Patent GB-718413-A (GB)
Title: Improvements in and relating to the continuous distillation of tars
IPC: C10C1/04
Filed: 1950-10-02
Abstract: <PICT:0718413/III/1> Coal tars and similar heavy hydrocarbon oils are fractionated using a plurality of fractionating columns connected in series so that liquid from the sump of each column (except the last) is delivered to the middle section of the following column, and the columns are maintained under successively increasing temperatures and diminishing pressures through the series, the last column being at 10 to 100 mm. absolute, heat being supplied to the system by providing each column (except the last) with an external heater through which sump-liquid is circulated, and by inserting a heater between the sump of the penultimate column and the middle section of the last column. Fractions are withdrawn from each column.  Coal tar is passed through heat-exchangers 1, 2, 3 wherein it is heated by the vapours from the heads of columns I, II, III.  The tar then passes through heat exchanger 4 wherein it is heated by a sidestream withdrawn from, and returned to, an upper section of column III.  The tar next passes through heat-exchanger 5 wherein it is heated by pitch withdrawn from the base of column III.  The tar is then introduced into a central section of column I, wherein an absolute pressure of about 1,000 mm. Hg is maintained.  Vapours of water and light oil are withdrawn from the head of the column and condensed; and the condensate is passed to decanter 7.  A portion of the light oil is returned to the head of the column; the quantity being adjusted so as to maintain the temperature of the head at 130 DEG .  Carbolic oil is withdrawn from an upper section of column I, and freed in column 10 from more volatile constituents which are returned to column I.  The residue collecting in the sump of column I is pumped through tubular furnace 12, and then returned to the column.  A portion of the residue is withdrawn, and introduced into a middle section of column II wherein an absolute pressure of 500 mm. Hg. is maintained by pump 16. Naphthalene oil is withdrawn from the head of column II; and a portion of the condensate is returned, by pump 17, to the head of column II, so that a temperature of about 230 DEG  is maintained there.  Naphthalene oil and washing oil are withdrawn from a middle section of column II, and rectified in columns 18 and 19 repectively. A portion of the residue in the sump of column II is continuously withdrawn, and introduced into column III wherein an absolute pressure of about 40 mm. Hg. is maintained by pump 26, assisted by the introduction of the cooled sidestream into an upper section of the column.  Anthracene oil is withdrawn from the head of column III, a portion of the condensate is returned in order to keep the temperature of the head of the column at about 250 DEG .  Anthracene oil is also withdrawn from a middle section of column III, and this oil is rectified in column 29.  The lower part of column III is maintained at an absolute pressure of about 10 mm. Hg. by pump 31; and pitch at a temperature of about 330 DEG  is withdrawn at the base.  A suitable tar oil fraction may be used as cooling-medium in coolers 14 and 24.  Subsidiary columns 10, 18, 19 and 29 may be heated by diverting portions of the vapours from furnaces 12, 21, 23. Specification 692,364 is referred to.