A European fertilizer manufacturer contacted Maintenance Partners to overhaul a multistage turbo expander. The expander was built in 1965 and was showing severe signs of wear and tear after years of use.
Turbo expander specifications
- Manufacturer: Worthington
- Process gas: tail gas nitric acid plant
- Power: 9843 kW
- RPM: 6600
- Rotor lay-out: 4 opposed flow (8 rows in total)
- Mass flow: 27900 kg/h
- Inlet conditions: 7,1 BARa / 675°C
- Exhaust conditions: 1,05 BARa / 350°C
- Year: 1965
New rotor vs repaired rotor
The rotor was considered irreparable by the original equipment manufacturer and a new rotor was offered. However, the delivery time of the new rotor was expected to be around 2,5 years. For the customer this was not acceptable and Maintenance Partners was contacted to check if a repair was possible in a shorter time frame.
Maintenance Partners offered to repair the turbo expander in 8 months time. The repair consisted of:
- Replacing 8 tie bolts
- Reblading 8 rows including riveting
- Laser cladding and grinding of 2 stub shafts
- Producing 3 new diaphragms
- Repairing 3 old diaphragms
- Renew white metal bearings
- High speed balancing
- Producing new steam turbine rotor for the same train
Reverse Engineering & parts manufacturing
Combining process and equipment knowledge allowed Maintenance Partners to re-engineer new diaphragms, bearings, labyrinths, nozzle and tie bolts and a complete new steam turbine rotor. In addition, all parts were manufactured in MP’s machine shop.
Rotor dynamic model & high speed balancing
To improve the turbo expander’s reliability a rotor dynamic model was created. This model is used to calculate right bearing clearances and to verify the required bearing type. It also predicts the rotor’s dynamic behavior at nominal speed.
This particular rotor had never high speed been balanced before (only incremental and low speed). This model helped to achieve very low vibrations of 0,06 mm/s rms during the final run in Maintenance Partners’ Schenck high speed balancing machine.
Benefits for the customer: Quick Delivery & Machine runs better than before
Instead of the 2,5 years it would take to order a new rotor, Maintenance Partners got the turbo expander running in perfect condition 8 months after the order was placed. The high speed balancing has significantly reduced rotor vibrations, as opposed to before the repair.
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