Hi Everyone,

My name is Mohamed Azlan, and I am a new member to this forum

I have a question regarding the operation of a compressor. Typically, in industrial practice, the maximum single-stage discharge temperature for a compressor is limited to about 150 degC. This restriction is mainly due to the durability of the seal as well as in reducing the thermal stresses acting on the compressor. However, is there any similar maximum limit placed on the temperature difference across a compressor?


In addition, I also recalled reading an article which mentioned that a compressor should also be designed with a maximum suction temperature to prevent excessive expansion of the suction side, but it does not give any numerical value for this. Can anyone verify to me as to whether this is true?


Thanks,
Mohamed Azlan

Mohamed:

Welcome to our Forums. I hope that you find fruitful and profitable responses to your queries here.

Please tell us all what TYPE of compressor you are describing: a Dynamic type (centrifugal) or a Positive Displacement type (reciprocating, etc.)? This is a detail that is very important in discussing compressors and one that I continue to repeat time-after-time. Also tell us if you are referring to a multiple-stage compressor. You have mentioned “single-stage discharge temperature for a compressor”, but that doesn’t mean it doesn’t have a subsequent compression stage directly afterwards.

I have discussed the effects and the discharge temperature limits imposed on compressors many times in these Forums. Please use the SEARCH feature in our search engine to find all the many past threads that discuss and resolve this query. As I have said in the past I always limit my reciprocating compressor discharge temperatures to 300 oF. As you state, this is done to maintain the durability of the seal as well as in reducing the thermal stresses. However, you left out the most important reason in the case of a lubricated cylinder: the degradation of lubricating oil and the subsequent damage to valves – leading to even higher and higher discharge temperatures

I don’t know what you mean by “maximum limit placed on the temperature difference across a compressor”. Do you mean to keep the discharge temperature constant and decrease the suction? Or do you mean to keep the suction temperature constant and increase the discharge? Please be specific. Compressor manufacturers are very specific in the temperature limitations imposed on their cylinders (in the case of reciprocating compressors) and they will tell you so. They do not dwell on a temperature difference; they base their calculations on specific temperature limits.

I have never heard of a compressor being designed with a maximum suction temperature to prevent excessive gas expansion on the suction side. A maximum temperature is imposed on the suction of each stage of compression in a reciprocating machine in order to prevent exorbitant discharge temperatures, protect the lubrication oil, and stay within the allowable design stress of the cylinder material. This is normal, expected engineering practice. If you have read this in an article, please make specific reference to it because I believe you have mis-read it or your interpretation is not correct.