If it is for the concern of air heater acid corrosion, You do need something to heat up the air before it goes to the air heater. As an alternative of SCAH, if you don't want to use it, you can consider 'hot air recirculation'. A certain percentage of air already heated up by the air heater is re-directed back to the FD fan inlet and goes through the air heater again. This further raises the inlet air temperature and protects the air heater from acid corrosion in cold winters. Even though your boiler will be installed in warm Africa, the system design might already want to take this advantage and use much lower gas outlet temperature to get higher boiler efficiency thus leaves you less room for inlet air temperature fluctuations at the air heater so the protection might still be needed. If the system is conservatively designed with high flue gas outlet temperature good for any weather condition then you should be okay without air-preheating.
I understand that SCAH adds complexities to the thermal system and is notorious for pluggings and water-hammer damages from condensate formations. Nevertheless, SCAH is still recommended mainly because it gives the systems higher efficiencies so has long-term benefits. I was reading about an improved design which avoids water-hammer problems. You might want to find out the details plus who supplies it.
I'd have to know a lot more about what type of boiler that you are going to construct before offering an opinion (tip).
What is downstream of the SCAH that it would have otherwise protected would it be there?
I come from the deep south of the USA and have seen lots of SCAH's rotting down from disuse. The small part of the year when they might have been beneficial, they were inoperative from lack of maintenance. Many just got taken out (or cut out.)
Most of the APH's downstream of the SCAH's were Ljungstroms and the buckets seem to have a decent life otherwise.
