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Project: 802 #G661

Activating spent sorbent from a once-through slurry injection process and recycling it to the furnace is a very effective way of improving sorbent utilization and reducing the cost of sulphur capture. The slurried spent sorbent can be reactivated by heating it at about 90°C for 2 - 3 hours in an agitated tank. The sulphur capture potential of the activated sorbent slurry is comparable to that of the fresh sorbent slurry; injecting the activated sorbent slurry alone, SO2 removal from a typical flue gas stream is up to 65% with Pt. Anne limestone slurry and 79% with dolomite doped Pt. Anne limestone slurry at Ca/S = 2.5. Grinding the waste before activating it resulted in 89% SO2 capture.

Additives such as hydrated lime and sodium bicarbonate can further

enhance the effectiveness of the activation process. Sorbent utilization (Ca/S=3) increases with increasing amounts of recycled waste. For the once-through process (no recycle), utilization is 23%, for 25% recycle it is 29%, for 50% recycle it is 36%. Assuming the use of the recycled waste only, the expected sorbent utilization is 46% at a Ca/S ratio of about 3.0. A waste sample from the Chatham circulating fluidized bed combustor also responded well to activation; sulphur capture using this activated slurried waste was 30%. The wastes from both the once-through and the recycle mode of operation are finer than the fly ash alone; they have higher ash resistivities, higher dust loading to the ESP and as a result ESP performance deteriorated by 2 to 5%.