EPA finalizes ACE rule, biomass co-firing not a compliance option

The U.S. EPA released its final rule for its Affordable Clean Energy program June 19. The ACE program replaces the Obama-era Clean Power Plan and establishes emissions guidelines for states to use when developing plans to limit carbon dioxide at coal-fired power plants. While biomass co-firing was discussed as a potential compliance option in the proposed rule, the final rule specifies that biomass co-firing cannot be used to comply with the ACE program.

The CPP was first proposed by the EPA in June 2014 under the Obama administration. Final rules for the program were released in August 2015. In March 2017, an executive order signed by President Trump ordered a review of the program. A few months later, in October 2017, the EPA issued a proposed rulemaking to repeal the CPP.

The EPA released the proposed ACE rule in August 2018. A public comment period was open through Oct. 31, 2019.

According to the EPA, the ACE rule identifies heat rate improvements (HRI) as the best system of emission reduction (BSER) for carbon dioxide from coal-fired power plants. Heat rate is a measure of the amount of energy required to generate a unit of electricity. The BSER must be applicable to, at, and on the premises of an affected facility. Within the rule, EPA lists six HRI candidate technologies, as well as additional operating and maintenance practices. The six HRI candidate technologies include neural network/intelligent sootblowers, boiler feed pumps, air heater and duct leakage control, variable frequency drives, blade path upgrade, and redesign/replace economizer.

States will establish unit-specific standards of performance that reflect the emission limitation achievable through the application of BSER technologies. States will have three years to submit plans under the program.

The EPA estimates the ACE rule will reduce carbon dioxide emissions by 11 million tons by 2030. Over the same time period, sulfur dioxide, nitrogen oxide, particulate matter 2.5, and mercury emissions are expected to be reduced by 5,700 tons, 7,100 tons, 400 tons and 59 pounds, respectively.

The ACE rule was finalized in conjunction with two related, but separate and distinct rulemakings. One repeals the CPP. The other contains new implementing regulations for ACE and future existing-source rules under Clean Air Act Section 111(d). The agency said these guidelines will inform states as they set unit-specific standards of performance. For example, EPA said states can take a particular source’s remaining useful life and other factors into account when establishing a standard of performance for that source.

The proposed ACE rule did include references to biomass. Specifically, it asked members of the public to comment on the inclusion of forest-derived biomass as a compliance option for affected units to meet state plan standards under the ACE rule. Public comments were also solicited regarding the inclusion of non-forest biomass as a compliance option, and what value to attribute the biogenic carbon dioxide emission associated with non-forest biomass feedstocks.

In the final ACE rule the EPA said it received comments both supporting and opposing the use of biomass for compliance. “Upon consideration of comments and in accordance with the plain language of CAA section 111…, the EPA is now clarifying that biomass does not qualify as a system of emission reduction that can be incorporated as part of, or in its entirely, as BSER,” the EPA wrote in the rule. “…[The] BSER determination must include systems of emission reduction that are achievable at the source. While firing of biomass occurs at a designated facility, biomass firing in and of itself does not reduce emissions of CO2 emitted from that source. Specifically, when measuring stack emissions, combustion of biomass emits more mass of emissions per Btu than that from combustion of fossil fuels, thereby increasing CO2 emissions at the source. Recognition of any potential CO2 emissions reductions associated with biomass utilization at a designated facility relies on accounting for activities not applied at and largely not under the control of that source, including consideration of offsite terrestrial carbon effects during biomass fuel growth, which are not a measure of emissions performance at the level of the individual designated facility. Use of biomass in affected units therefore not consistent with the plain meaning of ‘standard of performance’ and cannot be considered as part of the BSER.”

In a footnote regarding that statement, the EPA also notes it believes that a prevention of significant deterioration (PSD) permitting authority may conclude that some types of biomass is best available control technology (BACT) for greenhouse gases in the context of a PSD permit application where the applicant proposes to use biomass.

Within the rule, the EPA also states that “biomass fuel use opportunities are dependent upon many regional considerations and limitations—namely fuel supply proximity, reliability and cost—that prevent its adoption as BSER on a national level…Therefore, even is biomass firing could be considered a ‘system of emission reduction’ the EPA is not able to include the use of biomass fuels as part of the BSER in this action due to the current cost and achievability considerations and limitations discussed [within the rule].”

The EPA also said it received a range of comments both supporting and opposing the use of forest-derived and non-forest biomass feedstocks for compliance under the ACE rule, along with a range of comments regarding the valuation of CO2 emissions from biomass combustion. Some of those comments referenced the EPA’s 2018 policy statement regarding biogenic CO2 emissions in which the agency stated its intent to treat biogenic CO2 emissions from forest biomass and managed forests as carbon neutral in future agency actions.

“The construct of this final ACE rule necessitates that measures taken to meet compliance obligations for a source actually reduce its emission rate in that: (1) they can be applied to the source itself; and (2) they are measurable at the source of emissions using data, emissions monitoring equipment or other methods to demonstrate compliance, such that they can be easily monitored, reported and verified at a unit…” said the EPA in the rule. “While the firing of biomass occurs at a designated facility, biomass firing in and of itself does not reduce emissions of CO2 emitted from that source. Specifically, when measuring stack emissions, biomass emits more CO2 per Btu than fossil fuels, thereby increasing the CO2 emission rate at the source. Accordingly, recognition of any potential CO2 emissions reductions associated with biomass firing at a designated facilities relies on accounting for activities not applied at and largely not under control of that source…, including consideration of terrestrial carbon effects during the biomass fuel growth. Therefore, biomass fuels do not meet the compliance obligations and are not eligible for compliance under this rule.”

Additional information, including a full copy of the final rule, is available on the EPA website.