中文 3573 字 畢 業(yè) 設(shè) 計(jì) （ 論 文 ） 外 文 文 獻(xiàn) 翻 譯 翻譯題目 袋式除塵器在 DAP裝置中的應(yīng)用 學(xué) 院 機(jī)械工程學(xué)院 專 業(yè) 車輛工程 David M. Ivell / Procedia Engineering 46 ( 2012 ) 83 88 袋式除塵器在 DAP 裝置中的應(yīng)用 摘要：袋式除塵器雖然在磷銨廠沒有廣泛的應(yīng)用，但是，在某些情況下，使用他們代替氣旋跟洗滌器也是有可能的，本文探討最合適的氣流在廠袋式除塵器的應(yīng)用，分析它們在在每種情況下的優(yōu)點(diǎn)和缺點(diǎn)，包括對一個具體案例的經(jīng)濟(jì)評價，本文還討論了成功使用袋式除塵器必要的設(shè)計(jì)特點(diǎn)。 1.袋式除塵器的類型： 常用的袋式過濾器有三種基本類型 ,如下： 1.脈沖式 2.逆氣流清灰式 3.機(jī)械振動清灰式 機(jī)械振動式除塵器的濾袋固定在底部管板，袋子的底部是開放的，臟空氣進(jìn)入料斗并向上繼續(xù)運(yùn)動到濾袋，把灰塵沉積在里面。對于脈沖式，袋子的底部是封閉的，開放的頂部固定管板，臟空氣進(jìn)入料斗或袋式過濾器殼體的一側(cè)，從濾袋的外面到里面通過并把灰塵慢慢沉積下來。逆氣流清灰式袋式除塵器既可以收集在濾袋里面，也可在濾袋外面。 在逆氣流清灰式中，在清潔周期，袋式除塵器被劃分了跟其余部分隔離，目的是得到更好的清洗。袋的空氣由風(fēng)扇或風(fēng)扇大逆流清洗，取決于粉塵收集在濾袋內(nèi)或?yàn)V袋 外，同時，空氣在對濾袋增壓的過程也會使其得到清潔，袋的部分會產(chǎn)生折疊或者受壓，不管是濾餅產(chǎn)生裂縫還是袋子發(fā)生了脫落。 操作的原理如圖 1所示： 圖 1：使用袋式除塵器的基本類型 3 機(jī)械振動式袋式除塵器被再次劃分。當(dāng)水平桿穿過殼體的頂部時，濾袋被懸浮起來，通過電機(jī)驅(qū)動的凸輪使袋懸浮時產(chǎn)生的間歇運(yùn)動來進(jìn)行清灰。 而脈沖式袋除塵器的濾袋則由壓縮空氣產(chǎn)生的一個短沖擊進(jìn)行清灰，通常在7kg/cm2 g，通過位于每排袋頂部的一系列的公共頭注入。清潔的空氣被每個袋上的文丘里噴嘴加速，空氣短脈沖產(chǎn)生的沖 擊波使其在袋內(nèi)停留時間受到影響，從而造成了袋的變形以及濾餅的移位。濾袋被其里面的一個個金屬小籠支持起來，目的是為了防止器發(fā)生破裂，因?yàn)榍鍧嵉目諝飧饕募庸怏w比起來是微乎其微的，沒有必要單獨(dú)去劃分這種類型的袋除塵器。脈沖式清灰一般收非常有效的，因?yàn)樗写倪\(yùn)作是持續(xù)不斷的，而且空氣布率遠(yuǎn)高于其他兩種類型，因此在工廠所需空間更少。 由于粉塵有時具有粘性和吸濕性的性質(zhì)，施肥應(yīng)用并不容易，隨著不斷的發(fā)展，逆氣流清灰方式越來越少，而脈沖式清灰成為了工業(yè)清灰最有效的手段。因此，本文的剩余部分將著重闡述脈沖式清灰 袋式除塵器。 2.袋式除塵器設(shè)計(jì)特點(diǎn) 2.1過濾袋 /籠 理論上，過濾袋是可折疊或光滑的，袋可以是圓柱形或信封狀。這里我們只推薦光滑的圓筒袋，這些袋直徑通常約為 130mm,另外我們還建議，袋的長度限制在 12英尺（ 3657毫米）內(nèi)以確保有效的清洗。 材料和拋光將取決于被處理的粉塵性質(zhì)，對于 DAP，推薦使用帶釉面的聚丙烯 。 如前所述，金屬絲籠被插入每袋作為支撐。通常標(biāo)準(zhǔn)是鍍鋅籠，但這里我們建議不銹鋼籠。 我們曾經(jīng)遇到過單元內(nèi)最外層袋與外殼的橋接問題，為了避免這個問題我們已經(jīng)成功把邊緣的袋移除， 目的是增大殼與其最近的袋之間的空間，這有效的降低了從供應(yīng)商利率并避免了橋接問題。 2.2.脈沖式袋除塵器的清灰系統(tǒng) 壓縮空氣的噴射通常是由兩個定時器控制；一個控制頻率，另一個控制持續(xù)時間。 脈沖的持續(xù)時間很短而有序，僅為 0.1秒，頻率通過監(jiān)測壓力的升降來進(jìn)行設(shè)置，脈沖清灰通常足以防止一個預(yù)先設(shè)定的壓力降被超過。典型的壓力下降范圍在 75到 150毫米之間。它可以作為一個頻率定時器代替使壓降保持穩(wěn)定的壓力開關(guān)來使用，盡管我們沒有發(fā)現(xiàn)這是必要的，我們推薦使用雙隔膜電磁閥，因?yàn)樗峁┝藰O其快速 4 的開啟時間并且提 高了清灰效率。 2.3進(jìn)入排氣通風(fēng) 如果裝置被放置在戶外，一個步入式通風(fēng)裝置被指定安裝在空氣室出口，如果放置在室內(nèi)則不需要這個裝置，無論哪種方式，一系列的快速釋放的檢查 /維護(hù)艙口布置在裝置的頂部（見圖 2）。打開這些艙口開口，氣體就可以進(jìn)入脈沖管，文氏管，袋籠和袋。如果裝置是安裝在室內(nèi)，凈空必須進(jìn)行檢查以確保袋籠徹底的隔離。在凈空高度受限制的情況下，可以指定分包籠。 圖 2 文氏管通常連接到籠和袋帶有快速釋放彈簧鋼帶的地方（見圖 3以下） 圖 3 5 2.4.臟空氣入口 通常廠商 提供的臟空氣入口的是在殼體的一側(cè)或在漏斗的另一側(cè)，當(dāng)灰塵負(fù)載非常高或者灰塵非常重時，漏斗入口由生產(chǎn)商提供，這樣可以作為一個預(yù)集漏斗，我們之前遇到入口問題時沒有很好的解決辦法，所以推薦使用側(cè)殼體入口。 2.5.斗 供應(yīng)商的標(biāo)準(zhǔn)產(chǎn)品，通常有多個漏斗，每個都有它自己的流量，（特別是大的裝置），如圖 2所示。我們發(fā)現(xiàn)這樣安裝會干擾斗之間的工作，所以不推薦這種安排，相比而言，我們更喜歡一個長的需要放在外面墻上有且有加強(qiáng)筋的楔形料斗。 根據(jù)被處理的空氣條件（溫度，濕度等）我們會推薦蒸汽伴熱的料斗。 建立在 料斗壁也被證明是一個問題。使用的聲波號角，然而，已被證明有助于確保料斗壁保持干凈。 2.6集塵 /氣閘 收集的粉塵被螺旋輸送機(jī)回收參與造粒機(jī)的部分循環(huán)，從而達(dá)到除塵目的，在袋式除塵器的抽吸作用下，密封艙需要減少或消除周圍空氣進(jìn)入過程氣的泄漏。傳統(tǒng)的密封艙采用旋轉(zhuǎn)閥來解決這個問題，但是我們不這么做，因?yàn)橛泻芏嘟?jīng)驗(yàn)可以證明，主要從維護(hù)的立場： 堵塞，對葉片的磨損等。 2.7停機(jī)注意事項(xiàng) 大多數(shù)遇到的問題是停機(jī)時過程氣體溫度下降會導(dǎo)致空氣濕度上升，因此我們建議在再循環(huán)風(fēng)扇上再安裝一個可關(guān)閉的小加熱器 。 一個定時關(guān)機(jī)，關(guān)閉主風(fēng)機(jī)，關(guān)閉其入口擋板，加熱器風(fēng)扇啟動并和主機(jī)連線。風(fēng)扇循環(huán)空氣通過漏斗和袋出口增壓并再次回來。袋式除塵器單元內(nèi)的溫度由一個溫控器保持在某個設(shè)定點(diǎn)，當(dāng)然整個袋式除塵器單元是絕緣的。 2.8袋破損檢測 為了避免溫度的再循環(huán)，干凈的氣體經(jīng)濾袋的烘干機(jī)后直接作為燃燒室的稀釋氣體。我們建議安裝一個粉塵監(jiān)測裝置監(jiān)測在氣流離開濾袋時其負(fù)荷的增加。為了避免高濃度的粉塵被檢測到，在濾袋被更換或堵塞時，可以暫時的把氣流轉(zhuǎn)向大氣層。 6 3.DAP裝置的氣流 氣流經(jīng)烘干機(jī)，冷卻器和總廠除塵（設(shè) 備通風(fēng)口）是使用袋式除塵器粉塵回收的潛在途徑，典型的操作條件下，這些氣流在 DAP裝置中參數(shù)如下表 1 表 1 烘干機(jī)由于其自身的高濕度以及氣流最終被消除的事實(shí)，所以一般不認(rèn)為它是袋式除塵器的合適“接班人”，還有就是在任何情況下，其相對高的氨濃度剛好也成為了其的制約因 素。 人們通常要么考慮冷卻器要么考慮總廠除塵，在低粉塵濃度情況下較冷的氣流優(yōu)勢是很低的氨濃度。冷卻器的氣流跟烘干機(jī)差不多甚至超過它，所以所有的稀釋氣體由再生空氣冷卻器提供。在設(shè)備的通風(fēng)口，只能提供部分的稀釋氣體。下面的表 2提供了詳細(xì)的可回收的熱量回收，不管是總廠除塵還是冷卻器氣流到烘干機(jī)。在設(shè)備通風(fēng)系統(tǒng)的氨濃度意味著一些洗滌也可能被要求把濃度降至適當(dāng)范圍內(nèi)，除非從袋式過濾器的清潔空氣循環(huán)通過烘干機(jī)燃燒室中的空氣稀釋。 4.經(jīng)濟(jì)方面 更換干旋風(fēng)和濕式洗滌與袋式除塵器相比，以下兩個方面會對成本造成影響。 4.1冷卻器 冷卻器氣流中，只有旋風(fēng)尾氣洗滌器位于下游的旋風(fēng)才能被消除，通過氣旋和尾氣洗滌器的壓降約為 75毫米，高于預(yù)期單獨(dú)單獨(dú)通過袋式除塵器的壓降，導(dǎo)致一些積蓄在風(fēng)扇和相關(guān)電機(jī)中，由于較少的空氣會被清洗，尾氣洗滌塔的尺寸（直徑和高度）隨著洗滌循環(huán)泵能力變化也將大大減少。 烘干機(jī) 冷卻器 總廠除塵 溫度 , o C 88 58 72 濕度 ,kg/kg 0.135 0.02 0.02 相對濕度， % 11 15 7 粉塵負(fù)載， g/m3 30 3 50 氨負(fù)載， g/m3 4 忽略不計(jì) 1 7 下面的表 2總結(jié)了與氣旋 /濕式洗滌器與現(xiàn)代世界級的 DAP裝置額定 1000000噸袋除塵器選項(xiàng)相關(guān)聯(lián)的相對成本。 表 2 總之，袋式除塵器的選擇是大約 1000000美元，比傳統(tǒng)的旋風(fēng)和濕式除塵器的高。 4.2設(shè)備的通風(fēng)口 從設(shè)備排出氣流常將隨著來自反應(yīng)器 /造粒機(jī)的氣體在文丘里旋風(fēng)除塵器中得到清洗，在旋流器的壓降將類似于在袋式過濾器的壓降。因?yàn)榉磻?yīng)器 /造粒機(jī)氣體現(xiàn)在得到單獨(dú)處理，但是，他們都需要與風(fēng)扇隔離開，由于較少的空氣會被清洗，隨著循環(huán)泵容量變化的文丘里旋風(fēng)和尾氣洗滌器的大小也將減少。 下面的表 3用類似上表 2的方法 總結(jié)了相對成本 表 3 總安裝成本，美元?dú)庑?/濕式洗滌器 袋除塵器 氣旋 風(fēng)扇 尾氣洗滌器 Stack $6,450,000 $7,450,000 尾氣洗滌泵 袋除塵器 總安裝成本，美元?dú)庑?/濕式洗滌器 袋除塵器 R/G V型風(fēng)扇 R/G V型洗滌器 泵和洗滌器 $10,600,000 $10,600,000 尾氣洗滌器 Stack 尾氣清洗泵 袋除塵器 通風(fēng)口的風(fēng)扇 8 比較可知需要大致相同的資本支出 通過兩個方案比較可知，選用袋式除塵器可以節(jié)約能源，增加利用率，下面的表 4總結(jié)了袋式除塵器通過回收利用熱空氣作為烘干機(jī)燃燒室稀釋氣體以節(jié)約燃油，同時，降 低壓降也起到了節(jié)電的作用。 表 4 注：每噸消耗 400美元的燃油，每千瓦時花費(fèi) 2.5美分的電力成本假設(shè)都已包含在表內(nèi) 5.結(jié)論 冷卻器氣流中使用袋式除塵器的將需要大約 1000000美元的額外資本支出。 但在不超過 3年的時間，額外的支出將在節(jié)約能源中重新獲得 。 提供被回收的熱空氣作為烘干機(jī)燃燒室的稀釋氣體，對設(shè)備的通風(fēng)系統(tǒng)安裝袋式除塵器在經(jīng)濟(jì)上是非常有吸引力的。前期的資本支出跟濕式除塵器的差不多，1000000噸年 DAP裝置每年將節(jié)省約 450000美元。 至少 ，袋式過濾器應(yīng)在增加容量作為替代建設(shè)更多或更大的清洗裝置的改造情況下得到重視 冷卻器 設(shè)備的通風(fēng)口 每噸 DAP回收的熱量 (kcals /$） 8318 0.35 9416 0.39 每噸 DAP節(jié)約電量 (kWh / $) 1.6 0.04 2.3 0.06 每年節(jié)省 $390,000 $450,000 9 外 文 翻 譯 考核表 指導(dǎo)教師對 外文翻譯 的評語： 指導(dǎo)教師 （簽名） 年 月 日 建議成績（百分制） 評閱小組或評閱人對文獻(xiàn)綜述的評語： 評閱小組負(fù)責(zé)人或評閱人 （簽名） 年 月 日 建議成績 （百分制） 10 The Use of Bag Filters in a DAP Plant David M. Ivell a * Jacobs Engineering SA(JESA), 3149 Winter Lake Road., Lakeland, FL 33803, USA Abstract 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 types There are three basic types of bag filter available, namely: 1. Pulse Jet 2. Reverse Air 3. 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 of the 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 11 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 12 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 features 2.1 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 13 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 indoor locations, 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 2 Venturis are normally attached to the cages and the bags are held in place with quick release spring steel bands (See Figure 3 below). Figure 3 2.4 Dirty Air Inlet 14 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), as shown 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. 15 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 insulated 2.8 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 Vents Temperature, o C 88 58 72 Humidity,kg/kg 0.135 0.02 0.02 Relative Humidity,% 11 15 7 Dust Loading,g/m 3 30 3 50 Ammonia 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 the airstream ultimately needs to be scrubbed, in any case, due to its relatively high 16 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 cooler air. In the equipment vents case, only part of the dilution air requirements would be provided. Table 2 below provides details of the heat that can be recovered by recycling either the equipment vents or the cooler airstreams to the dryer. The ammonia concentration in the equipment vents system means that some scrubbing would probably also be required to bring the concentration down within proper limits, unless the clean air from the bag filter is recycled through the dryer as dilution air in the combustion chamber. 4. Economics The impact on capital cost of replacing dry cyclones and wet scrubbing with a bag filter is compared below for each of the two options. 4.1 Cooler The cooler airstream is typically scrubbed only in a cyclonic tail gas scrubber located downstream of the cyclones. The pressure drop across the cyclones and the tail gas scrubber is approximately 75 mm higher than would be expected across the bag filter alone, resulting in some savings on the fan and associated motor. Since less air will be scrubbed, the size (diameter and height) of the tail gas scrubber will also be significantly reduced along with the capacity of the scrubber circulating pumps Table 2 below summarizes the relative capital costs associated with the cyclones / wet scrubber versus the bag filter option for a modern world class DAP plant rated at 1 million tonnes per year. Table 2 Total Installed Costs, US $ Cyclones / Wet Scrubber Bag Filter 17 Cyclones Fan Tail Gas Scrubber Stack $6,450,000 $7,450,000 Tail Gas Scrubber Pumps Bag Filter In summary, the bag filter option is approximately $1 million more than the traditional cyclones and wet scrubber option. 4.2 Equipment Vents The airstream from the equipment vents is typically scrubbed in a venturi-cyclonic scrubber along with the gases from the reactor/granulator. The pressure drop across the cyclones is expected to be similar to the pressure drop across the bag filter. Since the reactor/granulator gases are now treated independently, however, both will necessitate separate fans. Since less air will be scrubbed, the size of both the venturi-cyclonic an