Life cycle assessment of natural gas power plants in Thailand

Abstract

The main primary energy for electricity in Thailand is natural gas, accounting for 73% of the grid mix. Electricity generation from natural gas combustion is associated with substantial air emissions. The two technologies currently used in Thailand, thermal and combined cycle power plant, have been evaluated for the potential environmental impacts in a “cradle-to-grid” study according to the life cycle assessment (LCA) method. This study evaluates the environmental impacts of each process of the natural gas power production over the entire life cycle and compares two different power plant technologies currently used in Thailand, namely, combined cycle and thermal. LCA is used as a tool for the assessment of resource consumption and associated impacts generated from utilization of natural gas in power production. The details follow the methodology outlined in ISO 14040. The scope of this research includes natural gas extraction, natural gas separation, natural gas transmission, and natural gas power production. Most of the inventory data have been collected from Thailand, except for the upstream of fuel oil and fuel transmission, which have been computed from Greenhouse gases, Regulated Emissions, and Energy use in Transportation version 1.7 and Global Emission Model for Integrated Systems version 4.3. The impact categories considered are global warming, acidification, photochemical ozone formation, and nutrient enrichment potential (NEP). The comparison reveals that the combined cycle power plant, which has a higher efficiency, performs better than the thermal power plant for global warming potential (GWP), acidification potential (ACP), and photochemical ozone formation potential (POCP), but not for NEP where the thermal power plant is preferable. For the thermal power plant, the most significant environmental impacts are from power production followed by upstream of fuel oil, natural gas extraction, separation, and transportation. For the combined cycle power plant, the most significant environmental impacts are from power production followed by natural gas extraction, separation, and transportation. The significant difference between the two types of power production is mainly from the combustion process and feedstock in power plant. The thermal power plant uses a mix of natural gas (56% by energy content) and fuel oil (44% by energy content); whereas, the combined cycle power plant operates primarily on natural gas. The largest contribution to GWP, ACP, and NEP is from power production for both thermal as well as combined cycle power plants. The POCP for the thermal power plant is also from power production; whereas, for combined cycle power plant, it is mainly from transmission of natural gas. In this research, we have examined the environmental impact of electricity generation technology between thermal and combined cycle natural gas power plants. This is the overview of the whole life cycle of natural gas power plant, which will help in decision making. The results of this study will be useful for future power plants as natural gas is the major feedstock being promoted in Thailand for power production. Also, these results will be used in further research for comparison with other feedstocks and power production technologies.