A numerical calculation method for efficient heat extraction from buried pipes in a backfilling mining working face

Abstract

This invention discloses a highly efficient numerical calculation method for buried pipe heat extraction in backfilled mining faces. The method obtains the thermophysical performance parameters of the roof and floor coal and rock masses to determine the calculation area; establishes a numerical calculation model including the backfill body, heat exchange pipes arranged within the backfill body, and the surrounding rock of the roof and floor; divides the model into a grid, sets symmetrical boundary conditions in the established numerical calculation model, and sets the initial and boundary conditions of the model according to the heat extraction conditions; runs the calculation model, determines the number of representative heat exchange pipes in the calculation model based on the heat exchange characteristics of buried pipes at different locations; and calculates the heat extraction performance of the entire backfilled mining face. This method is simple to operate, convenient, fast, accurate, and reliable in calculating the heat extraction performance of the entire backfilled space, evaluating the heat extraction capacity of backfilled mining faces, improving calculation efficiency, saving calculation costs, and effectively solving the problem of slow calculation speed for large-scale backfilled space buried pipe heat extraction simulation in underground mines. It provides a reference for efficient calculation of underground geothermal extraction.

Description

Technical Field

[0001] This invention relates to the field of geothermal development and utilization technology in mines, specifically to a highly efficient numerical calculation method for heat extraction from buried pipes in backfill mining faces. Background Technology

[0002] my country's energy endowment, characterized by abundant coal, scarce oil, and limited natural gas, dictates that coal remains the country's primary energy source. However, with the intensive exploitation of coal resources, shallow coal resources, primarily in eastern mines, are gradually being depleted. As mining depths increase, the temperature of the surrounding rock at the working face rises due to geothermal gradients, making the high-temperature environment a common feature of deep coal mining. Simultaneously, mine development facilitates the acquisition of geothermal resources, leading to increased attention and importance for geothermal energy in deep coal resource development. Scholars have proposed the coordinated development of deep mine geothermal and coal resources, treating geothermal energy as an equally important resource as coal, and jointly exploring, planning, and developing both to achieve comprehensive utilization of these resources.

[0003] Backfilled pipe heat extraction, a typical technology for the coordinated development of geothermal and coal resources, involves arranging heat exchange pipes within the goaf of a coal mining face and then filling it with a highly thermally conductive backfill. Heat from the high-temperature surrounding rock is transferred through the backfill to the heat exchange pipes and extracted for surface use. The effectiveness of backfilled pipe heat extraction is crucial to its widespread application. Due to the complexity of heat transfer processes in underground spaces, numerical simulation is currently the most effective method for calculating underground heat transfer. However, the heat extraction performance of heat exchange pipes at different locations within the backfill exhibits different patterns due to their positional relationships. Therefore, simulating the heat extraction of a single heat exchange pipe to represent all heat exchange pipes and calculating the heat extraction capacity of the entire backfill surface will lead to inaccurate results. Furthermore, due to the vast scale of underground spaces, simulating and analyzing the heat extraction performance of all heat exchange pipes across the entire backfill face presents significant challenges in terms of mesh generation and computational speed, making it difficult to implement.

[0004] Therefore, developing an efficient numerical calculation method for heat extraction from buried pipes in backfilled mining faces has become a major problem that urgently needs to be solved. It is of great significance for conveniently, quickly and accurately assessing the heat extraction capacity of buried pipes in underground backfilled spaces and guiding the co-development of underground thermal coal. Summary of the Invention

[0005] To address the aforementioned technical shortcomings, the purpose of this invention is to provide an efficient numerical calculation method for heat extraction from buried pipes in a backfilled mining face. This method is simple to operate, convenient, fast, accurate, and reliable in calculating the heat extraction performance of the entire backfilled space, evaluating the heat extraction capacity of the backfilled mining face, improving calculation efficiency, saving calculation costs, and effectively solving the problem of slow calculation speed for simulating heat extraction from buried pipes in large-scale backfilled spaces underground. It also provides a reference for efficient calculation of geothermal extraction in underground spaces.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention provides a numerical calculation method for efficient heat extraction from buried pipes in backfill mining faces, comprising the following steps:

[0008] S1: First, based on the collected engineering geological conditions and indoor experiments on rock properties of the backfilled coal mining face, obtain the thermophysical performance parameters of the roof and floor coal and rock mass, and determine the calculation area.

[0009] S2: A numerical calculation model is established based on the characteristics of the buried pipe heat extraction technology in the backfilling working face, including the backfilling body, the heat exchange pipes arranged in the backfilling body, and the surrounding rock of the top and bottom plates. The heat exchange pipes are divided into one Class A pipe at the boundary, one Class B pipe in the middle of the model, and two Class C pipes near the symmetrical boundary according to their positions. Initially, four heat exchange pipes are arranged at equal intervals l.

[0010] The S3 model is meshed, symmetric boundary conditions are set in the established numerical calculation model, and the initial and boundary conditions of the model are set according to the heat extraction conditions, including water flow temperature, water flow velocity and initial temperature of surrounding rock.

[0011] S4 runs the calculation model to simulate and analyze the outlet water temperature and the temperature distribution around each heat exchange tube. By gradually increasing the number of heat exchange tubes in the filling body of the model until the heat extraction performance of the two Class C tubes is consistent, the number N of representative heat exchange tubes in the calculation model is determined.

[0012] S5: Finally, based on the heat extraction characteristics of representative heat exchange pipes at different locations, calculate the heat extraction performance of the buried pipes in the entire filling working face.

[0013] Preferably, in step S4, the representative pipeline can represent the heat extraction performance of all heat exchange pipes in the entire filling working face, and the criterion for determining its quantity N is that the heat extraction performance of the two Class C pipes is consistent, that is, the outlet water temperature is consistent.

[0014] Preferably, in step S2, the initial equal spacing l can be set, and the setting range is 1 to 10 m.

[0015] Preferably, in step S5, the heat extraction performance of the C-type pipe is used to represent the heat exchange performance of the heat exchange pipes in the middle of the entire filling surface, and then the heat extraction Etot of all buried pipes in the entire filling working surface L is calculated. The calculation expression is as follows:

[0016]

[0017] Preferably, when meshing the model, the mesh around the heat exchange pipe is finer, while the mesh further away from the heat exchange pipe is relatively coarser, which improves computational efficiency without affecting computational accuracy.

[0018] Preferably, the heat output E of each heat exchange tube is calculated based on the simulated outlet water temperature. Specifically, E = specific heat capacity * flow rate * (outlet water temperature - inlet water temperature).

[0019] The beneficial effects of this invention are as follows:

[0020] This invention provides a simple, convenient, fast, low-cost, accurate, and reliable numerical calculation method for efficient heat extraction from buried pipes in filled mining faces. It has wide applicability. Based on the characteristics of buried pipe heat extraction technology in filled mining faces, it establishes a heat extraction model including the filling body, heat exchange pipes within the filling body, and surrounding rock. According to the heat exchange characteristics of buried pipes at different locations, it determines the number of representative heat exchange pipes and uses them to calculate the heat extraction performance of the entire filling space, evaluating the heat extraction capacity of the filled mining face. This reduces the modeling size and mesh number, improves computational efficiency, and significantly reduces the manpower and material resources consumed in model calculation. It effectively solves the problem of slow calculation speed for large-scale buried pipe heat extraction simulation in underground filled spaces, providing a reference for efficient calculation of underground geothermal extraction and promoting the development of geothermal resources in deep mines. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a flowchart of a high-efficiency numerical calculation method for heat extraction from buried pipes in a backfilling mining face, as described in Example 1.

[0023] Figure 2 This is the numerical calculation model for heat extraction from the buried pipe in Example 1;

[0024] Figure 3 This is a schematic diagram of the heat exchange tube classification in the buried tube heat extraction model of Example 1. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] like Figures 1 to 3As shown, this invention presents an efficient numerical calculation method for heat extraction from buried pipes in backfill mining faces. Based on the characteristics of heat extraction technology from buried pipes in backfill mining faces, this invention establishes a heat extraction model that includes the backfill body, heat exchange pipes within the backfill body, and surrounding rock. According to the heat exchange characteristics of buried pipes at different locations, the number of representative heat exchange pipes that can characterize the heat exchange performance of all buried pipes in the entire backfill space is determined and used to calculate the heat extraction performance of the entire backfill space, thereby reducing the modeling size and the number of grids and improving computational efficiency.

[0028] Taking a backfilling working face in a certain mine as an example, the specific implementation steps are as follows:

[0029] (1) First, based on the engineering geological conditions and comprehensive columnar section of the backfilled coal mining face, the range of the model calculation area was determined, and the thermophysical performance parameters of the roof and floor coal and rock mass were tested by sampling and making standard samples, as shown in Table 1;

[0030] Table 1. Thermal properties of the top and bottom plates of a filling face.

[0031]

[0032] (2) A numerical calculation model for heat extraction from buried pipes was established using SolidWorks software. The model has a length, width, and height of 80m, 40m, and 80m, respectively. The diameter of the heat exchange pipes in the model is set to 1 foot, the initial equal spacing l is set to 2m, and the number is set to 4; among them, there is 1 initial Class A pipe and 2 Class C pipes.

[0033] (3) When using the ANSYS mesh module to generate the mesh, the maximum size of the mesh around the heat exchange pipe is set to 0.0002m, and the maximum size of the surrounding rock mesh is set to 1m. After the mesh is generated, it is imported into Fluent software to set the boundary conditions and initial conditions, including a water flow temperature of 10℃, a water flow velocity of 0.1m / s, and an initial temperature of 40℃ for the surrounding rock.

[0034] (4) Run the calculation model, compare and analyze the outlet water temperature of each heat exchange tube and the temperature distribution around the tube, and gradually increase the number of heat exchange tubes in the filling body of the model until the heat extraction performance of the two Class C tubes is consistent. Determine the number of representative heat exchange tubes in the calculation model. When the number of heat exchange tubes in the model exceeds 10, the outlet water temperature of the added heat exchange tube is consistent with the previous one. Therefore, the number of representative heat exchange tubes is determined to be 10.

[0035] (5) The advancing length L of the filling face is 2000m, therefore there are a total of 999 heat exchange tubes in the entire filling face. The representative number of heat exchange tubes in the simulation is 10. Therefore, there are a total of 2 Class A tubes, 14 Class B tubes and 983 Class C tubes in the filling face. The heat extraction E of all buried tubes in the entire filling face is... tot Its calculation expression is:

[0036] E tot =2E A +14E B +983*E C

[0037] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A numerical calculation method for efficient heat extraction from buried pipes in backfill mining faces, characterized in that, Includes the following steps: S1: First, based on the collected engineering geological conditions and indoor experiments on rock properties of the backfilled coal mining face, obtain the thermophysical performance parameters of the roof and floor coal and rock mass, and determine the calculation area. S2: A numerical calculation model is established based on the characteristics of the buried pipe heat extraction technology in the backfilling working face, including the backfilling body, the heat exchange pipes arranged in the backfilling body, and the surrounding rock of the top and bottom plates. The heat exchange pipes are divided into one Class A pipe at the boundary, one Class B pipe in the middle of the model, and two Class C pipes near the symmetrical boundary according to their positions. Initially, four heat exchange pipes are arranged at equal intervals l. S3: Model meshing, setting symmetric boundary conditions in the established numerical calculation model, and setting the initial and boundary conditions of the model according to the heat extraction conditions, including water flow temperature, water flow velocity and initial temperature of surrounding rock. S4: Run the calculation model to simulate and analyze the outlet water temperature and the temperature distribution around each heat exchange tube. By gradually increasing the number of heat exchange tubes in the filling body of the model until the heat extraction performance of the added heat exchange tube is consistent with that of the previous heat exchange tube, determine the number N of representative heat exchange tubes in the calculation model. S5: Finally, based on the heat extraction characteristics of representative heat exchange pipes at different locations, calculate the heat extraction performance of the buried pipes in the entire filling working face.

2. The numerical calculation method for efficient heat extraction from buried pipes in a backfilling mining face as described in claim 1, characterized in that, In step S2, the initial equal spacing l can be set, and the setting range is 1 to 10m.

3. The method for efficient numerical calculation of heat extraction from buried pipes in a backfilling mining face as described in claim 1, characterized in that, In step S3, the mesh around the heat exchange pipe is finer, while the mesh further away from the heat exchange pipe is relatively coarser, which improves computational efficiency without affecting the computational accuracy.

4. The numerical calculation method for efficient heat extraction from buried pipes in a backfilling mining face as described in claim 1, characterized in that, In step S4, the representative heat exchange tube can represent the heat extraction performance of all heat exchange tubes in the entire filling working surface, and the criterion for determining its quantity N is that the heat extraction performance of the two Class C tubes is consistent.

5. The numerical calculation method for efficient heat extraction from buried pipes in a backfilling mining face as described in claim 1, characterized in that, In step S5, the heat extraction performance of type C pipes is used to represent the heat exchange performance of the heat exchange pipes in the middle of the entire filling surface. Then, the heat extraction Etot of all buried pipes in the entire filling working surface L is calculated, and its calculation expression is:

6. The numerical calculation method for efficient heat extraction from buried pipes in a backfilling mining face as described in claim 5, characterized in that, The heat E extracted by each heat exchange tube is calculated based on the simulated outlet water temperature.

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