Several variants of oxy-fuel combustion systems have been proposed and are under development for retrofit or for new applications in power plants. The initial process proposed for the first generation of these systems introduced the concept of burning fossil fuels with oxygen in a power-plant boiler. This is done using flue gas recycling to moderate the temperature, but without any integration of the air separation unit (ASU), the compression unit, and the different mass and heat streams within the overall process. Because this approach was not optimized, it led to an energy-intensive and costly approach to oxy-fuel combustion and system development.

The next step forward in developing an oxy-fuel system, which has currently been adopted by power plant designers, includes integration of the ASU and the compression unit, as well as mass and heat streams, in order to minimize energy loss and improve the overall system efficiency. Several studies, including bench- and pilot-scale research, are in pursuit of this goal. However, opportunities to further improve the oxy-fuel systems and their integration still remain open as areas for research and system development.

CanmetENERGY is currently working on the new generation (or third generation) of oxy-fuel systems to explore the possibilities of minimizing or totally eliminating the flue gas recycled from oxy-fuel systems. If successful, drastic reduction (up to 80%) of the plant size and further improvement in the plant efficiency and cost (both capital and operating) can be achieved. The objective of this research, which is still in its initial stages, is to eliminate the need for the temperature moderator. This requires extensive improvement in material and equipment design prior to system implementation.

Next Generation Hydroxy-Fuel Combustion Burner

Another variant of third generation oxy-fuel systems is hydroxy-fuel combustion. In this combustion mode, fuel and pure oxygen are combusted without flue gas recycling. The temperature moderator employed is either water or steam. This configuration has the advantage of lowering the gas mass flows in the system up to threefold, which achieves savings in capital costs while permitting the use of current materials. In turbine applications, hydroxy-fuel combustion will require the development of novel turbomachinery capable of generating power from the expansion of a steam/gas mixture.

At our state-of-the-art Vertical Combustor Pilot-Scale Research Facility, we have recently developed a novel hydroxy-fuel burner prototype. The burner has been designed for the combustion of various fuels, such as natural gas, oil, bitumen, emulsion, pulverized coal and coal slurry. The burner operates at 1mmBtu/hr (0.3MW_th), and its operational modes include air, oxygen/steam, oxygen/recycled flue gas, oxygen/CO₂, oxygen/steam/recycle flue gas, and oxygen/steam/CO₂. All aspects of the hydroxy-fuel design process, including technology development, and implementation were performed at CanmetENERGY.