Comparative Life-Cycle Air Emissions of Coal, Domestic Natural Gas, LNG, and SNG for Electricity Generation

Abstract

The U.S. Department of Energy (DOE) estimates that in the coming decades the United States' natural gas (NG) demand for electricity generation will increase. Estimates also suggest that NG supply will increasingly come from imported liquefied natural gas (LNG). Additional supplies of NG could come domestically from the production of synthetic natural gas (SNG) via coal gasification-methanation. The objective of this study is to compare greenhouse gas (GHG), SOx, and NOx life-cycle emissions of electricity generated with NG/LNG/SNG and coal. This life-cycle comparison of air emissions from different fuels can help us better understand the advantages and disadvantages of using coal versus globally sourced NG for electricity generation. Our estimates suggest that with the current fleet of power plants, a mix of domestic NG, LNG, and SNG would have lower GHG emissions than coal. If advanced technologies with carbon capture and sequestration (CCS) are used, however, coal and a mix of domestic NG, LNG, and SNG would have very similar life-cycle GHG emissions. For SOx and NOx we find there are significant emissions in the upstream stages of the NG/ LNG life-cycles, which contribute to a larger range in SOx and NOx emissions for NG/LNG than for coal and SNG.

Life Cycle Assessment of Greenhouse Gas Emissions from Plug-in Hybrid Vehicles: Implications for Policy

“…If new coal plants are untenable, increasing demand for natural gas, even in the absence of potential PHEV adoption, will likely require large increases in liquefied natural gas (LNG) imports. The life cycle GHG impacts of LNG for electricity are higher than for domestic natural gas (31). Hence large reliance on LNG to power PHEVs could increase emissions relative to using domestic natural gas and introduce additional energy security risks.…”

Comparative Analysis of the Production Costs and Life-Cycle GHG Emissions of FT Liquid Fuels from Coal and Natural Gas

“…Figure 1 shows the high-emissions scenario well-to-wheel GHG emission factors for gasoline. The error bars presented in these figures represent the uncertainty/variability in the upstream emission factors of coal, natural gas, and electricity reported by Jaramillo et al (7), as well as variability in the emissions from liquid fuel transport. The high-emissions scenario uses the current U.S. fuel mix for electricity generation (50% coal, 20% natural gas, and 30% low-carbon sources (12)) and does not consider CCS for the FT plants.…”

“…Emissions from the production, processing, and transport of coal, domestic natural gas, and LNG were obtained from Jaramillo et al (7). Values used for emissions from mining, processing, and transporting coal range between 3.5 and 7.0 g of CO2 equivalents per megajoule (g CO2e/MJ).…”

“…For domestic natural gas, the upstream use emissions range between 6.5 and 8.6 g CO 2e/MJ. For LNG these emissions range between 13 and 31 g CO 2e/MJ (7). For the case where the GTL fuels are produced in Qatar or Malaysia, the emissions for domestic natural gas are assumed to be representative of the emissions from production, processing, and transport of the gas used at these foreign plants, as suggested by Jaramillo et al (7).…”

Life Cycle Inventory of CO2 in an Enhanced Oil Recovery System

“…The upstream GHG emissions are associated with the coal life cycle from coal mining, processing, and transport ( Figure 1). According to Jaramillo et al (19), average emissions from coal mined, processed, and transported in the U.S. is 4.99 g CO 2 e per MJ. These emissions include methane emissions released from coal mining.…”