Production single contact

From an operational viewpoint, a single-contact removal of americium is most desirable. To avoid secondary problems caused by the production of magnesium (by Equations 2 and 3) in excess of its solubility in plutonium, americium removals are limited to about 85% per extraction stage. Multiple-stage extractions consequently are used when 85% or greater removal of americium is required. 

Fig. 21.1. Heat transfer flowsheet for single contact, sulfur burning sulfuric acid plant. It is simpler than industrial plants, which nearly always have 4 catalyst beds rather than 3. The gaseous product is cool, S03 rich gas, ready for H2S04 making. The heat transfer product is superheated steam. All calculations in this chapter are based on this figure s feed gas composition and catalyst bed input gas temperatures. All bed pressures are 1.2 bar. The catalyst bed output gas temperatures are the intercept temperatures calculated in Sections 12.2, 15.2 and 16.3.

Fig. 23.1. Simplified single contact sulfuric acid production flowsheet. Its inputs are moist feed gas and water. Its outputs are 98 mass% H2S04, 2 mass% H20 sulfuric acid and dilute S02, 02, N2 gas. The acid output combines gas dehydration tower acid, H2S04 making tower acid and liquid water. The equivalent sulfur burning acid plant sends moist air (rather than moist feed gas) to dehydration. Appendix V gives an example sulfur burning calculation.

Existing single-contact acid plants can also be converted to doublecontact plants (63). In such cases, however, using add-on scrubber systems is an alternative, and several such systems have been used commercially. The Cominco ammonia absorption process has been used for many years (22, 64). The Lurgi Sulfacid process (65) and Wellman-Lord process (66) have had more recent and limited use. The Mitsu-bishi-JECCO process has also been applied to acid plant tail gases (27, 67, 68), but the gypsum by-product would be essentially a waste in the United States. 

Figure 11.8 shows a simplified flow diagram for production of sulfuric acid from pyrites. The diagram shows a single-contact, single-absorption process. In most locations either stack gas scrubbing or a second contact-... 

Purity of Products. The maximum purity of A in the raffinate will be given by an operation in which the nth tie line, corresponding to the last stage, passes through S when extended. This necessarily requires n to be infinity. The absolute maximum purity of C in the solvent-stripped extract will correspond to the case for single contact (tangency of solvent-removal line to the solubility curve for the combined extracts). Since E ordinarily falls within the two-liquid-phase area, this cannot usually be realized, however. 

Solvent Recovery. Since but a single raflSnate and a single extract are the products of this type of operation, solvent-recovery calculations are identical with those of the single-contact operation described previously. The maximum purity of C in the finished extract will accordingly result if the solvent-removal line EiSe is tangent to the binodal curve. 

Calculate the compositions of solvent-free products for a single-contact doublesolvent extraction of 100 lb. of a solution containing 69.9% acetone (B), 30.1% acetic acid (C), with the double-solvent 106.3 lb. chloroform (A)-117.7 lb. water (D). Compare the results with the experimental data of Brancker, Hunter, and Nash, who show the results to be 42.25% B, 57.75% C 90.55% B, 9.45% C. 

Tail gas scrubbers are used to treat single contact and double contact acid plant tail gas. The choice of technology is based on a combination of required SO2 removal efficiency along with reagent costs and disposal or sale of wastes or by-products. 

The growth of solid films onto solid substrates allows for the production of artificial stmctures that can be used for many purposes. For example, film growth is used to create pn junctions and metal-semiconductor contacts during semiconductor manufacture, and to produce catalytic surfaces with properties that are not found in any single material. Lubrication can be applied to solid surfaces by the appropriate growth of a solid lubricating film. Film growth is also... 

Health and Safety Factors. VDE is a flammable gas its combustion products are toxic. Liquid VDE on contact with the skin can cause frostbite. Acute inhalation toxicity of VDE is low median lethal concentrations (LC q) for rats were 128,000 ppm after a single 4-h exposure (52) and 800,000 ppm after a 30-min exposure (53). Cumulative toxicity is low exposure of rats and mice at levels of up to 50,000 ppm for 90 days did not cause any... 

In the early 1970s, air pollution requirements led to the adoption of the double contact or double absorption process, which provides overall conversions of better than 99.7%. The double absorption process employs the principle of intermediate removal of the reaction product, ie, SO, to obtain favorable equiUbria and kinetics in later stages of the reaction. A few single absorption plants are stiU being built in some areas of the world, or where special circumstances exist, but most industriali2ed nations have emission standards that cannot be achieved without utili2ing double absorption or tad-gas scmbbers. A discussion of sulfuric acid plant air emissions, control measures, and emissions calculations can be found in Reference 98. 

Contact or ingestion of cyanamide must be avoided, and precautions taken to prevent inhalation of dust or spray mist. In rat studies cyanamide-100 toxicity ranges from a single oral dose LD q of 280 mg/kg to a single dermal dose LD q of 590 (420—820) mg/kg. The compound is, therefore, considered to be moderately toxic both by ingestion in single doses and by single-skin appHcations. An aqueous paste of the product is corrosive to rabbit skin. Small quantities of the dry product produced severe irritation when introduced into the conjunctival sac of the rabbit eye. 

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