Heat recovery investigation from dryer–thermal oxidizer system in corn-ethanol plants

• Mathematical model for dryer–oxidizer system in a corn ethanol plant was proposed.
• Three configurations were discussed: with intercooler, regenerator, and recuperator.
• Recovery rate of water condensed at various conditions and locations was quantified.
• Heat recovery possibilities at various temperatures and locations have been assessed.
• Energy savings in thermal oxidizer due to preliminary condensation were calculated.

In recent years, annual corn ethanol production in the U.S. has exceeded 13,298,000,000 gallons. However, net energy balance for this sector became a subject of controversy in many discussions.The aim of the presented research is an investigation of thermal improvement opportunities in a corn ethanol plant. For this purpose, a complex mathematical model was developed for a dryer–thermal oxidizer system. Three variants were subjected thermodynamic analyses: one state of the art system and two proposed system modifications. The properties of humid gas, a mixture of combustion products and moisture evaporated from distiller's grain, were updated based on the steam properties according to the formulation proposed by the International Association for the Properties of Water and Steam. All calculations were performed by uniquely-developed C++ code.The results indicate major potential for improvement in the following areas: (i) water recovery from humid gas; (ii) heat recovery from moisture condensation – max. 44% of total primary energy usage (TPEU); and (iii) fuel savings by reduction of humid gas flow through a thermal oxidizer – max. 1.4% of TPEU. Also the presented analysis can be a starting point for further modifications in real corn ethanol manufacturing applications, leading towards pilot system implementation.