Faced with the technical challenge of handling material with moisture content above 20% and in an environment with temperatures below -25˚C, engineers at SCHADE Lagertechnik have developed a stacking and reclaiming solution for a client in the cement industry in Eastern Europe. The combination of Luffing Stacker

and Bridge-Type Scraper Reclaimer has been demonstrating its reliability for more than five years now under highly demanding operating conditions. The construction of this installation is based on several decades of experience and knowhow in handling all kinds of sticky bulk material worldwide.

The cement plant operates a longitudinal blending stockyard equipped with a Luffing Stacker and a Bridge-Type Scraper Reclaimer developed and provided by SCHADE Lagertechnik (Figure 1).

The stacker serves a longitudinal storage bed with a capacity of 75 000 t split into two piles. The stockpile is roofed and thus protected against rain and other environmental influences. During the stacking process, the freshly delivered bulk material coming out of the crusher is passed through an analyser (Figure 2) controlling the moisture.

Moisture is a major issue at this plant. The raw material used in production might reach moisture contents of up to 21%. If the moisture content exceeds an upper limit,

STACKING AND RECLAIMING

HIGH-MOISTUREMATERIALSMARJAN BOJDYS, SALES DIRECTOR CEMENT,

SCHADE LAGERTECHNIK GMBH, GERMANY, HIGHLIGHTS A CASE

STUDY FROM EASTERN EUROPE THAT SHOWCASES THE ABILITY OF

THE RECLAIMER TO WORK WITH MATERIALS THAT HAVE MOISTURE

CONTENT ABOVE 20%.

Reprinted from November 2015 \ World Cement

material with less moisture is added to the stockpile. Small stockpiles of drier material are kept especially for this purpose in the quarry.

In case material with less moisture is not available, material is stored for a maximum period of approximately 3 days (Figure 3). The limited storage period is important in order to prevent compaction of the material at the pile bottom. This type of material management is one of the key factors of a successful production using raw material with high moisture levels.

Homogenisation of the raw materialEach batch of raw material has a different material quality due to varying sources. Among other factors, the chemical composition and the particle size of the material are relevant. These quality differences prevail

in the stockpile since the material is stored according to the Chevron Stacking Method. SCHADE delivered a stacker for a stacking rate of 2200 tph, at a travel speed of 25 m/min, which results in 295 layers of material. The number of layers grants a very good homogenisation of the raw material from the stockpile during reclaiming.

In order to reach the full performance of the bridge-type reclaimer, it is necessary to determine the material properties in advance of the machine being designed.

Based on the results, SCHADE engineers construct the scraper chain and the optimal harrow as a key part of the reclaimer design.

The Bridge-Type Scraper Reclaimer is equipped with large harrows on both sides and can therefore can operate in two directions. In order to achieve the best possible blending effect, the SCHADE active harrow covers nearly the total cross-section of the stockpile. It scrapes thin layers of material from the pile surface and transfers it as a free flowing material to the SCHADE scraper reclaimer chain system at the bottom of the cross-section. Due to its size being almost identical to the stockpile’s cross-section, the harrow only needs to move about 3 m in each direction. This means that all different material layers in the pile cross-section will flow down continuously to the SCHADE scraper reclaimer chain system. The shovel transports the material at the floor of the blending bed to the side via the concrete ramp (Figure 4). At the side of the ramp, belt conveyors installed in longitudinal direction along the stockpile move the reclaimed material on into the production stage. With a capacity of 800 tph, the SCHADE Bridge-Type Scraper Reclaimer installed onsite can easily fulfill the demand.

In contrast to those, SCHADE recommends the big harrows, which cover only a small cross-section of the stockpile, because of better pre-homogenisation

Figure 1. The SCHADE Bridge-Type Scraper Reclaimer in operation (photo SCHADE).

Figure 2. The analyser is essential for moisture control (photo SCHADE).

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and better constant material flow to the SCHADE Scraper Reclaimer Chain System. This blending is decisive for the quality of the cement at the end of the production process.

The harrow is the keyThere are two key elements to the successful operation of the SCHADE Bridge-Type Scraper Reclaimer: the material management and the tailor-made construction of the harrow.

A consistent material management is decisive in terms of keeping the moisture of the blended raw material within the operative range of the scraper reclaimer. However, the core feature of the Bridge-Type Scraper Reclaimer is the harrow. Based on several decades of experience with the development of machines for efficient bulk material stockpile operations, the engineers of SCHADE Lagertechnik developed the perfect harrow for this client’s challenging situation.

Harrows installed with all SCHADE Bridge-Type Scraper Reclaimers are full facing, which means they cover the total cross-section of the stockpile, resulting in optimum homogenisation of the material and substantially reduced wear and maintenance.

In the central part of the stockpile, the material is compacted the most by the weight of the material above. This effect is especially notable at high moisture levels. Naturally, this results in a more compact central part of the cross-section. Especially at high rates of reclaiming, fixed teeth alone might not be able to scrape the material properly off the cross-section. However, adjustable teeth in combination with scraper chains integrated into the harrow (Figure 5) handle the task flawlessly.

At the lower end of the teeth, flat steel plates are installed. Without these steel plates, the reclaimer might not reach the desired reclaiming rates at high moisture levels or in case of compacted material. The plates guarantee that the material loosened by the teeth of the harrow is removed, even under those conditions. With each transverse stroke of the harrow, the flat steel plates reliably scrape a fine stratum of material off the cross-section.

To be set for year-round operation, the inclination of the harrow has to be adjustable for winter and summer operations. In winter, the harrow has to be set one or two degrees more steeply to get the frozen material into a quick flow condition. If the flow is too slow, there might be an accumulation of material at the SCHADE Scraper Reclaimer Chain System. Warping or deflection of the rather large harrow during operations has been avoided by constructing its load bearing structure in two layers stabilised with framework beams.

The tailor-made design of the harrow for the client in Eastern Europe is not only based on a close analysis of the situation at the plant; a multitude of material samples from the customer’s material sources have also been analysed by an independent institute. This analysis provided additional facts and data for the

development of the harrow and the scraper plate form and liners. Further taking into account the internal shear forces caused by internal friction and the strength of the bulk solid, SCHADE engineers decide upon the optimum type of harrow construction and calculate the dimensions of the profiles and the drive unit accordingly. Close coordination and discussions with the client contribute to a solution considering all demands.

SCHADE drafts the harrow and the scraper chain. These construction drafts are passed to steel and mechanical engineers, who construct the machine in compliance with the specifications. In some instances the mechanical engineering takes place on the site where the machine will operate afterwards. Part of the entire production process is a thorough quality management by SCHADE. The installation is accompanied by a SCHADE chief supervisor. From the initial analysis of the material samples all the way through to the start of operation, SCHADE knowhow is part of the process, which means that the company can guarantee the best possible solution for the local situation.

Figure 3. Freshly stacked moist material on top of the pile (photo SCHADE).

Figure 4. The SCHADE Scraper Reclaimer Chain System (photo SCHADE).

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Ground-breaking technology for other industries The use of Bridge-Type Scraper Reclaimers is not limited to one industry. They are also destined for reclaiming limestone, gypsum, iron ore, coal and other bulk materials. This and other types of scraper reclaimers are essential for all kinds of bulk material storage, blending and reclaiming.

Though SCHADE bridge reclaimers can reach a capacity of more than 2200 tph and a span of up to 60 m, a high reclaiming capacity is not necessarily

the most important characteristic demanded from a bridge-type scraper reclaimer. For many industries the blending effect is of equal or even higher importance. Using the Chevron Stacking Method to create a stockpile, in combination with a correctly dimensioned reclaimer, provides for a highly homogenised raw material entering the production process. The reclaiming process is fully automatic and not only limited to longitudinal blending beds and stockpiles. SCHADE engineers are also able to construct circular blending beds according to the client’s demands.

SummaryOver the years, designing equipment to handle bulk materials with abrasive properties, high humidity, and in a deep-frozen or compacted state has evolved as a specialisation of the SCHADE engineers among their numerous other fields of competence. Up to now, the company has developed a solution to routinely handle material with moisture up to 21%, but it is only a matter of time until they raise the limits of the operative range for reclaiming bulk material.

Faced with a challenging situation at its client’s plant in Eastern Europe, SCHADE Lagertechnik found an engineering solution beyond the previously accepted standards. Despite -25˚C temperatures in winter and maximum moisture contents of 21%, the SCHADE machinery has worked reliably since 2009 and is still performing well.

Figure 5. Harrow with integrated scraper chain (photo SCHADE).