United States. Patent D

_‘ 2,831,762 United States. Patent D ice , Patented Apr.‘ 22, 1958 1 2 ately after leaving the converter to such an extent that 2,831,762 the oxidation of FeO to Fe2O3, possible only at a certain TREATING CONVERTER WASTE GASES temperature, cannot take place whereas the carbon r'non oxide is still oxidized to form carbon dioxide. Thus Roland Kemmetmuller, Vienna, and Rudolf Rinesch, Linz the heat-delivering combustion of the iron compounds to (Danube), Austria, assignors to Waagner-Biro Aktien gesellschaft, Vienna, Austria, an Austrian ?rm, and form Fe2O3 is prevented. Vereinigte Osterreichische Eisen- und Stahlwerke Ala Since the formation of Fe2O3 has been prevented the tiengesellschait, an Austrian ?rm exhaust gases contain only iron carbon compounds or iron oxygen compounds of black or grey colour and with N 0 Drawing. Application April 4, 1955 10 particle sizes much above that of Fe2O3. Serial No. 499,245 Furthermore, the concentration of dust in the exhaust Claims priority, application Austria April 6, 1954 gas stream is multiplied by the reduction of the quantities of gas compared to the previous processes. This facili 2 Claims. (Cl. 75-60) tates substantially the removal of the dust particles from In the conventional converters for re?ning iron or non 15 the exhaust gas stream. ferrous metals with air-oxygen-enriched air or pure oxy The reduction of the heat of the exhaust gases enables gen, the emaust gases from the converters were mixed a reduction in the size of the cooling plant and ‘a more with fresh air and the resulting mixed exhaust gas was favourable utilization of the dust recovered. All iron fed to exhaust gas cooling and gas cleaning plants. compounds excepting FezOa are readily utilized and can Exhaust gases from converter plants operating on pure 20 be returned to the steel making process. oxygen consist mainly of carbon monoxide and oxygen As has ‘been mentioned, extremely high temperatures and contain substantial quantities of metal vapours and are required for igniting the iron compounds leaving the solid metal particles entrained from the metal bath during converter, which are relatively slow in combustion so the re?ning process. In converter plants operating on that the previous process required waste heat utilization normal air or oxygen-enriched air the exhaust gases con plants having large combustion spaces and very large tain also nitrogen. In converters which are used, e. g, heating surfaces. for making steel, the solid particles escaping in the exhaust Thus the process according to the invention, in which gas consist mainly of FeO, FesC, FeCO3, in granular form. only the heat produced from the carbon monoxide is The exhaust gases leave the mouth of the converter at utilized, leads to much smaller and less expensive plants. temperatures between 1600 and 1800 deg. C. Behind, 30 The reduction of the quantity of gas entails also an i. e., after leaving the converter outlet the solid particles economy of power in the exhaust fans because in a given are oxidized in the presence of an excess of air to form plant the resistance varies with the square of the rate. mainly Fe2O3, which causes the known intensive red As has been mentioned the high dust concentrations colouring of these particles because Fe2O3 is the only iron due to the smaller quantities of exhaust gases are a spe oxygen compound of red colour. As has been mentioned 35 cial advantage particularly where wet cleaning plants vare the exhaust gases from converters operating on air or oxy used. The residual particles leaving the stacks behind such gen contain nitrogen, which retards the oxidation to Fe2O3 plants are grey in colour and thus give a pleasant appear so that in these plants the escaping particles do not or only ance compared to the previous plants, which discourage at a later time disintegrate to Fe2O3. The particle sizes dark-red smoke clouds from the stack. of the iron compounds FeO, Fe3C and FeCO3 are in the 40 In view of the great variation in the quantity of carbon order above 1 micron. When these compounds are oxi monoxide (CO) during the blowing period the invention dized to form Fe2O3 they disintegrate to form particles provides for controlling the oxygen supply in harmony smaller than 1 micron. That reduction in particle size with the quantity of carbon monoxide. In converters renders the removal of these particles from the exhaust fed with oxygen at an even rate the oxygen surplus in or gases most difficult. behind the converter will vary owing to the uneven for The disintegration of the afore-mentioned iron com mation of carbon monoxide. In another precess step pounds to form Fe2O3 takes place at temperatures be that surplus of oxygen may be compensated by a supply tween 1600 and 2000 deg. C. in the presence of surplus of substances such as carbon monoxide or other oxygen oxygen. combining gases. Plants have been constructed in which such exhaust We claim: gases containing these ?ne dust particles are conducted 1. A process for treating the exhaust gases from a steel through gas cooling and cleaning plants. All these proc making converter containing carbon monoxide and solid esses employ oxygen in a larger quantity than is necessary particles consisting mainly of FeO, Fe3C and FeCOs by for the theoretical combustion of the CO gas escaping admixing an oxygen containing gas with the exhaust gases from the converter. This is the cause of the afore formed in the converter and after such gases have left mentioned formation of Fe2O3, which involves the afore the converter, substantially in such an amount as is descri-bed disintegration of particles and intensive red required for the theoretical combustion of the carbon colouring of the escaping exhaust gases. The large excess monoxide but insu?icient to oxidize iron compounds to of air also causes a considerable increase in the quantities Fe2O3. of gas so that unduly large exhaust gas cooling and clean 2. A process for treating the exhaust gases from a. ing plants are required. steel making converter containing carbon monoxide, It may be mentioned that in plants Where the exhaust metal vapors and solid particles consisting mainly of FeO, gases contain also nitrogen the particle sizes are almost Fe3C and FeCO3 by admixing an oxygen containing gas ten times larger than in plants operating on pure oxygen. with the exhaust gases formed in the converter and after All disadvantages described hereinbefore are avoided such gases have left the converter, substantially in such according to the invention by admixing oxygen to the an amount as is required for the theoretical combustion carbon monoxide containing exhaust gases and vapours of the carbon monoxide and cooling the exhaust gases formed in the converter substantially only in such a quan from the converter immediately after leaving the con tity as is required for the theoretical combustion of the verter to a degree that oxidation of metal vapors and carbon monoxide formed in the converter. 70 metal particles to form Fe2O3 is inhibited in the presence In a development of the process the temperature of of surplus oxygen. the exhaust gases from the converter is reduced immedi (References on following page) M ‘3 > ‘ ' 2,831,782 ~ I. . .. > 4 Y j~ 1' ' References Cited in the ?le of this patent 1,889,757 Miller L. ______- Dec. ‘6, 19-32 _ , _ 1,902,160 Frazer et a1. ______.... Mar. 21, 1933 . UNITED STATES PATENTS 2,014,044 Haswell ______Sept. 10, 1935 981,280 Jones ______Jan. 10, 1911 2,107,549 Schmalfeldt ______Feb. 8, 1938 1,507,740 Kirby ______Sept. 9, 1924 5 2,373,244 Holz ______Apr. 10, 1945 1,742,750 1 ,Bradley ______Ian. 7, 1930 2,409,825 Ban'ngoltz ______.__ Oct. 22, 1946 1,780,833 McGurty ______..‘_._..-_ NOV. 4, 1930 ‘ 2,729,301 Ekstrom ______Jan. 3, 1956