US1933255A - Apparatus for recovering black liquors - Google Patents

Description

E. G. GOODELL #En DE Edward Goo ce.

APPARATUS FOR RECOVERING BLACK LIQUORS Original Filed July 25, 1931 Oct. 31, 1933.

mmnmun E www@ Patented Oct. '31, 1933 PdrEN'rv OFFICE APPARATUS FOR RECOVERING LIQUORS BLACK Edward G., Gooden, stevens ruim, wis.

Original application July 25,1931, Serial kNo. 553,041. Divided and this application" November 22, 1932. Serial No.v 643,939

' 11 Claims.

This invention relates to improvements in apparatus for regenerating black liquors vsuch as are obtained in the manufactureof sulfate or soda pulp.

More particularly this invention relates to improvements in smelting furnaces used in processes employed in the regeneration of spent black liquors including the recovery of their alkalimetal constituents and the utilization of the cal-oric value obtainable from the combustion of their organic contents. f

This application is a division of my prior application Serial No. 553,041, filed July 25, 1931.

In the manufacture of pulp by the sulfate process wood is treated in closed vessels runder pressure with steam and with cooking liquors. Sulfate cooking liquor isr composed principally of sodium hydroxide, sodium sulfide, and sodium carbonate. When this treatment is completed the contents of the closed vessels are blown into diffusers or wash tanks where the spent cooking liquor is separated from the pulp by drainage and washing. This spent liquor is known as black liquor andV is generally recovered by concentration in vacuum or direct heat evaporators producing a heavy syrup-like, black liquor high in organic content and containing nearly all of the sodium compounds used in the cooking process.

The final steps in the recoveryof the concentrated blackliquor are effected by various methods. In some cases the concentrated black liquor is fed into a rotary incinerator where it is dried and burned to form what is commonly called black ash. lIn other cases the heavy black liquor is sprayed directly into' a smelting furnace where it-is burned and the sodium compounds fused off and recovered. In the processes described in my Patents,V Numbers 1,779,535;

1,779,536; 1,779,537 yand 1,779,768 dated OctoberA 28, 1930, concentrated black liquor is first converted into a' moisture-free powderV and this powder is treated under controlled reducing conditions to reduce the sulfate to sulfide and to recover the fused sodium compounds while at the same time utilizing the heat of vcombustion to dehydrate the black liquor. In all the recovery processes, however, the final step consisted of burning the organic matter and of fusing the sodium compounds in the smelting furnace.

My present invention relates particularly to improvements in apparatus for burning'the black liquor in the form of a liquid spray or in the form of a dried black liquor powder or in the burning of both Vsprayed black liquor and dried black liquor powder in'combination. 1 j

I have found that in the operation of the above lmentioned processes according to my prior patents, it is advantageous to control the zone of combustion of both the sprayed black liquor and the black liquor powder. The high temperatures obtaining in the smelting furnace result in the volatilization of the combustible material at or very near the point of entrance of the sprayed black liquor or powder. If this volatilization takes place under oxidizing condition, it is accompanied almost immediately by combustion. This immediate combustion is not conducive to best results, as it reduces the overall efliciency of the reduction of the sulfate to sulfide.

I have no w found that it isV possible to control the combustion by introducing an inert gas into`v the smelting furnace at or near the point of entrance of the sprayed black liquor or dried black liquor powder. This inert gas has the effect of retarding the combustion of the organic constituents and permits the sprayed concentrated liquor or the dried black liquor powder to be projected into the smelting furnace for some distance before combustion of itsorganic content occurs.

A preferred embodiment of my novel controlV feature resides in the supplyingof heated inert gas which, in the case of spraying theblack liquor directly into the smelting furnace, hasthe additional advantage of acting as a dryingand evaporating agent to expel moisture fromrxthe sprayed black liquor prior to combustion of its organic contents.

It is therefore an object ofthis invention 'to providefapparatus for the regeneration of black liquor to recover valuable alkaline substances therefrom and utilize the heat of combustion of the organic constituents in the black liquor.

A further object of this invention is to provide apparatus for controlling the smelting furnace operation in the regeneration of black liquorl whereby the combustion of organic constituents in the black liquor is retarded to obtain a distinct and localized reduction zone and thereby produce a more efficient and economical operation.

Other and further important objects of this invention will be apparent from the disclosures in the specification and accompanying drawing. As shown onthe drawing:

The reference numeral 1 indicates a spray drier into which concentrated black liquor is vfed from spray devices 2. Evaporation in the spray drier 1 is effected by hot flue gases. The dried black liquor collects in the bottom of the spray drier 1,

when the nue to the drier is closed and vice versa dried black liquor and with concentrated black is removed therefrom by a spiral conveyor 30 or by other suitable means and is blown, together with the flue gases, through a duct or pipe 3 by means of a blower 4 suitably driven by any power means such as a motor 5. The dried black liquor and flue gases from the duct 3 are led into a cyclone powder collector 6 wherein the dried black liquor powder may be freed frorn'the flue gases. The cyclone powder collector may, if desired, be operated so that a part of the nue gases remain admixed with the dried black liquor by closing the damper 7 in the gas outlet stack 8.

The dried black liquor is in the form of a ne powder and is fed from the cyclonecollector by means of a spiral conveyor 9` or other suitable means into a smelting furnace 10. The conveyor 9 is driven by any suitable means such as by a belt 11 connected to a motor (not shown) Air is introduced into a smelting furnace l0 through a tuyre or blow pipe 12 located near the bottom thereof. The organic matter in the dried black liquor fed to the slnelting furnace Yis partially burned and the hot gases of` this partial combustion`are-directed into a steam boiler or generator 13 where additionalair is introduced through secondary air nozzles or openings 23 in the boiler setting. The additional air supplied through openings 23 allows complete combustion and sup plies sufficient air for complete combustion of the gases of the smelting furnace. Part of the calo`` According to my presentinvention, however, a

fan or blower 16 is provided for propelling a part of the fiuegases leaving the steam boiler through a duct 15. These gases are blown into the smeltingfurnace 19, as at 27. Another part ofthe fluev gases is allowed to pass through Vthe spray drier 1', where their caloric content is utilized in dehydrating the concentrated black liquor. A damper arrangement is provided at 17 to automatically release the flue gases to thev stack 14 toautcmatically close the passage to the stack 14 when the drier 1 is `in operation. A further damper arrangement 718 may be provided in the duct 15 to regulate the amount of gases passing through'the duct. sary sincesuch regulation is possible by the fan 16' which is Ipreferably provided with VariableI speed controls. Y

When the smelting furnace is` fed both with liquor, a spray device 19 is located near the top of the; `smelting furnace in the path of the incoming flue gases from the fan 16 through the pipe line or duct 2O.v The hot flue gases cause a partial dehydration of the concentrated black liquor without combustion of their organic content. Thepartially `dehydrated black vliquor then drops into the lower part of the smelting furnace where the organic products are volatilized and the volatile matter partially burned. Likewise the burning of the dried black liquor from the. feed 9 is retarded by the flue gases from the fan 16 as well as from the iiue gases from the cyclone separatorv 'l with which it may be admixed.

Ordinarily this 'is not necesV When the dried black liquor from the feed 9 as well as the partially dehydrated black liquor from the spray 19 reach the lower part of the smelting furnace 10 the organic material is burned off and the gaseous products of combustion pass into the steam boiler 13 and from thence partly through the duct 15 and partly through the spray drier 1.

In ordinary practice the flue gases of the steam boiler are discharged at temperatures of around ,500 to 6007F. Therefore, part of these flue e sible to completely shut off the stack 1li by closing the damper 17 to the stack and thus use practically all of the calorc value of the iiue gases from the steam boiler in the process of recovering the black liquor. The relatively cool gases may then finally be discharged from the apparatus through the exit 8 of the cyclone collector and thence through a` scrubber (not shown). y A f If desired, flue gases may be taken by fan 16 from the boiler region at a point where the temperature of these gases reaches 1,000 F. or even higher so that the difference in temperature mayV be expended in the evaporation'of the concentrated black liquor rather than in the formation of steam inthe boilers.

The cyclone separator is ordinarily operated under a back pressure in order to furnish a current of flue gases to the feed conveyor 9. In this operation the inert flue gaseshave no available calorific content but merely serve to assist in regulating the delivery of the dried black .Q

liquor powder to the furnace and in retarding its combustion `upon its introduction smelting furnace. v 1

into the The retarding of combustion of the organic materials present in the black liquor permits the substantially dehydrated black liquor to be de posited near the bottom of the smelting furnace `before substantial or complete combustion occurs. This causes a building up of a bed of burning dried black liquor and fused metallic values which flow fromthe bottom-fof the smelting furnace in a molten state. Being outY ofthe turbulent area of the smelting furnace created by the naming gases higher up in the furnace the alkali metal values are smoothly fused oif without being volatilized. This causes an increased efficiency in the recovery of the alkalies since their volatilization is reduced to `a minimum.

The building up of a bed of fused and burnl ing materials near the bottom of the smelting furnace also increases the reduction of sulfate bodies to sulde bodies in the event of regenerating black liquorv from sulfate pulp. l

I ainaware that many changes may be madel and numerous details of construction may be varied through a wide range' without `departing from the principles of this invention, and I therefore do not purpose limiting the patent granted hereon otherwise than necessitated by ,x

liquor kfrom said drying means tosaid furnace in admixture with the gaseous drying medium employed.

2. Apparatus for the regeneration of black liquor comprising, in combination, a smelting furnace, a steam generator, a spray drier, means for conveying the gaseous products of combustion from said smelting furnace into said steam generator, means for conveying a part of the exit gases from said steam generator into Ysaid spray drier to dehydrate black liquors sprayed therein, means for directing another part of the exit gases from said steam generator back into said smelting furnace in contact with black liquorV fed th'ereinto and means for conveying said dehydrated black liquor admixed with the drying gases from said spray drier to said smelting furnace. y

3. Apparatus for regeneration of black liquor comprising a smelting furnace provided with' a tuyre for supplying air thereto, a spray-device located near the top of said smelting furnace, means for enveloping the black liquor discharged from` said spray device with inert gases, and means for feeding dry black liquor powderY admixed with inert gas into said smelting furnace at a point below said spray device.

4. Apparatus for the recovery of alkaline Values and utilization of heat contents of black liquor comprising a vertical retort having walls defining a deep container for a bed of black liquor solid residues, a blow pipe in said container near the bottom thereof for supplying a limited amount of air to the bed, a conveyor for black liquor solids entering' the furnace on top of said bed, air nozzles in said retort above said black liquor feed for supplying additional air to the rising gases .rom the bed for their thorougheombustion, a steam generator for receiving the hotV gases of combustion, means for returning hot fiuegases from the steam generatorregion back to the smelting furnace, andmeans vfor spraying concentrated black liquor into said-retort in the path of said returned flue gases.

5. Apparatus for the regeneration of black liquor which comprises, in combination, a smelting furnace having aA relatively deep container for a bed of black liquor solids', means for supplying a limited amount of air to saidvcontainer, means for supplying black liquor solids to said bed, a combustion zone in said 'furnace above said bed, air nozzles opening into said combustion zone for supplying suiiicient air for thorough combustion of the rising gases from the fuel bed, a steam `generator for receiving the hot gases of combustion, means for transmitting part of the inert gases from the steam generator back to the smelting furnace, a spray device in the path of incoming inert gases in said smelting i furnace, a spray drying cabinet for the evaporation of black liquor and `means for transmitting flue gases from the steam generator to said spray Adrying cabinet.` v

f6. -Apparatus kfor the` regeneration of black liquor which comprises, in combination, a smelting furnace, a container in said .smelting furnace for receiving a bed of blackliquor solids, means for supplying a limited amount of air to said container, a steam generator, means for conveying hot gases of combustion from the bed of saidr smelting furnace to said steam' generator, air nozzles in the pathcf hot gases from the bed of the smelting furnace to the steam generator for supplying'sufficient air to said gases for their thorough combustion, means for transmitting part of the inert gases from the steam generator to the smelting furnace to prevent entrainment of solids from the bed in the rising gases, a spray drier for dehydration of black liquor and means for conveying flue gases from the steam generator to said spray drier.

'7. Apparatus for the regeneration of black liquor which comprises a vertical retort, a container for a bed of black liquor solids in vsaid vertical retort, a blow pipe in said container near the bottom thereof for supplying a limited amount of air to the bed, a tap hole in said container for allowing the removal ofv molten alkaline values from the bed, means for supplying black liquor solids'to said fuel bed, va steam Vgenerator for receiving hot gases of combustion the spray drier to said blacklliquor solids supply means. y

8. In an apparatus for the regeneration of black liquor `including a smelting furnace, a steam generator and a spray drier, means associated with said spray drier for receiving dried black liquor solids and inert gases therefrom and means for conducting said solids together with a portion of the inert gases to the smeltingfurnace.

9. In an apparatus for the regeneration of black liquor including a vsrnelting furnace, a steam generator and a spray drier, a powder and gas separating device associated with said spray drier for receiving dried black liquor powder and inert gases from theY spray drier, controlled means for releasing a part ofthe gasesin the separatorto the atmosphere, and a conveyor for conducting said powder admixed `with some o the inert gasesto the smelting furnace.

10. In an apparatus for the regeneration of black liquor including a steam generator and a furnace providedgwith a smelterv bed for black liquor substance, means for supplying a limited amount of air to said bed for partial combustion l25 ing furnace, means for transmitting heat from the furnace to said steam generator, arelatively f deep bed in the bottom of said furnace for black liquor' substance, means for supplying a Vlimited amount of air to said bed for partial combustion, under reducingk conditions, of the combustible' black liquor material therein, means for removing fused sodium compoundsr from the bottom of .said bed, means for re-circulating part of the v inert gases from the steam generator region back to the smelting furnacea spray device for black liquor in the path of the re-circulated gases for 1 depositing black liquor substance on the bed andV means for supplying additional air to complete Vcombustion of gasesl rising from the bed before saidl gases reach the steam generator.

' `EDWARD G. GOODELL. l

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