Leaching pressure drop

The present investigation was taken up to overcome all the above drawbacks. Deactivation of this catalyst mainly occurs due to crystal growth followed by fall in surface area and rise in pressure drop across the bed due to crumbling of catalyst but its chemical value remains almost intact. Acid leaching of the spent mass was expected to extract most of its metal / chemical values. This when achieved should ensure, apart from avoiding pollution. 

Solids feed preparation usually plays a crucial role in leaching processes. The use of line particles usually win spied up diffusive transfer of solutes from the solid to the extract. However, if too fine a size is used, extract may not be able to flow Ibrongh solid beds as rapidly as desired, flow pressure drop may be excessive and cause undesirable bed compaction, displacement instability will he enhanced, extract cling will increase, solid-liquid separation difficulty may increase, and excessive amocrats of intracellular colloidal material may be released. Therefore, the use of a compromise particle size is almost invariably desirable. Except for flaked oilseeds, where flake thicknesses of the order of 0.2 mat are necassery to obtain adequate oil release, particle diameters or thicknesses in the 2-5 mm range usually represent a good choioe for industrial scale extractions. 

Plugged seal legs are often a problem just after start-up. Minerals in the refractory are leached out by the moisture and acid produced during heat-up. These minerals, as well as corrosion products, accumulate on the liquid sulfur surface in the seal legs. A steady increase in pressure drop, shortly after start-up, is often caused when these deposits solidify in the seal legs. 

In the presence of sulfur (which is always present in the reactor beds after the unit is commissioned) and oxygen, sulfuric acid is formed. This acid leaches out minerals from the reactors refractory walls, corrodes the condenser tubes, forms a pressure drop-producing crust on the top of the catalyst beds, and may result in seal leg pluggage. 

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