CHEN 4470 – Process Design Practice Dr. Mario Richard Eden Department of Chemical Engineering Auburn University

1. Mass Integration CHEN 4470 – Process Design Practice Dr. Mario Richard EdenDepartment of Chemical EngineeringAuburn University Lecture No. 10 – Algebraic Mass Integration Techniques February 9, 2012

2. Why an Algebraic Approach? • Pinch Diagram • Useful tool for representing global transfer of mass • Identifies performance targets, e.g. MOC • Has accuracy problems for problems with wide ranging compositions or many streams • Algebraic Method • No accuracy problems • Can handle many streams easily • Can be programmed and formulated as optimization problems

3. Algebraic Mass Integration 1:7 • Composition Interval Diagram (CID) Number of intervals Nint≤ 2(NR+NSP) – 1 Equality is when no arrow heads or tails coincide!

4. Algebraic Mass Integration 2:7 • Table of Exchangeable Loads (TEL) • Exchangeable load of the i‘’th rich stream passing through the k’th interval is: • Exchangeable capacity of the j’th process MSA which passes through the k’th interval is calculated as:

5. Algebraic Mass Integration 3:7 • Table of Exchangeable Loads (TEL) (Cont’d) • Collective load of the rich streams passing through the k’th interval is: • Collective capacity of the lean streams passing through the k’th interval is:

6. Algebraic Mass Integration 4:7 • Mass Exchange Cascade Diagram • Within each composition interval it is possible to transfer a certain mass of pollutant from a rich to a lean stream • It is also possible to transfer mass from a rich stream in an interval to a lean stream in lower interval • Component material balance for interval k

7. Algebraic Mass Integration 5:7 • Mass Exchange Cascade Diagram (Cont’d)

8. Algebraic Mass Integration 6:7 • Comments • δ0 is zero (no rich streams exist above the first interval) • Feasibility is insured when all the δk's are nonnegative • The most negative δk corresponds to the excess capacity of the process MSA's in removing the targeted species. • After removing the excess capacity of MSA's, one can construct a revised TEL/cascade diagram in which the flowrates and/or outlet compositions of the process MSA's have been adjusted.

9. Algebraic Mass Integration 7:7 • Comments (Continued) • On the revised cascade diagram the location of residual mass = zero corresponds to the mass-exchange pinch composition. • Since an overall material balance for the network must be realized, the residual mass leaving the lowest composition interval of the revised cascade diagram must be removed by external MSA's.

10. Example No. 5 1:6 • Dephenolization of Aqueous Wastes • Same problem as solved in Example No. 2 (Lecture 5) • Composition Interval Diagram (CID)

11. Example No. 5 2:6 • Sample Calculations • Composition scales • Interval loads (rich in first interval, lean in second)

12. Example No. 5 3:6 • Table of Exchangeable Loads (TEL)

13. Elimination of Excess Capacity Lower flowrate of S2 to 2.08 kg/s as calculated in Example No.2 Example No. 5 4:6 • Cascade Diagram

14. Example No. 5 5:6 • Revised Table of Exchangeable Loads (TEL)

15. Example No. 5 6:6 • Revised Cascade Diagram Comments Pinch point is between intervals 4 and 5. Load to be removed by externals:0.0124 kg/s

16. Other Business • Next Lecture – February 16 • Advanced Column Design and Reactive Distillation • Reboiler Selection and Design • Design of Overhead Condensers and Air Cooled HX