Claims:We claim:
1. An apparatus for generation of thermoelectric power in steel plant and automobile applications; the apparatus comprising:
a plurality of thermoelectric generating (TEG) devices (8-10, 72-74) positioned proximate a boiler flue gas ducting system, for series and parallel electrical connections (1), wherein the plurality of TEG devices (8-10, 72-74) are grouped into a number of modules, each module consisting of a partial number of TEGs (11-22, 75-86);
wherein each of the TEG devices (8-10, 72-74) has a hot surface which is positioned in thermal contact with an outer surface of a flue gas duct (4) of a thermal power plant and a cold surface which is positioned proximate to the ambient environment such that the flue gas duct (4) is provided with an inlet (2) and an outlet (3) in the TEG devices (8-10, 72-74);
wherein the number of modules of the plurality of TEG devices (8-10, 72-74) are coupled to a plurality of DC-DC converters (62, 64, 65, 126, 128, 129) via a plurality of electrical terminals (32-34, 99-101), which is coupled to a power converter that is controlled by a maximum power point tracking (MPPT) device;
2. The apparatus as claimed in claim 1, wherein the hot surface and the cold surface of the plurality of TEG devices (8-10, 72-74) are formed of thermal interface materials.
3. The apparatus as claimed in claim 1, wherein the apparatus further comprises a power electronic switch which is connected across output terminals of each DC-DC converter from the plurality of DC-DC converters (62, 64, 65, 126, 128, 129).
4. The apparatus as claimed in claim 3, wherein the output terminal of each of the TEG devices (8-10) are connected to each other in series connections (23-31).

5. The apparatus as claimed in claim 3, wherein the output terminal of the each of plurality of TEG devices (72-74) are connected to each other in parallel connections (87-98).
6. The apparatus as claimed in claim 1, wherein the apparatus further comprises a plurality of maximum power point tracking (MPPT) controllers (61, 63, 66, 125, 127, 130) that extracts the maximum power from the plurality of TEG devices (8-10, 72-74).
7. The apparatus as claimed in claim 6, wherein the voltage (34) and current (40) values of the number of modules of TEG devices (8-10) are sensed by voltage (39) and current sensor (43) is fed to the MPPT controllers (61, 63, 66) in which Perturb and Observe (P&O) MPPT algorithm is stored on it.
8. The apparatus as claimed in claim 1, wherein the apparatus further comprises a plurality of heat sink projections (50, 51, 117, 120) which is positioned between the cold surface of plurality of TEG devices (8-10, 72-74) and the ambient environment.
9. The apparatus as claimed in claim 8, wherein a base plate of heat sink projections (50, 117) is positioned to the flue gas duct (4) using bolt and nuts (54, 118) and inside around nuts (55, 122) are welded to avoid the flue gas leakage.
10. The apparatus as claimed in claim 1, wherein the plurality of TEG devices (8-10, 72-74) generates the electricity at different voltage levels in response to different temperature differentials.
11. The apparatus as claimed in claim 1, wherein the peak power densities of the plurality of TEG devices (8-10, 72-74) are 19.86 W/m2 and 49.53 W/m2 for the operating temperature of 100ºC and 150ºC, respectively at a heat transfer coefficient of 5 W/m2C as a natural convection.
12. The apparatus as claimed in claim 1, wherein the peak power densities of plurality of TEG devices (8-10, 72-74) are 101.94 W/m2 and 257.45 W/m2 for the operating temperature of 100ºC and 150ºC respectively at a heat transfer coefficient of 25 W/m2C as a forced convection.
13. The apparatus as claimed in claim 1, wherein the hot surface of the plurality of TEG devices (8-10, 72-74) is 9.61 for the heat transfer coefficient of 5 W/m2C as a natural convection and operating temperature of 100ºC and 150ºC.
14. The apparatus as claimed in claim 1, wherein the hot surface of the plurality of TEG devices (8-10, 72-74) is 1.67 for the heat transfer coefficient of 25 W/m2C as a forced convection and operating temperature of 100ºC.
15. The apparatus as claimed in claim 1, wherein the hot surface of the plurality of TEG devices (8-10, 72-74) is 2.40 for the heat transfer coefficient of 25 W/m2C as a forced convection and operating temperature of 150ºC.
, Description:AN APPARATUS FOR GENEREATION OF THERMOELECTRIC POWER IN STEEL PLANT AND AUTOMOBILE APPLICATIONS
FIELD OF INVENTION
[001] The present invention relates to an apparatus for generation of thermoelectric power in steel plant and automobile applications. In particular, to the invention relates to electrical array configurations for ensuring the maximum power generation from Thermoelectric Generator (TEG) systems operating under non-uniform temperature gradients across the TEGs. More particularly the invention relates to optimize electrical array configuration, when a plurality of thermoelectric generators (TEGs) is mounted on the flue gas duct of a boiler/process plant where there is a variation in flue gas temperature with respect to time and drop in gas temperature along the gas flow path. Furthermore, the invention relates to extract maximum power from TEG system, when each TEG module or a group of TEG modules are exposed to dynamically varying temperature conditions.
BACKGROUND OF THE INVENTION
[002] Generally, the variable temperature gradients are commonly found in thermoelectric systems used especially in the boiler flue gas ducts of a thermal power plant/process plant for converting waste heat into electricity. Thermoelectric Generator (TEG) is placed on the outside of the duct instead of mineral wool insulation for such energy conversion. Due to the positional advantage, the TEG nearer to the inlet of the flue gas duct will have more difference in temperature across TEG resulting in higher heat transfer and generation of higher power. Also, the process variations lead to variations in flue gas temperature w.r.t time. Such variations result in variations in differential temperature across each TEG or a group of TEGs which lead to variations in the power output from each module of the system. When all TEGs modules are integrated to the power supply under such conditions, there is significant amount of power loss in the TEGs because of the inequality between internal resistance and load resistance. As per maximum power transfer theorem, maximum power is transferred from source to load when load resistance is equal to internal resistance of the source. Therefore, an impedance matching device is necessary to extract the maximum power available from TEG under dynamic temperature varying conditions. Electrical circuit configurations of series and parallel connections involving Maximum Power Point Tracking (MPPT) controller, boost dc-dc converter, etc. taking care of the above variations and ensuring steady peak power generation through a group of TEGs applied for recovering waste heat from flue gas have been proposed in the present invention.
[003] The Prior art US patent application number as 2013/0025644A1, apparatuses, methods and systems are disclosed to use thermoelectric generating (TEG) devices to generate electricity from heat generated by a power cable. An apparatus includes multiple thermoelectric generating (TEG) devices. Each of the TEG devices has a first surface configured to be positioned in thermal communication with an outer surface of the power cable and a second surface configured to be positioned proximate to an ambient environment around the power cable. The apparatus also includes a set of terminals electrically coupled to the TEG devices. When a temperature differential exists between the first surface and the second surface, the TEG devices convert heat into electricity presented at the set of terminals.
[004] A waste heat recovery from Power feeders in power distribution systems may generate significant heat due to Ohmic heating which is very low compared to this application.
[005] The above mentioned prior art is not related to Electrical circuit configurations of series and parallel connections involving Maximum Power Point Tracking (MPPT) controller, boost DC-DC converter, etc. taking care of the above variations and ensuring steady peak power generation through a group of TEGs applied for recovering waste heat from flue gas.
[006] The information disclosed in this background of the disclosure section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
OBJECTS OF THE INVENTION
[007] The principal object of the present invention is to provide an arrangement of TEG electrical terminals in array configurations like series, parallel and combinations of them applicable for recovering waste heat from flue gas.
[008] Another objective of the present invention is to present a TEG electrical array configuration, which gives the peak power output under varying temperature gradients.
[009] Yet another objective of the present invention is to specify the components involved in the circuits for distributed power in the (TEGs).
[0010] These and other objects and advantages of the present subject matter will be apparent to a person skilled in the art after consideration of the following detailed description taken into consideration with accompanying drawings in which preferred embodiments of the present subject matter are illustrated.
SUMMARY OF THE INVENTION
[0011] One or more drawbacks of conventional coal beneficiation process, and additional advantages are provided through the process as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be a part of the claimed disclosure.
[0012] The present subject matter relates to an apparatus for generation of thermoelectric power in steel plant and automobile applications. The apparatus has a plurality of thermoelectric generating (TEG) devices positioned proximate a boiler flue gas ducting system for series and parallel electrical connections, wherein the plurality of TEGs is grouped into a number of modules each consisting of a partial number of TEGs. Each of the TEG devices has a hot surface which is positioned in thermal contact with an outer surface of a flue gas duct of a thermal power plant and a cold surface which is positioned proximate to the ambient environment. The number of modules of TEG devices is coupled to a plurality of DC-DC converters via a plurality of electrical terminals, which is coupled to a power converter that is controlled by a maximum power point tracking (MPPT) device.
[0013] In an embodiment of the present subject matter relates to the apparatus further comprises a power electronic switch which is connected across output terminal of each DC-DC converter from the plurality of DC-DC converters, wherein the output terminals of each of the TEG devices are connected to each other in series and parallel connections, respectively.
[0014] In accordance with the embodiment of the present subject matter relates to the apparatus further comprises a plurality of maximum power point tracking (MPPT) controllers that extracts the maximum power from the plurality of TEG devices, wherein the voltage and current values of the number of modules of TEG devices are sensed by voltage and current sensor is fed to MPPT controllers in which Perturb and Observe (P&O) MPPT algorithm is stored on it.
[0015] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.
[0016] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods or structure in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
[0018] FIG. 1 illustrates series electrical array configuration of plurality of TEG devices, in accordance with a present subject matter;
[0019] FIG. 2 illustrates parallel electrical array configuration of plurality of TEG devices, in accordance with a present subject matter;
[0020] FIG. 3 illustrates cross section view for series electrical array configuration of individual TEG device for each of TEG devices on flue gas ducting system, in accordance with a present subject matter;
[0021] FIG. 4 illustrates cross section view for parallel electrical array configuration of individual TEG device for each of TEG devices on flue gas ducting system, in accordance with a present subject matter;
[0022] FIG. 5 illustrates elevation view of a structure having a TEG placing on flue gas ducting system in a boiler, in accordance with a present subject matter;
[0023] FIG. 6 illustrates plan view of a structure having a TEG placing on flue gas ducting system in a boiler, in accordance with a present subject matter;
[0024] FIG. 7 illustrates graph of the power-voltage (P-V) characteristics curve of a TEG device with different internal resistance under different temperature differential across TEG devices changing with respect to boiler load, in accordance with a present subject matter; and
[0025] FIG. 8 illustrates graph of comparisons for electrical power producing characteristics of different electrical array configurations with equal number of individual TEG devices in each TEG devices under constant and different small temperature differential across TEG devices, in accordance with a present subject matter.
[0026] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
[0027] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.
[0028] The terms “comprises”, “comprising”, or any other variations thereof used in the disclosure, are intended to cover a non-exclusive inclusion, such that a device, system, assembly that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such system, or assembly, or device. In other words, one or more elements in a system or device proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or device.
[0029] It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present subject matter. It should also be appreciated by those skilled in the art that by devising various arrangements that, although not explicitly described or shown herein, embody the principles of the present subject matter. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions. The novel features which are believed to be characteristic of the present subject matter, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures.
[0030] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
[0031] FIG. 1 and Fig. 2 illustrate series and parallel electrical array configurations of plurality of TEG devices, in accordance with a present subject matter. The present subject matter relates to an apparatus for generation of thermoelectric power in steel plant and automobile applications. The apparatus has a plurality of thermoelectric generating (TEG) devices 8-10, 72-74 that is positioned proximate a steam generator flue gas ducting system for series and parallel electrical connections 1, such that the plurality of TEGs devices 8-10, 72-74 is grouped into a number of modules each consisting of a partial number of TEGs 11-22. Each of the TEG devices 8-10, 72-74 includes multiple positive-type doped to negative type doped (P-N) thermoelectric pellet pairs. The multiple P-N thermoelectric pellet pairs are housed within a ceramic plate to form one of the TEG devices (not shown) and to insulate electrically.
[0032] Recovering the waste heat for TEG application ranges from fossil fuel fired boilers as derived from exhaust flue gases for Indian coal fired boilers. When the plurality of TEG devices 8-10 is mounted on the flue gas duct 4 of a thermal power plant, there is a drop in gas temperature from an inlet 2 to an outlet 3 of the flue gas duct 4, such as a first module of the plurality of TEG devices 8 for flue gas duct 4 from the duct inlet 2, a second module of the plurality of TEG devices 9 adjacent to the first module of the plurality of TEG devices 8 and so on nth module of the plurality of TEG devices 10 near to a chimney inlet for series connection, as shown in Fig. 1. Similarly, when the plurality of TEG devices 72-74 is mounted on the flue gas duct 4 of thermal power plant, there is a drop in gas temperature from the inlet 2 to outlet 3 of the flue gas duct 4, such as a first module of the plurality of TEG devices 72 for the flue gas duct 4 from the duct inlet 2, a second module of the plurality of TEG devices 73 adjacent to the first module of the plurality of TEG devices 72 and so on nth module of the plurality of TEG devices 74 near to the chimney inlet for parallel connection, as shown in Fig. 2. This drop in the gas temperature will lead to difference in operating temperatures for each TEG or TEG devices depending on its location in the flue gas duct 4 along the gas flow path. The temperature and heat transfer coefficient of the ambient may be nearly constant throughout the outside of the flue gas duct 4 along the gas flow path, and may be different in temperature each of the flue gas path. The first module of the plurality of TEG devices 8, including a number of TEGs 11-14, may be associated with the first flue gas path, a second module of the plurality of TEG devices 9, including a number of TEGs 15-18, may be associated with the flue gas path and a nth module of the plurality of TEG devices 10, including a number of TEGs 19-22, may be associated with the flue gas path for series electrical array configuration for each of the TEG devices 8-10 with another, as shown in Fig. 1.
[0033] Accordingly, the first module of the plurality of TEG devices 72, including a number of TEGs 75-78, may be associated with the first flue gas path, the second module of the plurality of TEG devices 73, including a number of TEGs 79-82, may be associated with the flue gas path, and a nth module of the plurality of TEG devices 74, including a number of TEGs 83-86, may be associated with the flue gas path for parallel electrical array configuration for each of the plurality of TEG devices 72-74 with another, as shown in Fig. 2. Each of the module of the TEG devices 8-10, 72-74 generates the electricity based on the temperature differential between the flue gas and the ambient environment with which the plurality of TEG devices 8-10, 72-74 is associated. Since the temperature differential experienced by each of the TEG devices 8-10, 72-74 may be different, characteristics of the electricity generated by each of the TEG devices 8-10, 72-74 may be different. For example, the plurality of TEG device 8-10, 72-74 generates the electricity at different voltage levels in response to different temperature differentials.
[0034] In an embodiment shown in Fig. 1, the modules of the TEG devices 8-10 are comprised the combinations of the number of TEGs 11-22. The length of each module of the TEG devices 8-10 may be arrived, when the flue gas temperature drop is at 1°C between the inlet 2 and the outlet 3 of each module of the TEG devices 8-10 to avoid the temperature mismatch effect on the TEG devices 8-10 in a series array connection. For example, the flue gas temperature difference between the first module of TEG device inlet 2, which may be located at the duct inlet and it is the maximum flue gas temperature and the outlet 5 of flue gas temperature for the first module of the TEG devices 8 may be at 1°C. The second module of the TEG devices 9, when the flue gas temperature difference between the second module inlet 5 and the outlet 6 of flue gas temperature may be at 1°C. The nth module (e.g. last module) of the TEG devices 10, when the flue gas temperature difference between the nth module inlet 6 and the outlet 7 of flue gas temperature may be at 1°C. Based on the available length of the individual TEG, the number of TEGs 11-22 are found the ratio between the length of each modules of the TEG devices 8-10 and the length of the individual TEG. The first module of the TEG devices 8 comprises the first 11, second 12, third 13 and last 14 of the TEGs, the second module of the TEG devices 9 comprises the first 15, second 16, third 17 and last 18 of the TEGs, and the nth module of the TEG devices 10 comprises the first 19, second 20, third 21 and last 22 of the TEGs.
[0035] Similarly, referring Fig. 2, the number of modules of the TEG devices 72-74 are comprised the combinations of the number of the TEGs 75-86. The length of each module of the TEG devices 72-74 is to be arrived, when the flue gas temperature drop is at 1°C between inlet 2 and outlet 3 of each module of the TEG devices 72-74 to avoid the temperature mismatch effect on the TEG devices 72-74 in a parallel array connection. For example, the flue gas temperature difference between the first module of TEG device inlet 2, which may be located in an air heater outlet 3 and it is the maximum flue gas temperature and the outlet 69 of flue gas temperature of the first module of the TEG devices 72 is at 1°C. The second module of the TEG devices 73, when the flue gas temperature difference between the second module inlet 69 and the outlet 70 of flue gas temperature is at 1°C, Similar to the nth module (e.g. last module) of the TEG devices 74, when the flue gas temperature difference between the nth module inlet 70 and the outlet 71 of flue gas temperature is at 1°C. Based on the available length of the individual TEGs, wherein the number of TEGs 75-86 are found the ratio between the length of each modules of the TEG devices 72-74 and the length of the individual TEGs. The first module of the TEG devices 72 comprises the first 75, second 76, third 77 and last 78 of the TEG s, and the second module of the TEG devices 73 comprises the first 79, second 80, third 81 and last 82 of the TEGs. Similarly, the nth module of the TEG devices 74 comprises the first 83, second 84, third 85 and last 86 the of TEGs.
[0036] Referring Fig. 3 and Fig. 4 illustrate cross-section view of a portion of the system of Fig. 1 and Fig. 2 for series and parallel configuration, respectively. Each of the TEG devices 8-10, 72-74 includes one or more positive-type doped to negative-type doped (P-N) thermoelectric pellet pairs that are configured thermally parallel and electrically series (not shown) to convert heat into electricity. Each of the TEG devices 8-10, 72-74 has a hot surface configured to be positioned in thermal contact with an outer surface of the flue gas duct 4 and a cold surface configured to be positioned proximate to the ambient environment. The temperature differential exists between the flue gas and the ambient environment. The TEG devices 8-10, 72-74 are driven by the temperature differential to convert the heat into the electricity. The TEG devices 8-10, 72-74 are directly positioned on a flat flue gas ducting system and flat TEG device may be used in this application.
[0037] In particular embodiments, the hot surfaces of the TEG devices 8-10, 72-74 and the cold surface of the TEG devices 8-10, 72-74 are formed of thermal interface materials to facilitate heat transfer. A plurality of heat sink projections 50, 51, 117, 120 improves the heat transfer between the cold surfaces of the TEG devices 8-10, 72-74 and the ambient environment. For example, the increased effective surface area may enable the outer surfaces of the TEG devices 8-10, 72-74 to achieve a lower temperature, increasing the temperature differential across the TEG devices 8-10, 72-74. Once TEG devices 8-10, 72-74 installed around a portion of the flue gas duct 4, the base plate of heat sink projections 50, 117 is positioned to the flue gas duct 4 using bolt and nuts 54, 118 and inside around nuts 55, 122 are welded to avoid the flue gas leakage. Thus, the TEG devices 8-10, 72-74 are installed on various portions of the flue gas duct 4, such as portions of the flue gas duct 4 that extend through the flue gas path.
[0038] The number of TEGs 11-22 of each of the TEG devices 8-10 are electrically connected in series in each individual TEG 52 as shown in Fig. 3. Similarly, the number of TEGs 75-86 of each of the TEG devices 72-74 may also be in parallel in each module 121 of the TEG devices 72-74 as shown in Fig. 4. The output terminal of each set of the TEGs 56, 57 for series connections, and the output terminal of each of the TEGs 123, 124 for parallel connections is connected to each other as discussed in detail below. The electrical terminals (32-34, 99-101) of each module of the TEG devices 8-10, 72-74 are coupled to a power converter that is controlled by a plurality of maximum power point (MPP) tracking devices 61, 63, 66, 125, 127, 130 as described with reference to Fig. 1 and Fig. 2 for series and parallel connections, respectively. For example, the plurality of MPP tracking devices 61, 63, 66, 125, 127, 130 is electrically coupled to the TEG array to extract the maximum power. The MPP tracking devices 61, 63, 66, 125, 127, 130 control a plurality of DC-DC converters 62, 64, 65, 126, 128, 129 to cause the TEG devices 8-10, 72-74 to generate the voltage and current presented at the electrical terminals (32-34, 99-101), near a maximum power point of the TEG devices 8-10, 72-74 at the temperature differential. The DC-DC converters 62, 64, 65, 126, 128, 129 are configured to receive the voltage and current presented at the electrical terminals (32-34, 99-101) and to convert the voltage and the current to an output voltage and the output current presented at a converter output. For example, the output of DC-DC converters 62, 64, 65, 126, 128, 129 are at a three-phase alternate current (AC) grid voltage. As described with reference to Fig. 1 and Fig. 2, there may be separate the TEG devices 8-10, 72-74 deployed around the flue gas duct 4 as the flue gas temperature drop along the flue gas path. The maximum power point (MPP) tracking devices 61, 63, 66, 125, 127, 130 independently control the power converters coupled to the separate module of TEG devices 8-10, 72-74 to enable each of the modules of TEG devices 8-10, 72-74 to operate at or near the MPP voltage.
[0039] In addition, conversion of heat to electricity by the TEG devices 8-10, 72-74 reduce a thermal pollution, may enhance the Electro static precipitator collection efficiency due to reducing the flue gas temperature and may reduce emission and carbon footprint through increasing plant overall efficiency.
[0040] Referring Fig. 1, illustrates the number of TEGs 11-14 that are electrically interconnected as in series array configuration 23-25 to one another and to the first electrical terminal 32 within the first module of TEG devices 8. The first module of TEG devices 8 is coupled to the first DC-DC convertor 62 via the first electrical terminal 32. The first DC-DC convertor 62 receives the power from the TEGs 11-14 of the first module of TEG system 8 via the first terminals 32. The electrical series configuration is followed for all other modules of TEG devices 8-10 (second module to nth module). The individual TEG device 53 along each section of each of TEGs 11-22 is electrically connected together in series to form a chain 52 as shown in Fig. 3. The output terminal of each of the TEGs 11-22 is connected together in series to form a chain 23-31 as shown in Fig. 1. Then, this connection may be called electrical series array configuration.
[0041] Each module of TEG devices 8-10, 72-74 is connected to the DC-DC converters 62, 64, 65, 126, 128, 129 and independently controlled by using separate MPPT controllers 61, 63, 66, 125, 127, 130. The DC-DC converters 62, 64, 65, 126, 128, 129 are cascaded together and is fed to a three-phase inverter which may convert the DC voltage into the AC voltage. The AC output of the inverter is stepped up using three-phase step up transformer and is injected to three-phase AC grid. A power electronic switch is connected across the output terminals of each DC-DC converters 62, 64, 65, 126, 128, 129 to ensure the continuity of supply during any fault in TEG arrays. Every set of the TEG devices 8-10, 72-74 is having equal number of individual TEG in each module of TEG devices 8-10, 72-74, but may or may not be same quantity between two modules of the TEG devices 8-10, 72-74. For example, in Fig. 1, if the first TEG 11 is positioned by “x” number of individual TEGs 53, then the each second 12, third 13 and last 14 of TEGs should be the same quantity (“x” number) of individual TEGs 53 as mentioned in the first TEG 11 in the first module of the TEG devices 8. When the first TEG 15 is positioned by “y” number of individual TEGs 53, then the second 16, third 17 and last 18 of TEGs should be the same quantity (“y” number) of individual TEGs 53 as mentioned in first TEG 15 in the second module of the TEG devices 9. Similarly, when the first TEG 19 is positioned by “z” number of individual TEGs 53, then the each second 20, third 21 and last 22 of TEGs should be the same quantity (“z” number) of individual TEGs 53 as mentioned in first TEG 19 in the nth module of the TEG devices 8-10.
[0042] In Fig. 2, illustrates the TEG devices 72-74 that are electrically interconnected as in parallel array configuration 87-98 to one another and to the first electrical terminal 99 within the first module of TEG devices 72. The first module of TEG devices 72 is coupled to the first DC-DC convertor 126 via the first electrical terminal 99. The first DC-DC convertor 126 receives the electricity from the TEGs 75-86 of the first module of TEG devices 72 via the first electrical terminal 99 and may process (e.g., invertor, transform or otherwise convert) the electricity before supplying the electricity to a three-phase alternate current grid. The electrical parallel configuration is followed for all other modules of TEG devices 72-74 (second module to nth module). The TEG devices 72-74 along each section of the flue gas duct 4 are electrically connected in parallel 121 as shown in Fig. 4. The output terminal of each of the TEG devices 72-74 is connected to each other in parallel connection 87-98 as shown in Fig. 2. Then, this connection is called the electrical parallel array configuration. Each of the TEG devices 72-74 is having equal number of individual TEGs 119 in each module of the TEG devices 72-74, but may or may not be the same quantity between two modules of the TEGs 75-86. For example, in Fig. 2, if the first TEG 75 is positioned by “x” number of individual TEGs 119, then the each second 76, third 77 and last 78 of TEGs should be same quantity (“x” number) of individual TEGs 119 as mentioned in the first TEG 75 in the first module of the TEG devices 72. When the first TEG 79 is positioned by “y” number of individual TEGs 119, then the each second 80, third 81 and last 82 of TEGs should be the same quantity (“y” number) of individual TEGs 119 as mentioned in the first TEG 79 in the second module of the TEG devices 73. If the first TEG 83 is positioned by “z” number of individual TEGs 119, then the each second 84, third 85 and last 86 of the TEGs should be the same quantity (“z” number) of individual TEGs 119 as mentioned in the first TEG 83 in the nth module of the TEG devices 74.
[0043] The TEGs 75-86 along each section of the flue gas duct 4 are electrically connected in parallel 121 as shown in Fig. 4. The output terminal of each of the TEG devices 8-10 is to be connected together in series to form a chain 23-31 as shown in Fig. 1. Then, this connection may be called electrical series array configuration. Each of the TEG devices 8-10 is having equal number of individual TEGs in each module of TEG devices 8-10, but may or may not be the same quantity between two modules of the TEGs 11-22. For example, in Fig. 1, if the first TEG 11 is positioned by “x” number of individual TEGs 53, then the each second 12, third 13 and last 14 of the TEGs should be the same quantity (“x” number) of individual TEGs 53 as mentioned in the first TEG 11 in the first module of the TEG devices 8. When the first TEG 15 is positioned by “y” number of individual TEGs 53, then the second 16, third 17 and last 18 of TEGs should be the same quantity (“y” number) of individual TEGs 53 as mentioned in the first TEG 15 in the second module of the TEG devices 9. Similarly, when the first TEG 19 is positioned by “z” number of individual TEGs 53, then the each second 20, third 21 and last 22 of TEGs should be the same quantity (“z” number) of individual TEGs 53 as mentioned in the first TEG 19 in the nth module of the TEG devices 10.
[0044] In case of boiler flue gas duct applications, the temperature of the flue gas is not constant and it changes with respect to boiler load, which changes based on demand. In such cases, there is significant amount of power loss in the TEG devices 8-10, 72-74 because of the inequality between internal resistance and load resistance. By Maximum power transfer theorem, maximum power is transferred from source to load when load resistance is equal to internal resistance of the source. Therefore, an impedance matching device is necessary to extract the maximum power available from the TEG devices 8-10, 72-74 under dynamic temperature varying conditions. This can be achieved by utilizing the DC-DC converters 62, 64, 65, 126, 128, 129 whose duty ratio is varied by using the MPPT controllers 61, 63, 66, 125, 127, 130. The DC-DC converters 62, 64, 65, 126, 128, 129 are used on the electrical load side and a TEG array is used to power this converter. The MPPT controllers 61, 63, 66, 125, 127, 130 push the operating point of the TEG devices 8-10, 72-74 to Maximum Power Point (MPP) where the load resistance is equal to internal resistance of the TEG devices 8-10, 72-74.
[0045] In series electric array configuration between each module of the TEG devices 8-10 as shown in Fig. 1, the first maximum power point tracking (MPPT) controller 61 extracts the maximum power from the TEGs 11-14 of the first module of TEG devices 8 that is connected to the first DC-DC converter 62. The voltage 35 and the current 36 values of the first module of TEG devices 8 is sensed by the voltage 32 and the current sensor 41 is fed to the first MPPT controller 61 in which the Perturb and Observe (P&O) MPPT algorithm is stored on it. The first MPPT controller 61 pushes the operating point of the first module of TEG devices 8 to the MPP by varying the duty ratio of the first DC-DC converter 62 based on perturb and observe process. Thus, the internal resistance of the first module of TEG devices 8 becomes equal to the load resistance and the devices operates at a voltage near to the MPP voltage. The TEGs 15-18 in the second module of TEG devices 9 is connected to the second DC-DC converter 64, which is controlled by the second MPPT controller 63. The voltage 37 and the current 38 values of the second module of TEGs 15-18 is sensed by the voltage 33 and the current sensor 42 is fed to the second MPPT controller 63 and it finds the optimal duty ratio of the second DC-DC converter 64 based on the perturb and observe process. Hence the operating point of the second module of TEG devices 9 moves to the MPP, wherein the MPP voltage is equal to the half of the open circuit voltage corresponding to a particular temperature differential along the flue gas path. Similarly, the nth dc-dc converter 65 is connected to the TEGs 19-22 of nth module of TEG devices 10, which is controlled by the nth MPPT controller 66. The voltage 34 and the current sensor 43 connected to the terminals of nth module of TEG devices 10 and senses the voltage 39 and the current 40 values, which are fed to the nth MPPT controller 66. Based on the perturb and observe algorithm stored in the memory of nth MPPT controller 66, it finds the duty ratio corresponding to MPP. Thus, the operating point of the nth module of TEG devices 10 moves near to the MPP point and maximum power is extracted from the devices. The MPP tracking devices control the operating voltages of the different module of TEGs 11-22 independently. The first 62, second 64 and nth 65 of the DC-DC converters are cascaded together and the output terminal is fed to a three-phase inverter which convert the DC power into the AC power such that the power is injected into a three-AC phase grid through a transformer.
[0046] In parallel electric array configuration between each module of TEG devices 72-74 as shown in Fig. 2, the first maximum power point tracking (MPPT) controller 125 extracts the maximum power from the TEGs 75-78 of the first module of TEG devices 72 that is connected to the first DC-DC converter 126. The voltage 102 and the current 103 values of the first module of TEG devices 72 is sensed by the voltage and current sensor 108 is fed to the first MPPT controller 125 in which the Perturb and Observe (P&O) MPPT algorithm is stored on it. The first MPPT controller 125 pushes the operating point of the first module of TEG devices 72 to the MPP by varying the duty ratio of the first DC-DC converter 126 based on perturb and observe process. Thus, the internal resistance of the first module of TEG devices 72 becomes equal to the load resistance and the devices operates at the voltage near to the MPP voltage. The TEGs 79-82 in the second module of TEG devices 73 is connected to the second DC-DC converter 128, which is controlled by a second MPPT controller 127. The voltage 104 and current 105 values of the second module of TEGs 79-82 is sensed by the voltage 100 and current sensor 109 is fed to the second MPPT controller 127 and it finds the optimal duty ratio of the second DC-DC converter 128 based on the perturb and observe process. Hence the operating point of the second module of TEG devices 73 moves to the MPP wherein the MPP voltage is equal to the half of the open circuit voltage corresponding to a particular temperature differential along the flue gas path. Similarly, the nth DC-DC converter 129 is connected to the TEGs 83-86 of nth module of TEG devices 74, which is controlled by nth MPPT controller 130. The voltage 101 and current sensor 110 connected to the terminals of nth module of TEG devices 74 senses the voltage 106 and the current 107 values, which are fed to the nth MPPT controller 130. Based on the perturb and observe algorithm is stored in the memory of nth MPPT controller 130, it finds the duty ratio corresponding to MPP. Thus, the operating point of the nth module of TEG devices 74 moves near to the MPP point and maximum power may be extracted from the devices. The MPP tracking devices may control the operating voltages of the different module of TEGs 75-86 independently. The first 126, second 128 and nth 129 of DC-DC converters are parallel connected together and the output terminal is fed to a three-phase inverter which converts the DC power into the AC power and the power is injected into a three-AC phase grid through a transformer.
[0047] Fig. 5 and Fig. 6 illustrate elevational and plan views for a structure of a flue gas ducting system extending through a different flue gas path 135, 137, 139 and included Electro Static Precipitator 136. For the purposes of description and as a particular non-limiting example, the structures are illustrated in Fig. 5 and Fig. 6 as a boiler; however, the structures include another type of flue gas path applications. For example, the structures include a steel plant (e.g., Corex gas plant, reheat furnace), an automobile, a train, and heat recovery steam generator flue gas or heat treatment furnaces which is generating flue gas, a food processing industries, a rice mills, a paper mill and a sugar plants.
[0048] Referring Fig. 5 and Fig 6, illustrate the flue gas which is flowing from an air heater 134 to a chimney 140 and in path of flue gas ducts 135, 137, 139, Electro static precipitator (ESP) 136, induced draft fan 138, etc. When the TEG devices 8-10, 72-74 are placed on the duct outer wall and side and top of Electro static precipitator (ESP) outer wall, the TEG devices 8-10, 72-74 nearer to the inlet (Air Heater outlet) of the flue gas ducts 135, 137, 139 will tend to absorb the heat resulting in generation of power leading to the reduction in the flue gas temperature along its flow path, such that the operating heat source temperature to the TEG devices 8-10, 72-74 will have an important part in exploring the amount of heat absorbed by the TEG devices 8-10, 72-74 and its contribution is further improved by introducing operating heat source temperature difference and electrical array configuration of the TEG devices 8-10, 72-74 playing a critical role in effective absorption of heat from flue gas. And of course, heat transfer coefficient between heat sink and ambient and ambient temperature may constant.
[0049] Fig. 7 shows the power-voltage (P-V) curve for the temperature differential across the TEG ?T1 151 and ?T2 152 and current –voltage (I-V) curve for the temperature differential across the TEG ?T1 149 and ?T2 150 and one load resistance line 163 in the I-V plane where ?T1 is the first temperature gradient across the TEG devices 149 and ?T2 is the second temperature gradient across TEG devices 150 due to the inconsistent temperature of the flue gas with respect to boiler load, which changes based on demand. The graphs are plotted by taking voltage 146 on the horizontal axis and power 145 and current 144 on the vertical axis. From Fig. 7 it can be seen that, the maximum power available from the TEG devices 8-10, 72-74 without MPPT corresponding to ?T1 and ?T2 temperature gradients are only P1 155, and P2 156 respectively corresponding to the load resistance line against the maximum possible powers of Pm1 153, and Pm2 154 respectively. The voltage corresponding to these temperature gradients are V1 159 and V2 160. The MPP voltage of ?T1 157 and ?T2 164 temperature gradients is half of the open circuit voltage at ?T1 161 and ?T2 162 temperature gradients respectively and MPP current at ?T1 and ?T2 temperature gradients is half of the short circuit current at ?T1 147 and ?T2 148 temperature gradients respectively. For the temperature gradient ?T1, the power transferred to the load is only P1 155 watts instead of Pm1 153 watts. Thus, there is Pm1- P1 watts power loss because of inequality between internal resistance and load resistance. Similar loss in power of Pm2- P2 watts is seen corresponding to ?T2 temperature gradients. This power loss is undesirable in case of TEG applications where the temperature gradient across individual TEG or TEG devices 8-10, 72-74 connected together is dynamically varying. The mismatching between the MPP and operating point corresponds to load line is obvious because the two operating points are not corresponding to each other. The matching of the two operating points occurs when the load resistance becomes equal to the internal resistance of the TEG array. Therefore, an impedance matching device is required to shift the load line corresponds to the MPP. Thus by transferring the load resistance from the load side of the converter to the TEG source side with a varying duty ratio D of the converter, the matching can be occurred.
[0050] In accordance with the embodiment of the present subject matter relates to the peak power densities of the TEG devices 8-10, 72-74 are at 19.86 W/m2 and 49.53 W/m2 for the operating temperature of 100ºC and 150ºC, respectively at the heat transfer coefficient of 5 W/m2C as a natural convection. Similarly, the peak power densities of the TEG devices 8-10, 72-74 are at 101.94 W/m2 and 257.45 W/m2 for the operating temperature of 100ºC and 150ºC respectively at a heat transfer coefficient of 25 W/m2C as a forced convection.
[0051] Accordingly, the hot surface of the TEG devices 8-10, 72-74 is at 9.61 for the heat transfer coefficient of 5 W/m2C as a natural convection and operating temperature of 100ºC and 150ºC, and the hot surface of the TEG devices 8-10, 72-74 is at 1.67 for the heat transfer coefficient of 25 W/m2C as a forced convection and operating temperature of 100ºC. Similar to, the hot surface of the TEG devices 8-10, 72-74 is at 2.40 for the heat transfer coefficient of 25 W/m2C as a forced convection and operating temperature of 150ºC.
[0052] Fig. 8 shows the (P-V) curves of different TEG electrical array configurations like series 165, series–parallel 166 and parallel 167 under uniform temperature gradient across TEG devices 8-10, 72-74 and (I-V) curves of different TEG electrical array configurations like series 168, series-parallel 169 and parallel 170 under uniform temperature gradient across TEG devices 8-10, 72-74. In addition, Fig. 8 shows (P-V) curves of different TEG electrical array configurations like series 172, series-parallel 173 and parallel 174 under non-uniform temperature gradient across TEG devices 8-10, 72-74 and (I-V) curves of different TEG electrical array configurations like series 175, series–parallel 176 and parallel 177 under uniform temperature gradient across the TEG devices 8-10, 72-74. It is clear that, the open circuit voltage and the internal resistance of the each TEG devices 8-10, 72-74 are remains equal due to uniform temperature of flue gas ?T1= ?T2= ?Tn. Therefore, the electrical characteristics of all the devices becomes identical and equal maximum power 171 can be obtained from series, parallel and series-parallel array configuration. But in practice this is not possible due to the non-uniform temperature differential across the modules. In non-uniform case, the TEGs 11-14 in the first module of TEG devices 8 are exposed to the temperature differential across individual TEG ?T1, the TEGs 15-18 in the second module of TEG devices 9 are exposed to the temperature differential across individual TEG ?T1 and the TEGs 19-22 in the nth module of TEG devices 10 are exposed to a temperature differential across individual TEG ?Tn for all electrical array configurations. Fig. 8 shows that, the series and series-parallel TEG array configuration gives equal power when the modules are connected according to Fig. 1 and Fig. 3 for series connection, Fig. 1 and Fig. 4 for series parallel connection and Fig. 2 and Fig. 4 for parallel connection. The each individual TEG in each module of TEG devices 8-10 is connected in series, as per Fig. 3 and each of the TEGs 11-22 in corresponding modules of TEG devices 8-10 is connected in series as per Fig. 1. The each TEGs 75-86 in each module of TEG devices 72-74 is connected in parallel, as per Fig. 4, and each TEGs 11-22 in corresponding modules of the TEG devices 8-10 is connected in series as per Fig. 1. The each individual TEG in each module of TEG devices 72-74 is connected in parallel, as per Fig. 4 and each TEG 75-86 in corresponding modules of TEG devices 72-74 is connected in parallel, as per Fig. 2. The number of TEGs 11-22, 75-88 in each TEG devices 8-10, 72-74 corresponding to module of TEG devices 8-10, 72-74 are equal for all array configurations. Hence, each module has identical electrical characteristics and the impact of non-uniform temperature differential distribution across the TEG devices 8-10, 72-74 along the flue gas path may be reduced. Therefore, the maximum power 178 obtained in series TEG array configuration is same as that obtained in series-parallel configuration. In case of series configuration, a single faulty device may affect the continuity of power supply from each module of TEG devices 8-10 but in series-parallel configuration even though one device becomes fault it may not affect the continuity of power supply and only that faulted TEG power may not receive in the load side. In parallel configuration, all the modules are connected in parallel and the effect of temperature mismatch is more. Therefore, the maximum power available in parallel configuration 179 is lesser when compared to series and series-parallel TEG array configuration.
[0053] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”
[0054] It will be further appreciated that functions or structures of a plurality of components or steps may be combined into a single component or step, or the functions or structures of one-step or component may be split among plural steps or components. The present invention contemplates all of these combinations. Unless stated otherwise, dimensions and geometries of the various structures depicted herein are not intended to be restrictive of the invention, and other dimensions or geometries are possible. In addition, while a feature of the present invention may have been described in the context of only one of the illustrated embodiments, such feature may be combined with one or more other features of other embodiments, for any given application. It will also be appreciated from the above that the fabrication of the unique structures herein and the operation thereof also constitute methods in accordance with the present invention. The present invention also encompasses intermediate and end products resulting from the practice of the methods herein. The use of “comprising” or “including” also contemplates embodiments that “consist essentially of” or “consist of” the recited feature.
[0055] Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/component of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter