The basic task of coal mine drainage design is to discharge all kinds of production wastewater, domestic sewage and rainwater generated by mine industrial plaza and residential area into the ground water body in an organized manner and in accordance with environmental protection requirements.
Coal mine drainage design and urban drainage design compared with many similarities but also has its own particularity. On the one hand, production and life need a lot of water, on the other hand, coal mining and greatly damaged groundwater resources. In the coal mine construction process, how to comply with the laws of the market economy, commercialization, urbanization drainage design, how to rationally use water resources, protect the ground water environment, is the coal mine drainage design workers must pay attention to the problem. This paper combines many years of practice in coal mine design, coal mine construction drainage design of a number of problems to put forward their own views.
1 water supply design
1.1 water source selection
Currently, most of the mines industrial sites and residential water supply to take the source wells groundwater as the main source of water supply, mine water purification reuse as an auxiliary source of water supply.
1.1.1 Problems
The following problems exist in the above water supply methods:
①In order to ensure that the mine production, living water, must be built in a number of water wells, Huainan mining area, for example, Pan San, Xieqiao Coal Mines have built more than 10 water wells, these wells of the pumping station and equipment investment, and each water wells have to be acquired to protect the land. Water wells water pipeline is long. In addition, the water source well water consumption is high, in the Huainan area, for example, the general depth of the well is more than 80m, and it needs 15-22KW deep-well pumps to elevate the groundwater to the industrial site and the residential area pools.
② industrial sites and residential water supply facilities are scattered, more duplication of construction. In particular, industrial sites mine water supply for non-potable water systems and water supply systems must be set up separately, even the pipeline is also a separate construction. Therefore, the water supply system investment is higher.
3 mine water utilization rate is low, serious waste of water resources.
1.1.2 Solutions
Therefore, in the coal mine water supply design should emancipate the mind, break the customary water supply mode, make full use of mine drainage resources, in the mine industrial site to build a centralized purification of water plant, mine drainage treatment for drinking water, responsible for the mine industrial site and the residential area of water supply. Take the mine drainage in the two Huaihuai areas of Anhui Province as an example, except for suspended solids and bacteria in the mine drainage, the rest of the physical, chemical and toxicological indicators are in line with the standard of drinking water. Most of the mine wastewater is reused after treatment, which is enough to ensure the production and living water supply for the industrial sites and residential areas of the mines. Some mines with sufficient water to meet their own water surplus, water purification plant can charge a certain amount of water capacity and pipe network construction costs, water supply to nearby residents. Mine water purification treatment process shown in Figure 2.
1.1.3 Advantages of adopting water purification
The advantages of adopting the water supply mode of purifying mine water mainly include:
①Making full use of groundwater resources, due to the different climatic conditions, geography, and geological environments, the spatial and temporal distribution of China's water resources is extremely uneven. Coal mine construction on the one hand, a large number of mine drainage pollution of the environment; on the other hand, due to the destruction of groundwater resources led to a serious shortage of water supply in the mining area; mine water purification and reuse, greatly reducing the amount of groundwater extraction, to avoid the contradiction of water scarcity, and is conducive to the further development of agriculture and industry around the mines, and thus the environmental and social benefits are significant.
②Greatly reduce the coal mine water supply and drainage facilities to repeat the construction, saving a lot of construction funds. Mine water reuse, industrial sites, water supply network, water supply structures and equipment, a single, the investment is greatly saved; at the same time reduce the new water wells, water pipelines, roads, land acquisition costs and a number of years due to coal mining caused by surface subsidence of the water wells, water pipelines and roads resulting in the reconstruction costs; reduce the cost of treatment of mine drainage [2].
3) Management and operation costs are reduced;
4) Water supply costs are reduced.
1.2 Underground water supply design issues to discuss
With the mechanization of the mining process, the degree of automation, in order to meet the requirements of production safety and dust control, the scope of underground water supply in coal mines is becoming more and more extensive, and the main water supply objects are summarized as follows: the mining process dust water, production water, water for firefighting. For the underground water point water equipment water consumption and water pressure requirements, in the coal mine design specifications have been stipulated, this paper will not repeat, the following mainly on the underground fire sprinkler design problems for some discussion.
1.2.1 Selection of water source
Currently most of the mine design will be the ground production and living water supply source as the underground water supply source. From the ground with a pipeline will lead the water to the underground, using a centralized water supply. The advantage is that the water quality can be guaranteed, do not need to increase the management personnel, for the development of vertical shafts and inclined shafts, the mine, the underground water pressure is larger, can meet the mining equipment and sprinkler water pressure requirements, generally do not need to be pressurized. The disadvantage is that the long pipeline in the shaft, some mines vertically down as high as 1,000m, the water pressure in the bottom of the alley is too large, the use of unsafe, especially for the deep shaft, the long shaft is particularly. In fact, underground water supply water source there are other options available: such as the use of deep underground subsoil water source, the use of underground drainage.
①Use of deep underground floor water source. If there is a good aquifer under the bottom plate in the underground alley, you can take the downward drilling of water source holes to draw water, borrowing the pressurized head of the groundwater to meet the water pressure requirements of the underground mining equipment, sprinklers and fire fighting water. Advantages of decentralized water supply by drilling holes in the deep basement: short downhole water supply pipeline, no power consumption, energy saving, low pressure of pipeline, safe to use. The disadvantage is that more hydrogeological work must be done, because not all locations in the well drilling holes can be taken to water.
②Use of underground drainage. When the underground drainage is large, and most of the dry bottom water, due to the large amount of water, the water is clearer, you can build a water warehouse in the well, a little precipitation, pumped to the underground water supply network.
In summary, we are in the mine underground water supply design, should carefully analyze the hydrogeological data, depending on the actual situation of each mine to suit the local conditions. When the underground water or bottom plate aquifer is close and large water, it is preferable to prioritize the choice of underground water or underground borehole water as a source of water. When the downhole water quality is very poor or does not have the conditions for water extraction, water should be supplied from the ground.
1.2.2 Underground dust sprinkling and its automation
The main purpose of underground dust sprinkling is to eliminate rock dust and coal dust, and try to make the concentration of rock dust in the underground wind flow below 2mg/m3 and coal dust below 10mg/m3, so as to ensure the safety of coal mine production and the health of workers. But the actual situation is that many mines underground coal dust concentration exceeds the standard, and dust sprinkler equipment is idle, analyze the reasons, there is insufficient production management and ideological awareness, not enough attention to the problem, but also the design can not make the sprinkler automation work, the management of inconvenient problems. Due to the uneven coal flow in underground transportation, especially the loading point or turning cage are intermittent work, sprinkler on and off, manual operation is not convenient and timely. When there is no coal, water is also sprinkled, resulting in water flowing everywhere or affecting the operation of the belt, etc. As a result, workers simply do not turn on the sprinkler. As a result, workers simply do not open the sprinkler. The design can take the following measures to achieve automatic opening and closing of sprinklers: add solenoid valves on the pipeline in front of the sprinkler and set up light sensors at the coal flow control point. When there is a coal flow through or the mine car arrives at the loading point and cage, the light is blocked, the light electric appliance acts to open the solenoid valve, the sprinkler spraying water, and vice versa immediately closed. This not only facilitates management, but also saves water, and more importantly, ensures production safety. Therefore, in the underground dust sprinkler system design, should strive to realize automation.
1.2.3 Underground water supply pipe anti-corrosion and pipe selection
Underground pipe anti-corrosion has always been a difficult problem in the design of underground water supply, due to the poor environmental conditions of the underground, high humidity in the air, the pipe is very easy to corrode. And because of the high pressure, often use seamless steel pipe or galvanized steel pipe. At present, civil buildings used to replace galvanized steel pipe pp-R pipe, its nominal pressure has reached 2.5mpa, the pipe does not exist anti-corrosion problems, in the future underground water supply design, when the pipe working pressure is not greater than 1.6mpa, you can do some trial research work.
1.3 Design of circulating cooling water system in industrial plaza
Because of the needs of coal mine ventilation, gas extraction and underground fire extinguishing, there are generally air compressor station, gas extraction station and nitrogen production station built in industrial plaza of the mine. The air compressor, gas pumping machine, nitrogen generator and other equipment need water cooling. Because of the large amount of water demand, circulating cooling water is used. Its water supply process is shown in Figure 3.
1.3.1 Repeated setup of circulating water system
At present, most of the mine circulating water design adopts air compressor station, nitrogen making station, gas pumping station and so on to set up their own circulating cooling water system. Using this decentralized set up the following disadvantages:
① cooling circulating water system pools, pumps and other structures and pumps, cooling towers, water softening and other equipment duplication of construction, occupies a large area, high investment;
② cooling pools, cooling equipment arranged in the workshop near the cooled equipment, resulting in a poor workshop hygiene environment;
③ decentralized set up a high energy consumption, high operating costs;
④ operation, management personnel are more, and the technical force is decentralized. Air compressor station, nitrogen station, gas pumping station on the cooling water quality requirements for softened water, cooling water temperature are required to be less than 35 ℃, the temperature of the water out of the equipment 39 ~ 42 ℃. Therefore, the mine construction design should be considered comprehensively, in the appropriate location of the mine industrial site design a circulating water center station, through the pipeline to the cooling equipment water supply, equipment cooling water through the pipeline self-flow to the circulating water center station. This setup can not only overcome the many shortcomings of the above decentralized setup, and equipment maintenance, replacement of small impact on production; energy saving and consumption reduction is obvious; easy to circulate the water supply of technical problems occurring in the organization of the strength of the research [3].
1.3.2 Reasonable Configuration of Cooling Equipment
From the use of circulating cooling water system has been put into operation to see the effect of the circulating cooling water equipment and the equipment being cooled configuration is unreasonable, resulting in poor cooling effect or energy saving effect is very poor, to the Huainan Coal Mine Pan San, Xieqiao mine air compressor station circulating cooling water system configuration as an example, air compressor station generally has 3 to 5 air compressors According to the underground ventilation, the number of air compressors can be reasonably adjusted, while the circulating water system pump configuration uses a cold water pump, a hot water pump, a standby pump for each other. Cold, hot water pump flow according to the air compressor group maximum ventilation cooling water required selection, the result of such a configuration, regardless of the air compressor group to open a few, cooling water pumps are running at maximum flow, and the number of air compressors open to switch frequently, the cooling water adjustment can only rely on frequent adjustment of the cold, hot water pump outlet pipeline valve opening degree, it is difficult to control, sometimes leading to the air compressor water phenomenon, in order to facilitate the adjustment, but also have to In order to facilitate the adjustment, and have to increase the bypass water return on the outlet pipe. This mode of operation has a great impact on the service life of the pump and high energy consumption. Therefore, in the design of the circulating water system, be sure to be cooled according to the operation of the equipment required for the change in the amount of water reasonable configuration of cooling equipment, such as cold, hot water pumps, cooling towers, water softening devices with the number of units and the flow rate and so on. If from the point of view of energy saving, you can also consider the circulating water system, cold, hot water pumps to increase the frequency control function, so that the flow regulation with the cooling equipment water demand changes more reasonable. Although the increase in frequency conversion adjustment function of the one-time investment has increased, but 4 ~ 5a energy-saving costs can recover the increased investment [4].
2 coal mine drainage design problems
The difficulty of coal mine drainage design is the design of domestic sewage treatment, coal system, the new mine attaches great importance to environmental protection construction, and invested a lot of money in environmental protection construction. Coal design departments have also carried out multi-process, multi-program comparison and exploration of domestic sewage treatment. For example, in the Huainan area, the biological aeration process of Pan No. 2 Mine, the biological turntable process of Pan No. 3 Mine, the surface aeration process of Xieqiao Mine, and the oxidation ditch process of Xinji Mine. But from the actual effect of putting into use and capital utilization are not ideal. Here are some analysis and discussion of coal mine sewage treatment.
2.1 Coal mine domestic sewage treatment facilities, the phenomenon of duplication of construction is common
Currently part of the coal mine industrial sites and residential areas to build a sewage treatment plant, so that the two places to requisition land, duplication of construction, the investment has increased greatly, the operation of the high energy consumption, high management costs, the technical force dispersed, the cost of tons of water treatment is high. Generally speaking, the mine industrial site and residential areas are not very far apart, the construction of a sewage treatment plant is more reasonable, considering the drainage from the residential area to the industrial site, the pipeline is buried too deep, can be set up in the middle of the sewage lifting pumping station, or in the middle of the industrial site and the residential area of the land acquisition and construction of sewage treatment plant. Take the joint construction method, not only can save investment, but also the main can greatly reduce operating costs.
2.2 Sewage treatment design parameters are not reasonable
The coal mine sewage treatment plant design, the sewage pollutant indicators BOD5, CODCr, SS value, not according to the actual measurements, not by analogy, but the city sewage pollutant indicators for the design of the basis to BOD5, for example, urban sewage for 200mg / L, while the actual Coal mine BOD5 value is generally only 70 ~ 80mg / L. Due to the domestic sewage organic content is too low, resulting in the original design of a number of activated sludge treatment process, in the operation of microorganisms do not get the minimum nutrients, and was "starved to death", decomposition, mineralization, the shape of the activated sludge. For this reason, many treatment plants to stop the reflux of activated sludge, maintaining the original design of the aeration link, so that the original design has lost the core link - activated sludge and its process, into a simple level of enhanced treatment. Even if the oxidation ditch sewage treatment process, there are the same problem, often the design process of reflux activated sludge reflux does not come up, resulting in the original oxidation ditch system into an additional aeration of the banded advection settling tank; the original design of a number of ancillary facilities to become redundant, such as defoamer tanks, sludge centralized treatment tanks and sludge drying field, resulting in a large amount of waste of funds [5].
Many mines in the Gujiao mining area in Shanxi use secondary biological contact oxidation to treat coal mine domestic wastewater, the effect is very good. This process is characterized by its ability to adapt to the low concentration and large variation of sewage in the mining area, as well as its investment saving and simpler operation and maintenance than the activated sludge method. Its principle is to utilize the biofilm formed on the surface of solid filter media to purify wastewater. The available filter media are various, such as slag, fiberglass or plastic honeycomb material, semi-soft fiber balls, etc. [6].
Therefore, when carrying out the design of coal mine wastewater, it is necessary to analyze the indicators of influent pollutants, select the wastewater treatment plan with strong applicability and high shock load resistance, and submit it to the expert group of environmental protection department for review to determine the final treatment process.
3 Conclusion
In short, the coal mine construction of water resources, coal mine water supply system, the rational configuration of the circulating water system, coal mine sewage treatment and environmental protection issues, it is worthwhile for the coal mine water supply and drainage design workers to study and explore.
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