Atmospheric and vacuum distillation unit tower top injection
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Dear sea friends: At present, many injection points at the bottom of vacuum distillation units (for water, corrosion inhibitors, and neutralizers) are located in the horizontal section at the top of the tower, that is, the horizontal portion between the first and second elbows at the tower top. Generally, this distance is quite short; is this method of injection reasonable? I’ve heard that there are requirements regarding the distance between the water injection point and the elbows before and after it? What are the specific requirements?
Only by injecting here can corrosion protection for the tower top system be achieved.
It is injected at the top of the tower. It’s just that it’s unclear whether the injection point is more suitable in the horizontal section or the straight pipe section. It is often observed on-site that the thinning of elbows after injection is particularly severe; hence, there is now a proposal to move the water injection points to the straight pipe sections
It is estimated that without reaching the horizontal section, the corrosion on the elbows will also be severe.
On-site thickness measurement showed no significant corrosion at the first elbow, while the second elbow was severely corroded, with only 3 mm remaining (originally 10 mm). This is likely due to the local dew point after water injection. So consider changing the location of the water injection point
The injection points at the top of the tower are separate! The first one is at the elbow at the top of the tower, the second one is in the section before the freezing point, and there’s another one behind the heat exchanger! Each one has its purpose! It’s not very reasonable to have only one injection point!
Why isn’t the first elbow corroded?
To verify the dew point temperatures of HCl and H2S, the injection point should be located in the pipe section at these temperatures. The amount of water added in the other case should be sufficient to dilute HCl and H2S ； The injection method needs to be considered, whether it is into the main airflow or sprayed onto the tube wall.