Backflow instrument

This post was last edited by ylb913 on 2018-8-5 at 20:34. I know about the instrument air used for backwashing in catalytic units, but I haven’t seen it in person. Back-blow instrument air is also used in sulfur recovery units; it has been my experience working with such units for over 20 years, and in all cases they are installed at a 90-degree angle. At a 45-degree angle, this is commonly seen in condensate systems, as there is an issue of pressure reduction, vaporization, and erosion associated with condensate ； I’ve also seen pipelines designed this way behind safety valves, in order to reduce pressure drop. In applications such as sulfur processing and catalytic cracking, where there should be no medium flow and blockages are to be prevented, the backflow air used does not pose any problems related to corrosion or erosion. The flow rate of this backflow air is very low, so there is no issue with pressure drops either; thus, there are absolutely no problems at all. Concepts such as 45 degrees at an angle, or even 15 degrees, 30 degrees, etc., have also been seen; this reflects the designer’s understanding of how to apply these concepts, and it’s possible that there are misunderstandings or excessive use of them. But here I don’t think there’s any harm; as long as there is reverse airflow, it works fine – the design simply specifies a default angle.

It is mainly to prevent dust blockage.

With the opening facing downward, the catalyst is less likely to clog the reverse air blast nozzle.

As a supplementary point, an appropriate backflow of air is beneficial for fluidization! The prerequisite for catalytic cracking is fluidization.