Huge amount of waste heat is generated in many industrial processes, in form of exhaust gases, water streams and/or solids (products and by-products). Representative sectors are steel and iron, concrete or glass production. Typically, it exists a mismatch between heat generation and demand that limits the potential application of the captured heat. Therefore, the implementation of a thermal energy storage becomes of paramount importance. If properly captured and stored, waste heat might be re-used in the same industry or commercialized externally, with the associated environmental and economic benefits. The challenge is to develop economically viable heat recovery systems that consider the heat capture, occasionally storage, and final application.

A viable heat recovery system must be simple, cost-effective and should not interfere with the industrial process. CIC energiGUNE and Sidenor I+D in the framework of the RFCS ECOSLAG project have developed a new heat recovery concept to capture the heat content of the molten slag using an underground heat exchanger in the slag pit. This solution accomplishes these requirements. The captured heat is then used to pre-heat water, reducing the gas consumption in the boilers.