Waste heat recovery system and method for blow-down water of steam boiler

Abstract

The invention relates to the technical field of energy recycling, in particular to a waste heat recovery system and method for steam boiler blow-down water, comprising a pressure flash tank, a blow-down cooling sedimentation tank, a first heat exchanger, a second heat exchanger, a water replenishing device and a pickling device; a steam boiler is communicated with the pressure flash tank and the pollution discharge cooling sedimentation tank, the pressure flash tank is communicated with the pollution discharge cooling sedimentation tank, the first heat exchanger and the second heat exchanger, the first heat exchanger is communicated with the steam boiler and the second heat exchanger, and the second heat exchanger is communicated with the steam boiler. The second heat exchanger is communicated with the pollution discharge cooling sedimentation tank, the water replenishing device is communicated with the second heat exchanger and the steam boiler, and the pickling device is communicated with the second heat exchanger. The technical problems that in the prior art, scale is difficult to remove, and heat utilization is low are solved, the cleaning efficiency of the recovery system is improved, and the utilization efficiency of waste heat of steam boiler blow-down water is improved.

Description

Technical Field

[0001] This invention relates to the field of energy recycling technology, and in particular to a waste heat recovery system and method for steam boiler wastewater. Background Technology

[0002] Existing patent CN106595022B discloses a method for energy-saving utilization of steam boiler heat recovery, using a steam boiler heat recovery and energy-saving system with a waste heat recovery mode: Periodic boiler blowdown heat recovery: High-temperature pressurized boiler water is discharged from boiler blowdown outlets 1# and 2#, a dual-color water level gauge, and a single-color water level gauge as drainage. This drainage enters the blowdown expansion tank through the inlet of the heat recovery energy-saving unit. The steam portion is discharged directly into the hot water exchange tank through the steam separator. High-temperature water is discharged through the outlet of the blowdown expansion tank. The heat recovery inlet four-way valves A1 and A4 are open, and A2 and A3 are closed. The heat recovery outlet four-way valves B2 and B4 are open, and B1 and B3 are closed. The high-temperature water passes through a tubular heat exchanger to the hot water tank. Heat recovery heating is performed; continuous boiler blowdown heat recovery: steam is continuously discharged from the steam boiler outlet, passes through the flash evaporator in the heat recovery energy-saving unit, and enters from the flash evaporator inlet. Steam is discharged from the flash evaporator steam outlet. Steam three-way valves C1 and C2 are open, and C3 is closed. Steam enters the hot water tank and is used directly to heat hot water. The high-temperature water discharged after steam-water separation in the flash evaporator is recovered again through the boiler periodic blowdown recovery path; low-temperature medium-pressure wastewater after heat recovery is discharged; steam separated from the blowdown expansion tank enters the hot water tank for further heating. When the hot water tank system is short of water, the electric valve for adding water to the hot water tank is opened to replenish the water tank; dry burning descaling operation mode: the intelligent controller controls the heat recovery heat exchange... Sensors at the inlet and outlet of the heat exchanger automatically detect and compare the data parameters of the heat exchange medium. When an abnormality is detected, the system automatically switches to dry-burning descaling mode. Steam from the flash evaporator outlet enters in reverse through the steam three-way valve C (C1 and C3 open, C2 closed), and then through the wastewater medium outlet and inlet of the heat recovery heat exchanger. This wastewater then flows through the heat recovery outlet four-way valve B (B3 and B4 open, B1 and B2 closed), and the heat recovery inlet four-way valve A (A2 and A4 open, A1 and A3 closed), performing flushing-type dry-burning descaling. Simultaneously, the heat from the dry-burning steam is recovered through the heat exchanger in the hot water tank. The system then switches back to heat exchange mode, and residual scale particles are further flushed away by high-pressure wastewater, completing the automatic dry-burning descaling process. Thermal deoxygenation is also performed. Operating Mode: Heat is recovered through energy-saving heat exchange in wastewater discharge. The high-temperature condensate from the flash evaporator undergoes heat exchange and energy-saving recovery along with the wastewater, raising the water tank temperature. Simultaneously, steam from the flash evaporator, through the opening of steam three-way valves C1 and C2 and the closing of C3, along with steam from the blowdown expansion tank, enters the hot water tank to heat the water. The hot water tank is connected to a silencer. Boiler Flue Gas Waste Heat Recovery and Energy-Saving Feedwater Operation Mode: The water in the hot water tank undergoes heat recovery and thermal deoxygenation, raising its temperature. Simultaneously, when the boiler control system issues a command to supply water, the hot water in the hot water tank is drawn by the feedwater pump, passes through the energy-saving device, and undergoes reverse convection heat exchange with the flue gas before entering the steam boiler feedwater inlet.

[0003] In practice, some components of scale, such as carbonates, sulfates, silicates, phosphates, and metal oxides, are difficult to remove effectively by dry burning descaling, which affects the heat exchange efficiency of the heat exchanger. At the same time, there is also recyclable heat energy in the exhaust gas between various mechanisms during waste heat recovery and utilization, but existing technologies are unable to effectively utilize this part of the energy. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in related technologies. To this end, this invention provides a waste heat recovery system and method for steam boiler wastewater, solving the technical problems of difficult scale removal and low heat utilization in the prior art, improving the cleaning efficiency of the recovery system, and increasing the utilization efficiency of waste heat from steam boiler wastewater.

[0005] This invention provides a waste heat recovery system for steam boiler wastewater, including a pressure flash tank, a wastewater cooling sedimentation tank, a first heat exchanger, a second heat exchanger, a water replenishment device, and an acid washing device. The steam boiler is connected to the pressure flash tank and the wastewater cooling sedimentation tank, and the pressure flash tank is connected to the wastewater cooling sedimentation tank, the first heat exchanger, and the second heat exchanger. The first heat exchanger is connected to the steam boiler and the second heat exchanger, the second heat exchanger is connected to the sewage cooling sedimentation tank, the water replenishment device is connected to the second heat exchanger and the steam boiler, and the acid washing device is connected to the second heat exchanger.

[0006] A further improvement of the waste heat recovery system for steam boiler wastewater of the present invention is that it further includes a wastewater expansion container, which is connected to the steam boiler and the wastewater cooling sedimentation tank.

[0007] A further improvement of the waste heat recovery system for steam boiler wastewater of the present invention is that the steam boiler has a continuous wastewater discharge pipe and a periodic wastewater discharge pipe; The continuous sewage pipe and the periodic sewage pipe are connected to a main sewage pipe. The main sewage pipe is connected to the pressure flash tank through a sewage waste heat recovery pipe. The main sewage pipe is connected to the sewage expansion tank through a backup sewage pipe. The sewage waste heat recovery pipe is equipped with a second control valve, and the backup sewage pipe is equipped with a first control valve. The pressure flash tank and the sewage cooling sedimentation tank are connected by a backup sewage pipe, which is equipped with a first valve.

[0008] A further improvement of the waste heat recovery system for steam boiler wastewater of the present invention is that the pressure flash tank and the first heat exchanger are connected through a waste steam discharge pipe, the pressure flash tank and the second heat exchanger are connected through a flash condensate pipe and a condensate header, a condensate pump is installed between the flash condensate pipe and the condensate header, a first manual gate valve is installed on the condensate header, and the first heat exchanger and the flash condensate pipe are connected through a waste steam condensate pipe.

[0009] A further improvement of the waste heat recovery system for steam boiler wastewater of the present invention is that the second heat exchanger and the first heat exchanger are connected by a secondary water inlet pipe.

[0010] A further improvement of the waste heat recovery system for steam boiler wastewater of the present invention is that the second heat exchanger and the wastewater cooling sedimentation tank are connected by a waste heat recovery discharge pipe, and the waste heat recovery discharge pipe is equipped with a second manual gate valve.

[0011] A further improvement of the waste heat recovery system for steam boiler wastewater of the present invention is that the water supply device is provided with a boiler water supply bypass pipe, the steam boiler is provided with a boiler water supply main pipe, and the boiler water supply bypass pipe and the boiler water supply main pipe are connected by a first water supply control valve. The first heat exchanger is connected to the boiler feedwater header via a secondary water outlet pipe; The second heat exchanger and the boiler water supply bypass pipe are connected through a primary water supply inlet pipe, which is equipped with a second water supply control valve.

[0012] A further improvement of the waste heat recovery system for steam boiler wastewater of the present invention is that the acid washing device is provided with an acid washing inlet pipe and an acid washing outlet pipe, the acid washing inlet pipe is connected to the second heat exchanger, the acid washing outlet pipe is connected to the waste heat recovery discharge pipe, the acid washing inlet pipe is provided with a first acid washing manual gate valve, and the acid washing outlet pipe is provided with a second acid washing manual gate valve.

[0013] The present invention also provides a method for recovering waste heat from steam boiler wastewater, wherein the waste heat recovery method is performed using the waste heat recovery system described above, and includes the following steps: The water supply device introduces water into the second heat exchanger, which then enters the first heat exchanger. After heat exchange in the first and second heat exchangers, the water temperature rises and is then supplied to the steam boiler. Alternatively, the water supply device can directly supply water to the steam boiler. The flash condensate in the pressure flash tank enters the second heat exchanger, where it exchanges heat with the water supplied by the water supply device before entering the wastewater cooling sedimentation tank. The secondary exhaust steam from the pressure flash tank enters the first heat exchanger, where it exchanges heat with the water supplied by the water supply device and becomes condensate. The condensate and flash condensate then merge and enter the second heat exchanger. The cleaning solution in the pickling unit enters the second heat exchanger. After the cleaning solution dissolves the scale in the second heat exchanger, it returns to the pickling unit to complete the cleaning of the second heat exchanger.

[0014] A further improvement of the waste heat recovery method for steam boiler wastewater of the present invention is that it further includes the following steps: when the steam boiler needs maintenance or malfunctions, the steam boiler wastewater enters the wastewater expansion tank, and then enters the wastewater cooling sedimentation tank, and the wastewater in the pressure flash tank enters the wastewater cooling sedimentation tank.

[0015] The above-described one or more technical solutions in the embodiments of the present invention have at least one of the following technical effects: This invention takes into account that the wastewater from steam boilers is saturated water with high pressure, high temperature, and high salt and alkali concentration, making it impossible for it to directly enter the heat exchanger. After being expanded, depressurized, and cooled by a pressure flash tank, it can meet the parameter requirements of subsequent equipment such as the first heat exchanger, the second heat exchanger, and the condensate pump, further reducing equipment manufacturing and maintenance costs.

[0016] In this invention, the flash-evaporated secondary exhaust steam enters the first heat exchanger and exchanges heat counter-currently with softened water. During this process, the flash-evaporated secondary exhaust steam undergoes a phase change, releasing latent heat and liquefying into higher-temperature condensate. This condensate then merges with the flash condensate from the pressure flash tank and enters the second heat exchanger for counter-current heat exchange with softened water, achieving deep recovery and utilization of waste heat from the wastewater. The softened water to be supplied to the steam boiler is replenished through the first and second heat exchangers, where waste heat from the wastewater is recovered. By increasing the boiler feedwater temperature, the fuel consumption for steam supply can be significantly reduced, improving overall energy efficiency.

[0017] The acid washing device in this invention can regularly descale and clean the heat exchange tubes of the second heat exchanger, which can improve the heat exchange efficiency of the second heat exchanger, reduce under-deposit corrosion damage to the second heat exchanger, and ensure the stability of the waste heat recovery system for steam boiler wastewater.

[0018] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of a waste heat recovery system for steam boiler wastewater provided by the present invention.

[0021] Figure label: 1. Steam boiler; 2. Blowout expansion tank; 3. Blowout cooling sedimentation tank; 4. Water makeup device; 5. Pressure flash tank; 6. Condensate pump; 81. First heat exchanger; 82. Second heat exchanger; 9. Pickling device; 111. Exhaust steam discharge pipe; 112. Flash condensate pipe; 113. Exhaust steam condensate pipe; 114. Condensate header pipe; 115. Waste heat recovery discharge pipe; 121. Primary makeup water inlet pipe; 122. Secondary makeup water inlet pipe; 123. Secondary makeup water outlet pipe; 124. Boiler makeup water bypass pipe; 125. Boiler makeup water header pipe; 131. Continuous blowdown pipe; 132. Periodic blowdown pipe; 133. Blowdown header pipe; 134. Blowdown waste heat recovery pipe; 135. Backup blowdown pipe; 136. Emergency discharge pipe; 137. Condensate discharge pipe; 141. Pickling inlet pipe; 142. Pickling outlet pipe; 711, First control valve; 712, Second control valve; 721, First water supply control valve; 722, Second water supply control valve; 731, First manual gate valve; 732, Second manual gate valve; 741, First pickling manual gate valve; 742, Second pickling manual gate valve. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. The following embodiments are used to illustrate this invention but should not be used to limit the scope of this invention.

[0023] The following is combined Figure 1 The present invention describes a waste heat recovery system for steam boiler wastewater, comprising a pressure flash tank 5, a wastewater cooling sedimentation tank 3, a first heat exchanger 81, a second heat exchanger 82, a water replenishment device 4, and an acid washing device 9. The steam boiler 1 is connected to the pressure flash tank 5 and the wastewater cooling sedimentation tank 3. The pressure flash tank 5 is connected to the wastewater cooling sedimentation tank 3, the first heat exchanger 81 and the second heat exchanger 82. The first heat exchanger 81 is connected to the steam boiler 1 and the second heat exchanger 82. The second heat exchanger 82 is connected to the wastewater cooling sedimentation tank 3. The water replenishment device 4 is connected to the second heat exchanger 82 and the steam boiler 1. The pickling device 9 is connected to the second heat exchanger 82.

[0024] In a preferred embodiment of the waste heat recovery system for steam boiler wastewater of the present invention, a wastewater expansion container 2 is further included. The wastewater expansion container 2 is connected to the steam boiler 1 and the wastewater cooling sedimentation tank 3. The wastewater expansion container 2 can receive high-temperature wastewater from the steam boiler 1, effectively relieving the system's wastewater discharge pressure. During system maintenance or malfunction, it can provide a temporary storage area for wastewater, ensuring the stability and safety of the system and avoiding safety accidents caused by wastewater overflow during maintenance or malfunction.

[0025] Furthermore, the steam boiler 1 has a continuous blowdown pipe 131 and a periodic blowdown pipe 132; The continuous sewage pipe 131 and the periodic sewage pipe 132 are connected to a sewage main pipe 133. The sewage main pipe 133 is connected to the pressure flash tank 5 through a sewage waste heat recovery pipe 134. The sewage main pipe 133 is connected to the sewage expansion tank 2 through a spare sewage pipe 135. The sewage waste heat recovery pipe 134 is equipped with a second control valve 712, and the spare sewage pipe 135 is equipped with a first control valve 711. The pressure flash tank 5 and the sewage cooling sedimentation tank 3 are connected by a spare sewage pipe 135, which is equipped with a first valve.

[0026] Furthermore, the pressure flash tank 5 and the first heat exchanger 81 are connected by a waste steam discharge pipe 111, the pressure flash tank 5 and the second heat exchanger 82 are connected by a flash condensate pipe 112 and a condensate header pipe 114, a condensate pump 6 is installed between the flash condensate pipe 112 and the condensate header pipe 114, a first manual gate valve 731 is installed on the condensate header pipe 114, and the first heat exchanger 81 and the flash condensate pipe 112 are connected by a waste steam condensate pipe 113.

[0027] Furthermore, the second heat exchanger 82 and the first heat exchanger 81 are connected by a secondary water inlet pipe 122.

[0028] Furthermore, the second heat exchanger 82 and the sewage cooling sedimentation tank 3 are connected by a waste heat recovery discharge pipe 115, and the waste heat recovery discharge pipe 115 is equipped with a second manual gate valve 732.

[0029] Furthermore, the water supply device 4 is provided with a boiler water supply bypass pipe 124, and the steam boiler 1 is provided with a boiler water supply header pipe 125. The boiler water supply bypass pipe 124 and the boiler water supply header pipe 125 are connected by a first water supply control valve 721. The first heat exchanger 81 is connected to the boiler water supply header 125 via a secondary water supply outlet pipe 123; The second heat exchanger 82 and the boiler water supply bypass pipe 124 are connected through a primary water supply inlet pipe 121, which is equipped with a second water supply control valve 722.

[0030] Furthermore, the pickling device 9 is provided with a pickling inlet pipe 141 and a pickling outlet pipe 142. The pickling inlet pipe 141 is connected to the second heat exchanger 82, and the pickling outlet pipe 142 is connected to the waste heat recovery discharge pipe 115. The pickling inlet pipe 141 is provided with a first pickling manual gate valve 741, and the pickling outlet pipe 142 is provided with a second pickling manual gate valve 742.

[0031] Preferably, the first heat exchanger 81 is a steam-water shell-and-tube heat exchanger, and the second heat exchanger 82 is a water-to-water shell-and-tube heat exchanger. The steam-water shell-and-tube heat exchanger is a two-stage heat exchanger with stainless steel heat exchange tubes. Waste steam flows through the shell side, and softened water flows through the tube side in a counter-current heat exchange process. The water-to-water shell-and-tube heat exchanger is a single-stage heat exchanger with silicon carbide heat exchange tubes. Silicon carbide heat exchange tubes have acid-resistant properties. In the water-to-water shell-and-tube heat exchanger, softened water flows through the shell side, and wastewater flows through the tube side in a counter-current heat exchange process.

[0032] Preferably, the first heat exchanger 81 is equipped with an exhaust valve pipe to improve the stability and safety of its operation. The exhaust valve pipe can effectively discharge non-condensable gases accumulated inside the heat exchanger, avoiding the problem of reduced heat exchange efficiency due to gas residue. At the same time, this design can prevent equipment vibration or noise caused by gas pressure buildup, extending the service life of the first heat exchanger. Through the automatic exhaust function, the system can maintain optimal heat exchange conditions without manual intervention, significantly improving overall operating efficiency.

[0033] Preferably, a safety valve is installed on the top of the pressure flash tank 5. This safety valve automatically opens when the internal pressure of the pressure flash tank 5 exceeds a set value, releasing excessive pressure and preventing equipment damage or safety accidents caused by excessive pressure. This ensures that the entire waste heat recovery system operates within a safe and stable pressure range. Simultaneously, a pressure sensor is also installed on the pressure flash tank 5 to monitor the internal pressure in real time. When abnormal pressure fluctuations occur, operators can take appropriate adjustment measures.

[0034] Preferably, the set pressure of the pressure flash tank 5 is 0.2 MPa. When the pressure sensor detects that the pressure is higher than 0.2 MPa, the safety valve opens to release the pressure.

[0035] Preferably, the condensate pump 6 is a high-temperature and corrosion-resistant pump, requiring the pressure flash tank 5 to have a certain installation height so that the condensate pump 6 has sufficient filling head to prevent cavitation from affecting normal water supply.

[0036] Preferably, the pickling device 9 is a chemical cleaning device that uses an external pump to force the cleaning solution to circulate, and periodically cleans the water-to-water shell-and-tube heat exchanger. The cleaning solution can be citric acid or nitric acid solution.

[0037] Preferably, the water supplied by the water replenishment device 4 to the steam boiler 1 and the second heat exchanger 82 is softened water, which is at room temperature.

[0038] Specifically, the steam boiler 1, continuous blowdown pipe 131, periodic blowdown pipe 132, blowdown header pipe 133, standby blowdown pipe 135, blowdown expansion container 2, and blowdown cooling sedimentation tank 3 constitute the standby blowdown system of the steam boiler 1. When the waste heat recovery system is under maintenance or malfunctions, the standby blowdown system of the steam boiler 1 can serve as a temporary blowdown measure to ensure that the steam boiler 1 can operate stably, safely, and efficiently for a long period of time.

[0039] Specifically, the pressure flash tank 5, the exhaust steam pipe 111, the first heat exchanger 81, and the exhaust steam condensate pipe 113 constitute the waste heat recovery heat-side system of the exhaust steam. The secondary exhaust steam after the steam boiler wastewater passes through the pressure flash tank 5 has less salt and higher purity, and there is no risk of scaling. In order to ensure the heat exchange effect, the secondary exhaust steam enters the first heat exchanger 81 for heat exchange.

[0040] Specifically, the waste steam condensate pipe 113, flash condensate pipe 112, condensate pump 6, condensate header 114, second heat exchanger 82, waste heat recovery discharge pipe 115, and sewage cooling sedimentation tank 3 constitute the sewage condensate waste heat recovery heat side system. The flash condensate obtained after treatment by the pressure flash tank 5 has a high concentration, so the flash condensate enters the second heat exchanger 82 for heat exchange.

[0041] Specifically, the steam boiler 1, continuous blowdown pipe 131, periodic blowdown pipe 132, blowdown header pipe 133, blowdown waste heat recovery pipe 134, pressure flash tank 5, and the blowdown exhaust steam waste heat recovery heat-side system and the blowdown condensate waste heat recovery heat-side system constitute the blowdown waste heat recovery heat-side system. The pressure of the steam boiler blowdown water is relatively high. The steam boiler blowdown water first enters the pressure flash tank 5, and the flashed secondary exhaust steam enters the first heat exchanger 81. The low-pressure saturated water in the pressure flash tank 5 and the condensate in the first heat exchanger 81 are combined and enter the second heat exchanger 82.

[0042] Specifically, the water supply device 4, the primary water supply inlet pipe 121, the second heat exchanger 82, the secondary water supply inlet pipe 122, the first heat exchanger 81, the secondary water supply outlet pipe 123, the boiler water supply header pipe 125, and the steam boiler 1 constitute a waste heat recovery cold side system. By preheating the softened water of the water supply device 4, the energy consumption of the steam boiler 1 is reduced. The secondary water supply inlet pipe 122 can also serve as the primary water supply outlet pipe.

[0043] Specifically, the pickling inlet pipe 141, the second heat exchanger 82, the pickling outlet pipe 142, and the pickling device 9 constitute the heat exchanger pickling system. The second heat exchanger 82 uses steam boiler wastewater as the heat carrier. As certain salts precipitate from the water when the temperature rises and the concentration is high, the scale layer gradually becomes thicker and harder with the increase of usage time and frequency. The heat exchanger needs to be descaled and cleaned regularly. The heat exchange tubes of the second heat exchanger 82 are made of silicon carbide.

[0044] The present invention also provides a method for recovering waste heat from steam boiler wastewater, wherein the waste heat recovery method is performed using the waste heat recovery system described above, and includes the following steps: Water supply device 4 introduces water into the second heat exchanger 82, and then into the first heat exchanger 81. After heat exchange in the first heat exchanger 81 and the second heat exchanger 82, the water temperature rises and is then supplied to the steam boiler 1. Alternatively, water supply device 4 can directly supply water to the steam boiler 1. The flash condensate in the pressure flash tank 5 enters the second heat exchanger 82, where it exchanges heat with the water supplied by the water supply device 4 before entering the sewage cooling sedimentation tank 3. The secondary exhaust steam from the flash tank 5 enters the first heat exchanger 81, where it exchanges heat with the water supplied by the water supply device 4 and becomes condensate. The condensate and flash condensate then merge and enter the second heat exchanger 82. The cleaning solution in the pickling device 9 enters the second heat exchanger 82. After the cleaning solution dissolves the scale in the second heat exchanger 82, it returns to the pickling device 9 to complete the cleaning of the second heat exchanger 82.

[0045] Specifically, it also includes the following steps: when the steam boiler 1 needs maintenance or malfunctions, the wastewater from the steam boiler 1 enters the wastewater discharge expansion container 2, and then enters the wastewater discharge cooling sedimentation tank 3. The wastewater in the pressure flash tank 5 enters the wastewater discharge cooling sedimentation tank 3.

[0046] In one specific implementation case, the temperature of the steam boiler wastewater is 200℃ and the pressure is 1.5MPa. Then the second control valve 712 is opened, and the steam boiler wastewater and steam enter the pressure flash tank 5. After the pressure flash tank 5 is expanded, depressurized and cooled, part of it becomes flash secondary exhaust steam and part of it becomes flash condensate. The pressure inside the pressure flash tank 5 is controlled below 0.2MPa. The room-temperature softened water from the water supply device 4 enters the second heat exchanger 82 through the boiler water supply bypass pipe 124, the second water supply control valve 722, and the first-stage water supply inlet pipe 121. It then enters the first heat exchanger 81 through the second-stage water supply inlet pipe 122, and finally enters the boiler water supply header 125 through the second-stage water supply outlet pipe 123. The room-temperature softened water undergoes heat exchange with the flash-evaporated secondary exhaust steam in the first heat exchanger 81 and with the flash-evaporated condensate in the second heat exchanger 82, resulting in a temperature increase. It then supplies water to the steam boiler 1 through the boiler water supply header 125. This process of heating the softened water through two heat exchanges effectively recovers and utilizes waste heat from the blowdown, reducing the energy consumption of the steam boiler. Flash condensate enters the second heat exchanger 82 through flash condensate pipe 112, condensate pump 6, condensate header 114, and first manual gate valve 731. After exchanging heat with softened water, it enters the sewage cooling sedimentation tank 3 through second manual gate valve 732 and waste heat recovery discharge pipe 115 to utilize the heat of flash condensate. The secondary exhaust steam from flash evaporation enters the first heat exchanger 81 through the exhaust steam discharge pipe 111. After heat exchange with softened water, it becomes condensate. The condensate then flows into the flash evaporation condensate pipe 112 through the exhaust steam condensate pipe 113. The acidic cleaning solution from the pickling device 9 enters the second heat exchanger 82 through the pickling inlet pipe 141 and the first pickling manual gate valve 741, and then returns to the pickling device 9 through the second pickling manual gate valve 742 and the pickling outlet pipe 142 to complete the cleaning of the second heat exchanger 82, thereby removing the scale in the second heat exchanger and improving the heat utilization rate of the flash condensate in the second heat exchanger.

[0047] In one specific embodiment, when the steam boiler 1 needs maintenance or malfunctions, the first control valve 711 is opened and the second control valve 712 is closed. The steam boiler wastewater enters the wastewater expansion tank 2 through the wastewater main pipe 133, the first control valve 711, and the backup wastewater pipe 135, and then enters the wastewater cooling sedimentation tank 3 through the condensate discharge pipe 137. The wastewater in the pressure flash tank 5 enters the wastewater cooling sedimentation tank 3 through the emergency discharge pipe 136.

[0048] In one specific embodiment, when the steam boiler 1 needs to be directly replenished with water or is severely short of water, the first water replenishment control valve 721 is opened, and room temperature water is directly replenished to the steam boiler 1 through the boiler water replenishment bypass pipe 124 and the boiler water replenishment header pipe 125.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A waste heat recovery system for steam boiler wastewater, characterized in that, It includes a pressure flash tank, a sludge cooling sedimentation tank, a first heat exchanger, a second heat exchanger, a water makeup device, and an acid washing device; The steam boiler is connected to the pressure flash tank and the wastewater cooling sedimentation tank, and the pressure flash tank is connected to the wastewater cooling sedimentation tank, the first heat exchanger, and the second heat exchanger. The first heat exchanger is connected to the steam boiler and the second heat exchanger, the second heat exchanger is connected to the sewage cooling sedimentation tank, the water replenishment device is connected to the second heat exchanger and the steam boiler, and the acid washing device is connected to the second heat exchanger.

2. The waste heat recovery system for steam boiler wastewater according to claim 1, characterized in that, It also includes a sewage expansion container, which is connected to the steam boiler and the sewage cooling sedimentation tank.

3. The waste heat recovery system for steam boiler wastewater according to claim 2, characterized in that, The steam boiler has a continuous blowdown pipe and a periodic blowdown pipe; The continuous sewage pipe and the periodic sewage pipe are connected to a main sewage pipe. The main sewage pipe is connected to the pressure flash tank through a sewage waste heat recovery pipe. The main sewage pipe is connected to the sewage expansion tank through a backup sewage pipe. The sewage waste heat recovery pipe is equipped with a second control valve, and the backup sewage pipe is equipped with a first control valve. The pressure flash tank and the sewage cooling sedimentation tank are connected by a backup sewage pipe, which is equipped with a first valve.

4. The waste heat recovery system for steam boiler wastewater according to claim 3, characterized in that, The pressure flash tank and the first heat exchanger are connected by a waste steam discharge pipe. The pressure flash tank and the second heat exchanger are connected by a flash condensate pipe and a condensate header. A condensate pump is installed between the flash condensate pipe and the condensate header. A first manual gate valve is installed on the condensate header. The first heat exchanger and the flash condensate pipe are connected by a waste steam condensate pipe.

5. A waste heat recovery system for steam boiler wastewater according to claim 4, characterized in that, The second heat exchanger and the first heat exchanger are connected by a secondary water inlet pipe.

6. The waste heat recovery system for steam boiler wastewater according to claim 5, characterized in that, The second heat exchanger and the sewage cooling sedimentation tank are connected by a waste heat recovery discharge pipe, which is equipped with a second manual gate valve.

7. A waste heat recovery system for steam boiler wastewater according to claim 6, characterized in that, The water supply device is equipped with a boiler water supply bypass pipe, and the steam boiler is equipped with a boiler water supply header pipe. The boiler water supply bypass pipe and the boiler water supply header pipe are connected by a first water supply control valve. The first heat exchanger is connected to the boiler feedwater header via a secondary water outlet pipe; The second heat exchanger and the boiler water supply bypass pipe are connected through a primary water supply inlet pipe, which is equipped with a second water supply control valve.

8. A waste heat recovery system for steam boiler wastewater according to claim 7, characterized in that, The pickling device is equipped with a pickling inlet pipe and a pickling outlet pipe. The pickling inlet pipe is connected to the second heat exchanger, and the pickling outlet pipe is connected to the waste heat recovery discharge pipe. The pickling inlet pipe is equipped with a first pickling manual gate valve, and the pickling outlet pipe is equipped with a second pickling manual gate valve.

9. A method for recovering waste heat from wastewater discharged from a steam boiler, characterized in that, Performing the waste heat recovery method using the waste heat recovery system as described in any one of claims 2 to 8 includes the following steps: The water supply device introduces water into the second heat exchanger, which then enters the first heat exchanger. After heat exchange in the first and second heat exchangers, the water temperature rises and is then supplied to the steam boiler. Alternatively, the water supply device can directly supply water to the steam boiler. The flash condensate in the pressure flash tank enters the second heat exchanger, where it exchanges heat with the water supplied by the water supply device before entering the wastewater cooling sedimentation tank. The secondary exhaust steam from the pressure flash tank enters the first heat exchanger, where it exchanges heat with the water supplied by the water supply device and becomes condensate. The condensate and flash condensate then merge and enter the second heat exchanger. The cleaning solution in the pickling unit enters the second heat exchanger. After the cleaning solution dissolves the scale in the second heat exchanger, it returns to the pickling unit to complete the cleaning of the second heat exchanger.

10. A method for recovering waste heat from steam boiler wastewater according to claim 9, characterized in that, It also includes the following steps: When the steam boiler needs maintenance or malfunctions, the steam boiler's wastewater enters the wastewater expansion tank, and then enters the wastewater cooling and sedimentation tank. The wastewater in the pressure flash tank also enters the wastewater cooling and sedimentation tank.

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