heat integration chapt. 10. costs heat exchanger purchase cost – c p =k(area) 0.6 annual cost –c...
TRANSCRIPT
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