Steam

[hakbrk]

OK asll you stem eng out there here is a question. Somebody asked me a question about a boiler the other day. A contract required a boiler rating of at least 4.3 MM BTU. They told me their boiler had the following data 1800 kg steam / hr, Working pressure 10 bar, temp 187 deg C. So they then proceeded to calculate that with a feedwater temp of 30 deg C their boiler would have a rating of 4.53 BTU / hr using cap/hr x (Enthalpy of steam at 11 bar absolute - Enthalpy of Water at 30 deg C). The boiler manufacturer stated the rating was 3.85 MM BTU. I then did some reserch and figured out the 1800 kg steam / hr and 3.85 MM BTU are both equal to 115 boiler HP. My problem is trying to explain why the boiler wouldn't be rated for the enthalpy of the steam minus the enthalpy of the feed water. Can somebody please help me get this staight. Thank you.

 

[hrsgguru]

Well, I think that your right to be a little confused here. For those conditions, the boiler should be rated for at least 4.53 MMBtu/hr heat input (that's a net figure). The gross heat input should be higher due to heat loss and other inefficiencies. So it should be rated at 135 HP or higher.

Now if the vendor is stating that their equipment is only rated for 3.85 MMBtu/hr, I would have to guess that whoever gave you the original data (1800 kg/hr @ 10 Bar with 30°C feedwater) is overstating the conditions for which this boiler was designed. For those pressure and temperature conditions, the boiler should only produce about 1530 kg/hr of steam, based on the manufacturer's rating.

Oh, and I don't agree that 1800 kg/hr = 115 HP - not at least at the stated conditions. 3.85 MMBtu/hr does equal 115 HP, though.

 

[hakbrk]

Thanks for the reply it was a mixture of misunderstanding and me being rusty on steam calculations. The Boiler is rated at 3.85 MM BTU or 1800 kg steam/hr based on the 100 deg C feed in steam out rating so you are correct the boiler would only be rated at 1350 kg steam/hour with 30 C feedwater. Thanks again.