CCB Generation and Use in Maryland 2004-2014.

摘要

Constellation Power Source Generation Inc., which owns and operates three coal-fired power plants in Maryland, has contracted with Charah Inc., an ash management company, to build a landfill to strict environmental requirements for the disposal of its plants’ coal combustion by-products that can’t be recycled for other uses. Coal-fired power plants produce approximately 40% of the electricity generated in Maryland. Constellation Power Source Generation Inc. (CPSGI), an affiliate of Baltimore-based Constellation Energy, owns and operates three of these plants that help meet the growing demand for electricity. Although more than half of the coal combustion by-products (CCBs) produced by these three plants is recycled for reuse in products such as cement and concrete, not all can be reused due to a lack of market demand. The remainder is placed in landfills permitted to dispose of such materials. Overview of Coal Combustion By-products Approximately 43% of CCBs were recycled for “beneficial uses” in 2008, according to the American Coal Ash Association. The remainder were landfilled, placed in mine shafts, or stored on site at coal-fired power plants. The University of North Dakota has extensively researched the characteristics of different types of CCBs typically produced by coal-fired power plants. Here are the main types of CCBs the university has identified: Boiler slag is a molten ash collected at the base of slag tap and cyclone boilers that is quenched with water and shatters into black, angular particles having a smooth glassy appearance. Bottom ash consists of agglomerated ash particles formed in pulverized coal boilers that are too large to be carried in the flue gases. Consequently, they impinge on the boiler walls or fall through open grates to an ash hopper at the bottom of the boiler. Bottom ash is typically gray to black in color, is quite angular, and has a porous surface structure. Fluidized bed combustion (FBC) materials consist of unburned coal, ash, and spent bed material used for sulfur control. The spent FBC material (removed as bottom ash) contains reaction products from the absorption of gaseous sulfur oxides (SO2 and SO3). Flue gas de-sulfurization (FGD) materials are derived from a variety of processes used to control sulfur emissions from boiler stacks. These FGD systems include wet scrubbers, spray dry scrubbers, sorbent injectors, and a combined sulfur oxide (SOx) and nitrogen oxide (NOx) process. Sorbents include lime, limestone, sodium-based compounds, and high-calcium coal fly ash. Fly ash is the coal ash that exits a combustion chamber in the flue gas and is captured by air pollution control equipment such as electrostatic precipitators, baghouses, and wet scrubbers. Charah’s Decision to Develop a CCB Landfill In the fall of 2007, CPSGI voluntarily began hauling and placing its nonbeneficially reused CCBs at privately owned lined landfills in Virginia and western Maryland as part of a consent decree signed with the Maryland Department of the Environment (MDE). At that time, CPSGI’s evaluation of alternative disposal locations to manage its CCBs in a manner that ensured the health, safety, and welfare of the community intensified. In addition, CPSGI was determined to secure a disposal site for its sole use, as a monofill for CCBs. To facilitate this evaluation, CPSGI turned to Charah Inc., a Louisville, Ky.–based leading ash management provider for the coal-fired electric utility industry. Charah was initially tasked with evaluating long-term, cost-effective CCB disposal opportunities, including beneficial mine reclamation, industrial waste landfills, and additional beneficial reuse applications. In 2008, more than 300 sites in four states were evaluated for environmental, regulatory, capacity, and operational feasibility. By late 2008, Charah presented CPSGI with a recommendation to purchase and develop an existing, unused 65-acre industrial waste landfill, located in Baltimore City, just miles away from the plants. The site identified by Charah was already permitted as an industrial waste landfill and was located within a heavy industrial zoning district separated from any residential land use. In addition, no private wells were located within the vicinity of the site. The site conformed to CPSGI’s strict environmental requirements and provided for long-term and cost-effective CCB disposal.