Ethanol Plant: Molecular Sieve Bed Precautions
6 Precautions to Consider While Dehydrating Ethanol
Purifying ethanol requires running your distilled ethanol through molecular sieve beds in order to produce over 99% pure ethanol. In order to dehydrate ethanol thoroughly most plants require that you have ten’s if not hundred’s of thousands of pounds of sieve installed in your vessels.
Making a significant mistake here could be hazardous to your co-workers and it could cost your plant a lot of money if you end up rolling your beds or if you have to shut down the vessels for awhile so here are six precautions to be aware of when running your sieve beds.
- Watch the temperature – The adsorption process creates a lot of heat energy; do not let temperatures exceed 600 degrees Fahrenheit at any time.
- Start the dehydration procedure with 200 proof ethanol, if you do not have 200 proof ethanol available, use extra caution until a stream with low water content is available for recirculation.
- Avoid massive slugs of liquid, these can stir the bed. Liquids may need to be drained while you are adding the wet feed.
- Avoid rapid pressure fluctuations, these can cause bumping or lifting in the bed. Pressure is normally released in order to control temperature. Be aware that as sieve and ethanol/water streams are in contact with one another intermolecular frictional heat can occur. Heat releases of up to 1,800 BTUs/lb of adsorbed water and 700 BTUs/lb of adsorbed ethanol can occur.
- Watch out for hot spots on the bed. This can be avoided by having a recirculating feed rate that is high enough to maintain a vigorous flow throughout the sieve beds.
- Make sure you purge the air. Ethanol is a flammable vapor and it is running through your beds at high temperatures and in the presence of oxygen. Purging the air can prevent fire hazards.