CA1232712A - Heat recovery in black liquor oxidation - Google Patents
Heat recovery in black liquor oxidationInfo
- Publication number
- CA1232712A CA1232712A CA000468627A CA468627A CA1232712A CA 1232712 A CA1232712 A CA 1232712A CA 000468627 A CA000468627 A CA 000468627A CA 468627 A CA468627 A CA 468627A CA 1232712 A CA1232712 A CA 1232712A
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- Prior art keywords
- multiple effect
- effect evaporation
- black liquor
- solids
- liquor
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- 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
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Abstract
ABSTRACT OF THE DISCLOSURE
The black liquor from a kraft pulping process after intermediate concentration and prior to its introduction into the conventional recovery furnace is subjected to wet oxidation with high purity oxygen.
The heat of such oxidation is used to flash the liquor to dry or semi-dry solids (80-100% solids concentration) and the resulting steam is available as process steam utilized upfitream in the evaporation sequence. The hazard of recovery boiler explosion is thus reduced or eliminated and net steam recovery is considerably improved.
The black liquor from a kraft pulping process after intermediate concentration and prior to its introduction into the conventional recovery furnace is subjected to wet oxidation with high purity oxygen.
The heat of such oxidation is used to flash the liquor to dry or semi-dry solids (80-100% solids concentration) and the resulting steam is available as process steam utilized upfitream in the evaporation sequence. The hazard of recovery boiler explosion is thus reduced or eliminated and net steam recovery is considerably improved.
Description
12~27~ Z
PUS
HEAT RECOVERY IN BLACK LIQUOR OXIDATION
TECHNICAL FIELD
The present invention relate to the treatment of black liquor from pulp mills.
BACKGROUND OF THE INVENTION
In the standard process for treatment of black liquor from the Raft Pulping Process, the weak black liquor containing about 15% solids is concentrated, typically in a multiple effect evaporation facility, to a concentration of about 45-50% solids. The thus obtained "ztron~" or "heavy" black liquor is further evaporated to a solid concentration of about 65% or more and in such highly concentrated state is subjected to combustion in a recovery boiler. In such systems wherein a direct contact evaporator it employed for concentrating the liquid from the multiple effect facility, flue gas from the recovery boiler is employed to supply heat to the direct contact evaporator (DOE). The smelt recovered from the boiler is sent to further processing to reclaim available chemical values therein, for use in the pulping process.
In other known Raft pulp mill recovery processes the strong black liquor from the multiple effect evaporation is further concentrated to about 65%
solids level by indirect contact (forced circulation) evaporator, before being fed to the recovery boiler.
327~2 In recent years it has been the prevailing practice to subject the black liquor to oxidation at some stage in the evaporation sequence, thereby converting sulfur values therein to more stable form such as thiosulfates and/or sulfates, which among other benefits obtained, significantly reduced the release of malodorous sulfur compounds to the atmosphere.
In US. Patents Nos. 4,239,589 and 4,313,788, black liquor treating systems are disclosed in which the oxidation of the black liquor is integrated into the multiple effect evaporation stage of the pulp mill recovery sequence. The heat of the oxidation reaction is recovered as flash steam and is employed in providing part of the heat requirement of the multiple effect evaporation system, thus reducing demand for outside steam.
In these prior art processes for treatment of black liquor, whether or not oxidation of the liquor is practiced, the concentrated liquor which is fed to the recovery furnace will normally contain about 35%
water, which reduces heat recovery efficiency by carrying away heat unproductively with the flue gases as latent heat of vaporization. In addition to the thermal effect, the presence of water poses an ever present danger of recovery boiler explosion because of reactions occurring in the smelt bed of the recovery boiler, which are difficult to control.
The pulping industry has been aware of the explosion hazard as well as of the relatively low heat recovery efficiency of the above described black liquor treating systems. A number of attempts have been described in prior art patents and scientific literature, directed to development of technology for solving the aforesaid problems. The most notable of ~327~2 these attempt have become known as: (1) St. Aegis Hydropyroly6i~ Process to Weyerhaeuser Dry Solids Pyrolyzes Process; and (3) Zimpro Wet Oxidation Process. None of Tao advocated prowesses has as yet received a general acceptance by the industry.
Details of the first two of these named processes are set out in the report by T. M. Grace, FORUM ON RAFT
RECOVERY ALTERNATIVES, Inst. of Paper Chemistry 1976, at pages 228 to 268. Halpern: (1975) Pulp Mill Processing, Notes Data Corporation, Park Ridge, NJ
1975, pp. 3Z2-325.
The Zimpro process was initially developed for the treatment and disposal of municipal sewage sludge and later extended for application to other areas of industrial waste disposal. In use of the Zimpro process for wet air oxidation of black liquor, the oxidation unit is said to achieve over 98% oxidation of COD in the liquor, while replacing conventional evaporators, furnaces, smelt dissever and other usual appurtenances of conventional black liquor treating systems. Steam recovered in the Zimpro process, in certain of toe designs, is recycled for ufie in the paper manufacturing process. The Zimpro process is described in Paper Trade Journal, May 15, 1979 at pages 34-36 and in Ellis, C. E., TAIPEI
PROCEEDINGS - 1982 Pulping Conference at pages glue.
Whereat in the described St. Aegis and Weyerhaeuser processes non-oxidative pyrolyzes it employed, in the Zimpro process the weak black liquor is completely oxidized by use of air as oxidant. All of these suggested alternative processes are comparatively complex and high in capital costs and represent significant departures from current technology of the industry.
1~32 I
SUMMARY OF THE INVENTION
In accordance with the present invention molecular oxygen of high purity it employed for partial oxidation of strong black liquor and the heat 5 of oxidation is utilized to flash the oxidized black liquor to dry or semi-dry old, which solids can be fed to a conventional recovery boiler for complete combustion of organic and recovery of contained inorganic chemicals. Part of the steam recovered in flashing the oxidized liquor is used upstream in concentration of the black liquor and the remainder made available for power generation or other desired use in the pulping plant or elsewhere. By operation in accordance with the invention improved efficiency of heat recovery is achieved, and, since most or all of the water normally contained in black liquor charged to the recovery boiler is eliminated, the explosion hazard is avoided or largely reduced.
The oxygen based recovery process of the present invention (OBRP) can be applied to the unoxidized strong black liquor effluent from the direct or indirect contact evaporator of a standard Raft recovery system, as well as in modified systems in which partial oxidation of the black liquor is carried out after the final stage in the multiple effect concentration of the liquor or at an intermediate stage of the multiple effect evaporation. In other hereinafter disclosed embodiments the process of the invention can be operated for partial oxidation of the strong black liquor effluent discharged from the multiple effect evaporation, thus replacing or eliminating the need for a direct or indirect contact evaporator in the recovery system.
~232'7~
GRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings illustrate by process flow diagrams systems for practice of the invention as compared with known prior art systems. In these drawings:
Figure 1 is a schematic flow diagram of a standard prior art black liquor treating system employing a direct contact evaporator:
Figure 2 ill a schematic flow diagram of a prior art system similar to that of Figure 1 but further incorporating means for partial oxidation of the black liquor prior to its introduction into the direct contact evaporator;
Figure 3 is a schematic flow diagram similar to that of Figure 2 wherein further oxidation of the black liquor is applied, in accordance with one embodiment of the invention, to the concentrated black liquor effluent discharged from the direct contact evaporator;
Figure 4 is a schematic flow diagram of a standard black liquor recovery system employing indirect contact evaporation (ICE);
Figure 5 is a schematic flow diagram similar to that of Figure 4 in which the concentrated liquor discharged from the indirect contact evaporation is subjected to partial oxidation in accordance with another embodiment of the invention:
Figure 6 is a schematic flow diagram in accordance with another embodiment of the invention wherein the conventional direct or indirect contact evaporator is eliminated and partial oxidation applied directly to the strong black liquor leaving the multiple effect evaporation system.
~23Z7~Z
DETAILED DESCRIPTION
In each of the 6y~tems illustrated in the accompanying drawings the numerical values shown are bayed on the treatment applied per ton of pulp in the black liquor discharged from the pulp worry. The heat content of the several streams it given in million of But (MM Btu3.
A shown in Figure 1, in a known standard system for treatment of black liquor from a Raft pulping plant the weak black liquor from the pulp wishers, containing a pulp concentration of about 15% by weight is brought to 50~ concentration by evaporation of liquid in a multiple effect evaporation system. The obtained strong black liquor it then further evaporated to a higher concentration and charged to the recovery boiler. -In the system illustrated in Figure 1, the strong black liquor from the multiple-effect evaporation system it brought to about 65% concentration in a direct contact evaporator and charged to the recovery boiler for combustion therein. As products of combustion in the recovery boiler there are obtained, (1) an inorganic smelt from which the contained chemical are recovered by caustic treatment, (2) flue gay at a temperature of about 600F which it utilized a the heat Ursa for the direct contact evaporator and recoverable exhaust team calculated to have a heat content of 11.7 million But. Of the team available from the recovery boiler 2.8 million But are used to supply required heat to the multiple effect evaporation system, leaving an available net steam product of I
million But for use in heat or power production in the pulping plant or elsewhere a desired. The spent flue gas discharged from the direct contact evaporator it ~X327~2 at a temperature of 325F (=163C) and will contain in the order of about 4175 pounds water.
The system of Figure 2 of the accompanying drawings employs an oxidizing reactor for oxidation of the strong black liquor enroot from the multiple effect evaporation system to the direct contact evaporator. In that respect the illustrated system it similar in operational sequence to systems such as are disclosed in US. Patents Nos. 3,928,531; 4,23g,589 and 4,313,788. I disclosed in Figure 2, oxidation of the partly concentrated black liquor with molecular oxygen upstream of the direct contact evaporator, will provide, from the heat evolved by the oxidizing reaction, a flash vapor (steam) which is utilized to provide part of the heat requirement in the multiple effect evaporation system.
The exhaust steam from the recovery boiler, however, will have a heat content of 11.1 million But, which it less than that of the corresponding Figure 1 operation. Since only 2.1 million But of the total steam product from the recovery boiler are needed for the multiple effect evaporator system to supplement that supplied by the oxidation reaction, there is available a net steam product of 9.0 million But for other desired use.
In the Figure 3 embodiment, in accordance with the present invention, the operational sequence and components of the system are similar to those employed in the process diagram of Figure 2, except that further oxidation with molecular oxygen is carried out on the concentrated black liquor (having 65% solids) discharged from the direct contact evaporation step.
As a result of such oxidation, designated by block OBRP in tyke flow diagram, the liquor is further concentrated to a dry solid content in the range of ~X327~2 80-100% and charged to combustion in the recovery furnace. The heat balance values of the several streams in Figure 3 are bayed on carrying the OBRP
oxidation to provide 100~ solids. While the same total steam production is had (11.1 MM But as in the Figure 2 example, the net steam available from the recovery boiler (10.9 MM But) is about 21 to over 22%
greater than that available from systems according to Figures 1 or 2.
Figure 4 illustrates a standard prior art system employing an indirect contact evaporation step applied to the strong black liquor discharged from the multiple effect evaporation system. In such systems there is a comparatively high total steam effluent ~lZ.7 MM But) discharged from the recovery boiler;
part of that discharged steam is utilized for heating the indirect contact evaporator (3.2 MM But), leaving a net steam make of only 9.5 MM But. A significant part of otherwise available heat is wasted in the wet flue gas discharged from the recovery boiler.
By partially oxidizing the concentrated black liquor discharged from the indirect contact evaporation step (65~ solids) in accordance with the invention, as illustrated at block OBRP of Figure 5, further evaporation of the liquid is had from the heat of the oxidation reaction, bringing the liquor to a solids concentration of 80~-100%, thus substantially reducing or eliminating the hazard of explosion in the recovery furnace. In the preferred example illustrated in Figure 5, the black liquor discharged from the indirect contact evaporation step is brought to 96% solids concentration by partial oxidation with high purity oxygen at OBRP before introduction into the recovery boiler.
~2327JL2 At this high solids concentration the total team production in the recovery furnace will provide a heat content ox 12.7 million But. An additional 1.8 million But becomes available from the heat of the oxidation reaction at OBRP which is utilized in the multiple effect evaporation system. Since 1.8 million But are withdrawn from the steam discharged from the recovery boiler, the net steam available from the boiler will provide 11.3 million But for other desired use. Thus, by incorporating the oxidation step in the line of liquid flow from the indirect contact evaporation and the recovery boiler, there is obtained about a 20% improvement in net available heat over the prior art system of Figure 4.
In the embodiment of the invention illustrated in Figure 6, the intermediate further concentration of the strong black liquor leaving the multiple effect evaporation system by resort to direct or indirect evaporators is eliminated and replaced by partly oxidizing the liquor effluent from the multiple effect evaporation system (50% iodize concentration) before its introduction into the recovery boiler. In the illustrated example of Figure I, the liquor leaving the multiple effect evaporation system is subjected to partial oxidation with high purity oxygen at OBRP.
The heat evolved by the oxidation reaction provides a net of 2.8 million But for use in providing the heat input required in the multiple effect evaporation system while evaporating the liquid during such oxidation to a solids concentration, in the illustrated example, to 83% solids concentration for introduction into the recovery boiler. Thus, in addition to savings in capital costs as a result of eliminating the direct or indirect contact evaporators, there is an additional plus in the 123Z~.2 available heat value of the net steam from the recovery boiler. The net steam product of 11.51 million But made available represents a 21-29~
improvement over the prior art systems of Figures 1,
PUS
HEAT RECOVERY IN BLACK LIQUOR OXIDATION
TECHNICAL FIELD
The present invention relate to the treatment of black liquor from pulp mills.
BACKGROUND OF THE INVENTION
In the standard process for treatment of black liquor from the Raft Pulping Process, the weak black liquor containing about 15% solids is concentrated, typically in a multiple effect evaporation facility, to a concentration of about 45-50% solids. The thus obtained "ztron~" or "heavy" black liquor is further evaporated to a solid concentration of about 65% or more and in such highly concentrated state is subjected to combustion in a recovery boiler. In such systems wherein a direct contact evaporator it employed for concentrating the liquid from the multiple effect facility, flue gas from the recovery boiler is employed to supply heat to the direct contact evaporator (DOE). The smelt recovered from the boiler is sent to further processing to reclaim available chemical values therein, for use in the pulping process.
In other known Raft pulp mill recovery processes the strong black liquor from the multiple effect evaporation is further concentrated to about 65%
solids level by indirect contact (forced circulation) evaporator, before being fed to the recovery boiler.
327~2 In recent years it has been the prevailing practice to subject the black liquor to oxidation at some stage in the evaporation sequence, thereby converting sulfur values therein to more stable form such as thiosulfates and/or sulfates, which among other benefits obtained, significantly reduced the release of malodorous sulfur compounds to the atmosphere.
In US. Patents Nos. 4,239,589 and 4,313,788, black liquor treating systems are disclosed in which the oxidation of the black liquor is integrated into the multiple effect evaporation stage of the pulp mill recovery sequence. The heat of the oxidation reaction is recovered as flash steam and is employed in providing part of the heat requirement of the multiple effect evaporation system, thus reducing demand for outside steam.
In these prior art processes for treatment of black liquor, whether or not oxidation of the liquor is practiced, the concentrated liquor which is fed to the recovery furnace will normally contain about 35%
water, which reduces heat recovery efficiency by carrying away heat unproductively with the flue gases as latent heat of vaporization. In addition to the thermal effect, the presence of water poses an ever present danger of recovery boiler explosion because of reactions occurring in the smelt bed of the recovery boiler, which are difficult to control.
The pulping industry has been aware of the explosion hazard as well as of the relatively low heat recovery efficiency of the above described black liquor treating systems. A number of attempts have been described in prior art patents and scientific literature, directed to development of technology for solving the aforesaid problems. The most notable of ~327~2 these attempt have become known as: (1) St. Aegis Hydropyroly6i~ Process to Weyerhaeuser Dry Solids Pyrolyzes Process; and (3) Zimpro Wet Oxidation Process. None of Tao advocated prowesses has as yet received a general acceptance by the industry.
Details of the first two of these named processes are set out in the report by T. M. Grace, FORUM ON RAFT
RECOVERY ALTERNATIVES, Inst. of Paper Chemistry 1976, at pages 228 to 268. Halpern: (1975) Pulp Mill Processing, Notes Data Corporation, Park Ridge, NJ
1975, pp. 3Z2-325.
The Zimpro process was initially developed for the treatment and disposal of municipal sewage sludge and later extended for application to other areas of industrial waste disposal. In use of the Zimpro process for wet air oxidation of black liquor, the oxidation unit is said to achieve over 98% oxidation of COD in the liquor, while replacing conventional evaporators, furnaces, smelt dissever and other usual appurtenances of conventional black liquor treating systems. Steam recovered in the Zimpro process, in certain of toe designs, is recycled for ufie in the paper manufacturing process. The Zimpro process is described in Paper Trade Journal, May 15, 1979 at pages 34-36 and in Ellis, C. E., TAIPEI
PROCEEDINGS - 1982 Pulping Conference at pages glue.
Whereat in the described St. Aegis and Weyerhaeuser processes non-oxidative pyrolyzes it employed, in the Zimpro process the weak black liquor is completely oxidized by use of air as oxidant. All of these suggested alternative processes are comparatively complex and high in capital costs and represent significant departures from current technology of the industry.
1~32 I
SUMMARY OF THE INVENTION
In accordance with the present invention molecular oxygen of high purity it employed for partial oxidation of strong black liquor and the heat 5 of oxidation is utilized to flash the oxidized black liquor to dry or semi-dry old, which solids can be fed to a conventional recovery boiler for complete combustion of organic and recovery of contained inorganic chemicals. Part of the steam recovered in flashing the oxidized liquor is used upstream in concentration of the black liquor and the remainder made available for power generation or other desired use in the pulping plant or elsewhere. By operation in accordance with the invention improved efficiency of heat recovery is achieved, and, since most or all of the water normally contained in black liquor charged to the recovery boiler is eliminated, the explosion hazard is avoided or largely reduced.
The oxygen based recovery process of the present invention (OBRP) can be applied to the unoxidized strong black liquor effluent from the direct or indirect contact evaporator of a standard Raft recovery system, as well as in modified systems in which partial oxidation of the black liquor is carried out after the final stage in the multiple effect concentration of the liquor or at an intermediate stage of the multiple effect evaporation. In other hereinafter disclosed embodiments the process of the invention can be operated for partial oxidation of the strong black liquor effluent discharged from the multiple effect evaporation, thus replacing or eliminating the need for a direct or indirect contact evaporator in the recovery system.
~232'7~
GRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings illustrate by process flow diagrams systems for practice of the invention as compared with known prior art systems. In these drawings:
Figure 1 is a schematic flow diagram of a standard prior art black liquor treating system employing a direct contact evaporator:
Figure 2 ill a schematic flow diagram of a prior art system similar to that of Figure 1 but further incorporating means for partial oxidation of the black liquor prior to its introduction into the direct contact evaporator;
Figure 3 is a schematic flow diagram similar to that of Figure 2 wherein further oxidation of the black liquor is applied, in accordance with one embodiment of the invention, to the concentrated black liquor effluent discharged from the direct contact evaporator;
Figure 4 is a schematic flow diagram of a standard black liquor recovery system employing indirect contact evaporation (ICE);
Figure 5 is a schematic flow diagram similar to that of Figure 4 in which the concentrated liquor discharged from the indirect contact evaporation is subjected to partial oxidation in accordance with another embodiment of the invention:
Figure 6 is a schematic flow diagram in accordance with another embodiment of the invention wherein the conventional direct or indirect contact evaporator is eliminated and partial oxidation applied directly to the strong black liquor leaving the multiple effect evaporation system.
~23Z7~Z
DETAILED DESCRIPTION
In each of the 6y~tems illustrated in the accompanying drawings the numerical values shown are bayed on the treatment applied per ton of pulp in the black liquor discharged from the pulp worry. The heat content of the several streams it given in million of But (MM Btu3.
A shown in Figure 1, in a known standard system for treatment of black liquor from a Raft pulping plant the weak black liquor from the pulp wishers, containing a pulp concentration of about 15% by weight is brought to 50~ concentration by evaporation of liquid in a multiple effect evaporation system. The obtained strong black liquor it then further evaporated to a higher concentration and charged to the recovery boiler. -In the system illustrated in Figure 1, the strong black liquor from the multiple-effect evaporation system it brought to about 65% concentration in a direct contact evaporator and charged to the recovery boiler for combustion therein. As products of combustion in the recovery boiler there are obtained, (1) an inorganic smelt from which the contained chemical are recovered by caustic treatment, (2) flue gay at a temperature of about 600F which it utilized a the heat Ursa for the direct contact evaporator and recoverable exhaust team calculated to have a heat content of 11.7 million But. Of the team available from the recovery boiler 2.8 million But are used to supply required heat to the multiple effect evaporation system, leaving an available net steam product of I
million But for use in heat or power production in the pulping plant or elsewhere a desired. The spent flue gas discharged from the direct contact evaporator it ~X327~2 at a temperature of 325F (=163C) and will contain in the order of about 4175 pounds water.
The system of Figure 2 of the accompanying drawings employs an oxidizing reactor for oxidation of the strong black liquor enroot from the multiple effect evaporation system to the direct contact evaporator. In that respect the illustrated system it similar in operational sequence to systems such as are disclosed in US. Patents Nos. 3,928,531; 4,23g,589 and 4,313,788. I disclosed in Figure 2, oxidation of the partly concentrated black liquor with molecular oxygen upstream of the direct contact evaporator, will provide, from the heat evolved by the oxidizing reaction, a flash vapor (steam) which is utilized to provide part of the heat requirement in the multiple effect evaporation system.
The exhaust steam from the recovery boiler, however, will have a heat content of 11.1 million But, which it less than that of the corresponding Figure 1 operation. Since only 2.1 million But of the total steam product from the recovery boiler are needed for the multiple effect evaporator system to supplement that supplied by the oxidation reaction, there is available a net steam product of 9.0 million But for other desired use.
In the Figure 3 embodiment, in accordance with the present invention, the operational sequence and components of the system are similar to those employed in the process diagram of Figure 2, except that further oxidation with molecular oxygen is carried out on the concentrated black liquor (having 65% solids) discharged from the direct contact evaporation step.
As a result of such oxidation, designated by block OBRP in tyke flow diagram, the liquor is further concentrated to a dry solid content in the range of ~X327~2 80-100% and charged to combustion in the recovery furnace. The heat balance values of the several streams in Figure 3 are bayed on carrying the OBRP
oxidation to provide 100~ solids. While the same total steam production is had (11.1 MM But as in the Figure 2 example, the net steam available from the recovery boiler (10.9 MM But) is about 21 to over 22%
greater than that available from systems according to Figures 1 or 2.
Figure 4 illustrates a standard prior art system employing an indirect contact evaporation step applied to the strong black liquor discharged from the multiple effect evaporation system. In such systems there is a comparatively high total steam effluent ~lZ.7 MM But) discharged from the recovery boiler;
part of that discharged steam is utilized for heating the indirect contact evaporator (3.2 MM But), leaving a net steam make of only 9.5 MM But. A significant part of otherwise available heat is wasted in the wet flue gas discharged from the recovery boiler.
By partially oxidizing the concentrated black liquor discharged from the indirect contact evaporation step (65~ solids) in accordance with the invention, as illustrated at block OBRP of Figure 5, further evaporation of the liquid is had from the heat of the oxidation reaction, bringing the liquor to a solids concentration of 80~-100%, thus substantially reducing or eliminating the hazard of explosion in the recovery furnace. In the preferred example illustrated in Figure 5, the black liquor discharged from the indirect contact evaporation step is brought to 96% solids concentration by partial oxidation with high purity oxygen at OBRP before introduction into the recovery boiler.
~2327JL2 At this high solids concentration the total team production in the recovery furnace will provide a heat content ox 12.7 million But. An additional 1.8 million But becomes available from the heat of the oxidation reaction at OBRP which is utilized in the multiple effect evaporation system. Since 1.8 million But are withdrawn from the steam discharged from the recovery boiler, the net steam available from the boiler will provide 11.3 million But for other desired use. Thus, by incorporating the oxidation step in the line of liquid flow from the indirect contact evaporation and the recovery boiler, there is obtained about a 20% improvement in net available heat over the prior art system of Figure 4.
In the embodiment of the invention illustrated in Figure 6, the intermediate further concentration of the strong black liquor leaving the multiple effect evaporation system by resort to direct or indirect evaporators is eliminated and replaced by partly oxidizing the liquor effluent from the multiple effect evaporation system (50% iodize concentration) before its introduction into the recovery boiler. In the illustrated example of Figure I, the liquor leaving the multiple effect evaporation system is subjected to partial oxidation with high purity oxygen at OBRP.
The heat evolved by the oxidation reaction provides a net of 2.8 million But for use in providing the heat input required in the multiple effect evaporation system while evaporating the liquid during such oxidation to a solids concentration, in the illustrated example, to 83% solids concentration for introduction into the recovery boiler. Thus, in addition to savings in capital costs as a result of eliminating the direct or indirect contact evaporators, there is an additional plus in the 123Z~.2 available heat value of the net steam from the recovery boiler. The net steam product of 11.51 million But made available represents a 21-29~
improvement over the prior art systems of Figures 1,
2, and 5.
The material and energy results from the illustrated systems are summarized in Table 1 on the basis MM But per ton of pulp.
Available Oxygen Steam System Figure % of Pulp MM BTU
Prior Art with DOE 1 0 8.93 Prior Art with DOE
and THY 2 6.0 8.96 Using DOE. THY and OBRP 3* 22.8 10.87 Prior Art using ICE 4 0 9.51 Using ICE with OBRP 5* 16.8 11.30 Using OBRP Alone 6* 24.6 11.51 *The processes according to the invention are indicated by asterisk.
The process energy balances are tabulated in Table 2. The indicated numerical values are on the basis of MM BTU/ton of pulp.
TABLE 2 12327~
OBRP PROCESS ENERGY BALANCE
(Bests 1 Ton Pulp all Values M~BTU/Ton) Figure # 1 2 3 4 5 6 Configuration DOE DOE DOE, THY ICE
Ho Box THY OBRP ICE OBRP OBRP
INPUTS
Gross Heat Value 19.80 19.12 19.12 19.8019.80 19.~0 Heat on I
Heat in liquor 0.63 .63 .63 .46 .46 .63 Air from SUE. .81 .81 Sal .83 .83 .72 BY Heater .19 19 --_ 08 -- --TOTAL INPUT 21.43 20.75 20.56 21.1721.09 21.15 LOSSES
Losses Common to Both Furnace Types 2.72 2.72 2.72 2.72 2.72 2.72 Dry Flue Gas* .97 .94 .88 1.29 1.21 1.14 ~olsture from Ho in Solids 1.12 1.12 1.12 1.16 1.16 1.03 Evaporation of water in Black liquor 3.47 3 47 1.62 1.93 14 75 TOTAL LOSSES 8.2S 8.25 6.34 7.10 5.23 5.64 Steam at SO 13.15 12.50 14.22 14.0715.8S 15.51 LESS
Soot Blower .19 .19 .19 .25 .25 .25 BY Heaters .19 .19 -- JOB .08 --St. Air Heaters 1.04 1.04 1 04 1.07 1.07 95 TOTAL STEAM DRAW 1.42 1.42 1.23 1.40 1.40 1.20 Steam to Evans 2.80 2.12 2.12 3.16 3.16 2.80 Steam Available for Process or Power Generatlon8.93 8.96 10.87 9.5111.30 11.51 *Temperatures of Flue Gas 325F 325F 325F ~00F 400F 400F(163C) (163C) (16~C) (204C)(204C) (204 1~327~2 As it teen from Table 2, by the addition of the oxidation step of Figure 3 following the usual direct contact evaporator, there is obtained an improvement in net steam made available of over 21%. In the case of systems employing indirect contact evaporation. the oxidation step (Figure 5) obtain an improvement in net steam production of about 19%. The system of Figure 6 also effects an improvement in net steam production by about 21-28~ as compared with conventional systems.
The material and energy results from the illustrated systems are summarized in Table 1 on the basis MM But per ton of pulp.
Available Oxygen Steam System Figure % of Pulp MM BTU
Prior Art with DOE 1 0 8.93 Prior Art with DOE
and THY 2 6.0 8.96 Using DOE. THY and OBRP 3* 22.8 10.87 Prior Art using ICE 4 0 9.51 Using ICE with OBRP 5* 16.8 11.30 Using OBRP Alone 6* 24.6 11.51 *The processes according to the invention are indicated by asterisk.
The process energy balances are tabulated in Table 2. The indicated numerical values are on the basis of MM BTU/ton of pulp.
TABLE 2 12327~
OBRP PROCESS ENERGY BALANCE
(Bests 1 Ton Pulp all Values M~BTU/Ton) Figure # 1 2 3 4 5 6 Configuration DOE DOE DOE, THY ICE
Ho Box THY OBRP ICE OBRP OBRP
INPUTS
Gross Heat Value 19.80 19.12 19.12 19.8019.80 19.~0 Heat on I
Heat in liquor 0.63 .63 .63 .46 .46 .63 Air from SUE. .81 .81 Sal .83 .83 .72 BY Heater .19 19 --_ 08 -- --TOTAL INPUT 21.43 20.75 20.56 21.1721.09 21.15 LOSSES
Losses Common to Both Furnace Types 2.72 2.72 2.72 2.72 2.72 2.72 Dry Flue Gas* .97 .94 .88 1.29 1.21 1.14 ~olsture from Ho in Solids 1.12 1.12 1.12 1.16 1.16 1.03 Evaporation of water in Black liquor 3.47 3 47 1.62 1.93 14 75 TOTAL LOSSES 8.2S 8.25 6.34 7.10 5.23 5.64 Steam at SO 13.15 12.50 14.22 14.0715.8S 15.51 LESS
Soot Blower .19 .19 .19 .25 .25 .25 BY Heaters .19 .19 -- JOB .08 --St. Air Heaters 1.04 1.04 1 04 1.07 1.07 95 TOTAL STEAM DRAW 1.42 1.42 1.23 1.40 1.40 1.20 Steam to Evans 2.80 2.12 2.12 3.16 3.16 2.80 Steam Available for Process or Power Generatlon8.93 8.96 10.87 9.5111.30 11.51 *Temperatures of Flue Gas 325F 325F 325F ~00F 400F 400F(163C) (163C) (16~C) (204C)(204C) (204 1~327~2 As it teen from Table 2, by the addition of the oxidation step of Figure 3 following the usual direct contact evaporator, there is obtained an improvement in net steam made available of over 21%. In the case of systems employing indirect contact evaporation. the oxidation step (Figure 5) obtain an improvement in net steam production of about 19%. The system of Figure 6 also effects an improvement in net steam production by about 21-28~ as compared with conventional systems.
Claims (7)
1. In the process of treating black liquor obtained from wood pulping with sulfur-containing compounds in a system employing multiple effect evaporation as a step in concentration of such liquor prior to introduction of the concentrated liquor into a recovery boiler for combustion of solids therein contained, the improvement which comprises the further step of bringing the liquid effluent from the multiple effect evaporation to a concentration of 80% to 100%
solids prior to its introduction into the recovery boiler, wherein at least part of the heat required for such further step is obtained by oxidizing the said liquid effluent with high purity oxygen and utilizing the vapor evolved in such oxidation to supply at least part of the heat requirement in the multiple effect evaporation; and recovering at least part of the heat of combustion from said boiler as net steam make.
solids prior to its introduction into the recovery boiler, wherein at least part of the heat required for such further step is obtained by oxidizing the said liquid effluent with high purity oxygen and utilizing the vapor evolved in such oxidation to supply at least part of the heat requirement in the multiple effect evaporation; and recovering at least part of the heat of combustion from said boiler as net steam make.
2. The improvement as defined in Claim 1 wherein said oxidizing it applied to the liquor effluent from the multiple effect evaporation having a solids content in the range of about 50% solids.
3. The improvement as defined in Claim 1 wherein said oxidizing is applied to the black liquor effluent from multiple effect evaporation which has been subjected to an intermediate concentration step to bring the same to a solids concentration in the order of about 65% prior to said oxidizing.
4. The improvement as defined in Claim 3 wherein said intermediate concentration of the effluent from said multiple effect evaporation is effected by direct contact with flue gas discharged from the recovery boiler.
5. The improvement as defined in Claim 4 wherein at least part of the heat requirement of said multiple effect evaporation is supplied by part of the steam produced in the recovery boiler.
6. The improvement as defined in Claim 3 wherein said intermediate concentration of the black liquor to the 65% solids range is applied to partially oxidized liquor effluent from said multiple effect evaporation.
7. The improvement as defined in Claim 3 wherein said intermediate concentration of the effluent from said multiple effect evaporation is effected by indirect heat exchange with a portion of the steam generated in the recovery boiler.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/468,627 US4574356A (en) | 1982-02-11 | 1983-02-22 | Peak dynamic stress calculator |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US55708283A | 1983-12-01 | 1983-12-01 | |
| US557,082 | 1983-12-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1232712A true CA1232712A (en) | 1988-02-16 |
Family
ID=24223990
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000468627A Expired CA1232712A (en) | 1982-02-11 | 1984-11-26 | Heat recovery in black liquor oxidation |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1232712A (en) |
-
1984
- 1984-11-26 CA CA000468627A patent/CA1232712A/en not_active Expired
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