Method of and apparatus for carrying out an exothermic process

A method of operating a plant for the combustion of a carbonaceous or sulfur-containing material, said plant comprising an upright fluidized-bed reactor, a fluidizing gas inlet at the bottom of said reactor, a secondary gas inlet opening into said reactor above the bottom thereof, an outlet at the top of said reactor for withdrawing exhaust gas and entrain solids therefrom, a gas-solids separator connected to said outlet for separating said exhaust gas from the solids entrained therewith, a recycling conduit connecting said separator with the interior of said reactor for recirculating separated solids thereto, and a fluidized-bed cooler, said method comprising the steps of:

• (a) feeding an oxygen-containing gas into said reactor on different levels in two partial streams whereby at least one of said streams is constituted as secondary gas and is introduced at least at one location above the level of introduction of fluidizing gas into the reactor;
• (b) maintaining the volume ratio of fluidizing the gas to secondary gas between 1:20 and 2:1;
• (c) adjusting the gas velocity and ratio of the fluidizing gas rate to the secondary gas rate to provide a continuous expanded-bed density gradient of the solids in the reactor from the bottom thereof to said outlet, the density above the secondary gas inlet being 10 to 40 kg/m.sup.3 ;
• (d) introducing combustibles into said reactor below said secondary gas inlet and into a space in said reactor substantially free from internal fixtures;
• (e) withdrawing solids from the circulating system consisting of said reactor, said separator and said conduit and cooling the withdrawn solids in said fluidized-bed cooler by direct and indirect heat exchange;
• (f) maintaining the temperature within said reactor substantially constant by feeding a controlled portion of the cooled solids from said fluidized-bed cooler thereto;
• and
• (g) heating at least a portion of said secondary gas by using said portion of said secondary gas as the fluidizing gas in said cooler and thereafter introducing the fluidizing gas from said cooler into said reactor through said secondary gas inlet.

A plant for the combustion of a combustible material which comprises:

• (a) an upright fluidized-bed reactor comprising:
• a fluidizing gas inlet at the bottom of said reactor, a secondary gas inlet opening into said reactor at a distance of at least one meter above said bottom of said reactor, the space within said reactor between said bottom and said secondary gas inlet being free from internal fixtures, and
• an outlet at the top of said reactor for exhaust gas entraining solids therewith;
• (b) a cyclone connected to said outlet for separating solids from said exhaust gas;
• (c) a recycling conduit connecting said cyclone with the interior of said reactor for returning said solids to said reactor;
• (d) means for withdrawing hot solids from the circulating system consisting of said reactor, said separator and said recycling conduit;
• (e) a fluidized-bed cooler receiving withdrawn solids from the last-mentioned means, said fluidized-bed cooler comprising:
• a plurality of compartments traversed by the solids to be cooled in succession,
• means for fluidizing the solids in each of said compartments,
• respective cooling registers in contact with the solids in each of said compartments,
• means for passing a coolant through said registers in succession and in a direction opposing the direction of movement of solids from compartment to compartment in said fluidized-bed cooler, and
• means for feeding fluidizing gas, heated in said cooler, to said secondary gas inlet;
• and
• (f) control means for feeding a proportion of cooled solids from said cooler to said reactor to maintain the temperature therein substantially constant.