Humidified Cycle Research Articles

Water and steam injection in micro gas turbine supplied by hydrogen enriched fuels: Numerical investigation and performance analysis

This paper investigates the energetic and environmental performance of micro gas turbine plant with two proposed concurrent improvements: the methane-based fuel enriched by hydrogen and the humidification of the plant cycle. The energetic and environmental benefits of both features are well-know, and the aim of this work is the analysis of their combined impact on the micro gas turbine operation. Despite enhancing fuel with H2 involves significant advantages like greenhouse emission reduction and a better combustion in case of low LHV fuels, most of commercial micro gas turbine combustors are not able to burn fuels with high hydrogen content unless structurally modified. On the contrary, has been demonstrated that humidified gas turbines (i.e., gas turbines with water injection, humid air turbine (HAT) and steam injection gas turbine (STIG) cycles) improve the combustion stability as well as electric power delivered and plant efficiency. Hence, in order to investigate the feasibility of the concurrent two features, the first step of this work was the thermodynamic analysis of a micro gas turbine supplied by methane-based fuels enriched with H2 up to 20%vol, considering both dry and humidified cycles. Since a combustion anomaly was detected, i.e., flashback, in the CFD study on the combustion chamber, a steam injection in the combustor has been added in the plant layout with the aim of overcoming the anomaly, and its effect on the combustion process has been analyzed also raising the hydrogen content up to 30%vol. The main outcome of this paper is the assessment of the feasibility of supplying the combustor of the proposed HGT-STIG micro gas turbine with a hydrogen enrichment up to 30%vol, achieving a safe and regular combustion mainly owing to a steam injection mass flow equal up to 125% of fuel flow.

TopCycle: A Novel High Performance and Fuel Flexible Gas Turbine Cycle

High pressure humidified cycles can combine high operational flexibility and high thermal efficiency. The current work introduces such a cycle, namely TopCycle, which provides the necessary combustion infrastructure to operate on a wide fuel variety in a steam-rich atmosphere. The cycle configuration is presented in detail, and its operation is exemplified on the basis of simulation results. Operation at design condition results in electric efficiencies higher than 50% (lower heating value (LHV)) and power densities higher than 2100 kW/kgair (referred to intake air flow). A sensitivity analysis identifies the cycle performance as a function of representative parameters, which provide the basis for future operation and design improvements. As for any gas turbine cycle, TopCycle’s electric efficiency can be effectively improved by increasing the turbine inlet temperature, optimizing the economizer heat recovery, as well as elevating the working pressure. Finally, TopCycle’s performance is compared to a state-of-the-art combined cycle (CC) at equivalent operation parameters. The TopCycle operates at an elevated electric efficiency and considerably higher power density, which can be transferred into smaller plant footprint and dimensions and thus lower investment costs at equal power output in comparison to a CC.

Reducing waste heat to the minimum: Thermodynamic assessment of the M-power cycle concept applied to micro Gas Turbines

To fully embrace its opportunities in future decentralized power production, the current mGT has to become more flexible in terms of operation, i.e. decoupling heat and power production. Cycle humidification during periods with low heat demand is a possible route to handle this issue. Indeed, cycle humidification has already been proven to increase the mGT electrical efficiency. Nevertheless, even when applying the most advanced humidified cycle concept, i.e. the REgenerative EVAPoration cycle, the electrical performance increase remains rather limited. In this perspective, the more recent Maisotsenko (or M-power) cycle concept offers a larger potential for humidification, even though its potential was only proven on large-scale gas turbine cycles and never applied to the smaller mGT scale. In this paper, the concept of this M-power cycle is applied to a 100 kWe mGT (Turbec T100) to assess its performance, using Aspen Plus® simulations. Moreover, the impact of various inputs, component performance and control parameters is studied using a sensitivity analysis. The numerical results highlight that the M-power cycle has the highest waste heat recovery and thus the highest electric efficiency (up to 147 kWe electric power output with an electric efficiency of 42.1% at constant rotational speed and 41.1%, corresponding to an 8.3%point absolute increase, at constant power output). Moreover, this cycle concept allows to approach the thermodynamic limit for cycle humidification. Indeed, a large exergy destruction is avoided by not going for direct water injection, but rather using a gradual injection and evaporation. Additionally, from a technological point of view, the M-power cycle is also preferable for the small-scale mGT. Indeed, in the M-power cycle, saturation tower, aftercooler, recuperator and economizer are combined in one single component, significantly reducing the complexity of the cycle. The main limitation is the saturator, that requires a wet bulb effectiveness of up to 98% to achieve the simulated performance, which can be technological very challenging.

Parametric Study of Various Thermodynamic Cycles for the Use of Unconventional Blends

This paper aims to conduct a parametric study for five gas turbine cycles (namely, simple, heat exchanged, free turbine and simple cycle, evaporative, and humidified) using a CO2-argon-steam-oxyfuel (CARSOXY) mixture as a working fluid to identify their optimal working conditions with respect to cycle efficiency and specific work output. The performance of the five cycles using CARSOXY is estimated for wet and dry compression, and a cycle is suggested for each range of working conditions. The results of this paper are based on MATLAB codes, which have been developed to conduct the cycle analysis for CARSOXY gas turbines, assuming a stoichiometric condition with an equivalence ratio of 1.0. Analyses are based on the higher heating value (HHV) of methane as fuel. This paper also identifies domains of operating conditions for each cycle, where the efficiency of CARSOXY cycles can be increased by up to 12% compared to air-driven cycles. The CARSOXY heat exchanged cycle has the highest efficiency among the other CARSOXY cycles in the compressor pressure ratio domain of 2–3 and 6–10, whereas, at 3–6, the humidified cycle has the highest efficiency. The evaporative cycle has intermediate efficiency values, while the simple cycle and the free turbine-simple cycle have the lowest efficiencies amongst the five cycles. Additionally, a 10% increase in the cycle efficiency can be theoretically achieved by using the newly suggested CARSOXY blend that has the molar fractions of 47% argon, 10% carbon dioxide, 10% H2O, and 33% oxyfuel at low compressor inlet temperatures, thus theoretically enabling the use of carbon capture technologies.

Micro Gas Turbine Cycle Humidification for Increased Flexibility: Numerical and Experimental Validation of Different Steam Injection Models

With the current shift from centralized to more decentralized power production, new opportunities arise for small-scale combined heat and power (CHP) production units like micro gas turbines (mGTs). However, to fully embrace these opportunities, the current mGT technology has to become more flexible in terms of operation—decoupling the heat and power production in CHP mode—and in terms of fuel utilization—showing flexibility in the operation with different lower heating value (LHV) fuels. Cycle humidification, e.g., by performing steam injection, is a possible route to handle these problems. Current simulation models are able to correctly assess the impact of humidification on the cycle performance, but they fail to provide detailed information on the combustion process. To fully quantify the potential of cycle humidification, more advanced numerical models—preferably validated—are necessary. These models are not only capable of correctly predicting the cycle performance, but they can also handle the complex chemical kinetics in the combustion chamber. In this paper, we compared and validated such a model with a typical steady-state model of the steam injected mGT cycle based on the Turbec T100. The advanced one is an in-house MATLAB model, based on the NIST database for the characterization of the properties of the gaseous compounds with the combustion mechanisms embedded according to the Gri-MEch 3.0 library. The validation one was constructed using commercial software (Aspen Plus), using the more advance Redlich-Kwong-Soave (RKS)- Boston-Mathias(BM) property method and assuming complete combustion by using a Gibbs reactor. Both models were compared considering steam injection in the compressor outlet or in the combustion chamber, focusing only on the global cycle performance. Simulation results of the steam injection cycle fueled with natural gas and syngas showed some differences between the two presented models (e.g., 5.9% on average for the efficiency increase over the simulated steam injection rates at nominal power output for injection in the compressor outlet); however, the general trends that could be observed are consistent. Additionally, the numerical results of the injection in the compressor outlet were also validated with steam-injection experiments in a Turbec T100, indicating that the advanced MATLAB model overestimates the efficiency improvement by 25–45%. The results show the potential of simulating the humidified cycle using more advanced models; however, in future work, special attention should be paid to the experimental tuning of the model parameters in general and the recuperator performance in particular to allow correct assessment of the cycle performance.

An analysis of the efficiency and economy of humidified gas turbines in district heating applications

In this article, the performance of gas turbine cycles operating with air/water working fluids, so-called humidified cycles, are examined in district heating applications. The investigated cycles are based on a GTX100 core from ALSTOM Power Sweden AB (ALSTOM) 1 1 Now member of the Siemens group. and utilise a two-stage flue gas condenser and an inlet air humidifier (pre-humidifier) to provide elevated quantities of district heating. Simulations have shown that electrical efficiencies up to 50% and total efficiencies above 100% can be reached calculated on the lower heating value (LHV) of the fuel. Based on cost data from ALSTOM, humidified cycles have a potential to give much lower (40% per kW el and 60% per kW DH) specific investment costs compared to combined cycles, mainly due to the absence of steam turbine. The humidified cycles are predicted to be cost-effective investments at market electricity prices € 5–8/MWh el lower than the conventional alternatives in district heating applications.