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Teg And Molecular Sieve Cost Comparison


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#1 mosayef

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Posted 17 March 2015 - 09:05 PM

hi all,

 

i need to dehydrate natural gas from 40 lb/mmscf to 10 lb/mmscf. according to GPSA engineering data book, it is clearly stated that it is enough to use TEG dehydrator because the capital and operating cost of TEG is lower than solid desiccant. but i need the exact number to prove TEG is cheaper than solid desiccant like molecular sieve. is there any report provide the cost comparison between TEG and Molecular sieve ?

 

or how to compare of this two ? i just think that i will calculate the system manually and i will use stanley walas chapter 20 to estimate the capital cost. i need your help if there is more simple way to solve my problem

 

thanks



#2 Zauberberg

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Posted 18 March 2015 - 05:07 AM

What I always recommend with regards to cost estimation, is to dig into project archive of your (or operator) company and look for Mol Sieve and TEG projects which contain cost information as well.

 

Other ways are to get quotation from technology suppliers, or as you say to do a preliminary design yourself and use whatever cost estimation methods available.

 

Based on my experience, the cost of Mol Sieve unit is 2-3 times the cost of a TEG unit.



#3 Napo

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Posted 18 March 2015 - 06:40 AM

Dear Mosayef,

 

In first you need consider the flow of gas (MMSCFD) and the gas composition. It has CO2, H2S. This composition is constant. Do you have a projection to future?.

 

Is your gas to feed to cryogenic process?.

 

You have to consider the operative cost and not only the installation.

 

We have a little MEG plant and the problems are corrosion, plugs, odor (vents).

 

Regards,

 

Napo.

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#4 Art Montemayor

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Posted 18 March 2015 - 10:31 AM

In my opinion, this query is devoid of proper background information - or a definitive scope of work for the assignment given.  This are typical student problems and mistakes.  By not focusing on the scope of work and the specific problem at hand, the query becomes lost in a maze of different options, methods, and generated work efforts without getting to the core of the expected resolution.  Specifics such as the raw gas flow rate, temperature, pressure, analysis, and other basic data are missing.

 

For example, lack of knowledge in the pre-selected processes being compared leaves the student with the idea that one process can serve as a legitimate replacement for the other.  In this specific case, this does not seem to be true.  TEG dehydration can be successfully used for a gas product having as low a water content as 3-4 lb/MM Scf of product gas.  Since your scope is to dehydrate the gas merely for 10 lb/MM Scf in the product gas, than TEG is a valid and logical selection.  That being the case, the adsorption process makes no common sense when viewed from practical, logical, and economic point of view.  Adsorption processes cannot be controlled in producing a pre-selected water content (10 lb) and holding it at that level on a constant basis.  Knowledge and familiarity with adsorption will yield concurrence with the fact that it is not a practical or logical process for pipeline transportation of large gas flow rates.  Adsorption (especially using Molecular Sieves) is used to yield a very, ultra-dry product gas - something that is not required in producing a relatively “wet” gas product.  It would logically be the process of choice if your scope was to treat the gas prior to liquefaction - especially at cryogenic temperatures - in order to avoid any freeze ups - but not for pipeline transport.

 

So, from a logical, common sense TEG is an obvious selection.  However, this is reached without considering the raw gas flow rate - which could make a difference.  If we are dealing with 1.0 MM Scfd, then adsorption could be considered - or deliquescence using calcium chloride.  My first advice to you would be to improve your communications skills.



#5 gegio1960

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Posted 19 March 2015 - 04:07 AM

only a little help...

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#6 mosayef

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Posted 25 March 2015 - 08:38 PM

thanks all for your information :)

 

 

 

 

dear all,

 

i need data about how much TEG make up per year and how long we usually replace molecular sieve due to poisioning or capacity reduction. i can't find it on internet . i need your help


Edited by mosayef, 25 March 2015 - 08:39 PM.


#7 Zauberberg

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Posted 26 March 2015 - 02:28 AM

A common life cycle of Mol Sieve is 3 years. Some operator companies replace it after 2 years during opportunity maintenance shutdowns.

Properly designed TEG unit should have around maximum 10-15g/1,000 Sm3 glycol losses.






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