Heatup Path-Equilibrium Curve Intercept Calculations

326

Appendix J

Heatup Path-Equilibrium Curve Intercept Calculations Figs. 11.7 and 12.1 indicate that maximum a feed gas's:

SO 2

oxidation in a catalyst bed occurs where

heatup path intercepts its: equilibrium curve. The point of interception may be determined: (a) by re-doing Table 12.1's calculations every 0.1 K (b) iteratively, using Excel's Goal Seek tool. This appendix describes (b).

J.l Calculation Strategy Our iterative intercept strategy is to find the temperature at which a feed gas's: heatup path % S02 oxidized, ~. equals its: equilibrium curve % S02 oxidized, f~E. This temperature and its equivalent % SO 2 oxidized define the intercept point. The next several pages provide an intercept calculation worksheet and instructions. The worksheet is for the specific case of:

10 volume% SO2 11 volume%

0 2

79 volume% N2 690 K

feed gas and 1.2 bar gas pressure. It is easily altered for different pressures and gas compositions and temperatures. All calculations are based on 1 kg-mole of 1st catalyst bed feed gas.

327 J.2 Worksheet

The top of worksheet Table J. 1 is similar to equilibrium curve worksheet Table D. 1. Its main components are:

(a) an equilibrium curve % S O 2 oxidized value in cell F 11 (b) Eqn. (10.13) in cell A14 (as shown to the right of that cell) (c) equilibrium pressure Pt specified in cell K6.

The middle of the worksheet is similar to heatup path Table 1.1. Its main components are:

(a) a matrix which contains Eqns. (11.1) to (11.6)- and Eqn. (11.7") with enthalpy equations in cells D28-J28 (b) feed gas temperature in cell F30 (copied from cell K5) (c) intercept gas temperature in cell J30 (copied from cell A14) (d) a matrix results column like that in Table I. 1 (e) a heatup path % S02 oxidized value calculated in cell I39 from the matrix results. The bottom of Table J.1 is the iterative part of the worksheet. It: (a) subtracts: heatup path % S02 oxidized (cell 139) from equilibrium curve % S O 2 oxidized (cell F 11) in cell G47 then: (b) uses Excel's Goal Seek tool to determine the value of: equilibrium curve % S02 oxidized in cell F 11 which gives a zero value to cell G47. The Goal Seek procedure is described in Section J.4.

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