Scrubbing processes with water

Sulphur dioxide is recovered from a smelter gas containing 3.5 per cent by volume of SO2, by scrubbing it with water in a countercurrent absorption tower. The gas is fed into the bottom of the tower, and in the exit gas from the top the SO2 exerts a partial pressure of 1.14 kN/m2. The water fed to the top of the tower is free from SO2, and the exit liquor from the base contains 0.001145 kmol SC /kmol water. The process takes place at 293 K, at which the vapour pressure of water is 2.3 kN/m2. The water flow rate is 0.43 kmol/s. 

Nitric acid is produced by the oxidation of NH3 in air at pressures up to 10 atm over a R catalyst to produce NO, followed by further air oxidation and hydration to produce Eff 03. This is a two-step process with water scrubbing to remove HNO3 fiom N2 and excess air. Since over 90% of the NH3 fed into the process is converted into HNO3, we can describe this process quahtatively as the overall single reaction... 

The soot formed as a byproduct in the partial oxidation process has to be scrubbed out with water and recycled in a fairly complex process. 

Sulfuric Acid Roasting. In this method, the copper slimes are mixed with sulfuric acid and roasted at 500-600 °C to produce selenium dioxide, which volatilizes readily at the roasting temperature. The selenium dioxide is reduced to elemental selenium during the scrubbing process with sulfur dioxide and water. The resultant commercial grade selenium can be purified to 99.5-99.7% (Hoffmann and King 1997). 

Old Production Process. The relevant steps of the old process are shown in the flow diagram in Figure 77. Hot crack gas from the electric arc furnace was quenched to ca. 200 C with water to enable most of the carbon black to be removed in cyclones. The quench water condensed in a further scrubbing step with water at ca. 50 C, and the remaining carbon black was removed at the same time. After mechanical removal of carbon black the heated wash water was cooled by direct contact with air in a cooling tower and recycled to the cooler. Excess water was fed to the wastewater treatment plant. Both carbon black fractions recovered were used as fuel. 

A schematic diagram of the water-absorption process for recovering chlorine from caustic-chlorine process sniff gas developed by the Hooker Electrochemical Company (Anon., 1957) is. shown in Figure 6-21. In this process, chlorine-containing noncondensable gas from the liquefaction stage of chlorine manufacture is scrubbed countercurrently with water in a packed absorber. The resulting chlorine-free gas can be vented to the atmosphere, and the... 

The composition of the gas mixture, which is introduced into the tube bundle reactor (tubes of 6-12 m length and 20-50 mm diameter, filled with the Ag catalyst) consists of 15-50 vol % ethylene, 5-9% oxygen, as much as 60% methane as dilution gas, and 10-15% carbon dioxide. The reaction therefore proceeds above the upper explosion limit. The ethylene conversion runs up to 10% per cycle through the reactor. The ethylene oxide selectivity amounts to 75-83 % maximum. The formed ethylene oxide is recovered by scrubbing with water and the newly formed carbon dioxide is separated from the cycle gas, e.g., by hot potash washing process. 

Aluminum fluoride is produced when partially dehydrated alumina hydrate reacts with hydrofluoric acids gas. The solid aluminum fluoride produced is cooled with noncontact cooling water prior to further processing, while the gases from the reactor are scrubbed with water to remove unreacted hydrofluoric acid from the gas stream. Aluminum fluoride is mainly used in the production of... 

Geminox A direct process for converting butane to 1,4-butanediol. The butane is first oxidized in the gas phase to maleic anhydride, using BP s fluidized bed technology. The maleic anhydride is scrubbed with water and then catalytically dehydrogenated to butanediol. Developed in 1994 by BP Chemicals and Lurgi. Modifications of the process can be used to make tetrahydrofiuan and y-butyrolactone. The first plant will probably be built on BP s site at Lima, OH, for completion in 2000. 

Schulte A process for removing ammonia from the gases produced in the coking of coal. The ammonia is removed by scrubbing with water, then distilled from the water and incinerated. Invented by E. V Schulte and commercialized by the Koppers Company. 

The throw-away processes with aqueous slurries of lime or limestone as the scrubbing media are the most extensively installed processes. These processes create a waste sludge containing calcium sulfite, calcium sulfate, fly ash, unreacted alkali, and other minor dissolved species in the free water contained in the sludge. Since flue gas contains oxygen, some of the dissolved sulfur dioxide is oxidized, and calcium sulfate is formed. 

However, as ammonia is very readily soluble in water, if the hydrogen produced in the process is scrubbed with water the ammonia is almost entirely removed and an exceedingly pure hydrogen results. 

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