Dry scrubbing of acid gases in recirculating cyclones

Abstract

This paper describes a laboratory-scale study on the use of recirculating cyclones as reaction chambers for dry scrubbing of gaseous HCl with solid slaked lime particles. This gas cleaning system combines a numerically optimized reverse flow gas cyclone (RS VHE geometry) with a straight-through cyclone concentrator, which simultaneously increases the capture of the solid particles and promotes their partial recirculation. A laboratory-scale study was undertaken to test this technology and to compare its performance to a modified Stairmand HE reverse flow cyclone without recirculation. The experimental conditions were: reaction temperature ≈326 K, gas flow rate ≈2.9 × 10 −4 N m 3 s −1 and relative humidity of the gas ≈8.5%. The experimental variables tested were the solids load (1.0-9.2 × 10 −7 kg s −1 ) and HCl concentration (0.4-2.8 × 10 −2 mol m −3 ) in the inlet gas.The experimentally obtained particulate removal efficiencies with the recirculating cyclones (≈98%) were higher than those obtained with the Stairmand HE cyclone (≈93%), with the additional advantage of having significantly lower pressure drop. As for the acid removal efficiencies (≈10-96%), no significant differences were found between the two systems tested under the same experimental conditions.The possibility of using optimized recirculating cyclones for gas cleaning in a dry scrubbing process is very promising, since this is a low cost technology, highly efficient both for the removal of acid gases and for the capture of solid particles, which has the advantage of not requiring a post-reaction de-duster.

Removal of chloride from MSWI fly ash

“…The XRD pattern shows that Ca(OH) 2 , CaCl 2 ·2H 2 O, and Ca(OH)Cl were present in the sample. Most of the studies reported in literature [11][12][13] assume that CaCl 2 ·2H 2 O and Ca(OH)Cl are both chlorinated products of the reaction between Ca(OH) 2 and HCl, according to the following equation:…”

Modeling dry-scrubbing of gaseous HCl with hydrated lime in cyclones with and without recirculation

“…(17). The equation describing the mass balance of the gaseous reactant in the ith CSTR takes the form:…”

“…(9) in the previous equation, and C A out i in the equation of the material balance of the solid reactant [Eq. (17)] and knowing that (…”

“…Assuming that in the cyclone concentrator the gas and the solid flows are well described by plug flow, the same cascade of CSTRs placed in series used in the cyclone reactor will be considered here, except the fact that solid capture does not occur. Thus, the variation of the HCl concentration, the molar flow rate and the quantity of B in this cyclone are determined in the same way as in the cyclone reactor (Equations (23), (17) and (11) considering Á fcap = 0, respectively). The quantity (number of grains) of B available to react in the 1st CSTR is given by:…”

Selecting Particulate and Gaseous Pollution Control Device

“…It was finally concluded that incorporation of various droplet interactions could refine the models for better prediction of removal efficiency. Chibante et al (2007) investigated on the dry scrubbing of gaseous HCl with solid slaked lime particles using recirculating cyclones as reaction chambers. This gas cleaning system basically combined a numerically optimized reverse flow gas cyclone with a straight-through cyclone concentrator that simultaneously increased the capture of the solid particles and partial recirculation.…”