Device designed for collecting solid debris in an electrolysis cell for the production of aluminium

Abstract

Bucket shovel type collection unit, used in an aluminum production cell, comprising: a) a means of fixing onto a mobile support; b) a connection actuated by a first actuator moving in relation to said mobile support in the vertical direction; c) a frame interdependent of said connection; d) at least one articulated bucket, swiveling around an axis assembled on said frame, having a blade and swiveling around said substantially horizontal axis. Said first actuator is connected to a programmable control system able to determine the altitude of said axis and the difference in altitude between said blade and said axis, define the vertical movement to be imposed on said collection unit, and define and transmit to said first actuator the appropriate control flow to impose said vertical movement. The control flow may be control current transmitted by a variable speed transmission to an electrical motor or an oil flow feeding the chamber of a hydraulic actuating cylinder, controlled by a servo-distributor.

1 . A collection unit designed to collect solid debris and mud in liquid media of a cell for producing aluminum, comprising:
 a) a means of fixing to fix said collection unit onto a mobile support able to move said collection unit above a zone to be cleaned;   b) a connection actuated by a first actuator which causes said connection to move in relation to said mobile support in a vertical direction;   c) a frame interdependent of said connection;   d) at least one articulated bucket, swiveling around a substantially horizontal axis, fitted to said frame, with a substantially horizontal blade, said bucket being actuated by a second actuator, interdependent with said frame, causing said bucket to adopt a rotary movement around said substantially horizontal axis,   
       characterized in that said first actuator is connected to a programmable control system able to:
 i) determine, directly or indirectly, the altitude of said substantially horizontal axis and a difference in altitude between said blade of said bucket and said substantially horizontal axis; 
 ii) define, from the altitude and the difference in altitude determined in i), a vertical movement which must be applied to said connection so that an altitude of said blade remains at least equal to a predetermined value; 
 iii) define and transmit to said first actuator a suitable control flow, so that the first actuator can apply said vertical movement to said connection. 
 
     
     
         2 . Collection unit according to  claim 1 , characterized in that said programmable control system includes:
 a) an instrumentation and control unit which is configured to acquire data relating to said altitude of said substantially horizontal axis and said difference in altitude between the bucket blade and the substantially horizontal axis, deduce from the data a set point to be imposed on the altitude of said substantially horizontal axis so that the altitude of the blade is at least equal to a predetermined value, which makes it possible to avoid any risk of contact between said blade and an obstacle located below said collection unit, and emits a signal representative of said set point;   b) a converter that is configured to translate said signal into a control flow and transmit said control flow to said first actuator.   
     
     
         3 . Collection unit according to  claim 1  or  2 , characterized in that said programmable control system is connected to a first sensor making it possible to measure the vertical movement of said connection in relation to a reference level and to a second sensor making it possible to directly or indirectly measure the difference in altitude between said blade of said bucket and said substantially horizontal axis. 
     
     
         4 . Collection unit according to  claim 3 , characterized in that said second actuator is a jack imposing a rotation on said bucket via a rod, and in that said second sensor is an incremental position sensor measuring movement of the rod of said jack in relation to the body of said jack. 
     
     
         5 . Collection unit according to  claim 3 , in which said instrumentation and control unit is an Programmable Logic Controller (or PLC) which is configured to:
 a) acquire the data provided by said first sensor and said second sensor at regular time intervals;   b) deduce from the data, using a computer program based on a kinematic model describing the trajectory of the blade in an appropriate reference frame, the value of the set point which it is necessary to impose on the altitude of the bucket's pivotal axis, and   c) transmit to said converter a signal representing said set point.   
     
     
         6 . Collection unit according to  claim 5 , in which said computer program implemented in said programmable controller is based on a kinematic model describing a trajectory of the blade which is deduced from the theoretical profile of the tank bottom by translation along a vector oriented vertically upwards, the intensity of which corresponds to a preset safety distance. 
     
     
         7 . Collection unit according to  claim 1 , characterized in that the collection unit includes a frame and two buckets assembled on said frame, laid out symmetrically in relation to a substantially vertical plane and articulated, swiveling around two substantially horizontal axes, each bucket having a blade opposite the blade of the other bucket, the second actuator, interdependent of said frame, imposing on each of said buckets a substantially symmetrical rotation movement in relation to said substantially vertical plane, so that the solid debris located between the two buckets is trapped by said buckets. 
     
     
         8 . Collection unit according to  claim 1 , characterized in that said second actuator is a hydraulic actuating cylinder fed by a circuit which has at least two operating configurations for closing the buckets:
 a) a first configuration, in which sufficient force is transmitted to the buckets to make it possible to entrain the solid debris encountered by the buckets,   b) a second configuration, corresponding to a differential assembly, in which sufficient kinetic energy is transmitted to the buckets for the slamming function to be carried out.   
     
     
         9 . Collection unit according to  claim 2 , characterized in that said first actuator includes an electrical motor interdependent with said mobile support, a connection interdependent with said collection unit and coupled to said motor so that rotation of said electrical motor causes the movement of said collection unit via said connection, in that said converter is a variable speed transmission which transmits to said electrical motor a control current, whose characteristics allow the electric motor to impose said vertical movement via said connection. 
     
     
         10 . Collection unit according to  claim 9 , in which said electric motor is the motor of an electromechanical jack and in which said connection is a rod of said electromechanical jack. 
     
     
         11 . Collection unit according to  claim 9 , in which said electric motor is the motor of an electric winch and in which said connection is a cable of said winch. 
     
     
         12 . Collection unit according to  claim 2 , in which said first actuator includes a hydraulic actuating cylinder including a body interdependent with said mobile support, said connection being a rod of said hydraulic actuating cylinder, and in which said converter is a distributor mounted on a portion of the hydraulic circuit which supplies a chamber on a rod side of said hydraulic actuating cylinder with a controlled flow. 
     
     
         13 . Collection unit according to  claim 12  in which said distributor is an electro-hydraulic servo-distributor with controlled flow to control a volume of oil inside the chamber on the rod side. 
     
     
         14 . Collection unit according to  claim 12 , in which said distributor is controlled by a Programmable Logic Controller which is configured to acquire, at regular time intervals, altitude H of the swiveling axis of the bucket and value L of the movement of the piston rod of the second actuator, deduce from these values, using a related computing memory, the set point which it is necessary to impose on the altitude of the pivotal axis of the bucket and inject a signal to said distributor in order to decrease or increase the volume of oil which feeds the chamber on the rod side and which is necessary to reach the right altitude. 
     
     
         15 . Collection unit according to  claim 12 , in which said hydraulic actuating cylinder is a double-acting jack, the rod of which is interdependent with said collection unit, with the chamber on the rod side able to constantly impose on said rod a vertical movement upwards and a chamber on the piston side able to constantly impose on said rod a vertical movement downwards, it being possible to connect the two chambers, via at least one distributor, to a source of pressure or a tank, the feeding circuit including several portions of circuits which make it possible to provide the following hydraulic feed configurations:
 a) a differential configuration, where the chamber on the rod side and the chamber on the piston side are connected to the pressure source, allowing the mast to descend at high speed;   b) a configuration corresponding to rest position, the collection unit remaining suspended, and the circuit arranged so that said collection unit can move vertically without effort should said collection unit encounter an obstacle;   c) a configuration in which the chamber on the rod side is connected to the pressure source, corresponding to the upward movement of the collection unit;   d) a configuration under controlled operation, in which the portion of circuit feeding the chamber on the rod side includes a distributor with controlled flow and controlled by a programmable control system including an instrumentation and control unit which is configured to acquire the data relating to the altitude of said substantially horizontal axis and the difference in altitude between the bucket blade and the substantially horizontal axis, deduce from these data the set point which it is necessary to impose on the altitude of said substantially horizontal axis and emit a signal representative of said set point to said distributor.   
     
     
         16 . Pot tending module designed to be used in a plant for the production of aluminum by igneous electrolysis and comprising a carriage and handling and servicing devices, characterized in that it also includes a collection unit according to  claim 1 . 
     
     
         17 . Pot tending assembly for a plant producing aluminum by igneous electrolysis including an overhead travelling crane characterized in that it includes also at least one pot tending module according to  claim 16 . 
     
     
         18 . Use of a pot tending module according to  claim 16  for work on electrolysis cells designed for the production of aluminum by igneous electrolysis, in which said first actuator is controlled by said programmable control system so that said substantially horizontal axis follows a pre-defined trajectory. 
     
     
         19 . Process for cleaning an anode hole during anode replacement, in which a collection unit according to  claim 1  is used, said first actuator being assembled interdependently with a pot tending machine; the method comprising:
 a. using the first and second actuators, said collection unit is brought in closed position, in line with said anode hole, said first actuator being at rest; 
 b. said first actuator is actuated to descend quickly as far as a predetermined altitude, higher than a level of a bath located in the tank, in order to authorize opening of the collection unit; 
 c. said second actuator is actuated so that it opens the buckets until said buckets reach a reference open position, typically close to the maximum opening permitted by the travel of the second actuator; 
 d. said first actuator is actuated in “slow” descent mode as far as a preset altitude; 
 e. from the altitude reached at the end of the previous stage, a height at which said blade must be is defined, taking a safety distance into account, and a trajectory that said blade must follow between said open reference position and the closed position is deduced; 
 f. said first actuator is actuated to raise said collection unit up to a point origin of the trajectory defined in the previous stage; 
 g. said second actuator is actuated, said first actuator being in controlled mode so that the blade follows the trajectory defined in e); 
 h. once the collection unit is closed, the first actuator is actuated in raise mode; then when the collection unit has reached a certain altitude, the first and second actuators are used to move the unit towards a zone which receives the collected debris.