Oxygen-enriched Air Combustion Research Articles

Effects of elevated oxygen content and temperature on the laminar burning velocity of the blast furnace gas in oxygen-enriched air condition

Oxygen-enriched air combustion holds promise as an effective method for harnessing blast furnace gas (BFG) in the steel industry. In this study, the laminar burning velocities of blast furnace gas were measured using the heat flux method under elevated oxygen mole fractions (0.3–1.0) and temperatures (303–353 K). Subsequently, the measured data were used to evaluate the GRI-Mech 3.0, Li, FFCM-1, and Konnov 2023 mechanisms. Comparisons between experimental and calculated laminar burning velocities revealed that the Konnov 2023 mechanism well predicts the experimental data at all conditions, while the predictions of the other three mechanisms deviate from the experimental data. The laminar burning velocities of blast furnace gas increased with elevated oxygen mole fraction and temperature. Interestingly, the peak of laminar burning velocity shifts from the fuel-rich side to the fuel-lean side with an increase in oxygen mole fraction, which is mainly due to the fuel-lean shift peak of adiabatic flame temperature and the higher diffusive properties of the gas mixture at fuel-rich side. The reaction CO+OH<=>CO2 + H emerges as the most significant reaction influencing laminar burning velocities. The elevated oxygen mole fraction reduces the dependence of the power exponent α on the fitted temperature range. Corresponding oxygen mole fractions for the blast furnace gas are determined to be 0.59 at φ = 0.8 and 0.93 at φ = 0.9, respectively, at which the laminar burning velocity of the BFG/O2/N2 mixture equals that of the CH4/Air mixture.

REDUCING THE СО2 ATMOSPHERIC EMISSION BY NATURAL GAS “OXY-FUEL COMBUSTION”, AS A MEANS OF PREVENTION THE GREENHOUSE IMPACT

At present, the relation to the fuel-energy complex as the main source of climatic changes of a planetary scale (global warming) has been formed. In view of the corresponding forecasts related to the greenhouse effect, mostly associated with emissions of carbon-containing combustion products (carbonization of the environment), the following ways of countering the climate threat are considered the last time: a — rejection of use of the organic fuel with a gradual transfer to using (burning) of carbon-free fuels (primarily hydrogen and hydrogen-containing mixtures); b — increasing an efficiency of use the organic fuel, first of all is the natural gas, which can provide a 2-times (sometimes more) reduction of total CO2 emissions in the industry; c — reducing the consumption of C-containing technological substances in the treatment of thermal and chemical-thermal processing of metallic materials (steel); d — ferrous recycling and maximum scrap using by iron and steel production. In the paper under consideration the methodology, based upon application the specific greenhouse (CʺСO2) and harmful (CʺNOx) substances issue per unit of useful energy as the determinative parameters, has been advanced for the first time from the standpoint of environment’s decarbonization and pollution. The proper solution for lowering СО2 issue is especially suitable by provision the high temperature processes with utilization the systems of gently oxygen-enriched combustion air. In contrast to traditional assessment of harmful (primarily NOx) and greenhouse (СО2) emissions per unit of generated or supplied energy (the corresponding indicators are C'NOx and C'СO2), application of more adequate values have been proposed by performing the relevant calculations per unit of useful energy Quse. The proper values of relevant indicators CʺNOx and CʺСO2 are objective characteristics by option the most suitable composition of fuel-oxidant mixture. This is approach makes the decisive solution by conditions of mutual substitution the fuels with purpose of account the energy utilization of exhaust gases. Thermodynamic principles and a methodology for calculation the relevant indicators of pollution the exhaust gases CʺNOx and CʺСO2 have been developed. Numerical calculations have been performed and the values of specific emissions of CʺNOx and CʺСO2 have been and determined in dependence on degree of enrichment an oxidizing air-oxidant with oxygen [O2], % (vol.), by account the operating temperature of the process. The possibility of reducing the CʺСO2 emissions by 2 to 3 times or more compared to natural gas with atmospheric air burning has been established even by the cases of a slight (till 30 % vol.) enrichment of the air with oxygen. Bibl. 33, Fig. 11, Tab. 1.

Numerical simulation of the influence of different oxygen concentration on the combustion characteristics of double tangential boiler at low load

In order to cope with the demand for deep peak regulation of high-parameter coal-fired units, this paper uses numerical simulation methods to systematically explore the influence of different secondary wind oxygen enrichment concentrations on the combustion performance and characteristics of singlefurnace double-cut round boilers during low-load operation, so as to provide theoretical support for the actual operation of power plants. The results are as follows: (1) The use of oxygen enriched secondary air combustion during low-load operation of the boiler can improve the overall temperature of the main combustion zone of the furnace and the local temperature of the burner nozzle section, and enhance the combustion stability of pulverized coal in the furnace. (2) When the secondary air oxygen concentration is 35% and 40%, the overall temperature of the main combustion area of the boiler increases the most obviously, and the combustion is the most stable. (3) Oxygen-enriched combustion effectively reduced the NOx emission concentration in the furnace, and the overall trend of NOx emission decreases first and then increases with the increasing trend of secondary air oxygen concentration.

Experimental study on NOx formation and burnout characteristics of pulverized coal in oxygen enriched and deep-staging combustion

Deep-staging combustion is an effective technology for reduction of NOx, but is often accompanied by the combustion worsening. Oxygen enriched and deep-staging combustion is a promising technology to realize both low NOx formation and high burnout rate. NOx reduction and burnout characteristics of pulverized coal in oxygen enriched combustion were experimentally investigated in this study with a drop-tube reactor. Results show that the NOx reduction is significantly promoted by elevated O2 concentration under deep-staging condition. The NOx formation of coal under 40% oxygen concentration condition is 40.7% lower than those in air combustion as the stoichiometric ratio in the fuel-rich zone (SR1) is 0.5. The thermal and fuel NOx formations were separately investigated. The fuel NOx reduction with increase of O2 concentration makes a major contribution to the total NOx reduction under deep-staging conditions. The elevated O2 concentration facilitates the release of fuel nitrogen in the fuel-rich zone, avoiding its oxidation in the fuel-lean zone. Moreover, the negative correlation between NOx formation and unburned carbon (UBC) in coal ash is evidently weakened with the increase of O2 concentration. Ultra-low NOx formation and high combustion efficiency could be concurrently achieved in oxygen enriched combustion under deep-staging condition. Furthermore, the comprehensive comparison of the oxygen enriched combustion, air combustion and oxy-fuel combustion was conducted. Low NOx formation can be reached in oxy-fuel combustion under non-staging condition, while oxygen enriched combustion performs much better in NOx reduction under deep-staging conditions.

Burning Resistance of Lignitic Coals Under Oxygen-Enriched Conditions

Abstract Oxygen-enriched air combustion of low-grade fuels with high inorganic matter is of great interest due to the efficient burning of such fuels and mitigation of emissions. For this purpose, this study aims to investigate the combined effects of oxygen enrichment and temperature on burnout levels. The oxygen-enriched air combustion performance of two Turkish lignites with different geological ages (early Miocene-Pliocene period Kutahya-Tuncbilek (KT) lignite and Pleistocene period Adiyaman-Golbasi (AG) lignite) was investigated in a horizontal tube reactor. The lignite samples were heated slowly (10 °C/min) to the temperatures of 200–600 °C for AG lignite and 200–800 °C for KT lignite under N2/O2 atmospheres with O2 ratios of 21, 30, 40, and 50 vol%. The solid residue remained after this oxidative heat treatment was characterized by proximate/ultimate analyses, higher heating value, (HHV) thermal analysis, Fourier transform infrared spectroscopy, (FTIR) X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. It was concluded that AG lignite that is relatively younger lignite is more susceptible to the O2-enriched conditions as the treatment temperature or O2 concentration increases. It was also determined that the combined effects of temperature and O2 concentration are much more profound than the individual effects of these parameters.

A comparative study on the air, the oxygen-enriched air and the oxy-fuel combustion of lignites in CFB

This paper deals with the comparative combustion processes of two lignites in the air, the oxygen-enriched air and the oxy-fuel-environments. Combustion experiments were conducted in a 30 kWth circulating fluidized bed (CFB) combustor. The air combustion and the oxygen-enriched air combustion were conducted with different excess air ratios and excess oxygen percentages, respectively. Emissions of major pollutants such as CO, CO2, NOx and SO2 were measured during experiments via on-line gas analysis systems. Similarly, temperatures along the combustor axis were measured at various positions. The oxy-fuel combustion experiments were done with O2/RFG mixture. In all environments the lignites sustained stable and steady combustion processes in the temperature range of 700–950 °C under the conditions applied. Emissions of both NOx and SO2 appeared to be considerably affected by combustion atmospheres. In the oxygen-enriched combustion both the NOx and SO2 emissions were higher than that in the air combustion and increased with increase in the O2 concentration in the feed gas. In comparison to the air and the oxygen-enriched air combustion processes, however, the NOx emissions were considerably depressed in the oxy-fuel combustion. In the oxyfuel combustion processes, CO2 concentrations of up to 96% in the flue gases were reached on dry basis.

Study of the post-combustion CO2 capture process by absorption-regeneration using amine solvents applied to cement plant flue gases with high CO2 contents

The present study is focusing on the investigation, for the cement industry, of the post-combustion CO2 capture process using amine(s)-based solvents. The novel aspect of the work is the flue gas considered, namely the high CO2 contents (between 20 and 60 vol.%), representative of flue gases coming from oxygen-enriched air combustion process (also called partial oxy-fuel combustion). Using the results of preliminary solvents screening tests at laboratory scale, absorption-regeneration micro-pilot experiments were carried out for the best solvents in order to characterize their respective absorption and regeneration performances. The use of the activated solution of DEA (diethanolamine) 30 wt.% with PZ (piperazine) 5 wt.% led to particularly high absorption performances in all CO2 concentration range. Besides the experimental measurements, Aspen Hysys™ simulations of the micro-pilot tests were performed for three solvents (monoethanolamine (MEA) as the reference case, then PZ and DEA + PZ) to validate the models implemented. Finally, the validated models were used to perform industrial scale simulations. These simulations confirmed that both the regeneration energy, the equivalent work and the operating costs are reduced when the absorption-regeneration process is implemented to flue gases with high CO2 contents.

Feasibility of Selective Exhaust Gas Recycle Process for Membrane-based CO2 Capture from Natural Gas Combined Cycles – Showstoppers and Alternative Process Configurations

This work presents the limitations of the Selective Exhaust Gas Recycle process for post-combustion capture from natural gas combined cycles using membranes and proposes a novel oxygen enriched air combustion with exhaust gas recirculation process that overcomes the limitations.

Combustion analysis of a light duty diesel engine using oxygen-enriched and humidified combustion air

The present work presents the results of 3D CFD combustion simulations of a current production 4-cylinder turbocharged Diesel engine using oxygen-enriched and humidified combustion air. Enriched Air (EA) is supposed to be produced by desorption from water, exploiting the different Henry constants of N2 and O2. Simulation results show that EA permits to increase the engine thermal efficiency (up to 10%) and drastically reduces soot emissions but increases in-cylinder peak pressure and NOx emissions. Combustion air humidification helps to reduce NOx increment, without losing the advantage in terms of thermal efficiency and in soot reduction, even if NOx emissions cannot be reported to the base case values.

Experimental investigation of NOx emissions during pulverized char combustion in oxygen-enriched air preheated with a circulating fluidized bed

An experimental investigation on NOx emissions of pulverized char combustion in oxygen-enriched air was carried out in a new test system consisting of a circulating fluidized bed (CFB) and a down-fired combustor (DFC). In this paper, the pulverized char combustion characteristics and NOx emission characteristics in the air conditions, the local oxygen-enriched air conditions in the CFB and the overall oxygen-enriched air conditions were studied. The results show that when the primary air oxygen concentration increased from 21.0% to 24.6% and to 28.2%, the ratio of fuel-nitrogen converted to nitrogen in the CFB increased from 39.7% to 45.0% and to 50.8%, respectively. This finding indicates that the preheating process in the CFB was one of the important reasons why the preheating combustion technology could significantly reduce NOx emissions. Compared with the air combustion conditions, the NO emissions decreased to almost half of the original emissions when only the primary air oxygen concentration increased. On this basis, the NO emissions increased slightly when the air oxygen concentration was also increased in the DFC. Under these conditions, the variations in the char combustion efficiency were consistent with the variations in the temperature distribution. The feasibility and superiority of integrating the preheating combustion technology and oxygen-enriched air combustion technology are verified.

Combustion characteristics of Turkish lignites at oxygen-enriched and oxy-fuel combustion conditions

Combustion and oxy-fuel combustion characteristics of two Turkish lignites (Orhaneli and Soma) were investigated by Thermogravimetric Analysis (TGA) method. Experiments were carried out under oxygen-enriched air and oxy-fuel combustion conditions with 21, 30, 40% oxygen concentrations. Three heating rates of 5, 10, and 20 °C/min were considered and the isoconversional kinetic methods of FWO, KAS, and Friedman were employed to estimate activation energies. The uncertainty assessment in obtaining the activation energy values was also considered. The obtained results indicated that the combustion of volatiles at both air and oxy-fuel conditions were approximately identical. However, at air combustion conditions, the decomposition of CaCO3 took place at temperatures above 700 °C. This decomposition process was independent of the oxygen concentration and took place when the temperature reached to a certain threshold. The decomposition of CaCO3 did not accomplish in oxy-fuel conditions as far as the temperature was higher than 900 °C. Combustion in oxy-fuel conditions had higher activation energy values comparing to conventional combustion atmosphere. The activation energy values were approximately unchanged at the start of combustion regardless of oxygen concentration or combustion atmosphere at about 165 kJ/mol and 150 kJ/mol for Orhaneli and Soma lignites, respectively. The apparent activation energies were higher at elevated oxygen concentrations. The uncertainties values related to FWO method were lower than KAS and Friedman methods. The calculated average uncertainty values were found to be at the range of 5–15% for most of the cases.

Empirical Model of Operating Temperature and Pressure Effect towards Pure and Binary O&lt;sub&gt;2&lt;/sub&gt;/ N&lt;sub&gt;2&lt;/sub&gt; Gas Permeability in Polysulfone Membrane

Oxygen (O2) enriched air combustion via adaption of polymeric membranes has been proposed to be a feasible alternative to increase combustion proficiency while minimizing the emission of greenhouse gases into the atmosphere. Nonetheless, majority of techno-economic assessment on the O2 enriched combustion evolving membrane separation process are confined to assumption of constant membrane permeance. In reality, it is well known that membrane permeance is highly dependent upon the temperature and pressure to which it is operated. Therefore, in this work, an empirical model, which includes the effect of temperature and pressure to permeance, has been evaluated based on own experimental work using polysulfone membrane. The empirical model has been further validated with published experimental results. It is found that the model is able to provide an excellent characterization of the membrane permeance across a wide range of operating conditions for both pure and binary gas with determination coefficient of minimally 0.99.

Fluidized Bed Incineration of Sewage Sludge in O2/N2 and O2/CO2 Atmospheres

Sewage sludge incineration in a fluidized bed is considered to be one of the most suitable ways of sewage sludge disposal. This process reduces the volume of the waste and causes the destruction of organic contaminants such as POPs, pharmaceuticals and other compounds with endocrine-disrupting potential. Oxygen-enriched air combustion and oxy-fuel combustion can increase the combustion efficiency, reduce the amount of flue gas and make possible CO2 capture more effective. However, the influence of incineration medium composition has not yet been thoroughly investigated in case of sewage sludge incineration. In this paper, the incineration of sewage sludge in a bubbling fluidized bed reactor was studied at oxygen-enriched air conditions, oxy-fuel conditions and oxy-fuel conditions with zero and non-zero concentrations of steam, CO, NO, N2O and SO2 in the inlet combustion medium. Consequently, the effects of various operating parameters on pollutants formation were comprehensively described with emphasis on...

Stability maps of non-premixed methane flames in different oxidizing environments of a gas turbine model combustor

Oxy-fuel combustion provides a promising solution to the problem of excessive NOx emissions generated by air-based combustion systems; NOx is potentially eliminated in the absence of air-based nitrogen. However, severe temperatures are reached if fuel is burned in pure oxygen. Dilution by CO2 is thus implemented to control the flame temperature. The addition of CO2, however, was found to retard chemical-kinetics rates and negatively affect the laminar burning velocity and combustion efficiency. This study thus set out to examine oxy-fuel combustion and compare it to oxygen-enriched air-fuel combustion based on flame stability and appearance. Experiments were conducted on a swirl-stabilized model gas-turbine combustor to determine the ranges of stable operation of methane flames in different oxidizer environments, including CO2-diluted oxy-combustion and oxygen-enriched air-combustion. Based on that, two sets of experiments were conducted over ranges of oxidizer Reynolds number, equivalence ratio, and oxygen fraction in the oxidizer mixture. The first set of experiments considered CO2-diluted oxy-combustion, while the second set considered oxygen-enriched air-combustion. For both sets, the results showed that the stability map widens as the oxygen fraction is increased in the oxidizer mixture. This can be attributed to higher flame speeds, which assist flame stabilization under lean operation. For the same oxygen fraction and Reynolds number, the oxy-combustion flames were found to stabilize at higher equivalence ratios and fuel flow rates when compared to the oxygen-enriched air flames. This difference in flame stability magnifies at smaller oxygen fractions and gradually diminishes as the oxygen fraction is increased.

Assessment on oxygen enriched air co-combustion performance of biomass/bituminous coal

The oxygen enriched air combustion performance and ash fusion characteristics of two typical agricultural and wood samples (corncob and hardwood) and bituminous coal were assessed using a thermal analysis technique. The effects of oxygen contents, sample kinds and blending ratios on the combustion performance were revealed, and the effects of sample properties and blending ratios on the ash fusion of samples were also evaluated. Biomasses showed better ignition performance and comprehensive combustion performance than bituminous coal. The ignition and comprehensive performance indices of corncob/coal blends were higher than those of hardwood/coal blends. Apparently, the combustion performances of biomass/coal blends improved with increasing the oxygen contents and blending ratios of biomass. Certain synergistic interactions were detected between Chinese bituminous coal and corncob or hardwood during the co-combustion at 100% and 80% oxygen contents. The ash fusion reactions of corncob, hardwood and bituminous coal mainly occurred in the ranges of 1036–1079 °C, 1046–1289 °C, and 1260–1290 °C, respectively, while the ash fusion reaction of corncob/coal blends occurred in the range of 1096–1289 °C.

Oxygen Enriched Air Effects on Combustion, Emission, and Distributed Reaction

A novel combustion technology which combines colorless distributed combustion (CDC) and oxygen enriched combustion (OEC) air is examined to achieve optimum benefits of both technologies and to foster novel technologies for cleaner environment. The influence of oxygen enriched air–methane flames under nonpremixed and premixed fuel-lean combustion conditions is examined with focus on emission of NO and CO, combustor exit temperature (Texit), and distribution of reaction zone in the combustor using OH* chemiluminescence intensity distribution. A cylindrical combustor was used at combustion intensity of 36 MW/m3·atm and heat load of 6.25 kW. Results are also reported with normal air (21% oxygen). Oxygen enrichment provided stable combustion operation at lower equivalence ratios than normal air and also reduced CO emission. Increase in oxygen concentration from 21% to 25% or 30% increased the NO and decreased CO emissions at all the equivalence ratios examined. Using 30% O2 enriched air in premixed case showed NO emissions of 11.4 ppm and 4.6 ppm at equivalence ratios of 0.5 and 0.4, respectively. Oxygen enrichment also reduced CO emission to 38 ppm at equivalence ratio of 0.5. Operating the combustor with normal air at these equivalence ratios resulted in unstable combustion. OH* chemiluminescence revealed increased intensity with the reaction zone to shift upstream at increased oxygen concentration. The exhaust temperature of the combustor increased with oxygen enrichment leading to lower CO concentration and increased combustion efficiency. The oxidizer injected at higher velocities moved the reaction zone to upstream location with simultaneous reduction of both NO and CO, specifically under nonpremixed combustion.

Thermogravimetric analysis and kinetics of the combustion of refining and chemicals wastewater in different oxygen concentrations

The oxygen-enriched air combustion behaviors and kinetics of refining and chemicals wastewater (RCW) solid were investigated using thermogravimetric analysis. The results showed that the combustion process of RCW solid was a four-stage reaction. The increase in O2 concentration had negligible effects on the overall first two stages and the vast majority of the third stage, while made the fourth stage shift to a lower temperature region. The kinetic triplets of each stage were determined by Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa, and the master-plots method. For the first three stages, the average E of each stage varied slightly with of O2 concentration increasing; while the fourth stage showed a rising trend. The most probable reaction models for the first and second stage were the simple order reaction model (Fn), while the random nucleation and nuclei growth model (An) for the third and fourth stage.

Modelling the cement process and cement clinker quality

This paper presents a recently developed simulation model that can be used as a tool for evaluating sustainable development measures for cement and lime production processes. Examples of such measures are introducing new combustion technologies such as oxy-fuel combustion, using biomass fuel and using alternative materials in the raw material feed. One major issue when introducing process changes is the need to maintain product quality. In some ways, oxygen-enriched air combustion resembles oxy-fuel combustion. The model results were validated and found to be consistent with full-scale operational data for normal running conditions and for a full-scale test with oxygen-enriched air. The model shows, for example, that with an additional 1500 m3/h of oxygen, fuel addition at the calciners can increase up to 108% and the raw material feed rate can increase up to 116% for a process with a raw meal feed of 335·5 t/h.

CO2 capture for gas turbines: an integrated energy-efficient process combining combustion in oxygen-enriched air, flue gas recirculation, and membrane separation

Carbon capture and storage for power generation systems is a major issue for achieving greenhouse gas emission reductions. Studies are usually dedicated to coal-fired power plants, but few efforts have addressed the challenge of CO2 capture for a gas turbine. In this paper, a recently reported hybrid process based on oxygen enriched air combustion, flue gas recycling and CO2 capture by membranes is explored for a 250MW open cycle gas turbine. An improved configuration based on an energy recovery system integrated with a heat exchanger offers superior performance compared to the reference gas turbine cycle. It is shown that an overall energy requirement below 2GJth/ton of CO2 captured (i.e. around 205kWhelectrical/ton CO2) can be achieved using a highly selective membrane (CO2/N2 selectivity of 200) operated under optimal process conditions.

Use of oxygen enriched air combustion to enhance combined effectiveness of oxyfuel combustion and post-combustion flue gas cleanup Part 1 - combustion

In this work, oxygen enriched air combustion is addressed. A 0·5 MW Doosan–Babcock burner was used and fired on the RWE npower combustion test facility located on the site of the Didcot ‘A’ Power Station in the UK. The present work concentrated on radiative and convective heat transfer measurements. Oxygen enrichment levels varied between circa 19 and 30% (v/v), dependent on the amount of recycled flue gas to give a constant furnace exit O2 level of 3%, although the furnace exit O2 was varied for carbon-in-ash measurements. Air was also used as comburent for baseline data acquisition. The recycled flue gas was dry and a Russian coal was fired. The results of this work has shown that oxygen enriched air combustion is a viable technique for carbon capture and storage providing CO2 enriched flue gas that will reduce the size of an amine scrubbing plant. The reduced level of oxygen enrichment compared to pure oxyfuel combustion also reduces the potential size of an air separation unit.