Wave of pollution control installations as EPA deadline approached favored activated carbon technology

Energize Weekly, October 4, 2017

A wave of mercury control technology installations—mainly lower-cost activated carbon systems—were made at coal-fired power plants just before the final April 2016 compliance deadline for new emission standards, according to the federal Energy Information Administration (EIA).

The EIA’s preliminary annual electric generator survey shows that there was an increase in installations just before the initial deadline in April 2015. At the time, more than 142 gigawatts (GW) of coal-fired generation had sought a one-year extension to complete their compliance strategy.

Between January 2015 and April 2016, about 87 GW of coal-fired plants installed pollution control equipment, with about 40 percent coming on online in April 2016.

“The nature and timing of control additions indicate a strategy to maintain the availability of affected coal-fired generators by requesting extensions to compliance deadlines and investing in flexible, low-cost environmental control technology,” according to the EIA.

The upgrades were prompted by the 2012 federal standard tightening mercury, acid gas and other toxic emissions from coal-fired plant smokestacks. The U.S. Environmental Protection Agency’s Mercury and Air Toxics Standards (MATS) required all coal- and oil-fired plants that sell power with a capacity of 25 megawatts or more to meet the emission limits for pollutants including mercury, arsenic and heavy metals.

About 60 percent of the 299 GW of coal-fired generation in the country did not add additional controls, for the remainder it meant either adding pollution controls or shuttering by April 2015.

An estimated 20 GW of coal-fired generation was retired, and 5.6 GW converted to natural gas between December 2014 and April 2016, according to EIA. There was also the option of seeking an additional 12-month extension. A few units got an additional one-year extension to April 2017.

“One-year MATS compliance extensions have been widely available, with state permitting agencies granting one-year extensions for myriad reasons, including for utilities to take additional time in determining appropriate compliance strategies,” according to an analysis by MJ Bradley & Associates, a Concord, Mass.-based consultant specializing in energy and air quality issues.

There are several pollution control technologies that can be added to a power plant to curb emissions including baghouses, electrostatic precipitators and activated carbon injection (ACI).

Baghouses and electrostatic precipitators reduce particle emissions and also help capture mercury, with baghouses generally providing greater reductions of both pollutants.

The most widely adopted and least costly technology, however, is the activated carbon systems, which were installed in 78 GWs of generation.

ACI injects powdered activated carbon—a highly porous absorptive medium—into the flue stack or exhaust of a coal-fired power plant. The activated carbon then absorbs the vaporized mercury from the flue gas and is collected from the plant’s pollution control for particulates.

ACI technologies have the shortest construction lead time of all the compliance control technologies—between 12 and 18 months—and the lowest installation cost—about $11 per kilowatt (kW). Baghouses and electrostatic precipitators have longer lead times, around 40 months for each, and installation costs of more than $100 per kW, according to the EIA.

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