Articles & Case Studies

KSB delivers water boosting pump solution for Italian power station

Posted: Thursday 22nd December 2011

There is no escaping the reality that power generation plants require considerable amounts of water for cooling purposes and that the water supply has to be constantly available. Where water is drawn from nearby rivers, it is to be hoped that the water volume of water remains sufficient to meet the power station’s cooling requirements all year round. In recent years many countries have recorded falling levels in their major rivers and for some power station operators this is becoming of major concern.

In Italy the River Po, some 652km long, is the country’s main natural waterway and supports the needs of industry and agriculture. Whilst occasionally subject to heavy flooding, the level of River Po has been falling in recent years and for some of the power stations along its course, this is leaving water intake pumps in shallow water at certain times of the year. The Edoardo Amaldi La Casella thermal power (Fig. 1) plant 15km to the west of Piacenza is one power station affected by this problem and now, with the assistance of KSB Italia, it is having to take steps to remedy the situation.

Built between 1971 and 1973, La Casella has a total nominal output of 1,500MW and over the past decade it has undergone a substantial development programme, changing from oil to natural gas. Today it contains four identical natural gas-powered combined cycle units of 375MW net output each, has EMAS (Eco-Management and Audit Scheme) registration and is fully compliant with EU environmental regulations. As to be expected with a power plant of this size, it requires considerable quantities of steam condensers cooling water and operators Enel are now taking action to ensure that its cooling water intake pumps are not left high and dry when river levels fall. For pump manufacturer KSB, this action has provided its Italian subsidiary - KSB Italia - with a great opportunity not just to supply its pump technology but also to demonstrate its all-round engineering and project management capabilities.

Each of the four power production plants has its own cooling water intake pump house on the river bank and when originally installed, each of the four pumps was sufficiently submerged in the river flow to ensure a constant supply of cooling water. The problem is that when the water level drops to below 47.5m above sea level, the water level at the point where the intake pumps are located is too low so the volume of water required cannot be guaranteed. The problem is further compounded by larger quantities of river bed silt being sucked into the pump chambers. In order to overcome the problem, Enel embarked on a year-long feasibility scheme that involved the technical and commercial co-operation of KSB Italia. The project devised was an ingenious system involving the installation of a booster pumping facility below the existing pump houses and located further into the main stream of the river.

Booster pumps

This booster pumping facility comprises four pump cells, each containing two KSB Amacan PA4 1500-1060 submersible pumps which raise water 2.2m and transfer it into the suction basin of the existing pump houses, thereby ensuring that the original pumps can continue feeding the steam condensers in the power production plants. The solution sounds straightforward, but in fact it proved to be more complex involving considerable civil works, the design and fabrication of special pump housings anchored to the river bed and the expertise of scuba divers.

The KSB Amacan PA is a wet-installed submersible motor pump featuring a single stage axial open impeller for installation in a discharge tube. Typical applications include irrigation, wastewater treatment, power station and industrial plant cooling and storm water pumping.

Providing a capacity of 4.4³m/sec, with a head of 3.2m at a speed of 420rpm each of the eight pumps (Fig.2) specified for the La Casella project has a 1660mm diameter impeller and a 1500mm DN discharge column. At 5.5 tonnes, the weight of the pump ensures self-centred seating in the discharge tube and is sealed in the tube by means of an ‘O’ ring. Because there are no anchoring or anti-rotation elements, the Amacan is quick to install and easy to remove.

Engineering design

Commencing in January 2010, the La Casella project has involved KSB in the design, civil engineering and logistical considerations necessary for the successful installation and commissioning of its pumps. For each of the eight pumps it was necessary to design and fabricate a special housing approximately 7m high comprising a screened intake, discharge tube to hold the pump and a discharge outlet. These housings were calculated by KSB AG using the ‘finite elements method’ in accordance with European anti-seismic rules (Fig.2).

Their construction was undertaken by KSB Italia and sub-contractor Tecno-Eettra Acque Srl. Particular care was taken in welding, with all welded points being checked using RT (Radiographic) and MT (magnetic particle) non-destructive test procedures according to Enel’s specifications. Because of their considerable size, each of the housing components had to be transported separately by lorry from the workshop to the La Casella site and finally mounted on site.

To enable the eight Amacan pumps and their housings to be installed, four water-filled cells were constructed in the river immediately in front of the existing water intake pump houses. These cells serve the purpose of eliminating any water turbulence in order for the concrete base platforms to be cast in the river bed followed by lowering the 15 tonne pump housings onto the base platforms (Fig.3). Ensuring that the housings were in the exact position for fixing to the base platforms was delegated to Tecno-Elettra Acque, this being an exacting procedure involving the skill of crane company Casella Autogru Srl using two heavy duty mobile cranes. The task of completing the fixing process involved three scuba divers from Sammozzatori Italia Srl, who performed a highly skilled and potentially hazardous task in poor visibility water. The entire mounting process was supervised on site by KSB Italia’s engineering foreman.

KSB Italia project manager Marco Beretta takes up the story: “The La Casella project has provided KSB Italia with the opportunity to demonstrate that its resources extend far beyond the supply of pumps. At the outset we drew on the hydrological resources of our colleagues in Germany in order to ensure that we would be selecting the best pumps for the duty and design the pump housings so that the water intake would match the suction basin requirements of the intake pumping stations. Considerable importance was given to the design of the pump housings, particularly in respect of the intake chamber as it was necessary to eliminate the risk of vortices and cavitation. It was our responsibility to get the housings fabricated, tested, delivered to site and finally installed.”

In developing the pumping solution KSB also had to take into account that the booster pumps would only be called into action when the river level falls to a critical point, that being 47.5m. At this level the power station lowers the dam locks and starts the booster pumps. Thus, it is possible that the pumps could remain idle underwater in their housings for several months and exposed to river bed silt build-up. The design of the housings takes this into account, so when called upon the pumps are in a state ready for operation.

Enel and KSB Italia also took on designing the engineering works for the four booster cells and the programme of installing the pumps and their housings without there being any disruption to the water intake needs of the power station. This involved building the four separate cells, each with a removable wall on the river side. This concept allowed the continuous availability of water to the intake pump stations, but also enabled each cell to be closed-off when the housings and pumps were being installed. Once the pumps and their housing were installed, the riverside walls were removed to allow river water to flow into the pump housings.

“It was absolutely critical that there was no water flowing into any of the cells during installation,” continues Marco Beretta. “Lowering the housing and pumps into position was an exacting operation, requiring millimetre precision. For the Amacan pumps to provide their designed performance their housings have to be true and securely mounted. Also it was a potentially dangerous for the team fixing the housings to the submerged base platforms, so safety was given the highest level of consideration. The divers were in constant communication to the above water team directing the crane operator.” (Fig. 4)

The actual installation was scheduled to commence in the second half of 2010, but rivers levels and environmental conditions along the River Po proved too hazardous, so it was in late March 2011that work commenced. This process involved the first two housings being lowered into position in the first cell and fixed to their mountings. The next stage was to lower the Amacan pumps into the discharge tube and ensure that they completely aligned within their housings. The installation procedure was finalised with the water-tight power connections and closure of the top of the housing.

“The time involved in completing the installation for each booster pump cell was three weeks,” says Marco Beretta. “Because it was necessary to shut down the relevant power plant unit, our schedule was largely dictated to us by the demands on the power station, so we had to work very closely with Enel. By careful planning, we ensured that our partners perfected the installation and commissioning procedures in the shortest time period and without any discernable interruption of the power station’s generating capacity.”

The success of the KSB pump solution could prove to be a blue-print for other powers stations along the River Po which could also become affected by the falling level of the river.

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