In this paper, the interaction between caking bituminous coal (HC) and two types of biomass, namely sunflower husks (SFHs) and walnut shells (WSs), was studied via lab-scale fixed-bed reactor experiments and thermogravimetric analysis (TGA). The dynamics of volatile matter composition and weight loss changes were analyzed for the initial biomass types and their 1:1 blends with HC during co-pyrolysis. Derivative thermogravimetry (DTG) revealed that during the co-pyrolysis of HC with biomass, the number of reaction stages increased to four, compared to three during individual pyrolysis, indicating synergistic thermal behavior. The apparent activation energy (E_a) of the blends was higher (62.8 kJ/mol for SFH/HC and 61.8 kJ/mol for WS/HC) than that of the individual HC (55.1 kJ/mol), SFHs (43.8 kJ/mol), and WSs (52.4 kJ/mol), confirming intensified reaction complexity. Co-pyrolysis resulted in higher methane (CH₄) production, with the CH₄:HAc (acetic acid) ratio increasing from 1.2 (WSs) and 1.7 (SFHs) to 1.9 (WS/HC) and 3.3 (SFH/HC). The non-additive behavior of blends is established, indicating the interactions between biomass and HC during co-pyrolysis. These findings support a more resilient and sustainable approach to producing fuels and reducing agents, particularly through the utilization of agricultural residues and waste biomass.

Compared to extensive studies on affecting parameters in sulfur removal with ZnO adsorbents from coal gasification syngas, similar studies conducted for biomass gasification syngas (BGS) are quite rare. Thus, considering the BGSs with high water content, this study was performed to investigate the effect of H₂O presence in syngas on sulfur removal capacity (SRC) of ZnO adsorbents. Initially, the effect of gas composition and temperature on SRC in binary gas mixture was investigated. While H₂O decreased the SRC, as expected, the highest reduction in the capacity occurred in the CO–H₂S gas mixture due to observed COS formation. Second, the SRCs and resulting COS formation were compared for synthetic syngas mixtures having different water contents and for different amounts of adsorbents. Finally, the separate and combined effects of temperature and H₂O on SRC and COS formation in synthetic syngas were investigated by comparing SRCs of typical syngas under wet and dry conditions. The results showed that increasing the amount of adsorbent and temperature results in higher SRC due to a reduction in COS formation through the reactions of COS with H₂ and H₂O. This indicates that it is critical to control the residence time of syngas and temperature to reduce COS formation during ZnO adsorption. GRAPHICAL ABSTRACT

This paper presents a techno-economic optimisation of supply-side transition pathways for the district heating system of Stadtwärme Kapfenberg GmbH (Austria), aiming at full decarbonisation by 2040. Conducted within the SUPPORT DHC project, the study assesses how industrial waste heat, renewable heat options, and Power-to-Heat (P2H) can be combined to provide cost-efficient and reliable heat supply under evolving boundary conditions. A detailed energy system model was implemented in energyPRO and optimised at hourly resolution over a full year using validated demand profiles and operator-specific constraints, including source availability, maintenance schedules, technology priority constraints, operational cost parameters, and fixed installed capacities for existing assets. The analysis pursues two objectives: one with identifying cost-optimal supply portfolios for the current and planned expanded system, and the other with sizing P2H under two operational modalities (PV-only and PV plus grid electricity – grid import is permitted only when day-ahead prices are at or below a threshold; proxying hours with high renewable availability and/or low marginal emissions) within predefined capacity ranges. Across the analysed scenarios, industrial waste heat remains the dominant component of the cost-optimal portfolio. For the PV capacities considered, PV-only P2H exhibits a limited system-wide impact, indicating that achievable benefits depend strongly on local generation scale. In contrast, grid-enabled P2H improves economic performance and operational flexibility under the applied electricity price threshold formulation. Minimum levelized cost of heat occurs at approximately 2 MW P2H capacity with a grid price threshold of around 40 €/MWh; beyond this point, marginal benefits diminish as low-price operating hours saturate. The paper provides decision support for municipal utilities by demonstrating an optimisation-based heat production planning workflow that informs EED-aligned transformation and investment planning for accelerated integration of industrial waste heat and low-grade renewable heat, with sector-coupling options assessed to strengthen operational feasibility.