Top 6 Signs It’s Time to Change out the Sieve in Your Ethanol Plant
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Posted on : 28-09-2011 | By : Mr. Ethanol | In : 3A, Ethanol Industry, Industry Issues, Molecular-Sieve-Mavens
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Loading ...A List of Signs That Say It Is Time for New Sieve
That time of year is rapidly approaching, and I don’t mean the winter holidays, it’s time for the Fall Shut Down for ethanol plants and managers have a crucial decision that needs to be made: should the molecular sieve in the dehydration beds be changed out or topped off?
While answering this question may be difficult, I have provided a list that could help you make this decision. These are the top six signs that topping off your sieve beds may not be enough anymore and a full change out of your molecular sieve beads may be in order.
- Age – If your ethanol dehydration beds are between 5-7 years old the beads begin to lose working capacity.
- Dust Starts to Show Up – If you start seeing dust or fractured particles show up in your regeneration condenser or your regeneration heat exchanger, it means the beads have been physically damaged either by fluidization or contamination.
- Frequent Filter Changes – Filters will always need to be changed out, but if you find yourself changing them out more frequently then it is a sign that the sieve beads are physically damaged.
- Decreasing the Cycle Time – Decreasing your cycle time in order to meet proof specification usually means that your bed is losing working capacity. This is a good sign that your sieve is losing its adsorption capacity, which happens as it ages.
- Reducing the Inlet Flow – If you are forced to reduce inlet flow to meet proof specification again it means your bed has lost some of its working capacity. This happens as sieve ages.
- Working Capacity Drops – When working capacity drops in the sieve beds you should calculate your dehydration efficiency. This can help you determine how well your sieve is currently adsorbing water. Please see the example and calculations below.
ethanol-plant-working-capacity
What about regeneration in vacuum? I have noticed that even if I regenerate at 200 C for hours under vacuum I do not recover the same level of absorption as fresh sieve. Do the guidelines for regeneration of sieve in vacuum conditions differ from those for regeneration in a hot gas flow?
Thanks!
Jack Singal
KIPAC / SLAC
2575 Sand Hill Road, ms 29
Menlo Park, CA 94025
It is virtually impossible to recover the sieve to its pristine moisture capacity under limited operational conditions. The molecular sieve as delivered has a given static water capacity measure at the factory immediately after processing. Typically this material is calcined at 550-600 degrees Celsius. This not only removes all adsorbed water but even the water of hydration in the crystal. Unless the zeolite that has been used in operation is exposed to the same extreme temperatures it will never be returned to its original capacity. In theory you could design a system with this sort of regeneration scenario but it is unlikely that this would be practical from an equipment or energy viewpoint.
Regardless of regeneration process, thermal swing, pressure swing or a combination of both the most recovered capacity you can expect can be derived from the isotheres and / or isotherms associated with that particular adsorbent. This is what is commonly referred to as the working capacity of a system rather than the static capacity of an adsorbent.