Claims:WE CLAIM:
1. An optimized segmented and cascaded thermoelectric element (17) for waste heat electric power generation, the thermoelectric element (17) comprising:
an electrical insulator (1);
a first stack (102) having p type legs (14) and n type legs (15) being sequentially laid vertically over the electrical insulator (1);
a copper electrode plate (4) being deployed above the first stack (102); and
a second stack (104) having p type legs (5) and n type legs (3) being horizontally coupled to the copper electrode plate (4).
2. The thermoelectric element (17) as claimed in claim 1, wherein the p type legs (14) includes two segments (7,8) formed of p type thermoelectric materials bismuth telluride and zinc antimonide.
3. The thermoelectric element (17) as claimed in claim 1, wherein the n type legs (15) includes two segments (10,11) formed of n type thermoelectric materials bismuth telluride and lead telluride.
4. The thermoelectric element (17) as claimed in claim 1, wherein number of couples of p type legs (14,5) and n type legs (15,3) in the first stack (102) and the second stack (104) is in the ratio 3:2 such that same electric current flows through both the first stack (102) and the second stack (104).
5. A thermoelectric power generation system (28) comprising:
thermoelectric power generation units (26) connected electrically in series to obtain a significant amount of power output, the thermoelectric power generation units (26) having:
a heat capturing plate (22),
a segmented and cascade thermoelectric module (23) formed using the thermoelectric element (17) as claimed in claim 1, and
a water based liquid cooling system (18); and
a frame (27) to hold the thermoelectric power generation units (26) above a heat source at a desired distance.
, Description:AN OPTIMIZED SEGMENTED AND CASCADED THERMOELECTRIC ELEMENT FOR WASTE HEAT ELECTRIC POWER GENERATION
FIELD OF INVENTION
[001] The present invention relates to thermoelectric generation, more particularly, the present subject matter relates to waste heat thermoelectric power generation.

BACKGROUND OF THE INVENTION

[002] Thermoelectric generator is a solid state material based device that converts temperature difference directly into electrical energy. The conversion efficiency of a thermoelectric generator depends on the temperature gradient across the hot and the cold side and also on the dimensionless figure-of-merit, zT, of the thermoelectric materials used inside them. To achieve high conversion efficiency, both high figure of merit materials and large temperature differences are desired. zT is a function of thermoelectric material properties and can be expressed as:
zT = (a^2 T) / ?k
[003] where ?, a and k are electrical resistivity, seebeck coefficient and thermal conductivity of materials used. T is absolute temperature. However, there is no single thermoelectric material that has high zT value throughout a wide temperature range. So, a single thermoelectric material cannot be used over the complete required temperature range. This leads to the use of different thermoelectric materials in each temperature range. There are two methods by which we can accomplish this - (a) The legs of the thermocouples can be segmented with different thermoelectric materials. (b) By using different thermoelectric materials in different stages such that each stage works over a fixed temperature range. In this way, the thermoelectric materials are working in their most efficient temperature range. Thus, the overall conversion efficiency of the thermoelectric generator module is enhanced.
[004] But only compatible thermoelectric materials can be segmented with each other because the thermoelectric material properties may change greatly from one segment to another. This issue can be solved by cascading the thermoelectric elements which are not compatible in different stages such that materials are thermally in contact but electrically insulated with the other stages. So, both segmenting and cascading thermoelectric materials in a thermoelectric generator module boosts the conversion efficiency.

[005] To keep the material in certain temperature interval, the optimization of the geometry i.e. length and cross sectional area of the materials in the legs of the thermocouples is required. Then, the materials will be operated at high efficiency. Swanson et al. and Harman et al. talks about the optimization of geometry of legs in the segmented and cascaded thermoelectric generator modules respectively. These algorithms are based on heat energy balance at interfaces between two different materials.

[006] The series connection of thermoelectric modules leads to the formation of a thermoelectric generator by which significant amount of power can be generated. The thermoelectric generators convert the waste heat radiated during various steel works like continuous casting of steel, hot rolling, wire drawing etc. into valuable electrical energy efficiently and economically.

SUMMARY OF THE INVENTION

[007] The present disclosure relates to an optimized segmented and cascaded thermoelectric element (17) for waste heat electric power generation, the thermoelectric element (17) including an electrical insulator (1); a first stack (102) having p type legs (14) and n type legs (15) being sequentially laid vertically over the electrical insulator (1); a copper electrode plate (4) being deployed above the first stack (102); and a second stack (104) having p type legs (5) and n type legs (3) being horizontally coupled to the copper electrode plate (4).

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[008] Further objects and advantages of this invention will be more apparent from the ensuing description when read in conjunction with the accompanying drawings of the exemplary embodiments and wherein:
FIG.1: shows a sectional schematic of a segmented and cascaded thermoelectric element;
FIG.2: shows a heat capturing plate for capturing the heat radiation from the steel works;
FIG.3: shows a water based cooling system with inlet and outlet;
FIG.4: shows a segmented and stacked thermoelectric module;
FIG.5: shows a thermoelectric power generation unit;
FIG.6: shows a thermoelectric power generation system for capturing and utilizing the waste heat during various steel works;
FIG.7: shows a flow chart for the conversion of waste heat energy to electrical energy;
FIG.8: shows an example of application of a thermoelectric power generation system in a steel slab continuous casting line for waste heat recovery;
FIG.9: shows another example of application of a thermoelectric power generation system in a tube or pipe forming line for waste heat recovery; and
FIG.10: shows another example of application of a thermoelectric power generation system in a blast furnace runner for waste heat recovery.

[009] The figure(s) 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.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS

[0010] The present invention, now be described more specifically with reference to the following specification.

[0011] 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 and are included within its spirit and scope. 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.

[0012] 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.

[0013] Thermoelectric generators can be used to recover waste heat energy through heat generation process for various steel works. To achieve high thermal to electrical conversion efficiency large temperature difference is desirable. The present invention enhances the conversion efficiency of a thermoelectric generator by segmenting and cascading different material in the n type and p type legs. The materials are selected so that they work in their most efficient temperature range. The segmented and cascaded thermoelectric generator consists different n type and p type materials in the legs joined together accordingly in different stacks. The selection of materials is based on the temperature of interest and the compatibility during segmentation. The thermoelectric materials include manganese silicide, zinc antimonide, bismuth telluride, half-heusler and lead telluride based alloy materials.

[0014] FIG. 1 is a schematic diagram of a segmented and cascaded thermoelectric element 17 in accordance with an embodiment of the present disclosure. In an example, the thermoelectric element 17 is formed of the aforementioned materials with a hot side temperature of 703 degrees K and cold side temperature of 303 degrees K. In FIG. 1, reference sign 1 shows an electrical insulator 1 placed on both sides of the thermoelectric element 17. Reference numerals 14 and 15 are p type and n type legs in a first stack 102 respectively with hot side temperature of 650 degrees K and cold side temperature of 303 degrees K having two segments namely 7 and 8 in p type 14 and 10 and 11 in n type 15.

[0015] Reference numerals 5 and 3 are the p type and n type legs in a second stack 104 respectively with hot side temperature of 703 degree K and cold side temperature of 650 degree K having only one segment. The legs 14, 15 and 5, 3 are electrically connected using copper electrodes 4. The first stack 102 and the second stack 104 are connected electrically in series but thermally in parallel. The geometry of the legs 14, 15 and 5, 3 both in the first stack 102 and the second stack 104 is optimized to keep the interface temperature between the segments and stacks at their desired level discussed above. A temperature profile of the interfaces is also shown in FIG. 1.

[0016] The leg 14 includes two segments 7 and 8. The segment 7 and 8 are formed of p type thermoelectric materials bismuth telluride and zinc antimonide respectively, bismuth telluride at its bottom and zinc antimonide at its top. The leg 15 includes two segments 10 and 11. The segments 10 and 11 are formed of n type thermoelectric materials bismuth telluride and lead telluride, bismuth telluride at its bottom and lead telluride at its top. The legs 5 and 3 are formed of p type material manganese silicide and n type material half-heusler respectively.

[0017] The number of couples of p type and n type in the first stack 102 and the second stack 104 is in the ratio 3:2 such that same electric current flows through both the stacks 102, 104. The load 16 is connected to the outputs 12 and 13 from the first stack 102. The theoretical conversion efficiency of 16.38% can be achieved by the thermoelectric element 17 considering no contact resistance.

[0018] FIG. 2 shows a heat capturing plate with reference sign 22 to capture the heat radiation from various steel works. The thickness and material of the plate 22 is selected to achieve high thermal conductivity, thermal stability and melting point.

[0019] FIG. 3 shows a water based cooling system 18 to maintain the temperature of the cold side to 303 degree K. In FIG. 3 reference sign 19 and 20 are the inlet and outlet for the water. In an example, a large number of fins with reference sign 21 are placed inside to enhance the efficiency of cooling.

[0020] FIG. 4 is a segmented and cascaded thermoelectric module 23 formed using the thermoelectric element 17. The number of thermoelectric elements 17 may vary depending upon the application and the desired power output. The thermoelectric elements 17 are connected electrically in series but thermally in parallel. In FIG. 5 a thermoelectric power generation unit 26 is shown which includes the heat capturing plate 22, a array of segmented and cascade thermoelectric module 23; and the water based liquid cooling system 18.

[0021] A thermoelectric power generation system 28 as shown in FIG. 6 is formed of thermoelectric power generation units 26 connected electrically in series to obtain a significant amount of power output. Reference numeral 27 is a frame to hold the thermoelectric power generation units 26 above the heat source at a desired distance. The distance is optimized to achieve high efficiency along with higher lifetime of the materials used.

[0022] The flow chart for the conversion of waste heat energy to electrical energy using a thermoelectric generator is shown in FIG. 7. Firstly, the waste heat energy is captured by heat capturing plate mostly through heat radiation. Then, the heat is conducted to the segmented and cascaded thermoelectric modules. A part of the heat energy is converted to electrical energy by the thermoelectric modules and the rest of the heat is carried away by the cooling system. The electrical energy produced by the thermoelectric generator can be stored in batteries or can be supplied to various steel processes. Also, at steady state the electrical energy generated by thermoelectric generator can itself power the cooling system to maintain a temperature of around 303 degree K to the colder side of the thermoelectric modules.

[0023] The thermoelectric power generation system 28 can be installed at positions 32 and 34 before or after slab cutting during continuous casting of steel slabs as shown in FIG. 8. In the figure, reference sign 28 is a ladle, 29 is a tundish, 30 is a mold, 31 is a roller, 33 is a slab cutting machine, 35 is heated slab before cutting and 36 is a slab after cutting.

[0024] In FIG. 9, reference sign 37 is a steel sheet, 38 is a reheating furnace, 42 is a pipe or tube formed the steel sheet 37 and 41 is a pipe or tube cutting machine. The thermoelectric power generation system 28 can be installed at positions 39 and 40 before or after the pipe or tube formation.

[0025] FIG. 10 shows the installation position 46 of the thermoelectric power generation system 28 above a blast furnace runner. In the figure, 43 is a blast furnace, 44 is molten iron at the bottom of the blast furnace and 45 is a blast furnace runner through which molten iron flows.

[0026] It is to be noted that the present invention is susceptible to modifications, adaptations and changes by those skilled in the art. Such variant embodiments employing the concepts and features of this invention are intended to be within the scope of the present invention, which is further set forth under the following claims.