Gas Technology: Renewable natural gas
We tend not to think of the origins of our natural gas resource. We instead consider issues of price, availability, and its usefulness in commerce, industry and in our homes. Today’s conventional natural gas originated with organic materials — mostly plants — that were buried in deep geological strata and were subjected to biological and thermal decomposition. This so-called “fossil fuel” is a cornerstone of our energy supply.
Looking at Renewable Sources
In recent years, we are seeing the potential for supplementing fossil fuel natural gas with gas produced in digesters by anaerobic decomposition of organic wastes, and by thermal processing of other organic material. These fuels not only have the potential to replace some fossil natural gas, but also help solve waste disposal issues and reduce total emissions of greenhouse gases.
At a recent Technology and Market Assessment Forum, this was the topic of a presentation by Donald Chahbazpour, Director of the Sustainable Gas Group of the northeastern utility National Grid. This corporation has instituted a major effort to identify and encourage development of renewable gas sources. Chahbazpour identified renewable gas as “Pipeline quality gas derived from biomass resources that is injected into the natural gas distribution network for direct use in existing natural gas equipment.” He explained that this fuel could originate from either anaerobic digestion or thermal gasification of biomass.
Variety of Sources
Sources of biomass include waste water treatment plants, landfills, wood waste, livestock manure, municipal solid waste, agricultural residues and energy crops. Regardless of the source of the gas, it needs to be treated to remove water vapor, carbon dioxide, sulfur oxides or other contaminants. After treatment, the renewable gas is essentially interchangeable and compatible with pipeline natural gas.
Chahbazpour indicated that in the four states served by National Grid, New York, Massachusetts, Hew Hampshire and Rhode Island, there is technical potential to produce 268 billion cubic feet of renewable gas. This represents 16% of the overall demand, and 25% of the demand without power generation. This is not a minor contribution.
Reducing Greenhouse Gas Emissions
A main driver for adoption of processes for recovering and using renewable gas is that it lowers greenhouse gas emissions. Because it is beneficially consuming methane that might otherwise have been emitted to the atmosphere, the impact of replacing fossil natural gas with renewable gas is a positive contribution. According to Chahbazpour, another benefit is diversity of fuel supply by using local renewable gas sources.
He adds that renewable gas stimulates the local economy, creates jobs, and reduces waste disposal impacts. An alternative use for biogas is to burn it directly — untreated — in engines or turbines for electric generation. However Chahbazpour feels that upgrading it to natural gas standards is a more efficient use of the resource.
Gas Must Meet Utility Standards
A wide range of systems are available for renewable gas collection and treatment. In all cases, the utilities accepting the renewable gas for injection in pipelines require it be treated and tested for complete compatibility with utility and downstream customer equipment. Suppliers of renewable gas can contract for deliveries to users using existing natural gas pipelines.
Renewable gas is an additional benefit to the already environmentally attractive features of natural gas as a fuel for the future. Suppliers of renewable gas continue to put facilities on the line, and the trend is for a major increase in the use of this valuable energy resource.
The Energy Solutions Center is a non-profit organization comprised of 50 energy utilities that work together to bring new, energy efficient, natural gas solutions to commercial and industrial energy users.