Process for the production of sulfur trioxide by the cold gas process

Claim 2

In a process for producing sulfuric acid by double absorption by burning pyrite to produce a gas at a temperature of about 750* to 950* C. containing about 10 to 14 percent SO2, about 8 to 2.8 percent O2 and the balance substantially nitrogen by utilizing a group of at least four series connected catalytic converter stages and a first and second absorber, wherein the SO2-containing gas is partially oxidized to SO3 in the first three stages to form a hot gas and the SO3 removed in the first absorber, and wherein cold tail gas from the first absorber is reheated and reoxidized in the last converter stage to SO3 which is recovered in the second absorber, the improvement which comprises, passing the hot gas from the furnace to a waste heat boiler where the gas is cooled to a temperature of about 520* to 620* C. which is then passed through a first heat exchanger and leaves the heat exchanger at a temperature of about 300* to 375* C., cleaning, cooling and drying said gas to a temperature of about 40* to 50* C. whereby to Provide cold gas, recycling said cold gas through a fourth heat exchanger serially coupled to the third catalytic converter stage, to preheat the cold gas to a temperature of about 225* to 300* C. following which the preheated gas is further heated in the first heat exchanger to a catalytic kindling temperature of about 410* to 450* C., passing said reheated cold gas through the first converter stage and partially oxidizing it to a temperature of about 560* to 620* C., passing the partially oxidized hot gas from the first converter stage through a serially connected second heat exchanger where the hot gas is cooled to a catalytic kindling temperature of about 440* to 480* C., passing the cooled oxidized gas through the second converter stage for further oxidation to a temperature of about 510* to 570* C. and from there through a third serially connected heat exchanger where the hot gas is cooled to a catalytic kindling temperature of about 420* to 450* C., further oxidizing the gas to a temperature of about 450* to 480* C. by passing it through the third converter stage, the hot gas leaving the third stage being cooled to a temperature of about 330* to 370* C. in said fourth heat exchanger, following which the gas is further cooled to 150* to 200* C. and passing through the first absorber, and removing cold tail gas from the first absorber at a temperature of about 60* to 90* C. and heating it to its kindling temperature of about 395* to 420* C. by passing it countercurrently and successively through the fourth, third and second heat exchangers, the heated tail gas being then passed through the last converter stage for final conversion to SO3 which is then recovered in the second absorber.

Claim 3

In an apparatus for producing sulfuric acid by the double absorption cold gas process using a group of at least four series-connected catalytic converters and a first and second absorber, wherein hot SO2 gas is first cooled, cleaned and dried to cold gas before subsequently reheating the cold gas, the catalytic conversion thereof to SO3, and recovery in the first absorber, the improvement characterized in: a. a furnace for generating hot SO2-containing gas, b. a waste boiler coupled to said furnace for receiving said hot SO2 gas, c. a first heat exchanger coupled to said waste heat boiler for removing heat from said hot gas, d. means for cooling, cleaning, and drying said hot gas series coupled to said first heat exchanger, said first heat exchanger being coupled to the input side of said cooling, cleaning and drying means, e. output means coupling said cooling, cleaning and drying means to said first heat exchanger, whereby to heat cold SO2 gas emanating therefrom to a catalytic kindling temperature, f. means coupling said first heat exchanger to the first converter, g. a second heat exchanger series connected between the first and second converter, for cooling the hot gas from the first converter, h. a third heat exchanger series connected between the second and third converter for cooling the hot gas from the second converter, i. a first absorber, j. means for conducting cold tail gas from the first absorber through a series connection through the third and second converter to heat said cold tail gas to its corresponding catalytic kindling temperature, k. means for conducting said heated cold tail gas from the second heat exchanger to the last converter for conversion to hot SO3, l. a second absorber, m. and means for conducting said hot SO3 gas from the last converter through a cooling means to the second absorber.