Steam boiler

Abstract

Conduction oil is adopted as a heat-carrying medium of a boiler tail flue gas heat recoverer and an external air pre-heater, flue gas low-temperature corrosion is effectively avoided, meanwhile, efficient recycling of waste heat of flue gas of the steam boiler is achieved, and the steam boiler 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] The invention belongs to the technical field of steam boilers, and in particular relates to a steam boiler using heat transfer oil as a heat carrier and utilizing a waste heat recovery technology for an air preheater outside a furnace. 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] 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 reasonably recycle and utilize the waste heat of steam boiler flue gas, utilize the large heat capacity of liquid media such as water or heat transfer oil compared to air, use heat transfer oil as the heat carrier of flue gas-heat transfer oil heat exchanger and air-heat transfer oil heat exchanger, realize the compact and convenient arrangement of the oil and gas heat exchanger in the tail flue of the steam boiler, realize the compact and simple arrangement of the air preheater outside the boiler, reduce the exhaust temperature of the steam boiler while effectively avoiding the low-temperature corrosion of the oil and gas heat exchanger in the tail flue, has become a hot topic of research in this field. Summary of the invention

[0007] The purpose of the present invention is to solve the shortcomings of the above-mentioned existing steam boiler air preheater technology. The oil-gas heat exchanger and the heat recovery technology of the air preheater outside the furnace, that is, the heat recovery system of the internal circulation of the heat transfer oil, are adopted to effectively avoid the low-temperature corrosion of the oil-gas heat exchanger in the flue, and realize the efficient and safe recovery and utilization of the heat of the steam boiler flue gas.

[0008] The purpose of the present invention is achieved by the following measures:

[0009] A steam boiler, wherein the heating surface of the steam boiler includes the heating surface of the boiler body 1 such as the water-cooled wall, the economizer 9, the oil-gas heat exchanger 10, the air preheater 2 and / or the superheater 7,

[0010] The economizer 9, the oil-gas 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 heating surface of the steam boiler body 1 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 enters the heating surface of the steam boiler body 1 and the superheater 7 through the economizer 9, the water supply pipeline 20, the steam boiler body 1, 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 hot air 3 formed by the blower 1 and the external air preheater 2 is transported to the steam boiler burner 4, and the heat transfer oil from the oil-gas heat exchanger 10 is used as the heat source of 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, and the pressurized heat transfer oil enters the oil-gas heat exchanger 10, is transported to the air preheater 2 outside the furnace after being heated by the flue gas, heats the air transported by the blower 1, and 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, or / and the superheater 7, the economizer 9, and the oil-gas heat exchanger 10, and the 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.

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

[0014] The heat transfer oil and air of 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.

[0015] The heat transfer oil and flue gas of the oil-gas heat exchanger 10 adopt an indirect heat exchange method, and the heat exchange tubes adopt smooth tubes, fin 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, and the filter 14 is used to filter out solid impurity particles in the imported heat transfer oil.

[0017] By controlling the inlet temperature of the heat transfer oil of the oil-gas heat exchanger 10 (for example, above 85°C, and the appropriate temperature is determined according to 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, 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.

[0018] The oil-gas separator 13 and the oil storage tank 16 may be of an integrated structure, and the oil storage tank 16 also serves as the oil-gas separator.

[0019] Preferably, the oil storage tank 16 is provided with a safety valve, an exhaust valve, and a discharge valve, and is sealed and protected by nitrogen and adopts heat preservation measures.

[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 of the heat transfer oil internal circulation heat recovery system.

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

[0022] 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.

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

[0024] 1. Energy saving: Using heat transfer oil as the heat carrier, combined with the heat regenerator and the heat regenerator technology outside the furnace, it can effectively avoid the low-temperature corrosion of the flue gas of the steam boiler and realize the efficient recovery and utilization of the flue gas waste heat. In essence, it is a composite heat carrier steam boiler that combines a traditional steam boiler using water as the heat carrier medium with a heat transfer oil furnace using heat transfer oil as the heat carrier medium;

[0025] 2. Easy and compact installation: The air preheater 2 outside the furnace and the oil-gas 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;

[0026] 3. Flexible and convenient operation and adjustment: The heat recovery system of thermal oil 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;

[0027] 4. Safety: The thermal oil heat recovery system combined with the steam boiler has mature and reliable operating experience in the industry. Because it is set up nearby, the amount of thermal oil used in the system is not large, and the flue gas temperature at the tail of the steam boiler is not high. Selecting the right thermal oil can ensure the long-term stable operation of the thermal oil heat recovery system. Preferably, the oil storage tank adopts nitrogen sealing and positive pressure operation mode. The oil storage tank 16 and the matching low-level oil tank 17 can be conveniently arranged in a safe place to increase safety;

[0028] 5. High efficiency of heat exchange: The heat exchange coefficient of the oil-gas heat exchanger 10 and the air preheater 2 outside the furnace is affected by many factors, such as the specific heat capacity of the heat transfer oil and the 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 oil-gas heat exchanger 10 and the air preheater outside the furnace 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;

[0029] 6. Compared with the prior art, the present invention is particularly suitable for the 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

[0030] Figure 1 It is a structural schematic diagram of a steam boiler of the present invention.

[0031] Figure 1 Among them, 1-blower, 2-air preheater outside the furnace, 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 feed water, 20-water supply pipeline, 21-flue, 22-low-temperature flue gas, 23-expansion tube, 24-fuel. DETAILED DESCRIPTION

[0032] The following is combined with Figure 1 The present invention is further described in detail with reference to the accompanying drawings and specific examples.

[0033] Embodiment 1:

[0034] A steam boiler, wherein the heating surface of the steam boiler includes the heating surface of the steam boiler body 1 such as a water-cooled wall, an economizer 9, an oil-gas heat exchanger 10, an air preheater 2 outside the furnace and a superheater 7,

[0035] The economizer 9, the oil-gas 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 heating surface of the steam boiler body 1, and the superheater 7 to generate superheated steam 8 for external heat supply.

[0036] The external air preheater 2 is arranged outside the steam boiler flue 21. The hot air 3 formed by the blower 1 and the external air preheater 2 is transported to the steam boiler burner 4, and the heat transfer oil from the oil-gas heat exchanger 10 is used as the heat source of 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, and the pressurized heat transfer oil enters the oil-gas heat exchanger 10, is transported to the air preheater 2 outside the furnace after being heated by the flue gas, heats the air transported by the blower 1, and 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, and the low-temperature flue gas 22 formed 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.

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

[0039] The heat transfer oil and air of 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.

[0040] The heat transfer oil and flue gas of the oil-gas heat exchanger 10 adopt an indirect heat exchange method, and the heat exchange tubes adopt smooth tubes, fin 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, and the filter 14 is used to filter out solid impurity particles in the imported heat transfer oil.

[0042] By controlling the inlet temperature of the heat transfer oil of the oil-gas heat exchanger 10 (for example, above 85°C, and the appropriate temperature is determined according to 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, 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.

[0043] The oil-gas separator 13 and the oil storage tank 16 may be of an integrated structure, and the oil storage tank 16 also serves as the oil-gas separator.

[0044] Preferably, the oil storage tank 16 is provided with a safety valve, an exhaust valve, and a discharge valve, and is sealed and protected by nitrogen and adopts heat preservation measures.

[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 of the heat transfer oil internal circulation heat recovery system.

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

[0047] 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.

[0048] 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 heating surface of the steam boiler comprises a heating surface of a steam boiler body (1), an economizer (9), an oil-gas heat exchanger (10), an external air preheater (2) and / or a superheater (7). The economizer (9), the oil-gas 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 heating surface of the steam boiler body (1) 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 heating surface of the steam boiler body (1), 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 heat transfer oil from the oil-gas heat exchanger (10) is used as a heat source for the external air preheater (2).

2. The steam boiler according to claim 1, characterized in that: The heat transfer oil separated by the oil-gas separator (13) is pressurized by a heat transfer oil pump (15), and the pressurized heat transfer oil enters the oil-gas heat exchanger (10), is heated by the flue gas, and is transported to the air preheater (2) outside the furnace to heat the air transported by the blower (1), and 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 (1), or / and the superheater (7), the economizer (9), and the oil-gas heat exchanger (10), and the low-temperature flue gas (22) is discharged to subsequent equipment for treatment, and then discharged from the chimney through the induced draft fan.

3. 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.

4. The steam boiler according to claim 1, characterized in that: The heat transfer oil and air of the external air preheater (2) adopt an indirect heat exchange method, and the heat exchange tubes adopt smooth tubes, fin tubes or spiral grooved tubes.

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

6. The steam boiler according to claim 1, characterized in that: The oil-gas separator (13) and the oil storage tank (16) adopt an integrated structure.

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) via an overflow pipe (23).

8. The steam boiler according to claim 1, 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 storage tank (16) is sealed and protected by nitrogen.

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

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