Producing Biomethane and Renewable Natural Gas (RNG) from Farm and Food-Based Biogas Systems
Table of Contents
- What is Biomethane or Renewable Natural Gas?
- How Much Energy is in Biomethane From Manure?
- Can Biomethane Be Produced on a Farm?
- How is Biomethane Used?
- Why Consider Renewable Natural Gas or Biomethane?
- Environmental and Societal Benefits of Using RNG from Farm and Food-Based Biogas Systems
- Building a Biomethane or RNG System On-Farm
This infosheet describes the potential opportunities related to the production and utilization of biomethane and renewable natural gas from biogas systems at farms and food processing facilities in Ontario. There is already one biogas system providing biogas to the natural gas pipeline in Canada (Figure 1), and a few more across North America and Europe. This infosheet explores some of the initial implications of engaging in these opportunities.
What is Biomethane or Renewable Natural Gas?
Biomethane is a gaseous fuel that contains between 55% to 99% methane, and is produced from biogas generated through the anaerobic digestion of organic materials, or from landfill gas production. Biomethane is biogas that is cleaned by removing contaminants such as hydrogen sulphide and moisture. In addition, biomethane may be "upgraded" to almost pure methane by eliminating carbon dioxide (CO2). Methane is the primary ingredient in conventional natural gas. Renewable natural gas (also known as RNG) is biomethane that has been cleaned to meet natural gas pipeline quality standards.
For more information on the basics of biogas production on the farm, read the OMAFRA Factsheet Anaerobic Digestion Basics (Order no. 07-057).
Figure 1. A farm-based biogas system producing renewable natural gas in British Columbia. The system that upgrades the gas to meet natural gas standards is located on the left hand side of picture.
How Much Energy is in Biomethane From Manure?
It is estimated that there is enough fuel from the manure from one milking cow to drive a pick-up truck roughly 5000 km per year. This calculation assumes that the manure from a milking cow (including its offspring) produces roughly 1350 cubic metres of biogas per year, and that 60% of the biogas is methane.
Can Biomethane Be Produced on a Farm?
Biomethane is currently being produced at the Catalyst Power facility at a dairy farm near Abbotsford, British Columbia. The biogas system became operational in 2010. Biogas is produced in four anaerobic digester tanks which are fed liquid manure, corn silage, and food wastes from the nearby communities. Biogas is upgraded to natural gas quality on a continuous basis, producing about 110,000 GigaJoules (GJ) per year. The upgraded gas (RNG) is sold to the local gas utility company.
How is Biomethane Used?
Once biomethane has been created it can be managed and used as a replacement for natural gas or other gaseous fuels. Some of the common uses for biomethane include:
Injection into the natural gas pipeline: Biomethane that has been upgraded into RNG must meet specific minimum or maximum levels for certain gases, moisture, and other constituents in order to be added into the pipeline. It must be pressurized, and it must meet a variety of safety and metering rules. Once RNG is added to the pipeline it is considered to be no different from natural gas. Depending on contractual models, it could be purchased by an end user, or by the gas utility. In Ontario, the process of pipeline injection is regulated by the Ontario Energy Board.
Figure 2. Injection system used to pump RNG into a natural gas line at a farm-based biogas system
Compressed for Non-pipeline Customers: Biomethane or RNG can be compressed as a gas and stored in pressurized containers to be used on-site or at remote locations. This may be attractive to fuel users who currently have more expensive fuel alternatives, for instance, when heating livestock facilities or greenhouses. In Europe compressed RNG from biogas is brought to vehicle fuelling stations in trailer-mounted pressurized containers. Local users of the fuel have vehicles designed or converted for natural gas use. Other European sites have RNG from a local biogas system piped directly to a nearby fuelling station without using the natural gas pipeline.
Biomethane: In some cases, biogas with only 60% methane content can be used to replace other fuels. To do so, some contaminant gases and water vapour must be adequately removed from the biogas. The remaining 40% of gas volume (other than methane) is made up primarily of carbon dioxide, meaning the fuel has a lower energy density than pure methane. This can be effectively accounted for in a properly designed fuel system, appliance, or engine. Figure 3 shows a prototype agricultural tractor that is designed to run on 60% methane biogas. The engine can operate on a blend biogas and diesel (called a dual fuel system). The prototype gets 70% to 80% of its 110 hp from cleaned biogas (containing 60% methane and 40% carbon dioxide). Other prototype tractors from Steyr (Case) and John Deere have also been demonstrated running on biogas.
Figure 3. Valtra's prototype biogas tractor that runs on farm-based biogas. Note the pressurized biogas storage system on lower side of tractor. Photo courtesy of Valtra and AGCO.
Why Consider Renewable Natural Gas or Biomethane?
With the recent breakthroughs in shale gas production, natural gas prices have dropped and may remain low compared to the prices in recent years. Despite this, there are a number of reasons why RNG production may be considered at biogas systems today:
RNG is not a fossil fuel. Fuel consumers may desire to purchase a fuel that has a lower greenhouse gas footprint than conventional fossil fuel-based natural gas. For instance, in 2011 an Ontario food processor signed an agreement to purchase landfill gas RNG via the natural gas pipeline so that its cookie production facility could be fully fuelled from a renewable source;
Efficient use of biogas. When biogas is generated for other purposes (waste management, wastewater treatment), upgrading biogas to RNG allows for an efficient use of the energy in the fuel, resulting in nearly all of the energy in the gas being converted for energy purposes. In comparison, using biogas or RNG in a cogeneration system to produce electricity may result in losses and inefficiency if there is not an on-site use for excess heat from a cogeneration system;
Availability of gas line connection. A biogas system may be located in an area that does not have sufficient electrical grid capacity to establish or expand the facility. The project developer might consider whether the natural gas line has capacity to use the RNG, or whether other gaseous fuel users might want to purchase the gas;
Cost effectiveness. In most cases it is not possible to produce RNG at a cost directly competitive to current natural gas prices. However, in some cases RNG use may be competitive to other sources of energy such as electricity, gasoline and diesel. This may be applicable at locations that are not currently serviced by conventional natural gas. Using RNG may also be a good way to keep using existing natural gas fuelled equipment (such as a boiler or furnace) but gaining the advantages of using a renewable fuel, such as reducing reliance on fossil fuels.
Environmental and Societal Benefits of Using RNG from Farm and Food-Based Biogas Systems
In addition to the climate change benefits associated with using methane from a non-fossil fuel source, when markets for RNG can be found, the operation of farm and food-based biogas systems results in benefits that include:
Emissions reduction: the storage, land application, or disposal of untreated manure and food waste can produce greenhouse gas or smog-forming emissions. By harvesting the carbon in a biogas system and using it as RNG, emissions from conventional processes are avoided.
Odour reduction: manure and food waste used in biogas systems might otherwise have contributed to odour emission when handled in other conventional manners. Digesting these materials in a biogas system results in odour reduction, contributing to reduced nuisance issues in rural and urban-fringe areas;
Pathogens: operating a biogas system with manure as a primary input results in a reduction in pathogens (such as E .coli). Reducing pathogens at the source adds another barrier to reduce risk for surface and groundwater drinking sources, contributing to source water protection objectives in the province;
Waste management for food wastes and by-products:
Avoid land filling: By using food waste as a biogas input, food waste and food processing by-products that are currently land-filled can be diverted. While a portion of the methane emissions from landfills can be captured once a landfill is capped, it is much more efficient to harvest this methane directly and fully in a biogas system.
Reduced waste management costs for the food sector: Directing food waste and by-products to biogas systems will in general result in lower handling costs for food waste compared to other management approaches (landfill, compost, and land-application). Conventional waste management approaches can be expensive since food wastes can be wet, sloppy, odorous, and may be generated through the winter (requiring storage solutions). Biogas systems have the ability to deal with all of these issues and potentially be a good destination at a lower cost. The result is that Ontario's food sector can avoid some costs and stay competitive with other jurisdictions.
Recycling of nutrients and carbon to the land: When food wastes are digested in biogas systems and the digestate effluent is returned to agricultural fields and spread like manure, the result is that agricultural nutrients like nitrogen, phosphorous and potassium are returned to the soil. The indigestible carbon component in food wastes will also contribute to soil health, building up organic matter. This is an improvement compared to land filling or sewer discharge of food wastes, where these nutrients and carbon are lost.
Rural economic development:
Local fuel production: Instead of sourcing energy from other jurisdictions, local companies become generators of fuel, meaning that energy dollars are kept in the province;
Local synergies: Locating biogas systems near the waste sources or near the destination for effluent end products means that jobs, transportation and tax revenue stay local. This approach closes the loop on the farm and food production system.
Building a Biomethane or RNG System On-Farm
A farm-based biogas system built for biomethane or RNG production will appear in most aspects like conventional biogas electricity-based systems. There are a few key differences apparent at RNG biogas systems (beyond the absence of electricity generation equipment):
Location near a natural gas line: For systems supplying RNG to the natural gas pipeline, construction of the facility within piping distance of natural gas pipeline will be necessary. Throughout many areas of rural Ontario there is no natural gas service, therefore pipeline injection may not be viable for many livestock farms simply due to their location.
Large size: In general, the upgrading technology currently on the market requires a higher gas production rate than would be available from most farm-based biogas systems built in Ontario today. In Ontario, building a sufficiently large system may be achieved with blends of off-farm materials, energy crops, and/or mixing manure from multiple farms to produce enough biogas.
Alternately, perhaps models can be developed for non-pipeline end use of biomethane such as vehicle refuelling or replacement of gaseous fuel via compressed gas trailer transport. Regulatory approval processes will have to be fleshed out for such systems. In addition, the following factors may be applicable for on-farm biomethane system construction and operation:
Seasonal variability: There are few consistent fuel users with constant daily demands. The biogas system may have to respond to daily or seasonal variations in fuel demand by changing input feeding rates, or by identifying alternative biogas uses to manage excess biogas.
Increased biogas storage: It is likely that there will be daily variations in fuel usage, whether the gas end user is a food processor or a fleet of vehicles, accounting for weekends and holidays and changes in business activities. Pressurized or non-pressurized gas storage may be required at the biogas system or at the end user site to facilitate the ongoing daily production of biogas.
This infosheet provides an introduction to biomethane and renewable natural gas production. These potential markets for biogas may be a new pathway to capture the environmental and economic benefits associated with farm and food-based biogas systems. Work remains to be done to demonstrate the economic value chain, technical needs, regulatory implications, and viability of these approaches.
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