Total reboilers

Maximum Conversion C = gift) Optimum Amount of Distillate Dj = g2(t) Optimum Reflux Ratio r = g3(t) Total Reboiler Heat Load QR = g4(t)... 

For a given product purity of x D = 0.70, Mujtaba and Macchietto (1997) solved the maximum profit problem for a number of cost parameters using the method described above. The results are presented in Table 9.3. For each case, Table 9.3 also shows the optimal batch time, amount of product, reflux ratio, total reboiler duty and maximum conversion (calculated using the polynomial equations). 

The next column parameters were imposed as follows feed specification liquid at bubble point feed flow rate 0.0053 kmol s" side stream flow rate 0.001455 kmol s" type of condenser total condenser pressure 760 mm Hg reflux ratio 3 type of reboiler total reboiler heat duty 417 kW bottom liquid volume 0.146 m tray surface (for top and bottom sections) 0.451 m tray surface (for right and left side of the dividing wall) 0.2255 m weir height 0.025 m hole diameter 0.002 m. 

Simple distillation Total condenser Total reboiler 15 Stages... 

Comparing the different options requires an economic analysis, although a good approach would be to compare the total reboiler duties required in each configuration to achieve similar separations and recoveries. The duty requirements for the different configurations are obtained from simulation and are shown in Figure 9.9. Based only on this criterion, the results appear to support the heuristic rules, which favor option A. This is followed closely by the recycle scheme, option D, which is not considered in the heuristic rules. 

When a finite value is specified for Lt and D is taken equal to F, the condition of total reboil (B = 0) in the stripping section is realized. The equations needed to apply the 2N Newton-Raphson method are formulated in a manner analogous to that demonstrated above for total reflux in the rectifying section. The condition that B = 0 is reflected by the equations for the Nth stage. The matrices of Eq. (10-38), the component-material balances, contain the following elements... 

If the distillation column is equipped with a partial reboiler, this reboiler is equivalent to a single theoretical contact since, in effect, the reboiler accepts a liquid feed stream and discharges liquid and vapor streams in equilibrium B and Vi in Fig. 8.10. However, not all reboilers operate this way. Some columns are equipped with total reboilers in which either all of the entering liquid from the bottom stage is vaporized and the bottoms are discharged as a vapor, or the liquid from the bottom stage is divided into a bottoms product and reboiler feed that is totally or partially vaporized. 

The equivalent work for the total reboiler is computed from (17-17) using T, equal to 680°R, the saturated steam temperature. Thus... 

Rg. 5.2. Distillation column with reactive total reboiler... 

The integration of the recycling reactor directly into the distillation column leads to the process configuration shown in Fig. 5.2, in which the reaction takes place within the column total reboiler. On top of the reboiler a fully non-RD section is installed. This process can be seen as a simple hybrid RD column with only one reactive tray. Comparing the curves in Fig. 5.4 and Fig. 5.6, the operational characteristics of the two processes, recycling system and distillation column with reactive reboiler, are identical at 93 = 00 and R = co. 

Comparing the performance of the three different RD processes considered, one can conclude that a non-RD section on top of reactive total reboiler seems to be the best configuration for both productivity and reliability of design. The minimum reflux ratio of this configuration can be estimated from (5.17) and (5.15). This R,ni value can be significantly reduced by installation of a pre-reactor 1). A fully RD column often suffers from splitting of the product in the upper column section owing to backward reaction. 

Equation (6.22) is the fixed point criteria for simple distillation and also for a continuous column at total reflux and total reboil. Since there is a symmetry in the rectifying and stripping maps, we can find the fixed points for both the rectifying and stripping cascades from equation (6.22). Thus, in this limit, our model recovers the criterion for fixed points in the well-known limit of no-reaction. At D = 1 (the chemical equilibrium limit), the fixed point criteria reduce to a single equation... 

Fig. 10.13 MTBE process at p = 11 bar. Bifurcation diagram for different reflux ratios R (left), O denotes total reboil. Multiplicity region in the R/Q parameter plane (right)...

D3. A distillation column separating ethanol from water is showm Pressure is 1 k cm. Instead of having a condenser, a stream of pure liquid ethanol is added directly to the column to serve as the reflux. This stream is a saturated liquid. The feed is 40 wt % ethanol and is at -20 °C. Feed flow rate is 2000 kg h. We desire a distillate concentration of 80 wt % ethanol and a bottoms conposition of 5 wt % ethanol. A total reboiler is used, and the boilup is a saturated vapor. The cooling stream is input at C = 1000 kg h. Find the external boilup rate, V. Note Set up the equations, solve in equation form for V including explicit equations for all required terms, read off all required enthalpies from the enthalpy conposition diagram IFigure 2-4V and then calculate a numerical answer. 

A total reboiler vaporizes the entire stream sent to it thus, the vapor conposition is the same as the liquid composition. This is illustrated in Figure 4-21. The mass balance and the bottom operating equation with a total reboiler are exactly the same as with a partial reboiler. The only difference is that a partial reboiler is an equilibrium contact and is labeled as such on the McCabe-Thiele diagram The total reboiler is not an equilibrium contact and appears on the McCabe-Thiele diagram as the single point y = x... 

A superheated direct steam input or a superheated boilup from a total reboiler will cause vaporization of liquid inside the column. This is equivalent to a net increase in the boilup ratio, E/B, and makes the slope of the stripping section operating line approach 1.0. Since superheated vapor inputs can be analyzed in the same fashion as the subcooled liquid reflux, it will be left as homework assignments 4.C14 and 4.C15. 

C2. Derive the bottom operating line for a column with a total reboiler. Show that this is the same result as is obtained with a partial reboiler. 

D24. We have a distillation column with a partial condenser and a total reboiler separating a feed of 200.0 kmol/h. The feed is 40.0 mol% acetone and 60.0 mol% ethanol. The feed is a two-phase mixture that is 80% liquid. We desire a distillate vapor that is 85.0 mol% acetone and a bottoms that is 5.0 mol% acetone. Column pressure is one atmosphere. Reflux is returned as a saturated liquid and L/D = 3.25. Assume CMO. Equilibrium data are in Problem 4.D7. 

D26. A distillation column with a partial condenser and a total reboiler is separating acetone and ethanol. There are two feeds. One feed is 50.0 mol% acetone, flows at 100.0 mol/min, and is a superheated vapor where approximately 1 mole of liquid will vaporize on the feed stage for each 20 moles of feed. The other feed is a saturated liquid, flows at 150.0 mol/min and is 35.0 mol% acetone. We desire a distillate product that is = 0.85 mole fraction acetone and a bottoms product that is Xg = 0.10 mole fraction acetone. The column has a partial condenser and a total reboiler. Boilup is returned as a saturated vapor. Column operates at a pressure of 1.0 atin. Assume CMO and use a McCabe-Thiele diagram. VLE data are given in Problem 4.D7. 

D30. A distillation column is separating methanol from water. The column has a total condenser that subcools the reflux so that 1 mole of vapor is condensed in the column for each 3 moles of reflux. Lq/D = 3. a liquid side stream is withdrawn from the second stage below the condenser. This side stream is vaporized to a saturated vapor and then mixed with the feed and input on stage 4. The side withdrawal rate is S = 500 kmol/h. The feed is a saturated vapor that is 48 mol% methanol. Feed rate is F = 1000 kmol/h. A total reboiler is used, which produces a saturated vapor boilup. We desire a distillate 92 mol% methanol and a bottoms 4 mol% methanol. Assume CMO. Equilibrium data are given in Table 2-7. Find ... 

E3. A distillation column with at total condenser and a total reboiler is separating ethanol from water. Reflux is returned as a saturated liquid, and boilup is returned as a saturated vapor. CMO can be assumed. Assume that the stages are equilibrium stages. Column pressure is 1 atm. A saturated liquid feed that is 32 mol% ethanol is fed to the column at 1000 kmol/h. The feed is to be input on the optimum feed stage. We desire a distillate conposition of 80 mol% ethanol and a bottoms conposition that is 2 mol% ethanol. A liquid side stream is removed on the eighth stage from the top of the column at a flow rate of S = 457.3 kmol/h. This liquid is sent to an intermediate reboiler and vaporized to a saturated vapor, which is returned to the column at its optimum feed location. The external reflux ratio is Lq/D = 1.86. Find the optimum feed locations of the feed and... 

D13. We have a column separating benzene, toluene, and cumene. The column has a total condenser and a total reboiler and has 9 equilibrium stages. The feed is 25 mol% benzene, 30 mol% toluene, and 45 mol% cumene. Feed rate is 100 mol/h and feed is a saturated liquid. The equilibrium data can be represented as constant relative volatilities = 2.5, a-j-j- = 1.0, and 0 = 0.21. We... 

C2. Assume that holdup in the column and in the total reboiler is negligible in an inverted batch distillation tFigure 9-RL... 

E3. In inverted batch distillation the charge of feed is placed in the accumulator at the top of the column fFigure 9-8). Liquid is fed to the top of the column. At the bottom of the column bottoms are continuously withdrawn and part of the stream is sent to a total reboiler, vaporized and sent back up the column. During the course of the batch distillation the less volatile component is slowly removed from the liquid in the accumulator and the mole fraction more volatile component increases. Assuming that holdup in the total reboiler, total condenser and the trays is small compared to the holdup in the accumulator, the Rayleigh equation for inverted batch distillation is. 

We feed the inverted batch system shown in the Figure 9-8 with F = 10 mole of a feed that is 50 mol% ethanol and 50% water. We desire a final distillate mole fraction of 0.63. There are 2 equilibrium stages in the column. The total reboiler, the total condenser and the accumulator are not equilibrium contacts. VLE are in Table 2-1. Find Dfjnaj, B o ai and Xg vg H boilup ratio is... 

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