Process Integration using Exergy Analysis in LNG Process Danahe Marmolejo Correa, Truls Gundersen Department of Energy and Process Engineering, Norwegian University of Sciences of Technology Extended Pinch Analysis and Design (ExPAnD) Exergy Classification and Decomposition Composite Curves, Exergy Composite Curves and a novel Exergy Diagram for Heat Recovery Systems Vertical Heat and Exergy Cascades LNG process design Norwegian University of Science and Technology Exergy Sources and Sinks in Heat Exchange Thermo-mechanical Exergy and Exergy of Heat International Process Integration Jubilee Conference Gothenburg Sweden, 18-20 March, 2012 Marmolejo−Correa, D. and Gundersen, T. (2012). A comparison of exergy efficiency definitions with focus on low temperature processes. Energy, 44, 477−89. T E 0 0 S Exergy, E S p 0 p 0 T 0 T T , Tp 0 , T p 0 0 , T p TM E . , Enthalpy H p E 0.0 0.5 1.0 1.5 2.0 0 1 2 3 4 5 0 Dimensionless Temperature, T T Exergy ratio of Heat, E Q / Q . . 0.5 0 0 , , , TM T p E Tp E Tp E T p -150.0 -100.0 -50.0 0.0 50.0 100.0 150.0 200.0 0 50 100 150 200 Temperature (°C) H (kW) Hot Stream (energy) Cold Stream (energy) 1 2 3 4 1 2 3 4 Source Sink Source Sink -150.0 -100.0 -50.0 0.0 50.0 100.0 150.0 200.0 0 50 100 150 Temperature (°C) E (kW) Hot Stream (exergy) Cold Stream (exergy) 1 2 3 4 2 1 4 3 Source Source Sink Sink Heat Transfer Exergy Transfer The Rule: • For process streams subject to a change in exergy, from supply (T s , p s ) to target (T t , p t ) conditions: • Negative changes in exergy are categorized as exergy Sources. • Positive changes in exergy are categorized as exergy Sinks. • For Work and Exergy accompanying Heat flows : • Supplied = Source • Produced = Sink • Both Supplied and Produced, then keep these separate as Source and Sink. Exergy Transfer Effectiveness (ETE) Exergy Sink ETE Exergy Source “Given a set of process streams with a supply state (temperature, pressure, and resulting phase) and a target state, as well as utilities for power, heating, and cooling; design a system of heat exchangers, expanders, compressors, pumps and valves in such a way that the irreversibilities (or some cost objective) are minimized” Using Exergy in Subambient Processes? Low Temperature Processes Heat Pinch Heat Recovery 0 , 0 CT , Surplus min Q , Deficit min Q , Enthalpy H , Destruction min E Carnot Factor, η C 0 0 0 ln 1 T T p E T T E T T c T T m Aspelund, A., Berstad D.O. and Gundersen, T. (2007). An extended pinch analysis and design procedure utilizing pressure based exergy for subambient cooling. Applied Thermal Engineering, 27(16): 2633-2649. “Drawbacks”: • The Carnot factor is in a non- linear relation with respect to enthalpy. • Multiple data points must be calculated between supply and target conditions. • The exergy targets are not explicitly shown in any of the diagrams. Exergetic Temperature, T E T (T > T 0 ) Exergy Pinch Exergy Recovery 0 T E min T , Deficit min E , Surplus min E , Rejection min E , T T based Exergy E , Requirement min E , Destruction min E 0 0 T E T T Composite Curves (CCs) New Exergy Diagram Some Characteristics: Heat Pinch min 0 T , Enthalpy H Heat Recovery , Surplus min Q , Deficit min Q Temperature, T (T > T 0 ) 0 T Reverse Brayton Process 6 (Natural gas) 7 3 AC-100 2 COM-100-5 1 (Nitrogen) 4 TUR-100 5 HX-100 LIQ-EXP-100 8 c b a d e b c • Linear relation between and ሶ . • Only supply and target conditions are required. • is always positive. • The heat and exergy pinch points are placed in corresponding enthalpy and exergy intervals. Exergy Composite Curves (ECCs) c p constant 0 0 0 ; 0 ; ; Carnot Q Carnot Q T T E T T Q T T CCs Initial New ECCs Initial CCs Final New ECCs Final Marmolejo−Correa, D. and Gundersen, T. A new graphical representation of exergy applied to low temperature process design. Submitted for a Special Issue (September 2012) of Industrial & Engineering Chemistry Research. -200 -150 -100 -50 0 50 0 5 10 15 20 25 30 35 40 Cold Hot Enthalpy MW 1 , 1 , 2 37.3 25 C H C H MW T T 2 , 2 , 1 13.8 92.5 168 C H C H MW T C T 2 1 1 2 3 Temperature (°C) 3 , 3 0 168 C H H MW T 0 25 50 75 100 125 150 0 5 10 15 20 25 Source Sink , 2 , 2 6.8 31.9 T H E H E MW T K , 1 , 1 14.3 117.7 T T C E C E MW T K , 3 , 3 22.4 117.7 T T H E H E MW T K 3 2 1 2 1 Exergetic Temperature (K) T based Exergy MW -175 -125 -75 -25 25 75 125 0 20 40 60 80 Cold Hot 3 , 3 , 1 0 165 168 H C H MW T C T C 1 , 1 70.0 85.7 H H MW T C 2 , 2 , 2 23.1 25 22 H C H MW T C T C 2 1 1 2 3 Enthalpy MW Temperature (°C) 0 25 50 75 100 125 150 0 5 10 15 20 Source (above T0) Source (below T0) Sink , 1 , 1 , 3 18.8 117.7 112.3 T T T C E C E H E MW T K T K , 2 , 2 9.4 0.0 T T H E H E MW T K , 1 6.1 T E H T K , 2 , 2 4.4 0.0 T T C E C E MW T K 2 1 3 2 1 Exergetic Temperature (K) T based Exergy MW , , N Des min Des i i E E Exergy Destruction , , , Above Pinch Req min Def min Des min E E E Exergy Requirement , , , Below Pinch Rej min Sur min Des min E E E Exergy Rejected , , , , Des Total Des min Des ST Des CW E E E E