Up-to-date life cycle assessment and comparison study of clean coal power generation technologies in China

Abstract

China has become the primary energy consumer in the world, consuming 48.2% of the world's coal in 2010. Of this percentage, 48.0% of China's coal consumption is used by the power generation industry, which causes unavoidable environmental problems in the country. This paper presents complete life cycle modeling and a comparative assessment of current clean coal power generation technologies in China, including a state-of-the-art commercial ultra super-critical system. In this study, a life cycle assessment (LCA) is adopted for energy and environment analysis, followed by a brief economic discussion. Incorporating up-to-date data and country-specific situations, the present work covers all up-stream stages of the electricity life cycle before final consumption: coal mining, coal transportation, and coal power generation. The modeling results show that ultra super-critical systems (USC) have the highest life cycle energy efficiency due to the highest net generating efficiency and the lowest plant auxiliary power consumption among the cases examined. The global warming potential (GWP) scores show reverse dependencies of net generating efficiency. An integrated gasification combined cycle (IGCC) was demonstrated to be the cleanest technology and has the lowest scores in most of the life cycle impact categories, in particular in acidification potential (AP) and photo-oxidant formation potential (POCP). IGCC ranks as the highest in capital costs due to its complexity, while USC and super-critical systems are among the lowest in capital cost because of their commercialization in China. Evaluation of coal power generation combined with carbon capture and sequestration (CCS) shows that the CCS technologies can reduce the total life cycle CO₂ emission from coal power plants substantially, although higher levels of CO₂ are generated from the extra energy consumption by the CCS.

Introduction

Global coal consumption grew by 7.6% in 2010, which is the fastest global growth rate since 2003. Coal now accounts for 29.6% of global energy consumption, which is an increase from 25.6% in 2000. During this time, China's consumption grew by 10.1%. China has become the biggest primary energy consumer in the world, and 70% of that consumption is from coal (British Petroleum, 2011). In 2010, China consumed 48.2% of the world's coal and accounted for nearly two-thirds of global consumption growth (British Petroleum, 2011). A total of 48.0% of China's coal consumption is delivered to the power generation industry. By the end of 2008, the total installed power generation capacity in China reached 793 GW. The total electricity generation in 2008 was 3.4 trillion kWh, of which coal-based thermal power accounted for 81.0%. China has the third largest proven coal reserves in the world and proven recoverable reserves of 114.5 billion tons (the equivalent of 57.3 billion tons of oil), which is 13.9% of the world's total (British Petroleum, 2011). Coal is expected to play a crucial role as an abundant energy source in China over the long term. However, the huge amount of coal being combusted brings negative environmental impacts. China's total SO₂ emissions increased from 14.1 million tons in 1981 to 25.5 million tons in 2005 (China Environment Protection Statistical Yearbook, 2007). Acid rain effects have extended from the southwest region of the country to south of the Yangtze River to form four major acid rain control areas, accounting for 30–40% of the area of the country. Pollution has caused severe ecological damage and severely affected people's health. Coal has been identified as the source of 90% of the SO₂ emissions, 70% of the dust emissions and 67% of the NO_x emissions (Chen and Xu, 2010). China has committed to reduce greenhouse gas (GHG) emissions by 40–45% per unit of gross domestic product (GDP) by 2020, and the Energy Saving and Emission Reduction Strategic Policy is set to be soon put into effect (General Office of the State Concil, 2010). Therefore, both clean and advanced coal technologies are needed to properly utilize coal in an environmentally responsible manner while improving efficiency.

Remarkable progress has been made to reduce environmental pollution in China's power industry (Chen and Xu, 2010). However, many researchers focus on the energy balance without a systematic appraisal of the whole effect in terms of life cycle. Life cycle assessment (LCA) is a systematic analytical method that evaluates the overall influence of a technology.

A few recent life cycle studies have been conducted on coal power generation (Babbitt and Lindner, 2005; Di et al., 2005; Koornneef et al., 2008; Korre et al., 2010; Liu et al., 2009; Nie et al., 2011; Odeh and Cockerill, 2008a,b; Ou et al., 2011; Xiao et al., 2011, 2005; Zhou and Liu, 2011). Nie et al. and Korre et al. performed life cycle assessments and comparisons of oxy-fuel and post-combustion carbon capture and sequestration technologies (Korre et al., 2010; Nie et al., 2011). Odeh and Cockerill created a life cycle model for UK coal power plants (Odeh and Cockerill, 2008a), and further investigated the reduction of GHG by implementing CCS technology (Odeh and Cockerill, 2008b). Koornneef et al. performed comprehensive research on pulverized coal power plants with post-combustion capture, transport and storage of CO₂ (Koornneef et al., 2008). Babbitt et al. reported on the life cycle inventory of coal electricity generation in Florida, U.S. (Babbitt and Lindner, 2005). Zhou et al., Xiao et al., and Di et al. have conducted life cycle studies on China's coal power generation (Di et al., 2005; Xiao et al., 2011; Zhou and Liu, 2011). However, these previous works either focus on GHG emissions (Korre et al., 2010; Nie et al., 2011; Odeh and Cockerill, 2008b) or only partially cover the complete life cycle of coal power generation. There are only two studies including ultra super-critical (USC) technology, which is the state-of-the-art and plays an important role in China's power industry (Koornneef et al., 2008; Zhou and Liu, 2011). However, the USC case examined in Koornneef et al. is set to be installed in the 2011–2013 timeframe, and emissions data from Zhou and Liu deviate considerably from current operating projects. The coal power generation technologies in Xiao et al. (2011) and Di et al. (2005) are mainly sub-critical units, and SO₂ and NO_x removing technologies, such as flue gas desulfurization (FGD) and selective catalytic reduction (SCR), are not included. There is no published researched on life cycle assessment that reports the current circumstances and development of clean coal power generation in China.

This paper presents complete life cycle modeling and a comparative assessment of clean coal power generation technologies. In this study, a life cycle assessment (LCA) is adopted for energy and environment analysis, followed by a brief economic discussion. By using up-to-date data and incorporating country-specific situations, this work covers all up-stream stages of the electricity life cycle before final consumption: coal mining, coal transportation, and coal power generation. It is intended to provide a systematic, effective and realistic judgment on China's coal power industry, which can then be used as a scientific basis for future development strategies and policies.