The flue gas temperature was usually approximately 350 °C; thus, a TUR inlet temperature of 320 °C
was selected with a proper minimum internal temperature approach, and the inlet pressure was 100 bar.
The cooling water temperature was 30 °C. The calculations were based on a unit mass flow rate (1 kg/s)
of the flue gas fed into the system.
Table 2 illustrates the thermodynamic performance of the proposed and reference systems. In the
proposed system, heat recovered from the 350 °C flue gas was 226.56 kW, and the refrigeration output
was 62.70 kW at an evaporation temperature of -55 °C. The COPt reached 0.277. The cooling capacity
per unit mass of flue gas Z was 62.70 kJ/kg. The simulation results for the reference system (derived
under the same assumptions) are shown in Table 3. With unit mass flow rate of the flue gas fed into the
system, the COPt was 0.185, andZ was 43.01kJ/kg. The COPt and Zof the proposed system increased by
49.73% and 45.78% over those of the reference system, respectively.
Besides an energy analysis, an exergy analysis was performed to reveal the irreversibility in each
process and to show the possibilities and methods for system performance improvement. The results of
the exergy analysis are presented in Table 3, and these data indicated where exergy destruction and loss
occurred. With the same exergy input (109.32 kW), the exergy outputs of the proposed and reference
systems were 21.03 and 14.25 kW, respectively. The exergy efficiency of the proposed system Kex was
21.03%, which was 6.78 percentage points higher than that of the reference system.
Exergy destruction and loss in the systems could be divided into four parts. The exergy efficiency
enhancement of the proposed system was primarily due to the decrease of exergy destruction and loss in
the first part. It included the exergy destruction in the components where working fluids absorb heat from
the heat source, such as in HRVG and GHEX of the proposed system and REB of the reference system.
The exergy destruction in this part of the
proposed system was 11.38 kW. The exergy
destruction in this part of the reference
system existed in REB and reached 33.83 kW,
which was much higher than that in the
proposed system.