Effect of hydrogen addition on combustion and emission characteristics of methane fuelled upward swirl can combustor

The present research aims to assess the potential of hydrogen in the form of a supplementary fuel to accelerate combustion chemistry and reduce CO emissions of methane fuelled upward swirl gas turbine combustor. Effects of hydrogen enrichment on flame characteristics and chemical kinetics are analysed using Large Eddy Simulations (LES). Flame visualization is performed and measurements of temperature and emissions at the exit of combustor are reported. For the same energy input, flames are relatively broader and shorter at higher hydrogen concentrations. Augmentation of hydrogen is advantageous in terms of flame velocity, temperature, rate of chemical reactions and CO emissions. Higher flame temperature favours NO_x emissions at higher hydrogen content. At a constant volumetric fuel flow, reduction in carbon-generated species is attributed to hydrocarbon substitution and chemical kinetic effects are less. Hydrogen addition increases flame temperature, decreases flame dimensions and reduces CO emissions with marginal increase in NO_x emissions.     

Effects of hydrogen addition on combustion characteristics of a methane fueled MILD model combustor

Combined with need of the carbon emissions, the feasibility of Moderate or Intense Low-oxygen Dilution (MILD) combustion fueled with hydrogen/methane blends needs to be investigated. This paper discusses the pollutant emissions, the stable operating range and the flame morphology for a jet-induced MILD model combustor. The hydrogen/methane volume ratios range 0:10 to 5:5. The NO_x emissions are less than 5 ppm@15%O₂ when the hydrogen content is less than 50% by volume in the atmospheric conditions. The calculation using chemical reactor network (CRN) model demonstrates that the effect of heat loss on NO_x emissions increases as the adiabatic combustion temperature increases, which is consistent with the experimental results. The maximum OH1 signal intensity increased at higher hydrogen content, especially when the hydrogen content exceeds 30% by volume. Due to the increase in turbulent burning velocity and the enhancement in the reaction intensity, the reaction zones shrink with increasing hydrogen content. In addition, with increasing hydrogen content, the stable operation range of the combustor becomes narrower, and the stable combustion is not maintained when the hydrogen content exceeds 50% by volume. The findings of the paper help to further understand the effect of hydrogen content on the formation of MILD combustion in the jet-induced combustor.     

Effects of hydrogen addition on methane catalytic combustion in a microtube

The objective of this paper is to study hydrogen-assisted catalytic combustion of hydrocarbon on a microscale experimentally. In the experiment, neither methane nor ethane can be ignited by itself, but hydrogen can be ignited and burn steadily in this tube. It is found that there is no significant difference between hydrogen added to the hydrocarbon and hydrogen alone as fuel without the platinum thermocouple, but the temperature will increase and the efficiency of methane combustion will increase considerably when the platinum thermocouple was put into the microtube. Methane can burn steadily without adding hydrogen after ignited by hydrogen. It can be concluded that the addition of hydrogen to hydrocarbon is favorable to ignition and the platinum thermocouple catalyzes the hydrocarbon combustion. The experiment result showed that the added hydrogen acts as an assistant for ignition and expands the range for methane steady burn. After igniting, methane can burn steadily alone at catalytic condition. This is useful for optimization microcombustion fuel.     

A numerical study on the combustion limits of mesoscale methane jet flames with hydrogen addition

A meso-scale jet flame model was established for the flame ports of domestic gas stoves. The influences of hydrogen addition ratio (β = 0%–25%) on the combustion limits were explored. The results show that with the increase of hydrogen addition ratio, the blow-off limit increases obviously, while the extinction limit decreases slightly, namely, the combustible range expands significantly. Quantitative analysis was carried out in terms of chemical effect and thermal effect. It was found that hydrogen addition will reduce O₂ fraction in the pre-mixture for a constant equivalence ratio. Under near-extinction limit condition, since the flame is located at the nozzle exit, the external O₂ cannot be entrained into or diffuse into the upstream of the flame, which leads to the decrease of reaction rate. However, for the near-blow-off cases, the external O₂ can be entrained and diffuse into the flame, which compensates the difference of O₂ content in the pre-mixture. Therefore, the combustion reaction is enhanced by hydrogen addition because more H radicals can be produced. In addition, as the flame is located closer to the tube with the increase of hydrogen addition ratio, heat transfer between flame and tube wall is augmented and the preheating of fresh mixture is strengthened by the inner tube wall. This heat recirculation effect becomes especially notable in low velocity cases. In conclusion, the extension of extinction limit by hydrogen addition is attributed to the thermal effect, while the increase of blow-off limit is mainly due to the intensification of chemical effect.     

辣椒厌氧发酵产H2和CH4的试验研究

以辣椒为原料,以实验室长期驯化的猪粪发酵残留物为底物的混合厌氧消化污泥作为接种物,在常温下进行批量发酵,发酵料液体积400 ml,RHT=86 d.TS质量分数为6.36%时,进行厌氧发酵产H2,产H2结束后使用NaOH溶液调节pH值为7.42,继续发酵产CH4.结果表明:辣椒产氢潜力(TS)为103.0L/kg,VS产氢潜力145.7 L/kg;TS产甲烷潜力为254.6 L/kg,VS产甲烷潜力为276.9 L/kg,其TS能量利用潜力达2 222.4 kJ/kg.     

掺氢比对低排放燃烧室性能影响研究

为了探究传统天然气燃气轮机对氢气燃料的适应性,基于现役某型工业低排放燃气轮机结构和性能,用数值模拟方法分析了燃料中氢气比例对低排放燃烧室性能的影响,确定了燃烧室燃用甲烷和氢气燃料的换用性能。研究表明：在1.0额定工况,掺氢比小于等于30%时,燃烧室不发生回火,喷嘴内部和火焰筒肩部回流区的温度以及燃烧室的总压损失随掺氢比的升高而升高,NOx排放体积分数小幅升高,CO排放体积分数减少;当掺氢比大于30%时,燃烧室发生回火,喷嘴和火焰筒肩部回流区温度、总压损失、NOx排放体积分数大幅升高,CO排放基本为零。在其他工况下,负荷变化对燃烧室边界条件影响较为复杂,对喷嘴回火边界影响无单调性变化规律。     

Experimental study of the effects of hydrogen addition on the thermoacoustic instability in a variable-length combustor

The current study examined the self-excited thermoacoustic instability of hydrogen/methane premixed flames using a variable-length combustor (300–1100 mm). The global dynamic pressure, heat release rate oscillation, together with the flame dynamics were studied. Results showed that both the hydrogen concentration and the chamber length were critical in determining the acoustic oscillation mode and instability trend. Low-frequency primary acoustic modes (<200 Hz) were mainly excited when the hydrogen concentration was low, whereas primary acoustic modes with relatively higher frequencies (~400 Hz) tended to occur in cases with a high hydrogen proportion (>40%). For primary acoustic modes lower than 200 Hz, the primary oscillation frequency tended to increase linearly with a rising hydrogen proportion. Heat release oscillation and flame dynamics analyses demonstrated that for the flame with large-scale shape deformation, the initial addition of hydrogen would intensify the heat release oscillation. Nevertheless, a further increase in the hydrogen level tended to inhibit the heat release oscillation by weakening the flame shape deformation. Eventually, a sufficient high-level of hydrogen addition would weaken the primary acoustic modes that have similar frequencies.     

Control of methane flame properties by hydrogen fuel addition: Application to power plant combustion chamber

This study presents a numerical investigation of the effects of mixing methane/hydrogen on turbulent combustion processes taking place in a burner similar to that integrated in gas turbine power plants. Thereby, in comparison to the reference case where the burner is fuelled by 100% of methane, the variations of the axial velocity field, temperature field and mass fraction of carbon monoxide field are examined for different percentages of hydrogen fuel injection. The computed results, obtained by using the software Fluent-CFD, are compared and validated against experimental reference data. Results show that the hydrogen addition to the methane has an impact on all physical and chemical parameters of the reactive system.     

Numerical study of hydrogen‐enriched methane–air combustion under ultra‐lean conditions

The demand for gas turbines that accept a variety of fuels has continuously increased over the last decade. Understanding the effects of varying fuel compositions on combustion characteristics and emissions is critical to designing fuel‐flexible combustors. In this study, the combustion characteristics and emissions of methane and hydrogen‐enriched methane were both experimentally and numerically investigated under ultra‐lean conditions (Ø ≤ 0.5). This study was performed using global mechanisms with a one‐step mechanism by Westbrook and Dryer and a two‐step mechanism with an irreversible and reversible CO/CO₂ step (2sCM1 and 2sCM2). Results show that the 2sCM2 mechanism under‐predicted the temperature, major species, and NO_x by more than 100% under ultra‐lean conditions; thus, we proposed a modified‐2sCM2 mechanism to better simulate the combustion characteristics. The mechanisms of Westbrook, 2sCM1, and modified 2sCM2 predicted the temperature and the CO₂ emission with an average deviation of about 5% from the experimental values. Westbrook and 2sCM1, however, over‐predicted the NO_x emission by approximately 81% and 152%, respectively, as compared with an average under‐prediction of 11% by the modified‐2sCM2 mechanism. The numerical results using the proposed modified‐2sCM2 mechanism shows that the presence of hydrogen in the fuel mixture inhibits the oxidation of methane that led to the formation of unburned hydrocarbons in the flame. We also showed that for any given fuel compositions of H₂/CH₄, there is an optimum equivalence ratio at which the pollutant emissions (CO and NO_x) from the combustor are minimal. Zero CO and 5 ppm NO_x emissions were observed at the optimal equivalence ratio of 0.45 for a fuel mixture containing 30% H₂. The present study provides a basis for ultra‐lean combustion toward achieving zero emissions from a fuel‐flexible combustor. Copyright © 2016 John Wiley & Sons, Ltd.     

甲烷催化制氢气的研究进展

阐述了甲烷催化制氢技术研究取得的主要进展，对各种制氢工艺方法、催化剂的种类和性能、反应器的类型、催化剂积炭等方面进行了详细的论述。     

Effect of hydrogen addition to intake gas on combustion and exhaust emission characteristics of a diesel engine

The present study experimentally investigated the performance and emission characteristics of the diesel engine with hydrogen added to the intake air at late diesel-fuel injection timings. The diesel-fuel injection timing and the hydrogen fraction in the intake mixture were varied while the available heat produced by diesel-fuel and hydrogen per second of diesel fuel and hydrogen was kept constant at a certain value. NO showed minimum at specific hydrogen fraction. The maximum rate of incylinder pressure rise also showed minimum at 10 vol. % hydrogen fraction. However, it is desirable to set the maximum rate of incylinder pressure rise less than 0.5 MPa/deg. to realize low level of combustion noise and NO emission. We attempt to reduce further NO and smoke emissions by EGR. As the result, in the case of the diesel-fuel injection timing of −2 °. ATDC with 3.9 vol. % hydrogen addition, the smoke emission value was 0%, NO emission was low, the cyclic variation was low, and the maximum rate of incylinder pressure rise was acceptable under a nearly stoichiometric condition without sacrificing indicated thermal efficiency.     

Co-firing hydrogen and dimethyl ether in a gas turbine model combustor: Influence of hydrogen content and comparison with methane

To promote the utilization of hydrogen (H₂) in existing gas turbines, dimethyl ether (DME) was used to co-fire with H₂ in a model combustor. The swirl combustion characteristics of DME/H₂ mixtures were measured under the varying H₂ content up to 0.7. The results show that the flow velocity elevates as the H₂ content increases, which is associated with the increased flame temperature. The OH level firstly increases and subsequently keeps nearly unchanged as the H₂ content increases. Meanwhile, the OH area nonlinearly increases with the increasing H₂ content. Moreover, the increasing H₂ content induces almost linearly decreased lean blowout limit (LBO), increased NO emission, and intensified combustion acoustics. Furthermore, the combustion characteristics of the 0.46DME/0.54H₂ mixture and CH₄ with the same volumetric heat value were compared. The 0.46DME/0.54H₂ flame displays lower LBO and higher NO emission than the CH₄ flame, which mainly results from the higher reactivity of 0.46DME/0.54H₂ mixture.     

Effects of hydrogen peroxide on combustion enhancement of premixed methane/air flames

Hydrogen peroxide is generally considered to be an effective combustion promoter for different fuels. The effects of hydrogen peroxide on the combustion enhancement of premixed methane/air flames are investigated numerically using the PREMIX code of Chemkin collection 3.5 with the GRI-Mech 3.0 chemical kinetic mechanisms and detailed transport properties. To study into the enhancement behavior, hydrogen peroxide is used for two different conditions: (1) as the oxidizer substituent by partial replacement of air and (2) as the oxidizer supplier by using different concentrations of H₂O₂. Results show that the laminar burning velocity and adiabatic flame temperature of methane flame are significantly enhanced with H₂O₂ addition. Besides, the addition of H₂O₂ increases the CH₄ consumption rate and CO production rate, but reduces CO₂ productions. Nevertheless, using a lower volumetric concentration of H₂O₂ as an oxidizer is prone to reduce CO formation. The OH concentration is increased with increasing H₂O₂ addition due to apparent shifting of major reaction pathways. The increase of OH concentration significantly enhances the reaction rate leading to enhanced laminar burning velocity and combustion. As to NO emission, using H₂O₂ as an oxidizer will never produce NO, but NO emission will increase due to enhanced flame temperature when air is partially replaced by H₂O_2.     

Optimization of a counter-flow microchannel reactor using hydrogen assisted catalytic combustion for steam reforming of methane

The objective of this study is to optimize a microchannel reactor using hydrogen assisted catalytic combustion for steam reforming of methane. Hydrogen assisted catalytic combustion does not require preheating because the catalytic combustion of hydrogen occurs at room temperature. After start-up by hydrogen catalytic combustion, fuels of hydrogen and methane were changed to methane. The geometric configuration of the counter-flow reactor was optimized by the simulation model under steady state condition. The hydrogen flow rate in the counter-flow reactor was also optimized by transient simulations using the response surface methodology. As a result, the counter-flow reactor showed extremely short start-up time because of the optimized configuration and the optimized hydrogen flow rate. Hot spots were avoided because of the hydrogen shut-off after start-up. The operating characteristics of the counter-flow reactor were compared with those of the co-flow reactor.     

Numerical study of the physical and chemical effects of hydrogen addition on laminar premixed combustion characteristics of methane and ethane

Methane and ethane are taken as the research objects. Using H₂ as diluent, based on Chemkin II/Premix Code and modified detailed chemical reaction mechanism: GRI 3.0*-Mech (introducing three hypothetical substances of FH₂, FO₂ and FN₂), the physical and chemical effects of hydrogen on laminar burning velocities (LBVs), adiabatic flame temperatures (AFTs), net heat release rates (NHRRs) and elementary reactions responsible for temperature changes of two alkanes under different equivalence ratios were analyzed and determined. Results showed that the chemical effect of H₂ promotes the LBVs and ATFs of methane and ethane, while the physical effect decreases the two parameters. In addition, the physical effects of H₂ inhibit the chemical reactions of methane and ethane, resulting in the decrease of NHRRs. The chemical effect of H₂ accelerates the process of chemical reaction and obviously increases the NHRRs. The two most vital elementary reactions that promote the temperature rise of methane and ethane are H + O₂ <=> OH + O and CO + OH <=> H + CO₂. The important reactions responsible for inhibiting the temperature rise are H + CH₃(+M) <=> CH₄(+M) and H + O₂ + H₂O <=> HO₂ + H₂O.     

Predicting radiative characteristics of hydrogen and hydrogen/methane jet fires using FireFOAM

A possible consequence of pressurized hydrogen release is an under-expanded jet fire. Knowledge of the flame length, radiative heat flux as well as the effects of variations in ground reflectance is important for safety assessment. The present study applies an open source CFD code FireFOAM to study the radiation characteristics of hydrogen and hydrogen/methane jet fires. For combustion, the eddy dissipation concept for multi-component fuels recently developed by the authors in the large eddy simulation (LES) framework is used. The radiative heat is computed with the finite volume discrete ordinates model in conjunction with the weighted sum of grey gas model for the absorption/emission coefficient. The pseudo-diameter approach is used in which the corresponding parameters are calculated using the formulations of Birch et al. [24] with the thermodynamic properties corrected by the Able-Noble equation of state. The predicted flame length and radiant fraction are in good agreement with the measurements of Schefer et al. [2], Studer et al. [3] and Ekoto et al. [6]. In order to account for the effects of variation in ground surface reflectance, the emissivity of hydrogen flames was modified following Ekoto et al. [6]. Four cases with different ground reflectance are computed. The predictions show that the ground surface reflectance only has minor effect on the surface emissive power of the smaller hydrogen jet fire of Ekoto et al. [6]. The radiant fractions fluctuate from 0.168 to 0.176 close to the suggested value of 0.16 by Ekoto et al. [6] based on the analysis of their measurements.     

Effects of hydrogen addition on the characteristics of a biogas diffusion flame

This work describes an experimental study of the effect of hydrogen addition on the stability and impingement heat transfer behaviors of a biogas diffusion flame. The amount of hydrogen added was varied from 5% to 10% of the biogas by volume. The results show that upon hydrogen addition in the biogas flame, there is a corresponding change in the appearance, stability and heat transfer characteristics of the flame.     

Thermodynamic analysis of hydrogen production via sorption-enhanced steam methane reforming in a new class of variable volume batch-membrane reactor

Combined reaction–separation processes are a widely explored method to produce hydrogen from endothermic steam reforming of hydrocarbon feedstock at a reduced reaction temperature and with fewer unit operation steps, both of which are key requirements for energy efficient, distributed hydrogen production. This work introduces a new class of variable volume batch reactors for production of hydrogen from catalytic steam reforming of methane that operates in a cycle similar to that of an internal combustion engine. It incorporates a CO₂ adsorbent and a selectively permeable hydrogen membrane for in situ removal of the two major products of the reversible steam methane reforming reaction. Thermodynamic analysis is employed to define an envelope of ideal reactor performance and to explore the tradeoff between thermal efficiency and hydrogen yield density with respect to critical operating parameters, including sorbent mass, steam to methane ratio and fraction of product gas recycled. Particular attention is paid to contrasting the variable volume batch-membrane reactor approach to a conventional fixed bed reaction–separation approach. The results indicates that the proposed reactor is a viable option for low temperature distributed production of hydrogen from methane, the primary component of natural gas feedstock, motivating a detailed study of reaction/adsorption kinetics and heat/mass transfer effects.     

Surface effects on flammable extent of hydrogen and methane jets

Studies on the effect of surfaces on the extent of the flammable cloud of high-pressure horizontal and vertical jets of hydrogen and methane are performed using CFD numerical simulations. For the horizontal jets, two scenarios pertaining to the location of the surface are studied: horizontal surface (the ground), and vertical surface (side wall). For a constant flow rate release, the extent of the flammable cloud is determined as a function of time. Effects of the proximity of the surface on the flammable extent along the axis of the jet and its impact on the maximum extent of the flammable cloud is explored and compared for both hydrogen and methane. The results are also compared to the predictions of the Birch correlations for flammable extents. It is found that the presence of a surface and its proximity to the jet centerline result in a pronounced increase in the extent of the flammable cloud compared to a free jet.