One of the methods of obtaining energy from renewable sources is the technology of indirect cofiring of biomass. It consists in the gasification of secondary fuel and combustion of the generated gas in the boiler together with its primary fuel. The paper presents a thermodynamic analysis of the use of the boiler flue gases as the converting medium in the process of indirect co-firing - a technology which is being developed at the Institute of Power Engineering and Turbomachinery of the Silesian University of Technology. The basis of the analysis are the data resulting from variant calculations conducted with the use of the Gaseq program. The calculations were made for various compositions of gasified fuel and the converting medium, variable fuel/oxidiser ratios and variable gasification temperatures. As a result, the equilibrium composition and the calorific value of the generated gas were obtained. The main optimisation objective adopted here was the nondimensional efficiency coefficient, which is the ratio of the chemical energy of products to the chemical energy of the process reactants.
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%.
Widely used CFD codes enable modelling of PC boilers operation. One of the areas where these numerical simulations are especially promising is predicting deposition on heat transfer surfaces, mostly superheaters. The basic goal of all simulations is to determine trajectories of ash particles in the vicinity of superheater tubes. It results in finding where on the surface the tube will be hit by particles, and what diameter and mass flow of the particles are. This paper presents results of CFD simulations for a single tube and a bundle of in-line tubes as well. It has been shown that available parameters like ash particle density, shape factor, reflection coefficients affect the trajectories in a different way. All the simulations were carried out with Fluent code of Ansys software.