IMPROVEMENTS IN SUPERHEATERS AND IN THE APPLICATION OF SUPERHEATED STEAM IN STEAM ENGINES, AND IN PACKINGS USED IN CONNECTION THEREWITH
Year: 1877

page_text: LETTERS PATENT to Alexander Melville Clark, of 53, Chancery Lane, in the
County of Middlesex, Patent Agent, for the Invention of "IMPROVEMENTS IN
SUPERHEATERS AND IN THE APPLICATION OF SUPERHEATED STEAM IN STEAM
ENGINES, AND IN PACKINGS USED IN CONNECTION THEREWITH."
A com-
munication from abroad by Le Baron Raymond Seillière and Louis Marie
Théophile Riot, both of Paris, France.
Sealed the 20th April 1878, and dated the 15th November 1877.
PROVISIONAL SPECIFICATION left by the said Alexander Melville Clark at
the Office of the Commissioners of Patents on the 15th November 1877.
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent. "IMPROVEMENTS IN SUPERHEATERS, AND IN THE APPLICATION
OF SUPERHEATED STEAM IN STEAM ENGINES, AND IN PACKINGS USED IN CON-
NECTION THEREWITH." [A communication from abroad by Le Baron Raymond
Seillière and Louis Marie Théophile Riot, both of Paris, France.]
Most of the steam engines at present employed use saturated steam, although
many attempts have been made and apparatus devised to substitute superheated
steam for saturated steam as the dynamic agent with a view to the more perfect
utilisation of the fuel.
The theory of the mechanical equivalent of heat first established by Joule in 1843,
and since then developed by others, proves that 1 kilogramme of saturated steam
having a tension of 6 atmospheres, for example, contains 655 units of heat, and that
1 kilogramme of saturated steam at the atmospheric pressure contains 637 units..
It is also proved that 1 kilogramme of superheated steam at the same tension of 6
atmospheres, and having a temperature of 300° Cent. contains 725 units of heat..
Thus, if 1 kilogramme of saturated steam at 6 atmospheres be introduced into a
cylinder, and if by means of suitable expansion apparatus it be exhausted at the
atmospheric tension, the difference between 655 and 637 units, vizt. 18 units, will
have been utilized by the engine. If, on the other hand, 1 kilogramme of super..

page_text: heated steam at 300° Cent. be admitted to a cylinder at a pressure of 6 atmospheres,
and if by a judicious expansion it be exhausted at the same tension as in the former
case, the difference between 725 and 637 units, or 88 units, will have been utilised
by the engine. Admitting that without any additional expenditure of fuel, this
kilogramme of steam may be superheated to 300° Cent. (which can be readily
effected by utilising the waste heat of the gases of combustion passing off through
the chimney) a profit should be realised equal to the difference between 18 and 88
units. This theoretical result is however, far from being easy to attain in practice,
and the many attempts which have been made to employ superheated steam, have
failed to give the looked-for result, owing to the phenomena not having been
sufficiently studied. Thus it has been hitherto assumed as a general principle in
physics that there is an equality of temperature between steam and its source so
long as these two remain in contact or in communication, and hence it has been
concluded that in order to superheat steam it must be isolated or separated from its
source, and all arrangements hitherto devised have been based on these data.
After a lengthened investigation of the subject it has been discovered that the
principle in physics above cited is only true so long as the channel of communica-
tion between the steam and its source is of sufficient size to allow of an equilibrium
of temperature being established, and it has been proved experimentally that, contrary
to the above principle, steam may be superheated during its passage from the
generator to the engine by reducing the area of the outlet from the boiler, and
augmenting the capacity of the superheater to the utmost extent possible.
By this
means superheated steam is obtained, having the same tension as the steam in
the generator, since it is in communication therewith, but having a higher
temperature notwithstanding. This superheated steam may be assimilated to steam
superheated in a closed receptacle to the same temperature and tension, as it
possesses the same density, the same clastic power, and the same temperature in the
one case as in the other; the result is, therefore, in exact conformity with the con-
ditions laid down in the theoretical introduction.
I will now proceed to describe the practical means which characterise the
Invention, and by the aid of which the advantages may be realised, which it has
been shown, are gained theoretically.
Take, for instance, an ordinary arrangement of portable engine, and without
otherwise altering it, interpose the superheating apparatus of this Invention
between the boiler and the cylinder. This superheating apparatus is, without the
interposition of any valves, in constant communication with the boiler by a pipe
leading from the steam dome to a distributing pipe connected with a suitable
number of independent concentric helical coils in the smoke box, and connected at
their other ends with a collecting tube in communication with a chamber
located centrally within the coils. This latter chamber communicates with another
coil beneath the crown of the fire-box by means of a pipe passing through one of
the boiler tubes which is plugged to prevent the passage of the flames. The latter
coil also communicates by a pipe with a chamber outside, forming a reservoir of
superheated steam, from which the cylinder is supplied. From this description it
will be seen that the superbeating apparatus of this Invention is not only subject
to the action of the heated gases in the smoke box, but also to the heat radiating
from the furnace itself. By this means the steam may be superheated to very high
temperatures, and herein lies the difference between the present plans and the
plans of others who have not deemed it proper to exceed the temperatures which
the adjuncts of the engine, such as the stuffing box packings and lubricants, are
capable of supporting without being destroyed, or which would cause those parts
of the engine subject to friction to bind. This difficulty is obviated by a judicious
employment of expansion based on the following phenomenon.
As the expansion of steam causes a diminution of temperature, if this expansion
be continued beyond the usual limits, for example, in the case of a non-conducting
engine to seven or eight times its volume, for superheated steam having a tension of
6 atmospheres, a certain quantity of water is caused to condense upon the sides of

page_text: the cylinder, which being heated by the contact of the superheated steam at the
moment of admission immediately vaporises the water of condensation. The cylinder
thus becomes a kind of generator from the moment the steam is cut off until it is
exhausted, and the surfaces are kept sufficiently cool to ensure proper working. It
is in consequence of this that saturated steam may be taken from the boiler at a
tension of 6 atmospheres, for example, or at a temperature of 155° Cent., caused to
circulate first through the series of coils in the smoke box, where it is raised to a
temperature of 300° Cent., and then through the coil in the fire-box, where the tem-
perature is increased to 450° Cent. (except in cases where the latter coil cannot be
made use of), the steam retaining throughout a tension of 6 atmospheres, and being
admitted at this temperature into the working cylinder, where it is expanded
during ths or the of the stroke. By thus raising the temperature of the super-
heated steam its use becomes still more advantageous, and in practice an economy
of 70 per cent. in fuel is obtainable by the application of this Invention to existing
engines. These high temperatures can only be employed in practice by using
metals capable of resisting them.
For temperatures ranging from 300° Cent. to 400° Cent., iron may be used, pre-
ferably galvanised or coated with zinc, to prevent oxidation, and fill up all cracks
which might occasion leakage; but iron if raised to a red heat decomposes the steam
by combining with its oxygen and becoming oxidised, leaving free hydrogen mixed
with the steam; this mixture on the one hand impedes the phenomenon of con-
densation by expansion in the cylinder, while on the other hand the oxidation is
destructive to the metal. Copper does not oxidise by the contact of the steam, but
it is very quickly damaged by the gases and flame of the furnace. Brass resists the
above causes of deterioration, especially if coated with zinc, and the use of this
metal in the construction of the different parts of the superheating apparatus con-
stitutes a novel application.
It now remains to set forth the great advantages resulting from this improved
arrangement of superheater.
The several coils of which the apparatus is composed must be of very small
diameter, 2 centimetres, for example, in order that the heat of the medium in which
they are placed may be transmitted to the whole body of steam to be superheated,
which is a very bad conductor of heat.
When the superheater is constructed of a single length of pipe as hitherto, there
is a considerable loss of power from the friction of the steam circulating in the pipe;
this loss has been found by experiment to amount to at least one atmosphere for
every hundred metres in length; that is to say, steam at 6 atmospheres on leaving
the boiler will have a pressure of but 5 atmospheres on leaving the superheater.
This loss is almost entirely prevented by the present Invention, which consists in
dividing the superheater into a number of tubes in the form of helical coils, of
which, say 5, each 20 metres in length, make up the total length of 100 metres,
whereby four-fifths of the friction is avoided, and the sectional area of the circu-
lation pipes is five times increased. Such form of superheater may be replaced by
an apparatus composed of straight tubes like a tubular boiler, the steam being
outside or inside the tubes.
In order to still further maintain the normal tension of the superheated steam it
is stored in a reservoir from which but a relatively small quantity is supplied to the
cylinder at each stroke of the piston, the result of which is that a regular and
constant circulation of the steam in the superheater is ensured.
By admitting the superheated steam directly into the cylinder, as heretofore,
without using such reservoir, it has been found by placing a gauge on the valve
chest that the pressure of the steam may fall as low as 14 atinosphere instead of
remaining at the normal pressure of 6 atmospheres. The reservoir also enables a
mixture of saturated steam and superheated steam to be used by placing it in direct
communication with the dome of the boiler by a pipe furnished with a cock, which
is opened, for example, in cases where the degree of expansion adopted for working
with highly superheated steam is found insufficient, and it is necessary to obtain

page_text: more power for starting the engine. This mixture furnishing steam less highly
superheated, the expansion may be less, and greater power consequently obtained,
since the pressure of the steam on its admission to the cylinder is always the same.
The direct communication between the dome of the boiler and the reservoir is also
of service when the engine is at rest, as owing to the difference between the dis-
tances to be traversed the steam from the boiler establishes a current in the opposite
direction through the surperheater, which prevents overheating.
The practical results of the improvements herein described are, first, to effect an
economy of 70 per cent.; and, secondly, as a consequence of such economy to allow
of a reduction in the size of boilers and engines; for example, a 4 horse-power
engine and boiler may with this system of superheating be made to develop 12 horse
power, and from this may be readily imagined the advantages which would result,
more particularly in the case of marine engines, where space is always so very
limited.
It will be understood that the arrangement of the various parts constituting the
superheater may vary according to the kind of boiler to which it is applied.
The superheating chamber and reservoir of superheated steam should always be
embedded in sand or other non-conductor to prevent loss of heat.
To prevent damage to the stuffing box packings of the piston and valve rods, at
the bottom of the stuffing boxes is first placed a packing made of a mixture of talc,
asbestos, and plumbago, and then over this the ordinary packing of greased hemp,
which is thus protected from the heat in the cylinder.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Alexander Melville Clark in the Great Seal Patent Office on the
15th May 1878.
"
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent. IMPROVEMENTS IN SUPERHEATERS, AND IN THE APPLICATION
OF SUPERHEATED STEAM IN STEAM ENGINES, AND IN PACKINGS USED IN CON-
NECTION THEREWITH." A communication from abroad by Le Baron Raymond
Seillière and Louis Marie Théophile Riot, both of Paris, France.
Most of the steam engines at present employed use saturated steam, although
many attempts have been made, and apparatus devised, to substitute superheated
steam for saturated steam as the dynamic agent, with a view to the more perfect
utilisation of the fuel.
The theory of the mechanical equivalent of heat first established by Joule
in 1843, and since then developed by others, proves that 1 kilogramme of saturated
steam, having a tension of 6 atmospheres, for example, contains 655 units of heat,
and that 1 kilogramme of saturated steam at the atmospheric pressure contains 637
units. It is also proved that 1 kilogramme of superheated steam at the same
tension of 6 atmospheres, and having a temperature of 300° C., contains 725 units.
of heat. Thus, if 1 kilogramme of saturated steam at 6 atmospheres be introduced
into a cylinder, and if by means of suitable expansion apparatus it be exhausted at
the atmospheric tension, the difference between 655 and 637 units, vizt. 18 units,
will have been utilised by the engine. If, on the other hand, 1 kilogramme of
superheated steam at 300° C. be admitted to a cylinder at a pressure of 6 atmos-
pheres, and if by a judicious expansion it be exhausted at the same tension as in
the former case, the difference between 725 and 637 units, or 88 units, will have
been utilised by the engine. Admitting that without any additional expenditure
of fuel this kilogramme of steam may be superheated to 300° C. (which can be
readily effected by utilizing the waste heat of the gases of combustion passing off
through the chimney) a profit should be realised equal to the difference between 18
and 88 units. This theoretical result is, however, far from being casy to attain in
practice, and the many attempts which have been made to employ superheated steam
have failed to give the looked-for results owing to the phenonema not having been
sufficiently studied. Thus, it has been hitherto assumed as a general principle in
physics that there is an equality of temperature between steam and its source so
long as these two remain in contact or in communication, and hence it has been
concluded that in order to superheat steam it must be isolated or separated from
its source, and all arrangements hitherto devised have been based on these data.
After a lengthened investigation of the subject it has been discovered that the
principle in physics above cited is only true so long as the channel of communi-
cation between the steam and its source is of sufficient size to allow of an equlibrium
of temperature being established; and it has been proved experimentally that con-
trary to the above principle steam may be superheated during its passage from the
generator to the engine by reducing the area of the outlet from the boiler, and
augmenting the capacity of the superheater to the utmost extent possible. By this
means superheated steam is obtained, having the same tension as the steam in the
generator, since it is in cominunication therewith, but having a higher temperature
notwithstanding. This superheated steam may be assimilated to steam superheated
in a closed receptacle to the same temperature and tension as it possesses the same
density, the same elastic power, and the same temperature, in the one case as in the
other. The result is therefore in exact conformity with the conditions laid down in
the theoretical introduction.
I will now proceed to describe the practical means which characterise the Invention,
and by the aid of which the advantages may be realised, which it has been shown
are gained theoretically.

page_text: The Invention is illustrated in the accompanying Drawings, Figure 1 of which
shows a sectional elevation of an ordinary arrangement of portable engine having
the superheating apparatus of this Invention placed between the boiler Gand cylinder
C. This superheating apparatus is, without the interposition of any valves, in
constant communication with the boiler G by a pipe T, leading from the steam dome
to a distributing pipe A, connected with a suitable number of independent con-
centric helical coils S in the smoke box F (see transverse section, Figure 2), and
connected at their other ends with a collecting tube B, in communication with a
chamber D, located centrally within the coils. The latter chamber communicates
with another coil E beneath the crown of the fire-box by means of a pipe d passing
through one of the boiler tubes which is plugged to prevent the passage of the
flames. The coil E also communicates by a pipe e with a chamber R, forming a
reservoir of superheated steam from which the cylinder C is supplied. From this
it will be seen that the superheating apparatus of this Invention commences at the
distributing pipe A and terminates at pipe e, and is consequently not only subject
to the action of the heated gases in the sinoke box F, but also to the heat radiating
from the furnace itself. By this means the steam may be superheated to very high
temperatures, and herein lies the difference between the present plan and the plans
of others who have not deemed it proper to exceed the temperatures which the
stuffing box packings, lubricants, and other adjuncts of the engine are capable of
supporting without being destroyed, or which would cause those parts of the engine
subject to friction to bind. This difficulty is obviated by a judicious employment
of expansion based on the following phenomenon.
As the expansion of steam causes a diminution of temperature if this expansion
be continued beyond the usual limits, for example, in the case of a non-condensing
engine, to seven or eight times its volume for superheated steam, having a tension of
6 atmospheres, a certain quantity of water is caused to condense upon the sides of
the cylinder, which being heated by the contact of the superheated steam at the
moment of admission, immediately vaporises this water of condensation. The
cylinder thus becomes a kind of generator from the moment the steam is cut off
until it is exhausted, and the surfaces are kept sufficiently cool to ensure proper
working. It is in consequence of this that saturated steam may be taken from
boiler G, at a tension of 6 atmospheres, for example, or at a temperature of 155° C.,
caused to circulate first through the series of coils in the smoke box F, where it is
raised to a temperature of 300° C., and then through the coil E in the fire-box,
where the temperature is increased to 450° C. (except in cases where the latter coil
cannot be made use of), the steam retaining throughout a tension of 6 atmospheres,
and being admitted at this temperature into the working cylinder C, where it is
expanded during 6/ths or 7/8ths of the stroke. By thus raising the temperature of
the superheated steam its use becomes still more advantageous, and in practice an
economy of 70 per cent. in fuel is obtainable by the application of the Invention to
existing engines. These high temperatures can only be employed in practice by
using metals capable of resisting them.
For temperatures ranging from 300° C. to 400° C. iron may be used, preferably
galvanised or coated with zinc to prevent oxidation and fill up all cracks which
might occasion leakage; but iron if raised to a red heat decomposes the steam by
combining with its oxygen and becoming oxidised, leaving free hydrogen mixed
with the steam; this mixture, on the one hand, impedes the phenomenon of con-
densation by expansion in the cylinder, while, on the other hand, the oxidation is
destructive to the metal. Copper does not oxidise by the contact of the steam, but
is very quickly damaged by the gases and flame of the furnace. Brass however
resists the above causes of deterioration, especially if coated with zinc, and the use
of this metal in the construction of the different parts of the superheating apparatus
constitutes a novel application.
It now remains to set forth the great advantages resulting from this improved
arrangement of superheater.
The coils of pipes S and E of which the apparatus is composed must be of very

page_text: small diameter, 2 centimetres for example, in order that the heat of the medium in
which they are placed may be transmitted to the whole body of steam to be super-
heated, which is a very bad conductor of heat.
When the superheater is constructed of a single length of pipe, as hitherto, there
is a considerable loss of power from the friction of the steam circulating in the pipe ;
this loss has been found by experiment to amount to at least one atmosphere for
every hundred metres in length, that is to say, steam at 6 atmospheres on leaving
the boiler will have a pressure of but 5 atmospheres on leaving the superheater;
this loss is almost entirely prevented by the present improvement, which consists in
dividing the superheater into a number of tubes S in the form of helical coils, of
which, say 5, each 20 metres in length, make up the total length of 100 metres,
whereby four-fifths of the friction is avoided, and the sectional area of the passage
afforded for the circulation of the steam is five times increased. This form of super-
heater may be replaced by an apparatus composed of straight tubes like a tubular
boiler, the steam being either inside or outside the tubes.
In order to still further maintain the normal tension of the superheated steam, it
is stored in a reservoir R, from which but a relatively small quantity is supplied to
the cylinder at each stroke of the piston, the result of which is that a regular and
constant circulation of the steam in the superheater is ensured.
By admitting the superheated steam directly into the cylinder, as heretofore,
without using such reservoir R, it has been found by placing a gauge on the valve
chest that the pressure of the steam may fall as low as 1 atmospheres, instead of
remaining at the normal pressure of 6 atmospheres. The reservoir R also enables
a mixture of saturated steam and superheated steam to be used by placing it in
direct communication with the dome of the boiler G by a pipe v, furnished with a
cock which is opened, for example, in cases where the degree of expansion adopted
for working with highly superheated steam is found insufficient, and it is necessary
to obtain more power for starting the engine. This mixture furnishing steam less
highly superheated, the expansion may be less, and greater power consequently
obtained, since the pressure of the steam on its admission to the cylinder is always
the same.
The direct communication between the dome of the boiler and the reser-
voir R is also of service when the engine is not working, as owing to the difference
between the distances to be traversed, the steam from the boiler establishes a
current in the opposite direction through the superheater, which prevents over-
heating.
The practical results of the improvements herein described are, first, to effect an
economy of 70 per cent.; and, secondly, as a consequence of such economy to allow
of a reduction in the size of boilers and engines; for example, a four-horse power
engine and boiler may with this system of superheating be made to develop 12
horse power, and from this may be readily imagined the advantages which would
result, more particularly in the case of marine engines, where space is always so very
limited.
It will be understood that the arrangement of the various parts constituting the
superheater may vary according to the kind of boiler to which it is applied.
The superheating chamber and reservoir of superheated steam should always be
embedded in sand or other non-conductor to prevent loss of heat.
To prevent damage to the stuffing-box packings of the piston and valve rods, at
the bottom of these stuffing boxes is first placed a packing made of a mixture of talc,
asbestos, and plumbago, and then over this the ordinary packing of greased hemp,
which is thus protected from the heat in the cylinder.
Having described the nature of the said Invention, and the manner of performing
the same, I declare that what I claim as the Invention to be protected by the herein-
before in part recited Letters Patent is,-
1st. Placing the superheater in constant communication with the boiler without
the intervention of any valve, substantially as shown for the purpose specified.
2nd. Constructing the superbeater of a number of comparatively short tubes in

page_text: order to multiply the passages for the circulation of the steam, and diminish the
friction resulting from such circulation, substantially as shown and described.
3rd. Working superheated steam to such a degree of expansion as to cause con-
densation and revaporization in the cylinder for cooling both it and the parts in
connection, as specified.
4th. The combination with the superheater of a reservoir for the superheated
steam, as shown and described, to prevent the fall of pressure which would otherwise
take place when the steam is admitted to the cylinder.
5th. The use of brass coated with zinc for making the tubes and other parts of the
superheater.
6th. Providing the stuffing boxes with a non-conducting packing at bottom to
protect the hemp packings from the heat of the superheated stean, as described.
In witness whereof, I, the said Alexander Melville Clark, have hereunto set
my hand and seal, this Fourteenth day of May, in the year of our Lord One
thousand eight hundred and seventy-eight.
A M CLARK
A. M. CLARK
(L.S.)