National Center for Sustainable Transportation

Renewable Natural Gas (RNG) is an important alternative fuel that can help the State of California meet several greenhouse gas (GHG) reduction and renewable energy targets. Despite considerable potential, current RNG use on national and state levels are not significant. RNG production potential in California through thermochemical conversion was evaluated as part of this project by assessing technical biomass availability in the state. Biomass feedstocks are defined broadly and include most carbonaceous matter including waste. The types of waste biomass available in the state are classified into three categories: municipal solid waste (MSW), agricultural residue and forest residue. A total of 32.1 million metric tonnes per year (MMT/year) of biomass is estimated to be technically available in the state. The energy content of this biomass is equivalent to approximately 602.4 million mmbtu/year. A survey of current renewable electricity generation and curtailment trends in California was conducted. Real-time data show significant curtailment throughout the year totaling more than 1,300 GWh from 2016 to early 2019. Power to gas and other forms of long-term storage integrated into the electric grid can mitigate these losses and enable smooth integration of additional renewables into the grid. Oxygen/air blown gasification, hydrogasification and pyrolysis are the three major technology options available for thermochemical biomass conversion to a gaseous fuel, including RNG. Although there are no commercial thermochemical biomass to RNG conversion facilities in operation, a number of gasification and pyrolysis technologies are undergoing pilot scale demonstration and development. Design basis for two thermochemical and power to gas conversion projects were developed as part of this project. Life cycle and economic analysis were conducted for the recommended processes.

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