化学化工专业英语翻译 reactor types.doc

Unit 4 Reaction EngineeringLesson 12 Reactor Types1. Stirred tank reactor A batch stirred tank reactor is the simplest type of reactor.It is composed of a reactor and a mixer such as a stirrer, a turbine wing or a propeller. The batch stirred tank reactor is illustrated below:This reactor is useful for substrate solutions of high viscosity and for immobilized enzymes with relatively low activity. However, a problem that arises is that an immobilized enzyme tends to decompose upon physical stirring. The batch system is generally suitable for the production of rather small amounts of chemicals. A continuous stirred tank reactor is shown above: The continuous stirred tank reactor is more efficient than a batch stirred tank reactor but the?equipment is slightly more complicated. 2. Tubular Reactor Tubular reactors are generally used for gaseous reactions, but are also suitable for some liquid-phase reactions.If high heat-transfer rates are required, small-diameter tubes are used to increase the surface area to volume ratio. Several tubes may be arranged in parallel, connected to a manifold or fitted into a tube sheet in a similar arrangement to a shell and tube heat exchanger. For high-temperature reactions the tubes may be arranged in a furnace.3. Fluidized bed ReactorA fluidized bed reactor (FBR) is a type of reactor device that can be used to carry out a variety of multiphase chemical reactions. In this type of reactor, a fluid (gas or liquid) is passed through a granular solid material (usually a catalyst possibly shaped as tiny spheres) at high enough velocities to suspend the solid and cause it to behave as though it were a fluid. This process, known as fluidization, imparts many important advantages to the FBR. As a result, the fluidized bed reactor is now used in many industrial applications.（1） Basic principlesThe solid substrate (the catalytic material upon which chemical species react) material in the fluidized bed reactor is typically supported by a porous plate, known as a distributor. The fluid is then forced through the distributor up through the solid material. At lower fluid velocities, the solids remain in place as the fluid passes through the voids in the material. This is known as a packed bed reactor. As the fluid velocity is increased, the reactor will reach a stage where the force of the fluid on the solids is enough to balance the weight of the solid material. This stage is known as incipient fluidization and occurs at this minimum fluidization velocity. Once this minimum velocity is surpassed, the contents of the reactor bed begin to expand and swirl around much like an agitated tank or boiling pot of water. The reactor is now a fluidized bed. Depending on the operating conditions and properties of solid phase various flow regimes can be observed in this reactor.（2） AdvantagesThe increase in fluidized bed reactor use in todays industrial world is largely due to the inherent advantages of the technology. Uniform Particle Mixing: Due to the intrinsic fluid-like behavior of the solid material, fluidized beds do not experience poor mixing as in packed beds. This complete mixing allows for a uniform product that can often be hard to achieve in other reactor designs. The elimination of radial and axial concentration gradients also allows for better fluid-solid contact, which is essential for reaction efficiency and quality. Uniform Temperature Gradients: Many chemical reactions produce or require the addition of heat. Local hot or cold spots within the reaction bed, often a problem in packed beds, are avoided in a fluidized situation such as an FBR. In other reactor types, these local temperature differences, especially hotspots, can result in product degradation. Thus FBRs are well suited to exothermic reactions. Researchers have also learned that the bed-to-surface heat transfer coefficients for FBRs are high. Ability to Operate Reactor in Continuous State: The fluidized bed nature of these reactors allows for the ability to continuously withdraw product and introduce new reactants into the reaction vessel. Operating at a continuous process state allows manufacturers to produce their various products more efficiently due to the removal of startup conditions in batch processes. ( 3 ) DisadvantagesAs in any design, the fluidized bed reactor does have it draw-backs, which any reactor designer must take into consideration. Increased Reactor Vessel Size: Because of the expansion of the bed materials in the reactor, a larger vessel is often required than that for a packed bed reactor. This larger vessel means that more must be spent on initial startup costs. Pumping Requirements and Pressure Drop: The requirement for the fluid to suspend the solid material necessitates that a higher fluid velocity is attained in the reactor. In order to achieve this, more pumping power and thus higher energy costs are needed. In addition, the pressure drop associated with deep beds also requires additional pumping power. Particle Entrainment: The high gas velocities present in this style of reactor often result in fine particles becoming entrained in the fluid. These captured particles are then carried out of the reactor with the fluid, where they must be separated. This can be a very difficult and expensive problem to address depending on the design and function of the reactor. This may often continue to be a problem even with other entrainment reducing technologies. Lack of Current Understanding: Current understanding of the actual behavior of the materials in a fluidized bed is rather limited. It is very difficult to predict and calculate the complex mass and heat flows within the bed. Due to this lack of understanding, a pilot plant for new processes is required. Even with pilot plants, the scale-up can be very difficult and may not reflect what was experienced in the pilot trial. Erosion of Internal Components: The fluid-like behavior of the fine solid particles within the bed eventually results in the wear of the reactor vessel. This can require expensive maintenance and upkeep for the reaction vessel and pipes. 4. Packed bed Reactor There are two basic types of packed-bed reactor: those in which the solid is a reactant, and those in which the solid is a catalyst. Many examples of the first type can be found in the extractive metallurgical industries.In the chemical process industries the designer will normally be concerned with the second type: catalytic reactors. Industrial packed-bed catalytic reactors range in size from small tubes, a few centimeters diameter to large diameter packed beds. Packed-bed reactors are used for gas and gas-liquid reactions. Heat-transfer rates in large diameter packed beds are poor and where high heat-transfer rates are required fluidized beds should be considered.Unit 4 REACTION ENGINEERINGLESSON 12 REACTOR TYPES1. 搅拌反应釜间歇搅拌反应釜是最简单的反应釜类型。它由一个反应器和例如混合机、涡轮翼或者推动器类的一个混合器组成。接着如下阐明间歇搅拌反应釜。这种反应釜是用于高粘性的溶液培养基和相对低活性的固定化酶。然而，随之产生的问题是固定化酶趋向于在活泼的物质上面分解。这种间歇系统是普遍适用于相当少量化学物质的生产。连续搅拌反应釜如上所示。连续搅拌反应釜比间歇搅拌反应釜更有高效率，但是它的装置略显得更复杂。2. 管式反应釜管式反应釜通常用于气体反应，也适用于一些液相反应。如果需要高热量传输效率，使用小直径的试管可以增加表面积与体积比。一些试管可能做相同的调整，与多部分相连，或者与管壳式换热器有相似调整的管板相符合。对于高温反应，试管应放在炉子中进行调整。3. 流动床反应釜流动床反应釜是用来操作多相化学反应的多样性的一种反应釜装置类型。在这种反应釜中，流体在足够高的速度时，被迫通过颗粒状固体材料，来延缓固体杂质和引起它运动，即使成流体态。这个过程，即流化作用，给予了流动床反应釜许多重要优点。结果了，流动床反应釜现在已在许多工业应用中使用。(1) 基本原则： 流动床反应釜中的固体培养基材料通常由多孔板支撑，称为经销商。这个流体在力的作用下通过多孔板向上运动再穿过固体材料。流体速度减小时，流体通过材料间的空隙，而固体杂质停留在了这里。这被称为填充床反应器。当增加流体速度时，反应器将达到一个阶段，即流体作用在固体杂质上的力能与固体材料的重量相平衡的地方。这个阶段称为初始流化作用，而且出现在最小流化作用速度的时候。一旦超过这个最小速度，流化床内部就开始扩张并成漩涡状，就像搅拌槽或水壶里沸腾的水一样。现在这个反应器叫做流化床。依赖于操作条件和固相性能，在这个反应器中，各种流量变化都能观察到。(2) 优点： 当今工业化世界流化床反应釜使用的增加是大幅度的，因为科技内在的优点。均匀的粒子混合： 由于固体材料固有的拟流化作用，流化床没有经历像填充床的贫混合。这种完全的混合允许在其他反应器设计中很难实现的产物。径向和轴向的浓度梯度的消除也允许了更好的流体固体接触，对高效的和高数量的反应是必要的。均匀的温度梯度： 许多化学反应产生或需要额外的温度。在反应床局部的热点或冷点，常常也是填充床中的问题，在流化情况下是要避免的，如流动床反应釜。在