Patent GB-767457-A (GB)
Title: Improved method of and plant for pulverising moisture-laden material
IPC: B65G53/06
Filed: 1955-02-04
Abstract: 767,457. Grinding-machines. BABCOCK & WILCOX. Ltd. Feb. 4. 1955 [Feb. 4, 1954], No. 3355/55. Class 59 A method of pulverizing moisture-laden material such as coal consists in passing a fluid carrier medium including superheated steam through a pulverizing zone from which it carries away the pulverized material, separating the medium from the pulverized material, recirculating the medium to the pulverizing zone after heating it to maintain the steam in superheated condition and evacuating excess medium from the circulating system. For producing pulverized coal for use as fuel in the plant shown in Fig. 1, screened coal is fed from a spout 14 by a feeder 11 to a pulverizing unit 10 and the carrier medium is introduced through a duct 12; this medium consists predominantly of steam with a minor proportion of non- condensable gases such as air and carbon dioxide which leak into the system. Upward passage of the medium through the feed spout 14 is prevented by sealing means in the form of high-pressure compressed air admitted into the spout from a manifold 15. The coal pulverized in the unit 10 is entrained in the medium and passes through a duct 13 for tangential discharge into a cyclone separator 16 where the coal is deposited through a sealed valve 24 on to a conveyer 25. The medium leaves the separator through a duct 30 connected through a blower 26 to a tubular heater 32 which discharges the heated medium to the duct 12 and pulverizer. The heater maintains the temperature of the medium above the saturation temperature of the steam and substantially constant despite variations' caused by the varying moisture content of the coal fed thereto; a temperaturesensitive device 46 arranged in the upper part of the pulverizer controls a damper 51 in the outlet duct of the heating fluid of the heater so that, if for example the moisture content of the entering coal is lowered, the device senses an increase in temperature of the medium and adjusts the damper 51 to reduce the heating effect of the heater. The carrier medium is initially introduced into the duct 12 through an inlet 58, but subsequently the supply of the medium is maintained by moisture evaporated from the material being pulverized. Excess carrier medium is withdrawn from the duct 30 by a fan 52 through a valved pipe 53 so as to maintian substantially constant pressure conditions in the system; automatic or manual adjustment may be provided for either the fan 52 or valve 54 in the pipe 53, and the discharged medium is cooled to condense the steam by radiation cooling or water jets. Should the entire system including the medium in the duct 30 be at super-atmospheric pressure, venting of excess fluid may be effected by a pressure relief valve arranged to open when the pressure of the medium exceeds a predetermined value. The plant shown in Fig. 2 is intended for the supply of pulverized coal to a cement kiln 82 and comprises as before, a pulverizer 60, blower 61, coal feeder 62, separator 63, heater 64 and vent fan 65; the blower 61 is, in this case, disposed between the heater and pulverizer and changes in fuel requirements may be met not only by variation of the rate of coal fed but by adjustment of a damper 76 in the duct 75 between the heater and blower. The pulverized coal is discharged from the separator 63 through a spout 70 provided with two counter-weighted valves 66, 67 into a T- connection 91 where it is entrained in the hot air which has been used for heating the heater 64 and then delivered through a pipe 92 and burner 93 into the kiln. The hot air for heating the heater 64 is obtained from the kiln hood 81, being withdrawn by a fan 86 through a dust separator 84 and the heater and then passed to the connection 91. The temperature of the carrier medium leaving the hot air passing from the separator 84 to the heater 64 by means of a proportioning valve 94 arranged to be manually or automatically operated to mix surrounding air with the hot air from the separator. A proportioning valve and flow control valve 95 are also provided in the flow from the heater 64 to the T-connection 91 to regulate the temperature and quantity of air supplied to the latter. Specification 523,753 is referred to.