Development and applications of Baosteel sintering flue gas desulphurization technology

Baosteel Technical ResearchEnergy conservation andvolume 4. Number 2, June 2010, Page 5emission reductionrefaceSenior researcherDr. Ll Xianwei Division. Research InstituteBaoshan Iron Steel Co.Ltd.e ron and steel are among the most important fundamental and functionalnaterials in human society. They have been making huge contributions to theprogress and development of human beings. By means of a cleaner productionand a material and non-material recycle economy, iron and steel enterprisesare able to produce high quality, high performance and long life productswithout generating significant negative impacts on the environment. Unfortunately, ironmaking and steelmaking are always considered as big consumers ofenergy and resources, and are constantly connected with heavy pollutionIssues in relation to eco-environment have become essential to the develoment of the iron and steel industry. Adhering to sustainable development anda recycle economy is the only way for the iron and steel industry. Based onthe fact of global warming and deterioration of the ecological-environmentalsystem, energy conservation and emission reduction have become commontargets for the entire international community. This demands the iron and steelindustry makes corresponding reform to adapt itself to the new challenges. Wemust minimize the environmental impacts of the iron and steel manufac-turingBaosteel underlines environmental protection, implements a clean produc-tion, develops a circular economy and pursues sustainable development. It isenterprise to pass the Iso 14001 environmental certification in theChinese metallurgical sector and also the first enterprise to earn the title ofThe national environmentally-friendly enterprise in both the Chinesemetallurgical sector and locally in the shan凵中国煤化工 s specialcolumn has gathered five articles in the fielCN MH Tion andemission reduction. All these articles present Baosteels latest researdy2010Baosteel Technical Research, Vol. 4, No. 2. Jun.development and practice in the fields of energy conservation and emissionreduction. Among them, two articles present the development and applicationsof the Baosteel sintering flue gas desulphurization(FGD)technology and theexperimental study of using the sintering FGD byproduct gypsum as a cementretarder. One article describes the two-stage treatment process developed forthe stainless steel cold-rolled product pickling wastewater, and one refers tothe energy conservation and applications of the waste heat recovery system inannealing furnaces. Based on a large number of dioxin analysis practices, thequick qualitative analysis method of polychlorinated dibenzo-dioxins andfurans( PCDD/Fs) for samples from the iron ore sintering process wasproposed and discussed in another article. These articles provide a glimpse ofthe efforts made by Baosteel in the fields of energy conservation and emissionreductionI would hereby like to express my great appreciation to the editors of thespecial column and the authors for their diligence and contributions. Letmake joint efforts and build a greener and world-class baosteel中国煤化工CNMHGBaosteel Technical Researchlume 4, Number 2, June 2010, Page 7Development and applications of Baosteel sinteringflue gas desulphurization technologySHEN Xiaolin, uU Daoging, LIN Yu, SHI Lei and WANG RuyiEnvironment Resources Division, Research Institute, Baoshan Iron Steel Co, Ltd Shanghai 201900, ChinaAbstract: The research background and technical features of Baosteel sintering flue gas desulphurization( FGD)-swirl-jet-absorbing wet limestone-gypsum sintering FGD technology, process and equipment are introduced in this paper Maincontents and achievements of the pilot experiment and the engineering practice of Baosteel FGD are analyzed anddiscussed systematically. Past engineering practice experiences indicate that Baosteel FGD has the following merits: wideapplicability to sintering flue gas features, such as frequently changing temperatures, unstable SO, concentration, intensivelyfluctuating flow rates, etc., high pollutants removal efficiency, low investment and energy consumption; stable and reliableKey words: sintering flue gas; desulphurization technology; engineering practicedoi:10.3969/j.issn.1674-3458.2010.02.0022 Main characteristics of sintering flue gas1 ntroductionThe characteristics of sintering flue gas, which areIn recent yearsofradically different from those of the coal-fired flue gasChina keeps increasing year by year, and the iron and from power plants, are mainly summarized as followssteel works have been one of the main sources of so,(1)The flow rate of the flue gas fluctuates violentlyemission, where SO, emitted from the sintering process (0. 5 to 1.5 times of the designed value)accounts for more than 60% of the total(2)The SO, concentration in the flue gaemission of the entire iron and steel industrygreatly. The SO, concentration responds to thefore, sintering flue gas desulphurization( FGD has in the mineral sulphur content, which are 300been the key issue to control SO, emission in China. 2000 mg/Nm in most cases, with the maximum beingDue to the complicacy ofthe agglomerating and over 7000 mg/Nm, and the minimum belowsintering process, the technology of FGD used in power 300 mg/Nmplants cannot be directly or simply applied to sintering(3) The flue gas temperature varies greatly, which isFGD. The FGD technologies used in the iron and steelnormally 80-160C, with the maximum being 180Cindustry of developed countries are either too expensive(4)The main components of sintering dust areto be accepted by the Chinese companies, such asminerals and their oxides, of which Fe,O, accounts foractivated carbon adsorption, ammonia-ammonium over 40%, with heavy metals, alkali metals, etc, andsulphate, etc, or their byproducts are not comprehen- the micron or sub-micron particles amount for oversively utilizable, such as maximized emission reduction 60%of sintering( MEROS ) circulating fluidized bed for(5)The contents of HCl and H are high, whichflue gas desulphurization(CFB-FGD )and limestone five times more than those of coal-fired flueemission control ( LEC ) etc. Therefore, the technormally from power plants.ologies of sintering FGD in China was listed as an(6)The oxygen content is high, which is aboutimportant research topic in The guideline of the 16%, much higher than that of coal-fired flue gas fromdevelopment of science and technology in the iron and power plants( which is normally 6%)steel industry until 2020. Since there has been veryTherefore, the FGD technologies utilized in powerlittle research and few technologies in this field, it is of plants cannot be directly or simply applied to sinteringgreat significance to develop novel sintering FGDFGD. It is of great urgency to develop a specialtechnologies with the characteristics of high efficiency, sintering FGD technology in conformity with China'shigh adaptability, cost-effectiveness, safety and reliabi- actual conditionsty in operation for the Chinese iron and steel中国煤化工companies. Against this background, Baosteel took the 3 CrFGDlead in the sintering FGD technology research andCNMHdevelopment in the beginning of 2005According to the manufacturing characteristics ofCorresponding author: SHEN Xiaolin: E-mail: xlshene baosteel comBaosteel Technical Research, VoL 4, No 2, Jun. 2010large-scaled sintering machines, with the consideration of 3.1 Process flowthe desulphurizer, the application of byproducts, and theflue gas from the main suction fan isactual conditions of the companies, we thoroughly pressurized by the booster fan. After being cooled andcompared and analyzed the existing FGD technologiespretreated in the cooling device, the flue gas enters theChina and abroad. In view of the characteristics of the swirl-jet absorber with the desulphurization reactionsintering flue gas,we chose the wet-type limestone- finishing there. Finally, the purified flue gas meetinggypsum sintering FGD technology as the basis of the the requirements of the standard is discharged fromtechnical route, and carried out the specific industrial the chimney after demisting. The auxiliary systemsperiments and research. Finally, we developed a such as the limestone slurry preparation and thepackage of key process and equipment technologies- gypsum dehydration systems are the same with otherBaosteel swirl-jet wet limestone-gypsum sintering FGD wet limestone FGD systems, which are mature(named Baosteel sintering FGD for short with self- techniques. The process flow diagram of Baosteelowned intellectual property rightsFGD is shown in Fig. 1sintering flue gas Cooling pretreatment devin. Swirl-ict absorberLimestone powder bunker1+留Process watcrFig 1 Process now diagram of Baosteel FGD3.2 Technical featureshave difficulties in adjusting large flue gas flow rate(1)Due to the characteristics of the sintering flue fluctuation. Furthermore, the sO, concentration isgas, which contains high contents of HF, HCl, heavy low, so the desulphurization efficiency of the absorbermetals and alkali metals, and is easily corrodible, must be high. Therefore, the reaction container wassticky and scalable, a cooling device is set up before designed as the swirl-jet absorber on the basis ofthe absorbing tower with the following functionsaerodynamic principle, which has the following(a) Cooling down the flue gas, ensuring the safetcharactensticsof the absorbing tower and providing the best tem- (a) The limestone slurry in theber isperature condition for desulphurization reaction. It continuous phase: the flue gas in a dispersion phasehelps prevent the gas-gas heater GGH ) from erupting from the gas-swirI-jet-hole is divided intoblocking in the conventional FGD process and fine bubbles in the absorber. Then the gas and theenhance the cooling efficiencylimestone slurry react thoroughly and violently at highb) The heavy metals, alkali metals and some dusts mass transition efficiency.in the flue gas are removed by the device, which is (b) This process can keep the system runninguseful to restrain the blocking problem and scale stable at high desulphurization and dust eliminatingformation in the absorbing tower and improve the efficiencies. The absorbing reaction can be completedquality of gypsum.at中国煤化工 cycle the limestone(c)Most of the HF and HCl in the flue gas are slurryremoved by the device, which can abbreviateCNMH Gs well-crystallizedcorrosion for the material of the absorbing tower and with a larger particle size and easy for utilizationother subsequent devices(3)The top of the absorbing tower has large space(2)The conventional spray tower and the CFB for the sudden expansion of the fluewhichSHEN Xiaolin, et al. Development and applications of Baosteel sintering flue gas desulphurization technologyoutside demisterform an operation exceeded two years, during which a series ofintegrated demister in order to guarantee high demis- difficult technical problems were tackled, and thetechnological processes and equipments were optim3.3 Mechanism of the chemical reactionized the design parameters and the operation controlexperiences of large-scaled engineering practices wereAfter being cooled and pretreated in the cooling finally achieveddevice, the sintering flue gas enters the pressure-stabilizing part in the middle of absorber. The flue gas 4.1 Pilot experiment plantdevice in the gas injecting pipes. Under the driving experiment plant is composed of six parts, inct. pilotthen is sprayed into the slurry tank via the swirl-jetAs a complete and typical processing unit, thegas pressure, the bubbles are injected from the pipes, the SO, absorption subsystem, the limestone slurrygenerating a fierce colliding, shearing, rotating and preparation subsystem, the flue gas subsystem,thegypsum dehydration subsystem, the water processblended and intensively interfered gas-liquid two-system and the distributed control system( DCShase turbulence zone and greatly elevating the gas- etc, and therefore, the experimental data derived fromiquid mass transition efficiency. During these proceit can represent the real conditions when applied tosses SO, in the flue gas dissolves in the liquid phase large-scaled engineering practices. The whole technto undergo chemical absorption reaction. The bubbles ological process can be briefly described as: afterin the turbulence zone continue to ascend until they pressurized by the booster fan, the sintering flue gasburst at the upper portion of the slurry surface, so the enters the preprocessor for cooling down, and thenwhole washing process of the flue gas is completedenters the swirljet-absorbing-tower for desulphtThe resultant calcium sulfite is further oxidized to be tion and dust removal: after released from thecalcium sulfate in the slurry tank by the oxidation air.absorption tower and defogged the clean gas is heatedThe ph value of the slurry tank is designed to be by the main gas duct and discharged through thebetween 4.2 and 5.5, which is relatively lowcompared with that of the conventional technologThis relatively low pH value makes the limestone 4.2 Technical development and achievements indissolute more quickly and completely, and the fast the pilot experiment plantoxidation and the perfect oxidation system under adesulphurizelow pH condition is one of the key factors to ensure ciency was studied, and the main factors and thethe absorbing tower runs safely. Air is blown into the essential knowledge of how to ensure a long-timeslurry to drive CO2 out and oxidize the reaction continuous and stable operation of this desulphurizaproducts to be utilizable gypsum. The matured gypsum tion system was capturedslurry is discharged from the bottom of the absorbing(2)A variety of swirl-jet-apparatuses and coolingtower and enters the subsequent gypsum dehydrating pretreatment methods were studied, technological procesystem,so that the slurry concentration can be sses, technological parameters and internal structuremaintained within the range from 10%0 to 20%configurations of key equipments were optimized,aThe retention time of the slurry in the tank is numerical simulation of the sintering FGD system wasdesigned to be 10 h to 20 h, in order to ensure developed, the optimal design parameters were ascersufficient time for the chemical reaction in thetained and a series of correlated thermodynamic andabsorbing tower. There are five reaction processes kinetic computation modules were establishedgoing on in the tank simultaneously, which occur inthe bubble region and finish in the reaction region(3) The pilot test was continuously conducted to(1)Absorption: SO2(8)+HyO+S02(1)+H, 0- the process of sintering FGD, such as the rules and aseek and identify all kinds of possible problems duriH·+HSO1→2H+SOsolutions of clogging, fouling, corrosion, etc., and the(2)Dissolution: H"+CaCO, Ca+hcO3control standards when the technology was put into(3)Neutralization: H"+HCO3-H,O+cO2;engineering practice, such as the key parameters, the(4)Oxidation: HSO,+1/2 02(1)S02+H* instrument arrangement and the control strategy wereSo+1/2O2(1)→SOformulated(5)Crystallization: Ca+S0,+1/2H,0-+(4)In order to deal with bottom slurry turbulenceCaSo, 1/2 H,O(s)uncertainty and to meet the requirement for liquidCa+SO:+2H, 0--CaSO,' 2H, O(s)surface smoothness, a side-entry slurry agitation andforced oxidation arrangement test was conducted,duringniels were established4 Pilot experimentvanos中国煤化工 re identified,thepackaglence and forcedIn October, 2006, a pilot experiment plant with a oxidatiCNMHGtimal engineeringcapacity of 90000 m/h flueeatment was built, allocation plan according to the flue gas processingand under real sintering flue gas conditions, capacity was formulatedomprehensive tests were carried out. The continuous(5)Corrosion coupons were put at the differentBaosteel Technical Research, Vol 4. No. 2. Jun. 2010positions eight positions in total ) to test over sintering FGD gypsum, it was found that, gypsum100 pieces of 48 kinds of anticorrosion materials produced with this technology had a large particlewithin this system, aiming at providing support for diameter, high-degree crystallization, low water con-engineering material selection; more than two kinds tent (s 10%, after dehydration ) low impurityof special anticorrosive clay material for the sintering content, high CasO, 2H2o content(> 90%),aFGD project were developed, and the engineering neutral pH value, and little heavy metal, and thereanticorrosion drafts throughout the system were fore, it met the utilization requirements. Moreoverfigured outrelative studies were carried out, such as mixing theOn the basis of the research and the test mentioned gypsum into fine steel slag powder or fine mineralabove, feasibility research approaches, project preli- slag powder to replace cement with a large utilizationminary designs and correlated key equipments design quantity and an excellent utilization effectproposals of three sets of large-scaled sintering mach(10)By analyzing the characteristics of sinteringines fGD projects with different flue gas processing desulphurization wastewater and developing watercapacities and flue gas characteristics were designedand formulatedtreatment and recycling technologies, special waste-(6) Research on the emergent procedures in thwater treatment technologies and proposalscase of unexpected problems occur during the operadifferent site conditions were figured outtion of large-scaled projects were conductedA.(7)A series of packaged technologies involving 5 Practical applications of Baosteel sinter-equipment of the desulphurization system wereing FGDevelopedAfter evaluated by experts, Baosteel decided to(8)On the basis of the pilot test, the operating commercialize the Baosteel sintering FGD technologyrules, the technical requirements and the criteria of theoverall commissioning program, the systems start-up 5.1 Scale of the desulphurization projectand shut-down under all kinds of conditions were Table I shows the basic conditions of threeformulated for large-scaled desulphurization projects(9)After analyzing the characteristics of theTable 1 Basic condition of three application projectsFull RGD project of Meishan Iron& Full FGD project of the Stainless Full FGD project ofSteel Company 3180 m2Steel Business Unit 1"224Baosteel3”450m2sintering machinesintering machinentering machDesigned flue gas tlow450000-900000500000-10000001000000-1800000ratc/(Nm3·h-)700000( Designed value)875000( Designed value) 1300000( Designed valueSo, concentration/1000-300000-11601800( Average)500( Average)Flue gas temperature/'C130-1705.2 Process performance guarantee valuesBaosteels 3 sintering FGD project and the 1Desulphurization efficiency >90%;Sintering desulphurization project of the StainlessSO, discharge concentration<100 mg/NmBusiness Unit were both completed and put intoDust discharge concentration $50 mg/Nmoperation by the end of October 2008, and all of theirCa/S≤1.03technical and economic indexes have met the designed&& Desulphurizer: ground limestone(250 meshes)andoned limestone mud from lime-roasting workFollowing are the operating conditions and results ofthe sintering FGd project of Meishan Iron SteelWater-drop content in demister exit gas <75 me/Nm':Company.Gypsum quality: CaSO, 2H,0>90%5.3.1 Pollutants removal effectsWater content≤10%pH value: 6-8As shown in Figs. 2-5, the automatic on-linemonitoring data are as follows the flue gas treatment5.3 Project operating conditions and resultscapacity fluctuates between 700000-500000 Nm/hThe 3" sintening FGD project of Meishan Iron & withinno Nm/h. the flueSteel Company reached a full-load operation on April g中国煤化工110-140℃.he20, 2008. The whole system has since then been keptCNMHGfluctuates aroundrunning stably and continuously for more than one and 1500 ing/tie average ou? outlet concentrationa half years, with the desulphurization efficiency and in the cleaned flue gas is below 70 mg/Nmand thethe synchronous running rate both exceeding 95%desulphurization efficiency maintains 95%SHEN Xiaolin, et al. Development and applications of Baosteel sintering flue gas desulphurization technologyx750675ErIcErFig. 2 Variations of the flue gas volumes at the inletg14210flue gas temperatures at the inletry的4小的Fig 4 Variations of the SO, concentrations at the inlet昌Fig 5 Variations of the SO, concentrations at the exitEven under the condition of violent fluctuation of average energy consumption is 2190 kWh, which isflue flow rates, flue temperatures and SO, concentra- less than the designed value of 2800 kWh. Thetions, the economical desulphurization efficiency is systems average water consumption and the waste-90%, and the system can run steadily at a desulph- water volume are 32 2 th and 2. 5 th respectivelyurization efficiency rate above 95%. The dust removal less than the designed values of 33 th and 3 thefficiency rate is over 85%, and the removal effici- respectively. Wastewater can be sent to the in-plantency rates of So,, HCl and HF are 2 50%, >80% wastewater treatment facility, then returned to theand 90%, respectively. Furthermore, the removal sintering process for recycling; meanwhile, the"whiteefficiency rate of dioxin ranges from 24% to 60% on smog" discharged from the chimney is collected andaverage of 40%. The pH value of the condensed fluid detected at the exit at a low temperature, and the phof"white smog"discharging from the chimney is 6.0 value of the condensate is over 6.0, ruling out theto6.5possibility of acid rainAs far as byproducts are concerned the sintering The synchronous operation rate of the FGD systemdesulphurization gypsum from the project is of high and the sintering machine is above 95%. After a longpurity( CaSO. 2H,0>90%)with excellent crys- time of operation, during a scheduled shutdown for thetallization and low impurities, and its quality is better maintenance of the sintering machine, inspection wasthan that of the desulphurization gypsum from coal- carried out with no damage of anticorrosive materialfired power plants and natural gypsum, fully meeting no rusting and spot corrosion near the welding seamsthe requirements for construction materials in China.er wall, inside theflue ga中国煤化了et hole found5. 3. 2 Project operation resultsTheOn the basis of the analysis of the data for long- operatiCNMHG requires simpleuIn ugi aimable logic contro-term operations, the systems operation drag loss is ller(PLC)control system is used in the desulphuri-around 3 100 Pa, and Ca/s is 1.03, both of which are zation system and the control operation of allin conformity with the original design. The systems equipment can be fulfilled at the PLc interface. ForBaosteel Technical Research, Vol 4, No. 2. Jun. 2010the 3 sintering FGD project of Meishan Iron Steel sintering flue gas, the three sintering FGD projectsCompany, the desulphurization system is maintained mentioned above can reduce about 13000 t of soy a collaborative company affiliated to Meishan iron emission, and save industrial discharge taxes of aboutSteel Company, and the operators were fully CNY 16. 38 million per year. A small amount ofcompetent after short-term trainingdischarged wastewater can be reused within the5. 3. 3 Investment and benefit analysissystem, and the byproducts of gypsum can be utilizedomprehensively. Therefore, Baosteel FGD is an energyAs far as the 3 sintering FGD project of Meishan saving and emission-reducing technology, which meetsIron Steel Company is concerned, its flue gas the requirements of a recycling econ-omy.treatment capacity is 700000 Nm/h and the initialinvestment is CNY 58 million. According to thestatistical analysis of the production report and the 6 Conclusioncalculations of energy consumption, water consump-The Baosteel sintering FGD technology wastion and limestone powder consumption, the desulphdeveloped especially for the complex characteristics ofurization cost per ton agglomerate is about CNY 5, sintering flue gas, which had many advantagesafter deducting the SO, pollution charge and the including high desulphurization and dust removalgypsum income, the desulphurization cost per ton efficiencies, stable operation, simple process, cheapagglomerate is only CNY 2. Under the condition of absorbent, utilizable byproducts, and advanced techno-processing the same quantity of exhaust gas, compared economic indicators, etcwith other wet FGD and CFB semi-dry FGD technTherefore. as a mature. reliable advanced, economologies, the initial investment and running cost of ical, environmentally-friendly and recyclable technBaosteel sintering FGD is 709-80% of those of ology, Baosteel FGD technology has an extensiveother FGD technologiesapplication value to the FGD of large and medium-In short, the 3 sintering FGD project of Meishan sized sinteringIron Steel Company has the following merits(1)This sintering FGD project has been ademonstrative project of environmental protection inthe Nanjing district, Jiarovince, which greatlyreduces SO2, dust and other pollutants emission andsignificantly improves the quality of ambient airsurrounding Meishan iron Steel CompanyAfter being put into operation, the 1"sintering FGDproject of the Stainless Steel Business Unit andBaosteel No. 3 sintering FGD project can fulfill theSHeN XiaolinLIU DaoqingLIN YUSO2 emission reduction task given by the MunicipalGovemment of Shanghai, and create sound environ-mental conditions for the sustainable development ofBaosteel(2) Through independent developition, Baosteel has solved a difficult problem in thesintering FGD project, which has not only filled thetechnical void in the iron and steel industry, but alsocreated a positive social image of BaosteelSHI LeiWANG Ruyi(3)According to the actual sulphur content in the中国煤化工CNMHG