Fired Heater PSV sizing

[pea13]

Hey there everyone,

I have a fired heater 150# steam generator. There is a PSV at the outlet of steam. How to calculate required capacity?? I used ASME 1 absorption rate / 1000 to find the required capacity. However, the data sheet for the PSV shows a much higher flowrate. I am a little weary with the ASME 1 as it says the formula finds "minimum" required capacity, so I don't think it is what should be used to size the PSV. Anyone knows how to find the required capacity for a fired heater PSV??

Thanks!

 

[ggordil]

The formula from ASME Sec I, assumes a latent heat of 1000 BTU/LB. At low pressures, around atmospheric, this is a reasonable assumption, however, the heat vaporization drops as the pressure goes up. If you want to calculate a more accurate rate find the heat of vaporization at the relief pressure, 1.06 times the MAWP. Then divide the heat produced by the generator by the latent heat of water. This is a more accurate method of calculating the relief rate and it may match what is on the data sheet.

 

[don1980]

For ASME Sec I equipment there are no calculations. Safety valves are sized prescriptively, based on the nameplate steam generation capacity of the boiler. It's simple, but you have to follow the rules exactly as stated. If you don't have a copy of Sec I you'll need one.