Propylene, ethylene and any other required comonomers are fed into the reactor(s). Hydrogen is added to control the molecular weight. Polymerization conditions (temperature, pressure and reactant concentrations) are set by the polymer grade to be produced. The reaction itself is exothermic. Reactor cooling is achieved by evaporation of liquefied reactor gas, which is injected into the reactor. Flash evaporation of the liquid in the polymer bed ensures the most efficient heat removal.