I would look into Hastelloy for the mixing tee and the other places where you have high temps. Hastelloy holds up to sulfuric over a wide ranges of conc and temps. You better contact your accountant and tell them to get a second mortgage on the plant so you can afford it, though.
PTFE...
One other point to mention:
Velocity
Sulfuric acid will not attack carbon/stainless steel if the passivated layer on the surface of the metal is in tact. Velocity of the fluid will wash off that layer. The limit to the fluid velocity is dependant on the metal. Rules of thumb that I have seen...
