GB577507A - Improvements in or relating to pulverising plant - Google Patents

Abstract

577.507. Furnace control apparatus. BABCOCK & WILCOX, Ltd. May 18, 1944, No. 9546. Convention date, May 22, 1943. [Class 51 (i)] [Also in Groups II, XXXV and XXXVII] In a pulverizing plant for supplying finely divided solid fuel or other material for transport by suspension in a current of air to a number of burners or other points of use, the excess is returned through a conduit to the pulveriser which is fed with the solid at a rate which is automatically controlled in accordance with the rate of flow of air to the pulverizer, the rate through the pulverizer, and the rate through the return conduit. As shown, the pulverizer 10 is fed with solid by a feeder 12 driven by a multi-speed motor 16, and with air by a pipe 18 the air current, with suspended solid, being extracted by a fan 26 and fed to a number of burners 46, the excess being returned by a conduit 52. The control of the feed motor is effected from a spring-influenced lever 102, a flexible extension 106 of which selectively engages contacts 140, 142, or 144, 146. The lever is engaged by a pin 114 carried by a diaphragm 90 subjected on opposite sides to the pressures at the entrance to and exit from the pulverizer by means of tube connections 86, 88. The. lever is also engaged by a pin 108 carried by a diaphragm 82 subjected to the pressure difference on opposite sides of a constriction 76 in the air conduit 18, through connections 78, 80. The pin 108 is also engaged by a spring-influenced lever 110 engaged by a pin 116 on a diaphragm 98 subjected to the pressure difference between widely spaced points in the return conduit 52 by means of tubes 94, 96. The A.C. three-phase supply is transformed down by a transformer 128 for the control circuits, the secondary terminal 130 being connected to a selector switch 138 connected by a lead 148 to the arm 106. The upper contacts 142, 140 are connected, the latter through a relay switch 156, to a relay 152 connected in turn to the transformer terminal 132. A second contact 166 of the selector switch 138 is connected to a relay switch 170 the other side of which is connectedthrough a relay switch 172 to a contactor coil 174, and through a relay switch 176 to a second contactor coil 178. The other terminals of the contactor coils are connected to the terminal 132 by a common return 158. The lower contacts 144, 146 are connected to a relay coil 160, the latter through a relay switch 164. The contactors 180, 182 are threepole switches for the motor 16, three wire connections 184, 186 leading to the high and low speed windings respectively. With the selector switch 138 set for automatic operation the motor will operate at low speed as long as the contact 106 is held clear, the coil 178 being energized to close the contactor switch 182 through the control circuit 130, 134, 136, 166, closed relay switches 170, 176 and return 158. Counter-clockwise movement of the lever 102 to the contacts 140 and 142 in succession operates the normally open relay switches 156, 172, and normally closed switch 176 and the motor runs at high speed, the control circuit being lead 134, switch arm 136, contact 150, lead 148, contacts 106, 142, lead 154, coil 152 and return 158. Closure of the switch 156 effects a maintaining circuit for the coil 152 through the contact 140. The motor will continue to run at high speed as long as the contact 106 remains in engagement with the contact 140. Clockwise movement of the lever 102 results in similar successive engagement with the contacts 144, 146 and the power supply to the motor is cut off. Additional contacts 188, 190 on the selector switch are for manual control.