Effect of Various Biowastes on Emissions in Combustion of Lignite Coal in a Circulating Fluidized Bed Combustor


Atimtay A., VAROL M., Olgun H., Kayahan U., Ünlü A., Atakül H.

6th International Conference on Environmental Science and Technology, Houston, United States Of America, 25 - 29 June 2012, pp.478

  • Publication Type: Conference Paper / Full Text
  • City: Houston
  • Country: United States Of America
  • Page Numbers: pp.478
  • Akdeniz University Affiliated: No

Abstract

In this study, combustion of biomass and coal was carried out in a circulating fluidized bed combustor. A lignite coal which has high sulfur content and three biomasses were used in the experiments. The biomasses were hazelnut shells; woodchips and olive cake which is a waste of olive oil industry. Olive cake is a quite common biomass in Mediterranean countries. The experimental setup consists of a circulating fluidized bed combustor column, a fuel feeding system, electrical heaters, and two cyclones. Its thermal capacity is 30 kW. The combustor column has an inside diameter of 108 mm and a height of 6 m. The temperatures along the column are observed with thermocouples located at specific heights. The temperature of the column is kept at 850 oC during the combustion experiments. The pressure drops along the combustor column, cyclone, downcomer, and loopseal are continuously measured and observed in order to determine the solid mass flux within the combustor. A series of combustion tests for each fuel was performed in order to investigate the effect of excess air ratio and secondary air ratio on the flue gas emissions and combustion efficiency. Optimum Ca/S ratio was determined for each combustion tests in order to minimize SO2 emissions. During the combustion experiments, CO2, CO, O2, NO, and SO2, emissions in the flue gas was continuously measured and recorded by Gasmet DX-4000 flue gas analyzer.

The results of the experiments showed that as the biomass ratio in the fuel mixture increases for co-combustion, the combustion takes place more in the freeboard of the main column. Therefore, the maximum temperatures are seen in the freeboard rather than in the bed. Also the CO and CmHn emissions increase as the biomass percentage increases in the fuel. Biomass fuels have high CO emission which indicates that a secondary air addition is required for the system. As the biomass content in the fuel mixture increases, a decrease in the overall combustion efficiency is observed. Secondary air injection into the freeboard has been a useful solution to decrease the CO and hydrocarbon emissions and to increase the combustion efficiency. Addition of secondary air during the combustion of biomass-coal mixtures is found to increase the NOx emissions slightly. These results suggest that during the design of the CFBC, one has to be careful about the VM content of the biomass. Agglomeration properties were also investigated. High sulfur content of lignite coal seemed to help to solve the agglomeration problem. The results are promising.