SUCTION GAS-PRODUCERS
The high cost and the complicated nature of the pressure gas-generators
which have just been discussed have led manufacturers to attempt in some
other way the generation of producer-gas intended for operating motors.
Several inventors, among whom we will mention Benier and A. Taylor (in
France), made some praiseworthy although not immediately very successful
attempts to simplify the manufacture of producer-gas.
=Advantages.=--In these systems the suction occasioned by the motor
itself has taken the place of a forced draft, produced in the generator
by an air-injector or a fan, so that the gas, instead of being stored
under pressure in a gas-holder, is kept in the apparatus under a
pressure below that of the atmosphere.
As the device for producing a draft by means of boiler pressure or of a
fan, and the gas-holder, are dispensed with, the result is a saving,
first in the cost of installation, consumption, and floor space.
Furthermore, the cooler and washer are supplanted by a single scrubber.
Manufacturers have succeeded in devising apparatus remarkable for the
simplicity of the processes employed and yielding economical results
which would never be obtained with pressure-generators employing
gas-holders and boilers, considering that the boiler alone calls for a
consumption of from 15 to 30 per cent. of the total amount of coal used
for making the gas.
The best results obtained by the author with pressure gas-producers have
indicated a consumption of not much less than 1 to 1-1/4 pounds of
anthracite per horse-power per hour at the motor, while with
suction-generators, under similar conditions and with the same grade of
fuel, he has repeatedly found a consumption of from 9/10 pounds per
effective horse-power per hour. In either case, the gas obtained
developed between 1,100 and 1,300 calories (4,365 and 5,158 B.T.U. per
35.31 cubic feet) if produced from anthracite yielding from 7,500 to
8,000 calories (29,763 to 31,746 B.T.U.) per 2.2 pounds.
The suction apparatus will also work very well with inferior coal
containing up to 6 to 8 per cent. of volatile matter and from 8 to 10
per cent. of ash. This great advantage added to all the others explains
the favorable reception which European manufacturers at once gave to
suction-producers. The petroleum engine itself will find a serious
competitor in the new system.
As regards the possibility of employing suction gas generators with
respect to the somewhat peculiar properties of the fuel, it may be said
at the outset that coke from gas works yielding from 6,000 to 6,500
calories (22,911 to 24,995 B.T.U.) and also charcoal are perfectly
available.
One horse-power per hour is obtained with a consumption of 1.1 to 1.3
pounds of coke.
Blast-furnace coke may be used in case of need, but its employment is
not to be recommended on account of the sulphides it contains, which
sulphides, being carried along by the gas, are liable to form sulphuric
acid with the steam, the corrosive action of which would soon destroy
the cylinder and other important parts of the engine.
=Qualities of Fuel.=--Anthracite coal is, upon the whole, so far the
best available fuel for generators. However, it should possess certain
qualities which will now be briefly indicated.
In suction gas-generators, above all, it is important that no harmful
resistance should be opposed to the passage of the air and of the gas
produced. It is therefore necessary to employ coal of a size that will
answer the foregoing condition, without being too expensive.
The size of the pieces, to a certain extent, determines the price; and
with coal of the same properties, pieces 1.1 to 2 inches may cost 1.4 of
the price for the ordinary size of 0.59 to 0.98 inches, which is very
well adapted for gas-generators. This is the size of a hazel-nut.
Moreover, it will be advisable to select the dryest coals, containing a
minimum of volatile matter and having no tendency to coke or to cohere,
in order that the volatilized products may not by distillation obstruct
the interstices through which the gases must pass. For the same reason
coal which breaks up and becomes pulverized under the action of the
fire is not to be recommended. The coal should also be such as to avoid
the formation of arches which would interfere with the proper settling
of the fuel during its combustion. It may be stated as a rule that, with
coal that does not cohere, the content of volatile matter should not
exceed 5 to 8 per cent.
Coal which contains more than 10 to 15 per cent. of ash should not be
used, for the reason that it chokes up and obstructs generators in which
the dropping and discharge of the ashes is done automatically, a fact
which should not pass unnoticed. The furnace cannot be cleaned safely
with a fire of this kind, where combustion takes place in an enclosed
space, without hindering the production of gas. Here again a point may
be raised very much in favor of suction gas-producers. In a good
generator, the ash-pit can be cleaned and the fire stoked without
interrupting the liberation of the gas drawn in and without appreciably
impairing the quality of the gas. These considerations are of importance
so far as the gas-generator itself is concerned. Other conditions which
should be noticed affect the engine fed by the generator, the grade of
coal used, and the purification of the gas obtained from it.
Unless special chemical cleaners and purifiers are employed, thereby
complicating the plant, the coal utilized should yield as little tar as
possible during distillation; for the tendency of the tar to choke up
the pipes and to clog the valves is one of the chief causes of defective
operation of producer-gas engines.
Tar changes the proper composition of the explosive mixture. When it
catches fire in the cylinder it causes premature ignition, which is so
dangerous in large engines.
From what has been said in the foregoing, it follows that, in the
present state of the art, the satisfactory operation of gas-generators
depends no longer on the use of pure anthracite, such as Pennsylvania
coal in America and Welsh coal in England, containing an amount of
carbon as high as 90 to 94 per cent. and having a thermal value of
33,529 B.T.U. On the contrary, good dry coal yielding from 29,763 to
31,746 B.T.U. is quite suitable for the generation of producer-gas.
A final, practical advantage which speaks in favor of a generator and
motor plant as compared with a steam-engine, is the small amount of
water required. Apart from the water used for cooling the engine, which
may be used over and over again if cooled, any water, whether it forms
scale or deposits, may be employed for cooling and washing the gas in
the scrubber.
According to the author's personal experience, an average of 3.3 gallons
of water per effective horse-power per hour is sufficient for this
purpose. This is about one-half of the amount required by a
non-condensing slide-valve engine of from 15 to 30 horse-power. The
difference in the consumption of water is quite important in city
plants, where water is rather expensive as a rule.
=General Arrangement.=--A suction gas-generator plant of the character
we have been discussing is shown in Fig. 91.
[Illustration: FIG. 91.--Engine and suction gas-producer.]
The apparatus _A_ is the generator proper, in which combustion takes
place. The gas produced passes into the apparatus _B_ through a series
of tubes, to be conveyed to the washer _C_. In the apparatus _B_, which
is the vaporizer, the water admitted at the top under atmospheric
pressure is vaporized by contact with a series of tubes, heated by the
gas coming from the generator. The steam, together with air, is drawn
into the lower part of the generator to support combustion. This
vaporizer is provided with an overflow for the outlet of the water which
has not been vaporized. The producer-gas pipe which leads from the
vaporizer to the washer has a branch _D_, for the temporary escape to
the atmosphere of the gas produced before and after the operation of the
engine. In the washer, as the drawing shows, the gas enters at the
bottom and leaves at the top to pass to the gas expansion-chamber _E_
and thence to the motor. The gas thus passes through the body of coke
in the opposite direction to the wash water, which then flows to the
waste-pipe. The coke and the water free the gas not only from the dust
carried along, but from the ammonia and other impurities contained in
the gas.
When firing the generator, a small hand ventilator _G_ is used for
blowing in air to fan the fire. The gas obtained at first, being
unsuitable for combustion, is allowed to escape through the branch _D_.
After injecting air for about 10 to 15 minutes, the engine can be
started after closing the branch _D_. The suction of the engine itself
will then gradually bring about the proper conditions for its regular
running, and after a quarter of an hour or half an hour the gas is rich
enough to run the engine under a full load.
The apparatus just described is the original type, upon which many
improvements have been made for the purpose of securing a uniform gas
production and of diminishing the interval of time elapsing between the
firing of the generator and the running of the engine under a full load.
Each of the elements of this apparatus--to wit, the generator,
vaporizer, super-heater, and washer--have been modified and improved
more or less successfully by the manufacturers; and in order that the
reader may perceive the merits and the drawbacks of the various
arrangements adopted, the most important ones will be separately
discussed.
=Generator.=--With respect to the general arrangement of parts,
generators may be divided into two classes:
First.--Generators with internal vaporizers, such as the Otto Deutz and
Wiedenfeld generators.
[Illustration: FIG. 92.--Old type of Winterthur producer.]
Second.--Generators with external vaporizers, such as the Taylor,
Bollinckx, Pintsch, Kinderlen, Benz, Wiedenfeld, Hille, and Goebels
generators.
=Cylindrical Body.=--The generator consists essentially of a mantle made
of sheet-iron or cast-iron and containing a refractory lining which
forms a retort, a grate, and an ash-pit. In the small size apparatus the
cast-iron mantle is often used, whereas in large sizes the mantle is
made of riveted sheet-iron so as to reduce its weight and its cost. In
the latter case the linings are securely riveted or bolted.
The Winterthur generator (Figs. 92 and 93), the Taylor generator (Fig.
94), and the Benz generator (Fig. 97), are made of cast-iron; the
Wiedenfeld generator (Fig. 95), the Pintsch generator (Fig. 96), are
made of sheet-iron; the Bollinckx (Fig. 98) is made partly of sheet-iron
and partly of cast-iron.
The different parts of a generator, if made of sheet-iron, are held
together by means of angle-irons forming yokes, and a sheet of asbestos
is interposed. If the parts are made of cast-iron, they are connected
after the manner of pipe-joints and packed with compressed asbestos.
This latter way of assembling the parts presents the advantage of
allowing them to be dismembered readily. Therefore, it allows the
several parts to expand freely and facilitates the securing of tight
joints. This last consideration is exceedingly important, particularly
for the joints which are beyond the zone in which the distillation of
the fuel takes place. Any entrance of air through these joints would
necessarily impair the quality of the gas, either by mingling therewith,
or by combustion. The air so admitted would also be liable to form an
explosive mixture which might become ignited in case of a premature
ignition of the cylinder charge during suction or through some other
cause.
[Illustration: FIG. 93.--New type of Winterthur producer.]
[Illustration: FIG. 94.--The A. Taylor producer.]
[Illustration: FIG. 95.--Wiedenfeld producer.]
[Illustration: FIG. 96.--Pintsch producer.]
[Illustration: FIG. 97.--Benz producer.]
[Illustration: FIG. 98.--Bollinckx producer.]
[Illustration: FIG. 99.--Lencauchez producer.]
=Refractory Lining.=--The interior lining of the generator should be
made of refractory clay of the best quality. It would seem advisable, in
order to facilitate repairs, to employ retorts made of pieces held
together instead of retorts made of a single piece. In the first case
the assembling should preferably be made by means of refractory cement,
and the inner surface should be covered with a coating so as to form a
practically continuous stone surface.
[Illustration: FIG. 100.--Goebels producer.]
Some manufacturers, in order to allow for the renewal of the part most
liable to be burnt, employ at the bottom of the tank a refractory
moulded ring (Lencauchez, Fig. 99).
It is always advisable to place between the shell or mantle of the
generator and the refractory lining a layer of a material which is a bad
conductor of heat as, for instance, asbestos or sand, in order to avoid
as much as possible loss of heat due to external radiation (Fig. 100).
[Illustration: FIG. 101.--Pierson producer.]
=Grate and Support for the Lining.=--These parts, owing to their contact
with the ashes and the hot embers, are liable to deteriorate rapidly. It
is therefore indispensable that they should be removable and easily
accessible, so that they may be renewed in case of need. From this point
of view, grates composed of independent bars would appear to be
preferable. The clearance between the bars depends, of course, on the
kind of ashes resulting from the different grades of fuel. It is
advisable to design the grate so that the free passage for the air is
about 60 to 70 per cent. of the total surface.
In generators having a cup-shaped ash-pit, containing water (Fig. 95),
the grate and the base of the retort are less liable to burn than in
apparatus having dry ash-pits. Certain apparatus, such as those of
Lencauchez (Fig. 99), Pierson (Fig. 101), and Taylor (Fig. 94), have no
grates; the fuel is held in the retort by the ashes, which form a cone
resting on a sheet-iron base, easy of access for cleaning and from which
the fuel slides down gradually.
The Pierson generator (Fig. 101) is provided with a poker comprising a
central fork, which is worked with a lever, in order to stir the fire
from below without entirely extinguishing the cone of ashes.
In some apparatus in which a grate is used (Fig. 92), a space is left
between the grate and the support of the retort. This arrangement has
the merit of allowing only finely divided and completely burnt ashes to
pass to the ash-pit. Moreover, a large surface grate can be employed,
thus facilitating the passage of the mixture of air and steam.
[Illustration: FIG. 102.--Kiderlen producer.]
The space above mentioned is provided with a cleaning-door through which
cinder and slag may be removed.
In other apparatus the grate rests either on the support of the
refractory lining, as in the old type invented by Wiedenfeld (Fig. 95),
or upon a projection embedded in the lining, as, for instance, in the
Kiderlen (Fig. 102) and Pintsch generators (Fig. 96).
In the Riche apparatus (Fig. 103) there is, besides the ordinary grate,
a grate with tiers on which the fuel spreads. This grate consists of
wide, hollow bars containing water. It should be noted that the
apparatus is of the blower type.
[Illustration: FIG. 103.--Riche combustion-producer.]
An interesting arrangement is found in Benier's generator (Fig. 104).
This consists of a grate formed of projections cast around a cylinder
which can be turned about its axis. The finely divided ashes which are
retained in the spaces between these projections are thus carried into the
ash-pit, and those which adhere to the metal are scraped away by a
metallic comb fastened to the lower part of the apparatus. The "Phoenix"
generator (Fig. 105) is fitted with a grate having a mechanical cleaning
device, worked by a lever from the outside.
[Illustration: FIG. 104.--Benier producer.]
[Illustration: FIG. 105.--Phoenix producer.]
=Ash-Pit.=--The ash-pits are exposed to the destructive effects of
heat and moisture, and should preferably be constructed of cast-iron,
since sheet-steel is liable to corrode quickly.
[Illustration: FIG. 106.--Otto Deutz producer.]
In most apparatus the ash-pit is hermetically sealed, and the air for
supporting combustion enters below the grate through a pipe leading
from the heater or the vaporizer. This arrangement seems best adapted to
prevent the leakage of gas which tends to take place by reaction after
each suction stroke of the engine.
Ash-pits formed as water-cups, such as the Deutz (Fig. 106), the
Wiedenfeld (Fig. 95), and the Bollinckx (Fig. 98), are fed by the
overflow from the vaporizer. These ash-pits are themselves provided with
an overflow consisting of a siphon-tube forming a water-seal.
Besides providing protection to the grate and other parts by this sheet
of water, a larger proportion of the heat radiated from the furnace is
utilized for the production of steam which contributes to enrich the
gas. The doors of the ash-pits and their fittings are likewise exposed
to a rapid deterioration.
For this reason these parts should be very strongly made, either of
cast-iron or cast-steel. Furthermore, they should, at joint surfaces, be
connected in an air-tight manner, which may be attained by carefully
finishing the engaging surfaces of the frame and the door proper, or by
cutting a dovetail groove in one of the sides of the frame which is
packed with asbestos and adapted to receive a sharp edged rib on the
other part.
The pintles of the hinges should also be carefully adjusted so that the
joint members of the door shall remain true. Hinges with horizontal axes
seem to be preferable in this respect to those having vertical axes. As
a means of closing the door, the arrangement here shown (Fig. 107) seems
to assure a proper engagement of the joint surfaces. It consists of a
yoke which straddles the door, and which, on the one hand, swings about
the hinge, and on the other hand engages a movable hoop. A screw,
fastened to the yoke, serves to tighten the door by pressure on its
center. This screw can also be fastened to the end of the yoke (Fig.
108).
[Illustration: FIGS. 107-108.--Fire-box doors.]
It is very advantageous to provide in each door a hole closed by an
air-tight plug, so that in case of need a tool may be introduced for
cleaning the grate. In this manner the grate may be cleaned without
opening doors and without causing a harmful entrance of air.
The door of the furnace, particularly, should be provided with an iron
counter-plate held by hinged bolts (Fig. 109); or, better still, this
door should be so constructed that it can be lined with refractory
material to protect it against the radiated heat of the fire.
=Charging-Box.=--Like the other parts of the generator the construction
of which has been discussed above, the charging-box should be absolutely
air-tight.
On account of their greater security, preference should be given to
double closure devices, which form a sort of preliminary chamber, owing
to which the filling of the generator is made in two operations. The
first operation consists in filling the preliminary chamber after
opening the outer door. Upon closing this outer door, the second
operation is performed, which consists in moving the inner door so as to
cause the fuel in the preliminary chamber to drop into the generator.
Stress has been laid on the greater safety of this type of charging-box
for the reason that, with devices having a single charging-door, a
sudden gust of air may rush in at the time of charging the furnace, and
bring about an explosion very dangerous to the workman entrusted with
stoking the furnace.
[Illustration: FIG. 109.--Door with refractory lining.]
The closure is generally simply a removable cover, or may be a lid
swinging about a hinge having a horizontal or vertical axis.
As regards the inner door, which is of great importance, in order to
insure an air-tight joint, there are three chief types of closure:
1. The Lift-Valve.
2. The Slide-Valve.
3. The Cock.
=The Lift-Valve.=--The lift-valve is formed by a disk of conical or
spherical shape moved up and down by means of a lever having a
counter-weight for adjustment. The valve is used in the Winterthur (Fig.
92) and Bollinckx (Fig. 98) generators.
This device serves as an automatic closure and insures a tight joint
irrespective of wear. Moreover, it presents the advantage that, at the
moment of opening, it distributes the fuel evenly in the generator; but
on the other hand, it has the drawback of not allowing the fuel to be
examined or shaken through the charging-box. In apparatus provided with
this kind of valve, it is therefore advisable to furnish the upper part
of the generator with agitating holes closed by an air-tight slide.
=Slide-Valve.=--The slide-valve closure consists of a smooth-finished
metallic plate movable below the charging-box proper. Operated as it is
from the outside, it is evident that the slightest play, the wearing of
the pivot, or the weight of the charge, will form spaces between the
plate and its seat through which air may rush in.
Furthermore, the manipulation of the slide-valve may be interfered with
if too much fuel is put in the generator.
The valve or damper may move parallel to itself or swing about the
operating axis. The Taylor apparatus (Fig. 94) and the Benier apparatus
(Fig. 104) are provided with such valves.
The Pintsch generator (Fig. 96) is provided with a device which,
properly speaking, is not a damper, but which consists of two boxes
movable about a vertical axis and arranged to be displaced alternately
above the shaft to effect the charging. This system effects only a
single closure, but explosions are scarcely to be feared with an
apparatus of this kind, owing to the considerable height of fuel
contained between the charging opening and the gas-producing zone.
=Cock.=--The cock is applied particularly in the modern apparatus of the
Otto Deutz Co. (Fig. 106) and the Pierson generator (Fig. 101). It
consists of a large cast-iron cone, having an operating handle and an
opening. The cone moves in a sleeve formed by the charging-box.
This arrangement appears to be preferable to the others on account of
its simplicity and of the ease with which it can be taken apart for
cleaning. Moreover, the fuel can be poked directly through the
feed-hopper. In apparatus provided with a cock, it is advisable to place
on the outside cover a mica pane through which the condition of the fuel
may be examined without danger.
=Feed-Hopper.=--Below the charging-box is arranged, as a rule, a hopper
tapered conically downward. This part of the generator should serve only
as a storage chamber for fuel. It can therefore be made of cast-iron,
and has the advantage of being removable, easily replaced, and of
allowing ready access to the retort for the purposes of examination and
repair.
The annular space surrounding this feed-hopper generally forms a chamber
for receiving the gas produced, as in the Winterthur (Fig. 92), the
Bollinckx (Fig. 98), and the Taylor apparatus (Fig. 99).
In generators having an internal vaporizing-tank, this tank itself
serves as a feed-hopper, which is the case in the Deutz apparatus (Fig.
106) and Wiedenfeld generator (Fig. 95).
=Connection of Parts.=--In order to facilitate the thorough cleaning of
the retort, preference is given to removable charging-boxes and
feed-hoppers. These are features of apparatus of the Bollinckx type
(Fig. 98), in which the charging-box is secured to the generator by
means of its yoke and by catches provided with knobs, and also of
apparatus of the Winterthur kind (Fig. 92), having a charging-box
pivoted about a vertical axis, or apparatus of the Duplex type (Fig.
110), in which the charging-box can swing about a horizontal hinge.
=Air Supply.=--We have seen that, when starting the generator, the gas
is produced with the aid of a fan. This fan may be operated
mechanically, but is generally operated by hand.
It is customary to convey the air-blast through a pipe leading to the
ash-pit, as in the Winterthur apparatus (Fig. 92). Often, however, the
air supply pipe is directly branched on that which leads from the
vaporizer to the ash-pit, as in the Deutz apparatus (Fig. 106). In this
case a set of valves or dampers permits the disconnection of the fan or
its connection with the ash-pit.
[Illustration: FIG. 110.--Duplex charging-hopper.]
In some apparatus an air inlet is provided immediately adjacent to the
ash-pit. This arrangement is faulty for the reason that it gives rise to
gaseous emanations which take place by reaction after each suction
stroke of the engine. Furthermore, it is advisable that the air supplied
below the ash-pit be as hot as possible. For this reason the employment
of preheaters is desirable. The dry air forced in by the fan stimulates
combustion, and the hot gas produced and mixed with smoke escapes
through a separate flue, generally arranged beyond the vaporizer and
serving as a chimney. This chimney should in all cases be extended to
the outside of the building, and should never terminate in a brick
chimney or similar smoke-flue. The direct escape of such gas and smoke
through a telescopic chimney above the charging-box has been generally
abandoned in modern structures.
[Illustration: FIG. 111.--Bollinckx flue and scrubber.]
[Illustration: FIG. 112.--Winterthur flue and air-reheater.]
The escape-pipe mentioned, being branched on the gas-pipe leading to the
engine, should be capable of disconnection when desired, by a thoroughly
tight system of closure. For this purpose, some employ a simple cock
(Bollinckx, Fig. 111), a three-way cock, a set of cocks, or, still
better, a double valve, as in the Winterthur apparatus (Fig. 112) and
the Deutz apparatus (Fig. 113). A double seated valve is also used, as
is the case in the Benz generator (Fig. 114).
[Illustration: FIG. 113.--Otto Deutz flue.]
[Illustration: FIG. 114.--Benz flue.]
=Vaporizer-Preheaters.=--As has been stated before, there are vaporizers
internal or external, relatively to the generator.
=Internal Vaporizers.=--The Deutz apparatus (Fig. 106), for example,
consists of an annular cast-iron tank mounted above the retort of the
generator.
The hot gases given off by the burning fuel travel around this tank and
vaporize the water which it contains. The air drawn in by the suction of
the engine enters through an opening located above the tank, travels
over the surface of the water which is being vaporized, and thus laden
with steam passes to the ash-pit.
The tank in question is supplied with water by means of a cock having a
sight feed, located on the outside, and the level is kept constant by
means of an overflow tube leading to the ash-pit. It is well to bend
this tube and to place a funnel on its lower member. The amount of
overflow may thus be regulated.
These vaporizers are simple and take up little room; but they are open
to the apparently well-founded objection that they heat up slowly and
require a considerable time to produce the steam necessary to enrich the
gas, this being due to the relatively large mass of cast-iron and the
amount of water contained therein.
The Pierson vaporizer (Fig. 101) and the Chavanon vaporizer (Fig. 115)
both consist of an annular tank forming the base of the generator. Steam
is formed near the outlet of the ashes, which, as has been described
above, leads to the outer air. The development of steam is regulated by
mechanical means controlled by the suction of the engine.
[Illustration: FIG. 115.--Chavanon producer.]
=External Vaporizers.=--External vaporizers are generally formed by a
cylinder with partitions constituting two series of chambers. In one of
these the hot gases from the generator travel, and in the others the
water to be vaporized is contained.
[Illustration: FIG. 116.--Taylor vaporizer.]
[Illustration: FIG. 117.--Deutz vaporizer.]
=Tubular Vaporizers.=--Different types of tubular vaporizers are
manufactured. The vaporizer with a series of tubes, as in Taylor's
apparatus (Fig. 116), Deutz's old model (Fig. 117), or with single tube
like Pintsch's generator (Fig. 118), is formed by three compartments
separated by two tube sheets or by plates which are connected by tubes.
In some cases the gases pass within the tubes, while the water to be
vaporized surrounds them; as in the Pintsch apparatus (Fig. 118), and
Taylor apparatus (Fig. 116), Benz (Fig. 119), and Koerting generators
(Fig. 120).
[Illustration: FIG. 118.--Pintsch vaporizer and scrubber.]
In other cases, the water lies inside and the gas outside. In this
latter case, a longitudinal baffle is employed to compel the gases to
heat the tubes in their whole length, as in the Deutz producer (Fig.
117). In a general way it may be said that such a series of tubes
presents the disadvantage of becoming clogged up rapidly by the deposit
of lime salts contained in water.
[Illustration: FIG. 119.--Benz vaporizer.]
[Illustration: FIG. 120.--Koerting vaporizer.]
If the set of tubes consists of fire-tubes, the deposit will form on the
outer surface, that is, on a portion not accessible for cleaning. From
this point of view, water-tubes are preferable, as they allow the
deposit or scale to be removed through the tubular heads or plates. On
the other hand, such water-tubes have the drawback that their exterior
surfaces are readily covered with pitch and soot. The tubular vaporizers
of the Field type (Bollinckx, Fig. 98) are composed of a single
sheet-iron tube or shell, in which the tubes are arranged, dipping into
a chamber through which the hot gases pass. This arrangement insures a
rapid production of steam, but the Field tubes are even more liable than
the others to become covered with deposits.
It will be seen that these types of vaporizers should all present the
following features: easy access, small quantity of the body of water
undergoing vaporization, and large heating surface with small volume.
The use of copper or brass tubes should be strictly avoided, as they
would be quickly corroded by the action of the ammonia and hydrogen
sulphide contained in the gas.
=Partition Vaporizers.=--Partition vaporizers comprise a cylindrical
shell, generally made of cast-iron and having a double wall in which the
water to be vaporized circulates. The gas coming from the generator
passes into the central portion, where it comes in contact with a hollow
baffle, also containing water (Wiedenfeld, Fig. 121). Vaporizers of this
kind are strong, simple, and easily cleaned.
=Operation of the Vaporizers.=--The general purpose of vaporizers,
whatever their construction may be, is to produce steam under
atmospheric pressure, by utilizing the heat of the generator gases
immediately after their production, or, as in the Chavanon system, by
utilizing the heat radiated from the furnace.
The air drawn by the engine through the generator generally passes
through the vaporizers and becomes laden with a certain amount of steam
which it carries along. The amount thus taken up depends chiefly upon
the temperature and the amount of gases coming from the generator, so
that the greater the amount drawn into the engine, the more energetic
will the vaporization be, and the richer the gas will become. It will be
understood that when a generator is working at its maximum production,
the interior temperature is highest and most favorable to the
decomposition of the largest amount of steam.
[Illustration: FIG. 121.--Wiedenfeld vaporizer.]
It follows that with the very simple vaporizers which have been
reviewed, a practically automatic regulation is obtained. However, some
manufacturers have deemed it advisable to regulate the amount of steam
more accurately, and to make it exactly proportionate to the power
developed by the motor. Thus in the Winterthur gas-producer (Figs. 92
and 112) the manufacturers have omitted the vaporizer proper, and use
instead an air-heater and a super-heater for air and steam.
The heater is formed by a cast-iron box having two compartments, through
one of which the hot gases from the generator pass, while in the other
the air intended to support combustion travels. At the inlet of the
super-heater a pipe terminates, which feeds, drop by drop, water
supplied by a feed device to be described presently. This water is
vaporized immediately upon contact with the wall of the super-heater and
is carried along with the air contained in it.
The super-heater comprises a hollow ring-shaped cast-iron piece arranged
in the chamber of the generator, in which the gases are developed, and
is thus heated to a high temperature. The mixture of air and steam
circulates in this super-heater before traveling to the ash-pit.
The feeder of the Winterthur gas-generator (Fig. 122) is composed of a
receptacle having the shape of a tank or basin containing water and
located below a closed cylindrical box. In this box a piston moves,
which is provided at its lower end with a needle-valve. The upper
portion of the box communicates with the gas-suction pipe through a
small tube. At each suction stroke of the engine, according to the force
of the suction, the needle-valve piston rises more or less and thus
allows a variable amount of water to pass.
[Illustration: FIG. 122.--Winterthur feeders.]
This apparatus--and all those based on the same principle--presents the
advantage of proportioning the amount of water to the work of the
engine; but in view of its rather sensitive operation it must be kept in
perfect repair and carefully watched. Obviously, should the water
contain impurities, the needle-valve will bind or the orifices will be
obstructed, and thus the feeding of the water will be interrupted. This
will not only result in the production of a poorer gas, but will lead to
greater wear of the grates, which in this case are not sufficiently
cooled by the introduction of steam.
[Illustration: FIG. 123.--Hille producer.]
=Air-Heaters.=--The preliminary heating of the air appears to be of
great utility for keeping up a good fire. This heating is very easily
accomplished, and is generally effected by utilizing a portion of the
waste heat of the gases, a procedure which also has the advantage of
cooling the gases before they pass through the washing apparatus.
The heating of the air for supporting combustion takes place either
before the addition of steam (Hille's generator, Fig. 123), or after the
mixture as in Wiedenfeld's apparatus (Fig. 95). In the first case, the
air passes through a sheet-iron shell concentric with the basin of the
generator, is there heated by the radiated heat, and is conveyed to the
ash-pit by a tube into which leads the steam-supply pipe extended from
the vaporizer. In the second type of heater, the mixture of air and
steam is super-heated during its passage through an annular piece
arranged in the ash-pit of the generator.
[Illustration: FIG. 124.--Benz dust-collector.]
=Dust-Collectors.=--Dust-collectors are generally placed between the
generator and the scrubber or washer. They may be formed of baffle-board
arrangements against which the gases laden with dust impinge, causing
the dust to be thrown down into a box provided with a cleaning opening
(Benz, Fig. 124, and Pintsch, Fig. 118).
Some collectors are formed either by the vaporizer itself, terminating
at its base in a tube which dips into water and forms a water-seal, as
in the Wiedenfeld generator (Fig. 121), or by a water-chamber into which
the gas-supply tube slightly dips (Bollinckx, Fig. 111). With this
arrangement, the gas will bubble through the water and will be partly
freed of the dust suspended in it. These water-chambers are generally
fed by the overflow from the spray of the scrubber. There is thus
produced a continuous circulation by which the dust, in the form of
slime, is carried toward the waste-pipe or sewer.
=Cooler, Washer, Scrubber.=--Some manufacturers cool the gas in a tower
with water circulation. Most manufacturers, however, simply cool the gas
in the washer or scrubber. This apparatus comprises a cylindrical body
of sheet-iron or cast-iron formed of two compartments separated by a
wooden or iron grate or perforated partition. The upper compartment up
to a certain level contains either coke, glass balls, stones, pieces of
wood, and the like. The top of the compartment is provided with a water
supply in the nature of a sprinkler or spray nozzle. The lower
compartment of the scrubber serves to collect the wash-water which has
passed through the substance filling the tower. An overflow in the shape
of a siphon, provided with a water seal, carries the water to the
waste-pipe either directly or after it has first passed through the dust
collector.
The gas drawn in enters the washer in the lower compartment either above
the water level (Deutz, Fig. 125; Winterthur, Fig. 126), or through an
elbow which dips slightly into the water (Benz, Fig. 127; Fichet and
Heurtey producer, Fig. 128).
The gas passes through the grate or partition which supports the
material filling the tower, and travels through the interstices in a
direction opposite to that of the water falling from the top. Under
these conditions, the gas is cooled, gives up the ammonia and the dust
which it may still contain in suspension, and is conveyed to the engine
either directly or after passing through certain purifiers. Care should
be taken to place the pieces of most regular shape along the walls, so
that the unevenness of their surfaces may not form upward channels along
the shell, through which channels the gas could pass without meeting the
wash-water.
[Illustration: FIG. 125.--Otto Deutz scrubber.]
[Illustration: FIG. 126.--Winterthur scrubber.]
[Illustration: FIG. 127.--Benz scrubber.]
The material most commonly employed in washers is coke in pieces of from
2-1/2 to 3-1/2 inches in size. This material is cheap and is very well
suited for retaining the impurities of the gas. The largest pieces of
coke should be placed at the bottom of the washer, and smaller pieces
should form at the top a layer from 6 to 8 inches deep. In this manner
the water is distributed more evenly and the gas is more thoroughly
washed. Blast-furnace coke is best suited for this washing, as it is
more porous and less brittle than gas-works coke. It is advisable to
put a baffle-board in front of the gas outlet to reduce the carrying
along of water in the conduits.
[Illustration: FIG. 128.--Fichet-Heurtey scrubber.]
[Illustration: FIG. 129.--Scrubber-doors.]
The tower of the washer should be provided with three openings having
air-tight closures, easily fastened by screws (Fig. 129). One of the
openings is located in the lower compartment, slightly above the water
level, to allow the deposits to be removed and to permit the cleaning of
the orifice of the gas-supply tube, which is particularly liable to be
obstructed. The second opening is placed above the grating which
supports the filtering material. The third opening is provided on the
top of the apparatus to permit the examination and cleaning of the water
feed device and the gas outlet without the necessity of taking the lid
of the washer apart, the joint of which is kept tight with difficulty.
The two openings last mentioned also serve for introducing and removing
the filtering material.
=Purifying Apparatus.=--In some cases, where it is necessary to have
very clean gas or where coal is employed which is softer than anthracite
coal, and which therefore produces an appreciable amount of tar,
supplementary purifying means must be employed. The apparatus for this
purpose may, like the washers, be based upon a physical action or upon a
chemical action. The physical action has for its purpose chiefly to
retain the pitch and the dust which may have passed through the washer.
This is accomplished by means of sawdust or wood shavings arranged in a
thin layer and capable of filtering the gas without opposing too great
a resistance to its passage. These materials are spread on one or more
shelves superposed to form successive compartments in a box closed in an
air-tight manner by an ordinary lid or a water seal cover (Pintsch, Fig.
130; Fichet and Heurtey, Fig. 131). It may be well to point out that the
presence of the water carried along will, in the end, destroy the
efficiency of the precipitated materials, because they swell up and
cease to be permeable to the gas. These materials must therefore be
renewed rather frequently. To obviate this drawback, vegetable moss may
be employed, which is much less affected by moisture than most filters
and keeps its spongy condition for a long time.
[Illustration: FIG. 130.--Pintsch purifier.]
The chemical action has for its chief object to rid the gas of the
carbonic acid and the hydrogen sulphide which certain fuels give off in
appreciable amounts. The purifying material, in this case, is formed
either by a mixture of hydrate of lime and natural iron oxide, or by the
so-called Laming mass, which consists of iron sulphide, slaked lime, and
sawdust, which last serves the purpose of rendering the material looser
and more permeable to the gas. The Laming mass as well as other
purifying materials will become exhausted in the course of chemical
reactions. It can be regenerated merely by exposure to the air.
[Illustration: FIG. 131.--Fichet-Heurtey purifier.]
=Gas-Holders.=--The purifiers by themselves constitute, to a certain
extent, storage chambers for the gas before it is supplied to the
engine; but in plants for the generation of gas without purifiers it is
advisable to provide a gas-holder on the suction conduit near the
engine.
[Illustration: FIG. 132.--Pintsch regulating-bell.]
In order to save floor space the gas-holder may be placed in the
basement. Preferably the capacity of the holder should be at least from
3 to 4 times the volume of the engine-cylinder. The holder should also
be provided with a drain-cock and with a hand-hole located at some
accessible point, so that the slimes and pitch which tend to accumulate
in the holder can be removed. In some cases the gas-holder is formed by
a small regulating bell, the function of which is to insure a uniform
pressure. This bell is emptied during the suction period and is filled
during the three succeeding periods of compression, explosion, and
exhaust (Pintsch, Fig. 132).
[Illustration: FIG. 133.--Types of gas-driers.]
=Drier.=--Sometimes, toward the end of a producer-gas pipe, a drier is
located for the purpose of keeping back the water carried along, the
drier being similar to that employed in steam conduits. It will, of
course, be understood that such driers are useful only in plants having
no purifiers (Fig. 133). The employment of the drier is advisable to
prevent the entrance of moist gas into the cylinder and the condensation
of moisture on the electric igniter.
[Illustration: FIG. 134.--Elbow with closure.]
=Pipes.=--The pipes connecting the several parts of a gas-producing
plant should be disposed with particular care to insure tightness and
cleanliness. It should be borne in mind that the gas is under a pressure
below that of the atmosphere, and that the least leakage will cause the
entrance of air, which will impair the quality of the gas. The greatest
care should therefore be taken in fitting the joints. These joints are
numerous, because there are joints wherever tubes are connected with
each other and with the apparatus. Furthermore, all elbows should be
provided with covers held in place by a yoke and compression screw, this
being done for the purpose of providing for the introduction of a brush
or other implement to remove the dust and pitch (Fig. 134).
For conduits of small diameter the elbows with covers may be replaced
with =T= connections, or connections provided with plugs.
Gas piping in the immediate neighborhood of the cock for admitting gas
to the motor should be provided with a conduit of proper diameter
leading to the open air and serving to clean the apparatus and to fill
them, during the operation of the fan, with gas suitable for combustion.
This conduit should be provided with a stop-cock. Test-cocks for the gas
should be placed on the piping immediately beyond the vaporizers, the
scrubber, and near the engine.
It will also be well to provide water-pressure gages before and after
the scrubber to enable the attendant to ascertain the vacuum in the
conduits and to adjust the running of the apparatus.
=Purifying-Brush.=--As an additional precaution against the carrying of
tar to the engine, metallic brushes are often employed, these brushes
being spiral in form and enclosed in a cast-iron box interposed in the
gas-supply pipe immediately after the engine. The gas will be broken up
into streams by the obstacles formed by these brushes and will be freed
of the suspended tar (Fig. 135). These brushes should be carefully
cleaned at regular intervals. The best way of doing this is to drop them
into kerosene or some other suitable solvent.
[Illustration: FIG. 135.--Metal purifying-brush.]
CONDITIONS OF PERFECT OPERATION OF GAS-PRODUCERS
These conditions depend upon the workmanship or upon the system of the
plant, on the care with which it has been erected, on the nature of the
fuel, on the condition of preservation of the apparatus, and upon the
manner in which the producers have been working.
=Workmanship and System.=--The workmanship itself, which term is meant
to include the choice of materials and the way they have been worked,
presents no difficulty. The producers which we have discussed are very
simple and offer absolutely no difficulties in their mechanical
execution. As regards the system, however, especially with respect to
the relative dimensions of the elements, it does not seem so far that it
is possible to indicate any principle or rule capable of a rigid general
application. It must be taken into account that the use of suction
gas-generators has become general only in the last three or four years;
the problem has therefore scarcely been adequately solved. However, some
hints may be given on this subject.
=Generator.=--In regard to the generator, it is possible to deduce from
the best existing plants the dimensions to be given to the generator
relatively to those of the engine to be supplied, upon the assumption
that the engine is single-acting and runs at a normal speed of from 160
to 230 revolutions per minute. The essential portion of the generator
which contributes to the production of a proper gas is that which
corresponds with the combustion zone. To this portion a cross-section is
given varying in size between one-half and one-quarter of the surface of
the engine-piston, sometimes between one-half and nine-tenths of this
surface, according to the nature and the size of the fuel that is used.
With small apparatus, however, ranging from 5 to 15 horse-power, the
size of the base cannot be reduced below a certain limit, since
otherwise the sinking of the fuel will be prevented. This danger always
exists in small generators and renders their operation rather uncertain,
such uncertainty being also due to the influence of the walls. It is to
be noted that most modern generators are rather too large than
otherwise.
Many manufacturers of no wide experience have been led to make their
apparatus rather large so as to insure a more plentiful production of
gas. As a matter of fact, the fire in such apparatus is liable to be
extinguished when the combustion is not very active. If the principles
of the formation of gas in suction-generators be kept in mind, it is
evident that the gas developed is the richer the "hotter" the operation
of the apparatus. Such operation also permits the decomposition of the
hydrogen and carbon monoxide.
The "hot" operation of a generator is accomplished best with active
combustion; and since this is a function of the rapidity with which the
air is fed, it obviously is advantageous to reduce the area of the
air-passage to a minimum as far as allowed by the amount of fuel to be
treated. As to the height of the fuel in use in the apparatus, this
varies as a rule between 4 and 5 times the diameter at the base.
=Vaporizer.=--The size of the vaporizer varies materially according to
its type. No hard-and-fast rule can therefore be adopted for determining
its heating surface; but this surface should in all cases be sufficient
to vaporize under atmospheric pressure from .66 to .83 pounds of water
per pound of anthracite coal consumed in the generator.
=Scrubber.=--For the scrubbers, the following dimensions may be deduced
from constructions now used by standard manufacturers.
The volume of a scrubber is generally from six to eight times the
anthracite capacity of the generator. A height of from three to four
times the diameter is considered sufficient in most cases. It should be
understood that in this height is included the water-pan chamber located
below the partition or grate, and the upper chamber through which the
gas escapes. The height of these two chambers depends necessarily upon
the arrangement used for leading the gas to the lower portion of the
washer and for the distribution of wash-water at the top.
=Assembling the Plant.=--The author has insisted strongly on the
necessity of having all the apparatus and pipe connections perfectly
tight. In order to ascertain if there is any leakage, the following
procedure may be adopted:
When starting the fire by means of wood, straw, or other fuel producing
smoke, instead of allowing this smoke to escape through the flue during
the operation of the fan, it may be caused to escape through the cock
which generally admits the gas to the motor, the cock being opened for
this purpose. The damper in the outlet flue is closed. In this manner
the smoke will fill all the apparatus and connecting pipes under a
certain pressure and will escape through any cracks, the presence of
which will thus be revealed.
Another test, which is made during the ordinary operation of the
generator, consists in passing a lighted candle along the joints; if
there is any leakage, this will be shown by a deviation of the flame
from a vertical position.
=Fuel.=--We have discussed the subject of fuel in a preceding chapter
(Chapter XIII) and have indicated the conditions to be fulfilled by low
grade or anthracite coal best adapted for use in suction gas-generators.
It may here be added that the coal used in the generator should be as
dry as possible and in pieces of from 1/2 inch to 1 inch. Very small
pieces, and particularly coal dust, are injurious and should be removed
by preliminary screening as far as possible. Screened coal is thrown in
with an ordinary grate shovel.
=How to Keep the Plant in Good Condition.=--In regard to the generator,
apart from the cleaning of the grate and of the ash-pit, which may be
done during operation, it is necessary to empty the apparatus entirely
once a week, if possible, in order to break off the clinkers adhering
to the retort. These clinkers destroy the refractory lining, form rough
projections interfering with the downward movement of the fuel, bring
about the formation of arches, and reduce the effective area of the
retort. At the time of this cleaning, tests are also made as to the
tightness of the doors of the combustion-chamber, of the charging-boxes,
etc.
The vaporizer should be cleaned every week or every other week,
according to the more or less bituminous character of the fuel and the
greater or smaller content of lime in the water used. Lime deposits may
be eliminated, or the salts may be precipitated in the form of
non-adhering slimes, by introducing regularly a small amount of caustic
potash or soda into the feed-water. If the deposits or incrustations are
very tenacious, the use of a dilute solution of hydrochloric acid may be
resorted to. Tar which may adhere to the conduits, pipes or gas
passages, is best removed while the apparatus is still hot, or a solvent
may be employed, such as kerosene, turpentine, etc. The connections
between the vaporizer and the scrubber are particularly liable to become
obstructed by the accumulation of tar or dust carried along by the gas.
It is advisable to examine the several parts of the plant once or twice
a week by opening the covers or the cleaning-plugs.
The lower compartment of the washer keeps back the greater part of the
dust which has not been retained in collectors or boxes provided
especially for this purpose. The dust takes the form of slime, and, in
some arrangements of apparatus, tends to clog up the overflow pipe,
thus arresting the passage of gas and causing the engine to stop. This
portion of the washer should be thoroughly cleaned once or twice a
month.
If very hard blast-furnace coke is used in the washer, it may be kept in
use for over a year without requiring removal. In order to free the
purifying materials from dust and lime sediments carried along by the
wash-water, it is well to let the wash-water flow as abundantly as
possible for about a half-hour at least once a month. At the time of
renewing the purifying material the precautions indicated in the section
dealing with these matters should be observed, and care should be taken
to have shelves or gratings on which the material is supported in layers
not too thick, so as to avoid any resistance to the passage of the gas.
In a general way it is advisable to test the drain-cocks on the several
apparatus daily, and to keep them in perfect condition. If, when open,
one of these cocks does not discharge any gas, water, or steam, a wire
should be introduced into the bore to make sure it is not clogged up.
=Care of the Apparatus.=--Each producer-gas plant will require special
instructions for running it, according to the system, the construction,
and the size of the plant. Such instructions are generally furnished by
the manufacturer. However, there are some general rules which are common
to the majority of suction gas-producers, and these will here be
enumerated.
=Starting the Fire for the Gas Generator.=--This operation calls for
the presence of the engineer of the plant and an assistant. The proper
procedure is as follows:
First: Open the doors of the furnace and of the ash-pit. Then open the
outlet flue and make sure that the grate of the generator is clear of
ashes and clinkers. It should also be seen to that the parts of the
charging-box work well and that the joints are tight.
Second: Ascertain whether there is the proper amount of water in the
vaporizer, in the scrubber, etc., and that the feed works properly.
Third: Through the door of the combustion-chamber introduce straw, wood
shavings, cotton waste, etc.; light them and fill the generator with dry
wood up to one-quarter or one-half of its height; then add a few
pailfuls of coal.
Fourth: Close the doors of the ash-pit and of the combustion-chamber and
start the draft by means of the fan. As soon as the draft is started, it
must be kept up without interruption until the engine begins to run,
which may be ten or twenty minutes after lighting the fire.
Fifth: After the draft has been continued for a few minutes, the coal
becomes sufficiently incandescent to start the production of gas, which
may be ascertained by trying to light the gas at the test-cock near the
generator. Then the opening in the outlet flue is half closed for the
purpose of producing pressure in the apparatus.
Sixth: Open the outlet flue adjacent to the engine for the purpose of
purging the apparatus and the conduits of the air which they contain
until the gas may be lighted at the test-cock placed near the motor.
Seventh: Adjust the normal outflow of wash-water for the scrubber.
Eighth: As soon as the gas burns continuously at the test-cock with an
orange-colored flame the engine may be started.
The gas at first burns with a blue flame; this color indicates that it
contains a certain amount of air. The opening of the test-cock should be
so regulated as to reduce the outlet pressure of the gas sufficiently to
prevent the flame from going out. During the production of the draft, as
well as during the ordinary running of the plant, the filling of the
apparatus with fuel should be done with care to prevent explosions of
gas due to the entrance of air. Particular care should be taken never to
open at the same time the lid of the charging-box and the device, be it
a cock, valve, or damper, which controls the connection of the
charging-box with the generator. All the operations which have been
mentioned above should be carried out as quickly as possible.
STARTING THE ENGINE
The manner of starting the engine depends on the type of the engine and
on the starting device with which it is provided, as we have already
explained in connection with engines working with gas from city mains.
It is, however, important for the production of a good explosive mixture
to regulate the amount of air supplied to the engine according to the
quality of the gas employed. It is advisable to continue the operation
of the fan until several explosions have taken place in the cylinder and
the engine has acquired a certain speed so as to be able to draw in the
normal amount of gas.
Naturally the gas-outlet tube near the admission-cock should be closed
after starting the engine, as well as the opening in the outlet flue of
the generator. When the motor is running properly, the amount of water
fed to the vaporizer and overflowing to the ash-pit is properly
adjusted. The generator is then filled up to the level indicated by the
manufacturer.
=Care of the Generator during Operation.=--As soon as the apparatus is
running under normal conditions, it presents the advantage of requiring
only very slight supervision and very little manual tending. The
supervision consists:
First: In regulating and keeping up a proper feed of water to the
vaporizer.
Second: In seeing to it that in apparatus provided with an overflow
leading to the ash-pit, the water should flow constantly but without
exceeding the proper amount.
Third: In keeping down temperature in the scrubber by properly
regulating the feed of the wash-water. This apparatus may be slightly
warm at its lower part, but must be quite cold at the top.
The manual tending to be done is limited to the regular filling up of
the generator with fuel and to the removal of ashes and clinkers. The
charging is effected at regular intervals, which, according to the
various types of anthracite-generators, vary from one to six hours.
Charging the apparatus at short intervals entails unnecessary labor,
while charging at too long intervals will often interfere with the
uniform production of the gas.
It will be obvious that the amount of fuel introduced will be the
larger, the greater the intervals between two fillings. This fuel is
cold and contains between its particles a certain amount of air;
furthermore, the layer of coal which covers the incandescent zone has
become relatively thin. The excess of air impoverishes the gas, and the
fresh fuel lowers the temperature of the mass undergoing combustion, so
that again the gas in process of formation is weakened. Experience seems
to show that as a rule it is best to fill up the generator at intervals
of from two to three hours, according to the work done by the engine. It
should be noted that the level of the fuel in the generator should not
sink below the bottom of the feed-hopper.
The author wishes again to emphasize that in order to prevent the
harmful entrance of air, the charging operations should be carried out
as quickly as possible; and for this reason the fuel should be
introduced not by means of the shovel, but by means of a pail, scuttle,
or other appropriate receptacle.
Care should be taken to fill the charging box to its upper edge and to
adjust its cover accurately before operating the device which closes the
feed-hopper (valve, cock).
The removal of the ashes and clinkers should be accomplished as
infrequently as possible, since opening the doors of the ash-pit and of
the combustion-chamber necessarily causes an inward suction of cold air
which is harmful.
As a rule with generators employing anthracite coal, it is sufficient to
empty the ash-pit twice daily; this should be preferably done during
stoppages. However, the cleaning of the grate by means of a poker passed
between the grate-bars or over them in order to bring about the falling
of the ashes, should be attended to every two to four hours, according
to the type of the generator and the nature of the fuel. In order that
this cleaning may be done without opening the doors, the latter should
be provided with apertures having closing devices.
This cleaning has for its chief object to allow the free passage of the
air for supporting combustion and to keep the incandescent zone in the
apparatus at the proper height. The accumulation of ashes and clinkers
at the bottom of the retort will shift this zone upward and impair the
quality of gas.
=Stoppages and Cleaning.=--After closing the gas-inlet to the engine,
the damper in the gas-outlet flue of the generator should be opened and
the cocks controlling the feed of water to the scrubber and to the
vaporizer should be closed.
If it is desired to keep up the fire of the generator during the
stoppage so as to be able to start again quickly, the ash-pit door
should be opened so as to produce a natural draft which will maintain
combustion. While the door is open, the clinkers which have accumulated
above the grate may be removed, as they are much more easily taken off
the grate when they are hot.
At least once a week the fire in the generator should be put out and the
generator completely cleaned--that is, when ordinary fuel is employed.
For this purpose, as soon as the apparatus is stopped, a portion
of the incandescent fuel is withdrawn through the doors of the
combustion-chamber, and the retort is allowed to cool before it is
emptied entirely. Too sudden a cooling of the retort may injure its
refractory lining. In order to prevent explosions caused by the entrance
of air, the feed-hopper should remain hermetically closed during the
removal of the incandescent fuel through the doors of the
combustion-chamber.
If the apparatus is placed in a room poorly ventilated, the cleaning
should be attended to by two men, so that one may assist the other in
case he is overcome by the gas. In all cases there should be a strict
prohibition against the use of any light having an exposed flame liable
to set on fire the explosive mixtures which may be formed.
When the generator, after cooling, is completely open, the charging-box
is taken apart, and, if necessary, the feed-hopper also; the grates are
taken out, if necessary; and, by means of a poker inserted from above,
the clinkers and slag adhering to the retort are broken off.
In the foregoing paragraphs the author has indicated how the several
apparatus, such as the vaporizer, the washer, the conduits, etc., should
be attended to and maintained in good working order.