Firetube Vs. Watertube 1

[Combustor1]

We currently have 4 boilers that we are going to replace in one of our paper mills and our consultant has suggested 3 firetube boilers (120,000 lbs/hr total - I am thinking why not one boiler).

My question is - what is more efficient watertube or firetube and what about maintenance which is more costly to maintain/operate. Does anyone have any direct experience with these issues.

Thanks in advance...

 

[Rjeffery]

Combuster,

"I am thinking why not one boiler"? What are you going to do for steam/heat/power if you have to take your only boiler down for maintenance/repairs?

 

[Combustor1]

Rjeffery,

The paper mill goes down every 5 to 6 weeks for a few days and once a year for a week. A boiler is a static machine and I do not believe that we need a spare - however the plant would like one if they could. This is the secondary question - I am more curious if anyone has operating experience in terms of maintenance costs for both types of boilers and efficiency.

Thanks...

 

[TBP]

Firetube boilers are physically large for their steaming capacity. They have a big water content which is good for peak loads - you've got a lot of hot water to flash to steam on a pressure drop, to help meet load spikes. They also have a large tolerance for crappy water treatment, as it's hard to plug them to the point where you have no circulation. They still corrode very nicely if you let things slide, though. They're also limited in capacity and operating pressure, as after a point, the shells get so large in diameter, and thick, it's not economical to make them. I'm not sure that you can FIND 40,000 #/hr firetube boilers. I think the largest I've ever seen are maybe 30,000 #/hr. I think you'll be looking at water tube boilers, in the size range you're talking about. If you're seriously thinking about a single boiler, it'll definately be water tube.

Many times, if you go with one large boiler, control valve, etc. you get into relatively short production runs, and the unit cost and delivery time takes a nasty jump.

While the boiler proper is essentially just a heat exchanger, there are LOTS of things to go wrong with auxiliary equipment like fans, controls, burner equipment, etc. If this was my plant, I'd be thinking a pair of 60's.

 

[linux]

hi combuster i like yourself work within a paper mill we have five boilers 4 water tube and 1 shell boiler as for size the water tube boilers are alot larger than the 50.000lb per hour shell boiler the water tube boiler are alot more reliable and less of a concern as the shell boiler which runs at 380 psi with rear end mods with superheaters luckly these only run for about 2/4 weeks a year now as we have a new 150 tonne per hour chp maybe a small chp would be a better option for you let me no what your electric needs are and i will give you a ruff idea how big a turbine would be to suit your steam requirements


how do you cope with paper breaks do you have a dump condenser or do you dump to air do you have a small steam turbine ?

 

[MJCronin]

Combustor,

TBP gives you good advice,

You havent mentioned your boiler operating pressure....this would help us out an awful lot

Also, what is your miniumum steam demand ? Firetube boilers have excellent turndown

Firetube boilers are commonly avalable to 1000 bhp ( see

http://www.johnstonboiler.com)

Operating pressures go to about 250 psig.....(depends on your selected size).....maximum steam flowrates go to about 34,000 lbs/hr

Firetube boilers are typically cheaper to purchase and quicker to deliver than watertube boilers

Download the DOE Steam Sourcebook for other details about the differences between these boiler types....

http://www.oit.doe.gov/bestpractices/steam/pdfs/steamsourcebook.pdf

let us know what you decide.........

(Where can we find these 40,000 lbs/hr firetube units !!??)


MJC

 

[KeItSiSt]

Burnham has firetube boilers up to 1500HP as standard which is 51750 #/hr.

 

[linux]

do you need super heated steam ?

what fuel do you intend on using?



you can find fire tube (shell) boilers of upto about 80.000 lbs here at

http://www.wellmanrobey.com/here

they also manufacture chp units (combined heat and power) or hrsg if you are american i belive this meens heat recovery steam generator

what are your enviromental requirements eg low nox burners and climate levey change tax ?

 

[Combustor1]

Thanks for all the info!

I have been working with a few contractors, our main contractor is pushing Firetube (Johnston) Claiming higher efficiency. From whay I can gather this is not true. He also has Firetubes slightly less expensive than Watertubes.

Our current demand is 80,000 lbs/hr and running 200# on the header. Our fuels is Nat gas.

Linux - I do not think we are heading for hsrg at this time.

TBP - Spares are nice I agree but we can not have a spare of everything. I am sure the plant would like a spare paper machine - but unfortunately that would not sit well with management! We have a few hundred combustions systems nation wide running almost 24/7 with minimal spares - we seem to do fine.

Thanks again for all you input!

 

[TBP]

How do you figure that a pair of 50% units vs a single 100% unit gives you a "spare" boiler? It's a matter of not having all of your eggs in one basket.

Even if you don't care about having the load spread between 2 boilers, check price & delivery on a single large unit, vs a pair of 50% boilers. I've seen cases where a pair of half size components were a total of 70% of a single large one, and delivery time was literally cut in half.

 

[Combustor1]

Thanks TBP - this is one of the things we are looking into - I just have difficulty believing it would be cheaper.

 

[TBP]

It's not ALWAYS cheaper, but it's always worth looking at. Use something like safety valves as an example. The boiler manufacturer won't make his own safeties, he'll buy them. If he needs a single, large 6" X 8", maybe it'll take 12 - 16 weeks to get it. If you can do the same job with a pair of 4" X 6" valves, they may be available in 4 - 6 weeks.

Even if the installed cost of a pair of 50% units is the same as a single large one (and I'd be surprised if it's not measureably cheaper), I'll bet you can chop one to two months off the time line for this project by going with the smaller boilers.