GB556864A - Improvements in or relating to the control of apparatus for supplying pulverised gas-entrained solid material - Google Patents

Abstract

556,864. Fluid-pressure servomotor-control systems. BAILEY METERS & CONTROLS, Ltd. April 22, 1942, No. 5419. Convention date, April 22, 1941. [Class 135] [Also in Group XXXV] The supply of solid fuel &c. to a pulverizing mill is except for the system shown in Fig. 16 (described later) controlled automatically by diaphragms. 11, 14, Fig. 5, responsive respectively to the pressure difference across an orifice 10 in a conduit supplying air to the mill to entrain the crushed particles and to the pressure difference partly or. wholly across a portion of the path traversed by the gas and entrained material. The diaphragms are differentially coupled to a lever 13 controlled additionally by an adjustable spring 18 opposing the first mentioned pressure difference. The lever may actuate electric contacts 17 controlling a reversible motor adjusting a variable speed gear to vary the rate of feed of material to the mill, a reversible motor 5 varying the speed of the feed motor or a pair of contacts short circuiting a resistance in the field circuit of the feed motor ; or it may operate a fluid pressure valve 25 (see Specification 425,507, [Group XII]), to effect similar control through a fluid pressure relay of the kind disclosed in Specification 461,389 or to adjust a speed controlling resistance by a fluid pressure actuator 49, Fig. 10, or it may operate jointly electric and fluid pressure controls to vary the speed of the feed motor 5 and the ratio of a variable speed transmission gear 4 to obtain an accentuated rate of fuel feed with increase of demand when the invention is applied to a furnace, an additional diaphragm 22, Figs. 5 and 6, or 48, Fig. 10, responsive respectively to the first-mentioned pressure difference or to the pressure in the conduit entering the mill (which is a measure of demand) may be used. These may be coupled directly to the lever 13 to assist the diaphragm 14 or the additional member may operate on a separate spring-controlled lever 21, Fig. 14, which may be arranged so that pressure is not applied to the lever 13 until it reaches a predetermined valve. The movements of the diaphragms 14, 22, 48 may be adjustable. In a system using a differential fluid pressure relay 27, Fig. 5, this additional control may be applied by an auxiliary controller coupled through valve 29 to this relay and the diaphragm 22 may act through a cam 30 or against a variable immersion element 32, Fig. 6, defining its operating law. When the furnace heats a steam generator the auxiliary controller may be a Bourdon tube 50, Fig. 11, subject to the steam pressure, of a differential diaphragm 22, Fig. 14, responsive to steam flow rate or a flow rate meter 58, Fig. 15, with a mercury immersed bell giving a straight line law. The Specification describes a variety of control systems adapted for a ball mill and a bowl mill (not shown) the entraining air being drawn through the furnace, and for the screw 41 feeding pulverized fuel from a hopper; one system is applied to a cement kiln furnace. Fig. 16 shows a system in which flow rate meters 61, 62 each having a straight line law and showing weight rate of flow are differentially coupled by a floating lever to a valve 70 and to a scale 71 reading directly in density of pit-coal stream ; the valve controls through a relay 27 a fluid pressure means 49 as in Fig. 10.