外文翻译煤低温氧化模型

1、英文原文:Coal oxidati on at low temperatures: oxyge n con sumpti on,oxidati on products, reacti on mecha nism and kin etic modelli ngThe conservation of mas and energy will be applied to the regions depicted in Figures 2a-2c. These con sist of the (a) the char, ) the vaporizati on in terface, and (c) th

2、e virg in solid. For mass con servati on with respect to a con trol volume, the rate of change of mass within the control volume plus the net rate of mass flow out of the contol volume is equal to zero. The conservation of energy for a control volume states that the rate of change of internal energy

3、 within the contol volume plus the net rate of enthalpy out is equal to the net rate of heat addition. Work is neglected, except for flow work, and combustion energy can be treated as an effective heat addition. Constant properties will be assumed for each distinet media, i.e. char and virgin materi

4、al; and the internal energy is refereneed at the initial temperature.The con servati on of mas for the solid in Figure 1 is give n by(1)1 dmmA dt, dm wheredtis the mass of cha nge of the solid,A is the surface area,And m is the mas flow rate of the gasified products per unit area.Hen ce, m is the ma

5、s loss rate per unit surface area, or which is more commomly referred to as the burning rate (per unit area). Eq.(1)is not essential to the governing equati ons which follow, but is only prese nted to show the relatio nship betwee n the rate of fuel gasses which flow out of the system and the rate o

6、f maw loss of the solid. Con servati on of mass for the charBy considering the conservation of mass for the char layer in Figure 2a, and assu ming that the vaporized fuel in sta ntan eously leaves the solid, it follows that where pc is the char density, and xh," is the char mass flow rate per u

7、nit area from the vaporizationplane. The accumulation of the fuel gases in the char matrix is taken to be n egligible, so that the rate of gaseous fuel en teri ng from the vaporizati on in terface is equal to the rate of fuel gaseswhich leave the solid to be burned. Conservation of mass for the vire

8、 in solidConsequently, a conservation of mass on the virgin fuel eleme nt in Figure 2c yieldsd cdys dt o c Ysmcddtc vdys(3a)Where p is the den sity of the virgin solid, and where the con trol volume surface moves at the speed of the vaporization plane, v = c v .It is assumed that the thick ness of t

9、he solid stays con sta nt as decompositi on occurs.Con servati on of mass for the vaporizati on in terface.A mass balanee at the vaporization plane together with Eq.(2), and assuming pc is con sta nt, gives(3b)This equati on states that the rate of mass from the virgin solid into the vaporizati on i

10、n terface is equal to the mass flow rate of char and fuel gases leav ing the vaporizati on in terface.The con servati on of en ergy for each regi on in Figure 2 is now con sidered. Con servati on of en ergy for the charFor the char regi on (2a),1 dUcA dtdT4m cg Ts T vmccc Tv T 0kgq f ,rq ext,rTsq vd

11、yy 0whereUcis the in ternal en ergy of the char layer,Cgis the specific heat of the vaporized fuel gas,Ccis the char specific heat,kgdTdyy 0is the flame conv ective heat flux,qf,ris the flame radiative heat flux,qext,ris the external radiative flux to the surface,4Tsis the surface reradiative heat f

12、lux (assumed to be a blackbody),qvis the heat flux to the plane of vaporization,TvTsis the vaporizatio n temperature,is the surface temperature,Tois the refere nee temperature.Con servati on of en ergy for the vaporizati on in terfaceThe conservation of energy applied to the vaporization plane of Fi

13、gure 2b yields:v Hv qv qkwhere Hv is the heat of vaporization (pyrolysis) for the solid at temperature Tvqk is the heat loss per unit area to the virgi n solid.The left side of Eq. (5) relates to the en ergy required to cha nge the virgin solid to vapor and char, and can be taken as a definition ofC

14、on servati on of en ergy for the virgin solidAn en ergy bala nee on the virg in solid gives£警vcTv To qk qbA dtwhere qb is the heat loss per unit area from the back of the solid,and Uv is the internal energy of the virgin solid.Since the density (p) and specific heat (c) of the virgin solid can

15、be considered con sta nts,c vUv cA T To dys(7)cEquations (2)- (7)constitute the governing equations for the solid phase. It is not en tirely obviouswhat are the unknown variables, and what is the strategy of sol ving for them. For now it can be no ted that by assu ming appropriate profiles for the t

16、emperature, the heat fluxes can be express edi ng terms of temperature by Fourier's Law. Also the variables involving the gas phase heat tran sfer n eed to be developed from the gas phase an alysis to follow in the next section. Now a digression is introduced to illustrate another approach for p

17、rese nti ng the solid phase equatio ns, and to offer a check on the above an alysis.Differential formulationCon sider pure con ductive heat tran sfer into the virgin solid with the space coordi nate(x), had tothe moving vaporizati on pla ne. This coord in ate system is show n in Figure 1,a nd is in

18、troduced toavoid confusion with the ys coordinate system used above. If x° is the initial fixed refere nee system,X Xowhere v is the velocity of the vaporizati on pla ne. The con duct ion equati on in the2tx2which tran sforms asTTT dxTT _vt xx0txx t dtt xx td 2t and22t2X0tX tfixed frame of refe

19、re nee is(8)(10)cTv t xTk -2t2 x txtwith the con diti ons:x0，kT qk xkTxv ，xqbfrom Eq. (8). Hence in the movi ng frame of refere nee.and(11)(12)t 0， T T0，the initial temperaturekdTdx(13)From Eq. (3) and since vdtdT m c一 dxkd2Tdx2(14)Case 1. Non-charri ng steady bur ningLet us consider the ideal case

20、of a non-charring material undergoing steady burning. If steady conditions prevail in the moving system, i.e., the temperature field is not changing in the virgin solid relative to the moving vaporization plane, and the back face con diti ons are n egligible,i.e., a very thick solid, the n Eq. (11)

21、becomesdT cv - dxwith conditions from Eq. (5) and (12)qv(15a)(15b)t 0，T Tvx ，TToUsing Eqns (fib) and (Ec)TToTvT。cmxk(15c)(16)and from Eq. (Ea)qvH v+ c TvTo(17)The denominator of Eq. (17)is commonly referred to as the steady state heat ofgasification ( Lg)(18)Lg H v + c TvToCase2. Tran sie nt charri

22、ngIn gen eral, other terms which will be con sidered below will affect the mass loss rate, m .If the process is not steady,we can consider Eq. (11) by integrating each item overvAlso for the charri ng case since at the vaporizatio n pla ne the above. Substituting in the integrated form of Eq.(11) gi

23、vesdtdt,and from Eq. (3b) it follows thatm should be replaced by mwhich is ide ntical to Eq. (6). This dem on strates that the con servati on of en ergy for the virgin solidis con siste nt with this differe ntial formulatio n.Soluti on strategyIn review, six in depe ndent equati ons have bee n prese

24、 nted con sist ing of con servati on of mass anden ergy for the char, vaporiz ing in terface, and virg in solid. These can be comb ined so that only twoenergy equations (4 and 6) are considered with the unknown variables: char depth, surface temperature, and a variable to be in troduced which repres

25、e ntsthe thermal effects in the virg in solid.The thick ness of the virg in solid and the mas burning rate can be related to the char depth, and the heat fluxes can be related to temperature profiles to be assumed in terms of the thick nesses of the char and virg in solid. A third equation will be f

26、ound from the gas phase flame analys is which will give a relati on ship for the bur ning rate. The flame conv ective and radiativeheat fluxes will be expressed in terms of the current variables from the gas phase flame analysis. Below, this sect ion will be con cluded with a derivati on of the conv

27、 ective flame heattransfer based on the above conservation equations which will serve as a boundary con diti on to the gas phase an alysis developed in the n ext secti on. This couples the solid and gas phase an alyses.From Eqns. (5) and (6)dc -dtTo dxm eTv To qv m c Hv qb(19)orThis is a departure f

28、rom the steady state results given by Eq.(17). It applies to the non-charring case if qv is regarded as the net surface heat flux,and = 0 .The more general charring case is considered by eliminating qv; from Eq.(19) by using Eq. (4).represe nted asFurthermore, the internalen ergyof the char isfollow

29、s:Ucvcucdys where uc is measured from the charring surface. The0where cc, is the charinternal energy per unit mass, uc,is represented as cc T Tospecific heat. By Eq.(2) it follows that1 dUA dtd cTcccTdt oTo dys(20)Comb ining all of the en ergy equati ons for the solid, or from Eqns. (4), (19) and (2

30、0)m LgkgdTdYqf,ry 0T 4qext,rI sdCcC 一 dtcT T0 dys m Cg0Ts Tvd v qb cdtT0 dysc m Cc TvT0(21aAlternatively,m LgdT kg d?+ qf ,rqext,r4Tvconv ective heat tran sferflow radiatio nexter nal radiati onreradiati on (non charri ng)Tv4dcccdt0T T0 dysserface reradiati on due to charri ngen ergy storage due to

31、charri ngm Cg TsTv + c m Q Tv T°qbEn ergy flow through chardc -dtTo dysback f a e heat lo.(21b)virgin SOU en ergy storage(The above labels are qualitative descripti ons of the terms.)Equation (21b) gives the thermal boundary condition for the g& phase analysis, Le.,whereLgdc -dtT0 dys qd cc

32、ccTdt 0T0 dys(24Tsq f,r q ext,r原始材料，都为其假定常量, 总质量图1中的质量守恒为内部热量参考自初始温度m Cg TsTv c m Cc TvT° /2) The form in Eq.(22)c on stitutes a boun dary con diti on for the gas phase problem to follow.中文译文:煤低温氧化模型氧气消耗、氧化产物、反应机理及动力学模型在图2a 2c种描述的区域应用了质量和能量守恒。其包括（a）炭化，（b） 气化表面，和（c）原始固体。对于一个控制体的质量守恒，控制体内的质量变 化速率

33、加上流出控制体的净质量流率等于零。控制体的能量守恒为控制体内的内 部能量变化加上流出控制体的净能量流率等于净增加热流率。 除了流动做功，忽 略了功的影响，另外燃烧热可视为有效增加热。 对每种特定媒介，如炭化材料和（1）m为单位面积上气化产物1 dmmA dt其中 如 是固体质量变化速率，A为表面面积, dt的质量流率因此，m是单位表面面积的质量损失速率，或更普遍地被称为燃烧速率（单 位面积）。方程（1）不是控制方程必须遵循的方程，但其可表现流出系统的燃烧 气化速率和固体质量损失速率之间的关系。炭化质量守恒考虑图2a中炭化层的质量守恒，并假定燃料气化后即刻离开固体，其遵循 下式：dtcdys其中

34、c是炭化层密度，mc为气化平面单位面积炭化质量流率。气化燃料在 炭化层的积累可不加以考虑，从进气化表面进入的气化燃料质量流率等于离开固 体将要燃烧的气化燃料的质量流率。原始材料质量守恒因此，在图2c中标出了原始燃料的质量守恒ddtc vdys(3a)其中为原始固体密度，其控制体表面移动速率等于气化平面移动速率plplv话，假定固体的厚度在热分界发生时保持不变气化表面的质量守恒结合方程（2）在气化平面存在质量平衡，假定c恒定，则v m mc m其中 =/ c此方程表示从原始固体进入气化表面的质量流率等于炭化和气化燃料离开 气化表面的质量流率。现在考虑图2中的各个区域的能量守恒。 炭化能量守恒对于

35、（2a）区域，1 dUcA dtT v mccc Tv T 0k dTt4Kgq f ,r q ext,rT sdy y 0(3b)qv其中：UcCgCc炭化层内部能量 气化燃料比热 炭化层比热kg?火焰对流热通量qf,rqext,r4TsqvTvTs火焰辐射热通旦对表面的外部辐射热通量表面辐射热通量（假定为黑体）对气化平面的热通量气化温度表面温度To参考温度气化表面的能量守恒图2b中表明了气化平面的能量守恒v Hv qv qk其中Hv 固体在温度Tv下气化（高温分解）热，qk单位面积散失到原始固体中的热量。方程（5）的左项为把原始固体变为蒸气和炭化材料所需能量, 的定义。原始固体能量守恒原始

36、固体有能量平衡：可作为1duA dtvcTv Toqk qb其中qb从固体背面单位面积热损失Uv原始固体内部能量由于原始固体的密度（）和比热（c）可视为常量，c vU v cA T To dysc方程（2）（7）建立了固相的控制方程。不是很明显能看出那些是未知变 量以及解出它们的方法。现在可以假定温度的大致分布，然后根据傅立叶定律就 可以用温度来表示热通量。而且和气相换热有关的变量在下一部分的气相分析中 也可以得到解答。现在介绍另外一个表征固相方程的公式，用以检验以上分析。 微分公式假定给原始固体的净传导热是沿着在移动的气化平面上建立的空间坐标 （x）的。 在图1中标出了坐标系，为避免上面所用

37、的 ys坐标混淆。如果X。是固定初始参 考系统，tX Xo v d（8）0其中v是气化平面的移动速度。在固定参考火焰下的传导方程是T c tk TXo(8)上式可变为TTTdXTTv(io)txot XXt dtt XX t2十2十和T2T2XotXt所以在参考移动火焰为c上式在下列条件下成立：TTv - t xxkt2tx2tx 0，kTxqkXv ，kTxqbt0，TT0，即初始温度(12)第一种情况：非炭化稳态燃烧让我们考虑一种非炭化材料稳态燃烧的理想情况。如果稳态条件在移动系统 中仍然成立，如温度场不随原始固体内气化平面的移动发生变化，且忽略背部条 件的影响，如一块非常厚的固体，则方程（11）变为(13)dT cv - dx由方程（3）和v JdTm ck叮