Full Length ArticleOxy-CFB combustion technology for use in power-generation applications
Introduction
It is true that coal has traditionally been identified as a key energy source for industrial development in several countries. However, its consumption has witnessed significant changes in recent years owing to increased greenhouse-gas (GHG) emissions and environmental pollution. Increase in shale-gas production in the United States (US) as well as advancements in the use of renewable energy sources have led to a rapid decline in coal-fired power generation. Twenty-three countries, states, and cities, including Britain, Canada, France, Italy, Mexico, Denmark, and California have announced their plans to end coal-power consumption by 2030 [1]. The global steam coal consumption in 2016 was reported to be 5622.3 million tons—a 3.9% (229.8 million tons) drop compared to 2015—with China reporting the largest drop—181.9 Mt. Additionally, coal consumption has declined in US, Japan, and Russia, whereas that in India and Indonesia has increased by 2% and 4.4%, respectively. It is noteworthy that US witnessed a 50.3-Mt drop in coal consumption, thereby demonstrating the impact of shale-gas production in the country [2].
Changes in global coal consumption are influenced by economic growth in emerging countries. In fact, because coal-power plays a major role in the industrial development of emerging economies, the demand for coal-based power generation is expected to increase, despite reduced coal consumption in organization for economic cooperation and development (OECD) countries. China and other emerging economies accounted for nearly 76% of the global demand for coal in 2016 owing to their focus on expansion of their installed coal-based power-generation capacity. In 2018, new coal-based power plants having 220-GWe capacity have been reportedly built in Asia. India is setting up new coal-based power plants of 50-GWe capacity, whereas Indonesia, Taiwan, Vietnam, Malaysia, and the Philippines are keen on expanding their existing fleet coal-based power-generation facilities. Unless carbon emissions are strictly regulated and implemented globally, emerging economies may not be able to reduce their coal consumption owing to increased cost of harnessing energy from other sources. Countries facing a high energy demand may find it difficult to build an energy portfolio based on natural gas or renewable energy [3].
By 2030, the Korean government is aiming to generate 20% of its total energy demand by harnessing power from renewable resources along with 37% reduction in GHG emissions, compared to business as usual (BAU), 2005. However, given that Korea fulfils 96% of its total energy demand via overseas import, and that the demand for electric power has witnessed a sudden rise, success of the government's above-mentioned energy policy depends on their future coal-fired power-plant utilization, which presently accounts for 40% of Korea's installed power-generation capacity [4]. Soon, intermittent renewable energy such as solar and wind dominates power stability, and the use of bioenergy in the power sector will continue to increase. This is because biomass is the most widely available alternative to fossil fuels, while at the same time enabling the most stable renewable energy-based generation to address the intermittence issues. In terms of large amounts of biomass to be utilized, CFB technology is an excellent option because it is suitable for low-rank fuel utilization, and flexible operation is possible through large-scale heat storage using external heat exchangers. Furthermore, Oxy-CFB technology is a promising technology to reduce GHG emissions by using coal or even replacing it with alternative fuels. In case of implementing bioenergy energy carbon capture and storage (BECCS) technology, it is the best thermal power generation option through negative carbon emission while facilitating renewable energy generation [5], [6].
The Future Energy Plant Convergence Research and Development Center (FEP CRC) was established in 2015 to develop ingenious thermal power-generation systems to solve problems associated with the Korean energy sector. Using their proposed Oxy-CFB technology, the said center aims to develop clean and efficient energy solutions in collaboration with four research institutes—the Korea Institute of Energy Research (KIER), Korea Institute of Industrial Technology (KITECH), Korea Institute of Standards and Science (KRISS), and Korea Institute of Machinery and Materials (KIMM). As part of this initiative, on-site research and development (R&D) is currently underway in the KIER campus. Moreover, several universities and corporate organizations contributed to this research project by performing basic research, numerical simulations, and R&D for commercialization of Oxy-CFB technology.
Table 1 summarizes R&D projects performed globally under the purview of the Oxy-CFB initiative. Most of these studies were performed in Europe, North America, and China. As a representative study, a 30 MWth Oxy-CFB system was developed by the Spain-based Fundación Ciudad de la Energia (CIUDEN). In collaboration with the European Union (EU), this project investigates design and operation technologies for testing the Flexi-Burn™ carbon capture CFB technology, thereby resulting in realization of a second-generation Oxy-CFB system capable of operating at oxygen concentrations of 40% or more in the oxidizer. Based on this, we proposed a 300-MWe commercialization project (Compostilla OxyCFB300) [7], [8], [9], which is still in its planning phase, because such a large-capacity oxy-combustion power plant requires a clear CCS site to handle emitted CO2 as well as the credit for CO2 reduction. CanmetEnergy in Canada has performed extensive research pertaining to the Oxy-CFB technology. Recently, Gas Technology Institute (GTI) and CanmetEnergy have developed a pressurized Oxy-CFB technology having 1-MWth capacity, and a 15-MWth class demonstration of the same is currently under development.
Tampere in Finland hosts the second-largest Oxy-CFB operational unit in the world with 4-MWth capacity, and Valmet operates the same. Studies have been performed to investigate the effect of solid concentration and temperature on in-furnace heat transfer at different oxygen concentrations. Moreover, a mathematical model has been developed to incorporate combustion, fluid-dynamic, and heat-transfer parameters, and the same has been validated using data from the demonstration plant. Performance tests have been performed to investigate commercial-scale Oxy-CFB boilers using an in-house 1.5-D model [10], [11], [12]. Owing to its large CFB-boiler market, China has the Oxy-CFB technology development underway across several organizations [13], [14], [15], [16]. The Institute of Engineering Thermophysics conducted a 1-MWth pilot plant experiment, and the Southwest University houses 2.5-MWth oxy-fuel combustion facilities, the experimental setup for which was manufactured by Babcox & Wilcox [17].
Section snippets
Research activities at FEP CRC
Fig. 1 shows the representative FEP CRC research topics. A wide range of usable fuels and environment-friendly combustion are major reasons for the increased popularity of CFB boilers in relevant markets—from large coal-fired power plants to small- and medium-sized biomass and waste-heat recovery systems. Despite several advantages afforded by CFB, its successful implementation involves few challenges—development of large USC-scale power plants; combustion problems caused by use of low-grade
Development of numerical-simulation technologies for CFB boilers
Numerical simulation of fluidized bed systems plays an important role in experimental result analysis as well as reactor-design verification. In this project, 1D and 3D numerical-simulation techniques have been developed. Based on experimental results obtained at the 0.1-MWth test rig, 2-MWe plant, and during commercial CFB boiler operations, numerical models of CFB boiler under air- and oxy-combustion conditions have been investigated. Additionally, numerical-simulation-based
Summary and future prospects of oxy-combustion technology
Although the introduction of CCUS technology is essential, as regards the future of thermal power plants, R&D efforts to this end have considerably reduced. This can be attributed to the lack of international cooperation with regard to reducing GHG emissions in response to climate change as well as the failure to develop technologies vital for successful implementation of CCUS. Commercialization of first-generation oxy-combustion technology failed owing to the efficiency-penalty problem
CRediT authorship contribution statement
Changwon Yang: Data curation, Software, Writing - original draft. Yongdoo Kim: Writing - review & editing. Byeongryeol Bang: Software, Validation. Soohwa Jeong: Formal analysis, Writing - review & editing. Jihong Moon: Investigation, Writing - original draft. Tae-Young Mun: Investigation, Writing - original draft. Sungho Jo: Investigation, Validation. Jaegoo Lee: Supervision. Uendo Lee: Validation, Writing - original draft, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was supported by the National Research Council of Science & Technology (NST) grant from the Government of Korea (MSIP) [grant no. CRC-15-07-KIER]. The authors thank Dr. J.K. Choi, for providing drawings describing FEP CRC research targets.
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