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Fuelling Farm Vehicles with Compressed Biogas

Executive Summary

This study investigates the technical feasibility and value of using compressed biogas (CBG) as a vehicle fuel to displace diesel in converted farm vehicles.  The entire process of fuelling farm vehicles with CBG is considered, including bolt-on biogas conditioning systems for existing biogas facilities to produce vehicle fuel, dual fuel vehicle conversion systems, capital and operating costs and considerations for improving future economics.

Most on farm biogas systems do not have a valuable option to utilize excess biogas that is produced beyond their energy contract requirements. The farmers consulted indicated their biogas systems could achieve additional biogas production of 50-200 m3/hour by increasing feedstock to the system.  There may be potential for Canadian biogas operators to produce more renewable energy from biogas systems, if the operators can identify economical pathways for using the biogas.  This study considers on-farm vehicle fuelling as an opportunity.   

Raw biogas is a mixture of 55%-65% methane (CH4), 35%-45% carbon dioxide (CO2) and small amounts of other gases such as hydrogen sulfide.  Minimally processed biogas can be combusted in stationary engines to produce electricity, but for current vehicle fuelling technology further conditioning is required.  Moisture and hydrogen sulfide must be removed to prevent engine corrosion and compressor damage. While CO2 does not have any energy value it technically does not need to be completely removed.  CO2 should be managed so the biogas has a predictable CH4 to CO2 ratio as current vehicle conversion technology require a stable fuel supply.  

Converting farm vehicles to a dual fuel configuration is a cost effective and convenient option that can displace 50-70% of diesel.  With a dual-fuel conversion, engines have the capability to co-combust natural gas, renewable natural gas, or biogas with diesel.  Dual fuel engines can also operate on diesel only, offering the flexibility to continue operating even if biogas fuel is unavailable.  The retro-fit is a non-invasive addition that can be added to any diesel engine.  It consists of adding on-board pressurized gas storage tanks, and a fuel injection system for the gas.  For a conversion to make economic sense, it is recommended to convert a vehicle used year-round that turns over a tank of fuel every day or few days.

The costs of biogas conditioning, compression, and vehicle conversion can vary based on configuration, size, and output gas quality.  Biogas conditioning systems that condition 85 m3/hour range in price from $200,000 to $400,000.  Vehicle conversion can range in price from $20,000 to $40,000.  Operational expenses include electricity demand and cost of consumable media, which is approximately $0.23/ diesel litre equivalent (DLE).  A farm vehicle that consumed 150 litres of diesel a day before conversion would spend $5,400 annually in operating costs, and have a total annual fuel savings of $14,300.

Converting biogas to vehicle fuel can be cost prohibitive for small-scale applications with current technology.  Further technology development for cost-effective, small-scale conditioning systems can help to minimize this barrier.  As carbon markets develop in Canada, there may be an option to claim offset credits from using biogas as fuel providing an additional revenue stream.  Theoretically, at $18/tCO2e, fueling one vehicle could generate $6,400 a year in carbon offsets.

While more work needs to be done to reduce cost barriers, fuelling farm vehicles with compressed biogas is technically feasible with existing technology. Converting biogas to vehicle fuel can be an option for farms looking to reduce diesel consumption and increase self-sufficiency by using a locally produced, low carbon fuel.

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