For the second type of calculations, the number of stages is specified. In this case the value of the solvent rate is adjusted upwards or downwards by increments until the number of calculated stages matches the specification. The Newton Method is used for iterating on the solvent rate.
Our program LEACH.BAS runs with any version of BASIC. It is part of the compressed collection that can be downloaded from our archive (see page for Dept. of Chemical Engr). The calculation portion was derived from a FORTRAN program written by Harry G. Folster. Our version has a built-in example, and it is easy to replace these numbers with those for an actual problem. Some demonstration data and results are shown below with comments added to the table printed by the program.
VALUES USED IN PROGRAM
BASIS IS 1 UNIT WEIGHT OF SOLIDS 'older version asks for amount
FRESH SOLVENT FEED 5 ' This is merely a starting guess, the program keeps adjusting
MASS FRACT. SOLUTE IN FEED .1 ' This + next 2 numbers must add up to 1
MASS FRACT. SOLVENT IN FEED .8
MASS FRACT. SOLID IN FEED 9.999996E-02 ' computerese
MASS FRACT SOLUTE IN FRESH SOLVENT 0
MF SOLVENT IN FRESH FEED 1
FRACT. SOLUTE IN SOLVENT EXTRACT .05 ' used when you ask how many stages
FRACT. SOLUTE IN FEED RECOVERED .9
WT. RATIO OF SOLVENT TO INERT SOLID 10 'based on inerts only
NO. OF AVAILABLE STAGES 9 ' specify zero to get no. of stages
STAGE CALCULATIONS FOR LEACHING
STAGE INPUT FRAC OUTPUT FRAC INPUT FRAC OUTPUT FR
T/D SOLUTE T/D SOLUTE T/D SOLUTE T/D SOLUTE
0 1 .1 1.11 .009009 1.022808 0 .9128084 9.859681E-02
A good way to get familiar with the program is to check the overall material balance using pencil and paper.