Effect Of Cellulose And Lignin On Co-combustion Characteristics And Emission Behavior Of Particles For Biomass And Coal

Biomass is a renewable and environmentally-friendly energy source. Its utilization is an effective way to alleviate the problems such as energy shortage and environmental pollution. Co-combustion of coal and biomass fuels has been popular in recent years because of its potential benefits for both the environment, such as to reduce CO2 emission, and the economics of power generation. However, there are still some problems with cofiring biomass with coal. For example, the effects of the components (cellulose and lignin) of biomass on combustion behavior of biomass and blends, and on particulate matter (PM) emissions during co-combustion are not very clear at present. They are discussed in some detail in this thesis.First, fundamental pyrolysis and combustion studies for sawdust and straw are conducted using a thermo-gravimetric (TG) analyzer in this thesis. Some mixtures of pure cellulose and lignin with different ratios, representing real biomass fuels, are also tested by the TG analyzer.Experimental results show that the lignin content is a good indicator for the pyrolysis characteristics of the simulated biomass, and can be used to predict its pyrolysis behavior. The combustion process of the actual biomass can be classified into two stages. The first stage shows a rapid decrease in mass due to cellulose decomposition. While the decrease in mass in the second stage is attributed to lignin decomposition and char burnout. Char morphologies are shown to affect combustion characteristics. By combustion of mixtures of coal and simulated biomass in the TG analyzer, cellulose is shown to enhance the co-combustion characteristics greatly.Second, to study PM emissions from co-combustion, both the real biomass and the simulated biomass are mixed with one coal with a mass ratio of 1:1, and are burnt in the Drop Tube Furnace. The results indicate that the distribution of the inhalable particulates (PM10) during co-combustion is similar to that from coal combustion. With the increase of lignin content, the concentrations of sub-micron particles (PM1.0) and super-micron particles (PM1.0+) increase.