Utility sulfur dioxide removal

Sulfur dioxide removal processes can be used to treat flue gas from industrial boilers, heaters, or other process gases where sulfur compounds are oxidized. These processes have generally been proven in utility applications. More recently, several industrial SO2 removal installations have been completed. 

Process Alternatives. Sulfur dioxide removal processes can be categorized as throwaway or recovery. Throwaway processes produce a liquid or solid waste that requires disposal. Recovery processes convert the sulfur dioxide to elemental sulfur or sulfuric acid. Throwaway processes have been used in most utility applications, but there could be greater incentives for using the recovery processes in industry. 

Research-Cottrell realized that the industrial and utility markets required different types of sulfur dioxide removal equipment. Therefore, it contracted with Ab Bahco Ventilation of Sweden to market their sulfur dioxide removal technology in the U.S. and Canada. Bahco technology is particularly applicable to industrial boiler and process applications (7, 8, 9). The first U.S. Bahco installation will handle seven stoker-type boilers at the Rickenbacker Air Force Base in Columbus, Ohio. 

Regenerative Aqueous Carbonate Process for Utility and Industrial Sulfur Dioxide Removal... 

There are several processes for the removal of sulfur dioxide from stack gas (Table 25.1) (Chapter 23) but to date scrubbing process utilizing limestone (CaCOj) or lime [Ca(OH)J slurries have received more attention than other stack gas scrubbing processes. Attempts have been made to use dry limestone or dolomite (CaCOs MgCOj) within the combustor as an in situ method for sulfur dioxide removal, thus eliminating the wet sludge from wet processes. This involves injection of dry carbonate mineral with the coal followed by recovery of the calcined product along with sulfite and sulfate salts. 

Operating data for four absorption systems of plants utilizing the Cominco process are presented in TaUe 7-25. Obsraved sulfor dioxide removal efficiencies vary fonn 8S to 97%. The degree of sulfur dioxide removal attainable in a system of this type is obviously d en-doit upon a large nuniba of variables. Chief among these are... 

Sulfur is widely distributed as sulfide ores, which include galena, PbS cinnabar, HgS iron pyrite, FeS, and sphalerite, ZnS (Fig. 15.11). Because these ores are so common, sulfur is a by-product of the extraction of a number of metals, especially copper. Sulfur is also found as deposits of the native element (called brimstone), which are formed by bacterial action on H,S. The low melting point of sulfur (115°C) is utilized in the Frasch process, in which superheated water is used to melt solid sulfur underground and compressed air pushes the resulting slurry to the surface. Sulfur is also commonly found in petroleum, and extracting it chemically has been made inexpensive and safe by the use of heterogeneous catalysts, particularly zeolites (see Section 13.14). One method used to remove sulfur in the form of H2S from petroleum and natural gas is the Claus process, in which some of the H2S is first oxidized to sulfur dioxide ... 

The thiophene ring system can be utilized as a synthetic scaffold for the preparation of nonthiophene materials as the sulfur moiety can be removed by reduction (desulfurization) or extrusion (loss of SO2). The extrusion of sulfur dioxide from 3-sulfolenes (2,5-dihydrothiophene 1,1-dioxides) give dienes (butadienes or o-quinodimethanes) that can be utilized to prepare six-membered rings by cycloaddition chemistry. For example, thermolysis of 3-sulfolene 120 provided tricyclic pyrazole 122 via an intramolecular cycloaddition of the o-quinodimethane 121 that results by extrusion of sulfur dioxide <00JOC5760>. Syntheses of 3-sulfolenes 123 and 124 <00S507> have recently been reported. 

During processing, affected fruit is generally removed or pressurized-water jets are utilized to remove damaged portions of fruit and contaminations (or both). These processes effectively eliminate patulin. However, if these procedures are not done properly, patulin may remain in the processed apple juice and apple products, where it is very stable. Pasteurization at 90°C only causes a reduction of 10%, however patulin is not stable in the presence of sulfur dioxide or sulfydryl compounds. The fermentation process for cider eliminates 99% of patulin. 

Tn 1970, 20 million tons of sulfur dioxide emitted from steam electric-power plants. Without control measures these emissions will increase to 40 million tons by 1980. With typical SO2 concentrations in stack gas currently in the range of 1000-2000 ppm, target levels for future control legislation correspond to 50-150 ppm SO2 in the stack, and there are not sufficient low sulfur fuels to meet these standards. To fill the gap between projected supplies of low sulfur fuels and our nation s energy requirements, an economical, high efficiency process to remove SO2 from the fiue gases of power plants is required. Such a process must also recover SO2 in a form which can be readily handled and sold, in recognition of the quantities involved. Furthermore such a process must be compatible with the many constraints public utilities face in its installation and operation. 

In addition to this wet scrubbing process, dry purification processes are also utilized for the removal of sulfur dioxide from furnace gases, such as the absorption of sulfur dioxide on activated charcoal (BF-process from Bergbau Forschung). 

Applications. In 1994 ca. 305 10 " t of liquid sulfur dioxide was consumed just in the USA, of which 40% was utilized in the manufacture of sulfur-containing chemicals such as sulfites, hydrogen sulfites, thiosulfites, dithionites and salts of hydroxyalkane sulfinic acid and alkane sulfonates. It is also utilized in cellulose manufacture, in the chemical dressing of manganese ores, in the removal of sulfur-containing impurities from mineral oils, for disinfection and preservation in the food industry and for the treatment of water. 

Spray-dry scrubbers are an alternative to conventional wet scrubbers. In this type of scrubber, an alkaline slurry or solution is sprayed in fine droplets into a reaction vessel, along with the flue gas. The droplefs rapidly react with the sulfur dioxide while drying to a fine powder of sulfite salts. This powder is entrained in the gas stream, and is carried to a dust precipitator where it is collected, as shown in Fig. 7. Most of the sulfur dioxide is collected in liquid-phase reactions while the droplets are drying, but 10-15 /o additional sulfur dioxide can be absorbed in gas/solid reactions, as the absorbent powder is swept through the ductwork and particulate collector. These are cocurrent devices, and so the limestone utilization and sulfur removal efficiency are inherently lower than those of countercurrent devices such as wet scrubbers. Partial recycle of the sorbent is often used to improve the sorbent utilization. 

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