The coupled combustion of biomass and organic solid wastes including oil sludge has attracted much attention. Although the optimal mixing ratio of different coal types and biomass has been extensively studied, little attention has been paid to oil sludge that has undergone co-combustion. In this study, the combustion characteristics of blended fuel for coal, biomass and oil sludge under different mixing ratios are studied via a thermogravimetric test and differential thermal analysis. Kinetic analysis of tri-fuel is performed using the Flynn–Wall–Ozawa (FWO) and Dolye methods. The results show that the bituminous coal combustion process mainly involves the combustion of fixed carbon (236.0–382.0 °C). Wood pellet combustion (383.0–610.0 °C) has two processes involving the combustion of compound carbon and fixed carbon. Blending wood pellets effectively enhances combustion efficiency. Wood pellets from Korla (KOL) have the most obvious effect on reducing the ignition temperature. The blending combustion of bituminous coal (SC), wood pellets from Hutubi (HTB) and oil sludge (OS) have significant synergistic effects. As the OS mixing ratio increases from 10% to 20% with 45% HTB, T_i and T_h decrease from 354.9 and 514.3 °C to 269.8 and 452.7 °C, respectively. In addition, f(α) is [−ln(1 − α)]² for tri-fuel in most mixing ratios when α < 0.5, while f(α) becomes [−ln(1 − α)]³ at α > 0.5. At a high-HTB-level mixing ratio, increasing the OS content causes a decrease in activation energy to 35.87 kJ mol⁻¹. The moderate blending of oil sludge improves the pre-finger factor and the combustion performance.

In this study, the co-combustion of coal and biomass, and the tri-combustion of coal, biomass, and oil sludge in a 130 t h⁻¹ circulating fluidized bed (CFB) boiler are investigated via the computational particle fluid dynamics (CPFD) approach. Furthermore, the effect of biomass feeding position is also comprehensively evaluated. The results show that for the co-combustion of coal and biomass, the O₂ mole fraction at the furnace outlet rises from 0.0541 to 0.0640 as the biomass blending ratio enhances from 40% to 100%, while the CO₂ mole fraction reduces from 0.1357 to 0.1267. The mole fraction of NO_x and SO₂ at the furnace outlet decreases from 4.5867 × 10⁻⁵ to 3.9096 × 10⁻⁵ and 2.8253 × 10⁻⁴ to 4.6635 × 10⁻⁵, respectively. For the tri-combustion of three fuels, the average NO_x mole fraction initially grows quickly and then declines gradually, ranging from 4.1173 × 10⁻⁵ to 4.2556 × 10⁻⁵. The mole fraction of SO₂ at the furnace outlet increases from 3.5176 × 10⁻⁴ to 4.7043 × 10⁻⁴ when the ratio of oil sludge rises from 10% to 20%. The uniformity of temperature and gas components distribution is “new inlet > secondary air inlet > feed inlet”. As for the three inlet positions, the mole fractions of NO_x at the furnace outlet are between 3.9096 × 10⁻⁵ and 5.1537 × 10⁻⁵, while those for SO₂ are between 2.5978 × 10⁻⁴ and 2.5278 × 10⁻⁴.

Ammonia is an ideal renewable, carbon-free fuel and hydrogen carrier, which produces nitrogen and water after complete combustion in the presence of oxygen. However, ammonia has low reactivity, slow flame-propagation speed, and carries risks of high nitrogen oxide (NO_x) emissions. Co-firing ammonia with an industrial by-product gas (with CH₄ and CO being the main combustible materials) is a cost-effective and convenient method of improving the combustion characteristics of ammonia, but attention still needs to be paid to the NO_x generation. Currently, the research on NO_x formation during co-firing of ammonia with other fuel gases is still insufficient. In this study, a high-temperature furnace reaction system was used to investigate the NO_x formation and inhibition mechanisms during the combustion of NH₃/CH₄ and NH₃/CO mixtures. By varying the ammonia blending ratio, excess air coefficient (α), temperature, residence time, and fuel concentration, the key factors influencing NO_x generation and inhibition were further analyzed. The results showed that when α was no less than 1, the production of NO_x initially increased and then decreased with an increasing proportion of ammonia in the fuel gas. Within the temperature range of 900 °C to 1500 °C, the amount of NO_x generated during the combustion of the mixed gas gradually decreased with the increase in temperature. Under the conditions of NH₃/CH₄ and NH₃/CO, the emissions of NO_x were higher than those during pure ammonia combustion.

The octagonal tangentially fired boiler can be utilized for burning lignite with high moisture. Co-firing biomass in an octagonal tangential boiler is considered a promising approach. A numerical simulation is carried out in this study to analyze the impact of flue gas recirculation (FGR) and the biomass blending ratio on heat and mass transfer in an octagonal tangentially fired boiler. When the FGR rate increases from 0 to 30%, the maximum temperature in the boiler decreases from 2162.8 to 2106.5 K. Simultaneously, the average temperature of the center longitudinal section decreases from 1589.0 to 1531.9 K. The maximum fluctuation of the outlet flue gas temperature remains within 10.9 K for the four calculated working conditions. Consequently, the efficiency of the boiler is basically unchanged. However, the flue gas temperature at the furnace outlet decreases significantly from 1605.9 to 1491.9 K. When the biomass blending ratio increases from 0 to 20%, the mean temperature of the primary combustion zone decreases from 1600.5 to 1571.2 K.

The opposed wall-fired boiler is widely used in Chinese power plants due to its adaptability. However, deviations from design conditions can cause the reduction of combustion efficiency and combustion stability, and the overheating of heating surfaces. This study conducted numerical simulations on a 600 MW supercritical opposed wall-fired boiler at 75%, 50%, and 30% Turbine Heat Acceptance (THA) load conditions. The variation of temperature field and heat flux in the furnace under different loads, and parameters such as distributions of heat flux, temperature, and the stress of the high-temperature heating surface are analyzed. Results indicate that reducing the load from 75% to 30% THA lowers the furnace outlet temperature from 1158 to 1009 K and reduces the average gas temperature of the high-temperature heating surface from 1800 to 1570 K. Under a high load, the maximum heat flux concentrates on the side water-cooled wall of the combustion zone. However, when the load decreases, the heat absorption shifts towards the main combustion zone. Furthermore, under a high load, the average wall temperature of the high-temperature heating surface remains at 1600 K with a uniform temperature distribution. In contrast, when the load drops to 30% THA, significant temperature differences appear on the heating surface, with a maximum difference of 400 K. This leads to excessive expansion and slagging on the high-temperature heating surface, particularly in the middle and lower sections, due to the increased stress. These findings offer valuable insights for optimizing the combustion characteristics of opposed wall-fired boilers and preventing overtemperature explosions on the platen heating surface.

Gas-fired boilers, gas stoves, and wall-mounted gas boilers are the main consumers of gas fuel, but they generally encounter problems when operating at high altitudes, such as reduced thermal efficiency and increased pollutant emissions. Previous studies on gas combustion characteristics under sub-atmospheric pressure were mostly carried out in a large space, which is quite different from chamber combustion equipment. Therefore, it is insufficient to guide the design and operation optimization of plateau gas equipment. In this paper, experimentations were carried out to explore the characteristics of a methane diffusion flame under sub-atmospheric pressures. The mass flow rates of methane and air remain consistent under different pressure conditions. The centerline temperature ($T_c$) distribution, flame appearance, smoke point, CO emission, and NO_x emission under different pressures (ranging from 61.66 to 97.75 kPa) were examined under both fuel rich and lean conditions. The results show that $T_c$ at the rear and front of furnace variation with pressure is opposite under fuel-lean and -rich combustion. The $T_c$ at the front of furnace decreases with decreasing pressure, whereas $T_c$ at the rear of furnace increases with decreasing pressure. With decreasing pressure, flame length decreases under lean combustion, but increases under rich combustion. The smoke point fuel flow rate, flame length, and residence time increases with decreasing pressure, following the law of negative exponent. The CO emission decreases with decreasing pressure, which indicates that the reduced pressure makes methane combustion more complete. For NO emission, the reduced pressure results in an opposite tendency under fuel-lean and -rich combustion. With decreasing pressure, the NO emission decreases under fuel-lean combustion but increases under fuel-rich combustion.