A device for concentrating wastewater using low-grade flue gas

Abstract

The present invention discloses a device for concentrating wastewater using low-grade flue gas. The device is used to solve the problems of flue gas waste heat recovery and wastewater concentration in power plants, and is composed of a dust removal unit, a desulfurization unit, a coal economizer, and a wastewater concentration system. The device uses the waste heat of flue gas from coal-fired power plants or other industries to concentrate wastewater. The concentration process has little effect on the humidity of the flue gas, converts wastewater into usable water, and finally transfers the recovered flue gas heat to the low-pressure heating system to achieve cascade utilization of thermal energy. The high-concentration wastewater after concentration and reduction can be sent to the evaporation and drying system, which greatly reduces the heat required by the evaporation and drying system and reduces the impact on the unit. The entire system has the advantages of low energy consumption, low investment, and low operating costs.

Description

Technical Field

[0001] The present invention belongs to the field of environmental protection technology, and specifically relates to a device for concentrating wastewater using low-grade flue gas, and in particular to a device for recovering flue gas waste heat in a thermal power plant and coordinating desulfurization wastewater treatment with flue gas waste heat recovery or coordinating wastewater treatment in other fields. Background Art

[0002] At present, the treatment of wet flue gas desulfurization wastewater mainly adopts the technology of three-tank pretreatment + clarifier + dehydrator, which can remove some heavy metals, reduce some SS and turbidity, but cannot remove chloride ions, and the treated wastewater has no outlet. The technologies currently under research include deep pretreatment + concentration reduction + evaporation drying.

[0003] Among them, deep pretreatment includes dosing, clarification and filtration; concentration and reduction can use thermal methods (MED, MVR, NED) and membrane methods (UF / RO); evaporative drying is to use steam or flue gas waste heat for drying. Steam evaporation is used to produce recyclable salt to achieve water reuse in wastewater. Its disadvantage is that the recovered salt is low-grade salt and difficult to reuse. At the same time, the evaporation process requires high-quality steam, which has high energy consumption, large investment and high operating requirements. The flue gas waste heat evaporation solution has low investment and low operating costs, and improves the downstream dust removal efficiency. Its disadvantage is that it consumes high-quality flue gas waste heat, affects the flue gas temperature of the air preheater, and reduces the unit efficiency. At the same time, it increases the load of the dust removal equipment. If concentration and reduction are not performed, a large amount of water will enter the desulfurization system, resulting in a decrease in the evaporation of the desulfurization tower, affecting the amount of desulfurization flushing water, and the amount of wastewater treated will also be limited by the flue gas temperature and load.

[0004] Therefore, the current desulfurization wastewater concentration technology consumes high-quality thermal energy, has high energy consumption, large investment costs, high operating requirements, and has adverse effects on unit efficiency. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is that the existing desulfurization wastewater concentration technology has the defects of consuming high-quality thermal energy, high energy consumption, large investment cost, high operation requirements, and adverse effects on unit efficiency. Therefore, a device for concentrating wastewater using low-grade flue gas is proposed.

[0006] To this end, the technical solution provided by the present invention is as follows:

[0007] The device for concentrating wastewater using low-grade flue gas provided by the present invention comprises a dust removal unit and a desulfurization unit which are connected and arranged, and also comprises a coal economizer which is arranged between the dust removal unit and the desulfurization unit or arranged upstream of the dust removal unit along the flue gas flow direction, and also comprises a wastewater concentration system, and the wastewater concentration system comprises:

[0008] a first heat exchanger, connected to the economizer, so as to exchange heat between the desulfurized wastewater and the first heat exchange medium from the economizer in the first heat exchanger;

[0009] A flash tank, comprising a shell and a concentrated wastewater outlet arranged at the lower part of the shell, wherein the shell is connected to the first heat exchanger to send the heated desulfurized wastewater into the flash tank for flash evaporation;

[0010] a second heat exchanger, connected to the concentrated wastewater outlet, so as to exchange heat between the concentrated wastewater and a second heat exchange medium in the second heat exchanger;

[0011] The sedimentation device is connected to the second heat exchanger to send the concentrated wastewater after cooling to the sedimentation device for sedimentation.

[0012] Furthermore, the sedimentation device includes at least two stages of sedimentation units, so that the concentrated wastewater after cooling can be subjected to multi-stage sedimentation;

[0013] The upper part of the sedimentation device is connected to the first heat exchanger, so that the supernatant and / or the added desulfurization wastewater in the sedimentation device enters the first heat exchanger and exchanges heat with the first heat exchange medium from the economizer in the first heat exchanger.

[0014] Furthermore, it also includes an evaporation drying unit, which is connected to the lower part of the settling device to send the concentrated desulfurization wastewater in the lower part of the settling device into the evaporation drying unit;

[0015] The air preheater is arranged on the upstream flue of the dust removal unit.

[0016] Furthermore, the evaporative drying unit is a flue spray evaporator, and along the flow direction of the flue gas, the flue spray evaporator is arranged in the upstream flue of the dust removal unit.

[0017] Furthermore, the evaporative drying unit is a rotary spray evaporator, a high-temperature dry flue gas inlet is arranged on the upper part thereof, and along the flow direction of the flue gas, the high-temperature dry flue gas inlet is connected with the upstream flue of the air preheater, so that the high-temperature dry flue gas in the upstream flue of the air preheater enters the rotary spray evaporator to exchange heat with the concentrated desulfurized wastewater;

[0018] A high-temperature wet flue gas outlet is provided at the lower part of the rotary spray evaporator, and the high-temperature wet flue gas outlet is connected to the flue between the air preheater and the dust removal unit. The connection point between the settling device and the rotary spray evaporator is located at the upper part of the rotary spray evaporator.

[0019] Furthermore, it also includes a third heat exchanger, which is connected to the secondary steam outlet on the upper part of the shell. The third heat exchanger is also connected to the second heat exchanger, so that the second heat exchange medium after the temperature is increased in the second heat exchanger enters the third heat exchanger and exchanges heat with the secondary steam from the flash tank again.

[0020] Furthermore, it also includes an air preheater, which is arranged on the upstream flue, and the nozzle is arranged in the upstream flue between the air preheater and the dust removal unit, or the high-temperature dry flue gas outlet is connected to the inlet flue of the air preheater.

[0021] Furthermore, it also includes a first pump, which is connected to the flash tank and is used to put the flash tank in a negative pressure state and control the vacuum degree therein;

[0022] a second pump, disposed on a pipeline between the settling device and the first heat exchanger, to deliver supernatant and / or added desulfurized wastewater into the first heat exchanger;

[0023] The third pump is arranged on the pipeline between the sedimentation device and the evaporation drying unit.

[0024] a fourth pump, disposed on a pipeline between the flash tank and the second heat exchanger;

[0025] The fifth pump is arranged on the return water pipe or the incoming water pipe of the low-pressure condensate water.

[0026] Furthermore, it also includes a chimney, wherein the chimney is connected to the desulfurization unit;

[0027] The dust removal unit is an electrostatic precipitator; the economizer is a low-temperature economizer; and the desulfurization unit is a desulfurization tower.

[0028] Furthermore, the first heat exchange medium is heat medium water; and the second heat exchange medium is low temperature condensate water.

[0029] The technical solution of the present invention has the following advantages: by setting up a dust removal unit, an economizer and a desulfurization unit connected in sequence, it also includes a wastewater concentration system, the wastewater concentration system includes a first heat exchanger connected to the economizer to exchange heat between the desulfurized wastewater and the first heat exchange medium from the economizer in the first heat exchanger; a flash tank, including a shell and a concentrated wastewater outlet arranged at the lower part of the shell, the shell is connected to the first heat exchanger to send the heated desulfurized wastewater into the flash tank for flash evaporation; a second heat exchanger is connected to the concentrated wastewater outlet to exchange heat between the concentrated wastewater and the second heat exchange medium in the second heat exchanger; a sedimentation device is connected to the second heat exchanger to send the cooled concentrated wastewater into the sedimentation device for sedimentation. The device uses the waste heat of flue gas from coal-fired power plants or other industries to concentrate wastewater, the concentration process will not cause significant changes in the humidity of the flue gas, the wastewater is converted into usable water, and finally the recovered flue gas heat is transferred to the low-pressure heating system of low-pressure heating condensation water to realize the cascade utilization of thermal energy. When the high-concentration desulfurization wastewater after concentration and reduction is subsequently evaporated and dried, the heat required for the evaporation and drying system is greatly reduced, reducing the impact on the unit. The entire system has the advantages of low energy consumption, low investment, and low operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 It is a structural schematic diagram of a device for concentrating wastewater using low-grade flue gas in an embodiment of the present invention;

[0032] Figure 2 is another structural schematic diagram of a device for concentrating wastewater using low-grade flue gas in an embodiment of the present invention;

[0033] Figure 3 is a schematic diagram of the structure of a wastewater concentration system in an embodiment of the present invention;

[0034] The reference numerals are as follows:

[0035] 0-air preheater; 1-dust removal unit; 2-desulfurization unit; 3-chimney; 4-economizer; 5-first heat exchanger; 6-flash tank; 7-third heat exchanger; 8-sedimentation device; 9-second heat exchanger; 10-nozzle; 11-first pump; 12-second pump; 13-third pump; 14-rotary spray evaporator; 15-fourth pump; 16-fifth pump. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0038] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0040] Example 1

[0041] This embodiment provides a device for concentrating wastewater using low-grade flue gas, such as Figure 1 and 3 As shown, it includes a dust removal unit 1 and a desulfurization unit 2 which are connected and arranged, and also includes an economizer 4, which is arranged between the dust removal unit 1 and the desulfurization unit 2 or arranged upstream of the dust removal unit 1 along the flue gas flow direction. In this embodiment, the dust removal unit 1 is an electrostatic precipitator, the economizer 4 is a low-temperature economizer, the desulfurization unit 2 is a desulfurization tower, and also includes a wastewater concentration system, which includes,

[0042] The first heat exchanger 5 is connected to the economizer 4 to exchange heat between the desulfurized wastewater and the first heat exchange medium from the economizer in the first heat exchanger 5. Specifically, the first heat exchange medium is the intermediate heat medium water obtained after heat exchange with the high-temperature flue gas;

[0043] The flash tank 6 comprises a shell and a concentrated wastewater outlet arranged at the lower part of the shell, and the shell is connected to the first heat exchanger 5 to send the heated desulfurized wastewater into the flash tank 6 for flash evaporation;

[0044] The second heat exchanger 9 is connected to the concentrated wastewater outlet to exchange heat between the concentrated wastewater and a second heat exchange medium in the second heat exchanger 9. Specifically, the second heat exchange medium is low-temperature condensate from the outside.

[0045] The settling device 8 is connected to the second heat exchanger 9 to send the concentrated wastewater after cooling to the settling device 8 for sedimentation; specifically, the settling device 8 includes at least two-stage settling units to allow the concentrated wastewater after cooling to undergo multi-stage sedimentation; the upper portion of the settling device 8 is connected to the first heat exchanger 5 to allow the supernatant and / or the added desulfurized wastewater in the settling device 8 to enter the first heat exchanger 5 and exchange heat with the first heat exchange medium from the economizer 4 in the first heat exchanger 5; more specifically, as Figure 3 As shown, the sedimentation device 8 is a three-stage sedimentation unit connected in sequence. The multi-stage sedimentation form is adopted to ensure that only a small amount of concentrated wastewater is sent to the evaporation and drying system to reduce the impact on the overall efficiency of the unit.

[0046] In the above device, waste heat from flue gas in coal-fired power plants or other industries is used to concentrate wastewater. The concentration process does not increase the humidity of flue gas, and the wastewater is converted into usable water. Finally, the recovered flue gas heat is transferred to the low-pressure heating system of low-pressure heating condensation water to achieve cascade utilization of thermal energy. When the concentrated and reduced high-concentration desulfurization wastewater is subsequently evaporated and dried, the heat required by the evaporation and drying system is greatly reduced, reducing the impact on the unit. The entire system has the advantages of low energy consumption, low investment, and low operating costs.

[0047] like Figure 1 As shown, it also includes a third heat exchanger 7, which is connected to the secondary steam outlet on the upper part of the shell. The third heat exchanger 7 is also connected to the second heat exchanger 9, so that the second heat exchange medium after heating from the second heat exchanger enters the third heat exchanger 7 and exchanges heat with the secondary steam from the flash tank 6 again, the secondary steam becomes secondary steam condensate, and the low-pressure heater condensate inlet water becomes the low-pressure heater condensate return water.

[0048] Furthermore, it also includes an evaporation and drying unit, which is connected to the lower part of the sedimentation device 8 to send the concentrated desulfurization wastewater in the lower part of the sedimentation device 8 into the evaporation and drying unit; specifically, the evaporation and drying unit is a flue spray evaporator (for example, it can be a nozzle 10), and along the flow direction of the flue gas, the nozzle 10 is arranged in the upstream flue of the dust removal unit 1.

[0049] Furthermore, it also includes an air preheater 0, which is arranged on the upstream flue of the dust removal unit 1, and the nozzle 10 is arranged in the upstream flue between the air preheater 0 and the dust removal unit 1; and a chimney 3, which is connected to the desulfurization unit 2.

[0050] In order to control the chloride ion concentration in the wastewater sedimentation tank, part of the concentrated wastewater is sent to the evaporative drying unit. The evaporative drying unit can use a flue sprayer (for example, a nozzle 10). The flue sprayer is generally arranged inside the flue between the air preheater 0 and the electrostatic precipitator. The high-temperature waste heat flue gas in the flue is used to evaporate the atomized concentrated water into water vapor. The steam enters the desulfurization tower with the flue gas after dust removal, and the evaporated crystals enter the electrostatic precipitator together with the dust and are discharged with the ash.

[0051] The device consists of a low-temperature economizer, a low-temperature phase-change wastewater concentration system and an evaporative drying unit. The low-temperature phase-change wastewater concentration system is mainly composed of a first heat exchanger 5 (wastewater heater), a flash tank 6 (wastewater flash tank), a second heat exchanger 9 (wastewater cooler), a third heat exchanger 7 (condenser), a sedimentation device 8 (wastewater sedimentation tank), a vacuum pump (first pump 11) and related wastewater delivery pumps and other equipment. The evaporative drying unit is composed of a flue sprayer (for example, a nozzle 10). If the original flue gas system has been installed with a low-temperature economizer, the flue gas system does not need to be modified. It is only necessary to modify the heat medium water pipeline of the low-temperature economizer, cut off the original pipeline directly sent to the low-temperature system, and connect it to the low-temperature phase-change wastewater concentration system. If the flue gas system is not equipped with a low-temperature economizer, a new low-temperature economizer needs to be added to recycle the original flue gas heat. Generally, the incoming water temperature of low-temperature intermediate heat medium water is above 70℃. In order to maximize the use of flue gas waste heat and prevent low-temperature corrosion, the incoming water temperature of the intermediate heat medium water is selected to be 70℃. After heat exchange with flue gas, its temperature rises to about 95℃. The intermediate heat medium water after heating is sent to the wastewater heater to exchange heat with the desulfurization wastewater. Generally, the incoming water temperature of the wastewater is about 35℃, and the desulfurization wastewater can be heated to 65-75℃. The heated wastewater enters the wastewater flash tank for negative pressure flash evaporation, and its flash temperature is between 55-65℃. The concentrated wastewater comes out from the bottom of the flash tank and is sent to the wastewater cooler to exchange heat with the low-pressure condensate. The low-pressure condensate of the initial heat exchange is heat exchanged with the secondary steam at the top of the wastewater flash tank in the condenser. The secondary steam condensate can be used for desulfurization tower process water replenishment. The heated low-pressure condensate returns to the low-pressure system to complete the recovery of flue gas waste heat. After cooling, the concentrated wastewater is sent to the wastewater sedimentation tank. After multiple stages of sedimentation, the supernatant and the newly desulfurized wastewater are sent to the wastewater heater for reheating and circulation concentration.

[0052] Example 2

[0053] This embodiment provides a device for concentrating wastewater using low-grade flue gas, such as Figure 2 and 3As shown, based on the above-mentioned embodiment 1, as a variable implementation mode, the evaporative drying unit is a rotary spray evaporator 14, a high-temperature dry flue gas inlet is arranged on the upper part thereof, and along the flow direction of the flue gas, the high-temperature dry flue gas inlet is connected with the upstream flue of the air preheater 0, so that the high-temperature dry flue gas in the upstream flue of the air preheater 0 enters the rotary spray evaporator to exchange heat with the concentrated desulfurized wastewater; specifically, the high-temperature dry flue gas inlet is connected with the inlet flue of the air preheater 0;

[0054] A high-temperature wet flue gas outlet is provided at the lower part of the rotary spray evaporator, and the high-temperature wet flue gas outlet is connected to the flue between the air preheater 0 and the dust removal unit 1. Specifically, the high-temperature wet flue gas outlet is connected to the inlet flue of the dust removal unit 1, and relative to the connection point between the high-temperature dry flue gas inlet and the upstream flue, the connection point between the high-temperature wet flue gas outlet and the upstream flue is close to the dust removal unit 1, and the connection point between the sedimentation device 8 and the rotary spray evaporator is located at the upper part of the rotary spray evaporator, specifically, the connection point between the sedimentation device 8 and the rotary spray evaporator is located at the top of the rotary spray evaporator.

[0055] In actual working conditions, the evaporative drying unit can use an independently rotating spray drying tower. The independently rotating spray drying tower is arranged outside the flue gas system, and a flue gas bypass is set up to extract a small amount of flue gas from the outlet of the denitrification SCR to the spray drying tower. The desulfurization wastewater is sprayed into the spray drying tower and the heat of the flue gas is used in the spray drying tower to evaporate the atomized concentrated water into water vapor. The flue gas at the outlet of the spray drying tower enters the inlet flue of the dust removal unit, and the steam enters the desulfurization tower with the flue gas after dust removal. The evaporated crystals enter the electrostatic precipitator together with the dust and are captured and discharged with the ash. The concentrated and dried solid salt is discharged from the bottom of the spray drying tower.

[0056] Example 3

[0057] The present embodiment provides a device for concentrating wastewater using low-grade flue gas. On the basis of the above-mentioned embodiment 1 or 2, it also includes a first pump 11, which is connected to the flash tank 6 and is used to make the flash tank 6 in a negative pressure state and control the vacuum degree therein; that is, in order to ensure that the wastewater after heating can be flash evaporated and concentrated, the low-temperature phase change concentration system needs to be equipped with a vacuum pump (that is, the first pump 11). The vacuum pump is connected in series with the wastewater flash tank and the condenser, and is located after the condenser. The secondary steam is first cooled in the condenser, and a phase change occurs during the cooling process to generate a negative pressure, which can maintain the negative pressure state of the system by itself. However, a vacuum pump needs to be set when the system is started and the vacuum degree is kept stable. The vacuum pump is evacuated when the system is started. During operation, only the non-condensable gas precipitated by the condensation of the secondary steam needs to be extracted, so as to reduce the power consumption of the vacuum pump while ensuring the stability of the vacuum degree of the system;

[0058] The second pump 12 is arranged on the pipeline between the settling device 8 and the first heat exchanger 5 to deliver the supernatant and / or the added desulfurized wastewater into the first heat exchanger 5;

[0059] The third pump 13 is arranged on the pipeline between the sedimentation device 8 and the evaporation drying unit.

[0060] The fourth pump 15 is arranged on the pipeline between the flash tank 6 and the second heat exchanger 9;

[0061] The fifth pump 16 is arranged on the return water pipe or the incoming water pipe of the low-pressure condensate water.

[0062] In addition, it should be noted that the water quality and quantity characteristics of desulfurization wastewater are related to many factors such as unit load, coal composition, operating conditions, desulfurization process water quality, limestone composition, etc. It has the characteristics of complex pollutant composition and large fluctuation range. Its pH value is low and it is acidic. The suspended solids content and salt content in the water are high, and there is a possibility of excessive heavy metals. The chloride content is very high and it is highly corrosive. It is the most difficult wastewater to dispose of in power plants. Reducing and concentrating the desulfurized wastewater requires a large amount of high-quality evaporation or flue gas, and the energy consumption is high. Whether the unit is extracted steam or the flue gas waste heat before the air preheater is used, it will have an adverse effect on the unit. In order to solve this problem, the present invention adopts a flue gas waste heat recovery and coordinated wastewater concentration device. The device recovers the original flue gas heat through a low-temperature economizer arranged before or after the electrostatic precipitator. The recovered heat is sent to the wastewater heater by the heat medium water, and the wastewater sent from the wastewater sedimentation tank is heated and heated. The heated wastewater enters the wastewater flash tank. The flash tank is in a negative pressure state, and its vacuum degree is provided by a vacuum pump. The vacuum pump is connected in series with the condenser and is located after the condenser. The concentrated wastewater after flash evaporation enters the wastewater cooler from the bottom of the flash tank, and the heat it carries is used to heat the condensate of the low-pressure heater for the first time. The cooled concentrated wastewater enters the wastewater sedimentation tank. After graded sedimentation, the supernatant and the newly arrived desulfurized wastewater are circulated to the wastewater heater again. A small amount of concentrated wastewater at the bottom of the wastewater sedimentation tank is sent to the flue sprayer in front of the electrostatic precipitator, and the high-temperature waste heat flue gas in the flue is used to evaporate the atomized concentrated water into water vapor. The steam enters the desulfurization tower with the flue gas after dust removal, and the evaporated and dried matter enters the electrostatic precipitator together with the dust and is discharged with the ash; or it is sent to an independently rotating spray evaporation tower for evaporation and drying, and a small amount of flue gas at the outlet of the denitrification SCR is extracted to the evaporation tower. The desulfurized wastewater is sprayed into the evaporation tower, and the heat of the flue gas is used to evaporate the atomized concentrated water into water vapor in the evaporation tower. The flue gas at the outlet of the evaporation tower enters the inlet flue of the dust collector, and the steam enters the desulfurization absorption tower with the flue gas after dust removal; the evaporated crystals enter the electrostatic precipitator together with the dust and are captured and discharged with the ash. The secondary steam obtained by flash evaporation comes out from the top of the flash tank and enters the condenser, where the low-pressure condensate is reheated. The low-pressure condensate after the secondary heating returns to the low-pressure circulating water system with a temperature close to that of the low-pressure condensate, and the secondary steam condensate is used for the desulfurization system process water replenishment. Through this device, the flue gas heat recovered by the low temperature is first used for desulfurization wastewater concentration, which solves the drawbacks of conventional routes using high-quality heat energy for evaporation. At the same time, after the wastewater is concentrated, the heat it contains is transferred to the low-pressure condensate system, so that the heat is not discharged and is fully utilized in stages, that is, the heat required for desulfurization treatment is met without losing much heat, and most of the heat is finally transferred to the low-pressure condensate, thereby reducing the energy consumption of the unit.

[0063] This device can make full use of the low-temperature economizer, an existing flue gas waste heat recovery device in the power plant. If the flue gas waste heat recovery modification is not carried out, a low-temperature economizer needs to be added before or after the electrostatic precipitator. The conventional technology is to recover the waste heat of the flue gas system through a low-temperature economizer to heat the low-pressure condensate or the heater. This device adds a desulfurization wastewater concentration system, first using the recovered heat to concentrate the wastewater, and then transferring the concentrated wastewater and secondary steam heat to the low-pressure condensate through the cooler and condenser. In the process, there is almost no loss of flue gas heat recovered, but the quality is reduced. The concentration system and evaporation crystallization system are independent of the flue gas system and can be adjusted according to the load changes of the unit.

[0064] The technical effect that can be achieved by the present invention is: by recovering flue gas waste heat through the low-temperature economizer arranged before or after the electrostatic precipitator, the dust removal capacity of the electrostatic precipitator can be improved and the process water replenishment of the desulfurization tower can be reduced. In the wastewater concentration system, the heat recovered from the flue gas is used to increase the temperature of the desulfurized wastewater. The wastewater after heating is flashed in the wastewater flash tank, thereby realizing the concentration of the desulfurized wastewater. The flash tank is in a negative pressure state, and its vacuum degree is provided by a vacuum pump. The recovered flue gas heat is taken out with the concentrated wastewater and secondary steam, and the heat contained in the concentrated wastewater and condensed secondary steam is recovered by low-pressure condensate, and finally the heat is returned to the low-pressure condensate system. In the case of almost no loss of the recovered heat, the use of heat is expanded, and the cascade utilization of thermal energy is realized. The condensed water of the secondary steam after condensation can be used for the process replenishment of the desulfurization system. The concentrated wastewater is pumped to the wastewater sedimentation tank. After multiple stages of sedimentation, the supernatant is recycled to the wastewater heater with the newly entered desulfurized wastewater, and a small amount of high-concentration wastewater is sent to the evaporation and drying unit to control the chloride ion concentration of the wastewater in the concentration system. When it is sent to the flue spray evaporator, the high-temperature waste heat flue gas in the flue is used to evaporate the atomized concentrated water into water vapor. The steam enters the desulfurization tower with the flue gas after dust removal, and the evaporated crystals enter the electrostatic precipitator with the dust and are discharged with the ash; or it is sent to an independent rotating spray evaporation tower for evaporation and drying, and a small part of the flue gas at the outlet of the denitrification SCR is extracted to the evaporation tower. The desulfurized wastewater is sprayed into the evaporation tower. The heat of the flue gas is used in the evaporation tower to evaporate the atomized concentrated water into water vapor. The flue gas at the outlet of the evaporation tower enters the inlet flue of the dust collector, and the steam enters the desulfurization absorption tower with the flue gas after dust removal; the evaporated crystals enter the electrostatic precipitator with the dust and are captured and discharged with the ash. The above method not only solves the problem of waste heat recovery of flue gas in coal-fired power plants or other industries, but also realizes wastewater concentration. The system has low energy consumption, low investment, low operating costs, and achieves environmental protection effects such as efficient energy conservation and emission reduction, and has a good social and economic impact.

[0065] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A device for concentrating wastewater using low-grade flue gas, comprising a dust removal unit and a desulfurization unit connected to each other, and also comprising an economizer, which is arranged between the dust removal unit and the desulfurization unit or along the flue gas flow direction, and is arranged upstream of the dust removal unit, characterized in that: Also included is a wastewater concentration system, the wastewater concentration system comprising: a first heat exchanger, connected to the economizer, so as to exchange heat between the desulfurized wastewater and the first heat exchange medium from the economizer in the first heat exchanger; A flash tank, comprising a shell and a concentrated wastewater outlet arranged at the lower part of the shell, wherein the shell is connected to the first heat exchanger to send the heated desulfurized wastewater into the flash tank for flash evaporation; a second heat exchanger, connected to the concentrated wastewater outlet, so as to exchange heat between the concentrated wastewater and a second heat exchange medium in the second heat exchanger; A settling device is connected to the second heat exchanger to send the concentrated wastewater after cooling to the settling device for sedimentation. The settling device includes at least two setstling units to allow the concentrated wastewater after cooling to undergo multi-stage precipitation. The upper portion of the settling device is connected to the first heat exchanger to allow the supernatant and / or the added desulfurized wastewater in the settling device to enter the first heat exchanger and exchange heat with the first heat exchange medium from the economizer in the first heat exchanger. An evaporation drying unit is connected to the lower part of the settling device to send the concentrated desulfurization wastewater in the lower part of the settling device into the evaporation drying unit; The air preheater is arranged on the upstream flue of the dust removal unit.

2. The device according to claim 1, characterized in that The evaporative drying unit is a flue spray evaporator, and along the flow direction of the flue gas, the flue spray evaporator is arranged in the upstream flue of the dust removal unit.

3. The device according to claim 1, characterized in that The evaporative drying unit is a rotary spray evaporator, a high-temperature dry flue gas inlet is arranged on the upper part thereof, and along the flow direction of the flue gas, the high-temperature dry flue gas inlet is connected with the upstream flue of the air preheater, so that the high-temperature dry flue gas in the upstream flue of the air preheater enters the rotary spray evaporator to exchange heat with the concentrated desulfurized wastewater; A high-temperature wet flue gas outlet is provided at the lower part of the rotary spray evaporator, and the high-temperature wet flue gas outlet is connected to the flue between the air preheater and the dust removal unit. The connection point between the settling device and the rotary spray evaporator is located at the upper part of the rotary spray evaporator.

4. The device according to claim 1, characterized in that Also includes, The third heat exchanger is connected to the secondary steam outlet at the upper part of the shell, and the third heat exchanger is also connected to the second heat exchanger, so that the second heat exchange medium after the temperature is increased from the second heat exchanger enters the third heat exchanger and exchanges heat with the secondary steam from the flash tank again.

5. The device according to claim 1, characterized in that Also includes, a first pump, connected to the flash tank, for placing the flash tank in a negative pressure state and controlling the vacuum degree therein; a second pump, disposed on a pipeline between the settling device and the first heat exchanger, to deliver supernatant and / or added desulfurized wastewater into the first heat exchanger; A third pump is provided on the pipeline between the settling device and the evaporative drying unit; a fourth pump, disposed on a pipeline between the flash tank and the second heat exchanger; The fifth pump is arranged on the return water pipe or the incoming water pipe of the low-pressure condensate water.

6. The device according to claim 5, characterized in that It also includes a chimney, which is connected to the desulfurization unit; The dust removal unit is an electrostatic precipitator; the economizer is a low-temperature economizer; and the desulfurization unit is a desulfurization tower.

7. The device according to any one of claims 1 to 6, characterized in that The first heat exchange medium is hot coal water; the second heat exchange medium is low temperature heater condensate.

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