Heat Integration Chapt. 10

Costs Heat Exchanger Purchase Cost – C P =K(Area) 0.6 Annual Cost –C A =i m [ΣC p,i + ΣC P,A,j ]+sF s +(cw)F cw i m =return on investment F s = Annual Flow of Steam, –$5.5/ston to $12.1/ston F cw =Annual Flow of Cold Water –$0.013/ston

Lost Work = Lost Money Transfer Heat from T 1 to T 2 ΔT approach Temp. for Heat Exchanger T o = Temperature of Environment Use 1 st and 2 nd laws of Thermodynamics LW=QT o ΔT/(T 1 T 2 ) T1T1 T2T2 Q

Minimize Utilities For 4 Streams

Simple HEN

Adjust Hot Stream Temperatures to Give ΔT min

Enthalpy Differences for Temperature Intervals

Interval Heat Loads

Pinch Analysis Minimum Utilities

Pinch Analysis

4 Heat Exchanger HEN for Min. Utilities

Minimum Utilities HEN

Too Many Heat Exchangers Sometimes fewer Heat exchangers and increased utilities leads to a lower annual cost N Hx,min = N s + N U - N NW –No. streams –No. discrete Utilities –No. independent Networks (1 above the pinch, 1 below the pinch Solution to Too Many Heat Exchangers –Break Heat Exchanger Loops –Stream Splitting Attack small Heat Exchangers First

Break Heat Exchanger Loops

Example

Change ΔT min C P =K(Area) 0.6 Area=Q/(UF ΔT min )

Distillation Columns

Position a Distillation Column Between Composite Heating and Cooling Curves

Heat Integration

Multi-effect Distillation Adjust Pressure in C2 for ΔT min

Heat Pumps in Distillation