Soot ash removal unit

The Soot Ash Removal Unit (SARU) is shown in Figure 5.23. In this step the carbon slurry is flashed to atmospheric pressure in the slurry tank. The slurry is then filtered to produce 1) a filter cake (with about 80% residual moisture) and 2) a clear water filtrate. The filter cake then goes through a controlled oxidation process in a multiple hearth furnace. The furnace allows the combustion of the carbon to take place under conditions where vanadium oxides neither melt nor corrode the furnace. The product is a vanadium concentrate that contains about 75% V2Os and can be sold to metals reclaiming companies. The process is autothermal because the heat of combustion of the carbon is sufficient to evaporate the moisture in the filter cake180. 

Figure. 23. Shell Gasification Plant - Soot Ash Removal Unit (SARU). 

SGP = Shell gasification process SARU = Soot ash removal unit PSA = pressure swing adsorption... 

Side-Stream Units. Wash water from particulate removal is treated in the soot ash removal unit described in more detail below. Carbon and ash are separated from the water by filtration. The filter cake is worked up by controlled oxidation to a salable vanadium concentrate. The bulk of the water is recycled to the water wash. 

Figure 100. Flow diagratn of a soot ash removal unit...

To prevent accumulation of ash and slag in the water circuit, some water is discharged continuously. In a combined chemical and physical treatment sulfides, cyanides and suspended solids (ash) are removed. A concentrated sludge has to be filtered off and disposed of. The run-off water from the filters is stripped of ammonia and after pH-adjustment sent to a biological treatment unit. Uhde [532] has developed an alternative route for soot treatment in which the soot is filtered off and subjected to combustion, and the filtered water is recycled to the quench and scrubbing circuits. Let down water is treated as described above. This soot treatment technique avoids not... 

If the partial oxidation unit is integrated in a coal gasification complex - as suggested in Chap. 7 - and the liquid products of coal gasification are used as a feedstock, the ash content of this feedstock will be extremely low and gasification can be performed in such a way that even less than 0.5 wt % of soot occur in the reformed gas. In this case, the expenditure for a carbon recycling system can be saved as the small carbon quantities can be more easily and with less expenditure be removed in the waste water treatment system of the complex. 

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