A dual-channel waste heat recovery system and method for flue gas from a gas generator set

Abstract

The present invention proposes a dual-channel waste heat recovery system and method for flue gas of a gas-fired power generation unit, comprising a boiler, an air heat exchange unit, a gas heat exchange unit and a chimney. The flue gas outlet of the boiler is connected to a flue gas recovery main pipe, and the flue gas recovery main pipe is respectively connected to the flue gas inlets of the air heat exchange unit and the gas heat exchange unit through two flue gas recovery branches. The flue gas outlets of the heat exchange unit and the gas heat exchange unit are both connected to the bottom inlet of the chimney through a flue gas exhaust pipe, and the top outlet of the chimney is connected to the atmosphere. The flue gas temperature of the present invention can be reduced to 80°C, thereby improving the 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 dual-channel 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, moisture and fine dust in the gas often adhere to the surface of the gas heater's heat exchange tubes, increasing heat transfer resistance and making it easier for sulfur dioxide in the gas to react and form acidic substances, which corrode the heat exchange tube surface. Because the dust is fine and contains water, it is difficult to remove it online with a soot blower during operation. The only option is to flush the front of the heat exchange tube with high-pressure water during shutdown. Corrosion damage to the gas inlet heat exchange tubes occurs within a short period of time, generally one to three years, severely limiting the service life of the gas heater and affecting 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] 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 elements 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 dual-channel 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 flue gas waste heat recovery system for a gas-fired power generation unit, which is characterized in that it includes a boiler, an air heat exchange unit, a gas heat exchange unit and a chimney. The flue gas outlet of the boiler is connected to a flue gas recovery main pipe, and the flue gas recovery main pipe is connected to the flue gas inlets of the air heat exchange unit and the gas heat exchange unit respectively through two flue gas recovery branches. The flue gas outlets of the heat exchange unit and the gas heat exchange unit are both connected to the bottom inlet of the chimney through a flue gas exhaust pipe, and the top outlet of the chimney is connected to the atmosphere.

[0013] In some optional embodiments, the air heat exchange unit includes a first air preheater, a second air preheater and a blower. The first and second air preheaters are sequentially arranged on the flue gas recovery branch along the flue gas flow direction. The air outlet of the second air preheater is connected to the air inlet of the first air preheater through an air duct. The air inlet of the second air preheater is provided with an air inlet pipe, and the air outlet of the first air preheater is provided with an air outlet pipe. The blower is connected to the air inlet pipe.

[0014] In some optional embodiments, the gas heat exchange unit includes a first gas heater and a second gas heater, and the first and second gas heaters are sequentially installed on the flue gas recovery branch along the flue gas flow direction. 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. A demister is provided on the gas inlet 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, the two flue gas recovery branch pipes are connected by providing a connecting pipe, and the pipe openings at both ends of the connecting pipe are respectively located between the first and second air preheaters and the first and second gas heaters.

[0017] In some optional embodiments, the first air preheater is a metal tube heat exchanger, and the end multiple rows of tube bundles use enameled metal tubes; the second air preheater is a non-metallic tube heat exchanger, and the heat exchange tubes use low-temperature corrosion-resistant glass tubes or fluoroplastic 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, a first regulating valve and a second regulating valve are respectively provided on the flue gas recovery branch pipes on the inlet sides of the first and second air preheaters, and a third regulating valve is provided on the connecting pipe.

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

[0021] A method for recovering waste heat from 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 main 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 is divided into two paths. One path of flue gas passes through the first air preheater, heating the air discharged from the second air preheater to reduce the flue gas temperature to 130℃~170℃. After passing through the first air preheater, the flue gas enters the second air preheater, heating the air sent in by the blower to reduce the flue gas temperature to 75℃~85℃. The other path of flue gas enters the first gas heater, heating the gas discharged from the second gas heater to reduce the flue gas temperature to 140℃~180℃. After exiting the first gas heater, the flue gas enters the second gas heater, heating the gas entering the demister to further reduce the flue gas temperature to 75℃~85℃. Finally, the two flue gases merge and are discharged through the chimney, completing the flue gas waste heat recovery of the entire unit.

[0023] The beneficial effects of the present application are: the present application provides a dual-channel waste heat recovery system and method for flue gas of a gas generator set, which can ultimately reduce the flue gas temperature to 80°C. By reducing the flue gas temperature from 140°C to 80°C, the power generation efficiency can be increased by 4 percentage points, increasing economic benefits and reducing carbon dioxide pollution; 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 require further definition or explanation 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 1 The present invention provides a dual-channel flue gas waste heat recovery system and method for a gas-fired generator set. The system comprises a boiler 1, an air heat exchange unit, a gas heat exchange unit, and a chimney 2. The boiler's flue gas outlet is connected to a flue gas recovery main 3, which is connected to the flue gas inlets of the air heat exchange unit and the gas heat exchange unit, respectively, via two flue gas recovery branch pipes 4. The flue gas outlets of both the heat exchange unit and the gas heat exchange unit are connected to the bottom inlet of the chimney via a flue gas exhaust pipe 5, while the top outlet of the chimney is connected to the atmosphere. The flue gas is divided into two paths: one for heating the air and the other for heating the gas. After the flue gas's waste heat has been utilized, the flue gas is combined into one path and discharged through the chimney.

[0035] The air heat exchange unit includes a first air preheater 6, a second air preheater 7 and a blower. The first and second air preheaters are sequentially arranged on the flue gas recovery branch along the flue gas flow direction. The air outlet of the second air preheater is connected to the air inlet of the first air preheater through an air duct 8. The air inlet of the second air preheater is provided with an air inlet pipe, and the air outlet of the first air preheater is provided with an air outlet pipe. The blower is connected to the air inlet pipe.

[0036] The gas heat exchange unit includes a first gas heater 9 and a second gas heater 10. The first and second gas heaters are sequentially installed on the flue gas recovery branch along the flue gas flow direction. The gas outlet of the second gas heater is connected to the gas inlet of the first gas heater through a gas pipeline 11. 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 12, a reheater 13 and an economizer 14 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 15, which is a glass fiber reinforced plastic corrugated plate demister, which effectively reduces the content of water, mist and dust at the gas inlet and reduces damage to the first and second gas heaters.

[0039] The two flue gas recovery branches are connected by a connecting pipe 16. The two end openings of the connecting pipe are respectively located between the first and second air preheaters and the first and second gas heaters. The flue gas recovery branches on the inlet sides of the first and second air preheaters are respectively provided with a first regulating valve 17 and a second regulating valve 18, and the connecting pipe is provided with a third regulating valve 19.

[0040] Under normal circumstances, the third regulating valve is in a closed state. A first regulating valve is provided on the flue gas inlet side of the first air preheater to adjust the amount of flue gas entering according to the demand ratio. When the boiler load changes, the flue gas in the air side pipeline can be directed to the gas side pipeline by opening the third regulating valve and closing the second regulating valve. Alternatively, the first regulating valve can be directly closed so that the flue gas only enters the gas side to ensure sufficient flue gas to heat the gas. Since resistance is generated when the flue gas enters the air preheater and the gas heater, pressure imbalance may occur in the two pipelines on the gas side and the air side. At this time, opening the third regulating valve allows the air side and the gas side pipelines to automatically divert the flue gas and adjust the pressure of the pipelines on both sides to achieve pressure balance on both sides.

[0041] The first air preheater is a metal tube heat exchanger, and the multiple rows of tube bundles at the end use enameled metal tubes to extend the service life of the first air preheater; the second air preheater is a non-metallic tube heat exchanger, and the heat exchange tubes use 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 of the flue gas of the gas generator set.

[0042] 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. Since the flue gas temperature here is relatively high, the medium in the heat exchange tubes uses thermal conductivity as the heat exchange medium of the heat exchange tubes; 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 of the flue gas of the gas generator set, and effectively prevent acidic water mist corrosion at the gas inlet.

[0043] A brief workflow for waste heat recovery from flue gas of a gas-fired generator set is as follows:

[0044] The flue gas generated by the combustion of coal gas in the boiler enters the flue gas recovery main pipe, 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 is divided into two paths. One path of flue gas passes through the first air preheater, heats the air coming out of the second air preheater and reduces the flue gas temperature to 130℃~170℃. After passing through the first air preheater, the flue gas enters the second air preheater and reduces the flue gas temperature to 75℃~85℃ by heating the air sent in by the blower. The flue gas on the air side is cooled; the other flue gas enters the first gas heater, and the flue gas temperature is reduced to 140℃~180℃ by heating the gas coming out of the second gas heater. After the flue gas comes out of the first gas heater, it enters the second gas heater, and the flue gas temperature is further reduced to 75℃~85℃ by heating the gas entering the demister, completing the flue gas cooling by each device and heating the gas at the same time. Finally, the two flue gases on the air side and the gas side are merged and discharged into the chimney, completing the flue gas waste heat recovery of the entire unit.

[0045] 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 dual-channel waste heat recovery system for flue gas from a gas generator set, characterized in that: The vents in the vents are routed through the vents to the fan and the fan is directed to the exhaust fan, which in turn is routed through the vents to the fan housing, the exhaust fan being routed through the vents to the fan housing, the fan being routed through the vents to the fan housing, and the fan being routed through the vents to the fan housing. There is 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; the gas heat exchange unit includes a first gas heater and a second gas heater, the first and second gas heaters are sequentially installed on the flue gas recovery branch pipe along the flue gas flow direction, 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, the gas outlet of the first gas heater is provided with a gas outlet pipe, and a demister is provided on the gas inlet pipe; the two flue gas recovery branches are connected by setting a connecting pipe, and the pipe ends of the connecting pipe are respectively located between the first and second air preheaters and the first and second gas heaters.

2. A dual-channel waste heat recovery system for flue gas from a gas generator set 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. A dual-channel waste heat recovery system for flue gas from a gas generator set according to claim 2, characterized in that: The first air preheater is a metal tube heat exchanger, and the end multi-row tube bundle adopts enameled metal tubes. The second air preheater is a non-metallic tube heat exchanger, and the heat exchange tubes adopt low-temperature corrosion-resistant glass tubes or fluoroplastic tubes.

4. A dual-channel waste heat recovery system for flue gas from a gas generator set according to claim 2, characterized in that: The first gas heater is a gravity heat pipe or a split heat pipe heat exchanger. 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 corrosion-resistant metal tubes are made of enamel, ND steel, and duplex stainless steel. 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.

5. The dual-channel waste heat recovery system for flue gas of a gas generator set according to claim 2 is characterized in that: A first regulating valve and a second regulating valve are respectively provided on the flue gas recovery branch pipes on the inlet sides of the first and second air preheaters, and a third regulating valve is provided on the connecting pipe.

6. A dual-channel waste heat recovery system for flue gas from a gas-fired generator set according to claim 2, characterized in that: The demister is a glass fiber reinforced plastic corrugated plate type demister.

7. A method for using the dual-channel waste heat recovery system for flue gas from a gas generator set according to claim 5, characterized in that: Includes the following: The flue gas generated by the combustion of coal gas in the boiler enters the flue gas recovery main 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 is divided into two paths. One path of flue gas passes through the first air preheater to heat the air coming out of the second air preheater to reduce the flue gas temperature to 130℃~170℃. Under normal circumstances, the third regulating valve is closed. After passing through the first air preheater, the flue gas enters the second air preheater, where the flue gas temperature is reduced to 75°C-85°C by heating the air supplied by the blower. The other flue gas enters the first gas heater, where the flue gas exiting the second gas heater is heated to reduce the flue gas temperature to 140°C-180°C. After exiting the first gas heater, the flue gas enters the second gas heater, where the flue gas temperature is further reduced to 75°C-85°C by heating the gas entering the demister. The two flue gases are finally combined and discharged through the chimney, completing the flue gas waste heat recovery for the entire unit. In the event of boiler load fluctuations, the third regulating valve is opened and the second regulating valve is closed to allow the flue gas from the air side pipeline to flow into the gas side pipeline, or the first regulating valve is directly closed to allow the flue gas to flow only into the gas side. When the pressures in the gas and air side pipelines are unbalanced, the third regulating valve is opened to automatically divert the flue gas from the air and gas sides, adjusting the pressures on both sides to achieve pressure balance.

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