CA1104764A - Black liquor recovery - Google Patents
Black liquor recoveryInfo
- Publication number
- CA1104764A CA1104764A CA276,409A CA276409A CA1104764A CA 1104764 A CA1104764 A CA 1104764A CA 276409 A CA276409 A CA 276409A CA 1104764 A CA1104764 A CA 1104764A
- Authority
- CA
- Canada
- Prior art keywords
- bed
- temperature
- black liquor
- furnace
- heat exchanger
- 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
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/10—Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working
Landscapes
- Paper (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Method and apparatus for oxidation of black liquor form an alkaline process for pulping cellulosic material in A fluid bed furnace wherein indirect heat exchange means are provided within the fluid bed in the furnace, means are provided to sense the temperature in the bed and to control the flow of fluid through the heat exchanger in accordance with the temperature sense thereby to maintain the tempera-ture in the bed substantially constant at a preselected value to form pellets of the inorganic chemical to be recovered and to recover heat from the bed.
Method and apparatus for oxidation of black liquor form an alkaline process for pulping cellulosic material in A fluid bed furnace wherein indirect heat exchange means are provided within the fluid bed in the furnace, means are provided to sense the temperature in the bed and to control the flow of fluid through the heat exchanger in accordance with the temperature sense thereby to maintain the tempera-ture in the bed substantially constant at a preselected value to form pellets of the inorganic chemical to be recovered and to recover heat from the bed.
Description
~1~4~4 The present invention relates to a fluidized bed burning of black liquors from the production of pulp from cellulosic raw material, for example, by the NSSC or the Kraft pulping processes for the recovery of heat and cooking chemicals.
Conventionally black liquors particularly from a Kraft process are recovered by concentrating the black li-quor using multiple effect evaporators and injecting this concentrated liquor into a recov~ry furnace having an oxida-tion zone and at the bottom thereof a smelting and reducingzone. The organics in the liquor are burned in the oxida-tion zone and the inorganic residue containing sodium sulfate is converted in the reducing zone into a smelt consisting primarly of sodium sulfide and sodium carbonate. The oxi-dation of organic materials generates heat some of which is recovered in the form of steam by a boiler section at the top and on the walls of the furnace.
Black liquors have also been recovered in fluid-ized bed recovery units wherein the organic materials are oxidized at a temperature lower than the melting point of the inorganics in the residue, and sodium carbonate and sodium sulphate pellets are formed. (For Kraft recovery these pellets must sub~equently be reduced by any convenient method to convert the sodium sulfate to sodium sulphide).
One of the prohlems with oxidation of black liquor in fluidized beds furnaces is the poor heat recovery. Fluid bed installations with heat recovery generally have the boiler section positioned remote fxom the fluidized bed furnace, i.e. the flue gases must be transported from the furnace through ducting and through a cyclone to the boiler section.
~ .
Oxidation of black liquor to form pellets in a fluidized bed requires accurate con~rol of the tempera~ure of the bed just below the eutectic temperature of the inor-ganic materials. No efficient manner of controlling the bed temperature is known. The methods currently in use in-clude varying the temperature of the fluidizing air, or vary-ing the concentration or amount of the spent black liquor bed to the bed, or a combination thereof. These controls, while adequate, are not thermally efficient.
The requirement for a relative low temperature in the bed (between about 1100 and 1400F) limits the concen-tration of dilute black liquor since the moisture content of the liquor is a signi~icant factor preventing unacceptably high bed temperatures. Thus the advantages of multiple effect evaporators are not available and water that could efficiently be evaporated in such evaporators must be evapo-rated within the furnace. This results in a significant decrease in the overall thermal efficiency of the system.
It is ~nown to utilize heat exchangers in a flui-dized bed coal burning furnaces both within the bed and above the bed. The purpose of these heat exchangers is simply to absorb as much heat as possible there being no control of the bed temperature.
In Canadian patent 925,657 issued May 8, 1973 to Shick a fluidized bed reactor is disclosed incorporating means for influencing the temperature of an exothermic re-action. The influence on bed temperature is obtained by submerging a heat exchange unit within the bed, setting the pressure of this unit and feeding fluid to the unit in accor-dance with the rate of evaporation of fluid from this system.Such an arrangement does not provide temperature control, ~4764 but simply slows the rate of temperature change and is unsa~
tisfactory for controlling the temperature in the fluidized ]bed at or close to the eutectic temperature of the pellets formed and for ensuring the eutectic temperature is not !
exceeded.
It is object of the present invention to control, by indirect heat exchanger means, the bed temperature of a fluidized bed black liquor recovery furnace at the required temperature based on the eutectic temperature of inorganic materials in the liquor being fired.
It is also an object of the present invention to cool the bed of a fluid bed black liquor recovery furnace and thereby incxease the capacity of the furnace by permit-ting more concentrated black liquor to be fed thereto and to generate steam and thereby increase the thermal efficiency of the system.
Broadly, the present invention relates to an im-proved fluid bed furnace for the oxidation of black li~uor from an alkaline process for pulping cellulosic material comprising; indirect heat exchange means within a fluid bed formed in the furnace, means to sense the temperature in the bed, a means to control the flow of fluid through the heat exchanger means in accordance with the temperature sensed thereby to maintain the temperature in the bed substantially constant at a temperature below eutectic temperature of the inorganics in the black li~uor while removing heat from the bed and forming pellets in s,aid bed.
Further features objects and advantages will be evident from the following detailed description of the pre-ferred embodiment of the present invention ta~en in con-junction with the accompanying drawings in which ' Figure 1 is a schematic illustration of one arran-47~4 gement incorporating a boiler in the bed of the conventional fluid bed furnace for oxidation of black liquor.
The fluidized bed furnace 10 is a conventional fur-nace having an air inlet 12 into a plenum chamber 14 at the bottom. Air from the plenum 14 passes through a diffuser plate 16 and forms a fluidized bed 18 of particles or pellets derived from the concentrated black liquor entering the fur-nace 10 via line 20. In the Figure 1 arrangement the line 20 leads to a nozzle 22 that injects the concentrated black liquor into the bed from above, alternatively this liquor may be injected directly into the bed.
A boiler section 24, is provided within the fluid bed 18 and used to absorb heat and regulate the temperature within the bed to that required for proper formation of pellets, e.g. in the Kraft process to a temperature of bet-ween about 1100 and 1400F and selected to be slightly be-low the combined eutec~ic temperature of the material in the bed. This temperature control is obtained by sensing the temperature within the bed by the sensor indicated at 26 which regulates the control 28 operating valve 30 so that if the temperature tends to rise the rate of flow of fluid through the boiler 24 will increase or if the temperature tends to drop slightly the rate of flow will be reduced there-by to hold the temperature within the bed substantially cons-tant within * 20F).
In the specific embodiment illustrated the hot gases from the fluid bed furnace 10 pass second boiler sec-tion 32, which cools the exhaust gases before they are clean-ed by the dust collector 34 and rejected to the atmosphere or further processing via line 36. Particulates from the dust collector 34 may be returned to the bed via line 38 to func-tion as ~ucleatio~ particles in the bed, ~1~4764 The boilers 32 and 24 are connected in series with the boiler 24 functioning as the preheater for feed water fecl to the boiler 32 i.e. in the arrangement illustrated boiler feed water enters the system by line 40 and a portion thereof is fed via line ~2 to the controller valve 30 and another portion is fed via line 44 to line 46 which carries the heated fluid leaving the boiler 24. The combined flow from line 46 forms the feed water to the boiler 32. The valve 48 in line 44 is controlled as indicated by line 50 from controller 52 in the normal manner to maintain the required ra~te of boiler feed and process steam leaves via line 54.
With this specific arrangement shown in the figure water heated in the boiler 2~ is intended to form significant portion of the feed water if not all of the feed water for the second boiler 32. Alternatively, the two boiler sections may be combined in the reverse order so that steam generated in boiler 32 would be super-heated in the boiler 24 with the amount of steam passing through the boiler 24 being control-led to maintain the temperature in the bed 18 as required.
It is extremely important that the temperature be controlled so that the temperature is not too high and yet the temperature should be as high as possible for efficient heat extraction. If the eutectic temperature of the material ; in the bed is exceeded there is a high probability that a smelt will be formed and that it will foul the operation of the bed and require shutdown and an extensive clean-up opera-tion.
The incorporation of the boiler coil within the ;~
bed and the control of flow rate of fluid through the coil to control the temperature to that required for pellet for- r matLon permits improvement of the operation of the fluidized 47~
bed and recovery of hea~ from the burning of the liquor.
Heat extracted from the bed 18 tends to lower the temperature o~ the bed and since the bed tempexature must be at or below the said eutectic temperature the concentration or amount of liquor iniected into the urnace may be lncreased and the capacity of the furnace signi.ficantly increased while heat is recovered from the process~ While the boiler 24 has been shown in series arran~ements with the boiler 3~ it may also be used independently~ However, the series arrangements are considerably more efficien~.
Modifica.ion may be made without departing from ; the spirit of the invention as defined in the appended claims.
Conventionally black liquors particularly from a Kraft process are recovered by concentrating the black li-quor using multiple effect evaporators and injecting this concentrated liquor into a recov~ry furnace having an oxida-tion zone and at the bottom thereof a smelting and reducingzone. The organics in the liquor are burned in the oxida-tion zone and the inorganic residue containing sodium sulfate is converted in the reducing zone into a smelt consisting primarly of sodium sulfide and sodium carbonate. The oxi-dation of organic materials generates heat some of which is recovered in the form of steam by a boiler section at the top and on the walls of the furnace.
Black liquors have also been recovered in fluid-ized bed recovery units wherein the organic materials are oxidized at a temperature lower than the melting point of the inorganics in the residue, and sodium carbonate and sodium sulphate pellets are formed. (For Kraft recovery these pellets must sub~equently be reduced by any convenient method to convert the sodium sulfate to sodium sulphide).
One of the prohlems with oxidation of black liquor in fluidized beds furnaces is the poor heat recovery. Fluid bed installations with heat recovery generally have the boiler section positioned remote fxom the fluidized bed furnace, i.e. the flue gases must be transported from the furnace through ducting and through a cyclone to the boiler section.
~ .
Oxidation of black liquor to form pellets in a fluidized bed requires accurate con~rol of the tempera~ure of the bed just below the eutectic temperature of the inor-ganic materials. No efficient manner of controlling the bed temperature is known. The methods currently in use in-clude varying the temperature of the fluidizing air, or vary-ing the concentration or amount of the spent black liquor bed to the bed, or a combination thereof. These controls, while adequate, are not thermally efficient.
The requirement for a relative low temperature in the bed (between about 1100 and 1400F) limits the concen-tration of dilute black liquor since the moisture content of the liquor is a signi~icant factor preventing unacceptably high bed temperatures. Thus the advantages of multiple effect evaporators are not available and water that could efficiently be evaporated in such evaporators must be evapo-rated within the furnace. This results in a significant decrease in the overall thermal efficiency of the system.
It is ~nown to utilize heat exchangers in a flui-dized bed coal burning furnaces both within the bed and above the bed. The purpose of these heat exchangers is simply to absorb as much heat as possible there being no control of the bed temperature.
In Canadian patent 925,657 issued May 8, 1973 to Shick a fluidized bed reactor is disclosed incorporating means for influencing the temperature of an exothermic re-action. The influence on bed temperature is obtained by submerging a heat exchange unit within the bed, setting the pressure of this unit and feeding fluid to the unit in accor-dance with the rate of evaporation of fluid from this system.Such an arrangement does not provide temperature control, ~4764 but simply slows the rate of temperature change and is unsa~
tisfactory for controlling the temperature in the fluidized ]bed at or close to the eutectic temperature of the pellets formed and for ensuring the eutectic temperature is not !
exceeded.
It is object of the present invention to control, by indirect heat exchanger means, the bed temperature of a fluidized bed black liquor recovery furnace at the required temperature based on the eutectic temperature of inorganic materials in the liquor being fired.
It is also an object of the present invention to cool the bed of a fluid bed black liquor recovery furnace and thereby incxease the capacity of the furnace by permit-ting more concentrated black liquor to be fed thereto and to generate steam and thereby increase the thermal efficiency of the system.
Broadly, the present invention relates to an im-proved fluid bed furnace for the oxidation of black li~uor from an alkaline process for pulping cellulosic material comprising; indirect heat exchange means within a fluid bed formed in the furnace, means to sense the temperature in the bed, a means to control the flow of fluid through the heat exchanger means in accordance with the temperature sensed thereby to maintain the temperature in the bed substantially constant at a temperature below eutectic temperature of the inorganics in the black li~uor while removing heat from the bed and forming pellets in s,aid bed.
Further features objects and advantages will be evident from the following detailed description of the pre-ferred embodiment of the present invention ta~en in con-junction with the accompanying drawings in which ' Figure 1 is a schematic illustration of one arran-47~4 gement incorporating a boiler in the bed of the conventional fluid bed furnace for oxidation of black liquor.
The fluidized bed furnace 10 is a conventional fur-nace having an air inlet 12 into a plenum chamber 14 at the bottom. Air from the plenum 14 passes through a diffuser plate 16 and forms a fluidized bed 18 of particles or pellets derived from the concentrated black liquor entering the fur-nace 10 via line 20. In the Figure 1 arrangement the line 20 leads to a nozzle 22 that injects the concentrated black liquor into the bed from above, alternatively this liquor may be injected directly into the bed.
A boiler section 24, is provided within the fluid bed 18 and used to absorb heat and regulate the temperature within the bed to that required for proper formation of pellets, e.g. in the Kraft process to a temperature of bet-ween about 1100 and 1400F and selected to be slightly be-low the combined eutec~ic temperature of the material in the bed. This temperature control is obtained by sensing the temperature within the bed by the sensor indicated at 26 which regulates the control 28 operating valve 30 so that if the temperature tends to rise the rate of flow of fluid through the boiler 24 will increase or if the temperature tends to drop slightly the rate of flow will be reduced there-by to hold the temperature within the bed substantially cons-tant within * 20F).
In the specific embodiment illustrated the hot gases from the fluid bed furnace 10 pass second boiler sec-tion 32, which cools the exhaust gases before they are clean-ed by the dust collector 34 and rejected to the atmosphere or further processing via line 36. Particulates from the dust collector 34 may be returned to the bed via line 38 to func-tion as ~ucleatio~ particles in the bed, ~1~4764 The boilers 32 and 24 are connected in series with the boiler 24 functioning as the preheater for feed water fecl to the boiler 32 i.e. in the arrangement illustrated boiler feed water enters the system by line 40 and a portion thereof is fed via line ~2 to the controller valve 30 and another portion is fed via line 44 to line 46 which carries the heated fluid leaving the boiler 24. The combined flow from line 46 forms the feed water to the boiler 32. The valve 48 in line 44 is controlled as indicated by line 50 from controller 52 in the normal manner to maintain the required ra~te of boiler feed and process steam leaves via line 54.
With this specific arrangement shown in the figure water heated in the boiler 2~ is intended to form significant portion of the feed water if not all of the feed water for the second boiler 32. Alternatively, the two boiler sections may be combined in the reverse order so that steam generated in boiler 32 would be super-heated in the boiler 24 with the amount of steam passing through the boiler 24 being control-led to maintain the temperature in the bed 18 as required.
It is extremely important that the temperature be controlled so that the temperature is not too high and yet the temperature should be as high as possible for efficient heat extraction. If the eutectic temperature of the material ; in the bed is exceeded there is a high probability that a smelt will be formed and that it will foul the operation of the bed and require shutdown and an extensive clean-up opera-tion.
The incorporation of the boiler coil within the ;~
bed and the control of flow rate of fluid through the coil to control the temperature to that required for pellet for- r matLon permits improvement of the operation of the fluidized 47~
bed and recovery of hea~ from the burning of the liquor.
Heat extracted from the bed 18 tends to lower the temperature o~ the bed and since the bed tempexature must be at or below the said eutectic temperature the concentration or amount of liquor iniected into the urnace may be lncreased and the capacity of the furnace signi.ficantly increased while heat is recovered from the process~ While the boiler 24 has been shown in series arran~ements with the boiler 3~ it may also be used independently~ However, the series arrangements are considerably more efficien~.
Modifica.ion may be made without departing from ; the spirit of the invention as defined in the appended claims.
Claims (7)
1. In a method for recovery of useful chemicals from black liquor formed in an alkaline pulping process for the digestion of cellulosic material to produce a pulp, wherein black liquor from the digestion process is concentrated and then fed into a fluidized bed recovery furnace wherein inorganics contained within the black liquor are agglomerated into pellets containing sodium compounds thereby to form the fluidized bed, and organic material in the black liquor is oxidized, the improvement comprising; further concentrat-ing said black liquor before injecting said further con-centrated black liquor into said fluidized bed, providing an indirect heat exchanger in said fluidized bed, sensing the temperature of said fluidized bed and controlling the flow of heat exchange fluid through said heat exchanger in accordance with the temperature sensed, thereby to maintain the temperature in said fluidized bed at a substantially constant value within the range of 1100 to 1400°F and below the eutectic temperature of said inorganics forming said pellets.
2. A method as defined in claim 1 wherein said heat exchange fluid is water.
3. A method as defined in claim 1 wherein said heat exchange fluid is steam.
4. A method as defined in claim 2 wherein said water after passing through said heat exchanger is introduced to a second boiler section heated by flue gas from said furance.
5. A method as defined in claim 3 wherein said steam is generated in a second boiler section heated by flue gas from said furnace.
6. An apparatus for oxidation of black liquor from an alkaline pulping process for digestion of cellulosic material comprising; a fluid bed recovery furnace an indirect heat exchanger within the area of said furnace wherein a fluid bed is formed, means for sensing the temperature of said fluid bed, control means for regulating flow of heat exchange fluid through said indirect heat exchanger means in accordance with the temperature sensed, thereby to main-tain the temperature in said bed substantially constant in the range of 1100 to 1400°F and below the combined eutectic temperature on the material in said bed.
7. An apparatus as defined in claim 6 further comprising a second boiler section in series with said heat exchanger, means for directing flue gases from said furnace through said second boiler section.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB16942/76 | 1976-04-27 | ||
| GB1694276 | 1976-04-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1104764A true CA1104764A (en) | 1981-07-14 |
Family
ID=10086445
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA276,409A Expired CA1104764A (en) | 1976-04-27 | 1977-04-18 | Black liquor recovery |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1104764A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5645616A (en) * | 1994-02-24 | 1997-07-08 | The Babcock & Wilcox Company | Black liquor gasifier |
-
1977
- 1977-04-18 CA CA276,409A patent/CA1104764A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5645616A (en) * | 1994-02-24 | 1997-07-08 | The Babcock & Wilcox Company | Black liquor gasifier |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |