Ahmed... please rephrase your question so that I may understand your real problem. The elements you've mentioned behave differently. If Cl is associated with Na and K (as chloride salts) they will remain in the solid... However, the question can not be understood clearly.
Some inorganic compound in biomass will be vaporized into aerosol form including KCl, K2SO4 and NaCl as most dominant fine particle compounds. When leaving cross section reaction area those temperature will gradually decrease and stick on wall column leading slagging formation. So, increasing high of column might be a consideration to make faster condensation of these aerosols. Thanks