Air Pollution Control Systems for Boiler and Incinerators.Unique control problems_7

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Air Pollution Control Systems for Boiler and Incinerators.Unique control problems_7Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 5-815-1/AFR 19-6 TM 10-5TM 5-815-1/AFR 19-6Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.comwith a solution of sodium carbonate or sodium hydrox- scrubber under controlled reactor conditions.ide to produce a solution of dissolved sodium sulfur The principal advantages of the dual alkalisalts. The solution is then oxidized to produce a neutral system are:solution of sodium sulfate. Because it is a throwaway (a) Scaling problems associated with directprocess, the cost of chemicals make it an unattractive calcium-based scrubbing processes areSOx removal process when burning high sulfur fuels significantly reduced.(greater than 1 percent). (b) A less expensive calcium base can be t. Dual alkali sodium scrubbing. used. (1) The dual alkali SOX removal system is a (c) Due to high solubility and concentration regenerative process designed for disposal of of active chemicals, lower liquid volumes wastes in a solid/slurry form. As shown in can be used thereby lowering equipment figure 10-6, the process consists of three costs. basic steps; gas scrubbing, a reactor system, (d) Slurries are eliminated from the and solids dewatering. The scrubbing system absorption loop, thereby reducing utilizes a sodium hydroxide and sodium plugging and erosion problems. sulfite solution. Upon absorption of SO2 in (e) A sludge waste, rather than a liquid waste, the scrubber, a solution of sodium bisulfite is produced for disposal. and sodium sulfite is produced. The scrubber (f) High SO2 removal efficiency (90% or effluent containing the dissolved sodium salts more). is reacted outside the scrubber with lime or u. Absorption of SO2. limestone to produce a precipitate of calcium (1) Activated carbon has been used as an absor- salts containing calcium sulfate. The bent for flue-gas desulfurization. Activated precipitate slurry from the reactor system is carbon affects a catalytic oxidation of 502 to dewatered and the solids are deposed of in a SO3, the latter having a critical temperature of landfill. The liquid fraction containing 425 degrees Fahrenheit. This allows absorp- soluable salts is recirculated to the absorber. tion to take place at operating temperatures. Double alkali systems can achieve efficiencies The carbon is subsequently regenerated in a of 90 - 95% and close to 100% reagent separate reactor to yield a waste which is used utilization. in the production of high grade sulfuric acid, (2) This system is designed to overcome the and the regenerated absorbent. There are inherent difficulties of direct calcium slurry serious problems involved in the regeneration scrubbing. All precipitation occurs outside the of the absorbent, including carbon losses due10-6Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 5-815-1/AFR 19-6 TM to attrition, chemical decomposition, serious subsequently store it as a sulphate in the pores corrosion problems, and danger of of the zeolite. combustion of the reactivated carbon. v. Cost of flue-gas desulfurization. The actual (2) Zeolites are a class of highly structured alumi- capital and operating costs for any specific installation num silicate compounds. Because of the reg- are a function of a number of factors quite specific to ular pore size of zeolites, molecules of less the plant and include: than a certain critical size may be — Plant size, age, configuration, and locations, incorporated into the structure, while those — Sulfur content of the fuel and emission greater are excluded. It is often possible to control requirements, specify a certain zeolite for the separation of — Local construction costs, plant labor costs, a particular material. Zeolites possesses and cost for chemicals, water, waste disposal, properties of attrition resistance, temperature etc., stability, inertness to regeneration techniques, — Type of FGD system and required equipment, and uniform pore size which make them ideal — Whether simultaneous particulate emission absorbents. However, they lack the ability to reduction is required. catalyze the oxidation of SO2 to SO3 and thus 10-3. Procedure to minimize SOX emission cannot desulfurize flue-gases at normal operating temperatures. Promising research is a. Efficiency requirement. The SOx removal effi- under way on the development of a zeolite ciency necessary for any given installation ...