搅拌式厌氧发酵反应器的CFD模拟及应用研究
发布时间：2018-07-28 08:56
【摘要】：厌氧发酵技术是废弃物资源化利用的核心技术之一,具有广阔的应用前景。本文以计算流体力学(CFD)为研究方法,系统研究了厌氧发酵体系物料混合过程的流体力学特征,为合理的工艺参数值选取及工业应用提供依据。本文选择玉米秸秆和牛粪的厌氧发酵体系为目标,建立了基于CFD的搅拌式厌氧发酵反应器数学模型;从物料性质、搅拌桨种类、搅拌设计参数等方面,模拟研究了搅拌混合体系的流场分布、固相浓度分布,以及发酵体系的能量产出与消耗。开展的创新性研究工作及取得的成果如下:首先,针对所研究的多相搅拌发酵反应器,建立了固(F)-固(S)-液三相CFD模型,通过速度场、矢量分布和局部颗粒浓度的对比,验证了所建CFD模型的可靠性;模拟研究了颗粒密度、颗粒直径和固体含量等因素对固相浓度分布的影响,结果表明,当颗粒密度大于液相时,固体会在反应器底部围绕釜底中心位置发生沉积;反之,则在近液面处围绕搅拌轴发生上浮积聚。颗粒的上浮和下沉现象随固体颗粒直径的增大而加剧;随着下沉颗粒S固含量由2.5%提高到10%,颗粒浓度的标准偏差变小,总体悬浮状况变好。之后,通过对所研究三相体系中RB桨、HE桨、PBU桨和PBD桨的数值模拟,研究了搅拌桨种类及其设计参数(搅拌桨直径、离底高度、叶片宽度)对流场的影响,得到了不同搅拌体系内流场的分布规律。研究结果表明,在搅拌反应器内采用不同桨型会产生不同的流场和流型:RB桨呈现典型的径流桨特征;HE、PBU和PBD在特定的几何结构配置下,出现主循环和二次循环流;搅拌桨叶直径变化直接导致釜内流场速度和流型均发生变化;搅拌桨离釜底高度变化,导致流场的排出位置随之改变:HE和PBD桨离底高度降低抑制了二次循环流,PBU桨的离底高度降低影响主循环流;叶片宽度变化直接影响流场速度分布,但流型不变。在湍流流域内,RB桨的功率准数Np最大,是PBU和PBD桨的1.6倍,HE桨的3.2倍。第三,系统研究了上述四种搅拌桨及其设计参数对固-固-液混合流场固相分布的影响,得到了上浮和下沉颗粒共存体系内固相分布规律:在搅拌桨下部反应釜的中心区域颗粒S发生沉积,颗粒F在液面附近围绕搅拌轴的中心区域发生积聚,颗粒S在流场中的混匀性优于颗粒F;轴向流动速度增大利于固体颗粒的均匀悬浮。随着搅拌转速的增加,上浮颗粒F和下沉颗粒S的悬浮均匀性提高。当转速为210 rpm时,固相F的混合优劣顺序为PBU PBD HE RB,而固相S的混合优劣顺序为PBD≈PBURBHE。在PBU搅拌体系中,根据CFD切线交汇法模拟得到上浮颗粒F和下沉颗粒S的临界悬浮转速分别为119 rpm和117 rpm,并分别推导出三相体系中下沉颗粒的临界离底悬浮转速Njs和上浮颗粒的临界下拉悬浮转速Njd的关联方程。第四,建立CFD模拟与析因分析相结合的方法,以搅拌桨直径、离底距离、桨叶宽度为设计因子,以上浮颗粒的悬浮质量σF、下沉颗粒的悬浮质量σS和能量输入MEL为响应值,经过系列化模拟研究,分别确定了四种搅拌体系中上浮颗粒与下沉颗粒悬浮质量的显著影响因子,并建立了搅拌桨设计因子与响应值间的关联方程。更加深入的模拟研究结果表明,在四种搅拌体系中,显著影响上浮颗粒/下沉颗粒悬浮质量的设计因子各自不同;而影响搅拌桨输入功率的设计因子均为桨叶直径、桨叶宽度和二者的交互作用值。对比PBD桨和RB桨的CFD模拟值与关联方程预测值,误差在1.6%～8.6%范围,关联方程可信。基于上述分析建立了耦合σF、σS和MEL三个响应值的无因次优化函数,并据此获得了四种搅拌桨体系中适合固-固-液三相体系的最优设计方案:采用PBU搅拌桨,桨叶直径、离底距离和桨叶宽度分别控制在0.1 m、0.078 m和0.04 m。最后,建立了一个适合厌氧发酵非牛顿体系的搅拌反应器数值模型,对玉米秸秆(CS)和牛粪(CM)的单一发酵体系及两者混合发酵体系的流场和能量消耗进行深入研究,提出了“净能量产出”指数概念,并获得了相应表达式。研究发现,在CS和CM单一发酵体系和二者混合发酵体系(CS+CM)反应器内流场的均匀程度为:CM CS+CM CS;本文提出的“净能量产出”指数可以用来优化发酵体系的投料比,对于连续搅拌、间歇搅拌INTER Ⅰ、间歇搅拌INTER Ⅱ三种搅拌方式的最优投料比分别为1:1,1:1和1:3。混合发酵体系的能量产出可以通过优化搅拌形式和投料比来提高。
[Abstract]:Anaerobic fermentation technology is one of the core technologies of waste resource utilization and has a broad application prospect. In this paper, the hydrodynamic characteristics of the material mixing process in anaerobic fermentation system are systematically studied by using computational fluid dynamics (CFD). This paper provides a basis for the selection of reasonable process parameters and the application of industrial application. The anaerobic fermentation system of stalk and cow dung is the goal. A mathematical model of stirred anaerobic fermentation reactor based on CFD is established. The flow field distribution, the distribution of solid state concentration and the energy production and consumption of the fermentation system are simulated and studied in the aspects of the material properties, the type of agitator and the parameters of the mixing design. The results are as follows: firstly, a solid (F) - solid (S) - liquid three phase CFD model is established for the multiphase stirred fermentation reactor studied. The reliability of the built CFD model is verified by the velocity field, the vector distribution and the local particle concentration, and the particle density, the particle diameter and the solid content are studied in the simulation. The effect of concentration distribution shows that when the particle density is larger than the liquid phase, the solid will be deposited around the bottom of the reactor at the bottom of the reactor, and on the contrary, the floating and the sinking of the particles are increased with the increase of the solid particle diameter at the near liquid surface. With the solid content of the sinking particle S, the solid content is raised by 2.5%. As high as 10%, the standard deviation of the particle concentration is smaller and the overall suspension condition becomes better. After the numerical simulation of the RB paddles, HE paddles, PBU paddles and PBD paddles in the three phase system, the influence of the type of impeller and its design parameters (impeller diameter, bottom height and blade width) on the flow field is studied, and the flow field in different mixing systems is obtained. The distribution rule. The results show that different flow fields and flow patterns are produced in the mixing reactor: RB propeller presents typical characteristics of runoff propeller; HE, PBU and PBD appear main circulation and two circulation flow under specific geometric configuration; the change of impeller diameter changes directly in the flow velocity and flow pattern in the reactor; The change of the height of the agitator at the bottom of the tank leads to the change of the discharge position of the flow field. The height of the HE and PBD oars decreases with the decrease of the two circulation flow, and the decrease of the height of the PBU paddle affects the main circulation. The blade width change directly affects the velocity distribution of the flow field, but the flow pattern is unchanged. In the turbulent basin, the maximum power of the RB paddle is Np, which is a PBU and PBD oar. 1.6 times and 3.2 times of HE paddle. Third. The effects of the above four agitators and their design parameters on the solid solid liquid mixed flow field are studied. The solid phase distribution in the coexistence system of the upper floating and sinking particles is obtained. The particle S is deposited in the central region of the bottom reaction kettle of the stirred propeller, and the particle F is around the mixing axis near the liquid surface. The agglomeration of the central region occurs. The mixing of particle S in the flow field is better than that of the particle F, and the axial flow velocity increases for the uniform suspension of solid particles. With the increase of the stirring speed, the suspension uniformity of the floating particles F and the sinking particle S increases. When the rotational speed is 210 rpm, the sequence of the mixing of the solid phase F is PBU PBD HE RB, while the solid phase S is the same. The sequence of mixing is PBD PBURBHE. in the PBU mixing system. The critical suspension speed of the floating particles F and the sinking particle S is 119 rpm and 117 RPM respectively according to the CFD tangent intersection method. The correlation between the critical off bottom suspension speed Njs and the critical drop off speed Njd of the floating particles in the three-phase system is deduced respectively. Fourth, the method of combining the CFD simulation with the factorial analysis is established, with the diameter of the impeller, the distance from the bottom, the blade width as the design factor, the suspended mass of the floating particles, the suspended mass of the floating particles, the mass of the suspended particles Sigma S and the energy input MEL as the response value. After a series of simulation studies, the floating particles in the four kinds of mixing systems are determined respectively. The correlation equation between the design factor of the impeller and the response value is established. The more in-depth simulation results show that in the four kinds of mixing systems, the design factors that significantly affect the suspension mass of the floating particles and the suspended particles are different, and the design factors that affect the input power of the agitation propeller Both the diameter of the blade, the width of the blade and the interaction value of the two, compared the CFD simulation value of the PBD paddle and the RB paddle with the predictive value of the correlation equation, the error is 1.6% to 8.6%, the correlation equation is credible. Based on the above analysis, the dimensionless optimization functions of the three response values of the coupling Sigma F, sigma S and MEL are established, and the suitable four kinds of stirred oar systems are obtained accordingly. The optimal design scheme of solid solid liquid three phase system: using PBU mixing paddle, blade diameter, bottom distance and blade width controlled at 0.1 M, 0.078 m and 0.04 M., a numerical model of stirred reactor suitable for anaerobic fermentation and non Newtonian system, a single fermentation system for corn straw (CS) and cow dung (CM) and their mixed hair, was established. The flow field and energy consumption of the fermentation system are deeply studied. The concept of "net energy output" is proposed and the corresponding expression is obtained. It is found that the uniformity of the flow field in the CS and CM single fermentation system and the two mixed fermentation system (CS+CM) reactor is CM CS+CM CS, and the "net energy output" index proposed in this paper can be used in this paper. In order to optimize the feeding ratio of the fermentation system, the energy output of the mixed fermentation system of 1:1,1:1 and 1:3. is improved by optimizing the mixing form and feeding ratio for the continuous stirring, intermittent stirring INTER I and the optimal feeding ratio of the batch mixing INTER II three mixing methods respectively.
【学位授予单位】：北京化工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：X71
[Abstract]:Anaerobic fermentation technology is one of the core technologies of waste resource utilization and has a broad application prospect. In this paper, the hydrodynamic characteristics of the material mixing process in anaerobic fermentation system are systematically studied by using computational fluid dynamics (CFD). This paper provides a basis for the selection of reasonable process parameters and the application of industrial application. The anaerobic fermentation system of stalk and cow dung is the goal. A mathematical model of stirred anaerobic fermentation reactor based on CFD is established. The flow field distribution, the distribution of solid state concentration and the energy production and consumption of the fermentation system are simulated and studied in the aspects of the material properties, the type of agitator and the parameters of the mixing design. The results are as follows: firstly, a solid (F) - solid (S) - liquid three phase CFD model is established for the multiphase stirred fermentation reactor studied. The reliability of the built CFD model is verified by the velocity field, the vector distribution and the local particle concentration, and the particle density, the particle diameter and the solid content are studied in the simulation. The effect of concentration distribution shows that when the particle density is larger than the liquid phase, the solid will be deposited around the bottom of the reactor at the bottom of the reactor, and on the contrary, the floating and the sinking of the particles are increased with the increase of the solid particle diameter at the near liquid surface. With the solid content of the sinking particle S, the solid content is raised by 2.5%. As high as 10%, the standard deviation of the particle concentration is smaller and the overall suspension condition becomes better. After the numerical simulation of the RB paddles, HE paddles, PBU paddles and PBD paddles in the three phase system, the influence of the type of impeller and its design parameters (impeller diameter, bottom height and blade width) on the flow field is studied, and the flow field in different mixing systems is obtained. The distribution rule. The results show that different flow fields and flow patterns are produced in the mixing reactor: RB propeller presents typical characteristics of runoff propeller; HE, PBU and PBD appear main circulation and two circulation flow under specific geometric configuration; the change of impeller diameter changes directly in the flow velocity and flow pattern in the reactor; The change of the height of the agitator at the bottom of the tank leads to the change of the discharge position of the flow field. The height of the HE and PBD oars decreases with the decrease of the two circulation flow, and the decrease of the height of the PBU paddle affects the main circulation. The blade width change directly affects the velocity distribution of the flow field, but the flow pattern is unchanged. In the turbulent basin, the maximum power of the RB paddle is Np, which is a PBU and PBD oar. 1.6 times and 3.2 times of HE paddle. Third. The effects of the above four agitators and their design parameters on the solid solid liquid mixed flow field are studied. The solid phase distribution in the coexistence system of the upper floating and sinking particles is obtained. The particle S is deposited in the central region of the bottom reaction kettle of the stirred propeller, and the particle F is around the mixing axis near the liquid surface. The agglomeration of the central region occurs. The mixing of particle S in the flow field is better than that of the particle F, and the axial flow velocity increases for the uniform suspension of solid particles. With the increase of the stirring speed, the suspension uniformity of the floating particles F and the sinking particle S increases. When the rotational speed is 210 rpm, the sequence of the mixing of the solid phase F is PBU PBD HE RB, while the solid phase S is the same. The sequence of mixing is PBD PBURBHE. in the PBU mixing system. The critical suspension speed of the floating particles F and the sinking particle S is 119 rpm and 117 RPM respectively according to the CFD tangent intersection method. The correlation between the critical off bottom suspension speed Njs and the critical drop off speed Njd of the floating particles in the three-phase system is deduced respectively. Fourth, the method of combining the CFD simulation with the factorial analysis is established, with the diameter of the impeller, the distance from the bottom, the blade width as the design factor, the suspended mass of the floating particles, the suspended mass of the floating particles, the mass of the suspended particles Sigma S and the energy input MEL as the response value. After a series of simulation studies, the floating particles in the four kinds of mixing systems are determined respectively. The correlation equation between the design factor of the impeller and the response value is established. The more in-depth simulation results show that in the four kinds of mixing systems, the design factors that significantly affect the suspension mass of the floating particles and the suspended particles are different, and the design factors that affect the input power of the agitation propeller Both the diameter of the blade, the width of the blade and the interaction value of the two, compared the CFD simulation value of the PBD paddle and the RB paddle with the predictive value of the correlation equation, the error is 1.6% to 8.6%, the correlation equation is credible. Based on the above analysis, the dimensionless optimization functions of the three response values of the coupling Sigma F, sigma S and MEL are established, and the suitable four kinds of stirred oar systems are obtained accordingly. The optimal design scheme of solid solid liquid three phase system: using PBU mixing paddle, blade diameter, bottom distance and blade width controlled at 0.1 M, 0.078 m and 0.04 M., a numerical model of stirred reactor suitable for anaerobic fermentation and non Newtonian system, a single fermentation system for corn straw (CS) and cow dung (CM) and their mixed hair, was established. The flow field and energy consumption of the fermentation system are deeply studied. The concept of "net energy output" is proposed and the corresponding expression is obtained. It is found that the uniformity of the flow field in the CS and CM single fermentation system and the two mixed fermentation system (CS+CM) reactor is CM CS+CM CS, and the "net energy output" index proposed in this paper can be used in this paper. In order to optimize the feeding ratio of the fermentation system, the energy output of the mixed fermentation system of 1:1,1:1 and 1:3. is improved by optimizing the mixing form and feeding ratio for the continuous stirring, intermittent stirring INTER I and the optimal feeding ratio of the batch mixing INTER II three mixing methods respectively.
【学位授予单位】：北京化工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：X71
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