Measurement of carbon black process

Citation

(2002), "Measurement of carbon black process", Pigment & Resin Technology, Vol. 31 No. 5. https://doi.org/10.1108/prt.2002.12931ead.006

Measurement of carbon black process

Measurement of carbon black process

Keywords: Powders, Carbon black, Measurement

The difficulty of accurately measuring carbon black powder deposits in a silo filled with swirling fine dust has reportedly been overcome by KROHNE's BM100A reflex radar level unit after other level measurement devices proved inadequate (Plate 1).

Columbian Chemicals Sevalco Ltd, is a major UK manufacturer of carbon black, a burnt oil residue with a very fine talc-like consistency used as a colourant.

Plate 1 The difficulty of accurately measuring carbon black powder deposits at Columbian Chemicals Sevalco Ltd has been overcome by KROHNE's BM100A reflex radar level unit

At the plant near Bristol the carbon black powder is cycloned into 10 × 4 m diameter silos. The hot powder is blown in from the top of the silo and builds up inside the vessel while agitator blades rotating in the middle of the silo ensures that the powder continues to flow freely. The settled powder is then pumped from the bottom of the silo, and is compacted into easy-to-handle pellets before being transported to customers.

The settled product needs to be accurately measured, but according to KROHNE other level measurement devices are confused by the dust cloud and are unable to differentiate it from the settled carbon black powder. Moreover, the company informs us that horn- type radar devices become clogged by the dust, rendering them useless.

KROHNE's BM 100A meter was installed in the top of a silo, with the cable probe descending some 3 m into the vessel ending just above the agitator blades. The BM 100A operates by emitting an electromagnetic pulse down the probe. When the pulse reaches a layer with a defined change in dielectric value, for example, between powder cloud and the powder deposit, part of the pulse is reflected back toward the sensor, where it is translated into a level measurement. For liquid applications the remainder of the pulse can then be used to monitor the next product layer, or interface.

This method of operation is said to ensure that the sensor probe continues to operate with a high degree of accuracy irrespective of the material being measured, while remaining insensitive to clogging or encrustation by deposits. Furthermore, KROHNE informs us that unlike traditional radar, detection of the reflected pulse is unaffected by the shape of the tank or silo in which it is positioned. Consequently, in the company's opinion the BM100A can be used in process conditions that render conventional level sensing techniques, such as ultrasonic, capacitance, or radar devices, unreliable or inaccurate.

The Reflex Radar BM 100A is believed to be ideal for the measurement of all liquids and powders with a dielectric constant greater than 1.05. It has no moving parts and offers low cost, with virtually maintenance free operation.

The BM100A claims high reliability and repeatability of 1 mm for liquids and powder. It can reportedly be used in conditions from −30°C to +240°C and from full vacuum to 100 bar, with ATEX certification for Zone 0 applications in liquids and Zone 20 dust approval for powders.

Various communication options are available including the Windows compatible "PC-Star" configuration and diagnostic software, HART "smart" protocol as standard and the option of Profibus PA, Fieldbus Foundation, or RS485 protocol. It can also be supplied with an explosion proof enclosure and an intrinsically safe output option where required.

Details available from: KROHNE. Tel: +44 (0) 1933 408500; Fax: +44 (0) 1933 408501; E-mail: info@krohne.co.uk