Ammonia synthesis volumes required

Resources for Nitrogen Fertilizers. The production of more than 95% of all nitrogen fertilizer begins with the synthesis of ammonia, thus it is the raw materials for ammonia synthesis that are of prime interest. Required feed to the synthesis process (synthesis gas) consists of an approximately 3 1 mixture (by volume) of hydrogen and nitrogen. 

Dehydration. Use of molecular sieve driers for final clean-up of the carbon oxides and water in the synthesis gas to less than 1 ppm levels has gained prominence in low energy ammonia plant designs. The sieves are usually located at the interstage of the synthesis gas compressor to reduce volume requirements. The purified make-up gas can then be combined with the recycle and routed direcdy to the converter. 

Converter Design. Design of ammonia synthesis reactors is not just the calculation of the required catalyst volume other parameters have to be considered, too, and for... 

Calculate the enthalpy of reaction for the ammonia synthesis at 450 C and a pressure of 600 atm using the value of the standard enthalpy of reaction at 450 °C in the ideal gas state calculated in Example 12.1. For the calculation of the residual enthalpies, the group contribution equation of state volume-translated Peng-Robinson (VTPR) should be applied. The required VTPR parameters are given in Appendix K. 

The ammonia synthesis reaction is an equilibrium reaction between hydrogen, nitrogen and ammonia, in the presence of magnetic iron oxide. The conversion is a function of pressure, temperature and the reactants ratio. Raising the reaction pressure increases the equilibrium conversion therefore increasing the heat of reaction produced inside the catalyst bed. This causes an increase in temperature resulting in a rise in spacial velocity. These results in a reduction in the reactor volume required compared to a reactor operating at lower pressure. The equilibrium reaction is defined by ... 

The reaction rate of the whole process in some reversible exothermic reactions, such as the carbon monoxide shift reaction, can be considerable. The heat needed to be extracted from unit volume of catalyst at the beginning and the ending stages of the reaction may vary by 10 times or more. These reactions require multi-stage heat exchange reactors. Other reactions, such as the ammonia synthesis... 

This plot shows the equilibrium line for ammonia synthesis, adiabatic reaction lines, lines with the same reaction rate (there is a difference of one order of magnitude between the rate lines) and the optimum reaction path (i.e. the temperature at which the reaction rate is maximum at each ammonia concentration). It is clear that if this optimum reaction path were followed from inlet to outlet concentration in the reactor system, then the minimum catalyst volume would be required. 

The oxides of carbon are poisons to the iron-based ammonia synthesis catalyst and mnst be removed from the synthesis gas before use. An important reaction that affected the economics of the manufacture of synthesis gas was the conversion of carbon monoxide into equal volumes of hydrogen and carbon dioxide by reaction with steam. This procedure, now cotrunonly referred to as the water-gas shift reaction required a catalyst based on iron and chromium oxides. 

The required amount of catalyst is not proportional to the increase of yield of ammonia. In the past decades, the amount of catalyst required per ton of ammonia has been reducing. One reason is that the quality or purification of syngas is continuously improved. Another is that the heat stability and antitoxic property of catalysts is increased which prolong the usage life of the catalyst. At the same time, by reducing the pressure class in synthesis loop, the volume of catalyst used is increased significantly. 

Since the successful commissioning of the first plant, the Haber-Bosch process for the manufacture of ammonia has required increasingly large volumes of synthesis gas as the demand, initially for explosives, and snbseqnently, fertilizers continned to grow. For abont 20 years, synthesis gas was made mainly from coke in water gas and producer gas units, as shown empirically below ... 

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