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!
  • Students Click Here

*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


De-Rating Vs Turn down the boiler to less than 20% MCR

De-Rating Vs Turn down the boiler to less than 20% MCR

De-Rating Vs Turn down the boiler to less than 20% MCR


We have foster wheeler water tube boiler operating pressure at 450psig with steam production of 250,000Lb/Hr. This boiler can only operate at a minimum of 20%MCR, i.e. 50,000Lb/Hr per the OEM. I was wondering if someone has converted these huge boilers to operate up to 10% MCR, i.e. 25,000Lb/Hr as we have no steam demand left. I understand bringing the pressure down will create other issues like higher steam velocities and may overwhelm the separators but not sure for such a huge size boiler. Is there anyone who has done this successfully and if yes, what is required to be done by keeping in mind that the circulation ratios are not affected and avoid the carry over as well. We may also have to look into the burner design to make sure we stay compliant from emissions stand point like NOX, CO etc. If anyone has any information or advice, please share.

RE: De-Rating Vs Turn down the boiler to less than 20% MCR

The de-rating or re-rating of the existing operation system are quite typical, but need a complete engineering study for the process and equipment in the system. The issues as you have mentioned are the items should be included in the study. IMO, the cost may also be one issue to be included in the proposal.

RE: De-Rating Vs Turn down the boiler to less than 20% MCR

Thanks for the reply.
We are also looking into purchasing the smaller once through boiler and looking at the cost Vs converting the existing boiler to run at lower MCR.

RE: De-Rating Vs Turn down the boiler to less than 20% MCR

I can state that during a 1986 Cleaver Brooks (C.B.) seminar at their Lebanon facility in PA, a 100 hp fire tube boiler with a rated steaming capacity 0f 3,450 lbs/hr (=28 gph fuel rate) can produce 850 lbs/hr (=7gph fuel rate) with a turn down ratio of four(4) or 25% of the rated value at 100%. The efficiency of fuel to steam at 100% to 25% firing rate dropped around 1%. At the time of the seminar, C.B. was introducing burners with a turn down ratio of ten(10) however, the steaming rate was not revealed, probably because no trials were yet conducted. I suspect though that the steaming rate at 10% will have a greater efficiency loss than the 1% ;by how much, I don't know. As mentioned by one of the responders a trial test would need to be conducted.

RE: De-Rating Vs Turn down the boiler to less than 20% MCR

We are not looking at this from the efficiency stand point; reason being, we need this boiler to start the combined cycle operation and shut down after the combined cycle is up and self sustaining. So for every start of the combined cycle, this boiler has to be running for a maximum of 4 hours and shut down after that and that may happen only 100 days of the whole year. Right now we have no choice as per the OEM to run at a minimum of 20% MCR, i.e. @ 50,000PPH where our demand to start the combined cycle is only ~10,000PPH and the remaining 40,000PPH of steam is being vented out through the sky vent.
We are going to talk to one of the company in our area and hoping that they have some experience without jeopardizing the circulation ratios on the water side but if any one have converted the huge boiler like that to low turndown and have any thing to share, please do so.
Thanking you all.

RE: De-Rating Vs Turn down the boiler to less than 20% MCR

From what you're saying that sounds like a significant waste of energy.

So basically in order to be able to re-start a CC gas turbine power plant? someone has decided to use a boiler sized at 25 times the required capacity??


I can't see any boiler being able to do that level of turndown.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: De-Rating Vs Turn down the boiler to less than 20% MCR

We had a host to whom we use to provide steam and the host is down now. Boilers were originally sized according to the load conditions but after the host is gone, they are too big for what we need the steam for.

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!


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