A standard top rubber seal, neoprene side seals, and a bottom loop seal
provide an effective barrier against energy loss.
It comprises medium-temperature cyclone, loop seal and ash cooler as well as convective heating surface, superheater, economizer and tubular air heater.
Unburned char and hot solids with high-temperature flue gas leave the convective pass and enter the medium-temperature cyclone, and the collected solids return to the furnace through the standpipe and the loop seal. The loop seal is controlled by high-pressure roots blower, and the solids recycle rate to the furnace is adjusted by changing both air flow rate and pressure drop.
Because of the plant elevations it was impractical to increase the height of the vertical leg of the L-valve, so the only option was to replace the L-valve by a loop seal
, see Figure 3, which is essentially a fluidized bed divided by a vertical baffle except for a gap at the bottom to allow solids to pass between the two side-by-side beds fluidized by separate air supplies.
A concentrated noncondensible gas (CNCG) system upgrade included new loop seals
, piping modifications, control valves, and an upgrade to DCS control.