Application of Baromembrane Processes in Distillation & Rectification Technologies
- Application of ceramic membranes for ethanol dehydration/absolutization
- Distiller's grain recovery
- Residue water (lutter water) recovery
Application of pervaporation membranes for ethanol dehydration, required for further use of ethanol or its components as biofuel, is an alternative to energy-consuming and environmentally dangerous conventional technologies of dehydration which are zeolite absorption and ternary azeotropic mixture distillation.
Ceramic pervaporation membrane allows separating water and ethanol mixtures containing 94.3%wt. ethanol into 99.8%wt. ethanol vapour and water vapour, containing only 0.2% wt. of ethanol.
In the process of pervaporation dehydration, BM concentration technology is implemented. It means that ethanol vapour is concentrated and withdrawn from the membrane unit together with 'permeate', therefore, after passing through the membrane, while water vapour is withdrawn together with 'concentrate', namely, from feed channel. The terms 'permeate' and 'concentrate' are quoted, as they commonly refer to liquid flows, while in membrane pervaporation both flows are in the form of VAPOUR.
Vapour pressure of inlet/feed stream is the moving force of BM pervaporation process. The process itself is implemented by SPECIAL non-porous ceramic membranes, usually assembled in multipass membrane module.
'Permeate' and 'concentrate' flow out of the membrane module as vapour phase and are condensed. The 'permeate' condensate, which is dehydrated/absolute ethanol, is used for biofuel production or other purposes. 'Concentrate' condensate, which actually distilled water, returns to the main process cycle of ethanol production.
Flow diagram of ethanol dehydration on the ceramic pervaporation membranes is shown in the figure below.
Distiller’s grain is one of the main and problematic waste products of distillation and rectification.
On one hand, distiller’s grain refers to EXTREMELY contaminated 'process wastewater'. According to different sources, distiller’s grain features the following characteristics:
If recovered by collecting and storing in settling basins, distiller’s grain can cause a real environmental hazard leading to pollution of air, soil, surface, and subterranean water.
On the other hand, distiller’s grain is EXTREMELY valuable feedstuff. Feeding quality of distiller’s grain is proven by the following characteristics:
The use of 'crude' distiller’s grain as feed is rather seasonal – during the warm seasons distiller’s grain almost is not used as feed. Furthermore, for such considerable volumes of distiller’s grain – 0.14 m3 per 1 dal of ethanol – the presence of large feeding complexes near the place of distiller’s grain formation are required.
Conventional technology of distiller’s grain recovery, which is evaporation followed by deliquefaction, is EXTREMELY energy-consuming, for there is a need in evaporating up to 80…85% of water from distiller’s grain. Moreover, there is a problem of condensate recovery. Even though the amount of condensate is smaller, it refers to much more contaminated production waste product.
Application of BM technologies enables to exclude consumption of heat energy and organic fuel required by evaporation and significantly reduces that one required by end product deliquefaction.
Flow chart of distiller’s grain recovery by means of ceramic ultrafiltration membranes is shown in figure below.
At the outlet of UF unit two USEFUL products can be obtained:
- Concentrate which can be used as animal feed or can enrich distillers grain cake being processed into Dried Distillers Grains with Soluble (DDGS);
- Permeate which is used for mash preparation, significantly reducing the volume of water used in technology, which is usually fresh potable water.
The results of BM technologies application for distiller's grain recovery are as follows:
- Substantial decrease in amount of heat energy required for technological process maintenance – there is no need to evaporate moisture of distiller's grain and to heat fresh potable water for mash preparation.
- Significant decrease of the environmental impact owing to ALMOST COMPLETE exclusion of the distillers grain disposal into settling basin.
- Production of high quality feed product which is distiller's grain concentrate, which has longer shelf-life, significantly smaller volume and cuts costs of the feed preparation.
Traditionally, lutter water is used only for fusel oil washing. In other words, it is used in process cycles which do not provide extraction of fusel oil as end product. Lutter water is usually not recovered, but disposed into industrial sewage network. The main components of lutter water refer to high-boiling ethers and organic acids.
In case of closed heating of columns (by heat-exchangers), the amount of lutter water is 1.0…1.5 l per dal. According to different sources and test reports, lutter water features the following characteristics:
We have developed and implemented recovery technology of lutter water which allows the following:
- To use lutter water permeate instead of some fresh potable water, thus reducing fresh potable water consumption for process needs by 10-15%.
- To reduce volume of waste water disposal.
- To reach 100% recovery of lutter water heat.
Lutter water is recovered by membrane unit with NF polymer membranes or RO membranes. Flow chart of lutter water recovery by polymer membranes is shown in figure below.
Permeate of lutter water recovery is taken to mash preparation, while concentrate is disposed into sewage facilities.