Combustion characteristics of lignite-fired oxy-fuel flames

This experimental work describes the combustion characteristics of lignite-fired oxy-fuel flames, in terms of temperature distribution, gas composition (O₂, CO₂, CO, total hydrocarbon concentration and NO) and ignition behaviour. The aim is to evaluate the flame structure of three oxy-fuel cases (obtained by changing the flue gas recycle rate) including a comparison with an air-fired reference case. Measurements were performed in Chalmers 100 kW test unit, which facilitates oxy-fuel combustion under flue gas recycling conditions. Temperature, O₂ and CO concentration profiles and images of the flames indicate that earlier ignition and more intense combustion with higher peak temperatures follow from reduction of the recycle rate during oxy-fuel operation. This is mostly due to higher O₂ concentration in the feed gas, reduced cooling from the recycled flue gas, and change in flow patterns between the cases. The air case and the oxy-fuel case with the highest recycle rate were most sensitive to changes in overall stoichiometry. Despite significant differences in local CO concentration between the cases, the stack concentrations of CO are comparable. Hence, limiting CO emissions from oxy-fuel combustion is not more challenging than during air-firing. The NO emission, as shown previously, was significantly reduced by flue gas recycling.     

Flame and radiation characteristics of gas-fired O2/CO2 combustion

This paper presents an experimental study on the flame properties of O₂/CO₂ combustion (oxy-fuel combustion) with focus on the radiation characteristics and the burn-out behaviour. The experiments were carried out in a 100 kWth test unit which facilitates O₂/CO₂ combustion with real flue gas recycle. The tests comprise a reference test in air and two O₂/CO₂ test cases with different recycled feed gas mixture concentrations of O₂ (OF 21 @ 21 vol.% O₂, 79 vol.% CO₂ and OF 27 @ 27 vol.% O₂, 73 vol.% CO₂). In-furnace gas concentration, temperature and total radiation (uni-directional) profiles are presented and discussed. The results show that the fuel burn-out is delayed for the OF 21 case compared to air-fired conditions as a consequence of reduced temperature levels. Instead, the OF 27 case results in more similar combustion behaviour compared to the reference conditions in terms of in-flame temperature and gas concentration levels, but with significantly increased flame radiation intensity. The information obtained from the radiation and temperature profiles show that the flame emissivity for the OF 21 and OF 27 cases both differ from air-fired conditions. The total emissivity and the gas emissivity of the OF 27 and the air-fired environment are discussed by means of an available model. The gas emissivity model shows that the increase in radiation intensity (up to 30%) of the OF 27 flame compared to the air flame can partly, but not solely, be explained by an increased gas emissivity. Hence, the results show that the OF 27 flame yields a higher radiative contribution from in-flame soot compared to the air-fired flame in addition to the known contribution from the elevated CO₂ partial pressure.     

Air and oxy-fuel combustion characteristics of biomass/lignite blends in TGA-FTIR

Pyrolysis and combustion behavior of indigenous lignite, olive residue and their 50/50 wt.% blend in air and oxy-fuel conditions were investigated by using thermogravimetric analyser (TGA) combined with Fourier-transform infrared (FTIR) spectrometer. Pyrolysis tests were carried out in nitrogen and carbon dioxide environments which are the main diluting gasses of air and oxy-fuel environment, respectively. Pyrolysis results of the parent fuels and the blend show that weight loss profiles are almost the same up to a temperature of 700 °C in these two environments, indicating that CO₂ behaves as an inert gas in this temperature range. However, further weight loss takes place in CO₂ atmosphere at higher temperatures due to CO₂-char gasification reaction which leads to significant increase in CO and COS formation as observed in FTIR evolution profiles. Comparison between experimental and theoretical pyrolysis profiles of the blend samples reveals that there is no synergy in both atmospheres. Combustion experiments were carried out in four different atmospheres; air, oxygen-enriched air environment (30% O2-70% N₂), oxy-fuel environment (21% O₂-79% CO₂) and oxygen-enriched oxy-fuel environment (30% O2-70% CO₂). Replacing N₂ in the combustion environment by CO₂ causes slight delay (lower maximum rate of weight loss and higher burnout temperature) in the combustion of all samples. However, this effect is found to be more significant for olive residue than lignite. Elevated oxygen levels shift combustion profiles to lower temperatures and increase the rate of weight loss. Combustion profiles of olive residue/lignite blends lie between those of individual fuels. Comparison between experimental and theoretical combustion profiles and characteristic temperatures of the blend samples indicates synergistic interactions between the parent fuels during co-combustion of olive residue and lignite.     

Experimental investigation of NOx emissions in oxycoal combustion

This work presents the results of an experimental investigation on NO_x emissions from coal combustion in a pilot scale test facility. Three oxidiser atmospheres have been compared, namely air, CO₂/O₂, and O₂ enriched recirculated flue gas. NO_x emissions from two different combustion modes have been studied, swirl flame and flameless combustion. The influence of the burner oxygen ratio and the oxidiser O₂ concentration on NO_x formation and reduction have been analysed. With increasing burner oxygen ratio, an increase of NO_x emissions has been obtained for air and CO₂/O₂ in both, swirl flame and flameless combustion. In case of the swirl flame, flue gas recirculation leads to a reduction of NO_x emissions up to 50%, whereas in case of flameless combustion this reduction is around 40% compared to CO₂/O₂. No significant impact of the oxidiser O₂ concentration in the CO₂/O₂ mixture on NO_x emissions is observed in the range between 18 and 27 vol.% in swirl flames. An analysis of NO_x formation and reduction mechanisms showed, that the observed reduction of NO_x emissions by flue gas recirculation cannot be attributed to the reduction of recirculated NO_x alone, but also to a reduced conversion of fuel-N to NO.     

Combustion characteristics of coal in a mixture of oxygen and recycled flue gas

The combustion of coal in a mixture of pure O₂ and recycled flue gas is one variant of a novel combustion approach called oxy-fuel combustion. With the absence of N₂, this approach leads to a flue gas stream highly enriched in CO₂. For many applications, this flue gas stream can then be compressed and sequestered without further separation. As a result, oxy-fuel combustion is an attractive way to capture CO₂ produced from fossil fuel combustion. When coal is burned in this O₂ and CO₂ rich environment, its combustion characteristics can be very different from conventional air-fired combustion. In CETC-O, a vertical combustor research facility has been used in the past years to investigate the combustion characteristics of several different coals with this variant of oxy-fuel combustion. This included flame stability, emissions of NO_x, SO_x and trace elements, heat transfer, in-furnace flame profiles and flue gas compositions. This paper will report some of the major findings obtained from these research activities.     

Modeling of oxy-fuel combustion for a western Canadian sub-bituminous coal

The motivation of this research is to develop practical oxy-coal combustion techniques in order to facilitate the conversion of coal-fired utility power plants so as to recover a CO₂ rich flue gas stream for use and/or sequestration. The objective of this study is to ascertain the applicability and accuracy of a modeling tool to assist with future pilot scale oxy-fuel combustion experiments and burner scale-up studies. Two modes of oxy-coal combustion, O₂ enriched air (OEA) and recycled flue gas (RFG), were experimentally tested in a 0.3 MW_th pilot-scale combustor using a western Canadian sub-bituminous coal. The computational fluid dynamic tool was utilized to model the combustion, heat transfer and pollutant formation characteristics of these test cases and to examine the impact due to changes in the combustion medium, burner swirl and burner configuration. The model provided insights for the observed variation in NO_x production among the test cases: the dramatic increase in the OEA mode, the drop at higher burner swirl settings and the surprisingly small reduction in the RFG mode. Overall the model results compared well with measured data in all test cases and established confidence in using the model to explore new design concepts for oxy-coal combustion.     

Development of an oxycoal swirl burner operating at low O2 concentrations

This work is to clarify the underlying mechanisms of burning pulverised coal in a mixture of CO₂/O₂. The performance of two different burner designs, single central orifice-type (SCO) and single annular orifice-type (SAO), under oxycoal conditions was examined in a down-fired test facility. Based on detailed in-flame measurements, combined with numerical simulations, the main parameters influencing the stability of a CO₂/O₂ pulverised coal swirl flame were investigated. The oxycoal flame was stabilised at the burner quarl by: increasing the O₂ concentration above 34 vol% without changes to the air-firing burner design and by modifications of the burner geometry thus changing its aerodynamics. The modification of the burner allowed a decrease of the O₂ concentrations to 23 vol% for SCO burner and to less than 21 vol% for SAO burner. Comprehensive measurement data for axial and tangential velocity, flue gas temperature and oxygen concentration for stable oxy-firing at 21 vol% O₂ is presented. The results reported can be used as a guideline for a development of an industrial swirl burner capable of stable operation in both regimes, namely: air and oxycoal.     

Pulverized coal combustion in air and in O2/CO2 mixtures with NOx recycle

This paper presents experimental results of a 20 kW vertical combustor equipped with a single pf-burner on pulverised coal combustion in air and O₂/CO₂ mixtures with NO_x recycle. Experimental results on combustion performance and NO_x emissions of seven international bituminous coals in air and in O₂/CO₂ mixtures confirm the previous findings of the authors that the O₂ concentration in the O₂/CO₂ mixture has to be 30% or higher to produce matching temperature profiles to those of coal-air combustion while coal combustion in 30% O₂/70% CO₂ leads to better coal burnout and less NO_x emissions than coal combustion in air. Experimental results with NO_x recycle reveal that the reduction of the recycled NO depends on the combustion media, combustion mode (staging or non-staging) and recycling location. Generally, more NO is reduced with coal combustion in 30% O₂/70% CO₂ than with coal combustion in air. Up to 88 and 92% reductions of the recycled NO can be achieved with coal combustion in air and in 30% O₂/70% CO₂ respectively. More NO is reduced with oxidant staging than without oxidant staging when NO is recycled through the burner. Much more NO is reduced when NO recycled through the burner (from 65 to 92%) than when NO is recycled through the staging tertiary oxidant ports (from 33 to 54%). The concentration of the recycled NO has little influence on the reduction efficiency of the recycled NO with both combustion media—air and 30% O₂/70% CO₂.     

CO2 capture using oxygen enhanced combustion strategies for natural gas power plants

This paper describes a series of experiments conducted with natural gas in air and in mixtures of oxygen and recycled flue gas, termed O₂/CO₂ recycle combustion. The objective is to enrich the flue gas with CO₂ to facilitate its capture and sequestration. Detailed measurements of gas composition, flame temperature and heat flux profiles were taken inside CANMET's 0.3 MWth down-fired vertical combustor fitted with a proprietary pilot scale burner. Flue gas composition was continuously monitored. The effects of burner operation, including swirling of secondary stream and air staging, on flame characteristics and NO_x emissions were also studied. The results of this work indicate that oxy-gas combustion techniques based on O₂/CO₂ combustion with flue gas recycle offer excellent potential for retrofit to conventional boilers for CO₂ emission abatement. Other benefits of the technology include considerable reduction and even elimination of NO_x emissions, improved plant efficiency due to lower gas volume and better operational flexibility.     

Numerical analysis of pulverized coal combustion characteristics using advanced low-NOx burner

A three-dimensional numerical simulation is applied to a pulverized coal combustion field in a test furnace equipped with an advanced low-NO_x burner called CI-α burner, and the detailed combustion characteristics are investigated. In addition, the validities of the existing NO_x formation and reduction models are examined. The results show that a recirculation flow is formed in the high-gas-temperature region near the CI-α burner outlet, and this lengthens the residence time of coal particles in this high-temperature region, promotes the evolution of volatile matter and the progress of char reaction, and produces an extremely low-O₂ region for effective NO reduction. It is also found that, by lessening the effect of NO reduction in Levy et al.'s model and taking the NO formation from char N into account, the accuracy of the NO prediction is improved. The efficiency factor of the conversion of char N to NO affects the total NO concentration downstream after the injection of staged combustion air.     

Chemistry and radiation in oxy-fuel combustion: A computational fluid dynamics modeling study

In order to investigate the role of combustion chemistry and radiation heat transfer in oxy-fuel combustion modeling, a computational fluid dynamics (CFD) modeling study has been performed for two different oxy-fuel furnaces. One is a lab-scale 0.8 MW oxy-natural gas flame furnace whose detailed in-flame measurement data are available; the other is a conventional 609 MW utility boiler which is assumed to be operating under oxy-fuel combustion condition with dry flue gas recycle. A new model for gaseous radiative properties is developed, validated, and then implemented in the CFD simulations. The CFD results are compared to those based on the widely used model in literature, as well as the in-flame measurement data. The importance and advantage of the new model for gaseous radiative properties have been well demonstrated. Different combustion mechanisms are also implemented and compared in the CFD simulations, from which significant difference in the predicted flame temperature and species is observed. This difference is consistent with those expected from the equilibrium calculation results. As a conclusion, the appropriate combustion mechanisms applicable to oxy-fuel combustion modeling are identified. Among the key issues in combustion modeling, e.g., mixing, radiation and chemistry, this paper derives useful guidelines on radiation and chemistry implementation for reliable CFD analyses of oxy-fuel combustion, particularly for industrial applications.     

Air and oxy-fuel combustion behaviour of petcoke/lignite blends

The pyrolysis and combustion behaviour of a petroleum coke (petcoke), an indigenous lignite and their 70/30 wt.% blend in air and oxy-fuel conditions were investigated by using non-isothermal thermo-gravimetric method (TGA) coupled with Fourier transform infrared (FTIR) spectrometer. Blend samples were prepared by mixing lignite, which has low calorific value, high ash and moisture contents with petcoke that has high calorific value, low ash and moisture content, in the proportion of 70:30. Pyrolysis tests were carried out in nitrogen and carbon dioxide environments which are the main diluting gases of air and oxy-fuel environments, respectively. Pyrolysis curves of parent fuels and their blend reveal close resemblance up to 700 °C in both N₂ and CO₂ environments. At higher temperatures, further weight loss taking place in N₂ and CO₂ atmospheres is attributed to calcite decomposition and CO₂-char gasification reaction, respectively. Gasification reaction leads to significant increase in CO and COS formation as observed in FTIR evolution profiles. Almost identical experimental and theoretical pyrolysis profiles of the blend samples show that there is no synergy between the parent fuels of the blend in both pyrolysis environments. Combustion experiments were carried out in four different atmospheres; air, oxygen-enriched air environment (30% O₂–70% N₂), oxy-fuel environment (21% O₂–79% CO₂) and oxygen-enriched oxy-fuel environment (30% O₂–70% CO₂). Combustion experiments show that replacing nitrogen in the gas mixture by the same concentration of CO₂ leads to delay in combustion (lower maximum rate of weight loss and higher burnout temperatures). Overall comparison of derivative thermogravimetry (DTG) profiles shows that effect of oxygen content on combustion characteristics is more significant than that of diluting gas in the combustion environment. At elevated oxygen levels, profiles shift through lower temperature zone, peak and burnout temperatures decrease, weight loss rate increases significantly and complete combustion is achieved at lower temperatures and shorter times. Theoretical and experimental combustion profiles of the blend mainly display different trends, which indicate synergistic interactions between lignite and petcoke during their combustion in different environments.     

Experimental study of ash formation during pulverized coal combustion in O2/CO2 mixtures

The present paper was addressed to mineral transformations and ash formation during O₂/CO₂ combustion of pulverized coal. Four Chinese thermal coals were burned in a drop tube furnace to generate ashes under various combustion conditions. The ash samples were characterized with XRD analysis and ⁵⁷Fe Mössbauer spectroscopy. The impacts of O₂/CO₂ combustion on mineral transformation and ash formation were explored through comparisons between O₂/CO₂ combustion and O₂/N₂ combustion. It was found that, O₂/CO₂ combustion did not significantly change the mineral phases formed in the residue ashes, but did affect the relative amounts of the mineral phases. The differences observed in the ashes formed in two atmospheres were attributed to the impact of the gas atmosphere on the combustion temperatures of coal char particles, which consequently influenced the ash formation behaviors of included minerals.     

Modeling char conversion under suspension fired conditions in O2/N2 and O2/CO2 atmospheres

The aim of this investigation has been to model combustion under suspension fired conditions in O₂/N₂ and O₂/CO₂ mixtures. Experiments used for model validation have been carried out in an electrically heated Entrained Flow Reactor (EFR) at temperatures between 1173 K and 1673 K with inlet O₂ concentrations between 5 and 28 vol.%. The COal COmbustion MOdel, COCOMO, includes the three char morphologies: cenospheric char, network char and dense char each divided between six discrete particle sizes. Both combustion and gasification with CO₂ are accounted for and reaction rates include thermal char deactivation, which was found to be important for combustion at high reactor temperatures and high O₂ concentrations. COCOMO show in general good agreement with experimental char conversion profiles at conditions covering zone I-III. From the experimental profiles no effect of CO₂ gasification on char conversion has been found. COCOMO does however suggest that CO₂ gasification in oxy-fuel combustion at low O₂ concentrations can account for as much as 70% of the overall char consumption rate during combustion in zone III.     

煤粉富氧燃烧着火温度预测的优化随机森林(GA-RF)模型

二氧化碳排放是造成温室效应的主要原因之一,富氧燃烧作为一种有效的碳减排与封存技术具有广泛的研究前景。在燃煤电厂中煤粉富氧燃烧的着火温度是燃烧器设计和运行安全的重要指标,并且与煤粉组成成分、煤粉粒径以及燃烧氛围都有复杂的相关性。因此,对煤粉富氧燃烧着火温度的预测模型研究意义重大。采用滴管炉分别测量了5种煤粉在O2体积分数为30%、35%、40%、50%、60%、70%、80%、90%、100%富氧条件下的着火温度,分析了氧气体积分数和煤粉的组成成分与着火温度之间的关系。研究发现,随着氧气体积分数分数的增加,5种煤样的着火温度均显著下降,且挥发分越高的煤,下降幅度越大。将45组试验着火温度数据与其他研究者采用同样方法测得的69组着火温度数据组成机器学习样品库,以煤粉的元素分析、工业分析、煤粉粒径及氧气体积分数为输入条件,以着火温度T为目标输出,构建了遗传算法优化的随机森林模型(GA-RF模型),准确预报了煤粉富氧燃烧的着火温度,其预报精度为:R2>0.99,RMSE<16,MAE<8。通过模型参数重要性分析发现,氢组分超过5%后,着火温度出现阶跃式上升,现有煤粉着火数据也证实了该现象。     

Impact of air staging along furnace height on NOx emissions from pulverized coal combustion

Experiments were carried out on an electrically heated multi-path air inlet one-dimensional furnace to assess NO_x emission characteristics of an overall air-staged (also termed air staging along furnace height) combustion of bituminous coal. The impact of main parameters of overall air-staged combustion technology, including burnout air position, air stoichiometric ratio, levels of burnout air (the number of burnout air arranged at different heights of the furnace), and the ratios of the burnout air flow rates and pulverized coal fineness of industrial interest, on NO_x emission were simulated to study in the experimental furnace, as well as the impact of air staging on the carbon content of the fly ash produced. These results suggest that air-staged combustion affects a pronounced reduction in NO_x emissions from the combustion of bituminous coal. The more deeply the air is staged, the further the NO_x emission is reduced. Two-level air staging yields a greater reduction in NO_x emission than single-level air staging. For pulverized coal of differing fineness, the best ratio between the burnout air rates in the two-level staging ranges from 0.6 to 0.3. In middle air-staged degree combustion with f_M = 0.75, pulverized coal fineness, R₉₀ (%), has a greater influence on NO_x emission, whereas R₉₀ has little influence on NO_x emission for deep air-staged degree with f_M = 0.61. Air-staged combustion with proper burnout air position has little effect on the burnout. For overall air-staged combustion, proper burnout air position and air-staged rate should be considered together in order to achieve high combustion efficiency.     

In situ diagnostics of Victorian brown coal combustion in O2/N2 and O2/CO2 mixtures in drop-tube furnace

Experimental investigation of the combustion of an air-dried Victorian brown coal in O₂/N₂ and O₂/CO₂ mixtures was conducted in a lab-scale drop-tube furnace (DTF). In situ diagnostics of coal burning transient phenomena were carried out with the use of high-speed camera and two-colour pyrometer for photographic observation and particle temperature measurement, respectively. The results indicate that the use of CO₂ in place of N₂ affected brown coal combustion behaviour through both its physical influence and chemical interaction with char. Distinct changes in coal pyrolysis behaviour, ignition extent, and the temperatures of volatile flame and burning char particles were observed. The large specific heat capacity of CO₂ relative to N₂ is the principal factor affecting brown coal combustion, which greatly quenched the ignition of individual coal particles. As a result, a high O₂ fraction of at least 30% in CO₂ is required to match air. Moreover, due to the accumulation of unburnt volatiles in the coal particle vicinity, coal ignition in O₂/CO₂ occurred as a form of volatile cloud rather than individual particles that occurred in air. The temperatures of volatile flame and char particles were reduced by CO₂ quenching throughout coal oxidation. Nevertheless, this negative factor was greatly offset by char-CO₂ gasification reaction which even occurred rapidly during coal pyrolysis. Up to 25% of the nascent char may undergo gasification to yield extra CO to improve the reactivity of local fuel/O₂ mixture. The subsequent homogeneous oxidation of CO released extra heat for the oxidation of both volatiles and char. As a result, the optical intensity of volatile flame in ∼27% O₂ in CO₂ was raised to a level twice that in air at the furnace temperature of 1273 K. Similar temperatures were achieved for burning char particles in 27% O₂/73% CO₂ and air. As this O₂/CO₂ ratio is lower than that for bituminous coal, 30-35%, a low consumption of O₂ is desirable for the oxy-firing of Victorian brown coal. Nevertheless, the distinct emission of volatile cloud and formation of strong reducing gas environment on char surface may affect radiative heat transfer and ash formation, which should be cautioned during the oxy-fuel combustion of Victorian brown coal.     

Flame temperatures and species concentrations in non-stoichiometric oxycoal flames

The oxyfuel technology offers the possibility for CO₂ sequestration from coal fired power plants. One drawback is the need for a high external flue gas recirculation to avoid inadmissible high flame temperatures. The concept of controlled staging with non-stoichiometric burners (CSNB) allows a significant reduction of the commonly proposed flue gas recirculation rate while fulfilling all requirements on temperature limitations. The concept aims at a more efficient oxyfuel process with a higher degree of freedom for heat-flux adjustments suitable for a new generation of oxyfuel boilers. The steam generator size could be reduced and in this way a more cost effective steam generator concept is possible. Additionally the energy demand for the flue gas recirculation is lowered.This paper presents the experimental investigations of non-stoichiometric oxycoal flames. Temperature and gas profiles were taken to analyze the combustion behavior of coal with high oxygen concentrations in the oxidizer under oxygen deficiency and accordingly oxygen excess. In addition an optical flame monitoring system allowed a comparison of ignition, flame shape and stability. In the test rig lignite was burned under different stoichiometries ranging from 0.5 to 2.5 and different oxygen concentrations in the oxidant ranging from 30 to 40 vol.%. The thermal input of the burner was 70 kW at a total thermal input of 140 kW and a dry flue gas recirculation was used. The results were compared to a conventional air-blown combustion and showed that similar temperature ranges can be reached even with oxygen concentrations in the oxidizer as high as 40 vol.%.     

Emission of suspended PM10 from laboratory-scale coal combustion and its correlation with coal mineral properties

Four pulverized coals were subjected to combustion in a laboratory-scale drop tube furnace to investigate the emission of suspended particulate matter smaller than 10 μm (PM₁₀) and to study the correlation of PM₁₀ emission with mineral properties of the coals. Combustion conditions of 1200 °C, 2.4 s and 20% atmospheric oxygen content were used and all the carbon was consumed under given conditions. The properties of PM₁₀ were studied including its concentration, particle size distribution and elemental composition. Two typical sizes were also subjected to Computer controlled scanning electron microscopy (CCSEM) analysis for determination of chemical species within them. To investigate the influence of coal mineral properties, the metallic elements in the raw coals were divided into three parts: organically bound, included inorganic particles and excluded ones. The results indicated that during coal combustion, about 0.5-2.5 wt% of inherent minerals changed into the suspended PM₁₀. With an increase in the coal ash content, the concentration of PM₁₀ increased proportionally. The resulting PM₁₀ had a bimodal size distribution with two peaks around 2.5 and 0.06 μm, respectively. SiO₂ and Al₂O₃ dominated the large mode around 2.5 μm, which is formed by the direct transformation of inherent minerals. On the other hand, SO₃ and P₂O₅ were prevalent in the small mode around 0.06 μm, which is formed by vaporization of these two elements. For other metals found in PM₁₀, the refractory metals were enriched in the large mode, with concentrations proportional to their content in the excluded minerals in the raw coal. Volatile metals were however enriched in the small mode since, they react with gaseous SO₂ and P₂O₅ to form sulfates and phosphates in the solid phase. The study showed that experimental observations agree with thermodynamic equilibrium considerations.     

Numerical investigation of the oxy-fuel combustion in large scale boilers adopting the ECO-Scrub technology

The present paper presents a three-dimensional numerical investigation of a pulverized-fuel, tangentially-fired utility boiler located at Florina/Greece under air, partial and full oxy-fuel conditions. Heat and mass transfer and major species concentration, such as CO₂, CO and O₂ are calculated; whilst the results for the reference air case scenario studied are in good agreement with the corresponding operational data measured in the plant, both for combustion calculations and NO_x emissions. Results for the partial and full oxy-fuel operation scenarios are in line with similar experimental and numerical investigations found in the recent literature. This numerical investigation of oxy-fuel conditions scenarios prior to their implementation under real scale conditions demonstrates the utmost of its importance, since significant results regarding the operation of a boiler in terms of lignite particle trajectories and burning rates are attained. Furthermore, NO_x calculations have been performed for all the examined case studies.