We use a very fine polymer powder that is extremely hydrophilic. Once exposed to moisture it becomes very adhesive and cohesive. So naturally we store it dry and limit exposure until it is time to use it.
The problem I have is delivering it to the dispersion unit we use. Right now, our only way to move it is to scoop it by hand. It sticks to absolutely everything and I have no humidity control in the area. So it is a “dirty” process needing full protective suits by the operators. The material isn’t hazardous, it just sticks to everything and is nasty.
What I thought might be attractive is to have a closed hopper (so it would be isolated from humidity) that would somehow allow the material to flow out. That way, nobody needs to physically handle the material and we can regulate the rate much better. This powder will flow under vacuum, but it will also bridge and stick. Aside from banging the sides to knock it loose, I am looking for the best way to keep it moving in a funnel/hopper.
Fluidizing by air would be very problematic, due to dust. Anyone deal with sticky, nasty powders in a way that made it less painfully inefficient? I had the thought of ultrasonic fluidizing, but I don’t really know too much about it. Before I start taking a deeper dive into this on my own, I figured posing the question here might give me a head start.
First thought. Can you visit the manufacturer of this polymer powder to see how they handle it? Do they have a “Handling Guide”? Can you arrange thru their sales and your purchasing to connect to the Engineer on the ground at their production facility?
Can you do anything electronically? else you have to provide a superdry environment and you may be able to remove/salvage ‘dust’ electrostatically.
I’m surprised that anything that hydrophilic would not be toxic and lethal…
@dik I was surprised about the toxicity, or lack thereof, too. I was assured it had been reviewed since I came on after this stuff was introduced, and I reviewed all the documents about a million times. Still, apparently safe despite it bugging my skin if I don’t wash it off by the end of the day.
@Latexman yeah, I’ve been trying to avoid contacting the mfg. because I’m going to be stepping on others’ toes to do so, but I’m just about at the point that I’m no longer concerned about that.
It has to do more to your lungs… moist environment, etc. I’d make sure the info was correct.
When a customer needs help with our products and on some customer complaints, my business usually sends me. I’ve built several entire plants and over a dozen reactor lines, plus I can smile while getting my ass chewed out. So, I’ve been there, done that, and have a closet full of t-shirts. Personally, I get a lot of satisfaction when helping a customer. If you help them out, they keep in touch and ask for advice before they get in trouble. So, I wouldn’t worry about the toes, you might learn something, create a lot of good will, and develop a contact you can call on when needed.
I’ve always prided myself in looking after clients… only one problem… about a year ago… had to do a sign foundation… and sent some prelim sketches to the client and he was p*ssed because he thought I should have sent him final drawings… lost him… two days after I started on the job. I didn’t know that the consultant that I was doing the work for had the project for 3 months before I got it. Only customer I lost.
A couple ideas I’ve seen.
This is a long shot, but is there a material that already goes into the final product that is/can be made into a bag? Then you could weigh-off what you need in a controlled environment into one of these bags, tie/close the bag, and 'bomb" the ingredient in when needed. In the polyethylene extrusion world the person that does this is known as the “bomber”.
Another way is if the powder can be sucked in using vacuum. Have the entrance in a controlled environment and terminate in the process where you want it.
We often utilize sodium bicarbonate in flue gas streams to remove HCl and SO2 (is there anything baking soda can’t do)? It behaves similarly to what you’re describing - it cakes when wet, but otherwise is not harmful. I’m sure your substance is “worse” in terms of becoming cohesive; however, you may be able to handle it similarly.
For the sodium bicarbonate, it’s typically stored in a silo (which is more a large, glorified hopper) with a rotary valve (sometimes two, for redundancy) at the bottom which loads the product into a metering screw. This screw delivers a defined volume at a defined rate to a blower system.
This blower system typically uses ambient air passed through a dehumidifier upstream of the blower and an aftercooler downstream. Immediately downstream of the aftercooler, the product is introduced from the metering screw. The system utilizes high velocity to keep the product in suspension (and flowing). The blower has a high flow rate (at relatively low pressure) and the downstream “piping” is specially manufactured. Normally, we would utilize large OD tubing (on the order of 3-1/2" to 5") with compression couplings where absolutely necessary. Joints are minimized and any elbows required are long, sweeping elbows with larger turn radii than typical fittings.
I understand you’re concerned with fluidizing it due to dust concerns (I assume at the dispersion unit), but I would suggest that concern may be alleviated with a smaller, local hopper at the dispersion unit. the product could be introduced with a rotary valve, precluding any dust from escaping the hopper.
I’m not sure how much of this information is truly applicable to your situation, but hopefully it’s somewhat helpful.
I appreciate all the replies. The cohesive and adhesive combination does make some of the solutions mentioned problematic, but I do have good takeaways from this already.
A little more info (I wish I could just say the material name but IP issues…ya know): I can’t make a “bomb” because it needs dispersion prior to mixing. If it goes in any larger than particle sized, it creates a layer of wetted powder that envelopes the dry powder inside and takes an extremely long time to wet all the way through and disperse even in 1-2 inch diameter balls (which happens a lot even with dispersion). The dispersion unit does pull vacuum actually so I am halfway to that solution you mentioned. It is the delivering it to the suction port that is my issue. That is where it is done by hand at the moment.
I think a lot of these things would be great if I had humidity control in the area. They require using this material but providing dry air is something I cannot get any commitment to no matter how I’ve explained to them how much of an improvement it would be. They want to stone age this process with stuff that simply needs a tiny bit of sophistication.
Thanks again for all the input so far.
I used to work, physically work, in an ice cream plant. When I lifted 50 and 100 lb. bags of whey to head level and “poured” it into the mixing vat, sometimes a small dust cloud was created. When the whey landed on me, it sucked the moisture from my body, balled up, and got sticky. I have a mental picture close to what you are talking about.
When we add HEC (hydroxyethyl cellulose) we have to add it to cold water, mix it, then heat it up. If you add it to hot water, you get footballs of HEC.
Would replacing the manual scooping at the dispersion unit with something like this help?
Woah, now that is something I like the look of
If I can get them to get serious about humidity control, that will be on my shortlist of options.
Depending on the container the polymer comes in, maybe you can make a collapsible booth/glovebox with glove ports that could create a controlled volume that you can more cheaply control humidity within?
I think that would be overkill actually, but I do like that you’re understanding how much I want to isolate this stuff.
It is in a sealed bag in a cardboard box. We use an entire box in the process so each container is used once unsealed.
My goal again is to be able to put the entire addition into a sealed container/hopper/whatever that I can then use to get it either to the hopper attached to the dispersion unit (which pulls vacuum) or replace that hopper. My problem is making sure:
- It all gets out of that container and
- it doesn’t just dump since I need to feed it at a certain rate for processing.
I think the eventual solution will be pretty simple. (If I get them to spend some money, it will be very simple ). I was just curious if anyone had experience with any apparatus for this type of process so I might avoid “shopping around for a solution” in an attempt to figure out the best method.
That looks a lot like the vacuum transfer systems I’ve seen and was imagining. We had a vacuum hose to clean up a powder testing station. It had it’s own fan and it tied in upstream of a process blower, so it was recycled back to the process. The vacuum hose didn’t really need it’s fan. The process blower could do the job, if you didn’t feed in too much at a time.
There are bag dump stations but unless you can get some time and money to see if they can be a little custom, they may not work for you. The customary grate interface, I think, might be a problem.
Can you get the powder supplied in different containers? If you got it in a lined fiber/plastic drum maybe you can use a wand with a shroud (keeps the volume of the drum somewhat isolated) that works with the dispersion vessel’s vacuum? The drum would give you something to support the weight of the wand and a rigid surface for the flexible shroud to extend over.
I work with chemicals where the hazard or cost makes premium conveying and isolation technologies mandatory and you save money on the bells and whistles. However, I have seen more modest plastic glove boxes do the job well enough for small quantity or short duration operations that they could be considered. You don’t need a top of the line isolator, but a “box” where you can keep the air cold and dry with some dry ice/LN2/window sized AC (a Class II Div 1 window shaker, of course) unit might work?
If the product is delivered in a sealed container, (say plastic bags), fashion a cover for your hopper and fit it with a sharpened tube, (think huge hypodermic needle). Simply drive the sealed bag down onto the tube to empty it into the hopper. If some vibratory action is needed to move the polymer, consider an audio exciter or transducer, (essentially magnet and voice coil without a speaker cone. Check out a company named Parts Express on-line). You will then need either a power oscillator or an oscillator and audio amplifier; all fairly cheap and easy to find. A lot of the tendency for a finely divided polymer to cling to surfaces is likely to be electrostatic. Assuming that the polymer particles are non-conductive, (electrically), charges will tend to build up on the surfaces of the particles and can not flow to find a neutralizing surface. You could try an ion spray to kill the trapped charges, but that would require some “cut and try” engineering.