【作者】 张凤鸣；

【导师】 马春元；

【作者基本信息】 山东大学 ， 热能工程， 2012， 博士

【摘要】 超临界水氧化是应用于有机废物无害化处理或产生多元热流体用于油田注采的新型技术。采用水膜反应器是解决超临界水氧化系统中腐蚀和盐沉积两大技术难题最为有效的方法。但是,基于水膜反应器的超临界水氧化系统中物料在预热段仍然存在结垢和堵塞问题,从而大大降低了系统的可靠性。此外,关于反应器设计所需要的相关数据十分缺乏。现有的实验或者工业反应器,一般都是根据燃料或有机废液的处理量及所需要的停留时间进行设计,但是没有考虑其他关键的设计参数,如：燃料的种类、燃料降解效率、反应器壁面的水膜保护、燃料的着火和灭火特性、无机盐的溶解排出等,容易造成反应器结构不合理。因此,本文设计一种内预热式超临界水氧化水膜反应器,将物料的预热从反应器外转移到反应器内,实现物料以常温注入反应器。通过对反应器内热液火焰的着火和灭火特性的研究,获取系统稳定运行的操作范围。考察各操作参数对反应器内的温度分布和反应器出口产物特性的影响规律,进而获得优化的操作参数。建立内预热式超临界水氧化水膜反应器的数值计算模型,分析各操作参数对反应器内的流场分布的影响；特别是在临界工况下,操作参数对反应器出口产物的影响规律。同时考察反应器结构(反应器直径和长度)对反应器内的温度分布和反应器出口产物特性的影响。最后提出利用反应器的热负荷参数(截面热负荷和容积热负荷)来指导反应器的设计方法,获取一定操作条件下水膜反应器的热负荷数据,为反应器设计提供指导。本文设计了一种内预热式超临界水氧化水膜反应器,该反应器是在水膜反应器结构的基础上,通过一个同轴射流燃烧器,利用辅助热源的射流卷吸作用来实现燃料的预热和着火,将燃料的预热由反应器外转移到反应器内,实现燃料常温注入反应器,从而解决了物料在预热段的结垢和堵塞问题。燃料能以常温注入水膜反应器的前提条件是水膜反应器内热液火焰的形成。水膜反应器内热液火焰的着火过程一般伴随着反应器内反应温度Trl急剧升高,以及反应器出口产物TOC(总有机碳)和CO浓度迅速下降,CO2浓度迅速升高。CO是甲醇超临界水氧化反应的主要中间产物。热液火焰的着火条件一般是燃烧器出口混合体系均相状态的形成。而水膜反应器内热液火焰的灭火过程一般伴随着反应器内反应温度Trl急剧下降至水的临界温度以下,以及反应器出口产物TOC和CO浓度迅速升高,CO2浓度迅速下降。辅助热源温度可降低至水的临界温度以下,并能保持反应器内的热液火焰稳定,说明燃烧器中心热水射流卷吸会引起组分的回流返混,使下游热液火焰的热量向上游的两相区传递。燃料浓度和燃料流量升高,着火温度降低；而燃料／辅助热源流量比升高,着火温度先升高后降低。燃料浓度、燃料／辅助热源流量比升高,灭火温度均降低；而燃料流量升高,灭火温度却呈上升趋势。在燃料浓度为25-45wt.%,燃料流量为2-5kg/h,燃料／辅助热源流量比为0.2-0.55时,对应的着火温度为450-600℃,灭火温度为250-400℃。对水膜反应器内热液火焰的研究结果表明：内预热式超临界水氧化水膜反应器不仅实现燃料以常温注入反应器,同时辅助热源亦可以亚临界温度注入反应器并保持热液火焰的稳定,从而降低系统能耗。燃料的性质也会影响热液火焰的着火和灭火温度。总体而言,单位质量反应热值较大的燃料,其对应的着火温度和灭火温度相对较低。在相同操作条件下,通过改变燃烧器结构来改变燃烧器出口流速的实验结果表明：燃烧器出口流速升高,有利于物料的射流混合,着火温度降低；但是燃烧器出口流速增高,对应的灭火温度升高。因此,物料流速降低有利于热液火焰的稳定。从系统稳定运行、节能和燃料的降解效率等角度出发,考察稳态运行条件下操作参数对反应器内温度分布和反应器出口气液相降解产物的影响规律,从而获得优化的操作参数。燃料/辅助热源流量比升高,反应器内的整体温度升高,而反应温度Trl几乎呈线性增加趋势。此外,燃料/辅助热源流量比增大,反应器内的超临界长度和有效反应时间均增加,燃料的降解更加彻底。本实验系统适宜的燃料/辅助热源流量比为0.3-0.5。辅助热源流量下降,也会增加燃料/辅助热源流量比,进而提高燃烧器出口混合体系中甲醇的浓度,反应温度Trl会明显升高。辅助热源流量仅为2.79kg/h时,反应温度接近900℃,非常接近反应器材质的耐温极限,不利于系统安全运行。辅助热源温度下降时,反应器内的整体温度均下降；而当辅助热源温度下降到一定程度时,反应器内的热液火焰会灭火。此外,辅助热源温度下降时,反应器内的超临界长度和有效反应时间均下降,不利于燃料的降解。因此,辅助热源入口温度一般控制在480-550℃。燃料流量增加会使反应器内的整体温度升高。反应温度一开始随燃料流量增加而增加,但是燃料增加到一定程度后,由于燃料和氧气的流速加快,两者不能充分混合反应,反应温度上升变缓甚至不再升高。燃料流量升高,反应器内的有效反应时间呈下降趋势,因此并不利于燃料的降解。为保证燃料降解效率高于99%,燃料流量应小于4kg/h。燃料浓度增加,反应器内的整体温度呈上升趋势,而反应温度上升最为明显。此外,燃料浓度增加,反应器内有效反应时间增加,燃料降解效率提高。蒸发系数增大时,反应温度变化不大。蒸发系数增大,会降低反应器内的整体温度水平和反应器内的有效反应时间。为保证燃料的降解和反应流体冷却至亚临界温度,蒸发系数控制在0.8-1.2较为合适。蒸发水温度降低时,超临界长度及有效反应时间减小。为保证燃料的彻底降解,蒸发水温度应大于250℃。以丙三醇、甲醇、乙醇和丙酮溶液作为模拟燃料的研究表明,反应器内的温度分布受燃料的单位质量反应热值影响非常大。单位质量反应热值较大的燃料在相同操作条件下,对应较长的超临界长度和有效反应时间,因而更有利于燃料的降解。通过有效反应时间来定量描述燃料的降解规律表明：当有效反应时间大于10.5s时,反应器出口液相产物中TOC浓度低于50ppm,对应降解效率大于99%,而气相产物中CO浓度低于0.1%,燃料能比较彻底的降解。由于超临界水氧化水膜反应器内的高温高压条件,反应器内测试非常困难。本文根据实验反应器的结构尺寸,建立了内预热式超临界水氧化水膜反应器的数值计算模型。燃料的超临界水氧化采用有限速率反应动力学模型,对燃料的氧化路径进行了假设和简化,燃料的氧化路径分为两步,并以CO作为主要的中间产物。数值计算结果和实验的温度场及反应器出口产物含量在趋势上是一致的,验证了模型的可靠性。反应器内流场的主要特征是反应器上部存在漩涡,该漩涡是由于燃烧器出口的射流卷吸作用及中心热流体和多孔内壁低温蒸发水的自然对流换热引起的。由于漩涡的存在,反应器上部像一个连续搅拌反应器。漩涡的存在虽然能强化反应流体的混合,但是燃料及其氧化的中间产物CO会扩散到低温的蒸发水区域,对反应器上部水膜形成和燃料降解形成不利影响。蒸发系数和蒸发水温度是多孔内壁亚临界水膜形成的主要影响因素。蒸发系数升高和蒸发水温度降低均有利于水膜的形成,其中蒸发水温度降低对水膜形成影响更为明显,但是会以反应器出口TOC和CO浓度升高为代价。在相同操作参数下,燃料浓度、燃料/辅助热源流量比和燃料流量对反应器内温度及反应器出口气液相产物分布的影响规律和实验结果是一致的。而在临界工况即反应器多孔内壁亚临界水膜存在的条件下,燃料浓度、燃料/辅助热源流量比和燃料流量升高时,由于有效反应时间不足,燃料降解效率下降,反应器出口TOC和CO浓度均呈上升趋势。在相同操作参数下,对不同燃料种类的数值计算结果与实验结果也能保持较好的一致性。在临界工况下,反应器出口产物中TOC和CO浓度随燃料单位质量反应热值的升高而升高。相同操作条件下,反应器直径增大,反应器的蒸发度也随之增大,有利于多孔内壁面水膜的形成；同时反应器内的有效反应时间会增长,有利于燃料的降解。反应器长度缩短也有利于多孔内壁的水膜的形成,但是会降低反应器内的有效反应时间和溶盐时间,不利于燃料降解和无机盐的溶解。考虑到当前水膜反应器的设计缺乏标准及指导参数的问题,提出了利用反应器的热负荷参数(截面热负荷和容积热负荷)来指导反应器设计的方法。水膜反应器的临界截面热负荷和临界容积热负荷是在一定条件下获得的,具体包括：燃料降解条件-燃料的有效反应时间大于11s；水膜形成条件-多孔内壁亚临界水膜的形成即多孔内壁温度均小于374℃；无机盐溶解条件-无机盐完全溶解排出反应器的溶盐时间为6s。燃料浓度、燃料流量和燃料/辅助热源流量比增大,对应的临界截面热负荷增加；此外,燃料单位质量的反应热值增大,对应的截面热负荷亦呈增加趋势。燃料浓度、燃料/辅助热源流量比和燃料单位质量反应热值增大,对应的临界有效容积热负荷和临界平均容积热负荷均增加；而燃料流量升高,对应的临界有效容积热负荷和临界平均容积热负荷却呈下降趋势。对燃料COD(化学需氧量)流量和临界截面热负荷的拟合结果表明,燃料初始COD流量增加,截面热负荷呈指数增加的趋势,两者之间的数学关系为qF=4.57×103COD0.12.对燃料COD流量和临界容积热负荷的拟合关系表明,随燃料输入COD流量的升高,水膜反应器的有效容积热负荷和平均容积热负荷呈指数下降的趋势。水膜反应器的有效容积热负荷和平均容积热负荷与燃料COD流量的数学关系分别为qV,r=2.50×104COD-0.09+ΔqV,r和qV,a=1.44×104COD-0.08+ΔqV,r。其中通过容积热负荷修正项ΔqV,r和ΔqV,a来修正燃料浓度、燃料种类和燃料/辅助热源流量比对容积热负荷的影响。更多还原

【Abstract】 Supercritical water oxidation is a new technology which is used for organic waste harmless treatment or producing multiple thermal fluids used for oilfield injection production. Transpiring wall reactor is the most effective solution to solve both the corrosion and plugging problems in the supercritical water oxidation process. However, corrosion and plugging still exist in the preheating section during the transition from subcritical to supercritical condition, and the reliability of the system is greatly reduced. The available experimental and industrial reactors are usually designed by the residence of the feed. However, other critical design parameters are neglected, such as:fuel type, degradation efficiency, the protection of the reactor wall by water film, the ignition and extinction characteristics of the feed, the dissolution and discharging of the inorganic salt, causing the irrational reactor structure. Thus, an inner preheating transpiring wall reactor for supercritical water oxidation was designed. The preheating of the feed can be transited from the exterior to the interior of the reactor. Therefore, the feed can be injected into the reactor at room temperature. Experimental study was conducted to investigate the ignition and extinction character of the hydrothermal flame inside the reactor, and the operating range of a stable operation were obtained. The effect of the operating parameters on the temperature profiles and the products of the reactor outlet were investigated to gain the optimized operating conditions. A computational fluid dynamic model of an inner preheating transpiring wall reactor for supercritical water oxidation was developed based on the real size of the reactor in the experiment. The effect of the operating parameters on the flow field of the reactor was analyzed, and the product characteristics of the reactor outlet at the critical condition were specially discussed. The influence of the reactor structure (reactor diameter and reactor length) on the temperature profile and product was also studied. A new method using the heat load parameters (the sectional heat load and the volume heat load) as criterion for the design of the transpiring wall reactor was proposed. And heat load data at certain conditions were obtained.An inner preheating transpiring wall reactor for supercritical water oxidation was firstly designed. A coaxial burner was introduced base on the structure of the transpiring wall reactor. The feed was preheated and ignited by the entertainment of the auxiliary heat source, and the preheating of the feed was transfered from the exterior to the interior of the reactor. Thus, the feed injected into the reactor at room temperature can be realized, and the problem of the corrosion and plugging in the preheating section can be solved.The prerequisite for the injection of the feed into the reactor at room temperature is the formation the hydrothermal flame inside the reactor. The ignition process of the hydrothermal flame accompanies by the sharp increase of the reaction temperature Trl and the concentration of CO2in the gaseous effluent, and the sharp decline of the concentration of TOC (Total Organic Carbon) in the aqueous effluent and CO in the gaseous effluent. It can be concluded that the most important prerequisite for ignition is the existence of a single-phase mixture at the outlet of the burner. The extinguishing process is on the contrast to the ignition process. The extinguishing process of the hydrothermal flame accompanies by the sharp decline of the reaction temperature Tr1and the concentration of CO2in the gaseous effluent, and the sharp increase of the concentration of TOC in the aqueous effluent and CO in the gaseous effluent. The stable hydrothermal flame can be kept even when the auxiliary heat source is lower than the critical temperature of the water. So it can be deduced that heat can be transfer from the downstream of the hydrothermal flame to the two-phase zone at the outlet of the burner by recirculation mixing and interdiffusion of species.The ignition temperature can be lowered when the increases of the feed concentration, the flux ration of the feed flow and the auxiliary heat source and the feed flow increase. The extinction temperature will also decrease when the feed concentration and the flux ration of the feed flow and the auxiliary heat source increase, while the extinction temperature increases when the feed flow increases. The ignition temperature of450-600℃and the extinction temperature of250-400℃are present at feed concentration of25-45wt.%, feed flow of2-5kg/h and the flux ration of the feed flow and the auxiliary heat source of0.2-0.55. The result based on the study of the hydrothermal flame characteristics shows that the feed injected into the reactor at room temperature can be realized by the inner preheating transpiring wall reactor, and at the same time, the temperature of the auxiliary heat source can be lower than the critical temperature to keep the hydrothermal flame stable, thus reducing the energy consumption of the system. The character of the fuel can also affect the ignition and extinction temperature of the feed. Generally, lower ignition temperatures and extinction temperatures will be present when the reaction heats per unit mass of the fuel are higher. The exit velocity of the burner was accelerated by changing the size of the burner. The increase of the exit velocity at the same operating parameters can enhance the mixing of the feed, thus lowering the ignition temperature. However, the extinction temperature will be increased when the exit velocity increases, which show that low velocity of the feed is favor for the stability of the hydrothermal flame.The effect of the operating parameters on the temperature profiles and the products of the reactor outlet were investigated based on the stable operation, energy saving, degradation efficiency, and the optimized operating conditions were obtained.The temperature of the whole reactor increases when the flux ration of the feed flow and the auxiliary heat source increases, and the reaction temperatures linearly increase. Besides, the supercritical length and the useful reaction time will increase when the flux ration of the feed flow and the auxiliary heat source increases, accompanying by higher degradation efficiency. The proper flux ration of the feed flow and the auxiliary heat source for the system is0.3-0.5. The decrease of the flow of the auxiliary heat source can also increase the flux ration of the feed flow and the auxiliary heat source. However, the reaction temperature can reach nearly900℃, which may exceed the temperature-resistance of the reactor material and is not conducive to the safety operation, when the flow of the auxiliary heat source is lowered to2.79kg/h. The auxiliary heat source flow for the experiment is selected at6-14kg/h. The supercritical length and the useful reaction time will be reduced when the temperature of the auxiliary heat source declines, causing lower degradation efficiency. So, the auxiliary heat source temperature is usually controlled at480-550℃.The temperature inside the reactor will also increase when the feed flow increases. The reaction temperature will increase firstly with the increase of the feed, but to certain feed flow, the reaction temperatures rise slowly or even no longer increase for the high velocity of the feed. The useful reaction time will decrease when the feed flow increases, thus are not conducive for the degradation of the fuel. The TOC removal efficiency of more than99%can be obtained at feed flow of less than4kg/h. The increase of the feed concentration will also increase the temperate of the whole reactor. The reaction temperature increases significantly with the increase of the feed concentration. Besides, the useful reaction time can be longer at high feed concentrations, and higher degradation efficiencies will be present.The transpiring flow relation has little influence on the reaction temperature, but the increase of the transpiring flow relation will lower the temperature of the reactor and the useful reaction time. The proper transpiring flow relation for the reactor is0.8-1.2. The increase of the transpiring water temperature, the temperature inside the reactor and the useful reaction time will increase. TOC removal efficiency of more than99%can be achieved when the transpiring water temperature exceeds250℃. The effect of the type of the fuel on the reactor was studied with the solution of glycerin, methanol, ethanol, acetone and water as artificial fuel. The temperature profile was greatly influenced by the reaction heat per unit mass of the fuel. Higher temperature profiles will present at higher reaction heats per unit mass. Besides, the length at supercritical temperature and the useful reaction time will increase at higher reaction heats per unit mass, which is conducive for the degradation of the feed.The quantitative description of the degradation law of the fuel by useful reaction time can be expressed as:the concentration of TOC in the aqueous effluent of the reactor can be lower than50ppm with the corresponding TOC removal efficiency higher than99%, and the concentration of CO in the gaseous effluent is less than0.1%, when the useful reaction time exceeds10.5s.The experimental measurement inside the reactor is difficult for the higher pressure and high temperature. A computational fluid dynamic model of an inner preheating transpiring wall reactor for supercritical water oxidation was developed based on the real size of the reactor in the experiment. The finite rate model was adopted in the simulation. And some assumption and simplification was made:the oxidation of fuel was divided into two steps with CO as the main intermediate product. The simulation results show a good agreement with the experimental temperature profiles and the aqueous and the gaseous products. An important characteristic of the flow field inside the reactor is the existence of the recirculation areas due to jet entrainment and natural convection in the upper part of the reactor. It is likely that a continuous stirred tank reactor (CSTR) is formed in the upper part of the reactor due to the existence of the eddy. The eddy is beneficial for the mixing of the feed, but it can destroy the water film in the upper section of the reactor and suppress the oxidation of fuel.The transpiring flow relation and the transpiring water temperature are two important factors which affect the formation of the subcritical water film. Compared with higher transpiration intensities, lower transpiring water temperatures are more conducive to the formation of water film, accompanied by a more significant decline of oxidation efficiency of the feed. The effect of the feed concentration, the flux ration of the feed flow and the auxiliary heat source and the feed flow on the flow fields well agree with the experimental result at the same operating conditions. But we are more interesting in the temperature profiles on the inner wall of the porous tube in the simulation which can’t be measured in the experiment. So the critical condition was defined which represents the existence of the ideal water film on the inner wall of the porous tube (keep the temperatures of the inner wall of the porous tube less or equal to374℃). The useful reaction time will decline when the feed concentration, the auxiliary heat source and the feed flow and the feed flow increase, resulting in the decreased efficiencies of fuel degradation, and the increased concentration of TOC and CO. Besides, the effect of the type of the fuel on the flow fields also agrees well with the experimental results at the same condition. However, the TOC and CO in the effluent will increase when the reaction heat per unit mass increase at critical conditions.Considering the irrational aspects in the design of the experimental reactor, different reactor diameters and lengths were test by numerical method for the optimization of the reactor structure. The increase of the reactor diameter.will increase the transpiration intensity, thus improving the formation of the water film on the inner porous wall. Besides, the increase of the reactor diameter can also prolong the useful reaction time, thus improving the degradation of the feed. The shortening of the reactor length can also increase the transpiration intensity, which is beneficial for the formation of the water film. However, the useful reaction time will be shortened at shorter reactor lengths. It can be concluded that a proper reactor diameter and length will be present for a certain operating condition.A new method using the heat load parameters (the sectional heat load and the volume heat load) as criterion for the design of the transpiring wall reactor was proposed. The heat load data at critical condition are obtained at certain criterions:a useful reaction time for fuel of11s; the formation of the subcritical water film; a dissolution time for inorganic salt of6s. The sectional heat load will increase when the feed concentration, the flux ration of the feed flow and the auxiliary heat source and the feed flow increase. Besides, the sectional heat load will also increase when the reaction heat per unit mass of the fuel increases.The fitting result of the initial chemical oxygen demand (COD) of the fuel and their sectional heat load shows that the sectional heat load is in an exponential growth relationship with the initial COD, and their relationship can be expressed by the formation:qF=4.57x103COD0.12. The volume heat load will increase when the feed flow and the flux ration of the feed flow and the auxiliary heat source increase, but decrease with the increase of the feed flow. Beside, the volume heat load will also increase when the reaction heat per unit mass of the fuel increases. The fitting result of the initial chemical oxygen demand (COD) of the fuel and the volume heat load shows that the e volume heat load is in an exponential downward relationship with the initial COD, and their relationship can be expressed by the formation:qv,r=2.50×104COD-0.09+Δqv,r and qv,a=1.44x104COD-0.08+Δqv,a.更多还原