The general subject of boiler room practice may be considered from two
aspects. The first is that of the broad plant economy, with a suggestion
as to the methods to be followed in securing the best economical results
with the apparatus at hand and procurable. The second deals rather with
specific recommendations which should be followed in plant practice,
recommendations leading not only to economy but also to safety and
continuity of service. Such recommendations are dictated from an
understanding of the nature of steam generating apparatus and its
operation, as covered previously in this book.
It has already been pointed out that the attention given in recent years
to steam generating practice has come with a realization of the wide
difference existing between the results being obtained in every-day
operation and those theoretically possible. The amount of such attention
and regulation given to the steam generating end of a power plant,
however, is comparatively small in relation to that given to the balance
of the plant, but it may be safely stated that it is here that there is
the greatest assurance of a return for the attention given.
In the endeavor to increase boiler room efficiency, it is of the utmost
importance that a standard basis be set by which average results are to
be judged. With the theoretical efficiency obtainable varying so widely,
this standard cannot be placed at the highest efficiency that has been
obtained regardless of operating conditions. It is better set at the
best obtainable results for each individual plant under its conditions
of installation and daily operation.
With an individual standard so set, present practice can only be
improved by a systematic effort to approach this standard. The degree
with which operating results will approximate such a standard will be
found to be directly proportional to the amount of intelligent
supervision given the operation. For such supervision to be given, it is
necessary to have not only a full realization of what the plant can do
under the best operating conditions but also a full and complete
knowledge of what it is doing under all of the different conditions that
may arise. What the plant is doing should be made a matter of continuous
record so arranged that the results may be directly compared for any
period or set of conditions, and where such results vary from the
standard set, steps must be taken immediately to remedy the causes of
such failings. Such a record is an important check in the losses in the
plant.
As the size of the plant and the fuel consumption increase, such a check
of losses and recording of results becomes a necessity. In the larger
plants, the saving of but a fraction of one per cent in the fuel bill
represents an amount running into thousands of dollars annually, while
the expense of the proper supervision to secure such saving is small.
The methods of supervision followed in the large plants are necessarily
elaborate and complete. In the smaller plants the same methods may be
followed on a more moderate scale with a corresponding saving in fuel
and an inappreciable increase in either plant organization or expense.
There has been within the last few years a great increase in the
practicability and reliability of the various types of apparatus by
which the records of plant operation may be secured. Much of this
apparatus is ingenious and, considering the work to be done, is
remarkably accurate. From the delicate nature of some of the apparatus,
the liability to error necessitates frequent calibration but even where
the accuracy is known to be only within limits of, say, 5 per cent
either way, the records obtained are of the greatest service in
considering relative results. Some of the records desirable and the
apparatus for securing them are given below.
[Illustration: 2400 Horse-power Installation of Cross Drum Babcock &
Wilcox Boilers and Superheaters at the Westinghouse Electric and
Manufacturing Co., East Pittsburgh, Pa.]
Inasmuch as the ultimate measure of the efficiency of the boiler plant
is the cost of steam generation, the important records are those of
steam generated and fuel consumed Records of temperature, analyses,
draft and the like, serve as a check on this consumption, indicating the
distribution of the losses and affording a means of remedying conditions
where improvement is possible.
Coal Records--There are many devices on the market for conveniently
weighing the coal used. These are ordinarily accurate within close
limits, and where the size or nature of the plant warrants the
investment in such a device, its use is to be recommended. The coal
consumption should be recorded by some other method than from the
weights of coal purchased. The total weight gives no way of dividing the
consumption into periods and it will unquestionably be found to be
profitable to put into operation some scheme by which the coal is
weighed as it is used. In this way, the coal consumption, during any
specific period of the plant's operation, can be readily seen. The
simplest of such methods which may be used in small plants is the actual
weighing on scales of the fuel as it is brought into the fire room and
the recording of such weights.
Aside from the actual weight of the fuel used, it is often advisable to
keep other coal records, coal and ash analyses and the like, for the
evaporation to be expected will be dependent upon the grade of fuel used
and its calorific value, fusibility of its ash, and like factors.
The highest calorific value for unit cost is not necessarily the
indication of the best commercial results. The cost of fuel is governed
by this calorific value only when such value is modified by local
conditions of capacity, labor and commercial efficiency. One of the
important factors entering into fuel cost is the consideration of the
cost of ash handling and the maintenance of ash handling apparatus if
such be installed. The value of a fuel, regardless of its calorific
value, is to be based only on the results obtained in every-day plant
operation.
Coal and ash analyses used in connection with the amount of fuel
consumed, are a direct indication of the relation between the results
being secured and the standard of results which has been set for the
plant. The methods of such analyses have already been described. The
apparatus is simple and the degree of scientific knowledge necessary is
only such as may be readily mastered by plant operatives.
The ash content of a fuel, as indicated from a coal analysis checked
against ash weights as actually found in plant operation, acts as a
check on grate efficiency. The effect of any saving in the ashes, that
is, the permissible ash to be allowed in the fuel purchased, is
determined by the point at which the cost of handling, combined with the
falling off in the evaporation, exceeds the saving of fuel cost through
the use of poorer coal.
Water Records--Water records with the coal consumption, form the basis
for judging the economic production of steam. The methods of securing
such records are of later introduction than for coal, but great advances
have been made in the apparatus to be used. Here possibly, to a greater
extent than in any recording device, are the records of value in
determining relative evaporation, that is, an error is rather allowable
provided such an error be reasonably constant.
The apparatus for recording such evaporation is of two general classes:
Those measuring water before it is fed to the boiler and those measuring
the steam as it leaves. Of the first, the venturi meter is perhaps the
best known, though recently there has come into considerable vogue an
apparatus utilizing a weir notch for the measuring of such water. Both
methods are reasonably accurate and apparatus of this description has an
advantage over one measuring steam in that it may be calibrated much
more readily. Of the steam measuring devices, the one in most common use
is the steam flow meter. Provided the instruments are selected for a
proper flow, etc., they are of inestimable value in indicating the steam
consumption. Where such instruments are placed on the various engine
room lines, they will immediately indicate an excessive consumption for
any one of the units. With a steam flow meter placed on each boiler, it
is possible to fix relatively the amount produced by each boiler and,
considered in connection with some of the "check" records described
below, clearly indicate whether its portion of the total steam produced
is up to the standard set for the over-all boiler room efficiency.
Flue Gas Analysis--The value of a flue gas analysis as a measure of
furnace efficiency has already been indicated. There are on the market a
number of instruments by which a continuous record of the carbon dioxide
in the flue gases may be secured and in general the results so recorded
are accurate. The limitations of an analysis showing only CO_{2} and the
necessity of completing such an analysis with an Orsat, or like
apparatus, and in this way checking the automatic device, have already
been pointed out, but where such records are properly checked from time
to time and are used in conjunction with a record of flue temperatures,
the losses due to excess air or incomplete combustion and the like may
be directly compared for any period. Such records act as a means for
controlling excess air and also as a check on individual firemen.
Where the size of a plant will not warrant the purchase of an expensive
continuous CO_{2} recorder, it is advisable to make analyses of samples
for various conditions of firing and to install an apparatus whereby a
sample of flue gas covering a period of, say, eight hours, may be
obtained and such a sample afterwards analyzed.
Temperature Records--Flue gas temperatures, feed water temperatures and
steam temperatures are all taken with recording thermometers, any number
of which will, when properly calibrated, give accurate results.
A record of flue temperatures is serviceable in checking stack losses
and, in general, the cleanliness of the boiler. A record of steam
temperatures, where superheaters are used, will indicate excessive
fluctuations and lead to an investigation of their cause. Feed
temperatures are valuable in showing that the full benefit of the
exhaust steam is being derived.
Draft Regulation--As the capacity of a boiler varies with the combustion
rate and this rate with the draft, an automatic apparatus satisfactorily
varying this draft with the capacity demands on the boiler will
obviously be advantageous.
As has been pointed out, any fuel has some rate of combustion at which
the best results will be obtained. In a properly designed plant where
the load is reasonably steady, the draft necessary to secure such a rate
may be regulated automatically.
Automatic apparatus for the regulation of draft has recently reached a
stage of perfection which in the larger plants at any rate makes its
installation advisable. The installation of a draft gauge or gauges is
strongly to be recommended and a record of such drafts should be kept as
being a check on the combustion rates.
An important feature to be considered in the installing of all recording
apparatus is its location. Thermometers, draft gauges and flue gas
sampling pipes should be so located as to give as nearly as possible an
average of the conditions, the gases flowing freely over the ends of the
thermometers, couples and sampling pipes. With the location permanent,
there is no security that the samples may be considered an average but
in any event comparative results will be secured which will be useful in
plant operation. The best permanent location of apparatus will vary
considerably with the design of the boiler.
It may not be out of place to refer briefly to some of the shortcomings
found in boiler room practice, with a suggestion as to a means of
overcoming them.
1st. It is sometimes found that the operating force is not fully
acquainted with the boilers and apparatus. Probably the most general of
such shortcomings is the fixed idea in the heads of the operatives that
boilers run above their rated capacity are operating under a state of
strain and that by operating at less than their rated capacity the most
economical service is assured, whereas, by determining what a boiler
will do, it may be found that the most economical rating under the
conditions of the plant will be considerably in excess of the builder's
rating. Such ideas can be dislodged only by demonstrating to the
operatives what maximum load the boilers can carry, showing how the
economy will vary with the load and the determining of the economical
load for the individual plant in question.
2nd. Stokers. With stoker-fired boilers, it is essential that the
operators know the limitations of their stokers as determined by their
individual installation. A thorough understanding of the requirements of
efficient handling must be insisted upon. The operatives must realize
that smokeless stacks are not necessarily the indication of good
combustion for, as has been pointed out, absolute smokelessness is
oftentimes secured at an enormous loss in efficiency through excess air.
Another feature in stoker-fired plants is in the cleaning of fires. It
must be impressed upon the operatives that before the fires are cleaned
they should be put into condition for such cleaning. If this cleaning is
done at a definite time, regardless of whether the fires are in the best
condition for cleaning, there will be a great loss of good fuel with the
ashes.
3rd. It is necessary that in each individual plant there be a basis on
which to judge the cleanliness of a boiler. From the operative's
standpoint, it is probably more necessary that there be a thorough
understanding of the relation between scale and tube difficulties than
between scale and efficiency. It is, of course, impossible to keep
boilers absolutely free from scale at all times, but experience in each
individual plant determines the limit to which scale can be allowed to
form before tube difficulties will begin or a perceptible falling off in
efficiency will take place. With such a limit of scale formation fixed,
the operatives should be impressed with the danger of allowing it to be
exceeded.
4th. The operatives should be instructed as to the losses resulting from
excess air due to leaks in the setting and as to losses in efficiency
and capacity due to the by-passing of gases through the setting, that
is, not following the path of the baffles as originally installed. In
replacing tubes and in cleaning the heating surfaces, care must be taken
not to dislodge baffle brick or tile.
[Illustration: 2000 Horse-power Installation of Babcock & Wilcox
Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers at the
Sunnyside Plant of the Pennsylvania Tunnel and Terminal Railroad Co.,
Long Island City, N. Y.]
5th. That an increase in the temperature of the feed reduces the amount
of work demanded from the boiler has been shown. The necessity of
keeping the feed temperature as high as the quantity of exhaust steam
will allow should be thoroughly understood. As an example of this, there
was a case brought to our attention where a large amount of exhaust
steam was wasted simply because the feed pump showed a tendency to leak
if the temperature of feed water was increased above 140 degrees. The
amount wasted was sufficient to increase the temperature to 180 degrees
but was not utilized simply because of the slight expense necessary to
overhaul the feed pump.
The highest return will be obtained when the speed of the feed pumps is
maintained reasonably constant for should the pumps run very slowly at
times, there may be a loss of the steam from other auxiliaries by
blowing off from the heaters.
6th. With a view to checking steam losses through the useless blowing of
safety valves, the operative should be made to realize the great amount
of steam that it is possible to get through a pipe of a given size.
Oftentimes the fireman feels a sense of security from objections to a
drop in steam simply because of the blowing of safety valves, not
considering the losses due to such a cause and makes no effort to check
this flow either by manipulation of dampers or regulation of fires.
The few of the numerous shortcomings outlined above, which may be found
in many plants, are almost entirely due to lack of knowledge on the part
of the operating crew as to the conditions existing in their own plants
and the better performances being secured in others. Such shortcomings
can be overcome only by the education of the operatives, the showing of
the defects of present methods, and instruction in better methods. Where
such instruction is necessary, the value of records is obvious. There is
fortunately a tendency toward the employment of a better class of labor
in the boiler room, a tendency which is becoming more and more marked as
the realization of the possible saving in this end of the plant
increases.
The second aspect of boiler room management, dealing with specific
recommendations as to the care and operation of the boilers, is dictated
largely by the nature of the apparatus. Some of the features to be
watched in considering this aspect follow.
Before placing a new boiler in service, a careful and thorough
examination should be made of the pressure parts and the setting. The
boiler as erected should correspond in its baffle openings, where
baffles are adjustable, with the prints furnished for its erection, and
such baffles should be tight. The setting should be so constructed that
the boiler is free to expand without interfering with the brickwork.
This ability to expand applies also to blow-off and other piping. After
erection all mortar and chips of brick should be cleaned from the
pressure parts. The tie rods should be set up snug and then slacked
slightly until the setting has become thoroughly warm after the first
firing. The boiler should be examined internally before starting to
insure the absence of dirt, any foreign material such as waste, and
tools. Oil and paint are sometimes found in the interior of a new boiler
and where such is the case, a quantity of soda ash should be placed
within it, the boiler filled with water to its normal level and a slow
fire started. After twelve hours of slow simmering, the fire should be
allowed to die out, the boiler cooled slowly and then opened and washed
out thoroughly. Such a proceeding will remove all oil and grease from
the interior and prevent the possibility of foaming and tube
difficulties when the boiler is placed in service.
The water column piping should be examined and known to be free and
clear. The water level, as indicated by the gauge glass, should be
checked by opening the gauge cocks.
The method of drying out a brick setting before placing a boiler in
operation is described later in the discussion of boiler settings.
A boiler should not be cut into the line with other boilers until the
pressure within it is approximately that in the steam main. The boiler
stop valve should be opened very slowly until it is fully opened. The
arrangement of piping should be such that there can be no possibility of
water collecting in a pocket between the boiler and the main, from which
it can be carried over into the steam line when a boiler is cut in.
In regular operation the safety valve and steam gauge should be checked
daily. In small plants the steam pressure should be raised sufficiently
to cause the safety valves to blow, at which time the steam gauge should
indicate the pressure at which the valve is known to be set. If it does
not, one is in error and the gauge should be compared with one of known
accuracy and any error at once rectified.
In large plants such a method of checking would result in losses too
great to be allowed. Here the gauges and valves are ordinarily checked
at the time a boiler is cut out, the valves being assured of not
sticking by daily instantaneous opening through manipulation by hand of
the valve lever. The daily blowing of the safety valve acts not only as
a check on the gauge but insures the valve against sticking.
The water column should be blown down thoroughly at least once on every
shift and the height of water indicated by the glass checked by the
gauge cocks. The bottom blow-offs should be kept tight. These should be
opened at least once daily to blow from the mud drum any sediment that
may have collected and to reduce the concentration. The amount of
blowing down and the frequency is, of course, determined by the nature
of the feed water used.
In case of low water, resulting either from carelessness or from some
unforeseen condition of operation, the essential object to be obtained
is the extinguishing of the fire in the quickest possible manner. Where
practicable, this is best accomplished by the playing of a heavy stream
of water from a hose on the fire. Another method, perhaps not so
efficient, but more generally recommended, is the covering of the fire
with wet ashes or fresh fuel. A boiler so treated should be cut out of
line after such an occurrence and a thorough inspection made to
ascertain what damage, if any, has been done before it is again placed
in service.
The efficiency and capacity depend to an extent very much greater than
is ordinarily realized upon the cleanliness of the heating surfaces,
both externally and internally, and too much stress cannot be put upon
the necessity for systematic cleaning as a regular feature in the plant
operation.
The outer surfaces of the tubes should be blown free from soot at
regular intervals, the frequency of such cleaning periods being
dependent upon the class of fuel used. The most efficient way of blowing
soot from the tubes is by means of a steam lance with which all parts of
the surfaces are reached and swept clean. There are numerous soot
blowing devices on the market which are designed to be permanently fixed
within the boiler setting. Where such devices are installed, there are
certain features that must be watched to avoid trouble. If there is any
leakage of water of condensation within the setting coming into contact
with the boiler tubes, it will tend toward corrosion, or if in contact
with the heated brickwork will cause rapid disintegration of the
setting. If the steam jets are so placed that they impinge directly
against the tubes, erosion may take place. Where such permanent soot
blowers are installed, too much care cannot be taken to guard against
these possibilities.
Internally, the tubes must be kept free from scale, the ingredients of
which a study of the chapter on the impurities of water indicates are
present in varying quantities in all feed waters. Not only has the
presence of scale a direct bearing on the efficiency and capacity to be
obtained from a boiler but its absence is an assurance against the
burning out of tubes.
In the absence of a blow-pipe action of the flames, it is impossible to
burn a metal surface where water is in intimate contact with that
surface.
In stoker-fired plants where a blast is used, and the furnace is not
properly designed, there is a danger of a blow-pipe action if the fires
are allowed to get too thin. The rapid formation of steam at such points
of localized heat may lead to the burning of the metal of the tubes.
Any formation of scale on the interior surface of a boiler keeps the
water from such a surface and increases its tendency to burn. Particles
of loose scale that may become detached will lodge at certain points in
the tubes and localize this tendency at such points. It is because of
the danger of detaching scale and causing loose flakes to be present
that the use of a boiler compound is not recommended for the removal of
scale that has already formed in a boiler. This question is covered in
the treatment of feed waters. If oil is allowed to enter a boiler, its
action is the same as that of scale in keeping the water away from the
metal surfaces.
[Illustration: Fig. 41]
It has been proven beyond a doubt that a very large percentage of tube
losses is due directly to the presence of scale which, in many
instances, has been so thin as to be considered of no moment, and the
importance of maintaining the boiler heating surfaces in a clean
condition cannot be emphasized too strongly.
The internal cleaning can best be accomplished by means of an air or
water-driven turbine, the cutter heads of which may be changed to handle
various thicknesses of scale. Fig. 41 shows a turbine cleaner with
various cutting heads, which has been found to give satisfactory
service.
Where a water-driven turbine is used, it should be connected to a pump
which will deliver at least 120 gallons per minute per cleaner at 150
pounds pressure. This pressure should never be less than 90 pounds if
satisfactory results are desired. Where an air-driven turbine is used,
the pressure should be at least 100 pounds, though 150 pounds is
preferable, and sufficient water should be introduced into the tube to
keep the cutting head cool and assist in washing down the scale as it is
chipped off.
Where scale has been allowed to accumulate to an excessive thickness,
the work of removal is difficult and tedious. Where such a heavy scale
is of sulphate formation, its removal may be assisted by filling the
boiler with water to which there has been added a quantity of soda ash,
a bucketful to each drum, starting a low fire and allowing the water to
boil for twenty-four hours with no pressure on the boiler. It should be
cooled slowly, drained, and the turbine cleaner used immediately, as the
scale will tend to harden rapidly under the action of the air.
Where oil has been allowed to get into a boiler, it should be removed
before placing the boiler in service, as described previously where
reference is made to its removal by boiling out with soda ash.
Where pitting or corrosion is noted, the parts affected should be
carefully cleaned and the interior of the drums should be painted with
white zinc if the boiler is to remain idle. The cause of such action
should be immediately ascertained and steps taken to apply the proper
remedy.
When making an internal inspection of a boiler or when cleaning the
interior heating surfaces, great care must be taken to guard against the
possibility of steam entering the boiler in question from other boilers
on the same line either through the careless opening of the boiler stop
valve or some auxiliary valve or from an open blow-off. Bad accidents
through scalding have resulted from the neglect of this precaution.
Boiler brickwork should be kept pointed up and all cracks filled. The
boiler baffles should be kept tight to prevent by-passing of any gases
through the heating surfaces.
Boilers should be taken out of service at regular intervals for cleaning
and repairs. When this is done, the boiler should be cooled slowly, and
when possible, be allowed to stand for twenty-four hours after the fire
is drawn before opening. The cooling process should not be hurried by
allowing cold air to rush through the setting as this will invariably
cause trouble with the brickwork. When a boiler is off for cleaning, a
careful examination should be made of its condition, both external and
internal, and all leaks of steam, water and air through the setting
stopped. If water is allowed to come into contact with brickwork that is
heated, rapid disintegration will take place. If water is allowed to
come into contact with the metal of the boiler when out of service,
there is a likelihood of corrosion.
If a boiler is to remain idle for some time, its deterioration may be
much more rapid than when in service. If the period for which it is to
be laid off is not to exceed three months, it may be filled with water
while out of service. The boiler should first be cleaned thoroughly,
internally and externally, all soot and ashes being removed from the
exterior of the pressure parts and any accumulation of scale removed
from the interior surfaces. It should then be filled with water, to
which five or six pails of soda ash have been added, a slow fire started
to drive the air from the boiler, the fire drawn and the boiler pumped
full. In this condition it may be kept for some time without bad
effects.
If the boiler is to be out of service for more than three months, it
should be emptied, drained and thoroughly dried after being cleaned. A
tray of quick lime should be placed in each drum, the boiler closed, the
grates covered and a quantity of quick lime placed on top of the
covering. Special care should be taken to prevent air, steam or water
leaks into the boiler or onto the pressure parts to obviate danger of
corrosion.
[Illustration: 3000 Horse-power Installation of Babcock & Wilcox Boilers
in the Main Power Plant, Chicago & Northwestern Ry. Depot, Chicago,
Ill.]