Digester tank with foam control cover

In apparatus for carrying out chemical reactions involving a liquid phase and a gas phase, wherein there is formation of foam above the liquid phase, the apparatus comprising a reactor vessel having an enclosed sidewall and bottom and designed to contain a liquid and a gas;

• a floating cover vertically movably maintained within the vessel and having a lower ceiling surface extending transversely across the vessel within the sidewall and designed to be supported above the level of liquid in the vessel;
• gas withdrawal conduit means located within the vessel and designed to permit the passage of gas between the vessel and the exterior of the vessel;
• and gas pressure controlling means for limiting the pressure below the floating cover within the vessel by controlling the flow of gas through the gas withdrawal conduit means;
• the improvement which comprises a gas-filled buoyancy chamber rigidly connected to and located below the floating cover and within the vessel and designed to partially support the floating cover above liquid within the vessel;
• and a variable level liquid/foam withdrawal member, ridigly supported from and below the floating cover, and defining a withdrawal opening, located within the vessel and below the uppermost portion of the buoyancy chamber, and withdrawal conduit means connecting the withdrawal opening to the exterior of the vessel, to control the passage of foam and liquid betwen the vessel and its exterior;
• wherein the floating cover and the withdrawal opening, moving together, can be maintained at a desired height relative to the surface of the liquid so as to permit the removal of any proportion of foam and sludge floating on the surface of the liquid.