| World Coal | Reprinted from October 2017

From stockpile to storage dome

Reprinted from October 2017 | World Coal |

Andreas Markiewicz and Dr Christoph Seifert, SCHADE Lagertechnic GmbH (Aumund Group), Germany, outline an environmentally friendly approach to storing and reclaiming coal.

It is now a fundamental requirement for all new power and industrial plant designs to pay careful attention to all aspects of environmental protection. Plant upgrades are aimed at minimising intrusion into the local surroundings and mitigating the impact of plant emissions on air quality and noise levels. In many

areas, particularly in Asia, standards for plant design are now driven by these demands for increased environmental standards from central power utilities. This has resulted in strict controls being put in place to ensure plants comply with the highest environmental standards. As a result, the use of open stockpiles in bulk terminals, power utilities and industrial plants are becoming problematic and driving operators to upgrade to enclosed storage facilities, where any pollution generated in the handling process may be contained and controlled.

While significant progress is being made in the Far East and China in relation to the use of alternative fuels and renewables, the vast majority of the base-load

Classical design of a coal storage facility at Kraftwerk Westfalen, Germany, including strategic and blending bed stockpiles using portal scrapers and reclaimers. The facility was installed in the 1980s.

power generated by coal-fired power generation accounting for around 60% of China's total energy (with similar levels in India).

The expanding use of wood pellets as a ‘green’ fuel is also an issue for plant

designers. In its present state, this material is very dusty and susceptible to self-ignition, which has caused some spectacular fires in recent years. When torrified pellet becomes commercially available, these problems may be

overcome but, currently, enclosed storage is the only viable option.

Traditionally the bucket wheel stacker-reclaimer was often the favoured solution, particularly in terminals, but it has many significant drawbacks: it is very heavy and expensive to install and operate and is also very time-consuming to repair or rebuild, particularly where a new slew bearing is required, often demanding a downtime of three months or more.

Although it is possible to enclose the system, it is difficult and expensive since the area required is high relative to the tonnage stored and therefore generally the bucket wheel is synonymous with outside storage and, whilst the system may stack and reclaim on the same unit, these functions may not be carried out simultaneously – generally requiring a separate stacker. The bucket wheel system may operate automatically but usually requires a full-time driver to control the unit and set the stockpile section to be recovered.

However, outside stockpiles are susceptible to adverse weather conditions and the equipment cannot operate in high wind speeds. Fugitive dust from the handling operation and wind blown from the stockpile surface is a persistent problem, and demands the intensive use of fogging systems to dampen the whole stockpile surface. Additionally, run-off water must be managed to prevent local pollution of ground water aquifers. Finally, external stockpiles are susceptible to spontaneous combustion, which is exacerbated by excessive water content and substantially increases the fire hazard.

Alternative storage solutionsSCHADE has a long history in the storage and reclaim of dry bulk materials, including metallurgical and thermal coal for the power industry mainly within Germany, but in recent decades increasingly within China and the Far East.

Over recent years, from the mid-1960s, SCHADE developed the circular storage concept with a radial stacking boom and cantilevered reclaimer boom, both mounted to a central column allowing simultaneous stacking and reclaim.

In the late 1980s, this concept was massively extended to achieve continuous

Circular storage system with cantilevered reclaimer discharging to a central outlet and underground conveyor system. Enclosed within a fabricated dome.

Circular storage system with bridge type reclaimer and reciprocating harrow to blend coal built up in a Chevcon stockpile.

| World Coal | Reprinted from October 2017

The latest design of enclosed storage using the semi-portal scraper reclaimer within a fabricated frame building (photo courtesy of SCHADE).

handling rates, typically of over 4000 tph incoming and over 2000 tph outgoing. These massive circular storage units now reach more than 130 m dia. and have storage capacities of about 360 000 t of thermal coal – able to satisfy the storage and intake demands of a typical 1000 MW power plant. Invariably the circular storage is typically fully enclosed within a high strength, light-weight geodesic style dome that is comprised of individual triangular elements.

At this level of performance, for shore side power plants, a single storage dome can be linked directly to a continuous ship unloader (CSU) via a system of enclosed jetty conveyors, providing full enclosure of the handling and storage facility and thus making the whole installation impervious to adverse weather conditions with no risk of fugitive dust pollution. Typically such an arrangement could work with vessels up to panamax size with sufficient capacity to hold a full vessel content and still provide over 90 000 t of online storage. The circular storage concept with a cantilevered boom reclaimer is generally reserved for strategic stockpiles where blending and homogenisation is not required. Using the cantilevered boom principle, the entire system is supported from the central column and no outer track is required thus simplifying the foundation demands, as only a ring beam plus containing walls is required to obtain the maximum stockpile volume and support the dome enclosure.

However, where blending is required, the circular storage is supplied with a bridge-style reclaimer, including inclined reciprocating harrows. The bridge is secured to the central column and also to a rail running around the periphery of the dome. Using the radial and luffing boom stacker a layered stockpile is generated automatically by the cone shell method (developed by SCHADE) such that at any point along the stockpile a cross section would yield samples of coal from every source. Using the circular concept, the output may be maintained without interruption as the blending bed is continuously generated and recovered as the stacker and reclaimer work together around the central column. With both the cantilevered and bridge style reclaimers, the recovered material is swept to the centre of the system and

discharged through an aperature in the concrete floor to an underground conveyor system installed in a tunnel beneath the storage. With over 50 units installed in and around China, the circular storage concept has proven very attractive and remains an effective

solution for both strategic and blending bed installations.

Exploring optionsHowever, there are other options, and in recent years, the operational benefit of the semi-portal reclaimer design has found

Reprinted from October 2017 | World Coal |

Longitudinal stockpile using a double sided harrow bridge type reclaimer for homogenisation of the stored material layered in a Chevcon stockpile.

Tripper car for feeding coal with a capacity of over 4500 tph from overhead belt conveyors into the storage.

Large semi-portal reclaimer at Taipeh Harbour including overhead conveyor system.

favour in many new installations where segregation and blending is required. The semi-portal design supporting beam is, in effect, half a standard portal frame supported at high level to a rail mounted to a concrete containing wall. At the lower end, the semi-portal is mounted to standard low level boogies running on a rail at ground level.

The reclaimer boom is secured to a through pivot at a low level and to the winch system at a high level, allowing the boom to be raised and lowered to follow the stockpile. In this manner, the stored material is conveyed over a concrete wharf onto a troughed belt collecting conveyor running parallel to the storage. Mounted at ground level the collecting conveyor requires no expensive underground tunnels thus reducing civil works cost and simplifying maintenance access.

InstallationThe system may be installed with back-to-back reclaimers using a mirror image arrangement either side of a central retaining wall to create two storage halls under a single enclosure. Individual storage bays may be created along the length of the storage hall allowing dissimilar materials to be stored and reclaimed from common equipment or, for example, for different grades of coal, which may be stored separately for subsequent blending during the reclaiming process.

Material is generally loaded into storage from overhead belt conveyors, including either a reversing shuttle belt or travelling tripper system, to deliver material to any point along the storage. For back-to-back installations, two lines of a tripper or shuttle system may be installed or, alternatively, a single tripper with an onboard reversing belt conveyor to discharge to either side of the central dividing wall. Clearly a twin conveyor offers the most flexibility but has cost implications. Alternatively a travelling boom stacker may be mounted to rails at ground level and travel along the full length of the stockpile passing over any intermediate retaining walls. The whole system is very cost-effective with a simplified reclaimer design and simplified enclosure demands, eliminating the need for very large self-supporting domes as would be required with a circular storage.

Where different grades are to be blended multiple reclaimers may be used, for instance one reclaimer per storage bay, allowing controlled volumes of each stored material to be metered by each reclaimer onto the common collecting conveyor. In this manner, the varying grades are layered onto the collecting belt and at each transfer point these layers mix to create a homogenous delivery to the boiler plant day bunkers. This solution is particularly suited to power plants receiving coal either by rail, sea or from multiple mine sites without going through an intermediate preparation plant. Each mine site will present a specific grade of fuel unique to that site with varying carbon, ash and sulfur content, and these grades may be stored separately and the final blend determined by the plant demand.

The world's biggest semi-portal reclaimer application, designed and recently commissioned by SCHADE for a power plant application, is designed for coal of density 0.72 and has a rail span of 58 m with a 55.5 m reclaimer boom based on a long travel rail distance of 380 m. Such a system would have a storage capacity of approximately 2 x 360 000 t and a typical recovery rate of 1980 tph. Semi-portal reclaimer designs on this scale are entirely compatible with multiple generator sets on a single site of approximately 2 x 1000 MW. As with the circular storage, the semi-portal storage may be directly connected to a deepwater

port that discharge big ships down to small barges or coal can be imported by rail from the hinterland, perhaps using a wagon tippler system discharging random flat bottom wagons.

SCHADE supply a complete package for its reclaimers, including all of the associated instrumentation and electrical controls including PLC and software to control the equipment and automatically recover the material within pre-set operational parameters. In addition, for multiple semi-portal reclaimers operating as blending units mixing dissimilar grades of the same base material, the company supply integrated control packages with a central PLC that may be integrated to the plant controls and deliver the desired blend ratios.

Generally the reclaimer will be supplied with cable winders for power and controls but alternatively the control system may be integrated with wireless communications to the central PLC. In addition to the control of the reclaimers the function of the tripper or shuttle system must also be integrated to define operating zones to ensure that material is not delivered above the reclaimer. The integration of the complete plant controls, including the intake and discharge systems, is equally important, and effective communication between the machinery supplier, client and site contractors is vital to deliver a dependable solution.

Using the semi-portal solution, the client has much greater flexibility to adjust the scope of supply to achieve the most economical solution. For example, the reclaimer supply package may include the tripper car but generally the belt conveyors will be sourced separately and again effective communication is mandatory to effectively integrate the packages. By maximising the local supply package combined with effective technical and quality control management, SCHADE delivers an economical working solution without compromise.

Conclusion In conclusion, the ability of any type of chain scraper reclaimer to operate autonomously and automatically has obvious environmental and operational benefits, and offers an economical and dependable alternative to open stockpiles.

| World Coal | Reprinted from October 2017

Typical and economical wagon tippler arrangement for bulk handling terminals with low requirements on the civil works.