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8 Life-Cycle Assessment of Carbon Utilization
Pages 165-182

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From page 165...
... While carbon utilization technologies take up CO2 and methane that would otherwise be emitted, the conversion of these greenhouse gases into products consumes energy and materials. Energy and materials consumption results in emissions of greenhouse gases which may or may not, on net, reduce overall emissions as a result of using the carbon utilization technology (Bruhn et al., 2016; von der Assen et al., 2013, 2014)
From page 166...
... In this report, the committee considered both technologies that lead to net-negative greenhouse gas emissions and technologies that lead to net greenhouse gas emission reductions, when displacement of business-as-usual technologies is included. Life Cycle GHG Emissions Comparison Between Product from Waste Gas Utilization and Business-As-Usual Technology Waste gaseous carbon utilization scenario Business as usual scenario GHGconversion > 0 Waste gaseous carbon: GHGconversion > 0 Other feedstock GHGin (fossil, biomass)
From page 167...
... • Which uses of waste gases (e.g., to chemicals or building materials) offer the greatest net greenhouse gas emissions abatement?
From page 168...
... Figure 8-1 depicts a system boundary appropriate for considering a single carbon utilization technology. In carbon utilization LCA, the system boundary must include the waste gas capture and any pretreatment steps prior to purification in addition to CO2 compression and transport to the point of conversion, if conversion is not co-located with capture (CO2 Sciences, Inc., 2016; Cuella-Franca et al., 2014; von der Assen et al., 2013, 2016)
From page 169...
... While energy consumption and greenhouse gas emissions are logical impacts to include in carbon utilization LCA, other impacts including water consumption and air pollutant emissions should not be ignored. However, with the exception of water consumption in the case of algal biofuel (Tu et al., 2017)
From page 170...
... For example, there may be synergies between the electricity generation process and the carbon utilization process if some of the heat normally wasted by a power plant is used to operate the utilization technology. A key methodological issue in LCA of carbon waste gas utilization systems is the treatment of the energy and emissions intensity of the waste gaseous carbon stream itself.
From page 171...
... Clearly, treatment of the waste gaseous carbon stream remains an area for examination. In any case, while the approach taken is subjective, consistency and transparency are essential if LCA results for carbon utilization processes are to be compared.
From page 172...
... Republished with permission of RSC Publishing, from Life-cycle assessment of carbon dioxide capture and utilization: Avoiding the pitfalls. von der Assen, N., J
From page 173...
... Republished with permission of RSC Publishing, from Life-cycle assessment of carbon dioxide capture and utilization: Avoiding the pitfalls. von der Assen, N., J
From page 174...
... This is relevant to waste gaseous carbon systems that co-produce a fuel (electricity or liquid fuel) and a chemical.
From page 175...
... Attributional and Consequential LCA The techniques discussed in previous sections of this chapter would be adopted in attributional LCA, in which the supply chain of a product or process is followed linearly as a series of steps over which inputs and outputs are accumulated and assigned to the product of interest. As carbon utilization technologies achieve widespread market penetration, they will impact the structure of product markets.
From page 176...
... after a useful life of just a few years, effective sequestration would be shorter.2 Moreover, if the waste gas were converted to a chemical that would be used for several years in a process with some percent lost to process inefficiencies and/or combustion of process waste streams, effective sequestration would again be much shorter. Finally, if the waste gas were converted to a liquid fuel, any sequestration would be very short lived because the fuel would likely be combusted in a vehicle or at a power plant shortly after production.
From page 177...
... As the field evolves and LCAs of various waste gaseous carbon utilization technologies grow in number and complexity, it will be critical for analysts to consider and document their approach to transparently reporting their data, data sources, and assumptions.
From page 178...
... their end of life For should be noted as outside the system boundary if the analysis time horizon does not incorporate their degradation Functional • CO2 emitted over • Direct displacement: per kilogram •  unit energy Per Units material lifetime product per unit mass Functional displacement: per •  • CO2 abated unit mass required for equivalent compared to a performance reference system Co-products • Limited co- • Treatment options include • Energy products products • Displacement could be treated • Energy with energy • Mass allocation • Market value • Other co product options are identical to those for chemicals and polymers 178
From page 179...
... LIFE-CYCLE ASSESSMENT OF CARBON UTILIZATION TABLE 8-2 Continued Building Polymers Chemicals Liquid Fuels Materials Temporal Long-term storage likely although •  • Waste carbon • Essentially no consideration of product lifetime storage duration storage of waste compared to conventional products dependent carbon warranted upon chemical • Carbon in fuel Choice of time horizon will determine •  application emitted to whether waste carbon effectively • Processes atmosphere sequestered for long-lived products such as upon evaporation or combustion decomposition (or incineration of waste chemicals) could lead to the carbon in the chemical being emitted to the atmosphere Attributional & Intent of analysis drives LCA approach •  Consequential Comparison of nearly identical systems or evaluation of nondisruptive systems •  LCA may be suitable for attributional LCA Evaluation of disruptive technology changes may be suitable for consequential •  LCA Potential Building materials Ongoing Alternative Electricity or Counterfactual such as wood, steel, widespread use emerging fossil- or biomassScenarios or aggregate that of fossil fuel– technologies (e.g., derived liquid fuels do not incorporate derived polymers new feedstock or a combination waste CO2 or some level of from biomass, thereof penetration of new catalysts, biomass-derived new separation polymers technologies)
From page 180...
... Priority areas include the following: Life-cycle assessment benchmarking Research is needed to develop benchmark life-cycle assessments of waste gas generation, waste gas cleanup, waste gas transport, electricity inputs, hydrogen inputs, and other enabling technologies to facilitate consistent and transparent assessments of the net greenhouse gas emissions of carbon utilization technologies. These benchmark assessments would include multiple environmental attributes of carbon utilization life cycles, such as greenhouse gas emissions, water use, air emissions, and materials use.
From page 181...
... International Journal of Greenhouse Gas Control 21:140-157.
From page 182...
... 2014. Scenarios for Assessing the Greenhouse Gas Impacts and Energy Input Require ments of Using North American Woody Biomass for Electricity Generation in the UK.


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