BACKGROUND

The disclosure relates to industrial heating equipment, and more particularly to a system and method for controlling a firing system.

Inhomogeneous temperature distributions are present in the firing zone at various industrial heating devices and process engineering systems. For instance, in known solutions all burners typically have flow patterns similar to each other, or at least it is typical to aim at having as similar flow patterns for all the burners as possible considering the local circumstances. Neighbouring burners are operated with similar or even the same power. Therefore, similar hot flow patterns occur at all burners as shown on the left side in Figures 2 and 3, where Figure 2 shows a furnace with slow burners and Figure 3 shows a furnace with fast burners. Due to the continuous movement of the pallet cars with the pellets through the furnace, stripe-like conditions result, where some pellets are mainly loaded with high temperature content, whereas other pellets are mainly loaded with lower temperature content, as shown on the right side in Figures 2 and 3. This results in products of varying quality.

BRIEF DESCRIPTION OF THE DISCLOSURE

An object of the present disclosure is to provide a new firing system and a new method for controlling a firing system.

The object of the disclosure is achieved by a method and an apparatus which are characterized by what is stated in the independent claims. Some embodiments of the disclosure are disclosed in the dependent claims.

The disclosure is based on the idea of providing burners with different type of flame characteristics in the firing system.

An advantage of the disclosure is that a better control of heating a material to be heated by the firing system over the width of the furnace can be achieved. Thereby, for instance a desired temperature distribution, such as a homogenous temperature distribution over the width of the furnace, of the material to be heated can be achieved by the firing system and the method.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the disclosure will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which Figure 1 illustrates schematically an industrial heating equipment according to an embodiment seen from an end of a furnace in cross section;

Figures 2 and 3 illustrate, seen from above, hot flow patterns on the left and resulting temperature ranges of the moving material on the right in furnaces heated in each case with a prior art firing system;

Figure 4 illustrates, seen from above, hot flow patterns on the left and resulting temperature ranges of the moving material on the right in a furnace heated with a firing system according to a first embodiment of this disclosure;

Figure 5 illustrates, seen from above, hot flow patterns on the left and resulting temperature ranges of the moving material on the right in a furnace heated with a firing system according to a second embodiment of this disclosure;

Figure 6 illustrates, seen from above, hot flow patterns on the left and resulting temperature ranges of the moving material on the right in a furnace heated with a firing system according to a third embodiment of this disclosure;

Figure 7 illustrates schematically a burner lance for an adjustable burner according to an embodiment seen from a side of the burner lance in cross section; and

Figure 8 illustrates a method for controlling a firing system.

The figures are provided for illustrating some features of the disclosure only and are not shown to scale. Same reference numbers are used for similar features in different figures and embodiments. Not all similar features are necessarily provided with reference numbers for the sake of clarity.

DETAILED DESCRIPTION OF THE DISCLOSURE

Figure 1 illustrates schematically an industrial heating equipment according to an embodiment seen from an end in cross section.

In industrial heating equipment 1 , burners 2 may be used for heating. Industrial heating equipment 1 may further comprise a combustion chamber 3, and one or more burners 2 may be provided on the combustion chamber 3. The combustion chamber 3 may, on the other hand, be mounted in an oven or a furnace 4.

A burner 2 may comprise a burner lance 10. A burner lance 10 according to an embodiment is illustrated in Figure 7. Referring for instance to the embodiments of Figures 1 and 7, fuel and primary air, in other words a primary air flow 25 and a fuel flow 26, may be configured to flow through the burner lance 10 and to enter, through the burner lance, the combustion chamber 3. Process air 5 may be configured to enter the combustion chamber through its own channels. After ignition of the fuel/air mixture, a flame 6 is created. The flame is provided at least partially in the combustion chamber 3, but in some embodiments, the flame may also extend into a furnace 4. The flame 6 is configured to create a heat flow 27, in other words a flow of hot gases. According to an embodiment, the furnace 4 may comprise moving means 7, such as a conveyor belt and chained pallet cars, for moving the material to be heated in the furnace 4. According to an embodiment, the heated material may then also be discharged from the furnace 4 by the moving means 7.

According to an embodiment, at least one end of the furnace 4, such as the second end 34, may have an opening and the hot flows 27 may exit the furnace 4 through the opening. According to an embodiment, the hot flow, and the heated material, in other words the product, may exit the furnace 4 through the same, end comprising the opening. According to another embodiment, such as an embodiment in connection with a pelletizing plant, the moving means 7 may comprise a porous material or a porous structure, and the hot flows 27 may exit the furnace 4 through the moving means.

Figure 4 illustrates, seen from above, hot flow patterns on the left and resulting temperature ranges of the moving material on the right in a furnace heated with a firing system according to a first embodiment of this disclosure, Figure 5 illustrates, seen from above, hot flow patterns on the left and resulting temperature ranges of the moving material on the right in a furnace heated with a firing system according to a second embodiment of this disclosure, and Figure 6 illustrates, seen from above, hot flow patterns on the left and resulting temperature ranges of the moving material on the right in a furnace heated with a firing system according to a third embodiment of this disclosure. According to an embodiment, the areas 32 shown on the right in Figures 2 to 6 are the hot areas, in other words areas where the material to be heated comprises the highest temperature, and in between and/or on the sides of the 32 areas the temperature is less hot.

An industrial heating equipment 1 may comprise a firing system 20. A firing system 20 may also be called a combustion system or a burner arrangement. A firing system 20 for a furnace 4, such as a firing system of Figure 4, Figure 5, or Figure 6, comprises a plurality of burners 2 provided spaced from each other along two opposing sides 31 of the furnace 4. The burners 2 are directed towards each other and the material to be heated. According to an embodiment, the sides 31 are configured to be provided at opposite sides of the material to be heated. According to an embodiment, the sides 31 , and thus the burners 2, are provided at opposite sides but horizontally upwards, in other words on a higher level in the vertical direction, in relation to the material to be heated. In the firing system 20, such as the firing system 20 of Figure 4, 5 or 6, a first portion of the burners are configured to provide a flame with first type of flame characteristics and a second portion of the burners are configured to provide a flame with a second type of flame characteristics. In the firing system 20, each side 31 is provided with at least one burner 2 belonging to the first portion of the burners and at least one burner belonging to the second portion of the burners.

In Figures 4, 5 and 6 these flames with different types of flame characteristics are illustrated by a heat flow 27 area of a certain shape. In other words, in Figure 4 for example, seen in the direction of the arrow, in other words in the direction of movement 35 of the material to be heated or from the bottom towards the top in the figure, the first burners 2 have a first type of flame characteristics, the second burners 2 have a second type of flame characteristics, the third burners 2 have a first type of flame characteristics and the fourth burners 2 have a second type of flame characteristics. In Figure 5, on the other hand, seen in the direction of the arrow, the first and third burner 2 on the right and the second and fourth burner 2 on the left have a first type of flame characteristics, whereas the first and third burner 2 on the left in the figure and the second and fourth burner 2 on the right have a second type of flame characteristics. It is clear for a person skilled in the art that the embodiments of Figures 4, 5 and 6 are schematical illustrations and arbitrary examples only with the purpose to explain concepts of this disclosure. It should also be understood that the first type of flame characteristics of Figures 4, 5 and 6, and the second type of flame characteristics of Figures 4, 5 and 6 may be different from each other, and that in firing systems 20 of this disclosure burners 2 with further types of flame characteristics may be included in addition to the first and second types.

According to an embodiment, in the firing system 20, at least two of the burners 2 may comprise adjustable burners 2. According to an embodiment, the adjustable burners 2 may be capable of generating different flame characteristics at a same firing rate. According to an embodiment, at least one of the adjustable burners 2, preferably at least two of the adjustable burners 2, may comprise an adjustable burner according to an embodiment or a combination of embodiments disclosed in this description and/or in the accompanying claims and/or figures. According to an embodiment, all of the adjustable burners 2 may comprise an adjustable burner according to an embodiment or a combination of embodiments disclosed in this description and/or in the accompanying claims and/or figures.

According to an embodiment at least 30 percent of the burners in the firing system are adjustable burners 2. According to another embodiment, at least 60 percent of the burners in the firing system are adjustable burners 2. According to an embodiment, all the burners 2 of the firing system 20 may comprise adjustable burners 2. Such embodiments may be beneficial especially in applications, in which a high adjustability of the heating and, thus, heat flow 27 and flame characteristics is needed.

According to an embodiment, the firing system also comprises non-adjustable burners 2. In other words, according to an embodiment, the firing system 20 comprises both adjustable and non-adjustable burners. Such embodiments may be beneficial in applications, in which a simpler structure is important and sufficient control and adjustability can be achieved by fewer adjustable burners 2.

According to an embodiment, at least two burners 2 may form a pair, also called a burner pair or a pair of burners. More particularly, at least two burners 2 may form a pair in such a manner that the two burners 2 are provided directly opposite to each other on opposing sides 31 of the furnace 4, such as in the embodiments of Figures 4 and 5. The sides 31 of the furnace 4 refer to the sides 31 extending on each side of the area, in which the material to be heated is provided. More particularly, the sides 31 extend from a first end 33 of the furnace 4, at which the material to be heated is configured to be provided into the furnace 4, to the second end 34 of the furnace 4, at which the material to be heated is configured to exit the furnace 4. The direction, in which a material to be heated may be configured to pass through the furnace 4 is shown by arrows, namely in the direction of movement 35, in Figures 2 to 6. According to an embodiment, the burners 2 are provided at the furnace 4 above the material to be heated in a vertical direction.

According to an embodiment, such as the embodiment of Figure 6, at least two burners 2 form a pair in such a manner that the two burners are provided offset from each other on opposing sides of the furnace. In other words, the two burners 2 forming a pair are spaced from each other also in the direction movement 35, as shown schematically in Figure 6 and emphasized by dashed lines. According to an embodiment, the firing system 20 comprises a plurality of such burner pairs each formed by a pair of burners 2 provided on opposing sides of the furnace. According to an embodiment, at least one burner pair comprises two adjustable burners 2.

According to an embodiment, in the direction of a side 31 of the furnace 4, after a maximum of two adjacent burner pairs with non-adjustable burners 2, at least one burner pair with adjustable burners 2 is provided adjacent to one of the burner pairs with non-adjustable burners 2. According to an embodiment, the two burners 2 of at least one burner pair may be configured to have flame characteristics that are different from each other. In other words, both burners 2 of a burner pair may comprise first type of flame characteristics, second type of flame characteristics or a further type of flame characteristics. According to an embodiment, the two burners 2 of at least one burner pair may be configured to have similar flame characteristics with each other and different from at least one adjacent burner on either side.

According to an embodiment, the flame characteristics may comprise at least one of a firing rate of the burner, a flow pattern of the burner and an average outlet velocity of the burner. The flow pattern of the burner 2 refers to the hot flow pattern configured to be generated by the burner 2.

According to an embodiment, the flame with the first type of flame characteristics may have an average outlet velocity of at least 150 m/s. According to an embodiment, the flame with the first type of flame characteristics may have an average outlet velocity of at least 200 m/s. According to an embodiment, both the flame with the first type of flame characteristics and the flame with the second type of flame characteristics may have an average outlet velocity of at least 150 m/s. A fast burner may comprise a burner configured to provide a high average outlet velocity, such as an average outlet velocity of at least 150 m/s, resulting in a hot flow reaching far in the furnace 4. Similarly, a burner configured to provide an average outlet velocity of at least 150 m/s may be called a fast burner, and a burner configured to provide an average outlet velocity of at least 200 m/s may be called a fast burner or a faster burner.

According to an embodiment, flame with the second type of flame characteristics has an average outlet velocity below 150 m/s, in other words less than 150 m/s. According to an embodiment, flame with the second type of flame characteristics has an average outlet velocity below 80 m/s. According to an embodiment, both the flame with the first type of flame characteristics and the flame with the second type of flame characteristics may have an average outlet velocity below 150 m/s. A slow burner may comprise a burner configured to provide a low average outlet velocity, such as an average outlet velocity below 150 m/s, resulting in a hot flow reaching a shorter distance in the furnace than a hot flow of a fast burner. A burner configured to provide an average outlet velocity below 80 m/s may be called a slow burner or a slower burner.

According to an embodiment, the flame with the first type of flame characteristics may have an average outlet velocity of at least 200 m/s, and the flame with the second type of flame characteristics may have an average outlet velocity of at least 150 m/s, for example. According to an embodiment, the flame with the first type of flame characteristics may have an average outlet velocity below 150 m/s, and the flame with the second type of flame characteristics may have an average outlet velocity below 80 m/s, for example.

According to an embodiment, the second type of flame characteristics may have an average outlet velocity that differs at least of 20 percent, preferably at least 30 percent, from the average outlet velocity of the flame with the first type of flame characteristics.

In this disclosure, the average outlet velocity refers to the average outlet velocity of fuel flow and/or primary air at the outlet end 13 of the burner 2 and, thus, the burner lance 10. In other words, the average outlet velocity refers to the average outlet velocity of fuel flow and/or primary air at outlet member(s) 12, 15, 17, such as nozzle(s).

According to an embodiment, the firing system 20 may further comprise at least one valve arrangement 22 for controlling at least one of primary air flow 25 and fuel flow 26 to the burners. According to an embodiment, in which the firing system 20 comprises adjustable burner(s) 2, the valve arrangement 22 may be configured to selectively enable and block flow of primary air from air supply and fuel from fuel supply to at least one of the air channel(s) 14 and fuel channels 11 , 16 respectively. According to an embodiment, where there are two fuel channels 11 , 16, in a use situation of the firing system 20 the ratio of fuel supply may be such that 100 percent of the fuel flow is supplied to one of the fuel channels and 0 percent to the other one, or the ratio may be 70 percent and 30 percent, and so on. Thus, enabling flow of fuel or primary air to a channel may comprise providing a percentage larger than 0 and a maximum of 100 percent of the total fuel or air flow to that channel. According to an embodiment, the valve arrangement 22 may be configured to control different ratios of fuel supply in different phases of using the firing system 20. According to an embodiment, a first ratio of fuel supply may be provided for a burner 2 of the firing system 20 to ignite a flame, and a second ratio of fuel supply may be provided to the same burner 2 after ignition. According to an embodiment, a third ratio of fuel supply may be provided for a burner 2 after the second ratio of fuel supply, for instance after a predetermined time of using the second ratio of fuel supply or after a predetermined temperature, for instance a predetermined temperature of the furnace and/or the material to be heated, is reached. According to another embodiment, a third ratio of fuel supply may be provided for a burner 2 of the firing system 20 at least partly simultaneously with providing a second ratio of fuel supply to another burner 2 of the firing system 20.

According to an embodiment, the firing system 20 further comprises a detector (not shown) for detecting the temperature of the material to be heated. According to an embodiment, the detector may be configured to measure the surface temperature of the material to be heated. According to an embodiment, the detector may comprise an optical measurement device. According to an embodiment, the firing system 20 may comprise a plurality of detectors for detecting the temperature of the material to be heated. According to an embodiment, the detector(s) may be configured to measure the temperature over the whole width of the furnace. According to an embodiment, at least one detector may be configured to measure the temperature from a sub-area of the width of the furnace. According to an embodiment, the firing system 20 may comprise at least one detector for detecting the temperature of the material to be heated after in each case a maximum of 6 burner pairs. Detectors for detecting temperatures may be configured to measure the temperatures, for instance surface temperatures, or detect temperatures or characteristics indicative of temperatures, such as hardness of the material, colour of the material, or radiation emitted by the material to be heated by optical detectors. Such detectors are known in the art and are, thus, not explained here in more detail.

According to an embodiment, the firing system 20 may further comprise at least one control unit (not shown) for controlling at least one of the primary air flow 25 and fuel flow 26 to burner(s) 2. According to an embodiment, the control unit may be configured to control flow of at least one of fuel and primary air to the burners. More particularly, the control unit may be configured to control flow of at least one of fuel and primary air to the burners, such as fuel supply ratios or air supply ratios, by controlling the valve arrangement 22.

According to an embodiment, the control unit may be configured to control at least one of the burners 2 based on temperature detected by at least one of the detectors, which detector is configured to detect a temperature. According to an embodiment, a feedback loop from the detected temperature, preferably a temperature of the material to be heated, may be used for the control, such as for controlling the flame characteristics provided by the burners.

According to an embodiment, a plurality of burners 2 of the firing system 20 may be configured to be controlled to generate such hot flow patterns that a desired temperature of the material to be heated, for instance the temperature distribution of the material to be heated over the width of the furnace, is achieved. According to an embodiment, the plurality of burners 2 may comprise adjustable burners and/or non-adjustable burners, at least some of which may be configured to be controlled to provide hot flow patterns different from each other. According to an embodiment, at least some of the adjacent burners 2 or burner pairs of the firing system 20 are controlled to generate hot flow patterns different from each other to provide the desired temperature of the material to be heated. These burners 2 or burner pairs may comprise a combination of fast, faster, slow and/or slower burners 2.

According to an embodiment, the firing system 20 may comprise at least 8 burners 2.

According to an embodiment, a furnace 4 may comprise a firing system 20 according to an embodiment or a combination of embodiments disclosed in this description and/or accompanying claims and/or figures. According to an embodiment, the furnace 4 may comprise moving means 7 for moving the material to be heated in a direction parallel to the sides 31 between the burners 2, in other words in the direction of movement 35. According to an embodiment, the moving means 7 may comprise at least one of the following: a conveyor belt and chained pallet cars.

According to an embodiment, the firing system 20 may be a firing system of a pellet plant and the moving means comprise chained pallet cars for pellets.

According to an embodiment, industrial heating equipment 1 may comprise a firing system 20 according to an embodiment or a combination of embodiments disclosed in this description and/or accompanying claims and/or figures.

Figure 7 illustrates schematically a burner lance 10 for an adjustable burner 2 according to an embodiment seen from a side of the burner lance in cross section. The burner lance 10 is, thus, seen in the same direction as the industrial heating equipment in Figure 1. According to an embodiment, at least one of the burners 2, preferably at least two burners 2, which burner(s) 2 comprise adjustable burner(s), comprise a burner lance 10 described in this description, for instance as described below referring to and illustrated schematically by Figure 7. It should be understood that the embodiment of Figure 7 is meant for explaining such a burner lance 10 and related features schematically only and that the actual construction of the burner lance 10 and, for instance, the number, order and structure of the fuel and primary air channels may vary within embodiments described in the description, accompanying claims and/or accompanying figures.

The burner lance 10, burner 2, firing system 20, and the method for controlling firing system may be used in industrial heating equipment and/or in process engineering systems.

According to an embodiment, the burner lance 10 and/or the burner 2 may be used for optimizing temperature in the furnace. According to an embodiment, the burner lance 10, the burner 2 and/or the firing system 20 may be used on straight grate pelletizing plants and, more particularly, used to optimize pellet quality. According to an embodiment, a burner lance 10 for industrial heating equipment, and more particularly for an adjustable burner 2 of a firing system 20 of this disclosure, such as the burner lance 10 of Figure 7, may comprise a first fuel channel 11 for fuel. The first fuel channel 11 may be provided with a first fuel outlet member 12 at an outlet end 13 of the burner lance 10. The burner lance 10 may further comprise a first air channel 14 for air, more particularly for primary air. The first air channel 14 may be provided with a first air outlet member 15 at the outlet end 13. The burner lance 10 may further comprise a second fuel channel 16 for fuel, which the second fuel channel 16 may be provided with a second fuel outlet member 17 at the outlet end 13.

The first air channel 14 may be provided radially outwards from at least two of the fuel channels 11 , 16 at the outlet end 13.

According to an embodiment, at least the second fuel outlet member 17 may be provided with a widening member configured to widen the angle 9 of the fuel flow exiting the burner lance 10 outwards from the longitudinal axis 8 of the burner lance 10. According to an embodiment, a widening member, such as the widening member of the second fuel outlet member 17, may comprise at least one of the following: a swirling member, a multi-hole plate with radially angled holes or a multi-hole plate with tangentially angled holes.

According to an embodiment, the first fuel outlet member 12 is not provided with a widening member. In other words, according to an embodiment, the first fuel outlet member 12 does not comprise a widening member and the second fuel outlet member 17 comprises a widening member. According to an embodiment, the burner lance 10 may comprise further fuel channels and fuel outlet members which may or may not comprise a widening member at the outlet end 13. According to an embodiment, the first fuel outlet member 12 may comprise an outlet member in a form of a nozzle, an annular opening, or a multi-hole plate.

According to an embodiment, a widening member, such as the widening member of the second fuel outlet member 17, is configured to cause a jet angle of at least 15 degrees with respect to a direction of the longitudinal axis 8 of the burner lance 10 at the outlet end 13. According to another embodiment, the widening member, such as the widening member of the second fuel outlet member 17, is configured to cause a jet angle of at least 17,5 degrees with respect to a direction of the longitudinal axis 8 of the burner lance 10 at the outlet end 13. According to a further embodiment, the widening member, such as the widening member of the second fuel outlet member 17, is configured to cause a jet angle of at least 20 degrees with respect to a direction of the longitudinal axis 8 of the burner lance 10 at the outlet end 13. According to an embodiment, the first fuel outlet member 12, the second fuel outlet member 17 and the first air outlet member 15 are provided concentrically with respect to one another. In other words, the first fuel channel 11 , the second fuel channel 16 and the first air channel 14 may be provided concentrically with respect to one another at least at the outlet end 13 of the burner lance 10. According to an embodiment, the first fuel outlet member 12, the second fuel outlet member 17 and the first air outlet member 15 are provided concentrically with one another and with the longitudinal axis 8 of the burner lance 10.

According to an embodiment, the first fuel channel 11 may comprise an innermost channel at the outlet end 13, and the second fuel channel 16 may be provided radially outwards from the first fuel channel 11 at the outlet end 13. In other words, the second fuel outlet member 17 may be provided radially outwards from the first fuel outlet member 12.

According to an embodiment, the first air channel 14 may be provided radially outwards from the second fuel channel 16 at the outlet end 13. In other words, the first air outlet member 15 may be provided radially outwards from the second fuel outlet member 17.

Figure 8 illustrates a method for controlling a firing system.

A method for controlling a firing system, such as the method of Figure 8, may comprise providing 81 a plurality of burners 2 spaced from each other along two opposing sides 31 of a furnace 4. The burners 2 may be directed towards each other and the material to be heated. The method further comprises configuring 83 a first portion of the burners 2 to provide a flame with first type of flame characteristics and a second portion of the burners 2 to provide a flame with a second type of flame characteristics; and providing 85 each side 31 with at least one burner belonging to the first portion of the burners and at least one burner belonging to the second portion of the burners.

According to an embodiment, the method for controlling a firing system 20 may be implemented by an embodiment or a combination of embodiments of a firing system 20 disclosed in this description, accompanying claims and/or accompanying drawings.

According to an embodiment, the method further comprises configuring the flame with the first type of flame characteristics and the flame with the second type of flame characteristics to have desired firing rates. According to an embodiment, the desired firing rates of the flame with the first type of flame characteristics and the flame with the second type of flame characteristics comprise firing rates according to an embodiment disclosed in connection with the firing system embodiments or a combination thereof. According to an embodiment, the method may further comprise controlling operation of the burners 2 by at least one valve arrangement 22.

According to an embodiment, the method further comprises moving a material to be heated between the burners 2 in a direction parallel to the sides 31 by moving means 7. More particularly, the material to be heated may be moved between the burners 2 but at a lower level in a vertical direction in relation to the burners 2. The direction, in which the material to be heated may be moved in the furnace 4, in other words the direction of movement, is indicated by an arrow in Figures 2 to 6.

According to an embodiment, the method may further comprise detecting the temperature of the material to be heated by at least one detector. The detector, detecting and/or the measurement may be in line with an embodiment, or a combination of embodiments disclosed in connection with the firing system 20 embodiments.

According to an embodiment, the method may further comprise controlling by at least one control unit at least one of the burners, a group of burners, or all the burners. According to an embodiment, controlling the burner(s) by the control unit may comprise controlling flow of at least one of fuel and primary air to the burner(s). According to an embodiment, controlling the burner(s) by the control unit may comprise controlling flow of at least one of fuel and primary air to the burners by controlling the valve arrangement. According to an embodiment, controlling the burner(s) 2 by the control unit may comprise controlling at least one of the burners 2 based on temperature detected by at least one of the detectors.

According to an embodiment, the moving means 7 may comprise at least one of the following: a conveyor belt and chained pallet cars.

According to an embodiment, the firing system 20 may be a firing system 20 of a pellet plant and the moving means 7 may comprise chained pallet cars for pellets.

According to an embodiment, the method may further comprise heating by the burners material to be heated provided in the furnace.