Semi-Turnkey Contracts and Equipment Packages for Cement Plants Worldwide
Martin Dalbert, Germany, 1. June 2018
Semi-Turnkey Contracts are offered by AUMUND to maximise the benefit of their detailed know-how in materials handling systems design but with the flexibility to allow clients, or EPC Contractors, to split responsibilities into discrete packages taking maximum advantage of specific suppliers niche products or services.
Very often the process systems (kiln and/or mills etc.) are separated from the transport and electrical equipment as well as civil works and these elements may be let by the client (or EPC Contractor) in separate but clearly linked packages. This gives the client the flexibility to choose favoured suppliers or specific equipment and services, particularly relevant for civil works and electrical controls, where local contractor’s experience of the site is a major advantage. For example an AUMUND Semi-Turnkey project could include the feeders, silos, conveying systems and storages along with the associated structures, bridges and transfer towers. Of course the materials handling and storage systems provider must work closely with the process equipment supplier to develop a plant layout that is both economical and satisfies the client’s general demands and local site topography.
As part of the Semi-Turnkey materials handling package AUMUND deliver all the associated loading plans for the civil works design and any plant interfaces plus the instrumentation and electrical control demands and control philosophy, respecting the plant norms and standards.
The process element within major plant development projects most likely will include, for the typical modern cement plant, such as crushing systems, mills and perhaps a new kiln. In these circumstances an EPC Contractor or the major equipment supplier (particularly the kiln supplier) will lead the project taking process and performance responsibility.
Once the major process plant is decided then the relative displacement of the major plant elements, raw material, raw meal, kiln, cooler, clinker storage, milling and dispatch must be shoehorned into the available space on site… This often demands some radical and often novel materials handling solutions to move materials between the process sections to deliver the performance and reliability demanded in this industry
With all Semi-Turnkey solutions clear battery limits are critical to exactly define the extent of supply and the specific responsibility of the EPC contractor. Such battery limits may be, for example, the outlet flange of an incoming belt conveyor and the inlet flange of a downstream storage silo, the contract may provide for the complete design not only of the materials handling equipment but also all of the associated structures, bridges, towers, access walkways, cladding, instrumentation, cable routing risers and trays etc. plus support for any services routed along the bridges etc..
Clearly close liaison with the EPC Contractor is vital to ensure all of the related activities, particularly control and power cabling, are provided with sufficient capacity to provide for the associated capital plant supplied by other specialist manufactures; mills for example. With the extensive use of 3D modelling the compatibility of such software across the contractors supplying each section of the plant is hyper critical allowing effective sharing of data on a common platform whilst respecting the individual manufacturers IP. Under the hieratical control of the EPC Contractor efficient document management is vital to ensure an effective engineering change permit system is rigorously managed and change data is distributed to the related contractors.
Whilst the Semi-Turnkey contract may include for the complete supply of mechanical conveying systems plus the associated supporting structures, transfer chutes, silos and access systems.
Very often the supply part may be restricted to the conveying equipment but the associated structures etc. may be given as an engineering only order. In this way the structural part of all of the semi-turnkey contracts may be combined by the EPC Contractor and let to a single favoured fabricator to maximise the volume and therefore minimise the rate per kilo both of the fabricators but also for the associated freight.
Of course effective quality control is essential and with a single fabricator a close relationship and trust may be more easily established and associated management costs mitigated. AUMUND are well versed in this modus operandi and extend the option for the EPC Contractor or client to arrange local manufacture of some elements of the conveyor systems such as elevator buckets, casings etc.. The clear purpose here being to minimise the cost without sacrificing quality and to this end AUMUND ensure parts fabricated locally remain interchangeable and are in fact no different to the same part manufactured at their works in Germany.
There are cement plants having its own peculiarities particularly related to the limestone sourcing and transportation. For the most part the limestone is quarried by blasting and run through a primary crusher to reduce the size for economical onward transportation.
Clearly the crusher is the key element here and is generally purchased from a specialist supplier outside the Semi-Turnkey contract system. However, once the crushed limestone, plus the necessary additives required adjusting the kiln chemistry, arrives at the cement plant then the first Semi-Turnkey packaged may be assembled taking the materials into the plant, tertiary crushing, automated storage and blending, conveying, elevating, silo storage for additives, blending and milling of the raw meal before being finally blended in silos and raised again to the pre-heater tower inlet. This package may be subdivided but in general the sections may be easily defined and the battery limits clearly specified terminating to the inlet flange of the pre-heater intake cyclone.
AUMUND offer the key materials handling plant at every stage of the process and in particular the chain and belt elevators required to raise the raw material and ground meal to silos. In addition SCHADE Lagertechnik GmbH (part of the AUMUND Group since 2001) can add their portal, semi-portal or circular storage systems, including chain based bridge type Reclaimers, into the package to homogenise the limestone before going into the raw meal mill. In this part of the process additives are blended into the limestone stream using weigh feeders, in the AUMUND package weigh feeder type DPB based on the apron or pan feeder concept offers a robust and reliable solution both for feeding and silo extraction. Based on the type KZB or BPB chain pan/plate concept but with a supporting roller at every chain pitch the load on the conveyor may be measured accurately on a weigh rail and the throughput computed from the chain speed.
From the raw meal the Pre-Heater, Pre-Calciner, Kiln, Clinker Cooler and Crusher are generally combined into a single source package almost invariably under the direct control of the EPC Contractor. However, from the cooler/crusher the Clinker section lends itself to a Semi-Turnkey package all the way to the finished cement mill bunkers including the clinker storage silos.
Generally the mechanical part of such a project will be the lead element defining the materials handling routing and the associated control and civil works. Over the last 95 years AUMUND have developed a wide range of pan conveyor designs, and in addition the bucket conveyor and bucket elevators providing the maximum flexibility in plant layout by giving the plant designer the option to select the most appropriate working angle and lift height to make the installation compact without sacrificing either performance or reliability. With the latest AUMUND conveyor chains conveying lift heights of 96 metres with a single lift are possible, with a working angle of 60 degrees using the BZB Bucket Apron Conveyor principle, often eliminating the need for any intermediate transfer point with consequent savings in structures, access provisions and control equipment. In addition the AUMUND type SPB Pivoting Pan conveyor concept offers a compact solution for loading dissimilar materials to the mill bunkers or longitudinal clinker storage hall.
Of particular interest illustrated herein a project for Holcim at Ste Genevieve on the Mississippi river in the USA and still the world’s largest kiln line with a proven performance of over 1,300 tons per day. In this plant AUMUND USA handled large sections of the Raw Meal plant and virtually the complete Clinker Transport from the cooler/crusher through to the twin storage silos and on to the mills plus the vertical elevators for the mill recirculation and finished cement handling.
The clinker handling specifically included twin AUMUND type KZB steep angle conveyors installed within a single gantry supported at high level from a clinker rejects silo. A diverter valve plus two high level transfer conveyors distribute the clinker to either of the two identical storage silos or the rejects silo between. From the adjacent silos four parallel AUMUND type KZB conveyors transfer the clinker to four identical vertical finished cement mills; each clinker conveyor is fitted with drive control allowing the output rate to be directly controlled to suit the mill demand.
Gypsum is added direct to the KZB conveyors at low level using small individual silos each with AUMUND extractors type CENTREX® plus weigh belt feeders. Using the combination of flow rate control on the main KZB conveyors and the gypsum additions the overall feed rate and blend ratio may be continuously and automatically monitored.
As referred herein the full EPC contract may be, and generally is, broken into many different Semi-Turnkey contracts each having to align with the adjacent parts plus electrical and instrumentation systems which from the clients viewpoint are seamless and fully integrated. Of course in most projects the client will be involved in the selection of Semi-Turnkey contracts since at some point the client must take-over the plant and be responsible for its operation and maintenance. From this viewpoint AUMUND are uniquely placed with a reputation for reliability and dependability unsurpassed in the industry.
Of course any Semi-Turnkey installation within the cement industry must perform 24/7 and deliver the dependability demanded in this most aggressive of applications often handling highly abrasive and hot materials such as cement clinker direct from the cooler. During a kiln flush accumulated dust and raw material may flow through the system uncontrollably and expose the ongoing conveyors to massive short term overloads and very high spot material temperatures. AUMUND steel pan conveyors are exceptional in this application being able to handle material temperatures to 700 degrees C. for short periods where a conventional belt conveyor would be a clear fire risk.
AUMUND offer an ongoing inspection and preventative maintenance package designed to expose potential faults at an early stage and, by continuous condition monitoring, determine the possible failure point. In this manner maintenance and refurbishment work may be planned into a regular outage period avoiding uncontrolled failures with associated expensive kiln downtime…
Conceptual design, materials handling systems, structures and storages, instrumentation and control philosophy along with associated dust plant and similar equipment may be part of the AUMUND Semi-Turnkey package supported by a wealth of knowhow.
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