Cleaning system of shale gas fracturing flow-back fluid MVR evaporation treatment equipment

Abstract

The invention relates to a cleaning system for shale gas fracturing flow-back fluid MVR (mechanical vapor recompression) evaporation treatment equipment, which is used for removing scales on the inner wall of a cavity through which fracturing flow-back fluid raw water flows in equipment to be cleaned, and comprises a carbon dioxide generation unit for supplying carbon dioxide; the gas dissolving unit is used for compressing the carbon dioxide supplied by the carbon dioxide generating unit into water to form carbon dioxide gas-dissolved water; the gas dissolving unit is provided with a cleaning input end, and the cleaning input end is used for being connected with one port of a cavity, through which the shale gas fracturing flow-back fluid raw water flows, in the to-be-cleaned equipment, so that the carbon dioxide gas dissolving water is introduced into the cavity. According to the cleaning system of the shale gas fracturing flow-back fluid MVR evaporation treatment equipment, scaling substances formed on the inner wall of a cavity through which raw water of shale gas fracturing flow-back fluid flows can be effectively removed, the cleaning effect is good, the cleaning time is short, the cost is low, and pollution to the environment is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of cleaning of shale gas fracturing flowback fluid processing equipment, and in particular to a cleaning system of shale gas fracturing flowback fluid MVR evaporation processing equipment. Background Art

[0002] Thermal method is one of the more effective methods for treating shale gas fracturing flowback fluid. The thermal method usually uses plate-type forced circulation MVR evaporation process to separate part of the water in the shale gas fracturing flowback fluid to obtain concentrated liquid, so that the organic matter and inorganic salts dissolved in the shale gas fracturing flowback fluid reach supersaturation and are separated, and then the obtained organic matter and crystal salt solid and water mixture are sent to the solid-liquid separation equipment for preliminary separation, and the separated concentrated liquid is returned to the evaporation system for further desalination treatment.

[0003] The plate-type forced circulation MVR evaporator has low adhesion, wide flow channel, forced turbulence design, low energy consumption, efficient online cleaning and quick disassembly and cleaning, more convenient maintenance, and solves problems such as equipment pipeline scaling and cleaning. The plate-type forced circulation MVR evaporation equipment includes a preheater, a main heat exchanger and a gas-liquid separator. Its working principle is as follows: after the front-end process treatment, the wastewater raw water will enter the raw water side pipeline of the preheater, and exchange heat with the high-temperature gas on the inner wall of its gas side pipeline, so that the water temperature of the inner wall of the raw water side pipeline is initially increased, and then enter the raw water side pipeline of the main heat exchanger, and exchange heat with the steam on the inner wall of the raw water side pipeline of the main heat exchanger and its gas side pipeline, further increasing the temperature of the water body, and then enter the gas-liquid separator for evaporation and concentration.

[0004] However, when the thermal method is used to evaporate and concentrate the raw water of shale gas fracturing flowback fluid, as the evaporation equipment runs for a long time, scaling will gradually accumulate on the raw water side pipeline of the preheater, the raw water side pipeline of the main heat exchanger, and the inner wall of the pipeline through which the raw water flows. As the scaling continues to accumulate, the raw water side pipeline is seriously blocked, and the heat exchange efficiency of the equipment is greatly reduced, affecting the normal operation of the equipment. There are two main existing descaling methods: one is physical flushing, which requires the equipment to be shut down and disassembled first, and then high-pressure water is passed into the cavity through which the raw water flows, and the scale adhered to the inner wall of the cavity is flushed away by the flushing force of the water flow and carried out with the water flow. However, this removal method is time-consuming, has poor cleaning effect, and consumes a lot of water; the other is chemical cleaning, which specifically involves passing chemicals into the pipeline to dissolve the scale to achieve the purpose of descaling. This method does not require disassembly of the equipment, but will introduce new chemical substances, and requires acidic and alkaline cleaning agents to clean the scale separately. After cleaning, the cleaning waste liquid needs to be additionally treated, and if not properly treated, it is easy to cause environmental pollution. Summary of the invention

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

[0006] A cleaning system for shale gas fracturing flowback fluid MVR evaporation treatment equipment is used to remove scale deposits on the inner wall of a cavity through which the raw water of the shale gas fracturing flowback fluid in the equipment to be cleaned flows, and comprises: a carbon dioxide generating unit for supplying carbon dioxide; a gas dissolving unit for compressing the carbon dioxide supplied by the carbon dioxide generating unit into water to form carbon dioxide dissolved gas water; the gas dissolving unit has a cleaning input end, and the cleaning input end is used to connect to a port of the cavity through which the raw water of the shale gas fracturing flowback fluid in the equipment to be cleaned flows, so as to pass the carbon dioxide dissolved gas water into the cavity.

[0007] Compared with the prior art, the cleaning system for pressure return fluid treatment described in the present invention is based on the fact that the scaling materials attached to the inner wall of the cavity through which the raw water flows in the treatment equipment are mainly composed of calcium carbonate, magnesium carbonate and organic viscous scaling materials. Carbon dioxide is dissolved in water through a dissolved gas unit to form carbon dioxide dissolved gas water containing carbonic acid, and this is used as a cleaning liquid to dissolve the scaling materials on the inner wall of the cavity, thereby effectively removing the scaling materials on the inner wall of the cavity. At the same time, the scaling materials are flushed by the carbon dioxide bubbles released during the decompression of the carbon dioxide dissolved gas water and the cleaning particles sprayed by the cleaning particle dosing unit, thereby 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 adding 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 are hollow structures.

[0011] In one embodiment, the cleaning system of the shale gas fracturing flowback fluid MVR evaporation treatment equipment further includes a collecting unit having a cleaning output end, and the cleaning output end is used to connect to another port of the cavity to collect the cleaning water.

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

[0013] In one embodiment, the water outlet of the sedimentation tank is connected to the gas dissolving unit so as to introduce the sedimentation water into the gas dissolving unit.

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

[0015] In one embodiment, the collection unit also includes a gas collecting hood arranged above the coagulation tank; the gas collecting hood has an air intake port facing the coagulation tank, which is used to collect carbon dioxide generated by the coagulation tank, and the air outlet of the gas collecting hood is connected to the gas dissolving unit to introduce the collected carbon dioxide into the gas dissolving unit.

[0016] In one embodiment, the collection unit also includes at least one filter connected to the sedimentation tank, and a separator connected to the filter; the filter is used to filter the sediment to obtain a filtrate containing the cleaning particles; the separator is connected to the cleaning particle adding unit to clean and separate the solid and liquid of the filtrate to obtain the cleaning particles, and add the obtained cleaning particles to the cleaning particle adding unit.

[0017] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic structural diagram of a cleaning system of a shale gas fracturing flowback fluid MVR evaporation treatment device according to the present invention;

[0019] Reference numerals:

[0020] 1. Equipment to be cleaned;

[0021] 10. Carbon dioxide generation unit; 100. Interlayer; 101. Dry ice storage bin; 102. Carbon dioxide storage bin;

[0022] 20. Dissolving gas unit; 200. Cleaning input end;

[0023] 30. Clean the particle 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 collecting hood. DETAILED DESCRIPTION

[0025] The existing plate-type forced circulation MVR evaporation equipment used for shale gas fracturing return fluid treatment includes preheaters, main heat exchangers, gas-liquid separators and other devices. As the equipment operation time continues to increase, the pipes of the preheater, main heat exchanger and gas-liquid separator through which the shale gas fracturing return fluid flows will gradually accumulate scale. The existing descaling methods are mostly physical flushing and chemical cleaning, but the cleaning effects of these two methods are not ideal, and the time cost and subsequent disposal costs are high.

[0026] In order to effectively remove scale, the inventors of the present invention conducted a composition analysis of the scale attached to the inner wall of the cavity through which the raw water flows in the shale gas fracturing return fluid treatment equipment (including the inner cavity of equipment such as heat exchangers, and pipes connecting various equipment), and found that the components of the scale attached to the inner wall of the cavity are mainly hardness scale and organic viscous scale: the hardness scale is specifically calcium carbonate and magnesium carbonate. This is because the shale gas fracturing return fluid has high hardness, and its raw water contains a large amount of calcium ions and magnesium ions, as well as carbonate and bicarbonate ions. The carbonate ions combine with calcium ions and magnesium ions to form water-insoluble calcium carbonate and magnesium carbonate, and the bicarbonate will produce carbonate when heated. The formed calcium carbonate and magnesium carbonate adhere to the inner wall of the cavity when flowing through the cavity and gradually accumulate, eventually forming hardness scale, and the formation of organic viscous scale is due to the gradual enrichment of some drag reducing components (such as high molecular guar gum, polyvinyl alcohol and polyacrylamide, etc.) in the shale gas fracturing return fluid during the treatment process.

[0027] Based on this, in order to remove hardness scaling materials such as calcium carbonate and magnesium carbonate and organic viscous scaling materials on the inner wall of the cavity through which the raw water of shale gas fracturing flowback fluid flows, the present 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, thereby achieving the purpose of descaling while ensuring that no pollutants are generated after the calcium carbonate and magnesium carbonate are dissolved; at the same time, after the carbon dioxide dissolved water is released under reduced pressure, a large number of dense bubbles will fully flush, break and peel off the organic viscous scaling materials; further, ceramic particles are introduced during the cleaning process to flush the organic viscous scaling materials and residual hardness scaling materials, so as to further improve the cleaning effect.

[0028] The scheme of the present invention is described in detail below with reference to the accompanying drawings.

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

[0030] Specifically, the carbon dioxide generating unit 10 is specifically a carbon dioxide storage tank, and a partition 100 is provided in the carbon dioxide storage tank, which divides the carbon dioxide storage tank into two upper and lower cavities, forming a dry ice storage bin 101 and a carbon dioxide storage bin 102 located above it. The partition 100 has a through hole for carbon dioxide to overflow. Dry ice is placed in the dry ice storage bin 101, and the dry ice gasifies at room temperature to form carbon dioxide, and the carbon dioxide enters the carbon dioxide storage bin 102 after passing through the partition 100. An air outlet is provided on the upper part of the carbon dioxide storage tank, and the air outlet is connected to the gas dissolving unit 20. In this way, the carbon dioxide in the carbon dioxide storage bin 102 can be passed into the gas dissolving unit 20. An air valve is provided on the pipeline between the carbon dioxide storage bin 102 and the gas dissolving unit 20, and the amount of carbon dioxide introduced is controlled by controlling the opening and closing of the air valve. Of course, carbon dioxide can also be supplied from the outside, such as collecting carbon dioxide generated in other sewage treatment processes and then passing it into the carbon dioxide storage bin 102. Here, the source of carbon dioxide can also be exogenous carbon dioxide gas, such as boiler exhaust gas, etc. A venturi ejector is used to absorb the boiler exhaust gas, and the boiler exhaust gas is used as the gas to be dissolved.

[0031] The gas dissolving unit 20 is specifically a pressure gas dissolving tank, which is provided with a compression device (not shown) that can pressurize the carbon dioxide introduced therein so that it dissolves into the water in the tank to generate carbon dioxide dissolved gas water. A water outlet is provided at the bottom of the pressure gas dissolving tank, and the water outlet is extended through a pipeline to form a cleaning input end 200. The cleaning input end 200 is used to be detachably connected to a port of the cavity through which the raw water of the equipment to be cleaned 1 flows, so as to introduce carbon dioxide dissolved gas water into the cavity through which the raw water in the equipment to be cleaned 1 flows, and the carbon dioxide dissolved gas water is used as a cleaning liquid to remove scale on the inner wall of the cavity. A regulating valve is provided on the pipeline between the pressure gas dissolving tank and the equipment to be cleaned 1, and the amount of carbon dioxide dissolved gas water introduced into the cavity is controlled by controlling the opening and closing of the regulating valve.

[0032] The following uses the main heat exchanger of the plate-type forced circulation MVR evaporation equipment as the equipment to be cleaned 1 as an example to illustrate the working process of the cleaning system of the shale gas fracturing return fluid MVR evaporation treatment equipment:

[0033] The main heat exchanger has a raw water side pipeline for the raw water of shale gas fracturing return fluid to flow in and out. Before use, the cleaning input end 200 is first connected to the water inlet of the raw water side pipeline of the equipment to be cleaned 1. During cleaning, the air valve is opened to allow the carbon dioxide generated by the carbon dioxide generating unit 10 to pass into the gas dissolving unit 20. The compression device (not shown) in the gas dissolving unit 20 is started to compress the carbon dioxide into the clean water in the pressure gas dissolving tank to form carbon dioxide dissolved gas water, and then the regulating valve is opened to pass the carbon dioxide dissolved gas water into the raw water side pipeline of the equipment to be cleaned 1 through the cleaning input end 200. The carbonic acid in the carbon dioxide dissolved gas water reacts with the calcium carbonate and magnesium carbonate in the scaling material to generate magnesium bicarbonate and calcium bicarbonate, and the 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 liquid to form cleaning water. In this way, the cleaning liquid is introduced into the cavity through which the raw water in the equipment to be cleaned 1 flows, so as to react 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 and peel off the organic viscous scaling and residual hardness scaling to achieve pipeline descaling.

[0034] Compared with the traditional physical flushing or chemical cleaning methods, the cleaning system of the shale gas fracturing flowback fluid MVR evaporation treatment equipment of the present invention is based on the fact that the main components of the scale are hardness scale and organic viscous scale: the hardness scale mainly includes calcium carbonate and magnesium carbonate, and carbonic acid with relatively mild acidity is generated by dissolving carbon dioxide in water, and then introduced into the pipeline of the equipment to be cleaned 1 to dissolve the calcium carbonate and magnesium carbonate scale attached to the inner wall of the cavity; while the organic viscous scale is some drag reduction components in the shale gas fracturing flowback fluid, and the carbon dioxide bubbles released during the decompression process of carbon dioxide dissolved gas water are used to flush, crush and peel off the organic viscous scale and the residual hardness scale, and finally achieve the purpose of descaling. In this process, the carbonic acid is relatively mild, making the entire reaction process more controllable and the raw material cost is low.

[0035] The inventor of the present invention has also found in practice that in some treatment processes, sulfate ions are introduced due to the addition of sulfuric acid to adjust the pH value. The sulfate ions combine with calcium ions to generate water-insoluble calcium sulfate, so that the hardness scaling material on the inner wall of the cavity through which the raw water of the shale gas fracturing return fluid flows contains calcium sulfate in addition to calcium carbonate and magnesium carbonate. For this mixed scaling material, in order to further improve the cleaning effect, the cleaning system of the shale gas fracturing return fluid MVR evaporation treatment equipment also includes a cleaning particle addition unit 30. The cleaning particle addition unit 30 is connected to the cleaning input end 200 to pass the cleaning particles into the pipeline of the equipment to be cleaned 1 through the cleaning input end 200. The cleaning particles are specifically ceramic particles with a hollow structure, and the particle size is 150 to 300 μm. Using solid particles made of ceramic material for cleaning can reduce the damage to the equipment to be cleaned 1 during the flushing process, and the hollow structure can reduce the weight of the cleaning particles, making it easy to flow out with the cleaning water and avoid accumulation on the inner wall of the cavity. The ceramic particles are specifically made of aluminum oxide. Alumina has good chemical inertness and can withstand corrosion from acids, alkalis, and most chemical solvents. This property allows it to remain stable in a variety of chemical environments and is not prone to reaction or decomposition. Alumina can maintain its physical and chemical properties unchanged in a high-temperature environment and is suitable for use under high-temperature conditions. Therefore, the present invention uses ceramic particles made of alumina as cleaning particles and uses carbon dioxide dissolved water to clean the pipeline. When the carbon dioxide dissolved water carrying cleaning particles is passed into the equipment to be cleaned 1, not only can the carbonic acid contained therein dissolve the calcium carbonate and magnesium carbonate scale, but the carbon dioxide dissolved water can also release high-density micro-nano carbon dioxide bubbles, which, combined with the cleaning particles, violently flush, crush, and peel off the calcium sulfate scale and organic viscous scale on the inner wall of the cavity, and the peeled pipe wall scale is discharged with the cleaning water. In this way, while the carbon dioxide dissolved water is passed into the equipment to be cleaned 1 to dissolve the scale, solid particles are sprayed into the pipeline to flush the scale, which can greatly improve the cleaning effect.

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

[0037] The cleaning produced water contains calcium bicarbonate, magnesium bicarbonate, cleaning particles and some scaling materials removed after being washed by the cleaning particles. In order to remove the solid scaling materials in the cleaning produced water and further recycle the cleaning produced water, the collection unit 40 of the cleaning system of the shale gas fracturing flowback fluid MVR evaporation treatment equipment comprises a coagulation tank 401, a flocculation tank 402 and a sedimentation tank 403 which are connected in sequence.

[0038] When the cleaning water containing cleaning particles flows into the coagulation tank 401, due to the porous structure of alumina, it has good adsorption capacity, so some cleaning particles can act as sedimentation cores in the coagulation tank 401, and the tiny particles in the water are bonded together to form larger flocs through adsorption. The formed flocs enter the flocculation tank 402. The flocculation tank 402 has a flocculant dosing device (not shown) for adding flocculants to the cleaning water. The flocculant is specifically PAM (polyacrylamide), which enlarges the solid particles in the water body and is conducive to the sinking of the solid particles. The cleaning water after coagulation flows into the sedimentation tank 403, and after sedimentation, the precipitated water and sediment are obtained. The precipitated water can be returned to the dissolved gas unit 20 and reused to generate carbon dioxide dissolved water with carbon dioxide, so as to realize the recycling of cleaning water, and the sediment is further processed to recover the cleaning particles.

[0039] Furthermore, to ensure the coagulation effect, a coagulant dosing device (not shown) can also be provided in the coagulation tank 401 to add a coagulant to the cleaning water. The coagulant can be PAC (polyaluminium chloride). PAC can form a mesh structure in the water body, cooperate with the cleaning particles, better bond the small solid particles in the water body together, and then precipitate the small particles in the water body together in the subsequent flocculation process, accelerate the sedimentation process, and better remove the solids contained in the water body.

[0040] Preferably, the coagulation tank 401 and the flocculation tank 402 are respectively provided with Figure 1 The agitator shown in the figure makes the added coagulant and flocculant fully contact with the cleaning water through the stirring action of the agitator.

[0041] In order to separate the cleaned particles in the sediment, the collection unit 40 further includes a first filter 404 , a second filter 405 and a separator 406 which are sequentially arranged downstream of the sedimentation tank 403 and are connected to each other.

[0042] Specifically, the first filter 404 has a filter screen or filter membrane with a pore size of 250 μm, and the second filter 405 has a filter screen or filter membrane with a pore size of 150 μm. The precipitate in the sedimentation tank 403 passes through the first filter 404 and the second filter 405 in sequence to obtain a filtrate; then the filtrate is passed into the separator 406, and after cleaning (such as ultrasonic cleaning) and centrifugation, clean cleaning particles are separated. These cleaning particles can be added to the cleaning particle addition unit 30 and reused for cleaning the equipment 1 to be cleaned. In this way, most of the scale and impurities are isolated by the two-stage filter to separate the cleaning particles, and then the scale and impurities on the surface are removed by the separator 406 to obtain cleaning particles that can be reused in the cleaning process, so as to realize the recycling of cleaning particles. Of course, the collection unit 40 can also be provided with only one filter to filter the precipitate. The first-stage filtration is easy to clog the filter screen, so the two-stage or multi-stage can better separate the cleaning particles and avoid filter clogging.

[0043] In addition, the carbonic acid that has not reacted with calcium carbonate and magnesium carbonate during the cleaning process will release carbon dioxide again in the coagulation tank 401 (especially under the action of the agitator), and the free carbon dioxide dissolved in the water due to pressure will also be released in the coagulation tank 401. In order to recover the carbon dioxide generated after cleaning, the above-mentioned collection unit 40 also includes a gas collecting hood 407 arranged above the coagulation tank 401. The gas collecting hood 407 has an air intake and an air outlet, the air intake of which is aligned with the coagulation tank 401, and the air outlet is connected to the gas dissolving unit 20. Preferably, the orthographic projection of the air intake of the gas collecting hood 407 on the plane where the opening of the coagulation tank 401 is located completely covers the opening of the coagulation tank 401 to ensure that all the carbon dioxide generated in the coagulation tank 401 can be collected by the gas collecting hood 407. The carbon dioxide generated in the coagulation tank 401 is collected by adsorption and passed into the gas dissolving 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 arranged as a whole in a closed space, and the air intake port of the air collecting hood 407 can extend to above the flocculation tank 402 and the sedimentation tank 403, and completely cover the flocculation tank 402 and the sedimentation tank 403, so as to absorb the carbon dioxide overflowing from the flocculation tank 402 and the sedimentation tank 403, and then re-introduce it into the dissolving unit 20 to generate carbon dioxide dissolved water.

[0045] Cleaning effect

[0046] When using thermal methods to treat shale gas fracturing flowback fluid, plate-type forced circulation MVR evaporation equipment is often used to evaporate the shale gas fracturing flowback fluid. Plate-type forced circulation MVR evaporation equipment usually includes a preheater and a main heat exchanger. The structure and working principle of the preheater and the main heat exchanger have been described in the previous article, so they will not be repeated here. In actual applications, both the preheater and the main heat exchanger are set with a minimum feed flow value. As the equipment runs for an increasing amount of time, the scale accumulated on the inner wall of the raw water side pipe in the preheater and the main heat exchanger will gradually clog the pipe, causing the feed flow of the preheater and the main heat exchanger to decrease. When the feed flow of the preheater and the main heat exchanger drops to the minimum feed flow value, it will affect production, so the raw water side pipe needs to be cleaned.

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

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

[0049] Three sets of preheaters of the same model were used to treat shale gas fracturing flowback fluid from the same source under the same conditions. After the preheater was operated for about 140 days, scaling materials accumulated on the inner wall of the raw water side pipeline of the preheater. The scaling materials included calcium carbonate and magnesium carbonate, as well as organic viscous scaling materials. The three preheaters were cleaned by disassembly and physical flushing, by passing 5% citric acid for cleaning, and by using the cleaning system of the wastewater treatment equipment of the present invention. The cleaning results are shown in Table 1:

[0050] Table 1

[0051]

[0052]

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

[0054] As can be seen from Table 1, the cleaning system of the wastewater treatment equipment of the present invention is used to clean the preheater. After cleaning, the feed amount of the preheater is completely restored, the cleaning effect is good, the time consumption is short, and no reagents need to be added during the cleaning process, so there is no residue after cleaning. Moreover, during cleaning, only the cleaning input end 200 and the cleaning output end 400 need to be connected to the water inlet and the water outlet of the raw water side pipeline of the preheater to be cleaned, respectively, so that online cleaning can be achieved;

[0055] The preheater was cleaned with 5% citric acid. After cleaning, the feed volume of the preheater could not be fully restored, indicating that the organic sticky scaling on the inner wall of the pipeline was not completely removed. The cleaning took a long time, and the residual reagents after cleaning were difficult to handle and the treatment cost was high.

[0056] Disassembling the preheater and cleaning it with a high-pressure water gun, a purely physical method, is not thorough due to the high hardness and dense accumulation of scale deposits, resulting in the lowest recovery of feed volume, poor cleaning effect, high water consumption, and a total time-consuming disassembly, cleaning, and installation.

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

[0058] Two sets of main heat exchangers of the same model were used to treat the same shale gas fracturing return fluid under the same conditions. The designed water output of the main heat exchanger was 10t / h. After the main heat exchanger was operated for about 140 days, scaling materials accumulated on the inner wall of the raw water side pipeline of the main heat exchanger. The scaling materials were mainly calcium carbonate and calcium sulfate, as well as organic viscous scaling materials, of which calcium carbonate accounted for 66.5%, calcium sulfate accounted for 20%, and the remaining components were organic viscous scaling materials. The two main heat exchangers were cleaned by two methods: introducing 5% citric acid and using the cleaning system of the wastewater treatment equipment of the present invention. The two cleaning methods and the data before cleaning are shown in Table 2:

[0059] Table 2

[0060]

[0061]

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

[0063] As can be seen from Table 2, when the cleaning system of the present invention is used for cleaning, the recovery degree of the feed amount of the main heat exchanger is close to 100%, and the parameters such as the temperature difference, inlet pressure, outlet pressure, inlet and outlet pressure difference and evaporation yield of the main heat exchanger are all restored to normal levels, indicating that the cleaning effect is extremely good. The reason for achieving such a cleaning effect is that the cleaning system of the present invention forms carbon dioxide-dissolved water containing carbonic acid by introducing carbon dioxide, and the carbonic acid gradually dissolves calcium carbonate and magnesium carbonate, making the scale loose and easy to peel off, and then the carbon dioxide bubbles released during the decompression process of the carbon dioxide-dissolved water and the ceramic cleaning particles flush the organic viscous scale and the residual hardness scale, which can effectively remove all the scale; while the cleaning with 5% citric acid has a feed amount recovery degree of only 89%, and the parameters such as the temperature difference, inlet pressure, outlet pressure, inlet and outlet pressure difference and evaporation yield of the main heat exchanger are all worse than those of the cleaning system of the present invention.

[0064] Compared with the prior art, the cleaning system of the pressure return liquid treatment equipment described in the present invention is based on the fact that the scaling materials attached to the inner wall of the cavity through which the raw water flows in the treatment equipment are mainly composed of calcium carbonate, magnesium carbonate and organic viscous scaling materials. Carbon dioxide is dissolved in water through a dissolving unit to form carbon dioxide dissolved gas water containing carbonic acid, and the water is used as a cleaning liquid to dissolve the scaling materials on the inner wall of the cavity, thereby effectively removing the scaling materials on the inner wall of the cavity. At the same time, the carbon dioxide bubbles released during the decompression of the carbon dioxide dissolved gas water and the cleaning particles dosing unit are used to spray the scaling materials to flush the scaling materials, thereby greatly improving the cleaning effect, shortening the cleaning time and reducing the cost. In addition, the cleaning particles, carbon dioxide and water in the cleaning water obtained after cleaning are separated from each other through a collecting unit and reused in the cleaning process, thereby realizing the three-phase circulation of liquid, gas and solid particles, which is economical and will not pollute the environment.

[0065] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the embodiments of the present invention. The singular forms of "a", "said" and "the" used in the embodiments of the present invention and the claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should also be understood that, unless otherwise specified, "multiple" refers to two or more; the terms "first", "second", "third", etc. are only used to distinguish, rather than to describe a specific order or sequence, and cannot be understood as indicating or implying relative importance. The term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items. When the above description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. In the description of the present invention, for those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0066] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A cleaning system for shale gas fracturing flowback fluid MVR evaporation treatment equipment, used to remove scale deposits on the inner wall of the cavity through which the shale gas fracturing flowback fluid raw water flows in the equipment to be cleaned (1), characterized in that: include: A carbon dioxide generating unit (10) for supplying carbon dioxide; The gas dissolving unit (20) is used to compress the carbon dioxide supplied by the carbon dioxide generating unit (10) into water to form carbon dioxide dissolved gas water; the gas dissolving unit (20) has a cleaning input end (200), and the cleaning input end (200) is used to connect to a port of the cavity through which the shale gas fracturing return fluid raw water in the equipment to be cleaned (1) flows, so as to pass the carbon dioxide dissolved gas water into the cavity.

2. The cleaning system of the shale gas fracturing flowback fluid MVR evaporation treatment equipment according to claim 1, characterized in that: It also comprises a cleaning particle dosing unit (30), which is in communication with the cleaning input end (200) and is used for introducing cleaning particles into the cavity through the cleaning input end (200).

3. The cleaning system of the shale gas fracturing flowback fluid MVR evaporation treatment equipment according to claim 2 is characterized by: The cleaning particles are made of ceramic.

4. The cleaning system of the shale gas fracturing flowback fluid MVR evaporation treatment equipment according to claim 3 is characterized by: The cleaning particles are hollow in structure.

5. The cleaning system of the shale gas fracturing flowback fluid MVR evaporation treatment equipment according to claim 1, characterized in that: It also comprises a collecting unit (40), wherein the collecting unit (40) has a cleaning output end (400), and the cleaning output end (400) is used to communicate with another port of the cavity to collect the cleaning produced water.

6. The cleaning system of the shale gas fracturing flowback fluid MVR evaporation treatment equipment according to claim 5, characterized in that: The collection unit (40) comprises a coagulation tank (401) and a sedimentation tank (403) which are connected in sequence; The water inlet of the coagulation tank (401) is in communication with the cleaning output end (400); The sedimentation tank (403) is used to precipitate solids contained in the cleaning produced water to form sedimentation produced water and sediment containing the cleaning particles.

7. The cleaning system of the shale gas fracturing flowback fluid MVR evaporation treatment equipment according to claim 6, characterized in that: The water outlet of the sedimentation tank (403) is in communication with the gas dissolving unit (20) so as to allow the sedimentation water to flow into the gas dissolving unit (20).

8. The cleaning system of the shale gas fracturing flowback fluid MVR evaporation treatment equipment according to claim 6, characterized in that: The collecting unit (40) further comprises a flocculation tank (402), wherein the flocculation tank (402) is located between the coagulation tank (401) and the sedimentation tank (403), and is respectively connected to the coagulation tank (401) and the sedimentation tank (403); The flocculation tank (402) is used to add flocculants to the cleaning produced water in the flocculation tank (402).

9. The cleaning system of the shale gas fracturing flowback fluid MVR evaporation treatment equipment according to claim 6, characterized in that: The collecting unit (40) further comprises a gas collecting hood (407) arranged above the coagulation tank (401); The gas collecting hood (407) has an air intake port facing the coagulation tank (401) for collecting carbon dioxide generated by the coagulation tank (401), and the air outlet of the gas collecting hood (407) is connected to the gas dissolving unit (20) to introduce the collected carbon dioxide into the gas dissolving unit (20).

10. The cleaning system of the shale gas fracturing flowback fluid MVR evaporation treatment equipment according to claim 6, characterized in that: The collection unit (40) further comprises at least one filter in communication with the sedimentation tank (403), and a separator (406) in communication with the filter; The filter is used to filter the precipitate to obtain a filtrate containing the cleaned particles; The separator (406) is connected to the cleaning particle dosing unit (30) and is used to clean and separate the solid from the liquid on the filtrate to obtain the cleaning particles, and to replenish the obtained cleaning particles to the cleaning particle dosing unit (30).

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