E3 releases report on decarbonizing pipeline gas in California

By Katie Fletcher | February 06, 2015

Energy and Environmental Economics Inc., or E3, released a study in January commissioned by Southern California Gas. The study investigates the potential role decarbonized pipeline gas and existing gas pipeline infrastructure can have in California to help meet the state’s 2050 greenhouse gas (GHG) reduction goals.

The study concludes that a technology pathway for decarbonized gas could feasibly meet the GHG emission reduction goals, and may even be easier to implement in some sectors. According to the report, “By 2050 traditional uses of oil and natural gas, including transportation fuels, water and space heating, and industrial boilers and process heating, will need to be mostly, if not fully, decarbonized.”

The study approaches the issue by looking at two “technology pathway” scenarios. The electrification scenario is where most energy end uses are electrified and powered by renewable electricity by 2050. The second scenario is mixed, where both electricity and decarbonized gas play significant roles in the state’s energy supply. In this scenario decarbonized gas replaces existing natural gas demand and fuels heavy-duty vehicles, but renewable energy is used to produce electricity and to power most light-duty vehicles.

In order to identify realistic sources of decarbonized gas, the study identifies three energy carriers for decarbonized gas, each with different primary energy sources: biogas, hydrogen and synthetic natural gas (SNG).

Biogas’ primary energy source is biomass. One of the challenges with biomass, the report specifies, is maintaining a sustainable feedstock supply. Biomass resources have competing uses, including food, fodder and fiber, so it remains uncertain whether biomass fuels could increase without negatively impacting the food supply or increasing GHG emissions from changes in the land.

Even with this identified challenge biogas and biomass play a large role in the low-carbon scenarios in the report. In the mixed scenario, biogas plays a large role in achieving the GHG emission target, and in the electrification scenario biomass is used to produce low-carbon electricity. Additionally, the study states current research and development efforts and policy initiatives have prioritized liquid biofuels, like ethanol, over biogas.

Biogas or renewable natural gas are produced through anaerobic digestion (AD) or gasification combined with methane synthesis. According to the study, the choice between the two is mainly driven by moisture content, feedstock biodegradability and cost.

As part of the research, input capital cost assumptions were made for generation technologies. The capital cost for biogas from now until 2026 is $3,189 per kW, and is assumed to have no change in real capital cost by 2050. That cost is based on 2012 dollar values.

Another set of data in the report compares biomass final product cost, feedstock and conversion costs and conversion efficiencies. Biogas electricity processed by AD is indicated to cost between $40 and $80 per ton for feedstock, $96 per ton for conversion at a 6.5 gigajoule (GJ) per ton conversion efficiency, which ultimately results in a product cost in the range of $21 to $27 per GJ. Pipeline biogas produced by gasification was also in the feedstock price range of $40 to $80 per ton, but had a $155 per ton conversion cost, 9.5 GJ per ton conversion efficiency and product cost range of $20 to $25 per GJ.

The two low-carbon scenarios evaluated in the study each present a different technically feasible strategy to decarbonize the state’s energy system.

The results of the study confirm prior conclusions that the electricity sector will be vital to achieving state goals, because in both scenarios the need for low-carbon electricity increases to power electric vehicles, electrification in buildings and as a fuel to produce decarbonized gases. For the mixed scenario to succeed the study indicates large quantities of biogas must be produced from sustainably sourced biomass.

The full report can be found here.