Particle withdrawal from fluidized bed systems

In a system wherein coal particles are fed into a vertically disposed vessel housing a fluidized bed formed from injection of said coal particles and a first fluidizing gas, to form a combustible product gas and agglomerated ash, said agglomerated ash tending to congregate at a lower portion of said vessel, improved apparatus for removing said agglomerated ash from said vessel, comprising:

• a. means for injecting a supplemental fluidizing gas into said vessel at a preselected elevation and at a temperature at least 500.degree. F. less than the average operating temperature of said fluidized bed so as to form a substantially discrete temperature interface region above said preselected elevation between said agglomerated ash and said fluidized bed, said interface region separating the mediums in said vessel into solids above said interface at a hot temperature and agglomerated ash below said interface at a cooler temperature;
• b. temperature sensitive means fixedly disposed at a selected elevation of said vessel for indicating said hot temperature and said cooler temperature;
• and
• c. means responsive to said temperature sensitive means indicating said cooler temperature for selectively removing some of said agglomerated ash from said vessel.

In a process wherein coal particles are fed into a vertically disposed vessel housing a fluidized bed formed from injection of said coal particles and a first fluidizing gas, to form a combustible product gas and agglomerated ash, said agglomerated ash tending to congregate at a lower portion of said vessel, an improved method for removing said agglomerated ash from said vessel, comprising:

• a. injecting a supplemental fluidizing gas into said vessel at a preselected elevation and at a temperature less than the average operating temperature of said fluidized bed so as to form a substantially discrete temperature interface region above said preselected elevation between said agglomerated ash and said fluidized bed;
• b. thermally monitoring the elevational position of said interface region;
• and
• c. selectively removing some of said agglomerated ash from said vessel in response to said thermal monitoring.