Sulfur dioxide scrubbing

Ashes and residues. These are the materials remaining from the burning of wood, coal, coke, and other combustible wastes. Residues from power plants normally are composed of fine powdery materials, cinders, clinkers, and small amounts of burned and partially burned materials. Fly ash from coal boilers and CKD (cement kiln dust) are frequently sold for stabilization of waste, waste bulking operations, and incorporation into building products such as gypsum from sulfur dioxide scrubbing. 

Figure 1 illustrates the components of a typical calcium-based sulfur dioxide scrubbing system. Flue gases enter a quenching section where... 

Figure 1. Typical calcium-based sulfur dioxide scrubbing system...

The ACP system combines a sulfur dioxide scrubbing system based on spray dryer technology with a regeneration system based on a unique reduction step coupled to chemical recovery and Claus technologies. This combination results in an efficient and reliable process for application to sulfur dioxide pollution problems. The remainder of this paper discusses the details of the process and typical installation characteristics and also presents process economics which indicate that the ACP system is economically feasible a well as technically sound. 

Alloy 625 has also been used in preheaters for sulfur dioxide scrubbing systems in coal-fired power plants and bottoms of electrostatic precipitators that are flushed with seawater. 

Recovery of iodine hy action of sulfur dioxide on aqueous sodium iodate Hydrogenation of vegetable oils with gaseous hydrogen Desulfurization of gases by scrubbing with aqueous ethauolamiues... 

In many cases, water is a poor scrubbing solvent. Sulfur dioxide, for example, is only slightly soluble in water, so a scrubber of very large liquid capacity would be required. SO2 is readily soluble in an alkaline solution, so scrubbing solutions containing ammonia or amines are used in commercial applications. 

If the gas to be measured contains sulfur dioxide, it has to be scrubbed from the gas before oxidation of the reduced compounds can occur. The gas is scrubbed using an SO2 scrubber. This may contain citrate buffer solution (potassium citrate or sodium citrate). The collection efficiency of the sulfur diox ide may be as high as 99%. 

Limestone scrubbing A process using a ground limestone and water mix to neutralize sulfur dioxide in waste gas products. 

Sulfur dioxide emissions from power plants can be reduced by spraying a water solution of calcium hydroxide directly into the smokestack. This "scrubbing" operation brings about the reaction... 

While the use of low-sulfur fuels is one mechanism to reduce sulfur dioxide emission, alternatively most approaches focus on scrubbing or ridding the emissions in smoke stacks of sulfur dioxide gas. A number of different types of scrubbers, i.e., sulfur dioxide removal systems, are available for industry. One system sprays the flue gas into a liquid solution of sodium hydroxide. The hydroxide combines with SO2 and O2 to form the corresponding sulfate which can be removed from the aqueous solution ... 

The 1970 s also brought about increased use of three-phase systems in environmental applications. A three-phase fluidized bed system, known as the Turbulent Bed Contactor, was commercially used in the 1970 s to remove sulfur dioxide and particulates from flue gas generated by coal combustion processes. This wet scrubbing process experienced several... 

ASR Sulfoxide [Alberta Sulfur Research] A process for removing residual sulfur dioxide and hydrogen sulfide from the tail gases from the Claus process by wet scrubbing with a solution containing an organic sulfoxide. Elemental sulfur is produced. It had not been piloted in 1983. 

Clauspol [Claus polyethylene glycol] A variation on the Claus process for removing hydrogen sulfide from gas streams, in which the tail gases are scrubbed with polyethylene glycol to remove residual sulfur dioxide. Clauspol 150 is a modification of this. Developed by the Institut Frangais du Petrole. 

Dual Alkali A flue-gas desulfurization process. The sulfur dioxide is absorbed in aqueous sodium hydroxide and partially oxidized, and this liquor is then treated with calcium hydroxide to regenerate the scrubbing solution and precipitate calcium sulfate. Developed by Combustion Equipment Associates and Arthur D. Little. 

Hanisch-Schroder A process for scrubbing sulfur dioxide from smelter gases using water. Developed in 1884 and still in use in 1950, although it was probably obsolete by 1990. It required 100 to 200 tons of water for each ton of sulfur recovered. 

Longmaid-Henderson A process for recovering copper from the residue from the roasting of pyrites to produce sulfur dioxide for the manufacture of sulfuric acid. The residue was roasted with sodium chloride at 500 to 600°C the evolved sulfur oxides and hydrochloric acid were scrubbed in water and the resulting solution was used to leach the copper from the solid residue. Copper was recovered from the leachate by adding scrap iron. The process became obsolete with the general adoption of elemental sulfur as the feedstock for sulfuric acid manufacture. 

North Thames Gas Board A process for removing organic sulfur compounds from coal gas by catalytic oxidation over nickel sulfide at 380°C. The sulfur dioxide produced is removed by scrubbing with dilute aqueous sodium hydroxide. Operated by the gasworks of the North Thames Gas Board, London, between 1937 and 1953. 

Stackpol 150 Also known as IFP Stackpol 150. A flue-gas desulfurization process. The sulfur dioxide is removed by scrubbing with aqueous ammonia, and the sulfur is then recovered by a four-stage process. Developed by the Institut Frangais du Petrole. 

Present theories of the origin of acid rain indicate that we can limit acid rain by reducing sulfur dioxide emissions and moving to low-sulfur fuels but, only about 20% of the world s petroleum reserves are low in sulfur. Switching U.S. midwestern power plants to low-sulfur coal could cause economic problems since much of the coal from the Midwest and Appalachia has a high sulfur content. Most of the electric power generated in the Midwest uses high-sulfur coal and it would cost tens of billions of dollars to scrub the sulfur out of coal. 

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. 

Several power plants have been equipped with dual alkali processes. These are throw-away processes with two liquid loops. In one common process, the scrubbing liquid is a clear solution of sodium sulfite. The absorption of sulfur dioxide converts the sodium sulfite to sodium bisulfite. In the regeneration loop, an alkali such as lime slurry is added the sodium sulfite solution is regenerated and a mixture of calcium sulfite and calcium sulfate is precipitated. The slurry is... 

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