In the ammonia synthesis system, why is the system pressure lower as the circulation rate increases?
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In an ammonia synthesis system, why does a higher circulation rate result in a lower system pressure? What is the principle behind it?
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This issue needs to be considered in the context of actual production. The increase in the circulation rate in actual production is due to the fact that the ammonia synthesis reaction proceeds well, generating a lot of heat; therefore, it is necessary to increase the circulation rate. We know that the ammonia synthesis reaction is a reaction that results in a decrease in volume, and as a result, the pressure must decrease when the reaction proceeds well.
Is it related to the reaction with ammonia? Check if the system’s performance has improved
Agree with the view from the third floor: the greater the circulation rate, the more gases participate in the reaction, and accordingly the system pressure decreases!
The system pressure in ammonia synthesis is determined by an equilibrium formed by the air intake volume of the cycle compressor unit and the gas consumption for the synthesis reaction in the ammonia synthesis tower (the volume reduction resulting from the reaction). When the circulation volume is increased, the space velocity rises, air consumption increases, so the pressure naturally drops, and at the same time the net ammonia value also decreases slightly.
I think it’s not that the higher the circulation volume, the lower the pressure, but rather that the lower the pressure, the higher the circulation volume. From the perspectives of chemical equilibrium and reaction kinetics, higher pressure shifts the equilibrium to the right, increasing the conversion rate; at the same time, the reaction rate also increases ； However, from a equipment perspective, the system operates under high pressure, which imposes high demands on materials and equipment, resulting in high investment costs. To control investment costs, the system pressure is set relatively low within a certain range; however, this leads to a decrease in reaction rate and conversion rate. To compensate for the resulting impact on production capacity, the space velocity is increased. An increase in spatial velocity further reduces the net ammonia level, thereby increasing the circulation rate. Therefore, to ensure a reasonable production capacity, it is necessary to select the appropriate pressure and space velocity, that is, the circulation rate.