December 1, 1916.

THE COLLIERY GUARDIAN.

1059

the pre-heater. It has also been found that the same
design is a good thing in a condenser. Gilled steam
pipes should be avoided in the construction of pre-
heaters, as they afford ready lodgment for solid matter
deposited from the oil, which soon interferes greatly
with their efficiency.

Experiences in Distillation and Refining.

The corrosion occurring on some benzol plants appears
to be due chiefly to ammonia in various forms of com-
bination, such as sulphide and chloride; the water in
the wash oil containing (at Staveley) as much as 5-5 per
cent, ammonia. An interesting but ominous occurrence
is the undoubted occasional conversion of some of this
ammonia to oxide of nitrogen, revealed by both smell
and appearance at the water and benzol outlets of the
separator.

The distillation of the crude benzol, before washing, is
effected by working two fractions, the first—the light
oil—embracing all that comes over up to direct steam
being required. The heavy oil which follows is col-
lected until naphthalene makes its appearance at the
outlet of the condenser. The residue is then run out
into the usual cooling pans.

A short time ago the manufacture of pure benzol was
taken up at Staveley, a still designed for this purpose
was put on order; but in the meantime, as the aniline
plant was about ready for starting up, and, conse-
quently, would be requiring supplies of pure benzol, an
attempt was made to produce it with the plant already
installed.

The first trouble occurred with the washing process.
The mixers -are of 4,000 gals, capacity, the usual charge
being 3,600 to 3,800 gals. After the initial troubles at
the starting up of the plant had been overcome, no
further difficulty was experienced in the washing of the
ordinary products. The mixers are fitted with inverted
cone agitators, running at 60 to 80 revolutions per
minute. The cones are set just low enough to ensure
the acid being picked up from the bottom of the vessel.
There is, consequently, with the full charge, a con-
siderable depth of benzol—roughly, 4^ ft.—above the
top of the cone; with the result that the agitation,
though quite sufficient for the washing of the light and
heavy oils, proved utterly inadequate for the much
more drastic washing required in the preparation of
pure benzol. It was found quite impossible to wash out
the thiophene, even with the most liberal use of acid,
except by working with a half-charge in the mixer, when
the benzol just about covered the top of the cone.
Working in this way, the agitation was all that could
be desired, though even then prolonged washing was
required to achieve .satisfactory results.

The practice is to give two washes with d.o.v., the
acid used being 3| per cent, by volume, and numerous
experiments in the way of varying the amounts of acid
used, and the time of agitation, have failed to bring
this figure any lower. The distillation of the washed
product, pending the erection of the new still, was
carried out in one of the old plate column stills, which
had only been designed for the production of ordinary
90’s. It was, however, thought possible that by working
at a very slow rate, and with severe dephlegmation, a
fairly pure benzol might be obtained. At the outset
it was found that the column would only pass back a
strictly limited amount of benzol without choking, and
even with taking several days over the distillation of
3,800 gals., it proved impossible to obtain anything like
a pure article, the best results being 44 per cent, of
benzol, testing as follows :—Specific gravity at 60degs.
Fahr., 0*884; drop, 79*4 degs. Cent.; 90 per cent, at
80-6degs. Cent.; 95 per cent, at 81-4degs. Cent.; dry
point, 82-8 degs. Cent.

The “ pure ” still, which has now been at work for
some time, has the bell type of column, with the usual
dephlegmator, and an analyser of the Coupler pattern.
A series of tests has been made to determine the work
done by this particular form of analyser, and the results
are given below. In addition to the water it takes,
which perhaps with many would be a small matter, the
analyser has the drawback of causing a lot more steam
to be required for distillation.

Three charges	Three charges

with analyser.	without analyser.*

As charged.	As charged.

Drop, 79-6° C.	Drop, 78*7° C.

Dry point, 99*5°	Dry point, 101°

Distillate	Gals.	Gals.

Total forerunnings... 960	...	1,106

Pure benzol ....... 9,101	...	8.718

To re-work ............ 516	...	746

90*s toluol ........... 156	...	195

Per cent pure benzol

in total distillate... 84’75	...	81T0

* The analyser con’d not be by-passed, but the term
“ without” is justified, as the water was cut off and the
siphons conveying the condensates back to the column were
all blanked off, >o that anything condensing in the analyser
was obliged to find its v\ay down the vapour pipe to the
condenser.

Note.—The dephlegmator, under both sets of conditions,
was worked at the same temperature.

The general experience at Staveley with perforated
plates a<s against the sealed hood, or bell, type of
column is all in favour of the latter. The intermediate
still, which is fitted with the bells, has given no trouble
—so far as the column is concerned—in over four years
of constant working; whereas the first one of the two
rectification stills, which are fitted with perforated
plates, has twice in the same period had to have its
column dismantled for cleaning, owing to the holes of
the trays and pockets of the overflows being choked ap
with rust. Apart from the trouble of dismantling and
re-erecting the column, the clearing of these holes is a
very tedious process, involving much time and labour.
The dephlegmation also, with the bells, appears to be
more searching than is the case with the perforated
plates.

Discussion.

Mr. J. T. Price (Manvers Main) asked what was the
comparative cost in the upkeep and efficiency of rotary
scrubbers as compared with tower scrubbers? What
was Mr. Wilson able to get his return gas down to, as
far as the benzol was concerned? What kind of packing
was used? This last, he said, was a very small ques-
tion, but it was one which had caused difficulty to
several people. With regard to the method of testing
the benzolised and de-benzolised oil, he noticed that Mr.
Wilson ran it up to 165 degs. Why 165 degs.? Why
not 160degs.? Why not 170 degs.? At every plant
that they went to, they found a different method of test-
ing. At Man vers Main, at one time, they ran up to
135 degs.—why, he did not know. Now, they went to
210 degs., and distilled at 120degs. At some works,
operating under identical conditions, one with the Wurtz
flask and one with the ordinary retort, they found, on
the same oil, a difference of about 12 per cent., running
up to 300 degs. Mr. Wilson recognised the need for
laboratory tests, and the speaker thought that something
should be done quickly, as far as that matter was con-
cerned. As to the oil that he put into circulation, and
the thick oil that he put out, Mr. Wilson ran it up to
92 per cent, at 315 degs. But Dr. Coleman, in his
specification, said it should not be more than 90 per
cent, at 300 degs. He supposed there would be very
little difference, but why not more than 90 per cent.?
Of course, he did not expect Mr. Wilson to answer Dr.
Coleman’s propositions, but, at the same time, he would
like some enlightenment on the point. Mr. Wilson
gave an inlet temperature of 140degs., and an outlet
temperature of 132 degs., and his main argument was
that this enabled them to keep the water out. On a
previous occasion, Mr. Lee gave them his temperatures
as 108 and 105 degs. respectively, and when they went
to Mr. Lee’s plant they found that the water content
was nil. Why keep the temperatures up, and deteriorate
the oil that way, simply by trying to avoid water, when
Mr. Lee could get the same results or better? As to
the 7 per cent, of water which refused to budge, they
had had the same experience at the plant with which he
was connected. He should also like to ask what Mr.
Wilson brought his crudes up to—60, or 55, or 50? If
he worked on nothing less than 65, could he give some
explanation as to the amount of the increase in toluol?

Scrubber Troubles.

Mr. Wilson, in reply, said the rotary scrubbers gave
trouble at the outset, with regard to the engines more
than anything else, but, with a suitable type of engine,
and a suitable weight, they found no trouble whatever.
Occasionally, they got trouble through the blocking of
the outlet by bristles that came loose, but that was all,
and only arose in one plant, in which they had a more
tortuous connection to the first tower scrubber, with
several bends in it. They had now put in a catch box,
with a series of grids—it was really a mud box adapted
from an ordinary pump—and they found that if they
cleaned that out every now and then they had no trouble.
They used ordinary board packing for the tower
scrubbers, and cotton for the glands in the pump. They
had tried asbestos, but found cotton the best. With
regard to the temperature for the distillation tests, he
had several times asked himself the question, “ Why
165?” They were now carrying out a series of experi-
ments to see whether it was necessary to go to such a
high temperature. He did not think it was, but, as Mr.
Price said, they got that temperature given them, and
they went on with it. It was only lately that they had
been investigating the matter much. He had pointed
out that his test was a comparative one. They must not
take it as being absolute; it was not a scientific test at
all. They might as well drop down to 130degs., or any-
thing they liked, really. He did not know why Dr.
Coleman fixed the figure of not more than 90 per cent,
at 300 degs. He did not know that there was any par-
ticular reason, except that they did not want to get the
oil too thick. Naturally, the higher the gravity, the
less likely they were to recover the benzol, particularly
in the summer time. With regard to the inlet and
outlet temperatures, he pointed out that he had asked
that tests should be conducted. He was in some doubt
as to whether it was necessary to go to such a high
point, and he thought they ought to compare experi-
ences. It was difficult to compare different plants if
they had different conditions in that respect. At
Staveley, they had always worked at the figure given,
and they found that if they came down low they got
water trouble. At the same time, they had been down
lower than 116 degs. without trouble. Why they should
have got it on that occasion he did not know, except
that, of course, the oil was getting very thick. He also
knew Mr. Lee’s practice, and that that gentleman got
very satisfactory results at a very much lower tempera-
ture, and he was bearing that in mind when he wrote
the paper. He was afraid he had given a wrong impres-
sion with regard to the reason for insisting on a high
point. This was not only on account of the water, but
it was also a question of clearing the oil. Mr. Price
said that Mr. Lee got nothing in his return oil. He
(Mr. Wilson) must admit to getting something, at any
rate, J per cent, of distillate; but he did not know
whether Mr. Lee used the same test as himself. It was
difficult for them to compare, results, because tests were
not standardised, and therefore they were at a loss in
talking with each other about these things. As to the
quality of the crude oil, they generally worked at about
60 to 65, and got good recovery with that; but in the
summer time it very often came down lower on its own
account. During the past summer, they had been
getting up to 60 and 65, and they had not been recover-
ing in proportion on the intermediate still; and as far
as they could see, that was due to an excessive amount

of naphthalene in the oil. At the 50-oven plant, they
were on 'the point of re-lining, and at that plant not
only had the tar got very bad, but a great deal of naph-
thalene was found. Of course, that was getting forward
into the oil. In fact, the residues from the inter-
mediate still, when they ran out and cooled, were prac-
tically solid, which was not the case formerly. As
regarded any increase in the toluol, that was a difficult
question to answer. The amount of toluol in their total
benzol was very small — only about 9| per cent., he
thought. He could not say he had noticed any increase.
He would like notice of the question.

Mr. G. Taylor (Silverwood) said, as to the trouble
with the bristles in the scrubber, that would be avoided
if they were pegged in, instead of being run in with
pitch. He had wondered whether, in the case of the
centrifugal pump, there was any trouble with the gases
liberated in the pump casing in the case of the rich oil.
(Mr. Wilson replied in the negative.) He noticed that
Mr. Wilson was rather in favour of determining the
benzol by means of the increase-in-weight method. In
that case, he thought the naphthalene would be deter-
mined as well as the benzol. He would like to know if
Mr. Wilson determined the naphthalene separately in
the liquid he got, or whether he let it go as such. Mr.
Wilson also said that there was trouble caused by varia-
tions, and that the variations were dependent upon the
high viscosity of the paraffin. He would like to know
what sort of paraffin they used, and whether they froze
it or not. If they froze their oil, they ought to get a
perfect stripping of the gas sample.

Mr. Wilson said the oil was prepared according to
the “ British Pharmacopoeia.” The absorption bulbs
were all immersed in ice.

Mr. Taylor, referring to the heat interchangers, asked
if they could not tell by means of thermometers
whether leakage took place.

Mr. Wilson replied that they had often found it by
means of thermometers, but a lot of the thermometers
got smashed.

Amount of Distillates.

Mr. Taylor said he had been looking at the figures
given for . the accumulated distillates, and he thought
they got a rather larger amount than they should do.
If they were working to 65 at 120 degs., their distil-
lates should approximate 65 at 120 degs. when they were
re-distilled. Mr. Wilson, however, got 38 at 120 degs. in
one case, and 9 at another, so that his amounts of distil-
lates in the first case must have been greatly excessive.
It seemed to him that the figures of temperature must
be found out by each plant for itself. In every coke
oven plant the gas varied. There were in it certain
amounts of benzol, or toluol, as the case might be, and
these amounts -would keep fairly constant so long as the
working conditions were kept fairly constant, which he
thought might be assumed. If tests were made, it was
not a difficult matter to find a temperature to take them
to. If they made their tests so that the re-distilled
distillates worked out at about 65 at 120 degs., they
could be pretty sure that they were representative.

Mr. Wilson said they would notice the point to
which he got practically all the oil over. It was a
pretty low temperature. He thought the bulk of the oil
had come over at about 107 degs. That was with a
large amount of water in; but up to 2 per cent, of water
at 105 degs. That would be the condition under which
the saturated oil test was made.

Mr. Taylor said, of course, they could get the water
out, say, by adding some plaster of paris.

Mr. Wilson agreed, and stated that they did not find
that the water in -their oil varied much, provided they
were working normally. They got about | per cent, of
water in the de-benzolised oil, and 1 to 1*2 per cent, in
the saturated oil.

Mr. Taylor thought the gas test would be rather
against Mr. Wilson’s plant. He might return smaller
tests than he was doing, and be more nearly correct
than the figures in the paper would tend to show. Say
they had a return gas of 0*02 gal., he thought they might
really put that down at 0-09 gal., and be nearer the mark
as expressed in 65’s. Mr. Wilson did not give any tem-
peratures of his washing oils to convey any comparative
figures.

Mr. Wilson said in the summer time they were up to
about 90 degs. Fahr, on the gas. In 1915 they had a series
taken for the water; and the oil temperature would be
a few degrees higher. The water temperature was
85 degs. in the summer time—sometimes higher—and
the gas ran about 90 to 95 degs. In winter they got
down pretty low. On one plant, they were often below
the normal temperature of 60 degs.; on the other plant,
where they cooled their water and used it over again,
they were not quite so low as that. There the tempera-
ture ran to 60 degs.

Mr. Taylor did not quite agree with the author with
regard to the quality of the wash oil. He thought this
should be lower in viscosity. If they had a very viscous
oil, they had trouble in the scrubbers, as it might glut
up in the grids, and things like that were bound to
interfere with the efficiency of the scrubber.

Mr. Wilson replied that he had not found it so. Of
course, if he could get a better oil, he would do so, but
he did not find that he could get a better at about 1’4,