Life cycle assessment (LCA) of liquefied natural gas (LNG) and its environmental impact as a low carbon energy source

Abstract

[Abstract]: A life cycle assessment is an environmental management methodology documented by the International Standards Organization (ISO2006) for researching the impact a product has on the environment. Liquefied natural gas is a product contributing to the emission of greenhouse gases such as carbon dioxide, methane and nitrous oxide. These emissions can be minimized by analysis of its source and adopting appropriate process technology throughout the product lifecycle. Natural gas for many years was regarded as a volatile waste product within the oil and coal industries, and was subsequently vented into the atmosphere resulting in pollution. Natural gas is now accepted as a source of low carbon energy assisting the transition from heavy fuels to renewable energy. Liquefying the natural gas has proved to be an economic method for transporting this energy to the market place where pipeline infrastructure is unavailable. Australia has large resources of natural gas in conventional off-shore wells and underground coal-seams. Demand for energy security has positioned Australia to capitalize on its natural resources and supply low carbon energy to fuel economic growth in Asia. The production of liquefied natural gas in Australia is forecast to grow above one hundred million tons per annum within the next five years, becoming the world’s second largest supplier behind Qatar. Natural gas has a calorific value of approximately 40 MJ/m3, with greater than eighty five percent Methane content. Liquefied natural gas is produced by cooling natural gas to its boiling point of minus 161°C, becoming 1/600th its original volume. It is stored in insulated tanks at normal atmospheric pressure before being loaded on-board ships and transported to market. Ships used to transport liquefied natural gas range in size between 135,000m³ and 265,000m³. Once delivered to market, liquefied natural gas is used for cryogenic storage and re-gasified for domestic gas supply, power generation and industrial manufacturing. This study assesses the environmental impact of liquefied natural gas during liquefaction, shipping and re-gasification using a life cycle assessment approach. Greenhouse gas emissions are quantified in the form of carbon dioxide equivalent emissions and recommendations are made for process and technology improvements. Liquefaction of natural gas produces emissions during the removal of carbon dioxide from inflow gas, fuel used in gas turbines compressors and fuel used by power generation turbines. Shipping liquefied natural gas generates emissions from fuel used by the ships engines and re-gasification generates emissions from fuel used to operate pumps and power turbines. A thirty eight percent improvement in efficiency has been identified in the lifecycle of liquefied natural gas from Australia compared to global production, resulting in only six and a half grams of carbon dioxide equivalent emissions per mega Joule of energy delivered to Asian markets.