An Improved Process and Apparatus for the Continuous Distillation of Tar.
Year: 1890

page_text: Date of Application, 24th Feb., 1890
Complete Specification Left, 24th Nov., 1890-Accepted, 7th Feb.,
1891
PROVISIONAL SPECIFICATION.
An Improved Process and Apparatus for the Continuous Distillation
of Tar.
I, HEINRICH PROPFE, of Mannheim, in the Empire of Germany, Doctor of
Philosophy, do hereby declare the nature of this invention to be as follows:-
In the fractional distillation of coal tar, as heretofore practised, it is necessary to
allow the residual pitch, remaining in the still after the distillation of each charge,
to cool down before removal, in consequence of its inflammability at the high
temperature attained. The loss of time and heat consequent on the intermittent
character of the operation is evident, and, owing to the danger of fire and other
causes, the process is not well adapted to be carried on at gas-works. Another
disadvantage is the intermittent character of the operation.
The process of this invention obviates these disadvantages as by it the tar may
be distilled continuously and that in gas works, preferably in a corner of the retort
house or outside. The tar as it deposits in the hydraulic main at a temperature
of 70° C., may be continuously conveyed to the apparatus of this invention and be
there quickly converted into hardening pitch whilst the volatile constituents are
concurrently distilled off. Moreover, the process enables the pitch to be con-
tinuously removed without risk of ignition and effects the greatest possible economy
of fuel.
In carrying out the process, the tar is caused to flow through a long vessel divided
into a series of stills or compartments in hydraulic communication and heated by an
inversely flowing current of gases from a furnace. During the passage of the tar,
first the more volatile and then the less easily volatile constituents are driven off
until those which boil at a high temperature are eliminated and collected. The tar
is, therefore, constantly becoming more inspissated and leaves the apparatus as
pitch. The heat of the pitch is utilised, by carrying its outlet pipe back through
the tar undergoing distillation.
An apparatus, adapted to carry out this process of distillation, consists of a
multiple still in the form of an elongated wrought iron box divided, by partitions
extending nearly to the bottom, into a number of separate stills or compartments,
eight for example, which communicate with each other below the partitions. Each
compartment is provided with a still head, for the purpose of carrying off the
distillate. The tar enters at the end farthest from the source of heat and the exit
of the pitch is at the same end and has an overflow swan neck or a cock by means
of which the level of the tar is kept constant in the still, the exit pipe extending
through all the compartments to the opposite end of the apparatus with the last
compartment of which it communicates. The furnace is situated beneath this last
chamber and the furnace gases are conveyed through flues extending beneath the
whole length of the apparatus. At starting, the apparatus is filled to about two-
thirds its height, the chambers then being separated from each other by the
hydraulic seal of the partitions dipping in the tar.
The distillation begins first in the compartment nearest the furnace and succes-
sively in the others whereby the contents of said compartment are gradually
converted into pitch by the continued heating. When this stage (which is easily
recognised by the nature of the distillate) is reached, the tar is supplied continuously
to the compartment farthest from the furnace whence it passes below the first
partition to the next compartment, and so on until it reaches the compartment
nearest the furnace. In its passage through the several compartments, the
temperature of the tar is constantly increasing and consequently the distillates
passing over from successive compartments, have progressively higher boiling points.

page_text: The inflow of the tar and the heating of the still are gradually regulated in such
manner that, for example, from the first to the fourth compartments only so called
fore-runnings and water distil continuously from the fifth and sixth so called light-
oil and from the seventh and eighth green-oil. It is desirable that a stream of
superheated steam be introduced into the two last chambers, because, as is known,
the distillation of the so called green-oil is thus considerably hastened. The pitch
passing out from the last compartment flows slowly through the outlet tube passing
through the several compartments in the inverse direction to the flow of tar through.
the compartments whereby it is gradually cooled and passes out at such a com-
paratively low temperature that it will not ignite. If when cold it be too hard, tar
oil, deprived of its valuable constituents is introduced into the last compartment by
a pipe.
The apparatus may be variously modified. For example, it may be arranged to
distil under diminished pressure, and, instead of heating by direct fire, superheated
steam, circulating through pipes in the still, may be employed. For the purpose of
ensuring uniform heating it is advantageous, when employing direct heat, to use a
regenerator, or gases of combustion from the gas-retort furnaces may be employed.
Dated this 24th day of February 1890.
HEINRICH PROPFE.
By A. M. & Wm. Clark,
53, Chancery Lane, London, Patent Agents.
COMPLETE SPECIFICATION.
An Improved Process and Apparatus for the Continuous Distillation
of Tar.
I, HEINRICH PROPFE, of Mannheim, in the Empire of Germany, Doctor of
Philosophy, do hereby declare the nature of this invention and in what manner
the same is to be performed, to be particularly described and ascertained in and by
the following statement :-
In the distillation of tars, as heretofore practised, it is necessary to allow the
residual pitch, remaining in the still after the distillation of each charge, to cool
down before removal, in consequence of its inflammability at the high temperature
attained. The loss of time and heat, consequent on the intermittent character of
the operation, is evident and, owing to the danger of fire and other causes, the
process is not well adapted to be carried on at gas works. Another disadvantage
is the intermittent character of the operation.
The process of this invention obviates these disadvantages, as by it the tar may
be distilled continuously and that in gas works, preferably in a corner of the retort
house or outside. The tar as it deposits for instance in the hydraulic main of gas
works at a temperature of 70° C., may be continuously conveyed to the apparatus
of this invention and be there quickly converted into hardening pitch whilst the
volatile constituents are concurrently distilled off. Moreover, the process enables
the pitch to be continuously removed without risk of ignition and effects the
greatest possible economy of fuel.
In carrying out the process, the tar is caused to flow through a long vessel
divided into a series of stills or compartments in hydraulic communication and
heated externally by an inversely-flowing current of gases from a furnace. These
compartments communicate with one another only by apertures below the partitions
which are hydraulically sealed so that only the heavy or unvolatilised constituents
can flow from one compartment to the next whilst the vapors pass over at the still
head. During the passage of the tar, first the more volatile, and then the less
easily volatile, constituents are driven off until those which boil at a high
temperature are eliminated and collected. The tar is, therefore, constantly
becoming more inspissated and leaves the apparatus as pitch. The heat of the
pitch is utilized, by carrying its outlet pipe back through the tar undergoing
distillation.

page_text: An apparatus, adapted to carry out this process of distillation is illustrated in
the accompanying drawing, forming part of this Specification, wherein Figure 1 is a
longitudinal sectional elevation, partly broken away. Figure 2 is a cross-section
on line a, b (Fig. 1) through the furnace and the last compartment of the series.
Figure 3 is a cross-section of a modification.
The apparatus consists of a multiple still, in the form of an elongated iron box,
divided, by partitions S extending nearly to the bottom, into a number of separate
stills or compartments eight for example A' A². ... A7 A8 which communicate
with each other below the partitions. Each compartment is provided with a still
head H¹ to Hs for the purpose of carrying off the distillate. The tar enters at T
at the end farthest from the source of heat and the exit of the pitch is at the same
end and has an overflow swan neck P or a cock by means of which the level of
the tar is kept constant in the still; the exit pipe extending through all the
compartments to the opposite end of the apparatus, with the last compartment A³
of which it communicates. The furnace is situated beneath this last chamber A
and the furnace gases are conveyed through flues extending beneath the whole
length of the apparatus. At starting, the apparatus is filled to about two-thirds
its height, the chambers then being separated from each other by the hydraulic seal
of the partitions dipping in the tar.
The distillation begins first in the compartment A³ nearest the furnace and
successively in the others, whereby the contents of said compartment are gradually
converted into pitch by the continued heating. When this stage (which is easily
recognised by the nature of the distillate) is reached the tar is supplied at T
continuously to the compartment A¹ farthest from the furnace whence it passes
below the first partition S to the next compartment A, and so on until it reaches
the compartment A nearest the furnace. In its passage through the several
compartments, the temperature of the tar is constantly increasing and consequently
the distillates passing over from successive compartments have progressively higher
boiling points. The inflow of the tar and the heating of the still are gradually
regulated in such manner, that, for example, from the first to the fourth com-
partments only so-called "fore-runnings" and water distil continuously; from the
fifth and sixth so called "light oil;" and from the seventh and eighth "green oil."
It is desirable that a stream of superheated steam be introduced into the two last
chambers, because, as is known, the distillation of the so-called "green oil" is thus
considerably hastened. The pitch passing out from the last compartment flows
slowly through the outlet tube passing through the several compartments in the
inverse direction to the flow of tar through the compartments whereby it is
gradually cooled and passes out at such a comparatively low temperature that it
will not ignite. If, when cold, it be too hard, tar oil, deprived of its valuable
constituents, is introduced into the last compartment by a pipe.
The form of apparatus may be variously modified. For instance, the apparatus
shewn in Figures 4 and 5 which is in the form of a boiler with one or two flues may
be employed. Or it may be arranged to distil under diminished pressure and
nstead of heating by direct fire, superheated steam circulating through pipes rin
he still (see Figure 3) may be employed. For the purpose of ensuring uniform
heating it is advantageous when employing direct heat to use a regenerator, or
rases of combustion from the gas retort furnaces may be employed.
Having now particularly described and ascertained the nature of the said
nvention and in what manner the same is to be performed, I would observe that I
m aware that continuous distilling apparatus having a series of hydraulically-
ommunicating chambers as herein described is not new and I lay no claim to such
pparatus, nor to the process of continuously distilling therein, but I declare that
that I do claim is ;-
1st. In the process of continuously-distilling tar in an apparatus such as herein-
escribed wherein the tar is caused to flow in the opposite direction to the heating
urrent through a series of hydraulically-communicating contiguous, but separated,

page_text: distilling chambers, conducting the pitch or residue from the final distilling chamber
through the contents of the whole series of compartments so as to give up its
surplus heat to the tar undergoing distillation therein, and pass off at a sufficiently
low temperature.
2nd. The herein-described apparatus for carrying out the herein described
continuous process of distillation of tar, wherein the several compartments are in
hydraulic communication only beneath the partitions, and in which piping leads
from the hottest compartment of the series back through the liquid contents of all
the other compartments, as and for the purpose specified.
Dated this 24th day of November 1890.
By A. M. & Wm. Clark,
53, Chancery Lane, London, Patent Agents.