Options for the Delivery and Use of Renewable Natural Gas (RNG)
There are two primary methods used to deliver renewable natural gas to the end user: it is either used locally onsite, for example to fuel vehicles; or it is injected into a pipeline for use elsewhere. Since the chemical structure of RNG is very similar to that of fossil natural gas, it can simply be dropped into existing natural gas pipelines. RNG and fossil natural gas have an identical methane component, however the trace constituents of each differ. RNG is a very versatile energy source that can be used to power vehicles, generate electricity, or for thermal energy applications in residential, commercial, industrial or institutional sectors.
Over the years, market demand has shaped how renewable natural gas is utilized. Ten years ago, most RNG projects in the US were supplying renewable natural gas for electricity generation offsite, largely due to Renewable Portfolio Standard programs implemented at state level. However, the introduction of new rules, as well as incentives, imposed by both state and federal governments saw the increased demand for renewable transportation fuels, together with a surge of growth in renewable natural gas projects to supply this emerging market. It also resulted in a dramatic shift of how RNG was being used. In 2017, only 24% of RNG projects were supplying renewable natural gas offsite to generate electricity, with the remaining 76% being converted into renewable transportation fuels.
Injecting Renewable Natural Gas into a Pipeline Network
Renewable natural gas can either be injected into a dedicated RNG pipeline, or it can be injected into an existing natural gas pipeline network. However, if the latter is used, the RNG first needs to meet the quality specifications required by the gas utility that will be receiving the RNG. This method of delivery can be costly as extensive planning is required, land needs to be purchased, permits need to be obtained, together with the cost of construction, interconnection equipment (point of receipt and pipeline extension to ensure quality control measures are met) and associated fees. However, injecting RNG into a pipeline enables it to be distributed further afield via the extensive natural gas pipeline network, providing flexibility of where and how it is ultimately used.Using Renewable Natural Gas as a Vehicle Fuel
Renewable natural gas can be converted into compressed natural gas (CNG) or liquefied natural gas (LNG) to fuel a wide range of vehicle types, supplying fuel stations much further afield. According to a report recently released by the EPA, â€œas of March 2020, the majority (91%) of LFG-sourced RNG pipeline injection projects were providing at least a portion of the RNG to a vehicle fuel market down the pipeline. In these cases, fueling stations far removed from the biogas source were receiving the RNG at the other end of a pipeline network.â€
Using Renewable Natural Gas to Generate Electricity
While many RNG projects use biogas that has been partially conditioned to generate electricity onsite, several RNG projects (primarily landfill gas projects) that inject RNG into a natural gas pipeline to be used to produce electricity offsite.
Using Renewable Natural Gas for Thermal Energy Applications
While biogas projects supplying RNG for use in thermal applications is relatively low compared to electricity generation and vehicle fuel, since there are more incentives for use in these areas, several projects do use untreated biogas to meet thermal energy demands in applications such as boilers, kilns and greenhouses for example. However, changing policies may see an increase in RNG being used in direct thermal applications in the future.
Using Renewable Natural Gas Locally Onsite
When utilized locally onsite, RNG is used predominantly as a vehicle fuel.
Utilizing Renewable Natural Gas Onsite as a Vehicle Fuel
When used as a vehicle fuel onsite, RNG project donâ€™t have to worry about meeting specifications laid out by the receiving gas utility. Typically the specifications required for vehicle fuel are less stringent than those required by pipeline operators. Using RNG onsite also alleviates the interconnection and transportation costs associated with pipeline injection. However, in order to be viable there needs to be sufficient demand for RNG vehicle fuel, and this demand needs to be consistent. This can be challenging, especially in rural areas that have a large supply of biogas, as large vehicle fleets tend to operate out of urban areas.
Very often, biogas producers have their own fleet of vehicles (including CNG-compatible vehicles), for example a municipality that operates a landfill or wastewater treatment facility. Having a fueling station onsite can provide a convenient and cost-effective source of fuel to run their fleets, and is sometimes also made available to outside fleets that operate in the area, providing a source of revenue. In cases such as this, where the vehicles that are used to transport the feedstock (waste) used in biogas production to the site are powered by RNG fuel derived from biogas generated by the waste delivered, are referred to as circular or â€˜closed loopâ€™ projects.
Transporting Renewable Natural Gas Via a Virtual Pipeline
When a renewable natural gas producer is located far from its end users or natural gas pipeline, a â€˜virtual pipelineâ€™ can be used to transport compressed RNG from the biogas plant either to fuel station where it will be available to end users, or to a point on the gas pipeline network where it can be injected into the pipeline for distribution to end users further afield. When a virtual pipeline is used, the RNG is compressed before being injected into a natural gas tube trailer, which is then transported to its destination by truck. When it arrives at the point of use/point of injection, it is decompressed to the pressure stipulated by the receiving entity. A virtual pipeline enables farms, landfills and other biogas producers that are located in remote areas to deliver their RNG to more populated urban areas. Transporting RNG via a virtual pipeline opens up markets further afield, however there are additional costs involved, including RNG processing equipment and infrastructure needed for the compression and decompression of the gas, as well as the transportation costs to haul the gas from source to point of delivery.
As we can see, there are several ways of delivering and utilizing renewable natural gas and RNG projects are not limited to any one specific delivery method or application. Some RNG projects may utilize more than one method for delivering their product to their end users, according to demand. For example, they may have a fuel station onsite to fuel their vehicle fleet and transport the surplus to a fuel station or natural gas pipeline offsite, making use of a virtual pipeline delivery service.
An Overview of Renewable Natural Gas from Biogas. July 2020, EPA 456-R-20-001.
Featured Image by IFCAR / Public domain