A system for coupling flue gas waste heat utilization with zero discharge of desulfurization wastewater

Abstract

The present invention is a system for coupling flue gas waste heat utilization with zero discharge of desulfurized wastewater, comprising a condensate heat recovery system, a desulfurized wastewater treatment system, and a flue gas waste heat utilization system; the condensate heat recovery system sequentially comprises a cold water outlet, a hot water outlet, and a return water outlet on the condensate mother pipe, and all three are connected to the condensate pipe; the flue gas waste heat utilization system comprises an SCR system and an FGD system, and the two are connected through a flue gas pipe; an air preheater, a dust collector, and an induced draft fan are sequentially arranged on the flue gas pipe; the desulfurized wastewater treatment system comprises a steam generator, a desulfurized wastewater evaporation and concentration system, and a desulfurized wastewater concentrate treatment system; and at least one low-temperature economizer is also arranged on the flue gas pipe. The present invention is a system for coupling flue gas waste heat utilization with zero discharge of desulfurized wastewater, realizing mutual coupling and coordination between the flue gas waste heat utilization system and the desulfurized wastewater zero discharge system, and achieving multiple benefits of energy saving, water saving, and environmental protection.

Description

Technical Field

[0001] The present invention relates to the field of energy conservation and environmental protection, and in particular to a system for coupling flue gas waste heat utilization with zero discharge of desulfurization wastewater. Background Art

[0002] In the process of wet desulfurization of boiler flue gas, in order to prevent the concentration of soluble chloride ions and fine dust particles in the slurry from being too high, a certain amount of desulfurization wastewater needs to be discharged from the absorption tower regularly to maintain the material balance in the desulfurization device. The impurities in wet desulfurization wastewater mainly come from flue gas, desulfurizer and desulfurization process water. The impurities in flue gas come from the combustion of coal, and the impurities in desulfurizer come from the dissolution of limestone. Coal contains a variety of elements including heavy metals. These elements generate a variety of compounds after combustion. Some of the compounds are discharged from the furnace with the slag, and the other part enters the desulfurization device absorption tower with the flue gas, dissolves in the absorption slurry, and is continuously concentrated during the circulation of the absorption slurry, resulting in a high impurity content in the desulfurization wastewater. The impurities contained in the desulfurization wastewater are mainly suspended solids, supersaturated sulfites, sulfates, chlorides and trace heavy metals, among which heavy metals are the first type of pollutants that require strict control in the national environmental protection standards. At present, the conventional desulfurization wastewater treatment process is neutralization, reaction, flocculation and precipitation treatment. Heavy metals and other suspended impurities in the desulfurization wastewater are precipitated and removed by adding reagents. The precipitated sludge is dehydrated to form a mud cake and transported outside the factory.

[0003] Conventional desulfurization wastewater treatment processes can only remove heavy metals and other suspended impurities contained in desulfurization wastewater, but cannot remove dissolved ions such as chloride ions and sodium ions in the water. The high salt content of desulfurization wastewater from power plants means that it can only be reused in the coal ash system after treatment. Therefore, most thermal power plant desulfurization wastewater now achieves "zero emission" by reusing it in the coal and ash system. However, some power plants use dry ash removal methods to save water and comprehensively utilize ash, which limits the reuse of desulfurization wastewater; coupled with the limitation of water consumption for spraying in coal yards, it is difficult for all desulfurization wastewater to be reused in the plant.

[0004] As the country's environmental protection requirements increase, new coal-fired power plants are gradually required to achieve "zero discharge" of desulfurized wastewater. In recent years, some domestic research institutions and power plants have tried and applied different "zero discharge" technical routes for desulfurized wastewater, including the "pretreatment + membrane concentration + evaporation crystallizer" technical route, the "concentration and evaporation using flue gas waste heat" technical route, the "direct evaporation of the main flue or bypass flue", and the "flue gas mixed evaporation" technical route. Among them, the "concentration and evaporation using flue gas waste heat" technical route has the advantages of moderate investment, low operating cost, and small land occupation, and has become a key technical route of concern in the industry, but its focus is on the desulfurized wastewater process and the demand for external heat sources.

[0005] At present, most thermal power plants have set up flue gas waste heat utilization systems, which heat condensate with flue gas waste heat through low-temperature economizers, thereby improving the thermal economy of the unit. The technical route of "using flue gas waste heat for concentration and evaporation" also requires flue gas waste heat. However, the overall consideration of the flue gas waste heat utilization system and the "zero emission" system of desulfurization wastewater, and the mutual coordination between the systems have not yet been achieved, which is also a problem that people urgently need to solve. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a system that couples flue gas waste heat utilization with zero discharge of desulfurized wastewater. The flue gas waste heat is used to heat the condensate drawn from the main condensate pipe of the heat recovery system. The heated condensate enters the steam generator to heat the closed-loop circulating water of a certain flow rate and a certain pressure into steam. The cooled condensate returns to the main condensate of the heat recovery system. The steam generated by the steam generator enters the desulfurized wastewater evaporation and concentration system to concentrate the desulfurized wastewater. After condensation, the steam returns to the steam generator to form a closed cycle, and the concentrated wastewater generated by the desulfurized wastewater evaporation and concentration system enters the desulfurized wastewater concentrated liquid treatment system for treatment. The flue gas waste heat utilization system and the desulfurized wastewater zero discharge system are coupled and coordinated with each other to achieve multiple benefits of energy saving, water saving, and environmental protection.

[0007] The technical means adopted by the present invention are described as follows.

[0008] The present invention relates to a system for coupling flue gas waste heat utilization with desulfurization wastewater zero discharge, which comprises a condensate heat recovery system, a desulfurization wastewater treatment system, and a flue gas waste heat utilization system;

[0009] The condensate heat recovery system includes a cold water outlet, a hot water outlet and a return water outlet in sequence on the condensate jellyfish tube, and the cold water outlet, the hot water outlet and the return water outlet are all connected to the condensate pipe, and the condensate pipes connected to the cold water outlet and the hot water outlet respectively merge at the outlet mixing port, and the condensate pipe connected to the outlet mixing port of the low-temperature economizer is provided with a return water inlet;

[0010] The flue gas waste heat utilization system comprises an SCR system and an FGD system; the SCR system and the FGD system are connected via a flue gas pipeline from the SCR system to the FGD system; the air preheater and the dust collector are sequentially arranged on the flue gas pipeline;

[0011] The desulfurization wastewater treatment system comprises a steam generator, a desulfurization wastewater evaporation and concentration system, and a desulfurization wastewater concentrate treatment system; the steam generator is connected to the desulfurization wastewater evaporation and concentration system through a circulating water pipeline; the concentrated wastewater outlet of the desulfurization wastewater evaporation and concentration system is connected to the concentrated wastewater inlet of the desulfurization wastewater concentrate treatment system; the wastewater inlet of the desulfurization wastewater evaporation and concentration system is connected to the wastewater pipeline; the desulfurization wastewater concentrate treatment system is arranged on the flue gas branch pipeline of the flue gas pipeline; the desulfurization wastewater concentrate treatment system is at least connected in parallel with the air preheater; the flue gas branch pipeline connected to the desulfurization wastewater concentrate treatment system is connected to the flue gas pipeline at the flue gas confluence;

[0012] At least one low-temperature economizer is also provided on the flue gas duct, which is arranged at the inlet and / or outlet of the dust collector 32. The condensate water pipe passes through the low-temperature economizer and the steam generator in sequence and then returns to the return water port. The condensate water pipe exchanges heat with the flue gas duct in the low-temperature economizer; the condensate water pipe exchanges heat with the circulating water pipe in the steam generator.

[0013] Preferably, a return water outlet is provided on the condensate pipe connected to the return water port of the steam generator; the return water outlet is connected to the return water inlet through the return water pipe.

[0014] Preferably, the high-temperature condensate outlet of the low-temperature economizer is connected to the return water port through a condensate pipe; a branch pipe is further provided between the low-temperature economizer and the return water port, and the branch pipe is connected to the return water inlet after passing through the steam generator.

[0015] Preferably, a second low-temperature economizer is arranged on the condensate pipe between the low-temperature economizer and the steam generator, and the second low-temperature economizer is also arranged on the flue gas pipe between the low-temperature economizer and the flue gas junction; the condensate pipe exchanges heat with the flue gas pipe in the second low-temperature economizer.

[0016] Preferably, a dust collector is provided on the flue gas duct between the air preheater and the flue gas confluence, and a second dust collector is provided on the flue gas branch duct between the desulfurization wastewater concentrate treatment system and the flue gas confluence.

[0017] Preferably, the desulfurization wastewater concentrate treatment system is provided with a waste residue outlet; the waste residue outlet is connected to the residue bin through a pipeline.

[0018] Preferably, the flue gas waste heat utilization system also includes an induced draft fan. When the low-temperature economizer is arranged at the outlet of the dust collector, the induced draft fan is arranged on the flue gas duct between the dust collector and the low-temperature economizer; when the low-temperature economizer is arranged at the inlet of the dust collector, the induced draft fan is arranged on the flue gas duct at the outlet of the dust collector.

[0019] The beneficial effects of the present invention are:

[0020] 1. The flue gas waste heat utilization system and the desulfurization wastewater zero discharge system are coupled with each other, with good coordination and easy adjustment;

[0021] 2. The desulfurization wastewater zero emission system utilizes part of the flue gas waste heat, and the remaining flue gas heat is returned to the heat recovery system through condensed water, which improves the thermal economy of the unit; at the same time, the temperature of the original flue gas entering the desulfurization system is further reduced, and the desulfurization water consumption is reduced, achieving multiple benefits of energy saving, water saving, and environmental protection.

[0022] 3. The desulfurization wastewater is first concentrated and then evaporated using high-temperature flue gas, which greatly reduces the consumption of high-temperature flue gas and the impact on boiler efficiency.

[0023] 4. The treatment method of high-temperature flue gas after utilization can be determined according to the comprehensive utilization of fly ash, and the form is flexible. This part of high-temperature dusty flue gas can be dedusted separately after utilization and then returned to the main flue, thus avoiding affecting the comprehensive utilization of fly ash. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 FIG. 1 is a schematic diagram of the system structure of the first embodiment of the present invention.

[0025] Figure 2 FIG. 4 is a schematic diagram of the system structure of the second embodiment of the present invention.

[0026] Figure 3 FIG. 4 is a schematic diagram of the system structure of the third embodiment of the present invention.

[0027] Figure 4 FIG. 4 is a schematic diagram of the system structure of the fourth embodiment of the present invention.

[0028] Figure 5 FIG. 5 is a schematic diagram of the system structure of the fifth embodiment of the present invention.

[0029] Figure 6 FIG. 4 is a schematic diagram of the system structure of the sixth embodiment of the present invention.

[0030] Explanation of the figure numbers: condensate heat recovery system 1, desulfurization wastewater treatment system 2, flue gas waste heat utilization system 3, condensate pipe 4, circulating water pipe 5, wastewater pipe 6, flue gas pipe 7, return water pipe 8, cold water outlet 11, hot water outlet 12, return water outlet 13, steam generator 21, desulfurization wastewater evaporation and concentration system 22, desulfurization wastewater concentrate treatment system 23, air preheater 31, dust collector 32, low-temperature economizer 33, second low-temperature economizer 34, second dust collector 35, induced draft fan 36, return water outlet 41, return water inlet 42, outlet mixing port 43, flue gas branch pipe 71, flue gas confluence port 72, flue gas confluence port 73, concentrated wastewater outlet 221, wastewater inlet 222, concentrated wastewater inlet 231, waste residue outlet 232, high-temperature condensate outlet 331. DETAILED DESCRIPTION

[0031] like Figure 1 It is a schematic diagram of the system structure of the first embodiment of the present invention, which includes a condensate heat recovery system 1, a desulfurization wastewater treatment system 2, and a flue gas waste heat utilization system 3.

[0032] The condensate heat recovery system 1 includes a cold water outlet 11, a hot water outlet 12 and a return water port 13 on the condensate mother pipe in sequence, and the cold water outlet 11, the hot water outlet 12 and the return water port 13 are all connected to the condensate pipe 4, and the condensate pipe 4 connected to the cold water outlet 11 and the hot water outlet 12 converges at a water outlet mixing port 43, and the cold water and hot water coming out of the cold water outlet 11 and the hot water outlet 12 are mixed at the water outlet mixing port 43, and the water output of the cold water and the hot water is controlled by adjusting the water outlet valves of the cold water outlet 11 and the hot water outlet 12, so as to achieve the purpose of controlling the water outlet temperature at the water outlet mixing port 43, and the condensate coming out of the water outlet mixing port 43 returns to the return water port 13 after passing through the steam generator 21 and the low-temperature economizer 33.

[0033] The flue gas waste heat utilization system 3 includes an SCR system and an FGD system. The SCR system and the FGD system are connected via a flue gas duct 7 from the SCR system to the FGD system. The flue gas duct 7 is provided with the air preheater 31, the dust collector 32, the induced draft fan 36 and the low-temperature economizer 33 in sequence. The air preheater 31 and the dust collector 32 further heat and remove dust from the flue gas in the flue gas duct 7. Then, in the low-temperature economizer 33, the flue gas duct 7 exchanges heat with the condensate water duct 4, further heats the condensate in the condensate water duct 4, and cools the flue gas in the flue gas duct 7. The cooled flue gas enters the FGD system for treatment.

[0034] The desulfurization wastewater treatment system 2 includes a steam generator 21, a desulfurization wastewater evaporation and concentration system 22, and a desulfurization wastewater concentrate treatment system 23. The steam generator 21 and the desulfurization wastewater evaporation and concentration system 22 are connected via a circulating water pipeline 5. The heated condensed water is exchanged with the closed circulating water in the circulating water pipeline 5 through the condensed water pipeline 4 in the steam generator 21, and the closed circulating water with a certain flow rate and a certain pressure is heated into steam. A return water outlet 41 is provided on the condensate water pipe 4 connecting the steam generator 21 with the return water port 13, and a return water inlet 42 is provided on the condensate water pipe 4 connecting the low-temperature economizer 33 with the outlet water mixing port 43. The return water outlet 41 is connected to the return water inlet 42 through a return water pipe 8. The condensate water cooled after passing through the steam generator 21 will be divided into two flow directions before returning to the return water port 13. One flow direction will directly return to the return water port 13, and the other flow direction will flow to the condensate water pipe 4 between the outlet water mixing port 43 and the low-temperature economizer 33 through the return water pipe 8 to mix with the condensate water inside. According to actual needs, the flow rate can be further adjusted by controlling the flow rate through a valve.

[0035] The concentrated wastewater outlet 221 of the desulfurization wastewater evaporation and concentration system 22 is connected to the concentrated wastewater inlet 231 of the desulfurization wastewater concentrated liquid treatment system 23, and the wastewater inlet 222 of the desulfurization wastewater evaporation and concentration system 22 is connected to the wastewater pipe 6. The wastewater enters the desulfurization wastewater evaporation and concentration system 22 through the wastewater pipe 6 for treatment, and the steam formed by the circulating water in the circulating water pipe 5 in the steam generator 21 is used for wastewater concentration and desulfurization in the desulfurization wastewater evaporation and concentration system 22, and then the steam is cooled and liquefied into liquid and returned to the steam generator 21 through the circulating water pipe 5 to be heated into steam again, and the concentrated wastewater enters the desulfurization wastewater concentrated liquid treatment system 23. The desulfurization wastewater concentrate treatment system 23 is arranged on the flue gas branch pipe 71 of the flue gas pipe 7. The desulfurization wastewater concentrate treatment system 23 is connected in parallel with the air preheater 31. The flue gas branch pipe 71 connected to the desulfurization wastewater concentrate treatment system 23 is connected to the flue gas pipe 7 at the flue gas junction 72. The desulfurization wastewater concentrate treatment system 23 utilizes the heat of the high-temperature flue gas generated by the SCR system to evaporate the concentrated wastewater, and the flue gas in the flue gas branch pipe 71 is mixed with the high-temperature flue gas in the flue gas pipe 7 at the flue gas junction 72.

[0036] like Figure 2 FIG. 2 is a schematic diagram of the system structure of the second embodiment of the present invention. Figure 2 and Figure 1Compared with the above, the same parts are not described here. The difference is that the high-temperature condensate outlet 331 of the low-temperature economizer 33 is connected to the return water port 13 through the condensate pipe 4. A branch pipe is provided on the condensate pipe 4 between the low-temperature economizer 33 and the return water port 13. The branch pipe is connected to the return water inlet 42 after passing through the steam generator 21. After heat exchange in the steam generator 21, the condensate in the branch pipe returns to the condensate pipe 4 between the water outlet mixing port 43 and the low-temperature economizer 33, and mixes with the condensate in the condensate pipe 4. Compared with the first embodiment, the temperature of the condensate returned to the condensate heat recovery system 1 is slightly higher than that of the first embodiment, but the control logic is slightly more complicated.

[0037] like Figure 3 The third embodiment of the present invention is a schematic diagram of the system structure. Compared with the first embodiment, the difference is that the low-temperature economizer 33 is arranged at the entrance of the dust collector 32 on the flue gas duct 7. In the third embodiment, the temperature of the flue gas entering the dust collector 32 is reduced, which is conducive to the collection of smoke dust, and at the same time reduces the flue gas volume of the induced draft fan 36 and reduces the power consumption of the induced draft fan 36. However, the waste heat of the flue gas caused by the temperature rise of the induced draft fan 36 cannot be used.

[0038] like Figure 4 The fourth embodiment of the present invention is a schematic diagram of the system structure. Compared with the first embodiment, the difference is that a second low-temperature economizer 34 is provided on the condensate pipe 4 between the low-temperature economizer 33 and the steam generator 21, and the second low-temperature economizer 34 is also provided on the flue gas pipe 7 between the low-temperature economizer 33 and the flue gas confluence port 72. The condensate pipe 4 exchanges heat with the flue gas pipe 7 in the second low-temperature economizer 34. In the third embodiment, the condensate is heated twice before entering the steam generator 21 for heat exchange with the circulating water. In this embodiment, the flue gas temperature entering the dust collector 32 is reduced, which is conducive to the collection of smoke dust. At the same time, the flue gas volume of the induced draft fan 36 is reduced, and the power consumption of the induced draft fan 36 is reduced. The flue gas waste heat of the induced draft fan 36 can be used to further improve the thermal economy of the unit.

[0039] like Figure 5 The diagram shows the system structure of the fifth embodiment of the present invention, the difference being that a dust collector 32 is provided on the flue gas pipeline 7 between the air preheater 31 and the flue gas confluence port 72, and a second dust collector 35 is provided on the flue gas branch pipeline 71 between the desulfurization wastewater concentrate treatment system 23 and the flue gas confluence port 72. In this embodiment, the salt-containing dust after passing through the desulfurization wastewater concentrate treatment system 23 is collected separately by the second dust collector 35 and will not enter the dust collector 32, thereby not affecting the comprehensive utilization of fly ash collected by the dust collector 32.

[0040] like Figure 6The figure shows a schematic diagram of the system structure of the sixth embodiment of the present invention, the difference being that the desulfurization wastewater concentrate treatment system 23 is provided with a waste residue outlet 232, and the waste residue outlet 232 is connected to the slag bin through a pipeline. In this embodiment, the desulfurization wastewater concentrate treatment system 23 can utilize the desulfurization system filter press to recover the filter cake, and the desulfurization wastewater concentrate is then evaporated by a high-temperature flue gas process or discharged to the slag bin. Under this scheme, the treatment method of the desulfurization wastewater concentrate is simple and flexible, and the treatment method of the desulfurization wastewater concentrate after the filter press can be selected according to the requirements of environmental protection emissions.

Claims

1. A system for coupling flue gas waste heat utilization with zero discharge of desulfurization wastewater, characterized in that: It includes a condensate heat recovery system (1), a desulfurization wastewater treatment system (2), and a flue gas waste heat utilization system (3); The condensate heat recovery system (1) comprises a cold water outlet (11), a hot water outlet (12) and a return water outlet (13) in sequence on the condensate jellyfish pipe, and the cold water outlet (11), the hot water outlet (12) and the return water outlet (13) are all connected to the condensate pipe (4), and the condensate pipe (4) respectively connected to the cold water outlet (11) and the hot water outlet (12) merges at the outlet mixing port (43); The flue gas waste heat utilization system (3) comprises an SCR system and an FGD system; the SCR system and the FGD system are connected via a flue gas pipeline (7) for the flow of flue gas from the SCR system to the FGD system; an air preheater (31) and a dust collector (32) are sequentially arranged on the flue gas pipeline (7); The desulfurization wastewater treatment system (2) comprises a steam generator (21), a desulfurization wastewater evaporation and concentration system (22), and a desulfurization wastewater concentrated liquid treatment system (23); the steam generator (21) and the desulfurization wastewater evaporation and concentration system (22) are connected via a circulating water pipeline (5); the concentrated wastewater outlet (221) of the desulfurization wastewater evaporation and concentration system (22) is connected to the concentrated wastewater inlet (231) of the desulfurization wastewater concentrated liquid treatment system (23); The wastewater inlet (222) of the desulfurization wastewater evaporation concentration system (22) is connected to the wastewater pipeline (6); the desulfurization wastewater concentrate treatment system (23) is arranged on the flue gas branch pipeline (71) of the flue gas pipeline (7); the desulfurization wastewater concentrate treatment system (23) is at least connected in parallel with the air preheater (31); the flue gas branch pipeline (71) connected to the desulfurization wastewater concentrate treatment system (23) is connected to the flue gas pipeline (7) at the flue gas confluence (72); The flue gas duct (7) is also provided with at least one low-temperature economizer, which is arranged at the inlet and / or outlet of the dust collector (32). The condensate water duct (4) passes through the low-temperature economizer (33) and the steam generator (21) in sequence and then returns to the water return port (13). The condensate water duct (4) exchanges heat with the flue gas duct (7) in the low-temperature economizer (33); the condensate water duct (4) exchanges heat with the circulating water duct (5) in the steam generator (21); The condensate pipe (4) connected to the low-temperature economizer (33) and the water outlet mixing port (43) is provided with a return water inlet (42); A return water outlet (41) is provided on the condensate pipe (4) connected to the steam generator (21) and the return water port (13); the return water outlet (41) is connected to the return water inlet (42) via a return water pipe (8); The high-temperature condensate outlet (331) of the low-temperature economizer (33) is connected to the return water port (13) via a condensate pipe (4); a branch pipe is provided on the condensate pipe (4) between the low-temperature economizer (33) and the return water port (13); the branch pipe is connected to the return water port (42) after passing through the steam generator (21); A second low-temperature economizer (34) is arranged on the condensate pipe (4) between the low-temperature economizer (33) and the steam generator (21), and the second low-temperature economizer (34) is also arranged on the flue gas pipe (7) between the low-temperature economizer (33) and the flue gas junction (72); the condensate pipe (4) exchanges heat with the flue gas pipe (7) in the second low-temperature economizer (34).

2. A system for coupling flue gas waste heat utilization with zero discharge of desulfurization wastewater as claimed in claim 1, characterized in that: A dust collector (32) is provided on the flue gas pipeline (7) between the air preheater (31) and the flue gas junction (72), and a second dust collector (35) is provided on the flue gas branch pipeline (71) between the desulfurization wastewater concentrate treatment system (23) and the flue gas junction (72).

3. A system for coupling flue gas waste heat utilization with zero discharge of desulfurization wastewater as claimed in claim 1, characterized in that: The desulfurization wastewater concentrate treatment system (23) is provided with a waste residue outlet (232); the waste residue outlet (232) is connected to the residue bin via a pipeline.

4. A system for coupling flue gas waste heat utilization with zero discharge of desulfurization wastewater as claimed in claim 1, characterized in that: The flue gas waste heat utilization system (3) further comprises an induced draft fan (36). When the low-temperature economizer (33) is arranged at the outlet of the dust collector (32), the induced draft fan (36) is arranged on the flue gas duct (7) between the dust collector (32) and the low-temperature economizer (33); when the low-temperature economizer (33) is arranged at the inlet of the dust collector (32), the induced draft fan (36) is arranged on the flue gas duct (7) at the outlet of the dust collector (32).

Images