Apparatus for continuous gravimetric metering of pourable material

1. An apparatus ( 1 ) for continuous gravimetric metering of pourable material, comprising:

a housing ( 2 ) comprising a first and a second mutually spaced wall ( 5 , 6 ), a charging port ( 7 ) through said first wall ( 5 ), a discharging port ( 8 ) through one of said walls displaced from said charging port ( 7 ) and at essentially same radius as said charging port ( 7 ) with respect to a predetermined vertical axis, a primary air port ( 10 ) through the other of said walls ( 6 ) and opposite to said discharging port ( 8 ), said primary air port ( 10 ) having a primary outlet opening ( 9 ) and being connected to a compressed air supply;

a rotor ( 3 ) mounted in and sealed to said housing ( 2 ) for rotation about said predetermined vertical axis including a plurality of pockets ( 13 ) extending therethrough at spaced locations separated by a rotor partition wall ( 14 ) having a thickness (t), said pockets ( 13 ) having a pocket opening front edge ( 38 ) as seen in the rotational direction of the rotor ( 3 ) and said pockets ( 13 ) forming a first ring ( 32 ) of pockets along the same radius as said charging and discharging ports ( 7 , 8 ), a circular measuring path (MP) being defined between the charging port ( 7 ) and the discharging port ( 8 ), the pockets ( 13 ) receiving material via the charging port ( 7 ) and material being emitted through said discharging port ( 8 ) during the rotation of the rotor ( 3 );

a drive motor ( 23 ) configured for rotating said rotor ( 3 ) in a rotational direction;

a control unit configured for speed indication and controlling the rotational speed of said rotor ( 3 );

a load cell ( 22 ) configured for measuring the weight of the material travelling along the measuring path (MP); and

a secondary air port ( 12 ) provided in the other of said walls ( 6 ), the secondary air port ( 12 ) having one or more secondary outlet openings including a first secondary outlet opening ( 11 ) and being connected to a compressed air supply, the secondary outlet opening(s) ( 11 ) of the secondary air port ( 12 ) having a secondary outlet opening front edge ( 36 ) and a total outlet area being substantially smaller than that of the primary outlet opening ( 9 );

wherein the improvement comprises:

the first secondary outlet opening ( 11 ) being displaced from the primary outlet opening ( 9 ) of the primary air port ( 10 ) in opposite direction to the rotational direction of the rotor ( 3 ) and being arranged opposite to said discharging port ( 8 );

wherein on rotation of the rotor ( 3 ), when the pockets ( 13 ) pass the first secondary outlet opening ( 11 ), a smaller first portion of material in the pockets ( 13 ) is discharged into the discharging port ( 8 ) by a smaller first amount of compressed air emitted through the first secondary outlet opening ( 11 ); and

wherein on rotation of the rotor ( 3 ), when the pockets ( 13 ) pass the primary outlet opening ( 9 ), a larger second amount of the material in said pockets ( 13 ) is discharged into the discharging port ( 8 ) by a larger second amount of compressed air emitted through the primary outlet opening ( 9 ).

2. The apparatus ( 1 ) according to claim 1 , wherein the total outlet area of the first secondary outlet opening ( 11 ) is 0.1% to 25% of the outlet area of the primary outlet opening ( 9 ).

3. The apparatus ( 1 ) according to claim 1 , wherein the front edge ( 36 ) of the first secondary outlet opening ( 11 ) is displaced at least a rotational angle X min of the rotor from the primary outlet opening ( 9 ), X min being defined as ¼ or ⅓×(360°/number of pockets in a pocket ring).

4. The apparatus ( 1 ) according to claim 1 , wherein the first secondary outlet opening ( 11 ) is displaced less than an angle of rotation X max of the rotor from the primary outlet opening ( 9 ), X max being defined as 5×(360°/number of pockets in a pocket ring).

5. The apparatus ( 1 ) according to claim 1 , wherein the displacement of the first secondary outlet opening ( 11 ) in respect to the primary outlet opening ( 9 ) and the thickness (t) of the rotor partition walls ( 14 ) are dimensioned so that when the first secondary outlet opening ( 11 ) is completely covered by one of the partition walls ( 14 ), the pocket opening front edge ( 38 ) of a pocket opening ( 37 ) is within the primary outlet opening ( 9 ) as seen in a vertical projection.

6. The apparatus ( 1 ) according to claim 1 , wherein the first secondary outlet opening ( 11 ) of the secondary air port ( 12 ) is oblong and extends towards the primary outlet opening ( 9 ) of the primary port ( 10 ).

7. The apparatus ( 1 ) according to claim 1 , wherein the primary air port ( 10 ) and the secondary air port ( 12 ) are configured as a single air port being provided with two separate and mutually spaced outlet openings in the form of the primary outlet opening ( 9 ) and the first secondary outlet opening ( 11 ).

8. The apparatus ( 1 ) according to claim 1 , wherein the primary air port ( 10 ) and the secondary air port ( 12 ) are separate air ports optionally separated by a common port partition wall ( 31 ).

9. The apparatus ( 1 ) according to claim 1 , wherein the first wall ( 5 ) is an upper wall and the second wall ( 6 ) is a lower wall.

10. The apparatus ( 1 ) according to claim 1 , wherein the discharging port ( 8 ) is provided in the first wall ( 5 ).

11. The apparatus according to claim 1 , wherein the pourable material comprises a fuel material.

12. The apparatus according to claim 11 , wherein the fuel material comprises coal.

13. The apparatus according to claim 2 , wherein the total outlet area of the secondary outlet opening ( 11 ) is 1% to 10% of the outlet area of the primary outlet opening ( 9 ).

14. The apparatus according to claim 13 , wherein the total outlet area of the secondary outlet opening ( 11 ) is 3% to 5% of the outlet area of the primary outlet opening ( 9 ).

15. The apparatus according to claim 8 , wherein the primary air port ( 10 ) and the secondary air port ( 12 ) are separate air ports formed by separate tubes or hoses.