EXPERIMENTAL SIMULATIONS OF VARIABLE THERMAL LOAD IN A MICROTURBINE BASED COGENERATIVE PLANT

Experimental results on a thermodynamic characterization of a micro-co-generative plant to assess performances under a variable thermal demand are presented in this paper. The generator is a microturbine Turbec T100-CHP integrated in a heat recovery system. For operation in standard conditions the maximum electrical and thermal power generated are respectively 105 and 167 kW. Operative conditions were realized by setting the set-point temperature at the outlet of the micro-turbine in the range 60 – 90°C, with 5°C step. Starting from an electrical power set-point, ranging between 60 and 100 kW, with 10 kW step, the heating power dissipated was varied in the range 70 – 170 kW, with 10 kW step. In every operating condition the measurement system allows the real-time calculation of the quantities needed for the energetic characterization of the plant, such as efficiency indices and PES (Primary Energy Saving index). The investigation of the effect of a variable thermal load at fixed electrical power set-point and water outlet temperature has shown that the machine can meet thermal demand by varying its rotation regime: transient duration is approximately a quarter of an hour. Energetic performances at partial thermal loads have been found of course to decrease: the electrical efficiency lose up to about 7% and thermal efficiency drop can be up to about 20%; nevertheless, the minimum first principle total efficiency ranges between 0.6 and 0.8 for all the investigated conditions. Eventually, in anticipation of the new European regulation, the analysis of PES values suggests that operation at partial thermal loads could be unprofitable, particularly for electrical power set-point less than 80 kW and cogenerative thermal power fraction less than 0.4.