|1. What is an IBC
and a FIBC
Factories processing bulk solids very often have to use intermediate bulk containers, either to bring raw materials to their process, store or move bulk within the factory or sell the finished product. These containers are designated under the generic denomination of Intermediate Bulk Containers - IBC - and can typically take 2 forms : either rigid IBC or Flexible IBC - FIBC. This page will 1st focus on FIBC which have taken a very important place in manufacturing facilities since 20-30 years.
FIBCs present different advantages for bulk solids operators. 1st of all the empty FIBCs when received to the factory from the manufacturer does not take any space, they are folded and several of them can be placed on a pallet. They are also lightweight and their cost is very low compared to rigid IBCs making it a packaging of choice for exporting the finished goods for example.
A FIBC shape is most of the time squarish also circular shapes also exist. FIBCs are equipped with lifting loops that can be hooked to a hoist. They are generally made of a woven outer layer, often in polypropylene and can be fitted with an inner liner for application requiring hygienic conditions - foodstuffs for examples - or just as an extra protection for the material against humidity especially.
For filling and discharge, FIBCs have spouts that can be connected to the process so that the material can be loaded or discharged efficiently while reducing the risk of dust or product spillage. It is advised to use well design Big Bag tipping stations or Big Bag filling station in order to perform these operations.
FIBCs are often called Big Bags or Super Sacks.
Single / Multiple use
Contrary to rigid IBCs which have a very long life span if handled properly, FIBCs cannot be used forever. Depending on their design and how strong they are built, they can be used one time - single use FIBCs - or several times - multiple use FIBCs. In any case, the recommendation of the FIBC supplier, in terms of maximal load and number of use must be strictly followed in order to ensure safety of the operation.
|FIBC type||Safety factor||Characteristics and usage instruction|
|Single trip||5:1||Those Big Bags may not be equipped with a discharging spout,
thus the operator has to cut open the bottom of the bag for
discharge. Such method of discharge may generate a lot of
|Standard duty||6:1||Those Big Bag can be reused, they have a discharge spout
allowing to have hygienic discharge, dust tightness and reuse
the Bag. The number of trips that the bag can do must be
checked based on the supplier specification but it is
generally 10-20 trips
|Heavy duty||8:1||Compared to standard duty, the number of trips is higher but
such bags are also designed to be re-usable
For the size of Big Bags, the biggest size are around 2 m high and
can hold in between 1 and 2 cubic meters. Usual maximum weight is
1000 kg, of course the actual specification is to be checked with
Handling bulk solids in FIBCs and specifically during filling and discharge can lead to dust explosion if some precautions are not taken properly.
Indeed, during loading or discharge a dust cloud is most likely to be created in the FIBC, if the dust can be ignited then an explosible atmosphere is created. This dust explosion risk must be identified in dust explosion risks analysis such as ATEX in Europe or DEA in US.
As the explosive atmosphere cannot be avoided, it is necessary to remove any potential source of explosion which, in the case of FIBC will mainly be :
- Spark discharge
- Brush discharge
- Propagating brush discharge
- Cone discharge
- Corona discharge
The following measure can be taken :
|Spark discharge||From a charged isolated equipment in the filling or tipping station||Energy depends on the size and capacitance of the equipment involved||All equipment on the process, and around including the platform and the operators must be earthed|
|Brush discharge||From the FIBC made of insulated material
||Max 4 mJ
||Use conductive Big Bags properly grounded during loading and
discharge if the material has an MIE less than mJ
|Propagating brush discharge||From the FIBC made of insulated material
||These discharges can be avoided if the material used for the
Big Bag and its liner has a breakdown voltage of less than 4
kV and if the resistivity is less than 108 Ohms
|Cone discharge||From the bulk material to the FIBC
||Max 10 mJ||Can be avoided by limiting the diameter of the big bag. As
for silo a calculation must be done to determine the critical
diameter above which an explosion can occur
|Corona discharge||Such discharges have not yet shown enough energy to be hazardous with dust cloud - to be noted however that if the dust is mixed with an explosive gas, corona discharges may be sufficient to ignite such a mixture|
Which ultimately translates in different classes for FIBC according to the ATEX risk to be considered :
|Big Bag Type||Characteristics|
|A||No specific properties to avoid the risk of dust explosion
Use only when no risk have been identified
|B||Breakdown voltage of the Big Bag fabric is less than 4 kV
If there is a liner, this property may not be valid anymore, requiring the use of a special liner. The breakdown voltage of both the liner and the outer layer must then be certified by the FIBC manufacturer
|C||Those Bags are made with conductive fabric. They thus
require to be grounded at any time during filling and
To be noted that in case of missing grounding, the bag will charge electrically and, being isolated, sparks discharges can happen and trigger and explosion. It is recommended, when having to use such bag, to have an automatic control making sure the bag is being grounded
|D||Type D Big Bags have been designed in order to be as efficient as type C Big Bag but without requiring grounding. A special fabric is used but some reports of explosion have been made for dusts having very low ignition energy, around 25 mJ [Holbrow]|
The use of FIBC, compared to IBC which are detailed in the second part of this page, has pros and cons. In order to help industrials to make a choice, those advantages and disadvantages are summarized in the table below :
|Cheap unit costs
Some types of Big Bags are re-usable
Can be used within a factory but also for exporting goods
|May be difficult to discharge, requires
a well designed tipping station
For type C Big Bags, requires strong procedure and / or automatic system to make sure the bag is grounded during filling and discharge
May be difficult to re-use hygienically Big Bags
Intermediate Bulk Container or IBC, designate mobile containers with hard walls, often in stainless steel for powder.
There are 2 dominant designs for IBCs : the tote design and another design with a conical discharge.
Totes : this design was introduced by the company Tote but has since become a generic term for this kind of design. The IBC is here of a squarish form, with a round top inlet and a rectangular outlet which takes the shape of a door at the bottom of the bin. Tote bins must then be tilted on a special equipment in order to discharge its content. The following question often pops up about tote IBCs : are IBC totes stackable ? Yes, tote bins can be staked easily and discharged easily which has helped for its success. However, for hygienic operations, the discharge door causes several challenges to avoid foreign body that led some food manufacturers to switch to conical IBCs
Conical IBC : The other type of IBC frequently found in powder handling industries is featuring a squared top part but welded to a conical bottom. The conical bottom can be fitted with difference kind of valves, from a simple manual butterfly valve, to split butterfly valves or cone valves. It is thus necessary to connect the IBC to a special station for allowing an efficient and clean discharge. This kind of IBC is very often preferred vs tote if it is also coupled with a blending step. Indeed, conical IBC can be rotated making it an interesting bulk solids blender.
From a dust explosion risk point of views, IBCs must be grounded during all loading and discharging. It can also be possible in some situation to have an explosion protection by venting the explosion from a nearby part of the process.
Regarding the sizes of IBCs, it is pretty flexible, it can come from around 100 l to 1-3 cubic meters. Rigid IBCs are usually made of stainless steel or aluminium. Aluminium is lighter and presents advantages for the handling but is also sensitive to foreign bodies as it is easy to chip off some small particles of aluminium when moving or tipping the bin.
|IBCs can be re-used
If properly designed, they can be hygienic
For conical IBC, IBCs can be integrated in a process including one mixing step
Requires specific docking stations for loading and discharge
[Holbrow] EXPLOSION HAZARDS AND PROTECTION IN THE USE OF
INTERMEDIATE BULK CONTAINERS, Holbrow, 2004, Crown