This invention relates to a method of purifying gases which are polluted by hydrocarbons and the like in an apparatus having two reactors. Each reactor contains a catalyst bed, a ceramic bed and a border layer located between the two beds. The polluted gas is forced to stream alternately through the first reactor and the second reactor (clock-wise streaming) and the second reactor and the first reactor, respectively (counter clock-wise streaming). The purification of said gas occurs when the hydrocarbons in the gas are oxidized to carbon dioxide and water in the catalyst beds. The temperature of the gas streaming through the upper portion of the reactors is measured. When the temperature exceeds a certain level, a portion of the gas is taken out from the apparatus during the passage over the border layer of the second reactor if said gas is streaming in a clock-wise direction, and a portion of said gas is taken out from the apparatus during the passage over the border layer of the first reactor if said gas is streaming in a counter clock-wise direction.
A process is provided for destroying organic contaminants, such as oil mists from workshop rooms, formaldehyde and aromatics, out of exhaust gases by passing the exhaust gas through two reactors connected in a parallel arrangement to a contaminated exhaust gas inlet. Each of the two reactors is equipped with a plurality of serially arranged reaction zones, wherein each reaction zone contains an upstream catalyst (such as a commercial wire knit catalyst); a downstream absorbent (such as Y zeolite or H-ZSM) and a heater. A major portion of the contaminated exhaust gas is passed through one of the two reactors, while, simultaneously, a minor portion of the contaminated exhaust gas is passed through the other reactor. After a period of time, the exhaust gas flow rate through the two reactors is reversed so that a major portion of the exhaust gas now flows through the reactor that previously had a minor portion of the exhaust gas flowing through it and a minor portion of the exhaust gas now flows through the reactor that previously had a major portion of the exhaust gas flowing through it, so that the process is cyclical in this manner. When a major portion of the exhaust gas flows through a reactor, the hydrocarbon contaminants are sorbed into the absorbent. When a minor portion of the exhaust gas flows through a reactor, the reactor is heated to the catalyst light-off temperature so that the contaminants within the exhaust gas and the contaminants released from the absorbent are catalytically destroyed in a downstream catalyst in an adjacent downstream reaction zone.
The present invention provides thermal oxidizers containing improved preheating designs and processes for improving the preheating of thermal oxidizers. The processes are practiced by preheating the matrix-bed of matrix materials in a flow path that is opposite in direction to the flow path for the processing fluids through the matrix bed. In such a process, there is a substantial reduction in the time and energy required for the preheating of the matrix bed in comparison to the prior processes using same flow direction preheating.
The gas phase exothermic reaction of a feed gas mixture is carried out by providing first and second chambers in fluid communication with one another and each containing a bed of solid heat exchange material and at least one bed of catalyst material, each chamber being selectively operable in cooling and heating modes. The feed gas mixture is introduced into a selected one of the chambers when the selected chamber is in the cooling mode and the other chamber is in the heating mode so that the feed gas mixture flowing through the selected chamber contacts the bed of heat exchange material before contacting the bed of catalyst material, the feed gas mixture being reacted in the catalyst bed to form a gaseous product. The gaseous product is conducted from the selected chamber to the other chamber so that the gaseous product flowing through the other chamber contacts the bed of catalyst material before contacting the bed of heat exchange material. The direction of gas flow through the chambers is periodically reversed so that the first and second chambers alternately operate in the cooling and heating modes, thereby forming between the first and second chambers a hot zone containing the gaseous products. A portion of the gaseous product is discharged from the hot zone so as to withdraw sufficient heat to maintain the reaction in the catalyst bed of the selected chamber at a temperature below a predetermined maximum temperature, while maintaining autothermicity.
An improved method and apparatus is provided for thermally reacting chemicals in a matrix bed of porous inert media. The reaction is conducted in an apparatus that is capable of establishing and maintaining a non-planar reaction wave within the matrix bed. The positioning of the non-planar reaction wave permits the interior surfaces of the vessel to be maintained at a temperature at least above 175.degree. F. The apparatus includes a vessel that contains the matrix bed; one or more feed tubes that extend into the matrix bed, where preferably an exterior portion of each of the feed tubes that passes through the vessel is insulated; an exhaust outlet; and a means for heating the matrix bed. The non-planar reaction wave is established by heating at least a portion of the matrix bed to at least the reaction temperature of the chemicals and feeding a process stream containing the chemicals to be reacted into the feed tubes. Upon exiting the feed tubes, the process stream is reacted in a non-planar reaction wave to produce heat and the reacted process stream. The heat from the non-planar reaction wave maintains the interior surfaces of the vessel at a temperature of at least 175.degree. F. during operation of the vessel. The reacted process stream is then directed to the exhaust outlet of the vessel.
