Note: Descriptions are shown in the official language in which they were submitted.
CA 02714097 2010-08-04
WO 2009/098580
PCT/1B2009/000208
"COGENERATION APPARATUS FOR HEAT AND ELECTRIC
POWER PRODUCTION"
BACKGROUND OF THE INVENTION
The present invention fits into that technical sector relating to the
combined production of heat and electric power.
More particularly the invention relates to a cogeneration apparatus
for generating heat and electric power, mostly for a domestic utilization
or for users not connected to the mains network.
BRIEF DESCRIPTION OF KNOWN ART
It is known that the combined generation of electric power and hot
water, for a house heating apparatus or for other house utilizations, is
considerably advantageous than producing power and hot water
separately, for the overall efficiency as well as for the convenience of
use, exploitation of the available space and purchasing costs of the
apparatus. This is also true with low-powered o medium-powered
apparatus, as those generally used for domestic purposes are. In this
case, in fact, in addition to the aforesaid advantages, it is also
zo convenient to exploit the government facilitations granted to those who
produce electric power by themselves. Another advantage arises from
the possibility to use the power company as a "energy bank": in fact, it
is now possible to convey the private power production exceeding the
consumption to the electric network when the production is greater than
the power consumption, and to draw it therefrom when the consumption
is greater than the current production.
Conventional cogenerator apparatus usually exploit the
mechanical energy generated by an internal combustion engine to drive
an electric power generator, in order to produce the desired electric
power. A part of the heat generated by said motor is subsequently
provided, by means of a heat exchanger, to a fluid circulating in a
CA 02714097 2010-08-04
WO 2009/098580
PCT/1B2009/000208
secondary circuit which serves a user (a heating system or the like) .
As the heat generated by the internal combustion engine must be
dissipated in any case, and then it would get lost, its use, even if only
partial, would allow a significant improve in the overall efficiency of the
whole cogeneration system.
A different, less common kind of cogeneration systems is also
known, wherein a Stirling engine, which is an external combustion
engine, is used instead of an internal combustion engine. The Stirling
cycle is well known since several years. It is based on a closed cycle
io operating principle. According to said cycle a thermodynamic fluid,
which consists of a gas, alternately moves between a hot area, wherein
it expands, and a cold area, wherein its volume decreases. The engine
operates correctly if there is created and kept a sufficiently high
temperature difference between the hot area and the cold area.
A Stirling engine is simple and cheap to manufacture; it has a few
moving parts and it is therefore extremely reliable, noiseless and easy
to maintain.
The apparatus for cogeneration of known art that use a Stirling
engine are substantially based on the same structural philosophy
already used for the cogenerators using an internal combustion engine.
That is, they are primarily designed for producing mechanical energy,
thus they exploit the residual heat for heating buildings or for some
other civil or industrial purposes only as a secondary effect.
Structures as those described above are not particularly suitable
for a domestic utilization, as the ratio between the electric power that is
produced and the heat that is made available is not optimised for such
use.
A problem that limits the use of a Stirling engine, mostly for small
sized cogeneration apparatus, arises from a difficult in achieving a good
efficiency in the mechanical energy production. In fact, although
performing a Stirling cycle in a motor allows in principle to achieve an
2
CA 02714097 2012-11-15
efficiency which approaches the theoretical maximum efficiency of that
thermodynamic cycle, the real efficiency that is normally achieved is
greatly limited by the objective difficult to keep the temperature difference
between the engine hot area and the engine cold area sufficiently high.
US Patent Application No. 2006/0213196 to Tetuo Sukioka discloses
a Stirling engine-cogeneration system featuring a burner unit provided with
a combustion chamber and with a liquid media jacket that envelopes the
combustion chamber. The exhaust gas coming from the combustion
chamber is evacuated through conducts passing inside the liquid media
jacket. Water flows within the jacket, and is heated both by the heat directly
coming from the combustion chamber and from the exhaust gas.
The heater belonging to a Stirling engine head is located into the
combustion chamber, in order to operate the same Stirling engine and
generate mechanic power. The Stirling engine is then connected to an
electric generator.
The above cogeneration system shows a good efficiency in
transferring the generated heat to water, but uses a substantially
conventional Stirling engine for producing electric power.
The characteristic feature of a Stirling engine to be operated by heat
coming from a combustion generated outside of the engine body makes it
particularly suited to be fuelled by a wide variety of combustible materials,
and particularly with non-conventional engine combustible materials, by
example with firewood or with its by-products, that could not be used with
any other kind of engine.
OBJECTS OF THE INVENTION
An object of the present invention is to provide a cogeneration
apparatus for generating heat and electric power, whose structure is
particularly suitable to be used in a domestic environment or in any
location not connected to the electric network.
3
CA 02714097 2012-11-15
A further object of the invention is to provide a cogeneration
apparatus which is capable to guarantee an excellent thermodynamic
efficiency and a continuous production of electric power.
Another object of the invention is to provide a cogenerator structure
that is capable to efficiently use combustible materials different from fossil
fuels, therein comprised low-environmental impact combustible materials.
A further object of the invention is to provide a cogeneration
apparatus wherein the section dedicated to electric power production is
substantially separated from that dedicated to heat production, and that is
io moreover easily integrable in an existing heat system for domestic use.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, there is provided an
is apparatus for cogeneration of heat and electric power, of the type
comprising a boiler 1, fit to generate heat by combusting a combustible
material inside a boiler furnace thereof and to convey it, by means of
suitable heat exchange means, toward a heating system and/or a heat
water production system, said cogeneration apparatus being characterized
20 in that it comprises, arranged into said boiler furnace, a hot section
of a
Stirling cycle engine, fit to be heated and kept to a high operating
temperature by the combustion of said combusting material inside said
boiler furnace, a corresponding cold section of said Stirling engine being
provided outside of said boiler furnace, said cold section being in a
25 thermodynamic fluid exchange relationship with said hot section, being
moreover separated from said hot section by at least one thermally
insulating wall, and being also mechanically connected to said hot section
by means of a transmission member, an electric generator being
mechanically connected to an output shaft of said Stirling engine so as to
30 convert a part of the mechanic power produced by said Stirling engine
into
electric power.
4
CA 02714097 2012-11-15
A corresponding cold section of the Stirling engine is located outside
the main boiler body. The cold section is thermally insulated from the hot
section, and it is kept in a thermodynamic fluid communication relationship
by means of a conduit. The hot and cold sections are moreover
mechanically connected one each other, and are also connected to an
electric generator, fit to convert a portion of the mechanic power generated
by the Stirling engine into electric power.
BRIEF DESCRIPTION OF THE DRAWINGS
io The
characteristic features of the present invention, as they will
appear from the appended Claims, are pointed out in the following detailed
description, with reference to the enclosed figures, wherein:
- figure 1 shows schematically a prospective view of a cogeneration
apparatus made according to the present invention;
- figure 2 shows a schematic configuration of a Stirling engine as
the one embedded in the cogeneration apparatus of figure 1.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
4a
CA 02714097 2010-08-04
WO 2009/098580
PCT/1B2009/000208
=
With reference to figures 1 and 2 and to a preferred, yet not
exclusive, embodiment of the invention, numeral 100 indicates, as a
whole, an apparatus for producing heat and electric power at the same
time.
The aforesaid cogeneration apparatus 100, as far as it regards the
preferred embodiment that will be described in the following, comprises
a boiler 1 of a kind normally used to drive a domestic heating system.
Advantageously, even this is not essential to the scopes of the
invention, the boiler 1 is a firewood fuelled boiler, more preferably
to fuelled
with pinewood or fir wood pellets. This makes the cogeneration
apparatus 100 suitable to exploit renewable energetic resources, which
are on the whole less polluting of the fossil fuels. Moreover, a
cogeneration apparatus 100 so structured fulfils to all the requirements
for exploiting the governmental facilitations provided to which efficiently
uses those energetic resources.
Boiler 1, whose structure is well known in itself and therefore it will
not be described in deep detail, comprises a main body 2, in the lower
portion of which a boiler furnace 11 or combustion chamber (figure 2) is
arranged. Pellets are burnt inside the boiler furnace 11, and heat is then
generated therein. Said pellets come to a burner 12 by falling through a
feed pipe 13, to which they are conveyed by a screw feeder 14. This
latter continuously draws pellets from a tank 15 arranged sideways of
the boiler main body 2.
At the upper portion of the main body 2 there is provided a heat
exchanger, not illustrated, inside which water flows to be heated and
then routed toward one or more load circuits by means of an electric
pump. Usually, a load circuit for house heating plus an additional load
circuit for heating water for domestic utilizations are provided in the
upper portion of the main body 2.
According to the present invention, the cogeneration apparatus
100 comprises a Stirling cycle engine 20, fit to exploit a portion of the
5
CA 02714097 2010-08-04
WO 2009/098580
PCT/1B2009/000208
heat produced by the boiler 1 for generating electric power to be
provided to the house electric network, in addition or instead of the
public electric network.
The aforesaid Stirling engine 20 comprises a hot section 21 and a
cold section 25, which are connected one each other by means of a
pipe 35 for exchanging a thermodynamic fluid, and which are also
mechanically connected by means of a mechanic transmission member
40, the structure of which will be detailed in the following.
According to the invention, the hot section 21 of the Stirling engine
Ici 20 is
arranged inside the boiler furnace 11, so as to be continuously
heated and kept at a high operating temperature by the heat produced
by the pellets combustion. The cold section 25 is, by contrary, arranged
outside the boiler furnace 11, inside a boiler's additional body 3, which
is arranged sideways of the main body 2, on the opposite side with
respect to the boiler side where the pellets tank 15 is located.
The hot section 21 and the cold section 25 are thermally insulated
by means of an interposing high thermal resistance wall 29. This wall
also acts as a separating wall between the boiler's main body 2 and
additional body 3, in the area wherein they face one each other.
The Stirling engine illustrated in figure 2 is a modular engine and,
by way of a non-limiting example, it comprises two identically structured
modules, arranged in parallel one each other. However it is to be
intended that, according to the required mechanical power to be
generated, the number of parallel modules can be greater or smaller
than those of the illustrated engine configuration.
For each of the aforesaid modules, the hot section 21 comprises a
first cylinder 22, made of a suitable thermally conducting material and
capable to be sufficiently resistant to high temperatures, fit to slidably
receive inside it a first piston 23. This latter is reciprocally slidable
inside
the first cylinder 22, with a stroke whose travel is defined by a first
piston rod-crank assembly 24 connected to the same piston 23. The
6
CA 02714097 2010-08-04
WO 2009/098580
PCT/1B2009/000208
aforesaid crank, together with the crank of the other hot section module,
defines a first drive shaft 24a. A first pulley 41 of the above cited
transmission member 40 is axially fit on a end of said first drive shaft
24a.
According to a similar construction technique, the Stirling engine
cold section 25 comprises a second cylinder 26, also made of a suitable
thermally conductive material, fit to slidably receive a second piston 27
inside it. This latter is reciprocally slidable inside the second cylinder 26,
with a stroke whose travel is defined by a second piston rod-crank
assembly 28 connected to the same second piston 27. The aforesaid
crank, together with the crank of the other cold section module, defines
a second drive shaft 28a. A second pulley 42 of the above cited
transmission member 40 is axially fit on a end of said second drive shaft
28a.
The first pulley 41 and the second pulley 42 are connected
together by means of a transmission belt 43, fit to define the above
mentioned mechanical connection between the hot section 21 and cold
section 25.
According to the conventional working cycle of a Stirling engine,
the first piston 23 and the second piston 27 are mechanically connected
so as to move counter-phased one each other; that means that, when
the first piston 23 reaches its top dead centre, the second piston 27
reaches its bottom dead centre.
Also according to the conventional working cycle of a Stirling
engine, inside the first cylinder 22 and the second cylinder 26 there is a
thermodynamic fluid, fit to collect heat while it is in the hot section 21,
inside the first cylinder 22, and to give heat while it is in the cold section
25. The thermodynamic fluid consists of a gas, by example Nitrogen
gas, but preferably Helium gas, which allows an optimum thermal
exchange.
In order to guarantee that the Stirling engine 20 operates correctly,
7
CA 02714097 2010-08-04
WO 2009/098580
PCT/1B2009/000208
it is necessary that the hot section 21 and the cold section 25
communicate one each other, in order to allow the thermodynamic fluid
to be transferred from one section the other one when a sufficient
temperature difference is set up between hot section 21 and cold
section 25. Therefore the first cylinder 22 and the second cylinder 26
are connected one each other by means of a pipe 35, which is external
to the cylinders walls.
Near the location where the pipe 35 reaches the cold section 25,
heat dissipating means 36 are provided, connected in series to the
io same pipe 35, whose function is to enhance the thermal exchange
surface between the thermodynamic fluid and the outside atmosphere.
Near the location where the pipe 35 reaches the hot section 22
there is moreover provided an expansion chamber 37, also connected
in series to the same pipe 35, fit to produce a first temperature fall in the
thermodynamic fluid coming from the Stirling engine hot section 22. At
one end of the second drive shaft 28a there is provided an output shaft
45, to which an electric generator 50 is mechanically connected by
means of a transmission group consisting of a bevel gear 46. The
generator 50 is fit to convert a portion of the mechanic power produced
by the Stirling engine into electric power, that can be subsequently
provided to the domestic electric network.
The above described positioning of the output shaft 45 is not to be
considered as a limitation of the characteristic features of the invention,
as well as it is not limiting the kind of the described transmission group
46. Different technical solutions can be suitably provided to connect the
Stirling engine to the electric generator 50.
The present invention provides several advantages over the
known art. First of all, the cogeneration apparatus 100 is installable in a
domestic environment, easily and without any undesired effect,
because of its small size and of its direct coupling to a commercial-type
boiler.
8
CA 02714097 2012-11-15
Moreover, the Stirling engine is made more efficient, and its
performances are provided more continuously, because of the particular
configuration and arrangement of the engine hot section and cold section.
More particularly, the total separation and the high thermal insulating grade
of the two sections allows to keep a high temperature difference between
them, and therefore allows the thermodynamic fluid to continuously
perform its expansion-contraction cycles, without the typical stall events
which are frequent in conventionally configured Stirling engines, with the
hot section and cold section arranged in mutual contact.
A further advantage offered by the invention is that it is easily
possible, if necessary, a conversion of an operating boiler to the
cogeneration apparatus of the invention, as the work which is necessary to
add the engine-electric generator assembly to the existing boiler are
somewhat simple, and do not interfere with the boiler operating parts.
Moreover, the engine-generator assembly can be easily mounted on
several types of conventional boiler at factory, in order to obtain a compact
and reliable cogeneration apparatus.
It is to be intended that what above has been described as a pure, not
limiting example. Therefore, possible changes and variations of the
invention are considered within the protective scope conceded to the
present invention, as defined in the appended claim.
9
