CA1100817A - Method of treating material in a fluidized bed reactor - Google Patents
Method of treating material in a fluidized bed reactorInfo
- Publication number
- CA1100817A CA1100817A CA284,402A CA284402A CA1100817A CA 1100817 A CA1100817 A CA 1100817A CA 284402 A CA284402 A CA 284402A CA 1100817 A CA1100817 A CA 1100817A
- Authority
- CA
- Canada
- Prior art keywords
- reactor
- liquor
- sodium
- fluidized bed
- particle fraction
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C11/00—Regeneration of pulp liquors or effluent waste waters
- D21C11/0085—Introduction of auxiliary substances into the regenerating system in order to improve the performance of certain steps of the latter, the presence of these substances being confined to the regeneration cycle
- D21C11/0092—Substances modifying the evaporation, combustion, or thermal decomposition processes of black liquor
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
- B01J8/18—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles
- B01J8/24—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles according to "fluidised-bed" technique
- B01J8/32—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles according to "fluidised-bed" technique with introduction into the fluidised bed of more than one kind of moving particles
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F11/00—Treatment of sludge; Devices therefor
- C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
- C02F11/13—Treatment of sludge; Devices therefor by de-watering, drying or thickening by heating
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- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
- C10B49/00—Destructive distillation of solid carbonaceous materials by direct heating with heat-carrying agents including the partial combustion of the solid material to be treated
- C10B49/16—Destructive distillation of solid carbonaceous materials by direct heating with heat-carrying agents including the partial combustion of the solid material to be treated with moving solid heat-carriers in divided form
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- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
- C10B53/00—Destructive distillation, specially adapted for particular solid raw materials or solid raw materials in special form
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
- F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
- F23G5/30—Incineration of waste; Incinerator constructions; Details, accessories or control therefor having a fluidised bed
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
- F23G2201/00—Pretreatment
- F23G2201/10—Drying by heat
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
- F23G2203/00—Furnace arrangements
- F23G2203/50—Fluidised bed furnace
- F23G2203/501—Fluidised bed furnace with external recirculation of entrained bed material
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Mechanical Engineering (AREA)
- Combustion & Propulsion (AREA)
- Materials Engineering (AREA)
- Hydrology & Water Resources (AREA)
- General Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Environmental & Geological Engineering (AREA)
- Water Supply & Treatment (AREA)
- Treating Waste Gases (AREA)
- Paper (AREA)
- Devices And Processes Conducted In The Presence Of Fluids And Solid Particles (AREA)
- Fluidized-Bed Combustion And Resonant Combustion (AREA)
- Meat, Egg Or Seafood Products (AREA)
- Treatment Of Sludge (AREA)
- Crucibles And Fluidized-Bed Furnaces (AREA)
- Drying Of Solid Materials (AREA)
- Heating, Cooling, Or Curing Plastics Or The Like In General (AREA)
- Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)
Abstract
ABSTRACT
A method or treating materials in a fluidized bed reactor, wherein the material to be treated is brought into contact with hot particles removed from the flue gases coming from the fluidized bad reactor to bring about chemical and/or thermal reactions in the material before it is introduced into the fluidized bed reactor together with recycled particles. Useful components can be recovered in the form of gases, solids or liquids in connection with this treatment.
A method or treating materials in a fluidized bed reactor, wherein the material to be treated is brought into contact with hot particles removed from the flue gases coming from the fluidized bad reactor to bring about chemical and/or thermal reactions in the material before it is introduced into the fluidized bed reactor together with recycled particles. Useful components can be recovered in the form of gases, solids or liquids in connection with this treatment.
Description
11()(t817 HOD OF TRE~TING ~IAT~RI~LS IN ~ FLUIDIZED BED ~EACTOR
BACKG~OUND 0~ TH~ INVENTION
1. ~ield of the invention The present invention relates to the treatment of materia~ in a flui-dized bed reactor and particularly to the treatment of various sludges, spent liquors from pulping processes and other combustible materials.
BACKG~OUND 0~ TH~ INVENTION
1. ~ield of the invention The present invention relates to the treatment of materia~ in a flui-dized bed reactor and particularly to the treatment of various sludges, spent liquors from pulping processes and other combustible materials.
2.~Description of the prior art It is ~rell known that a fluidized bed reactor can be used for the inci-ne~ating o~ v~rious matQri~3.~`he ~aterial is tl~en introduced into the bed of the reactor where it comes into contact with the hot fluidized particulate bed material. As an example of such an application the US-patent 3.319.586 can be cited, which describes incineration of waste sludges containing organic matters. Because of the high water content of these sludges after the mechanical dewatering process, the incineration of the sludges in a ~luidized bed reactor inv~ves problems.
By mechanical treatment lt is, for instance, possibl~ to remove so much ~ater from sewage sludge that itssolids content i~ ~bout 20 ~o. If appropriate chemica~s are added to the sludge such as e.g.
lime and ~err~chloride a solids content of about ~5 ~ can be achieved, whereby the combustion in a fluidized bed reactor will be autogenous.
If the solids content is lower, it is necessary to supply the reactor with auxlliary fuel in order to maintain combustion. ~rom most .
~ llOU817 indu~rial ~iaste -~UG~-qâ it i9 possil,le to remove only so much wateT~
by ~e na.lical llS~IlS ~ha-~ tns solids concentraiion will be lower tllan 20 ',c. ITlcineration of sucn sludges causes high operating costs, which increase ~ith the mois~ure content.
In order to l~provs the thermal econorny of the incineration pro-cess, the heat o~ the co~bustion gases can be utilizecl for predrying o~ the sludge either by direct or indirect heat transfer. In the direc~t method the combustion gases are brough into direct contact with the sludge and the exhaust gases will there~ore contain melodorous gases. As -tha volume of the gas is large, the burning of the smelling components will cause considerable expenses. In the indirect method large heat transfer sur~aces are needed, which causes lligh construction costs.
^ The Canadian patent 524,796 shows an example of a method where the sludge is predried by contacting it with the combustion gases.
Earl-ier, the chemi~ls in spent liquors frorn the 8Ul phate pulping processes have usually been recovered by combusting the s-pent liquors in a recovery boiler, whereby sodium and sulphur contained in the digestion chemicals are recovered form the smelt in the form of sodium carbonate and sodium sulphide. The sodium carbonate is ~len converte~ iT~
sodium hydroxide by causticizing the dissolved smelt. The combustion o~ the spent liquor takes place in three stages: drying, reducing combu~tion and oxidizing combustion. Because of this it is di~ficult to control the different stages carrie~ out in thç s~ule sP~e~,in such a way that tlle desired result will b~ achi~ed. This arr~ngel7lent is too c~pcrlsive ~or sm~ll pulp rnills A stealll bo~le~ is mo~3v~r not ~ully reali ble irl cperat~on,wh:;ch h~s b~eTI shown by many disastrous boiler explo-sions.
The ch0mical~in the spent liquors coming from a sulphite pulping process çan be recovered ~or instance as described in the Finnish pa-tent 45.880 where the carbonate and the sulphide sulphur in the ~ . . .
'
By mechanical treatment lt is, for instance, possibl~ to remove so much ~ater from sewage sludge that itssolids content i~ ~bout 20 ~o. If appropriate chemica~s are added to the sludge such as e.g.
lime and ~err~chloride a solids content of about ~5 ~ can be achieved, whereby the combustion in a fluidized bed reactor will be autogenous.
If the solids content is lower, it is necessary to supply the reactor with auxlliary fuel in order to maintain combustion. ~rom most .
~ llOU817 indu~rial ~iaste -~UG~-qâ it i9 possil,le to remove only so much wateT~
by ~e na.lical llS~IlS ~ha-~ tns solids concentraiion will be lower tllan 20 ',c. ITlcineration of sucn sludges causes high operating costs, which increase ~ith the mois~ure content.
In order to l~provs the thermal econorny of the incineration pro-cess, the heat o~ the co~bustion gases can be utilizecl for predrying o~ the sludge either by direct or indirect heat transfer. In the direc~t method the combustion gases are brough into direct contact with the sludge and the exhaust gases will there~ore contain melodorous gases. As -tha volume of the gas is large, the burning of the smelling components will cause considerable expenses. In the indirect method large heat transfer sur~aces are needed, which causes lligh construction costs.
^ The Canadian patent 524,796 shows an example of a method where the sludge is predried by contacting it with the combustion gases.
Earl-ier, the chemi~ls in spent liquors frorn the 8Ul phate pulping processes have usually been recovered by combusting the s-pent liquors in a recovery boiler, whereby sodium and sulphur contained in the digestion chemicals are recovered form the smelt in the form of sodium carbonate and sodium sulphide. The sodium carbonate is ~len converte~ iT~
sodium hydroxide by causticizing the dissolved smelt. The combustion o~ the spent liquor takes place in three stages: drying, reducing combu~tion and oxidizing combustion. Because of this it is di~ficult to control the different stages carrie~ out in thç s~ule sP~e~,in such a way that tlle desired result will b~ achi~ed. This arr~ngel7lent is too c~pcrlsive ~or sm~ll pulp rnills A stealll bo~le~ is mo~3v~r not ~ully reali ble irl cperat~on,wh:;ch h~s b~eTI shown by many disastrous boiler explo-sions.
The ch0mical~in the spent liquors coming from a sulphite pulping process çan be recovered ~or instance as described in the Finnish pa-tent 45.880 where the carbonate and the sulphide sulphur in the ~ . . .
'
3 llOU817 green liquor o~ ained I`rc,m the smelt coming from the recovery furnace are separated, and the sulphide-containing solut:ion is reacted l~ith a bisulphi-~c .iolution wherehy the released hydrogen sulphide is con-verted by combustion into dioxide. The sulphur dioxide from the com-b~lstion process is reacted with a carbonate water solution in an absorption to~i-er whereby bisulphite needed for the pulping liquor is formed.
P.yrolysis has been used for recovery of digestion chemicals from spent liquors, fo:r instance in the SCA-Billerud process, where the sodium s~ts in sodium sulphite spent liquors are conver-ted into sodium carbonate ~nd the sulphur components into hydrogen sulphide. The hydrogen sulphide is conver-ted by combus-tion into sulphur dioxide and absorbed into a sodium carbonate solut-ion. This method is described in the ~innish patQnt 45.518.
It has also been proposed to treat the spent liquor in a rotating furnace. The US-patent 3.787.283 describes a method for recovering che-micals,where a conce~ntratcd spunt liquo~ ~f`r~m a sodiurnbas~c1 pulpng pro-cess is m-lxed ~th reaotive aluulirla hydra~e and formed -~;o solid pe~ets by adding sodium alurninate. T,he pellets are fed into a rotating furnace where a temperature below the fusion temperature of sodium aluminate is maintained. A portion of the resulting sodium aluminate ash is dissolved in water and the solution is reacted with the sulphur dioxi-de-containing flue gases to form a slurry containing sodium sulphite, from which aluminium hydrate is separated. The remaining portion of the sodium aluminate ash is recycled and mixed into the spent liquor.
The operation of a rotating furnace involves several disadvantages.
It is expensive and requires a gl-eat deal of maintainance. Its thermal econorny is unsatisfactory because it is necessary to supply auxiliary fuel for maintaining the 1;~mperaa-tllre r~-quirec1 for ll~c ~e~c t.iOIl.
110~817 The nea; t~alls~er ~om ~tr`~ ~ctS in the f`uxnace to the trea-ted material ~s, as is ~-eil kno~-n, poor The furnace mus-t ther~ore be lar~e-sized.
In order to reduce the dust losses the material has to be ~ormed into pellets, for which r~ason auxiliary apparatures are required b~fore the f`urnace as wcll as after it. As a consequence of the pelletizing the solids contenl ol ~ne material supplied to the furnace must be high,which increases ~ne opera-tion costs.
It has also been p-oposed to incinerate spent liquors in fluidized bed reactors. As an example of an application of -this kind, the US-patent 3.635.790 can be cited. Because the combus-tion temperature has to be lower than the fusing temperature of the che~icals, for instance ~ irn~lly 750 C, ~ en incinorat~ng spen~ liquors containlng sodium the combustion has to be performed within a tempera-ture range where it is difficult to maintain stable combustion. The temperature can be re-duced by feeding to the furnace a liquor which has a low solids content or by cooling the process with a great amount of excess air. In both cases the furnace has to be~arge-sized and is difficult to control.
Gasification of solid organic material has earlier been per~or-INcd, for instance, by a method disclosed in the US-patent 3.840.353, wherein a granulated carbon-containing fuel is introduced into a fluidized bed reactor and solid par-ticles removed from the flue gases are returned to it. The combustion and the gaslfication of the carbon-containing material i9 b~ought about in the same reactor,for which reason it is difficult to control the reactions in a desired manner.
In order to avoid the aforesaid disad~antages, it has been proposed to subject the material to be treated to con~ct with hot material taken l`rolll ttl~ becl of the re~ctor b~fo-re it -ls introclucec-l irltO the flu;d~dled r~lctor. A method of this kind is described ~ the German patent appli-~ ~ .
cation ~5 3~ . O:le o^ the drawbacks of i;he arrangrement is that thehot ~ed ~aterial has ,Q be transI`erred ~rom 1;he reactor and back to it and al~o~ller d~al~b~ e ~he c(~n~-ol l~-r~l)1clrls c-)rlntec~e(l wi1;h i-l; w}len th cluarlt-l-ty ~r i;he moic~;lr? c~te~t ~f ti1~ n~aterial to b~ tr~at~d ~hanges.
Tlle w~ar o~ b~d ~la-terial and ~quiplrle]lt also CallSeS Prcblerns. l3ecau~
thermal energy for e~-a~oration of moisture in the material is taken from the bed, a corres?ondi~g amount of hea-t has to be transferred to it, i~.e. the combustion must take place in the bed which therefore has to be of l~ge volume. T~le supply to the bed must furthermore be distributed among several ducts, which will increase the construc-tion costs:
The exhaust gases from the combustion chamber of a fluidized bed reactor contain fine materia] which can be separated, for instance in a cyclone separator. The fine material contains ash, fine particles from the bed material and usually also usable chemicals. Its heat con-tent is considerable. Depending on the velocity of the air flowing through the fluidized bed reactor, it will function differently. The higher the velocity is, the more of the fluidized bed material is entrained in the uprising fluidizing ~iP and the more fine solids will be exhausted with the flue gases.
SUMMARY OF THE INVENTION
According to the invention, the material to be treated is subjected to contact with fine particles separated from the flue gases exhausted from the fluidized bed reactor, which preferably are mixed into the materlal before it is introduced into the reactor. In this connection also chemical and/or thermal reactions can occur. Useful components can bc recovered from the gases and vapors generated in connection with this treatment by known methods. The fluidized bed reactor is operated in such a way that the velocity of the air flowing through the reactor is between 1 and 10 m/s.
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~10()`817 In general terms, the present invention can also be defined as a method of treating a material in a fluidized bed reactor of the type wherein the treatment results in generation of a mixture of flue gas and hot particles, said method comprising the steps of: discharging said mixture from said reactor; sub-jecting at least a portion of the discharged mixture to separation to obtain a mainly gaseous fraction and a mainly solid hot particle fraction; feeding said material into a pre-reactor prior to the discharging of same from said pre-reactor into said reactor; feeding at least a part of said solid hot particle fraction for heat treatment of said material in said pre-reactor;
mixing said material within said pre-reactor with said part of said solid hot particle fraction thus causing a heat exchange between the two resulting in vaporization of a part of a liquid contained in said material; removing at least a portion of said vapor from said pre-reactor thereby reducing liquid content of said material; introducing said material into said reactor, whereby thermal energy contained in said mainly solid hot particle fraction is utilized in reducing liquid content in said material prior to the introduction thereof into the reactor.
According to one feature of the present invention, the volume and/or temperature of said part of solid particle fraction is such that thermal decomposition of organic components of the material to be treated is brought about before said mat-erial is introduced into said reactor. According to a still another feature of the present invention, the volume and/or temperature of said part of solid particle fraction is such that gasification of organic components in the material to be treated is brought about before said material is introduced into said reactor. Preferably, the volume and/or temperature of said parts of solid particle fraction is such that chemical reactions in the material to be treated are brought about before said material is - 5a -1~0(~`817 introduced into the reactor. According to another feature of the present invention, a part of the vapor removed from the pre-reactor is introduced into the reactor. In accordance with a yet another feature, aluminate hydrate and at least a portion of the sodium aluminate-containing particles removed from the flue gases coming from a fluidized bed reactor are mixed into a spent liquor from a pulping process based on an alkali compounds before said spent liquor is introduced into said reactor. In accordance with a still further feature of the present invention, alumina hydrate and at least a portion of sodium aluminate-containing particles removed from the flue gases coming from the fluidized bed reactor are mixed into a spent liquor from a pulping process based on alkali and sulphur compounds in order to convert the sulphur content of said spent liquor into hydrogen sulphide which is removed before said spent liquor is introduced into said reactor.
- 5b -The ad~antaf,,es of thc m~thod o,L this invent-ion ir. comparatlon with the fluid:.ze~ bed ~eci~rliqu~ o~' the ~pl:nior art, ar~3 as ~ollows:
The new method requires markedly less energy as ~u~i:L-iary f`n~l for burnill~ we~ sluAges thall tho prior at t`LIl-id-ized becl processes.
l`he volume of the flile gases in the new method is about 50 9~ of the volume of the flue gases in the prior art fluidized bed processes.
Consequently the size of the rluidized bed reactor and the gas cl,eaning equipment will be much smaller.
The mixing conditions in the new method are much bet-ter than in the prior art fluidizcd bed procffsses. Consequently the combustion densi-ty will be higher and the volume needed is smaller.
Due to the smalle~size of the fluidized bed reactor and the more e~ficient mixing, it is easier to ~eed the material to treated into ~he reactor. Especially the ~eeding of peat involves problems and high costs in the prior art fluidized bed processes.
Due to the radiating properties o~ the recycled particles, the combustion is stable also at low temperatures. The stabilizing in-fluence of the recycled particles also aids to this.
Because the moisture in the material to be treated is evapora+,ed before the combustion process, the combustion temperature will in-crease and because o~ the high heat transfe~ p,roperties of the fluidized bed material the heat t,r~nsfer surfaces for steam generation will be smaller.
The pressure losses in the fluidized bed reactor and the required power for the blower are smaller.
The new method makes it possible to use the evaporation heat for heating purposes.
The ~luidized bed reactor in which the new method is adapted is easily controllable.
- ' : ~:
', .
llOU817 It ~s there-lor? a ~eii-r~l object or the present invention to pro~
vide a method f~r t~e~in~ materials in a flui~i~ed bed reactor which avoids th~ above mGntioned disadvantages.
Another o~ct of` the in~-ention is to provide a method for the incine-rating of various alud~es.
A further objec of the invention is to provide a method for trea-ting spent liquors coming from pulping processes in order to recover the pulping chemicals in the spent liquors.
An additional object of the invention is to provide a method for thermal decomposition of or~anic materials in oder to obtain raw gases containing carbon monoxide, hydrogen and hydrogen sulphide.
DESCRIPTION OF 'I`llE DRAI~INGS - --The invention is described in more detail below with reference totho onclosed drawings in which:
FIG. 1 is a flow sheet of the method of the present invention as adapted for the incineration of sludges, FIG. 2 is a flow sheet of the method as applied to spent liquors from a sodium based pulping process,where sodium is reco~ered in the ~orm of Na2C03, FIG. 3 is a flow sheet of the method as applied to spent liquors from sodium-basèd pulping process,wher~ sodium is recovered in the form of NaOII, FIG. 4 is a flow sheet of the method as applied to spent liquors from a sulphlte pulping process, FIG. 5 is a flow sheet of the method as applied to spent liquors from a sulphate pulping process, and FIG. 6 is a flow sheet of the method as adapted for the thermal de-composition of organic material.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In l~'ig. l,there is shown a syste~ ~or l^hc inci~eration of slud~es,ir - 11~)t~817 wnlch rhe n~ eral. 1 ~ fe~ o a fluid:ized ~)ecl r~ cLor colnprising a windbox 2, a con3tric~:io~ plate 3 and a corrlbu.stion chamber l~. ~bove the consLriction pla~e ~-ere is h~t1 mate~ 5-~ icl-~ lu-i~ized and en-traineu by air supplied to i-t through-lhe constriction plate. Air for flu~i~ation and combustion is supplied to the windbo~ through con-duit 6. Auxiliary combus~ion air is supp:Lied to the combustion chamber through conduits 7, 8 and 9. The combustion gases and other gases generated by chemical reactions ~re cxhaustQd from the reactor thro-ugh conduit 10 from which the flue gases flow to a dust separa-tor 11, a preheater for the air 12,and a gas scrubber 13. In case of need auxiliary fuel can be supplied to the reactor through conduit 14. Bed material can be added through conduit 15 into a prc-r~actor 16.
Gas entrained solids are removed from the flue gases in the dust separator and conducted to the prercaotor wh~r~ they ~ro bro-ught into contact with the sludge supplied through conduit 17. The mixer is provided with -two agltator screws which rotate in opposite directions and in this manner bring about an effective mixing of the sludge with the hot particles while conveying it to the end o~ the pr~rcaetor,where-: from it is discharged to the reactor through conduit 18.In the prereactorjpreheating and drying of the sludge is brought about, in which connec-tion vapor is generated, which is passed through conduit 19 to a dust separator 20 and further to a oonde~oer 21.~ondcnsed liqu;d is discha~d -fr~m the lower part of th~ condenser,f`or ~tance to a w~r pu~cation plant,alld ~OI~-eO~lden9able ~a9cs are ~isch~rged frcm :it~ u~p~r part and pa~ed to the rcactor to bc burne~ bb~au~e th~y con-tain mclodorous compo-nent.~. A portiQrl of the ptlrtlcl~ rem~ by the dust scp~rator is dis-charg~d throu~l condlit 22 to control -the qualltity of the recycled mater~L
When the system illustrated in Fig. 1 is used for the gasification of moist organic material, the moist material 17 is supplied to the pre-hea~2r 16 where hot particles separated in the dust separator 11 are .
, ? l l~U817 rni~ed into -it. 1~ater e~-~poIcites and is di~schar~ed ~togcther wi-th possib-le evapora1:ed combusti~le components to the dust separator 20, where dust is separated from the gases. ~`rom -the separator, the gases flow to the condenser 2I kihere -t~le n~ost; -part (~ the stca1ll con~lens(?s. The remaiIling part of the gases is conducted to -the ~luidized bed reactor 1. The dried combustible materi~l and the particles which have been used for heating purposes are introduced into the fluidized bed reac-tor, wh~re the cornbustible material is partly cornbusted and the un-combusted portion 10 is oxh~u~tod ~ inly in gascous ~1~te, -throug;h the cyclono separator 1l t;o the plant wl1ere th~y are u~ed, e ~-.
. a steam boiler. The combustion gases pro-duced in this way have a considerably smaller content of inert gases than they would ha~e had i~ the combustible material had been supplied in a n;oist stato to the :~luidi~d kedbecause the water has been re-moved from the material before the actual gasi~ication is brought about. If the material had been dried directly by hot gases, a part of t1lG combuq~i~le conlponents would have been discharged with the drying gases. The generated combustible gases are thus o~ 1~etter quality and ~urthc~nore produced by simple means.
In ~ig. 2, there is shown a system ~or ~hc reoovery of chemicals from spent liquors coming from a NaOH-based pulping process,where sodium is recovered in the form of a NaC03-con~ining liquid from which a digestion liquor is obtained by causticizing.
In ~ig. 2, the numeral 24 re~ers to a fluidized bed reactor, which is supplied with air for fluidization and combustion through conduit 2~. The spent liquor is introduced through conduit 26into a mixer 27 to which also alumina hydrate separated in the filter 2~ is çorl~eyed, allCl thl~OUgll COlldUit 29, react-;v~ ~l(Oi-r)3 ~s m~e-up chel~l;c~ls. The alumina hydrate reacts partly with the sodium in the spent liquor forming sodium aluminate compounds which through conduit 30 are supp-, 110(~817 lied as a sludg-e h~ u~u- a ~io]ids cont;~nt oI` 30to 70 ~ to a prereacto:r 31. 'rhe hec;-t o,'` .he ~l ~ r,~es disc~ f-red frcr! the u~per ~art of the reac~or is utiliYed for producing steam in a waste heat boiler 32, from which they flow to a gas ccrubber. A portion of the clust in the flue gases, cooled dawrl to 300 ~, stt1es tc the bot-tom of the waste neat boiler, from which it is conducted -through conduit 34 to the prereactor 31,and another portion ~hereof` iH reillO~Cd in ths gas ~rubber.
A portion of the sodium aluminate-containing dust rcmovod f'rom the flue,gascs ln ~ waste heat boiler 32 is delivered to a dissolver 39.
From the dissolver sodium aluminate slurry is fed to -the gas scrub'ber 33 where it reacts with carbon dioxide in the flue gases, which neut-ralize it to a pFI-value of 9, whereby Al(OH)3 precipitates. From the dissolver the slurry is transmitted via an aging tank 41, where alu-mina hydrate crystallizes, to ~1~ fi~r 28 where aluminium hydrate is filtered out from the dissolved sodium salt. The sodium-containing solution is delivered throu~h conduit 42 to the digestion liquor pre-paration plant and the alumina hydrate through conduit 43 to the mixer 27.
In Fig. 3 there is shown a system forthe rccovery cif sodium,'in the form of NaOH-liquldj from spent liquo~ coming from a sodium-basecl pul-ping process.
In Fig. 3, the numeral 44 refers to a fluidized bed reactor wXich is supplied with preheated air through conduit 45. The spent liquor is ~ed through conduit 46 to a mixer 47 into which also alumina hydrate separated in filter 48 and through conduit 49 Al-salts such as Al(OH)3 and Al203 as make-up chemicals are lntroduced. The produced sodium aluminate slurry is conveyed to a prereactor 51 through conduit 50.
Into the prereactor, ~lso a po~tiorl oP the sodium alumlnQte-~onta:ini,ng 11C)(~817 dust r~?m(>~e(! L`rom ~h~ lul gas~s ol` tll~ tl~ ;ed Ije~ roclc-tor -Is -in-tro-cluce(l l1lrollm~ ~-~ndu-i-t ~3. '`~lo ~;rc~s~s gellerQ-tecl i~ 1he ~pror~acto~ are discharged through conduit 54 and steam can be separated from it and removed in form of condensate through conduit 55. The uncondensed gases are led to the reactor through conduit 56 -to be combusted.
'~he clr;ed materi~:L is introduced in-to the reactor through conduit 57. The gases generated in the combustion and other chemical reactions are discharged from the upper part of the reactor through condui-t 58, from which the flue gases flow to a dust~
separator 52, a waste heat boiler 59, and a gas scrubber 60.
A portion~of the sodium aluminate-containing dust removed from the flue gases by the dust separator 52 is conducted to a dissolver 62 to which wate:r is supplied through conduit 61. The for-med slurry is conducted to a sedimentation tank 64 where impurities are separated at a temperature of about 90 C. The impurities are re-moved through conduit 65 andaluminate liquor is fed through conduit 66 to a cooler 67. The numerals 68 and 69 refer to the inlet and outlet conduits for the cooling medium. The aluminate solution cooled to about 50 C is conducted to an aging tank 70 where Al(OH)3 precipitates in accordance with the following principal reactions:
3Na200 Al203~ 6H20 ~ ~ 6NaOH + 2Al(OH)3 Na20- Al203 ~ 4H20 ~- -~ 2NaOH + 2Al(OH)3 The precipitated Al(OH)3 is separated in the filter 48, washed with water from conduit 71 and fed to the mixer 47 through conduit 72. The sodium chemicals are removed through conduit 73 for reuse in the diges-tion liquor.
In ~ig. 4, there is shown a system for tll~? rcÇQ~Tery O.r~ chemicQlS ~rorrl spent liquor coming rom a sulphite pulping process, lvhe~e sodium and sulphur ls recovered in the form of sodium salts such as Na2S03, NaHS03, 1 ~ ~110(~817 Na2C03an~ a~lco3 in so u ion In Fig. 4, t~e num3ral 7'~ re~ers to a mixer into which concentrated spent liquor 75 fro~. a s-~lphit~ pulping process is introduced. To the mixer is conveyed al~min hydrate 76 separated in a filter 77 and dried in a dryer 7~. To the mixer is also deliver(od make-up chemicals 79, if necessary. From the mixer the spent liquor and the chemicals mixed into it are pumped through conduit 80 to a prereactor 81. To ihe prereactor is also conveyed sodium removed by a dust separator 83 from the flue gases corning from a fluidized bed reactor 8L~. In the pre-reactor pyrelysis of the spent liquor takes place whereby gases and steam are gencra~-ed.Air 85 can also be supplied to it, in which case partial combustion take~ place, The gases which contain the main part of the sulphur contained in the spent liquor, mostly in the form of hydrogen sulphide, and the steam are removed from the prereactor through conduit 86, and the solid components are introduced into the fluidized bed reactor through conduit 87. The gases and the steam generated in the prereactor and the air introduced into it bring about an effective intermixing of the spent liquor and the hot dust which can be intensi-fied by mechanical means. The temperature in the prereactor is maintai ned at between 200 and 900 C and preferably at about 700 C. The gases from the prereactor are alternatively passed through conduit 88 to the fluidized bed reactor or through conduit 89 to an after-burner 90 where they meet the flue gases exhausted from the fluidized bed reactor. The hydrogen sulphide burns to sulphur dioxide in the upper part of the fluidized bed reactor or the after-burner. The heat of the flue gases can be utilized in a waste heat boiler 91 from which they flow to gas scrubber 92 and 93.
A portion of the sodium aluminate containing dust ~emoved .
: . , ... . - . : ~ : . :
13 11C)0817 from the ~lst separa-~or 83 i~ p.ls~ed - -through a cooler 94 to a dissolver 9~ to which -~-ater 96 is suppl-ied. ~fter the dissolving step the dif~icultly solu~le co-~unc~s are separated in a sedimentation tank 97 and the sodium alumina-sontaining solution 98 is fed to the gas scrubber 93 in ~-h ch T;he solution is neutralized by sulphur dioxide-containing flue gases. ~, a result of the neutralization the alumina precipitates in the form of hydrate while the sodium salts remain in the sol~tion in the ~orm of Na2S03, NaHS03, Na-T~C03,an~ N.l2C03,dQp~l1cllng on the Na/S-ration and the pH-value.
The alumina hydrate is separated from the dissolved sodium salts in the filter.77. In order to improve the separation, the slurry 99 is first transferred to an aging tank 100 where the alumina hydrate crystallizes, before it is broug~ to the filter. After the separation, theal~mina hydrate is returned to the process through conduit 101 to be mixed into the s~ent liquor. The solution containing sodium salts is removed from the filter through conduit 102 to the digester house.
In Fig. 5, there is shown a system for the r~cover~ o~ chomicals coming from a sulphate pulping process, where sodium and sulphur is recovered mainly in the form of NaO~I and Na2S in solution.
In Fig. ~, a concentrated spent liquor 103 from a sulphate pulping process is convèyed to a mixer 104. To thc mi~er is also fed alumi2la hyd-r~e 105 separated ln a filte2r 106.~rom the mi~er ~he sp~nt liquor ~nd ~he cllemicals mixed i2~0 it are pumped to a ~reread~r 1O7.~Q th~ prereac-tor is also conveyed so~um alwninate-con1;ai~ng ho~t dust 108 removed y a dust separator 109 from the flue gases exhausted from a fluidized generated in the prereactor bed reac~or 110. The pyrolysis gases which contain sulphur, mainly in the form of hydrogen sulphide, are conveyed through conduit 111 to an absorption tower l12 into which also sodium hydroxide-containing solu~
tion from a sedim~ntation tank 113 is conveyed through conduit 114. The hydrogen sulphide is absorbed in the absorption tower, whereby a solu-- -.' , , ~ :
' , ' ', - ~': :
.. ~ .
"'~
, , 11~)(~817 tion, mainl~- conta:inin~r ~;aO~L an~ ~a2S is formed which is supplied to the filter lO~ throuOh collduit 115. ~ portion of the sodium aluminate-containing dust remo~-ed by -the dust separator 109 is brought through conduit 116 to a dissolver 117 to which also water 118 is supplied.
~ter the dissolving step alumina hydrate is separated by precipitation from the formed sodium hydroxide aluminate solution in the sedimenta-tion tank 113 and brought to the filter 1 o6 through conduit 119. ~n the fil-ter ~alumina hy~rate :is removcd to b~returned to the process while the solution containing sodium salts is transferred to the digester house through conduit 120.
In ~ig. .6, there is shown a system for -the thermal decomposition of organic material to obtain raw gases containing carborl monoxide, hydrogen and hydrogen sulphide. The heat-treatment can be carried out in t~e presence of oxygen or without it depending on the desired gasi-fication result and the material to be treated. The method can be appli~d to peat~ carbon and other solid fuels, oil s~nd or shale and various solid waste mcterials.By this method, raw gases can be pro-duced which can be used as such as combustible gases or be processed to synthetic gases fo~ use as raw materi~ :in the chemical industry or reducing gases for metallurgical purposes.
~ ccording to the invention, the gasification process and the com-bustion process are separated from each other for which reason the gasification can be effected at a lower temperature than the combustion .
The temperature of both processes can easily be controlled undepen-dently of each other. The heat required for the gasification is ob-tained mainly indirec-tly from the combustion process, i.e. from the hot dust removed from the flue gases and not, as in prior known methods, directly from the combustion process.
In ~ig. 6 moist material 121 is introduced into a dr-ier-mixer 122 to which also a portion of the ho-~ dus-t removed from the flue gascs :. , ,, . :: , - - -:
' . ' ' ' . ~
'~ ilO(~8~ 1 'by a cyclon 123 is con~-~-v-~ '.,hrough conduit 'i2~l~ In the drier-mixer the ho~ dust and ~he m,~erial to be ~reated are intermi,xed,whereby drying and preheating ~ the material is brought about at a temperature of about 100 C. ~renere~cl vapor~ ~lre discharged from the drier-mixer through conduit 1~ to a dust separator 126 from ~hich separatedsolids are returned rhro~gh condui-t 127 to the drier-mixer. ~ater is condensed from the ~-apors in a condenser 128 and discharged from the bottom par-t of the concenser -through conduit 129 and n~n-condensable gases are discharged from its upper end ~nd p~ssed t]lrou~l the conduit 130 to a ga~ scrubber 131. The dried and preheated material is then transferred to a prereactor 132 to which also the remaining portion of the hot dust removed from the flue gases is delivered. In the pre-reactor the temperature is main~ined at a desired value in the range '~
of ~L00 to 1000 C by controlling the rate of the incoming and dischar-ged quantities. The material is pyrolized in the prereactor and the carbonization residue is introduced through conduit 133 ~nto a fl~di~ed bed reactor 134 where its combustible components are burned under oxi-dizing conditions in a manner known per se. The pyrolysis gases are discharged from the prereactor through conduit 135 to a dust separator 136 and then passed to the gas scrubber 131. Air, steam and other gases can be introdùced into the prereactor through conduit 137. ~ ¦
If the heat value of the material introduced into the fluidized bed reactor is insufficient for maintaining a combustion temperature of between 600 and 1000 C, auxiliary fuel can be supplied to it through conduit 138.
The~invention is further illustrated by some examples:
E,'~M'~L~, 1 Incineration of sewage sludge (~ig. 1 Solids content of'the sludge 20 %
Dust content calculated on the total solids 30 Ss :
'~
'~ . .
.
Calor '' -' Q ',~C hea~ al ~ ~ 1 G ~I~J/~g of total solids Tempe~ a-e o~ Ih~ preheated air 500 C
Dust at a te~.pera ure of 800 C removed from the flue gases l~as mixed into the sludge and supplied to the fluidi~ed bed reactor at a temperaTure of 100 C.
Quantity of,dust mixed into the sludge kg/kg solids content 13,7 Ene~gy requirement KJ/kg~ 1440 -E~c~s air p 30 Quantity of flue gases k~/kg solids oontent 8;75 Composition of the flue gases 2 : oio 4 5 C2 0/g 12,0 2 o~0 72,7 - ~I20 c/~ ,t O, 8 Input energy ..
. - auxiliary energy yO 6,5 - sludge : /g 73,5 - air o~0 20,0 Output energ~
- flue gases from the reactor 70 . 45, 9 - steam .fr~n, th~ prereactor C/Jo 47,7 - dust in the flue gases 70 1,2 - heat losses J~ 5,~
As appears from the example, the combus-tion is almost autogenous ~rhen i-l accordance 1rith t;he L~ ntioTl~atel is removed from the sludge before it is fed to the reactor.
~ `, 2 Treatment of spent liquor from a sodium-based pulping.process and re-covery of sodilllrl in the form of ~azCo3 (~ig. 2) ' ~:
1, 24 ~g/s spellt liquor, ha~i.llg a solids content of about L~5 o/~, was fecl to the mixer to ~'hich O, 2 kg/s alumina ll~clrate was supplied. The alu-mina sperlt liquor mi~ture was i`ed to tlle prereactor to which 5,8 kg/s sodium alumina-te dus-t from the hea-t boi:Ler was added. About 0,53 kg/s water evapora-ted and the dried a:lurmirla spent liquor together with the recycled ash was supplied to the fluidized bed -reactor. The combustion took place at a temperature of about 1000 C. The sodium alumina com-poun~ convertod to sod:ium alumlnate, the main part of lrhich was removed from the fluidized bed reactor with the flue gases.
A portion of the sodium aluminate, i.e. 0,2 kg/s was conveyed to the dissolver where neutralization was effected by the flue gases, whereby a Na2C03-solution was produced. Precipitation of Al(Ofl)3 was brought about in the aging tank, alumina hydrate was then separated in thb filter,and 0,22 kg/s sodium carbonate solution was used for the preparation of digestion liquor. 0,8 kg/s water was supplied to the gas scrubber.
Treatment of spent liquor from a sulphite pulping process and recovery of sodium and sulphur in the form of Na2S03 and Na2C03(Fig. ~) 2L~ kg/s spent liquor, having a solids content of 8 50, was concentrated to a solids content of 36 /0 by a thermo compressor evaporation process and then concentrated to a solids content of 60 ~0 in a flue gas scrubber Into the concentrated spent liquor o,60 kg/s A1203 was mixed, corres-ponding to a mol ratio Na20/A1203 = 1 in the mixture. The mixture was pyrolyzed ln the prereactor at a temperature of about 700 C. The tempe-ra-ture was controlled by varying the quantity of the supplied hot dust removed from the flue gases. Partial cornbustion was brought about by blowing air into the prereactor. The spent liquor whlch contained Na-Al-sal-ts and unconobusted carbon was introduced into a fluidized bed :, , ' - ' :
reactor ihere the ~ l-s~ s were conver-teci into sodilun alwninate at a tempera.-lre a~ove 90~ C. The gases containing sulphur, mainly in the form of H2S, uncollibus~d Oas cornponents such as 1{2 and (~0, inert COill-pollents such as CO~, H~O and N2 were conveyed from the prcreactor to the fluidized bed reaclor or burner. Air and oil were supplied to the fluidized bed reactor. The cornbus-tion in the reactor was mildly reducing and the flue gases had ~he following composition:
2 = 1,3 %, C02 = 16,6 G/o~ N2 = 76 %~ CO = 1,3 ~/0, CH4 = 0~4 %~ H2 = 1,4 %, H2S = 1, 3 /o The after-burner of the flue gases was performed by adding 3,4 kg/s air, whereby H2S was converted into S02. Heat recovery was carried out in a waste heat boiler in which the temperature of the flue gases was redused from 1100 C to 400 C. The flue gases was then passed to a Venturi scrubber to concentrate the spent liquor and then to a second gas scrubber to absorb S02 in an alkaline sodium aluminate solution.
The sodium aluminate solution was formed by dissolving 1 kg/s dust re-moved from the flue gases in 5 kg/s water. When S02 and C02 were ab-sorbed in the water, Al(OH)3 precipitated, which was removed from the solution. The remaining solution, the concentration of which could be controlled by varying the quantity of the washing water supplied to the filter, which in this case was 5 kg/s, contained 1 o6 g/l Na2so3 38 g/l Na2C03 and could be used as such in the digestion liquor. The Al(OH)3 was mixed lnto the concentrated spent liquor.
Treatment of spent liquor from a sulphate pulping process and recovery of chemicals in the form of NaOH and Na2S (Eig. 5).
Into 2,2 kg/s concentrated spent liquor, havin~ a solids content of 1;` ~l~U8~7 65 ~c, 0,9 ~g/s ~((3~)3, contaiil:ing 0,7 kg/s water was mixed . To the m:lxturs was adclec1 du~t in a prereac-tor, havirlg a tempera-twre o~ about 1000 C,removed from the flue gases o~ a fluidi~ed bed reactor, whereby -a pyrolysis was brougnt about at a telrlperaturo be-tween 300 an~ 900 C.
A9 a result of the pyrolysis sulphur in the spent :liquor converted mainly into hydrogen sulphide which was absorbed in a solution contal-ning sodiwll hydroxide and sodiurn aluminate. The socliurn hydroxide alu-mirla~e solution l~as forlned by disso:Lving 0,9 l~g/s sodium alumina-te re-moved from the flue gases in the dust separator ancl the waste hea`t boi-ler. Before the absorption o~ H2S, 0,9 kg/s precipita-ted Al(OH)3 was removed and returned to the process. The remaining solution which con-ta,ned 2,9 mol/s sulphur and 5,7 mol/s soclium, mainly in the form o~
NaOH and Na2S, was used as a digestion liquor.
~ By the methcd according to the invention it is possible to reduce the sulphur in spent liquors under easily controllable conditions befo-re the combustion of the spent liquors. The pulping chemicals are re-covered in such a ~orm that they can be used as such in the digestion liquor. Depending on the pTI-value o~ the removed solution they can also appear in other ~orms as those described in the examples. It has been experimentally vari~ied that the sodium aluminate remaining in the solution has no detrimental ef~ects on the pulping process.
Pyrolysis o~ peat (Fig. 6) 15 g/s peat, having a solids content of 60 %, was dried in a drier-mixer to a solids content o~ about 99 /0. From the drier-mlxer 6 g1s water in the ~orm o~ steam was 1~ithdrawn to -the conclenser. 28 g/s dust removed froul the flue gases, having a temperature o~ ahout 900 C, WQS used for the drying. The dried peat together with the dust was introduced into the prereactor where the pyrolys:is was brought a~out at a temperature of about 700 C by us-ing 26 g/s dust. Steam was used .:
'-' 110(~817 rlS a .~,asirica~lon mcans. Tile cleanod pyrolysis gas contained =
2 = ' 5 '~' C0 = 30 '~o 2 = 4 4 o~/O
CHL~ = 4 S
H~S = 0,14 /0 H20 = 10,4 ~0 Its heat value was 13,1 MJ/m3. The carbonization resi~ue was burned in the fluidized bed reactor at a temperature of about 900 C.
Although the invention has been shown and described in connection with certain speci~ic embodiments, it is not intended to limit the invention to these particular embodiments, but on the contrary, it is intended to cover such alternati~es, modifications and equivalents as may be included within the spirit of the invention. It is, in parti-cular possible to apply the rnethod o~ the invention to spent liquor .
from pulping processes based on Ca or o-ther alkali rnetals.
P.yrolysis has been used for recovery of digestion chemicals from spent liquors, fo:r instance in the SCA-Billerud process, where the sodium s~ts in sodium sulphite spent liquors are conver-ted into sodium carbonate ~nd the sulphur components into hydrogen sulphide. The hydrogen sulphide is conver-ted by combus-tion into sulphur dioxide and absorbed into a sodium carbonate solut-ion. This method is described in the ~innish patQnt 45.518.
It has also been proposed to treat the spent liquor in a rotating furnace. The US-patent 3.787.283 describes a method for recovering che-micals,where a conce~ntratcd spunt liquo~ ~f`r~m a sodiurnbas~c1 pulpng pro-cess is m-lxed ~th reaotive aluulirla hydra~e and formed -~;o solid pe~ets by adding sodium alurninate. T,he pellets are fed into a rotating furnace where a temperature below the fusion temperature of sodium aluminate is maintained. A portion of the resulting sodium aluminate ash is dissolved in water and the solution is reacted with the sulphur dioxi-de-containing flue gases to form a slurry containing sodium sulphite, from which aluminium hydrate is separated. The remaining portion of the sodium aluminate ash is recycled and mixed into the spent liquor.
The operation of a rotating furnace involves several disadvantages.
It is expensive and requires a gl-eat deal of maintainance. Its thermal econorny is unsatisfactory because it is necessary to supply auxiliary fuel for maintaining the 1;~mperaa-tllre r~-quirec1 for ll~c ~e~c t.iOIl.
110~817 The nea; t~alls~er ~om ~tr`~ ~ctS in the f`uxnace to the trea-ted material ~s, as is ~-eil kno~-n, poor The furnace mus-t ther~ore be lar~e-sized.
In order to reduce the dust losses the material has to be ~ormed into pellets, for which r~ason auxiliary apparatures are required b~fore the f`urnace as wcll as after it. As a consequence of the pelletizing the solids contenl ol ~ne material supplied to the furnace must be high,which increases ~ne opera-tion costs.
It has also been p-oposed to incinerate spent liquors in fluidized bed reactors. As an example of an application of -this kind, the US-patent 3.635.790 can be cited. Because the combus-tion temperature has to be lower than the fusing temperature of the che~icals, for instance ~ irn~lly 750 C, ~ en incinorat~ng spen~ liquors containlng sodium the combustion has to be performed within a tempera-ture range where it is difficult to maintain stable combustion. The temperature can be re-duced by feeding to the furnace a liquor which has a low solids content or by cooling the process with a great amount of excess air. In both cases the furnace has to be~arge-sized and is difficult to control.
Gasification of solid organic material has earlier been per~or-INcd, for instance, by a method disclosed in the US-patent 3.840.353, wherein a granulated carbon-containing fuel is introduced into a fluidized bed reactor and solid par-ticles removed from the flue gases are returned to it. The combustion and the gaslfication of the carbon-containing material i9 b~ought about in the same reactor,for which reason it is difficult to control the reactions in a desired manner.
In order to avoid the aforesaid disad~antages, it has been proposed to subject the material to be treated to con~ct with hot material taken l`rolll ttl~ becl of the re~ctor b~fo-re it -ls introclucec-l irltO the flu;d~dled r~lctor. A method of this kind is described ~ the German patent appli-~ ~ .
cation ~5 3~ . O:le o^ the drawbacks of i;he arrangrement is that thehot ~ed ~aterial has ,Q be transI`erred ~rom 1;he reactor and back to it and al~o~ller d~al~b~ e ~he c(~n~-ol l~-r~l)1clrls c-)rlntec~e(l wi1;h i-l; w}len th cluarlt-l-ty ~r i;he moic~;lr? c~te~t ~f ti1~ n~aterial to b~ tr~at~d ~hanges.
Tlle w~ar o~ b~d ~la-terial and ~quiplrle]lt also CallSeS Prcblerns. l3ecau~
thermal energy for e~-a~oration of moisture in the material is taken from the bed, a corres?ondi~g amount of hea-t has to be transferred to it, i~.e. the combustion must take place in the bed which therefore has to be of l~ge volume. T~le supply to the bed must furthermore be distributed among several ducts, which will increase the construc-tion costs:
The exhaust gases from the combustion chamber of a fluidized bed reactor contain fine materia] which can be separated, for instance in a cyclone separator. The fine material contains ash, fine particles from the bed material and usually also usable chemicals. Its heat con-tent is considerable. Depending on the velocity of the air flowing through the fluidized bed reactor, it will function differently. The higher the velocity is, the more of the fluidized bed material is entrained in the uprising fluidizing ~iP and the more fine solids will be exhausted with the flue gases.
SUMMARY OF THE INVENTION
According to the invention, the material to be treated is subjected to contact with fine particles separated from the flue gases exhausted from the fluidized bed reactor, which preferably are mixed into the materlal before it is introduced into the reactor. In this connection also chemical and/or thermal reactions can occur. Useful components can bc recovered from the gases and vapors generated in connection with this treatment by known methods. The fluidized bed reactor is operated in such a way that the velocity of the air flowing through the reactor is between 1 and 10 m/s.
.
~10()`817 In general terms, the present invention can also be defined as a method of treating a material in a fluidized bed reactor of the type wherein the treatment results in generation of a mixture of flue gas and hot particles, said method comprising the steps of: discharging said mixture from said reactor; sub-jecting at least a portion of the discharged mixture to separation to obtain a mainly gaseous fraction and a mainly solid hot particle fraction; feeding said material into a pre-reactor prior to the discharging of same from said pre-reactor into said reactor; feeding at least a part of said solid hot particle fraction for heat treatment of said material in said pre-reactor;
mixing said material within said pre-reactor with said part of said solid hot particle fraction thus causing a heat exchange between the two resulting in vaporization of a part of a liquid contained in said material; removing at least a portion of said vapor from said pre-reactor thereby reducing liquid content of said material; introducing said material into said reactor, whereby thermal energy contained in said mainly solid hot particle fraction is utilized in reducing liquid content in said material prior to the introduction thereof into the reactor.
According to one feature of the present invention, the volume and/or temperature of said part of solid particle fraction is such that thermal decomposition of organic components of the material to be treated is brought about before said mat-erial is introduced into said reactor. According to a still another feature of the present invention, the volume and/or temperature of said part of solid particle fraction is such that gasification of organic components in the material to be treated is brought about before said material is introduced into said reactor. Preferably, the volume and/or temperature of said parts of solid particle fraction is such that chemical reactions in the material to be treated are brought about before said material is - 5a -1~0(~`817 introduced into the reactor. According to another feature of the present invention, a part of the vapor removed from the pre-reactor is introduced into the reactor. In accordance with a yet another feature, aluminate hydrate and at least a portion of the sodium aluminate-containing particles removed from the flue gases coming from a fluidized bed reactor are mixed into a spent liquor from a pulping process based on an alkali compounds before said spent liquor is introduced into said reactor. In accordance with a still further feature of the present invention, alumina hydrate and at least a portion of sodium aluminate-containing particles removed from the flue gases coming from the fluidized bed reactor are mixed into a spent liquor from a pulping process based on alkali and sulphur compounds in order to convert the sulphur content of said spent liquor into hydrogen sulphide which is removed before said spent liquor is introduced into said reactor.
- 5b -The ad~antaf,,es of thc m~thod o,L this invent-ion ir. comparatlon with the fluid:.ze~ bed ~eci~rliqu~ o~' the ~pl:nior art, ar~3 as ~ollows:
The new method requires markedly less energy as ~u~i:L-iary f`n~l for burnill~ we~ sluAges thall tho prior at t`LIl-id-ized becl processes.
l`he volume of the flile gases in the new method is about 50 9~ of the volume of the flue gases in the prior art fluidized bed processes.
Consequently the size of the rluidized bed reactor and the gas cl,eaning equipment will be much smaller.
The mixing conditions in the new method are much bet-ter than in the prior art fluidizcd bed procffsses. Consequently the combustion densi-ty will be higher and the volume needed is smaller.
Due to the smalle~size of the fluidized bed reactor and the more e~ficient mixing, it is easier to ~eed the material to treated into ~he reactor. Especially the ~eeding of peat involves problems and high costs in the prior art fluidized bed processes.
Due to the radiating properties o~ the recycled particles, the combustion is stable also at low temperatures. The stabilizing in-fluence of the recycled particles also aids to this.
Because the moisture in the material to be treated is evapora+,ed before the combustion process, the combustion temperature will in-crease and because o~ the high heat transfe~ p,roperties of the fluidized bed material the heat t,r~nsfer surfaces for steam generation will be smaller.
The pressure losses in the fluidized bed reactor and the required power for the blower are smaller.
The new method makes it possible to use the evaporation heat for heating purposes.
The ~luidized bed reactor in which the new method is adapted is easily controllable.
- ' : ~:
', .
llOU817 It ~s there-lor? a ~eii-r~l object or the present invention to pro~
vide a method f~r t~e~in~ materials in a flui~i~ed bed reactor which avoids th~ above mGntioned disadvantages.
Another o~ct of` the in~-ention is to provide a method for the incine-rating of various alud~es.
A further objec of the invention is to provide a method for trea-ting spent liquors coming from pulping processes in order to recover the pulping chemicals in the spent liquors.
An additional object of the invention is to provide a method for thermal decomposition of or~anic materials in oder to obtain raw gases containing carbon monoxide, hydrogen and hydrogen sulphide.
DESCRIPTION OF 'I`llE DRAI~INGS - --The invention is described in more detail below with reference totho onclosed drawings in which:
FIG. 1 is a flow sheet of the method of the present invention as adapted for the incineration of sludges, FIG. 2 is a flow sheet of the method as applied to spent liquors from a sodium based pulping process,where sodium is reco~ered in the ~orm of Na2C03, FIG. 3 is a flow sheet of the method as applied to spent liquors from sodium-basèd pulping process,wher~ sodium is recovered in the form of NaOII, FIG. 4 is a flow sheet of the method as applied to spent liquors from a sulphlte pulping process, FIG. 5 is a flow sheet of the method as applied to spent liquors from a sulphate pulping process, and FIG. 6 is a flow sheet of the method as adapted for the thermal de-composition of organic material.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In l~'ig. l,there is shown a syste~ ~or l^hc inci~eration of slud~es,ir - 11~)t~817 wnlch rhe n~ eral. 1 ~ fe~ o a fluid:ized ~)ecl r~ cLor colnprising a windbox 2, a con3tric~:io~ plate 3 and a corrlbu.stion chamber l~. ~bove the consLriction pla~e ~-ere is h~t1 mate~ 5-~ icl-~ lu-i~ized and en-traineu by air supplied to i-t through-lhe constriction plate. Air for flu~i~ation and combustion is supplied to the windbo~ through con-duit 6. Auxiliary combus~ion air is supp:Lied to the combustion chamber through conduits 7, 8 and 9. The combustion gases and other gases generated by chemical reactions ~re cxhaustQd from the reactor thro-ugh conduit 10 from which the flue gases flow to a dust separa-tor 11, a preheater for the air 12,and a gas scrubber 13. In case of need auxiliary fuel can be supplied to the reactor through conduit 14. Bed material can be added through conduit 15 into a prc-r~actor 16.
Gas entrained solids are removed from the flue gases in the dust separator and conducted to the prercaotor wh~r~ they ~ro bro-ught into contact with the sludge supplied through conduit 17. The mixer is provided with -two agltator screws which rotate in opposite directions and in this manner bring about an effective mixing of the sludge with the hot particles while conveying it to the end o~ the pr~rcaetor,where-: from it is discharged to the reactor through conduit 18.In the prereactorjpreheating and drying of the sludge is brought about, in which connec-tion vapor is generated, which is passed through conduit 19 to a dust separator 20 and further to a oonde~oer 21.~ondcnsed liqu;d is discha~d -fr~m the lower part of th~ condenser,f`or ~tance to a w~r pu~cation plant,alld ~OI~-eO~lden9able ~a9cs are ~isch~rged frcm :it~ u~p~r part and pa~ed to the rcactor to bc burne~ bb~au~e th~y con-tain mclodorous compo-nent.~. A portiQrl of the ptlrtlcl~ rem~ by the dust scp~rator is dis-charg~d throu~l condlit 22 to control -the qualltity of the recycled mater~L
When the system illustrated in Fig. 1 is used for the gasification of moist organic material, the moist material 17 is supplied to the pre-hea~2r 16 where hot particles separated in the dust separator 11 are .
, ? l l~U817 rni~ed into -it. 1~ater e~-~poIcites and is di~schar~ed ~togcther wi-th possib-le evapora1:ed combusti~le components to the dust separator 20, where dust is separated from the gases. ~`rom -the separator, the gases flow to the condenser 2I kihere -t~le n~ost; -part (~ the stca1ll con~lens(?s. The remaiIling part of the gases is conducted to -the ~luidized bed reactor 1. The dried combustible materi~l and the particles which have been used for heating purposes are introduced into the fluidized bed reac-tor, wh~re the cornbustible material is partly cornbusted and the un-combusted portion 10 is oxh~u~tod ~ inly in gascous ~1~te, -throug;h the cyclono separator 1l t;o the plant wl1ere th~y are u~ed, e ~-.
. a steam boiler. The combustion gases pro-duced in this way have a considerably smaller content of inert gases than they would ha~e had i~ the combustible material had been supplied in a n;oist stato to the :~luidi~d kedbecause the water has been re-moved from the material before the actual gasi~ication is brought about. If the material had been dried directly by hot gases, a part of t1lG combuq~i~le conlponents would have been discharged with the drying gases. The generated combustible gases are thus o~ 1~etter quality and ~urthc~nore produced by simple means.
In ~ig. 2, there is shown a system ~or ~hc reoovery of chemicals from spent liquors coming from a NaOH-based pulping process,where sodium is recovered in the form of a NaC03-con~ining liquid from which a digestion liquor is obtained by causticizing.
In ~ig. 2, the numeral 24 re~ers to a fluidized bed reactor, which is supplied with air for fluidization and combustion through conduit 2~. The spent liquor is introduced through conduit 26into a mixer 27 to which also alumina hydrate separated in the filter 2~ is çorl~eyed, allCl thl~OUgll COlldUit 29, react-;v~ ~l(Oi-r)3 ~s m~e-up chel~l;c~ls. The alumina hydrate reacts partly with the sodium in the spent liquor forming sodium aluminate compounds which through conduit 30 are supp-, 110(~817 lied as a sludg-e h~ u~u- a ~io]ids cont;~nt oI` 30to 70 ~ to a prereacto:r 31. 'rhe hec;-t o,'` .he ~l ~ r,~es disc~ f-red frcr! the u~per ~art of the reac~or is utiliYed for producing steam in a waste heat boiler 32, from which they flow to a gas ccrubber. A portion of the clust in the flue gases, cooled dawrl to 300 ~, stt1es tc the bot-tom of the waste neat boiler, from which it is conducted -through conduit 34 to the prereactor 31,and another portion ~hereof` iH reillO~Cd in ths gas ~rubber.
A portion of the sodium aluminate-containing dust rcmovod f'rom the flue,gascs ln ~ waste heat boiler 32 is delivered to a dissolver 39.
From the dissolver sodium aluminate slurry is fed to -the gas scrub'ber 33 where it reacts with carbon dioxide in the flue gases, which neut-ralize it to a pFI-value of 9, whereby Al(OH)3 precipitates. From the dissolver the slurry is transmitted via an aging tank 41, where alu-mina hydrate crystallizes, to ~1~ fi~r 28 where aluminium hydrate is filtered out from the dissolved sodium salt. The sodium-containing solution is delivered throu~h conduit 42 to the digestion liquor pre-paration plant and the alumina hydrate through conduit 43 to the mixer 27.
In Fig. 3 there is shown a system forthe rccovery cif sodium,'in the form of NaOH-liquldj from spent liquo~ coming from a sodium-basecl pul-ping process.
In Fig. 3, the numeral 44 refers to a fluidized bed reactor wXich is supplied with preheated air through conduit 45. The spent liquor is ~ed through conduit 46 to a mixer 47 into which also alumina hydrate separated in filter 48 and through conduit 49 Al-salts such as Al(OH)3 and Al203 as make-up chemicals are lntroduced. The produced sodium aluminate slurry is conveyed to a prereactor 51 through conduit 50.
Into the prereactor, ~lso a po~tiorl oP the sodium alumlnQte-~onta:ini,ng 11C)(~817 dust r~?m(>~e(! L`rom ~h~ lul gas~s ol` tll~ tl~ ;ed Ije~ roclc-tor -Is -in-tro-cluce(l l1lrollm~ ~-~ndu-i-t ~3. '`~lo ~;rc~s~s gellerQ-tecl i~ 1he ~pror~acto~ are discharged through conduit 54 and steam can be separated from it and removed in form of condensate through conduit 55. The uncondensed gases are led to the reactor through conduit 56 -to be combusted.
'~he clr;ed materi~:L is introduced in-to the reactor through conduit 57. The gases generated in the combustion and other chemical reactions are discharged from the upper part of the reactor through condui-t 58, from which the flue gases flow to a dust~
separator 52, a waste heat boiler 59, and a gas scrubber 60.
A portion~of the sodium aluminate-containing dust removed from the flue gases by the dust separator 52 is conducted to a dissolver 62 to which wate:r is supplied through conduit 61. The for-med slurry is conducted to a sedimentation tank 64 where impurities are separated at a temperature of about 90 C. The impurities are re-moved through conduit 65 andaluminate liquor is fed through conduit 66 to a cooler 67. The numerals 68 and 69 refer to the inlet and outlet conduits for the cooling medium. The aluminate solution cooled to about 50 C is conducted to an aging tank 70 where Al(OH)3 precipitates in accordance with the following principal reactions:
3Na200 Al203~ 6H20 ~ ~ 6NaOH + 2Al(OH)3 Na20- Al203 ~ 4H20 ~- -~ 2NaOH + 2Al(OH)3 The precipitated Al(OH)3 is separated in the filter 48, washed with water from conduit 71 and fed to the mixer 47 through conduit 72. The sodium chemicals are removed through conduit 73 for reuse in the diges-tion liquor.
In ~ig. 4, there is shown a system for tll~? rcÇQ~Tery O.r~ chemicQlS ~rorrl spent liquor coming rom a sulphite pulping process, lvhe~e sodium and sulphur ls recovered in the form of sodium salts such as Na2S03, NaHS03, 1 ~ ~110(~817 Na2C03an~ a~lco3 in so u ion In Fig. 4, t~e num3ral 7'~ re~ers to a mixer into which concentrated spent liquor 75 fro~. a s-~lphit~ pulping process is introduced. To the mixer is conveyed al~min hydrate 76 separated in a filter 77 and dried in a dryer 7~. To the mixer is also deliver(od make-up chemicals 79, if necessary. From the mixer the spent liquor and the chemicals mixed into it are pumped through conduit 80 to a prereactor 81. To ihe prereactor is also conveyed sodium removed by a dust separator 83 from the flue gases corning from a fluidized bed reactor 8L~. In the pre-reactor pyrelysis of the spent liquor takes place whereby gases and steam are gencra~-ed.Air 85 can also be supplied to it, in which case partial combustion take~ place, The gases which contain the main part of the sulphur contained in the spent liquor, mostly in the form of hydrogen sulphide, and the steam are removed from the prereactor through conduit 86, and the solid components are introduced into the fluidized bed reactor through conduit 87. The gases and the steam generated in the prereactor and the air introduced into it bring about an effective intermixing of the spent liquor and the hot dust which can be intensi-fied by mechanical means. The temperature in the prereactor is maintai ned at between 200 and 900 C and preferably at about 700 C. The gases from the prereactor are alternatively passed through conduit 88 to the fluidized bed reactor or through conduit 89 to an after-burner 90 where they meet the flue gases exhausted from the fluidized bed reactor. The hydrogen sulphide burns to sulphur dioxide in the upper part of the fluidized bed reactor or the after-burner. The heat of the flue gases can be utilized in a waste heat boiler 91 from which they flow to gas scrubber 92 and 93.
A portion of the sodium aluminate containing dust ~emoved .
: . , ... . - . : ~ : . :
13 11C)0817 from the ~lst separa-~or 83 i~ p.ls~ed - -through a cooler 94 to a dissolver 9~ to which -~-ater 96 is suppl-ied. ~fter the dissolving step the dif~icultly solu~le co-~unc~s are separated in a sedimentation tank 97 and the sodium alumina-sontaining solution 98 is fed to the gas scrubber 93 in ~-h ch T;he solution is neutralized by sulphur dioxide-containing flue gases. ~, a result of the neutralization the alumina precipitates in the form of hydrate while the sodium salts remain in the sol~tion in the ~orm of Na2S03, NaHS03, Na-T~C03,an~ N.l2C03,dQp~l1cllng on the Na/S-ration and the pH-value.
The alumina hydrate is separated from the dissolved sodium salts in the filter.77. In order to improve the separation, the slurry 99 is first transferred to an aging tank 100 where the alumina hydrate crystallizes, before it is broug~ to the filter. After the separation, theal~mina hydrate is returned to the process through conduit 101 to be mixed into the s~ent liquor. The solution containing sodium salts is removed from the filter through conduit 102 to the digester house.
In Fig. 5, there is shown a system for the r~cover~ o~ chomicals coming from a sulphate pulping process, where sodium and sulphur is recovered mainly in the form of NaO~I and Na2S in solution.
In Fig. ~, a concentrated spent liquor 103 from a sulphate pulping process is convèyed to a mixer 104. To thc mi~er is also fed alumi2la hyd-r~e 105 separated ln a filte2r 106.~rom the mi~er ~he sp~nt liquor ~nd ~he cllemicals mixed i2~0 it are pumped to a ~reread~r 1O7.~Q th~ prereac-tor is also conveyed so~um alwninate-con1;ai~ng ho~t dust 108 removed y a dust separator 109 from the flue gases exhausted from a fluidized generated in the prereactor bed reac~or 110. The pyrolysis gases which contain sulphur, mainly in the form of hydrogen sulphide, are conveyed through conduit 111 to an absorption tower l12 into which also sodium hydroxide-containing solu~
tion from a sedim~ntation tank 113 is conveyed through conduit 114. The hydrogen sulphide is absorbed in the absorption tower, whereby a solu-- -.' , , ~ :
' , ' ', - ~': :
.. ~ .
"'~
, , 11~)(~817 tion, mainl~- conta:inin~r ~;aO~L an~ ~a2S is formed which is supplied to the filter lO~ throuOh collduit 115. ~ portion of the sodium aluminate-containing dust remo~-ed by -the dust separator 109 is brought through conduit 116 to a dissolver 117 to which also water 118 is supplied.
~ter the dissolving step alumina hydrate is separated by precipitation from the formed sodium hydroxide aluminate solution in the sedimenta-tion tank 113 and brought to the filter 1 o6 through conduit 119. ~n the fil-ter ~alumina hy~rate :is removcd to b~returned to the process while the solution containing sodium salts is transferred to the digester house through conduit 120.
In ~ig. .6, there is shown a system for -the thermal decomposition of organic material to obtain raw gases containing carborl monoxide, hydrogen and hydrogen sulphide. The heat-treatment can be carried out in t~e presence of oxygen or without it depending on the desired gasi-fication result and the material to be treated. The method can be appli~d to peat~ carbon and other solid fuels, oil s~nd or shale and various solid waste mcterials.By this method, raw gases can be pro-duced which can be used as such as combustible gases or be processed to synthetic gases fo~ use as raw materi~ :in the chemical industry or reducing gases for metallurgical purposes.
~ ccording to the invention, the gasification process and the com-bustion process are separated from each other for which reason the gasification can be effected at a lower temperature than the combustion .
The temperature of both processes can easily be controlled undepen-dently of each other. The heat required for the gasification is ob-tained mainly indirec-tly from the combustion process, i.e. from the hot dust removed from the flue gases and not, as in prior known methods, directly from the combustion process.
In ~ig. 6 moist material 121 is introduced into a dr-ier-mixer 122 to which also a portion of the ho-~ dus-t removed from the flue gascs :. , ,, . :: , - - -:
' . ' ' ' . ~
'~ ilO(~8~ 1 'by a cyclon 123 is con~-~-v-~ '.,hrough conduit 'i2~l~ In the drier-mixer the ho~ dust and ~he m,~erial to be ~reated are intermi,xed,whereby drying and preheating ~ the material is brought about at a temperature of about 100 C. ~renere~cl vapor~ ~lre discharged from the drier-mixer through conduit 1~ to a dust separator 126 from ~hich separatedsolids are returned rhro~gh condui-t 127 to the drier-mixer. ~ater is condensed from the ~-apors in a condenser 128 and discharged from the bottom par-t of the concenser -through conduit 129 and n~n-condensable gases are discharged from its upper end ~nd p~ssed t]lrou~l the conduit 130 to a ga~ scrubber 131. The dried and preheated material is then transferred to a prereactor 132 to which also the remaining portion of the hot dust removed from the flue gases is delivered. In the pre-reactor the temperature is main~ined at a desired value in the range '~
of ~L00 to 1000 C by controlling the rate of the incoming and dischar-ged quantities. The material is pyrolized in the prereactor and the carbonization residue is introduced through conduit 133 ~nto a fl~di~ed bed reactor 134 where its combustible components are burned under oxi-dizing conditions in a manner known per se. The pyrolysis gases are discharged from the prereactor through conduit 135 to a dust separator 136 and then passed to the gas scrubber 131. Air, steam and other gases can be introdùced into the prereactor through conduit 137. ~ ¦
If the heat value of the material introduced into the fluidized bed reactor is insufficient for maintaining a combustion temperature of between 600 and 1000 C, auxiliary fuel can be supplied to it through conduit 138.
The~invention is further illustrated by some examples:
E,'~M'~L~, 1 Incineration of sewage sludge (~ig. 1 Solids content of'the sludge 20 %
Dust content calculated on the total solids 30 Ss :
'~
'~ . .
.
Calor '' -' Q ',~C hea~ al ~ ~ 1 G ~I~J/~g of total solids Tempe~ a-e o~ Ih~ preheated air 500 C
Dust at a te~.pera ure of 800 C removed from the flue gases l~as mixed into the sludge and supplied to the fluidi~ed bed reactor at a temperaTure of 100 C.
Quantity of,dust mixed into the sludge kg/kg solids content 13,7 Ene~gy requirement KJ/kg~ 1440 -E~c~s air p 30 Quantity of flue gases k~/kg solids oontent 8;75 Composition of the flue gases 2 : oio 4 5 C2 0/g 12,0 2 o~0 72,7 - ~I20 c/~ ,t O, 8 Input energy ..
. - auxiliary energy yO 6,5 - sludge : /g 73,5 - air o~0 20,0 Output energ~
- flue gases from the reactor 70 . 45, 9 - steam .fr~n, th~ prereactor C/Jo 47,7 - dust in the flue gases 70 1,2 - heat losses J~ 5,~
As appears from the example, the combus-tion is almost autogenous ~rhen i-l accordance 1rith t;he L~ ntioTl~atel is removed from the sludge before it is fed to the reactor.
~ `, 2 Treatment of spent liquor from a sodium-based pulping.process and re-covery of sodilllrl in the form of ~azCo3 (~ig. 2) ' ~:
1, 24 ~g/s spellt liquor, ha~i.llg a solids content of about L~5 o/~, was fecl to the mixer to ~'hich O, 2 kg/s alumina ll~clrate was supplied. The alu-mina sperlt liquor mi~ture was i`ed to tlle prereactor to which 5,8 kg/s sodium alumina-te dus-t from the hea-t boi:Ler was added. About 0,53 kg/s water evapora-ted and the dried a:lurmirla spent liquor together with the recycled ash was supplied to the fluidized bed -reactor. The combustion took place at a temperature of about 1000 C. The sodium alumina com-poun~ convertod to sod:ium alumlnate, the main part of lrhich was removed from the fluidized bed reactor with the flue gases.
A portion of the sodium aluminate, i.e. 0,2 kg/s was conveyed to the dissolver where neutralization was effected by the flue gases, whereby a Na2C03-solution was produced. Precipitation of Al(Ofl)3 was brought about in the aging tank, alumina hydrate was then separated in thb filter,and 0,22 kg/s sodium carbonate solution was used for the preparation of digestion liquor. 0,8 kg/s water was supplied to the gas scrubber.
Treatment of spent liquor from a sulphite pulping process and recovery of sodium and sulphur in the form of Na2S03 and Na2C03(Fig. ~) 2L~ kg/s spent liquor, having a solids content of 8 50, was concentrated to a solids content of 36 /0 by a thermo compressor evaporation process and then concentrated to a solids content of 60 ~0 in a flue gas scrubber Into the concentrated spent liquor o,60 kg/s A1203 was mixed, corres-ponding to a mol ratio Na20/A1203 = 1 in the mixture. The mixture was pyrolyzed ln the prereactor at a temperature of about 700 C. The tempe-ra-ture was controlled by varying the quantity of the supplied hot dust removed from the flue gases. Partial cornbustion was brought about by blowing air into the prereactor. The spent liquor whlch contained Na-Al-sal-ts and unconobusted carbon was introduced into a fluidized bed :, , ' - ' :
reactor ihere the ~ l-s~ s were conver-teci into sodilun alwninate at a tempera.-lre a~ove 90~ C. The gases containing sulphur, mainly in the form of H2S, uncollibus~d Oas cornponents such as 1{2 and (~0, inert COill-pollents such as CO~, H~O and N2 were conveyed from the prcreactor to the fluidized bed reaclor or burner. Air and oil were supplied to the fluidized bed reactor. The cornbus-tion in the reactor was mildly reducing and the flue gases had ~he following composition:
2 = 1,3 %, C02 = 16,6 G/o~ N2 = 76 %~ CO = 1,3 ~/0, CH4 = 0~4 %~ H2 = 1,4 %, H2S = 1, 3 /o The after-burner of the flue gases was performed by adding 3,4 kg/s air, whereby H2S was converted into S02. Heat recovery was carried out in a waste heat boiler in which the temperature of the flue gases was redused from 1100 C to 400 C. The flue gases was then passed to a Venturi scrubber to concentrate the spent liquor and then to a second gas scrubber to absorb S02 in an alkaline sodium aluminate solution.
The sodium aluminate solution was formed by dissolving 1 kg/s dust re-moved from the flue gases in 5 kg/s water. When S02 and C02 were ab-sorbed in the water, Al(OH)3 precipitated, which was removed from the solution. The remaining solution, the concentration of which could be controlled by varying the quantity of the washing water supplied to the filter, which in this case was 5 kg/s, contained 1 o6 g/l Na2so3 38 g/l Na2C03 and could be used as such in the digestion liquor. The Al(OH)3 was mixed lnto the concentrated spent liquor.
Treatment of spent liquor from a sulphate pulping process and recovery of chemicals in the form of NaOH and Na2S (Eig. 5).
Into 2,2 kg/s concentrated spent liquor, havin~ a solids content of 1;` ~l~U8~7 65 ~c, 0,9 ~g/s ~((3~)3, contaiil:ing 0,7 kg/s water was mixed . To the m:lxturs was adclec1 du~t in a prereac-tor, havirlg a tempera-twre o~ about 1000 C,removed from the flue gases o~ a fluidi~ed bed reactor, whereby -a pyrolysis was brougnt about at a telrlperaturo be-tween 300 an~ 900 C.
A9 a result of the pyrolysis sulphur in the spent :liquor converted mainly into hydrogen sulphide which was absorbed in a solution contal-ning sodiwll hydroxide and sodiurn aluminate. The socliurn hydroxide alu-mirla~e solution l~as forlned by disso:Lving 0,9 l~g/s sodium alumina-te re-moved from the flue gases in the dust separator ancl the waste hea`t boi-ler. Before the absorption o~ H2S, 0,9 kg/s precipita-ted Al(OH)3 was removed and returned to the process. The remaining solution which con-ta,ned 2,9 mol/s sulphur and 5,7 mol/s soclium, mainly in the form o~
NaOH and Na2S, was used as a digestion liquor.
~ By the methcd according to the invention it is possible to reduce the sulphur in spent liquors under easily controllable conditions befo-re the combustion of the spent liquors. The pulping chemicals are re-covered in such a ~orm that they can be used as such in the digestion liquor. Depending on the pTI-value o~ the removed solution they can also appear in other ~orms as those described in the examples. It has been experimentally vari~ied that the sodium aluminate remaining in the solution has no detrimental ef~ects on the pulping process.
Pyrolysis o~ peat (Fig. 6) 15 g/s peat, having a solids content of 60 %, was dried in a drier-mixer to a solids content o~ about 99 /0. From the drier-mlxer 6 g1s water in the ~orm o~ steam was 1~ithdrawn to -the conclenser. 28 g/s dust removed froul the flue gases, having a temperature o~ ahout 900 C, WQS used for the drying. The dried peat together with the dust was introduced into the prereactor where the pyrolys:is was brought a~out at a temperature of about 700 C by us-ing 26 g/s dust. Steam was used .:
'-' 110(~817 rlS a .~,asirica~lon mcans. Tile cleanod pyrolysis gas contained =
2 = ' 5 '~' C0 = 30 '~o 2 = 4 4 o~/O
CHL~ = 4 S
H~S = 0,14 /0 H20 = 10,4 ~0 Its heat value was 13,1 MJ/m3. The carbonization resi~ue was burned in the fluidized bed reactor at a temperature of about 900 C.
Although the invention has been shown and described in connection with certain speci~ic embodiments, it is not intended to limit the invention to these particular embodiments, but on the contrary, it is intended to cover such alternati~es, modifications and equivalents as may be included within the spirit of the invention. It is, in parti-cular possible to apply the rnethod o~ the invention to spent liquor .
from pulping processes based on Ca or o-ther alkali rnetals.
Claims (14)
1. A method of treating a material in a fluidized bed reactor of the type wherein the treatment results in generation of a mixture of flue gas and hot particles, said method comprising the steps of:
(a) discharging said mixture from said reactor;
(b) subjecting at least a portion of the discharged mixture to separation to obtain a mainly gaseous fraction and a mainly solid hot particle fraction;
(c) feeding said material into a pre-reactor prior to the discharging of same from said pre-reactor into said reactor;
(d) feeding at least a part of said solid hot particle fraction for heat treatment of said material in said pre-reactor;
(e) mixing said material within said pre-reactor with said part of said solid hot particle fraction thus causing a heat exchange between the two resulting in vaporization of a part of a liquid contained in said material;
(f) removing at least a portion of said vapor from said pre-reactor thereby reducing liquid content of said material;
(g) introducing said material into said reactor, whereby thermal energy contained in said mainly solid hot particle fraction is utilized in reducing liquid content in said material prior to the introduction thereof into the reactor.
(a) discharging said mixture from said reactor;
(b) subjecting at least a portion of the discharged mixture to separation to obtain a mainly gaseous fraction and a mainly solid hot particle fraction;
(c) feeding said material into a pre-reactor prior to the discharging of same from said pre-reactor into said reactor;
(d) feeding at least a part of said solid hot particle fraction for heat treatment of said material in said pre-reactor;
(e) mixing said material within said pre-reactor with said part of said solid hot particle fraction thus causing a heat exchange between the two resulting in vaporization of a part of a liquid contained in said material;
(f) removing at least a portion of said vapor from said pre-reactor thereby reducing liquid content of said material;
(g) introducing said material into said reactor, whereby thermal energy contained in said mainly solid hot particle fraction is utilized in reducing liquid content in said material prior to the introduction thereof into the reactor.
2. A method according to claim 1, wherein the volume and/or temperature of said part of solid particle fraction is such that thermal decomposition of organic components of the material to be treated is brought about before said material in introduced into said reactor.
3. A method according to claim 1, wherein the volume and/or temperature of said part of solid particle fraction is such that gasification of organic components in the material to be treated is brought about before said material is introduced into said reactor.
4. A method according to claim 3, wherein the material to be treated is preheated and at least partially dried by a portion of said hot particle fraction and then brought into contact with another portion of said hot particle fraction for the gasification of the organic components in said material.
5. A method according to claim 1, wherein the volume and/or temperature of said parts of solid particle fraction is such that chemical reactions in the material to be treated are brought about before said material is introduced into the reactor.
6. A method according to claim 1, wherein at least a part of the vapor removed from the pre-reactor is introduced into said reactor.
7. A method according to claim 1, wherein aluminate hydrate and at least a portion of the sodium aluminate-containing particles removed from the flue gases coming from a fluidized bed reactor are mixed into a spent liquor from a pulping process based on an alkali compounds before said spent liquor is introduced into said reactor.
8. A method according to claim 7, wherein another portion of said particles is dissolved in water, whereafter alumina hydrate is separated by precipitation from the produced solution and removed, whereby a digestion liquor containing NaOH is obtained.
9. A method according to claim 7, wherein another portion of said particles is dissolved in water, whereafter the produced solution is neutralized with carbon dioxide by contacting it with the flue gases in order to form alumina hydrate which is removed, whereby a liquor containing Na2CO3 is obtained.
10. A method according to claim 1, wherein alumina hydrate and at least a portion of sodium aluminate-containing particles removed from the flue gases coming from the fluidized bed reactor are mixed into a spent liquor from a pulping process based on alkali and sulphur compounds in order to convert the sulphur content of said spent liquor into hydro-gen sulphide which is removed before said spent liquor is introduced into said reactor.
11. A method according to claim 10, wherein the material to be treated is a spent liquor from a sulphite pulping process and the formed hydrogen sulfide is converted by combustion into sulphur dioxide which is absorbed in a solution containing sodium aluminate removed from the flue gases in order to form alumina hydrate.
12. A method according to claim 11, wherein said alumina hydrate is removed from the solution, whereby a sodium sulphite digestion liquor is obtained.
13. A method according to claim 10, wherein the material to be treated is a spent liquor from a sulphide pulping process and the formed hydrogen sulphide is absorbed in a solution containing sodium aluminate removed from the flue gases and sodium hydroxide in order to form alumina hydrate.
14. A method according to claim 13, wherein said aluminate hydrate is removed from the solution, whereby a sodium sulphate digestion liquor is obtained.
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI762695 | 1976-09-22 | ||
| FI762695A FI54160C (en) | 1976-09-22 | 1976-09-22 | FOERFARANDE FOER BEHANDLING AV MATERIAL I EN VIRVELBAEDDREAKTOR |
| FI770546 | 1977-02-21 | ||
| FI770546A FI62562C (en) | 1977-02-21 | 1977-02-21 | FOERFARANDE FOER BEHANDLING AV MATERIAL I EN VIRVELBAEDDREAKTOR |
| FI771247A FI60736C (en) | 1977-04-20 | 1977-04-20 | FOERFARANDE FOER BEHANDLING AV MATERIAL I EN VIRVELBAEDDSREAKTOR |
| FI771247 | 1977-04-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1100817A true CA1100817A (en) | 1981-05-12 |
Family
ID=27240976
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA284,402A Expired CA1100817A (en) | 1976-09-22 | 1977-08-10 | Method of treating material in a fluidized bed reactor |
Country Status (9)
| Country | Link |
|---|---|
| US (1) | US4311670A (en) |
| JP (1) | JPS5339670A (en) |
| AU (1) | AU512867B2 (en) |
| CA (1) | CA1100817A (en) |
| DE (2) | DE2759933C3 (en) |
| FR (1) | FR2365754A1 (en) |
| GB (1) | GB1561237A (en) |
| NO (2) | NO147529C (en) |
| SE (2) | SE430000B (en) |
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|---|---|---|---|---|
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| US8518219B2 (en) | 2008-01-02 | 2013-08-27 | Metal Tech Ltd. | Process for the treatment of organic waste and product obtained thereof |
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| GB2129010B (en) * | 1982-10-21 | 1987-03-04 | Shell Int Research | Combustion of coke present on solid particles |
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| US4597774A (en) * | 1984-10-22 | 1986-07-01 | Foster Wheeler Energy Corporation | Method for improving the operation of a fluidized bed |
| SE8405982L (en) * | 1984-11-27 | 1986-05-28 | Hans Theliander | WAY TO DRY PARTICULAR MATERIAL |
| FI75505C (en) * | 1985-01-11 | 1988-07-11 | Ahlstroem Oy | FARING MATERIALS FOR FISHING MATERIALS FROM FAST MATERIAL TO A FREON AND REACTOR WITH A CIRCULAR BEDD. |
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| US2503788A (en) * | 1945-11-29 | 1950-04-11 | Dorr Co | Reactor furnace |
| US2650084A (en) * | 1946-06-28 | 1953-08-25 | Dorr Co | Calcining lime bearing sludges |
| US2750276A (en) * | 1952-01-04 | 1956-06-12 | Armco Steel Corp | Method and apparatus for smelting fine iron ore |
| US3319586A (en) * | 1961-07-10 | 1967-05-16 | Dorr Oliver Inc | Treatment and disposal of waste sludges |
| US3309262A (en) * | 1963-12-03 | 1967-03-14 | Container Corp | Fluidized bed oxidation of waste liquors resulting from the digestion of cellulosic materials for paper making |
| US3635790A (en) * | 1969-07-02 | 1972-01-18 | Dorr Oliver Inc | Process for the thermal oxidation of spent liquor |
| US3787283A (en) * | 1972-03-28 | 1974-01-22 | Sonoco Products Co | Treatment of waste liquor from pulp production |
| JPS5135467B2 (en) * | 1972-12-14 | 1976-10-02 | ||
| JPS55439B2 (en) * | 1973-08-18 | 1980-01-08 | ||
| US4104129A (en) * | 1973-10-26 | 1978-08-01 | United States Steel Corporation | Low temperature carbonization and desulfurization of coal under elevated pressures |
| US4002535A (en) * | 1974-12-27 | 1977-01-11 | Union Carbide Corporation | Preconditioning treatment of coal to minimize agglomeration |
-
1977
- 1977-07-13 GB GB29339/77A patent/GB1561237A/en not_active Expired
- 1977-07-18 AU AU27092/77A patent/AU512867B2/en not_active Expired
- 1977-08-10 CA CA284,402A patent/CA1100817A/en not_active Expired
- 1977-08-19 SE SE7709375A patent/SE430000B/en not_active IP Right Cessation
- 1977-09-02 FR FR7726663A patent/FR2365754A1/en active Granted
- 1977-09-14 DE DE2759933A patent/DE2759933C3/en not_active Expired
- 1977-09-14 DE DE2741285A patent/DE2741285C3/en not_active Expired
- 1977-09-21 NO NO773236A patent/NO147529C/en unknown
- 1977-09-22 JP JP11343577A patent/JPS5339670A/en active Pending
-
1980
- 1980-01-04 US US06/109,604 patent/US4311670A/en not_active Expired - Lifetime
-
1982
- 1982-01-19 NO NO82820155A patent/NO161451C/en unknown
- 1982-12-08 SE SE8207014A patent/SE462398B/en not_active IP Right Cessation
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4781796A (en) * | 1983-09-13 | 1988-11-01 | Canadian Patents And Development Limited | Apparatus for the conversion of sludges |
| US8518219B2 (en) | 2008-01-02 | 2013-08-27 | Metal Tech Ltd. | Process for the treatment of organic waste and product obtained thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| NO147529C (en) | 1983-04-27 |
| NO161451B (en) | 1989-05-08 |
| DE2741285B2 (en) | 1979-09-27 |
| SE8207014L (en) | 1982-12-08 |
| AU2709277A (en) | 1979-01-25 |
| SE430000B (en) | 1983-10-10 |
| DE2741285A1 (en) | 1978-03-30 |
| DE2759933C3 (en) | 1986-01-02 |
| AU512867B2 (en) | 1980-10-30 |
| DE2741285C3 (en) | 1983-04-21 |
| SE8207014D0 (en) | 1982-12-08 |
| JPS5339670A (en) | 1978-04-11 |
| FR2365754B1 (en) | 1981-06-26 |
| SE7709375L (en) | 1978-03-23 |
| US4311670A (en) | 1982-01-19 |
| NO161451C (en) | 1989-08-16 |
| FR2365754A1 (en) | 1978-04-21 |
| SE462398B (en) | 1990-06-18 |
| NO820155L (en) | 1978-03-28 |
| GB1561237A (en) | 1980-02-13 |
| NO773236L (en) | 1978-03-28 |
| NO147529B (en) | 1983-01-17 |
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