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WO2008156397A1 - Procédé pour récupérer des produits chimiques et production de vapeur - Google Patents

Procédé pour récupérer des produits chimiques et production de vapeur Download PDF

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Publication number
WO2008156397A1
WO2008156397A1 PCT/SE2007/050443 SE2007050443W WO2008156397A1 WO 2008156397 A1 WO2008156397 A1 WO 2008156397A1 SE 2007050443 W SE2007050443 W SE 2007050443W WO 2008156397 A1 WO2008156397 A1 WO 2008156397A1
Authority
WO
WIPO (PCT)
Prior art keywords
lignin
furnace
steam
recovery boiler
black liquor
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.)
Ceased
Application number
PCT/SE2007/050443
Other languages
English (en)
Inventor
Ulf BERGSTRÖM
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Valmet Power AB
Original Assignee
Metso Power AB
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Metso Power AB filed Critical Metso Power AB
Priority to PCT/SE2007/050443 priority Critical patent/WO2008156397A1/fr
Publication of WO2008156397A1 publication Critical patent/WO2008156397A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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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
    • D21C11/12—Combustion of pulp liquors
    • D21C11/125—Decomposition of the pulp liquors in reducing atmosphere or in the absence of oxidants, i.e. gasification or pyrolysis
    • D21C11/127—Decomposition of the pulp liquors in reducing atmosphere or in the absence of oxidants, i.e. gasification or pyrolysis with post-combustion of the gases

Definitions

  • the present invention relates to a method for recovering chemicals and production of steam in a chemical pulp mill.
  • the process for converting the chemicals requires combustion temperatures around 1200°C, and during the process a chemical smelt is formed in the bottom of the boiler. This smelt is fed from the furnace floor out of the boiler to a dissolver where a green liquor is formed, which thereafter is subjected to a causticising process producing new white liquor to be used in the cooking process.
  • the primary objective with the invention is to enable a more energy efficient operation of the recovery boiler and its production of steam, not necessitating additional external fuels nor any wood material that better could be used in the pulping process.
  • the goal is to increase the amount of electricity that can be produced from black liquor available at the mill without sacrificing economy or loss of original wood.
  • Another objective is to enable an increase of the recovery boiler capacity while burning the main part of the black liquor with its main part of residual content of reusable cooking chemicals in the bottom part of the recovery boiler at less flue gas flow rates. If the flue gas velocity could be reduced in the lower part of the recovery boiler above the smelt bed, then the risks for withdrawing droplets of smelt and black liquor droplets in the flue gases is reduced.
  • the present invention relates to a process where the black liquor from the kraft pulping process is introduced to the recovery boiler in at least two forms: a lignin rich form and a lignin lean form where the method to introduce the two forms of liquor provides for the possibility to increase the inorganic recovery capacity of the boiler for a given size of furnace and at the same time provide for the possibility to increase the steam parameters for the boiler and also to reduce the super heater area that is needed.
  • a recovery boiler is a boiler where spent liquor from chemical pulp digestion is burnt.
  • the main objective of burning liquor in the recovery boiler is to recover the cooking chemicals but also to convert the organic substance in the spent liquor to steam.
  • the chemicals (inorganic matter) are reused in the chemical pulping process and the steam that is produced is used in the cooking process for heating and is also often used for electricity production in a steam turbine generator.
  • a recovery boiler is a vital part of the kraft pulping process.
  • the recovery boiler is also one of the most expensive individual machinery in a kraft pulp mill. For that reason there is normally a big commercial interest from pulp mill owners to maximise the capacity of the recovery boiler. Also due to increasing costs for energy most customers in the kraft pulping business seek for new solutions to maximize the amount of electricity that can be produced from the steam generated in the recovery boiler.
  • One of the methods to increase the electricity production in steam boiler processes is to increase the steam parameters. This means that the steam pressure and the steam temperature is increased. With higher steam parameters it is possible for the steam turbine to generate more electricity from the steam that is fed to the turbine. However increased steam parameters normally increases the corrosion rate in the superheater. The corrosion rate in recovery boiler superheaters is a well known problem and has forced recovery boiler manufactures to use more exotic superheater materials with higher material costs as a consequence.
  • the specific hearth heat rate in a boiler is defined as the ratio between heat input to the boiler and lower furnace cross section area.
  • the specific hearth heat ratio has by its definition a close relation to the flue gas velocities in the lower furnace. Flue gas velocities in the lower furnace has a direct relation on the amount of carry over that can be expected from the lower furnace to the superheater region. For that reason it can be assumed that if the specific hearth heat ratio becomes too high the carry over situation in the boiler will be worse and this will result in various problems such as reduced steam temperature, enhanced corrosion and general fouling of boiler heating surfaces. In many cases high carry over will lead to reduced availability of the boiler and imposes the need to shut down the boiler for manual cleaning or water wash.
  • the recovery boiler is a vital part of the kraft pulping process.
  • the spent liquor that is burnt in the recovery boiler is called black liquor.
  • Black liquor is the residue from the pulping process where the fibres has been separated from the lignin that is contained in the wood chips that forms the raw material in the pulping process.
  • the lignin contains mainly hydro carbons and is an energy rich substance.
  • the black liquor is a mixture of the lignin and the chemicals that has been used in the pulping process to achieve the right condition for separation of fibres and lignin.
  • Lignin act as the glue in the wood raw material and together with the fiber builds up the strength in wood. It has been well known that lignin as a refined product can be used in many applications. Lignin was refined from sulfite liquors during the 60s and was used as ingredient in many applications in oil industry, animal food industry and building material industry. Because the lack of sulfite liquor as raw material for lignin production, a process was developed during the 70s to extract lignin also from kraft pulp liquors. In this new process only part of the lignin was extracted hence forming both the lignin product and the remaining "lignin lean” product which also contains the inorganic compounds that is recovered in order to produce new chemicals for the cooking process. By this extraction process the "lignin lean" liquor would have a lower heating value than the original black liquor and the lignin product would have a higher heating value than the original black liquor.
  • lignin product Today with increased energy cost the lignin product is also thought of as a potential energy resource for various applications. However because the origin of the lignin product there are contaminations in the product. Normally inorganic material originating from the kraft pulping process is part of the lignin product. Since sulphur is a major compound in kraft pulping this will call for desulphuhsation need of the flue gases if lignin is burnt in a normal power boiler.
  • the present invention relates to a process where a "lignin lean" fraction of the black liquor is introduced in to the lower furnace in the traditional way while the "lignin rich” fraction is introduced to a separate or parallel furnace. Due to the fact that the "lignin lean” black liquor has a lower heating value more "lignin lean” liquor can be fired compared to if normal black liquor is fired, provided the same specific hearth heat rate.
  • the extracted lignin rich fraction is fired.
  • the extracted lignin contains lower levels of K and Cl compared to untreated black liquor. This means that the flue gas is not as corrosive as flue gas from untreated black liquor is.
  • the flue gas from the separate furnace can then be introduced to and mixed with the flue gas in the recovery boiler furnace.
  • the mixing point is preferably located at a position high up in the furnace so the carry over situation in the lower furnace is not affected.
  • the separate furnace can be equipped with final super heater elements that form part of the recovery boiler super heater system. The steam in the super heater panels in the separate furnace is heated by the flue gases produced by the combustion of the extracted lignin rich fraction.
  • the corrosion rate of the final super heater elements will be lower than if the final super heater elements would have been placed in the recovery boiler furnace. Also with the positioning of the super heater elements in the separate furnace where the fouling situation is better compared to the recovery boiler, the total installed superheater area can be reduced.
  • the present invention brings the following advantages to the recovery boiler process: • Steam parameters can be elevated since the final super heater stage will be heated with lignin fuel in the separate furnace. With lignin fuel in the separate furnace there is a much better possibility to control the flue gas chemistry close to the super heaters and hence reduce the corrosion rate.
  • Steam temperature control can with the present innovation be achieved in a much better way than in a traditional recovery boiler.
  • super heaters has to be "oversized" in order to account for gradually increased fouling of the super heater surfaces.
  • the steam temperature control is in traditional recovery boilers achieved with means for throttling the capacity that is extensive when the boiler is clean and which throttling is reduced the more fouled the super heater gets.
  • the final steam temperature can be controlled by controlling the amount of lignin that is fired in the separate furnace. Therefore with the present invention the total installed super heater area can be reduced compared to what is needed in a traditionally recovery boiler.
  • Figure 1 Show the principal layout of a system capable of operating according to the inventive method
  • FIG 1 is a principal layout shown of a system wherein the inventive method could be implemented.
  • the heart of the invention lies in the separation process of the lignin rich fraction from the black liquor emanating from the kraft cooking process.
  • the kraft cooking process is visualised as the stage 1 and the flow of black liquor is labelled BL.
  • the black liquor is first passing some evaporation stages 2a, and subsequent to this is the at least partially evaporated Black liquor subjected to a lignin separation process in stage 3.
  • the lignin separation process 3 is preferably a precipitation process where the lignin is made to precipitate by lowering the pH by addition of acid/Ac. This type of precipitation process is not requiring a lot of energy and requires only an addition of chemicals.
  • the lignin separation process results in a lignin rich fraction L RICH and a lignin lean fraction L LEAN -
  • the lignin lean fraction L LEAN is sent to the conventional black liquor guns 10 in the bottom area of the main furnace 20 recovery boiler 30.
  • the lignin rich fraction L RICH is sent to the parallel furnace 21 where a lignin burner 1 1 is installed.
  • the lignin separation process is separating the lignin lean fraction having the major part of the residual cooking chemicals left in this lignin lean fraction.
  • lignin lean fraction Typically is more than 75%, and preferably more than 90%, of the residual cooking chemicals from the original black liquor still kept in the lignin lean fraction, and in the lignin rich fraction is more than 75%, and preferably more than 90% of the content a lignin content, besides residual liquids from the separation process such as acids.
  • first heating surface HE1 In the conventional recovery boiler are the flue gases passing a first heating surface HE1.
  • This heating surface HE1 is cooled by circulating boiler water from the drum D and could preferably be the water cooled walls of the recovery boiler.
  • the flue gases thereafter pass a first superheater SH1 in the recovery boiler.
  • This superheater contains steam collected from the drum D heated by the flue gases and approaching a temperature in the range of 310-500°C. This high pressure steam could typically be sent to the high pressure steam net of the pulp mill, to be used in a power turbine.
  • first heating surface HE1 In this example is only one first heating surface HE1 , one superheater SH1 and one economiser ECO shown, but the number of heating surfaces, superheaters and economisers could be larger than one, and connected in a sequence differing from this embodiment. For example could in the direction of flue gases following sequence be installed; 1 ) a first heater surface, 2) a first superheater, 3) a second heater surface, 4) generating bank and economiser.
  • a parallel furnace 21 arranged close to or integrated with the ordinary recovery boiler structure.
  • this parallel furnace 21 is the lignin rich fraction L RICH burnt in a dedicated lignin burner 1 1 in the bottom of the parallel furnace.
  • the flue gases from this combustion are passing a superheater SH2 that is integrated with the steam generation system of the recovery boiler.
  • the superheater SH2 in the parallel furnace the second superheater of the steam generation system, and the steam already heated by the superheater SH1 in the recovery boiler is passed in series in this second or final superheating stage.
  • the steam parameters could be raised considerably in this final superheater, and the steam temperature could be elevated to 450-550 °C without risking the superheater tubes even if ordinary material is used in the tubes.
  • the flue gases in the parallel furnace could be merged into one flow with the remaining flue gases coming from the main furnace of the recovery boiler.
  • the merger could take place in a position after the first heating surfaces of the main furnace but before the final gas treatment stages of the main furnace (i.e. somewhere before final cleaning F).
  • the flue gases merged before the merged flue gases passes the superheater of the recovery boiler.
  • an additional fuel 40 be used as a additional or supplemental fuel in the parallel furnace as indicated in the figure.
  • This additional fuel could be burnt in a dedicated burner as shown, or possibly use the lignin burner 1 1 , and be activated if the steam heating requirements exceed the possibilities obtained from burning lignin only.

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Abstract

L'invention porte sur une génération améliorée de vapeur dans un procédé de récupération de produits chimiques dans une chaudière de récupération. La liqueur noire obtenue à partir d'un procédé Kraft est soumise à un procédé de séparation de lignine, formant une fraction riche en lignine et une fraction pauvre en lignine. La fraction riche en lignine est brûlée dans un four parallèle ayant des surchauffeurs, alors que la fraction pauvre en lignine est brûlée dans la chaudière de récupération ordinaire. Les gaz de combustion résultants provenant du four parallèle sont mélangés aux gaz de combustion au niveau d'une position de gaz de combustion ultérieure dans la chaudière de récupération, d'où une réduction des conditions chimiques dures dans la chaudière de récupération. Ceci conduit à une génération de vapeur plus efficace et à des possibilités de génération de vapeur à plus haute pression pour la production d'électricité.
PCT/SE2007/050443 2007-06-20 2007-06-20 Procédé pour récupérer des produits chimiques et production de vapeur Ceased WO2008156397A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/SE2007/050443 WO2008156397A1 (fr) 2007-06-20 2007-06-20 Procédé pour récupérer des produits chimiques et production de vapeur

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/SE2007/050443 WO2008156397A1 (fr) 2007-06-20 2007-06-20 Procédé pour récupérer des produits chimiques et production de vapeur

Publications (1)

Publication Number Publication Date
WO2008156397A1 true WO2008156397A1 (fr) 2008-12-24

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013188401A1 (fr) * 2012-06-13 2013-12-19 Liquid Lignin Company Procédé de production d'énergie à partir de lignine
EP3415816B1 (fr) 2017-05-10 2020-10-28 Valmet Technologies Oy Procédé et système permettant d'étendre la plage de charge d'une centrale électrique comprenant une chaudière fournissant de la vapeur à une turbine à vapeur

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2606103A (en) * 1947-06-13 1952-08-05 Comb Eng Superheater Inc Chemical recovery furnace with high-temperature superheater
US4470876A (en) * 1982-07-22 1984-09-11 Beaupre Marc F Kraft overload recovery process
US5707490A (en) * 1991-11-26 1998-01-13 Ahlstrom Machinery Oy Method of recovering energy from waste liquors from pulp processes
WO2006031175A1 (fr) * 2004-09-14 2006-03-23 Lignoboost Ab Methode pour separer de la lignine de liqueur residuaire

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2606103A (en) * 1947-06-13 1952-08-05 Comb Eng Superheater Inc Chemical recovery furnace with high-temperature superheater
US4470876A (en) * 1982-07-22 1984-09-11 Beaupre Marc F Kraft overload recovery process
US5707490A (en) * 1991-11-26 1998-01-13 Ahlstrom Machinery Oy Method of recovering energy from waste liquors from pulp processes
WO2006031175A1 (fr) * 2004-09-14 2006-03-23 Lignoboost Ab Methode pour separer de la lignine de liqueur residuaire

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013188401A1 (fr) * 2012-06-13 2013-12-19 Liquid Lignin Company Procédé de production d'énergie à partir de lignine
EP3415816B1 (fr) 2017-05-10 2020-10-28 Valmet Technologies Oy Procédé et système permettant d'étendre la plage de charge d'une centrale électrique comprenant une chaudière fournissant de la vapeur à une turbine à vapeur
EP3415816B2 (fr) † 2017-05-10 2025-09-24 Valmet Technologies Oy Procédé et système permettant d'étendre la plage de charge d'une centrale électrique comprenant une chaudière fournissant de la vapeur à une turbine à vapeur

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