I was reading about open hearth furnaces the other day.
Normally, combustion does not reach temperatures high enough to produce steel (from pig iron). But an open heart furnace uses the exhaust gasses to charge a thermal mass, and then the ports are switched, and the hot exhaust port becomes the air intake. The combustion air is now heated by the preheated walls, and even before combustion happens the fuel and air are already hot. Thus the flame is even hotter.
The open hearth furnace is not a technology i am excited about, but the idea of preheating the fuel and air is. A line concentrating solar collector can easily reach temperatures of 200C-300C (especially heating air rather than boiling water), which would increase the temperature of the flame by several hundreds of degrees as well. And if, on top of that, the flue gasses were heat exchanged with the incoming (already solar enriched) fuel and air before combustion, temperatures of >500C before combustion are possible (i would think much higher, but i am being conservative).
This is an excellent way of using medium temperature solar heat to enrich valuable fuels and enable higher temperature processes. Using hot air and fuel also helps combustion be more complete and efficent. Or the process could be tweaked to yield more nitric acid as a by product.