CA1319055C - Non-peripheral blowing of oxygen-containing gas in steam generating boilers - Google Patents
Non-peripheral blowing of oxygen-containing gas in steam generating boilersInfo
- Publication number
- CA1319055C CA1319055C CA000548516A CA548516A CA1319055C CA 1319055 C CA1319055 C CA 1319055C CA 000548516 A CA000548516 A CA 000548516A CA 548516 A CA548516 A CA 548516A CA 1319055 C CA1319055 C CA 1319055C
- Authority
- CA
- Canada
- Prior art keywords
- oxygen
- containing gas
- gas
- boiler
- sidewalls
- 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
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
- F23L7/00—Supplying non-combustible liquids or gases, other than air, to the fire, e.g. oxygen, steam
- F23L7/007—Supplying oxygen or oxygen-enriched air
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- 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
-
- 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
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E20/00—Combustion technologies with mitigation potential
- Y02E20/34—Indirect CO2mitigation, i.e. by acting on non CO2directly related matters of the process, e.g. pre-heating or heat recovery
Abstract
Abstract of the Disclosure In a steam generating boiler having a bottom wall supporting a char bed and sidewalls with ports through which air is admitted for combustion of combustible species in the char bed and emanating therefrom, combustion is improved by introducing an oxygen-containing gas into a lower central zone of the boiler, from at least one point remote from the sidewalls to thereby cause intimate mixing of the oxygen contained in the gas with the combustible species.
Description
The present invention relates to improvements in steam generating boilers. ~ore par-ticularly, the invention is directed toward improving combustion conditions in steam generatillg boilers such as the recovery boilers which are used in -the pulp and paper mills for the combus-tion of spen-t liquor frorn sodium-based pulping process.
The main objec-tives in operating a recovery boiler are to recover the pulping chemicals in the reduced s~ate and to recover -the heat released by the combustion of carbonaceous material to generate steam for the process. The spent liquor from the pulping process is sprayed in small drops over the cross section of the boiler furnace through the upwardly flowing combustion gases so as to dry the liquor droplets to a concentration where the heat value of the char material with the residual moisture is sufficient to keep a reasonably stable combustion going. The dry liquor solids settle on the bottom of the boiler forming a carbona-ceous char bed. The char bed has two functions: to reduce -the spen-t chemicals for further recycle and to supply heat by reacting with the oxygen in the air being blown horizon-tally over the char bed.
ln such boilers, the air is introduced peripher-ally through ports located in the boiler sidewalls and into the lower section of the boiler. ~n most designs, the total air supply is divided in two or more streams which are introduced peripherally at different levels of the boiler.
These air streams are referred to as primary, secondary and tertiary air, conventionally starting from the bottom of the boiler Because of the influence of the induced draft Ean and of the large size of the boiler, only a very small fraction of the peripherally introduced air reaches the central region of the boiler's cross-section.
Peripheral air is introduced either horizontally or slightly downwardly at subsonic velocities ranging from about 25 to 100 m/sec, which causes an upward deflection of the air along the walls of the boiler.
In cases where the fuel which supplies heat for the steam generation is concentrated towards the center of the boiler's cross-section, such as in the case where a char bed containing carbonaceous materials sits on the bottom of the boiler, the peripherally introduced air will not readily combine with the combustible species, either gaseous or finely divided solids, resulting in poor combustion in the lower section of the boiler.
A fundamental limitation to the burning capacity of these boilers is due to such poor mixing between the combustible species and the oxygen required as a comburant.
As the air is in-troduced peripherally through sidewall ports and blown into the lower section of the boiler, due to the relative low pressure and subsequent low velocity of the air flow, there is a preferential upward flow along the side-walls, leading to poor mixing with the combustible species.
The lack of intimate mixing of air with the combustible species in the lower section of the boiler limits its capacity not only because heat transfer to the boiler tubes is poor since peripheral air behaves as a coolant, but also because the lack of mixing lengthens the combustion zone, resulting in a vertical temperature profile _A 2 ;,~, which promotes carry over of unreacted inorganic ma-terial and in unnecessarily higher -temperatures in the upper section of -the boiler, where screen tubes and superhea-ter -tu~es are located.
Layers of carried over deposits on the screen and superheated tubes can be over 20 mm thick, thus drastically obstructing heat -transfer and reducing the sectional area for the passage of gases, eventually bottlenecking the boiler when the high pressure drop through the upper sec-tion limits the air blowing capacity of the boiler, forcing scheduled or non-scheduled shut-downs for deposit removal.
Another problem associated with poor mixing of the air with the combustible species is -the emission of reduced sulfur species in the exit gas. In conventional boilers, eventhough an overall 2 excess of over 2% may exist in the exit gas, some reduced sulfur species mix with the available oxygen only at the top of the boiler, where no-t enough time is available for a complete oxidation to occur and/or the gases are already at a lower temperature than necessary for complete oxidation.
From a thermochemical equilibrium view point, as long as there is more than 1~ vol. 2 in the flue gases exiting the boiler furnace, there should be less than 20 ppm total reduced sulfur ~TRS) speciesO However, because of imperfect gas mixing, equilibrium is not at-tained and therefore oxygen and combustible species coexist in the flue gases.
A better mixing of oxygen and the combustible species would modify -the ver-tical temperature profile of the boiler resulting in a temperature increase in the lower 1 31 qO55 section oE the boiler and consequent shorter combustion zone and lower exit gas tempera-cure in the upper section of the boiler wi-th -the following advan-tages:
1. Reduc-tlon of carried over deposits.
The main objec-tives in operating a recovery boiler are to recover the pulping chemicals in the reduced s~ate and to recover -the heat released by the combustion of carbonaceous material to generate steam for the process. The spent liquor from the pulping process is sprayed in small drops over the cross section of the boiler furnace through the upwardly flowing combustion gases so as to dry the liquor droplets to a concentration where the heat value of the char material with the residual moisture is sufficient to keep a reasonably stable combustion going. The dry liquor solids settle on the bottom of the boiler forming a carbona-ceous char bed. The char bed has two functions: to reduce -the spen-t chemicals for further recycle and to supply heat by reacting with the oxygen in the air being blown horizon-tally over the char bed.
ln such boilers, the air is introduced peripher-ally through ports located in the boiler sidewalls and into the lower section of the boiler. ~n most designs, the total air supply is divided in two or more streams which are introduced peripherally at different levels of the boiler.
These air streams are referred to as primary, secondary and tertiary air, conventionally starting from the bottom of the boiler Because of the influence of the induced draft Ean and of the large size of the boiler, only a very small fraction of the peripherally introduced air reaches the central region of the boiler's cross-section.
Peripheral air is introduced either horizontally or slightly downwardly at subsonic velocities ranging from about 25 to 100 m/sec, which causes an upward deflection of the air along the walls of the boiler.
In cases where the fuel which supplies heat for the steam generation is concentrated towards the center of the boiler's cross-section, such as in the case where a char bed containing carbonaceous materials sits on the bottom of the boiler, the peripherally introduced air will not readily combine with the combustible species, either gaseous or finely divided solids, resulting in poor combustion in the lower section of the boiler.
A fundamental limitation to the burning capacity of these boilers is due to such poor mixing between the combustible species and the oxygen required as a comburant.
As the air is in-troduced peripherally through sidewall ports and blown into the lower section of the boiler, due to the relative low pressure and subsequent low velocity of the air flow, there is a preferential upward flow along the side-walls, leading to poor mixing with the combustible species.
The lack of intimate mixing of air with the combustible species in the lower section of the boiler limits its capacity not only because heat transfer to the boiler tubes is poor since peripheral air behaves as a coolant, but also because the lack of mixing lengthens the combustion zone, resulting in a vertical temperature profile _A 2 ;,~, which promotes carry over of unreacted inorganic ma-terial and in unnecessarily higher -temperatures in the upper section of -the boiler, where screen tubes and superhea-ter -tu~es are located.
Layers of carried over deposits on the screen and superheated tubes can be over 20 mm thick, thus drastically obstructing heat -transfer and reducing the sectional area for the passage of gases, eventually bottlenecking the boiler when the high pressure drop through the upper sec-tion limits the air blowing capacity of the boiler, forcing scheduled or non-scheduled shut-downs for deposit removal.
Another problem associated with poor mixing of the air with the combustible species is -the emission of reduced sulfur species in the exit gas. In conventional boilers, eventhough an overall 2 excess of over 2% may exist in the exit gas, some reduced sulfur species mix with the available oxygen only at the top of the boiler, where no-t enough time is available for a complete oxidation to occur and/or the gases are already at a lower temperature than necessary for complete oxidation.
From a thermochemical equilibrium view point, as long as there is more than 1~ vol. 2 in the flue gases exiting the boiler furnace, there should be less than 20 ppm total reduced sulfur ~TRS) speciesO However, because of imperfect gas mixing, equilibrium is not at-tained and therefore oxygen and combustible species coexist in the flue gases.
A better mixing of oxygen and the combustible species would modify -the ver-tical temperature profile of the boiler resulting in a temperature increase in the lower 1 31 qO55 section oE the boiler and consequent shorter combustion zone and lower exit gas tempera-cure in the upper section of the boiler wi-th -the following advan-tages:
1. Reduc-tlon of carried over deposits.
2. Lowering of TRS emissions at similar excess 2 in flue gas.
3. Increased chemical recovery capacity.
4. Inereased steam generating capacity.
5. Reduced shut-down frequency for deposit re-moval.
6. Srnoother boiler operation.
Enriching the combus-tion air wi-th oxygen would -further allow burning capaeity increases without subsequen-t inerease in earry over deposits due -to lower gas veloeities relative to air eombustion.
It is -therefore an object of the presen-t inven-tion to improve the air distribution in che lower section of a s-team generating boiler so as to provide intimate mixing of the air with the combustion speeies, thereby improving combustion.
In accordance with one aspect of the invention, -there is provided a method of improving combustion in a steam genera-ting boiler having a bottom wall supporting a char bed and sidewalls with por-ts -through which air is admitted for combus-tion of combus-tible species in the char bed and emanating therefrom, which comprises introducing an oxygen-con-taining gas into a lower central zone of the boiler, from at least one point remote from the sidewalls to thereby cause intimate mixing of -the oxygen contained in the gas with the combustible species.
According to a further aspect of the invention, there is also provided in a steam generating boiler having a bot-tom wall supporting a char bed and sidewalls with ports through w'nich air is admitted for combustion of combustible species in the char bed and emanating therefrom, the impro-vement which comprises means for blowing an oxygen-contain-ing gas into a lower central zone of the boiler, from at least one point remote from the sidewalls to -thereby cause intimate mixing of the oxygen contained in the gas with the combustible species.
Applicant has found quite unexpectedly that by introducing an oxygen-containing gas into the lower central zone of the boiler, remotely from the sidewalls of the boiler, a better mixing of oxygen and combus-tible species could be achieved and that the oxygen deficient zone which is charac~eristic of boilers where air is introduced only peripherally through sidewall por-ts could be greatly reduced as a result of the improved mixing of the oxygen with the combustible species. This improvement can be attained without disrupcing the char oed formation which is essential to achieving chemical recovery. Due to the resulting tempe-rature increase in che lower section of the boiler, oxida-tion of Na2S, H2S or organic sulrides would occur in tha-t section of the boiler, thereby lowering TRS emissions.
Examples of suitable oxygen-containing gases which can be introduced non-peripherally include air, oxygen-enriched air and mixtures of oxygen with other gases 2' 2' CO, CE~4, C3E18, natural gas, H2O vapour N2O, flue gases, etc. It is of course also possible to use commercial 2 having a molecular oxygen content generally I ;~ 1 9055 between 90 and 99.5% by volume. On -the other hand, where -the oxygen-containing gas comprises a mixture of 2 and CO2, such a gaseous mix-ture is preferably nitrogen-free, -that is, havi.ng a N2 content of less than about 4% by volume, so as -to enable the CO2 to be recovered. Preferably, up to about 60~ of -the total oxygen re~uirement is introduced via the non-peripheral blowing of the oxygen-containing gas, the balance being supplied i.n the form of air introduced peri-pherally ~hrough the sidewall ports.
The oxygen-containing gas can be introduced non-peripherally by blowing the gas either downwardly from an upper section of the boiler or upwardly from above the char bed, or by a combined blowing of the gas both down-wardly froin an upper section of the boiler and upwardly from above the char bed. The oxygen-containing gas can be blown at any pressure, from atmospheric ~when a negative pressure exists in the boiler because of an induced draf-t fan) to about 10 atm., -the preferred pressure range being between about 1.2 and about 5 atm. (absolute). Thus, the gas veloci--ty can range from about 1 ft/sec to over sonic velocity, preferably from about 10 to about 1000 ft/sec.
The oxygen-containing gas is conveniently blown downwardly by means of at least one elongated lance arranged in the upper section of the boiler and ex-tending downwardly to discharge through at least one orifi.ce thereof at least one stream of the oxygen-containing gas, remotely from -the sidewalls of the boiler. For example, a single lance can be suspended from the top of the boiler to ex-tend vertically and centrally of the boiler, or can be mounted in the so-called "bull nose cavity" of the boiler, in which case 1 3 1 qO55 the lance is angularly inclined. Such a lance is preferably provided wi-th a plurality of di.scharge orifices spaced from one anothe~ and each oriented at an angle no-t greater than about 60 relative to the longi-tudinal axis of the lance. On the other hand, where a plurality of lances are used, the lances can be evenly distributed relative -to a central vertical axis of the boiler or they can extend in a common plane, in spaced-apart parallel relationship; in the latter case, -the lances may extend either vertically or at an angle relative -to the vertical.
Upward blowing of the oxygen-containing gas, on -the other hand, is advan-tageously effected by means of a-t least one injector arranged on the bottom wall oE the boiler remotely from the sidewalls thereof and extending through the char bed. Preferably, the injector protrudes from the surface of the char bed immediately surrounding -the injector a distance ranging from about 1 cm to about 30 cm, so as to not in-terfere with the chemical reactions occurring in the char bed and to prevent blockage of the gas discharge orifice of the injector by the liquid smelt.
According -to a particularly preferred embodiment, the injector comprises an elongated conduit of temperature and corrosion resistant metal extending through the bottom wall, and a protective refractory struc-ture surrounding the conduit, the conduit and refractory structure coextending from the bottom wall to above the char bed.
The pro-tective refractory structure should be made of a refractory material which is chemically resistant to the smel-t and capable of mechanically withstanding impac-ts caused hy falling deposits from the upper section of 1;~1'3055 the boiler. Examples of suitable refractory mate:rials include alumina, silica, silicon carbide, magnesite and chrome-magnesite.
In the case where a single injector is used, i-t is preferably disposed centrally of the boiler. In -the case of a plurali-ty of injectors, on the other hand, -these are preferably arranged to impart a swirling motion to the oxygen-containing gas.
It is also possible to pneumatically inject with the lance and/or injector particulate solids which can act as seeds to cause agglomeration of volatilized inorganic mat-ter, or as a source of heat to control furnace or char bed temperature, the oxygen-containing gas further serving in this case as a carrier gas. Such injection of particulate solids is also useful in removing accretion build-up from the gas discharge orifices of the lance or injector. For example, particles of sodium sulfate can be used as agglome-ration seeds whereas particles of carbonaceous materials such as coal or sawdust can be used as a source of heat.
However, where use is made of coal particles, the carrier gas should not contain more than about 21~ vol. oxygen.
The present invention finds application not only in recovery boilers used in pulp and paper mills, bu-t also in other types of steam generating boiler such as those opera-ted in coal fired power plants and boilers burning any mixture of biomass, hydrocarbons, fossils or by-product fuels for the purpose of generating steam and optionally recovering chemicals.
1 31 qO55 Further features and advantages of the invention will become more readil.y apparent from the following des-cription of preferred embodiments as illustrated by way of example in the accompanying drawings, in which:
Fig. 1 is a schematic vertical cross-section of a kraft recovery boiler equipped with a top blowing lance according to the invention;
Fig. 2 is a view similar to Fig. 1, illustrating a different location of the lance;
Fig. 3 is a fragmentary section view of the lance shown in Figs 1 and 2, illustrating -the discharge end thereof;
Fig. 4 is a bottom view of a lance according to another preferred embodiment;
Fig. 5 is a fragmentary section view taken along line 5-5 of Fig. 4;
Fig. 6 is a schematic vertical c,oss-section of a kraft recovery boiler equipped with a bottom blowing injec-tor according to the invention;
Fig. 7 is a fragmentary vertical section view illustrating the injector shown in Fig. 6i Fig. 8 is a fragmentary top view of the injector shown in Fig. 7;
Fig. 9 is a view similar to Fig. ~, illustrating an injector according to ano-ther preferred embodiment; and Figs 10, 11 and 12 which are on the same sheet as Fig. 6 are schematic horizontal section views illustrating different arrangements of injec-tors.
Referring first to Fig. 1, there is illustrated a kraft recovery boiler generally designated by reference numeral 20 and seen having a slan-ted bottom wall 22 and vertical sidewalls 24. The bottom wall 22 is formed of closely spaced tubes 26 with welded fins therebetween whereas the sidewalls 24 are lined with similar tubes 26 allowing circulation of water introduced through inlet 28 and fed to manifold 30 for distribution to the tubes 26.
slack liquor from the kraft pulping process is sprayed by means of spray nozzles 32 in small drops to collect as black liquor dry solids in a char bed 33 supported by the bottom wall 22. As water rises through the tubes 26, it is gradual-ly heated by the heat released by the combustion of the black liquor solids and vaporizes into steam to be collected in the upper drum 34 of the boiler tube bank 36 comprising a plurality of boiler tubes 38. Saturated steam is then sent from the upper drum 34 via line 40 to superheater tubes 42 for the generation of high-pressure dry steam which is discharged at the outlet 44 and may be used at various points in the pulp and paper mill.
Air for the combustion of the black liquor solids is supplied at three different levels in ~he boiler, by means of primary, secondary and tertiary windboxes 46,4~3 and S0 which respectively blow primary, secondary and tertiary air through ports 52,54 and 56 provided in the sidewalls 24.
The primary air is blown through por-ts 52 and which may account for up to 60~ of the total air supply serves to control the height and shape of the char bed 33. The char bed is a mixture of inorganic salts and carbonaceous mate-rials which provides a reducing environment to chemically 1, ) '331qO5~
reduce sodium sulfate -to sodi.um sulfide and sodium hydroxide -to sodium carbona-te, the active chemicals in the liquid smel-c produced and discharged through spout 5~. These cher,licals are subsequently recycled to the diges-tion stage of -the pulp mill for -the -trea-tmen-t of incoming wood.
The secondary air which is blown through ports 54 may account for up to 50% of the total air supply and provldes the oxidant which first meets the incoming black liquor from the spray nozzles 32. Besides causing flash dehydration of the black liquor salts, it supplies oxygen to burn carbon monoxide formed at the char bed 33 and should oxidize the reduced sulfur species either contained in the black liquor or genera-ted during the combus-tion of dry solids.
The tertiary air blown through ports 56 supplies the balance of air needed to attain an excess 2 in the exit gas represented by the arrow 60. The 2 concen-tration in the exit gas varies in practice from about 0.1 to about 6% by volume, but for the purpose of the present invention it is preferably within the range of 1.0 to 2.5~ by volume. The purpose of -the tertiary air is to take to completion the oxidation of combustible species emanating from the lower section of the boiler 20.
Hot gases and entrained volatilized matter are carried -to the upper section of the boiler 20. ~s temperatu-re decreases, the volatilized matter forms crusty deposits on screen tubes 62 and the boiler must therefore be periodi-cally shut down to remove such deposits. The screen tubes 62 1 31 qO55 form an independent hot water circui-t which -takes hot water from the lower drum 64 via line 66 and discharges steam via line 68 into -the upper drum 34 of the boiler -tube bank 36.
The hot gases containing mainly nitrogen, carbon dioxide and water vapor from the combus-tion of organic matter also carry ash and chemical fumes, which after the superheater tubes 42, cross the boiler tubes 38 and enter an economizer ~not shown). The economizer is a heat exchanger which uses the sensible heat in the exit gas 60 to indirec-tly preheat the feed water before it reaches the boilertubes 38 and subsequently the water introduced through the inlet 28 at the bottom of the boiler 20.
A fundamental characteristic of traditional steam generating boilers which limits efficient burning of combus-tible species is the lack of intimate mixing of the seconda-ry and tertiary air supplies with the intermediate products of combustion. The low velocity air tends to flow upwards peripherally along the sidewalls 24, resulting in a relatively cold gas containing large 2 excess. In the central zone, an 2 defficient plume 70 forms which may reach as high as the screen tubes 62 before complete mixing with the peripheral lean gas takes place.
The delayed mixing has important detrimental effects for the boiler operation. Should intimate mixing -take place at the tertiary air level, or not too high over it, complete combustion would be attained, thus the longitu-dinal temperature profile would change, resulting in a shorter but hotter combustion zone, with a subsequent lower temperature at the upper section of -the boiler.
i 3 1 9055 In order to overcome these drawbacks and to reduce the oxygen-defEicien-t zone 70, an oxygen-con-taining gas is blown downwardly into the lower central zone of the boiler by means of a water-cooled lance 72 suspended from -the top of the boiler by a retaining collar 74 and arranged centrally of the boiler. An oxygen-containing gas such as air or oxygen-enriched air is thus blown cen-trally into the lower section of the boiler, thereby causing intimate mixing of oxygen with the combustible species and resulting in a much shorter O2-defficient plume 70'.
Instead of posi-tioning the lance 72 vertically and centrally of the boiler, it is also possible to mount a shorter lance 76 in the so-called bull nose cavity 78 of the boiler, as shown in Fig. 2. In this case, the lance 76 is angularly inclined and s~ill provides non-peripheral down-ward blowing of oxygen-containing gas into the lower central zone of the boiler 20'.
Fig. 3 illustrates the structure of the water-cooled lance 72, which may also be the same for the lance 76 shown in Fig. 2. As shown, the lance 72 is formed with a central conduit 80 for conveying the oxygen-con-taining gas, which merges wi-th an outwardly diverging gas discharge orifice 82. Two concentric tubular conduits 84 and 86 are provided for circulating water -to cool the lance, the con-duits 84 and 86 communicating with one another at their lower ends by means of an annular elbow 88 formed in the tip 90 of the lance. The lance tip 90 can be made of a high thermally conductive metal, such as copper or a copper alloy. The ou-ter wall 92 of the lance, on -the other hand, can be made of corrosion resistant metal such as a ferrous alloy (e.g. stainless steel), whereas the inner walls 94 and 96 can be made oE thermally conductive metal such as carbon steel, for adequate cooling.
Figs 4 and 5 illustrate the discharge end of a similar water-cooled lance 72', but having a modified tip 90'. As shown, the tip 90' is formed with three gas dischar-ge orifices 82' equidistantly spaced from one another and each oriented at an angle of about 45 relative to the longitudinal axis of the lance.
In the recovery boiler 20" illustrated in Fig. 6, the non-peripheral blowing of oxygen-containing gas is effected by blowing the gas upwardly from above the char bed 33 into a substantially gaseous phase by means of an injec-tor 98 arranged on the bottom wall 22' and extending -through and above the char bed 33. The injector 98 comprises an elongated conduit 100 extending through -the bottom wall 22' for conveying the oxygen-containing gas and a protective refractory structure 102 surrounding the conduit 100, as best shown in Fig. 7. The conduit 100 and refractory s-truc-ture 102 coextend from the bottom wall 22' to above the char bed 33. The refractory structure 102 has a conical configu-ration, the gas discharge orifice 104 being located at the apex of such a conical structure. The flow of oxygen-con-taining gas can be regulated by means of the valve 106.
Where the oxygen-containing gas is air and it is desired to enrich the air with oxygen, molecular oxygen can be admixed via the conduit 108 connected to conduit 100 and provided with a valve 110 for regulating the flow of molecular oxygen admixed.
13190~i5 The bot-tom wall 22' is formecl of closely spaced tubes 26 wiLh welded fins 112 therebetween, as is -the bo-ttom wall 22 shown in Figs 1 and 2. However, in order to ins-tall -the injector 98 and enable the conduit 100 -thereof to extend between the bo-ttom wall tubes, -the two tubes 26' immediately adjacent the conduit 100 are ben-t downwardly and ou-twardly to provide sufficien-t spacing for accommodating the conduit 100; as best shown in Fig. 8. In order to also allow ther-mally induced deformations, the fins connected -to the tubes 26' are made in two parts 112' and 112" which are movably engaged with one another by means of a tongue and groove arrangement 11~.
Fig. 9 illustLaLes a similar bot-tom injector 98' with a protective refractory struc-ture 102' having a pyrami-dal configuration. As shown, the injector 98' is provided with four gas discharge orifices 104', one in each of the four upwardly converging sidewalls o:E the pyramidal refrac-tory struc~ure 102'.
As shown in Fig. 10, the injector 98 is arranged centrally of the boiler 20" so as to blow the oxygen-con-taining gas vertically upwardly in the center of -the boiler.
It is also possible to arrange the injector 98 off-center and to install two pyramidal--type injector 98" each having a single gas discharge orifice 104' in the refractory StLuc-ture 102" thereof such as to blow two streams of oxygen-con-taining gas angularly upwardly in a direction toward the vertical stream of oxygen-containing gas blown by the injector 98, as shown in Fig. 11. Four pyramidal-type injectors 98" can also be arranged in a manner such that the respective gas discharge orifices 104' thereof blow a stream ~ 3 1 ~055 of oxygen-containing gas angularly upwa:rdly while imparting to the oxygen-containing gas a swirling mo-tion, as shown in Fig. 12.
It should be noted in connec-tion with -the embodi-ments illustra-ted in Figs 1 and 2 that the lance 72 or 76 need not necessarily be wa-ter cooled as other types of cooling means can be utilised. For instance, -the lance can comprise a first tubular conduit for blowing the oxygen-con-taining gas and a second tubular condui-t concentrically arranyed with respect to the first conduit to defi.ne a channel of annular cross-section surrounding the first conduit for blowing a gas shrouding -the oxygen-containing gas. The shrouding gas can be any gas or mixture of gases which may serve as a coolant or as a gaseous shield to protect the tip of the lance from 2 attac]~. Examples of shrouding gas which may be used to this end include air, argon, N2, CO2, CO, CH4, C3M8, H2O vapour and flue gases.
With respect to the embodiments shown in Figs 8-12, the refractory s-truc-ture 102, 102' or 102" is entirely optional since when -the 2 concentration of the oxygen-con-taining gas blown by the injector 98,98' or 98" is less than about 35% by vol., a single s-teel pipe is adequate. For 2 concentrations of 35% by vol. and over, use can be made of an injector comprising a first tubular conduit of temperatu-re and corrosion resistant rnetal for blowing the oxygen-con-taining gas and a second -tubular conduit of temperature and corrosion resistant metal concentrically arranged with respect ~o the first conduit to define a channel of annular cross-section surrounding the firs-t conduit for blowing a gas shrouding the oxygen-con-taining gas, the Eirst and ~ 3~ qO55 second conduits coextending through the bottom wall and char bed. A refractory structure such as that represented by reference numeral 102 can optionally surround the second conduit, the refractory structure and second conduit coex-tending from the bottom wall through the char bed.
When solid carbonaceous or oxygen reactive ma-terials are pneumatically injected into the boiler, a concentric double condui-t type injector as described above can be advantaqeously utilized, wherein a gas which is non-reactive to the solid carbonaceous or oxygen reactive materials is used as a carrier and blown together with the solid carbonaceous or oxygen reactive materials through the central conduit while the oxygen-con-taining gas is blown through the annular channel defined between the condui-ts.
The carrier gas can consist of a hydrocarbon gas or of a gaseous mixture of hydrogen, carbon monoxide and hydrocar-bons. It is also possible to inject the solid carbonaceous or oxygen reactive ma-terials through the central conduit by means of a liquid hydrocarbon, the oxygen-containing gas being blown through -the annular channel between -the con-duits.
According to a further preferred embodiment, usecan be made of a concentric triple conduit injector, that is, an injector comprising a first tubular condui-t of temperature and corrosion resistan-t metal for pneumatically injecting a solid oxygen-reactive material in particulate form with a carrier gas which is non reactive to the oxygen reactive material, a second tubular conduit of temperature and corrosion resistant metal concentrically arranged with respect to the first conduit to define a first channel of 1 3 ~ ~ ~ 5 5 annular cross-sec-tion surrounding -the first conduit for blowing -the oxygen-containing gas, and a third tubular condui-t of -temperature and corrosion resistant metal concen-trically arranged wi-th respect -to -the second conduit to define a second channel of annular cross-section surrounding the second conduit for blowing a gas shrouding -the oxygen-containing gas, -the first, second and third conduits coex-tending through the bottom wall and the char bed.
Enriching the combus-tion air wi-th oxygen would -further allow burning capaeity increases without subsequen-t inerease in earry over deposits due -to lower gas veloeities relative to air eombustion.
It is -therefore an object of the presen-t inven-tion to improve the air distribution in che lower section of a s-team generating boiler so as to provide intimate mixing of the air with the combustion speeies, thereby improving combustion.
In accordance with one aspect of the invention, -there is provided a method of improving combustion in a steam genera-ting boiler having a bottom wall supporting a char bed and sidewalls with por-ts -through which air is admitted for combus-tion of combus-tible species in the char bed and emanating therefrom, which comprises introducing an oxygen-con-taining gas into a lower central zone of the boiler, from at least one point remote from the sidewalls to thereby cause intimate mixing of -the oxygen contained in the gas with the combustible species.
According to a further aspect of the invention, there is also provided in a steam generating boiler having a bot-tom wall supporting a char bed and sidewalls with ports through w'nich air is admitted for combustion of combustible species in the char bed and emanating therefrom, the impro-vement which comprises means for blowing an oxygen-contain-ing gas into a lower central zone of the boiler, from at least one point remote from the sidewalls to -thereby cause intimate mixing of the oxygen contained in the gas with the combustible species.
Applicant has found quite unexpectedly that by introducing an oxygen-containing gas into the lower central zone of the boiler, remotely from the sidewalls of the boiler, a better mixing of oxygen and combus-tible species could be achieved and that the oxygen deficient zone which is charac~eristic of boilers where air is introduced only peripherally through sidewall por-ts could be greatly reduced as a result of the improved mixing of the oxygen with the combustible species. This improvement can be attained without disrupcing the char oed formation which is essential to achieving chemical recovery. Due to the resulting tempe-rature increase in che lower section of the boiler, oxida-tion of Na2S, H2S or organic sulrides would occur in tha-t section of the boiler, thereby lowering TRS emissions.
Examples of suitable oxygen-containing gases which can be introduced non-peripherally include air, oxygen-enriched air and mixtures of oxygen with other gases 2' 2' CO, CE~4, C3E18, natural gas, H2O vapour N2O, flue gases, etc. It is of course also possible to use commercial 2 having a molecular oxygen content generally I ;~ 1 9055 between 90 and 99.5% by volume. On -the other hand, where -the oxygen-containing gas comprises a mixture of 2 and CO2, such a gaseous mix-ture is preferably nitrogen-free, -that is, havi.ng a N2 content of less than about 4% by volume, so as -to enable the CO2 to be recovered. Preferably, up to about 60~ of -the total oxygen re~uirement is introduced via the non-peripheral blowing of the oxygen-containing gas, the balance being supplied i.n the form of air introduced peri-pherally ~hrough the sidewall ports.
The oxygen-containing gas can be introduced non-peripherally by blowing the gas either downwardly from an upper section of the boiler or upwardly from above the char bed, or by a combined blowing of the gas both down-wardly froin an upper section of the boiler and upwardly from above the char bed. The oxygen-containing gas can be blown at any pressure, from atmospheric ~when a negative pressure exists in the boiler because of an induced draf-t fan) to about 10 atm., -the preferred pressure range being between about 1.2 and about 5 atm. (absolute). Thus, the gas veloci--ty can range from about 1 ft/sec to over sonic velocity, preferably from about 10 to about 1000 ft/sec.
The oxygen-containing gas is conveniently blown downwardly by means of at least one elongated lance arranged in the upper section of the boiler and ex-tending downwardly to discharge through at least one orifi.ce thereof at least one stream of the oxygen-containing gas, remotely from -the sidewalls of the boiler. For example, a single lance can be suspended from the top of the boiler to ex-tend vertically and centrally of the boiler, or can be mounted in the so-called "bull nose cavity" of the boiler, in which case 1 3 1 qO55 the lance is angularly inclined. Such a lance is preferably provided wi-th a plurality of di.scharge orifices spaced from one anothe~ and each oriented at an angle no-t greater than about 60 relative to the longi-tudinal axis of the lance. On the other hand, where a plurality of lances are used, the lances can be evenly distributed relative -to a central vertical axis of the boiler or they can extend in a common plane, in spaced-apart parallel relationship; in the latter case, -the lances may extend either vertically or at an angle relative -to the vertical.
Upward blowing of the oxygen-containing gas, on -the other hand, is advan-tageously effected by means of a-t least one injector arranged on the bottom wall oE the boiler remotely from the sidewalls thereof and extending through the char bed. Preferably, the injector protrudes from the surface of the char bed immediately surrounding -the injector a distance ranging from about 1 cm to about 30 cm, so as to not in-terfere with the chemical reactions occurring in the char bed and to prevent blockage of the gas discharge orifice of the injector by the liquid smelt.
According -to a particularly preferred embodiment, the injector comprises an elongated conduit of temperature and corrosion resistant metal extending through the bottom wall, and a protective refractory struc-ture surrounding the conduit, the conduit and refractory structure coextending from the bottom wall to above the char bed.
The pro-tective refractory structure should be made of a refractory material which is chemically resistant to the smel-t and capable of mechanically withstanding impac-ts caused hy falling deposits from the upper section of 1;~1'3055 the boiler. Examples of suitable refractory mate:rials include alumina, silica, silicon carbide, magnesite and chrome-magnesite.
In the case where a single injector is used, i-t is preferably disposed centrally of the boiler. In -the case of a plurali-ty of injectors, on the other hand, -these are preferably arranged to impart a swirling motion to the oxygen-containing gas.
It is also possible to pneumatically inject with the lance and/or injector particulate solids which can act as seeds to cause agglomeration of volatilized inorganic mat-ter, or as a source of heat to control furnace or char bed temperature, the oxygen-containing gas further serving in this case as a carrier gas. Such injection of particulate solids is also useful in removing accretion build-up from the gas discharge orifices of the lance or injector. For example, particles of sodium sulfate can be used as agglome-ration seeds whereas particles of carbonaceous materials such as coal or sawdust can be used as a source of heat.
However, where use is made of coal particles, the carrier gas should not contain more than about 21~ vol. oxygen.
The present invention finds application not only in recovery boilers used in pulp and paper mills, bu-t also in other types of steam generating boiler such as those opera-ted in coal fired power plants and boilers burning any mixture of biomass, hydrocarbons, fossils or by-product fuels for the purpose of generating steam and optionally recovering chemicals.
1 31 qO55 Further features and advantages of the invention will become more readil.y apparent from the following des-cription of preferred embodiments as illustrated by way of example in the accompanying drawings, in which:
Fig. 1 is a schematic vertical cross-section of a kraft recovery boiler equipped with a top blowing lance according to the invention;
Fig. 2 is a view similar to Fig. 1, illustrating a different location of the lance;
Fig. 3 is a fragmentary section view of the lance shown in Figs 1 and 2, illustrating -the discharge end thereof;
Fig. 4 is a bottom view of a lance according to another preferred embodiment;
Fig. 5 is a fragmentary section view taken along line 5-5 of Fig. 4;
Fig. 6 is a schematic vertical c,oss-section of a kraft recovery boiler equipped with a bottom blowing injec-tor according to the invention;
Fig. 7 is a fragmentary vertical section view illustrating the injector shown in Fig. 6i Fig. 8 is a fragmentary top view of the injector shown in Fig. 7;
Fig. 9 is a view similar to Fig. ~, illustrating an injector according to ano-ther preferred embodiment; and Figs 10, 11 and 12 which are on the same sheet as Fig. 6 are schematic horizontal section views illustrating different arrangements of injec-tors.
Referring first to Fig. 1, there is illustrated a kraft recovery boiler generally designated by reference numeral 20 and seen having a slan-ted bottom wall 22 and vertical sidewalls 24. The bottom wall 22 is formed of closely spaced tubes 26 with welded fins therebetween whereas the sidewalls 24 are lined with similar tubes 26 allowing circulation of water introduced through inlet 28 and fed to manifold 30 for distribution to the tubes 26.
slack liquor from the kraft pulping process is sprayed by means of spray nozzles 32 in small drops to collect as black liquor dry solids in a char bed 33 supported by the bottom wall 22. As water rises through the tubes 26, it is gradual-ly heated by the heat released by the combustion of the black liquor solids and vaporizes into steam to be collected in the upper drum 34 of the boiler tube bank 36 comprising a plurality of boiler tubes 38. Saturated steam is then sent from the upper drum 34 via line 40 to superheater tubes 42 for the generation of high-pressure dry steam which is discharged at the outlet 44 and may be used at various points in the pulp and paper mill.
Air for the combustion of the black liquor solids is supplied at three different levels in ~he boiler, by means of primary, secondary and tertiary windboxes 46,4~3 and S0 which respectively blow primary, secondary and tertiary air through ports 52,54 and 56 provided in the sidewalls 24.
The primary air is blown through por-ts 52 and which may account for up to 60~ of the total air supply serves to control the height and shape of the char bed 33. The char bed is a mixture of inorganic salts and carbonaceous mate-rials which provides a reducing environment to chemically 1, ) '331qO5~
reduce sodium sulfate -to sodi.um sulfide and sodium hydroxide -to sodium carbona-te, the active chemicals in the liquid smel-c produced and discharged through spout 5~. These cher,licals are subsequently recycled to the diges-tion stage of -the pulp mill for -the -trea-tmen-t of incoming wood.
The secondary air which is blown through ports 54 may account for up to 50% of the total air supply and provldes the oxidant which first meets the incoming black liquor from the spray nozzles 32. Besides causing flash dehydration of the black liquor salts, it supplies oxygen to burn carbon monoxide formed at the char bed 33 and should oxidize the reduced sulfur species either contained in the black liquor or genera-ted during the combus-tion of dry solids.
The tertiary air blown through ports 56 supplies the balance of air needed to attain an excess 2 in the exit gas represented by the arrow 60. The 2 concen-tration in the exit gas varies in practice from about 0.1 to about 6% by volume, but for the purpose of the present invention it is preferably within the range of 1.0 to 2.5~ by volume. The purpose of -the tertiary air is to take to completion the oxidation of combustible species emanating from the lower section of the boiler 20.
Hot gases and entrained volatilized matter are carried -to the upper section of the boiler 20. ~s temperatu-re decreases, the volatilized matter forms crusty deposits on screen tubes 62 and the boiler must therefore be periodi-cally shut down to remove such deposits. The screen tubes 62 1 31 qO55 form an independent hot water circui-t which -takes hot water from the lower drum 64 via line 66 and discharges steam via line 68 into -the upper drum 34 of the boiler -tube bank 36.
The hot gases containing mainly nitrogen, carbon dioxide and water vapor from the combus-tion of organic matter also carry ash and chemical fumes, which after the superheater tubes 42, cross the boiler tubes 38 and enter an economizer ~not shown). The economizer is a heat exchanger which uses the sensible heat in the exit gas 60 to indirec-tly preheat the feed water before it reaches the boilertubes 38 and subsequently the water introduced through the inlet 28 at the bottom of the boiler 20.
A fundamental characteristic of traditional steam generating boilers which limits efficient burning of combus-tible species is the lack of intimate mixing of the seconda-ry and tertiary air supplies with the intermediate products of combustion. The low velocity air tends to flow upwards peripherally along the sidewalls 24, resulting in a relatively cold gas containing large 2 excess. In the central zone, an 2 defficient plume 70 forms which may reach as high as the screen tubes 62 before complete mixing with the peripheral lean gas takes place.
The delayed mixing has important detrimental effects for the boiler operation. Should intimate mixing -take place at the tertiary air level, or not too high over it, complete combustion would be attained, thus the longitu-dinal temperature profile would change, resulting in a shorter but hotter combustion zone, with a subsequent lower temperature at the upper section of -the boiler.
i 3 1 9055 In order to overcome these drawbacks and to reduce the oxygen-defEicien-t zone 70, an oxygen-con-taining gas is blown downwardly into the lower central zone of the boiler by means of a water-cooled lance 72 suspended from -the top of the boiler by a retaining collar 74 and arranged centrally of the boiler. An oxygen-containing gas such as air or oxygen-enriched air is thus blown cen-trally into the lower section of the boiler, thereby causing intimate mixing of oxygen with the combustible species and resulting in a much shorter O2-defficient plume 70'.
Instead of posi-tioning the lance 72 vertically and centrally of the boiler, it is also possible to mount a shorter lance 76 in the so-called bull nose cavity 78 of the boiler, as shown in Fig. 2. In this case, the lance 76 is angularly inclined and s~ill provides non-peripheral down-ward blowing of oxygen-containing gas into the lower central zone of the boiler 20'.
Fig. 3 illustrates the structure of the water-cooled lance 72, which may also be the same for the lance 76 shown in Fig. 2. As shown, the lance 72 is formed with a central conduit 80 for conveying the oxygen-con-taining gas, which merges wi-th an outwardly diverging gas discharge orifice 82. Two concentric tubular conduits 84 and 86 are provided for circulating water -to cool the lance, the con-duits 84 and 86 communicating with one another at their lower ends by means of an annular elbow 88 formed in the tip 90 of the lance. The lance tip 90 can be made of a high thermally conductive metal, such as copper or a copper alloy. The ou-ter wall 92 of the lance, on -the other hand, can be made of corrosion resistant metal such as a ferrous alloy (e.g. stainless steel), whereas the inner walls 94 and 96 can be made oE thermally conductive metal such as carbon steel, for adequate cooling.
Figs 4 and 5 illustrate the discharge end of a similar water-cooled lance 72', but having a modified tip 90'. As shown, the tip 90' is formed with three gas dischar-ge orifices 82' equidistantly spaced from one another and each oriented at an angle of about 45 relative to the longitudinal axis of the lance.
In the recovery boiler 20" illustrated in Fig. 6, the non-peripheral blowing of oxygen-containing gas is effected by blowing the gas upwardly from above the char bed 33 into a substantially gaseous phase by means of an injec-tor 98 arranged on the bottom wall 22' and extending -through and above the char bed 33. The injector 98 comprises an elongated conduit 100 extending through -the bottom wall 22' for conveying the oxygen-containing gas and a protective refractory structure 102 surrounding the conduit 100, as best shown in Fig. 7. The conduit 100 and refractory s-truc-ture 102 coextend from the bottom wall 22' to above the char bed 33. The refractory structure 102 has a conical configu-ration, the gas discharge orifice 104 being located at the apex of such a conical structure. The flow of oxygen-con-taining gas can be regulated by means of the valve 106.
Where the oxygen-containing gas is air and it is desired to enrich the air with oxygen, molecular oxygen can be admixed via the conduit 108 connected to conduit 100 and provided with a valve 110 for regulating the flow of molecular oxygen admixed.
13190~i5 The bot-tom wall 22' is formecl of closely spaced tubes 26 wiLh welded fins 112 therebetween, as is -the bo-ttom wall 22 shown in Figs 1 and 2. However, in order to ins-tall -the injector 98 and enable the conduit 100 -thereof to extend between the bo-ttom wall tubes, -the two tubes 26' immediately adjacent the conduit 100 are ben-t downwardly and ou-twardly to provide sufficien-t spacing for accommodating the conduit 100; as best shown in Fig. 8. In order to also allow ther-mally induced deformations, the fins connected -to the tubes 26' are made in two parts 112' and 112" which are movably engaged with one another by means of a tongue and groove arrangement 11~.
Fig. 9 illustLaLes a similar bot-tom injector 98' with a protective refractory struc-ture 102' having a pyrami-dal configuration. As shown, the injector 98' is provided with four gas discharge orifices 104', one in each of the four upwardly converging sidewalls o:E the pyramidal refrac-tory struc~ure 102'.
As shown in Fig. 10, the injector 98 is arranged centrally of the boiler 20" so as to blow the oxygen-con-taining gas vertically upwardly in the center of -the boiler.
It is also possible to arrange the injector 98 off-center and to install two pyramidal--type injector 98" each having a single gas discharge orifice 104' in the refractory StLuc-ture 102" thereof such as to blow two streams of oxygen-con-taining gas angularly upwardly in a direction toward the vertical stream of oxygen-containing gas blown by the injector 98, as shown in Fig. 11. Four pyramidal-type injectors 98" can also be arranged in a manner such that the respective gas discharge orifices 104' thereof blow a stream ~ 3 1 ~055 of oxygen-containing gas angularly upwa:rdly while imparting to the oxygen-containing gas a swirling mo-tion, as shown in Fig. 12.
It should be noted in connec-tion with -the embodi-ments illustra-ted in Figs 1 and 2 that the lance 72 or 76 need not necessarily be wa-ter cooled as other types of cooling means can be utilised. For instance, -the lance can comprise a first tubular conduit for blowing the oxygen-con-taining gas and a second tubular condui-t concentrically arranyed with respect to the first conduit to defi.ne a channel of annular cross-section surrounding the first conduit for blowing a gas shrouding -the oxygen-containing gas. The shrouding gas can be any gas or mixture of gases which may serve as a coolant or as a gaseous shield to protect the tip of the lance from 2 attac]~. Examples of shrouding gas which may be used to this end include air, argon, N2, CO2, CO, CH4, C3M8, H2O vapour and flue gases.
With respect to the embodiments shown in Figs 8-12, the refractory s-truc-ture 102, 102' or 102" is entirely optional since when -the 2 concentration of the oxygen-con-taining gas blown by the injector 98,98' or 98" is less than about 35% by vol., a single s-teel pipe is adequate. For 2 concentrations of 35% by vol. and over, use can be made of an injector comprising a first tubular conduit of temperatu-re and corrosion resistant rnetal for blowing the oxygen-con-taining gas and a second -tubular conduit of temperature and corrosion resistant metal concentrically arranged with respect ~o the first conduit to define a channel of annular cross-section surrounding the firs-t conduit for blowing a gas shrouding the oxygen-con-taining gas, the Eirst and ~ 3~ qO55 second conduits coextending through the bottom wall and char bed. A refractory structure such as that represented by reference numeral 102 can optionally surround the second conduit, the refractory structure and second conduit coex-tending from the bottom wall through the char bed.
When solid carbonaceous or oxygen reactive ma-terials are pneumatically injected into the boiler, a concentric double condui-t type injector as described above can be advantaqeously utilized, wherein a gas which is non-reactive to the solid carbonaceous or oxygen reactive materials is used as a carrier and blown together with the solid carbonaceous or oxygen reactive materials through the central conduit while the oxygen-con-taining gas is blown through the annular channel defined between the condui-ts.
The carrier gas can consist of a hydrocarbon gas or of a gaseous mixture of hydrogen, carbon monoxide and hydrocar-bons. It is also possible to inject the solid carbonaceous or oxygen reactive ma-terials through the central conduit by means of a liquid hydrocarbon, the oxygen-containing gas being blown through -the annular channel between -the con-duits.
According to a further preferred embodiment, usecan be made of a concentric triple conduit injector, that is, an injector comprising a first tubular condui-t of temperature and corrosion resistan-t metal for pneumatically injecting a solid oxygen-reactive material in particulate form with a carrier gas which is non reactive to the oxygen reactive material, a second tubular conduit of temperature and corrosion resistant metal concentrically arranged with respect to the first conduit to define a first channel of 1 3 ~ ~ ~ 5 5 annular cross-sec-tion surrounding -the first conduit for blowing -the oxygen-containing gas, and a third tubular condui-t of -temperature and corrosion resistant metal concen-trically arranged wi-th respect -to -the second conduit to define a second channel of annular cross-section surrounding the second conduit for blowing a gas shrouding -the oxygen-containing gas, -the first, second and third conduits coex-tending through the bottom wall and the char bed.
Claims (81)
1. A method of improving combustion in a steam generating boiler having a bottom wall supporting a char bed and sidewalls with ports through which air is admitted for combustion of combustible species in the char bed and emanating therefrom, which comprises introducing an oxygen-containing gas into a lower central zone of the boiler, from at least one point remote from said sidewalls and from said char bed to thereby cause intimate mixing of the oxygen contained in said gas with said combustible species, said oxygen-containing gas being blown downwardly from an upper section of the boiler at a distance from said char bed sufficient to avoid oxidation of spent chemicals contained in said char bed.
2. A method according to claim 1, wherein said oxygen-containing gas is air.
3. A method according to claim 1, wherein said oxygen-containing gas is oxygen-enriched air.
4. A method according to claim 1, wherein said oxygen-containing gas is commercial 02 having a molecular oxygen content between about 90 and about 99.5% by volume.
5. A method according to claim 1, wherein said oxygen-containing gas comprises a mixture of oxygen with at least one other gas selected from the group consisting of N2, N2O, CO2, CO, CH4, C3H8, natural gas, flue gases and H2O
vapour.
vapour.
6. A method according to claim 1, wherein said oxygen-containing gas is substantially nitrogen-free.
7. A method according to claim 6, wherein said oxygen-containing gas has a nitrogen content of less than about 4% by volume.
8. A method according to claim 1, wherein up to about 60% of the total oxygen requirement is introduced non-peripherally, the balance being supplied in the form of air introduced peripherally through said sidewall ports.
9. A method according to claim 1, wherein said oxygen-containing gas is blown downwardly by means of at least one elongated lance arranged in said upper section and extending downwardly to discharge through at least one orifice thereof at least one stream of said oxygen-contain-ing gas, remotely from said sidewal.ls.
10. A method according to claim 9, wherein use is made of a single lance to blow said oxygen-containing gas, said lance extending vertically and centrally of said boiler.
11. A method according to claim 9, wherein use is made of a single lance to blow said oxygen-containing gas, said lance being angularly inclined.
12. A method according to claim 9, wherein use is made of a plurality of lances to blow said oxygen-containing gas, said lances being evenly distributed relative to a central vertical axis of said boiler.
13. A method according to claim 9, wherein use is made of a plurality of lances to blow said oxygen-containing gas, said lances extending in a common plane, in spaced-apart parallel relationship.
14. A method according to claim 12 or 13, wherein said lances extend vertically.
15. A method according to claim 13, wherein said lances are angularly inclined.
16. A method of improving combustion in a steam generating boiler having a bottom wall supporting a char bed and sidewalls with ports through which air is admitted for combustion of combustible species in the char bed and emanating therefrom, which comprises introducing an oxygen-containing gas into a lower central zone of the boiler, from at least one point remote from said sidewalls to thereby cause intimate mixing of the oxygen contained in said gas with said combustible species, said oxygen-containing gas being blown upwardly from above said char bed.
17. A method according to claim 16, wherein said oxygen-containing gas is blown upwardly by means of at least one injector arranged on said bottom wall remotely from said sidewalls and extending through said char bed.
18. A method according to claim 17, wherein said oxygen-containing gas is blown upwardly by means of a single injector disposed centrally of said boiler.
19. A method according to claim 17, wherein said oxygen-containing gas is blown upwardly by means of a plurality of injectors.
20. A method according to claim 19, wherein said injectors are arranged to impart a swirling motion to said oxygen-containing gas.
21. A method according to claim 1, wherein particula-te solids are pneumatically injected together with said oxygen-containing gas.
22. A method according to claim 21, wherein said solids are supplied as seeds to cause agglomeration of volatilized inorganic matter.
23. A method of improving combustion in a steam generating boiler having a bottom wall supporting a char bed and sidewalls with ports through which air is admitted for combustion of combustible species in the char bed and emanating therefrom, which comprises introducing an oxygen-containing gas into a lower central zone of the boiler, from at least one point remote from said sidewalls to thereby cause intimating mixing of the oxygen contained in said gas with said combustible species and pneumatically injecting particulate solids as seeds together with said oxygen-containing gas to cause agglomeration of volatized inorganic matter, said particulate solids comprising particles of sodium sulfate, or char bed temperature.
24. A method according to claim 21, wherein said solids are supplied as a source of heat to control furnace or char bed temperature.
25. A method according to claim 24, wherein said particulate solids comprise particles of a carbonaceous material.
26. A method of improving combustion in a steam generating boiler having a bottom wall supporting a char bed and sidewalls with ports through which air is admitted for combustion of combustible species in the char bed and emanating therefrom, which comprises introducing an oxygen-containing gas into a lower central zone of the boiler, from at least one point remote from said sidewalls to thereby cause intimate mixing of the oxygen contained in said gas with said combustible species, and pneumatically injecting a solid oxygen reactive material in particulate form into said boiler separately of said oxygen containing gas, by means of a carrier gas which is non-reactive to said oxygen reactive material.
27. A method according to claim 26, wherein said carrier gas is a hydrocarbon gas or a gaseous mixture of hydrogen, carbon monoxide and hydrocarbons.
28. A method of improving combustion in a steam generating boiler having a bottom wall supporting a char bed and sidewalls with ports through which air is admitted for combustion of combustible species in the char bed and emanating therefrom, which comprises introducing an oxygen-containing gas into a lower central zone of the boiler, from at least one point remote from said sidewalls to thereby cause intimate mixing of the oxygen contained in said gas with said combustible species, and injecting a solid oxygen reactive material in particulate form into said boiler by means of a liquid hydrocarbon.
29. A method according to claim 26 or 28, wherein said particulate oxygen reactive material comprises parti-cles of a carbonaceous material and is supplied as a source of heat to control furnace or char bed temperature.
30. A method according to claim 1 or 16, wherein said oxygen-containing gas is introduced at a pressure ranging from about 1 to about 10 atm. abs.
31. A method according to claim 1 or 16, wherein said oxygen-containing gas is introduced at a pressure ranging from about 1.2 to about 5 atm. abs.
32. A method according to claim 1 or 16, wherein said oxygen-containing gas has a velocity ranging from about 1 ft/sec to over sonic velocity.
33. A method according to claim 1 or 16, wherein said oxygen-containing gas has a velocity ranging from about 10 to about 1000 ft/sec.
34. In a steam generating boiler having a bottom wall supporting a char bed and sidewalls with ports through which air is admitted for combustion of combustible species in the char bed and emanating therefrom, the improvement which comprises means for blowing an oxygen-containing gas into a lower central zone of the boiler, from at least one point remote from an upper section thereof and from said sidewalls to thereby cause intimate mixing of the oxygen contained in said gas with said combustible species.
35. A steam generating boiler according to claim 34, wherein said gas blowing means is adapted to blow said oxygen-containing gas downwardly from an upper section of the boiler.
36. A steam generating boiler according to claim 35, wherein said gas blowing means comprises at least one elongated lance arranged in said upper section and extending downwardly to discharge through at least one orifice thereof at least one stream of said oxygen-containing gas, remotely from said sidewalls.
37. A steam generating boiler according to claim 36, wherein said at least one lance is angularly inclined.
38. A steam generating boiler according to claim 36, wherein there is a single lance extending vertically and centrally of the boiler.
39. A steam generating boiler according to claim 36, wherein there is a plurality of lances evenly distributed relative to a central vertical axis of said boiler.
40. A steam generating boiler according to claim 36, wherein there is a plurality of lances extending in a common plane, in spaced-apart parallel relationship.
41. A steam generating boiler according to claim 39 or 40, wherein said lances extend vertically.
42. A steam generating boiler according to claim 39 or 40, wherein said lances are angularly inclined.
43. In a steam generating boiler having a bottom wall supporting a char bed and sidewalls with ports through which air is admitted for combustion of combustible species in the char bed and emanating therefrom, the improvement which comprises means for blowing an oxygen-containing gas down-wardly from an upper section of the boiler into a lower central zone of the boiler from at least one point remote from said sidewalls to thereby cause intimate mixing of the oxygen contained in said gas with said combustible species, said gas blowing means comprising at least one elongated lance arranged in said upper section and extending down-wardly to discharge through a plurality of gas discharge orifices a plurality of streams of said oxygen-containing gas, remotely from said sidewalls, said gas discharge orifices being spaced from one another and each oriented at an angle not greater than about 60° relative to the longi-tudinal axis of the lance.
44. A steam generating boiler according to claim 43, wherein said at least one lance is provided with three gas discharge orifices equidistantly spaced from one another and each oriented at an angle of about 45° relative to said longitudinal axis.
45. In a steam generating boiler having a bottom wall supporting a char bed and sidewalls with ports through which air is admitted for combustion of combustible species in the char bed and emanating therefrom, the improvement which comprises means for blowing an oxygen-containing gas down-wardly from an upper section of the boiler into a lower central zone of the boiler from at least one point remote from said sidewalls to thereby cause intimate mixing of the oxygen contained in said gas with said combustible species, said gas blowing means comprising at least one water-cooled lance arranged in said upper section and extending down-wardly to discharge through at least one orifice thereof at least one stream of said oxygen-containing gas, remotely from said sidewalls.
46. In a stream generating boiler having a bottom wall supporting a char bed and sidewalls with ports through which air is admitted for combustion of combustible species in the char bed and emanating therefrom, the improvement which comprises means for blowing an oxygen-containing gas downwardly from an upper section of the boiler into a lower central zone of the boiler, from at least one point remote from said sidewalls to thereby cause intimate mixing of the oxygen contained in said gas with said combustible species, said gas blowing means comprising at least one elongated lance arranged in said upper section and extending down-wardly to discharge through at least one orifice thereof at least one stream of said oxygen-containing gas, remotely from said sidewalls, said at least one lance comprising a first tubular conduit for blowing said oxygen-containing gas and a second tubular conduit concentrically arranged with respect to said first conduit to define a channel of annular cross-section surrounding said first conduit for blowing a gas shrouding said oxygen-containing gas.
47. A steam generating boiler having a bottom wall supporting a char bed and sidewalls with ports through which air is admitted for combustion of combustible species in the char bed and emanating therefrom, the improvement which comprises means for blowing an oxygen-containing gas into a lower central zone of the boiler, from at least one point remote from said sidewalls to thereby cause intimate mixing of the oxygen contained in said gas with said combustible species, said gas blowing means being adapted to blow said oxygen-containing gas upwardly from above said char bed.
48. A steam generating boiler according to claim 47, wherein said gas blowing means comprises at least one injector arranged on said bottom wall remotely from said sidewalls and extending through said char bed.
49. A steam generating boiler according to claim 48, wherein said injector comprises a single conduit of tempera-ture and corrosion resistant metal.
50. A steam generating boiler according to claim 48, wherein said injector comprises a first tubular conduit of temperature and corrosion resistant metal for blowing said oxygen-containing gas and a second tubular conduit of temperature and corrosion resistant metal concentrically arranged with respect to said first conduit to define a channel of annular cross-section surrounding said first conduit for blowing a gas shrouding said oxygen-containing gas, said first and second conduits coextending through said bottom wall and said char bed.
51. A steam generating boiler according to claim 48, wherein said injector comprises an elongated conduit of temperature and corrosion resistant motley extending through said bottom wall, and a protective refractory structure surrounding said conduit, said conduit and refractory structure coextending from said bottom wall through said char bed.
52. A steam generating boiler according to claim 51, wherein said refractory structure has a conical configura-tion defining an apex, and wherein said conduit has a gas discharge orifice provided at said apex.
53. A steam generating boiler according to claim 51, wherein said refractory structure has a pyramidal configura-tion defining four upwardly converging sidewalls, and wherein said conduit has at least one gas discharge orifice provided in at least one of said upwardly converging side-walls.
54. A steam generating boiler according to claim 48, wherein said injector comprises a first tubular conduit of temperature and corrosion resistant metal for blowing said oxygen-containing gas and a second tubular conduit of temperature and corrosion resistant metal concentrically arranged with respect to said first conduit to define a channel of annular cross-section surrounding said first conduit for blowing a gas shrouding said oxygen-containing gas, said first and second conduits coextending through said bottom wall and said char bed, and wherein a protective refractory structure surrounds said second conduit, said refractory structure and said second conduit coextending from said bottom wall through said char bed.
55. A steam generating boiler according to claim 54, wherein said refractory structure has a conical configura-tion defining an apex, and wherein said conduits each have a gas discharge orifice provided at said apex.
56. A steam generating boiler according to claim 54, wherein said refractory structure has a pyramidal configura-tion defining four upwardly converging sidewalls, and wherein said conduits each have at least one gas discharge orifice provided in at least one of said upwardly converging sidewalls.
57. A steam generating boiler according to claim 48, wherein there is a single injector disposed centrally of the boiler.
58. A steam generating boiler according to claim 48, wherein there is a plurality of injectors arranged to impart a swirling motion to said oxygen-containing gas.
59. An injector for use in a steam generating boiler having a bottom wall supporting a char bed and sidewalls with ports through which air is admitted for combustion of combustible species in the char bed and emanating therefrom, said injector being mountable on said bottom wall remotely from said sidewalls for blowing an oxygen-containing gas in-to a lower central zone of said boiler and comprising an elongated conduit of temperature and corrosion resistant metal extending through said bottom wall, and a protective refractory structure surrounding said conduit, said conduit and refractory structure coextending from said bottom wall through said char bed.
60. An injector according to claim 59, wherein said refractory structure has a conical configuration defining an apex, and wherein said conduit has a gas discharge orifice provided at said apex.
61. An injector according to claim 59, wherein said refractory structure has a pyramidal configuration defining four upwardly converging sidewalls, and wherein said conduit has at least one gas discharge orifice provided in at least one of said upwardly converging sidewalls.
62. An injector according to claim 59, wherein said conduit is made of a ferrous alloy.
63. An injector according to claim 59 or 62, wherein said refractory structure is made of a refractory material selected from the group consisting of alumina, silica, silicon carbide, magnesite and chrome-magnesite.
64. An injector for use in a steam generating boiler having a bottom wall supporting a char bed and sidewalls with ports through which air is admitted for combustion of combustible species in the char bed and emanating therefrom, said injector being mountable on said bottom wall remotely from said sidewalls for blowing an oxygen-containing gas into a lower central zone of said boiler and comprising a first tubular conduit of temperature and corrosion resistant metal for blowing said oxygen-containing gas, a second tubular conduit of temperature and corrosion resistant metal concentrically arranged with respect to said first conduit to define an annular channel between said conduits for blowing a gas shrouding said oxygen-containing gas, said first and second conduits coextending through said bottom wall and said char bed, and a protective refractory struc-ture surrounding said second conduit, said refractory structure and said second conduit coextending from said bottom wall through said char bed.
65. An injector according to claim 64, wherein said refractory structure has a conical configuration defining an apex, and wherein said conduits each have a gas discharge orifice provided at said apex.
66. An injector according to claim 64, wherein said refractory structure has a pyramidal configuration defining four upwardly converging sidewalls, and wherein said con-duits each have at least one gas discharge orifice provided in at least one of said upwardly converging sidewalls.
67. An injector according to claim 64, wherein said conduits are made of ferrous alloy.
68. An injector for use in a steam generating boiler having a bottom wall supporting a char bed and sidewalls with ports through which air is admitted for combustion of combustible species in the char bed and emanating therefrom, said injector being mountable on said bottom wall remotely from said sidewalls for blowing an oxygen-containing gas into a lower central zone of said boiler and comprising a first tubular conduit of temperature and corrosion resistant metal for pneumatically injecting a solid oxygen reactive material in particulate form with a carrier gas which is non-reactive to said oxygen reactive material, a second tubular conduit of temperature and corrosion resistant metal concentrically arranged with respect to said first conduit to define a first channel of annular cross-section surround-ing said first conduit for blowing said oxygen-containing gas, and a third tubular conduit of temperature and corro-sion resistant metal concentrically arranged with respect to said second conduit to define a second channel of annular cross-section surrounding said second conduit for blowing a gas shrouding said oxygen-containing gas, said first, second and third conduits coextending through said bottom wall and said char bed.
69. An injector according to claim 68, wherein a protective refractory structure surrounds said third con-duit, said refractory structure and said third conduit coextending from said bottom wall through said char bed.
70. An injector according to claim 69, wherein said refractory structure has a conical configuration defining an apex, and wherein said conduits each have a gas discharge orifice provided at said apex.
71. An injector according to claim 69, wherein said refractory structure has a pyramidal configuration defining four upwardly converging sidewalls, and wherein said con-duits each have at least one gas discharge orifice provided in at least one of said upwardly converging sidewalls.
72. An injector according to claim 68, wherein said conduits are made of ferrous alloy.
73. An injector according to claim 64 or 69, wherein said refractory structure is made of a refractory material selected from the group consisting of alumina, silica, silicon carbide, magnesite and chrome-magnesite.
74. An injector according to claim 62, 67 or 72, wherein said ferrous alloy is stainless steel.
75. A method according to claim 16, wherein said oxygen-containing gas is air.
76. A method according to claim 16, wherein said oxygen-containing gas is oxygen-enriched air.
77. A method according to claim 16, wherein said oxygen-containing gas is commercial O2 having a molecular oxygen content between about 90 and about 99.5% by volume.
78. A method according to claim 16, wherein said oxygen-containing gas comprises a mixture of oxygen with a least one other gas from the group consisting of N2, N2O, CO2, CO, CH4, C3H8, natural gas, flue gases and H2O vapour.
79. A method according to claim 16, wherein said oxygen-containing gas is substantially nitrogen-free.
80. A method according to claim 79, wherein said oxygen-containing gas has a nitrogen content of less than about 4% by volume.
81. A method according to claim 16, wherein up to about 60% of the total oxygen requirement is introduced non-peripherally, the balance being supplied in the form of air introduced peripherally through said sidewall ports.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000548516A CA1319055C (en) | 1987-10-02 | 1987-10-02 | Non-peripheral blowing of oxygen-containing gas in steam generating boilers |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000548516A CA1319055C (en) | 1987-10-02 | 1987-10-02 | Non-peripheral blowing of oxygen-containing gas in steam generating boilers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1319055C true CA1319055C (en) | 1993-06-15 |
Family
ID=4136573
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000548516A Expired - Fee Related CA1319055C (en) | 1987-10-02 | 1987-10-02 | Non-peripheral blowing of oxygen-containing gas in steam generating boilers |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1319055C (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1537362A2 (en) * | 2002-05-15 | 2005-06-08 | Praxair Technology, Inc. | Low nox combustion |
| WO2012064545A3 (en) * | 2010-11-10 | 2013-11-28 | Praxair Technology, Inc. | Oxygen enhanced combustion of biomass |
| EP3798513A1 (en) | 2019-09-26 | 2021-03-31 | ÖKOFEN Forschungs- und Entwicklungsgesellschaft m.b.H. | Heating device |
-
1987
- 1987-10-02 CA CA000548516A patent/CA1319055C/en not_active Expired - Fee Related
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1537362A2 (en) * | 2002-05-15 | 2005-06-08 | Praxair Technology, Inc. | Low nox combustion |
| EP1537362A4 (en) * | 2002-05-15 | 2012-11-14 | Praxair Technology Inc | Low nox combustion |
| WO2012064545A3 (en) * | 2010-11-10 | 2013-11-28 | Praxair Technology, Inc. | Oxygen enhanced combustion of biomass |
| EP3798513A1 (en) | 2019-09-26 | 2021-03-31 | ÖKOFEN Forschungs- und Entwicklungsgesellschaft m.b.H. | Heating device |
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