1198

THE COLLIERY GUARDIAN.

December 6, 1918.

In the use of raw lignite, under present practice
thousands of tons of screenings are annually wasted.
The coal is forked over in the mine room and screened
again at the surface when being loaded into railroad
cars. If the problem is handled as outlined above, this
waste would be eliminated ; every pound of clean lig-
nite broken from the seam could be put to some
profitable use.

The raw lignite cannot be stored economically, the
treated product can ; and this results in another large
saving, in that it would enable the mines to operate
under stable conditions the year around, instead of
only during the winter months, as at present. Some
study should also be directed to designing appropriate
apparatus for the consumption of these classes of fuels
instead of using devices already on the market in-
tended to consume fuels of quite different character.

The experiments so far conducted open very large
economic and commercial possibilities, and it is be-
lieved that a little wider and more thorough investiga-
tion will point the way for the establishment of
cirbonising and briquetting plants in lignite-bearing
districts. The results will be not only the production
of a first-class solid fuel, but the saving of many
by-products valuable in war as well as peace, and
the easing of over-burdened transportation conditions.

THE POSSIBILITIES OF POWDERED
COAL.*

By W. G. Wilcox.

Among the more effi -lent types of combustion is the
use of powdered fuel. By considering the nature of
powdered coal as a fuel and its combustion charac-
teristics we can learn its possibilities in the present fuel
situation. The requirements necessary in perfect com-
b stion show the weaknesses of pre ent methods and
the possibilities of powdered ct al combustion.

Essentials of Good Combustion.

Assuming correct furnace and flue design, and proper
and controlled draught, the essentia’s of good combus-
tion are :—

Complete Oxidation of all the Combustible in the
Coal.—The loss of unburn^d carbon in the ash will vary
v\ith different types of fuel, different types of ash, and
the percentage of ash in the coal. It will also vary
with the type of stok-r used and boiler load carried.
Iti I'und-fired pra dice it will vary with the skill of the
fireman ; and in producer operation it will vary according
to the quality of the coal, type of producer and operating
conditions.

Using an Illinois coal of the following analysis :
Sulphur, 5’5 per cent.; volatile matter. 34'0; fixed
carbon, 42’0; ash, 18'5 per cent., the results of one of
the large users in the Middle West show the following
losses in the ash :

Actual per cent,
of coal lost.
Over-feed stokers—2 > per cent, unburned
carbon in the ash’................... 4’6 .

Chain grate stokers—35 per cent, un-

burned carbon in the ash .......... 6’5

Hand tired—35 per cent, upwards un-

burned carbon in the ash .......... 6’5 and upward.

This particular consumer has two different types of
stokers and also does a large amount of band-firing.
His consumption is over 100 carloads of coal per day;
operation is under the dire dion of skilled technical
men who have actual data as to losses.

In producer operation using a good-grade coal, 20
per cent, of unburned carbon in the ash is the minimum
figure. Under bad conditions when poor, fine, wet coal
was used and with variable steam pressure, as high as
55 per cent, un burned carbon will be found in the ash
even with a first-class modern producer.

With any type of stoker or producer the loss due to
unburned carbon in the ash increases with the in-
creasing ash content. Tins is not a straight-line func-
tion, partly due to the human element, while the inci ease
in unburned c-rbon with incre ising ash is affected
considerably by the natur e of the ash, its fusibility, etc.
Certain coals, although of high heating vahm, offer
enormous difficulties to efficient operation when put
through a producer, burned on grates or on stokers.
A case in point is a coal obtained in south-western
Virginia not far from Bristol, Tenn. This coal runs
over 14,000 B.Th.U. an 1 contains under 8 per cent. ash.
Occurring in this coal are fine laminations of pure
crystalline transparent calcite in just sufficient amount
t> flux the other ash materials and given continuous
trouble from clinkering. Even in a modern mechanical
producer this coal is a source of continuous trouble and
interruption of operation. Due to the mechanical
occurrence of the ash-washing does no good.

Another case is a Colorado coal of the following
analysis:—Ash, 6 66 per cent.; volatile matter, 43’76;
fixed carbon, 49’58; sulphur, 0’93; B Th.U., 12,886. The
ash of the coal melts, runs down on the grates and
freezes there while the coal itself disintegrates and
chokes up the fire.

There is, of course, also the loss of unburned carbon
up the stack which although as much as 1 or 2 per cent,
under some conditions, should be small with good
operation.

Control of Combustible and Air.—This is absolutely
essential, if we are to secure maximum flame tempera-
ture with a corresp nding increased rapidity of heat
transfer. The more lapid the beat transfer in the
furnace or boiler, the higher the capacity of the furnace
and, in general, the greater the efficiency. This may
well be shown by the following example: The theo-
retical flame temperature for hydrogen is 2,010 degs. C.;
while with 25 per cent, excess air, this figure drops to
1,764 degs. C. This factbasjlong been realised in boiler
practice and considerable emphasis has been placed on
high content of CO in the flue gases and a minimum
amount of excess air.

Control of Flame Length.—In order to maintain in a
furnace the conditions which the design of the furnace,

* Paper read before the Western New York Section of
the American Chemical Society.

the operation, or the metallurgical process occurring
therein, requires, it is essential that the length of the
flame be under control. An example is found in a
recent development in firing copper reverberatory
furnaces. For a long time it has been a practice to fire
copper reverberatories with an insufficient amount of
air, admitting the amount of air required to complete
combustion at ports along the side of the reverberatory.
It has recently been found with oil-fired reverberatories
that if the number of oil burners tiring into ihe furnace
is increased, and the mixture of < il and air so-adjusted
as to give complete combustion with a short hot flame,
the capacity of the furnace is increased in some cases as
much as 50 per cent., while the fuel ratio is better than
anything yet obt lined with oil in reverberatory practice.
This is also true of powdered coal-fired reverberatories.
In this particular operation it has been found that a
short h<>t flame leads to most efficient operat'on and
highest furnace capacity ; but theie are other processes
in which the re verse is true.

Improved Furnace Efficiency.

In changing types of fuel, for example in changing
from the hand-firing of coal to powdered coal combus-
tion, the economies met with are usually far greater
than those which < an be figuied from the known losses.
The increase in capacity is usually so great that it can
only be attributed to increased furnace efficiency. This
increased furnace efficiency in all probability follows
from the fact that the operator is now able to main-
tain the flame length and type of combustion for which
that particular furnace design is best suited. When,
in changing from hand-fired practice to powdered coal
combustion, it is found that only from 30 to 40 per
cent, as much coal is used as formerly, the greater pro-
portion of the saving is very evidently due to change in
the efficiency of the furnace.

Flexibility in Combustion.—This means rapid
response ; only in this way can a cold furnace be
brought to heat very quickly, or a standby boiler come
up to peak load rapidly, which makes for efficiency
because it reduces the fuel consumption during the
standby period. Many operations also require con-
siderable variation in heat input at different stages of
the operation; in order to secure highest efficiency
under these conditions, extreme flexibility as to “ com-
bustion load” is demanded.

Control of the Nature of the Combustion.—In many
operations it is not only necessary to heat uniformly,
quickly and efficiently, but it is equally important to
maintain a certain chemical condition i:a the furnace.
This condition may he oxidising, reducing or neutral.
In any case the control of combustion should be such
that the desiied condition may be maintained within
very close limits; failure to do so means a waste of
fuel. Maintaining an oxidising condition without
ability to control it within close limits, will result in
having present too much of an excess of air, which will
lower flame temperature, lessen output, lower furnace
efficiency and reduce fuel efficiency. Likewise a reducing
condition, unless maintained within close limits, means
that fuel is needlessly wasted. If the operation
demands a neutral condition, there may be some loss
due to spoiling of product, unless there is the ability to
maintain the neutral condition quite exactly.

One-Stage v. Two-Stage Combustion.

The best example of two-stage combustion is the
producer. The producer affords, in many of its appli-
cations, an over-all efficiency which is considerably
higher than that obtained by other methods. Never-
theless we should clearly realise that in the process
for making producer gas there is an inherent loss of
at least 20 per cent, because of the inability to
gasify without forming a certain percentage of CO2,
due to heat losses at the producer and losses in
sensible heat from the gas between the producer and
the point at which it is used.

There is another serious objection to two-stage
combustion. When combustion is completed, the final
flame temperature is lower than in a.one-stage process.
Unless we resort to such devices as the recuperator or
regenerator, high temperatures cannot be reached.
Furthermore, a two stage combustion results in “ crack-
ing ” some of the most valuable constituents of the
coal with the formation of smoke in the furnace and
soot in the producer. This has been shown very well
by Kreisinger, Augustine and Ovitz in Bulletin 135
of the Bureau of Mines in their study of the com-
bustion of coal and furnace design.

Having considered the essentials for efficient com-
bustion, we can correctly estimate the value of
powdered coal as an efficient fuel by studying its
characteristics- and seeing to what extent these make
it possible to maintain the essentials of good combus-
tion. In the same way we can also ascertain the
conditions demanded for success in the combustion of
pulverised fuel.

Fuel Characteristics of Powdered Coal.

The simplest way to regard the combustion of coal
is that it is a reaction between solid fuel and oxygen.
It is therefore a heterogeneous system; consequently
the velocity of the reaction and its completeness will
depend upon the surface exposed by the solid, the
pressure of the reacting gas, and the intimacy of the
mixture. By grinding an inch cube of coal so fine
that 85 per cent, will pass a 200 mesh screen, we have
increased the surface exposure from 6 sq. in. to
approximately 1,800 sq. in. We have therefore in-
creased the velocity of combustion approximately
300-fold. By doing so we have immediately changed
the characteristics of the fuel. We now have a fuel
relatively 300 times more active than the inch cube
of coal, a new type of fuel which has in it inherent
possibilities not met in lump or slack fuel. By in-
creasing the surface exposure 300-fold, we have
speeded up combustion proportionately. This carries
with it a further effect. The increase in combustion
velocity also increases the rapidity of heat evolution,
and consequently quickly raises the temperature of the
rest of the material. This temperature rise, which is
much more rapid than in the normal combustion of
coal, will double the velocity of combustion each rise

of 10 degs. Cent. The increased velocity due to
greater surface exposure and that due to temperature
rise are superimposed on each other, so that we have
with pulverised fuel a combustion which is hundreds
of times faster than when burning lump coal.

Having a finely divided fuel, it is possible to form
a mixture of fuel and air so intimate that each small
particle of coal is surrounded by the proper amount
of air. Tn this condition, by maintaining the proper
velocity of the air current, the fuel can be carried into
the furnace in suspension and there burned com-
pletely, efficiently, and rapidly.

Essentials for Combustion Efficiency.

It is, of course, a simple matter to control mechani-
cally the amount of powdered coal delivered to the
furnace in a given time. It is also quite possible to
control the amount of air delivered with the coal.
If, then, we deliver to the furnace an intimate mix-
ture of air and powdered coal, and have control of
the amount of coal dust and air delivered, we have
the prime essentials for highest combustion efficiency.
These are the possibilities in utilising coal in powdered
form. The degree to which they are attained depends
entirely upon how carefully we study the character-
istics of the fuel before and during combustion.

The amount of coal dust delivered to the furnace
can be controlled simply and positively by using as a
feeder a properly designed screw, operated at variable
speeds. It is also a simple matter to control the
volume of air admitted with the fuel. But the highest
efficiency possible with this type of fuel will not be
obtained unless we work out a correct way in which
to mix a finely divided solid with air.

(To be continued.')

LAW INTELLIGENCE.

HIGH COURT OF JUSTICE.

KING’S BENCH DI VISION.—December 5.

Before Mr. Justice Astbury.

Arbitrator’s Award Upheld.

Re the “ Snar.”—This was a case arising out of the
chartering and sub-chartering of the Norwegian vessel the
“ Snar.” By a charter party of March 9, 1916, the Nor-
wegian steamship “ Snar ” was chartered to the Federated
Coal Company for twelve months on hire at £5,000 a
month. By a sub-charter of March 25, 1916, the Federated
Coal Company sub-chartered the “ Snar ” to Blane,
Wright and Martinez for the same period at £5,355 a
month. In August ' 1916 Blane, Wright and Martinez
sub-sub-chartered the “ Snar ” to Quilard and Company
for the balance of the period in the head charter party
at £5,712 per month. Then Quilard and Company nego-
tiated direct with the owners of the “ Snar ” to arrange
for a further letting of the vessel to them at the expiry
of the existing charter party. The owmers were prepared
to let at 60s. per ton gross per month. That rate, said
counsel, was in excess of the limitation rate of 52s. 6d.
in force by the English and French authorities. The
“ Snar ” was then at Rouen, and the French Government
refused clearance to the vessel, and it was detained from
May 4, 1917, to May 22. A dispute arose regarding the
detention at Rouen. The matter went to arbitrators, who
found in favour of the owners of the “ Snar ” as against
the Federated Coal Company for £1,061 for the Federated
Coal Company as against Blane, Wright and Martinez
for £1,197, and for Blane, Wright and Martinez as
against Quilard and Company for £2,007.

His lordship upheld the award.

December 5.

Before Mr. Justice Rowlatt.

Marine Insurance.

Aktieselskabet Grenland v. Percy Janson.—The plaintiffs
in this case, Norwegian ship owners, claimed for a total
loss of the steamship “ Grenland ” under a policy of
marine insurance. The vessel was captured by a German
warship and condemned in the German Courts as a prize.

The defendant admitted the policy, and admitted that
he subscribed it for £187 10s., and that the vessel had
been totally lost, as alleged. But he said that in breach
of the warranty in the policy, “ warranted no mining
timber carried,” the vessel was carrying a cargo consist-
ing of crown trees and pit sleepers adapted and intended
for use in coal mines, and the whole or part of the
cargo was mining timber within the meaning of the
warranty. Alternatively, he said that the plaintiffs failed
to disclose before the contract was concluded a material
circumstance, that the cargo consisted of, or comprised,
crown trees and pit sleepers for use in mines. He also
said that during the negotiations for the contract the
plaintiffs represented that no mining timber would be
carried on the voyage, and the representation was
material.

Evidence was then called that pit props and mining
timber were different things in the understanding of
the Scandinavian trade. The words “ mining timber ”
were never applied to sawn goods, and generally meant
long beams of from 10 ft. to 30 ft. ; certainly they would
never include sleepers.

Further evidence was called to prove that sawn goods
were never classed as mining timber. In sawing wood it
was impossible to follow the grain, and the strength of
the wood was reduced. Sawn goods were measured in
a different way from that in which mining timber was
measured.

His lordship narrow’ed the matter down to the ques-
tion : What did the parties mean by “mining timber”?
He held that the plaintiffs were entitled to £187 10s., with
interest and cost.

Judgment accordingly. Stay of execution granted.

Damage to French Mine Installations. — The Petit
Parisien publishes a letter from M. Cuvinot, president
of the administrative council of the Anzin mines (Depart-
men of the Nord) to M. Clemenceau, in which he says:
The Germans, after using the mines up to last October,
began, as soon as they had to evacuate the country,
systematically to destroy with dynamite the surface instal-
lations. At a pit situated on the bank of the Scheldt
they damaged the lining in such a way as to cause a
flooding, which destroyed the work of several generations.