Coal char passivation process and apparatus

Abstract

A continuous process and apparatus for treating dried coal and coal char to promote passivation of the reactive carbon particles by forming a protective oxide coating and simultaneously adding moisture to rehydrate said particles. The passivation process is conducted in a novel apparatus providing for the staged control of the reaction temperature and the staged introduction of both oxygen and moisture. The fluidized bed apparatus has internal in-bed cooling means embedded within the fluidized coal or coal char particles so as to remove the heat energy as it is released by virtue of the exothermic passivation reactions.

What is claimed is: 
     
         1 . A fluidized passivation apparatus for passivating coal char, comprising
 a reaction chamber defining an interior and having a char inlet for receiving coal char into the interior and a char sump for allowing coal char to exit the interior;   the reaction chamber further including at least one gas inlet for admitting an oxygen-containing fluidizing gas into the interior, at least one gas outlet for allowing exit of the fluidizing gas from the interior, and a gas recirculation system comprising a source of fluidizing gas, one or more conduits and a pump, the conduits and pump arranged and adapted to recirculate the fluidizing gas from the gas outlet to the gas inlet under conditions to cause a fluidized state in the coal char within the interior of the reaction chamber;   at least one heat exchanger embedded within the interior of the reaction chamber, the heat exchanger having a coolant fluid inlet, a coolant fluid outlet and a plurality of contact surfaces for exchanging heat with coal char within the interior; and   a humidifier connected to a source of water and adapted for humidifying the coal char.   
     
     
         2 . The apparatus of  claim 1  wherein there are a plurality of heat exchangers and a plurality of gas inlets. 
     
     
         3 . The apparatus of  claim 1 , further comprising a cyclone in the gas recirculation system for removing entrained particulates from the gas stream and returning the particulates to the char. 
     
     
         4 . The apparatus of  claim 1  wherein the humidifier is configured to humidify the coal char by one or more of: (a) droplet spray onto char located in the interior of the reaction chamber; (b) droplet spray onto char at a location prior to its entry into the reaction chamber; (c) droplet spray into the interior of the fluidizing reaction chamber; and (d) droplet spray into the gas recirculation system so that the fluidizing gas is humidified. 
     
     
         5 . The apparatus of  claim 4  wherein the humidifier comprises a spray nozzle adapted to spray water into the interior of the reaction chamber. 
     
     
         6 . The apparatus of  claim 4  wherein the humidifier comprises a spray nozzle adapted to spray water into gas recirculation system. 
     
     
         7 . The apparatus of  claim 5  or  claim 6  wherein the humidifier further comprises a source of compressed gas for atomizing the sprayed water. 
     
     
         8 . The apparatus of  claim 1 , further comprising a source of oxygen for providing or supplementing the oxygen-containing fluidizing gas to passivate the coal char. 
     
     
         9 . A method for passivating coal char using a fluidized passivation bed according to  claim 1 . 
     
     
         10 . A method for passivating coal char using a fluidized bed reactor with an internal heat exchanger.