**Piotr Józwiak ´ 1,2,\*, Jarosław Hercog 1, Aleksandra Kiedrzy ´nska 1, Krzysztof Badyda <sup>2</sup> and Daniela Olevano <sup>3</sup>**


Received: 29 February 2020; Accepted: 1 April 2020; Published: 3 April 2020

**Abstract:** Preheating furnaces, which are commonly used in many production sectors (e.g., iron and steel), are simultaneously one of the most energy-intensive devices used in the industry. Partial replacement of natural gas with biomass-derived synthesis gas as a fuel used for heating would be an important step towards limiting industrial CO2 emissions. The time dependent computational fluid dynamics (CFD) model of an exemplary furnace was created to evaluate whether it is possible to obtain 40% of energy from syngas combustion without deterioration of thermal parameters of the treated load. As an outcome, a promising method to organize co-firing in the furnace was indicated. The obtained results show that the co-firing method (up to 40% thermal natural gas replacement with syngas), assuming low air-to-fuel equivalence ratio (λNG = 2.0) and even distribution of power among the furnace corners, lead to satisfactory efficiency of the heat treatment process—the heat transferred to the load exceeds 95% of the heat delivered to the load in the reference case), while carbon dioxide emission is reduced from 285.5 to 171.3 kg CO2/h. This study showed that it is feasible (from the heat transfer point of view) to decrease the environmental impact of the process industries by the use of renewable fuels.

**Keywords:** CFD modelling; heat treatment process; industrial furnaces; natural gas substitution; syngas co-firing
