cost of producing 600 psi steam vs 200 psi steam in boiler 3

[n7s3g9]

A boiler operating 24 Hr now produces 600 psi steam. If I need to use the same boiler for 200 psi steam only, how much minimum cost ( a factor like percent)in fuel cost, I can save?
Layman's Term please.

 

[quark]

No thumb rule for it and it all depends upon the boiler capacity, drum and pipe volume and load. In other words, if you have a boiler with a capacity of 1 ton/hr and you are constantly using 1 ton/hr, right from the start up, then your boiler can't develop any pressure and thus it is a wrong selection.

Secondly, you are not supposed to run your boiler at a reduced pressure than it is designed for. There will be steam quality problems and also energy inefficiency(I am not speaking about energy consumption).

Regards,

 

[zdas04]

The cost difference in producing 600 psi steam vs. 200 psi steam is all in the up front capital. Your fuel usage is a function of the demand, not the supply pressure. If the load requires about 200 psi dP, then there is a roughly fixed energy requirement to recover that dP, whether you are going from 0 to 200 or 400 to 600 psig.

David

 

[TBP]

You might get some marginal savings because you might be able to run lower flue gas temps, depending upon whether you've got an economizer and/or air heater. My experience with this kind of exercise is that it often looks FAR better than it really is, because of steam metering that is not pressure compensated. If it doesn't get recalibrated to the new, lower pressure, the meter reads high. There will also likely be steam quality issues at the lower pressure. Spirax Sarco has (or had) a video shot from inside the steam space of an operating boiler. You can actually watch the "fog" form inside the boiler when the pressure gets reduced from it's design operating pressure. You can also run into problems with system components (piping, control valves, traps, etc.) being sized for the current pressure, and not being big enough for the same #/hr at the lower pressure.

I can't think of too many plants that have tried this, that have actually had the headaches outweight the benefits. The ones that were convinced that they had acheived the greatest efficiency increases were typically being fooled by their steam meters.

 

[GeneratorGrrl]

You probably won't see enough in savings to make it worthwhile, because your boiler's efficiency will be drastically reduced. Not only is steam quality compromised but furnace efficiency is also compromised, and you may not get the full value of your fuel. If you have a requirement for 200 psi steam, it would be more efficient to keep your boiler running at its design pressure, and install pressure reducing stations where the lower pressure steam is needed.
I've seen that Spirax Sarco video and it is indeed dramatic. If energy efficiency and achieving maximum fuel value are your needs, then I would suggest looking up your local Spirax Sarco rep and having them in to do an energy audit on your plant. This is their bread'n'butter.

"Eat well, exercise regularly, die anyways."

 

[MJCronin]

n7f8g9,

Besides the metering/measurement issues noted above, there are also some design issues/problems in the distribution system.

If we assume that the same massflow of steam is being delivered at a much lower pressure, the steam velocity will increase dramatically. This will cause erosion in piping, elbows, valves etc.

On the plus side, any existing steam leaks will npt leak as much condensate.

MJC

 

[n7s3g9]

The boiler is generating superheated steam at 600 psig and 700 Deg F. Generation at boiler outlet is metered("T")and one metered customer("A") using this superheated steam less than half of total steam produced at boiler.There is no recycling of condensate from this customer. Steam is throttled to step down and another meter("B") measuring the use for Flare at 200 psig steam. Balance of the steam is charged to a customer "C" with some adjustment for recycled condensate. Flare "B" is shared 50% each by "A" and "C". The customer "C" needs steam for steam tracing, steam tracking etc ( probably 50 psig ). What would be "C"'s fair share of fuel cost for this steam? Is the total system heat loss dumped to "C" ? Any reference for boiler thermal balnces working spreadsheet?

 

[n7s3g9]

The boiler is generating superheated steam at 600 psig and 700 Deg F. Generation at boiler outlet is metered("T")and one metered customer("A") using this superheated steam less than half of total steam produced at boiler.There is no recycling of condensate from this customer. Steam is throttled to step down and another meter("B") measuring the use for Flare at 200 psig steam. Balance of the steam is charged to a customer "C" with some adjustment for recycled condensate. Flare "B" is shared 50% each by "A" and "C". The customer "C" needs steam for steam tracing, steam tracking etc ( probably 50 psig ). What would be "C"'s fair share of fuel cost for this steam? Is the total system heat loss dumped to "C" ? Any reference for boiler thermal balnces working spreadsheet?

 

[TBP]

I just noticed there's a typo in my post. The last paragraph SHOULD read "I can't think of too many plants that have tried this, and had the benefits outweight the headaches." Sorry.