We tailor the finned surfaces to the design temperature profile. We can use more economical materials and extended surfaces as the exhaust gas temperature reduces.
Using a range of finned surfaces from welded fins through to plate fins, we ensure the most compact arrangement while minimising the pressure drop required.
We design economisers to lower the gas temperature to a level marginally above the level at which condensation would occur. However, there is still a risk of corrosion under startup and shut down conditions. Therefore, we recommend appropriate materials and advise on the best operational parameters to minimise the potential for corrosion.
How it works
An economiser takes waste heat from the exhaust gases in a boiler flue and uses it to preheat the boiler feed water. The characteristics of the flue gas are subject to the fuel that is used and consequently can vary significantly.
Here are some key aspects that we consider in our designs.
Flue gas properties
We determine the on-coil fin configuration based on the calculated fin root and tip temperatures. We then progress to a secondary and tertiary phase of cooling ensuring that we remain within the design envelope of the selected fin form in each case.
The temperature of the boiler feed water inlet varies depending on ambient conditions and operational requirements. We work with our customers to review a range of operating points and ensure that the heat exchange characteristics permit easy control of the equipment as a whole.
Usually, the water is fed counter flow to the flue gas stream. This is the most efficient arrangement. However, when considering the control of fin and tube temperatures, we have found it advantageous to use co-current flow in a limited number of cases.
Note that, before discharge to the atmosphere, the flue gas may require a small amount of reheat to prevent the formation of a plume. Sterling Thermal Technology can also supply a heat exchanger designed to solve this issue.