Multi-parameter adjustable five-stage flue gas waste heat utilization system

Abstract

The invention relates to a multi-parameter adjustable five-stage flue gas waste heat utilization system which comprises an air preheater, a flue gas heat exchanger in front of an electric precipitator, a low-low temperature electric precipitator, an induced draft fan, a flue gas heat exchanger in front of an absorption tower, a desulfurizing tower and a chimney which are sequentially connected through pipelines. The air preheater is also connected with a cold primary air system and a cold secondary air heating system; the cold secondary air heating system comprises an air heater, and the air heater is further connected with a flue gas heat exchanger in front of an electric precipitator and a flue gas heat exchanger in front of an absorption tower; the air preheater is provided with a bypass system; and an expansion water tank is arranged between the electric dust remover front flue gas heat exchanger and the absorption tower front flue gas heat exchanger. The flue gas waste heat utilization system has the beneficial effects that the flue gas waste heat utilization rate can be effectively increased, energy is saved, and consumption is reduced; and cold secondary air is heated through the air heater, so that the cold end corrosion problem of the air pre-heater can be effectively relieved.

Description

Technical Field

[0001] The invention relates to the technical field of flue gas waste heat utilization, and more specifically, to a multi-parameter adjustable five-stage flue gas waste heat utilization system. Background Art

[0002] Heat loss from boiler flue gas is one of the main heat losses in thermal power plants, and when the type of coal used changes, it may also cause the boiler flue gas temperature to exceed the design value. Using the flue gas waste heat utilization system at the tail of the boiler to recover the waste heat from the flue gas can reduce the flue gas temperature, greatly reduce the heat loss from the flue gas, improve the economy of the power plant, and is one of the important ways to improve the thermal efficiency of the unit. There are operating results of large-capacity units using flue gas waste heat recovery systems both at home and abroad. Germany mostly adopts low-temperature economizer solutions, using condensed water to reduce the flue gas temperature and recover the waste heat to the heat recovery system; Germany also has power plants that use flue gas waste heat for water-based heaters to increase the temperature of the air entering the furnace; Japan uses a water-based medium flue gas-flue gas heat exchanger (MGGH), that is, the circulating cooling water absorbs the heat in the flue gas from the flue gas cooler arranged at the inlet of the dust collector, and then transfers the heat to the low-temperature flue gas in the flue gas heater arranged at the outlet of the desulfurization absorption tower. In order to save energy and improve the economic efficiency of power plants, many power plants use condensate or feed water to absorb exhaust heat in low-temperature economizers to reduce exhaust temperature. After being heated and raised in temperature, it returns to the steam turbine heater system, replacing part of the heater and forming a component of the steam turbine thermal system. Low-temperature economizers will save part of the steam turbine's heat recovery steam. When the steam inlet of the steam turbine remains unchanged, the saved steam returns to the steam turbine from the steam extraction port to continue to expand and do work. Therefore, the energy consumption of the unit can be saved when the power generation remains unchanged.

[0003] After some power plants adopt seawater desulfurization system, a big difference between seawater desulfurization and limestone-gypsum wet desulfurization is that there is no requirement for water balance in the desulfurization tower, which means that compared with limestone-gypsum wet desulfurization, the flue gas temperature before entering the desulfurization tower can be lowered, and there is more room for flue gas waste heat utilization. From this perspective, a flue gas heat exchanger is set in front of the absorption tower. Since the flue gas temperature is low there, the flue gas volume is large and the heat is large, but because of the low flue gas temperature, the overall heat exchange efficiency is low. After the flue gas is heated to the water temperature, the water temperature is still low. Conventionally, if it is used to heat the cold secondary air entering the furnace, the secondary air temperature is still low, and the exhaust gas temperature at the air preheater outlet cannot be effectively increased. Summary of the invention

[0004] The purpose of the present invention is to address the deficiencies of the prior art and to propose a five-stage flue gas waste heat utilization system with adjustable multiple parameters.

[0005] In the first aspect, a five-stage flue gas waste heat utilization system with adjustable multiple parameters is provided, comprising: an air preheater, a flue gas heat exchanger before an electrostatic precipitator, a low-temperature electrostatic precipitator, an induced draft fan, a flue gas heat exchanger before an absorption tower, a desulfurization tower and a chimney connected in sequence through pipelines;

[0006] Among them, the air preheater is also connected to the cold primary air system and the cold secondary air heating system; the cold secondary air heating system includes a heater, and the heater is also connected to the flue gas heat exchanger before the electrostatic precipitator and the flue gas heat exchanger before the absorption tower; the air preheater is provided with a bypass system; an expansion water tank is provided between the flue gas heat exchanger before the electrostatic precipitator and the flue gas heat exchanger before the absorption tower.

[0007] Preferably, the bypass system includes a bypass flue and a high-temperature economizer and a medium-temperature economizer arranged on the bypass flue; the high-temperature economizer and the medium-temperature economizer are connected in series.

[0008] Preferably, the flue gas heat exchanger before the electrostatic precipitator includes a high-temperature heat exchanger before the electrostatic precipitator and a low-temperature heat exchanger before the electrostatic precipitator; the high-temperature heat exchanger before the electrostatic precipitator is used to exchange heat between the output flue gas of the air preheater and the low-temperature water output by the flue gas heat exchanger before the absorption tower, and the low-temperature heat exchanger before the electrostatic precipitator is used to exchange heat between the flue gas treated by the high-temperature heat exchanger before the electrostatic precipitator and condensed water.

[0009] Preferably, a variable frequency pump for adjusting the water volume is provided on the condensate input side of the low-temperature heat exchanger before the electrostatic precipitator.

[0010] Preferably, the high-temperature heat exchanger before the electrostatic precipitator, the flue gas heat exchanger before the absorption tower and the heater are all provided with a variable frequency pump for controlling the air temperature of the cold secondary air outlet; the high-temperature heat exchanger before the electrostatic precipitator is also provided with a bypass for controlling the amount of heat absorption.

[0011] Preferably, the high-temperature economizer is used to heat feed water, and the medium-temperature economizer is used to heat condensate output from the low-temperature heat exchanger before the electrostatic precipitator; the condensate output end of the medium-temperature economizer is connected to the deaerator.

[0012] Preferably, the medium temperature economizer is provided with a bypass for adjusting the heat exchange amount.

[0013] In a second aspect, a five-stage flue gas waste heat utilization method with adjustable multiple parameters is provided, which is executed by any system described in the first aspect, and includes:

[0014] Step 1: Input flue gas, cold primary air and cold secondary air heated by a heater into an air preheater;

[0015] Step 2, the flue gas output from the air preheater is subjected to heat exchange treatment by the flue gas heat exchanger before the electrostatic precipitator;

[0016] Step 3, the flue gas outputted from the flue gas heat exchanger before the electrostatic precipitator passes through the low-temperature electrostatic precipitator, the induced draft fan and the flue gas heat exchanger before the absorption tower for heat exchange treatment;

[0017] Step 4: The flue gas output from the flue gas heat exchanger before the absorption tower is treated by the desulfurization tower and then discharged through the chimney.

[0018] Preferably, step 1 also includes: inputting flue gas into the bypass system of the air preheater, heating feed water through the high-temperature economizer of the bypass system, and heating condensate output from the low-temperature heat exchanger before the electrostatic precipitator through the medium-temperature economizer.

[0019] Preferably, in step 2 and step 3, the condensate input amount of the low-temperature heat exchanger before the electrostatic precipitator and the outlet air temperature of the cold secondary air are adjusted by corresponding variable frequency pumps.

[0020] The beneficial effects of the present invention are:

[0021] 1. The flue gas waste heat utilization system provided by the present invention can effectively improve the utilization rate of flue gas waste heat, save energy and reduce consumption.

[0022] 2. The present invention heats the cold secondary air through the heater, which can effectively alleviate the cold end corrosion problem of the air preheater.

[0023] 3. The flue gas heat exchanger provided by the present invention has a certain dust interception effect, reducing the dust concentration entering the seawater desulfurization tower.

[0024] 4. The present invention can further reduce the temperature of flue gas entering the desulfurization tower and improve the seawater desulfurization efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A structural schematic diagram of a five-stage flue gas waste heat utilization system with adjustable multiple parameters provided by the present invention;

[0026] Figure 2 A flow chart of a five-stage flue gas waste heat utilization method with adjustable multiple parameters provided by the present invention;

[0027] Explanation of the reference numerals: air preheater 1, flue gas heat exchanger 2 before electrostatic precipitator, high-temperature heat exchanger 201 before electrostatic precipitator, low-temperature heat exchanger 202 before electrostatic precipitator, low-temperature electrostatic precipitator 3, induced draft fan 4, flue gas heat exchanger 5 before absorption tower, desulfurization tower 6, chimney 7, high-temperature economizer 8, medium-temperature economizer 9, heater 10, expansion water tank 11. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with embodiments. The description of the following embodiments is only used to help understand the present invention. It should be noted that for ordinary persons in the art, without departing from the principle of the present invention, the present invention can also be modified in some ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0029] Embodiment 1:

[0030] Embodiment 1 of the present application provides a five-stage flue gas waste heat utilization system with adjustable multiple parameters, comprising: an air preheater 1, a flue gas heat exchanger 2 before an electrostatic precipitator, a low-temperature electrostatic precipitator 3, an induced draft fan 4, a flue gas heat exchanger 5 before an absorption tower, a desulfurization tower 6 and a chimney 7 connected in sequence through pipelines;

[0031] Among them, the air preheater 1 is also connected to the cold primary air system and the cold secondary air heating system; the cold secondary air heating system includes a heater 10, and the heater 10 is also connected to the flue gas heat exchanger 2 before the electrostatic precipitator and the flue gas heat exchanger 5 before the absorption tower; the air preheater 1 is provided with a bypass system; an expansion water tank 11 is provided between the flue gas heat exchanger 2 before the electrostatic precipitator and the flue gas heat exchanger 5 before the absorption tower.

[0032] The bypass system includes a bypass flue and a high-temperature economizer 8 and a medium-temperature economizer 9 arranged on the bypass flue; the high-temperature economizer 8 and the medium-temperature economizer 9 are connected in series.

[0033] Embodiment 2:

[0034] Based on Example 1, Example 2 of the present application provides a more specific five-stage flue gas waste heat utilization system with adjustable multiple parameters, such as Figure 1 As shown, it includes: an air preheater 1, a flue gas heat exchanger 2 before the electrostatic precipitator, a low-temperature electrostatic precipitator 3, an induced draft fan 4, a flue gas heat exchanger 5 before the absorption tower, a desulfurization tower 6 and a chimney 7 which are sequentially connected through pipelines;

[0035] Among them, the air preheater 1 is also connected to the cold primary air system and the cold secondary air heating system; the cold secondary air heating system includes a heater 10, and the heater 10 is also connected to the flue gas heat exchanger 2 before the electrostatic precipitator and the flue gas heat exchanger 5 before the absorption tower; the air preheater 1 is provided with a bypass system; an expansion water tank 11 is provided between the flue gas heat exchanger 2 before the electrostatic precipitator and the flue gas heat exchanger 5 before the absorption tower.

[0036] The flue gas discharged from the boiler needs to be cooled before the electrostatic precipitator. This part has a large amount of heat. If all of it is used to heat the secondary air entering the furnace after the heater exchange, the air temperature will be too high. Therefore, this part is optimized and divided into two sections. Specifically, the flue gas heat exchanger 2 before the electrostatic precipitator includes a high-temperature heat exchanger 201 before the electrostatic precipitator and a low-temperature heat exchanger 202 before the electrostatic precipitator; the high-temperature heat exchanger 201 before the electrostatic precipitator is used to exchange heat between the output flue gas of the air preheater 1 and the low-temperature water output by the flue gas heat exchanger 5 before the absorption tower, and the low-temperature heat exchanger 202 before the electrostatic precipitator is used to exchange heat between the flue gas treated by the high-temperature heat exchanger 201 before the electrostatic precipitator and condensed water.

[0037] A variable frequency pump for adjusting the water volume is provided on the condensate input side of the pre-ESP low-temperature heat exchanger 202, thereby adjusting the heat exchange ratio between the pre-ESP high-temperature heat exchanger 201 and the pre-ESP low-temperature heat exchanger 202.

[0038] The high-temperature heat exchanger 201 before the electrostatic precipitator, the flue gas heat exchanger 5 before the absorption tower, and the heater 10 are all provided with a variable frequency pump for controlling the air temperature at the cold secondary air outlet; the high-temperature heat exchanger 201 before the electrostatic precipitator is also provided with a bypass for controlling the amount of heat absorbed. The amount of heat absorbed by the high-temperature heat exchanger 201 before the electrostatic precipitator can be controlled by the bypass, and the heat exchange of the heat exchanger 5 before the absorption tower, the high-temperature heat exchanger 201 before the electrostatic precipitator, and the heater 10 can be controlled by the variable frequency pump, thereby controlling the air temperature at the secondary air outlet.

[0039] The high-temperature economizer 8 is used to heat feed water, and the medium-temperature economizer 9 is used to heat condensate output from the low-temperature heat exchanger 202 before the electrostatic precipitator; the condensate output end of the medium-temperature economizer 9 is connected to the deaerator.

[0040] The medium temperature economizer 9 is provided with a bypass for adjusting the heat exchange amount, and finally adjusting the temperature entering the deaerator.

[0041] It should be noted that the parts in this embodiment that are the same or similar to those in Embodiment 2 can be referenced to each other and will not be described in detail in this application.

[0042] Embodiment 3:

[0043] Based on Examples 1 and 2, Example 3 of the present application provides a five-stage flue gas waste heat utilization method with adjustable multiple parameters, such as Figure 2 As shown, including:

[0044] Step 1: Input flue gas, cold primary air and cold secondary air heated by heater 10 into air preheater 1.

[0045] Step 1 also includes: inputting flue gas into the bypass system of the air preheater 1, heating the feed water through the high-temperature economizer 8 of the bypass system, and heating the condensate output by the low-temperature heat exchanger 202 before the electrostatic precipitator through the medium-temperature economizer 9. For example, the outlet access temperature of the feed water pump connected to the high-temperature economizer 8 is 186.2°C, and the temperature after heating by the high-temperature economizer 8 is 330°C. The outlet access temperature of the No. 9 low-temperature heat pump connected to the medium-temperature economizer 9 is 101.8°C, and the temperature after heating by the high-temperature economizer 8 is 165°C. In addition, the outlet flue gas temperature of the air preheater 1 is 131°C.

[0046] The specific heating method of the cold secondary air is as follows: the heat of the flue gas in front of the desulfurization tower is used to heat the water temperature through the flue gas heat exchanger 5 in front of the absorption tower. The water temperature that is still relatively low after heating is further heated by the high-temperature heat exchanger 201 in front of the electrostatic precipitator and then heats the furnace cold secondary air.

[0047] For example, the temperature of the cold primary air is 27°C, the temperature of the cold secondary air before heating is 22°C, and the temperature of the cold secondary air after heating is 100°C.

[0048] Step 2: The flue gas output from the air preheater 1 is subjected to heat exchange treatment by the flue gas heat exchanger 2 before the electrostatic precipitator.

[0049] For example, the flue gas temperature after heat exchange treatment is 85°C.

[0050] Step 3: The flue gas output from the flue gas heat exchanger 2 before the electrostatic precipitator passes through the low-temperature electrostatic precipitator 3, the induced draft fan 4 and the flue gas heat exchanger 5 before the absorption tower for heat exchange treatment.

[0051] For example, the temperature of the flue gas output by the induced draft fan 4 is 95°C, and the temperature of the flue gas treated by the pre-tower flue gas heat exchanger 5 is 68°C.

[0052] In addition, in step 2 and step 3, the condensate input amount and the cold secondary air outlet temperature of the low-temperature heat exchanger 202 before the electrostatic precipitator are adjusted by the corresponding variable frequency pump.

[0053] Step 4: The flue gas output from the flue gas heat exchanger 5 before the absorption tower is treated by the desulfurization tower 6 and then discharged through the chimney 7.

[0054] It should be noted that the method provided in this embodiment is a method corresponding to the system provided in Embodiments 1 and 2. Therefore, the parts in this embodiment that are the same or similar to Embodiments 1 and 2 can be referenced to each other and will not be repeated in this application.

Claims

1. A five-stage flue gas waste heat utilization system with adjustable multi-parameters, characterized in that: include: An air preheater (1), a flue gas heat exchanger before an electrostatic precipitator (2), a low-temperature electrostatic precipitator (3), an induced draft fan (4), a flue gas heat exchanger before an absorption tower (5), a desulfurization tower (6) and a chimney (7) are sequentially connected through pipelines; The air preheater (1) is also connected to a cold primary air system and a cold secondary air heating system; the cold secondary air heating system comprises a heater (10), and the heater (10) is also connected to a flue gas heat exchanger (2) before the electrostatic precipitator and a flue gas heat exchanger (5) before the absorption tower; the air preheater (1) is provided with a bypass system; an expansion water tank (11) is provided between the flue gas heat exchanger (2) before the electrostatic precipitator and the flue gas heat exchanger (5) before the absorption tower.

2. The multi-parameter adjustable five-stage flue gas waste heat utilization system according to claim 1 is characterized in that: The bypass system comprises a bypass flue and a high-temperature economizer (8) and a medium-temperature economizer (9) arranged on the bypass flue; the high-temperature economizer (8) and the medium-temperature economizer (9) are connected in series.

3. The multi-parameter adjustable five-stage flue gas waste heat utilization system according to claim 2 is characterized in that: The pre-electrostatic precipitator flue gas heat exchanger (2) comprises a pre-electrostatic precipitator high-temperature heat exchanger (201) and a pre-electrostatic precipitator low-temperature heat exchanger (202); the pre-electrostatic precipitator high-temperature heat exchanger (201) is used to perform heat exchange between the flue gas output from the air preheater (1) and the low-temperature water output from the pre-absorption tower flue gas heat exchanger (5), and the pre-electrostatic precipitator low-temperature heat exchanger (202) is used to perform heat exchange between the flue gas treated by the pre-electrostatic precipitator high-temperature heat exchanger (201) and condensed water.

4. The multi-parameter adjustable five-stage flue gas waste heat utilization system according to claim 3 is characterized in that: A variable frequency pump for adjusting the water volume is provided on the condensate input side of the low-temperature heat exchanger (202) before the electrostatic precipitator.

5. The multi-parameter adjustable five-stage flue gas waste heat utilization system according to claim 4 is characterized in that: The high-temperature heat exchanger (201) before the electrostatic precipitator, the flue gas heat exchanger (5) before the absorption tower, and the heater (10) are all provided with a variable frequency pump for controlling the air temperature of the cold secondary air outlet; the high-temperature heat exchanger (201) before the electrostatic precipitator is also provided with a bypass for controlling the amount of heat absorbed.

6. The multi-parameter adjustable five-stage flue gas waste heat utilization system according to claim 5 is characterized in that: The high-temperature economizer (8) is used to heat feed water, and the medium-temperature economizer (9) is used to heat condensate output from the low-temperature heat exchanger (202) before the electrostatic precipitator; the condensate output end of the medium-temperature economizer (9) is connected to the deaerator.

7. The multi-parameter adjustable five-stage flue gas waste heat utilization system according to claim 6 is characterized in that: The medium-temperature economizer (9) is provided with a bypass for adjusting the heat exchange amount.

8. A five-stage flue gas waste heat utilization method with adjustable multi-parameters, characterized in that: Executed by the system according to any one of claims 1 to 7, comprising: Step 1, inputting flue gas, cold primary air and cold secondary air heated by a heater (10) into an air preheater (1); Step 2, the flue gas output from the air preheater (1) is subjected to heat exchange treatment by passing through the flue gas heat exchanger (2) before the electrostatic precipitator; Step 3, the flue gas output from the flue gas heat exchanger (2) before the electrostatic precipitator passes through the low-temperature electrostatic precipitator (3), the induced draft fan (4) and the flue gas heat exchanger (5) before the absorption tower for heat exchange treatment; Step 4: The flue gas output from the flue gas heat exchanger (5) before the absorption tower is treated by the desulfurization tower (6) and then discharged through the chimney (7).

9. The five-stage flue gas waste heat utilization method with adjustable multi-parameters according to claim 8 is characterized in that: Step 1 also includes: inputting flue gas into the bypass system of the air preheater (1), heating the feed water through the high-temperature economizer (8) of the bypass system, and heating the condensate output from the low-temperature heat exchanger (202) before the electrostatic precipitator through the medium-temperature economizer (9).

10. The five-stage flue gas waste heat utilization method with adjustable multi-parameters according to claim 9 is characterized in that: In step 2 and step 3, the condensate input amount and the cold secondary air outlet temperature of the low-temperature heat exchanger (202) before the electrostatic precipitator are adjusted by the corresponding variable frequency pump.

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