Oxy-fuel combustion, the burning of a fuel in the presence of oxygen instead of air, has been used previously and shows promise for becoming a successful post-combustion CO2 capture technique. It is currently being considered by the U.S. Department of Energy’s Innovations for Existing Plants Program to meet the goal of capturing 90 percent CO2 capture without increasing the cost of electricity more than 35 percent[1]. In a power generation system, implementing oxy-fuel combustion technology could potentially reduce negative environmental impacts of fossil fuel use and also encourage the use of reliable and domestic energy sources[1-3].
A major advantage of oxy-fuel combustion is the system’s ability to produce energy while minimizing the emission of greenhouse gases, which have been known to have a significant effect on the climate. The primary products of the oxy-fuel combustion system are CO2 and H2O. CO2 can be easily separated by condensing the water from the exhaust stream and eventually stored underground,
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The Jupitar Oxygen Corp. developed an oxy-fuel system that uses an untempered high temperature oxy-fuel flame, currently on the market for environmentally sound energy production[4-5]. The U.S. Department of Energy has investigated the performance of CO2 and H2O diluted oxy-fuel combustion systems in a high pressure combustor[6]. The equivalent air-flame temperature is achieved by the addition of recycled CO2 and H2O gases into the feed stream. The dynamic stability of oxy-fuel flame is primarily controlled by the percentage of oxygen in the fuel mixture[7]. For both turbine cycles and pulverized coal-fired plants, several combustor operability issues, such as heat transfer characteristics, heat loading, flame stability and flashback, become important with the transition from air to oxygen-based combustion[8-9]. To be used effectively and meet sequestration goals, however, the fundamental flame characteristics relevant to oxy-fuel combustion are needed to develop new designs and analyze retrofits on existing power generation plants. Therefore, this study presents the fundamental flame characteristics and combustor operability issues of oxy-fuel combustion.
Development of a burner system
A burner facility was designed and developed in order to investigate the flame stability characteristics using different diameter burners. A laboratory scale burner was designed and fabricated based on its capability to withstand the higher oxy-fuel flame temperatures, which were calculated to reach as high as 3,600K. A finite element analysis of the designed burner, under thermal stress, was carried out using NASTRAN 6.1. The purpose of this numerical analysis was to ensure that the burner could withstand the high thermal load. Figure 1 presents the final design of the tubular burner used for the experiments. The tubular burner system consists of three primary components: (a) platform, (b) mixing manifold and (c) burner tube assembly. The tube assembly section merges with the adapters to accommodate tubes of different diameters.
Experimental setup
Figure 2 shows the complete experimental setup for oxy-fuel flame stability and flame length measurements. The fuel used for these experiments were methane and oxidants O2 and CO2.
Research grade fuel and oxidant were delivered to the burners from pressurized tanks. Manual precision metering valves, in conjunction with low-torque-quarter-turn plug valves, were used to control and meter fuel and oxidant flow rates. A bank of digital mass flow controllers was used to measure mass flow rates of fuels and oxidant composition. Prior to each experiment, mass flow meters were calibrated using a laser-based mass flow meter calibrator. In the burner system, premixed fuel and oxidant entered into the manifold through 4 alternate injection holes. A flame arrestor device was positioned in the line before the manifold for safety. After the premixing section, the fuel and air mixture was ignited with an external ignition source. The resulting flame was analyzed with the use of a high-resolution digital camera set to a shutter speed of 1/5 second.
