A system and method for drying dewatered sludge from a power plant using exhaust steam waste heat

Abstract

The application discloses a system and method for drying sludge in power plants by using exhaust steam waste heat, which comprises a constant-discharge expander, a sludge drying device, a sludge cake crusher, a condensate tank and a steam heat storage unit; the sludge cake crusher is connected with the sludge drying device, the sludge drying device is connected with the condensate tank, and the condensate tank is connected with the steam heat storage unit; the steam heat storage unit is internally filled with heat storage materials; the constant-discharge expander is connected with the steam heat storage unit, and the steam heat storage unit is connected with the sludge drying device; the sludge drying device comprises a shell, a sludge drying device cylinder is arranged in the shell, and a plurality of rotary drying cylinders are uniformly arranged in the sludge drying device cylinder. The application combines boiler constant-discharge exhaust steam recovery treatment and power plant sludge treatment and disposal technology, solves the problems of white feather caused by waste of power plant boiler constant-discharge exhaust steam and equipment corrosion caused by exhaust steam emission, realizes conversion of discontinuous exhaust steam in power plants into stable heat source utilization, and solves the problems of high treatment cost and limited treatment capacity of power plant sludge external transportation.

Description

Technical Field

[0001] This invention belongs to the field of power plant sludge treatment and disposal technology, specifically relating to a system and method for drying power plant dewatered sludge using waste heat from exhaust steam. Background Technology

[0002] During the production process of thermal power plants, high-temperature and high-pressure steam, after releasing a certain amount of energy, becomes waste steam or low-parameter steam and is discharged from the system. Alternatively, hot water with a certain pressure and temperature, as well as continuous and periodic wastewater discharge and condensate from boilers, pressure vessels, and pipelines, undergo pressure reduction. Some water will undergo secondary evaporation due to the pressure reduction, forming flash steam. These waste steam, exhaust steam, or flash steam are collectively referred to as "exhaust steam." During unit operation, a large amount of steam (approximately 1-3 t / h) is discharged into the atmosphere from the boiler's blowdown expansion tank exhaust pipe. This steam contains the latent heat of vaporization of the working fluid from liquid water, absorbing heat to vaporize into steam, and thus contains low-grade waste heat resources. Because of its low pressure, exhaust steam cannot meet the requirements of steam-using equipment, so power plants usually discharge it directly, causing serious waste of heat and steam resources, resulting in huge economic losses for the enterprise and environmental pollution. Furthermore, the continuous nature of power plant exhaust steam discharge makes efficient and stable recovery and utilization a key issue that needs attention.

[0003] Due to national environmental policies, the off-site transportation and disposal of power plant sludge is restricted. On the one hand, municipalities are reluctant to accept it, and on the other hand, the cost of off-site sludge transportation and disposal is extremely high. The co-firing of coal-fired power units with sludge incineration provides a new approach to power plant sludge treatment and disposal, and there are already some successful implementation cases in power plants. The sludge generated by the raw water pretreatment system and biological treatment system of power plants has a moisture content of about 60% after dewatering. Further reduction of the sludge moisture content is needed for co-firing. Studies have shown that the moisture content requirement for sludge co-firing should not exceed 50%, and the dewatering requirements are relatively low. Therefore, further research and development of an economical and simple drying device is needed to dry the dewatered sludge, enabling coal-fired power plants to achieve the goals of resource conservation and environmental protection. Summary of the Invention

[0004] To address the technical problems of high cost and limited processing capacity in existing power plant sludge drying treatment technologies, the present invention aims to provide a system and method for drying power plant dewatered sludge using waste heat from exhaust steam. This method utilizes the exhaust steam generated by the power plant boiler during scheduled exhaust for sludge drying, avoiding waste of exhaust steam and the resulting plume and equipment corrosion. Simultaneously, it achieves efficient, stable, low-energy-consumption, and low-cost sludge drying, enabling the sludge to achieve a moisture content of up to 30%, meeting the requirements for co-firing, and helping coal-fired power plants achieve resource conservation and environmental protection.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A system for drying dewatered sludge from a power plant using waste heat from exhaust steam includes a fixed discharge expansion vessel, a sludge drying device, a sludge cake crusher, a condensate tank, and a steam heat storage unit.

[0007] The sludge cake crusher is connected to the sludge drying device, the lower part of the sludge drying device is connected to the condensate tank, and the condensate tank is connected to the steam heat storage unit; the steam heat storage unit is filled with expandable graphite-Ca(OH)2 composite heat storage material.

[0008] The fixed discharge expansion tank is connected to the steam thermal storage unit, and the steam thermal storage unit is connected to the sludge drying device;

[0009] The sludge drying device includes a sludge drying device cylinder, several rotary drying cylinders are evenly arranged inside the sludge drying device cylinder, and a circumferential steam distribution device is installed at the bottom of the sludge drying device cylinder.

[0010] Furthermore, a gas outlet is provided at the upper part of the shell, and a steam inlet is provided at the lower part of the shell. The gas outlet is connected to the steam thermal storage unit.

[0011] The circumferential steam distribution device includes a steam distribution branch pipe, which is either an annular steam distribution pipe or a straight steam distribution pipe. Several steam distribution holes are opened on the steam distribution branch pipe, and the diameter of the steam distribution holes is 80% of the diameter of the steam distribution branch pipe.

[0012] Furthermore, a steam circulation pipe is installed between the gas outlet and the steam thermal storage unit, and a steam circulation check valve is installed on the steam circulation pipe.

[0013] Furthermore, the fixed-discharge expansion vessel is equipped with a secondary steam recovery pipe and a safety valve, and the secondary steam recovery pipe is equipped with a steam recovery valve and a steam delivery check valve.

[0014] Furthermore, the steam thermal storage unit includes a steam inlet, a steam outlet, a cold water inlet, and a condensate outlet. The fixed-discharge expansion tank is connected to the steam inlet, the condensate tank is connected to the cold water inlet through a condensate delivery pipe, the steam outlet is connected to the sludge drying device through a steam delivery pipe, and the condensate outlet is connected to the condensate tank through a pipe.

[0015] Furthermore, a feed hopper is provided at the top of the rotary drying cylinder;

[0016] The rotary drying drum is equipped with a rotating scraper inside;

[0017] The bottom of the rotary drying drum is connected to the head section of the sludge drying device;

[0018] The sludge drying device also includes a sludge drying device head section connected to the sludge drying device cylinder, and an isolation plate is provided between the sludge drying device cylinder and the sludge drying device head section.

[0019] The bottom of the sludge drying unit's head section is equipped with an electric sector gate valve to control the discharge of dried sludge.

[0020] Furthermore, a support frame is welded onto the cylinder of the sludge drying device.

[0021] Furthermore, the sludge cake crusher adopts a double-roller structure, with a screw conveyor connected to the inlet of the sludge cake crusher and the outlet of the sludge cake crusher connected to the sludge drying device via a sludge distributor.

[0022] The mud cake crusher includes a circular roller, a scraper, and a rotary scraper, with the scraper and rotary scraper mounted on the circular roller.

[0023] Furthermore, the sludge distributor is arranged from top to bottom as follows: a corrugated feed plate, a pusher scraper in the middle, and a discharge plate.

[0024] Furthermore, the peak spacing of the corrugations on the corrugated feed plate is 5~10cm, and the rotation speed of the pusher scraper is 50~120 rpm.

[0025] A method for drying dewatered sludge from a power plant using waste heat from exhaust steam includes the following steps:

[0026] The dewatered sludge from the power plant enters the rotary drying drum inside the sludge drying device through the sludge cake crusher. The rotating scraper inside the rotary drying drum stirs and breaks up the sludge.

[0027] The boiler's exhaust steam enters the steam storage unit through the exhaust expansion container, where the latent heat of the steam is converted into chemical energy for storage. The expandable graphite-Ca(OH)2 composite heat storage material inside the steam storage unit undergoes an endothermic reaction to generate calcium oxide and water, thus completing the exhaust steam heat storage process.

[0028] The condensate in the condensate tank enters the steam heat storage unit and reacts with the expandable graphite-Ca(OH)2 composite heat storage material, releasing a large amount of heat. The heat enters the sludge drying device as high-temperature steam to achieve sludge drying.

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

[0030] This invention combines boiler exhaust steam recovery and treatment with power plant sludge treatment and disposal technologies by setting up a fixed-discharge expansion tank and a sludge drying device. It proposes a technical route for using boiler exhaust steam for power plant sludge drying, solving the problems of wasted boiler exhaust steam and plume and equipment corrosion caused by exhaust steam emissions. It also addresses the issues of high costs and limited processing capacity for transporting and disposing of power plant sludge. The steam thermal storage unit in this invention is filled with expandable graphite-Ca(OH)2 composite thermal storage material, which absorbs the calorific value of steam and stores it as chemical energy. When a heat source is needed, it releases heat by absorbing water and releasing heat, ultimately collecting, storing, and outputting the unstable exhaust steam as a stable heat source, solving the problem of difficulty in utilizing the discontinuous exhaust steam. The sludge drying device in this invention is equipped with multiple rotary drying cylinders, which, compared to conventional rotary sludge drying devices, provide a larger heat exchange area and higher mass transfer rate per unit volume of sludge. This invention can achieve a sludge moisture content of 30%, meeting the requirements for co-firing.

[0031] Furthermore, the sludge distributor in this invention adopts a corrugated feed plate-propulsion scraper-discharge plate structure, which can achieve uniform distribution of sludge feed.

[0032] Furthermore, the drying drum employs a rotating scraper cutting feed mode, which prevents sludge from clumping inside the drum, increases the sludge residence time, and achieves better sludge drying results. This device is suitable for power plant sludge systems with relatively small volumes, has low energy consumption, and is simple to operate and maintain. The dried sludge has a moisture content of less than 50%, making it suitable for co-firing with sludge from coal-fired power plants.

[0033] Furthermore, by setting a steam circulation check valve, it is possible to prevent discontinuous exhaust steam from directly entering the sludge drying unit's cylinder and forming a co-current flow, thereby reducing sludge drying efficiency.

[0034] Furthermore, the circumferential steam distribution device is located at the bottom of the sludge drying device. The steam flows from bottom to top in the sludge drying device and forms a countercurrent with the sludge flowing from top to bottom in the rotary drying drum. This can completely dry the sludge that initially enters, ensuring the drying effect. Attached Figure Description

[0035] Figure 1 This is a process flow diagram of the method for drying dewatered sludge from a power plant using waste heat from exhaust steam, as described in this invention.

[0036] Figure 2 This is a schematic diagram of a sludge drying device.

[0037] Figure 3 The diagram shows a circumferential steam distribution device; where (a) represents the number of rotary drying cylinders n=4, and (b) represents the number of rotary drying cylinders n=7.

[0038] Figure 4 The diagram shows the structure of a sludge distributor; (a) is a schematic diagram of a sludge distributor, (b) is a schematic diagram of a corrugated feed orifice plate, (c) is a schematic diagram of a pusher scraper, and (d) is a schematic diagram of a discharge orifice plate.

[0039] In the diagram: 1-Stationary discharge expansion container; 11-Steam recovery valve; 12-Secondary steam recovery pipe; 13-Steam conveying check valve; 14-Safety valve; 2-Sludge drying device; 21-Feed hopper; 22-Sludge drying device cylinder; 23-Rotary drying cylinder; 231-Rotary scraper; 24-Circumferential steam distribution device; 241-Steam distribution branch pipe; 242-Steam distribution hole; 243-Support; 25-Electric sector gate valve; 26-Steam circulation pipe; 27-Steam circulation check valve; 28-Sludge drying device end cap section; 3-Screw conveyor; 4-Sludge cake crusher; 41-Circular roller; 42-Scraper; 43-Rotary scraper; 5-Sludge distributor; 51-Corrugated feed orifice plate; 52-Propeller scraper; 53-Discharge orifice plate; 6-Condensate tank; 61-Automatic condensate valve; 62-Condensate conveying pipe; 7-Steam heat storage unit; 71-Automatic steam conveying valve; 72-Steam conveying pipe. Detailed Implementation

[0040] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0041] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and 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. Therefore, they should not be construed as limitations on this invention.

[0042] 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 indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0043] 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 communication connection; 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. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0044] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0045] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0046] This invention utilizes boiler exhaust steam recovery for power plant sludge drying, achieving exhaust steam recovery while reducing sludge moisture content, thereby meeting the requirements for sludge co-firing. This technology aligns with the concept of green and sustainable development.

[0047] See Figure 1 The present invention provides a system for drying dewatered sludge from a power plant using waste heat from exhaust steam. The system mainly includes a fixed discharge expansion container 1, a sludge drying device 2, a screw conveyor 3, a sludge cake crusher 4, a sludge distributor 5, a condensate tank 6, and a steam heat storage unit 7.

[0048] The fixed-discharge expansion vessel 1 is equipped with a secondary steam recovery pipe 12 and a safety valve 14. The secondary steam recovery pipe 12 is equipped with a steam recovery valve 11 and a steam transfer check valve 13.

[0049] The steam thermal storage unit 7 includes a steam inlet, a steam outlet, a cold water inlet, and a condensate outlet. A secondary steam recovery pipe 12 is connected to the steam inlet. The condensate tank 6 is connected to the cold water inlet via a condensate delivery pipe 62. The steam outlet is connected to the sludge drying device 2 via a steam delivery pipe 72, and the condensate outlet is connected to the condensate tank 6 via a pipe. The interior of the steam thermal storage unit 7 is filled with expandable graphite-Ca(OH)2 composite thermal storage material.

[0050] The sludge drying device 2 includes a feed hopper 21, a sludge drying device cylinder 22, a rotary drying cylinder 23, a circumferential steam distribution device 24, an electric sector gate valve 25, a steam circulation pipe 26, and a sludge drying device head section 28. An isolation plate is provided between the sludge drying device cylinder 22 and the sludge drying device head section 28, so that steam will not enter the sludge drying device head section 28 from the sludge drying device cylinder 22. The sludge drying device cylinder 22 is equipped with a feed hopper 21 at the top. Several rotary drying cylinders 23 are evenly arranged inside the sludge drying device cylinder 22. The feed hopper 21 is located at the top of the rotary drying cylinder 23. A circumferential steam distribution device 24 is set at the bottom inside the sludge drying device cylinder 22. A gas outlet is set at the top and a steam inlet is set at the bottom. The residual steam after heat exchange with the sludge inside the rotary drying cylinder 23 is connected to the steam inlet of the steam heat storage unit through the gas outlet, steam circulation pipe 26, and secondary steam recovery pipe 12. A steam circulation check valve 27 is set on the steam circulation pipe 26. The steam circulation check valve 27 can prevent the discontinuously discharged exhaust steam from directly entering the sludge drying device cylinder 22 of the sludge drying device 2 and forming a co-current flow, thereby reducing the sludge drying efficiency.

[0051] An electric sector gate valve 25 is installed at the bottom of the end cap section 28 of the sludge drying device to control the discharge of dried sludge.

[0052] The screw conveyor 3 is connected to the inlet of the sludge cake crusher 4, the outlet of the sludge cake crusher 4 is connected to the inlet of the sludge distributor 5, and the outlet of the sludge distributor 5 is connected to the feed hopper 21 of the sludge drying device 2. The dried sludge discharged from the outlet of the electric sector gate valve 25 at the bottom of the sludge drying device 2 can be directly transported to the sludge co-firing unit. The lower part of the sludge drying device 2 is also connected to the condensate tank 6.

[0053] See Figure 2 The rotary drying drum 23 is equipped with a rotating scraper 231, which rotates to convey the sludge downwards. By adjusting the rotation speed of the rotating scraper 231, the sludge drying time can be adjusted to ensure that the moisture content of the dried sludge meets the requirements. The rotation speed of the rotating scraper 231 is generally 30~100 rpm.

[0054] See Figure 3 In (a) and (b), the circumferential steam distribution device 24 has a slightly different structure depending on the number of rotary drying cylinders 23. The circumferential steam distribution device 24 includes steam distribution branch pipes 241, which are specifically either annular steam distribution pipes or straight steam distribution pipes. Several steam distribution holes 242 are opened on the steam distribution branch pipes 241, and the diameter of the steam distribution holes 242 is 80% of the diameter of the steam distribution branch pipes 241.

[0055] A support frame 243 is also welded onto the cylinder 22 of the sludge drying device to support the circumferential steam distribution device 24.

[0056] The circumferential steam distribution device 24 is located at the bottom of the sludge drying device 2. The steam flows from bottom to top in the sludge drying device 2 and forms a countercurrent with the sludge flowing from top to bottom in the rotary drying cylinder 23. This can completely dry the sludge that initially enters and ensure the drying effect.

[0057] See Figure 1 The mud cake crusher 4 adopts a double roller structure. The mud cake crusher 4 includes a circular roller 41, a scraper 42 and a rotary scraper 43. The circular roller 41 is equipped with a scraper 42 and a rotary scraper 43. During the crushing process, the circular roller 41 can remove the mud attached to its surface through the scraper 42, and the rotary scraper 43 can send the mud out of the mud cake crusher 4.

[0058] See Figure 4 The sludge distributor 5 consists of three parts: an upper, middle, and lower section. The upper section is a corrugated feed orifice plate 51, the middle section is a pusher scraper 52, and the bottom section is a discharge orifice plate 53. The peak spacing of the corrugations on the corrugated feed orifice plate 51 is 5-10 cm. The rotation speed of the pusher scraper 52 is 50-120 rpm. The position and number of openings in the bottom discharge orifice plate 53 are consistent with those in the rotary drying cylinder 23 of the sludge drying device 2. Moreover, the bottom of the discharge orifice plate 53 is connected to the feed hopper 21 at the top of the sludge drying device 2 via a pipe, ensuring that the sludge enters directly into the rotary drying cylinder 23 without contacting the steam.

[0059] A method for drying power plant dewatered sludge using waste heat from exhaust steam, based on the above system, is as follows: The power plant dewatered sludge (generally with a moisture content of around 60%) is conveyed to a sludge cake crusher 4 via a screw conveyor 3. The sludge cake crusher 4 can crush large sludge cakes into smaller lumps or granules. Then, the sludge passes through a sludge distributor 5. First, the lumps or granules are evenly distributed by a corrugated feed plate 51. Then, the sludge is pushed to a discharge plate 53 by a pushing scraper 52 in the middle section of the sludge distributor 5. The sludge then enters the rotary drying cylinder 23 inside the sludge drying device 2 through a pipe at the bottom of the discharge plate 53. The rotating scraper 231 inside the rotary drying cylinder 23 can stir and break up the sludge, preventing sludge clumping. The boiler's exhaust steam enters the steam storage unit 7 through the secondary steam recovery pipe 12 of the exhaust expansion vessel 1, converting the latent heat of the steam into chemical energy for storage. At this time, the expandable graphite-Ca(OH)₂ composite heat storage material inside the steam storage unit 7 undergoes an endothermic reaction, generating calcium oxide and water. The condensate is then transported to the condensate tank 6 through a pipeline. After the exhaust steam heat storage process is complete, energy release and sludge drying can proceed. The condensate in the condensate tank 6 enters the steam storage unit 7 through the condensate delivery pipe 62, reacting with the expandable graphite-Ca(OH)₂ composite heat storage material. The reaction of calcium oxide and water releases a large amount of heat, which is then delivered as high-temperature steam through the steam delivery pipe 72 to the sludge drying device 2. The steam is evenly distributed around the rotary drying cylinder 23 via the circumferential steam distribution device 24 at the bottom of the sludge drying device 2. The sludge is indirectly heated by the steam in the shell of the sludge drying device 2 through the cylinder wall in the rotary drying drum 23, thereby achieving sludge drying. During the heat exchange process, the steam condensate is discharged to the condensate tank 6 through the pipeline, and the remaining steam is recovered to the steam heat storage unit 7 through the steam circulation pipe 26. The dried sludge enters the head section 28 of the sludge drying device and is finally discharged through the electric fan-shaped gate valve 25 at the bottom before entering the subsequent co-firing unit.

[0060] Furthermore, by controlling the amount of cold water entering the steam storage unit 7, the steam temperature can be controlled, thereby controlling the sludge drying process. The final moisture content of the dried sludge can be adjusted to the range of 20% to 50% according to the co-firing requirements.

[0061] Example 1

[0062] The exhaust steam from a coal-fired power plant is transported to the sludge drying unit via pipeline, resulting in relatively low heat loss. The steam temperature measured at the steam inlet pipe of sludge drying unit 2 is approximately 100°C. The exhaust steam temperature of the power plant is 110°C, the pressure is approximately 0.12 kg (0.012 MPa), and the daily discharge time is approximately 1 hour.

[0063] The exhaust steam from the unit enters the steam thermal storage unit 7 after passing through the fixed-discharge expansion tank 1. The expandable graphite-Ca(OH)2 composite thermal storage material inside the steam thermal storage unit 7 absorbs and stores the heat from the instantaneously emitted exhaust steam as chemical energy. This process is the thermal storage process. After the thermal storage process is completed, energy release occurs, providing a stable heat source for the sludge drying process. During the energy release process, cold water in the condensate tank 6 is transported to the steam thermal storage unit 7 through pipelines. Calcium oxide reacts with water to release a large amount of heat, which is then transported to the sludge drying device 2 via steam to exchange heat with the sludge.

[0064] The raw water pretreatment system discharges 2 tons of sludge per day (calculated based on oven-dry sludge volume). The dewatered sludge typically has a moisture content of around 60%, therefore the dewatered sludge treatment capacity is 0.32 m³. 3 / h, with a daily processing capacity of approximately 8 m³ 3 .

[0065] The sludge from the raw water pretreatment system is squeezed and drained by a plate and frame dewatering machine, forming a mud cake. The mud cake is then conveyed to the mud cake crusher 4 by a screw conveyor 3. The mud cake is crushed into smaller blocks or granules by two round rollers 41. At this point, the average particle size of the sludge is about 3 cm. The crushed sludge is then output through the rotary scraper 43 at the outlet of the mud cake crusher 4 and enters the upper corrugated feed plate 51 of the sludge distributor 5. The corrugated plates on the corrugated feed plate 51 have a gap of 5 cm, which can ensure the passage of sludge. At the same time, when there is a lot of sludge entering the upper part of the sludge distributor 5, the corrugated feed plate 51 can achieve uniform distribution of sludge. Then, the sludge is pushed to the discharge plate 53 by the middle pusher scraper 52. The rotation speed of the pusher scraper 52 is set to 60 rpm.

[0066] The sludge enters the feed hopper 21 of the sludge drying device 2 through the opening of the discharge orifice plate 53. Then, the sludge material is driven into the rotary drying cylinder 23 by the rotation of the rotating scraper 231 inside the rotary drying cylinder 23. The sludge exchanges heat with the steam entering the cylinder 22 of the sludge drying device, thereby achieving the evaporation and removal of free water in the sludge.

[0067] For this system, there are 5 rotary drying cylinders 23, each with a diameter of 0.4m and a height of 2m. The rotation speed of the rotating scraper 231 is set to 80 rpm. The residence time of the sludge drying device is set to 30 min. When the moisture content of the sludge is reduced to less than 50% after drying, the electric sector gate valve 25 at the bottom of the drying device is opened to unload the dried sludge from the sludge drying device 2 and transport it to the incineration unit for co-combustion.

[0068] After the steam inside the sludge drying device cylinder 22 undergoes indirect heat exchange with the sludge, condensate is formed. The condensate is discharged to the condensate tank 6 through the condensate discharge pipe at the bottom of the sludge drying device 2.

[0069] This embodiment utilizes a sludge drying system to dry the dewatered sludge from the power plant's raw water pretreatment process using exhaust steam from the power plant's dewatered steam. The final sludge moisture content reaches 30%, meeting the requirements for co-firing. This technology is of great significance for the recovery and utilization of exhaust steam from power plants and for the resource-based treatment of power plant sludge.

[0070] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0071] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A system for drying dewatered sludge from a power plant using waste heat from exhaust steam, characterized in that, It includes a fixed discharge expansion container (1), a sludge drying device (2), a sludge cake crusher (4), a condensate tank (6), and a steam heat storage unit (7); The sludge cake crusher (4) is connected to the sludge drying device (2), the lower part of the sludge drying device (2) is connected to the condensate tank (6), and the condensate tank (6) is connected to the steam heat storage unit (7); the steam heat storage unit (7) is filled with expandable graphite-Ca(OH)2 composite heat storage material. The fixed discharge expansion container (1) is connected to the steam heat storage unit (7), and the steam heat storage unit (7) is connected to the sludge drying device (2); The sludge drying device (2) includes a sludge drying device cylinder (22) and a sludge drying device head section (28). Several rotary drying cylinders (23) are evenly arranged inside the sludge drying device cylinder (22). A circumferential steam distribution device (24) is provided at the bottom of the sludge drying device cylinder (22). The fixed discharge expansion vessel (1) is equipped with a secondary steam recovery pipe (12) and a safety valve (14). The secondary steam recovery pipe (12) is equipped with a steam recovery valve (11) and a steam delivery check valve (13). The steam storage unit (7) includes a steam inlet, a steam outlet, a cold water inlet and a condensate outlet. The fixed discharge expansion container (1) is connected to the steam inlet. The condensate tank (6) is connected to the cold water inlet through the condensate delivery pipe (62). The steam outlet is connected to the sludge drying device (2) through the steam delivery pipe (72). The condensate outlet is connected to the condensate tank (6) through a pipe.

2. The system for drying power plant dewatered sludge using waste heat from exhaust steam according to claim 1, characterized in that, A gas outlet is provided at the upper part of the shell, and a steam inlet is provided at the lower part of the shell. The gas outlet is connected to the steam heat storage unit (7). The circumferential steam distribution device (24) includes a steam distribution branch pipe (241), which is an annular steam distribution pipe or a straight steam distribution pipe. Several steam distribution holes (242) are opened on the steam distribution branch pipe (241), and the diameter of the steam distribution hole (242) is 80% of the diameter of the steam distribution branch pipe (241).

3. The system for drying power plant dewatered sludge using waste steam heat according to claim 1, characterized in that, A steam circulation pipe (26) is provided between the gas outlet and the steam storage unit (7), and a steam circulation check valve (27) is provided on the steam circulation pipe (26).

4. The system for drying power plant dewatered sludge using waste heat from exhaust steam according to claim 1, characterized in that, A feed hopper (21) is provided at the top of the rotary drying drum (23); A rotating scraper (231) is installed inside the rotary drying drum (23); The bottom of the rotary drying drum (23) is connected to the head section (28) of the sludge drying device; The sludge drying device (2) also includes a sludge drying device head section (28) connected to the sludge drying device cylinder (22), and an isolation plate is provided between the sludge drying device cylinder (22) and the sludge drying device head section (28); The bottom of the sludge drying device head section (28) is equipped with an electric sector gate valve (25) to control the discharge of dried sludge.

5. The system for drying power plant dewatered sludge using waste steam heat according to claim 1, characterized in that, The mud cake crusher (4) adopts a double roller structure. The inlet of the mud cake crusher (4) is connected to a screw conveyor (3), and the outlet of the mud cake crusher (4) is connected to the sludge drying device (2) via a sludge distributor (5). The mud cake crusher (4) includes a round roller (41), a scraper (42) and a rotary scraper (43), with the scraper (42) and the rotary scraper (43) mounted on the round roller (41).

6. The system for drying power plant dewatered sludge using waste heat from exhaust steam according to claim 1, characterized in that, The sludge distributor (5) consists of a corrugated feed plate (51), a pusher scraper (52), and a discharge plate (53) arranged sequentially from top to bottom.

7. The system for drying power plant dewatered sludge using waste heat from exhaust steam according to claim 6, characterized in that, The peak spacing of the corrugations on the corrugated feed plate (51) is 5~10cm, and the rotation speed of the pusher scraper (52) is 50~120 rpm.

8. A method for drying power plant dewatered sludge using waste heat from exhaust steam, based on the system described in claim 4, characterized in that, Includes the following steps: The dewatered sludge from the power plant enters the rotary drying drum (23) inside the sludge drying device (2) through the sludge cake crusher (4). The rotating scraper (231) inside the rotary drying drum (23) stirs and crushes the sludge. The boiler's exhaust steam enters the steam storage unit (7) through the exhaust expansion container (1), converting the latent heat of the steam into chemical energy for storage. The expandable graphite-Ca(OH)2 composite heat storage material inside the steam storage unit (7) undergoes an endothermic reaction to generate calcium oxide and water, thus completing the exhaust steam heat storage process. The condensate in the condensate tank (6) enters the steam heat storage unit (7) and reacts with the expandable graphite-Ca(OH)2 composite heat storage material to release a large amount of heat. The heat enters the sludge drying device (2) in the form of high-temperature steam to achieve sludge drying.

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