High Speed/ Low Effluent Process for Ethanol
Executive Summary: In this project, BPI demonstrated a new ethanol fermentation technology, termed the High Speed/ Low Effluent (HS/LE) process on both lab and large pilot scale as it would apply to wet mill and/or dry mill corn ethanol production. The HS/LE process allows very rapid fermentations, with 18 to 22% sugar syrups converted to 9 to 11% ethanol 'beers' in 6 to 12 hours using either a 'consecutive batch' or 'continuous cascade' implementation. This represents a 5 to 8X increase in
... entation speeds over conventional 72 hour batch fermentations which are the norm in the fuel ethanol industry today. The 'consecutive batch' technology was demonstrated on a large pilot scale (4,800 L) in a dry mill corn ethanol plant near Cedar Rapids, IA (Xethanol Biofuels). The pilot demonstrated that 12 hour fermentations can be accomplished on an industrial scale in a non-sterile industrial environment. Other objectives met in this project included development of a Low Energy (LE) Distillation process which reduces the energy requirements for distillation from about 14,000 BTU/gal steam ($0.126/gal with natural gas @ $9.00 MCF) to as low as 0.40 KW/gal electrical requirements ($0.022/gal with electricity @ $0.055/KWH). BPI also worked on the development of processes that would allow application of the HS/LE fermentation process to dry mill ethanol plants. A High-Value Corn ethanol plant concept was developed to produce 1) corn germ/oil, 2) corn bran, 3) ethanol, 4) zein protein, and 5) nutritional protein, giving multiple higher value products from the incoming corn stream. BPI is planning to implement and commercialize these technologies in the USA, and in cane producing areas around the world. Current projects in various stages of planning and execution include a 5,000 Liter/day cane juice ethanol demonstration project in Columbia, a 125,000 LPD molasses ethanol 'expansion project' in Pakistan, and a 30 million gal/yr dry mill ethanol facility near BPI's offices in Indiana. We further plan to promote the process to current wet mill corn processors (ADM, Cargill, and Staley's) Background: The High Speed/ Low Effluent (HS/LE) fermentation process allows very fast (6-12 hours) and complete fermentation of sugars by means of a self-aggregating yeast strain developed by BPI. This yeast allows a stable, high density yeast population to be maintained in the bio-reactors. In this project, lab and pilot scale studies were completed to permitthis technology to be confidently introduced into the US corn ethanol industry. There are three basic sections of this project: 1) application of the fermentation technology to the wet mill corn syrup/ethanol industry, 2) application to the dry mill corn ethanol industry, and 3) combining the fermentation technology with low energy distillation technology. In applying the HS/LE fermentation technology to wet mill corn syrup (Task 1), there were three major questions to be addressed. 1) Ensure complete conversion of dextrins to glucose in the short fermentation period: We must entirely saccharify the dextrins to glucose before the completion of the fermentation to ensure complete utilization of the starch/dextrins in the feed (Task 1.1), 2) Determine limits of 'back-set: We completed an effort to determine the limits of stillage recycle (back-set) with the goal of demonstrating successful back set at a high percentage of the feed make-up. This saves capital and energy associated with evaporation of the stillage (Task 1.2). 3) Demonstrate scalability of process to pilot and commercial scale: A major goal of this project was to scale-up and demonstrate the fermentation system at the 1,200 gallon scale. (Task 1.3) . Application of the HS/LE to dry mill syrup (Task 2) requires a fairly clear/clean syrup to be produced from the dry mill process. This goal could be attained by removing the corn fiber either before or after the cook process. Completed trials by project partner TEMA on a dry mill corn mash with a rinsing centrifuge indicated that finely ground corn tended to clog the screens of the rinsing centrifuge so that drainage rates of the rinse liquid through the retained solids slowed over time. Other solid separation technologies will be evaluated and tested in the future. Energy- Energy requirements in distillation can be reduced by integrating energy requirements throughout the ethanol plant (i.e. re-using steam from the evaporators), or by recompressing the overhead ethanol vapors and using these hot vapors to drive the reboiler. This MVR distillation concept can reduce energy usage for the distillation significantly (50% to as much as 75% reduction in utility costs), and even more energy savings and capital savings can be obtained when accompanied with design modifications of the distillation column itself. The design and modeling of the BPI Low Energy MVR system, along with the incorporation of energy saving technologies into corn ethanol plant, and modeling of the entire corn ethanol facility was completed as Task 3 of this project. In cooperation with Xethanol Biofuels and Xethanol, we designed and built two different pilot plants. Version 1 was designed and sited in Xethanol's small ethanol plant located in Hopkinton, IA during Q4 through Q7 of the project. Ethanol operations at this plant were stopped in February, 2005 (Q7), just as we were nearing completion of construction of our Version 1 pilot plant. In ensuing discussions with Xethanol, it was decided to site a second version of the pilot plant, (Version 2) in their plant in Blairstown, near Cedar Rapids, IA. Version 2 was then designed with the selection of vessels by Jim Stewart, GM, with a 4,800 Liter vessel selected as the HS/LE reactor. Dr. Dale completed a Process Flow Diagram (PFD), followed by a Piping and Instrumentation Diagram (P&ID). During the last 6 months of 2005, Xethanol pipefitters, electricians, and welders assembled and completed modifications to the vessels (including a large set of sight glasses), set the vessels, set pumps, piping, steam, water and electrical connections based on the P&ID. The pilot plant was completed in early February, 2006. Preliminary tests resulted in the failure of the drive one agitator in T-301, which was then repaired and replaced. A shake-down trial in March '06 was followed by performance trials in April. These trials were quite successful, with performance of the non-sterile, industrial scale HS/LE reactor closely matching performance of lab scale trials. A report on this work is attached as Appendix 1.3 A 'Material Transfer Agreement' was developed with ADM. BPI then provided the ADM research center with HS/ LE yeast. ADM completed some preliminary small scale trials of a continuous 3 stage CSTR implementation of the BPI technology on corn syrups from their Decatur IL facility. Yeast clogging of the tubing connecting the reactors caused operational problems. They may or may not pursue further trials based on conversations Dr. Dale has had with Dr. Charles Abbas, Director of Yeast and Renewable Research for ADM. Task 2.0 Application of HS/LE to Dry Mill Syrups Traditional dry mill corn ethanol production consists of grinding the corn, then adding liquid (a mix of water and thin stillage backset) to the milled corn to produce a mash. The mash is then liquefied (cooked w/ alpha-amylase and jet cooked @ 240 F followed by hold @ 195 F-where the starch granules are converted to dextrin polymers) and saccharified (addition of gluco-amylase after the mash is cooled to 140 F-where the dextrin polymers are converted to the glucose monomer). The whole mash is then taken to fermenters and the glucose converted to ethanol. To apply the HS/LE to dry mill ethanol, the fiber needs to be taken out before the fermentation. Our original design (P1) was to separate and rinse the insoluble corn solids/fiber after the cook using a rinsing centrifuge. We identified a project cooperator, TEMA Industries, a company that builds and markets rinsing centrifuges. The performance of the rinsing centrifuge on corn mash was determined in trials completed by TEMA (Task 2.1 -year 2). Task 2.1 Effect of Insoluble Solids- During Q5, we began some preliminary lab and pilot scale tests with centrifuges to determine the necessary processing equipment to achieve the required clarity in the dry mill dextrins fed to the HS/LE fermenter from a solids washing centrifuge as per BPI's DM-2 process. During Q6 we determined at what concentration Non-Soluble Solids (NSS) interfere with the long term performance of the HS/LE process: 1) Dry milled 'cooked' mash (converted to dextrins/glucose) was screened and rinsed using a 500 micron screen to separate the soluble dextrins from the corn fibers/NSS. The levels of NSS in the liquid fraction were measured and correlated with the optical density (OD) of the dextrin syrup. Fermentation trials in 250 ml shake flasks were performed to evaluate the effects of the NSS on the HS/LE yeast strain. During Q6, BPI began a series of lab scale centrifugations of whole mash to determine the centrifugal force needed to clarify the syrup, as well as the quality/clarity of the supernate from the mash. During Q9 we continued this separation work on Process P5, the BPI 'High value' process (see below) determining what degree of syrup clarity (Optical Density or OD) was required for good yeast pellet formation (Appendix 2.1). Task 2.2 Solids Separations Technology A variety of separation technologies were evaluated as a part of this I&I project. We have been evaluating several processes in addition to the P1 process (rinsing centrifuge separation of corn fibers/insoluble solids after cook of whole corn). Dr. Dale worked with two industrial cooperators, TEMA centrifuges and SEMO Milling to evaluate cost and performance of various improvements in corn ethanol processing.