The paper deals with numerical simulation of the retort boiler fired with solid fuel. Such constructions
are very popular for heating systems and their development is mostly based on the designer experience.
The simulations have been done in ANSYS/Fluent package and involved two numerical models. The
former deals with a fixed-bed combustion of the solid fuel and free-board gas combustion. Solid fuel
combustion is based on the coal kinetic parameters. This model encompasses chemical reactions, radiative
heat transfer and turbulence. Coal properties have been defined with user defined functions. The
latter model describes flow of water inside a water jacked that surrounds the combustion chamber and
flue gas ducts. The novelty of the proposed approach is separating of the combustion simulation from the
water flow. Such approach allows for reducing the number of degrees of freedom and thus lowering the
necessary numerical effort. Decoupling combustion from water flow requires defining interface
boundary condition. As this boundary condition is unknown it is adjusted iteratively. The results of the
numerical simulation have been successfully validated against measurement data.