Apparatus and method for the production of polyethylene and ethylene copolymers

An apparatus for the high pressure polymerization of ethylene which comprises:

• a tubular reactor;
• a conduit for supply of ethylene to the tubular reactor, the conduit being provided with a preheater for heating the ethylene;
• a waste heat boiler for the production of medium pressure steam using heat generated by the polymerization reaction;
• a high pressure steam boiler;
• and
• a steam distribution system comprising a medium pressure steam net for the distribution of steam from the waste heat boiler and a high pressure steam net for the distribution of steam from the high pressure steam boiler,
• in which the preheater comprises first, second and third sections, each section comprising at least one steam jacket, and in which the steam jacket or jackets of the first section of the preheater communicate with the medium pressure steam net, the steam jacket or jackets of the second section of the preheater communicate via block valves with both the medium pressure steam net and the high pressure steam net, and the steam jacket or jackets of the third section of the preheater communicate via a control valve with the high pressure steam net.

A method of heating ethylene in a preheater in a high pressure ethylene polymerization apparatus, in which the preheater comprises first, second and third sections and the method comprises:

• generating medium pressure steam using waste heat;
• providing high pressure steam from a source of high pressure steam;
• supplying medium pressure steam, optionally supplemented with high pressure steam, to the first section of the preheater;
• supplying to the second section of the preheater either the same steam as supplied to the first section of the preheater or high pressure steam;
• supplying high pressure steam to the third section of the preheater;
• and
• changing the heat input into the preheater by changing the steam supplied to the second section of the preheater from the same steam as supplied to the first section of the preheater to high pressure steam, or vice versa.

An apparatus for the high pressure polymerization of ethylene which comprises:

• a high pressure reactor for the polymerization of ethylene at a pressure of at least 1000 bar;
• a conduit for the supply of ethylene to the reactor,
• a preheater for heating the ethylene in the conduit to a temperature of from 130 to 220° C. having a first heating section, a second heating section and a third heating section;
• a waste heat boiler for the production of medium pressure steam at from 4 to 15 bar;
• a source of high pressure steam at from 15 to 70 bar;
• and
• a steam distribution system connecting the waste heat boiler and the source of high pressure steam to the preheater;
• a medium pressure steam net in said steam distribution system connected to receive medium pressure steam from the waste heat boiler and supply medium pressure steam to the first heating section and the second heating section,
• a high pressure steam net in said steam distribution system connected to receive high pressure steam from the high pressure steam source and supply high pressure steam to the second or third heating section;
• and
• a valve for controlling the supply of steam from the medium pressure steam net to the second heating section and a valve for controlling the supply of high pressure steam to the second heating section.