The Fragant power plant group is located in the Möll valley of the Tauern mountains in Austria and is operated by Kärntner Elek- trizitäts AG (KELAG). It is the company’s core for generating power and a mainstay for safe and reliable power supply in the federal province of Carinthia.
The power plant group consists of six large and several smaller alpine reservoirs, seven storage power plants and three run-of-the-river power plants. The total output is approximately 474 MW, which generates approximately 840 million kWh of electricity each year.
During phases of low network utilization, the storage pump, Oschenik 1, in the Innerfragant power plant, delivers water to the Oscheniksee reservoir located at an altitude of 2,953 ft (906 m). In cases of high power demand, the water is used to cover peaks. Andritz Hydro, Graz, one of the leading suppliers of equipment for hydroelectric power generation, received an order from KELAG to renew the Oschenik 1 machine unit and replace the 1968 pump with a much more powerful and larger model.
New Pump – Greater Efficiency
The Oschenik pump project included hydraulics, design, calculation, testing, production, assembly and commissioning. The operator’s requirement was a considerable boost in efficiency that was to be achieved, for example, by increasing the flow rate by approximately 18 percent. This was implemented by means of a horizontally split, 6-stage storage pump.
Fit for Extremes: Split Mechanical Seal
Andritz Hydro commissioned EagleBurgmann to design, calculate, produce, test and assemble a mechanical seal on the drive and non-drive side of the pump shaft. The fully split seal of the HGH/VGH series was selected for this application.
Split mechanical seals for pumps are used in applications where seal assembly is difficult. The seals are designed as partial or full axial split, which enables them to be mounted directly on the shaft of the completely installed pump. In the case of the semi-split EagleBurgmann HGH, the housing parts are split and the inner parts are not split during initial assembly. With the fully split EagleBurgmann VGH, all seal components are split. Both types of seals provide reliable performance in large pumps used in a wide variety of water projects worldwide.
Complex FEM Calculation
The mechanical seals for the Oschenik storage pump were redesigned based on FEM calculations and optimized for the extremely dynamic and static pressures. The typical pressure operating limit of the VGH is 116 PSI (8 bar) for a diameter of 17.72” (450 mm). However, the requirement for the new storage pump was 725 PSI (50 bar) static with a diameter of 22.05” (560 mm).
A particular challenge was to maintain the stability of the split seal housing and especially the metal-to-metal sealed coupling joint under the high pressure. This required the inclusion of structure mechanics (leakage, strength, screws, deformation at the joints, etc.) and sliding face design (lift-off behavior, leakage) in the complex calculations.
Test and Commissioning
The seals were tested at the EagleBurgmann test facility at 392 – 609 PSI (27 - 42 bar) in dynamic operation at 750 min–1 and static at 725 PSI (50 bar). The customer released the seals in March 2016.
Both seals were installed in December 2016 by EagleBurgmann installation engineers from Austria and Germany, and the pumps and seal system were put into operation in January 2017.
Flow rate: 3.32 m3/s
Manometric delivery head: 890 m
Rotational speed: 750 min-1
Output: Pmax , 34.5 MW
Housing pressure test: 3,843 PSI (225 bar)
Design for operation: Yearly 3,200 hr.s with approx.. 274,000 start/stop cycles
Expected service life: 75 years
Shaft diameter: 21.65” (550mm)
Temperature: +34 ˚F - +95 ˚F (+1 ˚C - +35 ˚C)
Pressure dynamic: p = 392 – 609 PSI (27 – 42 bar)
Starting pressure: 334 PSI (23 bar)
Pressure, static: max. 725 PSI (50 bar)
Rotational speed: 750 min-1
Sliding velocity: vg = 75 ft/s (23 m/s)
Seal face and seat: Silicon carbide (Q2)
Metal parts: CrNi steel 1.4301 (F)
Seal supply system: Plan 32 (injection of clean fluid from an external source) and Plan 62 (quench on the atmosphere side)
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