THE BASICS OF FOUL CONDENSATE

STRIPPING

Tom Burgess PEngSenior ManagerEnvironmental TechnologyGeorgiaPack Corporation133 Peachtree St NE

Atlanta Georgia 30303

This paper will cover the condensates thatare collected various stripping methodstypes of stripping columns basic theoryoperating problems the latest operatingprocedures and disposal of the stripper offgas SOG which contains the pollutantsremoved

ABSTRACT

Foul condensates from the digesters andevaporators contain reduced sulfur gas andorganic compounds such as methanolMeOH and turpentine which contributegreatly to pulp mill water pollution in the formof Biochemical Oxygen Demand BOD andtoxicity and air pollution in the form ofVolatile Organic Compounds VOC andodor

For this reason foul condensates are

collected and treated by stripping usingeither air or steam to remove the pollutantsIn many cases the pollutants can beeconomically used as a fossil fuel substitute

INTRODUCTION

The Cluster Rules resulting from the CleanAir Act Amendments CAAA of 1990 willrequire the collection and treatment of Kraftprocess condensates better know as foulcondensates or combined condensates

Steam stripping is one of the treatmentsaccepted by the Environmental ProtectionAgency EPA The others are hard piping tobiological treatment reusing the condensatesin a process where the vents are collectedand incinerated or any other process thatcan meet the required removal efficiencies

TABLE

Typical Pollutant Loads in Foul CondensatesBleached Kraft Mill

Based on Unbleached Digester Production

Source Total Flow

kgtonne lbton

McOH

kgt Ibt

Turpentine

kgtt Ibtt kgt

TRS

Ibt

Batch Digester Mill Softwood

Digester accumulator overflow 1125 2250 40 80 050 10 020 040

Turpentine decanter underfiow 250 500 15 30 050 10 015 030

Total Evaporator Condensate 7000 14000 42 84 025 05 100 200

Continuous Digester Mill Softwood

Turpentine decanter underflow 450 900 25 50 050 10 012 024

TotalEvaporator Condensate 8000 16000 75 150 050 10 120 240

41 1

Although the rules allow various methods ofdetermining removal efficiencies bleachedmills will have to collect selected

condensates and treat them to destroy 102pounds of methanol MeOH per oven dry tonof pulp ODTP 51 kilograms per oven drymegagram of pulp Unbleached mills willhave to destroy 66 pounds per ODTP 33kgMg

Most mills built or upgraded since 1980 havehad a condensate stripping system installedas an integral part of the overall mill processMany older mills have now added a foulcondensate stripper to meet the new EPACluster Rule

WHY STRIP FOUL CONDENSATES

The prime reason for stripping foulcondensates is pollution control Foul

condensates can contain 14 to 20 lb 7 to 10kg of BOD 2 to 4 lb 1 to 2 kg of turpentineand 2 t0 4 lb 1 to 2 kg of TRS per tontonne of pulp Table 1 If these foul

condensates are untreated they cannot bereused in the mill and are therefore sewered

putting a high load of BOD and toxicity intothe secondary treatment system and

frequently causing air pollution problems asthe TRS and McOH is released to the

atmosphere by flashing off from opensewers By collecting these foul condensatesand stripping them most of the pollutants canbe removed and burned reducing thepollution load to the air and to the secondarytreatment system

In most cases the stripped condensates canbe reused in the mill for such purposes asbrown stock washing and makeup water inthe recaust area Thus stripping also hasthe potential to reduce the total mill waterdemand Stripping will also be an integralpart of the effluent free mill of the future

Fortunately the stripped compounds areeasily burned Heat of combustion values forstripper overheads in the order of 120000Kcaltonne 475000 BTUTon pulp havebeen reported Table II These stripperoverheads can be transported as a gas orcondensed and transported as a liquid andused to replace fossil fuel in lime kilns boilersand incinerators In most cases the net heat

released by burning these pollutants isgreater than the heat energy required tooperate the stripper and can be used to helpeconomically justify installing the strippingsystem

TABLE II

Heat Value of Pollutants

Pollutant Net Heat of Combustion

kgcalkg BTULB

McOH 5037 9066

Alpha Pinene 9547 17200

H 3647 6565

CH 6229 11212

CH 7371 13268

CH 5638 10148

41 2

WHAT CONDENSATES ARE STRIPPED

The Cluster Rule requires collection andtreatment of the condensates from the

digester system the turpentine recoverysystem the evaporator systems the HVLCdilute NCG collection system and theLVHC concentrated NCG system

Batch Digester Blow Steam Condensate

The condensates from condensed blowsteam are rich in methanol and TRS In

order for these pollutants to be collectedhowever the blow steam system mustfunction correctly If the blow steam systemis undersized or operated incorrectly muchblow steam is vented with much of themethanol and TRS vented as well In some

mills fresh water is added to the accumulatorto keep the bottom temperature low Thisdilution of the blow steam condensate makescollection of these condensates undesirable

In a modem blow steam condensing systemthe direct contact primary condenser isfollowed by an indirect secondaryttertiarycondenser It has been found that up to 80of the pollutants can be segregated into the10 15 of condensed blow steam thatcomes from the secondaryttertiarycondenser This concentration of the

pollutants in a smaller flow greatly improvesthe efficiency and economics of stripping

The Cluster Rule will allow the treatment of

only the segregated stream provided that atleast 65 of the methanol in all the blowsteam condensates is contained in the

segregated stream

Batch Digester Relief Steam

During the cook noncondensible gasesNCG are vented from the digester TheNCG contains considerable amounts of

steam McOH and frequentlyturpentine This steam must be condensed in

order to collect the NCG The condensates

so formed must be collected and treated As

above this condensation can be done in two

stages and only the rich or segregatedstream collected and treated providing atleast 65 of the methanol in the relief gas isin the segregated stream

Continuous Digester Flash Steam

During the cook hot pressurized liquor isremoved from the digester and flashed toatmospheric pressure The flash steam

contains considerable amounts of NCG

McOH and frequently turpentine This

steam must be condensed in order to collect

the NCG The condensates so formed must

be collected and treated As above thiscondensation can be done in two stages andonly the rich or segregated stream collectedand treated providing at least 65 of themethanol in the flash steam is in the

segregated stream

Turpentine Decanter Underflow

In softwood mills batch digester relief steamcondensates and continuous digester flashsteam condensates go to a turpentinerecovery system The underflow from theturpentine decanter is a relatively low flowthat is rich in methanol turpentine and TRSmaking this foul condensate a primecandidate for stripping

Evaporator Condensates

The combined foul condensates from the

multiple effect evaporators contain methanolturpentine and TRS removed from blackliquor during evaporation The evaporatorsin effect act as strippers to remove thesepollutants from the black liquor

It has been found that most of the pollutants80 will collect in the condensates of the

effects and condensers following the effectswhere the weak black liquor is fed For

41 3

example if weak black liquor is fed to effects5 and 6 of a six effect evaporator the

pollutants will be found in the condensatesfrom the 6th effect and the surfacecondenser The Cluster Rule will allow

splitting out such condensates for treatmentthus reducing the amount of evaporatorcondensate to be treated by about two thirds

In modem multiple effect evaporatorsespecially those of the falling film design thathave been supplied since 1980 the majorityof the pollutants can be collected in 15 orless of the total condensate This is primarilydone by using twostage condensing withinternal condensate segregation This asmentioned above greatly reduces thecondensate to be treated and thus improvesthe efficiency and economics of stripping

In general there will be four condensatestreams generated in a modem falling filmevaporator The first is clean steamcondensate from the first effect The second

is combined condensates from the middle

effects and these will have methanol in the100 ppm range The third stream is

contaminated condensates from the lean

steam of segregated condensates from thefeed effects and these will have methanol

concentrations in the range of 1000 ppmThe final stream is foul condensates from the

rich stream of segregated condensates andthe methanol will be in the 5000 ppm range

The Cluster Rule will allow segregation ofcondensates providing that 65 or more ofthe methanol in all the evaporatorcondensates is in the segregated stream

NCG System Condensates

The condensates formed in NCG systemsalthough small in volume are veryconcentrated in methanol and TRS

compounds and contribute to odors in themill area if drained into open sewers TheCluster Rules may require collection andtreatment of these condensates

41 4

METHODS OF STRIPPING

There are two methods of stripping used inKraft pulp mills today One uses air and theother uses steam Both of these methods

can be further subdivided into two types ofstrippers stripping for TRS only and strippingfor methanol BOD TRS is easily strippedwhereas McOH is more difficult

consequently making the latter systemsbigger and more complex Further the newCluster Rules will not accept air stripping orstripping for TRS only

Air Stripping for TRS

This is the most basic form of stripping and isgenerally used to remove TRS fromcondensates so that they do not create odorproblems in the secondary treatment systemFigure 1 In this case the foul condensatesare stripped by air moving countercurrently ina stripper column About 3 5 weight of

air on condensate is required Higher airratios may be necessary if the TRSconcentration is high in order that thestripped gases are well below the LowerExplosive Limit LEL in the overheads Thetwo factors which have the greatest effect onair stripper efficiency are temperature and pHFigure 2 A pH of seven or less and acondensate temperature of 50C 120F ormore are required for good strippingefficiency Disposal of the high volume ofwarm moist overheads is the majordisadvantage of this system

F1i9T7irl

PUMP COLUMNFAN

FIGUREI AIR TRIPPER POR TRS

130F

13

J

i

0sW

COMOENSATE PN

FIGURE2 AIR STRIPPER ERIGERCT

Disposal is usually done by burning in aboiler kiln or incinerator The majoradvantages of this system are its simplicityand low cost

Air Stripping for BOD

This system is similar to air stripping for TRSexcept that much higher quantities of air arerequired in the range of 16 20 weight airon condensate Temperature is also veryimportant and temperatures in excess of70C 160 are required for good efficiencyThis form of stripping is not practical and is

not practiced

Steam Stripping for TRS

This system is similar to the air stripperexcept that two heat exchangers are addedto the system Figure 3 It is necessary topreheat the foul condensate before strippingotherwise the stripping steam would becondensed by the cold condensate Thispreheating is done by heat exchanging withthe hot stripped condensate The secondheat exchanger is used to condense thesteam out of the stripped TRS gas before it isincinerated The condensate is returned to

41 5

T

CLEAN

NEAT

ECNANOER

FOUL

P

FIGURE3 STEAM STRIPPER FOR TRS

the top of the stripping column About 3 5weight of steam is required oncondensate

Asp with air stripping efficiency is pHdependent Despite the disadvantage ofhigher capital and operating cost disposal ofthe overheads is much simpler Operatingcosts can be reduced if some use can bemade of the hot water generated in theoverhead condenser

Steam Stripping for BOD

This system is similar to the steam stripperfor TRS except that the overhead condenserbecomes a reflux condenser and the top ofthe column becomes a distillation column toconcentrate the methanol Figure 4 Thesteam requirement increases to 15 20

weight steam on condensate Figure 5

These systems have the advantage of highefficiency producing an overhead that isusable as a fuel The major disadvantagesare high capital and operating costs Theoperating costs can be reduced if some useof the heat from the reflux condenser can befound such as preheating boiler feed wateror making clean hot water for a bleach plant

The reflux tank shown in Figure 4 is optionaland many systems do not have themInstead the reflux condenser is positionedabove the column and reflux flows by gravityback to the column

We have examples of this type of strippingsystem at our mills in Palatka FL andBrunswick GA

REIwX

DISTILLATION

SECTION

TO

NEAT

EXCHANGER

STRIPPINGSECTION

FIGURE4 STEAM STRIPPER FOR S

100

GO

Go

AD

at

20

0 O S 10 a 20 20

Grur oDNOFraAn

FI oaTLLATmN EFFMIENCT

TYPES OF COLUMNS

In general two types of columns are used forstripping packed columns and valve traycolumns

Packed columns are generally cheaperespecially for small diameter columnsPacking material is either stainless steel pallrings or corrosion resistant plastic saddlesThe disadvantages of packed columns arepoor turndown ratio and plugging of thepacking by fibers carried in the condensate

Valve tray columns are an advanced form ofa bubble cap tray column They have theadvantages of maintaining high efficiencyover a wide operating range a constantpressure drop at varying vapor load ratesand selfcleaning of the trays These

advantages normally offset the higher capitalcost of the valve tray column

As a general rule packed columns are usedfor TRS strippers and very small BOOstrippers while valve tray columns are usedfor large BOD strippers The valve traycolumn has become the standard under the

Cluster Rule

INTEGRATED COLUMNS

In order to reduce the capital and operatingcosts of steam type BOD strippers they arenormally integrated into a set of multipleeffect evaporators There are two basic

ways to do this

Fully Integrated Figure 6

The stripping column is placed between twoeffects usually the 1 and 2 Steam fromthe 1 effect is run through the stripper andthen condensed in the 2 effect The 2

effect is the reflux condenser saving thiscapital cost The stripping steam isessentially free

41 6

To INCRYT1d

I1TUllTo 107JTCT

tn a

sear

ur

tcnAmn

MI ttCT nfI VRCT

COWM AM RIOT M X TAM

100

21golg YLLT toTnTO COLOM

it 11 PTtaux twas res COYIM

41 7

However there is an efficiency loss of about12 in the evaporators when the column isfully integrated In a system of this type forevery Kcal or BTU lost by integration two ormore Kcals or BTUs are returned by the heatvalue from burning the stripped BOD Thistype of full integration with respect to theevaporators can be used when a stripper isintegrated into an existing mill andwhere condensate flows are high comparedto the relative size of the evaporators

Partially Integrated Figure 7

In the case of a new mill with reduced foul

condensate flows and where the stripper ispart of the initial evaporator design onlypartial integration is required In this case

only part of the evaporator steam flow is usedfor stripping and the overheads arecondensed in either an external preheater orin a dedicated internal section of a

subsequent evaporator effect Such systemshave a much better energy return than fullyintegrated systems We have an example ofthis type of stripper at our mill in Leaf RiverMS

COLUMN OPERATION

Stripping columns are generally easy tooperate although control schemes forstrippers integrated into evaporators can becomplex due to their interdependence onevaporator operation Some problems incolumn operation are as follows

Foaming

Liquor in the foul condensate can cause thecondensate to foam when air or steam is

blown through it This results in a floodedcolumn where the condensate is carried out

the top of the column and steam orair flow isstopped This problem is handled bymeasuring the conductivity of the foulcondensate A high conductivity indicatesthe presence of liquor and the condensatecan be dumped before it gets to the column

41 8

This problem will show up as loss of steamflow to the stripper or high level in the refluxtank

At worst the foam will carry through thestripper off gas SOG system and into theincineration point where it may extinguishthe flame or cause other damage

Unstable Operation

In steam strippers where steam use iscontrolled and based on condensate flow

every change in flow upsets the system forseveral minutes In a continuous changesituation such as if the condensate feed flowis based on level control of a foul condensate

storage tank the system remains unstableTherefore flow changes should be made ona stepwise basis and made as seldom aspossible In the case of an integratedcolumn the evaporators used should be runas smoothly as possible If a mill has morethan one set of evaporators the set with thestripper should carry a constant base loadwhile the other set takes up the productionrate changes Unstable operation can alsocause problems if the stripper gas is burnedin a kiln or an incinerator Rapid changes inMcOH load can upset the heat balance in thekiln or incinerator

Unstable operation will result in low strippingefficiency

Steam Collapse

Once the column is started up it is full ofsteam If enough cold condensate enters thecolumn it will condense the steam where itenters the column causing an almostinstantaneous high vacuum in the top of thecolumn The hot condensate in the bottom of

the column will boil rapidly almost explodingThis sudden upward rush will buckle trayspop them out of their hold down clips orcarry packing out of the column Such asituation can happen on a startup when

1

there is insufficient hot condensate in the

bottom of the column to preheat the foulcondensate Great care must be taken to

avoid such situations Startups should bedone very slowly

Loss of trays results in loss of strippingefficiency

Control of Contaminant Removal

Condensing in the reflux condenser must becontrolled to maximise contaminant removal

while minimising steam loss At this point inthe process the system is a very complextwophase multicomponent system mainlymade up of water methanol reduced sulfurgases and turpentine but with several othercompounds such as ethanol and acetone inlesser quantities Good control depends on acombination of pressure and temperaturecontrol in the reflux condenser See

REFLUX CONTROL below

Fiber

The foul condensates tend to contain pulpfibers and these fibers can plug packedcolumns and heat exchangers especiallyplatetype heat exchangers Fortunatelyvalve tray columns are selfcleaning Thehandling of fiber can be done in two waysThe first is to install a good fiber filter beforethe heat exchanger The second is to designthe system to pass the fiber through usingvalve trays and heat exchangers with widegaps or large diameter tubes

This problem normally shows up as loss offlow through the heat exchangers especiallyplate type heat exchangers

Plugging of Heat Exchangers

Several mills have experienced a scale buildup on the stripped condensate side of theheat exchanger The reason for this is stillnot clear and the scale is very difficult to

41 9

remove For this reason the strippedcondensate should go through the tube sideof the heat exchanger to facilitate

mechanical cleaning Attempts to chemicallyremove the scale have been tried but with

mixed success Chemical cleaning shouldbe done before the tubes get too badlyscaled

This problem usually shows up as loss offlow of the stripper bottoms or high level inthe bottom of the stripper

Turpentine in Storage Tank

As there is turpentine in the condensatesthere is a tendency for the turpentine todecant in the storage tank and collect on topof the condensates If this happens and thestorage tank is pulled down lt is possible tosend a slug of turpentine to the stripper Theturpentine will easily strip and the turpentinewill go through the SOG system and causeproblems at the incineration point usually ahigh temperature trip

There are several means to avoid the

turpentine build up in the storage tank Thefirst is to send the turpentine decanterunderflow which can be rich in turpentinedirectly to the suction of the stripper feedpump The second method is to make surethere is agitation in the tank to prevent theturpentine decanting This can be done bymaking the incoming condensate linestangential recirculating feed condensateback to the tank or by adding an internalagitator

Skimming the turpentine can also be doneThis can either be done periodicallyreturning the turpentine to the turpentinerecovery system or by continuouslyskimming the turpentine into the stripper feedcondensate

REFLUX CONTROL

As mentioned above good control of thereflux cycle is required to operate the stripperefficiently both with respect to contaminantremoval and heat recovery

For any given operating pressure and anydesired stripper off gas SOG concentrationthere is fixed equilibrium temperature

Operating at the proper equilibriumtemperature and pressure is necessary inorder to control the overhead compositionFurther operating at the proper equilibriumconditions will ensure removal of the

turpenes and red oils with the SOG wherethey can be burned If the reflux condensateis allowed to sub cool the red oils will

separate out and build up in the reflux cycleuntil they give control problems

The concentration of methanol in the SOG is

a compromise between stripping efficiencyand heat recovery At higher methanolconcentrations heat recovery improves butstripping efficiency declines At lowermethanol concentrations stripping efficiencyimproves but heat recovery declines The

generally accepted optimum methanol

concentration in the overheads is 50 byweight

In a non integrated stripper it is possible tocontrol both the pressure and the

temperature Two methods of doing this areshown in Figures 8A and 8B With an

integrated stripper the evaporator operationwill fix the stripping temperature Thus it isnecessary to control the operating pressurebased on this temperature

Temperature control is done by controllingthe cooling water flow to the refluxcondenser Pressure control is done bycontrolling the back pressure on the SOGline

In the scheme shown in Figure 8A thetemperature of the reflux condensate is

41 10

measured rather than the gas which givesfaster response to temperature changesThis assumes that the condensate is not sub

cooled and is at the equilibrium temperatureThe condenser is mounted horizontally inorder to minimize sub cooling of thecondensate This scheme works well at

design conditions but sub cooling tends tooccur at reduced operating rates

In the scheme shown in figure 8B gastemperature is measured directly Vaporfrom the reflux condenser is bubbled throughthe condensate in the reflux tank which

ensures that liquid and gas phases are inequilibrium This gives better control but at acapital cost penalty

TRANSPORT AND DISPOSAL OF

CONTAMINANTS

Once the contaminants have been strippedout of the condensate and removed from the

system they must be disposed of The mostcommon way to do this is to carry them ingaseous form and bum them directly in a kilnboiler or separate incinerator The system fortransport is almost identical to a concentratedor low volume high concentration LVHCnoncondensible gas NCG system See

Figure 9

The major difference with a concentratedNCG system is that the stripper gas systemrequires makeup steam to ensure purging ofthe entire system on startup and to ensure aminimum velocity in the entire line at alltimes This is done by measuring the linevelocity near the incineration point andadding makeup steam as necessary nearthe pressure control valve at the stripperThe stripper gas system should be operatingwith SOG going to incineration before anyfoul condensate is sent to the stripper

The advantages of burning stripperoverheads are low cost simple operationand recovery of the high fuel value of thecontaminants

TO INCINERATION

P

CONDENSER

TFPEFLUX COOLING WATER

STRIPPER FIGURE 8A REFLUX CONTROL

41 11

VENT

PRESSURECONTROL

SEPARATOR TOWCWERATION

FLOWCONTROL FLAMEARRESTER

REFLUXCONDENSER

MAKEUPSTEAM

Figure 9 Stripper Off Gas system

The major disadvantage is that if this streamis ever vented it will create a severe odorproblem in the local area very quickly

It is also possible to collect the contaminantsas a liquid by use of an extra condenser Thisallows for storage of the contaminants

as a liquid which can be used for fuel or befurther refined for recovery of the chemicals

In the past the liquid McOH so collected fellunder Resource Conservation and RecoveryAct RCRA rules classifying it as ahazardous waste making this form ofcollection virtually illegal The Cluster Rule

reclassifies this liquid methanol as a cleanfuel and thus allow it to be collected and

stored as a liquid

In most cases the SOG will be furtherrectified to increase the methanol

concentration to 85 to 90 by weight

PROPER OPERATING PROCEDURES

The following procedures have been recentlydeveloped to reduce the possibility of steam

collapse and to eliminate venting of SOGduring startup and shutdown

The stripper should be started up with steamOnce the stripper is fully heated and all airpurged out of the system by cracking openthe back pressure control valve feeding ofcondensate can begin At a minimum steamflow of about 20 of design start with acondensate flow of about 10 of designAfter five minutes increase condensate flowto 20 of design Continue to increase bothcondensate and steam flow in 10

increments every five minutes until the fulloperating rate is achieved

The slow startup will prevent damage to thetrays due to steam collapse as well as givethe incineration point time to adjust to thechanging fuel load from the methanol in theSOG

As mentioned before any changes inoperating rate should be made in smallincrements maximum 10 and as seldom

as possible

For planned shutdowns condensate andsteam flow should be reduced slowly until20 of design is reached At this point stop

41 12

the condensate flow but leave the steamflow on

The SOG should continue to be sent to

incineration until the back pressure controlvalve goes closed At this point steam flow tothe stripper can be stopped and the SOGsystem which now contains no pollutantscan be shut down

In the emergency shutdown situation suchas when the fire goes out at the kiln orincinerator it is necessary to vent the gasescoming off the column To virtually eliminatethis venting condensate flow to the columnshould be stopped immediately and at thesame time the pressure control valve at thecolumn should be closed However steam

flow should remain unchanged This willkeep the system in thermal balance which isespecially important if integrated into theevaporator It will also speed up the restart ofthe system As before on the restart thecondensate flow must be brought on slowly

CONCLUSION

The Cluster Rule requires collection andtreatment of foul condensates to reduce Kraft

Pulp Mill pollution The stripping of foulcondensates is a good inplant method ofdoing this BOD toxicity and odor can bereduced by stripping In most cases thepollutants can be converted to a usable fuelgiving an economic return on investment

BIBLIOGRAPHY

Burgess T L and Voigt D Nekoosa CleansCondensates with Steam Distillation Pulpand Paper Canada 79 8 T268270 Aug1978

41 13

THE BASICS OF FOUL

CONDENSATE STRIPPING

TOM BURGESS

SENIOR MANAGER

ENVIRONMENTAL TECHNOLOGY

GEORGIA PACIFIC CORPORATION

ATLANTA GEORGIA

Most Kraft Mills Have

Foul Condensate Strippersin order to reduce

Hazardous Air Pollutants

under the Cluster Rule

4114

INPLANT POLLUTION

CONTROL FOR

BOD

14 to 20 1bton

7 to 10 kgltonne

INPLANT POLLUTION

CONTROL FOR

TOXICITY

Turpenes and Red Oils

2 to 4 1bton

1 to 2 kgltonne

4115

INPLANT POLLUTION

CONTROL FOR

ODOR

TRS

2 to 4 lbton

1 to 2 kgtonne

OTHER BENEFITS

REDUCED MILL WATER USE

REDUCED FOSSIL FUEL USE

4116

FOUL CONDENSATES FORSTRIPPING

CONDENSED BLOW STEAM

CONDENSED RELIEF STEAM

TURPENTINE UNDERFLOW

EVAPORATOR COMBINEDCONDENSATES

NCG SYSTEM CONDENSATES

BASIC STRIPPER

o

OFEED HEAT STRIPPER REFLUX

TANK EXCHANGER COLUMN CONDENSER

4117

BASIC STRIPPERSTRIPPER COLUMN

FOR 1000 TPD MILL 300 gpm 11501m

Column 6 ft2m diameter

Column 60 ft 18m high

Operates at 10 psig 170 kPa

Uses 20 valve trays

5 trays in top sectionSTRIPPER 15 trays in bottom sectionCOLUMN

300 series Stainless Steel

4118

BASIC STRIPPER

HEAT EXCHANGER

Standard is Shell and Tube with 300Series Stainless Steel tubes

Clean condensate on tube side foulon the shell side

Spirals may be better

Plate type plug quickly unlessdesigned for white water serviceMust heat condensate to within 20F10C of column temperature

41 19

BASIC STRIPPERFEED TANK

THE BIGGER THE BETTER

30 MINUTE RETENTION TIMEMINIMUM

SEVERAL HOURS BETTER

300 SERIES STAINLESS STEEL

MUST BE VENTED TOCONCENTRATED NCG

BASIC STRIPPERREFLUX CONDENSER

SHELL AND TUBE HEAT EXCHANGER

ALL 300 SERIES STAINLESS STEEL

MOUNTED HORIZONTALLY ORVERTICALLY

COOLANT THROUGH TUBES

USES WATER OR WEAK BLACKLIQUOR FOR COOLING

4120

BASIC STRIPPER

ffG

O

TOBURN

PROCESS

STEAM

FEED HEAT STRIPPER REFLUX

TANK EXCHANGER COLUMN CONDENSER

STEAM REQUIREMENT

Normally use steam ratio of 02pounds of steam per pound ofcondensate

For 300 gpm 1150 Im this is30000 lbhr13600 kghr steam

Require effective steam ratioof016 to 018 to get good efficiency

4121

STEAM REQUIREMENT

Some steam is condensed to

bring the incoming condensateup to the column operatingtemperature

What is left is the

EFFECTIVE STEAM

EFFECTIVE STEAM

20

16

12

08

04

0

0 20 40 60 80 100

TEMPERATURE DIFFERENCE F

4122

STRIPPER EFFICIENCY

Q 10o2 soW

60

2

iW

05 10 15 20

STEAM CONDENSATE RATIO

EFFECTIVE

COMPLIANCE MONITORING

We must show that the stripper is

operating with enough effective steamto ensure adequate methanol removal

For each stripper develop a curve fordesired efficiency at various steamratios and delta T

Operate below the curve

4123

COMPLIANCE MONITORING

70

60

50

OT 30 OPERATEOW THE

20 URVE

10

0

1 26

STEAM CONDENSATE RATIO

COMPLIANCE

MONITORING

70

so

50

OT 4030

20 J10

0

14 16 18 20 22 24 26

STEAM CONDENSATE RATIO

4124

INTEGRATED COLUMNS

AdvantagesLower Capital CostLower Operating Cos

Disadvantages

Loss of EvaporatorEfficiency

INTEGRATED COLUMNS

For every K Cal lost dueto integration two or moreK Cal are returned as

usable fuel

4125

FULLY INTEGRATED COLUMN

1 2

SOG

PARTIALLY INTEGRATED COLUMN

Steam

Main Section

Dedicated

Reflux

No1 Effect

Column

4126

OPERATING PROBLEMS

Foaming

Unstable Operation

Steam Collapse

Reflux Control

Fiber

Plugged Heat ExchangerTurpentine in Storage Tank

REFLUX CONTROLSimple

tATIONP

CONDENSER

r

REFLUX G WATER

STRIPPER

4127

REFLUX CONTROLBetter

CONDENSER

COOLING WATER

rO VAPORTO INCINERATION

rLIQUID

REFLUX

STRIPPER REFLUX TANK

STRIPPER GAS SYSTEM

Vent

PCFA

Insulated

0 meTo

Reflux FC Incineration

Condenser

Make up PurgeSteam Steam

4128

LIQUID METHANOL

CLUSTER RULE NOW

APPROVES

MANY ADVANTAGES

Higher Stripper uptimeStore McOH as a liquid fuel

Measure McOH flow for

compliance monitoring

OPERATING PROCEDURES

Start up on SteamAdd Condensate Slowly

Make Small Step Changes

4129

EMERGENCY SHUTDOWN

Close Pressure Control Valve

Stop Condensate FlowLeave Steam On

CONCLUSION

STRIPPING IS A GOODMETHOD OF MEETING

THE CLUSTER RULES

4130