Steam boiler

Abstract

A high-pressure water flue gas waste heat recovery system is adopted, flue gas low-temperature corrosion is effectively avoided, meanwhile, flue gas waste heat of the steam boiler is safely and efficiently recycled, installation and arrangement are compact and convenient, and essentially, the steam boiler adopts a hot water type waste heat recoverer and an external air pre-heater heat regeneration technology. Good application prospects are realized.

Description

Technical Field

[0001] The invention belongs to the technical field of steam boilers, and in particular relates to a steam boiler adopting a hot water type waste heat recovery device and an external air preheater heat recovery technology. Background Art

[0002] Steam boilers use coal, oil, natural gas, etc. as fuel. Since the fuel contains sulfur, sulfur oxides will be produced during combustion. The sulfur oxides combine with water vapor to form sulfurous acid or sulfuric acid vapor. If the metal wall temperature of the air preheater arranged 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 too low wall temperature often occur. Acid dew corrosion will occur in the air preheater after one to two years of operation, and even perforation and scrapping. This is a global problem that plagues steam boilers. Therefore, boiler design usually sacrifices heat recovery efficiency and alleviates (rather than eradicates) acid dew corrosion by increasing the exhaust temperature. However, too high an exhaust temperature is bound to cause a large amount of low-temperature heat source waste.

[0003] Existing steam boilers use corrosion-resistant low-temperature economizers or phase-change heat exchangers to recover flue gas waste heat, achieving good results, but there are also certain problems: for example, when hot water is used to recover waste heat, the generated hot water needs to have a reasonable consumption place, and heat balance organization is not easy.

[0004] The air preheater for recovering waste heat from flue gas arranged in the tail flue of the steam boiler requires space for the air duct arrangement for air entering and exiting the air preheater. The air and flue gas in the air preheater need to be heat exchanged in a cross-flow and rotational manner to effectively avoid heat transfer deviation of the air preheater. The distance for the air duct to enter the boiler burner is long, and the volume of the air preheater is large. In the economizer that uses low-temperature boiler feed water to recover waste heat from flue gas, the liquid feed water pipeline entering and exiting the economizer is compact and convenient to install and arrange, and occupies little space. The liquid feed water as a heat carrier has a large heat capacity, and the heat exchange coefficient between flue gas and liquid feed water in the economizer is much larger than the heat exchange coefficient between flue gas and air in the air preheater. For economizers and air preheaters with the same heat exchange conditions, the volume of the economizer is much smaller than that of the air preheater.

[0005] Therefore, how to reasonably recycle and utilize the waste heat of steam boiler flue gas, adopt a high-pressure water flue gas waste heat recovery system, use the characteristics of high-pressure water corresponding to a higher saturation temperature, use high-pressure water as the heat absorption medium of the flue gas-water heat exchanger, and use the high-temperature water from the gas-water heat exchanger that is lower than the pressure saturation temperature of the waste heat recovery system as the heat source of the air preheater outside the furnace, so as to realize the compact and convenient arrangement of the gas-water heat exchanger at the tail flue of the steam boiler, realize the compact and simple arrangement of the air preheater outside the steam boiler, reduce the exhaust temperature of the steam boiler, and effectively avoid the low-temperature corrosion of the gas-water heat exchanger at the tail flue, which has become a hot topic of research in this field. Summary of the invention

[0006] The purpose of the present invention is to solve the shortcomings of the above-mentioned existing steam boiler air preheater technology. A high-pressure water flue gas waste heat recovery system is adopted, that is, a combined system of an air-water heat exchanger in the flue and an air preheater outside the furnace, which effectively avoids low-temperature corrosion of the air-water heat exchanger in the flue and realizes efficient recovery of steam boiler flue gas waste heat.

[0007] The purpose of the present invention is achieved by the following measures:

[0008] A steam boiler, the steam boiler adopts a high-pressure water flue gas waste heat recovery system, the high-pressure water flue gas waste heat recovery system comprises an air-water heat exchanger 10, an air preheater 2 outside the furnace, a buffer water tank 13, a circulating water pump 15 and connecting pipes thereof,

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

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

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

[0012] The low-temperature water from the air preheater 2 outside the furnace enters the buffer water tank 13. The low-temperature water in the buffer water tank 13 is pressurized by the circulating water pump 15, enters the air-water heat exchanger 10, and then is transported to the air preheater 2 outside the furnace to heat the air transported by the blower 1, and returns to the buffer water tank 13. Alternatively, the high-temperature water from the air-water heat exchanger 10 enters the buffer water tank 13, and then is transported to the air preheater 2 outside the furnace through the circulating water pump 15, heats the air transported by the blower 1, and returns to the air-water heat exchanger 10, thereby forming a high-pressure water flue gas waste heat recovery system.

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

[0014] The buffer water tank 13 is provided with a pressure regulator 16, and the gas coming out of the pressure regulator 16 enters the buffer gas tank 13 through the pressure regulating 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 the connecting pipes at a relatively high pressure, so that the saturation temperature corresponding to the heat carrier medium in the high-pressure water flue gas waste heat recovery system, i.e., water, is relatively high, meeting the water temperature requirement for heating the external air preheater.

[0015] Preferably, the temperature of water coming out of the air-water heat exchanger is 10° C. to 30° C. lower than the corresponding saturated water temperature under the system pressure.

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

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

[0018] Preferably, nitrogen replaces the gas in the high-pressure water flue gas waste heat recovery system, and the system is closed after the replacement is completed; water is drawn from the outlet pipe of the boiler feed water pump 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 a set value. At this time, the buffer water tank 13 is equivalent to a gas-water co-containment chamber.

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

[0020] The water and air in the external air preheater 2 adopt an indirect heat exchange method, and the heat exchange tubes adopt smooth tubes, fin tubes or spiral groove tubes.

[0021] The water and flue gas in the gas-water heat exchanger 10 adopt an indirect heat exchange method, and the heat exchange tubes adopt smooth tubes, fin tubes or spiral grooved tubes.

[0022] By controlling the water inlet temperature of the air-water heat exchanger 10 (for example, above 85°C, the appropriate temperature is determined according to the sulfur content of the fuel), so that the average value of the water inlet temperature and the exhaust temperature of the air-water heat exchanger 10, that is, the metal wall temperature, is higher than the flue gas acid dew point temperature, low-temperature corrosion of the air-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 flue gas waste heat recovery device can operate economically and with high thermal efficiency, thereby achieving the purpose of energy saving and consumption reduction.

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

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

[0025] Parts not mentioned in the present invention may be implemented using existing technologies, that is, existing mature and reliable reasonable improvement measures may be introduced into the present 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 steam boiler flue gas waste heat recovery, combined with air-water heat exchanger and furnace air preheater heat recovery technology, which effectively avoids low-temperature corrosion of steam boiler flue gas and realizes safe and efficient recovery of flue gas waste heat;

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

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

[0030] 4. High efficiency of heat exchange: The heat exchange coefficient of the gas-water heat exchanger 10 and the external air preheater 2 is affected by many factors, such as the specific heat capacity of water and flue gas, thermal conductivity, viscosity, flow rate, flow velocity, material and structure of the waste heat recovery device, etc., and the numerical range will be different. According to relevant literature reports, when using tubular heat exchange tubes, the heat exchange coefficient is about 66.7W / (㎡·K); while the conventional steam boiler air preheater uses a tubular air preheater, and its heat exchange coefficient is 17.5W / (㎡·K) ~ 23.3W / (㎡·K). Therefore, for the same parameters of combustion-supporting air, the combination of the gas-water heat exchanger 10 and the external air preheater 2 is nearly twice the size of the conventional flue air preheater, and the metal consumption of the heat exchanger is greatly reduced, and the air short circuit (heat exchange tube leakage) of the traditional air preheater will not cause a false decrease in exhaust temperature and an increase in actual power consumption;

[0031] 5. Compared with the prior art, the present invention is particularly suitable for new construction or renovation of old systems of power station boilers and industrial steam boilers using coal or biomass fuels. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a structural schematic diagram of a steam boiler of the present invention.

[0033] Figure 1 Among them, 1-blower, 2-air preheater outside the furnace, 3-hot air, 4-burner, 5-heating surface of boiler furnace, 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 water tank, 14-return water pipeline, 15-circulating water pump, 16-regulator, 17-regulator pipeline, 18-regulator valve, 19-boiler feed water, 20-water supply pipeline, 21-flue, 22-low-temperature flue gas, 23-exhaust valve, 24-fuel. DETAILED DESCRIPTION

[0034] The following is combined with Figure 1 The present invention is further described in detail with reference to the accompanying drawings and specific examples.

[0035] Embodiment 1:

[0036] A steam boiler, wherein the heating surface of the steam boiler comprises a boiler furnace heating surface 5 (such as a water-cooled wall, a drum), an economizer 9, an air-water heat exchanger 10, an air preheater 2 outside the furnace and a superheater 7,

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

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

[0039] The low-temperature water from the air preheater 2 outside the furnace enters the buffer water tank 13 through the low-temperature water pipeline 12. The low-temperature water in the buffer water tank 13 is pressurized by the return water pipeline 14 and the circulating water pump 15, and then enters the air-water heat exchanger 10. After being heated by the flue gas, it is transported to the air preheater 2 outside the furnace through the high-temperature water pipeline 11 to heat the air transported by the blower 1, and then returns to the buffer water tank 13, thereby 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 down by the boiler furnace heating surface 5, superheater 7, economizer 9, and air-water heat exchanger 10. The formed low-temperature flue gas 22 is discharged to subsequent equipment (such as dust collector, desulfurization and denitrification equipment) for treatment, and then discharged from the chimney through the induced draft fan.

[0041] The buffer water tank 13 is provided with a pressure regulator 16, and the gas coming out of the pressure regulator 16 enters the buffer gas 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 the connecting pipes is at a relatively high pressure. Since the saturation temperature of the heat carrier medium in the high-pressure water flue gas waste heat recovery system, i.e., water, is relatively high, the water temperature requirement for heating the external air preheater is met.

[0042] Preferably, the temperature of water coming out of the air-water heat exchanger is 10° C. to 30° C. lower than the corresponding saturated water temperature under the system pressure.

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

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

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

[0046] The water and air in the external air preheater 2 adopt an indirect heat exchange method, and the heat exchange tubes adopt smooth tubes, fin tubes or spiral groove tubes.

[0047] The water and flue gas in the gas-water heat exchanger 10 adopt an indirect heat exchange method, and the heat exchange tubes adopt smooth tubes, fin tubes or spiral grooved tubes.

[0048] By controlling the water inlet temperature of the gas-water heat exchanger 10 (for example, above 85°C, the appropriate temperature is determined according to 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 flue gas waste heat can be utilized to the maximum extent, so that the flue gas waste heat recovery device can operate economically and with high thermal efficiency, thereby achieving the purpose of energy saving and consumption reduction.

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

[0050] Parts not mentioned in the present invention may be implemented using existing technologies, that is, existing mature and reliable reasonable improvement measures may be introduced into the present system, such as setting necessary valves, bypasses, automatic control facilities, etc.

[0051] Although the present invention has been disclosed as above with preferred embodiments, they are not intended to limit the present invention. Anyone familiar with the art can make various changes or modifications without departing from the spirit and scope of the present invention, which also belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the definition of the claims of this application.

Claims

1. A steam boiler, characterized in that: The steam boiler is provided with a high-pressure water flue gas waste heat recovery system, the high-pressure water flue gas waste heat recovery system comprising 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, The heating surface of the steam boiler comprises a boiler furnace heating surface (5), an economizer (9), an air-water heat exchanger (10), an external air preheater (2) and / or a superheater (7), The economizer (9), the air-water heat exchanger (10) and / or the superheater (7) are arranged in the flue (21) to perform heat exchange with the flue gas generated by the steam boiler burner (4); the boiler feed water (19) enters the boiler furnace heating surface (5) through the economizer (9) and the water supply pipeline (20) to generate saturated steam (6) for external heat supply, or the boiler feed water (19) passes through the economizer (9), the water supply pipeline (20), the boiler furnace heating surface (5) and the superheater (7) to generate superheated steam (8) for external heat supply. The external air preheater (2) is arranged outside the steam boiler flue (21), and the hot air (3) formed by the blower (1) and the external air preheater (2) is transported to the steam boiler burner (4) as combustion-supporting air, and the high-temperature water from the air-water heat exchanger (10) is used as a heat source for the external air preheater (2). Low-temperature water from the external air preheater (2) enters the buffer water tank (13). The low-temperature water in the buffer water tank (13) is pressurized by the circulating water pump (15) and enters the air-water heat exchanger (10). The water is then transported to the external air preheater (2) to heat the air transported by the blower (1) and returns to the buffer water tank (13). Alternatively, high-temperature water from the air-water heat exchanger (10) enters the buffer water tank (13) and is then transported to the external air preheater (2) by the circulating water pump (15) to heat the air transported by the blower (1) and returns to the air-water heat exchanger (10). Thus, a high-pressure flue gas waste heat recovery system is formed. The high-temperature flue gas generated by the steam boiler burner (4) is cooled by the boiler furnace heating surface (5), or / and the superheater (7), the economizer (9), and the air-water heat exchanger (10), and the resulting low-temperature flue gas (22) is discharged to subsequent equipment for treatment and then discharged from the chimney through the induced draft fan.

2. The steam boiler according to claim 1, characterized in that: The buffer water tank (13) is provided with a pressure regulator (16). The gas coming out of the pressure regulator (16) enters the buffer gas tank (13) through a pressure regulating 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 constant pressure device (16) is an inert gas.

5. The steam boiler according to claim 1, characterized in that: The fuel (24) of 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) adopt an indirect heat exchange method, and the heat exchange tubes adopt smooth tubes, finned tubes or spiral grooved tubes.

7. The steam boiler according to claim 1, characterized in that: The water and flue gas of the gas-water heat exchanger (10) adopt an indirect heat exchange method, and the heat exchange tubes adopt smooth tubes, finned tubes or spiral grooved tubes.

8. The steam boiler according to claim 1, characterized in that: The average value of the inlet water temperature and the exhaust gas 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 water tank (13) is provided with an exhaust valve (23), a pressure gauge and a safety valve.

10. The steam boiler according to claim 1, characterized in that: Nitrogen replacement is adopted in the high-pressure water flue gas waste heat recovery system, and the system is closed after the replacement is completed; feed water is introduced from the outlet pipe of the boiler feed water pump 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 controlled to a set value.

Images