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CHEMCAD Seminar Mass Transfer 2 John Edwards, P&I Design Ltd January, 2015. www.chemstations.com. MASS TRANSFER – ABSORPTION SESSION OBJECTIVES. SIMULATION SUITE. CHEMCAD SOFTWARE. www.chemstations.com. www.chemcad.co.uk. Basic Theory Thermodynamics CO 2 Amine System
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CHEMCAD Seminar Mass Transfer 2 John Edwards, P&I Design Ltd January, 2015 www.chemstations.com
MASS TRANSFER – ABSORPTIONSESSION OBJECTIVES SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com www.chemcad.co.uk • Basic Theory • Thermodynamics CO2 Amine System • Carbon capture simulation • Design considerations
MASS TRANSFER - ABSORPTIONBASIC THEORY ENHANCEMENT FACTOR SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com www.chemcad.co.uk Henry’s Law where m is slope of equilibrium line H=2950 bar for CO2 Stripping Factor CHEMCAD AMINE HG only Transfer Unit relationships reduces influence of liquid film Enhancement Factor E increasing E same as increasing PT Stripping Factor Mass Transfer Coefficients
MASS TRANSFER – ABSORPTIONCASE 8.01 CO2 ABSORPTION IN MEA SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com www.chemcad.co.uk Case 8.01 page 291 - 294
MASS TRANSFER – ABSORPTIONCASE 8.01 COLUMN OPERATION SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com www.chemcad.co.uk Case 8.01 page 291 - 294
MASS TRANSFER – ABSORPTIONCASE 8.01 PACKED COLUMN SIZING SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com www.chemcad.co.uk Case 8.01 page 291 - 294 HTU OV
MASS TRANSFER – ABSORPTIONPOST COMBUSTION CO2 / MEA SYSTEM SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com www.chemcad.co.uk Case 14.05 page 500 - 502 Cooled flue gas at 100°C is fed to an absorber re-circulating 30% MEA solution to absorb CO2 CO2 rich bottoms is fed via a cross heat exchanger for heat integration to a steam stripper
MASS TRANSFER – ABSORPTIONPOST COMBUSTION CO2/MEA PARAMETERS SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com www.chemcad.co.uk Case 14.05 page 500 - 502
MASS TRANSFER - ABSORPTION PROCESS REVIEW SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com www.chemcad.co.uk • Classification • Physical - exploits differences in physical properties • vapor pressure, solubility, molecular geometry, surface activity • Chemical - based on reaction kinetics and interfacial model • Mixture Classification • Homogeneous (V/L/S) - single phase gas or liquids • Air • Miscible Solvents • Heterogeneous (V/L/L/S) - immiscible phases • Liquid + Liquid • Liquid + Gas • Select Separation Process • Physical Absorption – Thermal Stripping • Reactive Absorption • Select Separating Agent • Solvent for Absorption • Stripping Method • Design Phases • Conceptual • Detailed • Final validation and release for construction
MASS TRANSFER - ABSORPTION DESIGN PRINCIPLES SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com www.chemcad.co.uk • Extent of separation • Number of equilibrium stages, predictable with reasonable confidence • Concept methods - Kremser equation, independent calculation • Rigorous methods - computer simulation, manufacturer’s software • Time of phase contact • Rate = (Driving Force) / Resistance • Driving Force = Departure from Equilibrium (Post combustion CC small) • Resistance (difficult to predict) • operating conditions: T, P, composition • physical properties of both phases • interfacial reaction mechanism • velocity, flow regime • Permissible pressure drop • Sets column diameter • Energy requirements • Heat • Heating and cooling • Heat of solution effects • Mechanical/Electrical • Prime movers for gas & liquids
MASS TRANSFER - ABSORPTION DESIGN PROCEDURE SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com www.chemcad.co.uk
MASS TRANSFER - ABSORPTION COLUMN DESIGN INTERNALS EFFICIENCY SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com www.chemcad.co.uk • Tray Column Murphree • Apply efficiency factor to theoretical plate • Obtain actual column profile for desired recovery • Apply safety factor for final number of trays • Packed Column Height Equivalent of Theoretical Plate (HETP) • Determine theoretical stages for desired separation • Obtain column profile • Multiply by HETP to get total height of packed section • Difficult to predict Murphree or HETP from theory • Depends on contacting device, phase equilibrium, hydraulics • Experimental data and correlations • Vendor information
MASS TRANSFER - ABSORPTION COLUMN DESIGN CONSIDERATIONS Weeping Flooding SIMULATION SUITE CHEMCAD SOFTWARE Liquid weeps at low gas velocity Liquid flow reverses at high velocity www.chemstations.com www.chemcad.co.uk • Column diameter is chosen to provide flexible operation between flooding and weeping. Typical operating range 60 to 70% of the flooding velocity. • The flooding velocity is determined by correlations. • Approach to flooding is used to get actual superficial velocity based on column diameter. • Minimum velocity to prevent plate weeping and wetting rate for packing • Plate column down-comers take up about 5-20% of column area • Packed columns require height allowance for liquid distribution and redistributors
MASS TRANSFER - ABSORPTION DESIGN TRAY COLUMNS SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com www.chemcad.co.uk • CHARACTERISTICS • Predictable hydraulic and mass transfer behaviour • Moderate to high pressure drop per tray • Can be scaled to large diameters • Suitable for fouling service • Feed point flexibility is easy • SPECIFICATION • Number of actual stages by applying Murphree plate efficiency • Feed tray location • Type of trays, tray spacing, tray layout • Column diameter • Column height • Feed / Side take-off arrangements / Nozzle sizes • Reboiler / Condenser sizing • COLUMN HEIGHT • Number actual stages x tray spacing + space allowance for feed/draws + sump + top volume • Tray spacing for most applications is 18-24 inches • Rule of thumb could be to add 1- 2 nozzle diameters to the total height for feeds and draws • Sumps sized on liquid residence time. Two to five minutes is reasonable.
MASS TRANSFER - ABSORPTION DESIGN PACKED COLUMNS SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com www.chemcad.co.uk • CHARACTERISTICS • Low pressure drop / smaller diameter / Feed point fixed • Random packing scale-up for HETP is difficult; structured packing scale-up is predictable • HETP prediction less well developed than for trays • Low to moderate cost for random packing; high cost for structured packing • Not suitable for fouling service • SPECIFICATION • Type of packing • Random packing • Structured packing • Trade-off pressure drop vs. HETP vs. cost • Column diameter – height of packing – feeds and off-takes • PACKED HEIGHT • HETP Replaces Tray Efficiency • Bed Height = No of Theoretical Stages x HETP • HETP is difficult to generalize and is a function of the type of packing, the system being separated and the hydraulics of the column. Experimental or vendor-supplied values are used.
MASS TRANSFER – SOLVENT EXTRACTIONCOLUMN STAGE SENSITIVITY SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com www.chemcad.co.uk Case Extraction Column Controller used to keep solvent feed at number of stages
MASS TRANSFER – SOLVENT EXTRACTIONSENSITIVITY STUDY SIMULATION SUITE CHEMCAD SOFTWARE www.chemstations.com www.chemcad.co.uk Case Extraction Column
MASS TRANSFER – ABSORPTIONDESIGN HEURISTICS Air / Gas Movers Pressure Rises Fans 12 in wg, blowers < 40 psig compressors > 40 psig Compressors: Reciprocating compressors: Efficiencies 65% at compression ratio of 1.5, 75% at 2.0 and 80-85% at 3-6 Efficiencies of large centrifugal compressors 76-78% and rotary compressors 70%. SIMULATION SUITE CHEMCAD SOFTWARE Centrifugal pumps: Single stage for 15-5000 gpm, 500 ft max head; Multistage for 20 – 11,000 gpm, 5500 ft max head. Efficiencies 45% at 100 gpm, 70% at 100 gpm and 80% at 10,000 gpm. www.chemstations.com www.chemcad.co.uk