【作者】 余波；

【导师】 傅培舫；

【作者基本信息】 华中科技大学 ， 热能工程， 2014， 博士

【摘要】 第三代SHELL高温(1500℃)高压(4.1MPa)干煤粉气化技术以其高转化率得到了广泛地应用,但由于采用合成气激冷,除了高昂的设备费,腐蚀和磨损也会导致极高的运行成本。采用水激冷可以降低设备投资和运行成本,但还没有在煤化工领域成功应用的报道。本文以高温(1500℃)高压(4.1MPa)上行干粉煤气化水激冷技术为背景,研究高温高背压条件下,射流喷嘴结构参数、喷射压力、背压和温度对水射流蒸发雾化的特征参数,如喷嘴流量系数、扩张角、粒径分布、速度场及穿透距离等的影响,为工业应用提供理论和技术支撑。喷嘴流量系数是喷嘴设计的一个重要参数,通过实验研究3支锥形进口喷嘴的流量系数与背压,喷射压力以及喷嘴结构参数之间的关系,结果表明：湍流条件下,流量系数受Re数控制,在一定背压下,当Re数达到第一临界Re数时,喷嘴内部流动由湍流状态转变为空穴流动状态,此时喷嘴流量系数受空穴数控制；当Re数达到第二临界值时,喷嘴内部流动转变为返回流,此时喷嘴流量系数保持不变；临界空穴数为喷嘴内部流动由湍流过度至空穴流时对应的空穴数,其随着背压升高而增加。本文通过数值方法研究高温高背压下水滴的蒸发特性,通过MIE理论研究了水滴的辐射特性,利用灰体模型计算水滴表面辐射换热,研究环境温度500℃-1500℃,背压1MPa-4MPa,水滴初始直径50μm-500μm以及不同来流速度下水滴蒸发过程,结果表明水滴的吸收系数随着环境温度升高而减小,随着水滴温度升高而减小,随着水滴直径增加而增加；静止条件下一定直径水滴蒸发寿命受背压和环境温度竞争控制；对流条件下,水滴寿命随着背压升高而缩短；在考虑水滴运动蒸发时,水滴直径对蒸发寿命和穿透距离起决定性作用。本文选取7支不同结构尺寸的锐边进口和锥形进口喷嘴为研究对象,研究喷嘴结构、环境压力(气体密度)和喷射压力对雾化锥角的影响,利用闪光摄影法获得喷雾图像,通过图像处理并利用CAD软件进行喷雾锥角测量,主要结论如下：锐边进口喷嘴在相同Re数下,在长径比1/d相差不大情况下,所获得喷雾锥角要大于锥形进口喷嘴；喷雾锥角随着Re数增加而增加；在相同Re数下,随着环境气体密度增加,喷雾锥角增加；喷嘴直径对射流刚性影响较为明显；喷雾锥角受环境密度影响要远大于喷嘴内部空穴的影响,但在喷嘴出口附近喷嘴内部的超空穴状态对雾化影响是非常重要的。最后对锥形进口喷嘴雾化性能影响因素进行研究,喷嘴直径为1.1mm,喷嘴长度为7mm,研究背压和喷射压力对射流雾化的影响,利用PIV(粒子图像速度仪)获得喷雾的瞬态图像和瞬时速度,结果表明：水射流雾化受到背压影响明显,随着背压升高,相同喷射压差下,雾化增强；较低背压的图像结果表明,射流破碎后水滴主要集中在射流轴线附近,雾化效果差；随着背压升高,水滴在喷雾锥角内实现了较均匀分布；低背压时射流径向速度沿半径衰减较快,而随着背压升高,径向速度衰减变慢；在利用动量定理计算射流破碎后速度沿前进距离衰减规律时,只有在雾化较充分时才可以假设喷雾角内水滴与气体速度相同。更多还原

【Abstract】 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.更多还原