UittrekselMicroturbines are an application of combined heat and power, based on the gas turbine technology and with a low electric power output in the range of 100kW. Using the same primary fuel to generate electricity as well as useful heat, they realize significant energy savings compared to the conventional schemes of separate production. During hot seasons they lose their advantage due to a limited heat demand, resulting in a temporary shutdown. This shutdown reduces the amount of operating hours. In an attempt to raise the economic feasibility of microturbine technology, the effect of steam injection is investigated by simulation and experimentation.
The influence of the steam injection on the stationary regime of the microturbine is studied by means of a perturbation analysis. At the hand of the analytical relationships between the thermodynamic variables, a Matlab model of the steam injection was set up, and this using only two accurately measurable variables: namely the shaft speed of the microturbine and the steam flow. Validation of the model was done by means of a simulation in the Aspen simulator. An efficiency rise of 0.44%per percent steam flow fraction is predicted at nominal electrical output. At 80 % of this output, the predicted rise is limited to 0.37 % per percent steam fraction. The mass flows, pressure ratios and shaft speeds of both the compressor and the turbine experience a reduction because of the steam injection at constant total electrical power output.
Steam is injected in the T100 microturbine at the VUB. The machine runs stable during steam injection; the maximum amount of steam, producible by the steam generator can be injected without any problems. Injection of steam at nominal power is however more complex, since this can’t be done directly. But by initiating the injection at 80 % of the nominal power and then slowly increasing the output power, injection at nominal power becomes possible. The steam injection reduces the shaft speed on the one hand and increases the electrical efficiency on the other hand, exactly as predicted. The analytical model of the steam injection is subsequently validated by the experimental data. However, this validation shows a difference between the simulations and the experiments. At partial power (80 %), the rise in efficiency was during the experiments limited to only 0.26 % per percent steam fraction. At nominal electrical power, the difference was less dramatically, namely 0.34 % per steam fraction. Possible explanations for this anomaly are the unknown mass flow, the decreasing compressor efficiency or an anomaly between the real compressor map and the one given by the fabricant of the microturbine. Nevertheless, continuing the measurement campaign and experimental validation of the compressor map might result in a conclusive explanation for the discrepancy between the measurements and the simulations.
|Begeleider||Jacques De Ruyck (Promotor) & Svend Bram (Co-promotor)|