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[Display omitted] • The co-firing of coal and municipal sludge with high moisture content was studied. • The more sludge co-fired, the less NO x emission. • There are higher flue gas temperature and NO x emission at lower moisture content. • Co-firing sludge from the medium-upper burner can reduce the layers of burner. • The shrunk-middle type is the optimum scheme of SA distribution. Using the current coal-fired power plant to treat sludge with large annual production is an efficient sludge treatment method. Nevertheless, the majority of the previous studies concentrated on sludge co-firing with low blending ratio and moisture content in utility boiler. Further analysis and discussion are necessary regarding the impact of sludge with high blending ratio and high moisture content on co-firing performance as well as the potential interactions between high moisture content sludge and coal during the co-firing process. The simulation results of the verified computational fluid dynamic (CFD) model can be regarded as numerical experiments. In the present research, CFD was used to analyze the co-firing characteristics of municipal sludge and coal in a 600 MW tangentially fired utility boiler. The impacts of sludge moisture content, blending ratio, blending strategy, and secondary air (SA) distribution on co-combustion characteristics and NO x emissions were investigated, and their potential synergistic effects were assessed. The co-firing of coal and sludge has little impact on the furnace outlet temperature while potentially lowering NO x emissions, provided that the net calorific value of the feeding of the mixture of sludge and coal is kept constant. The reduction of sludge moisture content can significantly improve co-combustion performance, but it also facilitates NO x production. Blending sludge from the position of the medium-upper burners can reduce the number of layers needed to burn the sludge in practical coal-fired boiler. Furthermore, the SA distribution has a major impact on the furnace outlet flue gas temperature and NO x content. The shrunk-middle type is the optimum scheme for SA distribution. This study contributes to a deeper knowledge of the actual co-firing of sludge and coal in the utility boiler and provides a possible theoretical foundation for the widespread, clean, and effective use of sludge. [ABSTRACT FROM AUTHOR]

The study on CO2 gasification behavior helps to promote the clean and efficient utilization of high-alkali fuels. The high-alkali fuels feature high contents of alkali metals, and sometimes they are also rich in alkali earth metals and iron. Though the influences of minerals on gasification characteristics have been extensively studied, few researchers have selected minerals based on the ash composition of high-alkali fuel. Moreover, the complex interactions among minerals could lead to inaccurate conclusions. In this paper, the CO2 gasification behavior of chars originated from one high-alkali biomass and three high-alkali coals was studied. The effects of principal minerals related to the high-alkali fuels, which were determined through the new plasma ashing method and traditional muffle ashing method, were also further evaluated via synthetic coal char. The synthetic coal char was free from any intrinsic minerals. The results indicate that the gasification reactivities of chars from high-alkali fuels are positively associated with the reaction temperature (900–1200 °C). The biomass char possesses the highest gasification reactivity, and three coal char samples are inferior to various degrees. The related chemicals offer their catalytic activities at 1000 °C in the sequence of K/Na-containing chemicals > Fe-containing chemicals > Ca-containing chemicals. The shrinking core model (SCM) and two-dimensional growth of nuclei model (2DGM) were chosen to conduct the kinetic analysis. The reaction constants of chars from different high-alkali fuels agree with their gasification behavior. Generally, the 2DGM is more suitable than SCM to predict the conversion of selected char samples. In most cases, the additions of chemicals increase the reaction constants. When Fe2O3 and CaCO3 are added into synthetic coal char, the SCM is more accurate to describe the gasification behavior at 900 °C, but the addition of Na2SO4 makes the 2DGM a better one. [ABSTRACT FROM AUTHOR]