Cement Americas

Fal 2017

Cement Americas provides comprehensive coverage of the North and South American cement markets from raw material extraction to delivery and tranportation to end user.

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16 CEMENT AMERICAS • Fall 2017 • www.cementamericas.com FEATURE The ultrasonic device was then replaced with the new contactless level measurement device. The Krohne ra- dar level meter, with a Polypropylene (PP) drop anten- na with a 6-in. nominal size, was placed directly on the silo's roof opening. Since the antenna was not affected by the angle of repose, it did not have to be aligned. Installation was further helped by the device's pre-con- figuration, which only required uploading a few more parameters into the device, including silo height, block distance and cone shape. In addition, the new device required less maintenance due to the lack of moving parts. The antenna's ellip- soidal and completely-enclosed shape, along with its smooth surface, minimized the need for dust protec- tion, regular flushing, and other periodic cleaning tasks. Measuring Cement Dust Levels The technology was also used at a Chinese cement plant, which uses ball mills to grind clinker. This pro- cess generates large volumes of cement dust, which is collected, stored, and then fed back into the production cycle. The 30-ft.-tall (9 m) dust storage silos are equipped with air injectors, which fluidize the dust and prevent it from forming up on the silo walls. This simplifies extraction, but the injectors lower the dust's dielectric constant to 1.4 Σr. Combined with the dust-laden air, the lowered dielectric makes it more difficult to obtain a reliable and accurate level measurement. Plant operators had previously tested ultrasonic, time-do- main reflectometer (TDR), and pulse radar devices, but found that none of these technologies could meet the cement plant's measurement requirements. To provide the required accuracy and reliability in level measurement, Krohne installed an OPTIWAVE 6300 C level meter with a 6-in. (150 mm) PP drop antenna and a 6-in. flange connection. Fitted to the silo roof, the two wire FMCW non-contact radar continuously measures the dust volume left in the silo. Several months of testing showed the device worked well, and the company equipped nine additional silos with similar measuring devices. Fly Ash Level Measurement One U.S. building materials producer previously used an ultrasonic level meter to monitor the amount of fine fly ash powder in a conical 20- x 65-ft. silo (6 x 20 m). How- ever, the company found it difficult to conduct accurate measurements due to the low reflective medium in a dusty environment. The challenging product surface has a low dielectric constant (3.3 Σr). There was also a tendency for the fly ash to build up on the silo walls and the level radar's antenna. This led to regular instrument failure, with subsequent process interruption. On several occasions, trucks were kept waiting for several hours. The producer sought out a reliable level meter that has an approval for use in hazardous dust areas. They opt- ed for the OPTIWAVE 6300 C level sensor, installing the device with a 6-in. (150 mm) drop PP antenna, using a 6-in. flange. The 24 to 26 gigahertz (GHz) FMCW level meter gener- ates a wave signal that enables the producer to accu- rately and reliably measure the product level in the dusty fly ash silo. The measuring signal is transmitted by a 4-20mA signal to a control room, where the silo level is constantly monitored. With the new level measurement technology, inefficient loading and costly delays due to false level indication are no longer an issue. In addition, workers no longer need to climb to the top of the silo to clean the sensor, thus substantially improving worker safety. Improved Performance Non-contact radar level meters incorporate technology that is not impeded by the dusty environment of cement storage facilities. In addition, accurate and reliable product level measurement is not affected by internal structural objects and build-ups in silos. Joe Incontri is Krohne's director of marketing and projects.

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