CERES :: Browsing by Author "Simms, Nigel J."

Browsing by Author "Simms, Nigel J."

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Open Access
Advanced reliability analysis of complex offshore Energy systems subject to condition based maintenance.
(Cranfield University, 2021-04) Elusakin, Tobiloba; Simms, Nigel J.; Shafiee, Mahmood
As the demand for energy in our world today continues to increase and conventional reserves become less available, energy companies find themselves moving further offshore and into more remote locations for the promise of higher recoverable reserves. This has been accompanied by increased technical, safety and economic risks as the unpredictable and dynamic conditions provide a challenge for the reliable and safe operation of both oil and gas (O&G) and offshore wind energy assets. Condition-based maintenance (CBM) is growing in popularity and application in offshore energy production, and its integration into the reliability analysis process allows for more accurate representation of system performance. Advanced reliability analysis while taking condition-based maintenance (CBM) into account can be employed by researchers and practitioners to develop a better understanding of complex system behaviour in order to improve reliability allocation as well as operation and maintenance (O&M). The aim of this study is therefore to develop models for reliability analysis which take into account dynamic offshore conditions as well as condition-based maintenance (CBM) for improved reliability and O&M. To achieve this aim, models based on the stochastic petri net (SPN) and dynamic Bayesian network (DBN) techniques are developed to analyse the reliability and optimise the O&M of complex offshore energy assets. These models are built to take into account the non-binary nature, maintenance regime and repairability of most offshore energy systems. The models are then tested using benchmark case studies such as a subsea blowout preventer, a floating offshore wind turbine (FOWT), an offshore wind turbine (OWT) gearbox and an OWT monopile. Results from these analyses reveal that the incorporation of degradation and CBM can indeed be done and significantly influence the reliability analysis and O&M planning of offshore energy assets.
Open Access
Analysis of combined static load and low temperature hot corrosion induced cracking in CMSX-4 at 550°C
(Elsevier, 2019-10-18) Brooking, Laurie; Gray, Simon; Dawson, K.; Nicholls, John R.; Simms, Nigel J.; Sumner, Joy; Tatlock, G. J.
A CMSX-4 3-point bend specimen was statically loaded under hot corrosion conditions and SEM, (S)TEM and EDX techniques were used to analyse the cracking generated. Sulphur, chlorine, sodium and oxygen were found at the crack tip, and an influence of loading on the corrosion mechanism’s preference to interact with either the γ or γʹ was observed. The microscopy analysis is in support of the corrosive mechanism being a combined stress and electrochemical corrosion linked with low temperature hot corrosion, where crack propagation occurs as a result of localised corrosion enhanced material degradation. High magnification EDX mapping identified W as segregating to the γʹ at room temperature.
Open Access
Analysis of high temperature steam oxidation of superheater steels used in coal fired boilers
(Springer, 2015-10-30) Dudziak, T.; Lukaszewicz, Mikolaj; Simms, Nigel J.; Nicholls, John R.
The present work compares the behaviour of four steels: (T23, T92, T347HFG, Super304H) in the temperature range 600–750 °C. This study focuses on the analysis of the oxidation kinetics in terms of mass change, metal loss and thickness change of the selected materials. In order to understand the differences in oxidation rates between the selected steels, the impact of chromium and the alloying elements were considered in this work. The obtained results show that the impact of alloying elements differs with exposure conditions and importance of the synergy effect.
Open Access
Approaches to modelling fireside corrosion of superheater / reheater tubes in coal and biomass fired combustion power plants
(ASM International, 2019-10-24) Simms, Nigel J.; Ekpe, Blessing; Riccio, Chiara; Mori, Stefano; Sumner, Joy; Oakey, John E.
The combustion of coal and biomass fuels in power plants generates deposits on the surfaces of superheater / reheater tubes that can lead onto fireside corrosion. This type of materials degradation can limit the lives of such tubes in the long term, and better methods are needed to produce predictive models for such damage. This paper reports on four different approaches that are being investigated to tackle the challenge of modelling fireside corrosion damage on superheaters / reheaters: (a) CFD models to predict deposition onto tube surfaces; (b) generation of a database of available fireside corrosion data; (c) development of mechanistic and statistically based models of fireside corrosion from laboratory exposures and dimensional metrology; (d) statistical analysis of plant derived fireside corrosion datasets using multi-variable statistical techniques, such as Partial Least Squares Regression (PLSR). An improved understanding of the factors that influence fireside corrosion is resulting from the use of a combination of these different approaches to develop a suite of models for fireside corrosion damage.
Open Access
Assessment of Coating Performance on Waterwalls and Superheaters in a Pulverised Fuel-Fired Power Station
(Springer, 2017-01-11) Simms, Nigel J.; Seraffon, Maud; Pidcock, Andrew; Davis, Colin
Protective coatings offer one route to increase the lives of heat exchangers in pulverised fuel power plants. A range of candidate coatings have been exposed on the waterwall and superheaters of a 500 MWe UK power station unit for periods of up to ~4 years (24,880 operating hours), during which time this unit was fired on a mixture of UK and world-traded coals. Both nickel- and iron-based candidate coatings were included, applied using high velocity oxy-fuel or arc-wire process; a selection of these also had a surface sealant applied to investigate its effectiveness. Dimensional metrology was used to evaluate coating performances, with SEM/EDX examinations used to investigate the various degradation mechanisms found. Both the waterwall and superheater environments generated their characteristic corrosion damage morphologies which depended on the radial positions around the tube. Coating performances were found to depend on the initial coating quality rather than composition, and were not improved by the use of a sealant.
Open Access
Assessment of corrosive attack of Fe9Cr1Mo alloys in pressurised CO2 for prediction of breakaway oxidation
(Elsevier, 2023-07-27) Gong, Yilun; Gill, Simon P. A.; Yan, Sabrina; Higginson, Rebecca; Sumner, Joy; Simms, Nigel J.; Larsson, Henrik; Shin, Aya; Pearson, Jonathan M.; Young, David J.; Atkinson, Colin; Cocks, Alan C. F.; Reed, Roger C.
To provide clarity on the poorly-understood mechanism of breakaway oxidation, corrosion of Fe9Cr1Mo steel in pressurised CO is quantified and modelled. The temperature range 400–640 , relevant to nuclear power plants, is emphasised. Attack is in the form of combined oxide scale growth and internal carburisation of the metal. Carbon activity in the metal at its surface exhibits a strong time dependence consistent with the kinetically-limited transport of carbon due to the slow Boudouard reaction. Breakaway is associated with the approach to saturation of the steel with respect to carbon. Diffusion modelling agrees well with steel carbide precipitation observations.
Open Access
Biomass thermal conversion : pelletisation of lignocelluloses and the effect on the gasification process
(Cranfield University, 2012-03) Kallis, Kyriakos Xenofon; Oakey, John; Simms, Nigel J.
Agricultural residues and energy crops constitute an important part of the energy chain although they are not being used extensively in the energy generation processes since they are associated with disadvantages such as low bulk and energy densities and handling problems. One solution is the pelletisation of these residues, which solves a great deal of these problems and enables the competition of biomass with other types of fuels. A large amount of work, concerning the combustion of biomass pellets, has been done previously, however, studies on biomass pellet gasification are still limited. An effort is made, in the current project, to connect the pelletisation and the gasification processes so that the work presented here could constitute a guide to the industry. The quality of the pellets to be gasified is affected by the initial pelleting parameters, namely the feedstock moisture content, the feedstock particle size and the die diameter. These parameters in turn, affect the process of gasification. These relationships were studied with the purpose of finding an optimum behaviour in the pelleting process that would allow high efficiencies of pellet gasification. The agricultural residue investigated was oilseed rape due to high cultivation in the UK. Oilseed rape straw (OSRS) was pelletised and used in two types of gasifiers; a downdraft and a spouted fluidised bed gasifier. Other types of biomass pellets such as Miscanthus pellets and Dried Distillers Grains with Solubles (DDGS) pellets were also studied. The gasification performance of the OSRS pellets was compared with the performance during gasification of Miscanthus and DDGS pellets. The results showed that dry and large pellets required more energy to be manufactured than the wet and small pellets. In addition, the results revealed the connection of the initial pelleting parameters and the quality of pellets which was assessed in terms of the pellet density, the bulk density and the pellet durability. The wet pellets with a small particle size had the highest density and the dry pellets had the highest bulk density and durability. The effect of the initial pelleting parameters on the gasification was also studied. It was found that the high feedstock moisture content negatively affected the gasification performance in both downdraft and spouted fluidised bed gasification. The feedstock particle size did not have an effect on the downdraft gasification but a minor effect was identified for the spouted fluidised bed. Large pellets were unable to be processed in the downdraft gasifier due to the increased bed porosity and pellet density and decreased amount of active carbon sites, while both large and small pellets were successfully processed in the spout bed gasifier. The gas higher heating value (HHV) produced in gasification was typically quite low, of between 2-4 MJ/m3. The comparison of the pellets showed that Miscanthus pellets had the highest gasification performance followed by the dry OSRS pellets, the wet OSRS pellets and finally the DDGS pellets. The most important reason for these differences was identified to be the ash content of the pellets.
Open Access
Characterization of full-scale carbon contactors for siloxane removal from biogas using online Fourier transform infrared spectroscopy
(Taylor & Francis, 2014-07-31) Hepburn, C. A.; Martin, B. D.; Simms, Nigel J.; McAdam, Ewan J.
In this study, online Fourier transform infrared (FTIR) spectroscopy has been used to generate the first comprehensive characterization of full-scale carbon contactors for siloxane removal from biogas. Using FTIR, two clear operational regions within the exhaustion cycle were evidenced: an initial period of pseudo-steady state where the outlet siloxane concentration was consistently below the proposed siloxane limits; and a second period characterized by a progressive rise in outlet siloxane concentration during and after breakthrough. Due to the sharp breakthrough front identified, existing detection methods (which comprise field sampling coupled with laboratory-based chromatographic determination) are insufficiently responsive to define breakthrough, thus carbon contactors currently remain in service while providing limited protection to the combined heat and power engine. Integration of the exhaustion cycle to breakthrough identified average specific media capacities of 8.5–21.5 gsiloxane , which are lower than that has been reported for vapour phase granular activated carbon (GAC). Further speciation of the biogas phase identified co-separation of organic compounds (alkanes and aromatics), which will inevitably reduce siloxane capacity. However, comparison of the five full-scale contactors identified that greater media capacity was accessible through operating contactors at velocities sufficient to diminish axial dispersion effects. In addition to enabling significant insight into gas phase GAC contactors, the use of FTIR for online control of GAC for siloxane removal is also presented.
Open Access
Co-firing fossil fuels and biomass: combustion, deposition and modelling
(Cranfield University, 2011-01) Khodier, Ala H. M.; Simms, Nigel J.
The application of advanced technologies employing combustion/co-firing of coal and biomass is seen as a promising approach to minimising the environmental impact and reducing CO2 emissions of heat/power production. The existing uncertainties in the combustion behaviour of such fuel mixes and the release of alkali metals with other elements during the combustion (or co-firing) of many bio-fuels are some of the main issues that are hindering its application. The potential presence of high levels of alkali chlorides and low levels of sulfates in the deposits formed on heat exchanger can cause enhanced corrosion and/or limit the heat transfer between the hot combustion gases and the water/steam system within the process plant. This work has investigated the detailed gas compositions and deposition characteristics of the combusted gas streams produced from fossil and biomass fuels pure and/or blend in a pilot-scale combustors (PF and FBC) at Cranfield University. Combustion gas analysis were obtained on-line by a high resolution multi-component Fourier Transform Infra-Red (FTIR) gas analyser and deposits samples were collected from the flue gas using air-cooled probes with surface temperatures of about 500, 600, 700 o C and analysed using SEM-EDX and XRD techniques. Fuels included several biomass fuels (cereal co-product (CCP) straw, miscanthus (pulverised), oil seed rape straw (against stored pellets), miscanthus (pellets), willow, fast pyrolysis bio-oil) and two commercially-used coals (El-cerrejon and Daw Mill). The results of the experimental studies have been compared with thermodynamic equilibrium predictions. High combustion efficiency was maintained throughout the range of fuel mixes. The SO2 and HCl levels were low in pure biomass combustion and increased as the biomass fraction of the fuel decreased when co-fired with these coals. However, the NOx output remained stable except for Miscanthus:Daw Mill mixtures and OSR stored pellet combustion. The deposition flux was highest on the coolest probes for each fuel. The lowest deposition fluxes were found for the combustion of either fast pyrolysis bio-oil or coppiced willow. There is evidence of significant differences deposition fluxes between El-cerrejon coal and Daw Mill coal mixed with CCP and/or miscanthus. The presence of chlorine was identified in deposits produced from combustion of pure biomass or high biomass mixes. The lowest levels found here in fast pyrolysis bio-oil combustion and only detected at higher shares (≥ 80 %) of biomass co-fired with Daw Mill coal, whereas, mixed biomass with El-cerrejon coal produced Cl in deposits at a low % biomass share. The application of thermodynamic equilibrium modelling has been found to be useful tool for providing a qualitative understanding of elements present and/or control by hot gas in modern combustion processes.
Open Access
Combined hot corrosion and static stress or fatigue of single crystal superalloys.
(2018-09) Brooking, Laurie Finian; Sumner, Joy; Gray, Simon; Simms, Nigel J.
It has been observed that gas turbine (GT) blades operating in harsh environments can undergo material degradation in the form of crack initiation and propagation before that predicted by fatigue lifing. It is thought that this degradation can occur partly as a result of the growing demands for improved GT efficiencies. This is because the requirement for improved GT efficiencies is commonly achieved through increases in operational temperatures and pressures which the turbine stages operate at. These increases in the operational temperatures can consequently lead to the extended effect of hot corrosion in locations of the blade which would not normally impacted, such as the under platform region. Therefore, GT blades are subjected to continuous developments in terms of blade design and material properties and selection in order to achieve improvement in the GT efficiencies, reduce emissions and lower life cycle costs. However, at start of this research project it was postulated that the mechanism causing premature material degradation is a result of the extended effects of low temperature hot corrosion (LTHC), interacting with both cyclic and static loading conditions. In order to experimentally study these interactions statically and cyclically loaded specimens were tested in environments representative of the under platform region of both industrial and aviation gas turbine (GT) blades. A range of geometries were studied: C-rings, three point bend and cylindrical fatigue specimens. Using these specimens experimental studies were conducted investigating the impact of deposit flux, dwell time, multiaxial stress state and load application rate. Further investigations into the microscopic mechanism occurring at the crack tip have been conducted using high magnification transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Detailed stress state data has been produced using finite element analysis (FEA), this data has then been used to assess the impact of the stress state on crack initiation and propagation. It was found that turbine blade materials were susceptible to a form of high temperature stress corrosion cracking (SCC). Additionally, enhanced fatigue crack initiation and propagation was observed with test conditions consistent with low temperature hot corrosion (LTHC) conditions. There was shown to be a detrimental impact with increased rates of LTHC on the high temperature cracking mechanism. Detailed microscopy and analysis of specimens informed a proposed fundamental mechanism behind the enhanced cracking observed in LTHC environments. The five research papers presented within this thesis provide contributions to knowledge and developments in the understanding of crack initiation and propagation within superalloys exposed to simultaneous LTHC environments and loading.
Open Access
Comparative evaluation of SRF and RDF co-combustion with coal in a fluidised bed combustor
(2007-10-01T00:00:00Z) Garg, A.; Smith, Richard; Longhurst, Philip J.; Pollard, Simon J. T.; Simms, Nigel J.; Hill, D.
The experimental study reported here was carried out to assess the feasibility of municipal solid waste (MSW) derived solid recovered fuel (SRF) in energy recovery applications. SRF was prepared by grinding and blending the major MSW constituents such as paper, plastics, wood and textile. The percentage of various constituents was the same as from the Ecodeco process employing bio- drying followed by mechanical treatment. The heating value of synthetic SRF was ca. 21 MJ/kg (as received basis). The metal emission results from the SRF co- combustion with coal were compared with that obtained from coal mono-combustion and refuse derived fuel (RDF) co-combustion with coal. RDF was also derived from MSW and was obtained from a local mechanical treatment waste facility. Use of SRF as co-fuel does not increase the emissions of metals to the environment in the flue gas stream when compared to coal mono-combustion. In addition, use of MSW derived fuel reduces the arsenic release to the atmosphere. The results showed that most of the metals are retained in the ash components (except mercury). The mobility of metals depends on the volatility and type of feedstock.
Open Access
Comparison of coal/solid recovered fuel (SRF) with coal/refuse derived fuel (RDF) in a fluidised bed reactor.
(Elsevier Science B.V., Amsterdam., 2011-06-01T00:00:00Z) Wagland, Stuart Thomas; Kilgallon, P.; Coveney, R.; Garg, A.; Smith, Richard; Longhurst, Philip J.; Pollard, Simon J. T.; Simms, Nigel J.
An experimental study was undertaken to compare the differences between municipal solid waste (MSW) derived solid recovered fuel (SRF) (complying with CEN standards) and refuse derived fuel (RDF). Both fuels were co-combusted with coal in a 50kW fluidised bed combustor and the metal emissions were compared. Synthetic SRF was prepared in the laboratory by grinding major constituents of MSW such as paper, plastic, textile and wood. RDF was obtained from a local mechanical treatment plant. Heavy metal emissions in flue gas and ash samples from the (coal+10% SRF) fuel mixture were found to be within the acceptable range and were generally lower than that obtained for coal+10% RDF fuel mixture. The relative distribution of heavy metals in ash components and the flue gas stream shows the presence of a large fraction (up to 98%) of most of the metals in the ash (except Hg and As). Thermo-gravimetric (TG) analysis of SRF constituents was performed to understand the behaviour of fuel mixtures in the absence and presence of air. The results obtained from the experimental study will enhance the confidence of fuel users towards using MSW-derived SRF as an alternative fuel.
Open Access
Concurrent combustion of biomass and municipal solid waste
(Cranfield University, 2010-09-30) Laryea-Goldsmith, Rene; Simms, Nigel J.
This PhD research project is primarily an investigation of the gaseous pollutant emissions arising from concurrent combustion of biomass and municipal solid wastes materials, using a fluidized bed combustor. Of the wide range of biomass energy resources available, dried distillers’ grains with solubles and wheat straw were chosen as two example agricultural by-products of the human food supply chain. To consider an integrated waste management programme, a residual waste resource from a materials recycling facility was identified as a waste materials source that could be utilized after materials recycling was performed (which is a higher priority activity with respect to energy recovery). Cont/d.
Open Access
Degradation of Environmental Protection Coatings for Gas Turbine Materials
(Cranfield University, 2008-12) Nalin, Laura; Simms, Nigel J.; Nicholls, J. R.
Nowadays, problems of component materials reliability in gas and oil-fired gas turbines focus on assessing the potential behaviour of commonly employed coatings, in order to avoid expensive and unpredictable failure in service and producing new materials whose performance meets life time and manufacturing/ repairing requirements. This MPhil project has investigated the oxidative and corrosive degradation mechanisms for some of the alloy/coatings systems (CMSX-4, CMSX-4/ RT22, CMSX-4/ CN91 and CMSX-4/ “LCO22”), which are currently used for turbines blades and vanes, in order to achieve a better knowledge of materials behaviour and to improve models for the prediction of turbine components’ lives. To achieve this target the study has made use of realistic simulations of turbine exposure conditions in combined with pre- and post-exposure metrology of bar shape materials samples, while optical microscopy has been applied to describe the microstructural evolution during the exposure and the products of the degradation for the hot corrosion. For high temperature oxidation, over extended periods of time (up to 10,000 hours), the research has allowed to describe the morphological changes in respect of the exposure time and temperature and to determine the oxidation kinetics experienced by the alloy and coatings. A model has been presented for predicting θ- α-Al2O3 growth. Moreover, using NASA COSP spalling model, with rate constants values coming from this study, a comparison between experimental mass change data and prediction has been shown. The hot corrosion study has provided new quantitative metal loss data and observations that extend/validate an existing model for materials life prediction, based on defining the severity of the corrosion conditions through measures of gas composition and contaminant deposition flux.
Open Access
Deposition onto heat exchanger surfaces from the co-firing of coal and biomass
(Cranfield University, 2011-12) Legrave, Nigel A; Simms, Nigel J.; Kilgallon, Paul; Villa, Raffaella
In the latter part of the 20th century, there has been a continuing global concern of the consumption of fossil fuels used in power production. There is further concern of the gaseous emissions that are created from this consumption and an awareness of climbing carbon dioxide (CO2) levels that are exhausted into the atmosphere. The concept of co-firing fossil fuel with varying levels of biomass species is not new but there is a requirement to explore its applications further in the interests of both the environment and power production. With dwindling fossil fuel resources, co-firing with biomass is a logical step forward as biomass is a generally a renewable product – whereas fossil fuels are not. More importantly, the study of effects of burning higher biomass percentages on the heat exchanger matrix of power plants requires more attention. This has been explored before in other studies that have resulted in inefficiencies within the power generation plant. The main of objectives of this research were to: co-fire coal with biomass over a wide range of mixes within a combustion environment; monitor the gaseous emissions and capture and analyse the deposits that are formed on deposit capture probes. The analysis of data obtained will enabled further research to be carried out and model deposit flux behaviour of simulated heat exchanger models and materials in the future.
Open Access
Development of a techno-economic framework for life extension decision making of safety critical installations
(Elsevier, 2016-09-22) Shafiee, Mahmood; Animah, Isaac; Simms, Nigel J.
One of the major decisions in management of the industrial assets is to ensure the feasibility of life extension process for safety critical components when they reach end-of-life. Most of the existing life extension decision-making models are restricted solely to either “technical” or “economic” feasibility analyses that may lead to inaccurate results or incorrect conclusions. In this paper, a comprehensive life extension feasibility assessment framework by taking into account both the technical and economic considerations is developed. The proposed techno-economic model for life extension of safety critical elements consists of three phases: preparation, assessment, and implementation. The technical assessment part of the framework incorporates all aspects of data collection and review, screening and prioritization of safety critical elements, condition assessment, estimation of remaining useful life, and risk analysis, while the economic assessment part deals with cost-beneﬁt analysis. The decision to qualify a safety critical element for continuous operation beyond its service life is made based on a “life extension measure (LEM)” which is calculated by combining two indexes of “equipment health condition” and “economic added-value” obtained respectively from the technical and economic assessments. The model is applied to support the life extension decision-making procedure for water deluge systems in offshore oil installations. The results of the study show that the model is highly capable of assisting asset owners to evaluate the technical and economic beneﬁts of extending the service life of components.
Open Access
Development of novel coatings to resist fireside corrosion in biomass-fired power plants
(Cranfield University, 2016-07) Orlicka, Dominika; Simms, Nigel J.; Nicholls, J. R.
The emission of CO2 to the atmosphere from firing conventional fossil fuels has become a major concern for the power industry, due to the enhanced greenhouse effect and global warming predictions. The increasing worldwide demand for electricity production is another issue. The replacement of fossil fuels with increasing quantities of biomass is of interest as biomass is considered to be carbon neutral and is widely distributed. Unfortunately, due to its composition, the risk of fireside corrosion found on heat exchangers (super- heaters and re-heaters) is greater than in coal-fired plants. Consequently, biomass-fired power plants operate at lower steam temperatures and pressures, leading to their poorer efficiency. Biomass-fired power plants suffer from alkali chloride-induced corrosion, considered faster and more severe than alkali sulphate-based corrosion common in traditional coal-fired plants. The main aim of this project was to develop a range of novel coating compositions which would be resistant to fireside corrosion found on boiler tubes in biomass-fired power plants. To accomplish this, studies were carried out into salt stabilities, coating oxidation and deposit corrosion. Salt stability experiments have resulted in improved understanding of the evaporation and sulphidation behaviour of KCl, NaCl, K2SO4 and Na2SO4 at high temperatures in environments containing HCl and SO2. KCl was chosen as a deposit for coating screening. Two-target magnetron co-sputtering was successfully used to deposit a range of coating compositions. These coatings were analysed at 550°C in corrosion environments containing combinations of HCl, KCl and water vapour. The addition of gaseous HCl did not have a significant influence on the coating degradation compared to similar tests in air. Deposited KCl significantly increased the corrosion rate, whereas adding 10% moisture to the environment with KCl had little additional effect. The growth of either protective Cr2O3 or less protective mixed oxides was observed on the different coating compositions. The best performing coatings had compositions in the range: 26.2 – 79.4 at% Cr, 12.1 – 62.9 at% Fe, 8.5 – 10.9 at% Al.
Open Access
Development of on-line FTIR spectroscopy for siloxane detection in biogas to enhance carbon contactor management
(Elsevier, 2015-04-04) Hepburn, Caroline; Vale, P.; Brown, A. S.; Simms, Nigel J.; McAdam, Ewan J.
Activated carbon filters are used to limit engine damage by siloxanes when biogas is utilised to provide electricity. However, carbon filter siloxane removal performance is poorly understood as until recently, it had not been possible to measure siloxanes on-line. In this study, on-line Fourier Transform Infrared (FTIR) spectroscopy was developed to measure siloxane concentration in real biogas both upstream (86.1–157.5 mg m−3) and downstream (2.2–4.3 mg m−3) of activated carbon filters. The FTIR provided reasonable precision upstream of the carbon vessel with a root mean square error of 10% using partial least squares analysis. However, positive interference from volatile organic carbons was observed in downstream gas measurements limiting precision at the outlet to an RMSE of 1.5 mg m−3 (47.8%). Importantly, a limit of detection of 3.2 mg m−3 was identified which is below the recommended siloxane limit and evidences the applicability of on-line FTIR for this application.
Open Access
Effect of co-firing coal and biomass blends on the gaseous environments and ash deposition during pilot-scale oxy-combustion trials
(Elsevier, 2017-02-20) Jurado Pontes, Nelia; Simms, Nigel J.; Anthony, Edward J.; Oakley, John
This paper presents the experimental results from co-firing blends of El Cerrejon (EC) coal and cereal co-product (CCP) using several ratios (100/0; 75/25; 50/50; 0/100 (w/w)) under air- and oxy-firing conditions, in a retrofitted 100 kWth pulverised fuel combustor. An on-line high-resolution multi-component Fourier Transform Infra-red (FTIR) analyser was used to measure CO2, O2, H2O, CO, NO, NO2, N2O, NH3, SO2, HCl, HF and CH4. A comprehensive evaluation of the major and minor species present in the flue gas was carried out to study the effects of the addition of biomass, the firing mode (air/oxy) and the type of recycle (wet/dry) on the gaseous environment in the combustor. It was found that similar CO2 levels can be reached when using pure coal or pure biomass, on a dry basis. For the minor species, the increase in the share of biomass had the effect of decreasing the SO2 levels reached in the flue gas and increasing the HCl content. No significant variation in the NOx levels was observed as a consequence of using high percentages of biomass. For ash deposit characterisation, two probes were used for which surface temperatures were controlled at 650° and 750 °C. Environmental scanning electron microscopy (ESEM) with energy dispersive X-ray (EDX) analysis, supported by X-ray diffraction (XRD), were used to study the deposits. The ESEM/EDX and XRD results showed similar sulphur levels in the deposits when varying the share of biomass even though EC coal contains 3.5 times more sulphur than CCP. This is thought to be a consequence of the reaction of sulphur with the alkalis, especially potassium, present at higher levels in the CCP, which produces higher levels of K2SO4 in the combustion gas. Chlorine was only found in the deposits generated using pure CCP under oxy-firing conditions. An evaluation of the different mineral species formed when varying the biomass share and the firing mode was also performed. Results obtained comparing the mineral species in deposits when using 100% CCP, switching from air to oxy-firing conditions, showed that in air-firing CCP deposits had higher levels of aluminium phosphate and arcanite (K2SO4). Also, under oxy-firing conditions, 100% CCP-derived deposits had a higher level of potassium magnesium chloride compared 100% EC.
Open Access
Effect of stress state and simultaneous hot corrosion on the crack propagation and fatigue life of single crystal superalloy CMSX-4
(Elsevier, 2018-05-03) Brooking, Laurie; Gray, Simon; Sumner, Joy; Nicholls, John R.; Marchant, G.; Simms, Nigel J.
Operating conditions within industrial gas turbines are changing in response to pressures to reduce environmental impact and enable use of renewable sources. This is driving an increase in the operational temperatures and pressures of combustion in turbine systems. Additionally, diverse operating environments can result in higher sulphur and trace metal contaminant levels, exacerbating hot corrosion in GT systems. Low cycle fatigue (LCF) cycling can also be intensified as a result of increased start/stop shutdowns. The combined effects of hot corrosion and stress are experimentally studied on CMSX-4 single crystal (SC) γ/γ' system under both fatigue and static stress conditions, with either a multi-axial bending or uniaxial stress state. The associated stress intensity thresholds (KTH) under the various stress conditions were evaluated using finite element analysis (FEA). Cracking was observed both under static and fatigue stress conditions in a hot corrosion environment. Crack morphologies were analysed using SEM techniques. Bending stresses and fatigue cycles demonstrated increased crack propagation in the presence of hot corrosion with static uniaxial stresses showing the longest nucleation times and lowest propagation rates.

Browsing by Author "Simms, Nigel J."

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