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John Edwards, P&I Design Ltd
CHEMCAD Seminar Mass Transfer 2 John Edwards, P&I Design Ltd January, 2015 1
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MASS TRANSFER – ABSORPTION SESSION OBJECTIVES
SIMULATION SUITE CHEMCAD SOFTWARE MASS TRANSFER – ABSORPTION SESSION OBJECTIVES Basic Theory Thermodynamics CO2 Amine System Carbon capture simulation Design considerations
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MASS TRANSFER - ABSORPTION BASIC THEORY ENHANCEMENT FACTOR
SIMULATION SUITE CHEMCAD SOFTWARE MASS TRANSFER - ABSORPTION BASIC THEORY ENHANCEMENT FACTOR reduces influence of liquid film Henry’s Law Stripping Factor where m is slope of equilibrium line H=2950 bar for CO2 Transfer Unit relationships Enhancement Factor E Mass Transfer Coefficients CHEMCAD AMINE HG only increasing E same as increasing PT
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MASS TRANSFER – ABSORPTION CASE 8.01 CO2 ABSORPTION IN MEA
SIMULATION SUITE CHEMCAD SOFTWARE MASS TRANSFER – ABSORPTION CASE 8.01 CO2 ABSORPTION IN MEA Case 8.01 page
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MASS TRANSFER – ABSORPTION CASE 8.01 COLUMN OPERATION
SIMULATION SUITE CHEMCAD SOFTWARE MASS TRANSFER – ABSORPTION CASE 8.01 COLUMN OPERATION Case 8.01 page
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MASS TRANSFER – ABSORPTION CASE 8.01 PACKED COLUMN SIZING
SIMULATION SUITE CHEMCAD SOFTWARE MASS TRANSFER – ABSORPTION CASE 8.01 PACKED COLUMN SIZING Case 8.01 page HTU OV
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MASS TRANSFER – ABSORPTION POST COMBUSTION CO2 / MEA SYSTEM
SIMULATION SUITE CHEMCAD SOFTWARE MASS TRANSFER – ABSORPTION POST COMBUSTION CO2 / MEA SYSTEM Case page 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
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MASS TRANSFER – ABSORPTION POST COMBUSTION CO2/MEA PARAMETERS
SIMULATION SUITE CHEMCAD SOFTWARE MASS TRANSFER – ABSORPTION POST COMBUSTION CO2/MEA PARAMETERS Case page
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MASS TRANSFER - ABSORPTION PROCESS REVIEW
SIMULATION SUITE CHEMCAD SOFTWARE MASS TRANSFER - ABSORPTION PROCESS REVIEW 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
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MASS TRANSFER - ABSORPTION DESIGN PRINCIPLES
SIMULATION SUITE CHEMCAD SOFTWARE MASS TRANSFER - ABSORPTION DESIGN PRINCIPLES 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
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MASS TRANSFER - ABSORPTION DESIGN PROCEDURE
SIMULATION SUITE CHEMCAD SOFTWARE MASS TRANSFER - ABSORPTION DESIGN PROCEDURE
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MASS TRANSFER - ABSORPTION COLUMN DESIGN INTERNALS EFFICIENCY
SIMULATION SUITE CHEMCAD SOFTWARE MASS TRANSFER - ABSORPTION COLUMN DESIGN INTERNALS EFFICIENCY 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
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MASS TRANSFER - ABSORPTION COLUMN DESIGN CONSIDERATIONS
SIMULATION SUITE CHEMCAD SOFTWARE MASS TRANSFER - ABSORPTION COLUMN DESIGN CONSIDERATIONS 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 Liquid weeps at low gas velocity Weeping Liquid flow reverses at high velocity Flooding
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MASS TRANSFER - ABSORPTION DESIGN TRAY COLUMNS
SIMULATION SUITE CHEMCAD SOFTWARE MASS TRANSFER - ABSORPTION DESIGN TRAY COLUMNS 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 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.
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MASS TRANSFER - ABSORPTION DESIGN PACKED COLUMNS
SIMULATION SUITE CHEMCAD SOFTWARE MASS TRANSFER - ABSORPTION DESIGN PACKED COLUMNS 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.
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MASS TRANSFER – SOLVENT EXTRACTION COLUMN STAGE SENSITIVITY
SIMULATION SUITE CHEMCAD SOFTWARE MASS TRANSFER – SOLVENT EXTRACTION COLUMN STAGE SENSITIVITY Case Extraction Column Controller used to keep solvent feed at number of stages
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MASS TRANSFER – SOLVENT EXTRACTION SENSITIVITY STUDY
SIMULATION SUITE CHEMCAD SOFTWARE MASS TRANSFER – SOLVENT EXTRACTION SENSITIVITY STUDY Case Extraction Column
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MASS TRANSFER – ABSORPTION DESIGN HEURISTICS
SIMULATION SUITE CHEMCAD SOFTWARE MASS TRANSFER – ABSORPTION DESIGN 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%. Centrifugal pumps: Single stage for 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.
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