Environmental impact of mixed fertilizer plant:
Mixed fertilizers contain two or more of the elements of nitrogen, phosphorus, and potassium (NPK), which are essential for good plant growth and high yields.
Ammonium phosphates are produced by mixing phosphoric acid and anhydrous ammonia in a reactor to produce slurry. This is the mixed-acid route for producing NPK fertilizers; potassium and other salts are added during the process. The principal pollutants from the production of Monoammonium phosphate (MAP) and Diammonium phosphate (DAP) are ammonia and fluorides. Fluorides and dust are released from materials-handling operations.
(i) Materials handling and milling of phosphate rock should be carried out in closed buildings. Fugitive emissions can be controlled by with capture of the dust in fabric filiters.
(ii) In the ammonium phosphate plant, the gas streams from the reactor, granulator, dryer, and cooler should be passed through cyclones and scrubbers, using phosphoric acid as the scrubbing liquid, to recover particulates, ammonia, and other materials for recycling.
(iii) In the nitrophosphate plant, nitrogen oxide (NOx) emissions should be avoided by adding urea to the digestion stage.
(iv) Fluoride emissions should be prevented by scrubbing the gases with water.
(v) Ammonia should be removed by scrubbing. Phosphoric acid may be used for scrubbing where the ammonia load is high.
(vi) The process-water system should be balanced, if necessary, by the use of holding tanks to avoid the discharge of an effluent.
The key production and control practices that leads to compliance with emissions requirements are:
• Maximize product recovery and minimize air emissions by appropriate maintenance and operation of scrubbers and baghouses.
• Eliminate effluent discharges by operating a balanced process water system.• Prepare and implement an emergency preparedness and response plan. Such a plan is required because of the large quantities of ammonia and other hazardous materials stored and handled on site.