Synergistic effects of co-combustion of coal and biomass
Biomass fuel is a promising alternative of fossil fuels.Co-combustion biomass in coal-fired power plants is currently a primary method of utilizing biomass energy.Due to the synergistic effect in the coupled combustion process of coal and biomass,the difference be-tween the combustion characteristics of co-combustion of biomass with coal and those of two alone cannot be determined through the arith-metic average of chemical composition or related properties.The high potassium content in biomass exacerbates the slagging tendency on the heating surface.To investigate the synergistic effects during the co-combustion of coal and biomass,Shenfu bituminous coal and chest-nut shell were selected as experimental samples.These materials were prepared into shaped pellets by mixing,grinding,and pressing for combustion experiments conducted on a Hencken flat-flame burner.The ignition delay time was determined via using high-speed cameras combined with image processing technology.The flame temperature and gaseous K concentration during the combustion process were meas-ured using a spectrometer based on flame emission spectrum theory.Then,the synergistic effects and reasons of ignition,combustion,and gaseous alkali metal release characteristics during co-combustion were investigated.Finally,the slagging index for various conditions was obtained using the results of ash analysis and the correlation between the release of gas-phase alkali metals and the slagging index was es-tablished.The results show that the ignition delay time under the co-combustion condition is lower than the theoretical value,confirming the existence of synergistic effects during ignition,which is characterized by the promotion of the ignition through the influence of cellulose pyrolysis and alkali metal catalysis.The difference between ignition delay time and theoretical value reaches the maximum value of 1.91 s under 50％biomass mass fraction,indicating the maximum synergistic effect.The release of gaseous alkali metals during co-combustion is lower than the theoretical value,indicating that the synergistic effect in gaseous alkali metal release during co-combustion acts as an in-hibitory factor.This inhibition effect is attributed to the volatile-coke interaction and the inorganic reactions in which the reactions of Si,Al with K dominates the synergistic effect.As the release of gaseous K increases,the values of base-acid ratio and silica ratio increase,the tendency of slagging also increases.The correlation coefficients between the slagging indices and the release of gaseous K are both more than 95％,indicating that the release amount of gaseous K is highly correlated with the slagging index.It can be seen that the release of gaseous K obtained by online monitoring has the potential to predict the slagging tendency.
co-combustion of coal and biomassignition characteristicK releaseslagging characteristicsynergistic effect
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