Sponge iron, 5.20

Iron silicate Iron-silicon alloys Iron-silicon-chromium Iron sponge... 

Iron Sponge. An old method for removal of sulfur compounds involves contacting gases containing H2S and H2O with CC- or y-ferric oxide... 

Physical solvent type Fluor solvents (propylene carbonate example), Selexol Physical/chemical type Sulfinol Carbonate type Potassium carbonate Solution batch type Lo-Cat, Chemsweet Bed batch type Iron Sponge, Mol Sieve... 

The iron sponge process is very old (introduced in England in the mid-19th century) and very simple. It removes only H S and mercaptans. It is good only for streams containing low H2S concentrations at pressures of 25 to l,200psig. Hydrated iron oxide containing water and of proper pH is supported on wood chips or other material. Water is injected with the gas. 

The iron sponge process uses the ehemical reaction of ferric oxide with Hi.S to sweeten gas streams. This process is applied to gases with low H S concentrations (300 ppm) operating at low to moderate pressures (. vO-SOO psig). Carbon dioxide is not removed by this process. 

The ferric oxide is impregnated on wood chips, which produces a solid bed with a large ferric oxide surface area. Several grades of treated wood chips are available, based on iron oxide content. The most common grades are 6.5-, 9.0-, 15.0-, and 20-lb iron oxide/bushel. The chips are contained in a vessel, and sour gas flows through the bed and reacts with the ferric oxide. Figure 7-3 shows a typical vessel for the iron sponge process. 

The zinc oxide process is similar to the iron sponge process. It uses a solid bed of granular zinc oxide to react with the H2S to form water and zinc sulfide ... 

It is difficult to remove H2S to pipeline quality with a membrane sy stem. Membrane systems have effectively been used as a first step to remove the CO2 and most of the H2S. An iron sponge or other H2S treating process is then used to remove the remainder of the H2S. 

The vessel is generally constructed of carbon steel that has been heat treated. Control of metal hardness is required because of the potential of sulfide-stress cracking. The iron-sponge vessel is either internally coated or clad with stainless steel. 

The superficial gas velocity (that is, gas flow rate divided by vessel cross-sectional area) through the iron-sponge bed is normally limited to a maximum of 10 ft/min at actual flow conditions to promote proper contact with the bed and to guard against excessive pressure drop. Thus, the vessel minimum diameter is given by ... 

Iron sponge is normally sold in the U.S. by the bushel. The volume in bushels can be determined from the following equation once the bed dimensions of diameter and height are known ... 

Bed life for the iron sponge between change outs is determined from ... 

The iron-sponge material is normally specified to have a size distribution with 0% retained on 16 mesh, 80% between 30 and 60 mesh, and 100% retained on 325 mesh. It is purchased with a moisture content of 20% by weight and buffering to meet a flood pH of 10. Because it is necessary to maintain a moist alkaline condition, provisions should be included in the design to add water and caustic. 

Pif iblem Design an Iron-Sponge Unit Solution ... 

Hydrogen sulfide is removed from natural gas by passage over iron sponge, when flammable iron sulfide is produced. Handling precautions during regeneration of the reactor beds are detailed. 

Iron Sponge Also called Dry box. An obsolete process for removing hydrogen sulfide from gas streams by reaction with iron oxide monohydrate. The ferric sulfide that is formed is periodically re-oxidized to regenerate ferric oxide and elemental sulfur. When this process becomes inefficient because of pore-blockage, the sulfur is either oxidized to sulfur dioxide for conversion to sulfuric acid, or is extracted with carbon disulfide. 

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