Semi-dry flue gas desulphurization in spray towers: a critical review of applicable models for computational fluid dynamics analysis

In semi-dry flue gas desulphurization in a spray dry scrubber, the desulphurization efficiency is a result of the competition between the spray droplets SO₂ absorption rate and the droplets drying rate. The complexity of the process is increased by the 3D nature of the hydrodynamics occurring within the dryer. For accurate optimization of the desulphurization efficiency, all these phenomena must be intricately modelled and the models solved. Computational fluid dynamics may be used in implementing the developed models and numerically solving the generated system of complex differential equations in a single platform. This paper presents a holistic appraisal of the models used in defining the semi-dry flue gas desulphurization process occurring in a spray dry scrubber. First, the hydrodynamic modelling of the process is addressed, with focus on the implementation of the atomization process in computational fluid dynamics platforms, including primary and secondary break-up, inter-droplet/particle interaction and wall-droplet/particle interaction. Secondly, the models used to define slurry droplet drying and the associated validation techniques are presented. Lastly, the models used to describe the absorption process of the sulphurous species into the droplet, taking into consideration the enhancement to the absorption by the reaction occurring within the droplet are discussed. A critical appraisal of the work done to date in modelling the semi-dry flue gas desulphurization process in a spray dry scrubber, and areas where further research is required is given at the end of each analysis.