CN212334983U - Mechanical vapor recompression drying system - Google Patents

Abstract

The utility model discloses a machinery vapor recompression drying system, it includes that mud storage pool, mud injection pump, thin layer evaporation desicator, extrusion divide strip make-up machine, guipure desiccator, dry mud storehouse, vapor compressor, cyclone, washing dust remover, comdenstion water buffer tank and link to each other with the comdenstion water buffer tank and be used for the suction system air to maintain the vacuum and discharge noncondensable gas's vacuum pump. The utility model discloses can save a large amount of energy resource consumptions and cooling water system consumption. In the process, no waste gas is discharged, and the system has no cooling water system, so that the evaporation loss of the water content of the cooling tower is saved.

Description

Mechanical vapor recompression drying system

Technical Field

The utility model relates to a sludge drying technical field, concretely relates to machinery vapor recompression drying system.

Background

A Mechanical Vapor recompression (Mechanical Vapor recompression) system, which is called MVR system for short, and is a novel efficient energy-saving system. The MVR evaporation technology has obvious energy-saving effect, compared with the multi-effect evaporation technology, the MVR system completely recovers the latent heat of secondary steam, and the heat efficiency is generally equivalent to that of 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 the water vapor is latent heat, and the sensible heat is only a small part. The mechanical steam recompression system effectively recovers the latent heat of the water vapor, thereby achieving the purposes of energy conservation and consumption reduction. The working principle is that the temperature, pressure and enthalpy of the steam generated by the evaporator are all improved after the steam is acted by the mechanical steam compressor, and the steam returns to the evaporator to be used as a heating source to supplement the heat energy required to be absorbed by the liquid evaporation and maintain the evaporation temperature. The system can basically achieve heat balance, and the fresh steam is only used for supplementing the heat loss of the system and the heat enthalpy of feeding and discharging, thereby greatly reducing the consumption of the evaporator to the fresh steam from outside and achieving the purpose of reducing the energy consumption. The MVR is applied less in the field of solid drying, and has the restriction factors of small heat transfer temperature difference, long drying time, high mechanical transmission energy consumption, system sealing requirement, high-performance compressor requirement and the like.

The common solid steam drying technology mostly adopts an indirect conduction heat exchange mode or a direct convection heat exchange mode. Indirect conduction heat exchange is commonly found in hollow blade machines, rotary disc dryers, drum dryers, double wall dryers, and the like. Direct convective heat transfer is commonly found in superheated steam drying, hot air drying, and the like. They all require large temperature differences and mechanical agitation or forced convection to enhance heat transfer.

The research shows that: the water in the solid is mainly free water, interstitial water, surface water and chemically combined water. In the evaporation drying process according to the water content, the evaporation rate is divided into a constant speed section, a speed reduction section and a final stage. After the water content of the general sludge is lower than about 65 percent, the 'constant speed section' finishes entering the 'speed reduction section' which is difficult to be used and consumes more energy for drying and evaporation.

The design and energy-saving analysis of a low-temperature drying system based on a vapor recompression technology of Zhou Lei of the university of aerospace in Nanjing shows that in the low-temperature drying process, the energy consumption of the system is reduced continuously along with the reduction of the evaporation temperature and the pressure ratio of a compressor theoretically; compared with the conventional low-temperature drying system under the same condition, the energy consumption of the low-temperature drying system based on the steam recompression technology is only 7.7% of that of the conventional low-temperature regenerative drying system. The MVR technology is applied based on the energy-saving principle and the limitation of the prior art, low pressure ratio compression and small temperature difference heat exchange are needed, the drying time is too long, the mechanical stirring for heat exchange enhancement and the transmission energy consumption are too high, and the energy-saving effect of the MVR is reduced. Meanwhile, the excessively high evaporation temperature causes more heat loss of the system, and the supplementary heat to the system is increased for heat balance of the system, resulting in further reduction of energy saving effect. Meanwhile, the screw vapor compressor capable of realizing the high pressure ratio is not common in the current market application, and is one of the reasons for the difficulty in MVR drying and energy-saving application. In order to ensure the drying effect, a certain drying speed needs to be controlled, the MVR technology and the vacuum low-temperature drying technology are combined to be the development direction of MVR drying, but after entering a speed reduction section, the evaporation rate is still unsatisfactory.

Superheated steam drying refers to a novel drying mode which utilizes superheated steam to directly contact with a dried material to remove moisture in the material. Compared with the hot air at the same temperature, the superheated steam carries much more heat per unit mass than the hot air due to the latent heat of the superheated steam, and when the superheated steam is used for drying the solid, no diffusion resistance exists due to the fact that the moisture on the surface of the solid is evaporated to the superheated steam. The speed of superheated steam drying and the temperature of the superheated steam are also relevant. Research and experiments of lucerty 'potato superheated steam and vacuum combined drying' of Fujian agriculture and forestry university show that low-temperature superheated steam can reach a relatively ideal drying speed in the drying process of potatoes.

Contaminants can enter the condensed water of the secondary steam along with the evaporation process in the drying process. The research on the characteristics of urban sludge superheated steam drying condensate liquid by the officer of the university of aviation in Nanchang and the research on the migration of pollutants in the distillation and compression process of high-salt organic wastewater by the flood and forever of the university of Shandong show that the pollutants entering the secondary steam condensate water through low-temperature evaporation are mainly alcohol organic matters, ammonia and the like, and the content of inorganic salts is extremely low. And in the high-temperature evaporation process, the pollutant components are complex and the pollution amount is more. In the traditional high-temperature sludge evaporation, the condensed water can reach the standard and be discharged or recycled after being treated in a sewage plant again.

In order to solve the above problems, the following patents "CN 103011546B", "CN 107098562A", "CN 106495427A", "CN 103708697B", "CN 103588375B", "CN 103285637B", "CN 105254147B" and "CN 110040935A" adopt corresponding technical means:

1) a two-stage sludge drying and energy recovery system and a drying process thereof adopt a two-stage drying process of a dividing wall type drying device and a belt type drying machine. The heat of the belt dryer is recovered from the secondary steam of the sludge of the dividing wall heat exchanger, which is equivalent to the two-effect evaporation of moisture, thereby realizing energy conservation.

2) The novel heat energy gradient recycling system of the two-stage sludge drying process comprises a thin-layer evaporator and a belt dryer which are used for two-stage drying. The heat input of the system comes from high-temperature steam of a thermal power plant. The primary steam condensate in the thin-layer evaporator at the section I is flashed into low-temperature low-pressure steam through the flash tank and is used for reheating hot air at the section II, so that the supplement amount of fresh steam can be reduced, and the purposes of saving steam and cooling water are achieved.

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

4) The mechanical vapor recompression heat pump MVR sludge drying system is characterized in that secondary vapor generated after sludge is dried by a hollow blade type dryer is compressed by a compressor and then returns to the inside of the hollow blade body, and all latent heat of the secondary vapor generated in the sludge drying process is recovered.

5) A MVC (mechanical vapor compression) evaporation drying system for sludge and a method for drying the sludge thereof are disclosed, wherein secondary steam in a sludge evaporation process enters a drying device through a steam compressor to serve as a steam supplementary heat source, and high-temperature condensed water is used for washing and purifying the steam.

6) The vacuum system vacuumizes a heated material cavity, and water vapor evaporated in the cavity is condensed into liquid water in a heat exchanger to be discharged, so that the aim of low-temperature evaporation is fulfilled.

7) The waste heat of the waste steam generated by drying the sludge by the superheated steam is utilized in a triple mode, the sensible heat and the latent heat of the waste steam are recovered, the waste water is recycled, and the waste gas is discharged in a zero-pollution mode. The whole device realizes the tertiary utilization of the waste heat of the waste steam of the sludge superheated steam drying. In the drying process, the sensible heat and the latent heat of the exhaust steam are simultaneously recovered, so that condensation in the drying process is prevented, and the drying time is shortened; in the drying process, only superheated steam is needed to be introduced in the initial stage, and the steam is recycled in the later stage, so that the input of a heat source is reduced, and the energy consumption is reduced.

8) The multilayer combined gravity-type sludge drying device and the drying method adopt a mode of combining indirect drying with superheated secondary steam to dry sludge, and effectively shorten the drying time by utilizing an MVR evaporation technology.

Although the above technical patents or related researches have solved the problems of energy saving in solid drying or application of MVR technology in the drying field, some of the problems have not been solved effectively. For example, the heat energy recycling process of the two-stage sludge drying process of "CN 103011546B" and "CN 107098562A" is equivalent to the energy-saving effect of "two-effect evaporation". High-temperature steam is adopted as energy in the drying process, and the energy consumption is still higher compared with that of an MVR technology. The CN106495427A MVR superheated steam sludge continuous drying system and the working method thereof, sensible heat and latent heat of secondary steam are used for preheating feed sludge. Based on the mass and heat balance, the latent heat of the secondary steam is far greater than the preheating heat of the sludge, and the heat recovery ratio is reduced. The CN103708697B and the CN103588375B dry the sludge by utilizing MVR evaporation technology through a hollow blade type or other indirect heat conduction drying devices, a large amount of heat needs to be supplemented to a system in the practical process, meanwhile, the evaporation time of the sludge after entering a speed reduction section is too long, and the energy saving benefit is reduced due to mechanical transmission or stirring enhanced heat transfer and heat loss. CN103285637B low-temperature vacuum dehydration and drying complete equipment and a process thereof, and CN105254147B sludge superheated steam drying exhaust steam waste heat are triple utilized, energy consumption is also from low-temperature (80-90 ℃) heat sources or steam, and the energy consumption is higher compared with MVR technology. "CN 110040935A" a multilayer combination falls from formula sludge drying device and drying method, the system supplements the heat and heats the compressed secondary steam directly, a part of secondary steam is used as superheated steam and enters the drying chamber directly and exchanges heat with the sludge convection, a part of secondary steam enters the indirect dryer cavity and exchanges heat with the sludge conduction. Compared with saturated steam, superheated steam in the inner cavity of the indirect dryer has a theoretically unsatisfactory heat transfer effect, and meanwhile, after secondary steam becomes condensed water, sensible heat of the secondary steam is not recovered more.

In view of the above, there is a need for a new mechanical vapor recompression drying system.

SUMMERY OF THE UTILITY MODEL

In view of this, the utility model provides an easy operation, dependable performance, low in manufacturing cost, dismantle easy maintenance, dry fast in succession, supplementary heat is little, the mechanical vapor recompression drying system that the system energy consumption is low.

According to the utility model discloses an aim, the utility model provides a following technical scheme: a mechanical vapor recompression drying system comprises a sludge storage pool for storing normal temperature sludge incoming materials and provided with a condensed water heat exchange coil inside, a sludge injection pump connected with the output of the sludge storage pool and provided with a jacketed heat exchanger, a thin-layer evaporation dryer connected with the output of the sludge injection pump, an extrusion slitting forming machine connected with the output of the thin-layer evaporation dryer, a mesh belt dryer connected with the output of the extrusion slitting forming machine, and a dry sludge bin connected with the output of the mesh belt dryer, the device comprises a steam compressor arranged between a thin-layer evaporation dryer and a mesh belt dryer, a cyclone dust collector connected with the mesh belt dryer and used for separating secondary steam and sludge dust, a water washing dust collector connected with the output of the cyclone dust collector and used for washing and cleaning the secondary steam, a condensed water buffer tank connected with the thin-layer evaporation dryer and used for collecting condensed water, and a vacuum pump connected with the condensed water buffer tank and used for pumping system air to maintain vacuum and discharging non-condensable gas.

On the basis of the technical scheme, the method further comprises the following subsidiary technical scheme:

the thin-layer evaporation dryer comprises at least one cylindrical heating bin, a scraper rotor, a motor, a steam inlet, a steam and condensate water outlet, a sludge feeding hole and a sludge outlet, wherein the scraper rotor is positioned on the inner side of the cylindrical heating bin, the surface of the scraper rotor is uniformly provided with a plurality of scrapers, the motor is positioned on the outer side of the cylindrical heating bin and drives the scraper rotor to rotate, the steam inlet is connected with the output of the water washing dust remover, the steam and condensate water outlet is connected with the input of the condensate water buffer tank, the sludge feeding hole is connected with the output of the.

The mesh belt dryer is of a closed structure, and a steam circulating fan and a heater are arranged in the mesh belt dryer.

The washing dust remover comprises a condensed water spray head, a demister positioned above the condensed water spray head, a dosing device connected with the condensed water spray head, a first circulating pump connected with the condensed water spray head, and a sewage pump for returning sludge to the sludge storage pool.

The device also comprises a granulator for extruding and granulating the dry mud in the dry mud bin and then discharging, a second circulating pump positioned between the sludge injection pump and the water washing dust remover, and a condensation water tank which is connected with the sludge storage tank and is internally provided with an electrochemical oxidation scale removal instrument.

The device also comprises a first filter arranged between the thin-layer evaporation dryer and the steam compressor and a second filter arranged between the thin-layer evaporation dryer and the water-washing dust remover.

Compared with the prior art, the technical scheme of the utility model has following advantage:

the MVR technology is applied to the field of solid drying, and compared with the traditional technology of heating and evaporating by utilizing a heat source, the MVR technology can save a large amount of energy consumption and cooling water system consumption. In the process, no waste gas is discharged, and the system has no cooling water system, so that the evaporation loss of the water content of the cooling tower is saved. The secondary steam condensate water evaporated at low temperature has low pollutant content and volatile organic matter as main component, and the condensate water after being treated in electrochemical oxidation and other methods in low cost may be exhausted directly. And the secondary steam condensate water evaporated at high temperature often needs to enter a sewage treatment plant again for treatment.

In the process of low-temperature vacuum evaporation, the material inlet temperature and the evaporation temperature are low, so that the preheating heat of the material is reduced; in the process of low-temperature superheated steam evaporation, the temperature of a material outlet is relatively low, the water content is low, and the heat loss of the material at the outlet is reduced; the temperature difference between the whole working temperature of the system and the ambient temperature is low, and the heat loss of the system is reduced.

In the whole evaporation process, only for the sludge with high viscosity and low evaporation speed (the water content is below 55-65%), the convection heat exchange is carried out by adopting a superheated steam evaporation mode with relatively large temperature and heat exchange temperature difference. The whole drying time is shortened, heat recovery is facilitated, and supplementary heat is small. The cost of the heat supplement of the system is irrelevant to the grade of energy, and is related to the quantity. The supplementary heat is mainly used for heating secondary steam to improve the sensible heat of the secondary steam. When superheated steam and sludge carry out convective heat exchange, the heat exchange temperature difference is high, and the heat exchange effect is good.

Under the condition of not influencing the continuous evaporation speed, sludge particles with different dryness can be generated by properly adjusting parameters of the superheated steam evaporation stage, and the drying range is 70-95%.

The whole latent heat of the evaporation of the water with the largest heat consumption can be recycled, and the whole or most of the heat of the high-temperature condensed water 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 both the pipeline and the container of the system are not pressure containers, thus effectively reducing the production, manufacture, use and maintenance costs. The gas directly contacted with the sludge is secondary steam, and no air pollution is discharged. In the low oxygen environment, the danger of combustion and dust explosion is avoided, and the safety is better.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

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

Detailed Description

Referring to fig. 1, the present invention provides a specific embodiment of a mechanical steam recompression drying system, which includes a sludge storage tank 110 for storing normal temperature sludge and having a condensed water heat exchange coil 111 therein, a sludge injection pump 120 connected to an output of the sludge storage tank 110 and having a jacketed heat exchanger 121, a first external heat source heater 122, a thin-layer evaporation dryer 130 connected to an output of the sludge injection pump 120, an extrusion slitting molding machine 140 connected to an output of the thin-layer evaporation dryer 130, a mesh belt dryer 150 connected to an output of the extrusion slitting molding machine 140, a dry sludge bin 160 connected to an output of the mesh belt dryer 150, a steam compressor 220 disposed between the thin-layer evaporation dryer 130 and the mesh belt dryer 150, a cyclone 230 connected to the mesh belt dryer 150 and used for separating secondary steam and sludge dust, and a water scrubber 240 connected to an output of the cyclone 230 and used for washing and cleaning the secondary steam, A condensate buffer tank 310 connected to the thin layer evaporation dryer 130 and collecting condensate, and a vacuum pump 400 connected to the condensate buffer tank 310 and pumping system air to maintain vacuum and discharge non-condensable gas.

The sludge storage tank 110 stores incoming normal-temperature sludge. And a condensed water heat exchange coil 111 is arranged on the inner wall of the sludge storage tank. The condensed water is arranged in the condensed water heat exchange coil 111, 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 convey sludge in the sludge storage tank 110 to the sludge inlet of the thin-layer evaporator 130, and the pressure of pushing and extruding internal solids can ensure that the inner cavities of the sludge storage tank 110 and the thin-layer evaporator 130 are closed without air leakage. The jacketed heat exchanger 121 is arranged outside the sludge conveying pipeline, condensed water is arranged inside the jacketed heat exchanger 121, and the condensed water and sludge are discharged into the sludge storage tank 110 after heat exchange. The external heat source heater 122 provides heat to provide supplemental heat to the system to heat the sludge to raise the temperature.

The thin-layer evaporation dryer 130 includes at least one cylindrical heating chamber and a scraper rotor disposed therein. One end of the cylindrical heating bin is provided with a motor, and the scraper rotor is driven by the motor. The scraper blades are uniformly distributed on the surface of the scraper rotor. The scraper blades push the sludge from one end of the thin-layer evaporation dryer 130 to the other end and spread the sludge evenly over the cylindrical inner 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 hole 133, and one end of the cylindrical heating bin is provided with a sludge outlet 134. Furthermore, the cylindrical heating bin is of a dividing wall type structure, and steam can flow in the cylindrical heating bin. The outer surface of the cylindrical heating bin is additionally provided with a heat preservation layer, and the inner surface of the cylindrical heating bin is coaxial with the scraper rotor.

The extrusion stripping forming machine 140 is a sludge extrusion device with a meshed net. The sludge from the sludge outlet 134 of the thin layer evaporator 130 is extruded and cut into strips by the extrusion and strip-dividing forming machine 140, and then is scattered on the conveying mesh belt of the mesh belt dryer 150. The solid extrusion pressure in the extrusion slitting forming machine 140 can ensure that the cavities of the thin layer evaporator 130 and the mesh belt dryer 150 are sealed without air leakage. The mesh belt dryer 150 has a closed structure, and has a circulation 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 inside the jacketed heat exchanger 121. The external heat source heaters 152 and 122 are preferably electric heating, high temperature heat pump, or externally directly introduced high temperature steam. Further, the mesh belt dryer 150 delivers the superheated steam heated by circulation to the steam compressor 220 for compression, and forms the water vapor with temperature and pressure increased, which is the secondary steam of the sludge evaporation of the thin layer evaporator 130. The superheated steam is forced to circulate under the action of the circulating fan 151, and the sludge on the mesh belt is subjected to convective heat exchange to dry the water of the sludge. The dry sludge bin 160 is used to store the dry sludge produced by the mesh belt dryer 150 and the cyclone 230. The granulator 161 extrudes and granulates the dry sludge in the dry sludge bin 160, and then discharges the dry sludge. The solids extrusion pressure within the pelletizer 161 can ensure that the pelletizer 161 is sealed from the outside atmosphere without air cross-talk. The first and second filters 210 and 250 are air filters for filtering fine dust in the air. The vapor compressor 220 is a water vapor compressor, preferably a twin screw vapor compressor, with a compression ratio of 2.0-4.5. The inlet of the vapor compressor 220 is injected with high-temperature condensate from a condensate buffer tank 310 for reducing the degree of superheat of the exhaust gas. The cyclone 230 is used to separate the secondary steam and sludge dust from the chamber of the mesh belt dryer 150. The secondary steam enters the water scrubber 240 and the sludge dust enters the dry sludge bin 160. The water scrubber 240 is used to wash clean the secondary steam and reduce its superheat. The system of the water scrubber 240 replenishes the high temperature condensate from the condensate buffer tank 310. The washing secondary steam is sprayed by the upper condensed water spray header 241 of the water scrubber 240 by the circulation pump 244. The chemical adding device 243 adds organic acid to the circulating water for cleaning and removing free ammonia in the secondary steam. The bottom of the water washing dust remover 240 is provided with a sewage discharge outlet which returns to the sludge storage tank 110 through a sewage discharge pump 245. The demister 242 is used for gas-water separation of the secondary steam after washing, and the secondary steam enters the second filter 250 after dust removal and ammonia removal. The cleaned and saturated secondary steam is returned to the steam jacket of the thin layer evaporator 130. The condensate buffer tank 310 is used to store condensate from 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 condensate tank 320 is a water storage tank with a closed structure, the upper part is gas, and the lower part is liquid water. Further, an electrochemical oxidation descaler 321 is arranged in the condensate water tank 320 and is used for reducing volatile organic compounds in the condensate water, reducing the COD of the condensate water and reaching the standard for discharge or recycling. The vacuum pump 400 is used to draw system air to maintain a vacuum and to remove non-condensable gases 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.

The embodiment also provides an MVR low-temperature vacuum combined superheated steam drying method, which utilizes the related structure and device to perform drying work, and specifically comprises the following steps:

s1: wet sludge is transferred from the sludge storage tank 110 to the thin-layer evaporative dryer 130 by transfer device sludge injection pump 120. In the process, wet sludge and condensed water exchange heat in the jacketed heat exchanger 121, the wet sludge and the condensed water are heated to 65-80 ℃ from 5-35 ℃ 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 ℃ at the inlet to 25-55 ℃ at the outlet, enters the heat exchange coil 111, is cooled to 15-45 ℃ and is discharged into the condensed water tank 320.

S2: the preheated sludge is formed into a thin layer in the thin layer evaporation dryer 130 and is adhered to the inner surface of the evaporator cylinder under the action of the rotating scraper blade. The cylinder body is internally provided with a negative pressure system, the pressure is set to be 25-47.5KPa, and the corresponding water evaporation temperature is 65-80 ℃. The sludge and the cylinder wall conduct heat exchange, saturated steam from the step S4 is filled in the cylinder jacket, and the preferable heat exchange temperature difference is set to be 18-33 ℃. The sludge begins to evaporate in the vacuum negative pressure environment, and the sludge is pushed by the rotation of the scraper blade to move on the cylinder wall and is enriched at the sludge outlet 134. The sludge is dried in the thin-layer evaporator 130 in a vacuum low-temperature drying process, and when the water content of the sludge is reduced from 80-95% to 55-65%, the drying process in the thin-layer evaporator 130 is completed. Saturated steam in the jacket of the thin-layer evaporator 130 exchanges heat to form liquid condensate which enters the condensate buffer tank 310.

S3: the extrusion stripping forming machine 140 extrudes and strips the sludge with the water content of 55% -65% at the sludge outlet 134 into thick strip-shaped sludge with the diameter of 2-5 mm, and the thick strip-shaped sludge enters the mesh belt dryer 150.

S4: the sludge entering the mesh belt dryer 150 is subjected to heat convection with superheated steam in the mesh belt transmission process, is further evaporated and dried, enters the dry sludge bin 160, is extruded and granulated by the granulator 161, and is discharged. The sludge is dried by superheated steam in the mesh belt dryer 150, the water content of the sludge is further evaporated and dried from 55 to 65 percent to be sludge with the water content of 20 to 45 percent, and the drying process in the mesh belt dryer 150 is completed. Saturated steam at the outlet of the compressor 220 enters the mesh belt dryer 150, is heated by the heater 152 to raise the superheat degree by 20-50 ℃, and is forced to circulate by the circulating fan 151 and subjected to convective heat transfer by sludge. The surplus superheated steam enters the cyclone 230, the water scrubber 240, and the filter 250 as clean saturated steam and again enters step S2.

S5: the secondary vapor generated in the evaporation process of step S2 is filtered by the filter 210, compressed by the compressor 220, and then processed to step S4. Condensate from the condensate surge tank 310 is injected into the suction inlet of the vapor compressor 220 for reducing the compressor rotor temperature and outlet vapor superheat. The preferable compression ratio is 2.0-4.5, and the steam temperature rises to 18-33 ℃;

s6: the temperature of the condensed water in the condensed water buffer tank 310 is 80-98 ℃. A portion of the flow proceeds to step S5 for reducing the degree of superheat of the compressor discharge gas; a part of the sludge is discharged to the sludge tank 110 after entering the water scrubber 240 in step S4; most of the condensed water enters the condensed water tank 320 after being subjected to heat exchange by the heat exchangers 121 and 111 in the step S1, and is discharged or recycled after trace organic matters are removed by the electrochemical oxidation descaler 321.

S7: the vacuum pump 400 exhausts the non-condensable gas in the condensed water buffer tank 310 and the condensed water tank 320 to ensure the vacuum degree and the evaporation pressure of the system. A small amount of non-condensable gas is discharged after being deodorized by the regenerable activated carbon filter 410.

The utility model has the advantages that:

based on the characteristics of the drying process, the optimal energy saving performance of the MVR technology in the field of moisture evaporation is combined, a constant-speed section drying process of drying and processing sludge by low-temperature vacuum evaporation is adopted, and a speed reduction section drying process of drying and processing moisture-containing solid materials by superheated steam is adopted. "superheated steam" is derived from reheated secondary steam of a "low temperature vacuum evaporation" process; the steam evaporated by the superheated steam enters the low-temperature vacuum evaporation dryer again to release the latent heat of all the water vapor to form high-temperature condensed water, and the sensible heat of the high-temperature condensed water is recovered by preheating the water-containing solid material.

In the whole evaporation process, the part with the largest heat consumption is recycled, namely all latent heat of secondary steam in the water evaporation process is recycled; in the drying process of the speed reduction section, steam temperature rise is only the process of sensible heat increase or release, the convective heat transfer temperature difference is obviously improved, the drying time is shortened, and the heat demand is minimum. All the steam sources in the convection heat exchange process are secondary steam generated by indirectly conducting and heating the sludge, namely the whole evaporation process is not wasted in the recovery of latent heat of the steam, and meanwhile, in the heating process of a supplementary heat source, the high grade of the energy sources is not wasted.

Secondary steam generated by superheated steam drying is subjected to cyclone dust removal, efficient filtration and washing and then indirectly exchanges heat with vacuum low-temperature drying sludge to generate condensed water. The washing process is provided with an automatic dosing device, and most of free ammonia is cleaned and eliminated to generate ammonium salt which is dissolved in sewage. The cleaning water source is condensed water from the system, and the sewage cleaned by water washing is discharged into the sludge storage pool, so that all heat and pollutants are recovered. A small amount of volatile organic compounds such as alcohols, esters and the like enter condensed water after being condensed with water vapor, and the condensed water is discharged or recycled after reaching the standard after removing trace volatile organic compounds in the condensed water in an electrochemical oxidation mode. The condensed water in the whole drying process is free from pollutant discharge. The superheated steam after washing reduces the pollutants in the steam and improves the saturation of the steam at the same time. The saturated steam is beneficial to improving the indirect heat transfer efficiency and saving the drying time of the low-temperature vacuum evaporation stage of indirect heat exchange.

The proportion of the evaporated water amount in the total sludge drying water amount is 10-25% in the superheated steam drying process, the system supplementary heat is completely used for sensible heat promotion of secondary steam, and the same supplementary heat can bring higher superheat degree and convection heat transfer temperature difference.

The speed regulation and the matching of the scraper plate or the mesh belt are used for controlling the water content of the sludge at the outlet, and the integral drying speed of the sludge is improved in a combined mode of vacuum low-temperature drying and superheated steam drying.

All secondary steam generated in the whole drying process recovers all latent heat and most sensible heat in the vacuum low-temperature drying stage and the sludge preheating stage. Compared with the traditional steam heating, drying and evaporating mode, the system does not need to be provided with a cooling water system.

Low temperature evaporation can avoid migration of contaminants to the condensate system. The condensate water system has low pollutant content, the main components are alcohols and esters of volatile organic compounds, and the condensate water can be discharged or recycled after reaching the standard through simple low-cost treatment. Compared with the traditional high-temperature drying evaporation mode, the condensed water does not need to return to a sewage treatment plant again or carry out complicated treatment on the 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 evaporating mode, the system safety is improved, and the equipment manufacturing cost and the system maintenance cost are reduced. The convection heat exchange mode of superheated steam is adopted, the oxygen content in the gas is extremely low, and the system explosion and fire hazard are avoided.

The above-mentioned embodiments are only for illustrating the technical concept and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and to implement the present invention, which should not be construed as limiting the scope of the present invention. All equivalent changes or modifications made according to the spirit of the main technical solution of the present invention should be covered within the protection scope of the present invention.

Claims (6)

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, The device comprises a water washing dust collector (240) which is connected with the output of the cyclone dust collector (230) and is used for washing and cleaning secondary steam, a condensed water buffer tank (310) which is connected with the thin-layer evaporation dryer (130) and is used for collecting condensed water, and a vacuum pump (400) which is connected with the condensed water buffer tank (310) and is used for pumping system air to maintain vacuum and discharging noncondensable 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).

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