Oxy-fuel technology is characterized by the use of pure oxygen or oxygen-enriched gas mixtures to replace air during combustion of (most often) fossil fuels. After the fuel is burned, flue gas with a high concentration of CO2 is generated, which facilitates the capture of CO2. First proposed by Abraham in 1982, the purpose of the technology was to produce CO2 for enhanced oil recovery (CO2-EOR).1 As concerns related to climate change have intensified, the need to control CO2 emissions (as the principal greenhouse gas) has also gradually increased in prominence. As a technology option with great potential for reducing CO2 emissions, oxyfuel combustion has become a focus of research worldwide.2
THE STATUS OF INTERNATIONAL OXY- FUEL TECHNOLOGY DEVELOPMENT
Figure 1 shows the development status and capacity of oxy-fuel projects at various research institutions; projects range in scope from laboratory scale to commercial applications. Some projects began as early as the 1980s. The principal research institutions and companies advancing oxy-fuel technologies include the following: Energy & Environmental Research Center, Argonne National Labs (ANL), Babcock & Wilcox (B&W), Air Products, and Jupiter Oxygen in the U.S.; IHI and Hitachi in Japan; Canmet in Canada; International Flame Research Foundation in the Netherlands; BHP Billiton, Newcastle University, and CS Energy in Australia; CIUDEN in Spain; Alstom in France; Doosan Babcock in the UK; and Vattenfall in Germany. Extensive research, development, and demonstrations are also occurring in China (shown in red in Figure 1), which are discussed in detail in later sections.
FIGURE 1. Status of international oxy-fuel project research. (Projects conducted in China are shown in red.)
“Following 30 years of development, oxy-fuel technology has matured and possesses the fundamental characteristics necessary for commercial application.”
Pilot-Scale Demonstrations
Since 2005, oxy-fuel pilot projects have significantly advanced the overall technology. Table 1 lists the pilot projects at the tens of MWe scale that are under construction or have been completed. These include the world’s first 10-MWe oxy-fuel comprehensive process test installation, built by Sweden’s Vattenfall in 2008 in Schwarze Pumpe, Germany. The world’s first 30-MWe oxy-fuel pilot power plant, which also boasted the world’s largest capacity, was completed by Australia’s CS Energy in 2011 in Callide. The 7-MWe oxy-fuel pulverized coal boiler and world’s first 10-MWe oxygen-enriched fluidized bed pilot were completed at CIUDEN’s Technology Development Center in 2012 in Spain. In China, the first 12-MWe oxy-fuel power installation will be completed by the end of 2014.
Large-Scale Demonstrations
Table 2 lists the large-scale oxy-fuel pilot projects being conducted globally. In 2003, the U.S. government announced plans to construct a zero-emission plant based on coal gasification; the project was named FutureGen. After more than seven years, the direction of this project changed. In August 2010, the U.S. Department of Energy launched FutureGen 2.0, which was based on carbon capture from oxy-fuel coal combustion. US$1 billion (the total budget for the project is now $1.3 billion) was allocated for the construction of a 200-MWe (now adjusted to 168-MWe) commercial-scale oxy-fuel power station. The objective is to obtain 90% carbon capture and remove most of the pollutants, including SOx, NOx, Hg, and particulate matter.
TABLE 1. Completed and planned oxy-fuel pilot projects
The UK power company Drax also announced its White Rose commercial-scale 426-MWe oxy-fuel carbon capture demonstration project. The Yorkshire-based project obtained official support from the UK’s Department of Energy & Climate Change in December 2013. A front-end engineering design (FEED) study is currently being conducted.
South Korea is also actively making progress on an oxygen- enriched coal-fired power station demonstration project—the country plans to build a 100-MWe pilot power station by 2015.
In China, several large-scale oxy-fuel projects are currently conducting pre-feasibility or feasibility studies, including the Shenhua Group’s 200-MWe Shenmu power plant, Sunlight Coking’s 350-MWe thermoelectric pilot, China Datang Corporation’s 350-MWe Daqing power plant, and Xinjiang Guanghui Energy’s 170-MWe pilot.
Among the aforementioned industrial-scale installations, a number of key components necessary for the oxy-fuel process have been verified. For instance, major power equipment manufacturers such as Alstom, IHI, Doosan Babcock, Hitachi, and B&W have completed evaluation tests on single 10-MWe oxy-fuel swirl burners that can be used in large-scale demonstrations.
Table 2. Large-scale oxy-fuel projects
Alstom has completed verification tests on a 15-MWth oxy-fuel tangential combustion system. Foster Wheeler has completed semi-industrial verification of a 10-MWe oxy-fuel CFB. Gas separation equipment suppliers Air Products, Linde, and Air Liquide have completed evaluation tests of compression/purification systems at the 10–30-MWth level. The success of these tests has laid the foundation for further large-scale projects.
THE CURRENT STATUS OF OXY- FUEL TECHNOLOGY IN CHINA
The foundation for Chinese oxy-fuel combustion research began in the mid-1990s. Huazhong University of Science and Technology (HUST) and Southeast University were the first institutions to focus on the desulfurization mechanisms and combustion properties of oxy-fuel combustion.4 In 2006, HUST obtained the support of the first National High Technology Research and Development Program for carbon emissions reduction and the first National Key Basic Research Development
Program for carbon emissions reduction, and launched a comprehensive national system for the research, development, and demonstration of oxy-fuel-based CO2 capture. Table 3 lists the major fundamental oxy-fuel combustion research projects supported by the Chinese government and industry.
HUST has already carried out much research and development work on basic oxy-fuel combustion, technology development, and pilot projects, which has largely driven oxy-fuel combustion technology development in China. Based on progress to date, HUST has developed a roadmap for oxy-fuel technology development in China (see Figure 2).
Laboratory- and Small-Scale Tests
Table 4 provides an overview of the oxy-fuel combustion small test systems (>10 kWth) that China has built or plans to build. Overall, there are two main approaches to oxy-fuel coal combustion (pulverized coal combustion and fluidized bed combustion). To support the development of the overall technology and key components, there has been significant oxy-fuel-related research activity and platform constructions.2
TABLE 3. Overview of fundamental oxy-fuel combustion research projects in China
FIGURE 2. Roadmap for research and development of oxy-fuel technology in China4
In 2006, HUST completed China’s first 300-kWth-test bed for oxy-fuel combustion and pollutant removal, achieving the objective of enriching high concentrations of CO2 (95%) and removing 85% of NOx and 90% of SO2.
In 2011, HUST completed construction of China’s first 3-MWth oxy-fuel whole process test platform in Wuhan (see Figure 3). This platform is currently China’s largest capacity oxy-fuel test platform, with a heat input of 3 MWth and an annual CO2 capture capacity of up to 7000 tonnes. This system first separates oxygen from air, then enriches, compresses, and purifies the CO2 generated during combustion. Thus the testing platform incorporates the comprehensive oxy-fuel combustion process. The system was designed in accordance with industry standards, and therefore possesses the capacity for deployment at increased scale. A number of key technological breakthroughs were achieved during the design, construction, and commissioning of the system.
Integrating the advantages and features of a circulating fluidized bed, Southeast University has conducted systematic studies of CFB oxy-fuel technology.6,7 A CFB oxy-fuel pilot test installation (50 kWth) was constructed, which was the first in China to genuinely achieve flue gas recirculation and the first internationally to be able to achieve wet flue gas circulation. The 2.5-MWth circulating fluidized bed oxy-fuel test system that Southeast University has built in partnership with B&W has been fully constructed and is currently being commissioned.
Industrial Pilots
In May 2011, HUST launched an industrial 12-MWe oxy-fuel pilot project (see Figure 4). The construction of this project was financially supported by China’s Ministry of Science and Technology, Dongfang Boiler Group Co., Ltd. (DBC), Sichuan Air Separation Equipment Co., Ltd., and Jiuda (Yingcheng) Salt Co., Ltd. The project involved rebuilding a 12-MWe oxy-fuel boiler in the salt company’s power plant. The system uses a swirl combustion system positioned on the front wall and is equipped with a cryogenic air separation system. The design of the boiler and system is compatible with oxy-fuel combustion. Evaluation tests can be conducted on air combustion as well as dry and wet circulation oxy-fuel combustion. After construction is complete, the pilot is expected to achieve a flue gas CO2 concentration higher than 80% and a CO2 capture rate greater than 90% at a CO2 capture capacity of 100,000 tonnes/ year. The captured CO2 can be stored in the mine shafts of the disused salt mine. In addition, some of the CO2 can also be used in the removal of calcium and magnesium during the salt manufacturing process. The project and its commissioning are expected to be completed by the end of 2014. CO2 capture, utilization, and storage (CCUS) will be incorporated during the second phase.
FIGURE 3. 3-MWth oxy-fuel comprehensive process test system (HUST)
TABLE 4. Overview of China’s oxy-fuel combustion small test systems (>10 kWth)
Demonstration-Scale Projects
Chinese companies are also actively preparing to launch large-scale oxy-fuel technology demonstration projects. Table 5 provides an overview of such projects.
In March 2012, Shenhua Group announced a project to integrate oxy-fuel combustion and carbon capture at the megatonne scale into a coal-fired power plant. To date more than 70 million RMB (US$11.5 million) has been invested.
FIGURE 4. Picture of 12-MWe semi-industrial oxy-fuel pilot installation (HUST)
This project aims to provide design and technology safeguards for the independent design, construction, and operation of megatonne-scale oxy-fuel projects. HUST, Dongfang Boiler Group Co., Ltd., and Southwest Electric Power Design Institute took part in the research for this project, which was officially launched in November 2012. To date, the project has involved comparing various options for new build and retrofit, techni- cal and economic evaluations, and preliminary research into key equipment such as boilers, burners, and smoke coolers.
Shanxi International Energy Group Ltd. (SIEG) has also announced a cooperative agreement with Air Products, under which Air Products’ exclusive oxy-fuel CO2 purification technology will be applied to SIEG’s 350-MWe oxy-fuel power generation demonstration project. Currently a feasibility study and the conceptual design of the installation are being completed. This project is based at SIEG’s power plant in Taiyuan, Shanxi and will be used to provide purified CO2 emissions for utilization and storage.
On 21 September 2011, China Datang Corporation signed a memorandum of understanding with France’s Alstom, forming a long-term strategic partnership to jointly develop CCS pilot projects in China. Under the memorandum, Alstom and China Datang Corporation will collaborate to develop two coal-fired power plant CCS demonstration projects. Of these, the 350-MWe coal-fired power plant located in Daqing will use Alstom’s oxy-fuel technology. A feasibility study is currently being carried out.
TABLE 5. Demonstration-scale oxy-fuel pilot projects in China
Xinjiang Guanghui New Energy Co., Ltd. has signed a strategic cooperation agreement with the U.S.-based Jupiter Oxygen Corporation for a carbon capture, energy conservation, and emissions reduction project. Jupiter plans to invest US$200 million in collaborating with Xinjiang Guanghui New Energy Co., Ltd. to build and develop a carbon capture and boiler retrofit project. Through this technical cooperation, Xinjiang Guanghui New Energy is expected to be able to reduce CO2 emissions by about 2.4 million tonnes yearly at its plant that produces 1.2 million tonnes of methanol and 800,000 tonnes of dimethyl ether plant each year.
OUTLOOK
Following 30 years of development, oxy-fuel technology has matured and possesses the fundamental characteristics necessary for commercial application. Importantly, it is suitable for existing coal-fired power plants. For China’s coal power-domi- nated energy mix to achieve greenhouse gas emission reduction targets, large-scale demonstrations must be launched as soon as possible, to allow for the greatest likelihood for the commercialization of oxy-fuel. At present, China has announced a succession of special CCUS plans. A number of ministries, including the National Development and Reform Commission, Ministry of Science and Technology, National Energy Administration, Ministry of Environmental Protection, and Ministry of Land and Resources, are promoting numerous strategies, including demonstration projects, technology research and development, environmental monitoring, storage uses, policies and regulations, and international cooperation.
Source: Zheng Chuguang - Professor, State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology Director, Advanced Coal Technology Consortium, Clean Energy Research Center
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