Ecological Research Series
A CASE STUDY OF THE
LOS ANGELES COUNTY
PALOS YERDES LANDFILL
GAS DEVELOPMENT PROJECT
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal spe-
cies, and materials. Problems are assessed for their long- and short-term influ-
ences. Investigations include formation, transport, and pathway studies to deter-
mine the fate of pollutants and their effects. This work provides the technical basis
for setting standards to minimize undesirable changes in living organisms in the
aquatic, terrestrial, and atmospheric environments.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/3-77-047
July 1977
A CASE STUDY OF THE
LOS ANGELES COUNTY PALOS VERDES LANDFILL
GAS DEVELOPMENT PROJECT
by
Frank R. Bowerman
Naresh K. Rohatgi
Kenneth Y. Chen
and
R. A. Lockwood
COM Inc. Environmental Engineers
Pasadena, California 91101
Contract No. 68-03-2143
Project Officer
Charles J. Rogers
Solid and Hazaradous Waste Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publica-
tion. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
n
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FOREWORD
The Environmental Protection Agency was created because of increasing
public and government concern about the dangers of pollution to the health
and welfare of the American people. Noxious air, foul water, and spoiled
land are tragic testimony to the deterioration of our natural environment.
The complexity of that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem solu-
tion 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, treat-
ment, 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 publica-
tion is one of the products of that research; a most vital communications
link between the researcher and the user community.
This report documents the first-ever-attempt to capture sanitary land-
fill gases and beneficiate them to natural gas pipeline quality—or very
nearly so.
Francis T. Mayo, Director
Municipal Environmental Research
Laboratory
m
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ABSTRACT
Life teaches many lessons, some through success and some through
a failure to succeed. This report documents the first-ever-attempt to
capture sanitary landfill gases and beneficiate them to natural gas pipe-
line quality - or very nearly so. For this reason the authors must credit
the entrepreneurs for a successful first full-scale demonstration of a
technology that produces very nearly pure methane and wish to compliment
the Los Angeles County Sanitation Districts for the willingness, coopera-
tion, and technical assistance that made the demonstration possible. Herein
lies an excellent example of local government and industry working together
to produce results that may have ultimate benefits for people throughout
the nation and the world.
That this demonstration failed to show an economic viability
during the twelve-month study period only suggests to the authors that
further consideration should be given to improving the dependability of the
molecular sieve process for landfill gas beneficiation, to the study of
alternative beneficiation processes, and/or alternative uses for less
modified landfill gases. Experiences since the completion of the data
collecting period, July 1976, indicates that the process has worked with
but little interruption for as much as 90 days. This is encouraging, but
the economics are still not favorable for molecular sieve beneficiation,
in the opinion of the authors.
Perhaps more serious consideration should be given to the use of
landfill gas with little or no modification, except perhaps moisture removal.
Reciprocating piston engines, rotary turbines, steam generators, air heaters,
and a host of other devices can be fueled successfully with mixtures of
methane, carbon dioxide, and small amounts of other gases, provided the heat
content is not below certain critical levels. Such uses date back to the
constantly-heated coffee pot warmed by the flame from a pipe stuck into the
landfill by the operators. Much more sophisticated, but economically viable
uses can be hypothesized; the authors are convinced that some of them will
prove to be practical and economical in use. Landfill gases present an
energy resource - modest as it is - that should be developed and utilized
wherever and whenever possible.
This report was submitted in fulfillment of Contract No. 68-
03-2143 by COM Inc. Environmental Engineers under the sponsorship of the
U.S. Environmental Protection Agency. This report covers the period October
1974 to July 1976.
IV
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TABLE OF CONTENTS
TITLE PAGE NO.
ABSTRACT iv
LIST OF FIGURES vii
LIST OF TABLES ix
CHAPTER I INTRODUCTION 1
A. History of Palos Verdes Landfill Gas Migration
and Recovery 1
B. Energy Shortage 4
C. Possible Significance of Sanitary Landfill Gas 5
D. Project Objectives 10
CHAPTER II LANDFILL EVALUATION FOR METHANE RECOVERY n
A. Refuse Characterization 11
B. Solid Waste Processing 12
C. Fill Characterization 12
D. Potential Total Gas Production 12
E. Kinetics of Gas Generation 15
F. Gas Recoverability 23
G. Evaluation of Operating Parameters for Landfill
Gas Extraction 23
CHAPTER III EVALUATION OF PHYSICAL PARAMETERS AT
PALOS VERDES LANDFILL 29
A. Refuse Types 34
B. Mode of Operation 34
C. Fill Characterization 37
D. Climatic Conditions 40
E. Geology 45
CHAPTER IV EVALUATION OF OPERATING CONDITIONS FOR 47
GAS WITHDRAWAL
A. Gas Composition 47
B. The Effects of Withdrawal Rates on Gas Composition 52
C. Effects of Gas Withdrawal Rates on Well Pressure
and Gas Pressure in Surrounding Fill Regions 52
D. Radius of Influence at a Selected Withdrawal Rate 55
.E. Total Energy Production 58
F. Permeability of Refuse Deposit 58
G. Theoretical Correlation of Operating Parameters for
Landfill Gas Extraction 60
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CONTENTS (continued)
TITLE PAGE NO.
CHAPTER V SELECTION OF TECHNIQUES FOR GAS
BENEFICIATION 65
A. Gas Purification Techniques 65
B. Design of an Adsorption Column for Sanitary
Landfill Gas Purification 71
CHAPTER VI RSF'S COMMERCIAL EXPERIENCE IN PALOS
VERGES LANDFILL GAS EXTRACTION AND
PURIFICATION 78
A. Landfill Gas Extraction 78
B. Gas Purification 78
C. Methane Gas Production and Consumption 85
D. Economic Evaluation 88
CHAPTER VII FIRE HAZARD AND SAFETY 89
CHAPTER VIII CONCLUSIONS 92
CHAPTER IX REFERENCES 94
CHAPTER X BIBLIOGRAPHY 97
APPENDIX
Theoretical Correlation of Operating Parameters
for Landfill Gas Extraction 101
vi
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LIST OF FIGURES
NUMBER PAGE NO.
1 Regional Map of Palos Verdes Sanitary
Landfill 2
2 Site Location Map 3
3 Future Total U.S. Energy Demand 6
4 Future Natural Gas Supplies and
Requirements 7
5 Existing Landfills in Los Angeles County 8
6 Sample Preparation Scheme for "As Received"
Solid Waste Characterization 13
7 Sample Preparation Scheme for Fill
Characterization 14
8 Plots of Theoretical Two-State Gas
Generation from Different Categories of
Solid Waste 18
9 Plots of Theoretical Cummulative Gas
Generation 19
10 Plots of Theoretical Rates of Landfill Gas
Generation 20
11 Ideal Landfill Gas Recovery System 24
12 Extraction and Monitoring Well Locations at
a Selected Portion of the Landfill 26
13 Landfill Methane Emissions Rate 31
14 Topographic Map of Palos Verdes Landfill,
June 20, 1957 32
15 Topographic Map of Palos Verdes Landfill, 33
16 Precipitation by Month, Long Beach,
California 41
17 Temperature by Month, Long Beach, California 42
18 Particle Size Distribution of
Diatomaceous Cover Soil ^6
vii
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NUMBER
FIGURES (continued)
PAGE NO.
19 Gas Well Locations at Palos Verdes
Landfill 48
20 Palos Verdes Landfill Gas Collection
System - Well and Telescoping Pipe 4g
Configuration
21 The Effects of Withdrawal Rates on Gas
Composition and Heating Values 53
22 Influence Area Study - Monitoring Well
Locations at Palos Verdes Landfill 54
23 Effects of Gas Withdrawal Rates on Well
Pressure 56
24 Monitoring Wells - Pressure Variation
Versus Time 57
25 Energy Production from a Well 59
26 Theoretical Correlation of Operating
Parameters for Landfill Gas Extraction 64
27 Ethanolamine Absorption Process for C0?
and H2S Removal 67
28 Phase Diagram for C02 - CH4 System 69
29 Liquefaction of Carbon Dioxide from
Landfill Gases 70
30 A Closed Cycle Molecular Sieve Adsorption
Process 72
31 Isotherms for Water Adsorption 73
32 Isotherms for Carbon-Dioxide and Hydrogen
Sulfide Adsorption 74
33 Determination of Mass-Transfer Fronts by
Dynamic Adsorption Test 7°
34 Schematic Diagram of Palos Verdes Landfill
Gas Purification Process '"
35 Palos Verdes Landfill - Commulative Methane
Production and Consumption 86
36 Ignition Temperature of Methane-Air Mixture ^0
viii
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LIST OF TABLES
NUMBER PAGE NO.
1 Existing Landfills - Los Angeles County as
of June, 1973 9
2 Average Refuse Composition - Hempstead, New
York 16
3 Mathematical Formulation of Landfill Gas
Generation 22
4 Schedule for Operating Parameters Evaluation 27
5 Refuse Survey - Types and Quantities of
Refuse Received 35
6 Percentage Moisture Content in Refuse
Deposits 36
7 Percentage Total Organic Carbon Content in
Refuse Deposits 38
8 Percentage Total Volatile Solids Content in
Refuse Deposits 39
9 Percentage Total Phosphorus Content in Refuse
Deposits 43
10 Percentage Kjeldhal Nitrogen Content (as N2)
in Refuse Deposits 44
11 Gas Analysis - Palos Verdes Sanitary Landfill 50
12 Gas Analysis - Palos Verdes Sanitary Landfill 51
13 Palos Verdes Landfill Gas Extraction and
Purification Operation 80
14 Composition and Flow Rates of Raw Gas Obtained
from Extraction Wells Located at Palos Verdes
Landfill 81
15 Sales and Combustion Gas Stream 87
16 Theoretical Correlation of Operating
Parameters for Landfill Gas Extraction 101
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CHAPTER I
INTRODUCTION
A. History of Palos Verdes Landfill Gas Migration and Recovery
The landfill site lies in coastal hills within the corporate limits
of the city of Rolling Hills Estates, Los Angeles County. A private company
mined diatomaceous earth from the site until about 1950. The Sanitation
Districts of Los Angeles County acquired the site in 1956 and since May 15,
1957, have operated a 289 acre sanitary landfill there. To date, the
Districts have deposited close to 15 million tons of solid wastes and liquid
industrial wastes within the Palos Verdes sanitary landfill.
The initial permit, for Class II (essentially household refuse)
landfill operation, was issued to the County Sanitation Districts on April 17,
1957. Filling proceeded at a rate of about 20,000 cubic yards per month until
one portion was completed in 1966 when the total weight of material deposited
was 4.1 million tons. At present this site is developed as the South Coast
Botanical Garden (Section A in Figure 2), a very attractive arboretum.
The present operating landfill lies between the section completed
in 1966 and Hawthorne Boulevard (Figures 1,2). As a result of favorable
geohydrological conditions at the current site, the Los Angeles Regional Water
Quality Control Board (LARWQCB) has adopted resolutions for waste discharge
requirements permitting the Districts,to operate this sanitary landfill as a
Class I (virtually unrestricted) disposal site. An average of 4810 tons per
day or 1.46 x 106 tons per year household, commercial, industrial, and liquid
wastes, including hazardous and toxic wastes, are now being deposited. The
presence of a large organic fraction and added moisture in the waste makes the
Palos Verdes landfill ideal for methane gas generation by anaerobic decomposi-
tion.
The Palos Verdes landfill has been the scene for recent experimen-
tation with both a gas migration control system and a gas recovery system.
A few years after the start of landfill operations it was determined that
refuse-generated gas had migrated across a public street which had been
constructed over a portion of the uncompleted mine tailings outside of the
site's boundary. The problem was remedied by the construction of a gravel-
filled cut-off trench to provide venting for the migrating gases.
Another problem arose in 1971 when a strong odor indicated that
gas had begun seeping through a crack in the concrete floor of a Sunday
School Church auditorium located about 150 feet outside of the landfill
property line. The District's gas survey and monitoring program indicated
that landfill gases were seeping through another area of loosely compacted
mine tailings to a maximum distance of 250 feet from the fill (Ref. 1).
This problem was solved by constructing a gas-collecting, well-withdrawal
system along the property line. Eighteen wells were constructed varying
in depth from 25-45 feet. The wells were connected by a collection pipeline
which terminates in a suction blower and gas burner station. This system
has operated successfully for over three years.
1
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i i
PALOS VERDES
SANITARY
ANDFILL
PACIFIC OCEAN
'IGURE I: REGIONAL MAP OF PALOS VERDES
SANITARY LANDFILL
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Q_
<
O
3
LU
(O
cvi
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a:
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As a result of the energy shortage and increasing prices for
natural gas, the Districts have instituted a Research Program aimed at
recovering gases for useful purposes. In early 1972, a 30-inch diameter
experimental gas well (which has since been backfilled) was dug in the
refuse to an approximate depth of 110 feet. A steel pipe was used for the
well casing with the bottom 80 feet perforated. This well became operative
on December 8, 1972. Several parameters were evaluated to design a landfill
gas collection system. Initial testing of the system was performed by with-
drawing approximately 300 SCFM of the refuse-generated gases using a one horse-
power centrifugal vacuum blower. Gas composition during this period was
approximately 53 percent methane and 45 percent carbon dioxide with a heating
value of 535 Btu/scf.
The Southern California Gas Company, a subsidiary of Pacific
Lighting Service Company, indicated a definite interest in the gas if it
could be economically purified to meet pipeline standards of 1000 Btu per
standard cubic feet. During this time, the Districts contacted the Reserve
Synthetic Fuels, Inc. (RSF), previously known as NRG Technology, Inc.,
Newport Beach, California to discuss possible acquisition of the gas rights.
RSF has developed a process for carbon dioxide removal by an adsorption pro-
cess based on the molecular sieve.
The inability of the Sanitation Districts to guarantee the volume
of gas production for a long term basis led to the current contract made with
RSF, dated October 31, 1973. The contract requires the Districts to drill a
sufficient number of wells so as to provide 1000 SCFM of unprocessed gas to
RSF. Under the terms of the contract, RSF shall at no cost to the Districts
design and construct all necessary facilities to receive and purify the well-
head gas. The initial program is designed for research and development. If
at any point in the program the process proves infeasible, RSF has the right
to cancel upon a 30-day notice. The research and development program was
set for a 12-month period; afterwards, if the process proves feasible, both
parties have agreed to negotiate in good faith for an expanded operation.
Should the experiment prove feasible for production of commercial quantities
of acceptably high Btu gas, the Southern California Gas Company has indicated
it will buy the gas from RSF and feed it into existing nearby pipelines serving
peninsula residents. If the negotiations fail to produce an expanded program,
the Districts have agreed to permit RSF to continue the 1000 SCFM withdrawal
system for an additional four year period in order to recover part of their
initial research investment. During this extended four year period, the
Districts would share in the royalties received from the sale of the gas,
based on 12-1/2 percent of the gross income.
B. Energy Shortage
Total energy consumption in the United States rose from 45
quadrillion (1015) Btu in 1960 to over 60* quadrillion Btu in 1970 and it
*During 1970, the total energy consumption in the United States was
approximately 67.5 quadrillion (IQl5) Btu (Ref. 5).
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was predicted in 1970 that usage would top the 90 quadrillion Btu mark in
1980. By the year 2000, the energy demand was predicted to reach 200 quadril-
lion Btu, Figure 3 (Ref. 2). The natural gas share of the total energy
market in the U.S. reached 31 percent in 1968, up from 14 percent in 1947
(Ref. 3). This total energy demand will exhaust the available natural gas
resources in the foreseeable future. Therefore, efforts should be made to
conserve energy and develop other sources of gas.
Gains in production of natural gas between 1947 and 1968 averaged
more than 6 percent a year or from 5.6 to 19.3 trillion (10'2) cubic feet.
During the same period, reserves increased an average of 2.5 percent annually
or from 165 to 282 trillion cubic feet. The reserves-to-production ratio
has declined from 29.5 to 14.6 years. By the end of 1969 the reserves were
down to 275.1 trillion cubic feet while production rose seven percent to
20.7 trillion cubic feet (Ref. 4). It is estimated that production of gas in
48 contiguous states will be limited to about 27 trillion cubic feet a year
from 1974 to 1990. With gas from Alaska, U.S. production could reach more
than 35 trillion cubic feet a year by 1990 and hold at this level for nearly
10 more years (Figure 4) before resource depletion would seriously affect
production rates of natural gas.
C. Possible Significance of Sanitary Landfill Gas Recovery
The 77 incorporated cities, together with the unincorporated
portions of Los Angeles County, have a combined population of approximately
7 million people (at the time of the 1970 census). An average of 30,000
tons of refuse are generated each day and disposed of entirely by landfill
methods (Table 1). These landfills are operated by county sanitation dis-
tricts and by municipal and private authorities (Figure 5).
It is probable that sanitary landfill gas can be collected and used
as an energy source by installing a properly engineered gas control and
processing system. Each year 10,119,000 tons of refuse are deposited in
the Districts' landfills. It is calculated that a sustained yield of 5.12
x 109 cubic feet per year of recoverable gases are produced, based on
generation capacity of 0.23 cubic feet of gas per year for each pound of refuse
[Ref. 6,7). Since the gas is approximately 50 percent methane, the total
generation capacity for methane is approximately 2.5 x 10" cubic feet per
year or 2.5 x 10^2 Btu per year. Using a value of $1.00 per million Btu,
this amount of energy has a gross value of $2.5 x 10^ per year.
The total natural gas consumption in the Los Angeles County area
is approximately 0.5 x lO^2 cubic feet per year (Ref. 8). Despite the fact that
the energy derived from landfill gas is considerable, the amount is only
approximately 0.5 percent of the total natural gas consumption in the
Los Angeles County area; this energy derived from solid waste is not a very
significant amount to the energy industry. On the other hand, it is a great
opportunity for landfill operators to convert a definite liability into a
financial asset.
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200-1
150-
o:
s
S
fi
O
100-
50-
RESIDENTIAL/COMMERCIAL
INDUSTRIAL
TRANSPORTATION
EXCLUDING ELECTRICAL
CONSUMPTION
REJECT
HEAT
ELECTRICAL
ENERGY
PRODUCED
I960
1970
I960
YEAR
1990 2000
ELECTRICAL
GENERATION
FIGURE 3: FUTURE TOTAL U.S. ENERGY DEMAND (Ref. 2)
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50-
W)
K-
UJ
m 40-
o
ffi
o
o
30-
20-
PRODUCTION IN CONTIGUOUS 48 STATES
PRODUCTION IN 48 STATES PLUS ALASKA
REQUIREMENTS
1968
1972
1976
I
1980
YEAR
1984
1988
1992
FIGURE 4: FUTURE NATURAL GAS SUPPLIES AND REQUIREMENTS (Ref. 3)
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.
SANTA MON'CA FRWY. /, 0
._LJV. COUNTY...
'"ORA'NGE COUNTY
PRIVATE
MUNICIPAL
C.S.D.
, .
FIGURE 5: EXISTING LANDFILLS IN LOS ANGELES COUNTY
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TABLE 1
EXISTING LANDFILLS
LOS ANGELES COUNTY AS OF JUNE, 1973 (Ref. 9)
NO. SITE
1 Palos Verdes Landfill
2 Sparda Landfill
3 Mission Canyon Landfill
4 Scholl Canyon Landfill
5 Calabasas Landfill -
6 Puente Hills Landfill
7 Sheldon-Arleta Pit
8 Toyon Canyon Landfill
9 Burbank City Landfill
10 City of Whittier Landfill
11 North Valley Refuse Center
12 Bradley Avenue Dump
13 Hewitt Pit
14 Penrose Pit (Replaced
Tuxford Pit, Tujunga Pit)
15 Azusa Rock & Sand
16 Owl Park
17 B.K.K. Co.
18 Operating Industries
19 ASCON
Total***
TONS/DAY
SOLID LIQUID
WASTE WASTE
4096 617
639 29
4381
1452
984 90
4281 74
2613**
2299**
252
352
900
1152
1300
971
1139
200
1081 719
2361 339
961 139
TOTAL*
TONS/YR
1 ,461 ,000
207,000
1 ,358,000
450,000
333,000
1,350,000
682,000
600,000
78,000
109,000
279,000
357,000
403,000
301 ,000
353,000
62,000
558,000
837,000
341 ,000
PREDICTED
YEAR OF
COMPLETION
1978
1998
2002
2015
2080
2090
1974
1976
2001
1983
2008
1975
1977
1979
1994
1979
2176
1975
1975
10,119,000
* Based on 310 operating days per year (6-day week)
** Based on 261 operating days per year (5-day week)
*** Does not include 131,000 tons per year of solid waste
disposed of in minor sites in Los Angeles County
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D. Project Objectives
Various types of field investigations are required to evaluate the
operation of a landfill gas extraction system and determine the potential
quality of gas which can be used as a new energy source. In this project,
the Palos Verdes landfill gas recovery and purification system is evaluated
with emphasis on the following objectives (presented in this report as
separate chapters):
1. Develop a landfill evaluation system based on landfill physical and
operating parameters that are significant in gas generation and
recovery.
2. Evaluate the physical parameters important in Palos Verdes landfill
gas generation and recovery.
3. Evaluate the operating conditions for gas withdrawal such as, drilling
of wells, collection system, withdrawal rate, amount of vacuum required
to produce gas at a given withdrawal rate, gas composition, radius of
influence (spherical, to determine the number of wells required at a
particular landfill site), and total energy production capacity. The
discussion will be totally based on the Los Angeles County Sanitation
Districts' experimental findings.
4. Evaluate the basis for selection of techniques for gas beneficiation.
General techniques for gas beneficiation will be discussed. The
criteria for the design of the adsorption system will also be discussed.
5. RSF's commercial experience in landfill gas extraction and purification
to boost the heating value to pipeline standards (1000 Btu/scf). The
discussion is limited by the information provided by RSF, Inc., Newport
Beach, California.
6. General discussion on the safety precautions required against fire and
explosion in operating a landfill gas recovery and purification system.
A discussion on cost analysis for a gas recovery and purification
system is not included in this report because of the unavailability of critical
information which concerned organizations thought to be proprietary. Readers
interested in this topic may find a paper prepared by Pacific Gas and Electric
Company (Ref. 10) of real value.
10
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CHAPTER II
LANDFILL EVALUATION SYSTEM FOR METHANE RECOVERY
Sanitary landfilling is the most popular method utilized for
disposal of both inorganic and organic solid waste. The organic waste dis-
posed of in this manner undergoes decomposition. Initially, as decomposition
proceeds, the organic matter is utilized in the metabolism of aerobic micro-
organism. Carbon dioxide and water are formed through consumption of the
oxygen trapped in the fill. After the atmospheric oxygen is used up, anerobic
decomposition of the waste results from fermatative reactions that produce
methane and carbon dioxide. The amount and composition of these gases of
decomposition depends upon the physical conditions existing in the landfill.
The recovery of methane for useful purposes requires development of
a landfill evaluation system. The purpose of this system is to evaluate the
following:
1. Gas generation, both total and time-dependent.
2. The percentage of the total gas generated that is actually recoverable.
3. Operating parameters for a gas recovery system to extract a high per-
centage of methane from a landfill without reducing the overall pro-
duction rate.
4. The variation in gas compositions and production rate.
5. The actual life of a well, operating under forced withdrawal conditions.
It is the purpose of this chapter to establish and discuss parameters
important in a landfill evaluation system for methane gas recovery. A proce-
dure is developed that can be followed to evaluate the potential recovery of
landfill methane gas.
A. Refuse Characterization
The total gas generation depends on the types and amount of waste
deposited in the fill. An estimate of methane gas production requires the
characterization of waste in terms of total organic carbon and volatile solids.
The presence of a high proportion of organic carbon and volatile solids in the
waste increases the volume of gas generation. The bacteria responsible for
organic waste decomposition also requires a certain amount of nitrogen and
phosphorous to obtain growth and methane production.
The solid waste composition is not only hetrogeneous, but also varies
with regard to seasonal and climatic changes. The precise and accurate
characterization of waste in terms of the above parameters requires a proper
selection of sampling and sample preparation procedure. Klee and Carruth
(Ref. 11) have developed a statistical method that may represent the weight
and composition of waste with a minimum degree of variance. Their technique
is based on the concept of random sampling.
11
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Figure 6 illustrates a sample preparation procedure that may be
used for refuse characterization. Three different groups* of samples are
collected from a truck load of solid waste. The desired weight of samples
are obtained from different waste pile locations. Initially, samples are
dried at 700 C. The selection of a low temperature is to prevent possible
loss of volatile organics. Each group of samples is separately ground and
pulverized until all of the particles can be passed through a No. 60 sieve.
It is assumed that after this process all samples are homogeneous. Each
group of samples are further subdivided into three groups and analyzed for
different parameters.
B. Solid Waste Processing
It is a general landfill practice to deposit wastes in whatever
condition they are collected. These wastes may consist of a variety of
materials ranging from organic waste residues to a wrecked car or dead
animals. In the interest of recovering methane gas from a landfill, it may
prove cost-effective to remove metalic, refractory organic (plastic, tires,
etc.), and inorganic wastes before filling.
In order to enhance the rate of gas generation and possibly the
in-place density, it may prove cost-effective to grind the solid waste before
filling. The rate of waste decomposition is a function of the surface area
of the particles; a large surface area will most likely increase the rate of
gas generation.
C. Fill Characterization
The fill characterization is performed to generate information such
as the degree of waste decomposition, moisture content, and level of nitrogen
and phosphorous present to support bacterial growth. The samples are collected
at various fill depths during well drilling. Fill characterization is determined
by analysis of sample taken according to the sample preparation scheme described
in Figure 7.
D. Potential Total Gas Production
An estimation of potential total methane gas production may be made
from the characterization of waste in terms of volatile solids content. How-
ever, a theoretical estimate may be made from the total organic carbon content
in the solid waste. A small portion of the total organic carbon will be
*The number of samples selected here is arbitrary. According to Klee (Ref. 11)
this parameter should be estimated based on the standard deviation of a system.
His findings on solid wastes indicated that sixteen number of samples of 200
pounds each will provide reliable results.
12
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GROUP I
*
DRYING AT 70°C
GRIND AND PULVER-
IZE UNTIL ALL
PARTICLES PASS
THROUGH A NO. 60
SIEVE.
I I I
ORGANIC CARBON
VOLATILE SOLIDS
NITROGEN
PHOSPHORUS
TRUCK LOAD OF
SOLID WASTE
RANDOM SAMPLING
GROUP H
DRYING AT 70°C
GRIND AND PULVER-
IZE UNTIL ALL
PARTICLES PASS
THROUGH A NO. 60
SIEVE.
ORGANIC CARBON
VOLATILE SOLIDS
NITROGEN
PHOSPHORUS
GROUP IE
DRYING AT 70°C
GRIND AND PULVER-
IZE UNTIL ALL
PARTICLES PASS
THROUGH A NO. 60
SIEVE.
I
ORGANIC CARBON
VOLATILE SOLIDS
NITROGEN
PHOSPHORUS
FIGURE 6»SAMPLE PREPARATION SCHEME FOR
"AS RECEIVED" SOLID WASTE CHARACTERIZATION
-------
FILL SAMPLE
MOISTURE CONTENT
GROUP I
ORGANIC CARBON
VOLATILE SOLIDS
NITROGEN
PHOSPHORUS
DRYING AT 70°C
GRIND AND PULVE-
RIZE UNTIL ALL
PARTICLES PASS
THROUGH A NO.
60 SIEVE.
GROUP IT
ORGANIC CARBON
VOLATILE SOLIDS
NITROGEN
PHOSPHORUS
GROUP HI
ORGANIC CARBON
VOLATILE SOLIDS
NITROGEN
PHOSPHORUS
FIGURE 7* SAMPLE PREPARATION
SCHEME FOR FILL CHARACTERIZATION
14
-------
used for bacterial cell formation, but most will be converted into methane
and carbon dioxide. The balance between the two depends upon the environ-
mental conditions. Under landfill conditions this parameter has yet to be
determined; therefore, the loss of carbon to bacterial cell formation will
not be included in the following calculations. Table 2 illustrates the
typical organic carbon, nitrogen, and hydrogen content in different solid
waste categories (Ref. 12). That reference determined that each pound of
particular sample of dry refuse contained approximately 0.25 pounds of
organic carbon.
Theoretically one mole of organic carbon will produce one mole of
methane and carbon dioxide mixture. Therefore, gas generation by decomposi-
tion of one pound of organic carbon will be as follows:
= nRT/P = (1.31) (298) _ 32.5 Cubic feet of CH4 and C02
1 mole x 12 Pound " 12~ Pound of Carbon
mole
where,
n = Moles of methane and carbon dioxide mixture
R = Gas constant
T = Absolute temperature, °K
p = Pressure, Atm.
or, (0.25) (32.5) = 8.1 Cubic feet of CH4 and C02
Pound of Dry Refuse
The gas production is time-dependent. The rate of gas generation
depends on refuse characteristics; the decomposition of refractory organic
carbon compounds will be extremely slow and decomposition might take 100
years or more. Therefore, actual gas production rates should be estimated
based on the kinetics of gas generation.
E. Kinetics of Gas Generation
The rate of gas generation is a dynamic process responding to various
physical parameters such as the concentration of oxygen present, moisture con-
tact of the fill, temperature, and surrounding pH. The landfill gas production
life may range from a few years to hundreds of years, depending upon these
environmental conditions and the characteristics of the fill material.
15
-------
TABLE 2
AVERAGE REFUSE COMPOSITION - HEMPSTEAD, NEW YORK
Cateoorv
***** j^ * J _
Cardboard
Newspaper
Misc. Paper
Plastic
Garbage
Grass
Textiles
Wood
Mineral
Metallic
% by Weight
(wet)
y t • v v /
5.33
13.81
24.16
2.83
11.13
17.94
3.2
3.24
9.73
8.63
100
Amount of
dry weight
0.8316
0.765
0.7365
0.8512
0.3644
0.6206
0.7621
0.8558
0.9704
0.934
% by Weight
(dry)
4.43
10.56
17.79
2.41
4.06
11.13
2.44
2.77
9.44
8.06
73.09
% Carbon
(dry basis)
2.02
5.11
7.83
1.62
1.69
4.03
1.13
1.34
0
0
24.77
% Nitrogen
(dry basis)
0.0071
0.015
0.076
0.029
0.11
0.23
0.053
0.008
0
0
0.528
% Hydrogen
(dry basis)
0.324
0.85
1.485
0.275
0.64
0.852
0.205
0.193
0
0
4.82
Source: "Municipal Refuse Disposal" American Public Works Association (Ref. 12)
-------
The actual kinetics of landfill gas generation is as yet unknown.
A theoretical concept may be developed, based on the assumption that a typical
solid waste falls in three categories such as readily decomposable (food, grass
etc.). moderately decomposable (paper, wood, textile etc.), and refractory
materials (plastic, rubber etc.). The metallic and mineral wastes do not
enter into the gas generation. With an assumption that half-lives, the time
required to produce 50 percent of the total estimated gas for categories such
as readily decomposable, moderately decomposable, and refractory materials are
1, 2, and 20 years respectively, by the end of 3-1/2, 6, and 60 years, 99 per-
cent of the total estimated gas will be produced.
Mathematical formulation is based on an assumed concept of two-stage
gas generation (Ref. 13). It is represented by a discontinuous unimolecular
reaction (first order) defined as constant rate of increase followed by a
discontinuous equation of constant rate of decrease. The first stage is
characterized by the following equation:
= KiG, or InG = K-|t + InC] (1)
and second stage by:
=-K2Gt, or lnGt = -K2t + lnC2, (2)
where,
G = Amount of gas produced in time t
Gt = Amount of gas remaining to be produced after decomposition
has proceeded for time t
L = Total amount of gas to be produced
KI & K2 = Gas generation rate constants
CT & C2 - Constants of integration
At the point of inflection (t = tt) when half of the total estimated
gas production has been reached (G = Gt = 1/2), the equation number 1 and 2 are
reduced to form:
In = K]tt + InCi (la)
In ir =-K2tt + lnC2 (2a)
17
-------
4.
2-
00
Ul
a
at
o
3
a
o
cc
a.
o
UJ -2-
5
0-
-6-
ASSUMED TOTAL GAS PRODUCTION: 3 CU. FT. OF GAS PER POUND OF REFUSE
BASIS'100 POUNDS OF DRY REFUSE
MODERATELY DECOMPOSABLE
READILY
DECOMPOSABLE
26
26
Z 4 6 8 10 12 14 16 18 20 22 24
TIME ELAPSED AFTER FILL COMPLETION-YEARS
FIGURE 8'PLOTS OF THEORETICAL TWO-STAGE GAS GENERATION
FROM DIFFERENT CATEGORIES OF SOLID WASTE
30
-------
500-
UJ
CO
ll_
LU
U.
O
400-
o
Q.
8
£300
0.
200-
o
i
100-
-6 CU.FT. PER POUND
• 3 CU. FT PER POUND
•I CU.FT. PER POUND
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
TIME ELAPSED AFTER FILL COMPLETION-YEARS
FIGURE 9: PLOTS OF THEORETICAL COMMULATIVE GAS GENERATION
-------
200-1
ro
o
> 160-
i
u.
o
£
g
e
80-
»**
g
fe
| 40-
BASIS: 100 POUNDS OF REFUSE
3 CU. FT. PER POUND
I CU.FT PER POUND
8 10 12 14 16 18 20 22
TIME ELAPSED AFTER FILL COMPLETION-YEARS
24 26 26 30
FIGURE 10: PLOTS OF THEORETICAL
RATES OF LANDFILL GAS GENERATION
-------
The combination of 1 with la and 2 with 2a provides the following
equations:
InG = Ir4 -K, (tt -t) (3)
lnGt = ln -K2 (t -tt)
A sample solid waste composition is shown in Table 3. It does not
include mineral and metallic content in the solid waste. Based on total gas
production and composition, the maximum possible gas generation by anaerobic
decomposition of each category of solid waste was estimated. First order rate
constants were calcinated based on half-lives and maximum time required to pro-
duce total estimated gas.
Equations 3 and 4 are plotted as a straight line, InG vs. t. For
purposes of illustration, the calculations are made for an assumed total gas
production of three cubic feet of gas per pound of dry refuse. As shown in
Figure 8, the gas production becomes discontinuous at the point of intersection
or at the half-life. The constants of the equation K] and InC] for both first
and second stages are given, respectively, by the slope of the line and its
intercepts on the Y-axis at t = 0.
The gas production with respect to time at selected total gas pro-
duction capacities of 1, 3, and 6 standard cubic feet of gas per pound of dry
refuse is shown in Figure 9. Within six years after the refuse placement,
approximately 95 percent of the total gas is produced. After that, gas
production capacity tails off and economical considerations will not permit
the continuation of gas recovery operation.
Figure 10 shows the rate of gas generation with respect to time,
calculated at various assumed gas production capacities. As expected, the
production will start with a small, but recognizable generation rate. The
theoretical curves indicate that approximately one percent of the total
expected gas production is generated during filling operation. After the
landfill has become completely anaerobic, methane is produced at an increased
generation rate until it reaches a maximum. Theoretical calculations indicate
that within two to three years after the fill completion, the methane genera-
tion rate reaches its peak. At this point approximately half of the total
estimated gas has been produced. The remaining gas is produced at a decreasing
generation rate.
The kinetics of gas generation is theoretically estimated and cannot
be reasonably extrapolated to all possible landfill conditions. However, a
landfill with an optimal moisture content (50-60 percent on wet weight basis
is often reported in the literature) will probably not show significant dis-
crepancies from the theoretically predicted kinetics.
21
-------
TABLE 3
MATHEMATICAL FORMULATION OF LANDFILL GAS GENERATION
(Ref. 12 for Solid Waste Composition)
Solid Solid
Waste Waste
Charact- Composition
eristic (Percentage)
Readily
Decompo- 35.4
sable
Moderately
Decompo- 61.0
sable
Refractory 3.6
Half-
Rate
P.n net ante
(Years) (Year)'1
•tt-
L max
V
|_max
tt-
[jmax
1 Kj_ = 3.9
3-1/21 K2 = 1.84
2 K, = 1.96
6~| K2 = 1.15
20 K, = 0.196
60] K2 = 0.115
InG = In^- -Kj_ (tt -t)
InG. = Ins- -1C, (t -t.)
U L C- I*
InG = 0.07 +3.9t
lnGt = 5.81 -1.84t
InG = 0.6 +1.96t
lnGt = 6.82 -1.15t
InG = 0.196t -2.21
lnGt =4.01 -0.115t
t = Half-life, time required to produce 50 percent of the total estimated gas.
« „
max
= Maximum time required to produce 99 percent of the total estimated gas.
Basis: 100 pounds of dry refuse
3 standard cubic feet of gas per pound of dry refuse (assumed).
Total Estimated Gas = 300 cubic feet.
22
-------
F. Gas Recoverabili'ty
The actual recovery of predicted methane gas production is of
particular concern in a landfill evaluation. The gas recoverability depends
on the following parameters:
1. The loss of gas prior to recovery operations.
2. The loss of gas caused by migration through the cover material and
sides.
3. The amount of gas which is not recovered as a result of poor economics in
continuing recovery operation after the production rate tails off in
later years.
The loss of landfill decomposed gases to the surrounding environment
occurs by the following two basic processes: convective flow in response to
pressure gradient; molecular diffusion, migration from high gas concentration
to low gas concentration regions (Ref. 14, 15, 16). In a landfill where the
compacted solid waste and-surrounding soil are of high permeability, the gas
migration is as a result of pressure gradient. The methane lost by this
process not only creates fire hazard problems in near-by properties, but C02
also enters groundwaters and creates a weak carbonic acid. The quantitative
determination of gas migration requires an investigation to determine perme-
abilities of cover soil and side and bottom soil.
To study potential gas generation, the landfill must be considered
as a closed system (Figure 11). An impermeable liner is theoretically used
to cover top, sides, and bottom of the fill. The gases generated inside the
fill by waste decomposition are withdrawn at the rate of their generation.
Under these circumstances the only possible loss is as a result of molecular
diffusion of gases. This loss is very small compared to the convective
migration.
G. Evaluation of Operating Parameters for Landfill Gas Extraction
The maximization of potential gas and energy production requires
the evaluation of several operating parameters. A thorough field investiga-
tion is required to determine optimal conditions for landfill gas extraction
without degrading the quality of the gas. The method utilized for gas
recovery is by pumping from extraction well. This will establish a pressure
gradient on a landfill, causing the gases produced in a region to flow into
the well. At the same time it may also create enough negative pressure to
allow atmospheric gases to flow into the fill through the cover soil. Aerobic
oxidation in the presence of atmospheric oxygen will increase the carbon
dioxide content resulting in low quality landfill gases. An effective gas
withdrawal system requires development of an evaluation system addressing
the number, size, and depth of wells that can be located at certain portions
of the landfill with maximum system efficiency. The development of such a
landfill gas extraction system requires experimental evaluation of the follow-
ing parameters:
23
-------
Connected to Header Pipe
Extraction Well
Impermeable Lining
\\\\\\\\\ \
FIGURE II:
SCHEMATIC DRAWING OF HYPOTHETICALLY IDEAL
LANDFILL GAS RECOVERY SYSTEM
24
-------
1. Selection of a "safe" withdrawal rate that can extract landfill gases
with maximum heating values.
2. Establish a differential pressure gradient to assure scavenging of the
landfill gases without interfering with the adjacent wells. This will
determine the radius of influence.
3. Optimization of energy required to operate a landfill gas withdrawal
system.
4. Determination of number of withdrawal wells that can be located at a
certain landfill configuration.
5. Total possible energy production from a gas withdrawal system.
The evaluation .of these parameters requires a thorough field
investigation. An experimental well should be constructed at a portion of
the landfill not older than one year, preferably within an age of six months
to one year. This selection is based on the assumption that a well-compacted
and covered landfill becomes completely anaerobic within six months of
completion. The bottom three-fourths of the experimental well should be
perforated. Materials of construction should be resistant to carbonic acid.
The well should be provided with a sampling device so that gases can be
extracted at various well depths. The experimental well should also be
equipped with various instruments to measure temperature, flow rate, and
absolute pressure. Around experimental well, various monitoring wells are
constructed to determine the pressure distribution at various landfill
locations (Figure 12).
Table 4 describes the schedule for operating parameter evaluation.
The described order of performance should be used to conduct the evaluation
tests. Prior to and after gas extraction, gas composition and landfill
pressure distribution are determined. This static test is performed to
determine the change caused in landfill gas quality parameters by gas
extraction (if any).
The purpose of the short-run test is to establish the initial
data on gas composition, landfill pressure distribution, and radius of
influence at various withdrawal rates and well depths. As indicated earlier,
gas composition is a function of withdrawal rate. The optimal situation
would appear to be to extract the gases at the rate of generation. Under
this circumstance not enough gradient would be developed between cover soil
and fill to allow atmospheric gases to penetrate. Experimentally, this
value may be determined by conducting a test for about 7 to 15 days at each of
several selected withdrawal rates. During this test gas composition and
heating values are determined. The maximum withdrawal rate that produces
gases with suitable constant heating value should be selected for a long-
run test. This test should also be conducted at various well depths to
minimize the total energy required to operate the gas withdrawal system.
The recovery of the greatest practical amount of gas in a landfill requires
construction of a number of extraction wells. The well spacing at a
25
-------
r300
•-200
-150'
-100'
•- 50
300'
200
150'
100
50' 2d
- 20'
EXTRACTION
WELL
FIGURE I2< EXTRACTION AND MONITORING WELLS LOCATIONS
AT A SELECTED PORTION OF THE LANDFILL
26
-------
TABLE 4
SCHEDULE FOR OPERATING PARAMETERS EVALUATION
CODE MODE OF TEST
Static
PARAMETERS
Landfill pressure profile
and gas composition prior
to initial extraction
DAYS REQUIRED
7*
Short-run
At different withdrawal
rate and well depths,
evaluate: (1) Extraction
well and monitoring wells
pressure distribution,
(2) Gas composition
Each withdrawal rate
and selected well
depth will take
approximately 7 to
15 days
C
D
Stati c
Long-run
Same parameters,as in "A"
At the selected withdrawal 150 to 180 days
rate: (1) Gas composition, (2)
Heating values, (3) Stability
of withdrawal rate
E
F
Stati c
Life of a
well
Same parameters as in "A"
Same parameters as in "D1
*The time schedule selected for operating parameter evaluation is
arbitrary. It may vary from landfill to landfill depending upon fill
depth, and chemical characteristics of waste deposited.
27
-------
particular landfill configuration is determined by obtaining the pressure
distribution data at a given withdrawal rate. The distance at which there
is no pressure effect from gas extraction (pressure gradient is approximately
zero) is called the neutral point and the distance between the well and this
point is called the radius of influence.
The long-term test is conducted by continuous extraction of gases
from a well at its production rate for a long period of time. This evaluation
test will provide information such as reliability and quality and quantity of
gas production from a well located at a particular landfill site. The
satisfactory performance of a landfill gas recovery system depends on the
following factors:
1. Minimize variations in gas composition during entire extraction period.
2. Practical life of a well operating under forced withdrawal conditions.
From the point of view of meeting a total energy requirement, as
well as designing a purification plant, it is important to have an idea about
variation in gas composition extracted from a landfill. The economic
feasibility of a gas recovery system can be determined, based on the life
of a well during which a selected desirable withdrawal rate can be sustained.
28
-------
CHAPTER III
EVALUATION OF PHYSICAL PARAMETERS AT PALOS VERDES LANDFILL
Initially, as decomposition proceeds, the organic matter is utilized
in the activity of aerobic micro-organisms. Carbon dioxide and water are
formed during the consumption of the oxygen initially trapped in the fill.
Following are the typical oxidation reactions for carbohydrates and fatty
materials (stearic acid):
CCH100,
D id D
C18H36°2
'6 0, = 6 CO, + 6
f. e.
26 °2 = 18 C02
H2°
After all atmospheric oxygen is used up, anaerobic decomposition of
the waste results from fermentative reactions that produce methane and carbon
dioxide gases. The overall anaerobic decomposition of complex organic materials
can be represented by the following two-step process:
Complex
Organic
Acid Formers
(Bacteria)
Organic
Acid
Methane Formers ^
(Bacteria)
CH4
+^
co2
In the first step, both facultative and anaerobic bacteria, known as
the "acid formers", act upon complex organic material such as fats, proteins,
cellulose, and carbohydrates and convert them to short chain organic acids.
This step is an essential prerequisite for the second step in which the forma-
tion of methane occurs.
In the -econd step, short chain organic acids are decomposed by a
strictly anaerobic group of bacteria, known as the "methane formers", and
converted to gaseous methane and carbon dioxide end products.
Under optimum operating conditions, a proper balance between the
two steps can be established to produce the maximum methane formation. The
important operating parameters are generalized below:
Strict Anaerobic Conditions The methane generating bacteria are obli-
gate anaerobes and even small amounts of free oxygen can be quite detri-
mental to them. At Palos Verdes landfill where waste deposits are up
to 125 feet deep, the existence of anaerobic conditions can be assumed.
29
-------
Temperature Two optimum temperature levels have been established
for methane formation. The mesophilic temperature ranqes from 260
to 37.5° C; thermophilic temperatures range from 50 to 55 C (Ref. 17).
Moisture Content Volume of gas production is related to the mois-
ture content of the refuse deposit. Merz (Ref. 7) has indicated the
effect of moisture content in gas production by conducting an experi-
ment containing 15 tons of refuse in a 10,000 gallon underground
storage tank. About 39.3 cubic feet of gas were produced during the
first three days after sealing. However, gas production was negligible
by the end of 60 days and continued so until about the 230th day.
Thereafter, production was resumed by addition of 450 gallons of water
to a moisture content of 69.9 percent, dry weight basis. A total of
2025 cubic feet of gas were produced during the period of 230 to 530
days after initiation.
Anaerobic decomposition can proceed quite well with a pH varying
from about 6.6 to 7.6 with an optimum range of about 7 to 7.2. At a
pH of 6.2 and lower, the acid conditions become toxic to the methane
formers. This will result in a drop in methane production, if not
death of the methanogens.
Nutrient Availability The bacteria responsible for waste decomposi-
tion require nitrogen, phosphorus, and all trace quantities of other
materials for growth. In cases where nutrients are lacking or inade-
quate in quantity they must be supplemented in the fill to obtain
growth and methane production.
The rate of gas production in landfills depends upon the type of
waste, age of landfill, and the operating parameters. General observations
in the landfills indicate that generation rates would range between 0.06 to
0.23 cubic feet per pound per year (Ref. 6). RSF (Reserve Synthetic Fuels)
also estimated the recoverable gas from any sanitary landfill as a function
of fill volume, so that the potential gas generation rate can be related to
the fill area and depth as shown in Figure 13. Under real conditions, the
generation rate starts out at its maximum value and decreases with time.
The actual kinetics of waste decomposition (or gas generation) with age of
the fill is an unknown factor. Landfills excavated 25 years after placing
have indicated that many materials, particularly cellulose, remain virtually
unchanged. Therefore, continuous production of gas at a certain flow rate
cannot easily be predicted.
The total volume of decomposition gases available under Palos Verdes
landfill conditions can be approximated by assuming that 1500 cubic feet of
gases will be produced by the decomposition of each ton of as received refuse
(Ref. 18). For example, consider parcel three in Figures 14 and 15; RSF is
using this area for gas withdrawal at Palos Verdes landfill. The landfill
surface area is approximately 1.91 x 10$ square feet or 44 acres. Fill depth
ranges from 53 to 140 feet. With the help of topographic maps prepared
June 20, 1957 and February 19, 1975, the volume of refuse deposited is
estimated to be approximately 1.6 x 108 cubic feet, with an average depth of
100 feet. Based on an average in-place refuse density of 1300 pounds per
cubic yard (determined by the Districts), a total of 7.6 x 109 pounds (3.8 x
106 tons) of solid waste will be producing gas.
30
-------
2OO
c/>
UJ
rr
*
<
UJ
5
UJ
Q
(O
O
<
EXAMPLE: A 75-ACRE LANDFILL
160 FEET DEEP WILL PRODUCE
3,750,000 CUBIC FEET OF
METHANE PER DAY
EMISSIONS
50% METHANE)
FIGURE 13= LANDFILL METHANE EMISSIONS RATE
Source: Reserve Synthetic
Fuels Inc.
-------
FIGURE 14'TOPOGRAPHIC MAP OF
PALOS VERDES LANDFILL
SCALE |">S6S'±CONTOUM MTtMVAL S*
WOTO«ll*^NT 0«TtD JUM M. rf*T
•JXIITTtP t|^ >>^| «OICT H*
*"" **
-------
1,.
FIGURE 15 = TOPOGRAPHIC MAP
OF PALOS VERDES LANDFILL
SCALE I'-SZO'i
CONTOUR INTERVAL 21
-------
A total of 4.5 x TO9 cubic feet of gases will be produced based
on the assumption that one ton of as received refuse produces 1500 cubic
feet of gases. From a withdrawal well system of 31.5 acres of surface area
and 100 feet deep, approximately 2 x 106 cubic feet per day of gases can be
extracted (Figure 6). At this production rate, flows could be sustained for
only six years. However, these calculations are estimates and may not repre-
sent the actual conditions in the landfill.
After a landfill is completed, the rate and volume of gas genera-
tion depends upon the types of waste deposited, age of landfill, mode of
operation, and climatic conditions. The amount of this potential production
which is actually recoverable depends upon the permeability of the soil
beneath the fill material, the permeability of the cover material, and the
permeability of the actual fill material. At a completed landfill site, such
as Palos Verdes, the only real control is on the permeability of cover material
Since local earth is being used as a cover material, it is important to study
both the geological characteristics of the Palos Verdes soil and its perme-
ability for methane gas movement. In this chapter, those physical parameters
pertinent to Palos Verdes landfill conditions will be discussed.
A. Refuse Types
The amounts and types of waste disposed of at Palos Verdes landfill
by the Districts are illustrated in Table 5. The data were complied by the
Districts during a month-long survey in March 1974, and show an average daily
input of 4810 tons of household and commercial waste. These categories com-
prise about 50 percent; liquid waste comprises about 19 percent of the total.
The presence of a high proportion of organic material in these types of waste
enhances the potential in the Palos Verdes landfill for methane gas generation.
B. Mode of Operation
The basic tool for placing and compacting the refuse is a crawler
tractor of about 65,000 pounds gross weight. The refuse is placed at the
bottom of the working face and compacted to the in-place density ranging
from 1000 to 1700 pounds per cubic yard. A maximum degree of compaction can
be achieved by the addition of water. This will not only help in regulating
the gas migration, but also enhances the rate of gas generation. At Palos
Verdes landfill since both liquid and solid waste are deposited, the addition
of water is not required.
The moisture content in the completed fill was analyzed at the
San Jose Creek Water Quality Laboratory of the County Sanitation Districts
of Los Angeles County. Grab samples at various depths ranging from 5 to
110 feet were collected by 30-inch bucket auger rigs. Table 6 shows the
moisture contents in well numbers 1 to 7 which RSF is operating for gas
extraction. It shows that on an average about 30 percent (wet weight basis)
of moisture is present in the fill except in the case of well number 7 which
taps a region used for dumping greater amounts of liquid waste. The distri-
bution of moisture content with respect to depth shows no clear pattern.
34
-------
TABLE 5
REFUSE SURVEY - TYPES AND
QUANTITIES OF REFUSE RECEIVED
TYPE
Household
Commercial
Solid Fill
Small Wood & Logs
Large Wood & Logs
Demolition Waste
Garden Wastes
State Park Wastes
Industrial Wastes
Bulky Items
Rubber Tires
Liquid Wastes
Agricultural Wastes
Daily Average
AMOUNT
(Tons per Day)
1198.1
1238.5
598.8
87.6
106.4
254.1
153.9
97.2
48.6
51.8
28.9
900.4
46.1
4810.4
PERCENTAGE
OF TOTAL
24.9
25.7
12.4
1.8
2.2
5.3
3.2
2.0
1.0
1.1
0.6
18.7
1.0
100.0
Period: March 4 through March 30, 1974
Source: County Sanitation Districts of Los Angeles County
35
-------
TABLE 6
PERCENTAGE MOISTURE CONTENT IN REFUSE DEPOSITS
(Wet Weight Basis)
DEPTH
(Ft.)
5**
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
TOO
105
110
WELL NUMBERS
1
31
32
-
40
-
23
-
26
-
33
-
34
-
25
-
29
-
54**
-
54**
-
45**
2
26
32
-
32
-
23
-
15
-
19
-
30
-
37
-
25
-
36
-
34
-
44**
3
54
26
-
30
-
-
-
37
-
39
-
29
-
26
-
30
-
22
-
29
-
51**
4
-
-
-
'
-
-
-
-
-
35
30
26
20
28
33
30
13
27
31
30
51**
-
5
26
28
23
38
30
28
28
37
41
22
25
33
25
23
26
22
22
36
30
22
-
-
6
20
32
34
33
34
40
39
33
30
30
29
31
31
32
38**
-
-
-
-
-
-
-
6A*
.19
19
-
29
-
23
-
14
-
37
34
-
-
34
-
62
57
-
-
44
-
-
7
25
20
45
36
31
25
25
23
34
47
36
28
29
33
37
62
64
56
50
51
65
63
9*
16
21
-
34
-
45
-
40
-
43
-
-
-
56
-
33
-
32
-
32
-
-
Source: Los Angeles County Sanitation Districts
* Analyses were conducted at the University of Southern California, Los Angeles
** Soil
36
-------
In addition to the application of water to achieve desired moisture
content, compaction and dust control, it is also necessary to cover the fill
with soil to reduce the loss of methane. At Palos Verdes landfill all final
surfaces of the fill are covered with a minimum of 3 feet of clean earth.
C. Fi 11 Character! zati on
Only two wells (Wells 6A and 9) were used for fill characterization.
These wells were more recently drilled by the Districts to increase the gas with-
drawal capacity. The samples were collected at various fill depths during
drilling operation. The analyses for total volatile solids, total organic
carbon, ammonia nitrogen, and total phosphorous were conducted at the
Environmental Engineering Laboratory of the University of Southern California,
Los Angeles, under the direction of Dr. Kenneth Y. Chen.
In order to perform statistical analyses of heterogenous refuse
deposits, each sample was divided into three groups weighing 500 grams per
subsample. Samples were dried at 70° C for 24 hours and ground to smaller
particle size by mortar. Once the moisture content of the sample was deter-
mined, the dried and ground samples were used for conducting other analyses.
The total volatile solids were determined by igniting the dried
samples in a 550° C muffle furnace for one hour. The loss in weight was
designated as volatile solids. The total organic carbon was determined by
the LECO-12 automatic carbon analyzer. Approximately 0.1 to 0.2 gram of
acid-treated, dried, ground sample was weighed into a LECO crucible. Iron
and copper catalysts were added to increase the rate of organic carbon
oxidation. The concentration was determined by comparing it with a standard
curve.
The procedures used for ammonia nitrogen (Kjeldahl method) and
total phosphorous are described in "Standard Methods for the Examination
of Water and Wastewater" (Ref. 19).
The total organic carbon in the refuse deposit does not follow any
pattern with respect to depth, Table 7. In the top 20 feet of refuse
deposits the organic carbon content is comparatively smaller. This is
probably because of two reasons: (1) The presence of natural soil used as
covering material. (2) The existence of aerobic conditions as a result of
the infiltration of atmospheric oxygen and the resulting faster oxidation
of organic carbon. The organic carbon content ranges from as high as 14.0
percent to as low as 0.4 percent on a dry weight basis. Since this fill is
approximately 4 to 5 years old, the organic portion of the fill has already
been partially decomposed, showing a relatively smaller concentration of
carbon content.
The volatile solids content range from 3.5 percent to 56 percent
on a dry weight basis (Table 8). The total volatile solids profile seems
to follow the same pattern as in the case of total organic carbon.
37
-------
TABLE 7
PERCENTAGE TOTAL ORGANIC CARBON CONTENT IN REFUSE DEPOSITS
(Dry Weight Basis)
WELL
NUMBER
6A
6A
6A
6A
6A
6A
6A
6A
6A
6A
6A
9
9
9
9
9
9
9
9
9
9
DEPTH
(FEET)
5
10
20
30
40
50
55
70
80
85
TOO
5
10
20
30
40
50
70
80
90
100
NO. OF
SAMPLES
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
MEAN
2.3
1.86
2.9
3.2
7.9
14.0
5.87
5.4
7.9
9.0
4.0
0.4
2.7
0.6
7.6
8.8
3.5
5.5
3.5
2.4
0.8
STANDARD
DEVIATION
0.2
0.26
1.5
0.3
1.1
2.4
1.31
0.5
2.4
0.8
0.6
0.1
0.4
0.06
0.4
2.5
0.5
1.3
0.6
0.2
0.3
COEFFICIENT
OF VARIATION
8.7
14.0
51.7
9.4
13.9
17.1
22.3
9.3
30.4
8.9
15.0
25.0
14.8
10.0
5.3
28.4
14.3
23.6
17.1
8.3
37.5
38
-------
TABLE 8
PERCENTAGE TOTAL VOLATILE SOLIDS CONTENT IN REFUSE DEPOSITS
(Dry Weight Basis)
WELL
NUMBER
6A
6A
6A
6A
6A
6A
6A
6A
6A
6A
6A
9
9
9
9
9
9
9
9
9
9
DEPTH
(FEET)
5
10
20
30
40
50
55
70
80
85
100
5
10
20
30
40
. 50
70
80
90
100
NO. OF
SAMPLES
3
3
- 3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
MEAN
7.6
10.6
12.7
11.8
50.9
43.8
21.23
29.0
44.2
32.1
16.5
3.5
10.4
6.3
44.5
40.2
42.7
55.9
32.8
32.3
32.3
STANDARD
DEVIATION
0.65
1.58
6.7
1.4
6.7
4.2
4.25
1.3
6.9
1.8
1.6
0.15
0.7
1.2
3.6
1.9
1.6
4.6
0.6
4.6
0.55
COEFFICIENT
OF VARIATION
8.6
14.9
52.8
11.9
13.2
9.6
20.0
4.5
15.6
5.6
9.7
4.3
6.7
19.0
8.1
4.7
3.7
8.2
1.8
14.2
1.7
39
-------
Tables 9 and 10 show the total phosphorous and Kjeldhal ammonia
nitrogen content in the refuse. In anaerobic decomposition, a portion of
the organic waste is converted to biological cells, while the remainder is
stabilized by conversion to methane and carbon dioxide. The biological
growth resulting from anaerobic decomposition is an unknown factor,
especially in the case of sanitary landfills. However, growth rate is pre-
dicated on the basis of waste strength and composition. Fatty acids produce
lowest biological growth compared to the carbohydrates. It is estimated that
approximately 0.1 Kg of biological solids are produced per Kg of BOD as a
result of methane fermentation (based on carbohydrates). In order to produce
a certain amount of biological growth, inorganic nutients such as nitrogen
and phosphorous are required. The requirements for nitrogen may be deter-
mined from the cell growth and the fraction of nitrogen in the cells. Based
on an average chemical formulation of biological cells of C5Hg03N, the nitro-
gen requirment is approximately 11 percent of the cell weight. The phosphorous
requirement is approximately one-fifth that of nitrogen or about 2 percent
of the biological solids weight. Based on the assumption that the ultimate
biological oxygen demand is the same as the average total organic carbon,
5 Kg per 100 Kg of dry refuse, approximately 0.5 Kg of biological cells per
100 Kg of dry refuse are formed. The nitrogen and phosphorous requirement
would be 0.05 and 0.01 Kg per 100 Kg of dry refuse respectively. Since the
nitrogen and phosphorous contents in refuse deposits are much higher than
required, it is believed an additional supply of nutrients will not be
needed.
D. Climatic Conditions
Meteorological data are reported for the Long Beach Airport,
approximately 11 miles to the east of the landfill site. These are the
bases for estimating the climatological situation at the Palos Verdes land-
fill. However, the climate at the landfill site may be influenced by local
topographic irregularities and climatological depictions should reflect this
orographic effect.
Precipitation is sparse during the summer months, with only an
average of about 0.35 inches falling between the months of May and October
(see Figure 16). With an annual average rainfall of nearly ten inches, it
is apparent that almost all of the rainfall occurs during the winter months.
Topography plays an important role in these precipitation totals. The Palos
Verdes Hills, in which the landfill lies, are sufficiently high to create
appreciable orographic precipitations, adding to the totals as recorded
at Long Beach. Occasionally heavy rains occur on the slopes of these
hills; in some instances flood damage has occurred.
In the winter months, maximum temperatures range in the middle and
high sixties, while the minimum temperatures usually range in the middle and
high forties (see Figure 17). In the summer months, maximum temperatures in
the high seventies are common, while low temperatures vary between the high
fifties and middle sixties. The mean annual temperature is approximately
630 F.
40
-------
2.0-1
1.5-
CO
UJ
1.0-
0.5-
\NI. NNI. K\l, K
J ' F ' M ' A ' M
ANNUAL AVERAGE (1941-1970):
9.56 INCHES
J J
MONTHS
A ' S 0 N D
FIGURE I6'PRECIPITATION BY MONTH, LONG BEACH, CALIFORNIA
Source: U.S. Weather Bureau
-------
110-
100-
90-
PO
-------
TABLE 9
PERCENTAGE TOTAL PHOSPHOROUS CONTENT IN REFUSE DEPOSITS
(Dry Weight Basis)
WELL
NUMBER
6A
6A
6A
6A
6A
6A
6A
6A
6A
6A
6A
9
9
9
9
9
9
9
9
9
9
DEPTH
(FEET)
5
10
20
30
40
50
55
70
80
85
100
5
10
20
30
40
50
70
80
90
100
NO. OF
SAMPLES
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
MEAN
0.333
0.246
0.145
0.314
0.202
0.182
0.33
0.387
0.136
0.244
0.283
0.293
0.295
0.296
0.180
0.208
0.306
0.295
0.706
0.485
0.181
STANDARD
DEVIATION
0.02
0.05
0.04
0.012
0.011
0.007
0.03
0.066
0.02
0.027
0.038
0.032
0.03
0.0016
0.033
0.019
0.012
0.05
0.18
0.055
0.026
COEFFICIENT
OF VARIATION
6.0
20.3
27.6
3.8
5.4
3.8
9.1
17.0
14.7
11.1
13.4
10.9
10.2
0.5
18.3
9.1
3.9
16.9
25.5
11.3
14.4
43
-------
TABLE 10
PERCENTAGE KJELDHAL NITROGEN CONTENT AS N~ IN REFUSE DEPOSIT
(Dry Weight Basis) c
WELL
NUMBER
6A
6A
6A
6A
6A
6A
6A
6A
6A
6A
6A
9
9
9
9
9
9
9
9
9
9
DEPTH
(FEET)
5
10
20
30
40
50
55
70
80
85
100
5
10
20
30
40
50
70
80
90
100
NO. OF
SAMPLES
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
MEAN
0.28
0.25
0.25
0.26
0.38
0.29
0.29
0.24
0.25
0.23
0.35
0.1
0.21
0.11
0.25
0.3
0.21
0.23
0.17
0.23
0.18
STANDARD
DEVIATION
0.029
0.01
0.014
0.028
0.035
0.027
0.011
0.028
0.02
0.044
0.003
0.0006
0.011
0.007
0.01
0.014
0.008
0.019
0.019
0.035
0.026
COEFFICIENT
OF VARIATION
10.4
4.0
5.6
10.8
9.2
9.3
3.8
11.7
8.0
19.1
0.9
0.6
5.2
6.4
4.0
4.7
3.8
8.3
11.2
15.2
14.4
44
-------
E. Geology
The main geologic unit comprising the Palos Verdes Hills is the
Monterey Shale formation of middle and upper Miocene age (18 to 11 million
years old), which lies upon highly altered Catalina Schist basement rocks
of early Mesozoic age (about 190 million years old). The Monterey forma-
tion consists of three members, the Altamira shale member, Valmonte
diatomite member, and the Malaga mud-stone member, from oldest to youngest.
At the northeast edge of the hills, Lower Pliocene age Repetlo siltstone
(6 to 11 million years old) are unconformably overlain by lower Pleistocene
age (less than 2 or 3 million years old), exposed in the syncline. These
latter are the Lomita marl, Timms point silt, and San Pedro sand (Ref. 20).
At the landfill site, only the Valmonte member of the Monterey
shale is found. This unit is composed of grey-brown to white diatomite,
diatomaceous claystone, siltstone, and thin beds of altered ash underlie
the entire property. The diatomite phases are composed of siliceous, very
fine grained, gritty, clay-like material with a porous texture. Because
of its relatively poor permeability and good stability, the Valmonte
diatomite is a satisfactory base for the present Class I sanitary landfill.
At the Palos Verdes Sanitary landfill, all final surfaces of the
landfill are covered with a minimum of three feet of clean earth consisting
partly of diatomaceous earth. The extent of migration of methane gas
through the cover soil depends upon the soil porosity and particle size.
Figure 18 shows that approximately 60 percent (by weight) of diatomaceous
soil particles are finer than 10 mm size. This cover soil is quite
impermeable to gas migration if compacted to the optimum moisture content
and maximum density.
45
-------
lOO-i
80-
60-
40-
20-
0-
QOI
0.05
O.I 0.5
PARTICLE SIZE IN MILLIMETERS
i
5
10
FIGURE 18' PARTICLE SIZE DISTRIBUTION
OF DIATOMACEOUS COVER SOIL (REF 14)
-------
CHAPTER IV
EVALUATION OF OPERATING CONDITIONS FOR GAS WITHDRAWAL
During 1972 to 1973, the Districts constructed well number 8 to
conduct an experiemental investigation. This well is approximately 110 feet
deep. The bottom 80 feet is perforated and lies within the fill of the
Class I portion of the landfill. Based on the experimental findings, the
Districts have constructed seven extraction wells at the Palos Verdes land-
fill (Figure 19 showing wells numbered 1 to 7). These wells are constructed
in the same way as the experimental well number 8. Each of these wells is
approximately 110 feet deep, spaced on 500 foot centers. During the past
year RSF operated only wells numbered 1, 2, 3, 4, 5, and 7 to meet a demand
of 1000 SCFM.
Figure 20 shows the wells and header pipe locations. Each well
utilizes alternate six-inch and four-inch diameter, 20-foot long polyvinyl
chloride pipe, coupled by burlap-wrapped joints. The well heads themselves
are buried. A buried concrete vault encloses a butterfly valve to adjust
flow rate and instrumentation consisting of a thermometer, a pressure tap,
and a pi tot tube device for measuring the flow rate.
The collection manifold connecting these wells is a 10-inch dia-
meter polyethylene pipe fabricated from 40-foot lengths fused together.
This manifold is buried approximately 35 inches below ground level. The
polyethylene pipe is flexible and will withstand differential settlement of
the landfill as well as seismic activity.
Experimental well number 8 was used for evaluating the operating
conditions for gas withdrawal. The findings reported in this chapter were
experimentally determined by Districts during 1973. These results were
determined for a short duration (maximum of four weeks) and they cannot be
reasonably extrapolated to continuous long-term operation.
A. Gas Composition
The landfill gas composition obtained from a depth of up to 110
feet is shown in Tables 11 and 12. Both the results obtained by Districts
and by the Reserve Synthetic Fuels, Inc. indicate that for a well producing
320 SCFM, the methane content in the landfill gases is approximately 53
percent. Carbon dioxide is the major impurity (approximately 45 percent).
However, operation of well number 8 indicated that composition depends upon
withdrawal rate. It was determined for the particular configuration that a
withdrawal rate of 320 SCFM will produce gases of heating value of approxi-
mately 500 Btu per SCF.
The high carbon dioxide concentration in landfill gases reduces
by dilution the heat of combustion compared to pipeline standards. Carbon
dioxide in conjunction with water, also makes landfill gases highly corro-
sive. It is therefore important to remove both water and carbon dioxide
before its use in commercial gas distribution systems.
47
-------
SOURCE: LOS ANGELES COUNTY SANITATION DISTRICTS
FIGURE 19 = GAS WELL LOCATIONS AT PALOS VERDES LANDFILL
-------
Connecting
Valve Box
O
z
CM
co
c
LJ
in
<&-
g»
tro.
Ur
00
C\JZ
<
e>_
CL
111
H
OJ
9tf
i O
0
f &
0
o*
«K
00
Rubber Couplings
(to provide flexibility)
V
PVC Header Pipe
—size for system
flow
'Gravel level should
be a minimum of 41
above first perforated
section
4" PVC pipe
To prevent grovel entry
wrap all Joints with
Burlap and fasten
With wire
PVC Ring cemented
to end of 4" PVC pipe
6"PVC pipe
Wire
GRAVEL
FIGURE 20=
TYP. JOINT DETAIL
PALOS VERDES LANDFILL GAS COLLECTION
SYSTEM
WELL S TELESCOPING PIPE
CONFIGURATION
30"Dia.
bore
SOURCE: LUS ANGELES COUNTY SANITATION DISTRICTS
49
-------
TABLE 11
GAS ANALYSIS*
PALOS VERDES -SANITARY LANDFILL
(January 31, 1973)
GAS
Methane (CH4)
Carbon Dioxide (CCL)
Hydrogen (H2)
Nitrogen (Np)
Oxygen (02)
Argon (A)
Hydrocarbon (Heptane, C7H,g)
Benzene
Toluene
VOLUME(%)
52.6
43.5
0.05
2.92
0.29
0.05
0.45
0.11
0.05
Heat of Combustion
(Btu/ft3)
585
Source: Los Angeles County Sanitation Districts
* Withdrawal Rate 320 SCFM
50
-------
TABLE 12
GAS ANALYSIS*
PALOS VERDES SANITARY LANDFILL
(June 8, 1974)
GAS
Oxygen
Nitrogen
Carbon Dioxide
Hydrogen
Hydrogen Sulfide
Methane
Ethane
Propane
Iso. Butane
N. Butane
Iso. Pentane
N. Pentane
Hexane
Heptane
Octane
Nonane
VOLUME (%)
0.070
0.272
45.588
0.056
0.0017
53.283
0.000
0.007
0.004
0.006
0.010
0.014
0.128
0.292
0.206
0.064
Heat of Combustion
(Btu/ft3)
Specific Gravity
(gram per
cubic centimeter)
580
1.017
Source: Reference 18
* Withdrawal Rate 320 SCFM
51
-------
B. The Effects of Withdrawal Rates on Gas Composition
The withdrawal of gases at higher flow rates may cause the migration
of air through the porous cover layer, resulting in the chanqe in gas composition.
The extent of air migration depends upon the permeability of the soil used in
final cover and also the inches of vacuum required to withdraw gases at a
certain flow rate. The increase in air concentration in landfill gases will
oxidize methane, resulting in hiaher carbon dioxide and nitrogen content and
in a reduction in the heatina value. The purpose of this test is to
determine a withdrawal rate at which CH4/C02 ratio is maximum and also remains
constant throughout the gas extraction.
In order to determine this parameter, Los Angeles County Sanitation
Districts conducted an experiment at the increased withdrawal rate from 320
to 600 SCFM. The experiment was conducted for a relatively short time (four
weeks). Figure 21 shows the influence of withdrawal rate upon gas composi-
tion and heating values with respect to time. After operating continuously
for a three-week period at the withdrawal rate of 600 SCFM, the methane to
carbon dioxide ratio of the gas decreased about 15 percent from 1.1 to 0.94.
In attempts to determine a withdrawal rate which would yield a
stable methane to carbon dioxide ratio and maximum heating value, the with-
drawal rate was reduced to 400 SCFM. After four weeks of continuous operation
at 400 SCFM withdrawal rate, the Btu value of the extracted gases began to
decline as the percentage of C02 began to rise. Therefore, composition data
would seem to indicate that a withdrawal rate of approximately 320 to 350 SCFM
will permit the gases to be collected with maximum heating values.
C. Effects of Gas Withdrawal Rates on Well Pressure and Gas Pressure in
Surrounding Fill Regions
The purpose of this test is to determine the amount of pressure drop
required to withdraw gases at certain flow rates. This parameter depends upon
the porosity and permeability of the fill. A 30-inch diameter experimental
well number 8 dug to 110 feet below the surface elevation was used for this
test (Figure 22). This experimental well is prototype for all extraction
wells on site. It was connected to a positive displacement blower equipped
with a nine-foot kittel muffler on the blower discharge.
The gas pressures in the surrounding landfill regions were deter-
mined from a remote well. This well is also 30 inches in diameter, dug to
125 feet below the surface elevation at a distance of 110 feet from an
experimental extraction well. This well is tightly caped to eliminate the
emission of gases to the atmosphere.
Gauge pressure readings (with respect to atmospheric pressure)
we re determined with a U-tube barometer filled with water. Results were
obtained up to a 0.01 inch accuracy (water column).
52
-------
60-
55-
50H
45-
40-
_o o o o-
-CO,
UJ
O
X
o
5 60
TIME IN WEEKS
WITHDRAWAL RATE=320 SCFM
50-|
UJ
UJ
40
-B.TU./FT3
~C02
CH4
1
2
TIME IN WEEKS
WITHDRAWAL RATE = 400 SCFM
60-
55-
50-
45-
40-
BIU./FT3
-o o o-
CH4
2 3
TIME IN WEEKS
WITHDRAWAL RATE = 600 SCFM
* QUESTIONABLE DATA
FIGURE 21: THE EFFECTS OF WITHDRAWAL RATES ON
GAS COMPOSITION AND HEATING VALUES
•600
•550
500
450
400
•600
-550
O
-500 5
o
-450
03
•400
600
-550
-500
-450
400
SOURCE: LOS ANGELES COUNTY
SANITATION DISTRICTS
53
-------
en
-Pi
1
"°^=
BLOWER^
GAS
EXTRACTION
WELL- -
— ^
jf
345'
265'
190'
125'
110'
55'
"o
*~
V
REN
^W®&^
MONITORING
WELLNo.l
*OTE GAS
^ WELL -^
CVI
(REFUSE)
—
V -«^-__
^
MONITORING
WELL No.2
+/
T" /^ n /^ p*
/TOP OF
/ REFUSE
/ FILL
MONITORING/
WELL No. 3 "4
^ 5
MONITORING
WELL No.5
-- ^^ £ MONITORING
— —
^"7 WELL No 6
APPARENT *•£$
TERMINATION FOR ^ (o c c >\ e c \
-p.jp 7muP r\c *• ruoci
(WITHDRAWAL RATE . _J>
OF320CFM) '*' C I.ALL
NOTES _
ss^S
. MONITORING WELLS ARE
•$r^*~ I2"IN DIAMETER» DUG TO 36*
^ J^a^^ BELOW SURFACE ELEVATION.
2. THE MONITORING WELL CASINGS
ARE 2"RV.C. PERFORATED PIPE.
-UNDISTURBED GROUND
FIGURE 22'INFLUENCE AREA STUDY
MONITORING WELL LOCATIONS AT PALOS VERDES LANDFILL
SOURCE: LOS ANGELES COUNTY SANITATION DISTRICTS
-------
Figure 23 shows the change in pressure with respect to time at
shutdown and restart of the blower, both in the case of experimental gas
extraction and remote wells. At 8:24 AM when the blower was shutdown,
pressure in the gas extraction and the remote well was increased to 0.6 and
0.9 inches of water respectively, in approximately 90 minutes. The remote
well follows a time-lag of approximately six minutes compared to the extrac-
tion well located at a distance of 110 feet. The increase in pressure is a
result of the accumulation of gases in the well.
On restart of the blower to withdraw gases at 320 SCFM, a velocity
head of 0.94 inches of water will be required. The pressure in the experi-
mental gas extraction well will drop by 3.3 percent of the atmospheric
pressure, whereas in the case of the remote well the reduction in pressure
is only 0.12 percent. The latter reduction in pressure is clearly due to
the influence of gas withdrawal from the extraction well.
D. Radius of Influence at a Selected Withdrawal Rate (320 SCFM)
In order to design an economical gas recovery system, it is
important to know the number of extraction wells that should be located in
a particular landfill configuration to extract the gases at their production
rate. The number of wells can be correlated with the radius of influence
(or sphere of influence), which depends upon withdrawal rate, depth, and
volume of refuse deposits. Los Angeles County Sanitation Districts did an
extensive survey at the Palos Verdes landfill to evaluate these parameters.
The following discussion is based on their results.
Figure 22 shows the schematic diagram indicating the number and
location of monitoring wells. All monitoring wells are 12 inches in dia-
meter and dug to 36 feet below the surface elevation. The monitoring well
casings are 2-inch PVC perforated pipe. Monitoring wells, numbers 1, 2, 3,
5, and 6, are located at a distance of 55, 125, 190, 265, and 345 feet
respectively from the extraction well. The extraction well was continuously
operated for three days at a withdrawal rate of 320 SCFM. The pressure changes
in monitoring wells, numbers 1, 3, and 5, were determined with respect to
time (Figure 24).
Pressure readings were first taken in the monitoring wells while
the suction blower was not operating. Those initial readings indicated
positive pressures for all wells to be approximately 0.25 inches of water
column. The blower was then started up and continuous hourly readings were
recorded over a 32-hour period after which hourly readings were made during
the regular working day. Within 12 hours after the start of the blower,
pressures in the monitoring wells, numbers 1, 3, and 5, were reduced by
0.31, 0.21, and 0.19 inches of water column respectively. Variation in the
gas pressures in the monitoring wells were observed to have a definite daily
cycle. These variations are not clearly understood at this moment because
it does not follow diurnal atmospheric pressure fluctuations. Maximum
pressure variation in wells 1, 3, and 5 is approximately 0.08 inches of water.
The data appear to show a measurable pressure influence up to 265 feet in
distance from the withdrawal well.
55
-------
12-1
10-
8-
6-
4-
I 2J
fe 0-
V)
Ul
a 2-
4-
6-
8-
10-
12-
14-
16
SHUTDOWN
WITHDRAWAL RATE - 320 cfm
REMOTE WELL
AM
10 II
JUNE 5, 1973
FIGURE 23'EFFECTS OF GAS WITHDRAWAL
RATES ON WELL PRESSURE
rL2
-1.0
-0.8
-0.6!
-0.4
-0.2
UJ
>
i
ho o
CO
UJ
1-0.2 O
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
•1.6
12 I
NOON PM
SOURCE: LOS ANGELES COUNTY
SANITATION DISTRICTS
56
-------
0.40-1
01
tr
1
fe
Q
0.30-
UJ
§5 0.20-
CO
CO
UJ
CT
CL
0.10-
0-
0.10-
0.20
4 6
START OF SUCTION BLOWER
320 SCFM WITHDRAWAL RATE
WELL No. 5
WELL No. I
CONTINUOUS MONITORING PERIOD
ASSUMED DATA
12 6
NOON
12 6 12
MIDNIGHT NOON
OCT. 10, 1973
6 12 6 12
MIDNIGHT NOON
OCT. II, 1973
6 12 6 12
MIDNIGHT NOON
OCT. 12, 1973
10
FIGURE 24*MONITORING WELLS
PRESSURE VARIATION VERSUS TIME
SOURCE: LOS ANGELES COUNTY SANITATION DISTRICTS
-------
From the data obtained in this study, a withdrawal rate of 320 SCFM
would appear to produce a radius of influence of approximately 250 feet.
These values correspond to the Palos Verdes landfill site containing an extrac-
tion well of 110 feet deep.
E. Total Energy Production
The gas quality evaluation test is conducted by continuously extrac-
ting gases from a well at its production rate for a long period of time. The
purpose of this test is to determine:
1. The total energy production from a well.
2. The actual life of a well operating under forced withdrawal.
The results reported here were obtained from a short run (one week)
and they do not satisfy any of the above purposes. However, it is shown that
at the withdrawal rate maintained within a range of 300 to 350 SCFM, gases with
an average heating value of 500 Btu per cubic feet can be extracted (Figure 25).
This will produce gases of approximately 1.5 x 10^ Btu by the end of one week
of operation.
F. Permeability of Refuse Deposit
A laboratory measurement of the permeability of porous refuse
deposit medium with suitable apparatus and with the proper technique will
undoubtedly give the most accurate results in a determination of this per-
meability constant (K). Theoretically this constant may be defined with the
help of Darcy's law (Ref. 21). For a radial flow (Vr) into a well, Darcy's law
can be written as:
Vr = . JLAP_ ; ft,
/
8r sec
Considering Q as volumetric flow rate in cc/sec and h and r are
the depth and radius of well respectively, we may calculate
Vr =
and, Q _ K_
2Trrh " " u.
8P
The radial flow system may be characterized by the conditions:
r = rw (radius of well); 8P =AP
r = re (radius of influence); 8P = 0
58
-------
en
CO
350-1
300-
350-
u. 200-
g 150-
-------
Whence, equation 2 may be written as:
K- Q/t1?". (3)
* 2 hT (*>
In equation 3 the resultant value for permeability constant (K)
will be in terms of Darcy's if p is expressed in centipoises, Q in cubic
centimeters per second, h in centimeters, and AP in atmosphere.
With the help of experimental data discussed earlier, we may
determine the permeability constant of Palos Verdes landfill refuse
deposits. A 110 foot deep experimental well withdrawing gases at a rate
of 320 CFM produces a 250-foot long radius of influence and 13.5 inches of
pressure drop. Assuming that this gas is composed of 50 percent of methane
and 50 percent of carbon dioxide, we may calculate the average viscosity of
landfill gas at standard temperature and pressure
= 0.011(0.5) + 0.0153(0.5) = 0.01315 centipoise
By substituting these values in equation 3 we may calculate the
permeability of refuse deposits:
K =
(0.01315) (320 x 472) In 250
0.25
(2ir) (HO x 12 x 2.54) (13.5 x 0.00245)
K = 20 Darcys
6. Theoretical Correlation of Operating Parameters for Landfill Gas Extraction
For the flow of ideal gases through landfill refuse deposits,
the operating parameters such as flow rate, pressure drop and radius of
influence may be theoretically correlated. Under steady conditions where the
generation rate is equal to the withdrawal rate, the following equation may
be written:
2 2
Q = IT (Re - Rw) Fg D h x 1 , CFM
(365) (24) (60)
Where,
Re is radius of influence, ft.
Rw is radius of a withdrawal well, ft.
Fg is generation rate, cu. ft.
(Yr) (Ib)
D is in-place density of refuse, Ib/cu.ft.
h is depth of a well, ft.
60
-------
The above equation may be reduced to:
S-= 5.97 x 10~6 (Re - Rw) Fg
(4)
C-| = h D, Assuming constant depth
and in-place density
With the help of equation 4 volumetric flow rate may be correlated
to the radius of influence and generation rate. The forced withdrawal of gas
will produce a pressure drop of (Pw-Pe). This value may be calculated by
making a mass-balance across a ring of radius r and depth h.
61
-------
2 2
The volume of refuse outside the ring is, ir(Re-r )h and volume
of gas generated in this segment in unit time, ?r(Re-r )h Fg. D.
Whence velocity at radius r is, Vr = 7r(Re"r )h F9- D
2^-rh
For radial flow into a well, Darcy's law may be written as:
Vr - K IE. - (Re-r2) Fg. D
vr LL 8r 2r
or,
Whence,
. D/
' 2
Re-r
r
8r
The above equation can be solved for the conditions:
r = Rw (radius of well); P = Pw
r = Re (radius of influence); P = Pe
- (Pe - Pw) = -AP = Fg.D
Re In §£ - 1 (Re - Rw)
Where,
or,
K is permeability of fill, Darcy,
ft is viscosity of gas, centipoise
(cm2)
/atm
/cm)
-AP = — x .' —. . v 929
n 2 x (365) (24) (60) (60) x y^y
£ Fg.D Re lr|| - -^(Re-Rw) ,atm.
-AP = 6x1 0'3 Fg ^ [Re2 ln|| - \ (Re-Rw)J • *
-^= 6x10'° Fg
L2
c - .
L2 K
inches of water
- \ (Re - Rw)]
(5)
62
-------
Equation 4 and 5 were solved for volumetric flow rate (Q) and
pressure drop (-AP) as a function of constants C] and C2, generation rate,
and radius of influence (Appendix A). In the case of a completed landfill,
constants CT and C2 can be calculated from average in-place density, depth,
and permeability of the fill; and viscosity of fill decomposed gases. If
rate of gas generation is known for a particular landfill site, Figure 26
can be used for operating parameters evaluation under steady-state conditions.
63
-------
CT>
25
5
u_
o
old
100
200
220
200-
RADIUS OF WELL =0.25 FEET
uD
K
300 400 0
RADIUS OF INFLUENCE (Re), FEET
200
300
FIGURE 26'THEORETICAL CORRELATION OF OPERATING PARAMETERS
FOR LANDFILL GAS EXTRACTION
400
-------
CHAPTER V
SELECTION OF TECHNIQUES FOR GAS BENEFICIATION
The fermentation process that is responsible for the decomposition
of combustible waste produces a mixture of gases. Methane gas withdrawn from
sanitary landfill deposits under slight vacuum is mainly contaminated with
carbon dioxide, with smaller fractions of nitrogen, water, hydrogen sulfide,
and other decomposition products. The methane is thus diluted with incom-
bustibles that lower the heating value. The acid gases are also corrosive
in the presence of water.
The low Btu raw gas from landfill sources cannot be mixed with pipe-
line gas because of its degraded performance in burners adjusted to the current
pipeline gas standard. Gas metering is performed on a volume basis, but the
heating value of 1000 Btu/SCF is guaranteed. Therefore, landfill gases should
be purified to meet the pipeline standard.
The raw landfill gases have higher specific gravity and lower heating
value compared to methane. Therefore, for its on-site efficient combustion, a
proper modification in burner design is required (Ref. 22).
Dehydration to reduce the corrosion problem may enhance the utility
of landfill gas where they can be used on site. Glycol and molecular sieve
dehydration processes are generally used. On the other hand, these gases may
also be processed to 99 percent methane purity to meet the pipeline standard,
thus upgrading the gas to a commercial product. Process selection obviously
will depend on the nature of the final product, requirements as they relate to
the actual composition of the raw gas. The first requirements of a processing
system are that the impurities of the raw gas may be removed to meet commercial
standards. Among the processes meeting these requirements the most attractive
economic choice may be made giving due consideration to any environmental impacts
involved. A number of gas purification processes are commercially available and
have had long use in the petroleum and the energy production industry (Ref. 23,
24, 25). A review of the operation of some of the most important techniques
is given here, followed by a section on the design procedure for an adsorption
column.
A. Gas Purification Techniques
Generally absorption, liquefaction, and adsorption processes are
used for bulk removal of carbon dioxide and hydrogen sulfide impurities.
1. Absorption
The ethanolamine absorption process is widely used for C02 and H2S
removal. Monoethanolamine (MEA) and diethanolamine (DEA) are the most widely
used solvents, but particularly the former (Ref. 26, 27, 28, 29).
65
-------
Figure 27 shows the simple process scheme where lean solvent
(ethanolamine) enters the top of the absorber at approximately 100° F and
contaminated landfill gas flows upward. Purified gas leaves the tower at
its top. The gas must be dehydrated before being fed into the distribution
pipeline. Since aqueous amine has very little affinity for the hydrocarbon
constituents of the gas to be purified, this process can be successfully used
for methane gas purification.
Ethanolamine solution is regenerated by stripping at a temperature
of approximately 230 to 240° F. The released gases and traces of solvent are
burnt in the flair burner and discharged to the atmosphere. The reactions
involved in absorption-regeneration processes are very complex, but may be
summarized by the following reversible reaction equations.
100° F
HO - CH, - CH0 - NH9 + H0S - * (HO - CH9 - CH9 - NH-) HS
• L t.
-------
en
-vl
DEHYORATOR
METHANE GAS
LANDFILL
GAS
COMPRESSOR
COOLER
ABSORBER
HEAT
EXCHANGER
COOLER
REFLUX
STRIPPER
( J PUMP
>--*\
STEAM
TO ATMOSPHERE
FLAIR BURNER
FIGURE 27'ETHANOLAMINE ABSORPTION PROCESS
FOR C02 AND H2S REMOVAL
-------
2. Liquefaction of Carbon Dioxide
Purification of landfill gases containing 50-50 percent of C02 and
CH4 can be achieved by liquefaction. Figure 28 shows the phase diagram for
the CH4-C02 system (Ref. 37). In order to produce methane of 90 percent
purity, it is necessary to operate the plant at 730-750 psia with temperature
no lower than -100° F. Methane (boiling point -259° F) vapor under these
conditions has a heating value of 900 Btu per SCF and contains 10 percent
C02- This does not meet pipeline standards; a second stage of purification
would be required.
Figure 29 illustrates the simplified process scheme for treating
the low Btu sanitary landfill gases containing about 50 volume percent of
C02- Water removal is accomplished by passing the gases through an adsorp-
tion tower (dehydrator) containing either molecular sieve or activated carbon.
Gas is cooled to the desired temperature and purified in the demethaniser, a
standard distillation type separator. C02 and CH4 are separately passed
through a heat pump cycle to recover energy which can be used in cooling the
feed gas.
The additional purification of landfill gas to boost the heating
value to acceptable pipeline standard can be achieved by one of the following
methods:
A second stage of liquefaction treatment involving freezing close
to the solid C02 vapor region, which will require an additional refrigeration
System. This process can be competitive only when a source of low cost
refrigeration is available.
Absorption of C02 into liquid: this process has the disadvantage of
re-introducing water back into the gas, thus requiring an additional drying
stage before entering the distribution pipeline.
Adsorption of C02 on solids: this process has the advantage of
removing the remaining 10 percent of C02 while keeping the gas dry.
3. Fixed-Bed Adsorption
Gas purification by adsorption process is based upon the physical
properties of specially prepared granular solids, the adsorbent. An adsorbent
will selectively attract and retain gases on its surfaces.
Adsorbents generally used for gas purification are molecular sieves,
activated carbon, silica gel, and activated alumina. Among all these adsor-
bents, molecular sieves are being most successfully used to purify gases
containing C02 and H2S (Ref. 38, 39, 40). They are particularly attractive
with gases containing relatively large quantities of C02 with small quantities
of H2S (Ref. 41).
68
-------
1400-
MOLE % CH4
SOLID C02
+ LIQUID
VAPOR
+ LIQUID
SOLID C02
+ VAPOR
-170 -150 -130 -110 -90 -70 -50 -30 -10 0 10 30 50 70 90
TEMPERATURE °F
FIGURE 28: PHASE DIAGRAM FOR C02-CH4 SYSTEM
-------
CH4
CONTAINING
10% C02
REFRIGERATION
SYSTEM
LANDFILL
GAS
DEHYDRATOR
COMPRESSOR
-IOO°F
730—750
Pisa
COo -*•
DEMETHANISER
HEAT PUMP
FOR ENERGY RECOVERY
FIGURE 29« LIQUEFACTION OF CARBON DIOXIDE
FROM LANDFILL GASES
-------
Figure 30 illustrates the simplified process scheme for gas purifi-
cation by the molecular sieve adsorption process working on the thermal-swing
regeneration cycle. Compressed landfill gas passes through filteration and
dehydration unit to remove dust and water respectively. The dried gases enter
at the top of one of the triple-beds unit. One bed is adsorbing contaminants
while the other two are at one of the two stages of regeneration (heating and
cooling). In a properly designed adsorption column, adsorption time is always
the same as the regeneration time so that this process can be continuously
operated. The gases produced by this process are of 99 percent purity and
they meet the pipeline standards.
Among all the process discussed earlier, the molecular sieve adsorp-
tion technique is considered to be one of the most economical for bulk land-
fill gas purification. The economic feasibility of this process depends upon
designing a proper purification system. Therefore, in the next section, the
criteria for adsorption column design are established.
B. Design of an Adsorption Column for Sanitary Landfill Gas Purification
The design of an adsorption column requires a detailed investigation
of the following items.
1. Selection of an Adsorbent
A number of commercially available adsorbents should be selected
which have the best adsorption properties for the gases to be removed.
Generally, molecular sieve, activated alumina, or silica gel are used to
remove water, carbon dioxide, and hydrogen sulfide by selective adsorption.
2. Static Adsorption Test
One of the important basis for adsorbent selection is its adsorptive
capacity. This is determined by running a series of static test to determine
the pounds of impurity that can be removed at equilibrium by each pound of
adsorbent. The extent of adsorption is highly temperature and pressure
dependent and it is usually represented by isotherms - gas phase concentration
versus specific adsorption on the solid at a given temperature (Figure 31 and
32).
Generally, molecular sieve type 5A and 13X is used for removal of
smaller molecules such as H20, C02 and H2S. Figure 22 shows that molecular
sieve 13X has almost five times the drying capacity of either alumina or
silica-type adsorbents when water is present in extremely low concentrations.
This is why exceptionally low dew points can be obtained with molecular sieves
in gas purification.
71
-------
PO
COMPRESSOR
FILTER
: CYCLE TIME CONTROLLER
(9
99% PURE
METHANE
PUMP
COOLER
o
o
o
HEATER
e
oo
VENT
GAS
[ FLASH TANK ]
PUMP
FIGURE 30'A CLOSED CYCLE MOLECULAR
SIEVE ADSORPTION PROCESS
-------
40-1
£
o
35-
UJ
m
oc
8 »'
Q
CO
o
o
Q
a
UJ
m
a:
25-
20-
15-
(£
I
U.
O
0) 10-
o
5-
TEMPERATURE: 25°C
SILICA GEL
MOLECULAR SIEVE TYPE I3X
iCTIVATED ALUMINA
5 10 15 20
WATER VAPOR PRESSURE-mm OF Hg
FIGURE 31' ISOTHERMS FOR
WATER ADSORPTION (REF42)
25
30
73
-------
>o
-IS*
20-
SI
m
12-
ife
ss
&'
2
o
Q
8-
4-
0.1
TEMPERATURE 25°C
Hj,S, TYPE I3X
COZ, TYPE 5A
:02, TYPE I3X
10
100
ADSORBATE PRESSURE-mm OF Hg
FIGURE 32'ISOTHERMS FOR CARBON-DIOXIDE
AND HYDROGEN SULFIDE ADSORPTION (REF42)
1000
-------
3. Dynamic Adsorption Test
In a gas purification process, the results obtained under static
adsorption only show the maximum loading attainable. The rate of attainment
of any fraction of the equilibrium loading of the adsorbent under dynamic
adsorption conditions remains to be determined. The purpose of this test
is to find the breakthrough time and capacity to reduce the adsorbate from
one concentration to another.
As the gas enters an activated adsorbent bed, the sorbable com-
ponent is attracted to and adsorbed on the adsorbent. Figure 33 shows the
adsorbate loading with respect to length of the bed (X-L) and concentration
of sorbable component in effluent with respect to time (Y-0). The portion
of the bed in which adsorbate loading is equal to equilibrium loading is
defined as the equilibrium zone (Area h a b k h). The portion of bed in
which the adsorbate concentration transition occurs is defined as the mass-
transfer zone (MTZ). The point at which adsorbent capacity is exhaused to
produce certain allowable concentration of effluent, is called breakthrough
point. This point advances through the column with time.
For a particular landfill gas, (X-L) and (Y-0) plots are experi-
mentally determined in the dynamic adsorption test. From this plot one can
determine the ratio of the weight of equilibrium bed (Area h k c f h) to
weight of unused bed (Area c d e f e), and breakthrough time (Ob) required
to reduce the adsorbate concentration to a desired level.
4. Gas Flow Rate
The superficial flow rate is fixed by the diameter of the column.
The pressure drop across the adsorbent bed becomes the limiting factor. Since
the cost of a pressure vessel tends to increase dramatically with the diameter,
the minimum diameter of an adsorption column is set by pressure drop limita-
tion. Generally, a superficial flow rate from 0.5 to 2 feet per second is
selected for a downward gas flow.
5. Heat of Adsorption
As the adsorption progresses the adsorbent is heated by the
exothermic heat of adsorption, and this heat is carried ahead of the adsorp-
tion zone by the gas. The effect of increase in temperature lowers the
capacity of the adsorbent. Therefore, gas flow rate should be controlled to
prevent over-heating.
6. Adsorbent Bed Arrangement
Generally adsorption-regeneration systems are dual-bed units, or
multiples of dual-bed units. In this arrangement one bed is adsorbing while
the other is regenerating.
75
-------
EQUILIBRIUM
CTI
FIGURE 33« DETERMINATION OF MASS-TRANSFER FRONTS
BY DYNAMIC ADSORPTION TEST
-------
In thermal-swing cycles, three-bed units are used with one adsorb-
ing while the other two are either heating or cooling. A bed spends a third
of its cycle time in each of the three positions.
7. Selection of a Regeneration Procedure
A procedure is selected on the basis of residual loading and
adsorption-regeneration cycle time. The following regeneration cycles are
used in gas purification:
Thermal-Swing Cycle Broadly defined as one in which desorption takes
place at a temperature higher than that of the adsorption step. Raising
the temperature of the adsorbent increases the equilibrium pressure of
the adsorbate. Cooling is required after regeneration before the adsor-
bent is ready for a subsequent adsorption step. The long regeneration
time makes this technique unattractive for use in bulk separation pro-
cesses such as COg removal from landfill gases.
Pressure-Swing Cycle Desorption is carried out at a pressure lower
than that of the adsorption step. Here, the partial pressure of the
sorbate in the gas is lowered instead of raising the equilibrium
pressure on the adsorbent as in the temperature swing cycle. The main
advantage of this technique is that desorbed materials can be recovered
as high purity products. The technique is very useful for bulk separa-
tion where short cycles and low residual loadings are required.
Purge-Gas-Stripping Cycle In this case a reduction of partial pressure
of sorbable component in fluid phase is achieved by dilution with an
inert gas to cause desorption. The purge gas may be heated to improve
efficiency and shorten the purge time required - the effects of thermal
swing may be enlisted.
77
-------
CHAPTER VI
RSF'S COMMERCIAL EXPERIENCE IN PALOS VERDES LANDFILL
GAS EXTRACTION AND PURIFICATION
As a result of the uncertainty on the part of the Los Angeles
County Sanitation Districts to guarantee a continuous supply of raw land-
fill gases to RSF's gas purification plant, a mutual agreement was reached
to extract and process 1.0 MMSCF per day of gases on an experimental basis.
It was decided that the District would only construct the withdrawal wells
required by RSF to meet the desired methane gas production; it would then
be the responsibility of RSF to operate and maintain a gas withdrawal and
purification system. On June 1, 1975 this sophisticated gas collection
system became operative to extract landfill gases under vacuum. These
gases are automatically routed to the purification plant or by-passed to
the waste burners. Carbon dioxide and hydrogen sulfide are removed by a
process based on the molecular sieve adsorption technique.
A. Landfill Gas Extraction
During the operation, an irregular supply of raw landfill gas at
variable withdrawal rates was experienced. Between June 1, 1975 and
February 12, 1976, on four different occasions gas extraction was stopped
as a result of mechanical and/or technical problems. Those problems were
mostly caused by the presence of corrosive carbonic acid. It was felt
that selection of a construction material resistant to carbonic acid would
partially solve this problem.
Table 13 indicates the total quantity of raw landfill gas with-
drawn to the end of December 1975. The extraction rate was acceptable only
during the months of November and December. A total of 91,239.2 MSCF of
raw landfill gas was extracted which is only 42.6 percent of the predicted
amount (based on a withdrawal rate of 1 MMSCF per day for 214 days).
During the month of December 1975 and part of January 1976, the
gas composition and flow rates of extraction wells numbered 1, 2, 3, 4, 5
and 7 were investigated (Table 14). These wells were pumped to supply
approximately 1000 SCFM of raw landfill gas. Generally, the flow rate of
an individual well ranged from as low as 75 SCFM to 310 SCFM. The methane
content in the raw landfill gas was always over 50 percent by volume. At
increased withdrawal rates, these gases contained substantial percentages
of nitrogen. An air leak.can be the result of three possible causes:
0) a broken header or branch header pipe, (2) a faulty connection at one
of the wells, and/or (3) an infiltration of air through the top cover of
the landfill.
B. Gas Purification
The purification of raw landfill gases require the following
five basic operations: initial and final compression, water removal, H2S
and water removal, carbon dioxide removal, and burning of contaminants to
form non-polluting products (Figure 34). The facilities to accomplish
this were built by RSF, costing approximately one million dollars.
78
-------
TO ATMOSPHERE
PRETREATER TOWERS
(H2S AND WATER REMOVALjv
RAW
LANDFILL
10
GAS
INITIAL
GAS
COMPRESSION
H20 REMOVAL
10-15 GPH CONDENSATE
RETURN TO LANDFILL
-HIGH EFFIENCY
WASTE GAS BURNER
.MOLECULAR SIEVE
ADSORPTION TOWERS
o
o
ooo
FINAL
COMPRESSION
(175 PSI)
SALES
GAS TO
SOUTHERN
CALIFORNIA
GAS COMPANY
-CONTAMINANT
REMOVAL
{WATER 8 ORGANICS)
FIGURE 34= SCHEMATIC DIAGRAM OF
PALOS VERGES LANDFILL GAS PURIFICATION PROCESS
SOURCErRESERVE SYNTHETIC FUELS, INC.
-------
TABLE 13
PALOS VERDES LANDFILL GAS EXTRACTION
AND PURIFICATION OPERATION
oo
o
June, 1975
July, 1975
August, 1975
September, 1975
October, 1975
November, 1975
December, 1975
January, 1976
February 12, 1976
RAW LANDFILL
GAS MSCF(A)*
6,165
11,669
11,333
11,035
4,317
20,738
25,982.2
-
-
AMOUNT OF
METHANE
PRODUCED
MSCF(B)**
3,242
4,838
6,490
4,576
495
5,504
4,108
2,273
314
B
A
0.53
0.42
0.57
0.42
0.12
0.27
0.16
-
-
AMOUNT OF
METHANE
CONSUMED
MSCF(C)**
3,274.8
5,558
2,561
1,879
896
1,309
2,716
1,202
490
C
B
1.01
1.15
0.39
0.41
1.81
0.24
0.66
0.53
1.56
NET AMOUNT OF
METHANE GAS SOLD
TO SOUTHERN CAL.
GAS CO., MSCF
- 32.8****
-720
3,929
2,697
-401
4,195
1,392
1,071
-176
91,239.2***
31,840
19,885.8
0.62
11,954.2
* Source: Los Angeles County Sanitation Districts
** Source: Southern California Gas Company, Los Angeles
*** The total quantity of gas withdrawn to the end of December, 1975
**** The negative sign indicates that methane consumption rate is higher compared to the production
rate.
Note: Readings were corrected for pressure. The heating values ranged from 968 to 1,030 Btu/SCF.
-------
TABLE 14
COMPOSITION AND FLOW RATES OF RAW GAS OBTAINED FROM EXTRACTION
WELLS LOCATED AT PALOS VERDES LANDFILL
WELL
DATE NO.
12/5/75 1
2
3
4
5
12/8/75 1
2
3
4
5
12/9/75 1
2
3
4
5
12/10/75 1
2
3
4
5
12/11/75 1
2
3
4
5
PERCENTAGE (VOLUME)
CO, CH4 No Op
"— -fc. T • •<- ^
40.6 59.4 Trace 0
38.7
40.5
33.9
34.6
49.0
45.1
-
38.9
41.4
40.1
40.8
-
39.8
39.7
42.2
42.4
34.4
39.4
35.9
47.8
43.8
41.0
43.9
39.5
61.3
57.1
56.2
62.4
49.1
54.9
-
57.4
58.6
57.7
59.2
-
60.2
56.7
57.8
57.6
65.6
60.6
58.4
50.8
56.2
59.0
56.1
57.1
0
2.4
8.1
3.0
1.9
Trace
-
3.7
0
2.2
Trace
-
Trace
3.6
0
0
0
0
5.7
1.4
Trace
Trace
0
3.4
81
0
0
1.8
0
0
0
-
0
0
0
0
-
0
0
0
0
0
0
0
0
0
0
0
0
WELL FLOW TOTAL FLOW RATE
RATE FROM ALL WELLS
SCFM SCFM
200
160
200
190
210
200
310
Shut Down
280
280
310
280
Shut Down
280
280
100
280
130
250
180
75
300
95
175
190
960
1070
1150
940
835
-------
TABLE 14 (continued)
DATE
12/12/76
12/13/75
12/16/75
12/17/75
12/18/76
WELL
NO.
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
PERCENTAGE (VOLl
C02 CH4 N2
42.1 56.9 1.0
36.3
41.0
39.1
36.4
38.3
38.8
40.3
38.1
43.5
41.7
40.4
44.1
44.3
40.6
37.3
38.9
38.2
44.1
38.8
39.4
40.7
42.4
38.4
41.3
63.0
58.4
60.7
58.0
58.2
60.4
58.9
61.6
52.1
55.9
59.2
55.4
55.5
53.8
59.4
60.6
61.1
55.7
56.2
57.1
58.8
57.1
61.4
53.3
0.7
0.5
0.2
5.6
3.2
0.8
0.6
0.3
4.4
2.4
0.4
0.5
0.2
5.4
3.1
0.5
0.6
0.2
5.0
3.3
0.5
0.4
0.2
5.4
IME) Wl
02
0
0.05
0.2
0.05
0
0.28
0.06
0.2
0.04
Trace
0.1
0.03
0.08
0.04
Trace
0.15
Trace
0.1
Trace
Trace
0.15
Trace
0.08
0.03
Trace
ELL FLOW TOTAL FLOW RATE
RATE FROM ALL WELLS
SCFM SCFM
75
250
95
200
200
95
290
95
200
220
75
250
no
180
210
75
250
95
175
250
75
270
95
180
210
820
900
825
845
830
82
-------
TABLE 14 (continued)
DATE
12/22/75
12/23/75
12/24/75
12/26/75
12/30/75
WELL
NO.
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
PERCENTAGE (VOLUME)
C02 CH.4 N£ 02
43.8 55.4 0.8 0.04
44.7
45.0
41.8
44.3
_
44.2 .
45.9
42.8
-
_
38.4
43.7
44.1
-
_
44.2
42.0
39.5
-
_
37.5
41.2
44.4
43.8
55.0
54.9
58.1
54.2
_
55.1
53.5
55.2
-
_
57.7
53.0
50.6
-
-
53.2
55.8
52.4
-
_
52.9
51.2
52.6
52.2
0.3
0.1
0.1
1.5
-
0.7
0.5
1.8
-
-
3.4
2.5
4.7
-
-
2.3
1.8
7.7
-
-
7.1
5.8
2.5
3.3
0.02
0.02
Trace
Trace
-
0.05
0.1
0.2
-
-
0.5
0.8
0.6
-
-
0.3
0.4
0.4
-
-
2.5
1.8
0.5
0.6
WELL FLOW TOTAL FLOW RATE
RATE FROM ALL WELLS
SCFM SCFM
110
280
160
200
230
Shut Down
360
330
310
Shut Down
Shut Down
260
250
310
Shut Down
Shut Down
310
290
350
Shut Down
Shut Down
290
265
310
90
980
1000
820
950
955
83
-------
TABLE 14 (continued)
WELL
DATE NO.
12/31/75 1
2
3
4
5
7
1/10/76 1
2
3
4
5
1/11/76 1
2
3
4
5
7
PERCENTAGE (VOLUME)
C02 CH_4 N£ 02
41.6
41.4
41.8
42.0
42.5
46.0
45.6
39.2
45.1
42.9
45.8
38.3
-
41.8
42.7
42.5
53.3
54.6
52.2
53.3
56.2
51.1
52.7
51.1
52.9
54.5
53.1
61.1
-
57.1
55.4
56.5
3.5
3.1
2.7
2.8
1.0
2.3
1.5
7.6
1.6
2.2
0.9
0.5
-
0.9
1.7
0.8
1.6
0.8
0.4
1.9
0.3
0.6
0.2
2.1
0.3
0.4
0.2
0.1
-
0.2
0.18
0.15
WELL FLOW TOTAL FLOW RATE
RATE FROM ALL WELLS
SCFM SCFM
Shut Down
290
290
310
75
75
58
250
95
172
90
75
240
Shut Down
165
84
75
1040
925
639
Source: Los Angeles County Sanitation Districts
84
-------
Water removal is accomplished by cooling the gases below the dew
point of water. This causes the water vapor to condense and separate from
the gas stream. This process has two advantages: (1) the load on the
adsorbent bed is reduced as a result of the water vapor being removed by
condensation in the cooler, and (2) the capacity of the adsorbent is
slightly increased because of the lower temperature. The water removed in
this fashion is collected and injected back into the landfill at depths
well below the ground level via an underground piping system. The quantity
of water will vary from 10 to 15 gallons per hour depending upon climatic
conditions and the volumetric flow rate of raw landfill gas.
The gas leaving the water removal operation then passes through
two pretreater towers which remove the adorous compound H2S and free water
vapor. The adsorbent used in the pretreater towers is a molecular sieve.
The regeneration of the adsorbent bed is accomplished by thermal-swing
cycle. In this process a heated gas stream is recirculated through the
towers, heating the beds to the temperature required to release the
adsorbed contaminants. Maximum energy saving is accomplished by using the
contaminated effluent from the pretreater and adsorption towers as fuel to
heat the regeneration system. The remaining contaminated gas stream is
incinerated in the waste gas burner, where the sulfur-bearing compounds
are oxidized to S02-
The purification plant also consists of six molecular sieve
adsorption towers to remove carbon dioxide. The molecular sieve adsorption
beds undergo an adsorption-desorption cycle on an intermittent basis to
provide continuous production of gas. On the desorption cycle the vessel
is depressurized to release the C02. The C02, which contains four percent
methane, is then routed to the waste gas'burner, where methane is oxidized
to C02 and water. The composition of the combusted exhaust gas is given in
Table 15. Upon completion of the desorption cycle the vessel is pressur-
ized and put back on stream.
The product gas undergoes the final stage of compression to 175
psi required by the Southern California Gas Company. The product gas
composition is given in Table 15.
C. Methane Gas Production and Consumption
Table 13 indicates the total amount of methane gas produced, the
amount of methane gas consumed (gas sold back to RSF to operate their
facilities), and the net amount of methane gas delivered to Southern
California Gas Company's pipeline (see Figure 35). During the months of
June, July, and October 1975 and part of February 1976, the methane con-
sumption rate was higher than the production rate. Out of a total of
31,840 MSCF of methane gas produced, approximately 19,886 MSCF (62 percent)
was consumed to operate the purification plant.
During the initial four months, approximately 50 percent by volume
of the total raw landfill gas extracted was produced as pure methane gas.
After that, this ratio dropped, ranging from 12 to 27 percent. The loss in
production capacity was blamed on an infiltration of air at an increased
85
-------
CO
> CONSUMPTION (MMSCF)
M A «
O O O
<
o
CUMMULATIVE GAS PRODUCT!
ZO 0 0
— — PROD
CONS
______
UCTION
UMPTION
W JUNE JULY AUGUST SEPTEMBER OCTOBER NOVEMBER DECEMBER JANUARY FEBRUARY
I97S 1976
FIGURE 35: PALOS VERDES LANDFILL-
CUMMULATIVE METHANE PRODUCTION AND CONSUMPTION
SOURCE: SOUTHERN CALIFORNIA GAS CO., LOS ANGELES
-------
TABLE 15
SALES AND COMBUSTION GAS STREAM
(Volume Percentage)
Hydrogen (H2)
Oxygen (02)
Nitrogen (N2)
Carbon Dioxide (C02)
Hydrogen Sulfide (H2S)
Methane (CH4)
Carbon Compounds
Water (H20)
Sulfur Dioxide (S02)
Free Air (by Difference)
SALES GAS (IN %) COMBUSTED GAS (IN %)
0.1047
0.1299
0.5072
75.0
99.2458
0.0124
6.999986
0.000014
18.0
100.0000
100.00000
Source: Reserve Synthetic Fuels, Inc.
87
-------
withdrawal rate causing an increase in nitrogen content in the landfill
gas. Since the existing RSF gas purification plant does not remove
nitrogen, the product methane gas is lower in heating value. As a result
of this problem, RSF was unable to sell a significant amount of product
gas to the Southern California Gas Company.
During the time span of 264 working days, the gas extraction
and purification system was under operation for only 204 days. A total
of approximately 31,840 MSCF of 99 percent methane gas was produced. The
purification plant was operating at 16.6 percent of its suggested produc-
tion capacity. The total saleable energy production during this period
was approximately 31.84 x 109 Btu based on the average heating value of
1000 Btu/SCF.
D. Economic Evaluation
The discussion on this gas purification system would be incom-
plete without conducting an economic evaluation. According to the contract,
the Los Angeles County Sanitation District is to receive the royalty after
RSF has extracted 525,600 MSCF of raw gas or 12 months from the date of
plant completion (June 1, 1975). Therefore, at this stage, the Sanitation
Districts are not yet earning any profit on the investment they have made
to drill and construct extraction wells. Based on the net energy production
(11.95 x 109 Btu) and maximum control price of $2.50 per million Btu, the
following conclusions can be drawn as of February 12, 1976:
Gross Income $29,886
Los Angeles County Sanitation
District's Royalty 0
Interest on one million dollars
for 264 days (based on 7.5 percent
annual rate) 54,246
Deficit $24,360
These calculations do not include operational, engineering, and
administrative expenses. It appears that RSF is not producing a net profit
at this stage of the operation. However, looking at the complexity of the
gas recovery and purification system it is advisable to wait another year
before a meaningful and rational economic evaluation can be made.
88
-------
CHAPTER VII
FIRE HAZARD AND SAFETY
The combustion and ignition of methane in air depends upon lower
and upper methane inflammability limits, pressure, and temperature (Ref. 43,
44). Based on these parameters, the possibility of fire and explosion at
various landfill locations may be evaluated. Therefore, in this section, the
mechanism of methane oxidation and ignition will be discussed.
The ignition of flame (such as of methane) is always a result of the
progressive auto acceleration of reaction, which becomes possible only under
definite thermal conditions brought about by an external source such as the
presence of flame, adiabatic compression, and possible spark from impact (flint
and steel). The rate of any chemical reaction increases with temperature accord-
ing to the Arrhenius equation:
^ = ko exp (- E/RT)
Where, E, the activation energy, is the energy required
for the internal reorientation of the reacting molecules.
And T, is the absolute temperature of the reacting mixture.
In the case of exothermic reaction, which includes all reactions of
fuel combustion, there is always some temperature at which the rate of heat
evolution due to the reaction begins to exceed the rate of heat removal from
the reacting gas mixture. This will cause the increase in temperature, reaction
rate and uncontrollable rate of heat evolution which is characterized as igni-
tion - at the ignition temperature. The ignition temperature is a function of
pressure and the concentration of methane in the air stream. Figure 36 illu-
strates the effect of pressure on the ignition temperature in an air mixture
containing 13 percent methane. At one atmosphere pressure, the ignition
temperature lies within the range of 800-900° C. At low methane concentration
(about 3 percent and less) the ignition temperature also depends on formation
of intermediate products such as carbon monoxide and formaldehyde. Sokolik
(Ref. 45) reported that the ignition process is retarded by the formation of
formaldehyde. The lower and upper inflammability limits of methane and air
mixture are between 5-15 percent at one atmosphere and 25° C.
In the landfill gas recovery and purification processes where the
methane concentration is very high, as well as temperature and pressure above
ambient conditions, the possibility of a fire hazard exists. Air leaks on the
suction side at landfill wells, pipeline, and suction blower may result in the
formation of an explosive mixture. At these locations, an oxygen analyzer may
be used to detect the oxygen content of the gas coming into the plant. This is
done to prevent the possibility of an explosive mixture of air and gas being
generated. In the case of excessive oxygen concentration, the compressor
should be shut down, thereby stopping all the processes.
89
-------
900-1
vo
o
800-
O
o
cc
K
O 600
E
CS
500-
400-
METHANE INFLAMMABILITY LIMITS (IN AIR)
LOWER- 5%
UPPER-15%
IGNITION TEMPERATURE = 800°C, AT latm.
ADIABATIC FLAME TEMPERATURE = 1862° C
•13% METHANE-AIR MIXTURE
10 15 20
PRESSURE IN ATMOSPHERE
25 28
FIGURE 36= IGNITION TEMPERATURE OF METHANE-AIR MIXTURE
-------
Gas leaks on the purification plant side at the compressor, pipe-
line, and different processing units into the atmosphere may also result in
fire and explosion. Various safety methods used at the Palos Verdes gas
purification plant are discussed in the EIR (Ref. 18).
91
-------
CHAPTER VIII
CONCLUSIONS
(1) The potential total energy that could be derived from sanitary land-
fills in Los Angeles County represents approximately 0.5 percent of
the total natural gas consumption in Los Angeles County.
(2) The generation and recovery of landfill methane gas requires evalua-
tion of both physical and operating parameters. The solid waste and
fill materials should be characterized in terms of organic carbon,
volatile solid, moisture, ammonia nitrogen, and phosphorus. The
amount and kinetics of gas generation is believed to be governed by
these physical parameters, including pH and temperature of the fill.
(3) A typical solid waste consists of 0.25 pound of organic carbon per
pound of dry refuse.
(4) Theoretically, the gas generation rate reaches its maximum after two
to three years from fill completion, and within six years approxi-
mately 95 percent of the total estimated gas is produced.
(5) The operating parameters are evaluated to determine gas withdrawal
rate, gas composition, radius of influence (to determine number of
wells that can be located at a certain landfill configuration), energy
required to operate the gas withdrawal system, and total possible
energy production.
*
(6) An average of 4810 tons per day of waste is disposed of at the Palos
Verdes landfill. Household and commercial waste categories comprise
about 50 percent and liquid wastes comprise about 19 percent of the
total. The wastes are compacted to an in-place density ranging from
1000 to 1700 pounds per cubic yard. Refuse deposits contain an
average of 30 percent (wet weight basis) of moisture.
(7) The nitrogen and phosphorus content in Palos Verdes fill deposits are
sufficient enough to meet biological growth.
(8) At the Palos Verdes landfill, the migration of gas is reduced by
covering the final surfaces with a minimum of three feet of clean
diatomaceous earth. This cover soil is quite impermeable to gas
migration if compacted to the optimum moisture content and maximum
density.
(9) From the parcel "three" located at the Palos Verdes landfill, an
estimated total of 5.2 x 10^ cubic feet of gases will be produced.
At a gas withdrawal rate of 2.25 x 106 cubic feet per day, flows
could be sustained for approximately six years.
(10) At a withdrawal rate of 320 CFM at an experimental well, the methane
and carbon dioxide content in landfill gases are approximately 53
percent and 45 percent respectively.
92
-------
(11) A withdrawal rate of 320 SCFM will produce a radius of influence of
approximately 250 feet in a 110-foot well.
(12) From a well dug to 110 feet below the surface elevation, a pressure
drop of -13.5 inches of water will be required to extract gases at
320 SCFM.
(13) Dehydration to reduce the corrosion problem may enhance the utility
of low Btu landfill gases where they can be used on site. However,
their efficient combustion may require a proper modification in
burner design.
(14) The low Btu landfill gases may also be processed to 99 percent methane
purity to meet the pipeline standards, thus up-grading the gas to a
commercial product. The molecular sieve adsorption technique with
pressure-swing regeneration cycle appears to be well-suited to bulk
gas purification.
(15) The gas withdrawal system which RSF is operating at Palos Verdes
landfill has pumped -approximately 91,239.2 MSCF of raw landfill gas
starting from June 1, 1975 to the end of December 1975. This amount
is about 42.6 percent of the predicted (based on a withdrawal rate
of 1 MMSCF per day for 214 days).
(16) At increased withdrawal rates, the landfill gases contained substan-
tial percentages of nitrogen resulting from air leaks. This is the
main problem which RSF is facing at the Palos Verdes gas recovery
operation. Since the removal of nitrogen from landfill gases is a
very expensive process, the final product may not meet the pipeline
standards. For that reason, a significant amount of purified gas was
not bought by the Southern California Gas Company (statement by RSF).
(17) During the months of June, July, and October 1975 and part of February
1976, the methane consumption rate was higher than the production
rate. Out of a total of 31,840 MSCF of methane gas produced, approx-
imately 19,886 MSCF (62 percent) was consumed to operate RSF's
purification plant.
(18) Economic evaluation indicates that RSF is not producing a net profit
at this stage of the operation. However, these evaluations are too
immature to predict any long-term profits.
93
-------
CHAPTER IX
REFERENCES
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llth Annual Seminar and Equipment Show of the Governmental Refuse
Collection and Disposal Association, Santa Cruz, California, November
7-9, 1973.
(2) Chemical and Engineering News, 48, 34-35, March 2, 1970.
(3) Chemical and Engineering News, 48, 8, March 30, 1970.
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Sacramento, 1965.
94
-------
(16) "In-Situ Investigation of Movements of Gases Produced from Decomposing
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,>
(24) Nonhebell, G., "Gas Purification Processes," George Newnes Limited,
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95
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(32) Dingman, J. C. and T. F. Moore, "Compare DGA and MEA Sweetening Methods,"
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Hot Potassium Carbonate Solutions," Chem. Engr. Progress, 50(7), 356, 1954.
(35) Maddox, R. N. and M. D. Burns, "Designing a Hot Carbonate Process," The
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The Oil and Gas Journal, pp. 167-173, October 9, 1967.
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Methane System," Industrial and Engineering Chemistry, Vol. 46, No. 3,
pp. 511-517, March 1954.
(38) Breck, D. W., "Zeolite Molecular Sieves," John Wiley and Sons, 1974.
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(40) Collins, J. J., "Molecular Sieves in the Process Industries," Chemical
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The Oil and Gas Journal, pp. 86-90, July 11, 1960.
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(43) Lewis, B. and G. Von Elbe, "Combustion, Flames and Explosions of Gases,"
Academic Press Inc., New York, 1961.
(44) Zabetakis, M. G., "Biological Formation of Flammable Atmospheres," Report
R. I. 6127, Washington, U. S. Department of the Interior, Bureau of Mines,
1962.
(45) Sokolik, A. S., "Self-Ignition, Flame and Detonation in Gases," Israel
Program of Scientific Translations, Jerusalem, 1963.
96
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CHAPTER X
BIBLIOGRAPHY
GENERAL
P & GO Staff Report, "Gas From Garbage - A Reality in Southern California,"
Pipeline and Gas Journal, September 1975.
"Oilfield Gas Processor Hunts Methane on Landfill," Solid Wastes Management,
May 1975.
"First Landfill Plant Dedicated; Shredding Approach Also Gets Nod," Solid
Waste Systems, July/August 1975.
Goeppner, J. and D. E. Hasselmann, "Digestion By-Products May Give Answer to
Energy Problem," Water and Wastes Engineering, pp. 30-35, April 1974.
Savery, W. and D. C. Cruzan,. "Methane Recovery from Chicken Manure Digestion,"
Journal of Water Pollution Control Federation, Vol. 44, No. 12, pp. 2349-2354,
December 1972.
Knight, M., "Landfill Site Provides Gas for 3,500 Homes," The Christian Science
Monitor, Wednesday, September 10, 1975.
Mandeville, R. T., "Fuel Gas from Landfill," Reserve Synthetic Fuels, Inc.,
Newport Beach, California.
"Supplemental Gas from Urban Sanitary Landfills," Gas Industries, October 1975.
"Methane Recovery - Palos Verdes Sanitary Landfill," Reserve Synthetic Fuels,
Inc., Newport Beach, California.
Peacock, H., "Methane Gas from Solid and Liquid Wastes in Rolling Hills Estates
Experiment," Western City, November 1975.
Nicholson, T., J. Bishop, and P. Greenberg, "Energy: How Scarce the Gas,"
Newsweek, October 20, 1975.
"LADWP Staff Report Recommends Expanding Methane Recovery from Landfills,"
Electrical Week, July 7, 1975.
LANDFILL GAS GENERATION AND RECOVERY
Carlson, J., "Methane Recovery from Sanitary Landfills," Presented at the
Seventh Annual Western Regional Solid Waste Symposium, San Jose, California,
April 7-8, 1975.
Jones, M. R,, "Methane Gas Recovery from Sanitary Landfills - A Promising
Energy Source," Presented at the Third National Congress on Waste Management
Technology and Resource Recovery, November 14-15, 1974.
97
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Merz, R. C., "Investigation to Determine the Quantity and Quality of Gases
Produced During Refuse Decomposition," Final Report, University of Southern
California, Los Angeles, Department of Civil Engineering, August 1964.
Merz, R. C. and R. Stone, "Gas Production in a Sanitary Landfill," Public Works,
95(2), February 1964.
Merz, R. C. and R. Stone, "Sanitary Landfill Behavior in an Aerobic Environment,"
Public Works, 97(1): 67-70, January 1966.
Fungaroli, A. A., "Instrumentation of Two Experimental Sanitary Landfills,"
IEEE Transactions on Geoscience Electronics, Vol. GE-8, No. 3, July 1970.
Carlson, J. A., "Shoreline Regional Park Gas Recovery Program," Progress Report
for Phase I, City of Mountain View, January 1975.
"Landfill Decomposition Gases - An Annotated Bibliography," National Technical
Information Service, U. S. Department of Commerce, PB-213487, June 1972.
Pacey, J. G., and R. S. Altmann, "Methane Gas in Landfills: Liability or Asset?",
Emcon Associates, San Jose, California, October 1975.
Lawrence, A. W. and P. L. McCarty, "Kinetics of Methane Fermentation in Anaerobic
Treatment," Journal of Water Pollution Control Federation, Vol. 41, No. 2, Part
2, February 1969.
McCarty, P. L., "Anaerobic Waste Treatment Fundamentals: Part One - Chemistry
and Microbiology," Public Works, September 1964.
McCarty, P. L., "Anaerobic Waste Treatment Fundamentals: Part Two - Environ-
mental Requirements and Control," Public Works, October 1964.
McCarty, P. L., "Anaerobic Waste Treatment Fundamentals: Part Three - Toxic
Materials and Their Control," Public Works, November 1964.
McCarty, P. L., "Anaerobic Waste Treatment Fundamentals: Part Four - Process
Design," Public Works, December 1964.
Rhyne, C. W., "Landfill Gas," Office of Solid Waste Management Programs, U. S.
Environmental Protection Agency, April 4, 1974.
Rhyne, C. W. and T. V. DeGeare, Jr., "Energy Recovery from Sanitary Landfills,"
Office of Solid Waste Management Programs, U. S. Environmental Protection Agency.
LANDFILL GAS MIGRATION
Bishop, W. D., R. C. Carter, and H. F. Ludwig, "Gas Movement in Landfilled
Rubbish," Public Works, 96(11): 64-68, November 1965.
Van Bavel, C.H.M., "Gaseous Diffusion and Porosity in Porous Media," Soil
Science, 73, 91-104, 1952.
98
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Callahan, G. P. and R. H. Gurske, "The Design and Installation of a Gas Migra-
tion Control System for a Sanitary Landfill," Presented at the First Annual
Symposium of the Los Angeles Forum on Solid Waste Management, Pasadena,
California, May 1971.
Blake, G. R. and J. B. Page, "Direct Measurement of Gaseous Diffusion in Soils,"
Soil Science Soc. Amer. Proc., 13, 37-42, 1948.
Perry, J. H., "Chemical Engineers Handbook," McGraw-Hill Chemical Engineering
Series, McGraw-Hill, New York, 1963.
Nosanov, M. E. and F. R. Bowerman, "Methods of Sensing Land Pollution from
Sanitary Landfills," Presented at the Joint Conference on Sensing of Environmental
Pollutants, Palo Alto, California, November 8-10, 1971.
Nosanov, M. E. and R. L. White, "Gas Control and Beneficial Use of Completed
Landfills," Public Works Magazine, November 1975.
FIRE HAZARD
MacFarlane, I. C., "Gas Explosion Hazards in Sanitary Landfills," Public Works,
pp. 76-78, May 1970.
"Methane Blamed for Fatal Blast in Sewer Tunnel," Engineering News-Record,
November 20, 1975.
"Methane Gas Explosions Delay Building on a Landfill," Solid Wastes Management-
Refuse Removal Journal, 12(7), July 20, 1969.
99
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APPENDIX
THEORETICAL CORRELATION OF OPERATING PARAMETERS
FOR LANDFILL GAS EXTRACTION
1 1 FORMAT ('I1,1 FG RE Q/C1 -DELTA P/C2 '/)
2 2 FORMAT (' ' F10.3, F 10.2, F14.5, F14.5)
3 DIMENSION RE(10)
4 WRITE (6,1)
5 RW = 0.25
6 READ, (RE(N), N=1.9)
7 READ, FG
8 5 DO 20 1=1,9
9 R = RE(I) *RE(I)
10 P = RW *RW
11 Q = 5.97* (R-P) *FG* 0.000001
12 DP = 0.006 *FG* (R*ALOG(RE(I)/RW)-0.5* (R-P)
13 20 WRITE (6,2) FG, RE(I), Q.DP
14 READ, FG
15 IF (FG.NE.0.0) GO TO 5
16 WRITE (6,1)
17 STOP
18 END
ENTRY
100
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TABLE 16
THEORETICAL CORRELATION OF OPERATING PARAMETERS
FOR LANDFILL GAS EXTRACTION
0
0.060
0.060
0.060
0.060
0.060
0.060
0.060
0.060
0.060
0.100
0.100
0.100
0.100
0.100
100
0.100
0.100
0.100
0.150
0.150
0.150
0.150
0.150
0.150
0.150
0.150
0.150
0.200
0.200
0.200
0.200
0.200
0.200
0.200
200
200
0.250
0.250
0.250
250
250
0.250
0.250
250
250
0.300
0.300
0.300
0.300
0.300
0.300
0.300
0.300
0.300
0.
0.
0.
0.
0.
0.
Re
0.25
50.00
100.00
150.00
200.00
250.00
300.00
350.00
400.00
0.25
50.00
100.00
150.00
200.00
250.00
300.00
350.00
400.00
0.25
50.00
100.00
150.00
200.00
250.00
300,00
350.00
400.00
0.25
50.00
100.00
150.00
200.00
250.00
300.00
350.00
400.00
0.25
50.00
100.00
150.00
200.00
250.00
300.00
350.00
400.00
0.25
50.00
100.00
150.00
200.00
250.00
300.00
350.00
400.00
Q/C1
0.00000
0.00090
0.00358
0.00806
0.01433
0.02239
0.03224
0.04388
0.05731
0.00000
0.00149
0.00597
0.01343
0.02388
0.03731
0.05373
0.07313
0.09552
0.00000
0.00224
0.00895
0.02015
0.03582
0.05597
-0.08059
0.10970
0.14328
0'. 00000
0.00298
0.01194
0.02686
0.04776
0.07462
0.10746
0.14626
0,19104
0.00000
0.00373
0.01492
0.03358
0.05970
0.09328
0.13432
0.18283
0.23880
0.00000
0.00448
0.01791
0.04030
0.07164
0.11194
0.16119
0.21940
0.28656
-DELTA P/C2
0.
4.
.00000
.31849
19.76927
47.76511
89.05838
144.17440
213.51840
297.42010
396.15860
0.00000
7.19749
32.94879
79.60854
148.43060
240.29080
355.86400
495.70060
660.26460
0.00000
10.79624
49.42319
119.41270
222.64590
360.43600
533.79580
743.55070
990.39670
0.00000
14.39498
65.89760
159.21700
296.86130
480.58150
711.72820
991.40130
1320.52900
0.00000
17.99373
82.37201
199.02130
371.07660
600.72680
889.66040
1239.25100
1650.66100
0.00000
21.59247
98.84641
238.82550
445.29190
720.87230
1067.59200
1487.10200
1980.79300
101
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
EPA-600/3-77-047
3. RECIPIENT'S ACCESSION-NO.
. TITLE AND SUBTITLE
A Case Study Of The Los Angeles County
Palos Verdes Landfill Gas Development Project
5. REPORT DATE
July 1977 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
. AUTHOR(S)
Frank R. Bowerman, Naresh K. Rohatgi, Kenneth Y. Chen,
and R. A. Lockwood
8. PERFORMING ORGANIZATION REPORT NO.
. PERFORMING ORGANIZATION NAME AND ADDRESS
COM, Inc., Environmental Engineers
283 South Lake Avenue
Pasadena, California 91101
10. PROGRAM ELEMENT NO.
IDB 314; 21BFS
11. CONTRACT/GRANT NO.
68-03-2143
.2. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
Municipal Environmental Research Laboratory--Cin.,OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
14. SPONSORING AGENCY CODE
EPA/600/14
5. SUPPLEMENTARY NOTES
Project Officer: Charles J. Rogers
e.ABSTRACT This report documents the first-ever-attempt to capture sanitary landfill
gases and beneficiate them to natural gas pipeline quality—or very nearly so. For
this reason the authors must credit the entrepreneurs for a successful first full-
scale demonstration of a technology that'produces very nearly pure methane and wish to
compliment the Los Angeles County Sanitation Districts for the willingness, coopera-
tion, and technical assistance that made the demonstration possible. Herein lies an
excellent example of local government and industry working together to produce results
that may have ultimate benefits for people throughout the nation and the world.
That this demonstration failed to show an economic viability during the twelve-month
study period only suggests that further consideration should be given to improving the
dependability of the molecular sieve process for landfill gas beneficiation, to the
study of alternative beneficiation processes, and/or alternative uses for less modified
landfill gases. Perhaps more serious consideration should be given to the use of
landfill gas with little or no modification, except perhaps moisture removal. Recipro-
cating piston engines, rotary turbines, steam generators, air heaters, and a host of
other devices can be fueled successfully with mixtures of methane, carbon dioxide, and
small amounts of other gases, provided the heat content is not below certain critical
levels. Landfill gases present an energy resource - modest as it is - that should be
d ut
d_uh
d-ub
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Methane, Carbon Dioxide
Anaerobic processes
Materials recovery
Cellulose
Decomposition
Gas benefication
Municipal solid waste
Methane production
13B
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)
112
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
102
OmC£H77-757-0 56/6471
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