In a fossil fuel waste incineration or plasma gasification process, waste heat generated by combustion of waste is captured by a heat transfer fluid and conveyed to an Organic Rankine Cycle (ORC) for energy recovery. In the case of a fossil fuel-fired waste incineration system, the heat transfer fluid captures waste heat from a double-walled combustion chamber, a heat exchanger being used to cool the hot process exhaust (gas cooler). In the case of a plasma waste gasification system, the heat transfer fluid captures waste heat from a plasma torch, a gasification chamber and combustion chamber cooling jackets as well as any other high-temperature components requiring cooling, and then a heat exchanger used to cool the hot process exhaust (gas cooler). The heat exchanger may take on several configurations, including plate or shell and tube configurations.