Valve system needed for a mill process unit

I am currently use a air acctuated double dump valve system on a mill process unit .The product is sub sea drill cuttings at a working temprature of 230c after processing.the dust is delivered from the mill then cyclone up a screw conveyor into the double dump discharge which is a two stage gate valve which alternates open closed.On the discharged side is a blow line at 140 milibar which takes the dust to two storage silos.The gas from the mill goes to two condensors steam and oil.I am looking for a more effective valve system that will eliminate back pressure to the screw side which is causing issue with the procees,Dust pollution Back pressure on the cyclone and steam and oil condensors.We have tried rotary valves and gate valves but do not get an effective seal and eccesive wearon seal faces.Manfactures hear the working tempratures and run scared.The valves need to be able to handle a through put of 5 ton per hour.Flap valves and butterfly valves have been eliminated due to temps.Does any one know of any suppliers who could handle this application the three main factors being temprature abrasion and effective sealing