Package fuel savings

[Dexter26]

Hi Can someone help with the calculations for the savings below. The package boiler output is 121.5 kpph, Heat input is 177.6 Mmbtu's


We are doing some energy reduction projects here in the plant. How much gas savings would there be for the following steam savings?


Steam sent to Heat Exchanger Annually. Heat lost to inefficiency of Heat exchanger Additional losses - Excess hot water production (approx 15% of total)
25,920 Klb 5,184 Klb 3,888 Klb

 

[TBP]

What is the fuel input to the boiler to make 1,000 lbs of steam? You can figure that off boiler efficiency (you've posted the annual numbers). What is your cost of a million BTU of fuel? Once you have that, then you can calculate the savings on each 1,000 lbs of steam not required by your process.

Before I spent any amount of money on other projects, I'd go through the steam traps to make sure that they're functioning properly, that they are the right size/type for the application, and are installed correctly. Fix any steam & condensate leaks. Make sure you're getting all the condensate back that you reasonably can - as in are your condensate pumps all working, etc.

 

[Dexter26]

Do you have a formula for what it takes to generate 1000 lbs of steam.

 

[TBP]

The boiler efficiency cannot count the heat value of the feedwater, so that must be subtracted from the heat output. What is the BTU/lb of steam leaving the boiler? What's the temperature of the feedwater entering the boiler? Get the heat values for each off the steam tables to see what the boiler is adding to each lb of water to generate a lb of steam. Apply that value to the annual steam produced numbers you provided. Then divide the BTUs out by the BTUs in - again from the number you provided. Multiply by 100, and you have the the boiler efficiency.

 

[Dexter26]

Output pressure 600 psi
Output Temp 725 deg F (1364.9 btu/lb)
FW Temp 228 deg F (405.7 btu)

(1364.9-405.7)*121.5 kpph / 177.6 Mmbtu's = .65*100 (65%)

So how would I figure how much fuel usage to produce 1000lbs of steam.

 

[TBP]

Not sure where you're getting your numbers. My steam tables say that 600 PSIG saturated steam has 1203 BTU/lb. 228*F feedwater will have about 196 BTU/lb.

 

[Dexter26]

I used the SH steam table for the steam.

 

[TBP]

You didn't say anything about a superheater. Is there an economizer as well?

 

[Dexter26]

There is 230 deg F in 323 deg out.

 

[TBP]

What about an air preheater - do you have one of those? ALL of these things matter.

 

[FacEngrPE]

ASME-PTC4.1 Steam-Generating Units is the standard method of determining boiler efficiency. It treats the boiler as a control volume with inputs and outputs. If you want to use this method get a copy of the standard, or search out one of the interpretations available on line.
Examples:

http://www.industrialboiler.ltd/boiler-efficiency-calculation-excel-sheet.html

https://beeindia.gov.in/sites/default/files/4Ch1.pdf

(this one is attached).

You really do need to know all of the details TPB is asking for.

Be aware boiler efficiency and combustion efficiency which are both important, are not the same thing.

 

[Dexter26]

If I know the boiler efficiency how would I find out how much fuel the boiler needs to produce 1000 lbs steam.

 

[MJCronin]

"I know nothing about boilers, efficiency or thermodynamics ... I am 20 years old and his is my first job indoors .... Please do my work for me"

MJCronin
Sr. Process Engineer

 

[FacEngrPE]

I put all of the calculations into a spreadsheet to do PTC4 calculations. Took several weeks part time. Finding the steam tables as an excel macro helped. thread770-56868. I don't have a copy I could share. It just duplicated the PTC 4 table and all the calculations.

However you need to figure out how to get all of the needed data. The instructions in PTC4 are straightforward, but require some equipment you might not have yet.

One of the thing engineers learn is when to say I do not know enough to successfully complete a task. Then we either spend the time to learn what is necessary, or find a way to give the task to someone that already has the necessary skill. If you know nothing about thermodynamics you likely will not ask enough correct answers to get a good result. It's time to find a mentor.

 

[Dexter26]

Thanks for all your help, I was able to work through it!