Evaporation system for high-salt organic wastewater treatment

Abstract

The invention discloses an evaporation system for high-salt organic wastewater treatment. The system comprises a preheating unit, a forced circulation evaporation crystallization unit, a secondary steam compression unit, a vacuum condensation unit and a solid-liquid separation unit, wherein the forced circulation evaporative crystallization unit comprises a crystallizer, an evaporator and a forced circulation pump; the secondary steam compression unit comprises at least one steam compressor; the preheating unit is formed by connecting a tail gas preheater and a condensate water preheater in series; the system further comprises an intelligent control system which is used for automatically monitoring and adjusting the liquid level, the temperature, the pressure, the vacuum degree and the discharging concentration. The forced circulation and the MVR technology are combined, and secondary steam is compressed and recycled, so that the energy consumption is greatly reduced; the multi-stage preheating system fully utilizes waste heat of the system; the vacuum system and the compressor work cooperatively, low-temperature evaporation is achieved, and thermal decomposition of organic matter is reduced; and crystal mush concentration real-time monitoring and intelligent discharging control are realized, so that the crystallization effect is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, in particular to an evaporation system for high-salinity organic wastewater treatment, which is a comprehensive treatment system combining forced circulation evaporation with mechanical vapor recompression (MVR) technology for treating high-salinity organic wastewater and realizing salt recovery. BACKGROUND

[0002] With the rapid development of industry, the treatment of high-salinity organic wastewater has become a key problem in the field of environmental protection. This type of wastewater usually contains high concentrations of salt (such as sodium chloride) and organic matter (COD > 10000 mg / L), and traditional biological treatment methods are difficult to effectively treat. Evaporation crystallization technology, as an effective treatment method, can crystallize and recover the salt in the wastewater, while producing reusable condensed water. However, traditional multi-effect evaporation systems have high energy consumption and high operating costs; and existing MVR evaporation systems are prone to scaling and clogging when treating high-salinity organic wastewater, and organic matter is easily decomposed at high temperatures to produce harmful gases, affecting the stable operation of the system.

[0003] In the prior art, CN107601789A discloses a high-concentration organic wastewater MVR evaporation treatment system, which uses a falling film evaporator, but is prone to scaling on the pipe wall when treating high-salinity wastewater, reducing heat transfer efficiency; CN108689574A discloses an MVR evaporation crystallization system and a method for treating salt-containing wastewater, but does not solve the problem of thermal decomposition of organic matter; CN109205822A discloses a forced circulation MVR evaporation system, but under high-salinity and high-organic conditions, the circulating pump is prone to wear and the system has poor stability.

[0004] Therefore, there is an urgent need to develop an evaporation system that can efficiently treat high-salinity organic wastewater, avoid scaling and clogging, reduce organic matter decomposition, and reduce energy consumption, to meet the current needs of industrial wastewater treatment. SUMMARY

[0005] The present application aims to solve the following problems existing in the prior art of high-salinity organic wastewater evaporation treatment systems:

[0006] High-salinity and high-organic wastewater is prone to scaling and clogging during evaporation, reducing system operating efficiency;

[0007] Organic matter is easily decomposed at high temperatures to produce harmful gases and coke, affecting the stable operation of the system;

[0008] Traditional evaporation systems have high energy consumption and high operating costs;

[0009] The system has small operational flexibility and is difficult to adapt to the treatment of wastewater with different concentrations and flow rates;

[0010] The crystallization effect is unstable and the salt recovery rate is low.

[0011] The technical scheme adopted by the present application to solve the above problems is: an evaporation system for high-salt organic wastewater treatment, comprising a preheating unit for preheating the high-salt organic wastewater to be treated;

[0012] A forced circulation evaporation crystallization unit comprising a crystallizer, an evaporator and a forced circulation pump, for evaporating and concentrating the preheated high-salt organic wastewater and crystallizing it;

[0013] A secondary vapor compression unit comprising at least one vapor compressor, for compressing the low-temperature secondary vapor generated by evaporation into high-temperature vapor and recycling it as the heat source for the evaporator;

[0014] A vacuum condensation unit comprising a condensate tank, a condensate pump, a vacuum cooler and a vacuum pump set, for maintaining the system vacuum degree and collecting condensate;

[0015] A solid-liquid separation unit for solid-liquid separation of the crystallized slurry to obtain crystalline salt and mother liquor;

[0016] An intelligent control system for automatic monitoring and adjustment of system liquid level, temperature, pressure, vacuum degree and discharge concentration.

[0017] Preferably, the preheating unit is composed of a tail gas preheater and a condensate preheater in series, the tail gas preheater uses system tail gas for primary preheating of the raw material, and the condensate preheater uses system condensate for secondary preheating of the raw material.

[0018] Preferably, in the forced circulation evaporation crystallization unit, the material circulates in the system at a flow rate of 1.2-3.0 m / s under the push of the forced circulation pump, and after being heated by the evaporator, it is flash evaporated and crystallized in the crystallizer.

[0019] Preferably, the secondary vapor compression unit comprises two Roots vapor compressors, the two compressors work in parallel, and each compressor is equipped with an adjustable bypass valve for adjusting the compressor load.

[0020] Preferably, the solid-liquid separation unit comprises a discharge pump, a hydrocyclone, a crystal slurry tank, a centrifuge and a mother liquor tank; wherein the crystal slurry is delivered to the hydrocyclone by the discharge pump for preliminary solid-liquid separation, the slurry with a higher solid-liquid ratio enters the crystal slurry tank, and the clear liquid enters the mother liquor tank; the slurry in the crystal slurry tank enters the centrifuge for further solid-liquid separation, the obtained salt enters the drying system, and the mother liquor after centrifugation is returned to the mother liquor tank and then delivered back to the forced circulation evaporation crystallization unit by the mother liquor pump.

[0021] Preferably, the intelligent control system comprises:

[0022] A liquid level control subsystem for controlling the crystallizer liquid level to be kept within the range of 15%-25%;

[0023] temperature control subsystem for controlling the evaporation system temperature in the range of 85-95℃;

[0024] vacuum control subsystem for controlling the system vacuum degree to the corresponding saturated vapor pressure level;

[0025] compressor control subsystem for controlling the compressor start-up and operation, starting at a frequency of 5Hz, and increasing to the working frequency at 2Hz / second after the current stabilizes, while gradually closing the bypass valve;

[0026] discharge control subsystem for monitoring the solid-liquid ratio of the crystal slurry, and starting the discharge program when the solid-liquid ratio reaches 18%-22%.

[0027] Preferably, the evaporator is made of corrosion-resistant materials, including TA2 and 316L stainless steel materials, and the heating chamber has horizontal and vertical structures, which can be selected and configured according to process requirements.

[0028] A control method of the above-mentioned evaporation system, characterized in that it comprises the following steps:

[0029] (1) Start the vacuum pump to draw the vacuum degree of the crystallization system to the saturated vapor pressure level;

[0030] (2) When the liquid level of the crystallizer reaches 20%, start the forced circulation pump to maintain the liquid level stable;

[0031] (3) Heat the materials in the system by steam compensation, and when the material temperature reaches 75℃, interlock the steam regulating valve with the material temperature, and set the temperature to 90℃;

[0032] (4) Start the condensate pump and the spraying pump, and adjust the compressor spraying flow;

[0033] (5) Start the compressor at a frequency of 5Hz, and after the current stabilizes, increase the frequency at 2Hz / second, and when it increases to about 30Hz, gradually close the compressor bypass valve;

[0034] (6) Monitor the solid-liquid ratio of the crystal slurry, and when the solid-liquid ratio reaches 20%, start the discharge pump for discharge, and adjust the discharge amount to maintain the system crystal balance;

[0035] (7) Control the liquid level of the condensate tank within the range of 60%-80%, and automatically discharge the condensate.

[0036] Preferably, in step (5), when the compressor current greatly exceeds the set value, immediately open the bypass valve, reduce the frequency, and check the system sealing.

[0037] Preferably, it further comprises a parking control step:

[0038] (1) Parking first close the steam regulating valve, and then stop the pump of each effect machine;

[0039] (2) When parking for a short time, empty the system of liquid, and clean the system with hot water;

[0040] (3) When parking for a long time, empty and clean the system, then close all the pumps and circulating water, and cut off the water, electricity and gas;

[0041] (4) When parking in winter, empty the system and the pump of residual materials, and keep the heat exchanger warm or stop the circulating water to prevent freezing and pipe blockage.

[0042] Compared with the prior art, the present application has the following advantages and effects:

[0043] (1) Forced circulation and MVR technology are combined, which not only prevents scaling and blockage, but also greatly reduces energy consumption, and the operation cost is reduced by more than 40%;

[0044] (2) The evaporation temperature is controlled at about 90°C through the vacuum system, which is much lower than the decomposition temperature of organic matter, effectively avoiding the problem of thermal decomposition of organic matter;

[0045] (3) The multi-stage preheating system fully utilizes the waste heat of the system, and the thermal energy utilization efficiency is improved by more than 30%;

[0046] (4) The compressor bypass control system can automatically adjust the load of the compressor to avoid overload and ensure stable operation of the system;

[0047] (5) The crystal slurry concentration is monitored in real time and the intelligent discharge control is controlled, the solid-liquid ratio is accurately controlled at about 20%, which ensures the crystallization effect and the salt recovery rate;

[0048] (6) The system operation is flexible, and can adapt to the wastewater treatment requirements of different concentrations and flow rates, and has a wide range of applications;

[0049] (7) Corrosion-resistant materials (TA2 and 316L stainless steel) are used to manufacture key equipment, prolonging the service life of the system;

[0050] (8) The full-automatic control system reduces the labor intensity of manual operation and improves the stability of the system. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 The figure is a process flow diagram of the evaporation system of the present application;

[0052] Figure 2 The figure is a structural schematic diagram of the forced circulation evaporation crystallization unit of the present application;

[0053] Figure 3 The figure is a principle diagram of the intelligent control system of the present application. DETAILED DESCRIPTION

[0054] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are explanations of the present invention, but the present invention is not limited to the following embodiments.

[0055] Example 1: System Composition

[0056] like Figure 1 As shown, the high-salt organic wastewater evaporation system of the present invention includes the following units:

[0057] Preheating unit: Composed of exhaust gas preheater E0101 and condensate preheater E0102 connected in series. The high-salt organic wastewater to be treated is first transported to exhaust gas preheater E0101 via MVR raw material tank V0101 and MVR feed pump P0101, where it undergoes primary preheating using the system's exhaust gas; then it enters condensate preheater E0102, where it undergoes secondary preheating using the system's condensate, fully recovering the system's waste heat.

[0058] Forced circulation evaporation crystallization unit: such as Figure 2 As shown, the system includes a crystallizer V0201, two evaporators E0201A / B (which can operate in parallel), and a forced circulation pump P0201. The preheated raw material enters the crystallizer V0201, where it circulates at a flow rate of 1.8 m / s under the influence of the forced circulation pump P0201. After being heated by the evaporators E0201A / B, the material undergoes flash crystallization within the crystallizer V0201. The heating chamber employs a vertical double-pass structure and is made of TA2 titanium alloy, offering excellent corrosion resistance.

[0059] Secondary steam compression unit: Includes two Roots steam compressors, Z0301 and Z0401. The low-temperature secondary steam generated by the crystallizer V0201 enters the two compressors respectively, and after compression and heating, it returns to the evaporators E0201A / B as a heat source. Each compressor is equipped with an adjustable bypass valve for load adjustment during startup and protection in abnormal conditions.

[0060] The vacuum condensation unit includes a condensate tank V0501, a condensate pump P0501, a vacuum cooler E0501, a vacuum pump unit P0502, and a gas-liquid separator V0502. The compressed high-temperature steam condenses into liquid in the evaporator and enters the condensate tank V0501. Non-condensable gases in the system are condensed by the vacuum cooler E0501; after gas-liquid separation, the liquid enters the condensate tank, and the gas is discharged to the exhaust gas treatment system by the vacuum pump P0502. By adjusting the operating status of the vacuum pump unit, the system vacuum level is maintained at the corresponding 90℃ saturated vapor pressure level (approximately 70 kPa).

[0061] Solid-liquid separation unit: including discharge pump P0202, hydrocyclone V0601, crystal slurry tank V0602, centrifuge D0601 and mother liquor tank V0603. When the solid-liquid ratio of the crystal slurry in the system reaches about 20%, the slurry is transported by the discharge pump P0202 to the hydrocyclone V0601 for preliminary solid-liquid separation, and the slurry with higher solid-liquid ratio is obtained to enter the crystal slurry tank V0602, and the clear liquid enters the mother liquor tank V0603. The slurry in the crystal slurry tank V0602 enters the centrifuge D0601 for further solid-liquid separation, and the salt obtained enters the drying system, and the mother liquor after centrifugation is returned to the mother liquor tank V0603, and then is transported back to the forced circulation system by the mother liquor pump P0601 for re-evaporation. In order to prevent enrichment of organic matter, part of the mother liquor is periodically discharged to the outside of the system for treatment.

[0062] Intelligent control system: as shown in Figure 3 , including PLC controller, various sensors (temperature, pressure, liquid level, flow, density, etc.) and actuators (control valve, frequency converter, etc.). The system adopts distributed control, and each subsystem can operate independently and cooperatively to realize automatic control.

[0063] Example 2: System control method

[0064] The control method of the application comprises the following steps:

[0065] 1. Start-up preparation:

[0066] (1) Check whether the emptying, drainage and blowdown valves of each device are closed;

[0067] (2) Check the air tightness of the system to ensure that there is no leakage;

[0068] (3) Check whether the lubricating oil level of each pump is normal;

[0069] (4) Ensure that the distilled water tank is pre-filled with half of the water.

[0070] 2. System start-up:

[0071] (1) Start the vacuum pump P0502 to draw the vacuum degree of the crystallization system V0201 to the saturated steam pressure level (corresponding to 90℃);

[0072] (2) Start the feed pump P0101 to start feeding, and when the liquid level of the crystallizer V0201 reaches 20%, start the forced circulation pump P0201 to interlock the liquid level LICV0201 and the regulating valve LV0201, and keep the liquid level stable at 20%;

[0073] (3) Open the steam compensation pipeline valve TV0201 to heat the material in the system, and when the material temperature reaches 75℃, interlock the steam regulating valve TV0201 and the material temperature TICV0201, and set the temperature to 90℃;

[0074] (4) Start the condensate pump P0501 and the spray pump P0503, and adjust the compressor spray flow to the design value;

[0075] (5) Start the compressor Z0301 / Z0401 at a frequency of 5 Hz, and after the current is stable, increase the frequency by 2 Hz each time until it reaches about 30 Hz. Gradually close the compressor bypass valve (10% each time), and closely monitor the change in compressor current. If the current significantly exceeds the set value, immediately open the bypass valve, reduce the frequency, or stop the machine for inspection;

[0076] (6) Adjust the vacuum valve before the vacuum pump to maintain stable system vacuum degree and avoid cavitation.

[0077] 3. Normal operation control:

[0078] (1) When the condensate tank V0501 liquid level reaches 70%, open the pneumatic valve LV0102 to discharge condensate water, and set a interlock with LICA-V501 to maintain stable liquid level;

[0079] (2) Take samples from the sampling port every 0.5-1 hour to monitor the crystal slurry solid-liquid ratio. When it reaches 20%, start the discharge pump P0202 for discharge, and adjust the discharge amount to maintain system crystal balance;

[0080] (3) When the mother liquor tank V0603 liquid level reaches the set value, start the mother liquor pump P0601 to transport part of the mother liquor back to the forced circulation system, and periodically discharge part of it to prevent organic enrichment;

[0081] (4) System operation parameters are automatically recorded, and abnormal conditions are automatically alarmed.

[0082] 4. Shutdown control:

[0083] (1) First close the fresh steam main valve, then stop each effect pump;

[0084] (2) Open all atmospheric vent valves;

[0085] (3) Empty all liquid in the system;

[0086] (4) Clean the system with cleaning water, and during the cleaning process, open the fresh steam to preheat the cleaning water, and use hot water for cleaning;

[0087] (5) For short-term shutdown (1-3 days), keep the system closed and check regularly;

[0088] (6) For long-term shutdown, empty and clean the system, then close all pumps and circulating water, and cut off the water, electricity, and gas main switch;

[0089] (7) For winter shutdown, empty the remaining material in the system and the pump, and insulate or stop circulating water for the heat exchanger to prevent freezing and pipe blockage.

[0090] Example 3: System operation effect

[0091] The system of the present application is actually operated in Shexian Circular Economy Park, and handles high-salinity wastewater from epoxy resin production, with the following operation parameters:

[0092] Feed quantity: 20 t / h

[0093] Evaporation quantity: 18.3 t / h

[0094] Influent water quality: COD < 12000 mg / L, calcium and magnesium ions < 100 mg / L, solid content 8%, pH 7-8

[0095] Steam pressure: 0.55 MPa (G)

[0096] Evaporation temperature: 90℃

[0097] Vacuum degree: 70 kPa

[0098] Crystal slurry solid-liquid ratio: 20%

[0099] Operation effect:

[0100] Energy consumption: steam consumption average 900 kg / h, reduced by more than 60% compared with traditional multi-effect evaporation system;

[0101] Output: condensate water quality COD < 100 mg / L, which can be reused or discharged into the later treatment; crystalline salt moisture content < 5%, purity > 95%, which can be shipped for resource utilization;

[0102] Stability: no fouling and plugging phenomenon for 180 days of continuous operation, and the system runs stably;

[0103] Economical efficiency: treatment cost reduced by 45%, and investment recovery period shortened to less than 3 years.

[0104] The present application solves the key technical problems in the treatment of high-salinity organic wastewater by the organic combination of forced circulation and MVR technology, realizes efficient, energy-saving and stable wastewater treatment and resource recovery, and has significant social and economic benefits.

[0105] The above described in the specification of the present application is only an example. Those skilled in the art of the present application can make various modifications or supplements to the described specific embodiments or replace them with similar ways, as long as they do not deviate from the content of the present application specification or exceed the scope defined by the present claims, which shall belong to the protection scope of the present application.

Claims

1. An evaporation system for the treatment of high-salinity organic wastewater, characterized in that, include: The preheating unit is used to preheat the high-salt organic wastewater to be treated; The forced circulation evaporation crystallization unit includes a crystallizer, an evaporator, and a forced circulation pump, which is used to evaporate, concentrate, and crystallize preheated high-salt organic wastewater. The secondary steam compression unit includes at least one steam compressor for compressing the low-temperature secondary steam generated by evaporation into high-temperature steam and returning it to the heat source of the evaporator. The vacuum condensation unit includes a condensate tank, a condensate pump, a vacuum cooler, and a vacuum pump unit, used to maintain the system vacuum and collect condensate. The solid-liquid separation unit is used to separate the solid and liquid components of the crystallized slurry to obtain crystalline salt and mother liquor; The intelligent control system is used to automatically monitor and adjust the system's liquid level, temperature, pressure, vacuum level, and discharge concentration.

2. The evaporation system of claim 1, wherein The preheating unit consists of an exhaust gas preheater and a condensate preheater connected in series. The exhaust gas preheater uses the system exhaust gas to preheat the raw materials in the first stage, and the condensate preheater uses the system condensate to preheat the raw materials in the second stage.

3. The evaporation system of claim 1 or 2, characterized in that In the forced circulation evaporation crystallization unit, the material is driven by a forced circulation pump and circulates within the system at a flow rate of 1.2 to 3.0 m / s. After being heated by the evaporator, it flashes and crystallizes in the crystallizer.

4. The evaporation system of claim 1, wherein The secondary steam compression unit includes two Roots steam compressors that operate in parallel. Each compressor is equipped with an adjustable bypass valve to regulate the compressor load.

5. The evaporation system of claim 1, wherein The solid-liquid separation unit includes a discharge pump, a hydrocyclone separator, a crystal slurry tank, a centrifuge, and a mother liquor tank. The crystal slurry is pumped to the hydrocyclone separator for preliminary solid-liquid separation, and the slurry with a higher solid-liquid ratio enters the crystal slurry tank, while the clear liquid enters the mother liquor tank. The slurry in the crystal slurry tank enters the centrifuge for further solid-liquid separation, and the resulting salt enters the drying system. The mother liquor after centrifugation is returned to the mother liquor tank and then pumped back to the forced circulation evaporation crystallization unit.

6. The evaporation system of claim 1, wherein The intelligent control system includes: The liquid level control subsystem is used to control the liquid level in the crystallizer to remain within the range of 15%–25%. The temperature control subsystem is used to control the temperature of the evaporation system within the range of 85-95℃; The vacuum control subsystem is used to control the system vacuum level at the corresponding saturated vapor pressure level. The compressor control subsystem is used to control the start-up and operation of the compressor. It starts at a frequency of 5Hz and then increases the frequency to the operating frequency at 2Hz per cycle after the current stabilizes, while gradually closing the bypass valve. The discharge control subsystem is used to monitor the solid-liquid ratio of the crystal slurry. When the solid-liquid ratio reaches 18%-22%, the discharge procedure is initiated.

7. The evaporation system of claim 1, wherein The evaporator is made of corrosion-resistant materials, including TA2 and 316L stainless steel. The heating chamber has both horizontal and vertical structures, which can be selected according to process requirements.

8. A method of controlling an evaporation system as claimed in any one of the claims 1-7, characterized in that Includes the following steps: (1) Turn on the vacuum pump and pump the vacuum level of the crystallization system to the saturated vapor pressure level; (2) When the liquid level in the crystallizer reaches 20%, turn on the forced circulation pump to keep the liquid level stable; (3) Heat the material in the system by steam compensation. When the material temperature reaches 75°C, interlock the steam regulating valve with the material temperature and set the temperature to 90°C. (4) Turn on the condensate pump and spray pump, and adjust the compressor spray flow rate; (5) Start the compressor, start at 5Hz frequency, after the current is stable, increase the frequency by 2Hz per time, and gradually close the compressor bypass valve when the frequency is increased to about 30Hz; (6) Monitor the solid-liquid ratio of the crystal slurry. When the solid-liquid ratio reaches 20%, open the discharge pump to discharge, and adjust the discharge amount to keep the system crystal balanced; (7) Control the liquid level of the condensate tank within the range of 60%-80%, and automatically discharge the condensate.

9. The control method according to claim 8, characterized by, In step (5), when the compressor current significantly exceeds the set value, immediately open the bypass valve, reduce the frequency, and check the system sealing.

10. The control method according to claim 8, characterized by, It also includes a parking control step: (1) When parking, first close the steam regulating valve, and then stop each effect pump; (2) When parking for a short time, empty the system liquid, and clean the system with hot water; (3) When parking for a long time, after emptying and cleaning the system, close all pumps and circulating water, and cut off the water and electricity total switch; (4) When parking in winter, empty the remaining material in the system and the pump, and insulate or stop circulating water for the heat exchanger to prevent freezing and pipe blockage.

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