Research on the Optimization Model of Energy Efficiency of Industrial Park

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1 Sed Orders for Reprits to The Ope Fuels & Eergy Sciece Joural, 2015, 8, Ope Access Research o the Optimizatio Model of Eergy Efficiecy of Idustrial Park He Xi * ad Wag Zhequa School of Ecoomics & Maagemet, Beijig Istitute of Petrochemical Techology, Beijig , Chia Abstract: I order to take the reductio of pollutio emissios as the target, this paper geerates the model parameters based o the iput-output relatioship betwee material flow ad eergy flow of regioal iter-idustry, ad builds the model of eergy efficiecy optimizatio of idustrial park with the distributio of regioal idustry structure as the cotrol variable. The modelig process is discussed i detail i model structure, elemets ad optimizatio objective ad cotrol variable etc. ad the suggestios o further research are give. Keywords: Eergy efficiecy, idustrial park, modelig, optimizatio model. 1. INTRODUCTION As a area marked out through admiistrative measure by the govermet of a coutry or a regio, the idustrial park is a moder productio area which gathers various productio factors, scietifically itegrates the resources, ad optimizes the fuctioal layout. The problems o the evaluatio ad modelig of the supply ad eed, utilizatio efficiecy of eergy resources are cocered by some scholars, ad may researches o the costructio, developmet, plaig ad evaluatio, etc. of eco-idustrial park appear [1-4]. Nevertheless, differet from the admiistrative regio, the idustrial park has o specific cetralized departmet to coduct statistics to the eergy cosumptio ad collect ad maage the statistic data, which is the mai difficulty of buildig the optimizatio model of eergy efficiecy of idustrial park. This paper theoretically discusses the buildig process of the optimizatio model of eergy efficiecy of idustrial park, ad presets some relevat suggestios. 2. MODELING PRINCIPLE AND FUNDAMENTAL ASSUMPTION 2.1. Optimizatio Objective ad Modelig Framework The evaluatio criterio of eergy efficiecy maily covers three aspects, amely livig, resources ad eviromet. The mai objective of the eergy efficiecy optimizatio of idustrial park is to save resources as far as possible ad protect the eviromet o coditio of guarateeig certai beefit of eterprise [5]. Uder certai techical coditio, some by-products geerated from productio ad processig ca directly substitute for raw material, or directly used for fial *Address correspodece to this author at the School of Ecoomics & Maagemet, Beijig Istitute of Petrochemical Techology, Beijig , Chia; Tel: ; Fax: ; hexi@bipt.edu.c cosumptio; some ca geerate ew recyclable by-products or by-products which caot be recycled after beig processed. Uder the existig techical coditio, the byproducts that caot be recycled are likely to cause certai ifluece o the eviromet through emissio, ad such byproduct is called as pollutat. I this way, the productio of sigle product ca be boiled dow to the iput-output process of raw material (eergy) product. I which, the recycle utilizatio of by-product is a key to improve its eergy efficiecy. The more the emitted by-products, the lower the eergy efficiecy, ad the positive relatioship betwee by-product utilizatio ratio ad eergy efficiecy idicates that the improvemet of by-product utilizatio ratio is the effective way to improve the comprehesive eergy efficiecy of the park, as show i Fig. (1). Therefore, the specific objective of eergy efficiecy optimizatio of idustrial park ca be idetified as the improvemet of by-product utilizatio ratio o coditio of guarateeig the gross output of the park; the geeral modelig framework ca be desiged to build a eergy optimizatio model with the productio process as ceter, icludig material flow coversio productio module, eergy coversio flow eergy module ad pollutat emissio eviromet module [6, 7] Fudametal Assumptio I order to be coveiet for describig the model, it is ecessary to perform fudametal assumptio to the productio structure of idustrial park. Assume that there is a sole correspodig relatio betwee product ad eterprise, amely that a eterprise oly maufactures a kid of product, ad a kid of mai product is oly maufactured by a eterprise i the park. Although a sigle eterprise i a park ofte maufactures multiple products, ad a same kid of product is ofte maufactured by may eterprises, this simplified processig does ot affect the descriptio of the productio structure i the park. I fact, the objective of busiess X/ Betham Ope

2 134 The Ope Fuels & Eergy Sciece Joural, 2015, Volume 8 Xi ad Zhequa! Raw!material! (Eergy!resource)! Productio! ad! processig! Product! Fial! product! By6product! Emissio! Evirometa l!pollutio! Fig. (1). Vector flow graph of sigle product productio. operatio is ecoomic accoutig ad eterprise developmet, ad the eergy optimizatio is to improve the eergy efficiecy of the whole park, which does ot ivolve the problems such ecoomic accoutig, ad has o coflict with the objective of improvig the profit of eterprise. I the survey period (also called as report period, it geerally takes fiscal year as uit, ad statistics should be coducted i ivestigatio period if there is o special statemet below), the total productio quatity of a product is called as the gross output of this product, cosistig of itermediate use, fial cosumptio ad imports from other places (imports for short), etc. Of which, itermediate use refers to the product used for productio iput, ad the fial cosumptio icludes eterprise cosumptio of the park, as well as the product exported to the outside of the park through market (exports for short). From Fig. (1), we ca see that the productio iput maily icludes raw material ad eergy, which ca be divided ito iitial iput ad recycled resource re-iput, excludig the product iput. Actually, the productio purpose is to obtai the fial product, while the product iput occupies the fial product, therefore, o the basis of the iput-output priciple of productio, for the productio module, it is assumed as follows: 1) For the give product, its productio techology remais uchaged, amely that the productio techology is exogeous, 2) What is reckoed i the fial cosumptio must be the product, 3) The product ad by-product etered i the productio process are ot reckoed i the iitial iput. The imports may be the material which is same as local product, also may be the resource differet from local product, ad all of them are called as imported product. The productio of it does ot occupy local resource, or pollute local eviromet. Therefore, for the imported product, it is assumed as follows: 1) The imported product is reckoed i itermediate use or fial cosumptio, ot reckoed i the iitial iput; 2) Oly the iitial iput of the imported resource is reckoed, ad the part used for the fial cosumptio is ot reckoed. For the processig of by-product, it is assumed as follows: 1) The by-product substituted for the raw material to participate i the productio eters ito the productio process for the secod time, which is reckoed i the iitial iput, ad correspodigly the replaced raw material should be deducted. 2) The by-product (such as idustrial hot water ad coal gas) substituted for the existig product ad directly used for the fial cosumptio is directly reckoed i the output of replaced product sice it does ot eter ito the productio process for the secod time; 3) The by-product which caot substitute for raw material ad the existig product ad is directly reckoed i the fial cosumptio may be exported to the outside of the park, or directly cosumed locally. Because it does ot eter ito the productio process for the secod time, it caot be directly reckoed i the productio iput, ad the processig method of it is to set a virtual productio uit ad recko this byproduct i its fial cosumptio; 4) The by-product which caot be used etirely is reckoed i the pollutat accordig to the pollutio level of its emissio to the eviromet. 3. MODEL STRUCTURE AND ELEMENTS 3.1. Mai Product ad Productio Module Assume that there are eterprises i the park which maufacture kids of products (mai product), ad the total output of No. k product is called as gross output, ad its distributio is show as follows: = j + y k z k, (k ) 1 (1) j=1 j is the quatity of No. k product cosumed to maufacture No. j product, ad the costituted matrix is called as itermediate use; y k is the quatity of products supplied to the market by the park, icludig fial cosumptio or fial product; z k is the quatity of this product imported (through market) from the outside of the park; If = 0, this park does ot maufacture this kid of product, ad its cosumptio ad itermediate use etirely 1 deotes set {1,2,,}, the same below.

3 Research o the Optimizatio Model of Eergy Efficiecy of Idustrial Park The Ope Fuels & Eergy Sciece Joural, 2015, Volume depeds o the import from the outside of the park, ow j=1 j + y k = z k, idicatig that this commodity should be deleted from the product list, thus > 0. Deote the quatity of No. k product directly cosumed to maufacture uit j product as a kj = j x j, which is called as direct cosumptio coefficiet, ad A = (a kj ) is called as direct cosumptio coefficiet matrix. Hece the vector formula of Formula (1) is: Y = (I A)X + Z (2) The above formula describes the compositio of product s fial cosumptio, which ca de rewritte as: X = (I A) 1 (Y Z) (3) 3.2. Iitial Iput ad Eergy Module For clarity, the eergy i the park oly refers to primary eergy, coal gas, electricity ad petrochemicals used as fuel (such as steam, diesel ad fuel oil), ad all these are called as arrow eergy; ad the pressure gas, cold ad hot source, etc are called as broad eergy. Assume that the first 1 eterprises i the park maufacture arrow eergy ad the followig 2 eterprises maufacture broad eergy, ad assume that the eterprises maufactured the eergy are professioal. Assume that there are r kids of iitial iputs i the park, divided ito two resources, amely eergy ad oeergy, of which, the first s kids are arrow eergy. If we leave out the o-eergy resource iitially iput ad the eergy which has bee cosumed before importig the product, the eergy cosumptio of the park is the gross eergy cotaied i iitially iput eergy substace [8]. Deote No. i Iitial iput material required by No. k uit product as t ik, ad deote T = (t ik ) r, which is called as resource cosumptio coefficiet matrix. O coditio of ot replacig iitial iput with by-product, the iitial iput quatity of No. i resource is u i = t ik,(i r), ad the correspodig iitial iput vector is U r = TX. However, the equivalet by-product utilizatio quatity should be deducted from actual iput quatity. Deote the eergy vector of iitial iput resource as η, leave out the eergy cosumed i the early iitial iput, ad the followig r s vectors are 0, simplified as ηs By-Product ad Eviromet Module Assume that m kids of by-products i all are maufactured durig the productio process of kids of mai products. If we deote the quatity of No. j byproduct geerated from maufacturig uit k product as b kj ad B = (b kj ) m is called as by-product productio matrix, the total quatity of No. j by-product geerated by the give productio structure is b j = b kj ( j m), ad the vector of by-product i the park is b = (b 1,,b m ) T = B T X. The by-product recycle utilizatio is realized through replacig the iitial iput, but the possible scheme of replacemet ad its result are complicated. Based o the above fudametal assumptio, the last scheme ca be boiled dow to direct substitutio. The idirect substitutio is obscure, therefore, oly the direct substitutio is take ito accout i the model. For the productio of product k, if No. j by-product ca substitute for No. i iitial iput, deote the quatity of No. j by-product equivalet to No. i uit iitial iput as h ij k, thus the iitial iput substitutio coefficiet matrix of the by-product substitutio realized through the productio of product k is H k = (h ij k ) r m,(k ). If it caot be replaced, make h ij k = 0. No. i iitial iput required by the productio of uit k product is tik, ad the equivalet No. j by-product is i d jk t ik h ij k (k, i r, j m). Hece the quatity of maximum by-product j used by the productio of uit k r k product is d jk t ik h i=1 ij. Call D = (d jk ) m as the byproduct cosumptio coefficiet matrix, its No. k colum vector is: D k = H k T T k,(k ) (4) Of which, T k is No. k colum of resource cosumptio coefficiet matrix T r. For the give product structure X, the maximum cosumptio vector of No. j by-product i the park is ˆd j = d jk, ad deote d max = ( ˆd 1,, ˆd m ) T = DX. Because the substitutio coefficiet matrix has 3 groups of subscripts, it caot be expressed with two-dimesioal matrix tool. For this, we expad the matrix expressio tool. A matrix is a two-dimesioal row-colum form, ad { H k : k } i fact is sheets of r m forms. Take its subscript as the third dimesio, called as k dimesio, ad the subscripts of each elemet of sigle H k are respectively take as i dimesio ad j dimesio, hece the relatioal formula ca be expressed with Fig. (2). I Fig. (2), matrix T = (t ik ) is at i k plae, D = (d jk ) is at j k plae, H 1 is at i j plae of k = 1, ad H is at i j plae of k =. The calculatio of Formula (4) D k = H k T T k,(k ) is carried out at correspodig i j plae, ad the obtaied vector D k costitutes matrix D = (d jk ) of j k plae.

4 136 The Ope Fuels & Eergy Sciece Joural, 2015, Volume 8 Xi ad Zhequa Table 1. Iput-output table of eergy- eviromet load of idustrial park. Iput Output Dept. Itermediate Use Fial Product Imports Gross Output By-Product Relatioal Formula Product Recycled product Iitial iput Eergy No-eergy Eergy No-eergy Eergy Fig. (2). Schematic diagram of three-dimesioal matrix operatio. The expressio of cotet ad symbol of the above three modules ca be boiled dow to the iput-output relatioship as show i Table 1, of which, all subscripts express the dimesios of vectors or matrixes, ad the superscript T expresses the traspositio of matrix or vector, ad d is the actual usage amout of by-product. 4. MODEL BUILDING 4.1. Costrait Coditios I order to use the parameters ad variables i Table 1 to build the optimizatio model, it is ecessary to further defie the structure of the parameters or variables. The parameter determied by productio techology is called as the parameter of productio techology, ad the parameter oly relates to the idustrial structure of the park is called as the parameter of idustrial structure; the variable chaged with the market demad is called as market variable, ad the parameter oly determied by the ature of material is called as the parameter of material ature. I this way, the sizes of A, B m, Dm ad Tr ad other parameters i Table 1 are determied by the process techology, but the cotets are determied by the idustrial structure of the park. Assume that the productio specificatios of the park remai uchaged, they are the parameters of idustrial structure. Eergy coversio coefficiet ηs ad cotamiatio coefficiet δm are the parameter of material ature. The attribute of H k = (h k ij ) r m relates to the product structure ad material ature. A Y Z X=XD+XT B m Y = (I A)X + Z Dm d = DX D Cotamiatio coefficiet δ b = B T X d max = DX Tr ηs No-eergy u = TX T H k = (h ij k ) r m The fial cosumptio Y of product is market variable, ad X = (I A) 1 (Y Z) is edogeous variable. Assume that the demad vector of the market to the product is Y d, we obtai the first costrait coditio: (I A)X + Z Y d (5) the productio scale of the park is limited by resources. The vector of regioal iitial iput of give product structure ad scale is deoted as U X = (E T,U T ) T. Of which, E is the eergy vector of s dimesio, ad U is other resource iput vector of r s dimesio. Whether eergy or o-eergy resource, ad whether local atural resources or exteral resources, the supply quatity withi certai period is restricted, ad is deoted as U c, hece we obtai the secod costrait coditio: U U c (6) Assume that the productio scale of the park is ot limited by techology, thus there is o explicit productio scale limit i the model. I productio, the by-product substitutes for iitial resource iput, which equivaletly icreases the resource supply quatity. O coditio that the resource is restricted ad the productio scale is ot restricted, it is i favor of the expasio of productio scale. However, the usage amout of by-product is limited by its output, thus we obtai the third costrait coditio d max b, i.e.: (B T D)X 0 (7) This coditio is too strict to the productio scale. O coditio that the iitial iput resource is permissible, we ca cosume the resource to improve the productio scale, ad geerally, the actual usage amout of by-product is d d max. Therefore, Formula (7) is uecessary costrait coditio, which ca be broadeed as: d b (8) Next, we will build the optimizatio mode through discussig the objective fuctio, cotrol variable Optimizatio Model The fial source of the park ecoomic icome is the fial cosumptio determied by its output level (leave out the

5 Research o the Optimizatio Model of Eergy Efficiecy of Idustrial Park The Ope Fuels & Eergy Sciece Joural, 2015, Volume product price), which is guarateed by the first costrait coditio Formula (5). Uder the objective coditio that the resource is limited, the by-product geerated from the productio process of the product of the park ot oly repleishes the resource supply of the park, but also reduces the resource price. Therefore, oe of the bases of determiig the optimizatio objective is that the usage amout of by-product is the maximum. Assume that d is the actual usage amout of by-product, for the give by-product utilizatio scheme, it is the fuctio of gross output i the park, ad the correspodig vector of regioal emissio is P X b d = B T X d. The pollutio level to eviromet due to idustrial emissio is measured accordig to the hazards of differet emissios, ad the uits of measuremet are differet, such as air pollutio, water pollutio ad soil pollutio, etc. I order to make the pollutio geerated from all by-product emissios have comparability, it is ecessary to determie the comparable coefficiets of differet pollutats to uify the measuremet criterio of regioal pollutio level, for example, we ca take the domai value of 100 credit system or equivalet [0-1] domai value. For clarity, we take the measuremet pollutio idex of [0-1] domai value i this model, ad assume that the eviromet pollutio of differet emissios has additive property, amely that the gross cotamiatio geerated from a kid of emissio is the simple accumulatio of uit emissio pollutio. For the give by-product (pollutat), the degree of cotamiatio geerated from uit emissio is determied. If we deote the pollutio idex of uit emissio of No. j byproduct as δj,δ = (δ 1,δ 2,,δ m ), uder the give parameter ad assumed coditio, the geeral pollutio idex of the regio is p = δ P X = δ B T X d, ad the optimized objective is mi p. Divide the gross output vector ito two parts: X = X T + X D, X T ad X D are respectively geerated with the iitial iput ad recycled material i Table 1 as raw material. Now the iitial iput vector is u = TX T the use vector of by-product is d = DX D, ad the objective fuctio is p = δ (B T X DX D ). Based o Formula (2), the optimizatio model is obtaied through combiig the costrait coditios Formulae (5), (6) ad (8): mi p = δ (B T X DX D ) X, X D s.t. (I A)X + Z Y d T(X X D ) U c DX D B T X X X D 0 X > 0 5. MODEL OPTIMAL SOLUTION The icompleteess of model (9) maily lies i its costrait coditios, ivolvig the existece of solutio ad trivial solutio (9) Z i the costrait coditio of Formula (5) is the vector of product imported from the outside of the park, maily used for regulatig the supply of this product of this park, but it does ot embody more effect i the objective fuctio or other costrait coditios, ad it may cause trivial optimal solutio, for example, as log as we take Z = Y d, X * will be the optimal solutio besides the fifth costrait coditio. There are two solutios to this problem. The first solutio is to correct Z ito et import (import-export), Y is the fial cosumptio of the regio, o the coditio that the market demad of the regio Y d ad the et import Z d are give, the first costrait coditio of Formula (9) becomes (I A)X Y d, thus we obtai the relatively complete plaig model: mi p = δ (B T X DX D ) X, X D s.t. (I A)X Y d T(X X D ) U c DX D B T X X X D 0 X > 0 (10) However, the cotradictio coditios (I A)X Y d ad TX T U c i the formula may cause o solutio. Thus it should be solved through improvig the iitial resource supply vector U c ad the by-product usage amout. I fact, TX T U c is equivalet to TX U c + TX D, of which, TX D is the vector of iitial resource equivalet to by-product, ad TX is the whole iput icludig byproduct. Therefore, as log as U c + TX D is big eough, the itersectio of (I A)X Y d ad TX T U c is oempty. The secod solutio is to set the import total products as less as possible mechaism i the model. I fact, the product import Z is oly used for compesatig the isufficiet product supply of the park, ad its criterio is as less as possible o coditio of meetig the primary demad. We ca set puishmet mechaism to hit the mark, amely take the imported product vector Z as the cotrol variable, ad put puishmet factor to the objective fuctio: mi p = δ (B T X DX D ) + MZ X, X D s.t. (I A)X + Z Y d T(X X D ) U c DX D B T X X X D 0 X > 0 (11)

6 138 The Ope Fuels & Eergy Sciece Joural, 2015, Volume 8 Xi ad Zhequa Of which, the elemet of row vector M of dimesio is equivalet to certai positive umber which is big eough. Differet from Formula (10), here we ca avoid the cotradictio of the first two costrait coditios through adjustig export vector Z. O coditio of ot takig techical capacity ito accout, based o the atural coditios of the regio, make DX D B T X as oempty with appropriate idustrial arragemet. We ca observe d max = D(X D + X T ) d, thus the costrait coditio of Formula (8) is looser tha that of Formula (7), ad guaratees p = δ (B T X DX D ) 0. Obviously, the ecessary ad sufficiet coditio that Formula (7) is equivalet to Formula (8) is DX T = 0, ow: d jk x Tk = 0,( j m) (12) If t ik x Tk = 0,(i r), it idicates that the productio iputs of all products use by-product or itermediate iput. O the above assumed coditio, the productio i this park does ot cosume ay atural resource of this park ad ay extraeous atural resource, which is a impossible park product structure, thus i r exists, makig t ik x Tk > 0. Of which, certai k must exist to make x Tk > 0. Because D is oegative matrix (each elemet is oegative), from Formula (12) we ca see d jk = 0,( j m), ow x Dk = 0 ; coversely, if certai d jk > 0, the x Tk = 0. Thus x Tk x Dk = 0,(k ), ad the ecessary ad sufficiet coditio that Formula (7) is equivalet to Formula (8) is that the process that the by-product maufactured from the productio of the product of the park is used for the iitial iput ca be separated, i.e. X T X D = 0. The fourth costrait coditio X X D 0 meas X T = X X D 0, ad coditio X > 0 shows that the regio maufactures the products i Table 1, all these meet the essetial requiremets i ormal circumstaces. I coclusio, through appropriate adjustmet, there is optimal solutio i model (9), ad there is better optimizatio operability. CONCLUSION The structure of the model built i this paper is simple, with preferable operability, which ca be take as the supplemetary mea ad sciece basis of idustrial structure plaig of idustrial park. However the fuctio ad resource edowmet of idustrial park are differet i thousads of ways, ad the model parameters should be determied accordig to the specific characteristics of the park, as well as that the effectiveess ad adaptatio of the model eed further ispectio. Fially, the applicatio ad further research for this model are described simply as follows: 1) Model (9) ad improved (10) or (11) are the framework plaig models with regioal product structure as cotrol variable. It is suggested that the survey should be carried out accordig to the idustrial layout of the park, ad determie the model variable ad parameter with the fuctioal orietatio ad resource edowmet of the park as basis. For the determiatio of parameter, may aspects of actual data should be cosidered comprehesively; 2) The applicatio of vector δ of cotamiatio coefficiet i the objective fuctio is the importat basis for Model (9) to stad. If this parameter does ot exist techically or caot be determied, it is suggested that other equivalet coefficiet should be used, ad the correspodig objective should be chaged ito other correspodig objective from the miimum eviromet pollutio; 3) The model assumes that the emissio is the waste of eergy, ad substitutes the idirect objective miimum emissio for the direct objective improve the eergy utilizatio efficiecy, thus it does ot embody or use eergy value coversio coefficiet i Table 1. It is suggested to cosider the direct eergy efficiecy objective i the further research; 4) For the eergy optimizatio, the comprehesive beefit of the park should be cocered, ad it is allroud. This model oly cotais evirometal beefit (the pollutio idex is the miimum) i the objective fuctio, ad idirectly cotais icome beefit i costrait coditio ( Y Y d ). It is suggested to do meticulous work i further research, cosiderig price, cost ad other regioal comprehesive ecoomic beefits, as well as commutig traffic, evirometal ifluece of grabbig atural resources ad other comprehesive social beefits of the park; 5) I view of the limitatio of data resource ad research deadlie, the optimizatio model built i this paper does ot give actual applicatio case study, which eeds further research. CONFLICT OF INTEREST The authors cofirm that this article cotet has o coflict of iterest. ACKNOWLEDGEMENTS Project supported by atioal atural sciece foudatio of Chia ( ). REFERENCES [1] Wu, Q.; Wu, C. The research o the developmet model of Chia eco-idustrial park. Chi. J. Popul. Resour. Eviro., 2012, 22(7), [2] Liu, H.; Yag, T. The research o the ifluece factors of eergy, ecoomy, eviromet coordiatio developmet of idustrial park. Eterprise Eco., 2013, 2013(3),

7 Research o the Optimizatio Model of Eergy Efficiecy of Idustrial Park The Ope Fuels & Eergy Sciece Joural, 2015, Volume [3] Sog, X.; She, J. Idustrial plaig modelig of eco-idustrial park ad NSGA-II-IFD algorithm based o multi-objective optimizatio. Chi. J. Popul. Resour. Eviro., 2014, 24(9), [4] Li X.; Peg N.; Zhou Y. Iteratioal sustaiable cosumptio practice ad policy implicatio. Chi. J. Popul. Resour. Eviro., 2014, 24(5), [5] Ha, Q.; Liu, Z. Total quatity cotrol-based bi-level plaig model of eergy distributio of idustry area. Chi. J. Maag. Sci., 2013, 21(2), [6] MacKezie, I.A.; Haley, N.; Korieko, T. Usig cotests to allocate pollutio rights. Eergy Policy 2009, 37(7), [7] Ohshita, S. Target allocatio methodology for Chia s provices: Eergy itesity i the 12th five-year pla. Califoria: Lawre Berkeley Natioal Laboratory, [8] Li, G.; Wag, Z. The estimatio of embodied eergy of Chia merchadise trade export based o iput-output method. J. Beijig Ist. Petrochem. Techol., 2013, 21(1), Received: December 5, 2014 Revised: Jauary 23, 2015 Accepted: March 5, 2015 Xi ad Zhequa; Licesee Betham Ope. This is a ope access article licesed uder the terms of the Creative Commos Attributio No-Commercial Licese ( which permits urestricted, o-commercial use, distributio ad reproductio i ay medium, provided the work is properly cited.