Ukraine has a significant potential for the production of solid recovered fuel (SRF/RDF) from household waste at a level of 2.5–3 million tons annually with a lower heating value within 13–16 MJ/kg. Thermal processing of such fuel generates energy that can be used for electricity and heat production (Waste-to-Energy technology). One of the methods of thermal utilization of SRF/RDF is their incineration, including co-incineration with fossil fuels, particularly in existing power boilers under conditions of their modernization. The involvement of SRF/RDF in energy production should occur while ensuring their thermal processing in an environmentally safe manner, in accordance with the requirements of Directive 201/75/EU on industrial emissions. The evaluation of the prospects for co-incineration of SRF/RDF of different quality classes according to DSTU EN 15,359:2018 with fossil fuels has been carried out using mathematical modeling methods in existing boiler equipment in an environmentally safe manner, in accordance with the requirements of Directive 201/75/EU on industrial emissions. It has been proven that it is possible to co-incinerate SRF of quality classes 1–2 with natural gas in the combustion chamber of a small capacity boiler KVGM-20, and SRF of quality classes 1, 2 and 3 with a coal in boiler TPP-312 while complying with the conditions for neutralizing harmful substances, in particular dioxins. The optimal combustion parameters have been determined to ensure stable boiler operation. The influence of SRF/RDF composition on the combustion process and atmospheric emissions has been assessed. Calculated dependencies of temperatures, velocities, distribution of gas component concentrations, carbon residue in solid phase, nitrogen oxides and carbon monoxide concentrations in the combustion chamber have been obtained.