INTRODUCTION
1
1.INTRODUCTION
1.1 1.1 GE GENE NERA RAL L
As the petroleum petroleum resources are depleting depleting and the crudes being refined are becoming higher in density and have higher content of hetero atoms (S,O,N etc) the need and demand for high-quality middle distillates has gron significantly over the past decade and continues to gro in the international mar!et" Stringent Stringent environment environment legislation legislation regarding regarding fuel specificati specifications ons has been imposed orldide over the last decade in order to improve the quality of diesel fuels ith a vie to reduce o#ides of sulphur(SO $), o#ides of nitrogen(NO$) and particulate matter (%&) in the diesel engine e#haust emissi emissions ons hich hich are ma'or ma'or contri contribut butors ors to enviro environme nmenta ntall pollut pollution ion"" n order to meet meet the the increased increased demand for
on-road diesel, diesel, the refiners refiners use
heavy distillates as blending components into the diesel pool" or the above reas reason ons, s, the the refi refini ning ng indu indust stry ry toda today y face facess on the the one one hand hand tigh tighte ter r specifications and on the other hand higher production demands for diesel" As a result, refiners orldide have started revamping or optimising the e#isting middle-distillate hydrotreaters to achieve deep desulphurisation" *he tightening of diesel fuel specifications began in 1++ hen the SA SA loe loere red d sulp sulphu hurr to .//p .//ppm pm ma#i ma#imu mum" m" *he *he 0ali 0alifo forn rnia ia Air esources 2oard (0A2) ent one step further by mandating a ma#imum aromatic aromatic level as ell as a minimum minimum cetane level" level" Similar Similar specificati specifications ons 3
are being being considered considered by the 4uropean 4uropean 0ommissi 0ommission on (40), hich requires requires a
ma#im ma#imum um
of ./ppm ./ppm sulphu sulphurr as ell ell
as ma#imu ma#imum m cetane cetane and
minimum polyaromatic levels" 5ermany is also considering ta# incentives to encourage refiners to produce and mar!et diesel fuel ith 1/ppm sulphur" n 6ecember 3///, the S 4nvironmental %rotection Agency (4%A) (4%A) introduced a ne mandate to further reduce the level of sulphur in on-road diesel by +7 percent (to 1.ppm ma#imum) starting in mid-3//8" n a typical refinery, diesel fuel is produced from one or more blending components co mponents derived from crude distillation and conversion units" *he main main blendi blending ng compon component entss are heavy heavy naphth naphtha, a, straig straight ht run diesel diesel,, hydrocrac!er diesel, 9ight 0ycle Oil (90O) from fluid catalytic crac!er (00), 0o!er diesel etc" *he desirability of these streams (for e#ample 90O) ould require much more severe treating then others eg: Straight un 9ight 5as Oil (S95O)" *he technologies for removing sulphur are not necessarily the same as the technologies required to upgrade other diesel fuel qualities" n the opin opinio ion n of many many refi refine ners rs and and proc process ess vend vendors ors,, the the tech techno nolo logi gies es for for removing sulphur from diesel fuel are probably the least e#pensive and easiest to implement compared to those required to upgrade other diesel fuel qualities" At pres presen ent, t, the the most most comm common on dies diesel el sulp sulphu hurr spec specif ific icat atio ions ns orldide are around .//ppm" ;oever, the sulphur specifications are being revised in many of the countries conforming to 4uro-<4uro-= specifications" n ndia, 24A O N6AN S*AN6A6S (2S) has
laid don specification for auto fuels" nline ith global specification, ndia has also reduced diesel fuel sulphur level from 1"/ t> (1////ppm) don to ./ppm (4uro- or 2harat- equivalent norms) over the last decade and is li!ely to be reduced further to ./ppm (4uro= or 2harat- equivalent norms) by April 1, 3/1/" nitially, the diesel hydrodesulphurisation units in ndia ere designed to produce .//ppm sulphur that consists of to reactors operating in series" *he typical operating conditions of the industrial units are as follos: reactor temperature of ?/ o0,eactor pressure of ?/!g
0urrent diesel specifications in ndia and proposed changer@s are compared ith 4uro- and 4uro-= specifications in table 1"1"
Table 1.1 Existing and future specificatins f diesel
?
C!aracteristics
6ensity 1.o 0 , !g
esidue ma#" *otal Sulphur, t"> ma#" %olycyclic Aromatic ;ydrocarbon (%A;), t"> , ma#" 6istillation , +. vol"> ecovery o0, ma#"
"!arat#III "!arat# $current% I& B3/-B?. B3/-B?. 3"/-?". 3"/-?".
Eur# III
Eur# I&
B3/-B?. 3"/-?".
B3/-B?. 3"/-?".
. 1.
-
. -
. -
.1 ?8 /"
.1 -
.1 ?8 /"
.1 ?B /"
/"/. 11
/"//. 11
/"/. 11
/"//. 11
7/
8/
8/
8/
1.'. CRUDE A((A) 0rude oil is defined as the mi#ture of naturally occurring hydrocarbons
that
is
refined in to diesel, gasoline, heating oil, 'et
fuels, !erosene and literally
thousands of
other products
called
petrochemicals" 0rude oil are named according to their contents and .
origins, and classified according to their per unit
eight (specific
gravity)" ;eavier crudes yield more heat upon burning, but have loer A% gravity and mar!et price in comparison to light (or seet) crudes. 1.'.1 CO*+O(ITION O, CRUDE OIL
*he composition of crude oil varies according to here it as obtained" *his largely has to do ith the type of ground in hich the oil as formed, and hat contaminants ere present and in hat relative concentrations" n addition to colour variations, there are also various contaminant levels and various floing properties" =ariations aside, crude oil, on average, has the composition shon belo" 0arbon (0)
B?-B+
;ydrogen (;) 11-1? Sulfur (S)
/"1-?".
Nitrogen (N) /"/1-/"B &etals
/"/-/"/1
Crude il is c-prised f
1"
%araffins
3"
Oleffins
"
Naphthenes 8
?"
Aromatics
1.'.' T)+E( O, CRUDE
*he different *ypes of 0rude oil have variations in viscosity and appearance from one oil field to another" *he variations range in odour, color and in the basic properties and qualities" Dhile all *ypes of crude oil are basically hydrocarbons, there are differences in their properties, especially in the variations in the molecular structure" *he many variations may also influence the suitability of the different types of crude oil for particular products and the resulting quality of the products"
*he different *ypes of crude oil are classified based on the American %etroleum 5ravity (A%) gravity and viscosity" *he properties may vary in terms of proportion of hydrocarbon elements, sulfur content etc as it is e#tracted from different geographical locations all over the orld" f the A% gravity of the crude oil is of 3/ degrees or less, it is graded as EheavyE, those ith an A% gravity of ?/"1 degrees or greater than that is !non as ElightE and if the oil ranges beteen 3/ and ?/"1 degrees, it is graded as EintermediateE" 0lassifications are made based on the sulfur content as ell" Crude il ith lo content of sulfur means EseetE and the presence of high content sulfur is !non as EsourE" *he purity of crude oil increases or decreases based on the sulfur content as sulfur is an acidic material"
1.'./.DI(TILLATION COLU*N
7
,igure 1.'./. distillatin clu-n
1.'.0.DE(CRI+TION O, DI(TILLATION +ROCE(( B
*he diagram above is a schematic flo diagram of a typical oil refinery that depicts the various unit processes and the flo of intermediate product streams that occurs beteen the inlet crude oil feedstoc! and the final end products" *he diagram depicts only one of the literally hundreds of different oil refinery configurations" *he diagram also does not include any of the usual refinery facilities providing utilities such as steam, cooling ater, and electric poer as ell as storage tan!s for crude oil feedstoc! and for intermediate products and end products" *he atmosphric distillation unit
is the first processing unit in
virtually all petroleum refineries" t distills the incoming crude oil into various fractions of different boiling ranges, each of hich are then processed further in the other refinery processing units" *he incoming crude oil is preheated by e#changing heat ith some of the hot, distilled fractions and other streams" t is then desalted to remove inorganic salts (primarily sodium chloride)" olloing the desalter, the crude oil is further heated by e#changing heat ith some of the hot, distilled fractions and other streams" t is then heated in a fuel-fired furnace (fired heater) to a temperature of about +B F0 and routed into the bottom of the distillation unit" *he cooling and condensing of the distillation toer overhead is provided partially by e#changing heat ith the incoming crude oil and partially by either an air-cooled or ater-cooled condenser" Additional heat is removed from the distillation column by a pump around system as shon in the diagram belo" +
As shon in the flo diagram, the overhead distillate fraction from the distillation column is naphtha" *he fractions removed from the side of the distillation column at various points beteen the column top and bottom are called sidecuts" 4ach of the sidecuts (i"e", the !erosene, light gas oil and heavy gas oil) is cooled by e#changing heat ith the incoming crude oil" All of the fractions (i"e", the overhead naphtha, the sidecuts and the bottom residue) are sent to intermediate storage tan!s before being processed further" *he reduced crude is sent to vacuum distillation , to obtain products such as asphalt , a#, tar etc, *he products obtained from distillation column are processed in respective units"
1.'..*A2OR +RODUCT(
%etroleum products are usually grouped into three categories: light distillates (9%5, gasoline, naphtha), middle distillates (!erosene, diesel), heavy distillates and residuum (heavy fuel oil, lubricating oils, a#, asphalt)" *his classification is based on the ay crude oil is distilled and separated into fractions (called distillates and residuum) as in the above draing" •
•
•
•
9iquified petroleum gas (9%5)
5asoline (also !non as petrol) Naphtha Cerosene and related 'et aircraft fuels 1/
•
6iesel fuel
•
uel oils
•
9ubricating oils
•
%araffin a#
•
Asphalt and tar
•
%etroleum co!e
11
LITERATURE RE&IE3
13
'.LITERATURE RE&IE3
'.1.GENERAL
2abich
and
&ouli'in (3//)
reported
that
organosulfur
compounds are usually present in almost all fractions of crude oil distillation" ;igher boiling point fractions contain relatively more sulfur and the sulfur compounds are
of higher molecular eight"
*he
reactivity of organosulfur compounds varies idely depending on their structure and local sulphur atom environment" *he lo boiling crude oil fraction
contains
mercaptans,
mainly the
aliphatic
organosulfur
compounds:
sulfides , and disulfides" *hey are very reactive in
conventional hydro treating processes and they can easily be completely removed from the fuel" Other processes li!e mero# can be applied to e#tract mercaptans
and disulfides from gasoline and light refinery
streams" or higher boiling crude oil fractions such as heavy straight run naphtha, straight run diesel and light 00 naphtha, the organosulfur compounds
predominantly
contain 1
thiophennic
rings" *hese
compounds
include
thiophenes
and benGothiophenes and
their
al!ylated derivatives" *hese thiophene containing compounds are more difficult than mercaptans and sulphides to convert via hydrotreating" *he heaviest fractions blended to the gasoline and diesel pools are bottom 00 naphtha , co!e naphtha , 00 and co!er diesel, contains mainly al!ylated
benGthiophenes,
al!ylbenGthiophenes,
as
dibenGothiophenes
ell
as
(62*)
polynuclear
organic
and sulphur
compounds,i"e" the least sulphur compounds in the ;6S rection" *he reactivity of sulphur compounds in the ;6S follos this order (from
most
rective
thiopheneI2*Ial!ylated
to
least
2*I62*
reactive)H and
thiopheneIal!ylated
al!ylated
62*
ithout
substituents at the ? and 8 positionsIal!ylated 62* ith one substituent at either the ? or 8 positionIal!ylated 62* ith al!yl substituents at the ? or 8 position" 6eep desulfurisation of the fuel implies that more and more of the least reactive sulphur compounds must be converted"
'.1.LIETERATURE RE&IE3 ON 4)DRODE(UL+4URI(ATION +ROCE((
*he conventional ;6S process is usually conducted over sulfided 0o-&O
desulfurisation level, activity and selectivity depends on the properties of the specific catalyst used , the reaction conditions, nature and concentrations of sulphur compounds present in the feed stream, and reactor and process design" 0hunsang song (3//) reported that the !ey
to ultra-deep
desulfurisation is the removal of refractory sulphur compounds from diesel fuels"
*hese
compounds
are
higher
molecular
eight
dibenGothiophenes(62*s) that contain substituents in positions ad'acent to the sulphur atom" n addition to straight-run gas oil , the light cycle oil from fluid catalytic crac!ing of heavy oils is a ma'or blend stoc! for diesel fuels hich tends to have the highest contents of refractory sulphur compounds especially ?,8-dimethyldibenGothiophene (?,8- 6&62*), ?,8diehtylbenGothiophene(?,8-6462*),
?-methyldibenGothiophene
(?-
&62*) and dibenGothiophene(62*)" Cnudsen et al"(1+++) reported that about four times more active catalysts are required to reduce the diesel fuel sulfur content from .// to ./ppm compared to a typical 0o-&o catalyst at constant 9;S= and the corresponding temperature increament is about BJ0" Cnudsen et al" (1+++) reported that the effect of process variables such as 9;S=, temperature, hydrogen partial pressure, hydrogen sulfide 1.
partial pressure and hydrogen to oil ratio on catalyst activity applied to deep desulfurisation could be predicted by a suitable !inetic e#pression" *hey found that the equation 3"1 could be used to describe the !inetics of 0o-&o and Ni-&o catalysts for very deep desulfurisation of diesel" n the e#pression for the rate of desulfurisation,the first term represents the direct e#traction route,hich is enhanced by an increase of the hydrogen partial pressure and inhibited by the presence of ;3S" *he second term represents the hydrogenation route, hich is also enhanced by an increase of hydrogen partial compounds,
pressure and inhibited
by the presence of aromatic
and in particular heterocyclic compounds (denoted by in
the equation)
'.'.LITERATURE RE&IE3 ON CATAL)(T
or 0o-&o catalysts, the second term can to a good appro#imation be neglected, and the rate constant k , can be determined by integration of the e#pression" *he partial pressure of hydrogen sulfide, % ; 3S
can be
e#pressed in terms of the sulfur concentration 0 S , hich means that an e#plicit e#pression can be obtained for k " *he rate constant of catalyst type, temperature and feedstoc!
18
or Ni-&o catalyst both terms are important, and the removal of the inhibitors has to be solves simultaneously in the rate equation" 9appas et al"(1+++) carried out hydrodesulfurisation of 90O and S5O blend in a continuous flo, tric!le bed hydrotreating pilot plant unit using a commercial 0o-&o catalyst and investigated the effect of operating parameters
(temperature,
pressure, eight hourly space velocity,
hydrogen-to Koil-ratio) on sulfur removal and aromatics saturation and reported that by decreasing the space velocity and by increasing the temperature, the pressure and the hydrogen-to -oil-ratio , the product density and the aromatics and sulfur content of diesel decreased" Sela!ovic and Lovanovic (3//1) carried out hydrodesulfurisation of middle distillates ith various blends of 95O-90O and 95O-9=5O using 0o-&o catalyst of different producers ith product sulfur specifications and determined the required severity in achieving lo sulfur levels" 9amourelle and Nelson (3//1) discussed various means to produce ultralo sulfur diesel products using ne generation Ni-&o and 0o-&o catalyst combinations" *hey studied various revamp options for ma!ing ultralo
sulphur diesel
from e#isting hydro treating units, hydrogen
strategy , reaction pathays , catalyst options"
17
2has!ar et al" (3//?) developed a three phase non-isothermal heterogeneous model to simulate the performance of pilot plant and industrial tric!le bed reactors applied to the hydrodesulfurisation of diesel fractions" *he developed model as found to simulate the performance of the industrial reactor adequately" *he model as also applied to study the influence of operating conditions on product quality" 2has!ar et al" (3//?) developed a three phase non- isothermal heterogeneous model to stimulate the performance of pilot plant and industrial tric!le-bed reactors applied to the hydrodesulphurisation of diesel fractions" *he developed model as found to stimulate the performance of the industrial reactor adequately" *he model as applied to study the influence of operating conditions on product quality" *he reactive reaction rates of various sulphur species are shon in table 3"1" *he more difficult sulphur species i"e" the substituted dibenGothiophenes, have the highest boiling points and are more prevalent in streams ith high end points"
1B
Table '.1. Relati5e reactin rates and biling pints f 5arius sulp!ur species (ulp!ur species
Relati5e Reactin
"iling +int6 ,
Rate *hiophene 1// 1B. 2enGothiophene / ?/ 6ibenGothiophene / .+/ ðyl 6ibenGothiophene . 8//-83/ 6imethyl 6ibenGothiophene 1 8/-8./ *rimethyl 6ibenGothiophene 1 88/-8B/ *he basic reactions that ta!e place during hydrodesulfurisaton are
as follos, &ercaptans
S; M ;3
Sulfides
3S; M 3;3
6isulfides
SS M ;3
Aromatics
ArS M3;3
; M;3S
3; M;3S
3; M3;3S
Aromatic M ;3S ( e#cluding ring saturation)
Aromatic ring saturation is a reversible reaction that is controlled by equilibrium"
1+
Salvatore and &ichael (3//?) reported that desulphurisation reactions can follo a number of paths, but to routes are generally favoured under typical hydro treating conditions" *he most common route for removing sulfur is the direct e#traction, or hydrogenolysis, reaction (carbon-sulfur bond brea!age)" *his mechanism is predominant hen the sulfur requirement is above ./ppm" At this level most of the sulfur in the more
reactive
compounds
(up
to
and
including
non-substituted
dibenGothiophene) has been removed" *ypically, conventional 0obaltmolybdenum (0o-&o) catalysts and lo-to-moderate reactor pressure are applied to favour this reaction mechanism" Salvatore and &ichael (3//?) reported that removing sulfur from most difficult compounds such as ?,8-dimethyldibenGothiophene, generally follos the hydrogenation route" t is easier to brea! the sterically hindered carbon-sulfur bond if one of the aromatic rings is first saturated" Saturating the ring changes the molecule@s spatial configuration and ma!es the sulfur atom more accessible to react ith the catalyst@s active sites" After the aromatic ring is hydrogenated, the sulfur atom can be removed via hydrogenolysis" Nic!el-molybdenum (Ni-&o) catalysts and higher pressure help promote the hydrogenation reaction mechanism"
3/
2has!ar et al" (3//?) reported that the hydrogenation route as found to be sloer than direct e#traction for most of al!yl-substituted 62* molecules but is much faster for sterically hindered 62*@S" Cnudsen et al" (1+++) reported that 0o-&o catalysts desulfurise primarily via the direct e#traction route" Ni-&o catalysts, e#hibit a higher hydrogenation activity,
have a relatively
higher
selectivity for
desulfurisation via the hydrogenation route" As compared ith the Ni-&o catalysts, the 0o-&o catalyst is not as good for the removal of ?,8-6&62*, but better than Ni-&o catalyst for removal of 62* and ?-&62*" LuareG et al" (1+++) carried out hydrotreating of S5O-90O blends to evaluate the effect of 90O on product quality at varied operating conditions over a commercial 0o-&o catalyst and determined apparent reaction orders and activation energies" 2has!ar et al" (3///) reported that the revised specification of diesel fuel can met by increasing the hydro treating capacity, operating the e#isting units at high severity levels and using a modified higher activity hydro desulphurisation catalysts "
31
446 S46
33
/.DIE(EL
6iesel is produced from the fractional distillation of crude oil beteen 3// F0
and B/ F0 at
atmospheric pressure , resulting in a
mi#ture of carbon chains that typically contain beteen B and 31 carbon atoms per molecule"
*he
best diesel fuels are straight-run
Stoc!s,
derived from simple distillation of crude oil" /.1.CO*+O(ITION
6iesel is composed of about (i) 7.>
saturated hydrocarbons (primarily paraffins including n, iso,
and cycloparaffins), (ii) 3.>
aromatic
hydrocarbons
(including
naphthalenes
and al!ylbenGenes)" *he average chemical formula for common diesel fuel is C1'4'/, ranging appro#imately from C174'7 t C14'8"
/.'T)+E( O, DIE(EL ,UEL
n ndia e have to types of diesel fuels: 1" ;igh speed diesel (;S6) used in automotive applications and 3" 9ight diesel oil (96O) used in stationary applications 3
/./.DIE(EL +RO+ERTIE(
Sulphur content Affects ear, depsits, and particulate emmissions" 6iesel fuels contain varying amounts of various sulphur compounds hich increase oil acidity" 9egislation has reduced sulphur content of highay fuels to /P.> by eight" Off road fuel has an average of /"3+> sulphur by eight" 0etane number A measure of the starting and arm-up characteristics of a fuel" n cold eather or in service ith prolonged lo loads, a higher cetane number is desirable" 9egislation dictates the 0etane nde# shoud be ?/ or above" Aromatic content 2y definition, aromatic content is characterised by the presence of the benGene family in hydrocarbon compounds that occur naturally in the refining of diesel fuel" n the chemical
ma!e up of fuel, the heavier
aromatic compounds of toluene, #ylene, and naphthalene are also present" 9imiting these aromatic compounds has the effect of reducing burning temperature and thus NO$ formation"
3?
0loud Q pour point Affect lo-temperature operation" *he cloud point of the fuel is the temperature at hich crystals of paraffin a# first appear" 0rystals can be detected by a cloudiness of the fuel" *hese crystals cause filters to plug"
A% gravity elated to heat content, affecting poer and economy" 5ravity is an indication of the energy content of the fuel" A fuel ith a high density (lo A% gravity) contains more 2*Es per gallon than a fuel ith a lo density (higher A% gravity)"
API gravity
=
1?1".
− 1,1".
specific gravity at 8/o F 8/o F
Ash &easures inorganic residues - *he small amount of noncombustable metallic material found in almost all petroleum products is commonly called ash" Ash content should not e#ceed /"/3 mass percent"
3.
Dater sediment Affect the life of fuel filters and in'ectors" *he amount of ater and solid debris in the fuel is generally classified as ater and sediment" t is good practice to filter fuel hile it is being put into the fuel tan!" &ore ater vapor condenses in partially filled tan!s due to tan! breathing caused by temperature changes" ilter elements, fuel screens in the fill pump, and fuel inlet connections on in'ectors must be cleaned or replaced hen they become dirty" *hese screens and filters, in performing intended function, ill become clogged hen using a poor or dirty fuel and ill need to be changed more often" Dater and sediments should not e#ceed /"1 volume percent"
=iscosity Affects in'ector lubrication and atomiGation" *he in'ector system or!s most effectively hen the fuel has the proper RbodyR or viscosity" uels that meet the requirements of 1-6 or 3-6 diesel fuels are satisfactory ith 0ummins fuel systems"
38
0arbon residue &easures residue in fuel - can influence combustion"
*he
tendency of a diesel fuel to form carbon deposits in an engine can be estimated by various tests to determine the carbon residue after +/> of the fuel has been evaporated "
/.0.IN,ERENCE
t is found that 1"
Specific gravity, flash point, viscosity, sulfur content, and
carbon residue increase ith increase in service severity" 3" *he cetane number (hich measures the fuel@s ignition quality) decreases ith increase in service severity" *here is also a decrease in volatility ith increase in service severity" " %roperties are, hoever, inter-related and it is difficult to isolate the effect of any single variable ?" t is found that the self-ignition temperature of the normal paraffins decreases as the length of the chain increases" ." Since the cetane rating of the fuel is a measure of the ignition characteristics of the fuel, it can be concluded that the heavier members of the paraffin family have higher cetane ratings" 8" n fact, cetane, 0 18;? (he#adecane) is the primary reference fuel in the cetane scale ith an arbitrary cetane rating of 1// hile other normal paraffins have cetane ratings that vary 37
almost linearly ith the length of the chain" /..C!aracteristics f 49drcarbns as Diesel ,uel (.N
GENERAL
4)DROCAR"ON
C4ARACTERI(TIC(
O 1"
,OR*ULA n-paraffins
0n;3nM3
9o specific gravity Q high
so-paraffins
(Straight chain) cetane number 0n;3nM3 (2ranch Same sp"gr as 1 but loer
0ycloparaffins
chain) 0n;3n
cetane no" Q 2"%" ;igher sp" 5r" *han 1 but
0n;3n-8
loer cetane number ;igher sp"gr Q 2"% but loer
0n;3n-13
cetane number than 1- ;ighest sp" 5r Q 2"%" Q
3"
"
?"
."
2enGenes
Naphthalenes
loest cetane no" I-prtant c!aracteristics f diesel fuel :nc; c!aracteristics#requires high cetane number
1"
(tarting c!aracteristics#requires high volatility but ill give loer
poer 3"
(-;ing and Odr# high volatility ill give better mi#ing and loer
smo!e but also loer poer "
Crrsin and 3ear#due to presence of sulfur and ash
?"
Ease f 4andling# should have lo pour point and viscosity for ease
of handling but high flash and fire point for safety and fire haGard" ."
Densit96 !eat f c-bustin and cleanliness.
3B
/.<.DIE(EL ,UEL (+ECI,ICATION( GENERAL ,UEL A(T* TE(T GRADE LO3 GRADE 4IG4 CLA((I,ICATION *ET4OD (UL+4UR (UL+4UR NO. NO. 1#D '#D ,las! pint7C *D =/ 3ater and sedi-ent6 D '>7= 5l6 -ax. Distillatin te-perature6 recrded *in
/8 7.7
' 7.7
# '88
'8' //8
D 8<
'88 1./#'.0
//8 1.=#0.1
D 00 D '<''
7.71 7.7
7.71 7.7
D 8< 7
C
*ax
&iscsit96 ;ine-atic --'?( at 07 7C *ax
As!6 *ax (ulp!ur @t6 -ax
3+
4)DROTREATING
0.14)DROTREATING
;ydrotreating (;6*) is a catalytic process , hich effectively removes sulphur and other impurities li!e nitrogen, o#ygen and metals from crude oil and petroleum distillates" A refining process
for
treating
petroleum
atmospheric or vacuum distillation units (e"g",
fractions
naphthas,
from middle
distillates, reformer feeds, residual fuel oil, and heavy gas oil) and other petroleum (e"g", cat crac!ed naphtha, co!er naphtha, gas oil, etc") in the /
presence of catalysts and substantial quantities of hydrogen" ;ydrotreating includes desulfuriGation, removal of substances (e"g", nitrogen compounds) that deactivate catalysts, conversion of olefins to paraffins to reduce gum formation in gasoline, and other processes to upgrade the quality of the fractions" ;ydrotreating applications include ;ydrodesulfurisation (;6S) of !erosene, ;ydrodesulfurisation (;6S) of naphtha, ;ydrodesulfurisation (;6S )of diesel, hydrofinishing of lube oil base stoc!s, hydrofinishing of a# etc"
0.'4)DROTREATING REACTION(
*he chemical reactions that are of primary interest in hydrotreating include 1" 3" " ?" ." 8"
;ydrodesulfurisation (;6S) ;ydrodenitrogenation (;6N) ;ydrodeo#ygenation (;6O) ;ydrogenation of aromatic compounds Saturation of olefins ;ydrodemetallation (;6&)
0.'.1.4)DRODE(UL+4URI(ATION
;ydrodesulfuriGation (;6S) is a catalytic chemical process idely used to remove sulfur (S)
from refined petroleum products such as
gasoline or petrol, 'et fuel, !erosene, diesel fuel" *he purpose of removing the sulfur is to reduce the sulfur dio#ide (SO3) emissions that result from using those fuels in automotive vehicles, aircraft, railroad locomotives, 1
ships, gas or oil burning poer plants, residential and industrial furnaces, and other forms of fuel combustion" -S-@ M 3;3 ; M @; M;3S
0.'.'.4)DRODENITROGENATION
*he hydrogenolysis reaction is also used to reduce the nitrogen content of a petroleum stream and removes as ammonia in a process referred to as !9drdenitrgenatin (;6N)" *he rate of ;6N reaction as little loer than the rate of ;6S reaction" TN-@M ;3 ; M @;
0.'./.4)DRODEO)GENATION
6uring hydrotreating, o#ygen compounds in the form of naphthenic acids, phenols, alcohols, aldehydes etc ere also removed as ater vapour from the feed" -O-@ M 3 ;3 ; M @; M; 3O
0.'.0.4)DRODE*ETALLATION
&etals li!e nic!el, vanadium, iron, copper, sodium etc present in traces get adsorbed over the catalyst 3
-& M U ;3 M A ; M &-A
0.'..4)DROGENATION O, ARO*ATIC CO*+OUND(
Aromatics combined ith hydrogen and get converted in to napthenes" 01/ ;B M 3 ;3 01/ ;13
0.'.<.(ATURATION O, OLE,IN(
Olefins combines ith hydrogen and get saturated T@ M ;3 ;-@;
0./.UNDE(IRA"LE REACTION(
*he undesirable reactions that occur in hydrotreating are 1" 3"
;ydrocrac!ing 0o!ing
*hese undesirable reactions reduce the yield of the product" At high temperature and pressure of ;6S reaction, ;ydrocrac!ing occurs as a side reaction" ;ydrocrac!ing reaction has to be minimised, because it consumes hydrogen, reduces the product yield and the hydrogen purity of the recycle gas" t is limited by the selection of catalyst ith lo hydrocrac!ing capacity and or!ing at lo temperature" 6uring ;6S reaction the heavy
molecules are adsorbed on the acidic site of the catalyst and reduce the catalytic activity
0.0.4)DROTREATING O+ERATING &ARIA"LE(
*he principle operating variables affecting the performance of hydrotreating reactions are as follos: 1" 3" " ?"
eaction temperature ;ydrogen partial pressure 9iquid hourly space velocity and ;ydrogen-to-oil ratio
Reactin te-perature
eactor temperature has
strong influence on hydrotreating
reactions" ncreasing reactor temperature increases conversion of sulphur, nitrogen and o#ygen compounds" 2ut increasing the reactor temperature also increases the side reactions namely, hydrocrac!ing and co!ing" 49drgen partial pressure
;ydrogen partial pressure can be increased by increasing the hydrogen recycle rate or hydrogen purity at a given feed rate" ncreasing hydrogen partial pressure reduces co!e formation by suppressing polymeriGation and condensation reactions" Adequate hydrogen-to-oil ratio is to be maintained to have desirable cycle length" ?
LiBuid !url9 space 5elcit9
ncreasing 9iquid ;ourly Space =elocity(9;S=) increases feed rate processed per unit volume of catalyst and hence reduces the severity of hydrotreating reactions" ;oever, loer 9;S= ill produce product ith lo sulphur, nitrogen and o#ygen" 9;S= is fi#ed based on the design feed rate of the unit" 49drgen#t#il rati
;ydrogen-to-oil ratio can be increased by increasing the hydrogen recycle rate or hydrogen purity at a given feed rate and should be !ept as high as possible to decrease the rate of undesirable gases and to improve the catalyst efficiency by avoiding co!e formation"
.
0A*A9VS* S46
.1. 4)DRO TREATING CATAL)(T
*here are to types of catalyst available for hydrotreating purposes" *hey are 0obalt-&olybdenum and Nic!el- &olybdenum on alumina support" 0obalt and Nic!el are responsible for catalytic action hereas &olybdenum acts as a promoter" Nic!el- &olybdenum catalyst e#hibits a higher hydrogenation activity than 0obalt- &olybdenum catalyst and is more suitable for treating crac!ed stoc!s" =ery often the support material also has catalytic action related to its chemical nature"
.'.CATAL)(T O+TION( ,OR +RODUCING ULTRA LO3 (UL+4UR DIE(EL(
8
%roper choice of catalyst is of paramount importance in the production of ltra 9o Sulphur 6iesel (9S6)" ecent advances in hydrotreating catalyst technologies have significantly improved the sulphur removal capability" *he use of the most advanced hydrotreating catalyst or catalyst system can significantly increase the desulphurisation capability of the e#isting hydrotreaters" Ne and improved ;6S catalyst for 9S6 production have been developed and mar!eted by A!Go Nobel(C 7.7, C B?B), 0riterion (0entury and 0entinel), ;aldor-*opsoe(*C .7, *C .7?), %, united catalyst
7
*he ne generation catalyst e#hibit /-?/> higher ;6S activity compared to previous generation catalyst (either 0o-&o or Ni-&o)" se of such high activity ne generation catalyst ill help in achieving ultra lo sulphur levels in e#isting units ithout shortening catalyst life" About 1.> more catalyst can be loaded using dense loading in place of soc! loading" *his result in a -? o0 reduction in start-of-run (SO) temperature for the same desulphurisation activity" 6ense loading result in a higher pressure-drop, hich combined ith a more uniform pac!ing normally obtained ith dense loading ill improve liquid distribution ithin the catalyst bed"
B
+ROCE(( ,LO3(4EET
+
54 ." ;V6O*4A*N5 %O04SS 9OD S;44*
?/
+ROCE(( DE(CRI+TION
?1
<.+ROCE(( DE(CRI+TION
*he e#periments have been carried out in a pilot plant that as designe designed d and assemble assembled d to perform perform hydrot hydrotrea reatin ting g operat operation ion " *he reactor of this pilot plant is a .// cm pressure of +/Cg
vessel vessel hich hich can operat operatee at (demonstrate (demonstratess the schematic schematic
process flo diagram (%6) of this pilot plant " As it is shon in this figure, the feed and hydrogen are mi#ed ith a certain ratio before floing floing into the reactor" *he mi#ed feed enters to the reactor ith definite pressure to achieve a predetermined temperature for performing the ;6S ;6S reactions"
*here are four thermocouple thermocoupless along the reactor reactor for determining determining the s!in and the inside inside reactor temperatur temperature" e" *he reactor reactor product stream stream is fed to a flash drum to separate gas and liquid liquid products" *he liquid product is accumulated in a drum and the gas product is transferred for online analysis to determine the ;3S and ;3 content of stream"
n addition addition to feed preparation preparation,, the catalyst catalyst should be presulfided presulfided before using it ith actual feed" %resulfiding of
catalyst is done by
dimethyl disulfide (6&6S), hich is added to the soma# gas oil, and circulated through the reactor bed"
*his *his is perfo perform rmed ed to stren strengt gthen hen the the acti activi vity ty and sele select ctiv ivit ity y of catalyst" *o e#ecute the procedure, an inert gas folloed by a pure ; 3 stream is fed to the reactor" *hen the reactor temperature is raised to a certain value"
?3
%resulfiding procedure as folloed by a set of e#periments hich as carried out to investigate the reproducibility of pilot plant setup and to find out a suitable procedure for carrying out the main set of e#periments"
*he *he liqu liquid id sampl samples es ere ere anal analyG yGed ed by ane aney y nic! nic!el el meth method od to dete determ rmin inee the the tota totall sulf sulfur ur cont conten ent" t" *he resu result ltss eluc elucid idat ated ed that that for for improv improveme ement nt of reprodu reproducib cibili ility ty of e#perim e#periment ental al result results, s, telve telve hours hours should pass to attain steady state of pilot plant system" 2y passing each si# hours the liquid sample is collected to analyGe" *he average total sulfur content for each e#periment is calculated by averaging the set of results hich are attained during the e#periment" 2y passing one day the operating condition can be changed to carry out another e#periment"
<.1.+ROCE(( O+TION ,OR UL(D +RODUCTION
*he main process option or types of improvements that may be required to produce 9S6 are listed and discussed belo" Some of these opti option onss can can be read readil ily y impl implem emen ente ted d and and may may not not have have seri seriou ouss cost cost impl implic icat atio ions ns hil hilee
some some othe otherr
opti option onss
requ requir iree
addi additi tion onal al capi capita tall
investments" All these process options can improve product sulphur and combination of them can be used to reduce sulphur significantly, but no single option is adequate in producing 9S6"
?
Raising reactr te-perature
*his is obvious option to increase the desulphurisation activity" *he ma#imum reactor temperature is limited by design furnace outlet temperature of the unit" ;igher reactor temperature ill also result in shorter catalyst run lengths and severely restrict its usefulness"
Reducing t!rug!puts
educing feed rates can decrease liquid hourly space velocities in the reactor and thus increase the rates of hydrodesulphurisation and result in loer product sulphur" *he required throughput reduction is estimated to be B times loer for the production of 9S6 from a current level of ./ ppm product sulphur ma!ing this option impractical"
Increasing !9drgen partial pressure
ncreasing the hydrogen partial pressure in the reactor can reduce the reactor SO temperature and also reduces the rate of catalyst deactivation" ;ydrogen partial pressure can be increased by increasing the purity of ma!eup hydrogen or purging the recycle gas and increasing its purity" ncreasing the hydrogen purity by 1/> of the recycle gas corresponds to about o0 decrease in average SO temperature, and a 3/-/> increase cycle length" *he effect of increasing hydrogen partial pressure by increasing total pressure is less than by increasing hydrogen purity: a 1/> increase in hydrogen partial pressure corresponds to about 1 o0 decrease in ??
average reactor temperature" *he reason for loer response is that ; 3S partial pressure is also increased and total pressure is increased"
Increasing !9drgen sulp!ide partial pressure
;ydrogen sulphide strongly inhibits ;6S reactions and its partial pressure has great impact on hydrogen partial pressure" SO temperature should be raised to achieve the same ;6S level hen the recycle gas contained large amount of hydrogen sulphide" *his effect is lager at higher total reactor pressure and more pronounced for 0o-&o catalysts than Ni&o catalysts" Scrubbing the recycle gas to remove hydrogen sulphide ill decreased ;3S partial pressure and increase hydrogen partial pressure" *he increased partial pressure of hydrogen can increase the catalyst life by reducing co!e formation"
Increasing !9drgen#t#il rati
ncreasing hydrogen-to-oil ratio ill reduce the inhibition effect of ;3S and ammonia and thereby increase the desulphurisation activity of catalyst" *his effect is rather small compared to the needs of achieving 9S6" ncreasing hydrogen-to-oil ratio by ./> may only gain ?-B> in catalyst activity" ncreasing the recycle gas-to-oil ratio also decreases the reactor average hydrogen sulphide partial pressure and thus in turn increases the apparent catalyst activity"
?.
Adding reactr 5lu-es
*he catalyst volume can be increased either by adding ne reactors to e#isting units or by installing ne dehydrosulphurisation units" 5enerally doubling the catalyst volume results, in a 3/ o0 decrease in average temperature, if all other operating conditions are unchanged" ncreased catalyst volume decreases the deactivation rate of the catalyst by reducing the start of run temperature in addition to the availability of more deactivation temperature span" n addition, lo 9;S= by itself reduces deactivation rate eve at the same SO average reactor temperature" *hough this option requires ne capital investment, it is the best option in terms of good fle#ibility of feed stoc! and product quality"
Reactr internals
eactor internals play a !ey role in improving the contact of the reactant ith the catalyst" mproper distribution of the reactants over the catalyst ill contribute to channelling through the catalyst bed, resulting in an inefficient utilisation of the catalyst, development of hot spots and premature catalyst deactivation due to co!e formation" t as reported that around one percent of bypassing of feed over catalyst an contribute ./ to 1./ ppm sulphur in the diesel product" %roperly designed reactor internals ith good distribution of reactants over catalyst surface is necessary hile producing ultra lo level of sulphur"
?8
E+ERI*ENTAL DETAIL(
?7
7"E+ERI*ENTAL DETAIL( %ilot plant studies ere carried out to evaluate the performance of 6;6* catalyst" *he ob'ective of the present or! is to evaluate the 6;6* catalyst to study the effect of temperature on the performance of 6iesel hydrotreating catalyst" *he catalyst evaluation studies ere carried out in a high pressure catatest unit %rocured from =inci *echnologies, rance" *he hydrotreating reactions ere carried out in co-current don flo mode of operation ithout hydrogen recycle"
,eedstc; Details
A straight run diesel sample collected from crude distillation column as used in the pilot plant study" *he characteristics of the straight run
diesel
feed
are
presented
in
table
1"
Catal9st e5aluated
*he 6;6* catalyst is from procatalyse is NiO-&oO
?B
Table>.1.C!aracteristics f prcatal9se !9drtreating catal9st. +rperties
Surface area , m3
3/8
%ore volume ,ml
/"..
2ul! density ,!g<9
/"77
9oss on ignition at ../ o ,t >
3"1
Single 5rain 0rushing Strength , 6aN
13"7
&a#
1B"/
&in
8"+
2ul! 0rushing strength &%a
1"/1
Ni O content ,t >
?"3
0o O content ,t >
-
&o O content ,t >
1B"/
Table >.'.+rperties f Diesel +rducts 49drtreated in +ilt +lant Reactr
eactor pressure - 77"7 !g
+rperties eactor *emp,o 0 9;S= , hr 6ensity 1.o 0
Operating cnditins 1/ 3/ / /"7 /"7 /"7 /"B?1/ /"B+3 /"B8.
g , o 0 2% 3?. . 3.B 1/ 38 3/ 371 / 37+ ./ 3+B 8/ 1/ 7/ 3. B/ ?? +/ 8+
?/ /"7 /"B?.
./ /"7 /"B1B
8/ /"7 /"B3B+
7"1 ?"?
7"7 ?"3
B"1 ?"31
B"7 ?"1+
+" ?"1
."? 17 78".
.?"? BB 7B
.."7 87 7+
.8"7 .. B1".
.7"7 ?3 B
3?1 3.8 381 38+ 377 3+7 /+ 3? ?3 8B
3B 3. 3.+ 38B 378 3+. /B 33 ?? 88
3. 3.. 381 38+ 377 3+8 /7 3 ?1 8.
3 3.? 3.+ 387 378 3+. /7 33 ?/ 8?
33 3?+ 3.8 38. 37 3+ /. 3/ + 83
*he e#perimental data obtained as a effect of temperature and pressure, on the sulfur content of products hydrotreated over different temperature is presented in the table" *he sulfur and nitrogen content of the hydrotreated products ere decreased due to the conversion of sulfur and nitrogen in the feed to hydrogen sulfide and ammonia respectively" *he aromatic content of the products as found to decrease oing to the hydrogenation of aromatics to naphthenes
results in the decrease of density and specific gravity of
hydrotreated products" *he decrease in density results in a higher A% gravity product" Saturation
of olefins also increases the percentage of
saturates in the hydrotreated product" *he increase in aniline point of the ./
hydrotreated products indicates that the product is highly paraffinic(more saturated or less aromatic) than the feed" *he decrease in aromatics reduces the amount of carbonaceous residue in the product" *he increase in aniline point and A% gravity results in a higher cetane number product , hich in turn indicates a loer ignition delay" *he viscosity of the hydrotreated products as also decreased hich in turn relates to ease of starting of diesel engine"
>.1.E,,ECT O, TE*+ERATURE
*he beteen
effect of reactor temperature on product quality as studied
1/o 0 and 8/oc at
/"7 liquid hourly space velocity and
77"7 Cg
the
effect of reactor temperature on product
sulfur hydrotreated over catalyst NiO-&oO
at a hydrogen-to-oil
ratio of 1./9<9" Dith catalyst and 77"7!g
254 ppm
to ?3 ppm as obtained at a reactor
temperature of 8/o0 and a 9;S= of /"7h -1 indicating a conversion of about +B"7 >" As e#pected ,highest conversion of sulfur compounds as achieved at the severe most operating conditions employed" rom the table , it is shon that increase in temperature has decreased the level of sulphur content in the feed" At a temperature of 1/o0 the sulfur content as 3.? ppm" As the temperature increases to 8/o0 sulphur content decreases to ?3 ppm" t as found that the sulfur content of the product decreases ith increasing reactor temperature at constant 9;S=" *he effect of reactor .1
temperature on product sulfur as more pronounced at higher liquid hourly space velocities and the sulfur conversion decrease at higher reactor temperature"
>.'.E,,ECT O, +RE((URE
*he data sho that the increase in the reactor pressure improved product quality" *he A% gravity and cetane number of the hydrotreated products increased and the sulfur and aromatic contents decreased ith increased reactor pressure" *he rate of hydrodesulfurisation reaction is faster at higher pressure" *he reason for this effect of pressure is considered to be that the higher the pressure better is the contact beteen hydrogen, and hydrocarbons and the catalyst" n general, the effect is considerably ea!er at higher pressures i"e", sulfur conversion decreases ith increasing pressure" ;oever, very high pressures reduce the activity of the catalyst, oing to the adhesion of carbon to its surface" At higher operating pressures, the effect of pressure on sulfur conversion
becomes
insignificant"
*he
partial
pressure
and
the
concentration of hydrogen sulfide in the gas phase goes up as the conversion of sulfur compounds increases" 2eyond a certain operating pressure, the concentration of hydrogen sulfide in the gas phase decreases because of the increase in solubility of hydrogen sulfide in liquid phase" n general, the hydrotreated products shoed a decrease in density, viscosity, sulfur, nitrogen and aromatic contents, and increase in A% gravity, aniline point, cetane number and saturates content hen the temperature is increased"
.3
*he polyaromatics content of the hydrotreated products as ell belo 11t> meeting 4uro- as ell as 4uro-= specifications"
>./.E,,ECT O, ANILINE +OINT
*his is an appro#imate measure of the aromatic content of a hydrocarbon fuel" t is defined as the loest temperature at hich a fuel oil is completely miscible ith an equal volume of aniline"
Aniline is an
aromatic compound and aromatics are more miscible in aniline than are paraffins" ;ence, the loer the aniline point, the higher the aromatics content in the fuel oil" *he higher the aromatics content, the loer the cetane number of the fuel" *he aniline point can thus be used to indicate the probable ignition behavior of a diesel fuel" aniline point increases from 78 to B"
>.0.E,,ECT O, I"+
According to American Society for *esting and &aterials petroleum- analysis distillation procedures, the recorded temperature hen the first drop of distilled vapor is liquefied and falls from the end of the condenser" *he initial boiling point in the feed is actually higher than that of the product" So hen the initial boiling point is ta!en for . vol > it has a certain higher temperature and finally if the temperature is noted for +/ vol > certainly it ill have a temperature less than the . vol >"
.
>..O&ERALL 4D( :INETIC(
*he !inetics for sulfur removal from real feedstoc!s are comple# and depend on the distribution of sulfur compounds and the degree of conversion" or industrial feedstoc!s, the structural differences beteen the sulfur containing molecules ma!e it impractical to produce a comple# rate equation to describe the ;6S !inetics" ;ence, in the present or! the folloing conventional poer la !inetic e#pression as used (LuareG et al"1+++):
1
1
S pn −1 Sf n −1
1 = !(n − 1) 9;S=
here S is the sulfur content in the feedstoc! (t>), S the sulfur content in the product (>)" n the apparent reaction order and ! is the !inetic constant" *he data at various space velocities, temperatures and product sulfur contents ere used for !inetic data analysis and to determine the folloing apparent reaction orders and activation energies"
Diesel indx
*he 6iesel nde# indicates the ignition quality of the fuel" t is found to correlate, appro#imately, to the cetane number of commercial fuels" t is obtained by the folloing equation
.?
Diesel Index
=
aniline po int ( o F ) x Degrees API gravity ( 8/ o F ) 1//
6iesel nde# and cetane number are usually about ./" 9oer values ill result in smo!y e#haust
Cetane i-pr5e-ent Cetane nu-ber or 0N is a measurement of the combustion quality
of diesel fuel during compression ignition" t is a significant e#pression of the quality of a diesel fuel" 0etane has improved significantly " as the temperature is increased the cetane number is increased .3"+ to .7"7"
Cetane i-pr5ers
*hese are compounds that readily decompose to give free radicals and thus enhance the rate of chain initiation in diesel combustion" *hey promote fast o#idation of fuels and thus improve their ignition characteristics" 0hemical compounds such as al!yl nitrates, ether nitrates, dinitrates of polyethylene glycols and certain pero#ides are ell !non cetane improvers" n general, hoever, in vie of their lo cost and ease of handling, most commercial significance has been attached to different primary al!yl nitrates"
Cetane index
..
Cetane index is used as a substitute for the cetane number of diesel
fuel" *he cetane inde# is calculated based on the fuelEs density and distillation range (AS*& 6B8)" *here are to methods used, AS*& 6+78 and 6?77"
.8
DE(IGN O, ,EED &E((EL (E+ERATOR O, A +ILOT +LANT
8.1. DE(IGN O, ,EED &E((EL Design f feed 5essel f !9dr treater in a pilt plant
.7
*he feed vessel is a unfired pressure vessel " %ressure vessels used in industry are lea!-tight pressure containers, usually cylindrical or spherical in shape, ith different head configurations" *hey are usually made from carbon or stainless steel and assembled by elding" 4arly operation of pressure vessels and boilers resulted in numerous e#plosions, causing loss of life and considerable property damage" n 1+3. the committee issued a set of rules for the design and construction of unfired pressure vessels"
8.'.DE(IGN CRITERIA
*he 0ode design criteria consist of basic rules specifying the design method, design load, alloable stress, acceptable material, and fabrication, inspection certification requirements for vessel construction"*he design method !non as design b9 rule uses design pressure, alloable stress, "
"
and a design formula compatible ith the geometry of the part to calculate the minimum required thic!ness of the part" *his procedure minimiGes the amount of analysis required to ensure that the vessel ill not rupture or undergo e#cessive distortion" n con'unction ith specifying the vessel thic!ness, the 0ode contains many construction details that must be folloed" Dhere vessels are sub'ected to comple# loadings such as cyclic, thermal, or localiGed loads, and here significant discontinuities e#ist, the 0ode requires a more rigorous analysis to be performed" *his method is !non as the design b9 anal9sis method" "
"
8./.(+ECI,ICATION(
.B
1" 3"
;ere the operation is considered to be running for 13 hours " &a#imum liquid flo rate : 8// ml e#cess for the N3 inert atmosphere"
." So W, e have to design the capacity of the vessel appro#imately to be 1/ litres" 8" 9et the feed vessel considered to be cylindrical" 7" =olume B"
T (X
9ength of the cylindrical vessel T 3/ mm
+" 6iameter of the cylindrical vessel T 3//m" 1/" so, the volume T 1/ litres 11. 9<6 ratio T 3/<3// T1"8
*ATERIAL O, CON(TRUCTION
1" 3"
*he material used here is SS18 " t is stainless steel and the ma#imum alloable stress is
1B1//" " t can ithstand temp of about .// o 0 Q pressure of about 1./ Cg
.+
TA"LE8.0.T!ic;ness calculatin DI*EN(ION( 6esign pressure 6esign temperature nside radius &a#imum alloable stress Loint efficiency (from table u13) 0irculated thic!ness (circular stress) 0irculated thic!ness (longitudinal stress) nternal corrosion alloance 4#ternal corrosion alloance *otal thic!ness 6esired thic!ness
UNIT Cg &m &m &m &m &m &m
&ALUE( 1./ 1// 1B1// /"7 "?3 1"71 / 1"3. ?"87 13
TA"LE 8.. *ax All@able stress in +(I
U+TO
U+TO
(( /1<
(( /1
(( /70
*(
177O, 3// // ?//
/>.>OC +" 1?B"B+ 3/?"??
1BB// 1B?// 1B1//
1?1// 137// 117//
1.7// 1?1// 13+//
11.// 11.// 11.//
8/
.// 8// 8./ 7// 7./ B// B./ +// +./
38/"// 1.".8 ?" 71"11 +B"B+ ?38"87 ?.?"?? ?B3"33 .1/"//
1B/// 17/// 187// 18// 181// 1.+// 1.7// 1.8// 1.?//
1/+// 1/?// 1/3// 1//// +B// +8// +?//
131// 11?// 113// 111// 1/B// 1/8// 1/?// 1/3// 1////
11.// 11.// 11.// 11.//
8.<.CALCULATION O, CIRCULAR T4IC:NE((
(i) (0ircular stress) ((6"% Y1?".) Y ("<3."?) <
((&"A"SYL"4) - /"8Y6"%Y1?".)) Y3."?
((1 Y 1?".) Y (1//<3."?) < ((1B1//Y/"7) - /"8Y1Y1?".))Y
3."? T
"?3
$ii% $Lngitudinal stress%
((6"%Y1?".)Y("<3."
?) <((3Y&"A"SYL"4) M (/"?Y6"%Y1?".))Y 3."? ((1Y1?".) Y (1//<3."?) < ((3Y1B1//Y/"7) M(/"?Y1Y1?".))Y3."? T 1"71
Ttal t!ic;ness
(0"*"0M"0"AM4"0"A) ("?3M / M 1"3. ) T ?"87 81
External pressure : /
8.>.DE(IGN O, GA( LIUID (E+ERATOR
83
igureB"7" 5AS 9Z6 S4%4A*O A vaporKliquid separator is a device used in several industrial applications to separate a vaporKliquid mi#ture" or the common variety, gravity is utiliGed in a vertical vessel to cause the liquid to settle to the
bottom
of
the
vessel,
here
it
is
ithdran"
n lo
gravity environments such as a space station, a common liquid separator ill not function because gravity is not usable as a separation mechanism" n this case, centrifugal force needs to be utiliGed in a spinning centrifugal separator to drive liquid toards the outer edge of the chamber for removal" 5aseous components migrate toards the center" *he gas outlet may itself be surrounding by a spinning mesh screen or grating, so that any liquid that does approach the outlet stri!es the grating, is accelerated, and thron aay from the outlet"
8
(+ECI,ICATION(
1"
Operation : 0ontinous 3" gas" " ?" ." 8" 7"
0onsider the seperator is occupied ith 8/> liquid Q ?/> =olume 9<6 ratio 9ength &"O"0
: 1 lt : 18.<+/ T 1"B : 18. mm 6iameter : +/ mm : SS18"
8.8.T!ic;ness calculatin
6&4NSONS 6esign pressure 6esign temperature nside radius &a#imum alloable stress Loint efficiency (from table u13) 0irculated thic!ness (circular stress) 0irculated thic!ness (longitudinal stress) nternal corrosion alloance 4#ternal corrosion alloance *otal thic!ness 6esired thic!ness
8.=.Calculatin f circular t!ic;ness
(i) (0ircular stress) 8?
N* Cg &m &m &m &m &m &m
=A94S 77"7 ?// ?. 1B1// /"7 1"8 1"8 / 1"3. 3"B. 13
((6"% Y1?".) Y ("<3."?) <
((&"A"SYL"4) /"8Y6"%Y1?".))Y3."? (
(77"7 Y 1?".) Y (?.<3."?) < ((1B1//Y/"7) - /"8Y77"7Y1?".))Y3."? T 1"8
(ii) (9ongitudinal stress):
((6"%Y1?".)Y("<3."?)<((3Y&"A"SYL"4) M (/"?Y6"%Y1?".))Y3."? ((77"7Y1?".) Y (?.<3."?) < ((3Y1B1//Y/"7) M(/"?Y77"7Y1?".))Y3."? T 1"8
Ttal t!ic;ness :
(0"*"0M"0"AM4"0"A) (1"8M / M 1"3. ) T 3"B.
External pressure : /
,IGURE 8.17 CETANE RE(+ON(E ,OR &ARIOU( CETANE I*+RO&ER(
8.
(cpe f t!e prect @r;
*he scope of the pro'ect or! includes the folloing: 1"
*o evaluate the performance of various activity ne
generation hydrotreating catalyst in a pilot plant tric!le-bed reactor
88
to determine the required severity level and different combination of catalyst for the production of ultra lo sulphur diesel" 3" *o study the effect of reactor temperature and liquid hourly space velocity on product quality at constant reactor pressure and hydrogen-to-oil ratio using different hydrotreating catalysts"
Applicatins
1"
seful in the production of ltra 9o Sulfur 6iesel
(9S6) as per fuel quality regulations assigned by government" 3" De are able to minimiGe pollution in the environment by reducing mainly sulfur Q also other impurities present in the diesel by hydro treating process"
87
RE(ULT( DI(CU((ION(
=.RE(ULT( DI(CU((ION(
*he hydrotreated products from pilot plant ere characteriGed in detail to study the e#tent ;ydrodesulphurisation and cetane improvement"
8B
1"
ncrease in temperature has increased the ;6S activity as
evidenced by reduction in sulphur content progressively of 3.? ppm to ?3ppm" 3" ncrease in temperature has beneficially increased the important property namely 0etane nde# also" *he 0etane nde# increase observed as ?". to 1/". units
CONCLU(ION(
*he pilot plant studies help in concluding the demand less than ./ppm product sulphur can be achieved from high sulphur a 6iesel Sample" *he 0etane improvement is remar!able from 6iesel feed hich has high aromatic content"
A++ENDI
1% Deter-inatin f Densit9 $A(T* D#07'%
*he density, specific gravity and A% volume (appro#imately /"7ml) of diesel as introduced into an oscillating sample tube" *he change in 8+
oscillating frequency caused by the change in mass of the tube as measured" sing the calibration data the density, specific gravity and A% gravity ere determined"
'%
Deter-inatin f :ine-atic &iscsit9 $A(T* D#00%
Cinematic viscosity is the resistance to flo of fluid under gravity" Cinematic =iscosity as determined at ?/o 0 using bbelohde@s =iscometer" *ime as measured for a fi#ed volume of liquid to flo under gravity through the capillary of a calibrated viscometer under a reproducible driving head and at a closely controlled and !non temperature" *he !inematic viscosity is the product of the measured flo time and the calibration constant of the viscometer"
/%
Deter-inatin f +ur +int $A(T* D#=>%
*he %our %oint is the loest temperature, e#pressed as a multiple of o 0 at hich the oil is observed to flo hen cooled and e#amined under prescribed conditions" *he %our %oint as determined using %our %oint apparatus" *he %our %oint is an inde# of the loest temperature of its utility for certain applications" After preliminary heating, the sample as cooled at a specified rate and e#amined at intervals of o 0 for its flo characteristics" *he loest temperature at hich movement of the sample occurred as observed and recorded as the pour point"
7/
0%
Deter-inatin f Aniline +int $A(T* D#<11%
Aniline %oint is the minimum equilibrium solution temperature, in degree 0elsius, of a mi#ture of equal volumes of aniline and the sample under test" *he aniline point is used to estimate the aromatic content of mi#ture" Specified equal volumes of aniline and sample ere placed in a tube and mi#ed mechanically" *he mi#ture as heated at a controlled rate and the temperature at hich to phases become miscible as noted" *he mi#ture as then cooled at a controlled rate and the temperature at hich to phases separate as recorded as the aniline point"
%
Deter-inatin f ,las! +int $A(T* D#=/%
lash %ont is the minimum temperature at hich the vapors from test sample ill give a momentary flash on application of a standard flame under specific test conditions" *he flash point is determined using %ens!y&artens closed cup apparatus" A brass test cup of specified dimensions, filled to the mar! ith test sample and fitted ith a cover of specified dimensions, as heated and the sample stirred at specified rates" An ignition source as directed into the test cup at regular intervals ith simultaneous interruption of the stirring, until a flash detected" *he temperature at hich flash as detected is reported as flash point"
<%
Deter-inatin f Ra-sbtt- Carbn Residue $A(T* D#'0%
71
t is the amount of carbonaceous residue formed by evaporation and thermal degradation (phyrolysis) of the sample" *he sample as eighed into a special glass bulb having a capillary opening and placed in a metal furnace maintained at appro#imately ../ o 0" *he sample as quic!ly heated to the point at hich all volatile matter is evaporated out of the bulb ith or ithout decomposition hile the heavier residue remaining in the bulb undergoes crac!ing and reactions" n the latter portion of the heating period, the cole or carbon residue as sub'ected to further decomposition or slight o#idation due to the possibility of breathing air in to the bulb" After a specified heating period, the bulb as removed from the bath, cooled in a dessicator, and the residue remaining as again eighed and e#pressed as a percentage of the original sample and reported as amsbottom 0arbon esidue" %rovision
is
made
for
determining
the
proper
operating
characteristics of the furnace ith a controlled bulb containing a thermocouple, hich must give a specified time-temperature relationship"
>%
Deter-inatin f Ttal (ulfur $A(T* D#'<''%
*he total sulfur content of diesel is determined by 4nergy 6ispersive S-ray luorescence spectrometry" *he diesel sample is placed in a beam emitted from the $-ray source" *he resultant e#cited characteristics $-radiation is measured and the accumulated count is compared ith counts from previously prepared calibration samples to obtain the sulfur concentration in mass>"
8%
Deter-inatin f Ttal Ar-atics and Ttal (aturates $I+#/=1%
73
6iesel sample contains monoaromatic, diaromatic and polyaromatic hydrocarbons" A !non mass of diesel sample as diluted in the mobile phase (n-
( 3/µ9 ) heptane) and a fi#ed volume
of the solution as in'ected into a ;igh
%erformance 9iquid 0hromatography (;%90) fitted ith a polar column" *his column has little affinity for the non-aromatic hydrocarbons hilst e#hibiting a pronounced selectivity for aromatic hydrocarbons" As a result of this selectivity the aromatic hydrocarbons are separated from the nonaromatic hydrocarbons into distinct bands according to their ring structure i"e", &A;, 6A;, %A; compounds" At a pre-determined time, after the elution of 6A;s the column as bac! flused to elute the %;As as a single Sharp band" *he column as connected to a refractive inde# detector that detects the components as they elute from the column" *he electronic signal from the detector as continually monitored by a data processor" *he amplitudes of the signal from the sample aromatics ere compared ith those obtained from previously run calibration standards in order to calculate > mass of &A;s, 6A;s, %A;s in the diesel" *he sum of &A;s, 6A;s and %A;s is reported as the total content of the aromatic contents in the sample" *he Saturates content of the sample is obtained by subtracting the total aromatics content from 1// percent"
=%
Deter-inatin f Nitrgen $A(T* D#0<'=%
7
N 3
AN*4C
analyGer as per AS*& 6-?83+ method determines the
Nitrogen content of the sample"
17%
Deter-inatin f A(T* Distillatin C!aracteristics $A(T* D#
8<%
*he distillation characteristics of the sample ere determined using AS*& 6-B8 6istillation apparatus" A 1// m9 specimen of the sample as distilled under prescribed conditions" *he distillation as performed in a laboratory batch distillation unit at ambient pressure under conditions that ere designed to provide appro#imately one theoretical plate fraction" Systematic observations of temperature readings and volumes of condensate ere made" *he volume of the residue and the losses ere also recorded" At the conclusion of
the distillation the observed vapor
temperatures can be corrected for barometric pressure and the data ere e#amined for conformance to procedural requirements, such as distillation rates" *he test as repeated if any specified conditions have not been met" *est results are commonly e#pressed as percentage recovered and corresponding temperature in a table"
7?
RE,ERENCE(
References
7.
1" 2abich "=" and &ouli'n L"A" (3//3), [ science and technology of novel processes for deep sulfurisation of oil refinery streams : a revie@, fuel, vol"B3,pp"8/7-81" 3" 2has!ar &",
=alavarasu 5", and 2alaraman C"S (3///), [deep
desulfuriGation of a diesel blend in a pilot plant tric!le bed reactor @, %etroleum Science and *echnology, vol"1B, No"7 Q B, pp"B.1-B8+" " 2has!ar &",
=alavarasu 5", Selvavathi =" and Sairam 2"(3//?),
[%roduction of ultra 9o Sulfur 6iesel-0atalyst and process options@, $ efinery *echnology &eet, 5oa, ndia, September3-3.,3//?Hpp"?7?-?B8" ?" 2has!ar &", =alavarasu 5", Sairam 2", 2alaraman C"S and 2alu C"(3//?), [*hree %hase eactor &odel to Simulate the performance of pilot-plant *ric!le K2ed
eactors Sustaining ;ydrotreating eactions@, nd"
4ng"0hem es", =ol"?,pp"88.?-888+" ." 0hunshan Song (3//), [An overvie of
ne approaches to deep
desulfuriGation for ultra-clean gasoline, diesel fuel and 'et fuel@, 0atalysis today , =ol"B8,pp"311-38" 8" 9amourelle A"% and Nelson 6"4"(3//1), [ ltra lo aromatic diesel@, %etroleum *echnology Zuarterly , 'une 3//1"
7.
Perry’s chemical engineers’ handbook. — 7th ed. /
prepared by a staf o specialists under the editorial direction o late editor Robert H. Perry : editor !on ". #reen : associate editor $ames %’Hara &aloney.
78
