Integration of a Melamine Plant

From a stoichiometric point of view, the melamine reaction decomposes half of the urea feedstock to carbon dioxide and ammonia, which are in turn the feedstocks to the urea process. The efficient recycle of such gases (off gas)is one of the key points for the profitability of a melamine project.

Many of the melamine processes (the so-called low pressure processes) produce off gases at low pressure, which cannot be easily recycled inside the urea plant. Off gases from low pressure melamine plants have to be condensed as lean carbamate solution, which has in turn to be concentrated in a multistep process before being sent to the urea plant. This procedure involves significant modifications to the urea plant, increases the consumption of utilities and, in any case, adds a notable amount of water to the stream feeding the urea reactor. An alternative way of re-processing the off gases from low pressure melamine plants is the separation between ammonia and carbon dioxide. Such procedure requires an investment that may easily jeopardize the economics of the whole melamine plant and also demands a full revamp of the urea plant in order to accommodate the increase in feedstock. Recycling the off gases from a low pressure melamine process is often so expensive that many melamine producers convert them to ammonium sulphate. This is not the case of Eurotecnica High Pressure Melamine Process. Off gases are produced at medium pressure and they can be condensed with just minor changes and additions in the equipment of the urea unit. As a result, the net urea consumption of an Eurotecnica Melamine Plant is just 1.43 kg/kg melamine: three molecules of urea per molecule of melamine