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The transition towards 100% renewable electricity production already raises several challenges at only 20-30% of renewable share. To match energy production and consumption, there will be a need for massive daily and seasonal electricity storage, in particular for fluctuating sources such as wind and solar. Power-to-fuel is one of the energy storage systems that allows long term storage such as season shifting. Electricity can be stored into fuels that are gaseous (hydrogen or methane), easily liquefiable (ammonia), or liquid (methanol). Still, these four fuels are regarded separately in terms of energy production, which reduces the flexibility of the power-to-fuel technology and its potential use as a storage mean. Our approach is to integrate these four fuels into a single technology for power and heat production: Homogeneous-Charge Compression-Ignition (HCCI) engines. Therefore, we developed a 0-Dimensional model to assess the suitability of a unique HCCI engine for the combustion of the four fuels of interest. This paper reports the feasibility of compression-ignition within achievable intake conditions (temperature and pressure) for various engine compression ratios, equivalence ratios and exhaust gas recirculation rates. For the four fuels, we obtained a proper ignition within a single engine design and for intake conditions (temperature and pressure) that can be sustained by recovering the heat losses of the engine only. As a consequence, power-to-fuel can effectively be used as a storage system when combined to a multifuel HCCI engine for the fuel reconversion to energy. Yet the low power densities estimated require further work on increased equivalence ratio and boosting conditions, as well as on the ringing risks associated with such techniques., SCOPUS: cp.p, info:eu-repo/semantics/published

info:eu-repo/semantics/nonPublished

The impact of multi-dimensional effects on the auto-ignition of the iso-octane was studied through comparison of 0-D and RANS simulations of the Argonne Rapid Compression Machines (RCM). A detailed kinetic mechanism was applied providing an accurate description of both the physical and chemical phenomena in an RCM context for a complex fuel. The effect of the inhomogeneities on the ignition delay was globally marginal except for the lowest temperature condition considered where the diffusive transport of intermediate species and radicals plays a crucial role. No significant effect of mass transfer to the crevices on the auto-ignition delay was noted under the test conditions. The sensitivity of the results to the turbulence level showed that turbulence may only exert a minimal effect on the auto-ignition delay., SCOPUS: ar.j, info:eu-repo/semantics/published

Climate change and the increasing demand for energy are important challenges of this century. Associated issues such as urban pollution due to automotive applications are also a major concern. To mitigate the impacts of our energy usage, a new mix based on renewable energies, including a substantial contribution from biomass, is required. Biofuels can be produced from biomass via biochemical and thermochemical processes. Valerate esters are synthetized from lignocellulose through hydrolysis, hydrogenation and esterification reactions. These biofuels present similar properties with the traditional fuels such as gasoline and diesel. They can be blended with them or fully substituted. Among these esters, methyl and ethyl valerates can be used in spark ignition engines thanks to their physicochemical properties. However, the formation of pollutants such as aldehydes (acetaldehyde and formaldehyde) is a disadvantage for its automotive applications. In this work, ethyl valerate, also called “ethyl pentanoate”, is studied. The understanding of its detailed combustion chemistry is crucial to control the pollutant formation. The main objective of this thesis is to investigate the flame structure of ethyl valerate at low pressure and for three equivalence ratios. Three premixed, laminar and one dimensional flames are stabilized on a Spalding-Botha burner. Gas chromatography is used to separate and to identify the reactants, the products and the intermediate species produced during this ester combustion. A new kinetic model named “Katshiatshia mechanism” is elaborated, tested and validated using the experimental data. This new detailed kinetic model is also assessed using experimental data of ethyl valerate laminar burning velocities (from Lund University) and using jet-stirred reactor experiments at high pressure (from the Université d’Orléans). The simulation results agree well with the jet-stirred reactor experimental results. For the laminar burning velocities, the kinetic, (FSA - Sciences de l'ingénieur) -- UCL, 2016

Fouling from the processing of residual biomass fuels in combustion applications is a major concern. This paper discusses the fouling behaviour of sunflower hulls with a high phosphorus (P) content by means of a broad fuel characterisation strategy including advanced predictive indices, the fuel selective leaching, multiple deposition tests in a Drop Tube Furnace (DTF) and deposits analysis with scanning electron microscopy–energy dispersive X-rays spectroscopy (SEM–EDS). First, we summarise the P-role in the ash chemistry, with a focus on the fouling mechanisms. Second, a characterisation strategy of the ash, based on three indices, including some details from the fuel selective leaching, is proposed to describe the P-rich fuels propensity to foul. The developed approach could be used as a complement to chemical equilibrium models. Thirdly, the characterisation strategy is applied to sunflower hulls. Deposition tests in an industrial scale DTF are performed for the raw fuel, and for the fuel with phosphoric acid (H3PO4H3PO4) water solution and calcium carbonate (CaCO3CaCO3) as additives, to obtain different P/K and P/Ca ratios in the fuel composition. The results show that increasing the fuel P-content allows to capture the alkali metals in alkali–alkaline earths–phosphates and alkali–phosphates phases, reducing the occurrence of deposits of S- and Cl-compounds. Low melting temperature phases can be reduced enhancing the formation of coarser, high melting temperatures ash particles formed by K/Na–Ca/Mg–phosphates, by means of an optimised addition of phosphorus- and active calcium-based additives. The experimental results confirmed the added value of the high-P fuels predictive characterisation strategy.

Fouling of heat exchangers in biomass combustion plants is an operational problem that can lead to a severe decrease of boilers efficiency and availability. To counteract deposition, additives are used to bind the vaporized alkali in high melting temperature structures, such as solid phosphates or aluminum-silicates. Fouling during the combustion of sunflower husks with a combination of P-and Ca-based additive (H 3 PO 4 and CaCO 3) and Al-silicates additives (kaolin or halloysite) was studied in a test campaign in a Drop Tube Furnace. Fouling tests with additives were compared with reference experiments with the raw fuel (two tests). Thermodynamic equilibrium computations with FactSage 7.0 and state-of-the-art databases were applied to quantify the ash molten fraction at 900°C, the mass of liquid per kg of biomass, the K-release rate to the gas phase and finally the condensed mass at 200°C. The use of additives decreased Cl and P (apart from the test with P addition) concentrations in the inner deposits and increased the amount of loose deposits on the probe. When computing the enrichment factors of the deposits with respect to the ash injected, K concentration in RAW1 deposits, with respect to RAW1 ash, is enriched of 14% (mol/mol). When using the P+Ca additive, K is depleted in deposits by 46%. With the use of aluminum-silicate additives, K is enriched by 4% for the HAL deposit and depleted of 21% for the KAO case.

Over the past 30 years, the Eddy Dissipation Concept (EDC) has been widely applied in the industry for the numerical simulations of turbulent combustion problems. The success of the EDC is mainly due to its ability to incorporate detailed chemical mechanisms at an affordable computational cost compared to some other models. Detailed kinetic schemes are necessary in order to capture turbulent flames where there is strong coupling between the turbulence and chemical kinetics. Such flames are found in Moderate and Intense Low-oxygen Dilution (MILD) combustion, where chemical time scales are increased compared with conventional combustion, mainly because of slower reactions (due to the dilution of reactants). Recent modelling studies have highlighted limitations of the standard EDC model when applied to the simulation of MILD systems, noticeably a significant overestimation of temperature levels. Modifications of the model coefficients were proposed to account for the specific features of MILD combustion, i.e. an extension of the reaction region and the reduction of maximum temperatures. The purpose of the present paper is to provide functional expressions showing the dependency of the EDC coefficients on dimensionless flow parameters such as the Reynolds and Damköhler numbers, taking into account the specific features of the MILD combustion regime, where the presence of hot diluent and its influence on the flow and mixing fields impacts on the reaction rate and thermal field. The approach is validated using detailed experimental data from flames stabilized on the Adelaide Jet in Hot Co-flow (JHC) burner at different co-flow compositions (3%, 6% and 9% O2 mass fraction) and fuel-jet Reynolds numbers (5000, 10,000 and 20,000). Results show promising improvement with respect to the standard EDC formulation, especially at diluted conditions and medium to low Reynolds numbers. © 2015 Elsevier Ltd.

Micro Gas Turbines (mGTs) appear as a promising technology for small-scale (up to 500. kW) Combined Heat and Power (CHP) production. However, their rather low electrical efficiency limits their profitability when the heat demand is low. Hot liquid water injection in mGTs-by means of a saturation tower within the micro Humid Air Turbine (mHAT) cycle-allows both improving the flexibility of heat production and the electrical efficiency of mGTs; two qualities that if enhanced would result in an increased economic feasibility of the technology.Based on simulations performed on a Turbec T100 mGT converted into an mHAT, this paper presents an assessment of the economic profitability of both an mGT (working as a CHP) and an mHAT unit operated in real network conditions. To that end, we have used net present value, internal rate of return and discounted cash flow stream methodologies. The input to the study consists of (1) hourly heat and electricity demand profiles of two distinctive users, one located in Brussels the other in San Francisco and (2) 25 electricity and natural gas price scenarios. Our aim is to investigate whether the increase in flexibility and electrical efficiency achieved when transforming an mGT into an mHAT offsets the additional costs.Results show that in scenarios with high electricity and low natural gas prices-the relationship between these two variables depending on the user, CHP and mHAT units are economically competitive. For all the price combinations where investing in mGT technology is feasible, it is worth transforming the unit into an mHAT. Moreover, the lower the electricity demand with respect to the nominal T100 production (100kWe), the more sensitive the user is to the price at which electricity is sold to the grid and therefore, the more the feasibility of mGT and mHAT technologies depends on subsidies or primes on surplus-electricity production. © 2015 Elsevier Ltd.

In this work, the results of simulating the ABL over a type III suburban terrain in the industrial wind tunnel of the Department of Mechanical Engineering of the Vrije Universiteit Brussel (VUB) are presented. Two different Roughness Barrier Mixing Device (RBMD) methods for simulating the ABL have been used (firstly, the well-known combination of Counihan quarter ellipses and roughness elements, and secondly, a new configuration based on truncated Irwin spires and roughness elements). Counihan quarter ellipses are generally considered as the optimal method for ABL simulation. However, its construction is quite complex. Therefore, an alternative setup, using truncated Irwin spires, was experimentally tested. The results of these two simulated ABLs were compared with international standard applicable for type III suburban terrain. Results showed good agreement between standards and experimental results showing that both techniques give a good representation of the ABL. Finally, the proposed truncated Irwin spires method/configuration is confirmed as a proper way to carry out ABL wind-tunnel simulations, as the results are practically the same as the ones obtained with the well-established Counihan method to simulate ABL in wind tunnels. © 2016 Elsevier Ltd

Coal devolatilization, as first step in thermochemical processes involving solid fuels, has been targeted in plenty of CFD investigations: despite the variety of models that were developed to define the rate of the process and the amount of volatile matter released, not all of them are suitable for CFD simulations of large-scale coal combustors. Empirical models ensure both simplicity and feasibility, but not full reliability for all coal types and operating conditions. CFD modeling results for coal conversion during devolatilization in an entrained flow reactor and oxy-conditions are presented and compared to experimental data. A benchmark assessment of one-step models on the accuracy of the volatile yield prediction is then performed. It is shown that the heating rate strongly influences the devolatilization process and its modeling, not only in terms of rate but also in terms of yield, which differs significantly from the proximate analysis value. This indicates the need for a model able to predict the variation of coal volatile yield with temperature and heating rate, in addition to the kinetic model. © 2016 Elsevier B.V.

Despite the potential of micro Gas Turbines (mGTs) for Combined Heat and Power (CHP), this technology still poses limitations that curb its widespread adoption, especially for applications with a variable heat demand. In fact, whenever the user heat demand is low, mGTs are generally shut down. Otherwise, the high temperature exhaust gases have to be blown off and the resulting electrical efficiency is not high enough to sustain a profitable operation. If, instead of released, the heat in the exhaust gases is re-inserted in the cycle by injecting hot water and transforming the mGT into a micro Humid Air Turbine (mHAT) the electrical efficiency can be increased during periods of reduced heat demand, thus improving the economics of the technology. Although the enhanced performance of the mHAT cycle has been thoroughly investigated from a numerical point of view, results regarding the experimental behaviour of this technology remain scarce. In this paper, we present the experimental characterisation of the mHAT located at the Vrije Universiteit Brussel (VUB): based on the T100 mGT and equipped with a spray saturation tower. These are the first experimental results of such an engine working at nominal load with water injection. In addi tion, the control system of the unit has been modified so that it can operate either at constant electrical power output (the default setting) or at constant rotational speed. The latter option allowed to better assess the effect of water injection. Eperimental results demonstrate the patent benefits of water injection on mGT performance: At fixed rotational speed, the power output of the mHAT increases by more than 30%while the fuel consumption rises only by 11%. Overall, the electrical efficiency in wet operation increases by up to 4:2% absolute points. Future work will involve further optimising the current facility to reduce pressure losses in the air and water circuits. In addition, we will carry out transient simulations and experime

From all fossil fuels, natural gas has the lowest carbon to hydrogen ratio, which enables Gas Turbines (GTs) running on natural gas to produce electricity with the lowest CO2 emissions per produced kWh. These lower emissions have pushed power production towards natural gas. However, if we want to move towards a carbon clean power production, the carbon in the exhaust must be captured. This leads to a major challenge since the low CO2 concentration in the exhaust of a GT makes carbon capture much more expensive compared to coal fired power production. The CO2 concentration can be increased by performing Exhaust Gas Recirculation (EGR). However, EGR on GT cycles negatively affects the efficiency. Using the concept of Humid Air Turbine (HAT), we investigate whether the efficiency losses can be compensated by introducing water in the cycle. This paper presents this novel approach by showing the impact of EGR on a flexible humidified micro Gas Turbine (mGT). It is based on results of simulations performed in Aspen® using the Turbec T100 mGT as reference case. Both the dry and wet operation of the Turbec T100 were simulated and validated with experimental results. For improved carbon capture, EGR was simulated in both the dry and the humidified mGT cycle. Simulation results indicate that EGR has no effect on the thermodynamic performance of the mGT and its components (compressor, turbine and recuperator), however efficiency is reduced significantly (up to 3.8% relative at nominal power output) because of additional losses to the fan blower installed to ensure the EGR. Additionally, the cycle performance strongly depends on the degree of cooling of the EGR stream before injection in the compressor inlet. Nevertheless, the simulation results also reveal that mGT humidification increases the total cycle efficiency, entirely compensating the EGR induced losses. Humidifying the mGT with EGR even leads to a higher electric efficiency than the standard mGT cycle, unlocking the i

Water introduction in the micro gas turbine (mGT) cycle is considered the optimal route for waste heat recovery and flexibility increase of such a small-scale combined heat and power (CHP) unit. However, humidification of the combustion air in a mGT affects combustion stability, efficiency, and exhaust gas emissions. This can lead to a non-stable, incomplete combustion, which will affect the global efficiency negatively. Additionally, CO emissions will increase. The non-stable, incomplete combustion might result in an engine shutdown due to a flameout. To study the impact of humidification on the combustion of methane in a humidified mGT, we performed combustion experiments in an atmospheric, variable-swirl, premixed combustion chamber. The results of these experiments are summarized in this article. The effect of the humidification of the combustion air was simulated by adding steam to the combustion air. The impact of the steam injection on methane combustion has been studied at variable swirl number and steam fraction. Experimental results showed a linearly increasing lean blowout (LBO) equivalence ratio for methane combustion with increasing steam fraction. In addition, CO emission levels started to rise at higher equivalence ratio for higher steam fractions compared to combustion under dry conditions. The CO emission levels at stable combustion were however still the same order of magnitude as for the dry combustion. The swirl number has little effect on the LBO limit. Final results indicated the possibility to maintain complete and stable combustion under humidified conditions with low CO emissions at higher equivalence ratio compared to the dry combustion. © 2016 Taylor & Francis.

Micro Gas Turbines (mGTs) offer valuable advantages for small-scale Combined Heat and Power (CHP) production compared to reciprocating Internal Combustion Engines (ICEs): lower maintenance costs per kWhe, cleaner exhaust, lower vibration levels and concentration of the residual heat in a single source (the exhaust gases). Nevertheless, mGTs have lower electrical efficiencies, fact that has prevented them from penetrating in the CHP market. Hot liquid water injection—by means of a saturation tower within the micro Humid Air Turbine (mHAT) cycle—allows both improving the flexibility of heat production and the electrical efficiency of mGTs; two qualities that if enhanced would increase the economic feasibility of the technology. Although the advantages of mHAT technology have been proven from a thermodynamic point of view, its economic performance has not yet been fully investigated. This paper presents a comparison of the economic profitability and the primary energy savings of an mGT, an ICE and an mHAT unit operating in real network conditions. Our aim is to investigate whether the increase in flexibility and electrical efficiency, achieved when transforming an mGT into an mHAT, allows this technology to economically outperform ICEs. Results show that the three units are viable in scenarios with high electricity and low natural gas prices. For the cases in which investment is feasible, the revenues with mHAT are the highest: thanks to their flexibility in heat generation, mHAT units are able to run all year long. On the other hand, the greatest primary energy savings are achieved with ICE units—which have the highest overall efficiencies—while mHAT savings are substantially lower. © 2016 Elsevier Ltd

In this work, the results of simulating the ABL over a type III suburban terrain in the industrial wind tunnel of the Department of Mechanical Engineering of the Vrije Universiteit Brussel (VUB) are presented. Two different Roughness Barrier Mixing Device (RBMD) methods for simulating the ABL have been used (firstly, the well-known combination of Counihan quarter ellipses and roughness elements, and secondly, a new configuration based on truncated Irwin spires and roughness elements). Counihan quarter ellipses are generally considered as the optimal method for ABL simulation. However, its construction is quite complex. Therefore, an alternative setup, using truncated Irwin spires, was experimentally tested. The results of these two simulated ABLs were compared with international standard applicable for type III suburban terrain. Results showed good agreement between standards and experimental results showing that both techniques give a good representation of the ABL. Finally, the proposed truncated Irwin spires method/configuration is confirmed as a proper way to carry out ABL wind-tunnel simulations, as the results are practically the same as the ones obtained with the well-established Counihan method to simulate ABL in wind tunnels.

info:eu-repo/semantics/nonPublished

info:eu-repo/semantics/published

Introduction of water in a micro Gas Turbine (mGT) has proven to be a very efficient way to introduce waste heat in the cycle. The injection of preheated water/steam in the mGT cycle will increase the efficiency of the cycle significantly. Different routes exist for water injection in an mGT cycle. Classical routes, like injection of steam/preheated water or the micro Humid Air Turbine (mHAT) cycle, where water is introduced in the cycle by means of a saturation tower, have shown to have high potential, however do not fully exploit the maximal potential for waste heat recovery. More advanced humidified gas turbine cycles exist on large scale, but these concepts have not yet been applied on mGT scale. In this paper, we study the impact of these different, more advanced, humidified gas turbine cycle concepts on the mGT performance. The different selected cycles – next to the classical Steam Injected Gas Turbine (STIG), injection of (preheated) water and the mHAT – were: mHAT-plus, Advanced Humid Air Turbine (AHAT) and the Regeneration EVAPoration cycle (REVAP®). Simulations indicated that humidifying the air of the mGT has a significant beneficial effect on the cycle performance, resulting in increased electrical power output and efficiency. Depending on the different used cycle layout, more waste heat could be recovered from the exhaust gas. The REVAP® cycle with feedwater preheat was identified as the optimal cycle layout within the selected cycles. Using this concept, the stack temperature could be lowered to 53 °C, corresponding to an increase in electrical power output of 128.7 kWe with a maximal absolute efficiency increase of 6.9% compared to the dry cycle layout (100.1 kWe electrical power output and 35.1% efficiency)., SCOPUS: cp.p, info:eu-repo/semantics/published

Despite appearing as a promising technology for decentralised Combined Heat and Power (CHP), the rather low electrical efficiency of micro Gas Turbines (mGTs) prevents them from being attractive for users with a variable heat demand. Hot water injection in mGTs, achieved by transforming the cycle into a micro Humid Air Turbine (mHAT), allows increasing the electrical efficiency of the units in moments of low heat demand— therefore decoupling heat and electricity production. In spite of previous research regarding simulations, experiments and economic assessments of mHAT technology, the detailed enthalpy and exergy flows between the components remained to be investigated. In the present paper, we introduce and compare the Sankey (enthalpy flow) and Grassmann (exergy flow) diagrams of an mGT based on the Turbec T100 and the corresponding mHAT cycle. Results show that the electrical efficiency of the T100 increases by 2.5% absolute points with water injection, while the total exergy efficiency decreases by only 4.1%. Although there is an enthalpy gain in the saturation tower, exergy actually decreases in this component due to the increase in entropy related to the evaporation of water. The benefits of water injection mostly rely on the increased heat capacity of the air-vapour mixture, the lower fuel consumption, the higher heat recovered in the recuperator, and the reduced power required by the compressor., info:eu-repo/semantics/published

With the increasing share of renewable energy in the total electricity production, the need for flexibility in electrical power production has increased. In some cases, flexibility has even become more important than high efficiency as a primary technology selection criterion. Micro Gas Turbines (mGTs) offer high flexibility for decentralised electricity production due to their limited power output (up to 500 kWe) and operation at variable shaft speed. However, the electrical efficiency of mGTs is rather low (30%). Therefore, mGTs are mainly used in Combined Heat and Power (CHP) applications in which case their total efficiency rises to 80%. In addition, like most CHP plants, mGT operation is mainly heat driven, which has a severe negative effect on the mGT’s flexibility.Humidifying the mGT–converting it into a micro Humid Air Turbine (mHAT)–offers a solution. The waste heat in the exhaust gases is recovered in the mHAT by evaporating auto-raised hot water behind the mGT compressor, resulting in an increased electrical efficiency and a more flexible mGT operation. The mHAT concept combines the high flexibility of the mGT with higher electrical efficiency. In this paper, we present a complete overview of the results of experiments performed on our humidified Turbec T100 mGT over the last three years. As a proof of concept, the mGT at the Vrije Universiteit Brussel has been equipped with a spray saturation tower to humidify the compressed air. The goal of these experiments was to evaluate the beneficial effect of compressed air humidification on the mGT performance at part and nominal load conditions. Stable runs both at constant power and constant rotational speed mode were achieved during water injection experiments. The latest results show a 4.2 percentage point electrical efficiency increase at constant rotational speed, info:eu-repo/semantics/published

Water introduction in the micro gas turbine (mGT) cycle is considered the optimal route for waste heat recovery and flexibility increase of such a small-scale combined heat and power (CHP) unit. However, humidification of the combustion air in a mGT affects combustion stability, efficiency, and exhaust gas emissions. This can lead to a non-stable, incomplete combustion, which will affect the global efficiency negatively. Additionally, CO emissions will increase. The non-stable, incomplete combustion might result in an engine shutdown due to a flameout. To study the impact of humidification on the combustion of methane in a humidified mGT, we performed combustion experiments in an atmospheric, variable-swirl, premixed combustion chamber. The results of these experiments are summarized in this article. The effect of the humidification of the combustion air was simulated by adding steam to the combustion air. The impact of the steam injection on methane combustion has been studied at variable swirl number and steam fraction. Experimental results showed a linearly increasing lean blowout (LBO) equivalence ratio for methane combustion with increasing steam fraction. In addition, CO emission levels started to rise at higher equivalence ratio for higher steam fractions compared to combustion under dry conditions. The CO emission levels at stable combustion were however still the same order of magnitude as for the dry combustion. The swirl number has little effect on the LBO limit. Final results indicated the possibility to maintain complete and stable combustion under humidified conditions with low CO emissions at higher equivalence ratio compared to the dry combustion., info:eu-repo/semantics/published

Despite the potential of micro Gas Turbines (mGTs) for Combined Heat and Power (CHP), this technology still poses limitations that curb its widespread adoption, especially for applications with a variable heat demand. In fact, whenever the user heat demand is low, mGTs are generally shut down. Otherwise, the high temperature exhaust gases have to be blown off and the resulting electrical efficiency is not high enough to sustain a profitable operation. If, instead of released, the heat in the exhaust gases is re-inserted in the cycle — by injecting hot water and transforming the mGT into a micro Humid Air Turbine (mHAT) — the electrical efficiency can be increased during periods of reduced heat demand, thus improving the economics of the technology.Although the enhanced performance of the mHAT cycle has been thoroughly investigated from a numerical point of view, results regarding the experimental behaviour of this technology remain scarce. In this paper, we present the experimental characterisation of the mHAT located at the Vrije Universiteit Brussel (VUB): based on the T100 mGT and equipped with a spray saturation tower. These are the first experimental results of such an engine working at nominal load with water injection. In addition, the control system of the unit has been modified so that it can operate either at constant electrical power output (the default setting) or at constant rotational speed. The latter option allowed to better assess the effect of water injection.Eperimental results demonstrate the patent benefits of water injection on mGT performance: at fixed rotational speed, the power output of the mHAT increases by more than 30%while the fuel consumption rises only by 11%. Overall, the electrical efficiency in wet operation increases by up to 4.2% absolute points. Future work will involve further optimising the current facility to reduce pressure losses in the air and water circuits. In addition, we will carry out transient simulations and experim, info:eu-repo/semantics/published

In this work, the results of simulating the ABL over a type III suburban terrain in the industrial wind tunnel of the Department of Mechanical Engineering of the Vrije Universiteit Brussel (VUB) are presented. Two different Roughness Barrier Mixing Device (RBMD) methods for simulating the ABL have been used (firstly, the well-known combination of Counihan quarter ellipses and roughness elements, and secondly, a new configuration based on truncated Irwin spires and roughness elements). Counihan quarter ellipses are generally considered as the optimal method for ABL simulation. However, its construction is quite complex. Therefore, an alternative setup, using truncated Irwin spires, was experimentally tested. The results of these two simulated ABLs were compared with international standard applicable for type III suburban terrain. Results showed good agreement between standards and experimental results showing that both techniques give a good representation of the ABL. Finally, the proposed truncated Irwin spires method/configuration is confirmed as a proper way to carry out ABL wind-tunnel simulations, as the results are practically the same as the ones obtained with the well-established Counihan method to simulate ABL in wind tunnels., info:eu-repo/semantics/published

From all fossil fuel power production routes, the electricity produced with Gas Turbines (GTs) running on natural gas has the lowest CO2 emissions. However, if we want to move towards full carbon clean power production, the CO2 in the exhaust must be captured. The energy impact of a Carbon Capture plant (CC) applied to the micro Gas Turbine (mGT) still remains unclear because few quantitative analyses are available. The low concentration of CO2 in the GT exhaust gas is disadvantageous from a CC point of view. Exhaust Gas Recirculation (EGR) is one of the technologies used to increase the CO2 concentration in the GT flue gas. It is potentially an effective method to reduce the high energy-penalty caused by the carbon capture. A typical capture method is an absorber–stripper system where the absorbent is commonly a 30wt% aqueous monoethanolamine (MEA) solution. In this work, a Turbec T100 mGT coupled with a chemical-absorption plant is considered. The entire plant has been simulated using Aspen Plus®. Simulation results show that the specific reboiler duty is rather constant (around 4.3 MJ/kgCO2) when varying the electrical power output of the mGT. The cycle performance is strongly affected by the thermal energy requirement for the stripping process, decreasing the global electric efficiency around 6.2 absolute percentage points. These results could be a starting point for future energy integrations between the mGT and the CC plant., info:eu-repo/semantics/published

Coal devolatilization, as first step in thermochemical processes involving solid fuels, has been targeted in plenty of CFD investigations: despite the variety of models that were developed to define the rate of the process and the amount of volatile matter released, not all of them are suitable for CFD simulations of large-scale coal combustors. Empirical models ensure both simplicity and feasibility, but not full reliability for all coal types and operating conditions. CFD modeling results for coal conversion during devolatilization in an entrained flow reactor and oxy-conditions are presented and compared to experimental data. A benchmark assessment of one-step models on the accuracy of the volatile yield prediction is then performed. It is shown that the heating rate strongly influences the devolatilization process and its modeling, not only in terms of rate but also in terms of yield, which differs significantly from the proximate analysis value. This indicates the need for a model able to predict the variation of coal volatile yield with temperature and heating rate, in addition to the kinetic model., SCOPUS: ar.j, info:eu-repo/semantics/published

0, info:eu-repo/semantics/nonPublished

info:eu-repo/semantics/nonPublished

From all fossil fuels, natural gas has the lowest carbon to hydrogen ratio, which enables Gas Turbines (GTs) running on natural gas to produce electricity with the lowest CO2 emissions per produced kWh. These lower emissions have pushed power production towards natural gas. However, if we want to move towards a carbon clean power production, the carbon in the exhaust must be captured. This leads to a major challenge since the low CO2 concentration in the exhaust of a GT makes carbon capture much more expensive compared to coal fired power production.The CO2 concentration can be increased by performing Exhaust Gas Recirculation (EGR). However, EGR on GT cycles negatively affects the efficiency. Using the concept of Humid Air Turbine (HAT), we investigate whether the efficiency losses can be compensated by introducing water in the cycle. This paper presents this novel approach by showing the impact of EGR on a flexible humidified micro Gas Turbine (mGT). It is based on results of simulations performed in Aspen® using the Turbec T100 mGT as reference case. Both the dry and wet operation of the Turbec T100 were simulated and validated with experimental results. For improved carbon capture, EGR was simulated in both the dry and the humidified mGT cycle. Simulation results indicate that EGR has no effect on the thermodynamic performance of the mGT and its components (compressor, turbine and recuperator), however efficiency is reduced significantly (up to 3.8% relative at nominal power output) because of additional losses to the fan blower installed to ensure the EGR. Additionally, the cycle performance strongly depends on the degree of cooling of the EGR stream before injection in the compressor inlet. Nevertheless, the simulation results also reveal that mGT humidification increases the total cycle efficiency, entirely compensating the EGR induced losses. Humidifying the mGT with EGR even leads to a higher electric efficiency than the standard mGT cycle, unlocking the id, info:eu-repo/semantics/published

Micro Gas Turbines (mGTs) offer valuable advantages for small-scale Combined Heat and Power (CHP) production compared to reciprocating Internal Combustion Engines (ICEs): lower maintenance costs per kWhe, cleaner exhaust, lower vibration levels and concentration of the residual heat in a single source (the exhaust gases). Nevertheless, mGTs have lower electrical efficiencies, fact that has prevented them from penetrating in the CHP market. Hot liquid water injection—by means of a saturation tower within the micro Humid Air Turbine (mHAT) cycle—allows both improving the flexibility of heat production and the electrical efficiency of mGTs; two qualities that if enhanced would increase the economic feasibility of the technology. Although the advantages of mHAT technology have been proven from a thermodynamic point of view, its economic performance has not yet been fully investigated. This paper presents a comparison of the economic profitability and the primary energy savings of an mGT, an ICE and an mHAT unit operating in real network conditions. Our aim is to investigate whether the increase in flexibility and electrical efficiency, achieved when transforming an mGT into an mHAT, allows this technology to economically outperform ICEs. Results show that the three units are viable in scenarios with high electricity and low natural gas prices. For the cases in which investment is feasible, the revenues with mHAT are the highest: thanks to their flexibility in heat generation, mHAT units are able to run all year long. On the other hand, the greatest primary energy savings are achieved with ICE units—which have the highest overall efficiencies—while mHAT savings are substantially lower., SCOPUS: ar.j, info:eu-repo/semantics/published

Fouling from the processing of residual biomass fuels in combustion applications is a major concern. This paper discusses the fouling behaviour of sunflower hulls with a high phosphorus (P) content by means of a broad fuel characterisation strategy including advanced predictive indices, the fuel selective leaching, multiple deposition tests in a Drop Tube Furnace (DTF) and deposits analysis with scanning electron microscopy-energy dispersive X-rays spectroscopy (SEM-EDS). First, we summarise the P-role in the ash chemistry, with a focus on the fouling mechanisms. Second, a characterisation strategy of the ash, based on three indices, including some details from the fuel selective leaching, is proposed to describe the P-rich fuels propensity to foul. The developed approach could be used as a complement to chemical equilibrium models. Thirdly, the characterisation strategy is applied to sunflower hulls. Deposition tests in an industrial scale DTF are performed for the raw fuel, and for the fuel with phosphoric acid (H3PO4) water solution and calcium carbonate (CaCO3) as additives, to obtain different P/K and P/Ca ratios in the fuel composition. The results show that increasing the fuel P-content allows to capture the alkali metals in alkali-alkaline earths-phosphates and alkali-phosphates phases, reducing the occurrence of deposits of S- and Cl-compounds. Low melting temperature phases can be reduced enhancing the formation of coarser, high melting temperatures ash particles formed by K/Na-Ca/Mg-phosphates, by means of an optimised addition of phosphorus- and active calcium-based additives. The experimental results confirmed the added value of the high-P fuels predictive characterisation strategy., SCOPUS: ar.j, info:eu-repo/semantics/published

Micro Gas Turbines (mGTs) appear as a promising technology for small-scale (up to 500 kW) Combined Heat and Power (CHP) production. However, their rather low electrical efficiency limits their profitability when the heat demand is low. Hot liquid water injection in mGTs—by means of a saturation tower within the micro Humid Air Turbine (mHAT) cycle—allows both improving the flexibility of heat production and the electrical efficiency of mGTs; two qualities that if enhanced would result in an increased economic feasibility of the technology.Based on simulations performed on a Turbec T100 mGT converted into an mHAT, this paper presents an assessment of the economic profitability of both an mGT (working as a CHP) and an mHAT unit operated in real network conditions. To that end, we have used net present value, internal rate of return and discounted cash flow stream methodologies. The input to the study consists of (1) hourly heat and electricity demand profiles of two distinctive users, one located in Brussels the other in San Francisco and (2) 25 electricity and natural gas price scenarios. Our aim is to investigate whether the increase in flexibility and electrical efficiency achieved when transforming an mGT into an mHAT offsets the additional costs.Results show that in scenarios with high electricity and low natural gas prices—the relationship between these two variables depending on the user, CHP and mHAT units are economically competitive. For all the price combinations where investing in mGT technology is feasible, it is worth transforming the unit into an mHAT. Moreover, the lower the electricity demand with respect to the nominal T100 production (100 kWe), the more sensitive the user is to the price at which electricity is sold to the grid and therefore, the more the feasibility of mGT and mHAT technologies depends on subsidies or primes on surplus-electricity production., SCOPUS: ar.j, info:eu-repo/semantics/published

Over the past 30 years, the Eddy Dissipation Concept (EDC) has been widely applied in the industry for the numerical simulations of turbulent combustion problems. The success of the EDC is mainly due to its ability to incorporate detailed chemical mechanisms at an affordable computational cost compared to some other models. Detailed kinetic schemes are necessary in order to capture turbulent flames where there is strong coupling between the turbulence and chemical kinetics. Such flames are found in Moderate and Intense Low-oxygen Dilution (MILD) combustion, where chemical time scales are increased compared with conventional combustion, mainly because of slower reactions (due to the dilution of reactants). Recent modelling studies have highlighted limitations of the standard EDC model when applied to the simulation of MILD systems, noticeably a significant overestimation of temperature levels. Modifications of the model coefficients were proposed to account for the specific features of MILD combustion, i.e. an extension of the reaction region and the reduction of maximum temperatures. The purpose of the present paper is to provide functional expressions showing the dependency of the EDC coefficients on dimensionless flow parameters such as the Reynolds and Damköhler numbers, taking into account the specific features of the MILD combustion regime, where the presence of hot diluent and its influence on the flow and mixing fields impacts on the reaction rate and thermal field. The approach is validated using detailed experimental data from flames stabilized on the Adelaide Jet in Hot Co-flow (JHC) burner at different co-flow compositions (3%, 6% and 9% O2 mass fraction) and fuel-jet Reynolds numbers (5000, 10,000 and 20,000). Results show promising improvement with respect to the standard EDC formulation, especially at diluted conditions and medium to low Reynolds numbers., SCOPUS: ar.j, info:eu-repo/semantics/published