Air cleaning units; gas handling systems, namely, spray tower or packed column scrubbers, fans, ejectors, flame arresters, mist eliminators, coolers, and heaters, all sold together as a unit, to transport and condition waste gas streams to control total reduced sulfur compounds, volatile organic compounds and hazardous air pollutants; thermal and catalytic oxidizers for industrial air pollution control, namely, for the destruction of volatile organic compounds (VOC), hazardous air pollutants (HAP) and total reduced sulfur (TRS) compounds from waste gas streams; chemical oxidation systems for the treatment of white and black liquors comprised of heat exchangers and mixed tank or plug flow reactors and mixers, all sold together as a unit; industrial air cleaning apparatuses for the collection of fine particle emission, namely, wet electrostatic precipitators and wet scrubbers; evaporators for chemical processing, namely, industrial process system apparatuses for black liquor evaporation, comprising of tubular or plate heat transfer equipment in various configurations for the removal of water from the black liquor to increase the solids content of the resultant black liquor; condensate treatment systems, namely, heat exchangers, filters, tray or packed stripping columns and condensers, all sold together as a unit for the removal of total reduced sulfur compounds and volatile organic compounds from process condensates; heat recovery systems, namely, heat exchangers, direct and indirect condensers, filters and waste heat boilers for heat recovery or reuse within industrial processes, all sold together as a unit; chemical recovery systems, comprising of separators, skimmers, indirect and direct condensers and decanters for the recovery of tall oil soaps and turpentine within the pulping process