Training at

onSoda Recovery

Ballarpur Industries ltd. Yamunanagar

Resham Kaur0805028

soda recovery

ABSTRACT

History-> The word paper derives from the Greek term for the ancient Egyptian writing material called papyrus, which was formed from beaten strips of papyrus plants. The soda process for making pulp from wood was developed by Watt & Burgess in 1851. NSSC pulping yields highest fibers up to 65%-80% which results in reduced stream pollution problems. But quality and bleachability is low.

Types-> Chemical pulp is of three types 1) Kraft or Sulfate Pulp (Alkaline) 2) Sulfite Pulp (Acid) 3) Neutral Sulfite Semi-Chemical (NSSC) Pulp Density->The density of paper ranges from 250 kgm-3 (16 lbft-3) for tissue

paper to 1500 kgm-3 (94 lbft-3) for some specialty paper. Printing paper is about 800 kgm-3 (50 lbft-3).

In BILT, Unit: Kraft Process is employed for pulping. Veneer, Veneer chips, Bamboo, Poplar wood and Poplar rulla, Eucalyptus wood & rulla etc. are the raw materials used in that unit due to their easily availability in nearby areas

SODA RECOVERY

INTRODUCTION :

Recovery of chemicals has always been considered as the backbone of pulp and paper industry in the

phase of increase of pulping chemicals. Strict laws of pollution control and power crisis arising from

mushrooming of industries the recovery of pulping chemicals has become more important.

THE KRAFT PROCESSINTRODUCTION:o Kraft process is one of the main chemical pulping . o Kraft or sulfate pulping is an alkaline process . o It is cooked with a strong (12%) solution of NaOH and Na2CO3.

The material added to the cooking liquor for the Kraft process is Na2SO4, hence the common name of sulfate process.

o The cooking however is done with a solution containing Na2S, NaOH and Na2CO3 formed from the sulfate during preparation and recovery of the cooking liquor.

o All sorts of wood can be cooked by the Kraft process and the fibers produced are bleachable and strong.

o It is very important that the chemicals used can be recovered and recycled, reducing or even eliminating stream pollution.

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soda recovery

Flow sheet of Kraft Process

soda recovery

ABBREVIATIONS USED: 1. Chipper House2. Chip Silo3. Digester4. Blow Tank5. Brown Stock Chest6. Pulp Washers7. Degassing Tank8. Stock Tank9. Knitters, Rifflers and Screens10. Beater11. Jordan12. Head Box13. Fourdrinier14. Dryer15. Calendar Stack16. Finished Paper Roll17. Weak B/L Storage18. Multiple Effect Evaporators

19. Steam Line20. To Sewer21. Condensate22. Strong B/L Storage23. Recovery Boilers24. ESP & Chimney25. Smelt Dissolving Tanks26. G/L Storage Tank27. G/L Clarifier28. Stationary Slaker29. Causticizing Tanks30. W/L Clarifier31. Mud Washers32. W/L Storage Tank33. Vacuum Drum Filter34. Lime Kiln35. Dregs36. Producer Gas Plant

soda recovery

Pulping Procedures in Kraft Process Cellulosic raw material : Almost any kind of wood,soft/hard

Principal reaction in the digester : Hydrolysis of lignin to alcohols and acids

Composition of cooking liquor : 12.5% solution of NaOH, Na2S;

58.6% NaOH, 27.1% Na2S, 14.3% Na2CO3.

Cooking conditions : Time 2-5 hours; Temperature 170 to 176˚C; Pressure 660-925kPa.

Chemical Recovery : through burning of organic matter dissolved in the liquor from the wood.

Material of construction : can be made of mild steel or stainless.

Pulp characteristics : Brown color, difficult to bleach, strong fibers, resistant to mechanical refining.

Paper products : Strong brown bag, gumming paper, building paper, strong white

paper, paperboards and liquid containers.

soda recovery

RECOVERY OF THE BLACK LIQUOR The B/L removed from the pulp washer contains 95 to

98% of the total chemicals charged to the digester. Organic sulfur compounds are presented in combination with sodium sulfide. Na2CO3 is present as are also small amounts of Na2SO4, salt, silica and traces of lime, Fe2O3, alumina and potash. Total solids usually average about 20%. Then black liquor is concentrated, burned and limed.

In the smelting furnace any remaining organic compounds are broken down, the carbon burned away and the inorganic chemicals melted. At the same time the following reaction takes place:

Na2SO4 + 2C Na2S + 2CO2

The carbon comes from the organics in the wood.

soda recovery

Soda Recovery-Flow Diagram:

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Soda Recovery sub-sections:

Evaporator Section

Boiler Section

Causticizing Plant

Lime Kiln

Producer Gas Plant

soda recovery

In this section black liquor is concentrated to a required concentration and sent to the recovery boilers for heat recovery & formation of green liquor.

The black liquor is concentrated with the help of evaporators. In this section there are mainly two types of evaporators, one is free flow falling film evaporator (FFFF) and other is short tube vertical effect evaporators (STVE).

Evaporator Section :

soda recovery

FORCED-CIRCULATION EVAPORATORS:

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SHORT-TUBE VERTICAL EVAPORATORS: Principal use :evaporation of

cane-sugar juice. Heating surface is induced by

boiling in the tubes, which are usually 50.8 to 76.2 mm (2 to 3 in) in diameter by 1.2 to 1.8 m (4 to 6 ft) long.

Body: vertical cylinder, usually of cast iron, and tubes are expanded into horizontal tube sheets

Circulation rate through the tubes is many times the feed rate; so there must be a return passage from above the top tube sheet to below the bottom tube sheet.

Most commonly used :central well or down-take

soda recovery

ROLE OF RECOVERY BOILERS

Feed - concentrated B/L coming from the evaporators. At both of these boilers B/L is fired to recover the heat content of the spent cooking liquor in form of production of high pressure steam. The lignin in the liquor is burnt away and what remain are the chemicals (in the form of smelt).

This smelt is then dissolved in weak white liquor coming from Causticizing Plant, which gives a characteristic green color (hence called green liquor; G/L).

This G/L contains some solid impurities which are separated out by means of a clarifier. The main aim of these boilers is to recover all unused chemicals from the B/L stream in form of G/L. Chemical composition of G/L is as follows:

Na2CO3 (70%); NaOH (15%); Na2S(15%)

soda recovery

Recovery Boilers

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RECOVERY BOILERS:

TYPES

ABL boiler JMW boiler

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Differences b/w ABL & JMW Boilers Points ABL

JMW

Firing wall firing centre base smelt Dissolving at the bottom at the top tank agitator FD fan after the ESP & gives fine gases to chimney before the ESP &

gives fine gases to ESP sump pump used for mixing salt cake for better mixing same mixing tank is

used for mixing of two both ESP ash & salt

cake. soot blowers all are retractable type only 5 are retractable type

and rest of 17 are

non-retractable Automatic soot blowing Soot blowing is done

manually Steam used for taken from the steam produced by itself uses steam produced

by other soot-blowing boiler for the same

ESP Two are used one is used Pumps four pumps being used; two for recirculation two to serve both the

purposes and two for transferring liquor to

Causticizing Plant

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CAUSTICIZING PLANT: Purpose-> To convert available Na2CO3 in useful NaOH by reacting it

with Ca(OH)2 thus converting the supplied G/L into W/L in a number of steps.

consists of-> causticizers, clarifiers, mud washers, filters, dreg washers and grit classifiers etc.

Process-> G/L at 500-600˚C from the smelt dissolving tank is pumped to

raw G/L storage tank. G/L is screened over the storage tank to separate solids. Screened G/L is allowed to fall in a clarifier to separate out dregs. The temperature is always kept at 95-100˚C so that slaking and causticizing reaction may take place in the causticizer tanks at desired rate. Clarified green liquor from the storage is supplied to splitting box. Lime is introduced in the slaker where G/L meets it from the splitter box in the slaker by two lines one in head and another in tale. Lime is transferred from lime bin. In the slaker causticizing reaction is completed around 80-90%.

The slaking reaction is as follows:- CaO + H2O Ca (OH) 2 + Heat (486 Btu/lb)

The resultant Ca(OH)2 reacts with sodium carbonate to form NaOH this reaction is called causticizing reaction:

Ca (OH) 2 + Na2CO3 2NaOH + CaCO3

Na2CO3(15%); NaOH(70%); Na2S(15%) 

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Details of Causticizing PlantDaily G/L intake (ABL) : 510 m3 (JMW), 810 m3

G/L clarifier capacity : 280 m3 (Both)Storage tank capacity : 165 m3 (All)Lime bin capacity : 150 tonW/L clarifier capacity (Old) : 650 m3(New), 400 m3

New mud washers capacity : 565 m3 (Both)Steam line used for heating : 3 Kgcm-2 & 7 Kgcm-2 Dryness of mud after filter : 64%Daily lime consumption : 77 tonNumber of clarifiers : 4Number of mud washers : 4Filter type filter : Rotary vacuum drumProduction(W/L ) : 855 m3 per dayTemperature in each step : 90-110˚C

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LIME KILN

Basic reaction that takes place inside a lime kiln is as follows:CaCO3 CaO + H2O + Δ

Basically consists of :mud filters, lime kiln, ESP

and chimneys etc

In this unit we have one filter (Rotary Vacuum Drum Filter type), one lime kiln, one ESP and an ID fan.

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Constructional & working details Length : 55 m Diameter : 2.5 m Feed end temperature : 200-250˚C Outlet zone temperature : 900-1000˚C Feed rate :

150 ton per day Average CaO in lime prepared from kin : 80-82 % Dryness of mud : 65-68 % % CaO in mud at feed end : 0.2 % % free NaOH in mud at feed end : 0.4 % Daily oil consumption : 6000 m3

Kiln speed : 0.667 rpm

Kiln motor speed : 1300-1400 rpm

Inlet & outlet draught for ESP : 12mmWC

& 120mmWC

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PRODUCER GAS PLANT:

Producer Gas (PG) is made by passing air stream through a bed of hot coal or coke. Temperature of the fuel bed depends on the fusion point of the fuel ash is to use up as much as possible, the exothermic energy from the reaction between C and O2 to supply the endothermic reaction between the C and steam:

C + Air CO2 + N2 (ΔH1000˚C= -395.4 MJ/ Kmol)

CO2 + C 2CO (ΔH1000˚C= +167.9 MJ/ Kmol)

C + H2O CO + H2 (ΔH1000˚C= +135.7 MJ/ Kmol)

CO + H2O CO2+ H2 (ΔH1000˚C= -32.18 MJ/ Kmol)

PG thus produced is used in lime kiln as fuel. Steam pressure

helps in maintaining axial flame length while oil atomization controls radial flame spread.

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PRODUCER GAS PLANT-Few details Coal feed rate : 20 ton per dayLCT-1 temperature : 135˚CLCT-2 temperature : 142˚CFurnace jacket temperature : 75˚CBlast Saturation Temperatur : 55˚CBlast Air pressure : 280 mmWCGas flow rate : 2730 m3/hourAir flow rate : 1170 m3/hourLCT-2 pressure : 125 mmWCSteam pressure : 0.4 Kgcm-2

CO leakage level : 10-250ppmGas outlet temperature : 106˚CDaily tar production : 1200 liter

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Thanks