Technical Information and References
Frequently Asked Questions
Fuel Heat Content: How many Btu's are there in a therm?
Fuel Heating Value Conversion: How do I convert from
Lower Heating Value (LHV) to Higher Heating Value (HHV) based emission factors?
Sulfur Specs - Natural Gas: What are the sulfur
specifications for PUC Quality natural gas?
Sulfur Specs - Propane: What are the sulfur
specifcations for propane?
Boiler Rating Conversion: How do I convert a boiler
rating from units of boiler horsepower (bhp) to heat input (lb/MMBtu)?
Q: How many Btus are there in a therm?
A: There are 100,000 British Thermal Units ("Btus") per therm. A therm is a
unit of gross heating value.
Q: How do I convert from Lower Heating Value (LHV) to Higher Heating Value
(HHV) based emission factors?
A: For gaseous fuels multiply the LHV value by 1.10 and for liquid fuels
multiply the LHV value by 1.06.
Q: What are the sulfur specifications for PUC Quality natural gas?
A: The Public Utilities Commission of the State of California has issued
General Order 58-A titled "Standards For Gas Service In The State of California"
(last revised April 12, 1989). Title 7 (Purity of Gas) of the General Order
specifies hydrogen sulfide and total sulfur standards for any gas supplied by a
utility. Section (a) limits hydrogen sulfide to 0.25 grain per 100 standard
cubic feet. Section (b) limits total sulfur to 5 grains per 100 standard cubic
feet (which is equivalent to 85 ppmv as S or 80 ppmv as H2S.
Q: What are the sulfur specifcations for propane?
A: The Gas Processors Association ("GPA") provides product specifications for
liquefied petroleum gases. These specifications may be found in Figure 2-1 (GPA
Liquefied Petroleum Gas Speficications - GPA Standard 2140-92) of the
Engineering Data Book (10th Edition, 1994) published by the Gas Processors
Suppliers Association. Total sulfur standards are provided in units of ppmw. For
commercial propane, the standard is 185 ppmw as S (254 ppmv as S, 239 ppmv as
H2S).
Q: How do I convert a boiler rating from units of boiler horsepower (bhp)
to heat input (lb/MMBtu)?
A: This conversion requires two steps. First the boiler horsepower value is
converted to an energy basis by muliplying by 33,446 Btu/hr per Bhp. Since Bhp
ratings are based on the amount on useful work a boiler performs, the efficiency
losses in converting the heat input to this useful work must be accounted for.
In general, a boiler is about 80 percent efficient in converting the fuel's
energy into useful work. Thus, the "Btu/hr" value must be corrected to account
for the 20 percent loss. Example: 500 Bhp = 20.904 MMBtu/hr (500 bhp * 33,446
Btu/hr/Bhp * 1/0.80).
For more information or assistance, call the Engineering Division at (805)
961-8800, or e-mail us at
engr@sbcapcd.org.
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