Lesson 7
第7课
Absorption of Gases
气体吸收
The removal去除of one or more selected选定的components from a mixture of gases混合气体by absorption吸收into a suitable liquid is the second major operation of chemical engineering that is based on基于interphase界面mass transfer质量传递controlled largely by rates of diffusion扩散速率控制1.
1、通过吸收将气体混合物中的一个或是几个组分脱除到合适的液体中去，是第二大基于扩散速率控制的相际传质的化工操作。
Thus因此, acetone丙酮can be recovered from an acetone-air mixture by passing the gas stream into water in which the acetone dissolves溶解while the air passes out.
2、因此，将丙酮和空气的混合气通入水中，丙酮发生了溶解而空气逸出，从而使丙酮得到恢复。
Similarly, ammonia氨气may be removed from an ammonia-air mixture by absorption in water.
3、同样，可以用水作为吸收剂将氨气从氨气和空气的混合其中移去。
In each of these examples the process o r absorption of the gas in the liquid can be treated as被当做  a physical process, the chemical reaction having no appreciable可感知的effect.
4、这些过程或在液体中气体吸收的例子被认为是物理过程，化学反应没有任何的影响。
However, when oxides of nitrogen氮的氧化物are absorbed in water to give nitric acid硝酸, or when carbon dioxide二氧化碳is absorbed in a solution溶液of sodium hydroxide氢氧化钠, a chemical reaction occurs, the nature性质of which influences影响the actual实际的rate of absorption.
5、然而，当氮的氧化物被水吸收变成硝酸，或是二氧化碳被氢氧化钠溶液吸收时，会发生化学反应，这种性质会对吸收的实际速率产生影响。
Absorption processes are therefore conveniently divided into two groups, those in which the process is solely独自地physical and those where a chemica l reaction is occurring.
6、因此，吸收被方便地分成了两类，一是只有物理变化的，另一个是伴有化学反应的。
In considering the design of equipment to achieve gas absorption, the main requirement is that the gas
be brought into intimate亲密的contact with the liquid, and the effectiveness of the equipment will largely be determined by the success with which it promotes contact between the two phases.
7、考虑设备的设计来实现气体的吸收，主要要求是气液两相要进行充分接触，设备的效果很大程度上取决于它能否促使气液两相可以充分接触。
The most useful concept概念of the process of absorption is given by two-film theory.
8、双膜理论是最有用的吸收概念理论。
According to the theory, material is transferred in the bulk体积、容积of the phases各相主体by convection currents对流运动, and concentration浓度differences浓度差异are regarded as negligible微不足道except除了in the vicinity附近of the interface界面between the phases2.
9、根据这一理论，在各相主体中，物质是通过对流运动来传递的，而且浓度差是可以忽略不计的，除了在相界面附近之外。
On either side of this interface界面it is supposed that人们推测the current s die out消失and that there exists a thin film膜of fluid through which the transfer is effected solely单独地by molecular diffusion.
10、在界面的两侧，人们推测运动会消失，在这里存在一个薄的流体膜（气膜和液膜），在薄膜中的传递仅受分子扩散的影响。
This film will be slightly稍稍thicker厚than the laminar sub-layer层流内层, because i t offers a resistance equivalent to that of the whole boundary layer边界层.
11、这个膜仅仅比层流内层厚些，因为它产生的阻力等同于整个边界层的阻力。
According to F ick's LaW the rate of transfer by diffusion is proportional正比to the concentration浓度gradient and to the area面积of interface over which the diffusion is occurring. ' 12、根据菲克定律，扩散的传递速率正比于浓度梯度以及发生扩散的界面面积大小。
The general form of equipment is similar to that described for distillation, and packed填料塔and plate板式塔towers are generally used for large installations装置.
13、吸收装置的一般形式和精馏类似，填料塔和板式塔一般用于大型装置
The method of operation is not the same.
14、然而操作方式却不相同。
In absorption, the feed is a gas and is introduced引入at the bottom底部of the column塔, and the solvent溶剂is fed to the top, as a liquid; the absorbed gas and solvent leave at the bottom, and the unabsorbed components leave as gas from the top.
reaction diffusion15、在吸收中，进料是气体，从塔底引入，溶剂做为液体从塔顶进入，被吸收气体与溶剂从塔底离开，不被吸收的气体组分从塔顶离开。
The essential difference between distillation and absorption is that in the former前者the vapor has to be produced in each stage by partial vaporization部分汽化of the liquid which is therefore at its boiling point, whereas然而in absorption the liquid is well远远地below its boiling point.
16、精馏和吸收本质的不同是前者不得不在每一块塔板上通过液体部分汽化来获得蒸汽，因此液体的温度要在其沸点处，然而再吸收中，液体却远远低于其沸点。
In distillation there is a diffusion of molecules in both directions, so that for an ideal system equimolecular等分子counter-diffusion反向扩散exists, but in absorption gas molecules are diffusing into the liquid, and the movement in the reverse相反的direction is negligible3.
17、在精馏过程中，分子扩散是双向的，因此，对于理想系统，存在等分子反向扩散，但是在吸收中，气体分子是扩散到液相，反向扩散是忽略不计的。
In general, the ratio比率of the liquid to the gas flowrate流率is considerably greater in absorption than in distillation with the result that layout布局of the trays is dif f erent in the two cases.
18、总的来说，相比精馏，吸收操作中液体的流率要大于气体流率，主要因为两种情况的塔板布局不同。
Furthermore, with the higher liquid rates in absorption, packed columns填料塔are much more commonly used.
19、而且，由于吸收操作液体流率高，所以填料塔被普遍使用。
As a result of the wide variety of purposes目的and specif i cation规格of absorbers吸收器, a large number of qui t e dif f erent types have been built and used.
20、由于各种各样的目的不同，吸收器的规格不同，大量不同种类的吸收器被制造和使用。
The various types of gas-absorption equipment may be divided roughly大致地into three groups: a) packed towers, b) bubble-cap towers, and c) miscellaneous其他types, including spray chambers and agitated vessels.
21、不同种类的气体吸收装置大致可以分为三类：a)填料塔，b）泡罩塔，和c）其他类型，包括喷雾室和搅拌釜。
The objective目标of each design, however, is the provision for提供intimate亲密的contact of gas and liquid over a large interphase surface相界面; with low first cost成本and low operating and maintenance维修expense发费.
22、但是，每种设计的目的都是要在低成本，低的操作和维修费用的条件下，在一个大的相界面上使气液两相可以充分接触。
The first cost includes foundations; tower shell; packing material; solvent charge, pumps, blowers, piping ducts, accessory heaters, coolers, and heat exchangers; and solvent-recovery system, if needed.
23、首要成本包括基建；塔体；填料物质；溶剂费用；泵；风机；输送管道；辅助加热器；冷却器，和热交换器；如有必要还需溶剂回收系统。
The operating costs include power for circulating gas and solvent, maintenance, labor, steam蒸汽for regenerating再生the solvent, cooling water, solvent make-up补给, and the value of the material which remains unabsorbed and is lost.
24、操作费用包括循环气体和溶剂所需要的能量，维修，劳动力，使溶剂再生的蒸汽，冷却水，溶剂补给，以及那些不被吸收的和损失掉的物质的价值。
Abbreviated简洁的methods for choosing the economically optimum最佳的operating conditions and equipment dimension s设备尺寸are needed.
25、选择最佳操作条件和设备尺寸的简单的凡是是需要的。
(J.M.Coulson andJ.F. Richardson)
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