Preheater Cone Valve stuck open and the Raw Mill Cone Valve stuck closed causing the Preheater to go positive. The Preheater Fans shut down and hot kiln feed fell out of the Preheat Tower and into the Kiln and Clinker Cooler, then onto the Pan Conveyor mixing with the clinker. This hot materal conveyed to the rubber conveyor belts which caught fire and were destroyed.