Sludge disposal system and method using solar energy coupled with exhaust heat

Abstract

The application discloses a sludge disposal system utilizing solar energy coupled with exhaust heat, which comprises a dissolving pool and a boiler, the inlet of the dissolving pool is connected with sludge, the hot water inlet of the dissolving pool is connected with the water side outlet of a flue gas-water heat exchanger, and the water side inlet of the flue gas-water heat exchanger is connected with the outlet of a condenser; a drying unit and a pyrolysis unit are arranged in a heat exchange box, and the sludge inlet of the drying unit is connected with the dissolving pool; a groove type solar heat collector, an oil pump and the oil side of an oil-steam heat exchanger are connected to form a heat conducting oil circulation loop, a photovoltaic panel is electrically connected with an electric heating device, the electric heating device, a high-temperature molten salt storage tank, a low-temperature molten salt storage tank and the molten salt side of a molten salt-steam heat exchanger are connected to form a molten salt circulation loop. The sludge disposal system utilizing solar energy coupled with exhaust heat provided by the application makes full use of flue gas waste heat and solar energy, reduces photoelectric fluctuation and lowers cost.

Description

Technical Field

[0001] This invention relates to the field of solid waste disposal technology, and in particular to a sludge disposal system and method that utilizes solar energy coupled with waste heat from flue gas exhaust. Background Technology

[0002] With the continued implementation of dual-carbon goals, the coordinated treatment of urban and industrial sludge—including harmlessness, volume reduction, and energy recovery—has become a crucial issue requiring improvement in the field of energy conservation and environmental protection. The process relying solely on solar thermal heating has inherent shortcomings. Solar energy is naturally intermittent and highly volatile, greatly affected by weather changes, day / night cycles, and solar irradiance, leading to frequent fluctuations in the temperature, pressure, and flow rate of solar thermal steam. This makes it impossible to provide continuous and stable thermal conditions for sludge drying and pyrolysis, resulting in unstable operation of the treatment process. Simultaneously, power plants continuously emit large amounts of flue gas during operation, containing significant low-grade waste heat resources. These resources can be converted into low-pressure, low-temperature saturated steam using conventional heat exchangers, possessing value as an auxiliary heat source. However, this waste heat cannot be effectively recovered and utilized; large amounts of low-grade waste heat are directly discharged into the atmosphere, resulting in the loss of high-quality energy. Even when the current solar thermal system generates sufficient heat, the industry still relies on a single, independent solar thermal power supply model, failing to achieve the fundamental principle of energy cascade utilization. High-grade solar energy is downgraded to bear the entire basic thermal load, resulting in a waste of clean energy. Increasing the scale of solar thermal power plant installations and redundant equipment configurations to offset the impact of solar radiation fluctuations significantly increases initial investment, land area, and subsequent operation and maintenance costs. Overall energy utilization efficiency is low, and it cannot simultaneously meet the multiple practical needs of stable processes, energy saving and consumption reduction, efficient resource utilization, and low-cost operation. Summary of the Invention

[0003] This invention is based on the inventor's discoveries and understanding of the following facts and problems: The waste heat from flue gas is not fully utilized, and the solar thermal heating supply is highly volatile.

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, embodiments of the present invention propose a sludge treatment system utilizing solar energy coupled with flue gas waste heat, comprising a dissolving tank and a boiler. Sludge is introduced into the dissolving tank through its inlet. The hot water inlet of the dissolving tank is connected to the water-side outlet of a flue gas-water heat exchanger. The water-side inlet of the flue gas-water heat exchanger is connected to the condenser outlet. The flue gas-side inlet of the flue gas-water heat exchanger is connected to the tail flue of the boiler. The material outlet of the dissolving tank is connected to a heat exchange box via a sludge pump. A drying unit and a pyrolysis unit are installed within the heat exchange box. The sludge inlet of the drying unit is connected to the dissolving tank. The steam-side inlet of the drying unit is connected to the mixed fluid outlet of a first ejector. The working fluid inlet of the first ejector is connected to the steam-side outlet of an oil-gas heat exchanger. The sludge outlet of the drying unit is connected to the sludge inlet of the pyrolysis unit, the steam-side inlet of the pyrolysis unit is connected to the mixed fluid outlet of the second ejector, the ejector fluid inlet of the second ejector is connected to the water-side outlet of the flue gas-water heat exchanger, the working fluid inlet of the second ejector is connected to the steam-side outlet of the molten salt-steam heat exchanger, the sludge outlet of the pyrolysis unit is connected to the coal mill, and the outlet of the coal mill is connected to the boiler. The trough solar collector, the oil pump, and the oil-side connection of the oil-steam heat exchanger form a heat transfer oil circulation loop. The photovoltaic panel is electrically connected to the electric heating device. The electric heating device, the high-temperature molten salt storage tank, the low-temperature molten salt storage tank, and the molten salt side connection of the molten salt-steam heat exchanger form a molten salt circulation loop.

[0006] The sludge treatment system utilizing solar energy coupled with flue gas waste heat, as described in this embodiment of the invention, fully leverages flue gas waste heat and solar energy, reducing photovoltaic fluctuations and lowering costs. This solution achieves the mixed utilization of solar thermal and flue gas waste heat through an ejector, which can mitigate operational disturbances caused by fluctuations in solar illumination, making the heat source conditions more stable throughout the sludge treatment process. Simultaneously, utilizing flue gas waste heat to share the base load reduces the installed capacity of the solar thermal system, lowering initial equipment investment and long-term operation and maintenance costs, thus balancing process stability and economic operation advantages. The ejector uses high-temperature solar thermal steam as the working fluid to eject a low-pressure fluid that absorbs flue gas waste heat. This eliminates the need for additional power equipment such as fans and compressors, resulting in no extra power consumption, a simple structure, and maintenance-free operation. It can efficiently recover low-grade flue gas waste heat, adhering to the principle of energy cascade utilization, avoiding the degradation and waste of high-grade solar energy, and improving the system's energy utilization efficiency.

[0007] In some embodiments, the water-side outlet of the flue gas-water heat exchanger has a first branch, which is connected to the inlet of a fifth regulating valve and the inlet of a sixth regulating valve, respectively. The outlet of the fifth regulating valve is connected to the inlet of the dissolving tank via a fifth shut-off valve, and the outlet of the sixth regulating valve is connected to the ejector fluid inlet of the first ejector via a sixth shut-off valve.

[0008] In some embodiments, the water-side outlet of the flue gas-water heat exchanger further has a second branch, which is connected to the ejector fluid inlet of the second ejector via a fourth shut-off valve and a fourth regulating valve.

[0009] In some embodiments, the system further includes a thermal oil buffer tank, the inlet of which is connected to the outlet of the trough solar collector, the outlet of which is connected to the oil-side inlet of the oil-vapor heat exchanger, the oil-side outlet of which is connected to the inlet of the oil pump, and the outlet of which is connected to the inlet of the trough solar collector; the steam-side outlet of the drying unit is connected to the steam-side inlet of the oil-vapor heat exchanger via a second regulating valve and a second shut-off valve.

[0010] In some embodiments, the outlet of the electric heating device is connected to the inlet of the high-temperature molten salt pump, the outlet of the high-temperature molten salt pump is connected to the inlet of the high-temperature molten salt storage tank, the first outlet of the high-temperature molten salt storage tank is connected to the inlet of the low-temperature molten salt storage tank, the second outlet of the high-temperature molten salt storage tank is connected to the molten salt side inlet of the molten salt-steam heat exchanger, the molten salt side outlet of the molten salt-steam heat exchanger is connected to the inlet of the low-temperature molten salt storage tank, the outlet of the low-temperature molten salt storage tank is connected to the inlet of the low-temperature molten salt pump, and the outlet of the low-temperature molten salt pump is connected to the inlet of the electric heating device.

[0011] In some embodiments, the steam-side outlet of the pyrolysis unit is connected to the steam-side inlet of the molten salt-steam heat exchanger via a third regulating valve and a third shut-off valve.

[0012] In some embodiments, the material outlet of the dissolving tank is connected to the inlet of the sludge pump via a first shut-off valve and a first regulating valve, and the outlet of the sludge pump is connected to the inlet of the heat exchange box.

[0013] In some embodiments, an air preheater is installed in the tail flue of the circulating fluidized bed boiler. The tail flue located behind the air preheater is provided with a flue gas intake port and a flue gas return port. The flue gas side inlet of the flue gas-water heat exchanger is connected to the tail flue via the flue gas intake port, and the flue gas side outlet of the flue gas-water heat exchanger is connected to the tail flue via the flue gas return port.

[0014] In some embodiments, the water temperature at the condenser outlet is 40-50°C, and after being heated by the flue gas-water heat exchanger, the temperature rises to 100°C. The mass mixing ratio of the water at the flue gas-water heat exchanger outlet to the sludge in the dissolving tank is 4:1. The temperature of the heat transfer oil in the trough solar collector is 300-350°C. After heat exchange by the oil-steam heat exchanger, the steam temperature formed is 250-280°C. After mixing by the first ejector, the steam temperature output is 180-210°C. The electric heating device heats the molten salt to 450-550°C. After heat exchange by the molten salt-steam heat exchanger, the steam temperature formed is 350-430°C. After mixing by the second ejector, the steam temperature output is 250-280°C.

[0015] An embodiment of the present invention proposes a sludge treatment method that utilizes solar energy coupled with waste heat from flue gas exhaust, comprising the following steps: Water from the condenser outlet is fed into the water side of the flue gas-water heat exchanger and heats up the flue gas discharged from the tail flue of the circulating fluidized bed boiler. The heated water is then fed into a dissolving tank and mixed with the sludge in the dissolving tank to dissolve the inorganic chlorine in the sludge. The sludge in the dissolving tank is pumped to the drying unit of the heat exchange box. The trough solar collector heats the heat transfer oil. After the heat transfer oil releases heat on the oil side of the oil-steam heat exchanger, it is pumped back to the trough solar collector for circulation and heat absorption. The steam side of the oil-steam heat exchanger absorbs heat and heats up to generate high-temperature steam. The high-temperature steam is used as the working fluid and enters the working fluid inlet of the first ejector. The high-temperature water from the flue gas-water heat exchanger is used as the ejector fluid and introduced into the ejector fluid inlet of the first ejector. The steam formed after mixing is passed into the drying unit to dry the sludge. The steam discharged from the drying unit flows back to the steam side of the oil-steam heat exchanger to absorb heat again. The dried sludge is sent to the pyrolysis unit. The photovoltaic panel generates electricity to drive the electric heating device to heat the molten salt. The high-temperature molten salt releases heat through the molten salt-steam heat exchanger and generates high-temperature steam which enters the second ejector. High-temperature water from the flue gas-water heat exchanger is introduced into the ejector fluid inlet of the second ejector as the ejector fluid. The steam formed after mixing is passed into the pyrolysis unit to pyrolyze the dried sludge. The sludge, after pyrolysis, is fed into a coal mill to be mixed and ground with coal, and then sent to a boiler for incineration through the coal feed port.

[0016] This application has the following advantages: Condenser outlet water is heated by a flue gas-water heat exchanger and then used for dechlorination in the dissolving tank. Combined with a trough-type solar thermal oil circuit and a photovoltaic electric heating molten salt circuit, it drives the first and second ejectors respectively to generate drying and pyrolysis steam, achieving multi-energy complementarity between low-grade waste heat and high-grade solar thermal / photovoltaic power. The first branch connects to the dissolving tank and the first ejector, enabling splitting and safe isolation of the high-temperature water flow at both ends of the water washing and dechlorination and drying ejector circuits. The second branch connects to the second ejector, enabling dynamic, on-demand allocation and independent safe isolation of low-grade flue gas waste water to the high-temperature pyrolysis ejector circuit. The thermal oil buffer tank forms a pressure-stabilizing thermal cycle, which, together with the steam return from the drying unit to the oil-steam heat exchanger, achieves the output of trough-type solar heating flow and pressure, as well as the heat-mass closed-loop recycling of the drying exhaust steam. The configuration of a high-temperature molten salt pump, a low-temperature molten salt pump, high- and low-temperature molten salt storage tanks, and a dual-outlet switching path enables cross-period, large-capacity storage and independent control of photovoltaic power converted into high-density thermal energy. The steam outlet of the pyrolysis unit is returned to the molten salt-steam heat exchanger to reuse the heat energy of the high-temperature exhaust steam from pyrolysis. A first shut-off valve and a first regulating valve are installed at the material outlet of the dissolution tank to achieve quantitative and continuous feeding of dechlorinated sludge slurry to the drying unit. A flue gas intake port and a flue gas return port are set at the tail flue after the air preheater to recover and utilize the waste heat of the low-temperature exhaust gas. The process sequentially executes steps such as waste water washing and dechlorination, solar working steam jet drying, photovoltaic molten salt working steam jet pyrolysis, and product co-firing in the furnace, achieving a full-chain continuous and harmless treatment of sludge, including efficient dechlorination at the source, efficient drying at medium temperature, deep pyrolysis at high temperature, and clean incineration for resource recovery. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a sludge treatment system that utilizes solar energy coupled with waste heat from flue gas according to an embodiment of the present invention.

[0018] Figure reference numerals: 1. Boiler; 2. Cyclone separator; 3. Tail flue; 4. Air preheater; 5. Steam turbine; 6. Condenser; 7. Flue gas-water heat exchanger; 8. Parabolic trough solar collector; 9. Oil pump; 10. Thermal oil buffer tank; 11. Oil-steam heat exchanger; 12. First ejector; 13. Second ejector; 14. Molten salt-steam heat exchanger; 15. Low-temperature molten salt storage tank; 16. Photovoltaic panel; 17. High-temperature molten salt storage tank; 18. High-temperature molten salt pump; 19. Low-temperature molten salt pump; 20. Electric heating device; 21. Sludge 21. Import; 22. Dissolving tank; 23. First shut-off valve; 24. First regulating valve; 25. Sludge pump; 26. Second shut-off valve; 27. Second regulating valve; 28. Third shut-off valve; 29. ​​Third regulating valve; 30. Heat exchange box; 31. Drying unit; 32. Pyrolysis unit; 33. Coal mill; 34. Coal feed port; 35. Flue gas outlet; 36. Flue gas return port; 37. Fourth shut-off valve; 38. Fourth regulating valve; 39. Fifth regulating valve; 40. Fifth shut-off valve; 41. Sixth regulating valve; 42. Sixth shut-off valve. Detailed Implementation

[0019] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0020] An embodiment of the present invention proposes a sludge treatment system utilizing solar energy coupled with flue gas waste heat, comprising a dissolving tank 22 and a boiler 1. Sludge is introduced into the inlet of the dissolving tank 22. The hot water inlet of the dissolving tank 22 is connected to the water-side outlet of a flue gas-water heat exchanger 7. The water-side inlet of the flue gas-water heat exchanger 7 is connected to the outlet of a condenser 6. The flue gas-side inlet of the flue gas-water heat exchanger 7 is connected to the tail flue duct 3 of the boiler 1. The material outlet of the dissolving tank 22 is connected to a heat exchange box 30 via a sludge pump 25. A drying unit 31 and a pyrolysis unit 32 are provided inside the heat exchange box 30. The sludge inlet 21 of the drying unit 31 is connected to the dissolving tank 22. The steam-side inlet of the drying unit 31 is connected to the mixed fluid outlet of a first ejector 12. The working fluid inlet of the first ejector 12 is connected to the steam-side outlet of an oil-gas heat exchanger 11. The sludge outlet of the drying unit 31 is connected to the sludge inlet 21 of the pyrolysis unit 32. The steam-side inlet of the pyrolysis unit 32 is connected to the mixed fluid outlet of the second ejector 13. The ejector fluid inlet of the second ejector 13 is connected to the water-side outlet of the flue gas-water heat exchanger 7. The working fluid inlet of the second ejector 13 is connected to the steam-side outlet of the molten salt-steam heat exchanger 14. The sludge outlet of the pyrolysis unit 32 is connected to the coal mill 33. The outlet of the coal mill 33 is connected to the boiler 1. The oil-side connection of the trough solar collector 8, the oil pump 9, and the oil-steam heat exchanger 11 forms a heat transfer oil circulation loop. The photovoltaic panel 16 is electrically connected to the electric heating device 20. The electric heating device 20, the high-temperature molten salt storage tank 17, the low-temperature molten salt storage tank 15, and the molten salt-steam heat exchanger 14 form a molten salt circulation loop. The boiler 1 is a circulating fluidized bed boiler 1. The top of boiler 1 is connected to cyclone separator 2, which separates coal particles and other materials in the flue gas into solid and gas components, extending the residence time of difficult-to-burn particles within boiler 1. Steam turbine 5, as the power unit, receives the main steam from boiler 1 and can use the steam to perform work. Condenser 6 is connected to the exhaust port of steam turbine 5, condensing the low-pressure exhaust steam into water to provide a low-grade heat source and recover water resources.

[0021] Pretreatment water washing is combined with waste heat recovery. Water from the condenser 6 outlet enters the water side of the flue gas-water heat exchanger 7 and exchanges heat with the exhaust gas from the tail flue duct 3 of the circulating fluidized bed boiler 1 to raise its temperature. The heated high-temperature water is then introduced into the dissolving tank 22 to mix with sludge, efficiently recovering low-grade flue gas waste heat and dissolving inorganic chlorine in the sludge, thus achieving pre-treatment of sludge dechlorination. The high-temperature water from the outlet of the flue gas-water heat exchanger 7 also serves as the ejector fluid for the first ejector 12 and the second ejector 13, respectively, avoiding the need for additional high-energy-consuming heating or steam extraction equipment and improving the overall system's energy utilization efficiency. High-temperature and high-pressure steam generated by trough solar collectors is used as the driving source. The high-temperature water generated by the first ejector 12 absorbs the waste heat from the flue gas and is mixed to produce steam with stable operating parameters, providing a stable heat source for sludge drying and mitigating the disturbances caused by the intermittency and fluctuations inherent in solar energy. The first ejector 12 has a simple structure and no energy consumption, eliminating the need for additional power equipment and reducing the system's power consumption and maintenance costs. Photovoltaic molten salt thermal storage and ejector-coupled pyrolysis work in synergy to achieve on-site consumption of photovoltaic green electricity and high-density thermal energy storage through molten salt energy storage units heated by photovoltaic power. High-temperature steam from molten salt heat exchange serves as the working steam source. The fluid absorbing waste heat from flue gas is ejected by the second ejector 13, and after mixing, forms high-temperature, high-pressure steam that meets the requirements for deep sludge pyrolysis. This reduces the installed capacity of photovoltaic and molten salt energy storage equipment, lowers initial investment, and achieves efficient deep sludge pyrolysis and volume reduction. The heat source quality is matched with the requirements of the sludge treatment process. The treated sludge is incinerated in boiler 1 as fuel, and the waste heat from the exhaust gas in the tail flue 3 feeds back to the water washing and ejector source, forming a closed-loop cascade utilization system, achieving harmless, reduced-volume, and resource-based treatment of sludge.

[0022] When the system starts up, the circulating fluidized bed boiler 1 and the flue gas-water heat exchanger 7 are first turned on to establish a basic water washing and dechlorination circuit. When there is sufficient sunlight, the trough solar collector 8 and the oil pump 9 are started, and the generated steam is injected into the first ejector 12 to begin sludge drying. When the photovoltaic panel 16 generates excess power, the electric heating device 20 and the high-temperature molten salt pump 18 are started to store heat. When pyrolysis is required, the molten salt-steam heat exchanger 14 and the second ejector 13 are turned on. When shutting down, the heat source is cut off in reverse order, and the high-temperature medium is completely discharged into the buffer tank and the low-temperature storage tank using the oil pump 9 and the molten salt pump to ensure equipment safety.

[0023] In some embodiments, the water-side outlet of the flue gas-water heat exchanger 7 has a first branch, which is connected to the inlet of the fifth regulating valve 39 and the inlet of the sixth regulating valve 41 respectively. The outlet of the fifth regulating valve 39 is connected to the inlet of the dissolving tank 22 via the fifth shut-off valve 40, and the outlet of the sixth regulating valve 41 is connected to the ejector fluid inlet of the first ejector 12 via the sixth shut-off valve.

[0024] Specifically, the first branch connects to the inlets of the fifth regulating valve 39 and the sixth regulating valve 41 respectively, enabling precise bidirectional distribution of the high-temperature water flow rate at the outlet of the flue gas-water heat exchanger 7. The fifth regulating valve 39 controls the high-temperature water flow rate entering the dissolving tank 22, ensuring the optimal water-solid mixing ratio during the sludge washing and dechlorination process. The sixth regulating valve 41 controls the ejector fluid flow rate entering the first ejector 12, ensuring that the first ejector 12 receives a matching ejector fluid volume under different light conditions and drying loads. When the solar heat collection is insufficient or the drying module is suspended, the sixth shut-off valve can close the ejector passage of the first ejector 12; when the dissolving tank 22 is shut down for maintenance, the fifth shut-off valve 40 can isolate the dissolving tank 22 independently to prevent fluid backflow. The two branches do not interfere with each other in flow distribution and are dynamically complementary, improving the operational flexibility and adaptability of the flue gas waste heat utilization system.

[0025] The first branch is a branch of the main branch at the water-side outlet of the flue gas-water heat exchanger 7. A tee joint or a diversion manifold can be installed at the branch. Temperature and pressure sensors can be installed on the first branch to monitor the vaporization degree and temperature state of the high-temperature water after heating by the flue gas-water heat exchanger 7. The fifth regulating valve 39 and the sixth regulating valve 41 can be electric regulating valves, pneumatic diaphragm regulating valves, or electro-hydraulic linkage regulating valves, used to receive feedback signals from the control mechanism and achieve continuous opening adjustment. The opening of the fifth regulating valve 39 forms a closed-loop feedback control loop with the sludge mass flow rate and temperature sensor in the dissolving tank 22; the opening of the sixth regulating valve 41 forms a closed-loop feedback control loop with the steam temperature and pressure sensor at the mixed fluid outlet of the first ejector 12.

[0026] In some embodiments, the water-side outlet of the flue gas-water heat exchanger 7 also has a second branch, which is connected to the ejector fluid inlet of the second ejector 13 via a fourth shut-off valve 37 and a fourth regulating valve 38.

[0027] Specifically, high-temperature water is injected and mixed with the high-temperature working steam generated by the molten salt-steam heat exchanger 14, directly participating in the high-temperature steam supply of the pyrolysis module. Compared to relying solely on molten salt heat storage to generate high-grade steam, utilizing the waste heat of low-grade flue gas as a supplementary load for the pyrolysis heat source reduces the green electricity consumption and equipment redundancy of the molten salt heat storage system. The second branch and the first branch together form a main-multiple water supply pattern at the outlet of the flue gas-water heat exchanger 7. The fourth regulating valve 38 can independently fine-tune the flow rate according to the actual injection requirements of the second ejector 13, forming a multi-node flow balance control network for the entire system together with the fifth regulating valve 39 and the sixth regulating valve 41 on the first branch. The fourth shut-off valve 37 provides an independent safety shut-off capability for the injection path of the second ejector 13. When the pyrolysis operation is cut off or the second ejector 13 needs maintenance, the second branch can be quickly shut off without affecting the normal operation of the dissolution tank 22 and the drying unit 31 of the first branch. The pipe diameter of the second branch is set according to the maximum injection flow requirements of the second ejector 13. The fourth regulating valve 38 can be a high-precision electric regulating valve or a pneumatic regulating valve with high-temperature sealing packing.

[0028] In some embodiments, the system further includes a thermal oil buffer tank 10, the inlet of which is connected to the outlet of the trough solar collector 8, the outlet of which is connected to the oil-side inlet of the oil-vapor heat exchanger 11, the oil-side outlet of which is connected to the inlet of the oil pump 9, and the outlet of which is connected to the inlet of the trough solar collector 8; the steam-side outlet of the drying unit 31 is connected to the steam-side inlet of the oil-vapor heat exchanger 11 via a second regulating valve 27 and a second shut-off valve 26.

[0029] Specifically, the heat transfer oil buffer tank 10 can absorb the volumetric thermal expansion of the high-temperature heat transfer oil during the heating process, effectively mitigating sudden changes in the outlet temperature and flow rate of the heat transfer oil caused by short-term drastic fluctuations in sunlight. Simultaneously, the buffer tank provides a stable liquid level difference, preventing cavitation at the inlet of the oil pump 9 and ensuring the continuous and stable operation of the heat transfer oil circulation loop. The exhaust steam or condensate after heat release in the drying unit 31 flows back to the oil-vapor heat exchanger 11 under the pressure control of the second regulating valve 27, re-absorbing heat and vaporizing, achieving a dual closed-loop reuse of water quality and heat energy, avoiding water waste and secondary pollution. Meanwhile, the second shut-off valve 26 provides reliable loop shut-off isolation. The heat transfer oil buffer tank 10 can be configured as a sealed pressure vessel with nitrogen sealing protection, equipped with a level gauge, safety valve, and high-temperature pressure gauge. The nitrogen seal effectively isolates air, preventing oxidation, deterioration, and explosive polymerization of the high-temperature heat transfer oil, extending its service life. The second regulating valve 27 can be an electric regulating valve with back pressure control function or a self-operated back pressure regulating valve, used to maintain the necessary heat exchange back pressure on the steam side inside the drying unit 31, ensuring that the steam fully condenses and releases heat in the drying unit 31 before flowing back to the oil-steam heat exchanger 11. The second shut-off valve 26 can be a high-temperature pneumatic gate valve or a hard-seal ball valve, used for closure and isolation during system shutdown or maintenance. The trough solar collector 8 heats the heat transfer oil to 300-350℃ and then sends it to the heat transfer oil buffer tank 10. The oil pump 9 maintains the heat transfer oil circulating on the oil side of the oil-steam heat exchanger 11 at the rated flow rate. The control system precisely controls the high-temperature steam temperature at the steam side outlet of the oil-steam heat exchanger 11 to 250-280℃ by adjusting the speed of the oil pump 9 and the opening of the oil inlet valve on the oil side of the oil-steam heat exchanger 11.

[0030] In some embodiments, the outlet of the electric heating device 20 is connected to the inlet of the high-temperature molten salt pump 18, the outlet of the high-temperature molten salt pump 18 is connected to the inlet of the high-temperature molten salt storage tank 17, the first outlet of the high-temperature molten salt storage tank 17 is connected to the inlet of the low-temperature molten salt storage tank 15, the second outlet of the high-temperature molten salt storage tank 17 is connected to the molten salt side inlet of the molten salt-steam heat exchanger 14, the molten salt side outlet of the molten salt-steam heat exchanger 14 is connected to the inlet of the low-temperature molten salt storage tank 15, the outlet of the low-temperature molten salt storage tank 15 is connected to the inlet of the low-temperature molten salt pump 19, and the outlet of the low-temperature molten salt pump 19 is connected to the inlet of the electric heating device 20.

[0031] Specifically, the photovoltaic panel 16 generates electricity to drive the electric heating device 20 to heat the molten salt, achieving stable and efficient conversion and large-capacity storage of the random and fluctuating photovoltaic electrical energy into high-density thermal energy. The high-temperature molten salt storage tank 17 completely decouples energy absorption and release in terms of time and load, ensuring a stable output of high-grade thermal energy even at night or during periods without sunlight. The high-temperature molten salt storage tank 17 has a first outlet and a second outlet. The first outlet is directly connected to the low-temperature molten salt storage tank 15 to form a self-circulating heat absorption within the molten salt during the heat storage stage where only photovoltaic heat storage is used. The second outlet is connected to the molten salt side inlet of the molten salt-steam heat exchanger 14, outputting high-temperature molten salt for heat exchange and release during the pyrolysis operation stage. The two outlet paths do not interfere with each other, and with the pressurization and delivery of the high-temperature molten salt pump 18 and the low-temperature molten salt pump 19, independent control of the heat storage and heat release processes is achieved. The cooled molten salt after heat release from the molten salt-steam heat exchanger 14, along with the molten salt from the first outlet of the high-temperature molten salt storage tank 17, are all collected in the low-temperature molten salt storage tank 15. The low-temperature molten salt is then pressurized by the low-temperature molten salt pump 19 and sent back to the electric heating device 20 for reheating, forming a closed-loop molten salt circulation loop with two tanks. This isolation between the cold and hot molten salts prevents thermal quality degradation caused by temperature mixing in a single tank, while ensuring that the molten salt remains above its safe crystallization temperature throughout the entire flow process, preventing the risk of "freezing" or pipe blockage due to solidification.

[0032] In some embodiments, the steam-side outlet of the pyrolysis unit 32 is connected to the steam-side inlet of the molten salt-steam heat exchanger 14 via a third regulating valve 29 and a third shut-off valve 28.

[0033] Specifically, the combination of the third regulating valve 29 and the third shut-off valve 28 provides pressure / flow control and safety isolation between the pyrolysis module and the molten salt thermal energy exchange system. The third regulating valve 29 maintains a stable outlet back pressure according to the heat exchange requirements within the pyrolysis module, ensuring sufficient high-temperature heat transfer of steam within the module. The third shut-off valve 28 can quickly and reliably cut off the steam return channel during pyrolysis shutdown, system maintenance, or sudden failures, protecting the molten salt-steam heat exchanger 14 from reverse impact. The photovoltaic molten salt thermal energy releases heat to the steam side within the molten salt-steam heat exchanger 14. The generated steam, after being ejected by the second ejector 13 to draw out the waste heat from the flue gas, enters the pyrolysis unit 32. After releasing heat, the exhaust steam returns to the steam side of the molten salt-steam heat exchanger 14 via the third regulating valve 29 and the third shut-off valve 28, completing the cycle.

[0034] In some embodiments, the material outlet of the dissolving tank 22 is connected to the inlet of the sludge pump 25 via a first shut-off valve 23 and a first regulating valve 24, and the outlet of the sludge pump 25 is connected to the inlet of the heat exchange box 30.

[0035] Specifically, the flow rate of the dechlorinated sludge slurry is adjusted according to the actual treatment load and moisture content requirements of the drying unit 31 within the heat exchange box 30. This, combined with the pressurized conveying of the sludge pump 25, ensures that the sludge enters the heat exchange box 30 at a stable and uniform flow rate, preventing thermal imbalance or blockage within the drying unit 31 due to fluctuating feed rates. The first shut-off valve 23 and the first regulating valve 24 are connected in series before the inlet of the sludge pump 25. When the sludge pump 25 needs maintenance, sludge cleaning, or the heat exchange box 30 suspends material reception, the first shut-off valve 23 can close and isolate the sludge slurry in the dissolving tank 22, preventing backflow or leakage of the sludge slurry due to gravity, ensuring safety between the front-end water washing and dechlorination unit and the rear-end pumping and conveying unit. The dissolving tank 22, as the pre-treatment unit for sludge water washing and dechlorination, sends the dechlorinated sludge slurry into the heat exchange box 30 via the first shut-off valve 23, the first regulating valve 24, and the sludge pump 25.

[0036] Optionally, a pulsed ultrasonic homogenizing mixing chamber can be added to the pipeline between the first regulating valve 24 and the inlet of the sludge pump 25. Before the sludge slurry enters the sludge pump 25, the fine flocs in the sludge are pre-dispersed and homogenized using pulsed ultrasonic waves. At the same time, a high-frequency micro-vibration anti-sticking layer is formed on the inner wall of the pipeline to prevent high-viscosity sludge from depositing, agglomerating, and clogging at the valve port of the first regulating valve 24 and the pump inlet.

[0037] In some embodiments, an air preheater 4 is installed in the tail flue 3 of the circulating fluidized bed boiler 1. The tail flue 3 located behind the air preheater 4 is provided with a flue gas inlet 35 and a flue gas return outlet 36. The flue gas side inlet of the flue gas-water heat exchanger 7 is connected to the tail flue 3 via the flue gas inlet 35, and the flue gas side outlet of the flue gas-water heat exchanger 7 is connected to the tail flue 3 via the flue gas return outlet 36.

[0038] Specifically, the low-temperature exhaust heat (typically 120-150℃) after the air preheater 4 is utilized. This low-grade waste heat, which would otherwise be directly discharged and lost, is extracted and converted into high-temperature water, reducing the exhaust temperature of boiler 1 and improving the thermal efficiency of circulating fluidized bed boiler 1 and the entire plant. The bypass heat exchange channel formed by the flue gas inlet 35 and the return flue gas inlet 36 on the tail flue duct 3 decouples the flue gas-water heat exchanger 7 from the main flue gas system of boiler 1. When the flue gas-water heat exchanger 7 needs to be shut down for maintenance, ash removal, or when the sludge disposal system is suspended, the bypass flue gas can be directly cut off. The flue gas flow in the main flue duct is completely unaffected by the normal operation of boiler 1. Bypass extraction avoids the huge flue gas resistance and ash accumulation blockage risk caused by directly installing a large heat exchanger inside the main flue duct. The smoke intake port 35 and the smoke return port 36 can be respectively equipped with high-temperature resistant and corrosion-resistant flue gas butterfly valves or shut-off baffle doors (such as electric double-layer pneumatic baffle doors) to control the flow rate of extracted flue gas or to achieve flue gas shut-off and isolation during maintenance.

[0039] In some embodiments, the water temperature at the outlet of the condenser 6 is 40-50°C, and after being heated by the flue gas-water heat exchanger 7, the temperature rises to 100°C. The mass mixing ratio of the water at the outlet of the flue gas-water heat exchanger 7 to the sludge in the dissolving tank 22 is 4:1. The temperature of the heat transfer oil in the trough solar collector 8 is 300-350°C. After heat exchange by the oil-steam heat exchanger 11, the steam temperature formed is 250-280°C. After mixing by the first ejector 12, the steam output temperature is 180-210°C. The electric heating device 20 heats the molten salt to 450-550°C. After heat exchange by the molten salt-steam heat exchanger 14, the steam temperature formed is 350-430°C. After mixing by the second ejector 13, the steam output temperature is 250-280°C.

[0040] Specifically, the water at the outlet of condenser 6 is heated by a heat exchanger and mixed with the sludge in dissolving tank 22 at a target mass mixing ratio. This efficiently absorbs the waste heat from low-grade flue gas. The 100°C high-temperature water increases the solubility and diffusion rate of inorganic chlorides (such as NaCl and KCl) in the sludge. The optimal water-to-solid ratio of 4:1 ensures sufficient sludge flow and efficient dechlorination, while avoiding the increased energy burden of subsequent drying and evaporation due to excessive water addition. A three-stage temperature gradient utilization system of "oil-steam-jet" is employed. The first ejector 12 uses high-grade steam to inject high-temperature water heated by the waste heat of the flue gas, increasing the steam flow rate and capacity while lowering the steam temperature to the optimal drying temperature range of 180-210°C, matching the heat and mass transfer requirements of the drying unit 31. The second ejector 13 uses high-grade steam to inject 100°C high-temperature water, stabilizing the steam temperature at 250-280°C, providing a suitable high-temperature heat source for deep pyrolysis and organic chlorine removal, achieving energy grade matching and synergy.

[0041] An embodiment of the present invention proposes a sludge treatment method that utilizes solar energy coupled with waste heat from flue gas exhaust, comprising the following steps: Water from the outlet of condenser 6 is fed into the water side of flue gas-water heat exchanger 7 and heated by exchanging heat with the flue gas discharged from the tail flue duct 3 of circulating fluidized bed boiler 1. The heated water is then fed into dissolving tank 22 to mix with the sludge inside, dissolving the inorganic chlorine in the sludge. Low-grade waste heat is used to raise the water temperature, improving the solubility and removal efficiency of inorganic chlorine (such as NaCl, KCl, etc.), thus solving the problem at its source that direct sludge incineration easily leads to high-temperature chlorine corrosion, coking, and excessive dioxin emissions on the heating surface of boiler 1. The water washing process in dissolving tank 22 can be combined with mechanical stirring, ultrasonic cavitation, or microbubble flotation to accelerate the stripping and dissolution of inorganic chloride salts on the surface and within the pores of sludge particles. A solid-liquid separation device (such as a belt filter press or centrifuge) can be added to the outlet of dissolving tank 22. The separated chlorine-containing waste liquid is treated and then discharged, while the wet sludge cake is then sent to heat exchange box 30 by sludge pump 25.

[0042] The sludge in the dissolving tank 22 is transported to the drying unit 31 of the heat exchange box 30 via the sludge pump 25. The trough solar collector 8 heats the heat transfer oil. After the heat transfer oil releases heat on the oil side of the oil-steam heat exchanger 11, it is pumped back to the trough solar collector 8 via the oil pump 9 for circulating heat absorption. The steam side of the oil-steam heat exchanger 11 absorbs heat and heats up to generate high-temperature steam. The high-temperature steam is used as the working fluid and enters the working fluid inlet of the first ejector 12. The high-temperature water from the flue gas-water heat exchanger 7 is used as the ejector fluid and introduced into the ejector fluid inlet of the first ejector 12. The steam formed after mixing is passed into the drying unit 31 to dry the sludge. The steam discharged from the drying unit 31 is returned to the steam side of the oil-steam heat exchanger 11 to absorb heat again. The introduction of the first ejector 12 realizes the deep coupling of high-grade solar thermal steam and low-grade flue gas waste water, increases the total mass flow rate of the drying steam, adjusts the steam to the optimal drying temperature, and allows for closed-loop utilization of the dried waste steam, thereby reducing the unit energy consumption of sludge drying.

[0043] The dried sludge is fed into the pyrolysis unit 32. Photovoltaic panels 16 generate electricity to drive an electric heating device 20 to heat molten salt. The high-temperature molten salt releases heat through a molten salt-steam heat exchanger 14, generating high-temperature steam which enters the second ejector 13. High-temperature water from a flue gas-water heat exchanger 7 is introduced as the ejector fluid into the inlet of the second ejector 13. The resulting steam is then fed into the pyrolysis unit 32 to pyrolyze the dried sludge. The photovoltaic power generation drives the electric heating device 20 to heat the molten salt, generating high-temperature steam through the molten salt-steam heat exchanger 14. This steam, after being ejected by the second ejector 13, is then fed into the pyrolysis unit 32 to further pyrolyze the dried sludge. The photovoltaic molten salt heat storage has high energy density and all-weather heat release capability. Combined with the high-temperature steam provided by the second ejector 13, the sludge undergoes pyrolysis in anoxic / anaerobic environments, efficiently removing residual bound organic chlorine and simultaneously modifying and upgrading the organic matter in the sludge.

[0044] After pyrolysis, the sludge is fed into a coal mill 33 and mixed with coal for grinding. The sludge is then fed into boiler 1 through coal feed inlet 34 for incineration. The calorific value of the sludge is increased after pyrolysis. The co-firing process does not affect the safe and stable operation of boiler 1. The waste heat from the flue gas and the power plant's condensate are fed back to the front-end washing and drying processes, forming a heat-material double closed loop. In the description of this invention, it should be understood that the terms "center," "longitudinal," "transverse," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention.

[0045] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0046] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0047] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0048] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0049] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A sludge treatment system utilizing solar energy coupled with waste heat from flue gas exhaust, characterized in that, include: The dissolving tank and the boiler are provided. Sludge is introduced into the inlet of the dissolving tank. The hot water inlet of the dissolving tank is connected to the water-side outlet of the flue gas-water heat exchanger. The water-side inlet of the flue gas-water heat exchanger is connected to the outlet of the condenser. The flue gas-side inlet of the flue gas-water heat exchanger is connected to the tail flue of the boiler. The material outlet of the dissolving tank is connected to the heat exchange box via a sludge pump. The heat exchange box is equipped with a drying unit and a pyrolysis unit. The sludge inlet of the drying unit is connected to the dissolving tank, the steam-side inlet of the drying unit is connected to the mixed fluid outlet of the first ejector, the working fluid inlet of the first ejector is connected to the steam-side outlet of the oil-steam heat exchanger, the sludge outlet of the drying unit is connected to the sludge inlet of the pyrolysis unit, the steam-side inlet of the pyrolysis unit is connected to the mixed fluid outlet of the second ejector, the ejector fluid inlet of the second ejector is connected to the water-side outlet of the flue gas-water heat exchanger, the working fluid inlet of the second ejector is connected to the steam-side outlet of the molten salt-steam heat exchanger, the sludge outlet of the pyrolysis unit is connected to the coal mill, and the outlet of the coal mill is connected to the boiler. The trough solar collector, the oil pump, and the oil-side connection of the oil-steam heat exchanger form a heat transfer oil circulation loop. The photovoltaic panel is electrically connected to the electric heating device. The electric heating device, the high-temperature molten salt storage tank, the low-temperature molten salt storage tank, and the molten salt side connection of the molten salt-steam heat exchanger form a molten salt circulation loop.

2. The sludge treatment system utilizing solar energy coupled with flue gas waste heat according to claim 1, characterized in that, The water-side outlet of the flue gas-water heat exchanger has a first branch, which is connected to the inlet of the fifth regulating valve and the inlet of the sixth regulating valve respectively. The outlet of the fifth regulating valve is connected to the inlet of the dissolving tank via the fifth shut-off valve, and the outlet of the sixth regulating valve is connected to the ejector fluid inlet of the first ejector via the sixth shut-off valve.

3. The sludge treatment system utilizing solar energy coupled with flue gas waste heat according to claim 2, characterized in that, The water-side outlet of the flue gas-water heat exchanger also has a second branch, which is connected to the ejector fluid inlet of the second ejector via a fourth shut-off valve and a fourth regulating valve.

4. The sludge treatment system utilizing solar energy coupled with flue gas waste heat according to claim 1, characterized in that, It also includes a thermal oil buffer tank, the inlet of which is connected to the outlet of the trough solar collector, the outlet of which is connected to the oil-side inlet of the oil-vapor heat exchanger, the oil-side outlet of which is connected to the inlet of the oil pump, and the outlet of which is connected to the inlet of the trough solar collector; the steam-side outlet of the drying unit is connected to the steam-side inlet of the oil-vapor heat exchanger via a second regulating valve and a second shut-off valve.

5. The sludge treatment system utilizing solar energy coupled with flue gas waste heat according to claim 1, characterized in that, The outlet of the electric heating device is connected to the inlet of the high-temperature molten salt pump, the outlet of the high-temperature molten salt pump is connected to the inlet of the high-temperature molten salt storage tank, the first outlet of the high-temperature molten salt storage tank is connected to the inlet of the low-temperature molten salt storage tank, the second outlet of the high-temperature molten salt storage tank is connected to the molten salt side inlet of the molten salt-steam heat exchanger, the molten salt side outlet of the molten salt-steam heat exchanger is connected to the inlet of the low-temperature molten salt storage tank, the outlet of the low-temperature molten salt storage tank is connected to the inlet of the low-temperature molten salt pump, and the outlet of the low-temperature molten salt pump is connected to the inlet of the electric heating device.

6. The sludge treatment system utilizing solar energy coupled with flue gas waste heat according to claim 1, characterized in that, The steam-side outlet of the pyrolysis unit is connected to the steam-side inlet of the molten salt-steam heat exchanger via a third regulating valve and a third shut-off valve.

7. The sludge treatment system utilizing solar energy coupled with flue gas waste heat according to claim 1, characterized in that, The material outlet of the dissolving tank is connected to the inlet of the sludge pump via a first shut-off valve and a first regulating valve, and the outlet of the sludge pump is connected to the inlet of the heat exchange box.

8. The sludge treatment system utilizing solar energy coupled with flue gas waste heat according to claim 1, characterized in that, An air preheater is installed in the tail flue of the circulating fluidized bed boiler. The tail flue located behind the air preheater has a flue gas intake port and a flue gas return port. The flue gas side inlet of the flue gas-water heat exchanger is connected to the tail flue via the flue gas intake port, and the flue gas side outlet of the flue gas-water heat exchanger is connected to the tail flue via the flue gas return port.

9. The sludge treatment system utilizing solar energy coupled with flue gas waste heat according to claim 1, characterized in that, The water temperature at the condenser outlet is 40-50℃, and after being heated to 100℃ by the flue gas-water heat exchanger, the mass mixing ratio of the water at the flue gas-water heat exchanger outlet to the sludge in the dissolving tank is 4:1; the temperature of the heat transfer oil in the trough solar collector is 300-350℃, and the steam temperature formed after heat exchange by the oil-steam heat exchanger is 250-280℃, and the steam temperature output after mixing by the first ejector is 180-210℃; the electric heating device heats the molten salt to 450-550℃, and the steam temperature formed after heat exchange by the molten salt-steam heat exchanger is 350-430℃, and the steam temperature output after mixing by the second ejector is 250-280℃.

10. A sludge treatment method utilizing solar energy coupled with flue gas waste heat, employing the system described in any one of claims 1-9, characterized in that, Includes the following steps: Water from the condenser outlet is fed into the water side of the flue gas-water heat exchanger and heats up the flue gas discharged from the tail flue of the circulating fluidized bed boiler. The heated water is then fed into a dissolving tank and mixed with the sludge in the dissolving tank to dissolve the inorganic chlorine in the sludge. The sludge in the dissolving tank is pumped to the drying unit of the heat exchange box. The trough solar collector heats the heat transfer oil. After the heat transfer oil releases heat on the oil side of the oil-steam heat exchanger, it is pumped back to the trough solar collector for circulation and heat absorption. The steam side of the oil-steam heat exchanger absorbs heat and heats up to generate high-temperature steam. The high-temperature steam is used as the working fluid and enters the working fluid inlet of the first ejector. The high-temperature water from the flue gas-water heat exchanger is used as the ejector fluid and introduced into the ejector fluid inlet of the first ejector. The steam formed after mixing is passed into the drying unit to dry the sludge. The steam discharged from the drying unit flows back to the steam side of the oil-steam heat exchanger to absorb heat again. The dried sludge is sent to the pyrolysis unit. The photovoltaic panel generates electricity to drive the electric heating device to heat the molten salt. The high-temperature molten salt releases heat through the molten salt-steam heat exchanger and generates high-temperature steam which enters the second ejector. High-temperature water from the flue gas-water heat exchanger is introduced into the ejector fluid inlet of the second ejector as the ejector fluid. The steam formed after mixing is passed into the pyrolysis unit to pyrolyze the dried sludge. The sludge, after pyrolysis, is fed into a coal mill to be mixed and ground with coal, and then sent to a boiler for incineration through the coal feed port.

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