Theoretic computing model of combustion process of asphalt smoke

Vol.12 Suppl 1J. CENT. SOUTH UNIV. TECHNOL.Oct.2005Article ID: 1005 - 9784(2005)S1 - 0088 - 06Theoretic computing model of combustion process of asphalt smoke"HUANG Rui(黄锐), CHAI Li-yuan(柴立元), HE Dewen(何德文), .PENG Bing(彭兵)， WANG Yun-yan(王云燕)(College of Metallurgical Science and Engineering,Central South University, Changsha 410083, China)bustion process of asphalt smoke is set by theoretic analysis. Through computer programming, the dynamic combus-tion process of asphalt smoke is calculated to simulate an experimental model. The computing result shows that thetemperature and the concentration of asphalt smoke influence its burning temperature in approximatively linear man-ner. The consumed quantity of fuel to ignite the asphalt smoke needs to be measured from the two factors.Key words; asphalt smoke; combustion; concentration; mathematical modelCLC number: X701.3Document code: A1 INTRODUCTIONbroken and oxidated, then the combustion productis discharged as clean gas. The device costs lessThe asphalt smoke is mainly produced by fluo-and the smoke is decontaminated ,out more fuel issolid furnace and dipping working procedure of car-consumed during the combustion process5,6]. Inbon industry, fluosolid furnace of aluminum indus-order to improve the advantage of combustion tech-try, sand and pitches mixture for road, asphaltnique, the relationship among parameters in theproduct working procedure of chemical industry,asphalt smoke combustion process is expressed bywaterproof of construction industry and so on[1,2.mathematic symbols based on combustion theory.It is composed of hydrocarbon granule as liquidThe combustion computing simulates an experi-state and hydrocarbon ramification as gas state, iment model, as shown in Fig. 1.which the multi-ring hydrocarbon is much hazardto people.TemperaturemeasureAs a complex pollution system, coal asphaltthat makes asphalt smoke is a mixture that con-Combustedtains thousandsf complex compounds[3].Asphalt smoke/airsmokeinleThrough the research literaturel2] that provides theAsphalt smokeresult of asphalt components by combined gas电chromatography &mass spectrum analysis meth-Aircombustionpump,deviceod, the asphalt smoke includes 196 contarminationsand the content of 81 contaminations can be sure tobe higher than others. These contaminations areElectce asphatCoal Combustiblemainly fluorene, acenaphthene, phenanthrene, an-heatergasthracites, naphthalene, glimmering anthracites,Fig.1 Sketch of asphalt combustionpyrene, furan, indene, biphenyl and ramificationexperiment device for numeric simulatingof these substances. At present, the research ofasphalt smoke components is only from the resultTo complete the calculation, the database ofof qualitative analysis, and less quantitative analy-main contaminations in asphalt smoke is set ac-sis work can be found to indicate the proportion ofcording to research literatures, and then the com-the main component.bustion product and the released heat can be calcu-Four ways to dispose the asphalt smoke in-lated as complete combustion by thermodynamicsclude: combustion, adsorption, electric dust re-with the data. Through the quantity of releasedmove and absorptionl,4-8]. These methods haveheat, the combustion temperature can be known.their respective benefit and disadvantage. As forThe中国煤化工tion to keep the as-combustion method, the asphalt smoke is burnedphalcan be studied,by supplied fuel and its macromolecule structure isthrfY片CNMHGhetwiththeheat①Recetved date: 2005 - 06 - 10; Accepted date; 2005 -07-10Corresponadence: HUANG Rui, PhD, Tel; + 86 - 731-8830875; E mial; huangrui@ ustc. eduHUANG Rui, et al; Theoretic computing model of combustion process of asphalt smoke●89.needed by asphalt smoke for combustion.relative literatures[10.1], and then the database isset to provide data for calculation The structure ofSPECIFICATION OF COMBUSTION MODEvector includes the important information con-AND DATABASEcerned on combustibility of asphalt smoke compo-nents, such as relative molecular mass, chemical2. 1 Specification of combustion mode of asphaltconstitution and enthalpy.smokeWith the database, the combustion enthalpyThe asphalt is composed of five elements andand generating enthalpy of the components are cal-those are carbon, hydrogen, oxygen, sulfur andculated by the method provided by reference litera-nitrogen, while asphalt smoke is produced byture-12. 18]. The method is briefly introduced as fol-pyrogenation of asphalt. From the foundation oflows.combustion technique, the voltilization substancesThe combustion enthalpy of organic sub-with lower relative molecular mass from asphaltstances can be calculated as Eqns. (3)-(5) accord-are mainly combustible hydrocarbon. Under differ-ing to its phase:ent combustion conditions ( including quantity ofAH{(g)/(kJ●mol-1)= -198.42- 615.14Noxygen supply, burn temperature, flow velocity of(3)smoke and so on), the combustion of asphaltAH?(I)/(kJ●mol-1)=- 196.98- 610.13Nsmoke can go by two modes: combustion com-pleteness or incompleteness. The chemical reactionAH!(g)/(kJ. mol-1)= - 206.21- 606.56Nequation of incompleteness combustion is(5)Cx+y+.HO,NS+(x+y/2+ m/4-where N is the length of the carbon chain ofn/2+j)O2一→xCO2 +yCO+zC+equivalent alkane. As for the alkane of single势H20+ BNz+jSO2(1)chain, N is just the number of carbon(C); but forother organic substances, N needs to be emendatedAnd the chemical reaction equation of completenessby the radical or branch chain in the molecularcombustion isstructure(ON,).CHO,NS;+(l+m/4-n/2+j)O2一The emendation factors ON; of radical or par-ICO2 +架H20+参Nz +jSO2(2)tial structure can be seen from some refer-enecel12,10:Inorganic gas is the main product of combus-N=C+ ZoN,(6)tion reaction, except some carbon ash and a fewsolid organic ashes in incomplete mode. In fact,Moreover, the database for combustion prod-the asphalt smoke is usually required to be com-ucts of hydrocarbon is set by some referencel1n.pletely burned to avoid new contaminations fromThe structure of vector is mainly relative molecularincomplete combustion. The calculation of asphaltmass, coefficients of specific heat (a, b, c), gener-smoke combustion will be accorded to the mode ofating enthalpy and so on. According to the Hess'scomplete combustion in the latter study.Law, the released heat of combustion reaction 0Qcan be calculated by the database.2.2 Database foundation of asphalt smokeWith the ceffcients of specific heat a, b andIn the calculation, the physical and chemicalc, the specific heat of complete combustion prod-properties of asphalt smoke and main combustionucts can be known according to the mathematic ex-products are expressed by vector. In the vectors,pression of specific heat (Eqn. (7)). Then thesome data can be read from database, and other pa-combustion temperature T can also be known byrameters can be computed by known data:the heat 0Q and Cp.Namec2,m/(J. mol-1●K-')=a+bT+cT (7)components o| Relative molecular massasphalt smokeNumber of CSIMULATING PROCESS OF ASPHALTMSMOKE COMBUSTION{ Enthalpy( NameAs to the combustion and flow of asphaltcomponents of| Relative molecular masssmol中国煤化rlevice changes dy-combustionCoefficient of specific heatnamiOn the discreteproductpoint|YHCNMHGribedasfllowingEnthalpysteps: (I) asphalt smoke transported by air pumpThrough the component information(2] of as-enters and mixes with the high temperature gas inphalt smoke, the physical and chemical propertiesthe combustion device; (2) the hydrocarbon com-of those components can be found out by referringbusts with oxygen and becomes inorganic product●90.Journal OSUT Vol 12 Suppl. 1 2005gas as well as heat; (3) the temperature and theThe temperature of mixture becomespressure in the device increase and smoke will ex-T+1_&.V。*C" T十h : v.Ot'Ce.Iihaust through vent, and then the density and thep●V.●cp+ps●v;Ot.cppressure of gas in device will decrease; (4) asphalt_些.V.. T:+Po●U;Ot. Ti(10)smoke continually enters the combustion devicep% .V.+po. U;Otand the temperature of mixed gas changes, andAt the same time, the asphalt smoke compo-then the former steps repeat.nents increase m●Ot(kg) as the subsequentTo computate the combustion process, severalsource of reactant in the calculation.parameters are taken to express the thermodynamicstate and geometrical size of asphalt smoke com-3.2 Calculation of combustion product and reac-bustion system, and the steps (1)-(4) are de-tion heatscribed by mathematical equations with these pa-According to the complete combustion moderameters. As a dynamic process of asphalt smoke(refer to Eqn. (2)), the combusting products arecombustion, we suppose that each circulation in-CO%，H2O, N2 and SO2. Based on the expressioncluding step (1)-(4) is completed in an intervalof reaction, the quantity of products of every kindOt. When less time St is set, the' computingof asphalt smoke components areprocess will be more continuous and the result ofl mol CO2calculation will be more accurate. Whereas more势mol H2Otime Ot is set, the process will be more discrete1 mol CH.O,NS, -→.(11)and the error of calculation will rise. In fact, themol N2interval can take Ot=0. 001 S according to the nu-merical precision in the computer program.[; mol(SO2)After the oxygen in air is reacted, the quantity3.1 Flow of asphalt smoke and mix of gasbecomesThe combustion of asphalt smoke needsNo =0.21.r/22.4- ENe.enough air by fan (refer to Fig.1), and this is be-cause: (1) complete combustion of asphalt smoke(l+四-n/2+j)(12)needs enough oxygen to get the chemical equivalentwhere No, is the quantity of O2 in combustionratio of asphalt smoke/air; (2) as the viscosity andthe relative molecular mass of asphalt smoke com-box; Ns is the quantity of the asphalt smoke com-ponents are heavier than those in air, the transpor-ponent i in combustion box.When the combustion reaction is completed,tation of asphalt smoke in device requires enoughdrive power. Then the flux of air needs to be ad-the quantities of every gas in box arejusted to realize the object.(Nco, =习(N; .l)Besides，the air should be rise to a propertemperature (> 200 C) to avoid the asphalt smoke|Nx,o= 2(Ne●驾sticking on the wall of vent pipe.Here suppose that the volume of combustionNsq, = Z(N& .i)box is V.(m), the temperature, density and pres-(13)Nx, = 0.78. u/22.4+sureof gas in box is T.(K), p.(kg/m') and p(Pa), the temperature of asphalt smoke is T:(K)，2(N'e●k/2)and the volume flux of air is u(m'/s); while theNq, = 0.21●n/22.4-total mass of asphalt smoke components is m:(kg/s). The T should be higher than 473 K at least.Z[N .(I +m/4-n/2+j)]The T. and V will be important in the combustionAccording to the Hess's Law, the heat ofprocess. As to the transportation of sticky asphaltsmoke in the whole device, the technical problemcombustion reaction is0Q= AHco, + 0Hno +△Hso, +won't be discussed in this paper. Moreover, the vola-tile of asphalt in asphalt smoke is usually lower than 10Hyq - 2oH。- 0Hq,(14)000 mg/m2 , the specific heat and the density of smokeare approximatively equal l0cp and Ao of air. In addi-3.3中国煤化工of gas in combus-tion, the oxygen supply can be calculated as 0. 21v ac-cording to the proportion of air components.MHCN MH Gn is completed,After the asphalt smoke is mixed with gas inthrough the spectic heat ot each gas component in box,combustion box during time Ot, the density Pe becomesthe total specific heat of all gas can be calculated asog+1_L.V.+B.切.Ot<9)c,= N:.cf .(15)HUANG Rui, et al; Theoretic computing model of combustion process of asphalt smoke●91●where N; is the quantity of gas componenti; c; isprocess and executing it on computer, the compu-the specific heat of the gas component i.ting result of different conditions can be gotten bySo the temperature variation of gas in box be-applying different paraneters.comesIf the concentration and the flux of asphaltOT = 0Q/cp,(16)smoke keep constant when entering the combustionWhile the temperature increases, the pressuredevice, the profile of combusting temperature inof gas increases, too. According to equation of gasbox is shown from igniting to steady combustion asstate, the pressure isFig. 3. The initial temperature in combustion boxp.=pt'●R. (T.+OT)(17)is room temperature (298 K), and the temperatureSince the vent of combustion device directlyof asphalt smoke is 500 K. When the asphaltconnects with the environment, the smoke flowssmoke combusts for a while, the temperature risesout by the pressure gradient between the combus-to 628.16 K and varies little.tion box and environment. In order to know thevolume of discharged smoke from combustion box,650 1suppose that the pressure of the gas remained indevice is equal to the pressure of environment ac-50cording to the analysis method of approximativestatic course ( setting the interval Ot smallenough). Then the volume of discharged gas is450oV = p.V。/po一Vc(18)wherep。 is the pressure of environment.350Through the data, the remained gas in box and itsdensity can be known. Moreover, the dischargingvelocity and the flux of combusted gas from com-bustion box can be known too.250--之-480 12Time/s3.4 Mixing of gas and circulation of processFig.3 Curve of combustion temperatureAccording to the analysis of the discreteprocess, when the smoke flows out, the sequentApplying different temperatures of asphaltaspbalt smoke mixes with the former remained gassmoke, the steady combusting temperature is dif-in box. The density and temperature of the mixedferent. The computing result shows that, the tem-gas in combustion box can be calculated as theperature of asphalt smoke before combustion afmethod in 3. 1.fects the latter steady combusting temperature asCirculating the computing of steps (1)-(4)，an approximative linearity (refer to Fig. 4). Fromthe dynamic process in combustion device can bethe computing result, if the temperature of asphaltnumerically described(Fig. 2). Through changingsmoke is 298 K, the steady combusting tempera-the parameters of the experiment conditions, theture will be 471.3 K. This shows that partial heateffect of combustion can be researched by this nu-releasedy reaction is consumed on increasing themerical experiment. The decontamination of as-temperature of sequent asphalt smoke. Accordingphalt smoke in actual device can also be studied byto the discourse in Refs.[6, 7, 15, 16], the scalethis way and the small scale experiment.of the temperature to burn the asphalt .smoke com-pletely is 873 - 973 K. Contraposing the curve inInputGasCombustionFig. 4, if the steady combustion temperature re-parmetersmixingreactionquired is 973 K, the temperature of asphalt smokemust be 892. 6 K.Changing the concentration of asphalt smoke ,the profile of combustion temperature can beResultSequentPressure increaseshown as Fig. 5. The result shows that the heat re-outputsmokeand smokeenteringdischargeleased by combustion is influenced by the concen-tration of asphalt smoke. If the concentration isFig.2 Ftow chart of recycle calculationhigh2mbusting tempera-ture中国煤化工tion is low, the heatis alsTYCHC N M H Gmbustion of asphalt4ANALYSIS OF COMPUTING RESULT ONsmoke, more Iuel IS requrea I0 De consumed to reachCOMBUSTION PROCESSthe steady combusting temperature.Since the components of asphalt smoke areThrough programming the former computingcomplex, the kindling point is different for each●92●Journal CSUT VoL 12 Suppl. 1 2005asphalt smoke is higher. On the other hand, if theconcentration of asphalt smoke is high ( condition(1) and (2)), the temperature supplied by addi-1000tional fuel decreases to 812.35 K (539.2 C) so as900to make the asphalt smoke combust effectively.8005 CONCLUSIONS700600Asphalt smoke is acombustible comprising500multifold organic component; and the differentkindling points of each component confine the scale4002001100of the combustion temperature. Based on the dataSmoke temperature/Kand method provided by references, a discreteprocess model of asphalt smoke combustion isFig. 4 Influence curve of combustion temperaturefound according to relative theory, and then theon asphalt smoke temperaturedynamic combustion process of asphalt smoke iscomputed by computer program to simulate an ex-perimental model.940 t1) The steady combustion temperature of as-phalt smoke is affected by supplied fuel. The quan-tity of supplied fuel is affected by the temperatureof asphalt smoke before combustion, and the; 860}mathematical model provides it quantificationally.2) The concentration of asphalt smoke is also20十an important factor to the quantity of supplied fu-el. If the concentration is higher, the reducedquantity of supplied fuel can be known by calcula-780tion; otherwise if the concentration is lower, the0.20.61.0additive fuel supplied to reach the combustion tem-Concentration of asphalU(g*m-3)perature of asphalt smoke can also be known byFig. 5 Influence curve of combustion temperaturecalculation.to asphalt smoke concentrationAccording to the computing result, if the tem-perature of asphalt smoke before combustion is 773component. The asphalt smoke must be requiredK, the concentration of asphalt smoke should lar-to be at certain temperature to combust effectively.ger than 0. 0249 kg/m3 to get the complete com-In fact, the temperature that the asphalt smokebustion temperature, then the asphalt smoke canshould be gotten before combustion just corre-persist in combusting itself without supplying fuel,sponds to the heat supplied by fuel. Comparing theThis concentration is higher than that of the indus-condition (1) and condition (3) in Fig. 6, it showstrial asphalt smoke, but when increasing the con-that less fuel is needed when the concentration ofcentration of asphalt smoke to decrease the fuel,the problem of air supplying and the driving power1 000of smoke will be difficult to resolve.In the actual applying, it requires not onlycombusting the asphalt smoke effectively, but alsoconsuming minimum fuel. The computing modelcan help it in a certain extent. The economical andthe practicability of the combustion technique canbe improved with synthetic research,!- 0.002 kg/m3 and 892.75 K-0.01 kg/m3 and 892.75 K3一0.02 kg/m3 and 812.35 KREFERENCES[1]中国煤化Inang, NIU Zhi-qinp.20f asphalt smoke in air682MH.CN M H Gnformation DeveloTime/sment & Economy, 2003, 13(4): 88 - 89.[2] SHI Bao-cheng, XU Guang, LIU Jingtai. CombinedFig. 6 Profile curve of combustion temperaturegas chromatography & mass spectrum analysis orto asphalt smoke concentrationschemical components of asphalt smoke[J]. Environ-HUANG Rui, et al; Theoretic computing model of combustion process of asphalt smoke●93●mental Chemistry, 2001, 20(2): 200 - 201.League[M]，Beijing; Chinese Industry Publishing[3] YAN Jjajl, Performance Study of Asphalt. MaterialCompany, 1957. 32 - 98.[M]. Beijing: People's Traffic Publishing Company,[11] Reid R C. Sherwood, Kilgore T, et al. The Proper-1990.145 - 149.ties of Gases and Liquids. 2nd ed[M]. New York:[4] DOU Bo. 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