A DESCRIPTION OF APPARATUS FOR PRODUCING CHEAP GAS, AND SOME NOTES ON
THE ECONOMICAL EFFECT OF USING SUCH GAS WITH GAS MOTORS, ETC.
[Footnote: Abstract of paper read in Section G. British Association,
York]
By MR. J. EMERSON DOWSON, C.E., of London.
In many countries and for many years past, inventors have sought
some cheap and easy means of decomposing steam in the presence of
incandescent carbon in order to produce a cheap heating gas; and working
with the same object the writer has devised an apparatus which has been
fitted up in the garden of the Industrial Exhibition, and is there
making gas for a 3½ horse power (nominal) Otto gas engine. The retort or
generator consists of a vertical cylindrical iron casing which incloses
a thick lining of ganister to prevent loss of heat and oxidation of the
metal, and at the bottom of this cylinder is a grate on which a fire is
built up. Under the grate is a closed chamber, and a jet of superheated
steam plays into this and carries with it by induction a continuous
current of air. The pressure of the steam forces the mixture of steam
and air upward through the fire, so that the combustion of the fuel is
maintained while a continuous current of steam is decomposed, and in
this way the working of the generator is constant, and the gas is
produced without fluctuations in quality. The well-known reactions
occur, the steam is decomposed, and the oxygen from the steam and air
combines with the carbon of the fuel to form carbon dioxide (CO_2),
which is reduced to the monoxide (CO) on ascending the fuel column.
In this way the resulting gases form a mixture of hydrogen, carbon,
monoxide, and nitrogen, with a small percentage of carbon dioxide which
usually escapes without reduction. The steam should have a pressure of
1½ to 2 atmospheres, and is produced and superheated in a zigzag coil
fed with water from a neighboring boiler. The quantity of water required
is very small, being only about 7 pints for each 1,000 cubic feet of
gas, and, except on the first occasion when the apparatus is started,
the coil is heated by some of the gas drawn from the holder, so that
after the gas is lighted under the coil the superheater requires no
attention.
For boiler and furnace work the gas can be used direct from the
generator; but where uniformity of pressure is essential, as for gas
engines, gas burners, etc., the gas should pass into a holder. The
latter somewhat retards the production, but the steam injector causes
gas to be made so rapidly that a holder is easily filled against a back
pressure of 1 in. to 1½ in. of water, and at this pressure the generator
can pass gas continuously into the holder, while at the same time it is
being drawn off for consumption.
The nature of the fuel required depends on the purpose for which the gas
is used. If for heating boilers, furnaces, etc, coke or any kind of coal
maybe used; but for gas engines or any application of the gas requiring
great cleanliness and freedom from sulphur and ammonia it is best to use
anthracite, as this does not yield condensable vapors, and is very free
from impurities. Good qualities of this fuel contain over 90 per cent of
carbon and so little sulphur that, for some purposes, purification is
not necessary. For gas engines, etc., it is, however, better to pass
the gas through some hydrated oxide of iron to remove the sulphureted
hydrogen. The oxide can be used over and over again after exposure to
the air, and the purifying is thus effected without smell or appreciable
expense. Gas made by this process and with anthracite coal has no tar
and no ammonia, and the small percentage of carbon dioxide present does
not sensibly affect the heating power. A further advantage of this gas
is that it cannot burn with a smoky flame, and there is no deposition of
soot even when the object to be heated is placed over or in the flame,
and this is of importance for the cylinder and valves of a gas engine.
To produce 1,000 cubic feet only 12 lb. of anthracite are required,
allowing 8 to 10 per cent, for impurities and waste; thus a generator
A size, which produces 1,000 cubic feet per hour, needs only 12 lb. in
that time, and this can be added once an hour or at longer intervals. No
skilled labor is necessary, and in practice it is usual to employ a man
who has other work to attend to near the generator, and to pay him a
small addition to his usual wages.
The comparative explosive force of coal gas and the Dowson gas
calculated in the usual way is as 3.4:1, i. e., coal gas has 3.4 times
more energy than the writer's gas. Messrs. Crossley, of Manchester, the
makers of the Otto gas engines, have made several careful trials of this
gas with some of their 3½ horse power (nominal) engines, and in one
trial they took diagrams every half-hour for nine consecutive days.
These practical trials have shown that without altering the cylinder of
the engine it is possible to admit enough of the Dowson gas to give
the same power as with ordinary coal gas. It has been seen that the
comparative explosive force of the two gases is as 3.4:1, but as it is
well known the combustion of carbon monoxide proceeds at a comparatively
slow rate, and for this reason, and because of the diluents present in
the cylinder which affect the weaker gas more than coal gas, experience
has shown that it is best to allow five volumes of the Dowson gas for
one volume of coal gas, and then the same uniform power is obtained as
with the latter.
This gives very important economical results; for if the cost of the
Dowson gas given in the tables as 4¼d., 3-1/3d., and 2¾d. per 1,000
cubic feet, be multiplied by 5 there will be 1s. 9¼d., 1s. 4¾d., and 1s.
2¾d., or a mean of 1s. 5½d. for the equivalent of 1,000 cubic feet of
coal gas, which usually costs from 3s. to 4s., and this represents an
actual saving of about 50 to 60 per cent, in working cost. Another
practical consideration is that coal gas requires 224 lb. to 250 lb. of
coal per 1,000 cubic feet of gas, but the writer requires only 12 lb.
per 1,000 cubic feet, and multiplying this by 5 to give the equivalent
of 1,000 cubic feet of coal gas, for engine work, there are 60 lb.
instead of 224 lb. to 250 lb. This is only 24 to 27 per cent, of the
weight of the coal required for coal gas, and in many outlying districts
this will effect an appreciable saving in the cost of transport.