GB871083A - Arrangement for the automatic regulation of turbo-compressors - Google Patents

Abstract

871,083. Fluid-pressure servomotor control systems. BROWN, BOVERI & CIE A.G. Dec. 16, 1957 [Dec. 14, 1956], No. 39070/57. Class 135. [Also in Group XXVI] In the automatic regulation of an axial-flow compressor for constant delivery pressure or flow, the regulation is divided into three ranges: a first range in which the regulation is done solely by a change of speed or in power supply to the driving machine; a second range in which the speed is approximately constant and guide blades or rotor blades are adjusted; and a third range in which instability is avoided by blowing off fluid while the blades remain at minimum opening and the speed remains constant. A compressor 2, Fig. 6, supplies blast air to three steel converters in a steel works. The pressure required by each converter is set by a corresponding hand valve H 1 , H 2 or H 3 downstream of a corresponding orifice O 1 , O 2 or O 3 connected to a source of constant air pressure p Hi , non- return valves R 1 , R 2 , R 3 ensuring that the highest pressure p Es of the three pressures prevails in piping leading to a bellows 12 and to one side of a diaphragm 3. The other side of diaphragm 3 is exposed to the compressor discharge p E . The diaphragm 3 actuates a valve to control the oil pressure p d developed downstream of an oil pump 30 and orifice O 4 , this pressure being used to actuate a blow-off valve 6 and variable compressor guide blading 8. A valve 13a actuated by a piston 13 exposed to the pressure p d controls an oil pressure p z so that p z varies in the reverse sense to P d . A differential piston exposed to the pressure p z and also to an oil pressure p nsg controlled by a valve actuated by bellows 12 actuates a sleeve 11 which co-operates with a valve member actuated by a centrifugal governor 10 to control an oil pressure p F which actuates the steam inlet valve 4 of turbine 1. During the first regulation range, pressure P d rises from 0 to 1.5 atmosphere and pressure p z falls from 5 to 0 atmosphere, and valve 4 decreases the supply of steam to turbine 1. During the second range, pressure p d further increases to 3 atmosphere, and the guide blades 8 are moved into the position of minimum opening. During the third range, P d further increases to 4.5 atmosphere, and blow-off valve 6 opens to increase the flow through the compressor 2 to avoid surging. A slight increase of speed occurs during the second range because of the reduction in air consumption and has the beneficial effect of reducing the tendency towards surging. The speed may be increased still further for this purpose by the provision of a further valve controlled by piston 13 and connected in series with valve 13a but acting in the opposite sense thereto, thereby causing pressure p z to increase during part of the second range. Alternatively, a separate piston-actuated valve, controlled by the oil pressure P d , may act on the pressure p z or p nsg for this purpose. The hydraulic system may be replaced wholly or partly by a pneumatic or electrical system, and the turbine 1 may be replaced by an electric motor. Fig. 9 shows an embodiment in which the regulation is in accordance with either delivery pressure or delivery flow. With valve 16b closed and valve 16a open, an oil pressure p ns is controlled in accordance with the delivery pressure p E by means of a valve actuated by bellows 3. The regulation of the plant is then in accordance with delivery pressure, the required value being set by means of a hand wheel 3a which adjusts the spring of the bellows 3. The bellows 3 may control the oil pressure P F directly instead of indirectly by way of sleeve 11. With valve 16a closed and valve 16b open, the pressure p ns is controlled by a valve actuated by a diaphragm 15 acted on by the pressure drop across a flowmeasuring nozzle 14. The regulation of the plant is then in accordance with delivery volume, the required value being set by a hand valve 16c. In either case, the pressure p ns determines the position of sleeve 11. The oil pressure P d for actuating the blow-off valve 6 and blades 8 is controlled by a valve actuated by a piston 19 which is subjected on one side to the delivery pressure p E and on the other side to an oil pressure P nist varying approximately quadratically with the speed and developed by a centrifugal pump 17. The regulation is divided into three ranges as in the previous embodiment. In a further embodiment, Fig. 6b (not shown), the regulation is in accordance with delivery flow, a flow-measuring nozzle 14 and a diaphragm being used as in Fig. 9, but in other respects the arrangement is as shown in Fig. 6.