| 摘要 |
Salt-containing waste waters (effluents) from exhaust gas scrubbers operated with lime or limestone for acidic pollutant gases frequently contain calcium chloride as the principal constituent. If discharge is still not possible after treatment, these waters must be evaporated. The salt product obtained is hardly utilisable and difficult to dispose of. The use of soda for a reprecipitation to give utilisable sodium chloride is frequently proposed. However, this solution only displaces the site of the disposal problems, since calcium chloride arises in turn in the production of soda. It is proposed to reduce the calcium content of the waste waters by interventions in the exhaust gas scrubber itself. This is possible by recycling the magnesium, precipitated in a waste water treatment in the form of Mg(OH)2, which is contained in virtually all waters of this type. As a further solution, the addition of sodium hydroxide solution or sodium sulphate directly to the scrubber is provided. Recycling or addition are carried out substoichiometrically with a stoichiometric factor of 0.5-0.99, based on the calcium content of the waste water with a conventional procedure. Fig. 1 shows a block diagram of the process according to the invention with recycling of Mg(OH)2 from the waste water treatment. Lime or limestone suspension (6), untreated gas (7) and make-up water (8) are fed to the exhaust gas scrubber (1). The purified gas (10), calcium sulphite and gypsum (9) and a waste water stream (11) leave the scrubber. The waste water is [lacuna] to a ... Original abstract incomplete. <IMAGE>
|
