Experimental characterisation of a micro Humid Air Turbine: assessment of the thermodynamic performance

Despite appearing as a promising technology for distributed generation, micro Gas Turbines (mGTs) have not yet managed to penetrate the small-scale Combined Heat and Power (CHP) market. The energy efficiency of mGTs amounts to 80% whenever both heat and electricity are required. However, when the heat demand is low, the hot exhaust gases have to be directly blown off and the electrical efficiency of the unit (∼30%) is not high enough to sustain profitable operation. Water injection, achieved when transforming the mGT into a micro Humid Air Turbine (mHAT), allows making use of the exhaust gas heat in such cases, thus increasing electrical efficiency of the technology and improving its feasibility. Although the enhanced performance of the mHAT cycle has been thoroughly investigated from a numerical point of view, results regarding the experimental behaviour of this technology remain scarce. In this paper, we present the experimental characterisation of the mHAT located at Vrije Universiteit Brussel (VUB) which is based on the T100 mGT equipped with a spray saturation tower. These are the first experimental results of such an engine working at nominal load with water injection. In addition, the control system of the unit has been modified so that it can operate either at constant electrical power output (the default setting) or at constant rotational speed. The latter option allowed better assessing the effect of water injection. Experimental results demonstrate the patent benefits of water injection on mGT performance: at fixed rotational speed, the power output of the mHAT increases by more than 30% while fuel consumption rises only by 11%. Overall, the electrical efficiency in wet operation increases by up to 4.2% absolute points.SCOPUS: ar.j