On nearly all plants we have used float, target plate and ultrasonic. This system is then used to give froth depth level control by twin outlets on graduated control 1 at 0-50% then 2 0-100% followed if 2 are fully open by 1 at 50-100%

The float ball sits on the interface between froth and slurry, plus froth cam does help with pulp level control.

There was a long conversation about this a few months back. Float ball and target is my favorite.

What you use. We used DPT and ULTRA SONIC

The float ball and target with an ultrasonic is a cheap accurate way to do level. DP can be inaccurate due to density changes. But if the pump box area is very steamy or dusty, the ultrasonic won't work. Steam was an issue in the oil sands and we ended up putting in 3 DPs on the pump boxes - that way we could adjust for density variations.

Thanks for the input everyone. We are bringing a new product to market here in Australia so it is always good to gauge people’s thoughts on the existing technology.

Used level sensing probes supplied to us in India by AMDEL- Mt. Isa- Australia in early 90' which was erroneous mall functioning due to froth adhering false coatings on probes. Needs flushing every 15 to 30 minutes to readjust to real requirements. You can measure top slurry level.

Commissioned Metso Rcs cell in copper and apatite plants, having PID programmed twin dart valve assembly, working on the inputs from floating bob targeted plated read by ultrasonic sensor. The sample reading frequency can also be varied to achieve stability of level control system. The advantage is that, this system programmed to monitors froth bed not slurry level. The best one I have seen.

On float cells the ultrasonic/target plate system is the most common. Its main advantage is it is cost effective, but its challenges are there are moving parts in contact with the froth/slurry and if incorrectly set up Ultrasonic signals can be slow and adversely affect loop response.

More recent developments are magnetostrictive, guided wave radar transmitters, and dual capacitive type sensors. Each of these has their limitations in application.

We have been using a level probe based on conductive principal in this application with huge success. Most concentrators where we have tested these have either converted from their current systems, which mentioned is a mixture of the technologies that he mentioned. The advantages that we have with these probes are that they are extremely accurate, on stable liquids can offer resolutions of 1mm and accuracy of >1% (Please bear in mind that due to the turbulence in the cells, these figures will not be achieved, we have however achieved figures within 5%), they are not affected by buildup on the rod, easily detects the interface between liquid and froth, are easy to set up, do not require maintenance (some of our customers have had them running for three years without maintenance). The only drawback we have had to date is that it is slightly more expensive than the ultrasonic devices; this cost is however recovered very quickly with the stability in control that these devices offer. The cost of the devices has also due to some new technology advancements come down slightly, so it is becoming more attractive to the customer. You are welcome to read a little more on the blog. http://is.gd/2yOS9H , in reality creating a stable environment for the level control, wheredevices do not get stuck due to mechanical restrictions just enhances control providing a more stable plant. The trends that you will see on the blog are a comparison between the probes and ultrasonic devices and the probes and magnetostrictive devices. In both cases the probe is the controlling device, with the other product acting as a follower to the probe to see what effect build up has on these devices. Also note that we have used these on concentrate sumps and mill feed sumps with huge success. Products and types of systems that we have these installed on include. Tank Cells, Bank Cells, and Column flotation. Products used on at present include, Copper, Nickel, Platinum and Gold, we have installed some in the fertilizer Industry and have tested on Coal washing plants with success.

Also check out Mintek FloatStar.

I am glad you mentioned FloatStar here, we have quite a few systems running with and without FloatStar (Feeding the signals into FloatStar), and the results have been very good in both instances. Unfortunately I do not have documentation that was published by any of these mines, but the feedback given from those to date has definitely indicated a remarkable improvement in control, and downstream in recoveries.

What technology does the Mintek FloatStar actually use to accurately measure pulp level?

On the website there is a lot of 'why you need it' but not much (none to be honest) 'how it does it'.

It looks like I am hijacking your discussion here. FloatStar in general just use the input signal from the field that is provided, it does not matter what type of Instrument is used, I have Differential Pressure, Ultrasonic, Radar, magnetostrictive and the level probes that we market, I am also sure that there must a few others that we are not even aware of. The important factor with FloatStar is that it is a predictive control system and reacts according to process changes that it sees. Keeping this in mind, we need to remember the very important thing with Instrumentation and Process control. If you get rubbish in, you get rubbish out (normally amplified), so it is very important to get a signal/ measurement that are as accurate as possible for FloatStar to react for optimal performance.

We have some exciting developments in the pipeline related to the flotation industry and I would like to keep you all up to date.

Good to see you are in consulting company. You need any help I can support you for all mineral processing form Mine to metal and Pollution control activities.

I think if you want 'hows' you need to specifically ask. Since you did to my understanding (a simple metallurgist's viewpoint) Floatstar is a clever circuit stabilization device. It combines feed forward and feedback control loops with the aim of minimizing any disturbance by reacting to it ahead of time.

Take an example of a float bank with three level controls A, B and C. When Sensor A sees a flow increases it sends a signal to the valves on tank A to open to maintain the level. It also sends a single to the level controller on B to open the valves, this signal is combined (in a certain ratio) with the level reading of tank B which the sends a signal to the valve in tank B to not only maintain the level of tank B by taking into account B's level but also what is happening in the previous tank. This way the valves on tank B are already adjusting for the upstream disturbance that is coming. Similarly the valve output on tank C is a function of the level in A, B and C. To my mind the trick is getting the ratio of the signals right and having the appropriate lag. I may be wrong and I'm happy to be corrected.

FloatStar may be more than that now but this was my understanding of its level control. I think it works well but as it says without good readings AND properly setup valves it is going to be a big mess.

I read the topic as being more on the monitoring and measurement side of pulp level, rather than the controlling side of things, which is what the FloatStar seems to be doing. This is why I asked what technology it actually uses to read level. As said, this correct level measurement is what the entire system relies upon so we must ensure it is done as accurately as possible. If monitoring flotation for example, you need to ensure the correct technologies are used to overcome problems like inaccurate measurement due to pulp density changes which can affect conventional shaped floats and differential pressure type units.

We have installed RIVS flotation cells. And level control of flotation cells is very good you can try it. And also they have automata tigon system for hall flotation circuit.

Absolutely correct, that is why we are aiming to provide as stable and accurate level signals as possible. Any Instrument can be used, as FloatStar just takes an input signal and processes it to perform the tasks that described. The accuracy of the Instrument has a direct effect on the outcome of the whole process. Thus the more accurate signals, the better your plant stability. Having said that, I have seen various different technologies employed, admittedly there are very accurate systems on the market, each one however has its different pros and cons. I believe that the level probes provide readout as accurate as is needed at an affordable price for the market. Being within roughly 5% of your exact level on a floatation cell that has a lot of turbulence is extremely good. Getting stuck in high and low positions just creates an upset in the whole system and considering that Floats uses feed forward and feedback control, any inaccurate/ unstable Instrument in the circuit will mess up your whole control system, which is a disaster on the metallurgical side, as this causes sludge, bumping, spillage and another point that is not always considered, it affects your retention time in the cells.

It's good and enthusiastic as the topic is extending from froth bed level accurate measurement to the roots contributing to the stability, stability criteria, performance and optimizing and ultimately improving metallurgical results or economics of flotation plants.

The flotation plants performance depends on

Optimum liberation grind size and (regrind size also) of minerals. Reagents used for effective uniform surface coatings, there sequence and residence time. Hydro dynamic parameters like froth bed, bubble size, bubble speed contributing to healthy pulling rate.

Under this factor froth bed level accurate measurement falls, froth bed depth maintenance with consistency, and taking care of upward bank cell underperformance with respect to time. I mean the missed valuable mineral particles. (Beautiful a simple or a situation of tank cell A, B, and C where tank C will pull the particle missed from tank B). At times the minor surging of slurry feed pumps to flotation cell needs and will be taken care by froth level controlling system. Now a day’s all these are controlled by good simulators with automated process control system based on Artificial intelligence and Neuro network process control systems.

The ultrasonic sensor with target plate is one of the most common methods of froth depth measurement in a flotation cell. The major problem with this method though is when the float-ball shaft tends to get stuck, and as such false level readings are transmitted to the PLC which takes "corrective action" that causes disturbances in the circuit. Not sure how these incidents can be reduced without getting operators to occasionally clean the shafts with wash water. 

You solve problem by tying thin film of rubber on the shaft up to top level with folding to avoid stretch of rubber.

In my comments earlier, I have spoken about the level probe that we have, this completely eliminates the stickiness, as there are no moving parts on these device.

Float Sensor for Level Control

This method, a float on the surface of the pulp changes position with level changes, depends on output of an electrical signal proportional to the angle that represents the position of support arm to the float from a fixed pedestal (see Fig. 113). The output of the sensor is an electrical signal from a variable capacitor or potentiometer that can be coupled directly to an electronic controller, or a pneumatic controller if the electrical signal is converted to air pressure.

Float buoyancy is sensitive partially to density of the froth layer, and to a lesser degree the pulp density. A disadvantage of the float buoyancy method is the possibility for accumulation of congealed froth on the float upper surface, adding weight to decrease float buoyancy. The float can be flushed with a water stream to overcome this difficulty. Fluctuations in level due to aeration is a more severe source of disturbance, an operating factor that can be overcome by placing the float sensor in a stilling box between the active cell and the tails box. The float system has the advantage that the level signal is modulated continuously in the range of cell level operation.

Fig. 113 illustrates the arrangement of equipment for a float-type level sensor driving an electrical dart valve position actuator attached to a dart valve stem.

source:

We are having a problem with float ball, shaft and target plate system. Mainly, the shaft gets stuck from time to time and that is causing a lot of disturbances in the circuit.