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EP1873450A2 - Procédé de réduction d'émissions d'oxyde d'azote pour une chaudière à récupération, et chaudière à récupération - Google Patents

Procédé de réduction d'émissions d'oxyde d'azote pour une chaudière à récupération, et chaudière à récupération Download PDF

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Publication number
EP1873450A2
EP1873450A2 EP07397020A EP07397020A EP1873450A2 EP 1873450 A2 EP1873450 A2 EP 1873450A2 EP 07397020 A EP07397020 A EP 07397020A EP 07397020 A EP07397020 A EP 07397020A EP 1873450 A2 EP1873450 A2 EP 1873450A2
Authority
EP
European Patent Office
Prior art keywords
nozzles
liquor
furnace
air
fed
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.)
Withdrawn
Application number
EP07397020A
Other languages
German (de)
English (en)
Other versions
EP1873450A3 (fr
Inventor
Antti Raukola
Matti Ylitalo
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 Oy
Original Assignee
Metso Power Oy
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 Oy filed Critical Metso Power Oy
Publication of EP1873450A2 publication Critical patent/EP1873450A2/fr
Publication of EP1873450A3 publication Critical patent/EP1873450A3/fr
Withdrawn legal-status Critical Current

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Classifications

    • 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
    • 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
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C6/00—Combustion apparatus characterised by the combination of two or more combustion chambers or combustion zones, e.g. for staged combustion
    • F23C6/04—Combustion apparatus characterised by the combination of two or more combustion chambers or combustion zones, e.g. for staged combustion in series connection
    • F23C6/045—Combustion apparatus characterised by the combination of two or more combustion chambers or combustion zones, e.g. for staged combustion in series connection with staged combustion in a single enclosure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C2201/00—Staged combustion
    • F23C2201/10—Furnace staging
    • F23C2201/101—Furnace staging in vertical direction, e.g. alternating lean and rich zones
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C2900/00—Special features of, or arrangements for combustion apparatus using fluid fuels or solid fuels suspended in air; Combustion processes therefor
    • F23C2900/06041—Staged supply of oxidant

Definitions

  • the invention relates to a method according to the preamble of the appended claim 1 for reducing the nitrogen oxide emissions of a recovery boiler.
  • the invention also relates to a recovery boiler according to the preamble of the appended claim 14.
  • a recovery boiler is used for burning spent liquor, so-called black liquor, obtained from the manufacture of sulfate pulp.
  • the function of the recovery boiler is not only to recover the energy contained in the black liquor but also to recover the chemicals contained in it, which can be recycled to pulping.
  • the combustion air required for the combustion of black liquor is normally supplied to the furnace from three different levels: primary air from the lower part of the furnace, secondary air from between the primary air level and the liquor nozzles, and tertiary air from above the liquor nozzles.
  • flue gases are produced which contain, among other things, nitrogen oxides. These oxides consist of both nitrogenous materials contained in the liquor and gaseous nitrogen contained in the combustion air.
  • combustion air staging This is based on the fact that by suitable stagewise combustion of the pyrolysis gases, an essential part of the nitrogen in the ammonia can be converted to molecular nitrogen.
  • combustion air is fed into the boiler from 3 to 5 different air levels. The aim is to burn the liquor in the boiler so that reducing substoichiometric air conditions are achieved in the furnace up to the last air supply stage, whereby the ammonia contained in the flue gases can be reduced to molecular nitrogen according to the following reaction formula:
  • HCN hydrogen cyanide
  • reaction equation (3) Part of the nitrogen originating from the fuel is reduced to molecular nitrogen, and part is oxidized to nitrogen oxides which are reduced further to molecular nitrogen as the hydrocarbon radicals formed in the pyrolysis participate in the reduction of the nitrogen oxides.
  • reaction equation (3) An example of such a reaction is shown in reaction equation (3), in which the hydrocarbon radical is -CHi.
  • Substoichiometric conditions in relation to oxygen are maintained in the furnace up to the uppermost air supply level, in which case the delay time needed for the reactions (1) and (2) is maximized and the amount of NH 3 and HCN is minimized.
  • the air required for burning out of the pyrolysis gases is supplied to the furnace at the last air supply stage, where excess air conditions are created.
  • SNCR selective non-catalytic reduction
  • a third method used for reducing the content of nitrogen oxides in flue gases from the recovery boiler is fuel staging.
  • the method is based on the ability of the radicals formed from the fuel to reduce nitrogen oxides to molecular nitrogen as shown in the reaction formula (3).
  • liquor is supplied into the furnace from several different supply levels with respect to the height of the furnace.
  • the liquor to be supplied to the lower part of the furnace is burnt primarily under reducing conditions prevailing in the lower part of the furnace.
  • the combustion of pyrolysis gases released from the liquor takes place underneath the liquor nozzles in an oxygenous air zone where excess amount of air is fed. As a result of the combustion with excess air, a small amount of nitrogen oxides are produced.
  • the aim is to remove these nitrogen oxides by reducing them to molecular nitrogen.
  • Finnish patent application 20040763 discloses a method for reducing the amount of nitrogen oxides produced in the combustion, whereby fuel is supplied to the furnace from two different feeding levels.
  • the liquor fed from the higher fuel feeding level in the furnace is to be burnt at such a temperature and under such reducing conditions that as much hydrogen cyanide is produced as possible.
  • the hydrogen cyanide is converted to molecular nitrogen by means of excess air fed to the upper part of the furnace.
  • a problem with this method is the fact that the tube systems and other equipment to be constructed for the requirements of the two liquor feeding levels are complex and expensive.
  • the method according to the invention is primarily characterized in what will be presented in the characterizing part of the independent claim 1.
  • the recovery boiler according to the invention is primarily characterized in what will be presented in the characterizing part of the independent claim 14.
  • the invention is based on the idea that black liquor is supplied to the furnace of the recovery boiler from one level so as to provide two combustion zones with respect to the height of the furnace. All the black liquor is supplied to the furnace substantially from the same level.
  • different types of liquor nozzles are used, installed substantially on the same level.
  • the droplet size of liquor to be fed from the first liquor nozzles is close to the liquor droplet size commonly used in a recovery boiler utilizing a single liquor feeding level.
  • the droplet size of the liquor to be fed from the second liquor nozzles is substantially smaller than the droplet size of the liquor to be fed from the first liquor nozzles.
  • the liquor to be fed from the first and second liquor nozzles is supplied from the same liquor tank.
  • the droplets from the first nozzles are larger in size than the droplets from the second nozzles.
  • the size and thereby also the weight of the droplets determine the location of the furnace where they will burn.
  • the droplets from the first nozzles fly to the char bed through air levels underneath them via different burning stages.
  • the droplets from the second nozzles are substantially smaller in size and thereby also in weight than the droplets produced by the first nozzles, and they are dried and burnt substantially at the same level with the second nozzles or slightly above them.
  • the nitrogen oxides produced by the fuel fed from the first nozzles can be reduced by the effect of reducing conditions generated by the fuel fed from the second nozzles.
  • the aim is to maintain substoichiometric conditions so that as little nitrogen oxides would form as possible. It is also an aim to totally reduce the NH 3 formed in the combustion to molecular nitrogen, if possible.
  • this combustion zone just before the liquor nozzles, there is a combustion zone in which the air coefficient is greater than 1.
  • this zone has excess air conditions, and its function is to guarantee the complete combustion of the liquor fed in the lower part of the furnace and of the pyrolysis gases generated therefrom.
  • some nitrogen oxides are also formed, for example NO.
  • the liquor droplets fed from the second liquor nozzles form a "droplet cloud" in the centre of the boiler, at the level of the liquor nozzles or slightly above them.
  • the droplet size is adjusted to be so large that the droplets also penetrate to the centre of the cross section of the boiler at the level of the nozzles. Because the droplets are small in size, their drying, pyrolysis and combustion take place almost immediately after the feeding of the liquor.
  • the quantity of the liquor to be fed from the second nozzles is significantly small; as a result, the afterburning zone above the liquor nozzles, where reducing conditions prevail, has a low temperature, about 950 to 1500 °C, preferably about 1050 to 1400 °C.
  • the combustion of the liquor fed from the second liquor nozzles in the furnace produces more hydrocarbon radicals than in prior art, which react with the nitrogen oxides contained in the flue gases coming from the lower furnace and reduce at least part of them to hydrogen cyanide (HCN).
  • HCN hydrogen cyanide
  • the burning out of the liquor fed from the second nozzles takes place in a burning-out zone by means of air supplied to the upper part of the furnace, which air is fed in such an amount that excess air conditions are generated.
  • the temperature is about 950 to 1200 °C, preferably about 950 to 1050 °C, and the conversion of the formed hydrogen cyanide to molecular nitrogen (N 2 ) takes place there.
  • FIG. 1 shows a recovery boiler 1 according to the invention, comprising a furnace 2 with a char bed 3 on its bottom.
  • the char bed 3 is formed when black liquor is fed in the form of droplets from liquor spray nozzles 6a into the furnace 2.
  • the liquor is dried, part of it is pyrolyzed, and part becomes coke.
  • smelt is formed which accumulates on the bottom of the furnace and is led from there to a smelt dissolving tank and into a chemical recovery plant.
  • combustion air is fed into the furnace from nozzles placed at several different levels with respect to the height of the furnace.
  • Primary air nozzles 4 are placed closest to the bottom of the furnace, at a distance from it.
  • Secondary air nozzles 5 are placed above the primary air nozzles 4 but still below the liquor nozzles 6a and 6b in the height direction of the furnace.
  • the secondary air 5 is divided into two parts to be fed from different levels into the furnace 2. Part of the secondary air is fed into the furnace 2 via so-called lower secondary air nozzles 5a, and the rest is fed into the furnace 2 via upper secondary air nozzles 5b.
  • liquor nozzles 6a and 6b are provided for feeding liquor into the furnace.
  • liquor nozzles 6a and 6b are provided for feeding liquor into the furnace.
  • tertiary air nozzles 7 are provided for feeding tertiary air into the furnace.
  • quaternary air nozzles 8 are provided for feeding quaternary air into the furnace.
  • an afterburning zone C Approximately at the level of the tertiary air nozzles 7 or slightly above them there is an afterburning zone C with substoichiometric, reducing conditions. Combustion air is fed from the tertiary air nozzles 7 into the afterburning zone C. Uppermost in the furnace 2 there is a burning-out zone D which is placed approximately at the level of the quaternary air nozzles 8 or above them. Combustion air is fed from the quaternary air nozzles 8 into the burning-out zone.
  • the zone D has an air coefficient well above 1, and its purpose is the afterburning of pyrolysis gases still left in the furnace by means of excess air.
  • Black liquor is fed into the furnace from one level so that two combustion zones are generated.
  • the first and second liquor nozzles 6a and 6b are provided between the secondary air nozzles 5 and the tertiary air nozzles 7.
  • the liquor nozzles 6a and 6b are placed substantially on the same level with respect to the height of the furnace.
  • the larger liquor droplets fed from the first liquor nozzles 6a fly downwards, and the liquor and the pyrolysis gases formed thereof are burnt in the reducing zone A and the combustion zone B prevailing underneath the liquor nozzles 6a and 6b.
  • the second nozzles 6b produce a liquor jet consisting of liquor droplets that are are substantially smaller than the liquor droplets generated by the first nozzles 6a.
  • the liquor droplets generated by the second liquor nozzles 6b and the pyrolysis gases formed of them are burnt in the afterburning zone C and the burning-out zone D prevailing at the level of the liquor nozzles and higher than them.
  • the first liquor nozzles may be spoon-shaped nozzles that are commonly used and which generate liquor droplets in the size of some millimetres.
  • the aim is that the formed droplets fall downwards, dry on their way down and are burnt as low down as possible in the furnace.
  • the second liquor nozzles are nozzles which are capable of generating substantially smaller liquor droplets than the first liquor nozzles.
  • the size of the liquor droplets is some hundreds of microns.
  • the droplet size is adjusted such that the liquor to be fed from the second nozzles forms a "liquor cloud" in the centre of the boiler, at the level of the liquor nozzles or slightly above them. However, the droplet size is adjusted to be so large that the droplets travel to the centre of the cross-sectional area of the boiler.
  • a carrier gas can be utilized for feeding the liquor.
  • the second liquor nozzles may be, for example, nozzles provided with a carrier gas channel surrounding the liquor channel in the nozzle and thereby forming a curtain of gas around the liquor. The carrier gas improves the penetrability of the liquor in the centre of the furnace and prevents the formation of a liquor cloud in the vicinity of the walls of the furnace.
  • the liquor to be fed from the second nozzles can be heated or treated to make the formation of small droplets easier.
  • the liquor to be fed from the nozzles is the same liquor as the liquor fed from the first nozzles.
  • the first and the second liquor nozzles can be arranged in different ways to the walls 9 of the furnace.
  • Figure 2 shows an embodiment for their placement.
  • the first nozzles 6a are placed symmetrically so that three nozzles are provided on each wall.
  • the second nozzles 6b are placed at the corners of the furnace 2.
  • two first nozzles 6a are provided on each wall 9.
  • the second nozzles 6b are placed between the first nozzles 6a, substantially in the center of the wall of the furnace.
  • the number and placement of the first and second liquor nozzles with respect to the walls of the furnace may vary from the examples shown in Figs. 2 and 3.

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  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Paper (AREA)
  • Treating Waste Gases (AREA)
  • Air Supply (AREA)
EP07397020.4A 2006-06-21 2007-06-12 Procédé de réduction d'émissions d'oxyde d'azote pour une chaudière à récupération, et chaudière à récupération Withdrawn EP1873450A3 (fr)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
FI20065429A FI122982B (fi) 2006-06-21 2006-06-21 Menetelmä soodakattilan typpioksidipäästöjen vähentämiseksi ja soodakattila

Publications (2)

Publication Number Publication Date
EP1873450A2 true EP1873450A2 (fr) 2008-01-02
EP1873450A3 EP1873450A3 (fr) 2013-07-31

Family

ID=36651524

Family Applications (1)

Application Number Title Priority Date Filing Date
EP07397020.4A Withdrawn EP1873450A3 (fr) 2006-06-21 2007-06-12 Procédé de réduction d'émissions d'oxyde d'azote pour une chaudière à récupération, et chaudière à récupération

Country Status (5)

Country Link
US (1) US20070295249A1 (fr)
EP (1) EP1873450A3 (fr)
BR (1) BRPI0705223A2 (fr)
CA (1) CA2592178A1 (fr)
FI (1) FI122982B (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FI123853B (fi) * 2009-03-06 2013-11-15 Metso Power Oy Menetelmä typenoksidipäästöjen vähentämiseksi happipoltossa
CN104748147B (zh) * 2015-02-28 2017-03-01 烟台龙源电力技术股份有限公司 墙式对冲燃烧锅炉的燃烧方法

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3574500A (en) * 1968-03-01 1971-04-13 Tampella Oy Ab Waste-liquor burner and disperser
EP0761871A1 (fr) * 1995-09-11 1997-03-12 The Mead Corporation Chaudière et four de récupération dans le procédé Kraft
WO2000037853A1 (fr) * 1998-12-21 2000-06-29 Alstom Power Inc. Procede de commande d'un systeme de cuisson tangentielle
WO2005118113A1 (fr) * 2004-06-03 2005-12-15 Andritz Oy Procede pour reduire les emissions d'oxyde d'azote

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5305698A (en) * 1989-04-04 1994-04-26 Blackwell Brian R Method and apparatus for improving fluid flow and gas mixing in boilers
FI925305A0 (fi) * 1992-11-23 1992-11-23 Polyrec Ab Oy Foerfarande och anordning foer inmatning av foerbraenningsluft i en eldstad
SE503453C2 (sv) * 1994-06-20 1996-06-17 Kvaerner Pulping Tech Sodapanna med ett sekundärlufttillflöde som åstadkommer en rotation av förbränningsgaserna och en förträngning av pannan ovanför lutinsprutningen samt ett förfarande vid en sådan panna
FI102410B1 (fi) * 1997-02-07 1998-11-30 Kvaerner Pulping Oy Menetelmä ja sovitelma ilman syöttämiseksi soodakattilaan
EP1654494A4 (fr) * 2003-07-03 2015-01-07 Clyde Bergemann Inc Procede et appareil pour ameliorer la combustion dans des chaudieres de recuperation
US8607718B2 (en) * 2007-03-28 2013-12-17 Babcock & Wilcox Power Generation Group, Inc. Recovery boiler combustion air system with intermediate air ports vertically aligned with multiple levels of tertiary air ports

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3574500A (en) * 1968-03-01 1971-04-13 Tampella Oy Ab Waste-liquor burner and disperser
EP0761871A1 (fr) * 1995-09-11 1997-03-12 The Mead Corporation Chaudière et four de récupération dans le procédé Kraft
WO2000037853A1 (fr) * 1998-12-21 2000-06-29 Alstom Power Inc. Procede de commande d'un systeme de cuisson tangentielle
WO2005118113A1 (fr) * 2004-06-03 2005-12-15 Andritz Oy Procede pour reduire les emissions d'oxyde d'azote

Also Published As

Publication number Publication date
FI20065429L (fi) 2007-12-22
CA2592178A1 (fr) 2007-12-21
EP1873450A3 (fr) 2013-07-31
FI20065429A0 (fi) 2006-06-21
FI122982B (fi) 2012-09-28
US20070295249A1 (en) 2007-12-27
BRPI0705223A2 (pt) 2008-12-16

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