21 replies to this topic

[PKS]

Dear Members,

 

We are in process of feasibility study for a new gas processing plant. We have been given an option for Modular Gas Processing Plant instead of conventional stick-built option. Definitely, modular option is better if we look into labor costs, time schedule of the project etc. 

 

I want to know, if there is any % recovery of products (C3, C4, C5+) comparison between Stick-built Vs Modular Gas Processing Plants. We got some information that Stick-built plants have more/better recovery of products than modular. This may turn the needle (selection) towards Stick-built option.

 

I am not able to find any matter relating to the recovery difference. Looking into better and enlightening points from you all.

 

 

Thanks and regards

 

PKS

[Neelakantan]

 point not clear is what exactly you mean by modular unit; modular units are also designed "fit-for-purpose";  I have done design for modular units for gas recovery plants, crude trains, fpso topsides, and mini-refinery. When we use the term modular, the idea is the construction mode and erection mode. the equipment are still to be designed for the specific project. Probably you meant en-sembling of off-the shelf units?

 

per se, no modular-unit sellers are going to say the difference in recovery between field constructed and modular erected units. even in modular units, the recovery level and power will vary as the feed composition, temp and pressure changes over the time of operation. This is essentially a sensitivity analysis.

 

I am also not clear how stick-built (used for house erection) can be interpreted for a gas plant. you may please elaborate the usage of this term.

 

regards

neelakantan

[PKS]

@Neelakantan

 

Thanks for your reply.

 

With modular gas plants I mean, the plants which are pre-engineered and are built off- the site location. e.g. click the link:  http://www.cbi.com/c...on-construction

[Bobby Strain]

Where is the plant located? What are your NGL recovery objectives? What is the capacity? When you have answers to these questions, and a few others, then you should evaluate the value of increased product recovery. You should evaluate the value of your alternatives with input from several plant providers. I would start with a general inquiry to several suppliers to get a perspective on the options available. You won't get true costs from any of the suppliers, and you have no way of comparison unless you have significant cost data for these facilities. In the final selection, you should not be concerned about the construction  implementation; only the cost. Sounds like you should engage the services of an independent party to help you with scoping and selection.

 

Bobby

[PKS]

Bobby

 

Thanks a lot for your reply. I fully agree with your points.

 

My concern is, if the % recovery of liquids better in stick-built option better than Modular (pre-engineered plants) option. Is there any such information found in literature or its just irrelevant to ask such question?

 

Off-course, it is the final cost which will govern the selection of one of the above discussed options. 

 

Regards

PKS

[Neelakantan]

precisely that is what I meant modular; the units are still to be designed, engineered and fabricated; to elaborate, based on the feed and product specifications, the units are pre-built (for that matter of fact, we have engineered even pipe racks so that the field erection is minimal) Thus modular units are designed based on the recovery specified by the client.

 

but how a "stick-built" unit is made for a gas plant?

 

regards

neelakantan

[ColinR33]

PKS, 

There is no inherent difference in recoveries between stick built and modular facilities as long as the designers of each are given the same specifications to meet.  Both can be designed and built as fit for purpose units that have the same recovery. 

 

Colin

[PKS]

Colin

 

Thanks for your input.

 

The licensor (stick-built) and the Modular (pre-engineered plants) vendor, when given our product specifications will definitely design the plants to meet the product specifications.

 

The question is of % recovery of liquids (C3+), as modular packages are for fixed capacity like 100/200/300 MMSCFD gas. If I need a capacity of 250 MMSCFD, the vendor may give me 1x100 MMSCFD + 1 x 200 MMSCFD (100+200=300>250) trains and a Stick-built Licensor will give me a plant designed for 250 MMSCFD gas. Here, is the doubt arises, about the %recovery. I hope my question is more elaborate now.

 

At the end I want to add that, at the end, it will be cost, which will decide which option is be opted. My question is academic point of view.

 

 

regards

PKS

Edited by PKS, 27 May 2014 - 01:44 AM.

[Neelakantan]

@ PKS

 

the fixed capacity plants are not "pre-engineered" modular plants; they are the off-the shelf units, designed generically; that is why I asked clearly in my earlier reply #2; for such units you have to or  supplier has to "rate" them for the feed and product conditions that you specify

 

regards

neelakantan

Edited by Neelakantan, 27 May 2014 - 12:45 AM.

[PKS]

@Neelkantan

 

My understanding of a:

 

Modular (Pre-engineered Plant) is a plant, which is already engineered with some range of feed gas composition, and are designed in modules of 100/200/300 MMSCFD etc. If a client desires 250 MMSCFD, the vendor may provide two gas plant trains, one of 100 MMSCFD and other for 200 MMSCFD (total=300 MMSCFD). 

 

Stick-built Plant: A plant designed for a given capacity and built on site.

 

As per your reply in #2, I understand that the Modular plants can be tailored to the required capacity and are constructed on shelf instead of at site.

 

Neelkantan, in most of the websites of vendors like UOP/Russel, (http://www.thomasrus...s/ngl-recovery/)

Please check this link. They mention about the recovery as well as their capacities of their design modules.

 

I am putting up what they UOP/Russel mentioned on their website "pre-engineered, factory-built modular NGL recovery plants can be delivered and installed at least six months faster than the traditional stick-built alternatives."

 

I want to say, modular plants are beneficial, in saving "time spent on engineering" (as these are pre-engineered) and "site-linked delaying constraints" (as these are factory built). If these are tailored, then they have to do engineering and I feel there is no difference with the stick-built option.

 

PKS

Edited by PKS, 27 May 2014 - 01:55 AM.

[ColinR33]

There certainly are pre-engineered sizes ("spec packages") but do not generalize all modular plants as such, many companies (such as the one I work for) design and fabricate fit for purpose (custom) plants designed for each individual case.   You do lose some of the cost and schedule savings but you have a facility that does exactly what you want. In the case of a spec package, the vendor can give you predicted performance, you cannot ask anyone outside of the vendor to predict the performance unless they have all of the design data, there are too many variables. 

[PKS]

I thank all the contributors!!

 

Let me conclude:

 

Modular Plant package may mean:

 

i) a Pre-engineered Plant, which is already designed, sized and engineered by a vendor for a range of composition of Natural Gas. Vendor may have sized the plant in various modules like 100/200/300 MMSCFD etc. They fit their modular design as per Feed Gas flow and composition. This approach saves time (means money) beacuse: They are already engineered and are built in factory instead of on-site, which helps saving time delays because of bad weather or labor upset, or remote location expensive labor etc. 

 

ii) a plant which is built in factory and is designed fit for purpose. Engineering is to be done and time is saved as it is factory built (benefits of factory-built are discussed in above point)

 

There is no pre-determined comparison based on % Recovery of liquids. One cannot predict, without working on the plant simulations.

Finally, its the overall cost which governs the selection of Stick-built or Package Gas Plants options.

 

 

Thanks and regards

PKS

Edited by PKS, 27 May 2014 - 01:50 PM.

[PKS]

Learned Members,

 

Please clear, if the above understanding is correct.

 

PKS

[ColinR33]

Yes, that is pretty much correct.  Stick built is typically the most expensive and longest lead time.  A "spec" packaged unit is the most economical and shortest delivery but you give up some flexibility and it may not be able to do exactly what you want and in general may not meet your company specifications.  A custom designed package unit will be between teh two in cost and delivery, but will be fit for purpose and will meet most or all of the company specifications.

 

Cheers,

Edited by ColinR33, 28 May 2014 - 05:26 PM.

[PKS]

Thanks a lot to all the contributors!!

 

PKS

[PKS]

I have one more query, what is used for the cleaning of equipment for shut-down before man entry, in a Gas plant. Nitrogen or steam out (off-course for hot section)? 

 

Some vendors give Nitrogen as cleaning medium for the same. I think steam is best to remove the residual hydrocarbons from the vessels/columns before man-entry. 

 

Anything on this will be helpful

 

Thanks

PKS

[Art Montemayor]

I don't understand your vendor's, or your logic.   Nitrogen is not a cleaning agent.  It is an asphyxiation hazard to humans and it doesn't "clean".   Who are the vendors that are claiming this?

 

I have always relied on steaming out vessels followed by cooling with forced air prior to human entry into a confined space.  This is all subject to a detailed and carefully supervised program that ensures that the entry is completely safe as to movement, breathing, and working capabilities.

[PKS]

Thanks a lot Art!!

 

There is a study going on to select between Stick-built option or Modular Gas Plants. We asked the vendors to include the requirement of steam (for steam-out) of hot section equipments during shutdown. But the vendors are considering N2 for the same. They say it is a gas plant and steam out is not required and N2 will solve the purpose (maybe followed by air purging). They say for the modular plants (pre-engineered ones), they have to design the equipments for steam-out, which ll be an extra effort to customize the unit for steam out. This is the exact situation. That's why I put the question here, to know if anywhere else also N2 is used instead of steam out. 

 

Our operations people say , they need steam to clean the equipment before man-entry. They say, they have experience of presence of pyrophoric material inside the equipments. To clean those steam out is required.

 

That's it!

 

Please guide.

 

Thanks and regards!!

PKS

Edited by PKS, 11 June 2014 - 05:11 AM.

[Art Montemayor]

PKS

 

Stick or modular, it doesn’t make any difference in having a safe, effective, and controllable cleaning process for any unit handling hydrocarbons.  Steam is universally used because it does clean while removing greases and other heavy hydrocarbons.  It is also inert, readily available, safe, and easily controllable.  The downside of steam is that it requires a boiler (usually available at most processing units), it is hot, and it can cause a partial vacuum if not adequately vented during the steam out.

 

As I stated, nitrogen is a potentially dangerous killer – particularly in confined spaces.  In the USA I believe nitrogen has caused more deaths in working environments than any thing else.  It operates like stealth; you are not aware of the asphyxiation until it is too late.  I personally would never use it as a “cleaning” agent because it simply does not clean.  All it lends is an inert atmosphere – and that is not what you are specifying.

 

 

My personal advice: stick to your basic specifications and needs.  You need a clean confined space before you send any person into it.  That is a basic need.  Nitrogen will not give you that – regardless of what your “vendors” state.  I asked for their identification to know who is out there in the engineering world who would be ignorant enough to state that nitrogen is a cleaning agent.  Your vendor doesn’t want to furnish a boiler and its controls – probably because it raises his bid.  However, you will be the owner and operator and it is your money.  I would not allow for any vendor to decide what is best for me or my operations.

[ColinR33]

Art has nailed it.

[Neelakantan]

@pks

 

i was thinking what the cleaning / man-entry has to to with modular units; and why not a separate thread for the same; and i am really surprised that a company on project level is looking at what vendor specifies?

 

my past is we specify and vendors comply; if for the modular units, vendor supply is different we "evaluate"; as ART has said clearly

"I would not allow for any vendor to decide what is best for me or my operations."

 

regards

neelakantan

 

(we do use nitrogen, as we cannot admit air directly after depressurization to flare; sequence is drain, depressurize, and steam; isolate positive, then N2 purge and finally air purge, then check again through your operations safety department to see if it is safe to open the manhole and air-blow; then follow safety norms for man-entry")

[PKS]

Thanks a lot!!

 

We have already asked the vendors to give a steam header and distribution system in the plant. We will use portable steam generator for steam (Steam is not available in the plant.) I wanted to know more views and opinions about the same.

 

The vendor say flushing with N2/water flush/Air is sufficient to clean the equipment for man-entry. Anyways we have asked them to go ahead as above.

 

Your vendor doesn’t want to furnish a boiler and its controls – probably because it raises his bid.  

@Art: Yes I also have same opinion. We have asked them to evaluate with equipments designed for steam out.

 

@Colin: Yes, Art has nailed it.

 

@Neelkantan: In stick built, the bidder is providing steam-out and for modular, the vendors are not providing. So, I had put the question here in this thread and thanks for the information.

 

Regards

PKS

Edited by PKS, 12 June 2014 - 12:00 AM.