Study on Combustion Characteristics of the Blast Furnace Gas in the Constant Volume Combustion Bomb

Transcription

1 Proceedings of the 7th WEA International Conference on Power ystems, Beijing, China, eptemer 15-17, tdy on Comstion Characteristics of the Blast Frnace Gas in the Constant Volme Comstion Bom IU YONGQI, WANG HAIFENG and I PING chool of Transportation and Vehicle Engineering handong University of Technology Zhangzho Road 12#, Zio CHINA liyq65@163.com, wanghaifeng198207@163.com, pinger2863@gmail.com Astract: - Blast frnace gas is the yprodct of smelting steel prodction process, and is the important secondary energy sorce. It is can e sed as fel for engines to generate electricity for most middle and small steel enterprises. In order to nderstand the comstion mechanism and provide the asis for the design of last frnace gas engine,premixed laminar comstion experiments of the last frnace gas-air mixtre were performed in the constant volme comstion om. The effects of the eqivalence ratio, the initial pressre, the initial temperatre and the diverse components of last frnace gas on laminar comstion velocity and flame transition velocity were investigated. The reslts indicate that the comstion velocity increases when the eqivalence ratio is close to the academic air-fel-ratio ( Φ =1. 0 ), and the maximm appears at the eqivalence ratio of Premixed laminar rning velocity of the last frnace gas-air mixtre decreases with increase in the initial pressre, and it increases with rising of initial temperatre. An increase of the amont of comstile gas in varios components last frnace gas can agment the nmerical vale of the laminar rning velocity and help to comstion. Key-Words: - Constant volme comstion om; Blast frnace gas; Comstion characteristic; aminar rning; Brning velocity; Premixed rning 1 Introdction Blast frnace gas is the yprodct of smelting steel prodction process in steel enterprises, and sally is composed of 22-26% CO, 16-19% CO 2, 1-4% H 2 and 58-60% of N 2 y volme. Becase CO and H 2 are comstile, last frnace gas is the important secondary energy sorce. In recent years, more and more attention is paid to the tilization of last frnace gas along with the high opinion to environmental protection and the redction energy consmption in China. It is regarded as an effective method to tilize last frnace gas to generate electricity [1]. The technology sing last frnace gas as fel for engines to generate electricity rings a new way for most middle and small steel enterprises to recycling and tilizing last frnace gas. Blast frnace gas is a kind of fel with low heat vale and varios components. The comstion characteristics of last frnace gas have important inflences on the performances and staility of engines. However, to the est knowledge of the athors, no stdy has een carried ot to systemically investigate the comstion characteristic of last frnace gas in engines. In this stdy, asic experiments were performed to investigate the comstion characteristics of last frnace gas in a constant volme comstion system, which facilitates nderstanding of the mechanism and provides the asis for the design of last frnace gas engine. 2 Experimental Detail 2.1 Experimental apparats Fig. 1. ketch of the experimental apparats

2 Proceedings of the 7th WEA International Conference on Power ystems, Beijing, China, eptemer 15-17, As shown in Fig. 1, the constant volme comstion test eqipment is composed of the constant volme comstion om ody, temperatre control system, mixtre spply system, ignition system, synchronal time series control system and comstion data captre and analysis system etc. The constant volme comstion om is the comstion chamer, in which last frnace gas and air mixtre is rned. There is a qartz glass oservation window at the side face of the om to facilitate captring the rning images. The temperatre control system was sed to heat premixed gas to the needed temperatre. Mixtre spply system was sed to confect varios composition mixed gas that consists of last frnace gas and air according to gas part pressre law. Ignition system was sed to ignite the mixtre, and synchronal time series control system was sed to keep synchronization of data collection with the ignition moment. The processes of ignation and flame transmission inside constant volme comstion ws screened and recorded y a high-speed camera with an image intensifier. The prssre of ning gas was measred y a pressre sensor, and was carried to high-speed data collection system (DEWE2010). 2.2 Experimental procedre Becase the component and concentration of the last frnace gas (BFG) is varios, three kinds of typical last frnace gas were tested in this paper, as shown in Tale 1. The effects of the eqivalence ratioφ, initial pressre P 0, initial temperatre T 0 and the components of the last frnace gases on the laminar comstion velocity was investigated. The eqivalence ratioφ ranged from 0.7 to 1.4. Initial pressre P 0 ranged from 100 to 2000kPa. Initial temperatre T 0 ranged from 300 to 700K. Tale 1. Three typical last frnace gas components BFG1 BFG2 BFG3 CO 20% 25% 25% CO 2 18% 18% 18% H 2 0% 0% 2% N 2 62% 57% 55% transition speed can e given as follow y the relation of the flame radis and time [2]: dr P = (1) dt in which, r is the flame radis otained from the high-speed images, and t is time. The expression of laminar rning velocity is ρ dr ρ = P = (2) ρ ρ dt In formla (2), P is spread flame transition speed. ρ is the rned gas density, which can e gotten y thermal eqilirim comptational procedre. ρ is the nrned gas density, which is characteristic parameter of initial state. Flame stretch rate α is defined that the logarithm of infinitely small area on the flame srface take derived nmer to time. d( ln A) 1 da 2 dr 2 α = = = = P (3) dt A dt r dt r aminar flame rning velocity and flame stretch rate are approximate linear relation[3], namely = α (4) in which, (or )is withot stretch (plane) flame laminar rning velocity in the formla. 3 Reslts and Discssion Fig. 1 shows the variale crve of the laminar flame radis with time for last frnace gas 2-air mixtre with Φ =1. 0, P 0 =100kPa and T 0 =300K. It is clearly that the laminar flame radis increases slowly in the eginning, then increases rapidly, and increases gently in the end. 2.3 Data Processing For premixed laminar comsting of the mixtres in constant volme comstion om, spread flame Fig.2. aminar flame radis verss time Fig.3 gives the variale crves of the comstion pressre with time for different eqivalence ratio for last frnace gas 2 and air mixtre with P 0 =100kPa

3 Proceedings of the 7th WEA International Conference on Power ystems, Beijing, China, eptemer 15-17, and T 0 =300K. It can e seen that the eqivalence ratio of mixtre has important effects on the pressre in chamer. For the eqivalence ratio of 1.0 and 1.15, the pressres rise qickly, and the maximm appears at the eqivalence ratio of The rning pressre vales of the very rich mixtre sch as Φ= 1. 4 and very lean mixtre sch asφ = 0. 7 are oviosly lower than that of the mixtre with eqivalence ratio of velocity of the last frnace-air mixtre decreases with increase in the initial pressre when the initial temperatre is constant. It s de to the integrated reflection of the diffsiility, the exothermic capacity and the chemic-reaction velocity. Fig.3. Comstion pressre verss time Fig.4 illstrates the variale crves of the laminar rning velocity for last frnace 2-air mixtre with eqivalence ratio. The initial condition is P 0 =100kPa and T 0 =300K. The laminar rning velocity increases when the eqivalence ratio is close to the vale of 1, and the maximm appears when the eqivalence ratio is eqal to On the contrary, the laminar rning velocity of the very dense or very rare mixtre decreases. The comparison of this stdy with other reslts of stdy [5] is also shown in the figre. They are similar. Fig.5. aminar rning velocity verss initial pressre Variation of the laminar rning velocity with initial temperatre is shown in Fig.6, with the initial condition of P 0 =100kPa andφ = 1. The laminar rning velocity increases with the increase in the initial temperatre. The reason is that rned gas temperatre T increases along with the increase of the reactant temperatre or named initial temperatre T, which reslts in the increase of laminar rning velocity. Fig.4. aminar rning velocity verss eqivalence ratio. The relationship etween the laminar rning velocity and the initial pressre at 300K is shown in Fig.5. The reslts indicate that the laminar rning Fig 6 aminar rning velocity verss initial temperatre Becase of the changeale particlarity of the last frnace gas composition, the effects of components of last frnace gas on comstion process shold e stdied. At the same time, the contents of CO and H 2 are mainly considered. Effects of the composition of the last frnace gas on the laminar rning velocity is shown in figre 7, with

4 Proceedings of the 7th WEA International Conference on Power ystems, Beijing, China, eptemer 15-17, the initial condition of Φ =1. 0, P 0 =100kPa and T 0 =300K. rning velocity or demonstrate the not changing mch t slowly increasing trend. The effect of temperatre on laminar rning velocity is a little igger than that of pressre after nfired area. Fig.7. aminar rning velocity verss composition of last frnace gas The reslts indicate that the more content of CO in last frnace gas, the rapider the laminar rning velocity rises. The main flammale composition in the last frnace gas is CO. N 2 and CO 2 in the last frnace gas can e regarded as the residal waste gas. Therefore, that the content of CO is high means less qantity of the residal waste gas in the last frnace gas. As well know, the smaller the residal waste gas, the larger the laminar rning velocity. If some hydrogen is mixed, comstion will e frther speeded. aminar rning velocity increases to some extent with the increase in the proportion of mixed hydrogen. It is de to the qicker rning velocity of the hydrogen than that ofco. Experimental reslts in an engine have already een proved that mixing hydrogen in fel can help to comstion, increase the reaction rate and improve the rning velocity [7]. Ths the performance of comstion and emission of the engine can e improved. It can also e fond from Fig. 7 that, with the increase of the flame radis, laminar rning velocity pts p the trend that slowly increases generally, t the range increased is qite small for the certain composition of last frnace gas-air mixtre. The reason is that the qality of fired mixed gas increases with the increase in the flame radis, and the pressre and the temperatre of nfired mixtre increase gradally ecase of the nfired mixtre is compressed y fired mixed gas. Otherwise, the laminar rning velocity redces when the pressre of nfired mixtre increases, t ecomes large when the temperatre increases. In this way, the common effects of the changes of pressre and temperatre of nfired mixed gas makes the vales of laminar 4 Conclsion The premixed comstion of the last frnace gas-air mixtres was investigated in the constant volme comstion experimental apparats, and the effects rle of the eqivalence ratio, the initial pressre, the initial temperatre and the variale components of last frnace gas on the laminar rning velocity was otained. The reslts show that the laminar rning velocity is effected seriosly y the eqivalence ratio, and its maximm appears when the vale of eqivalence ratio is aot The laminar rning velocity decreases with the increase in initial pressre and it increases with the increase in initial temperatre. The more amont of comstile gas (main to Caronic oxide), the igger laminar rning velocity or flame transition velocity is. The laminar rning velocity will increase with the increase in hydrogen fraction in mixtres. In a word, if the comstion ecomes etter, then the initial pressre shold e decreased, the initial temperatre shold e increased, the comstile gas fraction in mixtres shold e more mch and appropriate eqivalence ratio shold e chosen. Acknowledgements This stdy was financially spported y the Natre cience Fondation of handong Province (No. Y2006F63) and References: [1] C.G. i,.. n, Technology of tilizing last frnace gas to generate electricity, handong Internal Comstion Engine, No.4, 2004, pp [in Chinese]. [2].Y.iao, D.M. Jiang, J. Gao, et al., Measrements of Markstein nmers and laminar rning velecities for liqefied petrolem gas-air mixtres. Fel, Vol.83, 2004, pp [3] D.M. Jiang, Comstion and Emission of Internal Comstion Engine, Xi an Jiaotong University plishing hose, [in Chinese]. [4] T. Iijima and T. Takenno, Effects of Temperatre and Pressre on Brning Velocity, Comstion and Flame, Vol.65, 1986, pp [5] X.J.Yan, D.M. Jiang, A stdy on the laminar flame characteristics of methane-air-dilent

5 Proceedings of the 7th WEA International Conference on Power ystems, Beijing, China, eptemer 15-17, mixtre, Transactions of Chinese ociety for Internal Comstion Engine, Vol.18, No.4, 2000, pp [in Chinese]. [6] H.. G, tdy of comstion model for appliance on spark ignition engine felled y varios components coal ed methane, Chinese Internal Comstion Engine Engineering, Vol.25, No.5, 2004, pp [in Chinese]. [7] Y. Zhang, Z.H. Hang, Q.Wang, et al., Flame propagation characteristics of natral gashydrogen-air mixtres, Transactions of Chinese ociety for Internal Comstion Engine,Vol.24, No.6, 2006, pp [in Chinese].