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Screening machines and equipment:
Quality made in Germany.

Increasing capacities and improving quality in existing fertilizer plants

, Varna, Bulgaria
, RHEWUM GmbH

The leading manufacturer of nitrogen fertilizers in Southeastern Europe and leader in the production of phosphorus fertilizers on the Balkan Peninsula, Agropolychim AD, faced the task to upgrade a well-aged polishing screen and to improve the product quality to standards.

The feed capacity of 100 t/h should be maintained and at the same time the separation changed from 10 mm lump separation to 5 mm and additionally 1 mm dedusting of fertilizer added to the screening task.

Modification on the existing concrete steel beams was very limited and had to be respected in the new machine design. Installed at the top of the building with limitation in height, respecting on and off going connections and footprint, a tailor made design was the only solution which could be fitted, so the fertilizer producer decided for a customized flexible solution from Remscheid. To analyze the installed machine RHEWUM visited Agropolychim AD in Varna, Bulgaria to check the available area and provide fitting dimensions with the new machine. The available height for the screening machine was limited to 2.8 meters. Therefore, the distribution and outlet chutes were specially designed and integrated between the concrete floors.  

Fertilizer types

Agroplychim AD has an annual production capacity of:

  • Ammonium nitrate – 400,000 Mt or Urea Ammonium Nitrate – 800,000 Mt.
  • Mono/Diammonium phosphate – 300,000 Mt or Triple superphosphate – 330,000 Mt.

Further to its own production the company procures from its partners – about 300,000 Mt of nitrogen and phosphorus, mono/di-component and complex fertilizers annually. All these fertilizer types should be sieved by only one polishing screening machine. Therefore, the very flexible direct excited screening machine type WAF has been proposed for handling all the different screening tasks and save up unnecessary costs for additional equipment.

Decision for the RHEWUM WAF screening machine

The screening machine type WAF is a combination of a direct excited screen and a linear motion vibrating conveyor. This polishing screen is characterized by low down times, low space requirements as well as fast and easy maintenance. Additionally, it allows a maximum feed rate with maximum yield at a given purity which is the perfect combination for polishing fertilizer.

The linear motion is generated by two counter-rotating unbalanced motors that transports the fertilizer over the screen. The additional direct excitation of the screen cloth and the automatic self-cleaning cycle with high accelerations of up to 15 g helps to keep the cloth free reliably even when screening sticky materials. By this combination of drive and excitation difficult to sieve fertilizers are classified precisely and at high feed rates.

Reaching high product purities of at least 85 percent in all major fractions, especially the highly valuable fractions, amplified the arguments for the type WAF. Screening fine materials with a high efficiency at high feed rates requires a precise adjustment of all machine parts. The setting of the amplitude for each screen deck has to be adjusted individually to ensure and ideal screening process for each fraction. The electrical control of the WAF’s vibrating heads allows infinite control of the vibrator oscillation during operation and thus a perfect adaption of vibration amplitude to product variations.

One other major reason the client decided in favor of RHEWUM with the supply of the screening machines was that the screening plant can be retrofitted in the original space to keep the construction cost economical.

Trials

When designing and optimizing production plants, it is nowadays inevitable to carry out trials despite all new developments in this field. The RHEWUM testing facilities offer the possibility to compare the laboratory results with the respective product data. These results have a significant role in the design process of the respective machine guaranteeing the later success in the production.

The screen will be fed with 100 t/h of granulated fertilizer with a bulk density of 0.92 t/m³. Water content of the feed material is maximum 1.0 %wt. Due to space limitations at customer’s site a screening machine type WAF was tested with similar material to optimize the screening area as much as possible.

Several mesh types have been tested in order to find the best solution for the customer. Square meshes showed a slight clogging, but rectangular meshes were tested successfully. The reason for the clogging was the high specific load in the compact machine. The high material layer pushed the round particles into the square opening and clogged the mesh which was not the case with rectangular meshes.

Summary

Together with its customer RHEWUM designed, supplied and commissioned a highly efficient and flexible screen for polishing of various types of fertilizer at high capacities. The type WAF was chosen due to the good experiences with previously supplied machines to several fertilizer plants.