Designing a Fire Tube Boiler

[chicopee]

Someone is seeking a design of a fire tube boiler with a capcity of 50lbs/hr at 100psig. Dimensions are not to exceed 18"X18"X24". I dont think that it is possible to design such boiler. Any opinion from anybody?

 

[Montemayor]

I have designed and used this type of low pressure steam generator before. I patterned the design much like the conventional fired gas heater used in the oil patch - except that I allowed for the latent heat of evaporation and the disengagement space required in the shell side for steam generation.

It is notoriously very inefficient - I would expect a flue exhaust temperature of around 500 to 700 ^oF. But it works. Mine produced upwards of 1,000 pph of steam. I kinda doubt you can find a burner for 50 pph of steam product. It would approach the dimensions of a fine pencil.

But it can be done - albeit with an inhouse burner design yet to be developed.

 

[chicopee]

Montemayor, I thought that I had written it. This individual expects 90% and over efficiency and I think He is refering to the combined efficiency of combustion and heat transfer. I did not take his bid to design it nor do I think anybody else will do either.

 

[davefitz]

The burner capacity is similar to that of a home heating unit. I had seen some advertisements for a home hydronic heating hot water unit of the physical size and ratings indicated in the original question about 20 yrs ago- they used pulse ignition to reduce the NOx. I cannot remember teh name of the mfr.

To modify a hot water design to that of a boiler would require technical changes, espescially to meed the code rules- there is a big difference in code rules between hot water and steam boiler. The practical difference can be minimized if it is designed as a "once thru" unit without a steam drum pressure vessel, but the need for a smart and reliable control system would be paramount and might exceed the cost of everything else in the unit. The use of small dia tubes imlied pure feedwater quality, another issue. If you can ensure that no tube will exhuast fluid thaqt is more than 93% SBW, then the salty water issue can be dealt with eaily by simplyy using an outlet wteam/waetr seperator and a 7% blowdown.