Acetylene, The Principles Of Its Generation And Use

F >> F. H. Leeds and W. J. Atkinson Butterfield >> Acetylene, The Principles Of Its Generation And Use

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DUTY OF INCANDESCENT ACETYLENE BURNERS.--Granting that the petty troubles
and expenses incidental to incandescent lighting are not considered
prohibitive--and in careful hands they are not really serious--
and that mantles suitable for acetylene are employed, the gas may be
rendered considerably cheaper to use per unit of light evolved by
consuming it in incandescent burners. In Chapter VIII. it was shown that
the modern self-luminous, l/2-foot acetylene burner emits a light of
about 1.27 standard English candles per litre-hour. A large number of
incandescent burners, of German and French construction, consuming from
7.0 to 22.2 litres per hour at pressures ranging between 60 and 120
millimetres have been examined by Caro, who has found them to give lights
of from 10.8 to 104.5 Hefner units, and efficiencies of from 2.40 to 5.50
units per litre-hour. Averaging his results, it may be said that
incandescent burners consuming from 10 to 20 litres per hour at pressures
of 80 or 100 millimetres yield a light of 4.0 Hefner units per litre-
hour. Expressed in English terms, incandescent acetylene burners
consuming 0.5 cubic foot per hour at a pressure of 3 or 4 inches give the
duties shown in the following table, which may advantageously be compared
with that printed in Chapter VIII., page 239, for the self-luminous gas:

ILLUMINATING POWER OF INCANDESCENT ACETYLENE.
HALF-FOOT BURNERS.

1 litre = 3.65 candles | 1 candle = 0.274 litre.
1 cubic foot = 103.40 candles. | 1 candle = 0.0097 cubic foot.

A number of tests of the Guentner or Schimek incandescent burners of the
10 and 15 litres-per-hour sizes, made by one of the authors in 1906, gave
the following average results when tested at a pressure of 4 inches:
_________________________________________________________________
| | | | |
| Nominal size | Rate of Consumption per | Light in | Duty |
| of Burner. | Hour | Candles | Candles per |
| | | | Cubic Foot |
|______________|_________________________|__________|_____________|
| | | | | |
| Litres. | Cubic Foot | Litres | | |
| 10 | 0.472 | 13.35 | 46.0 | 97.4 |
| 15 | 0.663 | 18.80 | 70.0 | 105.5 |
|______________|____________|____________|__________|_____________|

These figures indicate that the duty increases slightly with the size of
the burner. Other tests showed that the duty increased more considerably
with an increase of pressure, so that mantles used, or which had been
previously used, at a pressure of 5 inches gave duties of 115 to 125
candles per cubic foot.

It should be noted that the burners so far considered are small, being
intended for domestic purposes only; larger burners exhibit higher
efficiencies. For instance, a set of French incandescent acetylene
burners examined by Fouche showed:

_________________________________________________________________
| | | | | |
| Size of Burner | Pressure | Cubic Feet | Light in | Candles per |
| in Litres. | Inches. | per Hour. | Candles. | Cubic Feet. |
|________________|__________|____________|__________|_____________|
| | | | | |
| 20 | 5.9 | 0.71 | 70 | 98.6 |
| 40 | 5.9 | 1.41 | 150 | 106.4 |
| 70 | 5.9 | 2.47 | 280 | 113.4 |
| 120 | 5.9 | 4.23 | 500 | 118.2 |
|________________|__________|____________|__________|_____________|

By increasing the pressure at which acetylene is introduced into burners
of this type, still larger duties may be obtained from them:

_________________________________________________________________
| | | | | |
| Size of Burner | Pressure | Cubic Feet | Light in | Candles per |
| in Litres. | Inches. | per Hour. | Candles. | Cubic Feet. |
|________________|__________|____________|__________|_____________|
| | | | | |
| 55 | 39.4 | 1.94 | 220 | 113.4 |
| 100 | 39.4 | 3.53 | 430 | 121.8 |
| 180 | 39.4 | 6.35 | 820 | 129.1 |
| 260 | 27.6 | 9.18 | 1300 | 141.6 |
|________________|__________|____________|__________|_____________|

High-power burners such as these are only fit for special purposes, such
as lighthouse illumination, or optical lantern work, &c.; and they
naturally require mantles of considerably greater tenacity than those
intended for employment with coal-gas. Nevertheless, suitable mantles can
be, and are being, made, and by their aid the illuminating duty of
acetylene can be raised from the 30 odd candles per foot of the common
0.5-foot self-luminous jet to 140 candles or more per foot, which is a
gain in efficiency of 367 per cent., or, neglecting upkeep and sundries
and considering only the gas consumed, an economy of nearly 79 per cent.

In 1902, working apparently with acetylene dissolved under pressure in
acetone (_cf._ Chapter XI.), Lewes obtained the annexed results with
the incandescent gas:

________________________________________________________
| | | | |
| Pressure. | Cubic Feet | Candle Power | Candles per |
| Inches. | per Hour. | Developed. | Cubic Foot. |
|___________|_____________|______________|______________|
| | | | |
| 8 | 0.883 | 65 | 73.6 |
| 9 | 0.94 | 72 | 76.0 |
| 10 | 1.00 | 146 | 146.0 |
| 12 | 1.06 | 150 | 141.2 |
| 15 | 1.25 | 150 | 120.0 |
| 20 | 1.33 | 166 | 124.8 |
| 25 | 1.50 | 186 | 123.3 |
| 40 | 2.12 | 257 | 121.2 |
|___________|_____________|______________|______________|

It will be seen that although the total candle-power developed increases
with the pressure, the duty of the burner attained a maximum at a
pressure of 10 inches. This is presumably due to the fact either that the
same burner was used throughout the tests, and was only intended to work
at a pressure of 10 inches or thereabouts, or that the larger burners
were not so well constructed as the smaller ones. Other investigators
have not given this maximum of duty with a medium-sized or medium-driven
burner; but Lewes has observed a similar phenomenon in the case of 0.7 to
0.8 cubic foot self-luminous jets.

Figures, however, which seem to show that the duty of incandescent
acetylene does not always rise with the size of the burner or with the
pressure at which the gas is delivered to it, have been published in
connexion with the installation at the French lighthouse at Chassiron,
the northern point of the Island of Oleron. Here the acetylene is
generated in hand-fed carbide-to-water generators so constructed as to
give any pressure up to nearly 200 inches of water column; purified by
means of heratol, and finally delivered to a burner composed of thirty-
seven small tubes, which raises to incandescence a mantle 55 millimetres
in diameter at its base. At a pressure of 7.77 inches of water, the
burner passes 3.9 cubic feet of acetylene per hour, and at a pressure of
49.2 inches (the head actually used) it consumes 20.06 cubic feet per
hour. As shown by the following table, such increment of gas pressure
raises the specific intensity of the light, _i.e._, the illuminating
power per unit of incandescent surface, but it does not appreciably raise
the duty or economy of the gas. Manifestly, in terms of duty alone, a
pressure of 23.6 inches of water-column is as advantageous as the higher
Chassiron figures; but since intensity of light is an important matter in
a lighthouse, it is found better on the whole to work the generators at a
pressure of 49.2 inches. In studying these figures referring to the
French lighthouse, it is interesting to bear in mind that when ordinary
six-wick petroleum oil burners wore used in the same place, the specific
intensity of the light developed was 75 candle-power per square inch, and
when that plant was abandoned in favour of an oil-gas apparatus, the
incandescent burner yielded 161 candle-power per square inch;
substitution of incandescent acetylene under pressure has doubled the
brilliancy of the light.

___________________________________________________________
| | | |
| | Duty. | Intensity. |
| Pressure in Inches. | Candle-power per | Candle-power per |
| | Cubic Foot. | Square Inch. |
|_____________________|__________________|__________________|
| | | |
| 7.77 | 105.5 | 126.0 |
| 23.60 | 106.0 | 226.0 |
| 31.50 | 110.0 | 277.0 |
| 39.40 | 110.0 | 301.0 |
| 47.30 | 106.0 | 317.0 |
| 49.20 | 104.0 | 324.9 |
| 196.80 | 110.0 | 383.0 |
|_____________________|__________________|__________________|

When tested in modern burners consuming between 12 and 18 litres per hour
at a pressure of 100 millimetres (4 inches), some special forms of
incandescent mantles constructed of ramie fibre, which in certain
respects appears to be better suited than cotton for use with acetylene,
have shown the following degree of loss in illuminating power after
prolonged employment (Caro):

_Luminosity in Hefner Units._

________________________________________________________
| | | | | |
| Mantle. | New. | After | After | After |
| | | 100 Hours. | 200 Hours. | 400 Hours. |
|_________|_______|____________|____________|____________|
| | | | | |
| No. 1. | 53.2 | 51.8 | 50.6 | 49.8 |
| No. 2. | 76.3 | 75.8 | 73.4 | 72.2 |
| No. 3. | 73.1 | 72.5 | 70.1 | 68.6 |
|_________|_______|____________|____________|____________|

It will be seen that the maximum loss of illuminating power in 400 hours
was 6.4 per cent., the average loss being 6.0 per cent.

TYPICAL INCANDESCENT BURNERS.--Of the many burners for lighting by the
use of incandescent mantles which have been devised, a few of the more
widely used types may be briefly referred to. There is no doubt that
finality in the design of these burners has not yet been reached, and
that improvements in the direction of simplification of construction and
in efficiency and durability will continue to be made.

Among the early incandescent burners, one made by the Allgemeine Carbid
und Acetylen Gesellschaft of Berlin in 1900 depended on the narrowness of
the mixing tube and the proportioning of the gas nipple and air inlets to
prevent lighting-back. There was a wider concentric tube round the upper
part of the mixing tube, and the lower part of the mantle fitted round
this. The mouth of the mixing tube of this 10-litres-per-hour burner was
0.11 inch in diameter, and the external diameter of the middle
cylindrical part of the mixing tube was 0.28 inch. There was no gauze
diaphragm or stuffing, and firing-back did not occur until the pressure
was reduced to about 1.5 inches. The same company later introduced a
burner differing in several important particulars from the one just
described. The comparatively narrow stem of the mixing tube and the
proportions of the gas nipple and air inlets were retained, but the
mixing tube was surmounted by a wide chamber or burner head, in which
naturally there was a considerable reduction in the rate of flow of the
gas. Consequently it was found necessary to introduce a gauze screen into
the burner head to prevent firing back. The alterations have resulted in
the lighting duty of the burner being considerably improved. Among other
burners designed about 1900 may be mentioned the Ackermann, the head of
which consisted of a series of tubes from each of which a jet of flame
was produced, the Fouche, the Weber, and the Trendel. Subsequently a
tubular-headed burner known as the Sirius has been produced for the
consumption of acetylene at high pressure (20 inches and upwards).

The more recent burners which have been somewhat extensively used include
the "Schimek," made by W. Guentner of Vienna, which is shown in Fig. 19.
It consists of a tapering narrow injecting nozzle within a conical
chamber C which is open below, and is surmounted by the mixing tube over
which telescopes a tube which carries the enlarged burner head G, and the
chimney gallery D. There are two diaphragms of gauze in the burner head
to prevent firing back, and one in the nozzle portion of the burner. The
conical chamber has a perforated base-plate below which is a circular
plate B which rotates on a screw cut on the lower part of the nozzle
portion A of the burner. This plate serves as a damper to control the
amount of air admitted through the base of the conical chamber to the
mixing tube. There are six small notches in the lower edge of the conical
chamber to prevent the inflow of air being cut of entirely by the damper.
The mixing tube in both the 10-litre and the 15-litre burner is about
0.24 inch in internal diameter but the burner head is nearly 0.42 inch in
the 10-litre and 0.48 inch in the 15-litre burner. The opening in the
head of the burner through which the mixture of gas and air escapes to
the flame is 0.15 and 0.17 inch in diameter in these two sizes
respectively. The results of some testings made with Schimek burners have
been already given.

[Illustration: FIG. 19.--"SCHIMEK" BURNER.]

The "Knappich" burner, made by the firm of Keller and Knappich of
Augsburg, somewhat resembles the later pattern of the Allgemeine Carbid
und Acetylen Gesellschaft. It has a narrow mixing tube, viz., 0.2 inch in
internal diameter, and a wide burner head, viz., 0.63 inch in internal
diameter for the 25-litre size. The only gauze diaphragm is in the upper
part of the burner head. The opening in the cap of the burner head, at
which the gas burns, is 0.22 inch in diameter. The gas nipple extends
into a domed chamber at the base of the mixing tube, and the internal air
is supplied through four holes in the base-plate of that chamber. No
means of regulating the effective area of the air inlet holes are
provided.

The "Zenith" burner, made by the firm of Gebrueder Jacob of Zwickau, more
closely resembles the Schimek, but the air inlets are in the side of the
lower widened portion of the mixing tube, and are more or less closed by
means of an outside loose collar which may be screwed up and down on a
thread on a collar fixed to the mixing tube. The mixing tube is 0.24
inch, and the burner head 0.475 inch in internal diameter. The opening in
the cap of the burner is 0.16 inch in diameter. There is a diaphragm of
double gauze in the cap, and this is the only gauze used in the burner.

All the incandescent burners hitherto mentioned ordinarily have the gas
nipple made in brass or other metal, which is liable to corrosion, and
the orifice to distortion by heat or if it becomes necessary to remove
any obstruction from it. The orifice in the nipple is extremely small--
usually less than 0.015 inch--and any slight obstruction or distortion
would alter to a serious extent the rate of flow of gas through it, and
so affect the working of the burner. In order to overcome this defect,
inherent to metal nipples, burners are now constructed for acetylene in
which the nipple is of hard incorrodible material. One of these burners
has been made on behalf of the Office Central de l'Acetylene of Paris,
and is commonly known as the "O.C.A." burner. In it the nipple is of
steatite. On the inner mixing tube of this burner is mounted an elongated
cone of wire wound spirally, which serves both to ensure proper admixture
of the gas and air, and to prevent firing-back. There is no gauze in this
burner, and the parts are readily detachable for cleaning when required.
Another burner, in which metal is abolished for the nipple, is made by
Geo. Bray and Co., Ltd., of Leeds, and is shown in Fig. 20. In this
burner the injecting nipple is of porcelain.

[Illustration: FIG. 20.--BRAY'S INCANDESCENT BURNER.]

ACETYLENE FOR HEATING AND COOKING.--Since the problem of constructing a
trustworthy atmospheric burner has been solved, acetylene is not only
available for use in incandescent lighting, but it can also be employed
for heating or cooking purposes, because all boiling, most warming, and
some roasting stoves are simply arrangements for utilising the heat of a
non-luminous flame in one particular way. With suitable alterations in
the dimensions of the burners, apparatus for consuming coal-gas may be
imitated and made fit to burn acetylene; and as a matter of fact several
firms are now constructing such appliances, which leave little or nothing
to be desired. It may perhaps be well to insist upon the elementary point
which is so frequently ignored in practice, viz., that no stove, except
perhaps a small portable boiling ring, ought ever to be used in an
occupied room unless it is connected with a chimney, free from down-
draughts, for the products of combustion to escape into the outer air;
and also that no chimney, however tall, can cause an up-draught in all
states of the weather unless there is free admission of fresh air into
the room at the base of the chimney. Still, at the prices for coal,
paraffin oil, and calcium carbide which exist in Great Britain, acetylene
is not an economical means of providing artificial heat. If a 0.7 cubic
foot luminous acetylene burner gives a light of 27 candles, and if
ordinary country coal-gas gives light of 12 to 13 candles in a 5-foot
burner, one volume of acetylene is equally valuable with 15 or 16 volumes
of coal-gas when both are consumed in self-luminous jets; and if, with
the mantle, acetylene develops 99 candles per cubic foot, while coal-gas
gives in common practice 15 to 20 candles, one volume of acetylene is
equally valuable with 5 to 6-1/2 volumes of coal-gas when both are
consumed on the incandescent system; whereas, if the acetylene is burnt
in a flat flame, and the coal-gas under the mantle, 1 volume of the
former is equally efficient with 2 volumes of coal-gas as an artificial
illuminant. This last method of comparison being manifestly unfair,
acetylene may be said to be at least five times as efficient per unit of
volume as coal-gas for the production of light. But from the table given
on a later page it appears that as a source of artificial heat, acetylene
is only equal to about 2-3 times its volume of ordinary coal-gas.
Nevertheless, the domestic advantages of gas firing are very marked; and
when a properly constructed stove is properly installed, the hygienic
advantages of gas-firing are alone equally conspicuous--for the disfavor
with which gas-firing is regarded by many physicians is due to experience
gained with apparatus warming principally by convection [Footnote:
Radiant heat is high-temperature heat, like the heat emitted by a mass of
red-hot coke; convected heat is low-temperature heat, invisible to the
eye. Radiant heat heats objects first, and leaves them to warm the air;
convected heat is heat applied directly to air, and leaves the air to
warm objects afterwards. On all hygienic grounds radiant heat is better
than convected heat, but the latter is more economical. By an absurd and
confusing custom, that particular warming apparatus (gas, steam, or hot
water) which yields practically no radiant heat, and does all its work by
convection, is known to the trade as a "radiator."] instead of radiation;
or to acquaintance with intrinsically better stoves either not connected
to any flues or connected to one deficient in exhausting power. In these
circumstances, whenever an installation of acetylene has been laid down
for the illumination of a house or district, the merit of convenience may
outweigh the defect of extravagance, and the gas may be judiciously
employed in a boiling ring, or for warming a bedroom; while, if pecuniary
considerations are not paramount, the acetylene may be used for every
purpose to which the townsman would apply his cheaper coal-gas.

The difficulty of constructing atmospheric acetylene burners in which the
flame would not be likely to strike back to the nipple has already been
referred to in connexion with the construction atmospheric burners for
incandescent lighting. Owing, however, to the large proportions of the
atmospheric burners of boiling rings and stove and in particular to the
larger bore of their mixing tube, the risk of the flame striking back is
greater with them, than with incandescent lighting burners. The greatest
trouble is presented at lighting, and when the pressure of the gas-supply
is low. The risk of firing-back when the burner is lighted is avoided in
some forms of boiling rings, &c., by providing a loose collar which can
be slipped over the air inlets of the Bunsen tube before applying a light
to the burner, and slipped clear of them as soon as the burner is alight.
Thus at the moment of lighting, the burner is converted temporarily into
one of the non-atmospheric type, and after the flame has thus been
established at the head or ring of the burner, the internal air-supply is
started by removing the loose collar from the air inlets, and the flame
is thus made atmospheric. In these conditions it does not travel
backwards to the nipple. In other heating burners it is generally
necessary to turn on the gas tap a few seconds before applying a light to
the burner or ring or stove; the gas streaming through the mixing tube
then fills it with acetylene and air mixed in the proper working
proportions, and when the light is applied, there is no explosion in the
mixing tube, or striking-back of the flame to the nipple.

Single or two-burner gas rings for boiling purposes, or for heating
cooking ovens, known as the "La Belle," made by Falk Stadelmann and Co.,
Ltd., of London, may be used at as low a gas pressure as 2 inches, though
they give better results at 3 inches, which is their normal working
pressure. The gas-inlet nozzle or nipple of the burner is set within a
spherical bulb in which are four air inlets. The mixing tube which is
placed at a proper distance in front of the nipple, is proportioned to
the rate of flow of the gas and air, and contains a mixing chamber with a
baffling pillar to further their admixture. A fine wire gauze insertion
serves to prevent striking-back of the flame. A "La Belle" boiling ring
consumes at 3 inches pressure about 48 litres or 1.7 cubic feet of
acetylene per hour.

ACETYLENE MOTORS.--The question as to the feasibility of developing
"power" from acetylene, _i.e._, of running an engine by means of the
gas, may be answered in essentially identical terms. Specially designed
gas-engines of 1, 3, 6, or even 10 h.p. work perfectly with acetylene,
and such motors are in regular employment in numerous situations, more
particularly for pumping water to feed the generators of a large village
acetylene installation. Acetylene is not an economical source of power,
partly for the theoretical reason that it is a richer fuel even than
coal-gas, and gas-engines would appear usually to be more efficient as
the fuel they burn is poorer in calorific intensity, _i.e._, in
heating power (which is explosive power) per unit of volume. The richer,
or more concentrated, any fuel in, the more rapidly does the explosion in
a mixture of that fuel with air proceed, because a rich fuel contains a
smaller proportion of non-inflammable gases which tend to retard
explosion than a poor one; and, in reason, a gas-engine works better the
more slowly the mixture of gas and air with which it is fed explodes.
Still, by properly designing the ports of a gas-engine cylinder, so that
the normal amount of compression of the charge and of expansion of the
exploded mixture which best suit coal-gas are modified to suit acetylene,
satisfactory engines can be constructed; and wherever an acetylene
installation for light exists, it becomes a mere question of expediency
whether the same fuel shall not be used to develop power, say, for
pumping up the water required in a large country house, instead of
employing hand labour, or the cheaper hot-air or petroleum motor. Taking
the mean of the results obtained by numerous investigators, it appears
that 1 h.p.-hour can be obtained for a consumption of 200 litres of
acetylene; whence it may be calculated that that amount of energy costs
about 3d. for gas only, neglecting upkeep, lubricating material
(which would be relatively expensive) and interest, &c.

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