Identification of combustion characteristics of high ash Indian coal, rice straw, rice straw char and their blends

The present investigation evaluates the co-combustion performance of rice straw (RS), rice straw char (RSC), high ash coal (HAC) to determine their suitability as blended fuels for power generation. Both the individual and blended fuels were characterized through proximate analysis, ash analysis, and the determination of gross calorific value (GCV). Experimental results indicate that RS and RSC possess higher GCV than HAC, improving overall GCV and combustion rate of the blends. Thermogravimetric analysis (TGA) reveals significant variations in the thermal properties of disproportionate mixtures (blends of HAC with RS or RSC). HAC has the highest ignition (Ti = 417°C), peak (Tp = 498°C), and burnout temperatures (Tf = 565°C), indicating weak thermal stability. In contrast, RS and RSC exhibit much lower Ti (226°C and 256°C, respectively) and Tf (420°C and 448°C), suggesting they ignite more easily and have moderate thermal stability. Blends with higher RS or RSC content progressively decrease Ti and Tf, but with a sharper DTGmax (maximum derivative thermogravimetry) and Pi (ignition index), highlighting more intense and quicker combustion. Increasing the RS content from 10 % to 90 % lowers the ignition temperature (Ti) from 416ºC to 222ºC and burnout temperature (Tf) from 564ºC to 417ºC. Performance index (Qf) increases, and rate of heat intensity (Sf) decreases as RS/RSC content increases, with RS9HAC1 and RSC9HAC1 having moderate stability and highest combustion intensity. This trend illustrates that increasing RS/RSC proportions enhance reactivity with moderate thermal stability. Thermodynamic analysis shows that blending RS and RSC with HAC decreases the enthalpy (ΔH) from 41.42 kJ/mol to 37.77 kJ/mol and from 42.02 kJ/mol to 31.74 kJ/mol as the RS and RSC content rises from 10 % to 90 % implying that individual combustion of coal is difficult while blending RS and RSC makes the combustion favorable. Adding 10 % RS and 20 % RSC can significantly improve combustion efficiency at various temperatures without major boiler modifications. The numerical study demonstrates the prospective for enhancing coal-biomass/biochar co-combustion by altering O2/CO2 gas levels, emphasizing the benefits of adding biomass and biochar, as well as substituting CO2 for N2 under specific conditions. © 2024 The Institution of Chemical Engineers