Markolenko T. Model and Method of Regulating the Thermal Power of a Boiler under Varying Calorific Value of Hydrocarbon Fuel to Improve Efficiency.

The dissertation addresses the pressing scientific and technical problem of increasing the energy efficiency and environmental safety of combustion processes involving mixtures of hydrocarbon fuels of variable composition in steam boilers. To achieve this goal, the study proposes an improved mathematical model for regulating boiler thermal power, taking into account the variable calorific value of the fuel. An adaptive method has been developed for controlling the volume and temperature of flue gases, with automatic regulation of the fuel mixture composition based on the current thermal load. The implementation of the proposed approach ensures thermal regime stability, increased boiler efficiency, and reduced specific CO2 emissions without requiring equipment modernization, thus meeting the current standards of sustainable energy development. The feasibility of the technical solutions is substantiated through numerical modeling, which demonstrated high energy efficiency, combustion stability, and reduced environmental impact. The proposed approaches are based on clearly defined combustion quality indicators and efficiency criteria for automated thermal power control, enabling an objective assessment of boiler optimization under conditions of variable fuel composition. Chapter 1 presents a review of current automated control systems for boilers, classification of hydrocarbon fuels, and their physicochemical characteristics. It substantiates the need for a new model capable of maintaining a stable flue gas volume under changing fuel composition. Chapter 2 describes the construction of a dynamic mathematical model of the boiler as a control object, incorporating variable fuel calorific value. A combustion simulation model was developed, considering chemical equilibrium. Verification using natural gas, wood, and biogas demonstrated the reliability and applicability of the model. Chapter 3 proposes a method for regulating thermal power by adjusting the ratio of methane to low-calorific gas at constant fuel mixture flow. This enables consistent flue gas parameters and thermal stability, even under variable load, which is essential to minimizing heat losses. Chapter 4 develops a method for automated thermal power regulation based on real-time calorific value measurement. A multi-level control system was proposed with cascade coordination of controllers, an online calorific value estimation module, and an adaptive fuel mixing algorithm. Numerical modeling confirmed the effectiveness of the approach across a wide load range (40–100%), maintaining constant flue gas flow and stable thermal power. The practical value of the dissertation lies in its applicability to existing boiler systems without retrofitting, enabling efficient use of mixed gaseous fuels and reducing environmental impact. Keywords: fuel mixture, energy efficiency, fuel calorific value, combustion, flue gas temperature, flue gas volume, power control, automation, classification, control system, mathematical model, quality indicators, efficiency criterion, environmental safety, environment.