While Georgia Power is still on hold with its conversion of the coal-fired Unit 3 at the Mitchell plant to burning biomass, the company and Southern Co. Services are making progress in testing direct injection (DI) methods for getting biomass into the converted plant.
Georgia Power, a unit of Southern Co. (NYSE: SO), filed its latest update Aug. 31 with the Georgia Public Service Commission on the project. In March 2009, the commission certified the Mitchell Biomass Facility, which covers a plan to convert a 155-MW coal-fired electric generating unit (Unit 3) to a 96-MW biomass-fired station. At the time the certificate was issued, the Mitchell Biomass Facility was anticipated to begin serving customers in the summer of 2012.
But, the U.S. Environmental Protection Agency then delayed several times the release of the final Industrial Boiler Maximum Achievable Control Technology (IB MACT) standard, the primary motivation behind the conversion. Also, the EPA released draft Coal Combustion Residuals (CCR) regulations for power plants. It was expected that both the IB MACT and the CCR regulations could impact the schedule and cost of the Mitchell Biomass Facility. IB MACT limits emissions by industrial boilers and applies to biomass-fired boilers. The Mitchell Biomass Facility certificate also contemplated disposal of the ash from biomass combustion in the existing coal ash impoundment. Depending upon the final CCR rule, other methods of ash disposal may be required and additional costs may result. The EPA also adopted greenhouse gas (GHG) permitting regulations for stationary sources, but proposed to defer the applicability of those regulations for biomass facilities for at least three years.
In February 2010, the commission approved a conversion delay until these regulatory factors were cleared up.
In December 2011, the EPA issued a proposed IB MACT rule. As with prior versions, the proposed IB MACT rule contains stringent emission limits for several hazardous air pollutants and surrogates of hazardous air pollutants. “Many of the proposed requirements are not sufficiently clear and will need further clarification and review,” Georgia Power said in the Aug. 31 filing. “However, it appears the revisions may make the IB MACT standards achievable for many biomass units, albeit with potential cost impacts. The EPA planned to issue the new IB MACT rule in the spring of 2012, but the rule has not been issued, and the EPA has not announced a new schedule.”
Biomass direct injection study began in May
Georgia Power has also promised the commission the results of a DI study, to be filed no later than the company’s 2013 Integrated Resource Plan (IRP) filing. Georgia Power began the DI study in May by selecting DNV KEMA as the outside engineering firm to provide a feasibility study including detailed boiler performance estimates, estimated equipment costs, estimated construction schedules, and emissions predictions. Southern Company Services (SCS) is managing the study, developing specifications and assembling required information for the study, interacting with DNV KEMA and reviewing the results of the study.
SCS is developing a complete cost estimate for the direct injection of biomass at Plant Mitchell. SCS tasks also include performance evaluations and cost estimates for additional items not included in the scope of the boiler study done by DNV KEMA. These items include revising the Woodyard equipment scope and cost, determining the required emissions control equipment and the related cost impacts as a result of the IB MACT rule, and any other balance of plant scope that would require changes or modifications. The study results (general arrangements, performance, emissions, cost estimates, schedule, and risk assessment) are necessary to fully evaluate the technical and economic feasibility of the DI approach.
At the time of the Aug. 31 filing, DNV KEMA and SCS continue to make progress on the DI study. For example, they have examined alternatives for the necessary process and equipment for drying the wood fuel from 50% moisture to about 10% moisture. Also, they have performed preliminary performance and emissions modeling. Georgia Power has provided PSC staff with informal monthly updates on the Mitchell Biomass Facility spending, and it will provide the final results of the DI study to staff no later than the 2013 IRP filing.
Within a 100-mile radius of Mitchell, there are 8 million acres of forest and timberlands, and 11 million tons/year of surplus supply wood fuel, said the Georgia Power website. Most of the wood fuel likely to be used in the plant is considered unusable waste by timber companies and therefore will not compete with their needed wood supply. About 1 million tons of the yearly 11-million-ton wood supply will be needed to operate the converted plant.