System and method for recovering exhaust gas in olefin polymer production

Abstract

The invention provides a system for recovering the emission of an olefin polymerization process. The system comprises a devolatilization device, a compression cooling unit, a first gas-liquid separation device, a first gas separation device and a second gas separation device, wherein the devolatilization device is used for receiving the emission and fresh purge gas from the olefin polymerization process and outputting a first fluid and polyolefin resin; the compression cooling unit comprises a compression device and a first heat exchange device and is used for receiving the first fluid and outputting a first gas-liquid mixture; the first gas-liquid separation device is used for performing gas-liquid separation on the first gas-liquid mixture and outputting a first recovery product and a first gas-phase component; the first gas separation device is used for receiving the first gas-phase component and removing small-molecular substances therein and outputting a component rich in small-molecular gases and a second gas-phase component rich in hydrocarbon substances; the second gas separation device comprises a second heat exchange device, a second gas-liquid separation device and a first gas expansion device.

Description

technical field [0001] The present invention relates to the production of olefin polymers, and more particularly to systems and methods for recovering vent gases in the production of olefin polymers. Background technique [0002] Resin devolatilization (removal of volatiles in resin) and vent gas recovery are important steps in the olefin polymer production process and have been studied in many literatures. For example, a resin devolatilization process and method are described in CN102171256. And in US5,391,656, disclose a kind of exhaust gas recovery method of compression condensation. [0003] The exhaust gas in the olefin polymerization production process refers to the gaseous stream containing reaction gas discharged from the reactor, flash tank, devolatilization unit, etc. For example, the exhaust gas of the slurry polyethylene production process mainly comes from the product flash tank and the devolatilization unit, while the exhaust gas of the gas phase process main...

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Problems solved by technology

However, as mentioned earlier, the exhaust gas contains only a small amount of condensable hydrocarbons, so a large amount of non-condensable gas is compressed and cooled ineffectively, thus affecting the economics of the compression condensation method

Therefore, the compression condensation method mainly has the following disadvantages: 1) The lower the content of condensable hydrocarbons in the exhaust gas, the lower the efficiency of the compression condensation method; 2) It is difficult to recover and purging gas (nitrogen) boiling point The recovery rate of close C1-C3 hydrocarbons is generally not more than 30%; 3) The concentration of purge gas in the uncondensed exhaust gas cannot meet the requirements of devolatilization, so it cannot be recycled and can only be discharged to the flare system

However, this method cannot be integrated in a satisfactory manner with the devolatilization process of the polyolefin process

For example, the pressure of the tail gas discharged by this method is low and cannot be further recycled.

At the same time, for the case of high hydrogen content, the recycling of purge gas will cause the accumulation of hydrogen in the system, resulting in a series of problems such as the decline of recovery efficiency.

[0011] It can be seen that although the existing methods and devices for recovering exhaust gas in the production of olefin polymers have their own characteristics, they cannot simultaneously realize the efficient recovery of hydrocarbons and the recycling of purge gas

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