Bulk Solids Conveying

We do not handle a process for controlling dust or spillage, but we have motor controllers that will reduce the energy consumption of your conveying system by up to 35 %. The payback time is usually less than 18 months.

Paul

M I T Energy, Inc.

E-mail: mitenergyserv@aol.com

Define cleaning up the system?

Basically the blowers in the silos, blow in a loop.

Once the air is up to speed/pressure a rotary valve sprinkles the carbon black [@ the bottom of the silo] into the moving airstream.

@ the mixer hopper a section of the pipe [diverter valve] turns 90° & allows the material to fall out of suspension from the air flow.

This continues until the hopper is full [ determined by weight or volume, depending on the system ], the diverter realighnes & the excess returns to the top of the silo.

the pressure/flow is relived w/a bag house on top, flow is the key, pressure being an indicator of the amount of material in the airstream.

There are of course variations, but this is a common layout.

A good place to start is the oem vendor.

Above is a Shick tube-veyor system for conveying flour.

Right... does "cleaning the system up" mean actually controlling leaks of carbon black, or does it mean simplifying and improving reliability of the process?

The last post was a good overview. For carbon black, you might also need an eductor under the rotary valve (following the silo and discharge feeder screw) because of the bulk density of the material. Its important to feed a metered stream to the rotary valve, and be able to let the rotary valve dump effortlessly. I always go for larger rotary valves running slower to avoid the "fan effects".

There are good nomographs for amount of conveying air needed in the Perry's Chemical Engineer's Handbook, or any OEM can do the calculation for you to keep the material in suspension for the length of pipe and diameter of pipe that you have. I always use blowers like Roots Blowers or some other lobe blower.

Elbows are important. Wear is always an issue with elbows in pneumatic systems as well as pressure drop. Several styles are available from long radius with ceramic linings to shorter radius with material dead spaces.

There is generally a receiver at the point of use, so the material can drop out of the airstream then be metered (again, a rotary valve or metering screw) into the mixer or reactor. This receiver has some sort of bin vent or baghouse or cyclone/baghouse to clean up the air stream.

I've done a lot of these systems from carbon to wood dust to plastic pellets to limestone and starches, and made about all the mistakes that can be made, and a good vendor will help you avoid a lot of late night phone calls from operations.

Good point, cleaning up the system was a little vague. The way I see it, this is a two prong approach. 1) literally clean up the system, control spills and leaks from the system to help clean up the plant and offices. The system is roughly 11 years old and I can't say much about the maintenance which I'm now in charge of. We utilize a bay in which semis will unload carbon black and it's then force fed into one of 4 silos. 2) Shore up the accuracy of the system, we constantly have overages which forces the operator to purge the system and start over. We bailed on the original logic and had a company called Mesabi write the controlling software (RS logix) Seems to be fairly solid.

Thank you all for the input. Our vendor happens to be in the UK, Chronos Richardson. I believe the system to be fairly good but could use some advancement. We utilize air slides which appear to be around 30 - 45 degrees, I was told they should be a min. of 60 degrees.. We also run into problems regarding the probes and sensors. This may be tied to bad/worn out fluidization cones on our rec. / weighing hoppers.

I'm not against bringing in an "expert" to help focus this project.... Any suggestions

Now I/m curious

Are the hoppers @ the mixers filled to volume [probes] or weight [hopper suspended on load cells]?

If acuracy is an issue & your batches are formulated by weight, suspended hoppers are the way to go!

I think you will find that the minimum angle for your air slides should be 6 degrees not 60, at that angle you would not need air assistance to move the material. if you are using FK pump to move the material through blow lines then there should be no spillage, unless the integrity of the pneumatic system has been compromised.

You're right, what I meant to say was the target angle should be 60 degrees...

We utilize a suspended hopper with a load cell, the system is smart enough to know when it measured wrong and will fault out, but I'm at a loss as to why it happened in the first place. Is CB prone to this? We pump CB from one of 4 silos into an SCV that utilizes a load cell. It's then transported to a recieving hopper located quite a distance away. The recieving hopper utilizes a bindicator probe, the material then drops into a surge hopper with a butterfly vavle before dropping into the mixer. Our facility is only 33,000sqft so I'm guessing it should be no problem to convey it anywhere in our building.

Why we're at it, has anyone ever cleaned their silos?

Cleaning, is a confined space operation & sould be handled by trained personel [OSHA rules], probably an outside contractor, to limit your liability.

Depending on your local climate, moisture can be an issue. You may have some sort of de-humidifacition system. Dry product & air will limit the amount of cleaning necessary. I can't imagine that you would have any fungal growth or bugs for that matter. Then again what the hell do I know about carbon black, other than it's hard to wash off your eyelids!

I'll throw some stuff out about the weighing issue.

If you can monitor the conveying line pressure [ somewhere down stream of the silo]& the rotary valve [ feeder ] @ the bottom of the silo & the weight @ the use bin [SCV?], it will help troubleshoot.

I'll assume carbon black has similar properties to flour, when the system is conveying the butterfly & feeder should run constant, pressure 5-7psi.

If the pressure is going to 9+ & dropping down, with the feeder cycling on & off, weight @ usebin climbing in spurts, try slowing down the feeder.

on top of the usebin there is some sort of fill/bypass [diverter] device, check for smooth, consistant operation.

if it's slow, sticking or partially open, this can cause the usebin to overfill.

Check the relief system for plugging, both on the usebin & on the silo.

When the usebin is either empty or full, the weight readout should be stable.

If unstable, the usual sort of troubleshooting, electrical connections, vibration....

A easy check [loadcells] is to monitor the scale readout while twisting the individual loadcells [no leaning on the usebin], if the system only has 1 loadcell, it will be very critical to proper operation, usually 3or4 are utilized for bakeries.

our accecptable accuracy is ± 3#s.

The Bindicator is probably used for hi-level [overfill/fault ] indication. If your not getting any bogus faults, It's probably well adjusted.

Hope some of this helps!