Production device and method for low-VOC (volatile organic compound) polyethylene product by slurry process
阅读说明：本技术 一种淤浆法低voc聚乙烯产品的生产装置及方法 (Production device and method for low-VOC (volatile organic compound) polyethylene product by slurry process ) 是由 吕世军 潘炯彬 何琨 项海定 张贤 刘兴冰 陈永强 崔春霞 朱彦博 高毕亚 余超 于 2019-10-18 设计创作，主要内容包括：本发明涉及一种淤浆法低VOC聚乙烯产品的生产装置及方法,主要解决现有技术中存在残留己烷溶剂VOC含量高的问题。本发明通过采用淤浆法低VOC聚乙烯产品的生产装置及方法,在淤浆法聚乙烯现有流程的滚筒干燥器后增加一套粉料脱气仓,进行“滚筒干燥器+粉料脱气仓”组合,能够很好地降低聚乙烯产品VOC的含量,产品粉末中己烷溶剂VOC含量从现有技术200ppm降低至本发明100ppm以下,较好地解决了上述问题,可应用于淤浆法低VOC食品级聚乙烯产品的生产中。(The invention relates to a production device and a production method of a slurry-process low-VOC polyethylene product, and mainly solves the problem that the content of residual hexane solvent VOC is high in the prior art. According to the production device and method for the low-VOC polyethylene product by the slurry method, a set of powder degassing bin is added behind a roller dryer in the existing flow of polyethylene by the slurry method, and the combination of the roller dryer and the powder degassing bin is carried out, so that the VOC content of the polyethylene product can be well reduced, the VOC content of a hexane solvent in product powder is reduced to be below 100ppm in the invention from 200ppm in the prior art, the problems are well solved, and the production device and method can be applied to production of the low-VOC polyethylene product by the slurry method.)
1. A production device for low VOC polyethylene products by a slurry method is characterized by comprising the following steps:
a roller dryer (2), wherein the inlet of the roller dryer (2) is communicated with a spiral feeder (1), the outlet of the roller dryer is communicated with a powder collector (3), a polyethylene wet cake (11) containing the hexane solvent VOC from an upstream section is in countercurrent contact with first dry nitrogen (13) in the roller dryer (2) to volatilize and remove the hexane solvent VOC, and the first VOC-containing nitrogen (12) leaves the roller dryer (2);
the powder degassing bin (7) is used for conveying nitrogen (16) into the top of the powder degassing bin (7) after being pressurized, enabling the nitrogen and dry powder (17) leaving the roller dryer (2) to flow in a reverse direction to a second dry nitrogen (19) blown from the lower part of the powder degassing bin (7) so as to volatilize and remove a hexane solvent VOC in the powder, and enabling product powder (20) to flow out from the bottom of the powder degassing bin (7) and be conveyed to a downstream working section; the second VOC-containing nitrogen (18) leaves the dust filter (6) and is treated and returned for reuse as dust conveying recycle gas.
2. A method for producing a slurry process low VOC polyethylene product using the production apparatus as claimed in claim 1, characterized in that it comprises the steps of:
step a) the polyethylene wet cake (11) containing the hexane solvent VOC from the upstream section enters the drum dryer (2) through the screw feeder (1), the first drying nitrogen (13) also enters the drum dryer (2) and is in countercurrent contact with the polyethylene wet cake (11) for a period of time, the hexane solvent VOC volatilizes, and the first VOC-containing nitrogen (12) leaves the drum dryer (2);
step b) the low-pressure steam (14) enters the drum dryer (2), indirectly heats the polyethylene wet cake (11) and the first dry nitrogen (13) to volatilize the hexane solvent VOC, and the low-pressure condensate (15) leaves the drum dryer (2);
step c) pressurizing the conveying nitrogen (16) through the powder conveying fan (5), allowing the conveying nitrogen to enter the top of the powder degassing bin (7) together with the dry powder (17) which leaves the roller dryer (2) and passes through the powder rotary valve (4) and flow out from top to bottom, and blowing in the second dry nitrogen (19) from the lower part of the powder degassing bin (7) and blowing out from bottom to top; the gas and the powder flow in the reverse direction, the hexane solvent VOC in the powder is volatilized and removed, the content of VOC adsorbed in the powder is reduced, and the product powder (20) flows out from the bottom of the powder degassing bin (7) and is sent to a downstream working section;
step d) the second VOC-containing nitrogen (18) leaves the dust filter (6) and is treated and returned for reuse as dust transport recycle gas.
3. A slurry process low VOC polyethylene product production method according to claim 2, characterized in that the polyethylene wet cake (11) containing hexane solvent VOC from upstream section enters the drum dryer (2) through the screw feeder (1), the first dry nitrogen (13) enters the drum dryer (2) through the powder collector (3), low pressure steam (14) enters the drum dryer (2), indirectly heats the polyethylene wet cake (11) and the first dry nitrogen (13), and low pressure condensate (15) leaves the drum dryer (2).
4. The method for producing a slurry process low VOC polyethylene product according to claim 2, wherein the conveying nitrogen (16) is pressurized by a powder conveying fan (5), and the dry powder (17) is mixed with the pressurized nitrogen at the outlet of the powder conveying fan (5) through a powder rotary valve (4) arranged at the outlet of the bottom of the powder collector (3); the mixed conveying nitrogen (16) and the dry powder (17) enter the top of the powder degassing bin (7) and flow out from top to bottom, and second dry nitrogen (19) is blown in from the lower part of the powder degassing bin (7) and blown out from bottom to top; and volatilizing and removing the hexane solvent VOC in the powder, and flowing out the product powder (20) from the bottom of the powder degassing bin (7) to be sent to a downstream working section.
5. The method for producing a slurry process low VOC polyethylene product of claim 2, wherein the production scale of said method is 1-60 million tons per year of slurry process polyethylene plant.
6. The slurry process low VOC polyethylene product production process according to claim 2 wherein the hexane solvent VOC mass fraction content in the polyethylene wet cake (11) from upstream section is between 5 and 50%; the hexane solvent VOC residue in the dry powder (17) leaving the drum dryer (2) and passing through the rotary powder valve (4) is between 2000 and 5000 ppm; the VOC content of the hexane solvent in the product powder (20) flowing out of the powder degassing bin (7) and sent to a downstream section is reduced to be below 100 ppm.
7. The method for producing a slurry process low VOC polyethylene product as claimed in claim 2, wherein the operating pressure of the drum dryer (2) is 2-6 KPaG, the operating temperature is 50-150 ℃, and the material residence time is 0.1-5.0 hours.
8. The method for producing low VOC polyethylene products by slurry process according to claim 2, wherein the operation pressure of the powder degassing bin (7) is 5-50 KPaG, the operation temperature is 20-80 ℃, and the material residence time is 0.1-5.0 hours.
9. The method for producing a slurry process low VOC polyethylene product as claimed in claim 2, wherein said nitrogen gas (16) is delivered at an operating pressure of 1-5 KPaG and an operating temperature of 0-40 ℃.
10. The method for producing a slurry process low VOC polyethylene product as claimed in claim 2, wherein the operating pressure of the second dry nitrogen (19) is 10-55 KPaG and the operating temperature is 30-90 ℃.
Technical Field
The invention relates to the technical field of polyethylene production, in particular to a production device and a production method for a slurry-process low-VOC polyethylene product, and specifically relates to a device and a method for reducing residual VOC in polyethylene powder by using a combination of a roller dryer and a powder degassing bin in a slurry-process polyethylene powder drying process, and the device and the method can be applied to slurry-process production of low-VOC food-grade polyethylene products.
Background
The slurry process polyethylene adopts parallel or serial polymerization process, high purity ethylene as main material, hexane as solvent, high efficiency catalyst and butene-1 or propylene as comonomer or functional assistant are added to obtain high density polyethylene product in dozens of grades. However, in the high-temperature processing process and daily use process of the high-density polyethylene product, harmful Volatile Organic Compounds (VOC) can be released to different degrees by the additives, and particularly in the high-density polyethylene product, about 2000-5000 ppm of hexane solvent remains, so that the quality of the food-grade polyethylene product is seriously influenced.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention adopts a production device and a production method of a slurry-process low-VOC polyethylene product to remove residual hexane solvent VOC in polyethylene powder so as to solve the problem of high VOC content in the slurry-process polyethylene product. The invention relates to a production device and a production method of a slurry-process low-VOC polyethylene product, which are characterized in that a powder degassing bin is added behind a roller dryer in the existing process flow of slurry-process polyethylene by taking the reference of the degassing process of gas-phase-process polyethylene powder, and the VOC content in the polyethylene product can be well reduced through the combination of the roller dryer and the powder degassing bin. The VOC-containing polyethylene powder discharged from the roller dryer is conveyed into the newly-added degassing bin through an air conveying system, and is subjected to gas-solid countercurrent contact with dry nitrogen to remove VOC impurities and then conveyed to a downstream working section, so that the VOC content of the obtained polyethylene product can be reduced to be below 100 ppm.
In order to achieve the purpose, the technical measures adopted by the invention comprise:
a first aspect of the present invention provides an apparatus for producing a slurry process low VOC polyethylene product, comprising:
the inlet of the roller dryer is communicated with the spiral feeder, the outlet of the roller dryer is communicated with the powder collector, the polyethylene wet cake containing the hexane solvent VOC from the upstream section is in countercurrent contact with first dry nitrogen in the roller dryer, so that the hexane solvent VOC is volatilized and removed, and the first VOC-containing nitrogen leaves the roller dryer;
the powder degassing bin is used for conveying nitrogen gas to enter the top of the powder degassing bin together with the dry powder leaving the roller dryer after being pressurized, the nitrogen gas and the second dry nitrogen gas blown from the lower part of the powder degassing bin flow in a reverse direction to volatilize and remove the hexane solvent VOC in the powder, and the product powder flows out of the bottom of the powder degassing bin and is conveyed to a downstream working section; the second VOC-containing nitrogen leaves the powder filter, is treated and then is returned for reuse as powder conveying circulating gas.
The second aspect of the invention provides a method for producing a low VOC polyethylene product by a slurry process, which adopts the production device and comprises the following steps:
step a) the polyethylene wet cake containing the hexane solvent VOC from the upstream section enters the roller dryer through the spiral feeder, the first drying nitrogen also enters the roller dryer and is in countercurrent contact with the polyethylene wet cake for a period of time, the hexane solvent VOC volatilizes and is removed, and the first VOC-containing nitrogen leaves the roller dryer;
step b) the low-pressure steam enters the roller dryer, the polyethylene wet cake and the first dry nitrogen are indirectly heated, the hexane solvent VOC is volatilized, and the low-pressure condensate liquid leaves the roller dryer;
step c) pressurizing the conveying nitrogen by the powder conveying fan, allowing the conveying nitrogen and the dry powder which leaves the roller dryer and passes through the powder rotary valve to enter the top of the powder degassing bin and flow out from top to bottom, and blowing in the second dry nitrogen from the lower part of the powder degassing bin and blowing out from bottom to top; the gas and the powder flow in reverse directions, the hexane solvent VOC in the powder is volatilized and removed, the content of VOC adsorbed in the powder is reduced, and the product powder flows out from the bottom of the powder degassing bin and is conveyed to a downstream working section;
and d) the second VOC-containing nitrogen gas leaves the powder filter, is treated and then is used as powder conveying circulating gas to return for reuse.
Further, in the above method, the polyethylene wet cake containing the hexane solvent VOC from the upstream section enters the drum dryer through the screw feeder, the first dry nitrogen gas enters the drum dryer through the powder collector, low-pressure steam enters the drum dryer, the polyethylene wet cake and the first dry nitrogen gas are indirectly heated, and low-pressure condensate exits the drum dryer.
Further, in the above method, the conveying nitrogen is pressurized by a powder conveying fan, and the dry powder is mixed with the pressurized nitrogen at the outlet of the powder conveying fan through a powder rotary valve arranged at the outlet at the bottom of the powder collector; the mixed conveying nitrogen and the dry powder enter the top of the powder degassing bin together and flow out from top to bottom, and the second dry nitrogen is blown in from the lower part of the powder degassing bin and blown out from bottom to top; and volatilizing the hexane solvent VOC in the powder, and delivering the product powder to a downstream working section from the bottom of the powder degassing bin.
Further, in the method, the production scale of the production device is 1-60 ten thousand tons per year of a slurry polyethylene device.
Further, in the method, the content of VOC (volatile organic compounds) of the hexane solvent in the polyethylene wet cake from the upstream section is 5-50%; the residual content of VOC (volatile organic Compounds) in the hexane solvent in the dried powder which leaves the roller dryer and passes through a rotary powder valve is 2000-5000 ppm; the VOC content of the hexane solvent in the product powder flowing out of the powder degassing bin and sent to a downstream section is reduced to be below 100 ppm.
Further, in the method, the operation pressure of the roller dryer is 2-6 KPaG, the operation temperature is 50-150 ℃, and the material retention time is 0.1-5.0 hours.
Further, in the method, the operation pressure of the powder degassing bin is 5-50 KPaG, the operation temperature is 20-80 ℃, and the material stays for 0.1-5.0 hours.
Further, in the method, the operation pressure of the nitrogen conveying is 1-5 KPaG, and the operation temperature is 0-40 ℃.
Further, in the method, the operation pressure of the second dry nitrogen is 10-55 KPaG, and the operation temperature is 30-90 ℃.
Compared with the prior art, the invention adopts the technical scheme that the invention has the following effects:
for a polyethylene device with the production scale of 1-60 ten thousand tons/year, the production device and the production method of the slurry-process low-VOC polyethylene product have the advantages that a set of powder degassing bin is added behind a roller dryer in the existing process flow of the slurry-process polyethylene, the VOC content in the polyethylene product can be well reduced through the combination of the roller dryer and the powder degassing bin, and the problems in the prior art are well solved. The VOC content of the hexane solvent in the product powder is reduced from about 200ppm in the prior art to less than 100ppm in the invention, and a good technical effect is achieved.
Drawings
FIG. 1 is a process flow diagram for the production of a slurry process low VOC polyethylene product of the invention;
FIG. 2 is a flow diagram of a prior art process for producing a low VOC polyethylene product using a slurry process;
wherein the reference numerals in the figures are:
a
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
The invention is further described with reference to the following drawings and specific examples, which are not intended to be limiting.