Heat Integration
Chapter 9 S,S&L
T&S Section 3.5
Terry Ring
University of Utah
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
Q
– ΔT=T1-T2
– To= Environment Temperature
• Q= UAΔTlm=UA (ΔT1-ΔT2)/ln(ΔT1/ΔT2)
T2
Simple Heat Exchange Network (HEN)
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 = s
• Fcw=Annual Flow of Cold Water
– $0.013/ston = cw
Capital and Operating Cost Optimization
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
2004
HPC MIX-2001
HPC XCHG- 2000
2042
2
2008
2039
2043
HPC XCHG-2004
Q-2004
MIX-100
2038
HPC XCHG-2009
2050
HPC XCHG-2007
2049
HPC FAXR-2000
2010
2009
HPC XCHG-2001
2040
2017
HPC SPLT-2000 2015
2044
2014
2041
2045
HPC FAXR-2002
2019
23
2018
1
7
HPC XCHG-2002
HPC XCHG-2003
2021
2005
2047
2046
2011
13
HPC CMPR-2000
Q-2006
2025
2027
28
30
XFS1
HPC SPLT-2001
2012
Q-2001
HPC VSSL-2003
2024HPC RCYL-2002
HPC VSSL-2001
2022
HPC XCHG-2006
2020
HPC VSSL-2000
Q-2007
HPC VSSL-2002
2029
HPC FAXR-2001
HPC REAC-2000
2053
HPC MIX-2002
2016 HPC XCHG-2005
Q-2003
6
2052
HPC XCHG-1008
Q-2005
Q-2002
3
2051
2048
HPC RCYL-2001
2002
HPC MIX-2000
HPC PUMP-2000
2032
2031
2026
2036
2037
HPC SPLT-2003
2035
HPC RCYL-2000
2034
2136
2102
2135
HPC XCHG-2014
2142
2033
Q-2104
HPC FAXR-2010 2117
2108
Q-2101
2103
HPC MIX-2011
2110
2109
HPC XCHG-2010
2143
HPC RCYL-2010
2104
2139
HPC MIX-2003
Q-2009
HPC MIX-2010
HPC CMPR-2010
2138
Q-2008
HPC CMPR-2001
2101
2115
HPC SPLT-2010
HPC XCHG-2011
HPC XCHG-2015
145
144
2114
2141
Q-2102
2116
2140
HPC REAC-2010
Q-2103
2107
HPC MIX-2012
2119
HPC XCHG-2013
2149
Q-2105
2150
HPC XCHG-2012
2151
HPC XCHG-2018
HPC XCHG-2016
2147 2121 HPC FAXR-2012
Q-2106
2123
2146
2105
125
2120
2129
113
HPC VSSL-2010
2112
2122
HPC VSSL-2011
HPC VSSL-2013
2127
HPC RCYL-2012
HPC VSSL-2012
2130
2124
2132
HPC SPLT-2011
2131
2126
2137
HPC RCYL-2011
2153
Q-107
HPC XCHG-2017
2148
2118
HPC FAXR-2011
2111
2106
HPC XCHG-2019
2128
2152
Q-2108
HPC PUMP-2010
XFS2
2004
HPC MIX-2001
HPC XCHG- 2000
2042
2
2008
2039
2043
HPC XCHG-2004
Q-2004
MIX-100
2038
HPC XCHG-2009
2050
HPC XCHG-2007
2049
HPC FAXR-2000
2010
2009
HPC XCHG-2001
2040
2017
HPC SPLT-2000 2015
2044
2014
2041
2045
HPC FAXR-2002
2019
23
2018
1
7
HPC XCHG-2002
HPC XCHG-2003
2021
2005
2047
2046
2011
13
HPC CMPR-2000
Q-2006
2025
2027
28
30
XFS1
HPC SPLT-2001
2012
Q-2001
HPC VSSL-2003
2024HPC RCYL-2002
HPC VSSL-2001
2022
HPC XCHG-2006
2020
HPC VSSL-2000
Q-2007
HPC VSSL-2002
2029
HPC FAXR-2001
HPC REAC-2000
2053
HPC MIX-2002
2016 HPC XCHG-2005
Q-2003
6
2052
HPC XCHG-1008
Q-2005
Q-2002
3
2051
2048
HPC RCYL-2001
2002
HPC MIX-2000
HPC PUMP-2000
2032
2031
2026
2036
2037
HPC SPLT-2003
2035
HPC RCYL-2000
2034
2136
2102
2135
HPC XCHG-2014
2142
2033
Q-2104
HPC FAXR-2010 2117
2108
Q-2101
2103
HPC MIX-2011
2110
2109
HPC XCHG-2010
2143
HPC RCYL-2010
2104
2139
HPC MIX-2003
Q-2009
HPC MIX-2010
HPC CMPR-2010
2138
Q-2008
HPC CMPR-2001
2101
2115
HPC SPLT-2010
HPC XCHG-2011
HPC XCHG-2015
145
144
2114
2141
Q-2102
2116
2140
HPC REAC-2010
Q-2103
2107
HPC MIX-2012
2119
HPC XCHG-2013
2149
Q-2105
2150
HPC XCHG-2012
2151
HPC XCHG-2018
HPC XCHG-2016
2147 2121 HPC FAXR-2012
Q-2106
2123
2146
2105
125
2120
2129
113
HPC VSSL-2010
2112
2122
HPC VSSL-2011
HPC VSSL-2013
2127
HPC RCYL-2012
HPC VSSL-2012
2130
2124
2132
HPC SPLT-2011
2131
2126
2137
HPC RCYL-2011
2153
Q-107
HPC XCHG-2017
2148
2118
HPC FAXR-2011
2111
2106
HPC XCHG-2019
2128
2152
Q-2108
HPC PUMP-2010
XFS2
Terms
•
•
•
•
•
HEN=Heat Exchanger Network
MER=Maximum Energy Recovery
Minimum Number of Heat Exchangers
Threshold Approach Temperature
Optimum Approach Temperature
Process
Minimize Utilities
For 4 Streams
470
480
Simple HEN
Minimize Utilities
For 4 Streams
470
480
Pinch Analysis
1) Adjust Hot Stream Temperatures to Give ΔTmin
Order T’s, 250, 240, 235, 180, 150, 120
Interval Heat Loads
Pinch Analysis
1) Adjust Hot Stream Temperatures to Give ΔTmin
Order T’s, 250, 240, 235, 180, 150, 120
Enthalpy Differences for
Temperature Intervals
Pinch Analysis
=ΔHi+50
Minimum
Utilities
Pinch Analysis
=ΔHi+50
Minimum
Utilities
Pinch Analysis
Actual Endpoint Temperatures!
ΔTapp
MER values
Process
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
Pinch Analysis
Cc≥Ch
Actual Endpoint Temperatures!
3*(260-190)=210
1.5*(250-190)=90
ΔTapp
2*(235-180)=110
4*(240-180)=240
MER values
Pinch Analysis
Actual Endpoint Temperatures!
Cc≥Ch
3*(260-190)=210
1.5*(250-190)=90
ΔTapp
2*(235-180)=110
90=2*(T-180)
T=225
4*(240-180)=240
210=4*(T-180)
T=232.5°F
2
0
3
0
MER values
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
Pinch Analysis
Actual Endpoint Temperatures!
Ch≥Cc
3*(190-160)=90
6
0
ΔTapp
1.5*(190-130)=90
30=1.5*(190-T)
T=170°F
2*(180-120)=120
90=2*(180-T)
T=135°F
2*(135-120)=30
MER values
4 Heat Exchanger
HEN for Min. Utilities
Cc≥Ch
Ch≥Cc
CW
MER
Values
Steam
Pinch Analysis
=ΔHi+50
Minimum
Utilities
Minimum Utilities HEN
Simple HEN
Comparison
Simple HEN
HEN with Min. Utilities
Saves
CW 7.5e4 BTU/hr
Steam 7.5e4 BTU/hr
Too Many Heat Exchangers
• Sometimes fewer Heat exchangers and increased
utilities leads to a lower annual cost
4+2-2=4
• 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
Break Heat Exchanger Loops
Stream Splitting
• Two streams
created from one
• one heat exchanger
on each split of
stream with
couplings
1
1
1b
1a
1b
1a
Example
CP=K(Area)0.6
Last Considerations
• How will HEN behave during startup?
• How will HEN behave during shutdown?
• Does HEN lead to unstable plant operation?
2004
HPC MIX-2001
HPC XCHG- 2000
2042
2
2008
2039
2043
HPC XCHG-2004
Q-2004
MIX-100
2038
HPC XCHG-2009
2050
HPC XCHG-2007
2049
HPC FAXR-2000
2010
2009
HPC XCHG-2001
2040
2017
HPC SPLT-2000 2015
2044
2014
2041
2045
HPC FAXR-2002
2019
23
2018
1
7
HPC XCHG-2002
HPC XCHG-2003
2021
2005
2047
2046
2011
13
HPC CMPR-2000
Q-2006
2025
2027
28
30
XFS1
HPC SPLT-2001
2012
Q-2001
HPC VSSL-2003
2024HPC RCYL-2002
HPC VSSL-2001
2022
HPC XCHG-2006
2020
HPC VSSL-2000
Q-2007
HPC VSSL-2002
2029
HPC FAXR-2001
HPC REAC-2000
2053
HPC MIX-2002
2016 HPC XCHG-2005
Q-2003
6
2052
HPC XCHG-1008
Q-2005
Q-2002
3
2051
2048
HPC RCYL-2001
2002
HPC MIX-2000
HPC PUMP-2000
2032
2031
2026
2036
2037
HPC SPLT-2003
2035
HPC RCYL-2000
2034
2136
2102
2135
HPC XCHG-2014
2142
2033
Q-2104
HPC FAXR-2010 2117
2108
Q-2101
2103
HPC MIX-2011
2110
2109
HPC XCHG-2010
2143
HPC RCYL-2010
2104
2139
HPC MIX-2003
Q-2009
HPC MIX-2010
HPC CMPR-2010
2138
Q-2008
HPC CMPR-2001
2101
2115
HPC SPLT-2010
HPC XCHG-2011
HPC XCHG-2015
145
144
2114
2141
Q-2102
2116
2140
HPC REAC-2010
Q-2103
2107
HPC MIX-2012
2119
HPC XCHG-2013
2149
Q-2105
2150
HPC XCHG-2012
2151
HPC XCHG-2018
HPC XCHG-2016
2147 2121 HPC FAXR-2012
Q-2106
2123
2146
2105
125
2120
2129
113
HPC VSSL-2010
2112
2122
HPC VSSL-2011
HPC VSSL-2013
2127
HPC RCYL-2012
HPC VSSL-2012
2130
2124
2132
HPC SPLT-2011
2131
2126
2137
HPC RCYL-2011
2153
Q-107
HPC XCHG-2017
2148
2118
HPC FAXR-2011
2111
2106
HPC XCHG-2019
2128
2152
Q-2108
HPC PUMP-2010
XFS2
Optimization of HEN
• How does approach ΔT >ΔTmin effect the
total cost of HEN?
• Q= UA ΔT
– Less capital cost
• LW=QToΔT/(T1T2)
– More Utility cost
ΔTmin
•
•
•
•
S
H1
H2
C1
T(C)
300
300
30
T(C)
200
250
200
LW=QToΔT/(T1T2)
C
1.5
2
1.2
Q(kW)
150
100
204
ΔTapp=10C
ΔTapp=105C
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
Change ΔTmin
Area=Q/(UF ΔTmin)
CP=K(Area)0.6
LW=QToΔT/(T1T2)
More Lost Work
Capital and Operating Cost Optimization
ΔTthres
Distillation Columns
Heuristic “Position a Distillation
Column Between Composite
Heating and Cooling Curves”
Heat Integration for Direct
Distillation Sequence
Multi-effect Distillation
Adjust Pressure in C2 for ΔTmin
• Heat Pumps in
Distillation
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.
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.
Heat Pumps
Where can they be used?
•Heuristic
•When positioning heat pumps, to reduce the total utilities,
place them across the pinch.
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