Autothermal

Autothermal refers to a class of thermal processes that are self-sustaining with respect to heat. In an autothermal process, heat required for the endothermic steps is supplied by the heat released by exothermic steps within the same process, so little or no external heating is needed.

A common example is autothermal reforming (ATR) of hydrocarbons, such as natural gas. ATR combines steam reforming (an endothermic reaction that consumes heat) with partial oxidation (an exothermic reaction that supplies heat). The feed typically includes a hydrocarbon, steam, and a controlled amount of oxygen or air. The reactor yields synthesis gas (primarily hydrogen and carbon monoxide) with a tailored H2/CO ratio for downstream processing.

The term can also apply to autothermal combustion, where a fuel oxidizes exothermically to provide the heat for a process or to sustain a reactor without an external heat source, often with heat integration to drive reforming, cracking, or destruction processes.

Advantages of autothermal operation include reduced energy input for external heating, simpler heat integration, potential for compact plant layouts, and faster startup. Challenges include maintaining stable temperature profiles, avoiding hot spots and carbon deposition, and controlling the oxygen supply to balance endothermic and exothermic reactions. Catalysts and heat exchanger design are important considerations.

Autothermal operation is used in hydrogen production, gasification, and syngas generation for chemicals and power systems, including integration with fuel cells and gas turbines. It represents a strategy to achieve thermally efficient processing by leveraging internal heat generation.