Solid material disposal requirements for integrated gasification combined cycle (IGCC) processes are expected to be similar to those for direct combustion of coal. An extensive study was conducted in preparation for the 1999 U.S. Environmental Protection Agency (EPA) Report to Congress on Wastes from the Combustion of Fossil Fuels (EPA 530-R-99-010, March, 1999)1. Recommendations resulting from the study concluded that disposal of coal utilization byproducts (CUBs) should remain exempt from Resource Conservation and Recovery Act (RCRA) Subtitle C hazardous waste management practices. Additionally, EPA determined that national Subtitle D regulations are warranted and are to be handled through the Land Disposal Restrictions (LDR) revised in August 2001. The LDR program identifies treatment standards for hazardous wastes and specifies requirements that generators, transporters, and owners or operators of treatment, storage, and disposal facilities (TSDFs) that manage restricted wastes destined for land disposal must meet.
Types of Waste Management and Control Measures2
Current management practices for solid wastes typically consist of onsite surface impoundments and landfills. Because of the economic value of IGCC slag, the use of temporary surface impoundments is the more likely storage practice.
Surface impoundments are natural depressions, excavated ponds, or diked basins. Materials managed in surface impoundments typically are sluiced with water from the point of generation to the impoundment. Solids gradually settle out and accumulate at the bottom of the impoundment, and may be left in place as a method of disposal. The impoundment also may be periodically dewatered and the solids removed for disposal in another unit, such as a landfill.
Landfills are facilities in which wastes are placed for disposal on land. Often landfills are comprised of natural depressions or excavations that are gradually filled with waste, although filling may continue to a level well above the natural grade. Wastes managed in landfills may be transported dry from the point of generation, or they may be placed after dredging from a surface impoundment. Some residual liquids may be placed along with the dredged solids. Also, liquids may be added during the construction of the landfill for dust control.
Specific storage and environmental control requirements are currently the responsibility of the states. Typical control measures include liners, covers, leachate collection systems and groundwater monitoring systems.
A Liner is a barrier placed underneath a landfill or on the bottom and/or sides of a surface impoundment. Depending on their construction, liners can slow or prevent the release of leachate from a landfill or liquids from a surface impoundment to underlying soils and ground water. Liners can consist of compacted soil, compacted clay, a synthetic material or membrane, or a combination of barrier types.
A cover, or cap, is a barrier placed over the top of a waste management unit. Covers can prevent precipitation runoff from becoming contaminated by contact with waste, prevent or slow percolation of precipitation into the unit, and prevent windblown transport of waste. Like liners, covers can consist of compacted clay, synthetic materials or membranes, or a combination of materials. Covers also may be a layer of soil or sand. Final covers are those placed upon closure of a unit.
A leachate collection system is a series of drains placed beneath a unit, typically a landfill.
These systems collect leachate for treatment or disposal, thus preventing it from reaching soils, ground water, or surface water.
Ground-water monitoring systems consist of one or several wells drilled in the vicinity of a unit. Samples from these wells are periodically collected and analyzed. Groundwater monitoring is not strictly an environment control but rather a warning system. Groundwater samples that display contamination may trigger regulatory requirements to mitigate or eliminate the source of contamination.
Solid Waste/Byproducts of Gasification