Nitrogen industry today is one of the leading industries. The use of ammonia has spread to refrigeration (R717, refrigerant), medicine (ammonia solution or ammonia), agriculture (fertilizers).
Primary attention is paid specifically to the production of nitrogen fertilizers (and therefore to their fundamentals, including ammonia, the demand for which has grown by 20% over the past two decades).
But ammonia production is distinguished, first of all, by high energy intensity. The whole history of this production is a struggle to lower the energies used (mechanical, thermal, electrical).
The synthesis of ammonia reveals the formula:
N2 + 3H2 = 2NH3 + Q
The reaction is exothermic, reversible, with a decrease in volume. Since the reaction is exothermic, lowering the temperature will shift the equilibrium to the formation of ammonia, however, the reaction rate will decrease significantly. Ammonia production should go at high temperatures (synthesis takes place at 500 degrees Celsius). Increasing t ° will lead to a reverse reaction. A pressure of 15 to 100 MPa allows you to counteract the influence of temperature (low pressure - from 10 to 15 MPa, medium pressure - from 25 to 30 MPa, high pressure - over 50 MPa). Of these, the average is preferable.
The catalyst is sponge iron with additives of calcium, silicon, potassium, and aluminum oxides.
Harmful impurities (carbon monoxide, water, hydrogen sulfide) adversely affect the reaction rate, poisoning the catalyst, thereby reducing its activity and reducing service life. This means that the hydrogen sulfide mixture must undergo thorough cleaning. But even after purification, only part of this mixture is converted to ammonia. Therefore, the remaining unreacted fraction is again sent to the reactor.
How is ammonia produced?
An already prepared mixture of three parts of hydrogen and one nitrogen is fed into the pipeline. It passes through a turbocharger, where it is compressed to the pressure indicated above, and sent to the synthesis column with a catalyst on the built-in shelves. The process, as we have found, is highly exothermic. The generated heat is heated by the nitrogen-hydrogen mixture. About 25 percent of ammonia and unreacted nitrogen with hydrogen come out of the column. The whole composition goes into the refrigerator, where the mixture is cooled. Ammonia becomes liquid under pressure. Now a separator comes into operation, the task of which is to separate the ammonia into the collector at the bottom and the unreacted mixture, which is returned by the circulation pump back to the column. Thanks to this circulation, the nitrogen-hydrogen mixture is used at 95 percent. Liquid ammonia is fed through an ammonia pipeline to a special warehouse.
All devices used in production are as tight as possible, which eliminates leakage. Only the energy occurring inside the exothermic reactions is used. The circuit is closed, low-waste. Costs are reduced through a continuous and automated process.
The production of ammonia cannot but affect the environment. Inevitable gas emissions, including ammonia, carbon oxides and nitrogen and other impurities. Low-grade heat is released. Water is discharged after flushing the cooling systems and the reactor itself.
Therefore, in the production of ammonia, it is necessary to include catalytic purification with the presence of a reducing gas. Wastewater reduction can be achieved by replacing reciprocating compressors with turbochargers. Low-grade heat can be utilized by introducing high-grade heat. However, this will increase flue gas pollution.
The energy technology scheme, including the combined cycle, where both steam heat and fuel combustion products are used, will simultaneously increase production efficiency and reduce emissions.