CA1324865C - Method for recovering chemicals from spent pulp liquors - Google Patents
Method for recovering chemicals from spent pulp liquorsInfo
- Publication number
- CA1324865C CA1324865C CA000567585A CA567585A CA1324865C CA 1324865 C CA1324865 C CA 1324865C CA 000567585 A CA000567585 A CA 000567585A CA 567585 A CA567585 A CA 567585A CA 1324865 C CA1324865 C CA 1324865C
- Authority
- CA
- Canada
- Prior art keywords
- energy
- gas
- reactor
- spent
- alkali
- 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 - Lifetime
Links
Classifications
-
- 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
- D21C11/12—Combustion of pulp liquors
- D21C11/125—Decomposition of the pulp liquors in reducing atmosphere or in the absence of oxidants, i.e. gasification or pyrolysis
Landscapes
- Paper (AREA)
Abstract
A b s t r a c t In order to recover chemicals from spent pulp liquors while at the same time making use of energy liberated in the process, the spent liquors are supplied to the reaction zone of a reactor while external thermal energy independent of the combustion, is simultaneously supplied, for instance, in the form of an energy-rich gas heated in a plasma generator, the temperature and oxygen potential in the zone being governed independently of each other by the controlled supply of said thermal energy, and possibly also the supply of carbonaceous material and/or gas containing oxygen, so that substantially all alkali and sulphur, i.e. 95 to 100% thereof, is bound in a molten phase which is separated from the gas phase and withdrawn via an outlet connected to the reactor, the organic portion of the spent liquor being withdrawn in the form of a gas.
Description
-`` 1 324865 The present invention relates to a method for recovering chemicals from spent pulp liquors while at the same time making use of energy liberated in the process, the spent liquors being supplied to the reaction zone S of a reactor while external thermal energy, independent of the combustion, is simultaneously supplied.
Within the paper and pulp industry the aim is to re-use chemicals and energy as far as possible, for both economic and environmental reasons. In principle the recovery processes for this are four part-processes, i.e. a sulphur-reduction process, a process for sepa-ration of inorganic products, an oxidation process for the organic substance with generation of energy and the processing of alkali to a usable form. These processes can be performed as separate part-processes or several may be performed in the same step. In a modern soda recovery boiler, the Tomlinson boiler, the first three processes are performed in one step whereas the alkali processing is performed in a subsequent causticizing step.
It is generally the soda recovery boiler which limits the possibility of expanding and/or increasing the capacity in an existing pulp factory. The capacity of the soda recovery boiler is usually limited by the volume of gas which can pass through its primary air zone without taking within too much of the solid and floating particles. Another limitation may be the thermal load of the steam part.
The soda recovery boiler may also be limited by the difficulty of optimizing both chemical recovery and combustion at the same time. This means that both alkali and sulphur will to a certain extent be released ' ,,.
.
.
.. .
' ' '- - ' : '~ .`' :
- .. , , ~ .
- ~ , - . -.. ..
~ . .
1 32486~
in gaseous phase. One solution to this problem is offered in Swedish patent 83 02 245-0 in which the whole recovery process is divided into three steps. The process starts with a high-temperature step where sulphur is reduced and withdrawn in the form of a melt, both alkali and organic material being gasified at the same time. Alkali is condensed in a second step, at the same time being converted to desired form, and finally a third step in which the gas from the organic portion is combusted and thereby generates energy.
The aim of the above-mentioned invention is thus to eliminate subsequent alkali processing~
Another process for recovering chemicals from pulp liquors is described in s~ 72 04 304-5. Here, melt and gas are separated in a pre-reactor and the process is entirely dependent on the energy developed at the partial combustion to obtain a sufficiently high tèmperature. In practice this entails considerable difficulties. If the partial combustion is insufficient the temperature will be too low to guarantee a flame whereas if it is too much, both sulphur and alkali will depart with the gas leaving.
In one aspect the invention provides a method for recovering chemicals and energy from spent pulp liquors, comprising: (a) feeding the pulp liquors to a reaction zone of a reactor; (b) supplying said reaction zone with thermal energy; (c) supplying said reaction zone with an oxygen containing gas, a carbonaceous material or a mixture thereof; and (d) controlling, independently, the temperature and oxygen potential of said reaction zone by the supply of thermal energy; wherein: (i) the temperature of said reaction zone is controlled at between 900 and 1,000C; (ii) by the controlled supply of components (c) reducing and binding in the melt essentially all sulfur contained in the pulp liquors, converting to sodium carbonate and binding in the melt most of the alkali contained in the spent liquors, and removing from the spent liquors the sulphur and alkali products; (iii) recovering gases, including organic components of the spent liquors, liberated in the process, said gases, when combusted, being the source of the energy recovered in the process; and (iv) said thermal energy source being independent of the energy recovered in (iii).
Thanks to a great number of experiments, we have now found that within a temperature interval of 900 - llOO~C and at a given oxygen potential in the liquor evaporation unit, all sulphur and alkali will be bound in a molten phase.
According to the present invention the recovery process is divided into three separate steps. In the first step the sulphur is reduced and withdrawn in a molten phase together with the inorganic portion of the spent liquor, the organic portion being si~ultaneously gaqified. This '`B - 2a -.
,` `
'`
step is optimized in order to obtain substantially total separation of sulphur and alkali. In the second step the gas is burned to generate energy. This can be achieved in many ways and for many purposes but since it is entirely separate from the recovery step it can easily be sub-optimized. The third step is conventional processing of alkali to the desired form.
( When performing the present invention the spent liquors are supplied to the reaction zone of a reactor while external thermal ener~y, independent of the combustion, is also supplied. Characteristic of the method according to the invention is that the temperature and oxygen potential in the zone are governed independently of each other and carbonaceous material and/or gas containing oxygen are possibly supplied so that substantially all alkali and sulphur is bound in a molten phase which is separated from the gas phase and withdrawn via an outlet connected to the reactor, the organic portion of the spent liquor being simultaneously withdrawn in the form of a gas.
( The external energy may advantageously be supplied in the form of an energy-rich gas heated in a plasma generator.
A temperature of 900C to 1100C is preferably main-tained in the liquor gasifier.
The method is preferably performed in such a manner that the melt withdrawn consists primarily of Na2S, NaOH and Na2CO3, 95~ to 100~ of the sulphur and alkali content of the liquor being in a molten phase within the stated temperature interval and at a given oxygen potential :- ;
.; ~
. ~ :
In the method according to the invention, as with the concept described in SE 83 02 245-9, a source of energy independent from the combustion is utilized, thus enabling the problems mentioned earlier which appear with a method according to SE 72 04 304-5 to be eliminated.
In the specific embodiment using a plasma generator, it has unexpectedly been discovered that the reaction rate for gasification of heavy black liquor is extremely high and the reactor can therefore be designed specifically to give maximum separation of the molten phase from the gas.
The possibility of accurately controlling the temperature according to the invention also allows optimum composition of the chemicals with respect to the digestion process without the melting point and fluidity of the molten phase necessarily giving rise to problems in the recovery step.
Example In experimental equipment 9 kg heavy black liquor was ( supplied to a cylindrical reactor before a plasma generator 20 B located tangentially on the cylinder~ 270 m3N air~a~
conducted through the plasma generator per hour. A further ( 120 m3N~;eupplied to the process through another tanqential inlet.
The heavy black liquor had the following composition:
Na 20.5% dry material S 4.5~ " "
H2 3.7~
2 37 ~ ~ .
C 34 ~ " "
Cl 0.3~ " ~
,. :'`.' . ~ ` ;' `,, ~,, :
65~ dry substance and calorimetric thermal value 13.89 MJ/kg DS.
The temperature in the reactor was maintained at 1000C.
Additionally 1260 kW energy was required to maintain this temperature, partly to cover losses in the reaction vessel. By keeping the swirl number higher than 0.6 and ~- the Reynolds number higher than 18000, as well as selecting suitable reactor dimensions, a substantially 100% separation of the melt can be obtained.
The melt was tapped continuously throughout the experiment and the quantity was 147.5 kg per hour. Analysi~s gave the following:
NaOH 2.1%
2 3 64.7 NaCl 0.7%
Na2S 31.5~
A gas was also obtained having the following dry gas composition:
CO 16.8% Na 0.03%
CO2 13.0% NaOH 0.04%
H2 23.5~ NaCl 0.02%
N2 46.6%
If the quantity of air were to be increased in order to decrease the energy addition, Na2S would to a great extent be oxidized - which is to be avoided at all costs.
;,. . . ~ ~
Within the paper and pulp industry the aim is to re-use chemicals and energy as far as possible, for both economic and environmental reasons. In principle the recovery processes for this are four part-processes, i.e. a sulphur-reduction process, a process for sepa-ration of inorganic products, an oxidation process for the organic substance with generation of energy and the processing of alkali to a usable form. These processes can be performed as separate part-processes or several may be performed in the same step. In a modern soda recovery boiler, the Tomlinson boiler, the first three processes are performed in one step whereas the alkali processing is performed in a subsequent causticizing step.
It is generally the soda recovery boiler which limits the possibility of expanding and/or increasing the capacity in an existing pulp factory. The capacity of the soda recovery boiler is usually limited by the volume of gas which can pass through its primary air zone without taking within too much of the solid and floating particles. Another limitation may be the thermal load of the steam part.
The soda recovery boiler may also be limited by the difficulty of optimizing both chemical recovery and combustion at the same time. This means that both alkali and sulphur will to a certain extent be released ' ,,.
.
.
.. .
' ' '- - ' : '~ .`' :
- .. , , ~ .
- ~ , - . -.. ..
~ . .
1 32486~
in gaseous phase. One solution to this problem is offered in Swedish patent 83 02 245-0 in which the whole recovery process is divided into three steps. The process starts with a high-temperature step where sulphur is reduced and withdrawn in the form of a melt, both alkali and organic material being gasified at the same time. Alkali is condensed in a second step, at the same time being converted to desired form, and finally a third step in which the gas from the organic portion is combusted and thereby generates energy.
The aim of the above-mentioned invention is thus to eliminate subsequent alkali processing~
Another process for recovering chemicals from pulp liquors is described in s~ 72 04 304-5. Here, melt and gas are separated in a pre-reactor and the process is entirely dependent on the energy developed at the partial combustion to obtain a sufficiently high tèmperature. In practice this entails considerable difficulties. If the partial combustion is insufficient the temperature will be too low to guarantee a flame whereas if it is too much, both sulphur and alkali will depart with the gas leaving.
In one aspect the invention provides a method for recovering chemicals and energy from spent pulp liquors, comprising: (a) feeding the pulp liquors to a reaction zone of a reactor; (b) supplying said reaction zone with thermal energy; (c) supplying said reaction zone with an oxygen containing gas, a carbonaceous material or a mixture thereof; and (d) controlling, independently, the temperature and oxygen potential of said reaction zone by the supply of thermal energy; wherein: (i) the temperature of said reaction zone is controlled at between 900 and 1,000C; (ii) by the controlled supply of components (c) reducing and binding in the melt essentially all sulfur contained in the pulp liquors, converting to sodium carbonate and binding in the melt most of the alkali contained in the spent liquors, and removing from the spent liquors the sulphur and alkali products; (iii) recovering gases, including organic components of the spent liquors, liberated in the process, said gases, when combusted, being the source of the energy recovered in the process; and (iv) said thermal energy source being independent of the energy recovered in (iii).
Thanks to a great number of experiments, we have now found that within a temperature interval of 900 - llOO~C and at a given oxygen potential in the liquor evaporation unit, all sulphur and alkali will be bound in a molten phase.
According to the present invention the recovery process is divided into three separate steps. In the first step the sulphur is reduced and withdrawn in a molten phase together with the inorganic portion of the spent liquor, the organic portion being si~ultaneously gaqified. This '`B - 2a -.
,` `
'`
step is optimized in order to obtain substantially total separation of sulphur and alkali. In the second step the gas is burned to generate energy. This can be achieved in many ways and for many purposes but since it is entirely separate from the recovery step it can easily be sub-optimized. The third step is conventional processing of alkali to the desired form.
( When performing the present invention the spent liquors are supplied to the reaction zone of a reactor while external thermal ener~y, independent of the combustion, is also supplied. Characteristic of the method according to the invention is that the temperature and oxygen potential in the zone are governed independently of each other and carbonaceous material and/or gas containing oxygen are possibly supplied so that substantially all alkali and sulphur is bound in a molten phase which is separated from the gas phase and withdrawn via an outlet connected to the reactor, the organic portion of the spent liquor being simultaneously withdrawn in the form of a gas.
( The external energy may advantageously be supplied in the form of an energy-rich gas heated in a plasma generator.
A temperature of 900C to 1100C is preferably main-tained in the liquor gasifier.
The method is preferably performed in such a manner that the melt withdrawn consists primarily of Na2S, NaOH and Na2CO3, 95~ to 100~ of the sulphur and alkali content of the liquor being in a molten phase within the stated temperature interval and at a given oxygen potential :- ;
.; ~
. ~ :
In the method according to the invention, as with the concept described in SE 83 02 245-9, a source of energy independent from the combustion is utilized, thus enabling the problems mentioned earlier which appear with a method according to SE 72 04 304-5 to be eliminated.
In the specific embodiment using a plasma generator, it has unexpectedly been discovered that the reaction rate for gasification of heavy black liquor is extremely high and the reactor can therefore be designed specifically to give maximum separation of the molten phase from the gas.
The possibility of accurately controlling the temperature according to the invention also allows optimum composition of the chemicals with respect to the digestion process without the melting point and fluidity of the molten phase necessarily giving rise to problems in the recovery step.
Example In experimental equipment 9 kg heavy black liquor was ( supplied to a cylindrical reactor before a plasma generator 20 B located tangentially on the cylinder~ 270 m3N air~a~
conducted through the plasma generator per hour. A further ( 120 m3N~;eupplied to the process through another tanqential inlet.
The heavy black liquor had the following composition:
Na 20.5% dry material S 4.5~ " "
H2 3.7~
2 37 ~ ~ .
C 34 ~ " "
Cl 0.3~ " ~
,. :'`.' . ~ ` ;' `,, ~,, :
65~ dry substance and calorimetric thermal value 13.89 MJ/kg DS.
The temperature in the reactor was maintained at 1000C.
Additionally 1260 kW energy was required to maintain this temperature, partly to cover losses in the reaction vessel. By keeping the swirl number higher than 0.6 and ~- the Reynolds number higher than 18000, as well as selecting suitable reactor dimensions, a substantially 100% separation of the melt can be obtained.
The melt was tapped continuously throughout the experiment and the quantity was 147.5 kg per hour. Analysi~s gave the following:
NaOH 2.1%
2 3 64.7 NaCl 0.7%
Na2S 31.5~
A gas was also obtained having the following dry gas composition:
CO 16.8% Na 0.03%
CO2 13.0% NaOH 0.04%
H2 23.5~ NaCl 0.02%
N2 46.6%
If the quantity of air were to be increased in order to decrease the energy addition, Na2S would to a great extent be oxidized - which is to be avoided at all costs.
;,. . . ~ ~
Claims (4)
1. A method for recovering chemicals from spent pulp liquors while simultaneously utilizing energy liberated in the process, wherein the spent pulp liquors are fed into a reaction zone of a reactor under simultaneous supply of external energy, said external energy being independent of combustion, wherein temperature and oxygen potential in the zone are controlled independently of each other by controlled supply of said thermal energy and/or carbonaceous material, c h a r a c t e r i z e d in that a temperature of 900° to 1100° C is maintained in the reactor and that the oxygen potential is controlled by a controlled supply of the oxygen-containing gas and/or the carbonaceous material, whereby sulfur contained in the spent pulp liquors is reduced and essentially all alkali and sulfur is bound in a molten phase, which molten phase is separated from the gas phase.
2. A method according to claim 1, c h a r a c t e r -i z e d in that the supplied gas is air and acts as carrier for external thermal energy supplied to the reactor.
3. A method according to claim 2, c h a r a c t e r -i z e d in that the external energy is supplied in form of a energy-rich gas heated in a plasma generator.
4. A method according to any of claims 1 - 3, c h a r a c t e r i z e d in that 95 to 100 % of all alkali and sulfur is bound in a molten phase.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE8702627A SE464921B (en) | 1987-06-25 | 1987-06-25 | SAVED TO RECOVER CHEMICALS FROM MASS DEVICES |
| SE8702627-4 | 1987-06-25 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1324865C true CA1324865C (en) | 1993-12-07 |
Family
ID=20368972
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000567585A Expired - Lifetime CA1324865C (en) | 1987-06-25 | 1988-05-25 | Method for recovering chemicals from spent pulp liquors |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS646191A (en) |
| CN (1) | CN1030107A (en) |
| CA (1) | CA1324865C (en) |
| FI (1) | FI85994B (en) |
| SE (1) | SE464921B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE9300199L (en) * | 1993-01-25 | 1994-07-26 | Kvaerner Pulping Tech | Method for recycling cellulosic liquids |
| US7494637B2 (en) | 2000-05-16 | 2009-02-24 | Massachusetts Institute Of Technology | Thermal conversion of biomass to valuable fuels, chemical feedstocks and chemicals |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE454188B (en) * | 1984-10-19 | 1988-04-11 | Skf Steel Eng Ab | MAKE RECYCLING CHEMICALS FROM MASS DISPENSER |
-
1987
- 1987-06-25 SE SE8702627A patent/SE464921B/en not_active IP Right Cessation
-
1988
- 1988-03-09 FI FI881088A patent/FI85994B/en not_active Application Discontinuation
- 1988-03-14 JP JP63058546A patent/JPS646191A/en active Pending
- 1988-03-29 CN CN88101785A patent/CN1030107A/en active Pending
- 1988-05-25 CA CA000567585A patent/CA1324865C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| FI881088A0 (en) | 1988-03-09 |
| CN1030107A (en) | 1989-01-04 |
| FI85994B (en) | 1992-03-13 |
| SE8702627L (en) | 1988-12-26 |
| SE464921B (en) | 1991-07-01 |
| FI881088A (en) | 1988-12-26 |
| SE8702627D0 (en) | 1987-06-25 |
| JPS646191A (en) | 1989-01-10 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |
Effective date: 20101207 |