REDU Service Transforms Failing Cooling Water Pumps
A power station in the Republic of Ireland had significant issues with high silt levels in the water being pumped by its two auxiliary cooling water pumps. High silt content had negatively affected the water quality and, in this case, also caused damage to the rotating elements and static parts of the pumps. This was a frequent and costly problem causing unwelcome downtime and pressures on resources.
At this power station, one pump serves as the main pump with the other used in stand-by. With the original design and material selection, the plant would run one of the pumps for a few weeks, then would have to switch to the backup as performance deteriorated and vibration increased. In 2019, Torishima Service Solutions Europe (TSSE) performed a basic overhaul of the lineshafts and intermediate bearings, utilising material upgrades to provide a temporary solution until new pumps could be ordered. However, when the site tendered for new pumps, on the basis of positive feedback to the temporary upgrade, TSSE proposed a permanent redesign of the existing pumps as opposed to purchasing new pumps.
This involved utilising TSSE’s exclusive Re Engineering and Design Up (REDU) service, which provides a review of pump specifications, regardless of the original supplier, and can lengthen the useful life of pumps. This service also includes the redesign and improvement of obsolete and worn parts, as well as providing a source for future spare parts requirements. Using the latest technology, the REDU service aims to increase the efficiency and reliability of existing pumps.
Scope of Work
TSSE proposed to retrofit the existing open lineshaft and packed gland design with an enclosed lineshaft and mechanical seal design. The design modifications required to retrofit the mechanical seal and line shaft enclosing tubes to the existing pump design were focused on minimising the effect on pump performance.
A detailed material analysis ensured that the risk of corrosion and premature wear was minimised.
The REDU design process began with the selection of a suitable Tori Seal, which was matched to the application and would be appropriate for the pressures and fluid type. The existing spider bearings had to be machined to create landing areas for the enclosing tube end caps. This was all designed with strict sealing requirements to protect the shafts from the pumped fluid.
As the widest rotating component inside the enclosing tube, the coupling design was re-developed to minimise the diameter. This resulted in a reduction of the enclosing tube diameter to maximise the pumped fluid area inside the column pipe. In redesigning the couplings, a new locking mechanism had to be devised to secure the shaft ends, this was developed from an existing Torishima design and illustrates how the depth of knowledge and experience of a world class OEM can be incorporated into the REDU process. Design input from Torishima Pump Mfg. Co. ensured that OEM standards were maintained throughout the process.
The next step was to re-machine the pump casing to ensure a mating face for the bottom enclosing tube.
The flushing lines for the mechanical seal and enclosing tube were combined to reduce water waste and minimize instrumentation and pipework. This involved complex fluid flow and pressure calculations to ensure lubrication and flushing flow requirements were met.
A flushing line control and instrumentation philosophy had to be developed. This included incorporating the following components:
- Pressure transmitter
- Solenoid Valve
- Air Vent
- Non-Return Valve
- Reverse Rotation Sensor
- Rotational Speed Detector
- ‘Black Box’ connection to existing site DCS
This new flushing line had to be integrated to site services and control systems. New instrumentation and valves were installed to control the flow and pressure of fresh water to keep the mechanical seal from running dry. An intermediary control panel with inbuilt safety protocols was implemented to integrate with minimum changes to the existing site control system.
There were delays faced in the supply chain on all components due to the global pandemic, which also slowed work on the unit itself to ensure strict safety protocols were followed. To reduce the overhaul window with the second pump REDU, all additional parts that were ordered for the first pump were pre-ordered for the second pump. The first REDU project required about seven months to complete under these conditions. However, due to careful planning, the backup pump with the same REDU requirements should be completed in less than two months, meaning that even in the face of the pandemic and design changes made to suit the customers DCS & SCADA, the REDU project was delivered on time.
After the REDU, the clean water from the external flushing line (which previously didn't exist) prevents the mechanical seal from running dry. The water filters down entirely into the enclosing tubes around the shafts and bearings, keeping them properly lubricated and protected from the pumped fluid.
This water runs through balance holes in the impeller into the suction area of the pump where it is then pumped along with the fluid through the system, minimizing water wastage.
The pump is not yet commissioned but it is expected the upgrades made to the material and the design drastically improve the meantime between failures, and thus, a reduced OPEX spend. The cost of new pumps would also have been higher, so this results in less initial CAPEX cost.
The REDU period was less than the turnaround time for a new pump based on the Torishima delivery window for an applicable new pump.
While the overall efficiency was not a driver behind the project (and is likely to be undetermined even on site), there are still efficiency results that can be noted. More uptime equals more plant efficiency.
TSSE expects the scope of work for the second pump to be identical (with the possible exception of minor tweaks), and it is due to be installed in early 2021. Any issues found in the first pump have been designed out of the second to make it easier to assemble. The project showed that a sophisticated and expert REDU provides a much less expensive solution to replacing with a brand new pump.
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