Each year Castle Cement sells more than three million tonnes of cement, satisfying 25 per cent of the UK’s need and providing employment for 1,200 people. Ketton works in Lincolnshire is one of the company’s 3 UK cement works. Obviously a company this size, with huge cement silos will need a highly accurate cement silo level indicator.

The Roman Emperor Hadrian was one of the first people to use a form of cement when he built the Pantheon, a temple to the gods of the pagan world as far back as AD117. There is also a great deal of history attached to Ketton Works too, back in August 1928 the Ketton Portland Cement Company was incorporated and the construction of a works began. Within a year it was producing cement from the first kiln and by the end of 1929 the 140 men – and 2 women – on the permanent payroll had despatched 8,500 tonnes of cement.

Today, two modern kilns produce some 1.4 million tonnes a year and Ketton is one of the most efficient cement works in Europe.  Castle continues to invest in modern plant and equipment at the works and is intent on improving the operation’s sustainability and efficiency.

 As with all cement works, 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.  With these conditions, careful consideration needs to be taken when choosing the correct cement silo level indicator.

At Ketton Works, the finished product silos are among the highest on the site and require the ‘longest range’ measurements. They are concrete construction and approximately 25m high and 10m in diameter. The cement silo level indicators used here were non-contact ultrasonic devices with large transducers (250-350mm diameter) 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 affecting 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, so the hunt for a more reliable cement silo level was on.

Of course, there are ‘contact, cable based’ technologies, such as capacitive or newer guided wave radar level gauges (TDR) based technologies available to use on these applications. However this type of cement silo level indicator will pose inevitable concerns, regarding roof loadings with a cable that is buried in the product of over the full height of a 25m silo (structural engineers may need consulting).

The wear on the cable by product, changing dielectrics (variations in humidity) and any cable ‘breakage’ consequences of would also have to be considered. With a cable based system requiring installation on an empty cement silo, the timing of installation is also a factor if silos are continually used.  If an electromechanical ‘plumb-bob’ device is applied, the potential for limited measurement (none during filling), high maintenance, risks of buried weights and cable breakage are potential concerns.

Castle Cement is always looking at new technologies and solutions to improve process and product quality and has evaluated a new technology, non-contact solids radar.  Their final choice of a cement silo level indicator was a VEGA radar transmitter, which has been tested and used ever since on this difficult long range finished product application.

VEGA developed solids radar devices from their experience with 100,000 radars already sold world-wide. For a cement silo level application, a special transmitter is needed for reliable performance.  VEGAPULS 68 radar 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 only 4 degrees. With improved dynamic range, it has 1000 times more sensitivity in signal processing and specially engineered ECHOFOX software for handling and tracking solids echoes.

 Radar is largely unaffected by in flight product and dust, this means VEGAPULS 68 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.

 An easy set-up for a silo level indicator is important too, so a simple to use plug in programmer with high-resolution graphics and easy to follow menus has been developed (remote HART or PC software PACTware are standard options) There are practical reasons, apart from enhanced reliability and range of measurement for using this radar technology. It is easier to install, with an integral aiming swivel and only a 100mm (4”) diameter antenna they are much easier to fit in a concrete topped silo.

Connection and supply (or even multi-dropping with a ‘field bus’ system) are also much easier with these 2-wire loop powered silo level indicators.  Level indicators with air cooling/cleaning can be used on high temperature applications such as clinker cooler beds or pre-heaters, or applications where high levels of build up can occur.

On this cement silo level application at Ketton works, the device has now been installed for almost a year and has worked reliably over the full height of the cement silo, reading during both filling and emptying, providing level accurate level indication of contents. Further devices have been also been ordered and used in applications across the site.  VEGA provided the best cement silo level indicator for the job.

The outcome of these solids radar developments has resulted in highly successful applications across a multitude of industries, proving to many users that non-contact level measurement can be reliable, working very well with fine, dusty products such as plastics, fly-ash, coal, sugar and flour for example.  The VEGAPULS 68 really is becoming the preferred silo level indicator.

VEGA are offering users to find out about this technology with a free trial on their applications. Contact VEGA for more details on 01444 870055 and ask for sales or e-mail info@uk.vega.com.