Due to significant enhancement in heat removal capacity of recirculating gas and space-time yield of fluidized bed reactors

condensed mode operation has become most popular in gas-phase ethylene polymerization. A mathematical model for condensing mode operation of gas phase ethylene polymerization process was established

which included fluidized-bed reactor model

stage heat exchanger model

and control model of reactor temperature

pressure

and component partial pressure of recirculating gas. Process simulation was applied to obtain steady state solution when reactor temperature was controlled by close-loop

and dynamic behavior of the system under small perturbation was used to qualitatively analyze stability of ethylene polymerization when reactor temperature was controlled by open-loop and close-loop. Finally

stepwise response characteristics of ethylene polymerization close-loop system was studied under consideration of 1-hexene partial pressure and catalyst feed rate. Simulation results show that the steady state solutions are stable within the scope of studied conditions when reactor temperature is close-loop controlled

whereas the steady state solutions are divided into stable and unstable zone by bifurcation points when reactor temperature is open-loop controlled. The long and short period oscillations observed in stepwise response of reactor temperature to 1-hexene partial pressure reveal that ethylene polymerization system under condensed mode operation is a complex process with multiple coupling control loops.