Thermal Evaluation of Using Thermosyphon Heat Exchangers Instead of Ljungstrom in Boiler of Mashhad Steam Power Plant

Document Type : Research Article

Authors

1 Faculty of Chemical and Materials Engineering, Shahrood University of Technology, Shahrood, I.R. IRAN

2 Faculty of Mechanical and Mechatronics Engineering, Shahrood University of Technology, Shahrood, I.R. IRAN

3 Department of Chemical Engineering, Hakim Sabzevari University, Sabzevar, I.R. IRAN

Abstract

Ljungstrom is used in steam power plants for heating of boiler’s air and increase its temperature to around combustion temperature by energy recovery of outlet smoke. Due to moving parts and therefore high depreciation, the main drawback of Ljungstroms is the possibility of air leakage into the smoke channel (more than 20%) which leads to an increase in the passing air through the fans and reduction of generating energy of power plants. On the other hand, a wickless heat pipe or thermosyphon is a thermal spreader with no moving parts and no external control. Thereforethe application of thermosyphon heat exchangers instead of conventional Ljungstroms can be considered as a reasonable suggestion. In this study, the  Ljungstrom of Mashhad steam power plant with specified geometry (surface area: 12040 m2) and operation conditions (thermal performance coefficient: 71%) is considered and the final goal is the design of thermosyphon heat exchanger systems with different geometries in case of pipe size and materials, working fluid, the number of pipes, and transverse and longitudinal pitch. The comparison of designed thermosyphon heat exchangers with Ljungstroms in case of required thermal surfaces and occupied volume is investigated too. In this research, two approaches with different working fluids have been considered. The second design with 522 heat pipes which were charged by mercury showed better performance than the first design which was made with 900 heat pipes and charged by thermex as the working media. Reduction of the required heat transfer surface, prevention of air leakage to the air stream, and elimination of electrical energy used by moving parts of Ljungstrom are some benefits of this study.

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References

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