Centrifuge Instrumentation 3

[shobi]

Hello everyone,
I am interested in instrumentation used to automate these type of centrifuges, especially in mining industry. If you have any first hand experience with them please write back. I am particularly interested in Bird's (manufacturer) centrifuges. I have found very little information on their actual design and operation. I would welcome any links, antecdotes, or personal experience.
Thanks in anticipation.

 

[dbaird]

Inter-lock system to ensure the cover cannot be opened while the rotor is spinning. Vibration and/or speed sensors for overspeed condition. Process media temperature, pressure and flow instrumentation.



David Baird
mrbaird@hotmail.com

Sr Controls Engineer

EET degree.

Journeyman Electrician.

 

[m777182]

I would include means to prevent a dangerous situation in a case of a power failure-at this moment you loose all information about the status of a centrifuge that is provided by electrical measurement. You cannot use electrical solenoid valves, oiling of the bearings is out and you cannot reposition the knive into a safe position.You cannot retard the rotor so it will move through the range of resonance frequency for a long time.If the power comes on again take care of where the process starts again!
M777182

 

[ischgl99]

I work in the centrifuge field and found a good book about centrifuges written by Wallace Leung from Bird, "Industrial Centrifugation Technology" It describes how the machines work, but may not be exactly what you are looking for.

As far as the instrumentation, which parts are you looking to automate? Unless the machine is old, it should already have an automated start and stop cycle. Some companies use a UPS in the case of a power failure for a controlled stop. Oil is used for all of the bigger sizes, grease cannot be used due to the speeds being run and the need for heat disapation. The UPS would be a good idea here to turn the oil pump back on after a power failure when the machine is coasting to a stop.

A speed sensor for over speed as well as underspeed is a must. Bearing temperature sensors are good ideas, torque overload, oil pressure if oil lubricated bearings.



Mike Bensema

http://www.dutchmenservices.com

 

[jmw]

So far everyone has looked at the instruumentation of the equipment but not the process. This is more difficult and would require some more infromation from you on what products you are centrifuging.

For some slurry streams you may need to consider density or viscosity measurement on the inlet and outlet streams. This information will help you measure the efficiency of the process.


JMW

http://www.viscoanalyser.com

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[shobi]

Thank you jmw, you finally got my drift. We have a 25 years old centrifuge process (26 birds all together in parallel configuration). They are used to centrifuge raw bitumen (oil sand industry) to remove solids (5 to 10% fines). Right now we don't have any kind of instrumentation on the process side (we do have safety instruments though). I am try to devise an instrument strategy to do a complete mass balance as well as to monitor tails line oil losses (wastage). My plan is to use one coriolis on feed (6" line), one coriolis on outlet (product) and one nuclear density meter on tails ( can't use coriolis due to higher solids contents, 25% and they are very abrasive). Is this sufficient for the process? Is there an oil monitoring device which can work on harsh tails stream? 25% sand, 70% water and 4-5% Hydrocarbons). I am sure now you all have a very clear picture. If you still have any more questions, please let me know and I will try to answer them.
Thanks everyone who took some time to consider my problem.

 

[jmw]

A couple of extra questions:
What temperature?
Any idea of viscosity at this temperature?
How do the density and viscosity of the "clean" bitumen compare with that of the untreated? and how stable are these values over time i.e. as the deposit is worked.

If you want to know how well the centrifuges are doing, then if the bitumen is of a stable consistency or shows only long term drift, then a downstream instrument is probably all you need. Laboratory data will give you the bitumens "clean" density. This, and the mean sand density lets you do a %mass display using a downstream density measurement or density and viscosity measurement.

You are already considering a nucleonics device.
However, a vibrating fork density sensor may also be suitable (upto 200degC, hence the temperature question and i am assuming you are heating to reduce the viscosity which will aid separation).

With 25% solids, I am going to ask if the viscosity shows a marked change between the solids laden and the clean bitumen. If density is insufficientlyly discriminating or you may get ambigous results, then viscosity may be a more sensitive indicator. These are questions a little bit of lab work will resolve before you have to spend any money.

The vibrating element sensors are very rugged and with good installation will give you good service.

If installed downstream of the centrifuges you will be measuring the relationship between the possible 0% solids and what you are getting. If the centrifuges are good, then presumably the sensor will not be seeing much in the way of solids anyway. These sensors are used in oil refineries and bitumen processing plant already, I just don't know of any on oil-sands.

I do know of there use in various mineral slurries inclduding chalk slurries from the extraction plant to the cement works. These slurrie sare usually well laden with extraneous material such as flints, sand and the odd bit of excavator.

I have a photo of a unit sent back for re-calibration that has evidently been hit by a large object with considerable force as well as being subject to long term erosion. The unit had been in service for some years. The sort of erosion sufered can be avoided by good installation.

These sensors are also installed in towed drones for river mud density and viscosity measurement and in downhole instrument strings. They also are used on bitumens in refinery produced bitumens for blending. Density (whatever the technology) and viscosity are popular choices for automating evaporatiors and centrifuges, sand separators, wash plant underflow monitoring and the like.

JMW

http://www.viscoanalyser.com

Eng-Tips: Pro bono publico, by engineers, for engineers.

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[SL1000]

Sorry to jump in on this thread but I found what jmw said very interesting. We have 5 product cents and 4 tailings cents (tails cents being replaced by a horizontal belt filter).

The product cents are a critical part of our process prior to rotary kiln gas fired dryers. The product is potasium cholride (potash). Tails from these is a brine solution. It would be useful if we too could improve our operating and control philosophy. It is physically difficult for us to measure any properties of the product falling into our dryers online and manual samples of the moisture are usually the only telltale of problems with the cent operation.

In your opinion would the measurement of density via the vibrating forks you have mentioned give an indication of efficiency/machine health. If so where can you get the probes? An ealry indication of screen wear or blockages would be useful.

Cheers

 

[jmw]

SL100,
if you have a solution or slurry then density measurement may be suitable (or viscosity).
The main criteria is resolution required.
The greater the density diference between the carrier and the entrainment the better the resolution.

Most manufacturers offer a variety of materials including titanium, monel, hasteloy (various) and stainless and augment these with non-stick coatings such as PTFE or PFA.

I would start with

http://www.solartronmobrey.com

(7826 and 7828) but do a search (I'm getting lazy!) to find other manufacturers such as Bopp & Reuther, PEEK (ONYX i think). In flow through systems Solartron again but also the mass flow meter companies who offer density as a secondary measurement.

The Solartron fork now comes with a long stem extension for top mounting in tanks (e.g. in Boraw production).



JMW

http://www.viscoanalyser.com

Eng-Tips: Pro bono publico, by engineers, for engineers.

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[SL1000]

Thanks jmw

certainly food for thought there. Your mention of mounting on a tank may be useful as the feed lines to the centrifuge don't need much of an escuse to sand out, a bit of runaway rubber lining would cause a nice blockage when introduced to a fork.
I think the feed is fairly consistant, it's the grade that changes mostly depending on the head grade to the plant and the insols level. I suppose it would be worth a try though to get the data and map the differential density overtime and then look for a meaningful relationship.

Talking of instruments for this sort of thing I recall using an ultrasonic probe that measured %solids in an ECAT thickener. I think dig some notes out.

Thanks

 

[jmw]

Ultra-sonics are often used for sewage treatment, you will find some information about these on the Solartron site as this is also in their product range and I should perhaps not mention them specifically as there are a number of other companies to look at including the mainstream instrument companies. But most are easily found by a web search and I mention the ones I know well.

There is a good comment in another website on density in bauxite or aluminium production which may be relevant. I will dig it out and post it.

PS for Boraw, read Borax.

JMW

http://www.viscoanalyser.com

Eng-Tips: Pro bono publico, by engineers, for engineers.

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[jmw]

Quite a bit of discussion here:

http://www.control.com/1026152447/index_html

and you may want to search that site for density as there are some good threads there.

JMW

http://www.viscoanalyser.com

Eng-Tips: Pro bono publico, by engineers, for engineers.

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[CARF]

Hi,

Coriolis massflowmeters can measure massflow, density, temperature and sometimes viscosity as well.

http://www.omega.com/literature/transactions/volume4/T9904-10-MASS.html

http://www.emersonprocess.com/micromotion/

The Endress + Hauser "PROline Promass 83I" can measure viscosity as well. This means you have 4 primary variables with only one sensor.

Hope this helps,
C.