Waste heat boiler adopting phase change heat exchanger

Abstract

The invention relates to a waste heat boiler adopting a phase change heat exchanger, the waste heat boiler comprises a body (3), a steam-water separator (4), the phase change heat exchanger (7) and a coal economizer (16), a steam-water mixture generated by heating of the body (3) of the waste heat boiler enters the steam-water separator (4), separated liquid water returns to the body (3), separated water vapor is fed into the phase change heat exchanger (7) through a main steam valve (5), and the phase change heat exchanger (7) is heated through the main steam valve (5). Clear water enters the purification water tank (14) after being purified by the water treatment equipment (13) and then is fed into the phase change heat exchanger (7) through the water feeding pump (15) and the coal economizer (16) to generate external supply steam (24), generated condensed water (8) returns to the phase change boiler body (3) directly or after being pressurized by the circulating water pump (9), and a waste heat source is conveyed to subsequent equipment for treatment after being cooled by the phase change boiler body (3) and the coal economizer (16). The product is obtained or discharged as three wastes.

Description

Technical Field

[0001] This invention belongs to the field of waste heat boilers, and specifically relates to a waste heat boiler employing a phase change heat exchanger. Background Technology

[0002] Currently used waste heat boilers all adopt an open-loop process, which means that clean water is purified by water treatment equipment and then pumped into the waste heat boiler by a feed water pump to absorb the heat from the waste heat source. The generated saturated or superheated steam is supplied externally for heating or to drive steam turbine generator sets to generate electricity.

[0003] In many parts of my country, the water quality supplied by waste heat boilers is poor. In addition, the operation and management level of water treatment equipment is not high, which causes scaling, oxygen corrosion and bulging in waste heat boilers, affecting their safe and economical operation.

[0004] Scale formation in waste heat boilers is a complex physicochemical process, primarily formed through the following mechanisms: Boiler feedwater contains hardness ions such as calcium and magnesium, as well as dissolved oxygen, which are difficult to remove completely by water treatment equipment. During the heating process in the waste heat boiler, these ions precipitate due to decreased solubility, chemical reactions, and concentration, forming insoluble solid deposits such as carbonates, sulfates, or silicates. These deposits adhere to the heating surface tube walls and gradually accumulate as scale. Dissolved oxygen introduced into the boiler feedwater leads to corrosion of the boiler's metal heating surfaces and the formation of oxides. Poor water quality, malfunctioning water treatment equipment, inadequate management, improper selection of chemicals, and oxides generated from corrosion of the waste heat boiler's metal heating surfaces all contribute to exacerbating scaling and under-scale corrosion, creating a vicious cycle that affects the safe and economical operation of the waste heat boiler and may even lead to major safety accidents.

[0005] Traditional waste heat boilers are used to recover the sensible or latent heat of gaseous, solid, or liquid waste heat sources. For example, the waste heat recovery devices and methods proposed by well-known domestic waste heat boiler manufacturers (Jiangsu Dongjiu Heavy Industry Co., Ltd.) include: 202520172730.3 - Waste heat recovery device for sensible heat of high-temperature magnesium slag, 202310573665.0 - Sensible heat waste heat recovery device and method for molten calcium carbide, 202122078113.1 Energy-saving device for tail gas exhaust of waste heat boiler for dry quenching coke flue gas, and 201911143005.9 - Cooling system and method for cement clinker, etc., which provide effective waste heat recovery devices and methods for gas, solid, and liquid heat sources. It is worth noting that the safe operation of waste heat boilers is crucial for heat sources in special forms, especially solid and liquid waste heat resources. For example, uneven scale formation on the heating surface (especially at the high-temperature end), or contaminants adhering to the outside of the heat exchange tubes, as well as the combined effects of contaminants and scale, can cause uneven heating of the local heating surface, high-temperature creep of the heat exchange tubes, etc., which affect the safe and long-term operation of the waste heat boiler. In severe cases, it can even lead to accidents such as tube rupture and explosion, causing significant property damage and casualties.

[0006] There are many uncontrollable factors affecting the waste heat source side. The scale buildup and oxygen corrosion on the inner side of the heat exchange surface of the waste heat boiler can be effectively controlled if appropriate processes are adopted.

[0007] Therefore, effectively mitigating the hazards of scale and oxygen corrosion on the heating surfaces of waste heat boilers under harsh operating conditions, and avoiding tube rupture and explosion accidents caused by scale and oxygen corrosion, is a challenging issue in waste heat boiler technology. How to solve this problem deserves in-depth consideration and research by boiler industry professionals. Summary of the Invention

[0008] The purpose of this invention is to solve the problem of scale and oxygen corrosion in existing waste heat boiler bodies. By adopting phase change heat exchanger technology, the scale and oxygen corrosion phenomena in existing waste heat boiler bodies (the body parts in contact with the high-temperature end of the waste heat source) are eliminated, so as to realize the safe, stable and efficient operation of waste heat boilers and the efficient recovery and utilization of waste heat.

[0009] The objective of this invention is achieved through the following measures:

[0010] A waste heat boiler employing a phase change heat exchanger is characterized in that: the waste heat boiler includes a main body 3, a steam-water separator 4, a phase change heat exchanger 7, an economizer 16, and connecting pipes thereof.

[0011] The main body 3 is heated by contact with the waste heat source, and the resulting steam-water mixture enters the steam-water separator 4 for steam-water separation. The separated liquid water returns to the main body 3, and the separated water vapor is sent to the phase change heat exchanger 7 via the main steam valve 5. The purified water enters the purified water tank 14 after being purified by the water treatment equipment 13, and is then sent to the phase change heat exchanger 7 via the feed water pump 15 and the economizer 16. In the phase change heat exchanger 7, heat is absorbed to generate externally supplied steam for output, or the externally supplied steam generated by heat absorption in the phase change heat exchanger 7 is further heated by the heat exchanger before being output. The water vapor from the main steam valve 5 heats the feed water in the phase change heat exchanger 7, and the resulting condensate 8 returns to the main body 3 directly or after being pressurized by the circulating water pump 9. The superheater is located in the waste heat source.

[0012] After the waste heat source is cooled by the main body 3 of the waste heat boiler and the economizer 16, it is transported to subsequent equipment (such as the next production process, dust collector, desulfurization and denitrification equipment, etc.) for treatment to obtain the corresponding products or to be discharged as waste.

[0013] Preferably, the purified water from the water treatment equipment 13 is deoxygenated by a normal temperature or thermal deaerator before being sent to the purified water tank 14.

[0014] Furthermore, the purified water tank 14 is integrated with the deaerator to form an integral structure. The purified water tank 14 is the deoxygenated water tank in the deaerator. The purified water from the water treatment equipment 13 is deoxygenated by the deaerator and then falls into the deoxygenated water tank in the deaerator.

[0015] The phase change heat exchanger 7 adopts a shell-and-tube heat exchange method, such as a shell-and-tube heat exchanger, a tube-and-shell heat exchanger, a spiral heat exchanger, etc. Preferably, the phase change heat exchanger 7 adopts a tube-and-shell heat exchanger, with steam flowing through the shell side and steam boiler feedwater flowing through the tube side.

[0016] The main body 3 of the waste heat boiler includes water-cooled wall tubes, downcomers, headers, steam-water separators, etc., and is designed according to the conventional natural circulation or forced circulation principle of waste heat boiler.

[0017] Preferably, the heated surface of the body 3 adopts enhanced heat transfer technology, such as internal finned tubes or internal spiral groove tubes.

[0018] The waste heat source may be one or more of gaseous, liquid or solid states, such as high-temperature magnesium slag, molten calcium carbide, high-temperature flue gas, etc.

[0019] The economizer 16 employs enhanced heat transfer measures, such as using finned tubes or spiral grooved tubes.

[0020] The phase change heat exchanger 7 is equipped with a safety valve, pressure gauge, etc. in the steam formation space of the external steam supply 24 to prevent high-pressure steam, which is used as a heat source, from leaking into the low-pressure side due to leakage from the heat exchange surface of the phase change heat exchanger 7, thus preventing the phase change heat exchanger 7 from operating under overpressure.

[0021] A water replenishment line is provided: softened water, demineralized water, or purified water is pumped into the water circulation loop of the waste heat boiler body 3 to compensate for steam and water losses caused by waste heat boiler blowdown. Softened water or demineralized water is produced through conventional water treatment equipment.

[0022] Preferably, pure water is used to supplement the steam and water loss in the water circulation of the waste heat boiler body 3. The pure water is obtained by cooling the externally supplied steam 24 generated by the phase change heat exchanger 7. The externally supplied steam 24 is cooled by the purified water from the water treatment equipment 13 to obtain pure water. The heated purified water is sent to the purified water tank 14. The pure water is sent into the water circulation loop of the phase change boiler body 3 by a booster pump.

[0023] A waste heat boiler employing a phase change heat exchanger is characterized in that: the waste heat boiler includes a main body 3, a steam-water separator 4, a phase change heat exchanger 7, an economizer 16, and connecting pipes thereof; the main body 3 of the waste heat boiler is a once-through boiler type; and the steam-water separator 4 is integrated with the main body 3 of the waste heat boiler.

[0024] The steam generated by the waste heat boiler body 3 is sent to the phase changer 7 via the main steam valve 5. The water in the purified water tank 14 is sent to the phase changer 7 via the feed water pump 15. In the phase changer 7, heat is absorbed to generate externally supplied steam 24. Alternatively, the externally supplied steam 24 generated by the phase changer 7 is further heated by the superheater before being output. The steam coming out of the main steam valve 5 is cooled by the phase changer 7, and the resulting condensate 8 is pressurized by the circulating water pump 9 and returned to the waste heat boiler body 3.

[0025] After the waste heat source is cooled by the main body 3 of the waste heat boiler and the economizer 16, it is transported to subsequent equipment (such as the next production process, dust collector, desulfurization and denitrification equipment, etc.) for treatment to obtain the corresponding products or to be discharged as waste.

[0026] For the parts not mentioned in this invention, existing technologies are used, that is, existing, well-known, mature, reliable and reasonable technical measures can be introduced into this system, such as setting up necessary pressure gauges, temperature control instruments, water level gauges, alarm instruments, automatic control facilities, etc.

[0027] The present invention has the following advantages over the prior art:

[0028] 1. Because the waste heat boiler body and phase changer adopt a closed-loop pure water circulation process, unlike the open circulation process in traditional waste heat boilers which requires continuous water replenishment to compensate for steam and water losses caused by continuous blowdown during operation, the heat exchange surfaces of the waste heat boiler body do not accumulate scale and oxygen corrosion. This can be considered as eliminating the possibility of scale and oxygen corrosion on the convective heat exchange surfaces of the waste heat boiler and the steam condensation side heat exchange surfaces of the phase changer. In essence, it shifts the main area of ​​scale and oxygen corrosion from the high-temperature and harsh environment of the waste heat boiler body. The scale and oxygen corrosion at the phase changer are moved outside the furnace. These can be efficiently treated through continuous blowdown, physical or chemical cleaning, feedwater deoxygenation, and the addition of deoxygenating agents or scale inhibitors. This effectively concentrates the scale and oxygen corrosion from the traditional waste heat boiler drum and convection heat exchange surfaces at the phase changer for treatment. Even if the heat exchange tubes of the phase changer perforate and leak, causing high-pressure steam to enter the shell side, it can be safely released through the safety valve located in the tube-side steam space of the phase changer, eliminating overpressure caused by the leak. The risks associated with this invention are far less than those of traditional waste heat boilers, where leaks can be detected promptly by monitoring the water level in the boiler body. The phase changer operates at a temperature below the critical temperature of water, within a stable medium-temperature range, preventing damage from overheating. Furthermore, the phase changer is a separate unit from the waste heat boiler body, unlike traditional waste heat boilers which are located inside flues or containers. This allows for maintenance and repair of the phase changer in a non-enclosed space. The overall optimization achieved by this invention significantly reduces the regulatory responsibilities of national regulatory authorities, the safety risks for users and operators, greatly extends the lifespan of the waste heat boiler body, reduces the risks associated with inspection, maintenance, and repair, and significantly reduces the costs of physical or chemical cleaning of the phase changer. The benefits of non-enclosed space inspection and repair operations far outweigh the costs of adding a phase changer, thus ensuring the safe, economical, and long-term operation of the waste heat boiler.

[0029] 2. An innovative economizer feedwater external circulation process is adopted, meaning that the economizer effluent after heating is no longer sent to the main body of the traditional waste heat boiler, but instead enters the phase change heat exchanger. The saturated steam generated by the phase change heat exchanger is supplied externally, or it is supplied externally after being superheated by a superheater located at the waste heat source. Therefore, it is significantly different from the water circulation process of the traditional waste heat boiler. Because the feedwater heated by the economizer reaches or approaches the saturation temperature, the heat transfer process of the phase change heat exchanger is more efficient.

[0030] 3. The phase change heat exchanger adopts a shell-and-tube heat exchanger. Because it is a strong heat transfer process in which phase change occurs on both sides, the overall heat transfer coefficient is extremely high, roughly ranging from 1500 to 3000 W / (m²). 2·K), in which steam flows through the shell side and feedwater flows through the tube side of the phase change heat exchanger. The tube side is easy to clean. By selecting appropriate pressures for the phase change boiler body and the phase change heat exchanger, the heat transfer temperature difference of the phase change heat exchanger is reasonable, the structure is compact, the heat transfer is efficient, and the cleaning is convenient.

[0031] 4. The waste heat boiler body adopts a closed-loop water circulation method. If a circulating water pump is installed, the circulating water pump does not need to be a multi-stage pump. Only the pressure resistance and overcoming the friction resistance need to be considered, and the power consumption is very small.

[0032] 5. This invention provides a variety of possibilities for optimizing the heating surface of the waste heat boiler body, such as using high circulation ratio once-through boiler technology, using small diameter tubes to increase the heat exchange area (avoiding pipe blockage, overheating deformation, tube rupture or explosion caused by scale and oxygen corrosion), and adopting enhanced heat transfer measures for the convective heat exchange surface.

[0033] 6. For existing waste heat boilers, the present invention can be used to modify the original waste heat boiler by adding a phase change heat exchanger. The saturated steam generated by the original waste heat boiler is introduced into the external phase change heat exchanger as a heat source. The saturated steam generated by the phase change heat exchanger is supplied externally or supplied externally after being superheated by the heat exchanger. The water inlet pipe from the economizer outlet of the original waste heat boiler to the main body is disconnected, and the economizer outlet water is connected to the phase change heat exchanger as feed water, thereby completing the new circulation process modification of the original waste heat boiler. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the waste heat boiler structure using a phase change heat exchanger according to the present invention.

[0035] Figure 1 In the middle section, 1-high temperature flue gas, 3-body, 4-steam-water separator, 5-main steam valve, 6-steam, 7-phase change heat exchanger, 8-condensate, 9-circulating water pump, 10-first safety valve, 11-second safety valve, 12-clean water, 13-water treatment equipment, 14-purified water tank, 15-feed water pump, 16-economizer, 22-flue, 23-low temperature flue gas, 24-external steam supply.

[0036] Figure 2 This is a schematic diagram of the DC-type waste heat boiler using a phase change heat exchanger according to the present invention.

[0037] Figure 2 In the middle section, 1-high temperature flue gas, 3-body, 4-steam-water separator, 5-main steam valve, 6-steam, 7-phase change heat exchanger, 8-condensate, 9-circulating water pump, 10-first safety valve, 11-second safety valve, 12-clean water, 13-water treatment equipment, 14-purified water tank, 15-feed water pump, 16-economizer, 22-flue, 23-low temperature flue gas, 24-external steam supply. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] Example 1:

[0040] As attached Figure 1 As shown, taking the recovery of heat from high-temperature flue gas using a waste heat boiler as an example, the waste heat boiler employs a phase change heat exchanger. The waste heat boiler includes a main body 3, a steam-water separator 4, a phase change heat exchanger 7, an economizer 16, and connecting pipes.

[0041] The main body 3 comes into contact with the high-temperature flue gas 1 and is heated. The resulting steam-water mixture enters the steam-water separator 4, where steam and water are separated. The separated liquid water returns to the main body 3, and the separated water vapor is sent to the phase change heat exchanger 7 via the main steam valve 5. The purified water enters the purified water tank 14 after being purified by the water treatment equipment 13, and then is sent to the phase change heat exchanger 7 via the feed water pump 15 and the economizer 16. In the phase change heat exchanger 7, heat is absorbed to generate externally supplied steam 24. The water vapor from the main steam valve 5 heats the feed water in the phase change heat exchanger 7, and the resulting condensate 8 returns to the main body 3 directly or after being pressurized by the circulating water pump 9.

[0042] After the high-temperature flue gas 1 is cooled by the heating surface of the waste heat boiler body 3 and the economizer 16, it is transported to subsequent equipment (such as dust collector, desulfurization or denitrification equipment, etc.) for treatment, and then discharged from the chimney by the induced draft fan.

[0043] The phase change heat exchanger 7 adopts an indirect heat exchange method, such as a shell-and-tube heat exchanger or a tube-and-tube heat exchanger. Preferably, the phase change heat exchanger 7 adopts a tube-and-tube heat exchanger, with steam flowing through the shell side and boiler feedwater flowing through the tube side. A safety valve is installed in the steam formation space of the externally supplied steam in the phase change heat exchanger 7 to prevent high-pressure heating steam from leaking into the low-pressure side due to leakage from the heat exchange surface of the phase change heat exchanger 7, which would cause the phase change heat exchanger 7 to operate under overpressure.

[0044] The main body 3 of the waste heat boiler includes water-cooled wall tubes, downcomers, headers, steam-water separators, etc., and is designed according to the conventional natural circulation principle of waste heat boiler.

[0045] A water replenishment line is provided: softened water, demineralized water, or purified water is replenished into the water circulation loop of the waste heat boiler body 3 via a booster water pump; the purified water is produced by cooling with externally supplied steam, and the externally supplied steam is cooled by the purified water produced by the water treatment equipment 13 to obtain purified water. The heated purified water returns to the purified water tank 14, and the purified water provides power to the water replenishment line via a booster water pump.

[0046] The purified water produced by the water treatment equipment 13 is deoxygenated by a room temperature or thermal deaerator before entering the purified water tank 14.

[0047] The purified water tank 14 and the deaerator can be integrated into one unit, that is, the purified water tank 14 is the deaerator water tank in the deaerator.

[0048] The steam space of the steam-water separator 4 leads out a safety valve connection pipe to prevent the waste heat boiler body 3 from operating under overpressure. The body 3 is equipped with a first safety valve 10 and a second safety valve 11, and the outlet pipes of the safety valves are connected to a safe location.

[0049] In accordance with the relevant safety management regulations for waste heat boilers, the space for forming external steam 24 in the phase change heat exchanger 7 is equipped with a safety valve, pressure gauge, water level gauge, etc.

[0050] Example 2:

[0051] As attached Figure 2 As shown, taking a waste heat boiler that recovers heat from high-temperature flue gas as an example, the waste heat boiler employs a phase change heat exchanger. The waste heat boiler includes a main body 3, a steam-water separator 4, a phase change heat exchanger 7, an economizer 16, and connecting pipes. The main body 3 of the waste heat boiler is a once-through boiler type, and the steam-water separator 4 is integrated with the main body 3 of the waste heat boiler.

[0052] The steam generated by the waste heat boiler body 3 is sent to the phase changer 7 via the main steam valve 5. The water in the purified water tank 14 is sent to the phase changer 7 via the feed water pump 15. In the phase changer 7, heat is absorbed to generate externally supplied steam for output. Alternatively, the externally supplied steam generated by the phase changer 7 is further heated by the superheater before being output. The steam coming out of the main steam valve 5 is cooled by the phase changer 7, and the resulting condensate 8 is pressurized by the circulating water pump 9 and returned to the waste heat boiler body 3.

[0053] After being cooled by the main body 3 of the waste heat boiler and the economizer 16, the high-temperature flue gas is transported to subsequent equipment (such as dust collectors, desulfurization and denitrification equipment, etc.) for treatment, and then discharged from the chimney by the induced draft fan.

[0054] The main body 3 of the waste heat boiler is designed as a waste heat boiler based on the forced circulation principle.

[0055] The rest is the same as in Example 1.

[0056] For the parts not mentioned in this invention, existing technologies are used, that is, existing, well-known, mature, reliable and reasonable technical measures can be introduced into this system, such as setting up necessary pressure gauges, temperature control instruments, water level gauges, alarm instruments, automatic control facilities, etc.

[0057] Although the present invention has been disclosed above with reference to preferred embodiments, these are not intended to limit the invention. Any person skilled in the art can make various changes, equivalent substitutions, or modifications without departing from the spirit and scope of the invention, and these modifications also fall within the protection scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims of this application.

Claims

1. A waste heat boiler using a phase-change heat exchanger, characterized in that: the waste heat boiler comprises a body (3), a steam-water separator (4), a phase-change heat exchanger (7), an economizer (16) and connecting pipelines thereof, the body (3) is heated by a waste heat source, a generated steam-water mixture enters the steam-water separator (4), steam-water separation is performed in the steam-water separator (4), separated water vapor is sent to the phase-change heat exchanger (7) through a main steam valve (5), water in a purified water tank (14) is sent to the phase-change heat exchanger (7) through a feed water pump (15) and the economizer (16), heat absorption in the phase-change heat exchanger (7) generates output export steam, or the export steam generated by heat absorption in the phase-change heat exchanger (7) is heated by a superheater and then output, water vapor from the main steam valve (5) is heated by the phase-change heat exchanger (7) to feed water, and generated condensate water (8) is directly or pressurized by a circulating water pump (9) and then returned to the body (3), the waste heat source is cooled by the body (3) and the economizer (16) of the waste heat boiler and then transported to subsequent equipment for treatment or discharged.

2. The waste heat boiler according to claim 1, characterized in that: the waste heat source is in one or more of gaseous, liquid or solid states, and the phase-change heat exchanger (7) uses a partition wall type heat exchange mode.

3. The waste heat boiler according to claim 1, characterized in that: a water supplement line is provided, in which softened water, desalted water or pure water is pressurized by a booster water pump and then supplemented into a water circulation loop of the body (3).

4. The waste heat boiler according to claim 3, characterized in that: the pure water is prepared by cooling of the export steam, the pure water is obtained by cooling of purified water generated by a water treatment device (13), and the purified water after temperature rise is returned to the purified water tank (14).

5. The waste heat boiler according to claim 4, characterized in that: the purified water prepared by the water treatment device (13) is deoxygenated by a normal temperature or thermal deaerator and then enters the purified water tank (14).

6. The waste heat boiler according to claim 5, characterized in that: the purified water tank (14) and the deaerator adopt an integrated structure.

7. A waste heat boiler using a phase-change heat exchanger, characterized in that: the waste heat boiler comprises a body (3), a steam-water separator (4), a phase-change heat exchanger (7), an economizer (16) and connecting pipelines thereof, the body (3) of the waste heat boiler adopts a once-through boiler type, and the steam-water separator (4) and the body (3) of the waste heat boiler adopt an integrated structure, the waste heat boiler body (3) generates water vapor which is sent to the phase-change heat exchanger (7) through a main steam valve (5), water in a purified water tank (14) is sent to the phase-change heat exchanger (7) through a feed water pump (15), heat absorption in the phase-change heat exchanger (7) generates export steam, or the export steam generated by the phase-change heat exchanger (7) is heated by a superheater and then output, water vapor from the main steam valve (5) is cooled by the phase-change heat exchanger (7), generated condensate water (8) is pressurized by a circulating water pump (9) and then returned to the body (3) of the waste heat boiler, ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The waste heat source is cooled by the body (3) and the economizer (16) of the waste heat boiler, and then is transported to subsequent equipment for treatment to obtain products or be discharged as three wastes.

8. The waste heat boiler according to claim 7, characterized in that: A water supplementing line is arranged, wherein softened water, desalted water or pure water is supplemented into the water circulation loop of the body (3) of the waste heat boiler by a booster pump; the pure water is prepared by cooling external steam, the pure water is obtained by cooling the purified water generated by a water treatment device (13), and the heated purified water returns to a purified water tank (14).

9. The waste heat boiler according to claim 8, characterized in that: The purified water prepared by the water treatment device (13) is deoxygenated by a normal-temperature or thermal deaerator, and enters the purified water tank (14).

10. The waste heat boiler according to claim 9, characterized in that: The purified water tank (14) and the deaerator are in an integrated structure.

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