Ultrahigh-pressure water bath type liquid nitrogen evaporator

Abstract

The invention relates to an ultrahigh pressure water bath type liquid nitrogen evaporator, and relates to the field of oil field equipment, the ultrahigh pressure water bath type liquid nitrogen evaporator comprises a shell, an end cover and a coil pipe, a heat exchange medium circulates in the shell, the shell is integrally placed in a phase change material to wrap the periphery, and the end cover is fixedly connected to the top of the shell to close the top of the shell; the coil pipes are a plurality of mosquito-repellent incense-shaped multi-layer tube pipes which are manufactured through a cold drawing process and are stacked up and down, and the coil pipes are arranged on one side in the shell; the inlet ends of the multiple coil pipes are fixedly connected with a liquid nitrogen inlet pipe, the length direction of the liquid nitrogen inlet pipe is vertical, the top of the liquid nitrogen inlet pipe extends out of the middle of the end cover, the outlet ends of the multiple coil pipes are fixedly connected with a nitrogen outlet pipe, the length direction of the nitrogen outlet pipe is vertical, and the top of the nitrogen outlet pipe extends out of one side of the end cover to output nitrogen with the pressure not higher than 140 MPa. The heat exchanger has the advantages of being small in size and high in heat exchange efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield equipment, and particularly to an ultra-high pressure water bath type liquid nitrogen evaporator. Background Art

[0002] In operations such as oilfield fracturing and gas lift oil production, it is necessary to evaporate liquid nitrogen into ultra-high pressure nitrogen gas, which is used to drive downhole tools, maintain formation pressure, or serve as a carrier for sand-carrying fluid. Currently, a water bath type evaporator is generally used for liquid nitrogen evaporation. Its principle is to use hot water as a heat medium to evaporate liquid nitrogen through coil heat exchange. This type of equipment can directly utilize the waste heat of the engine or the waste heat of boiler water to heat the liquid nitrogen to evaporate it, which can significantly reduce the energy consumption of electric heating and reduce carbon emissions, and has extremely high environmental protection. Among them, in ultra-high pressure fracturing operations, a relatively common liquid nitrogen evaporator uses TP304L stainless steel base tubes and 316L fins for high-frequency welding, and its design pressure can only reach a maximum of 15000 psi, approximately 103.4 MPa, with a relatively low upper limit. In addition, the waste heat is extremely unstable, and the waste heat of the engine will carry solid impurities and adhere to the coils. Due to the high mineral content of boiler water, scale will also accumulate on the coils, resulting in a significant reduction in heat exchange efficiency and unstable nitrogen pressure output.

[0003] Therefore, in view of the above deficiencies, it is necessary to provide an ultra-high pressure water bath type liquid nitrogen evaporator. Summary of the Invention

[0004] (I) Technical Problems to be Solved The technical problem to be solved by the present invention is to solve the problems of low pressure resistance strength and low thermal efficiency utilization rate of the traditional water bath type evaporator.

[0005] (II) Technical Solutions To solve the above technical problems, the present invention provides an ultra-high pressure water bath type liquid nitrogen evaporator, which includes a housing, an end cover, and coils. A heat exchange medium flows inside the housing, and the entire housing is placed inside a phase change material to wrap around the periphery. The end cover is fixedly connected to the top of the housing to seal the top of the housing. The coils are several mosquito coil-shaped multi-layer tubes stacked up and down made by a cold drawing process, with a length of not less than 2 m and a composition content of: C≤0.02, Mn≤1, Si≤0.5, P≤0.045, S≤0.03, 10.00≤Ni≤14.00, 16.00≤Cr≤17.00, 2.00≤Mo≤3.00. The coils are placed on one side inside the housing. The inlet ends of several coils are fixedly connected to a liquid nitrogen inlet pipe, the length direction of the liquid nitrogen inlet pipe is vertical, and the top extends outside the middle of the end cover. The outlet ends of several coils are fixedly connected to a nitrogen outlet pipe, the length direction of the nitrogen outlet pipe is vertical, and the top extends outside one side of the end cover to output nitrogen gas with a pressure not higher than 140 MPa.

[0006] As a further illustration of the present invention, preferably, a heat exchange medium inlet pipe is fixedly connected to one side of the middle part of the end cover and located on the side of the liquid nitrogen inlet pipe. The heat exchange medium inlet pipe is communicated with the middle space surrounded by the coil pipes; on one side of the end cover close to the nitrogen outlet pipe, a heat exchange medium outlet pipe is fixedly connected, and the heat exchange medium outlet pipe is communicated with the outer space surrounded by the coil pipes; the liquid nitrogen inlet pipe and the nitrogen outlet pipe adopt an Autoclave ultra-high pressure sealing design with a 60° conical surface seal so that the maximum pressure resistance is 700 MPa.

[0007] As a further illustration of the present invention, preferably, the heat exchange medium is engine cylinder jacket water or engine waste smoke, and the temperature is not lower than 80 °C; the length of the coil pipe is 6 m and the wall thickness is 2 mm.

[0008] As a further illustration of the present invention, preferably, a bottom plate is inserted into the bottom of the inner cavity of the housing. The bottom plate is in contact with the bottom of the coil pipe. An arc-shaped channel opening is formed on the bottom plate. One end of the channel opening is communicated with the middle space surrounded by the coil pipes, and the other end of the channel opening is communicated with the outer space surrounded by the coil pipes so that the heat exchange medium flows out from the bottom of the coil pipe to the area surrounded by the coil pipes.

[0009] As a further illustration of the present invention, preferably, an elastic pad is provided at the contact end between the top of the bottom plate and the coil pipe so that the contact surface between the bottom plate and the coil pipe is closed.

[0010] As a further illustration of the present invention, preferably, lifting lugs with holes are fixedly connected to both sides of the top of the end cover for hoisting.

[0011] As a further illustration of the present invention, preferably, the phase change material adopts paraffin-based composite PCM to make up for the heat when the heat of the heat exchange medium is insufficient.

[0012] As a further illustration of the present invention, preferably, the outer wall surface of the coil pipe, the inner end surfaces of the housing and the end cover are all coated with an isolation coating, and the isolation coating is a molybdenum disulfide coating; the melted phase change material is pumped into the housing through the heat exchange medium inlet pipe. A pulse vibration device is provided at the bottom of the bottom plate to generate vibration. After the phase change material is solidified, the housing is taken out to complete the cleaning.

[0013] As a further illustration of the present invention, preferably, there is no gap between the upper and lower spiral pipes of the coil pipe.

[0014] As a further illustration of the present invention, preferably, an exhaust port is provided on one side of the end cover to discharge the gas in the housing and stabilize the heat exchange effect of the evaporator.

[0015] (III) Beneficial effects The above technical solutions of the present invention have the following advantages: The present invention designs a multi-layer staggered welded coil of a mosquito coil-shaped screw coil pipe. Without changing the overall heat exchange power, the external dimensions are greatly reduced, realizing the miniaturized design of a high-power liquid nitrogen evaporator. By effectively utilizing the external waste heat for heat exchange in this evaporator, the maximum utilization of waste heat is achieved, turning waste into treasure and maximizing energy conservation and emission reduction. The entire housing is immersed in an environment with a phase change material, and the waste heat generated by other equipment is introduced to provide heat for the liquid nitrogen. Since each layer of the coil is in dense contact, the spiral coil directly forms a spiral fluid channel. The heat medium forms a circulating flow in the coil channel, and the external hot fluid can form an opposite convection with the high-pressure liquid nitrogen inside the coil along this spiral fluid channel, thereby increasing the contact area and time between the hot fluid and the liquid nitrogen. At the same time, the coil wall thickness is relatively thin, greatly improving the heat exchange area and heat exchange power. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is the overall assembly effect diagram of the present invention; Figure 2 is the top view of the present invention; Figure 3 is the coil structure diagram of the present invention; Figure 4 is the vertical cross-sectional view of the present invention; Figure 5 is the horizontal cross-sectional view of the present invention.

[0017] In the figure: 1. Housing; 11. Bottom plate; 12. Channel opening; 13. Elastic pad; 2. End cover; 21. Heat exchange medium inlet pipe; 22. Heat exchange medium outlet pipe; 23. Exhaust port; 3. Coil; 31. Liquid nitrogen inlet pipe; 32. Nitrogen outlet pipe; 4. Lifting lug. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0019] A super-high-pressure water-bath type liquid nitrogen evaporator, in combination with Figure 1 、 Figure 4 , includes a housing 1, an end cover 2, and a coil 3. The coil 3 is placed on one side inside the housing 1, and the end cover 2 is fixedly connected to the top of the housing 1 through a bolt pair and a sealing ring to seal the top of the housing 1. Liquid nitrogen is introduced into the coil 3, and a heat exchange medium is introduced into the housing 1 to exchange heat with the liquid nitrogen to evaporate it into super-high-pressure nitrogen. The heat exchange medium is preferably engine cylinder jacket water or engine waste smoke, and the temperature is not lower than 80 °C to ensure the environmental protection of the evaporator.

[0020] Combined with Figure 3 、 Figure 5 The coil pipe 3 is composed of 24 multi-layered tube pipes that are closely stacked in an up-and-down manner and are made by the cold drawing process. The length is not less than 2m, preferably 6m, and the wall thickness is 2mm. The component content of the coil pipe 3 is: C≤0.02, Mn≤1, Si≤0.5, P≤0.045, S≤0.03, 10.00≤Ni≤14.00, 16.00≤Cr≤17.00, 2.00≤Mo≤3.00; preferably in this application, C = 0.017, Mn = 0.67, Si = 0.33, P = 0.032, S = 0.002, Ni = 10.1, Cr = 16.63, Mo = 20.4. Each single tube pipe of the coil pipe 3 is bent into a mosquito coil-shaped structure. The outer wall surface of the coil pipe 3 is sprayed with an isolation coating, and the isolation coating is preferably a molybdenum disulfide coating. When the evaporator stops working, the low-temperature liquid nitrogen in the coil pipe 3 stops being supplied first, and the heat medium in the housing 1 is still in a high-temperature state. At the same time, the isolation coating on the surfaces of the liquid nitrogen inlet pipe 31 and the nitrogen outlet pipe 32 effectively avoids the probability that impurities in the heat medium adhere to the surfaces of the coil pipe 3, the liquid nitrogen inlet pipe 31, and the nitrogen outlet pipe 32 during thermal expansion and contraction, thereby affecting the service life of the heat exchanger. The maximum heat exchange area of a single tube pipe can reach 0.2m 2 , and the overall heat exchange power of the 24 coil pipes 3 can reach 450KW. The inlet ends of the 24 coil pipes 3 are all gathered into a liquid nitrogen inlet pipe 31 and fixedly connected to the liquid nitrogen inlet pipe 31. The length direction of the liquid nitrogen inlet pipe 31 is vertical and the top protruding end extends outside the middle of the end cover 2. The outlet ends of the 24 coil pipes 3 are all gathered into a nitrogen outlet pipe 32 and fixedly connected to the nitrogen outlet pipe 32. The length direction of the nitrogen outlet pipe 32 is vertical and the top protruding end extends outside one side of the end cover 2. Both the liquid nitrogen inlet pipe 31 and the nitrogen outlet pipe 32 adopt an Autoclave ultra-high pressure sealing design with a 60° conical surface seal, and the maximum pressure resistance can reach 700MPa.

[0021] By designing the coil pipe 3 into a mosquito coil-shaped multi-layered tube pipe that is closely stacked in an up-and-down manner and combined with the cold drawing process, not only effectively increases the arrangement quantity of the tube pipes, but also combines with the 6m length of the tube pipes to greatly increase the heat exchange area and improve the heat exchange efficiency. At the same time, it also increases the yield strength of the pipeline to more than 680MPa, which is 3 - 4 times that of ordinary stainless steel pipes, and the pressure resistance capacity can reach 140MPa. Furthermore, nitrogen with a pressure not higher than 140MPa can be output by the evaporator, and it can be applied to the working environment of oil fields. In addition, since the space decreases after the tube pipes are bent, the outer diameter of the housing 1 can also be reduced, which can reduce the overall volume of the evaporator and facilitate transportation and installation.

[0022] Combined with Figure 3 、 Figure 4, the housing 1 is cylindrical. At the bottom of the inner cavity of the housing 1, a bottom plate 11 is inserted. The bottom plate 11 is disc-shaped and its outer diameter is basically the same as the inner diameter of the housing 1. A pulse vibration device is provided at the bottom of the bottom plate 11 to generate vibration energy for subsequent cleaning work. The bottom plate 11 is in contact with the bottom of the coil 3. An arc-shaped channel opening 12 is formed on the bottom plate 11. One end of the channel opening 12 is connected to the middle space surrounded by the coil 3, and the other end of the channel opening 12 communicates with the outer space surrounded by the coil 3. The top of the coil 3 is in closed contact with the end cover 2. An elastic pad 13 is provided at the contact end between the top of the bottom plate 11 and the coil 3 to seal the contact surface between the bottom plate 11 and the coil 3, so that the heat exchange medium can only flow out from the channel opening 12 at the bottom of the coil 3 to the area outside the coil 3.

[0023] Combined with Figure 2 , Figure 4 , the end cover 2 is of a disc-shaped structure. On both sides of the top of the end cover 2, there are fixedly connected lifting lugs 4 with holes to facilitate the lifting of the end cover 2 or the housing 1 and the end cover 2. In the middle of the end cover 2, on one side of the liquid nitrogen inlet pipe 31, there is fixedly connected a heat exchange medium inlet pipe 21, and the heat exchange medium inlet pipe 21 is connected to the middle space surrounded by the coil 3. On one side of the end cover 2 close to the nitrogen outlet pipe 32, there is fixedly connected a heat exchange medium outlet pipe 22, and the heat exchange medium outlet pipe 22 communicates with the outer space surrounded by the coil 3. Since each layer of the coil 3 is in dense contact, the spiral pitch between the spiral coils 3 forms a circulation channel for the hot fluid. Combined with the channel opening 12, the heat exchange medium forms a circulation in the coil 3 channel. The external heat exchange medium can flow along this spiral fluid channel to form an opposite convection with the high-pressure liquid nitrogen inside the coil 3, thereby increasing the contact area and time between the heat exchange medium and the liquid nitrogen, and greatly improving the heat exchange efficiency.

[0024] The whole housing 1 is placed in the phase change material to wrap around the surroundings. The phase change material is preferably paraffin-based composite PCM. When the phase change material reaches above 80 °C, solid-liquid phase change will occur. At this time, it absorbs the heat in the heat exchange medium as latent heat and melts, while avoiding the sudden increase in the temperature of the heat exchange medium in the housing 1 resulting in a pressure mutation and affecting the safety of the evaporator. An exhaust port 23 is provided on one side of the end cover 2, which can be opened to release gas when the pressure in the housing 1 exceeds the standard to stabilize the pressure in the housing 1. When the heat input of the heat exchange medium is insufficient, the phase change material can release latent heat to compensate for the heat gap, so that the temperature of the heat exchange medium can be stabilized near the phase change temperature, thereby maintaining the liquid nitrogen evaporation rate.

[0025] An isolation coating is applied to the outer wall surface of the coil pipe 3, the inner end surfaces of the housing 1 and the end cover 2. After the liquid nitrogen evaporation for one cycle, the phase change material outside the housing 1 is melted by solar heating, and then the melted phase change material is pumped into the housing 1 through the heat exchange medium inlet pipe 21. The liquid phase change material penetrates into dead corners such as the spiral coil pipe gaps and the welding grooves by virtue of its low viscosity characteristics. The pulse vibration device on the bottom plate 11 is started synchronously, with a frequency of 20 - 50 Hz, to shake off the scale, dust or rust particles attached to the inner wall of the housing 1 and the coil pipe 3. At the same time, the vibration energy causes micro-scale vortices to be generated in the liquid phase change material, wrapping solid impurities such as scale, dust or rust particles.

[0026] Subsequently, the heating source is turned off, and low-temperature coolant is introduced into the coil pipe 3 and outside the housing 1. The phase change material solidifies gradually from the outside to the inside and from the inside to the outside, forming a solid inclusion, and solidifying the impurities in the phase change material lattice. Finally, the bolts on the end cover 2 are removed, and the end cover 2 is lifted by the lifting lug 4. Since the internal structure of the housing 1 is simple, the solid phase change material block can be taken out only by simple cutting and rotation methods. At this time, the impurities are removed together with the phase change material block, achieving "zero-residue cleaning" and effectively extending the service life of the evaporator. Then, the taken-out phase change material block is placed in the filtration box, melted again by solar secondary heating, and flows out from the bottom of the filtration box for secondary use, while the solid impurities remain in the filtration box for easy removal.

[0027] Through the above settings, not only can the evaporation efficiency be stabilized by the phase change material, but it can also be used as an environmentally friendly cleaning medium, thereby reducing the use of chemical cleaning agents and saving about 100,000 yuan in purchase costs annually. More importantly, there is no discharge of chemical agent-containing wastewater to pollute the environment, which conforms to the oilfield "zero-emission" policy and avoids the risk of environmental protection fines.

[0028] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A super high-pressure water bath type liquid nitrogen evaporator, characterized in that: It includes a housing (1), an end cover (2) and a coiled pipe (3). A heat exchange medium flows inside the housing (1), and the entire housing (1) is placed inside a phase change material to wrap around the surroundings. The end cover (2) is fixedly connected to the top of the housing (1) to seal the top of the housing (1); the coiled pipe (3) is composed of several mosquito coil-shaped multi-layer stacked tube pipes made by the cold drawing process, with a length of not less than 2m and the component content being: C≤0.02, Mn≤1, Si≤0.5, P≤0.045, S≤0.03, 10.00≤Ni≤14.00, 16.00≤Cr≤17.00, 2.00≤Mo≤3.00; the coiled pipe (3) is placed on one side inside the housing (1); the inlet ends of several coiled pipes (3) are fixedly connected to a liquid nitrogen inlet pipe (31), the length direction of the liquid nitrogen inlet pipe (31) is vertical and the top extends outside the middle of the end cover (2), the outlet ends of several coiled pipes (3) are fixedly connected to a nitrogen outlet pipe (32), the length direction of the nitrogen outlet pipe (32) is vertical and the top extends outside one side of the end cover (2) to output nitrogen with a pressure not higher than 140MPa.

2. The ultra-high pressure water bath type liquid nitrogen evaporator according to claim 1, characterized in that: On one side of the middle of the end cover (2) where the liquid nitrogen inlet pipe (31) is located, a heat exchange medium inlet pipe (21) is fixedly connected, and the heat exchange medium inlet pipe (21) is communicated with the middle space surrounded by the coiled pipe (3); on one side of the end cover (2) close to the nitrogen outlet pipe (32), a heat exchange medium outlet pipe (22) is fixedly connected, and the heat exchange medium outlet pipe (22) is communicated with the outer space surrounded by the coiled pipe (3); the liquid nitrogen inlet pipe (31) and the nitrogen outlet pipe (32) adopt an Autoclave ultra-high pressure seal design with a 60° conical surface seal to enable a maximum pressure bearing of 700MPa.

3. The super-high pressure water-bath type liquid nitrogen evaporator according to claim 2, wherein: The heat exchange medium is engine cylinder jacket water or engine waste smoke, with a temperature not lower than 80°C; the length of the coiled pipe (3) is 6m and the wall thickness is 2mm.

4. The super-high pressure water-bath type liquid nitrogen evaporator according to claim 3, wherein: A bottom plate (11) is inserted at the bottom of the inner cavity of the housing (1), the bottom plate (11) is in contact with the bottom of the coiled pipe (3), and an arc-shaped channel opening (12) is opened on the bottom plate (11). One end of the channel opening (12) is communicated with the middle space surrounded by the coiled pipe (3), and the other end of the channel opening (12) is communicated with the outer space surrounded by the coiled pipe (3) so that the heat exchange medium flows out from the bottom of the coiled pipe (3) to the area surrounded by the coiled pipe (3).

5. The super-high pressure water-bath type liquid nitrogen evaporator according to claim 4, characterized in that: An elastic pad (13) is provided at the contact end between the top of the bottom plate (11) and the coiled pipe (3) to seal the contact surface between the bottom plate (11) and the coiled pipe (3).

6. The ultra-high pressure water bath type liquid nitrogen evaporator according to claim 1, characterized in that: Lifting lugs (4) with holes are fixedly connected to both sides of the top of the end cover (2) for lifting.

7. The ultra-high pressure water bath type liquid nitrogen evaporator according to claim 1, wherein: The phase change material adopts a paraffin-based composite PCM to supplement heat when the heat of the heat exchange medium is insufficient.

8. The ultra-high pressure water-bath type liquid nitrogen evaporator according to claim 1, wherein: The outer wall surface of the coiled pipe (3), the inner end surfaces of the housing (1) and the end cover (2) are all coated with an isolation coating, and the isolation coating is a molybdenum disulfide coating; the melted phase change material is pumped into the housing (1) through the heat exchange medium inlet pipe (21), and a pulse vibration device is provided at the bottom of the bottom plate (11) to generate vibration. After the phase change material is solidified, the housing (1) is taken out to complete cleaning.

9. The super-high pressure water-bath type liquid nitrogen evaporator according to claim 8, characterized in that: There is no gap between the upper and lower spiral pipes of the coiled pipe (3).

10. The ultra-high pressure water bath type liquid nitrogen evaporator according to claim 1, characterized in that: An exhaust port (23) is opened on one side of the end cover (2) to discharge the gas inside the housing (1) to stabilize the heat exchange effect of the evaporator.

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