Projected Process Economics for Ethanol Production from Corn

Report Introduction: In order to identify technology which can reduce the cost of producing ethanol by fermentation using com as the raw material, an engineering and economic analysis was completed on the design for the base case of a typical existing dry mill/ethanol plant and three alternatives. The criteria for choosing an alternative are that the essential concepts of the technology have been demonstrated at a pilot plant scale or larger and that it is likely to be implemented in the next 3 to 5 years. This focus avoids getting into many innovative ideas that are in the laboratory stage, where reliable mass and energy balances and capital and operating costs are unavailable or self-promoting. The first alternative is the Biostil Process which was initially developed be Alfa-Laval in Sweden. The process has been acquired by Chematur of Sweden and is available in the U.S. from Weatherly, Inc. of Atlanta, Georgia. The process uses a single continuous fermentor with several on-line loops involving screens and centrifugal separators and mash column. The net result is a process that produces a stillage at about 30 wt% total solids at the bottom of the mash column. With the high total solids, there is no need for an evaporator and the high pressure steam to run the turbine for the vapor recompressor. Thus a cheaper low-pressure packaged boiler can be used. The process is used world-wide in cane molasses fermentation to ethanol. Also, two plants using wheat starch fermentation are in operation. It is an ideal concept to be applied to com based fermentation. The second alternative is a technology for dehydrating ethanol using com grits as an adsorbent for the water. The process was developed by Professor Ladisch of Purdue University and is used by the ADM Corporation in their plants. It is the only known adsorption dehydration technology that is practiced above an ethanol plant capacity of 30 million gallons per year (a limit for the use of molecular sieves). The adsorption columns and regeneration loop equipment replace the conventional azeotropic solvent distillation and solvent recovery columns. Naturally, there is no need for have the solvent, such benzene, in the plant. The third alternative is not so much a process alternative but a commentary of the role of fuels, boilers, cogeneration options and energy costs. There are trade-offs between capital cost and energy cost that change as fuel and electricity costs change. A quick summary chart comparing the capital and operating costs of the process alternatives is given in Table 1.