Vacuum rake type drying system for producing granular polyaluminum chloride

Abstract

The utility model discloses a vacuum rake type drying system for producing granular polyaluminum chloride, which comprises a steam source, a raw material tank, a multi-effect evaporator, a vacuum rake type drying machine, a surface condenser, a discharge pump, a vacuum pump, a condensate water tank and a condensate water pump, the multi-effect evaporator utilizes high-temperature steam to increase the concentration of the polyaluminum chloride solution from about 40% to about 70% thick slurry, then the thick slurry is sent into the vacuum rake dryer, the vacuum rake dryer utilizes the high-temperature steam to dry the polyaluminum chloride thick slurry, and granular polyaluminum chloride is produced. The particles are not easy to generate dust pollution in actual use, and the vacuum rake dryer is used for drying crystals, so that the steam consumption is low, the heat utilization rate is high, and the production cost is low.

Description

Technical Field

[0001] The utility model relates to the technical field of polyaluminium chloride production equipment, in particular to a vacuum rake drying system for producing granular polyaluminium chloride. Background Art

[0002] Polyaluminium chloride is a new type of water purification material, an inorganic polymer coagulant, also known as polyaluminium. It has a high degree of electrical neutralization and bridging effect on colloids and particles in water, and can strongly remove micro-toxic substances and heavy metal ions with stable properties. Due to the bridging effect of hydroxide ions and the polymerization of multivalent anions, the produced polyaluminium chloride is an inorganic polymer water treatment agent with a large relative molecular mass and a high charge. In terms of form, it can be divided into solid and liquid. Solids are divided into brown, beige, golden and white according to their colors, and liquids can be colorless and transparent, slightly yellow, light yellow to yellowish brown. Polyaluminium chloride of different colors also has great differences in application and production technology.

[0003] At present, the solid polyaluminium chloride is usually produced by a spray drying method, which is to directly send a polyaluminium chloride solution with a concentration of about 40% into a centrifugal spray drying tower, and then the polyaluminium chloride solution is atomized and dried into a powdered solid polyaluminium chloride under the action of hot air, and the powdered polyaluminium chloride enters a cyclone collector for collection under the action of a blower, and the tail gas discharged by the cyclone collector is discharged after spray washing. In this production method, atomization drying needs to heat the air first, and heating the air requires a large amount of energy. Moreover, the tail gas discharged by the cyclone collector contains a large amount of acidic substances, and the washing water used for spray washing must be purified before it can be discharged. This sewage purification is difficult and costly. In addition, the existing powdered polyaluminium chloride particles are small, and dust pollution is easily generated when actually used, affecting the health of the environment and users. Utility Model Content

[0004] In summary, in order to overcome the shortcomings of the prior art problems, the utility model provides a vacuum rake drying system for the production of granular polyaluminium chloride, which uses steam in an evaporation concentration system to increase the concentration of a polyaluminium chloride solution from about 40% to a concentrated slurry of about 70%, and then sends the concentrated slurry into a vacuum rake dryer for drying to produce granular polyaluminium chloride. The granular polyaluminium chloride is not prone to dust pollution during actual use, and a vacuum rake dryer is used for drying and crystallization, with less steam consumption, high heat utilization rate and low production cost.

[0005] In order to solve the above technical problems, the technical solution adopted by the utility model is:

[0006] A vacuum rake drying system for producing granular polyaluminium chloride, comprising: a steam source, a raw material tank, a multi-effect evaporator, a vacuum rake dryer, a surface condenser, a discharge pump, a vacuum pump, a condensate tank and a condensate pump,

[0007] The steam source provides high-temperature steam for the multiple-effect evaporator and the vacuum rake dryer, and is respectively connected to the air inlet of the multiple-effect evaporator and the air inlet of the vacuum rake dryer through pipelines. The raw material tank is used to collect and store low-concentration polyaluminium chloride liquid. The raw material tank is connected to the feed inlet of the multiple-effect evaporator through a feed pipeline, the discharge port of the multiple-effect evaporator is connected to the feed inlet of a discharge pump, the discharge port of the discharge pump is connected to the feed inlet of the vacuum rake dryer through a pipeline, the discharge port of the vacuum rake dryer is connected to the packaging system, the air outlet of the vacuum rake dryer and the air outlet of the multiple-effect evaporator are respectively connected to the air inlet of the surface condenser through pipelines, the air outlet of the surface condenser is connected to the air inlet of the vacuum pump, the air outlet of the vacuum pump is emptied, the condensate outlet of the surface condenser and the condensate outlet of the multiple-effect evaporator are connected to the water inlet of a condensate tank through pipelines, the water outlet of the condensate tank is connected to the water inlet of a condensate pump through a pipeline, and the water outlet of the condensate pump is connected to a sewage treatment system through a drainage pipeline.

[0008] Furthermore, the multi-effect evaporator comprises a first-effect evaporator, a second-effect evaporator and a third-effect evaporator connected in series, the first-effect evaporator is an external circulation evaporator, the second-effect evaporator and the third-effect evaporator are forced circulation evaporators,

[0009] The air inlet of the first-effect heater of the first-effect evaporator is connected to the steam source through the first-effect air inlet pipeline, the feed inlet of the first-effect separator of the first-effect evaporator is connected to the raw material tank through the first-effect feed pipeline, the discharge port of the first-effect separator is connected to the feed inlet of the first-effect heater through a pipeline, the air outlet of the first-effect separator is connected to the air inlet of the second-effect heater of the second-effect evaporator through the second-effect air inlet pipeline, and the discharge port at the upper end of the first-effect heater is connected to the feed inlet of the first-effect separator of the first-effect evaporator through a pipeline.

[0010] The feed port of the second-effect separator of the second-effect evaporator is connected to the discharge port of the first-effect separator through a second-effect feed pipeline, the discharge port of the second-effect separator is connected to the feed port of the second-effect circulation pump of the second-effect evaporator through a pipeline, the discharge port of the second-effect circulation pump is connected to the circulation feed port of the second-effect heater through a pipeline, the discharge port at the upper end of the second-effect heater is connected to the feed port of the second-effect separator through a pipeline, and the air outlet of the second-effect separator is connected to the air inlet of the three-effect heater of the three-effect evaporator through a three-effect air inlet pipeline.

[0011] The feed port of the triple-effect separator of the triple-effect evaporator is connected to the discharge port of the double-effect separator through a triple-effect feed pipeline, the discharge port of the triple-effect separator is connected to the feed port of the triple-effect circulation pump of the triple-effect evaporator through a pipeline, the discharge port of the triple-effect circulation pump is connected to the circulation feed port of the triple-effect heater and the feed port of the discharge pump through a pipeline, the discharge port at the upper end of the triple-effect heater is connected to the feed port of the triple-effect separator through a pipeline, and the air outlet of the triple-effect separator is connected to the air inlet of the surface condenser through a pipeline.

[0012] Furthermore, the first-effect feed pipeline is provided with a first-effect feed valve, the first-effect separator is provided with a first-effect material level meter, the first-effect material level meter is electrically connected to the first-effect feed valve, and the first-effect feed valve is controlled and adjusted by the first-effect material level meter;

[0013] A first-effect pressure sensor is provided on the first-effect heater, a first-effect air intake valve is provided on the first-effect air intake pipe, the first-effect air intake valve is electrically connected to the first-effect pressure sensor, and the first-effect air intake valve is controlled and adjusted by the first-effect pressure sensor;

[0014] The second-effect feed pipeline is provided with a second-effect feed valve, the second-effect separator is provided with a second-effect material level meter, the second-effect material level meter is electrically connected to the second-effect feed valve, and the second-effect feed valve is controlled and adjusted by the second-effect material level meter;

[0015] The three-effect feed pipeline is provided with a three-effect feed valve, the three-effect separator is provided with a three-effect material level meter, the three-effect material level meter is electrically connected to the three-effect feed valve, and the three-effect feed valve is controlled and adjusted by the three-effect material level meter.

[0016] Furthermore, the first-effect heater is connected to the feed port of the discharge pump through the first-effect drain pipeline, the second-effect heater is connected to the feed port of the discharge pump through the second-effect drain pipeline, and the third-effect heater is connected to the feed port of the discharge pump through the third-effect drain pipeline. The first-effect drain pipeline, the second-effect drain pipeline and the third-effect drain pipeline are all provided with drain valves.

[0017] Furthermore, the condensate outlet of the first-effect heater, the condensate outlet of the second-effect heater, the condensate outlet of the triple-effect heater, and the condensate outlet of the surface condenser are respectively connected to the water inlet of the condensate tank through pipelines.

[0018] Furthermore, the discharge port of the discharge pump is connected to the discharge main pipe, one end of the discharge main pipe is connected to the discharge port of the discharge pump, and the other end of the discharge main pipe is connected to the feed port of the three-effect separator. There are multiple vacuum rake dryers, and multiple vacuum rake dryers are arranged in parallel. The feed port of each vacuum rake dryer is connected to the discharge main pipe through a dry feed pipeline, and a dry feed valve is provided on the dry feed pipeline. The condensate outlet of the vacuum rake dryer is connected to the shell side of the first-effect heater through a pipeline.

[0019] Furthermore, the air inlet of the vacuum rake dryer is connected to the steam source through a dry air inlet pipeline, a dry air inlet valve is arranged on the dry air inlet pipeline, and the vacuum rake dryer is provided with a dry pressure sensor for detecting the steam pressure in the vacuum rake dryer. The dry pressure sensor is electrically connected to the dry air inlet valve, and the dry air inlet valve is controlled and regulated by the dry pressure sensor.

[0020] Furthermore, the condensate tank is provided with a condensate level gauge, the drain pipeline is provided with a drain valve, the condensate level gauge is electrically connected to the drain valve, and the drain valve is controlled and regulated by the condensate level gauge.

[0021] The beneficial effects of the utility model are:

[0022] 1. The utility model utilizes steam in an evaporation concentration system to increase the concentration of a polyaluminium chloride solution from about 40% to a concentrated slurry of about 70%, and then feeds the concentrated slurry into a vacuum rake dryer for drying to produce granular polyaluminium chloride. The granular polyaluminium chloride is not prone to dust pollution in actual use. The vacuum rake dryer is used for drying and crystallization, with less steam consumption, high heat utilization rate and low production cost.

[0023] 2. The multi-effect evaporator of the utility model includes three evaporators connected in series. The polyaluminium chloride solution entering the first-effect evaporator has a low concentration and good fluidity. Therefore, the first-effect evaporator adopts an external circulation evaporator. The concentration of the polyaluminium chloride solution after evaporation and concentration by the first-effect evaporator increases and the fluidity becomes worse. Therefore, the second-effect evaporator and the third-effect evaporator are both forced circulation evaporators. This arrangement saves the circulation pump of the first-effect evaporator, thereby reducing the system construction cost and operation cost.

[0024] 3. The condensed water generated by the vacuum rake dryer of the utility model is transported to the shell side of the first-effect heater through a pipeline. The steam heating chamber of the vacuum rake dryer is at positive pressure, while the shell side of the first-effect heater is at negative pressure. Moreover, the condensed water generated by the vacuum rake dryer has a high temperature. The high-temperature condensed water enters the low pressure from the high pressure. The condensed water flashes and releases heat, and heats the polyaluminium chloride solution in the tube side of the first-effect heater to evaporate and concentrate it, thereby achieving the purpose of recovering the heat of the condensed water, reducing the steam consumption of the first-effect heater, saving energy and reducing costs.

[0025] 4. The utility model has a simple structure, is easy to use, and has low cost, and can effectively realize the production of granular polyaluminium chloride. Moreover, the utility model is provided with a plurality of vacuum rake dryers arranged in parallel, which can effectively improve the drying efficiency, improve the production efficiency, reduce the steam consumption, and reduce the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the utility model. DETAILED DESCRIPTION

[0027] The utility model is further described in detail below in conjunction with the accompanying drawings.

[0028] like Figure 1As shown, a vacuum rake drying system for producing granular polyaluminium chloride comprises a steam source 1, a raw material tank 2, a multiple-effect evaporator, a vacuum rake dryer, a surface condenser 7, a discharge pump 6, a vacuum pump 11, a condensate tank 12 and a condensate pump 13. The steam source 1 provides high-temperature steam for the multiple-effect evaporator and the vacuum rake dryer. The multiple-effect evaporator comprises a first-effect evaporator 3, a second-effect evaporator 4 and a third-effect evaporator 5 connected in series. The first-effect evaporator 3 is an external circulation evaporator, and the second-effect evaporator 4 and the third-effect evaporator 5 are forced circulation evaporators. The air inlet of the first-effect heater 31 of the first-effect evaporator 3 is connected to the steam source 1 through a first-effect air inlet pipeline 32. The first-effect heater 31 is provided with a first-effect pressure sensor 33, and the first-effect air inlet pipeline 32 is provided with a first-effect air inlet valve 34. The first-effect air inlet valve 34 is connected to the first-effect pressure sensor 33. The first-effect pressure sensor 33 is used to control and adjust the first-effect air inlet valve 34. The feed port of the first-effect separator 35 of the first-effect evaporator 3 is connected to the raw material tank 2 through the first-effect feed pipeline 36. The raw material tank 2 is used to collect and store low-concentration polyaluminium chloride liquid. The first-effect feed pipeline 36 is provided with a first-effect feed valve 37. The first-effect material level meter 38 is provided on the first-effect separator 35. The first-effect material level meter 38 is electrically connected to the first-effect feed valve 37. The first-effect feed valve 37 is controlled and adjusted by the first-effect material level meter 38. The discharge port of the first-effect separator 35 is connected to the feed port of the first-effect heater 31 through a pipeline. The air outlet of the first-effect separator 35 is connected to the air inlet of the second-effect heater 41 of the second-effect evaporator 4 through the second-effect air inlet pipeline 43. The discharge port at the upper end of the first-effect heater 31 is connected to the feed port of the first-effect separator 35 of the first-effect evaporator 3 through a pipeline. The feed port of the second-effect separator 42 of the second-effect evaporator 4 is connected to the discharge port of the first-effect separator 35 through the second-effect feed pipeline 44, and the second-effect feed pipeline 44 is provided with a second-effect feed valve 46. The second-effect material level meter 47 is provided on the second-effect separator 42, and the second-effect material level meter 47 is electrically connected to the second-effect feed valve 46. The second-effect feed valve 46 is controlled and adjusted by the second-effect material level meter 47. The discharge port of the second-effect separator 42 is connected to the feed port of the second-effect circulation pump 45 of the second-effect evaporator 4 through a pipeline, and the discharge port of the second-effect circulation pump 45 is connected to the circulation feed port of the second-effect heater 41 through a pipeline, and the discharge port at the upper end of the second-effect heater 41 is connected to The feed port of the second-effect separator 42 and the air outlet of the second-effect separator 42 are connected to the air inlet of the three-effect heater 51 of the three-effect evaporator 5 through the three-effect air inlet pipeline 54. The feed port of the three-effect separator 52 of the three-effect evaporator 5 is connected to the discharge port of the second-effect separator 42 through the three-effect feed pipeline 55. The three-effect feed pipeline 55 is provided with a three-effect feed valve 56. The three-effect material level meter 57 is provided on the three-effect separator 52. The three-effect material level meter 57 is electrically connected to the three-effect feed valve 56. The three-effect feed valve 56 is controlled and adjusted by the three-effect material level meter 57. The discharge port of the three-effect separator 52 is connected to the feed port of the three-effect circulation pump 53 of the three-effect evaporator 5 through a pipeline.The discharge port of the triple-effect circulation pump 53 is connected to the circulation feed port of the triple-effect heater 51 and the feed port of the discharge pump 6 through a pipeline, the discharge port at the upper end of the triple-effect heater 51 is connected to the feed port of the triple-effect separator 52 through a pipeline, and the air outlet of the triple-effect separator 52 is connected to the air inlet of the surface condenser 7 through a pipeline.

[0029] The discharge port of the discharge pump 6 is connected to the discharge main pipe 8, one end of the discharge main pipe 8 is connected to the discharge port of the discharge pump 6, and the other end of the discharge main pipe 8 is connected to the feed port of the triple-effect separator 52. The discharge main pipe 8 is connected to the feed port of the vacuum rake dryer through a dry feed pipeline. The number of the vacuum rake dryers is two, and the two vacuum rake dryers are arranged in parallel, namely, a first vacuum rake dryer 9 and a second vacuum rake dryer 10. The feed port of the first vacuum rake dryer 9 is connected to the discharge main pipe 8 through a first dry feed pipeline 91, and a first dry feed valve 92 is provided on the first dry feed pipeline 91. The air inlet of the first vacuum rake dryer 9 is connected to the steam source 1 through a first dry air inlet pipeline 93, and a first dry air inlet valve 94 is provided on the first dry air inlet pipeline 93. The first vacuum rake dryer 9 is provided with a valve for detecting the steam in the first vacuum rake dryer 9. A first drying pressure sensor 95 for pressure is provided, the first drying pressure sensor 95 is electrically connected to the first drying air inlet valve 94, the first drying air inlet valve 94 is controlled and regulated by the first drying pressure sensor 95, the feed port of the second vacuum rake dryer 10 is connected to the discharge main pipe 8 through the second drying feed pipeline 101, the second drying feed pipeline 101 is provided with a second drying feed valve 102, the air inlet of the second vacuum rake dryer 10 is connected to the steam source 1 through the second drying air inlet pipeline 103, the second drying air inlet pipeline 103 is provided with a second drying air inlet valve 104, the second vacuum rake dryer 10 is provided with a second drying pressure sensor 105 for detecting the steam pressure in the second vacuum rake dryer 10, the second drying pressure sensor 105 is electrically connected to the second drying air inlet valve 104, the second drying air inlet valve 104 is controlled and regulated by the second drying pressure sensor 105. The discharge port of the first vacuum rake dryer 9 and the discharge port of the second vacuum rake dryer 10 are both connected to the packaging system, the air outlet of the first vacuum rake dryer 9 and the air outlet of the second vacuum rake dryer 10 are both connected to the air inlet of the surface condenser 7, the air outlet of the surface condenser 7 is connected to the air inlet of the vacuum pump 11, the air outlet of the vacuum pump 11 is emptied, the condensate outlet of the first vacuum rake dryer 9 and the condensate outlet of the second vacuum rake dryer 10 are connected to the shell side of the first effect heater 31 of the first effect evaporator 3 through a pipeline, and the first effect heater 31 The condensate outlet, the condensate outlet of the second-effect heater 41, the condensate outlet of the triple-effect heater 51, and the condensate outlet of the surface condenser 7 are respectively connected to the water inlet of the condensate tank 12 through pipelines, the water outlet of the condensate tank 12 is connected to the water inlet of the condensate pump 13 through a pipeline, and the water outlet of the condensate pump 13 is connected to the sewage treatment system through a drainage pipeline. A condensate level gauge 14 is provided on the condensate tank 12, and a drain valve 15 is provided on the drainage pipeline. The condensate level gauge 14 is electrically connected to the drain valve 15, and the drain valve 15 is controlled and regulated by the condensate level gauge 14.

[0030] The first-effect heater 31 is connected to the feed port of the discharge pump 6 through the first-effect drain pipeline 16, the second-effect heater 41 is connected to the feed port of the discharge pump 6 through the second-effect drain pipeline 17, and the triple-effect heater 51 is connected to the feed port of the discharge pump 6 through the triple-effect drain pipeline 18. The first-effect drain pipeline 16, the second-effect drain pipeline 17 and the triple-effect drain pipeline 18 are all provided with drain valves.

[0031] When in use, the first-effect air inlet valve 34, the first-effect feed valve 37, and the vacuum pump 11 are started, and the high-temperature steam provided by the steam source 1 enters the shell side of the first-effect heater 31 along the first-effect air inlet pipeline 32, and the polyaluminium chloride solution with a concentration of about 40% enters the first-effect separator 35 along the first-effect feed pipeline 36, and then flows out along the discharge port of the first-effect separator 35, and enters the shell side of the first-effect heater 31 from the lower part of the first-effect heater 31 along the pipeline. In the first-effect heater 31, after the polyaluminium chloride solution is heated to boiling by the high-temperature steam, the water in the solution is vaporized, generating kinetic energy for upward movement, so that the secondary steam and the solution with increased concentration enter the first-effect separator 35 together, and the secondary steam moves upward in the first-effect separator 35, and the solution continues to flow downward and enters the first-effect heater 31 again for heating, so that the self-circulation is carried out, and the polyaluminium chloride solution is evaporated and concentrated for the first time.

[0032] The secondary steam separated by the first-effect separator 35 enters the shell side of the second-effect heater 41 along the second-effect air inlet pipeline 43. Under the action of the vacuum pump 11, the secondary steam flows from bottom to top along the shell side of the second-effect heater 41. The second-effect feed valve 46 is opened, and the polyaluminium chloride solution after being concentrated by the first-effect evaporator 3 enters the second-effect separator 42 along the second-effect feed pipeline 44. The second-effect circulation pump 45 is started. The solution in the second-effect separator 42 enters the tube side of the second-effect heater 41 from the lower end of the second-effect heater 41 under the action of the second-effect circulation pump 45, and flows from bottom to top along the tube side. During the flow process, the solution is heated by the secondary steam, and the solution is evaporated and concentrated again. Then, the solution enters the second-effect separator 42 from the upper end of the second-effect heater 41 for gas-liquid separation. The secondary steam separated by the second-effect separator 42 enters the shell side of the triple-effect heater 51, and the separated solution continues to circulate into the second-effect heater 41 for heating. In this cycle, the polyaluminium chloride solution is evaporated and concentrated for the second time.

[0033] The triple-effect feed valve 56 is opened, and the solution after the second evaporation and concentration enters the triple-effect separator 52 along the triple-effect feed pipeline 55. Then, under the action of the triple-effect circulation pump 53, the solution circulates between the triple-effect heater 51 and the triple-effect separator 52. The solution is heated by the secondary steam separated by the second-effect separator 42 for evaporation and concentration, and the solution is evaporated and concentrated for the third time. The secondary steam separated by the triple-effect separator 52 enters the surface condenser 7 for condensation. Start the discharge pump 6, and the polyaluminium chloride solution after three evaporation concentration flows along the discharge main pipe 8, open the first drying feed valve 92 and the second drying feed valve 102, and the solution enters the first vacuum rake dryer 9 and the second vacuum rake dryer 10 along the first drying feed pipeline 91 and the second drying feed pipeline 101 respectively, open the first drying air inlet valve 94 and the second drying air inlet valve 104, and high-temperature steam enters the first vacuum rake dryer 9 and the second vacuum rake dryer 10, start the two vacuum rake dryers, and use high-temperature steam to dry the concentrated polyaluminium chloride solution, the water in the solution is evaporated, and granular polyaluminium chloride is produced, and then the granular polyaluminium chloride particles enter the packaging system for packaging, and the steam evaporated from the drying enters the surface condenser 7 for condensation.

[0034] The condensed water generated by the steam cooling in the shell side of the first-effect heater 31, the condensed water generated by the secondary steam cooling in the shell side of the second-effect heater 41, the condensed water generated by the secondary steam cooling in the shell side of the triple-effect heater 51 and the condensed water generated by the surface condenser 7 enter the condensed water tank 12, and then are drained under the action of the condensation pump, and then enter the sewage treatment system along the drainage pipeline.

[0035] The condensed water after the steam in the two vacuum rake dryers is cooled and condensed enters the shell side of the first-effect heater 31 along the pipeline. Under the pressure difference between the vacuum rake dryer and the first-effect heater 31, the high-temperature condensed water flashes in the shell side of the first-effect heater 31 to generate flash steam to participate in the heating of the solution, thereby achieving the purpose of condensed water heat recovery.

[0036] It should be noted that the above-described embodiments are illustrative rather than limiting of the technical solution of the utility model. Equivalent substitutions made by ordinary technicians in the relevant technical field or other modifications made according to the prior art should be included in the scope of rights required by the utility model as long as they do not exceed the idea and scope of the technical solution of the utility model.

Claims

1. A vacuum rake drying system for producing granular polyaluminium chloride, characterized in that: It includes a steam source (1), a raw material tank (2), a multiple-effect evaporator, a vacuum rake dryer, a surface condenser (7), a discharge pump (6), a vacuum pump (11), a condensate tank (12) and a condensate pump (13), The steam source (1) provides high-temperature steam for the multiple-effect evaporator and the vacuum rake dryer, and is connected to the air inlet of the multiple-effect evaporator and the air inlet of the vacuum rake dryer through pipelines. The raw material tank (2) is used to collect and store low-concentration polyaluminium chloride liquid. The raw material tank (2) is connected to the feed inlet of the multiple-effect evaporator through a feed pipeline. The discharge port of the multiple-effect evaporator is connected to the feed inlet of a discharge pump (6). The discharge port of the discharge pump (6) is connected to the feed inlet of the vacuum rake dryer through a pipeline. The discharge port of the vacuum rake dryer is connected to the packaging system. The air outlet of the dryer and the air outlet of the multi-effect evaporator are respectively connected to the air inlet of the surface condenser (7) through pipelines, the air outlet of the surface condenser (7) is connected to the air inlet of the vacuum pump (11), the air outlet of the vacuum pump (11) is emptied, the condensate outlet of the surface condenser (7) and the condensate outlet of the multi-effect evaporator are connected to the water inlet of the condensate tank (12) through pipelines, the water outlet of the condensate tank (12) is connected to the water inlet of the condensate pump (13) through pipelines, and the water outlet of the condensate pump (13) is connected to the sewage treatment system through a drainage pipeline.

2. The vacuum rake drying system for producing granular polyaluminium chloride according to claim 1, characterized in that: The multi-effect evaporator comprises a first-effect evaporator (3), a second-effect evaporator (4) and a third-effect evaporator (5) connected in series, wherein the first-effect evaporator (3) is an external circulation evaporator, and the second-effect evaporator (4) and the third-effect evaporator (5) are forced circulation evaporators. The air inlet of the first-effect heater (31) of the first-effect evaporator (3) is connected to the steam source (1) through a first-effect air inlet pipeline (32); the feed port of the first-effect separator (35) of the first-effect evaporator (3) is connected to the raw material tank (2) through a first-effect feed pipeline (36); the discharge port of the first-effect separator (35) is connected to the feed port of the first-effect heater (31) through a pipeline; the air outlet of the first-effect separator (35) is connected to the air inlet of the second-effect heater (41) of the second-effect evaporator (4) through a second-effect air inlet pipeline (43); the discharge port at the upper end of the first-effect heater (31) is connected to the feed port of the first-effect separator (35) of the first-effect evaporator (3) through a pipeline. The feed port of the second-effect separator (42) of the second-effect evaporator (4) is connected to the discharge port of the first-effect separator (35) through a second-effect feed pipeline (44); the discharge port of the second-effect separator (42) is connected to the feed port of the second-effect circulation pump (45) of the second-effect evaporator (4) through a pipeline; the discharge port of the second-effect circulation pump (45) is connected to the circulation feed port of the second-effect heater (41) through a pipeline; the discharge port at the upper end of the second-effect heater (41) is connected to the feed port of the second-effect separator (42) through a pipeline; the air outlet of the second-effect separator (42) is connected to the air inlet of the three-effect heater (51) of the three-effect evaporator (5) through a three-effect air inlet pipeline (54); The feed port of the triple-effect separator (52) of the triple-effect evaporator (5) is connected to the discharge port of the double-effect separator (42) through a triple-effect feed pipeline (55); the discharge port of the triple-effect separator (52) is connected to the feed port of the triple-effect circulation pump (53) of the triple-effect evaporator (5) through a pipeline; the discharge port of the triple-effect circulation pump (53) is connected to the circulation feed port of the triple-effect heater (51) and the feed port of the discharge pump (6) through a pipeline; the discharge port at the upper end of the triple-effect heater (51) is connected to the feed port of the triple-effect separator (52) through a pipeline; and the air outlet of the triple-effect separator (52) is connected to the air inlet of the surface condenser (7) through a pipeline.

3. The vacuum rake drying system for producing granular polyaluminium chloride according to claim 2, characterized in that: The first-effect feed pipeline (36) is provided with a first-effect feed valve (37), and the first-effect separator (35) is provided with a first-effect material level meter (38). The first-effect material level meter (38) is electrically connected to the first-effect feed valve (37), and the first-effect feed valve (37) is controlled and adjusted by the first-effect material level meter (38); A first-effect pressure sensor (33) is provided on the first-effect heater (31), a first-effect air intake valve (34) is provided on the first-effect air intake pipeline (32), the first-effect air intake valve (34) is electrically connected to the first-effect pressure sensor (33), and the first-effect air intake valve (34) is controlled and regulated by the first-effect pressure sensor (33); The second-effect feed pipeline (44) is provided with a second-effect feed valve (46), the second-effect separator (42) is provided with a second-effect material level meter (47), the second-effect material level meter (47) is electrically connected to the second-effect feed valve (46), and the second-effect feed valve (46) is controlled and adjusted by the second-effect material level meter (47); The three-effect feed pipeline (55) is provided with a three-effect feed valve (56), and the three-effect separator (52) is provided with a three-effect material level meter (57). The three-effect material level meter (57) is electrically connected to the three-effect feed valve (56), and the three-effect feed valve (56) is controlled and regulated by the three-effect material level meter (57).

4. The vacuum rake drying system for producing granular polyaluminium chloride according to claim 2, characterized in that: The first-effect heater (31) is connected to the feed port of the discharge pump (6) via the first-effect drain pipeline (16), the second-effect heater (41) is connected to the feed port of the discharge pump (6) via the second-effect drain pipeline (17), and the third-effect heater (51) is connected to the feed port of the discharge pump (6) via the third-effect drain pipeline (18). Drain valves are provided on the first-effect drain pipeline (16), the second-effect drain pipeline (17) and the third-effect drain pipeline (18).

5. The vacuum rake drying system for producing granular polyaluminium chloride according to claim 2, characterized in that: The condensate outlet of the first-effect heater (31), the condensate outlet of the second-effect heater (41), the condensate outlet of the third-effect heater (51), and the condensate outlet of the surface condenser (7) are respectively connected to the water inlet of the condensate tank (12) through pipelines.

6. The vacuum rake drying system for producing granular polyaluminium chloride according to claim 2, characterized in that: The discharge port of the discharge pump (6) is connected to the discharge main pipe (8), one end of the discharge main pipe (8) is connected to the discharge port of the discharge pump (6), and the other end of the discharge main pipe (8) is connected to the feed port of the three-effect separator (52). There are multiple vacuum rake dryers, and the multiple vacuum rake dryers are arranged in parallel. The feed port of each vacuum rake dryer is connected to the discharge main pipe (8) through a drying feed pipeline. The drying feed pipeline is provided with a drying feed valve. The condensate outlet of the vacuum rake dryer is connected to the shell side of the first-effect heater (31) through a pipeline.

7. The vacuum rake drying system for producing granular polyaluminium chloride according to claim 6, characterized in that: The air inlet of the vacuum rake dryer is connected to a steam source (1) via a dry air inlet pipeline, a dry air inlet valve is provided on the dry air inlet pipeline, and a dry pressure sensor for detecting the steam pressure in the vacuum rake dryer is provided on the vacuum rake dryer. The dry pressure sensor is electrically connected to the dry air inlet valve, and the dry air inlet valve is controlled and regulated by the dry pressure sensor.

8. The vacuum rake drying system for producing granular polyaluminium chloride according to claim 1, characterized in that: The condensate tank (12) is provided with a condensate level meter (14), the drain pipeline is provided with a drain valve (15), the condensate level meter (14) is electrically connected to the drain valve (15), and the drain valve (15) is controlled and regulated by the condensate level meter (14).

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