Regarding the Casale process, is it feasible to use variable-frequency motors for the liquid ammonia transfer pumps in the freezing section?
Thread Content
In the Casale ammonia synthesis process, an liquid ammonia pump is used in the chiller section; under normal conditions, this pump supplies liquid ammonia for low-pressure methanol washing. It is only when the plant produces chilled ammonia that it simultaneously generates chilled ammonia and supplies liquid ammonia for low-pressure methanol washing. Even under such operating conditions, this pump rarely operates at 100% capacity; thus, there is an issue with efficiency. Under normal circumstances, the pump’s efficiency is low, resulting in significant waste of capacity. Personally, I think using a variable-frequency motor with this pump would be more cost-effective and yield better economic benefits. Please everyone come and discuss it.
Our pump is being sent to the irrigation area; this part should be the low-pressure electrode. If energy conservation and reduced consumption are taken into consideration, variable frequency drives are the best choice. However, in terms of initial investment, variable frequency drives are relatively more expensive, though low-voltage ones are not much more costly. So it needs to be considered comprehensively.
The power of this pump is not high to begin with; if it operates under high load conditions frequently, using a variable frequency drive seems to be a worthwhile option. However, variable frequency drives are also efficient only to a certain extent – that is, they do not save electricity when the load deviates too much from the rated value. Considering this aspect alone, careful thought is needed. From a process perspective, variable frequency is primarily used to adjust the speed of the pump. When the cold ammonia pump operates under certain conditions, if its speed deviates too much, cavitation can occur. As for other impacts, opinions vary depending on individual perspectives. The above are my personal opinions.
The price of low-voltage variable-frequency motors is not very high. This pump has a power rating of around 30 KW; if the unnecessary energy consumption of the pump can be reduced, the economic benefits will be considerable. As for concerns about low flow rates and ammonia vaporization, there’s no need to worry too much; a lower rotation speed generates less heat, which in turn makes ammonia vaporization less likely to occur. There is a pressurization process inside the pump; under normal operation, the pressure and temperature of liquid ammonia increase only slightly within the pump. I believe the flow rate should not be low enough to cause the liquid ammonia to vaporize.
I have the same problem; I need to adjust the amount of ammonia delivered, and I am also considering using variable frequency speed control. I was wondering if there are any successful experiences in this regard.