Oxy-fuel Combustion Characteristics Research Articles

Computational fluid dynamics simulation on oxy-fuel combustion performance of a multiple-burner furnace firing coking dry gas

In heat production and power generation utilizing carbon-based fuels, oxy-fuel combustion is regarded as a potential method for carbon capture and sequestration. However, few studies, if any, have been performed on the impacts of exhaust dehydration efficiency and oxygen purity on the parameters of oxy-fuel combustion. In the current study, based on the experimental data, the oxy-fuel combustion characteristics of coking dry gas (CDG) in a gas-fired furnace were investigated using the computational fluid dynamics approach. The simulation results illustrate that the CO2 concentration in the flue gas could rise by nearly 14% as the dehydration efficiency increases from 0.60 to 0.95. The contents of CO2 elevate with the oxygen purity, while H2O and N2 show an opposite trend. Within the scope of the present study, an O2 content of 32% and an excess oxygen ratio of 1.1 are recommended given the combustion performance and economic issue. Due to the impacts of combustion performance, cost of ASU, CO2 enrichment, and so on, the selection of oxygen purity needs to be considered comprehensively. The content of N2 declines with the increase of the dehydration efficiency, which benefits the enrichment of CO2. The present work contributes to the clean and efficient utilization of combustible exhaust gas and provides further knowledge on green and low-carbon development.

Evaluation of numerical modeling and combustion characteristics of hydrogen oxy-fuel combustion in a semi-industrial furnace

The use of hydrogen (H2) in oxy-fuel combustion (OFC) systems is a promising concept for future high-temperature industries. However, the current literature lacks a comprehensive study on the numerical modeling aspects and the relevant flame characteristics. This was tackled in the present work, as the high-impulse OFC of pure H2 was analyzed for the first time in an industrial environment based on experiments, theoretical calculations and RANS simulations. A detailed 3D CFD model of a 180 kW furnace was developed in Fluent, focusing on an accurate prediction of the temperature field and heat transfer rates. An extensive model validation was accomplished using measurement data from the conventional OFC of methane (CH4), and highly precise results could be obtained. Then, the numerical modeling of H2 OFC was scrutinized, highlighting the influence of different CFD modeling options for turbulence, combustion chemistry and thermal radiation. In the end, a detailed analysis of the combustion characteristics has been performed, using the conventional OFC of CH4 as a reference.It was found that turbulence modeling has the dominating effect on the numerical representation of the flame, while only negligible changes were noticed with different combustion and radiation models. Precise simulation results were achieved only by incorporating novel adaptations of the k-ɛ model, since the turbulent diffusion was underestimated with all common turbulence models. In terms of the flame characteristics, H2 caused an increase in the peak flame temperature by 400 K relative to CH4, which led to an improved radiative heat transfer in the flame near region. At the same time, the flame length decreased by almost 10% despite three-times higher fuel nozzle velocities. Overall, thorough insights into both the numerical modeling and the combustion characteristics of H2 OFC were provided, which should support the move toward greater sustainability in high-temperature processes.

Numerical study on oxy-fuel combustion characteristics of industrial furnace firing coking dry gas

One of the most promising methods for clean utilization of hydrocarbon fuels and CO2 capture is oxy-fuel combustion. However, report on oxy-fuel burning of industrial gas is still limited. In the study, numerical simulation was conducted to explore the oxy-fuel combustion performance of a coking dry gas fired industrial furnace. A modified weighted sum gray gas (WSGG) model with a four-gray body and fourth-degree temperature polynomial was proposed for both air and oxy-fuel combustion with the introduction of the fourth graybody. The impacts of oxygen content, excess oxygen ratio, oxygen purity, and dehydration efficiency on combustion and heat transfer were mainly investigated. The maximum furnace temperature increases significantly, and the high temperature region inside the furnace shrinks and moves downward as the oxygen content rises. The H2O content increases from ∼20% to ∼37%, and the CO2 content decreases from ∼77% to ∼60%. The furnace temperature is up to 1835 K under air conditions, while the furnace temperature is reduced by 195 K under oxy-fuel condition of 21% O2 content. The composition of flue gas barely changes as the excess oxygen ratio increases from 1.02 to 1.20. Although the CO2 enrichment in flue gas and the improvement of oxy-fuel combustion performance benefit from an increase in oxygen purity, the combustion performance further advances little when it is raised to over 98%. Additionally, when dehydration efficiency grows, radiant heat transfer decreases and the flue gas temperature at the furnace outlet rises. The content of O2 and N2 has little relationship with dehydration efficiency. This study aids in understanding the actual oxy-fuel combustion process of an industrial gas-fired boiler and offers a possible theoretical basis for clean burning of petrochemical combustible gas and carbon capture.

Air and oxy-fuel combustion characteristics of coal gangue and weathered coal blends

Oxy-fuel combustion technology is suggested as one of the promising technologies for capturing CO2. The combustion characteristics of blends of a coal gangue and a weathered coal under air (21% O2/79% N2), oxy-fuel (20% O2/80% CO2) and oxygen-enriched oxy-fuel (40% O2/60% CO2) conditions were studied using a thermogravimetric analysis (TGA) technique operating at heating rate 10 oCmin−1 to a final temperature 900 °C, focussing on the effect of blending ratio and atmosphere. While the differential thermogravimetric (DTG) profiles of coal gangue in the three different atmospheres were very similar, the weathered coal showed a sharp peak in the temperature range 400–440 °C under oxygen-enriched oxy-fuel condition, which was different from DTG curves under air and oxy-fuel conditions. The blending of the coal gangue into the weathered coal gradually diminished this peak. The negligible deviations between the experimental DTG curves and theoretical DTG curves indicated that interactions were absent for all the coal gangue/weathered coal mixtures under air and oxy-fuel conditions. The obvious interactions between coal gangue and weathered coal were observed under oxygen-enriched oxy-fuel condition and the interaction may be related to thermal effect. The interactions increased as the increasing weathered coal ratio in blends and increasing oxygen concentration under oxy-fuel conditions.

Quantitative Analysis of Water Injection Mass and Timing Effects on Oxy-Fuel Combustion Characteristics in a GDI Engine Fuelled with E10

The climate change issue has become a growing concern due to the increasing greenhouse gas emissions. To achieve carbon neutrality for mitigating the climate problem, the oxy-fuel combustion (OFC) technique on internal combustion engines (ICEs) has attracted much attention. Furthermore, the water injection (WI) strategy was proven effective in improving the combustion process and thermal efficiency in engines under OFC mode. However, WI strategy effects on gasoline direct injection (GDI) engines fuelled with gasoline–alcohol blends have not been reported. This study quantitatively analysed WI mass and timing effects on oxy-fuel combustion performance from a GDI engine fuelled with E10 (10% ethanol and 90% gasoline in mass) by simulation. The results show that equivalent brake-specific fuel consumption (BSFCE) shows a monotonically decreasing trend with the increase in the water–fuel mass ratio (Rwf) from 0 to 0.2. However, further increasing Rwf would cause a deterioration in BSFCE due to the enhanced cooling effects of water vaporisation. Moreover, an appropriate water injection timing (tWI) could be explored for improving OFC performance, especially for large Rwf conditions. The difference in BSFCE between tWI = −100°CA and tWI = −60°CA can be up to around 6.3 g/kWh by increasing Rwf to 0.6.

Research on Oxy-Fuel Combustion Characteristics of Two Typical Chinese Coals

Oxy–fuel (O2/CO2) combustion technology shows great potential for carbon reduction. However, difference in the combustion atmosphere would affect coal combustion characteristics and pollutant emissions. In order to explore oxy–fuel combustion characteristics, two typical Chinese coals, sub–bituminous and lean coal, were utilized. Based on thermogravimetry and pilot–scale test, the ignition and burnout characteristics under oxy–fuel and air combustion atmosphere were investigated. Besides, the NOx emission characteristics were also investigated on the pilot–scale test. Through experimental results, these two kinds of coal showed different combustion characteristics, mainly due to differences in coal quality. Compared with air combustion, oxy–fuel combustion affected the coal combustion process. Firstly, the ignition temperature of sub–bituminous and lean coal decreased from 418 and 477 °C to 405 and 415 °C, respectively; the burnout temperature also decreased from 855 and 985 °C to 808 and 838 °C, respectively. Then, coal combustion performance was evaluated by comprehensive combustion characteristics (S); with an increase in S from, respectively, 3.659 and 2.013 to 4.826 and 3.545 × 10−8(min−2 × K−3), the combustion performance significantly improved. Then, the char burnout time was advanced for 1~3 min. Similar results were obtained on the pilot–scale test. The ignition temperatures decreased from 505 and 552 to 490 and 512 °C, respectively. Moreover, the char burnout rate increased by 0.5~5% and 2~11%, respectively. Lastly, the NOx concentration in flue gas was 2.2~2.6 and 2.0~2.3 times higher for the two kinds of coal under oxy–fuel combustion.

Effect of demineralization on pyrolysis semi-coke physical and chemical characteristics and oxy-fuel combustion characteristics

With global green and low-carbon development, carbon emission reduction is imminent. Oxy-fuel combustion technology is considered to be one of the most promising carbon capture and carbon sequestration technologies. In this work, the physical and chemical characteristics and oxy-fuel combustion characteristics of semi-coke (SC) and demineralized semi-coke (De-SC) were studied. The result shows that, compared with 20% O2/80% CO2, under 30% O2/70% CO2 atmosphere, the ignition temperature and burnout temperature of De-SC are lower, the maximum combustion rate is higher, and the main combustion process can be clearly divided into homogeneous and heterogeneous combustion stages. Compared with SC, De-SC has a less developed pore structure and lower alkali metal and volatile content, which lead to higher ignition temperatures for De-SC. The demineralization process makes the microcrystalline structure of carbon looser and increases the relative content of oxygen-containing functional groups, which are all beneficial to increasing the reactivity of De-SC. The combustion method of De-SC is mainly the particle surface reaction. Only in the atmosphere of 30% O2/70% CO2 and the heating rate of 30 °C/min the combustion mode of De-SC is on the surface and inside the particles. Under different atmospheres, compared with SC, De-SC has lower activation energy and higher pre-exponential factor. The activation and pre-exponential of De-SC have a kinetic compensation effect. The results of this paper provide a theoretical basis for an in-depth understanding of the application of De-SC under oxy-fuel conditions.

Comparison of oxy-fuel preheated combustion characteristics of high- and low- volatility carbon-based fuels

A comparative evaluation and analysis study of combustion characteristics, main pollutant emission behaviors, and fuel-N conversion paths of high- and low- volatility carbon-based fuels are conducted under O2/CO2 atmospheres in a preheating combustion reactor, i.e., CFB. Compared with conventional air combustion, the oxy combustion with high oxygen concentrations from 21% to 27.3% is studied. The studies show that the net calorific value of the preheated coal gas of semi-coke in O2/CO2 is up to 2 times that in air, and the net calorific value of the preheated coal gas of bituminous coal in O2/CO2 is up to 1.3 times that in air. During the preheating process of semi-coke, CH4 and HCN occupy a discreet proportions of preheating coal gas. Fuel characteristics and preheating atmosphere have no effect on the particle size of preheated coal char. Under an O2/CO2 atmosphere, the highest BET surface area of preheated coal char of bituminous coal is up to 30 times that of raw coal and that of semi-coke is up to 40 times that of raw coal. The carbon structure modification ratio of preheated coal char during the preheating process of bituminous coal is larger than that during the preheating process of semi-coke. With the increase in the concentration of oxygen in the primary stream, the NO emission decreased during the bituminous coal combustion process but increased during the semi-coke combustion process. In addition, the main generation path of NO in the reduction zone in O2/CO2 is NH3-NH2-NH-HNO-NO. In O2/CO2, the total promotion effect of reactions on NO formation in the combustion process of semi-coke preheated fuel is larger than that of bituminous coal.

Effects of Water Injection Strategies on Oxy-Fuel Combustion Characteristics of a Dual-Injection Spark Ignition Engine

Currently, global warming has been a serious issue, which is closely related to anthropogenic emission of Greenhouse Gas (GHG) in the atmosphere, particularly Carbon Dioxide (CO2). To help achieve carbon neutrality by decreasing CO2 emissions, Oxy-Fuel Combustion (OFC) technology is becoming a hot topic in recent years. However, few findings have been reported about the implementation of OFC in dual-injection Spark Ignition (SI) engines. This work numerically explores the effects of Water Injection (WI) strategies on OFC characteristics in a practical dual-injection engine, including GDI (only using GDI), P50-G50 (50% PFI and 50% GDI) and PFI (only using PFI). The findings will help build a conceptual and theoretical foundation for the implementation of OFC technology in dual-injection SI engines, as well as exploring a solution to increase engine efficiency. The results show that compared to Conventional Air Combustion (CAC), there is a significant increase in BSFC under OFC. Ignition delay (θF) is significantly prolonged, and the spark timing is obviously advanced. Combustion duration (θC) of PFI is a bit shorter than that of GDI and P50-G50. There is a small benefit to BSFC under a low water-fuel mass ratio (Rwf). However, with the further increase of Rwf from 0.2 to 0.9, there is an increment of 4.29%, 3.6% and 3.77% in BSFC for GDI, P50-G50 and PFI, respectively. As WI timing (tWI) postpones to around −30 °CA under the conditions of Rwf ≥ 0.8, BSFC has a sharp decrease of more than 6 g/kWh, and this decline is more evident under GDI injection strategy. The variation of maximum cylinder pressure (Pmax) and combustion phasing is less affected by WI temperature (TWI) compared to the effects of Rwf or tWI. BSFC just has a small decline with the increase of TWI from 298 K to 368 K regardless of the injection strategy. Consequently, appropriate WI strategies are beneficial to OFC combustion in a dual-injection SI engine, but the benefit in fuel economy is limited.

Effects of hydrogen addition to methane on the thermal and ignition delay characteristics of fuel-air, oxygen-enriched and oxy-fuel MILD combustion

The present study investigated the effect of adding hydrogen to methane on the thermal characteristics and ignition delay in methane-air, oxygen-enriched and oxy-fuel MILD combustion. For this purpose, numerical simulation of MILD furnace is performed by k-ε turbulence, modified EDC combustion, and DO radiation models. Additionally, a well stirred reactor (WSR) analysis alongside with CFD simulations is used for getting the better insight of combustion process and numerical results. The results show that H2 addition to CH4 provides a more uniform temperature field with higher peak and average temperatures under a similar oxidizer atmosphere. Also, more ignition delay time (IDT) obtained by the replacement of CO2 with N2, can be compensated by consideration of H2 in the fuel composition. This study implies that the use of H2 as an additive to methane is an effective strategy for conversion of methane-air to oxy-fuel combustion system with almost identical thermal and ignition characteristics.

Effects of CO2 and H2O on oxy-fuel combustion characteristics and structural evolutions of Zhundong coal pellet at fast heating rate

To comprehensively investigate the combustion characteristics and structural evolutions of Zhundong coal pellet at fast heating rate in O2/N2, O2/CO2 and O2/H2O atmospheres, the real-time mass loss, temperature and combustion images were directly obtained on a novel concentrating photothermal reactor with heating rate of 4800 °C/min. The structural features of the coal/char with different holding times were analyzed by FT-IR and Raman. The experimental results showed that the maximum temperature and the maximum mass loss rate of coal pellet increased with the increasing of H2O concentration but decreased with the increasing of CO2 concentration. Under the experimental condition with the fast heating rate, CO2 prolonged while H2O shortened the ignition delay of coal pellet. In the initial stage of coal combustion, faster consumption rates of all functional groups were evidenced in O2/H2O while slower consumption rates were evidenced in O2/CO2 compared with those in O2/N2. Raman band area ratio I(Gr+Vl+Vr)/ID of chars also exhibited that the less condensed char was observed in O2/CO2 but more condensed char was obtained in O2/H2O. Such results indicated that the coal conversion was slowed down with the addition of CO2 but accelerated with the addition of H2O in the initial stage at fast heating rate. The specific reaction rates were reasonably characterized by the Raman band area ratio of char in O2/N2, O2/CO2 and O2/H2O atmospheres, and they were accorded with the second-order function relationship expressions.

Numerical study on the auto-ignition characteristics of methane oxy-fuel combustion highly diluted by CO2

The methane oxy-fuel combustion highly diluted by CO2 at supercritical region has the best potential for its near-zero emission characteristics and high thermal efficiency, while its auto-ignition characteristic is still not clear. In current investigation, a model with detailed chemical kinetic mechanism was introduced to research its ignition delay times (IDs). Results showed that the fold points in low-temperature and high-pressure region is due to CH3O2 which only involved in Aramco-Mech 1.3. When temperature increases, the inhibition of the termination reactions plays a dominate role at low pressure, while the promotion of the branching reactions contributes more to the acceleration of ignition at high pressure. Five dominant pathways and their variations were clarified to depict the inhibition effect of the ratio of CO2/O2. Based on the newly proposed combustion mode, it was found that temperature dependence of the nonnegligible CO2 collision effect is opposite under low and high pressure with full-oxy combustion mode. This investigation extended the research region to higher pressure and comprehensively studied the relevant factors on the auto-ignition which not only provides theoretical reference for the chemical kinetics study of methane, but also contributes to the further researches of EGR, SCF and near-zero emissions technologies.

Experimental investigation and demonstration of pilot-scale combustion of oil-water emulsions and coal-water slurry with pronounced water contents at elevated temperatures with the use of pure oxygen

In this study, a high-temperature combustion chamber was fueled with oil-water-emulsions (OWE) and coal-water-slurry (CWS) from pyrolytic carbon black in order to experimentally examine the feasibility of co-processing low-calorific value fuels in industrial high-temperature applications by using pure oxygen as oxidizer. The present paper is the first report on the oxy-fuel combustion characteristics of liquid fuels with a pronounced water content including flame characteristics, temperature distribution, thermal output and emission measurements in a semi-industrial combustion chamber at a thermal input of 300 kW and ambient pressure. The obtained results demonstrated the beneficial character of oxy-fuel combustion and showed that co-processing of OWE and CWS from pCB with pronounced water contents is technically feasible. A stable oxy-fuel combustion of OWE was achieved with water contents of up to 75 wt%. In addition, a successful combustion of CWS with a water content of 65 wt% and oxygen concentrations above 50 vol.% was observed. The obtained results further demonstrated the beneficial character of oxy-fuel combustion of OWE and CWS especially with regard to reduced NOx emissions. The combustion of OWE with a water content of 75 wt% resulted in a significant reduction of the NOx concentration compared to pure heating oil, namely from 760 to 110 ppm, whereas the maximum temperature of the combustion chamber decreased only slightly, while in the case of CWS combustion, the concentration of CO emitted decreased significantly from 34 to 9 ppm by increasing the oxygen concentration in the oxidizer from 50 to 100 vol.%.

Study on scale-up characteristics of oxy-fuel combustion in circulating fluidized bed boiler by 3D CFD simulation

The oxy-fuel combustion CFB technology as a promising carbon capture technologies needs to study the scale-up process for the commercial diffusion. Numerical simulation would be a rational tool to investigate the gas-solid flow and oxy-fuel combustion process before constructing an expensive and complicated industry-scale plant. A three-dimensional (3D) CFD simulation according to the Eulerian-Lagrangian approach was applied to simulate the hydrodynamics of gas-solid flow and oxy-fuel combustion process in lab-scale, pilot-scale and industry-scale CFB boiler (from 0.1 MWth to 330 MWe). Results present the differences of the boiler configuration, the gas-solid flow and the oxy-fuel combustion characteristics between lab-scale, pilot-scale and industry-scale CFB boilers. The cross-section thermal load gradually decreased, while the cross-section area increased with the thermal inputs increased. In the lab-scale and pilot-scale oxy-fuel CFB, the particle velocity field was more uniform than that in the industry-scale CFB. The carbon conversion ratio increased with an increase in the thermal input. The emission of CO, NO and SO2 in the industry-scale oxy-fuel CFB boilers was lower than those in the lab-scale and pilot-scale. A larger oxy-fuel combustion power plant is beneficial to carbon capture and low pollutant emission. The results would be beneficial to the design and operation of industry-scale oxy-fuel CFB.

Oxy-Fuel Combustion Characteristics of Pulverized Coal under O2/Recirculated Flue Gas Atmospheres

Oxy-fuel combustion is an effective technology for carbon capture and storage (CCS). Oxy-combustion for coal-fired power stations is a promising technology by which to diminish CO2 emissions. Unfortunately, little attention has been paid to the oxy-combustion characteristics affected by the combustion atmosphere. This paper is aimed at investigating the oxy-fuel combustion characteristics of Australian coal in a 0.3 MWth furnace. In particular, the influences of various oxygen flow rates and recirculated flue gas (RFG) on heating performance and pollutant emissions are examined in O2/RFG environments. The results show that with increases in the secondary RFG flow rate, the temperatures in the radiative and convective sections decrease and increase, respectively. At a lower oxygen flow rate, burning Australian coal emits lower residual oxygen and NO concentrations. In the flue gas, a high CO2 concentration of up to 94.8% can be achieved. Compared to air combustion, NO emissions are dramatically reduced up to 74% for Australian coal under oxy-combustion. Note that the high CO2 concentrations in the flue gas under oxy-coal combustions suggest great potential for reducing CO2 emissions through carbon capture and storage.

Characteristics of Oxyfuel Combustion in Lean-Premixed Multihole Burners

This paper presents the results of an experimental investigation of combustion characteristics of nonswirl CH₄/CO₂/O₂ flames under atmospheric pressure in a lean-premixed multihole burner’s gas-turbine model combustor. The CO₂ and O₂ are well premixed and then channeled to a test rig, which is made up of a 2 in. diameter 1 m long pipe to premix the fuel and oxidizers before getting to the multihole burner. The burner consists of main holes and subholes that prevent flashbacks that may lead to rig explosion. The burner imparts jet to the premixed measured composition of CH₄/CO₂/O₂. The results indicated that the adiabatic flame temperature (Tₐd) is a strong controlling parameter in quantifying the stability map and combustor flame shape; variation in oxygen fraction and equivalence ratio influence the flame shape, whereas the equivalence ratio (ϕ) is the major controlling parameter of temperature distribution within the combustor. The results also indicated that the stability map does not follow the lines of constant power density, mass flow rate of the mixture (mₘᵢₓ), and Reynolds number (Re).

Pressurized oxy-fuel combustion characteristics of single coal particle in a visualized fluidized bed combustor

Pressurized oxy-fuel combustion (POFC) is recognized as the second generation of oxy-fuel combustion for the reduction of CO2 emissions, which has gradually gained more and more attention recently. In this work, the influence of pressure on the combustion characteristics (i.e., ignition, volatiles combustion, char combustion) of a single lignite particle was investigated in a pressurized visualized fluidized bed combustor under O2/N2 and O2/CO2 atmospheres. The combustion process was recorded by a color video camera, and the temperatures of volatiles flame and char particle were measured by pre-calibrated two-color pyrometry. The results indicated that increasing the overall pressure and increasing the oxygen volume fraction to a same partial pressure of oxygen will affect the ignition delay time (td) differently. td increased with the operating pressure at the same oxygen volume fraction, but decreased with the increase of oxygen volume fraction under atmospheric pressure. Pressurization significantly changes the coal flame shape and the volatiles flame becomes longer and thinner at a higher pressure. At the same oxygen volume fraction, higher flame and char temperatures and shorter burnout time (tb) of coal particle were observed under a higher pressure due to the better mass transfer of oxygen. With the same oxygen partial pressure, particle temperature is lower at high overall pressure than that at high oxygen volume fraction, which is probably a potential advantage of pressurized oxy-fuel combustion to resist agglomeration. Moreover, compared with atmospheric oxygen-combustion, the gasification of char particle in pressurized oxygen-combustion is more remarkable and cannot be neglected.

TGA and kinetic study of different torrefaction conditions of wood biomass under air and oxy-fuel combustion atmospheres

Combustion and oxy-fuel combustion characteristics of torrefied pine wood chips were investigated by Thermogravimetric Analysis (TGA). Three torrefaction temperatures (250, 300, and 350 °C) and two residence times (15 and 30 min) were considered. Experiments were carried out at three heating rates of 10, 20, and 40 °C/min. The isoconversional kinetic methods of FWO, KAS, and Friedman were employed to estimate the activation energies. The assessment of uncertainty in obtaining the activation energy values was also considered. The obtained results indicated that due to torrefaction, the O/C and H/C atomic ratios decreased, resulting the 300ºC-30 min and 350ºC-15 min torrefied biomass to be completely embedded in lignite region in van-Krevelen's diagram. Oxy-fuel combustion affected the decomposition of cellulose and lignin components of biomass while the impact on the hemicellulose component was negligible. The kinetic analysis revealed that with the evolution of conversion degree, the activation energy values increased during hemicellulose degradation, remained approximately constant during cellulose decomposition and showed a sharp decrease for lignin decomposition. The activation energy trends were comparable in both air and oxy-fuel combustion conditions, however slight changes in activation energy values were noticed. The highest activation energy value was obtained for 250ºC-30 min torrefied biomass at 183.40 kJ/mol and the lowest value was 72.93 kJ/mol for 350ºC-15 min biomass. The uncertainty values related to FWO method were lower than KAS and Friedman methods. The uncertainty values for FWO and KAS methods were at the range of 5–15%.

Performance Analysis of Air and Oxy-Fuel Laminar Combustion in a Porous Plate Reactor

Greenhouse gas emissions from the combustion of fossil fuels pose a serious threat to global warming. Mitigation measures to counter the exponential growth and harmful impact of these gases on the environment require techniques for the reduction and capturing of carbon. Oxy-fuel combustion is one such effective method, which is used for the carbon capture. In the present work, a numerical study was carried out to analyze characteristics of oxy-fuel combustion inside a porous plate reactor. The advantage of incorporating porous plates is to control local oxy-fuel ratio and to avoid hot spots inside the reactor. A modified two-steps reaction kinetics model was incorporated in the simulation for modeling of methane air-combustion and oxy-fuel combustion. Simulations were performed for different oxidizer ratios, mass flow rates, and reactor heights. Results showed that that oxy-combustion with an oxidizer ratio (OR) of 0.243 could have the same adiabatic flame temperature as that of air-combustion. It was found that not only does OR need to be changed, but also flow field or reactor dimensions should be changed to achieve similar combustion characteristics as that of air-combustion. Fifty percent higher mass flow rates or 40% reduction in reactor height may achieve comparable outlet temperature to air-combustion. It was concluded that not only does the oxidizer ratio of oxy-combustion need to be changed, but the velocity field is also required to be matched with air-combustion to attain similar outlet temperature.

Effect of oxygen concentration on oxy-fuel combustion characteristic and interactions of coal gangue and pine sawdust

Coal gangue is an inevitable coal waste from coal mine, which results in serious environmental problems. Oxy-fuel firing of coal waste and biomass waste is an alternative technology for efficient and clean utilization and CO2 reduction of coal waste. In this study, the oxy-fuel combustion characteristics and interactions of coal gangue and pine sawdust were investigated using thermogravimetric analysis, with a focus on the effect of oxygen concentration on interactions between coal gangue and pine sawdust during oxy-fuel combustion. The oxy-fuel combustion of pine sawdust had two obvious stages, including the release of volatile matter and the combustion of the remaining char, which differed from oxy-fuel combustion of coal gangue with one overlapped stage of devolatilization and char oxidation. Moreover, the addition of pine sawdust could improve the oxy-fuel combustion reactivity of coal gangue. The significant deviations between the experimental derivative thermogravimetric curves and theoretical derivative thermogravimetric curves for the blends indicated that interactions between coal gangue and pine sawdust had occurred in the temperature range of 400–600 °C. The interaction mechanism was primarily thermal effect between coal gangue and pine sawdust during oxy-fuel combustion. The oxygen concentration had a significant effect on the interactions between coal gangue and pine sawdust. The increase of oxygen concentration from 20% to 40% could improve interactions between coal gangue and pine sawdust obviously. However, relative small improvement of interactions was detected between coal gangue and pine sawdust when oxygen concentration was further increased from 60% to 80%. This was related to the difference of rate controlling factor for oxy-fuel combustion reaction under various oxygen concentrations.