A steam boiler

Abstract

The utility model relates to a kind of steam boiler using high-pressure water flue gas waste heat recovery system, including gas-water heat exchanger, external air preheater, buffer water tank, circulating water pump and its connecting pipeline: low-temperature water from external air preheater enters buffer water tank, then enters gas-water heat exchanger after boosting by circulating water pump, then returns to external air preheater, boiler feed water enters boiler furnace heating surface by economizer, produces saturated steam to heat externally, air enters burner by air blower, external air preheater, and high-temperature flue gas produced by fuel combustion, after being cooled by boiler furnace heating surface, economizer, gas-water heat exchanger, low-temperature flue gas formed is handled by subsequent equipment, then discharged from chimney by induced draft fan.

Description

Technical Field

[0001] This utility model belongs to the field of steam boiler technology, and specifically relates to a steam boiler that adopts hot water type waste heat recovery device and external air preheater reheating technology. Background Technology

[0002] Steam boilers use coal, oil, natural gas, etc., as fuels. Because these fuels contain sulfur, combustion produces sulfur oxides, which combine with water vapor to form sulfurous acid or sulfuric acid vapor. If the metal wall temperature of the air preheater located in the tail flue of the steam boiler is lower than the condensation point (acid dew point) of sulfuric acid vapor, liquid sulfuric acid (called acid dew) will form on its surface. Acid dew corrosion and ash blockage caused by excessively low wall temperatures frequently occur. Air preheaters often develop acid dew corrosion after one to two years of operation, sometimes even perforating and becoming unusable. This is a global problem plaguing steam boilers. Therefore, boiler design often sacrifices heat recovery efficiency by increasing the flue gas temperature to alleviate (rather than eliminate) acid dew corrosion. However, excessively high flue gas temperatures inevitably lead to a significant waste of low-temperature heat resources.

[0003] Existing steam boilers use corrosion-resistant low-temperature economizers or phase change heat exchangers to recover waste heat from flue gas, achieving good results, but there are also some problems: for example, when using hot water to recover waste heat, the generated hot water needs to be disposed of in a reasonable place, and it is not easy to organize the heat balance.

[0004] An air preheater for recovering waste heat from flue gas, located at the tail flue of a steam boiler, requires space for its air ducts. The air and flue gas in the air preheater need to exchange heat through cross-flow and rotation to effectively avoid heat transfer deviation. The ducts travel a long distance to the boiler burner, resulting in a large air preheater volume. In contrast, an economizer using low-temperature boiler feedwater to recover waste heat from flue gas has a compact, convenient, and space-saving installation of its liquid feedwater pipes. The liquid feedwater, as the heat transfer medium, has a large heat capacity, and the heat transfer coefficient between flue gas and liquid feedwater in the economizer is much greater than that between flue gas and air in the air preheater. Under the same heat exchange conditions, the economizer is much smaller than the air preheater.

[0005] Therefore, how to rationally recover and utilize the waste heat from steam boiler flue gas, and adopt a high-pressure water flue gas waste heat recovery system, taking advantage of the high saturation temperature of high-pressure water, using high-pressure water as the heat absorption medium in the flue gas-water heat exchanger, and using the high-temperature water from the gas-water heat exchanger (which is lower than the pressure saturation temperature of the waste heat recovery system) as the heat source for the external air preheater, has become a hot research topic in this field. This allows for a compact and convenient arrangement of the gas-water heat exchanger in the tail flue of the steam boiler, and a compact and simple arrangement of the external air preheater, reducing the exhaust temperature of the steam boiler while effectively avoiding low-temperature corrosion of the tail flue gas-water heat exchanger. Utility Model Content

[0006] The purpose of this invention is to overcome the shortcomings of existing steam boiler air preheater technology by adopting a high-pressure water flue gas waste heat recovery system, which is a combination system of gas-water heat exchanger in the flue and air preheater outside the furnace. This effectively avoids low-temperature corrosion of the gas-water heat exchanger in the flue and achieves efficient recovery of waste heat from steam boiler flue gas.

[0007] The objective of this utility model is achieved through the following measures:

[0008] A steam boiler employs a high-pressure flue gas waste heat recovery system, which includes a gas-water heat exchanger 10, an external air preheater 2, a buffer water tank 13, a circulating water pump 15, and connecting pipes thereof.

[0009] The heating surfaces of the steam boiler include the boiler furnace heating surface 5 (such as water-cooled walls and boiler drum), economizer 9, gas-water heat exchanger 10, external air preheater 2 and / or superheater 7.

[0010] The economizer 9, gas-water heat exchanger 10, and / or superheater 7 are arranged in the flue 21 to exchange heat with the flue gas generated by the steam boiler burner 4. Boiler feedwater 19 enters the boiler furnace heating surface 5 through the economizer 9 and water supply pipeline 20 to generate saturated steam 6 for external heating, or boiler feedwater 19 generates superheated steam 8 for external heating through the economizer 9, water supply pipeline 20, boiler furnace heating surface 5, and superheater 7.

[0011] The external air preheater 2 is arranged outside the flue 21 of the steam boiler. The hot air 3 formed by the blower 1 and the external air preheater 2 is transported to the steam boiler burner 4. The high-temperature water from the gas-water heat exchanger 10 enters the external air preheater 2 as the heat source of the external air preheater 2.

[0012] Low-temperature water from the external air preheater 2 enters the buffer water tank 13. After being pressurized by the circulating water pump 15, the low-temperature water in the buffer water tank 13 enters the gas-water heat exchanger 10, and is then transported to the external air preheater 2 to heat the air supplied by the blower 1, before returning to the buffer water tank 13. Alternatively, high-temperature water from the gas-water heat exchanger 10 enters the buffer water tank 13, is then transported by the circulating water pump 15 to the external air preheater 2, heats the air supplied by the blower 1, and then returns to the gas-water heat exchanger 10, thus forming a high-pressure water flue gas waste heat recovery system.

[0013] The high-temperature flue gas generated by the burner 4 of the steam boiler is cooled by the boiler furnace heating surface 5 and / or the superheater 7, economizer 9, and gas-water heat exchanger 10. The resulting low-temperature flue gas 22 is then discharged to subsequent equipment (such as dust collectors, desulfurization and denitrification equipment) for treatment, and then discharged from the chimney by an induced draft fan.

[0014] The buffer water tank 13 is equipped with a pressure regulator 16. The gas coming out of the pressure regulator 16 enters the buffer water tank 13 through the pressure regulator valve 18, thereby maintaining the liquid water in the gas-water heat exchanger 10, the external air preheater 2, the buffer water tank 13 and their connecting pipes at a high pressure, so that the heat transfer medium, i.e. water, in the high-pressure flue gas waste heat recovery system has a high saturation temperature, which meets the water temperature requirements for heating the external air preheater.

[0015] Preferably, the water temperature exiting the gas-water heat exchanger is 10°C to 30°C lower than the saturated water temperature corresponding to the system pressure.

[0016] The pressure regulator 16 is a high-pressure air storage tank or an air compressor.

[0017] Preferably, the gas exiting the pressure regulator 16 is an inert gas, such as nitrogen or argon.

[0018] Preferably, nitrogen is used to replace the gas in the high-pressure water flue gas waste heat recovery system, and the system is then sealed after the replacement is completed. Feedwater is drawn from the boiler feedwater pump outlet pipe and injected into the high-pressure water flue gas waste heat recovery system, and the pressure of the high-pressure water flue gas waste heat recovery system is slowly controlled to the set value. At this time, the buffer tank 13 is equivalent to a gas-water co-containment chamber.

[0019] The fuel 24 for the steam boiler burner 4 is coal, biomass, fuel oil or combustible gas.

[0020] The water and air in the external air preheater 2 are exchanged indirectly, and the heat exchange tubes are plain tubes, finned tubes or spiral groove tubes.

[0021] The water and flue gas in the gas-water heat exchanger 10 exchange heat indirectly, and the heat exchange tubes are plain tubes, finned tubes or spiral groove tubes.

[0022] By controlling the inlet water temperature of the gas-water heat exchanger 10 (for example, above 85℃, the appropriate temperature is determined according to the sulfur content of the fuel), so that the average value of the inlet water temperature and the exhaust temperature of the gas-water heat exchanger 10, i.e. the metal wall temperature, is higher than the acid dew point temperature of the flue gas, the low-temperature corrosion of the gas-water heat exchanger 10 can be effectively avoided. Under the premise of avoiding condensation, the waste heat of the flue gas can be utilized to the maximum extent, so that the waste heat recovery device of the flue gas can operate economically and with high thermal efficiency, achieving the purpose of energy saving and consumption reduction.

[0023] The buffer tank 13 is equipped with an exhaust valve 23, a pressure gauge, and a safety valve.

[0024] The pipelines of the high-temperature flue gas waste heat recovery system are insulated.

[0025] The parts of this utility model not mentioned are implemented using existing technology, that is, existing mature and reliable reasonable improvement measures can be introduced into this system, such as setting necessary valves, bypasses, automatic control facilities, etc.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] 1. Energy saving: High-pressure water is used as the heat carrier for the recovery of waste heat from the flue gas of steam boilers. Combined with the gas-water heat exchanger and the external air preheater regeneration technology, the low-temperature corrosion of the flue gas of steam boilers is effectively avoided, while realizing the safe and efficient recovery and utilization of waste heat from the flue gas.

[0028] 2. Easy and compact installation: The external air preheater 2 and the gas-water heat exchanger 10 are easy to install, which can effectively save and utilize space. The air conveying duct is simplified and concise, effectively reducing duct resistance and consumption.

[0029] 3. Flexible and convenient operation and adjustment: Through the high-pressure water flue gas waste heat recovery system, the internal circulation heat utilization of flue gas waste heat is realized. The operation and adjustment are flexible and convenient, and the waste heat recovery heat balance of flue gas is simple and reliable.

[0030] 4. High-efficiency heat exchange: The heat transfer coefficients of the gas-water heat exchanger 10 and the external air preheater 2 are affected by various factors, such as the specific heat capacity, thermal conductivity, viscosity, flow rate, flow velocity, and the material and structure of the waste heat recovery unit. These factors result in varying values. According to relevant literature, the heat transfer coefficient using tubular heat exchange tubes is approximately 66.7 W / (m²·K); while the heat transfer coefficient of conventional steam boiler air preheaters using tubular air preheaters ranges from 17.5 W / (m²·K) to 23.3 W / (m²·K). Therefore, for the same combustion air parameters, the combination of the gas-water heat exchanger 10 and the external air preheater 2 reduces the volume of the heat exchanger by nearly half compared to conventional in-flue air preheaters. This significantly reduces the metal consumption of the heat exchanger and avoids the false decrease in exhaust gas temperature and increased actual power consumption caused by air short-circuiting (air leakage in the heat exchange tubes) in traditional air preheaters.

[0031] 5. Compared with the prior art, this utility model is particularly suitable for the construction of new power plant boilers and industrial steam boilers that use coal or biomass fuel, or for the renovation of old systems. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of a steam boiler structure according to the present invention.

[0033] Figure 1In the middle, 1-blower, 2-external air preheater, 3-hot air, 4-burner, 5-boiler furnace heating surface, 6-saturated steam, 7-superheater, 8-superheated steam, 9-economizer, 10-gas-water heat exchanger, 11-high temperature water pipeline, 12-low temperature water pipeline, 13-buffer tank, 14-return water pipeline, 15-circulating water pump, 16-pressure regulator, 17-pressure regulating pipeline, 18-pressure regulating valve, 19-boiler feedwater, 20-water supply pipeline, 21-flue, 22-low temperature flue gas, 23-exhaust valve, 24-fuel. Detailed Implementation

[0034] The following is in conjunction with the appendix Figure 1 The present invention will be further described in detail with reference to specific embodiments.

[0035] Example 1:

[0036] A steam boiler, wherein the heating surfaces of the steam boiler include boiler furnace heating surfaces 5 (such as water-cooled walls, boiler drum), economizer 9, gas-water heat exchanger 10, external air preheater 2, and superheater 7.

[0037] The economizer 9, gas-water heat exchanger 10, and superheater 7 are arranged in the flue 21 to exchange heat with the flue gas generated by the steam boiler burner 4. The boiler feedwater 19 generates superheated steam 8 through the economizer 9, water supply pipeline 20, boiler furnace heating surface 5, and superheater 7 for external heating.

[0038] The external air preheater 2 is arranged outside the flue 21 of the steam boiler. The hot air 3 formed by the blower 1 and the external air preheater 2 is transported to the steam boiler burner 4. The high-temperature water from the gas-water heat exchanger 10 enters the external air preheater 2 through the high-temperature water pipeline 11, serving as the heat source for the external air preheater 2.

[0039] The low-temperature water from the external air preheater 2 enters the buffer water tank 13 via the low-temperature water pipeline 12. The low-temperature water in the buffer water tank 13 is pressurized via the return water pipeline 14 and the circulating water pump 15, then enters the gas-water heat exchanger 10. After being heated by the flue gas, it is then transported to the external air preheater 2 via the high-temperature water pipeline 11 to heat the air supplied by the blower 1, and then returns to the buffer water tank 13, thus forming a high-pressure water waste heat recovery process for the flue gas.

[0040] The high-temperature flue gas generated by the steam boiler burner 4 is cooled by the boiler furnace heating surface 5, superheater 7, economizer 9, and gas-water heat exchanger 10. The resulting low-temperature flue gas 22 is then discharged to subsequent equipment (such as dust collectors, desulfurization and denitrification equipment) for treatment, and then discharged from the chimney by an induced draft fan.

[0041] The buffer water tank 13 is equipped with a pressure regulator 16. The gas coming out of the pressure regulator 16 enters the buffer water tank 13 through the pressure regulator pipeline 17 and the pressure regulator valve 18, so that the liquid water in the gas-water heat exchanger 10, the external air preheater 2, the buffer water tank 13 and its connecting pipelines is at a high pressure. Because the heat transfer medium, i.e. water, in the high-pressure water flue gas waste heat recovery system has a high saturation temperature, it meets the water temperature requirements for heating the external air preheater.

[0042] Preferably, the water temperature exiting the gas-water heat exchanger is 10°C to 30°C lower than the saturated water temperature corresponding to the system pressure.

[0043] The pressure regulator 16 is a high-pressure gas storage tank or a compressor. Preferably, the pressure regulator 16 is a high-pressure gas storage tank.

[0044] Preferably, the gas exiting the pressure regulator 16 is an inert gas, such as nitrogen or argon.

[0045] The fuel 24 for the steam boiler burner 4 is coal, biomass, fuel oil or combustible gas.

[0046] The water and air in the external air preheater 2 are exchanged indirectly, and the heat exchange tubes are plain tubes, finned tubes or spiral groove tubes.

[0047] The water and flue gas in the gas-water heat exchanger 10 exchange heat indirectly, and the heat exchange tubes are plain tubes, finned tubes or spiral groove tubes.

[0048] By controlling the inlet water temperature of the gas-water heat exchanger 10 (for example, above 85°C, with the appropriate temperature determined based on the sulfur content of the fuel), low-temperature corrosion of the gas-water heat exchanger 10 can be effectively avoided. Under the premise of avoiding condensation, the waste heat of the flue gas can be utilized to the maximum extent, enabling the flue gas waste heat recovery device to operate economically and with high thermal efficiency, thereby achieving the goal of energy saving and consumption reduction.

[0049] The buffer tank 13 is equipped with an exhaust valve 23, a pressure gauge, and a safety valve. The pipeline of the high-pressure water waste heat recovery system is insulated.

[0050] The parts of this utility model not mentioned are implemented using existing technology, that is, existing mature and reliable reasonable improvement measures can be introduced into this system, such as setting necessary valves, bypasses, automatic control facilities, etc.

[0051] Although the present invention has been disclosed above with reference to preferred embodiments, these are not intended to limit the present invention. Any person skilled in the art can make various changes or modifications without departing from the spirit and scope of the present invention, and these changes and modifications also fall within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the claims of this application.

Claims

1. A steam boiler, characterized in that: The steam boiler is equipped with a high-pressure flue gas waste heat recovery system, which includes a gas-water heat exchanger (10), an external air preheater (2), a buffer water tank (13), a circulating water pump (15), and their connecting pipes: low-temperature water from the external air preheater (2) enters the buffer water tank (13), and the low-temperature water in the buffer water tank (13) is pressurized by the circulating water pump (15) and then enters the gas-water heat exchanger (10), and then returns to the buffer water tank (13) through the external air preheater (2); or high-temperature water from the gas-water heat exchanger (10) enters the buffer water tank (13), and then returns to the gas-water heat exchanger (10) through the circulating water pump (15) and the external air preheater (2). The heating surfaces of the steam boiler include the boiler furnace heating surface (5), economizer (9), gas-water heat exchanger (10), external air preheater (2), and / or superheater (7): boiler feedwater (19) enters the boiler furnace heating surface (5) through the economizer (9) and water supply pipeline (20) to generate saturated steam (6) for external heating, or boiler feedwater (19) generates superheated steam (8) for external heating through the economizer (9), water supply pipeline (20), boiler furnace heating surface (5), and superheater (7). Air enters the burner (4) via the blower (1) and the external air preheater (2). The high-temperature flue gas generated by the combustion of fuel (24) is cooled by the boiler furnace heating surface (5) and / or the superheater (7), economizer (9), and gas-water heat exchanger (10). The resulting low-temperature flue gas (22) is then discharged to the subsequent equipment for processing and then discharged from the chimney by the induced draft fan.

2. The steam boiler according to claim 1, characterized in that: The buffer tank (13) is equipped with a pressure regulator (16): the gas coming out of the pressure regulator (16) enters the buffer tank (13) through the pressure regulator valve (18).

3. The steam boiler according to claim 2, characterized in that: The pressure regulator (16) is a high-pressure gas storage tank or a gas compressor.

4. The steam boiler according to claim 2, characterized in that: The gas coming out of the pressure regulator (16) is an inert gas.

5. The steam boiler according to claim 1, characterized in that: The fuel (24) for the steam boiler burner (4) is coal, biomass, fuel oil or combustible gas.

6. The steam boiler according to claim 1, characterized in that: The water and air in the external air preheater (2) are exchanged indirectly, and the heat exchange tubes are plain tubes, finned tubes or spiral groove tubes.

7. The steam boiler according to claim 1, characterized in that: The water and flue gas in the gas-water heat exchanger (10) are exchanged indirectly, and the heat exchange tubes are plain tubes, finned tubes or spiral groove tubes.

8. The steam boiler according to claim 1, characterized in that: The average of the inlet water temperature and the exhaust temperature of the gas-water heat exchanger (10) is higher than the acid dew point temperature of the boiler flue gas.

9. The steam boiler according to claim 1, characterized in that: The buffer tank (13) is equipped with an exhaust valve (23), a pressure gauge and a safety valve.

10. The steam boiler according to claim 1, characterized in that: The high-pressure water flue gas waste heat recovery system uses nitrogen purging, and the system is sealed after the purging is completed. Feed water is drawn from the boiler feed water pump outlet pipe and injected into the high-pressure water flue gas waste heat recovery system to control the pressure of the high-pressure water flue gas waste heat recovery system to the set value.

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