Numerical investigation of the aerodynamic breakup of diesel droplets under various gas pressures

[EN] Abstract The present study investigates numerically the aerodynamic breakup of Diesel droplets for a wide range of ambient pressures encountered in engineering applications relevant to oil burners and internal combustion engines. The numerical model solves the Navier-Stokes equations coupled with the Volume of Fluid (VOF) methodology utilized for capturing the interface between the liquid and the surrounding gas. An adaptive local grid refinement technique is used to increase the accuracy of the numerical results around the interface. The Weber (We) numbers examined are in the range of 14 to 279 which correspond to bag, multimode and sheet-thinning breakup regimes. Model results are initially compared against published experimental data and show a good agreement in predicting the drop deformation and the different breakup modes. The predicted breakup initiation times for all cases lie within the theoretical limits given by empirical correlations based on the We number. Following the model validation, the effect of density ratio on the breakup process is examined by varying the gas density (or equivalently the ambient pressure), while the We number is kept almost constant equal to 270; ambient gas pressure varies from 1 up to 146bar and the corresponding density ratios (ε) range from 700 down to 5. Results indicate that the predicted breakup mode of sheet-thinning remains unchanged for changing the density ratio. Useful information about the instantaneous drag coefficient (Cd) and surface area as functions of the selected non-dimensional time is given. It is shown that the density ratio is affecting the drag coefficient, in agreement with previous numerical studies.Financial support from the MSCA-ITN-ETN of the European Union’s H2020 programme, under REA grant agreement n. 675676 is acknowledged.Stefanitsis, D.; Malgarinos, I.; Strotos, G.; Nikolopoulos, N.; Kakaras, E.; Gavaises, M. (2017). Numerical investigation of the aerodynamic breakup of diesel droplets under various gas pressures. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 1052-1059. https://doi.org/10.4995/ILASS2017.2017.4690OCS1052105

Report on comparison among current industrial scale lignite drying technologies

Lignite constitutes a major energy source and has long been used for energy production despite its contribution in greenhouse gas (GHG) emissions, as a fossil fuel. For example, 27.4% of Germany’s electricity originates from lignite power plants, while in Greece more than 55% of its electric energy consumption is provided by lignite. 45% of the total global coal reserves consist of low-rank coals (LRCs) such as lignite. With this background, the utilization of lignite for energy production is expected to remain a common practice in the decades to come since the availability of lignite is considerable in many countries of Europe and the world (e.g. Germany, Poland, Greece, USA, and Australia). Therefore, problems regarding the combustion and use of lignite should be addressed in a more efficient and environmentally friendly way. One of the main existing problems is the high moisture contained in raw lignite as received from the mine. The high moisture content results in higher CO2 emissions per unit of energy produced and is responsible for high capital and transport costs as well as other technical problems such as reduction in coal friability and difficulties in its blending and pneumatic transportation. Therefore, processing of lignite through drying is considered of great interest in the implementation of energy production in lignite power plants. Taking into account the significance of the subject and the usefulness of such an attempt, an overview of the currently existing drying technologies, including both evaporative and non-evaporative drying methods is reported in the present paper

NOVEL CONCEPTS FOR NEAR-ZERO EMISSIONS IGCC POWER PLANTS by

The pa per aims in ex am in ing and eval u at ing the state-of-the-art in tech no-log i cal con cepts to wards zero-emis sion coal-fired power plants. The dis-cus sion is based on the eval u a tion of a novel con cept deal ing with the car-bon ation-cal ci na tion pro cess of lime for CO2 cap ture from coal-fired power plants, com pared to the in te gra tion of CO2 cap ture in an In te grated Gasi fi-ca tion Com bined Cy cle power plant. Re sults from ther mo dy namic sim u la-tions deal ing with the most im por tant fea tures for CO2 re duc tion are pre-sented. Pre lim i nary eco nomic con sid er ations are made, tak ing into ac count in vest ment and op er at ing costs, in or der to as sess the elec tric ity cost re lated to the two dif fer ent tech no log i cal ap proaches. The cy cle cal cu la tions were per formed with the ther mo dy namic cy cle cal cu-la tion soft ware ENBIPRO (ENergie-BIllanz-PRO gram), a pow er ful tool for heat and mass bal ance solv ing of com plex ther mo dy namic cir cuits, cal cu la-tion of ef fi ciency, exergetic and exergoeconomic anal y sis of power plants. The soft ware code mod els all pieces of equip ment that usu ally ap pear in power plant in stal la tions and can ac cu rately cal cu late all ther mo dy namic prop er ties at each node of the ther mo dy namic cir cuit, power con sump tion of each com po nent, flue gas com po si tion etc. [1]. The code has proven its va lid ity by ac cu rately sim u lat ing a large num ber of power plants and through com par i son of the re sults with other com mer cial soft ware. Key words: IGCC power plants, CO2 captur

Novel concepts for near-zero emissions IGCC power plants

The paper aims in examining and evaluating the state-of-the-art in technological concepts towards zero-emission coal-fired power plants. The discussion is based on the evaluation of a novel concept dealing with the carbonation-calcination process of lime for CO2 capture from coal-fired power plants, compared to the integration of CO2 capture in an Integrated Gasification Combined Cycle power plant. Results from thermodynamic simulations dealing with the most important features for CO2 reduction are presented. Preliminary economic considerations are made, taking into account investment and operating costs, in order to assess the electricity cost related to the two different technological approaches. The cycle calculations were performed with the thermodynamic cycle calculation software ENBIPRO (ENergie-BIllanz-PROgram), a powerful tool for heat and mass balance solving of complex thermodynamic circuits, calculation of efficiency, exergetic and exergoeconomic analysis of power plants. The software code models all pieces of equipment that usually appear in power plant installations and can accurately calculate all thermodynamic properties at each node of the thermodynamic circuit, power consumption of each component, flue gas composition etc. [1]. The code has proven its validity by accurately simulating a large number of power plants and through comparison of the results with other commercial software.

AGGLOMERATION PROBLEMS DURING CARDOON FLUIDIZED BED GASIFICATION

Cynara Cardunculus, commonly known as cardoon is a potential energy crop native to th

Fly Ash Formation and Characteristics from (co-)Combustion of an Herbaceous Biomass and a Greek Lignite (Low-Rank Coal) in a Pulverized Fuel Pilot-Scale Test Facility

The lignite boilers are designed for lower quality fuels, and often the ash is not utilized. This work assessed the impact of combustion of an herbaceous biomass with a low-quality Greek lignite on the quality of the resulting fly ash. Test results were compared with those of fly ash samples from an industrial facility using the same fuel qualities. Inductively coupled plasma-optical (ICP) emission spectroscopy, X-ray powder diffraction (XRD), and scanning electron microscope (SEM) analyses were performed on the collected samples. Despite the significantly higher contents of K, Na and S in the biomass, at a 50% co-firing thermal share, the major and minor oxides in the fly ash were comparable to the lignite fly ash quality. This is attributed to the high ash content of the lignite, the low ash content of the biomass, and the much higher heating value of the biomass. There were improvements in fly ash performance characteristics with the herbaceous biomass in the fuel blend. The initial setting time and volume stability evaluations were improved with the biomass in the fuel blend. The work supports efforts of good practices in ash management, social responsibility, a circular economy, power plant renewable energy operations, and co-firing herbaceous biomass fuels in lignite power plants

Numerical investigation of the role of heat transfer in bubble dynamics

[EN] Bubble dynamics is generally described by the well-known Rayleigh-Plesset (R-P) equation in which the bubble pressure (or equivalently the bubble density) is predefined by assuming a polytropic gas equation of state with common assumptions to include either isothermal or adiabatic bubble behaviour. The present study examines the applicability of this assumption by assuming that the bubble density obeys the ideal gas equation of state, while the heat exchange with the surrounding liquid is estimated as part of the numerical solution. The numerical model employed includes the solution of the Navier-Stokes equations along with the energy equation, while the liquidgas interface is tracked using the Volume of Fluid (VOF) methodology; phase-change mechanism is assumed to be insignificant compared to bubble heat transfer mechanism. To assess the effect of heat transfer and gas equation of state on bubble behaviour, simulations are also performed for the same initial conditions by using a polytropic equation of state for the bubble phase without solving the energy equation. The accuracy of computations is enhanced by using a dynamic local grid refinement technique which reduces the computational cost and allows for the accurate representation of the interface for the whole duration of the phenomenon in which the bubble size changes significantly. A parametric study performed for various initial bubble sizes and ambient conditions reveals the cases for which the bubble behaviour resembles that of an isothermal or the adiabatic one. Additional to the CFD simulations, a 0-D model is proposed to predict the bubble dynamics. This combines the solution of a modified R-P equation assuming ideal gas bubble content along with an equation for the bubble temperature based on the 1st law of thermodynamics; a correction factor is used to represent accurately the heat transfer between the two phases.Financial support from the MSCA-ITN-ETN of the European Union’s H2020 programme, under REA grant agreement n. 675676 is acknowledged.Fostiropoulos, SR.; Malgarinos, I.; Strotos, G.; Nikolopoulos, N.; Kakaras, E.; Koukouvinis, P.; Gavaises, M. (2017). Role of heat transfer in bubble dynamics neglecting phase change. A numerical study. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 904-911. https://doi.org/10.4995/ILASS2017.2017.4691OCS90491