×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

large motor plus LCI for cracker compressors

large motor plus LCI for cracker compressors

large motor plus LCI for cracker compressors

(OP)
Dear colleagues,

Some crackers in France employ electric driven compressors for charge gas, C3R. TOTAL plant in Gonfreville has a 35MW electric driven CGC.

Why such practice is not so widespread (except in new LNG plants and compression stations))? CAPEX only? Reliability? It seems a very favorable energy balance can be obtained by electric motors (+ LCI) as steam condensation is avoided, lower steam flow during startup is necessary, etc.

have you ever discussed such point in this forum?

Do you know any cracker that is moving in this direction?

regards

fabio vincent
www.figener.com.br

RE: large motor plus LCI for cracker compressors

You have to input a fixed amount of work through the compressor shaft to compress a known amount of gas from a defined suction pressure and temperature to a known discharge pressure and temperature. I can generate that work with an internal combustion engine, an electric motor, a steam turbine, or a water wheel. In every case the amount of work input is fixed. The cost of that input is quite variable.

If I am running a gas turbine to generate electricity and I'm willing to spend the capital to recover the waste heat, then using steam is very inexpensive while using the electricity directly to run the compressor has a high opportunity cost (the power can be sold if not used). If I have to burn fuel to generate steam then steam turbines can be quite expensive to operate.

There are situations where I can use gas that would otherwise be vented to run an internal combustion engine, in countries with a carbon tax, the government is paying me to use that fuel instead of venting it, very cheap indeed.

Bottom line of the above discussion is that choice of driver for a particular compression operation in a particular location at a particular time is a complex economic analysis that does not lend itself to rules of thumb. You have to do the analysis honestly, without bias to decide what makes the most economic sense. Once you have that number it is quite appropriate to apply personal, corporate, or regulatory biases to add the consideration of intangibles--with an honest cost breakdown you can determine the cost of indulging in the biases to decide if pandering to them is justified. For example, if the NPV of your electric driven compressor is 80% of the NPV of a gas turbine driven compressor, but adding the turbine would increase the emissions output enough to force the entire plant into a non-attainment status (with accompanying potential for fines, capital expenditure required for other equipment, and bad press) then the lower NPV could easily be justified. In the same example, if the NPV of the electric was 10% of the gas turbine even considering fines and required capital expenditures then accepting the bad press might just be a cost of doing business as you install the turbine.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

RE: large motor plus LCI for cracker compressors

(OP)
Thanks, zdas04,

The project I refer to is a new cracker. The proposed design is to drive the main compressors with condensing steam turbines. However in the entire complex there companies that require process steam and so additional boilers beyond the furnaces steam generators are required. Residual fuel from cracker can be used to generate power in combined cycle and/or in integrated gas turbine (exhaust gases as comburent to furnaces). The point is: the entire cycle is more efficient if the large compressors were motorized (motor + LCI) and steam (produced in the furnaces) could be sent to other companies of the complex. I understand that local energy and fuel costs impact on the viability of any solution. What I could not up to now understand is why there is so few crackers with large motor driven compressors except in France.

Regards

fabio vincent
www.figener.com.br

RE: large motor plus LCI for cracker compressors

(OP)
Thanks, zdas04,

The project I refer to is a new cracker within a petrochemical complex. The proposed design is to drive the main compressors with condensing steam turbines. However in the entire complex there are other companies that require process steam and so additional boilers other than the furnaces steam generators are required. Residual fuel from cracker can be used to generate power in combined cycle and/or in integrated gas turbine (exhaust gases as comburent to furnaces). The point is: the entire cycle is more efficient if the large compressors were motorized (motor + LCI) and steam (produced in the furnaces) could be sent to other companies of the complex. I understand that local energy and fuel costs impact on the viability of any solution. What I could not up to now understand is why there is so few crackers with large motor driven compressors except in France. Any idea why?

Regards

fabio vincent
www.figener.com.br

RE: large motor plus LCI for cracker compressors

As I said, it is economics. If you have other profitable uses for the steam, the economics could easily favor running the compressor with electricity. If you have more steam generation capacity than loads then the economics will favor steam. I don't believe it is a country thing, I think it is an individual plant thing.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

RE: large motor plus LCI for cracker compressors

I am also working now on an ethylene cracker project. We are now on precommissioning stage. The main compressor charge gas compressor and the tertiary refrigerant compressor is using condensing turbine. One reason for this one is that steam turbine are variable speed that the main compresor needs. If we have to use electric motor, then we have to use variable frequency drive motors which are very expensive.

RE: large motor plus LCI for cracker compressors

Variable frequency drives and motors are not that much more expensive than fixed frequency and soft start equipment. I was quite surprised at how little variable frequency added to a project I did recently. If the numbers in your analysis were unbiased, and the decision favored steam drive then that's what I'd build. It has to be a case by case analysis.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close