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Low-NOx technologies are widely used in pulverized coal boilers, but they usually produce high levels of carbon in the fly ash. High levels of unburned carbon represent fuel loss, so the overall boiler efficiency is reduced. Additionally, the higher carbon content affects the suitability of fly ash for cement applications. The purpose of this paper is to provide a CFD approach for unburned carbon reduction by optimizing operating conditions. In this paper, three different boiler loads were simulated: 200 MW, 170 MW, and 140 MW. The air supply system was simulated previously for preparing as precise as possible boundary conditions. At last, unburned carbon level of every burner was investigated, and the effects of residue residence time and the local fuel-air momentum ratio are discussed in detail. According to the predicted results, operating conditions and the residence time of the coal particles affects the unburned carbon level in fly ash. Operating conditions plays a more significant role during the combustion process, while the residence time affects char burnout only when the burner's location is low. Therefore, it is concluded that a cost effective method could be developed for reducing the unburned carbon level in ash and correspondingly, the loss on ignition level. First, it is necessary to determine which burners are operating under poor conditions through CFD analysis. Then, the fuel air momentum ratios of those burners should be modified by changing the operating conditions, meanwhile, increasing residence time of coal particles to ensure complete combustion.

There has been a gradual increase in the field of parts recovery from cars that are withdrawn from use. However, the disposal of automotive shredder residue (ASR) still remains a significant problem. ASR is refuse derived fuel (RDF), which contains mainly plastics, fiber sponges, and rubbers in different proportions, and therefore a thermal treatment of selected waste samples is applied. The presented research includes thermogravimetry (TG) analysis and differential thermogravimetric (DTG) analysis, as well as a proximate and an ultimate analysis of the ASR samples. The obtained results were processed and used as an input for modelling. The numerical calculations focused on the identification of the ASR’s average composition, the raw pyrolysis process product, its dry pyrolytic gas composition, and the combustible properties of the pyrolytic gases. The TGA analysis with three heating rate levels covered the temperature range from ambient to 800 °C. The thermal decomposition of the studied samples was in three stages confirmed with three peaks observed at the temperatures 280, 470, and 670 °C. The amount of solid residue grew with the heating rates and was in the range of 27–32 wt%. The numerical calculation of the pyrolysis process showed that only 0.46 kg of dry gas were formed from 1 kg of ASR. The gas yield increased with the rising temperature, and, at the same time, its calorific value decreased from 19.22 down to 14.16 MJ/m3. This is due to the decomposition of C6+ hydrocarbons and the promotion of CO formation. The thermodynamic parameters of the combustion process for a pyrolytic gas air mixture, such as the adiabatic flame temperature and laminar flame speed, were higher than for methane and were, respectively, 2073 °C and 1.02 m/s.

Crude oil is still an attractive fuel for electricity production due to its low extraction costs in relation to other fuels. However, combustion of crude oil in modern gas turbines must meet certain criteria, which mainly include the reduction of harmful gas emissions, the elimination of harmful dust from the exhaust gas, the improvement of turbine efficiency, the limiting of the power degradation process and elimination of hard deposits. Experimental studies are always needed to meet these requirements because of common complexity in CFD crude oil combustion models. This paper presents experimental investigations of the combustion process of crude oil. Using different sorts of crude oil, all experiments are performed in the atmospheric test rig of a top-mounted combustor, which was scaled down from the baseline system. The test rig was optimized for the typical silo gas turbine boundary conditions. The combustion process is described and quantified with the measured temperature and velocity field distributions in the top-mounted combustion chamber for different injector design’s parameters. Additionally, measured profiles of the molar fraction of CO2, are discussed and compared with respect to the injector parameters. Finally, based upon the experimental results gathered, the possibility of fuel flexibility in the top-mounted combustor chamber is discussed.

The paper presents preliminary experimental analyses of combustion processes for crude oil. The research is started from investigation of combustion of gas in a strong swirl flow as is intended to be an introductory step in studying the mechanism of stability and emission of pollutants in combustion of crude oil occurring in gas turbines. The areas of recirculation and pollutant emission in a strong swirl flow have been studied for the following three cases: - isothermal flow without combustion; - combustion of gas mixture with CH4 and N2 differently composed; - combustion of crude oil. All experiments are performed in the atmospheric test rig of a top-mounted combustor, briefly described in the paper. The velocity field in the combustion chamber is measured by laser doppler anemometry. The measured profiles of temperature and molar fraction of NOx, CO, CO2, O2 are discussed for natural gas and crude oil. Depending on the degree of the swirl of the flow and on the temperature of entering air, the distribution of molar fraction of most important chemical species has been established. This allows for better understanding the process of combustion in a strong swirl flow. The established characteristics of the flame blow-out make it possible to calculate the limits of capacity power generation available from a given size of a gas burner. For the burner geometry, similar to that with the know characteristic of gas combustion, the parameters for CO and NOx have been established for crude oil. Also, characteristics have been found for a specially designed oil nozzle with a large spray angle — sufficiently large for the optimum supply of fuel into the area of strong swirl flow with combustion established on the basis of the analysis of the burning of gas. It has been found that in cases of combustion crude oil a relatively small increase of the temperature of air supplied for combustion results in a significant drop in CO emission what has an impact on lower NOx emission.

This paper presents numerical study on the combustion performance and NO x emissions of a 220 MW pulverized coal boiler. Three different loads have been simulated with combusting coal, 200, 170 and 140 MW, respectively. In order to get as precise as possible numerical analysis results, two-step simulation method has been adopted in this work, namely, air supply system simulation and furnace simulation. After air supply system simulation, the results have been taken as the initial and boundary conditions for furnace simulation. The comparison between the measured values and predicted results from 200 MW case shows much better agreement. According to the simulation results, the adopted two-step simulation method is reasonable and suitable for predicting the characters of the flow and combustion process. It is concluded that the distributions of temperature, O 2 and CO concentration inside furnace with different loads shows good similarly. The total NO x emissions decreased with the boiler load reducing, and fuel NO x has the same trend as total NO x , and fuel NO x account for about 66% in total NO x in all the three cases. More important, thermal NO x slowly decreased with the rise of boiler load. More detailed results presented in this paper enhance the understanding of combustion processes and complex flow patterns of front-wall pulverized coal boilers.

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