Study On The Properties Of Water Spray And Evaporation For The Quenching Of Pressurized Coal Gasification

Disadvantages of syngas quench for SHELL gasification are more investment needed and high running cost. Water quenching method can reduce cost of equipment investment and running cost. There is no mature technology of how to use water quenching. In this paper, we chose water quenching for SHELL coal gasification furnace as background. The plain orifice nozzle was chosed as quenching nozzle. This paper studied the effect of nozzle structure parameters, backpressue(environmental density), injection pressure on the nozzle discharge coefficient and atomization performance. And a single water drop evaporation process at high backpressure and high environmental temperature was studied by simulation method.Nozzle discharge coefficient is an important parameter for nozzle desigh. In this paper, experimental study on water spraying nozzles with120°taper inlet and different ratio of length/diameter at different injection pressure(≥10MPa) and back pressure(≤4.1MPa) were carried out. The results have shown that at different back pressure, the flow regimes are different under the condition of the same pressure difference. Cavitations occurring would be inhibited at high back pressure. In the turbulent flow regime, the discharge coefficient increases as the Reynolds number(Re) increases. When Re is more than the first critical Reynolds number at an assumed back pressure, the nozzle flow is in the cavitations flow regime, the discharge coefficient is decided by cavitation number. When Re increases further up to the second critical Reynolds number, the discharge coefficient keeps a constant for the flip flow takes place. The critical cavitations number increases as the back pressure increases.The single water droplet evaporation process under the stationary condition and convection condition were studied by simulation methods. The radiation property of water droplet was studied by MIE method. The effect of heat radiation on the droplet heat transfer was considered by a gray model method. The effect of ambient temperature (500℃-1500℃), backpressure(1MPa-4MPa) and initial water droplet diameter(50μm-500μm) on the evaporation process were studied. Results show that the water absorption coefficient decreases as the increasement of enviroment temperature and water droplet temperature, and increases as the droplet diameter increases. Under stationary condition, the water droplet evaporation life increases as backpressure increases at low eviromental tempreature, but the water droplet evaporation life decreases as backpressure increases at high eviromental tempreature. Under convection condition, the water droplet evaporation life decreases as backpressure increases. When consider the evaporation process of a moving water droplet, the diameter of water droplet is the key factor decided the evaporation life and the droplet penetration length.Spray angle of plain orifice nozzle is an important macro parameter of jet atomization. Seven nozzles with sharp edge inlet and tapper inlet was chosen to study the spray angle. The flash photography method was used to get spay images, and the AUTO-CAD soft was used to measure the spray angle. Results show that spray angle of sharp edge inlet nozzle is bigger at the same Re and1/d than taper inlet nozzle. For a nozzle, spray angle increas as backpressure(enviromental density) increases at the same Re. The nozzle diameter influences the jet rigidity obviously. The influence of backpressur(enviromental density) on the spray angle is greater than the influence of the nozzle inner cavitation, but the influece of cavitation on the jet atomization near the nozzle exit cann’t be neglected.At last, the PIV was used to research the taper inlet nozzle atomization performance at different backpressure(enviromental density) and injection pressure. The transient image of spray and instantaneous velocity field were obtained. Increasement of backpressure(enviromental density) can enhance the jet atomization at the same injection difference. At low backpressure(enviromental density), the atomized droplet of the jet concentrated around the jet axis. At high backpressure(enviromental density), the atomized droplets distribute evenly in the spray angle area. Big droplets(droplet diameter equal even bigger than nozzle diameter) can be founded in spray images especially at low backpressure(enviromental density), few big droplets could be saw in spray image at high backpressure(enviromental density). At low backpressure(enviromental density), spray velocity increase obviously as the injection pressure increases, but spray velocity increase inobviously as the injection pressure increases at high backpressure(enviromental density). inobviously as the injection pressure increases at high backpressure(enviromental density). When used momentum theorem to calculate the spray penetration, the assumption of droplet and gas are the same velocity in the spray angle area is only reasonable at sufficient atomization condition.