The IRmadillo for Monitoring the Alumina Refining Process
Alumina refining is a complex and hazardous process involving variable natural materials, hazardous and corrosive chemicals, high pressures and high temperatures – making traditional measuring and monitoring techniques almost impossible. Process improvement and optimisation requires an effective method of monitoring the process stream compositions, so how can this be achieved in such a harsh environment?
Taking samples off-line to a lab is one method, but by the time the results are available the process may well have already changed dramatically. At-line sampling is not safe as alumina refineries are dangerous places for staff to work in. Simple on-line measurements like temperature probes and flow meters are important for closing heat and mass balances, but more advanced analytical methods are needed to allow true, real-time, process optimisation. Up to now, these tools have not been available to the industry. All this changes with the introduction of the IRmadilloDiamond FTIR Spectrometer.
The Keit IRmadilloDiamond has been specifically designed for harsh, unforgiving and caustic environments, and is ideally suited for monitoring alumina refining – enabling real-time control, improved efficiency and therefore saving the refinery money.
The Bayer Process and Keit’s IRmadillo
The Bayer process is the dominant method of alumina production globally, and in its essence consists of dissolving bauxite in concentrated caustic soda (sodium hydroxide) solution, filtering out waste products and recrystalising aluminium hydroxide before calcining into alumina.
An overview of the Bayer process is shown below, with recommended installation points for the IRmadillo.
- Residue storage stream
- Spent liquor flow
What about other instruments – Raman, near infrared (NIR), refractive index monitors?
The process needs a very large amount of caustic soda, which is recycled as much as possible. Understanding the concentration of caustic soda at all points throughout the process is a key driver for cost savings and process improvement.
Organic chemicals and impurities present on the bauxite react with the caustic soda, using up a precious input to the process. Some of this can be regenerated by adding lime (which turns sodium carbonate back into sodium hydroxide), but other chemicals cannot be removed by lime and can cause problems further downstream – the IRmadillo helps identify and measure a huge range of chemicals – so you can optimise the process and save money.
- Raman spectroscopy is similar to the FTIR (mid infrared) that drives the IRmadillo’s process monitoring, but it can be very strongly and negatively affected by particles and bubbles in the solution, as well as showing strong fluorescence in many cases.
- Near infrared (NIR) technologies provide much less specific information than FTIR – they’re very good in some industries, but not up to the demanding job of alumina process monitoring.
- Refractive index monitors are cost effective instruments for simple systems, but they cannot cope with complicated mixtures such as those present in the Bayer process.
Raman, near infrared and refractive index monitors have been around for many years prior to the IRmadillo – put frankly, if they were the right tool wouldn’t you have one already?
The IRmadillo can easily monitor the following chemicals and properties:
- Alumina (as aluminium hydroxide)
- Total Caustic
- Total Alkalinity
How does the IRmadillo cope with build-up of scale?
Installations in spent liquor typically don’t exhibit scale-up on the IRmadilloDiamond.
Keit is also currently developing an in-situ descaling system for other installation sites, so you can install the instrument then walk away, knowing it will stop the build-up of scale. What’s more, the instrument checks every scan it takes for quality, and can be programmed to alert you if it detects a scale build-up for manual cleaning if something went very much out of specification on plant.
My process is exposed to the weather, hot and cold temperatures and possibly even caustic spray – how does the IRmadillo cope?
The IRmadillo was originally developed for the petrochemicals and oil and gas industries – so it can take a beating. It has an ambient temperature range of -20°C to +55°C so temperature variations aren’t a problem. It also has an IP65 rating meaning it doesn’t mind whatever the weather throws at it. It also has an optional additional enclosure for caustic environments.
Can you measure alumina and organic chemicals at the same time?
The IRmadillo is based on FTIR technology meaning it always measures everything that’s present in the mixture. So it can look for organic chemicals (such as oxalate and malonate), inorganic salts (such as sulphate) and the physical properties (such as total caustic and total alkalinity) all at the same time. It provides a reading every 2 minutes, giving you the tools you need to make changes in real time.
The IRmadillo for Alumina Process Monitoring
If you purchase the IRmadillo for monitoring alumina processing you will receive:
- IRmadilloDiamond process analyser
- Interface and mounting accessories to integrate with your process (following a consultation with your engineering team)
- IRmadillo controller PC
- Calibration services
- Ongoing technical and recalibration support (as per your warranty or maintenance contract)
If you like the sound of this, please contact us for more information. We can arrange a trial installation on your plant for several months so you can see you yourself just what the IRmadillo can do.