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 specifications for propane?

Boiler Rating Conversion: How do I convert a boiler rating from units of boiler horsepower (bhp) to heat input (lb/MMBtu)?


Fuel Heat Content:

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.


Fuel Heating Value Conversion

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.


Sulfur Specs – Natural Gas

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.


Sulfur Specs – Propane

Q: What are the sulfur specifications 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).


Boiler Rating Conversion

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 [email protected].