Vapour Boilup Rate

COLUMN FEEDRATE SATURATED LIQUID FEED FEED COMPOSITIONS REFLUX RATIO RELATIVE VOLATILITIES LIQUID HOLDUPS VAPOUR BOILUP RATE... 

The simulation is based on a fixed vapour boilup rate. Component balance equations are represented for benzene and toluene . The xylene concentrations are determined by difference, based on the sum of the mole fractions being equal to one. 

A liquid binary mixture with Bo = 10 kmol and xbo = <0.6, 0.4> molefraction is subject to conventional batch distillation shown in Figure 4.3. The relative volatility of the mixture over the operating temperature range is assumed constant with a value of (a=) 2. The total number of plates is, N = 20. The vapour boilup rate is, V = 5.0 kmol/hr and the reflux ratio is, r = 0.75. The condenser and total plate holdups are 0.2 and 0.2 kmol respectively. 

Table 5.2 summarises the results for two cases (i) constant vapour boil-up rate, (ii) variable vapour boilup rate. The initial and final time optimal reflux ratio values are shown in Table 5.2 for both cases. The optimal reflux ratios between these two points follow according to Equation P.13 for each case. See details in the original reference (Robinson, 1969). 

Equality constraints h(D°, D°) = 0 may include, for example, a ratio between the amounts of two products, etc. Inequality constraints g(u, D°) < 0 for the overall operation include Equations 7.14-7.18 (the first two of which are easily eliminated when m and H are specified) and possibly bounds on total batch time for individual mixtures, energy utilisation, etc. Any variables of D° and D° which are fixed are simply dropped from the decision variable list. Here, Strategy II was adopted for the multiple duty specification, requiring B0 to be fixed a priori. Similar considerations hold for V, the vapour boilup rate. The batch time is inversely proportional to V for a specified amount of distillate. Also alternatively, for a given batch time, the amount of product is directly proportional to V. This can be further explained through Equations 7.24-7.26) ... 

Two binary mixtures are being processed in a batch distillation column with 15 plates and vapour boilup rate of 250 moles/hr following the operation sequence given in Figure 7.7. The amount of distillate, batch time and profit of the operation are shown in Table 7.6 (base case). The optimal reflux ratio profiles are shown in Figure 7.8. It is desired to simultaneously optimise the design (number of plates) and operation (reflux ratio and batch time) for this multiple separation duties. The column operates with the same boil up rate as the base case and the sales values of different products are given in Table 7.6. 

Base Case Input Data The number of plates, N The vapour boilup rate, V moles/hr Column holdup = 15 = 250 = 0... 

Mujtaba and Macchietto (1992) investigated how productivity (kmol of product/hr) is affected by the proposed recycle policy. Consider a fixed vapour load to the condenser (or vapour boilup rate) and fixed product compositions (e.g. xlDi and x1 B2 for recycle loop 1 of Figure 8.13). Now scale the batch times (presented as... 

As presented in the earlier chapters, the operating policy for a batch distillation column can be determined in terms of reflux ratio, product recoveries and vapour boilup rate as a function of time (open-loop control). Under nominal conditions, the optimal operating policy may be specified equivalently in terms of a set-point trajectory for controllers manipulating these inputs. In the presence of uncertainty, these specifications for the optimal operating policy are no longer equivalent and it is important to evaluate and compare their performance. 

Vapour boilup rate, V, kmol/hr = 5.0 xD, molefraction = 0.90 Feed rate, Fp, kmol/hr = variable... 

It is evident that the operation in terms of product amount, reflux ratio, recovery, etc. of case 1 of Table 11.3 is very close to the operation of case 1 operation of Table 11.2. Also note that the energy consumption for CBD operation presented in Table 11.3 over a time period tp is same as that for corresponding SPSS operation over the same time period, since the vapour boilup rate in all cases used is 5 kmol/hr. Note that the results of case 2 of Table 11.3 are not close to those of case 4 of Table 11.2. The results (Table 11.2 and Table 11.3) clearly show that if the operation is restricted to one single reflux ratio or one single pass operation, it is possible to replace the CBD operation by continuous column operation using a very low feed flow rate. 

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