Method of reducing sulfur dioxide content in flue gas emanating from a circulating fluidized bed boiler plant

A method of reducing sulfur dioxide emissions of a circulating fluidized bed boiler plant, the method comprising the steps of:

• feeding a first stream of sulfur-containing carbonaceous fuel at a first feeding rate to a furnace of the boiler;
• feeding a second stream of calcium carbonate containing absorbent having a predetermined d50 particle size at a second feeding rate to the furnace;
• feeding oxygen containing gas to the furnace for fluidizing a bed of particles forming in the furnace;
• combusting the fuel with the oxygen, whereby the sulfur in the fuel is oxidized to sulfur dioxide;
• calcining the calcium carbonate to calcium oxide in the furnace and utilizing a portion of the calcium oxide to sulfate a first portion of the sulfur dioxide to calcium sulfate in the furnace;
• discharging flue gases, containing a second portion of the sulfur dioxide, and particles, including calcium oxide particles, entrained with the flue gases along a flue gas channel from the furnace;
• separating a first portion of the entrained particles, including a first portion of the entrained calcium oxide particles, from the flue gases in a particle separator having a cut-off size, and returning at least a portion of the separated particles via a return duct to the furnace;
• conveying a second portion of the entrained particles, including a second portion of the entrained calcium oxide particles, with the flue gases from the furnace to a semi-dry sulfur-reduction stage arranged downstream of the furnace;
• and
• reducing the sulfur dioxide content of the flue gases in the semi-dry sulfur-reduction stage,
• wherein the predetermined d50 particle size of the calcium carbonate containing absorbent is from 10 μm to 20 μm, and smaller than 50% of the cut-off size of the particle separator.