Bucket Wheel Reclaimers – Bridge Vs Slew

LinkedIn Pulse

01/05/2023

Selection CriteriaSelection criteria for stockpiles reclaim system: • Product blending quality,• Terminal annual throughput, • Numbers of different product grades, • Stockyard flexibility,• Operability • Maintainability• Effectiveness• Failure risk reduction• CAPEX and OPEX

Criteria Slewing Boom Mounted Bucket Wheel Reclaimer (SBWR)

Bridge Mounted Bucket Wheel Reclaimer

CAPEX High cost of reclaimer Low cost of reclaimer (approx. 66% of SBWR)

Stockyard arrangement

Very efficient stockyard formultiple product grades

Lower flexibility for stockyard with multiple products

Reclaim rate (Average to peak ratio)

Moderate to good. Average to peak ratio of 0.70 (approx.)

High. Average to peak ratio of 0.85 (approx.)

Product blending variability

High ship to ship and in-hatch variability

Medium ship to ship and in-hatch variability

Reliability Moderate to high HighOperating cost Moderate labour cost High labour costEquipmentutilisation time

High Moderate

Maintenance Higher level of maintenancerequired and somewhat more difficult to undertake

Lower maintenance hours and cost

Table 1 - Comparison of Stockyards Utilizing Slewing Vs Bridge Reclaimers

Definitions

Reclaim Capacities: Average Rate - The rate attained by a machine as a global average,

inclusive of all movements, motions and procedures required to complete a stockpile; also referred to as the stockpile average or through pile rate.

Nominal Rate - The rate required to attain the average rate when the stockyard and stockpile inefficiencies are taken into account. The nominal rate is calculated from an existing design as the water volume of a bucket times the number of buckets times the rotational frequency of the bucket wheel.

Peak Rate - The Instantaneous, maximum physical rate attained during an abnormal digging sequence and is inclusive of the ring chute volume and maximum heaped bucket volume.

Bridge Type Reclaimers

Bridge-type reclaimers have been manufactured mainly for steel mills, coal fired power plants and the cement industries. This is driven by the need for homogenisation. Configuration of a bridge reclaimer depends upon the specific project requirements. Reclaimers utilised by power plants have rather low reclaim rates and high product blending quality, whereas reclaimers at an export terminal or mine are designed for high reclaim rates.Bridge bucket wheels can be configured to reclaim product from stockpiles either from one direction or two directions (reversible mode). However, there are limitations with reversing the bucket wheel that may prove to be non-compatible with iron ore products. One issue is the bucket sealing faces, when reversed they become digging faces which would experience high wear rates when reclaiming iron ore.The major bridge reclaimer manufacturers are: KRUPP, SANDVIK, FAM, TAKRAF, TAIM WESER and SEMF.

Advantages and Disadvantages of Bridge Type ReclaimersAdvantages• Due to the inherent nature of a bridge type reclaimer, excellent product blending from

the stockpile can be achieved. This results in lower ship to ship and in-hatch variability.• High ratio of average/peak reclaim rate of approximately 0.85 or more.• Reclaiming can easily be fully automated and still maintain high efficiency levels.

However, reclaimer transfer would still require manual change-over of the electrical supply.

• High reliability.• Low maintenance hours and cost.• Good performance record.• Very stable, robust design that is not dependant on counterweights or structural tie

members for the overall balance of the machine.• Low risk of major machine structural failure or collapse.• Lower capital cost. Machine weight is approximately fifty percent (50%) of an

equivalent SBWR. Machine cost is approximately two-thirds that of a SBWR.

Disadvantages• Lower degree of flexibility.• Requires a higher level of scheduling, but lower level of stockyard management.

This is somewhat subject to final stockpile design configuration chosen.• Manual change-over is required to reposition reclaimer via the transfer car.• Additional infrastructure required such as, transfer cars and depending upon

configuration, additional conveyors.• The stockyard footprint can be larger than that for an equivalent SBWR type

yard.• Higher capacity machines have not yet been manufactured

Slewing Type Reclaimers

SBWR’s are widely used in open stockpile systems and are the most common type of reclaimer used in high capacity iron ore terminals.In terms of reclaiming product by bucket wheel, there are two reclaiming methods/procedures:• “Trencher” or “side-acting” machine: the bucket wheel travels along the entire

length of the stockpile and the boom is adjusted up and down to suit product height according to the reclaiming process.

• “Front–acting” machine: the bucket wheel is slewed in an arc across the cross section of the stockpile, in various benches and operating in a pilgrim step method.

Advantages and Disadvantages of Slewing Type Reclaimers

Advantages• High versatility, offering the potential to selectively reclaim product in different

stockpiles anywhere along its travel length.• Ability to slew and reclaim from stockpiles on either side of the central runway.• Provide economical solutions for a high capacity stockyard with multiple

products.• Capable of high reclaim rate.• Can be fully automated.• Flexibility and ease of mobility along its runway.• Low operating cost through automation.• Proven technology.

Disadvantages• Reduced product blending quality.• Lower ratio of average/peak reclaim rate, typically with long term average rates

of approximately fifty percent (50%) of peak rate or seventy percent (70%) of nominal bucket volumetric capacity.

• SBWR is a balanced machine.• Higher level of maintenance required, and maintenance is somewhat more

difficult to complete.• Slew bearing presents significant cost risk, if not maintained properly.

Slewing and Bridge Type Reclaimers: OverviewSBWR’s are highly versatile in terms of their ability to relocate along the rail to different piles.The reclaimer relocation to different product grade often coincides with shiploader hatch changes and there is no (or less) significant interruption to the ship loading operation. A stockyard with SBWR’s requires a windrow stacking method to achieve good product blending quality.The bridge reclaimers with a harrow (or rake) are suitable for stockyards with bed blending requirements where stacking is done in a simple chevron pattern.Currently, it is estimated that ninety percent (90%) of future terminal throughput will require bed blending, therefore uncoupled stacking and reclaiming operation for Lump and Fines is required and it is necessary to stack a complete pile before reclaiming in order to achieve the correct product blend.A stockyard with bridge reclaimers will achieve approximately a ten (10) to fifteen (15) percent higher average reclaim and shiploading rates over that of an SBWR yard with machines of the same bucket wheel volumetric capacity. The subject of high shipping rates is receiving attention by the International Maritime Organisation (IMO), with ship owners attempting to reduce the peak loading rates (often for the wrong reasons). The ability of the bridge type reclaimer to achieve the same average shiploading rate with lower peak rates may become increasingly important if maximum loading rates are imposed by the IMO.

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