Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/70—Furnaces for ingots, i.e. soaking pits
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D11/00—Process control or regulation for heat treatments
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
  • F27B17/00—Furnaces of a kind not covered by any preceding group
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D7/00—Forming, maintaining, or circulating atmospheres in heating chambers
  • F27D7/02—Supplying steam, vapour, gases, or liquids
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D99/00—Subject matter not provided for in other groups of this subclass
  • F27D99/0001—Heating elements or systems
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D99/00—Subject matter not provided for in other groups of this subclass
  • F27D99/0001—Heating elements or systems
  • F27D99/0033—Heating elements or systems using burners

Definitions

• the present invention relates to a method for increasing the temperature homogeneity in a pit furnace.
• the ingots are normally positioned leaning against opposite inner walls in the pit furnace, and resting on the furnace floor, often on a layer of oxide scale from previous runs.
• it is desirable to achieve good temperature homogeneity in other words to minimize temperature gradients inside the furnace.
• problems with the normally used furnace geometry in which the ingots are positioned leaning against the inner walls of the furnace.
• air burners are used to heat such pit furnaces.
• Such air burners turns over quite large volumes of air and fuel, leading to large volumes of hot combustion gases being circulated in the furnace.
• arrang-ing an air burner in one of the short sides of the furnace, and an exhaust port on the same short side, but below or above the burner lengthwise circulation along the whole furnace can be accomplished, whereby the gas volumes from the air burner can yield sufficient temperature homogeneity in the furnace.
• the present invention solves the above problems.
• the present invention relates to a method for increasing the temperature homogeneity in a pit furnace, in which at least two ingots to be heated are caused to lean against a respective one of first and second opposite inner walls of the pit furnace so that the ingots form an elongated space having a V-shaped cross-section between them as seen along the first and second walls, and is characterised in that at least one separate lance for an oxidant with an oxygen content of at least 85 percentages by weight and at least one separate lance for fuel are caused to be arranged in a furnace wall with their orifices arranged opening out into the furnace t a distance from each other and so that oxidant and fuel, respectively, are caused to be suppliable to said V- shaped space and to be combustible therein, and in that the orifice of the lance for oxidant is caused to be arranged above the orifice of the fuel lance and to be directed so that the oxidant flows obliquely downwards and along the longitudinal direction of said V
• Figure 1 is a partly cut away perspective view showing a conventional pit furnace
• Figure 2 shows the pit furnace of figure 1 from a long side
• Figure 3 shows the pit furnace of figure 1 from the top
• Figure 4 is a partly cut-away perspective view showing a pit furnace according to a first preferred embodiment of the present invention
• Figure 5 shows the pit furnace of figure 4 from a long side
• Figure 6 shows the pit furnace of figure 4 from a short side
• Figure 7 shows the pit furnace of figure 4 from the top
• Figure 8 is a view corresponding to that in figure 5, but which shows a pit furnace according to a second preferred embodiment according to the present invention as seen from a long side;
• Figure 9 shows the pit furnace of figure 8 from a short side
• Figure 10 shows the pit furnace of figure 8 from the top.
• Figures 1-3 illustrate, using a common set of reference numerals, a conventional pit furnace 100 in which ten ingots 101 are heated in two rows of five ingots each.
• the ingots rest upon a bed 102 of oxide scale from previous runs, and are standing leaning, over two rows, against the opposite inner walls of the respective long sides of the furnace 100, along the longitudinal direction 104 of the furnace 100.
• the furnace 100 is heated using a conventional air burner 103, directed along the longitudinal direction 104 of the furnace 100.
• the air burner 103 is arranged in the wall in one of the short ends of the furnace 100. Since the furnace is shown partly cut away in figures 1-3, said short end is not shown, together with the ceiling of the furnace 100 and one of its long sides.
• the hot combustion gases from the air burner 103 flow in the direction 104 along the rows of ingots 101, and turns over at a distal short end 105 of the furnace to then again flow back to the short end in which the air burner 103 is arranged, and there be evacuated through an exhaust channel 106 for flue gases. Since the air burner 103 and the exhaust channel 106 are arranged in the same wall in the furnace 100 but at different heights, natural convection arises resulting in sufficient temperature homogeneity throughout the whole furnace chamber.
• FIGS 4-7 show, with common reference numerals, a pit fur- nace 200 in which a method according to the present invention for increasing the temperature homogeneity is applied.
• the furnace 200 is largely similar to the furnace 100 shown in figures 1-3.
• the furnace 200 there is arranged a number of, at least two, ingots 201.
• the ingots 201 are arranged along two rows along the main longitudinal direction 250 of the furnace 200, each leaning against a respective first and second opposite inner walls of the pit furnace 200, so that the ingots 201 form a space 203 having a V-shaped cross- section (see figure 6) between and above them along said first and second inner walls.
• Said inner walls preferably constitute the inner walls of the long sides of the furnace 200.
• FIGS. 4-7 which are partly cut away, one of said walls is not shown.
• the ingots 201 rest upon a bed 202 of oxide scale similar to the bed 102.
• the ingots 201 may rest directly upon the furnace floor.
• An exhaust channel 206 for flue gases is arranged in one of the shorts sides of the furnace 200.
• At least one separate lance 211, 212 for oxidant, and at least one separate lance 210 for fuel are arranged in a furnace wall so that their orifices are arranged inside, opening out into, the furnace 200 at a distance from each other, and so that oxidant and fuel, respectively, can be supplied to the V-shaped space 203 between the ingots 201 and to react therein.
• the lower fuel lance 210 and the two oxidant lances 211, 212 arranged above the orifice of the fuel lance 210 together form a lance aggregate or group.
• the aggregate may also be designed with other configurations of lances for fuel and oxidant, as long as the orifice of at least one oxidant lance is arranged above at least one fuel lance.
• each oxidant and fuel lance is at least 5 cm.
• the oxidant being supplied via at least one, but preferably all, lances for oxidant has, according to the invention, an oxygen content of at least 85 percentages by weight, preferably at least 95 percentages by weight.
• the fuel may be any suitable, conventional, gaseous, liquid or solid fuel, such as oil or natural gas. It is preferred that the fuel is a gaseous or liquid fuel.
• At least one of the lances 211, 212 for oxidant is arranged with their orifice arranged above the orifice of at least one fuel lance 210, and is directed so that the oxidant flows obliquely downwards and along the longitudinal direction of the V-shaped space 203, essentially parallel to said first and second furnace walls.
• the oxidant is supplied to the V-shaped space 203 between the ingots 201, so that the downwards inclined stream of oxidant runs in the longitudinal direction 250 of the furnace 200.
• the stream of oxidant from each of the oxidant lances 211, 212 is arranged to cut through an area in the space 203 in which the fuel is supplied using the fuel lance 210.
• at least one stream of oxidant and at least one stream of fuel meet in the space 203.
• the oxidant Since the oxidant has such high oxygen content, the amount of hot combustion gases originating from the fuel and the oxidant being supplied through lances 210, 211, 212 will be substantially smaller than the corresponding amount of combustion gases originating from the air burner 103 for the corresponding heating powers. As described above, operation with such oxidant conventionally gives rise to deteriorated temperature homogeneity. Notably, it has proven difficult to achieve sufficiently high temperatures towards the bottom of the V-shaped space 203 between the ingots 201, i.e.
• the oxidant flows out from lances 211, 212, and meets the fuel flowing out from the fuel lance 210 in the V-shaped space 203 between the ingots 201. Since the oxidant is supplied this way, through a separate lance, the geometrical shape and the velocity of the oxidant stream may be controlled so that it may carry with it the resulting mixture of fuel and oxidant down towards the bottom of the V-shaped space 203. Thereby, the temperature there can be increased without any increased risk of overheating, which had been the case if for example an air burner had been positioned closer to the bottom or if a separate oxidant lance had been posi- tioned so that it opened out directly in close vicinity to the ingots 201.
• the fuel lance 210 may be arranged horizontally and so that the fuel stream is directed essentially straight along the main longitudinal direction of the V-shaped space. However, it is preferred that the fuel lance is somewhat inclined downwards as compared to the horizontal plane, at an angle of maximally 5°.
• the respective oxidant streams from lances 211, 212 are in this case directed with the same or a larger angle of inclination as compared to the horizontal plane.
• the downwards inclined oxidant stream can carry the combustion mixture with it downwards towards the bottom of the V- shaped space.
• At least one oxidant lance 211, 212 opens out above all supply locations for fuel, in the present example thus the fuel lance 210, which are arranged in the same furnace wall in which the orifice of the oxidant lance 211, 212 in question is arranged.
• the oxidant is supplied through at least one oxidant lance 211, 212, preferably the oxidant lance 212 the orifice of which is arranged at the top position in each respective aggregate, at high velocity. This results in increased convection in the furnace chamber, which compensates for the smaller amounts of combustion gases as compared to if one or several air burners had been used instead of the oxyfuel burner which is embodied by the lance aggregate 210, 211, 212.
• the lancing velocity is at least 100 m/s, which in many applications results in sufficient convection in the furnace chamber. Furnace atmosphere gases are sucked into the combustion mixture, which lowers the combus- tion temperature and thereby leads to less formed NO x . Then, in combination with the above described, downwards inclined oxidant stream, the whole furnace chamber, including the bottom of the V-shaped space 203, will be sufficiently warm without any risk for local overheating.
• oxidant is lanced through at least one oxidant lance 211, 121 at a velocity which is at least the sonic velocity. This results in heavily increased convection and recirculation throughout the whole furnace chamber, with corresponding improved temperature homogeneity and decreased CO and NO x rates. Such a method is especially preferred in larger furnaces.
• oxidant through at least one oxidant lance 211, 212 at a velocity of at least Mach 1.5.
• Such high lancing velocity has been found to result in convection which increases as a function of the velocity in a non-linear manner.
• combustion of flame- less type can be achieved, in which the combustion can take place in the majority of the furnace chamber simultaneously, with no clearly distinguishable flame. Therefore, this results in very good temperature homogeneity even in difficult to access parts of the furnace chamber.
• At least one oxidant lance 211, 212 is mounted so that the respective oxidant streams out into the furnace chamber at an angle of more than 0° and but more than 20°, most prefer between 3 and 5°, as compared to the horizontal plane.
• at least one oxidant lance 211, 212 is inclined from a horizontal position in the direction denoted by the arrow 251. This results, in a pit furnace 200 of normal size, in that the mixture of oxidant and fuel is conveyed sufficiently far towards the bottom of the V-shaped space 203 so that a desired temperature homogeneity can be achieved.
• more than one oxidant lance 211, 212, arranged with their respective orifices one above the other, is used as is illustrated in figures 4—7.
• the downwards inclined angle, in comparison to the horizontal plane, with which the resulting oxidant stream is directed is equal to or larger for oxidant lances 212 having respective orifices arranged further up than for oxidant lances 211 having respective orifices arranged further down.
• a lower oxidant lance 211 has an angle of more than 0° and not more than 10°
• an upper oxidant lance 212 has an angle of more than 0° and not more than 20°, however at least the same angle as the upper oxidant lance 212.
• a first group or aggregate of lances comprising a fuel lance 210 and two oxidant lances 211, 212, arranged in one of the short sides of the furnace 200
• a second lance aggregate comprising a fuel lance 220 and two oxidant lances 221, 222, is arranged in the other, opposite short side of the furnace 200.
• Both lance aggregates hence comprise a respective fuel lance 210, 220 above the orifice of which the orifices of two respective oxidant lances 211, 212, 221, 222 are arranged.
• Each such aggregate may be designed having other configurations of lances for fuel and oxidant, as long as at least one downwards inclined oxidant lance for oxidant with more than 85 percentages by weight oxygen has its orifice arranged above the level for at least one fuel lance in each aggregate .
• the two lance aggregates are arranged at different heights in the furnace 200. By such an arrangement, the temperature homogeneity can be further increased because of circulation effects arising in the furnace chamber.
• the fuel lance 210 having its orifice arranged at the lowest height in the first aggregate of lances 210, 211, 212 is arranged with its orifice at a height above the furnace floor which is between 0.7 and 1.2 meters above the level above the furnace floor at which the orifice of the lance 220, the orifice of which is arranged at the lowest height in a second aggregate of lances 220, 221, 222, is arranged.
• all such aggregates of fuel and oxidant lances 210, 211, 212, 220, 221, 222 the orifices of which are arranged so that the respective lance opens out into the V- shaped space 203 are arranged so that no lance orifice is arranged at a vertical level from the furnace floor so high so that overheating of the ingots 201 is risked as a direct consequence of the thermal energy being supplied locally as a result of the fuel or oxidant which is supplied through such a lance.
• What this vertical level is will depend upon the design of the furnace 200 as well as upon the positioning and shape of the ingots 201, but it is preferred that no such lance has its orifice arranged at a level below 1.5 meters above the floor.
• FIGS 8-10 illustrate an alternative embodiment, wherein a pit furnace 300, in a way which is similar to the above de- scribed in connection to figures 4-7, comprises ingots 301 supported by an oxide scale bed 302 and heated by two opposite aggregates of lances 310, 320 for fuel in combination with lances 311, 312, 321, 322 for oxidant.
• the arrow 350 denotes the longitudinal direction of the furnace 300.
• 306 is an exhaust channel for flue gases.
• the lances 311, 312 for oxidant are not, however, only inclined in relation to the horizontal plane in the direction of rotation pointed out by the arrow 351, similarly to the lances 211, 212 in figures 4-7, but lances 311, 312 are also inclined in the horizontal plane, in relation to a longitudinally arranged vertical plane and in a direction of rotation pointed out by the arrow 352.
• the resulting mixture of oxidant and fuel in the V-shaped space 303 (see figure 9) between ingots 301 can be spread more evenly than what is possible only by arranging the lances 311, 312 at an angle in relation to the horizontal plane according to the above.
• the lance angles for each individual lance for oxidant is adjusted depending on the actual application, so that the resulting temperature distribution in the V-shaped space 303 becomes as homogenous as possible. It is especially preferred that at least two lances 311, 312 for oxidant are mounted with their orifices arranged in the furnace chamber one above the other and so that their respective oxidant can stream out into the furnace chamber at different angels either in the horizontal plane and/or in the vertical plane. This results in even spread of the fuel/oxidant mixture but while still retaining the possibility to keep a low risk for local overheating because of the supplied oxidant. It is preferred that the angle in the horizontal plane, in the direction of rotation 352, between the oxidant stream from each individual oxidant lance and the main longitudinal direction of the V-shaped space 303, is 10° or less in any direction .
• At least one lance for oxi- dant 311, 312, 321, 322, preferably all such lances, are redirectable, so that it is possible to redirect their respective stream of oxidant in the horizontal plane and/or in the vertical plane. This will render the furnace 300 adjustable depending on changing operation prerequisites with for example different numbers of and/or differently sized ingots 301 to be heated.
• more than one lance for oxidant is used in the furnace, preferably in combination with one and the same lance for fuel, whereby the heating power in the furnace is controlled during operation by one or several lances being switched on or off, while the amount of supplied fuel is controlled so that it at each moment in time or at least over time stoichiometrically corresponds to the total oxygen supplied via the oxidant.
• an oxidant lance may be operated in a pulsating manner, where the switched on and switched off time periods are controlled so that the mean emitted power becomes the desired.
• one or several oxidant lances may be completely switched off.
• the total heating power is maximal.
• one or several oxidant lances may either be operated in a pulsating manner or alternatively be switched off.
• This decrease of the total heating power may be carried out in one or several steps, by altering the number of switched on oxidant lances and/or by altering the time periods for one or several oxidant lances being operated in a pulsating manner.
• the total heating power can be successively decreased in the same manner, at the same time as the operating temperature is maintained in the furnace and until the ingots have reached a desired final temperature. Then, the total heating power can be further decreased, still in the same manner as described above, so that temperature equilibrium prevails during a holding time with constant ingot temperature .
• At least one oxidant lance is operated with full power at each time.
• at least one oxidant lance being the oxidant lance having its orifice arranged furthest up in the furnace of the lances in an aggregate comprising at least a fuel lance and at least one oxidant lance, is oper- ated at full power. It is especially preferred that this at least one oxidant lance is operated with the above described high lancing velocities. This way, it is possible to control the total heating power over a broad power interval and at all times ensure satisfactory convection and therewith temperature homogeneity in the whole furnace chamber, including the V-shaped space between the ingots.
• This single oxidant lance is in this case preferably an oxidant lance which is the oxidant lance with its orifice arranged at the lowest height in an aggregate comprising at least one fuel lance and at least one oxidant lance, where the single lance has its orifice arranged above at least one fuel lance through which fuel is supplied.
• oxidant is supplied through different lances for oxidant, or through different constellations of lances for oxidant, in an alternating man- ner.
• one and the same total heating power can be maintained but using alternating oxidant lances.
• This leads to temperature homogenization over time, and decreases the risk of local overheating in so called "hot spots".
• the thermal homogeneity in the furnace 200 by arranging at least one lance 230 for an oxidant with an oxygen content of at least 85 percentages by weight in an furnace wall so that the orifice of the lance is arranged inside the furnace 200 and so that oxidant can be supplied directly to the space 205 having a triangular cross-section (see figure 6) which is present under at least one ingot 201 which in turn is leaning against an inner wall of the pit furnace 200, between the ingot 201 and the wall.
• the oxidant can be supplied directly to the space 205 is to be interpreted so that the stream of oxidant originating from the lance 230 streams into the space 205 without striking against any obstacles on its way.
• the lance 230 opens out in the space 205 itself, but it may also open out some ways outside and shoot the oxidant stream into the space 205.
• this space 205 of triangular cross-section will in general constitute an elongated, substantially cylinder-shaped body having triangular cross- section and being partly separated from the heated part of the furnace 200.
• oxyfuel used to heat the furnace 200
• the height of the bed 202 of oxide scale varies during operation, and also across time during several operating cycles.
• oxidant lances 230, 240 the orifices of which are ar- ranged opening out directly into the space 205 risk ending up below the level for the bed 202 when sufficient volumes of oxide scale are on the furnace floor, it is preferred to arrange all lances opening out into the space 205 under the ingots 201 at such height so that it is possible to surveil the oxide scale level and empty the furnace floor from oxide scale before it reaches the level for the orifices of installed lances.
• the oxidant lances 230, 240 are arranged with their orifices arranged at a height above the furnace floor which is above the maximum level for an oxide scale bed appearing in the furnace during operation. More specifically, it is preferred that they are arranged to at a height above the furnace floor of 0.5-1.0 meters.
• the oxidant supplied from the lance 230 similarly to that supplied from lances 211, 212, is supplied at elevated velocities, preferably at least 100 m/s, more preferably at least sonic velocity, most pref- erably at least Mach 1.5.
• elevated lancing velocities preferably at least 100 m/s, more preferably at least sonic velocity, most pref- erably at least Mach 1.5.
• the lance 230 can be positioned with its orifice arranged further up along the inner wall of the furnace 200 without the risk of it as a consequence giving rise to local overheating of ingots 201 at low oxide scale bed 202 depths.
• the lanced high velocity oxidant stream will suck hot furnace gases into the space 205 from surrounding parts of the furnace 200, which additionally increases the thermal homogeneity in the furnace 200 by distributing thermal energy to the space 205.
• the present inventors have surprisingly discovered that the formation of oxide scale during operation tends to consume large amounts of oxygen. It has been noted that this in some cases can lead to a lack of oxygen in the combustion reaction, whereby the concentration of CO in the furnace atmosphere very rapidly can be sharply increased.
• This CO is then oxidized in the space 205 by aid of additionally supplied oxidant with at least 85 percentages by weight oxygen, supplied through the oxidant lance 230 to the space 205.
• oxidant with at least 85 percentages by weight oxygen
• the oxidant supplied through the lance 230 is caused to react mainly with the CO formed during in- complete combustion of fuel in the furnace 200, using oxidant supplied to a part of the furnace which is not constituted by the space under the ingot.
• the combustion of the fuel takes place in two stages in the furnace 200, namely in a first stage during which CO is formed and a subsequent stage during which complete combustion to C0 2 takes place.
• FIG 8-10 An alternative embodiment is shown in figure 8-10, wherein a separate lance 331 for fuel supplies additional fuel, besides the fuel being supplied through lances 310, 320 to the V- shaped space 203 and to the rest of the furnace chamber, to the space 305 (see figure 9) , with which fuel the oxidant supplied through the lace 330 is caused to react.
• a separate lance 331 for fuel supplies additional fuel, besides the fuel being supplied through lances 310, 320 to the V- shaped space 203 and to the rest of the furnace chamber, to the space 305 (see figure 9) , with which fuel the oxidant supplied through the lace 330 is caused to react.
• no adjustment down of the amount of oxidant supplied to the rest of the furnace chamber is required to obtain under stoichiometric combustion.
• more than one lance for oxidant is arranged in the space 205, 305.
• a corresponding lance 230 is also arranged in the opposite short end of the furnace 200, in addition to the lance 230, so that it opens out into the space 205 under the ingots 201 which are leaning against the opposite long side of the furnace.
• the circulating flow motion will, starting out from lance 240, run in the direction 250 to the opposite short end, perpendicularly away from the orifice of the lance 230, thereafter back to the first short side and finally perpendicularly back to the orifice of the lance 240.
• Such an arrangement will result in good temperature homogeneity throughout the whole space 205 under all ingots arranged in the furnace 200.
• a corresponding arrangement comprising oxidant lances 330 and 340, respectively.
• the preferred but not required design with one respective fuel lance 331, 341 used in combination with each oxidant lance 330, 340 is also shown.
• alternating operation with several different oxidant lances for increasing temperature homogeneity is also valid for operation of lances 230, 240, 330, 340.
• alternating operation comprising both oxidant lances 230, 240, 330, 340 opening out into the space 205, 305 as well as oxidant lances 211, 212, 221, 222, 311, 312, 321, 322 opening out into the space 203, 303.
• the temperature homogeneity can be maximized over time, and local overheating can be avoided, in a way which easily can be adapted to current operating condi- tions.
• the temperature inside the furnace is measured using temperature sensors (not shown) , which are conventional as such, at different loca- tions where local overheating can be feared, and the alternating operation is controlled so that the heating power is decreased in places where the measured temperature is so high that overheating is risked, i.e. higher than a certain prede- termined value which is dependent upon the heated material.
• the control can for example take place by continuous control of the supply of oxidant through one or several oxidant lances or by operating one or several oxidant lances in a pulsating manner, with suitable relations between switched on time and switched off time. This results on the one hand in that the amount of CO in the flue gases can be controlled to desired low levels, on the other hand in that any afterburning in the space 205, 305 can be optimized.
• an oxyfuel combustion according to the present invention can be used as a complement to one or several existing air burners in a pit furnace, to increase the maximum capacity for the pit furnace or to decrease the power of the air burner with maintained capacity but smaller negative environmental impact.
• the lances for oxidant and fuel illustrated in figures 4-10 and described above can be arranged in other constellations. More oxidant lances can for instance be arranged so as to heat especially difficult to get at spaces and/or to create additional turbulence inside the furnace, depending on the actual operating conditions.
• the lances opening out into the V-shaped space do not need to be centrally arranged in said space, but can for example be arranged with their respective orifices somewhat displaced in the horizontal plane. In this case, it is preferred that the resulting downwards inclined oxidant stream cuts through an area to which fuel is supplied in the V-shaped space.
• more fuel lances may be used in each aggregate or group, alternatively in other places in the furnace so that fuel is supplied to a location being cut through by one or several high velocity streams of oxidant.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Crystallography & Structural Chemistry (AREA)
• Thermal Sciences (AREA)
• Physics & Mathematics (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Vertical, Hearth, Or Arc Furnaces (AREA)
• Furnace Details (AREA)
• Manufacture And Refinement Of Metals (AREA)
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