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Cost comparison of salt dryer vs molecular sieve

Cost comparison of salt dryer vs molecular sieve

(OP)
I have been asked to come up with a quick comparison of CaCl2 dryers and molecular sieves for drying of 200 t/h LPG. I think I have a good idea of the technical comparison and the operational considerations based on thread135-124876: CaCl2 Dehydration of LPG, but I have little experience with the capital cost comparison.

I am looking for a rough comparison, ie, 4x the cost for mol sieve vs others. I estimate the salt dryer option will cost about $700-800K.

Any input from the forum will help.

MT

RE: Cost comparison of salt dryer vs molecular sieve

It looks like you are trying to compare the cost of a Prius to a Locomotive.
  • Salt dryers at their very very best can get you a 20°F dewpoint depression. Mole Sieve can get you what every dew point you design for.
  • Salt dryers can remove about 3 lbm of water for every lbm of salt that is consumed. Mole Sieves are not consumed.
  • Salt dryer media is consumed. Mole Sieve media is regenerated. Think about this one, if you have 1 MMSCF/day of 600 lbm/MMSCF gas then you have to drain off 800 lbm of brine (call it 100 gallons) and add 200 lbm of salt EVERY SINGLE DAY. If you are talking more than a couple of MSCF/day the operators will hate you.
Cost is never the determining factor in this kind of decision. If it is big enough to consider a Mole Sieve (and it's attendant regeneration heat source) then there is no way that you would ever consider doing the job with salt.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

RE: Cost comparison of salt dryer vs molecular sieve

Sorry in advance for replying to an older thread, but I'm struggling to find information related to the actual performance of salt dryers in liquid propane service. My understanding of salt drier operation is that, depending on the type of salt used, the water removal varies to as low as 50% of the saturation point. This isn't anywhere near good enough to produce dry propane by the freeze valve test. I believe the water saturation point for C3 is about 180 ppmw @ 20°C. The question I'm struggling to answer or find information on is what we should expect out of a CaCl2 salt drier for water ppmw in the propane. I recognize that the inlet temperature of the C3 will also influence the product, but if we assume a temperature of say 100•F, what should we expect to get in the product?

I'm not a fan of salt driers and one of my primary concerns is whether or not they'll even work and produce a product that meets a standard C3 freeze valve test. However, many references indicate they are used quite often for drying liquid C3.

Thanks in advance for any information you can share.

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