A value is given in the model constants for the spiral plate heat exchanger to select a formula, and the resulting formula is used to adjust the fouling thermal resistance on the outer surface of the tube. However, this formula poses two problems:
Firstly, the calculation of the values of thermal conductivity, kinematic viscosity, and Prandtl number of flue gas involved in the formula is relatively complex, requiring the use of functions and regression formulas for computation, which is not suitable for simulation models
Secondly, this model is applied to training simulators, and the data provided by users are obtained using different calculation methods. Therefore, the calculation formulas and methods for boiler heat exchangers in literature and practice may differ, and relying solely on adjusting the fouling coefficient of the aforementioned formulas for simulation will introduce errors
The heat transfer process and heat dissipation of the additional heating surfaces are arranged in modern utility boilers with ceilings and numerous enclosed tubes, which absorb heat in parallel with the main heating surfaces. These constitute the additional heating surfaces of the single-phase medium heat exchangers serving as the main heating surfaces. These additional heating surfaces adopt the corrected heat transfer coefficient of the main heating surfaces, with the specific correction method being to add a thermal resistance, which is the reciprocal of the heat transfer coefficient of the tube wall to the working medium, to the denominator of the formula. For simplicity of calculation, the heat transfer coefficient of the tube wall to the working medium is taken as a constant
Regarding the heat transfer temperature difference of the spiral plate heat exchanger, since the temperature of the working medium within the additional heating surface is close to the saturation temperature under the pressure of the steam drum, the difference between the average temperature of the flue gas and the saturation temperature under the pressure of the steam drum is taken as the heat transfer temperature difference
       Enter the actual area of the additional heating surface as a constant. Calculate the heat absorption of the additional heating surface using a formula, and record this heat for future use. The heat dissipation of the boiler convection flue is actually mainly the heat dissipation of the additional heating surface of the enclosed wall tube. Therefore, when calculating heat dissipation, a formula is also used, taking a constant as the heat transfer coefficient of natural convection, using the temperature difference between the saturated temperature under drum pressure and the ambient temperature as the heat transfer temperature difference, and the area of the additional heating surface as the heat dissipation area
The heat balance model comprises three heat balances: one for the flue gas side, one for the steam side, and one for the metal tube wall. It should be noted that in the heat balance calculation, changes in flue gas temperature stored in the flue gas space of the heat exchanger, changes in the temperature of the working medium stored in the heat exchanger tubes, and changes in the metal temperature of the heat exchanger should be taken into account