Hydrocarbon cracking

Abstract

A method and apparatus for extending the operating life of a tube-type heat exchanger that has an upstream tube sheet face that carries a plurality of hollow tubes wherein the upstream side of the tube sheet face is coated with at least one refractory.

1 . In a method for thermally cracking a hydrocarbonaceous material to form a cracked product wherein said material is passed through at least one pyrolysis furnace to cause said cracking and form a furnace product, said product being transferred from said furnace to at least one tube-type heat exchanger which has a first upstream tube sheet face and a second downstream tube sheet face and which contains a plurality of longitudinally extending spaced apart hollow interior heat exchange tubes having an interior surface and upstream and downstream ends, said tubes extending in overall length from said upstream face sheet to said downstream face sheet for transporting said product through said heat exchanger, the longitudinal axes of said tubes extending from said upstream face sheet to said downstream tube sheet face, said upstream tube sheet face having an upstream side, said upstream ends of said tubes being product inlet ends that terminate with said upstream side of said upstream tube sheet face, the improvement comprising coating said upstream side of said upstream tube sheet face between said tube inlets with at least one refractory. 
     
     
         2 . The method of  claim 1  wherein said refractory contains at least about 40 wt. % alumina based on the total weight of said refractory. 
     
     
         3 . The method of  claim 1  wherein said interior surfaces of said exchange tubes are not coated with refractory. 
     
     
         4 . In a thermal cracking transfer line tube-type heat exchanger which has a first upstream tube sheet face and a downstream tube sheet face and which contains a plurality of longitudinally extending spaced apart hollow interior heat exchange tubes having an interior surface extending in overall length from said upstream tube sheet face to said downstream tube sheet face and upstream inlet and downstream outlet ends, the longitudinal axes of said tubes extending from said upstream tube sheet face to said downstream tube sheet face, said upstream tube sheet face having an upstream side, said upstream inlet ends of said tubes terminating with said upstream side of said upstream tube sheet face, the improvement comprising said upstream side of said upstream tube sheet face having a coating of at least one refractory. 
     
     
         5 . The apparatus of  claim 4  wherein said refractory coating is from about 0.25 to about 6 inches. 
     
     
         6 . The apparatus of  claim 4  wherein said refractory coating contains at least about 40 wt. % alumina based on the total weight of said refractory. 
     
     
         7 . The apparatus of  claim 4  wherein said refractory coating is supported by at least one ferrule that is carried at the inlet end of at least one of said exchange tubes. 
     
     
         8 . The apparatus of  claim 7  wherein said at least one ferrule carries at least one projection that extends away from said ferrule and into the interior of said refractory coating. 
     
     
         9 . The apparatus of  claim 4  wherein said interior surfaces of said exchange tubes are not coated with refractory.