| |
|
 |
 |
| Outokompu PSI 500 |
Malvern, UK -- On-line analysis generates data which leads to improved process knowledge and tighter process control and is therefore an important tool for both process and product optimization. In solids handling processes, particle size is typically an important variable, and therefore a change from off-line to on-line particle size frequently delivers variable cost savings, enhanced process efficiency, and/or improvements in product quality.
On-line particle size analysis is used across a range of wet processes to study the behaviour of diverse systems ranging from dilute oil-in-water emulsions to highly concentrated slurries. The properties of process streams, including particulate concentration, particle size, and the effects of dilution on the material being analyzed, can vary widely. Some streams may be suitable for direct analysis without any treatment, making an in-line system an option, but for others the on-line solution may involve sampling and then sample conditioning, such as dilution. For any given application a number of issues need to be considered carefully:
Analytical method
Various analytical methods have been used to determine the particle size of materials in a slurry but the particular benefits associated with low angle laser light scattering (laser diffraction) technology have resulted in it becoming the industry standard for many sectors.
As laser light is shone through a sample it is scattered to a degree determined by particle size. Particle size information can therefore be back-calculated from the observed diffraction pattern. The technique generates consistent volumetric particle size data with no requirement for external calibration. It is rapid and non-destructive in nature. The main limitation of the technology is that a proportion of the laser light must be able to penetrate through the stream and therefore for some applications dilution is required.
Sampling/sample conditioning and transport
The purpose of the sampling system is to remove a suitably sized, representative, flow or sample, from the process stream. The issues of settling and fouling need to be addressed in the design which also needs to take into account the required analytical regime, which may be either continuous, or batch if sample or diluent consumption needs to be minimized. Facilities for washing or back-flushing the sample line are important for maintaining data integrity.
The sample withdrawn from the process must be transferred appropriately to the analyzer and conditioned in a controlled way if necessary. Conditioning operations include dosing, with for example additives to prevent agglomeration, and dilution, to ensure that the sample can be analyzed accurately. Any tendency of the material to aggregate or dissolve need to be carefully considered.
System automation
Effective automation is needed to ensure minimal manual intervention, and in addition, to fully exploit the potential of an on-line system, the data produced needs to be presented in a useful form. Communication between any control package and existing plant systems needs to straight forward.
Insitec
The Malvern Insitec is an industrially robust on-line particle size analyzer, for wet or dry systems, based on laser diffraction technology. It can be used for particles in the size range range 0.5 – 1000 micron and can handle relatively concentrated samples as a result of a patented multiple scattering algorithm.
 |
| Figure 1: The Gulfstream continuous multi-stage diluter |
Insitec can be used in conjunction with the Gulfstream diluter (see below) for concentrated slurries with fine particles (in the range 0.5 – 100 micron), and forms an integral part of the Outokompu PSI 500 unit (see below) developed for the coarser materials (10 – 1000 micron), typical of the minerals industry. It is supplied with two software packages, RTsizer and Malvern Link, which present data in the required form and communicate with plant control systems, respectively. Data presentation can be customized to meet the requirements of the user. Sampling and analysis are fully automated.
The Gulfstream
The patented Gulfstream, a continuous multi-stage diluter (Figure 1), designed using computational fluid dynamics, uses a simple co-axial venturi/eductor to aspirate and dilute a sample. It can be operated continuously or in batch mode and is powered purely by the diluent flow. Figure 2 demonstrates the excellent repeatability achieved using the Gulfstream.
 |
| Figure 2: Particle size distribution data for a talcum slurry diluted to different concentrations. |
The Outokompu PSI 500
The Outokompu PSI 500 is a fully integrated unit, developed in a collaborative project between Malvern and Outokumpu, which incorporates sampling, conditioning and analysis. Sampling is a two-stage process - a primary representative sample flow of 50 – 170 l/min is cut from the process stream, from which a secondary sampling system cuts a representative slice every 10-30 seconds. This sample system is suitable for very high solids content systems (the only requirement is that the slurry must flow), for solids with a specific gravity ranging from 2 to 8. Flushing and cleaning of the sampler and the sample line is automated and there is an integral dilution unit for sample conditioning. Sample cutting frequency and dilution ratio are used to produce a suitable sample stream with the required flowrate.
Insitec technology has been used successfully to increase the efficiency of production of a broad range of materials including paints and pigments, chemicals, minerals, paper and toner. In the following case study the benefits achieved following the installation of a PSI 500 unit at a chromite concentrator plant in Finland are discussed.
Case study – monitoring cyclone operation at a chromite concentrator
The chromite concentrator plant at the Kemi mine of AvestaPolarit Chrome Oy in Finland produces upgraded lumpy ore and metallurgical grade chromite concentrate. Figure 3 shows the overall flowsheet for the plant. Material of the required size is produced using gravity separation, high gradient magnetic separation, and a battery of cyclones.
 |
| Figure 3: Flowsheet for Chromite fines concentrator section |
A PSI 500 unit was installed at the plant in December 2002, initially just to monitor the particle size of the feed to the high-gradient magnetic separation (HGMS) circuit. Following test work on the reliability and usability of the system under plant conditions a sample line was also installed to monitor the feed from the grinding circuit. A single PSI 500 unit monitors both streams resulting in an analysis cycle time of 5 minutes.
Particle size data for the feed from the grinding circuit (Sampling Point #1) provides a feedback signal to grinding control. Data for the feed stream to the HGMS circuit allows mal-operation in the cyclones to be rapidly observed. If any of the cyclones block and short cut to the overflow the feed becomes coarse and the circulating load in the HGMS circuit increases dramatically, resulting in recovery losses. Figure 4 shows how clearly this can be seen from data generated by the PSI 500.
 |
| Figure 4: Cyclone disturbance detection |
Operation at the plant has shown that the PSI 500 has great potential for the monitoring of wet slurries in minerals processes. The analyzer has worked reliably with minimal maintenance producing highly repeatable assays which can be correlated with off-line data generated using conventional techniques. The unit allows plant disturbances to be observed in real time and appropriate action to be taken much more rapidly.
Conclusions
The benefits of on-line particle size analysis for manufacturers handling slurries or emulsions are evident. Malvern has worked, together with partners with detailed industry knowledge, to develop technology specifically tailored to a wide range of applications. The benefits of on-line analysis can therefore be readily exploited by manufacturers from many different industrial sectors, allowing them to gain competitive advantage by improving process efficiency and product quality.
http://www.malvern.co.uk/
© Copyright 1998 - 2009 Powder and
Bulk Dot Com
Top of Page
|
|
| |
| Send news and case
histories to:
news@powderandbulk.com |
|
|
| |
|
|
|
I Live Newsfeed
I |
|
Increase traffic and add
content to your website
with our exclusive
newsfeed generator.
Our live newsfeed
allows you to
include news
headlines from our
News Center, right
on your homepage.
Headlines update in
real-time, automatically.
Click here to create
your own newsfeed! |
|
| |
|
 |
