Slag door arrangement and cleaning method

An electric arc furnace, comprising:

• a furnace vessel having a side wall and a slag tunnel extending laterally through the side wall of the furnace vessel, the slag tunnel having a rectangular opening cross section and side walls, an upper outer rim and a bottom,
• a furnace tilting device comprising a cradle on which the furnace vessel is supported, the furnace tilting device being configured to tilt the furnace vessel relative to a horizontal of a foundation on which the electric arc furnace stands, and
• a slag door assembly comprising:
• a slag door having a width that corresponds to a width of the rectangular opening cross-section of the slag tunnel with a first predetermined clearance between the slag door and the side walls of the slag tunnel so that the slag door is movable within the slag tunnel,
• a slag door pivoting device configured to be pivoted about a horizontal pivot axis, and
• a slag door lifter on which the slag door is mounted, the slag door lifter being configured to move the slag door between a lower minimum lifting position and an upper maximum lifting position perpendicular to the horizontal pivot axis,
• wherein:
• the slag door pivoting device is pivotable about the horizontal pivot axis through a range of pivot angles between a first pivot angle that spans from a vertical plane through the horizontal pivot axis toward the furnace vessel and a second pivot angle which is in the vertical plane or spans from the vertical plane through the horizontal pivot axis in a direction away from the furnace vessel, and
• the slag door lifter is mounted on the slag door pivoting device in a manner that a pivoting movement of the slag door about the horizontal pivot axis and a lifting movement of the slag door in the direction perpendicular to the horizontal pivot axis are independent of each other,
• the slag door assembly is attached to the furnace vessel and configured such that, in a horizontal tilt position of the furnace vessel, the vertical plane through the horizontal pivot axis is perpendicular to the horizontal,
• the horizontal pivot axis lies outside the furnace vessel,
• the slag door, in a position of the slag door pivoting device pivoted about the horizontal pivot axis by a third pivot angle corresponding to the first pivot angle minus 0 to 5°, and in a position of the slag door lifter, in which the slag door is moved in the direction of the lower minimum lifting position until the slag door contacts the bottom of the slag tunnel, projects obliquely into the slag tunnel from the outside at the top and faces the side walls of the slag tunnel with the first predetermined clearance therebetween;
• the slag door is plate shaped and extends in a slag door plane;
• the slag door pivoting device is configured to pivot the slag door between the first pivot angle and the second pivot angle,
• a first ray of the first and second pivot angles extends in the vertical plane, and
• a second ray of the first and second pivot angles extends from the horizontal pivot axis parallel to the slag door plane.

A method for cleaning a slag opening of an electric arc furnace comprising a furnace vessel having a side wall, a slag tunnel extending laterally through the side wall of the furnace vessel, the slag tunnel having a rectangular opening cross-section and side walls, an upper outer edge and a bottom, and a slag door assembly comprising:

• a slag door having a width that corresponds to a width of the rectangular opening cross-section of the slag tunnel with a first predetermined clearance between the slag door and the side walls of the slag tunnel so that the slag door is movable within the slag tunnel,
• a slag door pivoting device configured to be pivoted about a horizontal pivot axis, and
• a slag door lifter on which the slag door is mounted, the slag door lifter being configured to move the slag door between a lower minimum lifting position and an upper maximum lifting position perpendicular to the horizontal pivot axis,
• wherein:
• the slag door pivoting device is pivotable about the horizontal pivot axis through a range of pivot angles between a first pivot angle that spans from a vertical plane through the horizontal pivot axis toward the furnace vessel and a second pivot angle which is in the vertical plane or spans from the vertical plane through the horizontal pivot axis in a direction away from the furnace vessel, and
• the slag door lifter is mounted on the slag door pivoting device in a manner that a pivoting movement of the slag door about the horizontal pivot axis and a lifting movement of the slag door in the direction perpendicular to the horizontal pivot axis are independent of each other, and the horizontal pivot axis lies outside the furnace vessel,
• the method comprising:
• a) after a deslagging operation in which the slag door is moved by the slag door lifter to or close to the upper maximum lifting position, moving the slag door pivoting device to a position pivoted about the horizontal pivot axis by a third pivot angle corresponding to the first pivot angle minus 0 to 5°;
• b) moving the slag door using the slag door lifter in the direction of the lower minimum lifting position to a second predetermined clearance between the slag door and the bottom of the slag tunnel so that the slag door projects obliquely into the slag tunnel from the outside at the top and faces its side walls across the first predetermined clearance;
• c) moving the slag door lifter about the horizontal pivot axis in the direction of the second pivot angle to a fourth pivot angle corresponding to the second pivot angle minus 0 to 5°, either while simultaneously moving the slag door using the slag door lifter to maintain at least the second predetermined clearance from the bottom of the slag tunnel so that the slag door is moved parallel to and along the bottom at least at the second predetermined clearance, or in a movement on a circular section with a minimum clearance between the slag door and the bottom of the slag tunnel at a point of closest approach to the bottom of the slag tunnel;
• and
• d) moving the slag door pivoting device about the horizontal pivot axis in the direction of the first pivot angle to a position pivoted by a third pivot angle corresponding to the first pivot angle minus 0 to 5° with the slag door moved toward the upper maximum lift position such that the slag door is thereby moved a distance from the bottom of the slag tunnel greater than the second predetermined clearance or the minimum clearance;
• and
• e) moving the slag door using the slag door lifter in the direction of the lower minimum lifting position until it contacts the bottom of the slag tunnel, so that the slag door projects obliquely into the slag tunnel from the outside at the top and faces its side walls across the first predetermined clearance.

A slag door assembly for a metallurgical furnace that includes a furnace vessel having a slag tunnel with a rectangular opening cross-section extending laterally through the furnace vessel, the slag door assembly comprising:

• a slag door having a width corresponding to a width of the rectangular opening cross-section of the slag tunnel with a first predetermined clearance between the slag door and side walls of the slag tunnel so that the slag door is movable within the slag tunnel,
• a slag door pivoting device configured to be pivoted about a horizontal pivot axis,
• a slag door lifter on which the slag door is mounted, the slag door lifter being configured to move the slag door between a lower minimum lifting position and an upper maximum lifting position that is perpendicular to the horizontal pivot axis, and
• a control device connected to the slag door pivoting device and the slag door lifter and configured to input and store parameters for controlling pivot positions of the slag door pivoting device and lifting positions of the slag door lifter,
• wherein:
• the slag door pivoting device is pivotable about the horizontal pivot axis through a range of pivot angles between a first pivot angle that spans from a vertical plane through the horizontal pivot axis toward the furnace vessel and a second pivot angle which is in the vertical plane or spans from the vertical plane through the horizontal pivot axis in a direction away from the furnace vessel,
• the slag door lifter is mounted on the slag door pivoting device and is configured such that a pivoting movement of the slag door about the horizontal pivot axis and a lifting movement of the slag door in the direction perpendicular to the horizontal pivot axis are independent of each other, and
• the control device is further configured to:
• measure, during movement of the slag door, an applied force directly using transducers and/or indirectly by evaluating parameters of the actuators,
• in response to a determination that a predetermined first limit value of the measured applied force has been reached, stop the movement of the slag door towards the lower minimum lifting position, and
• in response to a determination that a predetermined second limit value of the measured applied force has been reached during movement of the slag door, abort the movement and issue a corresponding message.