Energy and a Cleaner Environment.....from waste coal



Since entering service in 1995, the Colver Power Project (CPP) has supplied electricity to a local utility with exceptional reliability. The facility also makes significant contributions to the region's environment and economy.

The CPP is situated about 100 miles east of Pittsburgh, USA, near the former mining town of Colver. This was the location of a bituminous-coal mine that closed in 1978. Typical of many similar mining operations, the Colver mine left behind high-ash bituminous-coal waste known as "gob".

CFB and PEDFA

The Colver Power Project uses a unique combination of technical, business, and environmental strategies to bring the largest independent power producer in Pennsylvania on-line. The heart of the Colver plant is Foster Wheeler's circulating fluidised-bed (CFB) steam generator. CFB steam generators burn a wide range of low-grade fuels, including bituminous gob, in an efficient and environmentally acceptable manner.

In a CFB steam generator, fuel is burned as it mixes with other material suspended in an upward flow of gas. At the Colver plant, the very hot "fluidised" bed consists of crushed gob, limestone to absorb sulphur, and ash. The vigorous mixing of these materials with air, the uniform combustion temperature throughout the furnace, and the long residence time of fluidised material in the furnace contribute to high combustion efficiency.

CFB technology allows the CPP to be fuelled exclusively with waste coal and yet operate under the most stringent air-emissions limits. Sulphur oxides and oxides of nitrogen, precursors of acid rain, are almost entirely captured and chemically converted into inert materials.

The project was financed by a combination of bank loans and tax-exempt bonds issued through the Pennsylvania Economic Development Financing Authority (PEDFA). The bonds received an investment-grade rating from both Finch's Investors Service and Standard & Poor's - the first time bonds for a waste-coal fuelled waste-to-energy plant under construction were given this rating.

Getting at the Gob The CPP safely fires more than 60,000 tons of gob annually, obtained from sites that include a major supply adjacent to the facility. Approximately 50% of the gob fired is trucked to the plant from more distant sources.

The Colver Refuse Site is another location with a substantial amount of coal waste. By mining this site for fuel over the next 15 years, the CPP will help to reclaim the land for other uses. Water for the CPP is drawn from a reservoir about two miles away. With the co-operation of the Cambria Township Water Authority the reservoir under went a $12 million expansion which resulted in a modern 82 surface-acre reservoir with a capacity of 427 million gallons. The reservoir project also created 20 acres of wetlands with numerous plant species, trees, shrubs, and woody vines. There are 25 duck boxes, over 100 bird boxes, and many types of game fish. Now a major community asset, the Vetera Dam and Reservoir has seen heavy recreational use since completion.

The water used at the Colver facility is recycled numerous times before being discharged from the plant. Wastewater is treated in two holding basins to meet environmental requirements for off-site discharge, in accordance with very stringent National Pollutant Discharge Effluent System (NPDES) standards.

Employment and Electricity

Along with adding to the area's supply of electricity, the CPP has created jobs in a region greatly impacted by mine closures. In addition to the work provided during construction, the CPP has created permanent jobs for area residents. Local hiring was a priority from the start of the project.

Fuel and Limestone Handling

Because fuel for the CPP comes from various waste sites and because Foster Wheeler's CFB technology is very flexible with regard to fuels, the CPP steam generator is able to handle wide variations in fuel properties that result from continuous blending. A conveyor transports the fuel to a storage building where a rake-reclaimer system is used for additional fuel blending.

In addition to firing some 600,000 tons of gob, the Colver CFB steam generator requires about 120,000 tons of limestone annually. In an arrangement beneficial to the local economy, the Colver Power Project supplies raw limestone to a local contractor who crushes the stone to the required size. CPP owners can thus change limestone suppliers if necessary while continuing to provide the local processor with business.

Very low SOx and Nox

Atmospheric emissions from the CPP are well below all applicable requirements. Sulphur-oxide emissions, particularly SO2 are controlled by the limestone injected into the fluidised bed. NOx emissions from Foster Wheeler's steam generators are inherently minimal due to the factors such as low combustion temperature. However, the Foster Wheeler ammonia-injection system installed at the Colver plant further reduces NOx emissions. NOx reduction systems can use either anhydrous ammonia or aqueous ammonia as reagents to reduce the nitrogen oxides formed during combustion to elemental nitrogen. Anhydrous ammonia injection is used at the CPP.

Atmospheric emissions from the CPP already meet the limits mandated by the U.S. Environmental Protection Agency for the year 2000.

By combining modern technology the CPP is producing energy and a cleaner environment from waste coal. This article has been adapted with permission from Foster Wheeler Corporation's magazine Heat Engineering

Source: World Coal Institute

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