Easily solved: Problems with agglomerated bulk solids
If you work with bulk solids you will know that agglomerates, lumps and other nuisances are not uncommon. They can form during transport, storage, repacking or packing processes and during production. Products may have specific properties that make them more susceptible to clumping.
Agglomerated material cannot be optimally processed. This can cause an unacceptable loss of quality and rejections in the end products. Luckily, problems with agglomerated bulk solids can be easily solved. We have compiled a list of screening and crushing machines that can help you in such cases.
There are two different procedures that you could use: You can either remove the agglomerates from the process, or break down of the agglomerates as part of the production process.
Do you want to remove lumps from your process?
The easiest, and often the most cost-effective solution is to separate the lumps by screening them off. The question here is: Which type of screening technology is the most suitable?
The main task of screening machines is to separate off product particles that are not the desired size: Remove small or large particles, separate into different groups according to size, protective screening. Any agglomerates and lumps are held back by the screen mesh. They are removed from the screening machine, ideally processed and then recycled, or disposed of as rejects.
An added plus: Depending on the product, the forces used during the screening process may be sufficient to break up some of the agglomerates and lumps. These will then pass through the screen mesh as good products. But this does not work with every product or screening machine. Whether a screening process is suitable for separating the agglomerates is determined by the properties of your products – we took a closer look.
» Fig. 1: Screens reliably separate agglomerates from the product. The “good” particles fall through the screen mesh, while the particles that are too large remain on the screen and are removed afterwards.
If you are working with “uncomplicated” products, vibration screening machines offer many advantages. You can achieve a high throughput rate – even with fine powders – with a very high rate of selectivity. The principle is simple: The vibration motors on the screen housing can generate high accelerations which are then transferred to the product via the screen mesh. The product particles on the screen insert are set in a "jumping" motion and either fall through the screen mesh (if they have the desired particle size), or remain on the screen insert (if they are too large) or they are discharged via the coarse material outlet.
Here are a few of our efficient vibration screening machines. They are particularly suitable for separating off oversized particles and agglomerates:
- JEL VibRS: High throughput and space-saving. Round screen with up to 5 screening levels.
- JEL Konti: Particularly versatile. Screen inserts can be changed in just a few minutes – for minimal downtimes.
- JEL Fix: Simple round screening machine for a maximum of 2 particle sizes. Ideal for installation in existing systems thanks to the low installation height. Can also be used as an easy-to-handle, mobile screening machine on a trolley.
» Fig. 2: The screen housing of the JEL Konti vibration screening machine (shown here with frame) is spring-mounted and is set into motion (both horizontally and vertically, depending on the motor inclination) by 2 vibration motors. The vibration amplitude can be varied by adjusting the imbalance.
However, the jumping movement of vibration screening machines cause problems if you are working with particularly fragile products and can even lead to particles being broken down. Linear and long-stroke screening machines, like the JEL Freischwinger screen bulk solids in a particularly gentle way. The horizontal screen movement moves the product gently across the surface of the screen mesh without causing it to jump up and down. This screening process also has a high rate of selectivity, making it very popular with our customers. Just like with the vibration screening machines, high throughput rates can be achieved with the appropriate screening surface, but they do require a little more space.
» Fig. 3: Particularly gentle screening: The oscillating drive of the JEL Freischwinger is connected to the screen housing with thrust rods. This makes the screen move horizontally.
The process is a little more complicated if you are working with a wet or fatty product with agglomerates. With any screening machine, there is always a risk that the screen mesh will become clogged and lose its permeability. If you need to separate and remove agglomerates from wet or fatty products, you can use one of our reliable centrifugal and cyclone screening machines, like the JEL Viro.
The heart of this machine is a round sieve basket with an internal rotor with rotating blades. The product is transferred to the sieve basket via a feed spiral and is then evenly spread across the surface by the rotor bars. Any agglomerates that cannot be broken up and that cannot pass through the sieve are conveyed to a separate outlet via the (adjustable) rotor bars.
» Fig. 4: Cyclone screening machines have a round sieve basket – in the case of the JEL Viro, this consists of two sieve semi-bowls. The product is transferred to the sieve basket and is then spread across the surface from the inside outwards by the inside rotor and rotor bars.
A typical example: Screening cocoa powder with the JEL Viro
Ideally, the separated agglomerates should be returned to production and reprocessed. If the production process does not allow for this, then they should be disposed of.
How can you dissolve lumps in your product?
Different factors come into play here: How hard are the lumps? How large are they? What size do the lumps need to be broken down to?
As a general rule, if the particles of the agglomerate are loosely clumped, only a small amount of energy is needed to dissolve them. Cyclone screening machines are also a good choice here. The centrifugal force that “throws” the product particles against the screen mesh from the center of the screening machine is often enough to break up soft agglomerates. Additional components, such as ultrasound cleaning systems vibrate the screen mesh and prevent it from becoming clogged when the lumps are broken up. This usually breaks up the majority of the agglomerate and significantly increases the amount of “good” product in the screening process.
» Fig. 5: With fatty products, the screen mesh becomes more and more clogged and loses its permeability. As such, in these cases the screening machine should have a screen mesh cleaning system. The most common types are vibration and ultrasound cleaning systems.
You can obtain very good results with simple straining sieves, like the JEL PS, if you need to break down softer or paste-like lumps. With these straining sieves, the lumpy product is gathered by a rotor with bars and is passed through the mesh. The product falls below the mesh in the desired particle size and can then be conveyed onto the next processing steps.
» Fig. 6: A view of the JEL PS straining sieve from the inside. The agglomerates are pressed through the mesh with the rotating bars. This only works with soft agglomerates and paste-like products.
A typical example: Straining agglomerates in plastic production
So, screening machine can also break down soft agglomerates. However, they quickly reach their limits if the lumps are hard and, in particular, very large. In cases like this, crushing machines, such as crushers or lump breakers, should be used: They generate enough energy to break down harder agglomerates and make them smaller so that they can be processed again in production.
Crushers, like the JEL UZ-2, consist of two parallel shafts equipped with rotor plates. The shafts move in opposite directions and pull in the lumpy material. Impact forces and friction, as well as the continuous rotating movement, ensure that even the most stubborn lumps can be broken down. The product then falls down through a crushing or sieve grate, where it can be caught, transported away and processed further. Different shaped crusher grates / grids and rotor plates are available so that you can tailor the process to the product or required particle size. Spacer sleeves can be placed between the rotor plates and help to ensure more variability. The fewer spacer sleeves installed between the rotor plates or the higher the number of rotor plates installed, the higher the force and achievable degree of size reduction.
» Fig. 7: Mobile, high-performing crusher with 2 strong shafts and a range of rotor plates. The surfaces of this machine that come into contact with the product are mirror polished as the crusher is used in the pharmaceutical sector.
Many crushers may be built on a mobile frame so that they can be used at different points in the production process. Often crushers and lump breakers are also permanently integrated into systems – e.g. as a single-shaft crusher underneath a big bag emptying station.
For example, single-shaft crushers are used as primary crushers for subsequent fine grinding, or as control crushers in pipelines. We have also installed it as a downstream device in dryers, centrifuges and stirring units. Or together with sack chutes and other emptying units.
Chemical and pharmaceutical customers in particular need devices like this due to the available product variety. The single-shaft crusher from Engelsmann has an internal shaft with sickle-shaped, interlocking crusher knives, the number of which depends on the task at hand. They take the material and crush the agglomerate with their rotary motion.
» Fig. 8: A single-shaft crusher from Engelsmann – here in the extendable pharmaceutical version.
As you have seen for yourself, dealing with lumps in the product depends on many different factors. In particular, however, it depends on the process-related objectives of the operator and the specific product properties. If agglomerates “only” need to be removed from the process, screening machines offer clear advantages with their selectivity, throughput rate and cost-effectiveness. However, if the agglomerates need to be broken down so that as much product remains in the production process as possible, screening machines are only suitable to a limited extent – namely only if the lumps are not too hard and not much force is required to break them down. If this is not the case, you can plan to use robust crushing technology such as crushers or single-shaft crushers.
You can determine which components and component combinations will best help you obtain optimal production results in technical trials. When it works reliably on a “small scale”, you can be sure to have the necessary process reliability for the “big picture” in your plant.
Do you have any questions about screening technology?
Tel.: +49(0)621 59002-42
Do you have any questions about crushers and lump breakers?
Tel.: +49(0)621 59002-47