A retort apparatus includes a primary rotating pipe within a second rotating pipe within a fixed pipe (27). The interior area of the primary rotating pipe is bounded by a heated pipe. A first annulus is formed between the primary and second rotating pipes. A second annulus is formed between the second rotating pipe and the heated pipe. A third annulus is formed between the primary rotating pipe and the fixed pipe. A heater is positioned within the interior area of said primary rotating pipe. In one embodiment, an inlet gate is provided for introducing a liquid and solid mixture into the first annulus proximate the second end thereof. A first conveyor is provided to move the mixture toward the hot end of the primary rotating pipe. A second conveyance is provided for transferring the mixture from the first annulus to the second annulus within the interior of the primary rotating pipe, and a third conveyance is provided to move the mixture within the second annulus in a direction toward the cooler end of the primary rotating pipe. A method according to the invention includes introducing a liquid and solid mixture into an annulus formed between the two rotating pipes and causing the mixture to move within the annulus toward one end of the pipe. The method also includes transferring the mixture from the annulus to the interior area of the inner rotating pipe, and causing the mixture within the interior area to move in a direction toward the other end of the rotating pipe.