Life Cycle Greenhouse Gas Emissions of Electricity Generated from Conventionally Produced Natural Gas

Abstract

SummaryThis research provides a systematic review and harmonization of the life cycle assessment (LCA) literature of electricity generated from conventionally produced natural gas. We focus on estimates of greenhouse gases (GHGs) emitted in the life cycle of electricity generation from natural gas-fired combustion turbine (NGCT) and combined-cycle (NGCC) systems. The smaller set of LCAs of liquefied natural gas power systems and natural gas plants with carbon capture and storage were also collected, but analyzed to a lesser extent. A meta-analytical process we term "harmonization" was employed to align several system boundaries and technical performance parameters to better allow for cross-study comparisons, with the aim of clarifying central tendency and reducing variability in estimates of life cycle GHG emissions.Of over 250 references identified, 42 passed screens for technological relevance and study quality, providing a total of 69 estimates for NGCT and NGCC. Harmonization increased the median estimates in each category as a result of several factors not typically considered in the previous research, including the regular clearing of liquids from a well, and consolidated the interquartile range for NGCC to 420 to 480 grams of carbon dioxide equivalent per kilowatt-hour (g CO 2 -eq/kWh) and for NGCT to 570 to 750 g CO 2 -eq/kWh, with medians of 450 and 670 CO 2 -eq/kWh, respectively. Harmonization of thermal efficiency had the largest effect in reducing variability; methane leakage rate is likely similarly influential, but was unharmonized in this assessment as a result of the significant current uncertainties in its estimation, an area that is justifiably receiving significant research attention. Keywords:combined cycle combustion turbine fossil fuels industrial ecology life cycle assessment (LCA) meta-analysis Supporting information is available on the JIE Web site

Harmonization of initial estimates of shale gas life cycle greenhouse gas emissions for electric power generation

“…After harmonization with consistent steps as implemented here for the eight shale gas LCAs, variability decreased (e.g., −13% in interquartile range), whereas the magnitude of estimates, in aggregate, remained constant, yielding a harmonized median of 450 g CO 2 e/kWh. Thus, the results from the larger set of conventional gas LCAs considered in O'Donoughue et al (26) suggests that the harmonized median estimate of life cycle GHG emissions from shale gas used to generation electricity in a modern combined cycle facility are slightly higher (3%) than those from conventional gas used for the same purpose. Considering the expected uncertainty ranges given the breadth of assumptions used in LCAs and that the results in O'Donoughue et al could not be updated to use the AR5 methane GWP (Methods), our conclusion is that based on current evidence, life cycle GHG emissions from shale and conventional gas are not significantly different (Fig.…”

“…O'Donoughue et al (26), considering all 42 references with life cycle GHG emission estimates for conventional gas-fired combined cycle (NGCC) facilities passing screens for relevance and quality (including all shale gas LCAs considered here that published an estimate for conventional gas), found that the published range of the middle 50% of 51 estimates v is ∼410-490 g CO 2 e/kWh (full range, ∼310-680 g CO 2 e/kWh), with a median of 450 g CO 2 e/kWh. After harmonization with consistent steps as implemented here for the eight shale gas LCAs, variability decreased (e.g., −13% in interquartile range), whereas the magnitude of estimates, in aggregate, remained constant, yielding a harmonized median of 450 g CO 2 e/kWh.…”

“…i,ii We compare results from these LCAs to prior harmonization of 200 estimates of life cycle GHG emissions for conventional gas and coal power generation (23,26). Our aim is to develop consistent comparisons of the results of each prior shale gas LCA, as well as for LCAs for conventional gas and coal and to pool results to provide insight into the question of which fuel source for power generation has lower life cycle GHG emissions: shale gas, conventional gas, or coal.…”

Life Cycle Energy Consumption and Greenhouse Gas Emissions Analysis of Natural Gas-Based Distributed Generation Projects in China

“…Life cycle GHG emissions associated with energy consumption can be calculated using the corresponding lifecycle emissions coefficient (Equations (11) and (12)). …”

“…The most frequently analyzed metrics of DG benefit include economy (net present value and internal return rate), GHG emissions, energy consumption reduction, and marginal abatement cost [10,11].…”