Patent GB-826514-A (GB)
Title: Apparatus for automatically distributing the air blast to blast furnaces
IPC: C21B7/16
Filed: 1957-03-22
Abstract: 826,514. Fluid-pressure servomotor control systems. UNITED STATES STEEL CORPORATION. March 22, 1957 [April 3, 1956], No. 9554/57. Class 135. Each tuyere of a blast furnace is supplied with air through a hot-blast main 2, bustle pipe 4 and individual lines 6, each embodying a Venturi 12; each line 6 includes a valve 10 controlled by the piston in a cylinder 14 and each valve 10 has a cable 18 attached thereto which is fixed to a counterweight 22, the cable passing over and being connected to a pulley 20 that carries a cam 24 which through a rod 30 actuates a relay 32. The latter produces an hydraulic pressure in a line 38 that is proportional to the position of the valve; line 38 is connected to pressure switches 40, 42. Pipes 44, 46 lead from the high- and low-pressure sides of each Venturi 12 to the opposite sides of one diaphragm 48 of an Askania regulator 50 whilst a second diaphragm 52 is actuated by pressure from an orifice plate 54 in a line 90, tapped from the main 2, in which line is a valve 92 with a bypass 94. The line 90 may be connected to a source of clean air. A pivoted oil jet 58 which is coupled to the diaphragms 48, 52 co-operates with lines 68, 66, the latter being provided with a solenoid-operated shut-off valve 70, and a twin-solenoid-actuated three-way valve 76 to control air flow to these lines which are connected to opposite ends of the cylinder 14; the solenoids are in circuit with a manual switch 88. The regulator also includes a limit switch 82 having a cam 84 and contacts 82c. The valve 92 is operated by an electric motor 96 having a switch 98 that is actuated at any selected frequency by an electric timing motor 102 to produce an intermittent operation of motor 96; the latter also has a speed control 104 adjusted by a reversible electric motor 106 provided with a control 108 incorporating a pressure-responsive element 109 in the pipe 4 or main 2 that is set to function at a given pressure. When the pressure is below the given value the motor 106 sets the speed control 104 to the slow position; when the pressure is above the given value the control 104 is set to the fast position. Another switch 120 controlled by a pressure element 122 stops the motor 96 should the pressure in the pipe 4 drop below a given minimum value. A further pressure element 128 is connected to a control 126 so that in the event of the pressure in pipe 4 exceeding a specific value, the valves 70 and 76 will be actuated and various alarms comprising bells 134, hooter 148 and lights 144 will be energized. Each switch 40 is set so that its contacts 40c are closed so long as the associated valve 10 is at least 50% open and each switch 42 is arranged with its contacts open until the associated valve 10 is more than 80% open. If the flow in one of the lines 6 decreases the jet 58 is moved to produce an air flow in line 68 and open the related valve 10 until the pressure differential in pipes 44, 46 again equals that in the other lines 6. An obstruction in one of the lines 6 will cause the corresponding valve 10 to open more than 80% thus closing contacts 42c so energizing a coil 122 and the motor 96 thereby closing the valve 92; concomitant energization of a coil 112 prevents movement of the control 104 to the fast position. The jet 58 is hence moved to cause an air flow in line 66 to close all the valves 10 except the one in the obstructed line 6 so that most of the air will then flow therethrough and clear the obstruction whereupon the increased flow causes the jet 58 to produce a flow in line 66 to close the valve 10 to the same position as the others; when it closes more than 50% contacts 40c will open and energize motor 96 to open valve 92 so that all the jets 58 moved leftwards to open the valves 10, which when they reach the control range, close contacts 40c and stop the motor 96. Upon complete opening of one valve 10 the associated pressure switch 138 energizes a green warning light 144. Upon complete closure of one valve 10 pressure switch 142 energizes a red warning light 146. In the event of a high-pressure condition in pipe 4 the control 126 both closes valves 70, to prevent the regulator 50 from operating automatically and valves 76 to permit air flow from a supply line 74 to line 68 and hence bring about opening of all the valves 10. When the furnace air is cut off the switch 120 ensures that the valves 10 do not completely close.