DE102012214538A1 - Combined heat and power plant - Google Patents

Abstract

A combined heat and power plant with an internal combustion engine (1), the power output of which can be regulated by varying the speed and which has a throttle element (35) in its intake system (22, 32, 34, 37), with an exhaust gas heat exchanger (11) for use the generated heat, with an electrical generator (2) and a converter (3) to adapt the voltage and frequency of the electrical energy to the requirements of the consumer (8) or the power grid (10) is with respect to an optimal efficiency and a quick adaptation of the The output power delivered to the required power is improved according to the invention in that a controllable exhaust gas recirculation (38) with an exhaust gas control valve (39) is provided on the internal combustion engine (1) that, in cooperation with the throttle element (35), the engine speed of the internal combustion engine (1) to the demand electrical power or the heat requirement can be adjusted, with a controller ensuring that the internal combustion engine (1) is preferred s wise is operated at an essentially constant mean pressure in the range of 5 bar to 8 bar.

Description

The present invention relates to a combined heat and power plant with an internal combustion engine, the power output is controlled by means of speed variation and having a throttle body in its intake, with at least one heat exchanger, which is connected to the internal combustion engine to the heat generated by the engine of a Use, with an internal combustion engine driven by the electric generator, with an inverter whose input terminal is connected to the electric generator and its output terminal to local consumers and / or a feed interface of a power network, wherein the inverter generates the electrical energy generated by the generator with respect Voltage, frequency and power requirements adapted to the values required by local consumers or the power grid.

Such a cogeneration plant is out of the EP 0 835 411 B1 known. This known system regulates the variable engine speed for adjusting the heat generated when the throttle is open by means of load on the generator via a corresponding control of the inverter. Such a control is not suitable for island operation with local consumers, because the active and reactive power resulting from the regulation must be delivered to the consumers, regardless of the power requirement. In island operation, however, it is expected that the power of the generated energy adapts to the consumers. Furthermore, a power supply structure with a large number of small energy producers requires that cogeneration plants of any capacity contribute to grid maintenance, thus in particular supporting grid parameters such as grid frequency, grid voltage and requested active and reactive power. However, this can not be guaranteed by the known system because the active and reactive power to be fed into a connected power grid is determined by the operating parameters of the known system, not the requirements of the network.

From the DE 10 2008 039 141 A1 is a combined heat and power plant known in which the output power of an internal combustion engine is made by means of a controllable exhaust gas recirculation. A throttle body is not provided. This system is intended for mains synchronous operation at constant engine speed. An inverter is not required. Therefore, this system can not contribute to the maintenance of the above network parameters.

The object of the invention is to provide a combined heat and power plant, which is suitable for island operation and is suitable in network operation for maintaining the network parameters and adjustment of the output power to the needs of consumers or the network and has a high efficiency.

The invention solves this problem in that a controllable exhaust gas recirculation is provided with an exhaust control valve on the internal combustion engine, by means of which the engine speed of the engine to the electric power demand or heat demand is adaptable, the throttle body is the adjustment of a suitable engine speed supportive controllable and the internal combustion engine is preferably operated at a substantially constant medium pressure in the range of 5 bar to 8 bar. In the range of the mentioned mean pressure of the internal combustion engine runs with a particularly high efficiency. A reduction in the mechanical power provided by the internal combustion engine is mainly caused by the controllable exhaust gas recirculation, wherein the throttle body only supports the adjustment of an engine speed suitable for the desired power output. As a result, the power adjustment is effected faster than by the controllable exhaust system alone. This minimizes the amount of internal combustion engine performance that is inappropriate for the demand for electrical power or requested heat demand and optimizes the adaptation of the power supply to the power requirement.

In an embodiment of the invention, it is provided that the throttle member is at least largely open in the region of the highest engine speed and at low engine speeds is always closed so far that associated with the throttling deterioration of the efficiency of the engine does not exceed a predetermined level. The throttling of an internal combustion engine inevitably leads to a deterioration of the efficiency. Therefore, the general aim is to operate internal combustion engines with the lowest possible throttling. However, the lower the engine speed, the lower the negative effect on the efficiency. In the present invention, except for the highest possible rotational speed, some throttling of the internal combustion engine is provided. However, the throttling remains, depending on the speed, always so low that the efficiency of the engine deteriorates only slightly so that this remains economically justifiable. It is therefore stored at any speed for the position of the throttle body, a limit that must not be exceeded in the control of the throttle body in the case of a constant power output of the engine. With appropriate specification of these speed-dependent limits, the mean pressure of the engine over the entire usable speed range does not change. A Deterioration of efficiency is limited to negligible values.

A further embodiment of the invention provides that for larger changes in the demand for electrical power Einregelung a suitable engine speed by a stronger or complete opening or closing of the throttle body is supported until the appropriate engine speed is reached. If, for example, a lot more electric power is suddenly requested, then the throttle element is preferably fully opened and brought back into a partially closed position only when approaching or reaching the target rotational speed, which does not or only slightly reduces the efficiency of the internal combustion engine. Conversely, in the case of a decreasing electric power demand, the throttle valve is closed to achieve the fastest possible reduction in engine speed. When approaching or reaching the appropriate engine speed, the throttle body is again brought into a largely open position, in which the efficiency of the internal combustion engine is not significantly reduced. In both cases, the achievement of the target speed is accelerated. The target speed is then held constant by regulation of the exhaust control valve until a new power adjustment is required.

In a preferred embodiment of the invention, the combined heat and power plant has a control unit which evaluates data on the operating state of the converter and / or the generator and / or signals from sensors, from which the electrical power requirement and / or the heat demand can be determined is, wherein the control unit is designed to control the output from the engine power to the throttle body and the exhaust control valve acting. In such a control unit can be realized with advantage complex control algorithms that take into account a variety of input parameters and can control several control elements of the system. In particular, the inverter can be provided with voltage and current sensors, from which voltage, current, frequency and phase shift and thus active power and reactive power of the electrical energy delivered to the consumers or a network can be determined. Corresponding sensors can also be provided in the generator. From the frequency of the generator voltage can also determine the speed of the generator and the internal combustion engine. By sensors of a heating circuit connected to the heat exchanger, in particular temperature sensors, the heat demand of the heating circuit can be determined. The throttle body and the exhaust valve or all other controllable actuators of the system are equipped with appropriate actuators, which are electrically controlled by the control unit.

In an advantageous embodiment, the combined heat and power plant according to the invention comprises a gas mixer for producing a fuel-air mixture to be supplied to the internal combustion engine from a combustible gas and air, wherein a gas control valve is provided to control the proportion of combustible gas in the mixture is controllable by the control unit. The control of the gas control valve has, among other factors such as the positions of throttle body and exhaust control valve and the speed of the engine influence on the output power and on the other hand in conjunction with the exhaust control valve influence on the exhaust gas temperature.

The invention is further improved by the measure that in the gas flow direction after the gas mixer, an intake damper is arranged, which consists of a plurality of chambers and a plurality of connecting the chambers overflow pipes. In the intake damper, the fuel gas-air mixture coming from the gas mixer, on the one hand, and the exhaust gas flowing from the exhaust gas recirculation are swirled and homogeneously mixed with one another, so that all cylinders receive the same mixture in a multi-cylinder internal combustion engine. This ensures a clean engine run, because in each cylinder an equally strong combustion takes place. This ensures that each piston or each exhaust valve is loaded to the same extent and in each cylinder equal temperatures prevail. This allows a finer tuning of operating parameters of the internal combustion engine such as in lean operation, where slightly richer mixture causes a higher exhaust gas temperature and slightly too lean mixture incomplete combustion.

The most uniform possible mixing of the fuel-air mixture from the gas mixer on the one hand and the exhaust gas from the exhaust gas recirculation on the other hand obtained when the exhaust gas recirculation flows into a connecting pipe between the gas mixer and the intake damper or directly into the first chamber of the intake manifold.

The invention can be further improved by a lambda probe is arranged in the exhaust gas stream downstream of the internal combustion engine, which is connected to the control unit, wherein the control unit is designed so acting on the gas control valve and / or the exhaust control valve that a predetermined ratio of non-combustible gases to combustible gas is maintained. In particular, in conjunction with a 3-way catalytic converter, this lambda control can ensure low NOx values in the exhaust gas. Incidentally, the lambda probe be used to control the internal combustion engine in lean operation.

An advantageous embodiment of the invention provides that in the exhaust stream to the engine at least one temperature sensor, preferably for each cylinder of the internal combustion engine, a separate temperature sensor is arranged and connected to the control unit and that the control unit acting on the gas control valve and / or the exhaust control valve acting is that a predetermined exhaust gas temperature or an exhaust gas temperature range is maintained. At low exhaust gas temperature extends the life of the exhaust valves of the engine. This embodiment can therefore increase the life of the combined heat and power plant and the required maintenance intervals. In the variant with separate temperature sensors for each cylinder of the internal combustion engine, it is possible to check a clean engine run with uniform combustion in all cylinders and to determine faults in individual cylinders which would not be noticeable in the case of a flat exhaust gas temperature monitoring.

The invention also encompasses a method for operating a cogeneration installation of the type described above, which is characterized in that, during a substantially stable operating state of the cogeneration installation, the control unit requires or requires the ones required by the consumers monitors the electrical power provided to the grid feed and keeps the speed of the engine or generator required to produce this electrical power constant by controlling the magnitude of the recirculated exhaust gas flow through the exhaust control valve, the throttle organ assisting control of the matching engine speed. The simultaneous control of throttle body and exhaust control valve allows the rapid achievement of a given engine speed and keeping constant while the efficiency of the engine is as high as possible.

The inventive method is optimized with respect to a fast power adjustment by the measure that the occurrence of a major change in the demand for electric power Einregelung a suitable for new power demand engine speed is accelerated by the fact that the control unit in addition to the exhaust control valve in the short term on the throttle body in terms of Changing the power requirement acts until the appropriate engine speed is reached.

The method can be further improved by the throttle body is always closed while maintaining the appropriate for the current need for electrical power or the current heat demand engine speed that caused by the throttling deterioration of the efficiency of the engine does not exceed a predetermined level. In this way, the mean pressure of the engine is not substantially changed from the minimum to the maximum usable speed and remains in an optimum range for the efficiency of the internal combustion engine.

To extend the life of the combined heat and power plant and extend the maintenance intervals, it is proposed that the internal combustion engine runs in lean operation and a required excess air is replaced by the admixture of cooled exhaust gas, preferably in the amount of about 20%. By this measure, the temperature of the exhaust gases can be limited to a maximum of 520 ° C, whereby the load and erosion of the exhaust valves is reduced. The resulting cooling of the exhaust gases is otherwise achieved only when operating with lambda> 1.5 by 50% excess air is added. When admixing exhaust gas instead of air, one obtains a positive performance effect from the larger percentage filling amount of fresh gas.

In a further development of the latter method measure, it is recommended that a predetermined exhaust gas temperature be adjusted by admixing cooled exhaust gas. The hot exhaust coming from the internal combustion engine is in any case passed through a heat exchanger to utilize the waste heat, where it is cooled down. In lean operation, therefore, the internal combustion engine can be advantageously operated with an addition of cooled exhaust gas instead of excess air.

A further embodiment of the method according to the invention provides that a required change in the engine speed is assisted by an activation of the converter, in which the electrical load of the generator is reduced to increase the engine speed and increased to reduce the engine speed. This regulation by electrical load of the generator is particularly well suited for stabilizing the constant engine speed when the quality of the supplied fuel gas changes in the short term, which has an effect on the output power of the internal combustion engine.

An embodiment of the invention will be explained in more detail with reference to the drawings. The figures show in detail:

1 : a schematic representation of a combined heat and power plant according to the invention;

2 a partially sectioned view of a Ansaugdämpfers for the system according to 1 ,

In the diagram of 1 you recognize a combustion engine 1 that works mechanically with an electric generator 2 is coupled. The generator is electric with a converter 3 connected, a first connection line 4 is shown in the diagram only as a simple line for the sake of simplicity. But it can depending on the design of the generator 2 also consist of several electrical wires for the transmission of polyphase alternating current. The first connection line 4 opens into an input connection 5 of the inverter 3 in which of the generator 2 generated AC rectified and converted in a known manner by means of power electronics in a single-phase or polyphase AC with fixed predetermined frequency, preferably 50 Hz or 60 Hz as needed. Also the voltage at the output terminal 6 of the inverter 3 Removable electrical energy is adapted to the requirements of energy consumers. Via a second connecting line 7 the converted AC becomes local consumers 8th or a feed-in interface 9 directed where the electrical energy generated in a power grid 10 arrives. The internal combustion engine 1 and the generator 2 can be operated within a usable variable speed engine speed range. This makes it possible to adapt the generated electrical energy or the heat generated to the requirements of the consumers 8th . 10 because the mechanical power output from the engine increases and decreases with engine speed. At variable engine speed but is also the frequency of the generator 2 generated alternating current variable. Also the electrical voltage at the output of the generator 2 depends on its speed. Because the consumers 8th . 10 usually need a constant frequency and a constant voltage is the inverter 3 required.

Since this is a combined heat and power plant, that of the internal combustion engine 1 utilized waste heat. For this purpose, an exhaust gas heat exchanger 11 provided by an exhaust pipe 12 with the exhaust of the internal combustion engine 1 connected is. The hot exhaust gases occur at the entrance 13 in the exhaust gas heat exchanger 11 and pass through a looped cooling coil 14 in which the exhaust gases are cooled. The cooling is carried out by a heat transfer medium, preferably water, which is the cooling coil 14 flows around. The water is heated. The heated water is via a flow line 16 to the heat consumers 17 pumped where it gives off its heat. As a heat consumer 17 For example, heating elements or hot water boilers or hot water heat exchangers are suitable, but they are not shown here in detail. Via a return line 18 the cooled water returns to the exhaust gas heat exchanger 11 where it is reheated. Also in a not shown cooling water circuit of the engine 1 Dissipated waste heat can be used 17 be supplied.

That from the exit 15 the exhaust gas heat exchanger 11 exiting cooled exhaust gas passes through an exhaust pipe 19 to a silencer 20 and from this via a starting pipe 21 into the atmosphere.

The required for the operation of the engine air is through an air inlet pipe 22 taken from the ambient air and passes through an air filter 23 in a gas mixer 24 , The gas mixer 24 consists essentially of a Venturi nozzle 25 with an entrance opening 26 and an exit opening 27 , The gas mixer 24 also has a gas control valve 28 on, through which fuel gas flows, which from a service line 29 via a first gas safety valve 30 and a second gas safety valve 31 to the gas control valve 28 arrives. The gas control valve 28 can regulate the strength of the gas flow. The fuel gas flows out of the gas control valve 28 to a side opening, not shown, of the Venturi nozzle in an area where the strongest negative pressure prevails. There, the fuel gas mixes with the air, so that at the outlet opening 27 the Venturi nozzle 25 a fuel-air mixture exits, which via a mixture pipe 32 in a suction damper 33 where it is swirled to mix fuel gas and air as homogeneously as possible. From the intake silencer 33 the mixture passes through a connecting pipe 34 to a throttle body 35 which is a throttle 36 to narrow the flow cross-section. From the throttle body 35 the mixture passes through an intake pipe 37 to the internal combustion engine 1 which sucks the mixture so that it enters the combustion chambers of the cylinders of the internal combustion engine 1 arrives.

From the exhaust pipe 19 branches a return pipe 38 which cooled exhaust gas via an exhaust control valve 39 to the mixture pipe 32 leads, where the cooled exhaust gas is added to the fuel-air mixture. Depending on the position of the exhaust gas control valve 39 Therefore, a more or less large flow of cooled exhaust gas into the mixture, which from the engine 1 is sucked. The more exhaust gas is added, the less combustible mixture, the internal combustion engine 1 suck in, so that from the combustion engine 1 delivered power is the lower, the more exhaust gas through the exhaust control valve 39 is added.

For controlling and regulating all plant components, the force Heat coupling system with a control unit 40 equipped. The control unit 40 Receives signals from devices or sensors with data on the operating status of the system via signal lines. In particular, it receives via a first signal line 41 Information about the generator 2 , In particular, the frequency of the generated alternating current and thus on the speed of the generator 2 and the internal combustion engine 1 , Via a second signal line 42 receives the control unit 40 Signals from a voltage and current sensor 45 , which contains data about electrical parameters at the output terminal 6 of the inverter 3 , in particular about frequency, current and voltage of the local consumers 8th or in the power grid 10 contain flowing electrical energy. Via a third signal line 43 receives the control unit 40 Signals from a lambda probe 46 containing the data on the composition of the exhaust gas of the internal combustion engine 1 in the exhaust pipe 12 transmitted. At the exhaust pipe 12 is also a temperature sensor 47 attached, whose signals via a fourth signal line 44 to the control unit 40 reach. In the heat consumer circle 16 . 17 . 18 is a heat meter 49 housed, whose signal is via the signal line 48 to the control unit to transmit data on the heat consumption.

The control unit 40 evaluates the incoming data and generates control signals for controlling and regulating the available actuators of the cogeneration plant. In particular, via a first control line 50 the opening of the gas control valve 28 controlled. A second control line 51 controls the exhaust control valve 39 and a third control line 52 the throttle body 35 , A fourth control line 53 is intended to control the inverter.

In 2 is the intake silencer 33 shown in detail. It consists of a first chamber 54 and a second chamber 55 passing through a partition 56 are separated from each other. About three different lengths connecting pipes 57 can the sucked fuel-air mixture from the first chamber 54 in the second chamber 55 enter, wherein the inlet openings of the connecting pipes 57 in different places within the first chamber 54 lie and the outlet openings of the connecting pipes 57 again at different depths of the volume of the second chamber 55 lead. In this way, the mixture is particularly well swirled, so mix possibly unevenly distributed combustion gases evenly with the air. The mixture passes from the gas mixer 24 over the mixture pipe 32 in the first chamber 54 of the intake silencer 33 , Unlike in 1 opens the return pipe 38 exhaust gas recirculation is not in the mixture pipe 32 but directly into the first chamber 54 of the intake silencer 33 ,

After the passage of the fuel-air mixture and the admixed exhaust gas into the second chamber 55 and after complete homogenization of all said components, these pass through an outlet opening 58 from the intake silencer 33 in the connecting pipe 34 to the throttle body 35 ,

The combined heat and power plant is operated according to the invention as follows:
The control unit 40 constantly checks whether the heat output or electrical power generated by the system meets the requirements. For this purpose, it evaluates the voltage and current sensor 45 and the heat meter 49 out. In island operation, if only the local consumers 8th must be supplied, recognizes the control unit 40 at a waste in the sensor 45 measured voltage that more electrical power is required. Conversely, it recognizes a lower power requirement for an increasing voltage. If the amount of heat generated is higher than that by means of heat meter 49 determined need of heat consumers 17 , the system can also be operated in island operation so that not all of the internal combustion engine 1 used heat generated, but for example in the form of hotter exhaust gases through the exhaust pipe 19 into the exit pipe 21 and thus gets into the ambient air.

However, if the combined heat and power plant is operated using heat, a total efficiency of> 80% must be achieved in order to comply with legal regulations. Therefore, the system must not be operated in such a way that heat generated during increased power consumption remains unused. In this case, the system according to the invention is superior to a cogeneration unit with a fixed engine speed, because when throttling the power at a fixed speed, the output electric power is reduced more than the heat output. Therefore, in such a case, there is nothing left but to turn off a system with fixed speed. In contrast, the system according to the invention has the advantage that by means of speed modulation, the electrical power can be reduced and adapted to the heat consumption to continue to operate the system at a total efficiency of <80%. The system according to the invention therefore does not have to be switched off and continues to supply power to the power grid 10 , which on the one hand positive for the support of the power grid 10 and on the other hand, overall a more economical operation of the system according to the invention is allowed, because of the power grid 10 fed-in electricity is paid extra.

After the control unit 40 has determined the power requirement, the internal combustion engine 1 be brought to a desired power corresponding engine speed. The Engine speed is determined by monitoring the frequency of the electric generator 2 generated electric current via the signal line 41 supervised. If the power requirement remains unchanged, the engine speed must be kept constant. The control unit 40 can over the control lines 50 - 53 Influence on the actuators, which in turn can change the engine speed.

This is how the control unit works 40 the gas control valve 28 so drive that the internal combustion engine 1 never operated with excess fuel to run as economically as possible. Preferably, the internal combustion engine 1 operated as Lambda 1 engine in which fuel and air in exactly stoichiometric ratio (lambda = 1) is mixed. The control unit evaluates this 40 the signals of the lambda probe 46 out. Furthermore, the control unit controls 40 over the second control line 51 the exhaust control valve 39 so that from the gas mixer 24 so much cooled exhaust gas is admixed to the flowing fuel-air mixture, that adjusts an exhaust gas temperature, which corresponds to a lean-burn engine with lambda ≈ 1.5. In contrast to air, the cooled exhaust gas contains practically no oxygen. Therefore, replacing air with exhaust gas achieves a desirable exhaust gas temperature of <520 ° C already with an exhaust gas content of 20% of the sucked mixture, while the same effect with air would only be achieved with an air excess of 50%. The mixture therefore contains a larger percentage of fresh gas. Due to the lower combustion temperature, the NOx formation is reduced, which is also the case with lean operation with excess air. However, with the addition of exhaust gas, the NOx content is reduced more because less oxygen is present for NOx formation. This is particularly important for the operation of the combined heat and power plant with biogas or sewage gas, since these fuels, the use of a catalyst is not possible and the lambda probes have a very short life.

Compliance with a low exhaust gas temperature is achieved by measuring the same by means of the temperature sensor 47 from the control unit 40 supervised. It is particularly advantageous if, instead of a single temperature sensor 47 , which generally measures the mixed temperature of the exhaust gases from all cylinders of the internal combustion engine, there is a separate temperature sensor for each cylinder. Thus, the exhaust gas temperature of each cylinder can be measured and evaluated separately. In this way, the control unit 40 detect, for example, faults in the ignition system, if this affects the exhaust gas temperature of a single cylinder. If, for example, a spark plug fails in a 4-cylinder engine, the control unit may 40 In many cases, change the mixture so that the remaining three cylinders still deliver the required power. However, these working cylinders have a higher exhaust gas temperature than permissible. This results in a restless engine run and the damage to the valves. By comparing the temperatures of the individual cylinders such failure can be detected early and engine damage can be avoided.

In operation with constant power requirement, the control unit 40 the speed of the internal combustion engine 1 alone via the exhaust control valve 39 in combination with the gas control valve 28 regulate and keep constant. In principle, a change in the engine speed with changed power requirements can be adjusted in this way. The system is regulated so that the medium pressure of the internal combustion engine 1 essentially preserves, so the internal combustion engine 1 operated with the highest possible efficiency. However, the adaptation of the engine speed can only be done relatively slowly. On the other hand, it is desirable to minimize the time while the engine is running 1 with mismatched engine speed is running.

To accelerate the setting of a changed engine speed is in the inventive combined heat and power plant, the throttle body 35 used. For example, if the engine speed is to be reduced rapidly, the throttle will 36 completely or at least partially closed, resulting in a rapid reduction in engine speed. If the lower engine speed is reached, the throttle body 35 again fully or partially open. Thereafter, the control unit regulates 40 the exhaust control valve 39 and the gas control valve 28 so that even with fully or partially open throttle body 35 the desired target speed is kept constant. Conversely, if the engine speed is to be increased rapidly, the throttle will 36 of the throttle body 35 more or less fully open, resulting in a rapid increase in engine speed. When the target speed is reached, the throttle will turn 36 again partially closed and the control unit 40 regulates the exhaust control valve 39 and the gas control valve 28 so that the engine speed remains constant. By opening or closing the throttle body 35 Thus, the adjustment of a suitable engine speed for adapting the engine power to the requested power can be accelerated.

Basically, the efficiency of the internal combustion engine 1 best if he can run unthrottled. A closing of the throttle 36 of the throttle body 35 degrades the engine efficiency. However, the effect is lower at low speeds than at high speeds. For each speed, there is an opening degree of the throttle body 35 , in which a deterioration of the Efficiency remains below an economically relevant extent. To the above-mentioned support of the change of engine speed by the throttle body 35 even when adapting to get higher speeds, the throttle must 36 of the throttle body 35 be partially closed, otherwise you could not open them to support the acceleration process. Quite open, the throttle body 35 only at the highest usable speed of the internal combustion engine 1 be. The lower the engine speed, the farther the throttle valve can get 36 be closed, without the reduction of the efficiency would have a noticeable economic impact.

One can therefore set a limit for the reduction of the efficiency, for example, tolerate a reduction in efficiency by one percent. Then you can determine at any speed of a throttle position, in which the efficiency is deteriorated by a maximum of one percent. The corresponding values are in the control unit 40 stored. If the engine speed is kept constant in the case of a constant power demand, the control unit controls 40 over the third control line 52 the throttle body 35 so on that the throttle 36 is closed to the stored for the current engine speed degree at which associated with the throttling deterioration of the efficiency of the internal combustion engine 1 the predetermined amount does not exceed, for example, one percent. In this way, the throttle body 35 always closed so far that although a throttling of the internal combustion engine 1 is effected, but not an economically significant effect on the efficiency of the internal combustion engine 1 Has. The engine speed is determined by the control unit 40 at a given position of the throttle body 35 through regulation exhaust control valve 39 and the gas control valve 28 kept constant.

The setting of a changed engine speed can also be achieved by controlling the inverter 3 get supported. For example, if you produce 20 kW of electrical power at 2300 rpm, and this is one of the highest levels of performance offered by the combined heat and power plant, there may be a problem when these 20 kW are actually requested, as fuel gas serving natural gas has a lower calorific value than usual, in which the required 2300 revolutions per minute are not achieved, because the engine can not produce this power with the bad natural gas. In this case, the control unit 40 the inverter 3 so drive that, for example, only 19 kW of electrical power into the mains 10 be fed. This ensures that the internal combustion engine 1 even with bad natural gas, the engine speed of 2300 revolutions per minute achieved. Although this does not produce the requested 20 kW, it does optimize the power output. Without the appropriate control of the inverter 3 For example, the engine speed would drop below 2300 rpm and the performance of the internal combustion engine 1 not fully utilized.

To optimize the combined heat and power plant in terms of efficiency, it is proposed that the generator 2 is designed as a permanent magnet generator. Although other designs are possible and possibly even cheaper to obtain, but only the permanent magnet generator achieves an electrical efficiency of 96% or more.

LIST OF REFERENCE NUMBERS

1

 internal combustion engine

2

 generator

3

 inverter

4

 first connection line

5

 input port

6

 output port

7

 second connection line

8th

 local consumers

9

 Infeed interface / mains supply

10

 power grid

11

 Exhaust gas heat exchanger

12

 Exhaust pipe / exhaust gas flow

13

 entrance

14

 cooling coil

15

 output

16

 supply line

17

 Heat consumer / heat utilization

18

 Return line

19

 exhaust pipe

20

 silencer

21

 outlet pipe

22

 Air inlet pipe

23

 air filter

24

 gas mixer

25

 venturi

26

 inlet opening

27

 outlet opening

28

 Gas control valve

29

 Service line

30

 first gas safety valve

31

 second gas safety valve

32

 mixture tube

33

 intake silencer

34

 connecting pipe

35

 throttle member

36

 throttle

37

 intake

38

 Return pipe / exhaust gas recirculation

39

 Exhaust gas control valve

40

 control unit

41

 first signal line

42

 second signal line

43

 third signal line

44

 fourth signal line

45

 Voltage / current sensor

46

 Lambda probe

47

 temperature sensor

48

 fifth signal line

49

 Heat meters

50

 first control line

51

 second control line

52

 third control line

53

 fourth control line

54

 first chamber

55

 second chamber

56

 partition wall

57

 overflow tubes

58

 outlet opening

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0835411 B1 [0002]
• DE 102008039141 A1 [0003]

Claims (15)

Combined heat and power plant with an internal combustion engine ( 1 ), whose power output can be regulated by means of speed variation and which is a throttle element ( 35 ) in its intake tract ( 22 . 32 . 34 . 37 ), with at least one exhaust gas heat exchanger ( 11 ), with the internal combustion engine ( 1 ) is connected to the engine ( 1 ) generated heat use of heat ( 17 ), with a by the internal combustion engine ( 1 ) powered electric generator ( 2 ), with an inverter ( 3 ), whose input terminal ( 5 ) with the generator ( 2 ) and its output terminal ( 6 ) with local consumers ( 8th ) and / or with a feed-in interface ( 9 ) of a power grid ( 10 ), the inverter ( 3 ) from the generator ( 2 ) produced electrical energy in terms of voltage, frequency and power consumption to those of local consumers ( 8th ) or the power grid ( 10 ), characterized in that a controllable exhaust gas recirculation ( 38 ) with an exhaust control valve ( 39 ), on the internal combustion engine ( 1 ) is provided that in cooperation with the throttle body ( 35 ) the engine speed of the internal combustion engine ( 1 ) is adaptable to the requirement of electrical power or the heat demand, whereby a control ensures that the internal combustion engine ( 1 ) is preferably operated at a substantially constant mean pressure in the range of 5 bar to 8 bar. Cogeneration plant according to claim 1, characterized in that the throttle body ( 35 ) is at least largely open in the region of the highest engine speed and is always closable at lower engine speeds to the extent that a deterioration in the efficiency of the internal combustion engine associated with the throttling ( 1 ) does not exceed a predetermined amount. Cogeneration plant according to claim 1 or 2, characterized in that for larger changes in the demand for electrical power Einregelung a suitable engine speed by a stronger or complete opening or closing of the throttle body ( 35 ) is supported until the appropriate engine speed is reached. Cogeneration plant according to one of the preceding claims, characterized in that it comprises a control unit ( 40 ), the data on the operating state of the inverter ( 3 ) and / or the generator ( 2 ) and / or signals from sensors ( 45 . 46 . 47 . 49 ), from which the electrical power requirement and / or the heat demand can be determined, and that the control unit ( 40 ) for controlling the combustion engine ( 1 ) delivered power to the throttle body ( 35 ) and the exhaust control valve ( 39 ) is formed acting. Cogeneration plant according to one of the preceding claims, characterized in that it comprises a gas mixer ( 24 ) for producing a combustion engine ( 1 ) comprises a fuel-air mixture of a combustible gas and air and that for controlling the proportion of combustible gas in the mixture, a gas control valve ( 28 ) provided by the control unit ( 40 ) is controllable. Cogeneration plant according to claim 5, characterized in that in the gas flow direction after the gas mixer ( 24 ) an intake damper ( 33 ), which consists of several chambers ( 54 . 55 ) and several the chambers ( 54 . 55 ) connecting overflow pipes ( 57 ) consists. Cogeneration plant according to claim 5 or 6, characterized in that the exhaust gas recirculation ( 38 ) into a mixture tube ( 32 ) between the gas mixer ( 24 ) and the intake silencer ( 33 ) or directly into the first chamber ( 54 ) of the intake damper ( 33 ) opens. Cogeneration plant according to one of the preceding claims, characterized in that in the exhaust gas flow to the internal combustion engine ( 1 ) a lambda probe ( 46 ) arranged with the control unit ( 40 ) and that the control unit is connected to the gas control valve ( 28 ) and / or the exhaust control valve ( 39 ) is designed so that a predetermined ratio of non-combustible gases to combustible gas is maintained. Cogeneration plant according to one of the preceding claims, characterized in that in the exhaust gas flow ( 12 ) after the combustion engine ( 1 ) at least one temperature sensor ( 47 ), preferably for each cylinder of the internal combustion engine ( 1 ) a separate temperature sensor, arranged and with the control unit ( 40 ) and that the control unit ( 40 ) in such a way on the exhaust gas control valve ( 39 ) and / or the gas control valve ( 28 ) is formed acting, that a predetermined exhaust gas temperature or an exhaust gas temperature range is maintained. Method for operating a combined heat and power plant according to one of the preceding claims, characterized in that during a substantially stable operating state of the cogeneration plant, the control unit ( 40 ) by consumers ( 8th ) or for the grid feed ( 9 ) provided electric power monitored and required for generating this electrical power speed of the internal combustion engine ( 1 ) or the generator ( 2 ) keeps constant, by the strength of the recirculated exhaust gas flow through the exhaust gas control valve ( 39 ) regulates, whereby the throttling organ ( 35 ) the adjustment of the appropriate engine speed is supported supportive. A method according to claim 10, characterized in that the controlling on matching to the new power demand motor speed is accelerated by the occurrence of a larger change in demand for electric power, that the control unit ( 40 ) in addition to the exhaust control valve ( 39 ) in the short term, the throttle body ( 35 ) in terms of changing the power demand until the appropriate engine speed is reached. A method according to claim 10 or 11, characterized in that the throttle member ( 35 ) while maintaining the appropriate for the current demand for electrical power or the current heat demand engine speed is always closed so far that caused by the throttling deterioration of the efficiency of the internal combustion engine ( 1 ) does not exceed a predetermined amount. Method according to one of claims 10 to 12, characterized in that the internal combustion engine ( 1 ) runs quasi in lean operation and a required excess air is replaced by an admixture of exhaust gas, preferably an admixture in the amount of 20%. A method according to claim 13, characterized in that a predetermined exhaust gas temperature is adjusted by admixing cooled exhaust gas. Method according to one of claims 10 to 14, characterized in that a required change in the engine speed by driving the inverter ( 3 ), in which the electrical load of the generator ( 2 ) is decreased to increase the engine speed and increased to reduce the engine speed.

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