By Xu Shisen
President, China Huaneng Clean Energy Research Institute
China has abundant coal reserves, but is short on oil and gas resources; therefore, its power generation fleet is expected to rely primarily on coal for the long term. However, coal-fired power generation can result in undesirable emissions such as particulate matter, SO2, NOx, Hg, and large quantities of CO2. As global environmental concerns mount, especially those related to climate change, controlling criteria emissions and greenhouse gas emissions has become increasingly important. How best to realize the goal of clean and efficient utilization of coal for electricity generation is a challenge facing China as well as the broader international energy community.
IGCC Can Be a Solution
Globally, integrated gasification and combined-cycle (IGCC) power plants are a potential option that would make possible lower-emissions, higher-efficiency coal utilization. However, costs must be decreased and reliability must improve before IGCC is ready for commercial application.
Emergence of IGCC
Research and development on IGCC began in the 1960s. Industry demonstrations started in the 1990s and commercial operation and further developments are now underway globally. IGCC technologies developed in the U.S., Europe,
and Japan share the following features:
- These countries regard IGCC technology development as an important part of their national energy strategies.
- Core technologies and key equipment are produced in their own countries or regions.
- Investment in demonstration projects has come from both governments and corporations.
- Through demonstration, project developers are hoping to commercialize their core technologies and become more competitive in the future.
To effectively meet the demands of the future IGCC market, GE (U.S.) and Siemens (Germany) respectively acquired their nationally developed coal gasification technologies. Along with the Mitsubishi Group (Japan), these companies have become global IGCC technology suppliers, offering two IGCC core technologies—coal gasification and syngas turbines.
State of IGCC in China
Currently, Chinese technology providers are able to design and optimize large IGCC power stations and provide gasification, syngas purification, waste heat boilers, steam turbines, air separation, and other systems and equipment for IGCC power stations. This lays a solid technical foundation for large-scale commercial construction and operation of IGCC power stations. In addition, China has recently seen breakthroughs in domestic gasification research and development. The two-stage dry pulverized coal pressurized gasification technology developed by the Huaneng Clean Energy Research Institute is competitive with internationally developed technologies in all key indices. Moreover, the design and manufacture of 1000-t/d and 2000-t/d gasifiers have been completed, which are being used in Inner Mongolia’s Shilin coal-to-methanol project and the CHNG GreenGen 250-MW IGCC power plant, respectively. The 1000-t/d and 2000-t/d multinozzle impinging stream coal-water slurry gasifiers developed by Yankuang and East China University of Science and Technology have also been placed into operation. However, gas turbine technology in China still lags behind systems developed internationally. Today the operating conditions for China’s systems are not yet suitable for the commercial application of low-heat-value syngas turbines for IGCC power stations. One ongoing project, however, is focused on the research, development, demonstration, and deployment necessary to advance Chinese IGCC systems.
The GreenGen Plan
In 2004, China Huaneng Group (CHNG) took the lead in putting forward the GreenGen Plan and joined with several power generation and coal-producing enterprises to launch an effort to demonstrate a coal-based power generation system with increased efficiency and near-zero emissions. The purpose of this plan was to research, develop, and demonstrate a new coal-based system that would include hydrogen production from coal gasification, power generation based on combined-cycle hydrogen turbines and fuel cells, and carbon capture, utilization, and storage (CCUS). The plan garnered support from China’s National 863 Program in the 11th and 12th Five-Year Plans.
The core technology for GreenGen is power generation based on IGCC—a well-known technology that includes gasification of coal to produce syngas, which is purified before being combusted to drive an electricity-generating gas turbine. The high-temperature exhaust gas from the gas turbine is utilized by a pre-boiler to produce steam, which then drives a steam turbine to produce additional electricity. Compared with supercritical pulverized coal combustion power generation, IGCC can be more efficient, may offer greater potential for improvements, and can be used to realize near-zero emissions, including increased ease of CO2 capture. Moreover, it can be combined with coal-derived hydrogen and fuel cell power generation technologies to form a more advanced and diversified energy production system. For these reasons, development of IGCC technologies is an important direction for the future of coal-based clean energy power generation in China.
GreenGen is being carried out in three phases. In Phase I, a 250-MW IGCC power station with proprietary technologies was constructed. In Phase II (currently underway), the key technologies involved in GreenGen will be further researched, developed, and demonstrated. Examples of key technologies include hydrogen production from coal gasification, the separation of H2 and CO2 (i.e., pre-combustion CO2 capture), fuel cell power generation, and CCUS. In Phase III, the plan is to build a 400-MW GreenGen demonstration project that will include full integration of key technologies, realizing high-efficiency coal utilization with near-zero emissions. During all phases the emphasis is on improving the technical reliability and economic feasibility of the GreenGen system in preparation for eventual deployment and widespread commercial use.
Progress to Date
From 2004 to 2008, CHNG completed the system design, equipment bidding, and all preliminary work for the 250-MW IGCC demonstration power station, which was sited in Tianjin. In May 2009, the project was approved by the National Development and Reform Commission, which made it clear that the core technologies should be domestically sourced. Construction began in July 2009 and was completed by September 2012. In November 2014 the plant successfully passed the standard test of 72 hours of continuous operation with another 24 hours of operation at full load. The IGCC facility was formally put into commercial operation in December 2012. Thus, as of late 2012, China joined the ranks of those countries that have mastered IGCC power station design, construction, and operation. This achievement marked a major breakthrough in China’s strategic effort to advance its clean coal power generation.
The overall system is based on a 2000-t/d two-stage dry pulverized coal pressurized gasification technology, a proprietary IGCC process design, and a power island with an E-class multi-shaft combined-cycle generating unit. This project realized independent development, design, manufacture, and construction. Many technologies had to be mastered to reach this stage, including the design of a large IGCC power station, gasification, purification, air separation, heat recovery boiler, and steam turbine power generation, all of which are important to further promoting clean coal power generation in China. As the technologies used for GreenGen were domestically sourced, China has also gained an enhanced capacity for independent innovation from project experience. Currently, the GreenGen IGCC demonstration power station has realized steady operation at high capacity (maximum 92% of design) for 29 consecutive days.
Since the successful completion of Phase I of the GreenGen Plan, CHNG has been actively pursuing Phase II: researching
and developing the key technologies within GreenGen. Specifically, with the support awarded under the 863 Program, CHNG is developing a pilot-scale system that will draw about 7% of the syngas from the GreenGen IGCC power station, shift CO and H2O to CO2 and H2, and then separate the CO2 from the H2 after desulfurization. The CO2 will be liquefied and used to explore how to enhance oil recovery with the end fate of the CO2 being geological storage. The separated H2-rich gas will be sent to the gas turbine for mixed firing after compression.
About 60,000–100,000 tonnes per year of CO2 will be captured and stored under the Phase II (CCUS) demonstration. Phase II will lay the foundation for subsequent research on CO2 capture for the entire IGCC power plant.
This demonstration of pre-combustion CCUS will boast the largest capacity and the most comprehensive process evaluation underway in China when it is in operation. Experiments will be undertaken under various loads and other operating conditions, paving the way for the exploration of low-energy consumption, high-recovery CCUS. With the research, development, and design of the demonstration plant for the CO2 capture technology already complete, the construction under Phase II began in early 2014. Since the sites for the oil displacement wells and CO2 storage were determined previously, CO2-EOR and CO2 storage experiments will be conducted as soon as the CO2 capture plant is ready.
Analysis of IGCC’s Technical Features
Table 1 lists the designed technical indices for the GreenGen IGCC Power Station. The designed power generation output is 265 MW, generating efficiency is 48%, power-supply efficiency is 41%, and coal consumption for power supply is 299 g/kWh.
Table 2 lists the actual technical indices of the GreenGen IGCC Power Station when it began operation. Compared with subcritical and most supercritical coal-fired units, GreenGen’s designed standard coal consumption of power supply is superior. However, it consumes more coal than a 1000-MW ultra-supercritical coal-fired unit. This can be attributed to the fact that the GreenGen IGCC power plant employs E-class turbines. If F-class, G-class, or even the higher-rated H-class gas turbines are subsequently employed, the efficiency of the GreenGen IGCC power station will increase markedly. In terms of parasitic power, the power consumption from the IGCC power station remains quite high as the air compressor and supercharger units of the power station are currently driven by electricity. If gas-fueled drives are adopted, the station’s power consumption rate is expected to fall from 28% to just 5%, making the plant even more efficient.
Table 3 includes a comparison of the designed indices of three typical advanced coal-fired power stations: the 1000-MW ultra-supercritical power plant of the Phase III Shanghai Waigaoqiao Power Plant, the 1000-MW ultra-supercritical air-cooled Ningxia Lingwu Power Plant, and the GreenGen 250-MW IGCC power plant. Currently, the GreenGen IGCC demonstration power station is competitive with the most advanced ultra-supercritical units in several technical indices. Similar to the standard coal consumption, use of higher-rated turbines would further improve the technical indices of the GreenGen IGCC facility.
Currently, the GreenGen IGCC Power Station emits 0.9, 47.87, and 0.6 mg/Nm3 of SO2, NOx, and particulate matter, respectively. The emission rates are far below the emissions of some of the most advanced coal-fired power stations in China and are competitive with advanced gas-fired units. With further possibility to improve on performance as the scale of the technology is increased, the GreenGen project has already demonstrated that gasification can be an efficient, low-emissions option for coal utilization in China and the world.
Plans for Future Development
Compared with the widely used and fully commercial pulverized coal-fired power plants, IGCC is less developed and in the demonstration stage in China. The high construction and operating costs are among the main obstacles for future development and deployment. It is a top priority to speed up development and demonstration of IGCC technology in China and to promote the technology based on the following:
- Use high-temperature and high-pressure gas turbines to improve IGCC efficiency. If G-class or even H-class gas turbines are used, IGCC power stations could become much more efficient (reaching 58%), making IGCC increasingly competitive.
- Reduce the construction costs for IGCC power stations. Increasing the scale of equipment produced in China, coupled with standardized designs and integration of chemical and power industry standards, will considerably reduce construction costs and thus accelerate the commercialization process.
- Increase the rate of the development of IGCC technology and the building of demonstration projects through support of several large-scale IGCC commercial demonstration power stations. This will advance relevant technologies and the mass production of equipment, so as to bring down specific investments and power generation costs.
- Develop integrated IGCC/polygeneration systems to realize diversified production of chemical products, fuels, and power as end products and thus improve the overall cost-effectiveness of the IGCC system.
- Strengthen research into and demonstration of IGCC-based CCUS technologies to lay a solid foundation to scale up coal-based energy power generation with near-zero emissions and drastic reductions of greenhouse gases in the future.
Future Plans for GreenGen
Based on the success of GreenGen Plan Phase I, CHNG is now executing Phase II with plans to subsequently move forward with Phase III. The steps involved in Phase II and Phase III are detailed below:
Phase II (2013–2017): Carry out trial operations and optimize to improve the existing systems and key equipment and further improve the operating safety, stability, and reliability of the individual units within the overall process. Research and develop IGCC-based CCUS technologies and advance fuel cell and hydrogen-enriched gas combustion technologies. Conduct feasibility studies on large-capacity, high-parameter IGCC and CCUS. Begin preliminary preparations for GreenGen Phase III.
Phase III (2018–2025): The plan is to build a 400–600-MW GreenGen demonstration plant that will include integration of key technologies such as IGCC, CCUS, fuel cell power generation, and combined-cycle power generation based on hydrogen-rich turbines and polygeneration. This demonstration plant will realize efficient coal-fired power generation with near-zero emissions of all major pollutants and CO2. Meanwhile, efforts will be made to continuously improve the cost-effectiveness and competitiveness of GreenGen-based IGCC units in preparation for widespread commercial deployment.
A Common Objective
With Phase I complete and Phase II successfully underway, the GreenGen project team is moving forward with the objective that this project can become the benchmark for commercial-scale, cost-effective, near-zero emissions, coal-based power generation. This is a goal that, if realized, would offer much strategic value not only to China, but to the world.