An ultra-high molecular weight polyethylene slurry filtering, washing, pre-drying system and processing method

Abstract

The application provides a kind of ultra-high molecular weight polyethylene slurry filtering, washing, pre-drying system and processing method, relating to ultra-high molecular weight polyethylene device, including pressure filter, the frame of pressure filter is divided into multiple independent filter units along circumference, drum is equipped in frame, control head is equipped in frame and drum;Multiple filter units are divided into filter unit group, washing unit group, pre-drying unit group and unloading unit.Compared with prior art, the application uses rotary pressure filter instead of the combination process of "centrifuge + stripping kettle + dehydrator" of existing ultra-high molecular weight polyethylene slurry post-treatment unit, separates the solvent of slurry, washes slurry and pre-dries slurry in one equipment, washes filter cake by using hexane solvent exchange and hot water washing combination, shortens process flow, and is more energy-saving compared with the way of completely evaporating solvent in stripping kettle by using hot water.

Description

TECHNICAL FIELD

[0001] The present application relates to an ultra-high molecular weight polyethylene device, in particular to an ultra-high molecular weight polyethylene slurry filtering, washing, pre-drying system and processing method. BACKGROUND

[0002] The existing ultra-high molecular weight polyethylene slurry post-treatment unit slurry washing and drying section is to send the slurry of the polymerization section into a centrifuge for solid-liquid separation, to preliminarily recover the solvent in the slurry, and to send the ultra-high molecular weight polyethylene filter cake after centrifugal separation into a stripping kettle for complete separation of the solvent through hot water distillation, to evaporate and remove the water in the product through pre-drying and drying processes, and to obtain the UHMWPE product. The process technology of "centrifuge - stripping kettle - dehydrator - dryer" has a process flow diagram as shown in Figure 1 .

[0003] The process technology has the following disadvantages:

[0004] (1) Long process flow: the "filtering, washing, drying" process of the ultra-high molecular weight polyethylene polymerization slurry needs to be completed in multiple sets of equipment such as "centrifuge, stripping kettle, dehydrator, bag collector, dryer", and needs auxiliary equipment such as conveying pump, fan, buffer tank, and matched pipelines, pipe fittings, valves, etc. between the equipment, so the process flow is long.

[0005] (2) High equipment failure rate: the ultra-high molecular weight polyethylene slurry uses a horizontal centrifuge for preliminary separation of the solvent. Since the particle size of the ultra-high molecular weight polyethylene powder is very small, in order to achieve good separation effect, the rotation speed of the centrifuge is very high, which is easy to cause the solid to be plasticized and caked by friction with the inner wall of the centrifuge. The centrifuge itself has a slow response to the adjustment mechanism, and if the discharge of the previous section fluctuates, the centrifuge is difficult to adapt to the rapid change of the feed, which increases the probability of centrifuge failure and affects normal production.

[0006] (3) Large equipment volume and high energy consumption: the ultra-high molecular weight polyethylene filter cake after centrifuge treatment needs to be washed and stripped by hot water to remove the solvent. This process is completed in two stripping kettles with hot water. The stripping kettle is not only large in size, but also needs to introduce a large amount of steam into the stripping kettle to evaporate the remaining solvent in the filter cake, which is high in energy consumption.

[0007] (4) Low capacity of a single line: the ultra-high molecular weight polyethylene wet material after washing in the stripping kettle needs to be sent into a dehydrator for pre-dewatering and then into a dryer for drying. Due to the limitation of the processing capacity of the dehydrator, the processing capacity of a single dehydrator can only reach 2.5 tons / hour, which is difficult to meet the increasing capacity demand. SUMMARY

[0008] To solve the above problems, the application provides a kind of ultra-high molecular weight polyethylene slurry filtering, washing, pre-drying system, using rotary pressure filter instead of the existing ultra-high molecular weight polyethylene slurry post-processing unit "centrifuge + stripping kettle + dehydrator" combined process, the solvent separation of slurry, slurry washing, slurry pre-drying is integrated in a device to complete, greatly shorten the original process.

[0009] The technical scheme adopted by the application is:

[0010] A kind of ultra-high molecular weight polyethylene slurry filtering, washing, pre-drying system, including pressure filter, the frame of pressure filter is divided into multiple independent filtration units along circumference, frame is equipped with drum for driving material rotation in filtration unit, control head is sleeved in frame and drum;Multiple filtration units are divided into filtration unit group for separating solid powder and mother liquor in slurry to form filter cake, washing unit group for washing filter cake multiple times to replace and evaporate hexane solvent in filter cake, pre-drying unit group for drying filter cake after washing and unloading unit for conveying filter cake after pre-drying;Filtration unit group is communicated with slurry conveying pump for conveying polyethylene and hexane slurry containing slurry, first nitrogen input port for inputting circulating nitrogen for first pressure filtration and mother liquor tank for receiving mother liquor generated after forming filter cake and mixing with nitrogen and hexane gas;Washing unit group is communicated with washing liquid conveying pump for conveying washing liquid and washing liquid supplementing pipeline for supplementing washing liquid, and washing liquid heater is communicated with washing liquid supplementing pipeline;Pre-drying unit group is communicated with second nitrogen input port for inputting circulating nitrogen for second pressure filtration;Washing unit group and pre-drying unit group are also communicated with oil-water separation tank for receiving mixed gas after pressure filtration and washing liquid after washing, and the gas phase of oil-water separation tank is communicated with the gas phase of mother liquor tank through pipeline, the gas phase outlet of oil-water separation tank is communicated with condenser and circulating gas compressor in sequence through pipeline, circulating gas compressor is communicated with first nitrogen input port and second nitrogen input port through pipeline, condenser is also communicated with oil-water separation tank through pipeline, the water phase outlet of oil-water separation tank is communicated with washing liquid conveying pump, and the oil phase outlet of oil-water separation tank is communicated with recovery solvent pump;The outlet of unloading unit is provided with screw conveyor below for conveying filter cake after drying to subsequent powder drying system.

[0011] Preferably, the discharge port of the unloading unit in the pressure filter is also communicated with a filter cloth flushing liquid tank for receiving filter cloth flushing liquid, and the filter cloth flushing liquid tank is communicated with the oil-water separation tank through a filter cloth flushing liquid pump.

[0012] Preferably, the pre-drying unit group is also communicated with a supplementary nitrogen inlet, and the supplementary nitrogen inlet is communicated with a compressed nitrogen pipeline.

[0013] Preferably, the frame of the pressure filter is divided into seven independent filter units, which are named as the first filter unit, the second filter unit, the third filter unit, the fourth filter unit, the fifth filter unit, the sixth filter unit and the seventh filter unit in the order of feeding; the first filter unit and the second filter unit form a filter unit group, the first filter unit is communicated with the slurry conveying pump, the first nitrogen input port is arranged in the second filter unit, and the first filter unit and the second filter unit are both communicated with the mother liquor tank; the third filter unit, the fourth filter unit and the fifth filter unit form a washing unit group, the washing liquid conveying pump communicated with the oil-water separation tank is communicated with the third filter unit, the fourth filter unit and the fifth filter unit through pipelines, and the third filter unit, the fourth filter unit and the fifth filter unit are also communicated with the oil-water separation tank through pipelines; the sixth filter unit is a pre-drying unit group, the second nitrogen input port is arranged in the sixth filter unit, and the sixth filter unit is also communicated with the oil-water separation tank through a pipeline; and the seventh filter unit is a discharging unit.

[0014] Preferably, the washing liquid heater is communicated with the fifth filter unit through a pipeline, and the washing liquid heater is provided with a hot water inlet and a hot water outlet.

[0015] The application also provides a post-processing method of an ultra-high molecular weight polyethylene polymer slurry based on a filtering and washing and pre-drying system of the slurry, which comprises the following steps:

[0016] In step (1), the slurry containing polyethylene and hexane is input into the filter unit group in the pressure filter through the slurry conveying pump for filtration, the solid powder in the slurry is separated from the mother liquor to form a filter cake, the first pressure filtration is performed on the filter cake by the circulating nitrogen input through the first nitrogen input port, and the separated mother liquor and the nitrogen containing hexane gas are conveyed into the mother liquor tank through the control head and the pipeline of the pressure filter;

[0017] In step (2), the filter cake formed in step (1) enters the washing unit group when the drum rotates, the washing liquid conveyed by the washing liquid conveying pump and the supplementary washing liquid heated by the washing liquid heater in the washing unit group are used to wash the filter cake, the hexane solvent in the filter cake is replaced and heated and evaporated, and the washed washing liquid and the azeotrope steam formed by evaporation enter the oil-water separation tank through the control head and the pipeline of the pressure filter;

[0018] In step (3), the washed filter cake in step (2) enters the pre-drying unit group when the drum rotates, the second pressure filtration is performed on the washed filter cake by the circulating nitrogen input through the second nitrogen input port of the pre-drying unit group to obtain the filter cake pre-removed of water and the separated washing liquid, and the separated washing liquid and the circulating nitrogen enter the oil-water separation tank through the control head and the pipeline of the pressure filter;

[0019] Step (4), the filter cake pre-dried in step (3) enters the unloading unit when the drum rotates, is discharged from the pressure filter by mechanical and gravitational action, and is transported to the subsequent powder drying system by a screw conveyor.

[0020] Preferably, the frame of the pressure filter is divided into seven independent filter units, which are distributed around the center of the frame and are named as the first filter unit, the second filter unit, the third filter unit, the fourth filter unit, the fifth filter unit, the sixth filter unit and the seventh filter unit in the order of feeding; the first filter unit and the second filter unit form the filter unit group in step (1), the third filter unit, the fourth filter unit and the fifth filter unit form the washing unit group in step (2), the sixth filter unit is the pre-drying unit group in step (3), and the seventh filter unit is the unloading unit in step (4).

[0021] More preferably, the first filter unit in step (1) is communicated with the slurry conveying pump, the second filter unit has a first nitrogen input port, and both the first filter unit and the second filter unit are communicated with the mother liquor tank.

[0022] More preferably, in step (2), the washing liquid from the bottom of the oil-water separation tank is pressurized by a washing liquid conveying pump and then proportionally introduced into the third filter unit, the fourth filter unit and the fifth filter unit to wash the filter cake and replace the hexane solvent in the filter cake, and the washed washing liquid enters the oil-water separation tank; the fifth filter unit is further communicated with a washing liquid supplement pipeline for supplementing the washing liquid, the washing liquid from the oil-water separation tank and the fresh washing liquid supplement are mixed and then heated by a washing liquid heater before being introduced into the fifth filter unit to wash the filter cake and evaporate the hexane solvent in the filter cake.

[0023] More preferably, the water phase outlet and the oil phase outlet of the oil-water separation tank are communicated with the washing liquid conveying pump and the recovered solvent pump, respectively; the gas phase of the oil-water separation tank is communicated with the gas phase of the mother liquor tank through a pipeline, and the gas phase outlet of the oil-water separation tank is further communicated with a condenser and a circulating gas compressor in sequence through a pipeline; the pressurized circulating nitrogen gas after the circulating gas compressor is divided into two parts, one part enters the first nitrogen input port of the second filter unit in step (1), and the other part enters the second nitrogen input port of the sixth filter unit in step (3); the hexane liquid condensed by the condenser is recovered to the oil-water separation tank through a pipeline.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] 1. This invention uses a rotary pressure filter to replace the existing combined process of "centrifuge + stripping kettle + dewatering machine" for the post-treatment unit of ultra-high molecular weight polyethylene sludge. The solvent separation, sludge washing and sludge pre-drying of the sludge are completed in one piece of equipment, which greatly shortens the original process flow.

[0026] 2. This invention employs a combination of solvent exchange and hot water washing to wash the filter cake: the first two washes use low-temperature hot water (below the boiling point of hexane) to exchange hexane solvent and preheat the filter cake, replacing most of the hexane solvent in the filter cake with water. The third wash uses hot water above 90°C. This method can effectively remove residual hexane solvent from the filter cake. At the same time, since most of the solvent does not undergo a vaporization process but is separated from the solid material in the form of solvent exchange, it is more energy-efficient than the method of completely evaporating the solvent in the stripping kettle using hot water.

[0027] 3. This invention uses a rotary filter press for slurry treatment, which avoids the drawback of low single-line capacity due to the limited processing capacity of dewatering machines in existing technologies, and greatly improves the material processing capacity of a single line. Attached Figure Description

[0028] Figure 1 This is a process flow diagram of the existing "centrifuge-stripping kettle-dehydrator-dryer" process technology;

[0029] Figure 2 This is a schematic diagram of an ultra-high molecular weight polyethylene slurry filtration, washing, and pre-drying system provided by the present invention.

[0030] Figure 3 This is a schematic diagram of the working process of a pressure filter in an ultra-high molecular weight polyethylene slurry filtration, washing, and pre-drying system provided by the present invention. Detailed Implementation

[0031] The specific embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0032] Figure 2 and Figure 3 This is a schematic diagram of an ultra-high molecular weight polyethylene slurry filtration, washing, and pre-drying system provided by the present invention. Figure 2 and Figure 3As shown, the system comprises a pressure filter, the frame of the pressure filter is divided into a plurality of independent filter units along the circumference, a rotating drum for driving the material in the filter unit to rotate is arranged in the frame, and a control head is arranged in the frame and the rotating drum; the plurality of filter units are divided into a filter unit group 10 for separating solid powder and mother liquor in the slurry to form filter cake, a washing unit group 20 for washing the filter cake for multiple times to replace and evaporate the hexane solvent in the filter cake, a pre-drying unit group 30 for drying the filter cake after washing, and a discharge unit 40 for conveying the filter cake after pre-drying; the filter unit group 10 is communicated with a slurry conveying pump 11 for conveying the slurry containing polyethylene and hexane, a first nitrogen gas input port 13 for inputting circulating nitrogen gas for the first pressure filtration, and a mother liquor tank 12 for receiving the mother liquor generated after forming the filter cake and mixed with nitrogen gas and hexane gas; the washing unit group 20 is communicated with a washing liquid conveying pump 21 for conveying the washing liquid and a washing liquid supplement pipeline for supplementing the washing liquid, and the washing liquid supplement pipeline is communicated with a washing liquid heater 26; the pre-drying unit group 30 is communicated with a second nitrogen gas input port 31 for inputting circulating nitrogen gas for the second pressure filtration; the washing unit group and the pre-drying unit group are further communicated with an oil-water separation tank 22 for receiving the mixed gas after pressure filtration and the washing liquid after washing, the gas phase of the oil-water separation tank 22 is communicated with the gas phase of the mother liquor tank 12 through a pipeline, the gas phase outlet of the oil-water separation tank 22 is communicated with a condenser 24 and a circulating gas compressor 25 in sequence through a pipeline, the circulating gas compressor 25 is communicated with the first nitrogen gas input port 13 and the second nitrogen gas input port 31 through a pipeline, the condenser 24 is further communicated with the oil-water separation tank 22 through a pipeline, the water phase outlet of the oil-water separation tank 22 is communicated with the washing liquid conveying pump 21, and the oil phase outlet of the oil-water separation tank 22 is communicated with a recovery solvent pump 23; a spiral conveyor 50 for conveying the filter cake after drying to a subsequent powder drying system is arranged below the outlet of the discharge unit 40, so that the separation of the solvent of the slurry, the washing of the slurry and the pre-drying of the slurry are integrated in the pressure filter and the original process flow is greatly shortened.

[0033] As a preferred embodiment, as shown in the figure, Figure 2 The frame of the pressure filter is divided into seven independent filter units, which are respectively named as a first filter unit 101, a second filter unit 102, a third filter unit 103, a fourth filter unit 104, a fifth filter unit 105, a sixth filter unit 106 and a seventh filter unit 107 according to the feeding sequence; the first filter unit 101 and the second filter unit 102 form the filter unit group 10, the third filter unit 103, the fourth filter unit 104 and the fifth filter unit 105 constitute the washing unit group 20, the sixth filter unit 106 is the pre-drying unit group 30, and the seventh filter unit 107 is the discharge unit 40.

[0034] The first filtering unit 101 is communicated with the slurry conveying pump 11 and the mother liquor tank 12; the UHMWPE (ultra high molecular weight polyethylene) slurry containing hexane, which is obtained by polymerization under the condition of slurry polymerization, is conveyed to the first filtering unit 101 through the slurry conveying pump 11, and the solid powder and the mother liquor in the slurry are continuously separated, the separated solid powder forms a filter cake on the filter cloth, the separated mother liquor is conveyed to the mother liquor tank 12 through the control head and pipeline of the pressure filter and is collected, and is sent into the mother liquor recovery system through the action of the mother liquor pump 121. Here, the UHMWPE (ultra high molecular weight polyethylene) slurry containing hexane contains hexane gas and hexane solvent.

[0035] The second filtering unit 102 is provided with a first nitrogen gas input port 13 and is also communicated with the mother liquor tank 12; the filter cake accumulated in the first filtering unit 101 enters the second filtering unit 102 along with the rotation of the rotating drum in the rotary pressure filter, the circulating nitrogen gas entering from the first nitrogen gas input port 13 performs the first pressure filtration on the filter cake, and further separates the mother liquor in the filter cake; the nitrogen gas mixed with hexane gas after pressure filtration and the separated mother liquor are conveyed to the mother liquor tank 12 through the control head and pipeline of the pressure filter.

[0036] The third filtering unit 103 is communicated with the washing liquid conveying pump 21 and the oil-water separation tank 22 through pipelines; the filter cake in the second filtering unit 102 in the rotary pressure filter enters the third filtering unit 103 along with the rotation of the rotating drum, and the washing liquid for washing the filter cake is added into the third filtering unit 103 through the washing liquid conveying pump 21 according to a certain volume ratio, so as to perform the first washing on the filter cake in the third filtering unit 103, the washed washing liquid is discharged from the third filtering unit 103 through the filter cloth, is discharged into the oil-water separation tank 22 through the control head and the washing liquid pipe connected with the third filtering unit 103; in the washing process in the third filtering unit 103, the washing liquid displaces the hexane solvent in the filter cake, and the filter cake is preheated.

[0037] The fourth filtering unit 104 is communicated with the washing liquid conveying pump 21 and the oil-water separation tank 22 through pipelines; the suspended matter after the first washing from the third filtering unit 103 in the rotary pressure filter enters the fourth filtering unit 104 along with the rotation of the rotating drum, and the washing liquid for washing the suspended matter is added into the fourth filtering unit 104 through the washing liquid conveying pump 21 according to a certain volume ratio, so as to perform the second washing on the suspended matter in the fourth filtering unit 104, the washing liquid is discharged from the fourth filtering unit 104 through the filter cloth, is discharged into the oil-water separation tank 22 together with the washing liquid produced by the first washing in the third filtering unit 103 through the control head and the washing liquid pipe connected with the fourth filtering unit 104. In the washing process in the fourth filtering unit 104, the washing liquid further displaces the hexane solvent in the suspended matter, and the filter cake is further heated.

[0038] The fifth filtering unit 105 is communicated with the washing liquid delivery pump 21 and the oil-water separation tank 22 through a pipeline, and is also communicated with a supplementary washing liquid pipeline for supplementing the washing liquid, the supplementary washing liquid pipeline is communicated with a washing liquid heater 26, the washing liquid heater 26 is provided with a hot water inlet and a hot water outlet; the suspended solids from the fourth filtering unit 104 in the rotary pressure filter after the secondary washing enter the fifth filtering unit 105 along with the rotation of the drum, the washing liquid input by the washing liquid delivery pump 21 is mixed with the fresh washing liquid input by the supplementary washing liquid pipeline, then is heated to 90 DEG C through the washing liquid heater 26, and then enters the fifth filtering unit 105 according to a certain volume ratio, so that the suspended solids in the fifth filtering unit 105 are washed for the third time, the washed washing liquid passes through the filter cloth and is discharged from the fifth filtering unit 105, and then is collected with the washing liquid produced by the primary washing in the third filtering unit 103 and the washing liquid produced by the secondary washing in the fourth filtering unit 104, and is discharged into the oil-water separation tank 22 through the control head connected with the fifth filtering unit 105 and the washing liquid pipeline. In the washing process in the fifth filtering unit 105, the hexane solvent in the suspended solids is evaporated to form the azeotrope steam of hexane and water under the heating action of the hot washing liquid, and the azeotrope steam is also discharged into the oil-water separation tank 22 along with the washed washing liquid.

[0039] It is worth noting that the washing process of the filter cake can be N (N≥1) times, the washing liquid can be a polymerization solvent or process water (hot water), and the temperature of the washing liquid can be controlled through a heat exchanger; in the washing process, multi-stage washing is adopted, the filter cake is replaced with the washing liquid, the content of the hexane solvent in the filter cake is further reduced, and the washing liquid has a heating effect on the hexane solvent in the filter cake, so that the temperature of the filter cake approaches the boiling point of the hexane solvent before entering the last stage of washing; in the last stage of washing, the washing liquid is further heated, so that the temperature of the washing liquid is higher than the boiling point of the hexane solvent, so that the filter cake enters the last stage of washing, and the replacement of the hexane solvent and the evaporation of the solvent exist simultaneously, the hexane solvent in the filter cake is completely removed, and the azeotrope steam formed by evaporation is discharged along with the washing liquid.

[0040] The washing liquid used in the third filtering unit 103, the fourth filtering unit 104 and the fifth filtering unit 105 can all be the washing solvent recovered from the oil-water separation tank 22, or all be fresh washing liquid from outside the system or a mixture of the recovered washing liquid and the fresh washing liquid in any proportion. According to the source of the washing liquid, the washing liquid recovered from the bottom of the oil-water separation tank 22 is pressurized by the washing liquid delivery pump 21 and then is proportionally introduced into the third filtering unit 103, the fourth filtering unit 104 and the fifth filtering unit 105 of the pressure filter, so as to perform cyclic washing on the filter cake, or is directly discharged without being recycled.

[0041] The sixth filtering unit 106 is a pre-drying unit group 30; the suspension after three times of washing from the fifth filtering unit 105 in the rotary pressure filter enters the sixth filtering unit 106 along with the rotation of the drum; meanwhile, the circulating nitrogen gas pressurized by the circulating gas compressor 25 is divided into two parts, one part enters the first nitrogen gas input port 13 of the second filtering unit 102, and the other part enters the second nitrogen gas input port 31 of the sixth filtering unit 106, to perform the second pressure filtration on the filter cake to achieve the effect of pre-drying the filter cake and remove the content of the washing liquid in the filter cake; the circulating compressed nitrogen gas after pressure filtration and the washing liquid are discharged from the sixth filtering unit 106 together through the filter cloth, and are discharged into the oil-water separation tank 22 together with the washing liquid generated by the three times of washing after being collected by the control head connected with the sixth filtering unit 106 and the washing liquid pipe. The gas for pressure filtration in the second filtering unit 102 and the sixth unit 106 can be nitrogen gas, water vapor or a mixture of nitrogen gas and water vapor.

[0042] The pre-drying unit group 30 is also connected with a supplementary nitrogen gas inlet, which is connected with the compressed nitrogen gas pipeline; when the nitrogen gas in the system is insufficient, the compressed nitrogen gas can be supplemented to perform pressure filtration on the filter cake.

[0043] The seventh filtering unit 107 is a discharging unit 40; the filter cake from the sixth filtering unit 106 of the rotary pressure filter enters the discharging unit 40 along with the rotation of the equipment; the discharging unit 40 is a non-pressure unit, the filter cake entering the discharging unit 40 falls off from the filter cloth under the joint action of the scraper and the compressed nitrogen gas for back blowing and is discharged from the discharging unit by gravity, and is transported to the subsequent drying system by the screw conveyor 50.

[0044] The lower discharge port of the pressure filter is also connected with a filter cloth washing liquid tank 51 for receiving filter cloth washing liquid; the filter cloth washing liquid tank 51 is connected with the oil-water separation tank 22 through a filter cloth washing liquid pump 52; after the discharging is completed, the pressure filter is washed using process water; the washing water is discharged from the lower discharge port of the pressure filter into the filter cloth washing liquid tank 51, and is then pressurized by the filter cloth washing liquid pump 52 and transported to the oil-water separation tank 22.

[0045] The gas phase of the oil-water separation tank 22 is communicated with the gas phase of the mother liquor tank 12 through a pipeline, the gas phase outlet at the top of the oil-water separation tank 22 is communicated with a condenser 24 and a circulating gas compressor 25 through a pipeline in sequence, the circulating gas compressor 25 is communicated with a first nitrogen input port 13 and a second nitrogen input port 31 through a pipeline, and the first condenser 24 is provided with a cooling water inlet and a cooling water outlet; the circulating nitrogen gas containing hexane gas in the mother liquor tank 12 and the mixed gas containing hexane and nitrogen in the oil-water separation tank 22 are collected and then enter the condenser 24, and the mixed gas is indirectly contacted with cooling water to exchange heat and is cooled, most of the hexane gas is condensed to form hexane liquid which returns to the oil-water separation tank 22 through a gravity flow pipeline, and the hexane gas and nitrogen which are not condensed are pressurized through the circulating gas compressor 25 and then are divided into two paths and return to the second filter unit 102 and the sixth filter unit 106 of the pressure filter as pressure filtration gas for recycling.

[0046] The bottom of the oil-water separation tank 22 is provided with a water phase outlet and an oil phase outlet, and the water phase outlet and the oil phase outlet are communicated with a washing liquid delivery pump 21 and a recovery solvent pump 23 respectively; the washing liquid collected in the oil-water separation tank 22 and the hexane liquid recovered after condensation are separated into a water phase and an oil phase-hexane liquid due to the density difference, wherein the water phase is discharged from the bottom of the tank through the washing water delivery pump 21, most of the water phase returns to the pressure filter through a pipeline for recycling, and a small part of the water phase is discharged as waste washing water; the oil phase-hexane liquid is discharged from the bottom of the tank through the recovery solvent pump 23 after being separated, enters a solvent recovery system, is treated and then is reused.

[0047] The application also provides a post-treatment method of an ultra-high molecular weight polyethylene polymer slurry based on an ultra-high molecular weight polyethylene slurry filtration, washing and pre-drying system, which comprises the following steps:

[0048] In step (1), the slurry containing polyethylene and hexane is input into the filter unit group 10 in the pressure filter through a slurry delivery pump 11 for filtration, the solid powder and the mother liquor in the slurry are separated to form a filter cake, and the filter cake is subjected to the first pressure filtration through the circulating nitrogen gas input through the first nitrogen input port 13, and the separated mother liquor and the nitrogen gas containing hexane gas are delivered into the mother liquor tank 12 through the control head and the pipeline of the pressure filter;

[0049] In step (2), the filter cake formed in step (1) enters the washing unit group 20 when the drum rotates, the washing liquid delivered through the washing liquid delivery pump 21 and the supplementary washing liquid heated through the washing liquid heater 26 in the washing unit group 20 are used to wash the filter cake, the hexane solvent in the filter cake is replaced and heated and evaporated, and the washed washing liquid and the azeotrope steam formed by evaporation enter the oil-water separation tank through the control head and the pipeline of the pressure filter;

[0050] Step (3), the filter cake after washing in step (2) enters the pre-drying unit group 30 when the drum rotates, the circulating nitrogen gas inputted from the second nitrogen gas input port 31 of the pre-drying unit group performs second pressure filtration on the filter cake after washing to obtain a pre-removed water filter cake and separated washing liquid, and the separated washing liquid and the circulating nitrogen gas enter the oil-water separation tank 22 through the control head and pipeline of the pressure filter.

[0051] Step (4), the pre-removed water filter cake in step (3) enters the unloading unit 40 when the drum rotates, is discharged from the pressure filter by mechanical and gravitational action, and is transported to a subsequent powder drying system by the screw conveyor 50.

[0052] The frame of the pressure filter is divided into seven independent filter units, which are distributed around the center of the frame and are respectively named as the first filter unit 101, the second filter unit 102, the third filter unit 103, the fourth filter unit 104, the fifth filter unit 105, the sixth filter unit 106 and the seventh filter unit 107 according to the feeding order; the first filter unit 101 and the second filter unit 102 form the filter unit group 10 in step (1), the third filter unit 103, the fourth filter unit 104 and the fifth filter unit 105 constitute the washing unit group 20 in step (2), the sixth filter unit 106 is the pre-drying unit group 30 in step (3), and the seventh filter unit 107 is the unloading unit 40 in step (4).

[0053] The first filter unit 101 in step (1) is in communication with the slurry conveying pump 11, the second filter unit 102 has a first nitrogen gas input port 13, and the first filter unit 101 and the second filter unit 102 are both in communication with the mother liquor tank 12. The UHMWPE (ultra-high molecular weight polyethylene) slurry containing hexane obtained by polymerization under slurry polymerization conditions is conveyed to the first filter unit 101 by the slurry conveying pump 11, and the solid powder and the mother liquor in the slurry are continuously separated, the separated solid powder forms a filter cake on the filter cloth, and the separated mother liquor is conveyed to the mother liquor tank 12 through the control head and pipeline of the pressure filter for collection and sent to the mother liquor recovery system by the action of the mother liquor pump 121; the filter cake accumulated in the first filter unit 101 enters the second filter unit 102 with the rotation of the rotating drum in the rotating pressure filter, the circulating nitrogen gas inputted from the first nitrogen gas input port 13 performs first pressure filtration on the filter cake to further separate the mother liquor in the filter cake; the nitrogen gas mixed with hexane gas and the mother liquor after pressure filtration enter the mother liquor tank 12 together through the control head and pipeline of the pressure filter.

[0054] The washing liquid from the bottom of the oil-water separation tank 22 in step (2) is pressurized by the washing liquid delivery pump 21 and then proportionally introduced into the third filter unit 103, the fourth filter unit 104 and the fifth filter unit 105 to wash the filter cake and replace the hexane solvent in the filter cake, and the washed washing liquid is introduced into the oil-water separation tank 22; the fifth filter unit 105 is also connected with a supplementary washing liquid pipeline for supplementing the washing liquid, the washing liquid from the oil-water separation tank and the fresh washing liquid supplement are mixed and then heated by the washing liquid heater 26 before being introduced into the fifth filter unit 105 to wash the filter cake and evaporate the hexane solvent in the filter cake to form hexane vapor.

[0055] The gas phase of the oil-water separation tank 22 is connected with the gas phase of the mother liquor tank 12 through a pipeline, and the gas outlet of the oil-water separation tank 22 is also connected with the condenser 24 and the circulating gas compressor 25 through a pipeline, the circulating nitrogen gas with hexane gas in the mother liquor tank 12 and the mixed gas with hexane and nitrogen in the oil-water separation tank 22 are collected and then introduced into the condenser 24 to be condensed, and the condensed gas is pressurized by the circulating gas compressor 25, and then divided into two parts, one part is introduced into the first nitrogen inlet 13 of the second filter unit 102 in step (1), and the other part is introduced into the second nitrogen inlet 31 of the sixth filter unit 106 in step (3), and the hexane liquid condensed by the condenser 24 is recycled to the oil-water separation tank 22 through a pipeline.

[0056] In step (3), the suspension after three times of washing enters the sixth filter unit 106 with the rotation of the drum; meanwhile, the circulating nitrogen gas pressurized by the circulating gas compressor 25 is divided into two parts, one part is introduced into the first nitrogen inlet 13 of the second filter unit 102, and the other part is introduced into the second nitrogen inlet 31 of the sixth filter unit 106 to perform second pressure filtration on the filter cake in the sixth filter unit 106 to separate the washing liquid in the filter cake and achieve the effect of pre-drying the filter cake, and the pressurized nitrogen gas and the washing liquid after pressure filtration pass through the filter cloth and are discharged from the sixth filter unit 106, and then are introduced into the oil-water separation tank 22 through the control head and the washing liquid pipeline connected with the sixth filter unit 106 and the washing liquid generated by the three times of washing.

[0057] In step (4), the filter cake from the sixth filter unit 106 of the rotary pressure filter machine enters the unloading unit with the rotation of the equipment, the unloading unit is a non-pressure unit, the filter cake entering the unloading unit is detached from the filter cloth under the joint action of the scraper and the compressed nitrogen gas for back blowing and is discharged from the unloading unit by gravity and then is conveyed to the subsequent drying unit by the screw conveyor 50.

[0058] The pressure filter further has a discharge port communicated with a filter cloth washing liquid tank 51 for receiving filter cloth washing liquid, and the filter cloth washing liquid tank 51 is communicated with the oil-water separation tank 22 through a filter cloth washing liquid pump 52; after the discharge is completed, the pressure filter is washed by using process water, the washing water is discharged into the filter cloth washing liquid tank 51 through the discharge port of the pressure filter, and then is delivered to the oil-water separation tank 22 through the filter cloth washing liquid pump 52.

[0059] The water phase outlet and the oil phase outlet of the oil-water separation tank 22 are respectively communicated with a washing liquid delivery pump 21 and a recovered solvent pump 23; the washing liquid and the hexane liquid collected in the oil-water separation tank 22 are stratified in the tank due to the density difference, the water phase is discharged from the bottom of the settling zone through the washing water delivery pump 21, most of which is returned to the pressure filter through a pipeline for recycling, and a small part is discharged as waste washing water; the stratified oil phase-hexane liquid is discharged from the bottom of the overflow zone through the recovered solvent pump 23 and enters a solvent recovery system for treatment and recycling.

[0060] In the present application, the washing liquid for washing the ultra-high molecular weight polyethylene filter cake can be hot water or solvent itself. When the solvent itself is used as the washing liquid, the oil-water separation tank will not be stratified, and all the washing liquid is discharged from one liquid outlet at the bottom of the tank and returned to the pressure filter for recycling after being pressurized by the washing liquid delivery pump. In addition, using the solvent itself to wash the slurry can effectively reduce the ash content in the product, and since the latent heat of the solvent is low, using the solvent to wash can effectively reduce the heat load required in the drying process, greatly reducing the energy consumption of the filter cake drying process. However, the organic volatile content (VOC) of the product is relatively high after using the solvent to wash. On the contrary, when hot water is used as the washing liquid, the hot water and the original solvent-hexane are not miscible, and when hot water is used to wash the filter cake, the hot water can replace the hexane in the filter cake and make the hexane evaporate to form hexane vapor. The hexane gas formed by evaporation can be recovered by sedimentation and stratification and condensation, which can reduce the ash content of the product and also greatly reduce the VOC content of the product.

[0061] The present application provides an ultra-high molecular weight polyethylene polymer slurry post-treatment method based on the ultra-high molecular weight polyethylene slurry filtration, washing and pre-drying system. The polymerization solvent or hot water is used to filter, wash and pre-dry the ultra-high molecular weight polyethylene polymer slurry in the pressure filter, which can effectively remove the ash and volatile content in the product and improve the quality of the ultra-high molecular weight polyethylene product. Compared with the traditional method of centrifuging the polymer slurry, stripping the solvent with hot water and then drying, the production capacity is improved and the energy consumption is reduced.

[0062] In summary, the technical scheme of the present application can effectively achieve the above-mentioned purposes, and the structure and function principle of the present application have been fully verified in the embodiments, and the expected effect and purpose can be achieved. Without departing from the principles and essence of the present application, various changes or modifications can be made to the embodiments of the present application. Therefore, the present application includes all alternatives within the scope mentioned in the patent application, and any equivalent changes made within the scope of the present application are within the scope of the present application.

Claims

1. A method for filtering, washing and pre-drying of ultra-high molecular weight polyethylene slurry, comprising a pressure filter, the frame of the pressure filter is divided into a plurality of independent filter units along the circumference, a rotating drum for driving the material in the filter unit to rotate is arranged in the frame, and a control head is arranged in the frame and the rotating drum; characterized in that: The plurality of filtering units are divided into a filtering unit group for separating solid powder and mother liquor in the slurry to form filter cake, a washing unit group for washing the filter cake multiple times to replace and evaporate the hexane solvent in the filter cake, a pre-drying unit group for drying the washed filter cake, and a discharge unit for conveying the pre-dried filter cake; the filtering unit group is connected with a slurry conveying pump for conveying the slurry containing polyethylene and hexane, a first nitrogen input port for inputting circulating nitrogen for the first pressure filtration, and a mother liquor tank for receiving the mother liquor generated after the formation of the filter cake and mixed with nitrogen and hexane gas; The washing unit group is connected with a washing liquid conveying pump for conveying the washing liquid and a washing liquid supplement pipeline for supplementing the washing liquid, and the washing liquid supplement pipeline is connected with a washing liquid heater; the pre-drying unit group is connected with a second nitrogen input port for inputting circulating nitrogen for the second pressure filtration; the washing unit group and the pre-drying unit group are also connected with an oil-water separation tank for receiving the mixed gas after the pressure filtration and the washing liquid after the washing, the gas phase of the oil-water separation tank is connected with the gas phase of the mother liquor tank through a pipeline, the gas phase outlet of the oil-water separation tank is connected with a condenser and a circulating gas compressor through a pipeline in sequence, the circulating gas compressor is connected with the first nitrogen input port and the second nitrogen input port through a pipeline, the condenser is also connected with the oil-water separation tank through a pipeline, the water phase outlet of the oil-water separation tank is connected with the washing liquid conveying pump, and the oil phase outlet of the oil-water separation tank is connected with a recovered solvent pump; a screw conveyor is arranged below the outlet of the discharge unit for conveying the dried filter cake to a subsequent powder drying system; the steps include: Step (1), the slurry containing polyethylene and hexane is input into the filtering unit group in the pressure filter through the slurry conveying pump for filtration, the solid powder in the slurry is separated from the mother liquor to form filter cake, the circulating nitrogen input through the first nitrogen input port is used for the first pressure filtration of the filter cake, and the separated mother liquor and the nitrogen gas containing hexane gas are conveyed into the mother liquor tank through the control head and the pipeline of the pressure filter; Step (2), the filter cake formed in step (1) enters the washing unit group when the drum rotates, the washing liquid conveyed by the washing liquid conveying pump and the supplemented washing liquid heated by the washing liquid heater in the washing unit group are used for washing the filter cake, the hexane solvent in the filter cake is replaced and heated and evaporated, and the washed washing liquid and the azeotrope steam formed by evaporation enter the oil-water separation tank through the control head and the pipeline of the pressure filter; Step (3), the washed filter cake in step (2) enters the pre-drying unit group when the drum rotates, the circulating nitrogen input through the second nitrogen input port of the pre-drying unit group is used for the second pressure filtration of the washed filter cake to obtain the filter cake pre-removed of water and the separated washing liquid, and the separated washing liquid and the circulating nitrogen enter the oil-water separation tank through the control head and the pipeline of the pressure filter; Step (4), the filter cake pre-removed of water in step (3) enters the discharge unit when the drum rotates, is discharged from the pressure filter through mechanical and gravitational action, and is conveyed to the subsequent powder drying system through the screw conveyor.

2. The ultra-high molecular weight polyethylene slurry filtration, washing, pre-drying process of claim 1, wherein: The pressure filter discharging unit is also connected with a filter cloth washing liquid tank for receiving filter cloth washing liquid, and the filter cloth washing liquid tank is connected with the oil-water separation tank through a filter cloth washing liquid pump.

3. The ultra-high molecular weight polyethylene slurry filtration, washing, pre-drying process of claim 1, wherein: The pre-drying unit group is also connected with a supplementary nitrogen gas inlet, which is connected with the compressed nitrogen gas pipeline.

4. The ultra-high molecular weight polyethylene slurry filtration, washing, pre-drying process of claim 1, wherein: The frame of the pressure filter is divided into seven independent filter units, which are named as the first filter unit, the second filter unit, the third filter unit, the fourth filter unit, the fifth filter unit, the sixth filter unit and the seventh filter unit according to the feeding sequence; the first filter unit and the second filter unit form a filter unit group, the first filter unit is connected with the slurry conveying pump, the first nitrogen gas inlet is arranged in the second filter unit, and the first filter unit and the second filter unit are connected with the mother liquor tank; the third filter unit, the fourth filter unit and the fifth filter unit form a washing unit group, the washing liquid conveying pump connected with the oil-water separation tank is connected with the third filter unit, the fourth filter unit and the fifth filter unit through pipelines, and the third filter unit, the fourth filter unit and the fifth filter unit are also connected with the oil-water separation tank through pipelines; the sixth filter unit is a pre-drying unit group, the second nitrogen gas inlet is arranged in the sixth filter unit, and the sixth filter unit is also connected with the oil-water separation tank through a pipeline; and the seventh filter unit is a discharging unit.

5. The ultra-high molecular weight polyethylene slurry filtration, washing, pre-drying process of claim 1, wherein: The washing liquid heater is connected with the fifth filter unit through a pipeline, and the washing liquid heater is provided with a hot water inlet and a hot water outlet.

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