Cooling conc. sulphuric is not as big a problem- the problem here is the dilution, the concentration range and the temperature.
Is silicon carbide an option? From a corrosion standpoint, I believe so. It's not cheap (we were quoted $400 US for a small thermowell tube, and small magdrive pump bushings are usually $250 or so, so I'd hate to see what a SiC exchanger would cost...). Even the best grades are sensitive to thermal shock, particularly to rapid cooling- it is a ceramic after all. The tubes can have quite high thermal conductivities, and the material is surprisingly strong- but the thermal shock and brittle fracture concerns tend to require that the tubes be made quite thick. Thermal resistance includes both thickness AND thermal conductivity, so you may not get the area reduction you want. And I have no idea how the tubes are mated to a tubesheet- if it's with fluoropolymer ferrules, you'll be in the same boat as you would be with the fluoropolymer exchanger.
You might get away with a lower alloy exchanger with anodic protection, but this method is for corrosion mitigation and control rather than elimination. Do it wrong and the unit may dissolve, rapidly. The same goes for spray-applied thin fluoropolymer coatings etc.- a pinhole through the coating will rapidly mean a pinhole through the metal.
The only metal I know will survive these conditions is tantalum. It's used for the tubes which add acid into hydrometallurgical autoclaves (i.e. units which dissolve metals like nickel and chromium...). Very, very expensive- 1/4"- 0.035" wall tubing is hundreds of dollars per foot. But also thermally conductive, metallic (i.e. not brittle), and possible to build an exchanger out of which will withstand 100 psig at these conditions. It can also be applied as a vapour deposited coating on other metals- with the same problems as other coatings wrt pinholes and scratches etc.
I think you either have to compromise on pressure handling, max temperature, size and/or cost. You're up against some hard physical limitations here...If you can compromise on your pressure and/or temperature a bit, you might get away with the Ametek unit- but make sure you baby the thing, because the fluoropolymer tubes will be like cooked spaghetti at these temperatures. The key is to find out what the expected temperature of the tubes themselves will be- they'll be somewhere between the shell and tubeside temperatures, and just where they end up will depend on the heat transfer conditions on each side. Careful design may yield an exchanger which, during normal operating conditions, keeps the tubes cool enough to be safe- but an upset may rupture the spaghetti, resulting in an acid-water dilution event that nobody will enjoy...
Agree that the Nickel Development Institute is a good place to go for advice in selecting a nickel superalloy for this service. I also suggest you speak with somebody in the acid plant business to see what they recommend- they have lots of contacts in various industries and they have a pretty good idea what works and what doesn't- plus their advice is generally free.