the entropy generation rate is multiplied with the real environmental
temperature, the power loss of the CHP plant becomes
too small.
In an earlier study, Holmberg et al. [9] have shown through a
simple steamturbine and condenser system (see Appendix A) that
the power loss of the system becomes too small if the entropy
generation rate is multiplied with the real environmental temperature
when vapor after the turbine condenses in a heat
exchanger at the higher temperature than the real environmental
temperature. The same example also shows that the law of
GouyeStodola gives exactly the correct power loss if the
condensing temperature of vapor is the same as the real environmental
temperature and there is no temperature difference
between vapor and cooling water in a condenser. In the previous
mentioned example, the entropy generation rate has been
multiplied with the so called effective temperature which has
been defined in Ref. [9] for an open flow system. The effective
temperature in Ref. [9] is quite similar to the thermodynamic
equivalent temperature of heat transfer that Woudstra et al. have
used for the thermodynamic evaluation of GTCC process in Ref.
[10]. Bejan [11] has also stated that the temperature in the law of
Gouy-Stodola should not be the real environmental temperature
when steam or gas expands in a turbine and entropy generation
occurs. Although some studies [12e14] related to the thermodynamic
analysis of the CHP processes have used the real environmental
temperature in the Second Law analysis or the
temperature has not been directly mentioned in the paper [15,16],
previous mentioned examples indicate that the entropy generation
rate should also be multiplied with a modified temperature to
be able to define the real power loss of the CHP plant based
ClausiuseRankine cycle. In this paper, themodified temperature is
called either the effective heat-emitting or the effective heatabsorbing
temperature depending on if the CHP plant emits or
absorbs heat.
The goal of this paper is to perform a thermal performance
analysis for a coal-fired CHP plant using the Second Law analysis
where the effective heat-absorbing and heat-emitting temperatures
are used. The general theory of the effective heat-absorbing
and heat-emitting temperatures is based on the theory presented
by Lampinen et al. in Ref. [17]. In this paper, temperatures will be
defined for the CHP plant undergoing ClausiuseRankine cycle. In
the thermal performance analysis, the maximum power to heat
ratio of the CHP plant and power losses over subsystems will be
calculated. The paper will also show that the real (not only the
theoretical maximum) power output of the CHP plant can b