| 摘要 |
Flue gas residues consisting predominantly of CaCl2, NaCl, CaSO4 and Na2SO4 together with small amounts of other impurities, are processed by (a) mixing the flue gas residues with an acid wash water to form a CaCl2 slurry; (b) filtering the slurry to give a first CaCl2 filtrate stream; (c) separating the filtrate stream into a first fraction with a CaCl2 concentration which is below a certain predetermined concentration and a second fraction with a CaCl2 concentration above the predetermined concentration, and (d) mixing the first fraction with the mixture formed in stage (a), wherein the predetermined concentration in stage (c) is such that after mixing the first fraction from step (c) with the mixture of flue gas residue and acid wash water from step (a) in step (d), a saturated (greater than 20 %) CaCl2 slurry is obtained. The second fraction from step (c) having a higher CaCl2 concentration is e.g. evaporated. The CaCl2 slurry may be subjected to aeration, preferably at a pH of above 8.3. The CaCl2 slurry may be subjected to air stripping. The CaCl2 filtrate stream may be subjected to successive neutralisation, reduction, addition of flocculating agent and sedimentation. The mixing of the flue gas residue with acid wash water is carried out e.g. at 60-80 (65-70) deg C. Filtration of the slurry is preferably carried out under reduced pressure e.g. of 0.2-0.4 bar absolute. An apparatus for carrying out the process is separately claimed.
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