Modeling the heat transfer processes in a thermosyphon-type heat recovery boiler

Abstract

Active investigations on elaborating energy-saving technologies and related equipment in different fields of technology, including heat consuming installations and production processes, were commenced approximately since the 1970s. In particular, special attention was paid to closed two-phase thermosyphons operating in accordance with a closed evaporation-condensation cycle without using coolant circulating pumps. The article considers the possibility of using the heat of flue gases from the heating system's main boiler unit for heating the return line water in a thermosyphon-based heat-recovery boiler having separate modules for evaporating and condensing the coolant (water). The heat-recovery boiler with a thermosyphon is intended for efficiently using the secondary source of energy. The closed thermosyphon is used as a device for transferring heat from flue gases to cold water via the evaporation--condensation cycle. The thermosyphon's tube bundle transfers heat from flue gases to the working fluid through the wall. The device can be used as part of various heat supply systems. Application of the heat-recovery boiler can make a number of technological processes more energy efficient. Despite the fact that the heat-recovery boiler is essentially a heat exchanger with an intermediate coolant and has a somewhat higher thermal resistance as compared with that of a regenerative heat exchanger, the prospects of using such a design are substantiated by the following factors: the device has only a slightly higher thermal resistance due to high intensity of the evaporation and condensation processes, and owing the possibility of transforming the heat flux in the network water heating zone; the heating system becomes more environmentally friendly owing to a lower probability of the ingress of corrosive sulfur-containing flue gases into the main system in case of degraded corrosion resistance of the heat exchanger material; and there are possibilities to reduce the pressure drop in the heated network water channel by properly choosing the flow path geometry, to shift the water heating condenser beyond the boundaries of the corrosive gaseous medium, and to use process production wastes from the boiler manufacturing plant as the heat exchanger structural material.