Sizing economiser safety valves

[athomas236]

I am sizing economiser safety valves using ASME Section I, clause PG-67.2.6 and seem to get different capacities if I use the US customary unit and the metric method.

For example, the maximum heat absorption of the economiser is 15.8MW which I convert to 53.9 million BTU/h. (Conversion factor is W * 3.412 = BTU/h)

Using the US unit method, the required capacity is BTU/h divided by 1000 which is 53900lh/h which I convert to 24450kg/h. (Conversion factor is lbs * 0.45359 = kg)

Using the metric method, the required capacity is W divided by 1.6, which is 9.9 million kg/h which converts to 21.8 million lb/h. (Conversion factor is kg * 2.2046 = lb)

Any advise/comments would be welcome.

athomas236

 

[JimCasey]

15.8 mw = 5.395983 e 13 BTU/hr
Using your 1000BTU/LB conversion which would be close >IF BOILING OCCURS IN THE ECONOMISER< , that gives you 5.396e10 Lb/H steam flow.= 2.4476 e 10 kg/h

 

[athomas236]

Jim,

Could you check your conversion from MW to BTU/h I get 5.39E7 not E13.

Also the conversion you mention is not mine but from the ASME code.

athomas236

 

[JimCasey]

I did my conversion using "convert.exe" which is freeware gleaned from the web.
MARKS' HANDBOOK shows 1 btu/hr=0.2928W
so 1 W=(1 BTU/hr /.2928 )=3.412 BTU/Hr
15.8MW=5.39 x 10e7 BTU/Hr.
So I apologize and agree with you there.

I still don't think you are boiling in the economiser, so the 1000 btu/lb (which is the vaporization energy of water), would not apply unless you are. If you are calling an economiser what I have seen others call a Heat Recovery Steam Generator (HRSG), then boiling would definitely occur. I am accustomed to thinking of an economiser as a heat exchanger that runs feedwater through the exhaust gas stack of a boiler.