Storage with a twist
Automated Solutions for Intake, Storage, Blending and Reclaiming
Since the very beginning of cement production the blending and proportioning of limestone, clay and trace additives was, and remains, the key to producing controlled and continuously repeatable qualities of cement to closely defined and internationally accepted standards.
In the early days sometimes blending was a hit and miss operation often based on counting shovel loads of various additives in a crude batch mixing operation. Similarly stockpile generation and reclaim would often be achieved simply using wheeled loaders where the raw material arrives by tipping truck and is then pushed up into a stockpile. The recovered material would be loaded to a hopper/feeder from which it could be elevated to bunkers, metered and ground and blended to form the raw meal.
In the modern cement plant these activities are automated using a combination of longitudinal and circular storage systems achieving a very high level of material homogenisation to ensure effective blending and therefore closely controlled clinker quality. A typical example is an early machine supplied in 1975 to Ketton Cement (now Hanson Group Heidelberg) in the UK for blending Limestone. The Bridge type Reclaimer with dual reciprocating Harrows recovers material from both directions of travel. Stacking and reclaim functions are integrated electronically to permit simultaneous operation using discrete stockpiles. The reclaimed limestone is taken by conventional belt conveyor from the storage to the raw meal mill bunkers.
The requirement for blending is now ever more important with an ever extending range of additions materials, often sourced from different locations, plus alternative raw materials such as granulated blast furnace slag. With kilns fired by coal or pet-coke there is in addition the requirement to store and blend large volumes of fuels often imported by sea or rail.
SCHADE are in the forefront of this technology delivering state of the art solutions at every level including circular strategic and blending storages for limestone and fuels plus both cantilevered boom and semi-portal designs for additions materials, corrective limestone and also solid fuels.
To illustrate these options we shall discuss three specific recent projects each with differing solutions.
Holcim Dotternhausen: Circular Limestone Storage and Blending
Installed in 2008 as part of an ongoing development of the cement plant this circular storage for Limestone incorporates a radial and luffing boom stacker plus an integral Bridge Reclaimer with single sided reciprocating harrow. The circular storage generates a layered stockpile using the Chevcon blending solution by travelling the boom stacker over the available radial working area back and forth controlled by a system of level and positional detectors. After each pass the boom is raised incrementally until the maximum stored depth is generated. To maximise the stored volume the stockpile is tapered off down to the reclaimer base level following the reclaimer as it traverses around the central column.
By generating a layered stockpile in this manner a cross section through the stockpile at any point would yield elements of every sample of material delivered evenly distributed over the length of the pile.
Using the reciprocating harrow system working on the full inclined face of the stockpile samples of every layer are delivered continuously to the lateral chain scraper conveyor working across the base of the stockpile and discharging through the centre of the storage to an underground belt conveyor system. In this application a reclaim rate of 200 tons per hour is provided but similar systems are available with much higher reclaim rates, typically to 1,200 tons per hour in the cement industry, or beyond.
The complete circular storage system including Stacker and Bridge Reclaimer is mounted to a central column which is extended upwards to support the incoming belt conveyor through a slew ring bearing. In this manner all loads are transferred to the foundations below and no loads are applied to the building structure allowing a light weight enclosure based on a fabricated or Geodesic design.
In general the circular storage offers the lowest footprint per ton stored and when the foundations and enclosure are factored in is generally the most economical solution both for Limestone and Fuel Blending. In addition, from an operational viewpoint, the circular storage offers the advantage of continuous, uninterrupted output from the full stockpile cross section. Since the stockpile is wrapped around the central column there is no starting and finishing point and by integrating the control of the stacker and reclaimer the system simply works endlessly around the central axis delivering a continuous supply of material from the storage to the process system...
Holcim Campulung: Longitudinal Storage, Blending and Reclaim:
Holcim Romania has recently commissioned a new kiln line at their Campulung plant using the best available technology with minimal environmental impact at the core of the design brief. As part of the new kiln line SCHADE were commissioned to design and supply a new limestone storage and blending facility in this case based on two parallel stockpiles serviced by a single central stacker and contained within a common enclosure envelope.
Using two parallel stockpiles material may be stacked on one side whilst being reclaimed from the other providing for a continuous output. Also, the longitudinal stockpile has in principle the flexibility of permitting absolute segregation of dissimilar materials that cannot be achieved using a circular storage.
The operating principle is similar to the circular storage in that the stacker traverses the working zone back and forth generating a new layer on each pass by incrementally increasing the stockpile height using the Chevron stacking pattern. Once the stockpile is completed the Bridge Reclaimer may then recover the material using the full size Harrows to ensure an even flow from every level of the inclined stockpile face providing complete homogenization of the output.
For this application the Reclaimer chain scraper conveyor is swept up at the discharge to simplify the transfer of material to the collecting conveyor running parallel to the stockpile and at the same relative level.
This is a classical stockpiling and reclaiming solution and when combined with a light weight building enclosure represents an economical and environmental friendly answer with the potential to easily extend should the need develop. Being full enclosed there is no risk of fugitive dust pollution and no possibility of contaminated water runoff polluting local waterways or aquifers.
For this project AUMUND also supplied a wide range of other conveyor equipment including Clinker Transport, Belt Elevators and Central Chain Elevators plus the type TKF Drag Chain Conveyors. The TKF application is particularly interesting since two units were installed side by side beneath track hoppers to receive granulated blast furnace slag from side discharge rail wagons.
Kelete Cement Turkmenistan: Segregated Storage and Reclaim.
Some of the earliest SCHADE designs were based on the cantilever boom reclaimer and in this application the latest SCHADE developments in scraper chain and shovel design are incorporated in this solution bringing the concept fully in line with current practice.
In this project Gypsum and other additives are stored in separate discrete bays with concrete dividing walls eliminating any risk of cross contamination. A single travelling Luffing Boom Stacker of length 15 metres services all of the storage bays with a loading rate of 400 tons per hour. The stacker boom may be raised clear of the diving walls allowing uninterrupted travel between storage bays.
For maximum flexibility in operation two Cantilevered Boom Reclaimers are provided, principally one for Gypsum and one for additives, and located on rails working from the opposite side of the building to the stacker unit. The reclaimer boom may be raised up clear of the stacker boom level allowing the two machines to pass each other during repositioning between working zones.
Whilst the cantilevered boom reclaimer may be swept up at the discharge in common with the bridge designs in this case a simple straight boom was employed simplifying the design but requiring a concrete wharf forming a ramp over which the recovered material is discharged to the collecting conveyor.
Each reclaimer is specified with a capacity of 200 tons per hour and this is a typical size in this type of application handling the additions and alternative raw materials that are added to the cement mix. Not only is this system used for additions materials of all types it may also be extended to store and reclaim solid fuels making maximum use of the facility providing the plant layout permits.
For the Kelete project in addition to the longitudinal storage an entirely separate circular storage and blending system was supplied uniquely for handling the Limestone and Clay mix with a reclaim rate of 300 tons per hour. By combining the segregated storage offered by the cantilevered boom Reclaimer and the blending benefits of the circular storage for the Limestone and Clay mix SCHADE were able to offer the client really the best of both concepts and overall an economical and environmentally sound solution.
Bulk Intake Systems
SCHADE have expanded into the Rail Wagon Tippler market with a new range of automated rail wagon unloading systems. These include the original AUMUND style tippler, now known as the “O” Frame, plus the new “C” Frame and “Pivot” Frame designs all available with a range of Wagon Positioners and Indexers allowing the complete automation of the raw material and fuel intake facility.
Either for use with Wagon Tipplers or where hopper bottom wagons are available within the AUMUND Group there are plentiful solutions for the feeding of any type of material from track hoppers of any size. Recently supplied to the Holcim Ste. Genevieve plant in the USA the type BPB heavy Apron feeders are used to receive clay and all additives direct from self discharging railcars.
In addition to the TKF Drag Chains already described at Campulung AUMUND offer the type PKF armoured chain feeder suitable for even wet and sticky materials with the added bonus, as with the TKF, it is totally enclosed and very compact requiring the minimum of pit depth and no external clean-up conveyor or dust extraction.
Finally the Samson under rail feeder may be installed to receive from self discharge wagons with the advantage of clean operation and a typical pit depth of only 3.5 metres. With the associated reduction in civil works costs and reduced material free fall this is an attractive option environmentally, operationally and economically.