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.