North China’s Inner Mongolia Autonomous Region plans to extinguish smoldering fires at nearly half of its coalfields with the problems by 2012. Smoldering coalfield fires have been raging on since 1960s due to factors including dry weather, improper coalmining practices which led to exposure of coal-bearing strata in the air, eventually leading to spontaneous combustions, Ya said. “More than 20 million tonnes of coal is wasted every year in our region due to the smoldering fires”. The regional government has earmarked an annual financing of 200 million yuan ($29.3 million) from 2009 to 2012 for fighting the fires, Ya said.
According to a harnessing plan, coal threatened by fire hazards is to be dug away to stop fires from spreading, while the fires are to be covered by sand. Other materials such as slurry are also pumped to help extinguish fires underground.
Inner Mongolia produced 637 million tonnes of coal last year, ranking the first in China.
Coal Seam Fires
Wikipedia discusses coal seam fires.
Extinguishing underground coal fires, which sometimes exceed temperatures of 540°C (1,000°F), is both highly dangerous and very expensive.
Near-surface coal seam fires are routinely extinguished in China following a standard method basically consisting of the following phases:
Smoothing the surface above the fire with heavy equipment to make it fit for traffic.
Drilling holes in the fire zone about 20 m apart down to the source of the fire, following a regular grid.
Injecting water or mud in the boreholes long term, usually 1 to 2 years.
Covering the entire area with an impermeable layer about 1 m thick, e.g., of loess.
Planting vegetation to the extent the climate allows.
Efforts are underway to refine this method, for example with additives to the quenching water or with alternative extinguishing agents.
Underground coal seam fires are customarily quenched by inertization through mine rescue personnel. Toward this end the affected area is isolated by dam constructions in the galleries. Then an inert gas, usually nitrogen, is introduced for a period of time, usually making use of available pipelines
It is estimated that China, the world’s largest coal-producing country, lost anywhere between 10 and 200 million tons of coal a year to wildfires, or between 0.5 and 10 percent of national production.
Team member Leonard Levin of the Electric Power Research Institute in Palo Alto, Calif., said that fires could emit 200 tons of mercury each year, but he called the figure a “wild guess.”
A report issued by the USGS earlier this year suggests just 48 tons are emitted annually, but even that is roughly equivalent to all of the mercury generated by coal-fired power plants in the United States.