I would like to ask about the issue of high outlet temperature in the propylene unit
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Dear seniors, I have a question. There are several aspects I’m not clear about regarding the reasons for the high outlet temperature of the propylene unit (which has 4 suction stages and 1 discharge stage). I would like to seek your advice. I saw a question about this earlier: the method to address high outlet temperature in an propylene reactor is to increase the suction pressure in Stage 1... What I’m not quite sure about is that, without using a return line, the way to increase the suction pressure is by reducing the rotation speed; thus, although the pressure in Stage 1 rises, the temperature will also increase, which shouldn’t it also raise the outlet temperature? From another perspective, if the speed is reduced thereby lowering the compressor load, the suction pressure increases and so does the discharge pressure; similarly, the temperature also rises, right? Thank you all; please help me resolve my doubts. .
Firstly, in cases where there are abnormalities in the suction temperatures at various stages, if the compressor is still able to operate normally, then any deviations of the suction temperatures at the various stages of the propylene compressor from their design values or any abnormalities are not caused by issues with the compressor’s operation. There’s no need to worry.
Secondly, the suction temperatures at various stages of the propylene compressor deviate from the design values, which is caused by changes in the load distribution across those stages
The temperatures in stages 2, 3, and 4 of the propylene compressor are low, which results in a shift of the cooling load to later stages and an increase in the load on the ethylene compressor. Therefore, adjustments need to be made to the propylene compressor and the process system to ensure a reasonable distribution of the cooling load. Otherwise, when the ethylene compressor is overloaded, the pre-cooling system will result in ethylene loss due to a shortage of refrigerant.
If the temperature in each section deviates from the design values, the return valve can be adjusted when there are no users present; when under high load conditions, only appropriate adjustments can be made to the process system to ensure a balanced distribution of cooling capacity. It’s impossible to make adjustments without activating the return trace
When the return line is activated, the pressure does increase, but inevitably the outlet temperature will rise as well. Even by activating the quenching line, it’s not possible to reduce the outlet temperature below its previous level
It mainly reduces the compression ratio; generally, the outlet temperature is related to the inlet temperature and the compression ratio
The relationship between compression ratio and temperature is that the higher the compression ratio, the higher the temperature; reducing the compression ratio naturally lowers the temperature