Patent GB-428573-A (GB)
Title: Improvements in and relating to coal dust mills and the like
IPC: F23K1/00
Filed: 1934-08-08
Abstract: 428,573. Impact pulverizers. AKT.-GES. BROWN, BOVERI, & CIE, Baden, Switzerland. Aug. 8, 1934, No. 22994. Convention date, Aug. 8, 1933. [Class 59] In a plant for the comminution and utilization of minerals, more particularly coal, the energy required for comminuting the coal is obtained indirectly or directly by the expansion of combustion products from an air and fuel mixture, and the whole or almost the whole of the remaining heat content of this air and fuel mixture is utilized for giving off heat in the same plant. As shown applied to a jet pulverizer 1, Fig. 1, a compressor 11 supplies compressed air to the nozzle 2 and the coal is projected onto an impact plate 4, the fines being discharged through a pipe 6 to the burner 6 of a boiler 7. The greater part of the combustion air is supplied by blower 8 driven by motor 9 and part may be diverted through pipe 10 to convey the dust to the burner. The compressor 11 is driven by a gas turbine 12, the exhaust gases in pipe 13 being led to the combustion chamber or boiler flues. The gas turbine may receive compressed air from the compressor 11 through pipe 14 and coal dust from the mill through pipe 15. With pressure firing the gas turbine takes its supply from the combustion chamber and exhausts through the superheater or preheater of the boiler. In Fig. 2 the gaseous pressure for projecting the coal onto the impact plate is developed in a combustion chamber 18 fed with compressed air and dust from compressor 19 driven by gas turbine or electric motor 20. With a pressure fired boiler a gas turbine 21 drives the charging compressor 22 which may be coupled to an electric motor 23 for starting and regulating purposes. The compressor 19 is charged from the compressor 22 and it may be coupled with it or form part of it. The compressed gases for the mill may be taken from the combustion chamber or the exhaust of a gas turbine such as 20. If the plant consists of a gas turbine instead of a steam generator then the working medium for the mill may be taken from the gas turbine. In Fig. 3 the combustion chamber 18 is supplied with compressed air through pipe 25 and with fuel such as coal dust, gas or liquid fuel from pipe 26, the mixture being ignited by electric igniter 27. The combustion products expand in the jet nozzle 2 and projects the coal onto impact plate 4, the coarse material returning to the jet whilst the fines are discharged through outlet 31. The coarse material separated out in the chamber 29 is returned through pipe 30 to the nozzle. A portion of combustion air may enter through pipe 32 and pass through annular gaps or nozzles 33 into the chamber 28 ; the coal is supplied through inlet 35. For starting up a small quantity of coal may be burnt in order to fill the chambers with waste gas free from oxygen. The pneumatic mill may disintegrate the coal in stages through a series of nozzles and impact plates. When, as in Fig. 2, the compressor 19 is charged from the compressor 22 the final pressure of the working medium changes in the same way as the charging pressure of the boiler or the counter-pressure of the jet so that with different loads of the boiler both the pressure drop of the jet nozzle and the volume of the working medium remain constant.