Welcome to

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Big Bag / Super Sack Discharge Stations

Also known as...

Big Bag tipping stations

Big Bag emptying stations

Big Bag unloading stations

Super Sack unloading system

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Section summary
1. What is a Big Bag tipping station
2. Design of Super Sack unloading stations
3. Performances
4. Important design points of Super Sack unloading systems
5. Safety
6. Common problems with Super Sack unloading stations
7. Super Sack unloading station manufacturers

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1. What is a Big Bag tipping station

Big Bag tipping stations (also named Big Bag unloading station, Big Bag emptying station, Super Sack unloading system - in US) constitute an important process equipment since they will allow to bring to the process the raw materials necessary to manufacture the desired product. All the subsequent process step depend on the feed of the raw materials, if those materials are brought by Big Bags or Super Sack (denomination in US), the tipping station must be well designed to allow a fast, clean and safe tipping.

Big Bag emptying stations allow to discharge large bulk bags of powder or granules, called FIBC, Big Bags or Super Sacks, in many industries and for many applications :

• Construction industry : cements, mortars
• Food industry : flours, maltodextrins, sugar
• Chemicals industry
• Plastics : polymer pellets

As there are different terms to designate large flexible bulk containers, the rest of the page is in-distinctively using the terms of FIBC, Big Bags, or Super Sacks.

2. Design of Super Sack unloading stations

The following items are to be taken into account when designing an unloading system for Super Sack / Big Bag.

Product properties

The flowability of the product to be discharged is a key parameter that will drive the design of the "upper" part of the tipping station. It is indeed of crucial importance that the product flows easily outside of the Big Bag, in order to make sure the capacity requirement of the line is met, while ensuring that 100 percent of the material is discharged from the tipping station, eliminating the material losses.

A powder rheology analysis of the powder(s) to be discharged must be done. If the product is very free flowing, no specific aid will be required. If issues are expected, a vibrating table can be chosen, however this will fit only products that are not compacting under the vibration. For very difficult product, it will be necessary to foresee the installation of automatic pushers.

It is common to have rods or a grid at the tipping station inlet (to avoid foreign bodies or for safety reasons). This feature may cause issue with product presenting a difficult flow, or being lumpy. Installation of such grid should be well considered in the design

Super Sacks (FIBC) dimensions

This looks obvious, but many time at the 1st use of the tipping station, the Big Bag is not fitting...

The min and max dimensions of the Big Bag must be well defined when ordering the tipping station. One particular dimension to check is the diameter and the length of the spout to be connected to the tipping station head.

Tipping head

The tipping head is the point where the Big Bag spout will be connected to the discharge tube.

The simplest form is just an open tube where the operator will introduce the discharge spout of the Big Bag. This is by no mean satisfactory since powder will leak, leading to Health and Safety issues. A clamping system must be foreseen. Commercial design can range from a simple manual mechanical clamp, to automatic clamping with pneumatic cylinder or inflatable seals.

Big Bag collapsing at end of discharge

Big Bag must be removed without spreading remaining powder to the environment. A system to collapse the Big Bag can be considered ; it is basically a fan located downstream the process, typically connected to the hopper to which the Big Bag discharges and that will induce a slight vacuum that will allow the Big Bag to collapse and be removed more hygienically.

Closing system

Closing a Big Bag being discharged is possible - although not easy. Some suppliers are proposing arms, operated with pneumatic cylinders, that can squeeze the discharge spout of a Big Bag and interrupt the flow of product, allowing to re-tighten a Big Bag and remove it from the station.

This can only work if product is flowing out of the Big Bag during the closing process.

Figure 1 : Typical design of a Big Bag Tipping Station

3. Performances

The Big Bag dumping platform must be designed to unload a certain number of Super Sack per hour. The cycle time achievable is made of the following components :

• Bringing a Big Bag to the tipping station
• Connecting the Big Bag to the tipping station
• Discharging the Big Bag
• Disconnecting the Big Bag
• Removing the Big Bag from the tipping station

Bringing Big Bag to tipping station

The duration of this activity will greatly depend on the setup and the number of operators. It can range from 2 minutes to 10 minutes.

• Shorter time will be achieved if a full Big Bag ready to be lifted is already in place

• Longer time will be necessary if a full Big Bag needs to be brough to the tipping station, prepared

The time necessary to lift and bring, transfer and put the Big Bag in position is dependent on the hoist speed. Typical values range from 6 to 9 m/min

Connecting the Big Bag to the tipping station

Opening the bottom of the Big Bag, adjusting the spout to the tipping point, untightening the spout and clamping it will take 2 to 3 minutes to a skilled operator.

Discharging the Big Bag

The discharge of the Big Bag is dependent on the process downstream

Table 1 : Estimation of the time needed to tip a Big Bag

Downstream	Time to tip
Direct discharge to a Buffer, no equipment in between	A big bag can be discharged in 2 to 5 minutes depending on the flowability of the powder
Discharge to a conveying line	It will depend on the conveying line throughput
Discharge to a vibrating sieve	The sieve must be designed to not impact the global process, the time should depend on the next process steps, typically a conveying line

Disconnecting the Big Bag

Stretching the Big Bag, disconnecting the spout and tightening it should take around 2 minutes to a skilled operator. Add 1 min if there is an option to collapse the Big Bag at the end of the discharge.

Removing the Big Bag from the tipping station

Bringing back the Big Bag at the lifting point - in order to remove it and hook a new one - will depend on the design of the hoist.

4. Important design points of Super Sack unloading systems

When reviewing the design of a Big Bag tipping station, the following points deserve full attention :

Table 2 : Key design points of a Big Bag Tipping Station

Design point	Recommendation
Big Bag station access	The access to the Big Bag station should be done without having the need of a platform in order to prevent occupational safety risks
Powder Properties	Design the station when knowing about the flow properties of the product, conduct tests if necessary
Understand the impact of downstream process	The equipment located after the station may have an impact on its operation, for example by creating pressure effects that disturb the flow of product

5. Safety

Big Bag tipping station have some inherent risks linked to the manipulation of large and heavy powder containers. It is necessary to manage those risks.

Risk : fall of Big Bag

An incorrectly hooked Big Bag can fall during the transfer process. The whole path of the Big Bag must be closed by a safety cage that prevent any people to stand close or even below the Big Bag in movement. Specific features must be put in place to make sure no people is present in the cage or try to open it (interlock on door, sufficiently high fences, control fixed outside the station...).

Risk : rotating equipment below tipping point

It is possible that a rotating equipment is located right below the tipping point (star valve, rotating magnet...). An operator could reach those equipment while trying to unblock powder for example and be amputated. Measures to ensure 0 access to the rotating element must be considered : welded grid if possible, enough distance not to be able to reach the rotating equipment with the hand, light curtain

Risk : ATEX

As every equipment processing powder, the ATEX risk needs to be considered when designing and sourcing a Big Bag station. The 1st condition is to prevent dust leaks, which means that the Big Bag station head clamping the spout must be well designed and tight. A system to collapse the Big Bag before removing can as well help reducing dust leaks. The training of the operator is key, procedures for tipping must be clear and applied. Finally, the ATEX rating of equipment must be performed and equipment sourced accordingly, with certification.

6. Common problems with Super Sack unloading stations

Big Bag tipping stations are usually reliable equipment, however a certain number of issues may require some corrections :

Table 3 : common problems with big bag tipping station

Issue	Recommendation
Spillage of product	Make sure the bag is well emptied at the end of discharge, train the operator to pull a bit a the big bag to help the flow of product out. Tighten immediately the spout
Dust emission during tipping	Make sure that the clamping head is properly tight
Collapse of big bag spout during tipping	Look for an equipment creating vacuum, make sure the tipping hopper below the station has a filter properly sized
Liner of Big Bag is falling in the station head with the product	Make sure the liner is well tightened at the top of the big bag Install a coarse grid to make sure no part of the bag can enter the process

7. Super Sack unloading stations manufacturers

Emptying stations for Big Bags are among the "must have" of every bulk handling equipment supplier. However not all stations have the same performance, thus the buyer should question the supplier on the design options available, and the experience of the Big Bag tipping station manufacturer with a particular product to handle. Specific discharging aids such as vibrating table, massaging device, or the possibility to pull down the tipping head are key.

The following companies can produce Big Bag unloading stations :

• Tetra Pak Powder Handling (Guerin Systems)
• Palamatic process
• Saultelma Rotolok
• De Dietrich process systems
• Serema

Note that powderprocess.net has no relation with those companies, the references are given as a help to the reader to find quickly suppliers.

Tipping bags

It is also possible to have stations designs for tipping bags of 25-50 kg.

Source

How to achieve efficient Big Bag Tipping, Thomas Lamotte, Processing Magazine, March 2019