1 Part-Load Simulations and Experiments of a Small Coal Gasifier

An oxygen-blown, coal powder-feed, entrained-flow demonstration gasifier was constructed and operated by the Industrial Technology Research Institute (ITRI) in Taiwan. Specific tests have been conducted to investigate the gasifier's performance and gain operation experience under part-load conditions either caused by reduced load demands or maintenance needs. Water spray near the exit of the gasifier was employed to test its feasibility in tuning H2 content or controlling gas exit temperature. To help understand the gasifying characteristics of various part-load conditions, computational simulation was conducted using the commercial CFD solver FLUENT. The 3-D Navier-Stokes equations and seven species transport equations were solved with eddy-dissipation combustion model. The simulation results provide the velocity, temperature, and species distributions inside the gasifier. The results indicate that water spray injection cools down the gas and increases H2 mole fraction at the cost of the reduction of CO and increased production of CO2. It is recommended that a better way to produce H2 is to inject steam near the feedstock injection ports where plenty carbon is available and temperature is high and favorable to produce H2 more efficiently via the gasification reaction without producing CO2. The simulated results were compared with the experimental data including situations when two of the three fuel injectors were under maintenance. Employing fuel injection through a single injector unexpectedly performs better than applying three injectors. The results indicate the injection velocity speed and momentum strength of each injector, rather than the total injection momentum, are more influential in affecting the gasification efficiency. The results of this study can be used to improve prediction of future part load performance