Vacuum drying system utilizing waste heat of low-temperature flue gas of coal-fired boiler

Abstract

The utility model provides a vacuum drying system utilizing waste heat of low-temperature flue gas of a coal-fired boiler. Comprising a horizontal vacuum dryer, an air pre-heater, a flue gas waste heat absorber, a boiler, a dust remover, a vacuum condenser, a vacuum pump, a circulating water pump, a low-pressure heater set, a measuring instrument, a vacuum drainage tank, a data processing and control system, a vacuum feeding device, a vacuum discharging device and a flow regulating valve. The hot water prepared by the flue gas waste heat with lower temperature is used as a drying heat source, and is used for heating wet materials in the vacuum disc dryer, so that the heat utilization efficiency of the waste heat is high; a hollow disc is used as a dryer in a drying machine cavity, and the occupied area of the whole equipment is much smaller than that of a traditional belt type drying machine; due to low pressure, the boiling point of water is reduced, a saturated state is easily achieved, the internal and external water pressure difference of sludge is increased, and the water migration efficiency is improved; therefore, the vacuum drying time is shorter than the drying time under normal pressure and micro-negative pressure, and the equipment size can also be controlled.

Description

Technical Field

[0001] The utility model relates to the field of treatment and disposal of sludge or waste residue with high moisture content, and mainly relates to a vacuum drying system utilizing the waste heat of low-temperature flue gas from a coal-fired boiler. Background Art

[0002] Existing waste heat recovery systems for coal-fired power plants primarily utilize exhaust heat (temperature 120°C to 160°C) after the air preheater to heat low-pressure condensate (via a low-temperature economizer), cool flue gas after the desulfurization tower (via a MGGH system), and air (via a heater). While these technologies offer some energy savings, their utilization is low. For example, using exhaust heat to heat low-pressure condensate only displaces the lower-temperature and pressure extraction steam from the heat recovery system back to the turbine for power generation, resulting in limited reductions in unit coal consumption (generally only 1-2g / KWh). Thermal energy utilization efficiency is only approximately 10%, with the vast majority of the heat being carried to the unit's cooling tower by circulating cooling water after inefficient power generation and released into the atmosphere.

[0003] With economic and social development, my country's urban population continues to grow, and with it, the amount of domestic wastewater. Consequently, the amount of sludge generated by water treatment is also increasing. After dehydration and filtration, the sludge in sewage treatment plants still has a high moisture content (60%-85%), which easily causes odor and harms the ecological environment. Further treatment is also difficult. Therefore, wet sludge generally needs to be dried. Over the years, two main technologies for drying wet sludge have emerged: disc drying, paddle drying, or thin-layer drying, which utilize steam as a heat source, and belt drying, which utilizes electricity and a compression heat pump system. The former is suitable for applications with steam heat sources, such as coal-fired power plants and waste incineration plants; the latter is suitable for applications without steam heat sources, such as sewage treatment plants.

[0004] Coal-fired power plants can use hot steam from the units to dry high-moisture materials. However, because they use high-temperature, high-pressure steam from triple or quad extraction, the steam thermal mass is relatively high. Using this steam, which could be used for efficient power generation, to dry sludge is relatively uneconomical. As mentioned earlier, conventional low-temperature economizer condensate heating technology can only squeeze out steam from the No. 7 and No. 8 low-pressure exhaust steam, resulting in poor thermal efficiency. Therefore, it is possible to consider using this low-temperature flue gas waste heat to heat high-moisture materials. However, due to the low flue gas temperature, sludge drying generally uses convection drying technology with higher heat transfer efficiency, rather than indirect heating drying technology. This results in large equipment footprints, high dust loads, and difficulty in subsequent exhaust gas treatment.

[0005] Vacuum drying technology involves placing the material being dried in a sealed drying chamber and continuously heating it while the vacuum system draws the vacuum. This process causes moisture within the material to diffuse to the surface through pressure and concentration differences. Water molecules gain sufficient kinetic energy on the surface to overcome the intermolecular attraction and escape into the low-pressure space within the chamber, where they are then pumped away by a vacuum pump. The degree of rarefaction of the gas under vacuum is called the vacuum degree. The higher the vacuum degree, the lower the pressure, the greater the pressure difference between the inside and outside of the material, and the faster the water evaporates.

[0006] Vacuum drying technology is currently mainly used in food, wood, and pharmaceutical processing. At present, the technology in this area has made certain progress, and vacuum belt dryers, vacuum rake dryers, vacuum drum dryers, etc. have appeared one after another.

[0007] However, the existing vacuum drying technology has the following main disadvantages:

[0008] The heat exchange area per unit volume is much lower than that of disc dryers or paddle dryers, resulting in a small processing capacity per unit;

[0009] In order to ensure the vacuum degree of the drying space, intermittent feeding and discharging of materials are required, which leads to frequent switching of other auxiliary equipment in the process (mainly feeding and discharging switching valves), reduced equipment reliability, and greatly limited processing capacity.

[0010] The patent (CN 217356904U) discloses a coal-fired coupled sludge power generation system, including a boiler, a sludge receiving bin and a steam turbine generator. The boiler pipeline is connected to a flue gas treatment system, and an air preheater is provided on the pipe section between the boiler and the flue gas treatment system. The sludge receiving bin pipeline is connected to a flue gas drying device, and the flue gas drying device exhaust pipe is connected to the pipe section between the air preheater and the flue gas treatment system. The steam turbine generator is connected to the boiler pipeline.

[0011] The above patents directly dry sludge by utilizing the waste heat of boiler flue gas. However, there are the following major problems: ① Extracting a portion of the medium- and high-temperature flue gas before the air preheater causes a decrease in boiler efficiency; ② Dust carried by the flue gas causes wear and contamination of pipelines and equipment, and corrosive gases in the flue gas corrode the flue and equipment. At the same time, the mixing of fly ash and sludge reduces the calorific value of the dry sludge; ③ The medium- and high-temperature drying process easily generates a large amount of VOCs that enter the tail gas, causing the COD in the desulfurization wastewater to exceed the standard; ④ The moisture of the dried tail gas is discharged into the flue gas treatment system of the unit, resulting in a high moisture content at the outlet of the desulfurization system and aggravated white smoke emission.

[0012] Patent (CN 2175169832U) discloses a system for drying sludge by deeply recovering waste heat from flue gas, comprising a flue gas waste heat deep recovery heat exchanger, a wet mud silo, a waste heat low-temperature dryer, and a dry mud silo. The flue gas waste heat deep recovery heat exchanger is connected to the waste heat low-temperature dryer through a pipeline, the feed port of the waste heat low-temperature dryer is connected to the discharge port of the wet mud silo, and the discharge port of the waste heat low-temperature dryer is provided with a dry mud conveying device, the end of which is connected to the dry mud silo.

[0013] The waste heat deep recovery device of the above patent uses cooling circulating water to transfer heat to indirectly dry the sludge. It mainly has the following problems: ① Since the flue gas temperature after the dust collector is relatively low, the water temperature after heat exchange is also relatively low, which results in poor sludge drying effect for conventional dryers and is difficult to implement on a large scale; ② Changes in the unit load can easily lead to large changes in the flue gas temperature (such as from 100% load to 40% load, the temperature drops from 140°C to 110°C), resulting in large changes in the water temperature and reduced sludge treatment capacity.

[0014] The patent (CN 207435292U) relates to a coupled power generation system that utilizes waste heat from flue gas to dry sludge. The wet sludge storage bin is connected to a low-temperature wet sludge drying device, the flue gas outlet of the boiler body is connected to a low-temperature flue gas heat exchanger, the low-temperature flue gas heat exchanger is connected to a heater, a circulating pump is provided on the pipeline between the low-temperature flue gas heat exchanger and the heater, the heater is connected to the low-temperature wet sludge drying device; the low-temperature wet sludge drying device is connected to a dry sludge bin, the dry sludge bin is connected to a raw coal hopper; the low-temperature wet sludge drying device is connected to an exhaust gas condensation recovery device, the exhaust gas condensation recovery device is connected to the boiler body, and the exhaust gas condensation recovery device is connected to the condensate water system of the coal-fired unit.

[0015] The above patent uses a belt-type low-temperature dryer for sludge drying. Although it solves the impact of low heat source temperature on the drying process, it has the following problems: ① The belt dryer occupies a large area (generally more than 3 times that of a disc dryer); ② Multiple heat exchanges lead to complex processes and low thermal efficiency; ③ High investment and operating costs. Utility Model Content

[0016] To address the aforementioned issues with existing technologies, the present invention provides a vacuum drying system that utilizes the waste heat from low-temperature flue gas from a coal-fired boiler. The system primarily comprises a vacuum dryer, a wet exhaust gas treatment system, and a flue gas waste heat water circulation system. The vacuum system reduces the evaporation temperature of the wet material to a low of 45°C to 75°C (corresponding to a pressure of -0.09 MPa to -0.06 MPa). This creates a significant heat transfer temperature difference between the 90°C to 110°C hot water generated by the low-temperature waste heat and the wet material, providing sufficient power for drying.

[0017] The technical solution of the utility model is as follows: a vacuum drying system utilizing the waste heat of low-temperature flue gas from a coal-fired boiler, comprising a flue gas waste heat utilization water circulation system, a wet tail gas treatment system and a vacuum drying system;

[0018] The flue gas waste heat utilization water circulation system includes: a low-pressure heater group, a circulating water pump, and a flue gas waste heat absorber are sequentially connected along the water flow direction; the water flow is a cold water flow composed of condensed water from the low-pressure heater group and cold circulating water after heat exchange in a horizontal vacuum dryer; the cold water flow is pressurized by the circulating water pump and enters the flue gas waste heat absorber as a heat exchange medium to absorb heat, and then enters the low-pressure heater group and the horizontal vacuum dryer respectively;

[0019] The wet tail gas treatment system includes: a dust collector and a vacuum condenser are sequentially connected along the direction of the flue gas, and then respectively connected to a vacuum pump and a vacuum drainage box; the flue gas is dust, water vapor and non-condensable gas;

[0020] The vacuum drying system comprises: a vacuum feeding device, a horizontal vacuum dryer and a vacuum discharging device which are sequentially connected along the material entry direction; the material is a high-moisture material.

[0021] Preferably, the horizontal vacuum dryer includes a shell, a dryer cavity, a hollow shaft, a hollow disc, a feed port, a discharge port, a drive device, and an exhaust port;

[0022] A jacket is provided inside the shell; a dryer inner cavity is provided inside the horizontal vacuum dryer, and a hollow shaft and a hollow disc are provided in the dryer inner cavity, and the hollow disc is arranged on the hollow shaft; a driving device is provided outside the horizontal vacuum dryer and connected to the hollow shaft, and the driving device drives the hollow shaft to rotate and drives the hollow disc to rotate.

[0023] Preferably, the water inlet connecting pipe of the horizontal vacuum dryer is divided into two routes in front of the dryer, one route is connected to the hollow disc through the hollow shaft, and the other route is connected to the water inlet of the jacket of the shell; the water outlet connecting pipe of the horizontal vacuum dryer also has two routes, which are respectively connected to the water outlet end of the hollow shaft of the dryer and the water outlet of the shell jacket.

[0024] Preferably, the circulating water pump is provided with a water pump inlet pipe and a water pump outlet pipe; the low-pressure heater group is provided with a heater inlet pipe, a first-level heater outlet pipe and a second-level heater outlet pipe.

[0025] Preferably, the flue gas waste heat utilization water circulation system is connected to the vacuum drying system via a pipeline, including connecting the water outlet pipeline of the circulating water pump to the water inlet connecting pipeline of the horizontal vacuum dryer along the water flow direction.

[0026] Preferably, a feed port is provided at the upper end of the horizontal vacuum dryer, and a pipe at the feed port is connected to a vacuum feeding device; a discharge port is provided at the lower end of the horizontal vacuum dryer, and a pipe at the discharge port is connected to a vacuum discharge device; two exhaust ports are also provided at the upper end of the horizontal vacuum dryer, which are connected to a dust collector.

[0027] Preferably, it further comprises a boiler, wherein the boiler pipeline is connected to a flue gas waste heat absorber, and an air preheater is provided between the flue gas pipe section between the boiler and the flue gas waste heat absorber and the air inlet end pipeline of the boiler.

[0028] Preferably, the water outlet pipe of the horizontal vacuum dryer is connected to a circulating water pump, and the circulating water pump is connected to the pipe section between the total water outlet pipe of the low-pressure heater group and the water inlet pipe of the flue gas waste heat absorber; the water outlet pipe of the flue gas waste heat absorber is respectively connected to the return water pipe of the low-pressure heater group and the water inlet pipe of the horizontal vacuum dryer;

[0029] The exhaust pipe of the horizontal vacuum dryer is connected to a vacuum condenser, and two dust collectors are provided on the exhaust pipe section between the horizontal vacuum dryer and the vacuum condenser; the lower end of the vacuum condenser is connected to a vacuum drainage box, and the upper end of the vacuum condenser is connected to a vacuum pump;

[0030] The vacuum pump, measuring instrument and flow regulating valve are respectively connected to the data processing and control system.

[0031] Preferably, the flow regulating valve includes a medium-temperature condensate regulating valve, a low-temperature condensate regulating valve and a return low-temperature condensate regulating valve;

[0032] The low-pressure heater group is provided with two water outlet ends, which are respectively connected to the medium-temperature condensate outlet pipe and the low-temperature condensate outlet pipe; the medium-temperature condensate outlet pipe and the low-temperature condensate outlet pipe merge to form the main water outlet pipe of the low-pressure heater group;

[0033] The medium-temperature condensate regulating valve is arranged on the medium-temperature condensate outlet pipe; the low-temperature condensate regulating valve is arranged on the low-temperature condensate outlet pipe; the return low-temperature heating condensate regulating valve is arranged on the low-temperature heating return pipe; the medium-temperature condensate regulating valve and the low-temperature condensate regulating valve are used to adjust the water volume in the outlet pipe and thus control the water temperature; the return low-temperature heating condensate regulating valve is used to adjust the flow distribution of hot water delivered to the horizontal vacuum dryer and the return low-temperature heating system.

[0034] Preferably, the horizontal vacuum dryer is further provided with a vacuum dryer internal pressure sensor for measuring the vacuum degree of the horizontal vacuum dryer.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] 1. Compared with the traditional disc or blade drying that can only use steam or thermal oil, this utility model can use hot water produced by flue gas waste heat at a lower temperature as the drying heat source;

[0037] 2. The utility model uses hot water produced by flue gas waste heat to heat the wet materials in the vacuum disc dryer, and the waste heat utilization efficiency is high;

[0038] 3. The utility model adopts a vacuum system, which avoids the odor overflow phenomenon that is easy to occur in conventional belt type;

[0039] 4. This utility model adopts a hollow disc as the dryer in the dryer cavity, and the overall equipment occupies a much smaller area than the traditional belt dryer;

[0040] 5. The vacuum drying method of this utility model accelerates the drying rate of sludge. Due to the low pressure, the boiling point of water is lowered, making it easier to reach saturation. The pressure difference between the water inside and outside the sludge is increased, and the water migration efficiency is improved. This will make vacuum drying take less time than drying under normal pressure and slightly negative pressure, and the equipment size can also be controlled.

[0041] 6. The utility model has a small device size, the corresponding heat dissipation is also small, and the amount of non-condensable gas in the exhaust gas under vacuum state is very small, so the sensible heat loss of the non-condensable gas is also very small, and the system energy consumption is lower than that of the conventional belt type;

[0042] 7. Due to the low-temperature vacuum drying adopted in the present invention, more organic matter in the material is retained in the dried material, thereby improving the material utilization rate (such as the calorific value of the sludge), and also reducing the organic matter in the dry tail gas, thereby reducing the difficulty of reprocessing the tail gas and tail gas condensate;

[0043] 8. Under the vacuum drying environment of the utility model, the dryer cavity is in an oxygen-deficient state, which can help kill most aerobic bacteria and harmful microorganisms in the sludge. The dried sludge product provides favorable conditions for sludge resource utilization;

[0044] 9. This utility model can process other heat-sensitive materials that require low-temperature drying, as well as hazardous materials such as those that are easily oxidized, explosive, and highly irritating. For conventional sludge, the absence of oxygen and low temperature eliminates the explosion risk of conventional disc or paddle drying.

[0045] 10. The utility model can adjust the vacuum degree in the dryer through a variable frequency vacuum pump to cope with the water temperature change caused by the load change of the unit, and has good load adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a schematic diagram of a vacuum drying system that utilizes low-temperature waste heat from a coal-fired boiler according to the present invention;

[0047] Figure 2 Schematic diagram of a vacuum dryer.

[0048] The reference numerals in the figure are as follows: 1-horizontal vacuum dryer; 2-air preheater; 3-flue gas waste heat absorber; 4-boiler; 5-dust collector; 6-vacuum condenser; 7-vacuum pump; 8-circulating water pump; 9-low-pressure heater group; 10-measuring instrument; 11-vacuum drainage tank; 12-data processing and control system; 13-vacuum feeding device; 14-vacuum discharging device; 15-flow regulating valve;

[0049] 1-Horizontal vacuum dryer includes: 1-1-shell; 1-2-dryer cavity; 1-3-hollow shaft; 1-4-hollow disc; 1-5-feed port; 1-6-discharge port; 1-7-drive device; 1-8-exhaust port;

[0050] 10- Measuring instruments include: 10-1- Circulating water return low-pressure flow meter; 10-2- Circulating water to dryer flow meter; 10-3- Hot circulating water temperature transmitter; 10-4- Vacuum dryer internal pressure sensor; 10-5- Vacuum drainage tank upper level gauge; 10-6- Vacuum drainage tank lower level gauge; 10-7- Exhaust gas temperature transmitter after condenser;

[0051] 15-Flow regulating valve includes: 15-1-Medium temperature condensate regulating valve; 15-2-Low temperature condensate regulating valve; 15-3-Return low temperature condensate regulating valve. DETAILED DESCRIPTION

[0052] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0053] See also Figure 1-2 The utility model provides the following technical solutions: a vacuum drying system utilizing the waste heat of low-temperature flue gas from a coal-fired boiler, comprising a horizontal vacuum dryer 1, an air preheater 2, a flue gas waste heat absorber 3, a boiler 4, a dust collector 5, a vacuum condenser 6, a vacuum pump 7, a circulating water pump 8, a low-pressure heater group 9, a measuring instrument 10, a vacuum drainage box 11, a data processing and control system 12, a vacuum feeding device 13, a vacuum discharging device 14, and a flow regulating valve 15;

[0054] A vacuum drying system that utilizes waste heat from low-temperature flue gas from a coal-fired boiler can be categorized into a flue gas waste heat utilization water circulation system, a wet tail gas treatment system, and a vacuum drying system according to its functions.

[0055] The flue gas waste heat utilization water circulation system includes: a low-pressure heater group 9, a circulating water pump 8, and a flue gas waste heat absorber 3 are sequentially connected along the water flow direction; the water flow is a cold water flow composed of condensed water from the low-pressure heater group 9 and cold circulating water after heat exchange in the horizontal vacuum dryer 1; the cold water flow is pressurized by the circulating water pump 8 and enters the flue gas waste heat absorber 3 as a heat exchange medium to absorb heat, and then enters the low-pressure heater group 9 and the horizontal vacuum dryer 1 respectively;

[0056] The wet tail gas treatment system includes: a dust collector 5 and a vacuum condenser 6 are sequentially connected along the direction of the flue gas, and then connected to a vacuum pump 7 and a vacuum drainage box 11 respectively; wherein the flue gas is dust, water vapor and non-condensable gas;

[0057] The vacuum drying system comprises: a vacuum feeding device 13, a horizontal vacuum dryer 1 and a vacuum discharging device 14 which are sequentially connected along the direction of material entry; wherein the material is a high-moisture material.

[0058] The horizontal vacuum dryer 1 includes a shell 1-1, a dryer cavity 1-2, a hollow shaft 1-3, a hollow disc 1-4, a feed port 1-5, a discharge port 1-6, a drive device 1-7, and an exhaust port 1-8; a jacket is provided inside the shell 1-1; the dryer cavity 1-2 is arranged inside the vacuum dryer 1, and is provided with a hollow shaft 1-3 and a hollow disc 1-4, and the hollow disc 1-4 is arranged on the hollow shaft 1-3; a drive device 1-7 is provided outside the horizontal vacuum dryer 1 and is connected to the hollow shaft 1-3, and the drive device 1-7 drives the hollow shaft 1-3 to rotate and drives the hollow disc 1-4 to rotate.

[0059] The water inlet connecting pipe of the horizontal vacuum dryer 1 is divided into two routes in front of the dryer, one route is connected to the hollow disc 1-4 through the hollow shaft 1-3, and the other route is connected to the water inlet of the jacket of the shell 1-1; the horizontal vacuum dryer 1 also has two water outlet connecting pipes, which are respectively connected to the water outlet end of the hollow shaft 1-3 of the dryer and the water outlet of the jacket of the shell 1-1.

[0060] The circulating water pump 8 is provided with a water pump inlet pipe and a water pump outlet pipe; the low-pressure heater group 9 is provided with a heater inlet pipe, a first-level heater outlet pipe and a second-level heater outlet pipe.

[0061] The flue gas waste heat utilization water circulation system and the vacuum drying system are connected via pipelines in the following manner: along the water flow direction, the water pump outlet pipeline of the circulating water pump 8 is connected to the water inlet connecting pipeline of the horizontal vacuum dryer 1.

[0062] A feed port 1-5 is provided at the upper end of the horizontal vacuum dryer 1, and a pipe at the feed port 1-5 is connected to a vacuum feeding device 13; a discharge port 1-6 is provided at the lower end of the horizontal vacuum dryer 1, and a pipe at the discharge port 1-6 is connected to a vacuum discharge device 14; two exhaust ports 1-8 are also provided at the upper end of the horizontal vacuum dryer 1, which are connected to the dust collector 5.

[0063] The vacuum drying system also includes a boiler 4 , the boiler 4 pipeline is connected to the flue gas waste heat absorber 3 , and an air preheater 2 is provided between the flue gas pipe section between the boiler 4 and the flue gas waste heat absorber 3 and the air inlet end pipeline of the boiler 4 .

[0064] The water outlet pipe of the horizontal vacuum dryer 1 is connected to a circulating water pump 8, which is connected to the pipe section between the total water outlet pipe of the low-pressure heater group 9 and the water inlet pipe of the flue gas waste heat absorber 3; the water outlet pipe of the flue gas waste heat absorber 3 is respectively connected to the return water pipe of the low-pressure heater group 9 and the water inlet pipe of the horizontal vacuum dryer 1;

[0065] The tail gas pipeline of the horizontal vacuum dryer 1 is connected to a vacuum condenser 6, and two dust collectors 5 are provided on the tail gas pipe section between the horizontal vacuum dryer 1 and the vacuum condenser 6; the lower end of the vacuum condenser 6 is connected to a vacuum drainage box 11, and the upper end of the vacuum condenser 6 is connected to a vacuum pump 7;

[0066] The vacuum pump 7 , the measuring instrument 10 and the flow regulating valve 15 are respectively connected to the data processing and control system 12 .

[0067] The flow control valve 15 includes a medium-temperature condensate control valve 15-1, a low-temperature condensate control valve 15-2, and a return low-temperature condensate control valve 15-3.

[0068] The low-pressure heater group 9 is provided with two water outlets, which are respectively connected to the medium-temperature condensate outlet pipe and the low-temperature condensate outlet pipe; the medium-temperature condensate outlet pipe and the low-temperature condensate outlet pipe merge to form the main water outlet pipe of the low-pressure heater group 9;

[0069] The medium-temperature condensate regulating valve 15-1 is arranged on the medium-temperature condensate outlet pipe; the low-temperature condensate regulating valve 15-2 is arranged on the low-temperature condensate outlet pipe; the return low-temperature heating condensate regulating valve 15-3 is arranged on the low-temperature heating return pipe; the medium-temperature condensate regulating valve 15-1 and the low-temperature condensate regulating valve 15-2 are used to adjust the water volume in the outlet pipe and thus control the water temperature; the return low-temperature heating condensate regulating valve 15-3 is used to adjust the flow distribution of hot water delivered to the horizontal vacuum dryer 1 and the return low-temperature heating system.

[0070] The horizontal vacuum dryer 1 is further provided with a vacuum dryer internal pressure sensor 10 - 4 for measuring the vacuum degree of the horizontal vacuum dryer 1 .

[0071] The working principle of this utility model is:

[0072] A vacuum drying system that utilizes the waste heat of low-temperature flue gas from a coal-fired boiler mainly includes a vacuum dryer, a wet tail gas treatment system, and a flue gas waste heat utilization water circulation system, as follows:

[0073] High-moisture materials (such as sludge) enter the dryer cavity 1-2 from the vacuum feeding system 13 through the dryer feed port 1-5. The driving device 1-7 drives the hollow shaft 1-3 to rotate, driving the hollow disc 1-4 on the shaft to rotate, while adhering the material to the surface of the hollow drying disc 1-4 in the cavity, and pushing the material to move toward the discharge port 1-6 at the other end.

[0074] Part of the hot water flowing into the dryer enters the hollow disc 1-4 from the hollow shaft 1-3 and exchanges heat with the material; part of the hot water flows into the jacket of the shell 1-1 to heat the material.

[0075] The flue gas waste heat water circulation system used to provide drying heat includes a circulating water pump 8, a low-pressure heater unit 9, a flue gas waste heat absorber 3, and associated piping and valves. First, condensate water, both medium-temperature (e.g., after 9-3) and low-temperature (e.g., before 9-2), is drawn from the unit's low-pressure heating system. This water is then combined with the cold circulating water from the vacuum dryer after heat exchange. The water flow is adjusted to meet the required water temperature by regulating valves 15-1 and 15-2. After being pressurized by circulating water pump 8, it enters the flue gas waste heat absorber 3, absorbing the flue gas heat. Part of the heated hot water returns to the low-pressure heating system (e.g., before 9-4), while the remaining portion is sent to the vacuum dryer 1 for material drying. The hot water flow to the dryer is regulated by the operating frequency of circulating water pump 8 and the opening of regulating valve 15-3 to meet drying requirements.

[0076] The 90℃~105℃ hot water generated by the flue gas waste heat absorber can use the vacuum system to reduce the evaporation temperature of the material to 45℃~75℃ (corresponding to the pressure of -0.09MPa to -0.06MPa). Therefore, a large heat transfer temperature difference is achieved between the hot water and the wet material, providing power for the drying of the wet material.

[0077] The wet exhaust gas treatment system mainly includes a dust collector 5, a vacuum condenser 6, a vacuum drainage box 11, and a vacuum pump 7. The exhaust gas after drying in the vacuum dryer is mainly composed of dust, water vapor, and a small amount of non-condensable gases. After the exhaust gas is discharged from the exhaust ports 1-8, it first passes through the dust collector 5 for dust removal. The dust collector 5 is directly connected to the dryer, and the separated dust falls directly back into the dryer. Generally, two outlets and two dust collectors are used for switching, which is convenient for ensuring the pressure inside the dryer when the dust collector is cleaned. The exhausted exhaust gas then passes through the condenser 6 to condense and remove water vapor. The latent heat of water vapor released by condensation is discharged or further recycled. Finally, the remaining non-condensable gases and water vapor are discharged by the vacuum pump 7. The vacuum pump provides a vacuum environment for the dryer to achieve vacuum drying and efficient condensation of the exhaust gas. The vacuum drainage box 11 switches the valve according to the water level in the box to discharge the exhaust condensate without affecting the vacuum in the condenser.

[0078] This system's process control: Under conditions of stable wet material moisture and a constant processing volume, when the boiler load decreases, the flue gas temperature decreases accordingly, and the drying output decreases, directly reflected in the slower change in the water level in the vacuum drain tank. At this point, the hot water flow to the dryer is first increased. If the amount of condensed water produced by drying still does not meet the requirements (i.e., the drying output is still insufficient), the variable frequency vacuum pump 7 adjusts the dryer's vacuum level (10-4), increasing the heat transfer temperature difference and thereby improving the drying output. This is achieved through relevant measuring instruments 10, control equipment (15 and 7), and data processing and control system 12.

[0079] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the description and drawings of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A vacuum drying system utilizing waste heat from low-temperature flue gas of a coal-fired boiler, characterized in that: Including flue gas waste heat utilization water circulation system, wet tail gas treatment system and vacuum drying system; The flue gas waste heat utilization water circulation system comprises: a low-pressure heater group (9), a circulating water pump (8) and a flue gas waste heat absorber (3) are sequentially connected along the water flow direction; the water flow is a cold water flow composed of condensed water of the low-pressure heater group (9) and cold circulating water after heat exchange in the horizontal vacuum dryer (1); the cold water flow is pressurized by the circulating water pump (8) and enters the flue gas waste heat absorber (3) as a heat exchange medium to absorb heat, and then enters the low-pressure heater group (9) and the horizontal vacuum dryer (1) respectively; The wet tail gas treatment system comprises: a dust collector (5) and a vacuum condenser (6) are sequentially connected along the direction of the flue gas, and then respectively connected to a vacuum pump (7) and a vacuum drainage box (11); the flue gas is dust, water vapor and non-condensable gas; The vacuum drying system comprises: a vacuum feeding device (13), a horizontal vacuum dryer (1) and a vacuum discharging device (14) which are sequentially connected along the material entry direction; the material is sludge.

2. The vacuum drying system utilizing waste heat from low-temperature flue gas of a coal-fired boiler according to claim 1, characterized in that: The horizontal vacuum dryer (1) comprises a housing (1-1), a dryer inner cavity (1-2), a hollow shaft (1-3), a hollow disc (1-4), a feed port (1-5), a discharge port (1-6), a driving device (1-7), and an exhaust port (1-8); A jacket is provided inside the shell (1-1); a dryer inner cavity (1-2) is provided inside the horizontal vacuum dryer (1), and a hollow shaft (1-3) and a hollow disc (1-4) are provided in the dryer inner cavity (1-2), and the hollow disc (1-4) is arranged on the hollow shaft (1-3); a driving device (1-7) is provided outside the horizontal vacuum dryer (1) and is connected to the hollow shaft (1-3); the driving device (1-7) drives the hollow shaft (1-3) to rotate and drives the hollow disc (1-4) to rotate.

3. The vacuum drying system utilizing waste heat from low-temperature flue gas of a coal-fired boiler according to claim 2, characterized in that: The water inlet connecting pipe of the horizontal vacuum dryer (1) is divided into two routes in front of the dryer, one route is connected to the hollow disc (1-4) through the hollow shaft (1-3), and the other route is connected to the water inlet of the jacket of the shell (1-1); the water outlet connecting pipe of the horizontal vacuum dryer (1) is also divided into two routes, which are respectively connected to the water outlet end of the hollow shaft (1-3) of the dryer and the water outlet of the jacket of the shell (1-1).

4. The vacuum drying system utilizing waste heat from low-temperature flue gas of a coal-fired boiler according to claim 1, characterized in that: The circulating water pump (8) is provided with a water pump inlet pipe and a water pump outlet pipe; the low-pressure heater group (9) is provided with a heater inlet pipe, a first-stage heater outlet pipe and a second-stage heater outlet pipe.

5. The vacuum drying system utilizing waste heat from low-temperature flue gas of a coal-fired boiler according to claim 1, characterized in that: The flue gas waste heat utilization water circulation system is connected to the vacuum drying system via a pipeline in the following manner: along the direction of water flow, the water pump outlet pipeline of the circulating water pump (8) is connected to the water inlet connection pipeline of the horizontal vacuum dryer (1).

6. The vacuum drying system utilizing waste heat from low-temperature flue gas of a coal-fired boiler according to claim 2, characterized in that: The upper end of the horizontal vacuum dryer (1) is provided with a feed port (1-5), and a pipeline at the feed port (1-5) is connected to a vacuum feed device (13); the lower end of the horizontal vacuum dryer (1) is provided with a discharge port (1-6), and a pipeline at the discharge port (1-6) is connected to a vacuum discharge device (14); the upper end of the horizontal vacuum dryer (1) is also provided with two exhaust ports (1-8), which are connected to a dust collector (5).

7. The vacuum drying system utilizing waste heat from low-temperature flue gas of a coal-fired boiler according to claim 1, characterized in that: It also includes a boiler (4), wherein the boiler (4) pipeline is connected to a flue gas waste heat absorber (3), and an air preheater (2) is provided between the flue gas pipe section between the boiler (4) and the flue gas waste heat absorber (3) and the air inlet end pipeline of the boiler (4).

8. The vacuum drying system utilizing waste heat from low-temperature flue gas of a coal-fired boiler according to claim 1, characterized in that: The water outlet pipe of the horizontal vacuum dryer (1) is connected to a circulating water pump (8), and the circulating water pump (8) is connected to the pipe section between the total water outlet pipe of the low-pressure heater group (9) and the water inlet pipe of the flue gas waste heat absorber (3); the water outlet pipe of the flue gas waste heat absorber (3) is respectively connected to the return water pipe of the low-pressure heater group (9) and the water inlet pipe of the horizontal vacuum dryer (1); The tail gas pipeline of the horizontal vacuum dryer (1) is connected to a vacuum condenser (6), and two dust collectors (5) are provided on the tail gas pipe section between the horizontal vacuum dryer (1) and the vacuum condenser (6); the lower end of the vacuum condenser (6) is connected to a vacuum drainage box (11), and the upper end of the vacuum condenser (6) is connected to a vacuum pump (7); The vacuum pump (7), measuring instrument (10) and flow regulating valve (15) are respectively connected to a data processing and control system (12).

9. The vacuum drying system utilizing waste heat from low-temperature flue gas of a coal-fired boiler according to claim 8, characterized in that: The flow regulating valve (15) comprises a medium-temperature condensate regulating valve (15-1), a low-temperature condensate regulating valve (15-2) and a return low-temperature condensate regulating valve (15-3); The low-pressure heater group (9) is provided with two water outlet ends, which are respectively connected to the medium-temperature condensate outlet pipe and the low-temperature condensate outlet pipe; the medium-temperature condensate outlet pipe and the low-temperature condensate outlet pipe are combined to form the main water outlet pipe of the low-pressure heater group (9); The medium-temperature condensate regulating valve (15-1) is arranged on the medium-temperature condensate outlet pipe; the low-temperature condensate regulating valve (15-2) is arranged on the low-temperature condensate outlet pipe; the return low-temperature heating condensate regulating valve (15-3) is arranged on the low-temperature heating return pipe; the medium-temperature condensate regulating valve (15-1) and the low-temperature condensate regulating valve (15-2) are used to regulate the water volume in the outlet pipe and thus control the water temperature; the return low-temperature heating condensate regulating valve (15-3) is used to regulate the flow distribution of hot water delivered to the horizontal vacuum dryer (1) and the return low-temperature heating system.

10. The vacuum drying system utilizing waste heat from low-temperature flue gas of a coal-fired boiler according to claim 1, characterized in that: The horizontal vacuum dryer (1) is further provided with a vacuum dryer internal pressure sensor (10-4) for measuring the vacuum degree of the horizontal vacuum dryer (1).

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