Renewable Natural Gas (RNG) offers a significant energy and environmental opportunity and, unlike geologic natural gas produced from oil and gas wells, RNG is produced in many states across the nation, not just limited to the states with favorable geology.
RNG is sourced primarily from gases emitted from wastewater recovery, organic material, landfills (LFG) and agricultural sources (“biogas”), the latter most commonly from animal wastes such as swine and dairy farms. With LFG and agricultural sources, the decay of organic material generates methane emissions and the recovery of this energy source not only reduces raw methane emissions but it also displaces the need for fossil fuel production, extending the life of finite geologic gas resources. As a result, landfill gas and biogas have lower carbon footprints than conventional fossil fuels.
The negative carbon intensity of agricultural biogas in particular can produce real rewards for operators. Under California’s Low Carbon Fuel Standard (LCFS) program, monetary premiums can be generated with lower carbon intensity fuel sources as an incentive to develop and supply these fuels. With average credit prices of approximately $120 in 2002, a biogas producer of bio-CNG with a carbon intensity score of -200 could realize a premium of $36.65 per MMBtu vs. $1.20 per MMBtu for an ethanol-blend with a carbon intensity of +80. Biogas has effectively displaced the use of fossil-based CNG in the state, and diary-produced biogas now represents over 40% of California’s biogas production compared to 3% in 2019. These incentives are one of the reasons that over 50% of transport RNG is sold in the California market.
Landfill gas (LFG) and biogas can be used for heating and electricity generation in addition to transport fuels. To provide an energy equivalent to conventional geologic natural gas production, however, the raw LFG or biogas must be purified of contaminants prior to sale or transfer into a local gathering or interstate pipeline. In the purification process, LFG or biogas is upgraded to remove moisture, carbon dioxide, oxygen, and other contaminants to create a high-quality methane that meets pipeline specifications. This upgraded biogas product is termed “biomethane”, otherwise known as RNG.
Several common contaminants such as carbon dioxide, hydrogen sulfide, oxygen, and siloxanes must be removed from LFG and biogas to upgrade it to RNG. In a report for the Northeast Gas Association, the Gas Technology Institute recommended specifications for pipeline-quality RNG as shown below.
Recommended Pipeline Specifications
| Constituent | Units | Recommended Limits |
| Heating Value | Btu/ft3 | 970 – 1110 |
| Carbon Dioxide | % | 2 |
| Oxygen | % | 0.1 to 0.4 |
| Nitrogen | % | 2 |
| Hydrogen Sulfide | Gr./100 scf | 0.25 |
| Total Sulfur | Gr./100 scf | 1 |
| Water | Lbs/MMSCF | <7 |
| Siloxanes (LFG) | mg per m3 | 0.5 |
Oxygen in particular is a serious issue for pipeline operators and gas systems downstream because it can result in severe corrosion in piping system components and downstream equipment, causing potentially serious pipeline leaks, damage to assets, and safety hazards.
Nearly all major pipelines in the U.S. have specifications limiting O2 content in purchased gas. The term “deoxo” is RNG industry shorthand for removing oxygen from the gas stream.
Approximately three-quarters of 39 major U.S. pipelines maintain oxygen limits of less than 2,000 ppm (0.2%) while one-quarter require oxygen levels below 1,000 ppm (0.1%). Some areas maintain an oxygen limit of 5 ppm or less. Direct treating of the gas to remove oxygen is typically required to meet the lower pipeline limits.
Oxygen Removal Methods
There are a variety of methods for treating RNG source gas for contaminants and the choice of alternative depends on the type of organic material and the production system design. Oxygen is a common problem with low pressure LFG and biogas production methods since the limited pressure differential naturally allows for oxygen ingress into the collection system and the fluid stream, often making oxygen removal a priority.
The use of adsorbents and membranes are often used to remove carbon dioxide, water, and hydrogen sulfide in the purification process. While these technologies have the capability to adsorb or remove some of the oxygen present in the gas stream, purification to the lower limits often requires direct treatment and catalytic removal of oxygen is the predominant technology.
Catalytic oxygen removal equipment employs a proprietary catalyst to treat the gas under controlled conditions to remove the elemental oxygen.
The advantages of catalytic removal include:
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- No harmful byproducts, only water vapor and trace amounts of carbon dioxide are emitted
- No hazardous disposal of treatment media
- No moving parts for enhanced production system reliability
The EcoVapor Advantage
EcoVapor is a primary supplier of oxygen removal technology to both the oil and gas production and RNG industries. We are actively involved in RNG projects across the country, from Texas to Maine to Washington state. Our proven catalytic technology used successfully for over a decade by oil and gas producers is now working for RNG developers.
Our modular biogas purification technology and flexible approach to deoxo for RNG makes EcoVapor the ideal choice for both small and medium-sized projects and makes it easy to scale up as your operations grow.
About EcoVapor
EcoVapor, a DNOW company, provides gas treating solutions to both geologic and biogas production problems. Our fleet of proprietary ZerO2 oxygen removal (deoxo) units has grown to a fleet of nearly 250 since 2010, operating reliably for leading producers in all major U.S. basins. ZerO2 technology helps Oil & Gas and biogas producers convert waste gas streams into revenue by treating gas to meet pipeline specifications so it can be sold instead of vented or flared, generating incremental value while reducing emissions and improving environmental performance.
EcoVapor is headquartered in Denver, Colorado and has field locations in Greeley, Colorado and Midland, Texas.
Contact
EcoVapor Recovery Systems (a DNOW Company)
Email: ecovapor.info@dnow.com
Phone: 844-NOFLARE (844-663-5273)
Sales: Joe Hedges (281-615-2072)
