Ammonia is one of the chemical constituents of industrial waste that must be removed in a treatment plant before the waste can safely be discharged into a river or estuary. Ammonia is normally present in wastewater as aqueous ammonium hydroxide NH 4 OH. A two-part process is frequently carried out to accomplish the removal. Lime (CaO) is first added to the wastewater, leading to the reaction CaO H2O! Ca2 2 OH The hydroxide ions produced in this reaction drive the following reaction to the right, resulting in the conversion of ammonium ions to dissolved ammonia: NH 4 OH NH3 g H2O l Air is then contacted with the wastewater, stripping out the ammonia. (a) One million gallons per day of alkaline wastewater containing 0.03 mole NH3/mole ammoniafree H2O is fed to a stripping tower that operates at 68°F. Air at 68°F and 21.3 psia contacts the wastewater countercurrently as it passes through the tower. The feed ratio is 300 ft3 air/gal wastewater, and 93% of the ammonia is stripped from the wastewater. Calculate the volumetric flow rate of the gas leaving the tower and the partial pressure of ammonia in this gas. (b) Briefly explain in terms a first-year chemistry student could understand how this process works. Include an equilibrium constant for the second reaction in your explanation

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

Chapter1: Introduction

Section: Chapter Questions

Problem 1.1P

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Ammonia is one of the chemical constituents of industrial waste that must be removed in a treatment plant before the waste can safely be discharged into a river or estuary. Ammonia is normally present in wastewater as aqueous ammonium hydroxide NH 4 OH. A two-part process is frequently carried out to accomplish the removal. Lime (CaO) is first added to the wastewater, leading to the reaction CaO H2O! Ca2 2 OH The hydroxide ions produced in this reaction drive the following reaction to the right, resulting in the conversion of ammonium ions to dissolved ammonia: NH 4 OH NH3 g H2O l Air is then contacted with the wastewater, stripping out the ammonia. (a) One million gallons per day of alkaline wastewater containing 0.03 mole NH3/mole ammoniafree H2O is fed to a stripping tower that operates at 68°F. Air at 68°F and 21.3 psia contacts the wastewater countercurrently as it passes through the tower. The feed ratio is 300 ft3 air/gal wastewater, and 93% of the ammonia is stripped from the wastewater. Calculate the volumetric flow rate of the gas leaving the tower and the partial pressure of ammonia in this gas. (b) Briefly explain in terms a first-year chemistry student could understand how this process works. Include an equilibrium constant for the second reaction in your explanation

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