Desert Basin Generating Station - Casa Grande Permit Summary

SALT RIVER PROJECT AGRICULTURAL IMPROVEMENT AND POWER DISTRICT CASA GRANDE

1. Introduction

This permit relates to an electrical power plant owned and operated by the Salt River Project Agricultural Improvement and Power District (SRP), a political subdivision of Arizona.
SIC Code: 4911
NAICS Code: 221100
Location: Desert Basin Generating Station (DBGS) at 1872 North Burris Road, Casa Grande, Arizona, parcel identified by Pinal County Assessor's Parcel #503-34-015B.
The facility lies in a PM10 non-attainment area with a gross generating capacity of 734 MW, comprising:
- Two combined cycle systems (CCS1 and CCS2)
- Two simple cycle combustion turbines (SCCT4 and SCCT5) rated approximately 49.5 MW each.
Each CCS consists of a combined cycle combustion turbine (CCCT) rated approximately 187 MW, and a supplementary-fired heat recovery steam generator (HRSG) feeding a shared steam turbine generator rated at approximately 262 MW.
Permit V20678.R02 was reopened due to an EPA order in response to a petition (No. IX-2022-3) from Sierra Club. The petition required revisions in specific sections of the permit.
- Permit Revision V20678.R02 authorizes the installation of two General Electric (GE) LM6000PC combustion turbines (SCCT4 and SCCT5) with a combined capacity of 99 MW.
Combustion gases exit SCCTs at 760 °F to 1,100 °F. An air injection system, also installed, reduces exhaust gas temperature for SCR systems to about 800 °F at catalyst inlet.
Exhaust undergoes post combustion treatment with:
- Oxidation catalysts for CO and VOC control
- High-temperature SCR systems for NOx emissions control
The upgrade involved physical changes at existing major stationary sources, quantified for purposes of determining major modification applicability. An Actual-to-Potential (ATP) analysis was conducted defining Project Emissions Increase (PEI) as the differences between Potential to Emit (PTE) and Baseline Actual Emissions (BAE).
- The PEI is equal to PTE for the new units, and thus, does not trigger New Source Review (NSR) or Prevention of Significant Deterioration (PSD) requirements.
- Permit Revision V20678.R01 details changes undertaken in the Power Systems Mfg., LLC (PSM) Combustion Turbine Upgrade Project affecting existing emission units.
Specific upgrades include:
- Flamesheet Combustion System
- Gas Turbine Optimization Packages (GTOP) 7
- Auto Tune System
- Inlet Bleed Heat System
- Part Load Performance Package
Following revisions, there were no increases in NSR pollutant emissions, thus exempting it from PSD review.
The plant maintains a major emitting source status for CO, NOx, PM2.5, and PM10, subjecting modifications to PSD requirements as per the Clean Air Act (1990).

2. Listing of (Federally Enforceable) Applicable Requirements

Governed by 40 CFR §70.5(c)(4), applicable regulations include:
- Pinal County Air Quality Control District (PCAQCD) Regulations:
- §3-1-040: Applicability and Classes of Permits
- §3-1-050: Permit Application Requirements
- §3-1-081: Permit Conditions
- §3-1-082: Emission Standards and Limitations
- §3-1-083: Compliance Provisions
- §3-1-103: Annual Emissions Inventory Questionnaire
- §3-1-132: Right of entry
- §3-1-150: Monitoring
- §3-1-160: Test Methods and Procedures
- §3-1-170: Performance Tests
- §3-1-173: Quality Assurance
- §3-1-177: Stack Height Limitation
- Permit Requirements for New Major Sources…
- Pinal-Gila Counties Air Quality Control District (PGCAQCD) Regulations (adopted March 31, 1975):
- 2-8-300: Visibility Limiting Standards
- 4-2-040: Fugitive Dust Standards
- 7-3-5.1: NOx Emissions - Fuel Burning Equipment
New Source Performance Standards (NSPS) 40 CFR Part 60:
- Subpart A: General Provisions
- Subpart JJJJ: Stationary Spark Internal Combustion Engines
- Subpart KKKK: Standards of Performance for Stationary Combustion Turbines
- Subpart TTTT: Standards of Performance for Greenhouse Gas Emissions
National Emission Standards for Hazardous Air Pollutants (NESHAP) 40 CFR Part 63 Subpart ZZZZ: Stationary Reciprocating Internal Combustion Engines (RICE)
40 CFR 63.1-63.15 as listed in the 63 Subpart ZZZZ table
Compliance Assurance Monitoring 40 CFR Part 64
Acid Rain Provisions; CAA Title IV:
- 40 CFR Part 72: Permit Regulation
- 40 CFR Part 73: Sulfur Dioxide Allowance System
- 40 CFR Part 75: Continuous Emission Monitoring which supports the Acid Rain Program
Ozone-depleting substances handling regulations under CAA §§608 & 611
National Emission Standards for Hazardous Air Pollutants (NESHAP) 40 CFR Part 51 Subpart M, Asbestos.

3. Prospective Compliance Requirements

A. Compliance Plan

The compliance plan ensures ongoing adherence to permit requirements and applicable regulations as mandated by 40 CFR §70.5(c)(8).

B. Compliance Schedule

Currently, compliance is being met and thus, no compliance schedule is necessary as indicated in 40 CFR §§70.5(c)(8) and 70.6(c)(3).

4. Authority to Construct

Emission sources detailed in the Equipment Schedule are governed by enforceable limitations in this permit, ensuring compliance with the ambient air quality standards.

A. Units CCS1 & CCS2 System Requirements

Each unit must:
1. Incorporate "Low-NOx" design turbines
2. Employ selective catalytic reduction systems for NOx reduction via an ammonia injection and catalyst system
3. Exhaust through stacks with specific configurations: not exceeding 20’ outlet diameter nor less than 160’ height
4. Include necessary platforms and sampling ports for testing
5. Use separate fuel-flow meters for turbines and duct burners
Fuel and Emission Limitations:
- Natural gas heat input for duct burners is limited to 1,824,000 mmBtu/year/unit, averaged over 12 months.
- Must limit startup events across both units to 638 events annually (with options for alternatives).

B. Units SCCT4 & SCCT5 System Requirements

Limit natural gas annual heat input to 1,996,000 mmBtu (12 month rolling average).
Continuous emissions monitoring systems must be installed on both units for monitoring NOx and CO emissions during operations.

C. Fuel Use Limitations

The only permissible fuel is pipeline natural gas with a maximum sulfur content of 0.0075 grains per dry standard cubic foot.

5. Emission Limitations and Controls

A. Applicable Limitations

The most stringent standard among various applicable standards or limitations in the permit will apply.

B. Allowable Emissions

Authorized emissions are specified in Section 4 of this permit; no emissions exceeding de minimis amounts in new modifications without appropriate permissions.

C. Emission Limits – SCCT4 and SCCT5

Start-up and Shutdown Limitations:
1. Definitions:
- Start-up: 30-min post initiation of fuel flow
- Shutdown: 9-min before fuel cutoff
- Malfunction: sudden unavoidable failure of control equipment not caused by maintenance.
1. Rolling limits for PM/PM10/PM2.5 emissions: not to exceed 4.99 tons/year.
2. NOx Rolling limits: not to exceed 19.99 tons/year.
3. VOC Rolling limits: not to exceed 19.99 tons/year.
4. CO Rolling limits: not to exceed 49.99 tons/year.

D. NOx Emission Limitations - NSPS Subpart KKKK

Limit for SCCT4 and SCCT5:
- 25 ppm at 15% O2 (1.2 lb/MWh) at >75% peak load, and
- 96 ppm at 15% O2 (4.7 lb/MWh) at <75% peak load.

E. CO2 Emission Limitation – NSPS TTTT (SCCT4 and SCCT5)

Limited to 50 kg CO2/GJ or less, based on certain operational conditions.

F. Emission Limits – CCS1 and CCS2

BACT Limitations: Specific definitions guiding the control of pollutants during start-up and shutdown phases, as well as operational guidelines concerning emissions.

(Note: The subsequent sections involve additional specific limitations, monitoring requirements, compliance measures, and procedural norms applicable to the facilities and their operations related to emissions and air quality management.)

6. Compliance Demonstration

A. Non-NSPS and NSPS Subpart KKKK NOX Tests

Periodic Performance Testing: Must be conducted at maximum heat input capacity. Continous monitoring systems must operate prior to testing. Tests cover:
- NOx emissions (Method 7E or CEMS RATA)
- CO emissions (Method 10)
- PM emissions (Method 5 or Method 201A)
- VOC emissions (Method 25a)
- Opacity (Method 9)

B. Test Protocols

Must be submitted 30 days prior to testing.

C. Performance Test Notifications

30 days notice required.

D. Test Reports

Due within 45 days post-testing and must detail specific emission rates.

E. Recurring Testing Cycle

Performance tests to repeat within five years of prior test; annual NOX performance tests if not using CEMS.

F. Elective Testing for Startup/Shutdown Impacts

Designed to quantify NOx emissions from start-up/shutdown events versus steady state operation and inform regulatory impacts, requires advance district approval.

G. Full-Speed-No-Load Testing Notification

Required notifications during maintenance/testing operations.