Integration And Modeling Of Biomass Gasification System And Coal-fired Circulating Fluidized Bed Boiler System

Shortage of fossil fuels and environmental problems concerning emission limitaions from use of fossil fuels have been paid much more attentions. The power generation of renewable energy instead of fuels becomes a hot issue in energy related field, and biogas and coal co-firing is an effective approach for biomass and fossil fuel complementary supply.In this paper, Aspen Plus software is used for modeling biomass gasification system and 300MW circulating fluidized bed boiler system, respectively. Biogas is used to replace some coal burning in the fluidized bed boiler, then integrated system of biogas reburning in circulating fluidized bed is established. The boiler operating conditions are simulated with three types of coal and four different operating modes in the article. Error and accuracy between the design values and calculated values about the import and export of the working fluid and flue gas temperature of heating surfaces, gas volume and boiler efficiency, are obtained.The results show that all the errors are small, and the maximum value is less than 9%, which confirms that the selected models and method are reasonable and can reflect the actual working process of the boiler suitably. Air gasification of rice husk is discussed in this study. Air ratio, agent preheated temperature and heat loss rate of unreacted carbon are found to influence the composition, heating value of the product gas and gasification efficiency. The optimized biogas with the temperature 597.988℃, heating value 5401.32kJ/Nm3 and gasification efficiency 72.25%is sent into the boiler, Moreover, by changing the reburning rate of the biogas energy in the input energy at the rated load, the research concludes this impact on the overall performance of boiler combustion system.The results reveal that with increase of the reburning rate, theoretical air volume decreases, fuel gas volume increases, combustion temperature and exhaust gas temperature improves, boiler effciency declines. Adding some heated surfaces at backpass can be used to improve boiler effciency.