Patent GB-703479-A (GB)
Title: Improvements in the continuous fractionation of tar
IPC: C10C1/04
Filed: 1950-10-06
Abstract: <PICT:0703479/III/1> <PICT:0703479/III/2> Tars, particularly coal tars, containing naphthalene, are submitted to a continuous fractionation process in two or more stages each consisting of heating, flash vaporization and rectification, characterized in that the tar is heated in the first stage to a temperature below about 320 DEG  C. but sufficiently high to ensure that the lower boiling components of the tar including substantially all the naphthalene are vaporized in the first flash vaporization stage, and that the residue from the first stage is further heated and then introduced into the second flash vaporization stage, which is maintained at reduced pressure (preferably below 100 mm. Hg.), to volatilize further components and leave pitch as residue.  Tar containing about 6 per cent. water is pumped via pipes 1 and 3, Fig. 1, through heat-exchanger 4, and then via pipe 5, through heat-exchangers 6 and 7.  The tar leaves heat-exchanger 7 at about 145 DEG  C., and is passed through pipe 8 into container 9, wherein laminar flow with separation of water containing ammonium chloride, takes place. The separated water is withdrawn through pipe 10 and cooler 43. The dehydrated tar is passed through piping 12 and 19 disposed in furnace 13 which is divided into two radiation zones and a central convection zone by walls 14, 15.  The furnace is heated by burners 16, 17; and the waste gas is withdrawn at the base of the convection zone.  The tar leaves the furnace at a temperature of about 320 DEG  C. and a pressure of 2 to 3 atm.  The tar is then introduced through pipe 20 into flash-chamber 21 near the base of fractionating-column 22 which operates at atmospheric pressure. Partial vaporization of the tar takes place in chamber 21, and the vapours are rectified in column 22.  Light oils and residual water are withdrawn from the head of the column, naphthalene oil is withdrawn through line 23, and phenol oil through line 24.  The naphthalene oil is rectified in column 29.  The bottoms from column 22 flow into chamber 21.  The liquid from chamber 21 is passed through vapour-liberation chamber 26, and is then used to heat the column 29 and heat-exchanger 6.  The liquid after leaving heat-exchanger 6, is raised to 350  DEG C. in the piping 31 disposed in the radiation zone of furnace 13, which is heated by burner 17 and communicates with the convection zone through an adjustable opening 32.  The heated liquid is passed through pipe 33 into flash-chamber 34 disposed in column 35 which is maintained at a pressure of about 70 mm. by pump 40; the liquid is partially vaporized and pitch is left as residue.  The pitch is withdrawn through line 36, cooled in heat-exchanger 7, and collected in a receiver 41.  The vapours liberated in chamber 34 are fractionated in column 35, from which washing-oil is withdrawn overhead while anthracene oil is withdrawn through line 37.  A column suitable for use in the process is shown in Fig. 2.  It comprises flash-chamber 52, vapour-liberation section 53, scrubbing section 51 containing Raschig rings arranged on grate-like base 69, and fractionating compartments 50 provided with bubble-trays 54.  The heated tar is introduced into chamber 52 through pipe 59 and tangential-opening 60.  The vapours liberated in chamber 52 are passed upwards through pipe 62.  The residual liquid accumulates on tray 63, and flows over the edge 64 into section 53. The residual volatile components are liberated from the liquid as it flows over the trays 66 in section 53.  The residual liquid is withdrawn through opening 68.