Study On Multistage Hybrid Process Of Salt Desorption-Absorption For Dilute Hydrochloric Acid Concentration

Millions of tons of dilute hydrochloric acid produced in chemical industry and other related industries in China,need to be concentrated on-site and recycled in order to realize the reuse of waste resources and eliminate the environmental pollution.At present,there are mainly three processing methods used in concentration of dilute hydrochloric acid,i.e.deep desorption,variable pressure rectification and extractive rectification,which are all high energy consuming and low efficient.So the research and development of more efficient and energy saving technologies has been paying much attention to in recent years.A new method,the multistage hybrid process of salt desorption-absorption was proposed and studied.For the new process,each stage consists of a desorption kettle and an absorption tower.The concentration is carried out stage by stage through controlling the salt concentration and other operating parameters during the process and the desired concentrated product can be obtained.The new method has the advantages of high efficiency and low energy consumption.The mathematical model of the multistage hybrid process of salt desorptionabsorption,based on the assumptions of vapor-liquid equilibrium in every desorption kettle,equal salt concentration in each desorption kettle,negligible heat loss of every desorption kettle and complete absorption of desorbed gas in each absorption tower,was developed firstly in this article,which is composed of MESH equations.In order to obtain the HCl+MgCl₂+H₂O vapor-liquid equilibrium mathematical model used in the multistage salt desorption-absorption hybrid process mathematical model,the experimental data from Perry’s book and Sako’s work is correlated and twelve model parameters of HCl+H₂O binary system and five model parameters of HCl+MgCl₂+H₂O ternary system are obtained on the basis of Sako’s HCl+MgCl₂+H₂O vapor-liquid equilibrium model.In this article,the parameters,such as the concentration of magnesium chloride,the concentration of dilute hydrochloric acid and the stage number of the hybrid process,are computed respectively according to the developed mathematical model of multistage hybrid process of salt desorption-absorption.Finally,the experiment of multistage hybrid process of salt desorption-absorption was carried out on a laboratory scale.When the stage number of the hybrid process was 3,the parameters influencing the product concentration,such as the concentration of magnesium chloride,the concentration of dilute hydrochloric acid were investigated and the experimental values were compared with the simulation results.The comparison results showed that the experimental values are in agreement with the simulation result and the effectiveness and reliability of the new process,i.e.the multistage hybrid process of salt desorption-absorption was proved.