Energy conservation by waste heat recovery in industry using thermosyphon heat exchangers

Conservation of energy by waste heat recovery is important not only for cost reasons, but also for reducing primary energy consumption as well as reducing carbon dioxide production. This paper explains and discusses the simulation, performance, and successful applications of thermosyphon heat exchangers (THE's) for recovering waste heat from exhaust gases in industrial plants. The advantages of this system are compactness, flexibility of system size, ease of operation, and minimum maintenance requirements. The thermosyphon heat exchanger can satisfactorily act as a pre-heater of air in boilers and furnaces using the heat recovered from the exhaust. In this work, one successful industrial practice is explained using thermosyphon heat exchanger. The THE was simulated to recover waste heat from the exhaust of a nearly 7 ton boiler in the SAMEN company. The energy recovered from the flue gas is used to preheat the incoming air to the boiler. The average rate of waste heat recovery and thermal effectiveness obtained from computer simulation are 100 kW and 40%, respectively. The payback period was less than two years. The evaluation of the thermal performance of the THE was based on the effectiveness-NTU and LMTD methods to obtain the heat transfer characteristics.