Vapor distillate

Liquid reaching the bottom of the column is partially vaporized in a heated r eboiler to provide boil-up, which is sent back up the column. The remainder of the bottom liquid is withdrawn as bottoms, or bottom product. Vapor reaching the top of the column is cooled and condensed to liquid in the over head conden.ser. Part of this liquid is returned to the column as r eflux to provide liquid overflow. The remainder of the overhead stream is withdrawn as distillate, or overhead product . In some cases only part of the vapor is condensed so that a vapor distillate can be withdrawn. 

In another alternative, shown in Fig. 13-3 7, the rectifying section may be operated at a pressure sufficiently higher than that of the stripping section such that heat can be transferred between any desired pairs of stages of the two sections. This technique, described by Mah et al. (op. cit.) and referred to as SRV (secondary reflux and vaporization) distillation, can result in a significant reduction in utihty requirements for the overhead condenser and bottoms reboiler. 

Example 4 Calculation of the BP Method Use the BP method with the SRK eqiiation-of-state for K values and enthalpy departures to compute stage temperatures, interstage vapor and hqiiid flow rates and compositions, and rehoiler and condenser duties for the light-hydrocarhon distdlation-coliimn specifications shown in Fig. 13-51 with feed at 260 psia. The specifications are selected to obtain three products, a vapor distillate rich in Cri and C3, a vapor side-stream rich in n-C4, and a bottoms rich in n-C and n-Cg. 

The IAEA monthly measurements show seasonal variations in that the heavy isotopes are depleted in precipitation when water vapor distills off cold oceans in the winters and enriched in precipitation when water vapor distills off warm oceans in the summers. See figure 3 for monthly isotope variations in precipitation, for example in Stuttgart. 

So, for rain (made from vapor distilled from the ocean),... 

To a flask equipped with stirrer, condenser, and dropping funnel is added 40.0 gm (0.61 gm-atom) of zinc dust in 40 ml of absolute ethanol. After the condenser outlet is connected to a series of Dry Ice-acetone traps cooled to —80° to —70°C, the mixture is heated to gentle reflux while 20.3 gm (0.0852 mole) of l,2-dibromo-l,l-difluoropropene in 30 ml of 95% ethanol is added dropwise over a 2 hr period. The reaction mixture is heated for an additional hour, and then the gaseous products which are condensed in the Dry Ice traps are purified by several vaporization distillations to afford 3.6 gm (56 %) b.p. 

The phosphorus vapor distills out of the furnace and is liquefied in a condenser, after which the liquid is filtered and cast into sticks in molds immersed in water. The molten calcium silicate is withdrawn from the bottom of the furnace and solidified as a slag. 

Optimization and vacuum control strategies (a) minimizing (floating) pressure by maximizing coolant valve opening, (b) floating pressure control of partial condenser with vapor distillate, (c) floating pressure control when the distillate is both vapor and liquid. 

Distillation with vapor product. When a partial condenser is used, the flash drum plays the role of a vapor/liquid separator. In the setup known as a stabilizer there is only vapor distillate, while the liquid is returned as reflux. The column has a pasteurization section when a gaseous stream leaves at the top, while the... 

Figure 8.12 Optimization of performance. The effect of catalyst mass holdup and vapor distillate flow on purity.

The first distillation column has 32 trays, with the feed on tray 12, being operated at a reflux rate of 50 000 kg/h. The column has a partial condenser and delivers 1000 kg/h vapor distillate (sent to the absorption column) and 32 000 kg/h liquid distillate. The liquid distillate contains mainly ethanol (77% weight) and water (20% weight), with furfural the main impurity. The recovery of ethanol is almost 100%. The bottoms stream (2.9 x 10s kg/h) consists mainly of water, the concentration of dissolved organic compounds being around 7% (weight). 

Pressure control with vapor distillate product... 

So what can we do in this case If column operation requires that we stick to this control structure, feedforward control will help to reduce the swings in distillate flowrate. However, better plantwide performance can be achieved if we can switch the control structure to one in which the vapor distillate is not used to control pressure. One possible alternative is shown in Fig. 6.27. Condenser cooling is used to control pressure, reflux flowrate controls reflux drum level (with P-only control), and the flowrate of the vapor distillate is ratioed to reflux flowrate. With this structure we allow the disturbances that the column energy... 

The specifications were selected to obtain three products a vapor distillate rich in C2 and C3, a vapor sidestream rich in n-C4, and a bottoms rich in n-Cj and n-Cp, as summarized in the table below. 

To obtain prodncts with a narrow composition range, a batch rectifying still is commonly nsed. The batch rectifier consists of a pot (or reboiler) as in simple distillation, pins a rectifying colnmn, a condenser, some means of accumulating and sphtting off a portion of the condensed vapor (distillate) for reflux, and one or more product receivers (Fig. 13-119). 

A process called distillation is often used to purify liquids. The liquid is heated to vaporize it, and then the vapor is cooled to condense it back to a liquid in a different place (Figure 14.5). Impurities that are less easily vaporized are left behind in the original container, and those that are more easily vaporized distill first and are discarded before the desired product distills. 

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