May 24, 1918.

THE COLLIERY GUARDIAN.

1049

overtime was worked. Trade unions with 315,036
members (mostly in skilled occupations) reported 0'1
per cent, unemployed at the end of April, compared
with 0’1 per cent, a month ago and 0T per cent, a
year ago.

Tinplate.—The number of tinplate mills working
at the end of April showed an increase of 16 on a
year ago. Difficulties in securing supplies of raw
material were still reported.

Wages.—In the four months, January-April, a net
increase of £500 in wages was granted, affecting 21,500
workpeople connected with coal mining. The net
increase in iron mining was £2,200 per week, affecting
8,000 persons, and in pig iron manufacturing £6,100,
affecting 32,000 persons.

Disputes.—Two new disputes occurred in April.
One near Worksop affected 1,990 miners and others,
and lasted for two days. It was settled by an agree-
ment that post-war miners were not to re-enter the
pits unless medically examined and passed into
Grade 3. The other dispute (near Newport) affected
1,588 workpeople, relative to the alleged non-payment
of war wage to certain men, and other grievances.
Work was resumed pending negotiations.

Fatalities.—In the four months the fatalities in
mines totalled 582, compared with 427 in 1917. The
mining fatalities (underground and surface) at mines
in April numbered 106, an increase of two on the
number in April 1917.

RECOVERING AMMONIA AT TAR-
DISTILLING PLANTS.*

By C. R. Woodward.

Although it has long been known to tar-distillers that
a certain amount of ammonia is present in the water
contained in ordinary coke-oven, gas-house or vertical
retort tars, very little has been done in the way of
experimenting to find the actual state in which the
ammonia is present, its strength or the possibilities of
recovery.

The writer has spent considerable time working on
this subject at the plant of a large tar distiller, and has
obtained results showing that not only can ammonia be
easily recovered, but that its recovery at these distilling
plants can be accomplished very profitably.

Sources of Ammonia.

At the tar works there are two sources from which
ammonia can be recovered—the liquor which settles out
on the top of the crude tar storage tanks, and the liquor
which conies over with the light oil in the process of
distilling the tar. As the storage tanks are both filled
and emptied from the bottom, this liquor, settling on
top of the tanks, is commonly allowed to accumulate
undisturbed until such time as the amount begins to
take valuable storage space, when it is run to waste.
The distilled liquor is by far the most profitable source,
due to its great volume and strength; but, as is the case
with the settled liquor, it has usually been allowed to
run to waste.

At the particular plant at which the experiments to
be described were made, the coal tar received in the
course of a year consisted of about 9,000,000 gals, coke-
oven tar, 4,000,000 gals, gas-house tar and 600,000 gals,
vertical-retort tar. About two-thirds of this tar was
distilled at the plant, the remainder being disposed of
in a crude state for road-building purposes, under trade
names tending to disguise its true composition.

Laboratory Tests.

Before any large scale operations were attempted,
laboratory tests for ammonia were made on the water
settling on the top of the storage tanks and on the
water distilled from the different kinds of tars in the
laboratory. The results given are expressed in ounces
of ammonia per gallon of liquor, and also in the per-
centage of anhydrous ammonia, the percentage being
obtained by dividing the number of ounces per gallon of
liquor by 3'88.

Tests of the liquor settling out from the tar in storage
are given in Table I.

Table I.—Liquors Settling on Tars.

Tank No. and	Volatile p- d Total Am-

class of tar.	ammonia. ea* ammonia, monia.

Oz.

No. 2	coke oven ..... 1*41

No. 3	gas-house ..... 0'705

No. 11	„	„	.... 0'82

No. 12	,,	„	.... 0'69

No. 22	vertical retort No w;

Oz. P. cent.

4'39	...	''80	...	1'50

1'77	...	2'48	...	0'64

1'58	...	2'40	...	3'62

2’22	...	2'81	...	0'73

settled out.

An examination of the liquor distilled in the labora-
tory from each of the three different classes of tar,
coke oven, vertical retort and gas house, showed an
average strength as follows:—

Table II.—Liquors Distilled from Tars.

Strength ammonia

from laboratory

Total
ammonia.
Per cent.

2'52
3'12
0'73

2'19

Class of tar.	sample.

Oz.

Coke oven................. 9'76

Coke oven plus NaOH...... 12’1

Gas-house................. 2'84

Vertical retort ............ 8’5

In the distillation of these tars the condenser was
kept at all times absolutely cold, so that never was there
any danger of ammonia loss. Under these conditions
the strength of the liquor obtained represents the maxi-
mum that can be recovered from these tars in practice.
The second test with NaOH was made for the purpose
of seeing if the fixed ammonia in the tar could be broken
up in the process of distilling.

Tbe results of the experiments on the settled liquor
indicated that with the exception of that on the coke
oven tar tbe strength in ammonia was very low. In
fact, were it not possible to mix them with stronger
liquors, recovery of the ammonia contained in them
would not be practicable regardless of the volume avail-
able. It should be noted that about 70 per cent, of the

* Metallurgical and Chemical Engineering.

ammonia in this liquor is fixed and would necessitate
using lime in the process of concentrating.

The water distilled from the tar, however, is found
to be considerably stronger in ammonia than tbe water
separated from the tar on standing, and suggests very
profitable recovery.

The great difference in the strength of these two
classes of liquor is noticeable, particularly in the tests
of the water from the coke oven tar, which contains
5'80 oz. ammonia in the settled liquor and 9'76 oz. in
the distilled liquor. This is probably due to evapora-
tion of ammonia from the surface of the water in the
storage tanks. The fact that the tar itself contains
some ammonium compounds, apart from those in the
water with which it is intimately mixed, causes a cor-
responding increase in the amount of ammonia in the
distilled liquor.

The reason why the water distilled from the coke
oven tar contains 9'76 oz. of free ammonia while the
water separating from tbe same tar on standing
contains only 1'41 free ammonia, is that the distilled
liquor contains only free ammonia, which passes over
with the water, the fixed ammonia remaining behind.
In the settled liquor the free ammonia has evaporated.

The result of the test with caustic soda indicates that
an additional amount of ammonia may be recovered
through the breaking up of the fixed ammonia remain-
ing in the tar. It was not, however, considered worth
while to try out this test on a large scale in view of the
difficulties likely to be encountered through the action
of the caustic on the tar.

Large-Scale Tests.

Ammonia tests were made on water obtained from
the distillation of tar on a large scale, 10,000 gals, direct-
fired stills being used. In making road-building material
and pitch it is customary at the plant in question to
mix coke oven tar and gas house tar in about equal
proportions. Most of tbe tests, therefore, were made
on the water distilled from such mixtures. However,
to make the experiment more complete, a special still of
straight coke oven tar and a still of vertical retort tar
were run to fuel pitch for the purpose of obtaining the
liquor from these particular tars. The strength of the
liquor only differs slightly from the tests obtained in the
laboratory. The ailimonia was found to be approximately
99 per cent, free and 1 per cent, fixed, this small amount
being probably due to combinations made with the gases
in the condenser, or with salt water leaking through the
condenser coils.

Liquor Recovered in Practice.

In order to ascertain if this ammonia liquor could
actually be recovered without loss in practice, an 18-day
test was run, during which time the liquor from all the
stills, instead of being allowed to run to waste, was
dumped into ground tanks and from there pumped into
a storage tank holding about 5,700 gals. When full this
tank was emptied, several samples being taken of the
liquor as it ran from the bottom. In this test the liquor
obtained was subject to some contamination from rain,
water, and from salt water dripping from the con-
densers, but the amount was not sufficient to affect the
results materially. The average yield of ammonia was
4'17 oz. per gallon.

The water was all taken from mixtures of gas-house
and coke-oven tars, and it is evident that, if care is used
to prevent evaporation, there is very little loss to be
anticipated in recovering the ammonia. The average
test of 4'17 oz. agrees very closely with the average
strength of 4'11 oz. in the liquor as it is given off from
the still, and before it is dumped into the ground tanks.

The composition of the distilled liquor, containing, as
it does, 99 per cent, of its ammonia in a free state, con-
stitutes a most favourable condition for concentrating—
no lime being required.

From these experiments, it appears that tbe bulk of the
liquor recovered at the stills when the usual tar products
are being made will average 4'11 oz. strength—a liquor
considered workable. To obtain a stronger liquor at
the expense of the total ammonia recovered, it is only
necessary to eliminate the last few tubs of weak liquor.
A strong ammonia liquor will always be obtained when
straight coke-oven and vertical-retort tars are distilled.

Estimate of Profit.

Records of the plant show that the total amount of
water distilled from the tar in the course of the year
averages about 700,000 gals. The water settling out of
the coke-oven tar in the course of a year is 76,000 gals,
and that on the gas-house tars 256,000 gals.

Assuming all the ammonia concentrated to a liquor
of 20 per cent, strength, which has at this time a value
of about 0 lOdol. a lb. at the works, the total amount
and value would be at this plant:—
Liquor settling on coke-oven tar:

76,000 X 8'35 x 15 p.c. — 9,520 lb. ammonia
Liquor settling on gas-house tar:

256,000 X 8'35 X 0'665p.c. =14,220 lb. ammonia
Distilled from tar : •

700,000 x 8'35 x 1058 p.c. = 61,840 lb. ammonia

Total ...............  85,580	lb. ammonia

Total value of ammonia, 0’10 dol. X 85,580 = 8,558 dols.

If any considerable amount of coke-oven tar or
vertical-retort tar is distilled without admixture of gas-
house tar, as is the case when ordinary fuel or briquette
pitch is made, the amount of ammonia recovered will be
greatly increased.

The only extra apparatus required is an ammonia
.concentrator for the weak liquor, a few small tanks and
a little additional piping. Tbe cost of the concentrator,
together with the tanks and including the labour of
setting up, would be about 4,000 do^s. Tbe operating
cost of concentrating the liquor per lb. of ammonia
recovered is estimated at 2 c. per lb. The total value of
the ammonia being approximately 8,558 dols., and the
cost of recovering ] ,712 dols., a profit of approximately
6,746 dols. a year is indicated.

It is stated that the Road Transport Board is about
to take over the whole of the road transport of the country.
The scheme arranges for a number of divisions of area.

THE SAFE STORAGE OF COAL.*

By W. D. Langtry and J. F. Kohout.

The storage pile tends to equalise the variable
demands for coal, especially for domestic consumption.
During the summer months there is but little burned
and many retailers start to stock for the winter. In
the winter months the demand is heavy and these
storage piles enable the dealers to make prompt
deliveries. These remarks also apply, in a sense, to
power fuel, as the generalisation may be made that
the storage pile acts as a reservoir which may be
drawn upon or left untouched as the needs and
occasion demand.

Broadly speaking, the larger sizes of coal store
without giving any trouble. This is due principally
to the fact that these sizes are drier and offer a
smaller surface, in proportion to their mass, to the
action of oxygen, than the finer sizes do.

Anthracite and semi-bituminous coals store well in
any size, but this is probably due to their chemical
composition. Oxidation occurs here also, but is much
slower in action and, therefore, smaller in amount for
any given length of time.

The finer sizes of coal, which are used pricipally for
power purposes, are generally high in moisture and
iron pyrites. These are deleterious ingredients
because of the ease of oxidation of the pyrites in the
presence of water vapour. The finer sizes, that is,
coal passing through 2 in. screen and smaller, expose
a great number of small surfaces to the air. These
several factors all tend to initiate oxidation and to
speed it along once it has started.

The methods of storage are three in number: —
under-water storage; storage in closed bins; and in
open piles. Under water any kind and size of coal
may be kept for any length of time without danger
of any sort from fire. This method is used by very
large consumers of coal, like the Western Electric
Company, of Chicago, and the United States Navy
Department. This provides a supply of coal which
may be safely held for an indefinite period of time.
All such concerns also hold coal in open piles for
immediate use.

Storage in closed bins is generally limited to small
quantities of fuel. These may be the winter supplies
in homes or stocks in small retail coal yards.

Storing in Open Piles.

The great bulk of storage coal is kept in open piles.
This is intended to be held readily available for use
and is seldom on the ground for more than a few
months. As a matter of fact, it should not be kept
for any great length of time, but the length of time
should depend on the kind of coal, since this is the
most dangerous form of storage. However, when
proper precautions are taken at the time the coal is
placed on the ground and maintained while the pile
lasts, losses may be eliminated, or, at any rate, reduced
to a minimum. These precautions will be taken up
later, since from now on only the finer sizes will be
considered. The losses which occur may be considered
to be due to oxidation.

In considering the mechanism of oxidation, the
general fact should be borne in mind that the rate
of oxidation increases with increase of temperature.
Also we must remember that coal is a poor conductor
of heat, so that any heat occurring or generated in
the interior of the coal pile stays there. These two
facts indicate that when oxidation starts, even though
at a low temperature, it generates a small amount
of heat; this heat is insulated from the outside air,
and, being retained, tends to increase the rate of
oxidation. Thus one action helps the other, and the
oxidation proceeds at a constantly accelerated speed,
the more easily oxidisable compounds or constituents
being attacked first.

Iron pyrites is oxidised in the presence of water
to ferrous sulphate and sulphuric acid, according to
the equation : —Iron pyrites + oxygen + water = iron
sulphate + sulphuric acid -p heat. This reaction takes
place with a considerable evolution of heat. It is
true that the oxidation really goes farther with the
evolution of still more heat, but, to consider this
matter from a more conservative viewpoint, this
additional heat, and also the heat due to the action of
sulphuric acid on lime or alkalies present in the coal,
or the heat generated by the dilution of the acid with
water are not considered.

It must be remembered that the water actually
enters into chemical combination with the pyrites and
oxygen, unless the water is present in sufficient amount
to exclude the air. This is the condition that prevails
in under-water storage, and is one of the reasons why
that method is best.

When coal is stored in the dry state, the equation
for the oxidation of the pyrites given above is
incomplete, since the moisture component is absent.
When it is stored under water the equation is again
incomplete, because the air is thus excluded and the
oxygen component is absent.

In other words, the oxidation in the dry state pro-
ceeds very slowly, since the only moisture available
is that in the coal and in the air. In dry coal the
moisture is very low, so in dry storage one of the
necessary constituents of the reaction is lacking to a
relatively large extent.

Spontaneous Heating.

The heat due to the oxidation of pyrites, helped
by that coming from external sources, if any, raises
the temperature of the pile to the point where the
carbon and hydrogen of the coal begin to be attacked.
This action is aided by the fact that coal, particularly
when freshly mined and when in a fine state of
division, has a strong affinity for oxygen. The oxygen
is absorbed much as water is taken up by a sponge.
This may be considered as the first stage of oxidation.
This supplies the oxygen needed for the oxidation of
the pyrites, and then of the carbon and hydrogen.
This action is not likely to occur until a temperature
of about 250 degs. Fahr, is reached. The temperature
of the coal is raised by these processes until it reaches

* The Black Diamond.