215489644 merox operating manual

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MEROX OPERATING MANUAL

INDEX

S. No. DESCRIPTION Page No.

1 INTRODUCTION

2 MEROX PROCESS DESCRIPTION MEROX PROCESS EQUIPMENT

PRETREATMENT

EXTRACTION SECTION

SWEETENING

POST TREATMENT

MEROX CATALYSTS

3 U-21 ATF /S MEROX

UNIT CAPACITY

FEED SPECIFICATIONS

PRODUCT SPECIFICATIONS

TYPE OF CATALYST USED

PROCESS DESCRIPTION

DETAILED DESCRIPTION OF P!ID

PRE-COMMISSIONING OPERATION

STARTUP PROCEDURE

REACTOR "ED WATER WAS#ING AND RE-

IMPREGNATION

S#UTDOWN PROCEDURE EMERGENCIES

OPERATING $ARIA"LES

C#EMICALS AND CATALYSTS

MODIFICATIONS

% U-22 STRAIG#T RUN LPG MEROX

UNIT CAPACITY

FEED SPECIFICATIONS


PROCESS DESCRIPTION DETAILED DESCRIPTION OF P!ID


STARTUP PROCEDURE

S#UTDOWN PROCEDURE

EMERGENCIES

OPERATING $ARIA"LES


MODIFICATIONS

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S. No. DESCRIPTION Page No.

& U-23 $"N MEROX

UNIT CAPACITY

FEED SPECIFICATIONS



PROCESS DESCRIPTION



STARTUP PROCEDURE

REACTOR "ED WATER WAS#ING AND RE-

IMPREGNATION

S#UTDOWN PROCEDURE

EMERGENCIES

OPERATING $ARIA"LES


6 U-2% CRACED LPG MEROX

UNIT CAPACITY

FEED SPECIFICATIONS



PROCESS DESCRIPTION



STARTUP PROCEDURE

S#UTDOWN PROCEDURE

EMERGENCIES

OPERATING $ARIA"LES

TROU"LE S#OOTING

7 U-2& CRACED FCCG MEROX

UNIT CAPACITY

FEED SPECIFICATIONS


PROCESS DESCRIPTION



STARTUP PROCEDURE

S#UTDOWN PROCEDURE

EMERGENCIES

OPERATING $ARIA"LES

MODIFICATIONS

8 SAFETY ! FIRE FIG#TING FACILITIES

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1. INTRODUCTION'

Straight-run LPG, gasoline and kerosene fractions obtained from atmosphericdistillation may contain hydrogen sulphide and mercaptans. the etent of !hichmainly depends upon the type of crude processed. Similar products from

secondary processes such as "## also contain hydrogen sulphide andmercaptans to a greater degree compared to straight-run products. $ydrogensulphide is corrosi%e and should be remo%e in order to meet specifications oncorrosion rate. &he specification for LPG, gasolene, 'erosene and (&" includecopper strip corrosion test !hich is a measure of rate of corrosion on coppercontaining materials.)ercaptans are substances !ith obnoious odour and,therefore, in order to handle and store them, mercaptan le%el !ill ha%e to bebrought do!n to a acceptable odour le%el. &he specifications of abo%e productsinclude *+octor &est* !hich must be negati%e and is generally related to the etentof mercaptan present. $ydrogen-sulphide can be easily remo%ed by !ashing !ithdilute caustic solution. $o!e%er, for reducing the mercaptans le%el manyprocesses are a%ailable like

Strong alkali-!ash

#opper s!eetening

+octor s!eetening

)ero process

$ydrodesulphurisation

(lkali-!ash is effecti%e only if lo! molecular !eight mercaptans are in%ol%ed.$ydrodesulphurisation is normally employed only if reduction of total sulphur le%elis also reuired. oth in%estment and operating costs are higher in case ofhydrodesulphurisation. /ut of other proceses a%ailable, )ero process isconsidered a superior and pro%en process.

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2. MEROX PROCESS DESCRIPTION

&he )ero process licensed by )0S 1ni%ersal /il Products #o., 21/P3, 1S(, is forthe chemical treatment of LPG, gasolene and distillates to remo%e mercaptans intodisulphides. &he remo%al of mercaptans may be either partial or full. &he chemicaltreatment is based on the ability of )ero catalysts to promote the oidation of

mercaptan to disulphide using air as the source of oygen. &he o%erall reaction isas follo!s

45S$ 04/4 - 5SS5 $4/

&he oidation is carried out in the presence of an aueous alkaline solution suchas either sodium hydroide or potassium hydroide. &he reaction proceeds at aneconomical rate at normal rundo!n temperature of refinery streams.

Lo! molecular !eight mercaptans are soluble in caustic solution and therefore!hen treating LPG and light gasoline fractions, the process can be used to etractmercaptan to the etent, they are soluble in caustic. 9traction of mercaptanreduces the sulphur content of the treated product. (lternati%ely mercaptans canbe con%erted to disulphides !ithout remo%ing any sulphur from the treated stock in!hich case the operation is referred to as s!eetening. :n the treatment of hea%ierboiling fractions such as hea%y naphtha and kerosene only s!eetening is possible.

MEROX PROCESS EQUIPMENT'

:n order to understand the function of %arious )ero process euipment. theeuipment can be broadly di%ided into follo!ing sections

Pretreatment for remo%al of hydrogen sulphide and naphthenic acids, if present.&he method %aries !ith properties and conditions of feedstock and in some casesmay not be reuired.

9traction section !here reuired, for remo%al of caustic soluble mercaptans andthus reduce sulphur in the treated product.

S!eetening for con%ersion of mercaptans to disulphides. "or a gi%en capacityplant, the )ero reactor si;e can %ary depending on the case of s!eetening due to

the type of mercaptans present and also on product reuirement.

Post-treatment to remo%e caustic ha;e and to control properties not affected by)ero process. $ence post-treatment needed depends on products, utilisation andtype of contaminants present in the feedstock.

&aking each section in turn, function of each euipment can be described.

PRETREATMENT

Petroleum fractions may contain hydrogen sulphide and stocks boiling higher than8


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!ith caustic. "urther it blocks some of the catalyst acti%ity sites slo!ing do!n thenormal reaction and also consumes part of the oygen a%ailable. $ence, it isrecommended that hydrogen sulphide is remo%ed by !ashing !ith dilute alkalisolution before the distillate is sent to reactor for treatment.

>aphthenic acids also interfere !ith treating operations and must be remo%ed priorto treatment. &he reactor contains caustic and if naphthenic acids are not remo%e

they form sodium naphthenates !hich coat the catalyst and block the pores. "orremo%al of napthenic acids, the procedure used is to !ash !ith dilute caustic.+ilute caustic is used so as to a%oid formation of emulsions. &here could, ho!e%er,be some carry-o%er of ha;e depending on the acidity of stock treated. &he ha;ecan easily be remo%ed by coalescing through a sand filter.

"eedstocks, !here carry-o%er of !ater from distillation units can be epected mustbe passed through a coalescer for remo%al of suspended !ater prior to caustic!ash, !hich !ould other!ise dilute the caustic used for pretreatment.

EXTRACTION SECTION

(s pre%iously stated, lo! molecular !eight marcaptans are caustic soluble and caneasily be remo%ed by !ashing !ith caustic in a counter current to!er. :mpro%edetraction is fa%ored by

Lo! temperature.

$igh concentration of caustic.

Lo!er molecular !t. of mercaptans

&ype of mercaptans, %i;. normal mercaptans are easily etractable, tertiarymercaptans least etractable and secondary being in bet!een.

&he mercaptan enters the caustic solution and reacts as follo!s

5S$ >a/$ ?- >aS5 $4/

&his is being a re%ersible reaction the degree of completion of reaction is go%ernedby normal euilibrium la!s.

&he sodium mercaptide is readily oidised to disulphide in the presence of )erocatalyst as sho!n

4>aS5 l04/4 $4/ - 4>a/$ 5SS5

&his is not a re%ersible reaction and the reaction rate is speeded up by

5aising the temperature.

1se of ecess air.

:ncreasing the intimacy of contact.

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:ncreasing the catalyst concentration.

&he oidation of mercaptides is carried out in oidiser in the presence of merocatalyst. &he disulfides oil, !hich is formed, separates out from caustic as it isinsoluble in caustic. #austic can be reused for etraction. &he presence of )erocatalyst in etraction caustic does not ho!e%er, affect the amount of mercaptans

etracted. and etraction is dependent only on parameters eplained earlier .

SWEETENING

S!eetening can be defined as con%ersion of mercaptan sulphur present in ahydrocarbon stream to disulphide sulphur !ithout actually reducing sulphur contentof treated stock. &he s!eetening process is based on the ability of )ero catalystto promote the oidation of mercaptans to disulphides using air as the source ofoygen. &he reaction is as follo!s

5S$ >a/$ ?- >aS5 $4/

4>aS5 l04/4 $4/ - 4>a/$ 5SS5

(s can be seen from reactions, the oidation is carried out only in the presence ofalkali solution.

&he S!eetening can be accomplished either in solid bed s!eetening, !here thehydrocarbons and caustic are simultaneously controlled o%er a solid supportimpregnated !ith )ero catalyst.

Liuid-liuid s!eetening !here hydrocarbon, air and caustic containing )erocatalyst, air simultaneously controlled in a mier.

Solid bed s!eetening consists of a reactor, !hich contains a bed of acti%atedcharcoal impregnated !ith )ero catalyst and kept !et !ith caustic solution.:mpregnation of catalyst on bed is achie%ed by dissol%ing the catalyst !ithammonia solution and pumping ammonia solution o%er charcoal. (ir is in@ectedahead of reactor and in the presence of mero catalyst the mercaptans areoidised to disulphides. &he reactor is follo!ed by a settler !hich ser%es asreser%oir of caustic. #austic is intermittently circulated from the settler o%er the

catalyst bed to !et the charcoal.

"or liuid-liuid s!eetening, the most common type of mier used is the orificeplate mier, !hich is a %essel, fitted !ith a series of plates !ith orifices. &he %esselpro%ides adeuate residence time and the orifice plates create enough turbulenceto bring about the intimate contact bet!een hydrocarbon, caustic, catalyst and air.&he problem of accomplishing liuid-liuid s!eetening is one of getting thedifficulty soluble mercaptans into the caustic phase for sufficient time to permittheir oidation. &he higher the molecular !eight or the more highly branched themercaptan is, the more difficult it is to accomplish necessary miing. $ence hea%ygasoline and 'erosene may ha%e to be treated using fied bed reactor.

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POST TREATMENT

&he product from the mero reactor !ill at times contain caustic ha;e. Posttreatment is reuired if the product is to go to storage, clear and bright. :n mostcases pro%ision of caustic settler and sand filter is adeuate to remo%e causticha;e. $o!e%er, for treatment of (&", !hich has to meet stringent specificationcaustic must be remo%ed by !ater !ash after caustic settling. Aater !ash

remo%es entrained caustic as !ell as !ater soluble surfactants, Aater !ash isfollo!ed by a salt filter to remo%e entrained !ater and part of the dissol%ed !ater.&his may be follo!ed by clay filter to remo%e copper and !ater insolublesurfactants, if present in feed.

MEROX CATALYSTS'

&here are t!o types of )ero catalyst, each one being used for specific ser%ice.#atalyst " is to be used on units euipped !ith solid bed s!eetening reactors.#atalyst AS is used for liuid-liuid s!eetening in miers. &his is a caustic

dispersible catalyst. &his is also used for oidation of etraction caustic inoidisers.

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3. U-21 ATF /S MEROX '

UNIT CAPACITY'

&he )ero 1nit for treating kerosene B (&" streams from the (tmospheric+istillation unit has been designed to feed .C million metric tons per year ofkerosene !hile processing a Corth 5umalia

crudes. &he 1nit shall operate for DEC stream days in a year.

FEED SPECIFICATIONS'

&he kerosene to be treated in the )ero 1nit shall ha%e substantially the follo!ingproperties

2i3 oiling 5ange :P0"P o# E


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2%ii3 &hermal stability2a3 "ilter pressure drop 4C.< maimum

in mm $g.2b3 &ube 5ating %isual Less than code D

2%iii3 Aater separameter inde F< minimum

2i3 (cidity, mg. '/$0Gm aphthenic acid etc.

S!eetening is achie%ed in supported catalyst bed reactor. &!o reactors in parallelha%e been pro%ided. (ir reuirement of all )ero units is supplied from a common

compressor. (lso, storage tanks for receipt, dilution and storage of caustic andstorage for methanol ha%e been pro%ided.

Post treatment for kero0(&" consists of caustic settling. !ater !ash to !ash of anycarry-o%er caustic salt drier for drying and clay filters for impro%ing colour stabilityof treated product. #lay adsorbs coloured nitrogen compounds.

DETAILED DESCRIPTION OF P!I DIAGRAM

'erosene0(&" as obtained from distillation unit stripper under flo! control ischarged to the unit charge pumps


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sulphide, etc. &he feed goes to coalescer


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!hich ensures constant pressure in the reactor and other %essels. &he treatedproduct is run-do!n to storage.

"eed stocks !hich do not call for complete treatment but !hich meet productspecifications after caustic pre-!ash, can be di%erted to storage after causticpre!ash, %essel


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/n completion of pressure test of the unit, !ater flushing of the different systems inthe unit is carried out !ith all the pumps running on line to flush out all muck, scaleand other construction debris contained in the lines. Suction screens must beinstalled on each pump to protect them from damage. :n the initial stages ofcommissioning of the unit, it is better to install a finer 26


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(fter inspection of salt drier internals for cleanliness and fittings, it is loaded !ithrock salt up to a height of 6


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(dd 7 bottles of )ero " after shaking. Stir the miture to help dispersing thecatalyst if reuired. )ake up the %olume to 8< litres.

Start educting the catalyst solution by routing the slip stream through the eductor4 G-4 from 4 P-4 discharge to suction.

5egulate the catalyst eduction rate to D to E litres0minute.

(fter establishing the abo%e rate, fill the drum from Pump discharge !ith a rateeual to eduction rate. (dd bottle of )ero " e%ery < minutes.(fter about 04 hrs. start checking the color of the circulating (mmonia at the pumpsuction before educting point. &his color should be clear or faint blue. :f the color isdark blue, it means that there is channeling in the charcoal bed :n such a case theimpregnation is to be stopped and 5eactor bed should be flushed !ith air to rectifythe bed channeling.

(dd EC bottles of )ero ".

(fter the last batch of solution is educted, flush the catalyst drum se%eral times!ith (mmonia solution and educt to the 5eactor .

#ontinue circulation for about E hrs.

Start transferring (mmonia solution to the second reactor 5 by opening theinlet block %al%e to top distributor !hen the solution le%el in 5 ( falls belo! topdistributor, shut off the inlet and continue to transfer all the circulating (mmoniasolution into 5.

Ahen the pump loses suction shut off the pump. lock in 5(. /pen hydrocarbonoutlet from 5 and start circulation back to the inlet. Start taking +) !ater to fill5 until the le%el is metre abo%e the distributor pipe.

Stop +) !ater flo! to the 5eactor, but continue the circulation. Sample thesolution and analy;e for (mmonia concentration.

:n@ect (mmonia gas again into the circulating solution to get


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>o! the reactors are ready for commissioning !ith 'ero0(&".

5euirement of #atalysts0#hemicals

2a3 )ero " catalyst -F< ottles.

2b3 (mmonia -C #ylinders of 6< 'g net !t.

2c3 +) !ater -4C< )D

$III. C#ARGING OF C#EMICALS'

&he caustic storage tanks


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Aater !ashing the product to remo%e the entrained caustic has to be done.$ence, start !ater-!ashing the product, pumping +) !ater into the !ater !ash%essel


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:t !as eperienced that !hile using !ater heater 24 3 lot of hammering !astaking place resulting se%ere %ibration of the lines and therefore it !as difficult tomaintain the !ater temp, Later on "A line connection !as gi%en d0s of +) Aater0H. &his does not reuire !ater heater ser%ices. "A temp. can be controlled bycontrolling the steam to deareator.

:nitially, the draining effluent !ill be dark bro!n and foamy !hich !ill change colourand e%entually becomes colourless. Ahen the !ater from the drain is clear andclean, the !ater !ashing can be stopped. Stop the !ater flo! and blo!out asmuch !ater as possible from the reactor beds !ith steam gi%en to reactor top.'eep the steam flo! through the beds for another D< minutes to remo%e as muchresidual hea%y oil as possible from the charcoal bed.

Stop steam in@ection and block off !ater heater. :ntroduce air into the reactors andblo! the reactors !ell for an hour or so that there is no !ater drip noticed from thebottom drain.

>et alkali;e the beds !ith fresh < deg. e caustic solution and then return theunit to normal !orking condition as discussed under IStart-up ProcedureI.

II. CATALYST REIMPREGNATION

&his step is necessary only !hen hot !ater !ashing, higher feed temperatures,stronger caustic saturation, reduced feed rates etc., do not help in mercaptanoidation and the product remains doctor positi%e. &he reimpregnation inter%al may%ary from three months to one year depending on proper pre!ashing feed

mercaptan content, crude source etc.

III. REIMPREGNATION OF EROSENE/ATF REACTORS

$ot !ater !ashing.

(cidising the reactor bed.

:mpregnation

I$. #OT WATER WAS#ING

:solate 5eactor 24 5- (3 from the rest of the unit. Start pumping out thekerosene, keep reactor under positi%e pressure by steam.

(fter kerosene is pumped out, start steam flo! from the !ater heater 24-3 to the5eactor 2'eep the bed temp. F< deg #. +rain out the condensate from 5eactorbottom. &his is to remo%e the residual kerosene and hea%y hydrocarbon in thebed.

Start introducing +) Aater through the !ater heater into 5eactor. 'eep the !ater

temp. 24 &-C3 around F


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Ahen the 5eactor is full, open reactor bottom to drain. 'eep the drain rate close tothe hot !ater fill rate i.e. about C< )D0hr.

>/&9 :nstead of using !ater heater, "A can directly be taken.

#heck the drain !ater color. Ahen the colour is clear, check the reactor effluentp$.

#ontinue hot !ater !ashing till reactor effluent p$ is do!n to 8,F.

"ollo! step . to .C for another reactor 245-3 and 4D5-.

$. ACIDISING OF REACTOR "ED'

Stop the !ater and steam flo!. "lush out the caustic circulation system by openingup the suction lines from the reactor bottom to the circulation pump 4 P-4 andpump discharge to spent caustic tank.

/pen the top man!ay of the 5eactor.

5efill reactor 24 5-(3 !ith +) !ater after the reactor has been pumped out till!ater le%el is ) belo! the distribution pipe, lock in 5eactor outlet line.

Start circulation from bottom to top of the reactor. oth the kerosene outlet and thebottom pump out of the reactor are open to the pump suction. #ontinue to fill +)Aater till !ater le%el is ) abo%e the distributor pipe.

:n@ect steam occasionally to keep the circulating !ater temp. at C


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$I. IMPREGNATION

Start filling reactor 4 5-( !ith +) !ater. lock in reactor outlet lines.

Start circulation pump 4 P-4 after reactor le%el is ) belo! the distributor pipe,#ontinue to fill +) !ater.

Ahen !ater le%el rises to ) abo%e the distributor. Stop !ater addition 2e carefulnot to flood the charcoal out of the reactor3.

#ontinue circulation for about 4-D hours.

Start (mmonia in@ection after the cylinder is connected. 5egulate the outletpressure at about D kg0cm4. :n@ect appro. C< kg of ammonia i.e about C-6 hours2one cylinder in 4-404hrs.3 )easure the rate by !eighing scale.

Put steam hose to pre%ent free;ing of pipe due to gas epansion.

#irculate ammonia for about 4-D hours keeping the rate at pump maimum i. e. C8)D0hr. Sample the solution and send to lab analysis. (mmonia concentrationshould be


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Start transfer ammonical solution to reactor 4 5- by opening the inletdistributor block %al%e. Ahen the le%el in reactor 45-( falls belo! the distributorpipe, shut off the inlet. #ontinue0transfer to ammonical solution into reactor 4 5-.

Ahen the pump loses suction, shut off the pump. lock in reactor 4 5-(. /pen$# outlet from reactor 45- and start circulation to its inlet. Start taking +)

!ater to fill the reactor until the le%el is ) abo%e distributor pipe.

Stop +) !ater flo! to the reactor but continue circulation. Sample the solution andanalyse for ammonia.

:n@ect ammonia to get


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:f the caustic is spent in settler ature and degree of emergency%aries from time to time and hence good @udgement and discretion should be

eercised to tackle such situations.

I. ELECTRIC POWER FAILURE'

:f it is a general po!er failure, feed to the unit !ill be interrupted !ith the failure ofthe pumps. $ence a shutdo!n of the unit is ine%itable. Shut off air in@ection to themier immediately and block off feed to the unit. Shut off discharge %al%e of unitpumps and close pressure controller at unit limits and hold system pressure. Startup the unit as per procedure !hen po!er supply is resumed.

II. STEAM FAILURE'

Local steam failure !ill not affect the unit running immediately, but if (H1 runningis affected by the emergency, feed to the unit might be interrupted. :n such a case,the unit !ill ha%e to be shutdo!n and kept in a standby condition pendingresumption of feed supply from (H1.

III. INSTRUMENT AIR FAILURE'

:nstrument air failure !ill result in all unit control %al%es operating in the fail-safeposition, i. e., they !ill all close. #lose off feed to the caustic pre-!ash %essel H-.

Shutdo!n caustic circulation pump P, circulation pump P4 and !ater in@ection

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pump PD and block le%el controllers !ith isolation %al%es. )onitor all le%els. $oldsystem pressure by blocking off pressure controller at unit limits.

5e%ert back to normal operations, starting the unit follo!ing standard procedure,once air supply to the instruments has been resumed.

I$. COOLING WATER FAILURE '

( total failure !ill effect feed supply to the unit and pumps. $ence, unit !ill ha%e tobe shutdo!n immediately. :solate all the pumps after stopping them. #lose thepressure controller and hold system pressure. )aintain le%els in the %essels. Start-up the unit in the normal !ay, !hen cooling !ater supply becomes a%ailable andfeed from (H1 is restored to the unit.

$. AIR COMPRESSOR FAILURE'

:f the duration of the failure is only short, the product may not go off specification.ut the mercaptan con%ersion efficiency drops off rapidly and the product !ill ha%eto be slopped as soon as it goes off uality. (ir in@ection block %al%e has to beimmediately shut-off to the reactors 5( and , on air compressor failure. /nresumption of air supply, check the product uality and !hen it is on specification,route it to storage tank. :f both the compressors are not a%ailable for a longerduration due to break-do!ns and maintenance, the 1nit !ill ha%e to be shut-do!n.

OPERATING $ARIA"LES'

&he caustic solution used for )ero treatment %i;. :n pre-!ash column and inreactors become spent e%entually. Aeak acids like #/4 picked up from air,

naphthenic acids and other aliphatic acids present in the feed stock make thealkalinity of the caustic lesser and its ability to etract mercaptans !ill suffer.$ence, it becomes necessary to remo%e part of the spent caustic and replace fromtime, to time to restore its alkalinity.

&he feed stock should be freed of all hydrogen sulphide by passing it through thepre-!ash column. /ther!ise the oidation reaction !ill be suppressed in thereactors. :t !ill gi%e rise to increased caustic consumption.

Lo!ering hydrocarbon feed rate and caustic temperature !ill impro%e mercaptan

etraction

>aphthenic acid in feed stock may gi%e rise to emulsion problems and hence mustbe remo%ed by pre!ash !ith D=e caustic solution.

/idation rate is increased by increasing the temperature and catalystconcentration. (bout D< cubic feet of free air is reuired for each pound ofmercaptan sulphur to be oidised.

&he amount of )ero #atalyst needed !ill be approimately one pound for


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Sufficient back pressure must be maintained at each etraction stage to pre%ent%aporisation and caustic entrainment.

Presence of acid oils upto a limit of 8 !ill increase solubility of mercaptans in thecaustic.

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C#EMICALS ! CATALYST

Sr Hessel>o.

:nitial fill,)D (ppro.le%el ofinitial fill

#austicstrength!t

)ake up 0 change out !henreuired

Juantity 9pected duration!ith design crude

#austic4H

F.D D


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MODIFICATIONS '

I. ANTISTATIC DOSING FACILITY

&his facility is gi%en to maintain (&" conducti%ity bet!een C< to EC< psm 2P:#/simen per meter3 to meet the specification.

(ntistatic (gent is stored in a small %essel 2


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%. U-22 STRAIG#T RUN LPG MEROX

UNIT CAPACITY'

&he )ero 9traction 1nit for straight run LPG has been designed to process7il#u #orrosion >o !orse than $4S "ree feed

PROCESS DESCRIPTION'

(mine absorber for remo%al of $4S and caustic pre!ash %essel are pro%ided forpretreatment.

&reatment for S5 LPG consists of only an etractor !ith caustic, as all mercaptanspresent in feed are in the etractable range. 9traction caustic is oidised in acommon oidiser section.

#austic settler has been pro%ided for settling and separation of carry-o%er causticfrom etractor.

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LPG obtained from crude unit stabiliser o%erhead is charged to unit by unit chargepumps


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PRE-COMMISSIONING OPERATIONS'

I. C#ECING COMPLETION OF CONSTRUCTION WORS( INSPECTIONAND "OXING UP OF EQUIPMENTS

&he follo!ing preliminary operations ha%e to be carried out to ensure a successful

start-up of the unit

#heck that all mechanical !orks of construction ha%e been completed, euipmentsinspected, boed up and signed off on unit check lists made for this purpose.

Scaffolding, debris, tools and other construction materials remo%ed from the unitarea.

)ake a final list of blinds !hich should be in position or taken out before startingpurging operations. )ake sure all blinds ha%e been installed at the proper sides of%al%es and signed off in the list.

#heck and ensure "ire-fighting and safety euipment is in place and in good!orking condition.

9nsure all utility systems and flare release headers are in ser%ice and ready foruse.

:solate the unit from other plants and tankages at the unit limits !ith block %al%es.

'eep the fuel gas and flare header isolated from the unit pending purging

operations.

:solate or remo%e orifice blocks of all flo! meters for flushing purposes.

II. WATER FLUS#ING OF T#E UNIT '

"or !ater flushing of a ne! unit, use ordinary !ater.

Aater flushing of the entire unit has to be done !ith all pumps running on line sothat all muck, scale and construction debris are !ashed out of all euipment and

unit pipelines. &he unit can be con%eniently taken in sections or indi%idualeuipment !ise and the flushing operation is carried out !ith temporaryconnections from the "ire !ater header. Suction screens ha%e to be installed onthe pumps during the flushing period to protect them from damage. &hey ha%e tobe run at least for 4E hours continuously to ensure their free and smooth ser%ice.+uring the flushing period, care should be taken to throttle the pump discharge%al%es suitably so as not to o%erload the motors. &he screens on the pump suctionlines ha%e to be cleared off all debris collected periodically after stopping thepumps. till they remain clear continuously at least for eight hours. +isconnect allinstruments lead lines and flush the leads thoroughly. )ake sure that all processlines, control %al%e loops are thoroughly flushed, to atmosphere to remo%e muck,

construction debris, etc. etter to drop each #0H and flush the assembly andbypass also thoroughly. &hen the #0H can be refied in position. )ake sure all lo!

- 29 -


30/76

points bleeders are clear and all columns and %essels %ents and drains should beclear.

Ahen !ater flushing operation is completed, !e ha%e to pressure test the entireunit !ith !ater as detailed belo!

:::. PRESSURE TEST OF EQUIPMENT ! LINES

:n order to check for leaks on euipment and lines after !ater flushing, they are allsub@ected to !ater pressure of about 6-4< kg0cm4 ."or this purpose LPG inlet toamine scrubber and its outlet after the pressure controller are isolated by block%al%es. 5ich amine and rich caustic outlets from scrubber 44#, pre-!ash %essel44H, etractor 44#4 must also be blocked off. :nitial filling of the entire unit can bedone !ith "ire !ater for remo%al of air. "or pressurising !e ha%e to use oiler feed!ater.

'eep running the pump out of F PE (00# group and through the permanentsupply line take "A to this unit and slo!ly pressurise the entire system to normaloperating pressure for a period of C to D< minutes. :f necessary one or t!o drainsmay be kept open to ha%e a small discharge from the pump.

+uring pressure test safety %al%e do!n-stream flanges may be kept !edge openor to check tight shut-off of safety %al%es before their set pressure.

&ighten all leaky flanges, %al%es glands etc. !here reuired. Gaskets may ha%e tobe replaced after pressure test. 'eep a record of such flange @oints for subseuenttesting before cutting in of feed LPG.

(fter the system pressure test is successfully completed depressurise the unit, butkeep the system filled !ith !ater. >o! the system is ready for taking in "uel gas.&his is the best !ay of keeping air out of the unit.

LPG can be taken in to the unit from (tmospheric 1nit in small uantities. LPG canbe lined up slo!ly to pressurise the unit to a slight positi%e pressure !ith gas. &hishas to be done slo!ly and carefully to a%oid chilling. :f. ho!e%er, fuel gas isa%ailable, gas can be taken directly. LPG %apourises slo!ly gi%ing positi%epressure. >o! drains off the !ater from the entire system under gas pressure.

:H. C#ARGING OF C#EMICALS

(fter pressurising the unit !ith fuel gas, inlet %al%e to the scrubber 44# is blockedoff. 9nsure that +9( inlet and outlet from 44# are also blocked off. Similarly,ensure that caustic charge line to 44 H and its eit as !ell as )ero coustic inletto etractor 44 #4 are all shut off. &he )ero regeneration system is alsopressured up !ith fuel gas upto the disulphide separator in cracked LPG )erounit and the etractor 44#4 bottom %al%e is blocked off. )ake sure air inlet %al%e tothe oidiser


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caustic solution in the storage tank pro%ided and transfer to disulphide separator


32/76

#ommission odorant in@ection to the rundo!n LPG after caustic settler at thespecified rate. #heck the odorant in@ection facility is ready in all respectsbeforehand. &hen start the in@ection pump 44P4 and set dosage. as instructed.

>/&9 /dorant in@ection is no more in use no!adays.

#heck freuently LPG for $.S after the pre!ash %esel 44H and replace caustic

as necessary. 44H caustic is be replaced !hen caustic becomes C


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EMERGENCY PROCEDURE

:. POWER FAILURE

:n case of general po!er failure LPG supply to the unit !ill stop and the unit pumpsrunning !ill be interrupted. +9( solution circulation also !ill stop.

lock off pressure controller at unit rundo!n line and hold pressure in the system.

)onitor all le%els.

Ahen po!er supply and LPG feed are restored, put the unit back into normaloperation, follo!ing standard procedure.

::. STEAM FAILURE

:n case of general steam failure, LPG to the unit !ill be affected and hence unit !illha%e to be shut do!n and kept under pressure till feed supply is resumed from(H1. :f the steam failure is confined to the )ero unit only then LPG )erosection can run !ithout any interruption.

:::. COOLING WATER FAILURE

"ailure of cooling !ater !ill affect the feed supply to the unit as !ell as the unitpumps. 1nit !ill ha%e to be shutdo!n and kept standby till !ater supply isrestored.

:H. INSTRUMENT AIR FAILURE

/n instrument air failure, all the control %al%es in the unit !ill close. :f (H1 is alsoaffected by air failure, feed to the unit !ill be interrupted. #lose off the pressurecontroller on LPG rundo!n line and maintain pressure in the system. )onitor allle%els till air supply is resumed to normal. 5e%ert to normal operation.

OPERATING $ARIA"LES

:. LPG PREWAS#

LPG is passed through amine scrubber 44# and caustic pre!ash %essel 44H toremo%e all traces of hydrogen sulphide. &he +9( solution should be kept at thespecified %alue of 4C by !t. &he amine circulation rate also should be at thedesign rate of about 8


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concentration in the caustic should be


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C#EMICALS ! CATALYSTS

Hessel no :nitial

fill )D

(ppro.

le%el ofinitial fill

#austic

strength !t.

)ake up0

charge out!hen red.

Juantity 9p.to

run!hendesigncrude

#austic


36/76

Scheme >o )50PS0D


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&. U-23 $IS"REAER NAP#T#A MEROX

UNIT CAPACITY

&he )ero treating unit for s!eetening the naphtha stream obtained from the%isbreaker unit has been designed to feed 6C,


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PROCESS DESCRIPTION

Caustic prewash vessel is provided for removal of hydroe! sulphide etc"

"or %isbreaker naphtha, both etraction and s!eetening sections are pro%ided.(fter caustic pre!ash naphtha goes to etraction to!er !here partial etraction of

mercaptans, to the etent possible are etracted. 9traction is follo!ed bys!eetening in reactor !ith supported mero catalyst bed. (ir reuirement is metfrom the common compressor .

Post treatment consists of a caustic settler, and a sand filter for remo%ing causticha;e. &he treated product reuires anti-oidant in@ection, since %isbreaker naphthais a cracked product.


Hisbreaker naphtha as obtained from Hisbreaker stabiliser bottom is fed to the unitby feed pumps


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&he treated product from settler is sent to storage %ia a sand filter


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9nsure free mo%ement in the unit area. Get scaffoldings, construction debris toolsand tackles etc. remo%ed from the unit area.

:solate the unit from other plants and storage tanks at the unit limits !ith block%al%es0blinds for carrying out flushing and purging operations.

:solate or remo%e instrument orifice blocks for flushing purposes.

II. WATER FLUS#ING OF T#E UNIT

:n preparation for start-up of the unit, !ater flushing of the entire unit has to becarried out to remo%e and !ash out all muck, scales construction debris etc. fromeuipment and lines for the purpose of !ater flushing, the unit can be taken up incon%enient sections as !ell as indi%idual euipment-!ise also. $ooking uptemporary fire !ater hose connections on euipment or lines, thorough flushing ofall euipment and lines are carried out.

(ll the unit pumps are tried out during !ater flushing !ith suitable !ire meshscreens 2 preferably


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(fter pressure test is satisfactorily completed, drain !ater from system at all lo!point and air blo! it thoroughly to remo%e all moisture.

I$. SCREENING AND LOADING OF C#EMICALS

(#&:H(&9+ #$(5#/(L

(cti%ated charcoal !hich mero catalyst impregnation !ill bescreened properly before it is loaded in the reactor 4D5. Standard (S&) Sie%e>os. < and D< screens ha%e to be used and charcoal coarser then >o.< andfines after >o.D< screen are separated out. &he charcoal thus screened is loadedin 4D5 after isolating it from other euipment. :ts top and side man!ays are keptopen. :ts inlet distributor pipe assembly has to be kept *#o%ered during loading topre%ent charcoal entry into the pipe. #harcoal loading is done through a hopperand ad@ustable can%ass chute, !hich etends to the bottom of the reactor. (sloading progresses, the length of the chute is ad@usted. >o cone formation is to beallo!ed on the charcoal surface in the reactor. :mproper le%eling !ill cause non-uniform distribution of hydrocarbon flo! through the charcoal bed.

Personnel must !ear dust masks co%ering their noses andmouths to pre%ent inhalation of charcoal dust, !hile loading for le%eling inside thereactor, the person entering must !ear a fresh air mask. Ahile loading, it has to beensured that the *bottom ohnson screen collector :s fully submerged in thecharcoal by physical checking, from the bottom man!ay. &he charcoal loading iscontinued till the inlet distributor pipe is about F


42/76

(fter the reactor is filled !ith charcoal to the reuired le%el and boed up proceedto impregnate charcoal !ith )ero catalyst " as detailed in the follo!ing steps.

"ill the reactor !ith +) !ater being careful not to add so much !ater as to floatcharcoal out of reactor.&o ensure this. reactor top man!ay can be kept open./nce le%el is ensured man!ay can be kept in closed position !ithout bolting to

enable inspection of bed after impregnation.

Stop + ) !ater supply and line up reactor bottom to reachcirculation pump 4D-P4 (. and establish from bottom of bed to top of bed.

9stimate the amount of !ater in the system i. e. reactor, lines etc. :f !ater ischarged from a tank, this can be estimated con%eniently from tank dips. 9stimateshould take into account piping, dead spaces etc. &he total uantity !ill be about6-7 )D.

#alculate the amount of ammonia reuired to raise theconcentration of !ater to a


43/76

$II. C#ARGING OF C#EMICALS

#austic reuirements of the unit is met from the storage facility a%ailable in thekerosene mero section. "resh caustic of 46.C e strength is recei%ed in storagetanks 4 &: B &4 and diluted !ith demineralised !ater to the desired strength.


44/76

:nitially, the product stream is routed to the slop tank till satisfactory results areobtained consistently for about 4 hours. &hen naphtha can be routed to the regularstorage tanks. Set the feed rate to normal consistent !ith other control systemsparameters.

REACTOR "ED WATER WAS#ING ! CATALYST REIMPREGNATION

/%er a period of time, catalyst in the reactor bed loses its acti%ity and e%en !etting!ith fresh caustic circulation does not help in restoring the acti%ity and the productcontinued to go off specifications. &hen the charcoal bed has to be hot !ater!ashed to remo%e the organic deposits on its pores. Aashing !ill bring back theacti%ity of the catalyst for reaction again. (s the loss of acti%ity by deposits oncharcoal surface occurs gradually the !ater !ashing operation can be plannedcon%eniently &he !ater used should be dust free and free from suspended matter.hardness, salts and acti%e chlorine. +) Aater is therefore, used in our plant forthis purpose. Aater !ashing procedure is as follo!s

Stop air in@ection and hydrocarbon charge to the reactor 4D 5.

Pump out all naphtha from 4D 5 under steam pressure. Steam out the reactor forabout an hour.

#ommission !ater heater 4D : and start introducing hot !ater into reactor at atemperature of 8C - FC=# at a rate of 8 gallons0minute for


45/76

"ollo! the steps C.. to C..E gi%en under I5eactor ed Aater !ashingI,ecepting the steaming of reactor. "ill up the reactor !ith hot !ater. &hen stop!ater and steam flo! to the !ater heater by blocking off the %al%es.

Line up reactor bottom drain line to caustic circulation pump 4D P4 (0 and flushout the lines free of caustic into the spent caustic disposal system.

#lose the reactor outlet %al%e and fill it up !ith hot !ater again. Start hot !atercirculation from reactor top to bottom, regulating !ater temperature !ith steamaround C


46/76

"lush out reactor 4D 5 !ith hot !ater thoroughly and drain off all !ater.

:solate all indi%idual euipment by blinds as reuired for maintenance. Steam and!ater !ash them thoroughly till they are hydrocarbons and chemicals free.

)aintain an upto date blind list of unit euipment.

"ollo! detailed instructions that !ill be gi%en at the time of shutdo!n for preparingeuipment and lines gas free and for maintenance.

9ntry to the %essels should be gi%en only after ensuring complete isolation byblinds, making gas free and free of chemicals. (lso, it must be ensured that the%essels are !ell %entilated and are safe to enter. Gas test must be taken beforeissuing clearance for entry into a %essel Safety euipments recommended must be!orn by personnel entering %essels !hich pre%iously contained caustic and otherchemicals.

EMERGENCIES

9mergencies result out of euipment failures and from interruption of utilities./perating personnel must be thoroughly familiar !ith the emergency proceduresso that uick actions can be taken in such situations. >ature and degree of anemergency %aries from time to time. $ence, good @udgement and discretion shouldbe eercised to tackle any emergency.

I. ELECTRIC POWER FAILURE

:f it is a general failure, naphtha feed to the unit !ill be lost and all unit pumps !ill

stop. 1nit !ill ha%e to be immediately shutdo!n. blocking off air in@ection to mier)M. #lose off the pressure controller at battery limit and hold the systempressure. Shut off the discharge %al%e of pumps. $old the le%els in the %essels.Start up the unit again follo!ing standard procedure. !hen po!er supply isrestored.

II. STEAM FAILURE

Local steam failure !ill not effect the unit immediately :f the naphtha feed supplyfrom %isbreaker is affected then unit !ill ha%e to be shutdo!n and kept standby till

the feed naphtha is a%ailable again.

III. INSTRUMENT AIR FAILURE

(ll control %al%es !ill operate to fail safe position i.e. they !ill close. Shut off the airto the reactor by the block %al%e to the mier )M. $old the pressure in the systemand monitor all le%els till air supply is restored to the instruments. Start-up the unitas per normal procedure and bring it back on stream.

I$. COOLING WATER FAILURE

( total !ater failure !ill affect feed supply to the unit as !ell as unit pumps. $ence.unit !ill ha%e to be shut do!n immediately. Stop the pumps. lock off pressure

- 46 -


47/76

#ontrollers and hold system pressure. )aintain all le%els in unit %essels. Ahencooling !ater becomes a%ailable, start up the unit, as per normal procedure.

"or a short duration, process air failure !ill not affect the treated naphtha uality.ut the mercaptan con%ersion efficiency drops off rapidly !ith no air for oidation.$ence the product !ill ha%e to be stopped as soon as it becomes doctor positi%e.Shut off air in@ection block %al%e to mier )M immediately on air failure.

OPERATING $ARIA"LES

#austic solutions used in pre!ash %essel 4D H and reactor 4D 5 become spente%entually and mercaptan etraction !ill suffer. $ence, periodically, part of thecaustic !ill ha%e to be replaced !ith fresh stock.

#austic concentration in the solution for etracting lighter mercaptans in 4D #must be 4


48/76

C#EMICALS ! CATALYSTS

Sr Hessel>o.

:nitialfill,)D

(ppro. le%el ofinitial fill

#austicstrength !t

)ake up 0 change out!hen reuired

Juantity 9pected duration!ith design crude

4DH 4.E D


49/76

. U-2% CRACED LPG MEROX

UNIT CAPACITY

#racked LPG )ero unit is designed to process ,EC,


50/76

PROCESS DESCRIPTION

&$9/5K /" )95/M &59(&)9>& /" #5(#'9+ LPG

&he etraction mode of )ero Process is for the treatment of light hydrocarbons inLPG and light naphtha streams. :t is designed to reduce the total sulfur content byetracting the mercaptan compounds in these streams. &he etracted mercaptan

compounds can be effecti%ely remo%ed after being oidi;ed to disulfide oils. &he$ydrocarbon stream is contacted !ith caustic solution in an etractor. 9tractedmercaptans are then oidi;ed and separated from the caustic. &hus the )eroprocess is easily described in t!o parts

)95#(P&(> 9M&5#&:/>

)ercaptans present in the LPG are readily dissol%ed in the caustic solution !henetracted by means of a high efficiency, counter flo! etractor. (s the hydrocarbonand caustic are intimately contacted, the mercaptans combine chemically !ith thesodium hydroide molecules.

5S$ >a/$ ?- >aS5 $4/

Since the reaction is re%ersible, the sodium mercaptide must be remo%ed from thecaustic solution from time to time. &he 1/P designed counter amount etractorpro%ides the effecti%e etraction of mercaptans in to the caustic solution and itsremo%al from cracked LPG.

)95/M #(1S&:# 59G9>95(&:/>

#austic regeneration is for the remo%al of sufficient mercaptides from the richcaustic solution to allo! the reuse of this caustic solution to continuously affect thedesired mercaptan remo%al from the hydrocarbon stream. Sodium mercaptides inthe rich caustic are readily oidi;ed to disulfide in the presence of oygen andenough )ero catalyst. Sodium hydroide reliberated. &his is represented as

)ero>aS5 0Ea/$

#atalyst

&his is an irre%ersible reaction.

&he disulfide oil produced is essentially in soluble in the caustic solution and thusallo! it to be gra%ity separated from the regenerated caustic before the leancaustic is allo!ed to return to the etractor.

&he composite reaction is

5S$ 04


51/76

necessary to remo%e maimum amount of $4S. &his is accomplished by (mineabsorption follo!ed by !ashing !ith dilute caustic of 7 by !t.

Post treatment is normally for the remo%al of entrained caustic solution due to itscorrosi%e nature to protect do!n stream process euipment and to meet productspecification.

DETAILED DESCRIPTION OF P ! I D

&he cracked LPG from "## gas concentration stabili;er o%erhead is recei%ed inamine scrubber 4E# 2E


52/76

section. LPG from top of settler is sent to storage. ack pressure controller


53/76

bet!een t!o support rings !hich hold !iremesh screens supported on gratingbars. "or searing of the supporting grids, nylon ropes are used. +isulfide oil !hichseparates out !hile passing through the anthracite packing floats on top of caustic"rom time to time as indicated by le%el disulfide oil shall be pumped out to sloptanks. "rom the disulfide outlet no;;le there is a line connecting to skim pot %entoff any air, !hich does not separate in the skim pot. Ahile pumping out disulfide oilfrom %essel. :t is ad%isable to check the le%el of caustic in skim pot and ensure that

the le%el is sufficiently belo! the %ent line @oining from disulfide outlet line./ther!ise there is a chance of draining out caustic along!ith disulfide oil.

&he #austic from the bottom of the separator is circulated back to etractor columnby caustic circulating pumps


54/76

4E-H-E $ori;ontal portion -E to 8 mesh anthracite coal

2D3 Hent tank -I steel 5asching rings

>/&9 - &he packing details should be checked !ith 1./.P original pro@ectbooks.

PRECOMMISSIONING OPERATION

#hecking completion of construction !orks, inspection and boing of euipment.

&he follo!ing preliminary checks should be carried out to ensure a successfulstartup of the unit.

#heck that all the mechanical !orks of construction ha%e been completed as perpro@ect book.

#heck the entire erection of the unit, euipment and lines and compare !ith theProcess and :nstrumentation diagrams and any discrepancies should be pointedout and corrected.

Scaffolding, debris, tools and other unnecessary construction material should beremo%ed from unit areas.

)ake a final list of blinds !hich should be in position or taken out before startingpurging operations. )ake sure all blinds ha%e been installed at the proper sides of%al%es and signed off in the list.

#heck and ensure "ire-fighting and safety euipment is in place and in good!orking condition.

9nsure all utility systems and flare release header is in ser%ice and ready for use.

:solate the unit from other plants and tanks at the unit limits !ith block %al%es.

'eep the fuel gas and flare header isolated from the unit pending purgingoperations.

:solate or remo%e orifice blocks of all flo! meters for flushing purposes.

A(&95 "L1S$:>G /" &$9 1>:&

Aater flushing of the unit is meant for thorough cleaning of euipment internals,and entire pipingO so that all muck, scale and construction debris are remo%edcompletely. Aater supply can be taken by temporary hoses from the fire hydrantsystems. &he unit can be con%eniently di%ided into small sections and the flushingoperations are to be carried out. (ll pumps suction screens should be fitted !ithfine mesh !ires during the flushing operations to protect the pumps* internals. &hefollo!ing precautions are %ery important during flushing out period.

- 55 -


55/76

:solate all instruments, disconnect the lead lines and flush thoroughly each leadline.

+rop control %al%es and flush through the inlet, outlet and bypass lines thoroughly.

+isconnect pumps* suction flangesO keep tin sheet to pre%ent !ater getting in tothe pumpsO open suction strainer flanges, pull out the strainer and flush each

suction line to outside thoroughly. &hen only !e can make up the pumps suctionflanges and run the pumps for further effecti%e flushing.

Ahile running the pumpsO the fine strainer gets choked uite oftenO and needsfreuent cleaning. &hese fine strainers can be totally remo%ed only after cleaningfreuency comes do!n to once in 8 to < hours.

Ahile flushing the entire system, make sure that all lo! point bleeders are pro%edclean.

P59SS159 &9S& /" 9J1:P)9>& (>+ L:>9S

&he cracked LPG unit contains t!o sections. &he LPG treatment section operatesat C to 6 kg0cm4 pressure, !hereas the 5egeneration section operates at Ckg0cm4. &he pressure testing of these t!o sections should be done independentlyto check for leak and for rectifying the same.

>/&9 -#austic regeneration being common to S5 LPG and H >aphtha )ero1nits in addition to #5 LPG )ero 1nit, it depends upon !hich )ero 1nit is beingcommissioned first. >aturally the first unit to be commissioned !ill be S5 LPGO soalso all the precommissioning and commissioning acti%ities of caustic.

5egeneration Section !ill ha%e to be done at this time.

&he procedural details are noted belo!

P59SS159 &9S& /" )95/M &59(&)9>& S9#&:/>

&he high-pressure section consists of (mine (bsorber, caustic pre!ash, )eroetractor, caustic settler and the %arious connected high-pressure lines andpumps.

&his system !ill be pressure tested after complete isolation from 5egenerationSection !ith !ater supply from F-P-E(00#. "or this purpose LPG inlet to (mineabsorber and its outlet after pressure controller are isolated by block %al%es. 5ichamine and rich caustic outlets from 4E-#-, pre!ash %essel H and 4E#-4 mustalso be blocked off.

:nitial filling of the )ero treatment section can be done from fire hydrant !ater!ith a temporary hose connection. "ill up the entire system and euipment !ith!ater and displace air completely. Pressuri;ing the system can then be done bytaking oiler feed !ater supply from F-P-E(00#. Slo!ly raise the system

pressure up to 8 to 4< kg0cm4. #heck for leaks in the entire high-pressure sectionand rectify the same. /ne or t!o bleeders can be kept slightly open so that oiler

- 56 -


56/76

feed !ater pump !ill ha%e some positi%e discharge. &he amine surge drum testpressure !ill be around to .C kg0cm4 only. So this needs pressure testingseparately from high-pressure section and can be done independently by initiallyfilling the %essel !ith !ater and then pressuring !ith hydraulic pumping. (fterpressure test fuel gas backing in to this %essel should be done by separate hoseconnection.

(fter successful completion of pressure testing, depressuri;e the section to aroundo! pullout all blinds in the unit as preparatory step for unit startup and keepsystem isolated by block %al%es only.

#ut in fuel gas or take small uantity of LPG into the system and let it e%aporate.Slo!ly the system !ater should be totally drained out under fuel gas pressure.

P59SS159 &9S& /" 59G9>95(&:/> S9#&:/>

&his section can be pressure tested !ith ser%ice air up to C kg0cm4. &he causticheater, oidi;er, disulfide separator and connecting lines and euipment aresub@ected to this pressure. Aith soap solution check for leaks and rectify the same.&hen depressuri;e the regeneration section to atmosphere. :n this section there isno need to displace air because later on air !ill be in@ected in to this system as perprocess needs.

#$(5G:>G /" #$9):#(LS

(fter pressuring up the unit !ith fuel gas, and total draining of !ater inlet %al%e to

the scrubber # is blocked off. 9nsure that +9( inlet and outlet from # are alsoblocked off. Similarly, ensure that caustic charge line to H and its eit as !ell as)ero caustic inlet to etractor #4 are all shut off.

Prepare 4


57/76

Ahile commissioning a fresh unit. there is no need to add catalyst in the beginning.Ae can add catalyst only !hen the circulating caustic becomes partly spent afterabsorption of )ercaptans from the LPG. ut !e !ill describe the steps for addingthe catalyst here.

#alculate the approimate uantity amount of caustic circulating from regeneration

to etractor 4E-#-4 and back. &his !ill be eual to 6 to 8 'L.

&he rate of addition of catalyst is approimately a bottle for e%ery E )D ofcirculating caustic.

Prepare slurry of catalyst in caustic taken in a bucket. &hen transfer the slurry tothe make-up pot. )i the slurry thoroughly in the pot by using (ir sparger pro%ided.

&ransfer the solution under air pressure in to the circulating caustic.

:t is desirable to add the total catalyst in small lots of to 4 bottles at a time toensure uniform distribution o%er the entire circulating caustic.

Same principle for catalyst addition !ill be follo!ed !hene%er part of the caustic isreplaced !ith "resh caustic to ensure minimum catalyst presence and acti%ity inthe caustic.

START-UP PROCEDURE

(fter the pre-commissioning acti%ities ha%e been completed the unit !ill becommissioned as per standard procedure noted belo!

#harge circulating caustic solution to top of etractor column #4 after establishinga !orking le%el in disulphide separator HE in cracked LPG )ero 1nit.

Ahen normal le%el of caustic is obtained in #4. commission the bottom le%elcontroller to regulate rich caustic flo! back to disulphide separator HE.

#harge lean amine in flo! control to the amine scrubber #. )aintain le%el at thebottom of # by commissioning the le%el controller regulating the rich amine flo!to regenerator section in S51.

>/5)(L S&(5&-1P P5/#9+159

(t this stage all the chemicals are charged to the unit and the unit ready for takingin hydrocarbon.

Line up cracked LPG flo! from battery limit to (mine scrubber - #austic pre!ash2bottom t!o distributors3 - 9tractor- #austic settler - ack pressure controller.#ommission the controller and set it at C kg0cm4.

/pen battery limit %al%e and direct LPG flo! to (mine scrubber. e prepared to

dra! more +9( from (mine regeneration unit as the (mine scrubber trays arebeing !ashed !ith (mine. Set the (mine flo! "5#.

- 58 -


58/76

"ill the scrubber, pre!ash and etractor %essels !ith LPG, (s etractor is beingfilled, caustic solution le%el in the regeneration section may be made to fill up thecirculating caustic in%entory. )ake sure there is al!ays some caustic le%el in theetractor. LPG should ne%er be allo!ed to enter regeneration section.

/nce the unit is filled !ith LPG and is at the operating pressure 2of to 44 kg0cm4 at

the inlet of the unit3, check LPG flo! rate and %erify all the gauge glasses.

#ommission steam to caustic heater to maintain the inlet temperature to oidiser atEC= #. Start air in@ection.

#ommission back pressure controller 4E-P#- 4E and set it at D.C kg0cm4. Send!aste air to %ent tank 4EH-C.

#ommission oygen analyser. /nce oygen concentration in the %ent air is belo!4 2by %ol3, start fuel gas. Set "5J:-46 at a flo! rate such that oygen contentafter dilution should fall belo! C 2 by %ol 3. Send air0fuel gas miture to thehighest disposal point in to the atmosphere.

(s disulphide0caustic inter phase appears in the hori;ontal body of the disulphideseparator, open disulphide oil disposal line to 4E-P-D. &he formation of disulphideoil !ill be %ery little and !ill be discharged to slop oil tank. &he pumping isepected to be intermittent. )ake sure that some disulphide oil is seen in the sightglass of disulphide separator. +o not pump out caustic also.

#heck the product after caustic settler for uality. Ahen it is doctor negati%e, it canbe routed to the regular storage bullets, kept ready for the purpose.

#ommission odorant in@ection to the rundo!n LPG after caustic settler at thespecified rate. #heck the odorant in@ection facility is ready in all respectsbeforehand. &hen start the :n@ection pump P-/4 and set the dosage as instructed.

#heck freuently LPG for $4S after the pre!ash %essel H and replace cautic asnecessary. #heck the acid oil content of the caustic solution once in a !eek. :f it ismore then 8-4 then some caustic from H- !ill ha%e to be replaced.

#heck the regenerated caustic being charged to the etractor #4. &his !ill gi%e anidea of the efficient operation of disulphide separator .

S#UTDOWN PROCEDURE

:nform all concerned of intention to shutdo!n the unit and proceed as follo!s

Shut off +9( charge pump to the scrubber #. Shut off LPG charge pump to #immediately after this. Stop odorant in@ection pump P/ 4.

Stop caustic circulation through the etractor #4 from the disulphide separator HE.

Stop caustic supply to pre-!ash %essel H.

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9mpty out caustic le%els from H #4 and H4 to spent caustic disposal or to thedisulphide separator HE as instructed.

9mpty out +9( le%el in # to its regeneration section in S51.

+epressure the %essels and columns slo!ly to the flare system, after isolation atunit limits.

:solate the %essel and column by blinds and make them gas and chemicals free bysteaming and !ater !ashing repeatedly, as per special instructions that !ill beissued at the time of shutdo!n.

'eep an upto date record of the blind list.

9ntry to the %essels has to be gi%en only after ensuring that they are absolutelyfree from all gases and chemicals used in the plant. Gas test must be done beforeentry permit is gi%en. Proper %entilation inside the %essels must be ensured.Personnel entering the %essels must !ear proper protecti%e euipment asmentioned in the clearance permits.

EMERGENCIES

I. POWER FAILURE

:n case of general po!er failure LPG supply to the unit !ill stop and the unit pumpsrunning !ill be interrupted. +9( solution circulation also !ill stop.

lock of pressure controller at unit rundo!n line and hold pressure in the system.

)onitor all le%els.

Ahen po!er supply and LPG feed are restored, put the unit back into normaloperation, follo!ing standard procedure.

II. STEAM FAILURE

:n case of general steam failure, LPG supply to the unit !ill be affected and henceunit !ill ha%e to be shut do!n and kept under pressure till feed supply is resumed

from "##.

III. COOLING WATER FAILURE

"ailure of cooling !ater !ill affect the feed supply to the unit as !ell as the unitpumps. 1nit !ill ha%e to be shutdo!n and kept standby till !ater supply isrestored.

I$. INSTRUMENT AIR FAILURE

/n instrument air failure, all the control %al%es in the unit !ill close. :f "## is also

affected by air failure. feed to the unit !ill be interrupted. #lose off the pressure

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controller on LPG rundo!n line and maintain pressure in the system. )onitor allle%els till air supply is resumed to normal. 5e%ert back to normal operation.

OPERATING $ARIA"LES

. (mine concentration -4C by !t. in !ater.

4. Lean +9( temperature -(s lo! as possible.

D. +9( circulation rate -< )D0$r.

E. LPG feed temperature -DC to E


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)ercaptan etractor #4 remo%es these undesirable components from LPG streamby intimate miing !ith a caustic solution containing )ero catalyst. &he causticconcentration for the circulation should be 4


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:mproper )ero #austic 5egeneration is caused by one or a combination of thefollo!ing

(ir :n@ection is insufficient. :nsufficient air in@ection is uickly ascertained by notingthe oygen content of the Hent Gas from the +isulfide Separator. ( %alue of lessthan 8 Hol. /ygen !ould confirm that insufficient air is being in@ected. $o!e%er,

this should be confirmed by a IShake &estI of the lean )ero #austic or byLaboratory (nalysis of the lean caustic for )ercaptide 2and Sulfide3.

:mmediately check the (ir :n@ection System to %erify that air is flo!ing to the5egeneration Section at the rate pre%iously established. :f there is reduced or noair flo!, re-establish proper air flo!. $o!e%er. if air in@ection is found to be at thepre%iously prescribed rate, then lack of sufficient regeneration air is probably dueto

III. SULFIDE CONTAMINATION

( lead acetate paper check on the pre!ash hydrocarbon stream !ill determine ifsulfide contamination is happening and determine its relati%e se%erity. :f thepresence of $4S in the etractor feed is confirmed, necessary steps mustimmediately be taken to re-establish proper hydrocarbon0+9( and pre!ashoperation.

:ncrease air in@ection in


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/n the other hand, should sulfide contamination be %erified but the source uicklyeliminated and the rich mero caustic analysis confirm lo! sulfide contamination.e. g. less than D


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!hich is ne! or long out of ser%ice should be thoroughly flushed and cleanedbefore being commissioned or it may be necessary to discard the first batch ofcaustic if it becomes subseuently loaded !ith iron sulfide scale from improperlyconditioned euipment.

(lso, certain corrosion inhibitors or the acid treatment of the inhibitor, promoteemulsion problems &he inhibitor is picked up by the )ero #austic from the LPG

being treated. &he presence of inhibitor or ecessi%e concentrations of inhibitorcan normally be traced to improper inhibitor in@ection and thus !ith proper additi%econtrol, the problem can be eliminated.

$III. INADEQUATE DISULFIDE SEPARATION

Poor disulfide separation from the lean )ero caustic in the disulfide separator canbe caused by surfactant materials, !hich keep the disulfide suspended in thecaustic. +isulfides in the )ero #austic can be analy;ed by 1/P )ethod DFD.

&he presence of surfactants in the lean )ero #austic can be determined by asurface tension test comparison bet!een plant and fresh )ero #austic. Plant and"resh )ero #austic are each shaken !ith eual %olume of isooctane. &he timereuired for the hydrocarbon-caustic phase to separate completely is noted in eachcase.

Significant difference in surface tension and settling time is indicati%e of thepresence of surfactant in the caustic. &he settling time for the plant )ero #austic!ill be significantly longer if surfacants are present.

:f the )ero #austic is not sufficiently regenerated !hen lea%ing the oidi;er, some

further mercaptan to disulfide may occur in the settling compartment of thedisulfide separator do!n stream of the coalescing section. (ny disulfide formedthere !ill not ha%e been coalesced into sufficiently large droplets to gra%ityseparate from the caustic and !ill remain suspended.

#omparison of the )ercaptan content of the #austic sampled at the oidi;er outletand disulfide separator caustic outlet !ill indicate the )ercaptan are oidi;ing todisulfides in the disulfide separator settling compartment. &his is usually caused byinsufficient mero catalyst. or miing. Slo!ly add etra )ero #atalyst and takesteps to keep the )ero #atalyst suspended !ill eliminate this problem.

:f insufficient separation is suspected, a Laboratory #oalescing &est can beconducted to check if dislfide separation could be impro%ed. :nsufficient separationis likely to be caused

:mproper installation of coalescing partition so that anthracite coal has migrated.

:mproper installation of anthracite coal, or

>o anthracite coal at all.

(t the earliest opportunity the %essel should be opened and the situation %erifiedand corrected. Proper disulfide remo%al from the lean )ero #austic is imperati%e

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if full benefit is to be recei%ed from the etraction operation. (ll of the disulfidecannot be gra%ity separated from the regenerated caustic. ( lo! re-entry sulfurconcentration 2less than < PP) in the $ydrocarbon3 is considered adeuate.

IX. INADEQUATE PREWAS#ING

(side from the ob%ious cause associated !ith the break-through of acidic

compounds due to ecessi%e uantities of $4S or #/4 in the feed or Spent#austic, the only remaining cause for a problem is inadeuate contacting or miingin the pre!ash. &his is caused by insufficient hydrocarbon flo!. $ydrocarbondistribution into the batch caustic is insufficient to assure proper miing andcontact. &his situation can only be corrected by plugging some distributor holes.&he number of holes to be plugged should be propertionate to the decrease infeed rate.

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4. U-2& CRACED FCCG MEROX

UNIT CAPACITY

#racked >aphtha )ero 1nit is designed to Process D


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Liuid-liuid s!eetening#austic settlingPassing through sand filter

#austic pre!ash is pro%ided on for straight 5un naphtha, as "## Gasolene afterstripper and +ebutaniser contains little or no $ydrogen Sulphide. "or s!eeteningproper a mier type of 5eactor has been pro%ided. Post treatment consists of a

caustic settler and sand filter. (nti-oidant in@ection facility is also pro%ided.

Straight-run naptha stabilisation from distillation unit stabiliser is Icharged to theunit by feed pumps


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back pressure in the unit by o.C antioidant !ith or!ithout copper deacti%ator is done by do;ing pumps 24DP-D(00#0+3 located in unit


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lines. "or this purpose, the unit can be con%eniently di%ided into sections andindi%idual euipment !ise !ater flushing can be done, &emporary fire !ater hoseconnections are made on unit euipment or lines at suitable points and thoroughflushing is done. Suitably !ire mesh strainers are to be installed on pump suctionspools during the !ater flushing operation to protect the pumps from damages.&he pumps are to be run at least for 4E hours continuously to ensure their free andsmooth functioning. +uring the !ater flushing operations, care should be taken to

see that pump discharge %al%es are sufficiently throttled so as not to o%erload theirmotors. &he suction screens installed !ill ha%e to be opened up and cleared of alldebris collected periodically after stopping the pumps, &his type of cleaning thescreens !ill ha%e to be continued till they remain free of any muck continuously atleast for 8 hours.

/n completion of !ater flushing the unit euipments and lines satisfactorily, !eha%e to pressure test entire system !ith steam.

III. PRESSURE TEST ! PURGE EQUIPMENT AND LINES

:n order to check for leaks on euipment and lines after !ater flushing they are alltested !ith steam pressure of about C kg0cm4proceed as follo!s

lock off caustic circulation pumps Pl ( B !ith their suction, discharge %al%es.

/pen !ide all %ents and drains in %essels Hl, H4, HD. :solate sand filter HE closingoff its inlet and outlet %al%es. &he sand fiter is to be purged !ith gas and testedunder gas pressure to a%oid caking of the sand bed.

$ook up steam hoses to the steam out connections of the %essels Hl, H4 and HD

and back up steam into the %essels and lines upto the unit limit block %al%e.

(fter sufficient steam purging for about C minutes from all possible %ents anddrains. #lose these points and pressure up the system to about C kg0cm4 !ithsteam. #heck up the entire unit for leaks and get them attended.

(fter successful completion of pressure test. continue !ith steam purging of theunit system till all air from euipment and lines ha%e been remo%ed. &he system isready for taking in hydrocarbon !hen all air from the system has been displacedby steam. )aintain a positi%e pressure of steam till fuel gas is taken into the unitand it is pressured up !ith gas.

"uel gas is slo!ly taken into the pre-!ash %essel H and then to mier H4 andcaustic settler HD. &he sand filter is also purged !ith gas first to displace all air andthen pressured up to fuel gas system pressure. #atalyst addition pot HC must beisolated from the gas purging lines. +rain all steam condensate from lo! pointsand drains. Ahen gas smell comes out of the %ents of the %essels. steam can becompletely shut off and system allo!ed to remain at


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I$. C#ARGING OF C#EMICALS AND CATALYST

efore actual start-up of the unit, the treatment systems should be made ready torecei%e LS5 gasoline from (H1. Prepare system as belo!

Pump in


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#ommission gasoline charge pumps and commence flo! !ith "5#-on line throughthe mier H4 after pre!ashing stage in H 5oute gasoline to storage passingthrough settler HD and sand filter HE, !ith the pressure in ser%ice.

Start in@ecting the reuired uality of mero catalyst into the caustic stream goingto the mier H4, taking care not to blo! air into the system.

ring operating conditions to normal. Ahen cracked gasoline becomes a%ailablefrom G#1, charge it to the mier H4.

Start anti-oidant in@ection into the treated gasoline stream at the stipulated rate.

&he abo%e procedure !as applicable !hen 4CH !as used as pre!ash %essel.>o! 4CH is being used as the additional 'nock /ut Pot for the sponge gasesfrom 4


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+isplace all gasoline from the %essels to the storage or slop tank !ith fire !ater."inally drain all the !ater and hydrocarbons from the %essel taking care not to pullany %acuum in them.

:solate %essels !ith blinds and steam them out thoroughly using the steam outconnections pro%ided. +rain all condensate from lo! points.

)aintain upto date record of blind list.

Aater !ash the caustic %essels and sand filter and mier !ith fire !ater repeatedlytill they are free of chemicals and clear !ater flo! out from the drains freely.

)ake sure that indi%idual euipment has been properly isolated by blinds andmade gas and chemicals free, as per laid do!n procedure. #onduct a gas testbefore allo!ing entry inside a %essel. :nsist on protecti%e euipment being !orn bypersonnel entering in %essels in caustic and other chemicals ser%ice.

EMERGENCIES

I. POWER FAILURE

:f it is a general po!er failure, all the pumps in the unit !ill stop. "eed to the unit!ill also be interrupted. :n this case the plant has to be shutdo!n. "ollo! the stepsgi%en belo!

Shut off air in@ection to mier H4.

#lose off the discharge %al%es of all pumps !hich ha%e stopped.

Shut off pressure controller at unit limits and hold pressure in the system, till po!ersupply is resumed.

Start-up the unit, as per standard procedure as soon as po!er supply is restored.

II. STEAM FAILURE

:f feed supply to the unit is interrupted due to general steam failureO unit !ill ha%e

to shutdo!n and !ait for resumption of feed supply from (H10G#1. :f it is a localfailure gasoline )ero treating section can continue to run, as long as possible.

III. COOLING WATER FAILURE

&he unit !ill ha%e to be shutdo!n as pumps cooling !ater supply !ill be affected.as !ell as feed supply from (H10G#1.

I$. INSTRUMENT AIR FAILURE

(ir failure !ill result in all the unit control %al%es operating in their fail safe

positions. i. e., they !ill all close. :f feed supply is interrupted unit !ill ha%e toshutdo!n. /ther!ise unit can be operated !ith the control %al%es blocked off and

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maintaining pressure and flo!s on bypass. Le%els in %essels !ill ha%e to bemonitored till air supply is restored.

$. UTILITY AIR FAILURE

:f the failure is only for a short duration unit operation can be continued normarly.:n the absence of oidising air in@ection, the mercaptan con%ersion efficiency drops

off uite rapidly. $ence, the product !ill ha%e to be slopped as soon as it is doctorpositi%e. >ormal operations can be re%erted to !hen air in@ection is restarted andthe product is on grade.

OPERATING $ARIA"LES

:n the mier H4, all hea%ier mercaptans are con%erted to disulphides. $ere, theoperating %ariables are air in@ection rate, )ero catalyst concentration in causticsolution and circulating caustic strength. (ir in@ection rate should be Q .7C>)D0kg of sulphur con%erted. &oo much air !ill gi%e rise to continuous %enting fromthe sand filter HD and increases the fire ha;ard. )ero catalyst concentrationshould be


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/perating instructions 1" #uta!e rich stream from 18C1 $ottom is $le!ded i!to%-25 &'( to $oost the )cta!e of *+" ,his also helps i!

upradatio! of additio!al aphtha i!to *+" ,he

$le!di! is do!e throuh a !ew co!trol valve 25-./C-

1109 provided at the dow!stream of %-25 #C"

2" #uta!e $le!d i!to *+ also poses some haards lie

additio! of more $uta!e i!to *+ ca! lead to *+ ualityfailure i! & / a!d ca! also lead to pote!tially

da!erous situatio! i! *+ ta!"

3" /!terlocs provided i! $uta!e $le!d facility are

25-./C-1109 would close at 18C1 $ottom temp less

tha! 92 (e C"

25-./C-1109 would close whe! 25-.&-4 .CC:

flow to *ero; < falls $elow 10 m3'hr"

4" 25-./C-1109 would !ormally remai! o! ratio co!trol"

&atio would $e set $etwee! 0"04 -0"07" ,his mea!s

$uta!e flow would $e 0"04-0"07 times sum of

&eformate a!d .CC: flow"But this facility is yet to be

created"

5" =t prese!t 25-./C-1109 would remai! o! =uto a!d

set poi!t has $ee! loced at 6 *3'hr ma;.CC%

asoli!e>)?C% aphtha>#< should $e limited to

3"5-4"0@w

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5. SAFETY ! FIRE FIG#TING FACILITIES

(ll the general safety rules and practices applicable to Petroleum 5efineryoperations are to be follo!ed in )ero &reating Plants also. (dditionally some ofthe safety precautions to be taken in each case are presented belo!

I. C#EMICAL #ANDLING

#hemicals, (mine B #austic are used in this unit. 5ubber glo%es, aprons and faceshields are supplied for any @ob in the chemical area of this unit and they should beused for any @ob here. (ny spillage of chemicals on the body can be !ashed off!ith copious amounts of !ater. ( safety sho!er is pro%ided in )ero 1nits for anychemical spillage-emergency on the body of any person. (ll safety euipmentshould be cleaned !ith !ater so that they can be safely re-used later on.

CAUSTIC SODA'

#austic solution, commonly called lye, used in )ero units is to be handledcarefully !ith due precautions. Glo%es, Goggles and face shields must al!ays beused in the treating area for any @ob. Painful in@ury and possible blindness canresult out of caustic splash into the eyes. ( safty sho!er is pro%ided in the treatingarea for !ashing the body immediately if an accident occur. :n case of causticsplash into the eyes, both the eyes must be thoroughly !ashed !ith plenty of!ater and the person should be sent for firstaid. (ll eye in@uries must be referred toproper medical attention after the first aid.

Aorkmen should be made a!are of the fact that caustic does not gi%e immediate!arning of its presence on the skin by burning or irritDtion. ut its presence on theskin can be recognised by its slippery, soapy feeling. ( doctor must be consultedimmediately in case of a se%ere skin burn. :n %ie! of the ha;ards mentionedabo%e, !orkmen must !ear rubber glo%es and apron besides goggles and faceshields !hen !orking in an area eposed to caustic. #austic is destructi%e toleather and it is ad%isable to !ear rubber foot!ear also !hile handling caustic.

!hen caustic comes into contact !ith the skin, the area must immediately be!ashed !ith plenty of !ater. +epending upon the se%erity of eposure, !ashing!ith a 4 solution of acetic acid can be follo!ed. "ecilities for immediate !ashing!ith !ater like safety sho!er must be readily a%ailable in the caustic handlingarea. Pumps, %al%es and process euipment scheduled for maintenance must beflushed thoroughly !ith !ater prior to opening. )aintenance !orkmen must !earall protecti%e euipment !hile doing @obs on euipment in caustic ser%ice.

CATALYST '

)ero catalyst has no harmful effect on the skin. $o!e%er, !orkman should bead%ised not to contaminate any part of their bodies !ith catalyst. Should any

contact takes place, the catalyst must be carefully !ashed off the skin !ith copious

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amount of soap and !ater until the blue colour is no longer seen. #atalyst shouldnot be taken internally nor breathing of its dust permitted.

DISULP#IDE

+isulphides are high boiling oily organic liuids ha%ing sp. gra%ity from

215489644 merox operating manual

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