The impact of the ethylene cracking gas compressor water injection system on the compressor
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After installing a water injection system in the cracking gas compressor of the ethylene plant, the outlet temperature can be effectively controlled to prevent coking of unsaturated hydrocarbons. However, some ethylene plants have also encountered some problems after adopting a water injection system. Please share your experiences regarding how the water injection system in your installations has affected the compressors. Through communication, a deeper understanding of the water injection system can be further promoted, to help operators optimize their operations better.
I’ve heard that water injection can cause acidic gases to dissolve in water, which may lead to corrosion of the compressor impellers, flow channels, as well as other pipelines and tanks. I haven’t seen any specific information on this topic. That’s why we have stopped using water injection in our equipment..
Injecting water between the compressor stages has proven very effective, as it reduces the temperature between stages. It reduces the coking of olefins; the outlet temperatures between various sections were above 95°C before water injection, but dropped to 85–95°C after injection, while also saving on the amount of CW water used. I disagree with what was said above. After water is injected, it vaporizes immediately between stages, and heat is absorbed through latent heat; therefore, there’s no way for acidic gases to dissolve in the water. Moreover, the pyrolysis gas itself contains water vapor and heavy hydrocarbons, which need to be removed between stages. The effect of inter-stage water injection combined with the addition of a polymerization inhibitor is far better than simply injecting water to flush the oil.
Changing to continuous water injection yields better results than intermittent oil flushing
Is water injection used in every section? What was said upstairs is also correct – after water is injected, it vaporizes, but after passing through the cooler, is it still gas? At this point, water may accumulate at the bottom of the remote heat exchanger. Care still needs to be taken when injecting water – your outlet temperature has decreased, but what about the efficiency of the compressor? Just looking at the temperature doesn’t tell us much.
Before water injection, the gas phase is saturated; after water injection, before alkali washing of the tower, acidic gases such as hydrogen sulfide and carbon dioxide dissolve in the water, thereby causing corrosion in the inter-stage heat exchangers and similar components.