Introduction B • The most common separation technique C • Consumes enormous amounts of energy, both in terms of cooling and A heating requirements • Contribute to more than 50% of plant operating costs D E • Definition: a process in which a liquid or vapour mixture of two or more substances is separated into its component fractions of desired purity,by the application (evaporation) and removal(condensation) of heat.
Influence of Pressure• Boiling points varies with pressure : keep it constant• Lower the partial pressure; lower the boiling pt.• Lighter components difficult to condense at low P; operates at higher P(10-12 bar)• Heavier components will have to be heated up to 400 degC for distillation to occur, hence HC bonds will start to break.• For heavier comps, distillation carried under vacuum condition to avoid the carbon chain from cracking
Separation• IBP, FBP• Gap• Overlap• Aim for: overlap Naphtha < 10 degC < Tops no gap & overlap between Naphtha and Kero overlap LGO < 10 degC < Kero overlap HGO < 10 degC < LGOSeparation efficiency is due to reflux ratio
Column Control For Product Spec• Control FBP of product by controlling the top temp of the column, higher top temp, heavier comps boils over, higher FBP, more product on overheads( at fixed pressure)• How to change production? for better separation, create more reflux,• How to top temp?(1) reduce/increase amount of heat removed from column @ (2) reduce/increase amount of heat supplied to column• Heat removed by reflux flow. reflux, remove more heat, top temperature • Heat supplied via (1) feed temperature & (2) bottom reboiler
Stripping Steam• Component A and B Ptotal = PA + PB• Introduce steam with same Ptotal Ptotal = PA new + PB new + Psteam• PA new < PA and PB new < PB• Hence enable comp A and B to vaporise at lower P and T (if low enough, no heat addition required)• Known as to lower the partial pressure of the component, applied in removing the light ends from fractions
Multi cut splitter and strippers• 2 cut splitter only gets 2 product, have to feed into another 2 columns to further separate• For instance to separate into 3 fractions, side stripper can be used Furnace