Fines reinjection

In operating a fluidized bed reactor such as a fluidized bed coal gasifier, fine particles tend to be elutriated from the fluidized bed. The elutriated fines, if not recovered, represent a significant carbon loss and thus a significant loss of reactor efficiency. In actual industrial practice, the fines are recycled back to the fluidized bed for further consumption. The location of the fines reinjection point into the fluidized bed reactor is important in order to maximize the consumption of fines in each pass. Otherwise, the fines will build up in the recycle loop and increase the heat load of the reactor operation. The fines reinjection location is selected to maximize the fines residence time in the bed and to provide an conducive environment for consumption, such as high temperature and an oxidizing atmosphere. 

Fossil-fuel and wood-waste fired industrial and commercial fuel combustion units commonly use multiple cyclones (generally upstream of a wet scrubber, ESP, or fabric filter) which collect fine PM (< 2.5 im) with greater efficiency than a single cyclone. In some cases, collected fly ash is reinjected into the combustion unit to improve PM control efficiency (AWMA, 1992 Avallone, 1996 STAPPA/ALAPCO, 1996 EPA, 1998). 

If in our model system, we had used 80% methylene chloride/hexane and the red peak had partially overlapped the backside of the blue peak, we would attempt to resolve it by reequilibrating in 40% methylene chloride/hexane and reinjecting. We could expect that we should see two well-resolved peaks if not, we could go to a 20% mixture. More than likely, we would have overshot on the first change and would have to fine-tune back toward the 80% mixture. Simply by modifying the solvent polarity, we are able to increase or decrease k and contract or spread our separation. This k development is our usual starting point in methods development. 

Figure 2A is representative of pressurized bubbling bed air blown partial oxidation of biomass fuel. The sketch indicates that fines recycling might be used, with nonmechanical valves to control the reinjection of fines into the fluidized bed gasifier. The vessel will drain a low-carbon ash product. The sketch also suggests that overbed air injection might be used for fuel gas partial oxidation as a means for fuel gas tar destruction. The... 

Carbon Reinjection. Partial suspension burning results in a greater carryover of particn-late matter in the flue gas than occurs with other types of stokers. In general the arrangement of the collection equipment is such that the coarse carbon-bearing particles can be returned to the furnace for further burning and the fine material discharged to the ash removal system. 

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