Experimental study of an economizer that recovers energy from the waste gas of a steam generator

An economizer is a type of heat exchanger produced from pipes that convert the sensible and latent heat of the waste gas from the boiler or furnace to water or air. The temperatures of waste gas from steam generators are usually 50-60oC higher than operating temperatures. The make-up water of steam generator can be heated by waste flue gas. Customers prefer devices that are economically inexpensive and trouble-free and do not take up much space in the boiler room. For this reason, end users prefer the steam generator because it takes up less space than the boiler. On the other hand, by employing an economizer, the waste heat of exhaust gas from the steam generator can heat feed water into the steam generator. Therefore, there was a demand for an economizer for boiler rooms with limited space. The present study, in line with this demand, designs, manufactures and tests an economizer which is more space-saving, more efficient, and easier to repair, compared to typical economizers in the market. In particular, this study has investigated the recovery of energy loss from the waste gas of LPG-fired steam generator. The economizer of the present study has been designed vertically instead of horizontally, and this vertical configuration saves more space in a boiler room. Additionally, it is on the same floor with the steam generator, and this makes it easier to repair. Moreover, the exhaust gas can bypass the economizer, thanks to the damper system, allowing the economizer to be repaired if needed without stopping the process. In the present study, the steam generator whose steam capacity is 300 kg/h is employed, and the waste stack gas is cooled to 110oC. As a result of employing the economizer, the energy of 16.20 kW is gained back from exhaust gas. This energy recovery results in saving 1.35 ₺ per operating hour and its payback period is determined to be 4.10 years. These results showed that, for further improvement, the economizer should have been designed for smaller pipe diameters that will provide turbulent flow.