Investigation Of Co-combustion Characteristics Of Non-inert Torrefied Rice Husk And Coal

The over-dependence of coal has caused severe global problems including energy security,environmental pollution and climate change.Co-combustion of coal with biomass waste is a promising way to mitigate these problems,due to the wide availability,renewability and carbon neutrality of biomass energy resources.And non-inert torrefaction of biomass can be used primarily to improve fuel properties of biomass with lower cost in contrast to traditional inert torrefaction,which can help to increase overall efficiency of the co-combustion system.But the fuel properties and co-combustion characteristics of non-inert torrefied biomass still need to be closely explored.As a kind of widely distributed agricultural biomass waste in China,rice husk was used in this work,as well as a bituminous coal and an anthracite coal.The torrefaction experiment was conducted on a fixed-bed reactor,and the influences of temperature and atmosphere on fuel properties of torrefied rice husk were studied.A non-isothermal thermogravimetric method was adopted to investigate the co-combustion characteristics of various coal/torrefied biomass blends at a heating rate of 20℃/min from 25℃to 1000℃.The experimental results of torrefaction show that the influence of oxidative atmosphere is distinctive only in high temperatures.The CO₂-torrefied rice husk is more similar to N₂-torrefied rich husk in mass/energy yields and fundamental combustion characteristics;the Flue-gas-torrefied rice husk is of slightly lower mass/energy yields,which are still above 75%;while the Air-torrefied rice husk is of the lowest mass/energy yields and highest ignition/burnout point.So the CO₂-torrefied and Flue-gas-torrefied rice husk under 260℃were chosen for co-combustion with coal.And the results show that during the co-combustion with bituminous coal,the beneficial effect of raw rice husk mainly appears in the beginning releasing stage of volatiles,while torrefied rice husk has advantageous influence in the later combustion stage of char.The DTG curves of oxy-fuel combustion were more stable than that of air combustion for all blends,but the addition of raw rice husk improved the overall reactivity of coal in a larger scale.When blended with anthracite coal,there is no significant difference observed between the co-combustion characteristics of raw and non-inert torrefied rice husks;and they all greatly improve the ignition properties and combustion reactivity of anthracite coal.To conclude,the non-inert torrefaction of rice husk for co-combustion utilization is feasible,especially for high substitution ratios in existing co-firing system.But the co-combustion performance varies with combustion atmosphere and the type of coal used.