I am curious to see the response to this question. I would think that direct injection of steam versus the reboiling of stripped sour water from within the tower would add water to the system, which is trying to process a waste stream, sour water. We are usually maxed out on sour water stripping capacity, so increasing the volume of water to be processed is a step in the wrong direction. We did consider going to live steam addition when we fouled a reboiler, but I don’t think we ever installed it.
We have a normal SWS, reboiled with steam. 6 years ago we had to retube the reboiler on the run. We would have gone out of service with half of the refinery if we stopped the SWS for the 2 weeks that were needed for repair, thus we decided to run the steam directly to the stripper through the reboiler return (2 small outages to disconnect the old and connect the new pipe and vice-versa).
It worked well, but we obviously lost some capacity and we had issues with high pH in SWS bottoms (pH of around 9 in BFW system). If you use your SWS rundown in the desalters this can create some problems.
Direct steam injection for SWS is typically historic. It was a cheap way to build strippers.
A reboiler is current state of the art.
Advantage of a reboiler:
Less process water (10-20%)
recovery of valuable condensate which is otherwise downgraded to effluent water.