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We have field diesel distillation unit and we have plan to inject pour point chemical to heavy oil product ( Residual) which goes to crude tanks for storage. I have some concerns about injection point orientation.
As good practice we normaly inject the chemical on the top of the pipe but in our case only we have a drain fitting at lower position 6 clocks (6 inch pipe).
It is ok to carry out this job.
For injecting liquid into liquid, it does not make much difference whether the injection flow is co-current or counter-current. There are some resources (A. Sloley) quoting that even in cases of injecting liquid into vapor stream the orientation does not have significant effects:
Top connections are preferred only for accessibility and maintenance reasons. Process wise, there is absolutely no difference.
The best thing to do is to provide injection point upstream of the pump or a control valve. Turbulence created across these devices will ensure proper mixing in all cases, regardless of the flow of main stream.