Technology for removal of carbon dioxide from flue gas streams was developed for use in the beverage industry. In 1989, Fluor Corp. purchased from Dow Chemical Co. the license for a CO2-capture technology. Today, post-combustion carbon capture is being considered as one of the technologies to reduce carbon emissions at coal-fired power plants. This represents challenges that impact many parts of modern power plants and has created activity and investment in research.
The most significant challenges for coal applications are approaches that reduce the requirements for process steam and electrical power. Affordable carbon-capture technologies with proven commercial experience will have the upper hand. Benefits to power generators that might be required to capture carbon will be in future developments and a potentially shorter scale-up timeline than other carbon-capture processes such as oxy-fuel and pre-combustion.
Econamine FG PlusSM Process Technology Background
The Econamine FG PlusSM technology is a proven technology of the carbon-capture industry. It is the first and most widely applied process that has extensive demonstrated operating experience in the removal of CO2 from high oxygen content flue gases (up to 15 volume percent). The flow diagram is similar to gas-treating processes, which have been practiced for many years. Simple, reliable equipment that is well-known to gas-treating operating personnel is used. Figure 1 shows a typical flow diagram. The technology does not require a custom-manufactured or expensive solvent. The main ingredient is readily available, inexpensive and produced worldwide.
While many CO2-removal technologies are being researched through laboratory and pilot-scale testing, this amine-based technology has a significant operating history at commercial facilities collecting CO2 from multiple sources, including low CO2 concentration flue gas (less than 3.1 volume percent) with high oxygen concentrations (greater than 13 volume percent). One of the most significant power applications of this CO2-removal system was the plant that captured 365 short tons per day of food-grade CO2 from the exhaust of the natural gas-fired power plant at the Bellingham (Mass.) Energy Center. Fluor designed and constructed the plant and maintained continuous operation from 1991 to 2005 (see Figure 2). The experience gained from the design, construction and more than 14 years of operation is used to further advance the technology.
Enhancements to the CO2-Capture Technology
An advanced simulator has been developed to account for mass transfer, heat transfer and reaction kinetics. This allows computerized testing of new configurations and advancements for further improvement. The Econamine FG PlusSM process has been improved through solvent and process enhancements to lower energy consumption and solvent loss. These enhancements along with advanced features are incorporated into the designs. The advanced features, most of which have been proven commercially, include:
- The solvent has been reformulated for greater CO2 carrying capacity (per solvent circulation rate), which results in lower energy cost for the CO2 capture.
- Absorber intercooling is used to optimize the temperature profile in the absorber for kinetic and thermodynamic (equilibrium) considerations.
- Lean vapor compression reduces the energy demand of regeneration.
- Advanced reclaiming technologies minimize reagent losses.
- Energy demand integration with the power plant cycle reduces the impact on the power plant.
- Large tower design reduces capital costs and space.
This list serves as a menu of some options from which a customized plant design can be developed. Each CO2-removal application has unique site requirements, flue gas conditions and operating parameters. Based on the given CO2-removal application, it might be beneficial to implement only some of the enhancement features. In this way, every plant will be optimized for its specific CO2-removal application.
Application at Coal-fired Power Plants
Provisions for addition of post-combustion CO2 capture can vary from being cognizant of the requirements for the design to full integration of the power, steam and cooling needs, as well as infrastructure for CO2 transportation.
At a minimum, the analysis and early decisions concerning CO2 capture with particular emphasis on the commercial post-combustion, carbon-capture technology should include in-depth analysis of the permitting requirements, plant arrangement and integration into the power plant (i.e., boiler, turbine, feedwater and condenser circuits, etc., to limit the impact on the power production of the generator and fully optimize the entire power generation system, carbon-capture system or both) and access for operation and maintenance.
Even with the deployment of proven technologies with high—efficiency, pollutant-removal technologies, impurities in the flue gas–particularly SOX, nitrogen dioxide (NO2), hydrogen chloride (HCl) and hydrogen fluoride (HF)–will lead to the formation of heat-stable salt (HSS) in the carbon-capture systems.
The HSS must be converted back into the base solvent in a reclaiming process. Fluor has assessed that it is often more cost-effective to reduce HSS precursors before the flue gas encounters the solvent.
The basic Econamine FG PlusSM technology has been demonstrated on coal-fired flue gas on a 5 Te/d CO2-capture test facility that processed a coal-fired flue gas for part of its limited test run at a Tokyo Electric Power (TEPCO) plant in Kawasaki, Japan.
In addition to extensive development programs, E.ON Energie AG is using the carbon-capture technology for a retrofitted demonstration plant that will commence operation in 2010 at E.ON’s coal-fired power plant in Wilhelmshaven, Germany. Econamine FG PlusSM advanced features will be incorporated into the demonstration plant that is designed to recover 70 Te/d CO2 from the flue gas produced by the Wilhelmshaven plant while processing 20,000 Nm3/h of power plant flue gas at a CO2 capture rate of at least 90 percent of the CO2 contained in that gas. This will be the first time that the advanced features of the Econamine FG PlusSM system are demonstrated on coal.
Further ongoing enhancements of the technology occur through select project applications. Numerous studies and proposals for applications have been completed for refineries, gas turbines and coal-fired power plants. Active engagement in the increasing wave of activity for potential implementation of CO2 capture to industry is essential. Table 1 shows a list of some of the studies and the range of potential application of post-combustion, carbon-capture systems for large and small plants and natural gas and coal-fired applications. It also illustrates the international concern for developing carbon-capture technologies.
Econamine FG PlusSM technology is a proven, cost-effective process for the removal of CO2 from low-pressure, oxygen-containing flue gas streams. The commercial performance has been demonstrated successfully for 20 years.
The consideration for integrating carbon capture into a power plant requires careful analysis and decision-making beyond adding space or capacity for electrical power and steam. These decisions can play an important part in reducing the impact to the plant and improve the economics of power production.
Important advances will reduce the steam and electric power requirements. Early decisions concerning CO2 capture should include in-depth analysis of the permitting requirements, plant arrangement and integration into the power plant (i.e., boiler, turbine, feedwater and condenser circuits, etc., to limit the impact on the power production of the generator and fully optimize the entire power generation system, carbon-capture system or both) and access for operation and maintenance.
Dennis W. Johnson is senior director of process specialty engineering, power, at Fluor Corp. Reach him at email@example.com.
Donald E. Broeils is vice president of plant betterment services, power, at Fluor Corp.
Satish Reddy is executive director of carbon-capture technologies at Fluor Corp. Reach him at firstname.lastname@example.org.
James H. Brown, PE, PMP, is director of engineering of the solid fueled projects business line, power, at Fluor Corp. Reach him at email@example.com.