Zuari’s NPK B plant was established in 1984. The plant manufactures DAP. The plant has an installed capacity of 1,100 metric tonnes per day. The technology adopted in the NPK B plant like the NPK A plant is based on the slurry granulation process. This process is highly efficient and produces the minimum amount of emissions. In addition to this, to be resource and environmentally friendly, the NPK B plant utilises process condensate from the Ammonia plant once it is passed through a hydrolyser stripper, recycling and reducing wastage in the process. The high standard of safety in the plant is achieved by a variety of well-established processes such as air monitoring. The NPK B stack is analysed for Sulphur dioxide, Ammonia and suspended particulate matter. The eco-friendliness of this plant and its zero effluent operations ensure that it is completely in accordance with Zuari’s environment policies.
The process adopted in NPK Plant ‘B’ is similar to the one in NPK Plant ‘A’. There are a few variations which are incorporated in the process described below:
Recycle solids consisting of crushed oversize as well as the fines separated in the process screens are routed back to the Ammoniator Granulator (AG) at the back end through a chute. All the fresh solid feeds like Potash, filler are also added to AG through the same chute. AG rotates at approx. 9 rpm causing a rolling/cascading bed which mixes the incoming solids uniformly. Hot slurry consisting of Ammonium Phosphates with a mole ratio of 1.4 is prayed on the rolling/cascading bed through slurry spray nozzles. Liquid ammonia is introduced below the rolling bed for further ammoniation and also supplies heat of reaction. The rolling/cascading action of the solids on which the slurry is sprayed causes the growth of granules through the process of agglomeration and accretion as well as rounding off of the granules to spherical shape.
Solids flowing into the dryer has a moisture content of 1.8 ~ 2.2%. The co-current dryer is a rotary equipment having specially designed flights to effect a good cascading of the solids across the maximum cross section so that the air is intimately contacted with the cascading solids and the solids are thus dried. Depending on the operating temperature at the exit of AG, the firing in the furnace generating hot air will vary. In the limiting case there will be no fuel combusted in the furnace and the internal heat of the solids will be adequate to dry the solids to a moisture content of 1.0 ~1.5% at the exit of dryer.
Dried solids having a moisture content of 1.0 ~ 1.5% moisture are then routed to 3 nos process screens and distributed on the entire width of the screen through a Screen Drag Feeder. The screens are double deck, vibrating type screens. The upper deck mesh has 4mm opening and separates the oversize. The lower deck mesh has an opening of 2mm and separates the undersize. The product is taken out from the top of the bottom deck mesh from where it flows to the product cooler through a conveyer belt.
Product is cooled in a rotary drum cooler using air in a counter-current flow and thereby the temperature of the product is reduced to 45 deg.C before sending the product to the storage bins or for bagging. Dehumidified air at about 15 deg.C is used as a cooling medium.
Dedusting system consisting of cyclones, fan and venturi scrubbers takes care of all the dust generated in various equipment like fines conveyor, crushers, belt transfer points to keep the plant free of dust.
Cyclones and Scrubbing
For effectively taking care of the dust and unreacted ammonia leaving with the air stream in different operations in the plant, high efficiency cyclones and venturi scrubbers as well as spray scrubber are employed. Dust and/or ammonia ingress is generated in the equipment like the Pre-neutraliser (If Operated) Ammoniator Granulator, Dryer, Product Cooler, Crushing Mills, Screens, Conveyers, etc. Cyclones separate most of the particulates from the air stream which are recycled back.