A new countercurrent double-effect evaporation crystallization device for high-salinity organic wastewater

Abstract

The invention discloses a novel countercurrent double-effect evaporation crystallization device for high-salt organic wastewater, comprising a circulating mother liquid storage tank, an evaporation tower, a circulating mother liquid delivery pump, a circulating mother liquid primary preheater, a circulating mother liquid secondary preheater, an evaporation tower, a wastewater delivery pump, a wastewater heater, a flash tank, a filter pump and a solid-liquid separator; a raw wastewater inlet is arranged on the circulating mother liquid storage tank, the evaporation tower generates a circulating mother liquid which is sent to the circulating mother liquid storage tank and mixed with the incoming raw wastewater, and then sent to the circulating mother liquid primary preheater and the circulating mother liquid secondary preheater in sequence through the circulating mother liquid delivery pump for preheating, and then sent from the circulating mother liquid secondary preheater to the top of the evaporation tower for spraying. The invention has three major circulation loops, less material loss in the overall circulation process, and no pollutants are generated during the treatment process. It is a novel countercurrent double-effect evaporation crystallization device that is efficient, clean and energy-saving.

Description

Technical Field

[0001] The invention relates to the technical field of energy conservation, environmental protection and chemical separation, and in particular to a novel countercurrent double-effect evaporation and crystallization device for high-salt wastewater containing organic matter generated in the process of chemical, pharmaceutical and food production. Background Art

[0002] In the existing technology, the generation of high-salt wastewater in industrial activities is inevitable, the generation channels are becoming more and more extensive, the total amount of generation is also increasing year by year, and its impact on the ecological environment is becoming more and more serious; in the early days, industry mainly used high-efficiency salt-tolerant bacteria and water dilution to treat high-salt wastewater, but this treatment method not only wasted a lot of water resources, but also could not control the total amount of salt emissions.

[0003] In order to better solve the problem of high-salt wastewater, the industry began to use evaporation and crystallization processes to comprehensively treat high-salt wastewater generated in industrial production activities; the evaporation process can be further divided into single-effect evaporation, multi-effect evaporation, rising film evaporation, falling film evaporation, etc.; and the crystallization process can be further divided into concentration crystallization, cooling crystallization, etc. Among the above-mentioned evaporation processes, the multi-effect evaporation process has won the favor of most factories for its advantages such as large operational flexibility and low power consumption.

[0004] The multi-effect evaporation process simply means that the steam generated by the previous evaporator is used as the heat source of the next evaporator. Each evaporator in the process constitutes a single-effect evaporation. Similarly, several evaporators connected in series to complete the evaporation task are called multi-effect evaporation. When naming each evaporator, we will add the corresponding effect number in front of the evaporator to make a distinction. Correspondingly, the steam generated by the multi-effect evaporator is called multi-effect steam or the secondary steam generated by the evaporator. As the name suggests, double-effect evaporation is to use two evaporators in series to complete the evaporation task. It is the most common form of multi-effect evaporation process in factories. Because of its simple process and single equipment, it has been used by various small and medium-sized factories to this day. However, in recent years, with the vigorous development of China's industry and the advocacy of "China Smart Manufacturing 2025", the advantages of the simple process of traditional countercurrent double-effect evaporation cannot cover up its shortcomings such as serious heat loss of the stream, high operating costs, and the need to maintain the vacuum condition of the single-effect evaporator at all times.

[0005] Therefore, it is extremely urgent to actively improve the original countercurrent double-effect evaporation process and seek a new and efficient process with small investment, mild working conditions, reduced energy consumption and increased heat reuse rate of the flow stream. Summary of the invention

[0006] The purpose of the present invention is to provide a novel countercurrent double-effect evaporation crystallization device for high-salt organic wastewater in view of the shortcomings of the prior art; the technical scheme is as follows:

[0007] A novel countercurrent double-effect evaporation crystallization device for high-salt organic wastewater, comprising a circulating mother liquid storage tank, an evaporation tower, a circulating mother liquid delivery pump, a circulating mother liquid primary preheater, a circulating mother liquid secondary preheater, an evaporation tower, a wastewater delivery pump, a wastewater heater, a flash tank, a filter pump and a solid-liquid separator;

[0008] The circulating mother liquid storage tank is provided with a raw material wastewater inlet, and the evaporation tower generates a circulating mother liquid which is sent to the circulating mother liquid storage tank and mixed with the incoming raw material wastewater, and then sent to the circulating mother liquid primary preheater and the circulating mother liquid secondary preheater in sequence through the circulating mother liquid delivery pump for preheating, and then sent from the circulating mother liquid secondary preheater to the top of the evaporation tower for spraying;

[0009] The circulating mother liquid obtained at the bottom of the evaporation tower is divided into two streams, one of which is refluxed to the circulating mother liquid storage tank via a wastewater delivery pump; the other is input into the wastewater heater via a wastewater delivery pump, and is delivered to the flash tank after being heated by the wastewater heater. The second-effect steam generated at the top of the flash tank is used as the heat source of the circulating mother liquid secondary preheater, and the purified water condensed by the circulating mother liquid secondary preheater after heat exchange is directly sent to sewage treatment;

[0010] The wastewater concentrate produced at the bottom of the flash tank is transported to the solid-liquid separator via a filter pump to remove solid salts, and the remaining filtrate is sent back to the wastewater heater for cyclic evaporation.

[0011] Furthermore, it also includes a water cooling tower, a circulating water cooler and a circulating water delivery pump; the mixed gas generated at the top of the evaporation tower is directly sent to the water cooling tower for cooling treatment, and the water vapor in the mixed gas is condensed accordingly, and the condensed hot water stored in the kettle of the water cooling tower overflows and is sent to the circulating mother liquid primary preheater via the circulating water delivery pump for heat exchange as a heat source, and the circulating water after heat exchange is divided into three streams, one of which is sent to the circulating water cooler for cooling and then sent to the top of the water cooling tower for recycling; one stream is directly sent back to the kettle of the water cooling tower for recycling; and the last stream is sent as purified water for sewage treatment.

[0012] Furthermore, an air supply pipe is provided at the bottom of the evaporation tower through an installed fan. When the circulating mother liquor secondary preheater sends waste water to the top of the evaporation tower for spraying, a supply gas is sent into the bottom supply pipe to transfer heat and mass with the sprayed waste water in the evaporation tower; and the supply gas is set to be a gas that is insoluble in water, which can be set to air, nitrogen or flue gas.

[0013] Furthermore, it also includes a gas-liquid cyclone separator, through which the gas at the top of the water cooling tower is passed to remove the liquid droplets entrained therein; and the gas after the liquid droplets are removed is adjusted by adding fresh air through the air supply pipeline and releasing an equal amount of gas, and finally the various indicators of the recycled gas must be consistent with the initial ones.

[0014] Furthermore, the pressures of the flash tank, circulating mother liquid storage tank, evaporation tower and water cooling tower are all at normal pressure; the circulating water cooler is also provided with a cooling water supply pipeline and a cooling water return pipeline.

[0015] Furthermore, the evaporation gas generated by the evaporation tower is set as first-effect steam, and the evaporation gas generated by the flash tank is set as second-effect steam, and the corresponding ratio of the second-effect steam generation amount to the first-effect steam generation amount is set in the range of 0.65-1.05:1.

[0016] Furthermore, the heat source of the wastewater heater is selected to be 6-10 bar low-pressure steam; and the wastewater heater 1 is also provided with a low-pressure steam inlet and a steam condensate outlet.

[0017] Furthermore, the evaporation tower and the water cooling tower are both configured as packed tower structures, and the packing in the tower body is provided with at least two sections, and distributors are correspondingly provided between each section of the packing.

[0018] Beneficial effects: The present invention has the following beneficial effects:

[0019] (1) The present invention has three major circulation loops, with little material loss in the overall circulation process and no pollutants generated during the treatment process. It is a new type of countercurrent double-effect evaporation crystallization device that is efficient, clean and energy-saving;

[0020] (2) The present invention replaces the vacuum first-effect evaporator in the traditional countercurrent double-effect evaporation with a heat and mass transfer evaporation tower that can operate efficiently under normal pressure, thereby avoiding the use of a vacuum system, reducing the material requirements and working condition requirements of the equipment, and expanding the application range and application field of double-effect evaporation;

[0021] (3) The present invention realizes the circulation of a part of the heat energy between the evaporation tower, the water cooling tower, and the circulating mother liquid primary preheater, which conforms to the law of energy balance; and this energy cycle solves the problem of steam heat waste in the well-known traditional countercurrent double-effect evaporation, thereby reducing the overall energy consumption of the process;

[0022] (4) The present invention is thorough in treatment, and the final product is crystallized and purified water; the organic pollutants in the purified water can be removed by subsequent elimination processes, and the purified water after subsequent treatment can be recycled as clean water;

[0023] (5) The present invention can be modified on the basis of the traditional countercurrent double-effect evaporation process, and a relatively small investment can be used to obtain a significant energy saving, and the investment payback period is within an acceptable range. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural diagram of the present invention;

[0025] Figure 2 It is a flow chart of the working principle of the present invention;

[0026] Figure 3 This is a coordinate diagram of the amount of saturated water vapor that 1 kg of dry air can carry at different temperatures. DETAILED DESCRIPTION

[0027] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. The embodiments are implemented based on the technical solution of the present invention. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0028] like Figure 1 and Figure 2 As shown, the technical scheme of the present invention involves fourteen equipments including a wastewater delivery pump 14, a wastewater heater 1, a flash tank 2, a circulating mother liquor storage tank 3, a circulating mother liquor delivery pump 4, a circulating mother liquor secondary preheater 5, a circulating mother liquor primary preheater 6, an evaporation tower 7, a solid-liquid separator 8, a water cooling tower 9, a gas-liquid cyclone separator 10, a fan 11, a circulating water cooler 12, and a circulating water delivery pump 13.

[0029] The present invention utilizes a water cooling tower 9 to recover waste heat from the hot mixed gas containing saturated water vapor from the evaporation tower 7, and the recovered heat is used as a partial heat source for the circulating mother liquid of the evaporation tower 7, thereby reducing the demand for secondary steam generated by the second-effect evaporation of the evaporation tower 7, and ultimately achieving the purpose of reducing operating energy consumption.

[0030] The present invention includes three major circulation loops, wherein an evaporation tower 7, a wastewater delivery pump 14, a circulating mother liquid storage tank 3, a circulating mother liquid delivery pump 4, a circulating mother liquid primary preheater 6 and a circulating mother liquid secondary preheater 5 constitute a mother liquid circulation loop; the evaporation tower 7, a water cooling tower 9, a gas-liquid cyclone separator 10 and a fan 11 constitute a gas circulation loop; and the water cooling tower 9, a circulating water delivery pump 13, a circulating mother liquid primary preheater 6 and a circulating water cooler 12 constitute a water circulation loop.

[0031] In the mother liquor circulation loop, the temperature of the circulating mother liquor should be between 60°C and 75°C when it enters the top of the evaporation tower 7. The evaporation amount of the circulating mother liquor in the evaporation tower 7 and the flash tank 2 will be supplemented by the raw wastewater in the circulating mother liquor storage tank 4.

[0032] In the gas circulation loop, because air, nitrogen, flue gas and other gases that are insoluble in water can carry different amounts of water vapor at different temperatures, and the higher the temperature, the greater the amount they can carry. Taking air as an example, Figure 3 As shown, 1 kg of 44°C dry air can carry a maximum of 57.7 g of water vapor, while 1 kg of 68°C dry air can carry a maximum of 195.8 g of water vapor. Based on the above physical laws, with the help of the evaporation tower 7 and the water cooling tower 9 with simultaneous heat and mass transfer, a similar "evaporation" operation under normal pressure can be achieved.

[0033] In the water circulation loop, especially when treating high-salt wastewater containing organic matter, it is inevitable that certain organic matter will be mixed into the hot mixed gas overflowing from the evaporation tower 7, and these organic matter will be washed off by water in the water cooling tower 9, which will lead to a certain accumulation of organic matter in the circulating water. This requires: firstly, the circulating water needs to be treated regularly to remove the accumulated organic matter in the circulating water; secondly, the circulating water cooler 12 is not suitable for direct mixing cooling, but should adopt indirect heat exchange to avoid the contamination of the refrigerant by the circulating water.

[0034] The present invention is specifically used as follows when treating organic high-salt wastewater:

[0035] The raw wastewater is transported into the circulating mother liquid storage tank 3, where it is directly mixed with the circulating mother liquid produced by the evaporation tower 7. The mixed circulating mother liquid is successively transported to the circulating mother liquid primary preheater 6 and the circulating mother liquid secondary preheater 5 for preheating through the circulating mother liquid delivery pump 4. The circulating mother liquid preheated to the corresponding temperature is directly sprayed from the top of the tower into the evaporation tower 7. At the same time, there is a circulating gas transported into the bottom of the evaporation tower 7 through the fan 11. The circulating gas and the wastewater are fully transferred to heat and mass in the tower.

[0036] The circulating mother liquor obtained at the bottom of the evaporation tower 7 is divided into two streams, which are respectively transported to the circulating mother liquor storage tank 3 and the wastewater heater 1 via the wastewater delivery pump 14; the circulating mother liquor transported to the wastewater heater 1 is heated here by low-pressure steam, and the heated circulating mother liquor is transported to the flash tank 2, and the second-effect steam produced at the top of the flash tank 2 is used as the heat source of the circulating mother liquor secondary preheater 5, and the purified water condensed after heat exchange is directly sent to sewage treatment; the wastewater concentrate produced at the bottom of the flash tank 2 is removed of solid salt by the solid-liquid separator 8, and the remaining filtrate is returned to the wastewater heater for circulating evaporation.

[0037] The mixed gas generated at the top of the evaporation tower 7 is directly passed into the water cooling tower 9 for cooling treatment. The purpose of the cooling treatment is to condense the water vapor in the mixed gas. The condensed hot water stored in the kettle of the water cooling tower 9 overflows and is passed into the circulating mother liquid primary preheater 6 through the circulating water delivery pump 13 for heat exchange as a heat source; the circulating water after heat exchange is divided into three streams, one of which is passed into the circulating water cooler 12 to be cooled to a preset temperature and then sent to the top of the water cooling tower 9 for recycling; one stream is directly sent back to the kettle of the water cooling tower 9 to maintain a certain temperature; the remaining stream is sent as purified water for sewage treatment.

[0038] The gas at the top of the water cooling tower 9 passes through the gas-liquid cyclone separator 10 to remove the entrained droplets therein; the gas without droplets is adjusted accordingly by appropriately adding fresh gas and releasing an equal amount of gas, and ultimately the various indicators of the recycled gas must be consistent with the initial ones.

[0039] For high-salt wastewater that is seriously acidic or alkaline, pH neutralization treatment should be given priority to prevent the above-mentioned process equipment from being corroded prematurely.

[0040] The wastewater heater 1, the circulating mother liquid primary preheater 6, the circulating mother liquid secondary preheater 5, and the circulating water cooler 12 all use shell and tube heat exchangers for countercurrent heat exchange, and the heat exchangers using steam as a heat source all use steam in the shell. The material of the heat exchanger should be stainless steel or titanium steel with good corrosion resistance.

[0041] The heat source of the wastewater heater 1 is 6-9 bar low-pressure steam, and the solid-liquid separation equipment can be a centrifuge, a filter press and other equipment.

[0042] The present invention is characterized in that an evaporation tower 7 is used to replace a single-effect evaporator of a conventional countercurrent double-effect evaporation, thereby avoiding the use of a vacuum system; and the present invention recovers waste heat in a mixed gas containing saturated water vapor at the top of the evaporation tower 7 through a water cooling tower 9, and uses the waste heat to preheat a circulating mother liquid of the evaporation tower 7, thereby saving the demand for steam produced by a flash tank 2 by a circulating mother liquid secondary preheater 5.

[0043] The ratio of the first-effect steam to the second-effect steam is affected by the salt concentration of the wastewater raw material itself. The higher the salt concentration of the wastewater raw material, the more second-effect steam is needed to obtain the first-effect steam; taking all factors into consideration, the ratio of the second-effect steam to the first-effect steam should be controlled between 0.65-1.05:1. The first-effect steam here refers to the evaporation amount of the evaporation tower 7; the second-effect steam refers to the secondary steam produced by the flash tank 2.

[0044] The evaporation tower in the present invention should be selected by fully considering the properties of the evaporation medium, and a packed tower with structured packing is preferred. At the same time, in order to evenly distribute the evaporation medium on the packing, the packing should be divided into two or more sections, and a redistributor should be provided between each section of the packing. The factors that need to be considered for a water cooling tower are basically the same as those for an evaporation tower. A packed tower with structured packing is also selected, and the packing in the packed tower is divided into two or more sections, and a redistributor should be provided between each section of the packing.

[0045] The gas used in the evaporation tower can be: air, nitrogen, flue gas and other gases that are insoluble in water. The specific process can be divided into a gas circulation process as in claim 1 and a non-circulation process in which the gas is directly discharged after passing through the water cooling tower 10. When the gas is a gas that is insoluble in water except air, the circulation process is preferred; when the gas is air, the non-circulation process that is directly discharged is preferred.

[0046] The technical content of the present invention is explained in detail with specific embodiments below. Figure 1 As shown, the present invention Figure 1 The reference numerals ak in the figure are monitoring point marks, and the data of each detection point can be recorded regularly.

[0047] Example 1

[0048] The high-salt wastewater first enters the pH neutralization sedimentation tank for pretreatment, neutralizing the pH to 7-7.5 while removing the suspended matter therein. After pretreatment, the wastewater has a salt content of 5% (salt is NaCl) and a DMF content of 2.5%, and enters the system of the present invention at a flow rate of 4571 kg / h for evaporation treatment.

[0049] The raw wastewater (4571kg, 25℃) is mixed with a circulating mother liquid (52709kg, 50℃) from the evaporation tower in the circulating mother liquid storage tank. Then the circulating mother liquid delivery pump extracts a circulating mother liquid (57280kg, 48℃) from the circulating mother liquid storage tank and delivers it to the circulating mother liquid primary preheater and the circulating mother liquid secondary preheater. The circulating mother liquid preheated to 79℃ is sprayed directly from the top of the evaporation tower. At the same time, a circulating air (11900kg, 44℃) is transported from the bottom of the evaporation tower into the evaporation tower through the fan, and heat and mass are transferred simultaneously with the circulating mother liquid.

[0050] The circulating mother liquid (54924kg, 50℃) obtained at the bottom of the evaporation tower is divided into two streams, one of which (52709kg, 50℃) is transported to the circulating mother liquid storage tank; the other (2216kg, 50℃) is transported to the wastewater heater and heated with 9bar low-pressure steam (2292kg, 175℃), and the heated circulating mother liquid is directly transported to the flash tank for two-phase flash evaporation. The second-effect steam obtained from this flash tank is used as the heat source of the circulating mother liquid secondary preheater. The concentrated liquid produced at the bottom of the flash tank is removed from the solid salt by the solid-liquid separator, and the remaining filtrate is sent back to the wastewater heater for circulation evaporation.

[0051] The saturated air (14256kg / h, 72℃) produced at the top of the evaporation tower is directly passed into the water cooling tower for cooling treatment. The purpose of the cooling treatment is to condense the water vapor in the saturated air. The condensed hot water stored in the kettle of the water cooling tower overflows (52749kg / h, 70℃) and is passed into the circulating mother liquid primary preheater through the circulating water delivery pump for heat exchange. The circulating water after heat exchange is divided into three streams. One stream (50394kg / h, 61℃) is passed into the circulating water cooler to cool to the preset temperature and then sent to the top of the water cooling tower for recycling; one stream is directly sent back to the kettle of the water cooling tower to maintain a certain temperature; the remaining stream (2356kg / h, 61℃) is sent as purified water for sewage treatment.

[0052] The gas at the top of the water cooling tower is passed through a gas-liquid cyclone separator to remove the entrained liquid droplets. The gas without liquid droplets is adjusted accordingly by appropriately adding fresh gas and releasing an equal amount of gas, and ultimately the various indicators of the recycled gas must be consistent with the initial ones.

[0053] Example results: The ah in the following table corresponds to Figure 1 The corresponding monitoring point ah.

[0054] Table 1 Sampling point material results

[0055]

[0056] The low-pressure steam consumed by the present invention and the traditional countercurrent double-effect evaporation is shown in the following table 5:

[0057] Table 2 List of low-pressure steam consumption and salt production

[0058]

[0059] Among them, the pressure of the first-effect evaporator of the traditional double-effect evaporation system is 0.3 bar, and the pressure of the second-effect evaporator is 0.7 bar; the evaporator and the flash tank of this embodiment are both operated at normal pressure.

[0060] The results of this embodiment show that the present invention can effectively reduce the low-pressure steam consumption by 12.5% ​​compared with the traditional countercurrent double-effect evaporation.

[0061] In this embodiment, the heat load of each stage of the circulating mother liquor preheater is shown in Table 6 below.

[0062] Table 3 Summary of heat loads of circulating mother liquor preheaters at all levels

[0063]

[0064] Compared with the current situation that the heat of the final steam in the conventional countercurrent double-effect evaporation process cannot be utilized, the energy saving of the present invention is mainly reflected in the use of a water cooling tower to recover the heat in the air at the top of the evaporation tower, and use this heat to preheat the circulating mother liquid. In other words, the greater the power of the primary circulating mother liquid preheater of the present invention, the better the energy saving effect in the actual working condition. In this embodiment, the power of the primary circulating mother liquid preheater accounts for 30.7% of the total power of the circulating mother liquid preheater.

[0065] Example 2

[0066] The high-salt wastewater first enters the pH neutralization sedimentation tank for pretreatment, neutralizing the pH to 7-7.5 while removing the suspended matter. After pretreatment, the wastewater has a salt content of 8% (salt is NaCl) and a DMF content of 2.5%, and enters the system of the present invention at a flow rate of 4571 kg / h for evaporation treatment.

[0067] The raw wastewater (4571kg, 25℃) is mixed with a circulating mother liquid (47154kg, 50℃) from the evaporation tower in the circulating mother liquid storage tank. Then the circulating mother liquid delivery pump extracts a circulating mother liquid (51725kg, 47℃) from the circulating mother liquid storage tank and delivers it to the circulating mother liquid primary preheater and the circulating mother liquid secondary preheater. The circulating mother liquid preheated to 82℃ is sprayed directly from the top of the evaporation tower. At the same time, a circulating air (11900kg, 44℃) is delivered to the evaporation tower from the bottom of the evaporation tower through the fan, and heat and mass are transferred simultaneously with the circulating mother liquid.

[0068] The circulating mother liquid (49451 kg, 50°C) obtained at the bottom of the evaporation tower is divided into two streams, one of which (47154 kg, 50°C) is transported to the circulating mother liquid storage tank (3); the other (2298 kg, 50°C) is transported to the wastewater heater and heated with 9 bar low-pressure steam (2228 kg, 175°C), and the heated circulating mother liquid is directly transported to the flash tank for two-phase flash evaporation. The second-effect steam obtained in the flash tank is used as the heat source of the circulating mother liquid secondary preheater. The concentrated liquid produced at the bottom of the flash tank is removed from the solid salt by the solid-liquid separator, and the remaining filtrate is returned to the wastewater heater for circulating evaporation.

[0069] The saturated air (14174kg / h, 72℃) produced at the top of the evaporation tower is directly passed into the water cooling tower for cooling treatment. The purpose of the cooling treatment is to condense the water vapor in the saturated air. The condensed hot water stored in the kettle of the water cooling tower overflows (52275kg / h, 69℃) and is passed into the circulating mother liquid primary preheater through the circulating water delivery pump for heat exchange. The circulating water after heat exchange is divided into three streams. One stream (50002kg / h, 61℃) is passed into the circulating water cooler to cool to the preset temperature and then sent to the top of the water cooling tower for recycling; one stream is directly sent back to the kettle of the water cooling tower to maintain a certain temperature; the remaining stream (2273kg / h, 61℃) is sent as purified water for sewage treatment.

[0070] The gas at the top of the water cooling tower is passed through a gas-liquid cyclone separator to remove the entrained liquid droplets. The gas without liquid droplets is adjusted accordingly by appropriately adding fresh gas and releasing an equal amount of gas, and ultimately the various indicators of the recycled gas must be consistent with the initial ones.

[0071] Example results: The ah in the following table corresponds to Figure 1 The corresponding monitoring point ah.

[0072] Table 4 Sampling point material results

[0073]

[0074] The low-pressure steam consumed by the present invention and the traditional countercurrent double-effect evaporator is shown in the following table 8:

[0075] Table 5 Summary of low-pressure steam consumption and salt production

[0076]

[0077] Among them, the pressure of the first-effect evaporator of the traditional double-effect evaporation system is 0.3 bar, and the pressure of the second-effect evaporator is 0.7 bar; the evaporator and the flash tank of this embodiment are both operated at normal pressure.

[0078] The results of this embodiment show that the present invention can effectively reduce the low-pressure steam consumption by 12.1% compared with the traditional countercurrent double-effect evaporation.

[0079] Table 6 Summary of heat loads of circulating mother liquor preheaters at all levels

[0080]

[0081] Compared with the current situation that the heat of the final steam in the conventional countercurrent double-effect evaporation process cannot be utilized, the energy saving of the present invention is mainly reflected in the use of a water cooling tower to recover the heat in the air at the top of the evaporation tower, and use this heat to preheat the circulating mother liquid. In other words, the greater the power of the primary circulating mother liquid preheater of the present invention, the better the energy saving effect in the actual working condition. In this embodiment, the power of the primary circulating mother liquid preheater accounts for 24.9% of the total power of the circulating mother liquid preheater.

[0082] Example 3

[0083] In this embodiment, high-salt wastewater first enters a pH neutralization sedimentation tank for pretreatment, and the pH is neutralized to 7-7.5 while removing suspended matter therein. After pretreatment, the salt content of the wastewater is 10% (the salt is NaCl) and the DMF content is 2.5%. It enters the system described in the present invention at a flow rate of 4571 kg / h for evaporation treatment.

[0084] The raw wastewater (4571kg, 25℃) is mixed with a circulating mother liquid (54503kg, 52℃) from the evaporation tower in the circulating mother liquid storage tank. Then the circulating mother liquid delivery pump extracts a circulating mother liquid (59074kg, 49℃) from the circulating mother liquid storage tank and delivers it to the circulating mother liquid primary preheater and the circulating mother liquid secondary preheater. The circulating mother liquid preheated to 80℃ is sprayed directly from the top of the evaporation tower. At the same time, a circulating air (11900kg, 44℃) is transported from the bottom of the evaporation tower into the evaporation tower through the fan, and heat and mass are transferred simultaneously with the circulating mother liquid.

[0085] The circulating mother liquid (56825kg, 52℃) obtained at the bottom of the evaporation tower is divided into two streams, one of which (54503, 52℃) is transported to the circulating mother liquid storage tank; the other (2322kg, 52℃) is transported to the wastewater heater and heated with 9bar low-pressure steam (2219kg, 175℃), and the heated circulating mother liquid is directly transported to the flash tank for two-phase flash evaporation. The second-effect steam obtained from this flash tank is used as the heat source of the circulating mother liquid secondary preheater. The concentrated liquid produced at the bottom of the flash tank is removed from the solid salt by the solid-liquid separator, and the remaining filtrate is sent back to the wastewater heater for circulation evaporation.

[0086] The saturated air (14149kg / h, 73℃) produced at the top of the evaporation tower is directly passed into the water cooling tower for cooling treatment. The purpose of the cooling treatment is to condense the water vapor in the saturated air. The condensed hot water stored in the kettle of the water cooling tower overflows (52761kg / h, 68℃) and is passed into the circulating mother liquid primary preheater through the circulating water delivery pump for heat exchange. The circulating water after heat exchange is divided into three streams. One stream (50512kg / h, 61℃) is passed into the circulating water cooler to cool to the preset temperature and then sent to the top of the water cooling tower for recycling; one stream is directly sent back to the kettle of the water cooling tower to maintain a certain temperature; the remaining stream (2249kg / h, 61℃) is sent as purified water for sewage treatment.

[0087] The gas at the top of the water cooling tower is passed through a gas-liquid cyclone separator to remove the entrained liquid droplets. The gas without liquid droplets is adjusted accordingly by appropriately adding fresh gas and releasing an equal amount of gas, and ultimately the various indicators of the recycled gas must be consistent with the initial ones.

[0088] Example results:

[0089] The ah in the following table corresponds to Figure 1 The corresponding monitoring point ah.

[0090] Table 7 Sampling point material results

[0091]

[0092] The low-pressure steam consumed by the present invention and the traditional countercurrent double-effect evaporation is shown in the following table:

[0093] Table 8 Summary of low-pressure steam consumption and salt production

[0094]

[0095] Among them, the pressure of the first-effect evaporator of the traditional double-effect evaporation system is 0.3 bar, and the pressure of the second-effect evaporator is 0.7 bar; the evaporator and the flash tank of this embodiment are both operated at normal pressure.

[0096] The results of this embodiment show that the present invention can effectively reduce the low-pressure steam consumption by 10.9% compared with the traditional countercurrent double-effect evaporation.

[0097] Table 9 Summary of heat loads of circulating mother liquor preheaters at all levels

[0098]

[0099] Compared with the current situation that the heat of the final steam effect in the traditional countercurrent double-effect evaporation process cannot be utilized, the energy saving of the present invention is mainly reflected in the use of a water cooling tower to recover the heat in the air at the top of the evaporation tower, and use this heat to preheat the circulating mother liquid. In other words, the greater the power of the primary circulating mother liquid preheater of the present invention, the better the energy saving effect in the actual working condition. In this embodiment, the power of the primary circulating mother liquid preheater accounts for 27.7% of the total power of the circulating mother liquid preheater.

[0100] Example 4

[0101] The high-salt wastewater first enters the pH neutralization sedimentation tank for pretreatment, neutralizing the pH to 7-7.5 while removing the suspended matter. After pretreatment, the wastewater has a salt content of 10% (salt is NaCl) and a DMF content of 5%, and enters the system of the present invention at a flow rate of 4571 kg / h for evaporation treatment.

[0102] The raw wastewater (4571kg, 25℃) is mixed with a circulating mother liquid (52868kg, 51℃) from the evaporation tower in the circulating mother liquid storage tank. Then the circulating mother liquid delivery pump extracts a circulating mother liquid (57439kg, 49℃) from the circulating mother liquid storage tank and delivers it to the circulating mother liquid primary preheater and the circulating mother liquid secondary preheater. The circulating mother liquid preheated to 80℃ is sprayed directly from the top of the evaporation tower. At the same time, a circulating air (11900kg, 44℃) is delivered to the evaporation tower from the bottom of the evaporation tower through the fan, and heat and mass are transferred with the circulating mother liquid.

[0103] The circulating mother liquid (55238kg, 51℃) obtained at the bottom of the evaporation tower is divided into two streams, one of which (52868kg, 51℃) is transported to the circulating mother liquid storage tank; the other (2370kg, 51℃) is transported to the wastewater heater and heated with 9bar low-pressure steam (2208kg, 175℃), and the heated circulating mother liquid is directly transported to the flash tank for two-phase flash evaporation. The second-effect steam obtained from this flash tank is used as the heat source of the circulating mother liquid secondary preheater. The concentrated liquid produced at the bottom of the flash tank is removed from the solid salt by the solid-liquid separator, and the remaining filtrate is sent back to the wastewater heater for circulation evaporation.

[0104] The saturated air (14101kg / h, 72℃) produced at the top of the evaporation tower is directly passed into the water cooling tower for cooling treatment. The purpose of the cooling treatment is to condense the water vapor in the saturated air. The condensed hot water stored in the kettle of the water cooling tower overflows (51092kg / h, 68℃) and is passed into the circulating mother liquid primary preheater through the circulating water delivery pump for heat exchange. The circulating water after heat exchange is divided into three streams. One stream (48891kg / h, 61℃) is passed into the circulating water cooler to cool to the preset temperature and then sent to the top of the water cooling tower for recycling; one stream is directly sent back to the kettle of the water cooling tower to maintain a certain temperature; the remaining stream (2202kg / h, 61℃) is sent as purified water for sewage treatment.

[0105] The gas at the top of the water cooling tower is passed through a gas-liquid cyclone separator to remove the entrained liquid droplets. The gas without liquid droplets is adjusted accordingly by appropriately adding fresh gas and releasing an equal amount of gas, and ultimately the various indicators of the recycled gas must be consistent with the initial ones.

[0106] Example results: The ah in the following table corresponds to Figure 1 The corresponding monitoring point ah.

[0107] Table 10 Sampling point material results

[0108]

[0109] The low-pressure steam consumed by the present invention and the traditional countercurrent double-effect evaporator is shown in the following table 11:

[0110] Table 11 Summary of low-pressure steam consumption and salt production

[0111]

[0112] Among them, the pressure of the first-effect evaporator of the traditional double-effect evaporation system is 0.3 bar, and the pressure of the second-effect evaporator is 0.7 bar; the evaporator and the flash tank of this embodiment are both operated at normal pressure.

[0113] The results of this embodiment show that the present invention can effectively reduce the low-pressure steam consumption by 11.1% compared with the traditional countercurrent double-effect evaporation.

[0114] In this embodiment, the heat load of each stage of the circulating mother liquor preheater is shown in Table 3 below.

[0115] Table 12 Summary of heat loads of circulating mother liquor preheaters at all levels

[0116]

[0117] Compared with the current situation that the heat of the final steam in the conventional countercurrent double-effect evaporation process cannot be utilized, the energy saving of the present invention is mainly reflected in the use of a water cooling tower to recover the heat in the air at the top of the evaporation tower, and use this heat to preheat the circulating mother liquid. In other words, the greater the power of the primary circulating mother liquid preheater of the present invention, the better the energy saving effect in the actual working condition. In this embodiment, the power of the primary circulating mother liquid preheater accounts for 27.5% of the total power of the circulating mother liquid preheater.

[0118] Embodiment 5:

[0119] The high-salinity wastewater first enters the pH neutralization sedimentation tank for pretreatment, neutralizing the pH to 7-7.5 while removing the suspended matter. After pretreatment, the wastewater has a salt content of 10% (salt is NaCl) and an ETOH content of 2.5%, and enters the system of the present invention at a flow rate of 4571 kg / h for evaporation treatment.

[0120] The raw wastewater (4571kg, 25℃) is mixed with a circulating mother liquid (52627kg, 51℃) from the evaporation tower in the circulating mother liquid storage tank. Then the circulating mother liquid delivery pump extracts a circulating mother liquid (57198kg, 49℃) from the circulating mother liquid storage tank and delivers it to the circulating mother liquid primary preheater and the circulating mother liquid secondary preheater. The circulating mother liquid preheated to 80℃ is sprayed directly from the top of the evaporation tower. At the same time, a circulating air (11900kg, 44℃) is delivered to the evaporation tower from the bottom of the evaporation tower through the fan, and heat and mass are transferred simultaneously with the circulating mother liquid.

[0121] The circulating mother liquid (54954kg, 51℃) obtained at the bottom of the evaporation tower is divided into two streams, one of which (52627kg, 51℃) is transported to the circulating mother liquid storage tank; the other (2328kg, 51℃) is transported to the wastewater heater and heated with 9bar low-pressure steam (2254kg, 175℃), and the heated circulating mother liquid is directly transported to the flash tank for two-phase flash evaporation. The second-effect steam obtained from this flash tank is used as the heat source of the circulating mother liquid secondary preheater. The concentrated liquid produced at the bottom of the flash tank is removed from the solid salt by the solid-liquid separator, and the remaining filtrate is sent back to the wastewater heater for circulation evaporation.

[0122] The saturated air (14143kg / h, 72℃) produced at the top of the evaporation tower is directly passed into the water cooling tower for cooling treatment. The purpose of the cooling treatment is to condense the water vapor in the saturated air. The condensed hot water stored in the kettle of the water cooling tower overflows (51891kg / h, 68℃) and is passed into the circulating mother liquid primary preheater through the circulating water delivery pump for heat exchange. The circulating water after heat exchange is divided into three streams. One stream (49648kg / h, 61℃) is passed into the circulating water cooler to cool to the preset temperature and then sent to the top of the water cooling tower for recycling; one stream is directly sent back to the kettle of the water cooling tower to maintain a certain temperature; the remaining stream (2243kg / h, 61℃) is sent as purified water for sewage treatment.

[0123] The gas at the top of the water cooling tower is passed through a gas-liquid cyclone separator to remove the entrained liquid droplets. The gas without liquid droplets is adjusted accordingly by appropriately adding fresh gas and releasing an equal amount of gas, and ultimately the various indicators of the recycled gas must be consistent with the initial ones.

[0124] Example results: The ah in the following table corresponds to Figure 1 The corresponding monitoring point ah.

[0125] Table 13 Sampling point material results

[0126]

[0127] The low-pressure steam consumed by the present invention and the traditional countercurrent double-effect evaporation is shown in the following table:

[0128] Table 14 Summary of low-pressure steam consumption and salt production

[0129]

[0130] The pressure of the first-effect evaporator in the conventional double-effect evaporation system is 0.3 bar, and the pressure of the second-effect evaporator is 0.7 bar; the evaporator and the flash tank in this embodiment are both operated at normal pressure.

[0131] The results of this embodiment show that the present invention can effectively reduce the low-pressure steam consumption by 11.6% compared with the traditional countercurrent double-effect evaporation.

[0132] In this embodiment, the heat load of each stage of the circulating mother liquor preheater is shown in Table 15 below.

[0133] Table 15 Summary of heat loads of circulating mother liquor preheaters at all levels

[0134]

[0135] Compared with the current situation that the heat of the final steam in the conventional countercurrent double-effect evaporation process cannot be utilized, the energy saving of the present invention is mainly reflected in the use of a water cooling tower to recover the heat in the air at the top of the evaporation tower, and use this heat to preheat the circulating mother liquid. In other words, the greater the power of the primary circulating mother liquid preheater of the present invention, the better the energy saving effect in the actual working condition. In this embodiment, the power of the primary circulating mother liquid preheater accounts for 28.2% of the total power of the circulating mother liquid preheater.

[0136] Embodiment 6:

[0137] The high-salinity wastewater first enters the pH neutralization sedimentation tank for pretreatment, neutralizes the pH to 7-7.5 and removes suspended matter. After pretreatment, the wastewater has a salt content of 10% (salt is NaCl), an ETOH content of 2.5%, and a DMF content of 2.5%, and enters the system of the present invention at a flow rate of 4571 kg / h for evaporation treatment.

[0138] The raw wastewater (4571kg, 25℃) is mixed with a circulating mother liquid (57986kg, 52℃) from the evaporation tower in the circulating mother liquid storage tank. Then the circulating mother liquid delivery pump extracts a circulating mother liquid (62557kg, 50℃) from the circulating mother liquid storage tank and delivers it to the circulating mother liquid primary preheater and the circulating mother liquid secondary preheater. The circulating mother liquid preheated to 78℃ is sprayed directly from the top of the evaporation tower. At the same time, a circulating air (11900kg, 44℃) is transported from the bottom of the evaporation tower into the evaporation tower through the fan, and heat and mass are transferred simultaneously with the circulating mother liquid.

[0139] The circulating mother liquid (60331kg, 52℃) obtained at the bottom of the evaporation tower is divided into two streams, one of which (57986kg, 52℃) is transported to the circulating mother liquid storage tank; the other (2345kg, 52℃) is transported to the wastewater heater and heated with 9bar low-pressure steam (2220kg, 175℃), and the heated circulating mother liquid is directly transported to the flash tank for two-phase flash evaporation. The second-effect steam obtained from this flash tank is used as the heat source of the circulating mother liquid secondary preheater. The concentrated liquid produced at the bottom of the flash tank is removed from the solid salt by the solid-liquid separator, and the remaining filtrate is sent back to the wastewater heater for circulation evaporation.

[0140] The saturated air (14126kg / h, 72°C) produced at the top of the evaporation tower is directly passed into the water cooling tower for cooling treatment. The purpose of the cooling treatment is to condense the water vapor in the saturated air. The condensed hot water stored in the kettle of the water cooling tower overflows (51211kg / h, 68°C) and is passed into the circulating mother liquid primary preheater through the circulating water delivery pump (14) for heat exchange as a heat source. The circulating water after heat exchange is divided into three streams, one stream (48986kg / h, 61°C) is passed into the circulating water cooler to be cooled to a preset temperature and then sent to the top of the water cooling tower for recycling; one stream is directly sent back to the kettle of the water cooling tower to maintain a certain temperature; the remaining stream (2226kg / h, 61°C) is sent as purified water to sewage treatment.

[0141] The gas at the top of the water cooling tower is passed through a gas-liquid cyclone separator to remove the entrained liquid droplets. The gas without liquid droplets is adjusted accordingly by appropriately adding fresh gas and releasing an equal amount of gas, and ultimately the various indicators of the recycled gas must be consistent with the initial ones.

[0142] Example results: The ah in the following table corresponds to Figure 1 The corresponding monitoring point ah.

[0143] Table 16 Sampling point material results

[0144]

[0145] The low-pressure steam consumed by the present invention and the traditional countercurrent double-effect evaporator is shown in the following table 17:

[0146] Table 17 Summary of low-pressure steam consumption and salt production

[0147]

[0148] The pressure of the first-effect evaporator in the conventional double-effect evaporation system is 0.3 bar, and the pressure of the second-effect evaporator is 0.7 bar; the evaporator and the flash tank in this embodiment are both operated at normal pressure.

[0149] The results of this embodiment show that the present invention can effectively reduce the low-pressure steam consumption by 11.0% compared with the traditional countercurrent double-effect evaporation.

[0150] In this embodiment, the heat load of each stage of the circulating mother liquid preheater is shown in Table 18 below;

[0151] Table 18 Summary of heat loads of circulating mother liquor preheaters at all levels

[0152]

[0153] Compared with the current situation that the heat of the final effect steam cannot be utilized in the conventional countercurrent double-effect evaporation process, the energy saving of the present invention is mainly reflected in the use of a water cooling tower (9) to recover the heat in the air at the top of the evaporation tower (7), and use this heat to preheat the circulating mother liquid. In other words, the greater the power of the primary circulating mother liquid preheater of the present invention, the better the energy saving effect in the actual working condition. In this embodiment, the power of the primary circulating mother liquid preheater accounts for 27.4% of the total power of the circulating mother liquid preheater.

[0154] The comparison of the above six embodiments is shown in Table 19 below:

[0155] Table 19 Comparison of various examples

[0156]

[0157] Energy saving characterization of the present invention = power of the first-stage circulating mother liquid preheater / total power of the circulating mother liquid preheater;

[0158] Estimated energy saving = (unit consumption of low-pressure steam of traditional double-effect evaporation - unit consumption of low-pressure steam of the present invention) / unit consumption of low-pressure steam of traditional double-effect evaporation.

[0159] The present invention has three major circulation loops, with less material loss in the overall circulation process and no pollutants generated during the treatment process. It is a new type of countercurrent double-effect evaporation crystallization device that is efficient, clean and energy-saving.

[0160] The present invention replaces the vacuum first-effect evaporator in the traditional countercurrent double-effect evaporation with a heat and mass transfer evaporation tower that can operate efficiently under normal pressure, thereby avoiding the use of a vacuum system, reducing the material requirements and working condition requirements of the equipment, and expanding the application range and application field of the double-effect evaporation.

[0161] The present invention realizes the circulation of a part of heat energy among the evaporation tower, the water cooling tower and the circulating mother liquid primary preheater, which conforms to the law of energy balance; and this energy circulation solves the problem of steam heat waste in the well-known traditional countercurrent double-effect evaporation, thereby reducing the overall energy consumption of the process.

[0162] The present invention provides thorough treatment, and the final product is crystallized and purified water; the organic pollutants in the purified water can be removed by subsequent elimination processes, and the purified water after subsequent treatment can be recycled as clean water.

[0163] The present invention can be modified on the basis of the traditional countercurrent double-effect evaporation process, and a relatively small investment can be exchanged for a significant energy saving, and the investment payback period is within an acceptable range.

[0164] The above specific implementation is only a preferred embodiment of the present invention and is not intended to limit the implementation of the present invention and the scope of the claims. All equivalent changes and modifications made according to the content of the patent protection scope of the present invention should be included in the scope of the patent application of the present invention.

Claims

1. A novel countercurrent double-effect evaporation crystallization device for high-salt organic wastewater, characterized in that: It comprises a circulating mother liquid storage tank (3), an evaporation tower (7), a circulating mother liquid delivery pump (4), a circulating mother liquid primary preheater (6), a circulating mother liquid secondary preheater (5), an evaporation tower (7), a waste water delivery pump (14), a waste water heater (1), a flash tank (2), a filter pump (15) and a solid-liquid separator (8); The circulating mother liquid storage tank (3) is provided with a raw material waste water inlet (31), and the evaporation tower (7) generates a circulating mother liquid which is sent to the circulating mother liquid storage tank (3) and mixed with the incoming raw material waste water. The circulating mother liquid is then sent to the circulating mother liquid primary preheater (6) and the circulating mother liquid secondary preheater (5) for preheating through a circulating mother liquid delivery pump (4), and then sent from the circulating mother liquid secondary preheater (5) to the top of the evaporation tower (7) for spraying; The circulating mother liquid obtained at the bottom of the evaporation tower (7) is further divided into two streams, one of which is refluxed into the circulating mother liquid storage tank (3) via the wastewater delivery pump (14); the other stream is input into the wastewater heater (1) via the wastewater delivery pump (14), and is delivered to the flash tank (2) after being heated by the wastewater heater (1). The second-effect steam generated at the top of the flash tank (2) is used as a heat source for the circulating mother liquid secondary preheater (5), and the purified water condensed by the circulating mother liquid secondary preheater (5) after heat exchange is directly delivered to sewage treatment; The wastewater concentrate produced at the bottom of the flash tank (2) is transported to the solid-liquid separator (8) via a filter pump (15) to remove solid salts, and the remaining filtrate is sent back to the wastewater heater (1) for cyclic evaporation.

2. A novel countercurrent double-effect evaporation crystallization device for high-salt organic wastewater according to claim 1, characterized in that: It also includes a water cooling tower (9), a circulating water cooler (12) and a circulating water delivery pump (13); the mixed gas generated at the top of the evaporation tower (7) is directly sent to the water cooling tower (9) for cooling treatment, and the water vapor in the mixed gas is condensed accordingly, and the condensed hot water stored in the bottom of the water cooling tower (9) overflows and is sent to the circulating mother liquid primary preheater (6) through the circulating water delivery pump (13) for heat exchange, and the circulating water after heat exchange is divided into three streams, the first stream is sent to the circulating water cooler (12) for cooling and then sent to the top of the water cooling tower (9) for recycling; the second stream is directly sent back to the bottom of the water cooling tower (9) for recycling; and the third stream is sent as purified water to sewage treatment.

3. A novel countercurrent double-effect evaporation crystallization device for high-salt organic wastewater according to claim 2, characterized in that: The bottom of the evaporation tower (7) is also provided with an air supply pipe (100) through an installed fan (11). When the circulating mother liquid secondary preheater (5) sends waste water to the top of the evaporation tower (7) for spraying, the bottom air supply pipe (100) sends a stream of air supply gas to transfer heat and mass with the sprayed waste water in the evaporation tower (7). The air supply gas is set to be a gas that is insoluble in water, and can be set to air, nitrogen or flue gas.

4. A novel countercurrent double-effect evaporation crystallization device for high-salt organic wastewater according to claim 3, characterized in that: It also includes a gas-liquid cyclone separator (10), through which the gas at the top of the water cooling tower (9) is passed to remove liquid droplets entrained therein; and the gas after the liquid droplets are removed is adjusted by adding fresh air through the air supply pipeline (100) and releasing an equal amount of gas, so that the various indicators of the circulated gas are finally consistent with those at the initial stage.

5. A novel countercurrent double-effect evaporation crystallization device for high-salt organic wastewater according to claim 2, characterized in that: The pressures of the flash tank (2), the circulating mother liquid storage tank (3), the evaporation tower (7) and the water cooling tower (9) are all at normal pressure; the circulating water cooler (12) is also provided with a cooling water supply pipe (121) and a cooling water return pipe (122).

6. A novel countercurrent double-effect evaporation crystallization device for high-salt organic wastewater according to claim 2, characterized in that: The evaporation gas generated by the evaporation tower (7) is set as first-effect steam, and the evaporation gas generated by the flash tank (2) is set as second-effect steam, and the ratio of the amount of second-effect steam generated to the amount of first-effect steam generated is set to be between 0.65-1.05:

1.

7. A novel countercurrent double-effect evaporation crystallization device for high-salt organic wastewater according to claim 6, characterized in that: The heat source of the wastewater heater (1) is low-pressure steam of 6-10 bar; and the wastewater heater (1) is also provided with a low-pressure steam inlet (101) and a steam condensate outlet (102).

8. A novel countercurrent double-effect evaporation crystallization device for high-salt organic wastewater according to claim 6, characterized in that: The evaporation tower (7) and the water cooling tower (9) are both configured as packed tower structures, and the packing in the tower body is provided with at least two sections, and a distributor is provided between each section of the packing.

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