PREPP rotary kiln seals: Problem and resolution

摘要

The Process Experimental Pilot Plant (PREPP) is a facility designed to demonstrate processing of low level chemical and transuranic hazardous waste. The plant includes equipment for handling the incoming waste containers, shredding, incineration and cooling the waste, grouting the residue and scrubbing and filtration of the off gas. The process incinerator is a rotary kiln approximately 8-(1/2) ft diameter and 25 ft long with a rotary seal assembly at each end. Each seal assembly consists of a primary, secondary and tertiary seal, with a positive air pressure between primary and secondary seals to prevent out-leakage from the kiln. The kiln operates at 0.5 inch water negative pressure. From the very outset the kiln seals exhibited excessive drag which taxed the kiln drive capacity and excessive in-leakage which limited kiln temperature. An engineering evaluation concluded that the original seals supplied by the kiln vendor could not accommodate expansion and centerline shift of the kiln resulting from heatup of the kiln and its support system. A totally new concept kiln seal design has been generated to replace the (modified) original seals. This new seal system has been designed to provide a very tight long lasting seal which will accommodate the 1.5 inch axial shift and up to 1 inch radial movement of the kiln shell. Design lifetime of the seal is 10,000 operating hours between major maintenance services while maintaining an acceptable leak rate hot or cold, rotating or stopped. The design appears adaptable to any size kiln and is suitable for retrofit to existing kilns. A one-third scale prototype seal assembly is being built to verify the concept prior to construction of the 10 ft diameter seals for the PREPP rotary kiln. 4 figs.