Abstract: A method and apparatus is provided for the thermolysis of solid waste within an enclosed thermolysis chamber in the absence of free oxygen which produces a thermolysis off-gas. The thermolysis off-gas is removed from the thermolysis chamber and injected into a cyclone where it is washed with water and cooled. The washed and cooled thermolysis off-gas is divided into two portions. One portion of the washed thermolysis off-gas is further cooled in a heat exchanger and then injected into a burner and combusted, while the remaining portion of the washed thermolysis off-gas is passed into indirect heat exchange with the hot off-gas resulting from the combustion of the other portion of the thermolysis off-gas in the burner and recycled back into the enclosed thermolysis chamber. This in-situ recycling of hot thermolysis off-gas helps prevent the creation of hot spots in the thermolysis chamber and the possibility of an explosive reaction between oxygen and hydrogen.