外文翻译-袋式除尘器在dap装置中的应用大学论文.doc

中文3573字 毕业设计（论文）外文文献翻译翻译题目袋式除尘器在DAP装置中的应用学 院机械工程学院专 业车辆工程18袋式除尘器在DAP装置中的应用摘要：袋式除尘器虽然在磷铵厂没有广泛的应用，但是，在某些情况下，使用他们代替气旋跟洗涤器也是有可能的，本文探讨最合适的气流在厂袋式除尘器的应用，分析它们在在每种情况下的优点和缺点，包括对一个具体案例的经济评价，本文还讨论了成功使用袋式除尘器必要的设计特点。1.袋式除尘器的类型：常用的袋式过滤器有三种基本类型,如下：1. 脉冲式2. 逆气流清灰式3. 机械振动清灰式 机械振动式除尘器的滤袋固定在底部管板，袋子的底部是开放的，脏空气进入料斗并向上继续运动到滤袋，把灰尘沉积在里面。对于脉冲式，袋子的底部是封闭的，开放的顶部固定管板，脏空气进入料斗或袋式过滤器壳体的一侧，从滤袋的外面到里面通过并把灰尘慢慢沉积下来。逆气流清灰式袋式除尘器既可以收集在滤袋里面，也可在滤袋外面。 在逆气流清灰式中，在清洁周期，袋式除尘器被划分了跟其余部分隔离，目的是得到更好的清洗。袋的空气由风扇或风扇大逆流清洗，取决于粉尘收集在滤袋内或滤袋外，同时，空气在对滤袋增压的过程也会使其得到清洁，袋的部分会产生折叠或者受压，不管是滤饼产生裂缝还是袋子发生了脱落。 操作的原理如图1所示：图1：使用袋式除尘器的基本类型 机械振动式袋式除尘器被再次划分。当水平杆穿过壳体的顶部时，滤袋被悬浮起来，通过电机驱动的凸轮使袋悬浮时产生的间歇运动来进行清灰。 而脉冲式袋除尘器的滤袋则由压缩空气产生的一个短冲击进行清灰，通常在7kg/cm2 g，通过位于每排袋顶部的一系列的公共头注入。清洁的空气被每个袋上的文丘里喷嘴加速，空气短脉冲产生的冲击波使其在袋内停留时间受到影响，从而造成了袋的变形以及滤饼的移位。滤袋被其里面的一个个金属小笼支持起来，目的是为了防止器发生破裂，因为清洁的空气跟主要的加工气体比起来是微乎其微的，没有必要单独去划分这种类型的袋除尘器。脉冲式清灰一般收非常有效的，因为所有袋的运作是持续不断的，而且空气布率远高于其他两种类型，因此在工厂所需空间更少。 由于粉尘有时具有粘性和吸湿性的性质，施肥应用并不容易，随着不断的发展，逆气流清灰方式越来越少，而脉冲式清灰成为了工业清灰最有效的手段。因此，本文的剩余部分将着重阐述脉冲式清灰袋式除尘器。2. 袋式除尘器设计特点2.1过滤袋/笼 理论上，过滤袋是可折叠或光滑的，袋可以是圆柱形或信封状。这里我们只推荐光滑的圆筒袋，这些袋直径通常约为130mm,另外我们还建议，袋的长度限制在12英尺（3657毫米）内以确保有效的清洗。 材料和抛光将取决于被处理的粉尘性质，对于DAP，推荐使用带釉面的聚丙烯 。 如前所述，金属丝笼被插入每袋作为支撑。通常标准是镀锌笼，但这里我们建议不锈钢笼。 我们曾经遇到过单元内最外层袋与外壳的桥接问题，为了避免这个问题我们已经成功把边缘的袋移除，目的是增大壳与其最近的袋之间的空间，这有效的降低了从供应商利率并避免了桥接问题。2.2.脉冲式袋除尘器的清灰系统 压缩空气的喷射通常是由两个定时器控制；一个控制频率，另一个控制持续时间。脉冲的持续时间很短而有序，仅为0.1秒，频率通过监测压力的升降来进行设置，脉冲清灰通常足以防止一个预先设定的压力降被超过。典型的压力下降范围在75到150毫米之间。它可以作为一个频率定时器代替使压降保持稳定的压力开关来使用，尽管我们没有发现这是必要的，我们推荐使用双隔膜电磁阀，因为它提供了极其快速的开启时间并且提高了清灰效率。2.3进入排气通风 如果装置被放置在户外，一个步入式通风装置被指定安装在空气室出口，如果放置在室内则不需要这个装置，无论哪种方式，一系列的快速释放的检查/维护舱口布置在装置的顶部（见图2）。打开这些舱口开口，气体就可以进入脉冲管，文氏管，袋笼和袋。如果装置是安装在室内，净空必须进行检查以确保袋笼彻底的隔离。在净空高度受限制的情况下，可以指定分包笼。图2 文氏管通常连接到笼和袋带有快速释放弹簧钢带的地方（见图3以下） 图32.4.脏空气入口 通常厂商提供的脏空气入口的是在壳体的一侧或在漏斗的另一侧，当灰尘负载非常高或者灰尘非常重时，漏斗入口由生产商提供，这样可以作为一个预集漏斗，我们之前遇到入口问题时没有很好的解决办法，所以推荐使用侧壳体入口。2.5.斗 供应商的标准产品，通常有多个漏斗，每个都有它自己的流量，（特别是大的装置），如图2所示。我们发现这样安装会干扰斗之间的工作，所以不推荐这种安排，相比而言，我们更喜欢一个长的需要放在外面墙上有且有加强筋的楔形料斗。 根据被处理的空气条件（温度，湿度等）我们会推荐蒸汽伴热的料斗。 建立在料斗壁也被证明是一个问题。使用的声波号角，然而，已被证明有助于确保料斗壁保持干净。2.6集尘/气闸 收集的粉尘被螺旋输送机回收参与造粒机的部分循环，从而达到除尘目的，在袋式除尘器的抽吸作用下，密封舱需要减少或消除周围空气进入过程气的泄漏。传统的密封舱采用旋转阀来解决这个问题，但是我们不这么做，因为有很多经验可以证明，主要从维护的立场：堵塞，对叶片的磨损等。2.7停机注意事项 大多数遇到的问题是停机时过程气体温度下降会导致空气湿度上升，因此我们建议在再循环风扇上再安装一个可关闭的小加热器。 一个定时关机，关闭主风机，关闭其入口挡板，加热器风扇启动并和主机连线。风扇循环空气通过漏斗和袋出口增压并再次回来。袋式除尘器单元内的温度由一个温控器保持在某个设定点，当然整个袋式除尘器单元是绝缘的。2.8袋破损检测 为了避免温度的再循环，干净的气体经滤袋的烘干机后直接作为燃烧室的稀释气体。我们建议安装一个粉尘监测装置监测在气流离开滤袋时其负荷的增加。为了避免高浓度的粉尘被检测到，在滤袋被更换或堵塞时，可以暂时的把气流转向大气层。3. DAP装置的气流 气流经烘干机，冷却器和总厂除尘（设备通风口）是使用袋式除尘器粉尘回收的潜在途径，典型的操作条件下，这些气流在DAP装置中参数如下表1表1 烘干机冷却器总厂除尘温度, o C885872湿度,kg/kg0.1350.020.02相对湿度，%11157粉尘负载，g/m330350氨负载，g/m34忽略不计1 烘干机由于其自身的高湿度以及气流最终被消除的事实，所以一般不认为它是袋式除尘器的合适“接班人”，还有就是在任何情况下，其相对高的氨浓度刚好也成为了其的制约因素。 人们通常要么考虑冷却器要么考虑总厂除尘，在低粉尘浓度情况下较冷的气流优势是很低的氨浓度。冷却器的气流跟烘干机差不多甚至超过它，所以所有的稀释气体由再生空气冷却器提供。在设备的通风口，只能提供部分的稀释气体。下面的表2提供了详细的可回收的热量回收，不管是总厂除尘还是冷却器气流到烘干机。在设备通风系统的氨浓度意味着一些洗涤也可能被要求把浓度降至适当范围内，除非从袋式过滤器的清洁空气循环通过烘干机燃烧室中的空气稀释。4. 经济方面 更换干旋风和湿式洗涤与袋式除尘器相比，以下两个方面会对成本造成影响。4.1冷却器 冷却器气流中，只有旋风尾气洗涤器位于下游的旋风才能被消除，通过气旋和尾气洗涤器的压降约为75毫米，高于预期单独单独通过袋式除尘器的压降，导致一些积蓄在风扇和相关电机中，由于较少的空气会被清洗，尾气洗涤塔的尺寸（直径和高度）随着洗涤循环泵能力变化也将大大减少。 下面的表2总结了与气旋/湿式洗涤器与现代世界级的DAP装置额定1000000吨袋除尘器选项相关联的相对成本。表2总安装成本，美元气旋/湿式洗涤器袋除尘器气旋风扇尾气洗涤器Stack$6,450,000$7,450,000尾气洗涤泵袋除尘器 总之，袋式除尘器的选择是大约1000000美元，比传统的旋风和湿式除尘器的高。4.2设备的通风口 从设备排出气流常将随着来自反应器/造粒机的气体在文丘里旋风除尘器中得到清洗，在旋流器的压降将类似于在袋式过滤器的压降。因为反应器/造粒机气体现在得到单独处理，但是，他们都需要与风扇隔离开，由于较少的空气会被清洗，随着循环泵容量变化的文丘里旋风和尾气洗涤器的大小也将减少。 下面的表3用类似上表2的方法总结了相对成本表3总安装成本，美元气旋/湿式洗涤器袋除尘器R/G V型风扇R/G V型洗涤器泵和洗涤器$10,600,000 $10,600,000尾气洗涤器Stack尾气清洗泵袋除尘器通风口的风扇 比较可知需要大致相同的资本支出 通过两个方案比较可知，选用袋式除尘器可以节约能源，增加利用率，下面的表4总结了袋式除尘器通过回收利用热空气作为烘干机燃烧室稀释气体以节约燃油，同时，降低压降也起到了节电的作用。表4冷却器设备的通风口每吨DAP回收的热量(kcals /$）83180.3594160.39每吨DAP节约电量 (kWh / $) 1.60.042.30.06每年节省$390,000 $450,000注：每吨消耗400美元的燃油，每千瓦时花费2.5美分的电力成本假设都已包含在表内5. 结论 冷却器气流中使用袋式除尘器的将需要大约1000000美元的额外资本支出。但在不超过3年的时间，额外的支出将在节约能源中重新获得。 提供被回收的热空气作为烘干机燃烧室的稀释气体，对设备的通风系统安装袋式除尘器在经济上是非常有吸引力的。前期的资本支出跟湿式除尘器的差不多，1000000吨年DAP装置每年将节省约450000美元。 至少，袋式过滤器应在增加容量作为替代建设更多或更大的清洗装置的改造情况下得到重视外文翻译考核表指导教师对外文翻译的评语： 指导教师 （签名） 年 月 日建议成绩（百分制）评阅小组或评阅人对文献综述的评语：评阅小组负责人或评阅人 （签名） 年 月 日建议成绩（百分制）The Use of Bag Filters in a DAP PlantDavid M. Ivell a *Jacobs Engineering SA(JESA), 3149 Winter Lake Road., Lakeland, FL 33803, USAAbstract Bag filters have not been commonly used in DAP plants. It is possible, however, to employ them as an alternative to cyclones and wet scrubbers in certain circumstances. This paper examines the most appropriate airstreams within the plant for the application of bag filters uses and discusses the pros and cons for their use in each case, including an economic assessment for a specific example. The paper also discusses the necessary design features for the successful use of bag filters. 1. Bag filter typesThere are three basic types of bag filter available, namely:1. Pulse Jet2. Reverse Air3. Mechanical Shaker The bags in mechanical shaker type filters are anchored to a bottom tube plate. The bottoms of the bags are open. The dirty air enters in the hopper and travels up the inside of the bags, depositing the dust on the inside. With the pulse jet type,the bottoms of the bags are closed and the open tops are anchored to a tube plate. The dirty air enters, either in the hopper or the side of the bag filter casing, and passes from the outside to the inside of the bags depositing the dust on the outside ofthe bags. Reverse air type filters can have either dust collection on the inside or outside of the bags. In the reverse air type, the bag filter is compartmentalized such that the bags being cleaned are isolated from the remainder of the unit during the cleaning cycle. The bags are cleaned by a large reverse flow of air supplied by a fan or fans. Depending on whether the dust is collected on the inside or outside of the bag, the air either pressurizes the compartment being cleaned and partially collapses the bags or pressurizes the bags. In either case the dust cake cracks and falls off the bags.The principle of operation of each is shown below in Figure 1:Figure 1: Basic types of bag filter available Mechanical shaker type bag filters are again compartmentalized. The bags are suspended from horizontal bars running across the top of the housing. The bags are cleaned by intermittently shaking the bars from which the bags are suspended using a motor driven cam. The bags in the pulse jet type filter are cleaned by a short burst of compressed air, typically at 7 kg/cm 2 g, injected through a series of common headers located over the top of each row of bags. The cleaning air is accelerated through venturi nozzles located above each bag. The short burst of air creates a shock wave effect traveling down the length of the bag causing the bags to flex and dislodge the cake. The bags are supported by a metal cage on the inside of each bag which prevents the bags from collapsing. Because the cleaning air is very small compared with the main process air, there is no need to compartmentalize this type of bag filter. The pulse jet cleaning is generally very efficient and, because the operation of all the bags is continuous, the air to cloth ratio is much higher than with the other two types and consequently requires less space within the plant Fertilizer applications are not the easiest due to the sometimes sticky and hygroscopic nature of the dust. Our experience with reverse air bag filters has been poor whereas pulse-jet type filters have been found to be the most effective for use in our industry. We will, therefore, concentrate on pulse jet filters for the remainder of this paper.2. Filter bag design features2.1 Filter Bags / Cages In theory filter bags can be pleated or smooth. Bags can be cylindrical or envelope shaped. We recommend only smooth, cylindrical bags. These bags are typically about 130 mm in diameter. We also recommend that bag length be limited to no more than 12 ft (3657 mm) to ensure efficient cleaning. The material and finish applied to the bag will depend on the properties of the dust being handled. However for DAP, polypropylene with a glazed finish is recommended. As mentioned earlier, a metal wire cage is inserted into each bag as a support. Galvanized cages are typically the standard, but we recommend stainless cages. We have experienced some problems with bridging between the outermost bags in the unit and the outside casing. To avoid this we have had success with removing all bags around the periphery to increase the space between the casing and the nearest bag. This effectively down-rates the standard offering from the vendor but does avoid the bridging problem.2.2 Pulse Jet Cleaning System The compressed air injection is normally controlled by two timers; one for frequency and the other for duration. The duration of the pulse is very short of the order of 0.1 seconds. The frequency is set by monitoring the rise in pressure drop and pulse cleaning often enough to prevent a pre-set pressure drop from being exceeded. Typical pressure drops are in the range of 75 to 150 mm. It is possible to replace the frequency timer with a pressure switch which actuates the pulse cleaning to maintain pressure drop although we have not found this to be necessary. Double diaphragm solenoid valves are recommended because they offer extremely quick opening times and improved bag cleaning.2.3 Access to the Outlet Air Plenum If the unit is to be placed outdoors, a walk-in plenum is specified to gain access to the outlet air plenum. For indoorlocations, a walk-in plenum is not required. Either way, a series of quick release inspection / maintenance hatches are provided in the top of the unit (see Figure 2 below). Opening of these hatches allows access to the pulse pipes, venturis, bag cages and bags. If the units are installed indoors, headroom must be checked to make sure that the bag cages can be fully removed. In case of headroom limitations, split bag cages can be specified.Figure 2Venturis are normally attached to the cages and the bags are held in place with quick release spring steel bands (See Figure3 below).Figure 32.4 Dirty Air Inlet Typically vendors provide the choice of dirty air inlets on the side of the housing or in the side of the hopper. Hopper entry is recommended by vendors when dust loadings are very high or the dust is very heavy. In this way the hopper supposedly functions as a pre-collector. Our experience with hopper entry has not been good with build up problems being encountered in the hopper. We therefore recommend side-housing entry.2.5 Hopper Vendors standard offerings typically have multiple hoppers each with its own discharge, (especially for larger units), asshown in Figure 2 above. We recommend against that arrangement as we have found that hopper build- up occurs where one hopper joins the other. We prefer one long, wedge-shaped hopper with any stiffeners that are required placed on the outside walls. Depending on the condition of the air being handled (temperature, humidity etc.) we may recommend steam tracing of the hopper. Build up on the walls of the hopper has also proven to be a problem. The use of sonic horns, however, has proved useful in ensuring that hopper walls are kept clean.2.6 Dust Collection / Airlock The dust collected in the hopper is removed by screw conveyor for recovery as part of the recycle to the granulator. Since the bag filter is under suction, an airlock is required to minimize or eliminate leakage of the surrounding air into the process airstream. The traditional airlock used in this duty has been a rotary valve. We do not, however, have good experience with rotary valves in fertilizer duty, mainly from a maintenance standpoint: blockages, wear on the vanes etc.2.7 Shutdown Precautions Most problems that are encountered with build up occur on shutdown when the temperature of the process air drops causing humidity to rise. We therefore recommend installing a small shutdown heater with recirculation fan. A shutdown timer shuts down the main fan and closes its inlet damper. The heater fan starts and the heater is brought on line. The fan circulates the air through the hopper and the bags to the outlet air plenum and back again. The temperature inside the bag filter unit is maintained at the desired set point by a thermostat. The entire bag filter unit, of course, is insulated2.8 Bag Breakage Detection In cases where the plan is to recycle the warm, clean gases from the bag filter to the dryer as dilution air in the combustion chamber, we recommend the installation of a dust monitor to detect any increase in dust loading in the airstream leaving the filter. In case high levels of dust are detected, the airstream is diverted to atmosphere temporarily until the bag can be replaced or plugged.3. DAP plant airstreams The airstreams from the dryer, cooler and general plant dedusting (equipment vents) are potential candidates for dust recovery using bag filters. Typical operating conditions for each of those airstreams in a DAP plant are given below in Table 1.Table 1 Dryer Cooler Equipment VentsTemperature, o C 88 58 72Humidity,kg/kg 0.135 0.02 0.02Relative Humidity,% 11 15 7Dust Loading,g/m 3 30 3 50Ammonia Loading,g/m3 4 Negligible 1 The dryer is not generally considered as a suitable candidate for a bag filter due to its high humidity and the fact that theairstream ultimately needs to be scrubbed, in any case, due to its relatively high ammonia concentration. Either the cooler or equipment vents airstreams could be considered. The very low ammonia concentration in the cooler airstream is an advantage as is the low dust concentration. The cooler airflow matches or exceeds that of the dryer so that all the dilution air requirements would be provided by recycled coo