Characterization of sulphuric acid aerosols in industrial processes such as the absorption in flue gas cleaning

Characterization of sulphuric acid aerosols in industrial processes such as the absorption in flue gas cleaning

Sulphuric acid aerosols may be formed with high number concentrations (>108 1/cm³) and small droplet diameters (<200 nm) in industrial processes during absorption, cooling or mixing processes. The aerosol formation based on spontaneous phase transition occurs as soon as a critical supersaturation in the gas phase is reached. Depending on the principle of nucleation, the required critical saturation differs: For homogeneous nucleation the needed supersaturations are higher whereas for heterogeneous nucleation the presence of foreign particles lowers the needed supersaturation. The binary system of sulphuric acid – water reveals a strong vapor pressure minimum which leads to high supersaturations and to the occurrence of homogeneous nucleation. The resulting sulphuric acid aerosol is difficult to precipitate and apart from higher emissions they may cause operational problems such as corrosion and fouling. Up to now, no validated method for the prediction of aerosol formation in a flue gas containing sulphuric acid is known. However, this is essential for the design of separator systems.

Rauchgasreinigungsanlage 

At the Institute for Technical Thermodynamics and Refrigeration a flue gas cleaning plant in pilot scale is in operation (see figure). There, the nucleation of the sulphuric acid aerosol during the quenching process of a hot glue gas is examined. The flue gas is charged with the sulphuric acid with the help of a microstructured reactor [1,2]. The flue gas is quenched in a packed column in order to generate the supersaturation. For the characterization of the formed aerosol a condensation particle counter is used. With this method, only the number concentration can be obtained. The results are compared with the simulations from the simulation tool „AerCoDe” which has been developed at the institute during the last years [3].
The aim of this project is the characterization of the sulpuric acid aerosol regarding number concentration, droplet diameters and acid content using a combination of experiments and simulations.  

 

References:
[1] P. Pfeifer, K. Haas-Santo, J. Thormann, K. Schubert, One pass synthesis of pure sulphur trioxide in microreactors, Chemistry Today, 2007, 25, 42-46
[2] L. Brachert, R. Riede, P. Pfeifer, K. Schaber (2012): Dosierung von Schwefeltrioxid und Erzeugung von Testaerosolen mithilfe eines Mikroreaktors, Chemie Ingenieur Technik, Volume 84, Issue 4, Pages 524-529
[3] A simulation tool for aerosol formation during sulphuric acid absorption in a gas cleaning process, A. Wix, L. Brachert, S. Sinanis, K. Schaber, Journal of Aerosol Science, Volume 41, Issue 12, Pages 1066-1079