Steam injection experiments in a microturbine - A thermodynamic performance analysis

This paper reports on a series of steam injection experiments on a Turbec T100
microturbine. Combined Heat and Power (CHP) systems, such as the considered T100 microturbine,
use one single primary fuel to simultaneously produce electric and thermal power. In doing so, they
realize significant energy savings compared to conventional schemes of separated production.
However, a reduction in the demand for heat (e.g. in summertime) will force this type of units to
shutdown. This significantly reduces the amount of operating hours and has a severe negative impact
on the net present value of such CHP investment projects.
The aim of this paper is to investigate and demonstrate the effects of steam injection in the compressor
outlet of a microturbine operating under reduced heat demand conditions, in order to keep the unit
running. The necessary steam can be auto-raised with heat available in the turbine exhaust
downstream of the recuperator. Such an injection will keep the unit running and thus avoid a forced
shutdown. Furthermore, it is expected that the electric efficiency will rise and that the power
production will become more economically viable as a result of the increasing operating hours.
This paper reports on the influence of steam injection on the electrical efficiency and shaft speed of a
T100 unit. ASPEN® simulations of the behaviour of the CHP unit are also presented. These simulations
predicted a 2.2% rise in electric efficiency at nominal electrical output when 5% of the mass flow rate
of air is replaced by steam.
The steam injection experiments resulted in stable runs of the unit, a predicted reduction in shaft
speed and increasing electrical efficiency. Validation of the ASPEN® simulations against the
experimental data revealed the necessity for a more accurate determination of the air mass flow rate
and more precise compressor characteristics.