A 10% by weight NaOH solution is being used for a caustic washing process. In order to smooth the variations in flow rate and concentration, a 10,000 gallon tank is being used as a surge tank (well mixed). The washing process requires a constant flow rate of 1500 gal/hr of the solution. Just before a plant upset, the tank contains 8000 gallons of a 10% NaOH solution, with an inlet flow to the tank of 1000 gal/hr of a 10.5% NaOH solution. Due to the upset, the inlet stream concentration drops to 5% NaOH instantaneously although the flow rate remains constant. An alarm will sound to warn the operator when the outlet concentration from the surge tank drops to 9.8% (or rises to 10.2%). The tank is well mixed and the density of all solutions is 8.3 lb/gal. All concentrations given above are on a weight basis. Find: a) how long it will take before the alarm sounds? b) if the alarm did not operate, how long it would take before the surge tank was empty?

Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
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A 10% by weight NaOH solution is being used for a caustic washing process. In order to smooth the variations in flow rate and concentration, a 10,000 gallon tank is being used as a surge tank (well mixed). The washing process requires a constant flow rate of 1500 gal/hr of the solution. Just before a plant upset, the tank contains 8000 gallons of a 10% NaOH solution, with an inlet flow to the tank of 1000 gal/hr of a 10.5% NaOH solution. Due to the upset, the inlet stream concentration drops to 5% NaOH instantaneously although the flow rate remains constant. An alarm will sound to warn the operator when the outlet concentration from the surge tank drops to 9.8% (or rises to 10.2%). The tank is well mixed and the density of all solutions is 8.3 lb/gal. All concentrations given above are on a weight basis. Find: a) how long it will take before the alarm sounds? b) if the alarm did not operate, how long it would take before the surge tank was empty?
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