EPA approves Colorado plan to control regional haze

The U.S. Environmental Protection Agency is proposing to approve a state implementation plan (SIP) for the state of Colorado that calls for various new emissions controls and unit shutdown for coal-fired power plants in the state.

EPA said in a March 26 Federal Register notice that plans to approve a revised SIP filed by Colorado in May 2011 that outlines what the state wants to do to comply with EPA’s regional haze program. States are required to assure reasonable progress toward the national goal of achieving natural visibility conditions in Class I areas. Written comments on the proposed approval will be taken until May 25.

In lieu of individual BART determinations, the state submitted a BART alternative for three of the subject-to-BART sources: Cherokee Unit 4, Pawnee Unit 1 and Valmont Unit 5. EPA is proposing to approve the BART alternative. For the rest of the subject-to-BART sources, the state provided analyses that took into consideration the five factors as required by the Clean Air Act (CAA). EPA is proposing to approve the BART determinations submitted by the state for Cemex Lyons Kiln and Dryer, Coors‘ CENC Units 4-5, Comanche Units 1-2, Craig Unit 2, Hayden Units 1-2 and Martin Drake Units 5-7.

Comanche Units 1-2 – BART-eligible facilities are Units 1-2 of Public Service Co. of Colorado’s (PSCO) Comanche plant. The plant consists of Units 1-3. Unit 1 is rated at 325 MW and Unit 2 is rated at 335 MW. The boilers burn sub-bituminous coal. Unit 3 is a new facility with a full suite of modern emissions controls already in place. As part of the Unit 3 project, PSCO proposed to install NOx and SO2 control devices on Unit 1 and Unit 2 and take new emission limits on those units. In November 2008, PSCO installed LNBs with OFA and a lime spray dryer (LSD) on Unit 1, and in November 2007, PSCO installed low-NOx burners (LNBs) with overfire air (OFA) and a LSD on Unit 2. PSCO told the state that due to the increased use of wind resources, the boilers will be required to cycle more frequently to accommodate intermittent wind resources, and, therefore the units will run at low loads more frequently. As a result, the SO2 reduction levels will be lower during those times.

Based on its analysis, the state determined that the SO2 BART emission limit for Comanche Unit 1 is 0.12 lb/MMBtu (30-day rolling average) and for Unit 2 is 0.12 lb/MMBtu (30-day rolling average). EPA agrees with the state’s conclusions.

Comanche Station Units 1-2 currently have a NOx permit limit of 0.20 lb/MMBtu on a 30-day rolling average for each unit and a combined annual average limit of 0.15 lb/MMBtu. PSCO conducted testing in the fall of 2008 on Unit 2 using a temporary selective non-catalytic (SNCR) system. During the test periods, NOx reductions were less than 10%, and in some cases during testing, an actual increase in NOx emissions was observed. Based on the results of PSCO’s test of SNCR, the state did not evaluate SNCR further as a control option. The state has determined that the NOx BART emission limit for Comanche Unit 1 is 0.20 lb/MMBtu (30-day rolling average) and for Unit 2 is 0.20 lb/MMBtu (30-day rolling average). The state assumes that the BART emission limits can be achieved through the operation of existing LNBs and EPA agreed with that conclusion.

Comanche Units 1-2 are each equipped with baghouses to control PM emissions with an emission limit of 0.03 lb/MMBtu. Stack tests show that the baghouses are achieving a 99% reduction in PM. The state assumes the BART limit can be met with the operation of the existing fabric filter baghouses and EPA agreed.

Craig Units 1-2 – The Tri-State Generation & Transmission Association’s Craig plant is a coal-fired facility with a total net capacity of 1,264 MW, consisting of three units. Only Units 1-2 are BART-eligible, with each rated at a net capacity of 428 MW.

Craig Units 1-2 are currently controlled with wet flue gas desulfurization (FGD). The units have a current SO2 emission limit of 0.16 lb/MMBtu on a 30-day rolling average and a requirement to achieve a 90% reduction of SO2 (90-day rolling average). The state determined that an emission limit of 0.11 lb/MMBtu would be achievable without additional capital investment. The state assumes that the BART limits can be achieved through the existing wet FGD and EPA agreed.

Craig Units 1-2 are currently controlled with ultra low-NOx burners (ULNBs) plus OFA, achieving emission reductions of about 54% each. The state determined that the NOx BART emission limit for Craig Unit 1 is 0.27 lb/MMBtu (30-day rolling average) and for Unit 2 is 0.27 lb/ MMBtu (30-day rolling average). The state assumed that the BART emission limits can be achieved through the operation of SNCR and EPA agreed with that conclusion. Tri-State and the state agreed to a NOx plan for Craig Units 1-2 that is more stringent overall. It consists of emission limits associated with the operation of SNCR for Unit 1 and the operation of selective catalytic reduction (SCR) for Unit 2. These NOx limits are 0.28 lb/MMBtu (30-day rolling average) for Craig Unit 1 and 0.08 lb/MMBtu (30-day rolling average) for Craig Unit 2.

Craig Units 1-2 are each equipped with baghouses to control PM emissions with an emission limit of 0.03 lb/MMBtu. Colorado determined that the PM BART emission limit is 0.03 lb/MMBtu (30-day rolling average) at Craig Unit 1 and Unit 2. The state assumes, and the EPA agrees, that the BART emission limits can be met through the operation of the current baghouses.

Hayden Units 1-2 – PSCO’s Hayden Units 1-2 are also covered by BART. Unit 1 is a pulverized-coal front-fired dry-bottom boiler. Unit 2 is a pulverized-coal tangentially-fired, dry-bottom boiler.

Hayden Units 1-2 are currently controlled with LSDs. Both units have a current SO2 emission limit of 0.16 lb/MMBtu (30-day rolling average) and a requirement to achieve an 82% reduction of SO2 (30-day rolling average). The state determined that additional equipment and maintenance was reasonable for SO2 BART controls and that a more stringent 30-day rolling SO2 limit represents an appropriate level of emissions control for both units. The state determined that the SO2 BART emission limit for Hayden Unit 1 is 0.13 lb/MMBtu (30-day rolling average) and for Unit 2 is 0.13 lb/MMBtu (30-day rolling average). It assumes these limits can be met with the operation of the existing LSD systems and EPA has agreed with that finding.

Hayden Units 1-2 are currently controlled with LNBs plus OFA, achieving emission reductions of 54% and 33%, respectively. The state decided that the NOx BART emission limit for Unit 1 is 0.08 lb/MMBtu (30-day rolling average) and for Unit 2 is 0.07 lb/MMBtu (30-day rolling average). Colorado assumes, and EPA agrees, that the BART emission limit can met through the installation and operation of SCR.

Hayden Units 1-2 are each equipped with baghouses with an emission limit of 0.03 lb/MMBtu. The state has determined that the PM BART emission limit is 0.03 lb/MMBtu (30-day rolling average) for these units. The state assumes the BART emission limit can be met through the operation of the current baghouses and EPA has agreed.

Martin Drake – Colorado Springs Utilities’ Martin Drake facility consists of three steam driven turbine/generator units, Units 5-7, which are the only BART-eligible units at the facility. These units fire coal as the primary fuel. All three boilers are pulverized-coal, dry-bottom, front-fired boilers.

Martin Drake Units 5-7 are currently uncontrolled for SO2. The state determined that dry sorbent injection (DSI) was technically feasible for all three units and that dry FGD was technically feasible for Units 6-7. The state determined dry FGD was not technically feasible for Unit 5 because of space constraints. The state established these SO2 BART limits: 0.26 lb/ MMBtu (30-day rolling average) for Unit 5; 0.13 lb/MMBtu (30-day rolling average) for Unit 6; and 0.13 lb/MMBtu (30-day rolling average) for Unit 7. The state assumes the BART limits can be met with DSI on Unit 5 and dry FGD on Units 6-7. EPA agreed with the state’s conclusions.

Martin Drake Units 5-7 are currently controlled with LNBs achieving 54.7%, 52.8%, and 57.7% control, respectively. The state determined that ULNBs plus OFA constitute BART based on the low dollars-per-ton control costs and the visibility improvement afforded by this control technology. The state determined that the following are the NOx BART limits: 0.31 lb/MMBtu (30-day rolling average) for Unit 5 and Unit 6; and 0.29 lb/MMBtu (30-day rolling average) for Unit 7. The state assumes these limits can be achieved through the installation and operation of ULNBs plus OFA, and EPA agreed with that finding.

Martin Drake Units 5-7 are each equipped with baghouses with an emission limit of 0.03 lb/MMBtu, which the state decided is the BART limit. The state assumes, and EPA agrees, that the limit can be met with the operation of the current baghouses.

BART alternative adopted for several coal units

Colorado has adopted the PSCO BART Alternative Program (BART alternative) to meet the requirements for BART for PSCO Cherokee Unit 4, Valmont Unit 5, and Pawnee Unit 1, and reasonable progress goals for PSCO Arapahoe Units 3-4 and Cherokee Units 1-3.

EPA is also proposing to approve the state’s reasonable progress (RP) determinations for: Platte River Power Authority’s (PRPA) Rawhide Unit 101; Coors‘ CENC Unit 3; Colorado Springs’ Nixon Unit 1; Black Hills Energy’s Clark Units 1-2; Holcim Florence Cement Plant; Tri-State’s Nucla plant; Tri-State’s Craig Unit 3; and PSCO’s Cameo plant.

Rawhide – The PRPA Rawhide plant is located in Larimer County. Rawhide Unit 101 is a coal-fired unit with a rated capacity of 305 MW (gross). Rawhide also has five natural gas-fired combustion turbines. Unit 101 is the only subject-to-RP unit at the facility.

Rawhide Unit 101 is currently controlled with a dry FGD achieving over 72% SO2 reduction with a current permit limit of 0.09 lb/MMBtu (annual average). The state has determined that the SO2 RP emission limit for Rawhide Unit 101 is 0.11 lb/MMBtu (30-day rolling average), reflecting the actual performance of the current controls. It represents a more stringent limit than the current limit of 0.13 lb/MMBtu (30-day rolling average). The state assumes, and EPA agrees, that the RP limit can be achieved by the operation of the current LSD.

Rawhide Unit 101 is currently controlled with LNB, close coupled over fire air and SOFA achieving a 49.6% control. The state decided that the NOx RP emission limit for Rawhide Unit 101 is 0.145 lb/MMBtu (30-day rolling average). The state assumes that this limit can be achieved through the operation of enhanced combustion control (ECC). EPA agreed.

Rawhide Unit 101 is equipped with baghouses with an emission limit of 0.03 lb/MMBtu. The state has determined that the PM RP emission limit for Rawhide Unit 101 is 0.03 lb/MMBtu (30-day rolling average) and assumes that this limit can be achieved through the existing baghouses. EPA agreed.

Nixon – Colorado Springs’ Nixon plant consists of one coal fired boiler (Unit 1), an auxiliary boiler, the associated equipment needed for generating electricity, and two natural-gas-fired simple cycle combustion turbines driving electricity generators. The state determined that Unit 1 and the two combustion turbines were subject to RP. Unit 1 is a 227-MW unit with a pulverized-coal, dry-bottom, front-fired boiler that fires low-sulfur western coal as the primary fuel.

Nixon Unit 1 is currently uncontrolled for SO2. The state set the SO2 RP emission limit for Nixon Unit 1 as 0.11 lb/MMBtu (30-day rolling average). The state assumes, and the EPA agrees, that the emission limit can be achieved with dry FGD.

Nixon Unit 1 is currently controlled for NOx emissions with LNBs. The state decided that the NOx RP emission limit for Nixon Unit 1 is 0.21 lb/MMBtu (30-day rolling average). The state assumes that the limit can be achieved with ultra-low NOx burners with overfire air control. EPA agreed with that conclusion.

Nixon Unit 1 has baghouses with an emission limit of 0.03 lb/MMBtu. The state has determined that the PM RP emission limit is that same level and that it can be achieved through the operation of the existing baghouses. EPA agreed.

Nucla – The Tri-State Nucla facility consists of one coal-fired unit, Unit 4, with a rated capacity of 110 MW (gross). Nucla is an atmospheric circulating fluidized bed (CFB) unit.

Unit 4 is currently controlled for SO2 emissions by limestone injection achieving a 70% reduction in emissions. Unit 4 has a current permit limit of 0.4 lbs/MMBtu (30-day rolling average). The state has determined that the SO2 RP emission limit for Nucla Unit 4 is 0.5 lb/MMBtu (30-day rolling average). It assumes, and EPA agrees, that the emission limit can be achieved through the operation of the current limestone injection system.

In 2006, Tri-State installed a small-scale SNCR system on Nucla Unit 4 that injects anhydrous ammonia to achieve NOx reductions. Tri-State does not operate the SNCR system frequently. The state has determined that NOx RP for Nucla Unit 4 is 0.5 lb/MMBtu (30-day rolling average). Due to the uncertainty of the control efficiency of SNCR, the state determined that it was not reasonable for NOX RP control at this time. EPA agreed.

Nucla Unit 4 is equipped with baghouses with an emission limit of 0.03 lb/MMBtu. The state has determined that the PM RP emission limit is the same level and that the existing baghouses can do that job. EPA agreed.

Craig Unit 3 – The Tri-State Craig plant is a three-unit, coal-fired facility. Craig Units 1-2 are subject to BART, while the state determined Craig Unit 3 was subject to RP. Craig Unit 3 is a dry-bottom pulverized coal-fired boiler.

Craig Unit 3 is currently controlled with a dry FGD achieving over 80% SO2 reduction. The state considered various dry FGD upgrades. Based on the design of Unit 3, the state could not identify any performance additives that could be used and determined that Tri- State cannot use a more reactive sorbent or increase the pulverization level of sorbent. The state has determined that a SO2 limit lower than 0.15 lbs/MMBtu would not result in significant visibility and EPA agreed.

Craig Unit 3 is currently controlled with LNBs and OFA that were installed in 2009. The state has determined that the NOx RP emission limit for Craig Unit 3 is 0.28 lb/MMBtu (30-day rolling average), which it assumes can be achieved through the operation of SNCR. EPA agreed.

Craig Unit 3 is equipped with baghouses with an emission limit of 0.013 lb/MMBtu for PM filterable and 0.012 lb/MMBtu for PM10. The state has established PM RP at those levels and assumes the baghouses can meet these limits. EPA agreed.

Clark, Cameo opt out due to retirements

Black Hills/Colorado Electric Utility informed the state that Clark Units 1-2 will be shut down by Dec. 31, 2013. The shutdown will result in SO2, NOx and PM reductions of about 1,457 tpy, 861 tpy, and 72 tpy, respectively. The state determined the shutdown by that date is RP for this source.

PSCO informed the state that the coal-fired Cameo plant would be shut by the end of 2011, resulting in SO2, NOx and PM reductions of about 2,618, 1,140, and 225 tons per year, respectively. The state, with the agreement of EPA, assumed the shutdown is RP for this source.

About Barry Cassell 20414 Articles
Barry Cassell is Chief Analyst for GenerationHub covering coal and emission controls issues, projects and policy. He has covered the coal and power generation industry for more than 24 years, beginning in November 2011 at GenerationHub and prior to that as editor of SNL Energy’s Coal Report. He was formerly with Coal Outlook for 15 years as the publication’s editor and contributing writer, and prior to that he was editor of Coal & Synfuels Technology and associate editor of The Energy Report. He has a bachelor’s degree from Central Michigan University.