The best Solution for Raw Material Storage and Blending

Related Vendors

DÜPERTHAL Sicherheitstechnik GmbH & Co. KG

Glatt Ingenieurtechnik GmbH

EDL Anlagenbau Gesellschaft mbH

Claudius Peters Technologies S.A.

Pile Change and Daily Bin Size

With a dual pile operation, there are interruptions to the flow every time the stacker and reclaimer swap locations. Therefore some storage capacity such as a bin or silo (often called a daily bin) needs to be provided between the stockyard and the main process to keep a continuous feed.

The flow interruption time to be covered by the daily bin is not only the time necessary for the relocation of the machines itself, but also the loss of reclaimer output due to the pile-end-effect, especially with frontal reclaimers when they operate in the end cones.

Alternative Feeding Route

Stackers and reclaimers are sturdy equipment and can be maintained during annual plant stoppages. However, there is also a need to provide an alternative possibility for feeding the process to allow for situations such as a failed reclaimer, especially in case where multiple processes are fed by single stockyard line that is required to operate continuously.

Gallery

Gallery with 10 images

The most common alternative feeding route are emergency hoppers that are fed by front loaders, which are both flexible and simple. However, where alternative feeding is for more than just emergencies, a cost effective by-pass option should be considered. This could include direct discharge by the stacker onto the reclaim belt.

Stockyards for Continuous Operation

With a continuous stockyard operation (circular stockyard, Fig. 3) there is only one stack revolving endlessly around the centre of the stockyard either clockwise or counter-clockwise. The stacker operates at one end while at the same time the reclaimer operates at the other end of the stack. The distance between the front and tail ends is a measure of the quantity currently held in the stockyard.

If the stacker is coming too close to the back end of the reclaimer, this means the pile is full and the feed must be interrupted. The instantaneous stacking rate is always higher than the reclaiming. Therefore, the reclaimer front end shall only come close to the stacker if it has stopped.

With continuous stockyards there is no interruption for relocating piles and therefore it may directly feed a continuous process, without the need for a daily bin.

Stacking Patterns

The most common stacking pattern for storage systems that have no homogenising purpose is the cone-shell method, Fig. 4. It is built by building a first cone with a height equal to the nominal height of the stack and then moving in one direction along a straight line for linear stockpiles or in a circle for circular stockpiles.

The chevron or "longitudinally layered pile" method can be used with circular and linear stockyards and consists in building a pile by spreading the material in layers along the centre line of the pile by travelling the stacker back and forth through the full length of the pile at a given speed. The thickness of material layer deposited during the process is given by the ratio between the volumetric stacking rate and the speed of the stacker travel.

The "chevcon" pattern is derived from the chevron and is exclusively suitable for circular continuous stockyards. It is like a chevron applied only to the tail end of a circular pile where each layer is shifted one after the other, always in the same direction. The result is a parabolic shaped crest called the construction ramp of the pile. The slope of the crest is mild near the top and increases toward the lower end. If it were a pure parabolic shape it would end in a vertical slope, but as it is limited to the natural angle of repose of the material it ends in a cone. Chevcon is the invention of an engineer of the original German company PHB, which unites the ideas of a combination of chevron and cone-shell.

Windrow stacking is similar to chevron but the position of the axis along which the material is deposited by the stacker is changing (by e.g. rotation of the stacker boom). This results in cords being piled up in a pyramidal way.

The Problem of Segregation

One important side effect of stacking is the well known effect of segregation, by which the bigger lumps tend to roll downhill while the finer material remains on top of a stack (Fig. 5). Segregation becomes all the more inconvenient when the grain size heterogeneity may follow an equal chemical heterogeneity, like for example with compound materials. Gypsum is a typical example where purity can vary significantly from bigger lumps to finer material.

In some cases, segregation is handled through the reclaiming process but windrow is the stacking pattern that best prevents this phenomenon from developing.

Reclaiming Modes

There are two different ways of reclaiming: frontal and side. If frontal reclaiming can be compared to cutting slices from a cake, side reclaiming could be compared to slicing up a potato into crisps.

Frontal reclaiming consists of bringing the material down following a cross section of the pile. The resulting output rate is the product of the cross sectional area by the speed of progression through the pile.

Side reclaiming (see Fig. 6) consists of taking a pass of only a small portion of the cross section, most of the time of triangular shape, along the whole length of the pile, before cutting the next pass until the pile is empty. The resulting output rate is the product of the cross sectional area of a pass multiplied by the speed of travel.

Side reclaimers are characterised by their lifting scraping boom. Various examples are shown below. The most common frontal reclaimers are bridge type with harrow raking systems. Other types include side reclaimers running in "pilgrim pace" mode and overhead excavators (ladder type) that are run on walls.

Stockyards for Homogenisation

Bed storage can achieve homogenisation, providing low extra capital expenditure compared to mere storage. Combining a specific stacking pattern and a specific reclaiming method, it is possible to a certain extent to shuffle a given amount of a material to obtain a significant reduction in the variations of its characteristics, as measured by defined quality parameters.

(ID:42575649)