KR20130075736A - Method for increasing the temperature homogeneity in a pit furnace - Google Patents

Abstract

Two or more ingots 201; 301 to be heated cause an inclination with respect to each of the opposing first and second inner walls of the pit furnace 200; 300 so that the ingots 201; When viewed along the second inner walls, a method of increasing temperature uniformity in a pit furnace (200; 300) is formed, forming an elongated space (203; 303) having a V-shaped cross section therebetween. The present invention provides one or more separate lances 211, 212, 221, 222; 311, 312, 321, 322 for oxidants having an oxygen content of at least 85% by weight and one or more separate lances 210, 220 for fuels. 310, 320 are arranged in the furnace wall with their orifices arranged to open into the furnace 200; 300 at a distance from each other, and the oxidant and the fuel, respectively, form the V-shaped space 203; Can be supplied and combustible in this space, and the orifices of the oxidant lances 211, 212, 221, 222; 311, 312, 321, 322 are the fuel lances 210, 220; 310, 320 The oxidant is directed to flow obliquely downward and along the longitudinal direction of the V-shaped spaces 203; 303.

Description

How to increase temperature uniformity in a pit furnace {METHOD FOR INCREASING THE TEMPERATURE HOMOGENEITY IN A PIT FURNACE}

The present invention relates to a method of increasing temperature uniformity in a pit furnace.

While heating the ingots in pit furnaces, the ingots are typically inclined with respect to the opposing inner wall of the pit furnace and placed in a furnace floor on an oxide scale layer from previous runs. do.

In such furnaces, it is desirable to obtain good temperature uniformity, in other words, to minimize temperature gradients inside the furnace. However, there are problems with commonly used furnace geometry in which the ingots are positioned at an angle to the inner walls of the furnace.

In the prior art, air burners are used to heat these pit furnaces. These air burners turn over with very large volumes of air and fuel, causing large volumes of hot combustion gases circulating in the furnace. For example, by arranging the air burners on one of the short sides of the furnace and the exhaust port on the same but short side below or above the burner, a lengthwise circulation along the entire furnace can be achieved, whereby This allows gas volumes from the air burner to produce sufficient temperature uniformity in the furnace.

However, oxyfuel combustion is more often used to reduce the amount of CO and Ox formation, and to increase energy efficiency, eg where high oxygen content oxidants are used to burn fuel. It is used. Because these oxidants contain significantly less ballast in the form of nitrogen than when air is used as the oxidant, fewer volumes of combustion gases occur in less than one fifth of the corresponding air burners in many cases. Therefore, it is more difficult to obtain sufficient temperature uniformity accordingly.

In particular, it is common that the lower portions of the ingots become too cold and the upper portions of the ingots are subject to overheating.

Due to the concern of local overheating close to the combustion location, there are limited possibilities for directing the combustion direction to cooler parts of the furnace. In general, it is also impossible to compensate for smaller amounts of combustion gases by increasing the power of oxyfuel burners. It is possible to arrange multiple oxygen fuel burners in one and the same furnace, but this is very expensive. In addition, because in other cases it is desired to heat different numbers of ingots in the same furnace, the result will still be inadequate.

The present invention solves the above problems.

Accordingly, the present invention provides a method of increasing temperature uniformity in a pit furnace, in which two or more ingots to be heated cause an inclination of each one of the opposing first and second inner walls of the pit furnace, whereby When viewed along the first and second inner walls, a method of increasing temperature uniformity in a pit furnace is formed, forming an elongated space having a V-shaped cross section therebetween. The present invention is directed to a furnace wall with one or more separate lances for oxidants having an oxygen content of at least 85% by weight and one or more separate lances for fuel being arranged to open into the furnace at a distance from each other. The arrangement allows each of the oxidant and fuel to be supplied to the V-shaped space and combustible within the space, and the orifice of the oxidant lance is arranged above the orifice of the fuel lance and the oxidant is It is characterized in that it is directed to flow obliquely along the longitudinal direction of the shape space and downward.

The invention will now be described in detail with reference to exemplary embodiments of the invention and the accompanying drawings.
1 is a partially cut perspective view showing a pit furnace of the prior art.
FIG. 2 is a view of the pit furnace of FIG. 1 viewed from the long side. FIG.
3 is a view of the pit furnace of FIG. 1 from above.
4 is a partially cut perspective view showing a pit furnace according to a first preferred embodiment of the present invention.
FIG. 5 is a view of the pit furnace of FIG. 4 seen from the long side. FIG.
FIG. 6 is a view of the pit furnace of FIG. 4 seen from the short side. FIG.
FIG. 7 is a view of the pit furnace of FIG. 4 from above. FIG.
Fig. 8 is a view corresponding to that of Fig. 5, but seen from the long side of the pit furnace according to the second preferred embodiment of the present invention.
FIG. 9 is a view of the pit furnace of FIG. 8 seen from the short side. FIG.
FIG. 10 is a view of the pit furnace of FIG. 8 seen from above. FIG.

1-3 illustrate a pit furnace 100 of the prior art, in which ten ingots 101 are heated in two rows of five ingots, using a set of common reference numerals. The ingots lie on an oxide scale bed 102 from previous runs, and opposing inner walls of the distinct long sides of the furnace 100 along the longitudinal direction 104 of the furnace 100. Erected inclined over two rows with respect to

The furnace 100 is heated using a prior art air burner 103 directed along the longitudinal direction 104 of the furnace 100. The air burner 103 is arranged on a wall at one end of one of the short ends of the furnace 100. Since the furnace is partially cut away in FIGS. 1-3, the short end is not shown with either the ceiling of the furnace 100 and one of the long sides of the furnace. The hot combustion gases from the air burner 103 flow along the rows of the ingots 101 in the direction 104, are passed to the distal short end 105 of the furnace and then the air burner 103 is again It flows back to the short end that is arranged and is emptied through the exhaust channel 106 for flue gases. The air burners 103 and exhaust channels 106 are arranged on the same wall in the furnace 100 with different heights, and natural convection occurs to ensure sufficient temperature uniformity over the entire furnace chamber.

4 to 7 show the pit furnace 200 to which the method according to the invention for increasing temperature uniformity is applied using common reference numerals. The furnace 200 is very similar to the pit furnace 100 shown in FIGS. In the furnace 200, two or more plurality of ingots 201 are arranged. The ingots 201 are arranged along two rows along the main longitudinal direction 250 of the furnace 200, each inclined with respect to the separate first and second opposing inner walls of the pit furnace 200. Ingots 201 form a space 203 having a V-shaped cross section (see FIG. 6) between the ingots and above the ingots along the first and second inner walls. The inner walls preferably constitute the inner walls of the long sides of the furnace 200. 4-7, one of the walls is not shown.

Ingots 201 lie in an oxide scale layer 202 similar to layer 102. Alternatively, the ingots 201 may be placed directly on the furnace.

An exhaust channel 206 for flue gases is disposed on one of the short sides of the furnace 200.

One or more separate lances 211, 212 for oxidant and one or more separate lances 210 for fuel are arranged in the furnace 200 with their orifices spaced from each other and into the furnace. It is preferably arranged on the furnace wall so that it is open and so that each of the oxidant and fuel can be supplied to and react in the V-shaped space 203 between the ingots 201.

The lower fuel lance 210 and the two oxidant lances 211, 212 disposed over the orifice of the fuel lance 210 together form a lance aggregate or group. As long as the orifices of one or more oxidant lances are arranged over one or more fuel lances, this assembly may also be designed with other configurations of lances for fuel and oxidant.

Preferably, the distance between each oxidant lance and the fuel lance is at least 5 cm.

The oxidant supplied through the lances for at least one, but preferably the whole, oxidant has, according to the invention, an oxygen content of at least 85% by weight, preferably at least 95% by weight. The fuel may be any suitable conventional gas, liquid or solid fuel such as oil or natural gas. The fuel is preferably a gas or liquid fuel.

One or more of the oxidant lances 211, 212, preferably all of the oxidant lances 211, 212 are arranged with their orifices arranged over the orifices of the one or more fuel lances 210, and the oxidant is It is preferred to be directed to flow along the longitudinal direction of the V-shaped space 203 essentially parallel to the first and second furnace walls and downwardly. In other words, the oxidant is supplied to the V-shaped space 203 between the ingots 201 such that a downwardly inclined stream of oxidant flows in the longitudinal direction 250 of the furnace 200. In addition, the stream of oxidant from each of the oxidant lances 211, 212 is preferably arranged to cut through the region of the space 203 to which fuel is supplied using the fuel lance 210. Preferably, at least one stream of oxidant and at least one stream of fuel meet in space 203.

Since the oxidant has such a high oxygen content, the amount of hot combustion gases originating from the oxidant and the fuel supplied through the lances 210, 211 and 212 is dependent on the air burner 103 for the corresponding heating powers. Will be substantially less than the corresponding amount of combustion gases originating from. As mentioned above, operation with such oxidants usually results in deteriorated temperature uniformity. Notably, notably, the bottom of the V-shaped space 203 between the ingots 201, ie near the oxide scale layer 202 at the bottom of the furnace 200, as well as each ingot 201 or Between the row of ingots and the furnace wall in which the ingots or ingots 201 are inclined, it is proved that it is difficult to obtain a sufficiently high temperature towards the space 205 (see FIG. 6) with the triangular cross section existing under the ingots 201. have.

Accordingly, the oxidant encounters the fuel flowing out of the lances 211 and 212 and flowing out of the fuel lance 210 of the V-shaped space 203 between the ingots 201. Since the oxidant is fed in this way through a separate lance, the geometry and velocity of the oxidant stream together with the final mixture of fuel and oxidant down towards the bottom of the V-shaped space 203 It can be controlled to be transportable. Thereby, if an oxidant lance had been positioned to open directly near the vicinity of the ingots 201 or if the air burner had been located closer to the bottom, in that case the temperature there would be any increase in overheating fear. Can be increased without.

The fuel lances 210 may be arranged horizontally, and may be arranged such that the fuel stream is directed essentially straight along the main longitudinal direction of the V-shaped space. However, the fuel lance is slightly inclined downward relative to the horizontal plane at an angle of up to 5 °. In this case, separate oxidant streams from the lances 211 and 212 are directed at the same or larger tilt angle relative to the horizontal plane. Thereby, the downwardly inclined oxidant stream can carry the combustion mixture therewith downwards towards the bottom of the V-shaped space.

According to a preferred embodiment, one or more oxidant lances 211, 212 are arranged in all supply positions for the fuel, in this embodiment the same furnace wall whereby the orifices of the oxidant lances 212, 212 are arranged accordingly. Fuel lance 210, open from above. This ensures that all fuel supplied through all of the lances 210, 211, and 212 assemblies is transported downward into the V-shaped space 203 using the oxidant stream from the lance.

According to a particularly preferred embodiment, the oxidant is fed at high speed to one or more oxidant lances 211, 212, preferably to an orifice of oxidant lance 212 arranged at an upper position of each separate aggregate. This causes an increase in convection of the furnace chamber that compensates for smaller amounts of combustion gases than when one or several air burners were used instead of the oxyfuel burners specified by the lance assemblies 210, 211, 212.

Preferably, the lancing speed is at least 100 m / s, which leads to sufficient convection of the furnace chamber in many applications. Furnace atmosphere gases are sucked into the combustion mixture, which lowers the combustion temperature, leading to less NOx formation. Then, in combination with the downwardly inclined oxide stream described above, the entire furnace chamber including the bottom of the V-shaped space 203 will be heated sufficiently without any concern for local overheating.

According to a particularly preferred embodiment, the oxidant is lanced through one or more oxidant lances 211, 212 at a rate of at least sonic velocity. This results in a very large increase in convection and recirculation over the entire furnace chamber, correspondingly improving temperature uniformity and reducing CO and NOx rates. This method is particularly desirable in large furnaces.

Most preferably, the oxidant is supplied through one or more oxidant lances 211, 212 at a rate of at least Mach 1.5. It has been found that such high lancing rates cause increasing convection as a function of the speed of the nonlinear manner. If it exceeds about Mach 1.5, a flame-less type of combustion can be achieved, which can occur simultaneously in most of the furnace chamber without a clearly distinguishable flame. Thus, this results in very good temperature uniformity even though it is difficult to access parts of the furnace chamber.

One or more oxidant lances 211, 212, more preferably each oxidant lance, into the furnace chamber at an angle of greater than 0 ° and no more than 20 °, most preferably 3 to 5 ° when the separate oxidant is compared with the horizontal plane. It is preferable to be mounted to flow in. As a result, one or more oxidant lances 211 and 212 are inclined from the horizontal position in the direction indicated by arrow 251. This allows the pit furnace 200 of normal size to be conveyed far enough towards the bottom of the V-shaped space 203 so that the desired temperature uniformity is obtained.

According to a particularly preferred embodiment, more than one oxidant lances 211, 212, in which each orifice of the oxidant lance is arranged one above the other, are illustrated as illustrated in FIGS. 4 to 7. Used. In this case, the angle inclined downward relative to the horizontal plane to which the final oxidant stream is directed has separate orifices arranged higher than for oxidant lances 211 having respective orifices arranged further below. The same or larger for the oxidant lances 212. In the exemplary case herein with two oxidant lances 211, 212, the lower oxidant lance 211 has an angle of greater than 0 ° and less than 10 °, while the upper oxidant lance 212 is greater than 0 ° and less than 20 °. Preferably at least the same angle as the upper oxidant lance 212. By arranging several oxidant lances up and down in this manner, the overall flow of fuel and oxidant can be controlled so that a good spread of fuel and oxidant can be achieved in space 205.

In the exemplary embodiment illustrated in FIGS. 4-7, a first group or collection of lances comprising a fuel lance 210 and two oxidant lances 211, 212 is one of the short sides of the furnace 200. And a second lance assembly comprising a fuel lance 220 and two oxidant lances 221, 222 is arranged on the other opposite short side of the furnace 200. Thus, both of the lance assemblies include respective fuel lances 210, 220 over the orifices in which the orifices of two separate oxidant lances 211, 212, 221, 222 are arranged. Each so as to have different configurations of fuel and oxidant lances, as long as the one or more downwardly inclined oxidant lances for the oxidant having more than 85% by weight oxygen have its orifices arranged above the level for one or more fuel lances of each aggregate. This collection of can be designed.

As is apparent from FIGS. 5 and 6, the two lance aggregates are arranged at different heights in the furnace 200. With this arrangement, the uniformity of temperature can be further increased due to the circulation effects occurring in the furnace chamber. In this case, the fuel lance 210 having its orifice arranged at the lowest height in the first assembly of lances 210, 211, 212 is at the lowest height in the second assembly of lances 220, 221, 222. It is preferred that the orifices of the arranged lances 220 are arranged to have their orifices at a height above the roadbed that is above 0.7-1.2 meters above the arranged roadbed level. All such assemblies of fuel and oxidant lances 210, 211, 212, 220, 221, 222 with their orifices arranged so that a separate lance opens into the V-shaped space 203, the overheat of the ingots 201 is fueled. Or it is more preferably arranged such that the lance orifice is not arranged from the hearth to a vertical level so high that there is a fear that the direct impact of thermal energy is locally supplied as a result of the oxidant being supplied through this lance. This vertical level will depend on the design of the furnace 200 as well as the location and shape of the ingots 201, but this lance preferably does not have its orifices disposed at a level of less than 1.5 meters above the floor.

8-10, which correspond to the views of FIGS. 5-7, in a manner similar to that described above in connection with FIGS. 4-7, the pit furnace 300 is provided with oxidant lances 311, 312. , An example of an alternative embodiment comprising ingots 301 heated by two opposing aggregates of fuel lances 310, 320 in combination with 321, 322 and supported by an oxide scale layer 302. do. Arrow 350 indicates the longitudinal direction of the furnace 300. Reference numeral 306 denotes an exhaust channel for the flue gases.

However, as can be seen most clearly in FIGS. 9 and 10, the oxidant lances 311, 312 are rotated in the direction of rotation indicated by arrow 351, similar to the lances 211, 212 of FIGS. 4-7. Not only inclined with respect to the horizontal plane of the lances 311 and 312 are also inclined with respect to the horizontal plane, in the longitudinally arranged vertical plane, and also in the direction of rotation indicated by the arrow 352. As a result, the final mixture of oxidant and fuel in the V-shaped space 303 (see FIG. 9) between the ingots 301 is only angled to the lances 311, 312 relative to the horizontal plane as mentioned above. Only by arranging can spread more evenly than is possible.

Since it is desirable to adjust the lance angles for each separate lance for the oxidant according to the practical application, the final temperature distribution in the V-shaped space 303 will be as uniform as possible. Two or more lances 311 and 312 for the oxidant are arranged up and down in the furnace chamber such that their separate oxidants can flow into the furnace chamber at different angles in either the horizontal plane and / or the vertical plane. It is particularly preferred to be mounted to these orifices. This leads to a uniform diffusion of the fuel / oxidant mixture, but still holds the possibility of keeping a low risk of local overheating due to the supplied oxidant. The angle of the horizontal plane of the direction of rotation 352 between the major longitudinal direction of the V-shaped space 303 and the oxidant stream from each individual oxidant lance is no more than 10 ° in either direction.

One or more lances 311, 312, 321, 322 for the oxidant, preferably all of these lances, can be redirected so that a separate stream of lances of oxidant to the horizontal and / or vertical surfaces can be redirected. It is especially preferable. This will allow the furnace 300 to be adjustable, for example, by varying the operating prerequisites of the different numbers and / or different sizes of ingots 301 to be heated.

According to a preferred embodiment, more than one lance for the oxidant is used in the furnace, preferably in combination with one and the same lance for the fuel, whereby the heating power in the furnace is switched on or off. Can be controlled during operation by one or several lances, while the amount of fuel supplied is stoichiometrically to the total oxygen supplied through the oxidant, at each instant in time or at least over the entire time. Control to correspond. In order to reduce the total heating power in the furnace from a predetermined high power level to a predetermined low power level, the oxidant lance is a pulsation scheme in which the switch on and switch off time periods are controlled so that mean emitted power is desired. can be operated in a pulsating manner. In addition or alternatively, one or several oxidant lances may be completely switched off.

In this context, it is preferred to disclose a heating method in which all oxidant lances are switched on so that the total heating power is maximized. If the furnace reaches a predetermined predetermined operating temperature, one or several oxidant lances can be operated either pulsatingly or alternately switched off. This reduction in overall heating power can be performed by changing the number of oxidant lances switched on and / or by changing the time periods for one or several oxidant lances that are operated in a pulsating manner.

In the following, the total heating power can be continuously reduced in the same manner while the operating temperature is maintained in the furnace and until the ingots reach the desired final temperature. The total heating power can then be further reduced in the same manner as described above, so that temperature equilibrium is effective at constant ingot temperature during the holding time.

During this entire procedure, it is preferred that at least one oxidant lance be operated at full power at each time. In addition, at least one oxidant lance, which is an oxidant lance having its orifice arranged farthest in the furnace of the lances of the assembly comprising at least one fuel lance and at least one oxidant lance, is preferably operated at full power. It is particularly preferred that such one or more oxidant lances are operated by the high lancing rates described above. This controls the overall heating power over a broad power interval and ensures satisfactory convection and at the same time temperature uniformity in the entire furnace chamber including the V-shaped space between the ingots. can do.

If it is desired that the total heating power be lower than that obtained when only one oxidant lance is operated at full power, it is preferable that only one oxidant lance be operated in a pulsating manner. One such oxidant lance is, in this case, an oxidant lance having one or more fuel lances and their orifices arranged at the lowest height in an assembly comprising one or more oxidant lances, wherein a single lance is one or more fueled Preference is given to oxidant lances having their orifices arranged above the fuel lances.

In order to further increase the thermal uniformity during the execution of the process according to the invention, the oxidant is further fed in an alternating manner through different lances for the oxidant or through different constellations for the oxidant. desirable. Thus, oxidant lances are used alternately but one and the same total heating power can be maintained. This causes temperature uniformity over time and reduces the risk of local overheating at the so-called "hot spots".

By installing one or several oxidant lances and one or several fuel lances operated according to the above, it is possible to operate using oxyfuel combustion in place of conventional pit furnaces operated by conventional air burners. Particular preference is given to switching. By this conversion following this operation, the existing pit can be converted cost-effectively into a more environmentally friendly oxyfuel operation, without resulting in problems with poor thermal uniformity in the furnace.

Referring back to the pit furnace 200 illustrated in FIGS. 4-7, the orifice of the lance is arranged inside the furnace 200 and below the one or more ingots 201, thus ingot 201 and the wall. At least one lance for an oxidant having an oxygen content of at least 85% by weight so that the oxidant can be supplied directly to the space 205 having a triangular cross section inclined relative to the inner wall of the pit furnace 200 (see FIG. 6). It is further desirable to increase thermal uniformity in the furnace 200 by arranging 230 on the furnace wall. The fact that an oxidant can be supplied directly to the space 205 is interpreted to mean that a stream of oxidant originating from the lance 230 will flow into the space 205 without hitting any obstacles on its path. Desirably, lance 230 may open into space 205 by itself, but also open outward in other ways to shoot oxidant stream into space 205.

If several ingots 201 are arranged in the furnace 200 along the same furnace wall, this space 205 of triangular cross section generally has a triangular cross section and partially from the heated portion of the furnace 200. It will constitute an elongated substantially cylindrical shape. If oxyfuel is used to heat the furnace 200, it is also difficult to obtain a sufficiently elevated temperature in the space 205. This is the case when one or several ingots 201 lean along a row against the same inner wall, as shown in FIGS. 4 to 7 and when both ingots lean against both long sides facing each other. Causes problems.

The height of the oxide scale layer 202 changes during operation and over time of several running cycles. Since the oxidant lances 230, 240, whose orifices are arranged to open directly into the space 205, may end up below the level for the layer 202 when sufficient volumes of oxide scale are on the road, Allow all lances to be opened into the space 205 below the ingots 201 at such a height so that it is possible to empty the oxide scale on the roadbed and monitor the oxide scale level before reaching the level for the orifices of the installed lances. It is preferable to arrange.

It is particularly desirable for the oxidant lances 230, 240 to be arranged in their orifices which are arranged at a height above the hearth in excess of the maximum level for the oxide scale layer appearing in the furnace during operation. More specifically, it is desirable for these lances to be arranged at a height above the roadbed of 0.5 to 1.0 meters.

In addition, the oxidant supplied from the lance 230, similar to the one supplied from the lances 211 and 212, most preferably at elevated speeds, preferably at least 100 m / s, more preferably at least sound speed, Is preferably supplied at least Mach 1.5. At these elevated lancing rates, the aforementioned advantages in terms of temperature uniformity and low flame temperatures are achieved, resulting in low CO and NOx ratios. This is particularly important for avoiding local overheating in the relatively narrow space 205 below the ingots 201 and further results in local overheating of the ingots 201 at low oxide scale layer 202 depths. It is caused that the orifices, which are arranged further along the inner wall of the furnace 200, can be located in the lance 230 without the same risk thereof. In addition, the lanced fast oxide stream can suck hot furnace gases from the peripheral portions of the furnace 200 into the space 205 and further heat the furnace 200 by distributing thermal energy to the space 205. Increase uniformity.

The inventors have surprisingly found that the formation of oxide scale during operation tends to consume large amounts of oxygen. It should be noted that in some cases this tendency results in a lack of oxygen in the combustion reaction, whereby the concentration of CO in the furnace atmosphere can be increased very quickly and rapidly. According to a preferred embodiment, the space 205 is such that the orifices are under stoichiometric by down-regulating the total amount of oxidant supplied through the oxidant lances 211, 212 arranged above the space 205. This phenomenon is exploited in that the main combustion in the chamber of the main furnace comprising these parts of the furnace 200 constituted by is continuously controlled. Thus, this will lead to an increase in the level of CO in the furnace atmosphere. This CO is then oxidized in the space 205 with the aid of an additionally supplied oxidant comprising at least 85 wt% oxygen, which is then supplied to the space 205 via the oxidant lance 230. As a result of this additional oxidant, overall stoichiometric equilibrium in the furnace 200 is achieved.

In this case, therefore, no additional fuel is supplied to the space 205. Instead, the oxidant supplied through the lance 230 is reacted primarily with CO formed during incomplete combustion of the fuel in the furnace 200, using the oxidant supplied as part of the furnace not constituted by the space under the ingot. do. Thereby, combustion of the fuel occurs in two stages in the furnace 200, the first stage during which CO is formed and the second stage during which complete combustion for CO ₂ occurs.

An alternative embodiment is shown in FIGS. 8-10, in which the separating lance 331 for fuel is supplied to the V-shaped space 203 and the rest of the furnace chamber via the lances 310, 320. In addition, additional fuel is supplied to the space 305 (see FIG. 9), and the fuel and the oxidant supplied through the lance 330 react. In this case, down regulation of the amount of oxidant supplied to the rest of the furnace chamber is not required to obtain substoichiometric combustion.

According to a preferred embodiment, more than one oxidant lance is arranged in the spaces 205 and 305. Thus, in FIGS. 4-7, in addition to the lance 230, the corresponding lance 230 is also below the ingots 201 inclined to the opposite long end of the furnace 200, against the opposite long side of the furnace 200. Are arranged to open into the space 205. In this case, the two or more ingots 201 to be heated are respectively separate first and second opposing insides of the pit furnace 200 such that separate spaces 205 having a triangular cross section are each formed under separate ingots. When inclined with respect to each one of the walls, one or more separate lances 230, 240 for an oxidant having an oxygen content of at least 85 wt% are arranged in one separate furnace wall, wherein the lances are furnace 200 The orifices are arranged so as to open inwardly and the oxidant can be supplied to a separate space 205, and the lances 230, 240 are arranged to open into each of the opposing furnace walls and the streams of oxidant It is generally desirable to be directed to bring about a cyclic flow motion within 200. Thus, in FIG. 7 the circulating flow motion starts from lance 240, in a direction 250 to the opposite short end, in a direction away from the orifice of lance 230, and then back to the first short side. Finally, it will proceed in the direction of returning perpendicular to the orifice of the lance 240. Such an arrangement will result in good temperature uniformity over the entire space 205 below all ingots arranged in the furnace 200.

8-10, a corresponding arrangement is illustrated that includes oxidant lances 330, 340, respectively. In this case, a preferred but not necessary design is also shown with one separate fuel lance 331, 341 used in combination with each oxidant lance 330, 340.

What is described above with respect to alternating operation for several different oxidant lances to increase temperature uniformity is also valid for the operation of lances 230, 240, 330, 340. Thus, for example, one lance 230 may be operated first followed by another lance 240 and then again one lance 230, while the lance that is not activated at each time point may be used instead. It is also possible to operate the lances 230 and 240 in an alternating manner that is switched off. Oxidant lances 211, 212, 221, 222, 311, 312, 321, 322, which are open to spaces 203, 303, as well as oxidant lances 230, 240, 330, 340 open to spaces 205, 305. It is also possible and desirable to carry out such alternating operations including all of these. In the case of such an operating mode, temperature uniformity can be maximized over time, local overheating can be avoided, and such a scheme can be easily applied to current operating conditions.

According to a preferred embodiment, the temperature in the furnace is measured using temperature sensors (not shown) in a conventional manner in different places where local overheating may be concerned, the measured temperature being so high that there is a risk of overheating, ie The alternating operation is controlled so that the heating force is reduced at a position at a temperature above a predetermined predetermined value depending on the material to be heated.

Due to the above point in consideration of the oxygen consumption of the oxide scale forming process, the oxygen level inside the furnace during operation using, for example, one or several conventional lambda sensors, to control the CO concentration in the furnace. And oxygen supplied through the oxidant lances 230, 240, 330, 340, 205, 305, 211, 212, 221, 222, 311, 312, 321 based on these or these measurements. It is desirable to keep the oxygen concentration in the furnace essentially constant by controlling the amount of. The control occurs, for example, by continuously controlling the supply of oxidant through one or several oxidant lances or by operating one or several oxidant lances in a pulsating manner, depending on a suitable relationship between the switch on time and the switch off time. . This allows on the one hand the amount of CO in the flue gases to be controlled at the desired low levels and on the other hand any afterburning in the spaces 205 and 305 can be optimized.

In the above, preferred embodiments have been described. However, it will be apparent to those skilled in the art that many modifications can be made in the above-described embodiments without departing from the spirit of the invention.

For example, oxyfuel combustion according to the present invention can be used as a complement to one or several existing air burners in a pit furnace, thereby increasing the maximum performance for the pit furnace or reducing the air burner's power. It maintains the burner's performance but can have less negative environmental impact.

In addition, the lances for oxidant and fuel shown in FIGS. 4-10 and described above can be arranged in different groups. For example, more oxidant lances can be arranged to heat the space which is particularly difficult to reach and / or to form additional turbulence inside the furnace depending on the actual operating conditions. The lances open to the V-shaped space need not be arranged in the center of the space, but can be arranged to have their separate orifices, for example, somewhat displaced within the horizontal plane. In such a case, it is desirable to have the santant stream inclined finally downward across the zone where the fuel is supplied in the V-shaped space. In addition, more fuel lances may be used in each assembly or group, or alternatively in other locations, allowing fuel to be fed to a location where one or several high velocity oxidant streams traverse.

Finally, it is also possible to arrange one oxidant lance at a lower height at each one of the corners in the furnace so that the oxidant can be supplied in both directions to the space under the ingots along both long sides of the furnace. .

Therefore, the present invention is not limited to the above-described embodiments, but may be modified within the scope of the appended claims.

Claims (14)

Two or more ingots 201; 301 to be heated cause an inclination with respect to each of the opposing first and second inner walls of the pit furnace 200; 300 so that the ingots 201; A method of increasing temperature uniformity in a pit furnace (200; 300), which forms an elongated space (203; 303) having a V-shaped cross section therebetween when viewed along the second inner walls:
One or more separate lances 211, 212, 221, 222; 311, 312, 321, 322 for an oxidant having an oxygen content of at least 85% by weight and one or more separate lances 210, 220; 310, for fuel 320 is arranged in the furnace wall with their orifices arranged to open into the furnace 200; 300 at a distance from each other such that each of the oxidant and fuel can be supplied to the V-shaped space 203; 303. And burnable in this space, and the orifices of the oxidant lances 211, 212, 221, 222; 311, 312, 321, 322 are arranged above the orifices of the fuel lances 210, 220; 310, 320. Characterized in that the oxidant is directed to flow obliquely along the longitudinal direction of the V-shaped spaces (203; 303) and downwards,
A method of increasing temperature uniformity in a pit furnace (200; 300).
The method of claim 1,
The oxidant lances (211, 212, 221, 222; 311, 312, 321, 322), the orifice of the oxidant lances (211, 212, 221, 222; 311, 312, 321, 322 is arranged Characterized in that it is caused to be arranged on all supply positions 210, 220; 310, 320 for fuel arranged on the same furnace wall,
A method of increasing temperature uniformity in a pit furnace (200; 300).
3. The method according to claim 1 or 2,
The oxidant is to be supplied at a speed of at least 100 m / s,
A method of increasing temperature uniformity in a pit furnace (200; 300).
The method of claim 3, wherein
Characterized in that the oxidant is supplied at a speed of sound or higher speed,
A method of increasing temperature uniformity in a pit furnace (200; 300).
The method according to any one of claims 1 to 4,
Each of the oxidant lances 211, 212, 221, 222; 311, 312, 321, 322 and the fuel lances 210, 220; 310, 320 are arranged so that separate streams meet in the V-shaped space 203; 303. Characterized by being oriented,
A method of increasing temperature uniformity in a pit furnace (200; 300).
6. The method according to any one of claims 1 to 5,
The oxidant lances (211, 212, 221, 222; 311, 312, 321, 322) is characterized in that the oxidant is mounted to flow into the furnace chamber at an angle of 0 to 20 ° with respect to the horizontal plane,
A method of increasing temperature uniformity in a pit furnace (200; 300). The method according to claim 6,
The oxidant lances (211, 212, 221, 222; 311, 312, 321, 322) is characterized in that the oxidant is mounted to flow into the furnace chamber at an angle of 3 to 5 ° with respect to the horizontal plane,
A method of increasing temperature uniformity in a pit furnace (200; 300).
The method according to any one of claims 1 to 7,
The oxidant lances 211, 212, 221, 222; 311, 312, 321, 322 are redirectable to control the angle for their oxidant flow in both the horizontal and vertical planes depending on the operating conditions. It is possible to be characterized by
A method of increasing temperature uniformity in a pit furnace (200; 300).
The method according to any one of claims 1 to 8,
The at least two oxidant lances 211, 212, 221, 222; 311, 312, 321, 322 are arranged such that their orifices are arranged up and down in the furnace chamber, and the lances 211, 212, 221, 222; 311, 312, 321, 322, characterized in that the separate oxidant is mounted such that it flows into the furnace chamber at different angles in the horizontal plane and / or vertical plane,
A method of increasing temperature uniformity in a pit furnace (200; 300).
The method of claim 9,
Orifices of the oxidant lances 212, 222; 312, 322 arranged relatively high are lances 211, 221; 311, 321 in which a separate oxidant from these lances is arranged at relatively low heights. Characterized in that it is arranged to be able to flow into the furnace chamber at an angle to a horizontal plane that is the same or relatively larger than the oxidant streams from
A method of increasing temperature uniformity in a pit furnace (200; 300).
11. The method according to claim 9 or 10,
The heating power in the furnace (200; 300) during operation is, firstly, one or several lances for the oxidant switched on or off (211, 212, 221, 222; 311, 312) , 321, 322, and secondly, by the amount of fuel controlled to stoichiometrically correspond to the oxygen supplied entirely through the oxidant,
A method of increasing temperature uniformity in a pit furnace (200; 300).
12. The method according to any one of claims 9 to 11,
The temperature uniformity in the furnace (200; 300) is characterized by the use of different lances (211, 212, 221, 222; 311, 312, 321, 322) for oxidants or constellations of lances for oxidants. Characterized in that it is further increased during operation by the alternating feeding method,
A method of increasing temperature uniformity in a pit furnace (200; 300).
13. The method according to any one of claims 1 to 12,
Oxygen levels in the furnace (200; 300) are measured, for example, using one or several lambda sensors, oxidizing lances 211, 212, 221, 222; 311, 312, 321, 322 during operation. Oxygen supplied through the) is controlled to maintain a substantially constant oxygen concentration in the furnace (200; 300),
A method of increasing temperature uniformity in a pit furnace (200; 300).
14. The method according to any one of claims 1 to 13,
The first group of lances 210, 211, 212; 310, 311, 312 consisting of one or more fuel lances as well as one or more oxidant lances having an oxygen content of at least 85% by weight of Arranged with their orifices on the short side,
An additional group of lances 220, 221, 222; 320, 321, and 322, consisting of one or more fuel lances as well as one or more oxidant lances having an oxygen content of at least 85% by weight, may face the furnace 200; 300. Are arranged with their orifices on the short side of and
All of the lances of the first group are arranged at a height above the roadbed which exceeds 0.9-1.5 meters above the level on the furnace floor where the orifices of the second group of lances are arranged whose orifices are arranged at the lowest height. Characterized in that it is arranged with the orifices of
A method of increasing temperature uniformity in a pit furnace (200; 300).

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