Combined Micro-Systems - Design for Micro-Combined Cooling, Heating and Power Systems - page 66

the microturbines are coupled to thermal components to recuperate the heat. The
heat lost in a microturbine is mainly contained in the hot exhaust gases. This heat
should be used to fuel a steam generator, to heat a residence or to fuel various
cooling absorption systems. The way in which the heat lost may be used depends on
the con

guration of the turbine. In a nonrecuperative turbine, the exhaust gas comes
out at a temperature of 538 C. A recuperative turbine capitalizes the heat lost

by using it to heat spaces or for the thermal agent in a cooling absorption system
where the exhaust temperature is around 271

- 594 °

C.
The exploitation of a microturbine has several advantages. The

°

first is that it has
less moving parts than a combustion engine. The limited number of moving parts
and the reasonable demands regarding the greasing make microturbines have a long
life cycle. Consequently, microturbines have low exploitation costs (seen as cost
per kW of power produced). The second advantage of microturbines is their rela-
tively small size, as compared to the power produced. Microturbines are light and
have a low level of noxe. The third, and maybe the most important advantage of
microturbines, is their capacity to use more types of fuel, including recuperated fuel
or bio fuel. The main disadvantages of microturbines are due to the fact that they
have low levels of electric ef

ciency. Moreover, in conditions of increased altitude
and environment temperature, microturbines observe a decrease in exhaust power
and ef ciency. Environment temperature directly affects the intake air temperature.

A gas turbine will work more efficiently when colder air is available at intake. The
performance characteristics of microturbines are given in Table 2 .
Micro Turbine Technology (MTT) is developing recuperated micro turbines up
to 30 kW electrical powers for CHP and other applications [ 9 ]. Automotive tur-
bocharger performance and ef ciency have increased signi cantly during recent

Table 2 Micro-turbine cogeneration system performance characteristics [ 8 ]
Capstone model
330 micro-turbine

IR energy systems
70LM (two shafts)

Turbec
T 100

Nominal electricity capacity (kW) 30 70 100

Electrical heat rate (Btu/kWh) HHV 15,075 13,540 12,639

Electrical ef ciency (%) HHV 22.6 25.2 27.0

Fuel input (MMBtu/h) 0.422 0.948 1.264

Required fuel gas pressure (psig) 75 55 75

Exhaust ow (Ibs/s) 0.69 1.40 1.74

GT exhaust temperature (F) 530 435 500

Heat exchanger exhaust temperature (F) 150 130 131

Heat output (MMBtu/h) 0.17 0.369 0.555

Heat output (kW equivalent) 51 108 163

Total overall ef ciency (%) HHV 73 64 71

Power/heat ratio 0.47 0.65 0.62

Net heat rate (Btu/kWh) 5509 6952 5703

Effective electrical ef ciency (%) HHV 46.7 49 60