SRI/USEPA-GHG-VR-32
September 2004
Environmental
Technology
Verification Report
NATCO Group, Inc. - Paques
THIOPAQ Gas Purification Technology
«EPA
Prepared by:
Greenhouse Gas Technology Center
Southern Research Institute
Under a Cooperative Agreement With
U.S. Environmental Protection Agency
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EPA REVIEW NOTICE
This report has been peer and administratively reviewed by the U.S. Environmental Protection Agency, and
approved for publication. Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
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THE ENVIRONMENTAL TECHNOLOGY VERIFICATION PROGRAM
oEPA
U.S. Environmental Protection Agency
SOUTHERN RESEARCH
INSTITUTE
ETV Joint Verification Statement
TECHNOLOGY TYPE:
APPLICATION:
TECHNOLOGY NAME:
COMPANY:
ADDRESS:
WEB ADDRESS:
Sour Gas Processing System
Biogas Purification
Paques THIOPAQ
NATCO Group, Inc.
Brookhollow Central III, 2950 N. Loop West, Suite,
100, Houston, Texas 77092
www. natcogroup. com
The U.S. Environmental Protection Agency (EPA) has created the Environmental Technology
Verification (ETV) program to facilitate the deployment of innovative or improved environmental
technologies through performance verification and dissemination of information. The goal of the ETV
program is to further environmental protection by accelerating the acceptance and use of improved and
cost-effective technologies. ETV seeks to achieve this goal by providing high-quality, peer-reviewed data
on technology performance to those involved in the purchase, design, distribution, financing, permitting,
and use of environmental technologies.
ETV works in partnership with recognized standards and testing organizations, stakeholder groups that
consist of buyers, vendor organizations, and permitters, and with the full participation of individual
technology developers. The program evaluates the performance of technologies by developing test plans
that are responsive to the needs of stakeholders, conducting field or laboratory tests, collecting and
analyzing data, and preparing peer-reviewed reports. All evaluations are conducted in accordance with
rigorous quality assurance protocols to ensure that data of known and adequate quality are generated and
that the results are defensible.
The Greenhouse Gas Technology Center (GHG Center), one of six verification organizations under the
ETV program, is operated by Southern Research Institute in cooperation with EPA's National Risk
Management Research Laboratory. A technology area of interest to some GHG Center stakeholders is
reliable renewable energy sources. The generation of heat and power at industrial, petrochemical,
agricultural, and waste-handling facilities with renewable energy sources such as anaerobic digester gas
(biogas) or landfill gas is a particular interest. Removal of the harmful components of biogases (primarily
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hydrogen sulfide and other sulfurous compounds) while minimizing the creation of secondary waste
streams and effluents is essential to development of these renewable energy sources. NATCO Group, Inc.
(NATCO), located in Houston, Texas, has requested that the GHG Center perform an independent
performance verification of the Paques THIOPAQ technology - a gas purification system.
TECHNOLOGY DESCRIPTION
The following technology description is based on information provided by NATCO and Paques and does
not represent verified information. This technology, developed in The Netherlands by Paques
BioSystems, is designed to safely and efficiently remove hydrogen sulfide (H2S) from biogas and other
sour gases while minimizing the generation of harmful emissions or effluents. The process is suitable to
applications where the processed biogas can be utilized as fuel. The system also allows the production of
elemental sulfur for subsequent sale or use. A variation of this technology is the Shell-Paques system,
which operates on the same principles as THIOPAQ, but includes system components that can process
low-, medium-, and high-pressure natural gas as well as acid gas and Claus tail gas.
The Paques desulfurization technology is a caustic scrubber-based system designed to maintain a high
level of H2S removal while addressing several shortcomings of conventional technologies. This
technology is designed by Paques Biosystems to: (1) reduce hazardous effluents from the scrubber by
aerobically digesting the waste into a more benign sulfurous product, and (2) regenerate and recycle
sodium hydroxide (NaOH) needed in the scrubber. The THIOPAQ system is specifically designed for
low-pressure biogas streams.
The THIOPAQ process begins with the input of biogas or sour gas into an absorber unit (or scrubber) at
ambient pressure. Scrubber design is site-specific in regards to vessel size, construction specifications,
and gas and solution flow capacities. System pH ranges from 8.2 to 9. The counter-current scrubber
design washes the sour gas or biogas with caustic solution in a packed bed or packed beds containing 2-
inch Pall rings. Treated gas (sweet gas) exits the scrubber top, enters a knockout drum, and is routed for
on-site use or to a sales gas stream.
The liquid stream is then sent to the bioreactor (ambient pressure) where caustic solution is regenerated
through a series of chemical reactions and biological oxidation of dissolved sulfide. A blower supplies air
to a distribution header in the bottom section of the reactor to enhance mixing. Some of the oxygen is
consumed in reactions with sulfide to produce sulfur by the actions of the Thiobacillus bacteria. The
bacteria are maintained using a continuous feed of proprietary nutrients supplied by Paques. These
nutrients are pumped into the bioreactor with a small metering pump. Regenerated solvent from the
bioreactor is pumped back to the scrubber for reuse.
VERIFICATION DESCRIPTION
The GHG Center tested a THIOPAQ system installed and operating at a 40 million gallons per day
(MGD) water pollution control facility (WPCF) designed to process industrial wastewater streams from
numerous local companies including grain and food processing plants and a paper mill. Approximately
three MGD of flow coming from the paper mill is pretreated in three upflow anaerobic sludge blankets
(UASBs). Each UASB generates around 100 to 200 cubic feet per minute (cfm) of biogas (generally 60
percent CH4, 38 percent CO2, and 1 to 2 percent H2S). The gas generated in each UASB is collected and
used to fuel a sludge incinerator within the plant that is capable of consuming all of the biogas generated
on-site under normal plant operations. The biogas is flared during rare occurrences when the incinerator
is not operating or is being fueled with natural gas.
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Field tests were performed on June 29 through July 1, 2004 on the THIOPAQ system to independently
verify the performance of this technology. One-month (June 1 through July 1, 2004) of process
monitoring data was provided by the facility to allow the GHG Center to evaluate system operations over
a longer term. The verification included evaluation of both environmental and operational performance
of the system.
Environmental Performance
• Air Emissions
• Liquid Effluent
Operational Performance
• H2S Removal Efficiency
• Gas Composition and Quality
• NaOH Consumption
• Sulfur Product Purity
Nine grab samples were collected during the verification period to directly measure the concentrations of
H2S and other sulfur compounds emitted to the atmosphere from the bioreactor vent. Vent gas flow rates
were not determined due to difficulties with cyclonic and highly variable flow. Therefore, vent gas
emissions are reported as estimates only. Seven bioreactor slurry samples were collected to determine the
sulfates, sulfides, and total suspended solids (TSS) content of liquids disposed from the system as
wastewater.
For verification of operational performance, nine corresponding biogas grab samples were collected on
both the upstream and downstream sides of the THIOPAQ system and submitted for analysis. Results of
the analyses were used with biogas flow rates through the system to evaluate system removal efficiency
for H2S and other sulfur compounds. The results also allowed the center to evaluate the effects of the
system on biogas composition and heating value. NaOH consumption rates were monitored and reported,
and composite solid waste samples from the system were collected for determination of elemental sulfur
content. Plans to measure the amount of solids produced by the system were abandoned during field
testing. The facility only wastes solids every three weeks or so on an as-needed basis. The frequency and
amount of solids removed varies widely depending on the amount of solids removed through the liquid
effluent. Removal of solids cake at this facility was operator specific and infrequent, therefore, it was
deemed too arbitrary for verification here. Because of this, a sulfur mass balance could not be completed
for the system.
Quality assurance (QA) oversight of the verification testing was provided following specifications in the
ETV Quality Management Plan (QMP). The GHG Center's quality manager conducted a technical
systems audit (TSA) and an audit of data quality (ADQ) on at least 10 percent of the data generated
during this verification. Two performance evaluation audits (PEAs) were also conducted. The GHG
Center field team leader and project manager have reviewed the data from the verification testing and
have concluded that the data quality objectives specified in the Test and Quality Assurance Plan were
attained for the verification parameters that were evaluated (excluding vent gas emission rates and solids
production rates).
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VERIFICATION OF PERFORMANCE
Environmental Performance
• Concentrations of H2S and total sulfur compounds in the air vented from the bioreactor were very low
averaging 929 and 1,961 ppbv, respectively. H2S typically comprised about half of the total sulfur
compound concentrations, and methyl mercaptan, dimethyl sulfide, and dimethyl disulfide were the other
prominent compounds.
• Vent gas flow rates were not determined due to difficulties with cyclonic and highly variable flow.
Using air flow rates into the reactor logged by the facility, the estimated average reactor vent emission
rates for H2S and total sulfur compounds were 0.0012 and 0.0026 pounds per hour, respectively.
• The average sulfate, sulfide, and TSS concentrations in the bioreactor effluent were 3,480, 2,030, and
20,130 milligrams per liter, respectively.
• The average bioreactor effluent disposal rate during the 1-month monitoring period was 110 gallons per
hour, or about 2,600 gallons per day. Resulting sulfate, sulfide, and TSS effluent disposal rates are 77,
45, and 444 pounds per day, respectively.
Operational Performance
• Biogas flow rates through the system during the three-day sampling period ranged from 119 to 504
standard cubic feet per minute (scfm) and averaged 322 scfm [or approximately 464 thousand cubic feet
perday(103cfd)].
• Table S-l summarizes the sour and processed gas average composition, H2S content, and heat content for
nine samples collected before and after the THIOPAQ system. The average H2S removal efficiency on a
mass basis was 99.8 percent. Biogas lower heating value (LHV) increased by approximately 8.6 percent
due to changes in gas composition, specifically, removal of some of the CO2 from the sour biogas.
Table S-l. Composition and Properties of Sour and Processed Biogas - Dry Basis
Avg. Sour Gas
Avg. Processed Gas
Gas Composition
CH4(%)
62.44
68.89
CO2(%)
33.75
28.71
N2(%)
1.89
2.03
H2S (ppm)
19318
27.5
Total S
(ppm)
19336
42.9
Higher and lower heating
values (Btu/scf)
HHV
633.9
685.6
LHV
568.6
617.2
Relative
Density
0.8970
0.8454
Compres-
sibility
0.9970
0.9972
During a continuous NaOH tank level monitoring period of 376 hours, a total of 947 gallons of 50-
percent NaOH solution was consumed for an average consumption rate of 2.52 gal/hr (60.5 gal/day). The
average sour biogas feed rate during that monitoring period was 355 scfm (or 511 x 103cfd) with an
average 1.93 percent sulfur content. The average 50-percent NaOH consumption normalized to biogas
feed rate was 0.12 gallons per thousand cubic foot of biogas processed, or 0.44 Ib NaOH per Ib sulfur.
The average elemental sulfur content of the solids cake samples was 43.6 percent (wet basis). On a dry
basis, elemental sulfur averaged 59.2 percent.
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Details on the verification test design, measurement test procedures, and Quality Assurance/Quality
Control (QA/QC) procedures can be found in the Test Plan titled Test and Quality Assurance Plan -
Paques THIOPAQ and Shell-Paques Gas Purification Technology (SRI 2004). Detailed results of the
verification are presented in the Final Report titled Environmental Technology Verification Report for The
Paques THIOPAQ Gas Purification Technology (SRI 2004). Both can be downloaded from the GHG
Center's web-site (www.sri-rtp.com) or the ETV Program web-site (www.epa.gov/etv).
Signed by Lawrence W. Reiter, Ph.D. 9/29/04 Signed by Stephen D. Piccot 9/20/04
Lawrence W. Reiter, Ph.D. Stephen D. Piccot
Acting Director Director
National Risk Management Research Laboratory Greenhouse Gas Technology Center
Office of Research and Development Southern Research Institute
Notice: GHG Center verifications are based on an evaluation of technology performance under specific,
predetermined criteria and the appropriate quality assurance procedures. The EPA and Southern Research Institute
make no expressed or implied warranties as to the performance of the technology and do not certify that a
technology will always operate at the levels verified. The end user is solely responsible for complying with any and
all applicable Federal, State, and Local requirements. Mention of commercial product names does not imply
endorsement or recommendation.
EPA REVIEW NOTICE
This report has been peer and administratively reviewed by the U.S. Environmental Protection Agency, and
approved for publication. Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
S-5
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SRI/USEPA-GHG-VR-32
September 2004
Greenhouse Gas Technology Center
A U.S. EPA Sponsored Environmental Technology Verification ( jrfif ) Organization
Environmental Technology Verification Report
NATCO Group, Inc. - Paques THIOPAQ Gas Purification
Technology
Prepared By:
Greenhouse Gas Technology Center
Southern Research Institute
PO Box 13825
Research Triangle Park, NC 27709 USA
Telephone: 919/806-3456
Under EPA Cooperative Agreement CR 829478
U.S. Environmental Protection Agency
Office of Research and Development
National Risk Management Research Laboratory
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711 USA
EPA Project Officer: David A. Kirchgessner
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TABLE OF CONTENTS
Page
LIST OF FIGURES iii
LIST OF TABLES iii
ACKNOWLEDGMENTS iv
ACRONYMS AND ABBREVIATIONS v
1.0 INTRODUCTION 1-2
1.1. BACKGROUND 1-2
1.2. PAQUES THIOPAQ TECHNOLOGY DESCRIPTION 1-3
1.2.1. THIOPAQ Process 1-3
1.2.2. Process Chemistry 1-4
1.2.3. Host Facility Description and THIOPAQ Integration 1-5
1.3. PERFORMANCE VERIFICATION OVERVIEW 1-7
1.3.1. Environmental Performance Parameters 1-7
1.3.2. Operational Performance Parameters 1-8
1.3.3. Modifications to TQAP 1-9
Vent Flow Measurement 1-9
Collection of Vent Gas 1-10
Collection of sour and processed biogas samples 1-10
Liquid NaOH Solution Flow Measurement 1-10
2.0 VERIFICATION RESULTS 2-1
2.1. ENVIRONMENTAL PERFORMANCE 2-1
2.1.1. Air Emissions 2-1
2.1.2. Liquid Effluent 2-3
2.2. OPERATIONAL PERFORMANCE 2-4
2.2.1. Gas Composition, Gas Quality, andH2S Removal Efficiency 2-4
2.2.2. NaOH Consumption 2-6
2.2.3. Sulfur Production and Purity 2-7
3.0 DATA QUALITY ASSESSMENT 3-1
3.1. DATA QUALITY OBJECTIVES 3-1
3.2. ENVIRONMENTAL PERFORMANCE PARAMETERS 3-1
3.3. OPERATIONAL PERFORMANCE PARAMETERS 3-3
3.4. VERIFICATION AUDITS 3-4
4.0 TECHNICAL AND PERFORMANCE DATA SUPPLIED BY NATCO GROUP 4-1
5.0 REFERENCES 5-1
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LIST OF FIGURES
Page
Figure 1-1 Simplified THIOPAQ System Schematic 1-3
Figure 1-2 THIOPAQ System Tested 1-5
Figure 2-1 Biogas and Reactor Air Flow Rates During Testing 2-2
Figure 2-2 Biogas Composition Before and After the THIOPAQ 2-5
Figure 2-3 NaOH Consumption During Verification Period 2-6
LIST OF TABLES
Page
Table 1-1 Host Site THIOPAQ Monitoring Instrumentation 1-6
Table 2-1 Sampling Matrix 2-1
Table 2-2 Summary of Sulfur Compounds in Vent Gas Samples 2-2
Table 2-3 Total Sulfate, Total Suspended Solids, and Total Sulfides in Reactor Slurry 2-3
Table 2-4 Composition and Properties of Sour and Processed Biogas 2-4
Table 2-4 Composition of Solids Removed From the THIOPAQ Process 2-6
Table 3-1 Verification Reference Methods 3-1
Table 3-2 Summary of Vent Gas Analytical QA/QC Checks 3-2
Table 3-3 Summary of Effluent Sulfate and Sulfide Analytical QA/QC Checks 3-3
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ACRONYMS AND ABBREVIATIONS
ADQ
ASTM
Btu
Btu/scf
CAR
cfm
DQI
DQO
EPA
ETV
gal
gal/day
gal/hr
GHG Center
Ib
Ib/hr
Ib/day
LHV
mg/1
MOD
NATCO
PEA
ppbv
ppmv
QA/QC
QMP
scfm
TQAP
TSA
103cfd
UASB
WPCF
Audit of Data Quality
American Society for Testing and Materials
British thermal units
British thermal units per standard cubic foot
Corrective Action Report
cubic feet per minute
data quality indicator
data quality objective
Environmental Protection Agency
Environmental Technology Verification
U.S. gallons
gallons per day
gallons per hour
Greenhouse Gas Technology Center
pound
pounds per hour
pounds per day
lower heating value
milligrams per liter
million gallons per day
NATCO Group, Inc.
Performance Evaluation Audit
parts per billion volume
parts per million volume
Quality Assurance/Quality Control
Quality Management Plan
standard cubic feet per minute
Test and Quality Assurance Plan
technical systems audit
thousand cubic feet per day
upflow anaerobic sludge blanket
Water Pollution Control Facility
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1.0 INTRODUCTION
1.1. BACKGROUND
The U.S. Environmental Protection Agency's Office of Research and Development operates the
Environmental Technology Verification (ETV) program to facilitate the deployment of innovative
technologies through performance verification and information dissemination. The goal of ETV is to
further environmental protection by accelerating the acceptance and use of improved and innovative
environmental technologies. Congress funds ETV in response to the belief that there are many viable
environmental technologies that are not being used for the lack of credible third-party performance data.
With performance data developed under this program, technology buyers, financiers, and permitters in the
United States and abroad will be better equipped to make informed decisions regarding environmental
technology purchase and use.
The Greenhouse Gas Technology Center (GHG Center) is one of six verification organizations operating
under the ETV program. The GHG Center is managed by EPA's partner verification organization,
Southern Research Institute (Southern), which conducts verification testing of promising greenhouse gas
mitigation and monitoring technologies. The GHG Center's verification process consists of developing
verification protocols, conducting field tests, collecting and interpreting field and other data, obtaining
independent peer-reviewed input, and reporting findings. Performance evaluations are conducted
according to externally reviewed verification Test and Quality Assurance Plans (TQAP) and established
protocols for quality assurance.
The GHG Center is guided by volunteer groups of stakeholders. These stakeholders guide the GHG
Center in selecting technologies that are most appropriate for testing, help to disseminate results, and
review test plans and technology verification reports. A technology area of interest to some GHG Center
stakeholders is reliable renewable energy sources. The generation of heat and power at industrial,
petrochemical, agricultural, and waste-handling facilities with renewable energy sources such as
anaerobic digester gas (biogas) or landfill gas is a particular interest. These gases, when released to the
atmosphere, contribute millions of tons of methane emissions annually in the U.S. Cost-effective
technologies are available that can curb these emissions by processing the gases to remove harmful
constituents, recovering the methane, and using it as an energy source. Removal of the harmful
components of biogases (primarily hydrogen sulfide and other sulfurous compounds) while minimizing
the creation of secondary waste streams and effluents is essential to development of these renewable
energy sources.
NATCO Group, Inc. (NATCO), located in Houston, Texas, requested that the GHG Center perform an
independent performance verification of the Paques THIOPAQ technology - a gas purification system.
This technology, developed in The Netherlands by Paques BioSystems, is designed to safely and
efficiently remove hydrogen sulfide (H2S) from biogas and other sour gases while minimizing the
generation of harmful emissions or effluents. The process is suitable to applications where the processed
biogas can be utilized as fuel. The system also allows the production of elemental sulfur for subsequent
sale or use. A variation of this technology is the Shell-Paques system, which operates on the same
principles as THIOPAQ, but includes system components that can process low-, medium-, and high-
pressure natural gas, as well as acid gas and Claus tail gas. The Shell-Paques version is of particular
interest to the natural gas, petrochemical, and refining industries. The two versions of the technology are
similar in principle and operation, but this verification applies only to the Paques THIOPAQ version. A
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THIOPAQ system installed and operating at a midwestern water pollution control facility (WPCF) was
selected for this verification.
Field tests were performed on the Paques THIOPAQ system to independently verify the performance of
this technology. The verification included evaluations of both environmental and operational
performance of the system. Details of the verification test design, measurement test procedures, and
Quality Assurance/Quality Control (QA/QC) procedures can be found in the Test and Quality Assurance
Plan (TQAP) titled Test and Quality Assurance Plan - Paques THIOPAQ and Shell-Paques Gas
Purification Technology [1]. The TQAP describes the rationale for the experimental design, the testing
and instrument calibration procedures planned for use, and specific QA/QC goals and procedures. The
TQAP was reviewed and revised based on comments received from industry experts and the EPA Quality
Assurance Team. The TQAP meets the requirements of the GHG Center's Quality Management Plan
(QMP) and satisfies the ETV QMP requirements.
The remainder of Section 1.0 describes the THIOPAQ system technology and test facility and outlines the
performance verification procedures that were followed. Section 2.0 presents test results, and Section 3.0
assesses the quality of the data obtained. Section 4.0, submitted by NATCO, presents additional
information regarding the THIOPAQ system. Information provided in Section 4.0 has not been
independently verified by the GHG Center.
1.2. PAQUES THIOPAQ TECHNOLOGY DESCRIPTION
Renewable biogas produced from the management of municipal and farm waste is a potentially viable
energy source. Operational performance data is needed to verify the ability of technologies to remove
contaminants in biologically generated gas streams. Biogas can be made more usable and
environmentally benign if contaminants (primarily H2S) are removed prior to their use as an energy
source. Conventional H2S removal technologies such as caustic scrubbers are available, but these systems
may be costly to operate and produce hazardous effluents. Redox processes are also available, but these
require use of chelating agents and generate potentially hazardous effluents.
1.2.1. THIOPAQ Process
THIOPAQ is a biotechnological process for removing H2S from gaseous streams by absorption into a
mild alkaline solution followed by the oxidation of the absorbed sulfide to elemental sulfur by naturally
occurring microorganisms. THIOPAQ is licensed by Paques for biogas applications. The Shell- Paques
version of the technology is used for refinery gas and other high pressure applications.
The Paques desulfurization technology is a caustic scrubber-based system designed to maintain a high
level of H2S removal while addressing several shortcomings of conventional technologies. According to
NATCO, this technology is designed to: (1) reduce hazardous effluents from the scrubber by aerobically
digesting the waste into a more benign sulfurous product, and (2) regenerate and recycle sodium
hydroxide (NaOH) needed in the scrubber. The THIOPAQ system is specifically designed for low-
pressure biogas streams. NATCO states that H2S to sulfur conversion efficiency is expected to be
between 95 to 99 percent.
The THIOPAQ process begins with the input of biogas or sour gas into an absorber unit (or scrubber) at
ambient pressure. Scrubber design is site-specific in regards to vessel size, construction specifications,
and gas and solution flow capacities. System pH ranges from 8.2 to 9. The counter-current scrubber
design washes the sour gas (or biogas) in a packed bed or packed beds containing 2-inch Pall rings. A
total draw-off tray combined with a liquid redistribution tray in-between the packed beds ensures proper
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liquid redistribution. Treated gas (sweet gas) exits the scrubber top, enters a knockout drum, and is routed
to the sales gas stream.
The liquid stream is then sent to the bioreactor (ambient pressure). A blower supplies air to a distribution
header in the bottom section of the reactor, enhancing mixing. Some of the oxygen is consumed in
reactions with sulfide to produce sulfur by the actions of the Thiobacillus bacteria. The bacteria are
maintained using a continuous feed of proprietary nutrients supplied by Paques. These nutrients are
pumped into the bioreactor with a small metering pump.
Regenerated solvent from the bioreactor is pumped back to the scrubber for reuse. A portion of the
solvent from the bioreactor is also pumped to a settling tank where solids are separated from the solution
and collected gravimetrically. NATCO estimates a potential elemental sulfur purity of 95 percent in the
sludge cake from the vacuum filter press. The solution is then recycled back to the bioreactor for reuse.
A general process flow diagram of the THIOPAQ process is shown in Figure 1-1.
Processed
Gas Out
Air Vent
Sour _
Gas In"
Scrubber
Recycled Caustic
Circulation
Pump
Air
NaOH Nutrients
I Vacuum Filteil
Effluent Bleed:
*• Water and
sodium salts
Sulfur Product
Figure 1-1. Simplified THIOPAQ System Schematic
1.2.2. Process Chemistry
The reactions that drive these processes occur primarily in the scrubber and the bioreactor. The first main
reaction in the scrubber (at feed gas pressure) is H2S absorption. The H2S is absorbed by the dilute
caustic scrubber solution (NaOH) in the scrubber according to the following chemical reaction:
H2S + NaOH -> NaHS + H2O
(a)
Reaction (a) shows that solution alkalinity is consumed during this process. The solution leaving the
scrubber (NaHS + H2O) is directed to the bioreactor.
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Hydroxide ions are also consumed in the scrubber during a CO2 absorption step:
CO2 + OH^HCO3 (b)
and a carbonate formation step:
HCO3 + OH -» CO32 + H2O (c)
Note: According to NATCO, the actual amount of CO2 removed from the sour gas generally is small.
The carbonate / bicarbonate buffer moderates the solution pH to the appropriate range, providing
hydroxide ions for H2S removal and allowing for the selective removal of H2S and the slip of CO2.
The liquid stream loses the OH- ion in the scrubber and gains the OH- ion back in the bioreactor. The
bioreactor operates near atmospheric pressure and is aerated (constant mix) with a controlled inflow of
ambient air. The bacteria react with the spent scrubber solution and convert the dissolved sulfide to solid
elemental sulfur as follows:
NaHS + V2O2 -> S° + NaOH (d)
This step relies on the biological oxidation of the dissolved sulfide into elemental sulfur using aerobic
bacteria (Thiobacillus). A small portion of the dissolved sulfide (less than 5 percent) is completely
oxidized to sulfate as follows:
2NaHS+4O2 -> 2NaHSO4 <-> Na2SO4 + H2SO4 (e)
Solution alkalinity is partially regenerated in the bioreactor via the reactions in equation (d). Caustic
solution regeneration eliminates the need for a large supply of NaOH to maintain pH above 8.2. Solution
regeneration is not 100 percent as shown in equation (e), so additional make-up NaOH is required. A
controlled amount of 50-percent NaOH is added to the system continuously using a small metering pump.
An automated level sensor detects when bioreactor solution level is high, and a controlled amount of
system effluent is bled to the wastewater treatment plant influent stream, restoring proper solution level.
This bleed stream also prevents the accumulation of sulfate ions. Air leaving the bioreactor is vented to
atmosphere.
According to NATCO, the sulfur produced has a hydrophilic nature, which significantly reduces the
chance of equipment fouling or blocking. This characteristic also makes the product suitable for
agricultural use as fertilizer. Alternatively, the sulfur can be melted to yield a high-purity product which
meets international Claus sulfur specifications.
1.2.3. Host Facility Description and THIOPAQ Integration
The WPCF that hosted the THIOPAQ verification is a 40-million gallon per day (MGD) wastewater
treatment facility specifically designed to process industrial wastewater streams from numerous local
industries including grain and food processing plants and a paper mill. Approximately three MGD of
flow coming from the paper mill is characterized as low-flow, high biological oxygen demand-type waste.
The facility uses three Biothane upflow anaerobic sludge blankets (UASBs) to pre-treat this wastewater
stream. The system was designed to handle an average of 818 and a maximum 1184 cubic feet per
minute (cfm) and was built in anticipation of future plant expansion. Currently, the three UASBs
generate around 300 to 600 cfm of biogas [or around 432 to 864 thousand cubic feet per day (103cfd)].
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Biogas composition can vary but is generally 60 percent CH4, 38 percent CO2, and 1 to 1.5 percent H2S.
The gas generated in each UASB is collected, combined, compressed, and used to fuel a sludge
incinerator within the plant. The sludge incinerator will consume all of the biogas generated on-site under
normal plant operations. The biogas is flared during rare occurrences when the incinerator is not
operating or is being fueled with natural gas.
The facility installed a THIOPAQ system in 2001 to efficiently scrub H2S from the biogas prior to its use
as fuel or incineration in the flares (Figure 1-2).
Figure 1-2. THIOPAQ System Tested
The THIOPAQ system tested here has a biogas treatment capacity of 1000 cubic feet per minute, is
largely automated and PLC-controlled, and includes numerous monitoring devices to record the system
parameters shown in Figure 1-1. Table 1-1 summarizes some of the monitoring instrumentation used at
the plant.
The system at this facility decants a liquid effluent batch only about once per week. Solids are removed
by a vacuum filter press (made by Straight-Line Filter Press) approximately once every three weeks. The
facility has not yet found a buyer or user of the solid waste containing sulfur, so the solids are collected in
a large bin and disposed of in a landfill. The bioreactor vent is a two-foot diameter rain-capped vent
emitting directly to atmosphere.
1-6
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Table 1-1. Host Site THIOPAQ Monitoring Instrumentation
Parameter
Biogas flow
(generation) rate
Scrubber solution
flow rate
NaOH consumption
rate
Typical Range
100-200acfmper
each UASB
800 to l,000gpm
Approximately
1,500 Ib/day
Instrumentation
Fluid Components International,
Model ST98 thermal mass flow
meters (three total)
Promag 50/53W electromagnetic
flow monitor
Milltronics level sensor
Location
One on the outlet of
each UASB
Scrubber pump
discharge
NaOH holding tank
1.3. PERFORMANCE VERIFICATION OVERVIEW
Field tests were performed on a Paques THIOPAQ system to independently verify the performance of this
technology. Field testing by the GHG Center was conducted over a three-day period at the facility. A
one-month period of process monitoring data including biogas flow rate, NaOH consumption, bioreactor
tank level, and air flow rates into the bioreactor was provided by the facility. These data allowed the
GHG Center to evaluate these system operations over a longer term. The verification included evaluation
of both environmental and operational performance of the system.
Environmental Performance
• Air Emissions
• Liquid Effluent
Operational Performance
• H2S Removal Efficiency
• Gas Composition and Quality
• NaOH Consumption
• Sulfur Purity
Sections 1.3.1 and 1.3.2 briefly describe the sampling and analytical procedures. Detailed descriptions of
the sample collection, handling, custody, and analytical procedures that were followed during this
verification can be found in the TQAP. Several modifications to the sampling and analytical procedures
specified in the TQAP were implemented during field testing. These changes in test procedures are
discussed in Section 1.3.3.
1.3.1. Environmental Performance Parameters
Air Emissions. The bioreactor vent continuously releases vent gases to the atmosphere. The GHG Center
conducted measurements on this vent to independently verify concentrations H2S and other sulfur
compounds, if any, that are liberated from the vent. GHG Center personnel collected three vent air
samples in Tedlar bags on each of three consecutive days for analysis. Collected samples were express
shipped to Air Toxics, Ltd. in Folsom, California for next day analysis. Concentrations of H2S and other
sulfur compounds were quantified following ASTM Method D5504 [2] and reported in units of parts per
billion by volume (ppbv). Vent gas flow rates were not independently verified (see Section 1.3.3).
However, the plant continuously monitors the amount of air injected into the bioreactor. These data were
1-7
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provided to the GHG Center for use here as a surrogate for the vent air release rate since the maximum
vent volumetric flow rate should be equivalent to or less than the volumetric air input.
Liquid Effluent. The THIOPAQ system includes only one liquid effluent point - the effluent bleed
stream used to regulate solution conductivity. The THIOPAQ system reduces the volume of hazardous
liquid effluent associated with conventional wet scrubbers, but small amounts of effluent must be bled
from the system intermittently to maintain proper system pH and conductivity. This effluent, consisting
mainly of water and small amounts of sulfate and sulfides, is directed back to the wastewater treatment
facility. Under normal plant operations, it is only necessary to remove liquid effluent from the system
every week or so. Rather than attempt to capture these events and measure the volume of effluent
removed, the facility provided tank level data for a one-month period. These data allowed the GHG
Center to calculate the amount of liquid removed from the system and then determine an average weekly
effluent rate.
A total of seven liquid effluent samples were collected during the verification period and analyzed for
total sulfates (EPA Method 300.0), total sulfides (EPA Method 376.1), and total suspended solids (EPA
Method 160.2) by CT Laboratories of Baraboo, Wisconsin.
1.3.2. Operational Performance Parameters
HZS Removal Efficiency. The Center conducted three tests per day to determine the system's H2S
removal efficiency. This was done in conjunction with the environmental testing outlined above. Time-
integrated biogas samples were collected in Tedlar bags simultaneously at the inlet and outlet of the
scrubber during each test. Collected samples were express-shipped to Empact Analytical in Brighton,
Colorado for determination of H2S and 17 other sulfur-based compounds by ASTM Method 5504.
Results of each species in each sample were standardized and reported in units of parts per million by
volume (ppmv). Removal efficiency was calculated based on the measured inlet and outlet
concentrations and the biogas throughput values provided by facility instrumentation.
Gas Composition and Quality. Gas processing by the THIOPAQ system is not expected to significantly
impact gas composition or quality other than removal of H2S. The center examined gas quality before
and after treatment in the THIOPAQ to verify that gas quality was not significantly affected by treatment.
The same sets of integrated biogas samples used to determine H2S removal were analyzed by Empact to
determine gas composition according to ASTM Method D1945 [3] and lower heating value using ASTM
D3588 [4]. Results of the analysis were examined to determine if the composition and lower heating
value (LHV) of the gas are significantly changed by THIOPAQ processing.
NaOH Consumption Rate. The THIOPAQ system reduces NaOH consumption through NaOH
regeneration in the bioreactor. The host facility uses a metering pump to add NaOH to the process and a
NaOH tank level sensor to continuously monitor consumption. The center evaluated the NaOH tank level
data for a one-month period to report the NaOH consumption rate at this facility.
Sulfur Production and Purity. The sulfur containing solids cake generated by the THIOPAQ system
represents a potentially salable product. The center collected a total of five solids cake samples from the
vacuum press for determination of moisture content and to estimate elemental sulfur content. Samples
were submitted to Core Laboratories of Houston, Texas for analysis.
Process Operations. Several key operational parameters that are logged by the facility were provided to
the GHG Center to aid in post-testing data analysis. These included biogas flow rate through the system,
scrubber water flow rate, bioreactor level, NaOH tank level, and air flow rate to the bioreactor. These
-------
data, all collected by site metering equipment (Table 1-1), are not used as primary verification parameters
but are included in this report to document system operations during testing. They also allowed the center
to evaluate operational stability or variation during the verification test periods.
1.3.3. Modifications to TQAP
The procedures and protocols described in the TQAP were selected prior to visiting the WPCF. When the
testing began at the site, several changes were necessary for successful implementation. These changes
were needed to adapt the procedures to site-specific operating practices and the characteristics of the
process streams that were measured. The changes to the verification protocol are described in Corrective
Action Reports that were submitted to the GHG Center QA Manager and filed at the GHG Center. A
summary of the changes that were adopted is presented here.
Upon arrival at the test site it was noted that the settling tank described in the system design
documentation was no longer an active component of the process. Consequently, suspended solids in the
bioreactor were higher than anticipated in the test plan. It was also noted that solids removal did not
occur daily, but rather every three weeks or so after manual measurements of suspended solids passed a
threshold value. These operations were highly operator dependant and were not conducted on a regular
basis. Some operators would instead route the solids slurry back to the plant and not to the filter press for
recovery. Therefore, regular, meaningful measurements of solids recovery were not possible. Liquid
bleed for pH and conductivity control was still triggered by the bioreactor tank level and was roughly a
fixed volume (approximately 6 inches in tank level or 1,590 gallons per event). This revision of the
discharge schedule prevented the planned measurement of smaller flows as presented in the TQAP.
These process modifications and other corrections of the initial information from the plant required
changes in verification parameters and test methods. In each case the proposed changes were reviewed
by the project QA Manager and approved upon his recommendation by GHG Center management.
These configuration and operational changes in the THIOPAQ process were addressed by the following
changes in experimental design and methods:
• Elimination of direct measurement of solids production rate as non-meaningful.
• Use of plant measurements for bioreactor vent flow rate, with spot verification using vane
anemometer.
• Change in procedure for effluent disposal rate using non-verified plant data. The planned
gravimetric measurement was deleted as unworkable and replaced with data from the plant
process instruments to detect bleed event, record the level change and to quantify the
resulting volume that was removed from the reactor (a 6-inch drop equals 1,590 gallons).
• Addition of total suspended solids measurement to liquid sample analysis, and change of
sample schedule.
• Addition of extended data period (one month of hourly averages) for plant process
measurements.
Other changes in the sampling and measurements approach were implemented in the field and are
described below. Documentation and QC checks were followed as outlined in the TQAP for setup and
measurement procedures for sample acquisition and sample handling.
Vent Flow Measurement: The field team leader attempted measurements and found that a standard pitot
traverse was impractical due to cyclonic flow, duct configuration, wind, and low flow rate. The
1-9
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measurement plan was changed to use plant process data with confirmatory check runs using vane
anemometer.
Collection of Vent Gas: Integrated 1-liter bag samples were collected over a 3- to 4- minute period rather
than the one-hour sample specified in the TQAP.
Collection of sour and processed biogas samples: In consultation with the analytical laboratory, cylinder
samples for gas quality were eliminated and the analyses were performed on bag samples used for sulfur
species (ASTM 5504) analysis. Use of Tedlar bags minimizes H2S sample deterioration. In addition, the
24-30 hour hold time limit was exceeded. Due to logistical issues such as sample packaging and
shipping, samples were held for up to 48 hours before analysis. This extended holding time may have
caused sample degradation or losses of H2S in the bags. Although the extent of the degradation, if any,
cannot be quantified, it is expected to be minimal. This is because results reported here are consistent
with sour and processed biogas H2S concentrations measured at the facility which are analyzed within an
hour of collection.
Liquid NaOH Solution Flow Measurement: The QC check was changed to use an onsite volume check
device(graduated sight glass)
1-10
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2.0
VERIFICATION RESULTS
The verification period was June 1 through July 1, 2004. Field testing was conducted by GHG Center
personnel over a 3-day test period from June 29 through July 1, 2004. Bioreactor vent gas, sour biogas,
processed biogas, liquid effluent, and solids samples collected during this 3-day test period are
summarized in Table 2-1. Follow-up effluent and solids samples were collected by facility personnel on
July 14. Key THIOPAQ operational data including biogas throughput, reactor air flow, reactor level, and
NaOH tank level were logged by the facility over the entire one-month verification period and provided to
the GHG Center. Results of the verification of THIOPAQ environmental and operational performance
are presented in Sections 2.1 and 2.2. The laboratory reports detailing sample analyses are on file at the
GHG Center and available on request, but too voluminous for inclusion here. A sulfur mass balance for
the technology could not be calculated because operational procedures at the facility were not appropriate
for measuring the sulfur solids production rate.
Table 2-1. Sampling Matrix
Date
6/29/04
6/30/04
7/1/04
7/14/04a
Sample Type (Sample ID and time collected)
Bioreactor
Vent Gas
Vent 1 (0920)
Vent 2 (11 15)
Vent 3 (13 15)
Vent 4 (1030)
Vent 5 (1130)
Vent 6 (1320)
Vent 7 (0840)
Vent 8 (0950)
Vent 9 (1120)
Sour Biogas
Sour gas 1 (0945)
Sour gas 2 (1125)
Sour gas 3 (1325)
Sour gas 4 (1055)
Sour gas 5 (1200)
Sour gas 6 (1330)
Sour gas 7 (0850)
Sour gas 8 (1000)
Sour gas 9 (1135)
Processed
Biogas
P gas 1 (0945)
P gas 2 (1120)
P gas 3 (1320)
P gas 4 (1050)
P gas 5 (1155)
P gas 6 (1325)
P gas 7 (0845)
P gas 8 (0955)
P gas 9 (1130)
Liquid Effluent
Effluent 1 (1000)
Effluent 2 (1030)
Effluent 3 (13 15)
Effluent 4 (1100)
Effluent 5 (1130)
Effluent 6
Effluent 7
Solids Cake
Solids 1 (0900)
Solids 2 (1000)
Solids 3 (1100)
Solids 4
Solids 5
Samples were collected by facility personnel on 7/14/04. Collection times were not recorded.
2.1. ENVIRONMENTAL PERFORMANCE
2.1.1. Air Emissions
Three vent gas samples were collected from the bioreactor on each of the three test days of the technology
verification. The schedule of vent gas sampling is included in Table 2-1. The results of the analyses of
these samples are summarized in Table 2-2. Full documentation of the laboratory analyses are maintained
in the GHG Center files. As shown in Table 2-2, concentrations of H2S and total sulfur compounds were
very low, averaging 929 and 1,961 ppbv, respectively. H2S typically comprised about half of the total
sulfur compound concentrations. Methyl mercaptan, dimethyl sulfide, and dimethyl disulfide were the
other prominent sulfur compounds.
2-1
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Table 2-2. Summary of Sulfur Compounds in Vent Gas Samples
Date
6/29/04
6/30/04
7/1/04
Average
Time
0920
1115
1315
1030
1130
1320
0840
0950
1120
H2S
ppbv
990
95
7.2
240
200
1300
3900
430
1200
929
Total S Compounds
ppbv
2154
1235
903
1105
738
2523
5120
1494
2381
1961
Difficulties with direct vent gas flow rate measurement forced the Center to use plant process data for the
air blower flow rates as a surrogate for the vent gas flow. After analyzing these data, it is apparent that
the air flow through the reactor is highly variable. The flow rates logged during the 3-day sampling
period are plotted as Figure 2-1 and summarized as follows:
Bioreactor Vent Gas Flow Rate Statistics
Statistic
Average
Maximum
Minimum
Standard Deviation
Value (scfm)
246.3
432.0
91.0
56.5
This level of variability was evident over the entire 1-month verification period and is reported by the
facility to be typical for this gas stream. The variable speed air blower is regulated by the THIOPAQ
control system to respond to changes in biogas throughput. Biogas flow rates through the system, also
plotted in Figure 2-1, are also highly variable. These variabilities complicated evaluation of vent gas flow
rates. GHG Center personnel also obtained vane anemometer readings in the vent as an independent
check on the air blower process data. The agreement between the two data sets is poor, further
complicating this measurement. Since the flow rate data is poor, only the concentrations of sulfur
compounds in the vent gas are summarized in Table 2-2.
To provide potential THIOPAQ system users with an estimate of potential bioreactor emissions, the
average concentrations shown in table 2-2, and the average vent gas flow rate for the 3-day test period
were used to calculate estimated average emission rates in units of pounds per hour (Ib/hr). The average
estimated H2S and total sulfur (quantified as H2S) emission rates for the bioreactor vent were 0.0012 and
0.0026 Ib/hr, respectively.
2-2
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600
500
£ 400
T3
I
I
5 300
O
0.
o
200
100
6/29/040:00 6/29/0412:00 6/30/040:00 6/30/0412:00 7/1/040:00 7/1/0412:00 7/2/040:00
Figure 2-1. Biogas and Reactor Air Flow Rates During Testing
2.1.2. Liquid Effluent
A total of seven samples of THIOPAQ effluent (reactor slurry) were collected during the verification for
determination of total sulfides, total sulfates, and total suspended solids. Results are summarized in Table
2-3.
Results of the sulfide analyses were much higher than expected and, after investigation of ion
chromatographs run by the laboratory, it is evident that thiosulfate was present in the samples.
Thiosulfate is a potential interference for the analytical method used here, so results presented here are
possibly biased high by the presence of thiosulfate.
One hour average tank levels were provided by the facility over the entire 1-month verification period. A
total of 81,600 gallons of effluent were released during the verification period. Based on these data, the
average effluent rate was approximately 110 gallons per hour (gal/hr), or about 2,600 gallons per day
(gal/day). These values were not independently verified by the GHG Center, but are used to estimate
mass emissions of sulfate, sulfide, and solids during the period.
2-3
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The average sulfate, sulfide, and TSS concentrations shown in Table 2-3 and the average effluent rate of
2,600 gal/day during the period were then used to estimate discharge rates. The estimated liquid disposal
rates for sulfate, sulfide, and solids during the verification period are 77, 45, and 444 Ib/day, respectively.
Table 2-3. Total Sulfate, Total Suspended Solids and Total Sulfide in Reactor Slurry
Date
6/29/04
6/30/04
7/1/04
7/14/04
Sample
Effluent #1
Effluent #2
Effluent # 3
Effluent # 4
Effluent # 5
Effluent # 6
Effluent # 7
Average
Total Sulfate
mg/1
3740
3710
3730
4020
3610
2850
2690
3480
Total Suspended
Solids
mg/1
22150
20940
21180
21560
20730
16800
17560
20130
Total Sulfide3
mg/1
1680
1770
2000
1820
1880
2470
2560
2030
Potential thiosulfate interference causing high bias in total sulfide test results.
2.2. OPERATIONAL PERFORMANCE
2.2.1. Gas Composition, Gas Quality, and H2S Removal Efficiency
The primary purpose of the THIOPAQ technology is to safely and efficiently remove H2S from sour gas.
A total of nine sour and processed biogas samples were collected by GHG Center personnel during the 3-
day verification period and analyzed for H2S content. Biogas flow rate through the system during the test
period ranged from 119 to 504 scfm and averaged 322 scfm (or 464 x 103cfd). The average throughput
was approximately 39 percent of design average capacity.
Average H2S removal efficiency (mass %) is calculated based on the average measured concentrations of
H2S in the sour biogas and the treated biogas as well as the average measured flow rate of biogas into the
scrubber and an estimated flow rate out of the scrubber. Changes in gas flow rate into and out of the
scrubber were expected to be negligible. Therefore, an equivalent biogas input and output flow rate was
assumed in the TQAP for determining the mass flows of H2S in and out of the scrubber, and the resulting
mass removal efficiency for the system. However, the biogas flow rate out of the scrubber is slightly less
than the input flow rate due to the removal of H2S and a portion of the CO2 in the scrubber. The biogas
flow rate out of the scrubber was estimated based on a material balance for the components of the biogas
(N2 and CH^ that were not impacted by the scrubber. Material balance calculations yield a maximum
change in biogas flow rate of 9.7 %.
Although significant changes were observed in biogas flow rate due to the scrubbing of the H2S and CO2,
a sensitivity analysis indicates that the maximum impact of the reduced biogas flow rate on the H2S
removal efficiency calculation is 0.01% because of the large change in H2S concentration. Therefore, the
assumption of equivalent flow rates in calculation of the H2S removal efficiency does not significantly
2-4
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impact the data quality, and is used in this report. H2S removal efficiency is then calculated as the change
in concentration of H2S across the scrubber.
The same samples were analyzed for basic gas composition and heating value to evaluate if gas treatment
by THIOPAQ impacted the quality of the gas. Results are summarized in Table 2-4. Figure 2-2
illustrates the gas composition before and after the treatment.
Table 2-4. Composition and Properties of Sour and Processed Biogas - Dry Basis
Sample ID
Sour Gas 1
Processed Gas 1
Sour Gas 2
Processed Gas 2
Sour Gas 3
Processed Gas 3
Sour Gas 4
Processed Gas 4
Sour Gas 5
Processed Gas 5
Sour Gas 6
Processed Gas 6
Sour Gas 7
Processed Gas 7
Sour Gas 8
Processed Gas 8
Sour Gas 9
Processed Gas 9
Avg. Sour Gas
Avg. Processed Gas
Gas Composition
CH4(%)
61.84
67.51
62.23
67.59
62.73
70.00
61.8
69.12
60.85
68.75
62.13
66.76
63.57
69.14
63.52
70.81
63.25
70.32
62.44
68.89
C02(%)
35.28
30.71
34.6
30.57
34.57
28.70
34.66
28.83
34.51
28.02
34.69
31.71
31.42
28.18
32.06
26.39
31.95
25.27
33.75
28.71
N2(%)
1.62
1.42
1.80
1.47
1.06
1.08
1.83
1.85
2.97
2.94
1.27
1.28
2.58
2.21
1.82
2.36
2.07
3.69
1.89
2.03
H2S (ppm)
12603
37.6
13869
36.1
16489
21.2
17156
26.0
16781
16.4
19180
31.7
24352
28.2
25957
31.5
27472
19.1
19318
27.5
TotalS
(ppm)
12619
53.8
13885
51.9
16503
35.0
17170
39.8
16792
32.8
19199
47.4
24369
44.3
25987
48.6
27497
32.5
19336
42.9
Heat Content (Btu/scf)
HHV
620.8
671.9
625.0
672.7
633.4
696.7
625.1
687.9
614.7
684.2
629.2
664.5
664.7
688.1
646.9
704.7
645.0
699.7
633.9
685.6
LHV
558.8
604.8
562.6
605.5
570.1
627.1
562.7
619.2
553.3
615.9
566.4
598.1
580.3
619.3
582.3
634.3
580.5
629.8
568.6
617.2
Relative
Density
0.9088
0.8604
0.9032
0.8592
0.9005
0.8385
0.9045
0.8430
0.9078
0.8400
0.9033
0.8690
0.8794
0.8397
0.8824
0.8227
0.8827
0.8188
0.8970
0.8454
Compres-
sibility
0.9970
0.9971
0.9970
0.9971
0.9970
0.9972
0.9970
0.9972
0.9970
0.9973
0.9970
0.9971
0.9971
0.9972
0.9971
0.9973
0.9971
0.9974
0.9970
0.9972
H2S concentrations in the sour biogas averaged 1.93 percent. Processed gas contained an average 27.5
ppm H2S. Based on these average concentrations, average H2S removal efficiency was 99.8 percent.
Analysis of the gas compositional data also indicates that the THIOPAQ system reduces the CO2
concentration of the biogas by an average 15 percent. This change in gas composition creates an increase
in methane concentration and heating value. The average LHV of the processed biogas was
approximately 8.6 percent higher than the sour gas.
2-5
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1.9%N2 1.9%H,S
33.8 % CO
2.0%N9
62.4 % CK,
28.7 % CO,
Sour Biogas
Processed Biogas
Figure 2-2. Biogas Composition Before and After THIOPAQ
2.2.2. NaOH Consumption
A primary benefit of THIOPAQ is the potential reduction in NaOH consumption, and subsequent
operating costs. NaOH consumption rates are site specific and will vary depending on the gas processing
rate, sour gas H2S concentrations, and the desired removal efficiency. Data presented here are
representative of the conditions experienced at this facility during the verification period.
Final adjustments to the NaOH feed rate were made by the facility engineer on June 16, 2004. One-hour
average tank level data collected from that point in time to the end of the verification period are plotted in
Figure 2-3 and are used to report NaOH consumption during the verification. Unless additional
adjustments are made to system operations, the NaOH feed rate is constant as illustrated in the figure.
During the 376-hour period shown, a total of 947 gallons of 50-percent NaOH solution were consumed
for an average consumption rate of 2.52 gal/hr (60.5 gal/day). This rate was field verified by GHG Center
personnel (see Section 3.3.2). The average sour biogas feed rate during the monitoring period was 355
scfm (511 x 103cfd), or about 39 percent of design capacity. The sour gas was an average 1.93 percent
sulfur. The average 50-percent NaOH consumption normalized to biogas feed rate was 0.12 gallons per
thousand cubic feet of biogas processed, or 0.44 Ib NaOH per Ib sulfur.
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2400
2200
Consumption of 50-percent
NaOH solution averaged
2.52 gal/hr
1000
6/14/040:00 6/16/040:00 6/18/040:00 6/20/040:00 6/22/040:00 6/24/040:00 6/26/040:00 6/28/040:00 6/30/040:00 7/2/040:00 7/4/040:00
Figure 2-3. NaOH Tank Volume During Verification Period.
2.2.3. Sulfur Production and Purity
A total of five samples of THIOPAQ solids cake were collected during the verification for estimation of
elemental sulfur and moisture content. The remaining solids were not identified. Results are ±10
percent and are summarized in Table 2-5.
Table 2-5. Composition of the Solids Removed From the THIOPAQ Process.
Date
7/1/04
7/14/04
Time
1000
1030
1100
1000
1030
Average
Sulfur
%
58
53
53
26
28
44
Other Solids
%
22
19
18
48
44
30
Water
%
20
27
29
26
27
26
The average elemental sulfur content of the samples as collected was 44 percent. On a dry basis,
elemental sulfur averaged 59 percent of the solids collected.
2-7
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Plans to measure the amount of solids produced by the system were abandoned during field testing. The
facility only removes solids every three weeks or so on an as-needed basis. The frequency and amount of
solids removed varies widely depending on the amount of solids removed through the liquid effluent (the
amount of liquids bled and the total suspended solids content of the liquid). Removal of solids cake at
this facility was so operator specific and infrequent that it was deemed too arbitrary for verification here.
Because of this, a sulfur mass balance could not be completed for the system.
Analysis of the liquid effluent composition and disposal rate indicated that the average total suspended
solids disposal rate via the effluent is 444 Ib/day. These solids are the same material that is collected on
as solids cake on the vacuum press, so it is estimated that 59.2 percent of the solids disposed of as effluent
(or 263 Ibs) is recoverable elemental sulfur. Since the THIOPAQ system tested here is not configured to
maximize solids recovery rate, the GHG Center could not determine how much of that sulfur is
recoverable for subsequent use.
2-8
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3.0
DATA QUALITY ASSESSMENT
3.1. DATA QUALITY OBJECTIVES
The GHG Center selects methodologies and instruments for all verifications to ensure that the desired
level of data quality in the final results is obtained. The GHG Center specifies DQOs for each
verification parameter before testing starts and uses these goals as a statement of data quality. Ideally,
quantitative DQOs are established based on the level of confidence in results needed by stakeholders or
potential users of a technology. In some cases, such as this verification, quantitative DQOs are not well
defined and therefore, qualitative DQOs are established.
During this verification, determination of each of the primary verification parameters was conducted
based on published reference methods. The methods used are summarized in Table 3-1.
Table 3-1. Verification Reference Methods
Verification Parameter
H2S air emissions (vent)
Sulfate emissions
Sulfide emissions
Total suspended solids
H2S removal efficiency
Gas Quality
NaOH consumption rate
Sulfur production
Required Measurements
H2S Concentrations
Sulfates in water
Sulfides in water
TSS in water
Sour gas H2S content
Processed gas H2S content
Gas composition
Gas heating value
NaOH consumption rate
Solids moisture content
Solids sulfur content
Applicable Reference
Methods
Modified ASTM D5504
EPA Method 300.0
EPA Methods 3 76.1
EPA Method 160. 2
ASTM D5504
ASTM D 1945
ASTMD3588
None, see Section 3.3.2
Internal laboratory
procedures
The qualitative DQOs for this verification, then, are to meet all of the QA/QC requirements of each
method. In some cases, the laboratory conducting the analyses has internal QA/QC checks that are
performed in addition to the method requirements. The analytical methods used here were introduced in
Section 1.3. Additional details regarding these methods can be found in the TQAP. A summary of the
QA/QC requirements and results for each method are provided in the following sections.
3.2. ENVIRONMENTAL PERFORMANCE PARAMETERS
The primary verification parameters for environmental performance were concentrations of H2S in the
vent gas and sulfate and sulfide concentrations in the effluent. QA/QC requirements for the methods used
to verify these two parameters are discussed below.
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3.2.1 H2S Concentrations in Vent Gas
Vent gas sample collection date, time, run number, and bag IDs were logged and laboratory chain of
custody forms were completed and shipped with the samples. Copies of the chain of custody forms and
results of the analyses are stored in the GHG Center project files. Collected samples were express
shipped to Air Toxics, Ltd., on each of the three days of sampling for next day analysis. A coordinated
effort minimized sample holding times, which ranged from 22 to 33 hours. Air Toxics analyzed collected
samples in accordance with a modified version of ASTM Method 5504. The QA/QC procedures
specified in the method were followed, and are summarized in Table 3-2.
Table 3-2. Summary of Vent Gas Analytical QA/QC Checks
QC Check
Five point
instrument
calibration (ICAL)
Laboratory control
sample (LCS)
Laboratory blank
Duplicate analyses
Minimum
Frequency
Prior to sample
analysis
After each ICAL
After the ICAL
10% of the
samples
Acceptance Criteria
Relative standard deviation < 30%
90 percent of the compounds
quantified must be within 70 -
130% of expected values
Results lower than reporting limit
Relative percent difference of <
25% for compounds detected 5
times higher than reporting limits
Results Achieved
Results acceptable
H2S within the range of 90
to 120% of expected
values
All compounds below
reporting limit
Relative difference < 25%
for compounds detected
As an additional QC check, the GHG Center supplied one blind/audit air sample to the laboratory for
analysis. The audit gas was an independent Reference Standard of H2S in air manufactured by Scott
Specialty Gases with a certified analytical accuracy of 25 ppm ± 5 percent. The audit sample was
collected, handled, and analyzed using the same procedures and equipment as the vent gas samples. The
laboratory result was 21 ppm, or approximately ±16 percent of the certified concentration. This QC
check served as a performance evaluation audit (PEA) for this verification, and was reported to the
Southern QA manager for inclusion in the audit report.
3.2.2 Sulfate and Sulfide Effluent Emissions
Concentrations of sulfates and sulfides in the liquid effluent samples were determined by CT Laboratories
using the methods identified in Table 3-1. The QA/QC procedures specified in the methods were
followed and are summarized in Table 3-3. Documentation from CT Laboratories that each of these QC
checks were conducted indicates that the qualitative DQO was met.
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Table 3-3. Summary of Effluent Sulfate and Sulfide Analytical QA/QC Checks
QC Check
Three-point
instrument calibration
Daily single -point
calibration
Duplicate analysis
Daily single -point
calibration reanalysis
Minimum Frequency
Before analyses
Daily, prior to sample
analyses
Two samples
Daily, after sample
analyses
Acceptance Criteria
None-establishes
instrument calibration curve
Result within 10% of
expected values
Not specified
Result within 5% of initial
response
Results Achieved
Calibration conducted
Result within 10%
Repeatability within
2%
Result within 5%
3.3. OPERATIONAL PERFORMANCE PARAMETERS
The primary verification parameters for operational performance were concentrations of H2S in the sour
and processed biogas, the biogas compositional analyses, and the NaOH consumption determination.
QA/QC requirements for the methods used to verify these two parameters are discussed below.
3.3.1 Biogas H2S, Composition, and Heating Value
For all biogas samples collected (Table 2-1), sample collection date, time, run number, and canister ID
were logged and laboratory chain of custody forms were completed and shipped with the samples.
Copies of the chain of custody forms and results of the analyses are stored in the GHG Center project
files. Collected samples were shipped to Empact for compositional analysis and determination of LHV
per ASTM Methods D1945 and D3588, as well as H2S analyses according to Method D5504. All
samples were analyzed within 48 hours of collection, which exceeds the 24 hour method
recommendation. Empact maintains strict continuous calibration criteria on the instrumentation used for
the sulfur and compositional analyses using certified reference standards. Copies of these calibration data
are stored in the GHG Center project files. As independent calibration checks, blind audits were
submitted to Empact on two similar verifications within the past year to evaluate analytical accuracy on
the methane analyses [5, 6]. These audits qualified as PEAs as required by the ETV QMP. Both audits
indicated analytical accuracy within 3.0. Since the same sampling and analytical procedures were used
here by the same laboratory analyst, the audit was not repeated a third time.
In addition to the blind audit samples, duplicate analyses were conducted on two of the sour biogas
samples and two of the processed biogas samples. Duplicate analysis is defined as the analysis performed
by the same operating procedure and using the same instrument for a given sample volume. Results of
the duplicate analyses showed an average analytical repeatability of 0.03 percent for both methane and
LHV. Duplicate analyses were also conducted on the sour gas samples to demonstrate H2S repeatability.
Average repeatability was approximately 4 percent.
3.3.2 NaOH Consumption
NaOH consumption rates were determined using data provided by the facility. GHG Center personnel
conducted a field check to verify the accuracy of the tank level sensor used to log NaOH consumption.
The NaOH tank is equipped with a graduated sight glass. Two sets of manual sight glass readings were
recorded along with the elapsed time of a given change in level. Calculated NaOH consumption rate
based on the manual readings averaged 2.62 gal/hr. The average rate reported by the facility (Section
2.2.2) was 2.52 gal/hr, a difference of approximately 4 percent.
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3.4. VERIFICATION AUDITS
In addition to the QA/QC activities discussed here, several audit activities were conducted in support of
this verification. Southern's QA manager conducted an on-site technical systems audit (TSA) of the
measurement equipment, techniques, and methods to ensure compliance with the requirements of the
TQAP. During the TSA, the QA manager and GHG Center field technician noted and documented all of
the changes in the TQAP procedures due to site operational differences on corrective action reports.
These reports are filed at the GHG Center.
Southern's QA manager also conducted an audit of data quality (ADQ) for this verification. The ADQ is
an evaluation of the measurement, processing, and data evaluation steps to determine if systematic errors
have been introduced. The QA manager randomly selected approximately 10 percent of the data and
followed through the analysis, processing, and reporting of the data to ensure accuracy. The ADQ also
included review of any problems, changes, or corrective actions documented during the test program to
verify that their impact on data quality has been assessed and documented.
Finally, the PEAs described in Sections 3.2.1 and 3.3.1 satisfied the PEA requirement from the GHG
Center's QMP.
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4.0 TECHNICAL AND PERFORMANCE DATA SUPPLIED BY NATCO GROUP
Note: This section provides an opportunity for NATCO and Paques to provide additional comments
concerning the THIOPAQ System and its features not addressed elsewhere in the Report. The GHG
Center has not independently verified the statements made in this section.
In anticipation of future plant expansion, the THIOPAQ system tested here was designed for higher
biogas throughputs than currently available. This means that the unit is currently operating at just 30 to
50 percent of capacity (50 to 70 percent turndown). According to NATCO and Paques, air blower
control is less efficient at these capacities and the technology will likely operate more efficiently at
throughputs closer to design capacity. It is expected that performance results presented here might further
improve at sulfur loads closer to design capacity. System turndown can also have a negative impact on
NaOH consumption rates. The rate verified here (0.36 Ib NaOH per Ib sulfur) may also improve at gas
throughput rates closer to design capacity.
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5.0 REFERENCES
[1] Southern Research Institute, Test and Quality Assurance Plan - Paques THIOPAQ and Shell-
Paques Gas Purification Technology, SRI/USEPA-GHG-QAP-32, www.sri-rtp.com. Greenhouse
Gas Technology Center, Southern Research Institute, Research Triangle Park, NC. June 2004.
[2] American Society for Testing and Materials, Standard Practice for Determination of Sulfur
Compounds in Natural Gas by Gas Chromatography and Chemiluminescense, ASTM D5 5 04-01.
West Conshohocken, PA. 2001.
[3] American Society for Testing and Materials, Standard Test Method for Analysis of Natural Gas
by Gas Chromatography, ASTM D1945-98, West Conshohocken, PA. 2001.
[4] American Society for Testing and Materials, Standard Practice for Calculating Heat Value,
Compressibility factor, and Relative Density of Gaseous Fuels, ASTM D3588-98. West
Conshohocken, PA. 2001.
[5] Southern Research Institute, Environmental Technology Verification Report: Combined Heat
and Power at a Commercial Supermarket - Capstone 60 kW Microturbine CHP System,
SRI/USEPA-GHG-QAP-27, www.sri-rtp.com. Greenhouse Gas Technology Center, Southern
Research Institute, Research Triangle Park, NC. September 2003.
[6] Southern Research Institute, Environmental Technology Verification Report: Residential Electric
Power Generation Using the Plug Power SUl Fuel Cell System, SRI/USEPA-GHG-QAP-25,
www.sri-rtp.com. Greenhouse Gas Technology Center, Southern Research Institute, Research
Triangle Park, NC. September 2003.
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