Natural gas as a renewable fuel
Amazingly, natural gas can be produced from a variety of sources—including a pile of garbage. The process from trash to gas makes natural gas a renewable fuel. Biogas is the term used for the methane that is developed from the breakdown of organic material in the absence of oxygen from sources such as sewage, municipal solid waste, and farm waste. Biomethane is the fuel that is produced by refining and removing any impurities from the biogas. And unlike fossil fuels, which are considered a finite resource, the natural gas produced from these sources is a renewable resource.
Compressed biogas (CBG) and CNG can be used interchangeably as a fuel in CNG vehicles. While pipeline gas is CNG-ready, biogas requires conditioning (cleaning) before compression. The conditioning process removes moisture (H2O), increases methane (CH4) content by removing carbon dioxide (CO2), and cleans the gas by removing hydrogen sulfide (H2S), siloxanes, and other trace elements. Although CBG is currently cheaper to produce than CNG—because the methane source is free—higher capital costs associated with CBG—due to conditioning—have the potential to offset this difference. One potential advantage of direct use of biomethane as opposed to those who inject gas back into the pipeline is that natural gas vehicles can tolerate somewhat higher levels of CO2, which can have a significant impact on gas cleanup costs. For injection into the pipeline, the biogas must be purified to about 98 to 99 percent methane. For direct use as a vehicle fuel, biogas may be cleaned to around 90 percent methane.
Renewable Fuel Credits
As a renewable gas, biomethane used as an alternative vehicle fuel, whether directly or after transportation by pipeline, may be a way to comply with the federal Renewable Fuel Standard (RFS) or California’s state-mandated Low Carbon Fuel Standard (LCFS). The federal RFS was created by Congress through the Energy Policy Act of 2005. It was updated in the Energy Independence and Security Act of 2007 (EISA). The new standard, known as RFS2, sets annual mandates for four types of alternative fuels, based on lifecycle GHG emissions levels relative to a 2005 baseline of petroleum. Biomethane qualifies as an Advanced Biofuel under the RFS which means that it is eligible for Green Tag Attributes or Renewable Identification Numbers (RINs). A RIN is a credit that is traded and can provide additional revenue for each unit of CBG fuel produced, a benefit to help commercialize this fuel.
Current CBG projects are generating $0.80/DGE to $1.15/DGE of additional revenue by selling RINs. The U.S. EPA recently expanded the definition of cellulosic biofuel to include CNG and LNG produced from biogas. This expanded definition allows biomethane to satisfy the federal biofuel mandate, which has traditionally been satisfied with fuels derived from sources like grass and wood. Traditional cellulosic biofuels were supposed to make up a growing portion of the Renewable Fuel Standard, but large-scale commercial production has been difficult to realize. Seventeen million gallons, less than 1 percent of the 1.75 billion gallons initially required by the Energy Independence and Security Act of 2007, is the revised target for cellulosic biofuel use in 2014. The expanded definition may be an additional driver for the development of biomethane projects and an important fuel source to satisfy cellulosic biofuel production requirements.
There are also tremendous environmental benefits.For example, there are 636 landfills in 48 states that are recovering energy from landfill gas, according to the Environmental Protection Agency’s Landfill Methane Outreach Program. The energy that’s captured is used in a variety of applications—including energy for power plants, manufacturing facilities, and homes.
According to the federal agency, landfills are the third largest human-made source of methane, which is 21 times more potent by weight that CO2. These landfill gases are either vented or often burned off or flared to reduce the emissions going into the atmosphere. The EPA has reported that all together these projects have captured 102 billion cubic feet of landfill gas. Biomethane has the added benefit of being a clean energy resource that reduces the country’s reliance on fossil fuels.
How do they do it?
The landfill gas is extracted using a series of wells and a blower/flare system. This system directs the collected gas to a central point where it can be processed and treated, including the potential to produce pipeline–quality gas that may be used directly or processed into an alternative vehicle fuel. For a complete description, click here to see the EPA’s pictures and graphs on how it’s done.
Real Life Application
In California, Waste Management’s Altamont Landfill near Livermore is producing natural gas that is being used to power its refuse trucks. It is one of a handful of projects exploring the possibilities of using landfill gas to produce either compressed natural gas as a vehicle fuel for light and medium duty vehicles or liquefied natural gas as a vehicle fuel for heavy duty trucks, such as refuse vehicles.
The Altamont project, which includes the world’s largest landfill natural gas plant, opened in November 2009, following almost 10 years of research. By July 2010, the plant was producing 1.7 million gallons of fuel. When the facility is at full capacity, it will produce 13,000 gallons of LNG per day, which will be enough fuel to power 300 heavy-duty refuse trucks serving 20 California communities. Because these trucks will not be using diesel fuel, the project is expected to reduce greenhouse gas emissions by 30,000 tons a year.
Waste Management and the Linde Group have partnered together to operate this $15 million facility, which collects, purifies, and liquefies landfill gas using technology developed by the Gas Technology Institute. The goal is to develop an efficient and low capital plant that can economically produce fuel on a small scale. The project is both technologically and economically challenging, but it has made significant progress in advancing the technology so that it could be implemented at other locations. Projects such as this are often done in conjunction with government support, since this helps reduce the risks and enables the acceleration of technology and market development. The Livermore project received support from four California agencies.