Steam boiler

Abstract

The utility model relates to a steam boiler, which adopts heat-conducting oil as a heat-carrying medium of a smoke heat recoverer of a tail flue of the boiler and an air pre-heater outside the boiler, effectively avoids low-temperature corrosion of smoke, realizes high-efficiency recycling of waste heat of smoke of the steam boiler, and is compact and convenient to install and arrange. The composite heat-carrying type steam boiler is characterized in that the steam boiler adopting water as a heat-carrying medium and the heat-conducting oil boiler adopting heat-conducting oil as a heat-carrying medium are combined, and the composite heat-carrying type steam boiler has a good application prospect.

Description

Technical Field

[0001] This utility model belongs to the field of steam boiler technology, and specifically relates to a steam boiler that uses thermal oil as the heat carrier and employs waste heat recovery technology in an external air preheater. 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] Thermal oil has the characteristics of "low pressure and high temperature". Heat exchangers that use thermal oil as a heat carrier have been widely and safely used in industry and have similar characteristics to boiler economizers that recover waste heat from flue gas.

[0006] Therefore, how to rationally recover and utilize the waste heat of steam boiler flue gas, taking advantage of the larger heat capacity of liquid media such as water or thermal oil compared to air, and using thermal oil as the heat carrier in flue gas-thermal oil heat exchangers and air-thermal oil heat exchangers, to achieve a compact and convenient arrangement of oil-gas heat exchangers in the tail flue of steam boilers, and to achieve a compact and simple arrangement of the boiler's external air preheater, thereby reducing the exhaust temperature of steam boilers while effectively avoiding low-temperature corrosion of the tail flue oil-gas heat exchangers, has become a research hotspot in this field. Utility Model Content

[0007] The purpose of this invention is to overcome the shortcomings of existing steam boiler air preheater technology by adopting oil-gas heat exchanger and external air preheater regeneration technology, namely, heat transfer oil internal circulation heat recovery system, which effectively avoids low-temperature corrosion of oil-gas heat exchanger in flue and realizes efficient and safe recovery and utilization of flue gas heat from steam boiler.

[0008] The objective of this utility model is achieved through the following measures:

[0009] A steam boiler, wherein the heating surfaces of the steam boiler body 5 include, for example, water-cooled walls, economizer 9, oil-gas heat exchanger 10, external air preheater 2 and / or superheater 7.

[0010] The economizer 9, oil-gas 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 heating surface of the steam boiler body 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, heating surface of the steam boiler body 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 heat transfer oil from the oil-gas heat exchanger 10 serves as the heat source for the external air preheater 2.

[0012] The heat transfer oil separated by the oil-gas separator 13 is pressurized by the heat transfer oil pump 15. The pressurized heat transfer oil enters the oil-gas heat exchanger 10, is heated by flue gas, and is then transported to the external air preheater 2 to heat the air delivered by the blower 1. The oil then returns to the oil-gas separator 13. The gas-liquid mixture generated by the oil-gas separator 13 enters the oil storage tank 16 through the expansion pipe 23. The high-temperature flue gas generated by the steam boiler burner 4 is cooled by the heating surface of the steam boiler body 5 and / or the superheater 7, economizer 9, and oil-gas heat exchanger 10. The resulting low-temperature flue gas 22 is discharged to subsequent equipment (such as dust collectors, desulfurization and denitrification equipment) for treatment, and then discharged from the chimney by the induced draft fan.

[0013] The fuel 24 for the steam boiler burner 4 is coal, biomass, fuel oil or combustible gas.

[0014] The heat transfer oil of the external air preheater 2 is exchanged with the air indirectly, and the heat exchange tubes are plain tubes, finned tubes or spiral groove tubes.

[0015] The heat transfer oil and flue gas in the oil-gas heat exchanger 10 are exchanged indirectly, and the heat exchange tubes are plain tubes, finned tubes or spiral grooved tubes.

[0016] A filter 14 is provided: the heat transfer oil coming out of the oil-gas separator 13 enters the heat transfer oil pump 15 through the filter 14. The filter 14 is used to filter out solid impurity particles in the inlet heat transfer oil.

[0017] By controlling the inlet temperature of the heat transfer oil in the oil-gas 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 oil-gas 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.

[0018] The oil-gas separator 13 and the oil storage tank 16 can be integrated into one unit, with the oil storage tank 16 also serving as the oil-gas separator.

[0019] Preferably, the oil storage tank 16 is equipped with a safety valve, an exhaust valve, and a discharge valve, is protected by nitrogen sealing, and is insulated.

[0020] A low-level oil tank 17 is provided: the low-level oil tank 17 is connected to the oil storage tank 16 through an overflow pipe 18, and the low-level oil tank 17 is used for the heat transfer oil in the heat transfer oil internal circulation heat recovery system.

[0021] The heat recovery system for internal circulation of thermal oil in the steam boiler is also applicable to hot water boilers.

[0022] For the parts not mentioned in this utility model, existing technologies can be used to implement them, 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.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. Energy saving: Using thermal oil as the heat carrier, combined with the regenerator and external air preheater regeneration technology, it effectively avoids low-temperature corrosion of flue gas in steam boilers while achieving efficient recovery and utilization of flue gas waste heat. In essence, it is a composite heat carrier type steam boiler that combines a traditional steam boiler that uses water as the heat carrier medium with a thermal oil furnace that uses thermal oil as the heat carrier medium.

[0025] 2. Easy and compact installation: The external air preheater 2 and oil-gas 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.

[0026] 3. Flexible and convenient operation and adjustment: Through the set heat transfer oil 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 heat balance of flue gas waste heat recovery is simple and reliable.

[0027] 4. Safety: The thermal oil heat recovery system integrated with the steam boiler has mature and reliable operating experience in industry. Due to its proximity to the boiler, the amount of thermal oil used in the system is not large, and the temperature of the flue gas at the tail end of the steam boiler is not high. By selecting a suitable thermal oil, the long-term stable operation of the thermal oil heat recovery system can be guaranteed. Preferably, the oil storage tank adopts a nitrogen-sealed, positive pressure operation mode. The oil storage tank 16 and the matching low-level oil tank 17 can be conveniently arranged in a safe location, increasing safety.

[0028] 5. High-efficiency heat exchange: The heat transfer coefficients of the oil-gas 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, with the same combustion air parameters, the combination of the oil-gas heat exchanger 10 and the external air preheater 2 reduces the volume of the heat exchanger by nearly half compared to conventional flue gas 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.

[0029] 6. 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

[0030] Figure 1 This is a schematic diagram of a steam boiler structure according to the present invention.

[0031] Figure 1In the middle, 1-blower, 2-external air preheater, 3-hot air, 4-burner, 5-steam boiler body, 6-saturated steam, 7-superheater, 8-superheated steam, 9-economizer, 10-oil-gas heat exchanger, 11-hot oil pipeline, 12-cold oil pipeline, 13-oil-gas separator, 14-filter, 15-thermal oil pump, 16-oil storage tank, 17-low-level oil tank, 18-overflow pipe, 19-boiler feedwater, 20-water supply pipeline, 21-flue, 22-low-temperature flue gas, 23-expansion pipe, 24-fuel. Detailed Implementation

[0032] The following is in conjunction with the appendix Figure 1 The present invention will be further described in detail with reference to specific embodiments.

[0033] Example 1:

[0034] A steam boiler, wherein the heating surfaces of the steam boiler body 5 include, for example, water-cooled walls, economizer 9, oil-gas heat exchanger 10, external air preheater 2, and superheater 7.

[0035] The economizer 9, oil-gas 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, the heating surface of the steam boiler body 5, and the superheater 7 for external heating.

[0036] 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 heat transfer oil from the oil-gas heat exchanger 10 serves as the heat source for the external air preheater 2.

[0037] The heat transfer oil separated by the oil-gas separator 13 is pressurized by the heat transfer oil pump 15. The pressurized heat transfer oil enters the oil-gas heat exchanger 10, is heated by flue gas, and is then transported to the external air preheater 2 to heat the air delivered by the blower 1. The oil then returns to the oil-gas separator 13. The gas-liquid mixture generated by the oil-gas separator 13 enters the oil storage tank 16 through the expansion pipe 23. The high-temperature flue gas generated by the steam boiler burner 4 is cooled by the heating surface of the steam boiler body 5, the superheater 7, the economizer 9, and the oil-gas heat exchanger 10. The resulting low-temperature flue gas 22 is discharged to subsequent equipment (such as dust collectors, desulfurization and denitrification equipment) for treatment, and then discharged from the chimney by the induced draft fan.

[0038] The fuel 24 for the steam boiler burner 4 is either coal or biomass.

[0039] The heat transfer oil of the external air preheater 2 is exchanged with the air indirectly, and the heat exchange tubes are plain tubes, finned tubes or spiral groove tubes.

[0040] The heat transfer oil and flue gas in the oil-gas heat exchanger 10 are exchanged indirectly, and the heat exchange tubes are plain tubes, finned tubes or spiral grooved tubes.

[0041] A filter 14 is provided: the heat transfer oil coming out of the oil-gas separator 13 enters the heat transfer oil pump 15 through the filter 14. The filter 14 is used to filter out solid impurity particles in the inlet heat transfer oil.

[0042] By controlling the inlet temperature of the heat transfer oil in the oil-gas 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 oil-gas 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.

[0043] The oil-gas separator 13 and the oil storage tank 16 can be integrated into one unit, with the oil storage tank 16 also serving as the oil-gas separator.

[0044] Preferably, the oil storage tank 16 is equipped with a safety valve, an exhaust valve, and a discharge valve, is protected by nitrogen sealing, and is insulated.

[0045] A low-level oil tank 17 is provided: the low-level oil tank 17 is connected to the oil storage tank 16 through an overflow pipe 18, and the low-level oil tank 17 is used for the heat transfer oil in the heat transfer oil internal circulation heat recovery system.

[0046] The heat recovery system for internal circulation of thermal oil in the steam boiler is also applicable to hot water boilers.

[0047] For the parts not mentioned in this utility model, existing technologies can be used to implement them, 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.

[0048] 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 heating surfaces of the steam boiler include the heating surfaces of the steam boiler body (5), the economizer (9), the oil-gas heat exchanger (10), the external air preheater (2), and / or the superheater (7). The economizer (9), oil-gas 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). The boiler feedwater (19) enters the heating surface of the steam boiler body (5) through the economizer (9) and the water supply pipeline (20) to generate saturated steam (6) for external heating. Alternatively, the boiler feedwater (19) generates superheated steam (8) for external heating through the economizer (9), the water supply pipeline (20), the heating surface of the steam boiler body (5), and the superheater (7). 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) as combustion air. The heat transfer oil coming out from the oil-gas heat exchanger (10) serves as the heat source of the external air preheater (2).

2. The steam boiler according to claim 1, characterized in that: The steam boiler includes an oil-gas separator (13). The heat transfer oil separated by the oil-gas separator (13) is pressurized by a heat transfer oil pump (15). The pressurized heat transfer oil enters the oil-gas heat exchanger (10), is heated by flue gas, and is then transported to the external air preheater (2) to heat the air delivered from the blower (1). The air then returns to the oil-gas separator (13). The gas-liquid mixture generated by the oil-gas separator (13) enters the oil storage tank (16) through the expansion pipe (23). The high-temperature flue gas generated by the steam boiler burner (4) is cooled by the heating surface of the steam boiler body (5) and / or the superheater (7), economizer (9), and oil-gas heat exchanger (10). The resulting low-temperature flue gas (22) is discharged to the subsequent equipment for processing and then discharged from the chimney by the induced draft fan.

3. 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.

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

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

6. The steam boiler according to claim 2, characterized in that: The oil-gas separator (13) and the oil storage tank (16) are integrated into one unit.

7. The steam boiler according to claim 1, characterized in that: A low-level oil tank (17) is provided: the low-level oil tank (17) is connected to the oil storage tank (16) through an overflow pipe (18).

8. The steam boiler according to claim 2, characterized in that: A filter (14) is provided: the heat transfer oil coming out of the oil-gas separator (13) enters the heat transfer oil pump (15) through the filter (14).

9. The steam boiler according to claim 2, characterized in that: The oil tank (16) is protected by nitrogen sealing.

10. The steam boiler according to claim 1, characterized in that: The heat recovery system of the steam boiler is also applicable to hot water boilers.

Images