Briyeo
Some info about sand furnaces on the GWR
I found some info in the GWR London Division Engine Sheds by Chris Hawkins & George Reeves
The sand furnace working discription
Sand Furnace - Many sand furnaces are constructed on the wrong principles. These have a firebrick lined furnace, above and below which ovens are fixed. into these the wet sand is thrown, and there lies sodden until all moisture is eliminated. The sand furnaces used on the GWR have a hot chamber between the furnace and the chimney, and above this chamber there is a receptacle for the wet sand. In the roof of the hot chamber one or more gratings are fixed, through which the sand falls gradually, and is dried through in detail by the hot gases passing through the chamber. These furnaces are automatic in action, and dry at lease five times he quantity of sand as the old fashioned oven furnaces would with the same expenditure of fuel.
The picture of the sand furnace being constructed at OOC south side shows the building and chimney.
There was a siding in front of the building where the wagons where parked.
The two opening where where the sand was shoved direct from a wagon into the hopper above the hat gas chamber.
The drawing of the sand furnace building show the gas path from the two fire boxes and the gas passes under the upper sand hoppers and then returns to the chimney. The sand fall through the grate and then rills sideways to the collection hoppers at floor level.