August 18, 1916.

THE COLLIERY GUARDIAN.

317

UTILISATION OF COKE BY-PRODUCTS.*

By C. G. Atwater.

There is probably no substance whose uses so fill the
scope of our engineering, manufacturing, chemical, and
social needs as do those of coal. Its consumption per
capita is fairly taken as the measure of a nation’s civili-
sation; its possession is the guarantee of a nation’s
future; in the development of its possibilities we appear
to have only crossed the threshold; in the application of
the possibilities we have demonstrated we are certainly
far behind what might be done.

The distillation of coal is practised in three general
types of apparatus, namely, the coal gas retort, the bee-
hive coke oven, and the by-product coke oven; therefore,
the industries dealing with the products of coal distilla-
tion are based on the operation of these three agencies.
The coal gas retort produces primarily coal gas for use
as an illuminating gas and also as by-products, coke,
tar, and ammonia, and in some instances benzol and
cyanides. The by-product coke oven produces coke as
its main product and as by-products, gas which may
be used for illumination, tar, ammonia, benzol, and
cyanides. The beehive oven produces only coke, and
should not perhaps be included in this catalogue except
that it comes under the general classification and is of
interest as occupying the industrial field, which we may
reasonably expect will ultimately be pre-empted by the
by-product coke oven. It is, as it were, a measure of
our immediate possibilities. The gas producer is not
included in this category, because coal is not, strictly
speaking, distilled destructively in this process, as air
enough is introduced to partly consume it and transform
it into carbonic oxide, which is attended with practically
the destruction of the by-products of distillation except
in the case of the recovery gas producers, where
ammonia and a small amount of tar are recovered.

The development of the industries based upon the
distillation of coal may be said, in America, to have
actually depended upon the introduction of the by-
product coke oven. This statement would not be true of
Great Britain, to any such extent at least. The great
extent to which coal gas is manufactured in England,
and has been for many years, had supplied the raw
materials for the chemical industries to work with,
aided by the limited territory, which facilitates the
assembling of supplies from different works. On the
other hand, it would be true of Germany, where coal
gas is not so widely used and where the introduction of
the by-product coke oven began at an earlier date. In
the United States the coal gas industry has long been in
existence, but has been, as it were, diluted so much by
the immense area of that country and the preponderance
of carburetted water gas that until the advent of the
by-product coke oven the supplies of raw material did
not encourage the development of an extensive industry
based on the products of coal.

The relative importance of these three methods of
destructive distillation may be gathered from the follow-
ing figures, calculated from the latest reports of the
United States Geological Survey :—

Tons. Per cent.

Coal distilled in by-product coke ovens 17,100,000 ... 23
Coal distilled in coal gas retorts . 4,000,000 ... 6

Coal distilled in beehive coke ovens... 52,100,000 ... 71

Total coal distilled ............ 73,200,000

As will be seen from these figures, the by-product coke
oven is about four times as great as the coal gas retort,
but both combined fall far short of the total of the
beehive coke oven. These figures indicate that a large
amount of by-products are recovered. They also show
that a still larger amount will ultimately be available
and must be reckoned with in our industrial calculations.

Coke.

The nature and varieties of coke are well known. Its
main use is in the smelting of pig iron, for which
approximately a ton must be manufactured for each ton
of pig iron produced, although the actual consumption
at the furnace is a little below this amount. For this
purpose metallurgical coke is required, that is to say,
coke having a strong cellular structure and reasonably
low in sulphur, phosphorus and ash. Metallurgical coke
is also used for re-melting pig iron in the foundry
cupola.

The softer coke produced by the coal gas retort has
found ready consumption for ordinary fuel purposes.
Apart from its lack of strength and liability to make
breeze, it is better fitted for ordinary fuel purposes than
the harder metallurgical coke, as it is not so difficult to
ignite.

A considerable .trade is being built up in certain
districts in domestic coke, which is usually the by-
product article crushed and sized and distributed in the
usual manner. It has been found very satisfactory for
all fuel purposes where a little attention is given to its
properties, as distinct from anthracite or bituminous
coal. It is quite probable that the future will see con-
siderable extension in this direction as the other pro-
ducts of coal distillation become more desired and justify
investment in coking plants. In this connection it may
be remarked that large quantities of coke are now con-
sumed in Germany in place of coal, it being desirable
to operate their by-product coke ovens for the produc-
tion of ammonia and of benzol, toluol, etc., although
the coke is not specially required.

Ammonia.

The usual way of obtaining ammonia in the by-
product coke oven system has until recently been by
washing the gas with water, which having a strong
affinity for ammonia, absorbed it, the product being
weak ammonia liquor. This ammonia liquor was dis-
tilled by steam in a column to form crude concentrated
liquor or led into the sulphuric acid saturator, where

* From Proceedings of the Engineers’ Society of Western
Pennsylvania.

by combination with sulphuric acid, sulphate of
ammonia was formed. The sulphate was then dipped
out of the saturating vessel, either by hand power or by
air lift, dried in a centrifugal dryer and stored for
shipping as the finished sulphate. Recent improve-
ments in coke oven by-product apparatus have modified
this method to the extent that the coke oven gas, after
being freed from tar, is led directly to the saturating
boxes and by the combination of the ammonia gas with
the sulphuric acid, sulphate of ammonia is formed
directly without the intervention of any washing water.
This is known as the semi-direct process, and produce's
an excellent quality of ammonia sulphate. In the plants
that are so far in operation in America, as those at
Joliet, Gary and elsewhere, where ovens of the Koppers
type are used, a certain amount of weak ammonia
liquor is ’also produced, due to the cooling of the gas
before passing through the saturator in order to remove
the tar. AVith the tar a certain amount of ammonia
liquor comes down. This ammonia liquor is usually in
the form of the fixed salts—chloride, sulphate, sulphite,
thiosulphate, and ferrocyanide, and must be freed by the
addition of lime or other alkali and distilled in the
usual column still. The ammonia vapour so obtained
is either returned to the gas main at a point just before
the gas enters the ammonia saturator, or it can be kept
apart and used for making ammonia liquor.

These two products, crude concentrated ammonia
liquor and ammonium sulphate, are the primary
ammonia products. From them the secondary products
are manufactured. These comprise principally
anhydrous ammonia and aqua ammonia, which are
used in refrigeration and chemical manufacture;
ammonium carbonate and ammonium bi-carbonate,
which are used as leavening agents in baking:
ammonium nitrate, which is used in the manufacture of
explosives; ammonium chloride, more generally known
as sal ammoniac, which is largely used in the manu-
facture of electric batteries and for various technical
purposes. The most important of the products, as far
as quantity goes, is ammonium sulphate. This is an
important carrier of nitrogen for agricultural use, and
is a component of most mixed fertilisers produced in
the United States. It is generally accepted as one of the
principal forms of nitrogen in all agricultural countries
and is shipped all over the world for this purpose.

Until the breaking out of the war, Germany was the
greatest producer of sulphate of ammonia of all the
countries, having surpassed the English production two
or three years ago. The total German output for the
year 1913 was 548,000 tons, England’s maximum pro-
duction being 432,000 tons, .reckoning all forms of
ammonia produced as the sulphate. The United States
stands third in this rank, having produced 220,000 tons
in the year 1915, the largest production recorded to date.
Chemically pure sulphate of ammonia will contain
about 25-8 per cent. NH3, and as ordinarily produced it
contains 25 per cent, or over, this being a high degree
of purity for a commercial article produced in large
quantities. It is of a dry, granular consistency, and
lends itself well to- use in fertiliser mixtures. Unfortu-
nately, all the nitrogen contained in the coal is not
available for recovery, a part being lost because of the
necessary amount of coal left in the mines and a further
portion being lost in the conversion of the coal to coke
and the recovery of ammonia. Allowing for all these
losses, however, there still remains enough nitrogen
recoverable in the form of ammonia sulphate to main-
tain the fertility of an acre for the period of 640 years.
With these figures in mind we can appreciate the impor-
tance of the waste that is now going on in the carbonisa-
tion of coal in the beehive coke oven, and, furthermore,
the great economic waste that takes place in the con-
sumption of bituminous coal in the ordinary manner.

The question of ammonia recovery has taken on new
importance because of the conditions developed by the
war, and the imperative need for nitric acid in water,
this acid being the sine qua non in the making of. modern
explosives.

A number of years ago Ostwald discovered a method
of oxidising ammonia to nitric acid by passing ammonia
gas, together with sufficient air, through a heated tube in
the presence of a platinum catalyser. This process was
never developed to any extent commercially until, on
the outbreak of the war, Germany was confronted with
a critical condition in her nitric acid supply, her annual
imports of nitrate, amounting to 850,000 tons, being
cut off. As the result, Germany turned to the Ostwald
process, or some development of it, and is now obtaining
her nitric acid from ammonia by oxidation. We are
told that she is now consuming from 250,000 to 300,000
tons of nitric acid per year for explosives, of which only
10,000 tons is obtained by the arc process of nitrogen
fixation, the balance being obtained from ammonia
derived from calcium cyanamide or produced syntheti-
cally by the Haber process.

Germany has for years recovered all the ammonia
available in coke production. Therefore no room existed
for expansion in that direction. But in the United
States over five hundred thousand tons of sulphate of
ammonia, produced in beehive coke manufacture but
not recovered, are annually wasted. If half of this were
recovered there would be a sufficient addition to the
present supply to equal the present German consump-
tion for munition purposes, as above stated.

The development of the arc process for the direct
recovery of nitrogen from the air, as done in Norway,
offers many difficulties in America. Chief among them
is the lack of large water powers where power in large
quantities could be produced at a price low enough to
make continuous operation feasible in time of peace,
even with Government support.

The production of calcium cyanamide, as done at
Niagara Falls, is more attractive, but Niagara
Falls is on the border and open to attack. More-
over, cyanamide only furnishes ammonia, which can
be more easily obtained from coal. The retort coke

oven plants lie at well-scattered points in the interior,
and are not open to enemy attack. It seems to the
author that the point on which stress should be laid,
and on which Government support should be elicited is
in the development of the process for ammonia oxida-
tion.

Gas.

The gas produced from the distillation of coal in the
by-product coke oven is essentially the same as ordinary
illuminating gas. A fair average analysis of such gas
is as follows: Hydrocarbons, 5*8 per cent.; methane,
40-8 per cent.; hydrogen, 37*6 per cent.; carbon
monoxide, 5-6 per cent.; carbon dioxide, 3-7 per cent.;
oxygen, 0-4 per cent.; nitrogen, 6-1 per cent.

Generally speaking, the gas will run from 600 to 700
British thermal units per cu.ft., and will have from 14
to 16 candle-power. It is capable of being used for all
the purposes to which ordinary city gas is put, that is
to say, not only may it be used in ordinary gas burners,
stoves, heating ovens, etc., but it can be used for power
in gas engines, and can be transported long distances
under pressure. Its illuminating value is due princi-
pally to the benzol and other higher hydrocarbons which
it contains. In order to obtain the maximum illumi-
nating value in coke oven gas a method of operation is
frequently resorted to, which is known as the division
of gases. The first portion of the gas given oft from an
oven of coke is, of course, the richest in illuminating as
well as in heat value. Therefore, it may be readily
understood that if the first portion of the gas from each
oven is kept by itself in one system of mains and the
later, leaner portion of the gas carried through a sepa-
rate system of mains, the first gas will be much more
valuable for general city purposes than the leaner gas.
It is understood, of course, that the present system of
heating the coke ovens is with a portion of their own gas.
For this purpose the illuminanfs are by no means neces-
sary, so the oven heating suffers no appreciable loss and
the disposable gas is afforded a decided gain where this
principle of the division of gases is practised. The two
gases remain distinct all the way through the condensing
and scrubbing processes, and the clean gas comes from
the condensing house in two separate mains. One is
led back to the ovens for firing them, the other is piped
away for whatever purpose it may be desired. Roughly
speaking, the proportion of gas under modern conditions
is about half and half, that is to say, of the 10,000 cu. ft.
of gas which a net ton of coal is usually supposed to
deliver, about 5,000 ft. is used for heating the ovens
and 5,000 ft. is disposable. With the shortened coking
time that now prevails a greater proportion of gas is
disposable, only about 4,000 ft. being necessary to heat
the ovens in some plants. Usually the separation of the
gases is made at the oven, proportioning the two quan-
tities as nearly as may be by manipulating the valves,
more rich gas being taken, if anything, than is neces-
sary. If more oven heating gas is needed the rich gas
can be by-passed in the fuel gas holder.

This plan of increasing the strength of the rich gas be-
taking the unessential portions from the poor gas has
been carried even further where benzol recovery is prac-
tised, by scrubbing the lean gas to obtain its benzol, and
adding this benzol as an enricher to the rich gas; in
fact, where benzol is recovered, it has been found expe-
dient to remove all the benzol from both gases and
deprive them of their troublesome naphthalene, and thus
greatly facilitate the transmission of the gas in cold
weather. After the benzol has been purified it is
returned to the rich portion of the gas and a better and
cleaner gas is thus obtained.

The usual type of condensing house for treating coke
oven gas does not include purifiers to remove the
sulphur. For the portion of gas used in heating the
ovens the presence of sulphur is of no moment, and if
it is possible to dispose of the surplus gas for usual city-
purposes, this in most cases has been done through the
existing gas company, and the purification from sulphur
is attended to by them. In a number of instances the
capacity of the district where the coke ovens are located
to consume illuminating gas is far behind the production
of the coke ovens, and other uses must necessarily be
found. In some cases this has been done in the 'open
hearth steel works, in the various heating furnaces,
soaking pits, etc., accessory to steel mills, or in ordinary
boiler firing. A much more desirable and economical
use is, of course, in the internal combustion engine,
where a great economy in the production of power mav
be obtained.

Although the by-product coke oven consumes nearly
one-half of its own gas production, the surplus gas pro-
duced is usually very large in quantity because of the
gieat amount of coal treated. The relation between the
surplus gas production at such a plant and the consum-
ing capacity of the ordinary sized town is not generallv
appreciated. A town, say, of 50,000 inhabitants, where
gas is generally used, may possibly consume 5,000 cu. ft.
per inhabitant per year, or about three-quarters of a
million feet per day, which could be supplied by the
by-product coke oven plant needed for a blast furnace
producing 100 tons of pig iron per dav. It will, of
course, be recognised that it is a great advantage to
by-product coke oven operation to be able to sell its gas
for city consumption, where the price ranges from 60c.
to Idol, per 1,000 to the ultimate consumer, rather than
for purely fuel purposes in competition with coal. This
may be the better appreciated when it is explained that
the value of coke oven gas is about four cents per
1,000 cu. ft. when used in competition with coal at
1-25 dols. per ton for firing boilers, or where the coal is
gasified in gas producers, so that from the economic
point of view, the use of such gas under steam boilers
is wasteful, and is a sacrifice of a high grade product to
a low grade use.

Benzol.

Coke oven gas is the main source of all the benzol
produced, although coal tar is usually credited with con-
taining the benzol which forms the foundation of so