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)– ΔT=T1-T2
– To= Environment Temperature
• Q= UAΔTlm=UA (ΔT1-ΔT2)/ln(ΔT1/ΔT2)
T1
T2
Q
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
2011
HPC REAC-2000
Q-2002
HPC VSSL-2000
2037
13
23
2024
XFS1
HPC SPLT-2001
30
2026
HPC PUMP-20002031
Q-2008
2012HPC RCYL-2001
2032
6
HPC MIX-2000
2009
3
1
2004
HPC XCHG-2002
HPC MIX-2001
2010
HPC CMPR-2000
2002Q-2001
7
2008HPC XCHG- 2000
HPC XCHG-2001
2038
2039
2040
2041
HPC XCHG-2003
2014
2025Q-2006
2050
2051
HPC XCHG-1008
HPC FAXR-2000
Q-2004
HPC FAXR-2002
Q-2005
HPC XCHG-2004
2042 2043
28
2052 2053HPC XCHG-2007
2048 2049
HPC FAXR-2001
HPC SPLT-2000
2016
2015
HPC MIX-2002
2018
2017
Q-2003HPC XCHG-2005
2044
2045
2019
HPC XCHG-20062020
2021
2046 2047 HPC VSSL-2001
HPC VSSL-2002
2022
HPC VSSL-2003
HPC XCHG-2009
Q-2007
2027
HPC RCYL-2002
2029
2101
HPC CMPR-2010
HPC MIX-20102102
HPC XCHG-2010
HPC XCHG-2011
2103
2104
2107
2108
HPC MIX-2011
2109 2110
HPC XCHG-2012
2114
2112
HPC VSSL-2010
HPC XCHG-2013
113
21052106
HPC SPLT-2010
HPC FAXR-2010
HPC FAXR-2011
HPC FAXR-2012
HPC MIX-2012
HPC VSSL-2011HPC VSSL-2012
HPC VSSL-2013
HPC XCHG-2016
2115
2116
2117
2118
2119
2120
2121
2122
21462147
2123
125
2124
2129
2128
2127
HPC RCYL-2012
HPC SPLT-2011
2130
2126
HPC PUMP-2010
2131
Q-21082137 HPC RCYL-2011
2132
2005
2111
HPC MIX-2003
HPC CMPR-2001
2033
2034
Q-2009
HPC XCHG-2014
HPC XCHG-2015
Q-2104
Q-2103
Q-2105
HPC XCHG-2017
2142 2143
144 145
2148 2149
2138 2139
2140
2141
Q-2101
HPC SPLT-2003
2135
2035
Q-2106
HPC XCHG-2018
2150 2151
Q-107
HPC XCHG-2019
2152 2153
Q-2102
HPC REAC-2010
HPC RCYL-2000
HPC RCYL-2010
2036
2136
XFS2
MIX-100
2
2011
HPC REAC-2000
Q-2002
HPC VSSL-2000
2037
13
23
2024
XFS1
HPC SPLT-2001
30
2026
HPC PUMP-20002031
Q-2008
2012HPC RCYL-2001
2032
6
HPC MIX-2000
2009
3
1
2004
HPC XCHG-2002
HPC MIX-2001
2010
HPC CMPR-2000
2002Q-2001
7
2008HPC XCHG- 2000
HPC XCHG-2001
2038
2039
2040
2041
HPC XCHG-2003
2014
2025Q-2006
2050
2051
HPC XCHG-1008
HPC FAXR-2000
Q-2004
HPC FAXR-2002
Q-2005
HPC XCHG-2004
2042 2043
28
2052 2053HPC XCHG-2007
2048 2049
HPC FAXR-2001
HPC SPLT-2000
2016
2015
HPC MIX-2002
2018
2017
Q-2003HPC XCHG-2005
2044
2045
2019
HPC XCHG-20062020
2021
2046 2047 HPC VSSL-2001
HPC VSSL-2002
2022
HPC VSSL-2003
HPC XCHG-2009
Q-2007
2027
HPC RCYL-2002
2029
2101
HPC CMPR-2010
HPC MIX-20102102
HPC XCHG-2010
HPC XCHG-2011
2103
2104
2107
2108
HPC MIX-2011
2109 2110
HPC XCHG-2012
2114
2112
HPC VSSL-2010
HPC XCHG-2013
113
21052106
HPC SPLT-2010
HPC FAXR-2010
HPC FAXR-2011
HPC FAXR-2012
HPC MIX-2012
HPC VSSL-2011HPC VSSL-2012
HPC VSSL-2013
HPC XCHG-2016
2115
2116
2117
2118
2119
2120
2121
2122
21462147
2123
125
2124
2129
2128
2127
HPC RCYL-2012
HPC SPLT-2011
2130
2126
HPC PUMP-2010
2131
Q-21082137 HPC RCYL-2011
2132
2005
2111
HPC MIX-2003
HPC CMPR-2001
2033
2034
Q-2009
HPC XCHG-2014
HPC XCHG-2015
Q-2104
Q-2103
Q-2105
HPC XCHG-2017
2142 2143
144 145
2148 2149
2138 2139
2140
2141
Q-2101
HPC SPLT-2003
2135
2035
Q-2106
HPC XCHG-2018
2150 2151
Q-107
HPC XCHG-2019
2152 2153
Q-2102
HPC REAC-2010
HPC RCYL-2000
HPC RCYL-2010
2036
2136
XFS2
MIX-100
2
Terms
• HEN=Heat Exchanger Network
• MER=Maximum Energy Recovery
• Minimum Number of Heat Exchangers
• Threshold Approach Temperature
• Optimum Approach Temperature
Process
Minimize UtilitiesFor 4 Streams
Simple HEN
Pinch Analysis1) Adjust Hot Stream Temperatures to Give ΔTmin
Order T’s, 250, 240, 235, 180, 150, 120
Interval Heat Loads
Enthalpy Differences for Temperature Intervals
Pinch Analysis
Minimum Utilities
=ΔHi+50
Pinch Analysis
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
4 Heat ExchangerHEN for Min. Utilities
Cc≥Ch Ch≥Cc
MER Values
Pinch Analysis
Minimum Utilities
=ΔHi+50
Minimum Utilities HEN
Simple HEN
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
Stream Splitting
• Two streams created from one
• one heat exchanger on each split of stream with couplings
1
1a
1b
1b
1a
1
Break Heat Exchanger Loops
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?
2011
HPC REAC-2000
Q-2002
HPC VSSL-2000
2037
13
23
2024
XFS1
HPC SPLT-2001
30
2026
HPC PUMP-20002031
Q-2008
2012HPC RCYL-2001
2032
6
HPC MIX-2000
2009
3
1
2004
HPC XCHG-2002
HPC MIX-2001
2010
HPC CMPR-2000
2002Q-2001
7
2008HPC XCHG- 2000
HPC XCHG-2001
2038
2039
2040
2041
HPC XCHG-2003
2014
2025Q-2006
2050
2051
HPC XCHG-1008
HPC FAXR-2000
Q-2004
HPC FAXR-2002
Q-2005
HPC XCHG-2004
2042 2043
28
2052 2053HPC XCHG-2007
2048 2049
HPC FAXR-2001
HPC SPLT-2000
2016
2015
HPC MIX-2002
2018
2017
Q-2003HPC XCHG-2005
2044
2045
2019
HPC XCHG-20062020
2021
2046 2047 HPC VSSL-2001
HPC VSSL-2002
2022
HPC VSSL-2003
HPC XCHG-2009
Q-2007
2027
HPC RCYL-2002
2029
2101
HPC CMPR-2010
HPC MIX-20102102
HPC XCHG-2010
HPC XCHG-2011
2103
2104
2107
2108
HPC MIX-2011
2109 2110
HPC XCHG-2012
2114
2112
HPC VSSL-2010
HPC XCHG-2013
113
21052106
HPC SPLT-2010
HPC FAXR-2010
HPC FAXR-2011
HPC FAXR-2012
HPC MIX-2012
HPC VSSL-2011HPC VSSL-2012
HPC VSSL-2013
HPC XCHG-2016
2115
2116
2117
2118
2119
2120
2121
2122
21462147
2123
125
2124
2129
2128
2127
HPC RCYL-2012
HPC SPLT-2011
2130
2126
HPC PUMP-2010
2131
Q-21082137 HPC RCYL-2011
2132
2005
2111
HPC MIX-2003
HPC CMPR-2001
2033
2034
Q-2009
HPC XCHG-2014
HPC XCHG-2015
Q-2104
Q-2103
Q-2105
HPC XCHG-2017
2142 2143
144 145
2148 2149
2138 2139
2140
2141
Q-2101
HPC SPLT-2003
2135
2035
Q-2106
HPC XCHG-2018
2150 2151
Q-107
HPC XCHG-2019
2152 2153
Q-2102
HPC REAC-2010
HPC RCYL-2000
HPC RCYL-2010
2036
2136
XFS2
MIX-100
2
Optimization of HEN
• How does approach ΔT (ΔTmin) effect the total cost of HEN?
• Q= UA ΔT
• LW=QToΔT/(T1T2)
– More Utility cost
ΔTmin
• S T(C) T(C) CQ(kW)
• H1 300 200 1.5 150
• H2 300 250 2 100
• C1 30 200 1.2 204
LW=QToΔT/(T1T2)
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
CP=K(Area)0.6
Area=Q/(UF ΔTmin)
More Lost Work
LW=QToΔT/(T1T2)
Capital and Operating Cost Optimization
ΔTthres
Distillation Columns
Heuristic “Position a Distillation Column Between Composite Heating and Cooling Curves”
Heat Integration for Indirect Distillation Sequence
Multi-effect DistillationAdjust Pressure in C2 for ΔTmin
• Heat Pumps in Distillation
Heat PumpsHow do they work?
Convert low temperature heat to high temperature heat.Must add work as heat can not go up hill.
Same as Air Conditioner
Carnot Efficiencyηmax= 1-Tc/Th
Endoreversibleη =1-√(Tc/Th)
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 PumpsWhere can they be used?
•Heuristic
•When positioning heat pumps, to reduce the total utilities, place them across the pinch.
Heat EnginesWhere can they be used?
•Heuristic
•When positioning heat engines, to reduce the cold utilities, place them entirely above or below the pinch
Tp
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