Abstract
The conversion of a waste heat energy to electricity is now becoming one
of the key points to improve the energy efficiency in a process
engineering. However, large losses of a low-temperature thermal energy are
also present in power engineering. One of such sources of waste heat in
power plants are exhaust gases at the outlet of boilers. Through usage of
a waste heat regeneration system it is possible to attain a heat rate of
approximately 200 MWth, under about 90°C, for a supercritical power block
of 900 MWelfuelled by a lignite. In the article, we propose to use the
waste heat to improve thermal efficiency of the Szewalski binary vapour
cycle. The Szewalski binary vapour cycle provides steam as the working
fluid in a high temperature part of the cycle, while another fluid –
organic working fluid – as the working substance substituting conventional
steam over the temperature range represented by the low pressure steam
expansion. In order to define in detail the efficiency of energy
conversion at various stages of the proposed cycle the exergy analysis was
performed. The steam cycle for reference conditions, the Szewalski binary
vapour cycle as well as the Szewalski hierarchic vapour cycle cooperating
with a system of waste heat recovery have been comprised.
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