Crane boom directly over a turbine exhaust stack

[CMcF]

I need advice on selecting a consultant to advise me on how hot a Crane boom directly over a turbine exhaust stack will get.
On oil rigs we have used cranes very close to exhaust stacks but not actually in the plume.
My concern is that heat transfer chages from radiation to cunduction.

Thanks in advance

CMcF

 

[gerhardl]

The question of who can help you is probably dependent on how complicated the questions and evaluations are formed. Perhaps an aircraft or spacecraft engineer could contribute, or an engineer for advanced military equipment.

In my opinion you could first try to set down possible and allowable limits for the critical input data, to simplify a worst case scenario, such as the obvious:

distance from flume source
temperature of flume at exposure point
temperature of material at exhaust outlet and distance
extension of flume and temperature 3- dimensional
surrounding temperature
influence of wind
timeframe for exposure and any variation over time for input data.


All data with max and min values, as you (or responsible safety engineer or project management/authorities) will have to agree on the 'worst case scenario'. Theoretically varying from full exposure, full flume, directly over the flume for 'years (?)' to minimum exposure: max distance away all the time at none or minimum flume.

Fire at exhaust stacks to be considered separatly together with fire conditions evaluation of total plant.

 

[CMcF]

Thanks gerhardl. That is a good list of criteria. I was also wondering about what effect the exhaust gas itself would have given that it will be mostly steam.
CMcF

 

[renderu]

I think you want a firm that can do a Computational Fluid Dynamics analysis. My thesis involved analysing a hot object in an airflow and this seems like a problem that I could set up using the tools I had.

 

[gerhardl]

For one reason or the other exhaust gas was in my mind.

Steam will change the problem a bit, and might not be that great problem.

Is this land-based or offshore?

Any outlet of steam with a large energy content (temperature of steam is pressure related- see steam tables), is wasted energy. Before starting calculations, check if energy recovery from the steam could give a positive contribution to the project, and this way keep the outlet temperature and amount down. (Steam consultant).

Neither should a simple deflection of steam outlet cost that much (stainless steel). In addition the white cloud you often see at steam outlet is actually a 'real cloud': moustly water drops, as steam will condense quite fast in a normal atmosphere.

The steam will also condense at colder metal constructions and could be a problem if the steam has a content of sulphur or other contents giving acids. On the other hand environment requirements require clean outlets.

 

[CMcF]

gerhardl,

The requirement is just for a one off job to install bigger lifeboats (average oil worker is a lot fatter now than in 1970's).
So I don't think energy recovery will be considered, but your idea for a deflector is worth looking at.

Thanks again.

CMcF

 

[chicopee]

I would first address this question to the crane operators.

 

[IRstuff]

> There is no conduction in the classical sense, unless your crane is touching the stack
> There will be convection, which is a combination of conduction to air, coupled with mass transport of the air.
> You could certainly worst-case it by making some gross assumptions about the plume and its dispersion.

TTFN
faq731-376

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[CMcF]

Thanks IRStuff,
In my head I was thinking that the boom was "touching" the plume so I said conduction, but of course this is convection.

CMcF

 

[StoneCold]

It seems like you could just lengthen the stack and have the whole problem solved without any fancy analysis and then coating for the crane, etc.

Regards
StoneCold

 

[CMcF]

???? But then the boom would hit the stack???

 

[StoneCold]

Not how I imagined the problem. It works fine. But since you are the one who presumably seen the real setup I will default to your guidance

Regards
StoneCold

 

[IRstuff]

Even with some simplifying assumptions, the analysis would be non-trivial. Nonetheless, one could postulate that the plume does not spread nor mix until after impinging on the crane (A definite worst-case). Use some plausible convection coefficient to transfer the heat to the crane and go on from there.

TTFN
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[renderu]

I like IRstuff's worse case scenerio. I'll propose that to simplify it further, you could take the heat generated from the plume (assuming you know it), and pretend it is being generated from within the crane. Then assume natural convection to the atmosphere. You can then figure out the crane temperature.

 

[MikeHalloran]

What kind of turbine? Steam or gas?

I have built watercooled exhaust stacks for helicopter-size gas turbines used in speedboats.

With 100 gpm of water forced through the jacket and then injected into the gas stream, you could stick your hand in the exhaust stream briefly and not get burned. Without the water injection, I wouldn't dare.

Absent extra injected water, here's still a bit more (combustion product) water coming out than fuel going in, but there's not enough to cool the gas stream much, and it's not cool enough to become visible steam; the gas is damn not, and the gas mass flow is impressive; maybe ten times as high as a Diesel that would use the same size exhaust pipe. Peak gas velocity in a Diesel stack would not exceed 100 mph. Peak velocity in a gas turbine stack probably wouldn't go below 100 mph. Heat transfer from the plume to anything in it would fall into the realm of 'forced convection', and the boundary layer would be pretty thin.

Gas turbines also become very unhappy with long stacks or tight elbows, and manifest their displeasure in expensive ways, most leading to self destruction.

Exhaust plume temperature profiles are commonly found in helicopter pilots' handbooks. ISTR the kill zone extends beyond the rotors, but you should check.

I have no experience with steam turbines.


Mike Halloran
Pembroke Pines, FL, USA

 

[CMcF]

Thank you all.
Your posts have given me considerable food for thought.
I have a couple of companies that will be do the job for me, your responses will help me sense check their results.

Many Thanks

CMcF