(France/Tunisia) — In October 2008, Polysius SAS, the French subsidiary of ThyssenKrupp Polysius, was awarded the EP contract for a 3600tpd cement plant in Tunisia by Sotacib Kairouan SA. To carry out this project while meeting the client’s requirement in a booming market proved a real challenge. However, close cooperation between Sotacib Kairouan and ThyssenKrupp Polysius ensured success and client satisfaction. By Patrick Brunelot and Jean-Christophe Lene, Polysius SAS, France.
Since the privatisation of the Tunisian cement industry in 1998 and up to the new Kairouan project, Polysius has been contracted for all previous projects in the country including:
Ciments de Djebel Oust – turnkey upgrade to 4000tpd
La Société des Ciments d’Enfidah – new 1900tpd turnkey clinker production line
Ciments de Djebel Oust and La Société des Ciments d’Enfidah – turnkey petcoke grinding plants
Sotacib Feriana – 1000tpd turnkey white clinker line
CIOK – turnkey petcoke conversion and grinding plant.
This impressive track record with Tunisian turnkey projects and the ongoing collaboration with Sotacib at its Feriana’s white cement kiln line encouraged the client to contact Polysius for the planned Rouissat project. With several ongoing investment projects in the MENA region in the booming market of late 2007, meeting customer expectations required flexibility and resource optimisation. In addition, the market-induced cost inflation with the associated difficulty to stay within customer budgets for full turnkey projects proved a further challenge. For these reasons Polysius offered Sotacib Kairouan the following alternatives:
a pre-engineered solution based on a ‘copy-plant’ concept with a slightly higher capacity than required
an original project management set-up.
Raw material preparation
As the raw materials quarries are located close to the plant, the company chose to prepare the raw mix at the crushing plant. The facility consists of a 1200tph double-hammer crusher with two feeders – one for limestone and one for clay components. To obtain an optimal raw mix chemical composition, an online analyser controls the feeder’s adjustments. Crushed raw materials are subsequently conveyed to a 41,000t circular mixing bed to complete the pre-homogenisation process.
In addition, a fully-automatic 25,000t correctives and additives storage is installed and includes one 500tph belt stacker and two 300tph side reclaimers.
Raw material grinding
Raw mixture materials are extracted from the storage with a 550tph conveying capacity which are also suitable to feed a second line in the future. A set of hoppers is provided for dosing the mix and corrective materials such as sand, iron ore and high-grade limestone.
For the grinding process, a RMR 51/26 vertical roller mill was selected to dry and grind 280tph of raw materials. The produced raw meal is then collected in two dedusting cyclones and stored in a 11,000t homogenisation silo.
The plant’s main fuel, petcoke, is dried and ground in a 3.6m x 6.5m ball mill, equipped with a 1100kW drive. The LMK 170 separator ensures the production of petcoke with a fineness of below five per cent R90m. The process gases are dedusted in one bag filter.
Moreover, the solid fuel preparation plant is fully equipped with safety devices and a CO2 inertisation system complying with ATEX regulations. A natural gas network with primary reduction station provides all the fuel for the kiln system.
The raw meal is dosed and fed into a five-stage preheater which includes a calciner with tertiary air and a separate combustion chamber which is able to burn up to 60 per cent of the total fuel requirement. This type of calciner is particularly suitable for low-reactivity fuel as petcoke and will offer considerable flexibility for future alternative fuel use. Clinkerisation is achieved in a 4.2m x 64m, three-pier 3600tpd kiln and a POLFLAMe® kiln burner allows combustion of fine petcoke.
Polysius’ latest-generation of clinker coolers, the POLYTRACK®, completes the clinker plant and ensures the heat recovery to the kiln process and final cooling of the clinker. The Polytrack is equipped with an intermediate roller crusher which guarantees a low temperature of the whole clinker fraction with an extremely-low wear rate. Clinker is then conveyed to a 50,000t storage hall.
Original dedusting concept
Only one bag filter is installed for kiln/mill and cooler process gases dedusting with dust emission <20mg/Nm3. No water or fresh air is required for gas conditioning, but an air-to-air heat exchanger on cooler gases is able to maintain the inlet filter temperature at <220C in any conditions. Furthermore, this air-to-air heat exchanger is stopped during compound mill + kiln mode to increase the inlet filter temperature, thus avoiding any corrosion development on the filter casing and saving electrical energy.
Cement grinding and packing
The clinker and additives are ground in a 5m x 13.25m ball mill driven by a 5300kW electrical motor and a COMBIFLEX® reducer. The ESV 290/0 separator ensures the cement separation and two bag filters complete the gas dedusting process.
Cement grinding is designed to produce up to 190tph of composite cement. This cement is then stored in a 20,000t multi-cell silo. Each of the five cells is able to feed the packing plant and one feeds a 250tph truck loading station.
A fully-automatic packing plant including two 2400 bags/h packing machines completes the cement dispatch system. The 50kg cement bags are loaded onto trucks or conveyed to the palletisation unit.
Quality control system
The POLAB® system ensures the quality control of the whole plant production. It includes fully-automatic sampling stations and sample transport system to the laboratory for raw material and cement.
The electrical scope includes the 225kV/5.5kV main power station which has been designed and installed by Mangin Egly/Omexom with Schneider Electric HV equipment and a power transformer from Getra (25MVA transformer). The overall electrical installation of the process part was realised and managed by Ibitek/CA2E, including the central automation which is based on Siemens PCS7.
Layout and building concept
The general layout was optimised to reduce conveying distances and required excavations according to site configuration and soil investigations, thus reducing investment and execution time. With the same targets, the building concept was optimised with the main structure in concrete and final elevation levels in steel structures.
Original project managemen
One of the key constraints for the project, in addition to the high overall workload in the cement plant engineering business at that time, was to optimise the capex and to keep it below the quoted budget figure for the full turnkey greenfield project. The offered copy plant played a significant role in ensuring this but additional solutions had to be implemented for further budget improvement.
Polysius offered an original project management set-up in which it would supply the mechanical equipment, civil and structural design, prepare requests for quotation and bid evaluations for local contracts (civil, structural steel, steel plate and erection works) as well as ensure overall project coordination. Local contractors would be contracted directly by the client.
Thanks to pre-engineered solutions, the client could be confident that the estimated quantities for civil and structural steel were accurate enough as a guarantee to secure its global budget for the project. Such a scheme allowed the customer to combine both the reduction of related project financial contingencies and the benefits of coordination and project management by an experienced company in turnkey projects. On this basis and with Polysius’ efforts to respond positively to the client’s requirements in exceptional market conditions Sotacib Kairouan was encouraged to entrust Polysius with its greenfield plant in Rouissat.
Two months after coming on-stream, the first clinker was produced and the plant was able to operate at nominal capacity. After a final adjustment, the plant achieved more than 4000tpd, thus confirming the high level of Polysius’ engineering quality, equipment reliability and commissioning team’s expertise.
This project – with involved such a different project management approach – was brought to life thanks to Sotacib Kairouan’s expertise in assessing the risk of such a solution. This was helped by the trust Sotacib Kairouan placed in Polysius for the turnkey project management and the competencies of Tunisian companies in handling local works.
Thanks to the active collaboration of the client and the partners selected, fast commissioning, the high quality of equipment supplied and, ultimately, the client’s satisfaction, this project counts as one additional major success for Polysius in the MENA region.