Combustion Characteristics of Polyethylene and Coal Powder at High Temperature

Availableonlineatwww.sciencedirect.SciencedirectJOURNAL OF IRON AND STEEL RESEARCH, INTERNATIONAL, 2008, 15(1): 06-09Combustion Characteristics of polyethylene andCoal Powder at High TemperatureLONG Shi-gang, CAO Feng, WANG Si-wei, sun Liu-henPANG Jian-ming, suN Yu-ping(School of Metallurgy and Resource, Anhui University of Technology, Ma'anshan 243002, Anhui, China)Abstract: To study the combustion characteristics of the polyethylene(PE)particle and coal powder at blast temper-ature of the blast furnace, the contents of Co and CO2 of off- gas during the combustion of Pe particle and coal pow-der at the 1 200 C and 1 250 C were measured using carbon monoxide and carbon dioxide infrared analyzer, andhen the corresponding combustion ratio was calculated. The results showed that when the temperature is high, thecombustion speed of Pe and coal powder is high and the corresponding combustion ratio is high. Whereas, the com-bustion speed and ratio of Pe are much higher than those of coal powder.Key words: polyethylene; coal powder; combustion characteristicThe process of injecting waste plastic into blastTable 1 Chemical composition of raw materialfurnace was first developed in Germany in 1994 andRaw materialHAshthen in JapanI 3. The process has been in operationPE85.6014.210.19for over 10 years. The practice revealed that,todate, the process is the best way for treating wasteCoal powder82.504.321.460.381.34plastic. The energy utilization of waste plastic canexceed 80%, and the percent of hazardous gas, suchThe simulated blast temperature in combustionas dioxins, produced are not higher than that pro- test was set at 1 200 C and 1 250C, respectively.duced without injecting waste plastic.The experiment apparatus is shown in Fig. 1. TheThe combustion of waste plastic injected in a mass of the sample was 0. 5 g in each single subblast furnace was investigated[3, 43. In this study, the stance combustion test with an airflow of 1 L/min.combustion characteristic of polyethylene (PE)and In the test, different amount of Pe and coal powdercoal powder at 1 200C and 1 250C was studied, were mixed according to the desired proportion toand the effect of grain size and reaction temperature observe the combustion characteristics of PE andon the combustion rate of PE and coal powder under coal powder mixture. The mass of the sample wasthe experimental condition was investigated1.0 g in each mixed sample combustion experimentwith an airflow rate of 1 L/min. The Co and cO21 Expermental Procedurecontents in the off-gas were determined using an inThe pe was granulated into particles of 0-3 mm, frared gas analyzer online. To compare the combus-3-5 mm, and 5-10 mm as the sample through the tion ratio of different samples, the CO and cO2 vol-light heating granulated plastification 5, 6 The coal umes in the off-gas were calculated as well as thepowder was collected from Ma'anshan Iron and Steel corresponding carbon contents in the samples. Thecompany. The chemical composition of raw materi- combustion ratio was defined as the ratio of the carbonals is shown in Table 1content value to the original carbon content valueFoundation Item, Item Sponsored by National Natural Science Foundation of China(50274001)Biography:LONGShi-gang(1941-),Male,Professor,E-mail:longs2004@yahoo.com:RevisedDateJanuary23,2007YH规Issue 1Combustion Characteristics of Polyethylene and Coal Powder at High Temperaturein the off-gas approaches zero and the co2 amountreaches a peak value of 4. 5%-6.0% after 4-6 min.The whole combustion reaction is complete in 30 minMeanwhile, it can be seen that the particle sizeof Pe has the obvious effect on the peak value and凶66the peak position of co and cOz content. The finer14the pe particles, the larger the peak value of COcontent and the nearer the peak position of co to thegrid origin. Whereas, the cOz content curve is com-Gas cylinder 2--Stabilizing valve: 3--Flow meter4-Electric resistance furnace, 5--Ceramic boat, 6-Sampleparatively scattered the larger the PE particles, the7-Temperature control device; tHermocouple;longer the time needed until the disappearance ofg--Pretreatment: 10-Filter 11--Sand-corefiltration ballCO2 in the off-gas. Thus, it can be seen that the lar12--Three-way valve: 13--Co infrared analysis instrument;ger the pe particles, the slower the combustion14-CO2 infrared analysis instrumentrate. The results of the effect of Pe particle size onFig. 1 Sketch of combustion experimental apparatusthe combustion rate in this study are in agreementRef [3 ]and Ref. [4]2 Results and discussionFig 2(b)shows that the combustion situationof different particle size of pe at 1 250C is similar2.1 CO and CO2 content in combustion off-gas of pe on the whole. The content of Co reaches a peak valwith different particle sizeue of about 3. 5% in less than 1 min and then decreaFig 2 shows the CO and Co contents in the off- ses gradually to zero in 2. 5 min, The CO2 content reagas after combustion of Pe at 1 200C and 1 250 C. ches a peak value of about 5% after 3 min, and thAss seen irlFig 2(a), the Pe decomposes quickly whole combustion reaction is complete in 25 minat a high temperature, The air supply amount is alwaysComparing Fig. 2 (a)with (b), it can be seenin a shortage state in the initial 100 s; therefore, the that the whole combustion reaction at 1 250C iscombustion is incomplete and the off-gas is mainly faster than that at 1 200 C. The combustion rateCO. The content of Co reaches a peak value of difference of PE with various particle size is much4.0%-4.5% after about 1 min with the little CO2. obvious at 1 200C and is not so obvious at 1250 CBut, after the combustion reaction, the amount of The reason is that the reaction speed is much fasterthe decomposed plastic decreases, which consumes at higher temperature, which weakens the influenceless oxygen than before. Therefore, the COz amount of PE itself. Therefore, at 1 250C, there is almostproduced from the combustion also increases, and the no influence on the combustion process for the Pecompleted combustion gradually occupies the domi- particles smaller than 10 mm.nant position. After about 3-4 min, the CO content2, 2 CO and cO2 content in off-gas produced by coal60a)Aa_CO2(0-8mm)760powder combustiona-CO(0-3 mmb一CO2(8-6mm){4.0Fig. 3 shows the CO and CO2 content in the offb-Co(8-5 mm)gas after combustion of coal powder at 1 250 C2.0c-CO2(5-10mm)2.0c-CO (5-10 mm)It can be seen from Fig 3 that the combustionca-cO2(0-3mm)60emho0of coal powder at 1 250C belongs to a complete com60bustion reaction, which produces almost no carbon monoxide. In addition, the combustion time (about 40 min)4.0b-0(5m0408of coal powder is longer than that of the Pe (aboutb-co 3-5 mm)20 min). It can be attributed to the fact that the PE20bC0(5-10mm)2.0can be decomposed to combustible gas at high tem0perature. Thus, the combustion of pyrolysis gas in0200600l00014001800the oxygen supply condition is a gas-gas reaction,hich carries out more quickly than the combustionFlg. 2 CO, and Co content in off-gas of different size ofof coal powder, Coal powder is mainly constituted bPE at I200℃(a) and at1250℃(b)carbon, and at high temperature the produced amountJournal of Iron and Steel Research, InternationaVol. 15is 75%,78%, and 82%, respectively.9090From Fig 4, it can be concluded that the finer707.0the Pe particles, the lower is the combustion ratio5.0of the pe. The reason for this is that the finer the3.0PE particles, the larger is the contact surface area ofCO1.0PE, and the faster is the burning speed at high tem5001000150020002500perature, which result in the partial unburned pyrolTime/sysis gas being taken out of the combustion area to-Fig 3 CO2 and Co content in off-gas ofgether with the off-gas.coal powder at1250℃By comparing Fig 4(a)and (b), it can be con-luded that the PE samples with the same particleof pyrolysis gas is much less than the plastic. There- size have a higher combustion ratio at 1 250C thanfore, the combustion of coal powder belongs mainly at 1 200 C. This is because the burning rate of PEto a gas-solid reaction, w hich has a very low comis higher at the higher temperature than at the lowerbustion speed. Meanwhile, the continuous in- temperature, which correspondingly leads to a high-troduction of fresh air in the com bustion area can er combustion ratio. Therefore, the reaction timesupply oxygen for the com bustion of coal pow- required to approach the highest combustion ratio isder, which leads to the output of only carbon di- also shortened, At 1 200 C, it needs 1 000 soxide in the off-gas during the com bustion of coal whereas at 1 250 C, it only needs 800 spowder.Fig 5 shows that the combustion ratios of PEare influenced by particle size, and the regularity is2. 3 Combustion ratio of pe and coal powdervery clear. In the initial period of burning, 200Fig 4 shows the combustion ratio of Pe with 600 s, the combustion ratio of small particles of PEdifferent particle sizes at1200℃and1250℃.is higher than that of large particles either at 1 200 CIt can be seen from Fig 4 (a) that at the tem- or 1 250C. But after 1 200s, the combustion ratioperature of 1 200C after 1 000 s, the final combus- of large particles of pe is higher than that of smalltion ratio of PE with thc particle size of 0-3 mm,3- particles of PE; just as the aforementioned reason,5 mm, and 5-10 mm is 73%,78%, and 80%, re- the experimental condition can not provide enoughspectively. Whereas, at the temperature of 1 250c oxygen to burn Pe.after 800 s, the final combustion ratio of pe withFrom Fig. 5, it can also be observed that ththe particle size of 0-3 mm, 3-5 mm, and 5-10 mm combustion ratio of coal powder is always lower thanthat of Pe before 1 200 s. Of course, rising temperature can increase the combustion speed and ratio of70coal powder such as PE50Particle size/mm5-10100Particle size/mum800100012000-3Time/s▲5-101-PE(0-3mm)1200℃;2-PE(3-5mm)1250℃;3-Coal1200℃;4-PE(0-3mm)1250℃20600800l0001200Time/s5-PE(5-10mmn)1200℃;6-Coal1250℃;7—PE(3-5mm)1200℃;8-PE(5-10mm)1250℃Fig4 Combustion ratio of pE with different particleFig 5 Comparison of combustion ratio betweensizes at1200℃(a) and at1250℃(b)PE and coal powder万数据Issue 1Combustion Characteristics of Polyethylene and Coal Powder at High Temperature(3) The combustion ratio of coal powder is lower3 Conclusionshan that of pe under the experimental condition(1)The particle size of pe has some influenceReferenceson the combustion process at 1 200 C. Namely, thecombustion speed of the small particles is higher [i] Janz ], Weiss W. Injection of Waste Plastics Into Blast Furnacethan that of the large particles. At 1 250C, the sizeof Stahlwerke Bremen [j]. La Revue de metallurgie-CIT1996,93(10):1219of Pe had little influence on the combustion process[2] Minoru Asanuma, Tatsuro Ariyama, Michtaka Sato, et al.Limited by the oxygen supply conditions in the testCombustion and gasfication Behavior of Waste Plastics Injec-tube, the larger the Pe particles, the longer the timeted Into blast Furnace [J]. 1998 ICST/Ironmaking Conferencerequired to finish the pyrolysis process. Therefore, theProceedings, 1998, 57: 525taking out of the unburned pyrolysis gas amount to- [3] Yoshitsugu lino, Steps Toward Building an EnvironmentallyAdvanced Steel Works [J]. NKK Technical Review, 2003gether with the off-gas is also less. The combustion(88);28ratio of pe is different in the initial 200-600 s, and [4] Dongsu Kim, Sunghye Shin, Seungman Sohn, et al.Wastethe ratio of smaller particles is higher than that ofPlastics as Supplemental Fuel in Blast Furnace Process: ImproPE with larger particles, but in contrast with the in-ving Combustion Efficiencies [J]. Journal of Hazardous Mate-rials,2002,94B(10):213itial period, after 600 s, the ratio of pe with larger[5] LONG Shi-gang, MENG Qing-min, WANG Zhi-quan, et al.particles is higher than that of PE with finer partiGranulating for Waste Plastics by light Heating Plasticizationcles.and Environment Protection J]. Journal of Anhui University(2) The combustion ratio of pe at 1 250C isof Technology, 2003, 20(4): 278(in Chinese)[6 MENG Qing-min, LONG Shi-gang, WANG Zhi-quan. Thehigher than that at 1 200 C. The experiment temStudy on the Softing Character and Light Heating [j. Journalperature has obvious influence on the combustion raof Anhui University of Technology, 2003, 10(4): 106(in Chitionese)