FEATURE FLOW, LEVEL & CONTROL
required, the process vacuum is protected by a valve, which closes while the cabinet door is open. This valve is also the portal that the level measurement must be made through, so the sensor has to be contactless to measure through it. Challenges faced include the ash density which varies considerably, very high temperatures, high levels of dust and fumes, vacuum, changing particle size and density. In addition, no ‘air purging or cooling’ would be allowed due to the combustion method, as well as the falling waste stream as it drops through the same valve into the barrel. The VEGAPULS 69 was installed to
replace radar level sensors. As this has much narrower focussing (3.5°), the device has no interfering echoes from the nozzle or the 6”/150mm diameter slide valve, which is approximately 0.8m away from the sensor. The set up was quick and simple, virtually no ‘false signal suppression’ was required, and it is able to measure directly right down into the barrel, with no loss of signal from the prevailing process conditions. This increased reliability means that the process is now more productive and change-overs only called for when needed. In addition, because the measurements are more accurate and the high levels can be more confidently anticipated, the operators can coordinate more efficient change over sequences, saving time and increasing safety. In another application, the VEGAPULS
69 has been installed at Kerneos’ production plant in Purfleet, Kent. Calcium aluminates, alumina cements or high alumina cements are obtained by the reaction at high temperature of lime (from limestone) and alumina (contained in natural minerals like bauxite). The product obtained after cooling is calcium aluminate clinker, a hard mineral which, after being crushed and screened, is used as an aggregate. When ground into a very fine powder, the clinker becomes calcium aluminate cement (CAC) which forms a paste when mixed with water. This hardens quickly, forming a rigid solid within 24 hours. However, the management of these
powders across the Kerneos production plant is a challenge. The fine powder is abrasive, adheres to everything and bulks out easily when pneumatically conveyed, so the weight is not always consistent with volume. One major part of the manufacturing system at the plant is handling reject alumina powders. There is a raw product silo for these returns at the heart of the plant, which handles inputs from these eventualities. The silo has four filling points, which can be unpredictable in their input – from road tankers, screens
16 OCTOBER 2015 | INSTRUMENTATION
and mills or vacuum lines, and often simultaneously. This can be at varying rates too, from a steady inflow from the manufacturing process or vacuum, to sudden fast fills from tankers and batch returns. If the silo overfills, the whole plant would need to shut down, so reliable measurement is critical. Many technologies have been tried
to monitor the level in the silo, which is only 4m in diameter by 8m high with a coned section, but the VEGAPULS 69 worked well. According to the company, its focussed signal, excellent responsiveness, resistance to build up and unrivalled signal to noise performance, means it can ignore unwanted filling noise, false signals and antenna build up (no air purging, even though every ‘PULS 69 sensor has this facility). Not only has the result been reliable,
long term level measurement, but being contactless it also negates any abrasion issues. In fact its performance has lead to the site planning to install this as the standard solution for level measurement in a number silos of all sizes across the site.
ON THE RIVER Meanwhile, VEGAPULS WL61 water radars were installed as test instruments in an application on the River Weaver. Here, the Dutton sluice site consists of eight large sluice gates lifted by Rotork actuators. The sluices operate depending on the water level. Here, level monitoring needs to be very accurate as
the navigation is closed to river traffic if the water level is too high. So, the river level is now measured by
four instruments. Two ultrasonic sensors (for redundancy) are mounted in stilling tubes which are required to reduce ‘loss of echo’ issues from weather and surface conditions. However, the tubes can require substantial engineering to install, and generally they need ongoing on-site maintenance to prevent blockages, or repairs to keep measurement errors to a minimum. According to the SCADA
maintenance engineer: “In recent years
Products such as the VEGAPULS 69 radar level sensor are being used in a variety of applications
we have experienced issues where either one or both of the ultrasonic sensors loses echo or ‘drifts’, causing level sensor failure alarms to be sent out.” As a result Canal & River Trust (CRT) has
installed two other devices alongside these - the VEGAPULS WL61 water radars - as test instruments. These were mounted on a unistrut adjacent to the stilling tubes and CRT has compared the data from both sets of instruments over several months. Since installation there has been no ‘drift’ with the WL61 water radars. The engineer commented: “As far as I can see, the WL61 radars provide more reliable data than the ultrasonic devices… I am pleased with the quality and performance of the VEGAPULS WL61 level radars. We will be installing these in place of the ultrasonic sensors at the other River Weaver sites and in other CRT sites as we replace older equipment.”
VEGA Controls T: 01444 870055
www.vega.com/uk
CONCENTRATING ON SHAMPOO PRODUCTION
The shampoos and conditioners manufactured by the personal and home care business of the Mibelle Group begin in concentrate form before being diluted from a 70% concentration down to 27%. As the dilution needs to be correct, the flow rate of the water needs to be precisely measured. While at an exhibition, Andy Crossley, Mibelle’s engineering manager, discovered the PF D550 Portable
Doppler Flow Meter from Micronics. This is used to monitor and balance flow, or to troubleshoot flow problems in full pipes. According to the company, quick to install and calibrate, this is ideal for evaluating the performance of in-line flow meters. It is particularly useful in projects where a permanent flowmeter is not required or to temporarily replace installed flow transmitters. The ultrasonic sensor straps onto the outside of pipes and
measures flow in any pipe that conducts ultrasound by injecting high frequency sound through the pipe wall and into the flowing liquid. Gas bubbles or solids suspended in the liquid reflect the ultrasonic signal back to the sensor at an altered frequency. This frequency shift is called the Doppler Effect. The PF D550 continuously measures the change from its transmitted frequency to the received frequency to accurately calculate flow. Commenting on the solution, Crossley said: “I’ve been very
impressed with the PF D550, it has proven to be a very useful tool and I would have no hesitation in recommending the use of more Micronics flow meters throughout Mibelle Group’s factories.”
Micronics T: 01628 810456
www.micronicsflowmeters.com
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