Nitrogen industry today is one of the leadingindustries. The use of ammonia has spread to refrigeration equipment (R717, refrigerant), medicine (ammonia solution or ammonia alcohol), agriculture (fertilizers).
Primary attention is paid to the production of nitrogen fertilizers (and hence - to their bases, including ammonia, demand for which has grown by 20% over the past two decades).
But ammonia production differs, first of all, by high energy intensity. The whole history of this production is the struggle for lowering the used energies (mechanical, thermal, electric).
Synthesis of ammonia reveals the formula:
N2 + 3H2 = 2NH3 + Q
The reaction is exothermic, reversible, with decreasingvolume. Since the reaction is exothermic, a decrease in temperature will shift the equilibrium to the formation of ammonia, however, the reaction rate will decrease significantly. The production of ammonia should go at high temperatures (synthesis takes place at 500 degrees Celsius). An increase in t will lead to a reverse reaction. Pressure from 15 to 100 MPa allows to counteract the influence of temperature (low pressure - from 10 to 15 MPa, average pressure - from 25 to 30 MPa, high pressure - above 50 MPa). Of these, the average is preferable.
The catalyst is iron spongy with additives of calcium, silicon, potassium, aluminum oxides.
Contaminants (carbon monoxide, water,hydrogen sulphide) have a negative effect on the reaction rate of the reaction, poisoning the catalyst, thereby reducing its activity and decreasing the service life. This means that the hydrogen sulphide mixture must necessarily undergo thorough cleaning. But even after purification, only a part of this mixture turns into ammonia. Therefore, the remaining unreacted fraction is again sent to the reactor.
How is ammonia produced?
The pipeline is supplied with an already prepared mixture ofthree parts hydrogen and one nitrogen. It passes through the turbocharger, where it compresses to the pressure indicated above, and is sent to the synthesis column with the catalyst on the built-in shelves. The process, as we found out, is highly exothermic. The nitric-hydrogen mixture is heated by the evolving heat. About 25 percent of ammonia and unreacted nitrogen with hydrogen emerge from the column. The whole composition is fed to the refrigerator, where the mixture is cooled. Ammonia under pressure becomes liquid. Now a separator enters the work, the task of which is to separate the ammonia into the collection at the bottom and the unreacted mixture, which is returned by the circulation pump back to the column. Due to this circulation, the nitric-hydrogen mixture is used by 95 percent. Liquid ammonia through the ammonia pipeline goes to a special warehouse.
All devices used in production,maximum hermetic, which eliminates leakage. Only the energy of the exothermic reactions taking place inside is used. The scheme is closed, low-waste. Costs are reduced through a continuous and automated process.
The production of ammonia can not but affectenvironment. Gas emissions are inevitable, including ammonia, carbon and nitrogen oxides and other impurities. Low-grade heat is released. Water is discarded after washing the cooling systems and the reactor itself.
Therefore, ammonia production isinclude catalytic cleaning with a gas-reducing agent. Reducing the amount of sewage can be achieved by replacing piston compressors with turbochargers. Low-potential heat can be utilized by introducing high-potential heat. However, this will increase the pollution by flue gases.
An energy-technological scheme involving a combined-cycle cycle where both steam heat and combustion products are used will simultaneously increase production efficiency and reduce emissions.