This document summarizes the processes at an acid regeneration plant and a PSA nitrogen and hydrogen gas production plant. The main objectives of the acid regeneration plant are to regenerate spent acid from steel pickling to over 99% purity and produce a valuable iron oxide byproduct. The PSA plant uses compressed air and ammonia cracking to produce high purity nitrogen and hydrogen gases for various industrial processes. Both plants utilize various unit operations like filtration, heating, cooling, absorption and adsorption to achieve the desired product specifications.

1. ACID REGENERATION PLANT
MAIN PROCESS
The main objective of this plant is to regenerate the spent acid which is coming from pickling .At pickling
the acid is showered at moving sheets of rusted steel due to which high amount of iron chloride become
mixed with this acid. Our plant is not only regenerating the acid upto 99% but also formed a valuable by-
product, i.e. Fe2O3.The flow diagram of the process is
MAIN FEATURES:
Thisis Pakistan’sonlyacidregenerationplantforuse insteel workspickling,hasprovidedconsiderably
processingadvantages,including:
 .Extremelylowemissionvalue.
 .The ironoxide by-producthasa highmarketvalue
 .Recoveryrate of HCl ishigherthan99%.
 .Constantacidqualityandcompositionensure uniformandhighqualitypickling.
 .Rinse waterinthe pickling line isusedinacidregenerationprocess,thusconsiderablyreducing
waste waterproduction.
 .The keydesignfeature of achievingextremelylow levelsof waste gasanddustemissionwhich
are belowcurrentlegislationlimits.
 .Adjustable acidconcentrationof regeneratedacid.
 .Independentfromchemical suppliers.
 .Automatedcontrol system.
FUEL:
Natural gas
Minimum calorific value 7400kcal/Nm3
Pressure 25 kPa.
CO2 2.485%
CH4 88.789%
N2 3.853%

2. RINSE WATER INDUSTRIAL WATER COMPRESSED AIR
Pressure 150kPa. Pressure 300kPa. Pressure 500kPa.
Temperature 60C Temperature 35C Dew point 10C
Fe 5g/l Hardness 200 ppm CaCO3 below minimum
HCl 15g/l Ph 7-8.2 ambient temp.
NITROGEN WASTE WATER REGENERATED ACID
Pressure 500-700kPa. Amount 250l/hr Amount 2000l/hr
Temperature ambient Cl- 25g/l Total HCl con. 25g/l
Purity 99.9% Fe++/+++ 15g/l Fe. 5g/l
MECHANICAL EQUIPMENTS USED AT ARP:
Spray roaster
1 spray unit
1 lump breaker
Rotary valve
Burner equipments
2 burners
2 uv-flame detector
1 combustion air blower
I set of burner piping
Dust separator
Cyclone separator
1 rotary valve
Pre concentrator with separator
Venturi
Separator
Absorption column
Exhaust fan
Gas cleaning system
Scrubber
Horizontal drop separator
Vertical drop separator
1 fume stack
Collecting bin

3. Oxide station
1 oxide bin
Gate valve
1 rotary valve
1 oxide separation filter
Oxide conveying pipes
Steel pipes
Conveying air fan
1 big bag fillng device
Storage tanks and pumps for ARP
1 tank for waste pickle liquor
1 tank for regenerated acid
1 tank for rinse water
1 tank for fresh acid
2 pumps for waste pickle liquor
2 pumps for regenerated acid
2 pumps for rinse water
1 pump for fresh acid
2 pumps for the sump pit
2 pumps for pre-concentrator
2 pumps for reactor feeding
2 pumps for absorber
2 pumps for gas scrubber
1 booster station. 2 pumps for water
Filters
1 filter for waste pickle liquor
2 filters for roaster charge

4. PROCESS DESCRIPTION:
OPERATION MODE:
ARPconsistof 4 modes
 No mode
 Freshwatermode
 Rinse watermode
 Waste water mode
START UP PROCEDURE:
The veryfirstthingwe have to do is to checkof leakage.Aftersatisfaction,we shall startthe suction
pumpwhichislocatedbelowthe roaster;the objective of startingthisfanistosuck all the unwanted
gaseswhichare presentinroaster,thenthe rotarypumpof lumpbreakeristurnon followedbythe
turningon of rotary pumpof venturi whichisinterlockedwiththe previouspump.
Thenopenthe industrial waterpump thenopenpreconcentratorpumpthenturnonthe circulationof
absorber,thiscause the removal of interlockonexhaustfan,simplyturniton thenstart the circulation
of scrubber. Adjustthe gasflowrate to the burners.Butonly1 burnershouldbe onbecause thisisthe
freshmode.
Aftersome hoursthe plantwouldbe tune to rinse watermode inwhich2nd
burnerwill alsobe started
and rinse waterpumpison withturningoff of ind.Waterpump.As soonthe temperature,inside the
roaster,reachedat 600oC, andthe topof the roasterreached400oC, insert1st
nozzle andstart spraying
the water.By doingthisthe temperature of the topside decreasedtocertainvalue butwill soonstart
increasing.Whentemperature of topof the roasterreacheditsset value again, insertanothernozzle
and run the plantfor several hoursonrinse mode.
Whenthe plantis switchedtowaste acidmode,we justhave to switchthe inletof separatorfromrinse
to waste acidline bysimplyopeningandclosingof waste acidand rinse waterpumprespectively.
WHAT IS ACTUALLY HAPPENING IN ARP??
In thisprocessthe spentacidis sprayatomizedintoadirectlyfiredfurnace and(bycontactwithoxygen)
and splittedintoFe2O3powder(solidphase)andHCl (gasphase).Reactiontemperaturesare inarange
of 400 to 700 degC. The gaseousHCl is absorbedinwaterto formregeneratedhydrochloricacidof
about17% strengthwhichcan be reusedforpickling.Itiscommonand attractive touse the slightly
acidicrinse waterfromthe picklinglineasabsorptionliquids.
The three basic processstepsof thisprocessare preconcentration,roastingandabsorption.Inthe
preconcentrationphase,the incomingwaste acidundergoesdirectheatandmassexchange withthe

5. hot exhaustgasfromthe roaster furnace.The directheatexchange isaccomplishedinaventuri
evaporatorwhere the waste acidisatomizedandturbulentlyintermixedwiththe roastgasat high
velocities.The waste gasisthuspartiallyevaporated,leavingbehindapreconcentrated waste acidtobe
usedas liquidfeedtothe sprayroastingfurnace. Inventuri 25% by volume of acidisevaporatedanditis
cooledfrom950c TO 400c and itis dedusted.
In the spray furnace,the preconcentratedwasteacidwhichisinjectedfromthe topbymeansof high
pressure atomizingnozzlesundergoesadropby dropevaporationof waterandHCl as well aspyro
hydrolysisreactionof remainingironchloridesandexcessoxygenprovidedbythe burners,whichare
tangentiallyalignedaroundthe furnace circumference inordertoforma specific‘swirl’flow pattern
whichincreasesthe dropletretentiontime byincreasingthe length of itspaththroughthe furnace.The
chemical reactionproductsof the pyrohydrolysisreactionconsistof HCl whichisextractedfromthe top
of the furnace togetherwiththe
steamand combustionproductsand
ferricoxide (Fe2O3) powderwhich
settlesatthe conical bottomof the
furnace ispneumaticallyconveyed
intoa storage bin forsuitable
disposal.The pyrohydrolysis
reactionsare as follows:
12FeCl2+3O2=8FeCl3+2Fe2O3
2FeCl3+3H2O=6HCl+Fe2O3

6. Afterthe streamof gassesescape the topof the
furnace theyallowedtopassthroughthe cyclone
separator.Incyclone separatorit entersatan angle
due to whicha cyclone isformedinit,whichcauses
veryhighvelocityatthe axisof cyclone and very
lowvelocityatthe side wallsof it,due towhichif
some particlesof ironoxide come alongwiththe
gas will move towardsthe wallsof separatorbythe
influenceof centrifugalforce andthusall the
particleswill leave the bottomof cyclone andshall
discharge againinthe roaster.
The dust free hotgas iswhenpassedthroughthe
cyclone itentersthe venturi where heattransfer,
mass transferandevaporationoccurs,whichis
alreadydescribedabove.
Thenthe gas is passedtoabsorber.
In thisabsorber,physical absorptionistakingplace.Thisnon-reactiveabsorptionismade betweenthe
twophasesi.e.the gas phase (fromthe topof separator) andthe liquidphase (dilute acid).Whenthese
twophasescome in contact witheachother,masstransfer
occurs at interphase atthe rate dependinguponthe flow
ratesof bothgas and liquid.Thistype of absorptiondepends
uponthe solubilityof gasin liquid, temperatureand
pressure.Thoughthe pressure isverylow butthiseffectcan
be balancedbyincreasingthe flow rate of liquiduptocertain
limit.
The absorptionalsodependsuponthe contacttime between
liquidingas,inthiscase betweendiluteacid andHCl gas
fumes.Forthiswe are usingstructuredpackinginside the
absorber.
The acid whichcomesfromthe bottomof the absorberis
thencollectedin“regeneratedacidtank”.
Afterabsorptioncolumn,there isanexhaustfanwhichis
responsible forthe suctionof roastedgasby creating

7. negative pressure.Asthe acidicgasis flowingthroughthe fan,we have toshowerwater atfast moving
impellersforsavingitfromcorrosion.
Gas is nowalmostfree of chlorine gas.The restof the chlorine ingasis thenremovedbypassingit
throughthe scrubberin whichall the chlorine isconvertedtoHCl andthe gas leavingthroughthe stack
to the atmosphere have concentrationof chlorineupto0.00%.
OTHER EQUIPMENTS USEDAT ARP
FLAP VALVE:
Designed for use on the discharge end of pipes to prevent backflow or intrusion into the pipe.
Typical applications include discharges to reservoirs, ponding basins and standpipes.
BALL VALVE:
A ball valve is a valve with a spherical disc, the part of the valve which controls the flow through it.
The sphere has a hole, or port, through the middle so that when the port is in line with both ends of
the valve, flow will occur. When the valve is closed, the hole is perpendicular to the ends of the
valve, and flow is blocked. The handle or lever will be in line with the port position letting you "see"
the valve's position. The ball valve, along with the butterfly valve and plug valve, are part of the
family of quarter turn valves.

8. SOLENOID VALVE:
A solenoid valve is
an electromechanically operated valve. The valve is controlled by an electric current through
a solenoid: in the case of a two-port valve the flow is switched on or off; in the case of a three-port
valve, the outflow is switched between the two outlet ports. Multiple solenoid valves can be placed
together on a manifold.
Solenoid valves are the most frequently used control elements
in fluidics. Their tasks are to shut off, release, dose, distribute or
mix fluids. They are found in many application areas. Solenoids
offer fast and safe switching, high reliability, long service life,
good medium compatibility of the materials used, low control
power and compact design.
DIAPHRAGM VALVE:
Diaphragm valves can be manual or automated. Their application is generally as shut-off valves in
process systems within the industrial, food and beverage, pharmaceutical and biotech industries.
The older generation of these valves is not suited for regulating and controlling process flows,
however newer developments in this area have successfully tackled this problem.

9. MATERIAL
OF PIPING AND
VALVES
Valvesare made up of
Niobiumwhich meltingpointis
2477oC, hence it isnot
sensitiveto heat.
Almostall the pipingismade
up of PP(Polypropylene) ratherthanPVC(Polyvinyl chloride),because PP’smeltingpointishigherthan
PVCand itis alsoa neutral polymer.
If it is exposedtofire,itsimplyconvertedintocarbondioxide andwaterwhile PVCshall formoxinsand
HCl gas whichare toxicto environment.
SAFETYANDMAINTAINANCE
GENEREL MAINTAINANACE:
 Cleanregularlyall workingareasexposedtooxide dustatleastevery2 days
 All the designedparameters(temperature,pressure,flow ratesetc.) of eachandevery
equipmentmustbe controlled withspecial care.
 Make sure and ironoxide formedmustbe inthe formof amorphousform, otherwise itwill
cause chockingeffect.
 Safetyshowers,eye rinsebottlesandfirstaidmaterial are tobe providedatappropriate places
inthe plant.
 Noise levelinthe workingareaswill notexceed85dBs.Anyequipmentproducinganoise level
higherthan85dBs (e.g.pumpsandfans) shouldbe installedinasecondprotectedroom.This
room isnot to be consideredinworkingareas.
 Industrial waterlining,whichisusedforcleaningpurposes,shouldbe of PVC(notof mildsteel).
PERSONAL SAFETY:
 Wear personal protectionequipmentnearchemicals.
 Avoidinhalingoxide dust.
 Close inspectioncoversordoorsduringoperation.

10. PSA PLANT
The PSA plantof ISL is producingpure N2and H2 gas and a mixture of them, whichisusedindifferent
processes.
Compressedairisusedasa raw material fornitrogenproductionasitcontains79% of it while ammonia
gas iscracked to produce hydrogengas.
DESIGN & OPERATING DATA
PRODUCTION GAS SPECIFICATION:
NITROGEN GASPLANT:
(a)Capacity: 300 NM3/hr.
(b)Composition…
O2: 5 PPM
H2: 0.5 % (Max.)
N2: Balance
(c)DewPoint: (-) 60ºC
(d)Op.Temperature: Ambient
(e) OutLet Pressure : 5.5 Kg/Cm2g
(Before Booster)
(f) Out LetPressure : 17.0 kg/cm2g (afterBooster)
HIGH PRESSURE AMMONIA CRACKER(1W+1S):
(a)Capacity: 12 NM3/HR
(b) ProductGas Pressure. : 6.0 Kg/cm2g
(c)ProductGas composition: Hydrogen – 75 %
Nitrogen–25 %
HIGH PRESSURE CRACKEDGAS PURIFICATION SYSTEM

11. (a)Capacity: 12 Nm/Hr.
(b)Hydrogen: 75 %
(c)Nitrogen: 25 %
(d) DewPoint : (-) 60 °C
(e) Res.NH3: Nil
(e) Pressure atBatteryLimit: 6.0 Kg/cm2g
LOW PRESSURE AMMONIA CRACKER(1W+1S)
(a)Capacity: 60 NM3/hr.
(b) ProductGas Pressure. : 0.2 Kg/cm2g
(c)ProductGas composition:
Hydrogen – 75 %
Nitrogen– 25 %
LOW PRESSURE CRACKEDGAS PURIFICATION SYSTEM – 2
Nos.
(a)Capacity: 60 Nm/Hr.
(b)Hydrogen: 75 %
(c)Nitrogen: 25 %
(d) DewPoint : (-) 70 °C
(e) Res.NH3: Nil
(e) Pressure atBatteryLimit: 0.2 Kg/cm2g
UTILITIES CONSUMPTION:
i) CoolingWater:(ForNitrogenGasPlant& AmmoniaCracker)
Flow: (16-18) NM3/Hr.
Pressure: 2.5 Kg/cm2
Temperature: 32°C

12. ii) ChilledWater:(ForNitrogenGasPlant)
Flow: (2 – 3) NM3/Hr.
Pressure: 2.5 kg/cm2g
Temperature: (5 – 10) °C
iii) CompressedAir:(ForNitrogenGasPlant)
Flow: 706 CFM
Pressure: (7.0 – 7.5) Kg/Cm2
Temperature: 20°C.
iv) AmmoniaGas(For Each 12 NM3/Hr. AmmoniaCracker):
FlowfromNH3 Tank : 5 Kgs./Hr.
Pressure atinlet(AfterPRV) 6.5 Kg/Cm2
Temperature : Ambient
v) AmmoniaGas(For Each 60 NM3/Hr. AmmoniaCracker):
FlowfromNH3 Tank : 24 Kgs./Hr.
Pressure atinlet(AfterPRV): 0.8 Kg/Cm2
Temperature : Ambient

13. DESCRIPTIONOF PROCESSES
Nitrogen production
AIR RECEIVER:
As itis discussedabove thatnitrogenisseparatedfromair,forthisair is
compressedto7.5 bars whichis receivedbyairreceiver,alsocalledasairbuffer.Asthe compressedair,
movingwithhighvelocitybythe influence of highpressure difference,entersthe receiver,the static
pressure increasesand,itsvelocitydecreases.Hence the excessmoisture condensedtothe bottomof
receiverwhichisremovedbyautodrainedvalve.The compressedairfree fromphysical moisture
particlesmovesupwardandflowstofilters.Itisadvisabletocheckthroughmanual drainvalve,once in
3-4 hoursfor anywater accumulationinthe airreceiver.
Airreceiverisprovidedwithinstrumentslike low
pressure switch,pressure indicator,safetyreliefvalve
and digital temperature indicatorwithsetpoint.
PRE-FILTER:
The compressedairthenentersa pre filterwhich
containssinteredbronze of 10 micronspore size.Inthis
filterlotsof moisture iscondensedbecause of slight
increase instaticpressure anddecrease invelocity.Auto
and manual drainvalve are providedatthe bottomof thisfilter.Autodrainvalve openforafixedtime
periodat regularintervalstodrainthe condensate.
FINE-FILTER:
In thisfilterborosilicate filterelementisusedof 2 microns pore
size.Thisfilterisusedtoremove oil andwaterdropletsfrom
airline.Asmoisture sizerangesfrom2-5micrones,itcaneasilybe
separatedbythisfilter.The condensatesmustbe drainedout
fromthe bottomof the filter.The air,whichpassedthroughfine
filter,isnowalmostfree fromanykindof moisture.Thisairis
thenpassedtothe carbon filter.
ACTIVATED CARBON FILTER AND AFTER FILTER:

14. Thisfilterisfilledwithactivatedcarbonwhichisusedtoremove remainingmoisture (if any) fromthe
compressedairlineandafterthis,the airpassesthroughafterfilterwhichwillremoveanydustparticle
if takenby air fromcarbon filter.
PRESSURE SWING ADSORPTION:
It comprisesof twotowersfilledwith2880L of CMS withbottomof towerfilledwith 1ftlayerof
alumina.Twolayersof ceramicballsare alsomaintainedinthese towerstogive itsome support.The
use of aluminaisprecautionaryasthe airis alreadydried.These towersare the heartof operationas
theyare performingthe mainrole by separatingnitrogenandoxygenfromdryair.
As molecularsize of nitrogenissmallerthanoxygen,whenairispassedfrombottomtotop,all the
nitrogengaspassedthroughCMS while oxygenmoleculesbecome adsorbonthe bed.The inside
temperature of towersis
approximately20-22o
C and
pressure is7.5 bar. The cycle time
isof 1+1 minute,meanswhen
one towerisin productionfor1
minute meanwhilethe another
towerisin regenerationmode
(The directionof gasin
adsorptionanddesorptionis
opposite,obviously).
After1 minute of productionthe
towersare depressurizedto
ambientpressure duringwhich
small amountof nitrogenis
passedfromtop to bottom,thisis
knownas equalizationof
pressure,topurge the adsorbed
oxygenoutwhichisstoredin
silencerthenpassedtoatmosphere.The processiscontinuous,when1st
towerisproducingN2 another
towerisremovingitsO2 and vice versa.
SURGE VESSEL:
Producednitrogenisthenstoredinalarge vessel whichabsorball the
surgesinpressure. Operatingpressureof nitrogensurge vessel is1.0to 1.5
kg/cm2g lowerthanthe maximumoperatingpressure of PSA unit.Pressure
difference withrespecttoPSA unitisto be maintainedbycontrolling
manual valve providedinnitrogenproductline fromPSA unittosurge
vessel.There isapressure re-equalizationlinefromnitrogensurge vessel to

15. PSA unitwithan orifice.Aftereverycycle change over,there isrushof nitrogengasfromsurge vessel to
PSA tower,resultinginfall inpressure by0.2to 0.5 kg/cm2g inthe surge vessel.Fromsurge vessel,raw-
nitrogentothe downstream –DE Oxosystemflow throughflow meteratconstantflow rate andpurity.
Purityof nitrogengas(raw-nitrogen)insurge vesselismaintainedupto99%.
DE-OXO UNIT:
Thisunitis usedtoremove the remaining1% oxygen.Forthisa mixture of hydrogennitrogengasis
introducedinthisvessel.Hydrogenreactwithoxygeninthe presence of palladiumcatalysttoform
water;
O2+2H2 2H2O
Thisis an exothermicreaction.Hence,with1% oxygencontents,the reactiontemperature remainsup
to 220°C (± 10°C). If oxygenpercentage ismore orless,the reactiontemperature will alsoincreaseor
decrease by21°C per0.1 % of oxygen.Double of hydrogenisrequired(byvolume)forremoval of
oxygencontents.Toavoidanyslippage of oxygentrace withoutreaction,hydrogenismaintainedslightly
higher(min.0.5%) or saysup to 2.5 timesof the oxygencontents(intotal).
NITROGEN DRYING UNIT:
Afterde-Oxounit,there isacoolerwhichcoolsdownthe streamcontainingwatervapors,at 200o
C, due
to cooling,the vaporscondensedandthenseparatedbymoistureseparator.
N2 gas leavingthe moisture separatorisalsosaturatedwith watervaporsshall enterthe 1st
NDU tower,
where itiscooledfor3 hours(on 1st
time usingNDU Plant).Atlow temperature adsorptionincreases
and all the moisture isadsorbedin4A sieves
while N2gas passthroughthe sievesand
drainout as product.These towersare
operatingat5.5 bar pressure.
The nextstreamof N2 whichpassesthrough
DE-Oxounitfollowthe same stepsuntil it
leavesthe moisture separation.Thisgasis
alsofull of H2O whichisabsorbedinN2
gas(leavingbehindexcessH2Oin moisture
separator).Nowthisgaswill alsoenterthe
towerwhichispreviouslyusedbutthistime
we don’tcool thisgas because the bedis
alreadyfull of moisture.Toremove this
moisture frombedsorto make the bed dry,
we must heatitfor 5 hours.Due to heating
the moisture capturingcapacityof N2 gas
increasesandalsothe hightemperature

16. increase the rate of desorptionof bed.Hence all the moistureconvertsintovaporsandabsorbinheated
N2 gas whichalreadycontainsome moisture.
Nowthisbedis completelydriedout,capable of adsorbingmore moisture.The heatedgasisthen
passedto coolers.Because of cooling,the watervaporswhichittakesfromthe towerscondensedout
and separatedbymoisture separator.Now the gascontainsthe same amountof moisture aswhenit
comesout from1st
moisture separator.Thisgasthenpassedtothe nextNDU towerwhichisnot yet
used(hence dry).Here gasiscool downfor3 hourscausingall the moisture toadsorbinbedand dry N2
iscollectedasproduct.
The third batchof N2 gas, afterpassingthroughmoisture separator,willenterthe 2nd
towerwhere itis
onlyusedforthe dryingof that towerandthenafterremovingall the moisture of 2nd
tower,itenters
the 1st
tower,whichisdriedoutbypreviousbatch.Here thisgas iscool downto dryN2 gas.The process
continuesanddrynitrogen,
whichcontains0.00% O2, is
collectedindistributiontank.
AMMONIA CRACKER:
The ISL PSA plantcontains9
crackers,4 of whichare being
usedto crack ammoniafor de-
Oxounit.
Ammoniagasafterpassing
throughfinsheatexchangerand
pressure reduce valvesis
maintainedat6bar pressure
and entersthe crackerfrom top.
In thisplant2 crackersare
operatingatlowpressure upto
0.5-0.8 bar but these crackersare onlyusedforHNx section.Before enteringthe crackeritpassthrough
anotherheatexchangerwhose taskisjustto pre heatthe gas andto cool downthe productgas. This
wouldsave the electrical energybyreducingthe time of heating.
The cracker containsretort tubesinwhichnickel catalystisusedtobreakthe bondsof ammoniaat880-
900o
C and convertingitintoa mixture of 75%H2+25%N2.

17. Duringcommissioning,initial 24-48hrs. periodiscalled“catalystconversionperiod”.Nickelcatalystis
available inthe formof nickel oxideandgetsconverttonickel duringinitialcommissioning/trial runof
the system.Reactiontakesplace asunder: -
NH3-75% H2 + 25% N2 (CrackedGas)
(Crackedgas) N2+ H2+ NiO Ni + H2O+N2
Afterall the catalystconvertsto nickel,the crackercan be usedfor production.
The product streamcontainsN2+H2+H2O(v).Vapors can be removedbydryingthisstreamin
CDU(crackedgas dryingunit).
CDU:
Thisunitalso
comprisesof 2
towersfilled
withA4 sieves
(A4 sievesare
usedto
separate
moisture).
Pressure of
towersis
maintainedat
6 bars.Before
the gas enters
the towersit
passes
throughfilter
whichshall remove all the dustparticlesfromit. Thenthe gaspassedtotwintowers.The operatingcycle
time of 24 + 24 hrs. Bothtowersare filledwithmolecularsievestoadsorbuncrackedammoniacontents
and dulyfittedwithindividual regenerationheaters.One
towerremainsunderdrying/purifyingoperationfor24 hrs.
Andsubsequentlyothertowerremainsunderregeneration
processfor the same period.After24 hrs.Change overtake
place throughautomaticchange overvalve withPLC.
Duringproductioncycle,the gaspassedthroughthe tower
frombottomto top causingall the uncrackedgas and
moisture toadsorbin the bedleavingasdrygas of nitrogen

18. hydrogenmixture.While duringregenerationprocess,thisbedisheated
upto150o
C witha small purgingof gas.This will desorbhe bedandall
the uncrackedgas and moisture shall be removedleavingbehindadry
towerwhichisthenreadyfor doingmore moisture separation.The dry
gas isthentransferredtode-Oxounit.
DISTRIBUTION VESSEL:
The capacity of thisvessel is10 m3
, providedwithinstruments like as
highpressure switch,pressure indicatorandsafetyvalve.Inthisvessel
N2 gas istemporallystoredthenthisgasistransferredtofollowingunits;
Mixingvessel
Suction pot
Instrumentair purging
SUCTION POT:
From here,dryN2 gas ispumped tostorage tanks.For thisoperation;two
positive displacementsimplexpumpsare used,one isinworkingcondition
while otherisof standby,whichincreasesthe pressure of gasupto17-18
bar. At thispressure,temperature of gasalsoincreaseswhichis reduced
by passingthe streamthroughcoolerandthentransferredtostorage
tanks.
MIXING VELLEL:
Pure N2 gas fromdistributionvesselandN2+H2 (25:75) fromlow
pressure CDU,whichis especiallyusedforproducingthismixture
for HNx,mix with eachotherina definite proportiontomaintain
the % of H2 at outletbe 25% and N2 be 75%. This HNx gas is

19. suppliedtoGP(galvanizingplant) whereitisusedtocontrol the amount of oxidesonthe sheet.
INSTRUMENT AIR PURGING:
At manyplaceswithinthe industrynitrogengasisusedforoperatingdifferentinstrumentsforexample
valves,pressure switches,pneumaticinstrumentsetc.thisnitrogengasisusedatthese places.
HYDROGEN PSA:
Its operationisexactlysame asnitrogenPSA onlythe difference isthe size of sieves.InnitrogenPSA
those sievesare usedwhichcanonlypassthe
moleculesof nitrogenthroughitandstopall the
large particles(whichare greaterthannitrogen).
Here such sievesare usedwhichsize issmallerthan
4A sievesso the pore size isalsoverysmall andonly
hydrogencanpass throughit while nitrogengasand
otherimpuritiesshalladsorbinthe bed.
The stream of gas from hydrogenCDUcontains75%
H2 and 25%N2, whenpassesthroughhydrogenPSA
unit,convertsinto100% hydrogengas.Fromthere
it passestotanks byboosterpumps.
The inside temperatureof PSA is150o
C and cycle
time is3+3 minutes.
SAFETY AND PRECAUTIONS:
 Properventilationsystemshouldbe providedatthisplantasammoniagas isused.
 CORROSIVE,COMPRESSEDGAS.May alsobe an EXPLOSION HAZARD,especiallyinconfined
spaces.Engineeringcontrols,propertraining,protective equipmentrequirementsandpersonal
hygiene measuresare essential.
 Neverworkalone onthisplant
 Use filtermasks,gloves,jacketwhenhandlingammonia.
 At hightemperature hydrogengasisflammable,hence “hydrogengasfire”extinguishersmust
be keptnear crackers.