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

Abstract

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.

Modelling of in-duct desulfurization reactors

“…The relevant decrease of the reaction rate with the solid conversion observed from experimental data, related to the interactions between SO 2 and the sorbent particles in the presence of water vapour, was described by an exponential dependence of the solid conversion [5][6][7], or a potential dependence reported with calcitic sorbents from recycling [8].…”

Hydrogen Chloride Removal from Flue Gas by Low-Temperature Reaction with Calcium Hydroxide

“…The selected temperature range is representative of the industrial operation of Ca-based DSI systems. , The HCl concentrations selected aim to represent HCl-rich flue gases, such as those generated by the cocombustion of municipal solid waste with relevant fractions of industrial or biomedical wastes, which is an increasingly common situation in European MSWI . The amounts of sorbent and inert in the fixed bed were chosen in order to obtain a bed thickness in the range 1.6–2.2 mm, which is representative of the average depth of the Ca­(OH) 2 cake adhered on the fabric filter bags in DSI systems . A gas flow rate of 180 N mL/min was adopted in order to have a superficial velocity of the gas in the reactor of 0.9 m/min at 180 °C, corresponding to a typical design value for fabric filters .…”

“…45 The amounts of sorbent and inert in the fixed bed were chosen in order to obtain a bed thickness in the range 1.6−2.2 mm, which is representative of the average depth of the Ca(OH) 2 cake adhered on the fabric filter bags in DSI systems. 46 A gas flow rate of 180 N mL/min was adopted in order to have a superficial velocity of the gas in the reactor of 0.9 m/min at 180 °C, corresponding to a typical design value for fabric filters. 47 Details on the laboratory apparatus, including the experimental procedure followed in FBR runs are reported in section S1 of the SI.…”