IMPROVEMENTS IN WORKING FURNACES BY MEANS OF COMPRESSED AIR
Year: 1886

page_text: Compressed Air.
I, CARL OTTO, residing at Greifenhagen, Kingdom of Prussia, do hereby declare
the nature of this invention for "IMPROVEMENTS IN WORKING FURNACES BY
MEANS OF COMPRESSED AIR," and in what manner the same is to be performed to
be particularly described and ascertained in and by the following statement :--
My invention relates to closed furnaces in which combustion is maintained by
compressed air, and the object of the same is to utilize the compressed combustion-
gases thus obtained, in the first place for the generation of steam, or in addition
thereto for other technical purposes, and, in the second place, for producing the
mechanical work, or a part thereof required to compress the air to be supplied to
the furnace. To this end my invention consists in the combination with a closed
furnace, of a steam-boiler receiving heat from the former, a pump for supplying
compressed air to the furnace, a hot-air engine worked by the compressed com-
bustion-gases from the said furnace and a motor cooperating with the hot-air
engine in driving the air-pump. The invention also comprises means for purifying
the combustion gases on their course from the furnace to the hot-air engine and
mixing them with ateam, and means for feeding the furnace with solid fuel.
If any fuel is burnt in a closed space under pressure, the temperature as well as
the quantity of heat developed increase considerably, and the combustion-gasos
produced are capable of exercising a greater calorific effect on a given surface, for
instance on the heating-surface of a steam-boiler, on account of their superior
calorific capacity (relatively to the unit of volume) originating from their greater
density. On issuing from the space or apparatus in which they have first given
off heat, there is still present in these gases the remaining heat and the whole
mechanical energy resulting from their expansive force, which are both lost if the
gases are allowed to escape into the atmosphere, so that under these conditions an
economical advantage does not arise from the use of compressed air.
A utilization of the said heat and mechanical energy may, however, be attained
by causing the issuing combustion-gases to operate expansively in a hot-air-engine,
and in employing the mechanical work thus produced for working the pump which
supplies the compressed air required for sustaining the combustion.
On the annexed three sheets of drawings an apparatus involving my invention
is represented by Fig. 1 in a vertical sectional elevation, and by Fig. 2 in plan
partly in section. Fig. 3 shows the fuel-feeder to a larger scale. Fig. 4 is a part
in detail. Fig. 5 is a section of the air-pump, and Fig. 6 represents a portion of -a
modified apparatus with furnace adapted for melting metals.
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page_text: In Figs. 1 and 2 A is a steam boiler provided with the inside furnace B; C is a
fuel-feeder adapted for introducing fuel into the furnace B while being under
pressure; D is an apparatus in which the combustion-gases issuing from the said
furnace are purified, and in which, if their temperature should be too high, they
are cooled down to the proper degree and impregnated with steam, E is the hot-air
engine, F a steam-engine coupled with the former, G the air-pump, H an air-vessel
inserted between the latter and the furnace and in which separates out any water
introduced into the air-pump for the purpose of refrigeration, and I a water-
reservoir from which the water evaporating in the purifier D, is replaced.
The boiler A is represented as a vertical cylindrical boiler with Field-tubes. In
the lower part of this boiler is formed, by means of a fire-proof lining, a shaft b,
into which air is introduced below the grate arranged therein through the pipe a,
the branch-pipe a¹ and the apertures a, while through the branch a² of the pipe a
and the nozzles a air is conveyed to the upper contracted portion or neck b¹.
A gas-furnace with generator is thus constituted, in which the main combustion
takes place in and immediately above the neck b¹. For heating the air supporting
the combustion, the pipes a¹ and a³ are formed in serpentines and imbedded in the
fire-proof lining. A cock inserted between the pipe a and the pipes a¹ a' serves
for the regulation of the admission of air to the latter, while the combustion at 6¹
may be so regulated by a fire-proof cone e, adjustable by the lever fand rod f¹,
that a clear flame will be produced even with the least possible admission of
air. The mixture of the air entering at a*, with the gas, and consequently
the intensity of combustion may be promoted by a platinum disk e¹ fixed upon
the cone e by a pin of like metal. In order to allow the flame to be observed,
a small window consisting of a pane of mica, is arranged at 62. i is a cock for
blowing off ashes.
.The furnace is first supplied with fuel and the fire kindled through the
-aperture c. During the working this aperture remains closed, the fuel being then
introduced by means of the contrivance C, or fuel-feeder, consisting in a cylinder d
with piston d¹ movable by hand, the hopper d' communicating with the said
cylinder and adapted to be closed against the inside pressure by the cover d', and
the piston-like valve d³ fitted with screw and hand-wheel. When the said valve
is in closed state, the hopper may be opened and filled with fuel. The hopper
having then been reclosed by the cover d, and the piston d drawn back, the
valve is raised, so that the contents of the hopper will drop into the cylinder d,
and thereupon screwed down again. The fuel may then be pushed by the piston
from the cylinder into the channel so that finally it will be conveyed into the
furnace. This operation does not require any considerable force, provided the
piston fits loosely enough as to allow the gas-pressure to act on both surfaces of the
Bame. Also the closing of the valve d' does not present any difficulty, as when
the valve is rotated, the guides d³ with which the same is provided, scrape off the
coals from the walls of the channel of connection between d and d², so that the
valve then easily enters into the said channel. The piston is preferably fitted with
a brush of wires.
same.
While the fire is being raised, air is allowed to enter through the cock i and¸
the aperture c, and the combustion-gases issue through the pipes and m into the
atmosphere or a chimney. After a sufficient steam-pressure has been attained the
steam-valve is opened for establishing communication between the boiler and
the cylinder of the steam-engine F through the pipe j, and thereby starting the
The said engine then puts in motion the air-pump G connected thereto, so
that compressed air will be forced through the pipe k into the air-vessel H and
thence through the pipes a, a¹ and a into the furnace. At the same time the
pipe m is closed by the valve m¹, the compressed combustion-gases, after having
given off the greater portion of their heat to the boiler for the generation of steam,
being thereby compelled to pass through the apparatus D (to be described
hereafter) to the cylinder of the hot-air engine E, where they are utilized
expansively to assist the steam-engine in its operation. Theoretically the hot-air

page_text: engine should do more work than the air-pump absorbs. But, on account of
the inevitable losses caused by leakage and radiation, the mechanical effect of the
.hot-air engine is ordinarily somewhat inferior to the power required for driving
the pump, and this deficiency must be compensated by the steam-engine, or by
any other motor. The remaining power of the steam-engine may be utilized for
other purposes.
The aforesaid apparatus D is but conditionally a necessary appurtenance. If
.the combustion-gases passing off from the boiler, are sufficiently pure, and if they
are not of too bigh temperature to be introduced directly into the hot-air engine,
the said apparatus may be dispensed with. But usually, especially if mineral coal
is employed as fuel, the gases contain ashes, vapours of tar and sulpherous acid,
which would injure and clog the engine; besides. the temperature of the gases is
not to be controlled sufficiently by the regulation of the combustion. In order to
separate out the said noxious admixtures and to prevent the temperature from
exceeding a certain limit, the gases are conducted through a watery alkaline
solution contained in the vessel D, and which on one hand retains the sulphurous
acid, the tarry vapours and the, ashes, while on the other hand it takes up the
surplus of free heat of the gases with generation of steam. If, for instance, the
temperature of the gases entering into D is 200° centigr., and that of the liquid,
which is under pressure, 150°, the quantity of heat corresponding to the difference
of 50° will become latent in the steam produced. Upon the expansion of the gases
in the cylinder of the hot-air engine, and the decrease of temperature resulting
therefrom, the steam will be condensed, and its latent heat, in becoming free again,
will be given back to the gases. In order to cause the gases to pass through the
said liquid in thin streams, the vessel D is provided with the baffle-plates g having
notches at their lower edge with which they dip into the liquid, see Fig. 4. The
inclined plates h have the purpose of separating out from the gas-current any
liquid carried along by the same, and to return it to the vessel D. The water
evaporated in D is replaced either at intervals or continuously from the reservoir I,
which is connected by the pipe o with the air-vessel H in order to produce therein
the same pressure as in D. On entering into the vessel D the water runs from I
over the inclined plates h. For preventing or diminishing radiation of heat the
apparatus D, the gas-pipes connected therewith and the hot-air cylinder are
surrounded by a jacket p, through which the exhaust steam from the steam-engine
is conducted to the pipe q, opening out into the pipe m.
For the purpose of reducing the power required for the compression of the air,
the air-pump is provided with means for diminishing the heat produced by the
said compression. Preferably these means consist in the arrangement shown by
Fig. 5 for injecting water in the form of spray into the cylinder of the pump
during the suction-period. This arrangement comprises a narrow channel x with
contracted ends connecting the two ends of the cylinder in the manner shown by
the drawing, and in the water-pipe y opening out with its ends, which. are also
contracted, at a right angle and close to the ends of the pipe..
Two spray
apparatuses are thus formed, which are actuated alternately by the air which is
being compressed. This arrangement, however, does not form any part of my
invention. The water thus mixed with the air separates out again in the
air-vessel H, whence it is blown off at intervals.
The cylinders of the air-pump and of the hot-air engine are preferably made of
the same size, and the expansion-gear of the latter is so adjusted that the gases will
expand to about atmospheric pressure. This degree of expansion is admissible
because the frictional resistances of the said engine are overcome by the steam-
engine, which in its turn profits by the economization of heat by means of the
joint arrangement. Considering that during each stroke the resistance in the
air-pump increases, while the pressure in the hot-air engine decreases, it is
advantageous to so connect the respective pistons that the piston of the hot-air
engine begins its stroke under full pressure somewhat before the maximum pres-
sure has been attained in the pump. The work produced in the former and that

page_text: consumed in the latter will, under these conditions, nearly balance each other in
the different portions of the stroke. In the arrangement shown by the drawing
and in which the air-pump is actuated directly by the piston rod of the steam-
engine, this relation between the said pistons is attained by placing the crank r of
the steam-engine at the requisite obtuse angle to the crank s of the hot-air engine.
The heat developed in the furnace may be utilized for other purposes besides
that of generating steam, for instance for, melting metals. An apparatus adapted
for this purpose is represented by Fig. 6. The gas-generator b provided with fuel-
magazine-shaft t, is placed below the melting-furnace u with hearth u¹. The gas
produced in b is conducted by the channel to the apertures v¹, and the air from
the pipe a to the apertures a'. The combustion-gases pass through the channels w
and winto a steam-boiler. The shaft is designed for the reception of a mold &¹,
into which the liquid metal may be run under pressure in view of producing
castings that are free from pores.
.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what
I claim is:
1. The combination, with a closed furnace, of a steam-boiler receiving heat from
the former, a pump for supplying compressed air to the furnace, a hot-air engine
worked by the compressed combustion-gases from the said furnace and a motor
cooperating with the hot-air engine in driving the air-pump, substantially as and
for the purpose described.
2. The combination, with a steam-boiler A, of a closed furnace B.an air-pump G
supplying compressed air to the furnace through the pipes a¹ and a², the hot-air
engine E worked by the compressed combustion-gases from the furnace, and a
steam-engine F connected to the boiler A and coupled with the engine E, the said
engines E and F driving the air-pump G, substantially as and for the purpose
specified.
3. The combination, with a closed furnace, a steam-boiler, a pump supplying
compressed air to the furnace, a hot-air engine connected to the furnace and a
motor cooperating with the hot-air engine in driving the air-pump, of means for
purifying the compressed combustion-gases on their course from the furnace to the
hot-air engine, for reducing their temperature and for mixing them with steam,
substantially as herein before set forth.
4. The combination, with the closed furnace B, steam-boiler A, air-compressing
pump G, hot-air engine E connected to the furnace and steam-engine F connected to
the boiler and coupled with the engine E, of the gas-purifyer D containing a watery
alkaline solution and provided with the baffle-plates g, substantially as described.
5. The combination, with the closed furnace B in which combustion is kept up
under pressure, of the fuel feeder C, comprising the cylinder d, piston d', hopper d²
with cover d', and valve d³ provided with means for operating it and keeping it
closed against the pressure acting thereon, substantially as and for the purpose
spécified.
6. The combination, with a steam-boiler A, the air-compressing pump G, the hot-
air engine E, and the steam-engine F, of a furnace adapted for melting metals,
substantially as set forth.
J. HENRY JOHNSON,
Agent.