A triple-effect evaporation system and process for evaporating and extracting salt from coking wastewater

Abstract

The present invention provides a triple-effect evaporation system and process for evaporating and extracting salt from coking wastewater, wherein the system comprises: a first-effect evaporation device, a second-effect evaporation device, a third-effect evaporation device, a first cyclone, a slurry centrifugal separation device, a gas-liquid separator, a main cooler, and an evaporation concentration condensation device; the evaporation concentration condensation device comprises a preheater and an evaporation condenser; the first-effect evaporation device comprises a first-effect separator, a first-effect heater, and a first-effect circulation pump forming a circulation path; the second-effect evaporation device comprises a second-effect separator, a second-effect heater, and a second-effect circulation pump forming a circulation path; the third-effect evaporation device comprises a third-effect separator, a third-effect heater, and a third-effect circulation pump forming a circulation path. The present invention can realize the evaporation and extraction of salt from coking wastewater, and can prevent calcium sulfate scaling and achieve excellent energy saving in the process of evaporating and extracting salt from coking wastewater.

Description

Technical Field

[0001] The invention relates to a triple-effect evaporation system and process for evaporating and extracting salt from coking wastewater, belonging to the technical field of evaporation and concentration. Background Art

[0002] Coking wastewater is a type of wastewater that is currently produced in large quantities during the coking production process and is extremely difficult to treat. Its composition is complex, containing not only toxic and highly toxic substances such as phenols and cyanides, but also aromatic hydrocarbons, polycyclic aromatic hydrocarbons, heterocyclic aromatic hydrocarbons, etc. that are difficult to biodegrade. It also contains high levels of suspended solids, chlorine, sulfate, calcium, and magnesium ions. Its main composition is shown in Table 1 below. It is a high-concentration organic industrial wastewater that is difficult to treat and is one of the environmental protection problems in the coking industry.

[0003] The use of evaporation and concentration to convert coking wastewater into solid salt is an emerging treatment method in recent years. The solid coking waste salt produced after treatment is mainly used for coke quenching and coal blending. As a traditional evaporation process, multi-effect evaporation is based on the cascade utilization of steam to operate multiple evaporators in series. It has high thermal energy utilization efficiency, obvious energy-saving effect, safe and reliable system operation, and has wide application value in zero discharge of coking wastewater.

[0004] Table 1 Main components of coking high-salt wastewater

[0005]

[0006] 1. Prior art related to the present invention

[0007] 1.1. Technical solution of prior art 1

[0008] Chinese patent CN111777118A discloses a triple-effect evaporation device for treating saline wastewater, wherein the triple-effect evaporation device for treating saline wastewater comprises a feed tank, a feed pump, a first-effect evaporation system, a second-effect evaporation system, a third-effect evaporation system, a discharge pump, a steam condenser, a condensed water tank and a vacuum device; wherein the first-effect evaporation system comprises a first-effect circulation pump, a first-effect separator and a first-effect heat exchanger, and the first-effect separator forms a circulation passage with the first-effect circulation pump and the first-effect heat exchanger through a pipeline; the second-effect evaporation system comprises a second-effect circulation pump, a second-effect separator and a second-effect heat exchanger, and the second-effect separator forms a circulation passage with the second-effect circulation pump and the second-effect heat exchanger through a pipeline; the triple-effect evaporation system comprises a triple-effect circulation pump, a triple-effect separator and a triple-effect heat exchanger, and the triple-effect separator forms a circulation passage with the triple-effect circulation pump and the triple-effect heat exchanger through a pipeline;

[0009] A feed port is provided at the top of the feed tank, and an outlet is provided at the bottom. The outlet is connected to the bottom discharge pipe of the first-effect separator through a feed pump and a pipeline. The discharge port of the first-effect circulation pump is connected to the bottom discharge pipe of the second-effect separator through a pipeline. The discharge port of the second-effect circulation pump is connected to the bottom discharge pipe of the triple-effect separator through a pipeline. The discharge port of the triple-effect circulation pump is connected to the discharge pump through a pipeline. A hydrometer is provided on the feed tank, and the measuring head of the hydrometer is deeply inside the feed tank.

[0010] The shell side inlet of the first-effect heat exchanger is connected to the steam pipeline, and the shell side outlet of the first-effect heat exchanger is connected to the steam condenser through a pipeline; the top outlet of the first-effect separator is connected to the shell side inlet of the second-effect heat exchanger, and the shell side outlet of the second-effect heat exchanger is connected to the steam condenser through a pipeline; the top outlet of the second-effect separator is connected to the shell side inlet of the triple-effect heat exchanger, and the shell side outlet of the triple-effect heat exchanger is connected to the steam condenser through a pipeline; the outlet of the steam condenser is connected to the condensate tank, and the top outlet and bottom outlet of the condensate tank are respectively connected to the vacuum pump and the condensate pump through pipelines.

[0011] The device has a simple structure. When it is used to treat saline wastewater, pretreatment steps such as softening can be omitted. On the one hand, the supersaturation of salts such as calcium sulfate can be eliminated in time by regularly adding calcium sulfate seeds to the feed tank. On the other hand, a forced circulation pump is used to ensure sufficient circulation flow rate and material circulation volume in the three evaporation units to achieve the purpose of preventing scaling. At the same time, the first-effect evaporation system uses steam as a heat source, and the second-effect evaporation system and the third-effect evaporation system respectively use the secondary steam of the first-effect evaporation system and the secondary steam of the second-effect evaporation system as heat sources, thereby making full use of thermal energy and having low steam energy consumption.

[0012] 1.2. Disadvantages of the prior art 1

[0013] (1) The heat recovery method is not set up properly. On the one hand, the heat carried by the hot distilled water generated by each effect heat exchanger is not recovered; on the other hand, the secondary steam extracted from the top of the three-effect separator is cooled by circulating water in the steam condenser. About 20%-25% of the heat of the whole device is wasted by evaporation of circulating water. A large amount of heat carried by the three-effect secondary steam is not recycled, which not only causes high steam consumption of the whole device, but also increases the amount of circulating water replenishment, resulting in a waste of resources;

[0014] (2) The device is not fully configured and cannot meet the process requirements of evaporation, concentration, crystallization and solid-liquid separation of coking wastewater. In addition, the coking wastewater contains high levels of suspended solids and organic matter. The device lacks pre-treatment methods such as flocculation and filtration of raw water, which can easily cause excessive levels of suspended solids and organic matter in the three-effect separator, causing the three-effect circulating fluid to boil over and thus resulting in unqualified distilled water. Excessive levels of suspended solids in the three-effect circulating fluid can also lead to overly fine three-effect crystals, resulting in poor centrifugal effects. In severe cases, it can even lead to the inability to achieve solid-liquid separation.

[0015] (3) Regularly adding calcium sulfate seeds to the feed tank not only increases the material consumption cost of concentrated water evaporation, but also increases the amount of solid waste discharged.

[0016] 2. Prior Art II Related to the Present Invention

[0017] 2.1. Technical solution of prior art 2

[0018] Chinese patent CN107151035A discloses a salt extraction system and a salt extraction method for coal chemical desulfurization wastewater, wherein the salt extraction system for coal chemical desulfurization wastewater comprises a multi-effect separator, a multi-effect heater, a condenser and a vacuum pump, wherein the multi-effect separator comprises three-effect forced circulation evaporation devices connected in sequence, the feed port of the first-effect forced circulation evaporation device is connected to a preheater, and the discharge end of the three-effect forced circulation evaporation device is connected to a cooling crystallizer; the multi-effect heater comprises three-effect heaters connected in sequence, the first-effect heater is also connected to the feed end of the first-effect forced circulation evaporation device, the air inlet of the second-effect heater is connected to the exhaust port at the top of the first-effect forced circulation evaporation device, the air outlet of the second-effect heater is connected to the feed end of the second-effect forced circulation evaporation device, and the air inlet of the three-effect heater is connected to the exhaust port at the top of the first-effect forced circulation evaporation device. The outlet is connected to the exhaust port on the top of the second-effect forced circulation evaporator, and the outlet of the triple-effect heater is connected to the feed end of the triple-effect forced circulation evaporator; and the condenser is connected to the exhaust port on the top of the triple-effect forced circulation evaporator through a pipeline, and the vacuum pump is arranged on the exhaust pipeline of the condenser; wherein, the system also includes a vapor-liquid separator arranged between the first-effect forced circulation evaporator and the second-effect heater, the air inlet of the vapor-liquid separator is connected to the exhaust port on the top of the first-effect forced circulation evaporator, and the air outlet of the vapor-liquid separator is connected to the air inlet of the second-effect heater; the system also includes a plurality of axial flow pumps arranged corresponding to the three-effect forced circulation evaporators connected in sequence, and the plurality of axial flow pumps are respectively arranged between each effect forced circulation evaporator and each effect heater.

[0019] 2.2. Disadvantages of the Second Prior Art

[0020] (1) The heat recovery of the device is not thorough enough, and the overall energy consumption is high. Specifically, although the device recycles the heat of the high-temperature condensed water separated by the vapor-liquid separator for heating the raw water, it does not explain that all the steam extracted from the top of the three-effect forced circulation evaporator is condensed and recovered in the condenser, and the large amount of heat carried by the steam is not recovered (the medium used for steam cooling is not explained). About 15%-20% of the heat of the entire device is wasted, which not only causes high steam consumption of the entire device, but also causes energy waste;

[0021] (2) The device lacks the necessary anti-calcium sulfate scaling device, making it difficult to treat coking wastewater containing high concentrations of calcium ions and sulfate ions, and there is a risk of not being able to obtain solid crystalline salt. On the one hand, the device has a high operating temperature, with the operating temperature of the first effect reaching 100-120°C, far exceeding the temperature control range of ≤80°C required for large-scale crystallization of calcium sulfate. The device operates at 100-120°C, which can easily cause the heat exchange tube of the first effect heater to be blocked, and in severe cases, it may even cause the first effect heater to be scrapped;

[0022] (3) The device is only suitable for treating saline wastewater with high ammonium sulfate content, low suspended solids content and low COD content, and cannot meet the process requirements for evaporation, concentration, crystallization and solid-liquid separation of coking wastewater. Specifically, the content of suspended solids and organic matter in coking wastewater is relatively high. The device lacks pre-treatment methods such as flocculation and filtration of raw water, which can easily cause excessive suspended solids and organic matter content in the three-effect separator, causing the three-effect circulating liquid to boil and resulting in unqualified distilled water. In addition, excessive suspended solids in the three-effect circulating liquid will also lead to overly fine three-effect crystals, which will lead to poor centrifugal effect and even make it impossible to achieve solid-liquid separation in severe cases.

[0023] Therefore, providing a new triple-effect evaporation system and process for evaporating and extracting salt from coking wastewater has become a technical problem that urgently needs to be solved in the field. Summary of the invention

[0024] In order to solve the above-mentioned shortcomings and deficiencies, an object of the present invention is to provide a triple-effect evaporation system for evaporating and extracting salt from coking wastewater.

[0025] Another object of the present invention is to provide a triple-effect evaporation process for evaporating and extracting salt from coking wastewater. The system and process provided by the present invention can realize evaporating and extracting salt from coking wastewater, and can prevent calcium sulfate scaling and achieve excellent energy saving in the process of evaporating and extracting salt from coking wastewater.

[0026] In order to achieve the above objectives, the present invention provides a triple-effect evaporation system for evaporating and extracting salt from coking wastewater, wherein the triple-effect evaporation system for evaporating and extracting salt from coking wastewater comprises:

[0027] A first-effect evaporation device, a second-effect evaporation device, and a third-effect evaporation device, wherein the first-effect evaporation device comprises a first-effect separator, a first-effect heater, and a first-effect circulation pump constituting a circulation path; the second-effect evaporation device comprises a second-effect separator, a second-effect heater, and a second-effect circulation pump constituting a circulation path; the third-effect evaporation device comprises a third-effect separator, a third-effect heater, and a third-effect circulation pump constituting a circulation path;

[0028] The system further comprises: a first cyclone, a slurry centrifugal separation device, a gas-liquid separator, a main cooler and an evaporation concentration condensation device; the evaporation concentration condensation device comprises a preheater and an evaporation condenser;

[0029] The cold side inlet of the preheater is connected to the coking wastewater pipeline, and the cold side outlet is connected to the inlet of the spray device at the top of the evaporative condenser. The circulating water tank at the bottom of the evaporative condenser is connected to the evaporative cold circulation pump and the spray device of the evaporative condenser through a pipeline to form a circulation passage; the outlet of the circulating water tank at the bottom of the evaporative condenser is also connected to the feed port of the first-effect separator through a pipeline;

[0030] The shell side inlet of the first effect heater is connected to the steam pipeline, and the shell side outlet of the first effect heater is connected to the condensate inlet of the second effect heater through a pipeline; the steam outlet of the first effect separator is connected to the steam inlet of the second effect heater, and the shell side outlet of the second effect heater is connected to the condensate inlet of the triple effect heater through a pipeline; the steam outlet of the second effect separator is connected to the steam inlet of the triple effect heater, and the shell side outlet of the triple effect heater is connected to the main cooler through a pipeline, and the steam outlet of the triple effect separator is connected to the heat exchange tube inlet of the evaporative condenser through the pipeline via the gas-liquid separator, and the heat exchange tube outlet is connected to the inlet of the main cooler;

[0031] The feed inlet of the first-effect circulation pump is connected to the inlet of the first cyclone through a pipeline via the first-effect concentrated liquid pump, and the light component outlet and the heavy component outlet of the first cyclone are respectively connected to the feed inlet of the second-effect separator and the feed inlet of the first-effect circulation pump through pipelines; the feed inlet of the second-effect circulation pump is connected to the feed inlet of the third-effect separator through a pipeline via the second-effect concentrated liquid pump; the feed inlet of the third-effect circulation pump is connected to the slurry centrifugal separation device through a pipeline via the slurry production pump.

[0032] In the present invention, a gas-liquid separator is added between the triple-effect separator and the evaporative condenser, so that the triple-effect secondary steam can be separated into gas and liquid before entering the evaporative condenser to avoid boiling inside the triple-effect separator and thus causing the conductivity of the distilled water outlet to exceed the standard.

[0033] In the present invention, the evaporative condenser (abbreviated as evaporative cooler) is a conventional device, and a fan, a spraying device and a heat exchange pipe are arranged on the upper part of the evaporative cooler, and a circulating water tank is arranged on the bottom.

[0034] In the present invention, the feed inlets of the first-effect separator, the second-effect separator and the third-effect separator are all located at the lower part of each effect separator. Furthermore, the feed inlets are all located below the liquid level of each effect separator.

[0035] In the present invention, the flow rate of each effect circulation pump used is relatively large, which can reach 2000m 3 / h or more, and at the same time, each effect circulation pump only needs a head of about 3-4m to meet the circulation requirements of each effect during operation, which will result in the outlet pressure of each effect circulation pump being only 0.03-0.04MPa, and the diversion effect of the cyclone is poor under this pressure. Therefore, a first-effect concentrated liquid pump, a second-effect concentrated liquid pump, and a slurry extraction pump are added to the system described in the present invention. The first-effect concentrated liquid pump, the second-effect concentrated liquid pump, and the slurry extraction pump are all used for the transfer of materials. The purpose of setting them is to minimize the head of the first-effect circulation pump, the second-effect circulation pump, and the third-effect circulation pump while ensuring the conveying pressure of the crystal-containing material and the diversion effect of the cyclone, so as to achieve the purpose of reducing power consumption.

[0036] In the present invention, a conductivity detector is provided at the bottom of the main cooler, and a probe of the conductivity detector penetrates below the liquid level in the main cooler.

[0037] As a specific embodiment of the above system of the present invention, the slurry centrifugal separation device includes a second cyclone, a cooling crystallizer and a centrifuge; the feed port of the triple-effect circulation pump is connected to the inlet of the second cyclone through a pipeline via the slurry production pump, and the light component outlet and the heavy component outlet of the second cyclone are respectively connected to the feed port of the triple-effect circulation pump and the inlet of the cooling crystallizer through pipelines; the outlet of the cooling crystallizer is connected to the inlet of the centrifuge through a pipeline.

[0038] In the present invention, the cooling crystallizer is a jacket structure, and concentrated water with a temperature of about 32° C. is used to cool the jacket. The heated concentrated water is sent to a first-effect separator as a raw material for evaporation and salt extraction.

[0039] In the present invention, a stirrer is provided on the top of the cooling crystallizer to prevent the crystallized material from settling and clogging pipelines and equipment.

[0040] In the present invention, the centrifuge is preferably a horizontal spiral sedimentation centrifuge.

[0041] As a specific embodiment of the above system of the present invention, the outlet of the circulating water tank at the bottom of the evaporative condenser is connected to the water side inlet of the main cooler and the water inlet of the cooling crystallizer through a pipeline via a concentrated water pump, and the water side outlet of the main cooler and the water outlet of the cooling crystallizer are connected to the feed port of the first effect separator through a pipeline after being collected. Correspondingly, the raw water is circulated and sprayed in the evaporative condenser, and concentrated water with a mass concentration of 8.5%-9.5% and a temperature of 20-35°C is obtained in the circulating water tank at the bottom of the evaporative condenser. The concentrated water is pressurized by the concentrated water pump and sent to the main cooler and the cooling crystallizer respectively, on the one hand to cool the two equipments, and on the other hand to heat the concentrated water to recover part of the heat. The heated concentrated water is sent to the feed port of the first effect separator as a raw material for evaporation and salt extraction.

[0042] As a specific embodiment of the above system of the present invention, a remote temperature meter is provided at the outlet of the concentrate pump to detect the temperature of the externally supplied concentrate.

[0043] As a specific embodiment of the above-mentioned system of the present invention, a distilled water tank is provided at the bottom of the main cooler, and the outlet of the distilled water tank is connected to the hot side inlet of the preheater through a pipeline via a distilled water pump, and the hot side outlet of the preheater is connected to the distilled water delivery pipeline.

[0044] As a specific embodiment of the above system of the present invention, the top outlet of the main cooler is connected to the vacuum pump through a pipeline to ensure that the vacuum gauge pressure of the system is -85kPa to -95kPa.

[0045] As a specific embodiment of the above system of the present invention, a steam regulating valve and a steam ejector are sequentially installed on the steam pipeline. In a specific embodiment of the present invention, the external steam enters the high-pressure inlet of the steam ejector after being pressure-regulated by the steam regulating valve, and the outlet of the steam ejector is connected to the shell side inlet of the first-effect heater through the steam pipeline to deliver the steam to the shell side of the first-effect heater.

[0046] As a specific embodiment of the above system of the present invention, the steam outlet of the second-effect separator is provided with a bypass interface, and the bypass interface is connected to the low-pressure steam inlet of the steam ejector through a pipeline.

[0047] As a specific embodiment of the above system of the present invention, the single-effect heater includes two heaters arranged in parallel. When the effect of one of the heaters decreases, it can be deactivated separately to achieve the cleaning of the heater without stopping production.

[0048] As a specific embodiment of the system described above in the present invention, the system also includes a pretreatment device, which includes a sedimentation tank, a raw water tank and a plate and frame filter press; wherein the sedimentation tank is provided with a feed port at the top, an outlet in the middle, and a mud discharge port at the bottom; the outlet of the sedimentation tank is connected to the inlet at the top of the raw water tank through a pipeline, and the bottom outlet of the raw water tank is connected to the cold side inlet of the preheater through a pipeline via a raw water pump; the mud discharge port is connected to the inlet of the plate and frame filter press through a pipeline via a filter pump, and the filtered water outlet of the plate and frame filter press is connected to the inlet at the top of the raw water tank through a pipeline.

[0049] As a specific embodiment of the above system of the present invention, a pH detector is provided on the side of the raw water tank, and the probe of the pH detector is inserted below the liquid level in the raw water tank to detect the pH value of the raw water.

[0050] As a specific embodiment of the system described above in the present invention, the slurry centrifugal separation device also includes a mother liquor tank and a mother liquor pump, the mother liquor outlet of the centrifuge is connected to the mother liquor tank inlet through a pipeline, and the outlet of the mother liquor tank is connected to the inlet of the sedimentation tank through a pipeline via the mother liquor pump.

[0051] As a specific embodiment of the above system of the present invention, the cooling water outlet of the gas-liquid separator is connected to the top inlet of the raw water tank through a pipeline to deliver the cooling water separated by the gas-liquid separator to the raw water tank.

[0052] As a specific embodiment of the above system of the present invention, the distilled water pipeline of the first-effect heater, the distilled water pipeline of the second-effect heater and the distilled water pipeline of the third-effect heater (i.e., the pipeline connected to the shell outlet of each effect heater) are respectively provided with U-shaped water seals to ensure that the steam pressure in the shell of each effect heater is in a stable state;

[0053] Preferably, the water seal height of the U-shaped water seal is not less than 1.5 m.

[0054] In the system provided by the present invention, the first-effect evaporator, the second-effect evaporator, the third-effect evaporator, the gas-liquid separator, the steam ejector, the cyclone, etc. are all conventional equipment.

[0055] On the other hand, the present invention also provides a triple-effect evaporation process for evaporating and extracting salt from coking wastewater, wherein the process comprises:

[0056] (1) After the pretreated coking wastewater is heated by heat exchange in a preheater, it is sent to an evaporative condenser and heat exchanged with triple-effect secondary steam in the evaporative condenser. During the heat exchange process, the pretreated coking wastewater is heated and continuously evaporated and concentrated to obtain concentrated water, which is sent to a single-effect separator as a raw material for evaporation and salt extraction;

[0057] (2) Concentrated water is continuously pumped out by the first-effect circulation pump and enters the first-effect separator for evaporation after heat exchange with external steam in the first-effect heater, generating first-effect secondary steam and first-effect concentrated liquid;

[0058] (3) The first-effect concentrated liquid is pumped out by the first-effect concentrated liquid pump and sent to the first cyclone for classification treatment. After the treatment, the upper layer is a low-solid content solution and the lower layer is a high-solid content calcium sulfate slurry; the calcium sulfate slurry is sent back to the feed port of the first-effect circulation pump to continue to participate in the circulation; the low-solid content solution enters the feed port of the second-effect separator and is continuously drawn by the second-effect circulation pump into the second-effect heater and heat-exchanged with the first-effect secondary steam and external steam to generate condensed water and a small amount of non-condensable gas, and then enters the second-effect separator for evaporation to generate second-effect secondary steam and second-effect concentrated liquid;

[0059] (4) The second-effect concentrated liquid is pumped out by the second-effect concentrated liquid pump and sent to the feed port of the three-effect separator. It is continuously pumped by the three-effect circulating pump into the three-effect heater and heat-exchanged with part of the second-effect secondary steam and the condensed water and a small amount of non-condensable gas generated in the second-effect heater. After heat exchange, it enters the three-effect separator for re-evaporation to generate three-effect secondary steam and three-effect crystal slurry. The condensed water and a small amount of non-condensable gas generated after heat exchange enter the main cooler for heat exchange and cooling to recover distilled water and heat.

[0060] (5) The crystal slurry is extracted by the crystal slurry extraction pump and then enters the crystal slurry centrifugal separation device, and solid salt and mother liquor are obtained after classification, cooling crystallization and centrifugal separation in the crystal slurry centrifugal separation device.

[0061] As a specific embodiment of the above process of the present invention, the mass concentration of total dissolved solids (TDS content) in the coking wastewater is about 6%-8%, and the suspended matter concentration is 100-300 mg / L.

[0062] As a specific embodiment of the process described above in the present invention, the process also includes pretreatment of coking wastewater, and the pretreatment includes: using the pretreatment device described above to settle and filter the coking wastewater to obtain pretreated coking wastewater (referred to as raw water) and filter residue, and the filter residue is mixed with coal after being squeezed and dehydrated.

[0063] As a specific embodiment of the process described above, the suspended solids concentration of the pretreated coking wastewater is less than 30 mg / L. In the present invention, the suspended solids concentration in the raw water is less than 30 mg / L, which can reduce the COD content of the three-effect crystal slurry, prevent the three-effect separator from boiling, and prevent the crystallized salt from being too small.

[0064] As a specific embodiment of the process described above, in step (1), the raw water heated by heat exchange is sent to an evaporative condenser and is heat exchanged with triple-effect secondary steam in the evaporative condenser. During the heat exchange process, the pretreated coking wastewater is heated and continuously evaporated and concentrated to obtain concentrated water, including:

[0065] The raw water heated by heat exchange is sent to the top of the evaporative condenser for spraying. The raw water is continuously extracted and sprayed by the evaporative cooling circulation pump, and heat is exchanged with the three-effect secondary steam in the heat exchange tube of the evaporative condenser. During the heat exchange process, the raw water is heated and continuously evaporated and concentrated, and concentrated water is continuously produced;

[0066] The triple-effect secondary steam in the heat exchange tube of the evaporative condenser is cooled into distilled water and a small amount of non-condensable gas, which are then sent to the main cooler for further cooling.

[0067] As a specific embodiment of the process described above in the present invention, in step (1), the temperature of the pretreated coking wastewater (i.e., raw water) is 30-50°C. Too low a temperature will increase the energy consumption of the system, while too high a temperature will reduce the pretreatment effect and increase odor volatilization.

[0068] As a specific embodiment of the above process of the present invention, in step (1), the triple-effect secondary steam is triple-effect secondary steam after gas-liquid separation in a gas-liquid separator, and the cooling water obtained by separation can be sent to the raw water tank of the pretreatment device for re-evaporation. In particular, the triple-effect secondary steam is sent to the evaporative condenser after gas-liquid separation to avoid excessive conductivity of distilled water outlet caused by explosive boiling inside the triple-effect separator.

[0069] In step (1), the raw water after heat exchange and temperature increase is exchanged with the triple-effect secondary steam after gas-liquid separation in the evaporative condenser. During the heat exchange process, the pretreated coking wastewater is heated and continuously evaporated and concentrated to obtain concentrated water; the triple-effect secondary steam is heat-exchanged with the raw water to obtain condensed water and a small amount of non-condensable gas, and the condensed water and the small amount of non-condensable gas are sent to the main cooler to exchange heat and cool the low-temperature concentrated water produced in the evaporative condenser. The temperature of the non-condensable gas after cooling is ≤35°C. The non-condensable gas after cooling is extracted by a vacuum pump to always maintain the vacuum degree in the triple-effect separator at -85kPa to -95kPa, such as about -90kPa; the recovered condensed water (distilled water) is collected in the distilled water tank at the bottom of the main cooler, pressurized by the distilled water pump, and then enters the preheater for heat exchange, and the generated distilled water is finally used for water replenishment in the production system.

[0070] As a specific embodiment of the above process of the present invention, the mass concentration of total dissolved solids in the concentrated water is 8.5%-9.5%, and the temperature is 20-35°C.

[0071] As a specific embodiment of the above process of the present invention, the heat exchange and temperature raising of the pretreated coking wastewater in the preheater comprises:

[0072] The raw water pump is turned on to heat the raw water with the distilled water in the preheater to increase the temperature. The distilled water may be the distilled water in the distilled water tank provided at the bottom of the main cooler, and the distilled water is delivered to the hot side inlet of the heat exchanger by the distilled water pump.

[0073] As a specific embodiment of the process described above in the present invention, the process further comprises, after step (1), the concentrated water is pressurized by the concentrated water pump and then subjected to heat exchange and temperature increase in the main cooler and the cooling crystallizer, and then the heated concentrated water is sent to the first-effect separator as a raw material.

[0074] As a specific embodiment of the process described above, in step (2), concentrated water is continuously extracted by a first-effect circulation pump and heat-exchanged with a mixed gas of external steam and part of the second-effect secondary steam in a first-effect heater before entering a first-effect separator for evaporation;

[0075] Preferably, the pressure of the mixed gas is 60-70 kPa and the temperature is 86-90°C.

[0076] As a specific embodiment of the process described above in the present invention, in step (2), the external steam (low-pressure waste heat steam) from the external network enters the high-pressure inlet of the steam ejector after being reduced in pressure by the steam regulating valve, and part of the second-effect secondary steam enters the low-pressure steam inlet of the steam ejector through the pipeline, and the external steam and part of the second-effect secondary steam are mixed in the steam ejector, and the resulting mixed gas enters the first-effect heater for heat exchange.

[0077] The present invention mixes external steam and part of the second-effect secondary steam to obtain a mixed gas, and sends the mixed gas to a first-effect heater for heat exchange, thereby recovering part of the heat of the second-effect secondary steam.

[0078] As a specific implementation of the process described above in the present invention, the mass concentration of total dissolved solids in the first-effect concentrated liquid is 12%-13%.

[0079] As a specific embodiment of the process described above, the temperature of the first-effect concentrated liquid is ≤78° C., preferably 76-78° C. In the present invention, controlling the temperature of the first-effect concentrated liquid to ≤78° C. can prevent excessive temperature from causing a large amount of calcium sulfate to precipitate and block the equipment.

[0080] Sulfate radicals and calcium ions in the coking wastewater will precipitate in the form of solid calcium sulfate in the first-effect evaporation device. After the first-effect concentrated liquid is treated by the first cyclone, the calcium sulfate slurry is sent back to the feed port of the first-effect circulating pump to continue to participate in the circulation, which can increase the concentration of solid calcium sulfate in the first-effect circulating liquid (i.e., the circulating liquid involved in the first-effect separator), that is, it can ensure that there are enough seed crystals in the first-effect flow. During the evaporation process, the calcium sulfate in the salt solution will not be deposited on the pipe wall, but will preferentially adhere to the surface of the suspended calcium sulfate seed crystals, thereby achieving the purpose of anti-scaling.

[0081] As a specific embodiment of the process described above of the present invention, the temperature of the condensed water and a small amount of non-condensable gas generated by the external steam in the first-effect heater after heat exchange is about 3-6°C higher than the temperature of the first-effect secondary steam. Therefore, in step (3), the condensed water and a small amount of non-condensable gas generated by the external steam after heat exchange can enter the shell side of the second-effect heater together with the first-effect secondary steam and the low-solid content solution in the tube side for heat exchange, so as to fully recover the heat of the condensed water and the non-condensable gas;

[0082] Among them, when a U-shaped water seal is provided on the distilled water pipeline of the first-effect heater, the condensed water and a small amount of non-condensable gas generated by the external steam after heat exchange enter the shell side of the second-effect heater through the U-shaped water seal for heat exchange and cooling. The setting of the U-shaped water seal can ensure that the steam pressure in the shell side of the first-effect heater is in a stable state.

[0083] As a specific embodiment of the above process of the present invention, in step (3), the temperature of the second-effect secondary steam is 64-68°C.

[0084] As a specific embodiment of the process described above, in step (3), the mass concentration of total dissolved solids in the second-effect concentrated liquid is 22%-22.5%.

[0085] Among them, the present invention does not make specific requirements on the solid contents of the low-solid content solution and the high-solid content calcium sulfate slurry in step (3). Those skilled in the art can routinely judge that the first-effect concentrated liquid is pumped out by the first-effect concentrated liquid pump and sent to the first cyclone for classification treatment, and the upper layer is the low-solid content solution, and the lower layer is the high-solid content calcium sulfate slurry.

[0086] As a specific embodiment of the process described above in the present invention, in step (4), the mass concentration of the total dissolved solids in the slurry is 45%-55%.

[0087] As a specific embodiment of the above process of the present invention, in step (4), the temperature of the triple-effect secondary steam is 48-52°C.

[0088] In step (4) of the above process of the present invention, the condensed water and a small amount of non-condensable gas generated after heat exchange enter the main cooler for heat exchange and cooling to recover distilled water and heat. Wherein, when a U-shaped water seal is provided on the distilled water pipeline of the triple-effect heater, the condensed water and a small amount of non-condensable gas generated after heat exchange enter the main cooler for heat exchange and cooling after passing through the U-shaped water seal. The setting of the U-shaped water seal can ensure that the steam pressure in the shell of the triple-effect heater is in a stable state; in addition, the cooling medium used for heat exchange and cooling can be the low-temperature concentrated water produced in the evaporative condenser, and the temperature of the non-condensable gas after cooling is ≤35°C. The non-condensable gas after cooling can be extracted by a vacuum pump to always keep the vacuum degree in the triple-effect separator at -85kPa to -95kPa, such as about -90kPa; the recovered condensed water (distilled water) is collected in the distilled water tank at the bottom of the main cooler, and is pressurized by the distilled water pump and then enters the preheater for heat exchange, and the generated distilled water is finally used for water replenishment in the production system.

[0089] As a specific embodiment of the process described above, the circulation flow rate of the circulating fluid in the tubes of the first-effect heater, the second-effect heater and the third-effect heater is ensured to be not less than 2 m / s by means of the circulation pumps of each effect, so as to achieve the purpose of anti-scaling.

[0090] As a specific embodiment of the process described above of the present invention, in step (5), the slurry is extracted by the slurry extraction pump and then enters the slurry centrifugal separation device, and solid salt and mother liquor are obtained after classification, cooling crystallization and centrifugal separation in the slurry centrifugal separation device, including:

[0091] The slurry is extracted by the slurry extraction pump and sent to the second cyclone for classification treatment. After the treatment, the upper layer is a low-solid content solution and the lower layer is a high-solid content solution. The low-solid content solution returns to the feed port of the triple-effect circulation pump to continue circulation, and the high-solid content solution enters the cooling crystallizer for cooling crystallization, and then centrifugally separated in a centrifuge to obtain solid salt and mother liquor.

[0092] Among them, the present invention does not make specific requirements on the solid content of the low-solid content solution and the high-solid content solution. Those skilled in the art can routinely judge that the upper layer of the slurry after the grading treatment in the second cyclone is a low-solid content solution, and the lower layer is a high-solid content solution.

[0093] In the process described above, returning the low-solid content solution to the outlet pipe of the triple-effect separator for continued circulation can, on the one hand, increase the discharge of solid materials in the triple-effect circulating liquid, especially solid suspended matter such as calcium sulfate and sludge, and reduce the probability of explosion in the triple-effect separator; on the other hand, it can increase the solid content in the cooling crystallizer and reduce the discharge of mother liquor generated after centrifugation.

[0094] As a specific embodiment of the process described above of the present invention, the temperature of the condensed water and a small amount of non-condensable gas generated after heat exchange in the second-effect heater is about 3-6°C higher than the temperature of the second-effect secondary steam. Therefore, in step (4), the condensed water and a small amount of non-condensable gas generated after heat exchange in the second-effect heater can enter the shell side of the three-effect heater and perform heat exchange with part of the second-effect secondary steam and the second-effect concentrated liquid in the tube side to fully recover the heat of the condensed water and the non-condensable gas.

[0095] Among them, when a U-shaped water seal is provided on the distilled water pipeline of the second-effect heater, the condensed water and a small amount of non-condensable gas generated after heat exchange in the second-effect heater enter the shell side of the three-effect heater after passing through the U-shaped water seal for heat exchange and cooling. The setting of the U-shaped water seal can ensure that the steam pressure in the shell side of the two-effect heater is in a stable state.

[0096] As a specific embodiment of the process described above, in the step (5), after cooling and crystallization, the temperature of the outlet slurry obtained is 35-45°C.

[0097] As a specific embodiment of the process described above, in step (5), after cooling and crystallization, the solid content of the obtained outlet slurry is 30%-50%, so that the salt dissolved in the slurry (salt slurry) can be precipitated quickly to increase the salt yield.

[0098] As a specific embodiment of the process described above, the cooling medium used for cooling crystallization in step (5) is low-temperature concentrated water produced in the evaporative condenser, and its temperature is 20-32°C.

[0099] In a specific embodiment of the present invention, step (5) includes the following specific steps:

[0100] The slurry is extracted by the slurry extraction pump and sent to the second cyclone for classification treatment. After the treatment, the upper layer is a low-solid content solution and the lower layer is a high-solid content solution. The low-solid content solution returns to the three-effect separator to continue to circulate, and the high-solid content solution enters the cooling crystallizer. Under stirring conditions, the high-solid content solution and the low-temperature concentrated water in the interlayer of the cooling crystallizer are heat exchanged. After cooling and crystallization, the temperature of the obtained outlet slurry is 35-45°C and the solid content is 30%-50%. The outlet slurry is then sent to a centrifuge for centrifugal separation to obtain solid salt and mother liquor;

[0101] Part of the mother liquor is sent back to the pretreatment process of coking wastewater. After mixing with the coking wastewater, it is re-sedimented and centrifuged to increase the solid salt output. Part of the mother liquor can also be regularly extracted for coal blending treatment to prevent the three-effect separator from boiling over due to excessive COD.

[0102] The triple-effect evaporation system and process for evaporating and extracting salt from coking wastewater provided by the present invention can achieve the following unexpected technical effects:

[0103] (1) The present invention adopts a unique energy-saving design, which greatly reduces the unit steam consumption of the system. Specifically, on the one hand, a set of steam ejectors is added to the system, using 0.6MPa external steam as power, and at the same time returning part of the second-effect secondary steam to the first-effect heater for heating, which greatly increases the pressure of the second-effect secondary steam and makes extensive use of the enthalpy value of the second-effect secondary steam, reducing the use of external steam; on the other hand, pre-treated raw water is used instead of circulating water or low-temperature water as circulating cooling water for evaporative cooling to cool the three-effect secondary steam, wherein the heat of the three-effect secondary steam is used for raw water heating and concentration, and the circulating evaporated raw water is used for cooling the three-effect secondary steam. One heat is used twice, and the heat utilization efficiency is greatly improved, so that both distilled water and a large amount of heat are recovered. In summary, the present invention makes full use of the thermal energy of steam, and the steam consumption of evaporating wastewater is only about 260kg / ton of water, which is more than 18% lower than the steam consumption of conventional three-effect evaporation systems (320-340kg / ton of water);

[0104] (2) The system provided by the present invention fully considers the characteristics of coking wastewater and eliminates the conventional softening pretreatment step; the use of the first cyclone to recover calcium sulfate seeds can timely eliminate the supersaturation of salts such as calcium sulfate, and at the same time, the purpose of anti-scaling is achieved by combining the control of the heating temperature (i.e., the temperature of the first-effect concentrated liquid, ≤78°C) and the reasonable design of the circulation flow rate; in addition, the first-effect heater that is prone to scaling is replaced by two units running in parallel, which realizes online cleaning without stopping production, and the whole system runs stably, and the cleaning cycle is greatly extended;

[0105] (3) The present invention recycles part of the mother liquor after centrifugation into the system for evaporation and salt production, and uses a pretreatment device to settle and filter the coking high-salt wastewater, thereby increasing the solid salt output, reducing the mother liquor discharge, avoiding the problems of boiling and excessive crystallization caused by excessive COD of the three-effect slurry, and ensuring the continuous and effective operation of the centrifuge. BRIEF DESCRIPTION OF THE DRAWINGS

[0106] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0107] Figure 1 A schematic structural diagram of a triple-effect evaporation system for evaporating and extracting salt from coking wastewater provided in an embodiment of the present invention.

[0108] Description of main figures:

[0109] Figure 1 middle:

[0110] 1. Evaporative condenser; 2. First-effect separator; 3. Second-effect separator; 4. Third-effect separator; 5. First-effect heater; 6. Second-effect heater; 7. Third-effect heater; 8. First-effect circulation pump; 9. Second-effect circulation pump; 10. Third-effect circulation pump; 11. First-effect concentrate pump; 12. Second-effect concentrate pump; 13. Slurry extraction pump; 14. Steam regulating valve; 15. Steam ejector; 16. Main cooler; 17. Vacuum pump; 18. Distilled water pump; 19. Cooling crystallizer; 20. Centrifuge; 21. First cyclone; 22. Second cyclone; 23. Evaporative cooling circulation pump; 24. Preheater; 25. Gas-liquid separator; 26. Concentrate pump. DETAILED DESCRIPTION

[0111] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical scheme of the present invention is now described in detail in conjunction with the following specific embodiments, but it should not be understood as limiting the applicable scope of the present invention.

[0112] It should be noted that the term "comprises" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, technique, system, product or equipment that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, techniques, systems, products or equipment.

[0113] In the present invention, the directions or positional relationships indicated by the terms "upper", "lower", "inner", "middle", "top" and "bottom" are based on the directions or positional relationships shown in the drawings. These terms are mainly used to better describe the present invention and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific direction, or to be constructed and operated in a specific direction.

[0114] In addition, some of the above terms may be used to express other meanings in addition to indicating orientation or positional relationship. For example, the term "on" may also be used to express a certain dependency or connection relationship in some cases. For those skilled in the art, the specific meanings of these terms in the present invention can be understood according to specific circumstances.

[0115] In addition, the terms "disposed" and "connected" should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection, or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, elements or components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0116] Example 1

[0117] This embodiment provides a triple-effect evaporation system for evaporating and extracting salt from coking wastewater, and its structural schematic diagram is shown in FIG. Figure 1 As shown, from Figure 1 It can be seen that the system includes: a first-effect evaporation device, a second-effect evaporation device, and a third-effect evaporation device. The first-effect evaporation device includes a first-effect separator 2, a first-effect heater 5, and a first-effect circulation pump 8. The first-effect separator 2 forms a circulation passage with the first-effect circulation pump 8 and the first-effect heater 5 through a pipeline;

[0118] The two-effect evaporation device comprises a two-effect separator 3, a two-effect heater 6 and a two-effect circulation pump 9. The two-effect separator 3 forms a circulation passage with the two-effect circulation pump 9 and the two-effect heater 6 through a pipeline;

[0119] The triple-effect evaporation device comprises a triple-effect separator 4, a triple-effect heater 7 and a triple-effect circulation pump 10. The triple-effect separator 4 forms a circulation passage with the triple-effect circulation pump 10 and the triple-effect heater 7 through a pipeline;

[0120] The system further comprises: a first-effect concentrated liquid pump 8, a second-effect concentrated liquid pump 9, a first cyclone 21, a slurry centrifugal separation device, a gas-liquid separator 25, a main cooler 16 and an evaporative concentration condensing device; the evaporative concentration condensing device comprises a preheater 24, an evaporative condenser 1 and an evaporative cooling circulation pump 23; the outlet of the circulating water tank at the bottom of the evaporative condenser 1 is connected to the water side inlet of the main cooler 16 and the water inlet of the cooling crystallizer 19 through a pipeline via a concentrated water pump 26, and the water side outlet of the main cooler 16 and the water outlet of the cooling crystallizer 19 are connected to the feed port of the first-effect separator 2 through a pipeline after being collected;

[0121] The outlet of the raw water pump is connected to the cold side inlet of the preheater 24 through a pipeline, and the cold side outlet is connected to the inlet of the spray device at the top of the evaporative condenser 1. The circulating water tank at the bottom of the evaporative condenser 1 is connected to the evaporative cold circulation pump 23 and the spray device of the evaporative condenser 1 through a pipeline to form a circulation passage;

[0122] The external steam enters the high-pressure inlet of the steam ejector 15 after being pressure-regulated by the steam regulating valve 14. The outlet of the steam ejector 15 is connected to the shell-side inlet of the first-effect heater 5 through a pipeline, and the shell-side outlet of the first-effect heater 5 is connected to the condensate inlet of the second-effect heater 6 through a pipeline; the top steam outlet of the first-effect separator 2 is connected to the steam inlet of the second-effect heater 6, and the shell-side outlet of the second-effect heater 6 is connected to the condensate inlet of the triple-effect heater 7 through a pipeline; the top steam outlet of the second-effect separator 3 is connected to the steam inlet of the triple-effect heater 7, and the shell-side outlet of the triple-effect heater 7 is connected to the main cooler 16 through a pipeline, and the steam outlet of the triple-effect separator 4 is connected to the inlet of the gas-liquid separator 25 through a pipeline, and the top gas outlet of the gas-liquid separator 25 is connected to the heat exchange tube inlet of the evaporative condenser 1 through a pipeline, and the heat exchange tube outlet is connected to the inlet of the main cooler 16;

[0123] The feed port of the first-effect circulation pump 8 is connected to the inlet of the first cyclone 21 through a pipeline via the first-effect concentrated liquid pump 11, and the top light component outlet and the bottom heavy component outlet of the first cyclone 21 are respectively connected to the lower feed port of the second-effect separator 3 and the feed port of the first-effect circulation pump 8 through pipelines; the feed port of the second-effect circulation pump 9 is connected to the lower feed port of the triple-effect separator 4 through a pipeline via the second-effect concentrated liquid pump 12; the feed port of the triple-effect circulation pump 10 is connected to the slurry centrifugal separation device through a pipeline via the slurry production pump 13.

[0124] In this embodiment, the slurry centrifugal separation device includes a second cyclone 22, a cooling crystallizer 19 and a centrifuge 20; the feed port of the triple-effect circulation pump 10 is respectively provided with a first bypass and a second bypass, the first bypass is connected to the inlet of the second cyclone 22 through a pipeline via the slurry extraction pump 13, and the top light component outlet of the second cyclone 22 is connected to the second bypass through a pipeline; wherein the first bypass is close to the bottom outlet of the triple-effect separator 4, and the second bypass is close to the feed port of the triple-effect circulation pump 10; this design enables the slurry extraction pump 13 to extract the slurry with a higher solid content at the bottom outlet of the triple-effect separator 4 for separation, and the separated light component with a lower solid content is directly returned to the outlet pipeline of the triple-effect separator 4 (or the feed port of the triple-effect circulation pump 10) and then directly enters the triple-effect circulation pump for reheating;

[0125] The bottom heavy component outlet of the second cyclone 22 is connected to the inlet of the cooling crystallizer 19 through a pipeline; the outlet of the cooling crystallizer 19 is connected to the inlet of the centrifuge 20 through a pipeline.

[0126] In this embodiment, a distilled water tank is provided at the bottom of the main cooler 16, and the outlet of the distilled water tank is connected to the hot side inlet of the preheater 24 through a pipeline via a distilled water pump 18, and the hot side outlet of the preheater 24 is connected to the distilled water delivery pipeline.

[0127] In this embodiment, the top outlet of the main cooler 16 is connected to the vacuum pump 17 through a pipeline to ensure that the vacuum gauge pressure of the system is -85 kPa to -95 kPa.

[0128] In this embodiment, a bypass interface is provided at the top steam outlet of the second-effect separator 3 , and the bypass interface is connected to the low-pressure steam inlet of the steam ejector 15 through a pipeline.

[0129] In this embodiment, the single-effect heater 5 includes two heaters arranged in parallel.

[0130] In this embodiment, the system also includes a pretreatment device, which includes a sedimentation tank, a raw water tank and a plate and frame filter press; wherein the sedimentation tank is provided with a feed port at the top, an outlet in the middle, and a mud discharge port at the bottom; the outlet of the sedimentation tank is connected to the top inlet of the raw water tank through a pipeline, and the bottom outlet of the raw water tank is connected to the cold side inlet of the preheater 24 through a pipeline via a raw water pump; the mud discharge port is connected to the inlet of the plate and frame filter press through a pipeline via a filter pump, and the filtered water outlet of the plate and frame filter press is connected to the top inlet of the raw water tank through a pipeline.

[0131] In this embodiment, a pH detector is provided on the side of the raw water tank, and a probe of the pH detector is inserted below the liquid level in the raw water tank to detect the pH value of the raw water.

[0132] In this embodiment, the slurry centrifugal separation device also includes a mother liquor tank and a mother liquor pump. The mother liquor outlet of the centrifuge 20 is connected to the mother liquor tank inlet through a pipeline, and the mother liquor tank outlet is connected to the top inlet of the sedimentation tank through a pipeline via the mother liquor pump.

[0133] In this embodiment, the feed inlets of the first-effect separator 2, the second-effect separator 3 and the third-effect separator 4 are all located below the liquid level of each effect separator.

[0134] In this embodiment, a conductivity detector is provided at the bottom of the main cooler 16, and a probe of the conductivity detector penetrates below the liquid level in the main cooler.

[0135] In this embodiment, the cooling crystallizer 19 is a jacket structure, and raw water with a temperature of about 32° C. is used for cooling in the jacket, and the heated raw water is sent to the lower feed port of the first-effect separator 2 .

[0136] In this embodiment, a stirrer is provided on the top of the cooling crystallizer 19 to prevent the crystallized material from settling and clogging the pipeline and equipment.

[0137] In this embodiment, the centrifuge 20 is a horizontal spiral sedimentation centrifuge.

[0138] In this embodiment, a remote temperature meter is provided at the outlet of the evaporative cooling circulation pump 23 to detect the temperature of the externally supplied cooling water.

[0139] In this embodiment, the cooling water outlet of the gas-liquid separator 25 is connected to the top inlet of the raw water tank through a pipeline, so as to deliver the cooling water separated by the gas-liquid separator 25 to the raw water tank.

[0140] In this embodiment, the distilled water pipeline of the first effect heater 5, the distilled water pipeline of the second effect heater 6 and the distilled water pipeline of the third effect heater 7 are respectively provided with U-shaped water seals to ensure that the steam pressure in the shell of each effect heater is in a stable state;

[0141] Wherein, the water seal height of the U-shaped water seal is not less than 1.5m.

[0142] In this embodiment, unless otherwise specified, all devices used in the system are conventional devices, which can be obtained by commercial purchase or self-built.

[0143] Example 2

[0144] This embodiment provides a triple-effect evaporation process for evaporating and extracting salt from coking wastewater, wherein the process is implemented using the triple-effect evaporation system for evaporating and extracting salt from coking wastewater provided in Example 1, and includes the following specific steps:

[0145] Step 1, pre-treating the coking wastewater, the pre-treatment comprising: using the pre-treatment device in the above embodiment 1 to settle and filter the coking wastewater to obtain pre-treated coking wastewater (referred to as raw water) and filter residue, and the filter residue is then subjected to coal blending after being squeezed and dehydrated;

[0146] The total dissolved solid content (mass concentration) of the coking wastewater is 7%-8%, and the suspended solid concentration is 100-300 mg / L; based on the total volume of the pretreated coking wastewater, the suspended solid concentration is <30 mg / L;

[0147] Step 2: Turn on the raw water pump, heat the pretreated coking wastewater in the preheater and heat it up, then send the raw water after heat exchange to the top of the evaporative condenser for spraying. The raw water is continuously extracted and sprayed by the evaporative cooling circulation pump, and heat is exchanged with the triple-effect secondary steam in the heat exchange tube of the evaporative condenser. During the heat exchange process, the raw water is heated and continuously evaporated and concentrated, and concentrated water is continuously produced. The mass concentration of total dissolved solids in the concentrated water is 9%, and the temperature is 20-35°C;

[0148] The triple-effect secondary steam in the heat exchange tube of the evaporative condenser is cooled into distilled water and a small amount of non-condensable gas, which are then sent to the main cooler for further cooling.

[0149] The triple-effect secondary steam in the heat exchange tube of the evaporative condenser is cooled into distilled water and a small amount of non-condensable gas, which are sent to the main cooler to exchange heat with the low-temperature concentrated water produced in the evaporative condenser. The temperature of the non-condensable gas after cooling is ≤35°C. The non-condensable gas after cooling is extracted by a vacuum pump to always keep the vacuum degree in the triple-effect separator at about -90kPa; the recovered condensed water (distilled water) is collected in the distilled water tank at the bottom of the main cooler, pressurized by the distilled water pump, and then re-enters the preheater for heat exchange with the pretreated coking wastewater. The generated distilled water is finally used for water replenishment in the production system;

[0150] The triple-effect secondary steam is triple-effect secondary steam after gas-liquid separation in a gas-liquid separator, and the cooling water obtained by separation can be sent to the raw water tank of the pretreatment device for re-evaporation;

[0151] The concentrated water is pressurized by the concentrated water pump and then heat exchanged and heated in the main cooler and cooling crystallizer. The heated concentrated water is then sent to the primary separator as the raw material for evaporation and salt extraction.

[0152] Step 3, concentrated water is continuously extracted by the first-effect circulation pump and enters the first-effect heater, the external steam (low-pressure waste heat steam) from the external network is decompressed and regulated by the steam regulating valve and enters the high-pressure inlet of the steam ejector, and part of the second-effect secondary steam enters the low-pressure steam inlet of the steam ejector through the pipeline, and the external steam inside and outside the steam ejector is mixed with part of the second-effect secondary steam, and the obtained mixed gas enters the shell side of the first-effect heater for heating, and the tube side temperature of the first-effect heater is controlled to be 78° C., so that the temperature of the first-effect secondary steam is 78° C., and the concentrated water and the mixed gas are heat-exchanged in the first-effect heater and enter the first-effect separator for evaporation to generate first-effect secondary steam and first-effect concentrated liquid;

[0153] Wherein, the pressure of the mixed gas is 60 kPa and the temperature is 88°C;

[0154] The mass concentration of total dissolved solids in the first-effect concentrated solution is 12.5%;

[0155] Step 4: The first-effect concentrated liquid is pumped out by the first-effect concentrated liquid pump and sent to the first cyclone for classification treatment. After the treatment, the upper layer is a low-solid content solution and the lower layer is a high-solid content calcium sulfate slurry; the calcium sulfate slurry is sent back to the feed port of the first-effect circulation pump to continue to participate in the circulation; the low-solid content solution enters the feed port of the second-effect separator and is continuously extracted by the second-effect circulation pump into the second-effect heater and heat-exchanged with the first-effect secondary steam and external steam to generate condensed water and a small amount of non-condensable gas, and then enters the second-effect separator for evaporation to generate second-effect secondary steam and second-effect concentrated liquid;

[0156] Wherein, the temperature of the second-effect secondary steam is 66°C;

[0157] The mass concentration of total dissolved solids in the second-effect concentrated liquid is 22.1%;

[0158] Step 5, the second-effect concentrated liquid is pumped out by the second-effect concentrated liquid pump and sent to the feed port of the three-effect separator, and is continuously pumped by the three-effect circulating pump into the three-effect heater, and the condensed water and a small amount of non-condensable gas generated after heat exchange with part of the second-effect secondary steam and the second-effect heater enter the three-effect separator for re-evaporation to generate three-effect secondary steam and three-effect crystal slurry;

[0159] The condensed water and a small amount of non-condensable gas generated after heat exchange in the triple-effect heater enter the main cooler for heat exchange and cooling after passing through a U-shaped water seal to recover distilled water and heat; in addition, the cooling medium used for heat exchange and cooling can be the low-temperature concentrated water (temperature of 20-32°C) produced in the evaporative condenser, and the temperature of the non-condensable gas after cooling is ≤35°C. The non-condensable gas after cooling can be extracted by a vacuum pump to always keep the vacuum degree in the triple-effect separator at about -85kPa to -90kPa; the recovered condensed water (distilled water) is collected in the distilled water tank at the bottom of the main cooler, pressurized by the distilled water pump, and then enters the preheater for heat exchange, and the generated distilled water is finally used for water replenishment in the production system;

[0160] Wherein, the mass concentration of total dissolved solids in the slurry is 45%-55%;

[0161] The temperature of the triple-effect secondary steam is 48°C;

[0162] In this embodiment, the circulation pumps of each effect are used to ensure that the circulation flow rate of the circulating fluid in the tubes of the first effect heater, the second effect heater and the third effect heater is not less than 2m / s, so as to achieve the purpose of anti-scaling;

[0163] Step 6, the slurry is produced by the slurry production pump and sent to the second cyclone for classification treatment. After the treatment, the upper layer is a low-solid content solution and the lower layer is a high-solid content solution. The low-solid content solution returns to the feed port of the triple-effect circulation pump to continue to circulate, and the high-solid content solution enters the cooling crystallizer. Under stirring conditions, the high-solid content solution and the low-temperature concentrated water in the interlayer of the cooling crystallizer are heat exchanged. After cooling and crystallization, the temperature of the obtained outlet slurry is 35-45°C, and the solid content is 30%-50%. The outlet slurry is then sent to a centrifuge for centrifugal separation to obtain solid salt and mother liquor;

[0164] The cooling medium used for cooling crystallization is the low-temperature concentrated water produced in the evaporative condenser;

[0165] Part of the mother liquor is sent back to the pretreatment process of coking wastewater. After mixing with the coking wastewater, it is re-sedimented and centrifuged to increase the solid salt output. Part of the mother liquor can also be regularly extracted for coal blending treatment to prevent the three-effect separator from boiling over due to excessive COD.

[0166] Through the above measures, in this embodiment, the COD content in the obtained three-effect slurry is ≤40000mg / L, the amount of mother liquor discharged is ≤150kg / h, and the coking solid waste salt can be stably produced; the system can operate continuously and stably for >90 days; the first-effect heater was overhauled and no obvious calcium sulfate precipitation was found, and the operating effect is good.

[0167] The above is only a specific embodiment of the present invention, and cannot be used to limit the scope of the invention. Therefore, the replacement of equivalent components, or equivalent changes and modifications made according to the protection scope of the patent of the present invention, should still fall within the scope of this patent. In addition, the technical features of the present invention can be freely combined with each other, with each other and with each other, and with each other.

Claims

1. A triple-effect evaporation process for evaporating and extracting salt from coking wastewater, characterized in that: The process is realized by using a triple-effect evaporation system for evaporating and extracting salt from coking wastewater. The system comprises a first-effect evaporation device, a second-effect evaporation device and a third-effect evaporation device. The first-effect evaporation device comprises a first-effect separator (2) forming a circulation path, a first-effect heater (5) and a first-effect circulation pump (8); the second-effect evaporation device comprises a second-effect separator (3) forming a circulation path, a second-effect heater (6) and a second-effect circulation pump (9); the third-effect evaporation device comprises a third-effect separator (4) forming a circulation path, a third-effect heater (7) and a third-effect circulation pump (10); The system further comprises: a first cyclone (21), a slurry centrifugal separation device, a gas-liquid separator (25), a main cooler (16), and an evaporation concentration condensation device; the evaporation concentration condensation device comprises a preheater (24) and an evaporation condenser (1); The cold side inlet of the preheater (24) is connected to the coking wastewater pipeline, and the cold side outlet is connected to the inlet of the spray device at the top of the evaporative condenser (1). The circulating water tank at the bottom of the evaporative condenser (1) is connected to the evaporative cold circulation pump (23) and the spray device of the evaporative condenser (1) through a pipeline to form a circulation passage; the circulating water tank outlet at the bottom of the evaporative condenser (1) is also connected to the feed port of the first-effect separator (2) through a pipeline; The shell side inlet of the first effect heater (5) is connected to the steam pipeline, and the shell side outlet of the first effect heater (5) is connected to the condensate inlet of the second effect heater (6) through a pipeline; the steam outlet of the first effect separator (2) is connected to the steam inlet of the second effect heater (6), and the shell side outlet of the second effect heater (6) is connected to the condensate inlet of the triple effect heater (7) through a pipeline; the steam outlet of the second effect separator (3) is connected to the steam inlet of the triple effect heater (7), and the shell side outlet of the triple effect heater (7) is connected to the main cooler (16) through a pipeline; the steam outlet of the triple effect separator (4) is connected to the heat exchange tube inlet of the evaporative condenser (1) through the pipeline via the gas-liquid separator (25), and the heat exchange tube outlet is connected to the inlet of the main cooler (16); The feed inlet of the first-effect circulation pump (8) is connected to the inlet of the first cyclone (21) through a pipeline via the first-effect concentrated liquid pump (11); the light component outlet and the heavy component outlet of the first cyclone (21) are respectively connected to the feed inlet of the second-effect separator (3) and the feed inlet of the first-effect circulation pump (8) through pipelines; the feed inlet of the second-effect circulation pump (9) is connected to the feed inlet of the third-effect separator (4) through a pipeline via the second-effect concentrated liquid pump (12); the feed inlet of the third-effect circulation pump (10) is connected to the slurry centrifugal separation device through a pipeline via the slurry extraction pump (13); The system further comprises a pretreatment device, which comprises a sedimentation tank, a raw water tank and a plate-frame filter press; wherein the sedimentation tank is provided with a feed inlet at the top, an outlet in the middle and a mud discharge outlet at the bottom; the outlet of the sedimentation tank is connected to the inlet at the top of the raw water tank via a pipeline, and the bottom outlet of the raw water tank is connected to the cold side inlet of the preheater (24) via a pipeline via a raw water pump; the mud discharge outlet is connected to the inlet of the plate-frame filter press via a pipeline via a filter pump, and the filtered water outlet of the plate-frame filter press is connected to the inlet at the top of the raw water tank via a pipeline; Wherein, the process comprises: (1) After the pretreated coking wastewater is heated by heat exchange in the preheater, it is sent to the evaporative condenser and heat exchanged with the three-effect secondary steam in the evaporative condenser. During the heat exchange process, the pretreated coking wastewater is heated and continuously evaporated and concentrated to obtain concentrated water, which is sent to the first-effect separator as a raw material for evaporation and salt extraction; (2) Concentrated water is continuously pumped out by the first-effect circulation pump and then enters the first-effect separator for evaporation after heat exchange with external steam in the first-effect heater, generating first-effect secondary steam and first-effect concentrated liquid; The temperature of the first-effect secondary steam is ≤78 o C; (3) The first-effect concentrated liquid is pumped out by the first-effect concentrated liquid pump and sent to the first cyclone for classification treatment. After treatment, the upper layer is a low-solid content solution and the lower layer is a high-solid content calcium sulfate slurry; the calcium sulfate slurry is sent back to the feed port of the first-effect circulation pump to continue to participate in the circulation; the low-solid content solution enters the feed port of the second-effect separator and is continuously drawn by the second-effect circulation pump to the second-effect heater and the condensed water and a small amount of non-condensable gas generated after heat exchange with the first-effect secondary steam and external steam, and then enters the second-effect separator for evaporation to generate second-effect secondary steam and second-effect concentrated liquid; The temperature of the second-effect secondary steam is 64-68 o C; (4) The second-effect concentrated liquid is pumped out by the second-effect concentrated liquid pump and sent to the feed port of the three-effect separator. It is continuously pumped by the three-effect circulating pump into the three-effect heater and heat-exchanged with part of the second-effect secondary steam and the condensed water and a small amount of non-condensable gas generated in the second-effect heater. After heat exchange, it enters the three-effect separator for re-evaporation to generate three-effect secondary steam and three-effect crystal slurry. The condensed water and a small amount of non-condensable gas generated after heat exchange enter the main cooler for heat exchange and cooling to recover distilled water and heat. The temperature of the triple-effect secondary steam is 48-52 o C; (5) The crystal slurry is extracted by the crystal slurry extraction pump and then enters the crystal slurry centrifugal separation device, where solid salt and mother liquor are obtained after classification, cooling, crystallization and centrifugal separation.

2. The process according to claim 1, characterized in that The slurry centrifugal separation device comprises a second cyclone (22), a cooling crystallizer (19) and a centrifuge (20); the feed port of the triple-effect circulation pump (10) is connected to the inlet of the second cyclone (22) via a pipeline via a slurry extraction pump (13); the light component outlet and the heavy component outlet of the second cyclone (22) are respectively connected to the feed port of the triple-effect circulation pump (10) and the inlet of the cooling crystallizer (19) via pipelines; the outlet of the cooling crystallizer (19) is connected to the inlet of the centrifuge (20) via a pipeline.

3. The process according to claim 2, characterized in that The outlet of the circulating water tank at the bottom of the evaporative condenser (1) is connected to the water side inlet of the main cooler (16) and the water inlet of the cooling crystallizer (19) through a pipeline via a concentrated water pump (26); the water side outlet of the main cooler (16) and the water outlet of the cooling crystallizer (19) are connected to the feed inlet of the first-effect separator (2) through a pipeline.

4. The process according to claim 1, characterized in that A distilled water tank is provided at the bottom of the main cooler (16); the outlet of the distilled water tank is connected to the hot side inlet of the preheater (24) via a pipeline via a distilled water pump (18); and the hot side outlet of the preheater (24) is connected to the distilled water delivery pipeline.

5. The process according to claim 4, characterized in that The top outlet of the main cooler (16) is connected to the vacuum pump (17) through a pipeline to ensure that the vacuum gauge pressure of the system is -85 kPa to -95 kPa.

6. The process according to claim 1, characterized in that A steam regulating valve (14) and a steam ejector (15) are sequentially installed on the steam pipeline.

7. The process according to claim 6, characterized in that The steam outlet of the second-effect separator (3) is provided with a bypass interface, and the bypass interface is connected to the low-pressure steam inlet of the steam ejector (15) through a pipeline.

8. The process according to claim 1, characterized in that The single-effect heater (5) comprises two heaters arranged in parallel.

9. The process according to claim 1, characterized in that A pH detector is provided on the side of the raw water tank, and a probe of the pH detector is inserted below the liquid level in the raw water tank to detect the pH value of the raw water.

10. The process according to claim 1, characterized in that The slurry centrifugal separation device also includes a mother liquor tank and a mother liquor pump. The mother liquor outlet of the centrifuge (20) is connected to the mother liquor tank inlet through a pipeline, and the mother liquor tank outlet is connected to the sedimentation tank inlet through a pipeline via the mother liquor pump.

11. The process according to claim 1, characterized in that In step (1), the suspended solids concentration in the pretreated coking wastewater is less than 30 mg / L.

12. The process according to claim 1 or 11, characterized in that In step (1), the mass concentration of total dissolved solids in the concentrated water is 8.5%-9.5%, and the temperature is 20-35 o C.

13. The process according to claim 1, characterized in that In step (2), the mass concentration of total dissolved solids in the first-effect concentrated solution is 12%-13%.

14. The process according to claim 1, characterized in that In step (2), the temperature of the first-effect secondary steam is 76-78 o C.

15. The process according to any one of claims 1, 13-14, characterized in that: In step (2), concentrated water is continuously extracted by the first-effect circulation pump and is heat-exchanged with a mixture of external steam and part of the second-effect secondary steam in the first-effect heater, and then enters the first-effect separator for evaporation.

16. The process according to claim 15, characterized in that The pressure of the mixed gas is 60-70 kPa and the temperature is 86-90 o C.

17. The process according to claim 1, characterized in that In step (3), the mass concentration of total dissolved solids in the second-effect concentrated liquid is 22%-22.5%.

18. The process according to claim 1, characterized in that In step (4), the mass concentration of total dissolved solids in the slurry is 45%-55%.

19. The process according to claim 1, characterized in that The circulation velocity of the circulating fluid in the tubes of the single-effect heater, the double-effect heater and the triple-effect heater shall not be less than 2m / s.

20. The process according to claim 1, characterized in that Step (5) The slurry is extracted by the slurry extraction pump and then enters the slurry centrifugal separation device, and solid salt and mother liquor are obtained after classification, cooling crystallization and centrifugal separation in the slurry centrifugal separation device, including: The slurry is extracted by the slurry extraction pump and sent to the second cyclone for classification treatment. After the treatment, the upper layer is a low-solid content solution and the lower layer is a high-solid content solution. The low-solid content solution returns to the feed port of the triple-effect circulation pump to continue circulation, and the high-solid content solution enters the cooling crystallizer for cooling crystallization, and then centrifugally separated in a centrifuge to obtain solid salt and mother liquor.

21. The process according to claim 20, characterized in that After cooling and crystallization, the temperature of the outlet slurry is 35-45 o C.

22. The process according to claim 20 or 21, characterized in that After cooling and crystallization, the solid content of the obtained outlet slurry is 30%-50%.

23. The process according to claim 20 or 21, characterized in that The cooling medium used for cooling crystallization is the low-temperature concentrated water produced in the evaporative condenser.

24. The process according to claim 1, characterized in that The process also includes: the concentrated water is pressurized by the concentrated water pump, and then heat exchanged and heated in the main cooler and the cooling crystallizer, and then the heated concentrated water is sent to the first-effect separator as raw material.

Images