Method of combusting oil shale in a circulating fluidized bed boiler

A method of combusting oil shale in a circulating fluidized bed boiler, the method comprising the steps of:

• (a) introducing fuel, comprising oil shale, into a furnace of the circulating fluidized bed boiler;
• (b) introducing primary oxygenous gas through a bottom grid of the furnace;
• and
• (c) introducing secondary oxygenous gas to the furnace at a first level above the level of the bottom grid,
• wherein (i) the primary oxygenous gas is introduced to the furnace at a rate providing below the first level a fluidizing velocity of less than 2.5 m/s, (ii) the primary and secondary oxygenous gases are introduced to the furnace in such a way that a circulating fluidized bed is formed, (iii) the fluidizing velocity at the first level is less than 70% of the fluidizing velocity in the upper portion of the furnace, and (iv) the proportion of the primary oxygenous gas is less than 40% of total oxygenous gas introduced to the furnace.