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Posted by steamplants on March 03, 2004 at 20:08:01:
In Reply to: Re: Fire tube Boiler Applications posted by Boiler Guy on February 28, 2004 at 06:06:22:
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: : Guys,
: : Johnston has been building 2500HP FT boilers for quite some time both single and multi burners. There is noting unsafe or bad about these boilers. Typically the major issue is shipping since these units are so large. There are many 1000HP+ units running today that have been in service for more than 5 years without a single problem. Most of which are 200 - 300 MWAP If any one has ideas that these boilers are dangerous contact the NBIC and search for any damage reports. As for other manufacturers building 1000+HP FT Boilers there are no others than Johnston. The others only try to build a large FT Boiler.
: We can all continue to go around and around for weeks. I'll end my contribution to this thread by saying in my humble opinion firetube boilers of this size are too large and are not as good a selection as a watertube boiler for a number of reasons as I have already put forward. The only advantage that the firetube proponets have countered with is a lower price than a watertube. While cost is certainly important the price difference between the two configurations is not so significant as to make a valid enough argument to convince me otherwise.
This discussion seems to pop up here on an annual basis!
First off, any vessel designed to retain pressure that is subject to heat, stress, corrosion, erosion, etc. is inherently dangerous and only through proper design, construction, operation and maintenance is that danger minimized.
Assuming all those parameters are equal - saying a large firetube is less safe than a watertube is like saying you will be less dead from standing in front of a rupturing mud drum than you will from standing in front of a rupturing fire tube shell. Neither event is likely to have a good outcome, yet neither boiler is any more likely or predisposed to have this type of occurrence than the other.
Large firetubes are not new, and saying they have no "track record" is groundless.
I installed (2) 1,500 HP units for a customer over (10) years ago and they are doing fine and I know these aren’t the only (2) out there.
I do agree that a complete engineering review should be done for any proposed installation and that only after careful consideration of all operating requirements, should the boiler be selected that best meets those requirements at the lowest life cycle costs.
Generally speaking - you would select a watertube over a large firetube if you need a higher capacity, higher operating pressure, superheated steam, faster startup or better response to a widely fluctuating load.
If none of those are issues, and If you have the space (a 1,500 HP firetube will require about twice the available building length, considering tube pull, than the same size water tube) The firetube will have a lower purchase price, be more efficient, will have a lower maintenance costs and be more forgiving to upsets in water chemistry.
Coming off the shop floor, relative safety will be the same for either unit, it's up to the owners/operators/inspectors to keep them that way.