Page 57 - Industrial Plants

critical speed is inside the critical operating range. This d) New HP and LP journal bearings
could lead to vibration issues if the shaft is not properly New HP and LP journal bearings with required reduced
balanced or if the alignment is not properly done. clearances according rotordynamic design (1,2‰
Lateral analysis turbine side (high-speed shaft line) with clearance), designed to improve stability and oil flow,
new turbine bearings having 1,2‰ clearance. having oil orifice inside the bearing housing.
Improvements are visible:
• Steam turbine first critical speed is still well below e) New thrust bearing
critical operating range, and second critical speed New thrust bearing, designed to withstand the axial
is still well above the same. forces all over the operating range of the turbine,
• Intermediate shaft first critical speed is now avoiding overheating or load limitation
outside the critical operating range (above
operating speed +15%) The retrofit will allow to upgrade quite considerably the
• Generator first and second critical speeds are power output and thermal efficiency, given the same
between the 1x and 2x operational speed and load conditions, in detail:
outside the critical operating range. • Nominal 21,5MWe case: actual required inlet
• Intermediate coupling first critical speed is above steam flow of 192,24 t/h (almost never reached
2x operational speed and just outside critical during plant life time) – retrofit solution 185,9 t/h
operating range. • Load case 1: actual measured power 13.080 kW
– retrofit solution up to 14.415 kW (+10,2%)
• Load case 2: actual measured power 14.064 kW
Advantages of the Retrofit Solution – retrofit solution up to 15.905 kW (+13,0%)
Upgrades of performances
• DPI is able to design and customize a retrofit
solution in order to increase the thermal efficiency
of the unit.
• Retrofit with performance improvement includes
the full redesign of the steam path using latest
advanced blade profile technologies with the
following new internal parts to be manufactured
accordingly:
a) New rotor and new stator blade carriers
The new internals, having foot print design to fit the
existing turbine casing axial and radial constraints, will
avoid major modifications. The steam path will be
redesigned as follows:
• HP control stage: new design to reduce reaction
grade and thrust forces
• HP blading section: 9 stages as the existing
configuration
• MP control stage: will not be installed as not
required
• MP blading section: 5 stages instead of then
existing 3 stages As a result of the study, the retrofit project showed the
following main benefits for the end-user:
b) New balancing piston • Higher Efficiency
New balancing piston, designed to better compensate With rising fuel prices and consumption and considering
the thrust forces of the blading and reduce the axial the increasingly stringent environmental regulations, the
forces on the thrust bearing. If possible with the actual improved thermal performance of a steam turbine is a
space constraints, spring loaded sealing rings will be key factor to reduce the carbon foot print of plants and
used as an upgrade to improve efficiency and reliability their OPEX
• Higher Power Output
c) New HP and LP gland bushes The increasing demand for power puts pressure to the
New HP and LP gland bushes designed to ensure existing plants to increase capacity. With this retrofit
proper leakage ratio. If possible with the actual space solution, we have been implementing the latest
constraints, spring loaded sealing rings will be used as technologies allowing for more power output with the
an upgrade to improve efficiency and reliability same steam input and output configuration.

IndustrIal Plants - May 2022
55