This instrument has been specifically engineered for operation in Red Mud Clarifiers, Thickeners, and Washers within Alumina Refineries. Its design integrates proprietary sensors, microprocessor-controlled electronics, and robust mechanics, resulting in an instrument that is a perfect fit for this demanding application. However, it can also be utilized in other applications where monitoring and control of sedimentation in settler tanks is needed.
We provide our customers with a low-maintenance solution capable of functioning in one of the harshest industrial environments, reliably delivering essential process information for online control or analysis of the settling process. The measurement ranges are extensive and specifically tailored to encompass the full operating range of the red mud settling tank. Our system does not compromise on performance; it consistently delivers accurate measurements regardless of the settling conditions within the tank. The Analyser not only reliably identifies and measures process parameters during normal operation but also maintains exceptional performance during disturbances in the settling process. This remarkably rugged instrument has been in service for several years in alumina refineries and is employed in various settler control schemes, ranging from simple manual setups to advanced fully automatic systems.
PORTABLE - Recognizing that repairing or maintaining electronic instruments in extreme weather conditions is impractical, we have designed our instrument with portability in mind. Our specialized cable gland, along with all plug-in connectors and a bayonet mounting system on the instrument stand, enables quick instrument changeovers in just 20 minutes.
SYNCHRONIZED - The Analyzer’s operation can be synchronized with the rotation of the Mud Rake, allowing the sensing probe to effectively scan the tank between the rake arms and reach the tank's bottom. This synchronization enhances measurement repeatability by consistently sampling the Solids Profile at the same reference point relative to the rake, thereby eliminating distortions caused by the rake's stirring effect.
MULTI-OUTPUT - Four independent, isolated 4-20 mA outputs provide critical parameters for a settling tank: Tank Level, Clarity, Light Mud Level, and Heavy Mud Level. A numerical analysis of data collected during the probe’s descent from the top to the bottom of the tank generates some of these values. Furthermore, all variables, along with the raw data, are accessible via a MODBUS RTU output through an opto-isolated RS485 connection. The raw data can be utilized to graphically display the vertical solids distribution within the tank. The three animated graphs above illustrate typical examples of such displays. The 4-20 mA outputs serve as a valuable backup in the event that a multidrop communication scheme is employed to control a series of tanks.
AUTOMATIC CONTROL - A classical feedforward and feedback control scheme is commonly employed for the two available control variables: managing Heavy Mud Level through modulation of Underflow Pump speed, and regulating Flocculation dosing via modulation of Flocculant flow. In the case of Heavy Mud Level control, the feedback process variable is derived from the Heavy Mud Level measurement obtained from the instrument. For Flocculation control, the feedback process variable is determined by the difference between Light Mud Level and Heavy Mud Level (LML-HML). Both control schemes have been successfully implemented in numerous plants. Additionally, raw data (solids profile) can be utilized to independently extract other parameters for control or monitoring purposes.
CLOUDY ZONE - Also referred to as the Light Mud Zone. Contrary to common assumptions, this zone is typically characterized by an abrupt transition in solids content, rather than a gradual decrease with depth. Empirical observations indicate that this transition is more akin to a knee than a slope. This characteristic makes the selection of the Light Mud threshold value critical, especially in cases where the Light Mud Zone has low suspended solids concentrations (approximately 1000-3000 mg/lt). Taking this issue into account, we have provided a wide range of Light Mud values available for user selection. Animated graphs 2 and 3 above illustrate examples of solids profiles with both small and large knees (cloudy zones). It can be seen that in both cases, the onboard numerical analysis accurately calculated the Light Mud Levels, as reflected by the time trends shown in the same graphs.
SOLIDS PROFILES - This term refers to a set of measurement data generated during the vertical scanning of the tank. The data consists of individual measurements taken approximately 1 cm apart. The high granularity of these measurements is crucial for flat-bottom tanks, where control ranges are narrow. For taller tanks, the spacing between points can be adjusted at the MODBUS command level to more suitable values to mitigate data handling. A graphic display of consecutive scans offers a dynamic visualization of the process.
Experienced personnel can gain valuable insights from visual observations of the Solids Profile. For instance, in the uppermost animated graph, it is clear that while the Light Mud Level remains relatively stable, the Heavy Mud Level shows a significant increase. Initially, this might suggest that the issue arises from low flocculant dosing. However, the absence of expansion in the Light Mud Zone points to an alternative source of the problem. Low mud compaction in the mud bed, potentially caused by inadequate blending of bauxite ore or insufficient addition of milk of lime, could lead to these results.
Graphical record of instrument readings, over period of time (Time Trend) is central to evaluation of the process.
For sedimentation process, Light Mud Level and Heavy Mud Level are the key variables used for monitoring of performance of a settling tank.
Example of time trend (as captured by the instrument) is displayed in the graph on the right, it shows an event where flocculant (polymer) flow has been temporarily interrupted.
