A low-energy-consumption two-stage drying system

Abstract

The present application discloses a low-energy-consumption secondary drying system, comprising a primary drying circulation system and a secondary drying circulation system. The primary drying circulation system comprises a screw feeder, a primary dryer, a silo a, a star-shaped discharger a, a superheated steam high-efficiency filter, a superheated steam circulation fan, a superheated steam heater and a secondary steam compressor. The secondary drying circulation system comprises a horizontal feeder, a secondary dryer, a silo b, a star-shaped discharger b, a circulation air filter, a circulation fan, a circulation air heater, an air filter and an induced draft fan. Superheated steam is used to preliminarily dry the material, and the moisture in the material evaporates to generate superheated steam, which is circulated. At the same time, part of the superheated steam is drawn out and used as a heat source for some equipment for the secondary drying circulation system, and the excess superheated steam is sent to other sections. The use of the secondary drying system of the present application can improve product quality, reduce energy consumption and reduce tail gas emissions. Compared with full hot air drying, the system has a considerable reduction in energy consumption.

Description

Technical Field

[0001] The invention relates to a low-energy-consumption two-stage drying system, belonging to the technical field of drying. Background Art

[0002] Drying is a high-energy consumption unit operation. Energy conservation and emission reduction in the drying process have always been the pursuit of drying. Traditional drying systems often use air or inert gas as the drying medium. Due to the physical properties of the drying medium itself, the energy consumption is relatively high.

[0003] Patent CN105779071A uses superheated steam as a drying medium to dehydrate lignite. The circulating superheated steam is first heated by the flue gas of a hot blast furnace and then heated by secondary steam pressurized by a steam turbine compressor. This is not ideal in terms of thermal energy utilization. The steam is compressed in multiple stages by a steam turbine compressor to a high temperature and pressure, and is used as the final heating heat source for the circulating superheated steam, which is not economical.

[0004] Patent CN105685200A uses superheated steam circulation to dry shrimp. Steam is generated by a steam generator and heated by a steam heater to become superheated steam. The superheated steam is sent to a superheated steam drying oven for primary drying of the shrimp. Part of the superheated steam exhaust is used to heat the air, condenses into water, and returns to the steam generator. The superheated steam from the superheated steam drying oven also returns to the steam generator, and the energy contained in the superheated steam is not well utilized. Summary of the Invention

[0005] In view of the above problems existing in the prior art, the purpose of this application is to provide a low-energy-consumption two-stage drying system.

[0006] The low-energy-consumption two-stage drying system comprises a primary drying circulation system and a secondary drying circulation system;

[0007] The primary drying circulation system is a closed-circuit superheated steam circulation system, including a screw feeder, a primary dryer, a silo a, a star-shaped discharger a, a superheated steam high-efficiency filter, a superheated steam circulation fan and a superheated steam heater;

[0008] The wet material is conveyed into the lower part of the primary dryer by a screw feeder. At the same time, the superheated steam conveyed by the superheated steam circulation fan is heated by the hot steam heater and then enters the bottom of the primary dryer. The wet material contacts the superheated steam in the primary dryer for preliminary drying. The preliminarily dried material and evaporated water are discharged from the top of the primary dryer along with the superheated steam into silo a for gas-solid separation. The material is discharged from the bottom of silo a through a star-shaped discharger a and enters the secondary drying circulation system. The superheated steam is discharged from the air outlet at the top of silo a. The excess superheated steam is sent to other sections. The rest is filtered by a hot steam high-efficiency filter and then divided into two paths: the first path is divided into two branches after passing through the hot steam circulation fan. The first branch is conveyed to the superheated steam heater for heating and then re-enters the primary dryer and silo a. The second branch is conveyed to the top bag a in the upper part of silo a for bag backwashing. The superheated steam from the two branches merges in silo a and is discharged from the air outlet at the top of silo a and recycled through the hot steam high-efficiency filter. The second branch of superheated steam is used as a heat source for some equipment.

[0009] The secondary drying circulation system is an air or inert gas partial circulation system, including a horizontal feeder, a secondary dryer, a silo b, a star-shaped discharger b, a circulating air filter, a circulating fan, a circulating air heater, an air filter and an induced draft fan;

[0010] The star-shaped discharger a at the bottom of silo a is connected to the horizontal feeder. After primary drying, the material is fed from the star-shaped discharger a into the horizontal feeder. At the same time, the circulating air delivered by the circulating fan is heated by the circulating air heater and then enters the horizontal feeder. The material enters the bottom of the secondary dryer with the circulating air for further drying. The dried product and evaporated water are discharged from the top of the secondary dryer with the circulating air and enter silo b for gas-solid separation. The material is discharged from the bottom of silo b through the star-shaped discharger b and the product is collected. The circulating air is discharged from the air outlet at the top of silo b and is divided into two paths: the first path is divided into two branches after passing through the circulating air filter and the circulating fan. The first branch is transported to the circulating air heater for heating and then re-enters the horizontal feeder to deliver the primary dried material to the secondary dryer and silo b. The second branch is transported to the top bag b in the upper part of silo b for bag back-blowing. The gas from the two branches converges in silo b, discharged from the air outlet at the top of silo b, and recycled through the circulating air filter. The second path is connected to the induced draft fan to discharge the exhaust gas.

[0011] Furthermore, the first-stage dryer is a rotary flash dryer or a cyclone dryer, which has a jacket on the outside and is heated by steam; the second-stage dryer is a cyclone dryer or a fluidized bed dryer, which has a jacket on the outside and is heated by steam.

[0012] Furthermore, the primary drying cycle system also includes a secondary steam compressor. The second superheated steam, after being filtered by the hot steam high-efficiency filter, is pressurized by the secondary steam compressor to form high-temperature and high-pressure steam, which is used as a heat source for some equipment, including a screw feeder, a circulating gas heater, and a secondary dryer. Heat exchange interlayers are provided on the outside of these equipment. The high-temperature and high-pressure steam pressurized by the secondary steam compressor is passed into the heat exchange interlayer outside the screw feeder to preheat the wet material in the screw feeder; the circulating gas heater is passed as a heat source to preliminarily heat the circulating gas; the heat exchange interlayer is passed into the heat exchange interlayer outside the secondary dryer to provide insulation and heat for the secondary dryer; the high-temperature and high-pressure steam is condensed and discharged after heat exchange. An exhaust pipe is provided on the pipeline between the top air outlet of the silo a and the superheated gas high-efficiency filter to send excess superheated steam to other work sections.

[0013] Furthermore, the second superheated steam is used as a heat source for several devices, including a screw feeder, a circulating air heater, and a secondary dryer, all of which are equipped with heat exchange interlayers. The superheated steam is passed into the heat exchange interlayer outside the screw feeder to preheat the wet material inside the screw feeder; passed into the circulating air heater as a heat source to heat the circulating air; and passed into the heat exchange interlayer outside the secondary dryer to insulate and heat the secondary dryer. After heat exchange, the superheated steam is condensed and discharged. An exhaust pipe is installed on the pipeline between the top outlet of silo A and the superheated air high-efficiency filter to transport excess superheated steam to other processing sections.

[0014] Furthermore, in the first-stage drying circulation system, the superheated steam heater uses raw steam or raw steam plus other heat sources to heat the circulating superheated steam to meet the first-stage drying temperature requirements; the other heat sources refer to electricity or thermal oil, or a combination of these heat sources.

[0015] Furthermore, in the two-stage drying circulation system, the hot channel of the circulating gas heater uses secondary steam or a combination of secondary steam and raw steam to heat the circulating gas in the cold channel of the circulating gas heater, thereby meeting the secondary drying temperature requirements of the product and making full use of the superheated steam generated by the primary drying system; the secondary steam refers to high-temperature and high-pressure steam pressurized by a secondary steam compressor, or superheated steam after passing through a hot steam high-efficiency filter;

[0016] Furthermore, an air filter is connected to the pipeline between the circulating air filter and the circulating fan through a pipeline to replenish fresh air into the secondary drying circulation system; the circulating air carries the material after preliminary drying into the secondary dryer for further drying, and the evaporated moisture is discharged from the top of the secondary dryer along with the circulating air and enters the silo b for gas-solid separation. The circulating air is discharged from the air outlet at the top of the silo b and then recycled. The humidity of the circulating air is regulated by discharging part of the exhaust gas from the induced draft fan and replenishing fresh air through the air filter to meet the material drying requirements.

[0017] Furthermore, the secondary dryer adopts a built-in bag-type fluidized bed dryer.

[0018] Furthermore, the circulating gas of the secondary drying circulation system is air or inert gas; for drying oxidizable materials, the circulating gas is inert gas, and the air filter is an inert gas supply port.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1) The present invention proposes a low-energy two-stage drying system. The first-stage drying cycle system adopts closed-loop circulation of superheated steam for drying, while the second-stage drying cycle system adopts partial exhaust circulation of air or inert gas for drying. The heat of secondary steam obtained in the first-stage drying process is used in the second-stage drying process. By controlling the amount of secondary steam, the first and second-stage drying capacities are adjusted, effectively reducing drying energy consumption and exhaust emissions, achieving excellent energy-saving and emission-reduction effects.

[0021] 2) Since superheated steam drying directly contacts wet materials with superheated steam, it can fully utilize the potential of steam, has high thermal efficiency and good energy-saving effect. At the same time, since superheated steam itself is high-temperature water vapor, there is no air film mass transfer resistance in the drying process, and it is easy to remove steam from the surface of material particles. The surface of the material has no hardening imagination and is not easy to deform. It is very suitable for materials that can withstand a certain temperature and have high requirements for product appearance and drying uniformity. The use of this two-stage drying system can improve product quality and reduce energy consumption. Compared with full hot air drying, this system has significantly reduced energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is one of the flow diagrams of a low-energy-consumption two-stage drying system of this application;

[0023] Figure 2 A schematic flow chart of a low-energy-consumption secondary drying system in this application, wherein the secondary dryer is a fluidized bed dryer;

[0024] Figure 3 This is the second flow diagram of a low-energy-consumption two-stage drying system of this application;

[0025] 1 Superheated steam circulation fan, 2 Superheated steam heater, 3 Primary dryer, 4 Silo a, 4-1 Silo roof bag a, 5 Superheated steam high-efficiency filter, 6 Secondary steam compressor, 7 Screw feeder, 8 Secondary dryer, 9 Circulating air heater, 10 Star-shaped discharger a, 11 Horizontal feeder, 12 Silo b, 12-1 Silo roof bag b, 13 Circulating air filter, 14 Circulating fan, 15 Star-shaped discharger b, 16 Air filter, 17 Induced draft fan, 18 Fluidized bed dryer, 19 Bag dust collector. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0027] Example: Control Figure 1 ;

[0028] A low-energy-consumption two-stage drying system comprises a primary drying circulation system and a secondary drying circulation system.

[0029] The primary drying circulation system includes a screw feeder 7, a primary dryer 3, a silo a 4, a star-shaped discharger a 10, a superheated steam high-efficiency filter 5, a superheated steam circulation fan 1, a superheated steam heater 2, and a secondary steam compressor 6. The secondary drying circulation system includes a horizontal feeder 11, a secondary dryer 8, a silo b 12, a star-shaped discharger b 15, a circulating air filter 13, a circulating air fan 14, a circulating air heater 9, an air filter 16, and an induced draft fan 17.

[0030] The working process of the primary drying circulation system of the present application is as follows: the wet material is transported into the lower part of the primary dryer 3 through the screw feeder 7; at the same time, the superheated steam transported by the superheated steam circulation fan 1 is heated by the hot steam heater 2 and then enters the bottom of the primary dryer 3; the wet material contacts the superheated steam in the primary dryer 3 for preliminary drying, and the preliminarily dried material and evaporated moisture are discharged from the top of the primary dryer 3 with the superheated steam into the silo a 4 for gas-solid separation; the material is discharged from the bottom of the silo a 4 through the star-shaped discharger a 10 and enters the secondary drying circulation system; the superheated steam is discharged from the air outlet at the top of the silo a 4, and the excess superheated steam is sent to other work sections, and the rest is filtered by the hot steam high-efficiency filter 5 and then divided into two paths: the first path is divided into two branches after passing through the hot steam circulation fan 1, the first branch is transported to the superheated steam heater 2 for heating and then re-enters the primary dryer 3 and the silo a 4; the second branch is transported to the silo top bag a in the upper part of the silo a 4 4-1 is used as bag back-blowing gas; the superheated steam from the two branches merges in silo a4, is discharged from the air outlet on the top of silo a4, and is recycled through the hot steam high-efficiency filter 5 to form a closed-loop circulation of superheated steam; the second route is pressurized by the secondary steam compressor 6 to form high-temperature and high-pressure steam used as a heat source for some equipment.

[0031] The working process of the secondary drying circulation system of the present application is as follows: the star-shaped discharger a 10 at the bottom of the silo a 4 is connected to the horizontal feeder 11, and the material is fed from the star-shaped discharger a 10 into the horizontal feeder 11 after primary drying; at the same time, the circulating air delivered by the circulating fan 14 is heated by the circulating air heater 9 and then enters the horizontal feeder 11; the material enters the bottom of the secondary dryer 8 with the circulating air for further drying, and the dried product and evaporated moisture are discharged from the top of the secondary dryer 8 with the circulating air and enter the silo b 12 for gas-solid separation; the material is discharged from the bottom of the silo b 12 through the star-shaped discharger b 15, and the product is collected; the circulating air is divided into two paths after being discharged from the air outlet at the top of the silo b 12: the first path is divided into two branches after passing through the circulating air filter 13 and the circulating fan 14. The first branch is transported to the circulating air heater 9 for heating and then re-enters the horizontal feeder 11 to send the primary dried material into the secondary dryer 8 and the silo b 12, and the second branch is transported to the silo b The top bag b12-1 in the upper part of 12 is used for bag back-blowing. The gases from the two branches merge in silo b12 and are discharged from the air outlet at the top of silo b12 and recycled through the circulating air filter 13. The second branch is connected to the induced draft fan 17 to discharge part of the exhaust gas, forming a closed loop.

[0032] The top outlet of silo a4 is connected to the air inlet of a superheated steam high-efficiency filter 5 via a pipeline. Silo a4 is equipped with a top bag a4-1. Superheated steam, discharged from the top of the primary dryer 3 and carrying material, enters silo a4, where it undergoes gas-solid separation. The superheated steam is then discharged from the top outlet of silo a4 and sent to the superheated steam high-efficiency filter 5 for filtration. A discharge pipe is installed on the pipeline between the top outlet of silo a4 and the superheated steam high-efficiency filter 5 to discharge excess superheated steam to other processing stages.

[0033] The circulating gas heater 9 in the present application is a heat exchanger structure. A heat exchange interlayer is provided on the outside of the secondary dryer 8, and a heat exchange interlayer is provided on the outside of the screw feeder 7. The high-temperature and high-pressure steam pressurized and heated by the secondary steam compressor 6 is divided into three paths. The first path enters the heat channel of the circulating gas heater 9 to heat the circulating gas, the second path enters the heat exchange interlayer on the outside of the secondary dryer 8 for insulation and heating, and the third path enters the heat exchange interlayer on the outside of the screw feeder 7 to preheat the wet material in the screw feeder 7. The high-temperature and high-pressure steam is discharged as condensed water after heat exchange.

[0034] In this application, the superheated steam generated during the drying process in the primary dryer 3 is increased in temperature and pressure by the secondary steam compressor 6 and then used to heat the air in the circulating air heater 9, to preheat the wet material by the spiral conveying jacket of the screw feeder 7, and to heat and insulate the secondary dryer 8 by the jacket. The secondary steam condensate generated in these three processes is discharged.

[0035] The top of silo b12 is equipped with a top bag b12-1. Recycled air, discharged from the top of the secondary dryer 8 and carrying material, enters silo b12, where it undergoes gas-solid separation. The recycle air is then discharged from the top outlet of silo b12 and sent to a recycle air filter 13 for filtration. A star-shaped discharger b15 is installed at the bottom outlet of silo b12 to discharge the product. The outlet of the recycle fan 14 is divided into two paths. The first path connects to the recycle air heater 9, where the recycle air is heated and then re-entered into the bottom of the secondary dryer 8. The second path connects to the air inlet at the top of silo b12, where the recycle air serves as backflush gas for the top bag b12-1 in the top of silo b12. The top outlet of silo b12 is connected to the air inlet of the recycle air filter 13 via a pipeline.

[0036] In the present application, an air filter 16 is further connected to the pipeline between the circulating air filter 13 and the circulating fan 14 through a pipeline to replenish fresh air into the secondary drying system; an induced draft fan 17 is further connected to the pipeline between the air outlet at the top of the silo b 12 and the air inlet of the circulating air filter 13 through a pipeline to discharge part of the exhaust gas. During the circulation process, the humidity of the circulating gas is controlled by the exhaust gas discharge of the induced draft fan 17 and the replenishment of fresh air from the air filter 16.

[0037] Furthermore, the secondary dryer 8 is a cyclone dryer or a fluidized bed dryer, and a jacket is provided on the outside thereof for passing steam for heating. If the secondary dryer 8 adopts a fluidized bed dryer, a built-in bag fluidized bed dryer can be provided.

[0038] During the air exhaust gas circulation process of the present application, the hot channel of the circulating gas heater 9 uses high-temperature and high-pressure secondary steam discharged by the secondary steam compressor 6 with pressurization and temperature increase, or uses superheated steam to heat the circulating gas in the cold channel of the circulating gas heater 9 to meet the temperature requirements for product drying.

[0039] In the closed-loop circulation process of superheated steam in this application, the superheated steam heater 2 uses raw steam provided by the enterprise, or uses electricity, thermal oil, and a combination of these heat sources to heat the circulating superheated steam to meet the temperature requirements for preliminary drying.

[0040] Furthermore, the primary dryer 3 is a rotary flash dryer or a cyclone dryer, which has a jacket on the outside and is heated by steam.

[0041] The low-energy consumption secondary drying system of the present application includes the following sub-processes when in operation:

[0042] 1) Material system:

[0043] The wet material is fed into the primary dryer 3 by the screw feeder 7 and comes into contact with the superheated steam for preliminary drying. It is discharged from the top of the primary dryer 3 into the silo a4 along with the superheated steam, and is separated from the superheated steam through the bag a4-1 on the top of the silo. The material enters the horizontal feeder 11 through the star-shaped discharger a10 and is sent to the secondary dryer 8 by the circulating air for further drying. Then, it enters the silo b12 along with the circulating air, and is separated from the circulating air through the bag b12-1 on the top of the silo. The material is packaged and stored through the star-shaped discharger b15.

[0044] 2) Superheated steam circulation system:

[0045] After being pressurized by the hot steam circulation fan 1, the superheated steam is split into two paths. One path is heated to a certain temperature by the hot steam heater 2 and sent to the primary dryer 3 for preliminary drying of the material. It then carries the preliminarily dried material and the superheated steam generated by the evaporated moisture into the silo a 4. The material is separated by the bag a 4-1 on the top of the silo. It is then filtered through the hot steam high-efficiency filter 5 and recycled. The other path is sent to the backflush air inlet of the bag a 4-1 on the top of the silo to backflush the bag. The backflush superheated steam and the superheated steam used for drying merge inside the silo a 4 and are discharged from the top outlet of the silo a 4. It is filtered through the hot steam high-efficiency filter 5 and recycled.

[0046] 3) Secondary steam reuse system:

[0047] The circulating superheated steam, including the superheated steam generated by evaporation of water in the primary dryer 3, is filtered through a hot steam high-efficiency filter 5. A portion of the superheated steam is then extracted and fed through a secondary steam compressor 6 to increase its temperature and pressure. Alternatively, a portion of the superheated steam is directly extracted and used to heat the circulating gas in the circulating gas heater 9, preheat the wet material in the spiral conveying jacket of the screw feeder 7, and maintain heat in the secondary dryer 8. During these three processes, the secondary steam releases heat, condenses into water, and is discharged.

[0048] 4) Air circulation system:

[0049] After being pressurized by circulating fan 14, air is split into two paths. One path is heated to a certain temperature by circulating air heater 9 and then fed to horizontal feeder 11, which blows the preliminarily dried material from star-shaped discharger a 10 to secondary dryer 8 for further drying. The air, along with the dried material and moisture evaporated during the secondary drying process, enters silo b 12. The material is separated by bag b 12-1 on the top of the silo, filtered by circulating air filter 13, and then recycled. The other path is fed to the backflush inlet of bag b 12-1 on the top of the silo to backflush the bag. The backflush air and the circulating drying air merge inside silo b 12, are discharged from the top outlet of silo b 12, filtered by circulating air filter 13, and then recycled.

[0050] 5) Silo roof bag backflush system:

[0051] The silo top bag a4-1 back-flushing system introduces part of the superheated steam after the superheated steam circulation fan 1 into the back-flushing air inlet of the silo top bag a4-1, performs back-flushing of the superheated steam in each chamber on the silo top bag a4-1, and the back-blown superheated steam is merged into the superheated steam circulation system.

[0052] The silo top bag b 12-1 backflush system introduces part of the circulating air after the circulating fan 14 into the backflush inlet of the silo top bag b 12, performs air chamber backflush on the silo top bag b 12, and the backflush circulating gas is merged into the air circulation system.

[0053] 6) Dehydration discharge system:

[0054] The moisture removed during the drying process is discharged through 6 points: 1) the condensate discharge port in the pipeline before the superheated steam circulation fan 1; 2) the secondary steam condensate discharge port of the circulating gas heater 9; 3) the condensate discharge port of the screw conveying jacket of the screw feeder 7; 4) the condensate discharge port of the external heating accompanying pipe of the secondary dryer; 5) the circulating superheated steam outlet a 4-1 on the top of the silo bag, which is partially discharged to supply other sections according to the system control requirements; 6) the circulating air outlet b 12-1 on the top of the silo bag to control the moisture content in the air circulation system.

[0055] Example 1 Simulation design calculation:

[0056] The initial moisture content of the dried material is 20%, the moisture content after primary drying is 9%, and the moisture content of the product after secondary drying is 5%.

[0057] Heat source: 10kg saturated steam (1.0MPa, 180℃);

[0058] Low energy consumption secondary drying system, calculation process see Figure 1 :

[0059] The primary drying adopts closed-loop superheated steam circulation, with an inlet flash temperature of 170°C (the temperature of the superheated steam entering the primary dryer 3 after passing through the superheated steam heater 2) and an outlet flash temperature of 120°C (the temperature of the superheated steam carrying the preliminarily dried material at the top outlet of the primary dryer 3). The superheated steam heater is a fin heat exchanger, and the heat source is 10kg saturated steam. The primary dryer is a flash dryer.

[0060] The secondary drying adopts partial exhaust gas circulation of air, with an inlet air temperature of 105°C (the circulating air temperature entering the secondary dryer 8) and an exhaust air temperature of 85°C (the circulating air temperature carrying materials at the top outlet of the secondary dryer 8). The secondary dryer is a cyclone dryer, and the cyclone cylinder is half-tube heated. The heat source is the secondary steam after pressurization by the steam compressor. The circulating air heater is a fin heat exchanger, and the heat source is the secondary steam after pressurization by the steam compressor.

[0061] Simulation calculation results show that the steam consumption for drying each ton of product is 10kg, the saturated steam is 200kg, and the electricity consumption for each ton of product is 9 kilowatts (energy consumption for the secondary steam compressor).

[0062] Example 2 Simulation design calculation:

[0063] The initial moisture content of the dried material is 20%, the moisture content after primary drying is 9%, and the moisture content of the product after secondary drying is 5%.

[0064] Heat source: 8 kg of saturated steam (0.8 MPa, 170°C) and 6 kg of saturated steam (0.6 MPa, 159°C).

[0065] Ordinary two-stage circulation drying system:

[0066] The first-level drying adopts closed-loop air circulation, with an inlet flash temperature of 150°C and an outlet flash temperature of 80°C. The superheated steam heater is a fin heat exchanger, and the heat source is 8 kg saturated steam. A dehumidifier is set to separate moisture from the circulating air. The inlet temperature of the dehumidified chilled water is 7°C, the return water temperature is 12°C, and the air temperature after dehumidification is 20°C.

[0067] Secondary drying uses air circulation, with an inlet air temperature of 95°C and an exhaust air temperature of 80°C. The circulating air heater is a fin heat exchanger, and the heat source is 6kg saturated steam.

[0068] Simulation calculation results show that drying each ton of product consumes 330 kg of 8 kg quality saturated steam, and consumes 130 kg of 6 kg quality saturated steam, and 40 tons of refrigerated brine is needed to circulate and dehumidify the air.

[0069] During the simulation, the power consumption of the fan, star-shaped discharger, and feeder was not included. Only the energy consumption for heating the drying medium was compared and calculated. Heat loss was converted to a uniform percentage.

[0070] The contents described in this specification are merely an enumeration of implementation forms of the inventive concept, and the protection scope of the present invention should not be considered as being limited to the specific forms described in the embodiments.

Claims

1. A low energy consumption two-stage drying system, characterized by: It includes a primary drying circulation system and a secondary drying circulation system; The primary drying circulation system comprises a screw feeder (7), a primary dryer (3), a silo a (4), a star-shaped discharger a (10), a superheated steam high efficiency filter (5), a superheated steam circulation fan (1) and a superheated steam heater (2); The wet material is conveyed into the lower part of the first-stage dryer (3) by the screw feeder (7); at the same time, the superheated steam conveyed by the superheated steam circulation fan (1) is heated by the hot steam heater (2) and then enters the bottom of the first-stage dryer (3); the wet material contacts the superheated steam in the first-stage dryer (3) for preliminary drying, and the preliminarily dried material and evaporated water are discharged from the top of the first-stage dryer (3) along with the superheated steam into the silo a (4) for gas-solid separation; the material is discharged from the bottom of the silo a (4) through the star-shaped discharger a (10) and enters the secondary drying circulation system; the superheated steam is discharged from the air outlet at the top of the silo a (4) The excess superheated steam is sent to other sections, and the rest is filtered by the hot steam high-efficiency filter (5) and then divided into two paths: the first path is divided into two branches after passing through the hot steam circulation fan (1). The first branch is sent to the superheated steam heater (2) for heating and then re-enters the primary dryer (3) and the silo a (4). The second branch is sent to the top bag a (4-1) in the upper part of the silo a (4) and used as bag backwash gas. The superheated steam of the two branches merges in the silo a (4); it is discharged from the air outlet at the top of the silo a (4) and recycled through the hot steam high-efficiency filter (5); the second branch of superheated steam is used as a heat source for some equipment; The secondary drying circulation system includes a horizontal feeder (11), a secondary dryer (8), a hopper b (12), a star-shaped discharger b (15), a circulating air filter (13), a circulating air fan (14), a circulating air heater (9), an air filter (16), and an induced draft fan (17); The star-shaped discharger a (10) at the bottom of the silo a (4) is connected to the horizontal feeder (11). After the material is dried at the first level, it is fed from the star-shaped discharger a (10) into the horizontal feeder (11). At the same time, the circulating air delivered by the circulating fan (14) is heated by the circulating air heater (9) and then enters the horizontal feeder (11). The material enters the bottom of the secondary dryer (8) with the circulating air for further drying. The dried product and evaporated water are discharged from the top of the secondary dryer (8) with the circulating air and enter the silo b (12) for gas-solid separation. The material is discharged from the bottom of the silo b (12) through the star-shaped discharger b (15) and the product is collected. The circulating air is discharged from the silo b (12) After the top outlet gas is discharged, it is divided into two paths: the first path is divided into two branches after passing through the circulating gas filter (13) and the circulating fan (14). The first branch is transported to the circulating gas heater (9) for heating and then re-enters the horizontal feeder (11) to send the primary dried material into the secondary dryer (8) and the silo b (12). The second branch is transported to the top bag b (12-1) in the upper part of the silo b (12) to be used as bag back-blowing gas. The gases of the two branches merge in the silo b (12) and are discharged from the top outlet of the silo b (12) and recycled through the circulating gas filter (13); the second path is connected to the induced draft fan (17) to discharge part of the tail gas; The primary drying cycle system also includes a secondary steam compressor (6), and the second superheated steam after being filtered by the hot steam high-efficiency filter (5) is pressurized by the secondary steam compressor (6) to form high-temperature and high-pressure steam to be used as a heat source for some equipment, including a screw feeder (7), a circulating gas heater (9) and a secondary dryer (8). Heat exchange interlayers are provided on the outside of these equipment; the high-temperature and high-pressure steam pressurized by the secondary steam compressor (6) is passed into the heat exchange interlayer outside the screw feeder (7) to preheat the wet material in the screw feeder (7); the circulating gas heater (9) is passed as a heat source to heat the circulating gas; the heat exchange interlayer outside the secondary dryer (8) is passed into the heat exchange interlayer outside the secondary dryer (8) to play a role in heat preservation and heat supply for the secondary dryer (8); the high-temperature and high-pressure steam is condensed and discharged after heat exchange; an exhaust gas discharge pipe is provided on the pipeline between the top air outlet of the silo a (4) and the superheated steam high-efficiency filter (5) to send excess superheated steam to other sections; In the primary drying cycle system, the superheated steam heater (2) uses raw steam or raw steam plus other heat sources to heat the circulating superheated steam to reach the primary drying temperature requirement; the other heat source refers to electricity or thermal oil, or a combination of these heat sources; The primary drying circulation system is a superheated steam circulation system.

2. A low-energy-consumption two-stage drying system according to claim 1, characterized in that: The first-stage dryer (3) is a rotary flash dryer or a cyclone dryer, which has a jacket on the outside and is heated by steam; the second-stage dryer (8) is a cyclone dryer or a fluidized bed dryer, which has a jacket on the outside and is heated by steam.

3. A low-energy-consumption two-stage drying system according to claim 1, characterized in that: The second superheated steam is used as a heat source for some equipment, including a screw feeder (7), a circulating gas heater (9) and a secondary dryer (8), and heat exchange interlayers are provided on the outside of these equipment; the superheated steam is passed into the heat exchange interlayer on the outside of the screw feeder (7) to preheat the wet material in the screw feeder (7); passed into the circulating gas heater (9) as a heat source to heat the circulating gas; passed into the heat exchange interlayer on the outside of the secondary dryer (8) to provide heat insulation and heating for the secondary dryer (8); the superheated steam is condensed and discharged after heat exchange; an exhaust gas discharge pipe is provided on the pipeline between the top air outlet of the silo a (4) and the superheated steam high-efficiency filter (5) to send excess superheated steam to other sections.

4. A low-energy-consumption two-stage drying system according to claim 1, characterized in that: In the secondary drying circulation system, the hot channel of the circulating gas heater (9) uses secondary steam or a combination of secondary steam and raw steam to heat the circulating gas in the cold channel of the circulating gas heater (9), thereby meeting the secondary drying temperature requirement of the product and making full use of the superheated steam generated by the primary drying system; the secondary steam refers to high-temperature and high-pressure steam pressurized by the secondary steam compressor (6), or superheated steam after passing through the hot steam high-efficiency filter (5).

5. The low-energy-consumption two-stage drying system according to claim 1, characterized in that: An air filter (16) is also connected to the pipeline between the circulating air filter (13) and the circulating fan (14) through a pipeline so as to replenish fresh air into the secondary drying circulation system; the circulating air carries the preliminarily dried material into the secondary dryer (8) for further drying, and the evaporated moisture is discharged from the top of the secondary dryer (8) along with the circulating air and enters the silo b (12) for gas-solid separation. The circulating air is discharged from the air outlet at the top of the silo b (12) and then recycled. The humidity of the circulating air is controlled by discharging part of the exhaust gas from the induced draft fan (17) and replenishing fresh air through the air filter (16) to meet the material drying requirements.

6. The low-energy-consumption two-stage drying system according to claim 1, characterized in that: The secondary dryer (8) adopts a built-in bag-type fluidized bed dryer.

7. The low-energy-consumption two-stage drying system according to claim 1, characterized in that: The circulating gas of the secondary drying circulation system is air or inert gas. For drying oxidizable materials, the circulating gas is inert gas, and the air filter (16) is an inert gas supply port.

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