CO-GASIFICATION OF DENSIFIED
SLUDGE AND SOLID WASTE IN A
DOWNDRAFT GASIFIER
by
S.A. Vigil and G. Tchobanogious
Department of Civil Engineering
University of California
Davis, California 95616
Grant No. R-S05-70-3010
Project Officer
Howard Wall
Office of Research Development
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
Cincinnati, Ohio 45268
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DISCLAIMER
This research project was co-sponsored in part by The Department of Civil
Engineering, University of California, Davis, the University of California Appropriate
Technology Program and the Municipal Environmental Research Laboratory, U.S.
Environmental Protection Agency. The contents do not necessarily reflect the views
of the University of California or the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
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FOREWORD
The Environmental Protection Agency was created because of increasing public
and government concern about the dangers of pollution to the health and welfare of
the American people. Noxious air, foul water, and spoiled land are tragic testimony
to the deterioration of our national environment. The complexity of that environment
and the interplay between its components require a concentrated and integrated attack
on the problem.
Research and development is that necessary first step in problem solution and
it involves defining the problem, measuring its impact, and searching for solutions.
The Municipal Environmental Research Laboratory develops new and improved
technology and systems for the prevention, treatment, and management of wastewater
and solid and hazardous waste pollutant discharges from municipal and community
sources, for the preservation and treatment of public drinking water supplies, and to
minimize the adverse economic, social, health, and aesthetic effects of pollution.
This publication is one of the products of that research; a most vital communications
link between the researcher and the user community.
Development of safe and economical methods for disposing of the sludges
produced from wastewater treatment operations is one of the most pressing
environmental needs. This publication provides much needed information on the
feasibility of one approach to dispose of sludge and solid wastes which generates a
gas that can be used to reduce the need for priority fuels.
Francis T. Mayo, Director
Municipal Environmental
Research Laboratory
111
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ABSTRACT
Thermal gasification, the subject of this report, is a new process for the
co-disposal of densified sludge and solid waste in a co-current flow, fixed bed reactor
(also called a downdraft gasifier). The advantages of this technology include lower
costs than other incineration or pyrolysis technologies, simple construction and
operation, and the ability to use a variety of fuels including agricultural wastes and
other biomass materials in addition to densified sludge and solid waste. These and
other related subjects are discussed in this report.
Essentially the gasification process involves the partial combustion of a
carbonaceous fuel to generate a low energy combustible gas and a char. Operationally
fuel flow is by gravity with air and fuel moving co-currently through the reactor.
The low energy gas produced is composed primarily of carbon monoxide, hydrogen
and nitrogen and trace amounts of methane and other hydrocarbons.
Although fixed bed gasifiers are mechanically simpler than other co-disposal
reactors such as multiple hearth furnaces or mass fired incinerators, they have more
exacting fuel requirements which include: 1) moisture content <_ 20 percent, 2) ash
content <_ 6 percent, and 3) relatively uniform grain size. Neither municipal solid
waste nor dewatered sludge meet these criteria without some front end processing.
Demonstrating that a suitable gasifier fuel could be made with a simple front end
system consisting of source separation of the solid waste, sludge dewatering, and fuel
densification has been one of the objectives of this project.
To study the gasification process a pilot scale gasifier was constructed. A
broad range of fuels have been tested with the gasifier including an agricultural
residue, densified waste paper, and densified waste paper and sludge mixtures containing
up to 25 percent sludge by wet weight. The sludge fuels were made from mixtures
of lagoon dried primary and secondary sludge and recycled newsprint (in full scale
systems a mixed paper fraction of solid waste would be used). The mixtures were
densified using commercially available agricultural cubing equipment.
The gasifier was operated with each fuel, and measurements of the variables
needed to characterize the process were made. Gas, fuel, and char analyses were
used to compute energy balances. These data were used to calculate efficiencies for
each run. Hot gas efficiency, which includes the sensible heat of the gas, ranged
from 85.2 to 40.0 percent. The cold gas efficiency, which does not include the gas
sensible heat, ranged from 37.1 to 80.7 percent. The dry, low energy gas produced
during the tests ranged in higher heating value from 4.52 to 6.79 MJ/m .
IV
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CONTENTS
FOREV/ORD iii
ABSTRACT iv
FIGURES vii
TABLES ix
ACKNOWLEDGEMENT x
CHAPTER
1. INTRODUCTION 1
Purpose of Present Study 2
Cited Literature 2
2. BACKGROUND 3
Conventional Approaches to Sludge Disposal 3
Resource Recovery from Solid Waste 11
Energy Recovery from Solid Waste 19
Co-Disposal of Sludge and Solid Waste 21
Gasification as a Co-Disposal Option 23
Gasification as a Unit Operation 27
Summary 31
3. EXPERIMENTAL APPARATUS, METHODS,
AND PROCEDURES 32
Experimental Gasification System 32
Laboratory Testing 3S
Field Testing 42
Preparation of Gasifier Fuels 42
Operation Procedures 44
Energy Balance Computations 46
4. EXPERIMENTAL RESULTS 55
Fuel Characteristics 55
Operational Data 55
Gas Analysis 69
Char, Condensate, and Slag Characteristics 69
Energy Balances - Run 06, 08, 11, and 12 76
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5. ENGINEERING SIGNIFICANCE 79
Economics of Co-Gasification 79
Large Scale Resource Recovery S7
Small Scale Gasification S7
Limitations to the Co-Gasification Process 88
6. CONCLUSIONS AND RECOMMENDATIONS FOR 89
FUTURE RESEARCH
Conclusions S9
Recommendations for Future Research 90
REFERENCES 91
APPENDIXES 96
A. Computer Program "GASEN" A-l
B. Computer Program "GASHEAT" B-l
C. Computer Program "ENERGY" C-l
VI
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FIGURES
Number Page
1. Typical flowsheets for sludge treatment 5
2. Cross section - multiple hearth sludge furnace 8
3. Cross section - fluidized bed sludge furnace 10
4. Cross section - electric sludge furnace 12
5. Cross section - cyclonic sludge furnace 13
6. Typical mixed waste recovery system 16
7. Materials recovery from source separated solid waste 18
8. Production of densified refuse derived fuel from
source separated solid waste 20
9. Gasification system for sludge and source separated
solid waste 24
10. An integrated gasification system for co-disposal of
various wastes 26
11. Schematic of a downdraft gasifier 30
12. Cross section - UCD sludge/solid waste gasifier 33
13. Exterior view - UCD sludge/solid waste gasifier 34
14. Interior view - UCD sludge/solid waste gasifier 35
15. Schematic of thermocouple system used to monitor
gasifier temperatures 37
16. Data analysis subsystem for monitoring gasifier
operation 37
17. Cross section - extrusion dies of the John Deere
Cubing Machine 39
18. Schematic of the Papakube densification system 40
vii
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FIGURES (continued)
Number Page
19. Schematic - dry gas sampling train 43
20. Schematic - gas moisture sampling train 43
21. Data required for mass balance 47
22. Data required for energy balance 47
23. Idealized psychrometric diagram for gas cooling 51
24. Temperature profiles for gasifier reduction zone and
low energy gas (RUN 08) 63
25. Temperature profiles for gasifier reduction zone and
low energy gas (RUN 09) 64
26. Temperature profiles for gasifier reduction zone and
low energy gas (RUN 10) 65
27. Temperature profiles for gasifier reduction zone and
low energy gas (RUN 10 continuation) 66
28. Temperature profiles for gasifier reduction zone and
low energy gas (RUN 11) 67
29. Temperature profiles for gasifier reduction zone and
low energy gas (RUN 12) 68
30. Sludge processing and disposal options SO
31. Annual costs of processing and disposal of sewage sludge
by various methods of a community of 10,000 persons S2
32. Annual costs of processing and disposal of sewage sludge
by various methods of a community of 30,000 persons S3
33. Annual costs of processing and disposal of sewage sludge
by various methods of a community of 50,000 persons S4
vni
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TABLES
Number Page
1. Summary of unit operations and processes for sludge
treatment and disposal 4
2. Characteristics of biological and thermal sludge
processing systems 7
3. Composition, moisture, and energy content of solid
waste 1 5
4. Planned co-disposal facilities in the United States 22
5. Summary of data collection and analysis equipment 41
6. Summary of fuel characteristics 56
7. Characteristics of typical coals and woods 58
8. Densities of gasifier fuels 59
9. Operation summary 60
10. Composition and energy content of low energy gas 70
11. Summary of gasifier char characteristics 71
12. Summary of condensate characteristics 74
13. Char and slag generation 75
1^. Energy balances 77
15. Cost of energy of hot producer gas and natural gas 86
IX
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ACKNOWLEDGEMENT
The assistance of 3. Goss, R. Couper, B. Jenkins, J.J. Mehlshau, N. Raubach,
and C.3. Redding of the Department of Agricultural Engineering, University of
California, Davis is gratefully acknowledged. The technical assistance of D. Vaughn,
Cal-Cube Corporation, and G. Nelson, Papakube Corporation is also gratefully
appreciated. Operation of the gasifier and conduct of laboratory analyses were assisted
by N. Sorbo, D.A. Bartley, D. Davis, and R. Healy, graduate students in the Department
of Civil Engineering, University of California, Davis. This report was typed by
B. Rutledge and D. Pfoutz. This research was co-sponsored by the University of
California Appropriate Technology Program. Their timely support made this project
possible.
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CHAPTER I
INTRODUCTION
Historically the civil engineer has been responsible for the protection of public
health and safety through the design of wastewater treatment systems and solid waste
disposal facilities. Originally the principal criterion placed on the civil engineer by
the public was the safe disposal of liquid and solid wastes in the most economic
manner possible.
Within the last decade, the public has demanded, and the government required,
through Federal laws, that liquid and solid wastes be disposed of in a safe manner
with minimum impact on the environment. In the environmental fervor of the day,
cost-effectiveness was not always considered.
More recently it has become recognized that it is not enough to protect the
environment. Systems for the disposal of liquid and solid wastes must also be both
cost and energy effective. This concept has been codified into law, The Clean Water
Act of 1977 (6). This law provides significant financial incentives to the states in
the form of additional Federal cost sharing funds to encourage the use of innovative
and/or alternate technology that is more cost effective and energy efficient than
conventional technology. Similarly in the Resource Conservation and Recovery Act
of 1976 (^5) the focus of solid waste management was-shifted from the disposal of
solid wastes in landfills to the recovery of energy and the recycling of resources.
Today the co-disposal of sludge (the solid residues of wastewater treatment)
and solid waste in a joint facility is acceptable from an environmental, economic,
and energy standpoint. However, the trend in development of such projects has been
towards very large systems. It has been assumed that the economics of scale precludes
the use of such technology by small communities (less than 50,000 population).
This report presents the development of a new process for the co-disposal of
sludge and solid waste, which unlike existing co-disposal technology, can be implemented
on a small scale. The process involves the co-gasification of densified mixtures of
sludge and source separated solid waste in a simple fixed bed reactor, also known as
moving packed bed reactors (27,28). Energy, in the form of a low energy gas, which
is produced by the process can be used to fuel boilers, heaters, engines, or turbines.
The process is air-blown gasification which has been widely applied to coal, wood,
and agricultural wastes, but has never before been used for the co-disposal of sludge
and solid waste.
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PURPOSE OF PRESENT STUDY
This study was undertaken to 1) review existing co-disposal technology, 2) assess
the potential for small scale'co-disposal and energy recovery, 3) explore the feasibility
of utilizing gasification technology in small communities, ^) design and construct a
pilot scale co-gasification system, 5) present and analyze data from co-gasification
experiments, 6) compare the economics of co-gasification with conventional sludge
disposal techniques, and 7) discuss how gasification technology can be best implemented
in an integrated waste management system for small communities.
CITED LITERATURE
Cited reports, studies, and other pertinent literature have been arranged
alphabetically and numbered sequentially, and may be found at the end of this report.
Where reference is made to this material in the text, the appropriate number or
numbers are enclosed in parentheses.
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CHAPTER II
BACKGROUND
The treatment of wastevvater, disposal of wastewater sludges, and collection
and disposal of municipal solid wastes are public works functions that should be
considered in an integrated fashion. All of these activities are energy intensive and
must be accomplished to protect both the public health and the environment. However
if the energy contained in municipal solid waste could be recovered and converted
to a usable form, it could subsitute for much of the energy consumed in the treatment
of wastewater and disposal of sludges.
Conventional methods for sludge and solid waste disposal are reviewed in this
chapter. The co-disposal of sludge and solid waste is also considered. Finally a new
concept for co-disposal, the co-gasification of densified mixtures of source separated
solid waste and sludge is presented.
CONVENTIONAL APPROACHES TO SLUDGE DISPOSAL
Sludge is the liquid or semi-liquid byproduct of wastewater treatment. Typically
the solids content of sludge ranges from 0.25 to 12 percent solids, depending on the
wastewater treatment process used. Dealing with sludge is complex and expensive
because it is composed of the solid constituents present originally in the wastewater
(primary sludge) and the organic matter contained in the wastewater converted to
bacterial cell tissue (biological sludge). Current sludge disposal practices are reviewed
in the following discussion.
Unit Operations of Sludge Processing and Disposal
The ultimate purpose of sludge processing is to dispose of sludge in as economic
and environmentally benign a manner as possible. To accomplish this goal, many unit
operations and processes are available. The principal unit operations and processes
used in sludge management are summarized in Table 1.
Typical Sludge Treatment Flowsheets
The unit operations and processes mentioned in Table 1 can be assembled in
an almost infinite variety of flowsheets. In general, two basic catagories of flowsheets
can be formulated, biological systems in which aerobic or anaerobic digestion is used
to stabilize sludge, and thermal systems in which incineration or pyrolysis. thermal
gasification, or liquefaction (PTGL) processes are used to reduce the volume and
sterilize the sludge. Typical flowsheets for each category are shown in Figure 1.
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Table 1
SUMMARY OF UNIT OPERATIONS AND PROCESSES FOR SLUDGE TREATMENT AND DISPOSAL
Unit Operation
or Process
Function
Typical Process or Operation
Thickening
Stabilization
Conditioning
De water ing
Drying
Composting
Thermal reduction
Ultimate disposal
Volume reduction to increase the
efficiency of downstream processes
Pathogen destruction, volume and
weight reduction, odor control
Improvement of dewatering or thickening
rate, improvement of solids capture,
improvement of compaction, stabilization
Water removal, volume and weight
reduction, reduction of fuel
requirements for incineration/drying
Water removal, sterilization,
utilization
Pathogen reduction, volume
reduction, product recovery
Destruction of solids, water removal,
sterilization, energy recovery
Utilization and disposal
Flotation and gravity
thickeners, centrifuges
Chlorine oxidation, lirne stabilization,
heat treatment, anaerobic digestion,
aerobic digestion
Chemical conditioning,
elutriation, heat treatment
Vacuum filter, filter press,
horizontal belt filter, centrifuge,
drying bed, lagoon
Flash dryer, spray dryer, rotary
dryer, multiple hearth dryer,
oil emersion dehydration
Composting (sludge only),
co-composting with solid waste
Multiple hearth incinerator, fluidized
bed incinerator, flash combustion,
pyrolysis-thermal gasification-
liquification (PTGL) processes,
co-disposal with solid wastes
Sanitary landfill, land application,
land reclamation
Adapted from References 33 and
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COMBINED
WASTE
ACTIVATED
PRIMARY
SLUDGE
c
TO
ANAEROBIC CHEMIC
DIGESTER * CONDIT
1
SUPERNATANT
PLANT INFLUENT
fc» CENTRIFUGE I
IONING "~ """ ~~~^
CENTRATE TO
PLANT INFLUENT
DEWATERED SLUDGE
TO ULTIMATE DISPOSAL
a) Biological
EXHAUST
GASES
WASTE
ACTIVATED
SLUDGE
PRIMARY
SLUDGE
FILTRATE TO
PLANT
INFLUENT
MULTIPLE-HEARTH
INCINERATOR
ASH TO
ULTIMATE
DISPOSAL
b) Physical - chemical
Figure I. Typical flowsheets for sludge treatment.
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Comparison Between Biological and Thermal Sludge Processing Systems
Biological processes have been used successfully to treat sludge for many years.
The advantages of these processes are relatively simple operation, proven performance,
and in the case of anaerobic digestion, the potential for energy recovery. On the
other hand, they are subject to upsets caused by variations in the sludge and fluctuations
in the biological flora and fauna in the reactor. For this reason, biological reactors
are often not fully automated, requiring close monitoring by skilled operators. Finally,
the end product of the biological stabilization process is a wet slurry which usually
must be dewatered for economic disposal.
Thermal sludge processing systems, while quite complex in some cases, can be
readily automated. The end product of thermal processing is a dry, sterile ash or
char which is a small fraction of the total influent solids. The principal disadvantages
to these systems are their relatively high capital cost, and the need for external fuel
(oil or natural gas). The principal differences between biological and thermal sludge
processing systems are summarized in Table 2.
Thermal Processing of Sludge
There are only four types of thermal sludge processing systems commercially
available. They include: multiple hearth furnaces, fluidized bed furnaces, electric
furnaces, and single hearth cyclonic furnaces. Only the first two types of systems
have been used extensively in the United States. There have also been many pyrolysis
and gasification processes tested with sludge, but there are currently no such projects
proposed or under development for sludge alone. All of the proposed projects in this
category are designed for solid waste alone, or for the co-disposal of solid waste and
sludge (41).
Multiple Hearth Furnace - The multiple hearth furnace (MHF) is the most widely used
method of thermal sludge processing. In 1977 over 340 units were in operation in
the United States (41). A typical MHF is shown in Figure 2. Dewatered sludge solids
are admitted to the upper hearth and progressively transported to the lower hearths
by the raking action of rotating rabble arms. Combustion air flow is counter to the
sludge flow. Because temperatures often exceed 900°C, the rabble arms and central
drive shaft are air cooled, and the outer shell of the furnace is refractory lined.
MHF's are designed for continuous operation. Because of the refractory lining,
24 to 30 hours are required to bring a cold furnace up to temperature or cool it.
For this reason MHF's are usually not installed at small treatment plants, many of
which are only manned eight hours per day.
In most MHF systems, auxiliary fuel is required to combust dewatered sludge
solids. If sludge can be dewatered enough, autogenous combustion of the sludge can
take place (i.e., self-sustaining combustion). The autogenous point can be estimated
with the following equation:
"' x 100%
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Table 2
CHARACTERISTICS OF BIOLOGICAL AND THERMAL
SLUDGE PROCESSING SYSTEMS
Type of System
Parameter
Biological
Thermal
Residence time
Start up time
Operational temperature
Operational complexity
Potential for automation
Preferred feedstock
Residue
Long (3 to 60 days)
Long (9 to 180 days)
Low (20 to 35°C)
Moderate
Moderate
Nutritionally
balanced,
wet slurry
Biologically active,
wet slurry
Short (lOsec to 1 hour)
Short (20min to 24 hours)
High (300 to 1100°C)
Low to high
Very high
Dry
Dry,sterile
ash or char
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COOLING AIR
DISCHARGE
SLUDGE CAKE,
SCREENINGS,
AND GRIT—,
SCUM
AUXILIARY
AIR PORTS
RABBLE ARM
2 OR 4 PER
HEARTH
BURNERS
SUPPLEMENTAL
FUEL
'COMBUSTION AIR
SHAFT COOLING
AIR RETURN
SOLIDS FLOW
DROP HOLES
:>$, COOLING AlR'1A>-'>- v"*::- •
Figure 2. Cross section - multiple hearth sludge furnace.
(After reference
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where:
P = Minimum percentage of solids in sludge for autogenous combustion
Q = Energy content of dry sludge, MJ/kg
W = Heat required to evaporate one kg of water in an MHF, MJ/kg
In an operating MHF the heat required to evaporate one kg of water is about 4.64
MJ/kg. However due to radiation losses and heating of the gas streams and sludge
solids a value of about 8.12 MJ/kg is used (41). The energy content of the dry sludge
solids, Q, is relatively high, typically about 18 MJ/kg. But this value is highly variable,
dependent on wastewater characteristics, operation of the wastewater treatment plant,
and the presence of chemicals such as lime or ferric chloride which are used to
condition sludge for dewatering.
For many wastewater treatment plant sludges the autogenous point is in the
range of 30 to 40 percent. However currently available sludge dewatering equipment
cannot consistently produce a dewatered sludge cake in this range. Thus MHF's (and
all other thermal sludge processing techniques) must have provisions for auxiliary fuel
to account for these variations. This requirement for expensive and scarce auxiliary
fuels such as natural gas or fuel oil has been the prime motivation for the development
of co-disposal systems which use municipal solid waste as the auxiliary fuel.
Due to stringent carbonyl and unburned hydrocarbon emission limitations in
many states, afterburning of MHF exhaust gases is usually required. This requires
additional auxiliary fuel. In this respect multiple hearth furnaces are at a disadvantage
compared to fluidized bed and single hearth cyclonic furnaces which do not require
afterburning.
Fluidized Bed Furnace - The fiuidized bed furnace (FBF) is the second most popular
thermal processing system for sludge in -the United States, with 60 units in operation
(41). As shown in Figure 3, an FBF is a vertically oriented, refractory lined steel
cylinder which contains a sand bed, a supporting grid plate, and air injection tuyeres.
The sand bed is typically about 0.8 m thick. Air is forced through the bed at a
pressure of 21 to 34 kPa gage, expanding the bed to twice its rest volume. Usually
FBF's are operated with 20 to 45 percent excess air. This is less excess air than
used with multiple hearth furnaces, so fluidized beds generally operate at higher heat
efficiencies for a given exhaust temperature. Bed temperature is maintained between
760 to 820°C by auxiliary burners. The bed has a heat storage effect, allowing for
rapid start-up after brief shut down periods (e.g., overnight).
Sludge is injected into the expanded bed at the bottom of the furnace. Turbulent
mixing in the expanded bed results in good heat transfer between the sand grains,
sludge, and hot combustion gases. The sand grains tend to have a comminuting effect
on the ash, preventing the buildup of clinkers. However, finely ground ash is carried
out of the furnace with the exhaust gases. Thus, air pollution control devices such
as wet scrubbers, must be used to meet particulate emission limitations. A portion
of the sand bed is also lost in the exhaust gases, about 5 percent of the bed volume
for every 300 hours of operation.
Fluidized bed furnaces have a minimum of mechanical components and are
relatively easy to operate. Most of the operating problems experienced with them
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SAND
FEED
THERMOCOUPLE
SLUDGE
INLET
FLUIDIZING
AIR INLET
FLUIDIZED A'.-.:
SAND BED ;.;:•:;.•'•;
EXHAUST AND ASH
PRESSURE TAP
^SIGHT
V GLASS
BURNER
TUYERES
FUEL
GUN
PRESSURE TAP
STARTUP
-i PREHEAT
DBURNER
JFOR HOT
WINDBOX
Figure 3. Cross section - fluidized bed sludge furnace.
(After reference
10
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have been with sludge feeding equipment and automatic temperature control systems.
As with the multiple hearth furnace, auxiliary fuel is required.
Electric Furnace - The electric furnace (EF) is a relatively new concept in thermal
sludge processing. The first unit was installed in the United States in 1975 (41). As
shown in Figure 4, sludge enters through an airlock and is distributed evenly over a
moving horizontal woven wire belt. Supplementary energy for non-autogenous sludge
is provided by infrared heating elements. Because this energy is in the form of
electricity, operating costs of an EF can be quite high. Also critical parts such as
the woven wire belt and the infrared elements have been shown to have a short life
(three to five years).
Single Hearth Cyclonic Furnace - Cyclonic furnaces were developed by the British
and several units are in operation in Great Britain (41). As shown in Figure 5, the
furnace consists of a vertical cylinder with a refractory lining. There is one rotating
hearth and a fixed plow which moves sludge towards the center of the hearth where
ash is collected. Combustion air and supplemental fuel are injected tangentially into
the furnace. Cyclonic furnaces have a relatively low capital cost due to their
mechanical simplicity. However maintenance problems have been experienced with
the sludge feed mechanism.
RESOURCE RECOVERY FROM SOLID WASTE
The need for supplemental fuel to thermally process sludge has been discussed.
An alternative to fossil fuels might be the use of municipal solid waste. The physical
characteristics of solid waste and how it can be processed into a fuel is reviewed
below.
Definition
Tchobanoglous, et_ al (52), have defined solid waste as:
". . . all the wastes arising from human and animal activities which are normally
solid and that are discarded as useless or unwanted."
The Resource, Conservation, and Recovery Act of 1976 (45) defines solid wastes as:
". . . any garbage, refuse, sludge from a waste treatment plant, water supply
treatment plant, or air pollution control facility and other discarded
material ..."
Note that the Resources, Conservation, and Recovery Act (RCRA) specifically defines
sludge as a solid waste. This is an important legal consideration because RCRA
clearly involves the solid waste manager with the sludge disposal problem and promotes
the concept of co-disposal of sludge and solid waste in a common facility.
Composition of Solid Waste
Solid waste has long been recognized as a misused resource. It contains valuable
components that can be recovered and reused or combusted for their energy content.
The most significant characteristics of municipal solid waste in the United States are
11
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CAS
EXHAUST
RADIANT
INFRARED
HEATING
ELEMENTS (TYP)
• WOVEN WIRE
CONTINUOUS BELT
COOLING
AIR
RABBLING I
DEVICE 1
COOLING
AIR
N>
1 —
*
U-, — ,T..,.
ttT
^- '
-k r*
N
y
«A\ i oooooooooooooooo 1
faff ^ ^ ^
^c
i r1-
i-i
L , . .. — 1
1 ..-.». . 1
F
ASH
J^DISC
1 COMBL
» Al
HARGE
Figure f. Cross section - electric sludge furnace.
(After reference 41)
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EXHAUST
COMBUSTION AIR
TANGENTIAL
AIR PORTS
CYCLONIC ACTION
ROTATING HEARTH
FIXED PLOW
SLUDGE
INLET
BURNER (TYP)
ASH DISCHARGE IN
CENTER OF FURNACE
Figure 5. Cross section - cyclonic sludge furnace.
(After reference
13
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summarized in Table 3. The percent by weight, moisture content, and energy content
of each component are given. Note that although municipal solid waste has an overall
energy content of only 10.5 MJ/kg at 20 percent moisture content, paper, which
typically makes up 40 percent of U.S. solid waste, has a much higher energy content
of 16.7 MJ/kg at a low moisture content of six percent.
Mixed Waste Recovery Systems
Mixed waste recovery is the mechanical separation of solid waste into its
various components. The primary function of mixed waste recovery is to produce a
combustible refuse derived fuel (RDF) which can be either burned on site for electricity
or steam production or sold to an adjacent government or industrial customer.
RDF is produced by a process train which separates solid waste into a
combustible light fraction consisting primarily of paper, plastics, and food wastes;
and a non-combustible heavy fraction containing metals, glass, and ash and dirt. A
typical process flowsheet for producing shredded RDF is shown in Figure 6.
Although the recovered materials have considerable value (e.g., ferrous scrap
$22/metric ton, aluminum $550/metric ton, clean glass cullet $22/metric ton), RDF
is the principal source of revenue for a mixed waste recovery system. At $17 to
$40/metric ton, RDF can represent 85 to 95 percent of project revenues (44). Several
large scale RDF systems have been economic failures because they either produced
a low quality RDF which the customer would not accept (Milwaukee, Wisconsin), or
they could not find a market at all for the RDF (New Orleans, Louisiana) (46).
Based on the limited operating experience which exists in the United States
with RDF systems, the following minimum criteria have been proposed for future
projects (46):
"1. Large scale resource recovery can only be economical in large metropolitan
areas where landfill sites are unavailable or very expensive, above
$25/metric ton.
2. There must be an adequate refuse supply committed to the facility (a
minimum of 1800 metric tons/day is required).
3. A customer must be obtained for the steam or power generated by the
plant and must be located close by. Firm contracts must be obtained for
both the refuse and the sale of energy.
4. If the customer is to be an industrial facility, it may be necessary to
design the facility with the capability of burning fossil fuel when refuse
is unavailable or when the plant cannot process the raw refuse due to
malfunctions of the processing equipment.
5. The logistics of delivering refuse to the resource recovery facility should
be planned long in advance."
These guidelines reflect the prevailing engineering philosophy towards RDF
systems which favors very large systems. Based on an average U.S. municipal solid
14
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Table 3
COMPOSITION, MOISTURE, AND ENERGY CONTENT OF SOLID WASTE
V/i
Percent by
Component
Food wastes
Paper
Cardboard
Plastics
Textiles
Rubber
Leather
Garden trimmings
Wood
Glass
Tin cans
Nonferrous metals
Ferrous metals
Dirt, ashes, brick, etc.
Overall value
Range
6
25
3
2
0
0
0
0
1
^
2
0
1
0
- 26
- 45
- 15
- 8
- k
- 2
2
- 20
- 4
- 16
- 8
- 1
- it
- 10
-
weight
Typical
15
40
4
3
2
0.5
0.5
12
2
8
6
1
2
4
-
Moisture,
Range
50
4
4
1
6
1
8
30
15
1
2
2
2
6
15
- 80
- 10
- 8
- it
- 15
- it
- 12
- 80
- 40
- 4
- 4
- 4
- 6
- 12
- 40
Percent Energy , MJ/kg
Typical
70
6
5
2
10
2
10
60
20
2
3
2
3
8
20
Range Typical
3.5
11.6
14.0
27.9
15.1
20.9
15.1
2.3
17.4
0.1
0.2
0.2
2.3
9.3
- 7.0
- 18.6
- 17.4
- 37.2
- 18.6
- 27.9
- 19.8
- 18.6
- 19.8
- 0.2
- 1.2
-
- 1.2
-11.6
- 12.8
4.7
16.7
16.3
32.6
17.4
23.3
17.4
6.5
18.6
0.1
0.7
-
0.7
7.0
10.5
After Reference 52
JAs discarded basis, HHV
-------
DUST
COLLECTOR
EXHAUST
FAN
MAGNETIC SEPARATOR
ROTARY SCREEN
SEPARATOR
Figure 6. Typical mixed waste recovery system.
(After reference 52)
-------
waste generation rate of 1.59 kg/cap*day, the recommended minimum size of 1800
metric tons/day of refuse mentioned in item 2 represents a service population of 1.13
million persons. The smallest RDF system in the United States, at Ames, Iowa, is
only a tenth of this size, processing 180 metric tons/day. But the Ames pJant operates
with a heavy city subsidy.
Densified Refuse Derived Fuel
Densified refuse derived fuel (d-RDF) is an alternative to conventional shredded
RDF. It is produced by compressing RDF into dense pellets or cubes. The primary
advantage of d-RDF is that it is storable and easy to transport in comparison to
conventional RDF which must be burned at the production site. An additional advantage
is that d-RDF can be burned in small stoker type boilers. These boiJers, in the 11,000
to 90,000 kg steam/hr range, are top small to be converted economically to run on
shredded RDF. However d-RDF can often be directly subsituted for coal in these
boilers (58).
One of the first d-RDF systems in the United States was operated during the
early 1970's by the City of Ft. Wayne, Indiana, to produce fuel for the municipal
power plant. A John Deere stationary alfalfa cuber was used to densify the light
fraction of municipal and industrial solid waste from a mixed waste recovery system.
The cubes were burned on a 1:3 ratio with coal in a 40,000 kW steam electric power
plant (21). A commercially produced solid waste densification system using a modified
John Deere cuber is currently being marketed by the Papakube Corporation of San
Diego, California (37,38).
Source Separation of Solid Waste
Source separation is an alternative resource recovery technique for small
communities. It can replace the high technology, capital intensive mixed waste
recovery systems previously discussed. Most source separation systems are operated
for materials recovery, not energy recovery. Thus their financial success is dependent
on the highly fluctuating secondary materials market.
In source separation systems, residents are requested to place bundles of
newspaper and containers with aluminum and steel cans out with their weekly trash
collection. The newspaper and other recyclables are picked up by the regular collectors
and carried in special containers or racks on the trash trucks. In other cities a
smaller separate vehicle is used to collect paper and other recyclable materials.
Usually, cities require that newspaper be tied into bundles. Magazines, paper bags,
and food packaging are not accepted. Such a system is currently operated by the
City of Davis, California (see Figure 7).
It has been assumed for the past few years that the recycling of waste paper
into newsprint or low quality paper is both economically and ecologically sound.
However, current energy prices, coupled with the fluctuating nature of newsprint
prices, are making energy recovery a viable option. Also, because only prime, hand
selected clean newsprint is suitable for recycling purposes, far more waste paper is
available for energy recovery as cleanliness is not as critical.
A source separation system designed to recover waste paper for use as a fuel
could be less restrictive. As a result, a higher proportion of a given community's
17
-------
00
NEWSPRINT
RECYCLABLES
TRUCK
TRASH
L
COMPACTOR
TRUCK
SANITARY
LANDFILL
Figure 7. Materials recovery from source separated solid waste.
-------
waste paper could be recovered. Such a system is shown in Figure S. In this system,
only a combustible fuel fraction is recovered. No attempt is made to recover steel
cans and glass because marketing of these components is difficult and seldom economic
for small communities. Aluminum, because of its high value could also be recovered.
ENERGY RECOVERY FROM SOLID WASTE
Energy can be recovered from municipal solid waste (MSW) in the form of
steam or electricity. There are two basic methods of approach: the mass burning
of unseparated solid waste, and the combustion of refuse derived fuel. The relative
merits of each approach are discussed below.
Mass Burning - Water Wall Incinerators
Mass burning of solid waste in a water wall incinerator is the most widely
used method of energy recovery. Eight units are being operated in the United States
while over 200 units are in use in Europe (54).
In a water wall incinerator, unseparated solid waste is fired on stoker grates
similar to those used in coal fired boilers. Energy recovery is accomplished by passing
hot combustion gases over water filled heat exchanger tubes for the generation of
steam. Because solid waste is unseparated prior to firing, metal, glass, and other
uncombustible materials are passed through the incinerator into the ashpit. These
materials become fused together into a slag-like mass which must be landfilled. Thus
the metal and glass originally in the waste are not recoverable. Metal in the waste
also tends to fuse on grate mechanisms, and ash handling equipment, requiring expensive
maintenance. A capacity of about 180 metric tons/day is considered to be the
minimum practical size by most manufacturers.
Mass Burning.- Modular Incinerators
Modular incinerators are batch fed, package units without continuous ash
removal. Originally designed for solid waste reduction only, recent units have
incorporated waste heat boilers for energy recovery. Twelve systems are in operation
or under construction in the United States, ranging in capacity from 15 to 21S metric
tons/day
They consist of a refractory lined cylinder containing a fixed grate. Unseparated
solid waste is loaded into the incinerator with a front end loader or similar equipment.
Two stage combustion is used in most units, with sub-stoichiometric air used in the
main combustion chamber, and excess air used in an afterburner section. After
completion of the combustion cycle, the unit is opened, and the ash removed manually.
Modular incinerators are factory built and highway shipable. Clusters of units
can be used to increase capacity. Operational problems have included poor combustion
performance, slagging of metals and glass, and deterioration of refractory liners. The
metal and glass in the ash are essentially non-recoverable.
19
-------
-T»- COMBUSTIBLES
NON-COMBUSTIBLES
8 FOOD WASTES
(j—tr
COMBUSTIBLES
TRUCK
PAPER
SHREDDER
DENSIFICATION
FUEL
CUBES
'O
COMPACTOR
TRUCK
SANITARY
LANDFILL
Figure 8. Production of densified refuse derived fuel from source separated
solid waste.
-------
Combustion of RDF
The combustion of refuse derived fuel (RDF) can reduce or eliminate many of
the problems encountered in mass firing of solid waste. Because the waste is separated
prior to combustion, recovery of aluminum, ferrous metals, and glass can be
accomplished. Removal of these materials also reduces the potential for slagging
and other maintenance problems which occur with the mass firing of unseparated solid
wastes.
Shredded RDF can be burned in suspension fired boilers at considerably higher
efficiencies than experienced with mass fired systems. Densified RDF can be burned
in conventional stoker fed coal boilers. The ability of standard boilers and steam
power plants to use shredded or densified RDF as a supplementary fuel is the greatest
advantatge of RDF combustion over the mass firing approach which requires a dedicated
solid waste combustion facility.
The principal disadvantages to RDF combustion include: high capital and
operating costs of RDF facilities, fluctuating quality of RDF which can adversely
affect combustion efficiency, and materials handling problems during RDF production.
Operational experience with RDF combustion is limited to five years operation with
shredded RDF at the Ames, Iowa, plant; a one year test with d-RDF at the Ft. Wayne,
Indiana, power plant; and one year test with d-RDF at the Union Electric power plant
in St. Louis, Missouri. Eight full scale RDF combustion systems are currently in the
design, construction, or start up stages in the United States (16,44, and 54).
CO-DISPOSAL OF SLUDGE AND SOLID WASTE
The main disadvantage to the thermal processing of sewage sludge is the need
for auxiliary fossil fuel. Co-disposal of sludge and solid waste in a common system
would eliminate or reduce the need for fossil fuels for the incineration of sludge,
while reducing the landfill requirements for solid waste. Currently available technology
for co-disposal, and several innovative co-disposal processes currently under
development are considered in the following discussion.
Review of Co-disposal Processes
Currently, there are no full scale co-disposal systems operating in the United
States, however, several facilities are under construction or in the design stage. These
projects are summarized in Table 4. Co-disposal processes are of two basic types:
in the first type, a mass fired solid waste incinerator is used to combust dried sludge
which has been mixed with unseparated municipal solid waste; in the second type, a
sewage sludge incinerator is modified to accept refuse derived fuel (RDF) as a
substitute for the natural gas or oil normally used in such 'furnaces.
Experience with full scale co-disposal systems has shown that external drying
or dewatering of sludge is required for the successful combustion of sludge in mass
fired incinerators (4S). Although direct injection of liquid sludge into incinerators
has been attempted in the past, it has failed in every application, probably due to
poor mixing between the sludge and solid waste in the incinerator, and the tendency
for the liquid sludge to form crusts on the stokers in the incinerator (4S). All of
21
-------
Table >t
PLANNED CO-DISPOSAL FACILITIES IN THE UNITED STATES3
Location
Type
Description
Status
NJ
Contra Costa County,
California
Duluth, Minnesota
Glen Cove, New York
Harrisburg,
Pennsylvania
Memphis, Tennessee
Sludge incinerator
utilizing RDF
Sludge incinerator
utilizing RDF
Mass fired solid
waste incinerator
Mass fired solid
waste incinerator
Sludge incinerator
utilizing RDF
Envirotech multiple hearth
furnace operated in the
gasification mode. Energy
recovery by steam turbine.
Fluidized bed sludge incinerator.
Energy recovery by steam
turbine.
Stoker grate furnace using
mixed solid waste and dewatered
sludge. Energy recovery by
steam turbine.
Existing mass fired incinerator
modified for sludge disposal.
Multiple hearth furnace
operated in the gasification
mode. Heat recovery boiler
with sale of steam.
Facility plan
completed
Under construction
Under EPA review
Under construction
Under EPA review
aAdapted from Reference 16
Status as of September 1979
-------
the proposed mass fired co-disposal systems discussed in Table 4 employ external
sludge drying or dewatering.
Modification of existing multiple hearth or fluidized bed sludge incinerators to
utilize RDF has proven successful in pilot testing. The Central Contra Costa County,
California AWT wastewater plant will utilize a modified multiple hearth furnace
operating in the gasification mode with RDF as the auxiliary fuel (16).
PTGL Processes for Co-disposal
There are many pyrolysis, thermal gasification, and liquifaction (PTGL) processes
being proposed for the conversion of biomass, sludge, and municipal, industrial, and
agricultural waste into solid, gaseous, and liquid fuels. An excellent overview of
many of the processes currently under development is given in Reference 27. Two
of the processes most often mentioned in connection with sludge disposal are the
Purox vertical shaft gasifier and the Envirotech multiple hearth gasifier.
The PUROX Vertical Shaft Gasifier - Although often referred to as a pyrolysis process
in the literature, the PUROX reactor is actually a vertical fixed bed, counter-current
flow gasifier. Pure oxygen is used as an oxidant and the output consists of a medium
energy gas (=13 MJ/m ) and a molten slag. After scrubbing, the gas can be combusted
in a heat recovery boiler. In a large scale test conducted at the Charleston, West
Virginia PUROX pilot plant, successful operation of the PUROX reactor in the
co-disposal mode was demonstrated. Test runs were made with mixed municipal solid
waste and dewatered raw primary sludge, and dewatered mixed biological and primary
sludges (35). In spite of this highly successful demonstration project, there are
currently no PUROX co-disposal systems in the planning or funding stages (16).
The Envirotech Multiple Hearth Gasifier - In 1976, the Envirotech Corporation in
conjunction with Brown and Caldwell Consulting Engineers, demonstrated the operation
of a multiple hearth sludge furnace using RDF as an auxiliary fuel (4). The furnace
was operated both in its original configuration as an incinerator and in the pyrolysis
mode. In actuality, the furnace was operated as a counter-current flow, air blown
gasifier. The multiple hearth gasifier produced a low energy gas (5.2-6.0 MJ/m )
which was combusted in an afterburner during the tests. Based on these highly
successful experiments, a full scale multiple hearth gasifier is in the final design
stages for the Contra Costa County, California and a similar facility is proposed for
Memphis, Tennessee (see Table 4).
GASIFICATION AS A CO-DISPOSAL OPTION
The refuse derived fuel systems, energy recovery units, and co-disposal processes
reviewed in the previous sections are designed for large communities on the order of
at least 100,000 population. However the ever increasing costs of energy and sludge
and solid waste disposal make small scale co-disposal attractive.
An alternate system for sludge disposal that could be used by small communities:
the co-gasification of sludge and source separated solid waste is considered in this
section. Such a system is shown schematically in Figure 9. The system consists of
the following components: a shredder to reduce the size of the waste paper and mix
it with dewatered sludge, a densification system to convert the sludge/waste paper
23
-------
GASIFIER
K>
-C-
WASTE
PAPER
SHREDDER
t
C
^.
(ENSIFICATION
/ \
Y
ENGINE -
GAS CLEANUP GENERATOR
GAS GAS
^ ^ ^^
DEWATERED Y
WASTEWATER CHAR
SLUDGE
ELECTRIC POWER
Figure 9. Gasification system for sludge and source separated solid waste.
-------
mixture into a dense fuel cube, the gasification reactor, a gas cleanup system, and
an engine-generator set to convert the gas to electrical energy.
Gasification of Sludge/Solid Waste Mixtures
Downdraft gasifiers are simple to construct and operate but they have exacting
fuel requirements which include:
1. moisture content < 20 percent
2. ash content < 6 percent
3. uniform particle size with good mechanical stability
Because waste can be dried prior to gasification, excessive moisture can be
overcome. However, ash content and particle size are more difficult to handle. When
the ash content is higher than 6 percent, there is a sufficient amount of ash to melt
and solidify into slag which can cause severe operational problems. Excessive fine
material in the fuel can cause mechanical bridging in the fuel hopper. One method
of overcoming these problems is to use more complex reactors such as the Envirotech
Multiple Hearth System or high temperature slagging gasifiers, such as the PUROX
process, in which the ash is melted. Although both of these approaches are operationally
feasible, they are costly and complex.
A lower cost approach is to utilize the simplest reactor type, the downdraft
gasifier, and tailor the fuel accordingly. A suitable fuel can be made by mixing
dewatered sludge with the paper fraction of source separated solid waste, and densifying
the mixture to produce a densified refuse derived fuel (d-RDF) that has low moisture
content, low ash content, and uniform particle size. The details of this operation
are discussed in a later chapter.
An Integrated Waste Management System for Small Communities
Although a gasification system could be operated in a small community strictly
with source separated solid waste and sludge, a more cost effective approach might
be to incorporate the gasification system with the other waste generating activities
of the city and its environs. An example of such a system is shown in Figure 10.
If the gasifier system is located at the site of the city waste water treatment plant,
the low energy gas produced could be used efficiently on-site to power pumps, blowers
and other equipment.
Provisions could also be made for the inclusion of urban biomass. Operation
of downdraft gasifiers with a wide range of agricultural wastes has already been
Demonstrated in previous gasification research conducted at the University of
California, Davis (26,59,60, and 61). In rural areas, agricultural wastes could be
obtained at little or no cost during some seasons. However, these wastes would still
require collection and densification prior to use. These supplemental biomass fuels
would increase the utilization of the system.
Use of Urban Biomass As a Fuel Source
Urban biomass can be defined as organic materials that are generated in an
urban environment as a by-product of landscaping and other horticultural activities.
25
-------
NJ
ON
COMBUSTIBLE
SOLID WASTE
URBAN BIOMASS
AGRICULTURAL
WASTE
WASTEWATER
SLUDGE
SEWAGE
TREATMENT
PLANT
ELECTRICITY
SHREDDER
DENSIFICATION
GASIFICATION
ENERGY
CONVERSION
CHAR
ELECTRICITY
TO POWER GRID
Figure 10. An integrated gasification system for co-disposal of various wastes.
-------
It is composed of tree trimmings, grass clippings, and other yard wastes. In many
communities this material is already collected in separately. The amounts collected
can be quite substantial. For example in Davis, California, a largely residential
community of 32,000 persons, in 1979, the urban biomass collected ranged for 213
metric tons in January to 263 metric tons in December (wet basis).
Preparation of Biomass Fuel
The use of biomass as a fuel source would probably require that it be dried,
shredded, and densified prior to use. The shredded and dried material could be blended
with waste paper and sludge in an integrated waste management system. Drying
could be accomplished with waste heat from the gasifier system, with solar energy
by spreading the biomass on a hard surface, or with forced, ambient air drying in a
large bin.
Utilization of Low Energy Gas
The low energy gas from a downdraft gasifier can be utilized in several ways.
The simplest technique is to burn the gas in a standard boiler designed for natural
gas. This requires a low energy gas burner designed for the greater gas and combustion
air volumes, and a larger gas feed line to account for the lower, energy content of
the gas (=: 5.6 MJ/m ) as compared to natural gas (= 37.3 MJ/m ).
Another approach is to cool and filter the gas and utilize it as an alternative
fuel for spark and compression ignition engines (24,47, and 60). Skov and Papworth
(47) described the operation of gasoline engine powered trucks, buses, and agricultural
equipment in Europe with gas produced using portable wood, charcoal, coal, and fueled
gasifiers. Gasifiers can also be used to fuel air heating burners. The amount of gas
clean-up is dependent on the use for the heated air.
In an integrated gasification system for small communities the low energy gas
could be burned in a stationary dual-fueled diesel engine-generator set. Two modes
of operation are possible. In the first case the gasifier-engine-generator set is located
at the fuel preparation site (the city wastewater treatment plant). Electricity produced
in excess of local requirements would be fed into the local power grid. In the second
case, fuel cubes 'could be produced at a central location and transported to satellite
gasifier systems in other locations.
GASIFICATION AS A UNIT OPERATION
Gasification is an energy efficient technique for reducing the volume of solid
waste and the recovery of energy. Essentially, the process.involves partial combustion
of a carbonaceous fuel to generate a combustible fuel gas rich in carbon monoxide,
hydrogen, and some saturated hydrocarbon gaes, principally methane. The historical
development, the basic theory of operation, and the types of reactors used in the
gasification process are discussed briefly below.
Definition
Gasification involves the partial combustion of a carbonaceous fuel to generate
a combustible gas containing carbon monoxide, hydrogen, and gaseous hydrocarbons.
27
-------
Currently, there is much confusion in the literature between the terms "pyrolysis"
and "gasification." In this thesis, the following definitions given by Lewis (29) are
used.
"Pyrolysis - Thermal processing of waste in the absence of oxygen, in (a)
indirectly heated retorts, and (b) furnaces that are directly heated by fuel
gases from a burner firing on a stoichiometric air/fuel ratio."
"Gasification - Thermal processing of waste where a fraction of the
stoichiometric oxygen required by the waste is admitted directly into the fuel
bed to liberate the heat required for endothermic gasification reactions. The
volatile portion of incoming waste will be pyrolyzed by the heat of the fuel
gases, and the outlet gas composition will reflect both processes."
Historical Development
Gasifers have been used since the 19th century. The first coal gasifiers were
built by Bischof in Germany, 1839, EbeJman in France, 1840, and Ekman in Sweden,
1845. This was followed by the Siemens brothers in Germany, 1861. The Siemens'
gasifiers were used primarily to fuel heavy industrial furnaces. The development of
gas cooling and cleaning equipment by Dowson in England, 1881, extended the use of
gasifiers to small furnaces and gas engines (42).
By the early 1900's, gasifier technology had advanced to the point where most
ligno cellulosic materials such as wood, fruit pits, straw, and walnut shells could be
gasified. These early gasifiers were used primarily to provide the fuel for stationary
gasoline engines. Portable gasifiers also emerged in the early 1900's. They were
used for ships, automobiles, trucks, and tractors. The real impetus for the development
of portable gasifier technology was World War II. During the war years, France had
over 60,000 charcoal burning cars while Sweden had about 75,000 wood burning gasifier
equipped buses, cars, tractors, and engine powered boats. With the return of relatively
cheap and plentiful gasoline and diesel oil, after the end of World War II, gasifier
technology was all but forgotten. However, in Sweden, research has continued into
the use of wood fueled gasifiers for diesel tractors and transport trucks. (39).
Furthermore the downdraft gasification of peat is being pursued actively in Finland
(24).
Although there has been considerable success reported with the gasification of
charcoal, coal, wood, and certain agricultural wastes (9,17,32,49,59,60, and 61), the
gasification of solid waste has not been as successful. It was stated in a recent
editorial in a leading solid waste trade magazine that (46):
"Pyrolysis [i.e., gasification] systems such as the Union Carbide Purox System,
the Landguard System, and the Occidental Flash Pyrolysis System have been
noble experiments, but are considered to be technical and economic failures."
It is felt that the principal causes for the failure of gasification technology in the
solid waste field has been the complexity of the systems, and a Jack of appreciation
of the heterogeneous nature of solid waste, mixed with air dried sludge. The approach
taken in this research, was to use as simple a reactor as possible, the vertical fixed
bed gasifier and fuel it with source separated paper, the cleanest form of solid waste.
The reader is referred to References 27 and 28 for an in-depth review of current
research into pyrolysis and gasification systems.
28
-------
Reactor Types
Four basic types of reactors are used in gasification. They are:
1. vertical packed bed
2. multiple hearth
3. rotary kiln
4. fiuidized bed
Most of the early gasification work in Europe was with the air-blown fixed bed type
reactors. The other types are favored in current United States practice, with the
exception of the PUROX oxygen blown gasifier (an updraft reactor).
The vertical, fixed bed, downdraft type reactor has a number of advantages
over the other types including simplicity and relatively low capital cost. However,
it is more sensitive to the mechanical characteristics of the fuel. The merits and
limitations of vertical bed gasifiers are discussed in detail in Reference 12. Fuel
flow is by gravity with air and fuel moving co-currently through the reactor (see
Figure 11). At steady state, four zones form in the reactor. In the hearth zone,
where air is injected radially into the reactor, partial combustion reactions predominate.
Some heat transfers from this zone upward into the fuel mass, causing pyrolysis
reactions in the distillation zone and partial drying of the fuel in the drying zone.
Actual production of the fuel gas occurs in the reduction zone, which is below the
partial combustion zone and where endothermic reactions predominate, forming CO
and H->. The hut carbon bed in the combustion zone and upper part of the reduction
zone cracks much of the volatile hydrocarbons produced into methane and a small
amount of other saturated and unsaturated hydrocarbon gases. The end products of
the process are a carbon rich char and the low energy gas.
Gasification Theory
A gasifier is basically an incinerator operating under reducing conditions. During
the gasification process, five principal reactions occur:
C + O2 = CO2 + 393.8 MJ/kg-mol exothermic
C + H2O = CO + H2 - 131.4 MJ/kg-mol endothermic
C + CO2 = 2CO - 172.6 MJ/kg-mol endothermic
C + 2H-, = CHL + 75.0 MJ/kg-mol exothermic
CO + H2O = CO2 + H2 + 41.2 MJ/kg-mol exothermic
The heats of reaction shown above are evaluated at 25°C and 1 atmosphere pressure.
The heat to sustain the process is derived from the exothermic reactions while the
combustible components of the low energy gas are primarily generated by the
endothermic reactions. Although the reaction kinetics of the gasification process are
quite complex and still the subject of considerable debate, the operation of air-blown,
downdraft gasifiers of the type used in this research is straightforward. For a further
discussion of gasification theory and reaction kinetics the reader is directed to
References 18, 20, 42, and 49.
29
-------
AIR
AIR
GAS
Figure 11. Schematic of a downdraft gasifier.
30
-------
Gas Composition
When a gasifier is operated at atmospheric pressure with air as the oxidant,
the end products of the gasification process are a iow energy gas (LEG) typically
containing (by volume) 10% CO2, 20% CO, 15% H-, 2% CH^ with balance being N2>
and a carbon rich char. Due to the diluting effect of the nitrogen in the input air,
the LEG has a energy content in the range of the 5.2 to 6.0 MJ/m . When pure
oxygen is used as the oxidant, & medium energy (MEG), with an energy content in
the range of 12.9 to 13.8 MJ/m , is produced (15). Because of their complexity and
high capital cost, oxygen blown gasifiers have not been applied commercially (16).
The simpler air blown gasifer has been used widely and is the subject of this research.
SUMMARY
The co-disposal of sludge and solid waste is a promising solution to an
environmental problem facing many communities. However current co-disposal
technology is not affordable by smaller communities. The co-gasification of densified
sludge and source separated solid waste in a simple fixed bed air-blown gasifier may
be a new co-disposal technique that is appropriate for use by small communities.
31
-------
CHAPTER III
EXPERIMENTAL APPARATUS, METHODS, AND PROCEDURES
The experimental work described in this report was conducted on the University
of California, Davis campus using the facilities, shops, and laboratories of the
Departments of Civil and Agricultural Engineering. The experimental gasification
system, the preparation of densified fuels, and the methods and procedures used in
the collection and analysis of the data are described in this chapter.
EXPERIMENTAL GASIFICATION SYSTEM
To investigate the co-gasification of densified sludge and solid waste, a pilot
scale gasification system was designed and constructed. The complete system consists
of three subsystems: 1) batch fed downdraft gasifier, 2) data acquisition, and 3) solid
waste shredding and densification.
Batch Fed Downdraft Gasifier
A pilot scale batch fed downdraft gasifier was designed and constructed for
the experiments. The design of the gasifier is based on laboratory and pilot scale
gasifiers built by the Department of Agricultural Engineering at the University of
California, Davis (59,60, and 61).
As shown in Figures 12, 13, and 14, the gasifier is built in three main assemblies,
fuel hopper, firebox, and ashpit. The fuel hopper is a double walled cylinder. The
inner wall is in the form of a truncated cone to reduce the tendency for fuel bridging.
The double wall acts as a condenser to remove water vapor from the fuel prior to
gasification. Condensed vapor is collected in a condensate gutter and drained off
after each run. The fuel hopper is mounted on the firebox with quick release clamps
to allow for easy inspection after experimental runs.
The firebox is also a double walled cylinder. The inner cylinder is the actual
firebox. Air is supplied by four air tubes to the annular space between the walls
which acts as an air plenum to distribute air evenly to the six tuyeres (air nozzles)
which supply air for partial combustion of the fuel. The choke plate acts as a large
orifice, replacing the venturi section previously used in earlier World War II and
Swedish gasifier designs. The firebox assembly is flange mounted to the ashpit.
The ashpit is used to collect char during, an experimental run. A rotating
eccentric grate is located in the ashpit immediately below the choke plate. The
grate supports the fuel bed, and allows passage of char and gas into the ashpit. Gas
is drawn off continuously through a pipe on the side of the ashpit.
32
-------
TUYERE
AIR
TUBE
ROTATING
GRATE
THERMOCOUPLE
LOCATIONS
(n) TUYERE
(ra) REDUCTION ZONE
(T3) ASHPIT
^5) FUEL HOPPER
(T6) AIR PLENUM
FUEL
HOPPER
CONDENSATE
GUTTER
AIR
AIR
CHAMBER
CHOKE
PLATE
GAS
ASH
REMOVAL
PORT
PACKING
GLAND
GRATE DRIVE
SPROCKET
Figure 12. Cross section - UCD sludge/solid waste gasifier.
33
-------
*.-^,*Znar**-l.l]vTriirjm*fnifti™rrrH i
rassT
Figure 13. Exterior view - UCD sludge/solid waste gasificr.
-------
Figure 14. Interior view - UCD sludge/solid waste gasifier.
-------
Gasifier Geometry - Little information is available in the literature concerning
the geometric design of a gasifier. The only detailed work on the subject is contained
in the report by Nordstrom (39). Between 1957 and 1963 his research group tried
various designs and arrived at some empirical relationships between tuyere diameter,
tuyere height relative to the venturi section and venturi diameter relative to firebox
diameter. Although these experiments were conducted on wood fueled gasifiers, it
was felt that Nordstrom's relationships could be used as a guide in the design of a
gasifier for solid waste.
Curves presented by Nordstrom (39) were used to estimate the relative sizes
of the choke plate, tuyere diameter, tuyere length, and distance between the tuyeres
and choke plate. Because the tuyeres, choke plate, and choke support plate and hoop
are removable, the internal geometry can be changed easily. The gasifier firebox is
45.7 cm in diameter. In the current configuration of the gasifier, a 7.6 cm choke
support hoop, 17.7 cm diameter choke plate, and 6.9 cm long by 1.4 cm inside diameter
tuyeres are installed.
Gasifier Construction - The choke plates and tuyeres were constructed from
Type 304 stainless steel. A temperature resistant alloy, ASTM Type AM 5 was used
for the firebox and the rotating grate. The remainder of the gasifier was constructed
from Type 1040 mild steel.
The gasifier was constructed in the College of Engineering machine shop. The
rolled cylindrical sections, the inner and outer walls of the firebox, the ashpit, and
the inner and outer walls of the fuel hopper were fabricated by commercial machine
shops. All other cutting, arc welding, and assembly were done in the College of
Engineering shops. Full sized gasifiers could easily be constructed in relatively
unsophisticated machine shops since exotic materials or complex machining are not
required.
Data Acquisition
The data acquisition subsystem is an automated temperature measurement
system. Temperatures are sensed with Type K thermocouples located as shown in
Figure 12. Additionally a Type T thermocouple is used in the air inlet line, a Type
K thermocouple is installed in the gas outlet pipe, and provision is made for three
magnetically mounted Type K thermocouples for surface temperature measurements.
Thermal emf from the thermocouples is converted to temperatures by a Digitec Model
1000 Datalogger. Channel number, temperature, and elapsed time are printed on the
paper tape output of the instrument. Because it was desired to monitor two critical
temperatures on a continuous basis, two additional thermocouple readout devices were
installed. These units permit continuous monitoring of the fuel hopper and tuyere
temperatures during operation. These temperatures are also recorded automatically
by the Datalogger. A schematic of the thermocouple system and a photograph of
the complete data analysis subsystem are shown in Figures 15 and 16.
Solid Waste Shredding and Densification
Densified fuels are required for the operation of fixed bed gasifiers. The
simplest type of densification system consists of a shredder followed by an agricultural
type cubing machine. Originally built to produce densified alfalfa hay, these machines
can be easily modified to produce solid waste fuel cubes.
36
-------
THERMOCOUPLE
Figure 15. Schematic of thermocouple system used
to monitor gasifier temperatures.
Figure 16. Data analysis subsystem for
monitoring gasifier operation.
-------
Because the capacity of commercially available densification systems is
relatively large (1.8 to
-------
ROTATING PRESSWHEEL
FREEWHEELING ABOUT
CENTER A.
ASSEMBLY DRIVEN AT
CENTER B.
i
EXTRUDED CUBE
EXTRUSION DIE
Figure 17. Cross section - extrusion dies of the John Deere Cubing Machine.
(Adapted from John Deere Model 390 Cubing Machine Catalog)
39
-------
CYCLONE
-p-
o
(±±r±f±±±±D--'
Figure 18. Schematic of the Papakube densification system.
-------
Table 5
SUMMARY OF DATA COLLECTION AND ANALYSIS EQUIPMENT
Test
Sampling
Technique
Apparatus
Reference
Proximate
analysis
Ultimate
analysis
Energy
content
Dry gas
composition
Gas
moisture
Cube physical
properties
Grab samples of
fuel and char
Grab samples of
fuel and char
Grab samples of
fuel and char
Grab sample of
gas
Grab sample of
gas
Grab sample of
fuel
Drying oven, muffle furnace,
desiccator
C, H, N w/ Perkin-Elmer
Gas Analyzer
S by Grote Combustion
Method ppt w/
Parr Adiabatic Oxygen
Bomb Calorimeter
Leeds and Northrup Multi-
Component Gas Analyzer
(H2, CO, COJ
Leeds & Norfhrup Thermo-
magnetic O-, Analyzer
Beckman Total Hydrocarbon
Analyzer
Leeds <5c Northrup Modular
Gas Sampling System
Ice water itnpingers, MI5CO
Model 7200 Source Sampler
Laboratory balance
ASTM D3172-73
"Standard Method for the Proximate
Analysis of Coke and Coal"
Micro-Analytical Laboratory
Department of Chemistry
University of California, Berkeley
ASTM D-2015-66
"Gross Calorific Value of
a Solid Fuel by the Adiabatic
Bomb Calorimeter"
Manufacturers operational
manuals. Calibration
by standard gas mixtures.
See Figure 19
Reference 8
and Figure 20
Reference 1
-------
Methods (see Table 5). Ultimate analysis for percent C, H, N, S, and O of the fuel,
char, and condensate was conducted by the Chemistry Department, University of
California, Berkeley campus. The energy content of the fuel and char was determined
with a Parr Oxygen Bomb Calorimeter.
Gas Sampling and Analysis
Gas samples were collected in Tedlar gas sampling bags. The gas samples
were analyzed on a Leeds and Northrup process analyzer system. Percent by volume
on a dry gas basis at ambient temperature were determined for CO, CO-,. O-,, H?
and total hydrocarbons. Samples were extracted from the gas flare using the sample
train shown in Figure 19. Moisture content of the gas was determined by the
condensation method as described in Reference 8. The moisture content sampling
train is shown in Figure 20.
FIELD TESTING
In addition to the gasifier temperatures that were recorded automatically by
the data analysis subsystem, the following data were recorded manually during test
runs.
Air and Gas Flows - Air and gas flows were measured using standard flange
mounted orifice plates in the air inlet and the gas flare line. The orifice plates
were calibrated both before and after each run. Because the gas flare orifice was
calibrated with air at ambient temperature, corrections for the temperature and
average density of the low energy gas were made.
Weight Loss - The entire gasifier is mounted on platform scales. The weight
of the gasifier was recorded at five minute intervals. Because only the producer gas
leaves the reactor, the weight loss during the run is1 a direct measure of gas generation.
Pressure Drop - The pressure drop across the fuel bed was measured periodically
during the run. When the pressure drop exceeded 20 cm of water the grate was
rotated, displacing char into the ashpit.
Char - Char samples were collected on the day following the run to allow the
gasifier to cool. Samples for analysis were collected from the reduction zone when
the gasifier was partially disassembled for inspection after each run.
Condensate - At the conclusion of each run, condensate was drained from the
gasifier, weighed, and a sample saved for later analysis.
Slag - To assess the potential of sludge/waste paper cubes to cause slagging,
the gasifier was partially disassembled after each run, and the residual char in the
firebox removed and sifted for slag agglomerations.
PREPARATION OF GASIFIER FUELS
The gasifier was fueled with six different types of fuels: wood chips, an
agricultural waste (almond shells), densified sludge/solid waste cubes (Cal-Cube
-------
Q
ICE
V
CONDENSER
GAS FLARE
CLASS
WOOL
MOLECULAR
SIEVE
PELLETS
-H HH h-
2O LITER TEDLAR
GAS SAMPLING BAG
THOMAS
DIAPHRAGM
PUMP
WATER
GAS FLARE
Figure 19. Schematic - dry gas sampling train.
IMPINGERS IN
ICEWATER BATH
MISCO MODEL 72OO
SOURCE SAMPLER
Figure 20. Schematic - gas moisture sampling train.
-------
machine), densified solid waste cubes (John Deere machine), and densified solid waste
and sludge/solid waste cubes (Papakube system). The preparation of these fuels is
described in this section. The characteristics of the fuels are described in a later
chapter.
Wood Chips and Almond Shells
The wood chips and almond shells were both fired in an as received condition.
They were obtained from the Agricultural Engineering Department at the University
of California, Davis. The wood chips were residues from a kiln dried wood
manufacturing operation. The almond shells from a California almond processing
plant, were screened to remove fines.
Densified Sludge/Solid Waste (Cal-Cube Machine)
Samples of source separated newsprint were obtained from the local solid waste
contractor, Davis Waste Removal, Inc. The newsprint was shredded with a hand fed
hammermill (2.5 cm round hole screen).
The shredded newsprint was mixed in a portable concrete mixer with lagoon
dried sludge from the University's sewage treatment plant (about 50 percent solids).
Sludge, water, and paper in the proportions of 1:1:8 (on a wet basis) was fed into
the Cal-Cube machine by hand. As described previously, only about 50 kg of cubes
were made due to mechanical problems with the cubing machine.
Densified Solid Waste (John Deere Machine)
Source separated newsprint was shredded with a hand fed hammermill and
densified with a John Deere Model 390 Stationary Cubing Machine. The shredded
newsprint, was hand fed into the feed hopper of the machine. About 100 kg of cubes
were prepared.
Densified Sludge/Solid Waste (Papakube System)
Samples of lagoon dried, mixed primary and secondary sludge (approximately
60 percent solids) from the University sewage treatment plant were collected and
trucked to the Papakube pilot plant in San Diego. Sludge/solid waste mixtures of
10, 15, 20, and 25 percent sludge (by wet weight) were prepared by placing preweighed
sludge and newsprint on the conveyor of the system (see Figure 18). It was assumed
that the shredder and blower provided adequate mixing of the sludge and solid waste.
Cubes of solid waste alone were also prepared with the Papakube system.
OPERATIONAL PROCEDURES
A standard operating protocol was used for each test run:
1. Weigh Empty Gasifier - The gasifier was weighed prior to
fueling. Char from the previous run was left remaining in
the gasifier up to the level of the tuyeres to facilitate
startup (see Figure 12).
-------
2. Fuel Gasifier - The fuel hopper was filled with fuel and
the combined weight of the gasifier and fuel recorded.
3. Turn on Gasification Air - The blower bypass valve was set
to supply to the desired flowrate as measured with the air
inlet orifice. The flow was manually regulated during the
run with the air bypass valve.
4. Ignite Gasifier Fuel - A steel rod was heated red hot with
an acetylene torch and inserted into the gasifier ignition
port. After smoke was emitted from the flare stack, the
rod was removed and the port closed.
5. Ignite Gas - After the fuel was ignited, a propane torch
was used to ignite the gas from the flare stack.
6. Record Data - The gasifier was weighed every 10 minutes,
differential and static pressures manually recorded, and
temperatures automatically recorded with the Datalogger.
7. Grate Rotation - The rotating grate was operated when the
pressure drop across the gasifier exceeded 20 cm hUO.
Operation of the grate causes the displacement of ash into
the ashpit and reduces pressure drop to a normal operating
range of 5 to 10 cm fyO.
8. Gas Moisture Content - After the gasifier reached steady
state conditions as defined by the appearance of the gas
flare and the reduction zone temperature, a sample of gas
was drawn off for gas moisture content with a MISCO Model
7200 Source Sampler (see Table 5 and Figure 20).
9. Gas Sample - Several grab samples of the gas were collected
in Tedlar gas sampling bags for later analysis (see Table 5
and Figure 19).
10. Shut Down - The blower was turned off after the gas
samples were collected. The blower valve was closed to
prevent backflow into the blower.
Post Experimental Run
After completion of each run the standardized procedure outlined below was
followed:
1. Calibrate Orifice Plates - After allowing the gasifier to
cool overnight, the orifice plates were recalibrated to
account for particulate buildup on the plates during the
run.
2. Unload Char - The rotating grate was run for one minute,
then char was unloaded from the ashpit and weighed.
15
-------
Unload Condcnsatc - Condensate from the fuel hopper gutter
was removed. A sample was obtained for ultimate analysis.
Partial Disassembly - The fuel hopper was removed from
the gasifier by loosening quick release bolts. All unburnt
fuel, and char were removed. The gasifier was inspected
for corrosion or damage. Samples of char were obtained.
All slag was removed, weighed, and retained for later
analysis. The char was reloaded into the gasifier to provide
a char bed above the level of the tuyeres.
ENERGY BALANCE COMPUTATIONS
In an energy balance, the energy input to the gasifier is compared with the
energy output. Energy inputs include: the sensible and latent heat of the air blast;
and the sensible heat and heat of combustion of the fuel. Energy outputs include:
the heat of combustion and sensible heat of the dry gas; the sensible and latent heat
of the steam in the gas; the sensible heat and heat of combustion of the char; the
sensible heat, heat of combustion, and latent heat of the condensate; and convection
and radiation losses. Significant data required for mass and energy balances are
summarized in Figures 21 and 22. Several simplifications that can be made to the
energy balance are discussed below.
Energy Inputs
The sensible heat of the air blast can be determined by measuring the
temperature of the input air. The latent heat of the air blast can be computed by
measuring the relative humidity of the ambient air and solving for the absolute
humidity at the temperature of the air blast. However, in energy balances conducted
on gasification tests of 30 types of agricultural residues, Jenkins (25) found that the
sensible and latent heat of the air blast was less than 0.1 percent of the heat of
combustion of the fuel. Therefore, the energy input of the air blast was ignored.
The principal input of energy to the gasifier is the heat of combustion of the
dry fuel. This must be reduced to account for the heat of vaporization of the bound
water in the dry fuel and the free moisture of the fuel as fired. The resultant net
energy is defined as:
Net
energy =
dry fuel
(M3/hr)
WF x FE x
r!00 - MCI
100 I
HHV dry fuel (MJ/hr)
WF x B\V
wr x DW
x 2.257
Latent heat bound water (MJ/hr)
WF x
flOO - MC1
^ 100 ;
Latent heat free moisture (MJ/hr)
-------
FUEL
AIR
' AIR
AIR
q, H2o
•/.HrDROCARBONS
V.N,
PROXIMATE
ANALTSia
V* A S H V. F C
1« = SENSIBLE HEAT
<>c ' HEAT OF COMBUST.ON
'l « LATENT HEAT
Figure 21. Data required for mass balance.
Figure 22. Data required for energy balance.
-------
where:
WF = wet fuel rate, kg/hr
FE = higher heating value dry fuel, M3/kg
MC = fuel moisture content, %
2.257 MJ/kg = Latent heat of vaporization of water, 100°C,
1 atmosphere
BW = bound water factor, dimensionless
BW, the bound water factor, is determined from the ultimate analysis of the dry fuel.
Two cases are possible:
BW = (% O + 0/8)/iOO
BW = (9 x %H)/100
The first case is typically encountered in most hydrocarbon fuels such as oil or coal,
where all the oxygen in the fuel combines with a portion of the hydrogen to form
water upon combustion. Hydrogen is present in excess (called available hydrogen).
In the second case, hydrogen is limiting, and excess oxygen exists in the fuel. This
is the case with many biomass based fuels such as wood or paper. This computation
is made using the computer program ENERGY, which is used to calculate energy
balances (see Appendix C).
Energy Output, Gas
The principal energy output of the gasifier is in the form of low energy gas.
The energy in the gas is contained in three forms: chemical energy, sensible heat,
and latent heat of the water vapor in the gas.
Chemical Energy, Gas
The chemical energy of the gas is computed by multiplying the volume fraction
of each gas component, as determined by the dry gas analysis, by the lower heating
value (LHV) of each component gas, (see Reference 19, p. 1937), and summing the
total. Thus, the gas energy content is defined as:
Gas energy
content = XCOECO + XH E + XCH ECH, + XC-HrEC9H,
(M3/m3) 2 2 * * 2626
.+ XC02EC02 + XN2EN2
-------
where:
X
CO'
ECQ = 12.71 MJ/m
EH2 = 10.81 MJ/m3
= 35.88 MJ/m3
= volume fraction of CO, H2,
3
(LHV, dry at 0°C, 762 mm Hg)
C2H6= 63.45
E - 0 ( " )
Cco2 ^ '
EM = ° ( " >
1N2
The gas energy content is computed by program "GASEN" (see Appendix A). The
program is also used to compute the higher heating value of the gas.
The chemical energy output of the gasifier is defined as:
Gas
chemical energy
output =
(MJ/hr)
where: GM = gas moisture content, %
Sensible Heat, Gas - The sensible heat in the gas is computed by first calculating
the mean specific heat at constant pressure for each gas component:
Cpi = aj + b.T + c.T
Gas energy
content
(MJ/m3)
X
Wet gas"
flow
(m /min)
X
100-GM
100
X
,0 min
hr
where Cp. = molar specific heat for gas component i
a., b., c. = specific heat constants for gas component i
T = absolute temperature
The constants a., b., c. can be found in Daniels and Alberty (10), Table 12.
The sensible heat of the gas is the change in enthalpy between the gas exit
temperature and a constant reference temperature. For this report, O°C (273 K) was
used. To calculate the sensible heat of a gas component, AH., the equation dH. =
Cp-dT is integrated between the reference temperature and, the average gas
temperature:
1 1
"C dT =
J (a. + b.
T + c. T) dT
273
273
-------
AH. = a. (Tj - 273) + ^ (T1 " (273)2) + F (T1 " (273)3)
where: AH. = sensible heat of gas component
T, = average gas temperature, K
273 = reference temperature, K
Then the sensible heat of the gas mixture is:
n
AH = I AHj • X
where: AH = sensible heat of gas mixture
AH. = sensible heat of gas component
X. = volume fraction of gas component i, volume basis
These calculations are performed with the computer program "GASHEAT" (in the
program, AH is assigned the variable name SH, see Appendix B).
Heat Loss, Condenser - To utilize low energy gas in an internal combustion
engine, the gas must first be dehumidified and cooled. This can be accomplished by
passing the moist gas stream through an air or water cooled condenser in which the
gas mixture is cooled below its dew point. The process is shown schematically on
the idealized psychrometric chart of Figure 23. The gas enters the condenser at dry
bulb temperature T. and is cooled at constant specific humidity from point 1 to 2 ",
at which point the vapor starts to condense. Further cooling reduces the specific
humidity of gas to point 2. The gas exits the condenser in a saturated state at dry
bulb temperature 7y.
Holman (22) suggested that such a constant pressure cooling process could be
treated analytically by writing an energy balance for the condenser system:
\ ~ V + H \ - ^ hv2} - «"! - ^ hf]
where q = heat removed by condenser,
h = enthalpy dry gas at T,, MJ/kg
sl
h = enthalpy dry gas at Tr MJ/kg
S2
to. = specific humidity at T,, kg water vapor/kg dry gas
-------
kJ
IT
W
CO
CC
O
I
DRY - BULB TEMPERATURE
Figure 23. Idealized psychrometric diagram for gas cooling.
(After reference 22)
51
-------
o^ = specific humidity at T-,, kg water vapor/kg dry gas
h = enthalpy of water vapor at T,, M3/kg
Vl 1
h = enthalpy of water vapor at T~, MJ/kg
V2
M = mass dry gas, kg
6
h, = enthalpy of liquid water at T-
The above expression rewritten as a rate expression is:
QC = MG [ (h - h ) + fo h - u, h ) - to. - uiJ h,]
gj §2 12 i * i
where: QC = heat removed by condenser, MJ/hr
MG = flow rate dry gas, kg/hr
The thermodynamic constants h , h , and h, can be found in standard steam tables
such as Table A7-M in Holman \22). The term (h - h ), the change in enthalpy
1 2
of the dry gas between T, and T_, is computed in the same fashion as the sensible
heat of the wet gas (see previous section). The specific humidity at T., w. , is
determined experimentally. The specific humidity at T^, CJLU, is found by assuming
that the exit gas is completely saturated. Then:
Pv
1.013-PV
where: P = saturated vapor pressure at T^i Dars
1.013 ' = 1 atmosphere, bars
18 = molecular weight, water vapor, kg
"M = molecular weight, dry gas, kg
gas
The dry gas flow rate, MG, is determined from the wet gas flow rate as follows:
m
kg-mole
52
-------
where:
MC
GS
GM
MD
= dry gas flow rate, kg/hr
= wet gas flow rate, m /min (at NTP)
= gas moisture content, %
= dry gas molecular weight, kg
These calculations are performed with the computer program "GASHEAT" (see
Appendix B).
Energy Output, Char
Energy also leaves the gasifier as sensible heat, latent heat, and heat of
combustion of the char. Because cool char is removed from the gasifier on the day
following the run, the sensible heat is ignored. The heat of combustion of the char
is determined by bomb calorimeter tests. The energy output of the char is defined
as:
Energy
output
char
(MJ/hr)
Energy Output, Condensate
Char
generation
rate
(kg/hr)
Char
energy
content
(MJ/kg)
The condensate is also an energy output. Because condensate is removed from
the gasifier at ambient temperature, the latent and sensible heat of the condensate
are ignored. The heat of combustion determined by Jenkins (25), 4.7.5 MJ/kg, is
assumed for all runs. The energy output of the condensate is defined as:
Energy
output
condensate
(MJ/hr)
Condensate
generation
rate
(kg/hr)
U.75 MJ/hrj
Losses
Energy losses from the gasifier include convection and radiation from the outer
surface of the gasifier. Losses are determined by balancing the net energy into the
gasifier against the energy outputs. Losses may also reflect errors in determining
the gas flow rate and the char generation rate. The energy losses are defined as:
Energy =
losses
Net
energy
input
-
Gas
chemical
energy
output
-
Gas
sensible
energy
output
-
i
Heat
loss,
condenser
-
— -
Char
energy
output
-
- "
Condensate
energy
output
53
-------
Efficiencies
The efficiency of a gasifier can be defined in two ways:
Hot gas
efficiency
Gas chemical Gas sensible
1 energy outputj + [energy output]
tNet energy
input
Gas chemical
Cold gas [ energy output
efficiency ~ pvlet energy!
input
x 100%
x 100%
The hot gas efficiency is the appropriate figure to use when the sensible heat of the
low energy gas can be utilized, such as in direct coupled boiler operation. The cold
gas efficiency represents the efficiency that could be expected when the low energy
gas is used to power an internal combustion engine, which requires that the gas be
cooled, thus wasting the sensible heat.
-------
CHAPTER IV
EXPERIMENTAL RESULTS
In the experimental phase of the project the gasifier was operated at a constant
air flow rate but fueled with five different types of fuels including: wood chips,
almond shells, densified source separated solid waste (two types), and densified mixtures
of sludge and solid waste (10, 15, 20, and 25 percent sludge by weight). The
characteristics of the fuels, operational data from the test runs, and energy balances
for the runs are presented and discussed in this chapter.
FUEL CHARACTERISTICS
All fuels except the wood chips were tested for proximate analysis, ultimate
analysis, and energy content (see Table 5 for the methods used). The results of these
analyses are summarized in Table 6. In general, the gasifier fuels tested were all
relatively high in volatile combustible matter (VCM), low in carbon content, and low
in energy content (HHV) as compared to coal, but similar to Douglas fir and Douglas
fir bark (see Table 7).
Both bulk and undividual particle densities of the fuels were also measured
(see Table S). The bulk density is a significant parameter in regards to storage and
transportation requirements. The densified fuels are over twice the bulk density of
the natural fuels (wood chips and almond shells).
OPERATIONAL DATA
The results of the gasification test series including the fuel, char, and condensate
rates; air and gas flows; weight and volume reductions; and temperature profiles are
discussed in this section.
An operational summary of the test series is given in Table 9. All test runs
were conducted at as close to the same air flow rate, as possible, 0.41 m /min (1
atmosphere, 0°C). Thus, the flow rate of fuel through the gasifier, the efficiency,
and gas quality are a function of the gasification characteristics of the fuel. The
significance of the data in Table 9 is discussed below.
Fuel, Char, and Condensate Rates
The fuel consumption rate is the primary parameter used to compare the
gasification potential of fuels. Since the entire gasifier is mounted on scales, the
-------
Table 6
SUMMARY OF FUEL CHARACTERISTICS
Item
RUN 06A
RUN 06B
RUN 08
Fuel description Almond
Shells
Proximate analyses0
VCM, % 68.04
FC, % 20.91
Ash, % 3.11
Moisture, % 7.94
Ultimate analyses
(Dry basis)
C, % 45.65
H, % 6.08
N, % 0.45
S, 96 0.05
O, % 44.57
Residue 3.20
A
Energy content , M3/kg
(Dry basis, HHV) 19.08
10% Sludge
Cubes
70.21
12.46
3.86
13.47
Solid Waste
Cubes
83.49
7.91
3.09
5.51
45.58
5.83
0.17
__
43.92
4.50
44.37
5.62
0.26
0.05
45.90
3.SO
19.03
18.92
Gasifier initially fueled with almond shells
5Gasifier fueled with sludge/solid waste for remainder of RUN 06
'Proximate analyses are the average of duplicate grab samples
Ultimate analyses are based on a single grab sample
*
'Bomb calorimeter results are the average of three tests on one grab sample
56
-------
Table 6 (cont.)
In
Item
Fuel description
Proximate analyses
VCM, %
FC, %
Ash, %
Moisture, %
Ultimate analyses
(Dry basis)
C, %
H, %
N, %
5, %
0, %
Residue
RUN 09
1096 Sludge
Cubes
83.87
8.19
1.11
6.83
46.46
5.98
0.19
0.14
45.33
1.90
RUN 10
15% Sludge
Cubes
75.10
12.19
2.62
10.09
45.99
5.89
0.19
0.10
44.83
3.00
RUN 11
20% Sludge
Cubes
74.54
13.05
3.07
9.34
45.24
5.81
0.13
0.11
46.81
1.90
RUN 12
2596 Sludge
Cubes
73.66
13.70
4.08
8.56
45.27
5.77
0.42
0.16
44.18
4.20
Energy content, MJ/kg
(Dry basis, HHV)
19.04
18.88
18.93
18.49
-------
Table 7
CHARACTERISTICS OF TYPICAL COALS AND WOODS3
Item
Pittsburgh Wyoming Lignite
Seam Coal Elkol Coal
Douglas Fir Douglas Fir
Bark
00
Proximate analyses
(Dry basis)
VCM, %
FC, %
Ash, %
Ultimate analyses
(Dry basis)
C, %
H, %
N, %
S, %
o, %
Residue, %
Energy content, MJ/kg
(Dry basis, HHV)
33.9
55.8
10.8
75.5
5.0
1.2
3.1
4.9
10.3
31.76
MA
51.4
4.2
71.5
5.3
1.2
0.9
16.9
4.2
29.57
43.0
46.6
10.4
64.0
4.2
0.9
1.3
19.2
10.4
24.92
86.2
13.7
0.1
52.3
6.3
0.1
0.0
40.5
0.8
21.05
70.6
27.2
2.2
56.2
5.9
0.0
0.0
36.7
1.2
22.10
After Reference 20
-------
Table 8
DENSITIES OF GASIFIER FUELS
Fuel Run No.
Wood chips
Almond shells
10% sludge cubes
Solid waste
10% Sludge cubes
15% Sludge cubes
20% Sludge cubes
25% Sludge cubes
02
06
06
08
09
10
11
12
Densification
process
Undensified
Undensified
Cal-Cube Machine
John Deere
Papakube
Papakube
Papakube
Papakube
Bulk
density
kg/m3
230
187
496
484
374
445
536
486
Unit
density
kg/m
—
—
1009
1041
738
932
1010
1014
59
-------
Table 9
OPERATIONAL SUMMARY
Item
Fuel description
Fuel consumption rate, kg/hr
Char production rate, kg/hr
Condensate production rate, kg/hr
Net run time, min
Gas flare ignition time, min
Air input rate, m /min
(0°C, 1 atm)
Gas output rate, m /min
(0°C, 1 atm)
Average reduction zone temperature, °C
Average gas outlet temperature, °C
Volume reduction, %
Weight reduction, %
RUN 02
Pine wood
chips
31.3
2.70
0.19
140
1
MO
N/Aa
669.9
I6tt.it
91
91
RUN 06
Almond
shells/
10% sludge
cubes
27.2
2.SO
•
0.18
223
13
.407
.773
752.0
197.8
N/A
88
RUN 08
Solid Waste
cubes
22.8
2.47
0.67
221
15
.412
.627
772.7
214.2
80
S6
Not available
60
-------
Table 9 (Continued)
o\
Item
Fuel description
Fuel consumption rate, kg/hr
Char production rate, kg/hr
Condensate production rate, kg/hr
Net run time, min
Gas flare ignition time, min
Air input rate, m /min
(0°C, 1 atm)
Gas output rate, m /min
(0°C, 1 atm)
Average reduction zone temperature, °C
Average gas outlet temperature, °C
Volume reduction, %
Weight reduction, %
RUN 09
10% Sludge
cubes
21.4
1.15
0.58
251
9
.405
N/Aa
828.8
193.5
81
91
RUN 10
15% Sludge
cubes
12.3
1.40
0.82
407
31
.408
N/A
656.4
149.1
73
80
RUN 11
20% Sludge
cubes
17.5
2.47
0.50
265
24
.407
.749
779.8
197.6
64
82
RUN 12
2596 Sludge
cubes
16.3
1.71
0.73
262
44
.415
.735
734.7
180.6
74
83
Not available
-------
weight loss is recorded at regular intervals during test runs. It is calculated as
shown:
Fuel consumption
rate
Weight loss
during run
+
Condensate
removed
+
Char
removed
+
Slag
removed)
Net run time
Where: Net run time = Run time - (Refueling time -t- Other down time)
As shown in Table 9, the undensified fuels were consumed at a higher rate
than the densified fuels. It was originally assumed that the fuel consumption rate
was inversely related to the bulk density. However, the densified fuel with the lowest
consumption rate, 15 percent sludge, was among the least dense of the densified fuels.
Char and condensate production rates were determined by weighing the char
and condensate removed after each run. The differences .between the rates for each
fuel were not significant.
Weight and Volume Reduction
In the gasification experiments, the weight reduction for sludge/solid waste
cubes ranged from 91 to S3 percent for 10 to 25 percent sludge mixtures, respectively.
Similarly, the volume reduction ranged from 6^ to 81 percent for 10 to 20 percent
sludge mixtures, respectively (see Table 9). Greater volume and weight reductions
may be possible by optimization of the gasification process.
Temperature Profiles
The most important temperatures from an operational viewpoint are the
reduction zone and gas outlet temperatures. The temperature of the reduction zone
is significant because the principal gasification reactions occur there. The gas outlet
temperature is important for the design of gas cleanup equipment and other peripheral
devices. It is also used to compute the sensible heat of the gas. The reduction zone
thermocouple is mounted just below the choke plate (sec Figure 12), and the gas
outlet thermocouple is mounted downstream of the gas outlet orifice plate.
Temperature profiles for RUNS 08, 09, 10, 11, and 12 are shown in Figures 2*f
through 29. The gasifier reduction zone heated rapidly, approaching steady state
temperature within 30 to 60 minutes in most cases. The dips in the temperature
profiles were due to refueling operations and pauses for the connection of gas sampling
equipment. The profiles are similar except for RUNS 10 and 12.
Due to gas sampling problems, RUN 10 was conducted in two parts with 3
hours of down time in between each part. The reduction zone temperature was S^3°C
when the first part of the run was terminated. When the run was restarted the
reduction zone had cooled to 230°C (see Figures 26 and 27). This allowed for an
extremely fast restart compared to a cold startup. Thus, fixed bed gasifiers exhibit
a heat reservoir effect similar to fluidized bed incinerators.
In RUN 12 difficulty was experienced with igniting the fuel. Once.the fuel
ignited, the reduction zone temperature curve for RUN 12 had a similar shape to the
62
-------
o
Ul
a: o
O o
K.
UJ
a.
5 X
UJ
h-
o
o
• REDUCTION ZONE
O CAS
ooo
,00'
l - 1 1 1 1
_l 1-
30 60 90 120 100 180
ELAPSED TIME.MIN
ZIO
240
270
300
Figure 2k. Temperature profiles for gasifier reduction zone and low energy gas.
(RUN 08)
63
-------
• REDUCTION ZONE
O GAS
I2O ISO ISO 2IO 24O 27O 3OO
CLAPSED TIME.MIN
Figure 25. Temperature profiles for gasifier reduction zone and low energy gas.
(RUN 09)
-------
I2O 150 tRO 210 240 270 300
CLflPSED TIME.MIN
Figure 26. Temperature profiles for gasifier reduction zone and Jow energy gas.
(RUN 10)
65
-------
UJ
a; o
~ o
u>
REDUCTION ZONE
tr
ui
o.
5
u
t-
O GAS
Pooc
>«/ \
O
X
,0
i—i—u_j—i i i i i i i i i
60 90 130 ISO ISO ZIO 24O 27O JOO
ELAPSED TIME. WIN
Figure 27. Temperature profiles for gasifier reduction zone and low energy gas.
(RUN 10 continuation)
66
-------
A /
,'V '".J
l 1 1 1 1 I I I I 1 1 , 1 1
• REDUCTION ZONE
O GAS
V
O
ooo
6O 9O 12O I5O IRO 2IO Z4O 2 FQ 3OO
ELAPSED TIME. WIN
Figure 28. Temperature profiles for gasifier reduction zone and low energy gas.
(RUN 11)
67
-------
re
I
5
UJ
I-
•"\J
.A..'
,0000
h* • • • • •
A\
J
• REDUCTION ZONE
O GAS
1 I I I - 1 - 1 - ' ' ' ' ' ' ' '
30 60 90 120 ISO ISO
ELAPSED TIME.MIN
210
240
270
JOO
Figure 29. Temperature profiles for gasifier reduction zone and low energy gas.
(RUN 12)
68
-------
reduction zone profiles for the other runs (see Figure 29). This problem was alleviated
in subsequent test runs by including a 10 cm layer of wood chips or shredded paper
in the combustion zone to act as tinder. Also the heated steel rod used for ignition
in these runs was replaced with an electric heating element.
GAS ANALYSES
Gas samples were collected for analysis during RUNS 06 through 12. However,
due to problems with the gas sampling train, analyses are only available for RUNS
06, 08, 11, and 12. As described in Chapter III, gas samples were collected in Tedlar
gas sampling bags and analyzed off-line with a Leeds and Northrup multicomponent
gas analyzer system. Gas moisture content was determined by the condensation
method (see Table 5 and Figures 19 and 20). Dry gas composition, gas moisture
content, and gas energy content are summarized in Table 10.
The dry gas compositions measured during RUNS 06, 11 and 12 were within
the normal range expected for air blown gasifiers. The gas collected in RUN OS was
lower in CO and H-, than expected. This was probably due to a gas leak in the
sample train as evidenced by the abnormally high percentage of 02 in the gas. The
energy content of the gas samples was within the typical range expected for low
energy gas except for RUN 08. However, as previously mentioned, the gas sample
collected during RUN 08 was probably contaminated.
CHAR, CONDENSATE, AND SLAG CHARACTERISTICS
Samples of char and condensate were collected after each run. The char
remaining in the ashpit after each run was sifted for slag agglomerations.
Char
Char samples were collected on the day following the run to allow the gasifier
to cool. The rotating grate (see Figure 12) was run for one minute to allow char
from the run to fall into the ashpit. During most runs the grate was also rotated
when the pressure drop across the gasifier exceeded about 20 cm of water.
Due to the basic design of a fixed bed gasifier, a considerable amount of char
must remain inside the gasifier, filling the area between the grate and the top of
the tuyere zone. Thus, char sampled from the ashpit may be representative of the
previous run and not of the current run. To account for this problem, char samples
for analysis were collected from the reduction zone when the gasifier was partially
dissembled for inspection after each run.
Significant characteristics of the chars are summarized in Table 11. The
proximate analyses of the chars indicates that relative to the gasifier fuels (see Table
6), the chars are low in volatile combustible matter (VCM) and high in fixed carbon
(FC). In this respect the chars are similar to coals which are also low in VCM (see
Table 7). The ash content of the chars is very high, ranging from 43 to 80 percent.
This would limit the use of char as a fuel.
Although char could be blended into the fuel of subsequent runs, a more
promising use of the chars may be to utilize them in the polishing of wastewater
69
-------
Table 10
COMPOSITION AND ENERGY CONTENT OF
LOW ENERGY GAS
Item
Dry Gas Composition
(By volume)
CO, %
U Qi.
H2, %
CH^a, %
C,H * 96
/ b
co2, %
o2, %
N-b, %
RUN 06
20.7
16.5
4.8
0.2
11.3
0
46.5
RUN 08
16.5
12.5
1.9
0.1
8.5
2.4
58.1
RUN 11
20.9
14.5
2.3
0.1
11.9
0.3
50.0
RUN 12
21.5
13.7
2.5
0.1
11.0
0.3
50.9
Gas Moisture Content
(By volume), 96
10.51
10.56
14.15
12.31
Gas Energy Content MJ/M"
(Dry gas, LHV, O°C,
762 mm Hg)
6.26
4.19
5.11
5.17
Measured as Total Hydrocarbons, CH. assumed to be 9596 of THC,
C2Hg assumed to be 596 of THC
N2 includes nitrogen, argon, and trace amounts of nitrogen oxides. NU is
determined by difference, N'2 = 100% - (CO + H2 + THC + CO2 + O2)
70
-------
Table 11
SUMMARY OF GASIFIER CHAR CHARACTERISTICS
Item
Fuel description
Proximate analyses
VCM, %
FC, %
Ash, %
Moisture, %
Ultimate analyses
(Dry basis)
C, %
H, %
N, %
S, %
0, %
Residue
Energy content, MJ/kg
(Dry basis, HHV)
RUN 06
Almond shells/
10% sludge cubes
1.23
37.63
60.89
0.25
45.31
0.48
0.20
0
0
62 .2a
13.11
RUN 08
Solid waste
cubes
5.51
20.73
72.57
1.19
28.81
0.29
0.17
0.05
3.78
66.90
S.52
RUN 09
10% Sludge
cubes
6.50
49.40
42.90
1.20
35.78
1.00
0.21
0.05
0
64.70a
22.15
As oxides, therefore total is greater than 100%.
71
-------
Table 11 (cont.)
Item
Fuel description
Proximate analyses
VCM, %
FC, %
Ash, %
Moisture, %
Ultimate analyses
(Dry basis)
C, 96
H, %
N, %
S, 96
0, %
Residue
RUN 10
15% Sludge
cubes
3.39
46.16
49.56
0.88
70.38
1.49
0.33
0.18
6.12
21.50
RUN 11
20% Sludge
cubes
2.60
16.90
79.80
0.70
79.01
0.75
0.27
0.20
2.37
17.40
RUN 12
25% Sludge
cubes
5.60
18.50
75.30
0.60
68.55
1.36
0.62
0.19
2.6S
26.60
Energy content, MJ/kg
(Dry basis, HHV)
24.37
27.60
24.3S
72
-------
treatment plant effluent as a substitute for activated carbon. This possibility is being
investigated separately under a research grant from the University of California
Appropriate Technology Program (11). Char samples from RUN'S 06, OS, 09, 10, 11,
and 12, as well as chars from agricultural residues, are being evaluated. Results
from this work are not available at this time.
Condensate
Condensate is produced in the gasifier by condensing vapors formed in the fuel
hopper. The vapors are condensed between the double walls of the fuel hopper and
collected in a Condensate gutter (see Figure 12). At the conclusion of each run, the
condensate is drained and a sample saved for analysis. Detailed chemical analyses
of the condensate were not conducted, but ultimate analyses for the condensate from
six runs are given in Table 12.
In gasification experiments with agricultural wastes, Jenkins (25) found that
condensate is about 80 percent water. He also observed that condensate was produced
mainly during start-up and shut-down. The average energy content of the condensate
was found to be 4.75 M3/kg.
Slag
The ash content of a fuel is an important parameter in the evaluation of
potential gasifier fuels because of the tendency for high ash content fuels to form
slag during the gasification process. Slag formation can reduce fuel flow through the
gasifier, increase firebox temperatures, and stress internal parts of the gasifier. In
extreme cases, the flow of fuel through the gasifier can be blocked off completely.
To assess the potential of sJudge/waste paper cubes to cause slagging, the
gasifier was partially disassembled after each run, and the residual char in the firebox
removed and sifted for slag agglomerations. The weight of the ash in the fuel and
char, and the amount of slag recovered after each run, are summarized in Table 13.
In all cases, the ash recovered in the char exceeded the total ash theoretically
contained in the fuel consumed during the run. This discrepancy was probably caused
by sampling errors as the amount of char generated during a run is not precisely
known. The slag generated in each run was approximately half the weight of the
ash originally in the fuel. Individual agglomerations were sometimes quite large,
exceeding ten centimeters in length. Although no operational problems were
experienced with the sludge/solid waste fuels tested, run times were relatively short.
Longer test runs will be needed to evaluate the slagging potential of sludge/solid
waste mixtures more fully.
Several techniques exist to control slagging. The easiest solution is to limit
the ash content of the sludge/solid waste cubes by controlling the ratio of sludge to
solid waste. Another technique is to operate the gasifier with a steam/air blast
instead of air. This will reduce temperatures in the combustion zone below the point
' where ash is melted. This method of temperature control is common in coal gasification
(IS).
73
-------
Table 12
SUMMARY OF CONDENSATE CHARACTERISTICS
Ultimate Analyses, %
RUN
06
08
09
10
11
12
C
12.83
7.13
7.56
7.12
6.06
7.55
H
9.62
10.08
10.25
10.31
10.2*
10.37
N
0.26
0.10
0.25
0.07
0.09
0.12
S
0.02
0.02
0.08
0.10
0.07
0.05
0
77.27
82.67
81.86
82.40
83.5*
81.91
-------
Table 13
CHAR AND SLAG GENERATION
T+A.—*.
1 LCI 11 ^~
Fuel
Sludge content, %
Ash, %
Total fuel, kg
Fuel ash, kg
Char
Ash, %
Total char, kg
Char ash, kg
Slag
Total slag, kg
Totals
Char ash + slag, kg
(Char ash + slag)/fuel ash, %
RUN
09
10
1.1
89.4
1.0
42.9
4.8
2.1
0.6
2.7
270
10
15
2.6
83.2
2.2
49.6
9.5
4.7
1.2
5.9
270
11
20
3.1
77.2
2.4
79.8
10.9
8.7
0.8
9.5
400
12
25
4.1
75.1
3.1
75.3
7.5
5.6
1.0
6.6
213
75
-------
ENERGY BALANCES - RUNS 06, 08, 11, and 12
Energy balances on four runs were calculated using computer programs "GASEN",
"GASHEAT", and "ENERGY". The output from the programs "GASEN" and "GASHEAT",
the fuel and char characteristics (Tables 6 and 11), and the operational data from
each run (Table 9) are used as input to the program "ENERGY", which, in turn, is
used to compute energy balances. Listings of the programs and printouts for each
run are attached as Appendixes A, B, and C. As previously mentioned, analyses of
low energy gas were only available for RUNS 06, 08, 11, and 12. Accordingly, energy
balances could only be computed for these runs. A summary of the energy balances
is shown in Table 14.
Referring to Table 14, energy balances for each run are given both in energy
units, MJ/hr, and percentages, assuming the fuel net energy as 100 percent. The gas
chemical energy is the most significant energy output, ranging from 37 to 81 percent
of the input net energy. The gas sensible heat is relatively minor, contributing only
3 to 5 percent to the energy output. The gas sensible heat could probably be increased
by insulation of the ashpit and gas piping to the flare. A far more significant energy
output is the char energy, which ranges from 6 to 25 percent of the input net energy.
As char generation is sensitive to fuel residence time and air flow rate, char energy
could be minimized by proper operation. Condensate energy is very minor varying
from 0.2 to 1.4- percent of the input net energy.
Energy losses ranged from 9 to 49 percent, with 20 percent being typical. The
extremely high Joss calculated for RUN 08, 49 percent, is most likely due to the
inaccurate gas analysis obtained on RUN 08. Hot and cold gas efficiencies ranged
from 40 to 37 percent, respectively for RUN OS, to 85 to 81 percent, respectively,
for RUN 12. Hot gas efficiencies in the upper 60 percent range are typical for the
runs. As mentioned previously, the high losses and low efficiencies calculated for
RUN 08 are probably more artifacts of the gas analysis problem with RUN 08, than
a measure of the actual performance of the gasifier.
The negative energy losses shown in RUNS 11 and 12 are most likely indicative
of errors made in determining the amount of char generated during each run. Due
to the relatively large storage volume for char in the gasifier above the grate, it
was difficult to exactly determine the amount of char generated during a short (2
to 3 hour) run. This could also account for the apparently lower char generation of
RUN 09 (see Table 13).
76
-------
Table 14
ENERGY BALANCES
Item
Gross Energy, dry fuel
Latent heat, combined water
Latent heat, fuel moisture
Net energy, fuel
Gas chemical energy
Gas sensible heat
Heat loss condenser
Char energy
Condensate energy
Energy Josses
Hot gas efficiency
Cold gas efficiency
Fuel description
RUN
MJ/hr
462.91
27.08
6.57
429.25
259.82
12.83
18.40
54.29
0.86
83.05
Almond
10% sludc
06
%
100.00
60.53
2.99
4.29
12.65
0.20
19.35
63.52
60.53
shells/
;e cubes
RUN
MJ/hr
407.61
24.59
2.84
380.18
140.98
11.09
15.78
21.30
2.85
188.18
08
%
100.00
37.08
2.92
4.15
5.60
0.75
49.50
40.00
37.08
Solid waste
cubes
77
-------
Table 14 (cont.)
RUN 11
Item
Gross Energy, dry fuel
Latent heat combined water
Latent heat, fuel moisture
Net energy, fuel
Gas chemical energy
Gas sensible heat
Heat loss condenser
Char energy
Condensate energy
Energy losses
Hot gas efficiency
Cold gas efficiency
Fuel description
MJ/hr
269.49
18.48
4.15
273.86
197.15
12.37
21.16
69.00
2.38
-28.19
%
100.00
71.99
4.52
7.73
25.20
0.87
. -10.30
76.51
71.99
20% sludge
cubes
RUN
M3/hr
268.08
16.26
4.07
247.75
199.93
11.03
19.27
41.45
3.33
-27.25
12
%
100.00
80.70
4.45
7.78
16.73
1.34
-11.00
85.15
80.70
25% sludge
cubes
78
-------
CHAPTER V
ENGINEERING SIGNIFICANCE
The economic and management issues that must be resolved if the co-gasification
process is to be used in a municipal environment are considered in this chapter.
These issues include: the economics of co-gasification compared to conventional
sludge disposal practices; the role of gasification in large municipalities; the use of
co-gasification in small communities; and limitations to the co-gasification process.
ECONOMICS OF CO-GASIFICATION
Although the gasification process itself is an old one, there is no operating
experience available for gasifiers fueled with solid waste operating in a municipal
environment. Therefore, to judge the economics of the co-gasification of sludge
relative to other more conventional disposal alternatives, many assumptions would
have to be made.
An economic evaluation of co-gasification was made by Bartley (2). He compared
a sludge co-gasification system to three conventional sludge processing systems (land
application, landfilling, and incineration). The systems studied are shown in Figure
30.
Sludge Processing and Disposal Alternatives
Referring to Figure 30, Option 1, the proposed co-gasification system consists
of a source separation program to recover waste paper, a processing system to produce
d-RDF from sludge (40 percent solids) and waste paper, a gasifier, and a dual-fuel
engine-generator installation to produce electrical power. The ash and char residue
from the gasification process will be disposed of in a sanitary landfill. Option 2
involves the land application of digested sludge (4 percent solids) with transport by
tank truck and application by subsurface injection. Option 3 provides for the transport
of dewatered (20 percent solids) digested sludge by dump truck for disposal to a
sanitary landfill. In Option 4 dewatered sludge at W percent solids is incinerated
autogenously in a multiple hearth furnace, and the resultant ash is hauled to and
disposed of in a sanitary landfill.
Sources of Cost Information
Literature and published reports, communications with manufacturers and
equipment suppliers, manufacturers catalogs, and consultations with practicing
engineers and researchers were used as sources of information and cost data. Due
to the different bases of the cost data obtained from the literature, all literature-
derived costs were updated to June 1979. Capital costs of structures and equipment
79
-------
SLUDGE -
(4%)
.CHEM. 125
FILTER
PRESS..
SLUDGE (40%)
-* 1 GASIFICATION
SYSTEM
d-RDF
PROCESSING
SOURCE SEPARATED WASTE PAPER
ELECTRICITY
TO SANITARY
" LANDFILL
a) Option 1
SLUDGE
(4%)
ANAEROBIC
DIGESTION
SLUDGE TRANSPORT
SLUDGE
(4%)
TO LAND
"APPLICATION
b) Option 2
SLUDGE
(4V.)
ANAEROBIC
DIGESTION
CHEM. 125 */mg
V
TO SLUDGE
LANDFILL
SLUDGE TRANSPORT
c) Option 3
SLUDGE
(4%)
TO SANITARY
*" LANDFILL
ASH TRANSPORT
d) Option
Figure 30. Sludge processing and disposal options.
(After reference 2)
SO
-------
were updated using an Engineering News Record Construction Cost (ENRCC) Index
value of 3,000 which corresponds to the value of the Index in June 1979. Other costs
were determined using 3une 1979 labor, power, and fuel costs.
Principal sources of cost data on gasification technology were References
14,40,43,49,55, and 56. Cost data for the conventional processes of digestion,
dewatering, incineration, land application, and landfilling were obtained from
References 23 and 57. Transportation costs for hauling sludge, char, and ash were
developed from Reference 13. Cost estimates for the recovery of source separated
waste paper were based on Hartley, et_ al (3).
Development of Costs
Hartley (2) calculated operating and capital costs for all four options shown in
Figure 30. In developing costs, Hartley made the following generalized assumptions
for all four options:
1. Cost of labor is $11/hour including fringe benefits. In cases where operating
personnel are not required full time it is assumed they would charge the
balance of their time to other operations.
2. Amortization rate is 8 percent.
3. Energy costs are electricity, $0.04/k\Vh; fuel oil, $0.50/gallon; and vehicle
fuel (gasoline and diesel), $1/gallon (June 1979).
4. Annual maintenance of facilities and equipment is 5 percent of the capital
cost of the item.
A complete summary of all the assumptions and the computations required is
beyond the scope of this thesis, The reader is referred to Hartley (2) for the details.
The results of his analysis are summarized below.
Annual Cost of Sludge Processing and Disposal Options
The annual costs of the four disposal options as a function of distance to
disposal site are presented graphically in Figures 31, 32, and 33 for cities of 10,000,
30,000 and 50,000 persons, respectively. The total annual costs of Option 1, the
proposed co-gasification system, reflect credit for the value of electrical power
produced by the system. The credit amounts to $58,000, $175,000, and $292,000
annually for cities of 10,000, 30,000, and 50,000 persons, respectively (based on an
energy credit of $0.04/kWh).
Hartley (2) made the following conclusions on the use of co-gasification (Option
1):
1. The annual costs of Options 2 and 3 (land application of liquid sludge and
landfilling of dewatered sludge) are effected significantly by the costs of
sludge transport. The transport of liquid sludge in Option 2 results in rapid
rise in costs as distance to the disposal site increases. Dewatering sludge
prior to transport as in Option 3 decreases overall costs of hauling. Transport
costs of the residues from the 'co-gasification and the incineration options
81
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300 r
V)
(X
250 -
o
o
Q 200
z
150
O
100
50
OPTION 4
INCINERATION
8=8=8:
L-OPTION I
CO-GASIFICATION
OPTION 2
LAND APPLICATION
20
40
60
80
ONE WAY DISTANCE TO DISPOSAL SITE
MILES
Figure 31. Annual costs of processing and disposal of sewage sludge by various
methods of a community of 10,000 persons.
(After reference 2)
82
-------
450
400
to
z
z
350
300
250
ZOO
150
OPTION 4
INCINERATION
OPTION I
CO-GASIFICATION
OPTION 3
LANDFILL
OPTION 2
LAND APPLICATION
20
40
60
80
ONE WAY DISTANCE TO DISPOSAL SITE
MILES
Figure 32. Annual costs of processing and disposal of sewage sludge by various
methods for a community of 30,000 persons.
(After reference 2)
S3
-------
550 r
500
en
o:
o
0
o
O
(O
to
o
o
z
<
450
400
350
300
250
200
OPTION 4
INCINERATION
OPTION I
CO-GASIFICATION
OPTION 2
LAND APPLICATION
20 40 60 80
ONE WAY DISTANCE TO DISPOSAL SITE
MILES
Figure 33. Annual costs of processing and disposal of sewage sludge by various
methods for a community of 50,000 persons.
(After reference 2)
-------
(Options 1 and 4, respectively) do not have significant effect upon annual
costs.
2. For cities of 10,000 persons, of the k options considered, Option 2, land
application of liquid digested sludge, would be least costly when the distance
to a disposal site was within approximately 80 miles of the wastewater
treatment plant. Beyond 80 miles landfilling of dewatered digested sludge
(Option 3) would be more cost effective. Option 1, the proposed co-
gasification system, while slightly less costly than the autogenous
incineration of dewatered sludge (Option 4), would be less cost effective
than either Option 2 and 3.
3. For communities of 30,000 persons, Option 2, land application, would be
the most economical system of sludge disposal when the land application
site was no more than 30-35 miles distance. Beyond this point Option 3,
sludge landfilling, would be more cost effective than Option 2. Option 1,
while more costly than Option 3, would have less cost than land application
of liquid sludge when the disposal site was 40 miles or more from the
community. For disposal site distances greater than 80 miles, Option 1
would be more economical than Option 3.
4. For cities of 50,000 persons, Option 2 is the most favorable option when
the disposal site is within about 20 miles from the communities. Beyond
20 miles, Option 1 would be more cost effective than either Option 2 or
Option 3. Option b, incineration, has annual costs greater than Options 1
and 3, but with a disposal site distance greater than approximately 35
miles, the costs of Option k are less than Option 2.
Alternate Gasification Strategies
Because the capital cost of sludge dewatering equipment represents up to 60
percent of the cost of preparing densified gasifier fuels, Bartley (2) looked at the
value of low energy gas made from densified paper alone. This approach also avoids
the high costs of an engine/generator set, which may be 70 percent of the cost of
the gasification system.
As shown in Table 15, the cost of producing low energy gas from densified
waste paper alone was almost competitive with natural gas prices in mid-1979. Thus,
direct use of hot, unfiltered low energy gas in a boiler may be a promising alternate
approach to energy recovery instead of the generation of electricity.
Economic Analysis
Although it would appear from Hartley's (2) analysis that co-gasification is only
marginally cost effective, several qualifications must be made to his conclusions:
1. Energy costs were based on mid-1979 values, (electricity $0.04/k\Vh, fuel
oil $0.50/gal, and vehicle fuel (gasoline and diescl) $1.00/gal).
2. Options 1, 3, and 4 utilized mechanical sludge dewatering devices. If
alternate lower cost means were used (i.e., lagoons or drying beds), capital
and operating costs would change dramatically.
85
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Table 15
COST OF ENERGY OF HOT PRODUCER GAS AND NATURAL GAS3
Fuel
Energy Cost, $/10b BTU
Size of community, persons
10,000
30,000
50,000
Hot, unfiltered producer gas
a. Sludge-waste paper d-RDF 15.35
b. Waste paper d-RDF 8.62
Natural gas 2.50
7.90
4.00
2.50
5.91
2.98
2.50
After Reference 2
86
-------
3. The cost of co-gasification were always Jess than conventional
incineration. Also the incineration costs assumed autogenous combustion
of the sludge. If this were not the case, expensive auxiliary fuel would
be needed in the incineration option.
4. Gasification and densification technology is in a developmental stage.
In contrast, conventional sludge processing equipment is well developed.
Thus, the costs of gasification equipment may include development costs
which have already been amortized in the more mature wastewater
treatment industry.
5. Bartley (2) assumed that gasifier char had no value and would be
disposed of in a sanitary landfill. If the char has value as a charcoal
feedstock or as a low cost substitute for activated carbon (11), the
overall cost of gasification would be reduced.
LARGE SCALE RESOURCE RECOVERY
Until recently, the availability of low cost landfills has negated the necessity
of finding alternatives to conventional solid waste disposal practices. It has only
been the scarcity and high cost of landfill sites in larger metropolitan areas that has
made resource recovery a viable alternative for large scale systems. Such pioneering
efforts as those in St. Louis (31) and Baltimore (51) are typical examples of the large
scale approach.
Large Scale Co-disposaJ of Sludge and Solid Waste
It has become more apparent in recent years that coupling treatment of the
liquid and solid waste streams of a community makes good sense from both an
economic and technical viewpoint (7). Several of the currently proposed co-disposal
systems were described previously in Table 4, Chapter II. These systems have two
characteristics in common with the earlier generation of municipal resource recovery
projects: they are relatively large scale; and they are technologically complex,
employing either mechanically intensive front end systems to produce RDF, or expensive
mass fired incinerators to handle unseparated solid waste.
The Role of Gasification in Large Municipalities
The relative simplicity of the gasification process lends itself to satellite
operation in larger cities. For example, source separated solid waste (or sludge/solid
waste mixtures) could be densified at a large central facility and trucked to satellite
gasifiers in other parts of the city. Or in the case of large urban areas with several
landfill sites and wastewater treatment plants, complete co-gasification systems could
be located at each site.
SMALL SCALE GASIFICATION
The technical feasibility of using simple downdraft gasifier to co-dispose of
sludge and source separated waste paper, while producing a low energy gas has been
87
-------
demonstrated in this study. The implementation of this technology in a small
community setting will require several commitments on the part of the community:
1. An institutional framework must be established for economic and
management cooperation between solid waste and wastewater treatment
authorities.
2. A community wide source separation system will be required for the
production of a suitable gasifier fuel.
3. The technical expertise to manage and operate a co-gasification system
will need to be developed, preferably within the existing staff of the
solid waste collection and wastewater treatment agencies.
Ultimately, an integrated waste management system, such as shown in Figure
10, Chapter II, could be developed. This would optimize usage of the system and
involve rural communities with surrounding agricultural producers. Such a system
might also involve the sale of gas, steam, or electricity to local industrial users.
Smaller communities could participate by pooling the costs of a central densification
system and operating small satellite gasifiers in their own communities to power
community owned facilities.
LIMITATIONS TO THE CO-GASIFICATION PROCESS
The co-gasification of sludge and solid waste is not a panacea. Although
gasification itself is an old technology, the application of gasification to municipal
uses is a relatively new concept. The hardware needed to implement the concept is
manufactured by several firms, but the equipment must still be considered to be in
the developmental stage. Questions on the environmental effects of gasification still
need to be resolved. Finally, the limitations inherent in the production of low energy
gas must be recognized. The gas should be used onsite, most efficiently in a boiler,
but can also be used, with an acceptable loss in efficiency, in a gas turbine or internal
combustion engine.
Important technical and economic questions that remain to be solved include:
optimization of gasifier operation; identification of slag control techniques;
determination of the fate of heavy metals in the gasification process; characterization
of particulate emissions; economics of co-gasification for small communities; the
economic break even point between direct combustion systems and gasification; and
the identification of component manufacturers.
38
-------
CHAPTER VI
CONCLUSIONS AND RECOMMENDATIONS
FOR FUTURE RESEARCH
An experimental gasifier has been designed, constructed, and operated
successfully with a variety of biomass and densified sludge/solid waste fuels.
Conclusions derived from the most significant results of this work and
recommendations for future research are presented below.
CONCLUSIONS
Based on the experimental work and a review of the literature in
co-disposal and gasification technology, the following conclusions can be drawn:
1. The co-disposal of sludge and solid waste is both
economically and technically viable. Several co-disposal
facilities are currently under construction in the United
States.
2. The preparation of densified sludge/solid waste mixtures
at a full scale pilot facility has been demonstrated.
3. A pilot scale downdraft gasifier was designed and
constructed. The gasifier design is based on agricultural
waste gasifiers built by the Department of Agricultural
Engineering at the University of California, Davis.
4. The gasifier was operated with various fuels including an
agricultural waste (almond shells), wood chips, densified
source separated solid waste, and densified mixtures of
sludge and source separated solid waste (10, 15, 20 and
25 percent sludge by wet weight). Low energy gas was
produced during the tests with an energy content ranging
from 4.19 to 6.26 M3/m at hot gas efficiencies from 40
to 85 percent.
5. The co-gasification of densified sludge and source
separated solid waste may be a new approach to co-disposal
that could be used by smaller communities. Compared to
conventional incineration, co-gasification is cost effective.
If mechanical sludge dewatering is used, co-gasification is
not competitive with landfilling unless landfill haul
89
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distances exceed 80 miles in communities of 30,000
population, or 15 miles in communities of 50,000 population.
Co-gasification does not appear to be a feasible option for
communities of 10,000. The use of alternate sludge drying
techniques would substantially reduce the cost of co-
gasification.
RECOMMENDATIONS FOR FUTURE RESEARCH
The technical feasibility of operating a fixed bed gasifier with densified
sludge/solid waste mixtures has been demonstrated. However, before the
co-gasification process can be considered operational, several key issues must
be addressed in future work. They are:
1. The optimum conditions for gasifier operations in terms
of fuel consumption, air flow, gas quality, and efficiency
need to be defined. These parameters can be used to
develop loading factors and specifications for the design
of full scale systems.
2. Conditions that cause slagging should be determined. Slag
control measures such as steam or water injection, or
continuous grate rotation should be investigated.
3. The fate of heavy metals during the gasification process
should be determined.
4. Mass emission rates and particle size distributions for
particulates in the low energy gas should be measured to
provide data for the design of gas cleaning equipment.
5. Emission data from engines, burners, and boilers fueled
with low energy gas should be measured. Emissions should
also be analyzed for potentially toxic compounds.
6. Manufacturers of system components should be identified.
This work will be assisted in part by a forthcoming survey
of gasifier manufacturers by the Solar Energy Research
Institute (50).
90
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APPENDIXES
96
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APPENDIX A
COMPUTER PROGRAM "GASEN"
Computer program "GASEN" is written in the BASIC language for the
Commodore PET 2001 mini-computer. The program uses dry gas analyses to calculate
the energy content of the low energy gas (HHV and LHV) at 60°F, 1 atmosphere and
0°C, 762 mm Hg. Results are reported in both English and metric units. A listing
of the program and printouts for the experiment runs are attached. Remark statements
(REM) are used throughout the program as comments to the user. Program variables
are identified in INPUT statements as they occur.
A-l
-------
3EABV.
5 PRINTS"
3 PRINT'MW
H PRINT" PROGRflh GfiSEN"
13 PRINT""
IS PRINT" EV"
It. PRINT""
17 PRINT "»»H»»»m«Hi.fiM VIGIL"
13 PRINT"". 'PRINT""
21 PRINT" DEC 14, 1380"
22 PRINT" REV JftH 25, 1381"
25 FOR I = 1 T05000 ' NEXT : PR I NT " I
23 PRINT""
31 PPI NT "PROGRAM GFiSEN COMPUTES THE LOWER HEAT ING"
32 PR I NT "VALUE vLHV> AND HIGHER HEATING WE"'PRINT'"1
34 PRINT" OF LOW ENERGV GAS FROM THE DRV GAS"
36 PRInT"iiNALVSIS. OUTPUT IS PRINTED IN BOTH SI "'PRINT1'"
38 PPIMT^ND ENGLISH CUSTOMARV UNITS. "'PRINT1'"'PRINT" "
40 PRINT"PLEASE SEE THE PROGRftM LISTING FOR"'PRINT'"1
42 PR I NT "DETAILS. " 'PRINT'"1
44 PPlNT'
4r; FOR i = i Tosoee : NEXT = PP i NT " ^"
4S PEM' LINES 5-44 SET UP TITLES
"?0 PR I -JT" »•:«*****»:»*#**#*#*##** **###if *###*###*#**#
?*> F'RInT";CNTER RUN «"
:•<-:• li-ipijT R
?3 °RIr
-------
130 PRINT"H2 =";H2;"
200 PRINT"CH4 =",C4,"
210 PF:IMT"C2H6=";C2.i"
212 PRINT"C02 =",CD,"
214 PR I NT "02 a";02;"'
216 PRIHT"N2 = ";N2.;"
213 PRIHT"H2G =".:AC!.:"
220 DEF FNR<;X::' = INT<,X*10e+.5>/100:REM ROUND OFF FUNCTION TO 0.01
222 PRINT fif
224 PRINT"OUTPUT DATA"
226 PRINT fit
228 REM •• ENERGY CONTENT VALUES FROM "HANDBOOK OF CHEMISTRY AND PHYSICS" ,42ND ED
230 REM'C.B. HODGMAN, EDITOR-IN-CHIEF,THE CHEMICAL RUBBER PUBLISHING CO.,
232 REM'CLEVELAND, OHIO,1961,.
234 H1 = (. C0*322. 6+H2*324.5+C4* 1013.2+C2*L??2Vl OO
236 PRIHT"HHV DRV GAS = ";FNR;"ETU/FT3,C30 IN HG,60 I€0 F>"
233 HM=H:*.0:<725?--REn CONVERTS BTU/FT3 TO M-J/M3
240 PRINT"HHV DRV GAS = " ,FNR>;HM>, "M,T,'M3, <30 IN HG-60 DEG F>"'PRINT'1"
242 L1=(C0*322.6+H2*275.OfC4*S13.1+C2*1641>/100
244 PRIHT"LHV DRV GAS = " ,FHRCL1 >; "BTU/FT3, <30 IN HC^cO DEG FV
246 L2=Ll*.037253'REh CONVERTS BTU/FTS TO NJ/M3
I'JS PRINT"LHV DP.V GnS = ":FNRCL2>; "MJ/M3, (30 IN HG,60 DEG F>"'PRINT""
252 ?RIHT"HHV DRV GnS ='" ;PNR; "BTU/FTs'. (30 IN HG,0 DEG C;"
254 H4=HJ*. 03725?-REfl CONVERTS BTU/FT3 TO MJ/M3
256 FRIHT"HHV DRY GAS = " ,FHR.; "MJ/M3, C30 IN HG,0 DEG C>"'PRINT""
2bO PPINT"LhV D'-V GflS = " ;FNR > "ETU/FT3.. (30 IM HG,0 DEG C>"
2t2 L4=i_3.*. 03725? 'REM CONVERTS BTU/FT3 TO MJ/M3
254 PP.INT-LHV DRV GRS = ";FNR"
I'M PRINT fl*
265 PRINT*f4'CLOSE 4
2TO REfl LHV VALUES FOR LINE 242 FROM "CHEMICflL ENGINEERS HAHHEOOK'S
272 REH 5TH EDITION,R.H. PERRV & C.H. CHILTON,EDITORS,
?74 REM:nCGRRw-HILL BOOK CO.,MEN VORK,1573.
276 EMU
A-3
-------
ORS EMEROV CONTENT RUM 4* •=.
INF'UT DRTA - DRV GflS RHRLVSIS
co = 20.7 ;:
H2 = iG.5 ;:
CH4 =4.3 .-;
CG2 = 11.3 /J
02 = o ••;
N2 = 46.5 X
H20 = 18.51 ;:
OUTPUT DflTfl
HHV DRV GAS = 172.54 ETU/FT3, <30 IN HG,oO DEG F)
HHV DRV GAS = 6.43 MJ/M3, (39 IN HG,6Q DEC F)
LHV DRV GAS = 159.2e ETU/FT3, (30 IN HG,fc"0 DEC F)
unV DRV GflS = 5.93 MJ/H3, C30 IN HO, 63 DEC F)
HHV DRV GfiS = 182.22 STU/FT3/ <38 IN HG,0 DEO C>
HHV DRV GflS = 6.79 I-1J/M3, <38 IN HG,S DEO C>
LHV DPV GAS = ltoS.67 STU/FT3, <30 IN HG,0 DEC C>
LriV DRV GAS = 6.2S MJ/M3, (30 IN HG,0 LEG C>
GRS EMERGV CONTENT RUN 4* :=:
IM="JT DflTfl - DPV GflS flr«'ftLVSIS
CO = Is. 5 y.
•12 = 12.5 ;:
CH4 « i . =i ;;
CSHS= .1 :•:
:02 = 5.5 r:
'•2 - 53*!"?:
OUTPUT
-Vv' p;;y r,pj = 114,5.5 B~U/FT3' <3Q
-IHV DSV OAS = 4. IS ••1.J/M3, (IS* IN
_,-V t'c:V Or'E - lC-r.5? ETIJ/FT3X33
ill.;. 1 E'lv'"}'. •• '3D IN J-0-0 DEO -I
^.52 VJ/»;.,:JO I t -I-,0 DEO C'
.-..;? .«.', •>!'/:. 130 IN HG>(t? DEO -I.'
-------
GRS ENERGV CONTENT RUN ** 11
->V I-'V Oh I- = i:?.37 E-(J.< "3.-<3S !••< HO-e'O I'£G r>
-V D5V .j^i. * 3.1' MJ/C3/C30 I.-i Ho,e-J DIG .->
—V DRV ij^:= = 1-17.4; E7U/-T3,C30 IN HG,3 DEC C>
--V DRY CI*-E. = 3.4S- KJ/f13, •. 30 Irl HG..0 DEG C>
...-iV IPV C-SS = 137.17 E7IJ/FT3, C?0 IN HG,0 DEG C>
..-:'-.' ERY -jnl - 5.11 '•U/r'13.''30 IN HC-,0 DEG C>
GRS ENERGV CONTENT RUN 4* 1
INPUT BRTfl - DRV OftS fiNftLVSIS
co = 1-1.5 ;:
n; = 13.7 ;;
CH4 = 2..°: X
c£H6= .1 r;
cos = : ; r;
N2 = so.:? ;;
OUTPUT D
-IHV DRV OrtS = 140.S4 BTU/FT3/ k30 IN HG^c'O DEG r>
HHV DRV GflS = 5.1'S KJ/M3X30 IN HO, 60 DEG F)
LHV DRV GAS = 131.5 ETU/FT3, C30 IN HG.60 DEG F)
LHV DRV GftS = 4.9 MJ/M3, <30 IN HG^SS Ii£G F>
-.riV IiRV :^5 = 14S.S? I:TLI/PT3,-;30 IN HC«,0 DEG C^
H-V IIPV Gni = 3.55 ."tJ/KS, <30 IN HG,0 DEG CJ
_HV IiPV Grti = 13.::. Si' FTU/FT3, •' 30 IrJ HG-0 DEG C >
_HV 5RV jfiS = 5.17 MJ.'M3,'.30 IM HG.-0 DEC- C>
A-5
-------
APPENDIX B
COMPUTER PROGRAM "GASHEAT"
Computer program "GA5HEAT" is written in the BASIC language for the
Commodore PET 2001 mini-computer. The program uses the dry gas analysis, gas
moisture content, average gas flow, average gas temperature, average condenser
temperature and thermodynamic data from standard tables to calculate the sensible
heat of the low energy gas and the latent heat lost when the gas is condensed. A
list of the program and printouts for the experimental runs are attached. Remark
(REM) statements are used throughout the program as comments to the user. Program
variables are identified in INPUT statements as they occur.
B-l
-------
1 PRINT ".T
10 PRINT
11 PRINT"MM8«iB
12 PRINT"
14 PRINT .....
16 PRINT""
18 PRINT"
26 PRINT""
£1 PRINT"
22 PRINT""
23 PRINT"
24 PRINT""
25 PRINT"
26 PRINT"": PR I NT""
27 PRINT"
29 PRINT"Hfl"
PROGRfiM GftSHEfiT"
BY"
SfiM VIGIL-
S'1
NELSON SORBO"
SEPT 23,1380"
.
32 FOR 1=1 T05000-- NEXT :PRINT"3"
34 PRINT "
36 PR I NT "MB"
3S PR I NT "PROGRAM GflSHEfiT COMPUTES THE HEfiT LOSS" : PRINT""
40 PRINT "FROM fl CONDENSER flND THE SENSIBLE" 'PRINT1111
41 PRINT "HEflT OF THE WET GflS. "
42 PR I NT "MUMS"
44 PRIHT"PLEflSE SEE THE PROGRfiM LISTING FOR" •' PRINT11"
46 PR I NT "DETAILED IHFORMflTION.
43 PRINT"!8KfeW"
49 PR I NT "*******#**•*.*»•:**#*.**•**********##*****#*# »
56 FOR I=lTQ8000:NEXT:PRINT":r
52 REM LINES 10-50 SET UP TITLES
121 PR I NT "rj": PR I NT "CENTER RUN NUMBER" = INPUT RU
122 PR I NT" ENTER DRY GftS flNflLVSIS flND GftS M/C"
130 PRINT ":€NTER KCO" = INPUT XI
290 PRINT "CENTER KH2" = INPUT X2
230 PRINT "rENTER
300 PRINT "CENTER'
320 PRINT "CENTER
;CH4":INPUT X3
.'C2H6": INPUT X4
iC02":INPUT X5
340 PRINT 'TENTER KQ2"'INPUT X6
360 PRINT "CENTER KN2"=INPUT X7
362 PR I NT "CENTER ?iH20" = INPUT XS
364 DEF FNR/106:REM ROUND OFF FUNCTION TH ii.rtl
366 REM LINES 36S-3S2 CONVERT THE DRV GftS flNfiLVSIS TO ft WET GftS E'flSIS
368 V1 ->'. 1*O 00-XS > /100: V1 =FNR (V1 >
370 V2=X2*<100-XS>/100:V2=FNRCV2>
372 V3=X3*C100-X3)/160:V3=FNR
374 V4*X4*< 100-X3>/KiO:V4=FNRCV4>
376 V5=X5*<100-X8>/100:V5»FNR
37S V6=X6#< 100-XS>/Ki0:V6=FNR
3SO V7=X7*
3S2 V8«X3:REM OflS MC IS THE SflME IN BOTH THE WET & DRY GftS fiNftLYSIS
3S3 PRINT "CENTER fiVO GfiS TEMP DEG C":INPUT Tl
3S4 PRINT 'TENTER ftVG COHD TEMP DEG C";INPUT T2
335 PR I NT "CENTER ENTHftLP1!1 SftT VflPOR flT Tl, MJ/KO" • INPUT HI
3S6 i='RINT":CHTER ENTHflLPY SrtT VflPOR flT T2, MJ/KG" : INPUT H2
387 PRINT'TENTER ENTHflLPV SflT WATER AT T2, MJ/KG"=INPUT HF
B-2
-------
388 PRINT":€NTEF: SflT VftPOR PRESSURE fiT T2, EARS" = INPUT PV
339 REM FOR LINES 338-385, SEE TABLE A-7M,PftGE 718
390 REM "THERMODVNfiMICS",THIRD ED., BY J.P. HGLMAN
351 PRINT" EENTER WET GftS FLOW M3/MIN"
392 PRINT"*! NTP <0 DEG C, 1 ATM)"'INPUT GS
39.3 OPEN 4,4
394 CMD 4
395 ftt=" "
396 PRINT fit
397 PRINT CHR*"GflS SENSIBLE 6 LATENT HEAT"-
398 PRINT CHR*a>"RUN #";RU
399 PRINT ft*
400 PRINT"INPUT DATA"
401 PRINT fit. ~
402'PRINT"GfiS FLOW =";FNX;"M3/MIN"
404 PRINT"GAS TEMP =";FNX(T1>;"DEG C"
406 PRINT"COND TEMP=";FNX;"LEG C"
408 PRINT"EN!HftLPV SflT VflPOR flT Tl ** ";H1; "MJ/KG"
410 PRINT"EN!HflLPV SftT VflPOR fiT T2 » ";H2;"MJ/KG"
412 PRIN!"EN!HRLPV Sft! Wfl!ER flT T2 = ";HF;"MJ/KG"
414 PRINT"SRT VAPOR PRESSURE flT T2 = M;PV;"BflRS"
420 PRINT""
422 PRINT "DRV GftS flNflLVSIS"
431 PRINT "m/.CO =";X1
432 PRINT "KH2 =";X2
433 PRINT "KCH4 ="JX3
435 PRINT "?:C2H&-";X4
437 PRINT "riC02 =";X5
43S PRINT T.Q2 «=";Xe
440 PRINT TiNZ =";X7
442 PRINT ";-;H20 =";X8
444 PRINT ft*
446 PRINT"OUTPUT LflTfl"
44S PRINT ft*
450 PRINT"ICT GflS flNftLVSIS"
454 PRINT'V-iCO =";V1
456 PRINT-KH2 =";V2
458 PRINT";:CH4 s";V3
460 PRINT"?-.'C2Ht-=";V4
462 PRINT":-.'C02 =".:V5
4-54 PRINT"K02 =";V6
466 PR1NT"XN2 ="A7
468 PRINT"KH20 =";V8
4?9 PRINT""
496 !1=! 1+273:REM CONVERT TO DEG K
497 T2=!2+2?3=REM CONVERT TO DEG K
498 REM LINES 500-540 CflLCULftTE flVG CP FROM T1-T2.THE CONSTANTS ftRE FROM TflBLE
499 PEM 1.2,"PHVSICflL CHEMISTRV",4TH ED,8V DflNIELS FIND ftLEERTV,JOHN WILEV,1975.
500 DIM A<8>,E(8),C<8)
502 POR I * 1 TO 8
504 REflD fia>,Ba>,ca>
509 NEXT I .
520 DflTfi 6.3424,1.8363E-3,-2.801E-7
522 DflTfl 6.9469,-.1999E-3,4.808E-7
524 DfiTft 3.422,17.845E-3,-'tl.65E-7
526 DflTft 1.373.41.S52E-3.-138.27E-7
523 DflTft 6.3957,10.1933E-3,-35.333E-7
530 DflTfl 6.0954,3.2533E-3,-10.171E-7
5?2 DflTft 6.4492,1.4125E-3,-.8G7E-7
534 DftTfl 7.1873,2.3733E-3,2.984E-7
540 REM LINE 542 CALCULATES MD,THE MOLECULftR MT C»P DRV GftS
542 MD= CXI*28+X2*2+X3*16+X4*30+X3*44+X6*32+X7*28)/1GO
544 PEM LINE 546 CALCULfiTES MU,!HE MOLECULflR W! OF WE! GflS
546 MW= (.V1 *28+V2*2+V3* 16+V4*30+V5*44+V6*32+V7*28+V8+18)/100
548 REM LINE 550 CflLCULA!ES MG,!HE FLOW OF DRV GflS IN KG/HR
556 MG-GS*SO*>*a/22.4>*MD
B-3
-------
352 REN IU=KG H20/KG DRV OhS AT Tl
554 wi=AMii*i00>
556 REM U2=KG H20/KG BRY GAS flT T2
553 U2= - « Ml -M2 > #HF »
5S8 REM LINES 5*0-620 CALCULflTE SH.THE SPECIFIC HEflT OF WET GflS flT Tl
5S5 REM RELflTIVE TO 0 DEG C
590 BT=Tl-273:D3=Tit2-273t2:DQ=Tlt3-273t3 .
591 S1 = »BT-k'B< 1 V£)#BS+CC< 1 )/3)#IJQ»/lCiO
592 S2=';V2*<:fl<2^*HTfa:(2>/2)*DS+/3)*DQ))/ie0
533 S3=';V3#/3)*DQ) J/ISQ
594 £4=*BS+(C(4>/3)#DQ»/100
595 S5= (! V5* <: A < 5 > * BT+ ( B < 5 ) /2 > * DS+ < C C 5 > /3 )*DQ > V 1 00
•596 S6= < V6# < A < 6 > * DT+ < B ( 6 > /2 > #BS+ < C ( 6 > /3 > *BQ > > / 1 00
597 S
593 S
606 SH=Sl+S2+S3+S4-»-S5+S6+S7*S8:REM SH IN GM-CAL/GM-MOLE
60S PEM SH*<4.1854 J/'GM-CAL>#
610 REM *<10E3 GM-MOLE/KG-MOLE)***<60 MIN/HR)
628 SH=SH*<4. 1854E-3>*GS*<1.-'22.4>*S0
622 PR I HT" HEAT LOSS CONDENSERS = ";FNX; "MJ/'HR"
646 PRINT""
648 PRINT A*
650 PRINTS: CLOSE 4
652 END
REflDV.
-------
C3RS SENSIBL.E & L-RTENT HERT
RUM 4* e
INPUT IlflTfl
OfiS FLOW = .77 113/MIN
GflS TEMP = 127.S BEG C
COND TENP= 13.* DEC C
EHTHflLPV JflT VftPOR A7 Tl = I'. 73 17 MJ/KO
EHTHflLPV JAT VfiPOR RT T£ = 2.5264 MJ/KO
EHTHflLPV SflT WATER AT T2 = .05711 MJ/KC
SfiT VflPOR PRESSURE flT T2 = .02161 EflRS
DRV OflS flNflLVSIS
:-;'CO = 20.7
:-:H2 =16.5
;.;CH4 =4.3
;-;co2 =11.3
;:o2 = s
MH2 =46.5
;-;H2o = 10.51
OUTPUT
WET CflS flHflLVSIS
;.'co = is. 5
KH2 =14.3
4.3
;.'02 = o
MH2 =41.6
XH2Q =10.51
HEAT LOSS CONDENSERS = IS. 4 MJ/HR
SENSIBLE HEflT WET GflS = 12. S3 MJ/HR
B-5
-------
INPUT DRTfi
GAS FLOW = .63 N3/MIH
GRS TEMP = 214.2 DEG C
COND TEMP= 12.1 DEO C
ENTHftLPV ShT VfiPOP RT Tl = 2.8 MJ/KG
ENTHftLPV SflT VfiFOR RT T2 = 2.3236 MJ/KG
EHTHflLPV SflT WATER RT T2 = .05632 MJ/KG
SflT VflPOR PRESSURE RT T2 = .31971 ERRS
DRV GftS RHRLVSIS
'.'CO =16.5
•:H2 * 12.5
;:CH4 » 1.9
:;co2 = s.s
XQ2 =2.4
;-:H2 = 53. i
.•:H20 = 10.56
OUTPUT DRTR
WET GRS flU fit VS IS
.'JCO = 14.S
:.'H2 =11.2
:-iCH4 = 1.7
'.'C2H6= . 1
= r.e.
=2.1
= 52
'JH20 = 10.56
HEflT LOSS COHDEMSERS = 15.78 MJ/HR
SENSIBLE HERT WET GRS = 11.09 MJ/HR
B-6
-------
SENSIBLE & L_FlTENT HERT
RUN *» 11
INPUT DflTfi
GftS FLOW = .75 M3/MIN
GflS TEMP = 137.6 DEO C
COND TEMP* 9.4 BEG C
ENTHflLPV SfiT VflPOfi fiT Tl = 2.7916 MJ/KG
ENTHflLPV SAT VflPOR ftT T2 = 2.51S7 MJ/KG
ENTHflLPV SfiT WflTER flT T2 = .03349 MJ/KG
SAT VflPOR PRESSURE ftT T2 « .01185 BARS
DRV GflS flHflLVSIS
•;co * 20.9
KH2 =14.5
2.3
;:co£ = 11.
y.02 = .3
KN2 = 56
OUTPUT DflTfl
WET GflS ftHflLVSIS
::co =17.9
;.'H2 =12.4
;;CH4 = 2
•;co2 = 10.2
K02 = .3
XN2 =42.9
KH20 * 14.15
HEftT LOSS COHLEMSERS = 21.16 MJ/HR
SENSIBLE HEflT WET OflS - 12.37 MJ/HR
B-7
-------
SENSIBLE: & L.FITENT HERT
R-UN # is
INPUT DRTfi
GfiS FLOW = .74 M3/MIN
GflS TEMP = 130.6 DEC. C
COND TEHP= 4.1 BEG C
EHTHHLPV SfiT VfiPOR HT Tl = 2.7737 MJ/KG
ENTHflLPV SfiT VfiPOR flT T2 = 2.50S3 MJ/KG
EHTHflLPV SftT WflTER flT T2 = .£U72 MJ/KG
SAT VflPOR PRESSURE *T T2 = S.25E-03 ERRS
DRV GfiS FlNRLVSIS
;-;c.o = 21.5
'.'H2 =13.7
.•iCH4 = 2.5
KC02 = 11
.-•:02 = .3
KH2 = 50.3
:-:H20 = 12.31
OUTPUT DftTfl
WET GftS rtNFJLVSIS
;:co = is.?
MH2 = 12
;:CH4 = 2.2
'.'C2H6= . 1
KC02 = ?.e
,'i02 » .3
,'.'H2 = 44.6
;.'H20 = 12.31
HEfiT LOSS CONDENSERS = 13.27 MJ/HR
SENSIBLE HEflT WET GftS = 11.03 MJ/HR
B-8
-------
APPENDIX C
COMPUTER PROGRAM "ENERGY"
Computer program "ENERGY" is written in the BASIC language for the
Commodore PET 2001 mini-computer. The program uses the dry gas analysis, gas
moisture content, wet fuel rate, dry fuel energy, air flow, wet gas flow, gas energy
content (computed by program "GASEN"), gas moisture content, char rate, char energy,
condensate rate, condensate energy, gas sensible heat and condenser energy loss
(computed by program "GASHEAT"), to calculate an energy balance. A listing of the
program and printouts for the experimental runs are attached. Remark statements
(REM) are used throughout the program as comments to the user. Program variables
are identified in INPUT statements as they occur.
C-l
-------
1 PRINT'TT
2 B$= "!M***##*#*******#*****#*#***************"
3 PRINT B*
4 PRINT"M«ttW"
6 PRINT" PROGRfiM ENERGY"
8 PRINT""
10 PRINT""
12 PRINT" BV"
14 PRINT""
16 PRINT""
18 PRINT" SftM VIGIL"
20 PRINT""
22 PRINT""
23 PRINT" 10/11/80 "
24 PRINT""
25 PRINT" REV 12/20/86, 2/17/81"
26 PRINT"a"
28 PRINT B*
30 FORI=1T05008:NEXT:PRINT".T
32 PRINT B*
34 PRINT"*W"
36 PRINT"PROGRfiM ENERGY COMPUTES FIN 'ENERGV" = PRINT'"1
33 PRINT"BflLANCE FOR THE UCD SLUDGE GflSIFIER." 'PRINT'"'
40 PRINT-'Madfl"
42 PRINT"PLEl=lSE SEE THE PROGRftM LISTING FOR" :PRINT""
44 PRIHT"DETflILED INFORMfiTION.
4(3 PRINT "K*M"
48 PRINT B*
50 FOR I=1T08000: NEXT'PRINT"::"
52 REM LINES 1-50 SET UP TITLES
60 PRINT":€HTER RUN ID #"
65 INPUT RU
100 PRINT"SENTER WET FUEL RflTE* KG/HR"
110 INPUT WF
120 PRINT":€NTER FUEL MOIST '/."
130 INPUT MC
140 PRINT":€NTER DRV FUEL ENERGV CONTENT MJ/KG"
150 INPUT FE
160 PRINT" :€NTER LHV DRV GflS C0 DEC C,30 IN HG> MJ/M3"
170 INPUT GE
180 PRINT":€NTER GftS MOIST Ji"
130 INPUT CM
192 PRINT'TENTER flIR FLOW RflTE M3/MIN AT 0 LEG C,1 fiTM"
193 INPUT OK
200 PRINT":€NTER WET GflS FLOW RflTE M3/MIN ftT 0 DEG C,1 flTM"
210 INPUT GF
212 PRINT'O"
220 PRINT":€NTER GflS SENS HEflT MJ/HR"
230 INPUT GS
232 PRINT":CNTER HEflT LOSS CONDENSER MJ/HR"
234 INPUT QC
240 PRINT"JENTER CHflR ENERGV MJ/KG"
250 INPUT Cl
260 PRINT"CENTER CHAR RflTE KG/HR"
270 INPUT C2
2S0 PRINT":€NTER COND RATE KG/HR"
281 INPUT C3
282 REM COND ENERGY « 4.75 MJ/KG
2S3 PRINTS"
290 PRINT"ENTER FUEL DRV ULTIMflTE flNflLVSIS":PRINT""
300 PRINT TENTER «C"
310 IUF'UT CR
C-2
-------
11 rCHTER KH11"
348 INPUT HR
360 PRINT" :€NTER KN"
370 INPUT NR
374 PRINT":€NTER KS"
376 INPUT SR
390 PRINT":€NTER KO"
400 INPUT OX
450 PRINT" :€NTER ^RESIDUE"
460 INPUT RR
470 PRINT"3"
471 OPEN 3,4
472 CMD 3
486 fi*=" '"
490 PRINT ft* ?"? '
510 PRINT CHR*U>" ENERGY BflLfiNCE RUN #";RU
530 PRINT K*
556 PRINT"RUN #";RU
560 PRINT-WET FUEL RflTE ";WF;"KG/HR"
570 PRINT-FUEL MOISTURE ";MC;"«"
560 PRINT"DRV FUEL ENERGY ";FE;"MJ/KG"
581 PRINT"fiIR FLOW IN";Oft;"M3/MIN"
530 PRINT"WET OftS FLOW RfiTE ";GF;"M3/MIN"
600 PRINT"LHV DRV GfiS <0 DEC C/30 IN HG>";GE;"MJ/M3"
601 PRINT"GfiS MOISTURE CONTENT" JGM; "?i"
610 PRINT'-CHflR RflTE";C2;"KG/HR"
611 PRINT"CHflft ENEROV";Cl;"MJ/KG"
620 PRINT-'COND RflTE";C3; "KG/HR"
630 PRINT'TOND ENERGV = 4.75 MJ/KG"
640 PRINT fl*
650 CF<=CR*10e/a0G-RR>:REM XC RESIDUE FREE EflSIS
660 HF«HR*100/<100-RR>:REM XH RESIDUE FREE BfiSIS
670 HF=NR*10Q/(100-RR>:REM ^^N RESIDUE FREE BftSIS
6S0 01=OX*100/<100-RR):REM %Q RESIDUE FREE BfiSIS
690 SF=SR*100A100-RR>:REM «S RESIDUE FREE BfiSIS
700 DEF FNRsINT(X*100+.5)/100:REM ROUND OFF FUNCTION TO 0.01
710 PRINT"FUEL RMflLVSES"
720 PRINT" ","DRV ULT","DRV ULT","STOICH"
730 PRINT" "i" "/"RES FREE","CONST"
740 CS»CF/12:REM STOICHIOMETRJC CONST C (RESIDUE FREE EflSIS)
750 HS=HF=REM STOICHIONETRIC CONST H (RESIDUE FREE ERSI3)
766 03=01/16=REM STOICHIOMETRIC CONST 0 (RESIDUE FREE BfiSIS)
770 PRINT"JiC", CR ,FNR,FNR(CS>
7S0 PRINT"/:H", HR ,FNRFNR
810 PRINT"«S% SR ,FNR
820 PRINT'T.'RES", RR
830 PRINT fi*
840 EO«WF*«ie0-MC)/'103>*FE:REM GROSS ENERGV DRV FUEL
842 IF HR-(OX/8X=0 THEN 854'REM TESTS H/0 RflTIO IN FUEL
S46 BM=OX+(OX/8>--REM BW-BOUND WflTER Y.> EXCESS H
850 GOTO 860
854 BW=?*HR:REM BW=BOUND WflTER ?i/H LIMITED/EXCESS 0
860 BW»BW/100:REM BW=BOUND WflTER FRRCTION
862 EL=WF*BW*«100-MC>/10Q>*2.257:REM LflTENT HEfiT IN BOUND WflTER
880 REM 8S2&890 ftSSUME LH H20 = 2.237 MJ/KG fiT 1 flTM/1D0 DEC C
890 EM=WF*MC*2.257/100:REM LflTENT HEflT IN M/C OF FUEL
900 EN»EO-EL-EM:REM NET ENERGV IN DRV FUEL
910 EC=GF*C(l00-Gf1>/l00)*GE*60:REri CHEMICflL ENERGV IN SfiTURflTED GftS
920 £1»C1*C2:REM ENERGV OUT CHfiR
930 E2=C3«4.75:REM ENERGV OUT CONDENSflTE
948 REM 930 ftSSUMES COND =4.75 MJ/KG
950 E3»EC+GS:REM ENERGV OUT HOT GflS
951 LO=EN-EC-GS-OC-E1-E2
952 REM LO»ENERGV LOSSES-CNET EN FUED-CCHEN EN GftS)--CHEflT LOSS
C-3
-------
";FNR(EL);"riJ/HR"
";FHR; "MJ/HR"
= ";FNR ; "MJ/HR
";FNR; "MJ/HR";FNR; '"/."
";FNR; "MJ/HR" ;FNR; "MJ/'HR" ;FNR; "MJ/'HR" ;FHR; "MJ/HR" ;FHR; "?.'"
";FNR(LO)J "MJ/HR" ;FNR(PL); "'/."
953 REH CONDENSER)"-*1 GO
992 PS=CGS/EN)*100
993 P1«(E1/'EH>*100
994 P2=CE2/EN>*100
995 PL<=*100
996 PG=(GC/£N>*100
1000 PRINT-NET ENERGV,DRV FUEL
1010 PRINT"CHEM ENERGV.GflS
1020 PRINT"SENS ENERGV,GfiS
1025 PRINT-'HEflTLOSS CONDENSER
1030 PRIKP'ENERGV OUT/CHflR
1040 PRINT"ENERGV OUT,CONLEHSflTE
1050 PRINT"EHERGV LOSSES
1060 PRINT fl*
1061 XX=EC+GS
1070 PRINT-'HOT GflS OUT = ";FNR; "MJXHR"
1030 PRINT "COLD GflS OUT « M;FNR; "MJ/HR"
1090 HG=; "Ji-
ll 10 CG=(EC/EN)*100
1120 PRIW'CQLD GflS EFF = "jFNRCCG); "Ji"
1130 PRINT fa
1240 fifi=<11.53*CR+34.34#/100>*(lX60>*/100>:REM GflSIFICflTIOH flIR/KG DRV FUEL
1302 PRINT"GflSIFICftTION flIR - ";FNR<«=lG>; "KG flIR/KG DRV FUEL"
1303 PRINT-GflSIFICATION flIR » M;FNR<:Gfl); "M3/MIN"
1310 PRINT-GflSIFlCflTION flIR ». ";FNR; "fi STOICH"
1320 PRINT n*
1321 PRINT#3=CLOSE 3
1330 END
REflDV.
-------
ENERGV ERL-ftNCE RUN 4*
RUN # 6
WET FUEL RflTE 27.2 KG/HR
FUEL MOISTURE 10.71 Y.
DRV FUEL ENERGY 19.06 MJ/KG
SIR FLOW IN .407 M3/MIN
WET GflS FLOW RflTE .773 M3/MIN
LHV DRV GflS (Q DEC C,30 IN HG> 6.2S MJ/M3
GflS MOISTURE CONTENT 10.51 Y.
CHflR RflTE 2.8 KG/HR
CHflR ENERGY 19.39 MJ/KG
COND RflTE .18 KG/HR
COND ENERGY -4.75 MJ/KG
FUEL fiNflLYSES
y.c -
JiH
>iO
>:H
y.s
XRES
DRY ULT
45.58
5.83
43.92
.17
0
4.5
DRY ULT
RES FREE
47.73
6.1
45.99
.18
0
STOICH
CONST
3.98
6.1
2.87
ENERGY BflLflNCE
GROSS ENERGY,DRV FUEL = 462.91 MJ/HR
LflTENT HEflT,COMB H20 = 27.08 MJ/HR
LftTENT HEflT,MOIST « 6.57 MJ/HR
NET ENERGY,DRY FUEL * 429.25 MJ/HR ' 160/i
CHEM ENERGY, GflS «= 259.32 MJ/HR 65.53 V.
SENS ENERGY, GflS - 12.83 MJ/HR 2.99 Y.
HEflT LOSS CONDENSER - 18.4 MJ/HR 4.29 JJ
ENERGY OUT^CHftR * 54.29 MJ/HR 12.65 Y.
ENERGY OUT,CONDENSftTE= .86 MJ/HR .2 X
ENERGY LOSSES » 83.05 MJ/HR 19.35 Ji
HOT GflS OUT « 272.65 MJ/HR
COLD GflS OUT « 259.82 MJ/HR
HOT GflS EFF * 63.52 K
COLD GflS EFF » 60.53 X
STOICH RIR = 5.37 KG flIR/KG DRY FUEL
STOICH RIR » 1.57 M3/MIN
GflSIFICflTION flIR « 1.39 KG flIR/KG DRY FUEL
GflSIFICflTION flIR = .41 M3/MIN
GflSIFICflTION flIR a 25.9 /.' STOICH
C-5
-------
ENERC3V BRL.RNCE RUN # S
RUN #8
WET FUEL RflTE 22.8 KG/HR
FUEL MOISTURE 5.51 %
DRV FUEL ENERGV 18.92 MJ/KG
FilR FLOW IN .412 M3/MIN
WET GflS FLOW RflTE .627 M3/MIN
LHV DRV GflS <0 DEO C.30 IN HG> 4.19 MJ/M3
GflS MOISTURE CONTENT 10.56 '/.
CHflR RflTE 2.3 KG/HR
CHflR ENERGV 8.52 MJ/KG
COND RfiTE .6 KG/HR
COND ENERGV =4.75 MJ/KG
FUEL
y.c
VM
y.o
XH
xs
XRES
ftNfiLVSES
DRV ULT
44.37
5.62
45.9
.26
.35
3.8
DRV ULT
RES FREE
46.12
5.84
47.71
.27
.05
STOICH
CONST
3. 84
5.84
2.98
— ^.^ — „_ -n-n
.ENERGV BflLflNCE
GROSS ENERGY-DRV FUEL
LflTEHT HEflT/COME H20
LflTENT HEflT,MOIST
NET ENERGV,DRV FUEL
CHEM ENERGV.GflS =
SENS ENERGV,GflS *
HEflT LOSS CONDENSER «
ENERGV OUT,CHflR »
ENERGV OUT,CONDENSflTE=
ENERGV LOSSES »
407.61 MJ/HR
24.59 MJ/HR
2.84 MJ/HR
= 3S0.18 MJ/HR 100Ji
140.98 MJ/HR 37.08 Y.
11.09 MJ/HR 2.92 '/.
15.78 MJ/HR 4.15 Y.
21.3 MJ/HR 5.6 Y.
2.85 MJ/HR .75 '/.
188. 18 MJ/HR 49.5 '/.
HOT GflS OUT *
COLD GflS OUT
HOT GflS EFF *
COLD GflS EFF
152.07 MJ/HR
140.98 MJ/HR
40 '/.
37.08 '/.
STOICH flIR » 5.08 KG ftlR/KG DRV FUEL
STOICH flIR = 1.32 M3/MIN
GflSIFICflTION flIR • 1.59 KG flIR/KG DRV FUEL
.41 M3/MIH
31.28 V. STOICH
GflSIFICflTION flIR
GflSIFICflTION flIR
C-6
-------
ENERGV BRL-FlNCE RUN 4* 11
RUN * 11
WET FUEL RflTE 17.5 KG/HR
FUEL MOISTURE 10.5 ^
DRV FUEL ENERGV 18.33 MJ/KG
flIR FLOU IN .407 M3/MIN.
WET GRS FLOW RflTE (SFTO .749 M3/MIN
LHV DRV GflS <0 DEC C,30 IN HO) 5.11 MJ/M3
GflS MOISTURE CONTENT 14.15 X
CHflR RftTE 2.5 KG/HR
CHflR ENERGV 27.6 MJ/KG
COND RflTE .5 KG/HR
COND ENERGV =4.75 MJ/KG
FUEL
XC
XH
xo
XH
X5
XRES
flNflLVSES
DRV ULT
45.24
5.81
46.81
.13
.11
1.91
DRV ULT
RES FREE
46.12
5.92
47.72
.13
.11
STOICH
CONST
3.84
5.92
2.98
ENERGV BflLflNCE
CROSS ENERGV,DRV FUEL
LflTENT HEflT,COMB H20
LflTENT HEflT,MOIST
NET ENERGV,DRV FUEL
CHEM ENERGV,GftS =
SENS ENERGV,OflS *
HEftT LOSS CONDENSER *
ENERGY OUT,CHflR .
ENERGV OUT,CONDENSflTE=
ENERGV LOSSES
= 296.49 MJ^HR
= 18.48 MJ/HR
« 4.15 MJ/HR
= 273.86 MJ/HR
197.15 MJ/HR 71.99 X
12.37 MJ/HR 4.52 X
21.16 MJ/HR 7.73 X
69 MJ/HR 25.2 X
2.38 MJ/HR .87 X
-28.13 MJ/HR-10.3 X
HOT GflS OUT «
COLD OflS OUT
HOT GflS EFF »
COLD GfiS EFF
209.52 MJ/HR
197.15 MJ/HR
76.51 X
71.99 X
STOICH flIR * 5.21 KG flIR/KG DRV FUEL
STOICH flIR - .98 M3/MIN
GfiSIFICRTION flIR = 2.16 KG flIR/KG DRV FUEL
GflSIFICflTION flIR » .41 M3/MIN
OflSIFICflTION flIR = 41.44 X STOICH
C-7
-------
ENERGV ERL.RHCE RUN **
RUN # 12
WET FUEL RflTE 16.3 KG/HR
FUEL MOISTURE 11.05 Y.
DRV FUEL ENERGV 13.49 MJ/KG
RIR FLOW IN .415 M3/MIN
UET GflS FLOW RfiTE .735 M3/MIN
LHV DRV GftS (8 DEC C,39 IN HO) 5.17 MJ/M3
GflS MOISTURE CONTENT 12.31 X
CHfiR RfiTE 1.7 KG/HR
CHfiR ENERGV 24.33 MJ/KG
CONI) RfiTE .7 KG/HR
COND ENERGV = 4.75 MJ/KG
FUEL flN*LVSE|v
RES FREE CONST
jiC 45.27 47.25 3;94
«H 5.77 6.82 5'2200
JJO 44.18 46.12 2.83
XN .42 .44
y.5 .16 .17
ENERGV BfiLRNCE
GROSS ENERGV, DRV FUEL = 268.08 MJ/HR
LflTENT HEhlT.COMB H20 = 16.26 MJ/-HR
LflTENT HEflT,MOIST » 4.07 MJ/^HR
NET ENERGV, DRV FUEL = 247.75 MJ/HR
CHEM ENERGV, GftS = 199.93 MJ/HR 80. 7 X
SENS ENERGV, GflS = 11.03 MJ/HR 4.45 Y.
HEfiT LOSS CONDENSER * 19.27 MJ/HR 7.78 X
ENERGV OUT, CHAR = 41.45 MJ/HR 16.73 '/.
ENERGV OUT,COHDENSflTE= 3.33 MJ/HR 1.34 Y.
ENERGV LOSSES • -27.25 MJ/HR-11 •%
HOT GflS OUT » 210.96 MJ/HR
COLD GflS OUT » 199.33 MJ/HR
HOT GflS EFF - 85. 15 Y.
COLD GflS EFF * 83.7 Ji
STOICH flIR * 5.31 KG flIR/KG DRV FUEL
STOICH flIR » .93 M3/MIH
GflSIFICflTION ftIR « 2.38 KG flIR/KG DRV FUEL
OflSIFICflTION flIR * .42 M3/MIN
GflSIFICfiTION flIR * 44.75 Y. STOICH
C-8
------- |