Power plant flue gas treatment system based on waste heat recovery

Abstract

The utility model discloses a power plant flue gas treatment system based on waste heat recovery, which comprises a boiler, a denitration device, a rotary air preheater, a dust remover, a flue gas air heater, an induced draft fan, a desulfurizing absorption tower, a chimney, a first bypass, a second bypass and a third bypass, the inlet end of the first bypass is connected to the flue between the denitration device and the rotary air preheater, and the outlet end of the first bypass is connected to the flue between the flue gas air heater and the rotary air preheater; the inlet end of the second bypass is connected with a primary warm air outlet of the smoke air heater, and the second bypass is connected with a primary air inlet and outlet of the rotary air preheater and connected into the boiler. The inlet end of the third bypass is connected with a secondary warm air outlet of the smoke air heater, and the third bypass is connected with a secondary air inlet and outlet of the rotary air preheater and connected into the boiler. Redistribution and optimization of the heat exchange load of the rotary air pre-heater are achieved, the rotary air pre-heater is made to work in a high-temperature area all the time, and long-period normal operation of the rotary air pre-heater is facilitated.

Description

Technical Field

[0001] The utility model relates to a boiler tail gas treatment system, in particular to a power plant flue gas treatment system based on waste heat recovery. Background Art

[0002] Some existing boiler tail gas treatment systems are as follows: Figure 1As shown, it consists of four parts: rotary air preheater, flue gas feed water heat exchanger (low-temperature economizer I), flue gas condensate water heat exchanger (low-temperature economizer II), flue gas heat medium water heat exchanger (dust collector inlet low-temperature economizer + heater). Based on the experience of many similar cases in the coal-fired power industry, this solution cannot guarantee the long-term safe and reliable operation of the equipment, and cannot maintain the design performance of long-term flue gas waste heat recovery and energy saving. There are many problems in its operation as follows: problems with the rotary air preheater. Due to the ammonia escape in denitrification and the presence of sulfur trioxide in the flue gas, ammonium bisulfate will inevitably be generated in the flue gas, causing ash accumulation and blockage in the rotary air preheater. There are currently many technical routes for the treatment of ammonium bisulfate blockage, but there is no complete solution. The designed flue gas temperature at the outlet of the rotary air preheater is 120°C, which causes the metal wall temperature of the low-temperature section of the heat storage element to be lower than the condensation and crystallization temperature of ammonium bisulfate. There will inevitably be ammonium bisulfate deposition and ash accumulation. The heat exchange capacity of the rotary air preheater will continue to decrease, the exhaust temperature will continue to rise, and the boiler efficiency will continue to decrease; problems with the flue gas feed water heat exchanger. The flue gas outside the tube will be horizontally eroded and worn, and the horizontal arrangement will cause certain ash accumulation; the feed water temperature is lower than 189.8°C (BRL). When operating at low load for a long time, the metal wall temperature in the feed water inlet area of ​​the flue gas feed water heat exchanger is low, and there is a certain risk of ammonium bisulfate deposition. Once blocked, it is difficult to remove, and the heat exchange tube cannot be replaced individually, and the entire module can only be replaced, which results in high maintenance costs. Problems with the flue gas condensate water heat exchanger: horizontal scouring of flue gas outside the tube will cause certain wear, and horizontal arrangement will cause certain dust accumulation. The inlet condensate temperature of the flue gas condensate water heat exchanger is lower than 80°C, and the outlet water temperature is lower than 161.9°C. The metal wall temperature is lower than the gasification temperature of ammonium bisulfate, and the inlet flue gas temperature is higher than the crystallization temperature of ammonium bisulfate. The viscous liquid ammonium bisulfate carried by the flue gas will produce ammonium bisulfate deposition under all operating conditions, which will definitely form a flue gas corridor and cause wear and leakage. Once blocked, it is difficult to remove, and the heat exchange tube cannot be replaced individually, and the entire module can only be replaced, which results in high maintenance costs. Problems with the flue gas heat medium water heat exchanger: horizontal scouring of flue gas outside the tube will cause certain wear, and horizontal arrangement will cause certain dust accumulation. Once blocked, it is difficult to remove, and the heat exchange tube cannot be replaced individually, and the entire module can only be replaced, which results in high maintenance costs. The heat of the secondary air heat medium water heater under all operating conditions cannot meet the demand, and external heat supplement is required. The flue gas treatment system of a power plant developed in the early stage (CN111895442A) includes a flue gas path mainly composed of a boiler, a rotary air preheater, a flue gas heater, an induced draft fan, a desulfurization tower and a chimney connected in sequence. The flue gas heater uses air as a cold medium. The air is introduced into the flue gas heater and exchanges heat with the flue gas flowing through the flue gas heater. The medium-temperature air obtained by the heat exchange is introduced into the rotary air preheater. The medium-temperature air exchanges heat with the flue gas flowing through the rotary air preheater. The first part of the hot air obtained by the heat exchange is introduced into the boiler as a heat source, and the second part of the hot air obtained by the heat exchange is cooled by heat exchange and recycled as part of the cold medium of the flue gas heater.Although this solution solves the problems of low-temperature corrosion and ammonium bisulfate blockage in the rotary air preheater, it needs to be further optimized in terms of waste heat recovery and heat exchange load distribution. Utility Model Content

[0003] At least in order to solve the technical problems mentioned in the background technology, the purpose of the utility model is to provide a flue gas treatment system for a power plant based on waste heat recovery.

[0004] In order to achieve the above-mentioned purpose, the utility model provides the following technical solutions.

[0005] A flue gas treatment system for a power plant based on waste heat recovery, comprising a boiler, a denitration device, a rotary air preheater, a dust collector, a flue gas heater, an induced draft fan, a desulfurization absorption tower and a chimney connected in sequence, and also comprising a first bypass, a second bypass and a third bypass; an inlet end of the first bypass is connected to the flue between the denitration device and the rotary air preheater, and an outlet end of the first bypass is connected to the flue between the flue gas heater and the rotary air preheater; an inlet end of the second bypass is connected to a primary warm air outlet of the flue gas heater, and the second bypass is connected to the primary air inlet and outlet of the rotary air preheater and connected to the boiler; an inlet end of the third bypass is connected to a secondary warm air outlet of the flue gas heater, and the third bypass is connected to the secondary air inlet and outlet of the rotary air preheater and connected to the boiler.

[0006] In order to further realize waste heat recovery and utilization, a heat exchanger is arranged on the pipeline of the first bypass, and the heat exchanger is connected to the water supply system. The low-temperature water in the water supply system forms high-temperature water after flowing through the heat exchanger.

[0007] Furthermore, a blower and a damper door are respectively provided on the second bypass and the third bypass.

[0008] As one of the preferred solutions of the utility model, the second bypass and the third bypass are respectively connected to the air intake system, which includes a pipeline connected to the cold air inlet of the flue gas heater, and a second damper door and a fan installed on the pipeline. In order to further realize the waste heat recovery, the air intake system is connected to the circulating water heater, and the hot water of the circulating water heater comes from the high-temperature water at the first bypass.

[0009] As the second preferred solution of the utility model, the second bypass and the third bypass each have an air intake system, each air intake system includes a pipeline connected to the cold air inlet of the flue gas heater, and a second baffle door and a fan installed on the pipeline, and the fan is connected to the circulating water heater through a pipeline.

[0010] In order to improve the heat exchange effect, the heat exchange tubes of the flue gas heater adopt three-dimensional fin heat exchange tubes.

[0011] Beneficial effects: The utility model realizes the redistribution and optimization of the heat exchange load of the rotary air preheater, and can increase the inlet air temperature of the rotary air preheater to above 70°C and the outlet flue gas temperature to above 150°C (the cold end comprehensive temperature is above 220°C), so that the rotary air preheater is always working in a relatively high temperature area, and ammonium bisulfate will not crystallize or corrode at low temperatures, thereby providing conditions for the long-term normal operation of the rotary air preheater; the flue gas heater is operated in a low temperature section, and the ammonium bisulfate is later moved to the flue gas heater to deposit and condense, so that the deposited ammonium bisulfate is completely removed by "dry burning" of the flue gas heater; the utility model can increase the inlet air temperature of the rotary air preheater to extract part of the high-temperature flue gas from the inlet of the rotary air preheater for heating the feed water without reducing the hot air temperature of the boiler, thereby achieving energy saving and in-depth utilization of waste heat recovery, and the exhaust gas temperature can be adjusted by adjusting the feed water amount during operation, which is very convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Schematic diagram of some existing boiler tail gas treatment systems;

[0013] Figure 2 This is a schematic diagram of the flue gas treatment system of a power plant in Example 1;

[0014] Figure 3 This is a schematic diagram of the flue gas treatment system of the power plant in Example 2. DETAILED DESCRIPTION

[0015] The following is a clear and complete description of the technical solutions in the embodiments of the utility model in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0016] Example 1: Figure 2As shown, a flue gas treatment system of a power plant based on waste heat recovery includes a boiler 1, a denitration device 2, a rotary air preheater 3, a dust collector 4, a flue gas heater 5, an induced draft fan 6, a desulfurization absorption tower 7 and a chimney 8 connected in sequence. The heat exchange tube of the flue gas heater 5 adopts a three-dimensional fin heat exchange tube, and also includes a first bypass 11, a second bypass 12, and a third bypass 13; the inlet end of the first bypass 11 is connected to the flue between the denitration device 2 and the rotary air preheater 3, and the outlet end of the first bypass 11 is connected to the flue between the dust collector 4 and the rotary air preheater 3; the inlet end of the second bypass 12 is connected to the primary warm air outlet of the flue gas heater 5, the second bypass 12 is connected to the primary air inlet and outlet of the rotary air preheater 3 and connected to the boiler 1; the inlet end of the third bypass 13 is connected to the secondary warm air outlet of the flue gas heater 5, the third bypass 13 is connected to the secondary air inlet and outlet of the rotary air preheater 3 and connected to the boiler 1.

[0017] In this embodiment, a heat exchanger 9 is provided on the pipeline of the first bypass 11, and the heat exchanger 9 is connected to the water supply system. The low-temperature water in the water supply system forms high-temperature water after flowing through the heat exchanger 9. The high-temperature flue gas flowing through the heat exchanger 9 in the pipeline of the first bypass 11 is introduced into the flue between the dust collector 4 and the rotary air preheater 3 after being cooled by heat exchange.

[0018] In this embodiment, a blower 10 and a damper door 14 are respectively provided on the second bypass 12 and the third bypass 13. The second bypass 12 and the third bypass 13 are respectively connected to an air intake system, which includes a pipeline connected to the cold air inlet of the flue gas heater 5, and a second damper door 16 and a blower 15 installed on the pipeline. The air intake system is connected to a circulating water heater, and the hot water of the circulating water heater comes from the high-temperature water at the first bypass 11.

[0019] Example 2: Figure 3 As shown, a flue gas treatment system of a power plant based on waste heat recovery includes a boiler 1, a denitration device 2, a rotary air preheater 3, a flue gas heater 5, a dust collector 4, an induced draft fan 6, a desulfurization absorption tower 7 and a chimney 8 connected in sequence. The heat exchange tube of the flue gas heater 5 adopts a three-dimensional fin heat exchange tube, and also includes a first bypass 11, a second bypass 12, and a third bypass 13; the inlet end of the first bypass 11 is connected to the flue between the denitration device 2 and the rotary air preheater 3, and the outlet end of the first bypass 11 is connected to the flue between the flue gas heater 5 and the rotary air preheater 3; the inlet end of the second bypass 12 is connected to the primary warm air outlet of the flue gas heater 5, the second bypass 12 is connected to the primary air inlet and outlet of the rotary air preheater 3 and connected to the boiler 1; the inlet end of the third bypass 13 is connected to the secondary warm air outlet of the flue gas heater 5, the third bypass 13 is connected to the secondary air inlet and outlet of the rotary air preheater 3 and connected to the boiler 1.

[0020] In this embodiment, a heat exchanger 9 is arranged on the pipeline of the first bypass 11, and the heat exchanger 9 is connected to the water supply system. The low-temperature water in the water supply system forms high-temperature water after flowing through the heat exchanger 9. The high-temperature flue gas flowing through the heat exchanger 9 in the pipeline of the first bypass 11 is introduced into the flue between the dust collector 4 and the rotary air preheater 3 after heat exchange and cooling. The second bypass 12 and the third bypass 13 each have a set of air intake systems, each of which includes a pipeline connected to the cold air inlet of the flue gas heater 5, and a second damper door 16 and a fan 15 installed on the pipeline. The fan 15 is connected to the circulating water heater 17 through a pipeline, and the hot water of the circulating water heater 17 can come from the high-temperature water at the first bypass 11.

[0021] During operation, the high-temperature flue gas discharged from the boiler 1 flows through the denitrification device 2, the rotary air preheater 3 (the flue gas is cooled for the first time in the rotary air preheater 3), the dust collector 4, the flue gas heater 5 (the flue gas is cooled for the second time in the air heater 5), the induced draft fan 6, the desulfurization absorption tower 7, and finally enters the chimney 8 for discharge; part of the high-temperature flue gas is extracted from the flue between the denitrification device 2 and the rotary air preheater 3 and introduced into the heat exchanger 9 to heat the low-temperature water to form high-temperature water. This part of the high-temperature water is further The circulating water heater is then used as a heat medium to heat the primary and secondary air; the air introduced through the air intake system is divided into primary air and secondary air, the primary air is heated by the flue gas heater 5 and then introduced into the primary air channel of the rotary air preheater 3 for secondary heating, and the high-temperature air after the secondary heating (i.e., hot primary air) is introduced into the boiler 1 for reuse, and the secondary air is heated by the flue gas heater 5 and then introduced into the secondary air channel of the rotary air preheater 3 for secondary heating, and the high-temperature air after the secondary heating (i.e., hot secondary air) is also introduced into the boiler 1 for reuse.

[0022] In this scheme, the inlet air temperature of the rotary air preheater is firstly increased, so that its outlet flue gas temperature is increased accordingly, so as to optimize the operating conditions of the rotary air preheater, prevent the rotary air preheater from low-temperature corrosion and condensation and ash accumulation of ammonium bisulfate and blockage, and ensure that the rotary air preheater maintains the design performance for a long period of time to achieve energy saving; on the other hand, after the inlet air temperature of the rotary air preheater is increased, part of the high-temperature flue gas can be extracted to heat the feed water without lowering the hot air temperature, thereby realizing the cascade utilization of waste heat and realizing the redistribution and optimization of the heat exchange load of the rotary air preheater.

[0023] The utility model realizes the redistribution and optimization of the heat exchange load of the rotary air preheater, and can increase the inlet air temperature of the rotary air preheater to above 70°C and the outlet flue gas temperature to above 150°C (the cold end comprehensive temperature is above 220°C), so that the rotary air preheater is always working in a relatively high temperature area, and ammonium bisulfate will not crystallize or corrode at low temperatures, thereby providing conditions for the long-term normal operation of the rotary air preheater; the flue gas heater is operated in a low temperature section, and the ammonium bisulfate is later moved to the flue gas heater to be deposited and condensed, so that the deposited ammonium bisulfate is completely removed by "dry burning" of the flue gas heater; the utility model can increase the inlet air temperature of the rotary air preheater, thereby extracting part of the high-temperature flue gas from the inlet of the rotary air preheater for heating the feed water without reducing the hot air temperature of the boiler, thereby realizing energy saving and deep utilization of waste heat recovery, and the exhaust gas temperature can be adjusted by adjusting the feed water amount during operation, which is very convenient.

Claims

1. A flue gas treatment system for a power plant based on waste heat recovery, comprising a boiler (1), a denitrification device (2), a rotary air preheater (3), a dust collector (4), a flue gas heater (5), an induced draft fan (6), a desulfurization absorption tower (7) and a chimney (8), characterized in that: The invention also comprises a first bypass (11), a second bypass (12), and a third bypass (13); the inlet end of the first bypass (11) is connected to the flue between the denitration device (2) and the rotary air preheater (3), and the outlet end of the first bypass (11) is connected to the flue between the flue gas heater (5) and the rotary air preheater (3); the inlet end of the second bypass (12) is connected to the primary warm air outlet of the flue gas heater (5), and the second bypass (12) is connected to the primary air inlet and outlet of the rotary air preheater (3) and connected to the boiler (1); the inlet end of the third bypass (13) is connected to the secondary warm air outlet of the flue gas heater (5), and the third bypass (13) is connected to the secondary air inlet and outlet of the rotary air preheater (3) and connected to the boiler (1).

2. The power plant flue gas treatment system according to claim 1, characterized in that: A heat exchanger (9) is arranged on the pipeline of the first bypass (11), and the heat exchanger (9) is connected to a water supply system. Low-temperature water in the water supply system flows through the heat exchanger (9) to form high-temperature water.

3. The power plant flue gas treatment system according to claim 2, characterized in that: A blower (10) and a baffle door (14) are respectively arranged on the second bypass (12) and the third bypass (13).

4. The power plant flue gas treatment system according to claim 3, characterized in that: The second bypass (12) and the third bypass (13) are respectively connected to an air intake system, wherein the air intake system comprises a pipeline connected to a cold air inlet of the flue gas heater (5), and a second damper door (16) and a fan (15) installed on the pipeline.

5. The power plant flue gas treatment system according to claim 4, characterized in that: The air inlet system is connected to a circulating water heater, and the hot water of the circulating water heater comes from the high-temperature water at the first bypass (11).

6. The power plant flue gas treatment system according to claim 2, characterized in that: The second bypass (12) and the third bypass (13) each have an air intake system, each air intake system comprising a pipeline connected to the cold air inlet of the flue gas heater (5), and a second damper door (16) and a fan (15) installed on the pipeline, and the fan (15) is connected to the circulating water heater (17) via a pipeline.

7. The power plant flue gas treatment system according to any one of claims 1 to 6, characterized in that: The heat exchange tubes of the flue gas heater (5) are three-dimensional fin heat exchange tubes.

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