Co-firing of pine chips with Turkish lignites in 750kWth circulating fluidized bed combustion system.

•Two Turkish lignites which have different sulfur levels (2–2.9% dry) and ash levels (17–25% dry) are combusted in a CFBC.•Forest red pine chips in a 750kW-thermal capacity CFBC system was co-combusted with lignites.•Limestone was added, Ca/S=3, to lignites to reduce SO2 emissions.•CO emissions are high at low excess air ratios, gets lower as the excess air ratio increases.•During co-firing experiments the temperature in the freeboard is 100–150°C higher as compared to coal combustion.