Sulfur single contact

Fig. 9.1. Single contact H2SO4 making flowsheet. SO3 rich gas from catalytic SO2 oxidation is reacted with strong sulfuric acid, Reaction (1.2). The reaction consumes H20(f) and makes H2S04(f), strengthening the acid. Double contact H2SO4 making is described in Fig. 9.6. A few plants lower the SO2 content of their tail gas by scrubbing the gas with basic solution (Hay et al., 2003).

Most sulfuric acid plants are double contact plants, Fig. 9.6, Tables 9.3, 19.3 and 23.2. They efficiently oxidize their feed S02(g) to S03(g) and efficiently make the resulting S03(g) into H2S04(f). Single contact plants (Fig. 9.1) are simpler and cheaper - but less efficient. 

Fig. 16.1. Schematic of single contact, 3 catalyst bed sulfuric acid plant. It is a single contact plant because it has only one H2S04 making step. Note gas cooling between catalyst beds. It permits additional S02 oxidation in the next catalyst bed.

Fig. 21.1 indicates how these requirements are achieved for a single contact sulfur-burning acid plant with 3 catalyst beds. It shows that ... 

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.

Single contact sulfuric acid plant including ... 

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.

In the conventional contact process (single contact process) the reaction gases are passed through the four trays without intermediate absorption and the gas is cooled after each tray to 450°C or 430°C for the lowest tray. After passage through the first tray 60 to 63% of the sulfur dioxide has been converted to sulfur trioxide, after the second tray 89 to 90% and after the fourth tray a maximum conversion of 98% is possible, based on sulfur dioxide. 

With the double contact process it is unnecessary to purify the tail gases to reduce their sulfur dioxide content still further, whereas tail gases from single contact plants have to be purified. This can be realized either by scrubbing with ammonia or with an aqueous solution of sodium sulfite and sodium hydrogen sulfite (Wellman-Lord process), absorption on activated charcoal (sulfacid process from Lurgi) or by oxidative gas purification such as in the peracidox process (oxidation of sulfur dioxide with hydrogen peroxide or peroxomonosulfuric acid). 

The S02-ladened off-gas from the cooler and the air from the stripper are compressed and sent to a single-contact, single-absorption sulfuric acid plant. Ninety-six percent of the SO2 is converted to 98 sulfuric acid. Ten percent of this byproduct acid is recycled and used in the MgO FGD process but most is stored onsite and eventually sold as a byproduct. The tail gas from the acid plant containing the unconverted SO2 is recycled to the flue gas ducts ahead of the FGD system. 

The Herculaneum smelter operates a 340-ton per day Monsanto type single contact acid plant on the site. This plant treats the sulfiir-rich gases produced in the sintering process. The 93% black sulfuric acid produced is stored in tanks on site. Sulfuric acid is shipped to customers from the smelter by truck, rail or river barge. The acid plant operates and performs maintenance on a schedule similar to the sinter plant. 

In the 1960s the environment protection laws made it prohibitive to expand the single contact single absorption plants. The conversion efficiency of SCSA process giving 96-96.5% conversion produced SO2 emission of 16-20 kg/tonne of sulfuric acid... 

In a typical sulfur-burning, single-contact sulfuric acid plant (Figure 11.1), the molten sulfur is burned with dry... 

Figure 11.1. Sulfur-Burning Single-Contact Sulfuric Acid Plant.

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-... 

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