Publications

Blowoff propensity, CRZs and flow turbulent nature using various syngases for gas turbines

This paper presents a series of experiments and numerical simulations using commercial software (ANSYS) to determine the behaviour and impact on the blowoff process with various geometries and simulated syngas compositions at fixed power outputs. Experiments were performed using a generic premixed swirl burner. The Central Recirculation Zone and the associated turbulent structure contained within it were obtained through CFD analyses providing details of the structures and the Damkolher Number (Da) close to blowoff limits. The results show how the strength and size of the recirculation zone are highly influenced by the blend, with a shift of Da and turbulence based on carbon-hydrogen ratio, shearing flows and Reynolds number. Instabilities such as thermoacoustics, flashback, autoignition and blowoff are highly affected by the flow structures and chemical reactions/diffusivity. Moreover, it has been observed that turbulence close to the boundaries of the central recirculation zone, a region of high stability for swirling flows, is highly altered by the chemical characteristics of the fuel blends. In terms of blowoff, the phenomenon is still not entirely understood. As the process occurs, its theoretical limits do not match its real behaviour. Therefore, one possibility could be the difference in turbulence and Da numbers across the flame, being critical at the base of the flame where the system is stabilized.

Investigation of boundary layer flashback enhancement in swirl burner using woven wire mesh

Experimental investigation of the Effect of Air Diffusive injection on premixing swirl flames

In recent decades there has been a strong trend towards the use of lean premixed combustion in order to produce gas turbine systems that are compliant with air quality regulations. Additional growing interest in using alternative fuels has drawn many problems in terms of operational stability, thus there have been extensive investigations to achieve more stable and reliable combustion systems. Flame flashback has been one of the major instability problems that have the potential of causing considerable damage to the combustion system hardware in addition to significant increase of emissions such as CO and NOx. Swirl combustors are proven as effective flame stabilisers over wide range of operation conditions due to swirl structures which provide a low velocity region that enables flame anchoring. However the interaction between swirl structures and swirl burner geometries can considerably alter the stability regime downstream the burner exit plane. Using central injectors either as a central bluff body or to inject fuel diffusively have been used successfully to achieve wide stability limits and prevent upstream flame propagation. However, central injectors in swirl combustors can be subject to large amounts of heat, which can cause flashback, subsequently increasing maintenance cost and reducing the predicted operating life of the system. This paper present a series of experiments using a well-characterised tangential swirl burner to investigate the effect of using diffusive air injection on flow field characteristics and how it can affect the lower instability limits through altering the flashback mechanism by Combustion Induced Vortex Breakdown (CIVB). Results show that using diffusive air stream injection affects flashback trends significantly by providing a wider range of stability limits both in terms of equivalence ratio and mass flow rate which implies the possibility of working at higher power outputs compared to the case when using a central body injector. This technique can be considered a promising technology in terms of flexibility of operation because it enables switching to another air stream diameter while maintaining full load operation as opposed to the use of central body injectors.

Experimental and Numerical Comparison of Currently Available Reaction Mechanisms for Laminar flame speed in Hydrogen/Ammonia Flames

No abstract is provided for this article.

Technologies for high-temperature batch annealing of grain-oriented electrical steel: An overview

The production of grain-oriented, electrical steel consists of a series of processes that lead to a product with superior magnetic properties used in transformers due to the low core loss. The unique properties are gained during the process of secondary recrystallization and abnormal grain growth. The abnormal grain growth occurs during a process of special thermal treatment with careful control over the heating rate, pressure, and type of gas used as atmospheric pressure during the process. The process of thermal treatment is known as high-temperature annealing. Investigating of developing the process hardware is crucially important to sustain energy-efficient processes and to maintain excellent final product properties. This research presents an overview of the technology of high-temperature coil annealing (HTCA) furnaces used at Cogent Power Orb, UK. The research focuses on some specific details of running, managing, and controlling the operation of the HTCA furnaces during the annealing process. The research provides energy analysis of the annealing process at Cogent Power Orb. Different factors were examined to identify the main factors that contribute to the high energy consumption. Actual data were collected from the annealing furnace control system. The raw data were processed and analyzed carefully to examine different factors, namely, steel charge weight, furnace on-time, and furnace heating elements. The study focused then on one specific factor, namely, annealing cycle time, and investigated further the way that this factor affects the process energy consumption. It was found that one of the main reasons for the long cycle duration and the high energy consumption is the failure of the heating elements during the cycle. The research discussed the area of improvements in the process hardware with a particular focus on the furnace design and the potential of introducing convection currents to overcome failure in the heating elements and thus reduce the process on time.

Effects of Reynolds number and ammonia fraction on combustion characteristics of premixed ammonia-hydrogen-air swirling flames

Several studies have investigated the effects of equivalence ratio and blending ratio in constant power cases for ammonia-based fuels as ammonia is being investigated extensively as an alternative zero-carbon fuel in recent years. However, in many fields, such as power generation, it is common to operate practical equipment at constant Reynolds number (Re) conditions. To that extent, this study investigates the impact of Re (4000 ≤ Re ≤ 7000), equivalence ratio (0.6 ≤ Φ ≤ 1.45), and ammonia volume ratio (0.55 ≤ XNH3 ≤ 0.9) on the combustion characteristics of NH3/H2 swirling flames. To supplement the experimental work, a previously developed Chemical Reactor Network (CRN) has been used to identify the reaction pathways affecting NOx emissions through reaction analysis. Sampled gas analysis (NO, NO2, N2O, NH3) at the exhaust was reported for the first time at a wide range of equivalence ratios and XNH3 at different Re. At constant Re = 6000, NO and NO2 peaked at around Φ = 0.8 – 0.9, while N2O became substantial at Φ ≤ 0.8 and unburnt ammonia became significant at Φ ≥ 1.05. The chemiluminescence images suggested that at Re = 6000, as XNH3 or Φ increases, the NH2* region expands, and reactions occur further downstream. Furthermore, with decreasing XNH3 at Re = 6000 and Φ = 0.9, the system becomes partially abundant in H2 and H but deficient in O2, suppressing the generation of O and OH radicals, and ultimately also suppressing HNO generation. This leads to the N/NH system reactions becoming dominant and increased NO consumption. NO emissions increased steadily with increasing Re at Φ = 0.8, while at stoichiometry, NO emissions remained somewhat unchanged with changing Re. Findings from this study will aid further in the development of carbon-free zero-emissions systems.

CO2-Argon-Steam Oxy-Fuel Production for (CARSOXY) Gas Turbines

Due to growing concerns about carbon emissions, Carbon Capture and Storage (CCS) techniques have become an interesting alternative to overcome this problem. CO2-Argon-Steam-Oxy (CARSOXY)-fuel gas turbines are an innovative example that integrates CCS with gas turbine powergen improvement. Replacing air-fuel combustion by CARSOXY combustion has been theoretically proven to increase gas turbine efficiency. Therefore, this paper provides a novel approach to continuously supply a gas turbine with a CARSOXY blend within required molar fractions. The approach involves H2 and N2 production, therefore having the potential of also producing ammonia. Thus, the concept allows CARSOXY cycles to be used to support production of ammonia whilst increasing power efficiency. An ASPEN PLUS model has been developed to demonstrate the approach. The model involves the integrations of an air separation unit (ASU), a steam methane reformer (SMR), water gas shift (WGS) reactors, pressure swing adsorption (PSA) units and heat exchanged gas turbines (HXGT) with a CCS unit. Sensitivity analyses were conducted on the ASU-SMR-WGS-PSA-CCS-HXGT model. The results provide a baseline to calibrate the model in order to produce the required CARSOXY molar fraction. A MATLAB code has also been developed to study CO2 compression effects on the CARSOXY gas turbine compressor. Thus, this paper provides a detailed flowsheet of the WGS-PSA-CCS-HXGT model. The paper provides the conditions in which the sensitivity analyses have been conducted to determine the best operable regime for CARSOXY production with other high valuable gases (i.e., hydrogen). Under these specifications, the sensitivity analyses on the (SMR) sub-model spots the H2O mass flow rates, which provides the maximum hydrogen level, the threshold which produces significant CO2 levels. Moreover, splitting the main CH4 supply to sub-supply a SMR reactor and a furnace reactor correlates to best practices for CARSOXY. The sensitivity analysis has also been performed on the (ASU) sub-model to characterise its response with respect to the variation of air flow rate, distillation/boiling rates, product/feed stage locations and the number of stages of the distillation columns. The sensitivity analyses have featured the response of the ASU-SMR-WGS-PSA-CCS-HXGT model. In return, the model has been qualified to be calibrated to produce CARSOXY within two operability modes, with hydrogen and nitrogen or with ammonia as by-products.

Central Recirculation Zone Visualization in Confined Swirl Combustors for Terrestrial Energy

This study characterizes the central recirculation zones formed under combustion conditions, with natural gas as fuel with different geometries and degrees of premixing using a swirl combustor firing into a confinement representative of gas turbine combustors. Phase-locked particle image velocimetry is used as the main method of characterization. The technique enables characterization of the time-dependent behavior of the central recirculation zone and a three-dimensional reconstruction of its boundaries. The central recirculation zone typically had an asymmetric lobed shape and precessed about the central axis. Partially premixed combustion at near-stoichiometric equivalence ratios reduced the coherence of the central recirculation zone and often caused it to nearly disappear, although a small remnant of recirculation could still be found in the three-dimensional space. Lower equivalence ratios strengthened the central recirculation zone considerably, for both non-premixed and partially premixed combustion. Although the central recirculation zone was asymmetric in shape and precessed about the central axis, the precessing vortex core, commonly found in these flows, was found to be significantly suppressed especially when central fuel injectors were used. Its occurrence then became intermittent and irregular. A quarl exit nozzle with a divergent lip was found to reduce flame attachment to the fuel injector.

Experimental and numerical investigation of the effect of diffusive air injection on turbulence generation and flashback propensity in swirl combustors

Combustion instabilities are considered one of the most serious challenges for developing combustion systems through the years. Undesirable issues linked to these phenomena represent a risk for such systems especially in gas turbines and propulsion devices where the propagation of these instabilities can even lead to considerable damages. Flame flashback from the combustion chamber into premixer represents one of the most important combustion instability issue in swirl combustors used in gas turbines. This study proposes an experimental and numerical approach to validate the use of a central air injection in swirl combustors to reduce flame flashback propensity via controlling the turbulence generation at the tip of the flame while pushing the CRZ, thus retarding the appearance of the CIVB, to mitigate the progression of combustion into the system. Results showed the potential of this technique to affect turbulence generation and pushing back the flame into the combustion chamber, increasing operability limits. Very good agreement was achieved between experimental and numerical results, demonstrating that the use of injection through the central core of the system not only controls the position of the recirculation zone but also affects turbulence and mitigates other forms of flame flashback.

Hydrodynamics During the Transient Evolution of Open Jet Flows from/to Wall Attached Jets

Swirl stabilized flows are the most widely deployed technology used to stabilize gas turbine combustion systems. However, there are some coherent structures that appear in these flows close to the nozzle whose occurrence and stability are still poorly understood during transition. The external recirculation zone and the Precessing Vortex Core to/from the Coanda effect are some of them. Thus, in this paper the transition of an Open Jet Flow-Medium Swirl flow pattern to/from a Coanda jet flow is studied using various geometries at a fixed Swirl number. Phase Locked Stereo Particle Image Velocimetry and High Speed Photography experiments were conducted to determine fundamental characteristics of the phenomenon. It was observed that the coherent structures in the field experience a complete annihilation during transition, with no dependency between the structures formed in each of the flow states. Moreover, transition occurs at a particular normalized step size whilst some acoustic shifts in the frequencies of the system were noticed, a phenomenon related to the strength of the vortical structures and vortices convection. It is concluded that a transient, precessing, Coanda Vortex Breakdown is formed, changing flow dynamics. The structure progresses to a less coherent Trapped Vortex between the two states. During the phenomenon there are different interactions between structures such as the Central Recirculation Zone, the High Momentum Flow Region and the Precessing Vortex Core that were also documented.

Fuel-lean ammonia/biogas combustion characteristics under the reacting swirl flow conditions

Ammonia has been identified as a viable energy vector for power generation. Using dual-fuel operation that mixes the ammonia with higher reactivity gaseous fuel can be vital in enhancing ammonia combustion. This study examined the fundamental swirl combustion characteristics of fuel-lean premixed ammonia/biogas via a numerical approach. The flame was established at an input thermal power of 7 kW and a global equivalence ratio of 0.8. The numerical model was validated with biogas emissions data acquired through experimental work. At 20 mm downstream the burner, increased carbon dioxide mass fraction in the biogas lowered the peak flame temperature by around 300 K. Moreover, the deformation of flame temperature radial profiles was also found aggravated as carbon dioxide concentration in the biogas elevated from 0 % to 40 %. The reduction in premixed reactant mixture reactivity not only initiated flame temperature profile deformation but also reduced the peak Damköhler number significantly. The peak Damköhler number was lowered by a factor of ∼ 1.5 when carbon dioxide dilution in the biogas elevated by 40 %. The premixed combustion was directed into the thin reaction flamelets zone with elevated carbon dioxide mass fraction, owing to the intensified flow fluctuation. This, in turn, elevates the normalised flame turbulent propagating speed, gas flow average velocities and turbulent kinetic energy, notwithstanding that heat release rate and averaged laminar flame speed declined. In all, the presence of carbon dioxide has been shown to lower the ammonia/methane mixture reactivity whilst escalating the reacting flow fluctuation.

Comparative effects of plasma and preheating in assisting premixed ammonia/air flames: A DNS study

In this study, Direct Numerical Simulations are utilized to investigate turbulent premixed NH3/air flames assisted by two distinct methods: non-equilibrium nanosecond plasma discharges and preheating, while maintaining equal input energy levels for both methods. The results show that plasma is more effective than preheating in increasing the turbulent burning velocity, namely by up to 31% under lean and by 26% in rich conditions. Furthermore, the flame structure is less affected by turbulence when using plasma. A negative correlation between flame displacement speed and local flame curvature is observed for all cases. Furthermore, negatively curved parts of the flame front are dominated by the reaction mode of combustion. In contrast, the positively curved parts are controlled by flame propagation mode in both preheated and plasma-assisted cases. It is shown that, when plasma is utilized, NO emissions are less sensitive to local heat release rate, and the amount of NO emissions is found to be 19% lower in comparison to the preheated case.

NH₃/CH₄ and NH₃/Biogas Swirl Combustion: Turbulent Flame Propagation and Sensitivity Analysis of NO Emissions

H&S implications, regulations and international scenarios

No abstract is provided for this article.

Numerical and Techno-Economic Analysis of Batch Annealing Performance Improvements in Tinplate Manufacturing

The present study examines the performance improvement in the batch annealing process used in tinplate manufacturing by enhancing the heat transfer towards the steel coils and altering annealing cycle parameters. Presently, the heat transfer in the furnace is non-uniform, resulting in non-uniform temperature profiles and recrystallisation inside the coils, affecting the final coated steel quality. This study modelled a current furnace and four improvement proposals utilising transient computational fluid dynamics, to produce coil temperature profiles and rank the cases by the highest coil temperature uniformity achieved at the end of soaking. By increasing the soaking temperature and time, as well as the coiling tension before annealing and altering the coil size, the aim was to achieve higher and more uniform coil temperatures that could ensure successful recrystallisation with less defects, especially at the cold spot area in the middle of the coil. Then, a techno-economic analysis compared the cost-effectiveness of the scenarios based on the associated costs and the improvement in the scratching defects of the batch-annealed steel. Overall, most cases exhibited positive results regarding temperature uniformity enhancement, but increasing the coiling tension was considered the most promising option, due to the combination of a large defect reduction potential and cost savings per cycle.

Flame characteristics of glycerol/methanol blends in a swirl-stabilised gas turbine burner

Finding alternative value-added usage for glycerol is imperative as existing uses are inadequate due to the vast excesses of glycerol generated mainly as a result of increased biodiesel production. This paper explores a mid-term, cost-efficient, technically viable utilisation in power generation applications and exposes the nature of its combustion. Blended with methanol to avoid the heat loss and fuel coking problems associated with preheating, glycerol was combusted in a model swirl-stabilised gas turbine burner utilising a standard pressure-swirl injector for fuel atomisation. Stable flames resulting from the tested blends – 70/30 and 50/50 combinations of methanol/glycerol by volume – were achieved over an equivalence ratio (ER) range between 0.29 and 0.51. The upper and lower limits of stable operating ER for the 70/30 case were accompanied by significant flame lift-off from the nozzle exit orifice – a phenomenon that was not pronounced in the 50/50 case. Also, the temporal variation of CH* species integral intensity suggested a reduction in the fluctuation of heat release rate, hence better flame stability, as ER increased for both blends. Overall, the 50/50 case showed greater flame stability compared with the 70/30 case based on the CH* chemiluminescence data and spectral analysis by means of fast Fourier transform.

Progress and Prospective of Nitrogen-Based Alternative Fuels

Alternative fuels are essential to enable the transition to a sustainable and environmentally friendly energy supply. Synthetic fuels derived from renewable energies can act as energy storage media, thus mitigating the effects of fossil fuels on environment and health. Their economic viability, environmental impact, and compatibility with current infrastructure and technologies are fuel and power source specific. Nitrogen-based fuels pose one possible synthetic fuel pathway. In this review, we discuss the progress and current research on utilization of nitrogen-based fuels in power applications, covering the complete fuel cycle. We cover the production, distribution, and storage of nitrogen-based fuels. We assess much of the existing literature on the reactions involved in the ammonia to nitrogen atom pathway in nitrogen-based fuel combustion. Furthermore, we discuss nitrogen-based fuel applications ranging from combustion engines to gas turbines, as well as their exploitation by suggested end-uses. Thereby, we evaluate the potential opportunities and challenges of expanding the role of nitrogen-based molecules in the energy sector, outlining their use as energy carriers in relevant fields.

Liquid biofuels production and emissions performance in gas turbines: A review

The increasing demand for clean and sustainable energy sources provides the impetus for the development of alternative fuels. Recent development of fuel-flexible gas turbine technologies enables the use of alternative non-fossil fuels that could play key roles in contributing to the global efforts in meeting emissions targets. This review highlights the current state-of-the-art production and properties of alternative fuels such as straight vegetable oil (SVO), biodiesel, bioethanol, bio-oil, hydrogenated vegetable oil (HVO) and Fischer-Tropsch (FT) fuel. This is followed by the evaluation of combustion performances in gas turbines. All of the alternative liquid biofuels have shown their potentials in reducing regulated emissions such as NOx, CO and soot under favourable operating conditions. Both HVO and FT fuels show comparable performance as that of jet fuel and can be used in aviation gas turbines, although the present day high production cost restricts the large-scale adoption, limiting its utility. They also have considerably higher cetane number than the rest, making it easier for the fuel to ignite. As for stationary power generation gas turbines that need not carry payloads, the other four alternative biofuels of biodiesel, bioethanol, bio-oil and SVO are possible candidates despite the physics-chemical properties variations when compared to fossil fuels. Amongst them, the use of SVO and bio-oil in gas turbines would require the parallel development of fuel supply systems and atomisation technologies to improve the combustion of the fuels. In all, the alternative liquid fuels reviewed provides realistic opportunities for cleaner and more sustainable operation of aviation and power generation gas turbines. Profound understanding on the fundamental combustion characteristics of the fuels are essential to expedite their mass adoption in gas turbine applications.

Experimental and Numerical Comparison of Currently Available Reaction Mechanisms for Laminar flame speed in Hydrogen/Ammonia Flames