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 (λ_NG = 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.

The transition to carbon-neutral power generation necessitates the development of innovative strategies to mitigate CO₂ emissions from coal-fired power plants. Ammonia, a carbon-free fuel, presents potential benefits but also poses challenges related to NOx emissions and combustion stability. This study assesses the feasibility of ammonia co-firing in a 200 MW pulverized coal boiler, with a particular focus on the impact of ammonia injection position on combustion stability and gas emissions. A 3D computational fluid dynamics (CFD) model in Ansys Fluent was used to simulate the co-combustion process, and it was validated using historical operational data. The simulations examined ammonia injection through burners and dedicated nozzles. The results indicated that injecting ammonia through the lower row burners (1 row burners) resulted in the lowest NOx emissions (<600 mg/m³), while injection at higher rows led to increased NOx levels. Moreover, ammonia co-firing at 40% thermal input reduced CO₂ emissions by nearly 50%, achieving an emission factor below 550 kg/MWh. These findings underscore ammonia co-firing as a promising low-carbon strategy, emphasizing the need for optimal injection locations to reduce NOx emissions and ensure efficient combustion. This research provides valuable insights for the design of future ammonia-coal co-firing systems.