I am interested if anyone has any experience with using nitrogen to force cool a turbine so it can be overhauled after a shutdown.

There is a company BJ Process and Piping Services that sya they can force cool a turbine in as little as 24 hours.

Thanks.

You don't mention the size of the turbine. We have a number of turbines throughout the refinery but, most would be considered donkey turbines. (Low pressure, lumpy steam)How important is it to start your repairs so soon after shutdown? Is there a time constraint? Is this turbine large enough to have gland sealing steam?
Will rapid cooling cause a rotor bow? If possible, could any insulating blankets be removed from the casing to facilitate cooling? If you’re just doing shaft bearings, the rotor will still be warm after 24 hours but I haven’t had any problems working on them. If you’re pulling the rotor the casing bolting could be a little tricky. Please leave a posting letting everybody know how you made out.

750 Mw units. We remove the insulation to help and keep the units on turning gear.

This is just something my management has heard about and I have some concerns about inducing stress in the turbine internals.

Just wondering if anyone has tried this or has any experience.

Ron,

While I have used Nitrogen cooling for reactors, I heve never used forced cooling for Rotating Machinery. You may wish to check independently some of the following points:

1. How cold is the Nitrogen, allowing for any J-T effects when entering the machine? If below -20C, some stressed internal parts may be exposed to brittle fracture.
2. Why Nitrogen, liquid air may be a cheaper medium.
3. Skip's point about possible cryogenic bending need review.
4. I assume the economic benefits of access within 24 hours is high. If it is on the critical path, I think you are right in seeking the views of others with such experience.

V.Narayan.

Yep, we do it quite often on our large compressor drive turbines (up to 60,000 HP) Works great, and definately shortens the maintenance outage.

The 60,000 HP would be about 45 Mw, thus roughly 1/16 the power of Ron's unit.
Depending upon the specifics of the cycles, the physical dimensions could be significantly larger. Larger dimension means there's less surface area for cooling per volume to be cooled, so it might be significantly slower. Also, thicker sections would seem to require more attention to detail to keep thermal stresses down to acceptable.
The vendors no doubt are very good at what they do. But if they are taking a first big step in unit size, it would seem prudent to ask the kind of questions Ron has in mind.

Steam Forced Cooling is I think standard practice on 350MW+ turbine generators here (Australia). I was involved in this 30 years ago on sets of HP-IP, 2 x LP casings.

The inlet main steam and reheat temperatures were set lower in steps over a few hours as unit load was reduced, taking care to keep steam temnperatures margins in superheater and reheater outlets above saturation (as required in operating instructions). (I think it was 25 C degrees). At no stage were operating limits exceeded.

A feasibility study I was involved in while working in the UK in 1971-73 showed that the technique could be used on all of the 500MW boiler-turbine design combinations at that time. I do not know if it was done, or if it was, is still done. The incentive then was to reduce time on turning gear as one machine had a shaft crack, with its fatigue growth attributed to many hours on turning gear.

In Australia, this method reduced the time to standstill by a day or more. Forced Air cooling was then tried, but was not successful on the HP-IP machines. It had been very good on 200MW non-reheat sets at another plant from mid-1960s.

As Ray mention forced air cooling was tried in reheat sets but not succesful.
If any one has succesful in air forced cooldown,can share the experience.