CN111908764A - Mechanical vapor recompression drying system and method - Google Patents

Abstract

The invention discloses a mechanical vapor recompression drying system and method, comprising a sludge storage tank, a sludge injection pump, a thin-layer evaporation dryer, an extrusion slitting machine, a mesh belt dryer, a dry mud silo, a steam A compressor, a cyclone, a water scrubber, a condensate buffer tank, and a vacuum pump connected to the condensate buffer tank and used to suck system air to maintain a vacuum and discharge non-condensable gases. The invention can save a lot of energy consumption and cooling water system consumption. There is no exhaust gas emission in the process, and the system has no cooling water system, which saves the evaporation loss of cooling tower water.

Description

Mechanical vapor recompression drying system and method

technical field

The invention relates to the technical field of sludge drying, in particular to a mechanical vapor recompression drying system and method.

Background technique

Mechanical vapor recompression (Mechanical Vapor Recom-pression) system, referred to as MVR system, is a new type of high-efficiency and energy-saving system. Compared with the multi-effect evaporation technology, the MVR system fully recovers the latent heat of the secondary steam, and the thermal efficiency is generally equivalent to a 5-10-effect evaporator.

In industrial fields such as drying and evaporative concentration, a large amount of water vapor is generated. Most of the energy carried by water vapor is latent heat, and sensible heat is only a small part. The mechanical vapor recompression system effectively recovers the latent heat of water vapor, thereby achieving the purpose of saving energy and reducing consumption. Its working principle is that the temperature, pressure and enthalpy value of the steam generated by the evaporator are increased after being acted by the mechanical steam compressor, and the steam is returned to the evaporator as a heating heat source to supplement the heat energy that needs to be absorbed by the liquid evaporation and maintain the evaporation temperature. The system itself can basically achieve thermal balance, and the fresh steam is only used to supplement the heat loss of the system and the enthalpy of incoming and outgoing materials, thereby greatly reducing the consumption of external fresh steam by the evaporator and achieving the purpose of reducing energy consumption. The application of MVR in the field of solid drying is less, the small heat transfer temperature difference, the long drying time, the large energy consumption of mechanical transmission, the need for sealing the system, and the need for high-performance compressors are all restricting factors for its application.

Common solid steam drying technologies mostly use indirect conduction heat transfer or direct convection heat transfer. Indirect conduction heat transfer is common in hollow blade dryers, rotary disk dryers, rotary drum dryers, sandwich wall dryers, etc. Direct convection heat transfer is common in superheated steam drying and hot air drying. They all require large temperature differences and mechanical agitation or forced convection to enhance heat exchange.

The research shows that the water in the solid is mainly free water, interstitial water, surface water and chemically bound water. According to the evaporation and drying process of these moisture, the evaporation rate is divided into "constant speed section", "speed reduction section" and "final stage". Generally, when the moisture content of the sludge is lower than about 65%, the "constant speed section" ends and enters the more difficult and more energy-consuming "speed reduction section" for drying and evaporation.

Zhou Lei, Nanjing University of Aeronautics and Astronautics, "Design and Energy-Saving Analysis of Low-Temperature Drying System Based on Vapor Recompression Technology" shows that in the low-temperature drying process, theoretically, the energy consumption of the system decreases with the decrease of the evaporation temperature and the compressor pressure ratio; with the same conditions Compared with the conventional low-temperature drying system under low temperature, the energy consumption of the low-temperature drying system based on vapor recompression technology is only 7.7% of that of the conventional low-temperature regenerative drying system. The application of MVR technology is based on the principle of energy saving and the limitation of existing technology, which requires low pressure ratio compression and small temperature difference heat exchange, which leads to long drying time, high energy consumption of mechanical stirring and transmission to strengthen heat exchange, and reduces the energy saving effect of MVR. At the same time, the excessively high evaporation temperature leads to more heat loss of the system, and the supplementary heat to the system is increased to balance the heat of the system, resulting in a further reduction of the energy saving effect. At the same time, the current market application of screw steam compressors that can achieve high pressure ratio is not common, which is also one of the reasons for the difficulty in the application of MVR drying and energy saving. In order to ensure the drying effect, it is necessary to control a certain drying speed. The combination of MVR technology and vacuum low-temperature drying technology is the development direction of MVR drying, but after entering the "speed reduction section", the evaporation rate is still unsatisfactory.

Superheated steam drying refers to a new drying method that uses superheated steam to directly contact the material to be dried to remove its internal moisture. At the same temperature, compared with hot air, superheated steam has latent heat, so the heat per unit mass of superheated steam is much greater than that of hot air, and when superheated steam is used to dry solids, because the surface of the solid is water evaporated to superheated Steam, there is no diffusion resistance. The speed of superheated steam drying and the temperature of the superheated steam are also related. The research and experiment of "Superheated Steam and Vacuum Combined Drying of Potatoes" by Lu Ye of Fujian Agriculture and Forestry University shows that low-temperature superheated steam can also achieve an ideal drying speed in the drying process of potatoes.

During the drying process, the pollutants will enter the condensed water of the secondary steam with the evaporation process. "Research on the Characteristics of Urban Sludge Superheated Steam Drying Condensate" by Guan Yong of Nanchang Aviation University and "Study on the Migration of Contaminants in the Distillation and Compression Process of High-Salt Organic Wastewater" by Hong Yongqiang of Shandong University show that the main pollutants entering the secondary steam condensate by low temperature evaporation are mainly It is organic alcohol and ammonia, etc., and the content of inorganic salts is extremely low. In the high-temperature evaporation process, the pollutant composition is complex and the amount of pollution is more. The traditional high-temperature sludge evaporates, and the condensed water needs to enter the sewage treatment plant again before it can be discharged or reused up to the standard.

In order to solve the above problems, the following patents "CN103011546B", "CN107098562A", "CN106495427A", "CN103708697B", "CN103588375B", "CN103285637B", "CN105254147B", "CN110040935A" adopted corresponding technical means:

1) "A two-stage sludge drying and energy recovery system and its drying process", which adopts a two-stage drying process of partition type drying equipment and belt dryer. The heat of the belt dryer is recovered from the secondary steam of the sludge in the partition heat exchanger, which is equivalent to the "two-effect evaporation" of water, thereby realizing energy saving.

2) "New-type thermal energy cascade reuse system for two-stage sludge drying process", the system includes a thin-layer evaporator and a belt dryer in two-stage drying process. The heat input of the system comes from the high temperature steam of the thermal power plant. The primary steam condensed water in the thin-layer evaporator of the first stage is flashed into low-temperature and low-pressure steam through the flash tank, which is used for the reheating of the hot air of the second stage, so as to reduce the supplementary amount of fresh steam and save both steam and cooling water. the goal of.

3) "MVR superheated steam sludge continuous drying system and working method", the system uses superheated steam as the drying medium, and the secondary steam generated in the drying process is divided into two paths: a small part of the steam is compressed by the compressor into high-pressure superheated steam It enters the hot end of the heat exchanger, and then enters the condensed water tank after heat exchange and condensation; the other way, most of the water vapor enters the cold end of the heat exchanger, and is sent back to the dryer after being heated. The drying system mainly adopts the compression method to recover the sensible heat and latent heat of the secondary steam generated in the drying process.

4) "Mechanical vapor recompression heat pump MVR sludge drying system", the secondary steam generated after the sludge is dried by the hollow paddle dryer, the secondary steam is compressed by the compressor and then returned to the hollow paddle body Inside, all the latent heat of the secondary steam generated during the sludge drying process is recovered.

5) "A sludge MVC evaporation drying system and method for drying sludge", the secondary steam in the sludge evaporation process passes through the steam compressor and enters the drying device as a steam supplementary heat source, using high temperature condensed water Washing purification steam.

6) "Low-temperature vacuum dehydration and drying equipment and its process", the vacuum system evacuates the heated material chamber, and the evaporated water vapor in the chamber is condensed into liquid water in the heat exchanger and discharged to achieve the purpose of low-temperature evaporation.

7) "Triple utilization of waste heat of waste steam drying with superheated steam of sludge", at the same time recovery of sensible heat and latent heat of spent steam, recycling of waste water, and zero pollution discharge of waste gas. The whole device realizes the three-time utilization of the waste heat of the waste steam from the superheated steam drying of the sludge. In the drying process, the sensible heat and latent heat of the exhausted steam are recovered at the same time to prevent condensation during the drying process and shorten the drying time; in the drying process, only superheated steam needs to be introduced in the initial stage, and the steam is recycled in the later stage, which reduces the input of heat source and reduces the energy consumption.

8) "A multi-layer combined self-falling sludge drying device and drying method" uses indirect drying combined with superheated secondary steam to dry sludge, and uses MVR evaporation technology to effectively shorten the drying time.

Although the above technical patents or related research have solved the application method of solid drying energy saving or MVR technology in the field of drying, there are many problems existing in the implementation process, and some problems have not been effectively solved. For example, "CN103011546B", "CN107098562A" two-stage sludge drying process heat energy recovery and utilization process, equivalent to "two-effect evaporation" energy-saving effect. The drying process uses high temperature steam as the energy source, and the energy consumption is still higher than that of the MVR technology. "CN106495427A" MVR superheated steam sludge continuous drying system and working method, the sensible heat and latent heat of secondary steam are used for the preheating of feed sludge. Based on the material quality and heat balance, the latent heat of the secondary steam is much larger than the preheating heat of the sludge, which reduces the heat recovery ratio. "CN103708697B" and "CN103588375B" use MVR evaporation technology to dry sludge through hollow paddle type or other indirect heat conduction drying devices. In practice, a large amount of heat needs to be added to the system. At the same time, after the sludge enters the "speed reduction section" Evaporation time is too long, mechanical transmission or stirring enhances heat transfer and heat loss, resulting in a decrease in energy-saving benefits. "CN103285637B" low temperature vacuum dehydration and drying complete equipment and its process and "CN105254147B" a kind of sludge superheated steam drying waste steam waste heat triple utilization, energy consumption also comes from low temperature (80 ℃-90 ℃) heat source or steam, energy consumption Compared with MVR technology, it is still higher. "CN110040935A" is a multi-layer combined self-falling sludge drying device and drying method. The system supplements heat to directly heat the compressed secondary steam, and a part of the secondary steam directly enters the drying chamber as superheated steam to exchange heat with the sludge by convection. , a part of the secondary steam enters the inner cavity of the indirect dryer and conducts heat exchange with the sludge. Compared with saturated steam, the heat transfer effect of the superheated steam in the inner cavity of the indirect dryer is not ideal in theory. At the same time, the supplementary heat to the system does not recover more sensible heat after the secondary steam becomes condensed water.

In summary, it is necessary to propose a new mechanical vapor recompression drying system and method.

SUMMARY OF THE INVENTION

In view of this, the present invention proposes a mechanical vapor recompression drying system and method with simple operation, reliable performance, low manufacturing cost, convenient disassembly and maintenance, fast drying continuous speed, small supplementary heat, and low system energy consumption.

According to the purpose of the present invention, the present invention provides a first technical solution: a mechanical vapor recompression drying system, which includes a sludge storage tank for storing incoming sludge at room temperature and having a condensed water heat exchange coil inside, and a sludge storage tank. The sludge injection pump connected to the output of the pool and provided with a jacket heat exchanger, the thin-layer evaporation dryer connected to the output of the sludge injection pump, the extrusion slitting machine connected to the output of the thin-layer evaporation dryer, and the extrusion A mesh belt dryer connected to the output of the slitting and forming machine, a dry mud silo connected to the output of the mesh belt dryer, a steam compressor arranged between the thin-layer evaporative dryer and the mesh belt dryer, connected to the mesh belt dryer and a cyclone dust collector for separating secondary steam and sludge dust, a water washing dust collector connected to the output of the cyclone dust collector and used for washing and cleaning the secondary steam, and a condensed water connected to the thin-layer evaporative dryer and collecting the condensed water A buffer tank, and a vacuum pump connected to the condensate buffer tank and used to suck system air to maintain vacuum and discharge non-condensable gas.

On the basis of the first technical solution, the following subsidiary technical solutions are further included:

The thin-layer evaporative dryer comprises at least one cylindrical heating bin, a scraper rotor located inside the cylindrical heating bin and a plurality of scrapers evenly distributed on the surface, a motor located outside the cylindrical heating bin and driving the scraper rotor to rotate, and The steam inlet connected to the output of the water washing dust collector, the steam and condensed water outlet connected to the input of the condensate buffer tank, the sludge inlet connected to the output of the sludge injection pump, and the sewage outlet connected to the input of the extrusion slitting machine. Mud export.

The mesh belt dryer is a closed structure with a steam circulating fan and a heater inside.

The water-washing dust collector includes a condensed water spray head, a demister located above the condensed water spray head, a dosing device connected to the condensed water spray head, a first circulating pump connected to the condensed water spray head, and Sewage pumps that return sludge to sludge storage tanks.

It also includes a granulator for extruding and granulating the dry mud in the dry mud silo, a second circulating pump located between the sludge injection pump and the water washing dust collector, and a sludge storage tank connected with an electrochemical device. Condensation sump of the oxidizing descaler.

It also includes a first filter disposed between the thin-layer evaporative dryer and the vapor compressor, and a second filter disposed between the thin-layer evaporative dryer and the water scrubber.

The present invention provides a second technical solution: a mechanical vapor recompression drying method, comprising:

S1: The wet sludge is transferred from the sludge storage tank to the thin-layer evaporative dryer through the transmission device. During the process, the wet sludge and condensed water are exchanged in the heat exchanger, and heated from 5-35 °C at the inlet to 65-80 °C ; The condensed water is cooled from 80-98 ℃ at the inlet to 15-45 ℃ at the outlet;

S2: The preheated sludge forms a thin layer in the thin-layer evaporative dryer under the action of the rotating scraper blade and adheres to the inner surface of the evaporative dryer cylinder. There is a negative pressure system in the cylinder, and the pressure is set to 25-47.5 KPa, the corresponding water evaporation temperature is 65-80 °C; the heat source for heat exchange between the sludge and the cylinder wall comes from the steam in step S4, the heat exchange temperature difference is 18-33 °C, and the sludge moisture content is 80%-95% reduced to 55%-65%;

S3: extrude the sludge with a moisture content of 55%-65% into sticky strips with a width of 2-5mm and then enter the mesh belt dryer;

S4: During the transmission process of the mesh belt, the sludge entering the mesh belt dryer exchanges heat with the superheated steam, and then enters the dry sludge bin after further evaporation and drying, and is extruded and granulated by the granulator. The drying rate is further evaporated from 55%-65% to sludge with a moisture content of 20%-45% to complete the drying process in the mesh belt dryer; after the saturated steam from the compressor outlet enters the mesh belt dryer, it is heated by a heater to lift After the temperature is 20-50°C, the circulating fan is forced to circulate and exchange heat with the sludge convection; the excess superheated steam enters the cyclone separation, washing and dedusting and filtering to become clean saturated steam and then enters step S2 again;

S5: After the secondary steam generated by the evaporation process in step S2 is filtered by the filter, it enters the steam compressor for compression and then enters step S4, and the condensed water from the condensed water buffer tank is sprayed into the suction inlet of the steam compressor, and the compression ratio is 2.0 -4.5, steam temperature rise 18-33℃;

S6: a part of the condensed water enters step S5 to reduce the superheat degree of the compressor exhaust; a part enters the water washing dust collector in step S4, and is discharged into the sludge tank; the remaining part of the condensed water passes through the heat exchanger in step S1 after heat exchange Enter the condensed water tank, remove trace organic matter through electrochemical oxidation descaling instrument, and then discharge or reuse;

S7: The non-condensable gas in the condensed water buffer tank and the condensed water tank is removed by the vacuum pump to the end.

Compared with the prior art, the technical scheme of the present invention has the following advantages:

Using MVR technology in the field of solid drying can save a lot of energy consumption and cooling water system consumption compared to the traditional heating and evaporation technology using heat sources. There is no exhaust gas emission in the process, and the system has no cooling water system, which saves the evaporation loss of cooling tower water. The secondary steam condensed water that uses low temperature evaporation has low pollutants, and its main component is volatile organic compounds. After low-cost treatment by "electrochemical oxidation" and other methods, the condensed water can be directly discharged up to the standard. The secondary steam condensate water evaporated at high temperature often needs to be re-entered into the sewage treatment plant for treatment.

In the process of "low temperature vacuum evaporation", the inlet temperature and evaporation temperature of the material are small, which reduces the preheating heat of the material; in the process of "low temperature superheated steam evaporation", the outlet temperature of the material is relatively low and the moisture content is low, which reduces the heat of the material at the outlet The temperature difference between the overall operating temperature of the system and the ambient temperature is low, which also reduces the heat loss of the system.

During the whole evaporation process, only for the sludge with high viscosity and low evaporation rate (water content below 55%-65%), the "superheated steam evaporation" method with relatively large temperature and heat exchange temperature difference is adopted for convective heat transfer. While shortening the overall drying time, it is beneficial to heat recovery and the supplementary heat is also small. The cost of supplementary heat in this system has nothing to do with the energy grade, but is related to the quantity. The supplementary heat is mainly used to heat the secondary steam to increase the sensible heat of the secondary steam. When superheated steam and sludge are convectively exchanged, the heat exchange temperature difference is high and the heat exchange effect is good.

Without affecting the continuous evaporation rate, by properly adjusting the parameters of the "superheated steam" evaporation stage, sludge particles of different dryness can be produced, and the drying range is 70%-95%.

All the latent heat of evaporation of the water with the largest heat consumption can be recycled, and all or most of the heat of the high-temperature condensate can be recycled.

The temperature of the secondary steam of the system can reach 120℃-150℃, but the pressure is lower than 0.1MPa, and the system pipelines and vessels are not "pressure vessels", which can effectively reduce the cost of production, use and maintenance. The gas in direct contact with the sludge is secondary steam, and there is no air pollution emission. In a low-oxygen environment, there is no danger of combustion and dust explosion, and the safety is better.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

FIG. 1 is a schematic structural diagram of the present invention.

Detailed ways

As shown in FIG. 1 , the present invention provides a first embodiment of a mechanical vapor recompression drying system, which includes a sludge storage tank 110 that stores incoming sludge at room temperature and has a condensed water heat exchange coil 111 inside, and a sludge storage tank 110 . The output of the pool 110 is connected and is provided with a jacket heat exchanger 121, a sludge injection pump 120 of the first external heat source heater 122, a thin layer evaporation dryer 130 connected to the output of the sludge injection pump 120, and a thin layer evaporation dryer 130. The extrusion slitting machine 140 connected to the output of the device 130, the mesh belt dryer 150 connected to the output of the extrusion slitting machine 140, the dry mud bin 160 connected to the output of the mesh belt dryer 150, and the The steam compressor 220 between the dryer 130 and the mesh belt dryer 150, the cyclone dust collector 230 connected to the mesh belt dryer 150 and used to separate secondary steam and sludge dust, and the output of the cyclone dust collector 230 connected to the The water washing dust collector 240 for cleaning the secondary steam water, the condensed water buffer tank 310 connected to the thin layer evaporative dryer 130 and collecting the condensed water, and the condensed water buffer tank 310 connected to the suction system air for maintaining vacuum and discharging Vacuum pump 400 for non-condensable gas.

The sludge storage tank 110 stores incoming sludge at room temperature. There is a condensed water heat exchange coil 111 on the inner wall of the sludge storage tank. The condensed water heat exchange coil 111 contains condensed water, and the condensed water and the sludge are discharged to the condensed water tank 320 after heat exchange. The sludge injection pump 120 provides power to transport the sludge in the sludge storage tank 110 to the sludge inlet of the thin-layer evaporator 130, and the pressure of the internal solid extrusion can ensure the sludge storage tank 110 and the thin-layer evaporator 130. The cavity is closed without gas. A jacket-type heat exchanger 121 is provided outside the sludge conveying pipeline, and the inside of the jacket-type heat exchanger 121 is condensed water, which is discharged into the sludge storage tank 110 after heat exchange between the condensed water and the sludge. The external heat source heater 122 provides heat for the system to supplement heat to heat the sludge to raise the temperature.

The thin-layer evaporative dryer 130 includes at least one cylindrical cylindrical heating chamber and a built-in scraper rotor. One end of the cylindrical heating bin is provided with a motor, and the scraper rotor is driven by the motor. Scraper blades are evenly distributed on the surface of the scraper rotor. The scraper blade pushes the sludge from one end of the thin-layer evaporative dryer 130 to the other end, and makes the sludge evenly spread over the inner cylindrical wall of the entire cylindrical heating chamber. One end of the cylindrical heating bin is provided with a steam inlet 131, and the other end of the cylindrical heating bin is provided with a steam and condensed water outlet 132. The other end of the cylindrical heating bin is provided with a sludge feeding port 133, and one end of the cylindrical heating bin is provided with a sludge outlet 134. Further, the cylindrical heating chamber is a partition structure, and steam can be circulated inside. An insulating layer is added on the outer surface of the cylindrical heating bin, and the inner surface of the cylindrical heating bin is coaxial with the scraper rotor.

The extrusion slitting machine 140 is a sludge extrusion equipment with a mesh of holes. The sludge from the sludge outlet 134 in the thin-layer evaporator 130 is extruded and chopped into "stripes" under the action of the extrusion slitting machine 140 and then scattered on the conveyor belt of the mesh belt dryer 150 superior. The solid pushing force in the extrusion slitting machine 140 can ensure that the cavities of the thin-layer evaporator 130 and the mesh belt dryer 150 are sealed without air. The mesh belt dryer 150 is a closed structure, with a circulating fan 151 with steam inside and a second external heat source heater 152 . Further, the circulating fan 151 of the mesh belt dryer 150 is located in the jacket heat exchanger 121 . The external heat source heaters 152 and 122 preferably have a heat source of electric heating, a high-temperature heat pump, or high-temperature steam directly introduced from the outside. Further, the mesh belt dryer 150 transports the circulating heated superheated steam to the steam compressor 220 for compression to form water vapor with temperature and pressure, which is the secondary steam from the evaporation of the sludge in the thin-layer evaporator 130 . The superheated steam is forced to circulate under the action of the circulating fan 151, and convectively exchanges heat with the sludge on the mesh belt to dry the sludge moisture. The dry sludge bin 160 is used to store the dry sludge produced by the mesh belt dryer 150 and the cyclone dust collector 230 . The granulator 161 extrudes and granulates the dry mud in the dry mud bin 160 before discharging. The solid pushing and extruding force in the granulator 161 can ensure that the granulator 161 and the external atmospheric environment are sealed without air. The first and second filters 210 and 250 are high-efficiency air filters for filtering fine dust in the gas. The steam compressor 220 is a steam compressor, preferably a twin-screw steam compressor, with a compression ratio of 2.0-4.5. The high temperature condensate water from the condensate water buffer tank 310 is injected into the inlet of the steam compressor 220 to reduce the superheat degree of the exhaust gas. The cyclone 230 is used to separate secondary steam and sludge dust from the chamber of the mesh belt dryer 150 . The secondary steam enters the water washing dust collector 240 , and the sludge dust enters the dry sludge bin 160 . The water washing dust collector 240 is used to wash and clean the secondary steam and reduce its superheat. The system replenishment water of the water-washing dust collector 240 comes from the high-temperature condensed water of the condensed water buffer tank 310 . Under the action of the circulating pump 244 , the secondary steam for washing is sprayed by the upper condensed water spray head 241 of the washing dust collector 240 . The dosing device 243 adds organic acid to the circulating water for cleaning and removing free ammonia in the secondary steam. There is a sewage outlet at the bottom of the water-washing dust remover 240 , which is returned to the sludge storage tank 110 through the sewage pump 245 . The demister 242 is used to separate the gas and water of the secondary steam after water washing, and the secondary steam enters the second filter 250 after dust removal and ammonia removal. The clean and saturated secondary steam is returned to the steam jacket of the thin layer evaporator 130 . The condensed water buffer tank 310 is used to store the condensed water of the thin-layer evaporator 130 . The upper part of the condensed water buffer tank 310 is gas, and the lower part is liquid water. The condensation water tank 320 is a water storage tank with a closed structure, the upper part is gas, and the lower part is liquid water. Further, there is an electrochemical oxidation descaling instrument 321 in the condensed water pool 320, which is used to reduce volatile organic compounds in the condensed water, reduce the COD of the condensed water, and discharge or reuse the condensed water. The vacuum pump 400 is used to suck system air to maintain vacuum and to remove non-condensable gas during operation. The regenerable activated carbon filter 410 is used for deodorizing and filtering a small amount of exhaust gas from the vacuum pump 400 .

This embodiment also provides an MVR low-temperature vacuum combined superheated steam drying method, which utilizes the above-mentioned related structures and devices to perform drying work, and specifically includes the following steps:

S1: The wet sludge is transported from the sludge storage tank 110 to the thin layer evaporative dryer 130 through the sludge injection pump 120 of the transport device. During the process, the wet sludge and the condensed water exchange heat in the jacket heat exchanger 121 , which is heated to 65-80° C. from 5-35° C. at the inlet, and the insufficient heat is supplemented by the first external heat source heater 122 . The condensed water is cooled from 80-98°C at the inlet to 25-55°C at the outlet, and then enters the heat exchange coil 111, and is cooled to 15-45°C and then discharged into the condensed water tank 320;

S2: The preheated sludge forms a thin layer and adheres to the inner surface of the evaporator cylinder under the action of the rotating scraper blade in the thin-layer evaporation dryer 130. There is a negative pressure system in the cylinder, the pressure is set to 25-47.5KPa, and the corresponding water evaporation temperature is 65-80℃. The sludge and the cylinder wall conduct heat exchange, the cylinder jacket is filled with saturated steam from step S4, and the preferred heat exchange temperature difference is set to 18-33°C. The sludge starts to evaporate in the vacuum negative pressure environment, and is moved on the cylinder wall by the rotation of the scraper blade and is enriched at the sludge outlet 134; the sludge in the thin-layer evaporator 130 is a "vacuum low temperature drying" process When the moisture content of the sludge is reduced from 80%-95% to 55%-65%, the drying process in the thin-layer evaporator 130 is completed; the saturated steam in the jacket of the thin-layer evaporator 130 becomes liquid condensed water after heat exchange and enters the condensation Water buffer tank 310;

S3: The extrusion slitting forming machine 140 extrudes and slits the sludge with a moisture content of 55%-65% at the sludge outlet 134 into viscous sticky sludge with a diameter of 2-5mm, and then enters the mesh belt dryer 150;

S4: The sludge entering the mesh belt dryer 150 exchanges heat with the superheated steam during the conveying process of the mesh belt. After further evaporation and drying, the sludge enters the dry sludge bin 160, and is extruded and granulated by the granulator 161 before discharging. The sludge in the mesh belt dryer 150 is a process of "superheated steam drying", the moisture content of the sludge is further evaporated from 55%-65% to the sludge with a moisture content of 20%-45%, and the drying process in the mesh belt dryer 150 is completed. . After the saturated steam at the outlet of the compressor 220 enters the mesh belt dryer 150, it is heated by the heater 152 to raise the superheat to 20-50°C, and then is forcedly circulated by the circulating fan 151 to exchange heat with the sludge by convection. The rich superheated steam enters the cyclone separator 230, the water washing dust collector 240, and the filter 250 to become clean saturated steam and enters step S2 again;

S5: After the secondary steam generated in the evaporation process in step S2 is filtered by the filter 210, it enters the compressor 220 for compression, and then proceeds to step S4. The condensed water from the condensed water buffer tank 310 is injected into the suction inlet of the steam compressor 220 to reduce the compressor rotor temperature and the outlet steam superheat. The preferred compression ratio is 2.0-4.5, and the steam temperature rise is 18-33°C;

S6: The temperature of the condensed water in the condensed water buffer tank 310 is 80-98°C. A part enters step S5 to reduce the superheat degree of the compressor exhaust gas; a part enters the water washing dust collector 240 in step S4, and then is discharged into the sludge tank 110; most of the condensed water is exchanged through the heat exchangers 121 and 111 in step S1 After being heated, it enters the condensed water tank 320, and is discharged or reused after removing trace organic matter by the electrochemical oxidation descaling instrument 321;

S7: The vacuum pump 400 removes the non-condensable gas in the condensed water buffer tank 310 and the condensed water tank 320 to ensure the vacuum degree and evaporation pressure of the system; a small amount of non-condensable gas is deodorized through the renewable activated carbon filter 410 and then discharged.

Advantages of the present invention:

Based on the characteristics of the drying process, combined with the optimal energy saving of MVR technology in the field of water evaporation, the "constant speed section" drying process of "low temperature vacuum evaporation" is used to dry the sludge, and the "superheated steam" is used to dry the water-containing solid materials. Slow down section" drying process. The "superheated steam" comes from the reheated secondary steam in the "low temperature vacuum evaporation" process; the evaporated steam of the "superheated steam" enters the "low temperature vacuum evaporation" dryer again to release the latent heat of all the water vapor and becomes high temperature condensed water. The sensible heat of the high temperature condensate is recovered by preheating the water-containing solid material.

In the whole evaporation process, the part with the largest heat consumption, that is, all the latent heat of the secondary steam in the process of water evaporation is recycled; in the drying process of the "speed reduction section", the steam heating is only the process of increasing or releasing the sensible heat, which is obviously improved. The convective heat transfer temperature difference is reduced, and the drying time is shortened while the heat requirement is minimized. The source of all the steam in the convective heat transfer process is the secondary steam generated by indirect conduction heating of the sludge, that is, the entire evaporation process is not wasted in the recovery of steam latent heat, and the high-grade energy is not wasted in the heating process of the supplementary heat source. .

The secondary steam generated by "superheated steam drying" is subjected to cyclone dust removal, high-efficiency filtration and washing and washing, and then indirectly heat-exchanges with the "vacuum low temperature drying" sludge to generate condensate water. In the washing process, an automatic dosing device is set to clean and eliminate most of the free ammonia to form ammonium salts that dissolve in the sewage. The cleaning water source comes from the system condensate water, and the washed and cleaned sewage is discharged into the sludge storage tank to recover all its heat and pollutants. A small amount of volatile organic compounds such as alcohols and esters are condensed with water vapor and then enter the condensed water. The condensed water in the whole drying process is free of pollutants. Through the "superheated steam" after washing with water, the pollutants in the steam are reduced, and the saturation of the steam is improved at the same time. Saturated steam is beneficial to improve the efficiency of indirect heat transfer and save the drying time of the "low temperature vacuum evaporation" stage of indirect heat transfer.

The amount of evaporated water in the process of "superheated steam drying" accounts for 10%-25% of the total water in sludge drying, and the system supplementary heat is all used to increase the sensible heat of "secondary steam". The same supplementary heat can bring higher superheat and Convective heat transfer temperature difference.

Through the speed adjustment and matching of the scraper or mesh belt to control the moisture content of the sludge at the outlet, the combination of "vacuum low temperature drying" and "superheated steam drying" improves the overall drying speed of the sludge.

All the secondary steam generated in the whole drying process recovers all its latent heat and most of its sensible heat in the stage of "vacuum low temperature drying" and sludge preheating. Compared with the traditional steam heating drying evaporation method, there is no need to set up a cooling water system.

Low temperature evaporation prevents contaminants from migrating to the condensate system. The condensate water system has low pollutant content, and the main components are alcohols and esters of volatile organic compounds, which can be discharged or reused according to the standard through simple and low-cost treatment. Compared with the traditional high-temperature drying and evaporation method, the condensed water does not need to be returned to the sewage treatment plant or complex treatment on site.

The condensing pressure of the system is less than 100KPa, and the system is not a "pressure vessel". Compared with the traditional high-temperature drying and evaporation method, the system safety is improved, and the equipment manufacturing cost and system maintenance cost are reduced. The convection heat transfer method of superheated steam is adopted, and the oxygen content in the gas is extremely low, which avoids the system explosion and fire hazard.

Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (7)

1. A mechanical steam recompression drying system is characterized by comprising a sludge storage tank (110) which stores normal-temperature sludge incoming materials and is internally provided with a condensed water heat exchange coil (111), a sludge injection pump (120) which is connected with the output of the sludge storage tank (110) and is provided with a jacketed heat exchanger (121), a thin-layer evaporation dryer (130) which is connected with the output of the sludge injection pump (120), an extrusion slitting forming machine (140) which is connected with the output of the thin-layer evaporation dryer (130), a mesh belt dryer (150) which is connected with the output of the extrusion slitting forming machine (140), a dry sludge bin (160) which is connected with the output of the mesh belt dryer (150), a steam compressor (220) which is arranged between the thin-layer evaporation dryer (130) and the mesh belt dryer (150), a cyclone dust collector (230) which is connected with the mesh belt dryer (150) and is used for separating secondary steam and sludge dust, and a cyclone dust collector (230, A water washing dust collector (240) connected with the output of the cyclone dust collector 230 and used for washing and cleaning secondary steam, a condensed water buffer tank (310) connected with the thin layer evaporation dryer (130) and used for collecting condensed water, and a vacuum pump (400) connected with the condensed water buffer tank (310) and used for pumping system air to maintain vacuum and discharging non-condensable gas.

2. The mechanical vapor recompression drying system as recited in claim 1, wherein: the thin-layer evaporation dryer (130) comprises at least one cylindrical heating bin, a scraper rotor, a motor, a steam inlet (131), a steam and condensed water outlet (132), a sludge feeding hole (133) and a sludge outlet (134), wherein the scraper rotor is positioned on the inner side of the cylindrical heating bin, a plurality of scrapers are uniformly distributed on the surface of the scraper rotor, the motor is positioned on the outer side of the cylindrical heating bin and drives the scraper rotor to rotate, the steam inlet (131) is connected with the output of a water washing dust collector (240), the steam and condensed water outlet (132) is connected with the input of a condensed water buffer tank (310), the sludge feeding hole (133) is connected with the output.

3. The mechanical vapor recompression drying system as recited in claim 2, wherein: the mesh belt dryer (150) is of a closed structure, and a steam circulating fan (151) and a heater (152) are arranged in the mesh belt dryer.

4. The mechanical vapor recompression drying system as recited in claim 1, wherein: the water washing dust remover (240) comprises a condensed water spray head (241), a demister (242) positioned above the condensed water spray head (241), a dosing device (243) connected with the condensed water spray head (241), a first circulating pump (244) connected with the condensed water spray head (241), and a sewage pump (245) for returning sludge to the sludge storage tank (110).

5. The mechanical steam recompression drying system as claimed in claim 1, further comprising a granulator (161) for extruding and granulating the dry sludge in the dry sludge bin (160) and discharging the dry sludge, a second circulation pump (311) between the sludge injection pump (120) and the water scrubber (240), and a condensed water tank (320) connected to the sludge storage tank (110) and having an electrochemical oxidation descaler (321) therein.

6. The mechanical vapor recompression drying system as claimed in claim 1, further comprising a first filter (210) disposed between the thin layer evaporation dryer (130) and the vapor compressor (220), and a second filter (250) disposed between the thin layer evaporation dryer (130) and the water scrubber (240).

7. A mechanical vapor recompression drying method, comprising:

s1: wet sludge is transmitted from a sludge storage tank to a thin-layer evaporation dryer through a transmission device, in the process, the wet sludge and condensed water exchange heat in a heat exchanger, and the wet sludge and the condensed water are heated to 65-80 ℃ from 5-35 ℃ at an inlet; cooling the condensed water from 80-98 deg.C at the inlet to 15-45 deg.C at the outlet;

s2: forming a thin layer of preheated sludge in a thin layer evaporation dryer under the action of a rotary scraper blade and adhering to the inner surface of a cylinder of the evaporation dryer, wherein a negative pressure system is arranged in the cylinder, the pressure is set to be 25-47.5KPa, and the corresponding water evaporation temperature is 65-80 ℃; wherein the heat source for conducting heat exchange between the sludge and the cylinder wall comes from the steam in the step S4, the heat exchange temperature difference is 18-33 ℃, and the water content of the sludge is reduced from 80-95% to 55-65%;

s3: extruding and stripping sludge with the water content of 55-65% into thick strip sludge with the width of 2-5mm, and then feeding the thick strip sludge into a mesh belt dryer;

s4: the sludge entering the mesh belt dryer is subjected to heat convection with superheated steam in the mesh belt transmission process, further evaporated and dried, enters a dry sludge bin, is extruded and granulated by a granulator, and is discharged, wherein the water content of the sludge is further evaporated and dried from 55-65% to form sludge with the water content of 20-45%, and the drying process in the mesh belt dryer is completed; after saturated steam at the outlet of the compressor enters a mesh belt dryer, the degree of superheat is raised by heating through a heater to 20-50 ℃, and forced circulation and sludge convection heat exchange are carried out through a circulating fan; the surplus superheated steam enters cyclone separation, water washing for dedusting and filtering to become clean saturated steam and then enters step S2 again;

s5: filtering the secondary steam generated in the evaporation process in the step S2 by using a filter, compressing the secondary steam by using a steam compressor, and then performing the step S4, wherein condensed water from a condensed water buffer tank is sprayed into a suction inlet of the steam compressor, the compression ratio is 2.0-4.5, and the temperature of the steam is raised by 18-33 ℃;

s6: a part of the condensed water enters step S5 to reduce the superheat degree of the compressor exhaust; after a part of the sludge enters the water washing dust remover in the step S4, discharging the part of the sludge into a sludge tank; the rest part of condensed water enters a condensed water tank after heat exchange through the heat exchanger in the step S1, and is discharged or recycled after trace organic matters are removed through an electrochemical oxidation descaler;

s7: and exhausting the non-condensable gas in the condensed water buffer tank and the condensed water tank by using a vacuum pump until the process is finished.

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