Thanks for the reply, SRS. From what we are hearing anyway, it appears to be quite rare to foul a waste heat boiler in a sulfur plant. I guess that makes us ‘special’, and not in a good way. It could be a collection of debris left behind at startup from the refractory repair in which case we hope to not see that again for twenty plus years. My fear is that it is somehow coming from the process under the right combination of flame temp in the furnace and composition of the acid gases. There is a large body of literature around the formation of fly ash and coal slag in coal-fired boilers that relate flame temp and mineral content of the coal to fouling potential. We have all the mineral components of fly ash in our refractory and in deposits found in the acid gas lines and amine systems. What we don’t know is how they get there and why haven’t we had problems in the past.