but if para-nitrobenzaldehyde be used in the above reaction and the
resulting nitro compound NO2.C6H4.CH(C6H4NH2)2 be reduced, then
pararosaniline is the final product, and consequently the third amino
group occupies the para position. Many derivatives of pararosaniline
and rosaniline are known, in which the hydrogen atoms of the amino
groups are replaced by alkyl groups; this has the effect of producing
a blue or violet shade, which becomes deeper as the number of groups
increases (see DYEING).
FUCINO, LAGO DI [Lat. _Lacus Fucinus_], a lake bed of the Abruzzi,
Italy, in the province of Aquila, 2 m. E. of the town of Avezzano. The
lake was 37 m. in circumference and 65 ft. deep. From the lack of an
outlet, the level of the lake was subject to great variations, often
fraught with disastrous consequences. As early as A.D. 52 the emperor
Claudius, realizing a project of Julius Caesar, constructed a tunnel
3-1/2 m. long, with 40 shafts at intervals, by which the surplus waters
found an outlet to the Liris (or Garigliano). No less than 30,000
workmen were employed for eleven years in driving this tunnel. In the
following reign the tunnel was allowed to fall into disrepair, but was
repaired by Trajan. When, however, it finally went out of use is
uncertain. The various attempts made to reopen it from 1240 onwards were
unsuccessful. By 1852 the lake had gradually risen until it was 30 ft.
above its original level, and had become a source of danger to the
surrounding countryside. A company undertook to drain it on condition of
becoming proprietors of the site when dry; in 1854, however, the rights
and privileges were purchased by Prince Giulio Torlonia (d. 1886), the
great Roman banker, who carried on the work at his own expense until, in
1876, the lake was finally drained at the cost of some L1,700,000. The
reclaimed area is 12-1/2 m. long, 7 m. broad, and is cultivated by
families from the Torlonia estates. The outlet by which it was drained
is 4 m. long and 24 sq. yds. in section.
See A. Brisse and L. de Rotron, _Le Dessechement du lac Fucin, execute
par S.E. le Prince A. Torlonia_ (Rome, 1876). (T. As.)
FUEL (O. Fr. _feuaile_, popular Lat. _focalia_, from _focus_, hearth,
fire), a term applicable to all substances that can be usefully employed
for the production of heat by combustion. Any element or combination of
elements susceptible of oxidation may under appropriate conditions be
made to burn; but only those that ignite at a moderate initial
temperature and burn with comparative rapidity, and, what is practically
of more importance, are obtainable in quantity at moderate prices, can
fairly be regarded as fuels. The elementary substances that can be so
classed are primarily hydrogen, carbon and sulphur, while others finding
more special applications are silicon, phosphorus, and the more readily
oxidizable metals, such as iron, manganese, aluminium and magnesium.
More important, however, than the elements are the carbohydrates or
compounds of carbon, oxygen and hydrogen, which form the bulk of the
natural fuels, wood, peat and coal, as well as of their liquid and
gaseous derivatives--coal-gas, coal-tar, pitch, oil, &c., which have
high values as fuel. Carbon in the elementary form has its nearest
representative in the carbonized fuels, charcoal from wood and coke from
coal.
_Solid Fuels._
Wood.
Wood may be considered as having the following average composition when
in the air-dried state: Carbon, 39.6; hydrogen, 4.8; oxygen, 34.8; ash,
1.0; water, 20%. When it is freshly felled, the water may be from 18 to
50%. Air-dried or even green wood ignites readily when a considerable
surface is exposed to the kindling flame, but in large masses with
regular or smooth surfaces it is often difficult to get it to burn. When
previously torrefied or scorched by heating to a temperature of about
200 deg., at which incipient charring is set up, it is exceedingly
inflammable. The ends of imperfectly charred boughs from the charcoal
heaps in this condition are used in Paris and other large towns in
France for kindling purposes, under the name of _fumerons_. The
inflammability, however, varies with the density,--the so-called hard
woods, oak, beech and maple, taking fire less readily than the softer,
and, more especially, the coniferous varieties rich in resin. The
calorific power of absolutely dry woods may as an average be taken at
about 4000 units, and when air-dried, i.e. containing 25% of water, at
2800 to 3000 units. Their evaporative values, i.e. the quantities of
water evaporated by unit weight, are 3.68 and 4.44.
Wood being essentially a flaming fuel is admirably adapted for use with
heat-receiving surfaces of large extent, such as locomotive and marine
boilers, and is also very clean in use. The absence of all cohesion in
the cinders or unburnt carbonized residue causes a large amount of
ignited particles to be projected from the chimney, when a rapid draught
is used, unless special spark-catchers of wire gauze or some analogous
contrivance are used. When burnt in open fireplaces the volatile
products given off in the apartment on the first heating have an acrid
penetrating odour, which is, however, very generally considered to be
agreeable. Owing to the large amount of water present, no very high
temperatures can be obtained by the direct combustion of wood, and to
produce these for metallurgical purposes it is necessary to convert it
previously either into charcoal or into inflammable gas.
Peat.
Peat includes a great number of substances of very unequal fuel value,
the most recently formed spongy light brown kind approximating in
composition to wood, while the dense pitchy brown compact substance,
obtained from the bottom of bogs of ancient formation, may be compared
with lignite or even in some instances with coal. Unlike wood, however,
it contains incombustible matter in variable but large quantity, from 5
to 15% or even more. Much of this, when the amount is large, is often
due to sand mechanically intermixed; when air-dried the proportion of
water is from 8 to 20%. When these constituents are deducted the average
composition may be stated to be--carbon, 52 to 66; hydrogen, 4.7 to
7.4; oxygen, 28 to 39; and nitrogen, 1.5 to 3%. Average air-dried peat
may be taken as having a calorific value of 3000 to 3500 units, and when
dried at 100 deg. C., and with a minimum of ash (4 to 5%), at about 5200
units, or from a quarter to one-third more than that of an equal weight
of wood. The lighter and more spongy varieties of peat when air-dried
are exceedingly inflammable, firing at a temperature of 200 deg. C.; the
denser pulpy kinds ignite less readily when in the natural state, and
often require a still higher temperature when prepared by pulping and
compression or partial carbonization. Most kinds burn with a red smoky
flame, developing a very strong odour, which, however, has its admirers
in the same way that wood smoke has. This arises from the destructive
distillation of imperfectly carbonized organic matter. The ash, like
that of wood, is light and powdery, except when much sand is present,
when it is of a denser character.
Peat is principally found in high latitudes, on exposed high tablelands
and treeless areas in more temperate climates, and in the valleys of
slow-flowing rivers,--as in Ireland, the west of Scotland, the tableland
of Bavaria, the North German plain, and parts of the valleys of the
Somme, Oise and a few other rivers in northern France. A principal
objection to its use is its extreme bulk, which for equal evaporative
effect is from 8 to 18 times that of coal. Various methods have been
proposed, and adopted more or less successfully, for the purpose of
increasing the density of raw peat by compression, either with or
without pulping; the latter process gives the heaviest products, but the
improvement is scarcely sufficient to compensate for the cost.
Lignite.
Lignite or brown coal is of intermediate character between peat and coal
proper. The best kinds are undistinguishable in quality from
free-burning coals, and the lowest earthy kinds are not equal to average
peat. When freshly raised, the proportion of water may be from 45 to 50%
and even more, which is reduced from 28 to 20% by exposure to dry air.
Most varieties, however, when fully dried, break up into powder, which
considerably diminishes their utility as fuel, as they cannot be
consolidated by coking. Lignite dust may, however, be compacted into
serviceable blocks for burning, by pressure in machines similar to those
used for brickmaking, either in the wet state as raised from the mines
or when kiln-dried at 200 deg. C. This method was adopted to a very large
extent in Prussian Saxony. The calorific value varies between 3500 and
5000 units, and the evaporative factor from 2.16 when freshly raised to
5.84 for the best kinds of lignite when perfectly dried.
Other natural fuels.
Of the other natural fuels, apart from coal (q.v.), the most important
is so-called vegetable refuse, such as cotton stalks, brushwood, straw,
and the woody residue of sugar-cane after the extraction of the
saccharine juice known as megasse or cane trash. These are extensively
used in countries where wood and coal are scarce, usually for providing
steam in the manufactures where they arise, e.g. straw for thrashing,
cotton stalks for ploughing, irrigating, or working presses, and cane
trash for boiling down sugar or driving the cane mill. According to J.
Head (_Proc. Inst. of Civil Engineers_, vol. xlviii. p. 75), the
evaporative values of 1 lb. of these different articles when burnt in a
tubular boiler are--coal, 8 lb.; dry peat, 4 lb.; dry wood, 3.58-3.52
lb.; cotton stalks or megasse, 3.2-2.7 lb.; straw, 2.46-2.30 lb.
Owing to the siliceous nature of the ash of straw, it is desirable to
have a means of clearing the grate bars from slags and clinkers at short
intervals, and to use a steam jet to clear the tubes from similar
deposits.
The common fuel of India and Egypt is derived from the dung of camels
and oxen, moulded into thin cakes, and dried in the sun. It has a very
low heating power, and in burning gives off acrid ammoniacal smoke and
vapour.
Somewhat similar are the tan cakes made from spent tanners' bark, which
are used to some extent in eastern France and in Germany. They are made
by moulding the spent bark into cakes, which are then slowly dried by
exposure to the air. Their effect is about equivalent to 80 and 30% of
equal weights of wood and coal respectively.
Sulphur, phosphorus and silicon, the other principal combustible
elements, are only of limited application as fuels. The first is used in
the liquidation of sulphur-bearing rocks. The ore is piled into large
heaps, which are ignited at the bottom, a certain proportion, from
one-fourth to one-third, of the sulphur content being sacrificed, in
order to raise the mass to a sufficient temperature to allow the
remainder to melt and run down to the collecting basin. Another
application is in the so-called "pyritic smelting," where ores of copper
(q.v.) containing iron pyrites, FeS2, are smelted with appropriate
fluxes in a hot blast, without preliminary roasting, the sulphur and
iron of the pyrites giving sufficient heat by oxidation to liquefy both
slag and metal. Phosphorus, which is of value from its low igniting
point, receives its only application in the manufacture of lucifer
matches. The high temperature produced by burning phosphorus is in part
due to the product of combustion (phosphoric acid) being solid, and
therefore there is less heat absorbed than would be the case with a
gaseous product. The same effect is observed in a still more striking
manner with silicon, which in the only special case of its application
to the production of heat, namely, in the Bessemer process of
steel-making, gives rise to an enormous increase of temperature in the
metal, sufficient indeed to keep the iron melted. The absolute calorific
value of silicon is lower than that of carbon, but the product of
combustion (silica) being non-volatile at all furnace temperatures, the
whole of the heat developed is available for heating the molten iron,
instead of a considerable part being consumed in the work of
volatilization, as is the case with carbonic oxide, which burns to waste
in the air.
Calorific power.
_Assay and Valuation of Carbonaceous Fuels._--The utility or value of
a fuel depends upon two principal factors, namely, its calorific power
and its calorific intensity or pyrometric effect, that is, the
sensible temperature of the products of combustion. The first of these
is constant for any particular product of combustion independently of
the method by which the burning is effected, whether by oxygen, air or
a reducible metallic oxide. It is most conveniently determined in the
laboratory by measuring the heat evolved during the combustion of a
given weight of the fuel. The method of Lewis Thompson is one of the
most useful. The calorimeter consists of a copper cylinder in which a
weighed quantity of coal intimately mixed with 10-12 parts of a
mixture of 3 parts of potassium chlorate and 1 of potassium nitrate is
deflagrated under a copper case like a diving-bell, placed at the
bottom of a deep glass jar filled with a known weight of water. The
mixture is fired by a fuse of lamp-cotton previously soaked in a nitre
solution and dried. The gases produced by the combustion rising
through the water are cooled, with a corresponding increase of
temperature in the latter, so that the difference between the
temperature observed before and after the experiment measures the heat
evolved. The instrument is so constructed that 30 grains (2 grammes)
of coal are burnt in 29,010 grains of water, or in the proportion of 1
to 937, these numbers being selected that the observed rise of
temperature in Fahrenheit degrees corresponds to the required
evaporative value in pounds, subject only to a correction for the
amount of heat absorbed by the mass of the instrument, for which a
special coefficient is required and must be experimentally determined.
The ordinary bomb calorimeter is also used. An approximate method is
based upon the reduction of lead oxide by the carbon and hydrogen of
the coal, the amount of lead reduced affording a measure of the oxygen
expended, whence the heating power may be calculated, 1 part of pure
carbon being capable of producing 34-1/2 times its weight of lead. The
operation is performed by mixing the weighed sample with a large
excess of litharge in a crucible, and exposing it to a bright red heat
for a short time. After cooling, the crucible is broken and the
reduced button of lead is cleaned and weighed. The results obtained by
this method are less accurate with coals containing much disposable
hydrogen and iron pyrites than with those approximating to anthracite,
as the heat equivalent of the hydrogen in excess of that required to
form water with the oxygen of the coal is calculated as carbon, while
it is really about four times as great. Sulphur in iron pyrites also
acts as a reducing agent upon litharge, and increases the apparent
effect in a similar manner.
The evaporative power of a coal found by the above methods, and also
by calculating the separate calorific factors of the components as
determined by the chemical analysis, is always considerably above that
obtained by actual combustion under a steam boiler, as in the latter
case numerous sources of loss, such as imperfect combustion of gases,
loss of unburnt coal in cinders, &c., come into play, which cannot be
allowed for in laboratory experiments. It is usual, therefore, to
determine the value of a coal by the combustion of a weighed quantity
in the furnace of a boiler, and measuring the amount of water
evaporated by the heat developed.
In a research upon the heating power and other properties of coal for
naval use, carried out by the German admiralty, the results tabulated
below were obtained with coals from different localities.
+-----------------------+-----------+------------+-----------+------------------+
| | Slag left | Ashes in | Soot in | Water evaporated |
| | in Grate. | Ashpit. | Flues. | by 1 lb. of Coal.|
+-----------------------+-----------+------------+-----------+------------------+
| Westphalian gas coals | 0.33-6.42 | 2.83- 6.53 | 0.32-0.46 | 6.60-7.45 lb. |
| Do. bituminous coals | 0.98-9.10 | 1.97- 9.63 | 0.24-0.88 | 7.30-8.66 |
| Do. dry coals | 1.93-5.70 | 4.37-10.63 | 0.24-0.48 | 7.03-8.51 |
| Silesian coals | 0.92-1.30 | 3.15- 3.50 | 0.24-0.30 | 6.73-7.10 |
| Welsh steam coals | 1.20-4.07 | 4.07 | 0.32 | 8.41 |
| Newcastle coals | 1.92 | 2.57 | 0.35 | 7.28 |
+-----------------------+-----------+------------+-----------+------------------+
The heats of combustion of elements and compounds will be found in
most of the larger works on physical and chemical constants; a
convenient series is given in the _Annuaire du Bureau des Longitudes_,
appearing in alternate years. The following figures for the principal
fuel elements are taken from the issue for 1908; they are expressed in
gramme "calories" or heat units, signifying the weight of water in
grammes that can be raised 1 deg. C. in temperature by the combustion
of 1 gramme of the substance, when it is oxidized to the condition
shown in the second column:
+----------------+---------------------------------+-----------+
| Element. | Product of Combustion. | Calories. |
+----------------+---------------------------------+-----------+
| Hydrogen \ | Water, H2O, condensed to liquid | 34,500 |
| / | " as vapour | 29,650 |
| Carbon-- | | |
| Diamond | Carbon Dioxide, CO2 | 7,868 |
| Graphite | " " | 7,900 |
| Amorphous | " " | 8,133 |
| Silicon-- | | |
| Amorphous | Silicon Dioxide, SiO2 | 6,414 |
| Crystallized | " " | 6,570 |
| Phosphorus | Phosphoric pentoxide, P2O5 | 5,958 |
| Sulphur | Sulphur dioxide, SO2, gaseous | 2,165 |
+----------------+---------------------------------+-----------+
The results may also be expressed in terms of the atomic equivalent of
the combustible by multiplying the above values by the atomic weight
of the substance, 12 for carbon, 28 for silicon, &c.
In all fuels containing hydrogen the calorific value as found by the
calorimeter is higher than that obtainable under working conditions by
an amount equal to the latent heat of volatilization of water which
reappears as heat when the vapour is condensed, though under ordinary
conditions of use the vapour passes away uncondensed. This gives rise
to the distinction of higher and lower calorific values for such
substances, the latter being those generally used in practice. The
differences for the more important compound gaseous fuels are as
follows:--
Calorific Value.
Higher. Lower.
Acetylene, C2H2 11,920 11,500
Ethylene, C2H4 11,880 11,120
Methane, CH4 13,240 11,910
Carbon monoxide, CO 2,440 2,440
Caloric intensity.
The calorific intensity or pyrometric effect of any particular fuel
depends upon so many variable elements that it cannot be determined
except by actual experiment. The older method was to multiply the
weight of the products of combustion by their specific heats, but this
gave untrustworthy results as a rule, on account of two
circumstances--the great increase in specific heat at high
temperatures in compound gases such as water and carbon dioxide, and
their instability when heated to 1800 deg. or 2000 deg. At such
temperatures dissociation to a notable extent takes place, especially
with the latter substance, which is also readily reduced to carbon
monoxide when brought in contact with carbon at a red heat--a change
which is attended with a large heat absorption. This effect is higher
with soft kinds of carbon, such as charcoal or soft coke, than with
dense coke, gas retort carbon or graphite. These latter substances,
therefore, are used when an intense local heat is required, as for
example, in the Deville furnace, to which air is supplied under
pressure. Such a method is, however, only of very special application,
the ordinary method being to supply air to the fire in excess of that
required to burn the fuel to prevent the reduction of the carbon
dioxide. The volume of flame, however, is increased by inert gas, and
there is a proportionate diminution of the heating effect. Under the
most favourable conditions, when the air employed has been previously
raised to a high temperature and pressure, the highest attainable
flame temperature from carbonaceous fuel seems to be about 2100
deg.-2300 deg. C.; this is realized in the bright spots or "eyes" of
the tuyeres of blast furnaces.
Very much higher temperatures may be reached when the products of
combustion are not volatile, and the operation can be effected by
using the fuel and oxidizing agent in the proportions exactly
required for perfect combustion and intimately mixed. These
conditions are met in the "Thermit" process of Goldschmidt, where
finely divided aluminium is oxidized by the oxide of some similar
metal, such as iron, manganese or chromium, the reaction being started
by a primer of magnesium and barium peroxide. The reaction is so
rapidly effected that there is an enormous rise in temperature,
estimated to be 5400 deg. F. (3000 deg. C.), which is sufficient to
melt the most refractory metals, such as chromium. The slag consists
of alumina which crystallizes in the forms of corundum and ruby, and
is utilized as an abrasive under the name of corubin.
The chemical examination includes the determination of (1) moisture,
(2) ash, (3) coke, (4) volatile matter, (5) fixed carbon in coke, (6)
sulphur, (7) chlorine, (8) phosphorus. Moisture is determined by
noting the loss in weight when a sample is heated at 100 deg. for
about one hour. The ash is determined by heating a sample in a muffle
furnace until all the combustible matter has been burnt off. The ash,
which generally contains silica, oxides of the alkaline earths, ferric
oxide (which gives the ash a red colour), sulphur, &c., is analysed by
the ordinary gravimetric methods. The determination of coke is very
important on account of the conclusions concerning the nature of the
coal which it permits to be drawn. A sample is finely powdered and
placed in a covered porcelain crucible, which is surrounded by an
outer one, the space between them being packed with small coke. The
crucibles are heated in a wind furnace for 1 to 1-1/2 hours, then
allowed to cool, the inner crucible removed, and the coke weighed. The
coke may be (1) pulverulent, (2) slightly fritted, (3) spongy and
swelled, (4) compact. Pulverulent cokes indicate a non-caking
bituminous coal, rich in oxygen if the amount be below 60%, but if the
amount be very much less it generally indicates a lignite; if the
amount be above 80% it indicates an anthracite containing little
oxygen or hydrogen. A fritted coke indicates a slightly coking coal,
while the spongy appearance points to a highly coking coal which has
been partly fused in the furnace. A compact coke is yielded by good
coking coals, and is usually large in amount. The volatile matters are
determined as the loss of weight on coking less the amount of
moisture. The "fixed carbon" is the carbon retained in the coke, which
contains in addition the ash already determined. The fixed carbon is
therefore the difference between the coke and the ash, and may be
determined from these figures; or it may be determined directly by
burning off the coke in a muffle and noting the loss in weight.
Sulphur may be present as (1) organic sulphur, (2) as iron pyrites or
other sulphides, (3) as the sulphates of calcium, aluminium and other
metals; but the amount is generally so small that only the total
sulphur is determined. This is effected by heating a mixture of the
fuel with lime and sodium carbonate in a porcelain dish to redness in
a muffle until all the carbonaceous matter has been burnt off. The
residue, which contains the sulphur as calcium sulphate, is
transferred to a beaker containing water to which a little bromine has
been added. Hydrochloric acid is carefully added, the liquid filtered
and the residue washed. To the filtrate ammonia is added, and then
barium chloride, which precipitates the sulphur as barium sulphate.
Sulphur existing in the form of sulphates may be removed by washing a
sample with boiling water and determining the sulphuric acid in the
solution. The washed sample is then fused in the usual way to
determine the proportion of sulphur existing as iron pyrites. The
distinction between sulphur present as sulphate and sulphide is of
importance in the examination of coals intended for iron smelting, as
the sulphates of the earthy metals are reduced by the gases of the
furnace to sulphides, which pass into the slag without affecting the
quality of the iron produced, while the sulphur of the metallic
sulphides in the ash acts prejudicially upon the metal. Coals for
gas-making should contain little sulphur, as the gases produced in the
combustion are noxious and have very corrosive properties. Chlorine is
rarely determined, but when present in quantity it corrodes copper and
brass boiler tubes, with which consequently chlorine-bearing coals
cannot be used. The element is determined by fusing with soda lime in
a muffle, dissolving the residue in water and precipitating with
silver nitrate. Phosphorus is determined in the ash by fusing it with
a mixture of sodium and potassium carbonates, extracting the residue
with hydrochloric acid, and twice evaporating to dryness with the same
acid. The residue is dissolved in hydrochloric acid, a few drops of
ferric chloride added, and then ammonia in excess. The precipitate of
ferric phosphate is then treated as in the ordinary estimation of
phosphates. If it be necessary to determine the absolute amount of
carbon and hydrogen in a fuel, the dried sample is treated with copper
oxide as in the ordinary estimation of these elements in organic
compounds. (H. B.)
_Liquid Fuel._
Vegetable oil is not used for fuel except for laboratory purposes,
partly because its constituent parts are less adaptable for combustion
under the conditions necessary for steam-raising, but chiefly because of
the commercial difficulty of producing it with sufficient economy to
compete with mineral fuel either solid or liquid.
The use of petroleum as fuel had long been recognized as a scientific
possibility, and some attempts had been made to adopt it in practice
upon a commercial scale, but the insufficiency, and still more the
irregularity, of the supplies prevented it from coming into practical
use to any important extent until about 1898, when discoveries of oil
specially adapted by chemical composition for fuel purposes changed the
aspect of the situation. These discoveries of special oil were made
first in Borneo and later in Texas, and experience in treating the oils
from both localities has shown that while not less adapted to produce
kerosene or illuminating oil, they are better adapted to produce fuel
oil than either the Russian or the Pennsylvanian products. Texas oil did
not hold its place in the market for long, because the influx of water
into the wells lowered their yield, but discoveries of fuel oil in
Mexico have come later and will help to maintain the balance of the
world's supply, although this is still a mere fraction of the assured
supply of coal.
With regard to the chemical properties of petroleum, it is not necessary
to say more in the present place than that the lighter and more volatile
constituents, known commercially as naphtha and benzene, must be removed
by distillation in order to leave a residue composed principally of
hydrocarbons which, while containing the necessary carbon for
combustion, shall be sufficiently free from volatile qualities to avoid
premature ignition and consequent danger of explosion. Attempts have
been made to use crude oil for fuel purposes, and these have had some
success in the neighbourhood of the oil wells and under boilers of
unusually good ventilation both as regards their chimneys and the
surroundings of their stokeholds; but for reasons both of commerce and
of safety it is not desirable to use crude oil where some distillation
is possible. The more complete the process of distillation, and the
consequent removal of the volatile constituents, the higher the
flash-point, and the more turgid and viscous is the fuel resulting; and
if the process is carried to an extreme, the residue or fuel becomes
difficult to ignite by the ordinary process of spraying or atomizing
mechanically at the moment immediately preceding combustion. The
proportions which have been found to work efficiently in practice are as
follows:--
Carbon 88.00 %
Hydrogen 10.75 %
Oxygen 1.25 %
---------
Total 100
The standards of safety for liquid fuel as determined by flash-point are
not yet finally settled, and are changing from time to time. The British
admiralty require a flash-point of 270 deg. F., and to this high
standard, and the consequent viscosity of the fuel used by vessels in
the British fleet, may partly be attributed the low rate of combustion
that was at first found possible in them. The German admiralty have
fixed a flash-point of 187 deg. F., and have used oil of this standard
with perfect safety, and at the same time with much higher measure of
evaporative duty than has been attained in British war-vessels. In the
British mercantile marine Lloyd's Register has permitted fuel with a
flash-point as low as 150 deg. F. as a minimum, and no harm has
resulted. The British Board of Trade, the department of the government
which controls the safety of passenger vessels, has fixed a higher
standard upon the basis of a minimum of 185 deg. In the case of
locomotives the flash-point as a standard of safety is of less
importance than in the case of stationary or marine boilers, because the
storage is more open, and the ventilation, both of the storage tanks and
the boilers during combustion, much more perfect than in any other class
of steam-boilers.
The process of refining by distillation is also necessary to reduce two
impurities which greatly retard storage and combustion, i.e. water and
sulphur. Water is found in all crude petroleum as it issues from the
wells, and sulphur exists in important quantities in oil from the Texas
wells. Its removal was at first found very expensive, but there no
longer exists difficulty in this respect, and large quantities of
petroleum fuel practically free from sulphur are now regularly exported
from Texas to New York and to Europe.
Water mixed with fuel is in intimate mechanical relation, and frequently
so remains in considerable quantities even after the process of
distillation. It is in fact so thoroughly mixed as to form an emulsion.
The effect of feeding such a mixture into a furnace is extremely
injurious, because the water must be decomposed chemically into its
constituents, hydrogen and oxygen, thus absorbing a large quantity of
heat which would otherwise be utilized for evaporation. Water also
directly delays combustion by producing from the jet a long, dull, red
flame instead of a short bright, white flame, and the process of
combustion, which should take place by vaporization of the oil near the
furnace mouth, is postponed and transferred to the upper part of the
combustion-box, the tubes, and even the base of the chimney, producing
loss of heat and injury to the boiler structure. The most effective
means of ridding the fuel of this dangerous impurity is by heat and
settlement. The coefficients of expansion of water and oil by heat are
substantially different, and a moderate rise of temperature therefore
separates the particles and precipitates the water, which is easily
drawn off--leaving the oil available for use. The heating and
precipitation are usually performed upon a patented system of settling
tanks and heating apparatus known as the Flannery-Boyd system, which has
proved itself indispensable for the successful use at sea of petroleum
fuel containing any large proportion of water.
Progress of liquid fuel.
The laboratory and mechanical use of petroleum for fuel has already been
referred to, but it was not until the year 1870 that petroleum was
applied upon a wider and commercial scale. In the course of distillation
of Russian crude petroleum for the production of kerosene or lamp oil,
large quantities of refuse were produced--known by the Russian name of
_astatki_--and these were found an incumbrance and useless for any
commercial purpose. To a Russian oil-refiner gifted with mechanical
instinct and the genius for invention occurred the idea of utilizing the
waste product as fuel by spraying or atomizing it with steam, so that,
the thick and sluggish fluid being broken up into particles, the air
necessary for combustion could have free access to it. The earliest
apparatus for this purpose was a simple piece of gas-tube, into which
the thick oil was fed; by another connexion steam at high pressure was
admitted to an inner and smaller tube, and, the end of the tube nearest
to the furnace being open, the pressure of the steam blew the oil into
the furnace, and by its velocity broke it up into spray. The apparatus
worked with success from the first. Experience pointed out the proper
proportionate sizes for the inlets of steam and oil, the proper pressure
for the steam, and the proportionate sizes for the orifices of admission
to the furnaces, as well as the sizes of air-openings and best
arrangements of fire-bricks in the furnaces themselves; and what had
been a waste product now became a by-product of great value. Practically
all the steam power in South Russia, both for factories and navigation
of the inland seas and rivers, is now raised from _astatki_ fuel.
In the Far East, including Burma and parts of China and Japan, the use
of liquid fuel spread rapidly during the years 1899, 1900 and 1901,
owing entirely to the development of the Borneo oil-fields by the
enterprise of Sir Marcus Samuel and the large British corporation known
as the Shell Transport and Trading Company, of which he is the head.
This corporation has since amalgamated with the Royal Dutch Petroleum
Company controlling the extensive wells in Dutch Borneo, and together
they supply large quantities of liquid fuel for use in the Far East. In
the United States of America liquid fuel is not only used for
practically the whole of the manufacturing and locomotive purposes of
the state of Texas, but factories in New York, and a still larger number
in California, are now discarding the use of coal and adopting
petroleum, because it is more economical in its consumption and also
more easily handled in transit, and saves nearly all the labour of
stoking. So far the supplies for China and Japan have been exported from
Borneo, but the discoveries of new oil-fields in California, of a
character specially adapted for fuel, have encouraged the belief that it
may be possible to supply Chile and Peru and other South American
countries, where coal is extremely expensive, with Californian fuel; and
it has also found its way across the Pacific to Japan. There are
believed to be large deposits in West Africa, but in the meantime the
only sources of supply to those parts of Africa where manufacture is
progressing, i.e. South Africa and Egypt, are the oil-fields of Borneo
and Texas, from which the import has well begun, from Texas to
Alexandria via the Mediterranean, and from Borneo to Cape Town via
Singapore.
In England, notwithstanding the fact that there exist the finest
coal-fields in the world, there has been a surprising development of the
use of petroleum as fuel. The Great Eastern railway adapted 120
locomotive engines to its use, and these ran with regularity and success
both on express passenger and goods trains until the increase in price
due to short supply compelled a return to coal fuel. The London,
Brighton & South Coast railway also began the adaptation of some of
their locomotive engines, but discontinued the use of liquid fuel from
the same cause. Several large firms of contractors and cement
manufacturers, chiefly on the banks of the Thames, made the same
adaptations which proved mechanically successful, but were not continued
when the price of liquid fuel increased with the increased demand.
[Illustration: FIG. 1.--Holden Burner.]
Economy of liquid fuel.
The chief factors of economy are the greater calorific value of oil than
coal (about 16 lb. of water per lb. of oil fuel evaporated from a
temperature of 212 deg. F.), not only in laboratory practice, but in
actual use on a large scale, and the saving of labour both in transit
from the source of supply to the place of use and in the act of stoking
the furnaces. The use of cranes, hand labour with shovels, wagons and
locomotives, horses and carts, is unavoidable for the transit of coal;
and labour to trim the coal, to stoke it when under combustion, and to
handle the residual ashes, are all indispensable to steam-raising by
coal. On the other hand, a system of pipes and pumps, and a limited
quantity of skilled labour to manage them, is all that is necessary for
the transit and combustion of petroleum fuel; and it is certain that
even in England will be found places which, from topographical and other
circumstances, will use petroleum more economically than coal as fuel
for manufacturing purposes under reasonable conditions of price for the
fuel.
[Illustration: FIG. 2.--Rusden and Eeles Burner.]
The theoretical calorific value of oil fuel is more nearly realized in
practice than the theoretical calorific value of coal, because the
facilities for complete combustion, due to the artificial admixture of
the air by the atomizing process, are greater in the case of oil than
coal, and for this reason, among others, the practical evaporative
results are proportionately higher with liquid fuel. In some cases the
work done in a steam-engine by 2 tons of coal has been performed by 1
ton of oil fuel, but in others the proportions have been as 3 to 2, and
these latter can be safely relied on in practice as a minimum. This
saving, combined with the savings of labour and transit already
explained, will in the near future make the use of liquid fuel
compulsory, except in places so near to coal-fields that the cost of
coal becomes sufficiently low to counterbalance the savings in weight of
fuel consumed and in labour in handling it. In some locomotives on the
Great Eastern railway the consumption of oil and coal for the same
development of horse-power was as 17 lb. oil is to 35 lb. coal; all,
however, did not realize so high a result.
Liquid fuel in locomotives.
The mechanical apparatus for applying petroleum to steam-raising in
locomotives is very simple. The space in the tender usually occupied by
coal is closed up by steel-plating closely riveted and tested, so as to
form a storage tank. From this tank a feed-pipe is led to a burner of
the combined steam-and-oil type already indicated, and this burner is so
arranged as to enter a short distance inside the furnace mouth. The
ordinary fire-bars are covered with a thin layer of coal, which starts
the ignition in the first place, and the whole apparatus is ready for
work. The burner best adapted for locomotive practice is the Holden
Burner (fig. 1), which was used on the Great Eastern railway. The
steam-pipe is connected at A, the oil-pipe at B, and the hand-wheels C
and D are for the adjustment of the internal orifices according to the
rate of combustion required. The nozzle E is directed towards the
furnace, and the external ring FF, supplied by the small pipe G and the
by-pass valve H, projects a series of steam jets into the furnace,
independent of the injections of atomized fuel, and so induces an
artificial inrush of air for the promotion of combustion. This type of
burner has also been tried on stationary boilers and on board ship. It
works well, although the great consumption of steam by the supplementary
ring is a difficulty at sea, where the water lost by the consumption of
steam cannot easily be made up.
Liquid fuel at sea.
Although the application of the new fuel for land and locomotive boilers
has already been large, the practice at sea has been far more extensive.
The reason is chiefly to be found in the fact that although the sources
of supply are at a distance from Great Britain, yet they are in
countries to whose neighbourhood British steamships regularly trade, and
in which British naval squadrons are regularly stationed, so that the
advantages of adopting liquid fuel have been more immediate and the
economy more direct. The certainty of continuous supply of the fuel and
the wide distribution of storage stations have so altered the conditions
that the general adoption of the new fuel for marine purposes becomes a
matter of urgency for the statesman, the merchant and the engineer. None
of these can afford to neglect the new conditions, lest they be noted
and acted upon by their competitors. Storage for supply now exists at a
number of sea ports: London, Barrow, Southampton, Amsterdam, Copenhagen,
New Orleans, Savannah, New York, Philadelphia, Singapore, Hong Kong,
Madras, Colombo, Suez, Hamburg, Port Arthur, Rangoon, Calcutta, Bombay,
Alexandria, Bangkok, Saigon, Penang, Batavia, Surabaya, Amoy, Swatow,
Fuchow, Shanghai, Hankow, Sydney, Melbourne, Adelaide, Zanzibar,
Mombasa, Yokohama, Kobe and Nagasaki; also in South African and South
American ports.
[Illustration: FIG. 3.--Storage of Liquid Fuel on Oil-carrying Steamers
(Flannery-Boyd System).]
The British admiralty have undertaken experiments with liquid fuel at
sea, and at the same time investigations of the possibility of supply
from sources within the regions of the British empire. There is an
enormous supply of shale under the north-eastern counties of England,
but no oil that can be pumped--still less oil with a pressure above it
so as to "gush" like the wells in America--and the only sources of
liquid supply under the British flag appear to be in Burma and Trinidad.
The Borneo fields are not under British control, although developed
entirely by British capital. The Italian admiralty have fitted several
large warships with boiler apparatus to burn petroleum. The German
admiralty are regularly using liquid fuel on the China station. The
Dutch navy have fitted coal fuel and liquid fuel furnaces in
combination, so that the smaller powers required may be developed by
coal alone, and the larger powers by supplementing coal fuel with oil
fuel. The speeds of some vessels of the destroyer type have by this
means been accelerated nearly two knots.
[Illustration: FIG. 4.--Installation on ss. "Trochas."]
[Illustration: FIG. 5.--Details of Furnace, Meyer System.]
[Illustration: FIG. 6.--Details of Exterior Elongation of Furnace, Meyer
System.]
Advantages in warships.
The questions which govern the use of fuel in warships are more largely
those of strategy and fighting efficiency than economy of evaporation.
Indeed, the cost of constructing and maintaining in fighting efficiency
a modern warship is so great that the utmost use strategically must be
obtained from the vessel, and in this comparison the cost of fuel is
relatively so small an item that its increase or decrease may be
considered almost a negligible quantity. The desideratum in a warship is
to obtain the greatest fighting efficiency based on the thickest
armour, the heaviest and most numerous guns, the highest maximum speed,
and, last and not least, the greatest range of effective action based
upon the maximum supplies of fuel, provisions and other consumable
stores that the ship can carry. Now, if by changing the type of fuel it
be possible to reduce its weight by 30%, and to abolish the stokers, who
are usually more than half the ship's company, the weight saved will be
represented not merely by the fuel, but by the consumable stores
otherwise necessary for the stokers. Conversely, the radius of effective
action of the ship will be doubled as regards consumable stores if the
crew be halved, and will be increased by 50% if the same weight of fuel
be carried in the form of liquid instead of coal. In space the gain by
using oil fuel is still greater, and 36 cubic feet of oil as stored are
equal in practical calorific value to 67 cubic feet of coal according to
the allowance usual for ship's bunkering. On the other hand, coal has
been relied upon, when placed in the side bunkers of unarmoured ships,
as a protection against shot and shell, and this advantage, if it really
exists, could not be claimed in regard to liquid fuel.
Recent experiments in coaling warships at sea have not been very
successful, as the least bad weather has prevented the safe transmission
of coal bags from the collier to the ship. The same difficulty does not
exist for oil fuel, which has been pumped through flexible tubing from
one ship to the other even in comparatively rough weather.
Smokelessness, so important a feature of sea strategy, has not always
been attained by liquid fuel, but where the combustion is complete, by
reason of suitable furnace arrangements and careful management, there is
no smoke. The great drawback, however, to the use of liquid fuel in fast
small vessels is the confined space allotted to the boilers, such
confinement being unavoidable in view of the high power concentrated in
a small hull. The British admiralty's experiments, however, have gone
far to solve the problem, and the quantity of oil which can be consumed
by forced draught in confined boilers now more nearly equals the
quantity of coal consumed under similar conditions. All recent vessels
built for the British navy are so constructed that the spaces between
their double bottoms are oil-tight and capable of storing liquid fuel in
the tanks so formed. Most recent battleships and cruisers have also
liquid fuel furnace fittings, and in 1910 it already appeared probable
that the use of oil fuel in warships would rapidly develop.
In view of recent accusations of insufficiency of coal storage in
foreign naval depots, by reason of the allegation that coal so stored
quickly perishes, it is interesting to note that liquid fuel may be
stored in tanks for an indefinite time without any deterioration
whatever.
Advantages in merchant ships.
In the case of merchant steamers large progress has also been made. The
Shell Transport and Trading Company have twenty-one vessels successfully
navigating in all parts of the world and using liquid fuel. The
Hamburg-American Steamship Company have four large vessels similarly
fitted for oil fuel, which, however, differ in furnace arrangements, as
will be hereafter described, although using coal when the fluctuation of
the market renders that the more economical fuel. One of the large
American transatlantic lines is adopting liquid fuel, and French,
German, Danish and American mercantile vessels are also beginning to use
it in considerable amounts.
In the case of very large passenger steamers, such as those of 20 knots
and upwards in the Atlantic trade, the saving in cost of fuel is
trifling compared with the advantage arising from the greater weight and
space available for freight. Adopting a basis of 3 to 2 as between coal
consumption and oil consumption, there is an increase of 1000 tons of
dead weight cargo in even a medium-sized Atlantic steamer, and a
collateral gain of about 100,000 cub. ft. of measurement cargo, by
reason of the ordinary bunkers being left quite free, and the oil being
stored in the double bottom spaces hitherto unutilized except for the
purpose of water ballast. The cleanliness and saving of time from
bunkering by the use of oil fuel is also an important factor in
passenger ships, whilst considerable additional speed is obtainable. The
cost of the installation, however, is very considerable, as it includes
not only burners and pipes for the furnaces, but also the construction
of oil-tight tanks, with pumps and numerous valves and pipe connexions.
[Illustration: FIG. 7.--Furnace on ss. "Ferdinand Laeisz." A, it is
proposed to do away with this ring of brickwork as being useless; B, it
is proposed to fill this space up, thus continuing lining of furnace to
combustion chamber, and also to fit protection bricks in way of saddle
plate.]
[Illustration: FIG. 8.--Fuel Tanks, &c., of ss. "Murex."]
[Illustration: FIG. 9.--Furnace Gear of ss. "Murex."]
Fig. 2 shows a burner of Rusden and Eeles' patent as generally used on
board ships for the purpose of injecting the oil. A is a movable cap
holding the packing B, which renders the annular spindle M oil and
steam tight. E is the outer casing containing the steam jacket from
which the steam, after being fed through the steam-supply pipe G,
passes into the annular space surrounding the spindle P. It will be
seen that if the spindle P be travelled inwards by turning the handle
N, the orifice at the nozzle RR will be opened so as to allow the
steam to flow out radially. If at the same time the annular spindle M
be drawn inwards by revolving the handle L, the oil which passes
through the supply pipe F will also have emission at RR, and, coming
in contact with the outflowing steam, will be pulverized and sprayed
into the furnace. Fig. 3 is a profile and plan of a steamer adapted
for carrying oil in bulk, and showing all the storage arrangements for
handling liquid fuel. Fig. 4 shows the interior arrangement of the
boiler furnace of the steamship "Trocas." A is broken fire-brick
resting on the ordinary fire-bars, B is a brick bridge, C a casing of
fire-brick intended to protect the riveted seam immediately above it
from the direct impact of the flame, and D is a lining of fire-brick
at the back of the combustion-box, also intended to protect the
plating from the direct impact of the petroleum flame. The arrangement
of the furnace on the Meyer system is shown in fig. 5, where E is an
annular projection built at the mouth of the furnace, and BB are
spiral passages for heating the air before it passes into the furnace.
Fig. 6 shows the rings CC and details of the casting which forms the
projection or exterior elongation of the furnace. The brickwork
arrangement adopted for the double-ended boilers on the
Hamburg-American Steamship Company's "Ferdinand Laeisz" is represented
in fig. 7. The whole furnace is lined with fire-brick, and the burner
is mounted upon a circular disk plate which covers the mouth of the
furnace. The oil is injected not by steam pulverization, but by
pressure due to a steam-pump. The oil is heated to about 60 deg. C.
before entering the pump, and further heated to 90 deg. C. after
leaving the pump. It is then filtered, and passes to the furnace
injector C at about 30-lb. pressure; and its passage through this
injector and the spiral passages of which it consists pulverizes the
oil into spray, in which form it readily ignites on reaching the
interior of the furnace. The injector is on the Korting principle,
that is, it atomizes by fracture of the liquid oil arising from its
own momentum under pressure. The advantage of this system as compared
with the steam-jet system is the saving of fresh water, the
abstraction of which is so injurious to the boiler by the formation of
scale.
[Illustration: FIG. 10.--Section through Furnace of ss. "Murex."]
The general arrangement of the fuel tanks and filling pipes on the ss.
"Murex" is shown in fig. 8; and fig. 9 represents the furnace gear of
the same vessel, A being the steam-pipe, B the oil-pipe, C the
injector, D the swivel upon which the injector is hung so that it may
be swung clear of the furnace, E the fire-door, and F the handle for
adjusting the injector. In fig. 10, which represents a section of the
furnace, H is a fire-brick pier and K a fire-brick baffling bridge.
It is found in practice that to leave out the fire-bars ordinarily
used for coal produces a better result with liquid fuel than the
alternative system of keeping them in place and protecting them by a
layer of broken fire-brick.
Boilers fitted upon all the above systems have been run for thousands
of miles without trouble. In new construction it is desirable to give
larger combustion chambers and longer and narrower boiler tubes than
in the case of boilers intended for the combustion of coal alone.
(F. F.*)
_Gaseous Fuel._
Strictly speaking, much, and sometimes even most, of the heating
effected by solid or liquid fuel is actually performed by the gases
given off during the combustion. We speak, however, of gaseous fuel only
in those cases where we supply a combustible gas from the outset, or
where we produce from ordinary solid (or liquid) fuel in one place a
stream of combustible gas which is burned in another place, more or less
distant from that where it has been generated.
The various descriptions of gaseous fuel employed in practice may be
classified under the following heads: