Use of Separators, Decanters in Biodiesel Processing
Usage of centrifuges in biodiesel processing began with Oelmühle Leer and Vogel & Noot in 1990 in Germany and Austria. Large-scale biodiesel production was still five to 10 years away. These companies developed their own continuous process at moderate temperature and ambient pressure to convert rapeseed (canola) oil into biodiesel by transesterification. Both processes utilized self-cleaning, explosion-proof centrifuges in the transesterification and water-wash sections to remove glycerin and other impurities instead of traditional gravity settling tanks. The patented technology has since been incorporated worldwide into 40 high-volume biodiesel plants by Westfalia/GEA Mechanical Equipment.
Europe was the leader in high-volume production of biofuels beginning in 1995, which was followed in North America in 2004-’05. Centrifuges and decanters were used in the pretreatment of feedstocks, mostly rapeseed (Europe) and soybean (North America) oils. Pretreatment degumming and neutralization reduced phosphorous and free fatty acids (FFA) to acceptable levels for efficient transesterification reactions.
In Europe, the esterification process for biodiesel was commercialized by Austria-based BDI-BioDiesel International AG (now BDI-BioEnergy International), which utilized lower quality feedstocks—tallow, lard, grease and used cooking oils. Today we find decanter centrifuges as the first stage in low-quality feedstock processing to remove bulk solids, followed by a centrifuge clarifier to produce a clean feed to traditional degumming/neutralization. The trademarked TOP Degumming process is frequently used to achieve phosphorous values of less than 10 parts per million prior to esterification or transesterification.
U.S. biodiesel production was initially based upon degummed or refined, bleached soybean oil using technologies from Crown Iron Works, Desmet Ballestra, Westfalia and a myriad of independents, which employed centrifuges in on-site pretreatment, and water-washing finished product. Smaller, used centrifuges saturated the low-volume production market where many were found to be mismatched to the application.
Soybean sterol glucosides moved into the spotlight as plants found the impurity to be a major factor in biodiesel quality problems involving low-temperature performance. Methods developed to meet the quality challenge include diatomaceous earth filtration, distillation and clarification via centrifuge at the end of the process. The clarifier centrifuge is gaining popularity due to its lower maintenance, no significant disposal costs, and continuous operation with low labor requirements. Simple water-washing of finished biodiesel is not effective. Similar glucoside problems were not noted in the rapeseed-based product, although additives were developed to improve cold flow properties in Europe. Downstream purification processing has moved to distillation for purity and color improvement. Although most biodiesel production uses sodium methylate as the catalyst, there are plants using potassium hydroxide, which produces salts and opportunities for decanter removal of the salts at high temperatures.
Higher priced soybean oil pushed many plants to shut down completely and exit the biodiesel market, or move to alternate feedstocks including tallow, lard, waste greases and corn oil recovered via centrifuge or three-stage decanter in ethanol plants. The recovered corn oil is roughly 4 to 5 percent of the ethanol plant capacity and is high in FFA and wax content, which presents challenges for use in transesterification. Centrifuges are used to dewax and degum the oil.
To further improve the efficiency of manufacturing biodiesel, companies focus on catalyst/feedstock, mixing techniques including high-shear mixers ( IKA, BWS, Fristam, Silverson) and cavitation mixers from Arisdyne, HydroDynamics and CTi. All work to upgrade product quality and reduce use of catalyst by increasing the reaction zone dynamics between catalyst and the reactant. Different disc stack designs and turbidity meters have been added to the biodiesel processing centrifuges to enhance process control and increase yields.
In the pretreatment area, the trademarked Alcohol Neutralization process was developed to optimize catalyst efficiency by taking excess sodium in the catalyst to be an FFA neutralization reagent instead of caustic soda. Explosion-proof separators designed for this activity include gear drive, direct couple drive and nitrogen blanketed machines. In some countries a belt-driven, frame-blanketed machine is installed.
Biodiesel plant centrifuges and decanters now exhibit heavy-duty, explosion-proof sight glasses, pneumatic operating water solenoids and higher-efficiency, intrinsically safe barriers in the control panels. All improvements are made with the Safety First incentive.
Technologies for process improvement move into the biofuel arena every day and will continue as the need for reduced costs is raised. Many of these, such as enzymatic and fixed bed catalyst systems, will require a purified feedstock and G Forces between 4,000 and 12,000 found in decanters, separators and clarifiers—a process parameter to be reckoned with and utilized by all.
Author: Ted Neuman
Market Manager, Oils & Fats Processing, North America
GEA Mechanical Equipment US Inc.