CONTROL OF THE HCL EMISSIONS FROM THE COMBUSTION OF PVC BY IN-FURNACEINJECTION OF CALCIUM-MAGNESIUM-BASED SORBENTS

This is a laboratory study on the reduction of hydrochloric acid (HCl) emissions from the combustion of poly(vinyl chloride) (PVC), by in-fu rnace injection of calcium- and magnesium-based sorbents. Experiments were conducted in a nearly isothermal, electrically heated, drop-tube furnace, at gas temperatures of 850 and 1050 degrees C. PVC and the so rbents were premixed in powder form and injected in the furnace, where combustion of the fuel, release of HCl, and chlorination of the sorbe nts took place. Combustion was globally fuel-lean, with bulk equivalen ce ratios in the range of 0.2-0.5; particle heating rates were 10(4)-1 0(5) K/sec; gas residence times were approximate to 1 sec. Experiments burned pure pulverized PVC (to serve as a baseline) or PVC mixed with pulverized Ca(OH)(2), Mg(OH)(2), calcium acetate (CA), magnesium acet ate (MA), calcium-magnesium acetate (CMA), calcium formate (CF), calci um propionate (CP), and calcium benzoate (CB). The particle size of PV C was in the range of 125-150 mu m, the size of the sorbents varied bu t it was typically <100 mu m. The Ca/Cl or Mg/Cl molar ratios were set to 1:2, reflecting a stoichiometric composition, except for CMA where the Ca/Cl ratio was set to either 1:6 or 1:3. The HCl reduction effic iency of the sorbents in these runs ranged from 3% to 98%. The calcium -based sorbents exhibited high HCl capture efficiencies (72-98%), espe cially the organic salts (89-98%). The latter compounds, upon devolati lization of their organic components, formed high-porosity cenospheric particles, which imposed minimal mass diffusion limitations. The magn esium-based sorbents did not react significantly (3-5%) with HCl in th is temperature range. However, a considerable fraction of the magnesiu m in CMA appears to have taken part in the chlorination reaction. Vary ing the gas temperature between 850 degrees C and 1050 degrees C did n ot significantly affect the HCl capture efficiency of the sorbents.