DESIGN AND CALCULATION OF A THERMOELECTRIC GENERATOR FOR SHIP POWER PLANTS
Authors:
1.
Astrakhan State Technical University
2.
University of Transport Technology
Hanoi, Vietnam
Hanoi, Vietnam
3.
Astrakhan State Technical University
(Candidate of Technical Sciences, Assistant Professor; Professor of the Department of Shipbuilding and Energy Complexes of Marine Engineering)
Russian Federation
Russian Federation
Type:
Article
Pages:
from 62
to 71
Status:
Published
Received:
20.11.2017
Accepted:
25.11.2017
Published:
25.11.2017
Subject area:
UDK 621.431.74.068.4:662.76
GRNTI 45.01 Общие вопросы электротехники
GRNTI 55.42 Двигателестроение
GRNTI 55.45 Судостроение
GRNTI 73.34 Водный транспорт
GRNTI 44.31 Теплоэнергетика. Теплотехника
GRNTI 45.01 Общие вопросы электротехники
GRNTI 55.42 Двигателестроение
GRNTI 55.45 Судостроение
GRNTI 73.34 Водный транспорт
GRNTI 44.31 Теплоэнергетика. Теплотехника
Language:
English
Keywords:
thermoelectric generator, RSD 49 project ship, Wartsila 6L20 diesel engine, heat utilization, exhaust gases, intensification of heat exchange
Abstract (English):
The article presents the design of a thermoelectric generator (TEG) for utilizing heat energy of exhaust gases of ship diesel engines. There have been chosen a TEG basic design and a technique for its efficiency raising. Geometric, heat and electric parameters of TEG have been calculated using RSD 49 ship project. Calculation of heat and electric parameters of TEG with intensive heat exchange on the surface of a hot node was made using sloping plates. The relation between TEG position (before and after exhaust boiler) and a Wartsila 6L20 main engine exhaust system has been determined. According to the analysis result, in case of TEG position after exhaust boiler and 100% load of main engine, estimates increased compared to a basic design: performance - 4%, capacity - 5%; output gas temperature decreased to 1%. At combined operation of TEGs positioned in the exhaust system of one main engine with exhaust boiler shut down and TEG positioned after exhaust boiler, estimates grew: capacity - 35%, performance - 14%; output gas temperature decreased to 19%. Total maximum capacity of TEGs positioned in the main engine exhaust systems makes 42.78 kW which is 1.78% of a ship power plant capacity.
The article presents the design of a thermoelectric generator (TEG) for utilizing heat energy of exhaust gases of ship diesel engines. There have been chosen a TEG basic design and a technique for its efficiency raising. Geometric, heat and electric parameters of TEG have been calculated using RSD 49 ship project. Calculation of heat and electric parameters of TEG with intensive heat exchange on the surface of a hot node was made using sloping plates. The relation between TEG position (before and after exhaust boiler) and a Wartsila 6L20 main engine exhaust system has been determined. According to the analysis result, in case of TEG position after exhaust boiler and 100% load of main engine, estimates increased compared to a basic design: performance - 4%, capacity - 5%; output gas temperature decreased to 1%. At combined operation of TEGs positioned in the exhaust system of one main engine with exhaust boiler shut down and TEG positioned after exhaust boiler, estimates grew: capacity - 35%, performance - 14%; output gas temperature decreased to 19%. Total maximum capacity of TEGs positioned in the main engine exhaust systems makes 42.78 kW which is 1.78% of a ship power plant capacity.
Keywords:
thermoelectric generator, RSD 49 project ship, Wartsila 6L20 diesel engine, heat utilization, exhaust gases, intensification of heat exchange
thermoelectric generator, RSD 49 project ship, Wartsila 6L20 diesel engine, heat utilization, exhaust gases, intensification of heat exchange
Introduction The issue of efficient use of fuel is of current importance for the fleet. It is known that in the main engines of the ship power plant (SPP), up to 50% of the combustion heat of the fuel is converted into mechanical energy. The rest of the energy is lost. Also, one of the solutions to this problem is the use of thermoelectric effect for converting heat energy of exhaust gases (EG) from marine diesel engines into electric ones. Thanks to the latest advances in the development of thermoelectric materials and systems, interest in the use of the thermoelectric generator TEG in SPP was renewed. Advantages of TEG are a significant resource, lack of moving parts, quiet operation, environmental cleanliness, versatility with regard to the methods of supply and removal of heat and the possibility of recovering the waste heat energy. The disadvantage of TEG is a low efficiency of 1-10%. Despite this, thermoelectric generators have been extensively utilized. This work is devoted to the issues of increasing the efficiency of TEG due to the intensification of heat transfer. The design of TEG with altered surfaces of the heat exchanger from the side of exhaust gases of the internal combustion engine is proposed, and changes are made in the method for calculating thermal and electrical parameters of TEG, taking into account the features of heat exchange processes with intensified TEG surfaces. Power plant of RSD 49 project vessel RSD 49 project vessels, in accordance with the classification adopted by Marine Engineering Bureau, belong to Volga-Don Max class. It means they have maximum displacement and dimensions for the Volga-Don shipping canal. Ships of the series can be used for transportation of general, bulk, timber, grain, bulky and dangerous goods in international traffic. Technical and operational characteristics of the vessel and engines are presented in Table 1. The propulsion system at "RSD 49 project vessel" consists of 2 Wartsila 6L20 engines, whose output flange is rigidly connected to the shafting and fixed-pitch propeller. The main engine (ME) gas system includes: a pipeline with an inner diameter of 420 mm and an outer diameter of 600 mm, thermal expansion joints, an AELBORG UNEX P-2 steam recovery boiler (SRB). Table 1 Operating characteristics of RSD 49 project vessel Characteristics Unit Value or response Calculated vessel length m 139.95 Width m 16.5 Hull height m 6.0 Draft m 4.70 Deadweight t 7143 Loaded sailing rate knots 11.5 Capacity of main propulsion of SPP kW 2 · 1200 Auxiliary diesel gases kW 2 · 292 Power plant type N/A Combustion engine Type of power delivery to propulsion shaft N/A Mechanic Since TEG is recommended to be installed vertically, two locations were chosen for its installation, after the engine and after the recovery boiler. As a basic version of TEG, the construction proposed by the authors in [1] was chosen. Table 2 Operating characteristics of exhaust gas system of Wartsila 6L20 engine Exhaust gas system Flow rate at 100% load kg/s 2.57 Flow rate at 85% load kg/s 2.25 Flow rate at 75% load kg/s 1.95 Temperature after turbo charger, 100% load (TE517) °C 305 Temperature after turbo charger, 85% load (TE517) °C 295 Temperature after turbo charger, 75% load (TE517) °C 305 Choosing thermo generator modules In this installation, thermo generator modules of ТГМ-287-1.0-1.5 type by KRYOTERM OJSC are used, whose design and electrical characteristics are presented in Tables 3 and 4 [2]. The construction of the thermo generator module is shown in Fig. 1. Table 3 Design characteristics of ТГМ-287-1,0-1,5 thermo generator module Module type Size range Electrical resistance, Rm Heat resistance Length, mm Width, mm Height, mm Ohm kW ТГМ-287-1.0-1.5 40 40 3.8 4.72 1.16 Table 4 Electrical characteristics of ТГМ-287-1.0-1.5 thermo generator module* Characteristics tc = 50°С, th = 150°С tc = 100°С, th = 200°С Voltage, V 4.77 4.52 Current rate, А 0.47 0.43 Capacity, W 2.23 1.93 Power efficiency, % 2.7 2.3 * tc - temperature of cold side; th - temperature of hot side. The parameters are indicated for the load resistance equal to the electrical resistance of the module. Fig. 1. Thermoelectric module Design and calculation of TEG with heat transfer augmentation on the surface of the hot unit for installation before UB The calculation procedure is similar to that specified in [3], with corrections that take into account the use of inclined plates on the surface of the hot unit. In particular, the calculation of the heat transfer coefficient of gas was changed. Cross-section area of flue, m2: where а - size of the wall face of the hot node, m; FH - cross-sectional area of inclined plates, m2. Cross-sectional area of inclined planes, m2: where h - height of the inclined plane, m; δ - element thickness, m; θ - inclination angle. Clearance between inclined planes, m2: where L - length of the heat exchanger, m; Ni-p - number of inclined planes in TEG. Gas rate, m/s: where Gg - gas consumption, kg/s. Heat transfer surface area, m2: where Fpsa - plate surface area; tag - average gas temperature. Reynolds number for gas where νg - kinematic viscosity of gas, m2/s; defd - equivalent flue diameter, m. Exhaust gas of the diesel engine moves in the pipeline in turbulent regime, therefore the Nusselt number for the gas is determined by the formula [4-6] where Prg - Prandtl number for gas. Coefficient of convective heat transfer for gas with augmentation of heat transfer on the surface of a hot unit: where λg - coefficient of thermal conductivity of gas, W/(m2 · K). It follows from the calculation results that the convective heat transfer coefficient for gas with augmentation of heat transfer on the surface of a hot unit is 7.3 times greater than convective heat transfer coefficient on a smooth surface of a hot part. According to the recommendations of the author of work [7], dimensions, slope angle, number and material of the plates were adopted. In accordance with the design of ME exhaust gas system, a TEG was designed with an heat transfer augmentation on the surface of the hot unit installed after the UB (Fig. 2).The calculation is performed for TEG at 75, 85 and 100% for ME loads. The results of calculations of the joint work of ME and TEG are given in Table 5. Table 5 Results of calculations for one TEG with the heat transfer augmentation on the surface of the hot unit installed before UB Ne, % P, kW I, А U, V Goutput. g, kg/s thoutput, ºС twoutput, ºС 75 5.8 16.72 352 1.95 240.9 38 85 5.75 16.62 346.43 2.25 240.5 38 100 6.09 16.92 360.12 2.57 255.3 38 Fig. 2. TEG design with heat transfer augmentation, established before UB Design and calculation of TEG with heat transfer augmentation for installation after UB Calculation procedure is similar to that specified in cl. [3], as amended in "Design and calculation of TEG with heat transfer augmentation on the surface of the hot unit for installation before UB". In accordance with Fig. 3, TEG design with heat transfer augmentation on the surface of the hot unit, installed after UB has been developed (Fig. 3). Fig. 3. TEG design with heat transfer augmentation, established after UB The results of the calculation of TEG with heat transfer augmentation established after UB are presented in Table 6. Table 6 Results of calculations for one TEG with the heat transfer augmentation on the surface of the hot unit installed after UB Ne, % P, kW I, А U, V Goutput. g, kg/s thoutput, ºС twoutput, ºС 100 9.7 45 216 2.57 98 26 Calculation of TEG collaboration indicators, when UB is off Calculation results of TEG collaboration indicators are presented in Table 7. Table 7 The results of calculations of TEG installed into the systems of gas hammer of one ME in joint operation with an idle UB TEG Ne, % P, kW I, А U, V Goutput. g, kg/s thoutput, ºС twoutput, ºС Before UB 100 6.09 16.92 360.12 2.57 255.3 38 After UB 100 15.3 56.6 270.4 2.57 122 28 Analysis of calculation results Based on the results of calculations, it can be concluded that the use of a heat transfer surface with inclined surfaces makes it possible to increase the efficiency of TEG operation. When TEG was installed before UB, the calculated values were increased in comparison with the basic design, in accordance with Fig. 4 and 5 - efficiency by 4%, power by 6%, and exhaust gas temperature at the outlet from TEG decreased by 1%. Gas rate has increased by 12%, but its value is within the permissible limits, which allows to conclude that the installation of inclined surfaces does not lead to significant aerodynamic resistance of the gas-sluice system. Fig. 4. Comparison of TEG power of the base version and TEG with modified heat transfer surface Fig. 5. Comparison of efficiency of TEG base version and TEG with modified surface When TEG was installed after UB at 100% ME load, calculated values increased: efficiency by 4%, power by 5%, and exhaust gas temperature at the outlet from TEG decreased by 1%, compared to the basic design in accordance with Fig. 6, 7. Fig. 6. Comparison of TEG power of the base version and TEG with modified heat exchange surface Fig. 7. Comparison of efficiency of TEG base version and TEG with modified surface The results of calculations of the joint operation of TEG, with UB off, in accordance with Fig. 8 and 9, showed an increase in TEG installed after UB: power by 35%, efficiency by 14%, exhaust gas temperature at the outlet from the TEG decreased by 19%. Fig. 8. Comparison of power of TEG installed after UB and in joint operation Fig. 9. Comparison of efficiency of TEG installed after UB and in joint operation Conclusion According to the calculation results obtained, the authors can infer: - the use of heat exchange surface when using inclined plates allows to increase the efficiency of TEG operation; - with TEG installed after UB at 100% ME load calculated values increased, compared to the basic design in accordance with Fig. 6, 7: efficiency by 4%, power by 5%, and exhaust gas temperature at the outlet from TEG decreased by 1%; - the results of calculations of the joint operation of TEG, with UB off, in accordance with Fig. 8 and 9, showed an increase in TEG installed after UB - power by 35%, efficiency by 14%, exhaust gas temperature at the outlet from the TEG decreased by 19%; - the total maximum power of TEG installed in the systems of ME exhaust gas systems is 42.78 kW, which comprises 1.78% of the power of SPP and 7.32% of the power of combustion engine; - TEG utilization is advisable for passenger and container vessels; - to convert DC electric current into alternating current, it is necessary to install an inverter with accumulators to store the TEG in the electrical system of the vessel. The article presents a new design of TEG with hot surfaces located in inclined panels. Results of calculations are presented in the article showing that when the surface area of a hot section heat exchanger changes, the convective heat transfer coefficient for gas with heat exchange augmentation on the surface of a hot unit is 7.3 times greater than the convective heat transfer coefficient on a smooth surface of a hot part. The authors investigated the influence of inclined plates on the exhaust gas flow; the study results will be presented in the next article.
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