FLOW BEHAVIORS IN A HIGH SOLID FLUX CIRCULATING FLUIDIZED BED COMPOSED OF A RISER, A DOWNER AND A BUBBLING FLUIDIZED BED

A circulating fluidized bed coal gasifier cold model which consists of an acrylic riser, a downer, and a bubbling fluidized bed were set up. Flow behaviors were investigated using silica sand with the solid mass flux up to 336 kg/m2•s. The effects of the solid inventory and the seals between the three reaction zones on the solid mass flux were investigated and discussed

An Improvement of Lean Combustion Characteristics of Heavy-Hydrocarbon Fuels with Hydrogen Addition

The Lewis numbers of lean heavy-hydrocarbon fuels are larger than unity, and hence, their flames are prone to extinction in a shear flow, which occurs in a turbulent combustion. Here, propane is used as a representative fuel of heavy-hydrocarbon fuels because the Lewis number of lean propane/air mixtures is larger than unity, and an attempt to improve its combustion characteristics by hydrogen addition has been made. A tubular flame burner is used to evaluate its improvement, since a rotating, streched vortex flow is established in the burner. The results show that with hydrogen additon, the fuel concentration, the flame diameter and the flame temperatuire at extinction are reduced and its combustion characteristics are imporved. However, it is found that the effective equivalence ration at extinction cannot become so small as that of lean methane/air mixture, which has a Lewis number less than unity

Temperatures of Positively and Negatively Stretched Flames

Both tubular flame temperature and Bunsen flame temperature have been measured for lean methane, hydrogen and propane/air mixtures. These temperatures have been compared with the adiabatic flame temperature, which is the typical temperature with no stretch. Results show that, the temperature of the tubular flame is almost the same as the adiabatic flame temperature for a lean methane/air mixture, considerably higher for a lean hydrogen/air mixture, and lower for a lean propane/air mixture. For the temperature around the Bunsen flame tip, this response is opposite to that of the tubular flame. To examine radiation effect, numerical simulation has been conducted. It is found that the radiative heat loss only reduces the flame temperature by 30 to 80℃. Thus, the different dependency of flame temperature on the mixtures is explained by stretch effect with the Lewis number considerations, and the response of these flames exhibits opposite behavior.・rights：日本機械学会・rights：本文データは学協会の許諾に基づきCiNiiから複製したものである・relation：isVersionOf：http://ci.nii.ac.jp/naid/110003479146

Structures of Tubular Flames : 1st Report, Structures of the Tubular Flames of Lean Methane/Air Mixtures in a Rotating Stretched-Flow Field

The tulular flames of lean methane/air mixtures in a rotating-flow field have been analyzed for their concentrations of stable species and temperature distributions, and their structures have been investigated. The results show that the tubular flame consists of an inner hot gas core of burned gas and an outer region of the unburned mixture, and that the flame structure is essentially the same as that of the one-dimensional, flat, premixed flame. As the extinction limit is approached, the flame diameter decreases and the concentrations of carbon monoxide and hydrogen behind the flame zone increase. Hence, the extinction of the tubular flame of lean methane/air mixtures is caused by incomplete combustion with stretch as it is with other stretched flames. As the density inside the flame is lower than that outside, the flame front is rendered smooth and cylindrical by the rotational motion of the flow

Pressure Change and Flame Characteristics in a Stretched, Rotating Flow

To investigate the pressure change and flame characteristics in a stretched, rotating flow, tubular flames of a lean hydrogen, methane, or propane-air mixture have been numerically simulated. Results show that, with rotation, the flame temperature of hydrogen and methane mixtures increases monotonically, while, that of a propane mixture decreases. With an increase of the fuel concentration, the position at which the reaction rate is maximum increases, and the temperature change becomes small. As seen in the pressure distribution, the pressure decreases around the center, and a pressure gradient is formed. This pressure gradient is steep near the center, but decreases as the radial distance is increased. The fuel flux decreases with the increase of circumferential velocities because of the decrease in the pressure gradient. For these reasons, this temperature change could be explained in terms of the pressure diffusion which results in mass transport due to the pressure gradient. However, it is also found that, with rotation, the pressure decreases and the density changes. The velocities increase due to flow expansion, resulting in an increase of flame stretch. Thus, the flame characteristic change with rotation is explained with the coupling of pressure diffusion and stretch effects