Gas Turbine Handbook : Principles and Practices

Case Study #2 255
year. This state-owned refinery has been modernized over the years
both in capacity output and plant efficiency.
The Refinery combined cycle/cogeneration plant was placed in
commercial operation on January 19, 1990. The cogeneration system
consists of two GT10 gas turbine-generator units, two dual pressure
Heat Recovery Steam Generators (HRSG) of forced circulation type
with by-pass stack, and one ABB condensing steam turbine-generator
unit. Saturated steam is also produced for general refinery purposes.
Figure 15-5 shows the general arrangement of the Aspropyrgos Cogeneration
Plant.
The GT10 unit electrical output is limited to 17 MW per
Customer’s specification. The steam turbine-generator is rated at 15
MW. The combined electrical output of the cogeneration system is
49 MW. The generated high pressure steam of 612 psia/760°F from
the HRSGs operates the condensing steam turbine-generator set.
Each HRSG also produces 18,520 lbs/hr of low pressure steam at 68
psia/342°F for refinery consumption.
Like the Corinth Motor Oil Refinery, the Aspropyrgos Cogeneration
Plant operates normally on refinery flare gas. The primary
fuel for the two GT10s has a heating value range of 18,360 Btu/lb to
23,580 Btu/lb; however, heating values of as high as 29,520 Btu/lb
has been recorded. The gas turbines are also capable of firing propane,
diesel oil, and a mixture of the various refinery by-product gas
streams. The two GT10s start up on diesel oil.
Similar to the Motor Oil Refinery, the factors that motivates
the Hellenic Refinery to install its own in-plant electrical power and
steam plant are the high purchase price of the electrical power and
the unreliability of the local electrical power supply, coupled with the
need to improve refinery efficiency and plant profitability. Since its
commercial operation, the Aspropyrgos Refinery has retired several
gas fired heaters and boilers. The Refinery average electrical consumption
is 33,300 kW, and, it exports its excess electrical generation;
thus further improves the Refinery profitability. Cogen plant reliability
has been close to 100% up to its first Major Inspection.
The first Major Inspection of the two GT10s was performed after
25,000 hours of operation (scheduled Major Inspection is 20,000
operating hours). Unit #2 was inspected and immediately returned
to service. More corrosion was found on Unit #1 then anticipated. It
was overhauled, the first two stages of turbine vanes and blades were