The implementation of a sustainable development concept that involves an improvement of resource use efficiency, whilst maximizing the utilization of locally available biomass resources, has contributed to an increased interest in the combined heat and power systems based on externally fired gas turbines. Since the high-temperature gas/gas heat exchangers intended to heat the turbine inlet air are the key components of such systems, intensified research on exchangers of this type has been observed over the last decade. This work presents the in-house calculation code developed to analyze the heat transfer between the hot-side and cold-side streams in the small-scale red-hot air furnace of a unique design. The performed calculations, based on the assumed thermal and flow operation parameters and technical specifications, allowed to determine the required heat exchange surface area of the furnace to achieve the target outlet conditions. The calculation code allows for determining the geometry of a furnace, including its overall dimensions, number of tubes, and their bent sections in the heat exchange parts. The study of the laboratory-scale furnace performance has demonstrated its good agreement with the simulation results, thereby proving the code a reliable tool in designing.

A one-dimensional transient mathematical model describing thermal and flow phenomena during coal coking in an oven chamber was studied in the paper. It also accounts for heat conduction in the ceramic oven wall when assuming a constant temperature at the heating channel side. The model was solved numerically using partly implicit methods for gas flow and heat transfer problems. The histories of temperature, gas evolution and internal pressure were presented and analysed. The theoretical predictions of temperature change in the centre plane of the coke oven were compared with industrialscale measurements. Both, the experimental data and obtained numerical results show that moisture content determines the coking process dynamics, lagging the temperature increase above the water steam evaporation temperature and in consequence the total coking time. The phenomenon of internal pressure generation in the context of overlapping effects of simultaneously occurring coal transitions - devolatilisation and coal permeability decrease under plastic stage - was also discussed.

In the present paper, the one-dimensional model for heat and mass transfer in fixed coal bed was proposed to describe the thermal and flow characteristics in a coke oven chamber. For the purpose of the studied problem, the analysis was limited to the calculations of temperature field and pyrolytic gas yield. In order to verify the model, its theoretical predictions for temperature distribution during wet coal charge carbonization were compared with the measurement results found in the literature. In general, the investigation shows good qualitative agreement between numerical and experimental data. However, some discrepancy regarding the temperature characteristics at the stage of evaporation was observed.