Waste heat recovery

A process for producing carbon black by pyrolysis of a feed hydrocarbon wherein a gas stream containing carbon black is passed through a means defining a flow path of an indirect heat exchanger, said process comprising preventing the substantial build up of carbon black deposits or cleaning carbon black deposits or both from said means defining a flow path by

• (a) providing a fixed bed of fluidizable particulate solids within said indirect heat exchanger,
• (b) positioning a shell-tube heat exchange section having a plurality of tubes within said bed of solids in such a manner that said bed of solids extends from below the inlet, through, and above the outlet of the tubes with the heat exchange fluid passing through the shell side and with said gas stream containing carbon black passing through the tubes which contain said particulate solids whereby heat is transferred from the gas stream containing the carbon black to the fluidized particulate solids and by way of the tubes to the shell fluid, said tubes being so sized as to have a length to diameter ratio sufficient to allow both upwardly and downwardly movement of said particulate solids within said tubes,
• (c) passing said gas containing carbon black through said bed of solids under conditions which cool said gas and fluidize said bed to maintain the inner peripheries of the tubes substantially freed from carbon black deposits to allow efficient heat exchange, and (d) withdrawing said cooled gas through a gas-solids separator positioned above said bed of solids within the cooling zone to prevent particulate solids from escaping with the cooled gas by recovering same and returning recovered entrained particulate solids to said fixed bed.