Based on the changes in the geological environment caused by coal development in the Tongchuan mining area, this paper discusses the issues from the perspectives of water resources protection, ground subsidence and ground fissure management, gangue mountain management, coal gangue resource utilization and coal mine gas utilization. Technical plan for geological environment protection in Tongchuan Mining Area.
1. Existing technical solutions for geological environmental protection
1. Mine water treatment
Among the existing 8 pairs of production mines in the Tongchuan mining area, only 4 There are sewage treatment facilities in the mines. Part of the treated mine water is used for underground water sprinkling to reduce dust, and part of it is discharged to the river. The mine water from the four mines without sewage treatment is discharged to the surface. After simple sedimentation treatment, most of it is used for underground production, and the rest is discharged.
2. Ground subsidence and ground fissures
All the goaf areas in the Tongchuan mining area have problems of ground subsidence and ground fissures. The occurrence of these problems has brought serious problems to people's production and life. difficulty. In order to understand the laws of coal mining subsidence and formulate reasonable prevention and treatment measures, the Tongchuan Mining Bureau commissioned Liaoning University of Engineering and Technology and the Mining Damage and Control Center to conduct research on the laws of ground subsidence in the Tongchuan Mining Area, and compiled the "Coal Mining in Tongchuan Mining Area of ??Shaanxi Province" Subsidence Report”. The report analyzes the causes of ground subsidence and the movement patterns of the ground surface, providing a theoretical basis for preventing and controlling ground subsidence. The ground subsidence and ground fissures in the mining area were investigated and observed, and the ground fissures that occurred were backfilled in a timely manner.
The "Three Downs" coal pressure in current production mines in the Tongchuan Mining Area is very serious (Table 5-6), accounting for 21.8% of the remaining geological reserves, and the Yakou Mine is the most serious, accounting for 32.8%. Among the “three” coal pressings, coal pressing under buildings accounts for the largest proportion, accounting for 89.8% of the total coal volume. Among coal pressing under buildings, coal pressing under buildings is dominated by coal pressing under buildings, accounting for 74.1% of the total. Under the current circumstances, it is impossible to relocate villages located in unmined areas of various mine fields, which will seriously affect the continuity of mine production and mining benefits. In order to rationally plan mining, improve the recovery rate of coal resources and coal mining benefits, minimize the impact of mining, and achieve coordinated development of resource development and environmental protection. To this end, Tongchuan Mining Bureau and Xi'an University of Science and Technology conducted a "Study on Mining Subsidence Patterns and Water Source Damage in Tongchuan Mining Area." The report summarizes the surface movement and deformation characteristics of the immovable trial mining working face under buildings in Tongchuan Mining Area and the large mining depth, small mining height and small working face. It demonstrates its mechanism and feasibility from both theoretical and experimental aspects. At the same time, it puts forward Safe mining dimensions of working faces under different geological and mining conditions.
Table 5-6 Current production mine reserves and "three lower" coal pressing conditions in the mining area. Unit: 10,000 tons
3. Treatment and utilization of coal gangue
Coal gangue in the Tongchuan mining area mainly exists in various valleys in the form of piles. Most of it has not been treated in any way, and a small part has been landfilled. As resources become increasingly scarce, coal gangue resource utilization has become an inevitable choice for green mines. Tongchuan Mining Bureau began to explore the utilization of coal gangue in the 1970s. According to relevant records, Wangjiahe Mine used coal gangue in the boiling furnace in 1978; in the 1980s, a Sanlidong internal gangue brick factory was built, but now these two mines have been bankrupt and closed.
At present, Tongchuan Mining Bureau has a cement plant of Aobo Company, which uses coal gangue as raw material to bake cement every year, and the annual utilization of coal gangue is 15,200 tons. Tongchuan Mining Bureau also sells part of the black gangue as fuel every year, with an annual utilization of about 35,000 tons. In 2006, a non-burning brick factory was established in Shijie Mine. It was completed and put into trial production in March 2007, with an annual utilization of 18,000 tons of coal gangue. Most of the gangue mountains in the Tongchuan mining area are in spontaneous combustion or have spontaneously combusted. The red gangue produced after spontaneous combustion is sold to cement plants as an additive to cement.
Although coal gangue has been comprehensively utilized through various methods mentioned above, the amount of utilization is negligible compared with the amount of production. In 2006, the coal output of Tongchuan mining area was 9.67 million tons, and 1.089 million tons of coal gangue was produced. It is still a very arduous task to increase the utilization of coal gangue and realize the resource utilization of coal gangue.
2. Key technical solutions for geological environment protection in Tongchuan Mining Area
1. Technical solutions for water resources protection
Water resources protection technology in Tongchuan Mining Area includes two aspects: One is the recycling of mine water; the other is protecting water resources in coal mining areas from damage.
The mine water shortage problem in Tongchuan District is prominent, and the mine water is mainly acidic water. Because the treatment cost of acidic mine water is high, the quality requirements of underground production water in mines are low. The current treatment method for acidic mine water is chemical neutralization. Therefore, the mine water in Tongchuan District is based on the neutralization method. Based on the specific conditions of each mine, direct input method, expansion filtration method and drum treatment method can be used. . The direct input method is to directly add alkaline neutralizers such as lime powder or lime milk to acidic mine water; the expansion filtration method is to use solid neutralizers such as limestone to neutralize acidic mine water using an upflow expansion filter; the drum treatment method Limestone and other solid neutralizers are placed in the drum of the processor to achieve neutralization during the continuous rolling, collision and grinding process.
Figure 5-16 Closed-circuit washing process flow
The mine water in Jiaoping District is treated and discharged after meeting the standards, so I will not go into details here. Yuhua Coal Washing Plant adopts water washing closed-circuit circulation technology to prevent coal slurry water from being discharged outside the plant and causing harm. The washing water in the coal preparation plant mainly includes three parts: filter press filtrate water, high-efficiency concentrator overflow water and coal slime sedimentation tank overflow water. Through the implementation of coal slime plant recycling and washing water closed-circuit circulation technology, washing water balance and washing water can be achieved. All reuse targets. The following is the closed-circuit washing process flow of a certain mine (Figure 5-16).
The impact of coal mining on surface water resources is mainly due to the decrease in groundwater levels caused by coal mining, the drying up of springs, and the drying up of some rivers. Substandard mine water discharge during coal mining causes pollution of surface water bodies. If mine waste such as coal gangue is piled up randomly without treatment measures, it will also cause surface water pollution. Therefore, the main issue in the protection of surface water resources is the management of mine water and coal gangue to eliminate pollution.
The impact of coal mining on groundwater resources is mainly the destruction of aquifers and aquicludes, resulting in changes in groundwater supply sources and runoff pathways, causing regional groundwater levels to drop, even to the aquiclude. Therefore, the technical solution for the protection of groundwater resources is to protect the aquifer and aquiclude from damage. This requires improving mining methods and roof management methods to prevent and reduce collapse, and the development of water-conducting fissure zones must not touch the overlying aquifer. Our country has done a lot of work in this area on how to prevent the occurrence of ground subsidence and the development height of fissure zones, which provides a basis for various mines in the Tongchuan mining area. However, the specific conditions of each mine are different, and the hydrogeological conditions of each mine in Tongchuan Mining Bureau are also different. The specific protection technical plan must be determined based on the hydrogeological conditions and coal mining methods of each mine. Therefore, in order to protect groundwater resources from damage as much as possible, it is necessary to combine industry, academia and research to find the best combination of groundwater resource protection and coal recovery rate.
2. Technical plan for the management of ground subsidence and ground fissure disasters
The technical plan for the management of ground subsidence and ground fissure disasters in the Tongchuan mining area also includes two aspects: First, the treatment of ground subsidence and ground fissure disasters that have occurred Technical solutions to control subsidence and ground fissures; one is a technical plan to reduce the occurrence of ground subsidence and ground fissures in the future.
For the subsidence areas in Tongchuan City, industrial land will still be mainly used after reclamation, and the subsidence areas will be mainly filled. Therefore, filling and reclamation can be used. Filling and reclamation can use coal gangue, fly ash, open-pit stripping waste, etc. near the mining area to fill the coal mining subsidence.
The reclamation of subsidence areas outside Tongchuan City is mainly ecological reclamation and biological reclamation. Ecological reclamation combines land reclamation engineering technology with ecological engineering technology, comprehensively uses the theories of biology, ecology, economics, environmental science, agricultural science, and systems engineering, and uses the species, organisms and materials of the ecosystem to Principles such as recycling and regeneration are combined with systems engineering methods to design multi-level utilization technology for destroying land.
Its purpose is to promote the optimal allocation of various production factors, achieve multi-level and hierarchical utilization of materials and energy, continuously improve its cycle conversion efficiency and land productivity, obtain better economic, ecological and social comprehensive benefits, and follow the path of sustainable development. . It includes the selection of various land reclamation engineering technologies, the selection of ecological engineering technologies such as agricultural three-dimensional planting, breeding, food chain structure, integration of agriculture, forestry, animal husbandry and sideline fisheries, which are often realized through graphic design, food chain design and reclamation engineering design. Biological reclamation technology is an emerging land reclamation technology and a current research hotspot at home and abroad. Biological reclamation is based on the land use direction of the reclamation area, using biological methods including fertilizing the soil, microbial fertilization, etc. to change the nutrient status and soil structure of the new cultivated layer of the soil, increase the water storage, water retention, and fertilizer retention capabilities, and create An environment suitable for the normal growth and development of crops and a technical system to maintain the ecological balance of the mining area. For example, the green manure method is the most effective way to improve reclaimed soil and increase organic matter and various nutrients such as nitrogen, phosphorus, and potassium. Green manure is mostly leguminous plants, generally containing 15 to 25% of organic matter and 0.3 to 0.6% of nitrogen. It is highly productive and can grow well on poorer and barren land with poor natural conditions. It has a well-developed root system and can absorb deep water. As nutrients in the soil, green manure also has the function of cementing and agglomerating soil particles after decay, thus improving the physical and chemical properties of the soil. Its application method is to plant green manure crops on the project reclamation land, and when they are mature, they are pressed into green manure and turned into the soil. Planting methods such as single planting, intercropping, and intercropping can be adopted. Ground cracks in ground subsidence areas must be backfilled in time to prevent the loss of soil nutrients and moisture.
The technology to prevent ground collapse and ground cracks is to improve mining methods and roof management methods. Our country has done a lot of work in this regard, and the Tongchuan Mining Bureau has also done a lot of work in an effort to reduce the occurrence of ground fissures caused by ground subsidence. In the early 1990s, the Tongchuan Mining Bureau used the regression prediction empirical formula obtained by applying the principle of least squares based on the measured maximum subsidence values ??of 7 observation stations, which can more accurately predict the maximum post-mining surface subsidence of general mining working faces. The subsidence value can continue to be used under similar geological and mining conditions. Tongchuan Mining Bureau jointly conducted the "Report on Coal Mining Subsidence in Tongchuan Mining Area, Shaanxi Province" and "Research on Mining Subsidence Laws and Water Source Damage in Tongchuan Mining Area" in conjunction with Liaoning University of Engineering and Xi'an University of Science and Technology. The influencing factors were simulated and analyzed, and research conclusions were given. The main research conclusions are: ① The ranking of the degree of influence of the surface subsidence coefficient in the Tongchuan mining area is the disturbance degree coefficient - the comprehensive hardness of the overlying rock - the thickness of the topsoil layer - the inclination length of the working face - the mining thickness. Among them, the coefficient of disturbance degree, the inclination length of the working face, and the mining thickness are positively related to the surface subsidence coefficient, and the comprehensive hardness of the overlying rock is negatively related to the surface subsidence coefficient. ② Mining depth is the main factor affecting the dynamic deformation of the ground surface. When the mining depth is small, the mining impact spreads to the surface faster, the surface subsidence changes have poor continuity, the maximum subsidence speed is fast, the active period is short, and the cumulative subsidence amount is larger. , the total surface movement time is shortened; when the mining depth is large, the surface movement starts slowly, the subsidence curve is gentle and continuous, the subsidence speed is small, the change is small, and the active period is short or no active period. ③ Mining speed and mining thickness have an important impact on the surface subsidence speed and duration. The greater the mining speed and thickness, the greater the maximum subsidence velocity, the shorter the active period and the greater the cumulative subsidence amount, and the total movement time is shortened accordingly. ④The thickness of the loess layer is an important factor affecting the dynamic movement of the surface. As the soil-rock ratio increases, the surface subsidence velocity tends to increase and the movement duration shortens. That is, the thicker the soil layer, the more intense the surface movement and deformation will be during the active period, and the more and larger surface cracks caused by movement and deformation will be.
3. Technical solutions for coal gangue utilization
(1) Black gangue and red gangue are used as cement mixing materials
Most of the coal gangue mountains in the Tongchuan mining area are prone to spontaneous combustion. Phenomenon, some gangue mountains have even spontaneously ignited for decades, and the burned coal gangue has turned into red gangue. Currently, red gangue is generally used as a mixing material for cement. Some of the red gangue in the Tongchuan mining area has been sold. Used as ingredients in cement plants.
To produce different types of cement, the coal gangue used as cement mixing material is required to be carbonaceous mudstone, mudstone, sandstone, and limestone (CaO content >70). Calcined coal gangue or spontaneous combustion of coal gangue is usually used. , Calcined coal gangue or spontaneous combustion coal gangue contains active silica and alumina, and can be used as active pozzolanic mixed materials. The coal gangue in the Tongchuan mining area is a high-quality gangue formed by the alteration of volcanic ash deposition. It is characterized by stable chemical composition and clay minerals with high silicon and aluminum content. Its chemical composition is shown in Table 5-7.
Table 5-7 Chemical composition of coal gangue in Tongchuan Mining Area (wB/)
The production process of using coal gangue as a mixed material to produce pozzolanic cement is basically the same as that of ordinary cement. , its production process is shown in Figure 5-17.
Figure 5-17 The process flow of using coal gangue as cement mixing material
(2) Producing Portland cement
Use coal gangue as raw material to produce cement. Mainly because the chemical composition of coal gangue and clay are similar, it can replace clay to provide silica-alumina raw materials, and coal gangue can release a certain amount of heat, which can save some fuel. Coal gangue is particularly easy to burn when replacing loess ingredients, mainly because it contains a variety of trace elements, such as sulfur, fluorine, titanium, vanadium, boron, strontium, barium, etc., which have a mineralizing effect. At the same time, coal gangue contains thermal energy, which enters the preheating process. The post-heater can accelerate the pre-decomposition of materials and greatly increase the output. During operation, the temperature of the preheater barrels at all levels is reduced accordingly, and the effect of an 8-level preheater can be achieved without investment.
According to the experience of Shaanxi Huafeng Building Materials Company in producing pozzolanic Portland cement, using coal gangue instead of loess as raw material to grow Portland cement has many advantages. The early and late strength reduction of cement after coal gangue is mixed with mixed materials is small. Compared with the amount of mixed materials increased by more than 15%, the amount of mixed materials was reduced by 15%, and the amount of red gangue was increased by 15%. The price of the raw material is 180 yuan/t, and the price of red gangue is 20 yuan/t. The price difference between pozzolanic Portland cement and ordinary Portland cement is 10 yuan/t. Calculation shows that the cost of cement per ton is reduced by 14 yuan. The annual output is 85,000 tons of cement, saving 1.19 million yuan.
Using coal gangue instead of loess as cement ingredients can improve the hourly output and cement quality of rotary kilns and cement mills, and has good economic and social benefits.
(3) Coal gangue as concrete admixture
The use of self-igniting coal gangue or burning coal gangue as concrete admixture has three advantages. First, it can reduce the amount of cement, thereby reducing energy consumption; second, it can use coal gangue in large quantities to reduce environmental pollution; third, it can improve the performance of cement concrete, increase its resistance to carbonization and sulfate erosion, and improve Concrete product quality and engineering quality. This is an important way to realize the resource utilization and harmless treatment of coal gangue.
Spontaneous coal gangue or coal-burning gangue has volcanic ash activity. Active silica and alumina can undergo a slow "secondary reaction" with the calcium hydroxide precipitated during the cement hydration process to generate hydration. Calcium silicate and calcium aluminate hydrate are firmly combined with the cement slurry hardener to improve the resistance and durability of concrete. Powdered gangue has special physical functions in concrete beyond the activity of volcanic ash, such as increasing the volume of the slurry, filling the pores of the slurry, etc., making the physical and chemical effects of gangue concrete reach a dynamic balance, and playing a role in improving the performance and quality of concrete. Improve the effect.
(4) Coal gangue is used as concrete aggregate
Coal gangue contains a large amount of silicon and aluminum substances. The combustible substances and siderite in it release gas and expand during the roasting process. Therefore, coal gangue is an ideal raw material for producing lightweight aggregate. Gangue lightweight aggregate is generally made from carbonaceous rock and argillaceous rock gangue with low carbon content by crushing, grinding, balling, burning and screening. The gangue can also be directly crushed to It is directly roasted in a certain proportion. Lightweight aggregate made from coal gangue is a new lightweight building material with good thermal insulation properties.
(5) White gangue is used as cement mixing material and building material
The main components of white gangue produced in coal production in Tongchuan mining area are limestone and sandstone.
Sandstone can be used as building materials after processing, and can also be used as underground filling materials. Limestone can also be used as a building material after processing, and can also be used as a raw material for the production of cement or quicklime.
(6) Gangue-free fired bricks
The traditional fired brick process causes secondary pollution to the environment and is highly selective for gangue. Coal gangue is used as raw material to produce non-burning bricks. The focus of raw material selection is coal gangue with high iron, sulfur, calcium, magnesium, etc. which is difficult or impossible to bake bricks. The use of coal gangue to make burn-free bricks avoids secondary pollution caused by traditional brick-making processes and significantly improves the adaptability of coal gangue raw materials. It is an important direction for coal gangue brick-making in the future.
The non-burning coal gangue is made of self-igniting coal gangue or burning coal gangue as the main raw material, combined with cement, stone and admixtures, etc., and is made by stirring, semi-dry pressing and natural curing. A kind of masonry material, its main process flow is shown in Figure 5-18.
(7) Gangue concrete block
Use spontaneous combustion or artificial calcined coal gangue as aggregate, cement and other cement as cementing materials, add a small amount of admixtures, add water, stir and shape, Solid or hollow blocks formed by natural curing are called gangue concrete blocks. Gangue concrete blocks have stable performance, have the advantages of light weight, high strength, simple process, low cost, high waste rate and good use effect. They are a promising new wall material. The production process of gangue concrete blocks is simple and easy to implement, and its process flow is shown in Figure 5-19.
The raw materials of gangue concrete blocks include aggregates, binders and admixtures. The aggregate is self-igniting coal gangue or coal gangue, which meets the requirements of JC/T541-94 "Spontaneous Coal Gangue Light Aggregate". Cementing materials include cement, fly ash, spontaneous combustion burnable coal gangue powder, etc. Admixtures include gypsum, quicklime, etc.
(8) Coal gangue power generation technology
Coal gangue with high carbon content (carbon content ≥ 20, calorific value between 6270 and 12550kJ/kg) can be directly used as a fluidized bed The fuel for the boiler is used to generate electricity. The process of burning coal gangue to generate electricity is simple: first, crush the mixture of coal gangue and low-quality coal and grind it to a particle size of less than 8 mm; then, it is sent to the circulating fluidized bed in the boiler by a belt conveyor for combustion, and the fluidized bed combustion The high-pressure air flow sent from the bottom of the bed causes the coal gangue powder to "boil" on the hearth, forming a fluidized state of a certain height; finally, the smoke and dust generated by combustion are sent to the flue through the dust collector, and the ash generated by combustion is The slag is pumped into the ash yard after being water-cooled.
Figure 5-18 Process flow chart of burn-free bricks
Figure 5-19 Process flow chart of coal gangue block production
4. Gas power generation technology
Gas power generation is an energy conversion process that uses gas as energy and converts the thermal energy contained in the gas into electrical energy. At present, there are three main methods of practical gas power generation: gas engine, gas turbine and steam turbine generator. Xiashijie Mine established a 3,000kWh gas self-contained power plant in May 2005.
5. Coal and gas mining technology The mining of coal seams will cause the surrounding rock layers to produce a "pressure relief and permeability increase" effect, that is, it will cause the destruction of the surrounding rock layers' in-situ stress sealing (reduction of in-situ stress-unloading). pressure, proliferation and opening of pores and cracks), damage to the sealing of interlayer rock layers (collapse, rupture, and subsidence of the overlying coal rock layers; cracking and bulging of the underlying coal rock layers), and damage to the sealing of geological structures (the sealing of geological structures due to The combination of the three results in a significant increase in the permeability coefficient of the surrounding rock and coal seams, creating prerequisites for high-yield and efficient extraction of pressure relief gas.
From the perspective of the pressure relief gas flow channel, the joint-creating effect of mining damage forms "three zones" in the vertical direction above the goaf: caving zone (forming cavities and cracks that penetrate the stope) Network channels), fault zones (forming layer-wise and vertical fracture network channels), and curved subsidence zones (forming layer-oriented fracture network channels within the layer).
From the perspective of pressure relief gas flow, the collapse of rock strata, the support and compaction of natural filling, etc., also produce "three zones" in the lateral direction above the goaf: the initial pressure relief, permeability and flow enhancement zone, pressure relief and Fully high permeability and high flow zone and ground pressure recovery and permeability and flow reduction zone. These horizontal "three zones" exist in the vertical "fault zone" and "bending subsidence zone".
The deformation, cracking and fissure expansion of the coal (rock) body caused by mining during the pressure relief of the coal seam will greatly improve the permeability of the coal (rock) body gas migration, resulting in "pressure relief and increased permeability". "Flow" effect, forming the conditions for gas "desorption-diffusion-seepage" activated flow. Due to the different distribution of coal and rock fissures in different areas, the desorption and flow conditions of gas are different. The use of reasonable and efficient gas drainage methods and drainage systems can achieve safe and efficient mining of gas resources. The mining of gas resources reduces the gas content of pressure-relief coal seams, eliminates the danger of coal and gas outbursts in pressure-relief coal seams, and reduces the amount of gas gushing into the wind flow of the working face, thereby creating the need for safe and efficient mining of pressure-relief coal seams. conditions.
The above is only the theoretical knowledge of coal and gas mining technology. The geological conditions and coal seam conditions of specific coal mines are different. The theory must be combined with practice, and industry, academia and research should be combined to explore Jiaoping District coal and gas mining technology. The National Engineering Research Center for Coal Mine Gas Control, Huainan Mining Group, China University of Mining and Technology, Anhui Institute of Construction Engineering, Anhui University of Science and Technology and other units have combined industry, education and research to jointly tackle key problems in the Huainan mining area, and systematically proposed the laneway drilling method for coal and gas* **The new mining method, based on the existing conditions of the coal seam group, first mines the key pressure relief layer, and implements continuous mining without coal pillars along the goaf lane along the edge of the goaf, and arranges upper and lower high and low drilling holes in the lane. Coal seam gas mining technology that extracts roof and floor decompression gas and gas enriched in goaf areas, and quickly builds gob-side lane filling wall technology through innovation, to achieve high coal and gas efficiency that is synchronized with the fully mechanized mining face* **Mining method of mining. It has innovated three projects including "Stability Control of Surrounding Rock Structure of Gobside Retention", "System Integration Innovation of Development of Roadside Filling Materials and Rapid Retention and Filling Technology" and "Gas Drainage of Remaining Lane Drilling". Gas mining technology. Jiaoping District can refer to the experience of Huainan Mining Area, combine the geological conditions, coal seam characteristics and gas characteristics of Jiaoping Mining Area and conduct scientific research to explore suitable coal and gas mining technology.