Combined Micro-Systems - Design for Micro-Combined Cooling, Heating and Power Systems - page 62

1.1.1 Method Based on Increasing the Pressure and Temperature
in the Warm Source

Increasing the pressure and temperature of the thermal agent delivered by the warm
source leads directly to the increase in thermal ef ciency. However, this method of

increasing ef ciency is subject to a series of technological restrictions, such as

the mechanical resistance of the thermal circuit components (especially those of the
steam generator). Increasing the initial pressure has the effect of increasing the
steam humidity in the

final area of the turbine. The presence of a large number of
water drops in the steam released at high speed (>200 m/s) leads to a phenomenon
of accentuated erosion and destruction of rotor blades in the final area of the

turbine.
Increasing the initial temperature has a contrary effect on the release humidity in
the steam turbine. Consequently, increasing the initial pressure must be accompa-
nied by increasing the initial temperature.
This method of increasing ef

ciency is achieved through the intermediary
overheating of the thermal agent, which comes from the warm source of the
thermodynamic cycle. The method presupposes the interruption of the steam release
in the turbine, for it to be then sent back to the steam generator. Here, it is over-
heated once again, up to a temperature comparable with the initial one and then it
continues to be released in the steam turbine. Figure 3 presents the simplified
scheme of an intermediary overheating system, where: GA

— steam generator, S Î I —

intermediary over-heater, CIP — high pressure body, CMJP — medium and low

pressure body, GE — electric generator, K — condenser, PA — circulation pump, PR

— regenerative pre-heater.

Intermediary overheating presupposes a complication of the thermal circuit and
of the steam generator, with direct effects on the initial investment. Consequently,
the scheme is generally justi

ed only for high power groups (>100 MW) with a

suf ciently high annual duration of installed power use.

Fig. 3 Intermediary
overheating system scheme

SII

CIP CMJP

GA

GE

K

PR

PA