Drying properties and product characteristics of desulfurization wastewater evaporation by medium-temperature flue gas

A medium-temperature flue gas evaporation technology was adopted to achieve the “ zero-emission” treat- ment of desulfurization wastewater ( DW). The temperature variation,drying product characteristics and particle ag- glomeration in the process of DW evaporation based on a pilot scale experiment system were investigated under the condition of coal-fired medium-temperature flue gas. The results show that adopting medium-temperature flue gas for DW evaporation,the outlet flue gas temperature of drying tower can be controlled flexibly,the temperature curve is smoother in the process of DW evaporation,and the DW can be dried more rapidly and reliably when compared to low temperature flue gas for DW evaporation. The main components of drying product of DW are MgSO4·H2 O,CaSO4· 0. 5H2 O and NaCl. It is a hollow spherical particle with coarse,porous or incomplete surface. The average diameter of particles is much larger than that of fly ash. The specific resistance of the fly ash first decreases and then slightly in- creases with the increase of temperature after the addition of the DW drying product to the fly ash,but the specific re- sistance is not so different with that of the original fly ash after 120 ℃ . The DW droplets and fly ash particles collide and agglomerate to form the chain,globular or irregular clusters agglomerate,increasing the particle size,which is con- ducive to improve the collection efficiency of ESP. The effect of a small amount of HCl from the DW evaporation process on flue gas system can be reduced through adjusting DW pH value,and the question of DW drying product af- fecting fly ash utilization can be resolved by increasing the number of dust collection equipment.