Sulfuric acid is the chemical produced in the United

Chapter 5, Problem 5.48

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Sulfuric acid is the chemical produced in the United States with the highest volume of production. In one of the earliest processes used to make it, an ore containing iron pyrites (FeS2) is roasted 226 Chapter 5 Single-Phase Systems (burned) with air. The following reactions take place in the roasting furnace: 2 FeS2(S) + Oz(g) -. FeZ03(S) + 4S0z(g) [1] 2 FeSz(s) + 1- 02(g) -. FeZ03(S) + 4 S03(g) [2] The gas leaving the reactor goes to a catalytic converter in which most of the SOz produced is further oxidized to S03: SOz + ~Oz -. S03 [3J Finally, the gas leaving the converter passes through an absorption tower, in which the S03 is absorbed in water to produce sulfuric acid (HzS04). (a) An ore containing 82 wt% FeSz and 18% inerts is fed to a roasting furnace. Dry air is fed to the furnace in 40% excess of the amount theoretically required to oxidize all of the sulfur in the ore to S03' An FeSz oxidation of 85% is obtained, with 40% of the FeSz converted forming sulfur dioxide and the rest forming sulfur trioxide. Two streams leave the roaster: a gas stream containing SOz, S03, Oz, and Nz, and a solid stream containing unconverted pyrites, ferric oxide, and inert material in the ore. Calculate the required feed rate of air in standard cubic meters per 100 kg of ore roasted and the molar composition and volume (SCM/1OO kg of are) of the gas leaving the roasting oven. (b) The gas leaving the roasting oven enters the catalytic converter, which operates at 1 atm. The conversion reaction [3] proceeds to an equilibrium point at which the component partial pressures satisfy the relation Ps03 = Kp(T) l/Z PS02P02 The gases are first heated to 600C, at which Kp = 9.53 atm-12, and are then cooled to 400C, where Kp = 397 atm-1/2. The rate of the forward reaction increases sharply with temperature and is several orders of magnitude greater at 600C than at 400C. Calculate the equilibrium fractional conversions of sulfur dioxide in the converter when the temperature is 600C and when it is 400C. Briefly explain why the converter gases are initially heated and then cooled. (c) Assuming complete conversion to sulfuric acid of the sulfur trioxide leaving the converter, how many kg of HzS04 will be produced per kg of sulfur in the ore? What would this ratio have. been if all of the sulfur in the ore had been converted? Summarize the factors responsible for the second number being larger than the first one