SO₂ Removal in the Filter Cake of a Jet-Pulsed Filter:  A Combined Filter and Fixed-Bed Reaction Model

Jet-pulsed filters are frequently used to separate fine solid particles from gas streams. An example for the application of the filter as both a solid separator and a fixed-bed reactor is a dry flue gas cleaning process, where the dry solid sorbent Ca(OH)₂ forms a filter cake that captures a major part of the SO₂ and HCl out of the flue gas. One important phenomenon concerning the formation of the filter cake on jet-pulsed filters is imperfect cake removal. Here a jet pulse tears off the entire filter cake from only a fraction of the exposed filter area, and only part of the total filter area is subjected to the jet-pulse cleaning. This property of jet-pulsed filters has a great influence on the chemical reaction simulation between gas and solid in the filter cake because the gas velocity through the cake, the cake thickness, and the residence time distribution of the solid forming the cake differ widely over the entire filter area. A recently developed filter model, in which different classes of cake thicknesses are understood to result from different cake generations, is used to determine the distributions of cake thickness, gas velocity, and residence time of the solid over the filter area. With the combination of the filter model and a fixed-bed reaction model using an empirical kinetic equation, the SO₂ removal in the fixed bed of the filter cake can be simulated. The combined filter and reaction model was successfully validated with an experiment from a pilot plant for dry flue gas cleaning, where solid Ca(OH)₂ was used as a sorbent. A sample of the partially reacted sorbent from the pilot plant had been used to derive the empirical kinetic equation for SO₂ sorption in fixed-bed laboratory experiments.