The paper presents the method of fouling degree evaluation of the heating surfaces in pulverized coal-fired boiler during coal combustion and biomass co-combustion. The fouling processes have a negative impact on the boiler operation by reducing the steam outlet temperature, increasing the mass flow rate of cooling spray water, and may be the reason for overheating of the superheater (SH) tube material. This leads to a reduction of the boiler efficiency and can cause shortening of a lifetime as well as damage of boiler heat exchangers, in particular, the steam SH. The basis of fouling degree assessment method are the dimensionless coefficients, which represent current values of heat absorbed by an individual heat exchanger in comparison to the value for a clean surface. The coefficients are determined based on the calculated heat power of individual heat exchanger taking into account the adjustment resulting from the flue gas temperature inside a combustion chamber. The results of the analysis showed a significant reduction of the amount of heat absorbed by the convection SH during continuous boiler operation. The next important conclusion is a large increase of the heat amount transferred to the radiant SH, which may result in exceeding the permissible temperature of the tube material. The proposed method together with on-line monitoring system installed on the boiler is used to calculate the fouling degree of individual heating surfaces. Accurate monitoring of boiler heating surface conditions can be used to optimize soot blowers operation and finally to improve process efficiency.

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