Eksperimentalno podprt numerični model za simulacijo zgorevanja lesnih pelet v mali kurilni napravi : doktorska disertacija

slovenian

doktorska dela

2022

combustion   combustion temperature   computational fluid dynamics (CFD)   emission measurements   empirical fuel bed model   experimental work   fixed grate   measurements of process parameters   small-scale boiler   wood pellets

Univerza v Mariboru, Fakulteta za strojništvo

The commercial wood pellet boiler was structurally modified so that it was possible to perform measurements of various parameters during operation. Several vital process parameters were determined: (1) basic boiler operating parameters such as cooling water temperature, cooling water flow, flue gas temperature and fuel supply, (2) emissions, i.e.. concentrations of several pollutants in the flue gases, (3) combustion temperatures and flue gases in the combustion chamber, and (4) airflows entering the combustion chamber. The results of the experimental work served to establish and validate a numerical combustion simulation. In this work, the combustion modelling is performed by introducing a two-way exchange between the fuel ned conversion model and the gas phase combustion simulation. Solid fuel conversion is modelled with an empirical 1D fuel layer model, which depends on the measured operating parameters, fuel properties and empirical description of the solid fuel conversion process. Two cases were investigated numerically. Example A is a representative of a “weak” staged air supply strategy, and example B is a “strong” strategy. The results showed that the temperatures predicted by the CFD followed the same trend as the measured values, although on average they were too high. The CFD forecasts of CO emissions showed the same trend as the measurements, but in the transition from a weak to a strong combustion strategy, a reduction of 69 % was predicted compared to the measured CO reduction. The CFD forecasts of NO emissions showed the same trend as the measurements, but in the transition from a weak to a strong staged combustion strategy, a 10 % higher reduction was predicted compared to the measured NO reduction. Despite the excessive temperature forecast, taking into account the engineering modelling approach with many simplifications and unknowns, the accuracy of emission forecasts can be considered sufficient for engineering purposes. The presented modelling approach could thus be used to evaluate new process parameters, geometric designs and configurations of secondary air supply nozzles.

08.08.2023