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

Abstract

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.

Rich-Quench-Lean model comparison for the clean use of humidified ammonia/hydrogen combustion systems

“…Simultaneously, a way to augment power and efficiency is to employ humidified cycles that enable the increase of mass through the system [25]. Humidification has also been employed in systems integrated with steam reforming [26], [27] and at different compressor stages [28], thus showing great versatility. Steam injection in a cycle is considered to be an optimal way for the recovery of waste heat [29].…”

Humidified ammonia/hydrogen RQL combustion in a trigeneration gas turbine cycle

“…Cycles of gas turbines with steam injection have been studied and improved over the years [32,33], especially for Combined Heat and Power (CHP) and Combined Cooling, Heat and Power (CCHP) configurations [34]. Humidification has also been employed in systems integrated with steam reforming [35,36] and at different compressor stages [37],…”

Prediction of Novel Humified Gas Turbine Cycle Parameters for Ammonia/Hydrogen Fuels

“…Steam-based gas turbine cycles have been employed over the years [19,20], especially for Combined Heat and Power (CHP) [21]. Humidification and steam reforming have also been used simultaneously [22,23], under various compressor stages [24], and under a great variety of conditions. To avoid combustion and ignition problems, humidified regimes need to be carefully understood [25].…”