The transition to sustainable energy sources is of critical importance in the context of global climate change, geopolitical instability in fuel supply, and the depletion of fossil energy resources. Biogas, produced through the anaerobic decomposition of organic matter, is considered a promising renewable alternative to natural gas in low-temperature heating systems. However, its variable composition, reduced calorific value, and high carbon dioxide content create significant technical limitations for its use in conventional burner equipment. These factors necessitate a comprehensive evaluation of the capability of existing boiler systems to operate effectively under conditions of fuel substitution. The article is dedicated to the analysis of the main operational challenges arising during the combustion of biogas in thermal energy systems. Issues related to flame stability, thermal efficiency, and emission control are examined. The study evaluates the substitution of natural gas with biogas under conditions close to real operation. Particular attention is paid to the influence of the physico-chemical properties of the fuel on combustion behavior and heat transfer efficiency. Computational fluid dynamics (CFD) methods are applied to model the thermochemical processes occurring within the combustion chamber of a fire-tube boiler. The study includes an assessment of the temperature field, fuel–air mixture interaction, and the formation of pollutants, particularly nitrogen oxides. The role of burner geometry in maintaining stable combustion during the transition to biogas is determined. The hydrodynamic behavior of fuel jets is investigated to assess their impact on flame stability and propagation. The influence of CO₂ dilution in the fuel mixture on temperature gradients and heat transfer processes is analyzed, as it may potentially lead to reduced efficiency. The interaction of fuel and oxidizer flows is discussed to evaluate jet penetration and mixing quality under varying fuel compositions. As a result, the possibility of adapting conventional thermal equipment to operate on renewable gaseous fuels is substantiated. A numerical approach to modeling the combustion process of biogas in a VK-32 boiler is proposed, which can be adapted for simulating heat exchange processes in similar types of fire-tube hot water boilers

Досліджено робочий процес водотрубно-димогарного котла ВК 32 при переході з природного газу на біогаз (70% CH₄, 30 % CO₂) із застосуванням CFD моделювання. Верифікована на експериментальних даних модель дозволила оцінити вплив зміни палива на процес горіння, структуру температурного поля та утворення оксидів азоту. Проаналізовано гідродинаміку паливно повітряних струменів і розраховано безрозмірний гідродинамічний параметр q. Підкреслено важливість модернізації існуючого теплотехнічного обладнання. Запропоновано адаптаційні заходи – коригування геометрії пальникового колектора – для забезпечення стабільності факела та ефективної роботи котла на паливі з нижчою теплотворною здатністю