Economisers to optimise the thermal efficiency of your process equipment
Economisers are used to recovering heat from the flue gases of boilers or other gaseous heat sources. The heat recovered is used to pre-heat the feed water, incoming combustion air or other streams that can benefit from the energy lost otherwise to the atmosphere. Improvements in the overall thermal efficiency of the process can be significant and should not be taken for granted.
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 economisers work
An economiser takes waste heat from the exhaust gases in a flue and uses it to preheat the incoming process fluid, such as 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 process fluid 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 heated medium 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.
As a recognised manufacturer of economisers, we can help you to get the best equipment for your application.