Utility Boiler Research Articles

Numerical Simulation of the OFA Effect on Combustion in a 600 MWe Boiler with Centrally Fuel Rich Burners

ABSTRACT With the rapid development of renewable energy, the traditional coal-fired power generation plays an important role in peak regulation, which requires the boilers to operate at low load or even ultra-low load. In order to investigate the effect of over-fire air (OFA) ratio on the flow, temperature and component concentration distribution and the furnace exit parameters for utility boilers at ultra-low loads, a 600 MWe utility boiler with centrally fuel rich (CFR) burner technology is taken as the object of study, and numerical simulations are carried out for five operating conditions with different OFA ratios (0%–40%) at 25% of the boiler’s maximum continuous rating (BMCR) load. The results show that no obvious high-temperature region is formed in the furnace and the flow field distribution in the furnace exit area is not conducive to the stable combustion of pulverized coal when the OFA ratio is 0% and 10%. When the OFA ratio is 30%, the area of the high-temperature region in the furnace reaches its maximum. When the OFA ratio is 40%, the furnace exit NO concentration is only 94.54 ppm. With the increase of the OFA ratio from 0% to 40%, the temperature of the flue gas at the furnace exit decreases by more than 100 K, which may affect the stable operation of the Selective Catalytic Reduction (SCR) denitrification equipment. Taking into consideration the flow in the furnace, the combustion, the NO x emission, and other factors, the recommended OFA ratio is 20% ~30%.

Numerical simulation of ammonia combustion with coal in a 135 MW tangentially fired boiler

This study conducted a simulation of coal and ammonia co-combustion in a 135 MW tangentially fired utility boiler using Fluent. The combustion process was modeled using a gas-phase non-premixed approach based on finite-rate/turbulent dissipation. Additionally, NO generation and conversion were simulated through multi-step chemical reactions. Upon verifying the accuracy of the proposed model, the effects of ammonia co-firing ratios and injection modes on boiler combustion characteristics and NO emissions were investigated. The results indicate that as the co-combustion ratio increases, the boiler temperature decreases. Concurrently, NO emissions from the furnace exhibit a trend of initial decrease followed by an increase, reaching a minimum of 136.21 ppm at a mixing ratio of 15 %. With a co-firing ratio of 30 %, a significant reduction in NO emissions can be achieved by decreasing the proportion of primary and secondary air. As the excess air factor of ammonia decreases from 0.3 to 0.1, NO emissions initially decrease, followed by a subsequent increase. Overall, optimizing the ammonia injection mode and air distribution ratio can reduce NO emissions to below 220 ppm when the ammonia co-combustion ratio is below 30 %. This study serves as a valuable reference for retrofitting utility boilers for coal-ammonia co-combustion.

Techno-economic and environmental feasibility study of MILD combustion in domestic utility boilers under partial load operation

This paper aims to achieve the benefits of MILD combustion, such as enhanced thermal efficiency with simultaneous NOx reduction in existing conventional domestic hot water utility boilers which encounter partial heat loads. For this purpose, a system based on waste heat recovery and flue gas recirculation (FGR) is introduced to perform techno-economic and environmental studies under continuous fluctuations of heat load demand in a typical building at various climate conditions. Technical investigations on several types of utility boilers revealed that MILD combustion could be implemented only in modulation boilers, which can serve combustion stability requirements in turndown conditions due to partial load demands. Up to 6 % fuel saving, which aligns with a commensurate decrease in CO2 emissions and a minimum 75 % reduction in NOx emissions, is foreseeable by manipulating optimal FGR for each specific boiler in various climate conditions. Finally, economic investigation demonstrated that the payback period for the proposed revamped system is less than one year for most climates.

Retrofit and application of pulverized coal burners with LNG and oxygen ignition in utility boiler under ultra-low load operation

An oxygen-rich and low NOx burner integrated with liquefied natural gas (LNG) was proposed to address unstable combustion and high NOx emissions from a 330 MW subcritical boiler under ultra-low load operation in China. To assess the effectiveness of the retrofit, Chemkin and Fluent softwares were utilized to construct a new NOx model and calculate NOx generation, based on the combustion of pulverized coal gas and LNG. Further, an eddy dissipation concept (EDC) model, which can reflect detailed chemical reactions, was applied to calculate gas-phase reactions in the furnace. The results showed that when performing the deep peak shaving after the retrofit, the combustion in the furnace was stable under 50% or more load, and NOx emission level at the furnace outlet was lower than 350 mg/m3 (6% O2 content, dry basis). Under 25% load, the oxygen-rich burner integrated with LNG was applied, and the pulverized coal flow entered the furnace in a state of high-intensity combustion, which effectively promoted the stability of combustion in the furnace. The reductive combustion state with reductive free radicals generated by LNG decomposition inhibited NOx formation. Consequently, NOx emissions from the furnace outlet decreased from 380 mg/m3 to 316 mg/m3.

Numerical investigation of stable combustion at ultra-low load for a 350 MW wall tangentially fired pulverized-coal boiler: Effect of burner adjustments and methane co-firing

In the context of deep peak regulation, utility boilers are often required to operate at ultra-low loads, significantly deviating from their designed conditions, which can lead to unstable combustion or even furnace flameout. However, their operating characteristics at 20 % or even lower loads remain unclear. This study focuses on a 350 MW wall tangentially fired pulverized-coal boiler, exploring its combustion characteristics and pollutant emission patterns at 20 % ultra-low load. Through numerical simulation analysis of 14 different combustion scenarios, this research investigates the impacts of burner arrangements, burner horizontal swing angles (ranging from 5° to 20°), and methane (CH4) co-firing ratios (ranging from 0 % to 20 %, calculated by heat value) on flue gas temperature and main flue gas components (O2, CO, NOx, etc.). The results indicate that as the boiler load decreases to 20 %, the average flue gas temperature inside the furnace drops by about 200 K, accompanied by widespread flame impingement on the water-cooled walls, leading to decreased combustion stability of the pulverized coal. Operating only the lower two layers of burners can achieve a higher average flue gas temperature (1540 K) and lower NO emissions (294 mg/m3). Furthermore, setting the horizontal swing angle of the burners to 15° can mitigate the impact of flames on the water-cooled walls and elevate the flame center, with the average flue gas temperature reaching 1559 K, making it the recommended burner swing angle setting. As the CH4 co-firing ratio increases from 0 % to 20 %, the average flue gas temperature rises by 50 K, and the emissions of NO and CO2 decrease by 15.3 % and 6.2 %, respectively, while H2O concentration increases by 21.3 %, potentially leading to low-temperature corrosion issues. The recommended CH4 co-firing ratio is 15 %.

Integrated Gasification of Biomass Residues (IBGCC)

A comprehensive outline of a new approach in integrated gasification of biomass residues including the material flow management in urban areas being targeted on the generation of electricity and district heating is presented. The feedstock is derived from civilian material by fully automated collection, sorting and separation. Thereby an outward transfer of inerts is executed, such as minerals, metals, glass and electronic scrap as well as sorted plastics being object to recycling. Finally a ligno cellulosic and a non-lignocellulosic fraction are gained. The for mer one is suitable for thermochemical conversion, the latter one for biological conversion into fuel gases which subsequently are oxidised completely at low air excess in a horizontally arranged cyclone combustion chamber. The heat recovered from the flue gases in the utility boiler is used to generate steam scooping in the supply of electricity and district heating. The basic design is scaled to an overall thermal capacity of 2-5 MW. This type is most capable of utilising renewable energy by converting the organic fractions of civilian material flows. The power plant is based on a reliable technology representing an on-site integrated biomass gasification combined cycle system including peripheral units specified for the treatment of complementary materials.

Direct numerical simulation of the drag, lift, and torque coefficients of high aspect ratio biomass cylindrical particles

Biomass straw fuel has the advantage of low-carbon sustainability, and therefore, it has been widely used in recent years in coupled blending combustion with coal-fired utility boilers for power generation. At present, the drag force FD, the lift force FL, and the torque T evaluation model are very limited. In this study, within a wide range of Reynolds numbers (10 ≤ Re ≤ 2000) and incident angles (0° ≤ θ ≤ 90°), the computational fluid dynamics open source code OpenFOAM-body-fitted mesh method is used to carry out the direct numerical simulation of the flow characteristics of large cylindrical biomass particles with a high aspect ratio of L/D = 9:1. The results show that (1) the projected area of the cylinder begins to decrease after reaching the maximum at θ = 15°, while the change in the incident angle causes the formation of a smaller recirculation zone on the leeward side of the structure, and the effect of the pressure difference on the drag coefficient (CD) is reduced. (2) The lift coefficient (CL) displays a parabolic symmetric distribution when θ = 45°, and then the distribution becomes asymmetrical when Re > 100. The torque coefficient (CT) exhibits a similar trend. (3) Based on the simulation data and the literature data, new models for CD, CL, and CT for cylinders with L/D = 9:1, 10 ≤ Re ≤ 2000 and 0° ≤ θ ≤ 90° are obtained, and the mean square errors are 2.4 × 10−2, 1.4 × 10−2, and 6.4 × 10−2, respectively. This new model can improve the accuracy and adaptability of the universal model of gas–solid dynamics for biomass particles.

A study of co-firing palm kernel shell on the Nagan Raya coal-fired power plant

Co-firing biomass with coal in existing utility boilers is seen as one strategy for promoting renewable energy with low upfront costs and little to no impact on the boilers' high efficiency. The purpose of this research is to analyse the fuel characteristics and performance of palm kernel shell co-firing at Nagan Raya Coal-Fired Power Plant (CFPP) at various percentages of palm kernel shell combination. The analysis is conducted based on the operational data obtained from Nagan Raya Power Plant. In this study, the characteristics of fuel and the performance of a power plant are analysed based on percentages of fuel variations, namely 100% coal, 95% coal-5% palm kernel shell, and 90% coal-10% palm kernel shell. The results reveal that co-firing's biomass ratio boosted operation parameters, including main steam pressure, temperature, and flow rate. Subsequently, co-firing with 90% coal-10% palm kernel shell has enhanced the power plant output to 90,7 MW compared to those with 100% coal, 95% coal-5% palm kernel shell, namely 89,3 MW and 90,4 MW, respectively

NOx formation model for utility boilers using robust two-step steady-state detection and multimodal residual convolutional auto-encoder

BackgroundTo achieve carbon neutrality, thermal power plants will take on greater peak-shaving responsibilities, resulting in utility boilers running at more frequently-changing states. This variation inevitably contributes to dirtier measurement data, and the data will follow new distributions that represent asynchronous operational characteristics. MethodTo predict the NOx formation concentration in this new context, a novel modelling framework is proposed. First, a two-step steady-state detection algorithm, including a basic and a precise identification procedure, is proposed to select steady-state samples from operational data. This algorithm also combines with a bayesian optimization–variational mode decomposition (BO–VMD) approach to enhance its robustness by eliminating high-frequency noise, and with an empirical cumulative distribution based outlier detection (ECOD) to remove outliers. Therefore, a high-quality steady-state dataset is acquired. Based on these data, a multimodal residual convolutional auto-encoder is developed to extract the latent variables that vary with the operation modes. These variables are then used to construct the multimodal NOx prediction model. Significant findingsThe findings on a 660 MW utility boiler reveal that, the proposed modelling framework has a lower misdiagnosis rate in steady-state identification compared to the one-step detection technique, and achieves higher fitting and generalization accuracy than the global modelling method.

Aerovalved Pulse Combustor for Enhancing Efficiency and Sustainability of Fossil Energy Conversion

Abstract The paper actualizes earlier research in developing a pulse combustion technique for enhancing the efficacy of utility and industrial boilers and furnaces. Some unpublished results of the experimental investigation of self-sustained pulsating combustion of a gas fuel in an aerovalved pulse combustor (PC) are presented. Relationships have been established between all important design and operating parameters and the combustion characteristics. It was demonstrated that a well-designed pulse combustor can operate efficiently in a stable self-pumping regime in a wide range of operating conditions with the loading from 20% to 100% of the maximum power. While a PC can operate autonomously as a gas burner, the present focus is on their use for mitigating slug and ash deposits on heating surfaces of coal- or biomass fired power and industrial boilers, thus providing an alternative to the proven detonation pulse (DPC) or other techniques for on-line cleaning of heating surfaces during the operation of power and industrial boilers.

Synergistic reduction of SO2 emissions while co-firing biomass with coal in pilot-scale (1.5 MWth) and full-scale (471 MWe) combustors

The objective of this study was to understand the synergistic effect of sulfur dioxide (SO2) emission reduction during the combustion of biomass-coal blends in comparison to pure coal by recording the gaseous SO2 concentrations, analyzing the composition of combustion ash by energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), and simulating and verifying the fate of sulfur by a thermodynamic equilibrium software (FactSage). In Set A experiments, five combinations of coal and steam-exploded biomass (100/0, 75/25, 50/50, 25/75, 0/100 in percentages by mass) were co-fired in a 1.5 MWth pilot-scale combustor. In Set B, pure coal (100/0) and an 85/15 percent mass blend of coal and torrefied biomass were co-fired in a 471 MWe utility boiler. Woody biomass contains lower amounts of sulfur compared to coal and the linear lowering of SO2 emissions as a result of co-firing is called the dilution effect. For Set A tests, FactSage predicted, and ash analysis confirmed that calcium was primarily responsible for the synergistic emission reduction (beyond dilution effect) in all the blends, except in pure biomass, where potassium was responsible. During pure coal combustion, 41.1% of the sulfur in the system was absorbed in the ash, compared to 97.0% during pure biomass testing. In Set B tests, the 85/15 coal-biomass blend, showed a 28.1% reduction in SO2 emissions along with a 22.1% reduction in the lime slurry utilization at flue gas desulfurization (FGD) towers compared to pure coal, which is equivalent to saving 7.4 L of lime slurry per MWe-hour. The results suggest that blending woody biomass with coal can help coal-fired utility boilers meet environmental emission standards and reduce desulfurization costs. These results are important since the current literature is deficient in research conducted at suspension-fired full-scale boilers to reduce SO2 emissions by co-firing coal and biomass blends.

Integration of carbon capture in a pulp mill—effect of strategic development towards better biomass resource utilization

The pulp and paper industry has an important role in the industrial transition towards net zero or negative emissions, given its renewable biomass-based feedstock and energy supply. In particular, pulp and paper mills have large existing sources of biogenic CO2, with a high potential to contribute to carbon dioxide removal through carbon capture and storage (CCS). To effectively navigate anticipated changes in feedstock and energy markets, there is a need for a better understanding of how different technology pathways for the pulp and paper industry interact with one another, for instance, how enhanced valorization of biomass side streams may affect the potential for carbon capture. This paper aims to investigate the effect of combining carbon capture with lignin extraction in a chemical pulp mill. Pinch analysis is used to study how the targets for heat recovery, fuel usage and electricity generation, are affected by different mill and capture configurations. Based on these results, the effect on carbon flows is evaluated. The results show that when carbon capture technology is implemented and fuel use is minimized at the case-study mill, there is still enough heat available from the recovery boilers to supply the process needs without requiring usage of a utility boiler. However, when carbon capture is combined with lignin extraction, the heat production of the recovery boilers is no longer sufficient to cover the process demands, and additional heat from a utility boiler is required. However, this case implies that some of the carbon leaves the mill embedded in the extracted lignin product, which can be expected to have a higher value than captured carbon dioxide. When back-pressure electricity production was maximized for the different mill configurations, a very high fuel-to-electricity efficiency could be achieved, but since the CO2 emissions from the utility boiler were not assumed to be captured, this would lead to more carbon being emitted compared to the capture scenarios with minimized fuel use.

Ammonia blend ratio impact on combustion characteristics and NOx emissions during co-firing with sludge and coal in a utility boiler

This study investigates the effects of the ammonia blend ratio and the number of nozzle layers on boiler combustion characteristics and NOx emissions by the computational fluid dynamics simulation method. The conclusions indicate that, as ammonia is injected from a single-layer of secondary air nozzles, with the ammonia blend ratio increases, the combustion temperature decreases, when the blend ratio is 60%, the combustion temperature decreases by about 300 K. When ammonia is injected into the furnace from multiple-layers of nozzles, and under the premise of the same ammonia blend ratio, the overall impact on the furnace temperature is smaller than that of ammonia entering from a single-layer of nozzles. When the blend ratio of the ammonia is 40%, the NOx emission of ammonia entering the furnace from two layers of secondary air nozzles is about 22.47% higher than when it is injected into the furnace from a single-layer of nozzles. After raising the ammonia mixing ratio, the NOx at the furnace outlet shows an inverted-parabola change, which first decreasing and then increasing.

Numerical simulation of ammonia combustion with sludge and coal in a utility boiler: Influence of ammonia distribution

The co-combustion of solid fuel and ammonia can effectively reduce carbon emissions. There is relatively little research on the co-combustion of ammonia and solid fuel in thermal power plants. The effect of ammonia distribution on co-combustion was studied by CFD simulations. Results show that in the main combustion region, solid fuel combustion with ammonia inevitably exacerbates incomplete combustion of fuels, and the maximum temperature difference in the same region of the furnace is about 18.8%. Ammonia can not only suppress NOx emissions but also promote NOx emissions, depending on the ammonia distribution method. Ammonia injected from secondary air nozzles in the top layer is the optimum distribution method of solid fuel co-combustion with ammonia. Compared to ammonia injected from secondary nozzles in the bottom layer, the emission of NOx is decreased by about 16.3%. This study will provide guidance and a theoretical basis for discussing the feasibility of co-combustion of solid fuel and ammonia in utility boilers.

Creating an Advanced Sensor Network to calculate real-time, mass-weighted flue gas composition and air heater leakage of a coal-fired utility boiler under dynamic operating conditions

Utilization of renewable energy sources to minimize the environmental impact of energy production has changed the way utility boilers operate, requiring frequent load cycling between full load and partial loads as low as 30%. Dynamic operation of coal-fired utility boilers significantly reduces boiler efficiency when compared to steady state at full load. Data-driven plant optimization has shown success with coal-fired utility boilers under dynamic operating conditions. The purpose of this work was to create an Advanced Sensor Network (ASN) to provide more extensive real-time data to inform dynamic plant optimization of Net Unit Heat Rate (NUHR). The ASN consists of gas sampling grids in the convective pass of the boiler and downstream of the air heater. These sampling grids allow for quantification of spatial variation of flue gas within the boiler and calculation of mass-weighted composition of flue gas through the combination of composition, velocity, and temperature measurements. The comparison of O2 between the inlet and outlet of the air heater is used to calculate air leakage in real time. Flue gas composition and air heater leakage are both important factors in boiler efficiency and NUHR.The results of this work support the value of mass-weighted averages for determining flue gas composition accurately. The measurements from the ASN show increased composition stratification during dynamic operation, with an average standard deviation 38% higher than observed during steady-state operation. Air heater leakage was also observed to increase from 2.8% to 5.1% following a load change. Prior to the installation of the ASN, these data would not have been available for dynamic control. These real-time data will be leveraged to calculate and optimize for NUHR during dynamic operation in future work.

Numerical research on ammonia-coal co-firing in a 1050 MW coal-fired utility boiler under ultra-low load: Effects of ammonia ratio and air staging condition

Co-firing ammonia (NH3) with coal for thermal power generation is a promising strategy for achieving global carbon neutrality. However, the drawbacks of NH3 combustion (e.g., narrow flammability limits, low theoretical flame temperature, high NOX emissions, etc.) can negatively impact the performance of coal-fired boilers, particularly for large-scale ones operating under ultra-low loads. As such, this study was conducted to investigate the ultra-low-load combustion characteristics of a 1050 MW coal-fired boiler when employing NH3-coal co-firing technology. Three-dimensional numerical simulations of ten combustion scenarios were performed to examine the effects of the NH3 co-firing ratio (ranging from 0% to 80%, by calorie) and air staging condition (Separated Over Fire Air (SOFA) ratio ranging from 4% to 24%) on temperature, gas species distributions, and emissions. Results show that as the NH3 co-firing ratio increases to 80%, the in-furnace average gas temperature decreases by 100 ∼ 200 K. The oxidation of NH3 takes precedence over the reduction of NO with NH3, leading to a surge in NO emissions· NH3 slip can be prevented at ultra-low loads due to the rapid consumption of NH3 near coal burners. Meanwhile, CO2 emissions reduce to 20% of that observed in pure coal firing. The increased H2O content in flue gas promotes coal burnout through the water–gas reaction, while the high H2O emissions may potentially cause low-temperature corrosion. At a SOFA ratio of 16%, a relatively large high-temperature region is achieved in the furnace, indicating more stable combustion under ultra-low loads. Excessively small or large SOFA ratios can reduce combustion intensity in the primary combustion zone while contributing to lower NO emissions.

Influence of Central Air on Flow and Combustion Characteristics and Low-Load Stabilization Performance of a Babcock Burner

On a cold single-phase test stand, the effect of central air on the exit flow field of Babcock, Germany, burner was investigated. Industrial measurements were taken for a 700 MW wall-fired pulverized-coal utility boiler with above burners. Gas temperature, gas composition and concentration in the burner area were measured at 444 MW, 522 MW and 645 MW loads, respectively. Only when the central air mass flow was zero did a center reflux zone exist in the burner outlet area. The steady combustion of faulty coal was aided by early mixing of primary and secondary air, which was made possible by the decreased central air mass flow. At all different loads, the pulverized coal in center region took a long distance to ignite. The temperature in center steadily dropped as central air mass flow decreased, while the temperature in secondary air region gradually rose. Within 1.5 m from the primary air duct outlet, the highest CO concentration was 25 ppm and the highest O2 concentration was close to 21% under all loads. The gas concentration near sidewall was more influenced by load. With all valves opening of burner center air at 30%, the boiler was able to operate safely and stably without oil at a load of 262 MW. The furnace chamber temperature in burner area reached 1056.1 °C.

A novel NOx emission prediction model for multimodal operational utility boilers considering local features and prior knowledge

This study proposed a data-driven NOx modelling framework that could capture the multimodal operational characteristics of a utility boiler, improve the training sample quality and strengthen the model interpretability. With this framework, to obtain a high-quality steady-state dataset from operational data, a multivariate F-test algorithm, which enhanced robustness by introducing the minimal number of stable units (MNSU) and the variational mode decomposition (VMD) outlier detection method, was first proposed. Based on the obtained sample, a Gaussian mixture model (GMM) was established to classify the data by their operational modes. In addition, the least absolute shrinkage and selection operator (LASSO) algorithm was employed to select specific features for each mode. Finally, the NOx prediction model was constructed using the light gradient boosting machine (LightGBM) model integrated with prior knowledge. The mechanistic relationships between the selected features (i.e., the oxygen content and separated overfire air damper opening) and target variable (i.e., NOx) were considered as the constraint conditions. By taking a 660 MW utility boiler as the research object, the proposed modelling framework obtained R2, RMSE and MAE values of 0.979, 3.573 mg/m3, and 2.586 mg/m3, respectively, performing better than five comparison models.

Intelligent Testing and Analysis of Dissimilar Steel Welds for Industrial Throttle Flowmeter

The throttling flowmeter used in utility boilers has been used as a measuring instrument for a long time. However, its safety performance, such as welding, lacks enough attention. The manufacturing welds of the throttling flowmeter are welded with austenitic stainless steel and pearlitic heat-resistant steel. Cracks and other defects are generally found in the inspection and detection of the manufacturing welds of throttling flowmeters in service, which have serious potential accidents. To find out the relationship between weldingdissimilar steels and defects, the microhardness indentation method was used to measure the residual stress of welding. Combined with the self-developed calculation software of microscopic indentation residual stress distribution, we used the difference between the color of the indentation area and the surrounding area to quickly measure the indentation strain collected by the microscope using the computer image recognition algorithm, which greatly improved the accuracy and speed of the microscopic indentation residual stress test. The results show that the residual stress at the weld of dissimilar steel is relatively large, and the mechanical property test is generally unqualified. The microindentation residual stress analysis method based on computer image recognition is used to quickly, intuitively, and accurately reveal the direct relationship between the combination of dissimilar steel welding materials and the generation of cracks and other defects.

An improved index to predict the slagging propensity of woody biomass on high-temperature regions in utility boilers

Ash deposition-related issues adversely affect the thermal transfer and cause corrosion to biomass fired utility boilers. Various models have been proposed to estimate the slagging propensities for firing biomass fuels of different origins. However, there is no reliable general applicable method that is available for assessing biomass fuel slagging propensities without carrying out extensive experimental testing. In addition, empirical correlations developed for coal produce large inaccuracies when applied to biomass. In this paper, a predictive slagging index, In, has been built by analysing the slagging formations of a range of woody biomass fuels, using the thermodynamic equilibrium modelling tool FactSage, together with the partial least squares regression (PLSR) coupled with cross-validation. The new index has been validated and supported by experimental observations from various literatures. The results obtained with the new index showed a substantially greater success rate in predicting the woody biomass ash slagging propensity when compared with the experimental observations from the literature than the other five conventional slagging indices. The predictive index, In, also successfully predicts the slagging propensities with high accuracy when extended to the application of herbaceous biomass and blended fuel between woody biomass and peat.