 40. The equivalent
values of wood shown in Figures 1 and 2 are based 'on wood-fired boiler
efficiencies of 78.5, 75, and 66 percent for moisture contents (wet basis)
of 5, 25, and 50 percent. The comparable values for coal and oil used to
develop Figures 1 and 2 are: 13,100 Btu/lb and 82 percent boiler effic-
iency for coal; and, 149,750 Btu/gal and 84 percent boiler efficiency
for residual oil.
The sensitivity calculations result in a pair of lines, corres-
ponding to 7,000 Btu/dry Ib (the upper line of each pair), and 8,500 Btu/
dry Ib (the lower line of each pair) for each assumed moisture content;
as shown in Figures 1 and 2. For example, if coal costs $55 per ton and
and oil costs $0.32 per gallon (about $2.10/10 Btu for each), the
equivalent value of wood as a boiler fuel as a function of heating value
and moisture content would be as follows:
Moisture Content, Value of Wood
Percent (wet basis) Equivalent to Coal at $55/ton
or Oil at $0.32/gallon
for 7.000 Btu/dry Ib for 8,500 Btu/dry Ib
5 $26.75 per ton $32.50 per ton
25 20.25 per ton 24.50 per ton
50 11.50 per ton 14.50 per ton
Viewed somewhat differently, Figures 1 and 2 show that if wood with a heating
value of 8,500 Btu/dry Ib and a moisture content of 25 percent (wet basis)
could be purchased for $12.50 per ton it would be competitive with coal
selling for $28.00 per ton or oil at 16.5 cents per gallon. On the other
hand, if the wood has a heating value of only 7,000 Btu per dry Ib, and
a moisture content of 50 percent (wet basis), the $12.50 per ton price
then would be competitive with coal at $47.50 per ton and oil at 28 cents
per gallon.
This analysis shows that wood with a moisture content of 25 percent
is about 75 percent more valuable than wood at 50 percent moisture, assuming
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the same heating value for the dry wood. It should be noted that this does
not mean that one could buy a ton of green wood with 50 percent moisture,
dry it to 25 percent moisture and, thereby, increase its value by 75 percent.
An example will serve to illustrate. Compared to coal at $55/ton, wood
with 8,500 Btu /dry Ib and 50 percent moisture is worth $14.50 per ton.
If a ton were dried to 25 percent moisture by removing 667 pounds of water,
it would be worth $24.50 per ton, but since only 2/3 of a ton is left, the
dried wood is worth only $16.33. The actual increase in value of nearly
13 percent results from the fact that the drier wood can now be burned with
greater efficiency under the boiler.
Basic Assumptions
In the assessment of the use of wood as a fuel as compared with
alternative fuels to be presented in subsequent sections, typical proper-
ties of wood were chosen as representative of wood fuel. These basic
assumptions are as follows:
• Heating value, 8,500 Btu per pound of dry wood
e Moisture content, 45 percent (wet basis)
• Heating value, as received, 4,675 Btu/lb or
9.35 x 10 Btu/ton
• Steam boiler efficiency, 68.4 percent
• Overall power plant efficiency, 27.4 percent
• Power plant heat rate, 12,450 Btu/kwhr
• Plant capacity, 50 MW
• Load factor, 70 percent
12
• Calculated annual heat input, 3.8 x 10 Btu/year
® Annual wood requirement, about 410,000 tons •
-------
10
SUMMARY OF FINDINGS
Overview
The use of forest surplus and waste wood to fuel a new 50~MW power
plant has been compared with the use of alternative fuels with respect to a
number of different considerations. The general conclusions may be stated
as follows:
• The use of forest surplus and waste wood is technically
feasible
• Pollutant emissions are controllable
• Net energy balances are favorable
• The cost is competitive
• With proper forest management, there is potentially
a net benefit to Vermont's forest ecosystem
• Wood is a renewable resource
• Therefore, a demonstration to advance the concept
toward commercial application is recommended.
A summary of the comparisons between alternative fuels which lead to these
conclusions is presented in Table 1. For each of several elements, quantitative
or qualitative comparisons among the alternative fuels are shown. For some
elements of comparison wood is better than other fuels, and for others it is
worse. A very simple method used to obtain a comparison considering all
elements is included in Table !„ For each element of comparison the alternative
fuels were assigned rankings ranging from 1 (best alternative) to 5 (worst
alternative). Where qualitative comparisons were found, or where subelements of
comparison existed, the rank values were assigned arbitrarily and, to a degree,
subjectively. Without attempting to assign weighting factors to the relative
importance of the elements of comparison, the rank values for each fuel were
summed to obtain an overall ranking. On this simplified basis the use of wood
as a power-plant fuel has the lowest total and the dual wood-coal system has
the second lowest total, therefore, both systems compare favorably with all of
-------
11
TABLE 1. SUMMARY COMPARISONS OF ALTERNATIVE FUELS
Alternative Fuels
Element of Comparison
1.
2.
3.
4.
5.
6.
SUM
General
1.1 Renewable resource
Rank
Boiler Technology
2.1 Equipment available
2.2 Boiler efficiency
Rank
Pollutant Emissions
3.1 "Source -to- Power Total Air
Emissions, 10 Tons/Year
3.2 Solid waste disposal problems
Rank
Energy Requirements
4.1 Initial fuel required,
1011 Btu
4.2 "Source-to-Power" Energy
Required, 1010 Btu
Rank
Cost
5.1 1980 Est. cost of electricity,
mils/kwhr
Rank
Ecological Impacts
6.1 Net benefit to ecosystem
Rank
OF RANK SCORES
Wood
Yes
1
Yes
.65-. 8
5
/ \
38(a)
No
3
38
24
2
I
[ 45
i
1
Yes
1
13
Low
Sulfur
Coal
No
3
Yes
.82
3
52
No
4
32
21
1
49
2
No
5
18
Physically
Cleaned
Coal
No
3
Yes
;82
3
37-41
Yes
4
36
47
4
52
3
No
4
21
HS Coal
with
Stack Gas
Cleaning
No
3
Yes
.82
3
24-26
Yes
2
35
34
3
56
4
No
3
18
Domestic
Residual
Oil
No
5
Yes
.84
1
24
No
1
32
63
5
N.D.
5
No
2
19
Dual,
75% Wood,
25% Cleaned
Coal
Yes /No
2
Yes
.69-. 81
4
. .
39 S
Yes
4
36
26
2
49
2
Yes /No
2
16
(a) These values are too high if the NOX emission factor has been overestimated.
See Table 16, Page 94.
(b) N.D. - Not determined in the analysis but assumed higher than the other fules.
-------
12
the alternative fuels. This result serves only to show that there are no
overriding factors to prevent consideration of the use of wood to fuel incre-
mental electric power generation capacity.
Specific Conclusions
Boiler Technology
1. The technology is available for burning wood under a boiler.
2. Vendors can supply wood-burning equipment. Between 1965
and March of 1975, 230 boilers with the capability to burn
wood as the primary fuel or as an alternative fuel were sold
in the United States„
3. Boilers for burning wood alone have not been sold in sizes
larger than 500,000 pounds of steam per hour, roughly
equivalent to 50 MWe0
4. Wood is often fired in combination with fossil fuels. This
mode can be used if the projected availability of wood in a
specific locale is insufficient to supply the input require-
ments for a large plant.
5. Drying the wood chips increases the boiler efficiency. It
would not be prudent to use auxiliary fuel for this purpose,
but waste heat from the plant could be used. The mechanics
of this refinement were not covered in this study, however,
a chip dryer, possibly of a fluidized-bed design, using heat
extracted from the stack gases appears feasible. The benefits
in reduced green wood handling and reduced fuel input warrant
a thorough analysis of this concept,
Pollutant Emissions and Control Technology
1. The use of waste wood to fuel boilers for the generation
of electricity is an environmentally acceptable method of
power generation.
-------
13
2. Total emissions for wood-fueled systems are significantly
less than acceptable alternative fuels such as physically
cleaned coal or low-sulfur Western coals0
3. Control technology for the collection of up to 99»9 percent
of the particulates is currently available. The most
promising control method identified is a multitubular cyclone
separator connected in series with a low-energy wet-impingement
scrubber,, This system has proven economical, dependable, and
effective in actual waste wood boiler application.
4. Emission of hazardous organic chemicals from the incomplete
combustion of wood should not present any significant problems
to the local air quality.
5. Environmentally acceptable disposal of boiler residues can be
accomplished by placing the relatively inert boiler ash and
fly ash in landfills or in lagoons.
Energy Balances
1. A larger fuel input is required because of reduced boiler
efficiency associated with firing wood. Wood with 45 percent
12
moisture (wet basis) requires 3,8 x 10 Btu/year compared
12
with 3.22 x 10 Btu/year for coal. Wood dried to 15 percent
12
moisture (wet basis) requires an input of 3.4 x 10 Btu/year.
This is less than the mined coal requirement for all coal
*
paths except low sulfur western coal.
2. Energy consumptions for recovery or procurement, for processing,
and for transportation of fuel are lower for green wood than
all other alternatives except low sulfur western coal and
imported oil. These quantities are even more favorable for
dried wood.
Cost Comparison
The cost of green wood chips delivered to the power plant is
estimated to be:
-------
14
Item
Stumpage or procurement 0. 36
Harvesting 7.60 10.65
Chipping 1.43 2.01
Transportation 1.25 -Jr',75
Total 10-64 14'91
2. The cost of electricity produced by alternative fuels is
estimated by this preliminary analysis to be:
Cost of electricity,
Fuel mils/kwhr in 1980
Green wood chips 45.2
Green wood and physically
cleaned coal 49.0
Low sulfur coal 49.2
Physically cleaned coal 51.9
HS coal with stack gas scrubbing 55.9
3. According to this preliminary analysis, green wood chips are
competitive in cost with all alternative fuels.
4. The estimated cost of electricity for a wood-fueled plant is
quite sensitive to wood fuel costs, and moderately sensitive
to plant size; but relatively insensitive to transportation
costs and pollution control costs. Harvesting accounts for
81 percent of wood fuel costs, whereas procurement accounts
for only 4 percent and chipping for 15 percent.
Environmental-Ecological Impacts
1. With sound forest management practice, the use of forest
surplus as fuel can, on balance, be of benefit to the
overall forest ecosystem.
2, The effect of nutrient removal by harvest is not completely
known at this time. Available data are site specific and
are difficult to project to other sites.
-------
15
3. Nutrient inputs to forests are variable and are not yet
fully quantified. Natural replacement of nutrients may be
entirely sufficient for projected management alternatives. The
natural process can be supplemented by fertilization if required.
4. Proper forest management practices have been defined for
mitigating potential impacts on water quality and soil errosion.
5o Properly planned cutting of timber stands tends to improve
wildlife habitat.
6. Good management can minimize visual impacts of timber cutting.
Applicability of the Concept
to Other Regions
1. Conservative estimates of surplus and waste forest biomass
show an availability equal to 23 to 103 percent of the utility
fuel requirements in the New England, South Atlantic, East
South Central, Mountain, and Pacific regions,
2. In the South Atlantic, Mountain, and Pacific regions, the
estimated surplus wood availability represents 77, 118, and
103 percent, respectively, of the combined oil and gas
consumption by utilities.
30 Wood fuel is cost competitive with other fuels in most of these
regions, therefore, the concept appears to be applicable in
at least five regions of the country for incremental electric
power capacity additions.
4. All-wood-fired boilers currently are not sold in sizes larger
than 500,000 pounds per hour of steam (approximately equal to
50 MWe). Larger plants could be built using multiple boilers.
The normal economies of scale would not apply.
5o Procurement, transportation, and storage problems may limit
the maximum size of a single wood-fired plant to 200-250 MWe.
-------
16
Use of Milton Plant for Demonstration
(1) The boilers, turbine-generator, and the plant auxiliaries
have been maintained well and seem to be adequate for a
few years of service under adequate care and operations.
(2) There are no apparent reasons why the plant cannot be
adapted to burn wood chips. However, the physical arrange-
ment of the boilers is not preferred for burning such fuel.
The deficiencies and countermeasures which may overcome
them are discussed in the report.
(3) Plant modifications are discussed including the systems
required for chip unloading and storage, chip retrieval
from storage and conveying into the existing boiler house,
chip feeding to the boilers, grate system, combustion air
supply, flyash collection, and ash removal.
(4) The equipment to modify the plant is currently available as
standard production items. Delivery may be as long as one
year for the stokers.
(5) The cost of the modification of the plant including
engineering is estimated at $680,000.
(6) With regard to the possibility that the planned research
program might include the development of design and per-
formance factors relative to burning wood chips to generate
steam, the value of data which can be obtained is question-
able because, as mentioned above, the boiler configuration
is not typical of modern design for burning such fuels. If
the research is extended into the fields of combustion and
pollution control, attention to the boiler deficiencies
will be imperative and qualified engineers should play a key
role in the entire project.
(7) Uncontrolled particulate emissions from the Milton Plant are
projected to yield particulate concentrations in excess of
allowable ambient air quality levels.
-------
17
(8) Increasing the stack height by 20 feet would not be expected
to alter the foregoing conclusion.
(9) Nominal 80 percent particulate control would reduce the
projected ambient particulate concentrations to acceptable
levels. However, at these control levels particulate and
odor emissions may prove to be pollution problems to the
town of Milton.
-------
18
SUMMARY OF BOILER TECHNOLOGY
A boiler by definition is a mechanical device for converting
water to steam. This steam can then be used for a variety of purposes
but the first and primary purpose in America was for powering steam
engines. The first American water tube boiler was patented by John
/i \ *
Stevens in 1803, for powering a riverboat on the Hudson River ^ > .
This first type of boiler, shown in Figure 3, consisted of a series
of tubes extending radially outward from a central reservoir which,
when heated, produced saturated steam. This design was limited and
enjoyed little success. In 1805, however, John Cox Stevens, son of John
Stevens, patented a two-drum boiler, shown in Figure 4, consisting of
a lower chamber connected to an upper chamber by a series of tubes. Water
in the lower chamber is converted to steam when heat is applied to the
connecting tubes and the steam is collected in the upper chamber.
This two-chamber or two-drum concept of boiler design is common in
many modern boilers manufactured today.
In 1881, the first central power station for generating electric
power from steam went into service at the Brush Electric Light Company
plant in Philadelphia, Pennsylvania . This plant consisted of four 73-
horsepower boilers which is roughly equivalent to 10,000 pounds of steam
**
per hour total or 1 megawatt at an overall cycle efficiency of 33 percent.
Over the years boiler size and complexity as well as steam temperatures
and pressures have increased dramatically. This evolution has taken place
most rapidly in the last 50 years with power plant unit sizes going from
60 megawatts in 1925, to units over 1000 megawatts in 1975.
One of the big factors allowing this drastic increase in boiler
size was the introduction of pulverized coal firing which began to replace
other forms of solid fuel firing in the 1930's.
Coal, when pulverized to talcom powder consistency, can be fired
into a boiler similar to a gas or liquid fuel eliminating the need for
grates and increasing the heat release possible in a given furnace volume.
* References for this section are given on page 57
** Lb^2le%h£rSe?°Wer " e<*u^lent to 34'5 P°unds of steam per hour or
10 ft* of heating surface (1).
-------
19
FIGURE 3. EARLY DESIGN OF WATER-TUBE BOILER
Source: Reference 1, Fig. 2, p 1-3.
FIGURE 4. IMPROVED DESIGN OF WATER-TUBE BOILER
Source: Reference 1, Fig. 3, p 1-4•
-------
20
Basic Roller Types
Boilers can generally be classified by design as either fire-
tube or watertube. In a firetube boiler (shown in Figure 5 ), as the
name implies, the combustion takes place on the inside of the heat transfer
tubes and this heat is absorbed by the water which is contained by the
boiler shell on the outside of the tubes. This type of boiler is generally
limited to small sizes (seldom exceeding 20,000 pounds steam per hour)
and to low pressure (less than 100 psig). Firetube boilers could
possibly be fired with solid fuels but in recent years almost all
firetube boilers sold were designed to fire natural gas or oil and
would be unsuitable for solid fuel firing.
In watertube boilers, water and steam is contained in the
heat-transfer tubes and the combustion takes place on the outside
contained by the furnace walls. In older watertube boiler designs,
the furnace walls were comprised of refactory brick which acted as
an insulator around the combustion zone. The trend in watertube
boiler design, however, has been towards the use of water tubes for
walls using the heat absorbed by the walls to raise steam. In the
case of hard-to-combust fuels with low volatility, low heat value,
or high moisture such as anthracite, municipal refuse, or wood,
refractory walls are still used to maintain sufficiently high furnace
temperatures to insure adequate combustion. Such designs, however,
limit the amount of heat that can be absorbed by the furnace, thus
decreasing boiler efficiency.
Watertube boilers are manufactured in a variety of configurations
depending on the fuels they are designed to fire. According to a recent
survey of watertube boilers sold in an 8-year period from 1965 to
1973 < ', 57 percent of all boilers sold were designed for natural gas
as a primary fuel, 28 percent were designed for oil, 6.4 percent for
bituminous coal, and 1.6 percent for wood bark.
It is important, however, to distinguish between boilers
above 500,000 pounds steam per hour or 50 megawatts (primarily utilities)
and those below 500,000 pounds steam per hour (primarily industrial
boilers). For boilers over 500,000 pounds steam per hour sold between
-------
FXCURE 5. FIRETUBE BOX^R (COURTESY OF SUPERIOR COKBUStM CORPOBAIM)
-------
22
1965 and 1973, 47 percent were coal fired, 25 percent oil fired, 21
percent gas fired, and 1.3 percent designed primarily for wood firing.
For boilers under 500,000 pounds steam per hour, only 3.9 percent were
designed primarily for coal, 27 percent for oil., 57 percent for gas,
and 1.4 percent for wcod. This comparison shows that in the larger
sizes dominated by utilities (over 50 megawatts electric generating
capacity) coal is the dominant fuel. In the smaller sizes, however,
coal and other solid fuels account for a relatively small fraction
of boiler sales.
Effect of Fuel Characteristics on Boiler Design
The particular fuel a boiler is designed to burn has a consider-
able effect on its design. Boilers designed for clean fuels such as
natural gas or oil generally have no provision for installation of grates
for firing lump-size solid fuels, nor do they have ash handling facilities
or soot blowers for cleaning ash deposits off heat transfer surfaces.
Also, to maintain compact, low cost design, tube spacing is usually kept
to a minimum allowing for no ash buildup on tube surfaces. As a result
it is not considered attractive to fire solid fuels such as coal or wood
in boilers specifically designed for clean fuels such as gas or oil.
(2)
According to the population survey made in 1973 only 0.1 percent of
boilers designed for natural gas list either coal or wood bark as an alternative
fuel. Of boilers designed for oil, only 0.4 percent can burn coal.
Boilers designed for dirty fuels such as coal and wood, however,
frequently are also capable of burning clean fuels as alternatives. For
instance, 7.0 percent of the boilers designed for coal sold between 1965
and 1973 list oil as an alternative fuel and 9.5 percent list natural gas.
Of the wood-burning boilers, 21 percent list oil as an alternative and 23
percent list natural gas. Boilers designed for wood, coal, or other ash-
containing fuels, have certain design features in common.
• Ash handling facilities for removing bottom ash
to disposal area.
• Soot blowing equipment for periodically cleaning
ash deposits off heat transfer surfaces.
-------
23
Wider tube spacings and more generous furnace
volumes to allow for ash deposits on heat-trans-
fer surfaces.
Allowances for installation of pollution control
equipment, particularly for fly ash control.
Fuel storage, handling, and preparation equipment
for receiving and storing an adequate fuel supply,
reducing it to a desired size and possibly re-
ducing its moisture content,and equipment for
conveying the fuel to the boiler for firing.
-------
24
Coal as a Fuel
Coal has its origin in wood and other cellulosic materials which,
after millions of years of compression, under the earth's surface, grad-
ually underwent evolution to various grades of coal. Compositions for the
common ranks of coal as they progress in time of evolution from the starting
material, wood are shown in Table 2. These various materials can be
generally classed as to their carbon content as a fuction of age. As the
age or evolutionary state increases, the fixed carbon (FC) content increases
from around 20 percent for wood to over 80 percent for meta-anthracite, the
oldest form of coal. The heat value also tends to increase up through the
bituminous series and then declines for the anthracites as the hydrogen
content decreases. An important difference between the starting material,
wood and the various forms of coal is the ash and sulfur which originates
from the soil conditions present in the coal deposit that become an integral
part of the coal. These constituents are present in wood in only small
amounts by comparison.
Coal has long been a standard fuel for utility boilers and will
continue to be for some time to come due to its relative low cost and
high availability compared to other fuels. Boilers designed for coal,
however, entail inherently higher cost than those designed for either
gas or oil. This higher cost can be justified in utility applications
due to long plant life and high plant utilization factors. In industrial
size boilers, under 500,000 Ibs steam per hour, coal fired boiler sales
have decreased considerably in the last 10 years in favor of gas and
oil-fired units. In 1965, 11 percent of all boilers sold under 500,000
Ibs steam per hour were coal fired whereas in 1972 only 1.1 percent were
coal fired ^2\
The type of firing method and equipment design employed for coal
burning depends both on coal properties and on boiler size. There is
a strong dependence of firing method on size particularly between
pulverized or suspension firing and firing on a grate with various types
of stokers.
-------
(3)
Table 2. Progressive Stages of Transformation of Vegetal Matter into Coal
Fuel Classification
by Rank
Wood
Peat
Lignite
Lignite
Subbituminous C
Subbituminous B
Subbituminous A
Bituminous High Volatile C
Bituminous High Volatile B
Bituminous High Volatile A
Bituminous Medium Volatile
Bituminous Low Volatile
Semianthracite
Anthracite
Meta-anthracite
Locality
Minnesota
North Dakota
Texas
Wyoming
Wyoming
Wyoming
Colorado
Illinois
Pennsylvania
West Virginia
West Virginia
Arkansas
Pennsylvania
Rhode Island
e|
11
i s
£ &
—
46.9
64.3
36.0
33.7
22.3
15.3
12.8
12.0
8.6
1.4
3.4
3.6
5.2
5.4
4.5
Analysis
on dry basis
Proximate
VM
78.1
67.3
49.8
44.1
40.4
39.7
39.0
38.9
35.4
34.3
22.2
16.0
11.0
7.4
3.2
FC
20.4
22.7
38.1
44.9
44.7
53.6
55.2
53.9
56.2
59.2
74.9
79.1
74.2
75.9
82.4
Ash
1.5
10.0
12.1
11.0
14.9
6.7
5.8
7.2
8.4
6.5
2.9
4.9
14.8
16.7
14.4
S
0.4
1.8
0.8
3.4
2.7
0.4
0.6
1.8
1.3
0.6
0.8
2.2
0.8
0.9
"'
6.0
5.3
4.0
4.6
4.1
5.2
5.2
5.0
4.8
5.2
4.9
4.8
3.4
2.6
0.5
Ultimate
C
51.4
52.2
64.7
64.1
61.7
67.3
73.1
73.1
74.6
79.5
86.4
85.4
76.4
76.8
82.4
N*
0.1
1.8
1.9
1.2
1.3
1.9
0.9
1.5
1.5
1.4
1.6
1.5
0.5
0.8
0.1
°«
41.0
30.3
15.5
18.3
14.6
16.2
14.6
12.6
8.9
6.1
3.6
2.6
2.7
2.3
1.7
« 'M'
2 '«
1-6
D
W 3
x S
8835
9057
11038
11084
10598
12096
12902
13063
13388
14396
15178
15000
13142
12737
11624
Ol
-------
26
In the size range above 500,000 Ibs steam per hour, 86 percent
of the boilers sold from 1965 to 1973 designed for coal were equipped
with pulverized coal fired systems. No stoker fired boilers were recorded
in this size range; however, in the size range under 500,000 Ibs steam
per hour 63 percent were stoker fired (41 percent spreader stoker,
9 percent underfeed stoker, and 13 percent overfeed stoker). In contrast
only 10 percent were pulverized fired in this size range.
Pulverized coal furnaces are fired in a similar fashion to gas
and oil fired furnaces. An example of a central station pulverized coal
fired boiler is shown in Figure 6. The coal first is reduced to a very
fine size usually gaged as the number of particles that will pass a 200
mesh screen having 200 openings per linear inch,or each opening 74 microns
in size. Normally, around 60 to 75 percent of the coal particles would
be required to pass a 200 mesh screen to be considered acceptable for
watertube boilers. This fine size allows rapid combustion and high
heat release rates.
The pulverizer itself normally consists of a set of steel balls
or rollers held between two races. As the races are rotated against each
other the coal is crushed between the ball surface and race surface. A
side view of a double ball and race pulverizer is shown in Figure 7. The
crushed coal is then picked up in an upward flowing air stream which
selects for smaller coal particles as the larger particles are not en-
trained and fall back into the pulverizer.
Pulverizer capacity is primarily a function of fuel moisture
content, size, and grindability. Hot air is usually supplied to the mill
to promote drying of the coal while pulverizing. If this air supply is
not sufficient then mill capacity may be reduced due to agglomeration of
the moist coal particles making it difficult to remove them from the mill.
Commercial pulverizers can commonly handle up to 20 percent total moisture
(15 percent surface moisture) without seriously affecting capacity.
-------
27
PULVERIZER
FIGURE 6. PULVERIZED COAL-FIRED BOILER
Source: Reference 1, Fig. 6, page 17-6.
-------
COAL-AND-AIR
DISCHARGE OPENING
A ^CLASSIFIER
RAW-COAL
FEEDER
AIR INLET-*
DRIVING
RING
FIGURE 7. BALL AND RACE TYPE COAL PULVERIZER
Source: Reference 1, Fig. 9, page 17-10.
-------
29
Coal size is also an important factor in determining pulverizer
capacity. Ideally the coal would be double screened to restrict the
size to about 3/4 x 1/4 inch. Usually coal is fed to pulverizers as
run of mine or screenings with lumps though large inconsistencies in
size will result in reduced capacity.
The grindablility of a coal is a measure of the relative ease with
which a coal can be crushed. The grindability is measured in a Hardgrove
grindability machine which is a standard ball and race type pulverizer
that is operated under a specific set of conditions'.. The power required
to pulverize a given amount of coal is a measure of its grindability
and is usually expressed as the Hardgrove Grindability Index. The effect
on mill capacity is about directly proportional to the index. Western
lignitic coals may have low grindabilities, around 50, whereas harder
Eastern coals may range to 100 or more.
Once the coal is pulverized it is pneumatically conveyed to
a series of burners and fired into the boiler.' Various firing configur-
ations can be used but the most common are to fire horizontally from
either one wall or opposing walls of the furnace or to fire tangentially
into the center of the furnace from the four corners. Approximately 10 to
15 percent excess air is customarily supplied with the fuel to insure
complete combustion.
After combustion about 80 percent of the ash in the fuel is carried
away with the flue gas' ^and must be removed in downstream particulate
removal devices. The remainder of the ash falls to the bottom of the
furnace where it is normally quenched in water and sluiced to an ash
settling pond.
Most all large and small coal fired boilers today operate in a so-
called dry bottom mode, where furnace temperatures are kept low enqugh
to prevent the ash from becoming molten, usually below the ash fusion
temperature of the coal. Some furnaces, however, are intentionally
operated at higher temperatures above the melting point of the ash in
a so called wet bottom or slagging mode. An example of this type of furnace
is the cyclone design shown in Figure 8. The cyclone burner itself is
-------
30
GAS
OUTLET
INTERMITTENT
SLA& REMOVAL
FIGURE 8. CYCLONE FURNACE
Source: Reference 1, Fig. 14, page 28-8.
-------
31
is shown in Figure 9. Coal, along with conveying air, is introduced
tangentially into the cyclone burner which consists of a water cooled
horizontal cylinder. The ash in the fuel melts and is thrown outward
to the burner walls where it is removed by a slag tap at the base of
the burner. The hot gases from the burner then go through a conventional
heat recovery boiler as is shown in Figure 8, Heat release rates of up
3
to 900,000 Btu/ft /hr and gas temperatures exceeding 3000 F are developed
in the burner section. Slagging furnaces are not recommended for fuels
with ash fluid temperatures over 2600 F or ash viscosity greater than
250 poises at 2600 F/1^
The cyclone boiler is the type of slagging boiler to be most
significantly employed on a utility scale though many older slagging
boilers are still operating that are not cyclones. Recently, however,
few of these boilers have been installed due to their interent propensity
for emitting high levels of NO to the atmosphere. The high gas tempera-
X
tures achieved in the burner causes fixation of airborne nitrogen to NO .
X
Stoker fired coal boilers are most commonly found in the size
range from about 25,000 to 250,000 Ibs steam per hour. Stokers offer
lower capital cost than pulverized fired systems because they don't require
pulverizers and related equipment.
The stoker itself is simply a means for conveying lump size
coal to the combustion zone and removing the ash to an ash pit on a
more or less continuous basis. Modern stokers can be classed into three
types, overfeed, spreader, and underfeed stokers.
Overfeed stokers are typified by the traveling grate arrangement
shown in Figure 10. The stoker consists of a continuous rotating belt.
Coal is deposited on one end of the belt and progresses through the
combustion zone where combustion air is supplied from plenum chambers
under the grate. The ash remaining after combustion is discharged to
an ash pit off the end,of the grate.
Another type of overfeed stoker is one involving a vibrating
grate shown in Figure 11. This stoker consists of an inclined grate with
a series of verticle plates that are free to move back and forth
-------
32
FIGURE 9. CYCLONE BURNER
Source: Reference 1, Fig. 1, page 28-2,
-------
33
O C O O O O O
o o o o o o o
0 O O O O O O
O 0 O O O O
0 0 O O O O O
Ho o o o o o o
o o o o o c o
oo o o o o o
o o o o o o o
O O 0 O O O O
O O C C O O O
o o o o o o o
FIGURE 10. TRAVELING GRATE STOKER
Source: Reference 4.
-------
COAL
HOPPER
FIGURE 11. VIBRATING GRATE STOKER
Source: Reference 1, Fig. 7, page 16-9.
-------
35
in a rectilinear motion. This motion causes the coal to descend down
the grate through the combustion zone to the end of the grate where
the ash is discharged to an ash pit.
A spreader stpker shown in Figure 12 is a special case of an
overfeed traveling grate, although stationary or intermittent dumping
grates may also be used. Instead of the coal being deposited on one end of
the grate, it is flipped or projected from one wall of the furnace
through the combustion zone in suspension. Much of the fuel burns
in suspension and the remainder falls to the grate where burning is
completed in a fast burning thin fuel bed. The advantages of this
type of operation are better response to load changes and greater ability
to handle a wide variety of coals.
The fuel bed on a spreader stoker is relatively thin and ususally
ranges from 2 to 4 inches. Heat release rates are high with stationary
fy
or dumping rates achieving 450,000 Btu/ft^/hr and traveling rates up to
e\
750,000 Btu/ftz/hr. The spreader stoker is limited in its ability to
handle low loads, however, as the fire tends to smoke at loads below
o (3)
125,000 Btu/hr/ft^. v
Underfeed stokers are somewhat different in principle than overfeed or
spreader types. An example of an underfeed unit is shown in Figure 13.
Coal is fed to the combustion zone by a screw type feeder from under
the bed, which is contained in a retort, and combusion takes place on
top of the bed . The ash is then removed off the sides.
Generally stokers require carefully sized coal for most efficient
operation. The most important considerations are to limit coal sizes over
2 inches and those less than 1/4 inch (referred to as slack). The
exception to this rule is the spreader stoker which operates best with
(3)
coal less than 3/4 inch including fines or slack . Also the traveling
grate stoker is limited to burning coals with low caking tendencies
such as anthracites, lignites and some free burning butiminous coals.
Also overfire air amounting to 5 to 15 percent of combustion air
or steam is generally injected just above the combustion zone in stoker
applications to promote turbulence and mixing. This practice stimulates
combustion and reduces smoke emissions.
-------
36
COAL
HOPPER
FEEDER
OVERTHROW
ROTOR
SIDE-WALL HEADER
)iffS^s21a^S3gfrni:CH;GZ^ySff!i^^
x,-,j,-vtf^r*s:-.--" .- - v -•---:—-—%/»-£.- -- rn - j+ -=•— .-V' - v-~ "••s- "~ ~- """" v i*-«-^7"^w
FIGURE 12. SPREADER STOKER
Source: Reference 1, Fig. 11, page 16-12.
-------
GEARBOX MOTOR
BOILER
BURNER
FAN a AIRDUCT
FEED SCREW
FIGURE 13. UNDERFEED STOKER
Source: Reference 4.
-------
38
Wood As A Fuel
Typical composition of various types of wood and the resulting
ash composition of the wood when burned are shown in Table 3. Wood consists
primarily of 90 to 95 percent cellulosic material with 5 to 10 percent
volatiles, resins, fatty acids and other non-cellulosic materials
Wood itself has a heating value of about 8,300 Btu/per dry Ib, whereas resins
and other materials have heating values of about 16,900 Btu per Ib. Woods
containing high amounts of resin material, therefore, have a higher
heating value than woods containing lesser amounts. As is shown in Table 3,
resinous woods, such as pine and fir, have heating values of close to
9,000 Btu per dry Ib, whereas harder woods, such as oak, having heating values
closer to 8,300 Btu per dry Ib.
In wood processing about 50 percent of the weight of the raw
wood ends up as residue or waste. This residue is broken down roughly
into 18 percent slabs edgings and trimmings, 10 percent bark, and 20
(3)
percent sawdust and shavings . Much of the residue, particularly slabs,
edgings and trimmings, is processed through a machine called the hogger,
which reduces the size of the wood making it more manageable and easier
to burn. This so called hog fuel may contain on the average about 50
percent moisture, but the moisture content can vary considerably, depending
on the particular type of wood processing involved. Other than the moisture
content wood shows a remarkably uniform composition. It usually contains
less than 1 percent ash and little or no sulfur, making it an ideal fuel.
Today, 43 percent of the world's wood is burned as a fuel which is its
largest single use.(9) The high moisture content in the wood has the
biggest effect on its value as a fuel. As the moisture content increases
the heating value of the wood correspondingly decreases. In addition to
reducing the heating value of wood, moisture also diminishes furnace
efficiency, as heat required to evaporate the water is lost in the stack
gases. This heat requirement is such that as the moisture content
approaches 60 percent, it becomes difficult to maintain steady combustion. As
the moisture content goes to 70 to 80 percent, the wood no longer has
sufficient heat content to support its own combustion and becomes useless
waste. Wood can be dried by a variety 6f means. For example large
presses can be used to squeeze excess moisture out of the wood and can
potentially reduce moisture from around 70 per cent down to 55 to 66
-------
39
TABLE 3. ANALYSES OF WOOD AND WOOD ASH'
Column No.'
Wood Analyses (Dry Basis ),£ by wt
Proximate
Volatile matter
Fixed carbon
Ash
Ultimate
H3 Hydrogen
C Carbon
S Sulfur
Ns + Os, Nitrogen + Oxy gen
A Ash
Heating value, Btu/lb
Ash Analvses, % by wt
Silica as SiO,
Iron as Fe2O3
Titanium as TiO»
Aluminum as A12O3
Manganese as MnaO4
Calcium as CaO
Magnesium as MgO
Alkalies as Na2O
Sulfate as SO8
Chloride as Cl
Carbonate as CO.,
Undetermined
Ash-fusion temperatures
"Col No. Kind of Wood
1 Southern pine bark
2 Oak bark
3 Oregon wood, hogged
4 ' White-fir bark, salt-water stored
5 Spruce bark, salt-water stored
6 Redwood bark, salt-water stored
72.9
24.2
2.9
5.6
53.4
0.1
38.0
2.9
9030
—
—
—
—
''—
—
—
—
—
—
-
—
f
76.0
18.7
5.3
5.4
49.7
0.1
39.5
5.3
8370
—
—
—
—
—
—
„
—
—
—
-
—
t
74.7
23.3
2.0
5.7
53.9
trace
38.4
2.0
9120
—
—
—
—
—
—
—
—
—
—
—
—
—
74.3
24.0
1.7
5.8
52.2
trace
40.3
1.7
8810
1.7
3.2
0.0
3.2
3.9
60.8
3.0
10.4
3.0
0.4
11.5
—
—
69.6
26.6
3.8
5.7
51.8
0.1
38.6
3.8
8740
32.0
6.4
0.8
11.0
1.5
25.3
4.1
10.4
2.1
trace
7.0
—
—
72.6
27.0
0.4
5.1
51.9
trace
42.6
0.4
8350
14.3
3.5
0.3
4.0
0.1
6.0
6.6
25.0
7.4
18.4
14.0
—
—
Ash-Fusion Temperatures, F
initial Deform.
Softening
Fluid
Reducing
t i
2180 2690
2220 2720
2340 2740
Oxidizing
f
2180
2220
2470
t
2680
2730
2750
* Reference 1, -page 3-A4.
-------
40
percent, making the wood acceptable to many types of fuel burning
equipment(10). Air drying can reduce moisture content of freshly cut
wood from 50 percent down to 25 percent in about a year . Hot air,
using heat from boiler flue gas, could be used to partially dry the
woods.
Heat losses in the burning of wood consists mainly of those due
to moisture in the stack gas and the heat left in the stack gas after
combustion. Other losses consist of radiation and miscellaneous heat -
losses from the boiler and carbon loss in the ash.
Loss in boiler efficiency as a function of moisture content -of
(9)
the wood is shown in Figure 14 ^ . This loss is a small function of the
temperature of the stack gases; however, the large bulk of the heat loss is
attributable to the latent heat of vaporization of the water vapor in the
stack gas. As can be seeij in Figure 14, this can amount to 13 percent
in efficiency loss for 50 percent moisture in the wood or up to 26 percent
loss for a moisture content of 67 percent. The heat loss in the dry stack
gases is a significant function of the amount and temperature of the stack
gas. The amount of stack gas is dependent upon the amount of excess air
used for combusting the wood and also the moisture content of the wood.
A moisture content of 50 percent can, in fact, increase the volume of flue
gas up to 50 percent . The loss in boiler efficiency due to heat in the
stack gases is around 9 percent for 500 degree stack gas and 40 percent
excess air, and this would increase to 14 percent for 100 percent excess
air. With heat recovery equipment,,such as combustion air preheaters
and economizers or feed water heaters, the stack gas temperature can be
reduced from 500 F down to 300 F. This would reduce the efficiency loss
to 5 percent for 40 percent excess air and 6 percent for 100 percent excess
air. A summary of these heat losses is given in Table 4. Data are given
for moisture content values of 5, 25, and 50 percent (wet basis). The
resulting boiler efficiencies are 78.5, 75, and 66 percent, respectively.
Wood is commonly burned in a variety of types of equipment.
Prior to about 1940 the most common method was to burn the wood in a
dutch oven which is shown in Figure 15. Wood is usually fed in through
the top of the oven and is left to pile up usually on some form of water.
cooled grate. Combustion air is fed through the sides of the cell and
grate causing the wood to be gasified and combusted. The hot gases are then
-------
41
30
c
0)
o
o.
•
«/>
V)
o
0>
X
o
CD
20
10
Stock gas
temperature.
400 F
25 50
Moisture, percent (wet basis)
75
FIGURE 14. BOILER HEAT LOSS VERSUS WOOD MOISTURE CONTENT
(9)
-------
42
TABLE 4. OVERALL BOILER EFFICIENCY AS A FUNCTION
OE WOOD MOISTURE CONTENT
Percent Lost
(a)
Heat Loss Factors
5% Moisture 25% Moisture 50% Moisture
Heat loss to dry stack gases
(b)
Heat loss to moisture in fuel
Heat loss from formation of
(c)
9
0.5
ture from hydrogen in the fuel
Heat loss from,, incomplete
combustion
Heat loss from radiation and
unaccounted for
^ 7-
8
21.5
Corresponding boiler Efficiency 78.5
9
4
7-8
.4
23
75
9
13
7-8
4
34
66
(a) Reference 9, heating.loss as a percentage of heating value.
(b) Based on 40% excess air, 400 - 500 F stack gas temperature.
(c) Based on stack gas temperature of 400 - 500 F.
(d) Based on Douglas fir bark fuel.
(e) Assumed.
-------
43
TO STACK
FUEL IN
ASK IN
. ... .
^&^:>-°-<«':+:^°^.?::*^
FIGURE 15. BOILER WITH A DUTCH-OVEN FURNACE
Source: Reference 9, Fig. 16, page 13.
-------
44
fed into the main boiler section where they are further combusted supplying
heat to raise steam. The dutch oven partially gasifies or distills the
wood and, therefore, can tolerate higher moisture contents than direct
combustion. This method, while still in common use, is not extensively
employed in modern units today.
Most modern applications of wood firing today utilize various
forms of stokers. The most common of these methods is the spreader stoker
showi in Figure 16. In this type of an arrangement the hog fuel or wood
chips are either flipped or blown into the combustion zone of the boiler
where a significant amount of burning takes place in suspension. A typical
pneumatic arrangement for blowing wood onto a spreader stoker is shown
in Figure 17. The wood that does not burn in suspension falls to some form
of grate where the remainder of combustion takes place. Various types of
grates can be employed for this purpose. In smaller sizes of boilers, up
to about 100,000 Ib of steam per hour, stationary or possibly intermittent
dumping grates are common. For units larger than this size, traveling
grates or self cleaning grates are used almost exclusively. Figure 16 shows
the boiler equipped with a traveling grate.
Heat release rates on spreader stoker type operations commonly
approach 1,000,000 Btu per hour per square foot of grate area with 35
to 70 excess air and 400 F air temperature . Usually, about 80 percent
of the combustion air is supplied through the grate and 10 to 20 percent is
injected over the grate to stimulate turbulence and mixing in the combustion
gases causing more rapid combustion and reduction of smoke emissions.
Spreader stoker type boilers can handle wood up to about 55 percent
/o\
moisture. Moisture contents above 45 percent, however, decrease the
combustion rate rapidly. ' Under these conditions furnace temperature
must be maintained above 750 to 1000 F to maintain stable combustion
conditions.
The thin fuel bed and rapid burning rates of the spreader stoker
result in its being very sensitive to changes in boiler load. Control is
*
necessary over boiler feed rates and air supply rates to maintain stable
combustion conditions. The inclined type grate shown in Figure 18
however, characteristically has a deeper fuel bed than a spreader stoker.
This large fuel inventory on the grate itself results in its being much
less sensitive to load changes.
-------
45
FIGURE 16. WOOD-FIRED SPREADER STOKER
Source: Reference 9, Fig. 20, page 16.
-------
46
DEFLECTOR PLATE
FIGURE 17. PNEUMATIC WOOD FEEDER FOR SPREADER STOKER
Source: Reference 12.
-------
47
ROTATING
DUST
DISCHARGERS
REFRACTORY
HEARTH
3-CAST
FEED CHUTE
NIPPLES
APPROXIMATE CONTOUR
OF WOOD REFUSE
FUEL BED
WATER COOLED
INCLINED GRATE
LATERAL
ZONING
WALL
3-GUILLOTINE TYPE
ASH REMOVAL DOORS
SHIELD
FOR PROTECTION
OF OPERATOR
WHILE REMOVING
ASH
EPARATELY
ONTROLLED
OVERFIRE
IR SUPPLY
FIGURE 18. WOOD-FIRED INCLINED GRATE
Source: Reference 9, Fig. 21, page 17.
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48
In all types of stoker applications care must be taken to prevent
overheating of the grate in localized areas. Often, the fuel becomes
unevenly distributed across the surface of the grate resulting in irregu-
larities in air flow. Overheating occurs in those areas where the air
flow is restricted and may cause grate damage. Many times grates are water
cooled to alleviate this problem. Careful control of fuel size is also an
important factor in preventing grate overheating by lessening the wide
variation in fuel density on the grate. Minimizing the amount of slack
or material under 1/4-inch diameter that enters in the fuel is most
important. Usually, fuel sizes of less than about 1-1/4 to 2 inches with a
(13)
maximum of 50 percent slack are specified for stoker applications.
Suspension firing of wood is similar to pulverized coal firing »
For successful suspension firing wood should be dried as much as possible
and reduced to as small a size as possible with a minimum of 50 percent
(13)
smaller than a 1/4 inchv . Suspension firing results in a simpler,
less expensive boiler than stoker firing, but requires more extensive
hoggingr'"Tt~is recommended that an auxiliary fossil fuel, such as oil,
natural gas, or pulverized coal, be fired in suspension along with the
(13)
wood. Normally, wood firing in suspension burning units should not
exceed 40 to 50 percent of the total heat input to the boiler, the rest
being carried by the auxiliary fossil fuel. A typical suspension fired
wood boiler normally has a small dumping type grate installed at the base
of the unit to handle excess wood ash or chips which may fall to the
bottom without burning.
Cyclone type boilers have seldom been used in wood firing
although in Sweden there is currently a cyclone boiler burning wood. The
cyclone type burners employed are basically the same as those used for coal
as shown in Figure 9. Some coal must be fired along with the wood in order
to maintain a slag coating on the outside of the burner. Wood must be
also processed to about the same size as required for suspension firing.
As mentioned previously, cyclone boilers have been employed less frequently
in recent years due to the high propensity for admitting high levels of
nitrogen oxides.
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49
Existing Wood-Burning Boilers
The percentages of boiler sales for various fuels in five dif-
ferent capacity categories sold between 1965 and 1973 are shown in Table 5.
Though small in sales compared with coal, oil, and natural gas, wood overall
ranks as the most significant fuel other than these three major fossil fuels.
The vast majority of wood burning boiler sales is in the size range of from
16,000 to 100,000 Ibs of steam per hour as shown in Table 6. The type of
firing most commonly employed in the different capacity categories is
shown in Table 7. The vast majority of boilers sold in the most common
size range (16,000 to 20,000 Ibs steam per hour) are of either spreader
stoker or overfeed stoker design. The category marked "Other" is
generally unspecified but probably contains boilers with dutch oven or
fuel cell type firing arrangements. In the larger sizes, over 500,000 Ibs
steam per hour, a few suspension fired units burning coal and wood have
been recorded sold in the sales period considered; however, the bulk of sales
were with a spreader stoker configuration.
Installed wood burning boiler capacity in the different capacity
ranges is shown in Figure 19. Though a relatively few number of boilers were
sold over 500,000 Ibs of steam per hour the total installed capacity is
greatest in this range (the largest unit being 1,700,000 Ibs of steam per
hour). In many of these units, however, a conventional fossil fuel would
normally be fired with the wood carrying a significant portion of the
boiler heat load. The most prevalent size range, however, is from about
15,000 Ibs per hour to 150,000 Ibs per hour.
Some basic conclusions can be drawn from sales of wood burning
boilers and other types of boilers in the last ten years.
- As can be seen from Table 5, the vast majority of
watertube boiler sales for all fuels for capacities
up to 500,000 Ibs of steam per hour used natural gas
or oil as a primary fuel. Wood is the most significant
fuel other than coal, oil, or natural gas.
- The most prevalent size for wood fired boilers is in the
range from about 15,000 to 150,000 Ibs steam per hour
(Figure 19). Some boilers burning fossil fuel plus wood have
ben installed in sizes greater than 500,000 Ibs steam per hour.
-------
50
TABLE 5. TOTAL BOILER SALES IN EACH CAPACITY CATEGORY FROM 1965
THROUGH 1973(2). Percent in each capacity range. W
(Capacities 103 Ibs. steam per hour)
FUEL
Bituminous Coal
Oil
Natural Gas
Wood bark
Other Fuels
10-16
1.9
27.1
66.9
0.6
3.6
16-100
3.5
27.5
63.6
1.6
2.9
100-250
6.5
31.8
48.7
1.7
9.8
250-500
9.4
24.9
24.2
1.0
35.3
over 500
46.7
24.8
21.3
1.3
5.4
(a) 10 Ibs. steam per hour
TABLE 6. WOOD BURNING BOILER SALES IN EACH CAPACITY RANGE FROM
1965 THROUGH 1973(2) (a)
Capacity Percent of
Range Boilers Sold
10 Ibs. steam/hr In Range
10-16 2.2
16-100 72.8
100-250 18.4
250-500 2.2
Over 500 4.4
(a) Statistics include all boilers with capability for wood firing. In
some cases, especially those in the size range over 500 x 103 Ibs
steam per hour, wood may serve as an auxiliary fuel with the bulk of
the boiler heat load being carried by conventional fossil fuels.
-------
51
Firing
Methods
Spreader
Stoker
Underfeed
Stoker
Overfeed
Stoker
Suspension
Other
10-16
50.0
0
0
0
50.0
16-100
34.6
1.9
34.0
0
29.5
100-250
72.5
i
0
20.0
2.5
5.0
250-500
100.0
0
0
0
0
Over 500
66.7
0
0
11.1
22.2
(a) Compiled from ABMA. data
-------
52
M
43
-------
53
- The most common firing method for wood fired boilers in
all size ranges is the spreader stoker with overfeed stokers
also being common in smaller sizes (less than 250,000 Ibs
steam per hour). Other types of firing such as dutch
ovens and fuel cells are also common in smaller sizes.
Suspension fired units are not common and those 'that have
been installed are in the larger sizes above 100,000 Ibs
steam per hour.
Nearly half of wood burning boilers sold between 1965 and 1973
list coal, oil,or natural gas as an alternate fuel' . The most common
alternates are oil and natural gas with coal accounting for only two
percent. Some basic considerations are necessary when firing wood in
combination with other fuels or substituting wood in boilers designed
for other fuels.
A major factor in the design of boiler furnaces is the fraction
of total heat released that is absorbed by furnace walls. Usually, about
half the heat of combustion is picked up by the furnace wall tubes, the
remainder going to the superheater, reheater, economizer, air heater, and
the stack. This fraction is important because it establishes the temp-
erature of the gases entering the superheater, thereby determining final
steam temperature. Hence any deposits formed in furnace wall tubes de-
crease heat transfer and lead to higher exit furnace temperature and to
higher steam temperature. Great care is taken in designing the furnaces
to provide sufficient heat-transfer surface to compensate for wall deposits
and to supply wall blowers properly placed to control the amount of deposit
that does form.
Natural-gas fired boilers do not have this problem. Boilers fired
with residual fuel oil do, but since the ash content of residual fuels
generally is less than 0.1 percent, the problem of deposits interfering
with heat transfer is usually less troublesome than the corrosive nature
of those deposits. With pulverized coal, the problem is very serious
since up to about half the ash in the coal may deposit on furnace wall
tubes, thereby greatly interfering with heat transfer. Under the worst
conditions, heat flux through a coal-ash-slag-covered wall tube may be
only a fourth that of a clean tube.
-------
54
These considerations become important when wood is substituted
for fuel oil or coal. Firstly, the ash content of wood is greater than that
of residual fuel oil, ranging from about 0.4 percent for redwood bark to
a reported 5.3 percent for oak bark(1). Other analyses indicate 2.0 percent
ash for birch and 4.3 percent ash for maple(3) , indicating roughly that an
ash content as high as 5 percent can be anticipated. And, since dry wood
has a heating value of 8000 to 9000 btu per pound, the total ash burden
in a wood-fired boiler furnace is about comparable to that with a 13,000
btu/lb bituminous coal containing 7 to 8 percent ash. Thus, the fouling
potential when burning wood is about comparable on a quantitative basis
to that of burning bituminous coal, and much greater - perhaps 50 to 100
times worse - than when burning residual fuel oil.
Qualitatively, wood ash differs radically from coal ash. Al-
though there is no such thing as a "typical" ash analysis, wood ash
generally is high in CaO (50-60 percent) and high in Na90 and K,0 (4-7
(13)
percent). ' Although ASTM cone fusion temperatures are sometimes
reported for wood ash, such data are meaningless except in the broadest
sense. What is significant is that wood ash is an excellent "flux" for
coal ash which is generally high in SiO? and Al-O.,. The viscosity of coal
£* £.3
ash slags decreases markedly as CaO increases, reaching a minimum at roughly
50 percent CaO in the slag. Therefore, if wood and coal are burned simul-
taneously, slagging and fouling might be expected, through the fluxing-
of the silicates in the coal ash with the CaO in the wood ash.
Further, the alkaline Na20 and K20 lead to serious fouling of
superheaters in coal-fired boiler furnaces when the alkali level exceeds
0.5 percent of the coal, or about 5 percent alkalies in the ash of a coal
containing 10 percent ash. In a wood such as maple with, say, 4 percent
ash containing 6 percent alkalies, and allowing for the difference in
calorific value, the fouling characteristics would be comparable with badly
fouling coals. An additional point here is that the alkalies in wood are
probably released in the flame more readily than the alkalies in coal ash,
which are generally tied up chemically with minerals such as feldspar or '
organically as salts of carboxylic acids. If the alkalies in wood are
sulfates or chlorides, their action would be more objectionable since
this would lead to increased volatilization of alkalies in the flame
-------
55
Generally speaking, substituting wood for residual fuel oil will
increase problems with fouled heat-receiving surfaces. Burning wood in
boiler furnaces designed for pulverized coal likely will not pose fouling
problems worse than with coal alone except that alkalies may tend to accumu-
late more rapidly in the cooler parts of the boiler, such as in the super-
heater. Burning wood in admixture with coal might be expected to lead
to problems with slagging because the principal constituents in wood
ash will react readily with the refractory elements in coal ash to form
low-viscosity, low-melting-point slags. Such interactions can be pre-
dicted with fair success, based on long experience with the fouling and
slagging characteristics of coal ash as a function of composition.
The substitution of wood firing in existing coal fired stoker
boilers presents the fewest problems. In most cases, only minor modifi-
cations to the boiler, such as addition of a wood feeding system or
firing ports, would be necessary. Hogged fuel of less than about two inches
in size, with a minimum of slack (less than 1/4 inches), should be
acceptable to most spreader and overfeed type stokers. Care should be
taken, however, in analyzing the effect of the combination of wood and
coal ash on the ash fusion temperature to insure that slagging or clinkering
does not occur as discussed earlier.
Wood can also be fired in suspension in boilers designed for
either pulverized coal or heavy oil. The wood should be reduced in size
below about 1/4 inch and dried as much as possible to insure rapid com-
bustion. Most all suspension wood fired boilers have a small grate at the
base of the unit to insure complete burnout of any wood chips that do not
burn in suspension. Pulverized coal and oil boilers generally do not have
such a grate and the addition of one may be necessary, though in firing
sawdust or very fine wood with relatively low moisture content such an
addition may not be necessary. In the case of some oil fired boilers,
soot blowers may have to be added or operated more frequently to allow for
the higher ash content of the wood (generally 10 to 20 times that of oil
by weight).
Substitution of wood in boilers designed for natural gas or
light oil represents a more difficult problem. Generally these boilers
are designed with minimum tube spacing and no provision for soot blowers
-------
56
the 1^..J.: ^^a-iSive, ui-^t compact design. Firing wut>U iu these
boilers would req~irt. extensive modification and is not considered an
attractive application.
In all cases where steady steam conditions are desired, it is
advisable to fire an auxiliary fossil fuel such as coal, oil, or gas with
the wood limiting the percent heat load carried by the wood. Variations
that may occur in wood moisture and heat content would otherwise cause
variations in steam conditions. Systems that are most sensitive to changes
in fuel composition are those with the minimum amount of fuel in the
furnace at any one time. Suspension fired systems are most sensitive and
in the past the recommended maximum heat load to be carried by wood was
(12)
40 to 50 percent . Spreader stokers are less sensitive and overfeed
stokers or dutch ovens with thick fuel beds are least sensitive.
-------
57
References
1. "Steam, Its Generation and Use", The Babcock & Wilcox Company, 37th
Edition, 1963.
2. Locklin, D. W., et al, "Design Trends and Operating Problems in
Combustion Modification of Industrial Boilers", Annual Progress
Report to U.S. EPA on Grant No. 802402, December 1973.
3. Fryling, G. R., "Combustion Engineering", Combustion Engineering, 1966.
4. Catton, J. L., "Combustion and Modern Coal Burning Equipment",
Sir Isaac Pitman & Sons, Ltd., 1946.
5. Leonard, J. W., "Coal Preparation", Third Edition, AIME, New York,
1968.
6. Duerbrouch, A. W., "Coal Preparation 1973", Mining Congress Journal,
Vol. 60, No. 2, pp 65-67, February 1974.
7. Duerbrouch, A. W., and Jacobsen, P. S., "Coal Cleaning--State of the
Art", paper presented at the Coal Utilization Symposium (S02 Emission
Control), Louisville, Kentucky, pp 1-10, October 22-24, 1974.
8. Prakash, C. B., and Murray, F. E., "A Review on Wood Waste Burning",
Technical Paper T170, Canadian Pulp and Paper Association, Pulp and
Paper Magazine of Canada, Vol. 23, No. 7, July 1972.
9. Corder, S. E., "Wood and Bark as Fuel", Research Bulletin 14, Oregon
State University, School of Forestry, August 1973.
10. Kazmerski, E. A., "Steam Generators for Multiple Fuel Firing",
TAPPI, Vol. 42, No. 4, pp 333-336, April 1959.
11. Miller, E. C. and Hansen, G. E., "Spreader Stoker Firing of Wood and
Coal in Multiple Fuel Furnaces", paper presented at the Fifth Annual
National Meeting of the Forest Products Research Society, May 1951.
12. Brown, 0. D., "Energy Generation From Wood Waste", National District
Heating Association, French Lick, Indiana, June 1973.
13. Roberson, J. E., "Bark Burning Methods1', TAPPI, Vol. 51, No. 6, June 1968.
14. Reid, W. T., "External Corrosion and Deposits in Boilers and Gas
Turbines", American Elsevier, New York, 1971, 199 pages.
-------
59
POLLUTANT EMISSIONS AND CONTROL TECHNOLOGY
The environmental aspects of wood combustion are presented in
the following paragraphs. Subjects included are: gaseous and particulate
boiler emissions, control equipment effectiveness and costs, potential
for hazardous organic emissions, and residue disposal problems and by-
product uses. In addition, emissions and control technology for fossil-
fueled boilers (coal and oil) are included for comparative purposes.
Gaseous and Particulate Boiler Emissions
Emissions to the atmosphere always accompany the combustion of
fuel for the generation of steam or electricity. In wood wastes combustion
the primary pollutant is particulate matter resulting from the entrainment
of ash and sand in the combustion gases. Wood is a relatively low ash
fuel compared to coal (see Table 8). Wood, unlike coal or oil, has a
negligible quantity of sulfur and sulfur dioxide emissions are therefore
very low. Nitrogen oxides emissions are higher relative to coal or oil,
according to EPA estimated emissions factors, even though nitrogen content
and combustion temperatures are generally lower.
Little emissions data other than particulate emissions have been
uncovered in a survey of the available literature. Emission factors
provided by the United States EPA for wood and bark combustion in boilers
with no ash reinjection or emission controls are presented in Table 9.
To obtain the emissions to the atmosphere, the emission factor must be
multiplied by the number of tons of wood burned, and, in the case of
particulates, reduced by the particulate collector efficiency. A con-
siderable amount of data have been located which specifies dust loading
to the collectors, these numbers are quite variable and range from 0.5
(D*
to 5.0 grains/scf. •
* References are listed on page
-------
TABLE 8. COMPARATIVE CHEMICAL ANALYSIS OF WOOD AND BARK, COAL, AND'OIL
Analyses
(dry basis), % by wt
Proximate
Volatile matter
- Fixed carbon
Ash
Ultimate
Hydrogen
Carbon
Sulfur
Nitrogen
Oxygen
Ash
Heating value, Btu/lb
Ash Analyses, % by wt
Si02
Fe2°3
Ti02
Al-O-
2 3
Mn-0
CaO
MgO
Na20
K2°
SO,
Cl3
Pine^.3^
Bark
72.9
24.2
2.9
5.6
53.4
0.1
0.1
37.9
2.9
9030
39.0
3.0
0.2
14.0
Trace
25.5
6.5
1.3
6.0
0.3
Trace
OakUJ
Bark
76.0
18.7
5.3
5.4
49.7
0.1
0.2
39.3
5.3
8370
11.1
3.3
0.1
0.1
Trace
64.5
1.2
8.9
0.2
2.0
Trace
• • i •
Spruced)
Bark
69.6
26.6
3.8
5.7
51.8
0.1
0.2
38.4
3.8
8740
32.0
6.4
0.8
11.0
1.5
25.3
4.1
8.0
2.4
2.1
Trace
Wood and Bark
Redwood (.*)
Bark
72.6
27.0
0.4
5.1
51.9
0.1
0.1
42.4
0.4
8350
14.3
3.5
0.3
4.0
0.1
6.0
6.6
18.0
10.6
7.4
18.4
Redwood
82.5
17.3
0.2
5.9
53.5
0
0.1
40.3
0.2
9220
.
Pine
79.4
20.1
0.5
6.3
51.8
0
0.1
41.3
0.5
9130
• •• i ^^»^^ • p" «
Washed
Penn . Coal
35.8
57.3
6.9
5.1
78.1
1.2
1.6
7.1
6.9
13,970
Coal
Western^)
Coal
43.4
51.7
4.9
6.4
54.6
0.4
1.0
33.8
3.3
9,420
30. 7 W
18.9
1.1
19.6
—
11.3
3.7
2.4
12.2
Penn. W
Coal
37.7
52.2
10.1
5.0
74.2
2.1
1.5
7.1
10.1
13,310
49. 7 (a;
11.4
1.2
26.8
4.2
0.8
2.9
2.5
Residual Fuel Oil
Range of (e>
No. 6 Oil
9.5 - 12.0
86.5 - 50.2
0.7 - :>.5
—
—
C.01 - 0.5
17,410 - 18,990
(2) Reference (22).
(b) Reference (11).
(c) Reference (23).
(d) Reference (24).
(e) Reference (22).
-------
61
TABLE 9. EMISSION FACTORS FOR WOOD AND BABK. COMBUSTION
IN BOILERS WITH NO REINJECTION*41''
Emission Factor Rating: C = Average Accuracy
— ' — ^ — — [M1MnnnrninnrrTT[r^1r — irnnmiinnm^iMmiMnmiiii • •!•
Pollutant
Par ticulates
Sulfur oxides (SO.) ^ '
Carbon monoxide
(e)
Hydrocarbons
Nitrogen oxides (NO )
1 u^^MmTrni^m^rv^-nrnrmmmniirH-r^Tr
Emissions ,
Ib/ton
25 to 30
0 to 3
2
2
10
(a) Reference (2).
(b) Approximately 50 percent moisture content.
(c) This number is the atmospheric emission
factor without fly ash reinjection. For
boilers with reinjection, the participate
loadings reaching the control equipment
are 30 to 35 Ib/ton (15 to 17.5 kg/MT)
fuel with 100 percent reinjection.
(d) Use 0 for most wood and higher values for
bark.
(e) Expressed as methane.
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62
Particulate Collection Efficiency
In contrast to coal, where collection efficiency is based on the
removal of a given percentage of the very small ash particles (10 microns
or less), the basis for hogged-fuel fly ash removal efficiency is speci-
fied on the actual material over (larger than) 325 mesh (44 microns) or
over 200 mesh (74 microns) collected. The reason for the different basis
is the lighter, larger average sized wood fly-ash particles. Figure 20
shows a typical size distribution of fly ash obtained from a bark boiler.
Also displayed for comparative purposes is a typical coal fly-ash size
distribution. Typical collection efficiencies for high-efficiency multi-
tube cyclone collectors are 93-95 percent for particles over 325 mesh
(44 microns), and 95-97 percent for particles over 200 mesh (74 microns).
The emission factors reported in Table 9 are acceptable to
calculate gaseous emissions for hogged fuel combustion. However, for
particulate matter the reported number is significantly higher than that
actually emitted. Assuming a 30 Ib particulate/ ton emission factor, 93
percent collection efficiency (for particles over 325 mesh) and that 85
percent of the dust loading is over 325 mesh, the effective particulate
emission factor is 6.3 Ib/ton. On the basis of 45 percent moisture fuel
and 8500 Btu/dry Ib, this factor can be converted to 0.67 lb/106 Btu. The
calculated numbers compares well with actual emission test data for
combined bark and gas (0.75, 0.76, 0.52 lb/10 Btu), bark and oil
firing (0.09, 0.15, 0.32 lb/106 Btu) .
Factors Affecting Particulate Emissions
Some of the reasons for the large range in the published data
for particulate emissions from wood-fired boilers include differences
in the extent of char reinjection, in boiler type, in grate heat release,
in excess air, in wood waste material type (e.g., logs, saw dust, chips)
and in wood moisture content. Probably the single most significant factor
is the extent of char reinjection utilized. Char reinjection systems,
which return collected particles to the combustion zone to achieve more
-------
1000
100
o
o
'e
*.
0)
CO
"o
S.
_jWood flyash- I
without reinjection
Wood flyash-
with reinfection
200 mesh
•-Hittri-i^-n't
-^•325 mesh
Co o I flyosh'.-•-- • •n.i.h-.4;;1'!t!
10 20 40 70 90
99 99.9 99.99
% Smaller Than
FIGURE 20. SIZE DISTRIBUTION OF WOOD AND COAL FLY ASH
(1,20)
-------
64
complete combustion of the carbon, represent a compromise between two
conflicting objectives. While reinjection increases boiler efficiency
and minimizes the emission of uncombusted carbon, it also increases boiler
maintenance requirements, decreases the average fly-ash particle size
(see Figure 20), increases the dust load to the collector, and makes
collection more difficult/ It has been reported that full injection
of collector catch (employed at many paper mills) can easily cause a
full 10-fold increase in dust loading to the collector.*- ' Properly
designed reinjection systems will separate the sand and the char from
the exhaust gases, pass the material over separatory screens and reinject
the larger carbon fraction to the boiler and reject the fine sand
particles to the ash disposal system.
Effectiveness and Costs of Particulate Control
Equipment Currently Employed for Wood-Fired Boilers
The effectiveness of air pollution control equipment can be
expressed in terms of total emissions per ton fired or in terms of the
collection efficiency of a piece of control equipment. Because of the
variation in boiler particulate emissions, resulting from ash reinjection
rate, boiler type, fuel characteristics, etc., the establishment of a
specific dust loading for all cases, is not possible. Data from a leading
U.S. dust collector manufacturer indicates that loadings can vary from
(4)
0.5 to 3.8 grains/scf. Another source reports loadings in the 0.5
to 5.0 grains/scf range. ' Because of these variations, calculations
of an accurate emission factor is difficult, therefore, collectors must
be evaluated in terms of efficiency. High-efficiency multitube cyclone
collectors can achieve collection efficiencies in the low to mid-nineties.
Currently, the use of multicyclones on hogged fuel boilers provides the
sole source of particulate removal for most plants. Costs for multi-
tubular cyclone collectors escalated to mid-1975 (originally reported in
1972) are $133 per 1000 Ib steam/hr (15
-------
65
and installed costs, respectively, for low-efficiency (single tube),
medium-efficiency (large diameter multitube), and high-efficiency (small
diameter multitube) centrifugal collectors are shown in Figures 21 and
22. These costs, although lower than actual mid-1975 costs which are
estimated to be approximately 1.6 times the costs shown in the figures,
show the wide variation in collector costs as a function of volumetric
flow rate and collector efficiency.
Assuming a 96 percent overall collection efficiency, dust
loadings cannot exceed 2.5 grains/scf and still meet a 0.1 grain/scf
emission regulation (currently the toughest control regulation in the
country). Since loadings can range as high as 5 grains/scf, it is
clear that additional control equipment may be required to meet the
new regulations. Currently, three systems are being employed for
secondary control of hogged fuel boiler particulate emissions: (1)
two multicyclone collectors in series, (2) multicyclone collector with
"shave off system" and scrubber on shave off, and (3) multicyclone
collector in series with a low energy scrubber.
Collectors in Series
Employing two collectors in series allows for a first collector
to remove the bulk of the dust and a second collector with special high-
efficiency vanes for the removal of the finer particles which passed
through the first unit. While a two-stage collection system is more
efficient than a single-stage system, overall collection efficiency is
not likely to exceed 97-98 percent. Costs and fan power requirements
are reported to be an additional $140 and 0.5 HP per 1000 Ib steam/hr
above those for single multitube collector.
Shave Off System
Another alternative for additional particulate control involves
a secondary shave off system. The principle involved is shown schematically
in Figure 23, The exhaust gases from the collector exit up the outlet
tube as a small-radius, high-velocity, spiral which centrifuges the
-------
66
100
in
jg
"5
•o
in
50
10
3
.§ 5
I—T-TTTTT
High efficiency
Medium efficiency
Low efficiency
i—I—r
100
so
Basis: 1968 dollars
, , , IMM!
300 500
, , I ,
10 50 100 500 1000
Gas Volume Through Col lector, I03 acf m
FIGURE 21. ANNUALIZED COST OF OPERATION OF
DRY CENTRIFUGAL COLLECTORS
Source: Reference 12.
100
50
in
k-
_o
"o
•o
K)
O
•»
S I®
TJ
= 5
o
• Medium efficiency
Low efficiency
Basis: 1968 dollars
, . . I....I
500 800
10
50 100
500 1000
Gas Volume Through Col lector, 10 acf m
FIGURE 22. INSTALLED COST OF DRY CENTRIFUGAL COLLECTORS
Source: Reference 12.
-------
67
Outlet
To scrubber
FIGURE 23. SECONDARY SHAVE OFF SYSTEM FOR(
ADDITIONAL PARTICULATE REMOVAL'
(1)
-------
uncollectecl dust into the outer boundary area. This outer layer is dust-
rich and is separated or "shaved off" from the clean exhaust gases and
sent to a low-energy scrubber for final cleaning. No cost data are available
for this alternative. Neither the two collectors in series or the
the shave off system is thought to have the "potential for continuous
efficient dust removal" that a mechanical collector and scrubber in
series offers.
Multitube Collector and Scrubber in Series
The best currently available system is a multitube cyclone
collector in series with a low energy wet impingement-type scrubber.
This system has proven successful in several commercial applications
such as the Rosebury Lumber Company in Eugene, Oregon, or the Hoeyner
Waldorf Corp. in Missoula, Montana. Equipped with such systems boilers
can easily meet emission regulation of 0.1 grains/set, Costs for this
system are an additional $120 (13C/ACFM) and 1.5 HP per 1000 Ib steam/hr
over mechanical collection.
Relative Performance and Cost of Alternative
Particulnte Removal Equipment
Although, at present, the use of multitube-cyclone separators
(and in a few locations secondary collection equipment) dominate in
particulate control for wood combustion, other collection devices tradi-
tionally used for particulate removal could be employed in the future.
There is currently available an abundance of information on the relative
efficiency of these alternative collection devices. Unfortunately, the
available data is not for the collection of waste wood fly ash. However,
this data can still be used to calculate the relative performance
capabilities of these particulate collectors. Average collection
efficiencies are summarized in Table 10 at different partile sizes for
various particulate control equipment, e.g., cyclones, electrostatic
precipitators, fabric filters (baghouse), scrubbers, etc. Note that,
for particles greater than 44 microns, or approximately 85-90 percent
-------
69
TABLE 10. DISTRIBUTION BY PARTICLE SIZE OF AVERAGE COLLECTION
EFFICIENCIES FOR VARIOUS PARTICIPATE CONTROL EQUIPMENT(a'(b)
Efficiency, %
Particle size range, ym
Type of collector
Baffled settling chamber
Simple cyclone
Long-cone cyclone
Multiple cyclone
(12-in. diameter)
Multiple cyclone
(6-in. diameter)
Irrigated long-cone
cyclone
Electrostatic
precipitator
Irrigated electrostatic
precipitator
Spray tower
Self-induced spray
Scrubber
Disintegrator scrubber
Venturi scrubber
Wet-impingement scrubber
Baghouse
(a) Reference 2.
Overall
58.6
65.3
84.2
74.2
93.8
91.0
97.0
99.0
94.5
93.6
98.5
99.5
97.9
99.7
.(b) Data based on standard silica
0 to
7.
12
40
25
63
63
72
97
90
85
93
99
96
99.
dust
5 5 to
5 22
33
79
54
95
93
94.
99
96
96
98
99.
98.
5 100
10 10 to
43
57
92
74
98
96
5 97
99.
98
98
99
5 100
5 99
100
with the following
20 20 to
80
82
95
95
99.
98.
99.
5 100
100
100
100
100
100
100
particle
44 >44
90
91
97
98
5 100
5 100
5 100
100
100
100
100
100
100
100
size and
weight distribution:
Particle size
range, ym
Percent
by weight
0 to 5
5 to 10
10 to 20
20 to 44
>44
20
10
15
20
35
-------
70
of wood fly ash (see Figure 20), collection efficiency for most of the
collectors is approximately 100 percent. The real differences in
collection efficiencies are for the smaller particle sizes. Approximately
94 percent of all the wood fly ash particles are.larger than 10 microns
and 96 percent are larger than 5 microns (extrapolation). Employing this
distribution of particle sizes and the reported efficiencies in Table 10,
the calculated collection efficiencies for wood fly ash are presented in
Table 11 for cyclones, multiple cyclones (6 in. diameter), electrostatic
precipitaters, wet-impingement scrubbers, venturi scrubbers, and fabric
filters. Annualized and installed costs (1968 dollars) for cyclone
separators were presented in Figures 21 and 22. Annualized and installed
costs (1968 dollars) are presented graphically for wet scrubbers (Figures 24
and 25), for electrostatic precipitators (Figures 26 and 27), and for
fabric filters (Figures 28 and 29).
With the available cost information assembled, and on the basis
of 500,000 Ib steam/hr or 316-440 x 103 ACFM (calculated from Table 14 in
Reference 8, based on twice the average flow rate), particulate control
costs for a 50 MWe power plant were calculated. Installed and annualized
costs for cyclones, wet scrubbers, fabric filters, and electrostatic
precipitators are presented in Table 12. The installed costs given are
for the collector alone. The required fan, ducting, and other instal-
lation costs will increase the total cost of the installed collector. The
large range in the numbers presented for each collector reflect both the
large variability in actual control costs and the fact that all the data
presented are not on the same basis (numbers in parentheses are on
different bases, which are identified in appropriate footnotes). While
there is significant variability in the cost data, the relative position
(in terms of lowest cost control method) of the alternative control
methods can be assessed. It can be concluded from Table 12 that of the
control methods capable of achieving <0.1 grain/scf particulate emissions,
the cyclone-scrubber system and electrostatic precipitator collectors
are the two most economical control systems.
As noted earlier, the use of multicyclone collectors alone
will not be sufficient to meet new emission limits of <0.1 grain/scf,
-------
71
TABLE 11. CALCULATED WOOD ASH COLLECTION EFFICIENCIES
FOR VARIOUS CONTROL EQUIPMENT
(a)
Type of Collector Efficiency ,
Long-cone cyclones 94.2
Multiple cyclone (6-in. dia) 98.4
Electrostatic precipitator 98.7
Wet-impingement scrubber 99.3
Venturi scrubber 99.96
Fabric filter 99.98
(a) Based on efficiencies per particle size reported
in Table 10, and the following size distribution.
Particle size Percent
fanges microns by weight
0 to 5
5 to 10
20 to 10
20 to 44
>44
4
2
2
2
90
-------
72
500
(A
o 100
"b 50
13
N
1
10
I I I Mlllj 1 I I | II
Basis: 1968 dollars
nn i ITH
5 10
50 100
500 1000
Gas Volume Through Collector, 10 acfm
FIGURE 24. ANNUALIZED COST OF OPERATION
OF WET COLLECTORS
Source: Reference 12.
1000
500
o ,00
*O 50
10
_ I II
I I I I I M L
— Basis: 1968 dollars
High
/effrciency
Medium
efficiency
I 5 10 50 100 500 1000
Gas Volume Through Collector, I03 acfm
FIGURE 25. INSTALLED COST OF WET COLLECTORS
Source: Reference 12.
-------
73
100
10 50 100 500 1000
Gas Volume Through Col lector, I03 acfm
FIGURE 26. ANNUALIZED COST OF OPERATION OF HIGH-
VOLTAGE ELECTROSTATIC PRECIPITATORS
Source: Reference 12.
IOOO
500
in
i_
J3
"o
13
ro
O
O
o
M
c
100
50
10
10
Basis: 1968 dollars
I I I I Mill I I I I Illl
50
100
500 IOOO
Gas Volume Through Col Iector,l03acfm
FIGURE 27. INSTALLED COST OF HIGH-VOLTAGE
ELECTROSTATIC PRECIPITATORS
Source: Reference 12.
-------
74
w
^
o
"o
•o
too
50
*- 10
O
o
o
c
I I I i-M
500
Basis: 1968 dollars
I 111 Mill I I I I III
10 50 100 500 1000
Gas Vol ume Through Col lector, I03 acfm
(a) High-temperature synthetics, woven and felt.
Continuous automatic cleaning.
(b) Medium-temperature synthetics, woven and felt.
Continuous automatic cleaning.
(c) Woven natural fibers. Intermittently cleaned -
single compartment.
FIGURE 28. ANNUALIZED COST OF OPERATION OF FABRIC FILTERS
Source: Reference 12.
100
in
i_
£
"o
TJ
m
O
in
O
O
(ft
C
10 50 100 500 1000
Gas Volume Through Collector, I03acfm
(a) High-temperature synthetics, woven and felt.
Continuous automatic cleaning.
(b) Medium-temperature synthetics, woven and felt.
Continuous automatic cleaning.
(c) Woven natural fibers. Intermittently cleaned
single compartment.
FIGURE 29. INSTALLED COST OF FABRIC FILTERS
Source: Reference 12.
-------
75
TABLE 12. PARTICULATE COLLECTOR COSTS FOR A. 50 MWe
COAL- OR WOOD-FIRED POWER
Installed Cost, Annualized Cost,
Collector Equipment
Cyclone - high efficiency
Cyclone with low energy
scrubber in series
Wet scrubbing - high efficiency
Electrostatic precipitator
Fabric filter (baghouse)
$1000
192 - 288
(66.5) (b)
422 - 633(c)
(258.5)(e)
480 - 752
(1500) (f }
(333) (h)
672 - 848
(692) (j)
752 - 1040
(1000) (1)
$1000
72 - 99
192 - 264(d)
800 - 1040
(130) (g)
(351) (i)
112 - 144
(130) (k)
240 - 288
(17.5) (m)
3
(a) Basis: 316-440 x 10 ACFM, and Tables from Reference 12 presented in
the text unless otherwise noted. All costs adjusted to mid-1975
dollars. Costs of fans, ducting, etc., are not included.
(b) Purchase cost basis from Reference 5: $133/1000 Ib steam/hr. At
500,000 Ib steam/hr this is equivalent to $66,500.
(c) Calculated installed cost based on the high efficiency cyclone
costs presented, and the information obtained from Reference 5,
that cyclone-scrubber systems are approximately 120 percent
greater than cyclone system alone.
(d) Calculated annualized cost based on cyclone annualized costs and
the estimate that cyclone-scrubber systems costs are approximately
167 percent greater than cyclones alone, Reference 5.
(e) No data available in terms of installed costs, but from Reference 5,
purchase cost basis is $192/1000 Ib steam/hr addition to cyclone
costs - or a total of $258,500.
(f) Investment cost rate from Reference 17 is $30/kw.
(g) Operating cost rate from Reference 17 is $2.6/kw/yr.
(h) Capital cost for collector from Reference 31.
(i) Annualized cost for collector from Reference 31.
(j) Capital cost for collector from Reference 31.
(k) Annualized cost for collector from Reference 31.
(1) Investment cost rate from Reference 17 is $20/kw.
(m) Operating cost rate from Reference 17 is $0.35/kw/yr.
-------
76
unless the inlet dust loading can be held to 2.5 grains/scf or less.
The three alternative control options capable of solving the problem:
(1) fabric filters, (2) electrostatic precipitators, and (3) wet scrubbers,
are discussed below. '
Fabric Filters; High capital and operating costs,
large size, and prone to fire hazards. (Some
vendors claim that the fire hazard can now be
eliminated.) Highest collection efficiency.
Electrostatic Precipitator; High capital and
operating costs, large size, and no proven per-
formance on waste wood boilers. High collection
efficiency.
Wet Scrubber-High Energy; Moderate capital costs
but high power requirements resulting in high
operating costs. High collection efficiency and
large quantities of scrubber sludge produced.
Wet Scrubber-Low Energy; Relatively low capital
costs, reasonable operating costs, sufficiently
high collection efficiency, ease of maintenance,
proven performance, and low generation of con-
centrated scrubber sludge.
In conclusion, of these alternative collection routes, the most promising
and the one being employed in new installations is the low energy
impingement-type scrubber connected in series with a multitube-cyclone
separator.
Emission of Potentially Hazardous Organic Compounds
No specific data on the types of organic compounds emitted from
hogged fuel combustion was found in a search of the literature. However,
data for a similar emission source, i.e., broadcast fire of forest slash
(branches and other residues left after cutting timer), show that most
components appear to be low molecular weight hydrocarbons and alcohols.
Acetone and simple aromatic compounds along with several short chain
unsaturated compounds (olefins) also are present. The estimated rate
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77
of hydrocarbon emissions was reported in Table 9 as 2 Ib/ton; however,
investigation of the basis for this number shows that it was not derived
from actual emission tests from hogged fueled boilers. Additional review
of the literature by researchers in Oregon has shown that 4 Ib/ton may
be a more realistic number, and that emissions as high as 55-85 Ib/ton
have been reported for wood waste boilers under conditions of very poor
(9)
combustion. During these periods of high hydrocarbon emissions,
potentially hazardous organic compounds such as carcinogenic compounds
and/or photochemically active compounds could be emitted.
Carcinogenic Compounds
Review of the available data and consultation with those
knowledgeable in the field indicate that very little direct information
on the carcinogenic nature of emission from wood waste combustion exists.
However, it is known that the production of various high boiling organic
compounds from the combustion of solid fuels such as coal are carcinogenic.
In addition, it is believed (because of the simularity between coal and
wood) that emissions of similar chemicals could result from waste wood
combustion. However, these emission should be in lower concentrations.
At present there are a number of organic compounds arising from the
combustion of solid fuels which are known or suspect carcinogens. As a
first approximation, these compounds can be limited to some of the compounds
with boiling points in the 250 C and higher range. This includes polycyclic
and methylated derivatives of polycyclic hydrocarbons, and nitrogen
(hetrocyclic) compounds. '
Because evidence for carcinogenity must be based on reports of
occupational exposure, epidemiological observations and extrapolations of
laboratory studies, only a few of the hundreds of compounds produced in
solid fuel conversion have been adequately investigated. Therefore, many
other chemicals emitted 'from the combustion process may be hazardous.
In conclusion, there appears to be evidence that carcinogenic
compounds may be emitted, but in a very low concentrations, from the
combustion of wood. While no detailed information is available, it can
be assumed that production of these compounds will be proportional, if not
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78
directly related to, the degree of incompleteness of the combustion process.
In comparison with the most abundant alternative fuel source, coal,
emission of carcinogenic compounds from the combustion of wood is estimated
to be less than that from a correspondingly sized coal-fired power plant.
Photochemically Active Compounds
Other hazardous organic compounds which could be emitted from .
wood waste boiler during periods of poor combustion are photochemically
active compounds. It has already been stated that hydrocarbon emissions,
during extremely poor combustion periods, can rise to twenty to forty
times the normal emission rate. It is possible under these conditions
that some of the hydrocarbons could react in the presence of sunlight to
form highly reactive peroxy compounds. These peroxy compounds interfere
with the normal nitrogen-oxygen photochemical cycle by oxidizing nitric
oxide to nitrogen dioxide, thereby preventing the destruction of ozone
(which is normally consumed in the oxidation of nitric oxide to nitrogen
dioxide) and allowing it to accumulate in higher than normal concentration.
This excess ozone concentration is a prime factor in the complex phenomena
called photochemical smog,
Unsaturated hydrocarbons are generally the most photochemically
active compounds. Fortunately olefins containing fewer than four carbon
atoms, like the compounds reported to be produced from combustion of
materials similar to wood, are much less reactive. The compounds showing
the greatest activity are multisubstituted aromatics and branch chained
olefins. While these compounds have not as yet been identified in wood
boiler emissions, there is evidence that such compounds exist in the
wood and bark itself, and could be emitted during periods of poor
combustion. Tunge and Kwan note in their paper that an unpublished
EPA report on wood waste emissions states that "forest fires and the
burning of agricultural wastes (a system where emissions should be
similar to wood burning under poor combustion conditions) produce hydro-
(Q)
carbons of which approximately 11 percent are considered reactive.
Therefore, information presented leads to the conclusions
that photochemically active hydrocarbons will probably be emitted in
low quantities during periods of poor combustion. If NO concentrations
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79
are sufficiently high this could lead to the formation of small quantities
of photochemical smog. However, the information does not suggest that
photochemical smog formation resulting from the combustion of waste wood
for the generation of electricity, especially when operated in compliance
with existing air pollution control regulation, is anticipated to be a
problem.
Solid Residue's From Burning Wood
Combustion of hogged fuel transforms wood's complex mixture of
cellulose, lignin, oils, resins, and other organic and inorganic compounds
into carbon dioxide, water, incompletely combusted char and ash. Residues
from the combustions process consist of boiler ash, clinker and slag,
and fly ash and carbon char. These residues are normally collected, mixed
together, and disposed.
Residue Characterization
Wood fly ash, once it has been collected from the combustion
gases, has not received a great deal of attention in the technical
literature. Boiler ash, clinker, and slag have also been neglected
except as their fusion temperature affects boiler design. Therefore,
technical information on boiler residues are somwhat limited. In addition
to the ash analyses presented in Table 8 the analysis of boiler ash from
an approximately 70 percent bark-30 percent wood fuel burned in the
Eugene, Oregon, power plant is presented in Table 13. As expected, the
major components are inert silicon (silica) and aluminum (alumina) oxides.
Because of the similarities of the elemental analysis of wood, regardless
of species or location (as noted in Table 8), the ash composition from
wood combusted in Vermont should be similar to the analysis in Tables 8
and 13. The wood ash can be characterized as a relative inert powdery
solid with a minor fraction of sodium, magnesium, and potassium along
with trace amounts of heavy metals.
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80
TABLE 13. SPECTROGSAPHIC ANALYSIS OF HOGGED FUEL ASH
(a)
Components
Silicon (Si.)
Aluminum (Al)
Calcium (Ca)
Sodium (Na)
Magnesium (Mg)
Potassium (K)
Titanium (Ti)
Manganese (Mn)
Zirconium (Zr)
Lead (Pb)
Barium (Ba)
Strontium (Sr)
Boron (B)
Chromium (Cr)
Vanadium (V)
Copper (Cu)
Nickel (Ni)
Mercury
Radioactivity
Concentration
19.6
3.6
2.9
2.1
0.8
0.3
0.1
0.016
0.006
0.003
0.010
0.002
0.003
Less than
Less than
Less than
Less than
Nil
Nil
, ppm
0.001
0.001
0.001
0.001
(a) Reference 18.
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81
Disposal Problems Of By-Product Uses
No disposal problems have been identified for the disposal of
wood boiler ash or fly ash. The normal procedure is to either transport
the collected ash to a sanitary landfill or dump for disposal, or slurry
the ash for disposal in lagoons. Analysis of the ash (Tables 8 and 13)
shows that the wood residues to be composed primarily of inert silica
and alumina. Disposal of this material in a safe and environmentally
acceptable manner should not require any special provisions.
Information on by-product uses for wood ash is at this time
limited. While several sources briefly mention the possibility of
employing boiler ash as a soil conditioner, no detailed information has
been presented. A test program was initiated in 1973 in Eugene, Oregon,
f 18)
to use the boiler ash from a wood-fired power plant as a soil conditioner.
A check on the progress of this program in August, 1975, showed that
because of poor participation (the farmers wanted the ash delivered to
their farms) only about 40 tons had been distributed. Consequently, very
little useful data have been obtained.
In Eugene, the soil conditioning value of the boiler ash is
twofold: (1) The ash helps "break up" the heavy clay soil, adding
permeability, and making the soil more manageable, and (2) the alkaline
ash helps raise the pH in the acidic soils to a more acceptable growth
(19)
promoting level.
In addition, there does appear to be some basis, because of the
similarity in the inorganic composition of bark and wood ash, for the
claims of boiler ash as a nutrient supplement. A considerable amount
of work has been done on the use of bark as a fertilizer and soil
conditioner. Howard reports in his review article that analyses showed
that, "except for nitrogen, the bark (both hardwoods and softwoods) had
all the necessary inorganic constituents of a first-class organic soil.
There is ample calcium, magnesium, phosphorus and potassium." These
same constituents are available in wood ash. Like bark, the fertilizer
value of wood ash would be increased by supplementing with extra nitrogen,
and depending on the plant crop to be grown, phosphorus, potassium and
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82
trace elements. There appears, then, to be a reasonable potential that
wood ash could be successfully employed as a soil nutrient and conditioner.
Another potential use of wood ash residues is the carbon cinders
recovered in the fly ash collectors. These materials can either be rein-
jacted into the boiler or collected and sold for use in charcoal briquet
manufacture.
A final use of wood ash residues noted in the literature is as
a spontaneous combustion preventative. The fly ash slurry coming from
the particulate removal scrubbers is combined with the sand and char from
the cyclone collectors to form a pasty mix. The sludge formed can be
easily disposed or employed as a combustion retardant.
Emission Control Technology for Fossil-Fuel Boilers
Included in this section are summaries of currently available
technology for the control of nitrogen oxides (NO ), sulfur oxides (S0»),
X 4*
and particulate emissions from coal and oil-fired power generation. This
material is presented to allow more comparative evaluation of the environ-
mental aspects of coal, oil, and wood combustion.
Nitrogen Oxides
Nitric oxide (NO) and nitrogen dioxide (N0_), commonly referred
to as NO , are important in the formation of smog. Nitrogen oxides in
X
the atmosphere come primarily from the internal combustion engine but a
(25)
significant fraction also is produced in power generation. The
formation of N0x results primarily from the high temperature oxidation
of atmospheric nitrogen in the combustion process. In addition, a smaller
but significant fraction comes from the oxidation of the chemically bound
nitrogen in the fuel.
High concentrations of NOX are considered harmful to plants,
animals, and humans, and in some cases corrosive to fibers and metals.
However, because the ambient concentration of NO in most locations is
X
low, there does not appear to be a need for absolute or uniform control
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83
of N0x from electric power stations throughout the country. Presently,
Los Angeles and Chicago are the only two cities requiring such control to
meet ambient air quality requirements set by the Federal Government. In
a low population density area such as Vermont, NO controls should probably
X
not be required. Should such requirements be set by the State or become
necessary to meet Federal ambient air quality requirements the present
state of the art calls for modification of the combustion process, rather
than use of collectors or scrubbers employed for other types of atmospheric
pollutants.
Four N0x control techniques (other than fuel substitution) are
possible for reduction of emissions from either coal fired dry-bottom
type furnaces (wet bottom boilers will require retrofitting to dry bottom
type prior to control) or oil-fired boilers. The four methods are as
follows:
(1) Low (or minimum) excess air firing
(2) Staged combustion and off-stoichiometric
firing
(3) Flue-gas recirculation
(4) Water injection.
In the first technique, the quantity of air above stoichiometric require-
ments admitted to the boiler is kept to an absolute minimum; NO reductions
X
as high as 50 percent have been experienced. Staged combustion and off-
stoichiometric firing involve running some or all the burners rich in
fuel, then introducing the balance of the air through special ports or
through fuel-lean burners. NO reductions as high as 60 percent are
X
possible with these techniques. Flue gas recirculation involves
recirculating a portion of the coal combustion products back to the firing
chamber. Little data are available for this technique in large-scale
boilers, but NO reductions similar to the other techniques are anticipated.
X *
A much less promising technique, compared to the other methods, is water
injection. In this control method the injected water reduces flame
temperature and consequently N0x formation. Unfortunately, the lower
temperature also results in a significantly lower thermal efficiency.
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84
The technology for NO removal is in its early stage of
X
development. Significant new developments can be anticipated in the
future. The technology to efficiently reduce N0x emissions (i.e.,
without unduly affecting boiler operation) from all power plants is
not currently available. The two most suitable methods to date for N0x
control in coal- or oil-fired boilers are staged combustion and off-
t
stoichiometric firing. Reductions as high as 60 percent are possible
without significantly derating (lowering the output efficiency) the
boiler.
Sulfur Dioxide
Although all the pollutants discharged to the atmosphere con-
tribute to the pollution hazard,sulfur dioxide is considered by health
authorities to pose the single most serious threat. Sulfur oxides pose
serious health effects to man, animals, and vegetation, and are corrosive
to materials and structures. Their odor can have detrimental effects,
both physiologically and psychologically. Because of the seriousness of
the problem, the Federal Government has set, in addition to ambient-air-
quality standards, new source performance standards for a number of
industrial activities including fossil-fueled power plants. To meet
the 1.2 lb S0_/10 Btu standard, efficient and unfortunately costly S0_
control techniques will be required. The primary means to reduce SO-
emissions are as follows:
(1) Fuel substitution
(2) Stack gas cleanup
(3) Physical cleaning of high pyritic sulfur coals.
Fuel Substitution. The use of an alternative fuel lower in
sulfur content has in the recent past been the most acceptable, lowest
cost method to reduce S02 emissions, i.e., natural gas or oil substitution
for high sulfur coal. However, with the growing depletion of domestic
supplies of natural gas and oil, and the recent dramatic increases in
fuel oil costs, this option is no longer economically viable. In light
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85
of these events, the use of coal is anticipated to increase substantially
in the near future. The only economical sources of low sulfur coal is
Western coal (low sulfur Eastern coal is reserved primarily for metal-
lurgical purposes). However, for Eastern utilities such as in Vermont,
the cost to transport low sulfur Western coal will likely make this option
economically unattractive (at least compared to stack gas cleanup). Another
alternative fuel option not normally considered is the use of waste wood
to generate power.
Stack Gas Cleanup. Assuming that high sulfur coal or residual
oil is employed to generate power, the remaining S0? control method is
stack gas cleanup. There is a continually growing number of companies
offering stack gas cleanup processes; however, they are basically all
very similar. In these processes the flue gases containing the SO- are
first cleaned of particulates, then set to a contracting device where
an aqueous-alkali solution and the flue gases are intimately mixed. In
regenerative-type processes, the S0« is recovered from the absorbing media
and converted to elemental sulfur or sulfuric acid while the absorbing
media is regenerated and recycled. In throwaway processes, the SO™ is
reacted with the alkali to form a slurry of insoluble sulfates or sulfites
of calcium which is pumped to a holding lagoon to be dewatered. The
large quantities of quick-sand-like scrubber sludge produced is currently
the major problem with throwaway processes.
The most commercially successful stack gas cleanup processes
have been of the throwaway type. The three most prominent are lime
(calcium oxide) scrubbing, limestone (calcium carbonate) scrubbing, and
double alkali (calcium oxide and soda ash) scrubbing. The principal
reasons for their successes over regenerative processes have been their
lower capital requirements and greater reliability. The three most
prominent of the regenerative processes are magnesia scrubbing (with
thermal regeneration), sodium sulfite scrubbing (with steam stripping
regeneration), and catalytic oxidation (of S02 to SOj) and absorption
in dilute sulfuric acid. All the processes noted above are capable of
reducing SO, emissions by at least 80 to 85 percent.
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86
The state-of-the-art of stack gas scrubbing is still rapdily
changing. While the United States EPA has concluded that the stack gas
cleaning is an efficient and sufficiently reliable control technology
many feel that no stack gas cleanup process has been sufficiently developed
and tested to guarantee acceptable performance. Because of these reser-
vations, and the fact that scrubbing systems are still in the demonstration
and development stage, new, lower cost, more efficient processes can be
anticipated to be developed in the future.
/
Physical Cleaning. The sulfur content of high sulfur Eastern
coals is composed of an inorganic (or pyritic) and an organic fraction.
The organic fraction is chemically bound into the structure of the coal
and cannot easily be removed. The pyritic fraction, often comprising a
significant part of the total sulfur content, can be removed by washing
or physically cleaning the coal. In most cases, the coal's sulfur content
can be reduced by at least one-third by this method. A recent study
indicates that approximately 25 percent of eastern bituminous coals are
either naturally occurring low-sulfur coals or can be washed to 1.2 Ib
SO-/10 Btu with a Btu recovery of 90 percent. Blending with a low-
sulfur fuel such as Western coal, municipal refuse, or wood could allow
an even greater percentage of the physically cleaned coals to meet the
SO. emission regulation.
Particulates
Particulate emissions are the most visible, and, therefore,
the most controlled, atmospheric pollutant. Particulate control is
required for all coal-fired units; fuel oil-fired boilers burning some
residual oils may also require controls. Control equipment for parti-
culate removal are either of the wet or dry type.
Wet type collections are scrubbing devices where the flue gas
and water are intimately mixed. The resultant slurry is clarified for
solids removal, neutralized, and the water recycled; the gas is reheated
(to increase buoyancy) and exhausted to the stack. Collection efficiencies
as high as 99.9 percent are possible.
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87
Dry type collectors can be classified as either mechanical or
electrostatic. Mechanical collectors include cyclones and fabric filters
(baghouses). In cyclones the solid particles are separated from the gas
stream by the centrifugal action on the gas created inside the device.
Cyclones are normally employed to remove the large particles from the
gas steam prior to entering a more efficient collector. Collection
efficiencies of cyclones are normally low, around 80 percent, but can
be increased by using longer, smaller diameter tubes such as in multi-
tubual cyclone collectors. Fabric filters are another mechanical dry
collector. The flue gas is cooled, then forced through cylindrical tubes
(bags) where the dust collects on the inside walls. The bags are cleaned
by either shaking or by the impingement of a blast of high pressure air.
Collection efficiencies are extremely high, 99.9 percent or greater.
Because of temperature limitations, fabric filters have not been accepted
by the electric power industry to the extent that electrostatic pre-
cipitators have.
The final particulate collection device to be discussed is the
electrostatic precipitator. In electrostatic separation, the flue gas
is passed between two high voltage electrodes where the entrained gas
particles become charged and are then drawn to and collected on the sur-
face of the electrodes. The buildup of particles is continued until the
efficiency of the unit falls to a predetermined level. The plates are
then rapped and the particles fall to a collection hopper. Precipitators,
the most common power plant particulate collection device, can be designed
to operate at collection efficiencies as high as 99.9 percent.
In conclusion, control technology for the removal of particulates
has been developed to the extent that it is possible to design and operate
particulate collection devices at efficiencies sufficient to meet all
Federal standards.
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88
Comparison of Wood and Fossil-Fuel Emissions
In the previous sections boiler emissions and control technology
for wood-fired and for fossil-fuel power plants were discussed. In this
section a "fuel-source-to-bus-bar" summation is presented of atmospheric
emissions for coal-, oil-, and wood-fueled systems taking into account
the emission associated with the procurement, transportation, processing,
and combustion of the fuel. The following 10 alternative fuel paths were
analysed.
(1) Low-sulfur Western coal, surface mined, and train
transported to Vermont
(2) High-sulfur (Pennsylvania bituminous) coal, deep
mined, physically cleaned, and train transported
to Vermont
(3) High-sulfur coal, deep mined, train transported to
Vermont and combusted with stack gas cleanup
(4) High-sulfur coal, surface mined, physically cleaned,
and train transported to Vermont
(5) High-sulfur coal, surface mined, train transported
to Vermont, and combusted with stack gas cleanup
(6) Imported oil refined in the Caribbean, tanker
transported to the east coast, and train trans-
ported to Vermont
(7) Domestic crude, pipeline transported from the
southwest to a New Jersey refinery, refined and
desulfurized, and train transported to Vermont
(8) Waste wood, harvested in Vermont, chipped, truck
transported to the power plant, and combusted
green
(9) Waste wood, harvested in Vermont, chipped,
trucked to the power plant, dried and combusted
(10) Combined coal and wood wastes, green wood
harvested, chipped, and truck transported. Coal
deep mined, physically cleaned, and train trans-
ported.
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89
Emission factors, in lb/10 Btu, are summarized in Table 14 for
N°x* S°2* C°' Particulates» a*"* total organics for each of the 10 alternative
fuel paths; rail and truck transport emission factors are expressed in
terms of lb/10 -ton-miles. Using the factors in Table 14 and the fuel
requirements, process efficiencies, transport distances, etc., discussed
in greater detail in the subsequent section on Energy Balances, total
emissions for each path were calculated and summarized in Table 15. The
basis for the calculations was the fuel requirement sufficient to supply
a 50 MWe power plant.
It should be noted that more than half of the total emissions
for wood-related systems shown in Table 15 is attributed to NO from the
A
combustion step. The NO emission factor for wood combustion has not
X.
been determined accurately as yet. These values may be too high.
Study of the total emission ranking of the alternative fuel paths,
displayed in Table 16, shows that the systems fall into three groups.
The first group, including residual oil combustion and high-sulfur coal-
fueled systems with stack gas cleanup, range in calculated emissions (total
of NO , S00, CO, particulates, and total organics) from 2,135 to 2,625
X ^
tons/year. The second or intermediate emissions group including wood
and high-sulfur, physically-cleaned coal systems have emissions that
range from 3,675 to 4,095 tons/year. The wood-related systems would
fall nearer the first group if the NO emissions during combustion are
X
overstated in this calculation. The third, high emissions group, including
low-sulfur Western coal and the combined wood- and coal-fired system have
emissions of 5,150 and 5,465 tons/year, respectively. Because of the
extremely high NO emission rates for wood-fired systems and the
A.
uncertainty in the NO emission factor, the emissions excluding N0x
were also included in Table 16. Comparing the 10 fuel supply paths
under this basis shows that the paths now fall into a low and a high
emission class. The low -emission class now includes both green and
dried wood along with oil and high-sulfur coal with stack gas scrubbing.
From these comparisons it can be concluded that wood-fueled systems can
compete favorably on an overall emissions (acceptability) basis with
either coal- or oil-fired systems.
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90
TABLE 14. SUMMARY OF "SOURCE-TO-POWER" UNIT AIR EMISSIONS
FOR COAL, OIL, AND WOOD FUEL SYSTEMS
Fuel Emissions lb/10 'Btu Output Refer-
Supply N0 so Partic- Total ence
Paths # Energy System x 2 CO ulates Organics No.
Low Sulfur Western Coal , v
1 Surface Mining 0.00008 Neg. ' Neg. 0.07 Neg. 14
Rail Transport (lb/
MM Ton-Mi) 0>) 1848.5 131.8 1425.6 142.6 145.3 14
Power Generation(°»d) 0.98 1.65 0.054 0.07 0.016 14
Pennsylvania Bituminous
Coal
2 Deep Mining 0 0 0 Neg. 0 14
Physical Cleaning 0.006 0.004 —(f) 0.01 — 14
Rail Transport 1848.5 131.8 1425.6 142.6 145.3 14
Power Generation^0'6) 0.68 1.443 0.038 0.044 0.011 14
3 Deep Mining 0 00 Neg. 0 14
Rail Transport'13) 1848.5 131.8 1425.6 142.6 145.3 14
Power Generation with
Stack Gas Cleanup(°) 0.60 0.50 0.042 0.1 0.013 14
4 Surface Mining 0.0002 Neg. Neg. 0.14: Neg. 14
Physical Cleaning 0.006 0.004 — 0.01 — 14
Rail TransportW 1848.5 131.8 1425.6 142.6 145.3 14
Power Generation^0*6) 0.68 1.443 0.038 0.044 0.011 14
5 Surface Mining 0.0002 Neg. Neg. 0.14 Neg. 14
Rail Transport^) 1848.5 131.8 1425.6 142.6 145.3 14
Power Generation with
Stack Gas Cleanup^0) 0.60 0.50 0.042 0.1 0.013 14
Crude Oil
6 Tanker Transport 0.0015 0.0016 0.0013 0.0021 9xlO~5 14
Rail Transport'1*) 1848.5 131.8 1425.6 142.6 145.3 14
Power Generation(°'8) 0.70 0.529 0 0.05 0.01 14
7 Domestic Oil Pipeline 0.009 0.016 2xlO~5 0.002 0.0003 14
New Jersey Refined
with Desulfurization 0.023 0.12 0.003 0.002 0.025 14
Rail Transport^) 1848.5 131.8 1425.6 142.6 145.3 14
Power Generation^0Ȥ) 0.70 0.529 0 0.05 0.01 14
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91
TABLE 14. (Continued)
Fuel Emissions lb/10 Btu Output
^PP1? NO SO
Paths # Energy System x 2
8
9
10
Waste Wood
Wood Recovery 0.05 0.004
Process Chipping 0.118 0.009
Truck Transport ft) 4595.0 364.5
Power Generation Q\
(Green Chips)
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92
TABLE 15. SUMMARY OF "SOURCE-TO-POWER" AIR EMISSIONS
FOR COAL, OIL, AND WOOD FUEL SYSTEMS
Fuel
Supply
Paths #
1
2
3
4
5
6
Emissions Ton/Year (Basis 50 MWe
NO
Energy System x
Low Sulfur Western Coal
Surface Mining 0.1
Rail Transport^) 282.8
Power Generation 1582.7
Total <-c<> 1865.6
Pennsylvania Bituminous
Coal :
Deep Mining^' 0
Physical Cleaning(d) 15.9
Rail Transport (e' 45.5
Power Generation 1098.2
Total (f) 1159.6
Deep Mining 1160.1
Surface Mining^) 0.3
Rail Transport ^ 49.1
Power Generation with
Stack Gas Cleanup 1144.1
Total^g) 1193.5
Crude Oil
Caribbean Refined o(n)
Tanker Transport 2.4
Rail Transport (*) 21.1
Power Generation 1130.5
Total (J) 1154.0
so2
-
20.2
2664.8
2685.0
0
10.6
3.2
2330.4
2344.2
0
3.5
870.1
873.6
10.6
3.2
2330.4
2344.2
3.5
870.1
873.6
0
2.6
1.5
854.3
858.4
CO
-
218.1
87.2
305.3
0
—
35.1
61.4
96.5
0
37.8
73.1
110.9
-
35.1
61.4
96.5
37.8
73.1
110.9
0
2.1
16.3
-
18.4
Partic-
ulates
113.1
21.8
113.1
248.0
-
26.5
3.5
71.1
101.1
—
3.8
174.0
177.8
371.2
26.5
3.5
71.1
472.3
243.6
3.8
174.0
421.4
0
3.4
1.6
80.8
85.8
Plant) (a)
Total
Organics
-
22.2
25.8
48.0
0
—
3.6
17.8
21.4
0
3.9
22.6
26.5
-
3.6
17.8
21.4
3.9
22.6
26.5
0
0.1
1.7
16.2
18.0
Grand
Total
5151.9
3722.8
2382.0
4094.5
2625.9
2134.6
-------
TABLE 15.
93
(Continued)
Fuel
Supply
Paths f Energy System
Emissions Ton/Year (Basis 50 MWe Plant)
m
Partic- Total Grand
CO ulates Organics Total
Domestic Oil Pipeline 14.5 25.8 0.0
New Jersey Refined
with Desulfurization 37.1 193.8 4.8
Rail Transport11' 21.1 1.5 16.3
Power Generation 1130.5 854.3 -
Total (J) 1203.2 1075.4 21.1
3.2
3.2
1.6
80.8
88.8
0.5
40.4
1.7
16.2
58.8
2447.3
8
9
10
Waste Wood
Wood Recovery ^ *•'
Process Chipping(k)
Truck Transport(l)
Power Generation
Total (k)
Wood Recovery'111'
Process Chipping (m'
Truck Transport^!)
Chip Drying
Power Generation
Total
-------
TABLE 16. AIR POLLUTION RANKING OF ALTERNATIVE FUEL PATHS
Total
Fuel Path Description
Imported residual oil
High sulfur coal, deep mined, stack gas
clean up
Domestic refined oil
High sulfur coal, surfaced mined, stack
gas clean up
Waste wood, dried
High sulfur coal, deep mined, physically
cleaned
Waste wood, green
Waste wood and physically cleaned coal
High sulfur coal, surfaced mined, physically
physically cleaned
Low sulfur western coal
Emissions , (a)
tons/yr
2135
2380
2450
2625
3675(b)
3725
3825 (b)
3852(b)
4095
5150
Rank
1
2
3
4
5
6
7
8
9
10
Emissions
Excluding N0x,
tons/yr
980
1190
1245
1430
1445
2565
1500
1848
2935
3285
Rank
1
2
3
4
5
8
6
7
9
10
(a) Includes NO , SO-, CO, participates, and total organics.
Jw ^
(b) Overestimated if NO emission factor from combustion is too high.
VO
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95
Summary
The following paragraphs summarize the previous discussions
relating to pollutant emissions and control technology for wood-fueled
power generation.
Air Pollution Emissions
Wood-fueled systems ranked fifth and seventh in total emissions
of the ten coal-, oil-, and wood-fuel paths considered. Partially dried
wood and green wood has the following calculated annual emissions for a
50 MWe power plant.
Emissions, ton/yr
Total
NOX S02 CK) Particulate Organics Total
Dried Wood
(280,000 ton wood/yr) 2,227 136 540 348 423 3,675
Green Wood
(410,000 ton wood/yr) 2,326 115 600 351 432 3,825
Wood-fueled systems had lower emissions than high sulfur, physically cleaned
coals (3,725-4,095 ton/yr), low-sulfur Western coal (5,150 ton/yr), and
combined wood and coal-fueled systems (3,852 ton/yr). Residual oil (2,135-
2,450 ton/yr) and coal-fueled systems with stack gas cleanup (2,380-2,625
ton/yr) had lower total emissions.
Emission rates for all pollutants appear to be low enough, or
controllable to meet all existing State or Federal air pollution regulations.
However, the estimated NO emission rate of 1.235 lb/10 Btu is significantly
X
higher than the 0.7 lb/10^ Btu Federal new source performance standards for
coal-fired power plants. While not in violation of new source standards,
which apply only to fossil-fuel power generation, the estimated N0x emission
rate is high enough for concern. Study of the data used to calculate the
NO emission rate shows that it was not obtained from actual testing, but
from estimates from similar combustion sources. The accuracy of this
factor is, therefore, uncertain at this time. In addition, the emission
-------
96
rate (originally expressed as Ib/ton) was converted to lb/10 Btu employing
an average heating value of 4200 Btu/lb. Use of a significantly higher
value would reduce the calculated NO emission rate. Therefore, the
X
significance of the difference between the calculated rate and the stan-
dard is questionable. In any event, modification of the boiler design
to restrict excess air could be employed to reduce N0x emissions.
The control of particulate emissions from wood-fueled power
generation can be accomplished by a number of control systems. Noted
below is a brief summary of the control method effectiveness and rough
estimates of collector costs excluding fans, ducting, etc., for a 50-MWe
wood-fueled power plant.
Collection
Efficiency,
percent
99.9
99.8
98.7
99.9
Installed
Cost, $1000
422-633
480-752
672-848
752-1040
Annual! zed
Cost, $1000
192-264
800-1040
112-144
240-288
Cyclone-scrubber
Wet scrubber
Electrostatic precipitator
Fabric filter
As can be seen, the cyclone-scrubber system and the electrostatic pre-
cipitator collector have the lowest annualized control costs. Of the
two, the multitubular cyclone in series with a low-energy scrubber system
is the overwhelming favorite. (There is no proven performance of electro-
static precipitators on waste wood boilers.) This choice is based on the
cyclone-scrubber system's relative low capital cost, reasonable operating
expenses, sufficiently high collection efficiency, ease of maintenance,
proven performance, and low generation of concentrated (easily disposed)
scrubber sludge.
During periods of incomplete combustion, organic chemicals
(primarily hydrocarbons) which are normally oxidized to CO and water
are released to the atmosphere. There is a potential that these chemicals
could react with each other to form either carcinogenic or photochemically
-------
97
active hazardous compounds. Investigation shows that while some small
fraction of these chemicals could be emitted, there is no evidence that
their emission will be significant to the local air quality or present
local health problems. Emissions of these materials, for example, are
estimated to be less with wood firing than for a correspondingly sized
coal-fired power plant.
Boiler Residue
Although available information on boiler residue disposal is
limited, disposal of the boiler ash, clinker, and fly ash is not con-
sidered to present a problem. The boiler residue is composed primarily
of inert alumina and silica with trace (part per billion) amounts of
heavy metals. Disposal of this material in an environmentally acceptable
manner is accomplished through disposal in landfills or, when collected
in slurry form, in lined lagoons.
/
Information on by-product uses is tentative. Attempts have
been made to employ the boiler residue as a soil conditioner; however,
at this time, no information is available regarding the success or
failure of these attempts.
Conclusions
These conclusions are summarized below:
e The use of waste wood to fuel boilers for the
generation of electricity is environmentally
acceptable method of power generation.
e Total air emissions for 100 percent wood-fueled
systems are comparable or less than alternative
fuels such as physically cleaned coal or low-
sulfur Western coals. The waste wood and coal
combination has comparable total air emissions.
e Control technology for the collection of up to
99 „ 9 percent of the particulates is currently
available. The most promising control method
-------
identified is a multitubular cyclone separator
connected in series with a low-energy wet-
impingement scrubber. This system has proven
economical, dependable, and effective'in actual
waste wood boiler application.
Emission of hazardous organic chemicals from the
incomplete combustion of wood should not present
any significant problems to the local air quality.
Environmentally acceptable disposal of boiler
residues can be accomplished by placing the
relatively inert boiler ash and fly ash in
landfills or in lined lagoons.
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99
References
(1) Barren, Mvah, Jr., "Studies in the Collection of Bark Char Throughout
the Industry", Tappi, _53 (8), pp 1441, 1448.
(2) Anonymous, "Wood Waste Combustion in Boilers", Compilation of Air
Pollution Emission Factors, 2nd Ed., United States EPA, Research
Triangle Park, North Carolina, 1973, p 1.6-2.
(3) Roberson, J. E., "Bark Burning Methods", Tappi, 51 (6), pp 90A-98A,
June, 1968.
(4) Brooks, R. R., "Trends in Wood Refuse-Fired Boiler Design", Heat
Engineer, 4£ (1), pp 8-11, January/February, 1973.
(5) Horzella, T. I. and Newton, L. R., "Hogged Fuel Boilers Air Pollution
Control to Meet Present Day Codes", presented November 15-17, 1972, at
Pacific Northwest International Section Air Pollution Control Authority
Meeting in Eugene, Oregon.
(6) Archibald, W. B. and Stewart, R. L., "Design of Air Emission Systems
for Modern Wood-Fired Boilers", presented November 17, 1972, at
Pacific Northwest International Section Air Pollution Control Assoc.,
Meeting in Eugene, Oregon.
(7) Effenberger, H. K. Cradle, D. D., and Tomany, J. P., "Control of
Hogged-Fuel Boiler Emissions, A Case History", Tappi, j6 (2), pp 111-115,
February, 1973.
(8) Corder, Stanely E., Wood and Bark as Fuel. Research Bulletin 14, Forest
Research Laboratory, School of Forestry, Oregon State University,
Corvallis, Oregon, August, 1973.
(9) Junge, D. C. and Kwan, K. T., "An Inventory of the Chemically Reactive
Constituents of Atmospheric Emissions from Hogged-Fuel-Fired Boilers
in Oregon", Forest Products Journal, 24 (10), pp 25-29, October 10, 1974.
(10) Stern, A. C., Air Pollution, 2nd Ed., Volumes I and II, Academic Press,
New York, New York (1968).
(11) Prakash, C. B. and Murray, F. E., "A Review on Wood Waste Burning",
Pulp and Paper Magazine of Canada, 23 (7), pp 70-75, July, 1972.
(12) Vandegrifts, A. E., et al, "Particulate Pollution Systems Study",
Handbook of Emission Properties, Vol. Ill, May, 1971 (Appendix A).
(13) Freudenthal, R. I., Lutz, G. A., Mitchell, R. I., "Carcinogenic
Potential of Coal and Coal Conversion Products , a Battelle Energy
Program Report, Columbus, Ohio (1975).
-------
100
References
(Continued)
(14) "Environmental Consideration in Future Energy Growth", Volume I,
prepared by Battelle Memorial Institute for the United States EPA,
April, 1973.
(15) Maugh, Thomas H., II, "Air Pollution: Where Do Hydrocarbons Come From?",
Science, 189 (4199), pp 277-278, July 25, 1975.
(16) Sproull, Reavis C., "Fiber, Chemical, and Agricultural Products from.
Southern Pine Bark", Forest Prod. J., 19 (10), pp 38-44, October, 1969.
(17) Anonymous, "Fossil Fuel Burning Sources", Draft copy of The Cost of
Clean Air, prepared by Battelle's Columbus Laboratories for the
United States EPA, 1975.
(18) Brown, Owen D., "Energy Generation from Wood Wastes" presented June 20,
1973, at International District Heating Association in French Lick,
Indiana.
(19) Private communication, Owen Brown, Steam System Superintendent,
Eugene Water and Electric Board, Eugene, Oregon, August 6, 1975.
'A
(20) Anonymous, "Sulfur Oxide Removal from Power Plant Stack Gas - Use of
Limestone in Wet Scrubbing Process", prepared for National Air
Pollution Control Administration by Tennessee Valley Authority,
Contract No. TV-29233A (1969).
(21) Howard, Edward J., "A Survey of the Utilization of Bark as Fertilizer
and Soil Conditioner", Pulp and Paper Magazine, Canada, TL_ (23-24),
pp 53-56, December 4-18, 1970.
(22) Anonymous, Steam - Its Generation and Use. 38th Ed., The Babcock &
Wilcox Company, New York, New York (1972), Chapter 5, pp 5-1-24.
(23) Diehl, R. C., Hattman, E. A., Schultz, H. S., and Haren, R. J., "Fate
of Trace Mercury in the Combustion of Coal", Technical Progress Report
54, Bureau of Mines Managing Coal Wastes and Pollution Program, p 4,
May, 1972.
(24) Perry, Robert H., Chemical Engineers Handbook. 4th Ed., McGraw-Hill
Book Company, New York, New York (1969), Chapter 9, p 9-3.
(25) Oxyley, J. H., et al, "Air Pollution: Control of Gaseous Emissions",
Equity Research Associates, ERA Environmental Issues, January 5, 1973.
(26) Oxley, H. J., et al, "Sulfur Emission Control for Industrial Boilers",
Proceedings of the American Power Conference, Vol 36, 1974.
-------
101
References
(Continued)
(27) Anonymous, "Energy Concepts for a New Era", Heat Engineer, pp 64, 69,
October/Decent er, 1973.
(28) Booth, John Barbon, "Some Guidelines to Aid in the Selection of
Collectors for Hogged Fuel Applications", Pulp and Paper, 40 (27),
pp 32-33, July 4, 1966.
(29) Powell, E. M., Ulmer, R. C., "Controlling Emissions from Fossil-Fueled
Power Plants", Confcustion, pp 24-34, January, 1974.
(30) Personal communication, R. I. Freudenthal, August 4, 1975.
(31) Hardison, L. C., Greathouse, C. A., "Air Pollution Control Technology
and Costs in Nine Selected Areas", By IGCI for US EPA, PB 227746,
Section 8, Kraft Mil Bark Boilers, pp 317-347, September, 1972.
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102
ENERGY. BALANCE ANALYSIS
Introduction ,
In considering the economic and technical feasibility of firing
an electric utility boiler with wood wastes in Central Vermont, it is .
appropriate to consider the overall energy use associated with wood fuel as
compared with that for alternate fueling options. This section sets out
the energy consumed in-the recovery, processing, and transport of fuel to
Central Vermont by the ten alternative fuel paths described in the preceding
analysis of overall atmospheric emissions.
Figure 30 is an illustration of the fueling paths which were
analyzed for their energy consumptions. Path 10 is not illustrated but
is a combination of Paths 1 (except Pennsylvania coal is substituted for
Wyoming coal) and 8. The estimated energy requirements, associated with
the conventional-fuel paths are compared with energy estimates for recover-
ing, processing, and transporting wood chips in the Central Vermont area.
Data for energy consumed in the various fuel recovery, preparation,
and transportation paths are presented first to establish the basis and
sources of the information. This is followed by an analysis of the'energy
consumption for the 10 fueling paths to supply a 50 MWe plant in Central
Vermont. In conclusion, summary data are presented for all fuel paths
investigated.
Basic Data and Sources of Information
Pennsylvania Bituminous Coal
A review of available Pennsylvania coal that may be physically
cleaned to produce a total sulfur content below 1 percent indicates that
only a few coalbeds in specific counties can qualify/ ' These counties
*References for this section are listed on Page 124
-------
Green
Waste-Wood
Fue
P ennsyIvania
_Bituminous
Coal
Dried
Waste Wood
Fuel
Domestic
Pipeline
Transport
Surface
Mining
Deep
Mining
Physical
Cleaning
Caribbean
Recovery,
50-Mile Radius
Surface Mining
Wyoming
/Tanker A
Desulfurized
Transport
\Transport J
Process
Chipping
Rail
Transport
Rail
Transport
Truck
Transport
Utility Boiler
50 MWe Output
Central Vermont
o
u>
FIGURE 30. FUEL PATHS FOR PUBLIC UTILITY
ELECTRIC POWER IN CENTRAL
VERMONT
Fuel Path Identification
1. Western (Wyoming) Coal
2. Penn. Bit. - Deep Mined - Physically Cleaned
3. Penn. Bit. - Deep Mined - Stack Gas Cleaned
4. Penn. Bit. - Surface Mined - Physically Cleaned
5. Penn. Bit. - Surface Mined - Stack Gas Cleaned
6. Caribbean Residual Fuel
7. Domestic Crude - Pipeline-Refined-Desulfurized
8. Green Wood Chips
9. Dried Wood Chips ,„ „ ,
10. Combined Coal/Green Wood Chips
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104
were identified and selected for energy balance analysis. Both surface and
deep mining operations were analyzed for the selected coalbeds.
Recovery - Deep Mining. Cost analysis of underground Eastern
coal mining has been reported. A mining capacity of 1.06 million tons
per year was selected as being representative of the Pennsylvania coalbed
operations. The total electric power for an operation of this size is
21.5 x 106 kwh per year and is equivalent to 69,000 Btu per ton of coal.
Fuels and lubricant consumptions represent an additional 81,000 Btu pers
ton of coal.*
Recovery - Surface Mining. Data for energy consumption for surface
(3)
mining for Pennsylvania were not located. Analyses of costs made in 1972
for contour surface mining in Northern West Virginia for a 1-million ton
per year capacity were considered acceptable for the purpose at hand. A separate
(4)
analysis was made in 1974 and it was also used for comparison purposes.
(3)
In the Northern West Virginia operation , the electrical con-
sumption amounts to 92,200 Btu per ton of raw coal. Fuels and lubricants
account for another 111,000 Btu per ton. The data for the Eastern Province
in Reference 4 is for a mining operation of 4.8 million tons per year. The
electric power consumption amounts to 45,600 Btu per ton of raw coal;
fuel and lubricants account for 34,400 Btu per ton. A 3-million-ton-per-year
Northern West Virginia mine was also examined.^ The electric power
value is 124,000 Btu/ton and fuel use is 60,000 Btu/ton. Inquiries con-
cerning these data indicate that the data of Reference 3 are more
appropriate for the present study.
Recovery - Wyoming Surface Mining. Reference 3 contains information
on the costs of power and fuel for a 5-million-ton-per-year low-sulfur coal
surface mine. The electric power consumption is calculated to be only
*The national average price of distillate fuel was taken as $2.61 per
million Btu.
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105
7060 Btu per ton of raw coal while the fuels, lubricants and so forth
account for 25,000 Btu per ton.
Data for a dozen Wyoming County coalbeds were examined^ and
the average mositure content was found to be about 16.5 percent. An
average heating value of 19 x 106 Btu per ton is considered appropriate.
Physical Cleaning of Pennsylvania Bituminous Coal
In the Northern Appalachian Region, the sulfur content of bituminous
coal averages about 3.07 percent total with the pyritic sulfur representing
2.03 percent. Consequently, it is essentially impossible to physically clean
the average coal to less than 1 percent. Some exceptions in the Pennsylvania
region are the Upper and Lower Freeport and Kittanning beds in certain
counties in which the average sulfur content is about 1.7 percent. The
losses of raw coal incurred in cleaning such coals to a sulfur content of
1 percent or less might not exceed 10 percent of the total raw coal
energy content, i.e., 90 percent energy recovery.*
The energy consumed by dewatering centrifuges, crushers, screen
vibrators and the like amount to about 24,000 Btu per ton of product. '
The energy for drying the coal consumes about 25 pounds of cleaned product
per ton of product. This will require about 28 pounds of raw coal or about
360,000 Btu per ton of product.
The remaining energy consumption is for the disposal/reclamation
of the refuse from the cleaned coal—pyritic sulfur plus tailings. It is
understood that this material could easily catch fire through spontaneous
combustion unless properly disposed. Alternate layers of refuse and
impervious clay have been utilized effectively and is probably entirely
appropriate for physical cleaning operations. It is estimated that 20 tons
of refuse disposed in this fashion would require a total of 380,000 Btu.
This includes loading, bulldozing refuse, shoveling clay and bulldozing clay.
(It does not include mulching, liming, fertilizing, and seeding .as this is
a surface mining reclamation operation.) This results in a consumption of
about 6,000 Btu per ton of product, a relatively small portion of the total.
* Cleaning of other Northern Appalachian coals to less than 1 percent sulfur
would entail total Btu losses of 20-30 percent or more.
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106
Stack Gas Scrubbing
Wet scrubbing stack gas cleanup systems have primary energy con-
sumption in the fans and pumps and these can amount to about 6 percent of
(0\ /
-------
107
Field data were used to determine the energy consumption for
pumping crude oil in a transcontinental pipeline. The operation was assumed
to be a 40-inch pipeline transporting 750,000 barrels of crude per day.
The crude had a viscosity of 100 SSU and a specific gravity of 0.85. Field
data analysis indicate that the energy consumption is 93 Btu per ton-
mile. This value is considered accurate to within 20 percent.
Green Wood Chip
Data on the energy consumption for the recovery and preparation
of green wood chips for boiler fuel were not readily available. Generally,
the literature which was reviewed contained information for smaller operations
performed on a laboratory basis and it was not considered to be necessarily
appropriate for theanalysis of interest here. Therefore, data were sought
from a variety of sources, all of which were actively engaged in forestry
management and commercial utilization of wood wastes as fuels. These
findings are summarized in the following paragraphs.
Recovery and Preparation. No specific information could be
obtained for the exact quantities of energy consumed in the recovery of
forest wood wastes. However, one source had what is believed to be very
(14)
good data for both recovery of wastes and their preparation and chipping.
During 1974, one diesel-powered disk-type Morbark chip harvester produced
52,000 tons of wood chips and complete cost records for fuel and energy
consumption were maintained. The operation included recovery, preparation,
chipping, and the blowing of the chips into a truck van. The mobile
chipper operated in good forestry conditions and forest wastes were trans-
ported a distance of the order of 1/4 mile to the chipper. The operations,
though not,exactingly separable in terms of energy consumption, could be
rather well estimated. Accordingly, it was estimated that 70 percent
of the total energy consumed was for wood preparation and chipping while
the balance was for recovery. This permits a breakdown of the energy
consumed per ton of green chips as follows:
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108
• recovery 140,000 Btu/ton
• preparation and chipping 330,000 Btu/ton
Another source of information had data for an operation producing
wood chips for pulp and paper production. Some 12 sets of production
figures and power consumptions were obtained. It was estimated by the
source that 15 percent of the total was for recovery. The range was as
presented below for recovery and preparation and chipping.
production, tons Btu per ton
• recovery
maximum 42,970 8,585
minimum 11,056 18,522
typical 38,245 9,686
• chipping
maximum 42,970 48,650
minimum 11,056 104,958
typical 38,245 54,888
Another source had collected much information from their member pulpwood
companies and this was being analyzed so that energy consumption values
could be established. They found that their data were often incomplete
but it broke down into 11 different kinds of logging operations represent-
ing pulpwood production regions. The range of energy consumed is as
follows:
• recovery 30,000 to 180,000 Btu per ton of chips
a chipping and trucking 300,000 Btu per ton of chips
The source advises that he distrusts the data at this stage of analysis.
Nonetheless, it appears to be of the right order.
Of these operations described, it is believed that the Total
(14)
Chips Incorporated operation is more closely related to the kind that
is proposed for the Central Vermont region. Good forestry practice was
utilized and wood types were somewhat similar to those in Vermont. For
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109
these reasons, the energy consumption data provided by Total Chips
Incorporated have been selected for energy balance analysis.
Transportation. The previously cited information was utilized
and the value of 1730 Btu per ton-mile was used. It was established that
the operation would be within 60 miles on the electric utility plant
and an average trip would be 40 miles one way or a weighted value of
60 miles per round trip (40 miles empty).
Quantity of Green Chips Required. The quantity will be
dependent upon the heating content per unit of weight and this, in turn,
is dependent upon moisture content. The basis of 9.35 x 10 Btu per ton
(45 percent moisture) was used.
For a heating value of 9.35 x 10 Btu per ton, about 410,000 tons
of green wood chips will be required annually for the 50 MWe plant with
the assumed load factor of 70 percent, and a power plant efficiency of 27.4
percent.
Annual Energy Consumption for Selected Paths
For purposes of comparison, the 10 fueling options were analyzed,
using the foregoing data, to determine the annual energy consumed in the
recovery, preparation, and transport of the fuel to Central Vermont in
the quantities required for a 50 MWe plant. The data for each are set
forth in a series of tables.
The quantity of each fuel required annually depends upon the
heating value of the fuel and the power plant efficiency for that fuel.
For the fossil fuels, an overall power plant efficiency of 32.5 perqent,
equivalent to a heat rate of 10,500 Btu/kwhr, was assumed. For a 50 MWe
plant operating at 70 percent load factor, the annual heat input require-
ment would be 3.22 x 1012 Btu. For green wood, the overall power plant
efficiency was assumed to be 27.4 percent, or about 12,450 Btu/kwhr^ The
annual heat input requirement in this case would be about 3.80 x 10 Btu/year,
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110
(1) Wyoming Low Sulfur Coal. The information on energy consumption
is presented in Table 17. As the sulfur content is below 1 percent no energy
is consumed in coal cleaning or stack gas cleanup.
(2) Pennsylvania Bituminous Coal. Deep Mined, and Physically
Cleaned. The detailed energy consumptions associated with the use of
physically cleaned high-sulfur coal are presented in Table 18. In the
cleaning of this coal the Btu content of the cleaned product and refuse
were treated as equal in this analysis. Actually, the product would be
expected to increase in heat content while the refuse would be consequently
lowered. When all refuse coal, dewatering and drying are taken into
account, nearly 13 percent of the raw mined high-sulfur coal is consumed
in preparation of clean coal.
(3) Pennsylvania Bituminous Coal, Deep Mined, and Stack Gas
Cleaned. As may be seen in Table 19, the energy consumption for stack gas
cleaning is significantly lower than for physically cleaned coal.
(4) Pennsylvania Bituminous Coal, Surface Mined, and Physically
Cleaned. The energy consumption for mining is overwhelmed by the physical
cleaning processing energy requirements. These details are shown in Table 20.
(5) Pennsylvania Bituminous Coal, Surface Mined, and Stack Gas
Cleaned. This fueling path is presented in Table 21. The energy consumed
in stack gas cleaning is significantly lower than for physically cleaned
coal.
(6) Caribbean Residual Fuel. The residual fuel is recovered,
processed, and transported by tanker to a nearby seaport. Hence, no
domestic energy is consumed by this fueling option other than for rail
transport of the fuel oil, Table 22.
(7) Domestic Crude Oil. This alternative path for obtaining
low-sulfur residual fuel was examined in the event a foreign curtailment
might prevent the procurement of the needed fuel. For this case, crude
was pipelined from the South-Central region of the U.S. to a New Jersey
refinery where it was processed into low-sulfur residual fuel. As may be
seen from Table 23, the energy consumed in preparation or processing
overwhelms the transportation energy consumption.
-------
TABLE 17. ENERGY CONSUMPTION FOR PATH 1, WYOMING LOW-SULFUR COAL
Heating Value: 19 x 10 Btu/ton
12
Quantity Required: 170,000 tons/year to provide 3.22 x 10 Btu
Activity
Annual Energy
Consumption,
106 Btu
Recovery
Surface Mining, Electric Power - 25,000 Btu/ton
Fuel and Lubricants - 7,100 Btu/ton
Preparation
Transportation
Rail - 170,000 tons, 1800 miles at 680 Btu/ton-mile
4,250
1,207
5,457
None
208,080
Total
213,573
-------
TABLE 18. ENERGY CONSUMPTION FOR PATH 2, PENNSYLVANIA BITUMINOUS COAL -
DEEP MINED AND PHYSICALLY CLEANED
Heating Value: 26.2 x 10 Btu/ton
12
Quantity Required: 123,000 tons/year of cleaned coal to provide 3.22 x 10 Btu
Activity
Annual Energy
Consumption,
106 Btu
Recovery
Deep mined, Mined Coal - 136,700 tons
Electric Power - 69,000 Btu/ton
Fuel and Lubricants - 81,000 Btu/ton
Preparation
9,432
11.072
Physical Cleaning (90% average Btu yield) ,
Coal rejected - 13,670 tons @ 26.2 x 10 Btu/ton
Electric Power (24,000 Btu/ton)
Drying Using cleaned coal, 25 Ibs/ton or
28 Ibs raw coal/ton = 360,000 Btu/ton
Rejected coal disposal - 6000 Btu/ton of product
Transportation
Rail - 123,000 ton, 400 miles @ 680 Btu/ton-mile
358,100
2,952
44,280
738
20,505
406,070
33,456
Total
460,030
-------
TABLE 19. ENERGY CONSUMPTION FOR PATH 3, PENNSYLVANIA BITUMINOUS COAL,
DEEP MINED, BURNED WITH STACK GAS CLEANING
Heating Value: 26.2 x 10 Btu/ton
Quantity Required: 133,700 tons/year to provide 3.22 x 10 Btu net input to power plant.
Activity
Annual Energy
Consumption,
10 Btu
Recovery
Deep Mined (mined coal 133,700 tons)
Electric, 69,000 Btu/ton
Fuel and Lubricants, 81,000 Btu/ton
Preparation
Stack Gas Cleaning 8% of input Btu's
Transportation
Rail - 133,700 tons, 400 miles @ 680 Btu/ton-mile
9,225
10.830
Total
20,055
280,000
36,366
336,421
u>
-------
TABLE 20. ENERGY CONSUMPTION FOR PATH 4, PENNSYLVANIA BITUMINOUS COAL,
SURFACE MINED AND PHYSICALLY CLEANED
Heating Value: 26.2 x 10 Btu/ton
Quantity Required: 123,000 tons/year of cleaned coal to provide 3.22 x 10 Btu
Annual Energy
Consumption,
Activity 106 Btu
Recovery
Surface Mined - mined coal 136,700 tons
Electric Power - 92,200 Btu/ton 12,603
Fuel and Lubricants - 111,000 Btu/ton 15.173
27,777
Preparation
Physical Cleaning - 90% average yield ,
Coal Rejected - 13,670 tons @ 26.2 x 10 Btu/ton 358,100
Electric Power - 24,000 Btu/ton 2,952
Drying using cleaned coal, 25 Ibs per ton or
28 Ibs of raw coal/ton = 360,000 Btu/ton 44,280
Rejected coal disposal - 6000 Btu/ton of product 738
406,070
Transportation
Rail - 123,000 ton, 400 miles @ 680 Btu/ton-mile 33,456
Total 467,300
-------
TABLE 21. ENERGY CONSUMPTION FOR PATH 5, PENNSYLVANIA BITUMINOUS COAL,
SURFACE MINED, BURNED WITH STACK GAS CLEANING
Heating Value: 26„2 x 10 Btu/ton
Quantity Required: 133,700 tons/year to provide 3,22 x 10*2 Btu net input to power plant.
Activity
Annual Energy
Consumption,
106 Btu
Recovery
Surface Mined - mined coal - 133,700 tons
Electric Power - 92,200 Btu/ton 12,327
Fuel and Lubricants - 111,000 Btu/ton 14.840
Preparation
Stack Gas Clean-up 8% of input Btu's
Transportation
Rail - 133,700 tons, 400 miles @ 680 Btu/ton-mile
Total
27,167
280,000
36,366
343,533
-------
TABLE 22. ENERGY CONSUMPTION FOR PATH 6, CARIBBEAN RESIDUAL FUEL -
TANKER TO NEW YORK/BOSTON
Heating Value: 6029 x 106 Btu/Bbl
12
Quantity Required: 511,760 bbl/year residual fuel oil to provide 3.22 x 10 Btu
Activity
Annual Energy
Consumption,
106 Btu
Recovery
Preparation
Transportation
Rail - 76,000 tons, 300 miles @ 680 Btu/ton-mile
None Domestically
None Domestically
15,500
Total
15,500
-------
TABLE 23. ENERGY CONSUMPTION FOR PATH 7, DOMESTIC CRUDE OIL - REFINED AND DESULFURIZED
Heating Value: 6.29 x 106 Btu/bbl 12
Quantity Required: 511,760 bbl/year residual fuel oil to provide 3.22 x 10 Btu
Activity
Annual Energy
Consumption,
106 Btu
Recovery (from well)
Transportation (.to refinery in New Jersey)
Pipeline - 76,000 tons, 1400 miles @ 93.1 Btu/ton-mile
Preparation
Refining (674,000 Btu/bbl)
Desulfurization (500,000 Btu/bbl)
Transportation
Rail - 76,000 tons, 300 miles @ 680 Btu/ton-mile
344,926
255.880
Negligible
9,906
600,806
15,504
Total
626,216
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118
(8) Green Wood Waste Chips. The energy consumed for the green
wood chip fueling of a boiler in Central Vermont is presented in Table 24.
The total annual energy consumption is estimated at 235,000 x 10 Btu for
recovery, chipping, and transportation. An independent, and preliminary,
analysis indicates that the annual consumption would be 168,300 x 10 Btu.
(18)
(9) Dried Wood Wastes (15 percent moisture). A review of a
paper company's operation of a newly designed wood-fired boiler revealed
that it should be possible to utilize stack gas heat to dry wood chips as
they are fed to the fuel feeding system of the boiler. Generally, the
moisture content of the wood wastes may run about 45 percent and this will
provide an overall steam-boiler conversion efficiency of about 68 percent.
A dryer could be installed using 750F stack gases to dry the wood chips to
a moisture content of about 15 percent. The heating value of the dried
chips would be raised to about 14.5 x 10 Btu/ton. In addition, the steam-
raising efficiency would increase to about 77 percent and the overall
power plant efficiency would increase to about 30.8 percent. The annual
wood requirement would be reduced more than 11 percent to 363,000 tons of
green wood (45 percent M.C.) which is equivalent to 235,000 tons of dried
wood (15 percent M.C.). As shown in Table 25 this will reduce the energy
consumption by the same percentage, to 208,000 x 10 Btu when compared with
green wood chip utilization.
(10) Combined Coal/Green Waste Wood. It was believed that a
fuel path in which both coal and wood chips were simultaneously fired
beneath a boiler at a ratio such as to provide not more than 1 percent
total sulfur content, would have a low recovery-to-boiler energy consumption.
The Pennsylvania coalbeds contain an average of 3.3 percent total sulfur.
Thus, to provide a 1 percent maximum of sulfur, the coal must be 0.303 times
the total heat input to the power plant. The balance must be wood. The
steam raising efficiency, estimated on a proportional basis, would be
about 72.5 percent, giving an overall power plant efficiency of 29 percent.
12
The heat input requirement thus becomes 3.60 x 10 Btu/year. A fuel mixture
12 19
of 1.09 x 10 Btu or 41,633 tons of coal per year plus 2.51 x 10 Btu or
268,363 tons of green wood chips per year would provide the equivalent of
a 1 percent sulfur fuel. As will be seen in Table 26, the annual energy
consumed by these combined paths is 173,771 x 10 Btu.
-------
TABLE 24, ENERGY CONSUMPTION FOR PATH 8, GREEN WASTE WOOD - CHIP AND TRUCK
Heating Value: 9.35 x 106 Btu/ton (45% M0C. wet, 8500 Btu/dry Ib)
Quantity Required: 410,000 tons/year (Plant efficiency - 27„6 percent)
Activity
Annual Energy
Consumption,
106 Btu
Recovery
410,000 tons @ 140,000 Btu/ton
Preparation
Chipping - 410,000 tons @ 330,000 Btu/ton
Transportation
Truck - 410,000 tons, 60 miles, 1730 Btu/ton-mile
Total
57,400
135,300
42,558
235,258
-------
TABLE 25. ENERGY CONSUMPTION FOR PATH 9, WASTE WOOD CHIPS DRIED AT THE POWER PLANT
Heating Value: 14.5 x 106 Btu/ton (15% M.C.) and 9.35 x 106 Btu/ton (45% M.C.)
Quantity Required: 363,000 tons/year of green wood = 235,000 tons/year of dried wood.
Activity
IIHI<^HMHW(i^
Recovery
363,000 tons of green wood @ 140,000 Btu/ton
Preparation
Chipping - 363,000 tons of green wood @ 330,000 Btu/ton
Trans portat ion
Truck - 363,000 tons of green wood, 60 miles, 1730 Btu/ton-mile
Annual Energy
Consumption,
106 Btu
50,820
119,790
37,680
K>
o
Total
208,290
-------
TABLE 26. ENERGY CONSUMPTION FOR PATH 10, COMBINED PENNSYLVANIA BITUMINOUS - GREEN WOOD CHIP FIRING
Heating Value: Coal - 26,2 x 10^ Btu/ton Tons required, 41,633
Wood - 9.35 x 106 Btu/ton Tons required, 268,363
Combined Heat Input to Boiler: 3.60 x 1012 Btu/year (Est. 29% efficiency)
Activity
Annual Energy
Consumption,
106 Btu
Recovery
Surface Mined Coal •
Wood - Fuel 140,000
Preparation
Coal
Wood, chipping 268
Transportat ion
Coal « 41,633 tons,
Wood - 268,363 tons
• Electric
Fuel and
Btu/ton
,363 tons,
400 miles
, 60 miles
92,200 Btu/ton 3,839
Lubricants 111,000 Btu/ton 4.621
330,000 Btu/ton
, 680 Btu/ton-mile
, 1730 Btu/ton«-mile
8,460
37,571
None
88,560
11,324
27,856
Total
173,771
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122
It should be noted that it was unnecessary to treat the coal and,
therefore, the energy losses and their costs are not incurred in the combined
firing process. Likewise, the 8 percent of the total energy production
consumed by stack gas cleaning is not lost nor is the sizable capital
cost incurred. A relatively low energy consumption value is obtained for
the combined firing paths.
Summary and Conclusions
A summary of the energy consumption balances is presented in
Table 27. The table includes energy consumption values for recovery,
processing, and transport of a sufficient quantity of fuel for a 50 MWe
power plant in Central Vermont at a 70 percent load factor. Totals for
these energy quantities for each fuel path, the path total, are given in
the last column of Table 27. In comparing the energy requirements for
alternate fuel paths, another important value to consider is the initial
quantity of fuel required, which is shown in the first column. This value
varies for the different fuel paths because of different power plant
efficiencies for different fuels, or, because some fuel is lost in pro-
cessing, as in the case of physical coal cleaning, or, in the case of ,
stack gas cleaning, because of the additional power requirement to operate
the scrubber. The use of green waste wood chips requires the initial
procurement of more fuel than any of the other paths. Since wood is a
renewable resource, this fact should not mitigate against its use. On
the other hand, the green waste wood path consumes less path-total energy,
which is derived from nonrenewable sources, than any of the coal paths
with the exception of low-sulfur Wyoming coal.
If the wood chips were dried by means of waste heat from the
power plant, the initial fuel requirement is lower than the Pennsylvania
coal paths, and the path-total energy becomes even more favorable with
respect to coal. The net benefits of chip drying are such that serious
consideration should be given to this concept in the design of the
commercial plant.
-------
TABLE 27. SUMMARY OF ANNUAL ENERGY CONSUMPTIONS FOR TEN FUELING PATHS
Recovery, 10 Btu Processing, 10 Btu
Fuel Required Mining Wood Physical Stack Gas Refining Desulfurization of Wood
Fuel Paths
Low-Sulfur
Wyoming Coal
Pennsylvania
Bituminous
Pennsylvania
Bituminous
Pennsylvania
Bituminous
Pennsylvania
Bituminous
Caribbean
Crude Oil
Domestic
Crude
Green Waste
Wood
Dried Waste
Wood
Combined Coal/
Waste Wood
10" Btu
3,220
3,590
3,510
3,590
3,510
3,220
3,220
3,800
3,400
| 3,600
10J tons Surface Deep Waste Cleaning Clean-up of Crude Residual Oil Chipping
170 mined 5,457
-
137 mined 20,505 406,070
134 mined 20,055 280,000
137 mined 27,777 406,070
134 mined 27,167 280,000
76
76 344,926 255,880
410 57,400 135,300
.
363 (green) • 50,820 119,790
42 8,460
268 37,571 88,560
Transportation, Path Total,
106 Btu 109 Btu
208,080
33,456
36,366
33,456
36,366
15,500
25,410
42,558
37,680
11,324
27,857
214
460
336
467 i-
N>
CO
343
15
626
235
208
I 174
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124
References
(1) Deurbrouck, A.W., Sulfur Reduction Potential of theCoals of the United
States, Bureau of Mines Report of Investigations, 7633, 1972.
(2) Katell, S., and Hemingway, E.L., Basic Estimated Capital Investment and
Operating Cost for Underground Bituminous Mines, U.S. Bureau of Mines,
I.C. 8632, 19747"
(3) Cost Analysis of Model Mines for Strip Mining of Coal in the U.S.,
Bureau of Mines, I.C. 8535, 1972.
(4) Katell, S., and Hemingway, E.L., Basic Estimated Capital Investment and
Operating Costs for Coal Strip Mines, Bureau of Mines, I.C. 8661, 1974.
(5) Walker, F.E., and Hartner, F.E., Forms of Sulfur in U.S. Coal, Bureau
of Mines, I.C. 8301, 1966.
(6) Anastas, M.Y., Physical Cleaning of Coal, unpublished Battelle Memorandum
of November 21, 1974.
(7) Personal communication with E. Hurst of the Lively Manufacturing and
Construction Co. of Beckley, West Virginia, June, 1974.
(8) Elliott, T.C., "S02 Removal from Stack Gas", Power, Sept., 1974, p. S-22.
(9) McGlamery, G.G., and Torstrick, R.L., "Cost Comparisons of Flue Gas
Desulfurization Systems" Proc. EPA Public. 650/2A, Volume I, 1975.
(10) Mineral Industries Survey: Crude Petroleum, Petroleum Products and
Natural Gas Liquids, Bureau of Mines, 1973.
(11) Creswick, F.A., Energy Requirements for the Movement of Intercity
Freight, Association of American Railroads, 1972.
(12) Energy Statistics; A Supplement to Summary of National Transportation
Statistics, Transportation Systems Center, Sept, 1973.
(13) Personal communication, Mr. Al Miller, Marathon, Findlay, Ohio.
(14) Personal communication, Mr. Harry Morey, Total Chips, Incorporated,
Sheppard, Michigan 48883, June 7, 1975.
(15) Personal communications, Mr. William Popadych, Mead Corporation,
Chillicothe, Ohio, June, 1975.
(16) Personal communication, Mr. J.E. Moore, Manager Forest Programs,
American Pulpwood Association, Washington, B.C., June, 1975.
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125
(17) Unpublished report, Appendix II Energy Balance, David Camp, Department
of Chemical Engineering, Massachusetts Institute of Technology, June,
1975.
(18) Personal communication, Mr. Robert Doerson, Kraft Paper Company,
Hawesville, Kentucky.
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126
COMPARATIVE COST ANALYSIS
Cost of Wood as Fuel
The fuel value of wood varies greatly with species, water
content, bark content, resin content, and other factors. On the basis of
/•i o o\ ft
heating values for wood from several sources ' ' and the approximate
(4)
composition of Vermont's forest lands, a heating value of 9.35 million
Btu per ton of green wood (45 percent moisture) was taken as an average
for Vermont woods. From some of the same sources and Wood Handbook,
54 pounds per cubic foot was calculated as the average weight of green
Vermont wood.
A 50-MW power plant operating at 27.4 percent efficiency with a
12
load factor of 70 percent will require 3.80 x 10 Btu of fuel energy per
year. At 9.35 x 10 Btu per ton, this requirement translates into about
410,000 tons of green wood per year. At 54 pounds per cubic foot, this
is equivalent to 15.185 x 10 cubic feet of green wood, or about 190,000
cords of wood per year.**
Availability of Wood as Fuel
Five counties in central Vermont (Washington, Orange, Addison,
Windsor, and Rutland) contain 1,921,000 acres of commercial or potentially
(4)
commercial forest land. Statistics relative to growing stock and
annual growth are shown in Table 28. An average acre of commercial forest
land in the five counties contains 1,060 cubic feet of growing stock (Table
28) and the net annual growth throughout the state is 24 cubic feet per
acre. At that rate, the regeneration time for Vermont forests is about
45 years.
Table 29 shows estimates of potential availability of green
wood fuel from the five counties on a sustained-harvest (45-year cycle)
basis. No differentiation is made as to ownership of the forest land,
whether it be private, corporate, Green Mountain National Forest, or
* References are listed on Page 161.
** A cord is considered to be equivalent to 80 cubic feet of solid wood,
excluding bark.
-------
TABLE 28. FOREST LANDS IN FIVE COUNTIES IN CENTRAL VERMONT
Addison Orange Rutland Washington Windsor Total
Total land area, 1000 acres
Commercial forest land area,
1000 acres
Softwood types, 1000 acres
Hardwood types, 1000 acres
6 3
Growing stock, 10 ft
6 3
Softwood, MM 10 ft
£ 3
Hardwood, MM 10 ft
2
Growing stock, ft /acre
Annual growth '
Gross, 1000 ft3
Cull, 1000 ft3
Mortality, 1000 ft
3
Net annual growth, 1000 ft
501.
285.
69.
216.
276.
68.
207.
967
11,758
2,938
1,941
6,879
5
8
5
3
5
7
8
441.
335.
140.
195.
352.
162.
189.
1,049
13,819
3,453
2,281
8,085
7
9
2
7
4
9
5
593.
444.
104.
340.
462.
119.
343.
1,040
18,303
4,574
3,021
10,709
3
9
5
4
8
3
5
452
361
137
224
404
176
228
1,120
14,864
3,714
2,453
8,696
.8
.3
.1
.2
.8
.5
.3
617.
•
492.
123.
369.
540.
151.
389.
1,098
20,266
5,064
3,345
11,857
8
6
6
0
7
2
5
2,607
1,920.5
575
1,346
2,037
679
1,358
1,060
79,010
19,743
13,040
46,226
Source: Reference 4.
a. Volumes of growing stock and annual growth are expressed as cubic feet of sound wood in the bole
from a 1-foot (height) stump to a 4-inch (diameter) top outside the bark (or to where the main
stem branches) of all commercial species trees at least 5-inch dbh (diameter at breast height).
b. These increments of annual growth were calculated for the five counties on the basis of the
following volumes for all of Vermont, as given in Reference 4:
Net Cubic Feet/Acre
Gross growth 41.14
Cull increment 10.28
Mortality 6.79
Net growth 24.07
Cull increment is the volume of trees that were classified as growing stock at the beginning
of the measurement period but were too poor in quality at the end of the period to be so classified.
Mortality is the volume of growing-stock trees that have died since the beginning of the
measurement period.
Net annual growth is gross growth minus cull increment and mortality.
N)
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128
TABLE 29. POTENTIAL AVAILABILITY OF GREEN WOOD FUEL
FROM FIVE VERMONT COUNTIES(a) ON A SUSTAINED-
HARVEST BASIS
Green Wood Available from Annual Growth on 1,920,500 Acres
Net Culls and
Growing Harvest Dead
Stock(b) Harvest(c) Residue(d) Trees(e) Total(f)
Volume ,
6 3
10 ft
1000 Cords (80 ft
Weight,
1000 tons
/cord)
(g)
46,226
578
1,248
43.915
549
1,186
8.783
110
237
26.102
326
705
78.800
985
2,128
a. Addison, Orange, Rutland, Washington, and Windsor Counties contain 1,920,520
acres defined as commercial forest land.
b. From Table 28.
c. Merchantable bole estimated as 95 percent of full tree bole on the basis of
information contained in Reference 6.
d. Slash (top, branches, and foliage) estimated as 20 percent of harvestable bole
on the basis of information contained in Reference 6.
e. Table 28 shows volume of cull trees to be 19.743 million cubic feet of full tree
bole. Slash from cull trees would be 19.743 x 106 x 0.95 x 0.20 = 3.751 ft3.
Total fuel volume would be (19.743 + 3.751)106 = 23.494 x 106 ft3. Table 28
also shows volume of trees that have died since 1966 to be 13.040 million ft3.
If 20 percent of this tree volume is useful for fuel, it would add another
2,608 million ft3, bringing the total fuel volume for culls and dead trees
to 26.102 million cubic feet.
f. Total includes harvest, harvest residue, culls and dead trees.
g. Based on average of 54 pounds per cubic foot of green wood.
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129
other. It can be seen from Table 29 that complete harvesting for fuel
equivalent to the annual growth of merchantable wood, tree residues, and
culls and dead trees throughout the five counties would yield about
2,128,000 tons of green wood, or about five times the requirement for a
50-MW power plant. This usage of the entire annual growth for fuel
would be uneconomic, because it ignores the much higher value of harvestable
sawlogs and poles.
If harvesting for fuel were limited to salvaging the residues
from conventional timber harvesting and removal of culls and dead trees,
the five counties could yield annually about 942,000 tons of green fuel
wood, or about 2.3 times the fuel requirements of a 50-MW power plant.
This appears to indicate that adequate green wood to fuel the power
plant should be available within a radius of about 25 miles. To the
extent that actual clearcutting is practiced and saplings less than 5
inch dbh* are used, that radius could be reduced.
The preceding estimate is based on harvesting green wood
equivalent to 100 percent of the net annual growth within a radius of
25 air miles from the proposed power plant. In 1972, the total wood
(4)
harvested in all of Vermont was only 45 percent of the net annual growth.
If this harvesting percentage is applicable to central Vermont and if
it persists despite the need for fuel for a 50-MW power plant, the
harvesting area would have to be increased to a radius of 35 air miles
from the plant.
It is not clear why only 45 percent of the net annual growth
of Vermont's commercial forest lands was harvested in 1972, in sharp
contrast with 71 percent in 1948 and 74 percent in 1966. Possible
reasons may include reduced markets available to Vermont wood, reduced
availability of forest workers, and inadequate stumpage prices to be
attractive to owners. On the assumptions that stumpage prices will be
attractive to owners, markets will exist for Vermont sawlogs and poles,
and adequate woodsmen will be available, it is estimated that adequate
green wood fuel to operate a 50-MW power plant will be available on a
45-year cycle from harvest residues and dead and cull trees within 30
* dbh - Diameter at breast height (4 feet)
-------
130
air miles of the plant. The average hauling distance should be about 25
miles and the maximum about 45 miles.
Wood Fuel Procurement Costs
Stumpage costs vary considerably with the value of wood being
harvested and the difficulty of harvesting. An average figure for Vermont
/0\
is said to be $2 per cord. At 80 cubic feet per cord and 54 pounds per
cubic foot for green wood, this figures to be $0.93 per ton. By 1980,
if inflation averages 7 percent per year, this value would be $1.30 per
ton. However, this is the value paid for the privilege of harvesting
valuable sawlogs and poles, although the harvest may, in some cases, include
the conversion of woodland residues to pulpwood chips. More commonly the
residues are left to decay on the forest floor (returning nutrients to the
soil) or are piled and burned (also returning nutrients to the soil).
Although not widely practiced in Vermont, the removal of dead
and cull trees for stand improvement costs the landowner about $25 per
acre. In this practice, the wastes are left to decay on the forest floor.
Some landowners may be willing to trade the value of future nutrients
against current improvement costs and permit the removal of dead and cull
trees at no stumpage cost.
It is estimated that the equivalent of stumpage costs for
collecting harvesting residues and dead and cull trees in 1980 will be
about $0.50 per ton. This stipend, added to stumpage for conventional
harvesting, would increase fees paid to the landowner for multiple harvest
by about 40 percent over the normal fees. This might be the inducement
needed to assure the continued availability of adequate fuel resources within
about 30 miles of the plant. Even if it were necessary to triple this
price to assure the availability of wood fuel, it would increase the
overall cost of the fuel by only about 12 percent.
Cost of Harvesting Wood Fuel
Timber in Vermont is currently harvested exclusively by chainsaw
and operator. There has been at least one experiment with mechanical
harvesting and total tree chipping in New Hampshire, ' but it does not
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131
seem likely that mechanical harvesting will soon make much inroad in
Vermont's forests.
Table 30 shows certain 1970 Census Bureau financial data for
SIC 24, Lumber and Wood Products, for New England and for Vermont, and
similar data for SIC 2411, Logging Camps and Logging Contractors, for
(10)*
New England. On the assumption that logging operations in Vermont
bear the same relationship to the lumber and wood products industry that
they do in New England as a whole, comparable figures for Vermont's
logging industry were calculated and these also are shown in Table 30.
Comparable 1972 data are available for New England but not for
Vermont. These data for logging camps and logging contractors are
combined in Table 31 with 1970 data for New England and Vermont to
facilitate calculation of appropriate 1972 data for logging operations
in Vermont.
In 1972, 47 million cubic feet of growing stock were harvested
in Vermont's forests. At 95 percent recovery of full tree bole as saw-
logs and poles, this represents 44.65 million cubic feet of merchantable
wood. From this figure and the estimates of costs shown in Table 31 for
1972, it was possible to calculate the incremental costs of harvesting
wood in Vermont, as shown in the following tabulation:
Payroll
Cost of materials
Taxes, profits, etc.
Value of shipments
$/Ft3,
1972
0.0708
0.1832
0.0862
0.3402
$/Ton
1972
2.62
6.79
3.19
1975(a)
3.30
8.55
4.02
12.60
15.87
(a) Based on inflation at 8 percent per year
* No data are given for SIC 2411 in Vermont. Data for 1971 could have
been used, but Vermont figures for SIC 24 are marked wxth an asterisk,
implying a low degree of reliability.
-------
132
TABLE 30. FINANCIAL DATA, 1970, LUMBER AND WOOD PRODUCTS,
FOR NEW ENGLAND AND VERMONT
Millions of Dollars
Cost of Value of
Payroll Materials Shipments
Lumber and Wood Products
New England 133.1 240.5 482.6
Vermont 13.4 22.1 48.2
Logging Camps, Contractors
New England 29.2 73.3 130.4
Vermont 2.94(a) 6.74(a) 13.02(a)
Source: Annual Survey of Manufactures (Reference 10).
(a) Figures for Vermont logging camps calculated as a ratio with figures
for New England. For example, for Payroll:
13 L
x 29.2 - 2.94.
133.1
-------
133
TABLE 31. FINANCIAL DATA, 1970 AND 1972, LOGGING CAMPS
AND LOGGING CONTRACTORS, FOR NEW ENGLAND AND
VERMONT
New England
1970
1972
Vermont
1970
1972
Millions of Dollars
Interest, Taxes,
Payroll Materials Profit, etc.^
29.2 73.3 27.9
31.4 89.0 31.7
2.94(b) 6.74(b) 3.34
3.16^c) 8.18(c^ 3.85
Value of
Shipments
130.4
152.1
13.02(b)
15.19(C)
Sources: 1970 New England data from Reference (10).
1972 New England data from Reference (11).
a. Interest, taxes, profit, etc. derived by subtracting payroll and
cost of materials from value of shipments.
b. 1970 Vermont data calculated by Battelle (see Table 30).
c. 1972 Vermont data calculated by Battelle as in Footnote (a),
Table 30.
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134
This harvesting cost of $15.87 per ton of wood is misleading
as a cost of harvesting green wood for fuel. It includes stumpage fees,
which were earlier estimated at $0«93 per ton of green wood. Deducting
this cost leaves a cost of $14.34 per ton for actual harvesting costs.
Furthermore, the harvesting of timber boles includes the handling of
approximately 20 percent of slash and a significant quantity of dead
trees, from which some timber is recovered.
It is estimated that the cost of collecting timber residues,
cull trees, and dead trees in conjunction with, but as a separate operation
from, conventional harvesting, would be only about 50 percent of the cost
of conventional harvesting. The use of full-tree chippers in the field
means that most of the cutting would be limited to felling cull trees
and dead trees from which no timber was harvested. Most of the cost
would be concerned with bunching and skidding material to the chipper.
Under these conditions, it is estimated that the cost in 1975 of harvesting
green fuel wood in Vermont would be about $7.60 per ton, exclusive of any
stumpage costs. By 1980, if inflation averages 7 percent per year, har-
vesting costs would be $10.65 per ton of green fuel wood.
Chipping Costs
An average acre of commercial forest land in central Vermont
contains 1,060 cubic feet of growing stock, equivalent to 28.62 tons of
harvestable green timber. The residues from harvesting this timber plus
culls and dead trees would amount to about 22.75 tons per acre (see
Table 29). Based on experience of an in-forest chipping operation in
Michigan, a chipper can operate economically within a radius of about
/-I ON
1/4 mile, or an area of about 125 acres, before moving to a new location.
Approximately 2,850 tons of chips could be produced before the chipper
was moved. The Michigan chipper averaged 200 tons of green chips per
day or 1000 tons per week, including all down time for maintenance,
repairs, moves, etc. On this basis, a chipper in Vermont would move to
a new location about every 3 weeks.
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135
A 50-MW power plant would require 410,000 tons per year of
green wood fuel or about 7900 tons per week. If chippers could operate
260 days per year, eight chippers would be required to fill this need.
Because of days lost to inclement weather, ten or more chippers would
be required.
In the New Hampshire experiment in total tree chipping in the
forest, five men were required in the yard, including the chipper
(Q)
operator. At $3 per hour for 1975 wages, plus 8 percent for manage-
ment, this would require a payroll of $650 per week.
In the Michigan experience in 1974, operating costs for the
yard machinery and chipper, including blowing chips into trucks, but
exclusive of labor, were $777 per 1000 tons of chips, including interest,
taxes, etc.
The cost of in-forest chipping in 1975 is thus estimated at
$1427 per thousand tons, or $1.43 per ton of green chips. By 1980, at
7 percent inflation per year, that cost would be $2.01 per ton.
Transportation Costs
The transportation of chips is best accomplished by truck,
preferably a tractor-trailer with nondumping box. Chips are blown in at
the chipper and the box is unloaded by small front-end loaders, or after
detachment from the tractor, by a tilting platform.
The going rate for hauling chips appears to average about $0.05
per ton mile. With an average hauling distance of 25 miles, hauling
charges in 1975 should average about $1.25 per ton. Inflating this value
by 7 percent per year gives a hauling cost of $1.75 per ton in 1980.
Replacement of Soil Nourishment
This subject is little understood and less practiced. In
normal woodland harvesting, residues are either allowed to decay on the
forest floor or are piled and burned. In either case, most of the
inorganic chemical content of the residues is returned to the soil,
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136
although much nitrogen content is lost, particularly when residues are
burned. The inorganic material that is hauled away in wood products is
completely removed from the forest.
A recent study in Wisconsin delineated the amounts of nitrogen,
phosphorus, potassium, and calcium removed from the forest by whole-tree
harvesting of a 40-year-old aspen-mixed hardwood second-growth forest.
Virtually all trees larger than 1 to 2 inches in diameter were harvested
by a feller-buncher. A total of 111,386 pounds (55.693 tons) of wood
products per acre were removed as chips, sawlogs, waste, and bark.
Elemental analyses were made of the wood products and the following nutrient
losses were calculated:
Wisconsin
Elements
Removed
Nitrogen
Phosphorus
Potassium
Calcium
The same authors estimated that inputs of nitrogen, phosphorus,
and potassium during the next 30 years from precipitation, mineralization,
and weathering would more than balance the amounts of those nutrients
removed at their particular Wisconsin location. The return of calcium
was estimated to be slightly insufficient, such that the calcium reserve
in the soil would support only nine 30-year cycles, and modest addition
of lime would be required.
With a 45-year regeneration cycle, Battelle believes that the
inputs of nutrients to Vermont's forest lands will compensate for
nutrients removed by multiple harvest. However, it is interesting to
see what the cost of such nutrients might be if they had to be replaced.
It was stated earlier that the average harvest of timber in
Vermont would be about 28.62 tons per acre and the average collection of
green wood accompanying such harvest about 22.75 tons per acre. Applying
Pounds
Per Acre
172
24
116
382
Pounds Per Ton
of Wood Product
3.09
0.43
2.08
6.86
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137
the findings in the Wisconsin investigation to the Vermont situation, the
following amount of nutrients would be removed by multiple harvesting:
Pounds Removed Per Acre in Harvesting
Vermont Forests
PrimaryFuelTotal
Nutrient Element Harvest Harvest Harvest
Nitrogen (N) 90 70 160
Phosphorus (^^ 12 10 22
Potassium (K20) 60 47 107
Calcium (CaO) 196 156 352
Fertilizer prices are published periodically by the U.S.
(14)
Department of Agriculture. The following tabulation shows fertilizer
ingredient prices in Vermont in April, 1975, from which the cost per
pound of the various nutrients is calculated:
Vermont. April. 1975
Price, Nutrient
Fertilizer Ingredient $/ton Ib/ton $/lb
Urea, 45.5% N 290 910 0.3187
Superphosphate, 20% P^ 135 400 0.3375
Potash, 60% K20 135 1200 0.1125
Limestone, 47% CaO 20* 940 0.0213*
Figures from these two tabulations were used to calculate the
1975 cost of nutrients removed from Vermont forest lands by multiple
harvest. These costs are shown in Table 32. The cost of buying fertilizer
materials to replace the removed nutrients would be about $1.45 per ton
of wood, with perhaps an additional $0.50 per ton of wood as the cost
of application. As mentioned earlier, Battelle believes that these nutrients
will be restored naturally, and the cost of fertilization is not included
in the sustained-harvest cost of wood fuel.
* For limestone, price includes cost of application.
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138
TABLE 32. COST OF NUTRIENTS REMOVED Bt MULTIPLE
HARVEST IN VERMONT'S FOREST LANDS
Dollars Per Acre
Nutrient
Nitrogen (urea)
Phosphorus (superphosphate)
Potassium (potash)
Calcium (limestone)
Primary
Harvest
28.68
4.05
6.75
39.48
1.96(a>
Fuel
Harvest
22.31
3.38
5.29
39.98
1.56(a>
Total
50.99
7.43
12.04
70.46
3.52(a)
Dollars
Per
Ton of
Wood
1.00
0.14
0.24
1.38
0.07(a)
(a) For limestone, cost includes cost of application.
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139
Power Plant Costs Using Wood Fuel
The operating costs of a power plant include costs of the basic
plant, fuel, operations and maintenance, emission controls, cooling
facilities, water, water conveyance, and transmission. For the hypo-
thetical 50-MW power plant in central Vermont, some of these factors
would be constant regardless of fuel, but difficult to determine without
a detailed, site-specific study. Consequently, estimates of power plant
nonfuel costs for burning the various fuels to generate electricity
include annual costs of the basic plant (once-through water cooling),
emission controls, and operation and maintenance, but do not include
costs of water, water conveyance, and transmission of electricity. Table
33 shows estimated costs of burning coal, oil, and wood in a 50-MW power
plant in 1980. The method for estimating these costs is discussed in
the following paragraphs.
Petruschell and Salter compared 1972 costs of nuclear, coal,
oil, and natural gas power plants and projected these costs to 1985.
They found the average capital investment for a 1000-MW coal plant in 1972
to be $143 million, and that for a 1000-MW oil plant to be $139 million.
Annual costs associated with these investments for a 70 percent load
factor would be $39.2 million for coal and $36.1 million for oil. Using
the 0.6 factor to adjust for plant size and escalating costs by 7 percent
per year, the capital investment in 1980 for a 50-MW coal plant should be $40.7
million and that for an oil plant should be $39.5 million. Annual costs
for a coal plant should be $6.50 million and those for an oil plant
$5.99 million. Battelle estimates the 1980 capital investment for a 50-
MW wood-fired plant to be $40 million and the annual cost to be $6.23 million.
Emission control costs are far from being firmly established.
McGlamery and Torstrick examined investment and operating costs for a
variety of flue gas desulfurization processes, including particulate
removal/153^ Based on 1974 construction costs and estimated 1975
operating costs, they estimated a capital cost of $27,452,000 and an average
annual cost of $8,101,900 for a typical lime slurry process for a new 500-
MW plant burning coal containing 3.5 percent sulfur. Adjusting for plant
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140
TABLE 33. ESTIMATED COSTS OF BURNING-VARIOUS FUELS
IN A 50-MW POWER PLANT - 1980
$. million
Capital
Investment
Annual
Cost
Mills/kwh
Basic Plant
Coal
Oil
Wood
Emission Control
Coal (SO. plus parti-
culates)
Low-sulfur coal (parti-
culates)
Oil (particulates)
Wood (particulates)
Dual, wood/low-sulfur
coal (particulates)
Operation and Maintenance
40.6
39.5
40.0
6.50
5.97
6.24
21.2
19.5
20.4
10.4
2.85
9.3
3.5
3.1
2.5
3.5
__
0.97
0.86
0.69
0.97
0.71
3.2
2.8
2.3
3.2
2.33
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141
size and escalating costs at 7 percent per year, the capital investment
in 1980 for emission control for a 50-MW coal plant should be $10.4 million
and the annual cost should be $2.85 million. Battelle estimates the 1980
investment for emission control for a 50-MW oil plant (particulates only)
will be $3.1 million and for a similar wood plant (particulates only) will
be $2.5 million. Annual costs will be $860,000 for oil and $690,000 for
wood.
Operation and maintenance costs should be essentially the same
for coal-fired, oil-fired, or wood-fired plants. On the basis of infor-
mation derived from Petruschell and Salter, 5^ these costs in 1980 for
a 50-MW plant should average $710,000.
The cost (within the plant) of generating electricity with a
particular fuel is the sum of the annual costs for plant, emission con-
trol, and operation and maintenance factors. For a 50-MW wood-burning
plant, the annual cost in 1980 of these factors from Table 33 is $7.63
million.
Summary of Wood Fuel Costs
The various cost elements of producing and burning wood to
generate electricity in a 50-MW power plant in central Vermont are sum-
marized in Table 34.
Costs of Various Coal Fuels
The 50-MW power plant in central Vermont might be fired with
other fuels under conditions that would meet environmental standards. The
alternative fuel systems to be considered here are low-sulfur coal,
physically cleaned coal from Pennsylvania, and high-sulfur coal with stack
gas desulfurization.
Low-Sulfur Coal
The nearest reliable source of low-sulfur coal to Vermont is
subbituminous coal in Wyoming. This coal contains less than 1 percent
sulfur and has an average heating value of 19 million Btu per ton.
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142
TABLE 34. THE COST OF WOOD AS A FUEL TO GENERATE
ELECTRICITY IN VERMONT - 1980
Cost Element
Procurement (stump age)
Harvesting
Chipping
Transportation
Basic plant
Emission control
Operation and mainte-
nance
Total
$/ton
0.50
10.65
2.01
1.75
—
—
—
14.91
Cost
$/year(a)
204,800
4,366,500
824,100
717,500
6,230,000
690,000
710,000
13,743,000
Mills /kwh
0.67
14.24
2.68
2.34
20.32
2.25
2.32
44.82
(a) A 50-MW power plant operating at 70 percent load factor
requires 410,000 tons of green wood per year.
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143
Mining Costs. Most Wyoming coal is recovered by strip mining.
The U.S. Bureau of Mines estimated capital investment, operating costs,
and selling price for a strip mine in the Northern Great Plains as of
May, 1974. This hypothetical mine was based on production of 9.2
million tons per year, with a life span of 20 years and a discounted
cash flow of 12 percent. The Bureau estimated initial capital investment
at $29,871,000 and total capital investment at $56,286,000. The operating
cost for such a mine was estimated at $2.27 per ton and the selling price
of the coal at $2.66 per ton.
The actual prices of several deliveries of Wyoming coal to
nearby electric utilities (in the same or adjacent county as the strip
mine) averaged $3.97 per ton from February through April of 1975. '
This figure was taken as the average FOB price of strip-mined Wyoming
subbituminous coal delivered to the rather sparse railroads. If coal
is to fill the energy need projected for it during the coming decades,
it seems likely that coal costs will increase by at least 10 percent per
year through 1980. At this inflation rate, the FOB price for Wyoming
strip-mined subbituminous coal should be about $6.40 per ton by 1980.
Shipping Costs. Battelle has found no record of shipments of
Wyoming coal to New England. Freight costs vary considerably with type
of shipment (unit train, complete train load, single car), size of
shipment, distance, geographical area, and time (seven rate increases
from January 1, 1974, to June 8, 1975). On the basis of a comprehensive
study of shipping costs, the U.S. Bureau of Mines estimated the 1970
cost for shipping coal from Cheyenne, Wyoming, to Boston, Massachusetts,
under "best practice" conditions (shipment greater than 80,000 tons) was
$0.523 per million Btu. (18) At 19 million Btu per ton, this would be
$9.94 per ton for Wyoming subbituminous coal. The Bureau also estimated
an average increase of $1.40 per ton for shipments less than 8000 tons,
bringing the average freight cost to $11.34 per ton. Battelle estimates
the additional cost of routing the shipment to central Vermont would
bring the 1970 freight to $12 per ton. The various ex parte freight
rate increases since 1970 bring the current average rate from Wyoming
to central Vermont to $19.25 per ton.
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144
An approach to estimating escalation of shipping costs based
on correlating elements of operating costs to the GNP deflator for the
(19)
period from 1960 to 1973 was used by Aude, et al. in comparing
slurry-pipeline systems with railroad systems for moving various solids.
At a general inflation rate of 7 percent per year, the escalation for
rail freight costs would be 11.9 percent per year. This escalation rate
checks very well for the period 1972 to 1975 ($19.25/ton versus $19.45/
ton with actual ex parte rate increases). Applying the same rate of
escalation to the $19.45 freight for 1975 gives $34.12 per ton for 1980.
Power Plant Costs. The information derived from Petruschell
and Salter and McGlamery and Torstrick was used to estimate the
nonfuel cost of generating electricity with low-sulfur coal as in the
section on Power Plant Costs Using Wood Fuel. The capital investment in
1980 for a 50-MW plant burning low-sulfur coal should be about the same
as that for a typical coal plant, or about $40.7 million. However, the
investment for emission controls should be about $3.5 million.
Annual costs in 1980 for a 50-MW plant burning low-sulfur coal
and operating at a 70 percent load factor should be about $6.5 million
for the basic plant and $970,000 for emission control, or about $8.2
million for plant, emission control, and operations and maintenance.
Summary of Low-Sulfur Coal Costs. The various cost elements
associated with using low-sulfur subbituminous coal from Wyoming to
generate electricity in a 50-MW power plant in central Vermont are sum-
marized in Table 35.
Physically Cleaned Coal
The most likely candidates as sources of high-sulfur coal that
can effectively be physically cleaned are the upper and lower Kittanriing
and upper and lower Freeport beds in southwestern Pennsylvania. Coal
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145
TABLE 35. THE COST OF LOW-SULFUR COAL FROM WYOMING TO
GENERATE ELECTRICITY IN VERMONT - 1980
Cost Element
Mining
Transportation (rail)
Basic plant
Emission control
Operation and mainte-
nance
Total
Cost
$/ton $/year(a)
6.40 1,088,000
34.12 5,800,400
6 , 500 , 000
970,000
710,000
40.52 15,068,000
Mills /kwh
3.55
18.92
21.20
3.16
2.32
49.15
(a) A 50-MW power plant operating at 70 percent load
factor requires 170,000 tons per year of low-sulfur
coal having a heating value of 19 million Btu/ton.
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146
losses ranging from 10 percent to 50 percent accompany physical cleaning
of coal. In the five Pennsylvania counties in which these coal beds are
mined most extensively, losses on cleaning coal from about 3 percent
sulfur to 1 percent or less average about 20 percent of the original
coal. However, the Kittanning and Freeport coals in these counties
average only about 1.7 percent sulfur. Battelle believes the losses
incurred in cleaning such coals to approximately 0.7 percent sulfur will
not exceed 10 percent.
Mining Costs. About 65 percent of the bituminous coal produced
in Pennsylvania comes from deep mines. Furthermore, 95 percent of the
State's reserves (28 inches or more in thickness to a maximum depth of
1000 feet) are in deep seams, and only 5 percent are recoverable by
surface mining. Consequently, the cost of Pennsylvania coal is high and
prospects are that it will continue to be high.
The U.S. Bureau of Mines estimated 1973 capital investments,
operating costs, and selling prices for several sizes of underground
bituminous coal mines operating in 72-inch coal beds. For a mine
producing 1.06 million tons per year, they estimated an initial capital
investment of $12,541,000 and a total capital investment of $21,851,000.
With a life of 20 years and assuming a 12 percent discounted cash flow,
they estimated operating cost at $7.35 per ton and selling price at
$8.76 per ton.
The actual prices of 31 deliveries of western Pennsylvania
coal to nearby electric utilities (within the same county) from January
through May of 1975 averaged $20.30 per ton. This figure was taken as
the average price of coal delivered to a coal cleaning plant, although
the increment for local transportation might actually be made after
cleaning rather than before. By 1980, at 10 percent escalation per year,
this price for mined and locally delivered coal, would be about $32.70
per ton.
Cleaning Costs. The hypothetical 50-MW power plant in central
Vermont will require 123,000 tons of cleaned Pennsylvania coal per year at
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147
26.2 million Btu per ton and containing 0.7 percent sulfur. With a 10
percent loss on cleaning, this will require a feed of 137,000 tons per
year of coal containing 1.7 percent sulfur, or 570 tons per day (240
working days per year). At 40 hours operation per week, a plant of
this size would not be very economic. Although cleaning plants of such
a size exist, they are generally not equipped adequately to do as good
a job of cleaning as is required here.
A cleaning plant that will handle 600 tons per hour of raw
coal should be equipped to do economically the required cleaning job.
On the basis of a study done at Battelle in 1974, the capital cost of
a 600-ton-per-hour physical cleaning coal plant in 1974 was $7.88 million.
On the basis of a coal feed containing 24 million Btu per ton, a loss of
15 percent, and a price for raw coal of $12 per ton, a cleaning cost of
$0.14 per million Btu or $3.36 per ton was found. Adjusting these costs
for the coal under consideration in this report (26.2 million Btu per
ton, 10 percent loss on cleaning, $20 per ton for raw coal) gives a current
cost of $0.17 per million Btu or $4.45 per ton for cleaning. At 9 percent
escalation per year (a compromise between coal at 10 percent and general
economy at 7 percent), the cost in 1980 for cleaning coal would be about
$6.85 per ton.
Shipping Costs. Utilizing information published by the U.S.
Bureau of Mines^18^ and Aude, et al. ^ and the technique discussed in
the subsection on Shipping Costs in the section on Low-Sulfur Coal,
Battelle estimates the average cost for shipping coal from western
Pennsylvania (District 2) to Vermont is currently $13.38 per ton. By
1980, this cost should be $23.48 per ton.
Power Plant Costs. The method described in the section on
Power Plant Costs Using-Wood Fuel, based on information published by
Petruschell and Salter(15) and McGlamery and Torstrick 15a , was used
to estimate the nonfuel cost of using cleaned coal (0.7 percent sulfur)
to generate electricity. The capital intrant in 1980 for a basic 50
MW plant burning physically cleaned coal should b- about the same as t
[-V
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148
for a typical basic coal plant, or abotst $40.7 million. The gaseous
effluent from burning coal with a sulfur content of 0.7 percent and
with a heating value of 26.2 million Btu per ton will not exceed the
limit on sulfur oxide emissions (1.2 pounds SO- per million Btu) imposed
by the Clean Air Act of 1970 on fossil fuel-burning equipment started
after August 17, 1971, and having a capacity of more than 250 million
Btu, which is equivalent to 1.15 pounds of S02 per million Btu. Battelle
estimates the investment for particulate emission control should be
about $3.5 million.
Annual costs in 1980 for a 50-MW plant burning physically
cleaned coal and operating at a 70 percent load factor should total
about $8.2 million for the basic plant, emission control, and operation
and maintenance.
Summary of Cleaned Coal Costs. The various costs associated
with using physically cleaned bituminous coal from western Pennsylvania
to generate electricity in a 50-MW power plant in central Vermont are
summarized in Table 36.
High-Sulfur Coal with Stack Gas Cleaning
The sulfur content of coal mined in west central Pennsylvania
ranges generally between 2.8 percent and 4.5 percent and the heating
value ranges from 24 million to 26 million Btu per ton. An average
sulfur content of 3.3 percent and heating value of 25 million Btu per
ton were assumed. Although this coal from District 1 is less amenable
to physical cleaning than the Kittanning and Freeport coals from District
2, it is located a little closer to Vermont and transportation costs will
be a little lower.
Mining Costs. Mining costs of the bituminous coal from District
1 should be essentially the same as those from District 2. Consequently,
the price of coal delivered to a railroad loading facility in the same
county should average about $32.70 per ton by 1980.
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149
TABLE 36. THE COST OF USING CLEANED PENNSYLVANIA BITUMINOUS
COAL TO GENERATE ELECTRICITY IN VERMONT - 1980
Cost Element
Mining
Cleaning
Transportation (rail)
Basic plant
Emission control
Operation and mainte-
nance
Total
Cost
$/ton $/year(a)
32.70 4,022,100
6.85 842,550
23.41 2,880,000
6,500,000
970,000
710 , 000
62.96 15,925,000
' Mills /kwh
13.12
2.75
9.39
21.20
3.16
2.32
51.94
(a) A 50-MW power plant operating at 70 percent load factor
requires 123,000 tons per year of physically cleaned coal
having a heating value of 26.2 million Btu/ton.
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150
(IB
Shipping Costs. Using the same sources ' and technique used
in the earlier estimates of shipping costs, Battelle estimates the average
cost for shipping coal from west central Pennsylvania (District 1) to
Vermont is currently $12.69 per ton and will be $22.26 per ton by 1980.
Power Plant Costs. Using the same sources ' and technique
used in the earlier estimates of nonfuel costs of generating electricity,
the cost was estimated for burning high-sulfur coal and employing stack
gas cleaning. The capital investment in 1980 for a basic 50-MW plant
burning high-sulfur coal should be about $40.7 million. However, the
investment for emission control (sulfur oxides and participates) should
be about $10.4 million.
Annual costs in 1980 for a 50-MW plant burning high-sulfur coal
and operating at a 70 percent load factor should be about $6.5 million
for the basic plant, $2.85 million for emission control, and $710,000
for operation and maintenance.
Summary of High-Sulfur Coal Costs. The various costs associated
with using high-sulfur bituminous coal from west central Pennsylvania with
stack gas cleaning to generate electricity in a 50-MW power plant in
central Vermont are summarized in Table 37.
Dual System - Green Wood Plus Cleaned Coal
It is possible that fresh supplies of green wood fuel could be
shut off for weeks or even months at a time. In such an event, it would
be desirable to have a system that could burn wood or coal interchangeably.
For this analysis, it will be assumed that 75 percent of the annual Btus
will be provided by green wood and 25 percent by physically cleaned coal.
Wood Fuel Costs. About 308,000 tons of green wood will be
required annually to provide 75 percent of the heat requirement for a 50-
MW p^wer plant operating at 70 percent load factor. It is anticipated that
the cost per ton for this wood will be the same as the cost per ton for
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151
TABLE 37. THE COST OF USING HIGH-SULFUR PENNSYLVANIA BITUMINOUS
COAL WITH STACK GAS CLEANING TO GENERATE ELECTRICITY
IN VERMONT - 1980
Cost Element
Mining
Transportation
Basic plant
Emission control
Operation and mainte-
nance
Total
Cost
$/ton $/year(a)
32.70 4,218,000
22.26 2,871,500
6,500,000
2,850,000
710,000
54.96 17,150,000
Mills /kwh
13.76
9-37
21.20
9.30
2.32
55.94
(a) A 50-MW power plant operating at 70 percent load factor
requires 129,000 tons per year of high-sulfur coal
having a heating value of 25 million Btu per ton.
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152
wood to supply 100 percent of the heat requirement for the power plant.
-j
Physically Cleaned Coal Costs. About 31,000 tons of physically
cleaned coal will be required annually to provide 25 percent of the heat
requirement for a 50-MW power plant operating at 70 percent load factor.
This is not a sufficient quantity of coal to attract a favorable contract
price. Battelle estimates the cost per ton for mining and cleaning this
small amount of coal will be about 10 percent higher than the costs would
be if cleaned coal were the only fuel used.
Power Plant Costs. The cost of a power plant to burn wood or
coal interchangeably will be somewhat greater than the cost of a power
plant to burn either fuel solely. Dual capabilities will be required for
receiving, storage, and conveyance of the fuels to a fuel hopper or
feeder. Fuel feeding and burning capabilities must be sufficiently flexi-
ble to handle either high-volume, low-density wood fuel or low-volume,
high-density coal. Probably a spreader-stoker firing system with water-
cooled grate would be employed, and ash handling capabilities would have
to be sufficient to handle 100 percent coal firing. Farticulate control
would have to be sufficient to handle 100 percent wood firing, but no
other emission controls would be required.
Battelle estimates the 1980 capital investment for a 50-MW
dual-fired (wood and cleaned coal) plant will be $40.9 million and the
annual cost will be $6.65 million. The investment for emission controls
will be about $3.5 million and annual costs will be about $970,000.
Summary of Dual System Costs. The various costs associated
with burning green wood and physically cleaned coal interchangeably to
generate electricity in a 50-MW power plant in central Vermont are sum-
marized in Table 38.
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153
TABLE 38. THE COST OF USING GREEN WOOD AND PHYSICALLY CLEANED
COAL INTERCHANGEABLY TO GENERATE ELECTRICITY IN
VERMONT - 1980
Cost Element
Procurement (stump age)
Harvesting
Chipping
Transportation (truck)
Mining
Cleaning
Transportation (rail)
Basic plant
Emission control
Operation and mainte-
nance
Total
$/ton
0.50
10.65
2.01
1.75
35.97
7.54
23.41
—
—
Cost
$/year(a)
154,000
3,280,000
619,000
5 39 , 000
1,115,000
234,000
726,000
6,650,000
970,000
750,000
15,037,000
Mills /kwh
0.50
10.70
2.02
1.76
3.64
0.76
2.37
21.70
3.16
2.45
49.06
(a) Assumes 75 percent of annual heat requirement will be
provided by wood and 25 percent by cleaned coal. A
50-MJ power plant operating at 70 percent load factor
will require 308,000 tons of green wood and 31,000 tons
of cleaned coal per year.
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154
Comparison of Various Solid Fuel Costs
Table 39 shows the estimated costs of using wood in Vermont to
fire a 50-MW power plant in 1980 compared with similar costs for using
low-sulfur subbituminous coal from Wyoming, cleaned bituminous coal from
Pennsylvania, high-sulfur bituminous coal from Pennsylvania with stack
gas cleaning, and a dual system comprising 75 percent wood and 25 percent
cleaned coal.
If all of the assumptions made in this analysis are valid, it
appears that the use of green wood fuel to generate electricity in Vermont
is economically feasible.
Sensitivity of Power Generation Costs toChanges
in Costs of Various Inputs
The effects on power generation costs of 25 percent increases
and 25 percent decreases in fuel costs, transportation costs, emission
control costs, and plant sizes were determined for 50-MW power plants
in central Vermont burning green wood, low-sulfur coal, cleaned coal,
high-sulfur coal with stack gas cleaning, and 75 percent green wood, 25
percent cleaned coal.
Effect of Changing Fuel Costs
The calculated impacts of 25 percent increases and decreases of
the various fuel costs on the costs of power generation are shown in Table 40.
Generation cost at the wood-fired plant is most sensitive to changes in
fuel costs and that at the plant fired with low-sulfur fuel is least
sensitive.
Effect of Changing Transportation Costs
The calculated impacts of 25 percent increases and decreases in
transportation costs on the costs of power generation are shown in Table 41.
Generation cost at the wood-fired plant is least sensitive to changes in
transportation costs and that at the plant fired with low-sulfur coal
-------
TABLE 39. THE ESTIMATED COSTS OF USING VARIOUS FUELS TO GENERATE ELECTRICITY IN VERMONT - 1980
Green Wood
Cost Elament
Procurement
Harvesting
Chipping
Mining
Cleaning
Transportation
Plant
Emission control
Operation and maintenance
Total
$M/year
205
- A, 366
824
718
6,230
690
710
13,743
Mills/tarn
0.67
14.24
2.68
2.34
20.32
2.25
2.32
44.82
Low-Sulfur
Coal (Wyoming)
$M/year
1.088
5,800
6,500
970
710
15,068
Mills
3.
18.
21.
3.
2.
49.
*
/kwh
55
92
20
16
32
15
Cleaned Coal
(Pennsylvania) ,
$M/year Mills/kwh
4,022
843
2,880
6,500
970
710
15,925
13.12
2.75
9.39
21.20
3.16
2.32
51.94
High-Sulfur Coal
Stack Gas Cleaning
(Pennsylvania) ,
$M/year
4,218
2,872
6,500
2,850
710
17,150
Mills/kwh
13.76
9.37
21.20
9.30
2.32
55.94
75% Green Wood
25% Cleaned Coal.
$M/year
154
3,280
619
1,115
234
1,265
6,650
970
750
15,037
Mills/kwh
0.50
10.70
2.02
3.64
0.76
4.13
21.70
3.16
2.45
49.06
-------
156
TABLE 40. SENSITIVITY OF POWER-GENERATION COSTS TO FUEL COSTS
50 MW POWER PLANT, CENTRAL VERMONT - 1980
Mills per kwh
Cost
Projected Fuel Cost
to Increased Decreased
1980 257o 257»
Percent Change In
Generation Cost
with Indicated
Change in Fuel Costs
257= 257=,
Increase Decrease
Green Wood
Fuel
Generation
17.59
44.82
21.99
49.22
13.19
40.42
+ 9.8
- 9.8
Low-Sulfur Coal
Fuel
Generation
3.55 4o44 2.66
49.15 50.04 48.26 + 1«8
- 1.8
Cleaned Coal
Fuel
Generation
High-Sulfur Coal with
Stack-Gas Cleaning
Fuel
Generation
15.87
51.94
19.84
55.91
11.90
47.97
13.76
55o94
17.20
59o38
10.32
52.50
+ 7.6
- 7.6
+ 6.2
- 6.2
75% Green Wood. 25%
Cleaned Coal
Fuel
Generation
17.62
49.06
22.06
53.48
13.22
44.60
+ 9.0
- 9.0
-------
1S7
TABLE 41. SENSITIVITY OF POWER-GENERATION COSTS TO TRANSPORTATION COSTS
50 MW POWER PLANT, CENTRAL VERMONT - 1980
Green Wood
Transportation
Generation
Low-Sulfur Coal
Transportation
Generation
Cleaned Coal
Transportation
Generation
High-Sulfur Coal with
Stack-Gas Cleaning
Transportation
Generation
75% Green Wood, 25%
Cleaned Coal
Transportation
Generation
Mills
Cost
Projected
to
1980
2.34
44.82
18o92
49.15
9.39
51.94
9.37
55.94
. 4.13
49.06
per kwh
Transportation Cost
Increased
25%
2.93
45.41
23.65
53.88
11.74
54.29
11.71
58.28
5..16
50.09
Decreased
257=
1.76
44.23
14.19
44.42
7o04
49.59
7.03
53.60
3.10
48.03
Percent Change in
Generation Cost with
Indicated Change in
Transportation Cost
25% 25%
Increase Decrease
+1.3 -1.3
+9.6 -9.6
+4.5 -4.5
+4o2 -4o2
+2.1 -2.1
-------
158
is most sensitive. When fuel costs and transportation costs are combined,
the changes in power generation costs tend to equalize for the five types
of plants, but costs at the plant using cleaned coal are the most sensitive
and those at the plant burning high-sulfur coal are least sensitive.
Effect of Changing Costs of Pollution Control
The calculated impacts of 25 percent increases and 25 percent
decreases in costs of pollution control on the costs of power generation are
shown in Table 42. Generation costs at the plant burning high-sulfur coal
with stack gas cleaning are more sensitive to changes in pollution control
costs than are those at any of the other plants.
Effect of Changing Plant Size
The calculated impacts of 25 percent increases and 25 percent
decreases in plant size on the costs of power generation are shown in
Table 43. Note that increased costs of generation are associated with
decreased plant size, and vice versa. Generation costs at the plant
burning high-sulfur coal are slightly more sensitive to plant size than
are generation costs at other types of plants.
-------
159
TABLE 42. SENSITIVITY OF POWER-GENERATION COSTS TO POLLUTION-CONTROL COSTS
50 MW Power Plant, Central Vermont - 1980
Mills
Cost
Projected
per kwh
Pollution-
Control Cost
to Increased
1980 25%
Green Wood
Emission -Control
Generation
Low-Sulfur Coal
Emission Control
Generation
Cleaned Coal
Emission Control
Generation
High-Sulfur Coal with
Stack-Gas Cleaning
Emission Control
Generation
75% Green Wood, 25%
Cleaned Coal
Emission control
Clano TTQ t" 4 rvn
2.25
44.82
3.16
49.15
3.16
51.94
9.30
55o94
3.16
49.06
2.81
45.38
3.95
49.94
3.95
52.73
11.63
58»27
3.95
40.85
Decreased
25%
1.69
44.26
2.37
48.36
2.37
51.15
6,98
53.62
2.37
48.27
Percent Change in
Generation Cost with
Indicated Change In
Emission-Control Cost
257= 257,
Increase Decrease
+1.2 -1.2
4-1.6 -1.6
+1.5 -1.5
+4.2 -4.2
+1.6 -1.6
-------
160
TABLE 43. SENSITIVITY OF POWER-GENERATION COSTS TO PLANT SIZE
50 MW Power Plant, Central Vermont - 1980
Mills
Cost
per kwh
/_\
Plant Costvs*'
Projected Size
to Increased
1980 25%
Green Wood
Plant
Generation
Low- Sulfur Coal
Plant
Generation
Cleaned Coal
Plant
Generation
High-Sulfur Coal with
Stack-Gas Cleaning
Plant
Generation
75% Green Wood, 25%
Cleaned Coal
Plant
Generation
22.57
44.82
23.45
49.15
23.45
51.94
30.50
55.94
23.95
49.06
20. ,64
42.89
21.45
47.15
21.45
49.94
27.89
53.33
21.89
47.00
Size
Decreased
25%
25.33
47.58
26.31
52.01
26.31
54.80
34.22
59.66
26.88
51.99
Percent Change in
Generation Cost with
Indicated Change in
Plant Size
25% 25%
Increase Decrease
-4.3 +6.2
-4'1 +5.8
-3-9 +5.5
-4.7 +6.6
•
-4.2 +6.0
(a) Plant costs include both the basic plant and emission control facilities,
which will change in size with the plant.
-------
161
References
(1) R. H. Perry, C. H. Chilton, and S. D. Kirkpatrick, Perry's Chemical
Engineers' Handbook, Fourth Edition, McGraw-Hill Book Company, New
York (1963), Section 9, p. 5.
(. ) J. K. Salisburg, Power Volume, Kent's Mechanical Engineers' Handbook,
C. Carmichael, editor, 12th Edition, John Wiley and Sons, New York
(1950), Section 2. p- 40.
(3) S. £. Corder, "Wood and Bark as Fuel", Research Bulletin 14, Forest
Research Laboratory, School of Forestry, Oregon State University,
Corvallis, Oregon (August, 1973), pp. 8-10.
(4) J. E. Barnard and T. M. Bowers, "A Preview of Vermont's Forest Resource",
U.D. Forest Service Note NE-196, Forest Service, U.S. Department of
Agriculture, Northeast Forest Experiment Station, Upper Darby, Penna.
(1974), 6 pps.
(5) Wood Handbook, Agriculture Handbook No. 72, The Forest Products
Laboratory, Forest Service, U.S. Department of Agriculture (1955),
pp. 55-57.
(6) J. L. Keays, "Complete-Tree Utilization, An Analysis of the Literature",
Part I: Unmerchantable Top of Bole, Information Report VP-X-69 and
Part IV: Crown and Slash, Information Report VP-X-77, Forest Products
Laboratory Canadian Forest Service, Department of Fisheries and Forestry,
Vancouver, B.C. (February and March, 1971).
(7) C. M. Newton, "Revised Report* on the Inventory of Vermont's Wood Supply",
Report to the Governor's Task Force on Wood as a Source of Energy
(1/16/75), Table 6.
(8) Leo Laferriere, Manager, Laird Properties and Ward Lumber Company,
Waterbury, Vt., draft of report on "Wood Procurement , (1975).
(9) A. W. Wimble, "Total Tree Chipping Study in New Hampshire", American
Pulpwood Association, Technical Release 73-R-24 (July 11, 1973), 7 pp.
(10) Annual Survey of Manufactures, 1970-1971, U.S. Department of Commerce,
Bureau of the Census (September, 1973), pp 172, 178.
the Census, February, 1975.
(12) Harry Morey, Total Chips, Inc., Shepard, Michigan, private communication.
1973).
-------
162
(14) Agricultural Prices, Pr 1 (4-75), U.S. Department of Agriculture,
Statistical Reporting Service, Crop Reporting Board (April 30, 1975),
p 27.
(15) R. L. Petruschell and R. G. Salter, "Electricity Generating Cost Model
for Comparison of California Power Plant Siting Alternatives", R-1087-
RF/CSA, Rand (January, 1973), 32 pp.
(15a) McGlamery, G. G. and Torstrick. R. L. , "Cost Comparisons of Flue Gas
Desulfurization Systems", paper prepared for presentation at Flue Gas
Desulfurization Symposium sponsored by the Environmental Protection
Agency, Atlanta, Georgia (November 4-7, 1974), 73 pp.
(16) Sidney Katell and E. L. Hemingway, "Basic Estimated Capital Investment
and Operating Costs for Coal Strip Mines", Information Circular 8661,
U.S. Department of the Interior, Bureau of Mines (1974), 31 pp.
(17) Coal Week, Vol. 1, several issues. A McGraw-Hill publication published
weekly by Coal Age/Keystone Coal Industry Manual/Oilgram News Service/
Oilgram Price Service.
(18) P. H. Mutschler, R. J. Evans, and G. M. Larwood, "Comparative Transportation
Costs of Supplying Low-Sulfur Fuels to Midwestern and Eastern Domestic
Energy Markets", Information Circular 8614, U.S. Department of the
Interior, Bureau of Mines (1973), 54 pp.
(19) T. C. Aude, T. L. Thompson, and E. J. Wasp, "Slurry-Pipeline Systems for
Coal, Other Solids Come of Age", Oil and Gas Journal (July 21, 1975),
pp 66-72.
(20) Sidney Katell and E. L. Hemingway, "Basic Estimated Capital Investment
and Operating Costs for Underground Bituminous Coal Mines'", Information
Circular 8632, U.S. Department of the Interior, Bureau of Mines (1974),
41 pp.
-------
163
ENVIRONMENTAL-ECOLOGICAL IMPACTS OF WOOD FUEL USE
The objectives of this effort are to review and evaluate existing
information on the environmental impacts of the forest management practices
which are proposed for the procurement of wood-derived fuels in Vermont.
Environmental effects considered are: (1) silvicultural practices: nutrient
budget; (2) stream water quality impacts of tree harvesting; (3) soil
erosion; (4) effects on wildlife; and (5) aesthetics. Recommendations for
(a) forest management practices needed to minimize environmental impacts,
and (b) additional studies which are needed to correlate wood procurement
practices with environmental impacts, are presented.
Silvicultural Practices; Nutrient Budget
The current interest in managing forest residuals has raised a
number of questions pertaining to the stability and longivity of American
forests. A review of the literature on environmental impacts of forest
management practices related to soil nutrient removal and its effects on
forest productivity indicate that definitive, comparable data are not
available. No studies of this kind have been published about the forests
of Vermont.
Three aspects of silvicultural practices - soil nutrient removal
are discussed: (1) nutrient removal; (2) nutrient inputs; and (3) rotation
periods.
Nutrient Removal
Forests remove definable amounts of nutrient materials from the
soil each year. The rate of uptake depends on many factors, i.e., stocking,
species of tree, age of stand, soil nutrient availability, available moisture,
etc. For example, Jorgensen et al(1)* indicate that a 16-year old pine
plantation, in North Carolina, removed 321 Kg/ha of nitrogen, 48 Kg/ha of
phosphorous and 226 Kg/ha of potassium (Table ,44). These trees were
growing at a stocking rate of 2,243 stems per hectare with a site index of
68 at age 25.
References for this Section are given on page 202
-------
164
TABLE 44. DISTRIBUTION OF TREE BIOMASS AND NUTRIENTS
IN A 16-YEAR-OLD LOBLOLLY PINE PLANTATION
IN THE NORTH CAROLINA PIEDMONT
Component
Trees
Needles
Branches
Stemwood
Stem Bark
Root Total
Total Tree
Forest Floor
Mineral Soil, 0-70 cm
Site Total
T/ha
Biomass
8.0
23.2
109.6
15.2
36.3
192.3
-
-
N
82
60
79
36
64
321
307
1,753
2,381
Kg/ha
p(a)
10
6
11
4
17
48
30
371
449
K(a
48
28
65
24
61
226
28
404
658
(a)
Total in vegetation and forest floor and extractable
in mineral soil
Source (1)
-------
165
As shown in Table 45, a wide variation exists in the amounts of
nutrients contained in the above ground portions of growing trees.
Rennie's(2) data represent growth on nutrient-poor soils; his, recommenda-
tion was to leave brush and stembark on the forest floor so that a minimum
of nutrients would be removed from the site. Morrison and Foster^
analyzed the vegetation growing on two soil types: till and sand. They
attribute the increased nutrient concentrations, in vegetation from the
till soils, to Increased soil moisture., increased soil depth, and a larger
percentage of silts and clays in the till soil. Deriegneau and Denaeyer-
DeSmet attribute the higher nutrient uptake associated with the mature
Quercus Fraxinus forest to available nutrient concentrations in the soil.
Several authors have related nutrient removal to harvest technique.
Malkonen compared whole tree harvesting, including roots, to normal
logging procedures in Findand (Table 46). His data indicate almost a three-
fold increase in nitrogen removal due to whole tree harvesting. The data
also indicate the differences due to species and site.
Jorgensen et al measured the effect of harvest method on
biomass and nutrients from a 16-year old Loblolly pine plantation in the
North Carolina Piedmont (Table 47). These data are most important in
that a management decision about market/residue-manipulation relationships
can be made. The authors state:
"At about 16 years of age, highly productive plantations can
be clearcut or thinned for pulpwood. In a 16-year old stand,
removal of needles, bark, branches, stems, and large roots
would yield 185 metric tons/ha of biomass. This material
would contain about 80 to 90 percent of the nutrients in
the tree biomass, 12 percent of the total nitrogen,
8 percent of the extractable phosphorous, and 31 percent of
the extractable potassium on the entire site. A much less
drastic harvest alternative now generally employed, removing
only the stemwood and bark to an 8-cm top, xrould yield 116
metric tons/ha. This form of harvest takes away only about
one-third as much nutrients as total-tree harvest, but yields
two-thirds as much biomass. Furthermore, the biomass left
-------
166
TABLE 45. NUTRIENT REMOVAL - ABOVE GROUND TREES
ONLY
Species
Pines
Other Conifers
Deciduous Hardwoods
N
-
-
-
Ca
ke/ha
283
676
1,283
K
noo vr
138
375
320
kg/ha/yr
Jack Pine Stand
(till)
Jack Pine Stand
(sand)
Fagus sylvatica
Pinus sylvestris
Quercus Fraxinus
Mixed Oak
Querce to- f raxinerum
Quercetum mix turn
Querecto-aegopodietum
Querecto-aegopodietum
Fagetum
Fagetum on diorite
Fagetum on granite
Betuletum verrucosae
Picea Forest
24
16
10
10
44
• 30
44
30
56
33
16
-
-
8
20.6
18
12
13
10
42
75
42
74
20
16
26
49
23.8
10
22.5
12
11
4
2
-
16
21
16
27
23
8.
4.
2.
3
6.
P Mg
rotation)
30
70
70
(a)
2 3
1 2
2
1
4 5
2.2 4.4
4 5
2.2 6
3 1
4 3
8 1.2 2.5
5 6.1 5.3
5 2.8 2.5
0.5 0.9
7 1.8 2.2
Source
Rennie (2)
Rennie (2)
Rennie (2)
Morrison and
Foster (3)
Morrison and
Foster (3)
Duvigneaud and /, %
Denaeyer-De Smet ; (4)
Duvigneaud and
Denaeyer-De Smet (4)
Duvigneaud and
Denaeyer-De Smet (4)
Duvigneaud and
Denaeyer-De Smel (4)
Duvigneaud and
Denaeyer-De Smet (4)
Duvigneaud and
Denaeyer-De Smet (4)
Duvigneaud and
Denaeyer-De Smet W
Duvigneaud and
Denaeyer-De Smet vO
Duvigneaud and
Denaeyer-De Smet W
Duvigneaud and
Denaeyer-De Smet W
Duvigneaud and
Denaeyer-De Smet W
Duvigneaud and
Denaeyer-De Smet W
Duvigneaud and
Denaeyer-De Smet (*)
(b)
kg/ha = 0.89218 Ib/acre
Literature reviewed by these authors.
-------
167
TABLE 46. COMPARISON OF TWO HARVESTING TECHNIQUES
IN FINLAND
Technique
Pine Forest
Timber Cut
Whole Tree Harvest
(including root)
Spruce Forest
Timber Cut
Whole Tree Harvest
(including root)
N
58
148
95
372
Ca
73
115
184
409
kg/ha
K
38
80
47
161
P
5.3
15.0
8.4
40.6
Source (5)
-------
TABLE 47. EFFECT OF HARVEST METHOD ON BIOMASS AND NUTRIENTS FROM A 16-YEAR-
OLD LOBLOLLY PINE PLANTATION
Nutrients in Biomass
Harvest Method
Debarked pulpwood
to 8-cm top
Pulpwood to 8-cm
top
Complete aerial
Complete aerial
+ roots 4-cm
and larger
Total biomass
aerial and below
ground
_ Tree
Weight
T/ha
102
116
156
185
192
Biomass
Percentage
53
60
81
96
100
Weight
N P K
kg /ha
74 13 61
104 14 80
254 30 165
282 37 202
321 48 226
Percentage
N
23
32
79
88
100
P K
27 27
29 35
63 73
77 89
100 100
Nutrients in
a percentage
N
3
4
11
12
13
biomass expressed as
of nutrients
pta?
3
3
7
8
11
on site
K(a)
9
12
25
31
34
Total nitrogen and forest floor and extractable in soil
Source (1)
00
-------
169
is mostly of low quality for manufacturing, and costs for
manufacturing and waste disposal may exceed the return re-
leased from harvest. Removing only debarked pulpwood takes
about 20 percent less N, P, and K from the site than a normal
pulpwood harvest, and reduces the weight yield by only 10
percent.
Patric and Smith calculated nutrient losses from several
West Virginia experimental watersheds under current silvicultural practices
(Table 48). The stands were uneven-aged, consisting of old second growth
oaks, maples, yellow poplar, black cherry and beech; residuals from a heavy
cutting in 1905 were present. These data indicate that repeated light
cuts tend to cause greater annual nutrient drain than does a single cut
per rotation.
Nutrient Input
Nutrient input to a forest system occurs primarily by (1)
mineralization of the solum and weathering of secondary materials in the
soil; (2) atmospheric inputs in the form of particulates, and dissolved
materials in precipitation; and (3) from organic inputs from the vegetation
itself. These inputs to the forest system, under normal circumstances,
are usually sufficient to balance losses/ In most soils, natural
weathering of soil materials along with low levels of nitrogen fixation
and atmospheric contributions seem ample to replace nutrient removals^ >.
Nutrient additions through fertilization or nitrogen-fixing
plants can establish high productivity rates in the forest ecosystem,
(8)
especially when deficiency conditions exist. More research is needed
to determine how widespread deficiencies may be, as well as to answer
(9)
questions of how much, when, and where fertilizer is to be applied.
These authors made an extensive survey of investigators currently doing
forest fertilization research in northeastern United States hardwoods.
Forest fertilization methods and quantities have been analyzed
by Groman(10) and recommendations are given. Few studies indicate no
-------
170
TABLE 48. ESTIMATED NUTRIENT LOSSES ACCOMPANYING SILVI-
CULTURAL PRACTICES ROUTINELY APPLIED ON THE
FERNOW EXPERIMENTAL FOREST, PARSONS, W. VA.
Intensive selection
(selected trees
over 12.5 cm dbh)
Extension selection
(selected trees
over 27.5 cm dbh)
Diameter limit
(all salable trees
over 43 cm dbh)
Commercial clearcutting
(all salable trees over
12.5 cm dbh)
Liquidation cutting
(all salable trees
branches and culls)
Cycle (a)
(vr.)
5
10
20
75
75
Harvested
Biomass
10,323
22,237
25,221
51,030
94,295
kg/ha
Nutrients ^ removed
per cycle
98
180
236
473
892
from soiHc>
per year
20
18
12
6
12
(a) Frequency of recutting
(b) N, P, K, Ca, Mg
(c) Computed as 88% of the harvested biomass as wood, 12% as bark; applying nutrient
content to biomass ratios for stemwood and bark (from Duvigneaud and Denaeyer-De
Smet). (4)
Source (6)
-------
171
substantial or long-term detrimental effects to the environment from forest
fertilization. Some examples of application rates
Sweden 132 kg /ha N
Pacific Northwest 150-200 kg/ha N
Southern Pines 90-112 kg/ha p o
Application of fertilizers to forests is a recent management
practice. It started in the 1950' s and by 1970 about 5 million acres in
the world were fertilized; it is projected that by 1980 the figure will
be 40 million acres. (11)
Available data for long-term results of application of N or
combinations of N, P, and K are not available. However, Stone ^12^ attributes the
reasons for fertilizer application to either acceleration of already
favorable growth rates on productive sites, or to allow reasonable normal
growth on soils either naturally deficient or depleted by an earlier cycle
of exploitive agriculture. Forest fertilization does offer a management
tool to offset any long-term effect of nutrient removal due to harvesting
practice.
Rotation Period
Man has been removing parts of forests, or complete forests for
centuries. Sometimes the results were disastrous (due primarily to erosion)
but in situations where soil conditions were favorable, the forest ecosystems
recovered. Stone ^12^ reviewed the literature and concludes that increased
nutrient removal is likely to be a minor problem from complete tree
utilization. There is increased nutrient loss, however, in such practices
as
Shorter rotations
Faster growing varieties
Closeness of tree plantings.
Boyle et al (13|) calculated a gross nutrient budget for a 40-year
old aspen-mixed hardwood second growth forest in Wisconsin (Table 49). The
authors calculate that nutrient inputs would more than sustain nutrient
removal due to whole tree harvesting for at least nine 30-year rotations.
The only potential limiting factor was calcium; this estimate was based on
-------
172
TABLE 49. GROSS NUTRIENT BUDGET FOR THE HARVEST SITE
N J? _ K _ Ca
N0 - N (- Extractable)
Soil reserves (top 6
inches) at time of
harvest (a> 24 102 115 586
Inputs expected
during next 30 years
from:
Precipitation
Mineralization &
weathering
Net Inputs
Outputs in whole tree
harvest at age 30
150
486
636
172
9
27
36
24
67
107
174
116
107
214
321
382
Input/Output index^ ' 3.7 1.5 1.5 0.8
(a)
These minimal reserves are supplemented by available
nutrients in soil horizons below 6 inches which are
penetrated by roots.
An index number greater than 1 indicates inputs during
the 30-year rotation are more than adequate to balance
harvest outputs. A value less than 1 indicates a
potential limiting supply when soil reserves are
exhausted.
Source: Reference 13.
-------
173
Ca content of the top 6 inches of soil. However, increased nutrient removal
due to increased runoff was not calculated.
Wells et al (14), as cited by Patrick and Smith(6) , calculated
the replenishment of soil nutrients in a North Carolina hardwood forest
(Table 50). Total annual input of N, P, K, Ca, and Mg equals 235.65 Kg/ha.
Patric and Smith calculated a maximum annual removal rate of N, P, K,
Ca, and Mg of 20 Kg/ha (Table 47). One could conclude that a net annual
increase of 215.65 Kg/ha of Ns Ps K, Ca, and Mg occurs under intensive
selection harvesting. However, losses due to erosion and runoff were not
included in the calculations=
Conclusions
1. Forests remove definable amounts of nutrients from the
soil. The rate of removal is dependent on: (1) species;
(2) stocking; (3) age of the stand; (4) available
moisture; and (5) soil nutrient availability.
2. The amount of nutrients removed from a site, due to
silvicultural practices, varies with the practice and
the variables mentioned in conclusion 1.
3. The effect of nutrient removal, by harvest, is not
known at this time. Available data are site specific
and are not amenable to comparisons or projections.
4. Nutrient inputs to forests are variable and are not
yet fully quantifiable.
5. Forest fertilization practices could serve as a
source of nutrients. However, fertilization
suggests good forest management. Due to the
land ownership patterns in Vermont, fertiliza-
tion may not be feasible on private lands; ferti-
lization would be feasible on state lands.
-------
174
TABLE 50. RE^LiifllSflMENT OF SOIL NUTRIENTS IN A IsOJiTH
CAROLINA. HARDWOOD FOREST
Nutrients (kg /ha)
Source
Rainfall
Canopy Drip
Stemf low
Litter
Annual Input
to Soil
N
3.53
4.86
0.23
45.98
54.60
P
0.28
0.61
0.01
3.26
4.16
K
0.88
17.48
0.65
14.16
33.17
Ca
3.42
12.47
2,02
94.99
120.90
Mg
0.72
3.75
0.24
18.11
22.82
Source (14)
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175
Stream Water Quality Impacts Of Timber Harvesting
The State of Vermont has the good fortune to have within its
borders many thousands of acres of relatively undisturbed forestland and
semi-wilderness areas. As watersheds, these areas are characterized by
consistently high stream water quality. With the proposed activity of
harvesting forests for energy production, the question arises as to what
effects this practice will have on water quality in the associated
streams.
The traditional parameter of quality in forest streams is
turbidity. Only in the last decade has it been recognized that this
criterion is an insufficient measure of the quality of forest streams,
because the chemical composition of identically turbid or nonturbid waters
may vary widely. Therefore, a number of different water quality parameters
must be assessed in an evaluation of these streams and of the impacts of
timber harvesting practices on stream quality. Impacts of timber har-
vesting on water quality values are reviewed as follows:
• Stream flow
• Water temperature
• Turbidity
• Nutrients and other ions
• Other parameters.
For clarification, the data are presented in three sections: (1)
impacts and mitigating measures; (2) policy implications in Vermont; and
(3) conclusions.
Impacts and Mitigating Measures
In general, there are at least three sets of variables influencing
how stream water quality -will be impacted by timber harvesting. The first
of these is the nature of the forested area before harvest - the composition
of the soil, the depth of the humus, the extent of forest cover in the area,
the species of trees affected, etc. Secondly, the original physical and
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176
and chemical composition of tlie associated streams will influence the final
result. The third set of factors centers on the harvest operation itself -
whether clearcutting or an alternate method is employed, whether a buffer
strip of trees is left next to the stream, and whether the slash is left
behind or somehow destroyed.
The studies conducted on this particular topic have not always
been careful to note all of these variables. Moreover, there is one
relatively well known study in which an additional factor was incorporated
within,the experimental designj, On one tract/within New Hampshire's
Hubbard Brook Experimental Forest, the trees and vegetation were killed
and left in place, and regrowth was prevented for 2 years by application
of an herbicide. Because of inconsistencies from one study to another,
the- results are not always directly comparable. In trying to predict
the outcome within a given Vermont forest and its watershed, one should
be cognizant of such pitfalls and assimilate as much information as
possible" about management decision.
Stream Flow. In an undisturbed forested area, the capacity of
the soil to accept rainwater is very high, usually higher than the
capacity of major intensity storms to deliver water to these areas.
Typically, heavy cutting of the forest will not affect this property of
the soil unless the soil itself is disturbed. This does not mean,
however, that the quantity of runoff is unaffected when the canopy is
removed, For example, see Figure 30a.
In the Hubbard Brook study, it was shown that annual runoff
from the area, which was deforested but which retained an undisturbed
soil layer, increased by 39 percent the first year and 28 percent the
second year over values that were based on a control area. June and
September runoff values were 414 percent and 380 percent higher than
for controls. Likens et al postulate that such results are a
function of the reduced canopy during these months. This conclusion is
(12)
accepted by Stone. According to Stone, destruction of leaves and
their transpiring surface area reduces the level of water intake necessary
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177
16
14
!•
i
< 6
COWEETA O
FERNOW X
LEADING RIDGE •
HUBBARD BROOK •
O
O
I
I
10 20 30 40 50 60 70
Reduction in Forest Stand
Basal Area (Percent)
80
90
100
FIGURE 30a. INCREASED STREAMFLOW IN THE FIRST YEAR OF CUTTING
Source: Reference 12.
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178
by vegetative roots. At the extreme, an absence of living vegetation in
the area which previously had been forested, such as Hubbard Brook, removes
the requirement for roots to take up any water at all. If the water
seepage through the soil is too slow to accommodate this increased
burden, then runoff and stream flow will also rise. On the other hand,
reestablishment of the foliage canopy will accompany increasing water
(12)
uptake by roots and a reduction in stream flow. This appears to
occur in a systematic and reoccurring pattern. In one experiment by
Hibbert , as cited by Stone, a clearcut forest in North Carolina
displayed the predicted increase in water yield, followed by a gradual
abatement over 23 years as the forest regrew; a subsequent clearcut
after that period of time then reproduced virtually an identical increase
in water yield.
Regardless of harvesting status, the period of greatest stream
flow discharge from a Vermont forest is likely to be in late March and
April, when snowmelt is fastest. Likens et al have documented
this result in neighboring New Hampshire. Snowmelt took place a few
days in advance in the denuded forest; the watershed discharge in 1968
was almost 30 percent greater in volume at its early spring peak than in
the continuously forested control area. The implications of this finding
are that any potential flood situation during this time of year might be
increased by the presence of widespread cleared forestland.
Water Temperature. The impacts of timber harvesting on ambient
stream temperatures within a watershed appear to be relatively well
understood. Removal of the forest cover permits direct solar radiation
into the stream. Brown reports that the solar heat load was increased
by six times after the shading overstory had been removed. The results
are twofold: not only will there be higher water temperatures, but the
daily fluctuation between maximum and minimum will be greater as well.
Such changes appear to be a function of solar radiation directly into
the stream, not increased air or soil temperatures.
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179
The degree of warming of a stream is not as well understood,
although several contributory factors have been identified. Levero and
Rothacher have found that temperature increases in streams, after
complete exposure to the sun, ranged up to as much as 8.3 degrees centigrade.
The variation in response by individual streams seems to be accounted
for by the length of channel exposed, the original width of the stream,
the volume of water and its initial temperature, and the amount of
canopy removed.
Stream water temperatures in New Hampshire's Hubbard Brook
area proved to be higher both in summer and in winter within the cleared
area than in the control area.^ Annual variation in the deforested
watershed was between 18 to 20 degrees C whereas in the control area it
ranged only about 16 degrees C. Daily fluctuations in summer were also
greater in the experimental area; mean hourly stream temperature, during
1 day in summer, went from approximately 18 degrees C to about 22
degrees C , while in the control watershed, temperature remained fairly
constant at 16 degrees C.
(19)
Experiments by Brown et al , in the Steamboat Creek drain-
age of Oregon's Cascade Mountains, have shown that the segment length
exposed to solar radiation is a very important factor in determining the
degree of temperature increase. On a very small stream, a 10-foot cut
along the stream produced a 1.1 degree C rise in temperature, a 30-
foot cut resulted in a 2.2 degree C increase, and a 150-foot cleared
stretch along another very small stream induced the temperature in that
stream to rise by 7.2 degrees C.
The fact that length of stream exposed to the sun is not the
only factor involved is demonstrated on another wider stream in the
Steamboat Creek area. A clearcut which exposed 1,100 feet of stream
produced a rise of only 2.2 degrees C , from 22.2 degrees C to 24.4 degrees
C. The two additional factors involved here were the relatively high
initial 22.2 degrees C reading, which was brought about by other clearcuts
upstream of the one studied, and the greater width of the stream segment.
One study conducted by Escher and Larmoyeux , in West
Virginia's Fernow Experimental Forest, reported that clearcutting in a
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180
given area resulted in temperatures greater than those which can be
tolerated by rainbow, brook, and brown trout. Water temperatures in
excess of 24 degrees C (75 degrees F ) were noted a number of times.
Many studies have pointed out that stream temperature increases,
after a clearcut, can be controlled and even prevented. Because of the
importance of shade, a buffer strip left adjacent to the stream has been
shown very effective in maintaining stream temperatures through a
clearcut area. In the Steamboat Creek area, a narrow strip of trees and
brush along a 1,680-foot exposure of stream prevented temperatures along
that segment from rising more than 1 degree F - from an initial 14.4
degrees C to a downstream reading of 15 degrees C. On another stream
where the upstream reading was 24.4 degrees C , there was no increase in
temperature when a buffer was left to protect the stream. Similar
results have been reported in a Southeastern forest when a thin strip
of vegetation had been left along the stream channel.
In West Virginia's Fernow Experimental Forest, a 10 to 20
meter wide protection strip was left on both sides of the channel along
a clearcut stretch approximately 730 meters long. Not only were stream
temperatures virtually unchanged along this length, but a comparison of
readings with those taken for several years before the cut indicated no
rise. Moreover, the increase in stream flow caused by the clearcut had
an additional result of extending the stream almost 200 meters upchannel
into the clearcut area; the presence of direct solar heating of this
water did not produce a downstream temperature rise.
Turbidity. The major cause of turbidity increases in a forested
watershed is not the harvesting practice but the building of logging
roads and skid trails. The degree of disturbance is related to the
slope of the terrain, the stability and erosiveness of the soils, and
the distance of disturbance activity from the stream channel. Most
observers are of the opinion that slight marginal improvements in planning
and construction of logging roads can prevent most of the increased
turbidity impairment to water quality.
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181
In the Hubbard Brook experiment(15), where the vegetation was
left in place after the tract was cut over and herbicided, no increases
in water turbidity were displayed. If anything, the values seemed
somewhat lower than in undisturbed watersheds.
Results from the Fernow Experimental Forest are also important.
According to Aubertin and Patric(21), most of the increase in tur-
bidity was related to storm activity. During nonstorm periods, tur-
bidity levels were generally low throughout the area, even in streams
adjacent to logging roads. Despite precautionary measures taken to
lessen road-related turbidity, highest levels were found in stormy
periods where logging roads were adjacent to protective buffers. During
one particularly intense storm, erosion control structures were damaged
next to a heavily used road; at the point that the resultant runoff
mingled with a stream, turbidity was at 550 Jackson turbidity units,
whereas several feet upstream of the mixing zone it was at only 25
Jackson turbidity units.
(22)
A study by Kochendeefer and Aubertinv ' in the West Virginia
forest demonstrated that a carefully planned, constructed, and main-
tained road system can keep turbidity increases to a very minor level.
In contrast, a nearby commercial clearcut in the same forest produced a
major rise in this parameter. The absence of logging road restrictions
in the latter tract was deemed the most important causative factor.
The United States Forest Service has been instrumental in
(23)
developing guidelines to reduce damage to watersheds caused by erosion.
These guidelines cover road locations and design, construction of
permanent roads, drainage control, and road maintenance. They should be
consulted during harvesting activities so that such impacts can be
minimized.
(24)
Nutrients and Other Ions. According to Likens and Bormann ,
it is the input of dissolved nutrients to a freshwater ecosystem which
determines that system's ultimate trophic status. In general, the
nutrient cycle within a forest ecosystem is a closed loop, and there is
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182
(25)
little loss of nutrients into drainage waters. Likens and Bormann
have shown, in fact, that an undisturbed forest ecosystem within the
Hubbard Brook area displayed an annual net gain in nitrogen and phos-
phorus and a near balance in potassium, despite the continuous mobility
of these nutrients in the ecosystem.
The degree of nutrient loss from a forested area after it has
been clearcut is important for two reasons. For one thing, a heavy loss
would contribute to an adverse water quality situation by resulting in
an accelerated rate of eutrophication. In addition, productivity of the
forest site might also be impaired.
The most dramatic example of nutrient losses following a
clearcut, though not all nutrients displayed tfie same pattern, took
place in the Hubbard Brook tract of New Hampshire. In this case, the
felled vegetation was left in place, the soil remained relatively undisturbed
owing to the lack of road construction and timber removal, and the area
was treated with herbicides for the three ensuing summers to prevent re-
growth. The undisturbed watershed showed a very low ammonium concen-
tration, and there was virtually no change after deforestation. These
data are explained by the fact that growing vegetation in the undis-
*
turbed forest may use the ammonium ions directly, thus depleting their
presence in stream flow, but when growing vegetation is absent, the j
process of biological nitrification converts the ammonium ions to
nitrite and then to nitrate ions. In both forest situations, therefore,
presence of the ammonium ions in the associated streams is minimal.
The nitrate ion, in contrast, increased markedly in the
tract's watershed after deforestation. Low levels of nitrate were
present in the drainage water of the undisturbed ecosystem, reflecting
both the efficiency of the conversion process from ammonium to nitrate
as well as the usage of these nitrates by the vegetation. After de-
forestation, ammonium was reduced to nitrates by the vegetative root
system. The result was continuous leaching of nitrates through the soil
and a significant rise in the concentration draining from the watershed.
Prior to the cutting, the average weighted value of the nitrate con-
centration was 0.9 mg/liter; 2 years after cutting it had increased
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183
to 53 mg/liter; the maximum monthly concentration after deforestation
was 82 mg/liter.
A related study by Pierce et al(26) examined the effects of
timber harvesting by commercial clearcut methods. On these tracts, also
located in the Hubbard Brook area, shrubs and saplings were left standing,
and herbicides were not applied to prevent regrowth. Again, concentrations
of nitrates rose significantly, but not nearly as much as in the water
draining the experimental tract. Maximum nitrate concentration in these
areas was 28 mg/liter, as compared with 82 mg/liter from the experimental
area. Total losses of nitrate-nitrogen were also substantially less
over the 2 years following the cut.
Studies from other Eastern forest areas do not corroborate the
results from New Hampshire. In West Virginia's Fernow Experimental
(21)
Forest, Aubertin and Patric observed the results after a tract had been
commercially clearcut. Nitrate-nitrogen levels increased only slightly
over a control watershed during the ensuing growing season; a somewhat
larger increase took place afterwards in the dormant season. Overall
nitrogen losses, however, were relatively small. The authors postulate
that the losses which did occur resulted from a buildup of nitrogen in
the soil during the growing season, which was leached during heavy
dormant season rainfall. Heavy nutrient shifts did not occur, though,
because timber was not left to decay on the forest floor, and regrowth
of the tract was both rapid and luxuriant.
(27)
Nutrient losses were also studied by Lynch et al in
Pennsylvania. After a three-phase clearcut was undertaken, herbicides
were applied to the tract to prevent regrowth of woody sprouts. A large
invasion of herbaceous vegetation took place, however, and much of the
available nitrogen was thus utilized. Significantly higher levels of
nitrate-nitrogen were not observed on the experimental tract.
Other nutrients displayed patterns similar to those of ammonium
and nitrate, and results differed depending on the experimental method.
In the Hubbard Brook area, calcium, magnesium, potassium, and sodium cations
all increased in average stream water concentrations following deforestation.
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184
In a comparison of clearcut and control areas of Fernow, however, these
four cations demonstrated minor increases in nutrient loss during the
growing season and similar values in the dormant seasons. Discrepancies
between the two experiments are thought to be based on the absence of
(2Q\
herbicide treatment in Fernow. Separate studies by Johnson and Swank ,
/29\
and Douglas and Swank ' in North Carolina's Coweeta National
Forest verify the results from West Virginia, with the predictable
exception that calcium concentrations increased substantially in the
watershed after a clearcut area received lime applications.
The sulfate ion is the only additional parameter studied both at
Hubbard Brook and in the Fernow Experimental Forest. Values varied,
although, in both cases ; the experimental tracts seemed to portray lower
sulfate concentrations in their respective watersheds. These decreases,
moreover, came about only after a several month lag. Complicated mechanisms
of precipitation chemistry and internal biological activity of the ecosystem
underlie the reasons for such changes
The impact of timber harvesting on phosphate concentrations was
examined in the Fernow forest, where a temporary increase in concentration
(21)
was found adjacent to the clearcut area. Aubertin and Patric do not
postulate any reasoning for this temporarily greater loss from the cut
area, but the same factors appear to be at work here as for nitrates.
Phosphates were not being taken up into root systems directly after the
clearcut, but as the vegetation began to regrow, this nutrient came more
and more into demand, and thus the increased losses into the water were
only short lived.
Other chemicals were studied in one of the two experiments.
Chloride concentrations increased in Hubbard Brook, mostly as a result
of the chlorine component of the herbicides. Aluminum and dissolved silica
also increased in Hubbard Brook; a decrease in the pH of the stream water
raised the solubility of both of these chemicals, and thus their concen-
trations rose. Another impact of this decrease in stream water pH centered
on a lowering of bicarbonate ion concentration to near zero. Copper,
zinc, and iron levels were all measured in the Fernow tracts, and none
seemed to be affected by the harvest.
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185
More recent studies at Hubbard Brook are attempting to pinpoint
methods for abating the increases in concentrations of nitrates, potassium,
and calcium. As reported by Hornbeck et al(30), a partial clearcutting
method known as strip cutting was applied in one tract. In this instance,
approximately 50 east-west strips were laid out on the tract, and every
third strip was cut during that year. The two sets of remaining strips
would be cut similarly in 2-year intervals. Results from this experiment
showed that nutrient losses from the forest could be mitigated significantly,
though losses were still substantial. Efforts are continuing in Hubbard
Brook to discover feasible methods for improvements in reducing nutrient
losses.
Other Parameters. The concentration of hydrogen ions in
stream water is affected by nutrient and other chemical release into the
water. Because such losses were relatively small in Fernow, the pH was
not changed. In Hubbard Brook, on the other hand, the weighted average
pH decreased from 5.1 to 4.3 over the space of 2 years. This change, as
has been mentioned above, resulted in rising solubility levels for
chloride and dissolved silica, which thereupon increased in concentration.
Total dissolved solid content in the Fernow watershed did not
change as a result of the timber harvest activity. The related parameter
of electrical conductivity was studied at Hubbard Brook. In the undisturbed
2
watershed, electrical conductivity averaged about 20 micrcmos/cm at 25
degrees C , and changed very little either daily or seasonally. At the
same time, conductivity in the denuded watershed was relatively variable
and ranged from 65 to 160 micromhos/cm2 at 25 degrees C. Timing and
duration of rainfall as well as other factors appeared to affect this
parameter.
Policy Implications in Vermont
The effects of timber harvesting practices on water quality is
a subject which falls within the purview of at least two major categories
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186
of environmental concern:
• Land use
• Water pollution.
The implications of this activity on environmental policy and law in the
State of Vermont will be discussed in the above order.
Land Use. Approaches to land use controls are both general
and specific in Vermont. The state's 1970 land use law, Act 250, is a
general outline of concern for these issues, and it contains certain
action-forcing mechanisms. More specific to the activity of timber
harvesting are certain practices and guidelines issued by the Vermont
Department of Forests and Parks.
Act 250, as originally adopted in 1970, created an environmental
board and district environmental commission to regulate land use. The
state board was directed to develop state land capability and land use
plans, as well as to set up a permit system to carry out the plans. The
"Capability and Development Plan" was thereupon prepared, and, in 1973,
the state legislature passed amendments to Act 250 to adopt the plan as
state policy and establish specific criteria for the issuance of permits.
As for the land use plan, it has been prepared, but the legislature has
not yet acted to adopt it formally.
The 1973 amendments to Act 250 place under state permitting
authority virtually all land development activities of significance. In
brief, anyone designing to "develop" land must procuce a 250 permit.
To determine if timber harvesting practices would require a permit, one
should look for the applicable definitions of "development", as expressed
in the adopted amendments. The relevant provisions are that "development"
encompasses the following:
• Construction for any purpose above 2,500 feet in elevation
• Quarrying and earth removal, with the stated exemption of
any construction for farming, logging, and forestry purposes
below 2,500 feet in elevation.
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187
It is possible, therefore, that the construction of logging roads and other
necessary facilities above 2,500 feet in elevation would create a require-
ment that the developer secure a 250 permit.
In cases where such a permit must be obtained, there are
environmental standards which must be addressed by the potential per-
mittee. In specific, a timber harvester would have to demonstrate that
his development:
• Does not interfere with headwaters within a watershed
• Contains proper waste disposal means and facilities
• Utilizes the best available technology to preserve
stream water quality
• Does not significantly interfere with flood waters
• Does not interfere with the natural condition of any
stream
• Is located on the shoreline of a body of water only
out of necessity and in conformance with shoreland
zoning requirements
• Does not unreasonably burden an existing water supply
• Does not unreasonably erode soil or reduce the water
holding capacity of the soil
• Does not adversely affect aesthetic, historic, or
natural areas
• Is in conformance with any local or regional zoning
• Is in conformance with the "Capability and Development
Plan", which provides, among other items, that (1)
the proposed development is not to affect significantly
a town's ability to provide for a reasonable rate of
growth; (2) the development must ensure that its
impact on agriculture and forestry potential is
minimized; and (3) the proposal must incorporate the
best available technology for efficient use of energy.
Permit applications are filed with the appropriate Office of
the District Commission or Regional Office of the Vermont Environmental
Conservation Agency. After the permit has been issued and construction
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188
is complete, the permittee may petition for a Certificate of Compliance,
which will foreclose any subsequent legal challenge of the permit issuance.
The relevance of Act 250 to timber harvesting practices need not
be overstated. It should be clear that certain such activities may implicate
this law and its attendant permit process, and in these cases the developer
will need to give the above mentioned environmental assurances.
In contrast to Act 250 and general state land use programs,
more specific but less formal procedures have been prepared by the Vermont
Department of Forests and Parks to evaluate nonpoint water pollution hazards
and to aid in prescribing appropriate erosion control measures. They are
included within the "Nonpoint Source Water Pollution Evaluation Handbook -
(31)
Erosion and Sedimentation". These are field procedures to be used
in the forested areas, and they are applicable not only to logging but to
most other types of disturbances that might potentially result in erosion
and sedimentation. Their emphasis is in determining areas where such dis-
turbances have taken place, the extent of current problems, and the result-
ing situation if given management practices are not implemented. This
document should be consulted along with other appropriate materials so
that adverse water quality impacts related to land use practices can be
mitigated during timber harvesting.
Water Pollution. Erosion control measures prescribed by the
Vermont Department of Forests and Parks, as well as permit procedures
pursuant to Act 250, represent important land use controls applicable to
timber harvesting in Vermont. At the other end of the process are
policies relating to Vermont's water quality and limitations to the
amount of material tolerated as stream pollution.
In general, Federal and state water quality policies have
been most responsive to pollution emanating from so-called "point"
sources such as municipal and industrial dischargers. "Nonpoint"
pollution, such as sediment and nutrients in the runoff from a logged-
over forest, have not been subject to effluent limitations in any strict
or standardized manner.
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189
This has taken place mostly because nonpoint sources are not amenable to
structural solutions at the point of discharge. Now that land use
practices and controls are becoming increasingly accepted, they are
being viewed as the key to the problem of nonpoint pollution. In other
words, because sediment and nutrients from the deforested area can not
be collected and treated as in a sewage treatment plant, forest managers
must institute standards for construction of logging roads and require-
ments for appropriate buffer strips, so that the creation of high
pollutant levels can be averted. In this way, treatment facilities will
not be needed.
Regardless of the type of solution to this particular pollution
problem, Vermont has adopted standards for the quality of the ambient waters
within the state. All waters are classified on the basis of actual or
intended use, and standards are assigned according to these designated uses.
Vermont's "Regulations Governing Water Classification and Control of Quality",
adopted by the Vermont Water Resources Board on December 20, 1973, establish
(32)
the following classes:
• Class A - suitable for public water supply with dis-
infection when necessary, character uniformly excellent
• Class B - suitable for bathing and recreation, irrigation
and agricultural uses; good fish habitat; good aesthetic
value, acceptable for public water supply with filtra-
tion disinfection
• Class C - suitable for recreational boating, irrigation
of crops not used for consumption without cooking,
habitat for wildlife and for common food and game
fishes indigenous to the region, and such industrial
uses as are consistent with other Class uses.
The State of Vermont has adopted for these classes standards for
the following parameters.:
• Dissolved oxygen
• Sludge deposits, solid refuse, floating solids, oil, grease,
and scum
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190
• Color and turbidity
• Coliform bacteria
• Taste and odor
• pH
• Temperature
« Unspecified other pollutants affecting the composition
of bottom fauna, affecting the physical or chemical
nature of the bottom, or interfering with the pro-
pagation of fish.
Additionally, the state has divided its waters into five manage-
ment types. Three types are for streams and rivers, and they differ accord-
ing to the fish populations they might sustain - whether they are warm-
or cold-water fisheries, and whether the fish are indigenous or stocked.
The other two management types are for lakes, ponds and reservoirs, one
being for a natural cold-water fishery, and the second being anything other
than that. Separate water quality standards for dissolved oxygen, temperature
and turbidity are assigned based on management types.
The ultimate effect of Vermont's water quality standards is
that discharges should not cause or contribute to violations of the ambient
standards. The emphasis throughout the regulations is on point sources
and effluent limitations, but there is no clear statement that nonpoint
sources are not meant for control as well. In all cases, state water
quality officials should be consulted for their views on the relationship
of forestry practices and ambient standards. They can also provide
information on designations applicable to specific streams.
Conclusion
It has been shown that timber harvesting can result in water
quality impacts. Important, however, is the concept that relatively simple
management techniques can mitigate or even eliminate many potentially
adverse effects. Adherence to these procedures will allow Vermont to
increase benefits from multiple-use lands without sacrificing any options.
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191
State policies in Vermont, moreover, lend weight to the need for
effective forestry management, for they are unusually strong in the area
of land use controls.
Soil Erosion
Silviculture, the art of producing and tending a forest,
necessitates management of a natural resource. One result of this
management is soil erosion, the degree and amount of soil erosion depend
on the quality of the management. Although soil erosion can result from
all aspects of a harvest (roads, skid trails, yarding and staging areas,
and the cut surface or harvested area), roads and skid trails have been
identified as the major sources of soil loss. 2' 33> 34> 35^ Data indicate
that tree cutting, even clearcutting, does not change the water handling
(33)
capacity of a forest soil. Even though the original canopy may be
totally removed, the litter cover and forest floor usually remain intact
/ *j / \
and furnish ample protection until a new canopy is established.
Although roads and skid trails can be identified as the major
sources of soil erosion associated with silviculture, magnitude of soil
loss is site specific. Each harvest has a potential for soil erosion
depending on several factors (slope, road design and maintenance, amount
and type of skiding, erosion prevention measures, soil type, etc.). For
example, Table 51 shows a summary of studies of the effect of logging on
erosion and sedimentation in the United States.
It must be remembered that each example in Table 51 reflects
a given set of conditions, thus making comparisons difficult. However,
erosion and sedimentation seem to be reported more from roads than from
cutting and skiding.(35) A review of the literature on the impact of
harvesting on forest environments and resources is presented in reference 36.
Soil erosion, resulting from silvicultural practices, need not be
a problem in Vermont. Ample data are available which document preventive
-l \JJ> J**» J-^J Jl > J
measures which can be incorporated into a harvesting plan.
In addition, the Vermont Department of Forests and Parks has published
criteria which list specifications required for various types of forest
-------
TABLE 51. SUMMARY OF STUDIES OF THE EFFECT OF LOGGING ON
EROSION AND SEDIMENTATION IN THE UNITED STATES
Study Location
N. C.
Mich.
Colo.
Wash.
Ore.
Alaska
Ore.
Calif.
Colo.
Calif.
Idaho
N. C.
W. Va.
Ore.
Ore.
Idaho
Accel. Location & Type Accelerated Erosion
Sediment Cut + Skid Roads
Production Surf. Mass Surf. Mass Not
Yes No eros. eros. eros. eros. Defined Comments
X X Cutting only; no roads,
no skidding
X X
X X Slight road erosion, no
sediment to streams
X X Sediment not "discerni-
ble"
X X Sediment not "discerni-
ble"
XXX No significant sediment
increase
X Regional, statistical
study
X Regional, statistical
study
X
X Mostly from channel
encroachment
XX X Accelerated sed. some
drainages, none in others
X X
XX X Varied with care in
logging
XX XX Cut & skid erosion due to
slash burning
XX XX
XX XX
VO
K>
Source: 35
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193
roads. The Vermont Department of Forests and Parks also provides the
woodlot owner with an example timber sale contract (used when state timber
is harvested) which specifies environmental protection measures.(41)
Adherence to the aforemer|tioned guidelines should provide satisfactory
erosion control for the projected feasibility study.
Effects on Wildlife
The general concern relative to the impacts that could result from
timber harvesting operations, and any mitigative measures that might lessen
these impacts, is to retain and/or improve the quantity and diversity of
wildlife and wildlife habitat that existed prior to these activities. Every
habitat must be capable of supplying its inhabitants with certain basic
necessities. Food and water in sufficient quality and quantity are obvious
requirements for maintenance and reproductive success. In addition, cover
is a necessity with a number of implications, including shelter and escape
cover from elements and predators, as well as resting and nest protection
cover. Added to the above, the habitat must also supply a seemingly end-
less list of specific individualistic requirements. Thus, the amount,
availability, and distribution of food, cover, water, and other special
requirements as affected by timber harvesting activities will determine the
carrying capacity a particular land unit has for a particular species.
While the word "impact" is normally associated with a negative
connotation, it can be positive as well. An activity that is detrimental
to one species could conceivably be beneficial to another. For instance,
the removal of tall trees would tend to improve the habitat of those species
living on or near the ground. On the other hand, such an action would result
in the elimination of habitat for those species which occupy the canopy.
Thus, forest management practices cannot be wholesalely judged as good or
bad for wildlife—only as.good or bad for certain species, at certain
times, in certain places.
Only rarely would wildlife be directly impacted by timber harvest-
ing or other forest management practices. More typically, such activities
directly impact wildlife habitats which, in turn, indirectly impact wildlife.
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194
For example, the removal of vegetation directly impacts the vegetation
which indirectly impacts wildlife by changing cover and food supply.
On an individual basis, an alteration in the accustomed composition
of the animal's environment, such as produced by a- timber harvesting operation,
would be expected to lead to either flight from the stress or an attempt
to cope with the changed environment. The latter response could conceivably
result in a short-term change in behavior which, for example, could affect
reproductive success such as abandonment of nesting sites. This behavior
would be expected to vary significantly between individuals of a species
and is not predictable. On a community basis, however, long-term changes
in species composition would be expected to follow the removal of timber
or brush. The magnitude of change will depend in large measure on the
life form of the disturbed community. The impacts would be greatest in
dense forests and brushlands as opposed to more open-type situations.
In general, variety and abundance of wildlife are enhanced in
forests that exhibit a variety of age classes and timber types and in
which silvicultural operations are active and widely dispersed through-
(42)
out the forests. The shade of dense old-growth forests is often too
great to provide the shrubs and herbs needed for food by birds and
animals. A well managed forest with openings can provide abundant
supplies. Wildlife also tend to work along the edge areas between the
woods and openings since both food and escape cover are readily avail-
(43)
able. Thus, many forms of wildlife would find the conditions created
by timber harvesting operations quite favorable for expansion. For instance,
small mammals would be favored by the new growth brought on by increased
sunlight. Most seed eating birds would also be favored by the openings
created by timber removal as opposed to conditions in deep woods. The
openings created in the densely wooded areas would also produce a variety
and quality of food for larger animals, such as deer, that would compensate
for seasonal deficiencies in surrounding areas.
Today, forestlands occupy some 4.5 million acres of Vermont and
account for about 75 percent of Vermont's total land area. Much of Vermont's
diverse and abundant wildlife population is of course found in these forested
(44)
areas. ' However, most of this woodland is in the pole stage or older
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195
categories. The early regeneration or succession stage, which is of pri
importance in the wildlife habitat spectrum, is noticeably lacking. As a
consequence, much of Vermont's wooded areas have grown beyond the stage
where they will support maximum or even minimum wildlife populations/44'
The loss of open lands reportedly has occurred at the rate of 20-25,000
acres per year and has a direct effect on the amount of forest "edge" which
is required by all wildlife species/ ' Commercial timber management practices
are effective, practical means of slowing the rate of edge loss and thus
improving or maintaining this important and productive wildlife habitat.
The quality and quantity of the range utilized by Vermont's
whitetail deer herd are of major concern. While less than 10 percent of
the total normal annual range serves as the herd's winter range, it is of
utmost importance as the deer population cannot survive without suitable
wintering areas. The abundance and availability of summer and winter browse
is a significant limiting factor for the deer herd. Presently, the deer
habitat and browse situation is reported to be in a poor and declining
itiat
(46)
state. This is substantiated by the decline in deer numbers from 250,000
in 1966 to 145,000 in 1973.
In order to remedy this situation, the State Forestry Planning
Committee of Vermont has recommended that the intensity of forest management,
including thinning and harvest cuts, be greatly increased. Such activities
would provide the necessary disturbances to stimulate the low woody growth
utilized for browse. In most instances, management of the woodlands for
improvement of deer habitat and browse would also be beneficial for
other wildlife species common to Vermont, such as black bear, ruffed grouse,
woodchuck, and snowshoe hare.(44) The State Forestry Planning Committee, in
its statement describing Vermont's forestry situation, has also recommended
a number of actions needed to enhance the wildlife potential of the State's
forests.(44) Briefly stated, these actions are:
• Integration pf wildlife habitat management with forest
resource management planning on both private and public
land.
• Development of wildlife habitat statistics and potentials
along with forest inventories.
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• Enlistment of the aid of competent authorities to
develop wildlife management guidelines for use
by both private and public ownerships.
• Implementation of intensified wildlife management
programs on the basis of well designed plans
developed cooperatively by professionals.
• Stimulation of the development of markets for
timber products so that stands can be economically
manipulated to provide the additional benefits of
habitat improvement.
Such actions, applied as part of the controlled commercial logging practices
discussed elsewhere in this report, will do much to maintain the young
productive forest stages that can provide the essential food and cover
requirements for wildlife.
Aesthetics
In recent years, public concern with aesthetics and environmental
quality has greatly increased, and aesthetic conflicts with an environmentally
aroused public are becoming more commonplace. One major focus of this
concern is the aesthetic impact of timbers harvesting operations which are
penetrating areas previously free from logging activities. Primarily as a
result of greater affluence and mobility, more and more people are now able
to visit forested areas in pursuit of recreation, scenery, and other
environmental amenities, and thus, are coming into more contact with forest
management operations. Unfortunately, people traveling through an area may
often only be aware of the regional landscape as a sequence of views along
a fairly narrow corridor such as a highway. The transiting viewer is thus
apt to be very sensitive to the visible presence of timber harvesting
operations. Public concern over timber harvesting practices is related
primarily to the visual impact; if it looks bad, people automatically
assume it is bad. Moreover, as most visitors to an area see it only once,
the fact that a cut over area can again be attractive is not visually
(42)
demonstrated to them. Complicating the program of aesthetic impacts
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197
is the fact that an individual's perception of a particular activity such
as timber harvesting is largely dependent upon what the individual knows
or believes. As a whole, the general public does not possess a specialized
knowledge or appreciation of regeneration, working circles, rotations,
sustained yields, etc. Thus, their opinion and reaction to timber harvesting
operations must be based largely on visual clues. As a result, forest
managers are becoming sensitive to appearances and are now modifying
harvesting practices to minimize aesthetic impacts. For example, in
addition to the size and stage of regrowth, the shape of a cutover area
is important. Cutover areas can often be made to harmonize with the
general landform by following the lay-of-the-land and/or leaving tree
cover in areas, such as saddles and selected portions of clearings.
Furthermore, edges which are the interfaces or boundary areas between
distinctly different landscape types are especially important and should
not suggest disharmony. The visual impact of such edge areas can be
lessened by timber harvesting techniques which (1) create small, irregular
openings which are similar to natural shapes already present, (2) arrange
openings for minimal visibility from likely viewing points, (3) use shelter-
wood harvesting to create a feathered edge, and 4) cut the boundary or
(47)
edge area several years ahead of the actual timber harvesting operation.
Wagner' has recently reviewed the environmental effects of forest manage-
ment and points out that "... perceiving is not equivalent to seeing" and
that "... perception depends on more than the stimulus present and the
capabilities of the sense organs. It also varies with the individual's
past history and present set or attitude acting through values, needs,
memories, moods, social circumstances, and expectations. Thus, what one
viewer perceives as desirable land management, another may perceive as
aesthetic degradation or even permanent devastation".
While more research is necessary to provide answers to aesthetically-
oriented forest management problems, Wagner<47) acknowledges that decisions
must be made now and suggests some interim guidelines to be considered
with respect to aesthetic values and forest management problems. Briefly
highlighted these guidelines are:
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198
1. Where possible, keep logging slash and amenity uses
of the forests separate in both space and time.
2. Lengthen rotations in critical view areas to reduce
the proportion of a working circle with exposed
slash or bare ground.
3. Reduce the scale of slash relative to nearby trees by
(a) using partial harvesting methods, (b) leaving islands
or clumps of trees within cutting areas, or (c) keeping
clearings small.
4. Where clearcutting is practiced, increase the "legibility"
of sustained yield forestry by dividing each working
circle into a series of "visual" management units.
5. Keep individual clearings small enough that a variety
of age classes will fit readily into a visual management
unit as mentioned in guideline 4.
6. Where highly productive sites are dedicated primarily
to even-aged timber management, create a coarse-textured
landscape so that new cuttings and areas of debris remain
a part of "ground" rather than becoming "figure".
7. Soften the edges of cutting and slash areas by (a) using
irregular shapes, (b) orienting openings for minimal
visibility from common viewing points, (c) using partial
harvesting systems where practicable, and (d) "feathering"
the edges of clearings.
8. Where volumes of debris are small, enhance the appearance
of naturalness and hasten rates of decomposition by (a)
leaving a residual stand, (b) lopping and scattering, (c)
crushing, (d) chipping, (e) piling and burning, or (f)
burying.
9. For heavy volumes of debris, create an appearance of
"managed concern" by (a) yarding unmerchantable material,
(b) windrowing, or (c) piling.
10. Avoid appearances of waste and inefficiency by increasing
utilization.
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11. Identify and mark "scenic routes" that avoid areas of
slash and bare ground along secondary road systems.
12. Relocate trails to avoid unsightly stages of rotations.
13. Create overlooks or short tours that permit a visitor
to see all stages of sustained yield timber management-
including slash and bare ground—within small area.
14. Use booklets, audio stations, cassette tape tours, short-
range radio transmitters (received through visitor's car
radio), or other means to help people understand what they
are seeing.
In the light of the above, it can be seen that it is in a context of com-
peting values (i.e.—the need for increased forest products and the
public's desire for unspoiled, aesthetically pleasing land) that timber
management decisions must now be made. Forest management decisions are
thus becoming more complex, and few management decisions can be made
without damaging someone's interests.
Summary
1. With sound forest management practice, the use of forest
surplus as fuel can, on balance, be of benefit to Vermont's
ecosystems.
2 . Forests remove definable amounts of nutrients from the
soil. The rate of removal depends on: (1) species; (2)
stocking; (3) age of the stand; (4) available moisture; and
(5) soil nutrient availability.
3 . The amount of nutrients removed from a site, due to
silvicultural practices, varies with the practice and
the variables mentioned in one above.
4. The effect'of nutrient removal, by harvest, is not known
at this time. Available data are site specific aud are
not amenable to comparisons or projections.
5. Nutrient inputs to forests are variable and are not yet
fully quantifiable.
6. Forest fertilization could serve as a source of nutrients.
However, fertilization implies good forest management. Due
to land-ownership patterns in Vermont, fertilization may
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not be feasible on private lands; fertilization would
be feasible on state lands.
7. Removing timber from a watershed will result in
temporary increases in stream flows depending on the
magnitude of cut and reestablishment time of the
forest cover.
8. Removal of the streamside canopy will result in
increased water temperatures. The magnitude of the
temperature fluctuation depends on the length of
channel exposed, the volume of water and initial water
temperature. Buffer strips, left adjacent to streams,
seem to be very effective in maintaining ambient water
temperatures within a clearcut area.
9. There is a tendency for nutrient flow, out of the
forest soil, to increase following harvest. The
magnitude and duration this loss depends on the amount
of time between cut and regeneration.
10. Vermont has very effective means of controlling
environmentally unacceptable forest harvesting
practices, i.e., land use law - Act 250, and regulations
governing water classification and control of quality.
11. Soil erosion, associated with silvicultural practices,
is due primarily to haul roads and skid trails.
Adherence to published guidelines should provide
satisfactory erosion control for the projected feasi-
bility study.
12. Much of Vermont's wooded areas have grown beyond the
stage where they will support maximum or even minimum
wildlife populations. As a result, the Vermont State
State Forestry Planning Committee has recommended
that timber stands be economically manipulated to
provide the additional benefits of habitat improve-
ments .
13. Public concern with timber harvesting practices is
related primarily to visual impact.
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14. Good management can reduce visual impacts.
Recommendations
1. Environmental impacts resulting from such silvicultural
practices as road construction, manipulation of wild-
life habitat, visual effects, etc., are well documented.
Also, sufficient management techniques are available to
diminish or curtail such impacts. It is suggested that
the Vermont Department of Forestry and Parks coordinate
procurement activities during the projected feasibility
study so that accepted silvicultural guidelines are
practiced.
2. The effects of residual management on the stability and
productivity of forest soils have not yet been resolved.
It is suggested that EPA initiate research to address
these problems. Such research would involve the
following variables:
• Identification and quantification of
nutrient inputs to Vermont's forest
soils.
• Identification and quantification of
nutrient outputs from Vermont's forest
soils.
However, this nutrient budget must be considered in view of the harvesting
techniques and rotation periods projected for wood, energy, procurement.
Such variables as: (1) site(s) potential; (2) species (mixture) selection;
(3) rotation projections (species; sites); and (4) amenability to manage-
ment (ownership, fertilization, etc.) must be considered before selection
of the experimental sites' can occur.
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REFERENCES
1. Jorgensen, J. R., C. G. Wells and L. J. Metz. 1975. The nutrient
cycle: key to continuous forest production. J. Forestry 73:400-403.
2. Rennie, P. J. 1955. The uptake of nutrients by mature forest
growth. Plant and Soil 7:49-95.
3. Morrison, I. K. and N. W. Foster. 1974. .Ecological aspects of
forest fertilization, p. 47-53. JEn F. Hegyi, chmn. Proceedings
of a workshop on forest fertilization in Canada. Canadian Forestry
Service Tech* Report 5. Great Lakes Forest Center, Sault Ste. Marie,
Ontario. 131 p.
4. Duvegneaud, P. and S. Denaeyen-De Smet. 1970. Biological cycling
of minerals in temperate deciduous forests, p. 199-225. In D. E.
Reichle, ed. Analysis of temperate forest ecosystems. Springer-
Verlay, N. Y. 304 p.
5. Malkonen, E. 1974. Effect of complete tree utilization on nutrient
reserves in forest soils, p. 377-386. JEn H. Young, ed. IUFRO
biomass studies. Univ. of Maine, Orono. 532 p.
6. Patric, J. H. and D. W. Smith. 1973. Forest management and
nutrient cycling in eastern hardwoods. U.S.D.A. Forest Service
Laboratory, Parsons, W. Va. (unpublished manuscript). 35 p.
7. Wilde, S. A. 1958. Forest soils: their properties and relation
to silviculture. Ronald Press, N.Y. 537 p.
8. Safford, L. 0. 1973. Forest fertilization in the eastern United
States; conifers, p. 206-210. In Forest fertilization symposium
proceedings. USDA Forest Service General Technical Report NE-3, Upper
Darby, Pa. 246 p.
9. Auchmoody, L. R. and S« M. Filip. 1973. Forest fertilization on the
eastern United States: hardwoods, p. 211-225. In Forest fertilization
symposium proceedings. USDA Forest Service General Technical Report
NE-3. Upper Darby, PA. 246 p.
10. Groman, W. A. 1972. Forest fertilization: state-of-the-art review
and description of environmental effects. U.S. Environmental
Protection Agency. EPA Techno Series R2-72-016. Corvallis, Oreg.
57 p.
11. Leaf, A. L. 1974. Where are we in forest fertilization? p. 1-5 JEn
F. Hegyi, ed. Proceedings of a workshop on forest fertilization in
Canada. Canadian Forestry Service Tecnn. Report 5. Great Lakes
Forest Center, Sault Ste. Marie, Ontario. 131 p.
12. Stone, E. 1973. The impact of timber harvest on soils and water.
p. 428-467. In F. A. Seaton, chmn. Report of the President's Advisory
Panel on Timber and the Environment. U. S. Government Printing Office,
Washington, D. C0 541 p.
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13. Boyle, J. R., j. j. Phillips, and A. R. Ek. 1973. Whole tree
harvesting: nutrient budget evaluation, j. Forestry 71:760-762.
14. Wells C. A., D. Whigham and H. Lieth. 1972. Investigations of
mineral nutrient cycling in an upland Piedmont forest, j. Elisha
Mitchell Scientific Soc . 88:66-78.
15. Likens, G. E., F. H. Bormann, N. H. Johnson, D. W. Fisher, and R. S.
Pierce. 1970. Effects of forest cutting and herbicide treatment
on nutrient budgets in the Hubbard Brook watershed-ecosystem.
Ecological Monographs 40:23-47.
16. Hibbert, A. R. 1967. Forest treatment effects on water yield.
p. 527-543. Jja W. E. Sopper and H. W. Lull, editors, Int. Symp.,
Forest Hydrology, Pergamon Press, New York.
17. Brown, G. W. 1969. Predicting temperatures of small streams. Water
Resources Research, 5:68-75.
18. Levno, A., and J. Rothacher. 1967. Increases in maximum stream
temperature after logging in old-growth Douglas-fir watersheds.
Pacific Northwest Forest and Range Exp. St. Res. Not PNW-65. 12 p.
19. Brown, G. W. , G. W. Swank, J. Rothacher. 1971. Water temperature
in the Steamboat drainage. U.S.D.A. Forest Service Research Paper
PNW-119. 18 p.
20. Eschner, A. R., and J. Larmoyeux. 1963. Logging and trout: four
experimental forests practices and their effect on water quality.
Prog. Fish Cult. 25:59-67.
21. Aubertin, G. M., and J. H. Patric. 1974. Water quality after clear-
cutting a small watershed in West Virginia. Journal of Environmental
Quality, 3:243-249.
22. Kochenderfer, J. N., and G. M. Aubertin. 1974. Effects of management
practices on water quality and quantity - Fernow Experimental Forest,
West Virginia. In Proc. Symp. Management Municipal Watersheds. U. S.
Forest Serv. Tech. Rept. NE. Upper Darby, Pa. (In Press)
23 U S D A. Forest Service. 1975. Protecting fish habitat during forest
road development. U. S. Govt. Printing Office, San Fransisco, Calif.
12 p.
24 Likens, G. E., and F. H. Bormann. 1974. Linkages between terrestrial
and aquatic ecosys'tems. Bioscience 24:447-456.
25 Likens, G. E., and F. H. Bormann. 1972. Nutrient cycling in ecosystems
p 25-67 lA J. Wiens, ed. Ecosystems: Structure and Function.
Oregon State University Press, Corvallis.
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26. Pierce, R. S., C. W. Martin, C. C. Reeves, G. E. Likens, and F. H.
Bormann. 1972. Nutrient loss from clearcuttings in New Hampshire
p. 285-295. JEn National symp. on Watersheds in Transition. Amer.
Water Resour. Ass. Proc. Series No. 14. Urbana, Illinois.
27. Lynch, J. A., W. E. Sopper, E. S. Corbett, and D. W. Aurand. 1974.
Effects of management practices on water quality and quantity -
Pennsylvania State Experimental Watersheds. Proc. Symp. Management
Municipal Watersheds. NE Forest Exp. Sta. Upper Darby, Pa. (In Press)
28. Johnson, P. L., and W. T. Swank. 1973. Studies of cation budgets in
the southern Appalachians on four experimental watersheds with con-
trasting vegetation. Ecology 54:70-80.
29. Douglass, J. E., and W. T. Swank. 1974. Effects of management
practices on water quality and quantity - Coweeta Hydrologic
Laboratory. .In Proc. Symp. Management Municipal Watersheds. U. S.
Forest Service Tech. Rept. N.E. Upper Darby, Pa. (In Press)
30. Hornbeck, J. W-, G. E. Likens, R. S. Pierce, and F. H. Bormann.
1975. Strip cutting as a means of protecting site and streamflow
quality when clearcutting northern hardwoods. Proc. 4th North
American Forest Soils Conf. Laval University, Quebec City, Canada.
(In Press)
31. State of Vermont, Department of Forests and Parks. 1975. Nonpoint
Source Water Pollution Evaluation Handbook - Erosion and Sedimentation.
State of Vermont, Montpelier. 43 p.
32. State of Vermont, Agency of Environmental Conservation, Water Resources
Board. 1973. Regulations governing water classification and control
of quality. State of Vermont, Montpelier. 25 p.
33. U.S. EPA. 1973. Processes, procedures and methods to control pollution
resulting from silvicultural activities. EPA Document 430/9-73-010.
Office of Air and Water Programs, Washington, D.C. 91 p.
34. Kochenderfer, J. N. 1970. Erosion control on logging roads in the
Appalachians. U.S.D.A. Forest Service Research Paper NE-158, Upper
Darby, Pa. 28 p.
35. Megahan, W. F. 1972. Logging, erosion, sedimentation: are they
dirty words? Journal of Forestry 70:403-407.
36. Bell, M.A.M., J. M. Beckett and W. F. Hubbard. 1975. Impact of
harvesting on forest environments and resources: a review of
literature and evaluation of research needs. Canada Dept. of the
Environment, Forestry Service. Pacific Forest Research Centre.
Victoria, B.C. 141 p.
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37. Leaf, C. F. 1974. A model for predicting erosion and sediment
yield from secondary forest road construction. U.S.D.A. Forest
Service Research note RM-274. 4 p.
38. Trimble, G. R. and R. S. Sartz. 1957. How far from a stream
should a logging road be located? j. Forestry 55:339-341.
39. Paker, P. E. 1967. Criteria for designing and locating logging
roads to control sediment. Forest Science 13:3-18.
40. Vermont Department of Forests and Parks. 1974. Forest Road
Classification. Montpelier, Vermont.
41. Vermont Department of Forests and Parks. 1974. Timber sale
contract. Montpelier, Vermont.
42. Webb, William L. 1973. Timber and Wildlife, p. 468^489. .In
F. A. Seaton, chmn. Report of the President's Advisory Panel on
Timber and the Environment, U.S. Government Printing Office,
Washington, D.C. 541 p.
43. Essentials of Forestry Practice. 1973. Timber and wildlife.
p. 568-489. In F. A. Seaton, chmn. Report of the President's
Advisory Panel on Timber and the Environment, U.S. Government
Printing Office, Washington, D.C. 541 p.
44. Vermont Forests. Resources for all. State Forestry Planning
Committee, State of Vermont, Agency of Environmental Conservation,
Department of Forests and Parks, 1972. 20 pp.
45. Hall, John. 1973. Vermont's State Wildlife Management Areas.
Reprinted from the Northern Logger and Timber Processor,
February, 1973. 3 p.
46. Vermont's 1974 Game Annual, Vermont Fish and Game Department,
Agency of Environmental Conservation, Bulletin 74-2.
47. Wagner, J. Alan. 1974. Recreational and esthetic considerations.
p> H-l-15. In Environmental Effects of Forest Residues Management
in the Pacific Northwest—A State-of-Knowledge Compendium. Pacific-
Northwest Forest and Range Experiment Station, USDA, Portland,
Oregon. USDA Forest Service General Technical Report PNW-24.
Various paging.
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APPLICABILITY OF WASTE WOOD FUEL CONCEPT TO OTHER
PLANT CAPACITIES AND REGIONS OF THE COUNTRY
The use of wood to fuel electricity generating plants at the 50 MWe
level has been shown to be both environmentally sound and cost effective. The
question remains as to whether wood fuel must be reserved for small incremental
power additions as contemplated in Vermont, or is feasible for larger capacity
facilities. More important is whether this rather unique solution to the
Vermont energy shortage is site specific or is applicable to other .sections of
the country.
Applicability to Other Plant Capacities
The waste wood fuel concept envisioned by GMPC calls for the employ-
ment of wood as the sole fuel for electricity generating stations. While this
concept has been shown both feasible and environmentally and economically
attractive, use of wood without supplementing with some conventional fossil fuel
places many limitations on the size and economy of this system.
Two major factors will tend to limit the size of any wood-fueled
power plant. First, procurement, transportation, and storage problems increase
dramatically with increasing plant capacity. Second, because of the variable
heat content of the wood chips, only boilers relatively insensitive to these
heat content changes such as stoker-fed boilers (maximum capacity approximately
50 MWe) can be employed. Because of the limited capacity per boiler, multiple-
boiler plants will be required to achieve Increased power rating or a dual
firing capability may be required.
In contrast to these limitations on plant size, there are inducements,
because of economies of scale, to build boilers as large as possible. Ultimately.
the size of any system will be determined by the community .requirements and the
economic trade-off between procurement system limitations and the economies of
scale. Rough estimates, based on transportation distances, suggest that the
maximum capacity of any wood-fueled plant will be from 200 to 250 MWe.
Significant increases in capacity, with accompanying economies of
scale, are possible through the use of suspension-fired boilers. However,
because of the nature of the boiler, the fuel must be of a more consistent
heating value than is possible with wood chips alone. The option recommended
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by many boiler manufacturers is to limit wood firing to 40.50 percent or less Qf
the total fuel content. The remaining fuel can be composed of coal, oil. or gas
Boilers employing combination wood-fossil fuels have been built as large'as
175 ^. The combined fuel concept can be utili2ed to bypass even this boiler
size limitation. By employing a 10 percent wood - 90 percent fossil fuel combin-
ation plant capacities as high as 500 to 1000 MWe would be possible with currently
available wood procurement technology,,
Applicability to Other
The potential viability of the waste wood for fuel concept can be
assessed by comparing the surplus or waste forest biomass available in the
different regions of the country with the current fuel requirements for these
regions.
Forest Biomass Waste
To facilitate this comparison, an estimate of the wood presently being
wasted in current forest harvesting operations and in forest product industries
was made. These numbers are rather conservative estimates of the total quantity
of wood available for fuel because they include no increase in the cutting of
commercial timber, and likely underestimate the quantity of wood available from
each category.
Noted below are the three major components of the biomass estimate,
along with the method of estimation. In each case the quantity is a fraction of
the quantity of commercial timber removed in the year 1970, as reported by the
U. S. Forestry Service„*
(1) Limbs and branches, stumps, and other
material normally left in the forest 50% of Removal
during three harvesting.
(2) Harvesting df "Rough and Rotten" old
non-prime trees and tree species which
are not used in the forest industry 25* of Removal
(this category includes all timber
harvested for stand improvement).
* References for this section are given on page 214
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(3) Use of forest industry plant wastes
such as saw mill residues, and wastes
from secondary industry such as furn- 20% of Removal
iture manufacture. Also included in
this category is waste bark.
In all cases only that fraction of the material which is currently
being wasted, i.e., not used in the pulp and paper or secondary industry, was
included to make these estimates„
Regional Fuel Requirements
Recent data on the quantities of fuel utilized in electric power
generation in each of nine regions of the United States are presented in
Figure 31. Steam-electric utilities consumption of coal, oil, and gas was
computed in terms of millions of coal-equivalent tons and plotted versus time,
starting in 1964. These numbers are compared in Table 52 (for the year 1970)
to the estimated quantity of waste forest biomass, expressed in terms of millions
of coal-equivalent tons, to determine those regions where the fuel wood concept
might be applicable. As shown in Table 52, the New England, South Atlantic,
East South Central, Mountain and Pacific regions all have waste forest biomass
totaling from 23 to 103 percent of the electric utility consumption of fossil
fuels in the region. Further, in the South Atlantic, Mountain, and Pacific
regions the estimated waste forest biomass represents 77, 118, and 103 percent,
respectively, of the combined oil and gas consumption by utilities.
Necessary Conditions for Fuel Wood Utilization
Three conditions are necessary before wood-burning power-plants can
become a reality:
(1) Supply - An adequate supply of fuel wood must be assured.
(2) Demand - There must be sufficient demand for additional
power in the region.
(3) Costs - The cost for electricity from fuel wood must be
lower or comparable to that from available fossil
fuels.
-------
FIGURE 31. STEAM-ELECTRIC UTILITIES1 FUEL CONSUMPTION TRENDS, COAL, OIL AND GAS, BY REGIONS
(Millions of Coal Equivalent Tons)
West North Central
1-rt »
1 Irt
75
50
25
i
-
\
r
U
i
.. ,.-
Pad
i
k.
i
me
1
I
-
-
-
~
125
100
75
25
1
I
-
-
-
\"'"
1
",
1
»- ****""
..JL_
'
r-—
;....
1
J...
-
-
-
-
-
I
East North Cental
_1_
IL-i-LJa>1
64 66 63 70 72 74 76
150
125
100
75 I-
50
25
L_
i • •
\- 1 Mountain
i- !
1
-
i
"
! i
-
-
64 66 68 70 72
Total U.S.
64 66 68 70 72 74 76
J<^
.^T
ro
O
vo
We»t Suulh Central
SCO
400
300
200
100
— 1 —
-
•^**
-
— r~
^
f
— i —
^
•-1 s=
•* * **
u— -
i
— i —
u-
• • *••
•""
— r~
'
•^
,
— I —
-
-
-
-
i
1JT
115 i ,„. .1
**•' i
i-
h
50 Ui-.r
25 L-
L
'!'!'!'
i 1 i
1 ...[..>-
-*•**? ! ]
_! _:
! • i
.1.1.1.
-i
-
-j
-i
t
-
.
i i i i "j-r—
U i I
i ' '
— r—
1 j ' i
66 68 70 72 74 76
•t: NCA Slnm Electric Flint Factofl,
64 !.« c-i 70 72 ~- 7j> t, .; ,.; 70 7; 7i ;4 {i tf
Nou: Co.1.0,l ra Cli n< not thown »he» connin|.lion a rtluMy mall.
-------
TABLE 52. COMPARISON OF CONVENTIONAL FUEL USAGE VERSUS QUANTITY OF
POTENTIALLY AVAILABLE WASTE WOOD FUEL, BY REGION
Potentially Available Waste Wood Fuel
Conventional Fuel Usage, s
10 Coal Equivalent TonsU;
Region
New England
Middle Atlantic
West North Central
East North Central
South Atlantic
East South Central
West South Central
Mountain
Pacific
(a) Reference (2).
(b) Reference (1).
Coal
4
45
25
115
65
50
—
14
—
Figures
Oil Gas
15
30
—
—
18
—
—
—
5
for
Total volume
0
4
15
—
13
—
76
6
25
1970.
calculated
Total
19
79
40
115
96
50
76
20
30
based
g 10" Coal
10 ,. , Equivalent
cu ft(b) ?onsM
534
341
335
752
2,946
1,815
1,762
875
3,818
on cu ft
4.3
2.8
2.7
6.1
23.9
14.7
14.3
7.1
30.9
removed in 1970.
Percent
of Total
23
4
7
5
25
29
19
36
103
The volume
Percent of
Oil and Gas
29
8
18
—
77
—
19
118
103
was composed <
three parts: (1) limbs and branches - 50 percent of removal, (2) rough and rotten - 25 percent of
removal, (3) plant residues - 20 percent of removal, including materials from primary, secondary
industry normally sent to waste.
(c) Volume of wood converted into equivalent tons of coal based on: (1) density of green chips, 54 lb/
ft^; (2) wood net heating value, 7.8 x 10° Btu/ton after correcting for the lower boiler efficiency
of wood as compared with coal (9.35 x 106 x 0.684/0.820 = 7.8 x 10°); (3) coal heating value, 26.2
10 Btu/ton.
to
-------
211
. There appears to'be, from the calculations presented in
Table 52, at least five regions where the quantity of waste wood is adequate
to supply wood-fired power plants. The questions exist, however, whether
(1) there exists a sufficient supply of wood within reasonable distance from
a proposed power plant site, and (2) there exists sufficient incentive to
induce the capital investment required to set up a reliable wood procurement
system in the area sufficient to supply a large electric power plant. Only
more detailed, site-specific study can determine these facts.
Demand. The demand for electric power, as shown in Figure 31, is
on the rise. Various estimates of electric power consumption show that demand
has been approximately doubling every ten years. With the depletion of the
world's reserves of natural gas and oil, the demand for a clean-burning, replen-
ishable fuel such as wood should be excellent.
According to Federal Power Commission statistics, two of the high
wood surplus regions, South Atlantic and East South Central, are near the lowest
in reserve electricity capacity of any of the regional electric reliability
(3)
councils. This low reserve should indicate the need for additional electric
generating capacity - capacity that could be, at least partially, supplied by
wood fuel.
Costs. The costs for electric power generation are composed of capital
costs for construction of the power generation facility, and operating costs
comprised mainly of fuel requirements. The capital costs for most fossil fuel
plants would be expected to be lower than for a comparable capacity wood fuel
plant due to the bulky nature of fuel wood and to boiler size limitations.
The capital costs for a plant with a dual capability for firing wood or coal
would be somewhat higher than for a plant firing wood alone because of the
need for dual fuel handling and storage. Required air pollution control equip-
ment, however, should be less for a wood-fired plant compared to a coal-fired
facility.
Fuel costs for fossil fuel vary by region. Data on fossil fuel costs in
dollars per million Btu are shown in Figure 32 for nine regions of the United States
from 1964 to 1973. While costs are reported only through 1973, the general trend
-------
FIGURE 32. STEAM-ELECTRIC UTILITIES' FUEL COST TRENDS, COAL, OIL AND GAS, BY REGIONS
("As Burned" Cost Per Million Btu)
West North Central
East North Central
Pacific
I.IU
1.00
80
60
40
20
1
-
-
-
£*~r
»"••"
(
^
'
/
X*
""T*
1
1
1
/
t
-
-
-
-
-
I
64 66 6S 70 72 74 76
1.20
1.00
eo
60
40
20
1
1
1
Mountain
-
-
•*•*»•
^£ w
Pi
!».—
_l
/'
/
r**""
_i —
'
'
1
1
1
f
•
.•"
(
-
,-
64 66 68 70 72 74 76
Total U.S.
New England
N>
I-1
N>
West South Central
East South Central
1.20
1.00
60
Art
20
1
" •"
-
"*"
,
"-'
i
X
,
/
-
-
-
-
-
1..
1.20
1.00
QM
Ln
-
•
-
•
-
i
,
'
'
»»*•».
r
f
t
**
•
-
-
-
-
i
1.20
l.CO
60
60
40
:o
1.20
1.00
80
60
40
20
• 64 66 68 70 72 74 74
Jf
'
64 66 68 70 .'2 74 76
/•»•-*- —
Source: NCA Smm-Elecuic Hani Ficlon.
66 68 70 72 74 76 64 66 66 70 72 74 76
Nat: CojJ. Oil TO G«i in not ihown where consumption is tebtively mail.
-------
213
of sky-rocketing costs is evident. This trend has increased even more rapidly in
the following years. With increases in imported oil costs, deregulation of oil
and eventual deregulation of natural gas, fuel costs including coal will continue
to rise. While certain areas, such as the low-sulfur coal Western states, will
continue to enjoy relatively low-cost fuel most of the country will be forced
to pay increasingly high fuel costs. Under this cost climate, waste wood selling
at $10-20/ton should be able to compete favorably with fossil fuels for incre-
mental electric power capacity additions.
Conclusions
The following conclusions have been drawn from study of estimates of
available waste forest biomass and current and projected levels of energy con-
sumption:
• The use of wood as the sole fuel for electric power
generation will limit maximum practical boiler size to
approximately 50 MWe. Larger capacity plants must be
comprised of relatively expensive, multiple boiler systems
or be based on the combined firing of wood and coal.
• The use of combined wood and fossil fuels will allow the
use of larger, more cost efficient, suspension-fired
boilers. Single boiler capacities of 175 MWe or larger
are possible.
• Procurement, transportation, and storage problems may
limit the maximum size of any single wood-fired plant
to approximately 200-250 MWe. Combined-fuel plants
could in theoy be constructed as large as 500-1000 We.
-------
214
• Five of the nine regions of the United States, New England
South Atlantic, East South Central, Mountain, and Pacific
have waste forest biomass which comprises from 23 to 103
percent of each region's electric utility consumption of
fossil fuels. Therefore, the applicability of the waste-
wood-for-fuel concept, based on waste wood availability,
is multiregionalo
• Demand for electric energy is growing steadily, and
therefore the opportunity for wood- or wood- and fossil-
fuel power plants is excellent.
• The cost of wood compared favorably with other fossil fuels
in many sections of the country° Wood's low polluting
composition and replenishable supply make wood an attractive
alternative to coal, oil, or gas for incremental capacity
additions.
• If a continuous supply of wood fuel cannot be assured, a
plant with dual fuel capability must be employed.
References
(1) Anon., The Outlook for Timber in the United States, Forest Resource Report
No. 20, U. S0 Department of Agriculture, Forest Service, Washington, D.C.
(October 1973).
(2) Anon., Steam-Electric Plant Factors. 1974 ed., National Coal Association,
Washington, D.C. (1974),
(3) Stout, James J., "Staff Report on 1975 Summer Load-Power Supply Situation
Contiguous United States", FPC News. Vol. 8, No. 24, June 13, 1975.
-------
215
EVALUATION OF THE USE OF THE MILTON
PLANT IM THE PROPOSED DEMONSTRATION
An assessment of the engineering modifications to the Milton
Plant required to successfully receive and burn wood fuel, and estimation
of the associated costs have been performed under subcontract by the
engineering firm of A. E. Stilson, Associates. The effort was intended
to be cursory and cost estimates were based on experience, data on-hand,
and unit prices of similar equipment. No engineering drawings were
prepared to describe the conversion or to assist in the cost estimates.
Consequently, considerable additional work will be required to establish
the construction details and the cost of the preferred method of adapting
the existing plant to buna wood chips. An estimate of these engineering
costs is included.
The report from A. E. Stilson, Associates is reproduced in
Appendix A. The basic conclusions reached are as follows:
(1) The boilers, turbine-generator, and the plant
auxiliaries have been maintained well and seem
to be adequate for a few years of service under
adequate care and operations.
(2) There are no apparent reasons why the plant cannot
be adapted to burn wood chips. However, the
physical arrangement of the boilers is not preferred
for burning such fuel. The deficiencies and
countermeasures which may overcome them are discussed
in the report.
(3) Plant modifications are described including the
( sySems required for chip unloading and storage,
chip retrieval from storage and conveying into
the existing boiler house, chip feeding to the
boilers, grate system, combustion air supply,
fly ash collection, and ash removal.
nit to modify the plant is currently
,anJ.B as standard production items. Delivery
_ be as long as 1 year for the stokers.
«) The cost of the modification including engineering
is estimated at $680,000.
•«-• «• —• •• —
-------
which can be obtained id questionable because.,
as mentioned above, the boiler configuration
is not typical of modern design for burning
such fuels. If the research is extended into
the fields of combustion and pollution control,
attention to the boiler deficiencies will be
imperative and qualified engineers should play
a key role in the entire project.
The following additional comments were made by Battelle engineers and were
discussed with a member of the Stilson staff.
(7) Occurrences of wood-dust explosions have been
reported* While the probability of such an
explosion is far lower for a system using wood
chips rather than sawdust, some fine material
is produced during chipping which might
accumulate sufficiently to create a problem.
Design of the Milton plant modifications and
of the projected 50-MW facility should provide
safe means for handling wood dust.
(8) A high-vanadium oil should be avoided when
burned in combination with wood chips. The
potential for ash fouling of the boiler tubes
is high for such a combination because of the
interaction of the vanadium in the oil and the
alkaline components in the wood ash.
Air Quality andStack Height Consideration
The question which has been .raised is whether raising the stack
at the Milton Power Plant from 185 ft- to 205 ft. will substantially affect
gound level concentrations of particulate resulting from the utilization
of wood in the Milton Power Plant boilers. If a mathematical examination
of the gound-level concentration equation is performed, it can be shown
that the maximum G.L.C. (ground level concentration) decreases 1% for every
1% increase in stack height, for the conditions of zero plume rise, infinite
mixing depth, and receptor heights equal to the stack base elevation.
With this formulation, the maximum G.L.C. would decrease by a
maximum of 11% by raising the stack 20 ft. This maximum G.L.C. decrease
is lessened for cases where there is a plume rise (as is typical with
power plants) and also for cases where the mixing depth interferes with
dispersion. In most real cases, therefore, the maximum G.L.C. decrease
due to increased stack height would be less than 11%.
-------
217
A computer program was used to verify the above results, and to
estimate the expected ground level concentrations. Power plant data
provided to the computer program included:
Mixing Depth
Stack Height
Stack Diameter
Stack Gas Temperature
Stack Gas Exit Velocity
Height of Receptor
1400 meters, an annual (afternoon)
average value for Milton
One set of cases at 185 feet,
and the other at 205 feet
Eight feet
550 degrees, allowing for some
temperature drop from the stack
inlet temperature of 600 degrees
We had a value of 3250 cfm. which
we first took as 3250 fpm. Later,
there was the probability that
3250 represented the 32500 cfm
capacity of each of two fans, with
a resultant velocity of 1293 fpm.
We used both values parametrically
noting that the latter value
appears more accurate from vis a vis
the energy content of the gas stream
There is an approximate correction
for elevation which we employed
to determine the effect of the bluff
behind the power plant. Thus,
receptor heights of 0 and 200 feet
above stack base elevation were
examined parametrically.
-------
218
The results for the most likely combination of parameters,
i.e., exit velocity of 1293 fpm, stack height of 185 feet, and receptor
height of 200 feet, are plotted as a function of wind speed and stability
on Figure 33. The results for a stack height of -205 feet for the smallest
and largest wind velocities are superimposed on Figure 33. It is seen that,
in general, the effect of increasing stack height by 6 20 feet is minimal.
The maximum ground level concentration predicted for each com-
bination of stack height, exist velocity, and receptor height is presented
in Figure 34. These results show that maximum G.L.C. is not very sensitive
to increased stack height, and somewhat more sensitive to stack gas exit
velocity, based upon the Briggs plume rise formulation. The maximum
G.L.C. is very sensitive to assumptions of terrain height, but the pre-
dicted concentrations for the two terrain heights are expected to bound
the actual observed values.
Finally, the actual predicted concentrations can be calculated
from the scaled parameters of Figures 33 and 34. Us.ing a wood-heat content
of 8 million BTU/ton, a suspended particulate emission factor of 30 Ibs/ton
wood (EPA AP-42), a heat output rate of 4 megawatts, and a input/output
conversion factor of 1 MW » 18 million BTU/hr., it was determined that the
heat input rate would be 72 million BTU/hr., requiring 9 tons wood/hr.,
with a suspended particulate emission of 270 Ibs/hr., or 34.0 grams/sec.
The absolute worst case G.L.C. predicted, then, would have a
value of 34.0 times 130 (Figure 35), or 4420 ug/m3 for a short time inter-
val (5-10 minutes). Since weather conditions do not remain invarient,
correlations have been drawn to relate maximum concentrations for differing
averaging times. In the Ohio River Valley, it has been observed that
the maximum 24-hour concentration is approximately 1/8 the maximum 5-
minute concentration (Reiquam). Thus, the maximum predicted 24-hour
3
concentration at the Milton plant is 553 ug/m , or more than the 24-hour
3
AAQ standard of 260 ug/m .
It is furthermore observed that a typical normalized concentration
(over all wind speeds and stabilities) in the first two kilometers is 10,
o
corresponding to an actual concentration of 340 ug/m . Thus, typical
ground level plume centerline concentrations can be expected to create
a nuisance in the immediate downwind neighborhood of the plant. Since
-------
219
the prevailing winds at the Milton site are westerly, and residences are
proximate to the east side of the plant, control of the emissions is
indicated. Nominal 80 percent participate control would reduce the maximum
o
predicted 24-hour concentration at the Milton plant to 110 ug/m , and the
3
typical ground level plume centerline concentration to 68 ug/m .
In conclusion, for all of the cases examined (for ranges of the
uncertain parameters) it was determined that a 24-hour violation of Federal
air quality standards could occur for uncontrolled emissions, and nuisance
effects could be expected at the residences near the plant. Raising the
stack by 20 feet is not expected to alter these conclusions. Therefore,
control of the emitted particulate is indicated.
-------
220
6 8
Downwind Distance, Kilometers
10
FIGURE 33. GROUND LEVEL CONCENTRATION AS A FUNCTION OF
DOWNWIND DISTANCE, WIND SPEED, AND STABILITY
-------
Stability; Unstabl
6 8
Kilometers
FIGURE 33. Continued
-------
222
Stability: Slightly Unstable
6 8
Kilometers
10
12
FIGURE 33. Continued
-------
223
Stability: Stable"
6 8
Kilometers
FIGURE 33. CONTINUED
-------
224
llfStability: Slightly Stable|-^p
6 8
Kilometers
FIGURE 33. CONTINUED
-------
225
Stability: Stable^ -r
Kilometers
FIGURE 33. CONTINUED
-------
226
FIGURE 34. GROUND LEVEL CONCENTRATION AS A FUNCTION OF
EXHAUST VELOCITY V AND TERRAIN HEIGHT H
6
-------
227
APPENDIX A
REPORT FROM A. E. STILSON, ASSOCIATES
on
CONVERSION OF THE MILTON PLANT
TO BURN WOOD CHIPS
-------
228
AldenEStilson & Associates
September 17, 1975
Page Two
SUMMARY
The results of the study are summarized as follows:
1) The boilers, turbine-genera tor, and the plant auxiliaries have
been maintained well and seem to be adequate for a few years
of service under adequate care and operations.
2) The existing oil-fired burners are manually ignited and operated
without flame safety equipment. A potential dangerous situation
could develop if oil flow were momentarily interrupted during
otherwise normal operation.
It is assumed that the oil burners will be operated at about
one fourth their design rate when the wood is burned. Wood
chips burning on a grate could provide an ignition source which
in turn would tend to reduce the hazard of operating oil burners
without flame safety equipment.
The costs presented in this report do not include adding flame
safety equipment to the burners. Several days of study would
be required to determine how this could be done and at what cost.
The legal and liability situations relative to operating safety should
be considered in view of not only the well being of the plant operators
but also the visitors which will likely be in the plant.
3) There are no apparent reasons why the plant cannot be adapted to
burn wood chips. However, the physical arrangement of the boilers
is not preferred for burning such fuel. The deficiencies and,counter-
measures which may overcome them are listed below.
a) The distance between the chips burning on the grate and the
boiler tubes is less than desired. This may be offset by
correct application of combustion air and turbulence to avoid
flame impingment on the tubes resulting in flame quenching
before complete burn out.
b) The combustion volume is about one half of that normally
designed into wood burning boilers. Again, proper proportions
and air flow patterns within the flame zone may be adequate to
provide acceptable combustion.
-------
229
AldenE.Stilson&Assoeiates
September 17, 1975
Page Three
SUMMARY
(continued)
c) Superheater surfaces are located on the rear wall of the
furnace and away from the flow of the hottest gases from the
burning of wood. The use of narrow angle oil burner nozzles
and proper setting of the air registers may provide adequate
heat over the superheater surfaces. It is assumed that a
minimum of one-fourth of the heat input to the boilers will be
from oil.
d) The boiler baffles being nearly horizontal provide a few areas
where flyash will deposit. Judicial use of adequate soot
blowers could likely be affective in avoiding excessive deposits.
The above situations need to be considered during the design of the
combustion air supply system. The design should permit adjustment
of the air input to achieve adequate combustion.
4) This report describes the plant modifications including the systems
required for:
a) Chip unloading and storage
b) Chip retrieval from storage and conveying into the existing
boiler house.
\
c) Chip feeding to the boilers
d) Grate system
e) Combustion air supply
f) Flyash collection
g) Ash removal
5) The equipment to modify the plant is currently available as standard
production items. Delivery may be as long as one year for the stokers,
-------
230
AldenE.Stilson& Associates
September 17, 1975
Page Four
SUMMARY
(continued)
6) The cost of the modification including engineering is estimated
at $680,000.
7) Assuming that 75% of the heat to operate the generator at full load,
the wood chip burning rate will be approximately 8000 Ib per hr
per boiler, 16000 Ib per hr total.
8) Dr. Beardsley indicated that the planned research program might
include the development of design and performance factors relative to
burning wood chips to generate steam. The value of data which can
be obtained is questionable because, as mentioned above, the boiler
configurations is not typical of modern design for burning such fuels.
If the research is extended into the fields of combustion and pollution
control, attention to the boiler deficiencies will be imperative and
qualified engineers should play a key role in the entire projects
CHIP HANDLING AND PLANT MODIFICATIONS
This section discusses the operating conditions and the selection of the equipment
and its arrangement to convert the existing boiler plant to burn wood chips. The
process starts with chips in a truck delivered to the site and concludes with
the flue gas being vented through the existing stack, the. discharge of flyash
into a container, and the discharge of ash from the boiler stokers into a container.
Operating Conditions
According to the operators of the existing plant burning oil, the turbine
generator functions well only when running at nearly the design load of
4 megawatts. This requires the steam from both boilers. Assuming that
an equivalent load would be maintained, the operating conditions would
be as follows:
1) Oil rate when burning only oil
2) Electrical output
3) Steam conditions
4) Heat input
5) Plant efficiency
6) Greenwood characteristics:
720 gal per hr total
4 megawatts
190 psi, 490F
100 x 106 Btuper hr
13.7 percent gross
Moisture 50 percent
Ash 1 percent
Heating value 5000 Btu per Ib
-------
September 17, 1975
Page Five
231
AldenRStilson & Associates
Operating Conditions (continued)
7) Assume 25 percent of total heat from oil when burning wood
chips.
8) Heat input from wood, 75 x 106 Btu per hr use 40 x 106 Btu per hr
to each boiler.
9) Chip feed rate to each boiler, 8000 Ib per hr.
10) Grate area in each boiler, 80 sq ft.
11) Burning rate of wood chips, 500,000 Btu per hr per sq ft of grate
area. This rate is reasonable.
12) Combustion volume with grates mounted low in the unit; 1600 cu ft.
13) Heat release rate from both oil and wood, 31,250 Btu per hr per cu ft.
A rate not exceeding 20,000 is considered good practice.
The heat release rate of 31,250 Btu per hr per cu ft is higher than considered
good practice for burning wood. However, good combustions can likely be
achieved with good design and control of the combustion air.
Chip Unloading and Storage
The chips would be delivered to the site in closed van semi-type trailers.
Standard equipment is available and would be used for unloading the trucks
and blowing the chips into a storage pile at the rear of the existing plant.
We expect that the nature of the chips would not result in a dust problem
to the neighborhood. However, this situation deserves additional consideration.
These chips would be stored outside on the ground, which would require
some leveling prior to the beginning of this operation. The chips would
serve as its own base, for operation on the surface of the ground.
There was some concern that the chips stored in this manner in the open
in the winter climates could freeze under some conditions and make the
retrieval of the chips for burning difficult if not impossible. However,
this was considered improbable by personnel at the Green Mountain Power
Company and also by other operators of paper mills who had experience
handling wood chips stored outside in temperatures as low as -50F.
Others planning this project considered dumping the chips at the top of the
Sufito theTeast of the plant. From here the chips would be shoved into a
chute and by gravity slide into the storage area. In our view, there is not
sufficient elevation difference to permit this considering that the storage
pile itself would likely be 15 to 30 feet high.
-------
232
AldenE.Stilson& Associates
September 17, 1975
Page Six
Chip Conveying to the Boiler Room
An operator, using a front end loader, would retrieve the chips from
the storage pile and dump them into a mechanical conveyor system
to deliver the chips into the boiler house. This system would consist
of the following:
1) An operator and a front end loader with a closed cab.
2) Hopper for receiving the chips from the front end loader and
distributing them to the conveyor. A vibrating or auger type
bottom might be required to meter the chips to the conveyor
and to reject or retain any large mass of chips Which might be
frozen together.
3) Conveyor to carry the chips from the storage area to the exterior
of the building at the northwest corner and high above the
operating floor. The conveyors and external hoppers for handling
the chips should be covered as much as possible, yet permitting
easy access for maintenance and operation.
4) Cross conveyor to carry the chips into the boiler house above in
front of the boilers. This conveyor would be equipped with a
system to unload the chips into a receiving hopper.
Chip Feeding
Chip storage and feeding to each boiler would be provided by the following
equipment:
1) Storage bin in front of the boilers and high in the boiler house.
2) An adjustable feed system consisting of dual sets of screws
and drives to meter chips independently to each boiler.
3) A swinging spout on each boiler to divide the flow of chips from
the feeder into two streams.
4) Gravity chutes to direct the flow to each of two air swept spouts
mounted on each boiler. The chips would be introduced at the front
of the boiler and below the existing operating floor.
5) Air swept spouts and the fan system to provide air to distribute the
chips on the grate.
-------
233
AldenEStilson & Associates
September 17, 1975
Page Seven
Chip Feeding (continued)
It would be the operators responsibility to control the feed rate from
the storage hoppers into each of the two boilers. The air swept spouts
would be adjusted in order to provide adequate distribution of the wood
chips on the grate system.
Grates
Each boiler would be equipped with a two-section dump type grate
which would be hand operated periodically to discharge the ashes into
the ash pits. Using a two-section stoker, only half of the furnace would
be cleaned at each time and this would continue to maintain fire in the
system.
To provide as much combustion volume as possible in the boiler, the
grates would be located as low under the boiler tubes as possible. This
will require some modification of the furnace and refractory linings in the
lower portion of the new combustion chamber.
Combustion Air Supply
The forced draft fans used for the existing oil burners should continue
to be used for this purpose.
For the burning of the wood chips, two additional fans would be installed
on each boiler. One fan would supply the under grate air and have a
static pressure capability of two inches of water at a flow rate of
7,500 cfm. The other would provide the overfire air for turbulence and the
distribution air to spread the wood chips over the grate. This fan would
have a pressure rating of 25 inches of water at a flow of 1500 cfm.
The combustion air from all fans would be manually controlled.
Superheat Control
It is anticipated the oil burners on ea ch boiler will have to remain in
service and be operated in conjunction with the burning of the wood
chips. The oil burners will supply about 25 percent of the required
boiler load They will also provide over fire turbulence for better
combustion and by directing the flame at the superheater give super-
heat control.
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AldenE.Stilson& Associates
September 17, 1975
Page Eight
Flyash Collection
As a means of particulate emission control, a mechanical dust collector
and induced draft fan would be required. The location of this equipment
would be exterior to the building in the vicinity of the existing coal silo.
Approximately a 100 HP fan would be required. Furnace draft would be
manually controlled by adjusting the damper at the fan inlet and the
balancing damper at the outlet of each boiler.
The existing breeching would be interrupted at the building wall and
replaced with new material up to the inlet of the elevated flyash collector.
Flue gas leaving the collector would be ducted to the electric motor driven
induced draft fan and thence back to the existing opening in the brick
stack.
The mechanical collector would have a bottom hopper for storage of
collected flyash material. Dust has burned in hoppers of collectors on
bark burning boilers. Therefore, continuous removal of the flyash through
a rotary valve is recommended.
The flyash would be discharged to a closed container to be picked up
and dumped at an acceptable location.
All of the outside duct work, flyash collector and induced draft fan would
be insulated.
Using the above technique 80 to 90 percent of the flyash will be collected.
Some steam plume may be visible at the top of the stack during cold weather
because of the high moisture in the wood.
Wet scrubber systems were considered undesirable because of the dense
steam plume and the tasks of treating and handling the water.
Ash Disposal
Ash from the wood burning would be dumped periodically into the ash pit
below the grates. From there they would be hand raked out of the furnace
into a container or conveyed out of the building to a receiver. The ash
content of wood is about 1 percent, so the quantity of ash to be handled
is not large. The ash would be hauled away with the flyash.
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AldenRStilson & Associates
September 17, 1975
Page Nine
Building Modifications
In order to install the stokers the concrete operating floor in front of
the boilers would be removed. The stokers would be brought into the
building through the windows above the operating floor and then lowered
through the new floor openings into the basement area for installation.
The concrete work now underneath the front of the boilers would also be
removed to receive the stokers, the front stoker plate, and the air swept
valves for the chip distribution onto the grate. Metal grating would be
reinstalled at the operating floor level and this would give the operator
at the floor level a view of the basement area where the air swept valves
would be installed.
DESCRIPTION OF THE EXISTING PLANT
The existing power generating station consists of two oil fired boilers and
one 4 megawatt General Electric steam turbine generator set. Each boiler is
equipped with two atomizing oil fired burners which have been installed in
what was originally an underfed coal fired unit. The coal stokers have been
removed and refractory floor installed in its place. Each boiler is equipped
with a forced draft fan and the flue gas exhausts into a common breeching
which is connected to a 135 ft. brick stack.
The boilers are natural circulating water tube type mounted in a brick setting.
The tubes and longitudinal-drum are installed inclined to the horizontal with
the downtake and uptake headers perpendicular to the tubes and the drum.
Gases make three passes, as directed by the refractory baffling arranged
parallel with the tubes, before exiting across the drum at the rear of the boiler.
The drum is suspended with hangers from overhead columns.
The superheaters consist of ten square tubes mounted horizontally across the
rear wall, thus only one side of each tube is exposed to the furnace. The flow
is parallel through the tubes and is combined in a header behind and external
to the boiler.
Other than boiler water level controls, there are no automatic controls and no
flame safety equipment on these boilers. The plant is started by manually
igniting a small quantity of No.2 fuel oil which is atomized by compressed air
during the warm-up period. As the boiler pressure increases the operators
manually admit steam to the turbine and then by increasing the burning rate
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AldenEStilson & Associates
September 17, 1975
Page Ten DESCRIPTION OF THE EXISTING PLANT
(continued)
and the turbine throttle setting they reach the equilibrium condition for
operation.
After the boiler is in operation, the No. 6 fuel oil is turned on and steam is
used for atomization. The No. 6 oil heater is located in the basement in front
of the boilers. Throughout the operating period, the fireman operates the
boiler maintaining pressure to satisfy the setting of the turbine throttle to
provide essentially a constant generator output. The quantity of combustion
air is set by the operator using the inlet damper on the forced draft fan.
The stack, approximately 135 feet high, provides the natural draft for the
furnace. The fireman adjusts the damper between the boiler and the breeching
to maintain the proper negative pressure in the furnace.
The boiler operates at 190 psi and about 490F. Superheat is achieved with
surface mounted superheater section at the rear of the boiler. The operator
stated that the fuel oil nozzle angle had to be reduced from 90 to 80 degrees
to extend the flame further towards the superheater in.order to maintain this
temperature.
According to the operators, the turbine does not run well unless both boilers
are fired and the unit is operated at nearly full load. Under such conditions,
the quantity of No.6 oil burned is about 720 gallons per hour and the generator
output is 4 megawatts.
The equipment is all in good working order and was fired for a period of about
seven hours late in August of 1975, This plant is operated very little and only
as needed to maintain the output of the power company.
No water treatment is used for either the make-up water or the boiler water of
this plant. According to the operators, it has been on line as much as 30-40%
of the time without any detrimental effects due to the lack of water treatment.
Make-up water is provided either by the river nearby or the municipal system.
Apparently this water is of such quality that treatment is not needed for this
boiler which is relatively low pressure for a power boiler.
According to the operators, the soot blowers are working adequately and do
provide the means for keeping the boiler surfaces clean. Also, they claim
that there was no substantial build-up of flyash on the horizontal baffles even
when the unit was firing on coal. The operator did mention that some portion
of the soot blower on one unit is not operating well and their attempts to repair
this were not successful.
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September 17, 1975 AldenE.Stilson&Associates
Page Eleven
DESCRIPTION OF THE EXISTING PLANT
(continued)
The building is constructed of poured concrete basement, walls and floor;
load bearing brick walls; and pre-cast concrete roof supported by steel
trusses.
The site is accessible by a good two lane road and there is a stone drive
along the north side of the steam plant which appears to be an all weather road
suited to handling heavy trucks. There is a bluff 30-50 feet on the east side
of the plant which is estimated to be 50-60 feet above the grade of the plant
site. A one lane drive at the top of the bluff is used by the oil hauling trucks
which discharge oil through a pipeline to the oil tanks below. A stone wall
which appeared to be the foundation for some other structure is on the top of
this bluff with the foundation remains of coal handling facilities. Others who
have been studying the conversion of this plant to burn wood chips have con-
sidered unloading the chips on the top of this bluff and then by gravity or
mechanical means convey them to storage below.
To the east of the building and north of the brick stack there is a coal silo
which has been abandoned. The foundation of this silo could likely be the
base for pollution control equipment of the plant converted to burn wood chips.
To the rear, which is south of the existing plant, is an area which could be used
for storing the wood chips outside. A few power line poles are located there
which might need to be moved. The transformers are located immediately adja-
cent to the building on the south side. Some protection will likely be required
to prevent the tractor operators handling the wood chips from hitting the trans-
formers .
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September 17, 1975
Page Twelve
238
AldenEStilson & Associates
COST ESTIMATES
The cost estimate for the plant modifications is shown below. A more detailed
engineering study and design will be required to develop cost estimates of
a preferred system. The plant modifications described above mention one
mechanical dust collector to be used for flyash control. If greater efficiency
in flyash collection would be required, a second mechanical collector could be
installed in series with the first and the purchase price of the second collector
is reflected by the contingency listed below. The costs are 1975 prices.
Item Installed Cost for Two Boilers
Chip unloading, storage and retrieval $ 90,000
Conveyors between the outside chip
storage and the hopper in the boiler house 40,000
Storage hopper and chip metering to
boilers 60,000
Stokers, including front wall furnace work 130,000
Refractory modifications 40,000
Building modifications 30,000
Induced draft fan and flyash collector 150,000
Electrical 20,000
Engineering 70,000
Contingency 50.000
TOTAL $680,000
Please let me know if you have any questions regarding this report.
Sincerely,
ALDEN E. STILSON & ASSOCIATES
JDH/mrd Jojrfii D. Hummell, P. E.
Enclosures (J
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239
TECHNICAL REPORT DATA
If lease read Instructions on the reverse before completing)
EPA-600/2-76-056
2.
3. RECIPIENT'S ACCESSION>NO.
«. TITLE AND SUBTITLE
Comparison of Fossil and Wood Fuels
5. REPORT DATE
March 1976
6. PERFORMING ORGANIZATION CODE
7. AU
o XT o ^•HvJ?am'TC-M-Allen> D-A. Ball, j.E.Burch,
H.N. Conkle, W.T. Lawhon, T. J. Thomas, and G.R
Smithson, Jr.
8. PERFORMING ORGANIZATION REPORT NO.
9, P
JG ORGANIZATION NAME AND ADDRESS
Battelle-Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
10, PROGRAM ELEMENT NO.
EHB-527; ROAP AAK-01A
11. CONTRACT/GRANT NO.
68-02-1323, Task 33
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OH REPORT AND.PERIOD COVERED
Task Final; 7-12/75
14. SPONSORING AGENCY CODE
EPA-ORD
^SUPPLEMENTARY NoTEsproject officer for this report is J.D. Kilgroe, Mail Drop 61,
Ext 2851.
16. ABSTRACT
The report gives results of a preliminary assessment, comparing the use
of wood as a fuel for a commercial electric power plant in Vermont, with that of
clean fossil fuels or fossil fuels with suitable polluation control technology. For the
study, wood fuel was derived from forest surplus; i.e., the tops and branches of
trees cut for commercial purposes, cull or noncommercial trees, and waste from
forest products industries. The comparison considered boiler technology, pollutant
emissions, control technology, energy balance, environmental/ecological impact, and
cost. Conclusions included: the use of forest surplus and waste wood is technically
feasible, pollutant emissions are controllable, net energy balances are favorable,
the preliminary estimated cost is competitive, with proper forest management, there
is potentially a net benefit to the ecology of Vermont's forest ecosystems, wood is a
renewable resource, and a demonstration is recommended to advance the concept
toward commercial application. Because wood is a competitive fuel, a cursory
study was made, showing the concept to be applicable to other regions of the country
for incremental electric power generation capacity.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air Pollution
Energy
Fossil Fuels
Wood Wastes
Cost Effectiveness
Electric Power Generation
8. DISTRIBUTION STATEMENT
Unlimited
EPA Form 2220-1 (9-73)
Air Pollution Control
Stationary Sources
19. SECURITY CLASS (This Report)
Unclassified
13B
21D
11L
14A
10A
21. NO. OF PAGES
254
20. SECURITY CLASS fThii r>a?c)
Unclassitied
22. PRICE
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