October 4, 1918.

THE COLLIERY GUARDIAN.

707

WEAR AND TEAR OF FUEL
ECONOMISERS.

By Edward Ingham, A.M.I.Meeh.E.

The Green’s type of fuel economiser, consisting of
an arrangement of vertical cast iron pipes through
which the boilei’ feed water is passed and heated by
the waste gases from the boiler furnaces, is nowadays
a recognised part of the steam plant at collieries.

As in the case of the boilers, a fuel economiser is
liable to deteriorate and eventually prove a source
of danger unless it be worked under satisfactory con-
ditions. In this article we shall consider the principal
causes of deterioration, and point out how, with care,
the life of an economiser may be considerably pro-
longed and the risk of explosion reduced to a
minimum.

The principal troubles which lead to deterioration
and explosion are: (1) External corrosion, (2) in-
ternal corrosion, (3) over-heating, (4) water-hammer,
and (5) flue gas explosions.

External Corrosion.

External corrosion is undoubtedly the principal
cause of deterioration. It is usually the result of
allowing the external surfaces of the vertical pipes
and the top and bottom boxes to become damp. In
general, it may be said that by keeping the external
surfaces dry, the trouble in question may be almost
entirely prevented.

Dampness may arise in a number of ways. The
economiser, for example, may be set in a damp situa-
tion, so that the whole of the brickwork setting is
always more or less damp. It should be remembered
that brickwork is porous and readily absorbs
moisture, so that every precaution should be taken
to prevent the setting from becoming damp. To this
end special attention should be given to the question
of preventing drainage or waste water from valves,
etc., soaking into the setting or from draining into
the soot chamber. It sometimes happens that the
soot chamber is below the level of the drains, so that
any water which collects therein cannot be satisfac-
torily removed. In such circumstances the lower por-
tions of the economiser are very liable to become
severely corroded. The difficulty may be overcome by
digging a well near to the economiser and providing
suitable arrangements for draining the water which
collects in the soot chamber into the well.

The principal cause of external wasting, however,
is condensation of steam on the external surfaces of
the vertical pipes. Most fuels contain a certain per-
centage of moisture, so that steam will be present in
the furnace gases. Immediately the gases come into
contact with the comparatively cold surfaces of the
vertical pipes at the feed inlet end of the economiser,
this steam condenses and settles on the lower portions
of the pipes. If the fuel also contains sulphur, corro-
sive acids are liable to be formed, which will attack
the metal and cause more or less severe wasting.

It is obvious that in order to obviate this trouble
condensation of steam in the gases should be pre-
vented. Experience has shown that if the tempera-
ture of the feed water entering the economiser is
not less than about 100 degs. Fahr, condensation is
not liable to take place in ordinary circumstances to
an objectionable extent. Hence it is very important
that in all cases the feed water should be raised in
temperature to at least 100 degs. before it enters the
economiser. If, of course, the feed water is the con-
densed steam from a surface-condensing engine, or
if it has been passed through a feed-water heater, its
temperature will generally be quite sufficient to pre-
vent any condensation, but otherwise some means
should be adopted for raising the temperature to the
desired amount. There are various ways of doing
this, one of the simplest being to connect the suction
pipe of the feed pump with the economiser outlet by
means of 1 in. wrought iron piping, so that some of
the hot feed may be introduced into the coal feed,
and the temperature of the latter thus raised as
desired. A small valve will, of course, be required
in the wrought iron piping in order that the quan-
tity of hot water passing through may be regulated.
There are also special devices for raising the tempera-
ture of the feed water.

It should be mentioned that although in most
cases external corrosion due to condensation of steam
on the pipes is not as a rule experienced when the
temperature of the water is raised to 100 degs.,
trouble is sometimes met with even when the tempera-
ture is as high as 140 degs. These, however, are ex-
ceptional cases, and occur, for example, when steam
jets are used in the furnaces, the jets giving rise
to the formation of a considerable quantity of steam
in the gases.

Internal Corrosion.

Internal corrosion is mostly caused by the acid
action of the feed water. When the water is corro-
sive, the internal surfaces of the vertical pipes and
of the top and bottom boxes become gradually wasted
away. In order to prevent this trouble it is necessary
to introduce certain reagents which will neutralise
the acid action of the water.

In many cases, however, internal corrosion appears
to take place mor^ or less rapidly, though the water
is comparatively pure. This kind of wasting is known
as graphitic wasting, and is of a very peculiar form.
The internal surfaces of the pipes remain apparently
unchanged, but if a chisel be applied, the wasted
material, which takes the form of black lead, may be
easily pared away. Obviously this form of cortosion
is ka dangerous one, since, owing to’ the fact that
the metal does not appear to have been affected in
any way, the wasting is liable to be overlooked. If
the feed water contains much scale-forming matter in
solution, this defect is not likely to be met with, the
formation of scale on the pipes apparently protecting
the metal from the corrosive action.

Overheating.

Overheating may be brought about in different
ways, a common cause of the trouble being the forma-

tion of scale on the internal surfaces of the pipes
and boxes. It is well known that most forms of scale
are bad conductors of heat, and interfere with the
free transmission of heat from the furnace gases to
the water in the economiser, the result being that
the metal becomes overheated, whilst the economiser
is rendered inefficient in working. In serious cases
the pipes may become overheated to such an extent
that they eventually fracture, involving risk of
serious explosion.

Another way in which overheating is brought about
is by passing the hot gases through the economiser
chamber when the water is not being pumped through
the economiser. For example, on starting up after
a stoppage, the attendant may forget for the moment
that the engines and feed pumps have not yet been
started, and open the dampers in the economiser
chamber to the full, so that the whole body of hot
gases is allowed to pass through the chamber. Since
the quantity of water contained in the pipes is com-
paratively small, the effect of the hot gases is to raise
the temperature of the water rapidly, and hence,
before long, some of the water may be evaporated
into steam. Under such circumstances the level of
the water in the vertical pipes will gradually fall,
leaving the upper portions of the pipes bared of water,
and thus liable to serious overheating.

Intermittent feeding may bring about a similar
result, and it is therefore desirable that continuous
feeding should be maintained as far as possible. Fre-
quent testing of the safety valve is useful in showing
whether any steam is being formed in the pipes. If
it is really necessary to work the economiser inter-
mittently, the furnace gases, or at least a portion of
them, should be by-passed, and at starting times this
precaution should always be observed.

Water Hammer.

This is not an uncommon trouble in- the working of
fuel economisers. It is usually a consequence of the
formation of steam in the economiser. When steam
forms, the opening of the outlet valve from the
economiser allows this steam to come into contact with
the water on the boiler side of the outlet valve, and
as a result crackling and water hammer action are
experienced. In serious cases this action may lead
to fracture of the top feed pipes and serious injury
to the engineer in charge. The obvious remedy for
water hammer is to avoid overheating and the forma-
tion of steam in the vertical pipes

Flue Gas Explosions.

Explosions of gas in conomiser chambers are not
uncommon occurrences, but in most cases they do not
give rise to very serious consequences. The brick-
work chamber may be more or less severely disturbed,
but apart from this there is, as a rule, no further
material damage. It is, however, conceivable that in
severe cases the shock of explosion may lead to rupture
of one or more of the vertical pipes, especially if the
pipes are much thinned by either internal or external
corrosion. A number of really disastrous economiser
explosions are believed to have been due to flue gas
explosions.

These explosions are usually brought about by air
and coal gas becoming mixed together in such pro-
portions as to form an explosive mixture, the mixture
being ignited by a spark or flame from the boiler
furnaces.

The manner in which an explosive mixture may
form is as follows: During the time the boilers are
shut down and the fires banked, the hydrocarbons dis-
tilled from the coal do not become wholly consumed,
and the unconsumed gases pass into the flues, where
they are liable to collect in any cavities which exist
in the flues, particularly in the upper portion of the
economiser chamber. Provided the accumulated gases
do not become mixed with air, there is no danger of
an explosion; but when the fireman, on starting up
the boilers, again opens the fire doors and breaks up
the fires, a quantity of cold air rushes into the fur-
naces, passing into the flues and the economiser
chamber, and so mixing with the accumulated gases.
The sparks and flame produced by the breaking up of
the fires ignite the explosive mixture, and so produce
an explosion.

In order to prevent flue explosions it is very desirable
that the dampers should be opened and allowed to
remain open for a minute or two before the fires are
disturbed. By so doing, any gases which may have
collected in the economiser chamber or elsewhere are
carried away to the chimney by the volume of cold
air which rushes through the flues.

In some cases, with the object of preventing damage
in case an explosion should occur, cast iron frames
provided with light doors are fitted into the top of
the economiser chamber. It is necessary that these
doors should be of fairly large area, say, approxi-
mately, 20 in. by 20 in., as otherwise they are liable
to prove more or less ineffective in preventing damage.
One frame and door will be required in each sloping
end of the economiser chamber, and in the case of
large economisers it is desirable that additional frames
and doors should be arranged in the sides of the
chamber.

Importance of Frequent Examination.

To prevent deterioration as far as possible, and to
safeguard the economiser against explosion, it is
obviously very necessary that frequent examination,
both internal and external, should be made. Un-
fortunately, an economiser is not by any means wholly
accessible. The vertical pipes, which are the parts
most liable to suffer, are so small that visual internal
inspection is quite out of the question, and the most
that can be done is to examine the pipes by means
of a light lowered down internally, all scale having
been removed as far as possible. A special look-out
should be kept for evidences of graphitic wasting,
and a chisel should be used, both on the pipes and
the boxes, with the object of discovering if the metal
is affected. It is recommended that if the metal has
become wasted to the extent of |in. in this way, the
pipe should be withdrawn and broken up for
examination.

As far as external examination is concerned, it is
only possible to examine the outer pipes, but, fortu-
nately, the pipes which suffer most are the outer ones
at the feed inlet end of the economiser, and these
are, as a rule, fully accessible. The extent of the
wasting which has taken place is best determined by
calipping the pipes and comparing the diameter with
the original diameter. Generally, it is the lower por-
tions which are most affected, and the wasting is
usually deepest within a few inches of the bottom
boxes. It is not wise to allow the pipes to become
reduced at any part to a diameter less than 43/16 in.

Whenever serious wasting, either internal or ex-
ternal, is suspected, it is advisable to withdraw a pipe
here and there and to break it up, so that a good
idea of the general condition of the economiser may
be obtained.

Hydraulic testing to a pressure 'of from 1J to twice
the working pressure is very useful for discovering
seriously wasted and fractured pipes.

Before concluding, it may be well to refer to the
somewhat common belief that an explosion of a fuel
economiser is a very remote possibility, and that,
even should an explosion occur, the results cannot
be of serious moment. It is quite true that an
economiser pipe, being of small diameter and con-
siderable thickness, is capable of withstanding an
enormous internal pressure; but it should be remem-
bered that the metal is liable to waste away both
internally and externally, whilst there is a further
possibility that the pipe may have been cast eccentri-
cally, so that it is thin at one side and thick at the
opposite side. Since the pipes are mostly inaccessible
for examination, it will be clear that corrosion may
continue until a pipe is practically wasted through,
whereupon failure is inevitable. Again, it is com-
monly believed that since an economiser contains only
water, no explosion can occur, because water is
practically incompressible. It must not be forgotten,
however, that immediately the water is relieved it
will, provided its temperature be over 212 degs. Fahr.,
immediately flash into steam of lower pressure, and
the shock of the explosion from one pipe may lead
to the explosion of other pipes, and consequent dis-
ruption of the whole economiser. That such accidents
are possible is well evidenced by an explosion which
occurred some time ago in South Wales, when one
group of an economiser containing 192 pipes was so
shattered that it could not be reassembled.

WATERPROOF PLUNGER GREASE.

By L. W. Brooks.

In the old days machinery did not always receive
as good attention as common sense would dictate,
especially in such matters as lubrication. Poor lubri-
cation was responsible for most of the repairs and
faulty operation. By this is not meant that cheap
lubricants were used, but the opinion is held that the
proper care was not used in selecting suitable lubri-
cants for each class of service. Cheap oil or grease
may be deemed satisfactory in some cases, such as
for the machinery in the breakers, but the power
house, hoists, cables, mine pumps, etc., require
lubricants selected with special reference to the
service. Even high-priced lubricants may be a
failure if they not designed to meet the con-
ditions under which they are used.

To illustrate this point, consider reciprocating mine
pumps handling dirty water. Grit works into the
packings and acts as an abrasive on the plungers,
scoring them badly. It also cuts out the packings,
so that they are an endless source of trouble.
Packings cost money, and it takes time to replace
them. Neither common black oil nor high-grade
cylinder oil will stop the excessive wear, because
neither has the necessary characteristics. The
problem is not solved merely by buying more expensive
lubricant.

The first consideration, therefore, is the fitness of
the lubricant for the purpose; the price is secondary.
Study each machine separately. In the case of mine
pump plungers the lubricant should be water-
proofed so it will not wash off. It must be adhesive
so the packing will not wipe it off and a man be
kept busy applying it. Such a necessity wastes
grease and time too. It must be of heavy body in
order to maintain a film that protects the plunger
from the cutting action of grit. It should contain
flake graphite to counteract the effect of grit and
add weeks to the life of the packing. Such a lubricant
is cheap at any price.

In a similar way the kind of lubricant most suit-
able for wire cables, for car wheels, for haulage loco-
motives, for pneumatic tools, etc., may be deter-
mined.—Coal Age,

Irregular Supply of Coal to Italy.—Coal arrivals in Italy,
says the Tribuna, were higher in the second quarter of
the year than in the first. Only about half the coal was
French, and of 20 per cent, less calorific value than
English. There are complaints of irregular quality and
unsuitable grades, the June arrivals of steam coal and
splint being short; but coking and gas coals were in
excess, whilst anthracite deliveries were three times the
required quantity. The State Railways are trying to
burn anthracite mixed with common coal, which is only
moderately successful. Suitable coke not being available
in required quantities, the metallurgical works suffer.

Roma Gas Bore, Queensland.—The Roma Gas bore,
according to the latest report, had reached a depth of
3,200 ft. In the old bore gas was met with at about
3,700 ft. If the gas stratum is found to be free of water,
is gas is likely to be in considerable volume. It is expected
that use will be made of the process of passing the gas,
under its own pressure, through a refined petroleum
product of a definite and suitable gravity which will
absorb the gasolene vapours. These vapours are then dis-
tilled off from the absorbent and condensed. A recent
publication of the United States Geological Survey shows
that the production of petrol by condensation methods
jumped from 43,000,000 gals, in 1914 to 65,000,000 gals,
in 1915, and was expected to be over 100,000,000 gals,
for 1916,