The present invention is directed to a hydrocarbon conversion apparatus. The apparatus comprises the following: a plurality of riser reactors, each of the riser reactors having a first end into which a catalyst can be fed and a second end through which the catalyst can exit the riser reactor; a separation zone provided to separate the catalyst from products of a reaction conducted in the hydrocarbon conversion apparatus; at least one transport conduit having a first end in fluid communication with at least two of the second ends of the riser reactors and a second end extending into the separation zone; and at least one catalyst return in fluid communication with the separation zone and the first ends of the riser reactors, the catalyst return being provided to transfer the catalyst from the separation zone to the first ends of the riser reactors.