Thermodynamic analysis of a micro turbine CHP system integrated with absorption-compression heat pump
2018
Micro gas turbine is a high-efficiency power generation
device, which is easy to realize miniaturization. Included compressor,
turbine and generator share only one shaft, thus reducing the required
moving parts and the unit size. It is widely used in civilian use,
industrial and agricultural sectors due to its low fuel consumption,
noise and emissions. Meanwhile, steam is widely used in industrial
processes such as iron and steel. Steam is generally generated by
coal-fired boiler or heat recover steam generator. It is estimated
that industrial boilers take up to 30% of the manufacturing industry
energy consumption. Micro gas turbine combined with waste heat boiler
is a common way to produce heat and electric power simultaneously.
However, large amount of waste flue gas with a high temperature above
170°C is rejected to ambient, causing large energy waste and
heat island effect. To solve this problem, a micro turbine CHP system
integrated with absorption-compression heat pump (ACHP) is proposed.
The waste flue gas of the Micro turbine CHP system is adopted as the
heat resource, which could produce 0.5 MPa saturated
steam in the proposed system. As a result, the energy and environmental
performance of the proposed system can be improved significantly. The thermodynamic performances of the proposed system are mathematically
investigated. The results show that the primary energy ratio and energy
saving ratio of the new system reach 67.3% and 23.56%, respectively,
which are 11.2% and 14.76% higher than those of a traditional micro
turbine CHP system. An exergy analysis is carried out to determine
the distribution of exergy destruction for further optimizing the
system performance. The exergy analysis shows that the irreversible
loss in the waste flue gas could be lowered by 78% in the proposed
system, and the exergy efficiency is 1.79% higher than that of the
reference system. Moreover, parametric analysis is conducted to study the effect
of the reboiler outlet temperature, partial condenser outlet temperature,
the rectifier inlet ammonia-water concentration and the generation
pressure on the system performance. Meanwhile, the coefficient of
the performance (COP) is selected to evaluate the performance of the
system. The outlet temperature of reboiler and the rectifier inlet
ammonia-water concentration have a great influence on the COP, while
the effect of the generation pressure and the outlet temperature of
the partial condenser is relatively small. The COP increase as the
outlet temperature of reboiler rises, while there is a peak value
(0.29) with the increase of the inlet ammonia-water concentration.
The COP changes slowly as the outlet temperature of the partial condenser
increases from 45°C to 75°C. The COP almost keeps constant
before generation pressure reaches 0.6 MPa, and then
decreases slightly afterwards.
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