ADVANCED COMBUSTION SYSTEMS - BASICS

• Q: What is advanced combustion?
  
  A: State-of-the-art, coal-fired boilers use air for the combustion of fuel. However, advanced combustion power generation burns fossil fuels in a high-oxygen concentration environment, rather than air. This strategy eliminates most, if not all, of the nitrogen found in air from the combustion process, resulting in flue gas composed of carbon dioxide (CO₂), water, contaminants from the fuel (including coal ash), and other gases that may infiltrate the combustion system. The high concentration of CO₂ (approximately 70 percent), along with the absence of nitrogen, simplify separation of CO₂ from the flue gas for storage or beneficial use. Thus, oxygen-fired combustion is an alternative approach to post-combustion capture for CO₂ storage from coal-fired systems. Examples of advanced combustion systems technology include oxy-combustion and chemical looping combustion. For further information, see:
  - Advanced Combustion Systems
  - Advanced Combustion Systems Technology Program Plan
  
  
• Q: How does oxy-combustion work?
  
  A: In oxy-combustion systems, oxygen is delivered to the boiler in a nearly pure state, rather than in air, eliminating nitrogen from the system and producing a flue gas composed primarily of carbon dioxide (CO₂) and water. The advantage of these advanced combustion systems is that the high concentration of CO₂ in the flue gas reduces the cost and improves the performance of the CO₂ capture process. Today’s oxy-combustion technology requires the recycle of about three-quarters of the flue gas to control combustion temperatures and employs conventional oxygen production technology, an air separation unit operating a cryogenic distillation process. For further information, see:
  - Oxy-Combustion
  - Advanced Combustion Systems Technology Program Plan
  
  
• Q: How does chemical looping combustion work?
  
  A: Chemical looping combustion systems produce the oxygen necessary for combustion internal to the process via the oxidation-reduction cycling of an oxygen carrier, usually a solid, metal-based compound. This allows the combustion process to be split into reduction and oxidation reactions in different reactors. The advantage of this technology is that oxygen can be separated from air without the large capital and energy costs associated with conventional oxygen production. Furthermore, combusting the fuel via oxygen supplied by the oxygen carrier prevents the introduction of nitrogen, resulting in a flue gas stream of concentrated carbon dioxide (CO₂) with water that can be purified, compressed, and sent for storage or beneficial use. For further information, see:
  - Chemical Looping Combustion
  - Advanced Combustion Systems Technology Program Plan
  
  
• Q: What could an advanced combustion power plant look like?
  
  A: An oxy-combustion power plant built today with equipment that is currently available at the scale necessary for power plant applications could include a cryogenic process for oxygen separation, atmospheric combustion for fuel conversion in a conventional supercritical pulverized coal boiler, substantial flue gas recycle, conventional pollution control technologies, and mechanical compression for carbon dioxide (CO₂) pressurization. An oxy-combustion power plant with advanced technologies still under research and development (R&D) could include advanced oxygen production such as a membrane-based oxygen separation process, a pressurized oxy-combustion boiler, minimal flue gas recycle, advanced pollution controls, and an advanced compression technology such as supersonic shockwave compression. Furthermore, a power plant employing chemical looping combustion would replace the air separation unit and oxy-combustion boiler with a chemical looping combustion system while also using advanced pollution controls and advanced compression technology. For further information, see: DOE/NETL Advanced CO₂ Capture R&D Program: Technology Update.
  

ADVANCED COMBUSTION SYSTEMS - ENVIRONMENT

• Q: What are the environmental benefits of advanced combustion?
  
  A: Advanced combustion systems have significant environmental benefits. Advanced combustion power plants produce flue gas that is rich in carbon dioxide (CO₂), but the separation of CO₂ from this concentrated stream is much simpler than for more dilute air-fired conventional combustion systems. A co-benefit of advanced combustion systems is the dramatic reduction in the emission of conventional pollutants (such as carbon monoxide, nitrogen oxides, volatile organic compounds, particulate matter, sulfur dioxide, and hazardous air pollutants) achieved through advanced flue gas purification. For further information, see: Advanced Combustion Systems Technology Program Plan.
  
  
• Q: What is the difference between advanced combustion and other technologies for capturing carbon dioxide?
  
  A: The primary advantage of advanced combustion systems is that the flue gas has a carbon dioxide (CO₂) concentration at or above 70 percent, with the remainder being primarily water. This simplifies the CO₂ capture process relative to fossil fuel-based power plants with post-combustion CO₂ capture, in which the proportion of CO₂ is much more dilute, ranging from approximately 4 to 15 percent. The high concentration of CO₂ in flue gas from advanced combustion power plants significantly decreases the cost and energy demands of the carbon capture system. For further information, see:
  - Advanced Combustion Systems Technology Program Plan
  - DOE/NETL Advanced CO₂ Capture R&D Program: Technology Update
  
  
• Q: How can advanced combustion performance be improved?
  
  A: Advanced combustion system performance can be improved by integrating advanced technologies which will reduce cost and improve efficiency. Advanced technologies under development include pressurized oxy-combustion, which will reduce boiler size and improve heat recovery, reducing cost and improving efficiency. Advanced membrane-based oxygen separation processes will reduce the cost and energy demands of oxygen production systems. Advanced flue gas purification technologies will leverage pressurized operation to capture pollutants at pressure, also reducing cost and improving efficiency. Chemical looping combustion will significantly reduce cost and improve efficiency by eliminating the oxygen production system. For further information, see:
  - Advanced Combustion Systems
  - Advanced Combustion Systems Technology Program Plan
  
  

ADVANCED COMBUSTION SYSTEMS - INDUSTRY

• Q: Are there any operating oxy-combustion power plants?
  
  A: There have been a number of pilot tests of oxy-combustion worldwide, including in the United States, Germany, Australia, Spain, China, and the United Kingdom. There are three commercial-scale demonstrations of oxy-combustion power plants which will capture and store carbon dioxide (CO₂) in various stages of planning: one each in the United Kingdom, China, and Korea. For further information, see:
  - Advanced Combustion Systems Projects
  - Power Plant Carbon Dioxide Capture and Storage Projects
  
  
• Q: Are there any operating chemical looping combustion power plants?
  
  A: No. While research and development (R&D) efforts in chemical looping combustion technology in the United States and worldwide are significant in number, the current testing of the technology is at a size far below commercial-scale power plants. For further information, see:
  - Advanced Combustion Systems Projects
  - Advanced Combustion Systems Technology Program Plan
  
  
• Q: Does advanced combustion have retrofit potential?
  
  A: Yes. Current oxy-combustion technology can be configured for retrofitting existing coal-fired power plants, as well as for use in new plants. However, advanced oxy-combustion or chemical looping combustion technologies would require new equipment for most major system components. For further information, see: Advanced Combustion Systems Technology Program Plan.
  
  

ADVANCED COMBUSTION SYSTEMS - NETL R&D

• Q: What is DOE doing to make advanced combustion technology less expensive and clean?
  
  A: The U.S. Department of Energy (DOE)/National Energy Technology Laboratory (NETL) is currently funding the development of advanced combustion technologies that have the potential to provide step-change improvements in both cost and performance as compared to the current state-of-the-art oxy-combustion systems. The research and development (R&D) efforts are focused on pressurized oxy-combustion, chemical looping combustion, and improvements to ancillary components, such as oxygen production and pollutant control. In addition, R&D efforts also focus on seeking out novel advanced combustion concepts that improve the cost and performance of power generation in a high-oxygen concentration environment and facilitate carbon capture and storage (CCS). For further information, see: Advanced Combustion Systems.