Sylwester Kalisz

Fouling and Its Mitigation in PC Boilers Co-Firing Forestry and Agricultural Biomass

This paper presents a study of the fouling properties of solid fuels based on analyses of ashes from hard coal, forestry biomass, and agricultural biomass, ash deposits collected directly from the boiler surfaces, and ash deposits collected from a deposition probe. All samples were collected in the area of the steam superheater/reheater of a OP 380 pulverized-coal boiler co-firing forestry and agricultural biomass. In addition, the study concerns mitigation of unwanted fouling through application of a silica-based fireside additive. An analysis was carried out to obtain the following information: physical and chemical properties of ash produced during co-firing of a biomass mixture (50 wt.% forestry/50 wt.% agricultural biomass) and coal in order to determine its propensity for fouling and slagging without the use of a fireside additive; slagging/fouling indices during co-firing of a biomass mixture (50 wt.% forestry/50 wt.% agricultural biomass) and coal with the use of a fireside additive; and slagging/fouling indices during co-firing of pure agricultural biomass (sunflower husk) and coal with the use of a fireside additive. The mass flow of co-fired biomass fuel supplied to the boiler during reference measurements and mass flow when the additive was fed were the same and amounted to 33 wt.% of the total fuel mass flow. Finally, the effectiveness of fouling mitigation is determined by comparing the results of the deposition rate obtained with the use of a deposition probe for all three cases of co-firing.

Review of Ash Deposition Coefficients for Selected Biomasses

Ambitious EU environmental policy decreasing CO2 emissions from combustion of fossil fuels impact on whole EU economy. Utilization of biomass as carbon neutral fuel helps to address these challenges Combustion and co-combustion of biomass, especially agriculture residue biomass, is associated with many technical problems such us: bed agglomeration, slagging and fouling, chlorine corrosion, decreased boiler efficiency which do not occur in conventional fossil fuels combustion. In this study six fuels were investigated on their deposition ability (2 types of straw, Miscanthus and herbaceous pellets, RDF—Refuse-Derived Fuel and reference coal). Biomasses were selected as the most commonly used in Polish and German power industry. Analysis comprised chlorine and sulphur contents of the fuel, ash oxides analysis and ash fusion temperatures. The main objectives of this work were to predict ash deposition tendency of chosen fuels using ash deposition indices and compare it with reference fuel. Next weaknesses of selected indicators are pointed out.

Numerical modelling of a stoker furnace operated under indirect co-firing of biomass

The subject of the CFD analysis presented in this paper is the process of biomass indirect co-firing carried out in a system composed of a stoker-fired furnace coupled with a gasification reactor. The installation is characterised by its compact structure, which makes it possible to minimise heat losses to the environment and enhance the physical enthalpy of the oxidising agent – flue gases – having a favourable chemical composition with oxygen and water vapour. The test results provided tools for modelling of biomass thermal processing using a non-standard oxidiser in the form of flue gases. The obtained models were used to optimise the indirect co-combustion process to reduce emissions. An overall effect of co-combustion of gas from biomass gasification in the stoker furnace is the substantial reduction in NO emissions by about 22%.