Milan Vujanović

Numerical study of co-firing pulverized coal and biomass inside a cement calciner

The use of waste wood biomass as fuel is increasingly gaining significance in the cement industry. The combustion of biomass and particularly co-firing of biomass and coal in existing pulverized-fuel burners still faces significant challenges. One possibility for the ex ante control and investigation of the co-firing process are computational fluid dynamics (CFD) simulations. The purpose of this paper is to present a numerical analysis of co-firing pulverized coal and biomass in a cement calciner. Numerical models of pulverized coal and biomass combustion were developed and implemented into a commercial CFD code FIRE, which was then used for the analysis. Three-dimensional geometry of a real industrial cement calciner was used for the analysis. Three different co-firing cases were analysed. The results obtained from this study can be used for assessing different co-firing cases, and for improving the understanding of the co-firing process inside the calculated calciner.

Numerical analysis of cement calciner fuel efficiency and pollutant emissions

Efficient mixing of pulverized fuel and limestone particles inside cement calciners is important due to the reason that the calcination process directly affects the final fuel consumption. The focus of this paper is on the numerical analysis of cement calciner’s operating conditions and pollutant emissions. The paper analyzes the influence of different amounts of fuel, mass flow of the tertiary air and the adiabatic wall condition on the decomposition rate of limestone particles, burnout rate of coal particles, and pollutant emissions of a newly designed cement calciner. Numerical models of calcination process and pulverized coal combustion were developed and implemented into a commercial computational fluid dynamics code, which was then used for the analysis. This code was used to simulate turbulent flow field, interaction of particles with the gas phase, temperature field, and concentrations of the reactants and products, by solving the set of conservation equations for mass, momentum, and enthalpy that govern these processes. A three-dimensional geometry of a real industrial cement calciner was used for numerical simulations. The results gained by these numerical simulations can be used for the optimization of cement calciner’s operating conditions, and for the reducing of its pollutant emissions.

Modelling pollutant emissions in diesel engines, influence of biofuel on pollutant formation

In order to reduce the harmful effect on the environment, European Union allowed using the biofuel blends as fuel for the internal combustion engines. Experimental studies have been carried on, dealing with the biodiesel influence on the emission concentrations, showing inconclusive results. In this paper numerical model for pollutant prediction in internal combustion engines is presented. It describes the processes leading towards the pollutant emissions, such as spray particles model, fuel disintegration and evaporation model, combustion and the chemical model for pollutant formation. Presented numerical model, implemented in proprietary software FIRE®, is able to capture chemical phenomena and to predict pollutant emission concentration trends. Using the presented model, numerical simulations of the diesel fuelled internal combustion engine have been performed, with the results validated against the experimental data. Additionally, biodiesel has been used as fuel and the levels of pollutant emissions have been compared to the diesel case. Results have shown that the biodiesel blends release lower nitrogen oxide emissions than the engines powered with the regular diesel.

Numerical analysis of ammonia homogenization for selective catalytic reduction application

Selective catalytic reduction based on urea water solution as ammonia precursor is a promising method for the NOx abatement form exhaust gasses of mobile diesel engine units. It consists of injecting the urea-water solution in the hot flue gas stream and reaction of its products with the NOx over the catalyst surface. During this process flue gas enthalpy is used for the urea-water droplet heating and for the evaporation of water content. After water evaporates, thermolysis of urea occurs, during which ammonia, a known NOx reductant, and isocyanic acid are generated. The uniformity of the ammonia before the catalyst as well as ammonia slip to the environment are important counteracting design requirements, optimization of which is crucial for development of efficient deNOx systems. The aim of this paper is to show capabilities of the developed mathematical framework implemented in the commercial CFD code AVL FIRE®, to simulate physical processes of all relevant phenomena occurring during the SCR process including chemical reactions taking part in the catalyst. First, mathematical models for description of SCR process are presented and afterwards, models are used on the 3D geometry of a real SCR reactor in order to predict ammonia generation, NOx reduction and resulting ammonia slip. Influence of the injection direction and droplet sizes was also investigated on the same geometry. The performed study indicates importance of droplet sizes on the SCR process and shows that counterflow injection is beneficial, especially in terms of minimizing harmful ammonia slip to environment.

Effects of deposition height and width on film cooling

ABSTRACT Because natural gas resources continue to be depleted for usage of gas turbines, it becomes important to search for alternate fuels. Coal-derived synthetic fuels contain traces of ash and other contaminants that result in deposition on vane and turbine surfaces. The present research shows a comparison of simulated results with and without a deposition configuration. Film cooling effectiveness distribution after the deposition was obtained to investigate the effects of various deposition heights and widths under the blowing ratios of 0.5, 0.75, and 1.0. The results indicated that the deposition near the hole exit can weaken the cooling performance. Moreover, it is revealed that the film cooling effectiveness deteriorates with increased deposition heights. The deposition width study revealed that a narrow deposition shows a good attachment of the coolant jet to the wall surface. It is found that an improvement of the film cooling effectiveness can be obtained by decreasing the blowing ratio.

CO2 emission reduction in the cement industry

The cement industry is one of the largest carbon emitting industrial sectors in the European Union (EU)and in the world. In line with the EU commitment to combat climate change, the cement industry needs to decrease significantly carbon emission. The cement manufacturing process is not only a source of combustion related CO2 emissions, but it is also a large source of industrial process related CO2 emissions. There are several effective measures which can be applied in cement manufacturing processes to achieve emissions reduction targets. Simultaneously, these measures can reduce the local environmental impacts and improve the competitiveness of the cement industry. In this paper, the following measures for CO2 emission reduction were analyzed in order to identify their environmental effectiveness: use of alternative fuels, more efficient kiln process, and co-production of synthetic fuels. The study was done on the case of a Macedonian cement plant. It was confirmed that the implementation of the selected mitigation measures results in substantial CO2 emission reduction.

CFD analysis of a cement calciner for a cleaner cement production

Cement calciners are pyroprocessing units found in modern cement plants. Inside of them occurs a strong endothermic reaction known as the calcination process, and the combustion of pulverized solid fuels. Controlling the mixing of limestone and pulverized fuel particles is of particular importance because it directly affects the energy consumption. The paper analyzes the impact of an axial and a swirl burner on the mixing of the particles, pollutant emissions and the operating conditions of a newly designed cement calciner. All necessary numerical models were developed and implemented into a commercial computational fluid dynamics code FIRE, which is then used for the analysis. This code is used to simulate turbulent flow field, temperature field, concentrations of the reactants and products as well as the interaction of particles with the gas phase, by solving the set of conservation equations for mass, momentum and enthalpy governing these processes. The results gained by these simulations can be used for the optimization of cement calciner’s operating conditions.

Two-phase flow simulation of mist film cooling with deposition for various boundary conditions

ABSTRACT Air film cooling is a conventional cooling technique that has been successfully used for gas turbine hot-section components, such as combustor liners, combustor transition pieces, and turbine vanes and blades. However, the increased benefit seems to approach a limit. This paper investigates the film cooling effectiveness considering mist injection. All the studies for various boundary conditions are conducted numerically, including the effects of droplet size, the flow rates of droplet injection, and the coolant air. Film cooling is also affected by the interaction between deposition and mist injection. A deposition configuration is located near the film hole with an inclination angle of 35°. Results show that the combined effect of injection and deposition is to weaken the film cooling effectiveness, especially upstream of x/d = 19. For the coolant air at a low speed, the mist injection cannot provide better cooling protection than without the mist injection.

Mitigation of Climate Change by Reducing Carbon Dioxide Emissions in Cement Industry

The cement industry is an energy intensive industry, and one of the largest carbon emitting industrial sectors. It is emitting 5 % of global anthropogenic carbon dioxide emissions, with especially high growth in Asia. While the energy efficiency of cement production has been increased significantly, the emissions can be further reduced by replacing conventional fossil fuels with alternative ones, mostly of waste origin. Due to the lower heating value of waste derived fuels than of the standardly used coal, the use of such fuels is possible where there is no need for very high process temperatures, e.g. in cement calciners where the desirable operating temperature is around 950 °C. Using waste derived fuels in cement calciners does not only reduce combustion related CO2 emissions in cement production by 10-30 %, depending on the amount of used waste derived fuels and the biogenic fraction in the used waste derived fuel, but is also an environmentally beneficial alternative to waste landfill disposal. However, incineration of high share of waste derived fuels in cement calciners still faces significant challenges. A possibility for the ex-ante control and investigation of the incineration process are Computational Fluid Dynamics - CFD simulations. Early comprehensive information, parametric studies and initial conclusions that can be gained from CFD simulations are very important in handling modern combustion units. The purpose of this paper is to present the benefit of using waste derived fuels in the cement industry, and to give some preliminary results on waste incineration numerical modelling.

Low NOx combustion and SCR flow field optimization in a low volatile coal fired boiler

Low NOx burner redesign and deep air staging have been carried out to optimize the poor ignition and reduce the NOx emissions in a low volatile coal fired 330 MWe boiler. Residual swirling flow in the tangentially-fired furnace caused flue gas velocity deviations at furnace exit, leading to flow field unevenness in the SCR (selective catalytic reduction) system and poor denitrification efficiency. Numerical simulations on the velocity field in the SCR system were carried out to determine the optimal flow deflector arrangement to improve flow field uniformity of SCR system. Full-scale experiment was performed to investigate the effect of low NOx combustion and SCR flow field optimization. Compared with the results before the optimization, the NOx emissions at furnace exit decreased from 550 to 650 mg/Nm³ to 330-430 mg/Nm³. The sample standard deviation of the NOx emissions at the outlet section of SCR decreased from 34.8 mg/Nm³ to 7.8 mg/Nm³. The consumption of liquid ammonia reduced from 150 to 200 kg/h to 100-150 kg/h after optimization.