Influence of Inert Gases on Characteristic Parameters of Combustion Process

The dissertation thesis is focused on the investigation of the influence of inert gases on characteristic parameters of the combustion process. Inert gases are usually standard components of alternative gaseous fuels such as the producer gas, coal gas or biogas. For a long period some of the fuels were considered as waste gases and their potential was not sufficiently utilised. Compared with noble fuels such as natural gas, alternative fuels have different physical-chemical properties. For example, their lower heating value (LHV) can be lower even than 10 MJ/mN3. The composition of the alternative gaseous fuels can be various during their production process. Lower LHV is a result of the occurrence of inert gases that does not take a part in the combustion reactions. Inert gases have the ability to accumulate the heat. Under certain conditions it is possible to combust alternative fuels on conventional burners, but due to their different properties, problems can occur during the combustion. E.g. to achieve the same heat output as with the noble fuel, it is necessary to burn bigger volume of the alternative fuel. However, the limiting factor could be the burner's head geometry. Theoretical introduction of the thesis summarizes research results in the field of low calorific gaseous fuels combustion and the addition of inert gases into the noble fuels. The thesis also describes the mechanisms of the NOx formation and summarizes techniques which can be used to reduce NOx formation. Furthermore, fuels from alternative sources are categorized and described, including their composition and characteristics. Their physical-chemical properties were obtained by means of the combustion simulation carried out in the simulation software. Two devices had to be designed and manufactured to fulfil goals of the dissertation thesis. The first is a gas mixing station capable of mixing 4 different components. The second device is a burner utilized for the combustion of low calorific fuels. The key section of this thesis is a chapter describing the experimental plan, the performance and the evaluation of the experiments. The goal of the experiments was to dilute the natural gas by two inert gases, namely carbon dioxide and nitrogen. The lowest LHV value achieved during the experiment was 10,7 MJ/mN3. The influence of the inert gases on the NOx emissions, the flame stability and characteristics, the flue gas temperature, the in-flame temperatures, the heat flux and the thermal efficiency was investigated and evaluated. Each parameter was measured and evaluated for three different burners: the burner with the staged gas, the burner with the staged air and the burner for low calorific fuels. Generally, after the addition of the inert gas into the noble fuel, the in-flame temperatures decreased. As a consequence, the NOx emissions decreased as well. The effects of carbon dioxide on the investigated combustion parameters were more substantial than the effects of nitrogen. Each measured parameter is strongly dependent on the burner geometry. The experiments revealed that in most cases the addition of the inert gas into the fuel influenced the flame length (flame shortened) and also more heat was transfered into the chamber's walls closer to the burner tile