Purity Recommendation

ABC RNG Purity Recommendation
Renewable natural gas is fully interchangeable with natural gas and satisfies the natural gas quality parameters that have been in place across the US for decades. Recently several gas utilities have either implemented new quality tariffs for RNG or changed previous RNG gas quality requirements to be far more stringent than for conventional natural gas sources. The ABC has surveyed the many dozens of US facilities adding RNG to natural gas pipelines, in some cases for more than twenty years, along with current natural gas quality parameters, and provided the following RNG purity recommendation that aligns both with typical natural gas quality requirements and the RNG produced from a number of upgrading processes.

Pipeline

The American Biogas Council (ABC) has identified a significant barrier to the growth of RNG generation: the lack of a consistent RNG purity specification. For RNG which is produced for use in CNG vehicles, the ABC is contacting CNG engine suppliers to obtain a recommendation. For RNG to natural gas pipeline facilities, in general the ABC advocates the use of the same specifications as conventional natural gas. Since these vary considerably within the continental US, the ABC through its RNG Committee and members has developed the gas purity specifications below for RNG projects injecting into gas distribution systems (for a PDF click here):

Physical Property

Units

Lower Limit

Upper Limit

Heating Value

BTU/ft3

960

1100

Carbon Dioxide

mol %

2

Oxygen

mol %

0.4

Total Inerts

mol %

5

Hydrogen Sulfide

gr./100 ft3

1/4

Total Sulfur

gr./100 ft3

1

Water

lbs/mmSft3

7

Siloxanes

ppm(v)

1

Hydrocarbon Dew Point

Fahrenheit

-40

Temperature

Fahrenheit

50

120

Dust, Particulate

commercially free*

Biologicals

commercially free*

Heavy Metals

commercially free*

*Commercially free is defined as equal or less than the levels present in conventional natural gas

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   CNG Vehicles

Since CNG specifications also vary considerably within the continental US, the ABC has developed the following gas purity specifications for RNG to CNG vehicle projects where the gas does not have to enter a conventional natural gas pipeline to be used in vehicles:

Physical Property

Units

Lower Limit

Upper Limit

Heating Value

BTU/ft3

940

1100

Carbon Dioxide + Nitrogen

mol %

4

Oxygen

mol %

1

Hydrogen

ppm(v)

300

Total Sulfur

wt%

0.001

Hydrogen Sulfide

ppm(v)

6

Siloxanes

ppm(v)

3

Liquids

commercially free*

Dust, Particulate

commercially free*

Chlorine Additives

commercially free*

Heavy Metals

commercially free*

*Commercially free is defined as equal or less than the levels present in conventional natural gas

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