1. Introduction - Firenze University Press

Abstract:
PROCEEDINGS OF ECOS 2012 - THE 25 TH INTERNATIONAL CONFERENCE ON
EFFICIENCY, COST, OPTIMIZATION, SIMULATION AND ENVIRONMENTAL IMPACT OF ENERGY SYSTEMS
JUNE 26-29, 2012, PERUGIA, ITALY
Method of increasing the efficiency of a
supercritical lignite-fired oxy-type fluidized bed
boiler and high-temperature three - end
membrane for air separation
Janusz Kotowicz a , Adrian Balicki a
a Institute of Power Engineering and Turbomachinery, Silesian University of Technology, ul.
Konarskiego 18 44-100 Gliwice, Poland, adrian.balicki@polsl.pl
In this paper a thermodynamic analysis of a supercritical power plant supplied with lignite was made. The
power plant consists of: a steam cycle at constant power of 600 MW, live steam parameters at
600 °C/29 MPa and reheated steam parameters at 620 °C/5 MPa; supercritical OXY type circulating fluidized
bed boiler and air separation unit. An air separation unit is based on a three – end type high temperature
membrane. Models of the steam cycle, circulating fluidized bed boiler and air separation unit were built using
a commercial computer program GateCycle and inhouse codes. After the integration of the listed above
models, CFB boiler thermal efficiency as a function of the oxygen recovery ratio in the high temperature
membrane for the variant without and with fuel drying were determined. The calculated thermal efficiency for
the variant with fuel drying increases from 76% to 87% with increasing oxygen recovery ratio from 0.45 to
0.9.
Keywords:
Thermodynamic analysis, Supercritical oxy-fuel boiler, High temperature membranes, Oxy-combustion,
Lignite drying
1. Introduction
The necessity of meeting the standards of flue gas emissions, introduced by both, EU and national
legislators, requires the continuous development of the technologies, which allow for maximum
limitation of the greenhouse gases emission. The group of these technologies includes oxy–
combustion technology, which, thanks to an almost complete elimination of nitrogen from the
process, substantially limits the flue gas stream generated by the power unit [1]. For uninterrupted
operation of the OXY type boiler it is necessary to provide a constant stream of oxidizer with the
highest possible oxygen content, which mixed with a stream of recirculated exhaust gas as an
oxidizing is mixture fed to the combustion chamber. The production of the technical oxygen with
the use of both currently available on an industrial scale cryogenic technology and considered
alternative technologies, is associated with the significant power consumption of the process, and
thus also with a decrease of the efficiency of the block [2]. For boilers fed with lignite, just like in
classical solutions, a possible way to improve the efficiency of electricity generation is to pre-dry
the fuel prior to the injection into the combustion chamber. The presence of large amounts of water
in the fuel reduces the lower heating value, enforces necessity to provide greater fuel mass flow to
the boiler and, which is particularly important in systems with wet type recirculation, increases the
probability of condensation of moisture from the flue gases. The drying process requires the
delivery of large quantities of the drying medium, of which a function is to raise the temperature
and the evaporation of the greatest possible amount of moisture from the fuel. In the classical
solutions as a drying medium hot air or exhaust gases leaving the boiler is used. In OXY type
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