Circulating Fluidized Bed Combustion Research Articles

Thermal-hydraulic calculation and analysis on evaporator system of a 660 MWe ultra-supercritical CFB boiler

Ultra-supercritical circulating fluidized bed (CFB) boilers have great commercial potential in large-scale clean utilization of low-quality fuels. Evaporator system is one of the keys in the combination of ultra-supercritical steam cycle with CFB combustion technology. Aiming at examining the thermal-hydraulic characteristic of the evaporator system of the conceptual design of a 660 MWe ultra-supercritical CFB boiler, a mathematical model was developed in this paper. A semi-empirical bed-to-wall heat flux model and a set of empirical correlations available for heat transfer and hydraulic resistance calculation were embedded in the thermal-hydraulic model. By iteratively solving the model, the thermal-hydraulic parameters of the evaporator system at different operating loads, including total pressure drops, mass flux distribution, and metal temperature were obtained. The results exhibit good flow distribution characteristic and low temperature deviations in the evaporator system. The outlet fluid temperature deviation and metal temperature in the evaporator system are both permissible, implying that the conceptual design of the evaporator system of the 660 MWe ultra-supercritical CFB boiler is acceptable.

Carbon dioxide fixation via accelerated carbonation of cement-based materials: Potential for construction materials applications

This study evaluated the CO2 absorption capacity of various inorganic materials commonly used as construction materials. This study compared and examined changes in the physicochemical properties of argon oxygen decarburization (AOD) slag, research cement (RC), ground granulated blast-furnace slag (GGBFS), and circulating fluidized-bed combustion (CFBC) ash in carbonation reactions. The carbon capture capacity was determined for all four materials. CFBC possessed the highest CO2 uptake (wt%), followed in descending order by RC, AOD slag, and GGBFS. However, the paste that 50% AOD slag mixed with 50% RC (AOD50RC50) featured the greatest improvement (92.95%) in strength development properties after carbonation curing. Compressive strength increased in RC100, GGBFS50RC50, and CFBC50RC50 by 6.05%, 3.29% and 15.92%, respectively. These results arose from differences in carbonation reaction mechanisms and products between the various materials. γ-C2S, the major component of AOD slag, produced CaCO3 and silica gel via carbonation; silica gel increased the compressive strength.

Utilization of CFBC Fly Ash as a Binder to Produce In-Furnace Desulfurization Sorbent

Circulating fluidized bed combustion (CFBC) power generation technology is known to efficiently reduce the emission of air pollutants, such as SO2 and NO2, from coal combustion. however, CFBC coal ash contains high contents of free CaO, making it difficult to recycle. This research has been conducted to find ways to use the self-hardening property of CFBC coal ash, one of its inherent characteristics. As part of these efforts, the present study intended to investigate the properties and desulfurization efficiency of Ca-based desulfurization sorbents using CFBC fly-ash as a binder. Limestone powder was mixed with CFBC fly-ash and Ca(OH)2 to fabricate desulfurization sorbents, and it generated hydrate of cement, including portlandite, ettringite, and calcium silicate, etc. The compressive strength of the desulfurization absorbent prepared by CFBC fly ash and Ca(OH)2 was 72–92% that of the desulfurized absorbent prepared by using general cement as a binder. These absorbents were then compared in terms of desulfurization efficiency using a high-temperature fluidized bed reactor. It was confirmed that the desulfurization absorbents fabricated using CFBC fly-ash as a binder achieved the best performance in terms of absorption time, which reflects the time taken for them to remove over 90% of high-concentration SO2 gas, and the conversion ratio, which refers to the ratio of CaO turning into CaSO4.

Effective adsorption of lead ions using fly ash obtained in the novel circulating fluidized bed combustion technology

Fly ash was examined for the separation efficiency of Pb2+ ions from water in batch experiments. Fly ash is industrial waste produced from the incineration of sewage sludge by the novel circulating fluidized bed combustion (CFBC) technology and was taken into the experiments. Physical and chemical properties of the material were characterized using several methods, such as fraction analysis, particle size distribution, bulk density, composition, morphology, surface and internal structure by elemental analysis, FT-IR, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis, comprehensive thermal analysis, fly ash texture by BET adsorption isotherms, specific surface area, volume of pores, average pore diameter and pore volume distribution by the BJH method. The influence of pH values on zeta potential of the fly ash surface before and after the adsorption process was conducted. The calculated maximum adsorption capacity of Pb2+ by fly ash reached 51.98 mg/g. The kinetic analysis revealed that the adsorption process is better described by the pseudo-second order equation and it is well fitted to the Freundlich model. In conclusion, fly ash obtained in the CFBC technology is a promising low cost adsorbent for the highly effective recovery of Pb2+ from wastewater.

Geopolymerization enhanced hydrothermal synthesis of analcime from steel slag and CFBC fly ash and heavy metal adsorption on analcime

ABSTRACTThis work is focused on crystal phase transition of solid wastes and functional application of crystal analcime in waste water purification, which provide a new environment-friendly route. In this paper, analcime was synthesized from steel slag and Circulating fluidized bed combustion (CFBC) fly ash (CFA) by hydrothermal method enhanced via geopolymerization (non-crystallized process). Then the analcimes were used for the removal of heavy metal ions (Pb2+, Cu2+) in aqueous solutions. Both the raw materials and products were characterized by XRF, XRD, FT-IR, SEM-EDS, and TEM. The results showed that non-crystallized process reduced the time of hydrothermal reaction and promoted the purity of analcime. The adsorption kinetics of analcime were all well fitted the pseudo-second-order model, and adsorption isotherms were well described by the Langmuir model. The maximum adsorption capacity of analcime for Pb2+ and Cu2+ were around 75.76, and 21.83 mg/g, respectively. The preference order observed for adsorption is Pb2+ > Cu2+.

STUDI KELAYAKAN PEMBANGUNAN PEMBANGKIT LISTRIK TENAGA UAP 2X50 MW DENGAN MENGGUNAKAN BOILER CIRCULATING FLUIDIZED BED COMBUSTION DI KENDARI, SULSELRABAR

This research is an explanation from feasibility study of the project; Which aims to analyze the feasibility of financially the development of Power Plant (PLTU) Capacity 2 × 50 MW by using boiler circulating fluidized bed combustion (CFB). Indicators used to analyze the feasibility of Power Plant (PLTU) Capacity 2 × 50 MW are: payback period, net present value (NPV), internal rate of return (IRR), sensitivity analysis, variable operating costs, and fixed operating costs. This research analyzes investment feasibility and risk from financial aspect by considering interest rate of loan (in USD) equal to 6% per year. The calculation of the value of investments made amounted to 1074.63 USD / kW, and net present value (NPV) of 61.8270 million USD with an internal rate of return (IRR equity) of 14 percent, and the results of this study has also been calculated payback period (PP) during 6.69 years, very feasible, because it is shorter than the project age (30 years); Then it can be concluded that the tariff of selling electricity after levelized is 8.1582 Cent US $

Combustion Characteristics and Pollutants in the Flue Gas During Shoe Manufacturing Waste Combustion in a 2.5 MWth Pilot-Scale Circulating Fluidized Bed

Shoe manufacturing waste (SMW) was combusted in a 2.5 MWth pilot-scale circulating fluidized bed combustor (CFBC) to demonstrate the feasibility of energy recovery and provide useful information for a fluidized bed combustor design specifically for this waste. The experimental results confirmed that the stable combustion could be achieved in this CFBC with a constant feed flow rate of 400 kg/h, a primary air flow rate of about 1650 Nm3/h and a second air flow rate of about 1800 Nm3/h. The pollutants in the flue gas (ITFG) were measured with the average values of CO2 at 9.9%, CO at 2145.04 ppm, NOx at 81.67 ppm, SO2 at 32.62 ppm, HCl at 3.12 ppm, HF at 0.57 ppm, Pb at 0.0029 mg/m3, Cd < 0.001 mg/m3, Hg at 20.938 ng/Nm3, and PCDD/ PCDF at 1.17E−03 ng TEQ/m3, respectively. CO and SO2 emissions exceeded the legal limits in China, while the combustion efficiency was relatively low. Therefore, in order to meet the CO emission limit, some useful suggestions were put forward for the future CFBC design to burn SMW. A flue gas desulfurization system is essential to reduce the SO2 emission. Very low Cu content, high level of residual carbon in the fly ash and high SO2 concentration ITFG resulted in low PCDD/PCDF emission.

Characteristics of co-combustion of strongly caking and non-caking coals in a pilot circulating fluidized bed combustor (CFBC)

Co-firing of Russian caking coal with non-caking coals (mixtures of Australian bituminous and Korean anthracite coals) was performed on a pilot scale using a circulating fluidized bed combustor (CFBC). The free swelling index (FSI) of caking coal was very high and the alkali index of non-caking coals was relatively high. However, stable fluidization and combustion were attained using various coal blends (containing up to 20 wt% of strongly caking coal). The average particle size in bottom ash increased slightly as the proportion of caking coal increased, triggering a slight temperature rise in the lower part of the combustor. Scanning electron microscopy/energy dispersive spectrometry and X-ray diffraction analyses of coarse particles showed that Al-rich bottom ash captured problematic K to form kalsilite (KAlSiO4), with a melting point much higher than the operating temperature of a typical CFBC. Such data strongly suggest that stable CFBC co-combustion is possible using mixtures featuring strongly caking coals. The unburnt carbon content of fly ash and the O2 concentration in flue gas at the steady state increased linearly as the proportion of caking coal increased, indicating reduced co-combustion of caking coal. Morphological analyses of unburnt carbon in bottom ash revealed that pore clogging progressed on addition of caking coal, decreasing char reactivity by blocking oxygen access during co-combustion. In terms of pollutants, NO emission from fuel N in flue gas increased slightly on addition of caking coal, but N2O emission decreased slightly, attributable to a temperature rise in the dense combustor bed. However, the conversion rate of fuel S to SO2 did not significantly change when the proportion of caking coal increased.

Failure evaluation of SA 210C riffle water wall tubes in 70 MW CFBC boiler

Abstract Boiler tubes used as water walls made up of ferritic steels is having some finite life, because of prolonged exposure in the furnace at elevated temperature, stress and aggressive environment, tube failure taking place. Now a day's premature failure of the boiler tube mainly in water walls is one of the very common phenomena in the thermal power plants. The present investigation was done on the as-received ASTM SA 210C failed boiler tube steel used as water walls in the Circulating Fluidized Bed Combustion (CFBC) coal fired thermal power plant. An attempt has been made to understand the cause, because identifying correct failure mechanism often helps to perform meaningful life assessment and also to prevent the future Boiler Tube Failure (BTF). The as-received of failed tube along with the parent (unused) tube from the water wall raiser panel were selected to study for mechanical and metallurgical properties. Tensile test and micro hardness examinations were carried out on both the parent tube and failed tube. Visual examination reveals “fish-mouth” appearance of the as-received failed tube because of short-term overheating. The micro structure of the parent metal has the conventional structure of ferrite (white constituent) and pearlite (dark constituent), whereas for the as- received failed tube reveals Widmanstatten ferrite. A detailed structure - property relationship has been made by using the combined techniques of Optical Microscopy (OM), SEM/EDAX and XRD. Tensile fractography depicts the presence of micro-voids coalescence in the fibrous network shows ductile mode failure in the as-received failed boiler tubes.

Effect of chemical additives on hard deposit formation and ash composition in a commercial circulating fluidized bed boiler firing Korean solid recycled fuel

Combustion of SRF (solid recycled fuel) and biomass with potassium (K), sodium (Na), and chlorine (Cl) contents can result in operational problems such as hard deposit formation and convection pass tube corrosion. Two types of commercially available chemical additives, ammonium sulfate [(NH4)2SO4] and borax solution, were examined to elucidate their effect on hard deposit formation and the particle composition of fly ash on the convection pass of a commercial CFBC (circulating fluidized bed combustion) boiler. The addition of ammonium sulfate/borax solution hindered metal chloride formation and reduced the amount of hard deposit formation on the convection pass tubes. Both the alkali and potassium chloride content and the point load hardness of the hard deposit were reduced, while the melting temperature increased according to the borax solution use. When chemical additives were employed, the particle size distribution of the fly ash shifted to coarse particles. In particular, SEM (scanning electron microscopy) images of the fly ash particles revealed the attachments of fine particles to the ash particles. These were assumed to be mineral salts attached to the coarse particles, which increased the overall particle size distribution.

Characteristics of Fly Ash under Oxy-Fuel Circulating Fluidized Bed Combustion

The objective of the present paper is to study the physiochemical properties of fly ash under oxy-fuel circulating fluidized bed (CFB) combustion mode. Tests were conducted in a 50 kW oxy-fuel CFB combustor under both air and oxy-fuel combustion. The analyses of the collected fly ash samples included particle size analysis, N₂ adsorption analysis, char carbon, inductively coupled plasma optical emission spectrometry (ICP-OES) , and X-ray diffraction (XRD). It was found that the d₁₀, d₅₀, and d₉₀ of fly ash under oxy-fuel combustion mode were larger than that under air combustion mode and increased with the rise of the inlet oxygen concentration. The Brunauer–Emmett–Teller (BET) surface area, pore volume, and pore size of fly ash under air combustion are almost the same with that at inlet oxygen concentration of 30%. The element mass concentrations were obviously different between the two combustion modes, but the main mineral phase was insignificantly different. Moreover, the inlet oxygen concentration has no significant effect on the element mass distribution in the fly ash, except for the alkaline earth metal under oxy-fuel combustion.

Influence of Indian lignite on gas solid hydrodynamics of a 210 MW CFB riser

The circulating fluidized bed combustion (CFBC) technology is better alternative to be adopted for generating power than PC fired boiler technology due to several advantages in which mainly fuel flexibility, environmentally friendly and low cost compared to combination of PC fired boiler with FGD for similar environmental performance. Unlike PC fired boilers, CFB boilers are suitable for low grade fuels like lignite. The huge availability of lignite in India reduces the import cost of bituminous coal which is regularly supplied as a fuel for PC fired boilers from other countries. The objective of the present paper is that the study of gas solid behaviour in 210 MW CFB riser by using mathematical equations. In this study, the key parameters of hydrodynamics (suspension density, local voidage, pressure drop) which are affecting the design and performance of CFB boiler are studied at different height levels of riser. Three Indian lignite samples (Tamilnadu, Gujarat and Rajasthan) which are successfully used in commercial operations of CFB boiler in India are assumed for this study with two mean particle diameters. This work is also determined and compared the heat transfer coefficients of boiler elements (water wall, wing wall and furnace superheater) placed in the riser.

Combustion as a Possible Solution to Pyrolytic Wastewater Utilization

Treatment of hazardous liquid wastes can never be considered as economically beneficial process. It often involves many different treatment steps, especially in the case of highly polluted industrial wastewaters like pyrolytic wastewater (WW) from shale oil production. Currently in Estonia approximately 0.15 million tonnes of this pyrolytic water is generated annually. In the future according to the Estonian National Development Plan for the Use of oil shale this amount is expected to increase by 5 to 6 times (Anon 2016). The current paper presents the experimental results of wastewater incineration as an alternative approach to water purification. Combustion of this pyrolytic WW was carried out in a pilot-scale 60 kWth circulating fluidized bed (CFB) combustor firing oil shale or with propane. The influence of the flow rate of pyrolytic water (up to 0.36 kgwater/kgos) on gaseous emissions was studied. The results show that incineration of this highly polluted pyrolytic water under studied conditions in CFB combustor fed with oil shale does not pose environmental risks as intensive heat and mass transfer allows almost complete combustion of VOC’s. Due to the chemical composition of oil shale ash, SO2 formed during WW incineration was bound to the oil shale ash resulting zero SO2 emissions. Only NOx emissions were increased by up to 1.8 times at highest pyrolytic water loading.

Effects of sulfate rich solid waste activator on engineering properties and durability of modified high volume fly ash cement based SCC

The engineering properties and durability of high volume low calcium fly ash (HVFA) cement based self-compacting concrete (SCC) modified with addition of circulating fluidized bed combustion (CFBC) fly ash were explored. Experimental results showed that an addition of CFBC fly ash did not influence the stability and passing and filling abilities of modified HVFA cement based SCCs. But its presence significantly improved the compressive strength, bonding behavior, and durability of the hardened SCC specimens. The added small amount of CFBC fly ash was found to increase the earlier compressive strength of hardened SCC specimen at one day of curing up to 43.8% higher than that of the control SCC specimen, which indicates a remarkable contribution of CFBC fly ash addition to shortening the time of construction. At ages of 3, 7, and 28 days, such increases were up to 30.2%, 22.3%, and 17.8%, respectively.

Mechanism for Migration and Layer Growth of Biomass Ash on Ilmenite Used for Oxygen Carrier Aided Combustion

Biomass is recognized as a CO2-neutral energy resource. However, biomass is a challenging fuel to combust because of its heterogeneity with regard to the content of inorganic constituents, volatiles, and moisture. Oxygen carrier aided combustion (OCAC) is a process advancement that provides enhanced combustion in existing circulating fluidized bed (CFB) units. The oxygen carrier has a central role in the OCAC concept through the oxygen transport it provides. The natural mineral ilmenite (FeTiO3) has been identified as a promising potential oxygen carrier. In order to ensure the feasibility even for long-term operation in industrial-scale processes, it is imperative to understand the evolution of the material during an OCAC process. In the present study, ilmenite was used as the bed material in the Chalmers 12 MWth CFB boiler during OCAC with woody biomass as fuel. Bed material samples were extracted from the bed inventory at different time intervals ranging from 5 to over 300 h. This paper proposes a mechanism for migration and layer growth of biomass ash on the ilmenite used as the oxygen carrier in a CFB combustor. It was found that with increased time of exposure, potassium migrated into the particle core. Longer process times led to the formation of a calcium layer around the particle, and simultaneously, migration of calcium inward on the particle was observed. Thermodynamic calculations were used along with analysis techniques in order to build a hypothesis for the possible mechanism of ash-bed material interaction.

Energy efficiency improvements of post-combustion CO2 capture based on reactive gas–liquid absorption applied for super-critical circulating fluidized bed combustion (CFBC) power plants

The environmental impact represents a significant constraint for fossil fuel-intensive industrial processes in transition to a low-carbon scenario. This paper is evaluating the potential energy efficiency improvements in reactive gas–liquid absorption process used for CO2 capture from coal-based super-critical CFBC power plants. Two improved configurations for Methyl diethanolamine (MDEA)-based post-combustion CO2 capture were assessed: absorption intercooling and lean vapour recompression as well as the combination of both. The improved MDEA gas–liquid absorption configurations were compared to conventional MDEA and MEA-based systems for post-combustion CO2 capture as well as the CFBC power plant without carbon capture to assess both the energy and cost penalties for CO2 capture. As the results show, the proposed innovative concepts exhibit better specific thermal energy consumptions for solvent regeneration (2.24–2.58 vs. 2.97 MJ/kg CO2), higher net electrical efficiency (34 vs. 32%) and improved economic indicators (e.g. 2403 vs. 2552 €/kW net power as specific capital investment, 39.2 vs. 41.6 €/MWh as O&M costs, 79 vs. 84 €/MWh as cost of electricity) compared to the conventional MDEA and MEA cases.

Design of a Circulating Fluidized Bed Combustor for Lignin- Rich Residue Derived From Second-Generation Bioethanol Production Plant

The present paper reports on the design of a pilot circulating fluidized bed combustor (CFB) for the conversion of lignin-rich residue derived from a second-generation bioethanol production plant. The designed combustor aims to improve the combustion efficiency of the lignin-rich residue, therefore increasing the heat recovery to partially cover the biorefinery’s heat consumption.Among the existing technologies, the fluidized bed combustion shows several advantages, in particular the fuel flexibility and the higher combustion efficiency mainly due to the presence of an inert material that uniforms the temperature and enhance the reactants mixing. The CFB differs from the bubbling fluidized bed (BFB) for the higher velocity of the oxidizer in the reactor, resulting in a better gas-solid mixing and higher burning rate (Basu 2015). Hence, by providing enhanced fuel conversion rate is and reduced reaction time, the characteristics of this apparatus meet the requirements for a more efficient combustion of the lignin-rich residue.The CFB combustor is mainly composed by a vertical combustion chamber (riser), a solid gas-particle separator (cyclone) and a solid particles recirculation system (recirculation valve or loop seal valve). The design process followed some consequential steps. The first step involved the theoretical 1D modeling of thereactor. Considering the project constraints of maximum plant capacity (5 kg h-1) and the consequentmaximum thermal power, the geometry was chosen correlating some literature data to obtain a riser diameter of DN100 and a riser height of 3500 mm. Besides, energy and mass balances were carried out to obtain air mass flowrate data, which has an impact on the hydrodynamic study of the fluidized bed. After the geometry selection and the stoichiometric calculation, a mono-dimensional empirical model was implemented to estimate the physical behavior of the bed particles (Basu 2015), (Kunii & Levenspiel 1991). The main output of the model is the voidage fraction profile along the riser. Further important outcomes of the model are the pressure drop along the riser and the solid recirculating rate. The latter is the main input parameter for the design of the cyclone and the loop seal valve. The second step was focused on the realization of the Piping and Instrumentation Diagram selecting the measurement instruments (thermocouples, pressure transducers and flowmeters) and the ancillary equipment (blower pumps, valves and pipes). In the third step, a three- dimensional CAD model was drawn for the design of the mechanical parts including the choice of the materials and the layout. The last step involved the project of the control logic and the hardware for the data acquisition system.The results of combustion tests on the circulating fluidized bed prototype will be used to gain insights into the combustion process of the lignin-rich residue, in the perspective of an industrial scale up to increase the efficiency of the energy recovery.

Development of non-sintered zero-OPC binders using circulating fluidized bed combustion ash

The aim of this study was to develop zero-OPC binders using two circulating fluidized bed combustion (CFBC) boiler ashes with different free-CaO contents. For this purpose, heat of hydration, setting time, compressive strength, microstructure assessment, and thermal analysis tests were conducted to analyze the effect of changing the mixture of zero-OPC binder on the hydration characteristics. Furthermore, the use of mineral admixtures such as fly ash, silica fume, and ground-granulated blast-furnace slag (GGBS) to improve the material’s strength was investigated. The hydration products of the zero-OPC binder were ettringite, portlandite, and calcium silicate hydrates components, which are similar to those of existing cements. From the test results, it was found that an optimal free-CaO content of 9.0%–17.0% ensured appropriate compressive strength and setting characteristics. Pre-hydration of CFBC ashes was found to effectively control the amount of free-CaO. The effect of mineral admixtures on improvements in strength confirmed that the CFBC ash-based zero-OPC binder is a highly promising alternative to existing cements.

Ash and Flue Gas from Oil Shale Oxy-Fuel Circulating Fluidized Bed Combustion

Carbon dioxide emissions are considered a major environmental threat. To enable power production from carbon-containing fuels, carbon capture is required. Oxy-fuel combustion technology facilitates carbon capture by increasing the carbon dioxide concentration in flue gas. This study reports the results of calcium rich oil shale combustion in a 60 kWth circulating fluidized bed (CFB) combustor. The focus was on the composition of the formed flue gas and ash during air and oxy-fuel combustion. The fuel was typical Estonian oil shale characterized by high volatile and ash contents. No additional bed material was used in the CFB; the formed ash was enough for the purpose. Two modes of oxy-fuel combustion were investigated and compared with combustion in air. When N2 in the oxidizer was replaced with CO2, the CFB temperatures decreased by up to 100 °C. When oil shale was fired in the CFB with increased O2 content in CO2, the temperatures in the furnace were similar to combustion in air. In air mode, the emissions of SO2 and NOx were low (&lt;14 and 141 mg/Nm3 @ 6% O2, respectively). Pollutant concentrations in the flue gas during oxy-fuel operations remained low (for OXY30 SO2 &lt; 14 and NOx 130 mg/Nm3 @ 6% O2 and for OXY21 SO2 23 and NOx 156 mg/Nm3 @ 6% O2). Analyses of the collected ash samples showed a decreased extent of carbonate minerals decomposition during both oxy-fuel experiments. This results in decreased carbon dioxide emissions. The outcomes show that oxy-fuel CFB combustion of the oil shale ensures sulfur binding and decreases CO2 production.

Influence of fly ash composition on non-gray particle radiation in combusting systems

In this study, chemical composition dependency of both radiative properties of ash particles and radiative heat exchange are investigated for conditions typically encountered in industrial coal-fired furnaces. For that purpose, chemical composition dependent / independent complex index of refraction models are utilized to evaluate (i) spectral particle absorption efficiencies, scattering efficiencies and asymmetry factors, (ii) particle cloud properties representing pulverized coal fired furnaces (PC-Fired), bubbling fluidized bed combustors (BFBC), circulating fluidized bed combustors (CFBC) and (iii) radiative heat flux and source term predictions for five different ash compositions. Results show that spectral particle radiation is of significant importance for accurate calculation of radiative heat transfer in combusting systems and it is originated from the spectral nature of the complex index of refraction rather than spectral nature of the incident radiation. It is also seen that chemical composition has a significant effect on particle absorption properties as well as heat flux/source term predictions. Hence complex index of refraction models used in radiative property estimations must take into consideration this composition dependency. Accordingly, one spectral and one gray complex index of refraction models are recommended for the evaluation of ash particle properties.