Disposal of Waste Plastics With Traditional Coking Process

Available online at www.sciencedirect.comBCIENCE)DIn.CT.@oJOURNAL OF IRON AND STEEL RESEARCH, INTERNATIONAL. 2006, 13(1): 05-09Disposal of Waste Plastics With Traditional Coking ProcessCAI Jiu-ju' ,YU Guang-wei'，LIAO Hong-qiang2 ，QIAN Kai，ZHAO Pen2，HE Ya-bin2(1. State Key Laboratory of Bioindustry, Northeastern University, Shenyang 110004，Liaoning, China;2. Shougang Technical Research Institute, Shougang Group, Beijing 100041, China)thermo- balance and a 10 g atmospheric fixed bed reactor, the thermo gravimetric behavior and product were studied dur-ing co-coking of WP with blended coal. And then, using a coke- oven with capacity of 200 kg, the characteristics of prod-ucts were assessed. The results showed that there is an overlapping temperature range (200 - - 550 C) of decompositionbetween WP and blended coal, and the pyrolysis synergism index η and synergism strength β proposed could evaluate thesynergism between them. 1% of added WP results in the maximum synergism in all series experiments. The increase ofadded WP decreases the synergism. Tar yield in co-coking is increased with the decrease of water yield for synergism.Moreover, it was also found that the quality indexes of coke, such as Mp, Mo，CRI and CSR, are degraded with the in-crease of WP until 4%，though the quality of tar and gas is optimized for WP addition.Key words: waste plastics; coal; cokingNowadays，the accumulation of mixed wastethe process was researched.plastics ( WP) results in a serious environmental and1Experimentaleconomic problem in the world. The conversion ofWP to useful products may be a promising method1.1 Compositionof solving the problem resulted from “white pollu-The composition of WP and blended coal used istion”. Presently， the most common ways to dealgiven in Table 1.with WP, such as landfilling，recycling and inciner-ation etc. ，do not appear to be the most adequate1.2 Apparatus .solution since all of them are associated with various(1) Thermo- balanceenvironmental problems， as second environmentalThe WCT- II thermo-balance produced by ATI-pollution-. Therefore, a new alternative technolo-CHAN Co，Ltd. of American was used. Its sensi-gy for treating WP with coking process was pro-tivity is 10-6 g and the sample weighs 200 mg. Theposed, which is characterized by high efficiency-2.3] .sample was heated from ambient temperature to 900By co-coking with blended coal, WP can be conver-Catarateof80"C/minandkeptat900Cfor7ted into coke, tar and gas. This process differs frommin. The atmosphere used was nitrogen at 0. 1 MPathe conventional plastics treatment in possibility ofwith a flowrate of 180 mL/ min.recovery of high added value products. In present(2) Atmospheric fixed bed reactorstudy，further investigation on co-coking of WFTypically, 5 g sample was fed into the fixed bedfrom municipal solid waste in Beijing and the blen-reactcetirote, the wield of pyrolysis prod-ded coal of Shougang coking plant was studied withucts,中国煤化工nperature to 900C ata thermo- balance and a 10 g atmospheric fixed beda rate.YHCNMHGergasusedwasnitro-reactor. Meanwhile, using a pilot 200 kg coke-oven,gen at 0.1 MPa with a flowrate about 10 mL/ min.Foundation Item: Item Sponsored by National Natural Science Foundation of China ( 50334020) and Foundation of Science and TechnologyComittee of Beiing of China ( H020620330310)Biography:CA1 Jjiu-ju(1948-)，Male, Doctor, Professor; E-mail: ygwneu@ sina. com; Revised Date: April 12. 2005●6.Journal of Iron and Steel Research, InternationalVol. 13Table 1 Composition of WP and blended coal in mass percent%_Component analysis (dry)Element analysisVolatileAshFixed carbonSHNOBlended coal23.409. 5267. 08.0.7975. 914.59 1. 1717. 54Waste plastics87. 965.326.72.0.0672.1111.46 0. 2016. 17(3) 200 kg coke-ovenblended coal more conveniently, new factors, namedA 200 kg coke-oven was used to study the char- as volatile release index D(%/ °C8) and pyrolysis syn-acteristics of product including coke, tar and gas.ergism index η, are defined by Eqn. (1) and Eqn. (2).Firstly，WP was cut into particles of 3- 5 mm byD=(dv/dt)ax/(tmxX Ot1/2)1)the crusher, and then the WP particles were mixed(2)with the blended coal by different ratios beforeφcharged into coke- oven. After co-coking ，the where ( dv/dt )max is maximum derivative of mass,strength and reactivity of coke were determined b(%/C); tmx is temperature at which maximum ratedrum tests and CO2 tests respectively. The tar wasof mass loss occurs, C; Ot1/2 is interval temperatureanalyzed by GC/MS and coke-oven gas was investi- zone at the temperature of (dv/dt)/(dv/dt)mx = 1/2，gated by gas detector.C; φ is percentage of added WP, %; D。is calculat-ed volatile release index, (%●"C- -3).2 Results and DiscussionBy calculation with Eqn. (1) and Eqn. (2)，the2.1 Thermo-gravimetric analysis resultspyrolysis characteristics are given in Table 2.The measured thermo- gravimetric TG and DTGFrom Fig. 1 (a) and Table 2, it can be seen thatcurves and theoretical ones for blended coal， wastefor the blended coal, tmax and tend are higher thanplastics and their mixtures with different ratios arethose of waste plastics， while ( du/dt)max is muchdisplayed in Fig. 1, where mixed powder 1 consistsless. The Ot1/2 for coal is 56 C larger than that ofof WP of 1% and coal of 99%; mixed powder 2 con-WP. Their difference in the thermal behavior couldsists of WP of 2% and coal of 98%，and mixed pow- obviously be attributed to different molecular struc-der 3 consists of WP of 4% and coal of 96%.tures. WP has relatively simple composition and unitIn order to study the effect of added WP on the molecular structure, and consequently, the tempera-100[ (a)- Coal72.0 105 F)0.161.30WP0.12,WP1.20.080.885Theoretical value---- Experimental vaJue0.0440} 0.47Coal20 L105@.20 105|(d| 0.24t 0.160.2095|95t 0.12| 0.1235 t0.08 85. Experimental valuI 0.04一1中国煤化工7576YHCNMHG=0L0100300700900500Temperature/C(a) WP or coal;(b) Mixed powder l;(c) Mixed powder 2; (d) Mixed powder 3Fig. 1 TG/DTG curvesNo. 1Disposal of Waste Plastics With Traditional Coking ProcessTable 2 Calculated pyrolysis characteristics of samplesItemCoalWP1%WP + 99%Coal 2% WP+ 98%Coal 4% WP+ 96 %CoalMeasured value0.144 11.787 90. 14200.14680. 1623(dv/dt)mx/(%●C-1)Theoretical value0.160 00. 17500. 2070513501519524527tmax/C9842108107101012/C939074DX10-6/(%. C-3)2. 809 084.966 32. 53282. 61863.049 23. 35373.952 15. 4528-0. 82090. 666 80. 600 9ture range of pyrolysis is relatively narrower. ButTable 3, it is clear that the main pyrolysis productsfor coal, it is a mixture of macromolecular skeletonfrom WP are 64% of tar, 30% of gas and 6% ofand mobile small molecules trapped in it，and its pycoke without water. The main pyrolysis productsrolysis temperature must be wider.from blended coal are 66. 2% of coke， 21.2% ofFig.1 (b) and (c) and Table 2 also obviouslygas，4% of tar and 8. 6% of water. The yield ofshow that with the increase of added WP, the values products from co- coking varied with the percentagesof (dv/dt)max，tmux and D are increased, but Ot/2 is of WP added. .decreased due to quite different pyrolysis characteris-Compared with the calculated values, the meas-tics of WP. Comparing TG/DTG curves, it can beured values of water yield is lower and tar yield isfound that the experimental value is greater than thehigher. The reason may be that there is a strong .theoretical one in the WP decomposition temperaturesynergism between coal and WP in the overlappingrange (200- 550 C)，which suggest that there is a decomposition temperature range (200一550 'C) whichstrong interaction between coal and WP with the in-have been described in the thermo- gravimetric analy-creased WP addition. In other words, the synergism sis. The radicals produced by WP act as a hydrogenoccurs between them， because different radicals donor to the radicals from coal because its hydrogenfrom coal and WP interact with each other in the o-is rich and more radicals like OH●and H●in coalverlapping temperature region during the co-cokingare transferred to the oil but not to H2O.of coal and WP. To better describe the synergismTheoretically, the difference of calculated andoccurring，the pyrolysis synergism index is proposedmeasured co- pyrolysis products shows the synergis-here. It was found that the maximum synergism istic behavior. In order to quantify the extent of theobtained with adding WP of 1%，and the synergism .synergistic effect between WP and coal in the fixedis decreased with the increase of WP added.. bed reactor， a term named “synergistic effectstrength”is proposed, which can be expressed bythe relative change between measured and calculated2.2 Product analysisvalues, and the formula is given as follows:Table 3 gives the products from co. coking op,=(W.- zk,W,.)/ zk,W.;X 100(3)WP and blended coal with the fixed- bed reactor. FromTable 3 Produets from co-coking of blended coal and WP with 10 g fixed-bed reactorWater/%Coke/ %Tar/%Gas/%TotalSamplemass/ gMeasuredCalculated Measured Caleulatedinred_ Calrulated Measured Caleulatedvalue中国煤化工value100%Coal5.08.666.2YHCNMHG21.2100% WP1.003099%Coal+ 1% WP4.95+0.057.28.5165. 45.606.44.602121. 2598%Coal+ 2% WP4.9+0. 18.4365. 165. 006.55. 2021.321. 3096%Coal+ 4% WP4.8+0.27.08.3264.663. 796.86.4021.621.39Note: Calculated value= XcmaX Woa+ XwpX Wwp. where Xcal，Xwp are percentage of blended coal and WP in the mixture of WPand coal, respectively; and Woul，, Wwp are yield of certain product from coal's pyrolysis and WP pyrolysis respectively.Journal of lron and Steel Research, InternationalVol. 13where p. is synergistic effect strength of the ith prod-yield. This agrees with the η obtained from that ofuct; Ww. is yield of the ith product from co pyroly-thermo-balance. Thus， the formulas proposed heremay be used as another parameter to quantify thesisof blended coal and WP; sk,W. is sumof yield synergistie fft ocuring in co coking of WP withof ith product from pyrolysis of the individual com-blended coal.ponent; k, is ratio of the jth component in theIn Fig.2，Mo and CSR of coke produced withblend; i is certain product; j is certain component.co- coking are decreased gradually while MIo and CRIAnd then, the total synergism strength, B，isare increased with the increase of WP added, whereproposed as follows:Mo，Mo are anti-cracking index and abrasion indexβ=Z|aβ: |of coke in normal state， %; CRI is coke reactivitywhere a, is coefficient equal to w...index of CO2，%; and CSR is coke strength after re-For co-coking of WP and coal, the synergisticaction with CO2，%. The reason may be as follows:effect strength of certain product and total synergis-(1) Large amount of contraction cavities was formedtic efect strength can be calculated bywhen the WP melts during co-coking; (2) During.=_w.c.W... +kwpWww.)](kwW...+the process of softening, de volatilization and swell-kwpWw.,)X 100(5)ing of coal and WP, the clusters or mosaics and thenporous coke structure are formed, and the pores andBased on above calculation， the synergisticanti-fissure are formed because the volatile is en-effect strength of the co-coking of coal and WP istrapped into the hardening viscous coal mass; (3)shown in Table 4.The added WP breaks the optical texture of coal andIn Table 4, the values of aerBreue and auspBur in-restrains the growth and coalescence of mesophase;dicate that the tar yield is increased and the water(4) The WP addition decreases the ability of the coals toyield is decreased with the increase of added WP.engulf the inert particles during this process, leading to aThe maximum of B. appears when adding WP of 1%，worse coherent coke with worse bonding between parti-accompanied with the most obvious‘ tar increasingcles; (5) The synergism as described hereinbefore hasand water decreasing' efect, which is decreased byimpact on coke properties for the radicals transfer.1. 31% for water yield and increased by 1.8% for tarTherefore, the mechanical strength (Mo and Mw) andCO2 resistance (CRI and CSR) of coke are worse thanTable 4 Synergistic strength between WP and blendedthose of coal.coal during co-cokingThe compositions of tar were analyzed by GC/ MS,TestsWaterCokeTarGasand the results are presented in Table 5. The resultsMixed powder1 -1.111 -0.196 2.504 - 0.245 4.057show that compared with the sample of blendedMixed powder2 -1.186 0.104 1.625 - -0.076 2.991coal, the yield of tar and the relative contents ofMixed powder3 -1.065 0.820 0.425 0.210 2.520 .benzene + toluene+ xylene (BTX) and naphthalene in70.6 [回)10.632.5 [7)70.210.431.5CRIMo69.8 t02; 30.5专。卷, CSR0.069.4-Mo29中国煤化工9.8MHCNMHG5269.028.568.8J 9.62034wP addition%Fig.2 Quality index of coke produced by co-coking of WP and blended coalNo.1Disposal of Waste Plastics With Traditional Coking ProcessTable 5 Tar yield and relative content of mainConclusionscomponent of tarRelative content of main component in tar/%(1) The interaction between coal and WP be-SamplesBenzene + Toluene+ Xylene Naphthalenecomes stronger with increasing WP addition in theCoal10.5417.1decomposition temperature range (200 一550 'C).Mixed powder 112. 4820. 88The tar yield is increased and water yield is de-creased.(2) The new idea and formulas of pyrolysisthe tar produced from the sample of mixed powder 1synergism index and synergism strength proposedare 1. 94% and more than 3. 78%，respectively. .could well evaluate the synergism between WP and .This phenomenon indicates that WP added to thecoal. Based on calculation， 1% addition of WP re-blended coal at certain ratio is helpful to increase thesults in the maximum synergism.valuable components of tar and increase its economic(3) For the coke produced from co-coking，value. During co-pyrolysis, the radicals produced by .M4o and CSR are decreased gradually while Mno andWP and coal interact with each other, improving theCRI are increased with the increase of WP added.formation of poly cyclic ring system. Furthermore,Thus, WP added to the blended coal for co-coking isthe raw gas is cracked on the way through the cokehelpful to improve economic value of tar and gas.mass and decomposes again at high temperature zoneto obtain some part of good quality oil.References:Besides，the contents of CO, CH，C。 H2n and[1] Pinto F, Costa P, Gulyurtlu I, et al. Pyrolysis of PlasticH2，and the caloric value of coke-oven gas from cWastes. 1. Effect of Plastic w aste Composition on Productcoking increase in the experiments. The reason mayYield [J]. 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