410

____________________________________________________________________________________________________________

THE COLLIERY GUARDIAN

March 3, 1916.

cent., whilst the free acid will be 1*4 per cent. I In the
first place, what about bags with this acid content? Some
years ago I experimented with nitre cake for this same
purpose, but could never reduce the sulphate of soda down
to anything like 15 per cent. To my mind it is ian open
question whether it is better to adopt this method or to make
as much sulphate -as possible by the ordinary method, and
waste the rest of the ammonia, or recover it in some other
form. I do not think the process is at all suitable for either
direct or semi-direct plants, as to work these with the liquor
at boiling point would be highly detrimental. On the other
hand, if the temperature is below boiling.point an excessive
amount of ■ sulphate of soda is deposited. The process
certainly cannot be launched into general practice in the off-
hand manner which the circular suggests.

Other Methods of Dealing with Ammonia.

The manufacture of nitrate of .ammonia is out of the
question, as nitric acid is more difficult to obtain than
sulphuric. Ammonium chloride occurs in all ammoniacal
liquor, and recovery of this, .under present conditions, is
well worth consideration. The production of crude
ammonium chloride is comparatively simple, but the manu-
facture of pure salt is not easy under ordinary coke oven
conditions. The most attractive propositions are (1) the
manufacture of liquefied ammonia., or pure ammonium
hydrate ; and (2) the manufacture of concentrated ammonia
liquor (containing about 15 per cent, of ammonia.) Of these
the latter is by far the simpler process. In this case it is
not always necessary to eliminate CO2 and H2S, though if
these are reduced a higher price can be obtained for the
liquor. The ordinary ammoniacal liquor is distilled, and the
steam, ammonia, carbon dioxide, sulphuretted hydrogen,
etc., are condensed in a water cooled condenser. The amount
of steam must be regulated in order to supply just sufficient
condensed water to dissolve the ammonia, etc., and to
maintain the strength of the condensed liquor at about
15 per cent, of ammonia. Concentrated liquor exerts a
moderate pressure at ordinary temperatures, so that great
precaution is necessary to avoid undue loss of ammonia. As
the liquor runs into the storage tank the displaced air will
carry away with it some ammonia, and in order to prevent
losing this I connect up the outlet pipe on the tank to the
suction side of the exhauster. Any ammonia therefrom
passes again into the scrubbers. The only trouble usually
experienced with this plant is the blocking up of the con-
denser tubes by ammonium carbonate. In order to obtain a
satisfactory effluent liquor more steam has to be put into the
still than is necessary to supply the amount of water required
to form the concentrated liquor. A reflux condenser must
therefore be employed, and with it the strength of the con-
centrated liquor can be regulated as desired. As conditions
are not always absolutely constant, the strength of the liquor
will occasionally rise above 15 per cent., and it is then that
trouble with blocked pipes begins. With about 20 per cent,
of ammonia the liquor will solidify at ordinary temperatures,
so that the condenser needs to be carefully watched, and
constant testing is necessary in order to keep the liquor at
the proper strength. The way in which the ovens are
worked with regard to suction has a very marked effect on
the working of the concentrated liquor plant. With suction
on the ovens, air is drawn in and carbon is burned. The
amount of CO2 in the gas is thereby considerably increased,
and this again results in the formation of more ammonium
carbonate in the ultimate concentrated liquor, the liability
to blockage increasing accordingly. By working our ovens
at a rather higher pressure than usual we have found that
carbonate troubles have disappeared, as neither air nor flue
gases are drawn in.

Many processes have been suggested for the partial elimina-
tion of CO2 and H2S, but the majority are unsuitable for
ordinary practice on account of unnecessarily complicating the
apparatus. By preheating the liquor, partial elimination of
both C02 and H2S can be obtained, but at the same time
some ammonia is also drawn off. To make it worth while,
the liquor must be pre-heated to at least 95 degs. Cent. The
following table shows the amounts of ammonia, CO2, and H2S
eliminated at various temperatures with a particular liquor :—

Composition of liquor :—

Free ammonia ............ 0-92 gm. per 100 c.c.

Carbon dioxide .......... 0-86	,,	,,

Sulphuretted hydrogen .... 0-122 ,,	,,

Quantities eliminated per 100 c.c. of liquor :—

Temperature.

85° Gent. 90° Cent. 95° Cent.

Ammonia ........... 0-054	.... 0-10	.... 0-152

Carbon dioxide ’.....	0-158	.... 0-16	.... 0-304

Sulphuretted hydrogen	0-069	.... 0-071	.... 0-074

The same test carried out under a suction of 60 mm. of
mercury gave the following results :—

Temperature.

85° Cent. 90° Cent. 95° Cent.

Ammonia ........... 0-061	.... 0-132	.... 0-196

Carbon dioxide ....... 0-184	.... 0-203	.... 0-378

Sulphuretted hydrogen	0-072	.... 0-074	.... 0-078

The Disposal of Pitch.

The accumulation throughout the country of large quanti-
ties of pitch has caused a slump in this product, which has
had a corresponding effect on the price realised for tar. The
question of the carbonisation of pitch in coke ovens has been
brought to notice as a possible means of reducing stocks, and
thus helping to improve the outlook for tar. The proposal
is that a proportion of pitch should be mixed with the coal
before charging. The effect, it is said, would be to improve
the quality of the coke, and also of'the gas, whilst there is
also the possibility of other advantages. The whole subject
is at present under investigation, and I would urge those
who are in a position to do so to make a trial, using, say,
5 to 10 per cent, of hard pitch, well mixed into the coal.
Experiments, both on a small anyl a large scale, have been
made, and the results are distinctly encouraging. If the
position with regard to pitch can be eased at all, it will be a
great benefit to tar producers.

In connection with this subject, it seems opportune to
refer to the possibility of State co-operation in technical
research. Prof. Bone has frequently called attention to the
urgent need for' the establishment of a national bureau to
deal with questions of fuel economy and allied matters. We
can easily imagine that a great deal of good would result
from such an establishment, and in the hands of the right
men it would prove to be an inestimable boon to the country.
But we must have practical men — men who know the
industry thoroughly, and who are fully aware of the nature
of all the difficulties we have to face.

Benzol Recovery.

One could not, under• present circumstances, omit some
reference to benzol recovery. Fortunately, I believe opera-
tion troubles are comparatively rare in this connection; but
m some cases there has been a difficulty in obtaining sup-
plies of suitable scrubbing oil. In my own case, by careful
attention to the elimination of naphthalene from the oil, I
have been able to prolong its working life very considerably.
In view of the importance of benzol in the present crisis, it
is rather surprising that we have not had some official
guidance with regard to the best method of working our
plants to produce the largest yield of benzol, etc. I think
that the first step which the Ministry of Munitions ought to
have taken was to appoint a committee of practical men to
investigate the question, and give us all the benefit of those
investigations. They should tell us not only what to do, but
how to do it.

I would like to mention the recovery of crude benzol of
less than 65 per cent. In my opinion, it is little short of
criminal at the present time to make 65 per cent, spirit, yet
we are more or less tied to it by custom and convention. We
know perfectly well that when the gas is scrubbed by creosote
oil, etc., the latter extracts a variety of products. The
general maximum temperature to which the oil is distilled
for the recovery of those products is about 135 degs. Cent.
Now, we also know quite well that the distillate so produced
in the majority of cases is not 65 per cent, spirit, but some-
thing less than that. To make it into 65 per cent, spirit, we
have to dephlegmate a portion of the vapours. This portion
is run back into the scrubbing oil, and almost invariably con-
tains both some benzene and some toluene. We ought to
recover the whole of the distillate as produced, and to get
the same price for it as for crude benzol at present. If our
usual buyers will not deal with it, the Government ought to
make them. On every hand we are told that more benzol
and toluol are required. The result of the adoption of this
proposal will be a net increase of several per cent, in the
production of toluene.

But the Government will not even deal with what benzol
we have got, let alone take steps to deal with what might be
recovered. For several weeks now I have carried a stock of
over 10,000 gals, of benzol, and I am absolutely unable to
get it moved, though, when I applied for special labels for
conveyance of benzol, etc., I was told that no special labels
were required, as tank wagons were always given preference.

I would like to press, therefore, the need for same con-
certed action on the part of this association in these matters.
What can we do to assist the production of .an increased
quantity of benzol. We can express our opinions as to the
best conditions for its formation and assist one another by
giving our experience of our own working. Chemically
speaking, benzol is a high-temperature product, and I have
found that our yield is substantially increased when car-
bonising at high temperature. The naphthalene also is
increased, but I do not think this -is any detriment, some,
indeed, considering it a distinct advantage. Working the
ovens at a pressure of about 5 mm. in the collecting main
I have found to be most satisfactory. Suction on the ovens
appears to me to be decidedly against a high yield of benzol.
The effect of moisture is, I think, also slightly detrimental.
In tests which I have carried out on the same class of coal
the best results were obtained from dry coal. At the same
time I would point out that it has been found that the
illuminating value of coal gas is higher from wet coal than
from dry, and it is urged, therefore, that the gas from the
former is richer in benzol than that from the latter. If,
therefore, in the subsequent discussion we can throw any
light on the formation of benzol we shall render a distinct
service to the country.

DISCUSSION.

Mr. E. M. Myers, in opening the discussion, said that
he was particularly interested in the references to pitch.
For about 18 'months he had been experimenting with
mixtures of pitch in the proportions of 5, 7|, and 10 per
cent, with coial, but had not got very encouraging results,
although other people seemed to have had better success.
He had found that when.he reached 10 per cent, pitch
mixed with slack, the moment the coal was charged in
the ovens it was absolutely impossible for the men to get
anywhere near the charging taps or to put the lids on for
the great volumes of flame and smoke, while as to the
effect on the coke, he could find no increase in quality
or decrease in the quantity of breeze, or anything to
warrant the trouble of mixing the pitch. He thought
some means ought to be devised for mixing the pitch
with small coke or breeze or breeze dust for the manu-
facture of an artificial fuel, having regard to the high
price of coal. He believed a very good market might be
found for the disposal of such briquettes. Thousands of
tons of pitch had been turned out every year in the form
of a patent fuel in South Wales especially, for the use of
the Belgian State Railways and the railways of France
and Italy, and he did not see why British railways should
not be forced to use patent fuel. The pitch difficulty was
an alarming one, for at his works they were storing some
80 or 90 tons of pitch per week, which, of course,
required a tremendous lot of storage space, labour and
cost. He had received a circular from the Ministry of
Munitions, and they had promised to send down a gas
engineer to show how the thing could be done, and he
was personally looking forward to a discussion with this
gentleman as to how best to eliminate the difficulty of
having huge quantities of pitch stored about the works.

Another interesting question was the recovery of
ammonium chloride. Why should this not be possible
without having to buy sulphuric acid, or splitting it up
into ammonia liquor. In some cases from 10 to 20 lb. of
ammonium chloride per ton were recoverable from coal,
without the addition of any acid or the use of stills, and
there was a ready market for it, if not in this country in
other parts of the world. Why should this salt not be
recovered direct in a marketable form?

Mr. Cooper, in reply, said he had carried out a con-
siderable amount of experimental work with regard to
the use of pitch, and he found exactly what Mr. Myers
said was quite true with regard to the smoke and flame.
He found that with intimate mixing there was less
trouble, and also that a moist was preferable to a dry
coal. The pitch should be exceedingly hard, which
meant that the oily constituents had been removed.

That was one of the difficulties to be overcome. He was
convinced, however, that there were possibilities in this
use of pitch, and that it would result in an improved
coke; but it was a matter for investigation, and not
likely to be solved without some trouble, and an
occasional failure might well be repaid in the ultimate
result. With regard to the recovery of ammonium
chloride, he quite agreed with Air. Myers that it was
foolish to start with ammonium chloride and then split
it up into something else; but that was the principle
at the root of all their progress—-they always began at
the wrong end first. He believed that, under normal
conditions, the recovery of ammonium chloride was
worth the candle. It was a question, after all, of £ s. d.,
and he thought as they were situated, in the majority of
cases, at present the recovery of ammonium chloride
was not the most satisfactory way of dealing with the
ammonium chloride which was in the liquor.

Mr. J. W. Lee asked if Mr. Cooper had worked the
pitch question on the same'basis of £ s. d.

Mr. Cooper : Yes. It was not worth bothering with
otherwise. They put in so much coke product and so
much volatile matter, which ultimately came back into
the tar, and unless the pitch question was sound from a
£ s. d. point of view it was not worth bothering with; but
he thought it was sound.

Mr. C. P. Finn felt that the Ministry of Munitions
had, from a national point of view, made a false step in
advising the use of pitch. He would have thought they
were more concerned with the carbonising of as much
coal as possible in coke ovens, and the recovery of as
much benzol and toluol as possible. Taking 10 per
cent, pitch, as suggested, and supposing that repre-
sented 10 per cent, of the coal which would normally
be charged—say, 300 tons per day—that would mean 30
tons of coal substituted by pitch. They did not get the
equivalent—3 to 3| gals, of crude benzol per ton of coal.
Therefore, they would not really be helping the Ministry
of Munitions. He quite sympathised with Air. Cooper
in thinking they should get the same price for 60 per
cent, as 65 per cent, benzol, but, of course, people who
were buying benzol thought differently. With regard to
the question of making sulphate of ammonia, and effect-
ing economies in the use of acid by substituting nitre
cake, he supposed anybody who had got a benzol recti-
fication plant would be using the waste acid from benzol
washing. He was doing so, and very successfully, by ■
boiling up this waste acid, skimming off the dirty tar,
and utilising what looked very strange coloured stuff
for making sulphate of ammonia—a raspberry coloured
liquor; but he could say that the use of this acid caused
a marked improvement in the appearance of the sulphate
—it was whiter and cleaner. That was one method of
utilising some of the acid otherwise wasted. With regard
to nitre cake, he had been making sulphate of ammonia
from nitre cake for just over two months—not wholly
from nitre cake; he had only been substituting a small
portion of sulphuric acid by nitre cake. It was well
knowm to all who had made sulphate of ammonia that,
in the past, a good deal of sulphate of soda had been
used for bringing down the percentage to 24-J-, which
wras the standard fixed by the buyer. This led him to
think that he could use large quantities of nitre cake,
and he arranged to get some for experimental purposes.
He used it by working the indirect process of recovery.
Normally, in making sulphate of ammonia, they made
up a bath of about 63 or 64 Twaddell, and started to
blow when they had sufficient salt—just over 60 Twaddell
free acids in the bath. They found now that if they had
281b. of nitre cake per bath, immediately they finished
blowing the salt they had to Twaddell up to about
10 degs. higher—about 74 made the percentage of free
acid about right for making salt which contained 24-6
of ammonia. The amount of free acid must have been
a mistake in the Ministry of Munitions circular, because
the amount of free acid, in his experience, was 0-19 per
cent., which was about the average; he had had 0-25 per
cent. They washed out in the centrifugal by means of a
small watering can, and obtained salt with about 0-19
per cent, of free acid. With regard to moisture, he had
never succeeded in getting below 2| per cent., and nor-
mally it was about 3 per cent. Making sulphate with
acid, and no nitre cake, he had been able to make it
lower.

Mr. G. W. Bradley alluded to published results on
the decomposition of, hydrocarbons, from which he
argued that it seemed impossible to obtain any valuable
hydrocarbons by the use of pitch; so that by diluting coal
with pitch they were simply displacing coal from the
ovens.

Mr. Cooper said that, with regard to the use of nitre
cake as referred to by Mr. Finn, the most important
point was the proportion of sulphuric acid that was
saved. To put in a few pounds of -nitre cake in such a
quantity that it only reduced the ammonia content of the
salt to 24'6 was not worth doing unless they were going
in for it on a scale at least as big as the Government
stated in the circular.

Mr. C. H. Oxley, touching on what Mr. Finn had said
with regard to moisture, said he had been used to the
wet system, and found that the sulphate contained
about 3J per cent, moisture. He had to- dry it artificially
to get it down to about 2 per cent, but it went to 2'5
on standing about a month; try as they would they
could not get it below 3^ per cent, on turning out.

Mr. G. A. Lant apprehended difficulty in getting into
the works the -chamber acid of about 110 Twaddell
■strength suggested in the Government circular on the
use of nitre cake. Chamber acid was also full of