Circular and longitudinal reclaimers, chevron and windrow stacking, conveyor belt mechanics, safety interlocks, and SOPs
Crushed material from the storage warehouse (≤10 cm) is transported by a network of conveyor belts to either circular or longitudinal reclaimer systems. These systems build and maintain long-term stockpiles of raw material that decouple the quarry and crushing operations from the raw mill, ensuring a continuous, homogenized feed despite upstream disruptions. The reclaimer's material handling system bridges the gap between the crushing stage (Step 2) and the raw mill feed stage (Step 4).
Chevron stacking: The stacker boom travels along the center line of the stockpile, depositing material in a continuous stream that creates a series of triangular cross-sections resembling chevrons. The coarse rock settles at the bottom and fine material accumulates at the top, creating a homogeneous cross-sectional profile. The chevron pattern is particularly beneficial for circular reclaimers because the reclaimer bucket cuts into the profile from different heights, generating a natural blend of coarse and fine fractions during reclaiming.
Windrow stacking: The stacker deposits material in parallel layers across the full width of the stockpile, building up layer by layer. Each pass creates a uniform thickness layer from bottom to top. Windrow stacking results in a horizontally homogeneous cross-section and is typically used with longitudinal reclaimers. The uniform thickness provides consistent feed chemistry to the raw mill when the reclaimer strips the pile face. However, window stacking does not provide the natural cross-sectional blending that chevron stacking offers.
A circular reclaimer consists of a boom mounted on a central pivot that rotates 360 degrees around a circular stockpile. The boom has a scraper, bucket chain, or rake that cuts into the material pile. As the boom rotates, the scraper or bucket chain pulls material from the pile and deposits it into a central hopper or onto a reclaim conveyor belt. The rotating pivot enables the boom to reach every part of the circular storage ring, extracting material evenly from all sides. Circular reclaimers are typically paired with chevron stacking because the rotating boom blends the coarse and fine fractions during reclaiming, producing a feed with consistent particle size distribution and chemistry.
Key control parameters include the boom rotational speed (typically 0.1-0.5 RPM), the scraper/bucket chain speed, and the reclaim rate setpoint from the raw mill. The reclaimer operates in full automatic mode, with the DCS adjusting the boom sweep speed to maintain the target reclaim rate. The feed rate is controlled by a variable frequency drive (VFD) on the reclaim conveyor that discharges onto the raw mill feed belt. Safety interlocks include boom limit switches (prevent over-travel), shear pin and torque monitoring, and body detection sensors in the operating zone.
A longitudinal reclaimer travels along a straight rail track parallel to a long rectangular stockpile. The boom swings laterally and vertically to access the material pile across its full face. As the reclaimer travels along the track, the boom sweeps across the pile, reclaiming material from the entire face. Longitudinal reclaimers are typically paired with window stacking and are used when large storage capacity is needed in a linear layout. The reclaimer has a portal or bridge structure with a scraper chain or bucket wheel that collects material from the pile and transfers it to a cross-belt conveyor mounted on the reclaimer frame.
Longitudinal reclaimers have two primary motion axes: travel along the rail track and boom swing across the pile face. Both motions are controlled by VFD-driven motors, and the positions are monitored by encoders and limit switches. The travel speed is typically 5-20 m/min, while the boom swing speed is slower to allow material to be properly scraped from the pile. The reclaiming sequence is programmed to move the reclaimer in steps, advancing after each full face sweep to prevent pile collapse and ensure complete reclaiming of the stockpile.
Conveyor belts are the primary transport infrastructure for material handling. Each belt consists of a rubber/fabric carcass belt (thickness 20-30 mm, width 1,200-1,800 mm) driven by a head pulley (drive pulley with motor and gearbox) and tensioned by a tail pulley. The belt speed (2-4 m/s) and width determine the transport capacity, with a 1,200 mm wide belt at 3 m/s capable of carrying up to 1,000 TPH. The drive motor power ranges from 75-200 kW depending on belt length, lift height, and loading. The belt is supported along its length by idler rollers (troughing idlers for the carrying side and flat return idlers for the return side).
Each conveyor belt has a substantial inertia - a heavy-duty belt can easily hold over 2,000 tonnes of material at any given time, with the transfer rate far exceeding the crusher's capacity, so hoppers and pend curves are designed to direct material centrally without spillage.
Each belt also has a standard start-up sequence: check pull cords and sway switches are clear, ensure zero-speed sensor is active, activate belt warning horn and flasher, start VFD ramp from 0 to operational speed, verify belt is tracking properly, and only then open feed gates to allow material onto the belt.
The following sequence is the SOP for starting the material handling system from a complete shutdown state. Each step is acknowledged in the DCS before the next step can proceed:
SEQ ACTION INTERLOCK CHECK --- ---------------------------------------- ------------------------------ 1 Visual inspection of all belts None 2 Check pull cords are reset Pull cords not reset 3 Check sway switches are AL Sway switches show misalignment 4 Cycle belt warning horn and flasher None 5 Start reclaim conveyor belt BELT running 6 Start mill/feeder conveyor belt FEEDER running 7 Start reclaimer boom swing None 8 Open feed gates MATERIAL on belt 9 Monitor feed rate and adjust None
If any step fails, the sequence holds and an alarm is triggered in the CCR. The same sequence in reverse is followed for shut-down. The safety interlock system is independent of the DCS and provides continuous monitoring of all belt protection devices. Any trip condition causes an immediate belt stop and prevents restart until the condition is cleared and reset manually.
Reclaimers have their own set of safety interlocks that must be checked before operation: