One could argue whether an impingement baffle for a gas inlet below a supported bed of solids is really necessary. For an inlet at the top of a solids bed it is necessary to prevent the gas blowing a crater in the solids bed. As this mol sieve bed is to be regenerated every now and then, whereby the regeneration gas enters through the top nozzle and flow through the bed in opposite direction of the normal air flow, there is an impingement device at the top nozzle, which is retractable with the elbow N2.
Here they found it necessary to also have an impingement plate at the bottom inlet, although there would be a distance of some 900 mm between nozzle and bottom of bed if the baffle were not there.
So be it, and now you think there is a lot of science behind this.....
In this case it seems to me that the diameter of the circular impingement baffle (750 mm) at the bottom is simply half the diameter of the vessel (1520 mm).
The 432 mm distance between inlet nozzle and impingement baffle is probably chosen such that the gas velocity through this distance is about the same as the gas velocity in the space around the impingement baffle.