An apparatus for improved removal of particulates and contaminants from a flue gas produced by the combustion of waste materials or fossil fuels in industrial processes having at least one horizontally oriented heat exchanger stage in which a wet scrubbing solution, such as an alkali reagent is sprayed in the same direction as the flue gas flow and a drain mechanism is located below the horizontally oriented heat exchanger. The horizontal orientation of the heat exchanger and the location of the drain mechanism increase the removal efficiency of very small particulates and contaminants. A collection tank is connected to the drain mechanism. A spray washing system is provided adjacent a mist eliminator and one or more additional heat exchanger stages for unplugging the heat exchanger and enhancing small particulate removal within the system.