Closed Water Circulation System in Phosphoric Acid and Fertilizer Plants

The article describes the water circulation system of the phosphoric acid and fertilizer plants at Siilinjarvi works of Rikkihappo Oy. Water arriving in and leaving the phosphoric acid and fertiliser plants has been connectd into a single closed water circulation system, thus avoiding discharge of waste water into the environment. The phosphoric acid plant operates on the hemi,hydrate-dehydrate system and has a capacity of 75,000 tons of P2O5 a year. The fertiliser plant produces 150,000 tons of monoammonium phosphate a year. The fertiliser plant produces 150,000 tons of monoammonium phosphate a year. Waste water containing nutrients coming from the plants is collected in one artificial basin which is about two hectares in area and two meters in depth. From the basin the water is pumped back to the plants for various purposes.The water in the closed circulation system is cooled by two cooling towers. The circulation system is also used to handle the runoff water from the storage area for the gypsum coming from the phosphoric acid plant, and from other areas which are liable to allow nutrients to enter the environment, such as unloading points for raw materials (apatite and ammonia) and product storage and loading areas. The circulation system handles also the nutrient containing water produced in the scrubbing of waste gases. These arrangements have made it possible to eliminate the environmental pollution effects oif the whole works area almost completely.