Difficult choice of industrial silos


How to choose a proper silo? This question is asked by many producers.

Along with increase in the field of ecological education during the last few decades, we have noticed a constant increase in using of biomass combusting boiler plants in various industry branches. Their advantage is undoubtedly a smaller threat to the environment. The combusted biomass emits less sulphur than comparable coal. However, it requires special storage conditions due to its humidity. One of the better ways to store biomass are steel silos that can be used in the open. They can stand independently or be set up in batteries. They are intended for storing of dry waste (max. 35% humidity).

For storing of wet waste, concrete silos and push rod out-feeders in form of a so-called movable floor are more suitable.

The silo is a long-term investment.

Anyone who chooses this storage method will quickly find out that saving of money and the choice of parameters based only on the price does not work when it comes to the long-term use. One of the problems is often too slow fuel collecting and slower fuel transport to the boiler.

How to choose a silo according to our needs?

The first choice should be its size. This parameter is very easy to determine, because it is known in advance what performance the boiler plant that is in-fed with biomass stored in silos will have.

When choosing the storage size, you must also take into account the possibility that the need for storing of additional fuel can increase in the future. You should consider whether to choose one larger silo or several smaller storages. An increased number of silos raises the investment price, but also directly improves the functionality, for example in the case when you are using various fuel types: straw, woodchips or pellets.

The next choice must be a type of the silo. The Runarsson company offers two solutions: conical silos and silos with flat bottom. Both types can be equipped with out-feeders and appropriate fuel conveyors.

It is difficult to indicate a better type of the silo. It depends on the individual needs of our customers. Of course, during conversations with our contractors, we try to suggest the best option for them regarding both the silo, the out-feeder and the conveyor.

Whom is a silo with flat bottom the best solution for?                           

We recommend it primarily for the customers who have building limitations in their area and the silo height is of key importance for them. In such a case, silos with flat bottom ensure the optimal capacity.

A flat bottom out-feeder collects material evenly from the entire silo bottom, which is its obvious advantage. It can also achieve higher out-feeding performances that are stable and easy to control by changing of the rotation speed of the out-feeder.

When to choose a silo with conical bottom?

If we have enough space, we can try to choose a higher and cheaper conical silo. However, it will be suitable for less demanding fuel. The fuel must be as loose as possible, rather not caking into larger pieces. We are talking for example about shavings or sawdust. The waste humidity should generally not exceed 20%.

When it comes to more demanding fuel, a conical bottom out-feeder is sometimes set up vertically, which can result in significant decrease of performance and collecting of material only from the central part. In an extreme case the out-feeder does not supply any material, which creates a threat if the material is supplied to the boiler. The risk of problems associated with the mentioned defects of the conical out-feeder increases with the material humidity.

So if our budget is limited, if we have enough space and if the boiler combusts loose fuel, a silo with conical bottom can be the right choice.

And what about conveyors?

And here again, the answer is not simple. Just as with silos, the price criterion should not be dominant in our choice. It is necessary to consider the conditions in which our conveyor will operate, what will be transported, what its service life should be and finally the price.

Screw conveyors

They will be best suitable when the investment cost is to be as low as possible. We try to achieve the lowest operating costs of the device together with its long service life.

Does it look perfect? Probably yes, but it is not a solution for everyone. When choosing a screw conveyor, we have to consider its length. This solution is best suitable for fuel transport up to 12-15 meters, preferably horizontally or at one angle. The screw conveyor is able to transport from 0 to 30 m3/h. 

If we need a longer-distance transport device with higher performance, we should choose redlers.

A chain conveyor – redler

The basic criterion for choosing of this type of conveyor is the length of the transport route and the performance. Redlers transport fuel over 30 m3/h. Therefore, they are much more efficient than screw conveyors. We can also use them when waste is divided into larger pieces – over 30 mm. In this type of conveyors, the material transport route is extended up to 50-60 m and the transport can take place at two different levels.

So if you need to transport small material amounts for short distances, you should choose a screw conveyor. For more complex solutions, a redler will be much better and more efficient.

When planning an investment regarding the purchase of a silo, a complex solution is worth considering. You can choose a silo that is adapted to your needs together with an appropriate out-feeder and conveyor. 

You are welcomed to contact our design office. We will suggest a solution that is best suitable for you. We invite you to check our wide offer.

Quality | Trust | Innovation

Let's build a greener future

Steel structures & mechanical equipment,
pressure & filtration equipment
pipelines & support constructions


Fuel in-feeding systems
Chain conveyors
Heat exchangers
Designing of mechanical equipment
Air and flue gas ducts
Chain conveyors transporting fuel or ash
Catwalks and stairs for operation and maintenance

Support constructions according to Eurocodes


Runarsson A/S
Krogagervej 2
DK-5240 Odense
CVR 36537450

Runarsson Engineering
Ostrowiec Świętokrzyski ul, Ignacego Boernera 6, 27-400 Ostrowiec Świętokrzyski

Runarsson Engineering (PL)

Tell us about your project

Runarsson A/S   

Krogagervej 2
5240 Odense DK
CVR: 36537450

+45 3841 3810

Runarsson Engineering Sp. z o.o.

Ignacego Boernera 6,
27-400 Ostrowiec Świętokrzyski PL
CVR: 661-237-70-12

+48 533-140-091