A system and method for recycling the waste heat of a cascade recovery wet desulfurization device

Abstract

The present invention discloses a system and method for recovering the waste heat of a wet desulfurization device for cascade recycling. The system includes a desulfurization tower, a circulating water pump and a water temperature regulating tank; the desulfurization tower includes a desulfurization tower body, in which a desulfurization slurry pool, a flue gas inlet, a slurry heat exchanger, a slurry sprayer, a wet flue gas heat exchanger, a demister and a flue gas outlet are sequentially arranged from bottom to top. The flue gas inlet is connected to an inlet flue, and an original flue gas heat exchanger is arranged in the horizontal straight section of the inlet flue; the water inlet of the wet flue gas heat exchanger is connected to a low-temperature hot water extraction pipeline, and the water outlet is connected to the water inlet of the slurry heat exchanger. The water outlet of the slurry heat exchanger is connected to the water temperature regulating tank, the water outlet of the water temperature regulating tank is connected to the water inlet of the circulating water pump, the water outlet of the circulating water pump is connected to the water inlet of the original flue gas heat exchanger, and the water outlet of the original flue gas heat exchanger is at least divided into two paths, and one of the paths is connected to the water temperature regulating tank. The present invention realizes the recovery of the waste heat of the wet desulfurization device and simultaneously realizes the transformation of low-grade hot water for extraction into high-grade high-temperature recycled water.

Description

Technical Field

[0001] The present invention relates to the fields of energy conservation and environmental protection, and particularly relates to a system and method for cascaded recovery of waste heat from a wet flue gas desulfurization device. Background Art

[0002] As one of the main devices for converting the chemical energy of fuel into heat energy, coal-fired boilers are widely used in high-energy-consuming industries such as electric power, metallurgy, and petrochemical. Since coal-fired flue gas contains a large amount of polluting components such as dust, nitrogen oxides, and sulfur dioxide, the discharged flue gas needs to be purified through processes such as denitrification, dust removal, and desulfurization before being discharged into the atmosphere through a chimney to reduce the pollution degree of the exhaust gas to the atmospheric environment. Considering the thermal efficiency of the boiler and the safety of various flue gas treatment processes comprehensively, the exhaust gas temperature at the outlet of the air preheater is usually set at 120 - 150°C, resulting in a large amount of flue gas waste heat not being effectively utilized, and the flue gas heat loss accounting for 80% or more of the total heat loss of the boiler. Therefore, there is an urgent need to find a scientific way for flue gas recovery and utilization to efficiently recover the waste heat in the flue gas, reduce energy consumption, and achieve energy conservation and emission reduction for enterprises.

[0003] And an indispensable device in the recovery of flue gas waste heat is the heat exchanger. When the flue gas drops below the sulfuric acid dew point temperature, sulfuric acid will precipitate on the surface of the waste heat recovery heat exchanger, thereby causing serious corrosion to the waste heat recovery heat exchanger. In addition, the strong viscosity of sulfuric acid droplets leads to ash accumulation on the surface of the heat exchanger, resulting in a sharp decline in the heat transfer efficiency of the heat exchanger and increasing the wind resistance of the heat exchanger. Generally, the acid dew point temperature of coal-fired boiler flue gas is between 80°C and 105°C. Using water as the heat transfer medium, it is necessary to control the water temperature entering the heat exchanger above 60°C to prevent the temperature of the side wall of the flue gas in the heat exchanger from being below the acid dew point, thereby causing the low-temperature hot water to be unable to extract heat. In addition, the temperature of the desulfurization slurry and saturated flue gas in the desulfurization tower is generally between 50 - 60°C, containing a large amount of low-grade heat energy, but the utilization path of its low-grade heat energy is limited after recovery.

[0004] There are the following problems in the recovery and utilization of waste heat in the tail gas emissions of coal-fired power plants and industrial boilers:

[0005] (1) There are problems of low-temperature corrosion and ash accumulation and blockage in the waste heat recovery heat exchanger at the inlet of the desulfurization tower flue, and the temperature of the heat transfer medium entering the heat exchanger is required to be relatively high; (2) The utilization path of the low-grade waste heat in the desulfurization slurry and wet flue gas in the desulfurization tower is limited; (3) Low-grade heat energy water cannot be directly converted into high-grade heat energy water. To solve these problems, there is an urgent need for a comprehensive waste heat recovery and utilization system for a wet flue gas desulfurization device that can achieve simple equipment, economy, and high waste heat recovery efficiency. Summary of the Invention

[0006] To solve the above-mentioned technical problems, the present invention provides a system and method for cascaded recovery of waste heat from a wet flue gas desulfurization device.

[0007] A system for recovering the waste heat of a wet flue gas desulfurization device with cascaded steps, comprising a desulfurization tower, a circulating water pump and a water temperature regulating tank;

[0008] The desulfurization tower includes a desulfurization tower body. A flue gas inlet is provided on the side wall of the desulfurization tower body, and a flue gas outlet is provided at the top. The flue gas inlet is connected to an inlet flue, and a raw flue gas heat exchanger is arranged in the horizontal straight section of the inlet flue;

[0009] At the bottom inside the desulfurization tower body, a desulfurization slurry pool is arranged. Above the desulfurization slurry pool, a slurry heat exchanger, a slurry sprayer, a wet flue gas heat exchanger and a demister are arranged in sequence along the flue gas flow direction. The desulfurization slurry pool is connected to the slurry sprayer through a slurry circulating pump. The flue gas inlet is located between the slurry heat exchanger and the slurry sprayer;

[0010] The water inlet of the wet flue gas heat exchanger is connected to a low-temperature hot water intake pipeline, and the water outlet is connected to the water inlet of the slurry heat exchanger through a pipeline. The water outlet of the slurry heat exchanger is connected to the water temperature regulating tank through a pipeline. The water outlet of the water temperature regulating tank is connected to the water inlet of the circulating water pump through a pipeline. The water outlet of the circulating water pump is connected to the water inlet of the raw flue gas heat exchanger through a pipeline. The water outlet of the raw flue gas heat exchanger is at least divided into two paths, and one of the paths is connected to the water temperature regulating tank through a pipeline.

[0011] The present invention recovers the waste heat in three forms of the waste heat of the wet flue gas, the waste heat of the desulfurization slurry and the waste heat above the acid dew point of the raw flue gas before the desulfurization device in a cascaded manner. Among them, the low-temperature hot water is used to exchange heat with the wet flue gas and the desulfurization slurry to increase the water temperature of the low-temperature water, and is mixed with the hot water heated by taking heat from a part of the raw flue gas to ensure that the raw flue gas heat exchanger operates above the acid dew point, realizing the cascaded recovery of the waste heat of the wet flue gas desulfurization device, and at the same time realizing the transformation from low-grade heat energy water to high-grade heat energy water.

[0012] The following also provides several optional ways, which are not additional limitations to the above overall solution, but are only further supplements or optimizations. On the premise of no technical or logical contradictions, each optional way can be combined with the above overall solution alone, or multiple optional ways can be combined with each other.

[0013] Optionally, the raw flue gas heat exchanger includes several layers of heat exchange tubes evenly distributed at equal intervals along the flue gas flow direction in the inlet flue. Each layer of heat exchange tubes includes several metal finned tubes. The single-layer heat exchange tubes are installed in the inlet flue with the axes of their metal finned tubes perpendicular to the flue gas flow direction and the axes of the metal finned tubes extending horizontally.

[0014] The axes of the metal finned tubes extend horizontally, and the heat exchange liquid circulates horizontally in the heat exchanger to perform primary heat exchange with the raw flue gas flowing through the gaps between the heat exchange tubes; the fins of the heat exchange tubes can be made of the same or different materials as the inner heat exchange tubes.

[0015] The wet flue gas heat exchanger can adopt a tube-and-shell heat exchanger. When a conventional tube-and-shell heat exchanger is used in the present invention, its outer shell needs to be removed, and the desulfurization slurry is directly sprayed on the surface of the tube bundle. Optionally, the wet flue gas heat exchanger includes at least one layer of heat exchange tubes. Each layer of heat exchange tubes includes several horizontally arranged metal tubes with a diameter of 15 mm - 30 mm and a wall thickness of 0.5 mm - 2.0 mm; the distance between adjacent metal tubes in the same layer is 1 / 3 - 1 times the diameter of the metal tube. The heat exchange tubes are made of corrosion-resistant stainless steel.

[0016] Optionally, the slurry heat exchanger is installed at a position 0.5 m - 2 m above the liquid level of the desulfurization slurry in the desulfurization slurry tank; the slurry heat exchanger includes several slurry heat exchange tubes. The slurry heat exchange tubes are double-layer tubes, where the outer layer is a hollow circular tube and the inner layer is a core rod with both ends sealed. One end of the outer hollow circular tube is the water inlet and the other end is the water outlet. The gap between the outer hollow circular tube and the inner core rod is the heat extraction liquid flow channel; the water inlets of all the outer hollow circular tubes are connected in parallel and then communicated with the water outlet of the wet flue gas heat exchanger, and the water outlets of all the outer hollow circular tubes are connected in parallel and then connected to the water temperature adjustment tank. The core rod can be of solid or hollow structure and is made of metal or non-metal materials.

[0017] Optionally, a spiral flow disturbing ring is wound on the outer surface of the inner core rod.

[0018] Optionally, the inner diameter of the outer tube of the slurry heat exchange tube is 30 - 100 mm, and the gap between the outer hollow circular tube and the inner core rod is 1 - 10 mm. The diameter of the core rod is 1 - 10 mm smaller than the inner diameter of the outer tube.

[0019] Optionally, a solenoid valve is provided on the connecting pipeline between the water outlet of the raw flue gas heat exchanger and the water temperature adjustment tank; a temperature sensor is provided in the water temperature adjustment tank; the temperature sensor and the solenoid valve are controlled jointly.

[0020] Optionally, process water flushing devices are provided both above and below the demister.

[0021] The present invention also provides a method for cascaded recovery of the waste heat of a wet flue gas desulfurization device, preferably completed by using the system of the present invention, including:

[0022] (1) Before the high-temperature raw flue gas enters the wet flue gas desulfurization tower, when it flows through the surface of the metal fin heat exchange tubes of the raw flue gas heat exchanger in the inlet flue, the low-temperature water in the metal fin tubes is heated to reduce the temperature of the raw flue gas to near the acid dew point, completing the first-stage heat exchange;

[0023] (2) After the raw flue gas that has completed the first-stage heat exchange enters the wet flue gas desulfurization tower and passes through the desulfurization sprayer, it directly contacts the desulfurization slurry droplets sprayed by the desulfurization nozzles. The moisture on the surface of the slurry droplets evaporates and the temperature rises, the temperature of the flue gas decreases and the humidity approaches the saturated state, completing the process of transferring part of the waste heat in the flue gas to the falling desulfurization slurry droplets;

[0024] (3) The slurry droplets that have completed heat exchange fall onto the surface of the heat exchange tubes of the slurry heat exchanger. The droplets flow downward layer by layer in the form of a liquid film on the surface of the heat exchange tubes, and at the same time, indirectly exchange heat with the low-temperature water inside the heat exchange tubes. The temperature of the slurry decreases and the low-temperature water heats up, completing the secondary heat exchange;

[0025] (4) The nearly saturated flue gas that has completed spray washing continues to rise. When passing through the wet flue gas heat exchanger, it contacts the low-temperature outer wall of the heat exchange tubes of the wet flue gas heat exchanger. The gaseous water in the flue gas condenses into liquid water and aggregates into large droplets, which fall to the bottom of the tower. The temperature of the nearly saturated flue gas decreases and the humidity reaches the saturated state. The low-temperature water inside the heat exchange tubes is heated and the temperature rises, completing the tertiary heat exchange;

[0026] (5) The condensed low-temperature saturated flue gas carrying some fine condensate droplets enters the demister layer. The fine droplets are captured by the demister blades and aggregated into large droplets, which fall to the bottom of the tower under the action of gravity;

[0027] The low-temperature heat extraction hot water is sent as a heat extraction medium into the heat exchange tubes of the wet flue gas heat exchanger to perform the tertiary heat exchange with the high-temperature wet flue gas flowing through the outer surface of the heat exchange tubes; the hot water heated by the wet flue gas heat exchanger enters the heat exchange tubes of the slurry heat exchanger as a heat extraction medium and performs the secondary heat exchange with the high-temperature desulfurized slurry falling onto the outer surface of the heat exchange tubes; the hot water heated again by the slurry heat exchanger is sent into the water temperature adjustment tank. After adjusting the water temperature to above 60 °C in the water temperature adjustment tank, it is sent into the heat exchange tubes of the original flue gas heat exchanger as a heat extraction medium to perform the primary heat exchange with the original flue gas flowing through the outer surface of the heat exchange tubes; a part of the high-temperature water heated by the original flue gas heat exchanger is sent into the water temperature adjustment tank to adjust the water temperature in the water temperature adjustment tank; the amount of water recycled from the original flue gas heat exchanger into the water temperature adjustment tank is adjusted by the solenoid valve according to the feedback water temperature of the temperature sensor in the water temperature adjustment tank.

[0028] In the present invention, the low-temperature water extracts heat from the high-temperature wet flue gas and the high-temperature desulfurized slurry through the wet flue gas heat exchanger and the slurry heat exchanger. The water temperature continuously rises and flows into the water temperature adjustment tank, and is transported to the original flue gas heat exchanger for heat extraction by the hot water circulation pump. A part of the heated hot water enters the hot water pipe network or the production workshop, and the other part returns to the water temperature adjustment tank. The amount of recycled water is adjusted by the solenoid valve according to the feedback water temperature data of the water temperature sensor in the water temperature adjustment tank, thereby realizing the cascaded recovery of the waste heat of the wet desulfurization device.

[0029] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0030] (1) The present invention provides a solution for recovering the waste heat of flue gas in a wet desulfurization device in a hierarchical manner: the raw flue gas heat exchanger in the inlet flue is used to exchange heat with the raw flue gas, the slurry heat exchanger is used to exchange heat with the desulfurization slurry, and the wet flue gas heat exchanger is used to extract heat from the nearly saturated wet flue gas after desulfurization washing. The high-temperature hot water after three-stage heat extraction is recycled to reduce the energy consumption of enterprise production.

[0031] (2) The present invention provides an efficient heat exchange device that does not occupy the space and operating resistance of the desulfurization tower. The slurry heat exchanger is installed from below the flue gas inlet of the desulfurization tower to above the slurry liquid level at the bottom of the tower. The slurry droplets sprayed by the spray layer flow in a film form outside the heat exchange tubes, greatly increasing the contact area of the slurry on the surface of the heat exchange tubes. In addition, the low-temperature water in the interlayer of the heat exchange tubes is under the action of the turbulence ring, strengthening the turbulence degree of the low-temperature water in the heat exchange tubes and enhancing the indirect heat exchange effect between the high-temperature slurry and the low-temperature water.

[0032] (3) The present invention provides a solution for converting low-grade heat energy water into high-grade heat energy water by using the waste heat recovery of a wet desulfurization device. After the low-temperature hot water extracts heat from the high-temperature wet flue gas and the desulfurization slurry and is heated up, it then enters the raw flue gas heat exchanger to extract heat, realizing the three-stage waste heat recovery of low-grade heat energy water into high-grade heat energy water and improving the application ways of high-temperature water.

[0033] (4) The present invention provides a solution for the coordinated treatment of multiple pollutions in the waste heat recovery of a wet desulfurization device. By extracting heat from the raw flue gas and the desulfurization slurry, it is beneficial to remove sulfur dioxide and sulfur trioxide in the flue gas. After the nearly saturated flue gas after desulfurization washing extracts heat again, part of the condensed water takes dust particles as crystallization nuclei and gradually aggregates and grows, and is captured by the demister, thereby reducing the emission of fine particles. Description of the Drawings

[0034] Figure 1 It is a schematic structural diagram of the waste heat recovery system of the wet desulfurization device in a stepped recovery manner according to the present invention.

[0035] Figure 2 is Figure 1 a schematic structural diagram of a single heat exchange tube in the raw flue gas heat exchanger in

[0036] Figure 3 is Figure 1 a schematic structural diagram of a single heat exchange tube in the slurry heat exchanger in

[0037] Figure 4 is Figure 1 a schematic structural diagram of the vertical cross-section of the wet flue gas heat exchanger in

[0038] The reference numerals shown in the figures are as follows:

[0039] 1 - Desulfurization tower 2 - Inlet flue 3 - Raw flue gas heat exchanger

[0040] 4 - slurry sprayer, 5 - wet flue gas heat exchanger, 6 - demister

[0041] 7 - flue gas outlet, 8 - slurry heat exchanger, 9 - water temperature regulating tank

[0042] 10 - water temperature sensor, 11 - circulation water pump, 12 - solenoid valve

[0043] 13 - desulfurization slurry tank

[0044] 31 - base pipe, 32 - metal fin

[0045] 51 - heat exchange pipe

[0046] 81 - water inlet, 82 - outer layer pipe, 83 - mandrel

[0047] 84 - spiral flow disturbing ring, 85 - water outlet Detailed implementation manners

[0048] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0049] For better describing and illustrating the embodiments of the present invention, one or more accompanying drawings may be referred to, but the additional details or examples used to describe the accompanying drawings should not be considered as limiting the scope of any one of the inventive concepts of the present invention, the currently described embodiments or the preferred modes.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments, and are not intended to limit the present invention.

[0051] As Figure 1 shown, a system for cascaded recovery of waste heat from a wet flue gas desulfurization device includes a desulfurization tower 1, a circulation water pump 11, and a water temperature regulating tank 9.

[0052] The desulfurization tower 1 includes a desulfurization tower body. A flue gas inlet is provided on the side wall of the desulfurization tower body, and a flue gas outlet 7 is provided at the top. The flue gas inlet communicates with an inlet flue 2, and a raw flue gas heat exchanger 3 is arranged in the horizontal straight section of the inlet flue 2.

[0053] At the bottom inside the desulfurization tower, a desulfurization slurry pool 13 is arranged. Above the desulfurization slurry pool 13, a slurry heat exchanger 8, a slurry sprayer 4, a wet flue gas heat exchanger 5 and a demister 6 are arranged in sequence along the flue gas flow direction. The desulfurization slurry pool 13 is communicated with the slurry sprayer 4 through a slurry circulation pump (not shown in the figure). The flue gas inlet is located between the slurry heat exchanger 8 and the slurry sprayer 4. That is, in the desulfurization tower 1, from bottom to top, there are the desulfurization slurry pool 13, the slurry heat exchanger 8, the flue gas inlet, the slurry sprayer 4, the wet flue gas heat exchanger 5, the demister 6 and the flue gas outlet 7 in sequence.

[0054] The water inlet of the wet flue gas heat exchanger 5 is communicated with a low-temperature heat extraction water input pipeline. The water outlet of the wet flue gas heat exchanger 5 is communicated with the water inlet of the slurry heat exchanger 8 through a pipeline. The water outlet of the slurry heat exchanger 8 is communicated with a water temperature regulating tank 9 through a pipeline. The water outlet of the water temperature regulating tank 9 is communicated with the water inlet of a circulating water pump 11 through a pipeline. The water outlet of the circulating water pump 11 is communicated with the water inlet of the raw flue gas heat exchanger 3 through a pipeline. The water outlet of the raw flue gas heat exchanger 3 is at least divided into two paths, and one of them is connected to the water temperature regulating tank 9 through a pipeline for regulating the water temperature entering the raw flue gas heat exchanger, and the other path can be connected to a high-temperature water pipe network.

[0055] The low-temperature heat extraction water sequentially recovers the waste heat of the wet flue gas, the waste heat of the desulfurization slurry and the waste heat above the acid dew point of the raw flue gas before the desulfurization device, realizes the recovery of the waste heat of the wet desulfurization device, and at the same time realizes the transformation of low-grade heat extraction water into high-grade high-temperature recycled water.

[0056] The raw flue gas heat extractor is arranged in the horizontal straight section of the inlet flue for primary heat exchange of the raw flue gas entering the desulfurization tower. A heat extraction medium flows through the raw flue gas heat extractor. When the raw flue gas flows through the outer wall of the heat extractor, indirect heat exchange is carried out with the heat extraction medium flowing in the heat extractor. In one implementation, the raw flue gas heat exchanger 3 includes several layers of heat exchange tubes equally spaced along the flue gas flow direction in the inlet flue. Each layer of heat exchange tubes includes several metal fin tubes. The single-layer heat exchange tubes are installed in the inlet flue with the axes of their metal fin tubes perpendicular to the flue gas flow direction and the axes of the metal fin tubes extending horizontally (that is, a single metal fin tube is horizontally installed in the inlet flue and its axis is perpendicular to the flue gas flow direction. Figure 1 It is for the convenience of showing that several layers of metal fin tubes are arranged along the flue gas flow direction). The adjacent layers of heat exchange tubes can be connected in series or in parallel. The series connection method can extend the travel of the heat extraction liquid in the heat exchanger.

[0057] As an implementation of the metal fin tube, such as Figure 2 shown, a single metal fin tube includes a base tube 31 and metal fins 32. The fins of the heat exchange tube can be made of the same or different materials as the inner heat exchange tube. The base tube is made of stainless steel with strong corrosion resistance. The metal fins can be made of stainless steel with strong corrosion resistance, or can be made of aluminum or copper with strong thermal conductivity. When aluminum fins or copper fins are selected, the outer surface of the metal heat exchange tube needs to be coated with an anti-corrosion coating.

[0058] In order to ensure that the flue gas temperature on the surface of the heat exchange tube of the original flue gas heat exchanger is above the acid dew point, a part of the high-temperature hot water after the original flue gas heat exchange needs to be returned to the water temperature regulating tank and mixed with the hot water after the slurry heat exchanger takes heat, so as to increase the temperature of the hot water entering the heat exchange tube of the original flue gas heat exchanger. The water outlet of the slurry heat exchanger is connected to the water inlet of the high-temperature water network and the side wall water inlet of the water temperature regulating tank through a three-way valve pipeline. A part of it enters the high-temperature water network and a part of it is sent back to the water temperature regulating tank. A solenoid valve 12 is provided on the pipeline between the water outlet of the original flue gas heat exchanger 3 and the water inlet of the water temperature regulating tank 9. A temperature sensor 10 is provided in the water temperature regulating tank 9. The temperature sensor 10 is controlled in conjunction with the regulating valve 12. The return water volume is adjusted through the solenoid valve according to the temperature data feedback of the temperature sensor in the water temperature regulating tank.

[0059] A water outlet is arranged on the lower half of the side wall of the water temperature regulating tank 9, and a pipeline connecting the circulating water pump 11 and the water temperature regulating tank is connected to the water outlet. Water inlets are arranged on the upper half and the top of the side wall of the water temperature regulating tank 9, and a pipeline connecting the slurry heat exchanger and the water temperature regulating tank is connected to the top water inlet, and a pipeline connecting the water outlet of the original flue gas heat exchanger and the water temperature regulating tank is connected to the side wall water inlet.

[0060] Before the high-temperature raw flue gas enters the wet desulfurization tower, when the high-temperature raw flue gas in the inlet flue flows through the surface of the metal fin heat exchange tube of the raw flue gas heat exchanger, the low-temperature water in the metal fin tube is heated, and the raw flue gas temperature drops to near the acid dew point, completing the first-level heat exchange.

[0061] After the flue gas that has completed the primary heat exchange enters the wet desulfurization tower, it directly contacts the desulfurization slurry droplets sprayed from the desulfurization nozzle when passing through the spray layer. The water on the surface of the slurry droplets evaporates and the temperature rises, the flue gas temperature decreases and the humidity is close to saturation, completing the process of transferring part of the residual heat in the flue gas to the falling desulfurization slurry droplets; the slurry droplets that have completed the heat exchange fall to the surface of the heat exchange tube of the slurry heat exchanger 8, and the droplets flow downward layer by layer in the state of liquid film on the surface of the heat exchange tube, and at the same time indirectly exchange heat with the water in the heat exchange tube, the slurry temperature decreases and the low-temperature water is heated, completing the secondary heat exchange.

[0062] The slurry heat exchanger is installed at a position 0.5m-2m above the desulfurization slurry liquid surface. As an embodiment of the slurry heat exchanger, the slurry heat exchanger 8 includes a plurality of slurry heat exchange tubes. The structure of a single slurry heat exchange tube is as follows: Figure 3 As shown, a single slurry heat exchange tube is a double-layer tube, including an outer tube 82 and a core rod 83, wherein the outer tube is a hollow circular tube and the inner tube is a core rod with sealed ends. One end of the outer hollow circular tube is the water inlet 81 of the heat exchange tube, and the other end is the water outlet 85 of the heat exchange tube.

[0063] The mandrel adopts a solid or hollow structure, and the material is made of metal or non-metal. To enhance the heat exchange efficiency of the slurry heat exchanger, in one implementation, a spiral turbulator ring 84 is wound around the outer surface of the inner mandrel.

[0064] In one implementation of the size of a single slurry heat exchange tube, the inner diameter of the outer tube of the slurry heat exchange tube is 30 - 100 mm, the diameter of the mandrel is 1 - 10 mm smaller than the inner diameter of the outer tube, that is, the gap between the outer hollow circular tube and the inner mandrel is 1 - 10 mm, and the gap between the outer hollow circular tube and the inner mandrel serves as the flow channel for the heat extraction liquid.

[0065] In one installation method of the slurry heat exchanger, the slurry heat exchanger 8 is horizontally installed above the desulfurization slurry tank in the desulfurization tower with the axis of its slurry heat exchange tube. The water inlets of all the outer hollow circular tubes are connected in parallel and then communicated with the water outlet of the wet flue gas heat exchanger 5, and the water outlets of all the outer hollow circular tubes are connected in parallel and then connected to the water temperature adjustment tank 9.

[0066] The slurry sprayer 4 is installed above the flue gas inlet, and the slurry sprayer adopts a conventional slurry sprayer in the desulfurization tower.

[0067] The wet flue gas heat exchanger is located between the slurry sprayer 4 and the demister 6. The low-temperature heat extraction water is sent into this heat exchanger. The nearly saturated flue gas that has completed spray washing continues to rise. When passing through the wet flue gas heat exchanger, the gaseous water in the flue gas condenses into liquid water when contacting the low-temperature outer wall of the heat exchange tube, aggregates into large droplets and falls to the bottom of the tower. The temperature of the nearly saturated flue gas drops and the humidity reaches the saturated state. The low-temperature water in the heat exchange tube is heated, completing three-stage heat exchange. As one implementation of the wet flue gas heat exchanger, as Figure 4 shown, the wet flue gas heat exchanger 5 includes several layers of heat exchange tubes 51. Each layer of heat exchange tubes includes several parallel metal tubes. The diameter of a single metal tube is 15 mm - 30 mm, and the wall thickness is 0.5 mm - 2.0 mm. The distance between adjacent metal tubes in the same layer of heat exchange tubes is 1 / 3 - 1 times the diameter of the heat exchange tube. The adjacent layers of heat exchange tubes can be connected in series or in parallel. Series connection can extend the travel of the heat extraction liquid in the heat exchanger. The heat exchange tubes are made of corrosion-resistant stainless steel. In other implementations, the wet flue gas heat exchanger 5 can adopt a tube-and-shell heat exchanger. When a conventional tube-and-shell heat exchanger is installed in the desulfurization tower, there is no need for an outer shell, and the flue gas directly passes through the tube bundle gap.

[0068] The condensed low-temperature saturated flue gas and carrying some fine condensate droplets enter the demister. The demister adopts a conventional demister structure in the desulfurization tower. Process water washing devices are arranged above and below the demister for cleaning the demister.

[0069] Based on the above waste heat recovery system, the process flow of waste heat recovery for the wet desulfurization device is as follows:

[0070] Before the high-temperature raw flue gas enters the desulfurization tower 1, when the high-temperature raw flue gas flows through the surface of the metal fin heat exchange tubes of the raw flue gas heat exchanger 3 in the inlet flue, it heats the low-temperature water in the metal fin tubes, and the temperature of the raw flue gas drops to near the acid dew point, completing the primary heat exchange;

[0071] After the flue gas that has completed the primary heat exchange enters the desulfurization tower 1 and passes through the slurry sprayer 4, it comes into direct contact with the desulfurization slurry droplets sprayed by the desulfurization nozzles. The moisture on the surface of the slurry droplets evaporates and the temperature rises, the temperature of the flue gas decreases and the humidity approaches the saturation state, completing the process of transferring part of the waste heat in the flue gas to the falling desulfurization slurry droplets;

[0072] The slurry droplets that have completed the heat exchange fall onto the surface of the heat exchange tubes of the slurry heat exchanger 8. The droplets flow downward layer by layer in the form of a liquid film on the surface of the heat exchange tubes, and at the same time indirectly exchange heat with the water in the heat exchange tubes, the temperature of the slurry decreases and the low-temperature water warms up, completing the secondary heat exchange;

[0073] The nearly saturated flue gas that has completed the spray washing continues to rise. When it passes through the wet flue gas heat exchanger 5, it comes into contact with the low-temperature outer wall of the heat exchange tubes, and the gaseous water in the flue gas condenses into liquid water and aggregates into large droplets and falls to the bottom of the tower. The temperature of the nearly saturated flue gas drops and the humidity reaches the saturation state, and the low-temperature water in the heat exchange tubes is heated, completing the tertiary heat exchange;

[0074] The condensed low-temperature saturated flue gas that has completed the heat exchange and carries some fine condensate droplets enters the demister 8. The fine droplets are captured by the demister blades and aggregated into large droplets, and fall to the bottom of the tower under the action of gravity.

[0075] The low-temperature hot water takes heat from the high-temperature wet flue gas and the high-temperature desulfurization slurry after passing through the wet flue gas heat exchanger 5 and the slurry heat exchanger 8. The water temperature continuously rises and flows into the water temperature adjustment tank 9. It is transported to the raw flue gas heat exchanger 3 by the circulating water pump 11 to take heat. Part of the heated hot water enters the hot water pipe network or the production workshop, and the other part returns to the water temperature adjustment tank 9. The return water volume is adjusted through the solenoid valve 12 according to the data feedback of the water temperature sensor 10 in the water temperature adjustment tank, so as to realize the cascade recovery of the waste heat of the wet desulfurization device.

[0076] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as these combinations of technical features do not conflict, they should all be considered to be within the scope described in this specification.

[0077] The above-described embodiments only represent several implementation manners of the present invention. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent should be subject to the appended claims.

Claims

1. A system for recovering the waste heat of a wet desulfurization device with stepped recycling, characterized in that, Including desulfurization tower, circulating water pump and water temperature regulating tank; The desulfurization tower comprises a desulfurization tower body, a flue gas inlet is arranged on the side wall of the desulfurization tower body, and a flue gas outlet is arranged on the top, the flue gas inlet is connected to the inlet flue, and an original flue gas heat exchanger is arranged in the horizontal straight section of the inlet flue; A desulfurization slurry pool is arranged at the bottom of the desulfurization tower body, and a slurry heat exchanger, a slurry sprayer, a wet flue gas heat exchanger and a demister are arranged in sequence above the desulfurization slurry pool along the flue gas flow direction. The desulfurization slurry pool and the slurry sprayer are connected through a slurry circulation pump. The slurry heat exchanger is installed at a position 0.5m-2m above the desulfurization slurry liquid level in the desulfurization slurry pool, and the flue gas inlet is located between the slurry heat exchanger and the slurry sprayer; The water inlet of the wet flue gas heat exchanger is connected to the low-temperature hot water pipeline, and the water outlet is connected to the water inlet of the slurry heat exchanger through a pipeline. The water outlet of the slurry heat exchanger is connected to the water temperature regulating tank through a pipeline. The water outlet of the water temperature regulating tank is connected to the water inlet of the circulating water pump through a pipeline. The water outlet of the circulating water pump is connected to the water inlet of the original flue gas heat exchanger through a pipeline. The water outlet of the original flue gas heat exchanger is divided into at least two paths, and one of them is connected to the water temperature regulating tank through a pipeline. A part of the high-temperature water heated by heat exchange in the original flue gas heat exchanger is sent to the water temperature regulating tank to adjust the water temperature in the water temperature regulating tank; A solenoid valve is arranged on the connecting pipeline between the water outlet of the original flue gas heat exchanger and the water temperature regulating tank; a temperature sensor is arranged in the water temperature regulating tank; and the temperature sensor is controlled in conjunction with the solenoid valve.

2. The system for recovering waste heat of the wet desulfurization device by steps according to claim 1, characterized in that The original flue gas heat exchanger includes several layers of heat exchange tubes distributed at equal intervals along the flue gas flow direction in the inlet flue, each layer of heat exchange tubes includes several metal fin tubes, and the single-layer heat exchange tubes are installed in the inlet flue with the axes of the metal fin tubes perpendicular to the flue gas flow direction and the axes of the metal fin tubes extending horizontally.

3. The system for recovering waste heat of the wet desulfurization device by the steps according to claim 1, characterized in that, The wet flue gas heat exchanger comprises at least one layer of heat exchange tubes, each layer of heat exchange tubes comprises a plurality of horizontally arranged metal tubes, the diameter of the metal tubes is 15mm-30mm, and the wall thickness is 0.5mm-2.0mm; the spacing between adjacent metal tubes in the same layer is 1 / 3-1 times the diameter of the metal tube.

4. The system for recovering the waste heat of the wet desulfurization device by steps according to any one of claims 1 to 3, characterized in that, The slurry heat exchanger includes a plurality of slurry heat exchange tubes, which are double-layer tubes, wherein the outer layer is a hollow circular tube and the inner layer is a core rod with sealed ends at both ends, one end of the outer hollow circular tube is a water inlet and the other end is a water outlet, and the gap between the outer hollow circular tube and the inner core rod is a heat-extracting liquid flow channel; the water inlets of all the outer hollow circular tubes are connected in parallel and connected to the water outlet of the wet flue gas heat exchanger, and the water outlets of all the outer hollow circular tubes are connected in parallel and connected to the water temperature regulating tank.

5. The system for recovering waste heat of the wet desulfurization device by steps according to claim 4, wherein, The outer surface of the inner core rod is wound with a spiral spoiler ring.

6. The system for recovering waste heat from the wet desulfurization device of the ladder according to claim 4, wherein The inner diameter of the outer tube of the slurry heat exchange tube is 30-100 mm, and the gap between the outer hollow circular tube and the inner core rod is 1-10 mm.

7. The system for recovering waste heat of the wet desulfurization device by steps according to claim 1, characterized in that, Process water flushing devices are arranged above and below the demister.

8. A method for recovering the waste heat of a wet flue gas desulfurization device with cascades, characterized in that, The method is accomplished by using the system of claim 1, comprising: (1) Before the high-temperature raw flue gas enters the wet flue gas desulfurization tower, when it flows through the surface of the metal fin heat exchange tubes of the raw flue gas heat exchanger in the inlet flue, it heats the low-temperature water in the metal fin tubes and reduces the temperature of the raw flue gas to near the acid dew point, completing the primary heat exchange; (2) After the raw flue gas that has completed the primary heat exchange enters the wet flue gas desulfurization tower and passes through the desulfurization sprayer, it comes into direct contact with the desulfurization slurry droplets sprayed from the desulfurization nozzles. The moisture on the surface of the slurry droplets evaporates and the temperature rises, the flue gas temperature decreases and the humidity approaches the saturated state, completing the process of transferring part of the waste heat in the flue gas to the falling desulfurization slurry droplets; (3) The slurry droplets that have completed the heat exchange fall onto the surface of the heat exchange tubes of the slurry heat exchanger. The droplets flow downward layer by layer in a liquid film state on the surface of the heat exchange tubes, and at the same time indirectly exchange heat with the low-temperature water in the heat exchange tubes. The temperature of the slurry decreases and the low-temperature water warms up, completing the secondary heat exchange; (4) The nearly saturated flue gas that has completed the spray washing continues to rise. When it passes through the wet flue gas heat exchanger, it contacts the low-temperature outer wall of the heat exchange tubes of the wet flue gas heat exchanger. The gaseous water in the flue gas condenses into liquid water and aggregates into large droplets that fall to the bottom of the tower. The temperature of the nearly saturated flue gas drops and the humidity reaches the saturated state. The low-temperature water in the heat exchange tubes is heated and warmed up, completing the tertiary heat exchange; (5) The condensed low-temperature saturated flue gas carrying some fine condensate droplets enters the demister layer. The fine droplets are captured by the demister blades and aggregated into large droplets, which fall to the bottom of the tower under the action of gravity; The low-temperature heat extraction water is sent as a heat extraction medium into the heat exchange tubes of the wet flue gas heat exchanger to conduct the said tertiary heat exchange with the high-temperature wet flue gas flowing through the outer surface of the heat exchange tubes; the heat extraction water heated and warmed up by the wet flue gas heat exchanger enters the heat exchange tubes of the slurry heat exchanger as a heat extraction medium, and conducts the said secondary heat exchange with the high-temperature desulfurization slurry falling onto the outer surface of the heat exchange tubes; the heat extraction water that is heated and warmed up again by the slurry heat exchanger is sent into the water temperature adjustment tank. After the water temperature is adjusted to above 60 °C in the water temperature adjustment tank, it is sent into the heat exchange tubes of the raw flue gas heat exchanger as a heat extraction medium to conduct the said primary heat exchange with the raw flue gas flowing through the outer surface of the heat exchange tubes; a part of the high-temperature water heated and warmed up by the raw flue gas heat exchanger is sent into the water temperature adjustment tank to adjust the water temperature in the water temperature adjustment tank; the amount of water recycled from the raw flue gas heat exchanger into the water temperature adjustment tank is adjusted by the solenoid valve according to the feedback water temperature of the temperature sensor in the water temperature adjustment tank.

Images