Teruyuki Okazaki

Improvements in Pyrolysis of Wastes in an Externally Heated Rotary Kiln

The effects of rotating speed and internal structure on the performance of an externally heated rotary kiln for waste pyrolysis were investigated. A newly developed method was adopted to evaluate the overall heat transfer coefficient km-w from the inner wall to the wastes for this purpose. The experimental results revealed that km-w monotonically increased with the number of lifters and their height. When six lifters 200 mm in height were attached to the inner wall of the kiln, the mean value of km-w increased from 38.6 W/mK to 45.3 W/mK at 2.7 rpm. In addition, km-w increased to 50.1 W/mK when the rotating speed was increased to 4.0 rpm. In the water vaporization phase during the course of the pyrolysis process, the height of the lifters had a significant influence on km-w. However, the number of lifters had a significant impact on km-w in the pyrolysis phase of the plastic-based wastes. According to measurements, a 10 % increase in km-w could be obtained when installing lifters to attain a ratio of lifter height Hl to the thickness of the waste layer Hw larger than 0.45 or when arc length between two lifters Ll to the arc length of the interface between the wastes and the kiln wall Lw was larger than 1.

LES of Pulverized Coal Combustion Furnaces

LES (large eddy simulation) is applied to combustion simulations of two large scale pulverized coal-fired furnaces. One application is a boiler furnace with the coal feed rate of 3,000 kg/h. The results of LES show good agreement in not only distributions of temperature, NO concentration, and CO concentration on the vertical center line but also NO and CO emissions and UBC (unburned carbon in ash). The calculation error of NO emission is 10%. The other application is a horizontal furnace with a low NOx burner with the coal feed rate of 560 kg/h. LES predicts temperatures and oxygen concentrations accurately; but the standard k-e model does not. The flame width calculated by the standard k-e model is narrower than that by LES. These calculated results indicate that the drawback of the standard k-e model is its low calculation accuracy for the coal jet flame decay and lift-off height.Copyright

Numerical Simulation of Turbulent Combustion Flows for Coaxial Jet Cluster Burner

We have developed a burner for the gas turbine combustor, which was high efficiency and low environmental load. This burner is named the “coaxial jet cluster burner” and, as the name indicates, it has multiple fuel nozzles and holes in a coaxial arrangement. To form lean premixed combustion, this burner mixes fuel and air in the multiple holes rapidly. The burner can change the combustion form between premixed and non-premixed combustion by controlling the mixing. However, the combustion field coexisting with premixed and non-premixed combustion is complicated. The phenomena that occur in the combustion field should be understood in detail.Therefore, we have developed the hybrid turbulent combustion (HTC) model to calculate the form in which non-premixed flame coexists with premixed flame. Turbulent flow has been simulated using a large eddy simulation (LES) with a dynamic sub grid scale (SGS) model coupled with the HTC model. These models were programmed to a simulation tool based on the OpenFOAM library. However, there were unclear points about their applicability to an actual machine evaluation and the predictive precision of CO concentration which affects burner performance. In this study, we validate the HTC model by comparing its results with measured gas temperature and gas concentration distributions obtained with a coaxial jet cluster burner test rig under atmospheric pressure. In addition, we analyze the CO generation mechanism for the lean premixed combustion in the burner.Copyright