The U.S. Environmental Protection Agency is proposing to partially approve and partially disapprove a revision to the Nebraska state implementation plan (SIP) related to mostly coal-fired emissions and their impacts on visibility at national parks and other protected areas.
EPA said in a March 2 Federal Register notice that this revised SIP under the federal agency’s regional haze program was submitted by the Nebraska Department of Environmental Quality in July 2011. EPA, which is taking comment on the decision until April 2, is proposing to approve a portion of this SIP revision as meeting certain requirements of the regional haze program and to partially approve and partially disapprove those portions addressing the requirements for best available retrofit technology (BART) and the long-term strategy (LTS).
EPA is proposing a federal implementation plan (FIP) relying on its Transport Rule to satisfy BART for SO2 at one source, the coal-fired Gerald Gentleman power plant, to address these issues.
States must identify all BART-eligible sources in their SIP. Sources are subject to BART under certain criteria. Nebraska used its database to identify facilities with emission units in one or more of the 26 BART categories. EPA proposes to find that Nebraska adequately identified all BART-eligible sources within the state.
Nebraska then screened out some BART-eligible sources from being subject to BART on the basis that they do not cause or contribute to visibility impairment in a Class I protected area. Nebraska identified eight sources with impacts less than that its threshold and were therefore determined not to be BART-subject: Beatrice Nitrogen Plant; Ash Grove Cement; Don Henry Power Center; Lon D. Wright Power Plant; CW Burdick Generating Station; North Denver Station; NPPD Sheldon Station; and OPPD North Omaha Station.
Two facilities had impacts above the BART threshold: Omaha Public Power District Nebraska City Station (NCS) Unit 1 and Nebraska Public Power District Gerald Gentleman Station (GGS) Units 1 and 2. EPA proposes to find that Nebraska adequately determined which sources in the state were subject to BART.
The NPPD website said that GGS is Nebraska’s largest generating plant. Located near Sutherland, the plant consists of two coal-fired generating units, which together have the capability to generate 1,365 MW. Coal from Wyoming’s Powder River Basin provides fuel for the plant.
The OPPD website said that the coal-fired NCS Unit 1 has 646 MW of capacity.
Nebraska City unit emerges from review in good shape
BART determinations are made on three separate pollutants, SO2, NOx and particulate matter (PM).
Nebraska found that for NCS Unit 1, direct PM emissions only accounted for minimal visibility impairment in the most impaired year, 2001, at the closest Class I area, Hercules Glades. Nebraska concluded that direct PM emissions from NCS do not significantly contribute to visibility impairment, and therefore, a full five factor BART analysis for PM was not needed.
For GGS Units 1 and 2, direct PM emissions only accounted for minimal impairment in the most impaired year, 2003, at the closest Class I area, Badlands. Nebraska concluded that direct PM emissions from GGS do not significantly contribute to visibility impairment.
EPA said it agrees with both of these PM conclusions by Nebraska regulators.
Nebraska and EPA, though, have reached different conclusions as to whether NCS Unit 1 is located at a power plant with a generating capacity in excess of 750 MW, or not. If NCS falls within this category, then the BART guidelines must be followed in determining BART limits and the presumptive limits in the guidelines would apply. In September 2008, Nebraska asked EPA for clarification on whether recently permitted units, such as the coal-fired NCS Unit 2, should be included in the total plant capacity for purposes of applying presumptive BART.
In a November 2008 response, EPA indicated it is reasonable to interpret the rule to mean that if the plant capacity is greater than 750 MW at the time the BART determination is made by the state (i.e., at the time the state places the BART determination on public notice), then the power plant is a facility with more than 750 MW of capacity and any unit at the plant greater than 200 MW is subject to presumptive BART.
The groundbreaking for construction of NCS Unit 2 was in September 2005. Nebraska put the NCS Unit 1 BART permit on public notice in December 2008. Unit 2 was operational in May 2009. Nebraska concluded that because NCS Unit 2 was not operational at the time of the BART determination for Unit 1, its capacity did not count towards the 750 MW threshold. “We concede that there is some question as to whether the NCS Unit 1 is a presumptive unit, requiring use of the BART guidelines, or not,” EPA wrote in the March 2 notice. “Regardless, Nebraska did proceed through a basic step-wise analysis of the costs and visibility impacts of available controls.”
NCS Unit 1 has existing overfire air (OFA) equipment for NOx control, so in determining BART for NOx at NCS unit 1, Nebraska considered low NOx burners (LNB) and selective catalytic reduction (SCR). Selective non-catalytic reduction (SNCR) was determined to be technically infeasible due to high furnace exit temperatures.
The cost effectiveness of LNB/OFA at an emissions rate of 0.23 lbs/MMBtu was $166 per ton; the cost effectiveness of LNB/OFA plus SCR at a rate of 0.08 lbs/MMBtu was $2,611 per ton. The addition of SCR would provide improvement at the Hercules Glades protected area, but because of the high incremental cost of $8,203 per ton and the level of visibility improvement, it was not chosen as BART. Nebraska determined BART for NOx at NCS unit 1 to be LNB with OFA at a rate of 0.23 lbs/MMBtu. EPA agreed that the state’s determination is reasonable given the relatively insignificant additional visibility improvement associated with SCR for the additional cost.
For SO2 control at NCS, Nebraska evaluated both dry and wet flue gas desulfurization (FGD). Nebraska concluded that dry FGD (spray dryer absorber (SDA)) has lower capital and operating costs than wet FGD and can achieve a similar control efficiency, so it focused its cost analysis on dry FGD. EPA noted that Nebraska did not evaluate dry sorbent injection (DSI) as a potential SO2 control for NCS Unit 1. Since DSI can generally achieve the same control efficiency as FGD, EPA said the state has appropriately evaluated the level of controls in its analysis.
The costs per ton for dry FGD were reasonable both at a rate of 0.15 lbs/MMBtu ($1,759 per ton) and 0.10 lbs/ MMBtu ($1,636 per ton). Nebraska determined that the minimal visibility improvement from installation of FGD at NCS Unit 1 did not warrant the additional cost ($34,770,000 or $1,759 per ton); therefore, no SO2 controls were proposed as BART for NCS Unit 1. EPA agreed that the state’s determination is not unreasonable given the minimal additional visibility improvement.
NOx not a big problem at Gerald Gentleman, SO2 is the issue
Nebraska evaluated LNB with OFA and SCR for NOx control at the Gerald Gentleman Station (GGS). In 2006, the Nebraska Public Power District (NPPD) installed LNB and OFA at Unit 1, but since this was after the 2001–2003 baseline modeling period, it was still evaluated in the BART analysis. SNCR was determined to be technically infeasible due to high furnace exit temperatures. LNB with OFA (at a rate of 0.23 lbs/MMBtu) had a cost effectiveness of $198 per ton, and LNB with OFA and SCR (at a rate of 0.08 lbs/MMBtu) had a cost effectiveness of $2,297 per ton.
GGS emissions affect six Class I areas. Nebraska concluded that based on the relatively low incremental visibility improvement of adding SCR to the LNB/OFA system for the additional cost ($5,445 incremental cost per ton), requiring SCR as BART was not warranted. NOx BART for GGS was determined to be the installation of LNB/OFA with an emission limitation of 0.23 lbs NOx/MMBtu, averaged across the two units. EPA agreed that the state’s NOx BART determination for GGS is reasonable.
Nebraska evaluated wet and dry FGD and also DSI for SO2 controls at GGS. All control options were evaluated at the presumptive rate of 0.15 lbs/MMBtu. The cost effectiveness for dry and wet FGD was nearly identical at $2,726 per ton and $2,724 per ton, respectively; the cost effectiveness of DSI was $2,058 per ton. All of these controls were determined by Nebraska to be reasonable on a cost per ton basis. FGD control would offer significant visibility improvements across the six Class I areas that GGS affects.
Nebraska regulators only provided visibility information for DSI at Badlands; therefore, the cumulative benefit of DSI is unknown. Nebraska raises water use of wet and dry FGD as a significant non-air environmental impact. In its SIP, Nebraska presents a description of the over-appropriation of water resources in the western part of Nebraska, where GGS is located. The state described that this over-appropriation means that any new use of groundwater requires an offset in water consumption in the same area. To do this, NPPD would have to purchase the groundwater rights from surrounding landowners.
Nebraska did not include the cost of obtaining these groundwater rights in the original BART analysis costs; however, in the narrative portion of the SIP, Nebraska describes both the costs of obtaining groundwater, and the loss of agricultural revenue due to taking land out of agricultural production. Nebraska concluded that the cost of obtaining water to operate wet FGD would add approximately 8.6% to the cost of controls. If these costs were added into the BART analysis, it would only increase the cost of control by $234 per ton. This brings the cost per ton to $2,958, which EPA believes is still a reasonable cost of control over both units.
Nebraska concluded that because of this unique situation, FGD controls are unreasonable for GGS Units 1 and 2. Nebraska concluded that BART is not having any SO2 controls at GGS. EPA disagreed with this conclusion.
“Using Nebraska’s analysis, we agree that the cost per ton for FGD control is reasonable, and Nebraska’s analysis shows significant visibility improvement, both at Badlands and on a cumulative basis,” the federal agency said. “We also believe that Nebraska inappropriately ruled out DSI. Costs for the control are reasonable at $2,058 per ton and visibility improvement at Badlands is significant…. Furthermore, DSI does not consume as much water as does FGD. Finally, even though the cost of FGD controls is reasonable, we believe that the costs of FGD control are overestimated. EPA conducted an independent review of the cost information presented by Nebraska in its BART analysis for dry scrubbers. We found several errors and deviations from EPA’s Cost Control Manual.”
EPA also found that Nebraska incorrectly calculated the SO2 emission rates. NPPD calculates its SO2 emission baseline based on applying a 24-hour maximum emission rate of 0.749 lbs/MMBtu (2001–2003) to a maximum heat input of 15,175.5 MMBtu/hr, based on a 100% capacity factor. This results in an emissions baseline of 49,785 tons/year.
“We believe this calculation does not appropriately represent GGS’s SO2 emission baseline, and is in fact too high,” said EPA. “We have downloaded emissions data for GGS from our Clean Air Markets Web site, and using the same emissions data from the three year averaging period of 2001-2003, we have calculated the three year average annual SO2 emissions for units 1 and 2 of the GGS to be 0.565 lbs/MMBtu. Reducing this to a controlled SO2 emissions level of 0.15 lbs/MMBtu results in a control efficiency of approximately 73.5 percent. Applying this level of control to our adjusted GGS SO2 emission baseline of 31,513 tons/year would reduce it to 8,366 tons/yr, resulting in a reduction of 23,147 tons of SO2 annually. Applying the same approximate 80 percent level of reduction GGS assumes to our adjusted GGS SO2 emission baseline of 31,513 tons/yr would reduce it to 6,311 tons/yr, resulting in a reduction of 25,202 tons of SO2 annually.”
Moreover, dry scrubbers are capable of much greater control efficiencies than the 80% level that GGS assumes, EPA added. Therefore, for the purpose of calculating the cost effectiveness of dry scrubbers at the GGS, the federal agency also analyzed an SO2 emission limit of 0.06 lbs/MMBtu, which results in a scrubber efficiency of about 89.4%. Applying this level of control to EPA’s adjusted GGS baseline of 31,513 tons/yr would reduce it to 3,347 tons/yr, resulting in a reduction of 28,166 tons of SO2 annually.
EPA said it believes that the cost per ton of SO2 controls ranging from $1,972 (its own analysis) to $2,958 (Nebraska’s analysis, plus water) is reasonable, and that the visibility benefits, whether considered just at Badlands or cumulatively, are significant. “Therefore, EPA proposes to disapprove Nebraska’s BART determination for SO2 controls at GGS,” the agency added.
EPA is also proposing to disapprove Nebraska’s LTS insofar as it relied on the deficient BART determination for SO2 at GGS. To address the deficiencies identified in these proposed disapprovals, EPA is also proposing its own federal implementation plan (FIP). On Dec. 30, 2011, EPA proposed to find that the trading programs in its Transport Rule would achieve greater reasonable progress towards the national goal than would BART in the states in which the Transport Rule applies, including Nebraska. EPA has not taken final action on that rule.
EPA wants its own plan to override Nebraska’s plan
EPA is proposing a partial FIP, relying on the Transport Rule as an alternative to BART for SO2 emissions from the GGS units. This limited FIP would satisfy the SO2 BART requirement for these units and remedy the deficiency in Nebraska’s LTS.
On Dec. 30, 2011, a federal appeals court stayed the Transport Rule, also known as the Cross-State Air Pollution Rule, while arguments on the rule are heard this spring. The court also indicated that EPA is expected to continue to administer the Clean Air Interstate Rule in the interim until the court rules on the Transport Rule. Under the regional haze rule, an alternative to BART does not need to be fully implemented until 2018. As that is well after EPA expects the stay to be lifted, EPA said in the March 2 notice that it believes it may still rely on the Transport Rule as an alternative to BART.