An economizer is a heat exchanger that recovers waste heat from hot gases coming from the stack or process outlet and transfers it to another fluid. Its operating principle is simple: high-temperature waste gases pass through a tube bundle or finned tubes, while feed water, process water, a glycol mixture, or fresh air are heated on the other side.

Economizers are used for waste heat recovery in steam boilers, oil and hot water circuits, cogeneration/trigeneration systems, drying ovens, chemical and pharmaceutical processes, and the food and beverage industry. They enable the same output to be achieved with less fuel or increase production capacity with existing fuel, thereby reducing burner load, exhaust gas temperature, and increasing efficiency while decreasing emissions.

The choice of economizer type depends on the process and the cleanliness of the gas. For relatively clean gases with a small temperature difference, finned economizers offer a compact solution. For pipelines with high levels of dust, soot, and particulate matter, finless (bare-tube) economizers are preferred. For applications where condensation is expected, condensing stainless steel economizers are used.

The choice of materials depends on the gas composition, temperature, dew point, and condensate chemistry. Carbon steel is economical for dry exhaust gases, while 304/316L stainless steel is preferred in the presence of acidic condensates. The design includes condensate collection and drainage systems, flow guidance to limit surface moisture, and corrosion-resistant coatings.

For optimal selection, it is necessary to communicate: the exhaust flow rate and inlet temperature, the target outlet temperature, the gas composition and the expected dew point, the permissible pressure drop on the gas side, the type of heat transfer fluid, the flow rate, the inlet and outlet temperatures, the operating regime, the site configuration and maintenance constraints, as well as the required design standards.

The return on investment is calculated by dividing the total investment cost by the annual energy savings. The results are influenced by fluctuations in energy prices, operating conditions, anticipated maintenance and cleaning costs, and, in the case of condensing systems, the cost of treating and disposing of condensate.