GB990582A - Improvements in and relating to the production of polyethylene - Google Patents

Abstract

The production of polyethylene from ethylene gas by a high pressure process is regulated by superimposing on the gas flow through a reactor pressure pulses, the reaction product being fed through a reduction valve into a trap operated at high pressure from which polyethylene and unreacted ethylene gas are withdrawn, measuring the pressure inside the reactor entrance and after analogue transformation this is fed as the momentary value into a pressure regulator connected with the reduction valve, measuring the temperature inside the reactor and after analogue transformation this is fed as the momentary value into a temperature set value regulator whose output reduces the set value of the pressure regulator when a predetermined temperature as adjusted on the temperature set value regulator is exceeded by the momentary temperature. The pressure measured in the reactor may be fed, after analogue transformation, into a derivative controller whose output is proportional to the momentary rate of change of the pressure and when the controller reaches a predetermined output a signal is produced by the controller whereby the reduction valve is opened to a predetermined extent through a switch. Alternatively, the pressure may be fed into a signal emitter of adjustable signal amplitude and the reduction valve is closed by this when a predetermined value is reached. The temperature measured in the reactor, after analogue transformation, may be made to act on the reduction valve through a derivative control, a switch and optionally a signal emitter. An electronic gate associated with a stable electronic oscillator may be opened by the switch and controlled synchronously with the signal and depending on the open time of the gate which is electronically measured, the cadence of the pressure pulses is adjusted so that the longer are the open periods, the more rapid is the cadence of the impulses and vice versa.