Investigation of combustion characteristics of biomass and coal mixtures in a circulating fluidized bed combustor

Thesis Type: Doctorate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Graduate School of Natural and Applied Sciences, Graduate School of Natural and Applied Sciences, Turkey

Approval Date: 2013




In this study, combustion and co-combustion tests of Bursa/Orhaneli lignite with two biomass fuels (olive cake and woodchips) were carried out in a laboratory scale Circulating Fluidized Bed (CFB) combustor, 6 m high and 108 mm inside diameter, in order to investigate the effect of excess air ratio (l), secondary air ratio (SAR) and location of secondary air injection along the combustor wall on the emissions. Optimum l and SAR was determined for each test. The flue gas emissions were compared with limits in the EU and Turkish Regulation. A series of co-combustion tests of olive cake (50% by wt.) with Bursa/Orhaneli lignite (Stotal < 2.7%) and with Denizli/Kale lignite (Stotal > 3.6%) were also done to investigate the effect of sulfur content of fuel and coal+biomass interaction on the ash composition. Olive cake was chosen to represent high alkali content biomass (50% K2O in ash). Samples taken from the bottom ash, fly ashes from cyclones and bag filter were subjected to XRF and XRD analyses. A Deposit Sampling Probe was used to simulate a heat exchanger surfaces in a boiler. The deposit accumulated on the probe and bottom ash samples were subjected to XRD and SEM-EDS analysis. The results showed that increasing share of biomass in the fuel mixture shifted combustion characteristics from char combustion to volatile combustion. Addition of biomass increased CO emission, reduced char formation and NO emission. It was proved that sulfur in coal helped to prevent agglomeration, slagging and fouling in the combustor. Optimum excess air ratio increased with addition of biomass to fuel mixture.