Economisers

Heat recovery to improve efficiency in thermal installations

An economiser is a heat exchanger that recovers residual heat from flue gases or process streams in order to increase the energy efficiency of a thermal installation. In steam boilers and other industrial processes, a significant proportion of the energy supplied leaves the system via hot flue gases. By using this heat to preheat feedwater or other process media, an economiser reduces the required fuel input and increases the overall system efficiency.

Economisers are widely used in power stations, chemical and petrochemical plants, and other energy-intensive industries. Depending on flue gas temperature, flow rates, pressure levels and the degree of fouling, various designs are possible, including tube bundle and finned tube designs. Finned tubes are used in particular where there are low heat transfer coefficients on the gas side, in order to increase the heat exchange surface area and thus achieve higher heat transfer.

Corrosion and fouling play a crucial role in the design and operation of economisers. When flue gas cooling results in temperatures below the acid dew point, condensation containing corrosive components may occur. This requires careful selection of materials, such as coated carbon steel or high-alloy steels, as well as a design that facilitates condensate drainage. Furthermore, fouling caused by soot, dust or ash deposits can adversely affect heat transfer and pressure drop, making inspection and periodic maintenance essential.

By making effective use of waste heat, economisers demonstrably contribute to lower specific fuel consumption, higher plant efficiency and a reduction in CO₂ emissions. They are therefore an integral part of modern, energy-efficient and sustainable process plants.