Well, the 1100-degree sand was used for testing purposes. It's a common lab technique, because the sand just brushes away.
In actual production, I would expect that the algae would be pumped through a pipe, which in turn is immersed in an oil bath. The pumping rate would be such that the algae slurry spends the right amount of time flowing through the heated section of the pipe (eg, if you wanted a minute of exposure, you could have ten feet of pipe, and pump at a 10ft/min flow rate). For large scale production, you'd have a large number of pipes running through that oil bath.
The oil would not need to be heated to 1100 degrees, as it transfers heat more efficiently than sand, and the metal pipe would already be hot before you started pumping the algae, so the added temperature needed to pre-heat the metal during the experiment would be absent. If you were trying to quickly heat the algae to 550 degrees, the oil would likely be something around 800 degrees. That's readily-achievable from a variety of energy sources: solar, solid biomass like wood chips, liquid biomass like vegetable oil, etc.