Patent GB-753529-A (GB)
Title: Improvements in or relating to mill installations
Inventor: HOLFORD-STREVENS LAWRENCE ST G
IPC: F23K1/00
Filed: 1953-11-27
Abstract: 753,529. Systems for reducing coal; beater mills. BABCOCK & WILCOX, Ltd. Nov. 23, 1954 [Nov. 27, 1953], No. 32949/53. Class 59. [Also in Group XIII] In a mill installation for providing fuel in pulverized or granular form and arranged to be swept by hot gaseous fluid, means for supplying the gaseous fluid to the mill 1 at a controlled temperature include a mixing duct 11 for the passage of gaseous fluid to the mill, a proportioning damper 31 in a duct 25 which connects a source 26 of hot air to the mixing duct, a duct 12 for the passage from a furnace chamber 15 to the mixing duct 11 of gaseous fluid at a temperature considerably greater than that of the hot air from the source 26, and a second damper 32 in the duct 25 which is adjustable by means of a control unit 34 so as to maintain the pressure in the duct 25a, i.e. between the dampers 31, 32, substantially equal to or greater than that in the furnace chamber adjacent the opening 13, whereby, during operation of the mill, with the damper 31 in a predetermined extreme open position, the gas pressure in the mixing duct 11 at the outlet from the duct 12 equals, or substantially equals, the gas pressure in the furnace chamber, whilst closing movements of the damper 31 result in the flow of gaseous fluid from the furnace chamber to the mixing duct. Coal slurry or relatively dry coal or a mixture of the two is supplied to the mill through an inlet 9. The mill is of the type in which a rotor mounted on a motor-driven horizontal shaft located in the lower part 2 of the mill carries several circumferential rows of beater arms and is surrounded by a fixed armour-plate casing. Gas is drawn through the mill by a fan 3 disposed in an outlet pipe 4, and the coarser of the particles entrained by the gas are separated in a classifier disposed in the upper part 5 of the mill and returned to the grinding zone. A damper 41 is provided in a duct 40 to control the flow of cold air into the duct 11. The dampers 31, 41 are adjusted by means of a control unit 43 responsive to the temperature of the gaseous fluid at the outlet from the mill so as to regulate that temperature, the damper 41 being arranged to remain closed until the damper 31 has reached its extreme open position. A damper 16 is provided in the mixing duct 11 and is adjusted by a control unit 18 which is responsive to a pressure drop across an orifice 20 in the outlet pipe 4 so that the damper maintains the mass rate of flow of gaseous fluid through the mill at a predetermined value. The control unit 43 is arranged to actuate visible and audible alarm signals upon the gas temperature at the outlet of the mill reaching a predetermined high value, and to cause movement of a damper 50, to block the entrance from the furnace chamber to the duct 12, and to stop the electric motors driving the fan 3, the means feeding fuel to the mill and the rotor of the mill upon the gas temperature at the mill outlet reaching a second and higher predetermined value. The furnace chamber is adapted to operate at a sub-atmospheric pressure of the order of 0À25 inches water gauge and the source 26 to supply hot air at a pressure of the order of five inches water gauge. Specifications 425,507, [Group XII] 528,735 and 626,223 [both Group XXIX] are referred to.