Advanced Gas Turbine cycles for high efficiency and sustainable future conventional generation

Lead Research Organisation: Imperial College London
Department Name: Dept of Mechanical Engineering

Abstract

Gas Turbines (GTs) will figure prominently in complimenting the intermittent power generated by renewables, while varied fuel sources by 2050 are likely to include biofuels (the former a mixture of methane, carbon mono- and di-oxide and nitrogen - essentially low calorific value fuel) and perhaps shale gas and hydrogen. In meeting CO2 emissions targets, there will be a premium on designs that (i) have the highest fuel conversion efficiency and (ii) integrate with carbon capture and storage. Such designs include either humid air turbines (HAT) or schemes with extensive exhaust, or flue, gas recirculation together with the use of oxygen-enriched air. There is extensive techno-economic evaluation of these designs with no preferred 'winner' and it is likely that each will find extensive application. Thus, there will be a need to design combustion chambers to burn low calorific gases, with "oxidant" streams including up to 30% (w/w) of steam, pure oxygen or oxygen heavily diluted with Carbon dioxide. Such changes present formidable difficulties to flame stability and extinction. The design of low NOx combustion chambers has shown the value of computational fluid dynamics (CFD) in developing commercially viable designs and this trend will strengthen. Finally, the value of suitable sensors during development has proved its worth. This research identifies the gaps in existing physical understanding, CFD and optical sensors, to be addressed by "fundamental research", that need to be filled so that step change GT technologies can be developed by industry. This proposal will develop tools and understanding as follows:
(i) On-line, near real time optical sensor to measure the 'Wobbe' index of fuel entering the gas turbine, since fast knowledge of the calorific value of highly variable bio- fuels is important for control of future GTs.
(ii) Flame stability and extinction is associated with the existence of a critical 'rate of stretch' and the largest laminar flame speed that the flame can experience due to the aerodynamic flow field of the combustors. Designers, using CFD for flow prediction in combustion chambers, need to know these critical values for the range of fuels and oxidants, which will be in use up to 2050. Thus, this proposal will obtain measurements of these values in premixed and non-premixed flames as a function of preheat and pressure and analyse the process of flame extinction in laboratory and pilot scale model combustors using, amongst other instruments, detection of CO and formaldehyde by planar laser induced fluorescence.
(iii) Low NOx emissions require the fuel to be well premixed and it is useful for development engineers to have access to an instrument, which can measure local fuel/air ratio on test stands. Building on previous successful development of an instrument based on natural chemiluminescent emissions from a flame, there will be an evaluation of its calibration as a function of pressure and humidity, the latter in the context of a HAT gas turbine design.
(iv) Thermoacoustic instability is a destructive high intensity 'limit cycle', which is either avoided operationally or designs are improved largely by cut and try methods. Until recently, the transition to this limit cycle and the limit cycle itself were characterised by frequency and phase spectral analysis. Our recent work has shown that non-linear time series analysis reveals that transition to high amplitude oscillations retains a structure as determined by chaos theory. We will use this form of analysis to identify the fluid mechanical structures responsible for this behaviour, with the aim of devising methods to at least warn gas turbine operators of impending thermoacoustic instability.
(v) The best available LES CFD methods will be evaluated using the measurements in the counterflow and model combustor geometries. There will also be direct assessment, through the measurements, of the 'sub-grid' contribution of LES methodology to calculations

Planned Impact

Using the RCUK Typology, this project has impact in the five fields shown below:
- Environmental sustainability, protection & impact
- Commercialisation & Exploitation
- Improving social welfare
- Evidence based policy making & influencing public policies
- Increasing public engagement with research & related societal issues
The social, environmental and economic importance of energy efficient and sustainable power generation is significant. This project will take an innovative and coordinated approach, pushing forward towards novel, energy efficient thermodynamic cycles for power generation using gas turbines and integration of biomass-derived low calorific value sustainable fuels. It will do so in a way which is both fundamental, by working on novel ideas which are applicable across a broad range of applications of whatever scale, and specific, by developing optical sensors for control of the operation process. The beneficiaries from this work will therefore be:

Society because of:
- The influence on improved evidence-based policy making
- Energy efficiency and sustainability
- The ideas underlying this project have the potential to deliver step change to current technology for power generation.

Industry and the UK Economy generally:
- The broad power generation industrial sector (e.g. gas turbine manufacturers, power generators) because of our detailed focus on the physical processes of the combustion technologies that will allow step change in the efficiency. During the project we will generate detailed information about a wide range of processes of direct relevance to the power generation industry. These will be of significant and immediate benefit as they fit directly into the Industry's own development plans. This is part of a strong national trend towards reduction of CO2 emissions.
- Transport and chemical processing industries through improved understanding of combustion processes, novel control tools (e.g. optical sensors) and improved computational models.
The above will generate impact across many sectors over the longer term because the UK will lead the way in developing new and validated methodologies for energy efficient power generation in the context of applying leading edge technology.

Publications

10 25 50
 
Description (i) A sensor has been developed that can monitor the variation of supplied fuel blends to gas turbine combustors. This can lead to the development of new control approaches for flexible fuel operation for power generation.
(ii) Chemiluminescence sensor for monitoring air-fuel ratio of gas turbine combustors flames has been developed and applied to flames of different fuel blends successfully. This can lead to an improved sensor for flame monitoring.
(iii) Forewarning algorithm developed that can predict forthcoming transition to thermoacoustic oscillations. This algorithm allows enough time to control appropriately the operation to avoid the initiation of thermoacoustic oscillations.
Exploitation Route The forwarning algorithm for prediction of transition to thermoacoustic oscillations has been tested successfully in an industrial environment. This is now considered for control of transition to combustion oscillations in commercial hardware. The sensor for monitoring variability of supplied fuel blends has been demonstrated to industrial partners, but this has not led yet to industrial implementation. The sensor for flame monitoring has been demonstrated to industrial partners, but this has not led yet to industrial implementation.
Sectors Aerospace, Defence and Marine,Education,Energy,Environment,Transport

 
Description The research has been planned together with industrial partners to ensure that the findings can influence the efficient operation of conventional power stations. Industrial co-supervision is also in place to guide the direction of the research towards the industrial interests. The developed data analysis of the time-dependent pressure of gas turbine combustors has been applied to commercial high pressure combustors. This analysis demonstrated the ability to predict the transition to combustion oscillations with about 1 second forewarning, which can be used for control of gas turbine combustors to avoid the initiation of combustion oscillations. A joined publication with industry has been completed in this field, following the industrial secondment of the PhD student to Siemens industrial site.
First Year Of Impact 2019
Sector Education,Energy,Environment
Impact Types Societal,Economic

 
Title Catalytic influence of water vapor on lean blowoff and NOx reduction for pressurized swirling syngas flames 
Description It has become increasingly cost-effective for the steel industry to invest in the capture of heavily carbonaceous BOF (Basic Oxygen Furnace) or converter gas, and use it to support the intensive energy demands of the integrated facility, or for surplus energy conversion in power plants. As industry strives for greater efficiency via ever more complex technologies, increased attention is being paid to investigate the complex behavior of by-product syngases. Recent studies have described and evidenced the enhancement of fundamental combustion parameters such as laminar flame speed due to the catalytic influence of H2O on heavily carbonaceous syngas mixtures. Direct formation of CO2 from CO is slow due to its high activation energy, and the presence of disassociated radical hydrogen facilitates chain branching species (such as OH), changing the dominant path for oxidation. The observed catalytic effect is non-monotonic, with the reduction in flame temperature eventually prevailing, and overall reaction rate quenched. The potential benefits of changes in water loading are explored in terms of delayed lean blowoff, and primary emission reduction in a premixed turbulent swirling flame, scaled for practical relevance at conditions of elevated temperature (423 K) and pressure (0.1-0.3 MPa). Chemical kinetic models are used initially to characterize the influence that H2O has on the burning characteristics of the fuel blend employed, modelling laminar flame speed and extinction strain rate across an experimental range with H2O vapor fraction increased to eventually diminish the catalytic effect. These modelled predictions are used as a foundation to investigate the experimental flame. OH* chemiluminescence and OH planar laser induced fluorescence (PLIF) are employed as optical diagnostic techniques to analyze changes in heat release structure resulting from the experimental variation in water loading. A comparison is made with a CH4/air flame and changes in lean blow off stability limits are quantified, measuring the incremental increase in air flow and again compared against chemical models. The compound benefit of CO and NOx reduction is quantified also, with production first decreasing due to the thermal effect of H2O addition from a reduction in flame temperature, coupled with the potential for further reduction from the change in lean stability limit. Power law correlations have been derived for change in pressure, and equivalent water loading. Hence, the catalytic effect of H2O on reaction pathways and reaction rate predicted and observed for laminar flames, are compared against the challenging environment of turbulent, swirl-stabilized flames at elevated temperature and pressure, characteristic of piratical systems. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
 
Description Siemens Industrial Turbomachinery Ltd 
Organisation Siemens AG
Department Siemens Industrial Turbomachinery Ltd
Country United Kingdom 
Sector Private 
PI Contribution Control of combustion oscillations in gas turbine combustors. Development of method for data analysis of measured pressure fluctuations in combustion chamber of industrial combustor. Ability to predict initiation of combustion oscillations with enough warning to be able to control the operation of combustor and avoid combustion oscillations.
Collaborator Contribution Supporting PhD student at our laboratory. Hosting of PhD student at industrial site. Engineering support during PhD student visit. Participation of personnel at meetings.
Impact Development of method for data analysis of measured pressure fluctuations in combustion chamber of industrial combustor. Ability to predict initiation of combustion oscillations with enough warning to be able to control the operation of combustor and avoid combustion oscillations.
Start Year 2015