By JOHN McCRAE, of Dundee.
About three years ago, when the sudden and serious fall took place in
the value of the secondary products produced in gas works, many gas
managers--ever desirous of doing their very best for their
employers--were forced to look around for some better market in which
to dispose of the products which had so seriously fallen in value.
This was no easy task; and even now it forms very uphill work indeed.
A comparatively new market has been created for the disposal of boiled
tar at several of the German ports. But the expense and difficulty of
loading ships with tar in casks take very much from the saving derived
from the new manner of disposal. It occurred to me, therefore, that we
must look nearer home for a remedy.
In all gas works of any magnitude, a considerable quantity of fuel
must be employed for the purpose of supplying the works with steam for
the exhauster engines, chemical apparatus, thawing purposes, etc.
Whether this fuel consists of coke or of coal, will not in the least
affect or alter my figures. I have no doubt if any manager discovers
that he is working more economically by selling the coke and using a
cheap small or other coal, he will adopt the cheapest process. In
Dundee, where we get a good price for coke, I found, for the purpose
of steam fuel, it would be far cheaper to buy small coal costing from
5s. to 5s. 6d. per ton delivered in the works, and dispose of the
coke. The question of fuel then lay between coal and tar; and I have
experimented somewhat extensively to ascertain the true relative
values of the two classes of fuel. For the purpose of this paper, and
within the last few days, I made a further examination into the
question; and the results arrived at will be those here quoted. The
coal we employed was what is known as Stravenhouse small coal, which
costs 5s. per ton delivered. The experiment in each case lasted 48
hours. The tar employed was what is known as boiled tar; the naphtha
having been previously removed, but the pitch oil left in the tar. The
value of this tar in Dundee is about 4s. per ton. The following are
the figures:
Coal, 10 tons 16 cwt., at 5s. £2 14 0
Tar, 1,460 gallons (or 9 tons 3 cwt.
160 gallons = 1 ton), at 4s. 1 16 7
-------
Saving per day by using tar. £0 17 5
And this at the longest day, when we are using a mere fraction of
steam, as compared with our winter requirements, and consequently the
profit is proportionally less than it will be when we are in full
work.
[Illustration]
And now allow me to direct your attention for a short time to the
appliance made use of in accomplishing this tar burning. On the wall
is shown a diagram giving in detail the injector known as C. & W.
Walker's patent tar sprayer burner; and it is supplied only by that
firm. The tar, which has been brought forward to the boilers in a
thoroughly liquid state, is discharged from the center of the injector
into the furnace of the boiler. Surrounding the center nozzle of the
injector is an annular space through which high pressure steam passes,
also into the furnace. The meaning of this steam moving along with the
tar is to force a draught, as well as to raise the temperature of the
tar, and so partially convert the tar into vapor; thereby making the
combustion more complete. The flow of the tar is regulated by the very
delicate sluices attached to the injectors. These valves consist of
elongated cones and plugs, and are constructed not only for the
purpose of regulating the flow of tar, but also for removing any
obstruction or incrustation which may accumulate in the nozzle. In
order to keep the tar in a liquid state (which in the winter time is
not an easy matter), a small steam pipe is passed through the center
of the tar pipe; but, of course, no steam is discharged among the tar,
as the presence of water in the injector prevents its correct working.
The steam pipe is simply passed through the tar pipe, and a steam trap
attached to its end. In changing from the coal or coke fuel to the
tar, little or no difficulty is experienced, and very rarely is a
shovelful of any kind of solid material required. The furnace bars
have only to be kept covered to prevent the waste of tar and the too
rapid ingress of air; and when the furnaces are in full work, and
being well and carefully attended to, the tar will be found to have
been nearly all consumed before reaching the solid material covering
the bars. The action is very much the same as in the paraffin oil
lamp. The wick is the medium by which the oil is brought to the point
of combustion, where it is developed into light; but the wick remains
little injured, although in close proximity to such intense heat. The
oil burns, not the wick. In the tar furnace, the tar itself burns, and
the tar only.
It will be easily understood that a little experience is necessary to
enable the attendant to fully understand the quantity of tar by which
complete combustion is to be obtained, and which in no case must be
exceeded. The moment one atom of tar is sent into the furnace beyond
that which can be thoroughly consumed, you have then the most hideous
discharge of black smoke (carbon) which it is difficult to describe,
but which can be easily understood, and, I believe, can be seen within
a few miles of where we now sit. I should mention that the injectors
are fitted on the furnace doors; but the connections are of such a
nature that the doors can be opened without disturbing any of the
permanent fittings.
And now I have told you that the results detailed in this short paper
were those obtained in the Dundee gas works. This is so; but were I to
leave the matter here, it might be inferred that I considered similar
results might be obtained in any and every gas works. I would not
mislead you; and therefore must detain you for a few moments longer in
order to show you how my town is different from many others. Dundee is
very peculiarly situated in this respect. It is a long distance from
any tar distiller's works capable of dealing with the large quantity
of tar we have for sale during the winter. A large portion of the
value of our tar must, therefore, go to the railway company, to cover
the cost of transit between the two points, and so the tar distiller
can allow us but a small figure for it at the starting point. Then
again, Dundee being far distant from the coal fields, the coal is
exceptionally high in price. I quite believe that in many of the west
country towns the coal for which we are paying 5s. per ton could be
had for 3s.; and the tar for which we are receiving 4s. per ton, they
would get not much under the double of this. Therefore, you see, in a
place so circumstanced, the figures I have given would be most
misleading. Still, I doubt not there are places as badly situated as
Dundee; and it is to such places that my remarks are directed. I
believe also that, in many towns distant from collieries, the tar
might be sold to manufacturers for use in their steam boilers; and
such an arrangement would, I think, prove advantageous both to the
seller and the user of this liquid fuel.
I think that as much has been said in regard to my subject as is
necessary; but permit me to add that I believe there is a future for
liquid fuels. I do not say tar, but more concentrated fuels, such as
crude naphthas, paraffins, and pitch oil. When you see one of our
large steamers taking coal into her bunker, it must have appeared to
you that there was great waste of power here. Every ton of coal laid
in must require a certain amount of power to carry it; and every ton
of coal so laid in reduces the cargo-carrying power to this extent. A
few gallons of oil will give you the steam-producing power of a ton of
coal; and this is a fact which the owners of non-paying steamships
should note. Take our locomotives also. Everything I have said in
regard to steamships applies to them; and the comfort to the stokers
and the general reduction in labor would be very marked indeed. Of
course, it may be argued that if there were such a large demand
created for oils for furnaces, the old fashioned law of supply and
demand might come into play, and so force up the price of the article
for which the increased demand had taken place. But I think this state
of matters is rather remote, when we bear in mind the great oil wells
only now becoming developed, and the oils from which can be run in
bulk direct from the wells into ships, and brought to this country at
very low rates.--_Journal of Gas Lighting._
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