Research on Mine Water Dispatching Mode Based on Maximization of Reuse Rate

Abstract

Coal mining not only produces a large amount of mine water but also may cause water pollution. Therefore, economic treatment and efficient reuse of mine water are the main research directions of the mine area at present, and the realization of optimal dispatching and efficient reuse of mine water is an urgent problem to be solved. Based on the Na Lin mining area as an example, based on maximizing the reuse rate of mine water, summarizes the mine water level fractionation utilization pathway and classification of mine water dispatching mode, build the Na Lin mining area water supply dispatching model, analyzed the Na Lin River No. 2 mining area water supply dispatching model and the space-time change of water dispatching, through comparing with traditional dispatching model, the results showed that: The constructed water dispatching model can significantly improve the mine water recycling rate in Na Lin river mine area, which provides a certain theoretical basis for the study of efficient utilization of mine water.

1. Introduction

In the process of coal mining in China, a large amount of mine water is generated [1]. Large amounts of mine water can lead to water damage in coal mines if it is not drained and left underground [2,3]. Such as high-pressure karst water, sudden water damage at the bottom of the main mining seam, sandstone and its loose layer pore water permeability, water damage at the top of the main mining seam and surface water backflow water damage, etc. [4]. Water damage in coal mines brings not only huge economic losses to the country and people [5], but also easily causes heavy casualties among underground workers [6,7]. The direct discharge of untreated mine water not only causes waste of water resources [8], but also causes environmental pollution in and around the mine site [9,10]. The main sources of coal mine wastewater are mine water, coal processing wastewater, coking plant wastewater and gas generating station wastewater and other polluted water [11], among which mine water accounts for the largest proportion [12]. At present, the utilization rate of mine water in China’s coal mines is obviously low [13]. According to the relevant research results of the Chinese Academy of Engineering, the total water resources of China’s coal mines were about 6.89 billion m³ in 2018, but the average utilization rate was only 35% [14]. The existence of this phenomenon of high emissions and low utilization rate has resulted in a serious waste of water resources [15]. Mine water is less polluted than other industrial wastewater [16] with simpler types of pollutants and is suitable for recycling [17]. The treatment and recycling of mine water can not only reduce water damage in mines and ensure mining safety [18], but also effectively alleviate the contradiction between increasing water consumption and increasing water shortage in mines, reduce pollution to the mines and their nearby environment [19], which is of great significance to promote ecological environmental protection [20]. In recent years, the issue of mine water treatment and utilization has received great attention from the state. National Development and Reform Commission Mine Water Utilization Development Plan (2013) [21], State Council Water Pollution Prevention and Control Action Plan (Water ten) (2014), clearly state “Promote the comprehensive use of mine water, and give priority to the use of mine water for supplementary water in coal mines, production and ecological water in surrounding areas” [22].

Optimizing mine water dispatching and utilization mode is an important way to improve mine water utilization [23]. Renfence [24] introduced new mine water treatment technologies, summarized key technologies for in-situ reuse of underground treatment and discussed a new model for mine water treatment. Renfence [25] summarized the classification of mine water development and utilization patterns and constructed a mine water classification index system. Renfence [26] analyzed the constraints on the utilization of mine water resources and proposed the development of high-quality mine water and the industrialization of mine water resources. Renfence [27] proposed the technical idea of constructing multiple underground reservoirs in the coal mine area based on the safety of coal mine production, connecting multiple underground reservoirs to each other through pipelines to form interconnected distributed underground reservoirs, and allowing joint dispatching of water between multiple reservoirs, on which the optimal dispatching of water resources in the mine area is carried out. Renfence [28] aimed at economic treatment and efficient reuse of mine water, using a variety of intelligent algorithms to achieve optimal allocation and economical reuse of mine water. Renfence [29] presented the damage to tailings dams due to 44 typical accidents and presented some advances and new insights on environmental sustainability and disaster control of tailings dams, and finally proposed a conceptual map of disaster prevention, disaster control, and environmental sustainability for safety management and environment to enhance the clean production of tailings dams. Renfence [30] evaluated the environmental performance of a new valorization strategy for needle iron ore residues in zinc production, avoiding landfill of needle iron ore by producing a clean by-product. The above literature does not address the study of specific mine water dispatching models.

Na Lin River No.2 Mine (Hereinafter called “The study area”) is located in Ordos, Inner Mongolia. The mine is located in the Wu Ding River basin, the first tributary of the Yellow River, with abundant water gushing [31]. Geological data provided by the mine gushing water, normal gushing water is 28,800 m³/d, and maximum gushing water is 36,000 m³/d. Together with the seepage of 2024 m³/d of yellow mud grouting, the normal gushing water of the mine is 30,824 m³/d, and the maximum gushing water is 38,024 m³/d. And the reuse amount of mine water is only 10,517 m³/d, accounting for 36.5%. The main problems of mine water utilization in this mine are large mine gush, imperfect mine water treatment process, and unreasonable mine water distribution and dispatching. In this paper, the relevant research work is carried out for the main problem.

The paper is structured as follows: Section 1 introduces the research background and current status; Section 2 introduces the graded and fractionated utilization of treated mine water, detailing the characteristics of normal water supply and the changes in water supply in case of abnormalities; Section 3 introduces the three main mine water models; Section 4 establishes a scheduling model and objective function that meets the characteristics of the Nalinhe No. 2 mine, taking into account the constraints according to its actual needs; Section 5 conducts experimental verification and compares the corrected results with the conventional scheduling model; Section 6 is the conclusions.

2. Mine Water Level Fractionation Utilization Pathway

Considering the water quality category of mine water, mine water treatment can be roughly divided into pre-treatment, secondary treatment, and deep treatment. Pre-treatment system in the conditioning pre-sinker can remove part of the large particles in suspension [32], and high-efficiency cyclone treatment can further reduce the suspended matter in the water. The secondary treatment unit is divided into four parts: hardness removal—coagulation and sedimentation PH (Hydrogen ion concentration) adjustment—filtration, except for SS (Suspended Substance) and COD(Chemical Oxygen Demand), which are partially reduced, and hardness is basically removed [33]; the deep treatment process unit, including self-cleaning filtration and ultrafiltration—reverse osmosis—disinfection, can effectively reduce the concentration of bacteria, salinity, colloids, and organic matter [34]. The flow chart of the mine water treatment process is shown in Figure 1.

Based on the three-stage treatment process of mine water, the preliminary construction of the mine in the normal water supply situation of the graded fractionated utilization path. The normal water supply situation refers to the situation where miners work in three normal shifts, the mine is in normal operation and is not in the transition period of the non-heating season, and the mine gushing water is sufficient to meet the water volume at each level of normal water supply. Due to the cold weather in the north of mainland China, the heating season refers to the season when heating is needed, and the non-heating season refers to the season when heating is not needed. The division between heating and non-heating seasons is based on the cyclical effects of different climates on production activities in northern China during the year and is carried out by the government to improve production activities through heating in the cold season. The heating and non-heating seasons are fixed every year. The amount of water required for this mine varies from season to season, and the temperature changes lead to different temperatures at the underground workings, so the work intensity varies, and therefore the reuse rate and treatment time of the mine water varies.According to the water supply conditions such as water quality, production, and safety, the water supply is divided into 1 to 7 water supply points. The first level water supply point is for underground fire-fighting water, the second level water supply point is for underground dust removal water, the third level water supply point is for underground industrial water, and the fourth level water supply point is the fire-fighting water on the well, the fifth level water supply point is the dust removal water on the well, the sixth level water supply point is the industrial water on the well, and the seventh level water supply point is the domestic water on the well.

2.1. Normal Water Supply Situation

Underground grading utilization: mine gushing water is used for underground fire-fighting water at the first level water supply point after underground treatment; mine water is supplied to underground dust removal water at the second level water supply point after satisfying underground fire-fighting water consumption; mine water is supplied to underground industrial water at the third level water supply point after satisfying underground dust removal water consumption (underground industrial water includes cooling water, grouting water, and hydraulic bracket water, etc.); the remaining mine water is used for up-hole water after satisfying underground industrial water consumption. Up-hole grading utilization: after pre-treatment, the mine water is first used for fire-fighting water at the fourth level water supply point and then supplied to the fifth level water supply point for dust removal water on the well after satisfying the amount of water used for dust removal water on the well, and then continued to be supplied to the sixth level water supply point for industrial water on the well after secondary treatment (industrial water at the well includes water for coal processing, boiler, and cooling water, etc.), and after satisfying the amount of industrial water on the well, the mine water is supplied to the seventh level water supply point for domestic water on the well after deep treatment (domestic water at the well includes water for greening and irrigation and other water, etc.). Among them, the mine water after underground treatment is stored in the clear water tank and supplied for underground fire-fighting water, underground industrial water, and underground dust removal water; the mine water after pre-treatment on the well is stored in the intermediate tank and supplied for fire-fighting water on the well and the dust removal water on the well; the mine water after secondary treatment is stored in the high-level tank and supplied for the industrial water on the well; the mine water after deep treatment is stored in the reuse tank and supplied for the domestic water on the well. After meeting all levels of water supply points, the remaining mine water is treated at three levels and discharged if the water quality meets the discharge standard; if it does not meet the discharge standard, it continues to be treated at three levels and then checked to see if it meets the discharge standard.

2.2. Irregular Water Supply Situation

The abnormal water supply situation refers to the abnormal situation where the water quantity at some water supply points changes and needs to be adjusted and controlled artificially to restore the normal water supply. There are three main situations that lead to abnormal water supply: (1) abnormal water supply caused by fire accidents; (2) abnormal water supply caused by the transition period of the non-heating season; (3) abnormal water supply caused by changes in production volume. Due to the large variety of anomalies, only a few typical abnormal water supply situations are listed in this paper and analyzed as follows.

2.2.1. The Fire-Fighting Incidents on the Well Lead to Increased Water Consumption for the Fire-Fighting Water on the Well

When a well firefighting accident occurs, the water consumption of the fourth water supply point (the fire-fighting water on the well) increases: (1) When a lighter degree of fire-fighting accident occurs on the well, underground, fifth, sixth, and seventh level water supply points remain unchanged, and the up-to-standard external drainage valve is turned down to call for up-to-standard external drainage to meet the water for fire-fighting on the well. (2) When a heavy fire accident occurs on the well, underground, the fifth and sixth level water supply points remain unchanged, the up-to-standard external drainage valve is closed, the water valve of the seventh level water supply point is closed, and the up-to-standard external drainage is called to meet the water for fire-fighting on the well. (3) When a very serious firefighting accident occurs on the well, the underground and the fifth level water supply point remain unchanged, the standard external drainage valve is closed, the sixth and seventh level water supply point water valve is closed and the standard external drainage is called to meet the fire-fighting water on the well.

2.2.2. Increased Water Consumption for Water Used for Dust Removal Underground and on the Well in the Non-Heating Season Compared to the Heating Season

During the transition from the heating season to the non-heating season, the water consumption of the second and fifth water supply points (water used for dust removal underground and on the well) increases: (1) When the amount of water used for dust removal increases less, the water supply points of the first, third, fourth, sixth, and seventh stages remain unchanged, and the up-to-standard external drainage valve is turned down to call for down-hole to up-hole external drainage to meet underground dust removal water, and for up-to-standard external drainage to meet dust removal water on the well. (2) When the amount of water for dust removal increases more, the water supply points of the first, third, fourth, and sixth levels remain unchanged, the standard external drainage valve is closed, and the water valve of the water supply point of the seventh level is closed, calling for the external drainage from down-hole to up-hole to meet the underground dust removal water, and calling for the standard external drainage to meet the water for dust removal on the well. (3) When the amount of water used for dust removal increases a lot, the first, third, and fourth stage water supply points remain unchanged, the standard external drainage valve is closed, and the water valves of the sixth and seventh stage water supply points are closed so that the down-hole to up-hole external drainage is called to meet the underground dust removal water, and the standard external drainage is called to meet the dust removal water on the well.

2.2.3. Increased Production during the Transition Period from Non-Heating to Heating Season

When the transition from the non-heating season to the heating season occurs, the amount of water used for domestic use on the well increases; when production increases, the amount of water used for production below the well and on the well increases. If the up-standard external drainage valve is closed or shut down, the reduction of up-standard external drainage can meet both the increase in the domestic water on the well and the increase in the underground industrial water, then the down-hole to up-hole external drainage is called to meet the underground industrial water, and the up-standard external drainage is called to meet the domestic water on the well and the industrial water on the well. If the standard external drainage valve is closed, the amount of standard external drainage cannot meet the increase in the domestic water on the well and the increase in the underground industrial water and the industrial water on the well at the same time. According to the condition that production is given priority, call for down-hole to up-hole external drainage to meet the underground industrial water first and call for the up-to-standard external drainage to meet the industrial water on the well first before considering the domestic water on the well.

3. Mine Water Dispatching Model

The study area is located in the southwest of Dong Sheng Coalfield, and there is user demand for mine water in this mine area [35]. Water is needed not only for cooling, coal processing, and dust removal in the mine but also for industrial parks, farmland irrigation, and aquaculture in the neighboring mines [36]. In consideration of economic applicability, the mine water dispatching mode of the mine is adapted to the dispatching mode of proximity utilization; in consideration of the requirement of two-way coordination between supply and demand, the mine water dispatching mode of the mine is adapted to the dispatching mode of the industrial chain oriented to the park. The Na Lin river mine area has a large amount of mine water gushing, unreasonable mine water distribution and dispatching, and a low utilization rate of mine water. It is necessary to discharge the remaining mine water that is well treated and meets the external discharge standard to the nearest lake. Therefore, the mine water dispatching mode of the study area is adapted to the dispatching mode that combines these three mine water dispatching modes. After a long period of development, there are three main classifications of mine water dispatching modes according to the utilization object, as follows:

3.1. Proximity Utilization Dispatching Model

After the collected mine water is treated, if it meets the water quality standards for mine working water, it is used nearby, and the water dispatching model aims to reduce the resources such as human and material resources needed to transport mine water. The chart of the proximity utilization dispatching model is shown in Figure 2.

3.2. Dispatching Mode for the Industrial Chain of the Park

After the collected mine water is treated, if it meets the water quality standards for user water, it is transported to the water dispatching mode of industrial park enterprises, surrounding agricultural irrigation, landscape greening, aquaculture, living and other water users. The chart of dispatching mode [37] for the industrial chain of the park is shown in Figure 3.

3.3. Dispatching Model to Achieve the Standard External Discharge

After the collected mine water is treated, if it meets the water quality standards for external discharge to the nearby lakes, the treated mine water is discharged to increase the ecological base-flow of rivers, replenish the flow of rivers and lakes, and return to the water dispatching mode for the purpose of rivers and lakes. The chart of dispatching mode to achieve the standard external discharge is shown in Figure 4.

4. Na Lin River No. 2 Mine Water Supply Dispatching Model

On the premise of no significant impact on the original water supply task, the corresponding mine water dispatching rules are set, taking into account the two-way coordination requirements of supply and demand: (1) the mine gush water is sufficient to meet the water volume at each level of normal water supply; (2) based on the premise of safety over production, the priority of water supply is: water for firefighting > water for dust removal > water for production > water for living; (3) miners work in three normal shifts. Due to the diversity of water supply, even if there is the same water supply situation, its degree varies. For this reason, this paper analyzes the mine water demand model and the mine water reuse dispatching model, and constructs the Na Lin River mine water supply dispatching model with the ecological goal of maximizing the mine water reuse rate, taking into account the requirement for two-way coordination between supply and demand.

4.1. Water Demand Model for Mining Sites

The water used in the mining area is mainly divided into two parts, namely underground water and the water on the well. This paper classifies the water consumption points according to the water consumption conditions in the mining area, which are divided into seven water consumption points: underground fire-fighting water and the fire-fighting water on the well, underground dust removal water, and the dust removal water on the well, underground industrial water and the industrial water on the well and the domestic water on the well.

(1) Underground fire-fighting water $X_1$. Its demand is

$$X_1=S\times n$$

(1)

In this formula: S indicates the average amount of water used for the occurrence of underground fires (m${}^3$/time); n indicates the average annual number of fires in the well.

(2) Underground dust removal water $X_2$. Its demand is

$$X_2=L\times t$$

(2)

In this formula: L indicates the average water consumption of underground dust removal equipment (m${}^3$/h); t indicates time (h).

(3) Underground industrial water $X_3$.Underground industrial water includes water for hydraulic support, water for grouting, and water for cooling. Its demand is

$$X_3=G\times \alpha +Y\times m+P$$

(3)

In this formula: G indicates the volume of grouting (m${}^3$); $\alpha$ indicates the water volume share, usually 0.6; Y indicates the average water consumption of hydraulic brackets (m${}^3$/pc); m indicates the number of hydraulic brackets (pc); P indicates the cooling water consumption (m${}^3$).

(4) The fire-fighting water on the well $X_4$. Its demand is

$$X_4=S\times n$$

(4)

In this formula: S indicates the average amount of water used for well fires (m${}^3$/time); n indicates the average number of well fires per year.

(5) The dust removal water on the well $X_5$. Its demand is

$$X_5=q\times D\times d$$

(5)

In this formula: q indicates the annual watering water quota(m${}^3$/m${}^2$·d); D indicates the area of the road (m${}^2$); d indicates the annual watering days.

(6) The industrial water on the well $X_6$. The industrial water on the well refers to the secondary processing of mined coal and the treatment of coal slurry, which mainly includes water for coal processing, water for heat exchange stations, water for boilers and water for cooling, etc. Its demand is

$$X_6=A\times t_1+B\times t_2+H\times t_3+E\times t_4+F\times t_5$$

(6)

In this formula: A and B indicate the average water consumption (m³/h) of the heavy dielectric process and the jigging process of the coal processing plant; H indicates the average evaporation and loss of water in the heat exchange station (m³/h); E indicates the water consumption of the coal-water slurry boiler system; F indicates the average water consumption of the cooling equipment ($m/h$); $t_i$ indicates the operation time of the corresponding equipment $\left(h\right)$.

(7) The domestic water on the well $X_7$. The domestic water on the well is mainly divided into the greening of the park and domestic drinking in the mine. Its demand is

$$X_7=N\times g+J\times l$$

(7)

In this formula: N indicates the total population of residents in the mine; g indicates the per capita water consumption standard in the mine (m${}^3$/person); J indicates the greening area in the mine (m${}^2$); l indicates the average water consumption for greening (m${}^3$/m${}^2$).

4.2. Dispatching Model for Reuse of Mine Water

The mine reuse basin is divided into four basins, namely, clear water basin, intermediate basin, high-level basin, and reuse basin. The clear water basin is the first reuse point in the mine, in which the water is transported to the underground fire-fighting water, underground dust removal water and underground industrial water; the intermediate basin is the second reuse point in the mine, in which the water is transported to the fire-fighting water on the well and the dust removal water on the well; the high-level basin is the third reuse point in the mine, in which the water is transported to the industrial water on the well; the reuse basin is the fourth reuse point in the mine, in which the water is transported to the domestic water on the well.

In the process of mine water reuse, the system is in a state of uninterrupted operation, with mine water constantly pouring into the treatment system. The use of mine water in underground and up-hole coal mines is in a random state. The mine water reuse dispatching system arranges the dispatching plan reasonably according to the underground—up-hole water demand and delivers the water from the treatment process to the water use points in the mine area. The mine water reuse rate $\eta$ is determined by measuring the reuse amount at each reuse point in the mine area.

The calculation formula is as follows:

$$\eta =\sum _{i=1}^4\frac{Q_i}{K}$$

(8)

In this formula: $Q_i$ indicates the amount of reuse at the i$th$ reuse point in the mine $\left(m\right)$, K indicates the amount of water gushing from the mine (${\mathrm{m}}^3$). Mine water reuse treatment time. The overall system treatment reuse operation time was calculated by using the treatment rate of each grade of the investigated mine water treatment system.

$$t_i=\sum _{i=1}^4\frac{Q_i}{V_i}$$

(9)

In this formula: $t_i$ indicates the treatment time of mine reuse water at the ith reuse point, $Q_i$ indicates the reuse amount of mine water at each reuse point, and $V_i$ indicates the treatment rate of reuse water at each reuse point. The treatment time of mine reuse water is taken as the maximum value calculated in each level. Mine water reuse rate. That is, the amount of mine water reused in the same time period, under different treatment reuse processes or different algorithm calculations.

$$v=\sum _{i=1}^4\frac{Q_i}{t_{m}ax}$$

(10)

In this formula: v indicates the reuse rate of mine water, i indicates the reuse point of mine water at all levels, $Q_i$ indicates the reuse amount of mine water at all levels and $t_{m}ax$ indicates the maximum treatment time of mine reuse water.

4.3. Objective Function

The lowest inverse of the sum of the mine water reuse and its treatment time consumption is taken as the objective function and the water quality and quantity of each water point are taken as the constraint. A mathematical model of system dispatching is established for a certain period of time T.

$$min\mathrm{fit}=\sum _{i=1}^4\left(\frac{1}{{\omega }_1\frac{C_i-Q_i}{S_i-Q_i}+{\omega }_2\frac{t_{imax}-t_{\mathrm{ic}}}{t_{imax}-t_{imin}}}\right)$$

(11)

In this formula:$S_i$ indicates the maximum amount of mine water reuse (m³), $C_i$ indicates the amount of reuse at the water use point i (m³), $Q_i$ indicates the amount of mine water reused in water use point i of the original system (m³), $t_{imax}$ indicates the time consumed to treat the maximum amount of mine water reuse (h), $t_{imin}$ indicates the minimum time consumed to treat the minimum amount of mine water reuse (h), and $t_{\mathrm{ic}}$ indicates the time consumed to reuse mine water at water use point i (h). ${\omega }_1$ and ${\omega }_2$ indicate the weighting coefficients, which are 0.6 and 0.4.

4.4. Binding Conditions

(1) Water supply and demand balance

$$R=\sum _{i=1}^M{X}_i+U$$

(12)

(2) Limitations on water supply capacity at all levels of mine water treatment

$$X_{min}\le X_i\le X_{max}$$

(13)

In this formula: $X_i$ indicates the water supply in the ith treatment stage (m³), $X_{min}$ indicates the minimum water supply in the ith stage (m³), and $X_{max}$ indicates the maximum water supply in the ith stage (m³).

(3) Water quality conditions for mining equipment

$$Z_{imin}<Z_i<Z_{imax}$$

(14)

In this formula: $Z_i$ indicates the water quality of the ith treatment stage, $Z_{imin}$ indicates the minimum water quality standard of the ith treatment stage, and $Z_{imax}$ indicates the maximum water quality standard of the ith treatment stage.

(4) Mine water treatment speed limit

$${V_{imin}<V}_i<V_{imax}$$

(15)

In this formula: $V_i$ indicates the mine water purification rate for the ith treatment stage $(m/h)$. $V_{imax}$ indicates the fastest treatment rate for the ith treatment stage (m³/h), and $V_{imin}$ indicates the minimum treatment rate for the ith stage (m³/h).

5. Mine Water Dispatching Scheme and Model Analysis

In this paper, we use the data and information of the mine water influx in the study area and the demand for reuse water in this mine and conduct experiments and tests based on three mine water dispatching preset rules and dispatching modes. The purpose of water supply dispatching in this paper is to maximize the reuse rate of mine water. To satisfy the original water supply task, we focus on analyzing the feasibility of this mine water dispatching mode to utilize mine water in the study area.

5.1. Mine Water Dispatching and the Relationship with Spatial and Temporal Variation

(1) The demand for reuse water at this mine varies greatly under different seasons. The main manifestations are: (a) the evaporation of mine water in the non-heating season is much larger than that in the heating season; (b) the water used in boilers is different between the heating and non-heating seasons, 51,840 m³/month and 8640 m³/month respectively; (c) the water used for dust removal, other water, and heat exchange stations increase in the non-heating season.

(2) The demand for reuse water at this mine site varies widely under different spaces. The main manifestation is that the demand for reusing water varies at different water supply points. Na Lin River No. 2 mine water point and water consumption is shown in

Table 1. Na Lin River No. 2 mine water point and water consumption.

Water Points	Position	Water Volume (Heating Season) m³/m	Water Volume (Non-Heating Season) m³/m
Underground fire-fighting water	underground	2880	2880
Grouting water	underground	17,280	17,280
Underground dust removal water	underground	4320	8640
Cooling water	underground	21,600	21,600
Hydraulic support water	underground	3456	3456
The dust removal water	underground	69,120	77,760
Fire-fighting water	ground	2880	2880
Coal processing water	ground	30,240	30,240
Heat exchange stations water	ground	25,920	38,880
Cooling water	ground	21,600	21,600
Greening water	ground	8640	8640
Boiler water	ground	51,840	8640
Domestic water	ground	1728	1728
Other Water	ground	43,200	51,840

.

5.2. Experimental and Test Results

In accordance with the established water supply dispatching rules, experiments and tests were conducted on the water supply and demand in the Na Lin River No. 2 mine, and the results of the experiments and tests were analyzed to evaluate the degree of effectiveness of the mine water dispatching model for the Na Lin River No. 2 mine and the effectiveness of the dispatching model.

Mine water reuse volume at all levels of mine reuse sites are shown as

Table 2. Mine water reuse volume at all levels of mine.

Dispatching Model	Clean Water Tank	Intermediate Tank	High Tank	Reuse Tank
Traditional dispatching (heating season)	160,700	-	-	51,840
Traditional dispatching (non-heating season)	160,700	-	-	58,875
Improved dispatching (heating season)	127,813.73	192,833.33	129,157.02	82,241.1
Improved dispatching (non-heating season)	134,530.75	154,986.77	134,246.52	9979.51

. Mine water treatment data for traditional and improved dispatching models are shown in

Table 3. Mine water treatment data for traditional and improved dispatching models.

Dispatching Model	Mine Water Reuse Rate (Month)	Mine Reuse Water Treatment Time	Reuse Rate (m³/h)
Traditional dispatching (heating season)	30.75%	720 h	295.29
Improved dispatching (heating season)	76.95%	572.41 h	929.48
Traditional dispatching (non-heating season)	17.95%	720 h	305.06
Improved dispatching (non-heating season)	35.45%	602.49 h	719.92

.

From the experimental data and test results, it can be seen that: The sum of the reused amount of the seven water points after optimization is much larger than that before optimization and the total amount of mine water reuse has been significantly improved. From a local point of view, the reuse amount of each water point has been redistributed, and the fire-fighting water on the well, the dust removal water on the well and the industrial water on the well have been greatly improved. The chart of comparison of mine water reuse volume at all levels of mine reuse sites are shown in Figure 5.

Compared with the traditional dispatching mode, the mine water reuse rate of this dispatching mode is increased, the processing time of mine reuse water is reduced, and the reuse rate is increased. The specific data are: the mine water reuse rate in the heating season increased by 46.2%, the mine water reuse treatment time decreased by 147.59 h/month, and the reuse rate increased by 634.19 m³/h; the mine water reuse rate in the non-heating season increased by 17.5%, the treatment time of mine reuse water was reduced by 117.51 h/month, and the reuse rate was increased by 414.86 m³/h. The chart comparison of traditional and improved dispatching models are shown in Figure 6.

It can be seen from the calculation results that the mine water dispatching mode can effectively improve the mine water reuse rate in the Na Lin River mining area.

6. Conclusions

Based on proposing the three-stage treatment process of mine water, and according to the total water inflow in the mining area and the water volume of each water supply point, this paper preliminarily constructed the method of graded and qualitative utilization of the mine in the normal water supply situation, and summarized the mine water dispatching mode of Na Lin River No. 2 mining area—the dispatching mode that is suitable for the combination of three mine water dispatching modes: the nearby utilization dispatching mode, the industrial chain-oriented dispatching mode and the standard discharge dispatching mode.

Based on the clarification of water supply dispatching rules and dispatching methods, the mine water demand model and mine water reuse dispatching models were analyzed, an ecological reuse target function was designed, and several constraints were established according to actual operating conditions, and a water supply dispatching model that takes into account the requirement of two-way coordination between supply and demand was proposed.

Compared with the traditional dispatching mode, the mine water reuse rate in the heating season is increased by 46.2%, the mine water reuse treatment time is reduced by 147.59 h/month, and the reuse rate is increased by 634.19 m³/h. The mine water reuse rate in the non-heating season is increased by 17.5%, the mine water reuse treatment time is reduced by 117.51 h/month, and the reuse rate is increased by 414.86 m³/h. Therefore, this mine water dispatching model can effectively improve the utilization rate of mine water in the Na Lin River mine.

This paper studied the spatial and temporal demand for mine water in mining areas and the periodic scheduling model of mine water, which can serve as a theoretical basis for the subsequent optimal scheduling of mine water for the purpose of reuse cost and reuse efficiency. Considering that the mine water informatization, resource-based treatment, and scheduling system is currently under construction, future research should analyze and study the scheduling mode for more specific scenarios of more complex mine water demand, such as temporary capacity increase and mega firefighting demand.