Tower Design in ProMax ChEN 4253 Design II Chapter 19 S,S&L Terry A. Ring University of Utah

Distillation Relative Volatility Equilibrium Line α=K L /K H

How To Determine the Column Pressure given coolant Cooling Water Available at 90ºF Distillate Can be cooled to 120ºF min. Calculate the Bubble Pt. Pressure of Distillate Composition at 120ºF –equals Distillate Pressure –Bottoms Pressure = Distillate Pressure +10 psia delta P Compute the Bubble Pt. Temp for an estimate of the Bottoms Composition at Distillate Pressure –Give Bottoms Temperature Not Near Critical Point for mixture

Short cut to Selecting a Column Design –Optimum Occurs at R= 1.2 R N/N min =2, N min =log[(d LK /b LK )(b HK /d HK )]/log[α LK,HK ] R min ~(F/D)/(α-1) –V=D (R+1) V= Vapor Flow Rate D= Distillate Flow Rate (=Production Rate) R=Reflux Ratio

HW3 – Tower 1 of Direct Sequence

Design Issues Packing vs Trays Column Diameter from flooding consideration –Trays, D T =[(4G)/((f U flood π(1-A down /A T )ρ G )] 1/2 eq U flood = f(dimensionless density difference), f = eq –Packed, D T =[(4G)/((f U flood πρ G )] 1/2 eq U flood = f(flow ratio), f = eq Column Height – N min =log[(d LK /b LK )(b HK /d HK )]/log[α LK,HK ]eq –N=N min /ε (or 2 N min / ε) Column Height = N*H tray Tray Height = typically 1 ft (or larger) Packed Height = N eq *HETP (or 2 N eq *HETP) –HETP(height equivalent of theoretical plate) –HETP random = 1.5 ft/in*D p Rule of thumbeq Tray Efficiency, ε = f(viscosity liquid * α LK,HK )Fig 19.3 Pressure Drop Tray, ΔP=ρ L g h L-wier N Packed, ΔP=Packed bed (weeping)

Tray Efficiency μ L * α LK,HK

Simulation Methods- ProMax Take feed into a 2 phase flash with X% vapor fraction Determine α LK,HK from flash data Calculate N min then N T =2*N min, N min =log[(d LK /b LK )(b HK /d HK )]/log[α LK,HK ] set ΔP on column, reboiler, condenser and separator set ΔT on condenser =0 Create a component recovery for HK in bottom with large ± –To be changed later Create a component recovery for LK in distillate with large ± –To be changed later May need to add pump around loop estimate. Determine α LK,HK * viscosity from successful distillation run (use Plots Tab to determine extra trays) determine N min and feed tray Use Fig to determine R min from R, N from N min Redo calc with tray efficiency defined see Figure 19.3 correlation. You may need to adjust column from here –Desired Split Fractions for HK and LK –More trays (less recycle ratio) Too many trays = flat composition profile

Column Costs Column – Material of Construction gives ρ metal –Pressure Vessel C p = F M C v (W)+C Platform –Height may include the reboiler accumulator tank –Tray Cost = N*C tray (D T ) –Packing Cost = V packing C packing + C distributors Reboiler C B α Area HX Condenser C B α Area HX Pumping Costs – feed, reflux, reboiler –Work = Q*ΔP Tanks –Surge tank before column, reboiler accumulator, condensate accumulator –Pressure Vessel C p = F M C v (W)+C Platform

CPI

Problem Methanol-Water Distillation Feed –10 gal/min –50/50 (mole) mixture Desired to get –High Purity MeOH in D –Pure Water in B

Simulation Methods- ProMax Take feed into a 2 phase flash with 50% vapor fraction Determine α LK,HK from flash data Calculate N min then N T =2*N min set ΔP on column, reboiler, condenser and separator set ΔT on condenser =0 Create a component recovery for HK in bottom with large ± –To be changed later Create a component recovery for LK in distillate with large ± –To be changed later May need to add pump around loop estimate. Determine α LK,HK * viscosity from successful distillation run (use Plots Tab to determine extra trays) determine N min and feed tray Use Fig to determine R min from R, N from N min Redo calc with tray efficiency defined see Figure 19.3 correlation. You may need to adjust column from here –Desired Split Fractions for HK and LK –More trays (less recycle ratio) Too many trays = flat composition profile

Tray Efficiency μ L * α LK,HK

Figure 19.1