Effect Of Alkali Metals On Release Characteristics Of PM₁₀ During Co-combustion Of Biomass And Coal

As one of effective ways to utilize biomass, co-combustion of coal and biomass fuels has been popular in recent years for its potential benefits for both environment, such as CO2 emission reduction, and economics of power generation. However, co-combustion could release fine particle matters which do great harm to environment and people's health. Alkali metals in biomass play an important role in PM₁₀ release during co-combustion, especially sub-micron particles. Thus, the study of alkali metals'effect on PM₁₀ release characteristics of co-combustion plays a very important significance to control the release of PM₁₀. Firstly, in this paper the biomass samples were washed by water and acid separately.Most of alkali metals in samples were removed. Then the combustion of biomass samples was studied experimentally by vertical thermal balance furnace and simulated by chemical and thermodynamic modeling. The results indicate that the release rate of alkali metals increases with temperature increasing during combustion process. And the alkali metals'release rate of untreated biomass is higher than that of water-washed and acid-washed samples. The factors are temperature, existed form of alkali metals and other elements. The simulated result which explains the alkalis'release characteristics well is similar to the experimental result.Then the biomass and coal were co-combusted in drop tube furnace to study the PM₁₀ release characteristics. The results indicate that the mass particle sizes of PM₁₀ present bi-modal distribution. The change of alkali metals'content and existed forms in samples affect the mass particle size distribution greatly, decrease the PM₁₀ release concentration and the mass concentration of K and Na in each rank of PM₁₀. In addition, the change trend of the mass concentration of K and Na with temperature is similar to the mass particles size distribution of PM₁₀. In a word, the release characteristics of PM₁₀ during co-firing of biomass and coal are related to the alkali metals'release characteristics closely.