Coal bed gas produced water resource utilization process

Abstract

The invention belongs to the technical field of safety and environmental protection, and provides a coalbed methane produced water resource utilization process which comprises the following steps: obtaining coalbed methane produced water containing various chloride salts, and pretreating the coalbed methane produced water containing various chloride salts to remove impurities; the method comprises the following steps: conveying coal bed gas produced water from which impurities are removed and which contains various salts such as chlorides and the like to a multi-effect evaporation assembly, and sequentially carrying out five-effect countercurrent evaporation, three-effect countercurrent evaporation and single-effect vacuum evaporation treatment, so as to obtain NaCl solids, KCl solids and salt slurry containing CaCl2; and feeding the salt slurry containing CaCl2 into a spray drying device, and drying to obtain a CaCl2 solid. NaCl solids, KCl solids and CaCl2 solids are obtained through five-effect countercurrent evaporation, three-effect countercurrent evaporation, single-effect vacuum evaporation and drying treatment, salt products meet the requirements of industrial salt, and coal bed gas produced water is utilized to a large extent.

Description

Technical Field

[0001] This invention belongs to the field of safety and environmental protection technology, specifically relating to a process for the resource utilization of coalbed methane produced water. Background Technology

[0003] The extraction of coalbed methane (CBM) requires addressing the issue of produced water discharge to prevent additional pollution. The main pollutants in CBM produced water include: high suspended solids, high mineralization, heavy metals, and other contaminants. High-mineralized CBM produced water discharged to the surface can cause soil salinization, affecting the survival of surface flora and fauna. CBM produced water containing heavy metals can harm plant and animal growth and human health. Therefore, the current stage of CBM extraction presents environmental impacts due to the need for salt treatment of produced water.

[0004] Currently, common processes for treating saline produced water include multi-effect evaporation, biological methods, SBR (Sequencing Batch Reactor Activated Sludge Process), and MBR (Membrane Bio-Reactor) technology, which combines activated sludge with membrane separation. However, biological desalination technology is still imperfect, and the technical proficiency is not high. SBR technology also has certain limitations, such as the need to adjust the reaction system and increase investment when the influent flow rate is large, and the need for appropriate process modifications when there are special requirements for effluent quality, such as nitrogen and phosphorus removal. MBR membranes are expensive, making the infrastructure investment of membrane bioreactors higher than that of traditional wastewater treatment processes. Membrane fouling is prone to occur, causing inconvenience to operation and management. It also has high energy consumption and high process requirements.

[0005] High-efficiency evaporation technology for high-salinity produced water is generally designed for high-salinity wastewater with a salt content of more than 40,000 mg / L. Therefore, for low-concentration high-salinity water with a salt content of 1% to 4%, the above methods cannot achieve a significant effect in treating saline wastewater, resulting in high costs and high energy consumption for evaporation and crystallization. Summary of the Invention

[0006] To address the above problems, this invention proposes a process for the resource utilization of coalbed methane produced water, comprising the following steps:

[0007] Obtain coalbed methane produced water containing various chloride salts, and pretreat the produced water containing various chloride salts to remove impurities;

[0008] Coalbed methane produced water with various chloride salts removed from impurities is sent to a multi-effect evaporation unit for sequential five-effect countercurrent evaporation, three-effect countercurrent evaporation and single-effect vacuum evaporation to obtain NaCl solid, KCl solid and salt slurry including CaCl2.

[0009] A salt slurry containing CaCl2 is fed into a spray drying device and dried to obtain solid CaCl2.

[0010] Furthermore, the pretreatment involves filtration, sedimentation, oil removal, COD removal, and then the addition of caustic soda for reaction. After adjusting the pH value, the water is then precipitated and filtered to obtain coalbed methane produced water with various chloride salts removed from impurities.

[0011] Furthermore, the five-effect countercurrent evaporation process involves preheating the coalbed methane produced water (after removing various chloride salts and impurities) in a waste steam preheater, then sending it to a condenser preheater for further preheating. After preheating, the water is sequentially sent to a five-effect evaporator (I), a four-effect evaporator (I), a three-effect evaporator (I), a two-effect evaporator (I), and a one-effect evaporator (I) for countercurrent evaporation to obtain a saturated chloride solution and NaCl crystals.

[0012] Furthermore, each of the first-effect evaporator (I), second-effect evaporator (I), and third-effect evaporator (I) is equipped with a salt collection leg (I). The saturated chloride solution is enriched and grown through the salt collection leg (I), and then transported to the thickener (I) for static sedimentation after passing through the first-effect evaporator (I), second-effect evaporator (I), and third-effect evaporator (I). After solid-liquid separation by a centrifuge (I), the mother liquor is transported to the fifth-effect evaporator (I) for evaporation and crystallization.

[0013] Furthermore, the triple-effect countercurrent evaporation involves exchanging heat between a saturated chloride solution and coalbed methane. After the heat exchange is completed, the solution is sequentially fed to a triple-effect evaporator (II), a second-effect evaporator (II), and a first-effect evaporator (II) for countercurrent circulation evaporation to obtain a solution containing crude NaCl crystals and small amounts of CaCl2 and KCl crystals, as well as a solution containing various salts including NaCl, KCl, and CaCl2.

[0014] Furthermore, each of the first-effect evaporator (II), the second-effect evaporator (II), and the third-effect evaporator (II) is equipped with a salt collection leg (II), and the third-effect evaporator (II) is equipped with a rinsing device. The solution containing multiple salts such as NaCl, KCl, and CaCl2 is enriched and grown through the salt collection leg (II), evaporated through the first-effect evaporator (II), the second-effect evaporator (II), and the third-effect evaporator (II), and rinsed by the rinsing device before being sent to a salt washing device for secondary salt washing. After the salt washing is completed, the solution is sent to a thickener (II) for static sedimentation, and then sent to a centrifuge (II) for solid-liquid separation before being sent to the third-effect evaporator (II) for evaporation and crystallization.

[0015] Furthermore, the single-effect vacuum evaporation involves feeding a solution containing multiple salts, including NaCl, KCl, and CaCl2, into a single-effect evaporator for evaporation to obtain a salt slurry containing CaCl2, as well as solid NaCl and solid KCl.

[0016] Furthermore, the single-effect evaporator is equipped with a salt collection leg (III), through which a solution containing multiple salts such as NaCl, KCl, and CaCl2 is exchanged with coalbed methane via heat exchanger II, then enriched and grown through the salt collection leg (III), and then transported to a thickener (III) for static sedimentation. After solid-liquid separation by a centrifuge (III), solid NaCl and solid KCl are obtained. The solution containing multiple salts such as NaCl, KCl, and CaCl2 is then transported to the single-effect evaporator for further evaporation and crystallization.

[0017] Furthermore, the vapor produced by evaporating the saturated chloride solution is drawn off by a vacuum system.

[0018] Furthermore, the NaCl solid and KCl solid are thermally dissolved in a hot dissolving tank during the recrystallization process. After dissolution, the clear liquid after centrifugation enters a cooling crystallizer heat exchanger to cool and precipitate potassium chloride crystals. The cooling crystallizer is equipped with a salt collecting leg (IV). The salt slurry is discharged from the salt collecting leg (IV) into a thickener (IV). After settling in the thickener (IV), it is sent to a centrifuge (IV) for solid-liquid separation. The separated KCl solid is dried by a potassium chloride drying device, while the NaCl solid after centrifugation in the hot dissolving tank is dried by a sodium chloride drying device.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1. Through five-effect countercurrent evaporation, three-effect countercurrent evaporation, and single-effect vacuum evaporation, as well as drying treatment, NaCl solid, KCl solid, and CaCl2 solid are obtained, and the salt products meet the requirements of industrial salt, realizing the maximum utilization of coalbed methane produced water.

[0021] 2. This invention pre-treats coalbed methane produced water containing various chloride salts to facilitate the separation of salt components. Then, it sequentially passes the water through a multi-effect evaporation assembly for five-effect countercurrent evaporation, three-effect countercurrent evaporation, and single-effect vacuum evaporation. This effectively utilizes the heat source, improves the thermal efficiency of steam, and successfully separates the salts and water from the coalbed methane produced water.

[0022] 3. Utilizing NaCl and KCl solids as resources is a more thorough method for treating coalbed methane produced water. Both methods use clean energy, resulting in high thermal efficiency, low power consumption, and no pollution. The process control is simplified, allowing for both manual and automated control. Furthermore, it can meet the requirements for long-term process operation, improving the operating efficiency of multi-effect evaporation components and overall economic benefits.

[0023] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 A flowchart illustrating the process steps for the resource utilization of coalbed methane produced water in an embodiment of the present invention is shown.

[0026] Figure 2 A process flow diagram of the multi-effect evaporation component in an embodiment of the present invention is shown;

[0027] Figure 3 A process flow diagram of an evaporation device in an embodiment of the present invention is shown;

[0028] Figure 4 A process flow diagram of the two-stage evaporation device in an embodiment of the present invention is shown;

[0029] Figure 5 A process flow diagram of a three-stage evaporation device in an embodiment of the present invention is shown. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] like Figure 1 As shown, the present invention provides a process for the resource utilization of coalbed methane produced water, including the following steps: obtaining coalbed methane produced water containing various chloride salts, and pre-treating the coalbed methane produced water containing various chloride salts to remove impurities;

[0032] Coalbed methane produced water with various chloride salts removed from impurities is sent to a multi-effect evaporation unit for sequential five-effect countercurrent evaporation, three-effect countercurrent evaporation and single-effect vacuum evaporation to obtain NaCl solid, KCl solid and salt slurry including CaCl2.

[0033] A salt slurry containing CaCl2 is fed into a spray drying device and dried to obtain solid CaCl2.

[0034] Produced water from coalbed methane (CBM) mainly originates during the extraction of CBM from coalbed methane wells. As water in the coal seam is extracted along with the CBM, the downhole water pressure decreases, causing the water to be drawn out and forming produced water. Produced water typically has high mineralization, hardness, and oil content, and may also contain various harmful substances such as heavy metals and radioactive materials. Therefore, the resource utilization of produced water from CBM is beneficial for both the sustainable development of CBM resources and environmental protection and ecological civilization construction.

[0035] Coalbed methane produced water containing various chloride salts contains a large number of impurities. Pretreatment can effectively remove impurities and improve the purity and quality of the raw solution, facilitating the separation of salt components and ensuring the smooth operation of subsequent processes. Filtration effectively removes particulate impurities and suspended solids, improving the purity of the feed solution; sedimentation removes larger particulate impurities and suspended solids, suitable for feed solutions with high levels of particulate impurities; oil removal removes grease and improves the transparency of the feed solution; pH adjustment involves adding acids and alkalis to alter the acidity or alkalinity of the feed solution, changing its chemical properties to some extent and facilitating subsequent processing.

[0036] COD (Chemical Oxygen Demand) is calculated by using chemical oxidants to oxidize and decompose oxidizable substances in water, and then calculating the oxygen consumption based on the amount of residual oxidant. COD is measured in ppm or mg / L. The lower the COD value, the less polluted the water. Currently, acidic potassium permanganate oxidation and potassium dichromate oxidation methods are commonly used to reduce the degree of water pollution.

[0037] Coalbed methane produced water containing various chloride salts is filtered, settled, deoiled, and deCOD removed. Then, caustic soda is added to react the mixture, and the pH value is adjusted before precipitation and filtration to obtain coalbed methane produced water with various chloride salts removed.

[0038] Preferably, after pretreatment, caustic soda is added to the coalbed methane produced water containing various chloride salts to react and adjust the pH value before precipitation to remove Mg from the original solution. 2+ The chemical reaction equation is:

[0039] 2NaOH+MgCl2=2NaCl+Mg(OH)2↓

[0040] Pre-treated and purified coalbed methane produced water, i.e., salt slurry with magnesium ions removed.

[0041] like Figure 2 As shown, the multi-effect evaporation assembly includes a first-stage evaporation unit, a second-stage evaporation unit, and a third-stage evaporation unit, wherein the first-stage evaporation unit, the second-stage evaporation unit, and the third-stage evaporation unit are connected in series; the coalbed methane produced water with various chloride salts removed from impurities is transported to the first-stage evaporation unit and saturated chloride solution and NaCl crystals are obtained by five-effect countercurrent evaporation.

[0042] A highly efficient utilization method for coalbed methane produced water containing various salts is proposed using a multi-effect evaporation component. This method treats the components in coalbed methane produced water containing various chloride salts to achieve resource utilization, making the salt products meet the requirements for industrial salt and realizing the maximum utilization of coalbed methane produced water.

[0043] The five-effect countercurrent evaporation, such as Figure 5 As shown, coalbed methane produced water with various chloride salts removed from impurities is preheated in a waste steam preheater and then sent to a condenser preheater for further preheating. After preheating, it is sequentially sent to a five-effect evaporator (I), a four-effect evaporator (I), a three-effect evaporator (I), a two-effect evaporator (I), and a one-effect evaporator (I) for counter-cyclic evaporation to obtain a saturated chloride solution and NaCl crystals.

[0044] Each of the first-effect evaporator (I), second-effect evaporator (I), and third-effect evaporator (I) is equipped with a salt collection leg (I). The saturated chloride solution is enriched and grown through the salt collection leg (I), and then transported to the thickener (I) for static sedimentation after passing through the first-effect evaporator (I), second-effect evaporator (I), and third-effect evaporator (I). After solid-liquid separation by the centrifuge (I), the mother liquor is transported to the fifth-effect evaporator (I) for evaporation and crystallization.

[0045] Multi-effect evaporation units refer to the simultaneous use of multiple evaporators connected in series. Hot steam passes through the evaporators one after another for evaporation, that is, the hot steam from the previous evaporation enters the next evaporation, and so on, evaporating in stages. This effectively utilizes the heat source to achieve the purpose of desalination of high-salt wastewater. Moreover, this technology can successfully separate salt and water in wastewater, and then treat them separately, which is a relatively thorough method for treating high-salt wastewater.

[0046] In this embodiment, the solution is transported using a transfer pump. The pressure from the transfer pump drives the solution from its initial position to its target location, which reduces friction loss during transport and lowers energy consumption.

[0047] The initial solution undergoes two-stage preheating: a waste steam preheater and a condensate preheater. The waste steam preheater utilizes high-temperature waste steam to preheat the initial solution, increasing its temperature and reducing its viscosity, thus facilitating subsequent processes and effectively recovering heat from the waste steam for energy conservation and recycling. The condensate preheater uses the high temperature of the condensate to preheat the solution, raising its temperature and making it easier for dissolved substances to crystallize and precipitate, thereby purifying and concentrating the initial solution. This two-stage preheating achieves highly efficient preheating of the initial solution, increasing its temperature, purity, and quality, while fully recovering and utilizing waste heat, reducing energy consumption, and enabling pollution-free production.

[0048] like Figure 3As shown, the coalbed methane produced water, after preheating and removal of various chloride salts and impurities, is transported to the five-effect evaporator (I) and then circulated in reverse to the first-effect evaporator (I) for evaporation. Specifically, the preheated coalbed methane produced water, after removal of various chloride salts and impurities, is transported to the five-effect evaporator (I) for evaporation. The finished liquid from the five-effect evaporator (I) is then transported by a five-effect transfer pump to the four-effect evaporator (I) for further evaporation. The finished liquid from the four-effect evaporator (I) is then transported by a four-effect transfer pump to the three-effect evaporator (I) for further evaporation. The finished liquid from the three-effect evaporator (I) is then transported by a three-effect transfer pump to the two-effect evaporator (I) for further evaporation. The finished liquid from the two-effect evaporator (I) is then transported by a two-effect transfer pump to the first-effect evaporator (I) for evaporation. Finally, the finished liquid is transported by a first-stage evaporation device transfer pump to the second-stage evaporation device. This process achieves a five-effect reverse circulation evaporation process and evaporates step by step, improving the resource utilization rate of the initial solution.

[0049] Furthermore, each of the first-effect evaporator (I), the second-effect evaporator (I), and the third-effect evaporator (I) is equipped with a salt collection leg (I). The remaining solution based on the saturated chloride solution is enriched and grown through the salt collection leg (I), and then transported to the thickener (I) for static sedimentation after passing through the first-effect evaporator (I), the second-effect evaporator (I), and the third-effect evaporator (I). After solid-liquid separation by the centrifuge (I), it is transported to the fifth-effect evaporator (I) for evaporation and crystallization.

[0050] In this embodiment, the salt collection legs are all devices that utilize the principle of gravity to separate and concentrate materials through the continuous flow of brine and materials, thereby achieving the purpose of purification and concentration. They are simple in structure, easy to operate, and have low maintenance costs.

[0051] Thickeners are devices used to adjust the concentration of solutions. By increasing the contact time between the material and the solution, the material is fully dispersed in the solution to increase the concentration and form a uniform suspension in the solution, which facilitates static sedimentation and subsequent process operations.

[0052] Centrifuges utilize centrifugal force to separate materials into solid-liquid, liquid-liquid, or gas-liquid forms under centrifugal force. They offer excellent separation results, high processing capacity, and easy operation.

[0053] Each of the first-effect evaporator (I), second-effect evaporator (I), and third-effect evaporator (I) is equipped with a high-efficiency salt collection leg (I). NaCl crystals continuously accumulate and grow from the salt collection leg (I). The salt slurry in the first-effect evaporator (I) is pumped to the second-effect evaporator (I) to recover part of the heat energy. The salt slurry in the second-effect evaporator (I) is pumped to the third-effect evaporator (I). The salt slurry in the third-effect evaporator (I) is pumped to the thickener (I) to collect the NaCl crystal solution through the discharge pump for static sedimentation. The settled solution is then separated into solid and liquid by a centrifuge (I). The separated NaCl is then dried in a fluidized bed drying process. The mother liquor after centrifugation is pumped to the five evaporators for further evaporation and crystallization.

[0054] like Figure 4 As shown, a saturated chloride solution is fed into a two-stage evaporator and subjected to triple-effect countercurrent evaporation to obtain crude NaCl crystals and small amounts of CaCl2 and KCl crystals, as well as a solution containing various salts including NaCl, KCl, and CaCl2.

[0055] Specifically, a saturated chloride solution is exchanged with coalbed methane via heat exchanger one. The two-stage evaporation device includes a first-effect evaporator (II), a second-effect evaporator (II), and a third-effect evaporator (II). After the heat exchange is completed, the saturated chloride solution is transported to the third-effect evaporator (II) and then circulated back to the first-effect evaporator (II) for evaporation to obtain a solution containing multiple salts such as NaCl, KCl, and CaCl2, as well as crude NaCl crystals and a small amount of CaCl2 and KCl crystals.

[0056] The heat exchangers in this embodiment are all devices used to transfer heat energy. By contacting two fluids at different temperatures, heat is transferred from the hot fluid to the cold fluid. The heat transfer is achieved through heat conduction, convection and radiation, which can efficiently transfer heat, improve energy utilization, and is suitable for heat exchange between different fluids.

[0057] It can be explained that after heat exchange, the saturated chloride solution is transported to the triple-effect evaporator (II) and then circulated in reverse to the first-effect evaporator (II) for evaporation. Specifically, after heat exchange, the saturated chloride solution is transported to the triple-effect evaporator (II) for evaporation. The evaporated solution is then pumped into the second-effect evaporator (II) for further evaporation by the feed pump. The evaporated solution is then pumped into the first-effect evaporator (II) for further evaporation by the feed pump. Finally, the evaporated solution is transported to the third-stage evaporation unit by the second-stage feed pump.

[0058] Furthermore, each of the first-effect evaporator (II), the second-effect evaporator (II), and the third-effect evaporator (II) is equipped with a salt collection leg (II), and the third-effect evaporator (II) is equipped with a rinsing device. The residual solution based on the solution containing multiple salts such as NaCl, KCl, and CaCl2 is enriched and grown through the salt collection leg (II), evaporated through the first-effect evaporator (II), the second-effect evaporator (II), and the third-effect evaporator (II), and after being rinsed by the rinsing device, it is sent to the salt washing device for secondary salt washing. After the salt washing is completed, the solution is sent to the thickener (II) for static sedimentation, and then sent to the centrifuge (II) for solid-liquid separation before being sent to the third-effect evaporator (II) for evaporation and crystallization.

[0059] Rinsing devices use high-pressure water jets to wash away dirt and bacteria from the surface of equipment to achieve a cleaning effect; salt conveyors are devices that evenly apply a salt solution to the surface of the object being cleaned, and are also used to remove dirt, oil stains and bacteria from the surface of industrial equipment to improve the quality of the products produced.

[0060] Specifically, the first-effect evaporator (II), second-effect evaporator (II), and third-effect evaporator (II) are equipped with high-efficiency salt collection legs (II), where coarse NaCl crystals are continuously enriched and grown from the salt collection legs. The salt slurry in the first-effect evaporator (II) is pumped to the second-effect evaporator (II) by the first-effect salt slurry pump to recover part of the heat energy. The salt slurry in the second-effect evaporator (II) is pumped to the third-effect evaporator (II) by the second-effect salt slurry pump. In addition, the salt collection legs of the third-effect evaporator (II) are equipped with a special rinsing device for rinsing. The rinsed salt slurry is pumped to the salt washing device for secondary rinsing after passing through the discharge pump, which contains the NaCl crystals. The salt slurry after secondary rinsing is discharged into the thickener (II) for static sedimentation. The statically settled solution is separated into solid and liquid by the centrifuge (II). The separated NaCl is dried in the fluidized bed drying process. The mother liquor after centrifugation is then pumped to the third-effect evaporator (II) by the mother liquor pump for further evaporation and crystallization.

[0061] like Figure 5 As shown, a solution containing multiple salts such as NaCl, KCl, and CaCl2 is fed into a three-stage evaporator and evaporated under single-effect vacuum to obtain a salt slurry containing CaCl2, as well as solid NaCl and solid KCl.

[0062] A solution containing multiple salts such as NaCl, KCl, and CaCl2 is heat-exchanged with coalbed methane through a heat exchanger (II). The three-stage evaporation device includes a single-effect evaporator, which is equipped with a salt collection leg (III). The solution containing multiple salts such as NaCl, KCl, and CaCl2 is enriched and grown through the salt collection leg (III) and then transported to a thickener (III) for static sedimentation. After solid-liquid separation by a centrifuge (III), it is transported back to the single-effect evaporator for further evaporation and crystallization.

[0063] Specifically, a solution containing multiple salts such as NaCl, KCl, and CaCl2 is fed into the heat exchanger of the three-stage evaporator of the three-stage evaporation unit by a two-stage feed pump. After exchanging heat with the steam from the boiler, the solution enters the three-stage evaporation unit for evaporation. The three-stage evaporation unit includes a single-effect evaporator, which is equipped with a high-efficiency salt collection leg (III). NaCl and KCl crystals are continuously enriched and grown from the salt collection leg (III). The salt slurry in the salt collection leg (III) is discharged into a thickener (III) for static sedimentation. The solution after static sedimentation is separated into solid and liquid by a centrifuge. The separated NaCl and KCl solids undergo a recrystallization process for salt separation. The mother liquor after centrifugation is then pumped to the single-effect evaporator for further evaporation and crystallization.

[0064] The recrystallization process refers to an important technique for purifying and separating the target compound in a mixture. It involves repeatedly crystallizing the target compound through steps such as dissolution, crystallization, and filtration to achieve high purity.

[0065] As an alternative implementation, the steam from the single-effect evaporator is returned to a suitable evaporator in a first-stage evaporation unit to fully utilize the steam's thermal energy; while the steam condensate discharged from the single-effect evaporator is buffered in a buffer tank and then pumped back to the boiler as boiler water.

[0066] The steam condensate discharged from the single-effect evaporator is buffered in a buffer tank and then pumped back to the boiler as boiler water. The buffer tank is used to balance pressure fluctuations in the system and prevent equipment damage caused by pressure changes. In the buffer tank, the steam condensate will stand for a period of time to separate impurities and gases. This setting is used to ensure the quality of boiler water supply, which can not only realize the recycling of resources and reduce production costs, but also reduce environmental pollution and improve the operating efficiency of the equipment.

[0067] NaCl and KCl are thermally dissolved in a hot dissolving tank based on a recrystallization process, and then centrifuged to obtain solid NaCl. The clear liquid after centrifugation is cooled by a cooling crystallizer and a heat exchanger (III) to precipitate KCl. The cooling crystallizer is equipped with a salt collecting leg (IV). The remaining solution after precipitation is discharged into a thickener (IV) through the salt collecting leg (IV). After settling in the thickener (IV), it is transferred to a centrifuge (IV) for solid-liquid separation. Both the separated solid KCl and solid NaCl are dried.

[0068] Specifically, a salt slurry containing CaCl2 is pumped to a spray drying process to obtain CaCl2 product. NaCl and KCl solids from a three-stage evaporation unit are thermally dissolved in a hot dissolving tank during recrystallization. After dissolution, the clear liquid after centrifugation enters a cooling crystallizer heat exchanger to cool and precipitate KCl crystals. The cooling crystallizer is equipped with a salt collection leg (IV). The salt slurry is discharged from the salt collection leg (IV) into a thickener (IV). After settling in the thickener (IV), it is sent to a centrifuge (IV) for solid-liquid separation. The separated KCl solids are dried by a potassium chloride drying device. Meanwhile, the NaCl solids separated by centrifugation in the hot dissolving tank are dried by a sodium chloride drying device.

[0069] The vapors from the saturated chloride solution, the solution containing multiple salts such as NaCl, KCl, and CaCl2, and the salt slurry containing CaCl2 are all drawn off by a vacuum system.

[0070] The evaporation unit also includes flash tanks (I) arranged sequentially for the first-effect evaporator (I) to the fifth-effect evaporator (I). When the steam generated by the extraction boiler based on coalbed methane produced water exchanges heat with the coalbed methane produced water (which has had various chloride salts removed) through the first-effect evaporator (I), the solution after heat exchange enters the second, third, fourth, and fifth-effect flash tanks (I) sequentially under the pressure difference between the effects for flashing. The flashed steam is then fed into the second-effect evaporator (I), the third-effect evaporator (I), and the fifth-effect evaporator (I), respectively. The system includes a four-effect evaporator (I), a five-effect evaporator (I), and a four-effect evaporator (I). The solution after flash evaporation is pumped back to the boiler as boiler water. The steam condensate from the two-effect evaporator (I), the three-effect evaporator (I), and the four-effect evaporator (I) is also cooled by a flash tank to recover heat energy before entering a condensate preheater to preheat the raw materials and then entering a condensate storage tank. In addition, the steam from the five-effect evaporator (I) is drawn in by a vacuum system, exchanges heat with the raw materials in a waste steam preheater, enters a condenser for condensation, and is discharged to a condensate storage tank by a vacuum system.

[0071] Among them, a flash evaporation tank refers to a liquid under high temperature and high pressure that suddenly decreases in pressure and rapidly vaporizes, and then undergoes water phase separation, so that the lower quality heat energy can be reused.

[0072] A condensate storage tank is a device that uses the condensation process of a coolant in a heat exchanger to convert steam into condensate for storage and treatment. It can effectively collect, store, and treat condensate to reduce energy consumption, reduce water waste, and protect the environment. Furthermore, the treated condensate can be reused in the production process, realizing the recycling of water resources.

[0073] The explanation is that the vacuum system is responsible for pumping water, which not only reduces the concentration of the solution but also discharges it to the condensate storage tank, enabling the reuse of water resources. This means that the treated coalbed methane produced water is reinjected into the coal seam, thereby increasing coalbed methane production. Furthermore, the vacuum system ensures that valuable components in the solution are not lost due to excessively rapid evaporation and can remove impurities from the solution, improving its quality.

[0074] The two-stage evaporation unit includes flash tanks (II) arranged sequentially from the first-effect evaporator (II) to the third-effect evaporator (II). The steam generated by the boiler exchanges heat with the first-effect solution through the first-effect evaporator (II). After the heat exchange is completed, the solution enters the second and third-effect flash tanks (II) sequentially under the pressure difference between the effects for flashing. The flashed steam is then fed into the second-effect evaporator (II) and the third-effect evaporator (II) respectively. The flashed solution is pumped back to the boiler by the condensate pump as boiler feedwater. The steam condensate from the second-effect evaporator (II) also recovers heat energy through the flash tank (II) and enters the condensate preheater to preheat the raw materials before entering the condensate storage tank. In addition, the steam from the third-effect evaporator (II) is drawn by the vacuum system, exchanges heat with the raw materials through the exhaust steam preheater, enters the condenser for condensation, and is discharged to the condensate storage tank by the vacuum system.

[0075] The steam evaporated in the three-stage evaporation unit is drawn off by a vacuum system and discharged into the condensate storage tank in the same way.

[0076] First, the coalbed methane produced water containing various chloride salts is pretreated to facilitate the separation of salt components. Then, it is sequentially evaporated through a multi-effect evaporator, achieving staged evaporation, effectively utilizing the heat source, and improving the thermal efficiency of steam. This process successfully separates the salts and water in the produced water. Finally, a mixed salt solution of NaCl and KCl is utilized for resource recovery, making it a relatively thorough method for treating coalbed methane produced water. Furthermore, the entire process uses clean energy, resulting in high thermal efficiency, low power consumption, and no pollution. The process control is simplified, allowing for both manual and automated control. It also enables long-term operation, improving the operating efficiency of the multi-effect evaporator and overall economic benefits.

[0077] KCl crystals have high value in agriculture, industry and other fields. Among them, KCl crystals are an important component of potash fertilizer. In the industrial field, they have good melting properties and high temperature stability. KCl is used to prepare ceramics, glass and other materials, as well as welding materials. It can also be used as an electrolyte in the production of electronic components such as batteries and capacitors. Therefore, it can enhance the utilization value of coalbed methane produced water resources on the basis of realizing the resource utilization of coalbed methane.

[0078] Optionally, the coalbed methane produced water resource utilization process proposed in this embodiment is relatively mature and simple, and can be controlled manually or automatically. Specifically, the automatic control is mainly based on a PLC system (Programmable Logic Controller). A PLC system is a digital computing and operating electronic device designed specifically for industrial production. It uses a type of programmable memory to store programs, execute user-oriented instructions such as logical operations, sequential control, timing, counting, and arithmetic operations, and control various types of machinery or production processes through digital or analog input / output. It is the core part of industrial control.

[0079] Specifically, a PLC system is used in conjunction with each step of the coalbed methane produced water resource utilization process. The PLC system controls the operation of the pretreatment process, specifically controlling the parameters of various reactors. It monitors and controls parameters such as temperature, pressure, liquid level, and flow rate in the first-stage evaporation unit to ensure the stability and effectiveness of the evaporation process. Sensors are installed in the first-stage evaporation unit, and the PLC system, upon receiving sensor signals, automatically controls the various devices within the unit. The processing methods for the second and third-stage evaporation units are similar to those for the first-stage unit. Furthermore, for the spray drying operation of the evaporated crystals, the PLC system controls the operation of each device in the spray drying unit and adjusts its parameters to achieve automatic control of the final product drying process. The PLC system can also automatically adjust the operating status of the equipment based on set process parameters and operating logic to ensure the stability of the entire process, guarantee the consistency of the final product, and improve the overall quality of the evaporation process.

[0080] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for the resource utilization of coalbed methane produced water, characterized in that: Includes the following steps: Obtain coalbed methane produced water containing various chloride salts, and pretreat the produced water containing various chloride salts to remove impurities; Coalbed methane produced water with various chloride salts removed from impurities is sent to a multi-effect evaporation unit for sequential five-effect countercurrent evaporation, three-effect countercurrent evaporation and single-effect vacuum evaporation to obtain NaCl solid, KCl solid and salt slurry including CaCl2. A salt slurry containing CaCl2 is fed into a spray drying device and dried to obtain solid CaCl2.

2. The coalbed methane produced water resource utilization process according to claim 1, characterized in that: The pretreatment process involves filtration, sedimentation, oil removal, COD removal, followed by the addition of caustic soda for reaction. After adjusting the pH value, the water is then precipitated and filtered to obtain coalbed methane produced water with various chloride salts removed from impurities.

3. The coalbed methane produced water resource utilization process according to claim 1, characterized in that: The five-effect countercurrent evaporation process involves preheating coalbed methane produced water (after removing impurities and various chloride salts) in a waste steam preheater, then sending it to a condenser preheater for further preheating. After preheating, the water is sequentially sent to a five-effect evaporator (I), a four-effect evaporator (I), a three-effect evaporator (I), a two-effect evaporator (I), and a one-effect evaporator (I) for countercurrent evaporation to obtain a saturated chloride solution and NaCl crystals.

4. The coalbed methane produced water resource utilization process according to claim 3, characterized in that: Each of the first-effect evaporator (I), second-effect evaporator (I), and third-effect evaporator (I) is equipped with a salt collection leg (I). The saturated chloride solution is enriched and grown through the salt collection leg (I), and then transported to the thickener (I) for static sedimentation after passing through the first-effect evaporator (I), second-effect evaporator (I), and third-effect evaporator (I). After solid-liquid separation by the centrifuge (I), the mother liquor is transported to the fifth-effect evaporator (I) for evaporation and crystallization.

5. The coalbed methane produced water resource utilization process according to claim 3, characterized in that: The triple-effect countercurrent evaporation method involves exchanging heat between a saturated chloride solution and coalbed methane. After the heat exchange is completed, the solution is sequentially fed to the triple-effect evaporator (II), the second-effect evaporator (II), and the first-effect evaporator (II) for countercurrent circulation evaporation to obtain a solution containing crude NaCl crystals and small amounts of CaCl2 and KCl crystals, as well as a solution containing various salts such as NaCl, KCl, and CaCl2. The vapor from the evaporated solution containing various salts such as NaCl, KCl, and CaCl2 is drawn off by a vacuum system.

6. The coalbed methane produced water resource utilization process according to claim 5, characterized in that: Each of the first-effect evaporator (II), second-effect evaporator (II), and third-effect evaporator (II) is equipped with a salt collection leg (II), and the third-effect evaporator (II) is equipped with a rinsing device. The solution containing multiple salts such as NaCl, KCl, and CaCl2 is enriched and grown by passing through the salt collection leg (II), then evaporated by the first-effect evaporator (II), second-effect evaporator (II), and third-effect evaporator (II), and after being rinsed by the rinsing device, it is sent to the salt washing device for secondary salt washing. After the salt washing is completed, the solution is sent to the thickener (II) for static sedimentation, and then sent to the centrifuge (II) for solid-liquid separation before being sent to the third-effect evaporator (II) for evaporation and crystallization.

7. The coalbed methane produced water resource utilization process according to claim 1, characterized in that: The single-effect vacuum evaporation process involves feeding a solution containing multiple salts, including NaCl, KCl, and CaCl2, into a single-effect evaporator for evaporation to obtain a salt slurry containing CaCl2, as well as solid NaCl and solid KCl. The vapor from the evaporated salt slurry containing CaCl2 is then drawn off by a vacuum system.

8. The coalbed methane produced water resource utilization process according to claim 7, characterized in that: The single-effect evaporator is equipped with a salt collection leg (III). A solution containing multiple salts such as NaCl, KCl, and CaCl2 is heat-exchanged with coalbed methane through heat exchanger II, then enriched and grown through the salt collection leg (III), and then transported to the thickener (III) for static sedimentation. After solid-liquid separation by centrifuge (III), solid NaCl and solid KCl are obtained. The solution containing multiple salts such as NaCl, KCl, and CaCl2 is then transported to the single-effect evaporator for further evaporation and crystallization.

9. The coalbed methane produced water resource utilization process according to claim 3, characterized in that: The vapor produced by evaporating the saturated chloride solution is drawn off by a vacuum system.

10. The coalbed methane produced water resource utilization process according to claim 1, characterized in that: The NaCl and KCl solids are thermally dissolved in a hot dissolving tank during the recrystallization process. After dissolution, the clear liquid after centrifugation enters a cooling crystallizer heat exchanger to cool and precipitate potassium chloride crystals. The cooling crystallizer is equipped with a salt collecting leg (IV). The salt slurry is discharged from the salt collecting leg (IV) into a thickener (IV). After settling in the thickener (IV), it is sent to a centrifuge (IV) for solid-liquid separation. The separated KCl solids are dried by a potassium chloride drying device, while the NaCl solids separated by centrifugation in the hot dissolving tank are dried by a sodium chloride drying device.

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