Back in June I mentioned that I was getting ready to head to the 2009 International Fuel Ethanol Workshop and Expo, which was held June 15-18 in Denver, CO. I had the opportunity to present a new ethanol scrubber design during the emissions abatement optimization session in the energy & environment track. My presentation dove- tailed well with other topics of the co-presenters, given below.
Track 2: Energy & Environment
Emissions Abatement Optimization
- Moderator: Monty McCoy, Technical Manager, US Water Services
- New Ethanol Scrubber Reduces Plant Capital and Operating Costs
Andrew Bartocci, National Sales Director, Envitech Inc.
- Fail-Safe Scrubber Emissions Compliance for Ethanol Biorefineries
Monty McCoy, Technical Manager, US Water Services; and Bob Elliott, Environmental Field Manager, American Engineering Testing Inc
- VOC, CO, and NOx Abatement and Optimization with RTO's
Andy Rodger, Engineer, Pro-Environmental Inc.
- Air Emissions Permit Compliance and Pollution Control Device Optimization Using Advanced Measurement Techniques
Thomas Dunder, GE Energy
I discussed a new ethanol scrubber used to recover ethanol from the fermentation and other vent streams. These streams contain CO2, ethanol and low concentrations of various volatile organic compounds (VOC's). Chilled water is commonly used to recover the ethanol, however, many of the VOC's (acetaldehyde, etheyl acetate, acrolein, and acetone) are highly insoluable in water and do not scrub out well. Post processing is often required to meet emission limits, which adds costs. I introduced a new, 2-stage scrubber design that uses re-circulated ethanol in the bottom stage and once-through chilled water in the top stage. Ethanol is an excellent solvent for the residual VOC's and it is readily available at ethanol plants. This approach eliminates the need for post processing and significantly reduces the plants capital and operating costs.
The presentations by Monty McCoy of US Water Services, Bob Elliot of American Engineering Testing, Inc., and Thomas Dunder of GE Energy showed test data from various ethanol scrubbers which illustrate how water flow rate, water temperature, and bisulfate injection rates impacts scrubber performance. The data also showed how the emission rate changes throughout the fermentation process.
Other issues of ethanol scrubber performance were discussed including channeling and fouled mist eliminators. Channeling is related to non uniform liquid to gas (L/G) ratio. When a limited amount of water is applied to the packing in a tall, narrow tower, uniform distribution of the water is critically important. If there are parts of the packed section where the L/G is lower than the average value, gas passing through those parts of the packing will not be scrubbed as efficiently. If any water runs down the tower walls, it won't spend as much time in contact with the gas and will absorb less ethanol than water trickling over the packing. A properly design scrubber should have internals that help maintain uniform distribution.
Fouled mist eliminators can result in excessive pressure drop. This can be caused by improper selection of the type of mist eliminator or from not having a proper wash system to keep the mist eliminators clean during operation. It's important to not view the fermentation scrubber as a simple can with packing in it. There are nuances to the scrubber design that enable it to operate at optimum performance with minimum maintenance.
To download the presentation click the icon below.
photo credit: stefanie says