2 replies to this topic

[ekar]

Dear All,

 

I am simulating a liquefaction plant in which the feed (natural gas) comes in at around 35 degC. After amine treatment, the saturated feed gas temperature is around 40 degC. Mol sieve dehydration unit manufacturer has trouble achieving the required removal of water at this inlet temperature, plus the regeneration gas required will be high. It was suggested to lower the gas temperature to around 25 degC. The challenge is in selecting the cooling method. The site's ambient air temperature is around 35 degC, and the seawater temperature is about 30 degC. Hence air & water cooling may not work. Another option is to use the cooled refrigerant, but this will increase the duty and potentially affect its operation & startup.

 

I would be grateful for any suggestion/advice you could give regarding the appropriate cooling method for this case.

 

Thanks,

ekar

[Bobby Strain]

The feed gas to the dehydrators is usually cooled to near hydrate formation temperature using propane refrigerant. Some liquid hydrocarbon may condense along with water. Provide a separator and absolute filter-separator ahead of the dehydrators. But everyone in the business knows to do this.

 

Bobby

[Art Montemayor]

ekar

 

I don’t know what Mol sieve dehydration unit manufacturer you are dealing with and what his problem is.  I think the problem is that the size of the adsorption towers gets uneconomically feasible.  Please be specific in what the problem is.

 

But Bobby Strain’s recommendation is correct and practical.  Propane mechanical refrigeration is usually applied before the adsorption step to a temperature is that is a little bit above the natural gas hydrate formation temperature.  This temperature is also usually calculated with simulation by inputting your feed gas properties and composition.

 

Your problem should be resolved by incorporating another unit operation – mechanical refrigeration and phase separation – into your simulation flow diagram.  Do that, and your problem is solved.