Treating gas with catalytic dust in panel bed

The method of treating a gas involving its contacting with a fine granular medium catalytic toward a chemical reaction by a chemical species present in the gas, comprising:

• a. arranging a granular material smaller than about 20 mesh in a panel bed having a plurality of transversely disposed upwardly spaced gas entry portions separated by interposed supporting members having outer and inner edges with respect to the bed wherein said gas entry portions have gas entry faces substantially contiguous with said outer edges and wherein said bed has gas exit portions spaced from said inner edges;
• b. forwardly flowing gas through the gas entry portions of the granular material bed and outwardly from the gas exit portions while adding to said gas a granular medium substantially smaller than about 120 mesh to separate and accumulate said medium in surface layer deposits at said gas entry faces wherein said gas enters said gas entry faces at a velocity greater than about 16 feet per minute during at least a part of this step (b);
• c. thereafter causing a transient flow of gas to move in the direction in reverse to the flow of said gas in (b);
• d. said transient reverse flow producing first a rise at a given rate of rise and subsequently a fall in the pressure difference between said gas exit portions and said gas entry portions, said difference produced by said transient reverse flow remaining greater than a first critical minimum difference for a time interval of less than about 150 milliseconds, said first critical difference being that difference at which a steady flow of gas in said reverse direction just produces a localized spill of granular material from said gas entry faces, and said difference produced by said transient reverse flow peaking to a top value beyond a second critical minimum difference, which is the pressure difference at which a transient flow of gas in said reverse direction producing said pressure difference at said rate of rise just initiates a body movement of said granular material toward said gas entry faces to spill a portion of the granular material and substantially all of said accumulated granular medium from the bed;
• e. supplying fresh granular material to replace material spilled from said gas entry portions;
• f. repeating the cycle of said steps (b), (c), (d), and (e) at least two times and then repeating step (b);
• g. forwardly flowing gas to be treated through the gas entry portions of the granular material bed and outwardly from the gas exit portions to treat said gas by contact with said surface layer deposits of said medium, wherein said medium is catalytically active toward a chemical reaction by a chemical species present in said gas to be treated, and wherein either at least a first part of this step (g) occurs simultaneously with a said step (b), the gas in (b) comprising the gas to be treated, or this step (g) is wholly subsequent to said step (b);
• and
• h. thereafter repeating steps (c), (d), (e), (b), and (g) in a cyclic manner.