Oxy-Fuel Combustion

With the ever rising concern of global warming, carbon
capture is gaining the reputation of one of the most challenging fields of research. A very promising technology to capture CO2 is oxy-combustion. Oxy-combustion offers several advantages over conventional combustion technologies, such as flue gas volume reduction, high combustion efficiency, low fuel consumption and significant reduction in NOx emissions. Liquid fuel is available and it is the most widely used source of energy in the world. Easy handling and transportation, less storage volume and higher flame temperature are some of the features of liquid fuel which give it an upper hand over other sources. In this study, an experimental work on oxygen enriched combustion of ethanol in a vertical reactor by Lacas F. et. al. has been modeled numerically. Non-premixed model using Probability Density Function has been incorporated to simulate the combustion process of ethanol droplets. Predicted combustion characteristics are found to be in good compliance with the experimental data. In addition to this, effects of dilution of carbon-dioxide in oxygen on the flame properties have also been presented. Combustion of ethanol in oxygen- carbon dioxide environment has been compared with that of the conventional air environment.

A critical review is presented of modern theoretical developments on problems of droplet vaporization in a high-temperature environment and of spray combustion. Emphasis is placed upon analytical and computational contributions to the theory with some mention of empirical evidence. Four areas of basic phenomena are discussed in some detail: (i)droplet slip and internal circulation, (ii) transient heating of the droplets, (iii) multicomponent fuel vaporization, and (iv) combustion and vaporization of droplet arrays, groups, and sprays. Various relationships amongst these phenomena are analyzed as well. Several other problem areas are given brief mention. Future directions are suggested.

Coal is the most important energy source for our country, which is dependent on foreign
energy sources. Moreover, it has reserve of about 200 years. Nevertheless, direct
utilization of coals brings about some challenges such as air pollution and higher emissions
of greenhouse gas which impact upon on health. For this reason, coal is gasified, and
cleaner, higher calorific synthetic fuels are obtained. In this thesis, coal gases (blast
furnace gas and generator gas) which are obtained by gasification or by product of coking
of coal have burned with pure oxygen, combustion and emission characteristics were
investigated experimentally and numerically. Furthermore, it is also aimed to ensure
dissemination of usage of local coal, as gaseous fuel, for different industries and the
integration of these gases with metal and glass industry, cutting, welding and so on
processes. For this purpose, low calorific coal gases have been properly oxy-combusted
experimentally by burner and combustion performances and emission values have been
measured in the first part of the work. The experimental results for existing burner have
shown that the burner wall was overheated due to the very high flame temperature (about
2000 K) in the flame holder zone. This undesirable situation has required the improvement
of the oxidizer inlet section of the existing burner for pure oxygen flow. Hence, the
oxidizer inlet section of the burner has been reduced approximately four times as
volumetric flow rate of oxygen is lower about 4 times than the air. The oxy-combustion
burner has been obtained by this modification. In the second part of study, the effect of this
improvement on the combustion characteristics of coal gases was investigated numerically
by a computational fluid dynamics software. The predicted temperature profiles have been
compared with the experimental data and it has been demonstrated that there is consistency
between the predicted and the measured results adequately. Studies have shown that low
calorific coal can be used effectively in our country.

Energy demand is increasing dramatically because of the fast industrial development, rising population, expanding urbanization, and economic growth in the world. To fulfill this energy demand, a large amount of fuel is widely used from different fossil resources. Burning of fossil fuels has caused serious detrimental environmental consequences. The application of biodiesel has shown a positive impact in resolving these issues. Edible vegetable oils are one of the potential feedstocks for biodiesel production. However, as the use of edible oils will jeopardize food supplies and biodiversity, non-edible vegetable oils, also known as second-generation feedstocks, are considered potential substitutes of edible food crops for biodiesel production. This paper introduces some species of non-edible vegetables whose oils are potential sources of biodiesel. These species are Pongamia pinnata (karanja), Calophyllum inophyllum (Polanga), Maduca indica (mahua), Hevea brasiliensis (rubber seed), Cotton seed, Simmondsia chinesnsis (Jojoba), Nicotianna tabacum (tobacco), Azadirachta indica (Neem), Linum usitatissimum (Linseed) and Jatropha curcas (Jatropha). Various aspects of non-edible feedstocks, such as biology, distribution, and chemistry, the biodiesel’s physicochemical properties, and its effect on engine performance and emission, are reviewed based on published articles. From the review, fuel properties are found to considerably vary depending on feedstocks. Analysis of the performance results revealed that most of the biodiesel generally give higher brake thermal efficiency and lower brake-specific fuel consumption. Emission results showed that in most cases, NOx emission is increased, and HC, CO, and PM emissions are decreases. It was reported that a diesel engine could be successfully run and could give excellent performance and the study revealed the most effective regulated emissions on the application of karanja, mahua, rubber seed, and tobacco biodiesel and their blends as fuel in a CI engine.

This study investigates the thermal and kinetic analysis of six diverse biomass fuels, in order to provide valuable information for power and energy generation. Pyrolytic, combustion and kinetic analyses of barley straw, miscanthus, waste wood, wheat straw, short rotation coppicing (SRC) willow and wood pellet were examined by non-isothermal thermogravimetry analyser (TGA), differential thermogravimetric (DTG) and differential scanning calorimetry (DSC) techniques. Biomass fuels were thermally degraded under N2, air, CO2 and the selected oxy-fuel (30% O2/70% CO2) reaction environments. The thermal degradation under inert N2 and CO2 atmospheres showed an almost identical rate of weight loss (R), reactivity (RM × 103) and activation energy (Ea) profiles. Similar profiles for R, RM and Ea were observed for the environments under air (21% O2/79% N2) and the oxy-fuel combustion. Results indicated that the thermal decomposition rate for biomass fuels in an oxidising condition was faster than in an inert atmosphere, favourable effect on thermal degradation of biomass fuels was observed when oxygen content increased from 21 to 30%. Higher activation energies with lower reactivity were observed for the biomass fuels that have low cellulosic contents as compared to the other fuels. Regression analysis confirmed that the reaction order 0.5 modelled fitted well for all biomass samples. All these findings will provide valuable information and promote the advancement of future researches in this field.

Oxy-fuel combustion has become as one of promising options for carbon dioxide capture in pulverized
coal power plant. Many investigations on oxy-fuel combustion in Drop Tube Furnace (DTF) have been
reported, but predicting oxy-fuel combustion using Computational Fluid Dynamic (CFD) is still needed
to be further studied. Different environment and combustion reaction in oxy-fuel combustion become
challenging in CFD modeling. Volatile and char combustion mechanisms have adopted in this CFD
modeling. The result is validated by experiment result in DTF. Sub-bituminous coal is used as coal
sample and running in air environment and oxy-fuel environment. Good agreement between CFD
result and the experiment result can be shown in this paper. Lower maximum gas temperature and
higher CO emission can be shown in oxy-fuel combustion

Integrated Gasification Combined Cycle (IGCC) with Pre-combustion has many advantages over post and oxy-combustion systems. This is because the CO 2 will be at higher pressure (requires smaller equipment) thereby making the separation process efficient and easy for sequestration. However the challenges remain to exploit this technology are; (i) it can only be applied for new plants since the separation process becomes integral part of combustion (results in higher down times), and existing plant cannot be retrofitted, (ii) the technology is not as mature as other counterparts and cannot be applied for large scale power production, (iii) higher energy penalty due to cooling of syngas for CO 2 separation with conventional methods.

The performance of industrial gas turbines is closely tied to the intake air temperature and component performance degradation caused by fouling, erosion, and foreign object damage (FOD). Generally, under hot and humid conditions an increase in the ambient intake air temperature induces a decline in gas turbines performance. With this regard, inlet air cooling (IAC) is an established technique that has been applied to reverse the deteriorating effects of high air temperatures. In this study, a steady-state off-design model for a single-shaft industrial gas turbine (Taurus 70) with a variable geometry has been developed to analyze a cumulative effect of fouling and variable ambient conditions on gas turbines performance. The validation of GasTurb 12, simulations was achieved by comparing the results with the Solar Turbines product catalog. The study has been segregated into four different scenarios: (i) with inlet air cooling, (ii) without inlet air cooling, (iii) with Variable Inlet Guide Vane (VIGV) schedule, and (iv) without VIGV schedule. With an increase in fouling severity level, thermal efficiency and specific fuel consumption (SFC) showed clear deterioration. However, with the integration of the IAC technique, the thermal efficiency and SFC improved that translate into economic gain. A novel idea has also been explored to investigate the effect of VIGV scheduling on performance improvement. It is observed that the deployment of the VIGV schedule improves the thermal efficiency and SFC that were previously deteriorating due to fouling. Hence, it is concluded that the integration of inlet air cooling with variable geometry engine can improve the performance of industrial gas turbines especially in hot climate regions such as the Middle East and Southeast Asian countries. Ó 2020 Faculty of Engineering, Alexandria University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Kinetics of bituminous coal and palm shells were evaluated using thermo-gravimetric analysis under different environments (N 2 /CO 2 /O 2 ). The observed percent mass loss of biomass was higher than mass loss percentage of coal because biomass had higher reactivity and volatile matter content. Ignition temperatures of pure coal, biomass and their blends were also investigated and it was observed that biomass blends had improved ignition properties in both air and oxy-fuel environments. However, the combustion mechanism wasn't affected. Different mixtures of CO 2 /O 2 were also used on 10% palm shelle90% coal samples and compared with air as the reference. At the same composition of oxygen in oxy-fuel as that of simulated air, ignition temperatures were slightly higher and mass loss percentages were marginally lower. However, this difference due to heat capacities of N 2 and CO 2 was meager and was considered negligible. Upon increasing O 2 content, lower ignition temperatures were observed. Kinetics of coal, palm shell and their blends were determined at different gas mixture compositions using Doyle's and Coats-Redfern's models. For both models, E was found to decrease with increasing palm shell composition in coal as well as increasing O 2 concentration in oxy-fuel. However, a reverse trend was observed for the pre-exponentional factor(A).

Oxy-fuel combustion is one of the promising carbon capture technologies considered to be suitable for future commercial applications with stationary combustion plants. Although more and more biomass and waste are now being burned in stationary combustion plants, research on oxy-fuel combustion of biomass has received much less attention in comparison to oxy-fuel combustion of coal. In this work, a series of tests was carried out in a 20 kWth fluidized bed combustor under oxy-fuel conditions firing two non-woody fuels (miscanthus and straw pellets) and one woody fuel (domestic wood pellet). The effects of the combustion atmosphere (air and oxy-fuel) and oxygen concentration in the oxidant of the oxy-fuel combustion on gas emissions and temperature profiles were systematically studied with the overall excess oxygen coefficient in the combustor being maintained roughly constant throughout the tests. The experimental results showed that replacing the air with an oxy-fuel oxidant of 21 vol% O2 and 79 vol% CO2 resulted in a significant decrease in combustion temperature and ultimately led to the extinction of the biomass flame due to the larger specific heat of CO2 compared to N2. To keep a similar temperature profile to that achieved under the air combustion conditions, the oxygen concentration in the oxidant of O2/CO2 mixture had to be increased to 30 vol%. A drastic decrease in CO emissions was observed for all three biomass fuels (up to 80% reduction when firing straw) under oxy-fuel combustion conditions providing that the oxygen concentration in the oxidant of O2/CO2 mixture was above 25 vol%. NOx emissions were found to decrease with the oxygen concentration in the oxy-fuel oxidant, due to i) the increase of bed temperature, which implies more volatile-N released and converted in the dense bed zone and ii) the less dilution of the gases inside the dense bed zone, which leads to a higher CO concentration in this region enhancing the reduction of NOx. Similar NOx emissions to those obtained with air combustion were found when the oxygen concentration in the oxy-fuel oxidant was kept at 30 vol%. Further analysis of the experimental results showed that the gas emissions when firing the non-woody fuels were controlled mainly by the freeboard temperature instead of the dense bed region temperature due to the characteristically high volatile matter content and fines of this kind of biomass fuels.

The aim of the present article is to present the achieved results on the experimental combustion aggregate. In the experimental measurement, the increased of the oxygen concentration in the oxidizing agent in the combustion of natural gas has been used. The results presented in this article are focused to achieve the thermal efficiency of the device, which is expressed by useful heat of the combustion aggregate. Part of the article is the analysis of the heating heat exchanger based on heat flow by convection and radiation and CFD mode of heat exchanger

Aluminium substituted cobalt-nickel ferrite nanoparticles were synthesized by citrate gel auto-combustion method followed by annealing at 1000 °C for 1 h in air. Scanning electron micrographs of all the samples show crystalline particles of irregular morphology with a small variation in particle sizes (~ 110–160 nm). From the analysis of the X-ray diffraction results we observed that the unit cell parameter decreases linearly with increase in aluminium concentration due to the smaller ionic radius of the Al 3+ ions substituting the other cations such as Co 2+ , Ni 2+ and Fe 3+ ions in the compounds. The room temperature Mössbauer spectra of the samples show Zeeman split sextet patterns corresponding to the tetrahedral (Th) and octahedral (Oh) interstitial iron (Fe 3+) cations. The observed magnetic hyperfine field (B hf) decreases with increase in Al-concentration due to the distribution of diamagnetic Al 3+ in the environment of 57 Fe probe atoms. The saturation magnetization measured by Vibrating Sample Magnetometer (VSM) shows a similar trend like that of B hf. The distributions of the cations obtained from the Rietveld refinement and Mössbauer spectroscopy results indicate an increase in Fe 3+ (Th)/Fe 3+ (Oh) occupancy-ratio on increasing Al 3+ concentration, and Ni 2+ cations prefer the octahedral site, whereas Co 2+ and Al 3+ ions redistribute themselves in tetrahedral and octahedral sites, in the ratio 2:3.

The scope of present research is to investigate the knowledge of the ongoing worldwide activities in the market and the state of the art technologies for emissions minimization in the combination of solid fuels. An effort will be made to evaluate the technologies, based on the available literature, considering the thermal conversion process that takes place in the boilers or furnaces, the emission level control and minimization potential and the specific characteristics of biomass as primary fuel.

The combustion characteristics of liquid ethanol in air and oxygen–carbon dioxide environments are investigated numerically inside a vertical reactor. Gambit 2.2 was used to construct the mesh and Fluent 12.1 was used to perform the
calculations. Different oxidizer environments were considered including pure air, oxygen-enriched air, in addition to the
cases of OF21 (21% O2 and 79% CO2) and OF29 (29% O2 and 71% CO2). Comparisons were performed between the
different cases and the results were validated against wide range of the experimental data. Nonpremixed combustion
model which utilizes probability density function to predict the scalar quantities was incorporated to simulate the combustion process. Two turbulence models, realizable k–" (RKE) model and Reynolds stress model (RSM), were applied and their results were compared. The Euler–Lagrange approach was utilized to solve the discrete phase model. The results showed the ability of the RKE model to predict much closer data to the  experimental data than the RSM which over predicts the temperature. For the case of OF21, the flame was lifted and the combustion temperature was reduced as compared to the air combustion case. However, the OF29 combustion case resulted in a very close performance to the case of air combustion.

Carbon dioxide emissions are considered one of the most important factors that cause global warming. For this reason, it is suggested to burn fuels using an oxidizer mixture consisting of oxygen and carbon dioxide rather than the conventional burning in air. This combustion technique ensures that the resulting products consist mainly of carbon dioxide and water vapor which facilitates capturing and sequestration of the carbon dioxide gas and thus eliminates its release into the atmosphere. One of the main challenges
that faces this technique is the need to ensure the flame stability in a wide range of operating conditions because of  he adverse effects of adding carbon dioxide to the oxidizer mixture on chemical kinetics. This study experimentally examines some of the conditions that must be met to ensure stable flame operation when burning compressed natural gas in a controlled mixture of oxygen and carbon dioxide stabilized over a perforated-plate burner at different equivalence ratios and at different oxygen fractions. Two sets of experiments are carried-out in this study. In the first set, the study identifies the range of equivalence ratios at constant oxygen fractions necessary for stable flame operation. In the second set, the study identifies the range of oxygen fraction at constant equivalence ratios necessary for stable flame operation. The study also documents the visual flame length and color and identifies the extinction mechanism outside the flammability limits for both sets. The first set of experiments reveals that, in the range of Reynolds number considered and at an oxygen fraction of  6%, stable flame operation is observed with flammability limits that are approximately 80% of the corresponding air-fuel combustion under the same Reynolds number. This ratio decreases as the oxygen fraction decreases. The visual flame length is longer than that of air-fuel combustion by approximately 15%. Extinction occurs by blow-off outside the upper and lower flammability limits. The second set of experiments reveals that for the burner and the range of  Reynolds numbers considered, operation below an oxygen fraction of 29% is not possible at all equivalence ratios considered (namely 0.7, 0.85, 1 and 1.15) while the upper flammability limit is a function of the equivalence ratio. Extinction occurs by blow-off below the lower flammability limit, and by flash-back above the upper flammability limit.
Keywords: Oxy-fuel combustion, CNG/O2/CO2 combustion, flammability limit, extinction mechanism, visual flame appearance and perforated-plate burner.

Integrated Gasification Combined Cycle (IGCC) with Pre-combustion has many advantages over post and oxy-combustion systems. This is because the CO 2 will be at higher pressure (requires smaller equipment) thereby making the separation process efficient and easy for sequestration. However the challenges remain to exploit this technology are; (i) it can only be applied for new plants since the separation process becomes integral part of combustion (results in higher down times), and existing plant cannot be retrofitted, (ii) the technology is not as mature as other counterparts and cannot be applied for large scale power production, (iii) higher energy penalty due to cooling of syngas for CO 2 separation with conventional methods. These issues have led worldwide researchers to focus on overcoming the challenges and make the technology of future. From the research of past decade, it is evident that CO 2 separation by adsorbents is best choice. Due to inherent disadvantages of process such as limited operating temperatures, recovery and purity of CO 2 , recovery &regeneration energy penalty, much of research in focused on developing enhanced adsorbents and processes. In this paper we present different techniques and materials developed by researchers in the past decade and also present future scope for pre-combustion capture applied to IGCC.

Dyes are an important class of pollutants, and can even be identified by the human eye. Disposal of dyes in precious water resources must be avoided, however, and for that various treatment technologies are in use. Among various methods, adsorption occupies a prominent place in dye removal. The growing demand for efficient and low-cost treatment methods and the importance of adsorption has given rise to low-cost alternative adsorbents.

Coal combustion was simulated in a lab-scale furnace and a full scale utility boiler at air-burn, oxycombustion with dry-and wet-flue gas recycles. Good agreement was obtained between the numerical predictions and experimental measurements. The study confirmed that certain dry and wet recycle ratios imitate the temperature and heat transfer characteristics found in air combustion. The performances of five gray models to predict the radiative properties of gases in the simulations were examined. Emissivity correlations developed for purely CO 2 media were not found to be suitable to predict the property at low H 2 O/ CO 2 ratios encountered during dry-recycle. Therefore, a new total emissivity correlation and a weighted-sum-of-gray-gases (WSGG) model were formulated to address the shortcomings and inaccuracies in existing gray gas models under oxy-firing. The new WSGG model with 4 band intervals was found to perform well in test cases that were representative of air-and oxy-firing conditions in boilers.

A piezocomposite generating element (PCGE) can be used to convert ambient vibrations into electrical energy that can be stored and used to power other devices. This paper introduces a design of a magnetic force exciter for a small-scale windmill that vibrates a PCGE to convert wind energy into electrical energy. A small-scale windmill was designed to be sensitive to low-speed wind in urban regions for the purpose of collecting wind energy. The magnetic force exciter consists of exciting magnets attached to the device's input rotor and a secondary magnet fixed at the tip of the PCGE. The PCGE is fixed to a clamp that can be adjusted to slide on the windmill's frame in order to change the gap between exciting and secondary magnets. Under an applied wind force, the input rotor rotates to create a magnetic force interaction that excites the PCGE. The deformation of the PCGE enables it to generate electric power. Experiments were performed with different numbers of exciting magnets and different gaps between the exciting and secondary magnets to determine the optimal configuration for generating the peak voltage and harvesting the maximum wind energy for the same range of wind speeds. In a battery-charging test, the charging time for a 40 mA h battery was approximately 3 h for natural wind in an urban region. The experimental results show that the prototype can harvest energy in urban regions with low wind speeds and convert the wasted wind energy into electricity for city use.

Carbon dioxide emissions are considered one of the most important factors that cause global warming. For this reason, it is suggested to burn fuels using an oxidizer mixture consisting of oxygen and carbon dioxide rather than the conventional burning in air. This combustion technique ensures that the resulting products consist mainly of carbon dioxide and water vapor which facilitates capturing and sequestration of the carbon dioxide gas and thus eliminates its release into the atmosphere. One of the main challenges
that faces this technique is the need to ensure the flame stability in a wide range of operating conditions because of  he adverse effects of adding carbon dioxide to the oxidizer mixture on chemical kinetics. This study experimentally examines some of the conditions that must be met to ensure stable flame operation when burning compressed natural gas in a controlled mixture of oxygen and carbon dioxide stabilized over a perforated-plate burner at different equivalence ratios and at different oxygen fractions. Two sets of experiments are carried-out in this study. In the first set, the study identifies the range of equivalence ratios at constant oxygen fractions necessary for stable flame operation. In the second set, the study identifies the range of oxygen fraction at constant equivalence ratios necessary for stable flame operation. The study also documents the visual flame length and color and identifies the extinction mechanism outside the flammability limits for both sets. The first set of experiments reveals that, in the range of Reynolds number considered and at an oxygen fraction of  6%, stable flame operation is observed with flammability limits that are approximately 80% of the corresponding air-fuel combustion under the same Reynolds number. This ratio decreases as the oxygen fraction decreases. The visual flame length is longer than that of air-fuel combustion by approximately 15%. Extinction occurs by blow-off outside the upper and lower flammability limits. The second set of experiments reveals that for the burner and the range of
Reynolds numbers considered, operation below an oxygen fraction of 29% is not possible at all equivalence ratios considered (namely 0.7, 0.85, 1 and 1.15) while the upper flammability limit is a function of the equivalence ratio. Extinction occurs by blow-off below the lower flammability limit, and by flash-back above the upper flammability limit.
Keywords: Oxy-fuel combustion, CNG/O2/CO2 combustion, flammability limit, extinction mechanism, visual flame appearance and perforated-plate burner.

In oxy-fuel combustion technology, the coal is burned in a mixture of pure oxygen and recycled flue gas with
high content of CO2 gas. Burning the coal in oxy-fuel combustion with O2 and CO2 environment will affect the
combustion performance compare with air (O2/N2) environment. Based on previous researches indicated that oxygen
concentration is required to be increased, so that the combustion behaviour similar as in air environment.
This paper describes the characteristics of coal ignition and combustion in oxy-fuel combustion applying the nonisothermal
thermogravimetric analysis. Experimental results find out the activation energy of three different coal
ranks in O2/N2 and O2/CO2 environment. Temperature of coal sample and inert reference material can simultaneously
measured in TG-DTA. Based on activation energy and TG-DTA data, predicted coal particle ignition temperature
can be calculated and then validated. The result is successfully applied both in air and O2/CO2 environment. In
comparison to the conventional combustion, thermogravimetric curves of coal combustion in O2/CO2 tend towards
higher temperature zone. The species in flue gas during burning test in TGA were determined and analyzed using the
Fourier-transform infrared (FTIR) spectrometer. Compared with pulverized coal combustion in O2/N2 environment,
much more CO is produced in O2/CO2 coal combustion process. Refer to two film model, the delay in oxy-fuel
combustion may be caused by the incoming O2 unbalance with much CO gas, and this can be solved with increasing
O2 concentration in O2/CO2 environment.

One of promising technology with zero CO2 emission at pulverized coal fired power plant is oxy-fuel combustion technology. In oxy-fuel combustion technology, the coal is burned in a mixture of pure oxygen and recycled flue gas with high content of CO2 gas. Burning the coal in oxy-fuel combustion with O2 and CO2 environment will affect the combustion performance compare with air (O2/N2) environment. Based on previous researches indicated that oxygen concentration is required to be increased, so that the combustion behavior similar as in air environment. This paper discusses the characteristics of coal ignition and combustion in oxy-fuel combustion applying Drop Tube Furnace (DTF). Three different Indonesian coal ranks of lignite, sub-bituminous and bituminous have been used as coal samples. Coal combustion test in DTF has been supplied with compressed air for air environment and mixing gas cylinder of 21%O2/CO2 for oxy-fuel environment. Experimental results indicated that the ignition time delay occurs in oxy-fuel combustion for all coal samples. Char combustion rate in oxy-fuel environment take longer time compared with in air environment. The different in physical gas properties influence on coal ignition and combustion characteristics.

The effect of mixing of natural gas with air and oxygen enriched air as the oxidising agents is described in this paper. The theoretical basics of the oxy/fuel combustion and the effect of increasing of oxygen content in the oxidising agent on the flue gas composition and theoretical temperature at natural gas combustion are briefly described. The burner of 2 kW thermal power with two types of mixing devices was designed. The mixing devices were tested using the mathematical model formulated on the basis of CFD-software and monitoring the flame temperatures on the physical models. In order to achieve a better comparison of the mixing devices, only their geometry were being modified, while the input parameters such as the mass flow of natural gas and oxidants remained the same. Using CFD modelling the different mixing chambers was also designed, of which the best results were achieved at the mixers with truncated cone shape. However, it has not been confirmed experimentally on the test apparatus. Key words: oxy/fuel combustion, oxygen enriched air, CFD mathematical model. Matematički i fizički model miješalice kod gorionika zrak/gorivo i kisikom obogaćen zrak/gorivo. U ovom radu opisan je učinak miješanja zemnog plina sa zrakom te kisikom obogaćenim zrakom kao oksidirajućim sredstvima. Sažeto su opisane teorijske osnove izgaranja kisik/gorivo i utjecaj povećanja sadržaja kisika u oksidirajućem sredstvu na sastav i teorijsku temperaturu plinova izgaranja pri izgaranju zemnog plina. Plamenik toplinske snage od 2 kW projektiran je s dvije vrste uređaja za miješanje čija funkcionalnost je istraživana pomoću matematičkog modela formuliranog na osnovi CFD programskog paketa i praćenjem temperature plamena na fizičkom modelima. Kako bi se postigla bolja usporedba uređaja za miješanje, modificirana je samo njihova geometrija dok su ulazni parametari, kao što su maseni protok zemnog plina i oksidirajućih sredstava, ostali isti. Korištenjem CFD modeliranja također su konstruirane komore za miješanje različitih oblika, od kojih su najbolji rezultati postignuti kod miješalica oblika krnjeg stošca. Međutim, to nije eksperimentalno potvrđeno na ispitnom uređaju. Ključne riječi: izgaranje kisik/gorivo, kisikom obogaćen zrak, CFD matematički model.

The performance of steam power plants, utilizing recovered waste heat from air-fuel and oxy-fuel combustion, are compared. Temperature profiles in the heat recovery steam generator (HRSG), steam production rate, network output and energy efficiency are simulated for different conditions. Investigations are made into the effect of varying pinch point on HRSG performance, network and energy efficiency for power generation utilizing oxy-fuel combustion. It is found that with increased pinch point there is an associated decrease in HRSG and steam plant efficiencies. Exhaust gas composition influences the energy efficiency of the power plant. When air-fuel and oxy-fuel combustion are compared there is a reduced amount of nitrogen in the oxidant stream in the latter case. When comparing air-fuel and oxy-fuel combustion, a considerable deviation in HRSG and steam power plant performance is exhibited, with oxy-fuel combustion offering benefits in system efficiency and plant output. The exhaust gas composition at the HRSG inlet contributes significantly the performance characteristics of the system. Raising the HRSG inlet temperature also increases power generation and system efficiency. The results provide insights into the use of oxy-fuel combustion for systems utilizing HRSG for power generation while demonstrating the influence of gas composition, pinch point, and exhaust gas temperature on system performance, and suggest that oxy-fuel combustion can help enhance the contribution to sustainable development of some energy systems.

Kinetics of bituminous coal and palm shells were evaluated using thermo-gravimetric analysis under different environments (N 2/CO 2/O 2). The observed percent mass loss of biomass was higher than mass loss percentage of coal because biomass had higher reactivity and volatile matter content. Ignition temperatures of pure coal, biomass and their blends were also investigated and it was observed that biomass blends had improved ignition properties in both air and oxy-fuel environments. However, the combustion mechanism wasn't affected. Different mixtures of CO 2/O 2 were also used on 10% palm shell-90% coal samples and compared with air as the reference. At the same composition of oxygen in oxy-fuel as that of simulated air, ignition temperatures were slightly higher and mass loss percentages were marginally lower. However, this difference due to heat capacities of N 2 and CO 2 was meager and was considered negligible. Upon increasing O 2 content, lower ignition temperatures were observed. Kinetics of coal, palm shell and their blends were determined at different gas mixture compositions using Doyle's and Coats-Redfern's models. For both models, E was found to decrease with increasing palm shell composition in coal as well as increasing O 2 concentration in oxy-fuel. However, a reverse trend was observed for the pre-exponentional factor(A). © 2011 Elsevier Ltd.

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This paper aims at investigating the performance of a cylindrical ion transport reactor designed for oxy-fuel combustion. The cylindrical reactor walls are made of dense, nonporous, mixed-conducting ceramic membranes that only allow oxygen permeation from the outside air into the combustion chamber. The sweep gas (CO 2 and CH 4 ) enters the reactor from one side and mixes with the oxygen permeate, and the products are discharged from the other side. The process of oxygen permeation through the reactor walls is influenced by the flow condition and composition of air at the feed side (inlet air side) and the gas mixture at the permeate side (sweep gas side). The modeling of the flow process is based on the numerical solution of the conservation equations of mass, momentum, energy, and species in the axisymmetric flow domain. The membrane is modeled as a selective layer in which the oxygen permeation depends on the prevailing temperatures as well as the oxygen partial pressure at both sides of the membrane. The CFD calculations were carried out using FLUENT 12.1 (ANSYS, Inc., Canonsburg, PA, USA), whereas the mass transfer of oxygen through the membrane is modeled by a set of user defined functions. The model results were validated against previous experimental data, and the comparison showed a good agreement. The study focused on the effect of oxygen partial pressure and temperature on the resulting combustion zones inside the reactor for the two cases of co-current and counter-current flow regimes. The results indicated that the oxygen to fuel mass ratio increases as the percentage of CO 2 increases in the inflow sweep gas for both co-current and counter-current flows. The obtained sweep mixture ratio (CO 2 /CH 4 ) of 24 is found within the stoichiometric limit over most of the reactor length in the co-current configuration, whereas the sweep mixture ratio of 15.67 is found in the counter-current configuration owing to the high O 2 permeation.

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Gaza Strip has a long history of critical shortage in its fuel supply due to the economic siege imposed by the Israeli national policy. Not surprisingly, therefore, alternative solutions have been sought ever since which replace the use of diesel in car engines with all kinds of vegetable oils. Nevertheless, such alternative shows drawbacks in relation to badly affecting the surrounding environment. This study focuses on these drawbacks in an effort to minimise environmental pollution emerged due to using vegetable oil as an alternative energy resource to fuel engine. In so doing, analysis in this article uses the Gaza Strip as a particular case. A comparison is utilised in this case through the lens of heat efficiency which compares between the proportions of environmental pollution, firstly emerged due to the combustion of vegetable oil and secondly occurred in the engine diesel. The next step seeks to minimize the proportion adopting handling heating that uses additional material...

Purpose: This study aims to investigate the effects of nozzle momentum flux distribution on the flow field characteristics.

Design/methodology/approach : The nozzle configuration consists of a central nozzle surrounded by four nozzles. All nozzles have same diameter and constant separation between nozzles. OpenFOAM® is used for simulating the jet flow. Reynolds Averaged Navier Stokes (RANS) equations are solved iteratively with a first order closure for turbulence. Pitot-static tube with differential pressure transducer is used for mean velocity measurements. The comparison of computed results with experimental data shows similar trend and acceptable validation.

Findings: According to the results, the momentum flux distribution significantly alters the near field of multiple turbulent round jets. Highly non-linear decay region in the near field is found for the cases having higher momentum in the outer jets. As a result of merging, increased positive pressure is found in the mixing region. Higher secondary flows and wider mixing region are reported as a result of momentum transfer from axial to lateral directions by Reynolds stresses.

Research limitations/implications : The present study is limited to isothermal flow of air jet in air medium.

Social implications: Optimum momentum flux distribution in multijet injector of a combustor can reap better mixing leading to better efficiency and lesser environmental pollution.

Originality/value: As summary, the contributions of this paper in the field of turbulent jets are following: simulations for various momentum distribution cases have been performed. In all the cases, the flow at the nozzle exit is subsonic along with constant velocity profile. To simulate proper flow field, a large cylinder type domain with structured grid is used with refinements towards the nozzle exit and jet axis. The results show that the non-linearity increases with increase in momentum of outer jets. Longer merging zones are reported for cases with higher momentum in outer nozzles using area averaged turbulent kinetic energy. Similarly, wider mixing regions are reported using secondary flow parameter and visualizations.

Luego de ciento cincuenta años de haberse perforado los primeros pozos comerciales de petróleo que condujeron al uso intensivo de combustibles líquidos para mover los vehículos de transporte, se está arribando al pico de las reservas de petróleo del planeta. Queda aún una buena porción por gastar, con la expectativa de que las consecuencias sean mejores que en la primera parte, la cual ha implicado varias guerras y deterioros del ambiente. Este ensayo aporta un resumen sobre la historia de los combustibles fósiles y sobre la prospectiva de las alternativas energéticas emergentes, poniendo énfasis en la bioenergía como una alternativa para la transición entre la actual era de la combustión y la nueva era de la energía limpia.

PACS: 89.30.A-, 88.20.D-, 88.20.Yq