CA2164328C - Combustion of black liquor and processing of lime sludge in a recovery boiler - Google Patents
Combustion of black liquor and processing of lime sludge in a recovery boiler Download PDFInfo
- Publication number
- CA2164328C CA2164328C CA002164328A CA2164328A CA2164328C CA 2164328 C CA2164328 C CA 2164328C CA 002164328 A CA002164328 A CA 002164328A CA 2164328 A CA2164328 A CA 2164328A CA 2164328 C CA2164328 C CA 2164328C
- Authority
- CA
- Canada
- Prior art keywords
- lime sludge
- recovery boiler
- black liquor
- combustion
- furnace cavity
- 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 - Fee Related
Links
- 235000008733 Citrus aurantifolia Nutrition 0.000 title claims abstract description 46
- 235000011941 Tilia x europaea Nutrition 0.000 title claims abstract description 46
- 239000004571 lime Substances 0.000 title claims abstract description 46
- 239000010802 sludge Substances 0.000 title claims abstract description 46
- 238000011084 recovery Methods 0.000 title claims abstract description 29
- 238000002485 combustion reaction Methods 0.000 title claims abstract description 26
- 238000000034 method Methods 0.000 claims abstract description 23
- 239000000126 substance Substances 0.000 claims abstract description 14
- 241001062472 Stokellia anisodon Species 0.000 claims abstract description 12
- AGVJBLHVMNHENQ-UHFFFAOYSA-N Calcium sulfide Chemical compound [S-2].[Ca+2] AGVJBLHVMNHENQ-UHFFFAOYSA-N 0.000 claims abstract description 9
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 7
- ODINCKMPIJJUCX-UHFFFAOYSA-N calcium oxide Inorganic materials [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 claims description 10
- 230000008569 process Effects 0.000 claims description 10
- 229910000019 calcium carbonate Inorganic materials 0.000 claims description 8
- 239000002245 particle Substances 0.000 claims description 8
- 239000003546 flue gas Substances 0.000 claims description 7
- 238000010411 cooking Methods 0.000 claims description 6
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims description 5
- 230000009467 reduction Effects 0.000 claims description 5
- 239000000292 calcium oxide Substances 0.000 claims description 4
- 230000003647 oxidation Effects 0.000 claims description 4
- 238000007254 oxidation reaction Methods 0.000 claims description 4
- 239000007787 solid Substances 0.000 claims description 4
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims description 3
- BRPQOXSCLDDYGP-UHFFFAOYSA-N calcium oxide Chemical compound [O-2].[Ca+2] BRPQOXSCLDDYGP-UHFFFAOYSA-N 0.000 claims description 3
- 229910021653 sulphate ion Inorganic materials 0.000 claims description 3
- 238000004140 cleaning Methods 0.000 claims description 2
- 239000012717 electrostatic precipitator Substances 0.000 claims description 2
- 239000007789 gas Substances 0.000 claims description 2
- 239000004071 soot Substances 0.000 claims description 2
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 claims 2
- 238000001354 calcination Methods 0.000 description 8
- 239000000446 fuel Substances 0.000 description 5
- 238000006243 chemical reaction Methods 0.000 description 4
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 3
- 239000005864 Sulphur Substances 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 230000001105 regulatory effect Effects 0.000 description 3
- 229910000029 sodium carbonate Inorganic materials 0.000 description 3
- 239000002023 wood Substances 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 239000012670 alkaline solution Substances 0.000 description 2
- 229910002092 carbon dioxide Inorganic materials 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000005855 radiation Effects 0.000 description 2
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- 229920003043 Cellulose fiber Polymers 0.000 description 1
- 101100348017 Drosophila melanogaster Nazo gene Proteins 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- 229920001131 Pulp (paper) Polymers 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 239000011575 calcium Substances 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000002309 gasification Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000009533 lab test Methods 0.000 description 1
- 229920005610 lignin Polymers 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- HYHCSLBZRBJJCH-UHFFFAOYSA-M sodium hydrosulfide Chemical compound [Na+].[SH-] HYHCSLBZRBJJCH-UHFFFAOYSA-M 0.000 description 1
- 229910052979 sodium sulfide Inorganic materials 0.000 description 1
- GRVFOGOEDUUMBP-UHFFFAOYSA-N sodium sulfide (anhydrous) Chemical compound [Na+].[Na+].[S-2] GRVFOGOEDUUMBP-UHFFFAOYSA-N 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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
- D21C11/04—Regeneration of pulp liquors or effluent waste waters of alkali lye
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C11/00—Regeneration of pulp liquors or effluent waste waters
- D21C11/0085—Introduction of auxiliary substances into the regenerating system in order to improve the performance of certain steps of the latter, the presence of these substances being confined to the regeneration cycle
- D21C11/0092—Substances modifying the evaporation, combustion, or thermal decomposition processes of black liquor
-
- 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
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
- F23G7/00—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals
- F23G7/04—Incinerators or other apparatus for consuming industrial waste, e.g. chemicals of waste liquors, e.g. sulfite liquors
Landscapes
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Paper (AREA)
- Gasification And Melting Of Waste (AREA)
- Heat Treatment Of Water, Waste Water Or Sewage (AREA)
Abstract
A method of modifying the course of combustion when evaporated black liquor is burnt in the furnace cavity of a recovery boiler is described. The method implies that lime sludge is supplied to the furnace cavity whereby the course of combustion is modified so that the temperature in the furnace cavity is raised. Also use of a recovery boil er for simultaneous combustion of black liquor and processing of lime sludge is described. In one embodiment of this use is disclosed that the processing of lime sludge is performed so that increased formation of calcium sulphide in the smelt of inorganic chemicals, which is formed in the recovery boiler, is obtained and/or so that the lime sludge is calcined.
Description
COMBUSTION OF BLACK LIQUOR AND PROCESSING OF
LIME SLUDGE IN A RECOVERY BOILER
The present invention relates to a method of modifying the course of combustion when evaporated black liquor is burnt. More precisely, the method involves supplying of lime sludge to the furnace cavity in such an amount that the course of combustion is modified. Further, the invention relates to the use of a recovering boiler.for simultaneous combustion of.black liquor and processing of lime sludge.
The processing of lime sludge implies a calcination of the lime sludge andlor an increase in the formation of calcium sulphide in the smelt of inorganic chemicals which is formed in the recovering boiler.
Background in the production of woodpulp in accordance with the sulphate process, the wood is treated in the form of wood chips in an alkaline solution, which mainly consists of NaOH and NaHS, in a cooking process at a temperature which in the final stage lies in the range of 150-175°C.
Upon separation of the cellulose fibres which have been detached in the cooking process, a solution of a recycled liquor is obtained, which is also called black liquor, and which in addition to the inorganic chemicals charged in the cooking process also contains from the wood released organic substanses, which mainly consist of lignin.
Thereafter, the black liquor is evaporated to a dry solids content which makes it possible to bum the organic contents without the need of supplying supplementary auxiliary fuel to the combustion plant.
LIME SLUDGE IN A RECOVERY BOILER
The present invention relates to a method of modifying the course of combustion when evaporated black liquor is burnt. More precisely, the method involves supplying of lime sludge to the furnace cavity in such an amount that the course of combustion is modified. Further, the invention relates to the use of a recovering boiler.for simultaneous combustion of.black liquor and processing of lime sludge.
The processing of lime sludge implies a calcination of the lime sludge andlor an increase in the formation of calcium sulphide in the smelt of inorganic chemicals which is formed in the recovering boiler.
Background in the production of woodpulp in accordance with the sulphate process, the wood is treated in the form of wood chips in an alkaline solution, which mainly consists of NaOH and NaHS, in a cooking process at a temperature which in the final stage lies in the range of 150-175°C.
Upon separation of the cellulose fibres which have been detached in the cooking process, a solution of a recycled liquor is obtained, which is also called black liquor, and which in addition to the inorganic chemicals charged in the cooking process also contains from the wood released organic substanses, which mainly consist of lignin.
Thereafter, the black liquor is evaporated to a dry solids content which makes it possible to bum the organic contents without the need of supplying supplementary auxiliary fuel to the combustion plant.
After evaporation of the black liquor, it is transported to a liquor combustion plant, which normally is a so called recovery boiler, but can also be a liquor gasification plant.
In a recovery boiler the burning of the black liquor is mainly effected in the furnace cavity which comprises an upper oxidation zone and a lower reduction zone, the temperature being higher in the oxidation zone than in the reduction zone.
In the combustion of the organic part of the black liquor the chemical energy is taken care of by the transformation to heat energy and electrical energy, and the inorganic chemicals are recovered. Normally, the sulphur content is converted to an active form for the cooking process, i. e. to sulphide. The portion of sodium which is not bound to the sulphur exists mainly in the form of carbonate.
The inorganic chemicals leave the combustion process mainly in melted form (e.g. at 750-850°C) and are further processed for recovery of the chemicals.
In such a further processing there is i.a. formed sparingly soluble CaC03, which is called lime sludge. Said lime sludge is washed with water prior to returning in a rotary kiln, whereby a weakly alkaline solution (weak liquor) is obtained. The returning of the lime sludge, i, e. the conversion of CaC03 into CaO, is energy-consuming and puts high demands on the quality of the fuel, so that a high flashing point can be maintained in the calcination zone of the rotary kiln. Normally approximately 40-45 % of the effective heat of the fuel is consumed by the calcination reaction, 15-20 % of the consumed fuel being lost by heat radiation from the mantle surface of the kiln and the lime cooler.
In experiments aiming at an improvement of the utilization of a recovery boiler it has now surprisingly been found that the recovery boiler may be used for simultaneous combustion of the black liquor and the processing of lime sludge. Most surprising i s however that the course of combustion is modified in the furnace cavity when blacf;
In a recovery boiler the burning of the black liquor is mainly effected in the furnace cavity which comprises an upper oxidation zone and a lower reduction zone, the temperature being higher in the oxidation zone than in the reduction zone.
In the combustion of the organic part of the black liquor the chemical energy is taken care of by the transformation to heat energy and electrical energy, and the inorganic chemicals are recovered. Normally, the sulphur content is converted to an active form for the cooking process, i. e. to sulphide. The portion of sodium which is not bound to the sulphur exists mainly in the form of carbonate.
The inorganic chemicals leave the combustion process mainly in melted form (e.g. at 750-850°C) and are further processed for recovery of the chemicals.
In such a further processing there is i.a. formed sparingly soluble CaC03, which is called lime sludge. Said lime sludge is washed with water prior to returning in a rotary kiln, whereby a weakly alkaline solution (weak liquor) is obtained. The returning of the lime sludge, i, e. the conversion of CaC03 into CaO, is energy-consuming and puts high demands on the quality of the fuel, so that a high flashing point can be maintained in the calcination zone of the rotary kiln. Normally approximately 40-45 % of the effective heat of the fuel is consumed by the calcination reaction, 15-20 % of the consumed fuel being lost by heat radiation from the mantle surface of the kiln and the lime cooler.
In experiments aiming at an improvement of the utilization of a recovery boiler it has now surprisingly been found that the recovery boiler may be used for simultaneous combustion of the black liquor and the processing of lime sludge. Most surprising i s however that the course of combustion is modified in the furnace cavity when blacf;
liquor is burnt in the presence of lime sludge, so that the temperature in said furnace cavity is raised even though the conversion of CaC03 to Ca0 is endothermic.
One aspect of the invention is directed to the use of a recovery boiler for simultaneous burning of black liquor and processing of lime sludge.
One embodiment of this aspect of the invention implies that the processing of the lime sludge is calcination of lime sludge and/or the processing of lime sludge is conducted so that increased formation of calcium sulphide in the smelt of inorganic chemicals, which is formed in the recovery boiler, is obtained.
The utilization of such calcium sulphide rich smelt of inorganic chemicals for the production of white liquor with enhanced and/or reduced sulphidity has been disclosed in the simultaneously filed patent application having the title "Preparation of white liquor".
Another aspect of the invention is directed to a method of modifying the course of combustion when evaporated black liquor is burnt in the furnace cavity of a recovery boiler by supplying lime sludge to the furnace cavity, whereby the course of combustion is modfied so that the temperature in the furnace cavity is raised, and at the same time the supplied lime sludge is processed.
In one embodiment of the invention the type of processing of the supplied lime sludge is controlled by regulation of the temperature in the furnace cavity.
The temperature may then be regulated so that the lime sludge will be at least partially calcined. Moreover, the temperature may be regulated so that the lime sludge will give increased formation of calcium sulphide in the smelt of inorganic chemicals which has been formed in the recovery boiler.
3a In a specific method aspect, the invention provides a method of modifying the course of combustion of evaporated black liquor obtained from a sulphate pulp cooking process in a recovery boiler having a furnace cavity with an upper oxidation zone, a lower reduction zone and a gas flue, which comprises supplying evaporated black liquor and lime sludge to the furnace cavity of the recovery boiler to regulate the temperature in the furnace cavity of the recovery boiler so that the lime sludge is at least partially calcined to calcium oxide and the lime sludge gives increased formation of calcium sulphide in a smelt of inorganic chemicals which is formed in the recovery boiler and wherein the black liquor and the lime sludge is premixed in an approximate dry solid content ratio of 15:1.
One aspect of the invention is directed to the use of a recovery boiler for simultaneous burning of black liquor and processing of lime sludge.
One embodiment of this aspect of the invention implies that the processing of the lime sludge is calcination of lime sludge and/or the processing of lime sludge is conducted so that increased formation of calcium sulphide in the smelt of inorganic chemicals, which is formed in the recovery boiler, is obtained.
The utilization of such calcium sulphide rich smelt of inorganic chemicals for the production of white liquor with enhanced and/or reduced sulphidity has been disclosed in the simultaneously filed patent application having the title "Preparation of white liquor".
Another aspect of the invention is directed to a method of modifying the course of combustion when evaporated black liquor is burnt in the furnace cavity of a recovery boiler by supplying lime sludge to the furnace cavity, whereby the course of combustion is modfied so that the temperature in the furnace cavity is raised, and at the same time the supplied lime sludge is processed.
In one embodiment of the invention the type of processing of the supplied lime sludge is controlled by regulation of the temperature in the furnace cavity.
The temperature may then be regulated so that the lime sludge will be at least partially calcined. Moreover, the temperature may be regulated so that the lime sludge will give increased formation of calcium sulphide in the smelt of inorganic chemicals which has been formed in the recovery boiler.
3a In a specific method aspect, the invention provides a method of modifying the course of combustion of evaporated black liquor obtained from a sulphate pulp cooking process in a recovery boiler having a furnace cavity with an upper oxidation zone, a lower reduction zone and a gas flue, which comprises supplying evaporated black liquor and lime sludge to the furnace cavity of the recovery boiler to regulate the temperature in the furnace cavity of the recovery boiler so that the lime sludge is at least partially calcined to calcium oxide and the lime sludge gives increased formation of calcium sulphide in a smelt of inorganic chemicals which is formed in the recovery boiler and wherein the black liquor and the lime sludge is premixed in an approximate dry solid content ratio of 15:1.
In a preferred embodiment of the invention the black liquor and the lime sludge are mixed before they are supplied to the furnace cavity.
The amount of lime sludge which is to be supplied in order to modify the course of combustion depends on several process parameters which may vary between different recovery boilers. However, a man of ordinary skill in the art may easily adapt the amount of lime sludge that is required to modify the course of combustion in the furnace cavity of a recovery boiler when the present invention is used, with the guidance of the present description of the invention.
The temperature in the furnace cavity may be controlled so that lime sludge wilt be at least partially calcined and/or so that lime sludge gives increased formation of calcium sulphide in the smelt of inorganic chemicals which is formed in the combustion plant. The determining factor is whether the temperature in the furnace cavity reaches calcination temperature for lime sludge, or whether the temperature is kept therebelow. In the formula below, which describe the reaction with lime sludge (CaC03) in the combustion of black liquor, the calcination temperature has been set at 800°C, but it can vary considerably e.g. by ~ 70°G.
1. CaC03 + Na2S > CaS + Na2C03 above 600°C
2. CaS + Na2C03 > Ca0 + NaZS + C02 above 800°C
3. Ca0 + NaZS > CaS + NazO below 800°C
The following relationship was established at a mill trial:
A
CaC03 > CaS ------- Ca0 B
0% (100-A+B)% (A-B)%
In the mill trial described below, A was =64.7 and B was =44.9, i.e. CaS=80.2 % and Ca0=19.8 %. In a laboratory experiment at 750°C, 15 minutes, 10 g smelt + 1.9 g lime sludge, A=0 and B=0, was obtained with 75 % of Ca as CaS.
At a mill trial the black liquor was premixed with lime sludge in an approximate dry solids content ratio of 15:1, (which corresponds to 20-30 % of the amount of lime 5 sludge that is produced in the process) and was supplied to the furnace cavity of the recovery boiler at normal capacity. The extensive follow-up of the analysis of the trial gave in summary the following results:
- The temperature of the smelt raised by approximately 100°C, which indicates a considerable raise of the temperature in the furnace cavity.
- The content of particles in the flue gases before the electrostatic precipitator was reduced by approximately 40%.
- Particles' pH increased from 9.8 to 10.4 despite a decreased content of Na2C03 in the particles.
- The temperature of outgoing superheated steam raised by approximately 15°C
during the trial, and returned thereafter to a tower level.
- Approximately 65 % of supplied CaC03 had reacted to Ca0 according to the formula 1 'above.
The reason for the modification of the course of combustion, which is expressed by the above observations, is not clarified, but the carbon dioxide formed at the simultaneous combustion of black liquor and processing of lime sludge (according to formula 2 above) is probably of importance for the modification.
Raised temperatures in the furnace cavity of a recovery boiler gives the following advantages for liquor combustion:
The heat recovery in the lower part of the furnace cavity is markedly improved.
The reduction of sulphur is improved.
The emission of particles with the flue gases from the level of the furnace cavity is considerably reduced (in the above example by approximately 40 %).
The amount of lime sludge which is to be supplied in order to modify the course of combustion depends on several process parameters which may vary between different recovery boilers. However, a man of ordinary skill in the art may easily adapt the amount of lime sludge that is required to modify the course of combustion in the furnace cavity of a recovery boiler when the present invention is used, with the guidance of the present description of the invention.
The temperature in the furnace cavity may be controlled so that lime sludge wilt be at least partially calcined and/or so that lime sludge gives increased formation of calcium sulphide in the smelt of inorganic chemicals which is formed in the combustion plant. The determining factor is whether the temperature in the furnace cavity reaches calcination temperature for lime sludge, or whether the temperature is kept therebelow. In the formula below, which describe the reaction with lime sludge (CaC03) in the combustion of black liquor, the calcination temperature has been set at 800°C, but it can vary considerably e.g. by ~ 70°G.
1. CaC03 + Na2S > CaS + Na2C03 above 600°C
2. CaS + Na2C03 > Ca0 + NaZS + C02 above 800°C
3. Ca0 + NaZS > CaS + NazO below 800°C
The following relationship was established at a mill trial:
A
CaC03 > CaS ------- Ca0 B
0% (100-A+B)% (A-B)%
In the mill trial described below, A was =64.7 and B was =44.9, i.e. CaS=80.2 % and Ca0=19.8 %. In a laboratory experiment at 750°C, 15 minutes, 10 g smelt + 1.9 g lime sludge, A=0 and B=0, was obtained with 75 % of Ca as CaS.
At a mill trial the black liquor was premixed with lime sludge in an approximate dry solids content ratio of 15:1, (which corresponds to 20-30 % of the amount of lime 5 sludge that is produced in the process) and was supplied to the furnace cavity of the recovery boiler at normal capacity. The extensive follow-up of the analysis of the trial gave in summary the following results:
- The temperature of the smelt raised by approximately 100°C, which indicates a considerable raise of the temperature in the furnace cavity.
- The content of particles in the flue gases before the electrostatic precipitator was reduced by approximately 40%.
- Particles' pH increased from 9.8 to 10.4 despite a decreased content of Na2C03 in the particles.
- The temperature of outgoing superheated steam raised by approximately 15°C
during the trial, and returned thereafter to a tower level.
- Approximately 65 % of supplied CaC03 had reacted to Ca0 according to the formula 1 'above.
The reason for the modification of the course of combustion, which is expressed by the above observations, is not clarified, but the carbon dioxide formed at the simultaneous combustion of black liquor and processing of lime sludge (according to formula 2 above) is probably of importance for the modification.
Raised temperatures in the furnace cavity of a recovery boiler gives the following advantages for liquor combustion:
The heat recovery in the lower part of the furnace cavity is markedly improved.
The reduction of sulphur is improved.
The emission of particles with the flue gases from the level of the furnace cavity is considerably reduced (in the above example by approximately 40 %).
- The nature of the particles is changed to the better, which reduces the clogging of the flue gas passages in the boiler and facilitates the cleaning of the heat surfaces and reduces the consumption of soot steam.
- Reduced amounts of deposits on the superheater surfaces give higher outgoing steam temperature and thus increased production of electricity.
- Increased calcination in the recovery boiler.
- An increase in the capacity of the liquor combustion.
Other advantages which can be obtained by conducting the processing of lime sludge in the recovery boiler is that the calcination can be done with a cheaper fuel and with lower energy consumption due to the fact that the high radiation losses that arise in a rotary kiln process are avoided. Moreover, the temperature in the furnace cavity may be regulated so that the processing of lime sludge is controlled so that increased amounts of calcium sulphide are formed in the smelt of inorganic chemicals, if this is considered to be desirable.
- Reduced amounts of deposits on the superheater surfaces give higher outgoing steam temperature and thus increased production of electricity.
- Increased calcination in the recovery boiler.
- An increase in the capacity of the liquor combustion.
Other advantages which can be obtained by conducting the processing of lime sludge in the recovery boiler is that the calcination can be done with a cheaper fuel and with lower energy consumption due to the fact that the high radiation losses that arise in a rotary kiln process are avoided. Moreover, the temperature in the furnace cavity may be regulated so that the processing of lime sludge is controlled so that increased amounts of calcium sulphide are formed in the smelt of inorganic chemicals, if this is considered to be desirable.
Claims (6)
1. A method of modifying the course of combustion of evaporated black liquor obtained from a sulphate pulp cooking process in a recovery boiler having a furnace cavity with an upper oxidation zone, a lower reduction zone and a gas flue, which comprises supplying evaporated black liquor and lime sludge to the furnace cavity of the recovery boiler to regulate the temperature in the furnace cavity of the recovery boiler so that the lime sludge is at least partially calcined to calcium oxide and the lime sludge gives increased formation of calcium sulphide in a smelt of inorganic chemicals which is formed in the recovery boiler and wherein the black liquor and the lime sludge is premixed in an approximate dry solid content ratio of 15:1.
2. The method of claim 1, wherein the temperature of the smelt is raised by approximately 100°C.
3. The method of claim 1 or 2, wherein the content of particles in the flue gas before contacting with an electrostatic precipitator are reduced by approximately 40%.
4. The method of claim 1, 2 or 3, wherein the particles in the flue gas have a pH of about 10.4.
5. The method of any one of claims 1 to 4, wherein approximately 65% of the supplied calcium carbonate lime sludge is reacted to calcium oxide.
6. The method of any one of claims 1 to 5, wherein flue gas particles reduce the clogging of flue gas passages in the boiler, facilitate the cleaning of heated surfaces and reduce the consumption of soot steam.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE9301920A SE505270C2 (en) | 1993-06-04 | 1993-06-04 | Black liquor combustion with mesate additive |
| SE9301920-6 | 1993-06-04 | ||
| PCT/SE1994/000536 WO1994029518A1 (en) | 1993-06-04 | 1994-06-03 | Combustion of black liquor and processing of lime sludge in a recovery boiler |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2164328A1 CA2164328A1 (en) | 1994-12-22 |
| CA2164328C true CA2164328C (en) | 2005-04-12 |
Family
ID=20390168
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002164328A Expired - Fee Related CA2164328C (en) | 1993-06-04 | 1994-06-03 | Combustion of black liquor and processing of lime sludge in a recovery boiler |
Country Status (4)
| Country | Link |
|---|---|
| CA (1) | CA2164328C (en) |
| FI (1) | FI117564B (en) |
| SE (1) | SE505270C2 (en) |
| WO (1) | WO1994029518A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE500660C2 (en) * | 1992-12-03 | 1994-08-01 | Mo Och Domsjoe Ab | Process for the production of green liquor in chemical recycling in sulphate and sulphite pulp mills |
| GB0325578D0 (en) * | 2003-11-03 | 2003-12-03 | Bioregional Minimills Uk Ltd | Method for treating black liquor |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3366535A (en) * | 1966-07-11 | 1968-01-30 | William T Neiman | Process for regenerating waste liquor for reuse in kraft pulping operation |
| FR2550245B3 (en) * | 1983-08-04 | 1986-02-28 | Nivelleau Bruniere Patrick M F | PROCESS FOR THE COMBUSTION OF WASTE BLACK LIQUORS FROM THE MANUFACTURE OF CELLULOSIC PASTE |
-
1993
- 1993-06-04 SE SE9301920A patent/SE505270C2/en unknown
-
1994
- 1994-06-03 WO PCT/SE1994/000536 patent/WO1994029518A1/en active IP Right Grant
- 1994-06-03 CA CA002164328A patent/CA2164328C/en not_active Expired - Fee Related
-
1995
- 1995-12-01 FI FI955806A patent/FI117564B/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| FI117564B (en) | 2006-11-30 |
| CA2164328A1 (en) | 1994-12-22 |
| SE9301920D0 (en) | 1993-06-04 |
| FI955806A0 (en) | 1995-12-01 |
| SE505270C2 (en) | 1997-07-28 |
| FI955806L (en) | 1995-12-01 |
| SE9301920L (en) | 1994-12-05 |
| WO1994029518A1 (en) | 1994-12-22 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |
Effective date: 20130604 |