Pinch Point Method in Optimization of Advanced Combined Cycles

The pinch point method has been
developed to identify energy saving opportunities in
industrial processes, The use of the composite curves
allows to compute the minimum energy requirement of a
process and to determine optimal heat exchange between
hot urd cold streams. The use of MILP (Mixed Integer
Linear Programming) optimisation method allows to
extend the approach to solve combined heat and power
problems. The method is applied here to determine the
optimal configuration of combined cycles, It allows to
maximize the mechanical power production without having
to consider the heat exchangersc onfiguration in the boiler
nor in the preheating section. The method is also used to
compute the steam extractions or productions and their
optimal pressure levels that maximize the mechanical
power produced From these results, the heat exchangers
network structure is then determined. Three situations are
analyzed: l) the heat recovery in a classical boiler using air
preheating, 2) the gas turbine combined cycle and. 3) the
" isothermal" gas turbine. The " isothermal" gas turbine is
an innovative promising technology that uses a partial
oxydation reactor followed by a staged combustion between
the expansion stages to reach a quasi isothermal profile
during the expansion. This allows to reduce the exergy
losses in the gas turbine. The resulting flue gases are used
in a combined cycle optimized with the method presented
here. Diffirent configurations are discussed We show that
the structure of combined cycles may strongly differ from
one to another.