How to control the sulfur dioxide produced by spontaneous combustion of gangue mountain

Coal gangue is a solid waste produced in the process of coal mining, with the continuous mining of coal, gangue accumulates day by day, piled up into a mountain. The gangue mountain not only contains a large amount of coal dust but also contains harmful substances such as FeS2, among which the heat generated during the oxidation process of Fes2 causes spontaneous combustion of the gangue mountain. For a long time, the SO2, H2S and other harmful gases produced by the spontaneous combustion of coal gangue and the dust of gangue have caused serious pollution to the surrounding environment, destroyed the local ecological balance, and threatened people's health.

1. Direct excavation method This method is relatively simple, but it is only suitable for the initial burning of gangue mountain. Generally, a machine or a high-pressure water gun is used to dig out the ignited gangue and hot gangue, cool it with water or let it cool naturally, backfill or re-pile it. In the early days, the United States used this method to extinguish fires on a large scale, and there were many accidents.

2. Grouting method Grouting method is the most commonly used method in China, which can be surface pouring, trench pouring and drilling grouting. Among them, borehole grouting has an ideal effect on large-area or deep combustion treatment and prevention of re-ignition. The method is to arrange a certain number of boreholes in the gangue mountain, and inject a certain concentration of grout into the fire area and self-heating area with grouting materials such as loess, fly ash, calcium carbide slag and lime.

Considering that the slurry is affected by gravity, its diffusion is mainly in the vertical direction, and it is difficult to control its flow direction. In recent years, there has been a treatment technology that combines grouting with foam fire extinguishing agent. The foam has a good oxygen insulation effect, which can not only save water, but also has a strong diffusion ability in the gangue void, and will not destroy the sealing belt formed by the slurry.

3. Irrigation method water forms steam at high temperature, absorbs a large amount of vaporization heat, and its endothermic cooling effect is very good, and it is an excellent fire extinguishing agent. However, this method must be chosen very carefully. On the one hand, the porosity of the gangue mountain increases after water injection, and the reactivity of the gangue after drying will also increase, making it difficult to prevent its recurrence.

On the other hand, for deep high-temperature red-hot fire areas or fire areas containing pyrite, water meets red-hot charcoal to produce a large amount of water gas, which increases the probability of deflagration. The addition of water will make the pyrite oxidation reaction more intense and complex, and the heat and gas generated will not have time to be released, resulting in accumulation and triggering an explosion. This has been proven by several post-rain gangue mountain accidents in China.

4. Surface sealing and compaction method The method is to lay soil and compact on the surface of the gangue mountain, isolate the air approach, and extinguish the air inside the gangue mountain after it is exhausted. The surface sealing and compaction method can reduce the combustion intensity and pollutant emission rate, which is mainly used to control the fire and pollution intensity of gangue mountain, and requires timely maintenance. In China, the method of layered stacking of gangue and layered compaction has achieved good results in preventing spontaneous combustion of gangue mountains, and its fire extinguishing effect is not ideal.

The United Kingdom and other European countries mainly use this method to prevent spontaneous combustion of gangue mountains.

5. Low-temperature inert gas method At present, the U.S. Bureau of Mines is conducting large-scale industrial tests on the low-temperature inert gas method. The method is to inject liquid nitrogen and solid 2CO mixture into the fire area, which can quickly reduce the temperature of the fire area, and the volume can be increased by 500 times during the phase change process, forming a cold pressure wave, which quickly spreads from the injection point to the whole area, discharges the low-density hot flue gas to the surface, and isolates the air at the same time, so as to achieve the purpose of cooling and extinguishing the fire.

From the perspective of engineering practice at home and abroad, the comprehensive measures of grouting method, supplemented by surface sealing and compaction, and infusion of foam fire extinguishing agent are the most mature and effective spontaneous combustion control technologies for gangue mountains. Areas with conditions can also learn from the methods of the U.S. Bureau of Mines and adopt low-temperature inert gas to extinguish fires.