A device for treating wastewater using low-grade flue gas

Abstract

The invention discloses a device for treating wastewater using low-grade flue gas. The device is provided with a dust removal unit, a coal economizer and a desulfurization unit connected in sequence, and also includes a first heat exchanger, a flash tank and a filter press device. The first heat exchanger is used to recover the waste heat of the flue gas, so as to improve the dust removal capacity of the dust removal unit and reduce the process water replenishment of the desulfurization unit. At the same time, the heat recovered from the flue gas is used to increase the temperature of the desulfurization wastewater. The wastewater after heating is flashed in the flash tank, so as to realize the concentration of the desulfurization wastewater. The flash tank is in a negative pressure state, and the recovered flue gas heat is taken out with the concentrated wastewater and secondary steam. The heat contained in the concentrated wastewater and the condensed secondary steam is recovered by the low-pressure condensate, and finally the heat is returned to the low-pressure condensate system, so as to realize the step-by-step utilization of heat energy. At the same time, the filter press device effectively treats the desulfurization wastewater. The device has low energy consumption, low investment, low operating cost, and achieves environmental protection effects such as efficient energy saving and emission reduction, and has a good social and economic impact.

Description

Technical Field

[0001] The present invention belongs to the field of environmental protection technology, and specifically relates to a device for treating 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 or for deep recovery of flue gas waste heat in other fields and coordinating wastewater treatment. 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 treating 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 treating wastewater by 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:

[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] The filter press device comprises a sedimentation unit and a filter press unit. The sedimentation unit is connected with the flash tank so as to send concentrated wastewater into the sedimentation unit for sedimentation. The filter press unit is provided with a concentrated wastewater inlet and a filtrate outlet. The concentrated wastewater inlet is connected with the lower part of the sedimentation unit, and the filtrate outlet is connected with the upper part of the sedimentation unit.

[0011] Furthermore, the sedimentation unit includes a straight section and a conical section which are connected in sequence, the top of the conical section is connected to the concentrated wastewater inlet, and the straight section is connected to the first heat exchanger, so that the supernatant and / or the added desulfurization wastewater in the sedimentation unit enters the first heat exchanger and exchanges heat with the first heat exchange medium from the economizer in the first heat exchanger.

[0012] Furthermore, the ratio of the length of the straight segment to the length of the tapered segment is (2-4):1.

[0013] Furthermore, it also includes a second heat exchanger, which is arranged between the flash tank and the precipitation unit, the inlet end of the second heat exchanger is connected to the concentrated wastewater outlet, and the outlet end is connected to the straight section, so as to exchange heat between the concentrated wastewater and the second heat exchange medium in the second heat exchanger.

[0014] 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.

[0015] 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;

[0016] a second pump, disposed on a pipeline between the sedimentation unit and the first heat exchanger, to deliver the supernatant and / or the added desulfurization wastewater into the first heat exchanger;

[0017] The third pump is arranged between the filter press unit and the straight section to deliver the filtrate into the straight section.

[0018] Furthermore, it also includes a fourth pump, which is arranged on the pipeline between the flash tank and the second heat exchanger to send the concentrated wastewater into the second heat exchanger;

[0019] The fifth pump is arranged on the pipeline between the sedimentation unit and the filter press unit to deliver the concentrated wastewater into the filter press unit.

[0020] Furthermore, it also includes a chimney, wherein the chimney is connected to the desulfurization unit;

[0021] The dust removal unit is an electrostatic precipitator; the economizer is a low-temperature economizer; the desulfurization unit is a desulfurization tower; and the filter press unit is a plate and frame filter press.

[0022] Furthermore, the first heat exchange medium is heat medium water; and the second heat exchange medium is low temperature condensate water.

[0023] The technical solution of the present invention has the following advantages: by setting a dust removal unit, a coal economizer and a desulfurization unit connected in sequence, it also includes a first heat exchanger, a flash tank and a filter press device, and the first heat exchanger is used to recover the flue gas waste heat, so as to improve the dust removal capacity of the dust removal unit and reduce the water replenishment of the desulfurization unit process water. At the same time, the heat recovered from the flue gas is used to increase the temperature of the desulfurization wastewater, and the wastewater after heating is flashed in the flash tank, so as to realize the concentration of the desulfurization 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 the condensed secondary steam is recovered by the low-pressure condensate, and finally the heat is returned to the low-pressure condensate system. Without losing the recovered heat, the cascade utilization of heat energy is realized, and the condensed secondary steam condensate can be used for the desulfurization system process water replenishment. The concentrated wastewater is sent to the filter press device. After precipitation, the supernatant is recycled to the wastewater heater with the newly entered desulfurized wastewater. A small amount of high-concentration wastewater is sent to the filter press unit for sediment treatment, which can carry out some chloride ions in the wastewater. The above method solves the problem of waste heat recovery of flue gas in coal-fired power plants or other industries, and at the same time achieves zero discharge of desulfurized wastewater. The device has low energy consumption, low investment, low operating costs, and achieves environmental protection effects such as efficient energy saving and emission reduction, and has a good social and economic impact. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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.

[0025] Figure 1Schematic diagram of the structure of a device for treating wastewater using low-grade flue gas in an embodiment of the present invention;

[0026] Figure 2 is a schematic structural diagram of the interconnection of the first heat exchanger, the flash tank and the filter press device in an embodiment of the present invention;

[0027] The reference numerals are as follows:

[0028] 1-dust removal unit; 2-desulfurization unit; 3-chimney; 4-economizer; 5-first heat exchanger; 6-flash tank; 7-third heat exchanger; 8-filter press device; 8-1-precipitation unit; 8-2-filter press unit; 9-second heat exchanger; 10-third pump; 11-first pump; 12-second pump; 13-fourth pump; 14-fifth pump. DETAILED DESCRIPTION

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] Example 1

[0034] This embodiment provides a device for treating wastewater using low-grade flue gas, such as Figure 1 and 2 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, and the desulfurization unit 2 is a desulfurization tower, and also includes,

[0035] 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;

[0036] 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;

[0037] The filter press device 8 includes a sedimentation unit 8-1 and a filter press unit 8-2. The sedimentation unit 8-1 is connected to the flash tank 6 to send concentrated wastewater to the sedimentation unit 8-1 for sedimentation. A concentrated wastewater inlet and a filtrate outlet are arranged on the filter press unit 8-2. The concentrated wastewater inlet is connected to the lower part of the sedimentation unit 8-1, and the filtrate outlet is connected to the upper part of the sedimentation unit 8-1. Specifically, the filter press unit 8-2 is a plate and frame filter press. In actual working conditions, the concentrated wastewater at the bottom of the sedimentation unit 8-1 is crystallized to form solids and then discharged. The plate and frame filter press is used for filter pressing. The filter cake after filtration is sent to the ash field, and the obtained filtrate is sent to the sedimentation unit 8-1 for continuous circulation and concentration.

[0038] In order to better treat desulfurization wastewater and reduce its solid content, such as Figure 2 As shown, the sedimentation unit includes a straight section and a conical section which are connected in sequence, the top of the conical section is connected to the concentrated wastewater inlet, and the straight section is connected to the first heat exchanger, so that the supernatant and / or the added desulfurization wastewater in the sedimentation unit enters the first heat exchanger and exchanges heat with the first heat exchange medium from the economizer in the first heat exchanger; preferably, the ratio of the length of the straight section and the conical section is (2-4): 1, the straight section is a straight cylinder, and the conical section is a conical cylinder.

[0039] The device consists of a low-temperature economizer, a low-temperature phase-change wastewater concentration system (the first heat exchanger 5 + flash tank 6, etc.) and a filter press. The low-temperature phase-change wastewater concentration system is mainly composed of the first heat exchanger 5 (wastewater heater), the flash tank 6 (wastewater flash tank), the second heat exchanger 9 (wastewater cooler), a vacuum pump and related wastewater delivery pumps and other equipment. The filter press device 2 includes a precipitation unit 8-1 and a filter press unit 8-2. 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. The concentrated wastewater after cooling is sent to the filter press device 8 for filter pressing to improve the treatment effect of the desulfurization wastewater.

[0040] The device uses the waste heat of flue gas from coal-fired power plants or other industries to treat wastewater. The concentration process has little effect on the humidity of the flue gas, turning the wastewater into usable water, and finally transferring 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 is sent to the sedimentation and filtration system. The whole system has the advantages of low energy consumption, low investment, and low operating costs.

[0041] Example 2

[0042] This embodiment provides a device for treating wastewater using low-grade flue gas, such as Figure 1 and 2 As shown, on the basis of the above-mentioned embodiment 1, in order to improve the heat utilization efficiency and the desulfurization wastewater treatment effect, a second heat exchanger 9 is further included, which is arranged between the flash tank 6 and the precipitation unit 8-1. The inlet end of the second heat exchanger 9 is connected to the concentrated wastewater outlet, and the outlet end is connected to the straight section, so that the concentrated wastewater is exchanged with the second heat exchange medium in the second heat exchanger 9. Specifically, the second heat exchange medium is low-temperature condensate from the outside;

[0043] like Figure 1As 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.

[0044] Example 3

[0045] The present embodiment provides a device for treating wastewater using low-grade flue gas. On the basis of the above-mentioned embodiment 1 or 2, it further includes a first pump 11, which is connected to the flash tank 6 and is used to put 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 to form secondary steam condensate. The cooling process undergoes a phase change to generate 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 secondary steam condensate needs to be extracted, so as to reduce the power consumption of the vacuum pump while ensuring the vacuum degree of the system is stable.

[0046] The second pump 12 is provided on the pipeline between the sedimentation unit 8-1 and the first heat exchanger 5 to deliver the supernatant and / or the added desulfurization wastewater into the first heat exchanger 5;

[0047] The third pump 10 is disposed between the filter press unit 8-2 and the straight section to deliver the filtrate into the straight section;

[0048] a fourth pump 13, disposed on the pipeline between the flash tank 6 and the second heat exchanger 9, to deliver the concentrated wastewater into the second heat exchanger 9;

[0049] The fifth pump 14 is provided on the pipeline between the sedimentation unit 8-1 and the filter press unit 8-2 to deliver the concentrated wastewater into the filter press unit 8-1;

[0050] It also includes a chimney 3 , which is connected to the desulfurization unit 2 .

[0051] 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 desulfurization wastewater requires a large amount of high-quality evaporation or flue gas, and the energy consumption is high. Whether using the unit's extraction steam or the flue gas waste heat before the air preheater, it will have an adverse effect on the unit. In order to solve this problem, the present invention adopts a device for deep recovery of flue gas and coordinated wastewater treatment. 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 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. The heat it carries is used to heat the low-pressure condensate for the first time. The cooled concentrated wastewater enters the filter press device. The supernatant and the new desulfurization wastewater are circulated to the wastewater heater again. A small amount of concentrated wastewater at the bottom of the sedimentation unit is sent to the filter press unit for further filtration. The filter cake particles obtained by filtration can be piled up or mixed with ash. The filtrate obtained is returned to the wastewater sedimentation tank and mixed with the new wastewater, and then enters the wastewater sedimentation tank, and is then sent to the wastewater heater for circulation and concentration. The secondary steam obtained by flash evaporation comes out from the top of the flash tank and enters the condenser. The low-pressure condensate is heated for the second time in the condenser. The low-pressure condensate after the second heating returns to the low-pressure circulating water system with a temperature similar to that of the low-pressure condensate. The secondary steam condensate is used for water replenishment in the desulfurization system process. Through this device, the flue gas heat recovered at low temperature is first used for desulfurization wastewater concentration, which solves the disadvantage 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 there is almost no heat loss, and the heat is fully utilized in a cascade manner. Most of the heat is finally transferred to the low-pressure condensate, thereby reducing the energy consumption of the unit.

[0052] 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 filter press are independent of the flue gas system and can be adjusted according to the load changes of the unit.

[0053] 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 treating 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 arranged upstream of the dust removal unit along the flue gas flow direction, characterized in that: Also includes, 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 filter press device, comprising a precipitation unit and a filter press unit, wherein the precipitation unit is connected to the flash tank so as to send concentrated wastewater into the precipitation unit for precipitation, and the filter press unit is provided with a concentrated wastewater inlet and a filtrate outlet, wherein the concentrated wastewater inlet is connected to the lower part of the precipitation unit, and the filtrate outlet is connected to the upper part of the precipitation unit; The precipitation unit comprises a straight section and a conical section which are sequentially connected, the top of the conical section is connected to the concentrated wastewater inlet, and the straight section is connected to the first heat exchanger, so that the supernatant and / or the added desulfurized wastewater in the precipitation unit enters the first heat exchanger and exchanges heat with the first heat exchange medium from the economizer in the first heat exchanger; A second heat exchanger is disposed between the flash tank and the precipitation unit, wherein the inlet end of the second heat exchanger is connected to the concentrated wastewater outlet, and the outlet end of the second heat exchanger is connected to the straight section, so as to exchange heat between the concentrated wastewater and the second heat exchange medium in the second heat exchanger; A 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 rises from the second heat exchanger enters the third heat exchanger and exchanges heat with the secondary steam from the flash tank again; The first pump is connected to the flash tank and is used to make the flash tank in a negative pressure state and control the vacuum degree therein. The first pump is connected in series with the second heat exchanger and is located after the second heat exchanger.

2. The device according to claim 1, characterized in that The ratio of the length of the straight segment to the length of the tapered segment is (2-4):

1.

3. The device according to any one of claims 1 to 2, characterized in that: Also includes, a second pump, disposed on a pipeline between the precipitation unit and the first heat exchanger, to deliver the supernatant and / or the added desulfurization wastewater into the first heat exchanger; The third pump is arranged between the filter press unit and the straight section to deliver the filtrate into the straight section.

4. The device according to any one of claims 1 to 2, characterized in that: Also includes, a fourth pump, disposed on the pipeline between the flash tank and the second heat exchanger, to deliver the concentrated wastewater into the second heat exchanger; The fifth pump is arranged on the pipeline between the sedimentation unit and the filter press unit to deliver the concentrated wastewater into the filter press unit.

5. The device according to claim 4, characterized in that It also includes a chimney, which is connected to the desulfurization unit.

6. The device according to any one of claims 1-2, characterized in that The dust removal unit is an electrostatic precipitator; the economizer is a low-temperature economizer; the desulfurization unit is a desulfurization tower; and the filter press unit is a plate and frame filter press.

7. The device according to claim 1, characterized in that The first heat exchange medium is heat medium water; the second heat exchange medium is low temperature condensate water.

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