Thermal oil boilers feature a high temperature (generally ranging between 200 and 250°C) due to the high oil return temperature, which in turn leads to a high temperature exhaust gas. The emission of these high temperatures no only wastes energy, but also pollutes the environment, and because of that, we designed the flue gas waste heat recovery boiler in order to recover energy. This boiler recovers heat from the flue gas in order to generate hot water and steam used in the boiler. It can also heat air to dry the materials, or be used as a boiler-combustion supporting air.