A cleaning system for shale gas fracturing flowback fluid MVR evaporation treatment equipment

Abstract

This invention relates to a cleaning system for a shale gas fracturing flowback fluid MVR evaporation treatment equipment, used to remove scale buildup on the inner wall of the cavity through which the raw fracturing flowback fluid flows in the equipment to be cleaned. The system includes: a carbon dioxide generating unit for supplying carbon dioxide; and a dissolved air unit for compressing the carbon dioxide supplied by the carbon dioxide generating unit into water to form dissolved carbon dioxide water. The dissolved air unit has a cleaning input end, which is connected to one port of the cavity through which the raw shale gas fracturing flowback fluid flows in the equipment to be cleaned, so as to introduce the dissolved carbon dioxide water into the cavity. The cleaning system for the shale gas fracturing flowback fluid MVR evaporation treatment equipment of this invention can effectively remove scale buildup formed on the inner wall of the cavity through which the raw shale gas fracturing flowback fluid flows, achieving good cleaning effect, short cleaning time, low cost, and no environmental pollution.

Description

Technical Field

[0001] This invention relates to the technical field of cleaning equipment for shale gas fracturing flowback fluid treatment, and in particular to a cleaning system for shale gas fracturing flowback fluid MVR evaporation treatment equipment. Background Technology

[0002] Thermal methods are currently one of the more effective methods for treating shale gas fracturing flowback fluid. Thermal methods typically employ a plate-type forced circulation MVR evaporation process to separate some of the water from the shale gas fracturing flowback fluid to obtain a concentrate. This concentrate causes the dissolved organic matter and inorganic salts in the shale gas fracturing flowback fluid to become supersaturated and separate. The resulting mixture of organic matter, crystalline salt solids, and product water is then sent to a solid-liquid separation device for preliminary separation. The resulting concentrate is then returned to the evaporation system for further desalination treatment.

[0003] Plate-type forced circulation MVR evaporators feature low adhesion, wide flow channels, and a forced turbulence design. They boast low energy consumption, efficient online cleaning, and quick disassembly for cleaning, making maintenance more convenient and solving problems such as scaling and cleaning of equipment pipelines. The plate-type forced circulation MVR evaporator includes a preheater, a main heat exchanger, and a gas-liquid separator. Its working principle is as follows: After initial treatment, raw wastewater enters the raw water side pipe of the preheater, where it exchanges heat with the high-temperature gas on the inner wall of its gas side pipe, initially raising the water temperature. It then enters the raw water side pipe of the main heat exchanger, where it exchanges heat again with the steam on the inner wall of its gas side pipe, further increasing the water temperature. Finally, it enters the gas-liquid separator for evaporation and concentration.

[0004] However, when using thermal methods to evaporate and concentrate raw water from shale gas fracturing flowback fluid, scale gradually accumulates on the inner walls of the raw water side pipes of the preheater, the main heat exchanger, and the pipes through which the raw water flows, as the evaporation equipment operates for extended periods. This continuous accumulation of scale causes severe blockage in the raw water side pipes, significantly reducing the heat exchange efficiency of the equipment and affecting its normal operation. There are two main existing descaling methods: one is physical flushing, which requires stopping and disassembling the equipment first, and then introducing high-pressure water into the cavity through which the raw water flows. The flushing force of the water flow washes off the scale adhering to the inner wall of the cavity and carries it out with the water flow. However, this method is time-consuming, has poor cleaning effect, and consumes a lot of water. The other method is chemical cleaning, which involves introducing chemical agents into the pipes to dissolve the scale and achieve the purpose of descaling. This method does not require disassembling the equipment, but it introduces new chemical substances. It requires the use of acidic and alkaline cleaning agents to clean the scale. After cleaning, the cleaning waste liquid needs to be treated separately. If not treated properly, it can easily cause environmental pollution. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to overcome the defects or deficiencies of the prior art and provide a cleaning system for a shale gas fracturing flowback fluid MVR evaporation treatment equipment, which can effectively remove scale from the inner wall of the cavity through which the raw water of the shale gas fracturing flowback fluid flows in the plate-type forced circulation MVR treatment equipment.

[0006] A cleaning system for a shale gas fracturing flowback fluid MVR evaporation treatment equipment is disclosed for removing scale buildup on the inner wall of the cavity through which the raw shale gas fracturing flowback fluid flows in the equipment to be cleaned. The system includes: a carbon dioxide generating unit for supplying carbon dioxide; and a dissolved air unit for compressing the carbon dioxide supplied by the carbon dioxide generating unit into water to form dissolved carbon dioxide water. The dissolved air unit has a cleaning input end, which is connected to one port of the cavity through which the raw shale gas fracturing flowback fluid flows in the equipment to be cleaned, so as to introduce the dissolved carbon dioxide water into the cavity.

[0007] Compared to existing technologies, the pressure backflow liquid treatment cleaning system of this invention is based on the fact that the scale adhering to the inner wall of the cavity through which the raw water flows in the treatment equipment is mainly composed of calcium carbonate, magnesium carbonate, and organic adhesive scale. The dissolved carbon dioxide unit dissolves carbon dioxide in water to form carbon dioxide dissolved water containing carbonic acid, which is used as a cleaning fluid to dissolve the scale on the inner wall of the cavity, effectively removing the scale. At the same time, carbon dioxide bubbles released during the decompression of the carbon dioxide dissolved water and cleaning particles sprayed by the cleaning particle dosing unit are used to flush the scale, greatly improving the cleaning effect.

[0008] In one embodiment, the cleaning system of the shale gas fracturing flowback fluid MVR evaporation treatment equipment further includes a cleaning particle dosing unit, which is connected to the cleaning input end and is used to introduce cleaning particles into the cavity through the cleaning input end.

[0009] In one embodiment, the cleaning particles are made of ceramic.

[0010] In one embodiment, the cleaning particles have a hollow structure.

[0011] In one embodiment, the cleaning system of the shale gas fracturing flowback fluid MVR evaporation treatment equipment further includes a collection unit, which has a cleaning output end for connecting to another port of the cavity to collect the cleaning product water.

[0012] In one embodiment, the collection unit includes a coagulation tank and a sedimentation tank connected in sequence; the inlet of the coagulation tank is connected to the cleaning output end; the sedimentation tank is used to settle the solids contained in the cleaning product water to form precipitated product water and precipitate containing the cleaning particles.

[0013] In one embodiment, the outlet of the sedimentation tank is connected to the dissolved air unit to introduce the precipitated water into the dissolved air unit.

[0014] In one embodiment, the collection unit further includes a flocculation tank located between the coagulation tank and the sedimentation tank, and connected to both the coagulation tank and the sedimentation tank respectively; the flocculation tank is used to add flocculant to the cleaning water in the flocculation tank.

[0015] In one embodiment, the collection unit further includes a gas collection hood disposed above the coagulation tank; the gas collection hood has an air intake facing the coagulation tank for collecting carbon dioxide generated by the coagulation tank, and the air outlet of the gas collection hood is connected to the dissolved gas unit to introduce the collected carbon dioxide into the dissolved gas unit.

[0016] In one embodiment, the collection unit further includes at least one filter communicating with the sedimentation tank and a separator communicating with the filter; the filter is used to filter the sediment to obtain a filter containing the cleaning particles; the separator is communicating with the cleaning particle dosing unit and is used to clean and separate the filter to obtain the cleaning particles, and to replenish the obtained cleaning particles to the cleaning particle dosing unit.

[0017] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0018] Figure 1 This is a schematic structural diagram of the cleaning system of the MVR evaporation treatment equipment for shale gas fracturing flowback fluid of the present invention;

[0019] Figure label:

[0020] 1. Equipment to be cleaned;

[0021] 10. Carbon dioxide generating unit; 100. Partition; 101. Dry ice storage chamber; 102. Carbon dioxide storage chamber;

[0022] 20. Dissolved gas unit; 200. Cleaning input terminal;

[0023] 30. Cleaning granule dosing unit;

[0024] 40. Collection unit; 400. Cleaning output end; 401. Coagulation tank; 402. Flocculation tank; 403. Sedimentation tank; 404. First filter; 405. Second filter; 406. Separator; 407. Gas collection hood. Detailed Implementation

[0025] Existing plate-type forced circulation MVR evaporation equipment used for shale gas fracturing flowback fluid treatment includes preheaters, main heat exchangers, and gas-liquid separators. As the equipment operates for extended periods, scale gradually accumulates in the pipes of the preheaters, main heat exchangers, and gas-liquid separators through which the raw shale gas fracturing flowback fluid flows. Current descaling methods primarily involve physical flushing and chemical cleaning, but both methods are not ideal in terms of cleaning effectiveness and incur high time and subsequent treatment costs.

[0026] To effectively remove scale, the inventors of this invention conducted a compositional analysis on the scale deposits adhering to the inner walls of the cavities (including the inner cavities of heat exchangers and other equipment, as well as the pipes connecting the various equipment) through which the raw water flows in the shale gas fracturing flowback fluid treatment equipment. The analysis revealed that the scale deposits adhering to the inner walls of the cavities mainly consist of hardness scale and organic viscous scale. The hardness scale is specifically composed of calcium carbonate and magnesium carbonate. This is because shale gas fracturing flowback fluid has high hardness, and its raw water contains a large amount of calcium and magnesium ions, as well as carbonate and bicarbonate ions. Carbonate ions combine with calcium and magnesium ions to form insoluble calcium carbonate and magnesium carbonate, while bicarbonate ions, when heated, will produce carbonate ions. The resulting calcium carbonate and magnesium carbonate adhere to the inner walls of the cavities as they flow through, gradually accumulating and eventually forming hardness scale. The organic viscous scale is formed due to the gradual enrichment of some drag-reducing components in the shale gas fracturing flowback fluid (such as high-molecular-weight guar gum, polyvinyl alcohol, and polyacrylamide) during the treatment process.

[0027] Based on this, in order to remove hard scale such as calcium carbonate and magnesium carbonate, as well as organic sticky scale, from the inner wall of the cavity through which the raw water from shale gas fracturing flowback flows, this invention introduces carbon dioxide dissolved water into the equipment to be cleaned. The carbonic acid in the carbon dioxide dissolved water can react with calcium carbonate and magnesium carbonate to generate water-soluble calcium bicarbonate, magnesium bicarbonate, and carbon dioxide, achieving the purpose of descaling while ensuring that no pollutants are generated after dissolving calcium carbonate and magnesium carbonate. At the same time, after the carbon dioxide dissolved water is released under reduced pressure, a large number of dense bubbles will thoroughly flush, break up, and peel off the organic sticky scale. Furthermore, ceramic particles are introduced during the cleaning process to flush away the organic sticky scale and residual hard scale, thereby further improving the cleaning effect.

[0028] The present invention will now be described in detail with reference to the accompanying drawings.

[0029] Figure 1 The specific structure of a cleaning system for an exemplary shale gas fracturing flowback fluid MVR evaporation treatment device of the present invention is shown. For example... Figure 1 As shown, the cleaning system of the shale gas fracturing flowback fluid MVR evaporation treatment equipment of one embodiment of the present invention includes a carbon dioxide generating unit 10 and a dissolved gas unit 20 connected to the carbon dioxide generating unit 10.

[0030] Specifically, the carbon dioxide generating unit 10 is a carbon dioxide storage tank. A partition 100 divides the storage tank into upper and lower chambers, forming a dry ice storage chamber 101 and an upper carbon dioxide storage chamber 102. The partition 100 has through holes for carbon dioxide to overflow. Dry ice is placed in the dry ice storage chamber 101, where it vaporizes at room temperature to form carbon dioxide. The carbon dioxide passes through the partition 100 and enters the carbon dioxide storage chamber 102. An outlet is located at the top of the carbon dioxide storage tank, connecting to the dissolved gas unit 20. Thus, carbon dioxide from the carbon dioxide storage chamber 102 can be introduced into the dissolved gas unit 20. A valve is installed on the pipeline between the carbon dioxide storage chamber 102 and the dissolved gas unit 20, controlling the amount of carbon dioxide introduced by opening and closing the valve. Alternatively, the carbon dioxide can be supplied externally, such as by collecting carbon dioxide generated during other wastewater treatment processes and then introducing it into the carbon dioxide storage chamber 102. Here, the source of carbon dioxide can also be external carbon dioxide gas, such as boiler exhaust gas. A Venturi jet is used to absorb the boiler exhaust gas, and the boiler exhaust gas is used as the gas to be dissolved.

[0031] The dissolved carbon dioxide unit 20 is specifically a pressure dissolved carbon dioxide tank. The pressure dissolved carbon dioxide tank is equipped with a compression device (not shown) to pressurize the carbon dioxide introduced into it, causing it to dissolve in the water inside the tank, generating dissolved carbon dioxide water. The bottom of the pressure dissolved carbon dioxide tank has an outlet, which extends through a pipe to form a cleaning input end 200. The cleaning input end 200 is detachably connected to one port of the cavity through which the raw water from the equipment 1 to be cleaned flows, so as to introduce dissolved carbon dioxide water into the cavity through which the raw water from the equipment 1 to be cleaned. This dissolved carbon dioxide water serves as a cleaning fluid to remove scale from the inner wall of the cavity. A regulating valve is installed on the pipeline between the pressure dissolved carbon dioxide tank and the equipment 1 to be cleaned. By controlling the opening and closing of the regulating valve, the amount of dissolved carbon dioxide water introduced into the cavity is controlled.

[0032] The following uses the main heat exchanger of the plate-type forced circulation MVR evaporator as an example to illustrate the working process of the cleaning system of the above-mentioned shale gas fracturing flowback fluid MVR evaporation treatment equipment:

[0033] The main heat exchanger has a raw water side pipeline for the inflow and outflow of raw water from shale gas fracturing flowback fluid. Before use, connect the cleaning input 200 to the inlet of the raw water side pipeline of the equipment to be cleaned 1. During cleaning, open the gas valve to allow the carbon dioxide generated by the carbon dioxide generating unit 10 to flow into the dissolved air unit 20. The compression device (not shown) in the dissolved air unit 20 is activated, compressing the carbon dioxide into the clean water in the pressure dissolved air tank to form carbon dioxide dissolved water. Then, open the regulating valve to allow the carbon dioxide dissolved water to flow into the raw water side pipeline of the equipment to be cleaned 1 through the cleaning input 200. The carbonic acid in the carbon dioxide dissolved water reacts with the calcium carbonate and magnesium carbonate in the scale to produce magnesium bicarbonate and calcium bicarbonate, respectively. Unreacted carbon dioxide is released with the bubbles. Since magnesium bicarbonate and calcium bicarbonate are soluble in water, they can be discharged with the cleaning fluid to form cleaning permeate. Thus, by introducing cleaning fluid into the cavity through which the raw water flows in the equipment 1 to be cleaned, the fluid reacts with the calcium carbonate and magnesium carbonate on the inner wall of the cavity to generate water-soluble calcium bicarbonate and magnesium bicarbonate. At the same time, the released carbon dioxide bubbles further flush, break up and peel off the organic sticky scale and residual hard scale, thereby achieving descaling of the pipeline.

[0034] Compared to traditional physical flushing or chemical cleaning methods, the cleaning system of the shale gas fracturing flowback fluid MVR evaporation treatment equipment of this invention is based on the fact that the main components of scale are hard scale and organic sticky scale. Hard scale mainly includes calcium carbonate and magnesium carbonate. Carbon dioxide is dissolved in water to generate milder carbonic acid, which is then introduced into the pipes of the equipment to be cleaned (1) to dissolve the calcium carbonate and magnesium carbonate scale adhering to the inner wall of the cavity. The organic sticky scale consists of drag-reducing components in the shale gas fracturing flowback fluid. Carbon dioxide bubbles released during the decompression process of dissolved carbon dioxide water flush, break up, and peel off the organic sticky scale and residual hard scale, ultimately achieving the purpose of scale removal. In this process, the relatively mild carbonic acid makes the entire reaction process more controllable and the raw material cost is low.

[0035] In practice, the inventors of this invention have also discovered that in some processing steps, the addition of sulfuric acid to adjust the pH value introduces sulfate ions. These sulfate ions combine with calcium ions to form water-insoluble calcium sulfate. Consequently, the hardness scale on the inner wall of the cavity through which the raw water from shale gas fracturing flowback fluid flows contains not only calcium carbonate and magnesium carbonate but also calcium sulfate. To further improve the cleaning effect for this mixed scale, the cleaning system of the aforementioned shale gas fracturing flowback fluid MVR evaporation treatment equipment also includes a cleaning particle dosing unit 30. The cleaning particle dosing unit 30 is connected to the cleaning input terminal 200 to introduce cleaning particles into the pipeline of the equipment 1 to be cleaned through the cleaning input terminal 200. Specifically, the cleaning particles are hollow ceramic particles with a particle size of 150–300 μm. Using solid ceramic particles for cleaning reduces damage to the equipment 1 to be cleaned during the rinsing process, while the hollow structure reduces the weight of the cleaning particles, making them easy to flow out with the cleaning water and preventing accumulation on the inner wall of the cavity. The ceramic particles are specifically made of alumina. Alumina possesses excellent chemical inertness, resisting corrosion from acids, alkalis, and most chemical solvents. This characteristic allows it to remain stable in various chemical environments, resisting reactions or decomposition. Alumina maintains its physical and chemical properties at high temperatures, making it suitable for use under such conditions. Therefore, this invention uses ceramic particles made of alumina as cleaning particles, combined with carbon dioxide dissolved in water to clean pipelines. When carbon dioxide dissolved in water carrying cleaning particles is introduced into the equipment 1 to be cleaned, not only does the carbonic acid it contains dissolve calcium carbonate and magnesium carbonate scale, but the carbon dioxide dissolved in water also releases high-density micro-nano carbon dioxide bubbles. These bubbles, combined with the cleaning particles, vigorously flush, break down, and peel off calcium sulfate scale and organic adhesive scale from the inner wall of the cavity. The peeled-off scale is then discharged with the cleaning water. Thus, by simultaneously introducing carbon dioxide dissolved in water to dissolve scale into the equipment 1 and spraying solid particles into the pipeline to flush away the scale, the cleaning effect is greatly improved.

[0036] Furthermore, the cleaning system of the above-mentioned shale gas fracturing flowback fluid MVR evaporation treatment equipment also includes a collection unit 40, which has a cleaning output end 400. The collection unit 40 is connected to the outlet of the raw water side pipeline of the equipment 1 to be cleaned through the cleaning output end 400 to collect the cleaning water formed after cleaning.

[0037] The cleaning permeate contains calcium bicarbonate, magnesium bicarbonate, cleaning particles, and some scale that has been sloughed off by the cleaning particles. To remove solid scale from the cleaning permeate for further recycling, the collection unit 40 of the cleaning system of the aforementioned shale gas fracturing flowback fluid MVR evaporation treatment equipment includes a coagulation tank 401, a flocculation tank 402, and a sedimentation tank connected in sequence.

[0038] When the cleaning water containing cleaning particles flows into the coagulation tank 401, the porous structure of alumina gives it excellent adsorption capacity. Therefore, some of the cleaning particles act as settling nuclei in the coagulation tank 401, binding together small particles in the water to form larger flocs through adsorption. These flocs then enter the flocculation tank 402. The flocculation tank 402 has a flocculant dosing device (not shown) for adding flocculant to the cleaning water. The flocculant is specifically PAM (polyacrylamide), which enlarges solid particles in the water, facilitating their settling. The cleaning water after coagulation flows into the sedimentation tank 403, where sedimentation produces precipitated water and sediment. The precipitated water can be returned to the dissolved air unit 20 for reuse in generating dissolved carbon dioxide water, achieving water recycling for cleaning. The sediment is further treated to recover the cleaning particles.

[0039] Furthermore, to ensure coagulation effectiveness, a coagulant dosing device (not shown) can be installed in coagulation tank 401 to add coagulant to the cleaning product water. PAC (polyaluminum chloride) can be used as the coagulant. PAC can form a network structure in the water, working in conjunction with the cleaning particles to better bind small solid particles together. These particles are then precipitated during subsequent flocculation treatment, accelerating the settling process and better removing solids from the water.

[0040] Preferably, the coagulation tank 401 and the flocculation tank 402 are respectively provided with the following: Figure 1 The agitator shown ensures that the added coagulant and flocculant come into full contact with the cleaning product water through agitation.

[0041] To separate the washing particles from the sediment, the collection unit 40 further includes a first filter 404, a second filter 405, and a separator 406, which are sequentially disposed downstream of the sedimentation tank 403 and connected in series.

[0042] Specifically, the first filter 404 has a filter screen or membrane with a pore size of 250 μm, and the second filter 405 has a filter screen or membrane with a pore size of 150 μm. The sediment in the sedimentation tank 403 passes sequentially through the first filter 404 and the second filter 405 to obtain filtered material. This filtered material is then passed into the separator 406, where it is washed (e.g., ultrasonically cleaned) and centrifuged to separate clean cleaning particles. These cleaning particles can be added to the cleaning particle feeding unit 30 and reused for cleaning the equipment 1 to be cleaned. In this way, most of the scale and impurities are isolated by two-stage filters to separate the cleaning particles. The separator 406 then removes the scale and impurities from the particles' surface, resulting in cleaning particles that can be reused in the cleaning process, thus achieving the recycling of cleaning particles. Of course, the collection unit 40 can also be equipped with only one filter to filter the sediment. Single-stage filtration is prone to clogging, so two or more stages can better separate the cleaning particles while avoiding filter clogging.

[0043] Furthermore, carbonic acid that did not react with calcium carbonate and magnesium carbonate during the cleaning process will re-release carbon dioxide in the coagulation tank 401 (especially under the action of the agitator), and free carbon dioxide dissolved in the water due to pressure will also be released in the coagulation tank 401. To recover the carbon dioxide generated after cleaning, the collection unit 40 also includes a gas collection hood 407 disposed above the coagulation tank 401. The gas collection hood 407 has an intake port and an outlet port; its intake port is aligned with the coagulation tank 401, and its outlet port is connected to the dissolved air unit 20. Preferably, the orthographic projection of the intake port of the gas collection hood 407 onto the plane containing the opening of the coagulation tank 401 completely covers the opening of the coagulation tank 401, ensuring that all carbon dioxide generated in the coagulation tank 401 can be collected by the gas collection hood 407. The carbon dioxide generated in the coagulation tank 401 is collected through adsorption and introduced into the dissolved air unit 20 to achieve the recycling of carbon dioxide.

[0044] To ensure that all carbon dioxide generated in the collection unit 40 can be collected, the collection unit 40 is set up in a sealed space, and the air intake of the gas collection hood 407 can extend to the top of the flocculation tank 402 and the sedimentation tank 403, and completely cover the flocculation tank 402 and the sedimentation tank 403, so as to adsorb the carbon dioxide overflowing from the flocculation tank 402 and the sedimentation tank 403, and then re-introduce it into the dissolved air unit 20 to generate carbon dioxide dissolved air water.

[0045] Cleaning effect

[0046] When treating shale gas fracturing flowback fluid using thermal methods, plate-type forced circulation MVR evaporation equipment is often employed. Plate-type forced circulation MVR evaporation equipment typically includes a preheater and a main heat exchanger. The structure and working principle of the preheater and main heat exchanger have been explained previously and will not be repeated here. In practical applications, both the preheater and the main heat exchanger are set with minimum feed flow rates. As the equipment operates for longer periods, scale accumulates on the inner walls of the raw water side pipes in the preheater and main heat exchanger, gradually clogging the pipes and causing a decrease in the feed flow rate. When the feed flow rate of the preheater and main heat exchanger drops to the minimum feed flow rate, production will be affected, thus requiring cleaning of the raw water side pipes.

[0047] The following describes the technical effects of the cleaning system of the wastewater treatment equipment of the present invention by using different cleaning methods to clean the preheater and the main heat exchanger:

[0048] 1. The equipment to be cleaned is the preheater of a plate-type forced circulation MVR evaporator.

[0049] Three identical preheaters were used to treat shale gas fracturing flowback fluid from the same source under identical conditions. After approximately 140 days of operation, scale accumulated on the inner walls of the raw water side pipes of the preheaters. This scale included calcium carbonate, magnesium carbonate, and organic adhesive scale. The three preheaters were cleaned using three methods: physical flushing after disassembly, cleaning with 5% citric acid, and cleaning using the wastewater treatment system of this invention. The cleaning results are shown in Table 1.

[0050] Table 1

[0051]

[0052]

[0053] Note: Since the degree of scale removal from heat exchange equipment is difficult to quantify, the degree of recovery of the feed rate of the heat exchange equipment after cleaning is used to measure the cleaning effect: the higher the degree of feed rate recovery, the better the cleaning effect.

[0054] As shown in Table 1, when the preheater is cleaned using the cleaning system of the wastewater treatment equipment of the present invention, the feed rate of the preheater is completely restored after cleaning. The cleaning effect is good and the time is short. No chemicals need to be added during the cleaning process, so there is no residue after cleaning. Moreover, during cleaning, it is only necessary to connect the cleaning input end 200 and the cleaning output end 400 to the inlet and outlet of the raw water side pipe of the preheater to be cleaned, respectively, to achieve online cleaning.

[0055] The preheater was cleaned with 5% citric acid. However, the feed rate of the preheater could not be fully restored after cleaning, indicating that the organic sticky scale on the inner wall of the pipe was not completely removed. In addition, the cleaning time was long and the residual agent after cleaning was difficult to treat and the treatment cost was high.

[0056] Disassembling the preheater and cleaning it using a purely physical method with a high-pressure water gun results in incomplete cleaning due to the high hardness and dense accumulation of scale. This leads to minimal recovery of feed volume, poor cleaning effect, high water consumption, and a long total time required for disassembly, cleaning, and installation.

[0057] 2. The equipment to be cleaned is the main heat exchanger of a plate-type forced circulation MVR evaporator.

[0058] Two identical main heat exchangers were used under identical conditions to treat the same shale gas fracturing flowback fluid. The main heat exchangers were designed to produce 10 t / h of water. After approximately 140 days of operation, scale accumulated on the inner walls of the raw water side pipes of the main heat exchangers. This scale mainly consisted of calcium carbonate and calcium sulfate, as well as organic sticky scale. Calcium carbonate accounted for 66.5%, calcium sulfate for 20%, and the remainder was organic sticky scale. The two main heat exchangers were cleaned using two methods: introducing 5% citric acid and using the cleaning system of the wastewater treatment equipment of this invention. The two cleaning methods and the data before cleaning are shown in Table 2.

[0059] Table 2

[0060]

[0061]

[0062] Note: Besides the degree of feed rate recovery, temperature difference, inlet pressure, outlet pressure, inlet-outlet pressure differential, and water production achievement rate (water production achievement rate = actual total water production / designed water production * 100%) are also key indicators for measuring heat exchanger efficiency. In actual production, heat exchanger scaling manifests as a decrease in heat exchange temperature difference, an increase in inlet-outlet pressure differential, and a decrease in equipment output. Here, temperature difference, inlet pressure, outlet pressure, inlet-outlet pressure differential, and water production achievement rate are used to compare the cleaning effects of different cleaning methods.

[0063] As shown in Table 2, when using the cleaning system of this invention, the feed rate of the main heat exchanger is restored to nearly 100%, and parameters such as the temperature difference, inlet pressure, outlet pressure, inlet-outlet pressure difference, and evaporation output of the main heat exchanger are all restored to normal levels, indicating an excellent cleaning effect. The reason for such a cleaning effect is that the cleaning system of this invention introduces carbon dioxide to form carbon dioxide dissolved water containing carbonic acid. The carbonic acid gradually dissolves calcium carbonate and magnesium carbonate, making the scale loose and easy to peel off. Combined with the carbon dioxide bubbles released during the decompression process of the carbon dioxide dissolved water and the scouring of organic sticky scale and residual hard scale by ceramic cleaning particles, the scale can be effectively removed completely. In contrast, when cleaning with 5% citric acid, the feed rate is only restored to 89%, and the parameters such as the temperature difference, inlet pressure, outlet pressure, inlet-outlet pressure difference, and evaporation output of the main heat exchanger are all worse than those cleaned with the cleaning system of this invention.

[0064] Compared to existing technologies, the cleaning system of the pressure backflow liquid treatment equipment described in this invention is based on the fact that the scale adhering to the inner wall of the cavity through which the raw water flows in the treatment equipment mainly consists of calcium carbonate, magnesium carbonate, and organic adhesive scale. A dissolved carbon dioxide unit dissolves carbon dioxide in water to form carbon dioxide dissolved water, which is then used as the cleaning fluid to dissolve the scale on the inner wall of the cavity, effectively removing the scale. Simultaneously, carbon dioxide bubbles released during the decompression process of the dissolved carbon dioxide dissolved water, along with cleaning particles sprayed by the cleaning particle dosing unit, further enhance the cleaning effect, shorten the cleaning time, and reduce costs. Furthermore, a collection unit separates the cleaning particles, carbon dioxide, and water in the resulting cleaning product water and reuses them in the cleaning process, achieving a three-phase cycle of liquid, gas, and solid particles. This is economical and does not pollute the environment.

[0065] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this invention. The singular forms “a,” “the,” and “the” used in the embodiments and claims of this invention are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that, unless otherwise stated, “a plurality” means two or more; the terms “first,” “second,” “third,” etc., are used only to distinguish and not to describe a particular order or sequence, nor should they be construed as indicating or implying relative importance. The term “and / or” as used herein refers to and includes any or all possible combinations of one or more associated listed items. When the above description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. In the description of this invention, those skilled in the art will understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0066] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A cleaning system for a shale gas fracturing flowback fluid MVR evaporation treatment device, used to remove scale from the inner wall of the cavity through which the raw water of the shale gas fracturing flowback fluid flows in the device to be cleaned (1), characterized in that: include: Carbon dioxide generating unit (10) is used to supply carbon dioxide; The dissolved gas unit (20) is used to pressurize the carbon dioxide supplied by the carbon dioxide generating unit (10) and compress the carbon dioxide into water to form dissolved carbon dioxide water; the dissolved gas unit (20) has a cleaning input end (200), which is used to connect to one port of the cavity through which the raw water of the shale gas fracturing flowback fluid in the equipment to be cleaned (1) flows, so as to introduce the dissolved carbon dioxide water into the cavity; A cleaning particle dosing unit (30) is connected to the cleaning input end (200) and is used to introduce cleaning particles into the cavity through the cleaning input end (200). The cleaning particles are hollow ceramic materials with a particle size of 150~300μm. A collection unit (40) has a cleaning output end (400) for connecting to another port of the cavity to collect cleaning water; The collection unit (40) includes a coagulation tank (401) and a sedimentation tank (403) connected in sequence, a gas collection hood (407) disposed above the coagulation tank (401), and a first filter and a second filter connected in sequence to the sedimentation tank, and a separator connected to the second filter. The inlet of the coagulation tank (401) is connected to the cleaning output end (400); The sedimentation tank (403) is used to settle the solids contained in the cleaning water, forming precipitated water and precipitate containing the cleaning particles. The outlet of the sedimentation tank (403) is connected to the dissolved air unit (20) to introduce the precipitated water into the dissolved air unit (20). The gas collection hood (407) has an air intake facing the coagulation tank (401) for collecting carbon dioxide generated by the coagulation tank (401), and the gas outlet of the gas collection hood (407) is connected to the dissolved gas unit (20) to introduce the collected carbon dioxide into the dissolved gas unit (20). The filter is used to filter the precipitate to obtain a filter containing the cleaning particles; The separator (406) is connected to the cleaning particle dosing unit (30) and is used to clean the filter material and separate the solid and liquid to obtain the cleaning particles, and to replenish the cleaning particles to the cleaning particle dosing unit (30).

2. The cleaning system of the shale gas fracturing flowback fluid MVR evaporation treatment equipment according to claim 1, characterized in that: The collection unit (40) further includes a flocculation tank (402), which is located between the coagulation tank (401) and the sedimentation tank (403) and is connected to the coagulation tank (401) and the sedimentation tank (403) respectively. The flocculation tank (402) is used to add flocculant to the cleaning water in the flocculation tank (402).

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