Drives move 55 million tonnes of gravel in China
In the remote south-western province of Yunnan, some 2000 km from Beijing and Shanghai, Sinohydro is constructing an important piece of China’s renewable energy program. The Xiang Jia Ba dam and hydropower scheme is the nation’s third-largest hydropower system and another major step forward in China’s sustainable energy and water resource management strategies.
When completed in 2015, the 30.7 billion kWh/year of electricity that will be generated by the Xiang Jia Ba hydro scheme will replace the equivalent of burning 13 million tonnes of coal per year. The follow-on effect of this renewable energy is also a significant reduction in emissions, equivalent to 23 million tonnes per year of carbon dioxide, 154,000 tonnes per year of nitrogen dioxide and 272,000 tonnes per year of sulfur dioxide.
Xiang Jia Ba will begin generating power in 2012 and the power will be transported by high-tension power lines to China’s central and eastern provinces. In addition to providing power, the 900+ million cubic metre reservoir on the Jin Sha Jiang River will help cities like Chongqing, Zhouzhou, Yibin and Shuifu (where the dam is located) and others to achieve national flood prevention standards. It will also provide water to irrigate approximately 250,000 hectares of land in 14 downstream regions.
To build this dam, Sinohydro chose Baldor’s CST (Controlled Start Transmission) as the best drives solution, installing 13 Baldor CST drives and two CSB (Controlled Stop Braking) units to deliver some 55 million tonnes of gravel over 31 km on five conveyor flights, laid through 29 km of tunnels.
The scale, rugged topography and sheer isolation of the Xiang Jia Ba project created numerous technological and logistical hurdles. Designing, developing, manufacturing, installing and supporting a reliable conveyor system on this scale presented an enormous challenge.
The Xiang Jia Ba project planning began in 2000, and soon presented a series of unique challenges. How to deliver gravel through such rugged mountains with very few opportunities to locate head/tail drives at surface locations meant that a 5-stage conveyor network was the preferred design. Sinohydro began construction of infrastructure in 2005 and finished boring the nine tunnels in 2Â½ years. After signing the contract, Baldor set about preparing designs, including extensive static and dynamic analysis of all five conveyors to ensure safe operation under all foreseeable start-up, shutdown, part-load conditions and power-out situations.
During the design stage, a number of issues were detected, and Baldor convened several meetings between other OEM suppliers and Sinohydro to ensure that these issues were overcome. One of the issues was the downhill grade of conveyor number 1. By integrating two Baldor CSB clutch only units and a CST drive in the design, Baldor was able to ensure control over the downhill acceleration profile.
Also during the dynamic analysis stage, a possible issue was discovered between conveyors 2, 3 and 4. The concern was that flywheels may be required on the head drives to balance the belt drift timing. Baldor’s analysis determined that a more economical solution was to use very high inertia motor rotors on conveyors 3 and 4 to allow more drift time for these conveyor belts, otherwise they would spill excess material if the preceding belt stopped too rapidly during a power outage scenario.
The design was completed in 12 months, and during this time Baldor also provided extensive data to other OEM suppliers so that their equipment such as winches and take-ups could be manufactured and installed to the required specifications.
The Baldor CST is a 2-in-1 drive that combines a planetary gear reducer and a hydro-viscous clutch specifically engineered to deliver and synchronise power from multiple drives, and to control acceleration of high-inertia loads such as long-haul conveyors.
There are more than 2000 CST units in operation around the world with 1433 of these in current operation throughout China, while there are nearly 200 in operation around Australia. CSTs have a proven track record on conveyors up to 30 km in length, in coal, gold, iron ore, copper and gravel mining operations, cement and power generation, as well as in bulk handling port facilities.
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