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Wood Wastes to Produce Renewable Natural Gas

Turning biomass into useful energy products such as biofuels or renewable natural gas has been one of the chief interests of scientists for many years. Forest residue, which includes all parts of the tree, can be converted into solid, liquid or gaseous biofuels that can then be burnt for energy or used as fuel substitutes for transportation or industrial processes.

Now (2019), the Gas Technology Institute has developed a site-specific engineering design titled Low-Carbon Renewable Natural Gas (RNG) from Wood Wastes. GTI have produced a “blueprint” for converting an existing biomass facility into an RNG production site that used the wood waste feedstock and some of the existing infrastructure. A biomass power plant in Stockton, California, was the host site for the production plant. The study provided data about the process technologies, the integrated plant and production costs, and proved that many environmental benefits and low-carbon fuel can be produced.

The team prepared a complete set of process-flow diagrams (PFDs) to show the process flow through the facility including the required auxiliary systems. Preliminary equipment specifications for the major equipment were compiled. Electrical loads were calculated and an electrical load list for all new equipment was created. A preliminary layout of major vessels, equipment and a set of preliminary general arrangement drawings were prepared. The gasification model which described input parameters such as temperature, pressure, fluidized bed material, velocities, residence time, char recycle, and feedstock moisture was optimised. The costs for the engineering, procurement, installation, and integration of the new equipment needed for RNG production were estimated. Based on the engineering work performed, resource assessment, and pipeline interconnection, an estimate for the cost of producing RNG was created, including a sensitivity analysis.

Research on the production of RNG has been carried out for several years. In 2016, a study examined the feasibility of producing large quantities of renewable natural gas fuels for use in transportation in California. The study’s results indicated that there were substantial sources of RNG in California which were commercially competitive with existing fossil fuel-based transportation fuels.

Finally, the study investigated the sensitivity of features influencing the climate performance of RNG on a life cycle analysis basis. The research results showed that vehicle-produced methane emissions constituted a large influence of overall carbon performance for LNG. Use of landfill gas on-site instead of being transported via pipeline reduced carbon emissions by up to 67%, indicating a clear climate benefit by avoiding pipeline transmission.

In 2017, two projects in Alberta and B.C. combined the forestry industry and wood wastes in profitable new ways by using new technology to convert biomass to biofuel and renewable natural gas. The company, G4 Insights, built a renewable natural gas (RNG) demonstration plant at an ATCO hosted site in Edmonton to test its conversion technology with a range of biomass types to generate technical operating and economic data.

G4 Insights’ proprietary PyroCatalytic Hydrogenation (PCH) launched a low temperature thermochemical process to produce a renewable replacement for fossil natural gas which could be supplied to end users through existing natural gas pipelines and used in any unmodified natural gas equipment, appliance, vehicle or industrial process.

The advantages of the new design are numerous: RNG production facilities using the commercial technologies outlined in the analysis produce 99% fewer conventional air pollutants compared to existing operational biomass power plants. The RNG product with very low carbon intensity could be used for carbon emission reductions in the transportation, industrial, commercial, and residential energy sectors. The gasification technology provides an additional option for utilizing woody biomass waste while providing a clean renewable energy source. The facility could produce RNG with a near zero or negative carbon footprint, depending on the equipment configuration of the wood waste-to-RNG production facility. In the base configuration in the study, one plant could offset approximately 170,000 tons of CO2 vehicle emissions each year, which is roughly equal to 400 million vehicle miles.

The scientists were convinced that it was possible to produce large quantities of RNG for use in all energy sectors. “We are confident that learning from the design study will help all stakeholders identify the most advantageous locations, in California and elsewhere, for converting from other biomass uses to RNG production.”