01 June 2007
The cement works in Lincolnshire is one of the company’s three UK works and contributes to the three million tonnes of cement sold by Castle each year. At Ketton two kilns produce 1.4 million tonnes a year. Castle continues to invest in modern plant and equipment at the works in a bid to improve the operations sustainability and efficiency.Raw and finished materials are stored across the site in a variety of silos, hoppers and bunkers. In the cement industry, materials measurement is very important and offers many challenges. The environment is harsh, the products are often handled at elevated temperatures, they are abrasive and generate very high levels of dust, material hangs up, ‘rat-holes’ and often forms ‘uneven’ surfaces.At 25m high and 10m in diameter, Ketton’s finished product silos are among the highest on the site and require the ‘longest range’ measurements. Non-contact ultrasonic devices with large transducers (250-350mm diameter) are installed through large holes in the concrete silo top. These systems have been used on site for a number of years, but despite high power transducers and sophisticated echo processing software, the sensors can still prove fallible to prevailing conditions. These include; filling, high product temperature effecting the efficiency of the transducers, air movement from conveying systems and in-flight dust weakening echoes. When these conditions are combined with the long ranges and sloping surface angles deflecting some of the signal, the systems can lose the ‘level echo’ altogether and misread.Castle turned to VEGA and tested its radar transmitter. VEGA says for solids applications a special transmitter is needed for reliable performance and suggested its VEGAPULS 68 radar. It is specifically designed for long-range applications, up to 70m, and uses high frequency K band (26GHz) to provide sharp focussing with beam angles from four degrees. Specially engineered ECHOFOX software was supplied for handling and tracking solids echoes. Radar is largely unaffected by in flight product and dust, this means the radar can be mounted close to fill points as well. It still gets a reliable signal return even from the sloping surfaces of fine powders, as the ultra high frequency can still reflect from the minute ‘horizontal’ surfaces of the finest particles to get a reflection back, whereas ultrasonic frequencies are too low to do this and are easily deflected. A plug in programmer, with high-resolution graphics and easy to follow menus was developed (remote HART or PC software PACTware are standard options) for the application. The radar technology is said to be easier to install, with an integral aiming swivel and only a 100mm (4”) diameter antenna. Connection and supply (or even multi-dropping with a ‘field bus’ system) are also much easier with 2-wire loop powered devices. The device has been installed at Ketton works for almost a year and Castle claims it has worked reliably over the full height of the silo, reading during both filling and emptying, providing level accurate level indication of contents. Further devices have also been ordered and used in applications across the site.
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