1. Chapter 9 S,S&L T&S Section 3.5 Terry Ring University of Utah
Heat Integration
Chapter 9 S,S&L
T&S Section 3.5
Terry Ring
University of Utah

2. 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)
ΔT=T1-T2
To= Environment Temperature
Q= UAΔTlm=UA (ΔT1-ΔT2)/ln(ΔT1/ΔT2) T1 Q T2

3. Simple Heat Exchange Network (HEN)
Use another stream for HX instead of a utility.
What happens when delta T in Exchanger is lowered? To Zero?

4. Costs Heat Exchanger Purchase Cost Annual Cost CP=K(Area)0.6
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 = s
Fcw=Annual Flow of Cold Water
$0.013/ston = cw
CpA is HX in auxiliary networks

5. Capital and Operating Cost Optimization
Capital cost goes down when A is less. This is caused by delta T being larger for Q to remain the same.

6. Heat Integration Make list of HX
Instead of using utilities can you use another stream to heat/cool any streams?
How much of this can you do without causing operational problems?
Can you use air to cool?
Air is a low cost coolant.
Less utilities = smaller cost of operations

9. Terms HEN=Heat Exchanger Network MER=Maximum Energy Recovery
Minimum Number of Heat Exchangers
Threshold Approach Temperature
Optimum Approach Temperature

10. Process

11. Minimize Utilities For 4 Streams

12. Simple HEN

13. Pinch Analysis 1) Adjust Hot Stream Temperatures to Give ΔTmin
Put T’s in order Max to Min
Order T’s, 250, 240, 235, 180, 150, 120

15. Interval Heat Loads

16. Enthalpy Differences for Temperature Intervals

17. Pinch Analysis Minimum Utilities
=ΔHi+50
Pinch Analysis Minimum Utilities
R’s = residulas

18. Pinch Analysis
ΔTapp
MER values

19. Process

20. How to combine hot with cold?
Big Exhangers 1st
1st HX at Pinch (temp touching pinch)
Above Pinch Connect
Cc≥Ch
Below Pinch Connect
Ch≥Cc
2nd Hx or not touching Pinch temp.
No requirement for Cc or Ch

21. 4 Heat Exchanger HEN for Min. Utilities
Cc≥Ch
Ch≥Cc
MER
Values

22. Pinch Analysis Minimum Utilities
=ΔHi+50
Pinch Analysis Minimum Utilities
R’s = residulas

23. Minimum Utilities HEN

24. Simple HEN

25. Too Many Heat Exchangers
Sometimes fewer Heat exchangers and increased utilities leads to a lower annual cost
NHx,min= Ns + NU - NNW
s=No. streams
U=No. discrete Utilities
NW=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

26. Stream Splitting Two streams created from one1
Two streams created from one
one heat exchanger on each split of stream with couplings 1 1b 1a 1b 1a

27. Break Heat Exchanger Loops

28. Example
CP=K(Area)0.6

29. Last Considerations How will HEN behave during startup?
How will HEN behave during shutdown?
Does HEN lead to unstable plant operation?

31. Optimization of HEN
How does approach ΔT (ΔTmin) effect the total cost of HEN?
Q= UA ΔT
LW=QToΔT/(T1T2)
More Utility cost

32. ΔTmin ΔTapp=10C ΔTapp=105C LW=QToΔT/(T1T2) S T(C) T(C) C Q(kW)H H C
ΔTapp=10C ΔTapp=105C
LW=QToΔT/(T1T2)

33. Costs Heat Exchanger Purchase Cost Annual Cost CP=K(Area)0.6
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

34. Change ΔTmin CP=K(Area)0.6 Area=Q/(UF ΔTmin) LW=QToΔT/(T1T2)
More Lost Work
ΔT =UA/Q
Utilities increase due to Lost work since it increases as ΔT increases
LW=QToΔT/(T1T2)

35. Capital and Operating Cost Optimization
Capital cost goes down when A is less. This is caused by delta T being larger for Q to remain the same.
ΔTthres

36. Distillation Columns

37. Heuristic “Position a Distillation Column Between Composite Heating and Cooling Curves”

38. Heat Integration for Indirect Distillation Sequence

39. Multi-effect Distillation Adjust Pressure in C2 for ΔTmin

40. Heat Pumps in Distillation

41. Heat Pumps How do they work?
Carnot Efficiency
ηmax= 1-Tc/Th
Endoreversible
η =1-√(Tc/Th)
Same as Air Conditioner
Convert low temperature heat to high temperature heat.
Must add work as heat can not go up hill.

42. Heat Pumps/Heat Engines Heurisitcs
When positioning heat engines, to reduce the cold utilities, place them entirely above or below the pinch
When positioning heat pumps, to reduce the total utilities, place them across the pinch.

43. Heat Pumps Where can they be used?
Heuristic
When positioning heat pumps, to reduce the total utilities, place them across the pinch.

44. Heat Engines Where can they be used?Tp
Heuristic
When positioning heat engines, to reduce the cold utilities, place them entirely above or below the pinch