Title: Unit 13 Readings and Lecture
Course: BFM 201 Ethanol Production > Section: BFM 201 Ethanol Production

Unit 13 Readings and Lecture

To Do:
Read Textbook: Ethanol Process Fundamentals – Chapter 8 pages 8.7 – 8.15
We discussed in Unit 12 the evaporation process and the circularity of the ethanol process, the goal to reuse and reclaim as much of the production material not consumed after making ethanol. As previously discussed, this would include the whole stillage, which is full of fat, protein, fiber, and minerals left behind after the starch has been fermented. It also includes process water and thermal energy. During the evaporation process the facility is striving to prepare co-products that are important to the profitability of the plant. Of particular interest is the preparation of the Dried Distillers Grain with Syrup. Additionally, the facility is reclaiming process water and thermal energy both of which contribute to the profitability and sustainability of the plant.

The evaporation process involves two distinct technologies to separate solids and liquids. The first step – and the step covered in unit 12 – is centrifuge separation which is a mechanical step utilizing the properties of specific gravity and separation force on the whole stillage (13 – 17% solids).  Two important products from this step are wet cake and thin stillage (4 – 5% solids). Half of the thin stillage went back to the slurry blehtender and the other half is going to the evaporators.

The second step – discussed more in this unit – is the evaporation system, which works on the principle of difference in boiling points for substances. Two important products from this step are syrup and flash vapors. Approximately 50% of the syrup will be added to the dried distillers grains and 50% sold as a high value protein. The flash vapors will be reused in the evaporators or condensed into cook water to be used in the slurry blender with the backset.

Our 50-mmgy facility will have six evaporators. The evaporators are “falling film” heat exchangers that are an efficient way to remove water by increasing vacuum across each unit. The evaporators work on the principle of differing boiling points for different substances. The multiple evaporators will have multiple effects by lowering pressure in each stage allowing vapors to flash off.  One pound of steam can remove several pounds of water in the multiple effect system. Evaporators 1, 2 and 3 are called first effect – the energy comes from outside sources. Evaporators 4, 5 and 6 are second effect getting their energy from flash vapors from the first effect. Flash vapors from the second effect is condensed and stored in the evaporator condensate receiver that is condensing the 200 proof ethanol vapors from the molecular sieves. This is yet another example of circularity.
References:

Chapter 8 (2006). In Ethanol process fundamentals: An introduction to ethanol processing. Granite Falls, MN: Minnesota Energy Enterprise Center.

Jacques, K. A., Lyons, T. P., & Kelsall, D. R. (2003). Chapter 26. In The alcohol textbook: A reference for the beverage, fuel and industrial alcohol industries. Nottingham: Nottingham University Press.