Engineering: Vorecons for Medupi Power Station
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Global drive component specialist, Voith Turbo, received an order from Sulzer in April 2008 for the supply of Vorecon drives to Eskom’s Medupi power station. These Vorecons will be built by Voith and weighs in at 50 tons, ten tons of which is oil content. With an impressive power output of between 18 to 20Mw, the units will be driving Sulzer boiler feed pumps at the power station.Martin Darrington, Voith Divisional Manager - Industry, says that rigorous testing showed that the Vorecon was unmatched for reliability, quality and longevity. “These are the three key elements that identified Voith as the preferred supplier of the variable speed planetary gears”, says Martin. “We are world leaders in hydrodynamic technology and the hydrodynamic Vorecon operates largely free of wear and offers unsurpassed efficiencies across wide speed ranges with a reliability rate of 99.97%”.
Eskom analysed the feasibility of the Vorecon together with three other products - a low speed VFD, a high speed VFD as well as an RK geared coupling to arrive at the best solution for the effective and efficient driving of boiler feed pumps. During a 12 month study which monitored and projected maintenance and operating costs over a 30 year cycle, the Vorecon performed seamlessly and without any maintenance costs. “In fact”, explains Martin, “the monitoring period revealed that the Vorecon could even exceed the maintenance-free 30 year life expectancy. This will, without a doubt, deliver excellent return on investment, a fact that was quickly recognised by Eskom. When Eskom Senior Management recognised and understood the incredible benefits and feasibility of the Vorecon as the best solution, they specified the units for driving the boiler feed pumps”.
Voith specially developed the Vorecon variable speed planetary gear in 1985 for power exceeding 1000kW and over 200 drives are in service worldwide. The Vorecon operates on the principle of power splitting, which permits high efficiencies over a wide range of speeds. Most of the power is transmitted hydrodynamically directly via the main shaft and the rotating planetary gear. At the heart of the Vorecon are a hydrodynamic torque converter and a superimposed gear. Only the power necessary for adjusting the speed of the driven machine is split off from the main shaft through the hydrodynamic torque converter and superimposed into the planetary gear. By using the majority of the mechanically transmitted power, the overall unit efficiency exceeds 95% and is therefore ideal for continuous speed regulation of heavy duty machines such as the control of pumps, fans and coal mills in power stations.
Pump technology expert, Sulzer, will supply three boiler feed pumps per boiler with one as standby for pumping water into the boilers at high pressure to generate steam for the turbines. Martin elaborates, “This is where the high efficiciency Vorecons really come into their own as high volumes of water generate more steam, increasing pressure for maximum power generation. In other words, high pressure is essential in order to pump the required volumes of water into the boiler and, by adjusting the planetary gear, the input can be increased from 1500rpm to a staggering 18000rpm. We have designed the Vorecon not to exceed noise levels at 95 dbA while vibration levels of the rotating machinery will run at 2.5.
“The total value of the order is calculated at approximately R250 million and”, continues Martin, “we expect this contract to increase spin off potential for the supply of our products in the Voith stable.
Delivery of the first Vorecon to Eskom Medupi will take place in December 2009 with one unit being delivered every month thereafter. Each Vorecon will be delivered as a complete unit.
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