Desalination system and desalination method for saline organic wastewater

Abstract

The present invention provides a desalination system and desalination method for saline organic wastewater, wherein the desalination system comprises a circulation path composed of a flash evaporator, a circulation pump, a heater, and a flash valve connected in series, wherein the liquid phase outlet of the flash evaporator is connected to the inlet of the circulation pump, the outlet of the heater is connected to the inlet of the flash valve, and the outlet of the flash valve is connected to the inlet of the flash evaporator. The desalination system and desalination method for saline organic wastewater provided by the present invention adopt the principle of combining cyclic flash evaporation with alcohol precipitation, and separate salt from other components through a two-step method of solid-liquid separation and vapor-liquid separation, effectively ensuring the separation effect while preventing the blockage of pipelines, valves, and equipment. The desalination system used is simple in device, low in cost, and has good adjustability. For heat sources of different qualities, the circulation ratio can be adjusted to adapt to different heat source temperatures; and the desalination system has good adaptability.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical wastewater pretreatment, in particular to a desalination system and a desalination method for saline organic wastewater. Background Art

[0002] In the chemical production process, after a series of unit operations such as raw material pretreatment, reaction, and refining, a stream of organic wastewater containing salt is often generated. If left untreated, the salt will be discharged into the sewage treatment plant along with the organic wastewater. On the one hand, it will affect the activity of the bacterial flora in the activated sludge of the sewage treatment plant. On the other hand, the salt discharged into the environment with the wastewater will cause environmental pollution, contaminating water bodies and soil. Therefore, it is necessary to separate the salt from the wastewater. At the same time, removing the salt from the wastewater also helps to recover organic matter from the organic wastewater, which can be recycled as a byproduct or returned as raw material to upstream processes. Recycling organic matter with high economic value, or with greater environmental harm or high toxicity is particularly necessary, realizing both economic and environmental benefits.

[0003] Typically, salt is separated from wastewater before organic matter. Otherwise, the salt will participate in the separation and refining of organic matter, potentially causing blockage in the separation and refining systems. Furthermore, the presence of salt increases the material requirements for the separation system, increasing separation costs. Therefore, it is essential to separate the salt in advance. Salt is usually removed from organic wastewater in the form of solids. The presence of solids can easily cause blockage and compaction in the desalination system, hindering the long-term stable operation of the system. Furthermore, if desalination is not thorough, small amounts of salt will enter the downstream system and accumulate. After the system has been running for a certain period of time, this can also cause problems such as blockage of distillation tower packing and corrosion of equipment and pipelines, preventing the long-term stable operation of the downstream system. Summary of the Invention

[0004] In view of the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a desalination system for saline organic wastewater and a desalination method for removing saline organic wastewater using the desalination system. The desalination system utilizes the principle of combining cyclic flash evaporation with alcohol precipitation, and adopts a two-step method of gas-liquid separation and solid-liquid separation to achieve complete separation of organic wastewater and salt, and effectively solve the problem of easy clogging of the system.

[0005] One of the objects of the present invention is to provide a desalination system for saline organic wastewater, comprising a heater, a flash valve, a flash evaporator and a circulation pump connected in sequence, wherein the liquid phase outlet of the flash evaporator is connected to the inlet of the circulation pump, the outlet of the heater is connected to the inlet of the flash valve, and the outlet of the flash valve is connected to the inlet of the flash evaporator; and a solid-liquid separation device is installed in series or in parallel with the heater.

[0006] According to some preferred embodiments of the desalination system of the present invention, the solid-liquid separation device is preferably located downstream of a mixing point of the saline organic wastewater and the circulating liquid of the desalination system.

[0007] According to some preferred embodiments of the desalination system described in the invention, when the solid-liquid separation device is connected in parallel with the heater, the heater, flash valve, flash evaporator and circulation pump are connected in series to form a circulation path, and a branch of the circulation pump outlet is connected to the inlet of the flash evaporator through the inlet of the salt-containing organic wastewater and the solid-liquid separation device in sequence.

[0008] According to some preferred embodiments of the desalination system of the invention, when the solid-liquid separation device is connected in series with the heater, the outlet of the circulation pump is connected in sequence through the inlet of the salt-containing organic wastewater and the inlet of the solid-liquid separation device and the heater to form a circulation path.

[0009] According to some preferred embodiments of the desalination system of the present invention, the solid-liquid separation device is selected from one or more of a filter, a centrifuge and a filter press.

[0010] According to some preferred embodiments of the desalination system of the present invention, the lower head of the flash evaporator is conical, elliptical or spherical, preferably conical.

[0011] A second object of the present invention is to provide a method for removing salt from saline organic wastewater using the above-mentioned desalination system, comprising:

[0012] S1. Add padding to the desalination system to a certain level, start the circulation pump, and establish circulation;

[0013] S2. A heat source is introduced into the heater. The circulating fluid is heated by the heater and then enters the flash evaporator through a flash valve for flash evaporation. The vapor phase obtained by the flash evaporation is discharged from the top of the flash evaporator to the desalination system. The liquid phase obtained by the flash evaporation is discharged from the liquid phase outlet of the flash evaporator and continues to circulate in the circulation path. The circulating fluid comprises at least one alcohol.

[0014] S3 continuously introduces fresh saline organic wastewater into the flash vessel to supplement the system material loss caused by the vapor phase discharge during the flash process, optionally, continuously introducing A alcohol into the flash vessel;

[0015] S4. The mixture of fresh salt-containing organic wastewater and circulating liquid is introduced into the solid-liquid separator. When the concentration of A alcohol in the circulating liquid in the system is high enough, the salt in the organic wastewater is analyzed and separated from the system by the solid-liquid separation process.

[0016] S5 repeat steps S1-S4, until the desalination system is operating stably, so that the fresh salt-containing organic wastewater feed, A alcohol feed, the discharge amount of precipitated salt, the flash vapor phase material discharge amount and the discharge composition tend to be stable;

[0017] The A alcohol is an alcohol or a mixture of alcohols containing at least one alcohol having a boiling point higher than the boiling point of water at the same operating pressure and not forming a low azeotrope with water. In addition to meeting this condition, the alcohol may also contain low-boiling alcohols having a boiling point lower than the boiling point of water at the same operating pressure or forming a low azeotrope with water, such as methanol, ethanol, etc.

[0018] According to the present invention, the circulating fluid has alcohol precipitation capability, forcing salts from fresh saline organic wastewater from upstream to precipitate as solids. During normal, continuous, and stable operation, the fresh saline organic wastewater from upstream enters the desalination system and immediately mixes with the circulating fluid, causing alcohol precipitation to precipitate solid salts. During normal, continuous, and stable operation, the solid salts, once precipitated, are immediately transferred to a solid-liquid separator for separation.

[0019] According to some preferred embodiments of the desalination method of the invention, the A alcohol is at least one of ethylene glycol or butanediol.

[0020] According to some preferred embodiments of the desalination method of the invention, the saline organic wastewater contains Al-alcohol, wherein the Al-alcohol concentration is 1 wt% to 20 wt% by weight;

[0021] According to some preferred embodiments of the desalination method of the invention, the saline organic wastewater does not contain retinol. Before step S1, the method further includes a pretreatment operation of the saline organic wastewater, wherein a certain amount of retinol is added to the saline organic wastewater. Preferably, the amount of retinol added satisfies the concentration of retinol of 1% to 20% by weight of the concentration of the mixed solution of the saline organic wastewater and retinol.

[0022] According to some preferred embodiments of the desalination method of the invention, when the desalination system operates continuously and stably, the salt-containing organic wastewater can be subjected to a cyclic flash evaporation process to produce an alcohol-rich circulating liquid with stable alcohol precipitation capability.

[0023] According to some preferred embodiments of the desalination method of the present invention, during the initial startup phase, the bedding material is selected from fresh saline organic wastewater containing Al-alcohol or Al-alcohol. When fresh saline organic wastewater is used as bedding material, the system needs to operate for a period of time and undergo cyclic flash concentration to form a stable alcohol-rich circulating liquid before it can be used for alcohol precipitation. However, when fresh Al-alcohol is used, the circulating liquid can be used for alcohol precipitation without the need for cyclic flash concentration.

[0024] According to some preferred embodiments of the desalination method of the invention, during normal continuous and stable operation, the circulating liquid is obtained by circulating heating and flash evaporation of saline organic wastewater. Since high-boiling-point substances will be enriched in the liquid phase, the saline organic wastewater is subjected to circulating heating and flash evaporation to form a stable alcohol-rich liquid with alcohol precipitation ability. When encountering fresh saline organic wastewater from upstream, the salt therein can be forced to precipitate in solid form, and then solid-liquid separation can be performed to separate the salt from the system in solid form.

[0025] According to some preferred embodiments of the desalination method of the present invention, the circulation ratio in the circulation path satisfies the requirement that, at this circulation ratio, the concentration of alcohol in the saturated liquid phase that achieves vapor-liquid equilibrium with the saturated organic wastewater vapor exiting the desalination system is sufficiently high, enabling the circulating liquid to have alcohol precipitation capability. Preferably, the circulation ratio is 0-100, more preferably 20-80, and even more preferably 30-80.

[0026] According to some preferred embodiments of the desalination method of the invention, the circulation ratio can be listed as 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100 and any value therebetween.

[0027] According to some preferred embodiments of the desalination method of the invention, in the saline organic wastewater, salt is discharged from the desalination system in the form of solid, and the remaining substances are discharged from the desalination system in the form of steam, thereby achieving complete desalination of the latter and preventing the latter from carrying solid salts into downstream devices.

[0028] In some preferred embodiments of the desalination method of the present invention, the circulation path operates in a continuous mode. The liquid phase in the circulation path is constantly circulating, which prevents solid salts from accumulating and potentially blocking the system. Furthermore, if incomplete solid-liquid separation results in leakage of solid salts into the liquid phase, repeated solid-liquid separation can be performed to prevent solid salts from accumulating and entering the flash steam discharge, potentially carrying with them the solid salts.

[0029] According to some preferred embodiments of the desalination method of the invention, under a specified flash steam pressure, the alcohol concentration in the alcohol-rich circulating liquid can be changed by adjusting the circulation ratio, and then the flash evaporation temperature can be adjusted to adapt to heat sources of different grades.

[0030] In some preferred embodiments of the desalination method according to the present invention, the flash steam pressure can be adjusted to accommodate different refining and separation methods in downstream devices.

[0031] A third object of the present invention is to provide an application of the above-mentioned desalination system or the above-mentioned method for removing salt from saline organic wastewater in the field of saline organic wastewater treatment.

[0032] As used herein, the term "azeotrope" refers to a mixture of two or more homogeneous solutions of different components, mixed in a specific ratio, that has a single boiling point at a fixed pressure. When the azeotrope reaches its azeotropic point, the composition ratios of the gaseous portion and the liquid portion are identical.

[0033] In the present invention, the term "low azeotrope" refers to an azeotrope whose boiling point is lower than the boiling points of the pure components constituting the azeotrope at the same operating pressure.

[0034] In the present invention, the term "high-boiling-point alcohol" refers to an alcohol substance having a boiling point higher than that of water at the same operating pressure and which does not form an azeotrope with water, such as ethylene glycol, butanediol, etc.

[0035] In the present invention, the term "low-boiling-point alcohol" refers to an alcohol having a boiling point lower than that of water at the same operating pressure, or an alcohol that forms a low azeotrope with water, such as methanol, ethanol, etc.

[0036] In the present invention, the term "circulation ratio" is the ratio of the mass flow rate of the logistics through the circulation pump to the mass flow rate of the system's saline organic wastewater feed.

[0037] The beneficial effects of the present invention are at least in the following aspects:

[0038] First, the desalination method for saline organic wastewater described in the present invention adopts a two-step method of solid-liquid separation and vapor-liquid separation to achieve complete separation of salt from other components. The existence of the circulation loop makes it possible to repeatedly perform solid-liquid separation on the solid salt leaking into the liquid phase, effectively preventing the salt from being entrained into the downstream device.

[0039] Secondly, in the desalination method for saline organic wastewater described in the present invention, the presence of solids in the desalination system is very small, and the solid-liquid system is always in a circulating flow state, avoiding solid sedimentation, accumulation, and compaction, effectively reducing the risk of blockage and improving the stability of the device.

[0040] Third, in the desalination method for saline organic wastewater of the present invention, the existence of circulating flash evaporation reduces the temperature rise of the system, and low-grade heat sources can be used for heating; for heat sources of different qualities, the circulation ratio can be adjusted to adapt to different heat source temperatures.

[0041] Fourthly, in the desalination method for salt-containing organic wastewater of the present invention, almost all of the heat consumed by the desalination system is used for vaporization of the organic wastewater. This heat can be further utilized in the downstream organic matter recovery device, thereby reducing energy waste and improving overall energy utilization.

[0042] Fifth, the desalination method for salt-containing organic wastewater of the present invention utilizes a desalination system with simple device, low cost and good adjustability; and the desalination system has good adaptability, and downstream operations such as pressure distillation, vacuum distillation or atmospheric distillation can be performed. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Flow chart of the desalination system equipment for saline organic wastewater involved in Examples 1-11;

[0044] Figure 2 This is a flow chart of the equipment for the desalination system for saline organic wastewater according to Example 12;

[0045] The above drawings include the following reference numerals:

[0046] 1-Flash evaporator; 2-Circulation pump; 3-Heater; 4-Flash valve; 5-Centrifuge; 6a-Filter; 6b-Filter. DETAILED DESCRIPTION

[0047] The present invention is described in detail below through examples, but the protection scope of the present invention is not limited to the following description.

[0048] If the specific conditions in the examples are not specified, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All equipment, instruments, valves, reagents, or apparatus used, if the manufacturer is not specified, are conventional products that can be obtained through commercial channels.

[0049] In the following embodiments, the desalination process of Examples 1-11 is as follows: Figure 1 As shown. The system used includes a circulation path consisting of a flash evaporator 1, a circulation pump 2, a heater 3 and a flash valve 4 connected in series. The liquid phase outlet of the flash evaporator 1 is connected to the inlet of the circulation pump 2, and the outlet of the flash valve 4 is connected to the inlet of the flash evaporator 1. A centrifuge 5 is used as a solid-liquid separator, and the flash valve 4 is used for pressure reduction. A branch of the outlet of the circulation pump 2 is connected to the inlet of the flash evaporator 1 through the centrifuge 5, and the clarified liquid obtained at the outlet of the centrifuge 5 is sent back to the flash evaporator 1. An inlet for salt-containing organic wastewater is set between the circulation pump 2 and the centrifuge 5. Fresh organic wastewater is also sent to the centrifuge, and the organic wastewater vapor is extracted from the top of the flash evaporator 1, and the salt is discharged from the centrifuge 5.

[0050] Example 1

[0051] The desalination process involved in this embodiment is as follows Figure 1 shown.

[0052] The saline organic wastewater to be treated has a flow rate of 2150 kg / h, a temperature of 50°C, and a pressure of 0.5 MPaG. The composition of the saline organic wastewater is: water, 83.72 wt%; ethylene glycol, 13.95 wt%; and sodium chloride, 2.33 wt%. Ethylene glycol has a standard boiling point of 193.2°C, which is higher than that of water and can be used to form an alcohol-rich circulating fluid.

[0053] S1. The salt-containing organic wastewater is introduced into the desalination system until the liquid level in the flash evaporator 1 reaches 50%, and the circulation pump 2 is started to establish a cycle;

[0054] S2. A heat source is introduced into heater 3. After the circulating liquid is heated, it enters flash evaporator 1 through flash valve 4 for flash evaporation. The flash vapor is discharged from the top of flash evaporator 1 to exit the desalination system, while the liquid phase is discharged from the bottom of flash evaporator 1 to continue circulating in the circulation path. The ethylene glycol concentration in the circulating liquid gradually increases as the flash evaporation cycle proceeds.

[0055] S3. A circulating liquid is separated from the outlet of the circulating pump 2 and merged with the fresh organic wastewater from upstream. The mixed liquid is introduced into the centrifuge 5, and the liquid discharged from the centrifuge 5 is returned to the flash evaporator 1. At this time, the flow rate of the fresh saline organic wastewater should maintain the liquid level in the flash evaporator 1 at a constant value to replenish the material discharged in the form of steam after the flash evaporation.

[0056] S4. As the flash evaporation proceeds, the ethylene glycol concentration in the circulating liquid gradually increases, the water content gradually decreases, and the salt precipitates from the circulating liquid, which is then gradually and completely separated in centrifuge 5. Meanwhile, the newly added saline organic wastewater, after being mixed with the alcohol-rich circulating liquid, continuously precipitates salt due to the alcohol precipitation process. These salts are immediately separated in centrifuge 5 after precipitation.

[0057] S5. Repeat steps S1-S4 until the desalination system is running stably and continuously.

[0058] Fresh, saline organic wastewater is continuously fed in, and salt and flash steam are continuously discharged. The flash steam composition and flow rate are close to those of the wastewater excluding salt. The alcohol-rich circulating liquid and the flash steam now form a vapor-liquid equilibrium. At this point, the ethylene glycol concentration in the circulating liquid rises to a stable value where alcohol precipitation occurs. This reaction with the continuously fed fresh wastewater precipitates salt, which is then separated in a centrifuge. Other components, as the circulating liquid heats and flashes, continuously evaporate into steam within the flash evaporator and continuously leave the system as gas, achieving complete desalination.

[0059] When the device is operating stably, the circulation ratio is 20.44, the operating temperature of flash evaporator 1 is 129.9℃, the operating pressure is 5kPaG; the outlet temperature of heater 3 is 147.8℃.

[0060] The relevant components in the circulating liquid are: water, 17.14% by weight; ethylene glycol, 82.86% by weight; the relevant components in the flash steam are: water, 86.37% by weight; ethylene glycol, 13.63% by weight. The circulating liquid and flash steam form a vapor-liquid equilibrium. After the flash distillation cycle, ethylene glycol, as a heavy component, is effectively enriched in the circulating liquid, significantly increasing its concentration. This can then be used for alcohol precipitation, forcing the salt in the saline organic wastewater to precipitate.

[0061] In this embodiment, salt leaves the system in solid form, and water and ethylene glycol leave the system in the form of flash steam after cyclic pressurization, heating, and reduced pressure flash evaporation. Due to the significant difference in physical properties between flash steam and solids, flash steam is less likely to carry solids into downstream devices compared to the situation where liquid-solid entrainment is more likely to occur. After the salt is precipitated, solid-liquid separation is performed, and the circulating liquid is flash evaporated and then vapor-liquid separation is performed. The two-step separation method of solid-liquid separation and vapor-liquid separation is used to finally separate the salt from other components. There is no direct contact between the vapor and the solid. Even if liquid-solid entrainment or vapor-liquid entrainment occurs, the possibility of flash steam carrying solid salts into downstream devices can be effectively reduced.

[0062] After the salt precipitates from the liquid, it immediately enters the liquid-solid separation equipment for separation, removing the solids from the system and allowing the clarified liquid to continue participating in the flash evaporation cycle. When the device is operating stably, the solids in the system are compressed to a very small area and are immediately removed as soon as they precipitate, effectively reducing the risk of blockage in components such as pipelines, valves, and heat exchange tubes.

[0063] For solid-liquid systems, low flow rates or static areas should be avoided to prevent solids from settling, accumulating, compacting, compacting, or clogging. Because the liquid in this desalination system is constantly circulating, these conditions are unlikely to occur. Furthermore, solids generated during startup, or leaking into the liquid phase due to incomplete solid-liquid separation, will recirculate with the circulating liquid and repeatedly enter the solid-liquid separator for solid-liquid separation, further ensuring effective solid-liquid separation and effectively reducing the risk of system clogging.

[0064] Examples 2-6

[0065] The desalination process involved in this embodiment is as follows Figure 1 shown.

[0066] The saline organic wastewater to be treated has a flow rate of 5600 kg / h, a temperature of 74.5°C, and a pressure of 0.1 MPaG. The composition of the saline organic wastewater is: water, 89.29% by weight; 1,4-butanediol, 8.93% by weight; and sodium chloride, 1.79% by weight. 1,4-Butanediol has a standard boiling point of 228°C, higher than that of water, and can be used to form an alcohol-rich circulating fluid.

[0067] The operation method is basically the same as that of Example 1, the only difference being that a different circulation ratio is used.

[0068] Changing the recycle ratio of the unit changes the required temperature of the circulating fluid before flash evaporation, and the required heat source quality for the heater. Considering that saturated steam is the most common heat source in actual production units, when using it as the heat source and specifying a 20°C heat transfer temperature difference at the process-side outlet of the heat exchanger, the changes in the required flash evaporation temperature, heat source temperature, and heat source pressure at different recycle ratios are shown in Table 1 below.

[0069] Table 1

[0070]

[0071] As shown in Table 1, when flash evaporation is not used, the organic wastewater needs to be heated to 215.7°C to vaporize it. At this time, saturated steam with a pressure of up to 3.0 MPaG is required as the heat source to ensure a 20°C heat transfer temperature difference at the heater outlet. When the circulation ratio is 28.2, the required saturated steam pressure is 0.94 MPaG; when the circulation ratio is gradually increased to 82.8, the required saturated steam pressure gradually decreases to 0.54 MPaG.

[0072] Therefore, the greater the recycle ratio, the lower the required temperature at the flash valve inlet (i.e., heater outlet), and the lower the heat source temperature requirement. When saturated steam is used as the heat source, the required saturated steam pressure is also lower. While producing an alcohol-rich liquid, the cyclic flash process also reduces the quality requirements of the heat source, enabling the use of less expensive low-pressure steam. This also reduces the wall thickness of equipment like heaters, lowering initial investment. If a factory only has a low-pressure steam pipeline network and no high-pressure steam network, this system can use low-pressure steam as the heat source, eliminating reliance on high-pressure steam.

[0073] Increasing the recycle ratio can lower the system's requirements for heat source quality, but the larger the recycle ratio, the higher the pump load. A higher recycle ratio is not necessarily better. In actual production, a matching recycle ratio can be calculated based on the plant's steam specifications, allowing for the design of an appropriate desalination system or ensuring the system operates at a reasonable operating point. This system also offers strong adaptability.

[0074] Furthermore, lowering the flash valve inlet temperature helps inhibit the self-polymerization of butanediol, reducing butanediol losses and preventing the self-polymerization products from disrupting the system, such as scaling and raising the system's saturation temperature and viscosity. If the system contains heat-sensitive materials that are susceptible to thermal decomposition, lowering the temperature can also help inhibit their decomposition. Therefore, this method is also suitable for saline wastewater containing heat-sensitive materials.

[0075] Examples 7-11

[0076] The desalination process involved in this embodiment is as follows Figure 1 shown.

[0077] The organic wastewater to be treated has a flow rate of 1090 kg / h, a temperature of 50°C, and a pressure of 0.5 MPaG. The composition of the saline organic wastewater is: water, 86.54% by weight; ethylene glycol, 4.81% by weight; ethanol, 4.81% by weight; and sodium chloride, 3.84% by weight. Ethylene glycol, with a standard boiling point of 193.2°C, is higher than that of water and is the primary component of the alcohol-rich circulating fluid. Ethanol, with a standard boiling point of 78°C, is lower than that of water and forms an azeotrope with water.

[0078] The operation method is essentially the same as in Example 1, differing only in that the flash evaporation process in the desalination system is performed at different pressures to accommodate different downstream separation methods. Because gases are difficult to compress, the vapor discharged from the flash evaporator is typically directed directly to a downstream distillation unit for refining. The flash vapor pressure only needs to be slightly higher than the operating pressure of the downstream refining unit to overcome the flow resistance.

[0079] By adjusting the flash steam pressure, a desalination system can be tailored to the downstream pressure. When saturated steam is used as the heat source and the heat transfer temperature difference at the process side outlet of the heat exchanger is set at 20°C, the changes in various parameters at different flash steam pressures are shown in the table below.

[0080] Table 2

[0081]

[0082] As shown in Table 2, when atmospheric distillation is carried out downstream, the flash steam pressure can be set to 5 kpaG to overcome the resistance of downstream pipelines, tower internals, etc. At this time, the flash steam temperature is 122.1 °C, and 0.53 MPaG saturated steam is required as the heat source.

[0083] When the downstream is subjected to -25kPaG vacuum distillation, the flash steam pressure is -20kPaG. At this time, the flash steam temperature is 115.5°C, and 0.22MPaG saturated steam is required as the heat source.

[0084] When 0.3MPaG pressurized distillation is performed downstream, the flash steam pressure is 305kPaG. No additional pressurization process is required for the flash steam, avoiding the use of complex and expensive gas compression machinery. For conditions where the downstream equipment is pressurized distillation, the increase in flash evaporation pressure leads to an increase in the flash evaporation temperature, which in turn increases the requirements for the quality of the heat source, requiring the use of 1.46MPaG saturated steam as the heat source. If the factory cannot provide this grade of steam, the required flash evaporation temperature can be reduced by increasing the circulation ratio in the same way, so that a lower-grade heat source can be used. When the circulation ratio increases from 31.3 to 61.2, the required saturated steam pressure decreases from 1.46MPaG to 1.15MPaG. Therefore, this circulating flash desalination method has strong adaptability.

[0085] Furthermore, regardless of the distillation method used in downstream units, wastewater and organic matter enter the downstream units as flash steam. Compared to liquid-phase feed, saturated vapor-phase feed reduces the heat load on the bottom reboiler. This means that the heat consumed in the cyclic flash desalination process can be reused in downstream processes, improving energy efficiency.

[0086] Example 12

[0087] The desalination process involved in this embodiment is as follows Figure 2 As shown. The system used includes a circulation circuit consisting of a flash evaporator 1, a circulation pump 2, a filter 6a, a filter 6b, a heater 3, and a flash valve 4, connected in series. The liquid phase outlet of the flash evaporator 1 is connected to the inlet of the circulation pump 2, the outlet of the circulation pump 2 is connected to the inlets of the filters 6a and 6b, the outlets of the filters 6a and 6b are connected to the inlet of the heater 3, and the outlet of the heater 3 is connected to the inlet of the flash valve 4. Filters 6a and 6b serve as solid-liquid separators, and the flash valve 4 is used for pressure reduction. Flash steam is discharged from the gas phase outlet of the flash evaporator 1; solid salts are discharged from the filter. Filters 6a and 6b are connected in parallel, serving as backup for each other. When one is shut down for cleaning, the other maintains normal operation. Fresh saline organic wastewater is fed from an upstream device into a pipeline connecting the outlet of the circulation pump 2 and the inlets of the filters 6a and 6b. After merging with the circulating liquid, it is sent to the filters.

[0088] The composition and flow rate of the organic wastewater to be treated are the same as those in Example 1.

[0089] S1 using fresh ethylene glycol for padding, add ethylene glycol from the outside to the flash vessel 1 once to 50% liquid level, start the circulation pump 2, establish circulation;

[0090] S2. A heat source is introduced into heater 3. After the circulating fluid is heated, it enters flash evaporator 1 through flash valve 4 for flash evaporation. The flash vapor is discharged from the top of the flash evaporator to exit the desalination system. The liquid phase obtained by the flash evaporation is discharged from the bottom of the flash evaporator and continues to circulate in the circulation path.

[0091] S3 after step S2 flash, the introduction of fresh saline organic wastewater into the system, fresh wastewater is used to supplement the flash discharge desalination system material, to maintain a stable flash evaporator liquid level;

[0092] S4. Because the circulating fluid contains a large amount of ethylene glycol, the salt in the organic wastewater immediately precipitates as a solid upon contact with the circulating fluid. This salt is then separated in a filter. The remaining components of the organic wastewater discharged from the circulating system are then added to the circulating fluid and recirculated.

[0093] S5. Repeat steps S1-S4 until the desalination system operates stably.

[0094] During this process, as organic wastewater is continuously added, the concentration of ethylene glycol in the circulating liquid will gradually decrease, but its concentration will still be much higher than the concentration of ethylene glycol in the organic wastewater feed; other components in the wastewater except salt flash in the flash evaporator and leave the system in the form of steam, achieving complete desalination.

[0095] By using ethylene glycol instead of fresh organic wastewater as a bedding material before commissioning, the circulating fluid has the ability to undergo alcohol precipitation during the initial startup phase, avoiding salt precipitation in the flash evaporator during the initial flash concentration process and reducing the startup time. When the system reaches steady state, the relevant operating parameters of each device remain the same as in Example 1, and the composition of the circulating fluid remains the same as in Example 1.

[0096] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation of the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for desalting saline organic wastewater, characterized in that: include: S1. Add padding to the desalination system to a certain level and establish circulation; S2. The circulating fluid is heated by the heater and then enters the flash evaporator through the flash valve for flash evaporation. The vapor phase obtained by the flash evaporation is discharged from the top of the flash evaporator to the desalination system, and the liquid phase obtained by the flash evaporation is discharged from the liquid phase outlet of the flash evaporator and continues to circulate in the circulation path; the circulating fluid contains at least one alcohol A; S3 continuously introducing fresh saline organic wastewater into the flash vessel; S4. The mixture of fresh salt-containing organic wastewater and circulating liquid is introduced into the solid-liquid separator. When the concentration of A alcohol in the circulating liquid in the system is high enough, the salt in the organic wastewater is analyzed and separated from the system by the solid-liquid separation process. S5 repeat steps S1-S4, until the desalination system is operating stably, so that the fresh salt-containing organic wastewater feed, A alcohol feed, the discharge amount of precipitated salt, the flash vapor phase material discharge amount and the discharge composition tend to be stable; The A alcohol is an alcohol or a mixture of alcohols comprising at least one alcohol having a boiling point higher than that of water at the same operating pressure and not forming a low azeotrope with water; When the desalination system operates continuously and stably, the salt-containing organic wastewater is flash-evaporated to produce an alcohol-rich circulating liquid with stable alcohol precipitation ability; Fresh saline organic wastewater enters the desalination system and is immediately mixed with the circulating liquid, causing alcohol precipitation to precipitate solid salts. Once the solid salts are precipitated, they are sent to a solid-liquid separator for separation. The circulation ratio in the circulation path satisfies the requirement that the concentration of alcohol substances in the saturated liquid phase that reaches vapor-liquid equilibrium with the saturated organic wastewater vapor exiting the desalination system is sufficiently high at this circulation ratio, so that the circulating liquid has alcohol precipitation capability. The desalination method utilizes the following system, which includes a heater, a flash valve, a flash evaporator and a circulation pump connected in sequence, wherein the liquid phase outlet of the flash evaporator is connected to the inlet of the circulation pump, the outlet of the heater is connected to the inlet of the flash valve, and the outlet of the flash valve is connected to the inlet of the flash evaporator; a solid-liquid separation device is installed in series or in parallel with the heater, When the solid-liquid separation device is connected in parallel with the heater, the heater, flash valve, flash evaporator and circulation pump are connected in series to form a circulation path, and a branch of the circulation pump outlet is connected to the inlet of the flash evaporator through the inlet of the saline organic wastewater and the solid-liquid separation device in sequence; When the solid-liquid separation device is connected in series with the heater, the outlet of the circulation pump is connected in sequence through the salt-containing organic wastewater inlet and the solid-liquid separation device and the inlet of the heater to form a circulation path; The solid-liquid separation device is located downstream of the mixing point of the saline organic wastewater and the circulating liquid of the desalination system.

2. The desalination method according to claim 1, characterized in that The saline organic wastewater may contain or not contain A alcohol.

3. The desalination method according to claim 1, wherein The saline organic wastewater contains Al-alcohol, wherein the concentration of Al-alcohol is 1 wt % to 20 wt % in terms of weight percentage.

4. The desalination method according to claim 1, wherein The saline organic wastewater does not contain A-alcohol. Before step S1, a pretreatment operation of the saline organic wastewater is also included, in which a certain amount of A-alcohol is added to the saline organic wastewater.

5. The desalination method according to claim 4, characterized in that: The amount of A alcohol added is such that the concentration of A alcohol is 1% to 20% by weight of the mixed solution of salt-containing organic wastewater and A alcohol.

6. The desalination method according to any one of claims 1 to 5, characterized in that: The padding material is selected from fresh saline organic wastewater containing A-alcohol or A-alcohol.

7. The desalination method according to claim 6, characterized in that: The circulation ratio is 20~80.

8. The desalination method according to claim 7, characterized in that: The circulation ratio is 30~80.

9. The desalination method according to claim 1, characterized in that: The solid-liquid separation device is selected from one or more of a filter, a centrifuge and a filter press.

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