a GTCC (gas turbine combined cycle) process, in which case the
power to heat ratio may even be over 1.
Basically, most CHP plants based on ClausiuseRankine cycle
operate in the same way as power plants producing only electricity.
The main difference is the steam pressure after the steam
turbine which is higher than in a condensing power plant. In
addition, the heat production must constantly cover the heat
demand of the process where heat is supplied. The thermal
performance of the power plant is usually analyzed using either
the energy (First Law) or the exergy (Second Law) analysis. The
First Law analysis is typically used to calculate power plant efficiencies
as well as power and heat outputs of the power plant.
The Second Law Analysis is based on the calculation of exergy
losses or exergy destruction rate over the subsystems of the
power plant and in several cases the exergetic efficiency of the
power plant is defined on the basis of these losses. Compared to
the First Law analysis, the Second Law Analysis reveals in which
subsystems the largest irreversibility occurs, and it also gives
information what the improvement potential of the system is.
When discussing power plants the exergy loss may also be called
the power loss and from now on the term power loss is used in
this paper.
For condensing power plants based on ClausiuseRankine cycle
(either conventional thermal power plant or nuclear power plant
process) power losses are usually calculated using the law of
GouyeStodola by multiplying the entropy generation rate with the
real environmental temperature (e.g. temperature of cooling water
or air), see e.g. Refs. [2e8]. In the connection of ClausiuseRankine
cycle the law of GouyeStodola reveals how much power/work is
lost in the power plant process (the thermodynamic system) due to
irreversibilities when the power plant emits heat into the environment
at the same temperature as the real environmental temperature.
For condensing power plants, it is usually reasonable to
use the law of GouyeStodola, because the power plant emits heat
into the environment in a condenser or a cooling tower where the
temperature of the cooling water or air remains almost the same as
the real environmental temperature.
Compared to condensing power plants, CHP plants (and many
other thermodynamic systems) emit heat into the environment
at higher temperature level than the real environmental temperature.
In addition, the temperature of the environment is
usually not constant but may rise considerably when the system
emits heat into it. For example, the temperature of the district
heating water (environment) may rise from c. 50 C to over
110 C when it is heated at a municipal CHP plant (system). If
a GTCC (gas turbine combined cycle) process, in which case the
power to heat ratio may even be over 1.
Basically, most CHP plants based on ClausiuseRankine cycle
operate in the same way as power plants producing only electricity.
The main difference is the steam pressure after the steam
turbine which is higher than in a condensing power plant. In
addition, the heat production must constantly cover the heat
demand of the process where heat is supplied. The thermal
performance of the power plant is usually analyzed using either
the energy (First Law) or the exergy (Second Law) analysis. The
First Law analysis is typically used to calculate power plant efficiencies
as well as power and heat outputs of the power plant.
The Second Law Analysis is based on the calculation of exergy
losses or exergy destruction rate over the subsystems of the
power plant and in several cases the exergetic efficiency of the
power plant is defined on the basis of these losses. Compared to
the First Law analysis, the Second Law Analysis reveals in which
subsystems the largest irreversibility occurs, and it also gives
information what the improvement potential of the system is.
When discussing power plants the exergy loss may also be called
the power loss and from now on the term power loss is used in
this paper.
For condensing power plants based on ClausiuseRankine cycle
(either conventional thermal power plant or nuclear power plant
process) power losses are usually calculated using the law of
GouyeStodola by multiplying the entropy generation rate with the
real environmental temperature (e.g. temperature of cooling water
or air), see e.g. Refs. [2e8]. In the connection of ClausiuseRankine
cycle the law of GouyeStodola reveals how much power/work is
lost in the power plant process (the thermodynamic system) due to
irreversibilities when the power plant emits heat into the environment
at the same temperature as the real environmental temperature.
For condensing power plants, it is usually reasonable to
use the law of GouyeStodola, because the power plant emits heat
into the environment in a condenser or a cooling tower where the
temperature of the cooling water or air remains almost the same as
the real environmental temperature.
Compared to condensing power plants, CHP plants (and many
other thermodynamic systems) emit heat into the environment
at higher temperature level than the real environmental temperature.
In addition, the temperature of the environment is
usually not constant but may rise considerably when the system
emits heat into it. For example, the temperature of the district
heating water (environment) may rise from c. 50 C to over
110 C when it is heated at a municipal CHP plant (system). If
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