Patent GB-876431-A (GB)
Title: Apparatus for controlling the flow of hot blast to the tuyeres of blast furnaces
IPC: G05D11/035
Filed: 1959-05-28
Abstract: 876,431. Fluid-pressure servomotor control systems. HAGAN CHEMICALS & CONTROLS Inc. May 28, 1959 [June 26, 1958], No. 18256/59. Class 135. Each tuyere pipe 15, 16, 17, 18n, &c., Fig. 1, of a blast furnace has a flow control valve 15b actuated by a servomotor 135 under the control of a flow regulator 15d subject to the pressure difference across an orifice plate 15a and adjusted to modifv the controlled flow rate in response to a pressure signal fed simultaneously to all of the flow regulators and generated in response to a measure of total flow available from a bustle pipe 10, e.g. bustle pipe pressure, by a regulator 20 the ratio between the signal pressure of which and the bustle pipe pressure is adjustable by the output from a ratio totalizer 21 the input 30 to which is obtained from a cascaded series of totalizers 15e, 16e, 17e, 18en. The system is such that a selected flow control valve, say 15b, is arranged to be fully open and the other valves are adjusted to maintain the flows in their respective tuyere pipes equal to the flow in the pipe 15. So long as the signal transmitted from the regulator 15d to the servomotor 135 is such as to maintain the valve 15b fully open the signal pressure, which is also fed to the totalizer 15e, is insufficient to cause that totalizer to transmit a signal to the other totalizers. Should, however, the flow in the tuyere pipe increase whereby the regulator 15d transmits a higher signal pressure to cause partial closure of the valve 15b the totalizer 15e transmits a pressure to the next totalizer 16e, the outlet pressure of which is dependent upon the setting of the valve 16b in the tuyere pipe 16. Due to the cascade arrangement of the totalizers an output pressure is delivered to a diaphragm 239 of the ratio totalizer causing motion of a beam 220 to operate valves 231, 232 to increase the pressure in a conduit 31 leading to the ratio regulator 20 whereby the ratio between the bustle pipe pressure and the signal fed to the regulators 15d &c. is modified. The diaphragm 239 of the ratio totalizer is adjustably loaded by a spring 242, a second diaphragm may be subject to a modifying signal, and another diaphragm 225 is connected to the conduit 31 through a restriction 253 and capacity 254 for automatic reset and rate action. The conduit 31 is connected to a diaphragm chamber 209, Fig. 5, the diaphragm 206 of which modifies the effect of a feedback connection 193, 196, 198, 201, &c., between a diaphragm 188 subject to the outlet or signal pressure of the regulator 20 and a lever 177 connecting a diaphragm 165 with a control valve 166. The diaphragm 165 is responsive to the difference between bustle pipe pressure and tuyere pipe, i.e. atmospheric, pressure and the feedback connection includes a cam 195 for extracting the square root so that the signal pressure, which is delivered through a conduit 114 connected to each regulator 15d &c. is proportional to the total flow from the bustle pipe. Each regulator 15d comprises a diaphragm 85, Fig. 3, subject to the pressure difference across the corresponding tuyere pipe orifice plate 15a &c. and actuating a valve 94 which determines the signal pressure transmitted through a conduit 118 to the corresponding servomotor 135. The diaphragm 85 is acted upon, through a lever 102 &c. by a biasing force developed by a diaphragm 109 which is subject to the signal pressure in the conduit 114. The pressure in the conduit 118 is also fed to a stabilizer consisting of a spring-loaded bellows 124 having a leaky hydraulic link with a piston 128 connected by a spring 120 to the diaphragm 85. The servomotor 135 comprises a piston and cylinder controlled by a relay valve actuated by a spring-loaded diaphragm subject to the pressure in the conduit 118 and a follow-up connection between the piston and the loading-spring of the diaphragm.