Affecting Factors and Improving Measures for Converter Gas Recovery

Availableonlineatwww.sciencedirect.com° ScienceDirectJOURNAL OF IRON AND STEEL RESEARCH, INTERNATIONAL. 2007, 14(6):22-26Affecting Factors and Improving Measures for Converter Gas RecoveryWANG Ai-hua, CAI Jiur-ju', LI Xiu-ping, WANG Ding Zhou Qing-an(1, School of Materials and Metallurgy, Northeastern University, Shenyang 110004, Liaoning, China;2. Energy Department, Baoshan Steel Co Ltd, Shanghai 201900, China)Abstract: To change the undesirable present situation of recovering and using converter gas in steel plants in China,the basic approaches to improving the converter gas recovery rate were analyzed theoretically along with the changecurves of the converter gas component content, based on the converter gas recovery system of Baosteel No. 2steel-making plant. The effects of converter device, raw material, air imbibed quantity, recovery restricted condition, andintensity of oxygen blowing on the converter gas recovery rate were studied. Among these, the effects of the air im-bibed quantity, recovery restricted condition, and intensity of oxygen blowing are remarkable. Comprehensive meas-ures were put forward for improving the converter gas recovery from the point of devices, etc, and good resultswere aKey words: steel plant; converter gas, recovery rate; affecting factorConverter gas is an important secondary energy common task of most domestic steel plants s)resource for steel enterprises, and is also one of theBased on the lt converter gas recovery systemeak points in the recovery and utilization of sec- of Baosteel No. 2 steelmaking plant, the factors andondary energy resources. Improving the converter the comprehensive measures of improving thecon-gas recovery rate can effectively reduce the produc-. verter gas recovery rate were investigated in thistion cost of steelmaking, laying the basis for"minus study.energy steelmaking",. and can remarkably decrease 1 Brief Introduction of Converter Gas Recov-the total quantities of pollutant emissions to realizecleaner production. Thus, " converter gas recoveryery Systemis an important technology in modern converterThe converter gas recovery system in No. 2steelmaking, and is regarded as one of the important steelmaking plant is an Lt system introduced fromtechnologies spread emphatically during the 10th Australia, and its working principlefive-year plan -a1Fig1(6. It mainly consists of flue gas coolingThe converter gas recovery system has long cleaning and recovcry, and dust pressing. Comparedpipes and complicated equipment, and several affect- with the traditional wet dust removal systeing factors. The literatures show that the recovery main technique traits are as follows. First, its highand utilization of converter gas are not satisfactory dust removal efficiency with the dust content in re-in most domestic steel plants, and its recovery rate covered gas less than 10 mg/mallows the converterlags behind the international advanced levell. This gas to be utilized directly by users. Secondly, it canwastes abundant energy resources and seriously pol- recover ferrous dust block of 50 000 t per year,andlutes the environment. Therefore, quick mastery of returns to the converter to replace iron ore for rawthe converter gas recovery technology, the complete materials. Thirdly, it does not cause secondary polexhaustion of equipment potential, and the safe and lution and sewage retreatment, and thus saves theeffective recovery of converter gas have become the energ中国煤化工 renter gas recoveryFoundation Item: Item Sponsored by National Natural Science Foundation of ChinaCNMHGBiography:WANGAi-hua(1976-),Male,DoctorCandidate:E-mail:wangaibua1976@yahoo.com.en:RevisedDateMay24,2006No 6Affecting Factors and Improving Measures for Converter Gas Recovery23·2 Analysis of Factors Affecting Converter Gas/tera arang conn DirrDissipation furnelRecoIn the smelting process, the converter producesDhrst ratchera large quantity of hot flue gas, which can becomethe available converter gas through the recovery sys-pe嶼tem. The data for the change of CO and O2 contentCoarse dust Rotary kInein converter gas during the smelting process areFg 1 Converter gas recovery process of LT systemnormal production conditions, and the scatter dia-grams of the content changing with the smeltingrate is very high. Therefore, the recovery process of time are obtained from the data, as shown in Fighe"LT"method has greater economic benefits andFig 2 indicates that: (1)during the smeltinenvironmental benefitsprocess, the Co and O2 content dots are always dis-O, content changeFlg 2 Change of Co content(a) and O, content(b)in converter gas with smelting timeributed on both sides of the two average curves, converter gas recovery quantity wasf obtainedwhich represent the rule of the content of CO and O2. through the gas caloric value multiplying the flowchanging with the smelting time. (2) Both the pro- rate of flue gas and converted by standard heatingduction quantity of CO and the content in converter value(8 360 kJ/m ) Fig 3 indicates that since thegas are different because of the different reaction flow rate of flue gas remains stable, the changing inmechanisms in the forepart, metaphase, and telo- stances of converter gas recovery can be known byphase of converter smelting, and the CO quantity investigating the changes of unit volume caloric val-and its content in converter gas reach the highest ue of converter gas. In Fig. 3, t, is beginning time oflevel in the smelting metaphasegas recovery and tr is ending time in the present re-covery condition. The unit volume caloric value of2.1 Approaches for improving converter gas recov- converter gas can be obtained by the area connectingery rateabc-d-ef-a in the Fig 3. Improving the unit vold Whether the converter gas must be recovered ume caloric value of converter gas indicates the im-pends on the content of Co and O, in the flue gas. provement of the converter gas recovery rate, name-The converter gas recovery restricted condition of ly, requirement to increase the integral area of theNo. 2 steelmaking plant is that the content of Co is changing curve of the co content to the smeltinggreater than or equal to 40% while that of O, is less time under the recovery conditions. Under the nor-than 1%. according to the content change average mal--.L- L-sic measures to in-curves of CO and O2 in Fig. 2, Fig 3 is obtained.中国煤化工creasprove the converterAccording to the integral principlethe unit gasCNMHG()The extensivolume caloric value of converter gas was obtained of recovery time, which indicates that the added are-by integrating the changing curves of the CO content as of polygons a-b-ba-a and effe are the inin recovery time with the smelting time, and the. creasing amount of unit volume caloric value of con-Journal of Iron and Steel Research, InternationalVol. 14molten iron. According to the operational data underthe normal production situation in No 2 steelmakiplant, the effects of raw material and carbon contentin molten steel are given in Table 1. according toTable 1, raw material and carbon content obviously20ANd erde wuaffect the converter gas recovery rate per ton steelespecially the molten iron ratio in raw material2. 2. 3 Air imbibed quantitySmelting time/minuring converter smelting, the entering ofFig. 3 Analysts of improving means for converter gas recoverysmall quantity of air into the inteeen themobile smoke cover and the converter mouth mayverter gas, if the beginning time r, is brought for- easily cause the second burning of gas so as to dete-ward to t, while the ending time tr delayed to ty,. riorate it in quality. Here, the concept of"air im-(2)On this basis, increasing the ascending rate of bibed cocfficicnt", represented by a, is introduced toCO content(namely, the slope k,=tan& represen- describe the effect of the air imbibed quantity fromting the ascending rate)during the smelting forepart the converter mouth on the converter gas recoveryand the descending rate during the telophase (name- rate. The air imbibed coefficient indicates the pro-ly, the slope k2=-tanB representing the descend- portion between the air imbibed quantity from theing rate), thereby decreasing the time required by converter mouth and the theoretical air quantity re-the CO content to reach the metaphase, namely, the quired to burn all the converter gas, a affects bothascending curve bc of the Co content is changedthe gas quantity and its unit volume caloric value,b-c, and the descending curve d-e is changed to d'- The increase of a causes CO in the gas to fire, ande, and thus, the added areas of polygons b-bc-c'-b' the caloric value of gas and the converter gas recov-and e - are the increasing amount of unit ery rate to decrease. Theoretically, if a=1y, CO involume caloric value of converter gas. (3) Finally, if the gas is burnt completely, and the caloric value ofthe Co content value is increased from cd to gh gas is zero if a=0, the Co content in the gas readuring the smelting metaphase, the integral area is ches the highest, and the recovery quantity conver-added with the area of the polygon cd'-h-g-c, and ted to the standard caloric value of gas is also thethus, the caloric value and recovery rate of converter highest. At present, the air imbibed coefficient ofgas are improved correspondingly.converter smelting in No. 2 steelmaking plant is be-tween 0.09 and 0. 16, weakening the converter gas2.2 Factors affecting converter gas recovery raterecovery leveL. Therefore, the smaller the a, theSeveral factors affect the converter gas recovery larger is the converter gas recovery rate. Accordingrate, which must be researched from aspects such as to the computational analysis, the converter gas reconverter device, raw material, carbon content in covery rate per ton steel can be increased by 0. 92 m/tmolten steel, air imbibed quantity, recovery re- if a is decreased by 0. 01.stricted condition, and intensity of oxygen blowing 2. 2.4 Recovery restricted conditionbased on the above theoretic analysis.To ensure the safety of gas2. 2. 1 Converter equipmentthe requirement of gas quality by users, relevant re-Whether the converter runs well or not directly stricted condition must be set, The restricted condi-affects the quantity of converter gas recovery, espe- tion directly affects the beginning and ending time ofcially the allotment state of gas tank capacity and thesers'application amount. The situation of supplyTable 1 ErEcts of raw material and carbon content inbeing more than demand will not allow complete re-molten steel on converter gas recovery ratey of converter gas andConverter gaspointlessly. The low Co content in the gas analyzerJyH中国煤化工recovery rate/also affects the converter gas recovery rate.2.2.2 Raw material and carbon content in molten steelCNMHG士1%±1016The converter gas is mainly produced by the Carbon content change in raw material of *o 17. *0.650carbon oxidation of the decarburization process from Carbon content change in molten steel of #o 1%to650No 6ffecting Factors and Improving Measures for Converter Gas Recoveryrecovery, namely, the length of the recovery time.(1) Consummating soft and hard wares and re-Improving the restricted condition will prolong the alizing total recovery from every convertertime and increase the quantity of converter gas re-Good operation of the gas recovery system is thecovery. For instance, Masteel changes its recovery basic premise for the gas's high efficient recovcryrestricted conditions of converter gas from CO grea- Since the measure scope of co content in the Ltter than or equal to 30% and O2 less than 1. 5% to converter gas analyzer is only 85%, the gas contai-co greater than or equal to 18% and O2 less than ning more than 85% of Co content is ignore1.5%, so as to add 0. 5 min of recovery time and in- Therefore, the measure scope of co content in thecrease 3 m of the converter gas recovery rate per ton analyzer must be modified to 100%, and then thesteel in a safe situation[7. If the recovery restricted converter gas recovery per ton steel can be increasedcondition in No. 2 steelmaking plant is improved by 1.8msuch that co is greater than or equal to 30% and O,At the same time, the connecting pipes can beis less than 1%, the converter gas recovery rate per constructed between the converter gas tank in No. 2ton steel can be increased by 1.52 msteelmaking plant and other gas tanks, which can2. 2.5 Intensity of oxygen blowingsolve the gas dissipation problems and relieve theIn the converter smelting metaphase, a large gas tension of other gas tanks in supply.quantity of carbon begins to be oxygenated in the2) Lowering smoke cover appropriately whilemelting pool. Here decarburization is the main reac- controlling slight differential pressure in convertertion in the converter, and the speed of decarburiza- mouth and improving quality of recovered gastion mainly depends on the intensity of oxygen blo-In the production operation, the afr imbibedwing. The higher intensity will improve the ascend- quantity is mainly affected by the size of interspaceing speed of the co content in the prophase and the between the mobile smoke cover and the converterdescending speed in the telophase, and thus increase mouth and the slight differential pressure in the conrthe converter gas recovery rates. If the intensity of verter mouth. Therefore, in the converter smeltingoxygen blowing of No. 2 steelmaking plant is in- process, the smoke cover must be strictly lowered increased from 2.9 m/(mint)to 3. 5 m /(mint), the lowest position as early as possible, and be keptthe smelting time can be shortened within 1l min at zero distance from the converter to prevent the airand the converter gas recovery per ton steel is in- from being imbibed to cause the second barning andcreased by 7to ensure the quality of the recovered gas. At the3 Improving measures for Converter Gas re- same time, the slight differential pressure in theconverter mouth must be appropriately controlledcovery Ratekeep the mouth in a slight positive pressure, to limitTo define the potential of converter gas recovery is the negative effect of air imbibed, and to improveof guiding significance to analyze and solve the prob- the quality of the converter gas.lems existing in the gas recovery and to take relevant(3)Optimizing oxygen blowing system and ac-measures. Here, the concept of"ideal converter gas tualizing high efficient smeltingrecovery ratio"is introduced to describe the maxi-The converter gas recovery can be efficientlymum potential of the gas recovery quantity, which improved by optimizing the oxygen blowing systemimplies that the quantity of converter gas is recov- appropriately controlling the oxygen lance positionered from the production of per ton molten steel un- while considering the relationship between converterder the ideal conditions. For instance, in the con- decarburization and gas recovery,. reducing convertverter of No. 2 steelmaking plant, the ideal gas re- ers second pouring down, and increasing the endcovery rate per ton steel is calculated as 128. 8 m point hitting rate At present, the intensity of oxy-under the ideal conditions]. Based on the compari- gen blowing is about 2. 9 m/(mint), and is ustson between the ideal quantity and the actual data ally b5 m/( min.t)aver the safety con-106.5 m/t, the present converter gas recovery cerns中国煤化工 premise, the con-udy can be developed more intensively. Therefore,vertCN MH Gan be increased byit is necessary to consider the weakness of the pres- 7 m /min.t) if the intensity ot oxygen blowing isent production and take related measures to signifi- increased to 3. 5 m/(min t)cantly improve the converter gas recovery rate.(4)Improving measures and operation of re-Journal of Iron and Steel Research, InternationalVoL 14covery and prolonging converter gas recovery time. ' sent converter gas recovery level in No. 2 steelmak-The practice shows that part of the converter ing plant is not satisfactory. The situation of con-gas cannot be recovered for the lag effect, because verter gas recovery and energy saving can be greatlysome time is required to switch the valve from accep- improved using compressive measures such as bette-ting the command to acting completely. Therefore, ring the technology and equipment, lowering theaccording to the successful experience in Masteel], converter mouth appropriately while controlling thethe present condition for gas recovery in No. 2 steel- slight differential pressure in the mouth, and opti-making plant can be modified to co greater than or mizing the oxygen blowing system, etc.equal to 30% and O less than 2%, and the begin- Referencesning timethe ending time is de[1 LIU Liu, YU Zhi-xiang, XIAO Zhong-min. Development andlayed so as to increase nearly l min of recovery timeProspect of Converter Steel Making Technology [J].Chinaand then the gas recovery per ton steel can be in-Metallurgy, 2001,(1):17creased by 2.52 m"/(mint)[2] WENG Yu-qing. Scientific and Technological Progress of MetFurthermore, it is also necessary to reinforceallurgical Industry in China at the Beginning of 21st Centurthe management and promote the information ex[J]. Iron and Steel, 2004, 39(1): 1-8, 16(in Chinese).[3] YIN Ruiyu. Steel Plant Models and Industrial Ecological Chi-changing and cooperation between the operators ofa-on Future Development Model of Steel Industry [A].Ironthe converter recovery system and the energy re-d Steel, 2003, 38(Supplement): 1-12.source center to ensure safe and efficient converter [4] WENG Yuqing. Current Status and Prospect of Energy Savingand Environment Protection of Chinese Steel Industry [J]. Chi-na Metallurgy, 2003,(11) 1-7(in Chinese).4 Conclusions[5 YU Bo. Comprehensive Measures for Improving Rate of coverter Gas Recovery [n]. China Metallurgy, 2003,(10): 14-(1)The basic measures of improving the convert17(in Chinese)er gas recovery rate are theoretically defined alor[6] CHEN Zhi-bin, The Current State and Development of Recov-ery and Utilization Technology of Domestic Converter Gas U]with the changing curves of the converter gas comMetallurgic Power, 2003.(1):9-12 (in Chineseponent content.[7] SHI Cuibi, CHEN Guang-yan, SHI De-ming, ct al. Minus(2) The factors affecting the converter gas re-Energy Steel Making Practice of Magang 95 Ton Convertercovery include the converter device, raw materialU]. Metallurgical Environmental Protection, 20043(in Chircarbon content of molten steel, air imbibed quanti- [8] YU Xiao-fang, YANG WeZHENG Cong-jie, Study onty, recovery restricted condition, and intensity ofIncreasing the Intensity of Supplying Oxygen in Converter [J].oxygen blowing; the effects of the air imbibed quanJournal of Iron and Steel Research, 2000, 12(2): 6-9(in Chi-tity, restricted condition, and intensity of oxygenblowing are especially remarkable.[9] LI Xiu-ping, CAI Jiu-ju, YIN Rui-yu, et al. Study on mini-mum Energy Coi of Converter Procedure [I]. Iron(3)Compared to the ideal recovery rate, the pre-and Steel, 2003, 38(5):50-52 (in Chinet中国煤化工CNMHG