Concentrating dilute sulfuric acid by spray evaporator

Large quantities of dilute spent sulfuric acid are released in many chemical processes. Recovering the dilute acid is not only profitable to the manufacturer but also imperative to environmental protection. This paper proposes a spray evaporator with a Venturi-type nozzle to concentrate the dilute sulfuric acid. Both hot air and dilute acid flow concurrently upwards through the nozzle. Water involved in the droplets is vaporized in the chamber and the dilute acid is concentrated. The bench-scale experimental results show that the dilute acid with initial concentration 18 wt% can be easily concentrated to 40–75 wt%. The measured parameters, such as concentration of outlet sulfuric acid, outlet air temperature and total pressure drop, are in accordance with those estimated from a mathematical model incorporating momentum, mass and heat transfer between the acid and air. The model is also applied to simulate the performance of the concentrator, including variations of droplet diameter, droplet velocity, droplet temperature, air temperature, air absolute humidity as well as pressure drop along the concentrator.