1.Introduction

Ethylene,propylene,butadiene,and aromatics are the basic chemicals which are mainly produced by steam pyrolysis of petroleum hydrocarbons in the steam crackers.Petroleum hydrocarbons are preheated by superheated steam in the convection section of the furnace,and then the pyrolysis process takes place mainly in the radiant section of the furnace,where tubes are externally heated to 750–900 °C.Then the pyrolysis products are separated into hydrogen,ethylene,propylene,butadiene,aromatics and so on.The operating conditions,such as residence time,ratio of steam to oil,coil outlet pressure and coil outlet temperature,would affect the pyrolysis product yields.Therefore,the building of pyrolysis model to simulate hydrocarbons pyrolysis in cracking furnace is important for the technology development,furnace design,and operating optimization.

五是保障措施方面的问题。“一站式”司法确认机制是一种矛盾纠纷多元化解机制。它的运行，不仅需要司法机关、司法行政机关在工作机制、人员配备等方面提供保障，还需要在办公场地、办公设备、办公耗材、人员工资、职业保障等方面作出合理安排。这就需要各级党委、政府和相关部门在政策、财政及相关场所建设方面予以支持。

那个时候的农村人，一辈子能盖上一处房子已经是大事，几间祖屋就是几代人生活的居所。小学一年级的时候，家里房子，帮工的邻居对放学回来的他说“黑健儿，我们这可是给你盖房子呢，过几年你娶媳妇得记得我们！”黑健翻了个白眼，“才不是！我长大了要盖高楼！”顿时引起一阵大笑，有赞许也有不屑。村里人没想到，这一句话，十几年后便成了现实，再回到村里，一些长辈一脸欣慰地说“臭小子，从小就喜欢盖房子，如今真的能天天盖楼房了！”

During the establishment of the pyrolysis model,the key step is the simulation of the reaction process from reactants to products and the core is the kinetic model of the pyrolysis.The pyrolysis reaction kinetic model always is the focus of the research.Based on the research results,the kinetic model of pyrolysis can be divided into three categories generally.They are simple empirical model,semi-empirical model(molecular model),and theoretical model(the free radical model).The empirical model is a prediction model based on the relationship between the operating parameters(e.g.temperature,residence time)and the material properties(e.g.specific gravity and family composition)and the product yields[1–5].According to the molecular model,the free radical reaction is generally incorporated into a molecular reaction,or a number of molecular reactions are combined into average molecular reactions.The relatively simplified kinetic model was obtained by calculating the relevant kinetic parameters[6–10].These above two models are easier to build up and run quickly.However,both models should have sufficient experimental data and they are just suitable for test conditions.The free radical model is based on Rice's free radical theory[11],and the reaction network is constructed by the elementary reaction[12–15].The free radical model can better reflect pyrolysis process with good adaptability and external ductility.But the reactants and reaction types are complex,and the number of reaction kinetic parameters is large.So the establishment and solution of the model is more difficult.

In this paper,the free radical reaction model was studied with the n-pentane pyrolysis process as an example.

2.Pyrolysis Model Development

2.1.Parameters' solution

The kinetic parameters were generally obtained from experimental study in the previous research[16].According to the pyrolysis process of petroleum hydrocarbon,lots of free radicals need to be caught and analyzed.Recently,the development of quantum chemistry has provided a new way to solve this problem by theoretical calculation[17,18].Here,the n-pentane pyrolysis process is investigated by means of quantum chemistry and Gaussian 03 Software is used to calculate the thermodynamic parameters of reactants and products.Then the kinetic parameters of the reactions are obtained.At last,pyrolysis reaction network consisting of a large amount of reactions and free radicals is constructed and the free radical reaction model for n-pentane pyrolysis is built.

2.1.1.Calculation of thermodynamic parameters

The structure of the reactants and the products involved in the reaction is optimized by Gaussian03 Software to obtain the optimized structures(the stationary points)and to calculate the frequency and the thermodynamic parameters.Then,the structure of the van der Waals complex composed of the reactants and products is optimized.The optimized structure of the reaction initiation and termination is obtained to optimize the reaction transition state.The following is the choice of calculation method in the Gaussian03 Software:Calculation accuracy and calculation amount being evaluated,UB3LYP method applies to calculate the bimolecular reactions,and UMP2 is used to calculate the unimolecular reactions.The basis set of the calculation is the level of 6-31G+(d,p).

The structure of the reaction transition state is configuration optimized with QST2&QST3 method of Gaussian03.The frequency characteristic value of the transition state of the optimized structure is calculated,and the saddle point type of the structure is determined by the imaginary number to verify the reaction transition state.Then the IRC(intrinsic reaction coordinate)is used to search the reactants in the both ends of the reaction transition state to verify whether the transition state is in the intermediate state.At last,the thermodynamic parameters are calculated under the same calculation method and basis set.

Based on the above thermodynamic parameters,the ground state energy,enthalpy of formation,entropy of formation and Gibbs free energy of the reactants,reaction transition state and the products are obtained,and the activation enthalpy(ΔH≠),the activation free energy(ΔG≠)and the activation entropy(ΔS≠)are calculated[19].

2.1.2.Solution of the reaction kinetic parameters

According to the obtained thermodynamic parameters,the reaction kinetic parameters can be calculated from the transition state theory,and the formula can be derived:

In comparison with Arrhenius Eq.(2),

The first half of the Eq.(1)is combined to the frequency factor A,and the activation enthalpy(ΔH≠)is equal to that of the Arrhenius equation.Therefore,the activation energy can be calculated from the thermodynamic parameters of quantitative chemistry calculation,and the frequency factor A can be obtained from the following equations.

By adjusting the three parameters of rtol,Atol and h,the average time of semi implicit Eular algorithm can be reduced to less than 300 ms.The calculation efficiency is increased by 10 times.

The initiation reaction is taken as the example.There are two kinds of bond cleavage in the initiation reaction of n-pentane pyrolysis,i.e.C-H bond cleavage and C--C bond cleavage.The C--H bond cleavage can occur on α carbon,β carbon and γ carbon,respectively.Since the C--C bond is σ bond,the C-H bonds on the carbon atom are axisymmetric and the reactions are equivalent.Then C-H bond cleavage of n-pentane can be divided into three different situations to calculate the kinetic parameters.According to the C--C bond cleavage,the kinetic parameters can be calculated under two conditions of α carbon-β carbon bond and β carbon-γ bond breaking,respectively(Fig.1).

Fig.1.Diagram of reaction sites for pentane.

The kinetic parameters of initiation reaction of the n-pentane pyrolysis calculated under five conditions are listed in Table 1.

Table 1 Kinetic parameters of initiation reaction of the n-pentane pyrolysis

Reaction E a/kJ·mol−1 A 1 CH3CH2CH2CH2CH3→CH3CH2CH2CH2CH2·+H 402.4 1.24×10−16 2 CH3CH2CH2CH2CH3→CH3CH2CH2CH·CH3+H 392.8 8.22×10−15 3 CH3CH2CH2CH2CH3→CH3CH2CH·CH2CH3+H 394.4 8.25× 10−15 4 CH3CH2CH2CH2CH3→CH3CH2CH2CH2·+CH3 368.2 8.91× 10−15 5 CH3CH2CH2CH2CH3→CH3CH2CH2·+CH3CH2 374.4 1.25× 10−16

The reaction rate constants of the above five reactions under the temperature range of the common pyrolysis are calculated by Arrhenius equation.The dependence of reaction rate constant on the temperature is shown in Fig.2.The figure shows that the activation energies of these five reactions are larger,and the reaction rate increases obviously when the reaction temperature exceeds 850°C,and its absolute value is small.

既然如此，对于人工智能，我们是否也可作如是观？进一步说，特别是当人工智能发展到“类人”阶段之时，其和人类的不同究竟还有多大？这种不同，是否必定比女性和男性的不同更大？如果我们不应因女性和男性的差异而否认女性的法律人格，那至少在逻辑上说，差异也不能成为否认人工智能之法律人格的理由。

In hydrogen abstraction reaction stag 60 reactions are considered,in the β cleavage reaction stage 10 β cleavage reactions and 10 reverse cleavage reactions are considered,in the free radical coupling reaction stage 9 free radical coupling reactions are considered.The reaction kinetic parameters of the above reactions are calculated.The changes of the reaction rate constants with the pyrolysis temperature are shown in Figs.3–5.

From Figs.2 to 5,it can be seen that the reaction rate constant k of the initiation reaction(Fig.2)is significantly smaller than that of the other three reaction stages in the reaction temperature range.It is indicated that the initiation reaction is the speed control step of the n-pentane pyrolysis process.

The kinetic parameters of four types of reactions,i.e.the free radical initiation reaction,hydrogen abstraction reaction,β cleavage reaction,and free radical coupling reaction,are obtained by quantum chemistry method.The obtained reaction is combined with the reaction of the pyrolysis model of C4 hydrocarbon[20],and the reaction network of pentane pyrolysis consisted of 199 free radicals reactions.

Fig.2.Rate constants of the initiate reactions[reaction rate constant,s−1(unimolecular reaction)or m3·mol−1·s−1(bimolecular reaction)].

Fig.3.Rate constants of hydrogen absorption reactions[reaction rate constant,s−1(unimolecular reaction)or m3·mol−1·s−1(bimolecular reaction)].

2.2.Pyrolyisis model formulation

A plug flow model is used to simulate the radiant coil of the cracking furnace(Fig.6).The setofcontinuity equations is written with the mass,energy and momentum conservation as follows[21].

On the basis of the obtained kinetic parameters,the above set of equations is solved.The material composition,pressure,temperature and heat intensity of the reactor are calculated.The pyrolysis model is established.

3.Solution and Optimization of Kinetic Model

In the kinetic network of molecular reaction model,the set of ODEs(ordinary differential equation)consisted of fewer involved species and reactions isn't stiff.Such equation set can be solved by four-order Runge–Kutta method.

Fig.4.Rate constants of β-fracture reactions[reaction rate constant,s−1(unimolecular reaction)or m3·mol−1·s−1(bimolecular reaction)].

Fig.5.Rate constants of radical coupling reactions[reaction rate constant,s−1(unimolecular reaction)or m3·mol−1·s−1(bimolecular reaction)].

ΔG≠ Gibbs activation free energy,kJ·mol−1

Fig.6.Schematic diagram of the reaction tube in radiant section

So the stiff of the set of free radical reaction ODEs brings large difficulty for the solving,and the Runge–Kutta method isn't efficient for such ODE set.It is necessary to find new method to solve such ODE set.

3.1.Solution of kinetic model

The semi implicit Eularmethod is applied to solve the stiffODEs[25].The ODE d Y/d t=M(Y)+N(Y)is taken as an example.The right term M(Y)of the equation is a non-rigid term and N(Y)is a rigid term.

Explicit algorithm is as follows.

The solution of this algorithm does not need iteration,but it is not suitable for rigid problems.

Implicit algorithm is as follows.

The algorithm needs to be solved iteratively with a lot of computing resources.

By means of semi implicit method,the term M(Y)is calculated by explicit algorithm and the N(Y)is calculated by the semi implicit scheme.Such solution will not only solve the problem of rigid equations,but also reduce the consumption of computing resources to improve the efficiency of the solution.

The semi implicit Eular method is used to solve the pyrolysis example,and the yield of the product is obtained,as shown in Fig.7.It can be seen that the semi implicit Eular method can solve the stiff ODEs.

Fig.7.Chart for results from semi-Eular methods*:Others stand for minor products e.g.methane,hydrogen,propylene,butadiene,etc.

Although the solution to the problem of stiff ODEs is solved,the current calculation takes a long time.The solution shown in Fig.7 takes more than 3400 ms.The computational efficiency needs to be improved.

3.2.Optimization of solution method

The operation efficiency is improved by multi-core CPU parallel computing with OpenMP assemblies.OpenMP is a parallel processing of program assemblies presented by OpenMP Architecture Review Board[26].It can describe a high-level abstract interface for parallel calculations to reduce the difficulty and complexity of parallel programming.This software can be used in parallel computing programs to support multi-core computing system.

After the addition of the support for OpenMP in programming environment,the program blocks for parallel operation are searched.The parameters ofOpenMP are configured,such as the number of automatic opening process.Then the compiler can process these loops and call the OpenMP assembly to configure the thread granularity and load.The compiled program is running on the computer with quad-core CPU.It shows that threads optimized with OpenMP can use all the CPU resources and the execution time decrease.

K overall thermal conductivity,kJ·s−1·m−2·K−1

Fig.8.Comparison chart of time-consuming of optimized semi-implicit Eular.

After comparison,the code segment with significant optimization is selected to be optimized,and the code segment without obvious optimization is keeping the serial execution.The system resource for creating threads in parallel is reduced and the delay of the inter thread information exchange is also reduced.At last,the average consuming time of the serial semi-implicit Euler method is reduced from nearly 3500 ms to 1200 ms.

3.3.Parameter optimization

In the semi implicit Eular algorithm,there are three important parameters to control the amount of calculation and the calculation accuracy of ODEs' solution,i.e.the absolute error convergence(atol),the relative error(rtol)and the initial step size(h).In the coded program,two of the above three parameters are fixed and the average time of semi implicit Eularalgorithm is scanned under the fixed interval parameter changes.The influence of parameter changes on the average time is presented in Fig.9.

Fig.9.Influence of calculation parameters on consuming time.

Fig.9 shows that with the increase of h value,the average time of the algorithm is obviously reduced,and the inflection pointis reached when the value of h is 0.1 that is the optimized value of h.With the increase of rtol and Atol parameters,the average time of algorithm is decreased obviously without obvious inflection point.But with the increase of the two parameters,the calculation accuracy of semi implicit Eular algorithm decreases.The values of two parameters are selected as those higher values in the range of accuracy requirements.

Fig.10.Schematic device of bench scale pyrolysis unit.

Table 2 Operating conditions of n-pentane pyrolysis experiments

Operating conditions Residence time/s 0.22 Mass ratio of steam to n-pentane 0.50 Coil outlet temperature/°C 650 700 750 800 810 820 830 840 850 860 870

The free radical reaction of the pyrolysis of n-pentane is mainly divided into four type,i.e.initiation reaction,hydrogen absorption reaction,beta cleavage reaction and free radical coupling reaction.Here the kinetic parameters E a and A of the four radical reactions involved in n-pentane pyrolysis are calculated,and the reaction rate constant k at different temperatures can be obtained.

在全国层面，商品房建设逐年增加，房地产开发企业房屋建筑施工面积从1997年的44 985.46万平方米逐步增长至2017年的781 483.73万平方米，房地产开发企业房屋建筑竣工面积从1997年的15 819.7万平方米逐步增长至2017年的101 486.41万平方米。如图3所示。

4.Model Verification

The verification of the kinetic scheme was performed on the basis of n-pentane pyrolysis experiments in the bench scale pyrolysis unit under the temperature range of 650 °C to 875 °C.Fig.10 is the schematic device of the bench scale pyrolysis unit.The unit can predict the yields for most of cracking coils and most of operating conditions and this unit provides valuable lots of suggestions to the ethylene plant about the operation[27].Table 2 is the operating conditions of experiments.

The comparison between measured and calculated yields of hydrogen,ethylene and propylene are presented in Figs.11–13.

通过调查研究，我国90%左右的餐饮企业都是中低档企业，因此，餐饮企业有广阔的发展空间。但由于企业的规模较小，在发展的过程中，其向银行货款或进行融资都有一定的困难，这给企业发展造成一定的影响。

推荐理由:本书讨论了社会热点问题和人们普遍关注的话题中的化学基本知识及化学所发挥的作用，并介绍了一些基础化学知识，让读者更好地了解并对其潜在性和危险性做出合理的评判。

Fig.11.Hydrogen yield of n-pentane pyrolysis from model simulation and experimentation.

Fig.12.Ethylene yield of n-pentane pyrolysis from model simulation and experimentation.

Fig.13.Propylene yield of n-pentane pyrolysis from model simulation and experimentation.

The figures show the general favorable agreement between the predicted data and the experimental data.The experimental yields of main products are consistent with the simulated results from the above kinetic model.The validity of the above built free radical reaction model and its solution method is confirmed.On the basis,the pyrolysis network can be explored,such as increasing the number of reactions and the reaction path,to apply to more complex pyrolysis process.

利用SPSS软件进行描述性统计分析；利用Aquachem水化学软件绘制Piper三线图进行水化学类型分析；选取超标较严重的硫酸盐(SO2-4)、亚硝酸盐(NO-2)、硝酸盐(NO-3)、总硬度和溶解性总固体(TDS)共5项评价指标，利用熵权密切值法对地下水水质进行评价。评价的标准采用《地下水质量标准》(GB/T14848—93)将地下水质量划分为5类(Ⅰ—Ⅴ)，见表1。

5.Conclusions

A method of the establishment and solution of the hydrocarbon pyrolysis model based on free radical reaction mechanism is presented.The n-pentane pyrolysis process is taken as an example.The pyrolysis kinetic parameters are obtained by quantum chemistry and the free radical reaction net is established.The pyrolysis model is developed on the basis of the plug flow reactor model.During the solution of the model,the stiff ODEs are solved by semi implicit Eular algorithm and the computational efficiency increases 10 times by algorithm optimization.

The method is applicable to building free radical reaction model of pyrolysis process of n-pentane.It can accurately simulate hydrocarbon pyrolysis process,and effectively improve calculation speed of reaction model.Itprovides an effective method for the accurate prediction of the yields of pyrolysis products.

A frequency factor,s−1(unimolecularreaction)orm3·mol−1·s−1(bimolecular reaction)

Nomenclature

(3)领导职权执行的差异.有的国际化经营企业在领导管理上遵循一系列严格、明确的管理规则，做到职责分明；有的则重视感情的维系和礼仪的规范.因此，不同的职权分配方式形成国际化经营企业的文化冲突.文化冲突影响了跨文化管理者与员工之间的和谐关系，管理者需要用原有文化背景下的死板的规章制度来控制企业以及企业管理的运行，而员工则会消极应付工作，管理陷入困境.

d i inside diameter,m

d o outside diameter,m

E a activation energy,kJ·mol−1

f friction coefficient

由于国际碳交易市场前景的不确定性，众多参与方将希望寄托于国内碳交易市场的建立。受2012年1月1日起欧盟对飞经欧洲的航空公司征收“碳关税”以及我国自主承诺单位国内生产总值二氧化碳排放比2005年下降40%～45%等因素影响，近两年建立国内碳交易市场的呼声很高。

G mass flow,kg·m−2·s−1

In the above kinetic model,free radical species with very low concentration emerge.It brings the stiffness for the set of ODEs.In such an ODE set,some species' concentrations change rapidly and some change slowly.The rapidly changing component can quickly reach its steady value,while the slowly changing component reaches its steady value slowly.From the view of numerical solution,when the change is fast,the small step length should be selected for the integral,when the changing component reaches its steady value,larger step integration should been chosen.But in common method such as Runge–Kutta method,the step length couldn't be enlarged with the component change,otherwise the numerical instability will occur,i.e.the error will increase rapidly,so that the solving process cannot continue[22–24].

S cross-sectional area of tube,m2

H o heat out of micro element,kJ·s−1

H r reaction heat of micro element,kJ·s−1

为进一步促进核桃生产向丰产、优质、高效发展，实现产业化，要充分认识核桃生产的地位和作用，核桃生产的发展对振兴绿汁镇农村经济、增加农民收入、致富奔小康发挥重大作用。

ΔH≠ activation enthalpy,kJ·mol−1

h Planck constant,6.626196 × 10−34 J·s

After the multi-core CPU parallel computing function is implemented,the code segment of the model is processed in serial and parallel respectively,and the calculation efficiency is tested.The time consuming of optimization is presented in Fig.8.

k reaction rate constant,s−1(unimolecular reaction)or m3·mol−1·s−1(bimolecular reaction)

k B Boltzmann constant,1.3806505 × 10−23 J·K−1

L length of the reaction tube,m

Nk molar flow rate of component k,mol·s−1

这是当前我国农村面临的普遍现象，农村的收入较低，青壮年劳动力多外出打工，在农村留守的多是老人和儿童，农村电商发展中主要依赖的青壮年群体的流失，对农村电商发展不利。年轻化群体拥有良好的信息获取能力和主动学习能力，但是在当前农村运营团队中，重庆忠县凉泉村依赖村干部和年龄较大的村民，在电商知识和技能获取学习方面都力不从心，限制了忠县农村电商的发展。

P reaction pressure,Pa

R ideal gas constant,8.314 J·mol−1·K−1

r j reaction rate of reaction j,mol·m−3·s−1

在当今信息高速发达的社会，教师知识的传授已经不再是学生获得知识和能力的唯一方式和途径。同时信息社会也为学生提供了不受时间和空间局限的受教育机会。在互联网+的教育时代背景下，学生可以在不同的地域环境享受来自其它地方的优质教育，这对于乡村教育来讲，无疑给乡村儿童提供了更多接触和了解新世界、新思想和新知识的机会。加强学校互联网建设，提高乡村学校的硬件设施，使乡村学校学生也能享受到高质量的网络教育。

H i heat into micro element,kJ·s−1

T temperature,K

T f flow temperature,K

T w wall temperature,K

V m molar volume,m3·mol−1

βj,k stoichiometric coefficients of component k in reaction j

当代瓷画创作者多为写实派，我说的写实不是艺术风格，而是作品内容。当代瓷画创作者们都非常关注现实生活，非常关注当代人的所思所想。因此，当代瓷画多为表现当代人的思想情感而作，或表达个人情怀，或表达家国情怀。

Δυ≠ molar change of active compounds

κ(T) Wigner tunnel effect correct factor

ρ fluid density,kg·m−3

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