Method for controlling maintenance equipment for a recovery boiler and maintenance equipment

Abstract

The present invention relates to a method for controlling a maintenance work device (10) of a recovery boiler (11) to perform maintenance work on at least one object to be maintained (S1 to S14) in the recovery boiler (11), wherein the maintenance work device (10) comprises a maintenance tool (13) and tool moving devices (R1 to R5) for moving the maintenance tool (13) to accomplish the maintenance work, and the method comprises a) a method step of defining the position in a fixed world coordinate system (20) in the recovery boiler (11), and b) at the initial temperature of the recovery boiler (11) the position of at least one object to be maintained (S1 to S14) determined in the fixed world coordinate system (20) The present invention relates to a method comprising: a method step of defining the position of an initial base coordinate system (21) of at least one object to be maintained (12) at a selected point in (4) a fixed world coordinate system (20); a method step of defining the position of a corrected base coordinate system (22) of at least one object to be maintained (S1~S14) in a fixed world coordinate system (20) at the position of a selected point in the fixed world coordinate system (20) at the transition temperature of the recovery boiler (11); and a method step of controlling tool movement devices (R1~R5) to perform maintenance work on at least one object to be maintained (S1~S14) within the corrected base coordinate system (22). The present invention also relates to a maintenance work device (10).

Description

Technical Field

[0001] The present invention relates to a method for controlling a maintenance work device of a recovery boiler and a maintenance work device.

Background Art

[0002] The main fuel burned in a recovery boiler is black liquor. Secondary fuels such as oil, natural gas, or some renewable fuels such as tar or tall oil are used during startup and shutdown. In normal operation, only black liquor is ignited by using a special nozzle designed to spray liquid fuel for optimal combustion. The purpose of spraying is to enable rapid drying and volatilization of the organic materials in the fuel, which mainly consist of lignin and hemicellulose separated from wood fibers in the pulping process.

[0003] In addition to the organic materials, black liquor contains chemicals used in the kraft pulp process. These inorganic materials, mainly sodium sulfate and sodium carbonate, melt with the heat of the burning organic materials. The molten salts (smelt) flow from the boiler through the smelt spout at the bottom of the boiler furnace to the dissolving tank.

[0004] Black liquor combustion is a sensitive process that requires maintaining a balance between ignition temperature and pressure, nozzle angle and type, and black liquor quality. The effects of black liquor ignition failure include the accumulation of deposits within the hot surface, inefficient char and smelt bed reactions, and increased fuel gas contaminants. To avoid improper ignition and ensure successful operation, burners must be kept free of smelt and char deposits. These deposits are particularly prone to buildup and can easily clog uneven boiler furnace surfaces such as smelt spouts, black liquor gun openings, and cleaning and inspection hatches. Therefore, regular cleaning of these surfaces is essential for optimal and uninterrupted process performance. Traditionally, such maintenance work was performed manually using appropriate hand tools, but due to the high safety risks involved in working in areas with potential high-temperature smelt splashes, automated and / or robotic maintenance equipment for these tasks has been increasingly used over the past few decades.

[0005] For example, known automated maintenance systems and devices, such as those described in International Publication No. 2018 / 229334, European Patent No. 1914477, European Patent No. 2024559, or U.S. Patent No. 555425650, have been used in recent years to reduce the employee safety risks mentioned above. However, further improvements to such devices are still needed in several respects. For example, one drawback of currently applied known automated solutions concerns their position control methods. This is because, when the combustion process is switched between different stages of operation, namely between startup and normal operation, and between normal operation and shutdown, known maintenance devices are not adapted to compensate for the large thermal changes and thermal expansion that typically occur within the recovery boiler walls. The effects of such thermal expansion are, in most cases, unpredictable due to the nonlinearity of the phenomenon caused, in particular, by the structural complexity of the boiler. Therefore, pre-defined compensation based on simple linear calculation models, for example, may not adequately solve these problems. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2018 / 229334 [Patent Document 2] European Patent No. 1914477 [Patent Document 3] European Patent No. 2024559 [Patent Document 4] U.S. Patent No. 555425650 [Overview of the project] [Problems that the invention aims to solve]

[0007] The object of the present invention is to provide an improved method for controlling a maintenance device for a recovery boiler, wherein the maintenance work performed by the device can be controlled by taking into account the displacement of the object to be maintained caused by thermal expansion occurring within the recovery boiler wall due to temperature transitions during different operating stages of the recovery boiler. Furthermore, the object of the present invention is to provide a device for performing the maintenance work controlled by the method of the present invention. [Means for solving the problem]

[0008] The drawbacks described above are corrected by the method of the present invention, for the reason that in this method, the initial base coordinate system, which coincides with the object to be preserved in a fixed world coordinate system and in which the preservation work device performs the preservation work within it, is determined to shift from its initial position and orientation to its actual position and orientation, i.e., to the position where the initial base coordinate system actually is located after the occurrence of displacement caused by thermal expansion occurring within the recovery boiler during recovery boiler operation. More precisely, the method according to the present invention is characterized by the apparatus described in independent claim 1 and independent claim 16. Dependent claims 2 to 15 describe advantageous embodiments of the method and advantageous embodiments of the apparatus of dependent claims 17 and 18.

[0009] The advantage of the method according to the present invention is that the control system of the maintenance device can compensate for displacement and misalignment of the object to be maintained caused by thermal expansion. Therefore, by the method according to the present invention, maintenance work performed on the object to be maintained in the recovery boiler is safely and reliably achieved regardless of the displacement of the object caused by temperature transitions occurring in the recovery boiler. In fact, this means that the maintenance work device is always automatically adapted to operate according to the dominant temperature of the recovery boiler. Therefore, for example, when cleaning a smelt spout, the smelt spout cleaning tool moved by the smelt spout cleaning device is always accurately positioned at the desired location on the smelt spout to be cleaned, regardless of the operating stage of the recovery boiler. This ensures a smooth and effective cleaning cycle and prevents uncertainty and potential damage to the control of the smelt spout and / or cleaning tool as is the case with known control methods.

[0010] The present invention will be described in more detail below with reference to the accompanying figures. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram illustrating the principle of determining the temperature-corrected base coordinate system from the initial base coordinate system in the world coordinate system. [Figure 2] This figure shows an exemplary embodiment of a smelt spout cleaning device for a recovery boiler, viewed obliquely from above, and a maintenance work device controlled by the method of the present invention. [Figure 3] This is an enlarged view of the smelt spout of the recovery boiler, seen from above at an angle, showing how the initial base coordinate system is positioned on the smelt spout in the case of the smelt spout cleaning device shown in Figure 2. [Figure 4] This is a schematic diagram showing the location of the smelt spout in the world coordinate system and the location of the initial base coordinate system in a method for controlling a maintenance work device applied to the embodiments shown in Figures 2 and 3. [Figure 5]This is a top view of the maintenance work device, showing how the measuring sensors for determining the position of the smelt spout are positioned relative to the smelt spout and the recovery boiler. [Figure 6] Figures 2 to 5 are top views of embodiments of the maintenance work device, illustrating the principle of displacement caused by the rotation of the recovery boiler wall along the Y-axis due to thermal expansion. [Figure 7] Figures 2 to 6 are front views of an embodiment of the maintenance work device, and are schematic diagrams showing the displacement caused by the rotation of the recovery boiler wall along the X-axis due to thermal expansion. [Modes for carrying out the invention]

[0012] The method according to the present invention can be applied to several different maintenance tasks of a recovery boiler, such as smelt spout cleaning, black liquor gun opening cleaning, or inspection hatch opening cleaning. In this regard, the method is generally discussed in terms of controlling maintenance tasks performed by maintenance equipment, where maintenance tasks mean any such tasks performed on the recovery boiler regularly or occasionally.

[0013] In this application, a maintenance work apparatus means an apparatus comprising a control unit, by which the physical (movable) parts of the apparatus can be automatically controlled according to a control program executed within the control unit. Thus, the control unit comprises, for example, a computer or other data processing device, and the control program can be programmed and / or installed within the computer or other data processing device and executed as appropriate. The control unit is further equipped with control hardware suitable for controlling electrically, pneumatically, and / or hydraulically operated actuators, which are arranged to move the physical parts of the maintenance work apparatus, referred herein as tool moving devices. Typically, the tool moving devices of a maintenance apparatus may be formed, for example, by an articulated industrial robot with appropriate degrees of freedom. A single maintenance work apparatus may include one or more tool moving devices.

[0014] The maintenance tools applied to a maintenance task may be selected according to the maintenance task. For example, in smelt spout cleaning, a smelt spout cleaning tool is used. However, the maintenance tools may also be several multipurpose tools suitable for several different maintenance tasks, or any specific maintenance tools designed for their intended purpose. A maintenance work apparatus may include several maintenance tools. Preferably, the maintenance work apparatus has at least one maintenance tool per tool moving device.

[0015] In general, the methods for controlling maintenance work are at least a) A step of defining the position in a fixed world coordinate system in the recovery boiler, b) A step of defining the position in the initial base coordinate system of at least one protected object at a selected point determined in a fixed world coordinate system at the initial temperature of the recovery boiler, c) defining the position of the corrected base coordinate system of at least one object to be maintained, which is at the position of the selected point in the fixed world coordinate system, at the transition temperature of the recovery boiler; d) controlling a tool movement device to perform maintenance work on at least one object to be maintained within the corrected base coordinate system.

[0016] The step of defining the position of the corrected base coordinate system may be achieved, for example, by controlling the tool movement device to move the maintenance tool to the position of the selected point on at least one object to be maintained at the transition temperature, and recording the coordinates of the selected point in the fixed world coordinate system. Such control may be achieved manually or automatically. Manual definition may be achieved by controlling the tool movement device to move the tool to a predetermined reference position. Automatic definition may be achieved, for example, by an appropriate position identification device (such as an RFID tag) on the object indicating the reference position of the object to be maintained to the control unit.

[0017] In an embodiment of the method, the position of the corrected base coordinate system is at least partially determined by calculating the displacement of the initial base coordinate system caused by the thermal expansion of the recovery boiler wall due to temperature transition.

[0018] In an embodiment of the method, at least the fixed world coordinate system is a three-dimensional orthogonal coordinate system, and the determination of the position coordinates (i.e., the original position coordinates) of the corrected base coordinate system is calculated using the following equations. X’ = X + ΔX (1) Y’ = Y + ΔY (2) Z’ = Z + ΔZ (3) where the X’, Y’, and Z’ coordinates are the position coordinates of the corrected base coordinate system in the fixed world coordinate system. the X, Y, and Z coordinates are the position coordinates of the initial base coordinate system in the fixed world coordinate system. ΔX, ΔY, and ΔZ are the positional displacements of the initial base coordinate system due to thermal expansion in a fixed world coordinate system.

[0019] If the method involves controlling maintenance work on at least two objects to be maintained that are adjacent to each other in a recovery boiler, the Y-axis indicates the direction along the line between the at least two adjacent objects to be maintained, the X-axis indicates the direction perpendicular to the Y-axis and in the same plane as the X-axis, and the Z-axis indicates the direction perpendicular to the plane defined by the X-axis and Y-axis. Typically, for each of at least two objects to be maintained, one initial base coordinate system and one corrected base coordinate system are determined. Thus, the tool moving device is controlled to perform maintenance work for each of the at least two objects to be maintained within its respective corrected base coordinate system. Furthermore, in such embodiments, i.e., in addition to the positional coordinate displacements ΔX, ΔY and ΔZ, the correction includes rotation of the coordinate axes of the initial base coordinate system due to the rotation of the recovery boiler wall caused by thermal expansion. Thermal expansion of other parts of the recovery boiler other than the recovery boiler wall may also be considered, but in most cases these are considered negligible. The rotation angles A and C of the coordinate axes of the initial base coordinate system shown in Figure 1 are given by the equation A=arctan(ΔX2-ΔX1) / (Y2-Y1) (4) C=arctan(ΔZ2-ΔZ1 / (Y2-Y1) (5) It is determined by [the following]. During the ceremony, A is the rotation angle of the Y-axis with respect to the X-axis. C is the rotation angle of the Y-axis with respect to the Z-axis. Y1 is the first Y position. Y2 is the second Y position. ΔX1 is the displacement in the X direction that occurs at position Y1. ΔX2 is the displacement in the X direction that occurs at position Y2. ΔZ1 is the displacement in the Z direction that occurs at position Y1. ΔZ2 is the displacement in the Z direction that occurs at position Y2.

[0020] In this embodiment, deformation of the recovery boiler wall caused by temperature transitions is measured by at least one displacement sensor placed at a known location in the recovery boiler. The measurement results from at least one displacement sensor are used in determining the initial base coordinate system displacement to determine the position of the corrected base coordinate system. If at least two displacement sensors are present, placed at least two different locations, they may be used to determine displacements occurring at at least two different locations in the recovery boiler. This makes it possible to determine the rotation angle of the corrected base coordinate system, in which case the rotation of the initial base coordinate system due to displacement changes occurring at different locations in the recovery boiler is calculated based on the measured displacements at at least two different locations.

[0021] example In this example, whose configuration is shown in Figure 2, the maintenance work device 10 is responsible for cleaning the smelt spouts S1-S14 of the recovery boiler 11 by applying the method according to the present invention. This includes five tool-moving devices R1-R5, which are articulated industrial robots in this example. As can be seen from the figure, the recovery boiler 11 has 14 smelt spouts S1-S14 in this case. Therefore, each robot R1-R5 only needs to clean a maximum of three smelt spouts, which ensures that the time required for the cleaning process remains short compared to, for example, when only one tool-moving device is used for all the smelt spouts. The smelt spouts S1-S14 are divided among the robots R1-R5 in the manner described in Table 1 below. [Table 1]

[0022] World Coordinate System The displacement of smelt spouts S1-S14 caused by thermal expansion is determined in a world coordinate system 20 located at a fixed position. For a single robot, the robot's frame mounting point and world coordinate system are typically located in the same position. In the case of multiple robots as specified herein, the world coordinate system 20 for each robot R1-R5 is located at a predetermined point that is the same for each robot. In this example, the world coordinate system 20 is located between the two closest smelt spouts S7 and S8 in the center.

[0023] Initial base coordinate system The cleaning movement of the smelt spouts S1-S14 is carried out within a corrected base coordinate system 22 (also called the “work coordinate system”). In this example, the initial base coordinate system 21 and the corrected base coordinate system 22 are positioned as shown in Figure 3 (i.e., at the lower ends of the smelt spouts S1-S14). Alternatively, they may be positioned at any suitable location, for example, on a plate with holes, provided that its position is appropriately considered in the calculations. In any case, the position and orientation of the initial base coordinate system 21 are corrected by applying the principles described above to form the corrected base coordinate system 22, thereby compensating for the effects of thermal expansion in the control of the smelt spout cleaning operation.

[0024] Figure 4 shows how the initial base coordinate system 21 is selected in this example. The original base coordinate system 21 is defined in the world coordinate system 20. In fact, these can be determined, for example, by actual robots and smelt spout cleaning tools, by applying the following procedure. 1. The smelt spout cleaning tool 13 is brought close to each smelt spout S1 to S14 by the normal control program of each robot R1 to R5. 2. From this close position, the smelt spout cleaning tools S1-S14 are moved to the desired point by manually controlling the respective robots R1-R5. 3. At the desired location, its coordinates are defined in the world coordinate system 20 as they were in the original initial base coordinate system 21. 4. These coordinates are stored in the memory of the control unit of the maintenance work device 10 as they were in their respective initial coordinate systems 21.

[0025] Displaced and corrected base coordinate system The displacements occurring in the recovery boiler 11 due to thermal expansion (mostly occurring in the recovery boiler walls 12) are measured in three dimensions (X, Y, and Z) using three measuring sensors M1-M3. The measuring sensors M1-M3 can be any suitable measuring sensors capable of directly measuring or determining their position (e.g., optical sensors or cameras), or any suitable measuring sensors capable of indirectly measuring or determining their position (e.g., strain gauges or other types of displacement sensors). The displacements also change the positions of the smelt spouts S1 through S14. These changes are compensated for by controlling the movement of each smelt spout cleaning tool 13 within a corrected base coordinate system 22 that takes the displacements into account.

[0026] The positions of the measurement sensors M1, M2, and M3 are shown in Figure 5. As can be seen in Figure 5, in this example, the Y direction is the horizontal direction, which is transverse to the longitudinal direction of the smelt spouts S1-S14. Therefore, thermal expansion causing displacement in the Y direction changes the distance between adjacent spouts S1-S14, and in this example, between the measurement sensors M1, M2, and M3 as shown in Figure 5. It should also be noted that the change in the Y-direction distance between the measurement sensors (i.e., ΔY1, ΔY2, ΔY3) also affects the calculation of displacement in the X and Z directions, as these distances are also used to calculate rotations with respect to the Z and X axes.

[0027] The changed distance between the measurement sensors in the Y direction can be calculated for spouts S1 to S7 using the following method. M1'(Y) = M1(Y) + ΔY1(6) M2'(Y) = M1(Y) + ΔY2(7) M'12dist=ABS(M1'(Y)-M2'(Y)) (8) During the ceremony, M1'(Y) is the changed Y coordinate of sensor M1. M2'(Y) is the changed Y-coordinate of the measurement sensor M2. M1(Y) is the original Y coordinate of the measurement sensor M1. M2(Y) is the original Y coordinate of the measurement sensor M2. ΔY1 is the displacement of the measurement sensor M1 in the Y direction. ΔY2 is the displacement of the measurement sensor M2 in the Y direction. M12'dist is the changed distance between the measuring sensors M1 and M2. The smelt spout S8-S14 can be calculated using the following method. M1'(Y) = M1(Y) + ΔY1 (9) M2'(Y) = M1(Y) + ΔY2 (10) M23'dist=ABS(M1'(Y)-M2'(Y)) (11) During the ceremony, M3'(Y) is the changed Y-coordinate of the measurement sensor M3. M3(Y) is the original Y coordinate of the measurement sensor M3. ΔY3 is the displacement of sensor M3 in the Y direction. M23'dist is the changed distance between the measuring sensors M2 and M3.

[0028] Therefore, assuming that thermal expansion is uniform in the Y direction, the displacement of the smelt spouts S1 to S14 in the Y direction can be calculated from the following equation.

number

[0029] The recovery boiler wall 12 may also twist with respect to the Z-axis, causing the amount of displacement in the X-direction at adjacent smelt spouts to vary. Figure 6 shows a situation where the X-direction displacements ΔX1, ΔX2, and ΔX3 of the measuring sensors M1, M2, and M3 in Figure 6 are not equal. In such cases, the wall is twisted with respect to the Z-axis, and the displacement due to thermal expansion for each smelt spout (S1-S14) must be calculated separately.

[0030] In the region of spouts S1 to S7, the wall rotation angle A1 can be calculated from the following equation.

number

[0031] Within the regions of the smelt spout S8 to S14, the rotation angle A2 can be calculated from the following equations.

number

[0032] Given that rotation angles A1 and A2 are known, the displacement in the X direction of each spout S1...S14 can be calculated from the following equation. ΔXsi=ΔX2+tanA1·Ysi(i=1…7) (16) ΔXsi=ΔX2+tanA2·Ysi(i=8…14) (17) During the ceremony, ΔXsi is the displacement of the smelt spout Si caused by the rotation of the recovery boiler wall 12 relative to axis X. Ysi is the distance in the Y direction of the smelt spout Si from the original in world coordinate system 20.

[0033] The recovery boiler wall 12 may also twist with respect to the X-axis, causing the amount of displacement in the Z-direction at adjacent spouts to vary. Figure 7 shows a situation where the Z-direction displacements ΔZ1, ΔZ2, and ΔZ3 of the measurement sensors M1, M2, and M3 in Figure 7 are not equal. In such cases, the wall is twisted with respect to the X-axis, and the Z-direction displacement for each smelt spout S1 to S14 must be calculated separately.

[0034] In the region of the smelt spout S1-S7, the rotation angle C1 of the wall with respect to the X-axis can be calculated from the following equation.

number

[0035] Within the regions of the smelt spout S8 to S14, the rotation angle A2 can be calculated from the following equations.

number

[0036] Given that rotation angles C1 and C2 are known, the displacement in the Z direction of each smelt spout S1...S14 can be calculated from the following equation. When ΔZsi = ΔZ2 + tanC1·Ysi, i = 1...7, (20) When ΔZsi = ΔZ² + tanC²·Ysi and i = 8...14, (21) During the ceremony, ΔZsi is the displacement of the smelt spout Si in the Z direction caused by the rotation of the wall about axis X. Ysi is the distance in the Y direction of the smelt spout Si from the original in world coordinate system 20.

[0037] Therefore, by using these equations, the displacements ΔXSi, ΔYSi, and ΔZSi of each smelt spout S1 to S14 can be calculated in all three coordinate axes X, Y, and Z directions. Thus, in this example, the position and orientation of the corrected base coordinate system 22 (i.e., the work coordinate system) that coincides with the smelt spout Si can be determined in the world coordinate system 20 by adding the respective displacements in each direction (i.e., ΔXSi, ΔYSi, and ΔZSi) to the coordinates of each initial base coordinate system 21 and taking into account the angles of the coordinate axes (angles A1, A2, C1, and C2).

[0038] Therefore, by applying the corrected base coordinate system 22 determined by the method described above, the robots R1…R5 can be controlled to perform the cleaning movement of the smelt spout cleaning tool 13 such that all effects of thermal expansion are compensated for and control uncertainties caused by thermal expansion can be avoided.

[0039] Without a doubt, the method for controlling the maintenance work apparatus according to the present invention may be implemented in several different ways, different from the examples described above. For example, the position of each initial base coordinate system can be selected differently, which also affects the corrected base coordinate system. When different objects are being maintained, the control method may be adapted according to their characteristics. For example, when inspecting a hatch, the initial base coordinate system may be positioned at one of its corners or another suitable position, preferably such that its determination can be reproducibly made using the respective maintenance tool moving device (e.g., a robot) (i.e., including some physical point of discontinuity to which the maintenance tool can be moved by the tool moving device).

[0040] Consequently, the present invention is not limited to the embodiments described above, but can be modified within the scope of the accompanying claims.

Claims

1. A method for controlling a maintenance device (10) of a recovery boiler (11) to perform maintenance work on at least one object to be maintained (S1 to S14) in the recovery boiler (11), wherein the maintenance device (10) comprises a maintenance tool (13) and tool moving devices (R1 to R5) for moving the maintenance tool (13) to accomplish the maintenance work, and the method is a) A method for defining the position of the recovery boiler (11) in a fixed world coordinate system (20), b) A method step of defining the position of the initial base coordinate system (21) of the at least one object to be preserved (S1 to S14) at a selected point of the at least one object to be preserved (S1 to S14) determined in the fixed world coordinate system (20) at the initial temperature of the recovery boiler (11), c) A method step of defining the position of the corrected base coordinate system (22) of the at least one object to be preserved (S1 to S14) at the selected point of the at least one object to be preserved (S1 to S14) determined in the fixed world coordinate system (20) at the transition temperature of the recovery boiler (11), d) A method comprising the step of controlling the tool moving devices (R1 to R5) to perform the maintenance work on the at least one object to be maintained (S1 to S14) within the corrected base coordinate system (22).

2. The method according to claim 1, wherein the position in the corrected base coordinate system (22) is determined by the tool moving devices (R1 to R5) by controlling the tool moving devices (R1 to R5) to move the maintenance tool (13) to the position of the selected point in the at least one maintenance object (S1 to S4) at the transition temperature and by recording the coordinates of the selected point in the fixed world coordinate system (20).

3. The method according to claim 1 or 2, wherein the position of the corrected base coordinate system (22) is determined at least partially by calculating the displacement of the initial base coordinate system (21) caused by thermal expansion of the recovery boiler wall (12) due to temperature transitions.

4. At least the fixed world coordinate system (20) is a three-dimensional Cartesian coordinate system, and the position coordinates of the corrected base coordinate system are calculated using the following equation: X' = ​​X + ΔX Y' = Y + ΔY Z' = Z + ΔZ During the ceremony, The X', Y', and Z' coordinates are the position coordinates of the corrected base coordinate system (22) in the fixed world coordinate system (20). The X, Y, and Z coordinates are the position coordinates of the initial base coordinate system (21) in the fixed world coordinate system (20), The method according to any one of claims 1 to 3, wherein ΔX, ΔY, and ΔZ are positional coordinate displacements of the initial base coordinate system (21) due to thermal expansion in the fixed world coordinate system (20).

5. The method according to claim 4, comprising controlling the maintenance work on at least two objects to be maintained (S1 to S14) arranged adjacent to each other in the recovery boiler (11).

6. The method according to claim 5, wherein the Y-axis indicates a direction along the line between the at least two adjacent objects to be protected (S1 to S14), the X-axis indicates a direction perpendicular to the Y-axis which lies in the same plane as the X-axis, and the Z-axis indicates a direction perpendicular to the plane defined by the X-axis and the Y-axis.

7. The method according to any one of claims 4 to 6, wherein the positional coordinate displacements ΔX, ΔY, and ΔZ include the rotation of the coordinate axes of the initial base coordinate system (21) due to the rotation of the recovery boiler wall (12) caused by the thermal expansion.

8. The rotation angles A and C of the coordinate axes of the initial base coordinate system (21) due to the rotation of the recovery boiler wall (12) caused by the thermal expansion are given by the equation A=arctan(ΔX ２ -ΔX １ ) / (Y ２ -Y １ ( C=arctan(ΔZ2-ΔZ1 / (Y ２ -Y １ ) Determined by, During the ceremony, A is the rotation angle of the Y-axis with respect to the X-axis, C is the rotation angle of the Y-axis with respect to the Z-axis. Y １ This is the first Y position, Y ２ This is the second Y position, ΔX １ is the displacement in the X direction that occurs at the position Y １ and ΔX ２ This is the position Y ２ This is the displacement in the X direction that occurs at, ΔZ １ This is the position Y １ This is the displacement in the Z direction that occurs at, ΔZ ２ This is the position Y ２ The method according to claim 7, wherein the displacement in the Z direction occurs.

9. The method according to any one of claims 5 to 8, wherein for each of the at least two objects to be protected (S1 to S14), one initial base coordinate system (21) and one corrected base coordinate system (22) are determined.

10. The method according to any one of claims 5 to 9, wherein the tool moving devices (R1 to R5) are controlled to perform the maintenance work for each of the at least two objects to be maintained (S1 to S14) within their respective corrected base coordinate systems (22).

11. The method according to any one of claims 1 to 10, wherein the displacement generated in the recovery boiler (11) due to the temperature transition is measured by at least one displacement measuring sensor (M1 to M3) placed in a known position in the recovery boiler (11).

12. The method according to claim 11, wherein the measurement results of at least one displacement measuring sensor (M1 to M3) are used in determining the displacement of the position in the initial base coordinate system (21) in order to determine the position in the corrected base coordinate system (22).

13. The method according to claim 11 or 12, wherein at least two displacement sensors (M1 to M3) placed at at least two different positions are used to determine displacements occurring at at least two different positions in the recovery boiler (11).

14. The method according to claim 13, wherein the rotation of the initial base coordinate system (21) due to the change in displacement at different positions in the recovery boiler (11) is determined based on the measured displacement at at least two different positions.

15. The method according to any one of claims 1 to 14, wherein the maintenance work is at least one of the following: smelt spout cleaning, black liquor gun opening cleaning, or inspection hatch opening cleaning, and the maintenance tool is one of the following tools: smelt spout cleaning tool (13), black liquor gun opening cleaning tool, or inspection hatch opening cleaning tool.

16. A maintenance work device (10) for performing at least one maintenance operation on at least one object to be maintained (S1 to S14) in the recovery boiler wall (12), wherein the device comprises a maintenance tool (13) and tool moving devices (R1 to R5) for moving the maintenance tool (13) to accomplish the maintenance operation, and the maintenance work device (10) comprises a control device for controlling the maintenance work device (10) by the method according to any one of claims 1 to 15.

17. The maintenance work device (10) according to claim 16, wherein the tool moving devices (R1 to R5) are articulated industrial robots.

18. The maintenance work device (10) according to claim 16 or 17, further comprising at least one displacement measuring sensor (M1 to M3) for measuring the displacement generated in the recovery boiler (11).

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