Fuel flexibility will drive the energy demand in the near future. The use of different syngas compositions from various sources will play a major role in the global fuel mix. CO2 in the blends will also be added as a mechanism to improve carbon capture and storage technologies. However, this can trigger instabilities such as thermoacoustics, flashback, autoignition and blowoff. In terms of blowoff, the phenomenon is still not entirely understood. This project presents a series of experiments to determine the behaviour and impact on the blowoff process at various swirl numbers, nozzle geometries and gas compositions. The Central Recirculation Zone was analyzed just before blowoff. The results show how the strength and size of the recirculation zones are highly influenced by these parameters. However, it seems that the CRZ dimensions/strength does not play an important role in the blowoff, whilst the composition of the mixture shows high correlation. Nevertheless, the CRZ intensity using these compositions can increase residence time, important for combustion improvement of other blends.
Recently, ammonia is being considered for fuelling gas turbines as a new sustainable source. It can undergo thermal cracking producing nitrogen, hydrogen and unburned ammonia, thus enabling the use of these chemicals most efficiently for combustion purposes. Ammonia being carbon-free may allow the transition towards a hydrogen economy. However, one of the main constraints of this fuelling technique is that although the combustion of ammonia produces no CO2, there is a large NOx proportion of emissions using this fuel. In this work, cracked ammonia obtained from a modified combustion rig designed at Cardiff University was used to simulate a swirl burner under preheating conditions via heat exchangers. The primary objective of this system is to find new ways for the reduction of NOx emissions by injecting various amounts of ammonia/hydrogen at different mixtures downstream of the primary flame zone. The amount of injected ammonia/hydrogen mixture (X) taken from the thermal cracking system was ranged from 0%-4% (vol %) of the total available fuel in the system while the remaining gas (1.00-X) was then employed as primary fuel into the burner. CHEMKIN- PRO calculations were conducted by employing a novel chemical reaction code developed at Cardiff University to achieve the goal of this paper. The predictions were performed under low pressure and rich conditions with an equivalence ratio ϕ =1.2 in a swirl burner previously characterised at output powers of ~10 kW. Ammonia and hydrogen blends were evaluated from 50% NH3 (vol %) with the remaining gas as hydrogen, continuing in steps of 10% (vol %) NH3 increments. Results showed that the minimum unburned ammonia and higher flame temperature were achieved at 60%-40% NH3-H2 when compared to other blends but with high NO emissions. These NO levels were reduced by injecting a small amount of NH3/H2 mixture (X=4 %) downstream the primary zone in a generated circulations promoted by the new design of the burner which affecting the residence time hence reducing the NO emission in the exhaust gas.
‘Fuel-flexible’ gas turbines will be required over the next 20 years at least. However, this contrasts with recent experiences of global operators who report increasing emissions and difficult combustion dynamics with even moderate variations in the fuel supply. Swirl stabilized combustion, being the most widely spread technology to control combustion in gas turbines, will be a technology needed for dynamic stabilization of the flow field. However, the features of the recirculation zone are highly complex, three dimensional and time dependent, depending on a variety of parameters. A high momentum flow region inherent to swir ling flows has attracted the attention of several groups interested in blowoff and stretch flame phenomena. Therefore, this study focuses on experimental results obtained to characterise the relation between the central recirculation zone and the high momentum flow region under moderate swirl levels using a well-studied tangential swirl burner for power generation applications. As to be expected the recirculation zone and the high momentum flow region rotate together about the central axis. Moreover, the interaction between them produces high, intense local velocities. This region of High Momentum (shearing flow) also presents a complex geometry that seems to be based on the geometrical features of the burner, different to previous findings on the burner where the system was thought to have a unique shearing flow region. The high three dimensional interaction of these structure is confirmed at the point where the precessing vortex core losses its strength. .
Ammonia and hydrogen are examples of zero-carbon fuels of high interest for implementation in gas turbine technologies. However, large emissions of nitrogen oxides are still a major detrimental for the implementation of these technologies. Therefore, various techniques have been presented as potential solutions to mitigate this problem. Rich-Quench-Lean systems combined with humidified atmospheres are amongst the most promising with the reduction of emissions as a consequence of recombinations of species and lower combustion temperatures. However, limited scrutiny exists around the chemical progression of species in systems like these whilst being fuelled with ammonia blends. Furthermore, any chemical study currently faces a challenge for the selection of a chemical kinetic mechanism due to the great variety of available mechanisms for ammonia combustion, each with different characteristics for the resolution of this fuel. Thus, a Chemical Reactor Network (CRN) has been developed to numerically assess an industry scale humidified Rich-Quench Lean system, utilising five of the most used chemical kinetic models in humidified ammonia combustion whilst informing developers of the differences between those selected. The results displayed significant differences between the mechanisms as the flame progresses. Sensitivity analyses of [OH] and [NH3] displayed similar reactions having opposing effects for these two species at various points of the burner. Quantitative Reaction Path Diagrams (QRDP) for NO showed both similarities and differences between the mechanisms in terms of paths taken and rates of production.
Ever-increasing energy demand, limited non-renewable resources, requirement for increased operational flexibility, and the need for reduction of pollutant emissions are the critical factors that drive the development of next generation fuel flexible gas turbine combustors. The use of hydrogen and hydrogen-rich fuels such as syngas helps in achieving decarbonisation. However, high temperatures and flame speeds associated with hydrogen might increase the NOx emissions. Humidified combustion presents a promising approach for NOx control. Humidification inhibits the formation of NOx and also allows for operating on hydrogen and hydrogen-rich fuels. The challenge in the implementation of this technology is the combustor (burner) design, which must provide a stable combustion process at high hydrogen content and ultra-wet conditions. In the present work, we investigate the flow field and combustion characteristics of a generic triple swirl burner running on humidified and hydrogen enriched methane-air mixtures. The investigated burner consists of three co-axial co-rotating swirling passages: outer radial swirler stage, and two inner concentric axial swirler stages. Reynold’s Averaged Navier-Stokes (RANS) simulation approach has been utilized here for flow description within the burner and inside the combustor. We present the flow fields from isothermal and lean pre-mixed methane-air reactive simulations based on the characterization of velocity profiles, streamwise shear layers, temperature fields and NOx emissions. Subsequently, we investigate the effect of combustion on flow fields, and flame stabilization for hydrogen enriched methane-air mixtures as a function of hydrogen content. We also investigate the effect of humidified combustion on methane-hydrogen blends and present comparison of temperature estimations and NOx emissions.
The research involves an experimental investigation into the laser surface texturing (LST) of stainless steel 316L parts to explore the correlation between the laser process parameters and the dimensional accuracy of the textured designs. A full factorial experimental design was used to analyse the impact of the input parameters via main effects plot and analysis of variance (ANOVA) test. The results indicated that laser track distance along the traverse scanning direction had the most significant effects on all the output responses, i.e. width and depth of the textured grooves and width of the riblet (unmachined region). Laser intensity also had significant effect on the riblet width and groove depth, while scanning velocity did not exhibit any statistically significant influence on any of the responses. The deviations in the riblet and groove widths from the nominal CAD design were the least when using a track distance of 10 μm, whereas the deviations in the groove depth was minimum for a track distance of 100 μm.
Microstructured surfaces have been found to be energy efficient and cost effective through enhancement of heat transfer, drag reduction and anti-fouling in areas such as thermal engineering, fluid mechanics, microelectronics and transportation.However, their use with the condensation phenomenon has yet to receive considerable attention.Therefore, based on a new approach to recover energy in humid environments, the influence of different geometries manufactured on stainless steel inserts via micro-wire electro discharge machining (µ-WEDM) on condensation was analysed.The experimental work was carried out in a chamber with a high percentage of relative humidity (% RH) comparing the geometries against an unstructured surface.The experimental results showed a differential temperature (ΔT), 26% higher than the unstructured surface.Thus, it is reasonable to believe that this experimental study could be used in the design of energy recovery systems to enhance condensation heat transfer.
No abstract is provided for this article.
The reduction of greenhouse gas (GHG) emissions requires the deployment of a large portfolio of alternatives. While the electrification of activities based on renewable sources represents the main option for accomplishing the latter, the use of energy vectors such as hydrogen or ammonia will also play an important role to reduce emissions in activities that are hard to decarbonise. The United Kingdom (UK) has already established several goals for producing hydrogen from offshore wind energy resources. However, the transport of this energy is still not known. Based on this context, this work was aimed at analysing ammonia as an energy carrier that could help the UK to exploit and move these resources by quantifying its techno-economics. The objective of this work was also to analyse the case for only considering hydrogen as the energy carrier. Six scenarios were studied, and the results show that the alternative with the lowest levelised cost of hydrogen (LCOH) was the use of ammonia as the energy carrier from Orkney (Scotland) to the Milford Haven Port (Wales) via maritime transportation and its decomposition back to hydrogen without its purification. The LCOH for this scenario was 9.93 USD per kg of H2, which was 0.93 USD per kg of H2 and 2.53 USD per kg of H2 lower in comparison to directly transporting liquid hydrogen or considering the purification of hydrogen via ammonia, respectively. The construction of a hydrogen pipeline from Orkney (Flotta Oil Terminal) to the Milford Haven Port was the next best alternative (11.23 USD per kg of H2), while transporting hydrogen or ammonia via the Teesside Free Port (England) with maritime carrier and pipeline were the highest cost alternatives. A sensitivity analysis was carried out considering different levels of grid electricity and offshore wind costs highlighting an important impact of the first particularly on hydrogen production costs. As a conclusion, we show that ammonia is a feasible energy carrier that represents a large-scale solution comparable to hydrogen in terms of costs, that has the advantage of a relatively rapid deployment while hydrogen (particularly its transport and storage) reaches a more mature stage of development.
Although technological development has been focused on achieving more reliable, efficient and safe energy vectors, social sciences studies have been analysing the role of public attitudes to these developments in order to secure a future for zero-carbon alternatives. Public perception is a key element for the transition to renewable energies. These technologies can offer many benefits for both people and the environment, but if people are not willing to accept a new technology, then the development might be threatened. For this reason, it is fundamental to understand people's beliefs and attitudes at any stage of the technological process. In addition, for upstream technologies like ammonia, where its effectiveness, cost and risks are uncertain, public perception studies can highlight ethical and value issues people consider important. Therefore, this chapter is focused on the importance of understanding these complex interactions between public and the development of new energy alternative technologies, specifically ammonia as energy vector. The chapter discusses the importance of examining public acceptance of new energy technologies. It then concludes with a case study focused on ammonia-based technologies, providing the foundations for the recognition of public perceptions around the subject, enabling future groups to consider the findings throughout the development of new technologies fuelled by NH3.
While thermomechanical analyses in solid and combustion processes in the gas phase are intensively studied separately, their interaction is less investigated. On one hand, the combustion system can be affected by the solid as a result of, for example, the heat conduction. On the other hand, the high-temperature flame can induce the thermal load in the solid, which significantly affects the mechanical stress field in the material. This work focuses on the coupling between the solid and flame and the combustion-induced mechanical stress in the material. The influence of the solid on the flame structures and properties and also the influence of the flame on the thermomechanical behavior in the solid are investigated. A stagnation flow NH3–H2–air flame to a plane wall is considered as a representative model, which is simple but also realistic in many engineering conditions. It is mainly found that an increase of the flame strain rate leads to an increase of thermomechanical stress in the wall, and the system pressure improves the flame stability against extinction but enlarges the induced thermomechanical stress at the same time. Furthermore, it is observed that the hydrogen content in the gas mixture does not affect the thermomechanical stress in the wall if the flames with different hydrogen additions are imposed with the same strain rate. On the basis of various flame parameters, it is also shown that the solid would also flow plastically under certain conditions, such as high pressures. From the viewpoint of the wall, it is mainly shown that the flame stability against extinction can be improved using wall materials with larger heat conductivities.
