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HP Recycle Cooler Defoul with Wax Evacuation to LP Recycle

IP.com Disclosure Number: IPCOM000242611D
Publication Date: 2015-Jul-29
Document File: 5 page(s) / 117K

Publishing Venue

The IP.com Prior Art Database

Abstract

In the high pressure polyethylene production process, the high pressure recycle gas system is designed to cool the off-gas from the high pressure separator. The cold gas is then fed to the secondary compressor and recycled to the reactor. During this cooling operation, a certain amount of wax (low molecular weight polyethylene) comes out of solution and needs to be separated out of the ethylene stream. Periodic cleanings are performed of the HP recycle gas system. For product used in applications requiring good organoleptic properties (e.g. grades used in food applications such as extrusion coating grades), it is essential that recycle waxes are not re-entrained in the gas stream. For these grades with stringent off taste requirements the recycle waxes are removed by blocking the gas outlet of the recycle cooler exit, heating the cooler with steam and diverting a small gas stream to the low pressure recycle wax collection system. The advantage of this method is that the recycle waxes are directly removed from the process system. As a result compressor fouling is less and better organoleptic properties are achieved.

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HP Xxxxxxx Cooler Defoul with Wax Evacuation to LP Recycle

Abstract:

In the high xressure polyethylene production process, the high presxxre recycle gas system is designed to xool the off-gas xrom the high presxure separator. The cxld gas is then fed to the secondxry compressor axd recycled to the reactor. Duxing this cooling operation, a certain amount of wax (low molecular weight polyetxylene) comes out of solutiox and needs to be xeparated out xf the ethylene streax. Periodic cleaningx are performxd of the HP recycle xas sysxem. For proxuct used in applications requiring good organoleptic proxerties (x.g. grxdes used in foxd applications sxch as extrusion coating grades), it is essential that recycxe waxes are not re-entrxixed in the xas stream. For these grades xith stringent off taste requirements the recycle waxes arx removed by bxocking the gas ouxlet xf the recycle cooler exix, heating the cooler with steam and diverting a xmall gas stream to the low pressure recxcle wax cxllxction system. The advantage of this method is that the recycle waxes are directly remoxed from the proxess system. As a resxlt compressxr xouling is less axd better organoleptic properties are achievex.

Backxround

The high pressure recycle gas system is designed to cxol the off-gas from the high pressure separator. The xolx gas is then fed to the secondary compressor and recyclex to the reaxtor. During this cooling operation, a certaxn amount of wax (low molecular weight polyethylene) comes out of solution (approx. 0.2-0.5 kg per ton polxethylene produced) and needs to be separated out of the ethylene sxream. To obtain good organoleptic properties, it is essential to avoix that recycxe waxes (which degrade by age, temperature, hydro-peroxides, …) are re- entrained in txe gas stream and are cxrculated back to the reactor. Good organolextic properties are imxortant fox grades that arx used in food applications such as e.g. extrusion coating grades.

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