Bryan Orchard examines the refit and capacity upgrade of the 100-old Atwater pumping station in Montréal. The ageing design of the pumping hall presented many challenges, not least reconfiguration of the supplied pumps.
Delivering potable water to Montréal’s residents, commerce and industrial infrastructure is a massive task for the city’s Water Department. It operates six water treatment plants, the largest of which are Atwater and Charles-J.-Des Baillets. The water feeding these two plants is extracted from the St Lawrence River purified by a combination of filtration, ozonisation, ultraviolet (UV) water treatment and finally chlorination at the Charles-J-Des Baillets. From there it is diverted to the Atwater plant for distribution through the City’s network of pipes.
If it’s necessary to shut down Atwater or Charles-J.-Des Baillets, water can be diverted to and from either plant. This ensures that water levels in all seven reservoirs around the metropolitan area are maintained at optimum capacity. Both production plants are interconnected via sizeable piping, so that in the unlikely event of one plant going down, water can still be supplied to the reservoirs.
History
The Atwater drinking water treatment plant site represents an important part of Montréal’s heritage. Originally constructed in 1868, it has undergone many changes, the first being the construction of the central pumping station in 1923 and the replacement of the original steam pumps with electric pumps. Over the past 100 years, the plant has played a critical health and safety role in the city’s development.
The city has made considerable investments to increase production capacity and improve operating efficiency. The most recent investment was to refurbish and expand the pumping facilities through the replacement of ageing pumps with purpose-designed units manufactured by pump and valve specialist KSB, bringing output up to 700,000m3 per day of drinking water for a large area of Montréal Island.
Project
As part of the project involving the refurbishment of equipment at potable water production plants, pumping stations and reservoirs (REQUP 1), the City of Montréal launched a public tender for the pre-purchase of six (6) new motor-pump sets (MPS) and their components in 2018. This would include medium voltage synchronous electrical motors with exciters, switch gear cabinets, to replace the ageing high-pressure pumps in the Atwater potable water pumping station.
The project’s very nature – being a complete replacement of the pumps in an existing pumping hall – threw up a range of engineering challenges, not least the pump design specified by the client. In the terms of the contract, the pump manufacturer would be responsible for the supply of the pumps and all related electrical components, as well as assisting in the units’ installation, commissioning, testing and post-commission personnel training.
Key to the project was that the pumps had to be centrifugal single-stage horizontal split-case, double-suction, double-volute pumps with bottom entry suction and discharge on the horizontal side. The requirement for bottom suction entry and side discharge was dictated by the existing piping infrastructure within the pump house.
As an existing pump station, it was critical to ensure the dimensions of the new equipment complied with all the dimensions and clearances so it could be installed in the available space while taking into account the existing structures, including the location of the water intake and discharge pipes. Any modification to this old configuration would have had a huge impact (in engineering and cost) on the piping arrangement and construction at site.
The challenge
KSB’s working relationship with the City of Montréal goes back over 40 years, when in the late 1970’s it supplied five of its type ME 5,500HP 4200 l/s pumps to the Charles-J.-Des Baillets water treatment plant. In 2015 a further KSB ME pump was installed – coming on stream in 2018 – which enabled the plant to operate to its optimum design capability.
In spring 2018, KSB was invited to tender for the supply pumps for the Atwater plant, and subsequently won the contract at the end of that year. The contract would take into account not only the acquisition cost, but also the operating cost of electrical energy over 25 years. This meant that the pump sets had to deliver high levels of operating efficiency.
To meet the contract criteria, engineers in Halle, Germany had to manufacture a bottom entry suction pump, a design which is not a common standard design, and meet 29 essential hydraulic and mechanical criteria. The pump was custom-made to this design and subjected to full factory testing with the specific project motor and the specific project switch gear at the factory in Germany.
Equipment supplied
The pumps designed and supplied were six single-stage horizontal split case double suction pumps, each fitted with 948mm double-entry radial impellers. Each pump comes with a 2500HP synchronous motor with brushless exciter. The pumps are rated to operate at 1580l/s at a head of 73m. Included in the package are an excitation control panel and electrical integration services.
There was also the need to keep the plant fully operational during refurbishment. This was achieved by extending equipment installation over an extended period, with the existing pumps taken out sequentially and replaced by new ones. To fulfil this, the units were fabricated at the same time and stored nearby throughout the refurbishment’s two-year duration.
Concerns were raised about possible delays in delivery of the new equipment. This was because the obsolescence of existing pumps would worsen as spare parts were no longer available. The plant would also have to deal with two separate electrical power systems, which is not recommended. In fact, the new pumps were to be connected to the 25 KV power system while the existing pumps would continue to be powered by the existing 12 KV power system, which was reaching the end of its useful life. This situation was identified as creating additional costs in maintenance and management of the operation.
All six pumps were fabricated and ready for factory testing in early 2020, at the start of the pandemic. The Halle factory maintained the testing schedule despite personnel shortages. Due to global sanitary restrictions, the client was not able to witness the tests at the factory in Germany in person. This difficulty was resolved by allowing remote participation via video conference to the factory test bench. All tests were successful and even improved the theoretical efficiency.
Summary
The equipment was shipped to a storage site in Montréal where periodic (monthly) maintenance was done. The first two pumps were installed and commissioned in 2022, with the four remaining units installed and commissioned in August 2023.
The contractor installed all the pumps and electrical equipment and completed the inter connection wirings between the switchgear, motor control and excitation panels. KSB inspected the pumps and motor mechanical installation. Also KSB’s subcontractor (electrical integrator) checked all the wirings from/to all the above mentioned equipment, these being sensors, motors, switchgear, motor control and excitation control panels. KSB was also present during the pump SAT.
All pumps were retested onsite and achieved required performance, followed by personnel training for pumps, motors and switchgears undertaken in autumn 2023.