An Improved Tubulous Boiler with Superheater.
Year: 1894

page_text: Date of Application, 10th Aug., 1894
Con plete Specification Left, 24th Apr., 1895-Accepted, 24th May, 1895
An Improved Tubulous Boiler with Superheater.
I, WILHELM SCHMIDT, of Wilhelmshöhe near Cassel, Villa Henkel, in the
Province of Hesse-Nassau, Germany, Civil Engineer, do hereby declare the nature
of this invention to be as follows:-
This invention relates to steam-generators of the kind, in which a tubulous boiler
is combined with a superheater, and forms an improvement on the steam-generator
described in my English Patent No. 23171, 1893. In order to facilitate under-
standing of my present improvement, and avoid taking reference to the said
Letters Patent, I will first expose the principles according to which said former
steam-generator has been constructed.
There is employed in the latter a continuous coil heated directly by the furnace
and generating the steam, and another continuous coil heated by the boiler-gases
and superheating the steam.
Said two coils are combined with a reservoir, which is connected with both ends
of the boiler-coil, and with one end of the superheating-coil. The feed-water is
introduced into said reservoir from whence it is entering the boiler-coil through
the lower end of the latter. The hot water is led back into the reservoir through
the upper end of the boiler-coil, together with the steam evolved, and water and
steam are now separating within said reservoir, the former commencing its circuit
anew, and the steam being led off through the other coil within which it is
superheated.
In devising the afore described arrangement, I proceeded from the experience
that to obtain superheated steam of a temperature of about 300° C., the heating-
gases ought to possess a temperature of from 500 to 600° C.; experiments proved,
that said degree of superheating is obtained in the most efficacious way by
arranging the superheater in that zone of the heating gases, which commences with
a temperature of 600° C. The superheating-coil is thus arranged behind the boiler-
coil with regard to the direction of the furnace-gases; the latter, therefore, need be
cooled down by the boiler-coil to about 600° C. only, the further exhaustion of the
heat of the furnace-gases (down to 250° C.) being effected by the superheater.
Generally, an exhaustion of the furnace gases down to 250° C. is demanded also
of steam-generators having no superheater. The greatest portion of the steam is,
however, produced in the fore- or front-part of a generator ie. in that part by which
an exhaustion of the furnace-gases down to 600° C. is effected. The quantity of
steam produced by exhausting the furnace-gases from 600 down to 250° C. is a
comparatively small one, there being, moreover, required, comparatively large
surfaces for taking up that heat. It has been proved by extensive trials, that
about 50% of the steam is produced in the small part of a generator within which
the fire-box is enclosed.
It will be seen from this, that a generator if combined with a superheater of
high efficiency not only may have a comparatively small heating-surface, but
should have such a one; and, further, that a generator of that kind will yield the
same results as a larger boiler having no superheater, in that the waste-heat of the
furnace-gases is in both cases the same, i.e. about 250° C. The great advantage
obtained by superheating the steam to a high degree is, first, that the volume of
the steam is considerably increased; and second, that by the use of that highly
حيم

page_text: superheated steam any condensation of the latter within the cylinder is perfectly
prevented.
Especially in consequence of the great increase of volume of the steam
by superheating the same to a high degree of temperature I am enabled to
reduce the size of the generator proper in a comparatively like degree, and to
employ for the generator coiled pipes, which although possessing some well-known
advantages could not be used for larger plants on account of the following
reasons:
A principal point to be considered in the use of coils as a generator is the rapid
circulation of the water, or of the mixture of water and steam respectively. There
is, however, the friction arising between the water and the walls of the coiled-
pipes counteracting that circulation, especially, if the length of the pipes is a great,
their section, however, a small one. If, to overcome this drawback, pipes of
sufficiently larger section were to be used, the practical differences caused by
bending wrought iron pipes of that section would, in view of the present state of
the art, soon become insurmountable. If, on the other hand, pipes with but small
section are employed, the length of the pipes, in order to provide the necessary
largeness of heating-surface, must be a correspondingly greater one. There, then,
is so great a friction between water and pipes, and so great a retardation of the
circulation of the water within the pipes, that the remaining circulation is
insufficient for a regular and shockless evolvement of the steam.
All this is wholly changed, if a generator consisting of coiled pipes is combined
with a superheater. There is no necessity any more for giving so large a surface
to the boiler-coil, as the furnace-gases are to be cooled down to normal waste heat
not by the boiler-coil, but by the superheating-coil. The size of the boiler-coil
need be but a fifth or a sixth of that used heretofore.
The bighest effect of said combination of a boiler-coil with a superheating-coil
is, however, attained, if said coils are connected with a reservoir preventing the
mixture of water and steam escaping from the boiler-coil from flowing directly into
the superheating-coil, and causing a separation of said medium (compare the third
paragraph of my present Specification). The more rapid the circulation of the
water, or of the mixture of water and steam respectively, within the boiler-coil, the
more heat is given off by said mixture to the water contained within the reservoir,
and the more steam is evolved. The circulation in its turn will be the more rapid,
the greater the difference of pressure between the contents of the reservoir and the
boiler-coil, and the smaller the friction within the latter. Owing, therefore, to
said rapid circulation, the water flowing through the boiler-coil will not wholly be
turned into steam; there will be produced a mixture of steam and hot water,
which needs separation into its two components. If that mixture would directly be
led into the coils of the superheater, there could, perhaps, be obtained dried steam,
but no superheated one.
If, now, very large quantities of superheated steam are to be produced by means
of a steam generating plant of the kind above treated, some alterations of the
tubulous boiler as well as of the superheater, become requisite. It is to be con-
sidered, that in that case correspondingly large quantities of water were to be
driven through the boiler-coil, and therefore a corresponding increase in the size
of the latter had to be made. That increase can, however, be effected by the use
of longer pipes only, as an increase in. the section of the pipes is hindered by the
immense difficulty of bending the same. By employing longer pipes than normally
used, the drawbacks that were overcome just by the shortening of the pipes would
anew be caused.
The improved arrangement is represented in the accompanying drawing.
Concerning, first, the improvements in the tubulous boiler-proper, the same are to
be seen in both the figures. Instead of using but one boiler-coil, as formerly,
there are now employed three of them (a, b, c) each of which is with both its ends
connected with the reservoir by means of the hollow pieces a c¹. The lower
ends of said three coils communicate directly with the water-chamber of said

page_text: reservoir; the upper ends of the coils communicate by means of pipe y with the
dome of the same.
The action of each of said coils is the same as that of the one
coil hitherto used; each coil is but short, and, in consequence thereof, offers but a
slight frictional resistance to the water flowing through it.
Besides the number of the coils, there is also a special configuration and
arrangement of the same. Coil a is shaped like a cone, and forms a vault by
which the noxious effect of the thin flames is greatly reduced. Moreover, the fire-
gases are contracted by reason of that shape, and on streaming to the coil b, they
are again expanding. The gases after having washed the inner side of coil & enter
the annular space between the coils and c, from whence they are flowing to the
superheater.
There is attained by that arrangement of the coils a nearly smokeless combustion
of the fuel.
The way described is made by the gases only if coil is closed at its upper end
by the cover d. If that cover is raised, the greatest portion of the gases will flow
directly through the coil b, thus leaving coil c untouched. There may be attained
by that means a regulation of the degree of superheating, as will be seen by the
following.
If cover d is closed, all the gases are compelled to wash coil 6 as well as coil c;
owing to the greater surface offered by both the coils, the temperature of the gases
is, as a matter of course, reduced more as if the cover is raised, and coil b is the
only one washed by the gases. There is, consequently, in the former case, the
superheating less intense, and thus by raising the cover more or less, or perfectly
closing it, the degree of superheating may be varied or regulated.
The superheater shown in Fig. 1 consists of two superposed coils & ¹ connected
with each other, and with the reservoir, in such a manner that in spiral k the steam
is flowing in a direction equal to that of the furnace-gases, whilst in the other spiral
it is flowing in a direction opposite to that of the furnace gases. This construction
of superheater is not new. The whole arrangement has been improved, however,
in the manner shown in Fig. 2. There are arranged in the superheating-chamber
two coils connected with each other by the pipe 2. Coil serves as heater
for the feed-water, and is arranged above the superheating-coil; coil h serves as a
fore-evaporator, and is arranged below the superheating-coil. Coil is connected
with the feed-pump. Coil his connected with the upper portion of the reservoir
by means of the vertical pipe y¹.
a,
The
The feed-water thus is forced by the feed-pump (not shown) first through the
heating-coil h, and thereafter into the fore-evaporator h. The mixture of water
and steam escaping out of pipe y' separates within the reservoir. The water mixes
with the water already contained within the reservoir, whilst the steam is entering
b and c.
the superheater together with the steam produced within the coils
steam after having passed the superheating coil is led directly to the engine.
It will be seen, that part of the steam is produced already by the fore-
evaporator h. In consequence of this, the boiler coils proper may be reduced still
more in size, i.e. in their lengths, so that friction is kept on the smallest degree
This circulation within
possible, and therefore the circulation is a very rapid one.
the coils hand is maintained by the action of the force-pump.
Coil besides its action as a fore-evaporator forms, however, a protection for the
superheating coil proper, in that the intense heat of the boiler-gases is broken by
said coil h. The boiler-gases after leaving the space containing the superheating
coil proper, are still more exhausted by coil ', so that the waste heat of said gases
is but a very low one.
Dated this 10th day of August 1894.
WILHELM SCHMIDT,
By Geo. Thos. Hyde,
1, Broad Street Buildings, Liverpool Street, London, E.C.,
Agent for the Applicant.

page_text: You ous Doller with Superneater.
I, WILHELM SCHMIDT, of Wilhelmshöhe near Cassel, Villa Henkel, in the
Province of Hesse-Nassau, Germany, Civil Engineer, do hereby declare the nature
of this invention, and in what manner the same is to be performed, to be
particularly described and ascertained in and by the following statement:-
This invention relates to steam-generators of the kind, in which a tubulous boiler
is combined with a superheater, and forms an improvement on the steam-generator
described in my English Patent No. 23171/1893. In order to facilitate under-
standing of my present improvement, and avoid taking reference to the said
Letters Patent, I will first lay down the principles according to which said former
steam-generator has been constructed.
There is employed in the latter a continuous coil treated directly by the furnace,
and generating the steam, and another continuous coil heated by the boiler-gases,
and superheating the steam. Said two coils are combined with a reservoir, which
is connected with both ends of the boiler-coil, and with one end of the superheating-
coil. The feed-water is introduced into said reservoir, from whence it enters the
boiler-coil through the lower end of the latter. The hot water is led back into the
reservoir through the upper end of the boiler-coil, together with the steam evolved,
and water and steam now separate within said reservoir, the former commencing its
circuit anew, and the steam being led off through the other coil within which it is
superheated.
In devising the afore described arrangement, I proceeded from the experience
that to obtain superheated steam of a temperature of about 300° C., the heating-
gases ought to possess a temperature of from 500° to 600°C.; experiments proved,
that said degree of superheating is obtained in the most efficacious way by arranging
the superheater in that zone of the heating gases, which commences with a tem-
perature of 600° C. The superheating-coil is thus arranged behind the boiler-coil
with regard to the direction of the furnace-gases; the latter, therefore, need be
cooled down by the boiler-coil to about 600° C. only, the further exhaustion of the
heat of the furnace-gases (down to 250° C.) being effected by the superheater.
Generally, an exhaustion of the furnace gases down to 250° C. is demanded also
of steam-generators having no superheater. The greatest portion of the steam is,
however, produced in the fore- or front-part of a generator, i.e. in that part by
which an exhaustion of the furnace-gases down to 600° C. is effected. The quantity
of steam produced by exhausting the furnace-gases from 600° down to 250° C. is a
comparatively small one, there being, moreover, required comparatively large
surfaces for taking up that heat. It has been proved by extensive trials, that
about 50% of the steam are produced in the small part of a generator within which
the fire-box is enclosed.
It will be seen from this, that a generator if combined with a superheater of high
efficiency not only may have a comparatively small heating-surface, but should have
such a one; and, further, that a generator of that kind will yield the same results
as a larger boiler having no superheater, in that the waste-heat of the furnace-gases
is in both cases the same, i.e. about 250° C. The great advantage obtained by
superheating the steam to a high degree is, first, that the volume of the steam is
considerably increased; and second, that by the use of that highly superheated
steam any condensation of the latter within the cylinder is perfectly prevented.
Especially in consequence of the great increase of volume of the steam by
superbeating the same to a high degree of temperature I am enabled to reduce the
size of the generator proper in a comparatively equal degree, and to employ for
"

page_text: the generator coiled pipes, which although possessing some well-known advantages
could not be used for larger plants on account of the following reasons:
A principal point to be considered in the use of coils as a generator is the rapid
circulation of the water, or of the mixture of water and steam respectively.
The friction arising between the water and the walls of the coiled-pipes
counteracts, that circulation, especially, if the length of the pipes is a great, their
section, however, a small one. If, to overcome this drawback, pipes of sufficiently
larger section were to be used, the practical differences caused by bending wrought
iron pipes of that section would, in view of the present state of the art, become
soon insurmountable. If, on the other hand, pipes with but small section are
employed, the length of the pipes, in order to provide the necessary largeness of
heating-surface, must be a correspondingly greater one. There is then so great a
friction between water and pipes, and so great a retardation of the circulation of
the water within the pipes, that the remaining circulation is insufficient for a
regular and shockless evolvement of the steam.
All this is wholly changed, if a generator consisting of coiled pipes is combined
with a superheater. There is no necessity any more for giving so large a surface
to the boiler-coil, as the furnace-gases are to be cooled down to normal waste heat
not by the boiler-coil, but by the superheating-coil. The size of the boiler-coil
need be but a fifth or a sixth of that used heretofore.
The highest effect of said combination of a boiler-coil with a superheating-coil is,
however, attained, if said coils are connected with a reservoir preventing the
mixture of water and steam escaping from the boiler-coil from flowing directly into
the superheating-coil, and causing a separation of said medium (compare the third
paragraph of my present Specification). The more rapid the circulation of the
water, or of the mixture of water and steam respectively, within the boiler-coil,
the more heat is given off by said mixture to the water contained within the
reservoir, and the more steam is evolved. The circulation in its turn will be
the more rapid, the greater the difference of pressure between the contents of the
reservoir and the boiler-coil, and the smaller the friction within the latter. Owing,
therefore, to said rapid circulation, the water flowing through the boiler-coil will
not wholly be turned into steam-; there will be produced a mixture of steam and
hot water, which needs separation into its two components. If that mixture would
directly be led into the coils of the superheater, there could, perhaps, be obtained
dried steam, but no superheated one.
if, now, very large quantities of superheated steam are to be produced by means
of a steam generating plant of the kind above treated, some alterations of the
tubulous boiler as well as of the superheater become requisite. It is to be considered,
that in that case correspondingly large quantities of water were to be driven through
the boiler-coil, and therefore a corresponding increase in the size of the latter had
to be made. That increase can, however, be effected by the use of longer pipes
only, as an increase in the section of the pipes is hindered by the immense difficulty
of bending the same. By employing longer pipes than normally used, the drawbacks
that were overcome just by the shortening of the pipes would anew be caused.
The improved arrangement is represented in the drawings sent in with Provisional
Application.
Concerning first, the improvements in the tubulous boiler-proper, the same are to
be seen in both the figures. Instead of using but one boiler-coil, as formerly, there
are now employed three of them (a b c) each of which is with both its ends connected
with the reservoir f by means of the hollow pieces a¹. The lower ends of said
three coils communicate directly with the water-chamber of said reservoir; the
upper ends of the coils communicate by means of pipe y with the dome of the same.
The action of each of said coils is the same as that of the one coil hitherto used
each coil is but short, and, in consequence thereof, offers but a slight frictional
resistance to the water flowing through it.
;
Besides the number of the coils, there is also a special configuration and arrange-
ment of the same. Coil a is shaped like a cone, and forms a vault by which the

page_text: noxious effect of the thin flames is greatly reduced. Moreover, the fire-gases are
contracted by reason of that shape, and on streaming to the coil b, they expand
again. The
gases after having washed the inner side of coil benter the annular
space between the coils b and c, from whence they flow to the superheater.
There is attained by that arrangement of the coils a nearly smokeless combustion
of the fuel.
The way described is made by the gases only if coil is closed at its upper end
by the cover d. If that cover is raised, the greatest portion of the gases will flow
directly through the coil b, thus leaving coil c untouched. There may be attained
by that means a regulation of the degree of superbeating, as will be seen by the
following.
If cover d is closed, all the gases are compelled to wash coil as well as coil c;
owing to the greater surface offered by both the coils, the temperature of the gases
is, as a matter of course, reduced more as if the cover is raised, and coil b is the
only one washed by the gases. There is, consequently, in the former case, the
superheating less intense, and thus by raising the cover more or less, or perfectly
closing it, the degree of superheating may be varied or regulated.
The superheater shown in Fig. 1 consists of two superposed coils kk' connected
with each other, and with the reservoir, in such a manner, that in spiral k the steam
flows in a direction equal to that of the furnace-gases, whilst in the other spiral it
flows in a direction opposite to that of the furnace gases. This construction of
superheater is not new. The whole arrangement has been improved, however, in
the manner shown in Fig. 2. There are arranged in the superheating-chamber two
coils connected with each other by the pipe 2. Coil serves as a heater for
the feed-water, and is arranged above the superheating-coil; coil serves as a
fore-evaporator, and is arranged below the superheating-coil. Coil ¹ is connected
with the feed-pump. Coil is connected with the upper portion of the reservoir
by means of the vertical pipe y¹.
The feed-water is thus forced by the feed-pump (not shown) first through the
beating-coil h', and thereafter into the fore-evaporator h. The mixture of water
and steam escaping out of pipe y separates within the reservoir. The water mixes
with the water already contained within the reservoir, whilst the steam enters the
superheater together with the steam produced within the coils a b & c. The steam
after having passed the superheating coil is led directly to the engine.
It will be seen, that part of the steam is produced already by the fore-
evaporator . In consequence of this, the boiler coils proper may be reduced still
more in size, i.e. in their lengths, so that friction is kept on the smallest degree
possible, and therefore the circulation is a very rapid one. This circulation within
the coils and ¹ is maintained by the action of the force-pump.
Coil besides its action as a fore-evaporator forms, morcover, a protection for
the superheating coil proper, in that the intense heat of the boiler-gases is broken
by said coil. The boiler-gases after leaving the space containing the superheating
coil proper, are still more exhausted, by coil ', so that the waste heat of said gases
is but a very low one.
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. In a generator for superheated steam, the combination with a reservoir, of two
or more boiler-coils connected each by both its ends with said reservoir, one (a) of
said boiler-coils forming a conical vault adapted to contract the furnace-gases, said
reservoir being connected with one end of the superheating coil arranged above, or
behind, the boiler-coil, substantially and for the purpose as described.
2. In a generator for superheated steam, the combination with a reservoir, of two
or more boiler-coils connected each by both its ends with said reservoir, one (a) of
said boiler-coils forming a conical vault adapted to contract the furnace gases,
another boiler-coil (b) arranged above the former forming a vault adapted to

page_text: distribute the furnace-gases, said reservoir being connected with one end of a
superheating coil arranged above, or behind, the boiler-coil, substantially and for
the purpose as described.
3. In a generator for superheated steam, the combination with a reservoir, of
three or more boiler-coils connected each by both its ends with said reservoir, the
lowest (a) of said boiler-coils forming a conical vault adapted to contract the
furnace-gases, the second boiler-coil (6) arranged above the former forming a vault
adapted to distribute the furnace-gases, the third boiler-coil (c) embracing said
coil (b) forming a fire-mantle, said reservoir being connected with one end of a
superheating coil arranged above, or behind, the boiler-coil, substantially and for
the purpose as described.
4. In a generator for superheated steam, the combination with the superheating
coil or coils, of two other coils (h h¹) arranged one above, the other below said
superheating coil or coils, and connected with each other, the upper (¹) of said
coils being adapted to exhaust the furnace-gases still more by letting them heat
the feed-water, the lower (h) of said coils being adapted to relieve the boiler-coils
by evaporating part of said feed-water, substantially and for the purpose as
described.
5. In a generator for superheated steam, the combination with a superheating-
coil kk (Fig. 1), or 2 (Fig. 2) respectively, of two or more boiler-coils, each of
which is shorter than the superheating-coil, and is connected by both its ends with
a reservoir connected with one end of the superheating coils; a coil h¹ adapted to
exhaust the furnace gases still more by letting them heat the feed-water being
arranged above the superheating-coil; another coil adapted to relieve the
boiler-coils by evaporating part of said feed-water being arranged below the
superheating-coil, substantially and for the purpose as described.
6. In a generator for superheated steam, the combination with a reservoir, of
two or more boiler-coils connected each by both its ends with said reservoir, one (a)
of said boiler-coils forming a conical vault adapted to contract the furnace-gases,
another boiler-coil (b) arranged above the former forming a vault adapted to
distribute the furnace-gases, said reservoir being connected with one end of a
superheating-coil arranged above, or behind, the boiler-coil; said second vault
having a cover adapted to close the upper opening of the respective-coil,
substantially and for the purpose as described.
Doted this 24th dow of rail 1905
WILHELM SCHMIDT,
By Geo. Thos. Hyde,
Agent for the Applicant.