Sulfur burning

About 70% of sulfuric acid is made from elemental sulfur. All the sulfur is obtained as a byproduct from refining natural gas and petroleum. 

The sulfur is made into SO2 acid plant feed by  

Very little S03(g) forms at the 1400 K flame temperature of this reaction. Fig. 7.4. This explains Fig. 1.4 s two-step oxidation, i.e.  

The product of sulfur burning is hot, dry SO2, O2, N2 gas. After cooling to 700 K, it is ready for catalytic SO2 oxidation and subsequent H2S04-making. 

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By 1987, sulfur trioxide reagent use in the United States exceeded that of oleum for sulfonation. Sulfur trioxide source is divided between Hquid SO and in situ sulfur burning. The latter is integrated into sulfonation production faciUties. 

Fig. 3. Process flow diagram for a continuous falling film SO sulfonation plant, equipped with a sulfur-burning SO converter unit. See text.

In early years the contact process frequentiy employed only two or three catalyst stages (passes) to obtain overall SO2 conversions of approximately 95—96%. Later, four pass converters were used to obtain conversions of from 97% to slightiy better than 98%. For sulfur-burning plants, this typically resulted in sulfur dioxide stack emissions of 1500—2000 ppm. 

Process air in sulfur-burning plants is dried by contacting it with 93—98 wt % sulfuric acid in a countercurrent packed tower. Dry process air is used to minimise sulfuric acid mist formation in downstream equipment, thus reducing corrosion problems and stack mist emissions. 

Fig. 22. Flow sheet for a dual absorption sulfur-burning plant.

In drying towers of sulfur-burning plants, mesh pads or inertial impaction-type mist eliminators are usually adequate. High efficiency mist eliminators are usually used in drying towers of spent acid or metallurgical plants. 

As of 1993—1994, over 70% of sulfuric acid production was not sold as such, but used captively to make other materials. At almost all large fertilizer plants, sulfuric acid is made on site, and by-product steam from these sulfur-burning plants is generally used for concentrating phosphoric acid ia evaporators. Most of the fertilizer plants are located ia Florida, Georgia, Idaho, Louisiana, and North Carolina. In the production of phosphate fertilizers, the primary role of sulfuric acid is to convert phosphate rock to phosphoric acid and soHd calcium sulfates, which are removed by filtration. 

The number of moles of sulfur burned equals the number of moles of sulfur dioxide produced. The atomic weight of sulfur is 32 and molecular weight of sulfur dioxide is 64. Therefore ... 

The first step in the manufacture of H2SO4 is to burn sulfur to sulfur dioxide. Sulfur burns spontaneously in air, liberating heat. 

S03/air can be raised from sulfur burning and subsequent oxidation to S03 or S03 can be stripped from 65 % oleum with dry air or S03 can be obtained by evaporation of liquid-stabilized S03, subsequently mixed with dry process air. 

FIGURE C.1 Elemental sulfur burns in air with a blue flame and produces the dense gas sulfur dioxide, a compound of sulfur and oxygen. 

Sulfur forms several oxides that in atmospheric chemistry are referred to collectively as SOx (read sox ). The most important oxides and oxoacids of sulfur are the dioxide and trioxide and the corresponding sulfurous and sulfuric acids. Sulfur burns in air to form sulfur dioxide, S02 (11), a colorless, choking, poisonous gas (recall Fig. C.1). About 7 X 1010 kg of sulfur dioxide is produced annually from the decomposition of vegetation and from volcanic emissions. In addition, approximately 1 X 1011 kg of naturally occurring hydrogen sulfide is oxidized each year to the dioxide by atmospheric oxygen ... 

In order to explore composition modulation of the final stage of a converter further, Briggs et al. (1978) added a second integral reactor, also holding about 30 g of the vanadia catalyst. With the preconverter in place, this system was operated on a typical feed from sulfur burning, with a S02 02 N2 composition in vol% of 10.8 15.2 74, and from a smelter effluent with a composition of 8.0 6.2 85.8. The cycled beds of vanadia catalyst were held in a fluidized sand bath at 401°C for the former feed and at 405°C for the latter one. The space velocity for both the air and the S03/S02 mixture was about 24 min 1 (STP). Table II summarizes the experimental results for the cycle periods tested. 

S02 emitted from the modulated bed goes through a minimum after switching to the S03/S02 mixture. Lowest values are obtained 2 min after the composition change for the sulfur burning feed and they are about 8% of the steady-state emission, whereas for the smelter effluent feed, the lowest emission is about 13% of the steady-state value. Evidently, a cycle period of 4 to 5 min would be optimum for the conditions used, yielding a performance some 10% better than that shown at r = 10 in Table II. 

If a section cut through a small sulfur-burned area of a lemon injured on the tree is examined microscopically, coagulation of protoplasm and cell collapse are apparent. Also, the injured tissue stains abnormally dark with safranin indicating the protoplasm has become more acidic than in normal tissue (18). Sides of the peel of lemons burned by sulfur on the tree were found to be higher in total sulfate than were uninjured sides of the same peel. The high total sulfate content of the peel was subsequently found to be due in part to soluble sulfate, as shown by analyses of the expressed cell solution (18). 

Air temperature and vapor density are two factors which influence the rate of dissipation of radiant energy received by plants from the sun, and they determine in a large measure the temperature of the plant part and consequently sunburn and sulfur burn (18), other factors, such as particle size of the sulfur, being constant. 

While it is conceivable that an excess of bases in the cell solution might be protective against mild sulfur burn, this possibility has not yet been tested. On the other hand, a small increase in buffer capacity might reduce sulfur burn. An example of this effect may be seen in the buffer curves of the leaf sap in two of the United States Department of Agriculture s muskmelon varieties. No. 5, which is susceptible to sulfur burn, has a buffer curve which lies 0.2 to 0.3 pH unit closer to the acid side than the buffer curve of the sulfur burn-resistant variety, No. 11353 (Figure 1). 

Figure 1. Titration Curves of Leaf Tissue Fluids of Sulfur Burn-Susceptible and Sulfur Burn-Resistant Muskmelon Leaves...

Converted starches, 4 720 Converter passes, in sulfur burning, 23 774-776... 

Double absorption sulfur burning plant, flow sheet for, 23 775 Double-arm kneading mixers, 16 722 Double-barrier structure, in RTDs, 22 170-171... 

Non-sulfur burning plants, 23 778 Nonthermoplastic linear polymers,... 

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