How to make Adsorption Dehydration Performane Monitoring
How to make Adsorption Dehydration Performane Monitoring
(OP)
My plants have sorbead(Alumino-silica gel) to desorb water from nat. gas stream from 45 to 0.5 lb/MMscfd (gas flowrate 127 MMscfd) and we wonder that we can extend life for 1-2 years if we can find that the Mass Transfer Zone is enough. Some methods are using Gamma ray to determine bed density or using neutron backscatter (which I don't know how they work). Any suggestion 'lb be very appreciated.
Thank you
Thank you





RE: How to make Adsorption Dehydration Performane Monitoring
We had a lead/guard bed of mol sieve in an ethylene plant and we monitored the time in lead, gas flow, dP and time until breakthrough. This was plotted, on a normalized flow basis, to give us an idea what the deterioration in bed's performance was like. One difference here is that it doesn't sound like you have a guard bed. Without that, running to breakthrough versus a fixed cycle does entail a risk to the plant.
Also, we had a fixed inlet temperature and so we didn't bother correcting for inlet water content. If your inlet temperature varies, that can increase the water load to the bed significantly.
RE: How to make Adsorption Dehydration Performane Monitoring
Please elaborate your dehydration plant working,i.e intermitent operation with regeneration cycle or contineous operation ,procedure of regeneration (if any), change of any physical parameter which is being monitored,any equipment or process downstream of dehydration unit for further treatment etc.Do you use cryogenic process downstream of this unit.
RE: How to make Adsorption Dehydration Performane Monitoring
G. Gordon Stewart, P.Eng.
Gas & Oil Process Engineering Consultant
http://www.ggordonstewart.com/
ggstewar@telusplanet.net
RE: How to make Adsorption Dehydration Performane Monitoring
There was no 'guard bed' to catch carryover or slugs of liquid from the upstream equipment (though there were separators of course).
RE: How to make Adsorption Dehydration Performane Monitoring
You may ask the supplier of the adsorbent material about the characteristics and recommended operating parameters like maximum velocity, maximum allowable depth of bed, etc. and compare against your actual operating parameters. You will then know if you are violating any of the norms set by the supplier of the adsorbent bed. You can then take corrrective action. If you find that your actual operating parameters are well within the specified norms, then the supplier has to explain why his material is giving short life.
RE: How to make Adsorption Dehydration Performane Monitoring
You can also do a breakthough test - this allows you to determine the remaining life of the sieves. This needs expertise.
You can do a gamma scan to determine the health of the beds. Sometimes the beds can be fluidized and displaced which will cause channelling and premature breakthrough.
Regeneration profiles can give clue to what is happening. You'll find a plateau period when all the water is driven off.Monitor the time interval. Increase of this interval will tell you you're getting more liquid. Sometimes heat loss thru insulation can be substantial. Normally expect 15-30 C drop in regen gas inlet temp & outlet temp.
RE: How to make Adsorption Dehydration Performane Monitoring
We have 4 dehydrators (ID 76", H 16.5 ft) for 127 MMscfd natural gas from 45 to 0.5 lb/MMscfd. Desiccant is 97%Silica 3%Alumina. Switching valves to operate 20 hrs cycle time (drying 10 and regen 10 hrs) Two beds always in drying mode about 65F, 657 psig. We use the same gas for cooling and heating beds at 500F 566 psig.
How can I do a breakthrough test or monitor mass transfer zone ? Unfortunately we can't shut down this unit and no bed moisture probes. Does gamma ray provide the reliable results because I'm afraid the difference in density profile between MTZ and active zone is not enough to interpret the moisture content in each zone. Do you know Neutron Backscatter ? Does it provide moisture results directly ?
Thank you very much for every comments.
RE: How to make Adsorption Dehydration Performane Monitoring
We did have problems with 'some' molecular sieves prematurely failing but concluded it was due to sodium and calcium being leached from the clay binder during regenerations (we regened countercurrently and had a phenomena called the reflux effect occuring) until essentially the mol sieve bead or extrudate fell apart.
That's not true for silica gel I agree, that will shatter if hit with free water.
RE: How to make Adsorption Dehydration Performane Monitoring
nong- Gamma scan will tell you whether the beds are lifted or not . It will not tell anything else.I do not know about neutron back scatter. If you get any info please let me know.
Breakthru test can be done online if you've bed probes - or if you've one probe at the end of the bed ( about 1 m above the vessel bottom). It is better to do offline - that is you have to divert the gas to flare downstream.
RE: How to make Adsorption Dehydration Performane Monitoring
I suspect this is one of those 'agree to disagree' positions.