Coal mine water supply and drainage design analysis?

The basic task of coal mine water supply design is to meet the requirements of mine construction and production for water quantity, water pressure and water quality. It mainly includes water for production, living and fire fighting in the mine industrial square; Cooling circulating water of various industrial equipment; Water for living and fire fighting in mine residential areas; Mine groundwater supply.

The basic task of coal mine drainage design is to discharge all kinds of production wastewater, domestic sewage and rainwater produced by mine industrial square and residential area into surface water body in an organized way and in line with environmental protection requirements.

Compared with urban water supply and drainage design, coal mine water supply and drainage design has many similarities, but it also has its particularity. On the one hand, production and life need a lot of water, on the other hand, coal mining has greatly destroyed groundwater resources. In the process of coal mine construction, how to comply with the laws of market economy, carry out commercialized and urbanized water supply and drainage design, and how to make rational use of water resources and protect surface water environment are issues that coal mine water supply and drainage designers must pay attention to. Based on many years' experience in coal mine design, this paper puts forward some views on some problems existing in water supply and drainage design of coal mine buildings.

1 water supply design

1. 1 Selection of water source

At present, most mine industrial sites and residential areas use groundwater from water source wells as the main water supply source, and mine water is reused as an auxiliary water supply source after purification.

1. 1. 1 has a problem.

The above water supply method has the following problems:

(1) In order to ensure the mine production and domestic water, many water source wells must be built. Take Huainan mining area as an example. There are more than 10 water source wells in Pansan and Xie Qiao coal mines. The pump house and equipment of these water source wells are heavily invested, and each water source well needs land acquisition and protection. The water pipeline of the water source well is long. In addition, the energy consumption of water intake from water source wells is high. Taking Huainan as an example, the depth of well completion is generally more than 80m, and a deep well pump of 15 ~ 22kW is needed to lift groundwater to industrial sites and residential pools.

② The water supply facilities in industrial sites and residential areas are scattered, and there are many redundant constructions. In particular, the mine water supply system of industrial sites is non-drinking water system and the water supply system of water source wells must be set up separately, and even the pipes should be built separately. Therefore, the investment in water supply system is very high.

③ The utilization rate of mine water is low, and water resources are seriously wasted.

1. 1.2 solution

Therefore, in the design of coal mine water supply, we should emancipate our minds, break the usual water supply mode, make full use of mine drainage resources, build centralized purification water plants in mine industrial sites, treat mine drainage as domestic drinking water, and be responsible for supplying water to mine industrial sites and residential areas. Taking mine water in Huaibei area of Anhui Province as an example, the physicochemical and toxicological indexes of mine water meet the drinking water standard except suspended solids and bacteria. Most of mine drainage is reused after treatment, which is enough to ensure the production and living water of mine industrial sites and residential areas. Some mines with sufficient water have surplus besides meeting their own water demand. Water purification plants can supply water to nearby residents after charging a certain water capacity increase fee and pipe network construction fee. The purification process of mine water is shown in Figure 2.

1. 1.3 Advantages of using purified water

The advantages of purifying mine water supply mainly include:

① Groundwater resources are fully utilized. Due to different climatic conditions, geographical and geological environments, the temporal and spatial distribution of water resources in China is extremely uneven. On the one hand, a large number of mine drainage pollutes the environment; On the other hand, due to the destruction of groundwater resources, the water supply in mining areas is seriously insufficient; The purification and reuse of mine water greatly reduces the exploitation of groundwater, avoids the contradiction of water shortage, and is conducive to the further development of industry and agriculture around the mine, thus achieving remarkable environmental and social benefits.

② The repeated construction of water supply and drainage facilities in coal mines has been greatly reduced, and a lot of construction funds have been saved. The mine water is fully reused, which simplifies the water supply pipe network, water supply structures and equipment in industrial sites and greatly saves investment; At the same time, reduce the cost of new water source wells, water pipelines, roads, land acquisition and the reconstruction cost of water source wells, water pipelines and roads caused by surface subsidence caused by coal mining several years later; The treatment cost of mine water is reduced [2].

(3) Reduce management and operation costs;

(4) reduce the cost of water supply.

1.2 Discussion on underground water supply design

With the improvement of mechanization and automation of coal mining technology, in order to meet the requirements of safe production and dust prevention, the scope of underground water supply in coal mines is becoming wider and wider. The main water supply objects are summarized as follows: dust prevention water for coal mining technology, production water and fire water. The requirements of underground water points for water consumption and water pressure of water equipment have been stipulated in the Code for Design of Coal Mines, so I won't repeat them here. The following mainly discusses the problems existing in the design of underground fire sprinkler.

1.2. 1 water source selection

At present, in most mine designs, the surface water supply source for production and life is used as the underground water supply source. Water is piped from the ground to the underground, and centralized water supply is adopted. Its advantage is that it can ensure the water quality and does not need to increase management personnel. For the mine developed by vertical shaft and inclined shaft, the underground water pressure is relatively high, which can meet the water pressure requirements of mining equipment and sprinklers, and generally does not need pressurization. The disadvantage is that the pipeline in the wellbore is long, and some mines are as high as 1000m vertically. The water pressure in the roadway at the bottom of the well is too high, which is unsafe to use, especially for the elderly in the deep well and roadway. In fact, there are other schemes for underground water supply, such as using deep underground water and underground drainage.

(1) Utilize deep underground water. If there is a good aquifer under the floor of the bottom roadway, water can be taken from the confined water head of groundwater by drilling the water source hole to meet the water pressure requirements of underground mining equipment, sprinkler and fire water. The advantages of decentralized water supply by drilling in deep floor are: short underground water supply pipeline, no power consumption, energy saving, low pressure on pipeline and safe use. The disadvantage is that more hydrogeological work must be done, because it is impossible to drill holes for water at all underground locations.

② Underground drainage is adopted. When the underground drainage is large, and most of it is the discharged floor water, because of the large amount of water and clear water, a water warehouse can be built underground, and after a little precipitation, it can be pumped to the underground water supply pipe network by a pump.

To sum up, when designing underground water supply, we should carefully analyze hydrogeological data according to the actual situation of each mine and adjust measures to local conditions. When there is drainage water underground or the bottom aquifer is close and the water quantity is large, it is advisable to give priority to drainage water underground or borehole water underground as the water source. When the underground water quality is poor or does not have the conditions for water intake, water should be supplied from underground.

1.2.2 underground dustproof sprinkler and its automation

Dust prevention and water spraying in underground is mainly to eliminate rock dust and coal dust, and try to control the concentration of rock dust in underground airflow below 2mg/m3 and coal dust below 10mg/m3 to ensure the safety of coal mine production and the health of workers. However, the actual situation is that many mine coal dust concentrations exceed the standard, but dust-proof sprinkler equipment is idle. Analysis of the reasons shows that there are some problems such as insufficient production management and ideological understanding, insufficient attention to problems, design can not make the nozzle work automatically, inconvenient management and so on. Because of the uneven coal flow in underground transportation, especially when the coal loading point or the can is turned over, and the sprinkler is intermittent, the manual operation is inconvenient and untimely. Sprinkle water when there is no coal, causing water overflow or affecting belt operation. As a result, the workers simply didn't turn on the sprinklers. In the design, the following measures can be taken to realize the automatic opening and closing of the nozzle: an electromagnetic valve is added to the pipeline in front of the nozzle, and an optical sensor is set at the coal flow control point. When a coal flow passes by or the mine car reaches the loading point and cage, the light is blocked, the photoelectric device opens the electromagnetic valve, and the sprinkler sprays water, otherwise it will be closed immediately. This not only facilitates management, but also saves water, mainly ensuring production safety. Therefore, in the design of underground dustproof sprinkler system, we should strive to realize automation.

1.2.3 anticorrosion of underground water supply pipeline and pipe selection

The anticorrosion of underground pipelines has always been a difficult problem in the design of underground water supply. Due to poor underground environment and high air humidity, pipelines are easy to be corroded. And because of the high pressure, seamless steel pipes or galvanized steel pipes are often used. At present, the nominal pressure of PP-R pipe used to replace galvanized steel pipe in civil buildings has reached 2.5mpa, and there is no corrosion problem in the pipe. In the future design of underground water supply, when the working pressure of the pipeline is not greater than 1.6mpa, some experimental research work can be done.

1.3 design of circulating cooling water system in industrial plaza

Due to the needs of ventilation, gas extraction and underground fire fighting in coal mines, air compressor stations, gas extraction stations and nitrogen production stations are generally built in mine industrial squares. Air compressor, air extractor, nitrogen generator and other equipment need to be cooled with water. Because of the large water demand, circulating cooling water is used. The water supply process is shown in Figure 3.

1.3. 1 Repeated setting of circulating water system

At present, air compressor station, nitrogen making station, gas drainage station and other supporting circulating cooling water systems are mostly used in mine circulating water design. Adopting this decentralized arrangement has the following disadvantages:

(1) The water pool, pump house and other structures of the cooling circulating water system, as well as water pumps, cooling towers, softened water and other equipment are repeatedly constructed, occupying a large area and with high investment;

(2) The cooling pool and cooling equipment are arranged near the workshop of the cooled equipment, resulting in poor sanitary environment of the workshop;

③ Decentralized setting has high energy consumption and running cost;

(4) there are many operators and managers, and the technical force is scattered. The air compressor station, nitrogen generator station and exhaust station all require softened water for the quality of cooling water. The inlet temperature of cooling water is required to be less than 35℃, and the outlet temperature of equipment is 39 ~ 42℃. Therefore, the design of mine construction should be considered comprehensively, and a central station of circulating water should be designed at an appropriate position in the mine industrial site to supply water to the cooled equipment through pipelines, and the cooling water from the equipment will flow to the central station of circulating water by itself through pipelines. This arrangement can not only overcome many shortcomings of the above-mentioned decentralized arrangement, but also has little impact on production due to the maintenance and replacement of equipment; Energy saving and consumption reduction are obvious; It is convenient to organize forces to solve technical problems in circulating water supply [3].

1.3.2 Reasonable configuration of cooling equipment

Judging from the use effect of the circulating cooling water system that has been put into operation, the configuration of circulating cooling water equipment and cooled equipment is unreasonable, resulting in poor cooling effect or poor energy saving effect. Take the configuration of circulating cooling water system in Pansan and Xie Qiao coal mines of Huainan Coal Mine as an example. Generally, there are 3-5 air compressors in the air compressor station, and the number of air compressors can be reasonably adjusted according to the underground ventilation. The water pump configuration of circulating water system adopts a cold water pump, a hot water pump and a standby pump. The flow rates of cold and hot water pumps are selected according to the cooling water required for the maximum ventilation rate of the air compressor unit. As a result of this configuration, no matter how many air compressors are turned on, the cooling water pump runs at the maximum flow. When the number of air compressors changes frequently, the cooling water can only be adjusted by frequently adjusting the opening of the outlet pipeline valves of the cold and hot water pumps, which is difficult to control and sometimes leads to water leakage of the air compressors. In order to facilitate adjustment, bypass backwater must be added to the outlet pipe. This operation mode has great influence on the service life of the pump and high energy consumption. Therefore, in the design of circulating water system, it is necessary to reasonably configure cooling equipment, such as the number and flow matching of cold and hot water pumps, cooling towers and desalting water devices, according to the change of water demand during the operation of the cooled equipment. From the point of view of energy saving, we can also consider adding frequency conversion adjustment function to the cold and hot water pumps of the circulating water system to make the flow adjustment more reasonable with the change of water demand of the cooled equipment. Although the one-time investment of frequency conversion regulation function is increased, the increased investment can be recovered by saving energy for 4 ~ 5 years [4].

2 coal mine drainage design problems

The difficulty of coal mine drainage design is the design of domestic sewage treatment. New coal mines in coal system attach great importance to environmental protection construction and invest a lot of funds for environmental protection construction. The coal design department has also made a comparison and exploration of multi-process and multi-scheme for domestic sewage treatment. For example, biological aeration process in Pan Er Mine, biological rotary table process in Pansan Mine, surface aeration process in Xie Qiao Mine and oxidation ditch process in Xinji Mine in Huainan area. However, the actual effect and capital utilization rate are not ideal. The treatment of domestic sewage in coal mines is analyzed and discussed below.

2. 1 Repeated construction of domestic sewage treatment facilities in coal mines is common.

At present, some coal mines have built sewage treatment plants in their industrial sites and residential areas, which leads to land acquisition and repeated construction, a substantial increase in investment, high energy consumption in operation, high management cost, scattered technical force and high cost per ton of water treatment. Generally speaking, the mine industrial site is not far from residential areas, so it is more reasonable to jointly build a sewage treatment plant. Considering that the drainage from residential area to industrial site is too deep, a sewage pumping station can be set in the middle, or a sewage treatment plant can be built by land acquisition between industrial site and residential area. Joint construction can not only save investment, but also greatly reduce operating costs.

2.2 The selection of design parameters for sewage treatment is unreasonable.

When designing coal mine domestic sewage treatment plant, the values of pollutant indexes BOD5, CODCr and SS in sewage are not measured or analogized, but based on the pollutant indexes of urban domestic sewage. Take BOD5 as an example, the value of urban domestic sewage is 200mg/L, while the actual BOD5 value of coal mine is generally only 70 ~ 80 mg/L. Because the organic matter content in domestic sewage is too low, many originally designed activated sludge treatment processes can not get the minimum nutrients in operation, but are "starved to death", decomposed and mineralized, and cannot form activated sludge. For this reason, many treatment plants stopped the backflow of activated sludge in the original design, and kept the aeration link, which made the original design lose the core link-activated sludge and its process flow, and became a simple primary enhanced treatment. Even in the oxidation ditch sewage treatment process, there are the same problems, often in the design process, the returned activated sludge can not return, resulting in the original oxidation ditch system becoming a ribbon advection sedimentation tank with additional aeration; Many supporting facilities in the original design became redundant, such as defoaming pool, sludge centralized treatment pool, sludge drying field, etc., which caused a lot of waste of funds [5].

Many mines in Gujiao mining area of Shanxi province use two-stage biological contact oxidation method to treat domestic sewage of coal mines, and the effect is very good. The characteristics of this process are that it can adapt to the sewage with low concentration and great variation in mining areas, and at the same time, it is less expensive and simpler to operate and maintain than the activated sludge process. Its principle is to use the biofilm formed on the surface of solid filter material to purify wastewater. Available filter materials are various, such as slag, glass fiber reinforced plastic or plastic honeycomb materials, semi-soft fiber balls, etc. [6].

Therefore, when designing coal mine sewage, it is necessary to analyze the indexes of influent pollutants, select a sewage treatment scheme with strong applicability and high impact load, and submit it to the expert group of environmental protection department for review to determine the final treatment process.

3 Conclusion

In a word, the utilization of water resources in coal mine construction, the rational allocation of coal mine water supply system and circulating water system, coal mine sewage treatment and environmental protection are all worthy of in-depth study and discussion by coal mine water supply and drainage designers.

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