11 Gas recovery apparatus; gas scrubbing and purification apparatus; gas purification installations; separators for scrubbing gas; heat exchangers for chemical processing; distillation apparatus for chemical processing; evaporators for chemical processing; distillation columns; vacuum distillation columns for industrial use; gas scrubbers [parts of gas installations]; heat exchangers, other than parts of machines; gas and air purification installations and machines relating thereto, namely mechanical filters for cleaning industrial gases, dust separators, parts for the aforesaid filters, included in this class; electric separators for filter and flue gas purification installations; flue gas purification installations and parts therefor, included in this class; gas scrubbers, namely machines and mechanical filters for purifying gases; superheaters; filters for gas and fume extractors; air cleaning filters; flues and installations for conveying exhaust gases; flue gas cleaning apparatus; flues and installations for conveying gases and emissions.