You are trying to evaluate whether an existing, idle distillation column can be used for a separation for which it was not originally designed. Answer the following questions about this column:

a. The reflux pump (there are two in parallel) must pump fluid from the reflux drum to the top of the column. The fluid density is \(775 \mathrm{~kg} / \mathrm{m}^{3}\). The reflux drum is \(6 \mathrm{~m}\) above the pump inlet. The top of the tower is \(42 \mathrm{~m}\) above the pump discharge. Frictional pressure drop for the entire length of pipe is calculated to be \(130 \mathrm{kPa}\). The desired flowrate is \(7 \mathrm{~L} / \mathrm{s}\). The pump curve and

\(\mathrm{NPSH}_{R}\) curves are in Figure P22.21. Determine whether this pump can be used for this job and, if so, what configuration is necessary. The frictional pressure drop seems high. Suggest a possible explanation.

Figure P 22.21

b. The reboiler is connected to the low-pressure steam line \(\left(160^{\circ} \mathrm{C}ight)\). However, there is also a desuperheater. The area of the exchanger is \(300 \mathrm{~m}^{2}\), and the heat transfer coefficients have been estimated to be \(5000 \mathrm{~W} / \mathrm{m}^{2} \mathrm{~K}\) and \(3000 \mathrm{~W} / \mathrm{m}^{2} \mathrm{~K}\) for the boiling side and the condensing side, respectively. The boiling point of the process fluid is \(87^{\circ} \mathrm{C}\), and the required heat load is \(6000 \mathrm{~kW}\). What is the saturated steam temperature required at the desuperheater exit?

c. List at least three items you would investigate regarding the ability of this column to do the desired separation. For each item, discuss what you would look for or calculate to determine the suitability of the column for this duty.

Transcribed Image Text:

NJ NPSH, m of liquid DO 0 Head, kPa 800 Pump Curve 700 600 500 400 300 200 100 10 5 0 0 2 8 10 12 14 Flowrate, L/s 2 Flowrate, Lis NPSHR 8 10 12 14