GB678933A - Improvements in and relating to the continuous distillation of coal tar - Google Patents

Abstract

<PICT:0678933/III/1> Coal tar is continuously distilled by heating it in a continuous heater to temperatures from 335 DEG C to 350 DEG C, flashing the heated tar at an absolute pressure of between 300 and 400 mm. of mercury in a chamber into which steam is injected and fractionating the vapours in an adjoining bubble-cap column under a corresponding vacuum, the required fractions being taken off at various points in the column. Reflux for the column is obtained from the phenol oil fraction. As described crude tar enters at 1 and is preheated in the heat exchanger 2 by pitch from the flash chamber 20 before passing successively to heater 3, dehydrator 5, and topping column 9 for light oils operated substantially at normal pressure The light oils are condensed at 11 and reflux returned to column 9 by pipe 12. The condensate flows through cooler 13 to separator 14 where separation of water occurs. The topped tar is pumped through heater 17 and pressure control valve 19 to flash chamber 20, operated at 300-400 mm. pressure into which steam is introduced by pipe 21 and from which pitch flows away through exchanger 2 while steam and vapours pass into the base of fractionating column 23. Anthracene oil is taken off as bottom product at 26, phenol oil as top product at 29 and washing and naphthalene oils as side streams at 27 and 28 respectively. Side columns 30 and 31 are provided for the rectification of the last two fractions steam being introduced at 32 into the column 30 for distilling the lighter constituents of the washing oil while heat for the column 31 is supplied by the circulatory heater 35. The phenol oil vapours and steam passing over at 29 are cooled at 38 and the condensate flows to a receiver 39 connected to a vacuum pump 41 and by run-off pipe 42 to separator 43 where the phenol oil and water separate. The phenol oil is partly returned by pump 44 to the top of column 23 as reflux and partly to an auxiliary column 46 provided with circulatory heater 47 where it is completely freed from water and drawn off at 48, water vapour passing over to pipe 29. Water from separator 43 is forced by pump 51 through evaparator 52 which feeds by pipes 54, 21 and 32 and pressure reducing valves 53 to flash column 20 and side column 30. The parts of the apparatus under reduced pressure are at a higher level than those at normal pressure and fluid columns form in the run-off pipes 24, 26, 33, 37 and 48 in accordance with the vacuum in the various columns.