A multi-stage waste heat recovery system and method for flue gas of a gas generator set

Abstract

The present invention proposes a multi-stage waste heat recovery system and method for flue gas of a gas-fired power generation unit, comprising a boiler, a primary air heat exchange unit, a secondary gas heat exchange unit, a tertiary gas heat exchange unit and a chimney. The flue gas outlet of the boiler is connected to the bottom inlet of the chimney through a flue gas recovery pipe, and the top outlet of the chimney is connected to the atmosphere. A primary air heat exchange unit, a secondary gas heat exchange unit and a tertiary gas heat exchange unit are sequentially arranged on the flue gas recovery pipe along the direction of flue gas flow. The flue gas temperature of the present invention can be reduced to 80°C, thereby improving power generation efficiency. In addition, the waste heat recovery system has good corrosion resistance, is reliable and stable, and has a long service life.

Description

Technical Field

[0001] The present application relates to the technical field of waste heat recovery of flue gas from power generation, and in particular to a multi-stage waste heat recovery system and method for flue gas from a gas generator set. Background Art

[0002] Steel mills produce a large amount of by-product gas, such as blast furnace gas, converter gas, coke oven gas, etc. Using by-product gas to generate electricity is an effective way for steel mills to reduce costs, increase efficiency and achieve efficient utilization of by-product gas.

[0003] In the field of waste heat recovery from flue gas generated by steel mill by-product gas power generation, its utilization directly impacts the overall unit's power generation efficiency. Currently, waste heat recovery systems for gas-fired generators primarily utilize flue gas generated by boiler combustion, passing it through a superheater, reheater, and economizer to utilize the heat from the medium- and high-temperature flue gas. The flue gas then enters a metal tubular air preheater and then a heat pipe gas heater, reducing its temperature to approximately 140°C before being discharged into the atmosphere.

[0004] Since flue gas contains corrosive gases such as sulfur oxides and nitrogen oxides, when the flue gas temperature is below 140℃, the dew point corrosion of SOx and NOx will be aggravated, causing great damage to the waste heat recovery equipment. Therefore, after the flue gas waste heat is recovered from the current gas-fired power generation units, the flue gas temperature is generally discharged at around 140℃, which restricts the further recovery and utilization of the flue gas waste heat.

[0005] At the same time, due to the influence of acidic water mist in the gas, the gas inlet heat exchange tube will be corroded and damaged in a short period of time, generally 1 to 3 years, which seriously restricts the service life of the gas heater and affects the power generation efficiency of the entire unit.

[0006] The current waste heat recovery system for by-product gas power generation in steel plants has the following problems:

[0007] 1. The exhaust temperature of flue gas is 140℃, and the waste heat of flue gas is not fully utilized, so there is still room for utilization and value;

[0008] 2. The flue gas outlet temperature of the gas heater is 140°C. Low-temperature corrosion occurs during low-load operation, which will destroy the vacuum degree of the heat pipe element on the flue gas outlet side of the gas heater, causing leakage of the heat pipe working fluid and resulting in a decrease in the heat exchange performance of the equipment;

[0009] 3. The temperature on the gas inlet side of the gas heater is relatively low (generally 30-50°C). The gas contains acidic water mist, which causes low-temperature corrosion. This will destroy the vacuum degree of the heat pipe components on the gas inlet side of the gas heater, causing leakage of the heat pipe working fluid and a decrease in the heat exchange performance of the equipment. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a multi-stage waste heat recovery system and method for flue gas of a gas generator set in response to the above-mentioned problems.

[0011] The embodiment of the present application is implemented as follows:

[0012] An embodiment of the present application provides a multi-stage waste heat recovery system for flue gas from a gas-fired power generation unit, which is characterized in that it includes a boiler, a primary air heat exchange unit, a secondary gas heat exchange unit, a tertiary gas heat exchange unit and a chimney. The flue gas outlet of the boiler is connected to the bottom inlet of the chimney through a flue gas recovery pipe, and the top outlet of the chimney is connected to the atmosphere. The primary air heat exchange unit, the secondary gas heat exchange unit and the tertiary gas heat exchange unit are sequentially arranged on the flue gas recovery pipe along the direction of flue gas flow.

[0013] In some optional embodiments, the primary air heat exchange unit is an air preheater and a blower, the air inlet of the air preheater is provided with an air inlet pipe, the air outlet of the first air preheater is provided with an air outlet pipe, and the blower is connected to the air inlet pipe.

[0014] In some optional embodiments, the secondary gas heat exchange unit and the tertiary gas heat exchange unit are respectively the first gas heater and the second gas heater, the gas outlet of the second gas heater is connected to the gas inlet of the first gas heater through a gas pipeline, the gas inlet of the second gas heater is provided with a gas inlet pipe, and the gas outlet of the first gas heater is provided with a gas outlet pipe.

[0015] In some optional embodiments, a superheater, a reheater and an economizer are sequentially installed on the flue gas recovery main pipe along the flue gas flow direction.

[0016] In some optional embodiments, a demister is provided on the gas inlet pipe.

[0017] In some optional embodiments, the air preheater is a metal tube heat exchanger, and the terminal multiple rows of tube bundles are made of enameled metal tubes.

[0018] In some optional embodiments, the first gas heater is a gravity heat pipe or a split heat pipe heat exchanger, and several rows of heat exchange tubes on the flue gas outlet side and the gas inlet side are made of corrosion-resistant metal tubes; the second gas heater is a non-metallic tube heat exchanger, and the heat exchange tubes are made of low-temperature corrosion-resistant glass tubes or fluoroplastic tubes.

[0019] In some optional embodiments, the corrosion-resistant metal pipe is made of enamel plating, ND steel, or duplex stainless steel.

[0020] In some optional embodiments, the demister is a fiberglass corrugated plate demister.

[0021] A multi-stage waste heat recovery method for flue gas of a gas-fired power generation unit, characterized by comprising the following contents:

[0022] The flue gas generated by the combustion of coal gas in the boiler enters the flue gas recovery pipe and passes through the superheater, reheater and economizer in sequence. The flue gas temperature at the economizer outlet is 250℃~300℃. The flue gas at the economizer outlet enters the air preheater, heats the air sent in by the blower, and then enters the first gas heater. The flue gas temperature is reduced to 140℃~180℃ by heating the coal gas coming out of the second gas heater. After exiting the first gas heater, the flue gas enters the second gas heater and heats the coal gas entering the demister to further reduce the flue gas temperature to 75℃~85℃. Finally, the flue gas is discharged from the chimney, completing the flue gas waste heat recovery of the entire unit.

[0023] The beneficial effects of the present application are as follows: the present application provides a multi-stage waste heat recovery system and method for flue gas of a gas-fired power generation unit, in which the high-temperature flue gas passes through an air preheater and a gas heater in sequence for heat exchange, realizing multi-stage heat exchange and cooling, and the flue gas temperature can be reduced to 80°C, and the power generation efficiency can be increased by 4 percentage points. In addition, the waste heat recovery system has good corrosion resistance, which solves the low-temperature corrosion problem on the flue gas outlet side and the gas inlet side of the gas heater, and the waste heat recovery system operates reliably and stably and has a long service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 This is a flowchart of the waste heat recovery process of an embodiment of the present application. DETAILED DESCRIPTION

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0027] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without creative work are within the scope of protection of the present application.

[0028] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0029] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the product of this application is typically placed when in use. These terms are intended only to facilitate the description of this application and simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0030] Furthermore, terms such as "horizontal," "vertical," and "overhanging" do not necessarily imply that a component must be absolutely horizontal or overhanging, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but rather that it can be slightly tilted.

[0031] It should also be noted that, in the description of this application, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0032] In this application, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Moreover, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0033] The features and performance of the present application are further described in detail below with reference to the embodiments.

[0034] like Figure 1The present invention provides a multi-stage waste heat recovery system for flue gas from a gas-fired power generation unit, comprising a boiler 1, a primary air heat exchange unit 2, a secondary gas heat exchange unit 3, a tertiary gas heat exchange unit 4, and a chimney 5. The boiler's flue gas outlet is connected to the chimney's bottom inlet via a flue gas recovery pipe 6, while the chimney's top outlet is connected to the atmosphere. The primary air heat exchange unit, the secondary gas heat exchange unit, and the tertiary gas heat exchange unit are sequentially installed on the flue gas recovery pipe along the flue gas flow direction. The flue gas is used to heat the air and gas, and finally, after the waste heat of the flue gas is fully utilized, it is discharged from the chimney.

[0035] The primary air heat exchange unit is an air preheater and a blower. The air inlet of the air preheater is provided with an air inlet pipe, the air outlet of the first air preheater is provided with an air outlet pipe, and the blower is connected to the air inlet pipe.

[0036] The secondary gas heat exchange unit and the tertiary gas heat exchange unit are respectively the first gas heater and the second gas heater. The gas outlet of the second gas heater is connected to the gas inlet of the first gas heater through a gas pipeline 7. The gas inlet of the second gas heater is provided with a gas inlet pipe, and the gas outlet of the first gas heater is provided with a gas outlet pipe.

[0037] A superheater 8, a reheater 9 and an economizer 10 are arranged in sequence on the flue gas recovery main pipe along the flue gas flow direction.

[0038] The gas inlet pipe is provided with a demister 11, which is a glass fiber reinforced plastic corrugated plate demister, which effectively reduces the content of water, fog and dust at the gas inlet and reduces damage to the first and second gas heaters.

[0039] The first air preheater is a metal tube heat exchanger, and the end multi-row tube bundle uses enameled metal tubes to extend the service life of the first air preheater.

[0040] The first gas heater is a gravity-type heat pipe or split heat pipe heat exchanger. Several rows of heat exchange tubes on the flue gas outlet and gas inlet sides are made of corrosion-resistant metal tubes, made of enamel, ND steel, and duplex stainless steel, to extend the service life of the first gas preheater. Due to the relatively high flue gas temperature here, the medium in the heat exchange tubes is desalted water; the second gas heater is a non-metallic tubular heat exchanger. The heat exchange tubes are made of low-temperature corrosion-resistant glass tubes or fluoroplastic tubes. Glass tube heat exchangers or fluoroplastic heat exchangers can effectively prevent low-temperature sulfuric acid dew point corrosion in the flue gas of the gas generator set, and effectively prevent acidic water mist corrosion at the gas inlet.

[0041] A brief workflow for multi-stage waste heat recovery of flue gas from a gas-fired generator set is as follows:

[0042] The flue gas generated by the combustion of coal gas in the boiler enters the flue gas recovery pipe and passes through the superheater, reheater and economizer in sequence. The flue gas temperature at the economizer outlet is 250℃~300℃. The flue gas at the economizer outlet enters the air preheater, heats the air sent in by the blower, and then enters the first gas heater. The flue gas temperature is reduced to 140℃~180℃ by heating the coal gas coming out of the second gas heater. After exiting the first gas heater, the flue gas enters the second gas heater and heats the coal gas entering the demister to further reduce the flue gas temperature to 75℃~85℃. Finally, the flue gas is discharged from the chimney, completing the flue gas waste heat recovery of the entire unit.

[0043] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A multi-stage waste heat recovery system for flue gas of a gas generator set, characterized in that: The smoke exhaust fan is connected to the smoke exhaust pipe, and the smoke exhaust pipe is connected to the smoke exhaust pipe of the second stage. The thermal units are respectively a first gas heater and a second gas heater. The gas outlet of the second gas heater is connected to the gas inlet of the first gas heater through a gas pipeline. The gas inlet of the second gas heater is provided with a gas inlet pipe, and the gas outlet of the first gas heater is provided with a gas outlet pipe. The air preheater is a metal tube heat exchanger, and the multiple rows of tube bundles at the end are made of enameled metal tubes. The first gas heater is a gravity heat pipe or a split heat pipe heat exchanger, and several rows of heat exchange tubes on the flue gas outlet side and the gas inlet side are made of corrosion-resistant metal tubes. The second gas heater is a non-metallic tube heat exchanger, and the heat exchange tubes are made of low-temperature corrosion-resistant glass tubes or fluoroplastic tubes.

2. A multi-stage waste heat recovery system for flue gas from a gas-fired power generation unit according to claim 1, characterized in that: A superheater, a reheater and an economizer are arranged in sequence on the flue gas recovery main pipe along the flue gas flow direction.

3. The multi-stage waste heat recovery system for flue gas of a gas-fired power generation unit according to claim 2, characterized in that: The gas inlet pipe is provided with a demister.

4. A multi-stage waste heat recovery system for flue gas from a gas-fired power generation unit according to claim 3, characterized in that: The corrosion-resistant metal pipe is made of enamel plating, ND steel, and duplex stainless steel.

5. A multi-stage waste heat recovery system for flue gas from a gas-fired power generation unit according to claim 3 or 4, characterized in that: The demister is a glass fiber reinforced plastic corrugated plate type demister.

6. A multi-stage waste heat recovery method for flue gas of a gas-fired power generation unit, characterized in that: Includes the following: The flue gas generated by the combustion of coal gas in the boiler enters the flue gas recovery pipe and passes through the superheater, reheater and economizer in sequence. The flue gas temperature at the economizer outlet is 250℃~300℃. The flue gas at the economizer outlet enters the air preheater, heats the air sent in by the blower, and then enters the first gas heater. The flue gas temperature is reduced to 140℃~180℃ by heating the coal gas coming out of the second gas heater. After exiting the first gas heater, the flue gas enters the second gas heater and heats the coal gas entering the demister to further reduce the flue gas temperature to 75℃~85℃. Finally, the flue gas is discharged from the chimney, completing the flue gas waste heat recovery of the entire unit.

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