CA2714097C

CA2714097C - Cogeneration apparatus for heat and electric power production

Info

Publication number: CA2714097C
Application number: CA2714097A
Authority: CA
Inventors: Marinella Maurizzi
Original assignee: TRADEWAVE AG
Current assignee: TRADEWAVE AG
Priority date: 2008-02-06
Filing date: 2009-02-05
Publication date: 2013-10-08
Anticipated expiration: 2029-02-05
Also published as: CA2714097A1; EP2337938A2; WO2009098580A3; WO2009098580A2; ITBO20080079A1

Abstract

The cogeneration apparatus for producing heat and electric power comprises a boiler (1), fit to generate heat inside a boiler furnace or combustion chamber (11). Inside the boiler furnace (11) there is provided the hot section (21) of a Stirling cycle engine (20), fit to be heated and kept at a high operating temperature by the heat generated inside the same boiler furnace (11). A
corresponding Stirling engine cold section (25) is provided outside the main body (2) of boiler (1). The cold section (25) is thermally insulated by the hot section (21), and it is kept in a thermodynamic fluid communication relationship with this latter by means of a pipe (35). The hot section (21) and cold section (25) are moreover mechanically connected one each other, and they are also mechanically connected to an electric generator (50), fit to convert a part of the mechanic power produced by the Stirling engine into electric power.

Description

"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 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 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.

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.

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 =
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 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 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, 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.

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.

Claims

1. 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 (11) 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 (100) being characterized in that it comprises, arranged into said boiler furnace (11), a hot section (21) of a Stirling cycle engine (20), fit to be heated and kept to a high operating temperature by the combustion of said combusting material inside said boiler furnace (11), a corresponding cold section (25) of said Stirling engine (20) being provided outside of said boiler furnace (11), said cold section (25) being in a thermodynamic fluid exchange relationship with said hot section (21), being moreover separated from said hot section (21) by at least one thermally insulating wall (29), and being also mechanically connected to said hot section (21) by means of a transmission member (40), an electric generator (50) being mechanically connected to an output shaft of said Stirling engine (20) so as to convert a part of the mechanic power produced by said Stirling engine (20) into electric power.

2. Apparatus according to claim 1, characterized in that said boiler (1) is a wood pellets powered boiler.

3. Apparatus according to claim 1 or 2, characterized in that said boiler (1) comprises a main body (2) and an additional body (3), arranged sideways with respect to said main body (2) near to said boiler furnace (11), said cold section (21) and said electric generator (50) being located inside said additional body (3).

4. Apparatus according to claim 1, characterized in that said Stirling engine (20) comprises: at least a first cylinder (22), made in said hot section (21) and fit to slidably receive a first piston (23), reciprocally slidable inside of said first cylinder (22); a second cylinder (26), made in said cold section (25) and fit to slidably receive a second piston (27), reciprocally slidable inside of said second cylinder (26);
said first cylinder (22) and second cylinder (25) being capable to exchange a fluid between each other by means of a pipe (35), with interposition of heat dissipating means (36) arranged outside of said boiler furnace (11); said first piston (23) and second piston (27) being moreover mechanically connected, by means of corresponding piston rod-crank assemblies (24, 28), to said mechanic transmission member (40).

5. Apparatus according to claim 4, characterized in that said mechanic transmission member (40) comprises a first pulley (41), located outside of said hot section (21), a second pulley, located outside of said cold section (25), and a transmission belt (43), arranged between said pulleys (41,42) and fit to mechanically connect the aforesaid pistons (23,27).

6. Apparatus according to claim 5, characterized in that said heat dissipating means (36) comprises a helical pipe, fit to enhance the thermal exchange surface between said thermodynamic fluid and the atmosphere.

7. Apparatus according to claim 5, characterized in that said pipe (35) moreover comprises an expansion chamber (37), fit to give a first temperature fall to the hot thermodynamic fluid coming from said Stirling engine hot section (21).

8. Apparatus according to claim 1 to 5, characterized in that said Stirling engine (20) comprises a plurality of operating modules, each one of those comprising a cited hot section and a cited cold section, working in parallel and in mutual mechanic coupling.

9. Apparatus according to claim 1, characterized in that said electric generator (50) is connected to said output shaft (45) of the Stirling engine (20) by means of a bevel gear (46).