Heat Integration

Chapt. 10

Costs

• Heat Exchanger Purchase Cost– CP=K(Area)0.6

• Annual Cost– CA=im[ΣCp,i+ ΣCP,A,j]+sFs+(cw)Fcw

• im=return on investment• Fs= Annual Flow of Steam,

– $5.5/ston to $12.1/ston

• Fcw=Annual Flow of Cold Water– $0.013/ston

Lost Work = Lost Money

• Transfer Heat from T1 to T2

• ΔT approach Temp. for Heat Exchanger

• To= Temperature of Environment

• Use 1st and 2nd laws of Thermodynamics

• LW=QToΔT/(T1T2)

T1

T2

Q

Minimize UtilitiesFor 4 Streams

Simple HEN

Adjust Hot Stream Temperatures to Give ΔTmin

Enthalpy Differences for Temperature Intervals

Interval Heat Loads

Pinch Analysis

Minimum Utilities

Pinch Analysis

4 Heat ExchangerHEN for Min. Utilities

Minimum Utilities HEN

Too Many Heat Exchangers

• Sometimes fewer Heat exchangers and increased utilities leads to a lower annual cost

• NHx,min= Ns + NU - NNW

– 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 ΔTmin

CP=K(Area)0.6

Area=Q/(UF ΔTmin)

Distillation Columns

Position a Distillation Column Between Composite Heating and

Cooling Curves

Heat Integration

Multi-effect DistillationAdjust Pressure in C2 for ΔTmin

• Heat Pumps in Distillation