兰州理工大学石油化工学院毕业设计(论文)
solution back to the storage tank at the end of the experiment. Further, a filter can be installed for
clarification of the solution.
6. 2 Measurement of the concentration，supersaturation and solubility
The concentration of the solution was determined by means of an immersion refractometer. A sample of the solution was diluted by addition of about the same amount of water. The masses of the water and the solution were measured. The refractive index of the new solution was measured after the solution was heated to 38°C. The concentration of the solution was determined from the known relation between refractive index and concentration, which was determined with the same equipment using solutions with a known concentration. The initial concentration was calculated using the concentration of the diluted solution and the masses of the water and solution. The precision was about 0.1 g/l00g H2O.
Measurement of the refractive index can be used to follow the concentration of the solution with time in a batch crystallizer. The supersaturation can be determined when the solubility curve is known. In view of the fact that the crystal size distribution is mainly determined by the period that the supersaturation reaches its maximum and then drops to a more or less constant value, it is essential that the measuring instrument be able to follow rapid change in supersaturation accurately. Further, the accuracy of the supersaturation had to be sufficient, especially at low supersaturation, in order to be able to compare these results with the ones from the continuous crystallizer and the fluidized bed. A standard instrument was bought which seemed to satisfy both requirements. The transition between light and dark was measured by means of a light sensitive resistance. Three problems arose: The instrument reading was dependent on the room temperature (the temperature of the solution was kept constant),The instrument reading was dependent on the light intensity of the lamp, and the instrument reading was not independent of the stirred vessel in which the measurement was made.The first two problems were solved to some extend by keeping the temperature of the light sensitive resistance as constant as possible and by stabilizing the power fed to the lamp. The third problem, which was probably caused by re-entry of light into the prism, required a reconstruction of the measuring device. This time consuming and laborious reconstruction has not been carried out.
The solubility of potassium dichromate has been measured by placing a highly concentrated, warm solution in a constant temperature bath. The suspension was agitated for 6 to 12 hours in order to attain equilibrium between solution and crystals. Then agitation was stopped and at least 10 hours later two samples of the solution were withdrawn , These samples were boiled dry to determine the concentration. The results are shown in table 5.2.
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兰州理工大学石油化工学院毕业设计(论文)
6.3 Thermodynamics of separation operations
Thermodynamic properties and equations play a major role in separation operations, particularly with respect to energy requirements, phase equilibria, and sizing equipment. This
chapter discusses applied thermodynamics for separation processes. Equations for energy balances, entropy and availability balances, and for determining phase densities and phase compositions at equilibrium are developed. These involve thermodynamic properties, including specific volume or density, enthalpy, entropy, availability, and fugacities and activities together with their coefficients, all as functions of temperature, pressure, and phase composition.Methods for estimating properties for ideal and non-ideal mixtures are summarized.
6.3.1Energy, entropy, and availability balances
Most commercial separation operations utilize large quantities of energy in the form of heat and/or shaft work. For example, the energy consumption by distillation in the US is approximately $10 trillion per year (1991). Thus, it is of considerable interest to know the extent of energy consumption in a separation process, and to what degree energy requirements might be reduced. Such energy estimates can be made by applying the first and second laws of thermodynamics.Consider the continuous, steady-state flow system for a general separation process in Fig. 2.1.
One or more feed streams flowing into the system are separated into two or more product streams that flow out of the system.
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兰州理工大学石油化工学院毕业设计(论文)
n- molar flow rates， zi- the component mole fractions
T- temperature, b- molar availabilities h- molar enthalpies, s- molar entropies
P- pressure, Q- heat flows in or out, W- shaft work crossing the boundary of the system
At steady state, if kinetic, potential, and surface energy changes are neglected, the first law of thermodynamics (also referred to as the conservation of energy or the energy balance), states that the sum of all forms of energy flowing into the system equals the sum of the energy flows leaving the system:
(stream enthalpy flows + heat transfer + shaft work) leaving system- (stream enthalpy flows + heat transfer + shaft work) entering system =0
All separation processes must satisfy the energy balance. Inefficient separation processes require large transfer of heat and/or shaft work both into and out of the process; efficient processes require smaller levels of heat transfer and/or shaft work. The first law of thermodynamics provides no information on energy efficiency, but the second law of thermodynamics (also referred to as the entropy balance) does.The entropy balance is:
(stream entropy flows + entropy flows by heat transfer) leaving system- (stream entropy flows + entropy flows by heat transfer) entering system= production of entropy by the process.
Note that the entropy balance contains no terms related to shaft work.
* Although the production of entropy, ?Sirr, is a measure of energy inefficiency, it is difficult to relate to this measure because it does not have the units of energy/time (power).
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兰州理工大学石油化工学院毕业设计(论文)
附录B: 外文翻译 6.实验过程分析
6.1 .42L连续结晶生产过程和流化床
连续结晶生产实验中的成核速率和流化床实验中的生长速率可以用于成批的结晶实
验。下面将讨论两种实验仪器。
作为48L结晶罐，连续化的结晶罐几乎有相同的尺寸。不锈钢生产罐（42L，?395mm）安装有6个隔板，三桨叶的螺旋搅拌装置（?152mm，径长比：0.81，功率：0.16）和一个冷凝盘管（面积：0.44m2）。悬浮液从一个玻璃化的装置流出，该装置固定在罐壁和罐体中部的冷凝盘管之间的环形空间内。确定罐体与流出管道（10mm）轴线之间的距离，是为了获取典型样品（同样见附录5），三个流出装置的内直径分别为5.9mm,6.7mm和10.3mm, 当为了保证理想产品的取出时，设置这些流出装置是为了满足液体保留时间内的期望变化值。图6.4中展示的流出管道的结构较小。
图6.9 连续结晶生产的流出示意图
连续生产系统的流出方式由图6.9给出。储罐上部隔间中的溶液被输送进晶体罐中。通过冷却悬浮液来获得晶体。悬浮液从储罐中下面的隔间或者溶解罐中流出，溶解罐是晶体溶解的容器。储罐/溶解罐中的溶液温度至少比溶液的饱和温度高10℃。这里运用一个
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兰州理工大学石油化工学院毕业设计(论文)
特殊的冷却系统是为了在不同温度下进行试验。为了避免冷凝盘管上附着沉淀，冷却水的
温度被要求尽量与结晶温度相近，但仍要保证热量的转移。结晶罐中悬浮液温度的精确控制通过调节冷却水的流速来完成。冷却水储罐可以通过电子加热装置（在图6.9中未表示出来）加热。这个加热装置实在实验结束时为了溶解晶体而设置的。由浓度可以计算出晶罐中晶体的质量浓度，这里的质量浓度是指晶体溶解之前和溶解之后的浓度。
晶体生长实验是在流化床中进行的。图6.10给出了流化床的流出示意图。晶种悬浮在圆柱形的玻璃管（?25mm璃管的底部有压缩物，顶部是端口扩大。饱和溶液较高的速率是的晶种既不会停留在径窄的部位也不会停留在径宽的部位。在饱和溶液中析出的晶体被输送到储罐或溶解在溶解罐（60L）中。储罐或溶解罐中的溶液保持恒定的温度，较溶液的饱和温度高2℃。溶液被输送到溶解罐的上部隔板中，通过一个流量仪表和一个冷却装置，然后进入流化床。溶液的流动速率和冷却水的温度要保持恒定，这是为了确保溶液的恒定温度。晶体通过改变旋塞阀的位置和分离晶体和溶液可以是晶体生长停止。实验结束时可以将原料液（图6.10中未示出）输送回储罐中。并且，为了澄清溶液可以安装一个过滤器。
6.2溶解度、饱和度和浓度的测量
借助于沉浸在溶液中的折射仪可以测量溶液的浓度。通过加入与溶液等量的水可以稀释溶液。同时要测量所加入水的质量和溶液的质量。当稀释的溶液加热到38℃时就测量此时的折射指数。从已知相关溶液的折射指数和浓度可以得知溶液的浓度，这些相关的溶液的参数是用同样的设备测量已知浓度得到的。原溶液浓度由稀释溶液的浓度和水与溶液的质量来决定的。精确到0.1g/100g水。
测量折射指数可以用于追踪连续晶体生产中随时间变化的溶液的浓度。当溶解度曲线确定时溶液的饱和度便可以确定。这里有一个共识，当溶液饱和度达到最大值并且回落到尽可能稳定的值时，此时确定晶体尺寸的分布，这样可以保证测量仪器可以精准的追踪到饱和度的变化。并且此时饱和度的精度是有效的，特别是在低浓度时，这也是为了对比连续生产的结晶罐和流化床中的相同数据。一个标准的设备或许可以满足生产寻求。通过光敏电阻测量转换器的亮与暗。 这里仍然有三个需要解决的问题：
观察仪器实在室温下进行（溶液的温度要保持恒温）； 观察仪器是依据灯泡的光亮强度； 观察仪器不能是在搅拌的过程中进行。
解决前两个问题可以通过尽可能保持光敏电阻的温度和向灯泡输送稳定的电力。第三个问题，可能是由灯光进入棱镜的折射引起的，这需要重新改造测量仪器。这些时间的消耗和复杂的改造是不可能完成的。
重铬酸钾的浓度是在浓缩后和溶液保持恒定温度时测量的。悬浮液搅拌6到12小时是为
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