MACHINING & MACHINERY THE ROTOR RETURNS
SULZER
Sulzer identifies faulty OEM replacement compressor rotors ensuring an optimum repair
Ever ordered something online , only to discover on delivery it ’ s not right and needs to be sent back ? While this is annoying for personal items , when it ’ s a rotor for your chlorine compressor , it can potentially have significant consequences for production . Thankfully for Nobian Industrial Chemicals B . V ., Sulzer ’ s Venlo Service Center was there to spot and solve the problem before things could go spinning out of control .
As a global leader in the production of specialty chemicals , Nobian manufactures and moves large quantities of chlorine . To allow delivery to customers , this key ingredient for many industrial and chemical processes is often liquefied . An important enabler of this process at Nobian ’ s Rotterdam plant is a 4-stage chlorine compressor and its back-up spare . This means that when the main compressor needs attention from the maintenance team after prolonged service with this materially corrosive element , it is swapped out for repairs and the spare takes its place .
To make sure it had its spare ready , Nobian contacted Sulzer in the Netherlands to perform a complete overhaul . With its turnkey service for the maintenance and upgrade of compressors and other rotating equipment , the local team was ready to take this on .
A comprehensive compressor overhaul
The results of the compressor inspection showed that the casing could be re-used . This would be achieved by welding some erosion marks and machining the entire split line to remove corrosion , with the entire casing to be re-bored afterwards . Furthermore , the new diaphragms from the compressor OEM did not meet Nobian ’ s specifications , but the used items were found to be in reasonable condition .
Considering this , the final project scope encompassed machining the casing , the reuse of the existing diaphragms and the replacement of all other internals . These included the rotor and impellers , internal labyrinth seals , bearings , oil seals , the variable inlet guide vanes ( VIGV ) assembly and stuffing boxes .
Consequently , Sulzer in the Netherlands subcontracted the compressor casing machining , installed the used diaphragms and replaced all other internals with new items supplied by Nobian . However , during a trial fit of the rotor from the OEM , it appeared that its balance drum was wrongly installed , being twisted at 180 °. Consequently , the rotor was shipped by Nobian back to the OEM , with final reassembly put on hold .
Identifying more rotor issues
As this was the spare compressor , Nobian opted to wait for this rotor to be repaired . When it did finally appear , Sulzer ’ s Venlo Service Center resumed the project to finish the compressor overhaul . However , the refurbished rotor was delivered with some minor nonconformities such as rust and broken , incorrectly secured labyrinth seals .
As a consolation , the balance drum was now in the correct position and in terms of dimensions at least , the rotor was fit for purpose . Sulzer commenced with machining the shims to the correct thickness to achieve the right axial clearances for the rotor . Since the labyrinth seals might be replaced by the OEM , it was decided to not machine the stuffing box to the required internal diameter until the refurbished rotor was inspected and the outer diameter of the labyrinth seals were measured again . Despite this progress , the faulty rotor still presented positioning problems .
Why rotor position is important
The positioning of the rotor is absolutely vital in any compressor . As the split line of casing had been machined to remove the corrosion , the internal packaging of the unit had changed . To compensate for this , the internal bores of the casing had been modified to ensure that the central shaft would be properly aligned . However , the faulty rotor could potentially make contact with other elements in the compressor such as the labyrinth seals or stuffing boxes - regardless of the other modifications .
Collaborating on a customer problem
Sulzer invited Nobian to the Venlo Service Center so that they could share their unwelcome discoveries regarding the rotor . The team presented its inspection results and comprehensive 3D scans of the compressor casing and rotor , conforming that there was a positional offset between the center line of the casing and rotor shaft . Because of that , the internals would need to be machined to compensate for this offset . Representatives from both businesses sat down to review the measurements and Nobian agreed with Sulzer ’ s diagnosis .
Both parties confirmed that the replacement rotor sent by the original equipment manufacturer ( OEM ) had to be returned again , so the project was put on hold for a second time until it was repaired . Nobian was invited to return to Sulzer for the unboxing and inspection of the rotor when it arrived .
Getting the right rotor
Better late than never , the refurbished rotor arrived at the Venlo Service Center to be welcomed by experts from both businesses . Thankfully for everyone involved , it was a case of third time lucky . A close inspection and a 3D scan confirmed the rotor was finally fit for purpose and would sit in the right position .
To complete the overhaul , the last stuffing box was machined within tolerances . The rotor was installed and the entire unit reassembled , all witnessed by Nobian . Using its engineering expertise and identifying the nonconformities on the refurbished rotor , the team at the Venlo Service Center had ensured that the spare compressor was brought back to optimum condition . Plant operators at Nobian could breathe a sigh of relief .
Sulzer secures compressor availability
With the compressor now fixed , Nobian has access to a spare that can step up when required . As a result , compressor availability is assured , protecting process uptime , profitability and chlorine production .
For further information , please visit www . sulzer . com
76 PECM Issue 59