The accompanying figure depicts a distillation column that is used in a petroleum plant to fractionate...

  

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The accompanying figure depicts a distillation column that is used in a petroleum plant to fractionate (i.e. separate) a liquid feed stream containing equimolar amounts of benzene and toluene. The 'overhead product' (from the reflux drum) contains mostly the lighter benzene component while the 'bottoms product' (from the reboiler) contains mostly the heavier toluene component. In the bottom half of the column (known as the 'stripping section'), there is always some 'bottoms liquid' (approximately 10% benzene and 90% toluene with corresponding density of 791 kg/m) that sits in the base of the column. A 23-10 centrifugal pump with an 8" impeller (see pump performance curve below) is used to transfer 275 gal/min of this hot 'bottoms liquid' to a reboiler where a portion of it gets vaporized and sent back to the column and the rest gets removed as the 'bottoms product. a. Determine the value of NPSH, (m) for the 'bottoms liquid' pump to operate at the desired flow rate of 275 gal/min. b. If the average height of the 'bottoms liquid' at the base of the column is 2 m, determine what is the appropriate vertical position (m) of the 23-10 centrifugal pump relative to the bottom of the column for the following conditions: Feed- Condenser Bottoms Cooling water Reflux Reflux Drum Pump Overhead product Distillation plate Vapor Reboler Steam Condensate liquid Pump The pressure inside the column is fairly constant at 1.5 atm throughout the column Bottoms product Upflowing vapor Downflowing liquid The temperature varies inside the column; the temperature at the bottom is approximately 100 C and the corresponding vapour pressure of the 'bottoms liquid' is 75 kPa It has been determined that the total head loss (i.e. all friction and minor losses) for the suction piping into the pump can be appropriately described by the equation H = 6.83 Q2, where H,, is in m and Q is in m/min. 100 Impeller diameter 140 450 10 in 31-36-4 2x3-10 54 56 57 58 3500 RPM 400 120 9 in 350 8 Total head (m) 80 Total head (f) 300 250 200 31 150 6 in- 30 HP 40 40 100 36 41 46 -3 HP- 25 HP 20 HP 5 HP 46 15 HP- 75HP 10 HP NPSH, (m) 420 NPSH, (f) 20 10 50 HP 40 HP 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 8 in 9 in 10 in 6 in 7 in 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 Capacity (gal/min) 200 400 600 800 Capacity (L/min) 1000 1200 1400 The accompanying figure depicts a distillation column that is used in a petroleum plant to fractionate (i.e. separate) a liquid feed stream containing equimolar amounts of benzene and toluene. The 'overhead product' (from the reflux drum) contains mostly the lighter benzene component while the 'bottoms product' (from the reboiler) contains mostly the heavier toluene component. In the bottom half of the column (known as the 'stripping section'), there is always some 'bottoms liquid' (approximately 10% benzene and 90% toluene with corresponding density of 791 kg/m) that sits in the base of the column. A 23-10 centrifugal pump with an 8" impeller (see pump performance curve below) is used to transfer 275 gal/min of this hot 'bottoms liquid' to a reboiler where a portion of it gets vaporized and sent back to the column and the rest gets removed as the 'bottoms product. a. Determine the value of NPSH, (m) for the 'bottoms liquid' pump to operate at the desired flow rate of 275 gal/min. b. If the average height of the 'bottoms liquid' at the base of the column is 2 m, determine what is the appropriate vertical position (m) of the 23-10 centrifugal pump relative to the bottom of the column for the following conditions: Feed- Condenser Bottoms Cooling water Reflux Reflux Drum Pump Overhead product Distillation plate Vapor Reboler Steam Condensate liquid Pump The pressure inside the column is fairly constant at 1.5 atm throughout the column Bottoms product Upflowing vapor Downflowing liquid The temperature varies inside the column; the temperature at the bottom is approximately 100 C and the corresponding vapour pressure of the 'bottoms liquid' is 75 kPa It has been determined that the total head loss (i.e. all friction and minor losses) for the suction piping into the pump can be appropriately described by the equation H = 6.83 Q2, where H,, is in m and Q is in m/min. 100 Impeller diameter 140 450 10 in 31-36-4 2x3-10 54 56 57 58 3500 RPM 400 120 9 in 350 8 Total head (m) 80 Total head (f) 300 250 200 31 150 6 in- 30 HP 40 40 100 36 41 46 -3 HP- 25 HP 20 HP 5 HP 46 15 HP- 75HP 10 HP NPSH, (m) 420 NPSH, (f) 20 10 50 HP 40 HP 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 8 in 9 in 10 in 6 in 7 in 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 Capacity (gal/min) 200 400 600 800 Capacity (L/min) 1000 1200 1400