Abstract: A sealing system primarily for use with a superatmospheric upflow oil shale retort is comprised of a first and second vertical vessel, with a first sealing screw being employed to transport the particles as a continuous bed from the first to the second vessel, and with a second sealing screw to transport the particles from the second vessel to discharge. In the first vessel, shale particles are cooled by contact with water, which usually generates noxious gases, such as hydrogen sulfide. These noxious gases are removed from the sealing system by the purging action of two sealing gas streams, the first sealing gas removing the bulk of the noxious gases from the first vessel, and the second sealing gas removing residual noxious gases from the second vessel.The shale particles are discharged to the environment from the second sealing screw in a dry condition, with a minimum emission of noxious gases.