Abstract
Ash behavior is a key operational aspect of industrial-scale power generation by means of biomass combustion. In this work, FactSageTM 6.4 software was used to develop and assess three models of wheat straw combustion in a vibrating grate-fired commercial boiler of 16 MWth, aiming to describe the inorganic elements release as well as fly ash melting behavior and composition. Simulations were carried out solving four consecutive calculation stages corresponding to the main plant sections. Chemical fractionation was adopted in order to distinguish between reactive, inert and partially reactive biomass fractions. The developed models allow take into account different levels of partial reactivity, values of the temperature for each sub-stage on the grate, and ways to apply entrained streams based on data from the elemental analyses of the fly ashes. To this end, two one-week experimental campaigns were conducted in the plant to carry out the sampling. It has been found that considering chemical fractionation is indispensable to describe the entrainment of solid particles in the gas stream. In addition, the best results are obtained by adopting a small reactivity (2%) of the inert fraction. As for fly ash composition, the concentrations of the major elements showed good agreement with the results from the chemical analyses. In the case of S and Cl, calculations revealed a match with gas cooling effects in the superheaters as well as an entrainment effect. The melting behavior together with the presence of KCl and K2SO4 condensates, point out at possible corrosion phenomena in walls at temperatures of 700–750 °C.
Highlights
Combined heat and power (CHP) generation by biomass combustion constitutes an important share of the energy mix worldwide
Error bars correspond to the standard deviations from the data obtained in the analyses of series of n samples taken in both tests, being n = 5 in Test 1 and n = 3 in Test 2
Three different predictive models were considered to predict fly ash behavior from the experimental data taken in a 16 MWth biomass vibrating-grate firing boiler
Summary
Combined heat and power (CHP) generation by biomass combustion constitutes an important share of the energy mix worldwide. The most extended use of biomass, around 90%, is heat generation through its direct combustion. Forecasts for biomass exploitation in industrial CHP and tri-generation plants highlight the ever-increasing role of bioenergy in the energy system. The deployment of bioenergy in the European Union is expected to double by 2030 [1], whether by the substitution of fossil fuels or through new advanced biomass combustion plants. Different biomass firing technologies are available, with varying installed capacities ranging from a few electric megawatts (MWe ) to high-throughput plants of around 100 MWe or even higher. Grate furnaces and fluidized beds are the prevalent technologies for large-scale
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