Biomineralization cementation backfill body buried pipe heat exchange system, filling technology and evaluation method

Abstract

The invention provides a biomineralization cemented backfill buried pipe heat exchange system, a filling process and an evaluation method, relates to the field of ground source heat pump engineering and geotechnical engineering reinforcement, and aims to solve the problems that traditional cement-based and bentonite-based backfill materials are unstable in heat-conducting property, easy to crack, poor in compactness and the like. The system comprises a water insulation and heat preservation box body, a drainage assembly, a backfilling body and a heat exchange assembly. The filling process comprises the steps of (1) EICP treating fluid preparation, (2) sand treatment of a backfill body, (3) laying of a drainage assembly and a heat exchange assembly, and (4) filling of the backfill body. And evaluation is carried out through the unit well depth heat exchange amount and the energy efficiency coefficient of the buried pipe. Based on an environment-friendly EICP technology, urea is hydrolyzed by soybean urease to generate NH4 < + > and CO3 < 2->, the NH4 < + > and CO3 < 2-> react with an external calcium source to form calcium carbonate precipitates, calcium carbonate crystals can not only bond soil particles, but also construct more heat conduction paths, and the heat conductivity coefficient of the backfill material is remarkably improved.

Description

Technical Field

[0001] This invention relates to the fields of ground source heat pump engineering and geotechnical engineering reinforcement technology, and in particular to a biomineralized cemented backfill buried pipe heat exchange system, filling process and evaluation method. Background Technology

[0002] A ground source heat pump system is a technology that uses shallow geothermal energy to power buildings. Through heat exchange pipes buried in the ground, the circulating medium (usually water) exchanges heat with the surrounding soil and rock, achieving cooling in summer and heating in winter. The system mainly consists of three parts: a buried pipe heat exchanger system, a ground source heat pump main unit system, and an indoor air conditioning terminal system. The buried pipe heat exchanger, as the core component of the system, directly affects the overall system performance due to its heat exchange efficiency with the surrounding backfill material. In traditional underground energy structures, backfill materials are often reinforced with cement-based or bentonite-based binders. Cement-based materials have high thermal conductivity and compressive strength, but their thermal conductivity is significantly affected by the water-cement ratio; while bentonite-based materials (such as bentonite mortar) can be used as backfill, they are prone to cracking and shrinkage under dehydration conditions, severely affecting their thermal conductivity.

[0003] Therefore, developing a green, environmentally friendly, efficient, and easy-to-construct ground source heat pump system is of great significance for promoting the sustainable development and practical engineering application of underground energy structures. Summary of the Invention

[0004] This invention proposes a biomineralized cemented backfill buried pipe heat exchange system, filling process and evaluation method, which solves the problems of unstable thermal conductivity, easy cracking and poor compaction of traditional ground source heat pump systems using cement-based and bentonite-based backfill materials.

[0005] The specific technical solution of the present invention is as follows:

[0006] This invention first proposes a heat exchange system for buried pipes in biomineralized cemented backfill, comprising a waterproof and insulated box, a drainage assembly, a backfill, and a heat exchange assembly. The waterproof and insulated box includes a box body and a box cover, and from the inner surface to the outer surface, it includes a waterproof membrane layer and an insulation board layer. The inner surface of the waterproof and insulated box is also covered with an inner geotextile. The drainage assembly includes several drainage pipes, one end of which is located at the inner bottom of the waterproof and insulated box, and the other end is connected to a drainage pump located outside the waterproof and insulated box. The drain pipe at the bottom of the insulated box is a perforated pipe wrapped with filter cloth. The backfill consists of several layers of permeable sand and gravel, which are laid from bottom to top inside the box. Each layer of permeable sand and gravel is sprayed with EICP treatment solution before laying another layer. The permeable sand and gravel consists of sand soaked in EICP treatment solution. The heat exchange assembly includes heat exchange tubes, which are laid in the middle of the backfill. The inlet and outlet of the heat exchange tubes are connected to the constant temperature circulating water tank. Temperature sensors are installed on the inlet and outlet of the heat exchange tubes.

[0007] Furthermore, the outer surface of the thermal insulation and water-proof box is covered with an outer geotextile.

[0008] Furthermore, the impermeable membrane layer is a waterproof plastic membrane layer, and the insulation board layer is a foam board layer.

[0009] Furthermore, the inner diameter of the flower tube is 4 cm, and several drainage holes are provided on the flower tube.

[0010] Furthermore, the drain pump is a vacuum pump, and the filter cloth is gauze.

[0011] Furthermore, the height of each layer of the permeable sand and gravel layer is less than 200 mm, and the particle size of the sand is less than 1 mm.

[0012] Furthermore, the portion of the heat exchange tube located inside the water-insulated box is a U-shaped or corrugated tube, the heat exchange tube is an HDPE tube, the inlet and outlet of the heat exchange tube are connected to the constant temperature circulating water tank through connecting pipes, and the portion of the heat exchange tube located outside the water-insulated box and the connecting pipe are wrapped with insulation cotton.

[0013] The present invention further proposes a filling process for a buried pipe heat exchange system with biomineralized cemented backfill as described above, comprising the following steps:

[0014] (1) EICP treatment solution preparation

[0015] Soybean flour and water are mixed at a mass ratio of 1:10. 0.05 mol of calcium chloride is added per liter of solution and stirred. After stirring, ε-polylysine hydrochloride is added to the soybean flour suspension at a mass ratio of 0.8 g / kg. Stirring is continued. After standing at room temperature and separating into layers, the supernatant is taken, which is the soybean urease solution.

[0016] Calcium chloride and urea, both with a molar concentration of 2.0 mol / L, are mixed at a volume ratio of 1:1 to form a cementing solution.

[0017] The EICP treatment solution is prepared by mixing soybean urease solution and cementing solution at a volume ratio of 1:1.

[0018] (2) Sand treatment of backfill

[0019] Pour the EICP treatment solution into the sand of the backfill, stir and soak thoroughly, and ensure the sand particle size is less than 1mm;

[0020] (3) Laying of drainage components and heat exchange components

[0021] A geotextile is laid inside the box, and the perforated part of the drainage pipe is laid on top of the inner geotextile at the bottom of the box. The outside of the perforated pipe is wrapped with filter cloth. The other end of the drainage pipe extends out of the box and is connected to the drainage pump. The inlet and outlet of the heat exchange pipe are connected to the constant temperature circulating water tank. Temperature sensors are installed on the inlet and outlet of the heat exchange pipe. The middle part of the heat exchange pipe is inserted into the middle of the box. The part of the heat exchange pipe outside the water-proof and heat-insulating box is wrapped with heat-insulating cotton.

[0022] (4) Backfilling

[0023] The soaked sand from step (2) is layered and filled into the box. Each layer is a permeable sand and gravel layer, and the height of each permeable sand and gravel layer is less than 200mm. After each layer of permeable sand and gravel is filled, EICP treatment liquid is sprayed on the surface, and the drainage pump is started to drain the liquid. After spraying EICP treatment liquid, the next layer of permeable sand and gravel layer is filled until the filling is completed. Then, geotextile is laid on the surface of the backfill, the box cover is placed and fixed.

[0024] Further, in step (1), after adding calcium chloride, stir at 200 rpm / min for 40 min, add ε-polylysine hydrochloride and continue stirring for 5 min, let the soybean urease solution stand at room temperature for 8 h to separate into layers, let calcium chloride and urea with a molar concentration of 2.0 mol / L stand until the temperature is consistent with room temperature, and then mix them at a volume ratio of 1:1 to prevent calcium chloride from dissolving in water and releasing a large amount of heat that affects the concentration of the solution; in step (2), after pouring the ICP cementing liquid into the sand of the backfill, stir it thoroughly and soak it for 1 hour; in step (3), the inlet and outlet of the heat exchange tube are connected to the constant temperature circulating water tank through connecting pipes; in step (4), finally wrap the water-proof and heat-insulating box with an outer geotextile.

[0025] This invention further proposes an evaluation method for the aforementioned biomineralized cemented backfill buried pipe heat exchange system. The evaluation is based on the heat transfer per unit well depth and the energy efficiency coefficient of the buried pipe. The formula for the heat transfer per unit well depth of the buried pipe is as follows:

[0026]

[0027] Where: q is the heat transfer per unit well depth of the buried pipe (W / m); G is the mass flow rate of the fluid in the heat exchange pipe (kg / s); c p Specific heat capacity of the fluid inside the heat exchanger tube (J / (kg·K)); t in t out ...

[0028] The formula for the coefficient of performance (COP) is as follows:

[0029]

[0030] In the formula: t in t out The inlet and outlet water temperatures of the heat exchanger tubes are t ave t0 is the average water temperature at the inlet and outlet of the heat exchange tubes, and t0 is the initial temperature of the backfill.

[0031] The heat transfer per unit well depth and the energy efficiency coefficient were calculated to evaluate the performance of the buried pipe heat exchange system in the biomineralized cemented backfill.

[0032] The beneficial effects of this invention: This invention addresses the problems of unstable thermal conductivity, easy cracking, and poor compaction of traditional cement-based and bentonite-based backfill materials. Based on the environmentally friendly EICP (enzyme-induced calcium carbonate precipitation) technology, it biomineralizes and binds the backfill material, significantly improving its thermal conductivity and uniformity. Enzyme-induced calcium carbonate precipitation (EICP) technology is an environmentally friendly and efficient soil reinforcement method. This technology utilizes soybean urease to hydrolyze urea to generate NH4. + and CO3 2- The calcium carbonate crystals react with the added calcium source to form calcium carbonate precipitate. These calcium carbonate crystals not only cement soil particles but also create more heat conduction paths, thus significantly improving the thermal conductivity of the backfill material. Therefore, increasing the calcium carbonate content in the material is an effective way to enhance its thermal conductivity. In addition, due to the good fluidity of EICP treatment fluid, this technology has advantages over traditional cementing materials in cementing fine porous materials. Therefore, a biomineralized cemented backfill buried pipe heat exchange system was constructed, and corresponding filling technology and evaluation methods were provided, providing reliable methods and technical support for its performance evaluation and optimization in actual buried pipe heat exchange projects. Attached Figure Description

[0033] 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, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the buried pipe heat exchange system of the biomineralized cemented backfill body of the present invention.

[0035] Figure 2 This is a schematic diagram of the filling process of the present invention;

[0036] Figure 3 These are partial actual diagrams of the filling process of the present invention;

[0037] Figure 4 This is a diagram showing the heat exchange per unit well depth for the buried pipe in Example 3;

[0038] Figure 5 This is the energy efficiency coefficient diagram for Example 3.

[0039] In the diagram: 1. Backfill; 2. Heat exchange pipe; 3. Connecting pipe; 4. Temperature-controlled circulating water tank; 5. Permeable sand and gravel layer; 6. Drainage pipe; 7. Drainage pump; 8. Waterproof and heat-insulating box; 9. Inner geotextile; 10. Impermeable membrane; 11. Insulation board; 12. Temperature sensor; 13. Outer geotextile. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1

[0042] Reference Figure 1A biomineralized cemented backfill buried pipe heat exchange system includes a waterproof and heat-insulating box 8, a drainage assembly, a backfill 1, and a heat exchange assembly. The waterproof and heat-insulating box 8 includes a box body and a box cover. From the inner surface to the outer surface, the waterproof and heat-insulating box 8 includes a waterproof membrane layer 10 and a heat-insulating board layer 11. The inner surface of the waterproof and heat-insulating box 8 is also covered with an inner geotextile 9. The drainage assembly includes several drainage pipes 6. One end of each drainage pipe 6 is located at the inner bottom of the waterproof and heat-insulating box 8, and the other end is connected to a drainage pump 7. The drainage pump 7 is located outside the waterproof and heat-insulating box 8. The drain pipe 6 at the bottom of the body 8 is a perforated pipe and is wrapped with filter cloth on the outside; the backfill body 1 includes several layers of sand and gravel permeable layer 5, which are laid from bottom to top in the box. Each layer of sand and gravel permeable layer 5 is sprayed with EICP treatment liquid before laying another layer. The sand and gravel permeable layer 5 is made of sand soaked in EICP treatment liquid; the heat exchange component includes heat exchange tube 2, which is laid in the middle of the backfill body 1. The inlet and outlet of the heat exchange tube 2 are connected to the constant temperature circulating water tank 4. Temperature sensors 12 are installed on the inlet and outlet of the heat exchange tube 2.

[0043] As a further implementation, the outer surface of the thermal insulation and water-proof box 8 is covered with an outer geotextile 13, which can protect the thermal insulation and water-proof box 8.

[0044] The geomembrane layer 10 can be a waterproof plastic membrane layer, or, depending on the needs, a geomembrane layer made of other geomembrane materials such as aluminum foil, as long as it achieves the effect of preventing water seepage. The insulation board layer 11 can be a foam board layer, an insulation board layer made of other insulation materials, or a multi-layer composite insulation board layer, as long as it achieves the effect of heat preservation.

[0045] The inner diameter of the flower tube can be selected as 4 cm, but other inner diameters can also be selected according to actual needs, not limited to 4 cm. Several drainage holes are opened on the flower tube.

[0046] The drainage pump 7 can be a vacuum pump, or other drainage pumps as needed, not limited to a vacuum pump. The filter cloth can be gauze, or other filter cloths as needed, not limited to gauze.

[0047] The height of each layer of the permeable sand and gravel layer 5 is less than 200mm, such as 50mm, 100mm, 120mm, 150mm, 180mm, etc., and the particle size of the sand is less than 1mm, such as 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, etc.

[0048] The portion of the heat exchange tube 2 located inside the water-insulated box 8 is U-shaped, or it can be a continuous U-shaped or corrugated tube. The heat exchange tube 2 is an HDPE pipe. The inlet and outlet of the heat exchange tube 2 are connected to the constant temperature circulating water tank 4 through the connecting pipe 3. The portion of the heat exchange tube 2 located outside the water-insulated box 8 and the connecting pipe 3 are wrapped with insulation cotton.

[0049] Among them, the permeable sand and gravel layer 5 can be 7 layers or other numbers, depending on the needs.

[0050] Example 2

[0051] Reference Figure 2 and 3 A filling process for a buried pipe heat exchange system with biomineralized cemented backfill as described in Example 1, comprising the following steps:

[0052] (1) EICP treatment solution preparation

[0053] Soybean flour and water are mixed at a mass ratio of 1:10. 0.05 mol of calcium chloride is added per liter of solution and stirred. After stirring, ε-polylysine hydrochloride is added to the soybean flour suspension at a mass ratio of 0.8 g / kg. Stirring is continued. After standing at room temperature and separating into layers, the supernatant is taken, which is the soybean urease solution.

[0054] Calcium chloride and urea, both with a molar concentration of 2.0 mol / L, are mixed at a volume ratio of 1:1 to form a cementing solution.

[0055] The EICP treatment solution is prepared by mixing soybean urease solution and cementing solution at a volume ratio of 1:1.

[0056] (2) Sand treatment of backfill

[0057] Pour the EICP treatment solution into the sand of the backfill, stir and soak thoroughly, and ensure the sand particle size is less than 1mm;

[0058] (3) Laying of drainage components and heat exchange components

[0059] A geotextile is laid inside the box, and the perforated part of the drainage pipe is laid on top of the inner geotextile at the bottom of the box. The outside of the perforated pipe is wrapped with filter cloth. The other end of the drainage pipe extends out of the box and is connected to the drainage pump. The inlet and outlet of the heat exchange pipe are connected to the constant temperature circulating water tank. Temperature sensors are installed on the inlet and outlet of the heat exchange pipe. The middle part of the heat exchange pipe is inserted into the middle of the box. The part of the heat exchange pipe outside the water-proof and heat-insulating box is wrapped with heat-insulating cotton.

[0060] (4) Backfilling

[0061] The soaked sand from step (2) is layered and filled into the box. Each layer is a permeable sand and gravel layer, and the height of each permeable sand and gravel layer is less than 200mm. After each layer of permeable sand and gravel is filled, EICP treatment liquid is sprayed on the surface, and the drainage pump is started to drain the liquid. After spraying EICP treatment liquid, the next layer of permeable sand and gravel layer is filled until the filling is completed. Then, geotextile is laid on the surface of the backfill, the box cover is placed and fixed.

[0062] As a further implementation scheme, in step (1), after adding calcium chloride, stir at 200 rpm / min for 40 min, add ε-polylysine hydrochloride and continue stirring for 5 minutes, let the soybean urease solution stand at room temperature for 8 hours to separate into layers, let calcium chloride and urea with a molar concentration of 2.0 mol / L stand until the temperature is consistent with room temperature, and then mix them at a volume ratio of 1:1 to prevent calcium chloride from dissolving in water and releasing a large amount of heat that affects the concentration of the solution; in step (2), after pouring the ICP cementing liquid into the sand of the backfill, stir it thoroughly and soak it for 1 hour; in step (3), the inlet and outlet of the heat exchange tube are connected to the constant temperature circulating water tank through connecting pipes; in step (4), finally wrap the water-proof and heat-insulating box with an outer geotextile.

[0063] Example 3

[0064] An evaluation method is provided for the evaluation of the buried pipe heat exchange system of the biomineralized cemented backfill body described in Example 1, used in Example 2. The evaluation is based on the heat transfer per unit well depth of the buried pipe and its energy efficiency coefficient. The formula for the heat transfer per unit well depth of the buried pipe is as follows:

[0065]

[0066] Where: q is the heat transfer per unit well depth of the buried pipe (W / m); G is the mass flow rate of the fluid in the heat exchange pipe (kg / s); c p Specific heat capacity of the fluid inside the heat exchanger tube (J / (kg·K)); t in t out ...

[0067] The formula for the coefficient of performance (COP) is as follows:

[0068]

[0069] In the formula: t in t out The inlet and outlet water temperatures of the heat exchanger tubes are t ave t0 represents the average water temperature at the inlet and outlet of the heat exchange tubes, and t0 represents the initial temperature of the backfill. The heat exchange per unit well depth and the energy efficiency coefficient are calculated to evaluate the performance of the buried pipe heat exchange system in the biomineralized cemented backfill.

[0070] The initial temperature of the backfill was set to 29℃±0.5℃. The temperature of the circulating medium was set to 5℃, 15℃ and 35℃ respectively through a constant temperature circulating water tank. The heat exchange tube was buried at a depth of 750 mm and exposed at a height of 250 mm. Water was selected as the circulating medium. The inlet and outlet temperatures of the heat exchange tube were recorded by temperature sensors on the inlet and outlet of the heat exchange tube. The heat exchange capacity per unit well depth and energy efficiency coefficient of the buried pipe were calculated using the above formula.

[0071] like Figure 4 The figure represents the heat transfer per unit well depth of the biomineralized cemented backfill buried pipe heat exchange system under different influent water temperatures. It is evident from the figure that the heat transfer per unit well depth increases significantly with increasing temperature difference. When the temperature difference is +5℃, the heat transfer per unit well depth is 39.6 W / m; when the temperature difference is -15℃, it is 123.2 W / m; and when the temperature difference becomes -25℃, the heat transfer per unit well depth at 72 hours is 184.8 W / m. In actual engineering projects, the heat transfer per unit well depth of heat exchangers is 30~80 W / m, while in this biomineralized cemented backfill, it can reach a maximum of 185 W / m. This is mainly due to two factors: firstly, the heat transfer efficiency between the backfill and the heat exchange pipe is high; secondly, the heat exchange pipe is relatively short, resulting in a higher heat transfer per unit well depth.

[0072] like Figure 5 When the inlet water temperature is 5℃, 15℃ and 35℃, the system energy efficiency coefficients are 0.066, 0.061 and 0.055 respectively, indicating that the heat exchange also increases when the temperature difference increases.

[0073] All of the above results indicate that the backfill material bonded by biomineralization technology has superior heat transfer performance.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A buried pipe heat exchange system for biomineralized cemented backfill, characterized in that: include The waterproof and heat-insulating box includes a box body and a box cover. The waterproof and heat-insulating box includes a waterproof membrane layer and a heat-insulating board layer from the inner surface to the outer surface. The inner surface of the waterproof and heat-insulating box is also covered with an inner geotextile. The drainage assembly includes several drainage pipes. One end of the drainage pipe is located at the bottom of the inner part of the water-proof and heat-insulating box, and the other end is connected to a drain pump. The drain pump is located outside the water-proof and heat-insulating box. The drainage pipe located at the bottom of the inner part of the water-proof and heat-insulating box is a perforated pipe and is wrapped with filter cloth on the outside. The backfill consists of several layers of permeable sand and gravel, which are laid from bottom to top inside the box. Each layer of permeable sand and gravel is laid and sprayed with EICP treatment solution before laying another layer. The permeable sand and gravel consists of sand that has been soaked in EICP treatment solution. The heat exchange assembly includes heat exchange tubes, which are laid in the middle of the backfill. The inlet and outlet of the heat exchange tubes are connected to a constant temperature circulating water tank, and temperature sensors are installed on the inlet and outlet of the heat exchange tubes.

2. The system as described in claim 1, characterized in that: The outer surface of the thermal insulation and water-proof box is covered with an outer geotextile.

3. The system as described in claim 1, characterized in that: The impermeable membrane layer is a waterproof plastic membrane layer, and the insulation board layer is a foam board layer.

4. The system as described in claim 1, characterized in that: The inner diameter of the flower tube is 4 cm, and several drainage holes are provided on the flower tube.

5. The system as described in claim 1, characterized in that: The drain pump is a vacuum pump, and the filter cloth is gauze.

6. The system as described in claim 1, characterized in that: The height of each layer of the permeable sand and gravel layer is less than 200 mm, and the particle size of the sand is less than 1 mm.

7. The system as described in claim 1, characterized in that: The portion of the heat exchange tube inside the water-insulated box is a U-shaped or corrugated tube. The heat exchange tube is an HDPE tube. The inlet and outlet of the heat exchange tube are connected to the constant temperature circulating water tank through connecting pipes. The portion of the heat exchange tube outside the water-insulated box and the connecting pipe are wrapped with insulation cotton.

8. A filling process, characterized in that: The filling process for the buried pipe heat exchange system of biomineralized cemented backfill as described in any one of claims 1-7 includes the following steps: (1) EICP treatment solution preparation Soybean flour and water are mixed at a mass ratio of 1:

10. 0.05 mol of calcium chloride is added per liter of solution and stirred. After stirring, ε-polylysine hydrochloride is added to the soybean flour suspension at a mass ratio of 0.8 g / kg. Stirring is continued. After standing at room temperature and separating into layers, the supernatant is taken, which is the soybean urease solution. Calcium chloride and urea, both with a molar concentration of 2.0 mol / L, are mixed at a volume ratio of 1:1 to form a cementing solution. The EICP treatment solution is prepared by mixing soybean urease solution and cementing solution at a volume ratio of 1:

1. (2) Sand treatment of backfill Pour the EICP treatment solution into the sand of the backfill, stir and soak thoroughly, and ensure the sand particle size is less than 1mm; (3) Laying of drainage components and heat exchange components A geotextile is laid inside the box, and the perforated part of the drainage pipe is laid on top of the inner geotextile at the bottom of the box. The outside of the perforated pipe is wrapped with filter cloth. The other end of the drainage pipe extends out of the box and is connected to the drainage pump. The inlet and outlet of the heat exchange pipe are connected to the constant temperature circulating water tank. Temperature sensors are installed on the inlet and outlet of the heat exchange pipe. The middle part of the heat exchange pipe is inserted into the middle of the box. The part of the heat exchange pipe outside the water-proof and heat-insulating box is wrapped with heat-insulating cotton. (4) Backfilling The soaked sand from step (2) is layered and filled into the box. Each layer is a permeable sand and gravel layer, and the height of each permeable sand and gravel layer is less than 200mm. After each layer of permeable sand and gravel is filled, EICP treatment liquid is sprayed on the surface, and the drainage pump is started to drain the liquid. After spraying EICP treatment liquid, the next layer of permeable sand and gravel layer is filled until the filling is completed. Then, geotextile is laid on the surface of the backfill, the box cover is placed and fixed.

9. The process as described in claim 1, characterized in that: In step (1), after adding calcium chloride, stir at 200 rpm / min for 40 min, add ε-polylysine hydrochloride and continue stirring for 5 min, let the soybean urease solution stand at room temperature for 8 h to separate into layers, let calcium chloride and urea with a molar concentration of 2.0 mol / L stand until the temperature is consistent with room temperature, and then mix them at a volume ratio of 1:1 to prevent calcium chloride from dissolving in water and releasing a large amount of heat that affects the concentration of the solution; in step (2), after pouring the ICP cementing solution into the sand of the backfill, stir it thoroughly and soak it for 1 hour; in step (3), the inlet and outlet of the heat exchange tube are connected to the constant temperature circulating water tank through connecting pipes; in step (4), finally wrap the water-proof and heat-insulating box with an outer geotextile.

10. An evaluation method, characterized in that: The evaluation method for the buried pipe heat exchange system of the biomineralized cemented backfill as described in any one of claims 1-7 evaluates the system by the heat transfer per unit well depth of the buried pipe and the energy efficiency coefficient. The formula for the heat transfer per unit well depth of the buried pipe is as follows: Where: q is the heat transfer per unit well depth of the buried pipe (W / m); G is the mass flow rate of the fluid in the heat exchange pipe (kg / s); c p Specific heat capacity of the fluid inside the heat exchanger tube (J / (kg·K)); t in t out ... The formula for the coefficient of performance (COP) is as follows: In the formula: t in t out The inlet and outlet water temperatures of the heat exchanger tubes are t ave t0 is the average water temperature at the inlet and outlet of the heat exchange tubes, and t0 is the initial temperature of the backfill. The heat transfer per unit well depth and the energy efficiency coefficient were calculated to evaluate the performance of the buried pipe heat exchange system in the biomineralized cemented backfill.

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