TAIM WESER has designed and supplied a dual phosphate conveying circuit for the TIFERT (Tunisian Indian Fertilizers) phosphoric acid production plant located in Skhira, in Southern Tunisia.
The phosphoric acid plant built by TIFERT (Tunisian Indian Fertilizers) in La Skhira, 300km south of the Tunisian capital, has been completed at last. After the delays encountered by the project due to the political instability in the area during the spring of 2011, the new plant is expected to start operating in the first few months of this year.
TIFERT entrusted the TAIM WESER Group with the design and assembly of the continuous conveying circuit which will carry phosphate mineral to the plant for subsequent treatment and transformation into fertilizer. This circuit is made up of 12 belts and has a total length of 1,317m and a belt width of 1,200mm. The belts travel at a speed of 1.5 m/s and have a conveying capacity of 800tph (tonnes per hour). The new plant will be capable of producing 360,000 tonnes of phosphoric acid
per year and is part of TIFERT’s overall plan for supplying fertilizers to the Indian market for the next 30 years.
For this turnkey project, TAIM WESER leads a joint venture together with the firm Socomenin, a top-level Tunisian company which specializes in industrial engineering and construction and has been in charge of manufacturing the local structures, assembly and commissioning, always under TAIM WESER’s supervision. On the other hand,TAIM WESER has been responsible for designing and supplying the commercial elements and key components as well as for supervising all the processes. Assembly has already been completed, and testing is to take place in the near future; the no-load tests in the first place, and then the appropriate load tests.
TIFERT is the first company to be made up of two Tunisian state enterprises and two Indian companies. This plant will permit to transform the mineral and to directly export the fertilizer instead of the raw material. This will generate a significant added value, boosting the Tunisian industry’s competitiveness and encouraging the inflow of capital and the creation of jobs.
 
THE PHOSPHATE CONVEYING PROCESS STEP BY STEP
The process starts in the goods-wagon unloading station, measuring 300m in length, which is equipped with a hopper capable of unloading up to two 20-wagon trains. A total of 117 pneumatically actuated gates have been installed at the bottom of the hopper, whose opening/closing and opening degree can be controlled from a computer programme installed on a PLC. The extraction capacity of the conveyor belt underneath the seals can be thereby controlled. The said control programme has been integrally developed at TAIM WESER.
Next, the phosphate is dropped onto the extractor belt, which is installed in a 10m-deep concrete tunnel, and is then transferred to another conveyor that takes it to the surface. From there, the material goes through a vibrating screen in order to remove possible foreign material that might have accidentally entered the product, and is subsequently carried by two circuits: the first one leads to the plant, and the second goes to an intermediate buffer yard where it is stored. This yard has a capacity of 60,000 tonnes and is made up by a 100m belt that circles through drums. The material at the yard is collected by means of power loaders that feed two hoppers which discharge onto a circuit belt.
Finally, before entering the production process proper, there is another 500m3 concrete silo which is fed through the top by a moving belt, which is reversible so as to increase the silo’s loading capacity. Beneath it, two rotating extractors are
installed, the purpose of which is to preserve the integrity and properties of the material. Lastly, these extractors dump onto two belts that take the phosphate inside the plant in order for it to be transformed.
 
THE CIRCUIT WITH ALL ITS COMPONENTS
On designing the phosphate conveying system for the La Skhira plant, TAIM WESER took into account both the material to be conveyed (wet phosphate, phosphogypsum and neutralizing salt) and the moisture thereof — around 15% — and the desert climate of the area. Based on this, the company has supplied the components needed to build the circuit, which includes: the unloading station with 117 gates, including an opening, closing and flow-control pneumatic and electronic control system as well as its (2, 110kW) compressors, tanks, piping, valves and the PLC. In addition, two rotary extractors, 12 conveyor belts of different lengths — two of which convey two process by- products (neutralizing salt and phosphogypsum), seven transfer towers, one screen, one radial stacker to make up the buffer yard, two loading hoppers, one moving silo-loading belt, one magnetic separator, and ten block and tackles.
As mentioned above, the assembly of the circuit was affected by the events that took place in Tunisia at the beginning of 2011, which paralysed the country’s activity for over a month. This standstill especially affected industrial activity and, in particular, the progress of the onsite assembly works, so much so that normal work rate did not resume until four month later. All in all, the plant is expected to come into operation halfway through 2012.