If I have a LPS entering a coil, but I can not return by gravity. I have to pump the condensate pump back to the bfu, how do I calculate gpm.
Do I just find lbs/hr and then calculate using 1lb-water/hr = 8.34 gallons/lb-water x 60min/hr x SG
which gives me 1lb-water/hr = 500 gpm
or do I calculate gpm by:
btu/h = gpm x 500 x Tdiff
with btu/h = 960 x lbs/hr
You’re multiplying instead of dividing.
GPM Cond = (#/hr steam)/(8.35 #/gal)/(60min/hr)
So 1#/hr equals only 0.002 GPM
Since you have LP steam, flash loss in the condensate pump won’t be enough to affect the GPM selection. If you know your steam load, you can calculate GPM.
Additionally, remember is the warm-up load. I would suggest a 2:1 safety factor, although I have seen it as high as 2.5:1. It all depends on how fast you are warming up. For each 1 Lb/Hr of rated load, figure 2 or 2.5 lb/hr required for warm-up. Your condensate pump will have to handle this additional load and must be sized accordingly. So your max pump load will then be 0.004 or 0.005 GMP for each lb/hr of running steam load.
Above is a snippet.