Thermal resistance by slagging and its relationship with ash properties for six coal blends in a commercial coal-fired boiler

• Published in: Fuel (Guildford) 2019-01, Vol.235, p.1377-1386
• Main Authors: Park, Ho Young, Lee, Jeong Eun, Kim, Hyun Hee, Park, Sangbin, Baek, Se Hyun, Ye, Insoo, Ryu, Changkook
• Format: Article
• Language: English
• Subjects: Ash viscosity; Ashes; Boilers; Coal; Growth rate; Heat resistance; Heat transfer; Mathematical models; Operational problems; Slag; Slagging; Superheaters; Temperature effects; Thermal resistance; Thermo-mechanical analysis; Thermomechanical analysis; Viscosity
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2018.08.134

•Operating data of a commercial coal-fired boiler was analyzed for six coal blends.•Thermal resistance (Rslag) was determined as the extent of slagging by ash deposition.•Second peaks of TMA matched with the trend in Rslag on superheaters.•Third peaks of TMA were inversely correlated with Rslag on furnace walls.•Temperature at 25 Pa·s of ash viscosity was correlated with Rslag on furnace walls. Evaluating ash slagging can alleviate the operational problems and improve the efficiency of coal-fired boilers. This paper presents methods to quantify the extent of slagging in a 500 MWe tangential firing boiler by determining the thermal resistance and relating it to ash properties. To determine the thermal resistance by slagging, the operational data of the boiler were extracted for six coal-blend cases and analyzed using a one-dimensional process model. Although the conventional slagging indices based on ash composition have generated conflicting results, new indices based on thermo-mechanical analysis (TMA) of the coal-blend samples provided reasonable agreement with the operational data. In particular, the second peak of the TMA associated with the growth rate was correlated with the thermal resistance of the superheaters, and the third peak representing the slag melting was inversely correlated with that of the furnace wall. It was also found from the numerical modeling of the slag flow on the furnace wall that the critical viscosity temperature at 25 Pa·s can be positively related with the thermal resistance, and consequently, with the slagging propensity of specific coal ashes.