Patent GB-628385-A (GB)
Title: Improvements in or relating to method and means for washing coal
IPC: B03B5/44
Filed: 1945-04-17
Abstract: 628,385. Washing granular materials. COMPAGNIE. DES MINES D'ANZIN. April 17, 1945, No. 9598. Convention date, Nov. 9, 1943. [Class 82(ii)] In a method and plant for washing coal according to the sink and float principle, the heavy suspension contains a mixture of ''carbon" (coal dust), and attle or tailings from schists together with an amount of barytes which is less than 10 per cent of the suspended solids and may be zero, their proportions and granular composition being predetermined so that their size and average specific gravity are substantially the same as for a suspension containing barytes as a main ingredient. The "carbon" content of the suspension medium is kept at or below 24 per cent when no barytes is present, or up to 27 per cent with 10 per cent barytes, despite continuous feed of "carbon" from the raw coal, by continuous removal of particles of high "carbon" content, e.g. by passing through a froth flotation-vessel the diluted suspension obtained from rinsing washed coal, middlings and schists before sending it to thickeners for rebuilding the heavy suspension. There is also a continuous addition of crushed schist at any point in the cycle to compensate the lack of barytes and maintain the necessary suspension density, such addition being made preferably either to the feed tank for concentrated suspension from the thickeners (in the case of adding dry schist), or to the storage tank supplied with diluted suspension for rinsing washed coal &c. before sending for froth flotation; alternatively schisteous water from an adjacent plant for slime and coal-dust flotation, may be used the said water being concentrated and added to diluted suspension to be sent to a froth-flotation vessel for removal of "carbon." For carrying out the process, for each grain size of coal are provided regulating tanks 2, 3, having stirrers 2a, 3a, together with a washing vessel 5 preferably of the de Vooys type (see Figs. 2, 4), for classifying into three products and three ringing appliances 20, 12, 21, respectively for coal, middlings and schists, diagrammatically indicated in Fig. 1 by the rectangle 1. For the combination of grain sizes there are in addition, in series, a storage tank 44 for receiving the whole of the diluted suspensions from the rinsing appliances and if necessary some heavy suspension; a froth flotation-vessel 49 for removal of carbon from the liquids collected in the storage tank; a concentrating cone 51 for classifying solid particles after froth flotation; filtering devices (Callow trommels 52) for separating the coarser particles; and thickeners 64 for re-building heavy suspension before returning it to the washing vessels. Raw coal enters the washing vessel 5 via a chute 25; heavy suspension from the tank 3 enters at 6 and flows partly upwardly and over the weir 7 but mostly downwardly to the foot of the elevator 9. Coal is raked by the rake-band 26 over a gratirig 8 to a screen 20 where it is rinsed, clean coal being, collected at 29. Middlings and schists fall to the bottom of the vessel 5 where, the speed of upward flow of the liquid stream in the part 18 being adjusted-by means of the weir 22a in conjunction with the propellor 24-to carry along with it only the middlings, the middlings rise, pass over the weir 22a into the vessel 17 and thence by a rake 32 are carried to a rinsing screen 12, the rinsed middlings leaving at 34. Schists are carried from the bottom upwardly by the conveyer 9 to a third rinsing screen 21, rinsed schists leaving at 41. The rinsing devices are supplied with clarified water which is raised by pump 65 from thickeners 64, at 28, 33, 39; with clean water at 28a and 40; and with heavy suspension overflowing from the weirs 7, 10, at 11, Fig. 4. Some of the diluted suspension leaves the rinsing device 12 at 16 and is returned to the tank 3 direct; diluted suspension from 31, 36, 43 is led to a storage tank 44 into which also may be led a portion of heavy suspension from the inlet 6 via the pipe 47. Schisteous water from an adjacent froth flotation plant for slime and coal-dust (diagrammatically shown as 71) and concentration cone 67, or wet crushed schists at 48, may also be iritroduced into the tank 44; alternatively dry schist may be introduced into the schisteous water at any other point such as 76 from a concentrating cone 51. Liquid from the tank 44 is raised by a pump 50 via a filter fabric 73 into the "carbon"-removing froth flotation apparatus 49 wherein "carbon" is removed at 74, the suspension leaving at 75 being led to a concentrating cone 51 the overflow from which passes via pipe 79 to thickeners 64 and the dense liquid passing through a calibrated nozzle 76. A flow of clean water 77 carries the latter into a series of Callow trommels 52 which filter out the coarsest particles and from which the filtered liquid is led via collectors 58 to thickeners 64. Excess water leaves the thickeners at 81 whilst the treated dense suspension is pumped by the pump 66 into the regulating tanks 2. Specification 420,427 is referred to. The Specification as open to inspection under Sect. 91 comprises also the washing of minerals other than coal by the above process and apparatus. This subject-matter does not appear in the Specification as accepted