Syngas feed of micro gas turbines with steam injection: Effects on performance, combustion and pollutants formation
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In this work, the performance of a 100 kW Micro Gas Turbine (MGT) fed by biomass-derived Synthesis gas (S) have been assessed using a simulation algorithm, consisting of a set of equations describing the behavior of the turbomachines, the pressure losses in each component, as well as the consumption of the other auxiliary devices. An additional algorithm using Cantera’s library has been developed in order to study the combustion kinetics and to assess the MGT emissions with S and with natural gas (NG) feed. The electric power output, achieved using S with a Lower Heating Value (LHV) of about 9 MJ/kg, turns out to be similar to that achieved with NG, if a proper fuel injection strategy is adopted; efficiency is slightly lower, mainly because of the variation of the working fluid composition which involves an increase of the heat required to run the machine. In this work, the effect of the steam injection on the MGT performance characteristics has been also investigated with both NG and S. Steam injection allows to obtain higher power and efficiencies at the rated rotational speed. Attention must be paid to the risk of the compressor stall, especially when using S, as the mass flow rate processed by the compressor decreases significantly. As regards the pollutants’ emission, S combustion involves a reduction of NOX emissions of about 75%, while CO emissions slightly increase with respect to natural gas combustion. However, it was found that, with a proper fuel and steam injection strategy, the concentration of the polluting compounds can be further reduced. Moreover, another advantage of adopting the steam injection technique lies in the increased flexibility of the system: according to the users’ needs, the discharged heat can be exploited to generate steam, thus to enhance the electric performance, or to supply thermal power.