Big Bag Filling

[JoeNava]

In a polymer plant, a hopper feeds two different filling systems for packing. A big bag filling system has to be added. The existing two filling system are fed by means of a 2-way valve, being each outlet independently controlled. No major room is available below hopper. Before to recommend a major area revamp to accommodate the 3rd line. Any of you, have succesfull experience with 3 way valves, to handle the 3 filling system, 2 existing and one new?. What can be recommended?

Joe

 

[azertyuiop]

I do not see any problems with this solution , excepted that I would foresee some flow control mechanism on each outlet , to be able to divide the hopper gravity flow into three separate inequal flow streams , each one being calibrated to the needed filling rate capacity of their respective system.

See , a good bigbag filling system needs a high flow rate for a short period (10t/h or much more) , having then a large time lapse without any flow required , because the full BB has to be removed and a new empty BB installed manually , taking 'lots' of idle time that can be used to fill up other packaging with less high flow rate demands.

This require a short time span / high BB flow rate feed , that may not apply to your other filling machines.

I would analyse the three required flow rates , choose the required valve outlet that goes with each system and build a screw conveyor under the one that shall feed the BB installation. This allows you then to place your new BB installation somewhere else , out of the way of your current operating systems. And just have a short operational shutdown to install the new three way valve system and screw conveyor inbetween your existing hopper and the new BB installation , before restarting everything.
Keep in mind that screws usually are not longer than 10meter/30feet , and if you want to go further , a row of similar screws will be required , that are feeding each other in row till they reach the BB installation.

I had a client in the past with a similar problem. We kept it simple. Each system was fed sequentially , the sequence being decided in flow rate requirements. When the BB needed feeding , the other small bags systems were allowed to finish their current filling operation , then their valves were shut down during the 20 sec BB filling operation , and released again for operation after the filling cyclus of the BB. This was required , simply because the hopper outlet feeding couldn't cope with such a high flow rate for the three systems simultaneously. The client wanted it that way , because BB's were his main product line. We could have fed the three lines simultaneously , but the available flow rate for the BB would have been much lower , requiring a 4 minutes BB fill up period , instead of the 20sec. That was not acceptable for the client.

I guess you will have to decide your own priorities , but your problem is certainly not a big issue mechanically speaking.

If you change regularly from hopper recipe , then you also will have to take into account that the BB screw feeder will always have a residue of the previous recipe on the bottom of the screw tube. Simply because there is always a small gap between the archimedes screw and the surrounding tube body , to allow for mechanical tolerance. Most companies simply solve the issue by flushing the screw with the new recipe , and fill e.g. a half BB with the mix up recipe before really starting the batch sequence of the new recipe. That generates wastes that you didn't have previously , and you have to get rid of them , which cost monies. I don't think you will be able to avoid this , not having space under your hopper to directly place the BB system under it. Someone with lots of small batch runs and therefore lots of wastes used this product residue , which had a high calorific value, as a fuel to heat up a furnace and recycle it into CO2 going though the stack and lots of heat for their process installations.

If this is really a problem , then a way out is a vibrating table system for your product conveying toward your BB system , because you then don't have residues. I don't have much expertise with those systems , but I know that you are even able to let your product climb up on a vibrating downward hill ramp , when applying the right vibrating frequency. This can be an option for you , if you can't accept the waste problem going with a screw conveyor. Although vibrating table conveying systems are major noise making devices , and lots of people are reluctant to use them simply for this issue.

Another possibility is to place a rotating valve system underneath your third outlet (doesn't require lots of height) , install a dense phase conveying system blowing the powder falling from that rotary valve to the BB installation. Advantages : you can go 100's of meters/yards without 'any' problem. Disadvantages : much lower flow feed rate than with a screw system + compressed air requirement that are not minimal , this air being used as a piston to blow props of products toward your BB receiving installation. Other possible disadvantages : static electricity build up and bridge forming above the rotating valve due to blowby leak air from underneath the RV , leading to installation shutdowns. Transport pipe clogging , requiring emptying of the whole blow pipe routing because of product in them that can't be blown away anymore , is also a hazard.

You have a variety of solutions for your problem , but the specifics are in your hand. If the hopper recipe doesn't change , go for screw conveying. Simple , rustic , maintenance friendly, clean. If the recipe changes sometimes , go for screw conveying. If the recipe changes every shift , go for pneumatic transport , and demand steel hard work guaranty for the products you want to transport.

 

[JoeNava]

azertyuiop,

Thanks for your well documented repply, I really feel very confident with my initial thoughts.

In your experience, what is your best recommendation for the 3 way valve ( I mean one inlet from the hopper and 3 outlets, one is for the BB)?SO I can check some preliminary sizes and utilities needed

Regards

 

[azertyuiop]

\ /
\ / hopper outlet
\ A1 /
A1 (----) hopper valve
/ / /\ / /--\ \ 45°->70° expansion cone with 70° chinese hat
/ / A1 \A2\ Area A2 > area A1
| | | |
| | | | start of 3-way valve system

I personnally would create an expansion space right under your hopper outlet , before dividing the flow into three parts. It is always good to allow the powder to flow more easily after having been compressed toward an hopper outlet.

The flow divider under that expansion cone , could be a 'chinese hat' conical part build in that expansion cone , under which three openings are available. The chinese hat has to have a steep inclination (70°) to avoid bridge forming and be minimally of the same diameter as the hopper outlet valve , to capture all the falling powder. It has to be placed under the valve , so that the valve can open (of course) , and be at least 15cm under the lowest valve opening circle , to allow the powder to get some speed while falling (kinetic energy). You also have to make sure there is enough space in between the conical chinese hat and the expansion piece wall , to avoid clogging. That space must be bigger in 'donut' area than the circular hopper valve outlet area , simply to avoid re-compression of the powder : A1 < A2.

Dimensions are not my speciality , that's the job of the 3-way valves supplier. I integrate various existing systems to create fully functioning process lines.