a fluid bed reactor system and process employing a silyl chromate catalyst therein wherein the reactor system comprises a vertical reactor having a fluidizing medium permeable distribution plate towards the base thereof , a fluidizing medium supply line to supply fluidizing medium to the base of the reactor , a catalyst injection means to supply particulate catalyst to the side of the reactor , a polymer product recovery means to recover polymer product from the reactor and beneath the distribution plate , a fluidizing medium recycle line to recycle the fluidizing medium from and to the reactor , and a heat exchanger in the recycle line to remove heat of reaction from the recycled fluidizing medium .