What’s wrong with the ammonia cooling temperature!

An ammonia cooling temperature of -6 degrees is sufficient to reduce the concentration of ammonia in the inlet stream to very low levels. Lowering the ammonia cooling temperature further has little practical significance; it only leads to increased energy consumption.

What should be the appropriate level of ammonia content in imports? At 15 MPa and -6°C, what can the inlet ammonia content reach?

At 15 MPa and -6°C, the ammonia content at the inlet can be reduced to below 4.0%; if ultrafiltration is used for ammonia separation, it can be brought down to below 3.5%

The ammonia cooling temperature plays a positive role in reducing the inlet ammonia content and increasing the yield of synthetic ammonia; its determination depends on the synthesis pressure. According to the synthesis process designed by a renowned domestic design company, it is quite confusing: the synthesis pressure is 15 MPa, there are two stages of ammonia cooling, and the temperature during ammonia cooling is only –6°C. Personal opinion: The determination of the ammonia cooling temperature is generally based on the volume of circulating gas, but it is also related to the ammonia synthesis process rather than the synthesis pressure! ““At 15 MPa and at —6°C, the ammonia content at the inlet can be kept below 4.0%,” that’s what is generally said; however, in actual production, the temperature is usually controlled below —8°C to ensure stability of the system.

The content of saturated ammonia in the gas phase at equilibrium with liquid ammonia under high pressure can be approximated by the Larson equation: lg y NH3 = 4.1856 + 1.903/√P – 1099.5/T. It follows from this equation that the amount of gaseous ammonia after condensation depends on the operating pressure and the temperature of the ammonia cooler. Increasing pressure and decreasing temperature both reduce the ammonia content in the gas phase.

With a synthesis pressure of 15 MPa, the ammonia production should be over 180,000 tons; a high ammonia cooling temperature will result in a high ammonia content at the inlet of the synthesis tower. The level of ammonia content at the inlet of the synthesis tower also depends on the ammonia separation method. For example, if molecular sieves are used to remove moisture from the make-up gas, and ammonia separation takes place after the tower, with the make-up gas being introduced into the compressor cycle stage, then, at the same ammonia cooling temperature, the ammonia content at the inlet of the synthesis tower will be lower than when ammonia separation occurs before the tower. I’m not sure which ammonia separation process your plant uses.

The process used by the poster is likely a synthesis loop following low-temperature methanol-liquid nitrogen washing; since the inert gas content in such a loop is low, the circulation volume is also low. Additionally, low-temperature cooling capacity is required for the methanol washing process, and it’s not strange that it is designed in this way to work in conjunction with the compressor.

We use a system with 15 Mpa pressure, featuring two-stage cooling and two-stage separation technology. When the outlet temperature of the second ammonia cooler is below zero degrees, the ammonia concentration in the gas entering the tower is around 3%, which is sufficient for achieving separation effects. Of course, the lower the temperature, the better the separation performance; however, extremely low temperatures place higher demands on the internal structure of the system. If the synthesis pressure is high, it is possible to reduce the temperature accordingly

Our factory uses two-stage ammonia cooling, with the outlet temperature of the ammonia cooling system being around -10 degrees Celsius.

For our 15MPa secondary ammonia cooling system, the temperature is generally around -10 degrees; the ammonia content at the inlet is a little over 2%, but less than 3%

Our factory uses 300 kilograms, with ammonia cooling at -5 degrees

For our 27MPA unit, the ammonia cooling temperature is generally between -5 and -12 degrees Celsius. The ammonia concentration at the exit of the synthesis tower is around 15%, while it’s about 2.5% at the inlet; this level is sufficient to meet the production requirements without any issues. The owner’s question is about low pressure; I think perhaps using two-stage ammonia cooling could be used to compensate for the insufficient cooling capacity and thus reduce power consumption This post was last edited by *aoye613 on 2009-4-23 14:32.]

Theoretically, the higher the pressure and the lower the ammonia cooling temperature, the better; according to the Larson value, the corresponding saturated vapor pressure of ammonia will be lower. However, in practical operation, it is impossible to achieve an ideal state due to process requirements; low- and medium-pressure synthesis is not conducive to the ammonia synthesis reaction, but a low compressor back pressure results in lower power consumption ； Similarly, with a higher ammonia cooling temperature, the refrigeration load is reduced, and the occurrence of ammonia carryover can be avoided. Therefore, various balance calculations should be carried out during the design phase of a process; as for whether further adjustments are needed during production, this depends on the specific condition of the process equipment.

We use a system with 15 Mpa pressure, featuring two-stage ammonia cooling and two-stage separation. The outlet temperature of the second ammonia cooler is around -5 degrees Celsius, and the ammonia content in the tower is about 2.6%, which indicates that separation has been achieved. Of course, the lower the temperature, the better for separation; however, this results in higher load on the ice machines and much lower energy efficiency, making it uneconomical.