DEVICE AND METHOD FOR CONTROLLING THE FUEL-AIR RATIO IN THE COMBUSTION OF GROUND COAL IN A FIRING SYSTEM OF A COAL-FIRED POWER STATION

摘要

The invention relates to a device and to a method for controlling the fuel-air ratio in the combustion of ground coal in a firing system of a coal-fired power station, which comprises means for pneumatically conveying the ground coal to the burners (16) of the firing system of a coal-fired power station and means for supplying air for combustion to the burners (16) or into the furnace (15) of the firing system of a coal-fired power station, and in which the quantity of air for combustion and the quantity of carrier air are controlled. The aim of the invention is high reliability of the control of the fuel-air ratio, wherein the measurement of the quantity of air for combustion and the measurement of the quantity of carrier air are carried out according to the correlation measurement method by evaluating electrical signals obtained by means of sensors (11) arranged in the air stream. According to the invention, said aim is achieved by a measuring device for measuring the quantity of air, said device comprising a correlation measurement device (12) that evaluates signals generated by electrostatic induction on two sensors (11) arranged one after the other in the air stream,in the air flow direction (s). An electrode (10) having an electrode contour, which has an average radius (rm) with 0.1 mm = rm = 1.2 mm, is arranged in the flow direction (s) of the air in front of the sensors (11) at a distance (I) that is larger than 1 x the inner width of the flow cross-section of the conduit conveying the air and smaller than 10 x the inner width of the flow cross-section of the conduit conveying the air in the region of the sensors (11) in the flow cross-section of the conduit conveying the air. The counter-electrode (13, 25), which acts electrically with respect to the electrode (10), is arranged in the flow direction (s) of the air between the electrode (10) and the sensors (11), and the electrode (10) and the counter-electrode (13, 25) are connected to the poles of a high voltage source (9) having a voltage (U) of 12 kV = U = 20 kV. The electrode (10) and the counter-electrode (13, 25) are connected to the high voltage source (9) in particular only during the starting phase of the firing system of a coal-fired power station or at air flow rates < 10 m/s or for checking purposes.