GB2376271A

GB2376271A - Plant for generating electricity and heat comprising a thermoelectric converter such as a Stirling engine

Info

Publication number: GB2376271A
Application number: GB0205428A
Authority: GB
Inventors: Datong Wu; Stephan Kohl; Juergen Waidner; Hans-Werner Zimmermann; Andreas Schall
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2001-03-08
Filing date: 2002-03-07
Publication date: 2002-12-11
Anticipated expiration: 2022-03-07
Also published as: DE10111072A1; GB0205428D0; GB2376271B; DE10111072B4

Abstract

The invention relates to a plant (1) for generating electricity and heat, with a heat-generating unit (2), having a first burner (6) and a first heat exchanger (8), which is linked to a first circuit loop (9) and which transfers heat generated by the first burner (6) to a heat transfer medium of a heating circuit, and with a combined electricity- and heat-generating unit (3), having a second burner (15), a second heat exchanger (17), which is linked to a second circuit loop (18) and which transfers some of the heat generated by the second burner (15) to the heat transfer medium, and a thermoelectric converter (21), which converts some of the heat generated by the second burner (15) into electrical energy which can be tapped via appropriate electrical terminals (22) on the plant (1), there being provided a control and regulating system (27) which controls and/or regulates the electricity- and heat-generating unit (3) for generating heat base loads and controls the heat-generating unit (2) for generating heat peak loads.

Description

237627 1

Plant for generating electricity and heat Prior art

10 The invention relates to a plant for generating electricity and heat. A plant of this type is commonly employed in a building in order for example to heat a heating circuit for a central-heating system and/or for a hot-water supply.

Furthermore, such a plant can additionally generate 15 electricity, which can be used for example to meet a base load of a current demand of the building.

Heat-generating units, having a burner and a heat exchanger, which is linked to a circuit loop, connected to 20 a flow and a return of the heatgenerating unit, and which transfers heat generated by the burner to a heat transfer medium of a heating circuit, are known. A heating circuit can thus be heated with the aid of such of a heat-

generating unit. Heat-generating units of this type, which 25 are used exclusively for generating heat, are well known.

Furthermore, relatively modern combined electricity- and heat-generating units, likewise having a burner and a heat exchanger, which is linked to a circuit loop, connected to 30 a flow and a return of the plant, and which transfers at least some of the heat generated by the burner to a heat transfer medium of a heating circuit, are known.

Furthermore, electricity- and heat-generating units of this type are equipped with a thermoelectric converter, e.g. a

Stirling engine, which converts at least some of the heat generated by the burner into electrical energy which can be tapped via appropriate electrical terminals on the electricity- and heat-generating unit. A heating circuit, 5 G.9. of building, can thus be heated in the usual way with the aid of such an electricity- and heat-generating unit, while at the same time electricity is also generated, which can be utilized directly for example in this building. The electricity generation in situ means that 10 there are no line losses, with the result that the ecological energy balance is improved. In particular, Stirling engines operate with a far better efficiency than a conventional power plant.

15 Such an electricity- and heat-generating unit works as follows: a combustion mixture is burnt in the burner, whereby heat is released. At least some of this heat is converted into electrical energy by the thermoelectric converter. In the heat exchanger, at least some of the heat 20 remaining in the waste combustion gases can then be transferred to the heat transfer medium, e.g. water.

Furthermore, the heat exchanger serves at the same time for cooling the thermoelectric converter, whereby additional heat is transferred to the heat transfer medium. In the use 25 of such a conventional electricityand heat-generating unit for a heating installation in a building, the unit must be suitable both for generating heat base loads and for generating heat peak loads, e.g. in winter. To enable such an electricityand heat-generating unit to generate 30 sufficient thermal energy for heat peak loads as well, the associated burner and the associated heat exchanger must be of correspondingly large dimension. However, this has the result that burner and heat exchanger are overdimensioned in operating states in which merely a heat base load is

required, so that the electricity- and heat-generating unit operates with a reduced efficiency in this case.

5 Advantages of the invention The plant for generating electricity and heat according to the invention, with the features of Claim 1, has, in

contrast, the advantage that the plant can operate with 10 relatively high efficiencies both at heat base loads and at heat peak loads. The invention is based on the idea of equipping the plant with an electricity- and heat-

generating unit for generating heat base loads and additionally with a (purely) heat-generating unit for 15 generating heat peak loads. This measure provides the possibility of equipping the electricity- and heat-

generating unit with a relatively small burner and with a relatively small heat exchanger, so that a relatively compact construction can be realised for the electricity 20 and heat-generating unit. In this regard, the invention makes use of the fact that a smaller or more compact electricity- and heat-generating unit has a smaller surface, thereby radiates less heat, consequently exhibits less heat loss and thus has a higher efficiency. The 25 invention additionally takes account of the fact that the heat losses dependent on the volume of the heat-generating unit are approximately the same size when generating heat base loads and when generating heat peak loads. This relationship will be illustrated with the aid of a 30 numerical example: a conventional electricity- and heat-

generating unit is dimensioned so that it can generate for example a heat base load of 2000 watts and a heat peak load of 20,000 watts. The losses radiated to the environment in particular via its surface amount to 200 watts for example,

regardless of the load state. When generating heat peak loads, the known electricity- and heat-generating unit thus exhibits relatively low losses of about 1%. On the other hand, the losses when generating heat base loads are 5 relatively high and amount to abort And To contrast in the case of the plant according to the invention, the electricity- and heatgenerating unit can be constructed so compactly that it radiates for example only 20 watts to the environment as a loss, whereas the heatgenerating unit 10 combined with it as before exhibits a loss of 200 watts.

Consequently, the plant according to the invention exhibits a relatively low loss of about 1\ in the numerical example when generating heat base loads, i.e. with the heat-

generating unit inactive. A relatively low loss of about 1% 15 in the numerical example also results when generating heat peak loads.

A particular advantage of the present invention is that the plant according to the invention can also be produced by 20 retroactively adding an electricity- and heat-generating unit to an existing heat- generating unit, the plant thus combined using an appropriate control and regulating system to control and/or regulate the retroactively added electricity- and heat-generating unit for generating heat 25 base loads and to control and/or regulate the already present heat-generating unit for generating heat peak loads. The electricity- and heat-generating unit is expediently 30 designed essentially for the heat base loads, whereas the heat-generating unit is dimensioned for the heat peak loads. This enables a particularly economical operation of the plant.

In accordance with a preferred embodiment, the electricity-

and heat-generating unit can have a standard connection for supplying a combustion medium and/or for discharging the waste combustion gases. This measure enables the 5 electricity- and heat-generating unit to be coupled to different known, standardized heat-generating units. This enables a simplified production of the plant according to the invention, since the compact electricity- and heat-

generating unit can be easily combined with conventional, 10 seriesproduced heat-generating units. This is particularly advantageous in the case where a compact electricity- and heat-generating unit according to the invention is retroactively added to a conventional heat-generating unit which is already installed, so as to produce the plant 15 according to the invention.

According to another embodiment, valve means are provided, by which a flow and/or a return of the plant can be connected to a first circuit loop assigned to the heat 20 generating unit and/or to a second circuit loop assigned to the electricity- and heat-generating unit. By this measure, the two separate units, namely the heat-generating unit and the electricity- and heat-generating unit, are hydraulically coupled to each other.

According to a development, a control and regulating system of the plant can be connected to these valve means for the actuation thereof, the control and regulating system switching the valve means, for generating heat base loads, 30 so that the heat transfer medium circulates in the second circuit loop and not in the first circuit loop, and, for generating heat peak loads, so that the heat transfer medium circulates both in the first circuit loop and in the second circuit loop. This measure prevents, when generating

heat base loads, the heat transfer medium from flowing also through the heat exchanger of the heat-generating unit, which is in this case inactive. Radiation losses due to the heat-generating unit can thus be reduced.

Further important features and advantages of the plant according to the invention emerge from the subclaims, the drawings and the associated description of the figures with

reference to the drawings.

Drawings Exemplary embodiments of the plant according to the 15 invention are illustrated in the drawings and are explained in more detail below. In the drawings, Fig. 1 shows, schematically, a basic illustration of a plant according to the invention in a first 20 embodiment and Fig. 2 shows, schematically, an illustration as in Fig. 1, but in a second embodiment.

25 Description of the exemplary embodiments

In accordance with Figs. 1 and 2, a plant 1 for generating electricity and heat according to the invention has a heat-

generating unit 2 and a combined electricity- and heat 30 generating unit 3. The plant 1 possesses a flow 4 symbolized by an arrow and a return 5 likewise symbolised by an arrow. The plant 1 can be connected by way of flow 4 and return 5 to a heating circuit (not illustrated), by which for example a building is to be heated or supplied

with hot water. Accordingly, heat transfer medium, e.g. water, heated by the plant 1 leaves the plant 1 through the flow 4, whereas the cooled heat transfer medium of the heating circuit is introduced into the plant 1 through the 5 return 5 for renewed heating.

The heat-generating unit 2 has a first burner 6, which is supplied with a combustible combustion-gas mixture via a first fresh-gas line 7. The heatgenerating unit 2 10 additionally has a first heat exchanger 8, which transfers heat generated by the first burner 6 to the heat transfer medium. For this purpose, the first heat exchanger 8 is linked to a first circuit loop 9, which is connected to the flow 4 and to the return 5 of the plant 1. In this 15 arrangement, a supply line TO is connected to the return 5 of the plant 1 via valve means 11, whereas a discharge line 12 communicates directly with the flow 4.

The waste combustion gases produced by the first burner 6 20 are cooled by the first heat exchanger 8 and enter a waste gas-collecting line 14 via a first waste-gas line 13.

The electricity- and heat-generating unit 3 has a second burner 15, which is supplied with the combustible gas 25 mixture by a second fresh-gas line 16. The electricity- and heat-generating unit 3 possesses a second heat exchanger 17, which is connected to the flow 4 and the return 5 of the plant 1 in a second circuit loop 18 with a supply line 19 and a discharge line 20. Here, too, the supply line 19 30 is coupled to the return 5 via the valve means 11, whereas the discharge line 20 communicates directly with the flow 4. The electricity- and heat- generating unit 3 additionally has a thermoelectric converter 21, which is preferably designed in the manner of a Stirling engine. In the

operation of the second burner 15, the thermoelectric converter 21 converts some of the heat generated by the second burner 15 into electrical energy, which can be tapped as current via appropriate electrical terminals 22 5 on the plant '. In this procedure, the second heat exchanger 17 cools the thermoelectric converter 21 and a third heat exchanger 41 extracts still further heat from the waste combustion gases, in order thereby to heat the heat transfer medium. The cooled waste combustion gases 10 then leave the electricity- and heat-generating unit 3 via a second waste-gas line 23. In the embodiment according to Fig. 1, this second waste-gas line 23 can be connected to the first waste-gas line 13 of the heat-generating unit 2.

In accordance with the embodiment according to Fig. 2, the 15 second waste-gas line 23 can also be connected directly to the waste gascollecting line 14.

What is particularly important here is the hydraulic connection of the units 2 and 3, which in both embodiments 20 is chosen such that both units 2 and 3 are connected to the flow 4 and return 5 in parallel, that is are connected to the heating circuit in parallel with each other.

In accordance with Fig. 1, the heat-generating unit 2 and 25 the electricity- and heat-generating unit 3 are accommodated, in accordance with a first embodiment, in a common housing 24. In order to supply the two burners 6 and 15 with fresh gas, a common blower 25 is assigned to both units 2 and 3 here. Furthermore, a common control unit 26 30 including a control and regulating system 27 is provided for both units 2 and 3. The control unit 26 is connected to the two units 2 and 3 and also to the valve means 11 via corresponding control lines 28.

The plant 1 according to Fig. 1 works as follows: In order to generate heat base loads, the control and regulating system 27 is designed such that it switches the 5 valve means 11 so that the return 5 is connected only to the supply line 19 of the second circuit loop 18, but not to the supply line 10 of the first circuit loop 9.

Furthermore, in order to generate heat base loads, only the electricityand heat-generating unit 3 is activated, 10 whereas the heat-generating unit 2 is deactivated.

When heat peak loads are to be generated by the plant 1, the control and regulating system 27 switches the valve means 11 so that both the supply line 10 of the first 15 conductor loop 9 and the supply line 19 of the second conductor loop 18 are connected to the return 5. Both conductor loops 9 and 18 are then connected in parallel.

The control and regulating system 27 then controls and regulates the heatgenerating apparatus 2 in the required 20 manner. Accordingly, in order to generate heat peak loads, both the heat-generating unit 2 and the electricity- and heat-generating unit 3 are activated. In other words: in order to generate larger heat loads, the heat-generating unit 2 is connected to the electricity- and heat-generating 25 unit 3.

In the second embodiment, illustrated in Fig. 2, the heat-

generating unit 2 and the electricity- and heat-generating unit 3 are each accommodated in a separate housing 29 and 30 30, respectively. In order to supply the burners 6 and 15 with fresh gas, a separate blower 31 and 32 is likewise assigned to each unit 2 and 3, respectively. Accommodated in the first housing 29 of the heat-generating unit 2 is a first control unit 37 including first control and

regulating means 38. The first control unit 37 is connected to the heatgenerating unit 2 via a corresponding control line 39. In addition, the first control unit 37 is connected via a corresponding signal line 36 to a second 5 control unit 33 accommodated i n the second housing 30. This second control unit 33 includes second control and regulating means 34 and is connected via corresponding control lines 35 to the electricity- and heat-generating unit 3 and also to the valve means 11, which are 10 accommodated in the second housing 30. The control units 33 and 37, and their control and regulating means 34, 38, respectively, cooperate via the signal line 36 to form a control and regulating system 40 which enables the operation of the plant 1. In another embodiment, the second IS control unit 33 of the electricity- and heat-generating unit 3 can take over the control and regulation of the heat-generating unit 2, in which case the first control unit 37 can then be dispensed with. As can be seen particularly clearly from Fig. 2, a heat-generating unit 2 20 which is already installed can be supplemented in a simple manner, by the retroactive addition of the electricity- and heat-generating unit 3, to form the plant 1 according to the invention. For this purpose, all that is required is for the valve means 11 to be connected to the return 5 and 25 to the supply line 10 of the first conductor loop 9, for the discharge line 20 of the second conductor loop 18 to be connected to the flow 4 and for the two control units 33 and 37 to be connected to each other. In addition, the second waste-gas line 23 is connected to the waste gas 30 collecting line 14.

The plant 1 according to Fig. 2 works as follows:

In order to generate heat base loads, the control and regulating system 40 switches the valve means 11 so that the return 5 is connected only to the second conductor loop 18 and not to the first conductor loop 9. For the heat base 5 loads, the heat-generating unit 2 is deactivated, whereas the electricity- and heat-generating unit 3 is activated.

In order to generate larger heat loads, in particular heat peak loads, the heat-generating unit 2 is then switched on, i.e. activated. At the same time, the valve means 11 are 10 also actuated so that now the first conductor loop 9 also communicates with the return 5.

The particular advantage of the plant according to the invention is that, in order to generate heat base loads, 15 only the very compactly constructed electricity- and heat-

generating unit 3 is active, and can operate with a relatively low heat loss at these heat loads. Only at larger heat loads is the heatgenerating unit 2 switched on, and likewise operates with a relatively low heat loss 20 at large heat loads.

A further important aspect of the present invention is that the electricity- and heat-generating unit 3 is designed so that it can easily be combined with different heat 25 generating units 2. As a result, the electricity- and heat generating unit 3 has a modular nature, and can be connected, in particular also retroactively, to an existing heatgenerating unit 2. In order to simplify this, the electricity- and heatgenerating unit 3 has a standard 30 connection for supplying the combustion medium and/or for discharging the waste combustion gases.

List of reference symbols 1 Plant 2 Heat-generating unit 10 3 Electricityand heat-generating unit 4 Flow 5 Return 6 First burner 7 First fresh- gas line 15 8 First heat exchanger 9 First circuit loop 10 Supply line of 9 11 Valve means 12 Discharge line of 9 20 13 First waste-gas line 14 Waste gas-collecting line 15 Second burner 16 Second fresh-gas line 17 Second heat exchanger 25 18 Second circuit loop 19 Supply line of 18 20 Discharge line of 18 21 Thermoelectric converter 22 Electrical terminal 30 23 Second waste-gas line 24 Common housing 25 Common blower 26 Common control unit 27 Control and regulating system

28 Control line 29 First housing 30 Second housing 31 First blower 5 32 Second blower 33 Second control unit 34 Second control and regulating means 35 Control line 36 Signal line 10 37 First control unit 38 First control and regulating means 39 Control line 40 Control and regulating system 41 Third heat exchanger

Claims

Claims 1. Plant for generating electricity and heat, with a heat-

generating unit (2), having a first burner (6) and a 10 first heat exchanger (8), which is linked to a first circuit loop (9), connected to a flow (4) and a return (5) of the plant (1), and which transfers heat generated by the first burner (6) to a heat transfer medium of a heating circuit, and with a combined electricity- and heat 15 generating unit (3), having a second burner (15), a second heat exchanger (17), which is linked to a second circuit loop (18), connected to the flow (4) and the return (5) of the plant (1), and which transfers at least some of the heat generated by the second burner (15) to the heat 20 transfer medium, and a thermoelectric converter (21), which converts at least some of the heat generated by the second burner (15) into electrical energy which can be tapped via appropriate electrical terminals (22) on the plant (1), there being provided a control and regulating system (27; 25 40) which controls and/or regulates the electricity- and heat-generating unit (3) for generating heat base loads and controls and/or regulates the heatgenerating unit (2) for generating heat peak loads.

30
2. Plant according to Claim 1, characterized in that the electricityand heat-generating unit (3) is designed to generate heat base loads and in that the heat-generating unit (2) is designed to generate heat peak loads.
3. Plant according to Claim 1 or 2, characterized in that the electricityand heat-generating unit (3) has standardized connection means for supplying a combustion medium and/or for discharging the waste combustion gases.
4. Plant according to one of Claims 1 to 3, characterized in that the heat-generating unit (2) and the electricity-

and heat-generating unit (3) are supplied with a combustion medium by a common blower (25).
5. Plant according to one of Claims 1 to 4, characterized in that the heat-generating unit (2) and the electricity and heat-generating unit (3) are accommodated in a common housing (24).
6. Plant according to one of Claims 1 to 5, characterized in that a common control unit (26) including the control and regulating system (27) is provided for the heat generating unit (2) and for the electricity- and heat 20 generating unit.
7. Plant according to one of Claims 1 to 3, characterized in that the heat-generating unit (2) is supplied with a combustion medium by a first blower (31) and in that the 25 electricity- and heat-generating unit (3) is supplied with a combustion medium by a second blower (32).
8. Plant according to one of Claims 1 to 3, 7, characterized in that the heat-generating unit (2) is 30 accommodated in a first housing (29), and in that the electricity- and heat-generating unit (3) is accommodated in a second housing (30).
9. Plant according to one of Claims 1 to 3, 7, 8, characterized in that a first control unit (37) is provided for the heat-generating unit (2) and in that a second control unit (33) is provided for the electricity- and 5 heat-generating unit (3)! the two control units (33' 37) cooperating to form the control and regulating system (40).
10. Plant according to one of Claims 1 to 9, characterized in that valve means (11) are provided, by which the flow 10 (4) and/or the return (5) of the plant (1) can be connected to the first circuit loop (9) and/or to the second circuit loop (18).
11. Plant according to Claim 10, characterized in that the 15 control and regulating system (27; 40) is connected to the valve means (11) for the actuation thereof, the control and regulating system (27; 40) switching the valve means (11), when generating heat base loads, so that the heat transfer medium circulates in the second circuit loop (18) and not 20 in the first circuit loop (9), and, when generating heat peak loads, so that the heat transfer medium circulates both in the first circuit loop (9) and in the second circuit loop (18).

25
12. Plant according to Claim 11, characterized in that the control and regulating system (27; 40) actuates the valve means (11), when generating heat peak loads, so that the first circuit loop (9) and the second circuit loop (18) are connected in parallel.
13. Plant substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.
14. Plant substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.