SE453408B

SE453408B - Sulphate cellulose process

Info

Publication number: SE453408B
Application number: SE8402753A
Authority: SE
Inventors: Punya B Chaudhuri
Original assignee: Punya B Chaudhuri
Priority date: 1984-05-22
Filing date: 1984-05-22
Publication date: 1988-02-01
Also published as: SE8402753D0; SE8402753L

Abstract

Lignin and other organic substances are precipitated in a carbonising tower. Black lye enters the tower at the top and passes downwards. Carbon dioxide from flue gases (e.g. from the lime sludge furnace) enters the tower further down and flows upwards to meet the black lye. Both the tower and flue gas are at 65-80 deg. C. The pH of the liquid having the tower is measured and adjusted to be 8.7-9.6 by controlling the supply of lye and carbon dioxide to the tower.

Description

15 20 25 30 35 453 408 svaveldioxid till atmosfären, bidrar till försurning av marker och vattendrag genom sur nederbörd. Alternativt kan detta extra svavel fångas upp i utrustningar för avgasrening men utgör i alla händelser ett extra hanteringsproblem. 15 20 25 30 35 453 408 sulfur dioxide to the atmosphere, contributes to acidification of soils and watercourses through acid rain. Alternatively, this extra sulfur can be captured in exhaust gas purification equipment but in any case constitutes an extra handling problem.

Rßnocönttse sön UPPFINNINGEN Ändamålet med uppfinningen är att ytterligare förbättra sulfat- cellulosaprocessen genom att helt eller delvis ersätta eldningsoljan vid mesabränningen med organiska substanser i svartluten. Uppfinningen kännetecknas härvid av att den lösta organiska substansen i svart- luten, främst lignin, fälls med hjälp av koldioxid genom att svart- luten, företrädesvis efter viss indunstning och avskumning av såpa, inleds i övre delen av ett första torn som utgörs av ett karbonise- ringstorn, att svartluten bringas att falla nedåt i detta första torn för att möta koldioxid som inleds längre ned och som strömmar uppåt i tornet, att svavelväte som bildas i det första tornet avleds till ett andra torn i vilket svavelvätet absorberas genom att detta andra torn genomströmmas med vitlut, att svartlut och den utfällda organiska sub- stansen leds från det första tornet till en separeringsenhet, i vilken fällningen avskiljs, att den avskilda organiska substansen urvattnas och homogeniseras till en suspension, och att denna suspension används och bränns som flytande bränsle i mesaugnen/-ugnarna. Ytterligare kännetecken och aspekter på uppfinningen framgår av patentkraven samt av följande beskrivning av en föredragen utföringsform.THE INVENTION The object of the invention is to further improve the sulphate cellulose process by completely or partially replacing the fuel oil in the mesa firing with organic substances in the black liquor. The invention is characterized in this case that the dissolved organic substance in the black liquor, mainly lignin, is precipitated by means of carbon dioxide by the black liquor, preferably after some evaporation and skimming of soap, being introduced into the upper part of a first tower which consists of a carbonise ring tower, that the black liquor is caused to fall downwards in this first tower to meet carbon dioxide which starts further down and which flows upwards in the tower, that hydrogen sulphide formed in the first tower is diverted to a second tower in which the hydrogen sulphide is absorbed by this second tower through white liquor, that black liquor and the precipitated organic substance are passed from the first tower to a separation unit, in which the precipitate is separated, that the separated organic substance is diluted and homogenized to a suspension, and that this suspension is used and burned as liquid fuel in mesaugnen / -ugnarna. Further features and aspects of the invention appear from the claims and from the following description of a preferred embodiment.

BESKRIVNING AV FÖREDRAGEN UTFÖRINGSFORM En utföringsform av sättet enligt uppfinningen skall i det följande beskrivas med hänvisning till ritningsfiguren, som i form av ett diagram visar flödesvägarna och apparaturen. Från en behållare 1 leds svartluten från kokningsprocessen med hjälp av en pump 2 och en led- ning 3 till en indunstare 4. I indunstaren 4 ökas torrhalten till cirka 22 à 23 2 och pumpas sedan via en ledning 5 till ett kar 6.DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the method according to the invention will be described in the following with reference to the drawing figure, which in the form of a diagram shows the flow paths and the apparatus. From a container 1, the black liquor from the boiling process is led by means of a pump 2 and a line 3 to an evaporator 4. In the evaporator 4, the dry content is increased to about 22 to 23 2 and then pumped via a line 5 to a vessel 6.

Huvuddelen av svartluten pumpas därefter med hjälp av en pump 7 via en ledning 8, eventuellt efter avskumning av såpa, till en andra induns- tare 9 och därifrån till sodapannan. 10 15 25 30 35 453 408 En delström av svartluten från karet 6 pumpas emellertid via en ledning 10 och en ventil 11 till toppen av ett karboniseringstorn 12.The main part of the black liquor is then pumped by means of a pump 7 via a line 8, possibly after skimming of soap, to a second evaporator 9 and from there to the recovery boiler. However, a partial stream of the black liquor from the vessel 6 is pumped via a line 10 and a valve 11 to the top of a carbonization tower 12.

En lämplig temperatur på svartluten som inleds i tornet 12 är 65-80°C.A suitable temperature for the black liquor which begins in the tower 12 is 65-80 ° C.

I samma torn 12 inleds även rökgas från en mesaugn på en nivå som räknat från bottnen ungefär motsvarar en tredjedel av tornets höjd.In the same tower 12, flue gas is also started from a lime kiln at a level which, from the bottom, corresponds approximately to one third of the height of the tower.

Rökgasen bör ha en temperatur inom samma temperaturomrâde som svart- luten, det vill säga 65-80°C, lämpligen ca 70°C. Rökgasen innehåller cirka 20 % koldioxid. Inloppsledningen för rökgas har betecknats 13 och en ventil i denna ledning har betecknats 14. Rökgasen strömmar upp genom tornet 12 och möter den långsamt nedåtfallande svartluten.The flue gas should have a temperature within the same temperature range as the black liquor, ie 65-80 ° C, preferably about 70 ° C. The flue gas contains about 20% carbon dioxide. The flue gas inlet line has been designated 13 and a valve in this line has been designated 14. The flue gas flows up through the tower 12 and meets the slowly descending black liquor.

Tornet 12 är konstruerat som ett fyllkroppstorn med vätskespridare för svartluten och gasspridare för rökgasen.The tower 12 is designed as a filler tower with a liquid spreader for the black liquor and a gas spreader for the flue gas.

Koldioxiden reagerar med svartluten i tornet 12, varvid lösta orga- niska substanser i svartluten, främst lignin, fälls ut. Svartluten jämte utfällt lignin ansamlas efter hand i bottnen på tornet 12.The carbon dioxide reacts with the black liquor in tower 12, whereby dissolved organic substances in the black liquor, mainly lignin, precipitate. The black liquor and precipitated lignin gradually accumulate in the bottom of the tower 12.

Vid reaktionen mellan svartluten och koldioxíden i tornet 12 bildas även svavelväte som frigörs. För att avdriva detta svavelväte inleds ånga i tornets bottendel, vilken arbetar som en strippingkolonn för avdrivning av bundet och löst svavelväte genom ånga. Denna del av tornet 12 har betecknats 15, och àngledningen har betecknats 16. De svavelvätehaltiga gaserna avleds på tornets 12 topp genom en ledning 17 till ett separat torn 18, som genomströmmas av vitlut, som reabsorberar svavelvätet, varefter luten recirkuleras till kokeriet.During the reaction between the black liquor and the carbon dioxide in the tower 12, hydrogen sulphide is also formed which is released. To evaporate this hydrogen sulphide, steam is introduced into the bottom part of the tower, which acts as a stripping column for the evaporation of bound and dissolved hydrogen sulphide through steam. This part of the tower 12 has been designated 15, and the steam line has been designated 16. The hydrogen sulfide-containing gases are diverted at the top of the tower 12 through a line 17 to a separate tower 18, which is passed through white liquor, which reabsorbs the hydrogen sulfide, after which the liquor is recycled to the boiler.

Svartluten jämte utfällt lignin utmatas från tornets 12 bottendel genom en ledning 20. pH-värdet i vätskan som utmatas genom ledningen 20 kontrolleras genom en pH-mätare 21, som via manöverledningar 22 och 23 styr ventilerna 11 och 14 för reglering av lut- och koldioxidin- taget, så att önskat pH upprätthålls i processen. Ett lämpligt pH i avgående vätska från tornet bör ligga mellan 8.7 och 9.6.The black liquor together with precipitated lignin is discharged from the bottom part of the tower 12 through a line 20. The pH value in the liquid discharged through the line 20 is controlled by a pH meter 21, which controls the valves 11 and 14 for regulating the liquor and carbon dioxide via control lines 22 and 23 taken, so that the desired pH is maintained in the process. A suitable pH in liquid leaving the tower should be between 8.7 and 9.6.

Med hjälp av en pump 24 pumpas svartluten jämte det utfällda ligninet till en sedimenteringsapparat 25. Ligninet sedimenterar och pumpas via en ledning 26 och en pump 27 till ett filter 28 för tvättning och urvattning. Det urvattnade ligninet leds till tank 29, i vilken 10 15 20 453 408 ligninet homogeniseras och lagras. För att hindra separation av lignin och vatcenfas kan ett medel tillsättes i homogeníseríngstanken 29, exempelvis en organisk högmolekulär polymer. Genom homogeniseringen får ligninet formen av en suspension i vattenfas och används som flytande bränsle i en mesaugn 30. Det homogeniserade lignínet leds till mesaugnen 30 med hjälp av en pump 31 och en ledning 32 och insprutas i mesaugnen med en lämplig specíalbrännare 33. Den klarade vätskan från sedimenteringstanken 25 avleds till en behållare 34, till vilken även förs filtrat från filtret 28. De båda kombinerade vätskor- na förs från behållaren 34 med hjälp av en pump 35 och en ledning 36 till behållaren 1 för recirkulation. e.~By means of a pump 24, the black liquor together with the precipitated lignin is pumped to a sedimentation apparatus 25. The lignin settles and is pumped via a line 26 and a pump 27 to a filter 28 for washing and dewatering. The dehydrated lignin is passed to tank 29, in which the lignin is homogenized and stored. To prevent separation of lignin and aqueous phase, an agent may be added to the homogenization tank 29, for example an organic high molecular weight polymer. Through the homogenization, the lignin takes the form of a suspension in aqueous phase and is used as liquid fuel in a lime kiln 30. The homogenized lignin is led to the lime kiln 30 by means of a pump 31 and a line 32 and injected into the lime kiln with a suitable special burner 33. The clarified liquid from the sedimentation tank 25 is diverted to a container 34, to which filtrate is also fed from the filter 28. The two combined liquids are fed from the container 34 by means of a pump 35 and a line 36 to the container 1 for recirculation. e. ~

Claims

10 15 20 25 30 35 455 408 PATENT REQUIREMENTS

Process in the sulphate cellulose process to produce lignin suspension with a low content of sulfur from black liquor substantially without emission of sulfur to the ambient atmosphere, characterized in that the dissolved organic substance in the black liquor, mainly lignin, is precipitated by carbon dioxide by the black liquor, preferably after some evaporation and defoaming of soap, it begins in the upper part of a first tower which consists of a carbonation tower (12), that the black liquor is caused to fall downwards in this first tower to meet carbon dioxide which starts further down (13) and which flows upwards in the tower, that hydrogen sulphide formed in the first tower is diverted to a second tower (18) in which the hydrogen sulphide is absorbed by flowing through this second tower with white liquor, that black liquor and the precipitated organic substance are led from the first tower to a separation unit (25) , in which the precipitate is separated, that the separated organic substance is diluted and homogenized to a suspension, and that it The suspension is used and burned as liquid fuel in the lime kiln (s).

2. A method according to claim 1, characterized in that the carbon dioxide is wholly or partly in the form of flue gas which is obtained at least in part from one or more lime kilns (30).

3. A method according to claim 1 or 2, characterized in that the black liquor which is led to the first tower has a temperature between 65 and 80 ° C, and that the carbon dioxide-containing gas also has a temperature within the same temperature range.

4. A method according to claim 3, characterized in that the pH value of the liquid discharged from the first tower is adjusted to between 8.7 and 9.6 by measuring said pH, wherein measured value is caused to regulate the supply of black liquor and / or carbon dioxide to the tower.

5. A method according to claim 3, characterized in that hydrogen sulphide formed is evaporated in a lower part (15) of the first tower at a level below the carbon dioxide intake. 10 15 20 455 408

6. A method according to any one of claims 2-5, characterized in that the separation unit consists of a sedimentation apparatus, in which the precipitated organic substance is sedimented in the bottom, while the clarified liquid from the sedimentation apparatus is pumped back to the main stream of black liquor for further evaporation, combustion and causticization.

7. A method according to claim 3, characterized in that the first tower consists of a filling body tower with a liquid spreader for the black liquor and a gas spreader for the carbon dioxide.