過程裝備與控制工程專業(yè)英語

1、Reading Material 16 Pressure Vessel CodesHistory of Pressure Vessel Codes in the United States Through the late 1800s and early 1900s, explosions in boilers and pressure vessels were frequent. A firetube boiler explosion on the Mississippi River steamboat Sultana on April 27, 1865, resulted in the b

2、oat's sinking within 20 minuted and the death of 1500 soldiers going home after the Civil War. This type of catastrophe continued unabated into the early 1900s. In 1905, a destructive explosion of a firetube boiler in a shoe factory in Brockton, Massachusetts, killed 58 people, injured 117 other

3、s, and did $400000 in property damage. In 1906, another explosion in a shoe factory in Lynn, Massachusetts, resulted in death, injury, and extensive property damage. After this accident, the Massachusetts governor directed the formation of a Board of Boiler Rules. The first set of rules for the desi

4、gn and construction of boilers was approved in Massachusetts on August 30, 1907. This code was three pages long. In 1911, Colonel E. D. Meier, the president of the American Society of Mechanical Engineers, established a committee to write a set of rules for the design and construction of boilers and

5、 pressure vessels. On February 13, 1915, the first ASMEBoiler Code was issued. It was entitled "Boiler Construction Code, 1914 Edition". This was the beginning of the various sections of the ASME Boiler and Pressure Vessel Code, which ultimately became Section 1, Power Boilers. The first A

6、SME Code for pressure vessels was issued as "Rules for the Construction of Unfired Pressure Vessels", Section , 1925 edition. The rules applied to vessels over 6 in. in diameter, volume over 1.5 , and pressure over 30 psi. In December 1931, a Joint API-ASME Committee was formed to develop

7、an unfired pressure vessel code for the petroleum industry. The first edition was issued in 1934. For the nest 17 years, two separated unfired pressure vessel codes existed. In 1951, the last API-ASME Code was issued as a separated document. In 1952, the two codes were consolidated into one code-the

8、 ASME Unfired Pressure Vessel Code, Section . This continued until the 1968 edition. At that time, the original code became Section , Division 1, Pressure Vessels, and another new part was issued, which was Section , Division 2, Alternative Rules for Pressure Vessels. The ANSI/ASME Boiler and Pressu

9、re Vessel Code is issued by the American Society of Mechanical Engineers with approval by the American National Standards Institute (ANSI) as an ANSI/ASME document. One or more sections of the ANSI/ASME Boiler and Pressure Vessel Code have been established as the legal requirements in 47 states in t

10、he United Stated and in all provinces of Canada. Also, in many other countries of the world, the ASME Boiler and Pressure Vessel Code is used to construct boilers and pressure vessels. Organization of the ASME Boiler and Pressure Vessel Code The ASME Boiler and Pressure Vessel Code is divided into m

11、any sections, divisions, parts, and subparts. Some of these sections relate to a specific kind of equipment and application; others relate to specific materials and methods for application and control of equipment; and others relate to care and inspection of installed equipment. The following Sectio

12、ns specifically relate to boiler and pressure vessel design and construction. Section Power Boilers (1 volume) Section Division 1 Nuclear Power Plant Components (7 volumes) Division 2 Concrete Reactor Vessels and Containment (1 volume) Code Case Case 1 Components in Elevated Temperature service (in

13、Nuclear Code N-47 Case book) Section Heating Boilers (1 volume) Section Division 1 Pressure Vessels (1 volume) Division 2 Alternative Rules for Pressure Vessels (1 volume) Section Fiberglass-Reinforced Plastic Pressure Vessels (1 volume) A new edition of the ASME Boiler and Pressure Vessel Code is i

14、ssued on July 1 every three years and new addenda are issued every six months on January 1 and July 1. The new edition of the code becomes mandatory when it appears. The addenda are permissive at the date of issuance and become mandatory six months after that date. Worldwide Pressure Vessel Codes In

15、 addition to the ASME Boiler and Pressure Vessel Code, which is used worldwide, many other pressure vessel codes have been legally adopted in various countries. Difficulty often occurs when vessels are designed in one country, built in another country, and installed in still a different country. Wit

16、h this worldwide construction this is often the case. The following list is a partial summary of some of the various codes used in different countries: Australia Australian Code for Boilers and Pressure Vessels, SAA Boiler Code (Series AS 1200):AS 1210, Unfired Pressure Vessels and Class 1 H, Pressu

17、re Vessels of Advanced Design and Construction, Standards Association of Australia. France Construction Code Calculation Rules for Unfired Pressure Vessels, Syndicat National de la Chaudronnerie et de la Tuyauterie Industrielle (SNCT), Paris, France. United Kingdom British Code BS. 5500, British Sta

18、ndards Institution, London, England. Japan Japanese Pressure Vessel Code, Ministry of Labour, published by Japan Boiler Association, Tokyo, Japan; Japanese Standard, Construction of Pressure Vessels, JIS B 8243, published by the Japan Standards Association, Tokyo, Japan; Japanese High Pressure Gas C

19、ontrol Law, Ministry of International Trade and Industry, published by The Institution for Safety of High Pressure Gas Engineering, Tokyo, Japan. Italy Italian Pressure Vessel Code, National Association for Combustion Control (ANNCC), Milan, Italy. Belgium Code for Good Practice for the Construction

20、 of Pressure Vessels, Belgian Standard Institute (IBN), Brussels, Belgium. Sweden Swedish Pressure Vessel Code, Tryckkarls kommissioner, the Swedish Pressure Vessel Commission, Stockholm, Sweden.壓力容器準(zhǔn)則美國的壓力容器規(guī)范歷史 在19世紀(jì)和20世紀(jì)初期，鍋爐和壓力容器頻繁發(fā)生爆炸事件。1865年4月27日，蘇丹輪船的火管鍋爐在密士西比河爆炸，導(dǎo)致輪船在20分鐘內(nèi)沉沒，且參加南北戰(zhàn)爭的1500準(zhǔn)備回家

21、的士兵全部死忙。這類大災(zāi)難一直持續(xù)到20世紀(jì)初期。1905年，馬薩諸塞州布拉克頓一鞋廠發(fā)生毀滅性的火管鍋爐爆炸事件，造成58人死亡，117人受傷，財(cái)產(chǎn)損失400000$。1906年，馬薩諸塞州林恩一個(gè)鞋廠發(fā)生爆炸，導(dǎo)致死亡，受傷，且持續(xù)性損失。這次意外后，馬薩諸塞州州長組織成立鍋爐標(biāo)準(zhǔn)委員會。1907年8月30日，第一部鍋爐設(shè)計(jì)及結(jié)構(gòu)規(guī)范獲得通過，長達(dá)3頁。 1911年，德梅爾上校，美國機(jī)械工程師學(xué)會主席，成立一個(gè)委員會來編寫鍋爐及壓力容器的設(shè)計(jì)和結(jié)構(gòu)規(guī)范。1915 2月13日，第一個(gè)美國機(jī)械工程師學(xué)會鍋爐規(guī)范發(fā)布，叫做鍋爐構(gòu)造規(guī)范，1914版本。這是系列美國機(jī)械工程師學(xué)會鍋爐及壓力容器規(guī)范的

22、開端，最終變成第一章電站鍋爐。 第一部關(guān)于壓力容器的機(jī)械工程師協(xié)會標(biāo)準(zhǔn)作為熱交換器結(jié)構(gòu)規(guī)則發(fā)布，共8章，1925版本。規(guī)定容器直徑為6英尺，體積為1.5英尺，并且壓力為 每平方英寸30磅。1931年12月，美國石油組織-美國機(jī)械工程師學(xué)會委員會成立并致力于研究用于石油工業(yè)的熱交換器規(guī)則。1934開始發(fā)行第一個(gè)版本。接下來的17年，就有兩部分離熱交換器規(guī)則。1951年，美國石油組織與美國機(jī)械工程師協(xié)會標(biāo)準(zhǔn)作為單獨(dú)文件發(fā)布。1952年，這兩部規(guī)則合并成一部-美國機(jī)械工程師學(xué)會熱交換器規(guī)則，共8章。一直延續(xù)到1968年版。那時(shí)，原始的規(guī)則變成8章，1部是壓力容器，另一部分是2章的壓力容器替換規(guī)則。

23、美國國家標(biāo)準(zhǔn)協(xié)會美國機(jī)械工程師學(xué)會鍋爐及壓力容器規(guī)則由美國機(jī)械工程師學(xué)會發(fā)布，由美國國家標(biāo)準(zhǔn)協(xié)會批準(zhǔn)的作為美國國家標(biāo)準(zhǔn)協(xié)會美國機(jī)械工程師學(xué)會文件。更多的美國國家標(biāo)準(zhǔn)協(xié)會美國機(jī)械工程師學(xué)會鍋爐及壓力容器規(guī)則在美國47州和加拿大所有城市作為法定使用。同時(shí)，世界上許多其他國家使用美國機(jī)械工程師學(xué)會鍋爐及壓力容器規(guī)則來制造造鍋爐及壓力容器。 ASME 鍋爐及壓力容器規(guī)范 美國機(jī)械工程師學(xué)會鍋爐及壓力容器規(guī)則分成許多章。有些章節(jié)涉及到一些特殊設(shè)備及使用；有些涉及到特殊材料和設(shè)備的操作和控制方法；其他的涉及到設(shè)備的安裝及維護(hù)等。下面的章節(jié)與鍋爐及壓力容器設(shè)計(jì)和結(jié)構(gòu)有關(guān)。 第一章 電站鍋爐（1卷） 第3章

24、節(jié)1 核電站元件（卷） 節(jié)2 混凝土電抗器容器及防范（1卷） 規(guī)則事例 事例1，高溫保養(yǎng)元件（核的規(guī)則手冊的氮-47） 第7章 鍋爐供暖（1卷） 第8章 節(jié)1 壓力容器（1卷） 節(jié) 壓力容器替換規(guī)則（1卷） 第9章 玻璃鋼壓力容器（1卷） 每三年發(fā)布一次新版美國機(jī)械工程師學(xué)會鍋爐及壓力容器規(guī)則，每六個(gè)月發(fā)布新的附錄，分別是1月1日和7月1日。每當(dāng)新版規(guī)則發(fā)布就強(qiáng)制執(zhí)行，附錄的發(fā)行允許不執(zhí)行，但即日起六個(gè)月后腰強(qiáng)制執(zhí)行。 壓力容器國際規(guī)范 除國際使用的美國機(jī)械工程師學(xué)會鍋爐及壓力容器規(guī)則外，許多其他的壓力容器規(guī)范在多個(gè)國家可以使用。在一個(gè)國家設(shè)計(jì)的容器在他國使用時(shí)經(jīng)常發(fā)生故障，這種情況常發(fā)生在國

25、際性結(jié)構(gòu)。 下面的目錄是被用于列國中的各種規(guī)則的一部分的一些摘要信息： 澳大利亞 鍋爐及壓力容器的澳大利亞規(guī)則，表面活性劑鍋爐規(guī)范（1200系列）:系列1210，熱交換器，先進(jìn)的壓力容器設(shè)計(jì)和結(jié)構(gòu)，澳大利亞標(biāo)準(zhǔn)協(xié)會。 法國 熱交換器結(jié)構(gòu)規(guī)則計(jì)算規(guī)則，巴黎，法國。 英國 反散射能譜法英國規(guī)則。5500，英國標(biāo)準(zhǔn)協(xié)會，倫敦，英國。 日本 日本壓力容器規(guī)范，勞工部，由日本鍋爐協(xié)會出版，東京，日本；日本標(biāo)準(zhǔn)，壓力容器結(jié)構(gòu)，日本工業(yè)標(biāo)準(zhǔn)B，8243，由日本標(biāo)準(zhǔn)協(xié)會出版，東京，日本；日本高壓氣體管制法，日本通商產(chǎn)業(yè)省，由安全的高壓氣體工程師協(xié)會出版，東京，日本。 意大利 意大利壓力容器規(guī)范，燃燒過程控制（

26、anncc）國家協(xié)會，米蘭，意大利。 比利時(shí) 國際慣例壓力容器結(jié)構(gòu)規(guī)則，比利時(shí)的標(biāo)準(zhǔn)協(xié)會，布魯塞爾，比利時(shí)。 瑞典 瑞典壓力容器規(guī)范，tryckkarls kommissioner，瑞典壓力容器試運(yùn)行，斯德哥爾摩，瑞典。 Reading Material 17Stress CategoriesThe various possible modes of failure which confront the pressure vessel designer are:(1)Excessive elastic deformation including elastic instability.(2)E

27、xcessive plastic deformation.(3)Brittle fracture.(4)Stress rupture/creep deformation (inelastic).(5)Plastic instability-incremental collapse.(6)High strain-low cycle fatigue. (7)Stress corrosion.(8)Corrosion fatigue.In dealing with these various modes of failure, we assume that the designer has at h

28、is disposal a picture of the state of stress within the part in question. This would be obtained either through calculation or measurements of the both mechanical and thermal stresses which could occur throughout the entire vessel during transient and steady state operations. The question one must a

29、sk is what do these numbers mean in relation to the adequacy of the design? Will they insure safe and satisfactory performance of a component? It is against these various failure modes that the pressure vessel designer must compare and interpret stress values. For example, elastic deformation and el

30、astic instability (buckling) cannot be controlled by imposing upper limits to the calculated stress alone. One must consider, in addition, the geometry and stiffness of a component as well as properties of the material.The plastic deformation mode of failure can, on the other hand, be controlled by

31、imposing limits on calculated stresses, but unlike the fatigue and stress corrosion modes of failure, peak stress does not tell the whole story. Careful consideration must be given to the consequences of yielding, and therefore the type of loading and the distribution of stress resulting therefrom m

32、ust be carefully studied. The designer must consider, in addition to setting limits for allowable stress, some adequate and proper failure theory in order to define how the various stresses in a component react and contribute to the strength of that part.As mentioned previously, different types of s

33、tress require different limits, and before establishing these limits it was necessary to choose the stress categories to which limits should be applied. The categories and sub-categories chosen were as follows:A.Primary Stress.(a) General primary membrane stress.(b) Local primary membrane stress.(c)

34、 Primary bending stress.B.Secondary Stress.C.Peak Stress.The major stress categories are primary, sec9ondary, and peak. Their chief characteristics may be described briefly as follows:(a) Primary stress is a stress developed by the imposed loading which is necessary to satisfy the laws of equilibriu

35、m between external and internal forces and moments. The basic characteristic of a primary stress is that it is not self-limiting. If a primary stress exceeds the yield strength of the material through the entire thickness, the prevention of failure is entirely dependent on the strain-hardening prope

36、rties of the material.(b) Secondary stress is a stress developed by the self-constraint of a structure. It must satisfy an imposed strain pattern rather than being in equilibrium with an external load. The basic characteristic of a secondary stress is that it is self-limiting. Local yielding and min

37、or distortion can satisfy the discontinuity conditions or thermal expansions which cause the stress to occur.(c) Peak stress is the highest stress in the region under consideration. The basic characteristic of a peak stress is that it causes no significant distortion and is objectionable mostly as a

38、 possible source of fatigue failure. The need for dividing primary stress into membrane and bending components is that, as will be discussed later, limit design theory shows that the calculated value of a primary bending stress may be allowed to go higher than the calculated value of a primary membr

39、ane stress. The placing in the primary category of local membrane stress produced by mechanical loads, however, requires some explanation because this type of stress really has the basic characteristics of a secondary stress. It is self-limiting and when it exceeds yield, the external load will be r

40、esisted by other parts of the structure, but this shift may involve intolerable distortion and it was felt that must be limited to a lower value than other secondary stresses, such as discontinuity bending stress and thermal stress.Secondary stress could be divided into membrane and bending componen

41、ts, just as was done for primary stress, but after the removal of local membrane stress to the primary category, kit appeared that all the remaining secondary stresses could be controlled by the same limit and this division was unnecessary.Thermal stress are never classed as primary stresses, but th

42、ey appear in both of the other categories, secondary and peak. Thermal stresses which can produce distortion of the most complete suppression of the differential expansion, and thus cause no significant distortion, are classed as peak stresses.One of the commonest types of peak stress is that produc

43、ed by a notch, which might be a small hole or a fillet. The phenomenon of stress concentration is well-known and requires no further explanation here. Many cases arise in which it is not obvious which category a stress should be placed in, and considerable judgment is required. In order to standardi

44、ze this procedure and use the judgment of the writers of the Code rather than the judgment of individual designers, a table was prepared covering most of the situations which arise in pressure vessel design and specifying which category each stress must be placed in.The potential failure modes and v

45、arious stress categories are related to the Code provisions as follows:(a) The primary stress limits are intended to prevent plastic deformation and to provide a nominal factor of safety of the ductile burst pressure.(b) The primary plus secondary stress limits are intended to prevent excessive plas

46、tic deformation leading to incremental collapse, and to validate the application of the elastic analysis when performing the fatigue evaluation.(c) The peak stress limit is intended to prevent fatigue failure as a result of cyclic loading.(d) Special stress limits are provided for elastic and inelas

47、tic instability.Protection against brittle fracture are provided by material selection, rather than by analysis. Protection against environmental conditions such as corrosion and radiation effects are the responsibility of the designer. The creep and stress rupture temperature range will be consider

48、ed in later condition.應(yīng)力類型壓力容器設(shè)計(jì)者遇到的多種可能的失效形式：（1） 過度彈性變形包括彈性失穩(wěn)。（2） 過度塑性變性。（3） 脆性斷裂。（4） 應(yīng)力斷裂/蠕變變形（非彈性的）。（5） 塑性不穩(wěn)性增加失穩(wěn)。（6） 高應(yīng)變低周期疲勞。（7） 應(yīng)力腐蝕。（8） 疲勞腐蝕。在處理這些不同的失效形式上，我們假設(shè)設(shè)計(jì)者在局部問題的處理上，有一副應(yīng)力狀態(tài)圖。這需要通過對機(jī)械和熱應(yīng)力的計(jì)算或測量來得到，它們（應(yīng)力）在短暫穩(wěn)定的狀態(tài)操作期間，存在于整個(gè)容器中。有人會問，這些數(shù)據(jù)與設(shè)計(jì)的合理性有什么關(guān)系？它們能確保一個(gè)構(gòu)件的安全和滿意的性能嗎？它與這些各種各樣的失效形式對立，壓力容器

49、設(shè)計(jì)者必須比較和說明應(yīng)力值。例如，通過單獨(dú)計(jì)算應(yīng)力來強(qiáng)加上限，是不能控制彈性變形和彈性失穩(wěn)。此外，還必須考慮構(gòu)件的幾何形狀和硬度，以及材料的特性。從另一方面來看，塑性變形失效形式可以通過在計(jì)算的應(yīng)力上強(qiáng)加極限來控制，但不象疲勞和應(yīng)力腐蝕失效形式，峰值應(yīng)力不做整體描述。必須對屈服結(jié)果進(jìn)行仔細(xì)考慮。因此，載荷的類型和由那里引起的應(yīng)力分布，必須被仔細(xì)研究。除了限制許用應(yīng)力外，設(shè)計(jì)者還必須考慮一些適當(dāng)?shù)氖Ю碚?，來解釋各種應(yīng)力怎樣在構(gòu)件內(nèi)起作用和對那些部分的強(qiáng)度所做的貢獻(xiàn)。正如前面所涉及的，不同類型的應(yīng)力需要不同的限制，在確定這些限制之前，選擇應(yīng)用于什么限制的應(yīng)力類型是必要的。供選擇的應(yīng)力類型如下：A

50、、 主應(yīng)力。（a）普通的薄膜主應(yīng)力（b）內(nèi)部薄膜主應(yīng)力（c）主要彎曲應(yīng)力B、 副應(yīng)力 C、 最大應(yīng)力應(yīng)力類型是主應(yīng)力、副應(yīng)力及最大應(yīng)力。它們的主要特征簡略描述如下：（a） 主應(yīng)力是由施加載荷產(chǎn)生的應(yīng)力，載荷在滿足外部和內(nèi)部的作用力和力矩之間的平衡規(guī)律是必要。一次應(yīng)力的基本特征是自身不受限制。在整個(gè)厚度上，如果一次應(yīng)力超過了材料的屈服強(qiáng)度，防止失效必須完全依賴材料的變形硬化性質(zhì)。（b） 副應(yīng)力是由結(jié)構(gòu)的自身約束二產(chǎn)生的應(yīng)力。它必須滿足一個(gè)強(qiáng)加應(yīng)變的式樣，而不是與一個(gè)外載荷平衡。副應(yīng)力的基本特征是自身受限制。局部屈服和較小變形，能夠滿足引起應(yīng)力產(chǎn)生的不連續(xù)條件或者熱膨脹。（c） 最大應(yīng)力是所考慮范

51、圍內(nèi)的最高應(yīng)力。峰值應(yīng)力的基本特征，是不會引起大的變形和作為疲勞失效一個(gè)可能的源頭是令人討厭的。將主應(yīng)力分成薄膜和彎曲部分的必要，以后再討論，極限設(shè)計(jì)理論表明主彎曲應(yīng)力的計(jì)算值允許高于主薄膜應(yīng)力的計(jì)算值。然而，我們應(yīng)該解釋一下由機(jī)械載荷產(chǎn)生的局部薄膜應(yīng)力的主要種類的位置，因?yàn)檫@種應(yīng)力確實(shí)有副應(yīng)力的基本特征。它是自身受限制的，而且當(dāng)它超過屈服極限后，外載荷將受到結(jié)構(gòu)的其他部分抵抗，但這種轉(zhuǎn)變可能會產(chǎn)生嚴(yán)重變形，因此必須將它限制在比其他副應(yīng)力更小的值，例如不連續(xù)彎曲應(yīng)力和熱應(yīng)力。正如主應(yīng)力那樣，副應(yīng)力被分為薄膜和彎曲部分，但是，在將局部薄膜應(yīng)力歸到主應(yīng)力類型后，就會有所有剩余的副應(yīng)力被相同的限制控

52、制，這種分劃是沒有必要的。熱應(yīng)力從來不被歸類為主應(yīng)力，但它卻出現(xiàn)在其他兩種類型中，副和最大應(yīng)力中。能夠通過大部分抑制小膨脹而產(chǎn)生變形，以及不會引起嚴(yán)重變形的熱應(yīng)力，被歸為最大應(yīng)力。最大應(yīng)力的一個(gè)最普通的類型，是由缺口引起的，它可能是一個(gè)小洞或一條裂痕。我們都知道應(yīng)力集中現(xiàn)象，這里不做進(jìn)一步解釋。許多情況出現(xiàn)在不明顯的地方，一種應(yīng)力該歸納為哪種，需要考慮到判斷能力。為了使這個(gè)程序規(guī)范化，并且使用規(guī)范作者的判斷法，而不是個(gè)別設(shè)計(jì)者的判斷法，準(zhǔn)備一份能夠包括大多數(shù)情況的表格，這些情況出現(xiàn)在壓力容器設(shè)計(jì)和詳細(xì)說明中，每種應(yīng)力都必須填入其中。潛在的失效形式和各種應(yīng)力類型，與規(guī)范條款有如下的聯(lián)系：（a）主

53、應(yīng)力的限制，目的是防止塑性變形，并在韌性爆破壓力上提供一個(gè)名義安全因素。(b)主應(yīng)力和副應(yīng)力的限制，目的是防止導(dǎo)致失穩(wěn)增加的過量塑性變形和做疲勞估算時(shí)， 確認(rèn)彈性分析的應(yīng)用。(c)最大應(yīng)力的極限，目的是防止因周期載荷產(chǎn)生的疲勞失效。(d)特殊應(yīng)力的限制，提供給彈性和非彈性失穩(wěn)。應(yīng)對脆性斷裂的保護(hù)，是通過材料的選擇，而不是分析提供的。對環(huán)境條件比如腐蝕和輻射的保護(hù)，是每個(gè)設(shè)計(jì)者的職責(zé)。蠕變和應(yīng)力斷裂的溫度范圍，將在以后的章節(jié)中考慮。Reading Material 18Packed TowersIn comparison with tray towers, packed towers are s

54、uited to small diameters (24 in. or less), whenever low pressure is desirable, whenever low holdup is necessary, and whenever plastic or ceramic construction is required. Applications unfavorable to packings are large diameter towers, especially those with low liquid and high vapour rates, because o

55、f problems with liquid distribution, and whenever high turndown is required. In large towers, random packing may cost more than twice as much as sieve or valve trays. Depth of packing without intermediate supports is limited by its deformability; metal construction is limited to depths of 20 25 ft,

56、and plastic to 10 15 ft. Intermediate supports and liquid redistributors usually are needed every 2.5 3 tower diameters for Raschig rings and every 5 10 diameters for Pall rings, but at least every 20 ft. The various kinds of internals of packed towers are represented in Fig. 4.2 whose individual pa

57、rts may be described one-by-one. (a) is an example column showing the inlet and outlet connections and some of the kinds of internals in place. (b) is a combination packing support and redistributor that can also serve as a sump for withdrawal of the liquid from the tower. (c) is a trough-type distributor that is suitable for liquid rates in excess of 2 gpm/sqft in towers 2 feet and more in diameter. They can be made in ceramics or plastics. (d) is an example of a perforated pipe distributor which is available in a variety