Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Pulverised coal firing is physically a very complicated process. The behaviour of a certain coal from a certain mine depends on a number of parameters for example temperature, composition of the coal, porosity of coal particle and oxygen content. It turns out that two coals with quite similar compositions fired at the same conditions still may behave completely different. Thus, the burning of the coal particle cannot be predicted unless experiments with the coal in controlled conditions are carried out. The speeds at which it burns and the rate at which volatile content of the particles are released are crucial properties for the prediction of the behaviour of the coal. These properties were determined by the experiments. The prediction of the burning is done with models, and the experiments are used to predict a number of parameters in these models. The experiments were carried out in an Isothermal Plug Flow Reactor (IPFR). This reactor ensures completely isothermal conditions in terms of temperature and oxygen content. It also allows the coal to be inside the reactor for a controlled time, called the residence time, which can be varied. While the coal particles are inside the reactor, they will lose weight because of the combustion process. Since the residence time can be varied, it is possible to plot the weight-loss against time. The parameters were then determined by fitting each model to the experimental results. A number of models were chosen, most of which are represented in the most common CFD-programs. An Excel sheet was created for each model where the weight-loss was calculated in time steps for a number of particle size classes with the equation of the model. Adding the classes together gave the total weight-loss for a certain time step. This was then compared with the experimental results. Two coal-based fuels were to be characterised, a coal and a petroleum coke, but it turned out that the petroleum coke had too low ash content for the analysis procedure. The accuracy of the procedure was too low. So the experiments with the coke were terminated. What could be said about the coke anyway is that it probably needs another fuel to aid ignition of the particles. The coal was completely characterised and the parameters were determined. This coals burns rather slowly and there may be some problems with the stability of the flame especially at lower temperatures since the volatile content of the particles are released rather slowly.
Place, publisher, year, edition, pages
IdentifiersURN: urn:nbn:se:ltu:diva-51045ISRN: LTU-EX--02/182--SELocal ID: 8459bf69-e5d9-46e8-b52d-df60cae4d3a1OAI: oai:DiVA.org:ltu-51045DiVA: diva2:1024408
Subject / course
Student thesis, at least 30 credits
Mechanical Engineering, master's level
Validerat; 20101217 (root)2016-10-042016-10-04Bibliographically approved