What impacts does the shutdown of a refrigerated ammonia chiller have on the ammonia synthesis system during its normal operation? ! !

If there is a backup unit, it is recommended to activate it immediately; this will not cause too much impact in the short term. In our factory, ammonia coolers are only available for the ammonia synthesis process, so I will discuss this aspect specifically. When the chiller stops working, there are no significant changes in the temperature and pressure of the synthesis tower in the short term. However, when the liquid level in the ammonia cooler approaches zero, the temperature at the outlet of the ammonia cooler rises, the pressure in the synthesis tower increases, and the temperature of the catalyst layer drops rapidly. The temperature can be controlled by increasing the amount of ammonia circulated and reducing the amount of cooling gas used. After restarting the tower, the system pressure can be reduced by releasing inert gases, and operations can also be adjusted to keep the system pressure from rising above safe levels. Open the vent valve to prevent overpressure in the ammonia gas pipeline. During major overhauls, we stop adding ammonia a few hours in advance. This post was last edited by snowdfr on 2009-3-18 20:49]

It’s sufficient to use a backup unit; in the case of a failure in the chiller, the synthesis system first experiences a rapid increase in pressure, resulting in low production. The temperature of the ammonia cooling system rises quickly, and it’s difficult to control the temperature of the low-temperature methanol wash. Over time, the composition of the products can become abnormal.

As long as the chiller stops operating, the synthesis process must be halted; otherwise, the pressure in the refrigeration system rises too rapidly. The temperature of the methanol washing process is not greatly affected in the short term, and this can be controlled by reducing the flow rate. At such times, the temperature of the methanol may rise, resulting in slight excess levels. In such cases, it is possible to release air from the system to keep the methanol system functioning, and in severe situations, air must be released from the methanol washing process as well. The impact of short-term air separation is minimal; the water flow rate can be increased, and if there is a nitrogen tower, then there is basically no impact at all.

For synthetic systems alone, the sequence of impacts caused by the chugging of the refrigeration unit is as follows: an increase in gaseous ammonia pressure leading to overpressure; an increase in the temperature of the ammonia-cooled fluid beyond the process requirements; a decrease in the liquid level in the ammonia-cooled separator; effects on the reactions within the synthetic system; and an increase in the pressure of the synthetic system, resulting in overpressure, and so on. If all the chillers fail to operate, the only option is to quickly start up backup units or restart them (if the equipment permits), but this will definitely take at least ten minutes or so. Meanwhile, the load should be reduced; ammonia gas can be absorbed through water washing. If that doesn’t work, then venting is necessary (but if the venting pipe isn’t high enough, it won’t be possible to do this for an extended period of time). If it cannot be started, an emergency stop is necessary. If only a part has been skipped, reducing the load usually suffices to deal with it.

“\"Handling the situation where all chillers stop operating under full load\" was one of the exam questions when I first started working as a dispatcher. I later dealt with such incidents myself; however, our methanol washing refrigeration system is independent, and the nitric acid production unit in the ammonia processing plant takes care of about 50% of the chiller’s workload. In such cases, it is sufficient to shut down only the synthesis tower. The biggest risk associated with an emergency shutdown of the refrigeration system is overpressure in the ammonia gas system. As mentioned by the original poster, while ensuring that the ammonia gas pipelines do not experience overpressure, what needs to be preserved above all is the ammonia cooling system used in air separation. Therefore, during handling, the synthesis tower should be shut down first, the amount of gas being vaporized should be reduced, and the methanol washing unit should also be stopped (gas release is allowed, but the circulation process continues).

Firstly, it is necessary to prevent overpressure in the main ammonia pipeline, while also avoiding a complete shutdown of the system; therefore, the ammonia feed to the ammonia coolers used in ammonia synthesis, those that use copper washing, and those that use alcohol washing should be reduced or stopped. And promptly activate the backup machine or arrange for the faulty machine to be repaired; if it cannot be activated in time nor repaired, the only option is to continue operating according to the actual conditions of the production process until production can no longer be maintained, at which point the system must be shut down.

The ice makers in our plant use centrifugal compressors driven by steam turbines to supply ammonia to the purification and decarburization ammonia coolers, the ammonia coolers of the syngas compressor, as well as the ammonia coolers in stages 1 and 2 of the synthesis system. When an ice maker stops operating, the purification system and the synthesis system are put into emergency shutdown mode, while the syngas compressor continues to operate in circulation mode. Arrange the system start-up and shutdown times based on the reasons for the chiller trip.

We only have one chiller here, and I’ll explain our approach. When the chiller stops working, it mainly affects the refrigeration system; the pressure in the ammonia cooler rises rapidly, which can easily lead to overpressure (triggering the safety valve). The proper course of action is to quickly cut off the air supply to the previous stage, thereby preventing a rapid increase in pressure in the synthesis system. The circulation pump in the synthesis system should be stopped immediately, so as to minimize the amount of heat that reaches the ammonia cooler. The synthesis system should be brought to a complete stop, and the gas exiting it should be vented into the ammonia washing tank. In the previous stage, the system pressure should be maintained stable first, with further actions taken depending on the condition of the chiller

I. Situations where gaseous ammonia has a place to go: For example, in factories with ammonia processing workshops, if an ice machine stops working, proper coordination is sufficient; it has little impact on the system. It’s enough to reduce the operation of the ammonia evaporator to prevent the pressure of gaseous ammonia from rising. II. For factories that do not have ammonia processing workshops or no way to dispose of gaseous ammonia, if the pressure of gaseous ammonia rises rapidly before the refrigeration machine is restarted, in order to prevent overpressure in the system, it is sufficient to follow the emergency shutdown procedure for the synthesis system. In general, in such situations, the reduction is carried out first, while preparations for an emergency stop are made.