PROCESS AND SYSTEM FOR REMOVING HEAVIES FROM DILUENT RECYCLED TO A SLURRY POLYMERIZATION REACTOR

A recovery and purification system for a liquid medium from a slurry polymerization, the system comprising:

a first fluid passage connected at one end to a slurry polymerization reactor;

a flash gas separator connected to an opposite end of the first fluid passage, for separating a vapor stream comprising solid polymer particles in a liquid medium;

a vapor removal line connected at a top portion of the flash gas separator, for transporting the vapor stream from the flash gas separator;

a first condenser downstream of the vapor removal line;

a collection tank downstream of the first condenser;

a vapor bypass line providing a bypass for a portion of the vapor stream around the condenser to the collection tank;

a bypass valve for controlling the flow of vapor through the vapor bypass line;

a liquid delivery line at a bottom portion of the collection tank;

a vapor recycle line at a top portion of the collection tank;

a second condenser fluidly connected to the vapor recycle line; and

a second fluid passage connecting the output of the second condenser to the slurry polymerization reactor.

The recovery and purification system of claim 1, wherein the bypass valve is in informational communication with at least one of a temperature controller downstream of the collection tank and a level controller positioned within the collection tank.

The recovery and purification system of claim 2, wherein the level controller is in informational communication with the temperature controller, and the temperature controller is in informational communication with the bypass valve.

The recovery and purification system of claim 1, comprising a heavies column connected at an opposite end of the liquid delivery line.

The recovery and purification system of claim 1, comprising a recycle tank disposed along the diluent recycle line downstream of the second condenser.

The recovery and purification system of claim 1, comprising a purge column fluidly connected to receive solid polymer particles from the flash gas separator.

A process for recycling a liquid medium withdrawn from a slurry polymerization reactor, using a recovery and purification system as defined in any of claims 1 to 6, the process comprising:

separating a first vapor stream from a slurry comprising a liquid medium and solid polymer particles, wherein the vapor stream comprises at least the medium and heavies;

condensing a first portion of the first vapor stream in a first condenser to form a first liquid;

passing a second portion of the first vapor stream to a collection tank without passing through the first condenser;

separating a second liquid and a second vapor stream in the liquid collection tank;

passing the second liquid to a heavies purification zone; and

recycling the condensed medium to the slurry polymerization reactor without fractionating to remove heavies.

The recycling process of claim 7, comprising mixing together the first liquid and the second portion of the first vapor stream before passing to the collection tank.

The recycling process of claim 7, comprising:

separating a solid polymer fluff from the slurry, the solid polymer fluff having entrained diluent; and

passing the solid polymer fluff to a purge zone, wherein the purge zone extracts entrained diluent from the solid polymer fluff.

The recycling process of claim 9, wherein at least 1% of the heavies in the first vapor stream are condensed into the second liquid.

The recycling process of claim 9, wherein at least 2% of the oligomers in the first vapor stream are condensed into the second liquid.

The recycling process of claim 9, comprising:

measuring the level of liquid in the liquid collection tank; and

controlling the condensing of the vapor stream based on the measured liquid level.

A process for operating a slurry polymerization system comprising a recovery and purification system as defined in any of claims 1 to 6, the process comprising the steps of:

forming a slurry comprising solid polyolefin particles in a liquid medium in a polymerization reaction zone;

withdrawing a portion of the slurry from the polymerization reaction zone;

vaporizing the liquid medium to form a first vapor stream comprising at least the medium and heavies;

separating the first vapor stream from the solid polyolefin particles;

passing a first portion of the first vapor stream to a first condenser whereby a first liquid stream is formed;

passing a second portion of the vapor stream to a collection tank without passing through the first condenser;

collecting the liquid stream and the second portion in the liquid collection tank;

separating a second vapor stream from a second liquid stream in the liquid collection tank;

condensing and recycling the second vapor stream back into the polymerization reaction zone without further heavies removal treatment; and

passing a second liquid stream to heavies removal treatment.

The operating process of claim 13, wherein the liquid medium comprises an inert diluent, and the solid polyolefin particles comprise polyethylene.

The operating process of claim 13, wherein the liquid medium comprises propylene, and the solid polyolefin particles comprise polypropylene.

The operating process of claim 13, wherein the second liquid stream is held in the liquid collection zone for a time sufficient to allow heavies from the vapor to transfer to the liquid.