The IRmadillo for Monitoring Pulp & Paper Processes
Pulp and paper manufacturing is a chain of complex chemical processes involving hazardous chemicals, different temperature profiles and variable natural materials. This can make process monitoring and control difficult, and traditional approaches have significant drawbacks and issues.
Paper mills use substantial amounts of chemicals, water and energy, and require effective recycling of these resources to be financially viable. Real-time process analytics can dramatically improve the efficiency of this process, so how can this be achieved with the hazardous chemicals and complicated processes present in mills?
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. There are some instruments designed for monitoring specific elements of the manufacturing process, but they either require sample conditioning (such as filtering or cooling), they may struggle with suspended solids or are not compatible with fluctuating temperatures. 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 pulp and paper manufacture – enabling real-time control, improved efficiency and therefore saving the mill money.
The Kraft Process, Paper Bleaching & Keit’s IRmadillo
The Kraft process is the dominant method of pulp manufacture globally, which consists of treating wood chips with steam, sodium sulphide (Na2S) and caustic soda (sodium hydroxide – NaOH). This produces pulp and a by-product known as dilute black liquor containing a variety of chemicals including NaOH, sodium sulphate (Na2SO4) and sodium sulphite (Na2SO3). This can be converted back to Na2S through a recausticizing process, involving many different steps – shown in more detail below.
The washed pulp can either be used directly to make board or packaging, or after bleaching can be used to make paper or tissue. Bleaching involves a range of chemicals such as NaOH, chlorine dioxide (ClO2) and hydrogen peroxide (H2O2). Lastly, the bleached pulp is mixed with chemical additives (for example cellulose derivatives or polymer additives) to achieve the desired properties in the finished product before rolling into paper. The waste white water from the paper making machine is recycled and topped up with additional chemical additives.
An overview of the Kraft process is shown below, with recommended installation points for the IRmadillo.
- Kraft Process:
- White liquor stream
- Green liquor stream
- Weak black liquor stream
- Concentrated black liquor stream
- Entry to bleaching plant
- Paper Making Process:
- Chemical blend chest
- White water chest
The Kraft process relies on being able to efficiently recover the inorganic chemicals from the black liquor for reuse in the digester and this is done by converting first to green liquor and then to white liquor in the recovery circuit, also recovering energy in the process. Beacause of the wide variety of chemical reactions involved, this opens up multiple opportunities for the process to go wrong and quickly drift away from effective and efficient conditions. Understanding exactly what is happening inside the boiler and the causticizers is a key driver for cost savings and process improvement.
Chemicals are added during the paper manufacturing process to achieve the desired end product (for example, wet strength additives for tissue products). These can be expensive chemicals, and measuring their concentration in white water can ensure that the minimum amount of chemicals required are being used, dramatically reducing costs for the mill. The IRmadillo helps you optimise every stage in the process, improving efficiency and saving money.
What about other Instruments – Raman, Near Infrared (NIR), and Refractive Index Monitors?
- Raman spectroscopy is similar to the FTIR that drives the IRmadillo’s process monitoring, but it can be very strongly and negatively affected by fibres, pulp and bubbles in the solution, as well as showing strong fluorescence in many cases. Controlling pulp and paper with Raman would be an extremely difficult thing to do.
- Near infrared (NIR) technologies are good at measuring solids (for example monitoring the wood chips themselves) but cannot differentiate between similar chemicals (for example between sulphate and sulphite ions), meaning they’re not good enough for fine control of the Kraft process.
- Refractive index monitors are cost effective instruments for simple systems, but they cannot cope with complicated mixtures or temperature variations giving them limited use in the Kraft 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 properties:
- EA: Effective alkali
- AA: Active alkali
- TTA: Total titratable alkali
- TDS: Total dissolved solids
- TDD: Total dissolved deadload
- RE: Reduction efficiency
- REA: Residual effective alkali
- RAA: residual active alkali
- Paper additives
Pulp & Paper FAQs
How does the IRmadillo cope with build-up of scale (such as pirssonite) in green liquor?
Keit is currently developing an in-situ descaling system for installation sites that suffer from scaling, 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.
What sort of sample preparation or conditioning is required?
The IRmadillo was developed to install directly into your process, with no need for filters, sample conditioning systems or anything else. During installation scoping conversations, our engineers will discuss how best to seal the instrument into your process (such as an ANSI or DIN flange). If your process operates at a very high temperature then we may need to bring the temperature down to a manageable level.
Can you measure multiple chemicals at the same time?
The IRmadillo is based on FTIR technology meaning it continuously measures everything that’s present in the mixture – all the time, every time. For you, this means it can look for organic chemicals (such as cellulose and polymers), inorganic salts (such as sulphate) and the physical properties (such as effective alkali and total dissolved solids) 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 Monitoring Pulp & Paper Processes
If you purchase the IRmadillo for monitoring pulp processing and paper manufacturing, 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.