Miy 2, 1913.

THE COLLIERY GUARDIAN.

905

that year, since which time various improvements have
been effected. The chief advantages claimed for the
process are :—Saving of steam and water, and concen-
tration of the operations into a small space ; simplicity
of working, with electric drive; independence of the
yield of ammonia on the external temperature; gas
quite free from higher tar constituents, and consequent
absence of contamination of the scrubbing oil in the
benzol process; perfectly pure lighting and power gas
after the removal of the naphthalene; perfectly dry salt
from the hydro-extractor (no artificial drying being
required), owing to the high temperature of the acid
bath; no need for milk of lime, clarifying tanks, &c.,
with ordinary coal, and no calcareous effluent water ;
perfect working, even with coal rich in common salt, and
fixed ammonia compounds in the gas; suppression of
effluent by utilising the heat of the gases for evaporating
the water in the cooling towers.

The gas is freed from tar and ammonia; then cooled,
if necessary, to deposit a portion of the contained
moisture, and returned to the ovens, for heating
purposes. As shown in fig. 5, the crude gas from the
ovens, after being air-cooled in the main down to
between 100 and 200 degrees Cent., is passed through
the tar-spraying device, in which a circulation of tar
water is maintained by a centrifugal pump. This
spraying removes all the tar from the gas. A portion
of the separated tar runs off, through an overflow, to the
tar pit, the rest being returned to the sprayer by the
pump, the delivery pipe of which is provided with a coil
enabling the temperature of the tar water to be
regulated to dew point in the separation of the air.
Under ordinary conditions, this temperature is about
160 degs. Fahr., the tar temperature varying between
120 and 175 degs. Fahr., according to the weather.

The hot gas next passes through hoods with serrated
edges, into the closed saturator, which is half filled with
dilute sulphuric acid. The heat of the reaction in the
bath heats the gas up sufficiently to prevent any dilution
of the liquor by the water vapour in the gas. On the

Fig. 6.—Diagram of the Collin Process.

a, Cooler; b> tar separator; c, suction fan ; d, e,f, saturator ; g, still.

other hand, water is introduced into the saturator from
the dilute sulphuric acid (60 degs. strength) employed,
and also through the rinsing water for the hydro-
extractors, &c., so that in many cases the bath requires
to be heated. The gas liquor from the tar sprayer is
frequently used for rinsing purposes, since, during its
circulation in the sprayer, it absorbs a portion of the
fixed ammonia compounds from the gas. To prevent
supersaturation, and the consequent deposition of salts
in the tar, a portion of the circulating liquor has to be
drawn off all the time, and this can be used for rinsing.
In large plants, these fixed compounds can be decom-
posed with lime in a small still plant, the ammonia being
driven off by steam and returned to the gas. With
this method of working, the quantity of water to be
evaporated per ton of dry coal is | cwt., as compared
with 400 lb. in the semi-direct process and 880 lb. with
the indirect process ; and the annual cost of steam for
80 ovens amounts to £115, against £825 and £1,825
respectively. The calcareous effluent waters of the three
processes are in the same proportion. Again by con-
centrating the circulation water of the spraying
apparatus in simple apparatus, sal-ammoniac can be
recovered therefrom direct, and no effluent water is
formed.

In the saturator, the sulphate of ammonia crystallises
out, and is transferred to a drainer by means of an
ejector, being afterwards passed through a hydro-
extractor and put into store. The finished salt is pure
white and contains at least 25’25 percent, of ammonia
and 0’2 per cent, of free sulphuric acid. Owing to its
low percentage of moisture it stores better than the salt
obtained by the semi-direct process. From the saturator
the wet gas passes through a separator to retain any
particles of liquor that may have been carried over, and

then goes to the condensers, which may be either of the
tubular pattern or the injection type. In the former
case, which is suitable for plants where hot boiler-feed
water or fashing water is required, the cooling water
flows through cross tubes interposed in the path of the
gas. The tar oils condensed in the top of the apparatus,
flow over the surface of the tubes, and prevent the
deposition of naphthalene. When direct cooling is
practised, the condensed products run off in the water and
are removed in a separator. In the re-cooling apparatus
the volume of water is reduced to about its initial
quantity by evaporation, so that there is practically no
effluent to be disposed of.

A suction fan draws the gas through the whole
apparatus, and delivers it back to the coke ovens, &c.;
and since the fan and other machinery can be driven by
electricity, the whole of the heat energy recovered in
the coking plant can be utilised in a power house, either
in large gas engines or in steam turbines and waste
heat turbines.

The Collin Process.—This semi-direct process (fig. 6)
is of the same general character as that of Koppers,
the chief differences being that no pre-heaters are used,
and there is no gas heater of the kind employed by
Koppers between the tar separator and the suction fan.
The gas from the ovens is cooled down in the cooler a,
so that the tar is effectually separated in b. It is then
delivered by the suction fan c into the saturator d, and
thence to the benzol plant, or returned to the coke
ovens. The condensed liquor in a is treated in known
manner in the still, g, the ammoniacal vapours being
led into the saturator in such a way as to prevent any
intermixture with the coke oven gas. The pressure
generated in the still forces these vapours through the
acid bath into the bell e, whence they are returned to
the gas current, or delivered to the benzol plant or gas
engines as required. In this way the gas is protected
from contamination with sulphur dioxide fumes. The
hot still vapours render heating the acid bath
unnecessary, and also saves motive power, the kinetic

energy of the vapours enabling them to overcome the
resistance of the bath liquor. Another advantage of
the method is that it furnishes a sulphate of ammonia
quite free from tar and in large crystals, the recovered
tat being also free from contamination. The inventor
claims as an important advantage the possibility of the
troublesome waste gases being discharged directly into
the chimney stack. The saving of steam in the ammonia
plant is stated to be about 4Jd. per hundredweight of
sulphate.

Partnerships Dissolved.—The London Gazette announces
the dissolution of the following partnerships:—J. E. Noirit
and A. Noirit, carrying on business as saddlery merchants
and manufacturers, at Darwall-street, Walsall, under the
style of E. and A. Noirit, and as malleable iron founders, at
Hatherton-etreet, Walsall, under the style of Broadhurst
and Co., so far as regards A. Noirit; Alice Skelding, H. E.
Guest and W. E. Guest, carrying on business as coal
merchants, at Vale-street, Dennis-park, Stourbridge, under
the style of Guest and Co.

Hull Coal Export!. — The official return of the exports of
coal from Hull for the week ending Tuesday, April 22, 1913,
is as follows:—Amsterdam, 2,334 tons ; Antwerp, 660;
Allinge, 166 ; Aquila, 1,021; Arendal, 1,045; Bruges, 1,601;
Bandholm, 895; Brunsbuttel, 1,425 ; Bremen, 6,035;
Christiania, 2,065; Copenhagen, 254; Calais, 1,416; Civita
Vecchia 4,952; Drontheim, 250; Tuborg, 1,478; Gefle, 1,400;
Genoa, 2,455; Gothenburg, 569; Harlingen, 1,068; Hamburg,
9,462; Harburg, 499; Hamas, 1,832; Libau, 5,925; Mar-
seilles, 605; Naples, 1,353 ; Newfairwater, 443; Malmo, 423 ;
Nakskov, 1,610; Oporto, 1,490; Oxelosund,2,299; Riga,2,731;
Randers, 901; Rouen, 1,563; Rotterdam, 15,526; Revai,
4,927; Stettin, 250; Stockholm, 1,261 ; St. Petersburg,
2,959; St. Peters, 725; Stege, 769; Videy, 1,371; Venice,
822; total, 90,835 tons. Corresponding period last year
(strike period) nil, 1911 61,008 tons.

THE THIRD REPORT OF THE EXPLOSIONS IN
MINES COMMITTEE

The Appendices.

We give below a short summary of the appendices to
the Third Report of the Explosions in Mines Committee
on “ The Influence of Incombustible Dusts on the
Inflammation of Gaseous Mixtures.”*

I. The Lower Limit of Inflammation of Mixtures of the
Paraffin Hydrocarbons with Air.f

By R. V. Wheeler, D.Sc., Chief Chemist, and M. J.
Burgess, Assistant Chemist.

The first systematic determinations of the limits of
inflammation were made in 1816 for “ firedamp ” by
Davy. These experiments place the lower limit of
inflammation of the particular sample of “ firedamp ”
that Davy used at between 6 3 and 67 per cent. Davy’s
determinations were repeated in 1876 by Coquillon, who
ignited the mixtures in a closed vessel by means of an
electric spark. His results, and his description of them,
are similar to Davy’s, but he places the lower limit at
about 5 8 per cent. Later determinations of the limits
of inflammation of “ firedamp,” and of a number of pure
gases and vapours, have been made by Le Chatelier, in
conjunction with Mallard and Boudouard. The figure
given for firedamp (assumed to be pure methane) is
6 per cent. This figure has received general acceptance
throughout the coalmining world. The most recent
results that have appeared are those published by Teclu.
Teclu states that the lower limit of inflammation of
methane, prepared from sodium acetate, lies between
3 20 and 3’67 per cent.

Dr. Perman states that he obtained much wider limits
than those usually given, and he gives for methane
2 5 per cent, as the lower limit of explosibility (inflam-
mation) when mixed with air, evidenced by a “ distinct
movement ” of the mercury gauge; but it does not
necessarily follow therefrom that the mixture experi-
mented with was explosive or even inflammable. The
expansion caused by the heat of combustion of only a
trace of inflammable gas would be sufficient to affect
a sufficiently delicate gauge.

In connection with the work on coaldust explosions it
was essential to know with certainty what was the
smallest amount of firedamp which, when present in
dust-free air at ordinary temperature and pressure,
would enable flame to be propagated when a source of
heat was introduced, and it was found necessary to make
fresh determinations under conditions which would, as
far as possible, eliminate sources of error, such as
cooling by the walls of the vessel in which the inflam-
mable mixtures were ignited. Moreover, there was
reason to believe that “ firedamp ” should not be regarded
as consisting of pure methane, or methane diluted with
a greater or lesser quantity of air, but that in many
samples other hydrocarbons are present in appreciable
(and by no means negligible) quantities.

Dr. Gray (Transactions Institution of Mining Engi-
neers, 39, 286,1910) points out that since the proportion of
firedamp in the atmosphere of a well-ventilated mine is
usually small, it is quite likely that the relatively much
smaller proportion of other inflammable gases has
escaped recognition; and he places on record the
analysis of a sample which contained noteworthy quan-
tities of higher paraffins. Further, when it is remem-
bered that the major portion of the inflammable gases
that find their way into the ventilating current of a
coalmine issues from minute fissures in the coal; and
that the gases that can be extracted from coal at
ordinary temperatures, either by exhaustion or by
simply crushing, contain not only ethane but higher
members of the paraffin series of hydrocarbons, it will
be seen that the limits of inflammability of every sample
of “ firedamp ” must not be regarded as identical with
those of any one particular sample.

These considerations led to the determination of the
lower limit of inflammation of the higher members of
the paraffin series of hydrocarbons when mixed with
air, as well as that of methane. At the same time it
appeared that it should be possible, by obtaining a
sufficiency of data, to establish some definite relationship
between the lower limit of inflammation of any gas and
its known physical qualities.

A “ lower-limit mixture ” is one such that a given
volume must, under the conditions of its combustion,
evolve just sufficient heat to raise an equal volume to
its ignition-temperature. There are at least three
factors which must obviously determine this necessary
condition: (1) the calorific power of the gas; (2) the
volume and specific heat of the diluent gases; and (3)
the ignition-temperature of the mixture. Of these three

* Colliery Guardian, April 8, 1913, p. 812, and April 25,
1913, p. 848.

t Abstracted from the Transactions of the Chemical
Society, Vol. 99, 1911.