USTUTT cold model DFB system is shown in the figure below. All dimensions of the cold model are downscaled by a factor of 2.33 in regard to the 10 kWth CaL DFB system.The cold model riser carbonator is 5.3 m high and has a diameter of 30 mm, while the cold model BFB has a diameter of 49 mm.
Solids are entrained through the different regions of the riser (1-3) and are separated by the cyclone separator (4). Consecutively, the riser entrainment proceeds to the double exit loop seal (6) via the upper standpipe (5) of the DFB system. The double exit loop seal used in this facility is essentially a typical loop seal with an orifice at its bottom. The size of the opening of the orifice is controlled with use of a cone valve (7), thus controlling the solid looping rate through the orifice. The weir (8) of the loop seal leads the solids back to the riser while the cone valve discharge leads to the BFB (9). The absolute pressure of the BFB is controlled through a pressure control valve (10). Solids proceed through the BFB overflow (11) to the lower loop seal (13) via the lower standpipe (12) and from there back to the riser, thereby closing the solid loop of the DFB system. The return legs of the double exit and lower loop seals enter the riser at a slightly elevated position in regard to the distributor.
Cold model schematic. 1- dense region; 2- lean core-annulus region; 3- riser exit region; 4- cyclone; 5- upper standpipe; 6- double exit loop seal; 7- cone valve; 8- weir; 9- BFB; 10- BFB pressure control valve; 11- BFB overflow; 12- lower standpipe; 13- lower loop seal (Charitos et al; 2009)