The drop in gas flow is likely due to sulfur crystals forming in line since you are able to ‘heat soak’ the problem away. This means that it is a heat loss problem so I would check all of the steam traps for all piping from the pit to the incinerator. Steam jacketing (or contro trace) of the inlet sweep air lines to ‘pre-heat’ the air is a sound idea. Also, CSI can custom steam jacket the eductors which is an excellent idea. Nobody ever checks steam traps so there is very high chance for these lines to get totally corroded out. you will see total failure when steam starts crossing over and backing into the pit and coming out of the look boxes. I have seen lines completely corroded from this phenomena.