Prevention, control and/or extinguishment of coal seam fires using cellular grout

Abstract

Coal fires are difficult and persistent problems throughout the world wherever coal is at or near the surface. Coal fires can be associated with mining activities including underground and surface mine operations, coal stockpiles and coal waste piles, and they can also occur in unmined areas along coal seam outcrops. Environmental safety and health hazards are posed by coal fires in the form of ground surface subsidence, air pollution, forest and brush fires, and destruction of property and surface improvements, in addition to the potential massive loss of energy resources. While many causes exist, the most common source of coal fire ignition is spontaneous combustion as weathered, or broken/pulverized coal oxidizes and the temperature rises to the ignition point. This process can occur before any mining in the case of outcrop fires, or anytime during and after the mining cycle. The magnitude of coal fire problems varies worldwide depending on reserves available, extent of mining, population, political/economic situations, and a host of other influencing factors. Mining and environmental regulations imposed in the United States have heightened awareness regarding coal fire problems and resulted in efforts to control the most problematic existing fires and extinguish small fires before they escalate. Coal fires in other major coal-bearing countries, such as China and India, pose a significantly greater problem in terms of worldwide impact. Figures for China vary dramatically but estimates indicate that as much as 100–200 million tons of coal reserves are consumed annually as a result of coal fires. Similar estimates for the Jharia Coal Field in India indicate that about 40 million tons of coal reserves were burned during the 1990s. These data point to a significant source of global pollution, in addition to substantial economic losses. Goodson & Associates, Inc. (G & AI), a Lakewood, CO engineering firm, has developed a technology utilizing cellular (foam containing) grout to mitigate coal fires from the perspectives of prevention, control and extinguishment. The variable combination of portland cement, waste fly ash, aggregates and special foams create a highly flowable, high-heat resistant grout that is used to simultaneously address each of the three necessary fire elements: fuel, oxygen and heat. Coal fire prevention can be achieved by spraying the material on the exposed surface of coal seams following completion of strip mining. Control is enabled by grout injection into cracks, vents and cut-off trenches to stall or prevent continued growth. Extinguishment can be accomplished by grout injection directly into the fire zone, air intakes and exhausts. The benefits of using this technology are numerous. Cellular grout injection is safer at lower cost than conventional techniques such as complete excavation, while causing less environmental disruption and providing for quicker applications. The use of large quantities of fly ash in the process is economically and environmentally sound, by providing for disposal of a waste material while addressing the worldwide problem of coal fires.