Solid accumulation characteristics was examined in a 240mm dia. and 2720mm high reactor of 2.4ton/day NKK direct coal liquefaction process. The characteristics was largely influenced by gas flowrate. No solid accumulation was observed at gas feedrates higher than 400Nm3·h-1. At a low gas feedrate of 300Nm3·h-1, the axial temperature profile in the reactor was not uniform and solid accumulation occurred due to insufficient fluid mixing. The accumulated solids were found to be mainly composed of two types of compound, which were small pieces of metal iron generated from ball mill for coal slurry prearation and agglomerates of sulfides of liquefaction catalyst and metal iron. The composition of solids obtaind in the present reactor was diffrent from those in other coal liquefaction plants, which mainly arised from formation and agglomeration of mineral matter such as CaCO3. The characteristics of solid accumulation was well simulated by a sedimentation-diffusion model with densities and linear velocities of gas and liquid under coal liquefaction condition, which were estimated on the basis of gas-liquid equilibrium. It was suggested from the model that ash accumulation is more hardly to occur in the present reactor under the conventional operating conditions than in the other coal liquefaction reactors.
In this study, we investigated the combustion characteristics of a gas turbine combustor using the spray combustion simulation method which had been developed by our group.As a result of the simulation, it was clear that the temperature distribution in the combustor was closely related to the combustion gas flow and the fuel droplets behaviors. We measured, moreover, the averaged temperature at the outlet and the mean temperature profile along the centerline of the combustor, and compared the measured data with the calculated results. As for the averaged temperature at the outlet, the simulation agreed with the measurements, but it could not predict well the temperature profile along the centerline, especially in the lower fuel feed rate. It was guessed that the discrepancy was caused by the measurement error of temperature due to the difficulty of measurement in the closed system and the calculation error in the complex flow field. We also tried to predict the NOx formation characteristic in the combustor and compared with the measured data of the NOx concentration in the exhaust gas. As a result, it was necessary to simulate both of thermal NOx and prompt NOx formation. Thus, we developed the prompt NOx formation model in which its complex formation mechanism was modeled simply.
The effects of operating conditions, air staging, limestone feed and coal types on N2O and NOx emissions were examined using an experimental bubbling fluidized-bed combustor. N2O emission level increased with decreasing in bed temperature and increasing in residual oxygen concentration and superficial gas velocity. Both of air staging and limestone feed into the bed were effective for reduction of N2O emission. In general, N2O emission increased with nitrogen content in coal, though no reasonable correlation has been found between NOx emissions and the nitrogen content. The emission levels of N2O and NOx from the bubbling combustion were compared with those from circulating combustion, which was reported previously. Although total emissions of N2O and NOx from both types of combustion were almost same level, N2O emission from the bubbling combustion showed lower level than that from the circulating combustion. The reason for the difference in the emission levels of N2O and NOx from both types of combution was qualitatively discussed to take into account both differences in flow dynamics of bubbling and circulating beds and in chemical reactions under heterogeneous and homogeneous systems.