Ten years ago, during the modernisation of the power plant, a combined cycle gas turbine (CCGT) plant was constructed. This supplies the power plant with electricity (approximately 70% of the demand) and heat as well as space heating by means of cogeneration. The natural gas-fired power plant also supplies a large part of the district heating requirement for the nearby town.
The central components of the plant include feedwater pumps, which supply water to the steam generators at the power plant. As the reliability and availability of the pump groups are essential for the operation of the power plant, the CCGT plant has a total of three of these pumps available. While two of them are in operation, one is held in reserve so that in the event of a breakdown, the downtime of the power plant is kept to a minimum.
These important components were due to undergo maintenance for the first time in autumn 2019. In the interest of operational safety, the plant wanted to avoid being without the back-up pump any longer than absolutely necessary and therefore a short lead time was of paramount importance. After careful consideration of the competitive bids, the contract was awarded to Sulzer.
The project included the maintenance of the whole pump group consisting of the centrifugal pump, its drive motor and the connecting variable-speed coupling that controls the pump speed. All three components are made by different manufacturers. While the motor was being inspected, the Sulzer service center in Neuss overhauled the pump. The variable-speed coupling was sent to the facility in Schkopau, which specializes in the maintenance of gears and couplings.
As part of the standard maintenance programme, the condition of all three components was assessed and wearing parts were replaced. In the case of the variable-speed coupling, one component had to be replaced on the drive side, while a magnetic particle test certified the integrity of the remaining parts.
In this case, due to entrained dirt particles and air bubbles in the water, the pump is exposed to higher loads than the other components. The inspection made after dismantling and cleaning during the assessment found a shaft heavily damaged by scoring, and a destroyed impeller. Sulzer completed the reconstruction of the shaft and the replacement impeller was obtained from the original equipment manufacturer (OEM), enabling the rest of the overhaul to continue without interruption.
The remaining repairs could be carried out as required at the service centre. These activities were performed by the in-house mechanical production facility and included reworking the wear rings, producing new gauge rings for connection to these with an interference fit, producing a new throttling bush and reworking an impeller hub.
The project was completed on time in around two months and the maintenance of the second pump is scheduled to take place this year. “The customer was extremely satisfied with the handling of the project and found Sulzer to be a reliable partner”, says Andreas Holzaht, sales engineer at the Neuss Service Centre. “When the time comes, the second of the three pumps due for maintenance will also be overhauled to guarantee continued operational safety at the power plant and thus a reliable supply of electricity for the plant as well as district heating.”