Ariel Green; Taylor Schroedter, Brigham Young University
Most high-pressure combustion systems use water slurries to transport coal particles to the combustor. This is inefficient as a fraction of the energy released during combustion must be used to vaporize the water. Transporting coal with a gas would minimize this energy loss and improve combustor efficiency. However, transporting densely packed particles with gas at high pressure is challenging. This research evaluated the feasibility of using gas to transport dense phase coal through a simple pipe and identified the preferred initial coal distribution in the pipe to reduce particle removal times. CO2 was used to push coal through a 10-cm long, 0.635-cm diameter pipe to test the removal time when the gas mass flow rate and the initial position of coal particles was changed. Using Barracuda computational fluid dynamics (CFD) software, cases with differing flow rates and initial coal positions were simulated until 99% of the coal particles had exited the pipe. The time for removal was compared for each case. It was found that a greater gas mass flow rate will remove the coal particles from the pipe faster. At lower mass flow rates, a large amount of particles exited quickly, but the coal remaining trickled out very slowly, elongating the removal time and weakening the transport efficiency. More total energy would be required at the lower mass flow rates for the remaining particles to be slowly removed. Furthermore, the initial position of the coal particles proved to be a very impactful variable. When the mass of particles was distributed in half of the pipe from bottom to top, more time was required for 99% removal at every gas mass flow rate. Because of the set-up, particles had to essentially climb over one another to leave the pipe. This caused a build-up at the end of the pipe that took a long time to empty. Distributing the same amount of particle mass in the first half of the pipe from left to right resulted in much shorter times to empty. The trends identified with the test data can be extrapolated to larger systems to find the ideal method to fully remove coal from a pipeline and into a combustion chamber when using carbon dioxide gas.