What are the temperature requirements for the seal gas in the cracking gas compressor of an ethylene plant?
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At present, the first-stage seal gas pipeline of the pyrolysis gas compressor in this unit is frosting due to the throttling effect of the valves; presumably the temperature of the seal gas is also low. I would like to ask experts whether a low temperature of the seal gas can cause damage to the dry gas seal
3.jpg The temperature of the sealing gas is low and frosting occurs, indicating that the sealing gas contains liquid, which can easily cause damage to the dry gas seal! The plant I work in is an 1.8 million-ton DMTO plant; the primary sealing gas used for the reaction gas compressors used in olefin separation is the process gas from the fourth stage outlet of the compressor, and the pipelines are equipped with electric heating to prevent the formation of liquid!
There are limits on the temperature of the sealing gas; the specific design temperature range depends on the composition of the sealing gas used and the specific requirements of the dry gas seal. The sealing gases commonly used in ethylene cracking gas compressors include self-sealing gas, high-pressure ethylene from the atmosphere, and medium-pressure nitrogen. Electric heating will be installed on the dry gas seal pipeline. Too low a temperature poses a risk of liquid entrainment in the sealing gas, leading to damage to the dry gas seal.
We also encountered similar problems with the dry gas seal system of our previous pyrolysis gas compressors; frosting tended to occur in the primary seal gas line, especially in the low-pressure cylinder section. After checking the design of our propylene plant, we found that it had a heating sleeve in the primary seal gas line, which used low-pressure steam for heating, thereby solving this issue effectively.
Isn’t it supposed to operate in a normal mode without cutting off the real gas? Another thing: HN, as the primary sealing gas, is equipped with an electric heater – don’t you have one?