YOUSUF Ch. 4

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CHAPTER 4 RESULTS AND DISCUSSION This section discusses all the results of the study, which were obtained by applying the six selected index methods on the three process routes of benzene synthesis case study. After understanding the criteria and requirement of all the index methods in detail, the first step was to collect or estimate the data needed for the index calculation. The data for all the parameters is provided in Appendices D F. Then, the scoring of the hazard parameter was done based on the penalty system of each index method, as described in Chapter 2 of this thesis. It should also be noted that the penalty system for all indexes is consistent, in that a higher penalty score indicates a more unsafe or severe (more hazardous) situation. 4.1 Benzene Synthesis Routes case study The six selected index methods were used to examine the inherent properties for the three process routes of benzene production. The process routes are; toluene hydrodealkylation (TDA), pyrolysis gasoline hydrogenation (Pygas) and catalytic reforming of naphtha

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result discussion of master project .. A STUDY ON CORRELATION OF SAFETY, HEALTH AND ENVIRONMENTAL PROPERTIES AT INHERENT LEVEL: BENZENE SYNTHESIS ROUTES

Transcript of YOUSUF Ch. 4

CHAPTER 4RESULTS AND DISCUSSIONThissectiondiscussesalltheresultsofthestudy,whichwereobtainedbyapplyingthesixselectedindexmethodsonthethreeprocessroutesofbenzenesynthesiscasestudy. Afterunderstandingthecriteria andrequirementofalltheindexmethodsindetail, thefirststepwastocollectorestimatethedataneededforthe index calculation. The data for all the parameters is provided in Appendices D F. Then, the scoring of the hazard parameter was done based on the penalty systemofeachindexmethod,asdescribedinChapter2ofthisthesis. Itshouldalsobenotedthatthepenaltysystemforallindexesisconsistent,inthatahigher penaltyscore indicates a more unsafe or severe (more hazardous) situation.4.1 Benzene Synthesis Routes case studyThe six selected index methods were used to examine the inherent propertiesforthe threeprocessroutesofbenzeneproduction. Theprocessroutesare;toluenehydrodealkylation(TDA),pyrolysis gasolinehydrogenation(Pygas)andcatalyticreforming of naphtha764.1.1 Case study 1: Toluene hydrodealkylation process route (TDA)In the TDA process, toluene reacts with hydrogen to produce benzene and methane.Thereactiontakesplaceat630 C and23bar(Turtonet.al. 1998). TheTDAprocessroutecomprisesoftwonon-catalyticvapor-phasereactions. Thefirstreactionistheonlymainreactionwhichisaccompaniedbythesidereactionasshown below. The TDA process route is described in more details in Section 2.9.Main reaction: Toluene + Hydrogen Benzene + Methane (4.1)Side reaction: Benzene Diphenyl + Hydrogen (4.2)4.1.2 Case study 2: Pyrolysis gasoline hydrogenation process route (Pygas)Pyrolysis gasoline (Pygas) contains a mixture of about 100 chemicals so thatmanyhydrogenationreactionstakeplaceinthereactor. However,theC6cutrepresents 26.23% of the total chemicals fed to the reactor. This is the second largestfeedafterbenzene46.4%(materialbalancetable in Chapter2). Cyclohexeneisconsidered to be the key component of C6cut (Mostoufi et al., 2005). Based on that,the hydrogenation of cyclohexene is selected to be the main reaction chosen for thiscasestudy. Sincebenzenerepresents46%ofthetotalfeedintothereactor,itwasinvolvedintheassessmentofthiscasestudy. Methylcyclohexanewasselectedtorepresent the C7cut in the assessment. The selection of methylcyclohexane is basedon the availability of the data needed for the assessment.In pyrolysis gasoline hydrogenation, the C5cut is removed first by distillation(depentanizer) and sent via the overhead of the depentanizer column to the refinery.TheC9+cutisalsoremovedintheBTX(benzene,toluene&xylene)distillationcolumnandsentviathebottomtotherefinery. The central C6 C8cutisthen77transportedasatopoutletfromBTXdistillationcolumntothereactorforhydrogenation. Thehydrogenationinthereactorisdoneinvaporphaseattemperatureof230 Candpressureof26bar. However,thebottomoutletis thentransportedthroughdifferentdistillationcolumnsformorepurificationandthentoproducebenzene(thePFDanddetaileddescriptionoftheprocess isprovided inChapter 2). The formula below shows the hydrogenation of cyclohexene.C6H10+ H2C6H12(4.3)4.1.3 Catalytic reforming of naphtha process routeNaphthafeednormallycontainsabout300chemicalcompounds.Componentsliken-heptane,n-octane,methylcyclohexane,toluene,ethylbenzene,andxylenesareusuallypresentinsignicantconcentrations. Thesecomponentsrepresent more than 63% of naphtha cut. The other components are present in muchsmaller amounts. All the compounds are present in the naphtha feed as paraffins (40 70 wt. %), naphthenes (20 50 wt. %), aromatics (2 20 wt. %) and olefins only(0 2 wt. %) (Antos and Aitani, 1997). This is the composition of typical straight-run medium naphtha.As shown in Figure 2.8 for the reforming process, naphtha feed is heated upto400 540 Candthenfedunderpressureof10 20 bar. Naphthafeedpassesthroughseriesofcatalyst-equippedreactorsandfurnacesbetweenthereactorstokeep the reactions temperature at desired level. The reactions that take place in thisprocessare;hydrogenationofolefins,isomerizationofparaffinstoiso-paraffins,dehydrocyclizationofparaffinstonaphthenesandthentoaromaticsanddehydrogenationofnaphthenestoaromatics. Asthereactionstakeplaceineachreactor, there is gradually increase in the aromatics concentration from the first to the78final reactor. The formulas below show some of the reactions that take place in thereactors.2 6 6 14 64 ) ( H H C H C Hexane nlization Dehydrocyc+ (4.4)2 6 7 14 73 ) ( H H C H C ohexane Methylcyclation Dehydrogen+ (4.5)The product from the last reactor is called reformate which is transported intoahigh-pressureseparatortoremovethelightcutC1-C2 (AntosandAitani,1997).Reformate is then sent via the bottom outlet into a stabilizer for more purification byseparatingtheC3-C4cutsfromreformatecut(C5-C8+) (Yang etal., 2008).Reformate is then transported into a reformate process unit for further processing toproduce benzene as the desired product. More details on catalytic naphtha reformingprocess route are provided in Chapter 2.4.2 Calculation and discussion of inherent SHE indexesInthisstudy,sixindexbasedmethodswereselectedforconductingtheassessment on the three process routes of benzene.From the six methods, each twomethods represent one aspect of the three main aspects of inherent safety, health, orenvironment. Forinherentsafety,twobasedindexmethods;InherentSafetyIndex(ISI) (Heikkila et al., 1996) and iSafe (Palaniappan et al., 2004) were selected. Foroccupationalhealthassessment,ProcessRouteHealthinessIndex(PRHI)(HassimandEdwards,2006)and InherentOccupationalHealthIndex(IOHI) (HassimandHurme,2010) wereselected.Thesemethodsassesstheinherentoccupationalhealthinessofaprocess. Theinherentenvironmentalevaluationmethodsare; theenvironmentalhazardindex(EHI) (Cave and Edwards, 1997), and InherentEnvironmental Toxicity Hazard; IETH (Gunasekera and Edwards, 2006).794.2.1 Inherent safety index (ISI) calculationAs mentioned earlier in Chapter 2, the inherent safety index (ISI) consists oftwomainindexes. The chemicalinherentsafetyindex(ICI)andprocessinherentsafety index (IPI). For this case study, the calculation of the ICIindex is summarizedin Table 4.1.Table 4.1: Calculation of the sub-indexes of chemical inherent safety index ICIforthe TDA, Pygas and naphtha reforming case studiesTDA processroutesCalculations of the ISISub-indexes of the ICIChemicals IINTICORIRMIRSIFIEITIFETMainreactionToluene 3 04 03 1 2 5Hydrogen 4 0 NA 4 0 4Benzene 3 0 4 1 4 9Methane 4 0 4 1 0 4Penalty of worst chemical 4 0 4 0 4 1 4 9Total ICIfor the step; ICI= 4 + 0 + 4 + 0 + 9 = 17Pygas processroutes Sub-indexes of the ICIChemicals IINTICORIRMIFIEITIFETCyclohexene 4 034 1 2 7Hydrogen 4 0 NA 4 0 4Cyclohexane 3 0 4 1 2 7Benzene 4 0 4 1 4 9Methylcyclohexane 3 0 4 1 1 6Penalty of worst chemical 4 1 3 4 1 4 9Total ICIfor the step; ICI= 4 + 1 + 3 + (4 + 1 + 4) = 17Naphtha reformingroute Sub-indexes of the ICIChemicals IINTICORIRMIFIEITIFETn-Hexane 3 044 1 2 7Methyl cyclohexane 3 0 4 1 1 6Hydrogen 4 0 NA 4 0 4Benzene 4 0 4 1 4 9Toluene 3 0 3 1 2 6Penalty of worst chemical 4 1 3 4 1 4 9Total ICIfor the step; ICI= 4 + 1 + 3 + 9 =17Forthecorrosivenesssub-index (ICOR),based onthedataprovidedinAppendices D1, E1andF1 nochemical involvedinthethree processroutes has80corrosivenesspropertyonmetals;thereforethe ICORisassignedapenaltyof(0).This value is determined based on the penalty system of the ICORwhich is providedinChapter2 (seeTable2.4). IntheTDAcasestudy,thetwoheatreactionsub-indexes for main IRMand side reactions IRSwere calculated to be (- 4134.65 j/g) and(0 j/g) and hence are given penalties of 4 and 0, respectively. In Pygas and naphthareforming case studies no side reactions take place so that only the heat reaction forthemainreaction werecalculatedtobe - 1405j/g forPygasand3005.8j/gfornaphthareforming. Hence,the IRMwas given apenalty of3 foreach. Theheatreactionforthemainandsidereactionswascalculated usingEquation (4.3). Thecalculation in more details is provided in Appendix D1., , ts reac ts reacfproductdproductsfH H Htan tan_ _ = A (4.3)Where;H, is the heat of a reactionHf, is the heat formation of a chemicalThesub-indicesforhazardouspropertiesincludingflammability(IF),explosiveness(IE)andtoxicity(IT)areeachdescribedbytheflashpoint,explosionlimits and threshold limit value TLV-15 min for each chemical substance. First, thepenaltyfor each sub-index is assigned forall chemicals in the process route. Then,the largest penalty sum of these sub-indexes, which represents the worst chemical inthe process, is taken to calculate the ICIindex. The largest sum which is 9 was givenby benzene. Benzene was assigned a penalty of (4) as a highly flammable chemicalwithalowflashpointtemperature(-11.1 C). Ontheotherhand,benzenewasassignedapenaltyof(1)foritsexplosionlimits(1.2% - 7.8%). FortheIT,benzenewasassignedapenaltyof(4)ascarcinogenicchemicalwithaTLV-15minof 2.5ppm. This result is generalized to all three case studies since benzene presents in allthreeprocessroutes. Thesepenaltiesweregivenbasedonthepenaltysystemprovided in Table 2.4.In the same manner, Penalties are assigned to each sub-indexfor all chemicals as shown in Table 4.1 above. Data is provided in Append D1, E1and F1.81, 9 4 1 4 = + + = + +benzene T E FI I I (4.4)After determining the penalties for all chemical sub-indexes, the ICIvalue wasobtained for each process route by applying Equation (2.2) as shown in Table 4.1. Inthe TDA and naphtha reforming case studies the ICIwas given a value of 17 for each.On the other hand, ICIwas given a value of 16 in the Pygas case study. This can beinterpreted by that the reactions in the three process routes take place with differentheatreaction asmentionedearlierandhence theIRMsub-indexwasassignedapenalty of 4 in both TDA and naphtha reforming case studies, while it was assigned apenalty of 3 in Pygas case study.The process inherent safety index (IPI) was also calculated as shown in Table4-2 below. This index consists of five sub-indexes which are; inventory (II), processtemperature (IT), pressure (IT), equipment safety (IEQ) and process structure (IST).IntheTDAprocess,thereactiontakesplaceat 630 C and 23bar,whichcontributetothepenaltyof4and 1totheITandIP,respectively. InPygashydrogenationprocess,theoperatingtemperatureis230 Candtheoperatingpressure is 26 and hence ITand IPwere assigned a penalty of 2 for each. In naphthareforming process, the feed is heated up to 400 540 C and then fed under pressureof10 20bar. Basedonthat,penaltiesof3and1were assignedtoITandIPrespectively. Theequipmentsafetysub-index(IEQ)wasgivenapenaltyof 3theTDAprocess,whileitwasgivenapenaltyof4bothPygasandnaphthareformingprocess. Thisisbecause;theTDA,Pygasandnaphthareformingprocessinvolvehighhazardequipmentsuchasanexothermicreactor(TDAprocess),furnace,compressor,andseparationanddistillationsystems(seetheprocessflowdiagramFig.2-6,2-7 and2.8). Theprocessintheseroutesisconsideredunsafeforhavingsuchhazardousequipments. Hence,theISTwasassignedapenaltyof3fortheprocessroutesexceptforthe naphthareforming routewherethe processincludethreefurnacesinserieswhichmeans repeatedreheatisrequired sothattheISTwasgiven a penalty of 4 (data is provided in Appendices D2, E2 and F2).82Table 4.2: Calculation of the sub-indexes of process inherent safety index IPIfor theTDA, Pygas and naphtha reforming case studiesTDA processroutesCalculations of the ISISub-indexes of the IPIMainreactionChemicals IIITIPIEQISTToluene3 4 1 3 3HydrogenBenzeneMethaneTotal IPIfor the route = 3 + 4 + 1 + 3 + 3 = 14Pygas process route Sub-indexes of the IPIChemicals IIITIPIEQISTCyclohexene4 2 2 4 3HydrogenCyclohexaneBenzeneMethylcyclohexaneTotal IPIfor the route = 4 + 2 + 2 + 4 + 3 = 15Naphtha reforming route Sub-indexes of the IPIChemicals IIITIPIEQISTn-Hexane3 3 1 4 4Methyl cyclohexaneHydrogenBenzeneTolueneTotal IPIfor the route = 3 + 3 + 1 + 4 + 4 = 15The inventory (Q) of chemicals was calculated to be 73 ton for TDA process,318.5tonforPygasprocessand127.6tonfornaphthareformingprocess. Thegreater is the inventory the higher is the penalty. Based on that, the IIwas assigned apenalty of 3 for the TDA and naphtha reforming routes, while it is assigned a penaltyof4forthePygasprocessroute. Thecalculationoftheinventorywasdone bymultiplyingthethroughputintothemajorvessels(F)withtheresidencetime()ofthese vessels(seeEquation4.1). Majorvesselsforeachprocessrouteareasillustrated in Figures 2.6, 2.7 and 2.8. The calculation of the inventory for all routesis shown in Table 4.3. = F Q (4-1)83Table 4.3: Calculation of the inventory in the TDA, Pygas and naphtha reformingprocess routesToluene hydrodealkylation process routUnit Feed (t/h) (h) Inventory, Q (ton)Mixer (V-101) 13.27 1 13.27Reactor (R-101) 20.86 0.083 1.73Flash drum(V-102) 20.9 1 20.9Flash drum(V-103) 11.6 1 11.6Distillation column (T-101) 25.6 1 25.6Total inventory 73.1Pygas hydrogenation process routeUnit Feed (t/h) (h) Inventory, Q (ton)Depentanizer(DA-17002) 24124BTX-Tower (DA-17003) 18.428118.428DPG-2 reactor (DC-17101) 16.410.0831.362Flash (FA-17201) 16.412116.412Stabilizer(DA-17202) 11.864111.864Splitter (DA-17001) 11.839111.839Ex. distillation (DA-17901) 31.84131.84Stripper (DA-17902) 148.5971148.597Distillation C. (DA-17203) 18.053118.053Clay Tower(FA-17203) 18.053118.053Clay Tower(FA-17204) 18.053118.053Total inventory Q 318.5Naphtha reformingUnit Feed (t/h) (h) Inventory, Q (ton)Reactor(R-100) 27.3211 0.083 2.267Reactor(R-100) 27.3211 0.083 2.267Reactor(R-100) 27.3211 0.083 2.267Flash drum(V-100) 27.3211 1 27.3211Stabilizer (V-101) 25.9023 1 25.9023Splitter(V-102) 25.901 1 25.901Ex. Distillation tower (T-100) 25.901 1 25.901Benzene tower(T-101) 17.358 1 17.358Total inventory Q 129.1844Afterdeterminingthepenaltyofeachsub-index,theIPIvalueswerecalculatedtobe15forbothTDAandPygasprocessroutesand14fornaphthareforming route as shown in Table 4.2 above. The total inherent safety index value(IISI) was obtained for all process routes by using (Eq. 2-1) as follows;84, 31 14 17 = + = + =PI CI TDA ISII I I, 32 15 17 = + = + =PI CI Pygas ISII I I, 32 15 17 = + = + =PI CI TDA ISII I I4.2.2 i-Safe index calculationTheiSafeindexmethodconsistsoftwoindexeswhicharetheindividualchemicalindex(ICI)andtheindividualreactionindex(IRI). TheICIconsistsofreactivity(Nr),flammability(Nf),explosiveness(Ne)andtoxicity(Nt)sub-indexes.Meanwhile,theIRI consistsof processyield(Ry),temperature(Rt),pressure(Rp),and the heat reaction (Rh) sub-indexes (Palaniappan et al., 2004). The iSafe methodisalmostsimilartotheISImethodexceptfortheprocessyieldsub-indexwhichisfromthe PIIS (EdwardsandLawrence,1993). TheiSafesub-indexesarescoredbased on the same penalty system developed for the ISI.As shown in Table 4.4 for the ICI index, a penalty was assigned to each sub-indexbasedonthedatacollectedforthe relevant parameter. Thepenaltyofthereactivitysub-index (Nr) isbasedontheNFPAreactivityratingdataforeachchemicalsubstance,whereastheotherthreesub-indexes(Nf, Ne, Nt)areevaluatedbasedonthedataofflashpoint,explosionlimitsandthresholdlimitvalueTLV-15min, respectively foreach chemical. The ICI is then calculated by summing up thepenaltiesofthefoursub-indexesforeachchemical. The ICImaxrepresentsthemaximumsummationvalueofthefoursub-indexes. Thechemicalwiththe ICImaxvalue is considered as the worst chemical in the process route.Becauseofitseffectsonhealthasacarcinogenicchemical, benzeneisconsidered to be the worst chemical in all the three process routes and also used as an85example to show how the four sub-indexes are calculated. The reactivity of benzeneis 0 and hence is given a penalty of 0, while it was assigned a penalty of 4 as a highlyflammablewith lowflashpointtemperature -11.1 C. Ontheotherhand,benzenewasassignedapenaltyof 1 foritsexplosionlimits 1.2% - 7.8%. Foritstoxicity,benzenewasassignedapenaltyof 4basedonitsTLV-15minwhichis 2.5 ppm.These penalties were given based on the penalty system provided in Table 2.4. Thesame calculation of the rest of the sub-indexes is conducted for each chemical basedon the data provided in Appendices D3, E3 and F3.Table 4.4: Calculation of the iSafe sub-indexes for the TDA, Pygas and naphthareforming process routesTDA processroutesCalculation of i-SafeICI sub-indexes IRI sub-indexesChemicals NrNfNeNtICI ICImaxRyRtRpRhIRIMainreactionToluene 0 3 1 3 79 0 4 1 4 9Hydrogen 0 NA 4 0 4Benzene 0 4 1 4 9Methane 0 4 1 0 5Pygas processroutes ICI sub-indexes IRI sub-indexesChemicals NrNfNeNtICI ICImaxRyRtRpRhIRICyclohexene 0 4 1 2 79 3 3 2 3 11Hydrogen 0 NA 4 0 4Cyclohexane 0 4 1 2 7Benzene 0 4 1 4 9Methylcyclohexane 0 4 1 1 6Naphtha reforming route ICI sub-indexes IRI sub-indexesChemicals NrNfNeNtICI ICImaxRyRtRpRhIRIn-Hexane 0 4 1 2 79 2 3 1 3 9Methyl cyclohexane 0 4 1 1 6Hydrogen 0 NA 4 0 4Benzene 0 4 1 4 9Toluene 0 3 1 2 6For the calculation of IRI sub-indexes, the process yield of benzene from thethreeprocessrouteis 98% fromtheTDAprocess, 75.22%fromPygasprocessand82.76% from naphtha reforming process. Based on that, the Rywas given penaltiesof 0,3and2for thethreecases respectively. Thisisbecauseahighyieldisgoodfrominherentsafetyperspectivebecausemoreofthereactantsareturnedintothe86desired product. Thus the associated penalty value will be smaller for a higher yieldvalue (indicates less hazardous condition). The other three sub-indexes (temperatureRt, pressure Rp, and the heat reaction Rh) are penalized based on the exact approachas used in the ISI. The calculation of IRI sub-indexes is shown in Table 4.4 above.The total reaction index for the all examined process routes TRI was obtained using(Eq.2-5). The overallsafetyindex(OSI) isthesumoftheTRIforeachstepinvolvedintheprocessbut, sincethereisonlyonereactionstep foreachprocessroute, the (OSI) value is equal to the TRI value.18 9 9max= + = + = IRI ICI TRITDA18 = X = TRI OSITDA20 11 9max= + = + = IRI ICI TRIPygas20 = X = TRI OSIPygas18 9 9max= + = + = IRI ICI TRINaphtha18 = X = TRI OSINaphtha4.2.3 Inherent occupational health index (IOHI) calculationInherent occupational health index (IOHI) consists of two indexes which arephysical and process hazards index (IPPH) and index for health hazards (IHH). Thesetwoindexes are calculatedseparatelyandthenthevaluesofthetwoindexesaretotalled up to give the IOHI value. The IPPHindex consists of six sub-indexes whichare; the mode of process (IPM), material phase (IMS), volatility (IV), pressure (IP) (bar),corrosiveness(IC)andtemperature(IT). Ontheotherhand,theIHHindexisformulatedfromtwosub-indexeswhichare;exposurelimitbasedsub-index(IEL),giving information on the chronic hazards of the chemicals in the working air and theR-phrase based sub-index (IR) which describes the type of health effect that might becaused by the chemical (Hassim and Hurme, 2010a).87For the IPPHsub-indexes, the IC, IVand IMSsub-indices are penalized based onthe chemicals corrosiveness, boiling point andmaterial phase data respectively. InTDA process, for the IC, no chemical has corrosiveness property on metals and hencethe ICisassignedapenaltyof 0foreachchemical. ForbothPygasandnaphthaprocess, theICwasassigned a penalty of 1 due to the availability of H2S which hascorrosivenesspropertyonmetals. FortheIV,thehighertheboilingpointofachemicalthelowertheIVpenaltywillbe. Thisisbecause;thechemicalwithhighboilingpointismorestableatthereactiontemperature. IntheTDAprocess,hydrogenhas thelowestboilingpointsof -259.2C. Basedonthat,theIVwasassignedapenaltyof 3 asamaximum penalty for thewholeprocess. Thesame IVpenaltywasassignedtothePygasandnaphthareformingroutessincehydrogenisinvolvedintheprocess. The threeprocessroutesinvolve chemicalswhichareinliquid phaseandhencetheIMSwas assigneda maximum penaltyof 2,whileitwasassignedapenaltyof1forchemicals in vaporphase. AsinISIandi-Safe,thepenaltyofworstchemicalisconsideredforIPPHcalculation. Ontheotherhand,modeofprocess(IPM),pressure(IP),andtemperature(IT)wereobtainedforthewhole step. The mode of process is continuous in all process routes so that the IPMwasassignedapenaltyof1. Despitehavingdifferentoperatingpressureandtemperature, the three process routes were assigned penalties of 1 and 3. This is dueto the nature of the associated penalty system as shown in Table 2.8. The calculationof IPPHis summarized in Table 4.5.For IHH, both IELand IRpenalties were determined for each chemical based onits occupational exposure limits (OEL-8h) value and R-phrase. The value of the IHHwas then calculated by the summation of the maximum IELand IRpenalties receivedbythechemicalsubstanceintheprocess. Inallstudiedprocessroutes,benzenegives the largest penalties for both IELand IRsince it is a carcinogenic chemical. Theoverall value ofIOHI was obtained to be (21) for TDA, (22) for Pygas and (22) fornaphtha reforming process. This is shown in Table 4.5.88Table 4.5: Calculations of the IOHI index for the TDA, Pygas and naphthareforming process routesTDA processroutesCalculation of IOHIIPPHsub-indexes IHHsub-indexesChemicals ICIVIMSITIPIPMIELIR(acute)IR(chronic)IRMainreactionToluene 0 1 23 1 12 1 3 4Hydrogen 0 3 1 0 0 0 0Benzene 0 1 2 4 2 5 7Methane 0 3 1 0 0 0 0Maximum penalties 0 3 2 3 1 1 4 2 5 7Total IPPHand IHH10 11Overall value of IIOHI21Pygas processroutes IPPHsub-indexes IHHsub-indexesChemicals ICIVIMSITIPIPMIELIR(acute)IR(chronic)IRCyclohexene 0 1 23 1 11 1 3 4Hydrogen 0 3 1 0 0 0 0Cyclohexane 0 1 2 1 4 3 4Benzene 0 1 2 4 2 5 7Methylcyclohexane 0 1 2 1 1 3 4Maximum penalties 1 3 2 3 1 1 4 2 5 7Total IPPHand IHH11 11Overall value of IIOHI22Naphtha reforming route IPPHsub-indexes IHHsub-indexesChemicals ICIVIMSITIPIPMIELIR(acute)IR(chronic)IRn-Hexane 0 1 23 1 11 2 4 6Methyl cyclohexane 0 1 1 1 1 3 4Hydrogen 0 3 1 0 0 0 0Benzene 0 1 2 4 2 5 7Toluene 0 1 2 2 1 3 4Maximum penalties 1 3 2 3 1 1 4 2 5 7Total IPPHand IHH11 11Overall value of IIOHI224.2.4 Process route healthiness index (PRHI) calculationThePRHIindexismorecomplicatedthantheotherindicesdiscussedpreviously. The calculation of the PRHI includes the following sub-indices: inherentchemicalandprocesshazardindex(ICPHI),health hazardindex(HHI), material89harmindex(MHI),workerexposureconcentration(WEC)andtheoccupationalexposure limit (OEL). Details of the PRHI index are discussed in Chapter 2.4.2.4.1 Inherent Chemical and Process Hazard Index (ICPHI) calculationThisindexassessestheprocessactivities(AP)andprocessconditions(CP)thatareinvolvedinachemicalprocessroutebyassigningapenaltyforeach.Ahigherpenaltyindicatesahigherhazardposedbytheactivityortheprocesscondition.Theprobabilityofthereleasethatcanbecausedbyanactivityoraprocess condition assigns the penalty.The higher the probability of therelease, thehigher the penalty will be. Equation (2.13) is used to calculateICPHI [20]. Tables2.6 and 2.7 summarize the penalties for process activities and process conditions.The ICPHI was calculated for all process routes by summing up the penaltiesreceivedbytheprocessactivities(AP)andtheprocessconditions(CP). Thepenaltiesreceived bythe APandCPare 5 and 4 inTDAprocesscase,while thepenalty receivedby thesamesub-indexes inbothPygasandnaphtha is5 foreach.Tables 4.6 and 4.7 summarized the AP and CP calculation.TheAPcalculationpartitselfconsistsoffiveactivities. For allstudiedprocess routes, since the materials are in liquid and gas phase, material transportationis conducted via pipes, therefore this activity was assigned with the penalty of 1. Themode of process in all routes is considered to be continuous and hence is assigned apenalty of 1. All the process routesinclude flaringbutabove occupiableplatformlevelsothatthisactivitywasassignedapenaltyof2. Maintenanceworksarerequired in these process routes so this activity assigned a penalty of 1. The value ofthe AP was obtained by summing up the penalties of all these activities as shown inTable 2.6.90Table 4.6: Calculations of ICPHI - Penalties for Activities (PA) for TDA, Pygas andnaphtha reforming process routesPenalties for Activities (PA) TDAProcessActivities Operation PenaltyTransportPipe 1 1Bag 2Drum 3Vibration 4Mode of processContinuous 1 1Semi-continuous 2Semi-batch 2Batch 3Venting or flaringNoneScrub vent effluent 1Above occupiable platform level 2 2occupiable platform level 3MaintenanceNo 0Yes 1 1OtherAgitation 10Others (seiving, filtering ...) 1Solid handling 2Size reduction 2Extrusion 3Air open mixing 3Total (AP) for the step = 1 + 1 + 2 + 1 + 0 = 5FortheCP,thereareeightparametersinvolvedwhicharetemperature(0C),pressure (atm), viscosity (cp), ability to precipitate, density difference (sg), ability tocausecorrosion, solubility and materialstate. Inspiteofhavingdifferent operatingtemperature and pressure as mentioned earlier, the three process routes were assignedthesamepenaltiesof1and0 forthesetwoparameters. Thisisduetothe penaltyrangeofthetemperatureandpressure in theassociatedpenaltysystemasshowninTable2.7. Thecalculationofviscosity(Vis),density(Den),corrosiveness(Cor),solubility(Sol)andmaterialstate(MS)isbasedontheworstchemicalassumption.The viscosity of the chemicals involved in the three process range from 0.009 to 0.98(cp) and hence was assigned a penalty of 1 for each chemical. The density of thesechemicals range from 0.069 to 0.87 and based on that it was assigned a penalty of 1foreachchemical. Asdiscussedearlier,inTDAprocess, nochemical has91corrosivenesspropertyonmetalsandhencethe Cor isassignedapenaltyof 0foreach chemical. For both Pygas and naphtha process, the Cor was assigned a penaltyof 1 due to the availability of H2S which has corrosiveness property on metals. Allchemicalsinthese process routes havelow solubilitysothattheSol sub-indexwasassigned a penalty of 0. Except for hydrogen and methane all chemicals involved inall the studied process routes are in liquid state. Due to that, the MS was assigned apenalty of 1 for each chemical in liquid state.Table4.7: Calculationsof ICPHI - Penaltiesfor processconditions (PC) forTDA,Pygas and naphtha reforming process routesTDA processroutesCalculation of CPDescription of conditionsChemicals T C P atm Vis(cp) Den Cor Sol MSMainreactionToluene1 01 1 0 0 1Hydrogen 1 1 0 0 0Benzene 1 1 0 0 1Methane 1 1 0 0 0Total PC for the route 1 + 0 + 1 + 1 + 0 + 0 + 1 = 4ICPHI = AP + PC = 5 + 4 = 9Pygas processroutes Description of conditionsChemicals T C P atm Vis(cp) Den Cor Sol MSCyclohexene1 01 1 0 0 1Hydrogen 1 1 0 0 0Cyclohexane 1 1 0 0 1Benzene 1 1 0 0 1Methylcyclohexane 1 1 0 0 1Total PC for the route 1 + 0 + 1 + 1 + 1 + 0 + 1 = 5ICPHI = AP + PC = 5 + 5 = 10Naphtha reforming route Description of conditionsChemicals T C P atm Vis(cp) Den Cor Sol MSn-Hexane1 01 1 0 0 1Methyl cyclohexane 1 1 0 0 1Hydrogen 1 1 0 0 0Benzene 1 1 0 0 1Toluene 1 1 0 0 1Total PC for the route 1 + 0 + 1 + 1 + 1 + 0 + 1 = 5ICPHI = AP + PC = 5 + 5 = 10924.2.4.2 The HHI and MHI calculationThehealthhazardindexHHIwascalculatedforeachchemicalsubstanceinvolved in the process based on its effect to human health. The penalty system wasdevelopedbasedonhealtheffectHEvalues.TheHEliststheprincipleeffectsofexposuretoa chemicalanditsvaluesrangefrom1to20,where1representingthemostseverehealtheffectsand20indicatesthelowesthealtheffects(seeappendixA).ThepenaltysystemofPRHIanditsotherindexesisconsistent,inthatahighvalueindicatesthe moresevereorworsesituation.TomakethevaluesofHHIconsistentwiththispenaltysystem,anewscaleofminimum0andmaximum5iscreated.AvalueofHHIistakenbydividingthesubtractionproductof(21- HEcode) by the maximum ranking value of 20 and finally multiplying it with maximumscale of 5.This is done by using (Eq. 2.14).IntheTDAcasestudy, benzenehasthelargestHHIvalue 17.9 sinceitisacarcinogenic chemical. This is followed by 7.3 assigned to toluene. Hydrogen andmethaneareconsideredasasphyxiantchemicalsthereforetheywereassignedwithlower penalties of 1.8 for each. The total value of the HHI for the TDA process routeis 28.8 as shown in Table 4.8.93Table 4.8: Calculation of the Health Hazard Index (HHI) TDA process routeTDA Process routeHealth Effect (HE)* 21-HEScaledPenaltyHHI forchemicalMainreactionChemicalsTolueneIrritation to Eye, Nose,Throat, Skin Moderate(HE15)6 1.57.3 Narcosis (HE8) 13 3.3Acute pulmonary edema,chemical pneumonitis(HE11)10 2.5HydrogenAsphyxiant (HE17) 4 11.8Explosive (HE18) 3 0.8BenzeneLeukemia (HE1) 20 517.9CNS depression (HE7) 14 3.5Narcosis (HE8) 13 3.3respiratory arrest (HE11) 10 2.5cardiovascular collapse;aplastic anemia (HE12)9 2.3Irritation (HE16) 5 1.3MethaneSimple asphyxiant(HE17)4 11.8Explosive (HE18) 3 0.8Total HHI for TDA process route = 7.3 + 1.8 + 17.9 + 1.8 = 28.8InthePygascasestudy, benzene also hasthelargestHHIvalue 17.9.Methylcyclohexanetookthesecondplacewithapenaltyof 13.1. Cyclohexene,hydrogen and cyclohexane assigned penalties of (9.3), (4.8) and (1.8) for each. Thetotal value of the HHI for the Pygas hydrogenation process route is 46.9 as shown inTable 4.9.94Table4.9: CalculationoftheHealthHazardIndex(HHI) Pygashydrogenationprocess routePygas Process routesHealth Effect (HE)* 21-HEScaledPenaltyHHI forchemical Step ChemicalsMainreactionCyclohexeneCumulative systemictoxicity (HE3)18 4.59.3Narcosis (HE8) 13 3.3Irritation-Eye, Nose,Throat, Skin-Moderate(HE15)6 1.5HydrogenAsphyxiant (HE17) 4 11.8Explosive (HE18) 3 0.8CyclohexaneNarcosis (HE8) 13 3.34.8Irritation-Eye, Nose,Throat, Skin-Moderate(HE15)6 1.5BenzeneLeukemia (HE1) 20 517.9CNS depression (HE7) 14 3.5Narcosis (HE8) 13 3.3respiratory arrest(HE11)10 2.5cardiovascular collapse;aplastic anemia (HE12)9 2.3Irritation (HE16) 5 1.3methylcyclohexaneIrritation-Eyes, Nose,Throat, Skin---Mild(HE16)5 1.313.1Respiratorysensitization (asthma,rhinitis) (HE9)12 3Suspect teratogen(HE5)16 4Mutagen (HE2)19 4.8Total HHI for the step process route =9.3 + 1.8 + 4.8 + 17.9 + 13.1 = 46.9For naphtha reforming process, benzene also has the largest HHI value 17.9.Methylcyclohexanetookthesecondplacewithapenaltyof 13.1. Hexane,tolueneand hydrogen were assigned penalties of 8.9, 7.3 and 1.8 for each. The total value ofthe HHI for naphtha reforming process route is 53.8 as shown in Table 4.10.95Table4.10: CalculationoftheHealthHazardIndex(HHI) naphthareformingprocess routeBenzene Process routesHealth Effect (HE)* 21-HEScaledPenaltyHHI forchemicalProcessrouteChemicalsNaphthareformingn-HexaneIrritation-Eye, Nose,Throat, Skin---Mild(HE16)5 1.38.9Nervous systemdisturbances---Polyneuropathy (HE7)14 3.5Narcosis (HE8) 13 3.3Explosive, flammable(HE18)3 0.8Narcosis (HE8) 13 3.3MethylcyclohexaneIrritation-Eyes, Nose,Throat, Skin---Mild(HE16)51.313.1Respiratorysensitization (asthma,rhinitis) (HE9)12 3Suspect teratogen(HE5)16 4Mutagen (HE2) 19 4.8HydrogenAsphyxiant (HE17) 4 11.8Explosive (HE18) 3 0.8BenzeneLeukemia (HE1) 20 517.9CNS depression (HE7) 14 3.5Narcosis (HE8) 13 3.3respiratory arrest(HE11)10 2.5cardiovascularcollapse; aplasticanemia (HE12)9 2.3Irritation (HE16) 5 1.3TolueneIrritation to Eye, Nose,Throat, Skin Moderate(HE15)6 1.57.3 Narcosis (HE8) 13 3.3Acute pulmonaryedema, chemicalpneumonitis (HE11)10 2.553.8For materialharmfulindexMHI,eachchemical ineachprocessroute wasassignedapenaltybasedonitsNFPAhealthranking(seeAppendixB). TheMHIvalue was obtained to be 5 for the TDA route, 7 for the Pygas route and 7 for naphtha96reforming process route. The calculation of the MHI for chemicals involved in eachprocess route is presented in Table 4.11 below.Table4.11: Calculationofmaterialharmfulindex(MHI) forthe TDA,Pygasandnaphtha reforming process routesTDA processroutesNFPA healthrankingPenaltyMainreactionToluene 2 2Hydrogen 0 0Benzene 2 2Methane 1 1Total MHI for TDA process route = 2 + 0 + 2 + 1 = 5Pygas processroutesNFPA healthrankingPenaltyCyclohexene 2 2Hydrogen 0 0Cyclohexane 2 2Benzene 1 1Methylcyclohexane 2 2Total MHI for TDA process route = 2 + 0 + 2 + 1 + 2= 7Naphtha reforming routeNFPA healthrankingPenaltyn-Hexane 1 1Methyl cyclohexane 2 2Hydrogen 0 0Benzene 2 2Toluene 2 2Total MHI for naptha reforming process route;1+ 2 + 0 +2 + 2 = 74.2.4.3 The work exposure concentration (WEC) calculationThecalculationprocedureoftheWECstartswithcalculatingtheemissionrateofchemicalsfromsmallleaks(SM)andestimatingthefugitiveemissions(FE)intheprocess. TheSM canbecalculatedthroughtheairbornequantityofreleasedgasAQg,airbornematerialfromflashingliquidsAQfandtheairbornematerialevaporatingfromapoolsurfaceAQP. However,inthisstudy onlyAQgwascalculatedsinceallprocessrouteshave vapourphasereactiononly. TheAQgiscalculated by using Equation (Eq. 4.2).97273 / 10 751 . 42 6+ =T MW P D x AQavg a g(4.2)Where,D is the diameter (mm) of a hole with a maximum value of 0.25 inch,Pa is the absolute pressure (kpa) = (Pg+101.35);Pgis the gauge pressure (kpa gauge),MWavgistheaveragemolecularweight (mol/g) for materialsineachprocessroute(Eq. 4.3)T is the operating temperature, C._= MWxMF MWavg(4.3)Where,MW is the molecular weight of each chemical in the processMF is the mole fraction of the same chemical.Themolefractionforchemicalsiscalculatedbasedontheirflowratefromthereactorsoutlet(seeAppendix D9forTDA,E8forPygasandF8fornaphthareforming). ThevalueofgAQ wascalculatedtobe 0.06418kg/s fortheTDAprocess, 0.07992 kg/s forPygasprocessand 0.07095 kg/s fornaphthareformingprocess. Asummaryofairbornequantitycalculationfor allprocessroutesisprovided in Appendices D8, E7 and F7.For the FE, since at the R&D stage no piping diagram isyet available, basicassumptionsontheleakingpointsintheprocessaremade. Thetypicalleakpointsfrom valves, pumps, compressor, pressure relief valves, sampling points and flangesareconsidered (seeAppendix D9forTDA,E8forPygasandF8fornaphthareforming). Once the type and number of leak points have been determined in eachprocess,theFEsareestimatedbasedontheemissionfactorsestablishedbytheenvironmental protection agency (EPA). The total fugitive emissions in each processroute are then estimated by summing up the emissions from all the leak points. Forthe TDA process route the total fugitive emission is 0.7943 kg/h, while it is 1.15 kg/h98forPygasprocessand 1.080kg/h. Asummaryof fugitiveemissionscalculationisincluded in Table 4.12.Table 2.12: Estimation of fugitive emissions in the TDA, Pygas hydrogenation andnaphtha reforming processThe TDA process routeType of leak pointNumber of leakpointsEmission factor(kg/h)Total rate (kg/h)Valves 10 0.00597 0.0597Pumps 2 0.0199 0.0398Compressor 1 0.228 0.228Pressure reliefvalves3 0.104 0.312Sampling points 3 0.015 0.045Flanges 60 0.00183 0.1098Total FEs = 0.0597+0.0398+0.228+0.312+0.045+0.1098= 0.7943 kg/hThe Pygas hydrogenation process routeType of leak pointNumber of leakpointsEmission factor(kg/h)Total rate (kg/h)Valves 16 0.00597 0.09552Pumps 2 0.0199 0.0398Compressor 0 0.228 0Pressure reliefvalves8 0.104 0.832Sampling points 4 0.015 0.06Flanges 68 0.00183 0.12444Total FEs = 0.09552 + 0.0398 + 0.832 + 0.06 + 0.12444 = 1.15 kg/hNaphtha reforming process routeType of leak pointNumber of leakpointsEmission factor(kg/h)Total rate (kg/h)Valves 18 0.00597 0.10746Pumps 2 0.0199 0.0398Compressor 1 0.228 0.228Pressure reliefvalves5 0.104 0.52Sampling points 5 0.015 0.075Flanges 60 0.00183 0.1098Total FEs = 0.10746+0.0398+0.228+0.52+0.075+0.1098= 1.080 kg/hAftercalculatingTheSMandFE,theworkplaceconcentration(WC)iscalculated by using Eq. 4.4 and Eq. 4.5 as shown below. The ventilation rate (Q) iscalculatedbymultiplying theairchangerate(ACH)bytheroomvolumeof10m3.The ACH is estimated to have two values of 0.2 h-1and 30 h-1as worst-case and best-99case scenario respectively(Michael, 1997). Hence, the Q has two values which areQ=2m3h-1andQ=300m3h-1. Sincetheworstcasescenarioisconsidered,theminimum workplace concentration (WCmin) wascalculated by applying the Q valueof 300 m3h-1(Eq. 4.5). The value of WC was calculated for the TDA to be 0.7728kg/m3, while it was obtained for the Pygas to be 0.9628 kg m-3and 0.8551 kg m-3fornaphtha reforming.1 31minmax2=+=h mh kgQFE SMWC (4.4)1 31maxmin300=+=h mh kgQFE SMWC (4.5)Finally,theworkexposureconcentration(WEC)iscalculatedforminimumormaximumworkplace concentrationbyusingEq. 4.6 asshownbelow. Inthisequation, the estimated exposure time (EET) is estimated to be 6 hours compared tothenormalaverageworktimeperday(AWD)whichis8hours. FortheTDAprocess, the value of WEC was calculated to be 0.5796 kg/m3, while it was obtainedforthePygastobe 0.722 kgm-3and 0.6413 kgm-3fornaphthareforming. Table4.12 summarizes the calculation of the WEC value in all process routes.AWDEETWC WECi=max(4.6)Table4.13: Calculationoftheworkerexposureconcentration(WECmax) fortheTDA, Pygas and naphtha reforming process routesThe TDA process routeSM (AQg) x3600 (kg/h)FE (kg/h)SM+FE(kg/h)WC= SM+ FE/300(kg/m)WEC= WC x 6/8( kg/m3)0.06418 x 3600= 231.0480.7943 231.84 0.7728 0.5796The Pygas hydrogenation process route0.07992 x 3600= 287.71.15 288.85 0.9628 0.722Naphtha reforming process route0.0709593 x 3600= 255.453481.080 256.53 0.8551 0.64133381004.2.4.4 The occupational exposure limit (OELavg) calculationFortheOELavg,itwasobtainedusingtheOEL-8hvaluesofthechemicalsinvolved in the selected process routes. First the mass fraction for each chemical iscalculated based on the material balance data (see Appendix D8, E7 and F7). Afterthat, the mass fraction for the OEL is calculated for chemicals that have the OEL-8havailable. ThemassfractionforOELofeachchemicalisthenmultipliedwithitsOEL-8hvalue. Finally,thevalueofOELavgis calculatedbysumminguptheproductsofmultiplyingthemassfractionforOELwithOEL-8hforallchemicals.The obtained values of OELavgare 51.52 x 10-6kg m-3for the TDA route, 44.52 x 10-5kg m-3 for Pygas and 61.30 x 10-5kg m-3for naphtha reforming. A summary of theOELavgcalculation is included in Table 2.14.4.2.4.5 The overall PRHI calculationThe PRHI value was obtained by applying Equation (2.12) which is describedpreviously in Chapter 2. The PRHI value obtained for the TDA, Pygas and naphthareformingprocessroutesare 14580000, 5326575 and 3939862, respectively. Inorder to get a manageable numbers, each value of PRHI is divided by 108(Hassim et.al.,2006). ThevaluesofPRHIforthethreeroutesbecome 0.1458,0.05326 and0.03939. These valueswere thenscaledtoobtainmorepresentablevalues ofthePRHI. Thescalingisdonebydividingtheobtainedvalues ofPRHIbythehighestindexvaluecalculatedforthethreebenzeneprocessroutes whichisinthisstudy0.1458(seeEq.2.27).Thescaledvalues ofPRHIforthe threeprocessroutesare100, 36.5 and 27. Table 4.15 below shows the overall calculation of the PRHI index.101Table 2.14: Calculation of OELavgfor the TDA, Pygas and naphtha reforming process routesThe TDA process routeMaterialMassfractionOEL-8h (mg m-3) Mass fraction for OEL OELavgToluene 0.16 188 mg/ m30.16/(0.16 + 0.435)= 0.269 0.269 (188) + 0.731 (1.3)= 51.52 mg m-3= 51.52 x 10-6kg m-3 Benzene 0.435 1.3 mg/m3 0.435/(0.16 + 0.435) = 0.731The Pygas hydrogenation process routeCyclohexane 0.312 1032.64 mg/m30.312/ (0.312 + 0.533 + 0.0036) =0.3670.367(1032.6) + 0.628(1.3) +0.0408 (1600 )= 378.97 + 1.004 + 65.28= 445 mg m-3= 44.52 x 10-5kg m-3Benzene 0.5331 1.6 mg/m3 0.533/ (0.312 + 0.533 + 0.0036) =0.628Methylcyclohexane 0.036 1600 mg/ m30.036/ (0.312 + 0.533 + 0.036) =0.0408Naphtha reforming process routen-Hexane 0.2809 17600.2809/(0.2809 + 0.0096 + 0.2324 +0.4455) = 0.29 (0.29 * 1760) + (0.00991 * 1600)+(0.23998 * 1.3) + (0.46003 * 188)= 510.4 + 15.856 + 0.311974+86.48564= 61.30536 mg m-3= 61.30536 x 10-5kg m-3Methylcyclohexane 0.0096 16000.0096/(0.2809 + 0.0096 + 0.2324 +0.4455) = 0.00991Benzene 0.2324 1.30.2324/(0.2809 + 0.0096 + 0.2324 +0.4455) = 0.23998Toluene 0.4455 1880.4455/(0.2809 + 0.0096 + 0.2324 +0.4455) = 0.46003102Table 4.15: Calculation of PRHI for the TDA, Pygas and naphtha reforming processroutes4.2.5 The inherent environmental toxicity hazard (IETH) assessmentTheIETHindexmethodisproposedtoestimatetheinherentenvironmentalfriendliness ofa chemical process plant by considering the potential toxicity impactontheaquatic,terrestrialandatmosphericenvironments (GunasekeraandEdwards,2006). TheIETHinvolvesseveralparametersthatshouldbecalculatedforeachchemicalintheprocess. Firstthepredictedenvironmentalconcentration(PEC)(mol/m3) is calculated for each chemical in the process. The obtained PEC is appliedintheprobitequationto obtaintheatmosphericimpacthazard(HAi) foreachchemical (see Equation 2.35). Then, the specific water hazard index (SWHIi) and thespecificterrestrialhazardindex(STHIi)arecalculatedforeachchemicalusingEquations(2.37) and (2.38)asdescribedinChapter2. Datarequiredforthecalculationistakenfrom(HSDB,HazardousSubstancesDataBank,http://toxnet.nlm.nih.gov). Afterthat,theobtainedSWHIiandSTHIiareappliedinEquations (2.39) and (2.40)tocalculatetheaquaticenvironmentalhazards(WHIi)andtheterrestrialenvironmentalhazards(THIi),respectively. TheobtainedWHIiand THIiare then applied in Equations (2.41) and (2.43) to estimate the values of thepredictedfish killed(FK)andtheterrestrialanimalskilled(AK).TheFKvalueisthenappliedinEquations(2.42)tocalculatethevaluesofaquaticimpacthazard(HWi). TheAKvaluerepresentstheterrestrialimpacthazard(HTi). The obtainedvalue ofHAiforeach chemicalisappliedon animpactseverityscale(see Equation2.36), while thevaluesof HWiandHTiforeachchemicalare appliedonanimpactProcessroutePRHI indicesICPHI HHI MHI WEC OELavgPRHI PRHI/108PRHIscaledTDA 9 28.8 5 0.5796 51.5 x10-614,580,000 0.1458 100Pygas 10 46.9 7 0.722 44.5 x 10-55326575.28 0.05326 36.53Naphtha 10 53.8 7 0.6413 61.3 x 10-53939862.64 0.03939 27103severity scale (as shown in Eq. 2.44 and 2.45) to obtain the values of the atmospherictoxicityimpactofa chemical(YAi),theaquatictoxicityimpact(YWi)andtheterrestrialtoxicityimpact(YTi). ThesethreevaluesaresummeduptoobtainthevalueofthechemicalenvironmentaltoxicityhazardCETHforeachchemicalinvolvedintheprocess (Eq.2.47). Finally,IETHvalueisobtainedforthewholeprocessbysumminguptheCETHvaluesobtainedforallchemicalsintheprocess(Eq. 2.47).Inthe TDA casestudy,theCETHwascalculatedforbenzeneandtolueneonly. This is because; hydrogen and methane lack the important data that is requiredfortheIETHcalculationsuchasTLV,LC50andLD50forhydrogenandLD50formethane. TheCETHvalueforbenzeneis 12.815, while fortolueneis 13.57. Thisresult indicates that toluene has more severe impact to the environment compared tobenzene,whichisamorehazardoussubstancefromhealthimpactpointofview.Thisresultcouldbecontributedbytheamountofinventory,whichsignificantlyaffects the IETH calculation. In this case study, the inventory of toluene is to someextant more than that of benzene (2800 t vs. 3381 t). The inventory is calculated bythesamewayinISIbutforeachindividualchemical(benzeneandtolueneinthiscasestudy). Inadditiontothat,thestorageinventoryforthetwochemicaliscalculated by using Equation 4.7. By summing up the CETH values for benzene andtoluene, theIETH valuefortheTDAprocesswasobtainedtobe26.3. Thecalculation of benzene CETH value is shown in more details in Appendix D10, whiletoluene CETH value calculation is shown in Appendix D11.Storage inventory (kg) = 14 days * daily flow rate (t/h) (4.7)In Pygashydrogenation casestudy, theCETHwascalculatedforcyclohexene, benzene and methylcyclohexane. The CETH value for cyclohexene is7.615andfor benzeneis 15.055 whereasfor methylcyclohexane is 0. The valueobtainedformethylcyclohexanecouldbecontributedbyitssmall inventory, whichsignificantlyaffectstheCETHcalculation. The IETHwas then calculatedbysumming up the CETH values. The obtained IETH for Pygas process is 22.66. The104detailedcalculationsofthe CETH forthethree chemicalsareprovidedinAppendices E10, E11 and E12.In naphthareforming casestudy,theCETHwascalculatedfor n-hexane,methylcyclohexane, benzeneandtoluene. The obtainedvaluesofCETH for thesechemicals are 9.88, 3.607, 12.7 and 14.8 respectively. The IETH was then calculatedbysumminguptheCETHvalues. The obtainedIETHfor naphthaprocessroute is40.98. The detailed calculations of the CETH for the four chemicals are provided inAppendices F8, F9, F10 and F11.4.2.6 Environmental hazard index (EHI) assessmentTheEnvironmentalHazardIndex(EHI)ranksroutesbytheestimatedenvironmental impact of a total release of chemical inventory. For the purpose of theEHIcalculation,thespecificenvironmentalhazardindex(SEHI)valueneedstobecalculatedforeachchemicalinvolvedina processroute. TheSEHIconsistsofthespecific water hazard index (SWHIi) and the specific terrestrial hazard index (STHIi).TheSWHIiandSTHIiarecalculatedforeachchemicalusingEquations(2.48) and(2.49)asdescribedinChapter2. Datarequiredforthecalculationistakenfrom(HSDB, Hazardous Substances Data Bank, http://toxnet.nlm.nih.gov). After that, theobtainedSWHIiandSTHIiareappliedinEquation (2.50)tocalculateSEHIi. Theobtainedvalues ofSEHIiforchemicalsintheprocessare thenappliedinEquation(2.51) to calculate the EHI for the whole process. In the TDA case study, the valuesofSEHIforbothbenzeneandtolueneare 2.48x10-4t-1and 2.08x10-4t-1respectively. ThesevalueswereobtainedbysummingupthevaluesoftheSWHIandtheSTHIforeachchemical. Finally,byapplyingEquation (2.51) thevalueofthe EHI for the TDA process was obtained to be 1.46.105In Pygas casestudy,the calculation ofSEHI wasdone for cyclohexene,benzeneandmethylcyclohexane. TheobtainedvaluesofSEHIforthesechemicalsare 1.95254 x 10-3t-1, 2.715 x 10-4t-1and 1.6008 x 10-4t-1respectively. Each valuewas multiplied by the associated chemical inventory to obtain the EHI value for eachchemical in the process. The obtained EHI values are then summed up to be 5.637,which is for the whole process.In naphthareforming casestudy,the calculation ofSEHI wasdone for n-hexane, methylcyclohexane, benzene and toluene. The obtained values of SEHI forthesechemicalsare 0.002852t-1, 1.6 x10-4t-1, 2.715 x10-4t-1and2.08x10-4t-1respectively. Eachvalue wasmultipliedbytheassociatedchemicalinventorytoobtaintheEHIvalueforeachchemicalintheprocess. The obtained EHIvalueswere thensummed up tobe 16.37,whichis thetotalEHI forthewholeprocess.Calculation in more details for each chemical in the three process routes is shown inTables 4.16, 4.17, 4.18, 4.19 and 4.20.106Table4.16: Calculationoftheenvironmentalhazardindex(EHI)for benzene TDA, Pygas and catalytic naphtha reforming process routes1. Calculation of SWHIbenzene650benzene10 SWHI xLCPECWbenzene=LC50(24 h) goldfish = 0.589 mol m-3WbenzenePSEC = 1.46 x 10-4mol m-3t-1SWHIbenzene= 2.47 x 10-4t-12. Calculation of STHIbenzeneSTHIbenzene=d[ ]x 10LD50Rat (oral) = 3306 mg/kgWtrat = 0.2 kgd = 4 daysTDIflrat= 1 x 10-5m3TDIfrat= 2.5 x 10-5m3PSECWtoluene=1.2x10-4molm-3t-1PSECStoluene= 5.8x 10-5mol m-3t-1By applying the equation:STHIbenzene= 1.5 x 10-6t-13. Calculation of SEHIbenzenebenzene benzene benzeneSTHI SWHI SEHI + =) t 10 x 1.5 ( ) 10 47 . 2 (-1 -6 1 4+ = t x SEHIbenzene1 410 715 . 2 = t x SEHIbenzene4. calculation of EHIbenzeneEHIbenzene= Qi* SEHIbenzeneEHIbenzene (TDA)= 2800 * (2.715 x 10-4t-1) = 0.760EHIbenzene (Pygas)= 8656.6 * (2.715 x 10-4t-1) = 2.35EHIbenzene (Naphtha)= 2658.54 * (2.715 x 10-4t-1) = 0.721107Table 4.17: Calculation of the environmental hazard index (EHI) for toluene TDAand catalytic naphtha reforming process routes1. Calculation of SWHItoluene650toluenetoluene10 SWHI xLCPSECW=LC50(96 h) goldfish 0.626 mol m-3toluene WPSEC = 1.24x 10-4mol m-3t-1SWHItoluene= 1.98 x 10-4t-12. Calculation of STHItolueneSTHItoluene=d [ ]x 10LD50Rat (oral) = 5000 mg/kgWtrat = 0.2 kgd = 4 daysTDIflrat= 1 x 10-5m3TDIfrat= 2.5 x 10-5m3PSECWtoluene= 1.24x 10-4mol m-3t-1PSECStoluene= 5.85 x 10-5mol m-3t-1By applying the equation:STHItoluene= 9.96 x 10-6t-13. Calculation of SEHItoluenetoluene toluene tolueneSTHI SWHI SEHI + =) 10 96 . 9 ( ) 10 98 . 1 (1 6 1 4 + = t x t x SEHItoluene1 410 08 . 2 = t x SEHItoluene4. Calculation of EHItolueneEHItoluene= Qi* SEHItolueneEHItoluene (TDA)= 3381 * (2.08 x 10-4t-1) = 0.703EHItoluene(Naphtha)= 5097.82 * (2.08 x 10-4t-1) = 1.0603108Table4.18: Calculationoftheenvironmentalhazardindex(EHI)formethylcyclohexane Pygas and catalytic naphtha reforming process routes1. Calculation of SWHImethylcyclohexane650ohexane methylcyclohexane methylcycl10 SWHI xLCPSECW=LC50(96 h) golden shrine = 0.733 mol m-3ohexane methylcycl WPSEC = 1.16 x 10-4mol m-3t-1SWHImethylcyclohexane= 1.58 x 10-4t-12. Calculation of STHImethylcyclohexaneSTHImethylcyclohexane= d [ ]x 10PSECWmethylcyclohexane= 1.16 x 10-4mol m-3t-1PSECSmethylcyclohexane= 5.48 x 10-5mol m-3t-1LD50mouse (oral) = 2250 mg/kgTDIflmosue= 1 x 10-5m3TDIfmosue= 2.5 x 10-5m3,Wtmouse = 0.2 kg,d = 4 daysBy applying the equation:STHImethylcyclohexane=2.208 x 10-6t-13. Calculation of SEHImethylcyclohexaneohexane methylcycl ohexane methylcycl ohexane methylcyclSTHI SWHI SEHI + =) t 10 x 2.208 ( ) t 10 x 1.58 (-1 -6 -1 -4ohexane methylcycl+ = SEHI1 4ohexane methylcycl10 6008 . 1 = t x SEHI4. calculation of EHImethylcyclohexaneEHImethylcyclohexane= Qi* SEHImethylcyclohexaneEHImethylcyclohexane (Pygas)= 194 * (1.6008 x 10-4t-1) = 0.031EHImethylcyclohexane (Naphtha)= 1501.3 * (1.6008 x 10-4t-1) = 0.2403109Table 4.19: Calculation of the environmental hazard index (EHI) for cyclohexene Pygas process route1. Calculation of SWHIcyclohexene650e cyclohexene cyclohexen10 SWHI xLCPSECW=LC50(96 h) goldfish = 0.0706 mol m-3e cyclohexen WPSEC = 1.38 x 10-4mol m-3t-1SWHIcyclohexene= 1.95 x 10-3t-12. Calculation of STHIcyclohexeneSTHIcyclohexene=d[ ]x 10TDIflrat= 1 x 10-5m3TDIfrat= 2.5 x 10-5m3PSECWcyclohexene= 1.38 x 10-4mol m-3t-1PSECScyclohexene= 6.55 x 10-5mol m-3t-1LD50Rat (oral) = 1946 mg/kgWtrat = 0.2 kgd = 4 daysBy applying the equation:STHIcyclohexene= 2.54 x 10-6t-13. Calculation of SEHIcyclohexenee cyclohexen e cyclohexen e cyclohexenSTHI SWHI SEHI + =) t 10 x 2.54 ( ) t 10 x 1.95 (-1 -6 -1 -3e cyclohexen+ = SEHI1 3e cyclohexen10 95254 . 1 = t x SEHI4. calculation of EHIcyclohexeneEHIcyclohexene= Qi* SEHIcyclohexeneEHIcyclohexene (Pygas)= 1668 * (1.95254 x 10-3t-1), EHIcyclohexene= 3.256110Table 4.20: Calculationoftheenvironmentalhazardindex(EHI)for n-Hexane catalytic naphtha reforming process route1. Calculation of SWHIn-Hexane650Hexane - ne cyclohexen10 SWHI xLCPSECW=LC50(24 h) goldfish = 0.0464 mol m-3Hexane - n WPSEC = 1.3229 x 10-4mol m-3t-1SWHIn-Hexane= 2.851x 10-3 t-12. Calculation of STHIcyclohexeneSTHIn-Hexane=d[ ]x 10TDIflrat= 1 x 10-5m3TDIfrat= 2.5 x 10-5m3PSECW n-Hexane= 1.3229 x 10-4mol m-3t-1PSECS n-Hexane= 6.246 x 10-5mol m-3t-1LD50Rat (oral) = 28,710 mg/kgWtrat = 0.2 kgd = 4 daysBy applying the equation:STHIn-Hexane= 9.5 x 10-8t-13. Calculation of SEHIn-HexaneHexane - n Hexane - n Hexane - nSTHI SWHI SEHI + =) t 10 x 1.24 ( ) t 10 2.851x (-1 -6 -1 -3Hexane - n+ = SEHI1Hexane - n0.002852 = t SEHI4. calculation of EHIn-HexaneEHIn-Hexane= Qi* SEHIn-HexaneEHIn-Hexane= 5031.718 * (0.002852 t-1), EHIn-Hexane= 14.355. Calculation of EHI for the whole process_= =ton ii iSEHI Q EHI1EHITDA= 0.760 + 0.703 = 1.463EHIPygas= 3.256 + 2.35 + 0.031 = 5.637EHINaphtha route= 14.35 + 0.2403 + 0.721 + 1.0603 = 16.37161114.3 Discussion of the indexes valuesBased on the inherent safety index assessment, both pygas hydrogenation andcatalyticnaphthareformingareconsideredtobethemosthazardousroutes. Theyboth have the same ISI index value of 32. On the other hand, TDA route has the ISIindexvalueof31andhenceitisconsideredtobelesshazardousamongthethreeroutes. These results are contributed by the IPand ICOsub-indexes penalties in pygascase andICO,IEQand ISTsub-indexes penalties in naphtha reforming case. In pygascase, theIPandICOare assigned penalties of 2 and 1 respectively whereas the samesub-indexes are assigned 1 and 0 for TDA case study. Naphtha reforming route hastheIEQandISTsub-indexespenaltiesof4foreachwhereasinTDAroutethesamesub-indexesareassignedapenaltyof3foreach.Table 4.21summarizestheISIassessment.Table4.21: Evaluationofbenzeneproductionprocessroutesbasedoninherentsafety index (ISI)ProcessrouteCalculation of inherent safety index (ISI)Sub-indexes of ICISub-indexes of ICITDAprocessIINTICORIRMIRSIFETIIITIPIEQIST4 0 4 0 9 3 4 1 3 3ICI= 4 + 0 + 4 + 0 + 9 = 17 IPI= 3 + 4 + 1 + 3 + 3 = 14IISI= 17 + 14 = 31Pygasprocess4 1 3 0 9 4 3 2 3 3ICI= 4 + 1 + 3 + 0 + 9 = 17 IPI= 4 + 3 + 2 + 3 + 3 = 15IISI= 16 + 16 = 32Catalyticnaphthareforming4 1 3 0 9 3 3 1 4 4ICI= 4 + 1 + 3 + 0 + 9 = 17 IPI= 3 + 3 + 1 + 4 + 4 = 15IISI= 17 + 14 = 32ForiSafeindex,IncontrasttoISIindexmethodassessment, Pygas isconsidered to be the most hazardous route with iSafe index value of 20. Both TDAand naphtha reforming routes have the same iSafe index value of 18 and hence theyareconsideredtobethelesshazardousthanPygasroute. TheseresultsarecontributedbyRy. InTDAcasestudy,Ry was assignedapenaltyof 0,whereas it112was assigned penalties of 3 and 2 in both case studies pygas and naphtha reformingroutes as in Table 4.22.Table 4.22: Evaluation of benzene production process routes iSafe index methodProcessrouteCalculation of iSafe indexSub-indexes of ICI Sub-indexes of IRITDANr Nf Ne Nt ICImax, (FET)Ry Rt Rp Rh0 4 1 4904 1 4ICI = 0 + 9 = 9 IRI = 0 + 4 + 1 + 4 = 10OSI = 9 + 9 = 18Pygas0 4 1 4 9 3 3 2 3ICI = 0 + 9 = 9 IRI = 3 + 3 + 2 + 3 = 11OSI = 9 + 11= 20Catalyticnaphthareforming0 4 1 4 9 2 3 1 3ICI = 0 + 9 = 9 IRI = 2 + 3 + 1 + 3 = 9OSI = 9 + 9 = 18In the IOHI assessment, Pygas hydrogenation and naphtha reforming have thehighest IOHI index value of 22 and hence are considered to be the worst two routes,whereas TDA is considered to be less hazardous route with IOHI value of 21. Theseresults are contributed by the ICsub-index penalty. The ICis assigned a penalty of 1in both pygas and naphtha routes, while it is assigned a penalty of 0 in TDA route asshown in Table 4.23.113Table4.23: Assessment ofbenzeneproductionprocessroutesbasedoninherentoccupational health index (IOHI)ProcessrouteCalculation of IOHI indexSub-indexes of IPPHSub-indexes of IHH(TDA)ICIVIMSITIPIPMIELIR0 3 2 3 1 1 4 7IPPH= 0 + 3 + 2 + 3 + 1 + 1 = 10 IHH= IEL+ IR= 4 + 5 = 9HH PPH IOHII I I + = = 10 + 11 = 21(Pygas)1 3 2 3 1 1 4 7IPPH= 1 + 3 + 2 + 3 + 1 + 1 = 11 IHH= IEL+ IR= 4 + 5 = 9HH PPH IOHII I I + = = 11 + 11 = 22Catalyticnaphthareforming1 3 2 3 1 1 4 7IPPH= 1 + 3 + 2 + 3 + 1 + 1 = 11 IHH= IEL+ IR= 4 + 5 = 9HH PPH IOHII I I + = = 11 + 11 = 22As in Table 4.24 for PRHI index, TDA process route is considered to be themosthazardousroutewithPRHIindexvalueof100. Thisisfollowedby PygasprocessroutewithPRHIindexvalueof 36. Naphthareforming isconsideredtobethe least hazardous route with PRHI index value of 27. In TDA case, the low valueof OELavgcontributes to a higher value of the PRHI than that in pygas and naphthacase studies.Table 4.24: Assessment of benzene production process routes based on process routehealthiness index (PRHI)ProcessroutePRHI indicesICPHI HHI MHI WEC OELavgPRHI PRHI/108PRHIscaledTDA 9 28.8 5 0.5796 0.000051 14,580,000 0.1458 100Pygas 10 46.9 7 0.722 0.00044 5,324,182 0.0532 36Naphtha 10 55.5 11 0.6453 0.00061 30,421,285 0.3042 27114BasedontheIETHassessment, naphthareformingprocessroute isconsideredtobethemosthazardousroutewith IETH indexvalueof 41. Thisisfollowed by the TDA process route with IETH value of 26. The Pygas process route,withIETH indexvalueof 23,isconsideredtobetheleasthazardousroute. Thisresult is contributed by the chemical inventory, the more the inventory the higher thehazard and hence the greater the penalty assigned to the chemical. For Pygas processroute,theverysmallinventoryofmethylcyclohexane,194ton,contributedto therank of this route as the least hazardous among the routes selected for this case study.Also the calculation approaches of this method contributed to such outcomes.Table4.25: Assessment ofbenzeneproductionprocessroutesbasedon inherentenvironmental toxicity hazard (IETH)The TDA process routeChemicals YAiYWiYTiCETH IETHBenzene 7.57 5.245 0 12.81526.385Toluene 5.806 5.1954 2.57 13.57The Pygas process routeCyclohexene 0 7.615 0 7.61522.67 Benzene 8.085 6.97 0 15.055Methylcyclohexane 0 0 0 0Catalytic naphtha reformingn-Hexane 0 9.88 0 9.8840.987Methylcyclohexane 0 3.606 0 3.607Benzene 7.528 5.1659 0 12.7Toluene6.097 5.823 2.88 14.8In the EHI assessment, naphthareformingprocessroute isconsideredtobethe most hazardous route with EHI index value of 16, while the Pygas process routetakethesecondplace with EHI indexvalueof 5. TheTDAprocessroute isconsideredtobetheleasthazardousroute withEHIvalueof1.5.AsfortheIETH,the chemical inventory contributed to the assessment outcomes.115Table4.26: Assessment ofbenzeneproductionprocessroutesbasedon inherentenvironmental toxicity hazard (EHI)The TDA process routeChemicals SWHIiSTHIiSEHIiEHIiEHIprocessBenzene 2.4 x 10-4t-11.5 x 10-6 t-11 410 7 . 2 t x 0.7601.463Toluene 1.9 x 10-4t-19.9 x 10-6t-11 410 08 . 2 t x 0.703The Pygas process routeCyclohexene 1.9 x 10-3t-12.5 x 10-6t-11 310 9 . 1 t x 3.2565.637 Benzene 2.4 x 10-4t-11.5 x 10-6t-11 410 7 . 2 t x 2.35M. cyclohexane 1.5 x 10-4t-12.2 x 10-6t-11 410 6 . 1 t x 0.031Catalytic naphtha reformingn-Hexane 2.8 x 10-3t-19.5 x 10-8t-110.002852 t 14.3516.3716M. cyclohexane 1.5 x 10-4t-12.2 x 10-6t-11 410 6 . 1 t x 0.2403Benzene 2.4 x 10-4t-11.5 x 10-6t-11 410 7 . 2 t x 0.721Toluene1.9 x 10-4t-19.9 x 10-6t-11 410 08 . 2 t x1.06034.4 Correlation of index methodsThevaluesofthe six indexmethodsforthecasestudyprocessroutesarepresentedinTable 4.27.Thehighertheindexvaluethegreaterthehazard. Theassessment results were correlatedbypair-wiselinearregressiontodeterminethecorrelationamongthe six indexmethods. Table4.28presentsthecorrelationcoefficientR2values. ThehighertheR2value,thecloserto1,thestrongerthecorrelation (Hassim et al., 2008).116Table 4.27: Values of the ISHE index methodsProcess route ISI iSafe IOHI PRHI IETH EHITDA 31 18 21 10027 2Pygas 32 20 22 36 23 6Naphtha reforming 32 18 22 27 41 16Table 4.28: Correlation R2of benzene production route index values by linearregressionIndex iSafe IOHI PRHIIETH EHIISI 0.25 1 0 0.069 0.51iSafe ------ 0.25 0 0 0Average------ 0.63 0 0.035 0.26------ 0.31 0.15IOHI ------- ------- 0 0.069 0.51PRHI ------- ------- ------- 0 0Average------ ------ ------ 0.035 0.26------ ------ 0.15IETH------ ------ ------ ------ 0.73EHI ------------ ------ 0.73 ------4.4.1 Correlation between safety and health index methodsAsshowninTable 2.28,theonly significantcorrelation between safetyandhealthindexeswasshownby ISI with IOHIindexeswithcorrelationcoefficientR2of1. TheISIandiSafeshow poorcorrelationwithR2valueof 0.25despitethesimilarity of their sub-indexes. This poor correlation is contributed by the differenceinISIandiSafeconsiderations. E.g.theISIhighlyconsiderscorrosiveness(ICOR),inventory(II),safetyequipment(IEQ)andthesafetystructure(IST).TheiSafedoes117notconsiderthesepropertiesatall. Instead,itconsiders theprocessyield(Ry),reaction temperature (Rt) and the heat of reaction (Rh). The ICOR, II, IEQand ISTsub-indexes were assigned penalties in naphtha reforming higher than that in TDA route(see Table 4.21). The IIwas also assigned a penalty in pygas and higher than that inTDA route. Hence, the TDA, pygas and naphtha reforming were assigned penaltiesof 31, 32 and 32 respectively (see Table 4.27). In iSafe index assessment, the valuesare influenced by the process yield sub-index. The Rywas assigned a penalty of 0 inTDAcase study,whileitwasassignedpenaltiesof 3 and4 inbothpygasandnaphtha case studies (see Table 4.22).In IOHI index assessment, the corrosiveness sub-index (IC) is the determinantsub-index which was assigned a penalty of 0 for TDA route, whereas it was assignedapenaltyof1forpygasandnaphtharoutes. SimilarlytotheISIindexanddifferently from iSafe index, IOHI ranks the TDA as the least hazardous route whileitrankspygasandnaphthareformingroutesasthemosttwohazardousrouteswithpenaltiesof21,22 and22 respectively. Asaresult,IOHIshowed anexcellentcorrelation with ISI and poor correlation with iSafe index.Nocorrelationwith PRHI wasshown,becausethis methods is fugitiveemissionbasedanddo not havecommonparameterswithinherent safetymethods.AccordingtothePRHIassessment,theTDA wasindicatedasamosthazardousprocess route with PRHI value of 100 followed by pygas process route with value of36,whereas naphthareforming was assigned apenalty of 27 astheleasthazardousprocessroute. Asaresult, nocorrelationatallwasshownbetween thePRHI andanyothermethod. ThisresultcouldbecontributedbyAlsoitshouldbenotedthatthepoorcorrelationisbecausePRHIincludesfugitiveemissionandaleakfactorwhich make the correlation weak as discussed by Hassim et al. (2008).1184.4.2 Correlation between safety and environmental index methodsThe ISIhas a moderatecorrelationwithEHI(R2value0.52) andworsecorrelation with IETH (R2 value 0.07). However, no correlation was shown by iSafewith the environmental methods. The correlation between safety and environmentalindexes is bad with average R2value of 0.15. The reason is, even though both safetyandenvironmentalcriteriaconsiderthecatastrophicandshort-termscenario,theyhavenocommonparameters. Inspiteofhavingthesamecalculationapproaches,environmental index methods showed a moderate correlation with R2value of 0.73.4.4.3 Correlation between health and environmental index methodsAs with the ISI index, the IOHI correlates moderately with EHI (R2= 0.51),while it has poor correlation with IETH (R2= 0.07). This can be interpreted by that;environmental index methods are based on different scenarios which are catastrophicandshort-term eventswhereasoccupationalhealthmethodsarebasedonlong-termexposureduringthenormaloperation. ThePHRIshowednocorrelationwiththetwoenvironmentalindexmethods. Inadditiontothereasonsabove,thePHRIconsiders the fugitive emissions which could contribute to the poor correlation.4.4.4 Average correlation between safety, health and environmental criteriaAsshownaboveinTable4.28 thecorrelationofSHE indexesinthe casestudyispoor. The correlationbetweensafety and healthcriteria isweakwithaverage R2valueof 0.31. When excludingthePRHIthetwocriteria correlate119reasonably with an averageR2valueof0.63. ThisshowsthatPRHIusesdifferentbasisduringtheassessmente.g.fugitiveemissionsaspectandhencecontributetopoor correlation with other inherent index based methods. From Table 4.28 it can beseenthat the correlation oftheenvironmentalcriterion withboth safetyandhealthcriteria isverypoorwith an averageR2valueof0.15. Thisisbecause;theenvironmental methods have no common parameters with safety and health methods.Besides, thedifferentassessmentcharacteristics,e.g.catastrophicandsort-termscenarioinenvironmentalcriterionvs.normaloperationandlong-termscenarioinhealth criterion, might have contributed to this low poor correlation. The correlationof the ISIwithIOHI(R2=1),ISIwithEHI(R2=0.51)andIOHIwithEHI(R2=0.51) could make a selection of either ISI or IOHI to be the single method that can beused to assess the three S, H and E criteria.