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新型攪拌反應(yīng)器設(shè)計(jì)畢業(yè)設(shè)計(jì)-資料下載頁

2025-06-29 02:01本頁面
  

【正文】 pattern has less swirl, and baffles may not be needed, particularly at low viscosity.Draft Tubes A draft tube is a cylindrical housing around and slightly larger in diameter than the impeller. Its height may be little more than the diameter of the impeller or it may extend the full depth of the liquid, depending on the flow pattern that is required. Usually draft tubes are used with axial impellers to direct suction and discharge streams. An impellerdraft tube system behaves as an axial flow pump of somewhat low efficiency. Its top to bottom circulation behavior is of particular valve in deep tanks to suspension of solids and for dispersion of gases.Impeller Size This depends on the kind of impeller and operating conditions described by the Roynolds, Froude, and Power numbers as well as individual characteristics whose effects have been correlated. For the popular turbine impeller, the ratio of diameters of impeller and vessel falls in the range ,d/D=~, the lower values at high rpm, in gas dispersion, for example.Impeller Speed With mercially available motors and speed reducers, standard speeds are 37,45,56,68,84,100,125,155,190,and 320 rpm. Power requirements usually are not great enough to justify the use of continuously adjustable stream turbine drives. Twospeed drives may be required when starting torques are high, as with a settled slurry.Impeller Location As a first approximation, the impeller can be placed at 1/6 the liquid level off the bottom. In some cases there is provision for changing the position of the impeller on the shaft. For offbottom suspension of solids, an impeller location of 1/3 the impeller diameter off the bottom may be satisfactory.Kinds of Impellers A rotating impeller in a fluid imparts flow and shear to it, the shear resulting from the flow of one portion of the fluid past another. Limiting cases of flow are in the axial or radical directions so that impellers are classified conveniently according to which of the flows is dominant. By reason of reflections from vessel surfaces and obstruction by baffles and other internals, however, flow patterns in most cases are mixed. Because the performance of a particular shape of impeller usually cannot be predicted quantitatively, impeller design is largely an exercise of judgment so a considerable variety has been put forth by various manufacturers. A few mon types are described as follows:1. The threebladed mixing propeller is modeled on the marine propellers but has a pitch selected for maximum turbulence. They are used at relatively high speeds with low viscosity fluids, up to about 4000 Cp.2. The turbine with flat vertical blades is suited to the vast majority of mixing duties up to 100000 Cp .3. The horizontal plate to which the impeller blades of this turbine are attached has a stabilizing effect.4. Turbine with blades are inclined 45176。.Constructions with two to eight blades are used, six being most mon. Combined axial and radial flow are achieved. Especially effective for heat exchange with vessel walls or internal coils.5. Curved blade turbines effectively disperse fibrous materials without fouling. The swept back blades have a lower starting torque than straight ones, which is important when starting up settled slurries.6. Shrouded turbines consisting of a rotor and a stator ensure a high degree of radial flow and shearing action, and are well adapted to emulsification and dispersion.7. Anchor paddles fit the contour of the container, prevent sticking of pasty materials, and promote good heat transfer with wall.8. Gate paddles are used in wide, shallow tanks and for materials of high viscosity when low shear is adequate. Shaft speeds are low.反應(yīng)器摘要:在一段時(shí)間內(nèi),幾乎所有種類的盛裝設(shè)備都已經(jīng)被當(dāng)做化學(xué)反應(yīng)器,例如從混合噴嘴離心泵到最精細(xì)的塔和管組件。本節(jié)專門討論一般特征的主要類型的反應(yīng)器及其設(shè)計(jì)。關(guān)鍵詞:反應(yīng)器 類型 設(shè)計(jì)正文:反應(yīng)器類型間歇式和半間歇式反應(yīng)器 間歇式反應(yīng)器通常用于液相反應(yīng)。當(dāng)固體催化劑必須保持懸浮狀或有兩個(gè)液相時(shí),就需要一個(gè)攪拌器,例如在芳烴的硝基化反應(yīng)中。為了使得反應(yīng)器內(nèi)的溫度均勻,以及為了使得通過夾套或內(nèi)部蛇管的有效交換而將溫度保持在所需的數(shù)值上,攪拌是必需的。所以,一般認(rèn)為間歇式反應(yīng)器的濃度和溫度在空間上是均勻的,但是濃度隨時(shí)間變化。而溫度的順序變化則有利于選擇性或安全地實(shí)現(xiàn)充分的轉(zhuǎn)化。 在純粹的間歇式操作中,反應(yīng)物在開始時(shí)就完全加到反應(yīng)器中。為了更好地控制溫度,這種操作方式并不適合,而反應(yīng)物可能不得不逐漸加到容器內(nèi)。這樣反應(yīng)器被認(rèn)為是在半間歇式狀態(tài)下操作?;蛘?,為了實(shí)現(xiàn)反應(yīng)物的完全轉(zhuǎn)化,可以去除一種產(chǎn)品,例如在酯化反應(yīng)中的水。最明顯的區(qū)別是間歇操作和連續(xù)操作模式以及正在聯(lián)系的某種階段。間歇操作主要應(yīng)用于當(dāng)反應(yīng)時(shí)間很長(zhǎng)或所需的日常生產(chǎn)規(guī)模小的情況。相同的間歇式設(shè)備往往是在不同的時(shí)間用來制造各種產(chǎn)品的。否則,間歇操作不可能比連續(xù)操作來得經(jīng)濟(jì)。在一個(gè)日常的或長(zhǎng)的基本設(shè)備上安裝一個(gè)或多個(gè)間歇式反應(yīng)器配以適當(dāng)?shù)恼{(diào)壓槽就可以被用來模擬連續(xù)運(yùn)轉(zhuǎn)。 當(dāng)多相混合物參與時(shí),轉(zhuǎn)換率通常受限于界面物質(zhì)傳播的速度,以致于更大的接觸表面是可取的。因此,固體物或催化劑被精細(xì)分割,并且流體充分接觸是通過機(jī)械攪拌或離心泵來實(shí)現(xiàn)的。反應(yīng)器的迅速發(fā)展使得反應(yīng)器通過攪拌或離心泵增強(qiáng)傳熱和降低有害的溫度梯度。 攪拌反應(yīng)器 攪拌反應(yīng)器是最常見的間歇式反應(yīng)器。攪拌是為了混合原材料,在反應(yīng)期間保持統(tǒng)一性,以及在容器表面增快傳熱速度。無論是單容器或多容器,許多應(yīng)用中的攪拌反應(yīng)器是用于連續(xù)的處理。了解攪拌反應(yīng)器所達(dá)到的完全混合程度,對(duì)預(yù)測(cè)它作為反應(yīng)器的性能來說是極為必要的。間歇式和半間歇式反應(yīng)器最多用于低產(chǎn)量的情況,這時(shí)勞動(dòng)力費(fèi)用和空載時(shí)間僅是產(chǎn)品單位價(jià)格的很小一部分。它們通常出現(xiàn)在特殊化學(xué)品和聚合物以及藥物領(lǐng)域,特別是在產(chǎn)品種類種類眾多的工廠中?;钊鞣磻?yīng)器活塞流是一種簡(jiǎn)化的和理想化的流體流動(dòng),其中所有流體的單元都以相同的速度沿著品行的流線移動(dòng)。這種完全有序的流動(dòng)是唯一一個(gè)在活塞流反應(yīng)器模型中得到解釋的移動(dòng)機(jī)理。完全混流反應(yīng)器這種反應(yīng)器正好是上面所說的活塞流反應(yīng)器的反面極端。其基本的特點(diǎn)是假設(shè)整個(gè)反應(yīng)器中濃度和溫度的完全均勻性,與此相反的是進(jìn)入活塞流反應(yīng)器的流體前后分子相互之間沒有混合的假設(shè)。所以在完全混流反應(yīng)器中,轉(zhuǎn)化是在單一的濃度水平上發(fā)生的,當(dāng)然這個(gè)濃度就是流出物的濃度。為了接近這個(gè)理想混合流模型,在與流體流過容器的平均滯留時(shí)間相比很小的時(shí)間內(nèi),物料必須和反應(yīng)器中的流體充分混合。它和理想流動(dòng)模型的差別將在以后進(jìn)一步討論。當(dāng)溫度控制是關(guān)鍵的問題時(shí),則經(jīng)常地選用攪拌式連續(xù)流反應(yīng)器,例如在芳烴或甘油的硝基化反應(yīng)中。攪拌式連續(xù)流反應(yīng)器也被用在當(dāng)反應(yīng)必須在固定濃度下進(jìn)行時(shí),例如丁二烯與苯乙烯的共聚合,或者當(dāng)反應(yīng)必須在兩相間進(jìn)行,或者當(dāng)催化劑必須處于懸浮狀時(shí),例如用齊格勒催化劑時(shí)乙烯的聚合、甲基苯乙烯加氫轉(zhuǎn)化成異丙基苯的空氣氧化轉(zhuǎn)化成丙酮或苯酚等反應(yīng)。這里被稱為完全混流的反應(yīng)器有幾種不同的名稱。最早的一種叫“連續(xù)攪拌槽式反應(yīng)器” 或者CSTR,也有人將他改稱為“連續(xù)流動(dòng)攪拌槽式反應(yīng)器”或者CFSTR。其他一些名字是“返混反應(yīng)器”、“混合流動(dòng)反應(yīng)器”和“理想攪拌槽式反應(yīng)器”。所有這些名字都出現(xiàn)在文獻(xiàn)中,所以必須知道。攪拌槽反應(yīng)器優(yōu)先用于由于放熱多而采用很大液氣比的反應(yīng),因?yàn)閿嚢杩筛纳苽鳠?,并且也容易安裝內(nèi)換熱器。它們也能達(dá)到大的界面積。當(dāng)細(xì)分過的催化劑必須保持懸浮態(tài)時(shí),攪拌也是常用的。這樣反應(yīng)器就是“泥漿”類的反應(yīng)器。但是也有不攪拌的操作。有許多氫化、氧化和氯化的例子是在攪拌槽反應(yīng)器中進(jìn)行的??梢允情g歇的、半間歇的,也可以是連續(xù)的。固定床催化反應(yīng)器 本世紀(jì)初的固體催化劑的發(fā)現(xiàn)及其在化工中的應(yīng)用是化學(xué)工業(yè)的一次突破。從那時(shí)起,這個(gè)工業(yè)通過新過程的開發(fā)和已有過程的改造以一種特殊的方式不斷變化和發(fā)展,其中大多數(shù)過程依賴于固體催化劑的使用。 催化過程的大多數(shù)是在固定反應(yīng)器中進(jìn)行的。除了粗柴油的催化裂化在流化床反應(yīng)器中進(jìn)行以實(shí)現(xiàn)催化劑的連續(xù)再生外,現(xiàn)今化學(xué)和石油煉制工業(yè)中的大多數(shù)固體催化過程都采用固定床催化反應(yīng)器。目前的固定床反應(yīng)器主要是大容器裝置。反應(yīng)器容器的這種大幅度的增長(zhǎng)明顯地和不斷增長(zhǎng)的市場(chǎng)需求有關(guān),但是這種增長(zhǎng)的實(shí)現(xiàn)也毫無疑問地反映了世界上欣欣向榮的建設(shè)活動(dòng)所引起的在技術(shù)和基礎(chǔ)領(lǐng)域中的進(jìn)步。其他類型反應(yīng)器 還有其它不太普遍的類型,用于特殊的任務(wù)。例如文丘里反應(yīng)器用在抗污染的設(shè)施中以苛性堿洗掉少量的殘余SO2。這種反應(yīng)器的有點(diǎn)是它們的壓降低,原因是文丘里管將氣體排到液體中。落膜反應(yīng)器或濕壁反應(yīng)器可以用于發(fā)熱量極大的反應(yīng)。另外,有限的和精確的界面積使得可以很好地控制很快速的反應(yīng)?;緮嚢璺磻?yīng)器的設(shè)計(jì) 液體壓力容器的大小與攪拌器的大小和安裝位置,檔板和其他內(nèi)部的因素是影響大量攪拌或混合質(zhì)量所需的能量的因素。內(nèi)部安裝取決于操作的目的:是保持同質(zhì)性的
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