A fertiliser factory links several processes together, and each one makes a raw material for the next. Ammonium nitrate and ammonium sulfate both start with ammonia, which is made by the Haber process from nitrogen in the air and hydrogen from natural gas.
To make ammonium nitrate, some of the ammonia is oxidised with air and water to make nitric acid. The rest of the ammonia is then neutralised by the nitric acid: NH3 + HNO3 → NH4NO3. To make ammonium sulfate, ammonia is neutralised by sulfuric acid: 2NH3 + H2SO4 → (NH4)2SO4. The sulfuric acid is made by the Contact process from sulfur, air and water.
Neutralisation gives out heat. In an integrated factory this heat is used to evaporate water from the solution so that the fertiliser can be crystallised or made into granules. Sharing products and heat between the processes saves energy and money, and means the factory needs only a few basic raw materials: air, water, natural gas and sulfur.
