Pollutant (HAP) Major Source [FCAA § 112(g)] Permit HAP-14, which would establish Case-By-Case Maximum Achievable Control Technology (MACT) requirements for the Limestone Electric Generating Station (LMS) - Unit 3 Boiler (LMS3) and auxiliary boiler (AUX) located approximately 9 miles north of Jewett, Texas on FM 39, Jewett, Limestone County, Texas. These new boilers are also subject to State Air Quality and federal Prevention of Significant Deterioration (PSD) preconstruction permitting requirements. The TCEQ has prepared draft State Air Quality Permit 79188 and PSD Air Quality Permit PSD-TX-1072, which establishes additional conditions under which the proposed facility must operate. A pending contested case hearing for permits 79188 and PSD-TX-1072 has been abated for this HAP review. LMS3 is an 800 MW boiler firing sub-bituminous coal, petroleum coke, or bituminous coal with a maximum heat input rate of 8,000 MMBtu/hr at their Limestone Electric Generating Station which has two existing solid fuel fired boilers. LMS3 will fire either 100 percent sub-bituminous coal, or a nominal blend (by weight) of 20% petroleum coke with 80% sub-bituminous, or a 40% bituminous coal with 60% sub-bituminous coal blend
MACT Case-by-Case Review: NRG recognizes that the vacatur of the Clean Air Mercury Rule, along with the absence of a source category MACT standard for the proposed PC boiler, and the vacatur of the Industrial Boiler MACT (40 CFR 63 Subpart DDDDD) that applied to the auxiliary boiler necessitates the need for NRG to accomplish a case-by-case MACT analysis.
NRG has provided a Clean Air Act Section 112(g) case by-case MACT analysis for LMS3 and a Section 112(j) case-by-case MACT analysis for AUX. Permit HAP-14 establishes federally enforceable MACT emission limitations for carbon monoxide [(CO) as a surrogate for organic hazardous air pollutants (HAPs)], filterable particulate matter [(PM) as a surrogate for non-mercury HAP metals], hydrogen fluoride (HF), hydrogen chloride (HCl), and mercury (Hg) for LMS3. The analysis by NRG Texas confirms that the control technologies and emissions limits proposed by NRG Texas in its June 2006 state PSD permit application for the PC Boiler meet case-by-case MACT requirements, with the exception that slightly reduced emissions limits for mercury, HF, and filterable PM are indicated due to recent emissions compliance demonstrations at similar sources. Had a case-by-case MACT analysis been an applicable requirement when the 2006 state/PSD application was submitted, the emission limits proposed as BACT to the TCEQ for mercury and other hazardous air pollutants would have satisfied that requirement. The Hg emission limit of 0.020 lb/GWh was reduced to the MACT floor determined to be 0.015 lb/GWh when firing subbituminous coal and 0.0075 lb/GWh when firing only bituminous coal. Filterable PM emission limit was lowered to 0.012 lb/MMBtu. The HCI emission limit remains 0.0023 lb/MMBtu. The HF emission limit was lowered to 0.0005 lb/MMBtu. CO as a surrogate for organic HAPS remains 0.15 lb/MMBtu.
This permit also establishes federally enforceable MACT emission limitations for CO as a surrogate for organic HAPs and filterable PM as a surrogate for non-mercury HAP metals for AUX. MACT for HAPs is the use of good combustion practices and the use of natural gas as the fuel. CO is a surrogate for organic HAPs and was lowered to 0.04 lb/MMBtu.
ADDITIONAL IMPACTS: The impact on air quality resulting from any commercial or industrial growth associated with Permit HAP-14 were accounted for the review of Draft Permit Nos. 79188 and PSD-TX-1072.
SPECIAL CONDITIONS Permit Number HAP-14
MAXIMUM ACHIEVABLE CONTROL TECHNOLOGY (MACT) APPROVAL
1. This case-by-case MACT permit (HAP-14) establishes federally enforceable MACT emission limitations for carbon monoxide (CO) (CO is a surrogate for organic hazardous air pollutants [HAPs]), filterable particulate matter (PM) (filterable PM is a surrogate for non-mercury HAP metals), hydrogen fluoride (HF), hydrogen chloride (HCl), and mercury (Hg) for the Limestone 3 Pulverized Coal Boiler (LMS3). This permit also establishes federally enforceable MACT emission limitations for CO (CO is a surrogate for organic HAPs) and filterable PM (filterable PM is a surrogate for non-mercury HAP metals) for the natural gas-fired auxiliary boiler (AUX).
2. Emission limits are based upon representations in the case-by-case MACT permit application dated May 12, 2008 and subsequent updates.
3. These facilities shall comply with all applicable requirements of Title 30 Texas Administrative Code (30 TAC) Chapter 113, 30 TAC Chapter 116, and the U.S. Environmental Protection Agency (EPA) regulations on National Emission Standards for Hazardous Air Pollutants for Source Categories in Title 40 Code of Federal Regulations Part 63 (40 CFR Part 63), promulgated for:
A. Applicable General Provisions, Subpart A.
B. Clean Air Act Section 112(g) case-by-case MACT determination for the PC Boiler (EPN LMS3) and a Section 112(j) case-by-case MACT determination for the Auxiliary Boiler (EPN AUX).
4. If any condition of this case-by-case MACT permit, HAP-14, conflicts with a condition of Permit 79188 and PSD-TX-1072 or any other authorization for the facilities covered by permit HAP-14, the most stringent permit condition shall govern.
FUEL SPECIFICATIONS, OPERATING LIMITATIONS, PERFORMANCE STANDARDS, AND CONSTRUCTION SPECIFICATIONS
5. Fuel fired in the Unit 3 Boiler, EPN LMS3, shall be limited to a maximum heat input of 8,000 million British thermal units per hour (MMBtu/hr), averaged over a 30-day period, based on the higher heating value (HHV) of the fuel and the fuel fired shall be limited to:
A. Sub bituminous coal, bituminous coal and petroleum coke. The maximum bituminous coal/subbituminous coal blend could be up to 40 percent/60 percent by weight respectively and the petroleum coke/subbituminous coal blend could be up to 20 percent/80 percent by weight, respectively.
B. Pipeline-quality natural gas.
C. Use of any other fuel will require prior approval from the permitting authority.
D. Upon request by the Executive Director of the Texas Commission on Environmental Quality (TCEQ) or any air pollution control program having jurisdiction, the holder of this permit shall provide a sample and/or an analysis of the fuel fired in the PC Boiler or shall allow air pollution control agency representatives to obtain a sample for analysis.
6. Emissions from the Limestone Unit 3 Utility Boiler exhausting through EPN LMS3 shall not exceed the performance standards identified in the table below. The performance standards of this permit condition shall apply at all times, except during periods of planned start-up and shutdown. During periods of planned start-up and shutdown, the holder of this permit shall not exceed the hourly mass emission limits in the maximum allowable emission rates table (MAERT), and the holder of the permit shall operate the Limestone Unit 3 Utility Boiler and associated air pollution control equipment in accordance with good air pollution control practices to minimize emissions. The permit holder shall retain records of planned start-up and shutdown periods in which the emission specifications identified below are exceeded and shall identify all measures taken to mitigate emissions. Initial compliance with the performance standards of this special condition shall be demonstrated in the initial determination of compliance stack sampling utilizing EPA Reference Method testing and shall be determined based upon the average of three stack sampling test runs. Continuous compliance thereafter shall be either via Continuous Monitoring Systems (CMS) for the pollutants monitored by CMS or via stack sampling described by Special Condition No. 11. Compliance with the HAP emission limits for non-mercury HAP metals and organic HAPs shall be demonstrated by using the surrogate’s filterable particulate matter (PM) for non-mercury HAP metals and CO for organic HAPs. The averaging periods identified in Table A below shall be the basis for continuous compliance.
SPECIAL CONDITIONS Permit Number HAP-14 Page 3
A. Standards demonstrated by Continuous Monitoring Systems (CMS)
Pollutant1 Performance Standard Compliance Averaging Period
CO 0.15 lb/MMBtu2 30-day rolling
Hg 0.012 to 0.015 lb/GWh* 12-month rolling *
When firing subbituminous coal, or a blend of subbituminous coal and petroleum coke, an output-based emission limit of 0.015 lb/GWh, based on a monthly rolling 12-month average.
When firing a blend that includes both subbituminous coal and bituminous coal, a weighted, output-based emission limit, based on a monthly rolling 12-month average, computed as follows:
Where:
ELb = Total allowable Hg in lb/GWh that can be emitted to the atmosphere during any12-month period when a blend of fuels was burned.
ELi = Hg emissions limit for the subcategory i (coal rank), 0.015 lb/GWh for subbituminous coal and petroleum coke and 0.0075 lb/GWh for bituminous coal;
HHi = GWh contributed by the corresponding subcategory i (coal rank) burned during the compliance period; and
n = Number of subcategories (coal ranks) being averaged.
During 12-month periods when a blend of fuels including bituminous coal is burned, the applicable Hg emission limit will vary with the amount of bituminous coal. For example, if a 60/40 blend of subbituminous and bituminous coals is burned, the Hg emission limit will be 0.012 lb/GWh; for an 80/20 blend, the limit will be 0.0135 lb/GWh.
B. Standards demonstrated by Reference Method3(RM) testing Pollutant1 Performance Standard (lb/MMBtu)2 Compliance Demonstration Period
PM (front-half catch) 0.012 annual
HCl 0.0023 annual
HF 0.0005 annual
Notes:
1 PM - particulate matter CO - carbon monoxide
Hg - mercury HF - hydrogen fluoride HCl - hydrogen chloride
2 lb/MMBtu - pounds of emissions per million Btu of heat input. Heat input is based on fuel HHV. 3 RM - EPA Reference Methods, based on the average of three stack sampling runs to be
conducted as prescribed by Special Condition No. 11.
7. The holder of this permit shall operate the boilers and associated air pollution control equipment in accordance with good air pollution control practices to minimize emissions during start-up and shutdown, by operating in accordance with a written start-up and shutdown plan. The plan shall include detailed procedures for review of relevant operating parameters of the boilers and associated air pollution control equipment during start-up and shutdown to make adjustments and corrections to reduce or eliminate any excess emissions. The plan shall also address readily foreseeable start-up scenarios, including hot start-ups, when the operation of the boiler is only temporarily interrupted, and provide for appropriate review of the operational condition of the boilers before initiating start-up. 8. The 155 MMBtu/hr Auxiliary Boiler (EPN AUX) shall meet the following specifications:
A. Emissions of CO shall not exceed 0.04 lb/MMBtu, averaged over 3 hours of operation except during start-up and shutdown.
B. Emissions of filterable PM shall not exceed 0.0022 lb/MMBtu, averaged over 3 hours of operation except during start-up and shutdown.
C. Fuel shall be limited to pipeline quality natural gas.
D. Operation of the auxiliary boiler shall be limited to a maximum annual heat input of 135,780 MMBtu/yr, which is the equivalent of a 10 percent annual capacity factor.
SPECIAL CONDITIONS Permit Number HAP-14 Page 5
9. Stack sampling ports and platform(s) as specified in the attachment entitled AChapter 2,
Stack Sampling Facilities,@ or an alternate design may be required at a later date if
determined necessary by the TCEQ Regional Director or the TCEQ Austin Compliance Support Division.
INITIAL DEMONSTRATION OF COMPLIANCE
10. The holder of this permit shall perform initial stack sampling and other testing to establish the actual quantities of air contaminants being emitted into the atmosphere. Unless otherwise specified in this special condition, the sampling and testing shall be conducted in accordance with the methods and procedures specified in Special Condition No. 11. The holder of this permit is responsible for providing sampling and testing facilities and conducting the sampling and testing operations at his expense. The TCEQ Executive Director or his designated representative shall be afforded the opportunity to observe all such sampling.
A. For the PC Boiler, EPN LMS3:
(1) Demonstrate compliance with the performance standards of Special Condition No. 6 and the hourly emission rates of the MAERT, using the average of three one-hour stack sampling test runs for each contaminant.
(2) Air contaminants to be sampled and analyzed include: CO, HCl, HF, filterable PM, and Hg. Diluents to be measured include O2or carbon dioxide (CO2). (3) Boiler load during testing shall be maintained as follows.
a. Operate at maximum firing rates for the atmospheric conditions occurring during the test as measured by millions of pounds of steam generated per hour or MW of electric generator output. If the steam generating unit is unable to operate at maximum rates during testing, then additional stack testing may be required when higher production rates are achieved.
b. During 30-day average emission testing, the boiler load does not have to be at maximum, but the load must be representative of future operating conditions and must include at least one 24-hour period at full load. If the steam generating unit is unable to operate at maximum rates during testing, then additional stack testing may be required when higher production rates are achieved.
B. For the Auxiliary Boiler (EPN AUX) demonstrate compliance with the CO and filterable PM performance standards of Special Condition No. 8 using the average of three one-hour stack sampling test runs for each contaminant.
C. Requests to waive testing for any pollutant specified in this condition shall be submitted to the TCEQ Office of Permitting, Remediation, and Registration, Air Permits Division. Test waivers and alternate or equivalent procedure proposals for New Source Performance Standards testing which must have EPA approval shall be submitted to the TCEQ Field Operations Support Division, MC-174.
D. Sampling as required by this condition shall occur within 60 days after achieving the maximum fuel firing rate at which the PC Boiler will be operated but no later than 180 days after initial start-up. The first boiler operating day of 30-day average initial performance testing required by 40 CFR § 60.48Da(f) must commence within this time.
TEST METHODS AND PROCEDURES
11. Sampling Methods Required and Pre-test meeting requirements:
A. Sampling shall be conducted in accordance with the appropriate procedures of the TCEQ Sampling Procedures Manual, EPA Methods in 40 CFR Part 60, Appendix A and 40 CFR Part 51, Appendix M, EPA Conditional Test Methods, and American Society for Testing and Materials (ASTM) as follows:
(1) Appendix A, Methods 1 through 4, as appropriate, for exhaust flow, diluent, and moisture concentration;
(2) Appendix A, Method 5 or 17, for the filterable concentration of PM (front-half catch);
(3) Appendix A, Method 10 for the concentration of CO;
(4) Appendix A, Method 19, for applicable calculation methods; (5) Appendix A, Method 26 or 26A for HCl and HF;
(6) Appendix M, Methods 201A or Appendix A, Reference Method 5, for the filterable concentration of particulate matter less than 10 microns in diameter, PM10 (front-half catch);
SPECIAL CONDITIONS Permit Number HAP-14 Page 7
(7) ASTM D6784-02, Standard Test Method for Elemental, Oxidized, Particle-Bound, and Total Mercury in Flue Gas Generated from Coal-Fired Stationary Sources (also known as the Ontario Hydro Method), or other approved EPA methods.
(8) Any deviations from those procedures must be approved by the Executive Director of the TCEQ prior to sampling.
B. The TCEQ Waco Regional Office shall be given notice as soon as testing is scheduled but not less than 30 days prior to sampling to schedule a pretest meeting. (1) The notice shall include:
(a) Date for pretest meeting. (b) Date sampling will occur.
(c) Name of firm conducting sampling. (d) Type of sampling equipment to be used. (e) Method or procedure to be used in sampling.
(2) The purpose of the pretest meeting is to review the necessary sampling and testing procedures, to provide the proper data forms for recording pertinent data, and to review the format procedures for submitting the test reports. The permit holder shall present at the pretest meeting the manner in which stack sampling will be executed in order to demonstrate compliance with emission standards found in this permit.
(3) Prior to the pretest meeting, a written proposed description of any deviation from sampling procedures specified in permit conditions or TCEQ, EPA or ASTM sampling procedures shall be made available to the TCEQ. The TCEQ Regional Director or the TCEQ Field Operations Support Division, MC-174 shall approve or disapprove of any deviation from specified sampling procedures.
C. Information in the initial test report for the PC boiler, EPN LMS3, shall include the following data for each test run:
(1) hourly coal and petroleum coke firing rate (in tons);
(2) average coal and petroleum coke Btu/lb as-received and dry weight; (3) average steam generation rate in millions of pounds per hour;
(4) average generator output in MW;
(5) control device operating rates, including SCR reagent injection and solids injection rates (fresh lime, recycle lime/ash);
(6) emissions in the units of the limits of this permit, lb/hr and lb/MMBtu, three-hour or 30-day average, as appropriate; and
(7) any additional records deemed necessary during the stack sampling pre-test meeting.
D. Three copies of the final sampling report shall be forwarded to the TCEQ within 60 days after sampling is completed. Sampling reports shall comply with the attached conditions of Chapter 14 of the TCEQ Sampling Procedures Manual. The reports shall be distributed as follows:
One copy to the TCEQ Waco Regional Office. One copy to EPA Region 6 Office, Dallas.
One copy to the TCEQ Austin Office of Permitting, Remediation, and Registration, Air Permits Division.
CONTINUOUS DEMONSTRATION OF COMPLIANCE
12. The holder of this permit shall install, calibrate, maintain, and operate a continuous emission monitoring system (CEMS) to measure and record the concentrations of CO from EPN LMS3. Diluents to be measured include O2or CO2. The CEMS data shall be used to determine continuous compliance with the CO, emission limitations in Special Condition No. 6 and the attached MAERT.
13. The holder of this permit shall install, calibrate, operate, and maintain a CEMS to measure and record the concentration of mercury from EPN LMS3, unless another means of compliance is prescribed by federal rules. The CEMS data (or data from other means prescribed by federal rules) shall be used to demonstrate continuous compliance with the emission limitations of Special Condition No. 6 and the MAERT
14. If any emission monitor fails to meet specified performance, it shall be repaired or replaced as soon as reasonably possible.
SPECIAL CONDITIONS Permit Number HAP-14 Page 9
15. After the initial demonstration of compliance, on-going stack sampling of EPN LMS3 for HCl, HF, and filterable PM shall be used to demonstrate ongoing compliance and shall meet the following specifications:
A. Stack sampling shall be performed once annually during periods of normal operation, except as follows:
(1) If the annual test does not establish compliance with a performance standard of Special Condition No. 6, the holder of this permit may conduct additional tests during the year to be averaged with the previous test(s) to demonstrate compliance; or
(2) If, after two years of stack sampling, the average of the two annual stack sampling results for a pollutant is less than 70 percent of the applicable performance standard identified in Special Condition No. 6, then compliance stack sampling for such pollutant may be conducted once every three years.
B. Sampling required in this special condition shall demonstrate compliance with the performance standards of Special Condition No. 6.
C. Sampling required in this special condition shall be conducted in accordance with the methods, procedures, and notification protocol specified in Special Condition No. 11.
D. Ongoing compliance with the HF, HCl, and filterable PM tons-per-year emission rates in the MAERT shall be demonstrated by calculating rolling 12-month annual emissions from emission factors (lb/MMBtu, HHV) obtained from the sampling required in this condition and the monthly total heat input (MMBtu, HHV) from coal and petroleum coke.
E. To demonstrate proper operation of the baghouse, pressure drop shall be monitored and recorded.
16. Compliance with the applicable filterable PM and CO emission limits for the PC Boiler (EPN LMS3) will be demonstrated as follows for periods of start-up and shutdown:
A. Compliance with the filterable PM emission rates in Special Condition No. 6 will be demonstrated, when firing solid fuels, if the recorded pressure drop across the baghouse meets manufacturer guidelines for proper operation during start-up and shutdown.
B. Compliance with the CO emission rate in the MAERT applicable during start-up and shutdown will be demonstrated if the CO emissions during start-up and shutdown are in compliance with the CO emission rate in the MAERT for planned start-up and shutdown.
17. Following the initial demonstration of compliance, ongoing compliance with the emission limits shall be through source operation in accordance with manufacturer’s specifications, or in accordance with written procedures that are shown to maintain operating conditions necessary for emission compliance. The Executive Director of the TCEQ or his designated representative may also require direct measurement of emissions using the sampling methods and procedures specified in Special Condition No. 11 to establish compliance with the limitations, in which case the sampled emission rate will be used to determine compliance.
RECORDKEEPING REQUIREMENTS
18. The following records shall be kept at the plant for the life of the permit. All records required in this permit shall be made available at the request of personnel from the TCEQ, the EPA, or any air pollution control agency with jurisdiction.
A. A copy of this permit.
B. Permit application dated May, 12, 2008 and subsequent updates submitted to the TCEQ.
C. A complete copy of the testing reports and records of the initial performance testing completed pursuant to Special Condition No. 10 to demonstrate initial compliance. 19. Records shall be kept for a minimum of five years after collection and shall be made
immediately available upon request to representatives of the TCEQ, the EPA, or any local air pollution control program having jurisdiction. The most recent two years shall be maintained on-site and shall be available for inspection. The remaining three years of records may be maintained off site. Records shall be legible and maintained in an orderly manner. The following records shall be maintained:
SPECIAL CONDITIONS Permit Number HAP-14 Page 11
A. Continuous monitoring data for CO, Hg and diluent gases, O2or CO2, from CEMS to demonstrate compliance with the emission rates listed in the MAERT and performance standards listed in Special Condition No. 6 for pollutants that are monitored by CMS. Records should identify the times when emissions data have been excluded from the calculation of average emission rates because of planned start-up and shutdown periods along with the justification for excluding data. The CEMS data retention at intervals less than one hour is not required. The permit holder shall retain additional records of planned start-up and shutdown periods in which the emission specifications identified in Special Condition No. 6 are exceeded and shall identify all measures taken to mitigate emissions. All records should also identify factors used in calculations that are used to demonstrate compliance with emissions limits and performance standards.
B. Files of all CMS quality assurance measures, calibration checks, adjustments and maintenance performed on these systems.
C. Steam turbine generator hourly gross electrical output in MW, including identification of shutdown intervals, for compliance with output based performance specifications of this permit.
D. Average coal and petroleum coke feed rate to the PC Boiler in tons per hour and the corresponding average heat input (HHV) in MMBtu/hr, based upon an average over each calendar month.
E. Hourly average pressure drop records for the baghouse.
F. Tons of coal and petroleum coke fired in the PC Boiler, EPN LMS3, monthly to show compliance with the fuel throughput requirements of this permit.
G. Required stack sampling results or other air emissions testing (other than CMS data) that may be conducted on units authorized under this permit after the date of issuance of this permit.
REPORTING
20. The holder of this permit shall submit to the TCEQ Waco Regional Office and the Air Enforcement Branch of EPA in Dallas semi-annual reports for each emission unit which is required to be continuously monitored pursuant to this permit.
AS-BUILT INFORMATION
21. The holder of this permit shall submit to the TCEQ Waco Regional Office and the TCEQ Air Permits Division change pages to the permit application reflective of the final plans and engineering specifications on the PC Boiler and auxiliary boiler, including their respective control equipment, no later than 30 days before initial start-up of the PC Boiler. This information shall include:
A. All TCEQ Tables in the permit application, updated with manufacturer and other specified data.
B. Revised plot plans and equipment drawings as required to reflect the constructed facility.
C. Identification of any maximum inputs of raw materials for the as-built facility that is lower than the values represented in the permit application and used for calculating or establishing emissions. Accompanying this information shall be a request for permit alteration. The TCEQ shall alter the permit special conditions and MAERT to reflect any such reduction in emissions. Increases in allowable emission rates require a permit amendment before construction begins.
EMISSION SOURCES - MAXIMUM ALLOWABLE EMISSION RATES Permit Number HAP-14
This table lists the maximum allowable emission rates and all sources of air contaminants on the applicant’s property covered by this permit. The emission rates shown are those derived from information submitted as part of the application for permit and are the maximum rates allowed for these facilities. Any proposed increase in emission rates may require an application for a modification of the facilities covered by this permit.
AIR CONTAMINANTS DATA
Emission Rates * Emission
Point No. (1) Source Name (2) Air Contaminant Name (3) lb/hr TPY**
NORMAL OPERATIONS
LMS3 Unit 3 Pulverized Coal Boiler 8,000-MMBtu/hr Nominal 800-MW Gross CO PM (filterable) HF HCl Hg 1,200 (6) 5,256 420 (5) 17.5 (5) 81.7 0.053 (5)
AUX Auxiliary Boiler
155-MMBtu/hr CO PM (filterable) 2.7 0.15 (5) (5)
PLANNED START-UP AND SHUTDOWN LMS3 Unit 3 Pulverized Coal Boiler
8,000-MMBtu/hr
Nominal 800-MW Gross
EMISSION SOURCES - MAXIMUM ALLOWABLE EMISSION RATES
(1) Emission point identification - either specific equipment designation or emission point number from a plot plan.
(2) Specific point source names. For fugitive sources, use an area name or fugitive source name. (3) CO - carbon monoxide
PM - particulate matter, suspended in the atmosphere, including PM10 and PM2.5 PM10 - particulate matter equal to or less than 10 microns in diameter
HCl - hydrogen chloride HF - hydrogen fluoride Hg - mercury
(4) Fugitive emissions are an estimate only and should not be considered as a maximum allowable emission rate.
(5) Emission rates reflect the case-by-case MACT determination for the issuance of Permit HAP-14. (6) Compliance with hourly emission limit for CO is based on a rolling 30-day average.
* Emission rates are based on and the facilities are limited by the following maximum operating schedule: 24 Hrs/day 7 Days/week 52 Weeks/year or 8,760 Hrs/year
PRELIMINARY DETERMINATION SUMMARY
NRG Texas Power, LLC Permit No. HAP-14 I. APPLICANT
NRG Texas Power LLC 1301 McKinney, Suite 2300 Houston, Texas 77010 II. PROJECT LOCATION
The proposed project, new Unit 3 Boiler, at the Limestone Electric Generating Station will be located approximately nine miles north of Jewett on Farm-to Market Road 39 in Limestone County, Texas.
III. PROJECT DESCRIPTION
NRG Texas Power LLC (NRG Texas) has requested a Hazardous Air Pollutant (HAP) Major Source [FCAA § 112(g)] Permit HAP-14, which would establish Case-By-Case Maximum Achievable Control Technology (MACT) requirements for the Limestone Electric Generating Station - Unit 3 Boiler (LMS3) and auxiliary boiler (AUX) near Jewett in Limestone County, Texas. These new boilers are also subject to State Air Quality and Federal Prevention of Significant Deterioration (PSD) preconstruction permitting requirements. The TCEQ has prepared draft State Air Quality Permit 79188 and PSD Air Quality Permit PSD-TX-1072, which establishes additional conditions under which the proposed facility must operate. A pending contested case hearing for permits 79188 and PSD-TX-1072 has been abated for this HAP review. The PC Boiler is an 800 MW boiler firing sub-bituminous coal, petroleum coke, or bituminous coal with a maximum heat input rate of 8,000 MMBtu/hr at their Limestone Electric Generating Station (LMS) which has two existing solid fuel fired boilers. LMS3 will fire either 100 percent sub-bituminous coal, or a nominal blend (by weight) of 20% petroleum coke with 80% sub-bituminous, or a 40% bituminous coal with 60% sub-bituminous coal blend
IV. EMISSIONS
Permit HAP-14 establishes federally enforceable MACT emission limitations for carbon monoxide [(CO) as a surrogate for organic hazardous air pollutants (HAPs)], filterable particulate matter [(PM) as a surrogate for non-mercury HAP metals], hydrogen fluoride (HF), hydrogen chloride (HCl), and mercury (Hg) for LMS3. This permit also establishes federally enforceable MACT emission limitations for CO as a surrogate for organic HAPs and filterable PM as a surrogate for non-mercury HAP metals for AUX.
Annual potential emissions of surrogate HAP pollutants, in tons per year (tpy), for CO, and filterable PM for LMS3 are summarized in the following table:
Surrogate Pollutants tpy
CO Filterable PM
5,256 420*
Annual potential emissions of other HAP pollutants in tpy, for LMS3 are identified in the following table:
Other HAP Pollutants in tpy Fluorides
(as HF) Mercury (Hg) Hydrogen Chloride (HCl)
17.5* 0.053* 81.7
* - indicates emission rates reduced by case-by-case MACT analysis
Annual potential emissions of surrogate HAP pollutants for AUX, for CO is 2.7 tpy, and for filterable PM is 0.15 tpy.
V. FEDERAL APPLICABILITY
Recent federal court vacatur of both EPA's delisting of electric utility steam generating units (EUSGUs) as sources subject to MACT standards and the Clean Air Mercury Rule (CAMR) require that MACT emission limitations separately be established for coal-fired electric generating units such as the proposed PC Boiler LMS3. LMS3 is now subject to the requirements for case-by-case MACT pursuant to Clean Air Act Section 112(g).
Additionally, the U.S. Court of Appeals for the D.C. Circuit vacated the National Emissions Standard for Hazardous Air Pollutants [40 CFR 63 Subpart DDDDD (Boiler MACT)] that applied to the proposed auxiliary boiler. Vacatur of the Boiler MACT may subject the proposed auxiliary boiler to case-by-case MACT requirements under Clean Air Act Section 112(j). NRG Texas elected to submit a case-by-case analysis for both the PC and auxiliary boiler in this application.
VI. CONTROL TECHNOLOGY REVIEW
The analysis by NRG Texas confirms that the control technologies and emissions limits proposed by NRG Texas in its June 2006 state PSD permit application for the PC Boiler meet case-by-case MACT requirements, with the exception that slightly reduced emissions limits for mercury, HF, and PM (the surrogate for non-mercury HAP metals) are indicated due to recent emissions compliance demonstrations at similar sources. Had a case-by-case
Preliminary Determination Summary Permit Number HAP-14
Page 3
MACT analysis been an applicable requirement when the 2006 state/PSD application was submitted, the emission limits proposed as BACT to the TCEQ for mercury and other hazardous air pollutants (emission limits that are now stipulated in the draft State/PSD permit for the PC Boiler) would have satisfied that requirement.
Additionally, the analysis confirms that the control technologies and emissions limits proposed by NRG Texas in its June 2006 state/PSD permit application for the auxiliary boiler meet case-by-case MACT requirements, with the exception of a more stringent emission limit for CO, the proposed surrogate for organic HAPs.
The EPA definition of MACT for a new source in 40 CFR § 63.41 is:
“Maximum achievable control technology (MACT) emission limitation for new sources means the emission limitation which is not less stringent that the emission limitation achieved in practice by the best controlled similar source, and which reflects the maximum degree of deduction in emissions that the permitting authority, taking into consideration the cost of achieving such emission reduction, and any non-air quality health and environmental impacts and energy requirements, determines is achievable by the constructed or reconstructed major source.”
The EPA definition of MACT for an existing source in 40 CFR § 63.51 is:
“Maximum achievable control technology (MACT) emission limitation for existing sources means the emission limitation reflecting the maximum degree of reduction in emissions of hazardous air pollutants (including a prohibition on such emissions, where achievable) that the Administrator, taking into consideration the cost of achieving such emission reductions, and any non-air quality health and environmental impacts and energy requirements, determines is achievable by sources in the category or subcategory to which such emission standard applies. This limitation shall not be less stringent than the MACT floor.”
The HAPs potentially emitted by LMS3 can be classified in broad categories, based on the effective methods of controlling their emissions: mercury, non-mercury HAP metals, acid gases (hydrogen chloride and hydrogen fluoride), and organic HAPs. The HAPs potentially emitted by AUX can be classified into two broad categories: metal HAPs and organic HAPs NRG Texas performed the case-by-case MACT analyses in two steps. First, they established the "MACT floor" or most stringent emission limitation achieved in practice by the best controlled similar source. Next, NRG Texas performed a "beyond the floor" analysis of the other methods for potentially reducing emissions to a greater degree, considering factors such as the cost of achieving such emissions reductions and any non-air quality health and environmental impacts and energy requirements to establish whether these reductions are achievable.
Of particular relevance to the case-by-case MACT analyses is the requirement of 40 CFR § 63.43(d)(4) that case-by-case MACT determinations must take into consideration emissions standards that may have been proposed by EPA pursuant to § 112(d) of the Clean Air Act for the pertinent source category. In the case of the PC Boiler, the relevant proposed (and later rescinded) rule is Subpart UUUUU of 40 CFR Part 63. For the auxiliary boiler, the relevant proposed and promulgated (later rescinded) rule is Subpart DDDDD of 40 CFR Part 63. NRG Texas considered the emissions standards under these rules in establishing the case-by-case MACT emissions limitations presented in their application. In addition, NRG Texas considered the following materials in identifying and evaluating available control options, emission limits, and averaging periods: 1) The Clean Air Mercury Rule, 2) BACT determinations made by TCEQ, 3) Entries in the RACT/BACT/LAER Clearinghouse maintained by EPA, and 4) Control technology determinations and emission limits imposed by air quality permitting authorities outside Texas.
To be consistent with the draft state/PSD permit, proposed Subpart UUUUU, and CAMR, all case-by-case MACT limitations established for the PC Boiler are also expressed as 12-month rolling averages, except for the organic HAP surrogate, CO, which is expressed as a 30-day average. For the auxiliary boiler, the MACT limitations in today's application were established in the averaging period units expressed in the previous Subpart DDDDD Boiler MACT standard.
The proposed suite of controls to limit HAP emission from the PC Boiler are a selective catalytic reduction system, a wet flue gas desulfurization system, state-of-the art mercury controls, and a fabric filter. These control technologies will meet the MACT emission limitations established pursuant to 30 TAC § 116.404 and meet the definition of MACT set forth in 30 TAC § 116.15(7).
LMS3 BOILER CASE-BY-CASE MACT
Mercury (Hg) - is the HAP of primary concern from coal-fired PC Boilers as demonstrated by EPA in their proposed Subpart UUUUU. NRG Texas first established the MACT floor, or the most stringent mercury emission limit that has been achieved in practice by the best controlled similar source. The LMS3 main boiler will be a PC Boiler with a nominal 800-MW generating capacity, burning subbituminous coal and blends of subbituminous coal with up to 20 percent by weight petroleum coke or up to 40 percent by weight bituminous coal. The universe of similar sources includes all PC Boilers burning subbituminous coal or blends of primarily subbituminous coal and lesser amounts of petroleum coke or bituminous coal.
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NRG Texas provided a detailed evaluation of mercury emission controls and recent permit limits for mercury emissions from PC Boilers in a June 2007 technical supplement to the initial state/PSD permit application. Based on information then available, NRG Texas determined that a mercury emission limit of 0.020 pounds per gigawatts-hour (lb/GWh) represented BACT for LMS3 for all fuel types. That emission limit is included in the draft of Permit Nos. 79188 and PSD-TX-1072 and remains more stringent than nearly all mercury emission limits for PC Boilers that have made initial compliance demonstrations.
To date, the most stringent mercury emission limit identified for any facility that burns, primarily, subbituminous coal and has made an initial compliance demonstration is a heat input based limit of 1.7 x 10-6 lb/MMBtu for Unit 4 at the Walter Scott, Jr. Energy Center in
Iowa. Based on a maximum heat input rate of 7,675 MMBtu/hr and a gross rating of 870 MW, this unit has a gross heat rate of approximately 8,820 Btu/kWh and its equivalent output-based limit is 0.015 lb/GWh. Although this unit has been operating for less than one year, NRG Texas conservatively concluded that the mercury emission limit of 0.015 lb/GWh has been demonstrated in practice and represents the MACT floor for boilers burning only subbituminous coal.
NRG Texas's evaluation did not reveal any PC Boiler burning a blend of subbituminous coal and a lesser amount of bituminous coal that achieves a mercury emission limit more stringent than that achieved by Walter Scott Unit 4. However, PC Boilers burning bituminous coal are known to be able to achieve lower mercury emissions rates than boilers burning subbituminous coal, and NRG Texas has taken this into account in establishing the MACT floor for mercury emissions from the PC Boiler. Specifically, NRG Texas has reviewed regulatory agency information to identify the most stringent mercury emission limit for any facility that burns primarily bituminous coal and has made an initial compliance demonstration as of May 2008. The results of this review indicate that the most stringent mercury emission limit identified is an output-based limit of 0.0075 lb/GWh pursuant to §7.29(5)(a)3.e of the Massachusetts Air Pollution Control Regulations. This limit took effect in January 2008 and is currently being achieved by the three bituminous PC Boilers at the Brayton Point Station. Although this limit has been in effect for only two months, NRG Texas conservatively concludes that the mercury emission limit of 0.0075 lb/GWh has been demonstrated in practice and would represent the MACT floor for boilers burning only bituminous coal.
To reflect the most stringent mercury emission limits demonstrated in practice for both subbituminous coal firing and firing of subbituminous coal blends, this analysis indicates that the MACT floor for mercury emissions from the PC Boiler should be defined as follows:
When firing a blend that includes both subbituminous coal and bituminous coal, a weighted, output-based emission limit, based on a monthly rolling 12-month average, computed as follows:
Where:
ELb = Total allowable Hg in lb/GWh that can be emitted to the atmosphere during
any12-month period when a blend of fuels was burned.
ELi = Hg emissions limit for the subcategory i (coal rank), 0.015 lb/GWh for
subbituminous coal and petroleum coke and 0.0075 lb/GWh for bituminous coal;
HHi = GWh contributed by the corresponding subcategory i (coal rank) burned
during the compliance period; and
n = Number of subcategories (coal ranks) being averaged.
During 12-month periods when a blend of fuels including bituminous coal is burned, the applicable Hg emission limit will vary with the amount of bituminous coal. For example, if a 60/40 blend of subbituminous and bituminous coals is burned, the Hg emission limit will be 0.012 lb/GWh; for an 80/20 blend, the limit will be 0.0135 lb/GWh.
NRG Texas and the TCEQ also reviewed the available literature to identify whether a "beyond-the-floor" MACT emission limit would be appropriate for mercury emissions from the PC boiler. This review identified no other methods for potentially reducing emissions to a greater degree. Thus, the MACT floor represents the most stringent limit achievable. It should be noted that the mercury emission limits presented above, Unit 4 at the Walter Scott, Jr., Energy Center in Iowa for subbituminous coal firing and the three bituminous coal fired boilers at the Brayton Point Station are based on the use of activated carbon injection in conjunction with state-of-the-art control equipment for reducing emissions of NOX, SO2, and
particulate matter. This is the most effective of all identified mercury emission control strategies, irrespective of cost, and is consistent with the planned air pollution control technologies for the LMS3 PC boiler.
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It should be noted that this case-by-case MACT emission limit for mercury emissions from LMS 3 is based on new compliance demonstration data generated after NRG Texas submitted the LMS3 permit application in June 2006. The mercury emission limit of 0.02 lb/GWh established as BACT in the draft of Permit Nos. 79188 and PSD-TX-1072 would have represented case-by-case MACT for Limestone Unit 3 at the time of permit application submittal if a case-by-case MACT determination had been an applicable requirement at that time.
Non-Mercury HAP Metals - HAP metals other than mercury are emitted in the form of particulate matter, and particulate matter air pollution control devices are the only identified control technology for non-mercury HAP metals emissions. The design and operation of these devices is not based on the control of emissions of individual metals to meet target levels; rather these devices are designed and operated to meet emission limits for the particulate matter category as a whole. Therefore, NRG Texas proposes the use of filterable particulate matter emissions as a surrogate for non mercury HAP metals emissions. As such, a filterable particulate matter emission limit can be established which represents the case-by-case MACT for all non-mercury HAP metals, as has been EPA's practice when establishing MACT emission standards for source categories emitting HAP metals.
NRG Texas provided a detailed evaluation of particulate matter emission controls and recent permit limits for particulate matter emissions from coal-fired PC Boilers in the state/PSD permit application technical supplement submitted in June 2007 that established a filterable particulate matter emission limit of 0.015 lb/MMBtu as BACT for the PC boiler for all fuel types. That emission limit is included in the draft of Permit Nos. 79188 and PSD-TX-1072 to represent BACT and neither NRG Texas nor the TCEQ found any more stringent emission limit for a pulverized coal-fired PC Boilers that has made its initial compliance demonstration. Accordingly, the MACT floor for emissions of non-mercury HAP metals from the PC boiler is a filterable particulate matter emission limit of 0.015 lb/MMBtu. As part of this analysis, a review of the available literature was performed to determine whether a "beyond-the-floor" MACT emission limit would be appropriate for emissions of non-mercury HAP metals from the PC boiler. This review shows through advances in fabric filter technology and in the continued commercialization of wet electrostatic precipitator technology, a more stringent filterable particulate matter emission limit of 0.012 lb/MMBtu is achievable. NRG Texas has determined that the cost of achieving this additional emission reduction through the use of advanced fabric filter baghouse technology at LMS3 is acceptable. Fabric filter baghouses do not cause any appreciable non-air quality health or environmental impacts, nor are they characterized by unacceptable energy requirements. Accordingly, a filterable particulate matter emission limit of 0.012 lb/MMBtu has been
determined to represent beyond-the-floor MACT for the PC boiler. This emission limit will be achieved using the planned air pollution control technologies represented in the application for Permit Nos. 79188 and PSD-TX-1072.
As noted above, wet electrostatic precipitator technology was identified as another add-on control technology that could be used to achieve a beyond-the-floor filterable particulate matter emission limit of 0.012 lb/MMBtu. The wet electrostatic precipitator is less preferred than the fabric filter baghouse upgrade because of its unacceptable economic costs. The annualized cost of installing, maintaining and operating a wet electrostatic precipitator is estimated to be $22.4 million (a detailed cost estimate is provided in Appendix C of the application). Adding a wet electrostatic precipitator to the planned air pollution control technologies for the PC boiler would not achieve a more stringent limit than the proposed 0.012 lb/MMBtu. However, the emission reduction achievable with this technology is not material, as the economic costs are unacceptable in any event. Even assuming that the wet electrostatic precipitator in this configuration could achieve a further 50 percent reduction, the cost effectiveness would be more than $100,000 per ton of reduction in filterable particulate matter emissions and approximately $10 million per ton of non-mercury HAP metals emissions.
No direct comparison can be made between the case-by-case MACT emission limit for the PC boiler and the new source MACT proposed by EPA under Subpart UUUUU because EPA elected not to propose an emission standard for non-mercury HAP metals from coal-fired EUSGUs. An emission limit of 0.012 lb/MMBtu for filterable particulate matter should be established as the beyond-the-floor MACT limit for emissions of non-mercury HAP metals from the PC boiler.
Acid Gases - Hydrogen chloride (HCl) and hydrogen fluoride (HF) are inorganic, vapor phase HAPs formed from combustion of trace quantities of the halogens chlorine and fluorine in the fuel.
NRG Texas provided a detailed evaluation of acid gas emission controls and recent permit limits for HCl and HF emissions from coal-fired PC Boilers in the state/PSD application technical supplement submitted in June 2007. Based on that evaluation, NRG Texas determined that HCl and HF emission limits of 0.0023 lb/MMBtu and 0.0007 lb/MMBtu, respectively, represent BACT for the PC boiler for all fuel types. Those emission rates were agreed to by the TCEQ and included in the draft of Permit Nos. 79188 and PSD-TX-1072.
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HCl - To date, available information shows that the most stringent HCl emission limit identified for any facility that burns primarily subbituminous coal and has made an initial compliance demonstration is 0.0029 lb/MMBtu for Unit 4 at the Walter Scott, Jr., Energy Center in Iowa. Although this unit has been operating for less than one year, NRG Texas has conservatively concluded that the HCl emission limit of 0.0029 lb/MMBtu has been demonstrated in practice and represents the MACT floor for boilers burning only subbituminous coal. To date, available information shows that the most stringent HCl emission limit identified for any facility that burns primarily bituminous coal and has made an initial compliance demonstration is 0.0024 lb/MMBtu for Unit 3 at the Cross Generating Station in South Carolina." Based on this emission limit, NRG Texas concludes that an HCl emission limit of 0.0024 lb/MMBtu has been demonstrated in practice and represents the MACT floor for boilers burning primarily bituminous coal.
Because continuous monitoring for HCl emissions is not feasible, the MACT floor for HCl emissions from the PC boiler should be established based on the use of a worst-case blend containing 60 percent by weight subbituminous coal and 40 percent by weight bituminous coal. The corresponding proposed MACT floor emission limit is 0.0027 lb/MMBtu. HF - To date, available information shows that emissions, based on the use of subbituminous coals primarily from New Mexico with very low fluoride content of 86 parts per million by weight or less. Applying this control efficiency of 95.72 percent to the HF emission calculations for the PC boiler, and considering the average coal fluoride concentrations of the coals proposed to be burned at this unit, results in an annual average HF emission rate of 0.0005 lb/MMBtu. This value represents the MACT floor for the PC boiler.
NRG Texas reviewed available literature to determine whether a beyond-the-floor MACT emission limit would be appropriate for emissions of acid gases from the PC boiler. This review shows that, due to the continued commercialization of wet electrostatic precipitator technology, lower hydrogen chloride and hydrogen fluoride emissions are likely achievable through the addition of a wet electrostatic precipitator to the planned air pollution control technologies for Limestone Unit 3. The hydrogen chloride and hydrogen fluoride emission reductions achievable with this technology addition are unknown, because there are no performance data for any similarly configured existing facility. However, the precise level of emission reduction achievable with this technology is not material to the case-by-case MACT determination, as the economic costs are unacceptable in any event. The required total capital investment for a wet electrostatic precipitator at LMS3 is $128 million and the total annualized cost of installing, maintaining and operating this technology is estimated to be $22.4 million (details are in Appendix C of the application). Even assuming that the wet electrostatic precipitator in this configuration could remove all the remaining HCl and HF,
which overstates the achievable reductions by a substantial amount, the cost effectiveness would be more than $200,000 per ton of reduction in combined emissions of these pollutants.
The BACT emission limit for HCl of 0.0023 lb/MMBtu included in the draft of Permit Nos. 79188and PSD-TX-1072 should be established as the case-by-case MACT emission limit for HCl from the PC boiler. An HF emission limit of 0.0005 lb/MMBtu, which is more stringent than the BACT emission limit included in the draft permit, should be established as the case-by-case MACT emission limit for HF. It should be noted that this case-by-case MACT emission limit for HF is based on new compliance demonstration data generated after NRG Texas submitted the state/PSD permit application for the LMS3 project in June 2006. The BACT emissions limit for HF of 0.0007 lb/MMBtu included in the draft Permit Nos. 79188 and PSD-TX-1072 would have represented case-by-case MACT for the PC boiler at the time of the initial state/PSD permit application submittal if a case-by-case MACT determination had been an applicable requirement at that time.
No direct comparison can be made between the case-by-case MACT emission limits for HCl and HF for the PC boiler and the new source MACT proposed by EPA under Subpart UUUUU because EPA elected not to propose emission standards for acid gases from coal-fired PC Boilers.
Organic HAPs - Coal-fired PC Boilers emit organic HAPs due to incomplete combustion of the fuel, the same mechanism by which CO and VOC emissions are produced. As set forth in Sections 4.2.4 and 4.2.5 of the initial state/PSD permit application submitted in June 2006 and in Sections 4.4 and 4.5 of the permit application technical supplement submitted in June 2007, good combustion practices represent the only technically feasible control technology or technique for organic HAP emissions. Thus, NRG Texas concludes that CO emissions are an effective surrogate for emissions of organic HAP emissions. As such, a CO emission limit can be established which represents the case-by-case MACT for all organic HAPs. This is consistent with EPA's practice when establishing MACT emission standards for source categories emitting organic HAPs from combustion processes.
NRG Texas presented a detailed evaluation of CO and organic HAP emission controls and recent permit limits for CO emissions from PC Boilers fired primarily with subbituminous coal in Section 4.4 of the permit application technical supplement submitted to the TCEQ in June 2007. Based on that evaluation, NRG Texas determined that a CO emission limit of 0.15 lb/MMBtu, based on a 30-day average and excluding periods of planned start-up and shutdown, was BACT for the PC boiler. That emission limit is included in the draft of Permit Nos. 79188 and PSD-TX-1072. NRG Texas's case-by-case MACT analysis did not reveal any more stringent emission limit for any PC Boilers that fires primarily
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subbituminous coal, uses low-NOx burners to achieve a low NOx emission rate, and has made its initial compliance demonstration. Those projects with a lower CO limit have higher NOXshort-term limits which reflects the balancing needed between NOXand CO in
low-NOX burners. Accordingly, the MACT floor for emissions of organic HAPs from
LMS3 corresponds to a CO emission limit of 0.15 lb/MMBtu, based on a 30-day average and excluding periods of planned start-up and shutdown.
As part of this case-by-case MACT analysis, NRG Texas performed a review to determine whether a "beyond-the-floor" MACT emission limit would be appropriate for emissions of organic HAPs from the PC boiler. This review shows that the MACT floor represents the most stringent limit achievable. The best-controlled similar sources all use good combustion practices to control particulate matter emissions. This is the most effective of all identified control strategies for emissions of CO and organic HAPs, irrespective of cost. The BACT emission limit for CO of 0.15 lb/MMBtu, as a 30-day average and excluding periods of planned start-up and shutdown, included in the draft of Draft Permit Nos. 79188 and PSD-TX-1072 should be established as the case-by-case MACT emission limit for emissions of organic HAPs from the PC boiler. No direct comparison can be made between the case-by-case MACT emission limit for the PC boiler and the new source MACT proposed by EPA under Subpart UUUUU because EPA elected not to propose an emission standard for organic HAPs from coal-fired EUSGU.
Planned Start-Up and Shutdown emissions were addressed in Draft Permit Nos. 79188 and PSD-TX-1072 and where necessary were identified in the MAERT. LMS3 will start-up on natural gas which will minimize emissions and allow the various control devices to be brought to operating temperature before coal is fired. The baghouse to control filterable PM as a surrogate for non-mercury HAP metals will operate during planned start-up and shutdown and delaying the firing of coal minimizes Hg emissions. The scrubber will also be operating during planned start-up and shutdown to control acid gases HCl and HF. Natural gas also allows for better combustion control during planned start-up and shutdown to minimize CO the surrogate for organic HAPs. Maintenance activities were not addressed by the applicant and are not part of this permit. They will be addressed in a future permit action.
AUXILIARY BOILER CASE-BY-CASE MACT
NRG Texas is proposing no add-on controls to achieve MACT emissions limits for the auxiliary boiler. As discussed in the following sections, MACT will be achieved through the use of sweet natural gas as the fuel and through good combustion practices.
Emissions of metal HAPs are predominantly in the form of particulate matter, and air pollution control devices are the only identified control technology for metal HAP emissions. However, particulate control devices are not applied to natural gas-fired boilers because metal HAPs are present in negligible quantities in the fuel, and the quantity and size of the particles do not lend themselves to effective removal. Therefore, NRG Texas is proposing, as means to achieve case-by-case MACT for metal HAPs, the use of good combustion practices and the use of natural gas as the fuel. This proposal is consistent with EPA's promulgated Subpart DDDDD Boiler MACT, which places no limits on the emissions of PM (the surrogate for non-gaseous metal HAPs) from natural gas-fired boilers and process heaters.
NRG Texas reviewed EPA's RBLC database for the 10-year period from April 1998 through April 2008 to identify metal HAP emission limits for gas fired auxiliary boilers. Although eleven natural gas-fired auxiliary boiler units were identified, metal HAP limits were not listed with any of the entries. The PM limits for ten of the eleven units varied from a minimum of 0.0022 lb/MMBtu to a maximum of 0.0200 lb/MMBtu with an average of 0.0071 lb/MMBtu. For eight of these units, either the use of good combustion practice, use of natural gas, or use of low ash fuel was listed as the control technology basis.
NRG Texas did not propose a PM BACT limit for the auxiliary boiler in its June 2006 application for Permit No. 79188/PSD-TX-1017, although an emission factor of 0.0075 lb/MMBtu was used to estimate total PM emissions from the auxiliary boiler. This emission factor, taken from EPA's AP-42 Chapter 1.4, pertaining to natural gas firing in boilers, is for total PM, which is the sum of the condensable emission factor (5.7 lb/106 scf) and the filterable emission factor (1.9 lb/106 scf). The filterable PM emission rate corresponding to the AP-42 filterable PM emission factor is approximately 0.002 lb/MMBtu. As part of this analysis, NRG Texas reviewed the available literature to identify whether a "beyond-the-floor" MACT emission limit would be appropriate for emissions of metal HAPs from the auxiliary boiler. This review showed no better level of control than what is established at the MACT floor; that is, the use of good combustion practices and clean gaseous fuels is the most effective among all identified particulate matter emission control strategies, irrespective of cost, and is consistent with the planned air pollution control technologies for the auxiliary boiler.
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Although the RBLC database search and review identified a range of PM emissions limits, all the limits are based in the use of natural gas. Because no other control option either exists or is cost effective for the control of the very fine particulate emissions from the firing of natural gas, there is no way to effectively control PM emissions other than through good combustion control. As such, the following work practices and limit are proposed as case-by-case MACT for the emission of metal HAPs for the auxiliary boiler: a filterable PM limit of 0.0022 lb/MMBtu along with the use of natural gas as fuel and good combustion practices. This filterable emission limit is consistent with the lowest PM BACT limit identified in the RBLC database.
Organic HAPs are emitted from natural gas-fired auxiliary boilers due to incomplete combustion of the fuel. The promulgated and vacated Subpart DDDDD Boiler MACT used the monitoring of carbon monoxide emissions as the surrogate for determining the effectiveness of the combustion of organic HAPs from boilers because of the direct correlation between CO and the formation of organic HAPs. CO is a good indicator of incomplete combustion and easily monitored. Minimizing CO emissions will minimize organic HAPs.
Although the Boiler MACT has been vacated, CO remains an appropriate surrogate for organic HAPs. Irrespective of the Boiler MACT vacatur, it has been established in precedent that CO is a surrogate for organic HAPs. Therefore, a review of the "best controlled similar source" for CO emissions can be performed to establish the MACT floor for organic HAP emissions from the proposed auxiliary boiler.
NRG Texas conducted a review of EPA's RBLC database for the ten-year period from April 1998 through April 2008 to identify organic HAP emission limits for gas-fired auxiliary boilers. Eight units were identified with CO limits that varied from a minimum of 0.040 lb/MMBtu to a maximum of 0.087 lb/MMBtu with an average of 0.073 lb/MMBtu. For five of these units the control technology was listed as either the use of good combustion practice, and/or use of natural gas. Oxidation catalysts were listed as the control technology for one unit, with an associated CO limit of 100 ppm (by volume, on a dry basis, and at 7 percent oxygen). The lowest CO limit reported for any unit was a BACT level of 0.04 lb/MMBtu, or approximately 50 ppm (by volume, on a dry basis, at 3 percent oxygen, and for a 3-hour average), with good combustion practice and the use of natural gas as the method of meeting this limit. This level is one-half of the California South Coast Air Quality District limit of 100 ppmv at 3 percent percent oxygen for a 3-hour average.
These RBLC limits compare to the promulgated and rescinded Boiler MACT limit for CO of 400 ppm (by volume, on a dry basis, and at 3 percent oxygen), or about 0.3 lb/MMBtu. NRG Texas proposed a BACT limit for the auxiliary boiler of 0.08 lb/MMBtu in the 2006 application for Permit Nos. 79188 and PSD-TX-1072.
The range of emissions limits identified above - from 50 ppm to 400 ppm - reflects that minimizing CO emissions is not the primary pollution control objective for well controlled and properly operated natural gas-fired auxiliary boilers. Rather, the proper design, tuning, and operation of these units to minimize NO, emissions is of primary importance, and effective control of NOX, is accomplished at the expense of increasing CO emissions. This
suggests that the MACT floor for organic HAPS is more reasonably set as the use of good combustion practice and the use of natural gas as fuel.
NRG Texas performed the following "beyond the floor" analysis for organic HAPs from the auxiliary boiler, evaluating technically feasible alternatives for the control of organic HAPS based a comparison of their energy, environmental, and economic impacts to the corresponding impacts with the use of good combustion practices only.
Technical Feasible Alternatives - the use of oxidation catalysts could reduce emissions of organic HAPs, and that there are no technical obstacles to the use of this technology with natural gas-fired boilers. No other technically feasible alternatives to good combustion practices were identified.
Energy Impacts of Alternatives - No significant energy impacts would preclude the use of good combustion practices or oxidation catalysts for the control of CO emissions. However, catalytic oxidation systems consume electrical energy to overcome catalytic oxidation draft losses because of the pressure drop across the catalyst. While the energy costs of such systems are real and quantifiable, they do not in and of themselves eliminate this control technology from further consideration.
Environmental Impacts of Alternatives - No significant environmental impacts would preclude the use of good combustion practices as the means to control organic HAP emissions. The oxidation catalysts will have a minor environmental impact due to the disposal of the waste that is generated from the spent catalyst. In addition, oxidation catalysts will promote the conversion of the trace amounts of sulfur in the natural gas to sulfuric acid mist. However, the amounts of sulfur in natural gas are so small as to make the impact of sulfuric acid mist formation insufficient to eliminate the use of oxidation catalyst from an environmental standpoint.
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Economic Impacts of Alternatives - Because all new gas-fired boilers would be designed with good combustion practice as the baseline, the economic impact of good combustion practices is zero. The typical oxidation catalyst for CO is a rhodium or platinum (noble metal) catalyst on an alumina support material. This catalyst is installed in an enlarged duct or reactor with flue gas inlet and outlet distribution plates. Acceptable catalyst operating temperatures range from 400°F to 1250°F, with the optimum temperature range being 850°F to 1100 °F. Below 600°F, a greater catalyst volume would be required to achieve the same reduction. To achieve this temperature range in the proposed auxiliary boiler, the catalyst would need to be installed in the boiler before the economizer. Because the proposed boiler is small by boiler standards, it will be a package boiler of standard design. Standard design package boilers do not come with oxidation catalyst installed in the economizer section. Typical flue gas temperatures leaving a standard design package boiler are much lower than the acceptable minimum operating temperature for oxidation catalyst. As such, a standard design package boiler would not be obtainable, and a special design boiler would be required. This, in turn, would significantly increase the cost of oxidation catalyst technology for a unit as small as the proposed auxiliary boiler - a cost that would be prohibitive within the context of the size and limited use of the boiler. This conclusion is consistent with the now rescinded Industrial Boiler MACT standards and work practices, which did not require the use of oxidation catalysts.
A CO emission limit of 0.04 lb/MMBtu is proposed as the case-by-case MACT surrogate for emissions of organic HAPs from the proposed auxiliary boiler. This level is consistent with the lowest CO BACT limit identified in the RBLC database. Limiting the AUX boiler to 10 percent annual capacity also impacts the cost effectiveness of additional controls. Planned Start-Up and Shutdown emissions were addressed in draft Permit Nos. 79188 and PSD-TX-1072 for AUX and where necessary were identified in the MAERT. Natural gas also allows for better combustion control during planned start-up and shutdown to minimize CO the surrogate for organic HAPs. Natural gas also contains no quantifiable HAP metals. Maintenance activities were not addressed by the applicant and are not part of this permit. They will be addressed in a future permit action.
VII. AIR QUALITY ANALYSIS
A full air quality analysis was performed for draft Permit Nos. 79188 and PSD-TX-1072 and is not required for this case-by-case MACT permit.
VIII. NATIONAL AMBIENT AIR QUALITY STANDARDS ANALYSIS
A full NAAQS analysis was performed for draft Permit Nos. 79188 and PSD-TX-1072 and is not required for this case-by-case MACT permit.
IX. INCREMENT ANALYSIS
An increment analysis was performed for draft Permit Nos. 79188 and PSD-TX-1072 and is not required for this case-by-case MACT permit..
X. AIR QUALITY MONITORING
Not required for this case by case MACT permit. XI. ADDITIONAL IMPACTS ANALYSIS
The impact on air quality resulting from any commercial or industrial growth associated with Permit HAP-14 were accounted for the review of draft Permit Nos. 79188 and PSD-TX-1072.
XII. AIR TOXICS REVIEW
A modeling evaluation, using full dispersion modeling, of site wide emissions was conducted for draft Permit Nos. 79188 and PSD-TX-1072 and the analysis only resulted in small reductions in filterable PM, HF and Hg emission rates.
XIII. CONCLUSION
NRG TEXAS has provided a detailed case-by-case analysis to establish federally enforceable MACT emission limitations for CO as a surrogate for organic HAPs, filterable PM as a surrogate for non-mercury HAP metals, HF, HCl, and Hg for LMS3. It also establishes federally enforceable MACT emission limitations for CO as a surrogate for organic HAPs and filterable PM as a surrogate for non-mercury HAP metals for AUX. Therefore, the TCEQ Executive Director has made a preliminary determination to issue this HAP-14 MACT air permit to NRG TEXAS at its Limestone Electric Generating Station near Jewett in Limestone County, Texas.
