There are several different methods of making fertilizer. The job of fertilizer is to replace the chemicals that growing plants leech out of the soil. The key ingredients of a fertilizer, therefore, are things that are essential to the healthy growth of plants – such as nitrogen, calcium, sulfur, and magnesium.
Fertilizer Manufacturing and Pan Granulation
The way that fertilizer is made has evolved a lot over the years. The pan granulation process was introduced in the 1970s by Norsk Hydro as a way to produce large amounts of coarse grade ammonium nitrate-based fertilizer. This type of fertilizer is used for forest fertilization.
The process uses water-free melt, is inexpensive, and makes fertilizer that is easy to transport and store. The process requires hot nitrogenous melt, and cooled solids which are fed into a rotating pan.
The rotation of the pan will help to form the fertilizer into a rolling, tumbling particles which form a crescent-shaped bed. The cooled solid particles should enter the pan at a point where there is not a lot of existing material so that they can be covered by the melt. Warmer particles will tumble over the cooler particles to cover them, and as the material moves through and exits the pan it will stabilize at a temperature that is below the melting point of the material.
The objective is to gradually build up the size of the particles by rotating the solids so that they pick up melt, which cools onto them.
When to Use Pan Granulation?
Pan granulation technology was originally intended to use to convert dry pulverant and other material, into bigger granules that are easier to work with. When the process is performed properly, it should be seen that it produces strong particles that are of uniform size and a similar shape.
Temperature and Concentration
It is difficult to produce large pellets with pan granulation, but for smaller pellets, it is a good solution. Many common methods of pan granulation rely on the water content of the solution being about 5-8 percent by weight. This ensures that at the correct temperature a certain amount of water will evaporate rapidly, and the layer that is added to the process solidifies on the granules almost immediately. Note that if the water content is insufficient, then the rolling particles on the bed will become a sticky mass which is difficult to handle, separate, and transport. The water content is important to allow for the heat removal caused by evaporation since this is what keeps the granules in an optimum state.
The maximum concentration limit for the solution is 95 percent by weight, and this works well for melts of ammonium nitrate and urea, that is sprayed onto appropriately sized, fast-moving solids.
The size of the rotating drum, and the pressure with which the solution is sprayed onto the solids will also impact upon the outcome. The pan manufacturer will provide instructions for the appropriate speed, pressure and temperature depending on the type of fertilizer to be produced.