Soda ash, one of the most important basic chemical raw materials, is widely used in chemicals, detergent and soap, petrochemical, pulp and paper, glass, metal, ceramic and food industries. Soda ash is mainly produced from natural trona and other sodium carbonate-containing minerals, in addition to the ammonia-soda and ammonium sulfate-soda methods. In the production of soda ash based on mirabilite, the ammonium sulfate-soda method is considered the most suitable one because of its high utilization degree of mirabilite, low energy consumption, and production of ammonium sulfate as a byproduct.
The depletion of nonrenewable energy resources and the high cost associated with it have made energy conservation and more efficient use of energy an urgent matter. Consequently, it is important to find a way of reducing energy consumption in the production of soda ash.
The solution is exergy analysis, which helps understand the energy distribution, detect the location of energy consumption and provide a direction for energy saving of a system.
The difficulty in exergy analysis of electrolyte systems is to accurately estimate the chemical exergy of substances or species involved in aqueous electrolyte solution. Furthermore, as for the soda ash production process by the ammonium sulfate-soda method, the gas-liquid reaction and salt precipitation reaction occur simultaneously in the Na2SO4-NH3-CO2-H2O electrolyte system, so exergy analysis cannot be carried out using the chemical exergy of elements and substances presented by preceding researchers.
Pak Kyong Song, a researcher at the Faculty of Chemical Engineering, has proposed a novel approach to calculate the chemical exergy of an aqueous electrolyte system accompanied by gas-liquid reaction and salt precipitation reaction, based on the Pitzer equation.
He simulated a soda ash production process using Aspen Plus and performed an exergy analysis based on the thermodynamic data obtained from the simulation.
The result showed that the exergy destruction of the entire process is 99.945kW and exergy efficiency is 59.57%. In addition, he found that the units with low exergy efficiency in the process are condenser and absorption towers such as NH3 absorption tower, carbonation tower and water washing tower, which are the primary targets of energy saving.
For more details, you can refer to his paper “Study on Exergy Analysis of the Soda Ash Production Process by the Ammonium Sulfate-Soda Method” in “ACS Omega” (SCI).