Abstract: A scrubber comprises a casing (1) with an inlet (2) and an outlet (3) for flue gases, and with an outlet (4) for water and substances separated from the flue gases, and water injection nozzles. The casing (1) is divided, by means of a partition having a throughflow opening for flue gases, into an evaporation zone (11) in which injected water is caused to cool the flue gases by heat absorption and evaporation, simultaneously as the water adsorbs any substances carried along by the flue gases, and a condensation zone (12) in which flue gases and steam from said first zone are condensed. The flue gas outlet from the condensation zone is provided with a drop separator (8), and the partition (151) separating the two zones is arranged as a collector of water which has not evaporated in said evaporation zone and which by means of a pump (16) and further nozzles (17), is reinjected into said evaporation zone (11).

Abstract: Apparatus for controlling the combustion of natural gas in a natural gas fired appliance is described. Exhaust gases are sampled and maintained at a predetermined constant temperature between the dew point and the steam point. The relative humity of the constant temperature gas is monitored by a hygrometer. Relative humidity deviations from a predetermined value result in output signals from the hygrometer to a control circuit. The control circuit is connected to regulators in the air intake or chimney of the appliance which regulate air intake to keep the relative humidity substantially constant and hence control combustion of the gas. In another embodiment the relative humidity of the exhaust gases and the combustion air intake are monitored by separate hygrometers which are linked to each other so that a change in the relative humidity of a gas affecting one hygrometer will compensate the other hygrometer and control combustion as before.