Pipe diameter calculation method of geothermal well heat exchange system and one open section structure

Abstract

The application relates to a pipe diameter calculation method of a geothermal well heat exchange system and an open section structure, and relates to the field of geothermal well construction. The application comprises the following steps: based on the heat exchange demand of a user, the circulating water quantity and the heat exchange quantity of the geothermal well are obtained; according to the relationship among the circulating water quantity, the inner diameter of the pumping pipe and the flow velocity, the energy required by the total pressure drop along the pumping pipe, and the relationship between the heat exchange quantity and the energy required by the total friction pressure drop, the minimum pipe diameter of the pumping pipe is determined; the inner diameter of the heat exchange sleeve pipe is measured, and the maximum pipe diameter of the pumping pipe is obtained by combining the minimum wall thickness of the pumping pipe, so that the value range of the inner diameter of the pumping pipe is determined. The application can obtain the value range of the inner diameter of the pumping pipe on the basis of the user demand, so that the heat supply demand of the geothermal well to the surrounding residents and the economic requirement are met.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of geothermal well construction, in particular to a pipe diameter calculation method of a geothermal well heat exchange system and an open section structure. BACKGROUND

[0002] Geothermal heating, geothermal power generation, geothermal agriculture, ground source heat pump and other geothermal energy use projects cannot do without corresponding geothermal development technology. At present, most of the geothermal spring resources rely on artificial excavation of geothermal wells to transfer geothermal resources in the deep underground to the ground for heat exchange heating.

[0003] The coaxial casing heat exchange system is a device for collecting underground heat energy. According to different principles, it can be divided into closed coaxial casing heat exchange system and open coaxial casing heat exchange system. The open coaxial casing heat exchange system has higher heat exchange capacity and better heat exchange efficiency than the closed coaxial casing heat exchange system, thus having great and far-reaching research significance. However, in the actual construction process of the open coaxial casing heat exchange system, there are often cases of excessive heat conversion leading to heat waste, or insufficient heat conversion leading to failure to meet the heat demand of users.

[0004] In the open coaxial casing heat exchange system, the selection of the pipe diameter of the water pumping pipe and the water injection pipe is one of the main factors affecting the heat exchange efficiency of the open coaxial casing heat exchange system. Therefore, it is necessary to reasonably calculate and select the pipe diameter of the inner pipe in the open coaxial casing heat exchange system according to the actual situation, so as to maximize the utilization rate of geothermal energy. SUMMARY

[0005] In order to reduce the cases of excessive heat conversion leading to heat waste, or insufficient heat conversion leading to failure to meet the heat demand of users, the present application provides a pipe diameter calculation method of a geothermal well heat exchange system and an open section structure.

[0006] The present application provides a pipe diameter calculation method of a geothermal well heat exchange system and an open section structure, comprising the following steps: based on the heat exchange demand of users, obtaining the circulating water quantity and heat exchange power of the geothermal well;

[0007] According to the relationship between the circulating water quantity and the inner diameter and flow rate of the water pumping pipe, the energy required by the total pressure drop along the water pumping pipe, and the relationship between the heat exchange power and the energy required by the total friction pressure drop, the minimum pipe diameter of the water pumping pipe is determined;

[0008] The inner diameter of the heat exchange casing is measured, and the maximum pipe diameter of the water pumping pipe is obtained by combining the minimum wall thickness of the water pumping pipe. Thus, the value range of the inner diameter of the water pumping pipe is determined.

[0009] By adopting the above technical solution, the range of values ​​for the inner diameter of the pumping pipe can be determined based on user needs, thereby meeting the geothermal well's requirements for heating supply to surrounding residents and economic efficiency, reducing the situation where the heat exchange system converts too much heat, resulting in heat waste, or converts too little heat, resulting in the inability to meet the user's heating needs.

[0010] Optionally, based on the user's heat exchange requirements, the circulating water volume Q of the geothermal well can be obtained. w With heat exchange power P;

[0011] Q w =V o ·S o

[0012] Where V o S is the flow velocity of the water in the pumping pipe. o S represents the effective flow area of ​​the pumping pipe. o =π((d) o ÷2) 2 ), d o This refers to the inner diameter of the water pump pipe.

[0013] Descent caused by pumping pipe resistance

[0014] The energy required for the total pressure drop along the pipeline of the water pump is: W = ρ * g * 1.1 * H * Q w ÷1000;

[0015] Where λ is the resistance coefficient, which can be obtained by looking up a table or by sampling; ρ is the density of geothermal water, which can be measured by sampling; g is the gravitational acceleration of the working surface; and L is the insertion length of the pumping pipe in the geothermal well, which can be determined according to the depth of the geothermal well.

[0016] And P ≥ 4R per unit time;

[0017] Select a section of coaxial casing based on the inner diameter of the geothermal well, and measure the inner diameter d of the coaxial casing in the pump chamber section of the geothermal well. t , and d o +h o ≤d t ÷2,h o The minimum wall thickness of the water pump pipe is 6mm.

[0018] Based on the above formula, the appropriate range of inner diameters for the pumping pipe can be calculated.

[0019] By adopting the above technical solution, the supply demand of users around the geothermal well can be obtained. o The minimum value is determined by the relationship between the energy required for the total pressure drop along the pump pipeline and the circulating water volume.

[0020] Optionally, the Q w =v i ·S i The number of water injection pipes is n, and the inner diameter of the water injection pipes is d. i The effective flow area of ​​the water injection pipe is S. i S i =n·π((d i ÷2) 2 );

[0021] And the d t -d o -2h o -2(d ｉ -2h i )≥40mm, where h i The minimum wall thickness of the water injection pipe is 4mm; the range of pipe diameters for the water injection pipe can be calculated.

[0022] By adopting the above technical solution, the structure employs multiple small-diameter water injection pipes, tubular cable ducts, and water level monitoring equipment arranged around the pumping pipe. The pipe diameter was calculated while maintaining the spacing between any two adjacent pipes, thus limiting the range of possible pipe diameter values. This ensures sufficient working space for installation during construction.

[0023] Optionally, according to formula 2π(d t -d o -h o )≥α(n+2)(d i +h i ), where a is the interval coefficient, and 1.5≤a≤3; the range of values ​​for the number of water injection pipes is calculated.

[0024] By adopting the above technical solution, the water flow velocity in the water injection pipe is reduced, thereby reducing the pressure received in the water injection pipe, and the range of values ​​for n can be calculated accordingly.

[0025] Optionally, according to formula S i =δ·S o The number of water injection pipes is calculated from δ≥1.

[0026] By adopting the above technical solution, the range of values ​​for n is further restricted.

[0027] Preferably, δ = 1.5.

[0028] By adopting the above technical solution, the value of n is determined.

[0029] On the other hand, this application discloses a heat exchange well section structure, including a coaxial sleeve coaxially embedded in the heat exchange well, a pumping pipe for extracting geothermal water from the geothermal well installed in the coaxial sleeve, the pumping pipe being vertically installed in the heat exchange well, and a submersible pump being installed on the pumping pipe.

[0030] Multiple water injection pipes are vertically arranged inside the coaxial sleeve.

[0031] By adopting the above technical solution, the space of the first section is maximized, heat loss in the first section is reduced, and the pipe resistance during water pumping is lowered.

[0032] Optionally, a partition plate is provided inside the coaxial sleeve, and multiple through holes are opened on the partition plate. The water injection pipe and the water extraction pipe are respectively inserted and fixed in the through holes.

[0033] By adopting the above technical solution, heat loss in the first section is further reduced, and contact and collision between the water pumping pipe and the water injection pipe caused by shaking are reduced.

[0034] In summary, this application includes at least one of the following beneficial technical effects:

[0035] 1. A model is established based on the needs of users around the heat exchange well to obtain the users' heat exchange power and circulating water volume requirements. Based on the relationship between heat exchange power and the energy required for the total pressure drop along the friction, and combined with the diameter of the first section of the heat exchange well, a suitable range of pumping pipe inner diameter is obtained.

[0036] 2. By limiting the flow area of ​​the pumping pipe and the injection pipe, the specific number of injection pipes and the range of pipe diameter values ​​are determined.

[0037] 3. Select the appropriate pumping or injection pipe diameter by taking the maximum radial value of the pumping or injection pipe downwards. Attached Figure Description

[0038] Figure 1 This is a structural schematic diagram of the heat exchange well pump chamber section in this application.

[0039] Figure 2 yes Figure 1 Cross-sectional view of section AA.

[0040] Explanation of reference numerals in the attached drawings: 1. Open section; 2. Coaxial sleeve; 3. Pumping pipe; 31. Submersible pump; 4. Injection pipe; 5. Cable conduit; 6. Water level monitoring equipment; 7. Divider plate; 71. Through hole. Detailed Implementation

[0041] The following is in conjunction with the appendix Figures 1-2 This application will be described in further detail.

[0042] This application discloses a section structure of a geothermal well. (Refer to...) Figure 1 This is a schematic diagram of the structure of a section 1 of the heat exchange well in this embodiment of the present application. Section 1 is the wellhead section with a larger inner diameter at the top of the heat exchange well. Section 1 includes a coaxial sleeve 2 coaxially embedded in the heat exchange well. A pumping pipe 3 for extracting geothermal water from the geothermal well is installed inside the coaxial sleeve 2. The pumping pipe 3 is vertically installed in the heat exchange well, and a submersible pump 31 is installed on the pumping pipe 3.

[0043] Multiple water injection pipes 4 are vertically arranged inside the coaxial sleeve 2. In this embodiment, the total depth of the heat exchange well is approximately 2500m-3000m, and the total depth of the first section is 500m. The groundwater level is 200m below ground, the wellhead inner diameter of the first section 1 of the heat exchange well is 311mm, and the submersible pump 31 is installed below the water surface at a location 210m-230m below ground in the first section.

[0044] To ensure the temperature of the water pumped out by the pumping pipe 3, and considering the total depth of the heat exchange well, the length of the pumping pipe 3 extending into the heat exchange well is 2100m.

[0045] To maximize the space utilization of the first section, multiple water injection pipes 4 are provided, with the bottom end of the water injection pipes 4 located above the submersible pump 31. The multiple water injection pipes 4, as well as the strip-shaped cable pipe 5 and the water level monitoring equipment 6, are evenly arranged around the pumping pipe 3, thereby maximizing the use of the internal space of the first section 1 and balancing the spacing between any two adjacent pipes.

[0046] The selection of the coaxial sleeve 2 is based on the inner diameter of the first section. On one hand, the coaxial sleeve 2 can insulate the heat exchange well, reducing heat loss; on the other hand, it reinforces the first section 1 of the heat exchange well, reducing the possibility of collapse. In this application, the inner diameter d of the coaxial sleeve 2 is selected. t =224mm insulated steel pipe.

[0047] Multiple partition plates 7 are fixedly installed inside the coaxial sleeve 2 above the submersible pump 31. Each partition plate 7 has a through hole 71 corresponding to the pumping pipe 3, the injection pipe 4, the cable pipe 5, and the water level monitoring device 6. The through hole 71 corresponding to the pumping pipe 3 is coaxial with the partition plate 7, while the other through holes 71 are evenly distributed around the axis of the partition plate 7. The pumping pipe 3, the injection pipe 4, the cable pipe 5, and the water level monitoring device 6 pass through their respective through holes 71, thereby reducing contact and collisions between the pipes and the cable pipe 5 and the water level monitoring device 6 within the first section 1 due to shaking.

[0048] On the other hand, based on the above-mentioned open section structure of the heat exchange well, the pipe diameter calculation method of the geothermal well heat exchange system provided in this application adopts the following steps:

[0049] First, a usage model for the heat exchange system is established based on actual supply and demand. This embodiment is based on the Beijing operating scenario, considering an initial two months of operation and a four-month heating season. Continuous operation is considered in all calculations, without considering intermittent pump shutdowns. According to preliminary calculations, due to the small well diameter and relatively small inner diameter of the pumping pipe, the circulation flow rate Q is... w Defined as Q w =20m 3 / h.

[0050] The heat exchange system initially operates for 60 days, during which the temperature drops rapidly, then decreases more slowly, reaching an outlet temperature of 29.8℃ after 60 days. The heat exchange power P of the system can reach 240KW. The fluid in the pumping pipe increases approximately linearly with depth, primarily relying on ground heat conduction. Due to the thermal insulation performance of the coaxial sleeve, the temperature drop across the entire depth is only 1℃. After 120 days of operation, the fluid temperature decreases compared to 60 days, but the overall decrease is not significant. The inlet fluid temperature still relies on heat conduction to extract heat, and the temperature drop in the inner pipe remains around 1℃; therefore, P = 240KW is included in the calculation.

[0051] Circulating water volume Q w The relationship between the pumping pipe and the injection pipe is shown in the following formula:

[0052] Q w =v o ·S o =v i ·S i (1);

[0053] Where v o S is the flow velocity of the water in the pumping pipe. o Let S be the effective flow area of ​​the pumping pipe, n be the number of injection pipes, and d0 be the inner diameter of the injection pipe; S be the effective flow area of ​​the injection pipe. i The number of water injection pipes is n, and the inner diameter of the water injection pipes is d. i ;

[0054] And S i =n·π((d ｉ ÷2) 2 );S o =π((d) o ÷2) 2 (2);

[0055] The relationship between the circulating water volume and the energy required for the total pressure drop due to friction along the friction path conforms to the following formula:

[0056] Descent caused by pumping pipe resistance

[0057] The energy required for the total pressure drop along the pipeline of the water pump is: W = ρ * g * 1.1 * H * Qw ÷1000(4);

[0058] Where λ is the drag coefficient, which can be obtained by looking up a table; in this embodiment, λ is 0.043. ρ is the density of the geothermal water, which can be measured by sampling; in this embodiment, the density of the geothermal water is calculated to be 1000 kg / m³. g is the gravitational acceleration constant of the working surface, with a selected value of 9.8 m / s². 2 L is the length of the pumping pipe extending into the geothermal well, which can be determined according to the depth of the geothermal well. Based on the above structure, L = 2100m.

[0059] In order to ensure the economy of the heat exchange system and avoid excessive energy consumption due to frictional resistance along the pipeline during the pumping process, which would reduce the economic efficiency of the heat exchange, the frictional resistance along the pipeline and the heat exchange power should satisfy the formula: P≥4W(5).

[0060] To allow space for water injection pipes and other equipment or pipelines, the maximum outer diameter of the pumping pipe must not exceed half the inner diameter of the coaxial sleeve.

[0061] d o +h o ≤d÷2(6);

[0062] In the formula h o The minimum wall thickness of the water pump pipe is 6mm.

[0063] Based on the above formula, the suitable inner diameter range for the water pumping pipe can be calculated as: 54mm ≤ d o ≤106mm.

[0064] Within the above range, d o Starting from the maximum value, select the largest water pipe diameter available on the market: an outer diameter of 89mm and an inner diameter of 62mm.

[0065] At this time, d o =62mm,d o +h ｏ =89mm

[0066] To ensure the spacing between two adjacent water injection pipes, the following formula is used: 2π(d ｔ +d o +h o )÷2≥α(n+2)(d i +h i (7),

[0067] α is the interval coefficient, and 1.5≤a≤3.

[0068] Furthermore, to ensure sufficient installation space for the pipes within the initial section, the diameters of the pumping and injection pipes should meet the following formula:

[0069] d t -d o -2h o -2(d ｉ -2h i ≥40mm(8)

[0070] According to formula (8), the pipe diameter range d of the water injection pipe is obtained. i ≤43.5mm,

[0071] Within the range of water injection pipe diameters, taking the maximum value downwards, we obtain the water injection pipe diameters that meet the requirements on the market: inner diameter 32.6mm, outer diameter 40.8mm.

[0072] At this time d i =32.6mm,d ｉ +h i =40.8mm,

[0073] Substituting into formula (7) and rounding down, we get: 5≤n≤12.

[0074] Furthermore, considering the flow area of ​​the pumping and injection pipes, it is necessary to ensure that the water flow velocity in the injection pipe is lower than that in the pumping pipe. Therefore, the number of injection pipes is limited, and the following formula is used:

[0075] S i =δ·S o , where δ≥1(9)

[0076] Preferably, δ = 1.5. Substituting into formula (9) and combining with formula (2), rounding up yields the number of water injection pipes: n = 6.

[0077] The above steps complete the calculation and selection of the diameters of the first-section water injection pipe and the water extraction pipe to achieve the expected heating effect.

[0078] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for calculating the pipe diameter of a geothermal well heat exchange system, characterized in that: A section (1) of the geothermal well heat exchange system includes a coaxial sleeve (2) coaxially embedded in the heat exchange well. A pumping pipe (3) for extracting geothermal water from the geothermal well is installed inside the coaxial sleeve (2). The pumping pipe (3) is vertically installed inside the heat exchange well and a submersible pump is installed on the pumping pipe (3). Multiple injection pipes (4) are vertically arranged inside the coaxial sleeve (2). A partition plate (7) is provided inside the coaxial sleeve (2). Multiple through holes (71) are opened on the partition plate (7). The injection pipes (4) and the pumping pipes (3) are correspondingly inserted and fixed in the through holes (71). The method for calculating the pipe diameter of a geothermal well heat exchange system includes the following steps: Based on the user's heat exchange requirements, obtain the circulating water volume and heat exchange power of the geothermal well; Based on the relationship between circulating water volume and pump pipe inner diameter and flow velocity, the energy required for total pressure drop along the pump pipe, and the relationship between heat exchange power and energy required for total pressure drop along the friction, the minimum pipe diameter of the pump pipe is determined. Specifically, the relationship is: the heat exchange power P and the energy W required for total pressure drop along the pump pipe satisfy P≥4W. Measure the inner diameter of the heat exchanger jacket, and combine it with the minimum wall thickness of the pumping pipe to obtain the maximum diameter of the pumping pipe, thereby determining the range of values ​​for the inner diameter of the pumping pipe.

2. The method for calculating the pipe diameter of a geothermal well heat exchange system according to claim 1, characterized in that: Based on the user's heat exchange requirements, the circulating water volume Q of the geothermal well is obtained. w With heat exchange power P; Q w =v o ·S o Among them, v o S is the flow velocity of the water in the pumping pipe. o S represents the effective flow area of ​​the pumping pipe. o =π(d o ÷2) 2 d o This refers to the inner diameter of the water pump pipe. Drawdown caused by pumping pipe resistance ; The energy required for the total pressure drop along the pipeline of the water pump is: W = ρ·g·1.1·H·Q w ÷1000; in The drag coefficient is obtained by looking up a table or through sampling inspection; The density of the geothermal water was measured through sampling. The gravitational acceleration of the working surface. The length of the pumping pipe extending into the geothermal well is determined according to the depth of the geothermal well; Select the coaxial casing for the pump chamber section based on the inner diameter of the geothermal well, and measure the inner diameter of the coaxial casing in the pump chamber section of the geothermal well. ,and , The minimum wall thickness for the water pump pipe is 6mm. Based on the above formula, the appropriate range of inner diameters for the pumping pipe can be calculated.

3. The method for calculating the pipe diameter of a geothermal well heat exchange system according to claim 2, characterized in that: The , where v i The water flow velocity inside the water injection pipe is [value], and the number of water injection pipes is [value]. The inner diameter of the water injection pipe is The effective flow area of ​​the water injection pipe is ; ; And the ,in The minimum wall thickness of the water injection pipe is 4mm. The diameter range of the water injection pipe was calculated.

4. The method for calculating the pipe diameter of a geothermal well heat exchange system according to claim 3, characterized in that: According to the formula The range of possible values ​​for the number of water injection pipes was calculated, where, It is the interval coefficient, and .

5. The method for calculating the pipe diameter of a geothermal well heat exchange system according to claim 4, characterized in that: According to the formula The number of water injection pipes was calculated, among which .

6. The method for calculating the pipe diameter of a geothermal well heat exchange system according to claim 5, characterized in that: The .

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