Presentation on theme: "Chapter10 Equilibrium-Based Methods for Multicomponent Absorption, Stripping, Distillation, and Extraction."— Presentation transcript:
1 Chapter10Equilibrium-Based Methods for Multicomponent Absorption, Stripping, Distillation, and Extraction
2 Purpose and Requirements: Know Equilibrium-Based Methods for MulticomponentLearn to use ASPEN PLUS, ChemCAD, HYSIM, PRO/IIKey and Difficult Points:Key PointsTheoretical Model for an Equilibrium StageGeneral Strategy of Mathematical SolutionDifficult PointsEquation-Tearing ProceduresSimultaneous Correction ProceduresInside-Out Method
3 Outline 10.1 THEORETICAL MODEL FOR AN EQUILIBRIUM STAGE 10.2 GENERAL STRATEGY OF MATHEMATICAL SOLUTION10.3 EQUATION-TEARING PROCEDURES10.4 SIMULTANEOUS CORRECTION PROCEDURES10.5 INSIDE-OUT METHOD
4 Absorption (Gas Absorption/Gas Scrubbing/Gas Washing吸收) Gas Mixture (Solutes or Absorbate)Liquid (Solvent or Absorbent)Separate Gas MixturesRemove Impurities, Contaminants, Pollutants, or Catalyst Poisons from a Gas(H2S/Natural Gas)Recover Valuable Chemicals
6 Absorption Factor (A吸收因子) A = L/KVComponent A = L/KV K-valueWaterAcetoneOxygen ,000Nitrogen ,000Argon ,000Larger the value of A，Fewer the number of stages required1.25 to 2.0 ，1.4 being a frequently recommended value
8 6.1 EQUIPMENTtrayed towerpacked columnbubble columnspray towercentrifugal contactorFigure 6.2 Industrial Equipment for Absorption and Stripping
9 Trayed Tower (Plate Clolumns板式塔) Figure 6.3 Details of a contacting tray in a trayed tower
10 (d) Tray with valve caps (a) perforation(b) valve cap(c) bubble cap(d) Tray with valve capsFigure 6.4 Three types of tray openings forpassage of vapor up into liquid
11 Froth (a) Spray(b) Froth(c) Emulsion(d) Bubble(e)Cellular Foam Liquid carries no vapor bubblesto the tray belowVapor carries no liquid dropletsto the tray aboveNo weeping of liquid through theopenings of the trayEquilibrium between the exitingvapor and liquid phasesis approached on each tray.(a) Spray(b) Froth(c) Emulsion(d) Bubble(e)Cellular FoamFigure 6.5 Possible vapor-liquid flow regimes for a contacting tray
12 Packed ColumnsFigure 6.6 Details of internalsused in a packed column
13 Packing Materails (a) Random Packing Materials (b) Structured Packing More surface area for mass transferHigher flow capacityLower pressure dropPacking Materails(a) Random PackingMaterials(b) Structured PackingMaterialsExpensiveFar less pressure dropHigher efficiency and capacityFigure 6.7 Typical materials used in a packed column
14 6.2 ABSORBER/STRIPPER DESIGN General Design ConsiderationsTrayed TowersGraphical Equilibrium-StageAlgebraic Method for Determiningthe Number of EquilibriumStage Efficiency6.2.3 Packed ColumnsRate-based MethodPacked Column Efficiency, Capacity,and Pressure Drop
15 6.2.1 General Design Considerations Design or analysis of an absorber (or stripper) requiresconsideration of a number of factors, including:1. Entering gas (liquid) flow rate, composition, temperature, and pressure2. Desired degree of recovery of one or more solutes3. Choice of absorbent (stripping agent)4. Operating pressure and temperature, and allowable gas pressure drop5. Minimum absorbent (stripping agent) flow rate and actual absorbent (stripping agent) flow rate as a multiple of the minimum rate needed to make the separation6. Number of equilibrium stages7. Heat effects and need for cooling (heating)8. Type of absorber (stripper) equipment9. Height of absorber (stripper)10. Diameter of absorber (stripper)
16 SUMMARY1. Rigorous methods are readily available for computer-solution of equilibrium-based models for multicomponent, multistage absorption, stripping, distillation, and liquid-liquid extraction.2. The equilibrium-based model for a countercurrent-flow cascade provides for multiple feeds, vapor side streams, liquid side streams, and intermediate heat exchangers. Thus, the model can handle almost any type of column configuration.3. The model equations include component material balances, total material balances, phase equilibria relations, and energy balances.4. Some or all of the model equations can usually he grouped so as to obtain tridiagonal matrix equations, for which an efficient solution algorithm is available.5. Widely used methods for iteratively solving all of the model equations are the bubble-point (BP) method, the sum-rales (SR) method, the simultaneous correction (SO method, and the inside-out method.
17 6. The BP method is generally restricted to distillation problems involving narrow-boiling feed mixtures.7. The SR method is generally restricted to absorption and stripping problems involving wide-boiling feed mixtures or in the ISR form to extraction problems.8. The SC and inside-out methods are designed to solve any type of column configuration for any type of feed mixture. Because of its computational efficiency, the inside-oi method is often the method of choice; however, it may fail to converge when highly! nonideal liquid mixtures are involved, in which case the slower SC method should j be tried. Both methods permit considerable flexibility in specifications.9. When both the SC and inside-out methods fail, resort can be made to the much slower relaxation and continuation methods.
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