Benchmarking of a micro gas turbine model integrated with post-combustion CO2 capture
Introduction
Higher living standards and population growth demand higher energy supplies, especially in the form of electricity. For secure energy distribution to the user, power generation currently relies heavily on fossil fuels, with a relatively small share of renewable resources [1]. Despite an increasing share of renewable energy sources in power generation, competitive prices and viable resources still make fossil-based fuels, such as coal and natural gas, an economically attractive option for electricity producers. Therefore, there is a strong need for the development and deployment of low carbon emission technologies, including carbon capture and storage (CCS) to commit to the target of limiting global temperature rise of 2 °C compared to pre-industrial levels [2], [3]. Post-combustion capture is one potential route to mitigate CO2 emissions from industrial plants, including power stations. Instead of releasing the CO2 in the exhaust gas to the atmosphere, the captured carbon can be transported and stored safely in a number of locations, including geological formations, saline aquifers, unmineable coal beds and depleted oil and gas reserves [4].
One major challenge identified in the implementation of post-combustion carbon capture is the high-energy requirement imposed by solvent regeneration, which brings down the net electrical efficiency by approximately 8–10% points [5], [6], [7], [8], [9]. Hence, options for the utilization of internal and external heat extraction to meet the energy demands have been considered to outweigh the resulting energy penalty [6], [7]. Evaluation of such technical limitations and constraints is needed to improve the overall thermodynamic and economic performance of the whole system.
The CO2 content in the exhaust of natural-gas-fired gas turbines (GT) typically varies from 3.8 to 4.4 mol% [10], [11]. Due to the low CO2 concentration, and thus partial pressure in the exhaust gas, its integration with a post-combustion carbon capture plant introduces a major efficiency penalty [12], [13], [14]. Various innovations have been proposed, with modifications to the configuration of the basic gas turbine cycle [15], [16]; these include activities aimed at efficiency enhancements, such as steam injection and humid air turbine cycles (HAT) [17], [18], [19], and those increasing the CO2 content of the exhaust gas, such as through adaptations like exhaust gas recirculation (EGR) [20]. This study is dedicated to the latter option as one of the best novel solutions under discussion.
In an EGR cycle, part of the exhaust gas is recirculated back to the oxidizer inlet after cooling and condensing out the moisture, while the rest is emitted or alternatively sent to the carbon capture unit. The enhanced CO2 content in the exhaust gas with a reduced flowrate is beneficial for the integration of an EGR cycle with a CO2 capture system. However, despite these advantages, the EGR cycle poses several technical problems that restrict the maximum amount of exhaust gas that can be recycled; for example, the increase in EGR ratio results in oxygen (O2) starvation at the combustor inlet and thus narrow flame stability limits. Ditaranto et al. [21] reported an increase in unburned hydrocarbons (UHC) and CO emissions along with flame instability, when O2 concentration at the combustor inlet decreases to 14 mol%. Further, experiments by Elkady et al. [22] showed stable operation for a dry low NOx (oxides of nitrogen) GE's F-class turbine combustor for EGR ratios of 35%. It has been recommended that the O2 concentration at the combustor inlet should be kept higher than 16 mol% to maintain stable combustion and safe operation, as well as minimize unburned species [21], [22], [23].
Studies on the effect of EGR on the performance of the gas turbine and post-combustion capture system have focused on the energy penalty and cost reduction of the carbon capture system on its integration [6], [7], [11], [24], [25], [26], [27], [28], [29], [30], [31]. Most of the literature pertains towards the studies encompassing the natural-gas-fired power plants in EGR mode with post-combustion capture system.
In order to assess different GT modifications to facilitate CO2 capture on gas-fired power plants, micro gas turbines (MGTs) have been used due to their operational flexibility and adaptability for research in academia. However, the CO2 concentration of the MGT is even leaner than industrial-scale natural-gas-fired gas turbines. Cameretti et al. [32], [33] showed the reduction in NOx emissions for the MGT by studying the effect of EGR on its performance by varying fuel types. With EGR in place, the efficiency of the capture process for large-scale GTs could be further improved [34], [35], [36], [37]. The effect of the EGR ratio (varying from 40 to 55%) on the system performance and degree of CO2 enhancement, as well as the effects of ambient conditions, are also reported in the literature, explored through the use of various process modelling tools [17], [34], [38], [39].
To support the underpinning research on CO2 capture for GT-based plants, our research teams have developed models for a 100 kWe micro gas turbine and integrated amine capture plant using two different software tools, namely IPSEpro and Aspen Hysys. The operational baseline for both models has been previously validated against experimental work conducted on two different Turbec T100 micro gas turbine in two different locations. However, the boundary conditions used, such as the ambient temperature and humidity, limit the comparability of both models. Therefore, through this collaboration, the MGT and amine capture models previously developed have been validated again using experimental data from a common test facility. Providing a common basis, the benchmarking results from both models, i.e. micro gas turbine and the capture process, are presented in this study. Models were first validated individually, and then adapted and integrated for EGR condition. The goal of this study is to highlight features of different software tools with different capabilities for the performance analysis of GT cycles with integrated post-combustion capture. The main objective is to deliver a reliable model at a sufficient level of detail, providing guidance for our future experimental campaigns on other innovative cycles including HAT.
Section snippets
Micro gas turbine experiments
The UK Carbon Capture and Storage Research Centre's (UKCCSRC) Pilot-Scale Advanced CO2 Capture Technology (PACT) National Core Facilities has two natural gas-fuelled micro-turbines, both of which are Turbec T100 PH (power and heat) designs. These can be coupled with the on-site post-combustion CO2 capture plant, explored in Section 2.2. Series 1 gas turbine at PACT is used for these experiments and can produce up to 100 kWe of electrical power and up to 165 kWth of thermal power. The electrical
Gas turbine experimental results
3. Table 4 summarises the experimental data gained from Series 1 Turbec T100 PH gas turbine tests at the PACT Core Facility, outlining the results for the gas turbine parameters and flue gas analysis over its operating envelope. As shown, there are distinct trends for a number of key parameters. The fuel and air flowrates (FR4) increased with power output, as did the engine speed. O2 levels decreased with increasing power output, as more oxygen was consumed due to the higher fuel flowrates; a
Conclusions
Carbon capture on natural gas-fired power plants is in the process of being commercially demonstrated. In order to support research on this area and aid its deployment, a micro gas turbine has been selected to carry out experimental and theoretical studies, integrated with an amine-based post combustion CO2 capture unit, due to its operational flexibility and affordability. MGT and amine capture models were developed using two different software tools, IPSEpro and Aspen Hysys. The baseline
Acknowledgements
The authors would like to thank for their financial support of this project: EPSRC Gas-FACTS: Gas – Future Advanced Capture Technology Options, EP/J020788/1.
U. Ali acknowledges the grant provided by the University of Engineering and Technology, Lahore Pakistan: Faculty Development Programme Scholarship-2012 and the partial support by the University of Sheffield, UK for this research. M. Mansouri Majoumerd acknowledges the financial support provided by the International Research Institute of
References (52)
- et al.
CO2-free power generation in combined cycles - integration of post-combustion separation of carbon dioxide in the steam cycle
Energy
(2006) - et al.
On the off-design of a natural gas-fired combined cycle with CO2 capture
Energy
(2007) - et al.
Natural gas combined cycle power plants with CO2 capture – opportunities to reduce cost
Int J Greenh Gas Control
(2012) - et al.
Integrating a full carbon capture scheme onto a 450MWe NGCC electric power generation hub for offshore operations: presenting the Sevan GTW concept
Appl Energy
(2009) - et al.
Integration aspects of reactive absorption for post-combustion CO2 capture from NGCC (natural gas combined cycle) power plants
Energy
(2014) - et al.
Techno-economic analysis of natural gas combined cycles with post-combustion CO2 absorption, including a detailed evaluation of the development potential
Int J Greenh Gas Control
(2007) Advanced gas turbine cycles for power generation: a critical review
Appl Therm Eng
(1998)An overview of current and future sustainable gas turbine technologies
Renew Sustain Energy Rev
(2005)- et al.
Process simulation and thermodynamic analysis of a micro turbine with post-combustion CO2 capture and exhaust gas recirculation
Energy Procedia
(2014) - et al.
Investigation on the in-flame NO reburning in turbine exhaust gas
Proc Combust Inst
(2009)
Comparison of two CO2 removal options in combined cycle power plants
Energy Convers Manag
Techno-economic analysis of a natural gas combined cycle power plant with CO2 capture
Evaluation of natural gas combined cycle power plant for post-combustion CO2 capture integration
Int J Greenh Gas Control
Impacts of exhaust gas recirculation (EGR) on the natural gas combined cycle integrated with chemical absorption CO2 capture technology
Energy Procedia
Technologies for increasing CO2 concentration in exhaust gas from natural gas-fired power production with post-combustion, amine-based CO2 capture
Energy
CO2 capture for gas turbines: an integrated energy-efficient process combining combustion in oxygen-enriched air, flue gas recirculation, and membrane separation
Chem Eng Sci
Effects of exhaust gas recirculation on the thermal efficiency and combustion characteristics for premixed combustion system
Energy
Study of an exhaust gas recirculation equipped micro gas turbine supplied with bio-fuels
Appl Therm Eng
Process simulation and thermodynamic analysis of a micro turbine with post-combustion CO2 capture and exhaust gas recirculation
Energy Procedia
On the performance and operability of GE's dry low NOx combustors utilizing exhaust gas recirculation for postcombustion carbon capture
Energy Procedia
Retrofitting micro gas turbines for wet operation. A way to increase operational flexibility in distributed CHP plants
Appl Energy
Performance evaluation of PACT pilot-plant for CO2 capture from gas turbines with exhaust gas recycle
Int J Greenh Gas Control
Performance analysis of a biogas-fueled micro gas turbine using a validated thermodynamic model
Appl Therm Eng
Effect of the CO2 enhancement on the performance of a micro gas turbine with a pilot-scale CO2 capture plant
Chem Eng Res Des
Impact of the operating conditions and position of exhaust gas recirculation on the performance of a micro gas turbine
Updated energy and emissions projections 2015
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Trends and advances in micro gas turbine technology for sustainable energy solutions: A detailed review
2023, Energy Conversion and Management: XOptimal design and operating strategy of a carbon-clean micro gas turbine for combined heat and power applications
2019, International Journal of Greenhouse Gas ControlCitation Excerpt :However, although their CO2 emissions when burning natural gas are lower than those of other fossil fuels, the constraint of a zero/negative carbon emissions will anyhow drive the deployment of CCUS, even on small- and large-scale turbine cycles. Considering their traditional configurations, mGTs and GTs are not suitable for CC applications: the low concentration of CO2 in the exhaust gases, due to the high excess of air used to limit the turbine inlet temperature (TIT), is disadvantageous for the capture process, demanding a higher CC energy input leading to a major overall efficiency penalty (Ali et al., 2017b). As a matter of fact, the flue gas produced by a GT contains 3–5% CO2 concentration which is very low compared to 13–15% CO2 concentration in the exhaust gas produced by coal fired power plants, where CC is traditionally envisioned (Akram et al., 2015).
Natural gas combined cycle with exhaust gas recirculation and CO <inf>2</inf> capture at part-load operation
2019, Journal of the Energy InstituteCitation Excerpt :Rezazadeh et al. [33] concluded that it is viable to operate a NGCC plant with CO2 capture at part load down to 60% of the nominal load of the gas turbine, but with a penalty in power output and efficiency. Ali et al. [2] presented a study related to a micro-turbine with EGR at part-load. However, there is a lack of information related to EGR in an industrial NGCC integrated with CO2 capture at part load.
The effects of internal leakage on the performance of a micro gas turbine
2018, Applied EnergyCitation Excerpt :Best et al. analyzed the effects on the capture performance of increased CO2 concentration in the exhaust gas due to exhaust gas recirculation [21]. Ali et al. examined the possibility of applying post-combustion CO2 capture to an MGT [22]. Giorgetti et al. compared performance of dry and wet MGT cycles with carbon capture [23].
Carbon capture on micro gas turbine cycles: Assessment of the performance on dry and wet operations
2017, Applied EnergyCitation Excerpt :Akram, et al. [13] observed that the SRD was reduced by around 7.1% per unit percentage increase in CO2 concentration in the exhaust gas [13]. Ali et al. [20] demonstrated that a mGT with 55% EGR produced an exhaust gas with 2.2 times the CO2 compared to the mGT without EGR, promoting a 40% decrease in the SRD. In order to increase the efficiency and the flexibility of mGTs, the waste heat in the exhaust gas (whenever not used for cogeneration) can be used to heat up water which is then injected into the engine.
Thermodynamic model validation of Capstone C30 micro gas turbine
2017, Energy Procedia