At Tarmac's Cairneyhill quarry in Scotland, a solids radar device has proven successful in yet another difficult application on solids level measurement. Although some solids radar devices are able to handle ranges up to 70 m, this application was only over a small range in a crusher.
Vega's solids radar device overcame the difficulties being experienced with an existing ultrasonic level device, resulting in increased productivity for the plant.
Radar vs ultrasonic level: what is the difference?
If looked at from the application point of view, most solids level applications present some harsh or difficult operating conditions. The preference, where possible, is for non-contact measurement especially in a quarry, as it avoids any mechanical issues such as wear, roof loading and damage associated with cable-based systems. However, there are additional challenges for a non-contact system such as high levels of dust, build up, air turbulence, noise from machinery or falling product and often structures inside the vessel to be measured.
To date, ultrasonic sound-based measurement has been the traditional solution, but this can be hampered by all the conditions mentioned above. Sound pulses need to physically move the air to transmit the signal. This can become difficult or impossible in very dusty or turbulent air, and high levels of process noise can also interfere with and confuse a system. Radar uses microwave signals, which are almost completely immune to these environments, to detect the level. The microwave signal travels electronically and does not have to create this 'wave' of air. Turbulence, noise and dust are generally not even seen, even when sited close to a fill point in a pneumatically filled silo. It is also worth noting that solids radar are specifically designed for these applications, with increased sensitivity, sharper focusing and software able to handle uneven product surfaces.
The application
The gyratory secondary crusher application is at the heart of the Tarmac quarry in Cairneyhill. It feeds the screening plant which sizes the stone and stores it in the main silos ready for the subsequent despatch or processing on site. Almost all stone passes through here, so maintaining the correct level in the crusher is an important control, as it affects the efficiency of the whole plant.
It is a difficult measurement, due to the dust and noise as well as the narrow area required to be measured into the crusher down the side of the crusher table. An ultrasonic device was used as the system to control the level of feed into the crusher, but it delivered unreliable performance. This was because of the dust and process noise interfering with the sound-based signal, which meant that lost level signals were causing the crusher to overload, or run out completely. This often caused the crusher to choke and become blocked and the quarry was suffering regular, long down-time periods resulting in lower throughput, while digging out trapped 300 mm sized pieces.
The solution
A better solution was sought by the site electrical and instrumentation engineers, and they chose to trial a new technology in a radar level device from Vega. It was installed positioned above the inlet bowl, using its higher focused signal to look down the side of the crusher table. The device was also commissioned to adapt to tracking the fast changing level and has proved reliable ever since. The feed rate can now be read over a longer range throughout the process and can be more accurately controlled, resulting in an increase of crusher utilisation, capacity and availability of up to 12%.
Although radar for level measurement is a slightly more expensive option to ultrasound-based devices, it clearly performs in difficult applications and this reliability quickly pays back. Microwave-based measurement is being used in ever widening application areas in silos, hoppers and bins. Recently the head of engineering for a large European cement manufacturer commented: "Following previous experiences with many manufacturers and technologies ...we could not believe there is now something so reliable for (non-contact) silo level measurement." It seems radar for solids level is fast becoming the preferred technology for many companies involved in solids handling.
Free trial system for your application
Vega Instruments are offering users the opportunity to try this solids radar technology for themselves with a free trial, subject to a 'no obligation' site survey on a suitable application.
For more information contact John Groom on +27 (0)11 958 1901 or e-mail john.groom@za.vega.com
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