Coal-fired boiler exhaust smoke waste heat recycling system and working method

Abstract

The invention discloses a coal-fired boiler exhaust smoke waste heat recycling system and a working method. The working method comprises the steps that a bypass flue is led out from an inlet flue of an air pre-heater to an outlet flue of the air pre-heater; a bypass flue gas heat exchanger high-temperature section and a bypass flue gas heat exchanger low-temperature section are arranged on the bypass flue, and the bypass flue gas heat exchanger high-temperature section is communicated with the steam turbine regenerative system through a high-temperature section heating water supply water inlet pipeline and a high-temperature section heating water supply water return pipeline; the low-temperature section of the bypass flue gas heat exchanger is communicated with a steam turbine regenerative system through a low-temperature section heating condensed water inlet pipeline and a low-temperature section heating condensed water return pipeline; a tail flue gas heat exchanger high-temperature section and a tail flue gas heat exchanger low-temperature section are arranged on the flue; a primary air heater and a secondary air heater are additionally arranged on the air duct; and an internal circulating water pipeline is connected between the high-temperature section of the tail flue gas heat exchanger and the primary air heater as well as between the low-temperature section of the tail flue gas heat exchanger and the secondary air heater.

Description

Technical Field

[0001] The present invention relates to the technical field of wind power generation, and in particular to a system and a working method for recovering waste heat from exhaust gas of a coal-fired boiler. Background Art

[0002] The waste heat loss from boiler exhaust is the main energy loss of coal-fired units in modern large-scale thermal power plants, accounting for about 4% of the heat released by the fuel. According to the traditional production process of thermal power plants, the heat of this part of the waste heat from exhaust is discharged into the atmosphere along with the flue gas, causing great pollution to the environment. As a flue gas waste heat resource, boiler flue gas waste heat has the characteristics of high source temperature, large quantity, and easy recycling. The effective recovery and efficient utilization of boiler flue gas waste heat has always been a topic of continuous innovative research by technical personnel in this field. In the prior art, the method of recovering boiler flue gas waste heat is mainly to install a low-temperature economizer after the air preheater and before the desulfurization tower to recover waste heat for heating condensate in the heat recovery system. Some power plants combine low-temperature economizers with heaters to indirectly increase the flue gas temperature by increasing the air inlet temperature of the air preheater, thereby heating the condensate and improving the quality of waste heat recovery. However, it was found in the study that the work capacity of the low-pressure heater exhaust is already very low. After the flue gas waste heat replaces part of the low-pressure heater exhaust to heat the condensate and enters the turbine thermal system, most of the energy will be lost to the environment in the form of cold source loss, resulting in a low comprehensive utilization efficiency of boiler flue gas waste heat. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present invention provides a coal-fired boiler exhaust waste heat recovery system and working method. The present invention fully utilizes the boiler exhaust waste heat and improves the waste heat quality for feed water heating and deaerator heating.

[0004] In order to achieve the above object, the present invention adopts the following technical solution:

[0005] In a first aspect, the present invention provides a system for recovering and utilizing waste heat from flue gas of a coal-fired boiler, comprising: a boiler flue gas system and a steam turbine heat recovery system, wherein the boiler flue gas system comprises an air preheater, an electrostatic precipitator, an induced draft fan, a desulfurization tower, and primary and secondary fans correspondingly arranged on the primary and secondary air ducts of the air preheater; the steam turbine heat recovery system comprises high pressure heaters 1-3, low pressure heaters 5-8, a feed water pump, and a deaerator, wherein a bypass flue is led out from the inlet flue of the air preheater to the outlet flue of the air preheater;

[0006] The bypass flue is provided with a high-temperature section of a bypass flue gas heat exchanger and a low-temperature section of a bypass flue gas heat exchanger. The high-temperature section of the bypass flue gas heat exchanger is connected to the steam turbine heat recovery system through a high-temperature section heating feed water inlet pipe and a high-temperature section heating feed water return pipe. The low-temperature section of the bypass flue gas heat exchanger is connected to the steam turbine heat recovery system through a low-temperature section heating condensate water inlet pipe and a low-temperature section heating condensate water return pipe.

[0007] A high-temperature section of a tail flue gas heat exchanger is arranged on the flue between the electrostatic precipitator and the induced draft fan, and a low-temperature section of a tail flue gas heat exchanger is arranged on the flue between the induced draft fan and the desulfurization tower; a primary air heater is installed on the primary air duct, and a secondary air heater is installed on the secondary air duct, and an internal circulation water pipe is connected between the high-temperature section of the tail flue gas heat exchanger and the low-temperature section of the tail flue gas heat exchanger and the primary air heater and the secondary air heater.

[0008] As a further technical solution, the inlet of the bypass flue is connected to the inlet flue of the air preheater, and the outlet of the bypass flue is connected to the outlet flue of the air preheater.

[0009] As a further technical solution, one end of the low-temperature section heating condensate inlet pipe is connected to the No. 5 low-temperature heater outlet, and the other end is connected to the low-temperature section of the bypass flue gas heat exchanger; a condensate booster pump is installed on the low-temperature section heating condensate inlet pipe.

[0010] As a further technical solution, one end of the low-temperature section heated condensate return pipe is connected to the deaerator inlet, and the other end is connected to the low-temperature section of the bypass flue gas heat exchanger.

[0011] As a further technical solution, one end of the high-temperature section heating water inlet pipe is connected to the outlet of the water pump, and the other end is connected to the high-temperature section of the bypass flue gas heat exchanger.

[0012] As a further technical solution, one end of the high-temperature section heating water return pipe is connected to the outlet of the No. 1 high-pressure heater, and the other end is connected to the high-temperature section of the bypass flue gas heat exchanger.

[0013] As a further technical solution, the internal circulation water pipeline connects the high-temperature section of the tail flue gas heat exchanger, the low-temperature section of the tail flue gas heat exchanger, the primary air heater and the secondary air heater.

[0014] As a further technical solution, the internal circulation water pipeline includes a first pipeline, a second pipeline and a third pipeline, one end of the first pipeline is connected to the outlet end of the low-temperature section of the tail flue gas heat exchanger, and the other end is connected to the inlet end of the high-temperature section of the tail flue gas heat exchanger; after the second pipeline and the third pipeline are connected in parallel, one end is connected to the inlet end of the low-temperature section of the tail flue gas heat exchanger, and the other end is connected to the outlet end of the high-temperature section of the tail flue gas heat exchanger, and the second pipeline and the third pipeline pass through the primary air heater and the secondary air heater respectively.

[0015] As a further technical solution, an internal circulation water pump is arranged on the first pipeline between the high-temperature section of the tail flue gas heat exchanger and the low-temperature section of the tail flue gas heat exchanger.

[0016] In a second aspect, the present invention provides a working method based on a high-grade recovery and utilization system of waste heat from exhaust gas of a coal-fired boiler, and the working method is as follows:

[0017] The low-temperature section of the tail flue gas heat exchanger preheats the primary air and secondary air to increase the primary air and secondary air at the air preheater inlet; the high-temperature section of the bypass flue gas heat exchanger heats the feed water through the high-temperature section heating feed water inlet pipe and the high-temperature section heating feed water return pipe, and the low-temperature section of the bypass flue gas heat exchanger heats the condensate at the deaerator inlet through the low-temperature section heating condensate inlet pipe and the low-temperature section heating condensate return pipe.

[0018] One or more technical solutions of the present invention have the following beneficial effects:

[0019] 1. Preheat the primary and secondary air through the waste heat from the low-temperature section of the flue gas to increase the inlet air temperature of the air preheater, so that the flue gas heat of the air preheater becomes abundant. Bypass part of the flue gas through the bypass flue to achieve the heat balance of the air preheater, and then set the high-temperature section of the bypass flue gas heat exchanger on the bypass flue to heat the feed water, and set the low-temperature section of the bypass flue gas heat exchanger to heat the condensate at the inlet of the deaerator, so as to achieve high-grade recovery of flue gas waste heat.

[0020] 2. The present invention coordinates the heat energy transfer and utilization process in the boiler and turbine system of the thermal power plant, reduces the flue gas temperature to below 90°C, and at the same time increases the temperature of the recovered waste heat to above 300°C, which is used as a heat source for water heating and a heat source for heating the deaerator, greatly improving the recovery and utilization grade and comprehensive utilization efficiency of the flue gas waste heat. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0022] Figure 1 It is a schematic diagram of the flue gas system and steam turbine thermal system of a thermal power plant boiler in the prior art;

[0023] Figure 2 This is a schematic diagram of the structure of the waste heat recovery system of coal-fired boiler exhaust gas;

[0024] Among them: 1. Air preheater inlet flue, 2. Bypass flue, 3. Bypass flue gas heat exchanger high temperature section, 4. Bypass flue gas heat exchanger low temperature section, 5. High temperature section heating feed water return pipe, 6. High temperature section heating feed water inlet pipe, 7. Low temperature section heating condensate return pipe, 8. Condensate booster pump, 9. Low temperature section heating condensate inlet pipe, 10. Air preheater flue gas outlet, 11. Tail flue gas heat exchanger high temperature section, 12. Internal circulation water pipe, 13. Secondary air heater, 14. Primary air heater, 15. Internal circulation water pump, 16. Tail flue gas heat exchanger low temperature section. DETAILED DESCRIPTION

[0025] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0026] Glossary:

[0027] High-pressure heater: a proprietary name in this field, high-pressure heater

[0028] Low-pressure heater: a proprietary name in this field, high-pressure heater

[0029] Embodiment 1

[0030] like Figure 1 As shown, it is a schematic diagram of the boiler smoke and air system and the turbine thermal system of a thermal power plant in the prior art. It can be seen that the existing thermal power unit includes a boiler smoke and air system and a turbine heat recovery system, wherein the boiler smoke and air system includes an air preheater, an electrostatic precipitator, an induced draft fan, a desulfurization tower arranged in sequence on the air preheater flue, and a primary fan and a secondary fan correspondingly arranged on the primary air duct and the secondary air duct of the air preheater, and the turbine heat recovery system includes No. 1 high pressure heater, No. 2 high pressure heater, No. 3 high pressure heater, a feed water pump, a deaerator, No. 5 low pressure heater, No. 6 low pressure heater, No. 7 low pressure heater and No. 8 low pressure heater.

[0031] like Figure 2 As shown, a coal-fired boiler exhaust waste heat recovery system mentioned in this embodiment is improved on the existing boiler smoke and air system and turbine heat recovery system, and a bypass flue 2 is led out from the air preheater inlet flue 1 to the air preheater outlet flue 10. Specifically: Figure 2As shown, the inlet of the bypass flue 2 is connected to the air preheater inlet flue 1, and the outlet of the bypass flue 2 is connected to the air preheater outlet flue 10. The bypass flue 2 is provided with a bypass flue gas heat exchanger high temperature section 3 and a bypass flue gas heat exchanger low temperature section 4, wherein the bypass flue gas heat exchanger high temperature section 4 is connected to the steam turbine heat recovery system through a high temperature section heating feed water inlet pipe 6 and a high temperature section heating feed water return pipe 5, and the bypass flue gas heat exchanger low temperature section 4 is connected to the steam turbine heat recovery system through a low temperature section heating condensate water inlet pipe 9 and a low temperature section heating condensate water return pipe 7. Specifically: Figure 2 As shown, one end of the high-temperature section heating feed water inlet pipe 6 is connected to the outlet of the feed water pump, and the other end is connected to the bypass flue gas heat exchanger high temperature section 3, one end of the high-temperature section heating feed water return pipe 5 is connected to the outlet of the No. 1 high-pressure heater, and the other end is connected to the bypass flue gas heat exchanger high temperature section 3, one end of the low-temperature section heating condensate water inlet pipe 9 is connected to the outlet of the No. 5 low-pressure heater, and the other end is connected to the bypass flue gas heat exchanger low temperature section 4; and a condensate booster pump 8 is installed on the low-temperature section heating condensate water inlet pipe 9, and part of the flue gas is bypassed through the bypass flue to achieve thermal balance of the air preheater, and then a bypass flue gas heat exchanger high temperature section is set on the bypass flue for heating the feed water, and a bypass flue gas heat exchanger low temperature section is set for heating the condensate at the deaerator inlet, so as to achieve high-grade recovery of flue gas waste heat.

[0032] In addition to the above improvements, Figure 2As shown, a high temperature section 11 of a tail flue gas heat exchanger is arranged on the flue between the electrostatic precipitator and the induced draft fan, a low temperature section 16 of a tail flue gas heat exchanger is arranged on the flue between the induced draft fan and the desulfurization tower, a primary air heater 14 is installed on the primary air duct, a secondary air heater 13 is installed on the secondary air duct, and an internal circulation water pipe 12 is connected between the high temperature section 11 of the tail flue gas heat exchanger and the low temperature section 16 of the tail flue gas heat exchanger and the primary air heater 14 and the secondary air heater 13, wherein the internal circulation water pipe 12 connects the high temperature section 11 of the tail flue gas heat exchanger, the low temperature section 16 of the tail flue gas heat exchanger, and the primary air heater 14. 4 is connected to the secondary air heater 13, specifically: the internal circulation water pipeline 12 includes a first pipeline, a second pipeline and a third pipeline, one end of the first pipeline is connected to the outlet end of the low temperature section 16 of the tail flue gas heat exchanger, and the other end is connected to the inlet end of the high temperature section 11 of the tail flue gas heat exchanger; the second pipeline and the third pipeline are connected in parallel, one end of which is connected to the inlet end of the low temperature section 16 of the tail flue gas heat exchanger, and the other end is connected to the outlet end of the high temperature section 11 of the tail flue gas heat exchanger, and the second pipeline and the third pipeline pass through the primary air heater 14 and the secondary air heater 13 respectively, and are used to preheat the primary air and the secondary air by the waste heat of the low temperature section of the flue gas. The primary air and secondary air are preheated by the waste heat of the flue gas low temperature section to increase the air temperature at the air preheater inlet, so that the flue gas heat of the air preheater becomes abundant, and the air preheater heat balance is achieved by bypassing part of the flue gas through the bypass flue, and then the bypass flue gas heat exchanger high temperature section is set on the bypass flue for heating the feed water, and the bypass flue gas heat exchanger low temperature section is set for heating the condensed water at the deaerator inlet, so as to achieve high-grade recovery of flue gas waste heat. An internal circulation water pump 15 is set on the first pipeline between the high temperature section of the tail flue gas heat exchanger and the low temperature section of the tail flue gas heat exchanger. The specific working principle of the internal circulation water pipeline 12 is: the internal circulation water pipeline 12 first enters the low temperature section 16 of the tail flue gas heat exchanger, and then is pressurized by the internal circulation water pump 15, enters the high temperature section 11 of the tail flue gas heat exchanger, leaves the high temperature section 11 of the tail flue gas heat exchanger, and then enters the primary air heater 14 and the secondary air heater 13 at the same time, and finally returns to the low temperature section 16 of the tail flue gas heat exchanger, and circulates back and forth.

[0033] Based on the high-grade recovery and utilization system of waste heat from flue gas of a coal-fired boiler mentioned in this embodiment, its specific working method is as follows: the low-temperature section of the tail flue gas heat exchanger preheats the primary air and the secondary air, and increases the primary air and the secondary air at the inlet of the air preheater; the high-temperature section of the bypass flue gas heat exchanger on the bypass flue heats the feed water by heating the feed water inlet pipe and the feed water return pipe at the high temperature section, and the low-temperature section of the bypass flue gas heat exchanger heats the condensate water inlet pipe and the condensate return pipe at the low temperature section to heat the condensate at the inlet of the deaerator, so as to achieve high-grade recovery of waste heat from flue gas. By coordinating the heat energy transfer and utilization process in the boiler and steam turbine system of the thermal power plant, the flue gas temperature is reduced to below 90°C, and the temperature of the recovered waste heat is increased to above 300°C, which is used as the heat source for heating feed water and the heat source for heating the deaerator, greatly improving the recovery and utilization grade and comprehensive utilization efficiency of waste heat from flue gas.

[0034] The above description is only a preferred embodiment of the present embodiment and is not intended to limit the present embodiment. For those skilled in the art, the present embodiment may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present embodiment shall be included in the protection scope of the present embodiment.

Claims

1. A coal-fired boiler exhaust waste heat recovery system, comprising: A boiler flue gas system and a steam turbine heat recovery system, wherein the boiler flue gas system comprises an air preheater, an electrostatic precipitator, an induced draft fan, a desulfurization tower and primary and secondary fans correspondingly arranged on the primary and secondary air ducts of the air preheater; the steam turbine heat recovery system comprises high pressure heaters 1-3, low pressure heaters 5-8, a feed water pump and a deaerator, and is characterized in that: a bypass flue is led out from the inlet flue of the air preheater to the outlet flue of the air preheater; The bypass flue is provided with a high-temperature section of a bypass flue gas heat exchanger and a low-temperature section of a bypass flue gas heat exchanger. The high-temperature section of the bypass flue gas heat exchanger is connected to the steam turbine heat recovery system through a high-temperature section heating feed water inlet pipe and a high-temperature section heating feed water return pipe. The low-temperature section of the bypass flue gas heat exchanger is connected to the steam turbine heat recovery system through a low-temperature section heating condensate water inlet pipe and a low-temperature section heating condensate water return pipe. A high-temperature section of a tail flue gas heat exchanger is arranged on the flue between the electrostatic precipitator and the induced draft fan, and a low-temperature section of a tail flue gas heat exchanger is arranged on the flue between the induced draft fan and the desulfurization tower; a primary air heater is installed on the primary air duct, and a secondary air heater is installed on the secondary air duct, and an internal circulation water pipe is connected between the high-temperature section of the tail flue gas heat exchanger and the low-temperature section of the tail flue gas heat exchanger and the primary air heater and the secondary air heater.

2. A coal-fired boiler exhaust waste heat recovery system as claimed in claim 1, characterized in that: The inlet of the bypass flue is connected to the inlet flue of the air preheater, and the outlet of the bypass flue is connected to the outlet flue of the air preheater.

3. A coal-fired boiler exhaust waste heat recovery system as claimed in claim 1, characterized in that: One end of the low-temperature section heating condensate water inlet pipe is connected to the No. 5 low-temperature heater outlet, and the other end is connected to the low-temperature section of the bypass flue gas heat exchanger; a condensate water booster pump is installed on the low-temperature section heating condensate water inlet pipe.

4. A coal-fired boiler exhaust waste heat recovery system as claimed in claim 1, characterized in that: One end of the low-temperature section heated condensate return pipe is connected to the deaerator inlet, and the other end is connected to the bypass flue gas heat exchanger low-temperature section.

5. A coal-fired boiler exhaust waste heat recovery system as claimed in claim 1, characterized in that: One end of the high temperature section heating water inlet pipe is connected to the outlet of the water pump, and the other end is connected to the high temperature section of the bypass flue gas heat exchanger.

6. A coal-fired boiler exhaust waste heat recovery system as claimed in claim 1, characterized in that: One end of the high temperature section heating water supply return pipe is connected to the outlet of the No. 1 high pressure heater, and the other end is connected to the high temperature section of the bypass flue gas heat exchanger.

7. A coal-fired boiler exhaust waste heat recovery system as claimed in claim 1, characterized in that: The internal circulation water pipeline connects the high temperature section of the tail flue gas heat exchanger, the low temperature section of the tail flue gas heat exchanger, the primary air heater and the secondary air heater.

8. A coal-fired boiler exhaust waste heat recovery system as claimed in claim 7, characterized in that: The internal circulation water pipeline includes a first pipeline, a second pipeline and a third pipeline, one end of the first pipeline is connected to the outlet end of the low-temperature section of the tail flue gas heat exchanger, and the other end is connected to the inlet end of the high-temperature section of the tail flue gas heat exchanger; after the second pipeline and the third pipeline are connected in parallel, one end is connected to the inlet end of the low-temperature section of the tail flue gas heat exchanger, and the other end is connected to the outlet end of the high-temperature section of the tail flue gas heat exchanger, and the second pipeline and the third pipeline pass through the primary air heater and the secondary air heater respectively.

9. A coal-fired boiler exhaust waste heat recovery system as claimed in claim 8, characterized in that: An internal circulation water pump is arranged on the first pipeline between the high temperature section of the tail flue gas heat exchanger and the low temperature section of the tail flue gas heat exchanger.

10. A working method of a high-grade recovery and utilization system of waste heat from exhaust gas of a coal-fired boiler based on any one of claims 1 to 9, the working method being as follows: the low-temperature section of the tail flue gas heat exchanger preheats the primary air and the secondary air to increase the primary air and the secondary air at the inlet of the air preheater; the high-temperature section of the bypass flue gas heat exchanger on the bypass flue heats the feed water through the high-temperature section heating feed water inlet pipe and the high-temperature section heating feed water return pipe, and the low-temperature section of the bypass flue gas heat exchanger heats the condensate at the inlet of the deaerator through the low-temperature section heating condensate inlet pipe and the low-temperature section heating condensate return pipe.

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