y Christina Borgese and Marc Privitera, PE
Practical advice for cash-strapped community-scale biodiesel plants
Feedstock characterization, process conversion and fuel finishing are the building blocks of biodiesel production. Of the three, feedstock characterization is usually underestimated. The lack of depth in the understanding of feedstock’s impact on the business plan has lead to challenges that might have been avoided for smaller scale producers. This article on feedstock is the first of three installments to discuss the building blocks of biodiesel production.
Nontraditional methods to process higher free fatty acid (FFA) feedstocks are more technically complex compared to traditional systems. High FFA feedstocks include yellow grease, brown grease, tallows, and algal oils. Yellow grease is primarily comprised of restaurant and cooking wastes. Brown grease typically comes from grease trap waste, dissolved air flotation skimmings, agricultural spoils and meat cut waste. Algal oil is only now emerging as another feedstock. Tallows and rendered fats typically have a high existing market value.
The National Renderers Association defines yellow grease as no more than 15 percent FFA and no more than 2 percent MIU (moisture, insolubles and unsaponifiables). The historical reference on FOG, Bailey’s Industrial Oil and Fat Products, defines brown grease as having an FFA level between 15 and 50 percent. There is much debate throughout the industry on how exactly to define brown grease. In reality the nomenclature is inconsequential. What really matters is the actual FFA and MIU content received at the plant and whether or not the system is capable of processing the material. A rookie mistake is negotiating a contract to buy yellow or brown grease without the needed characterization.