Bubbling Fluidized Bed Combustor Research Articles

Alternative sorbents for mercury capture in flue gas from lignite combustion

This paper presents an experimental study of two of alternative sorbents for mercury capture from the lignite combustion flue gas. The sorbents are based on calcium hydroxide and aluminosilicate, using different modifications. A commercially available activated carbon (AC) with bromine impregnation was selected as the reference sorbent. This sorbent is a state-of-the-art solution for mercury removal in industrial combustion facilities. However, its application is costly for power plants because of the market price of the AC and because the presence of carbon in the fly ash can complicate its further use, which gives a strong motivation for exploring new alternatives. Experimental investigation was carried out in a 500 kW pilot-scale bubbling fluidized bed combustor using a lignite with naturally high mercury content. A injection system of our own design and construction was used to supply the sorbents to the flue gas downstream of the combustor at a flow rate in the range of 100–500 mg/m3N of the flue gas. Continuous measurement of mercury concentration was used upstream the sorbent injection and downstream the fabric filter, simultaneously. Different sorbent injection rates and flue gas temperatures at the sorbent injection point were examined.The mercury capture ratio was evaluated considering the Hg balance in the combustor. It was shown that the mercury self-capture by the fly ash in the fluidized bed combustion system varies approximately from 30 to 90 %, depending on the SO2 concentration. The Hg capture ratio for calcium hydroxide was in a range of approximately 15–25 %, while for aluminosilicate it was 25–45 %, determined by the actual conditions of the flue gas and the initial Hg concentration. This is in the range of the reference AC, which typically reaches from 25 – 95%. The increased injection rate of the sorbents was reflected in the Hg capture ratio, but its promotion was observed only in the case of the aluminosilicate sorbent. A correlation of the Hg capture ratio with the flue gas temperature at the injection point was also clearly identified only for the aluminosilicate sorbent, when an increase in the temperature led to increasing in the capture ratio.

Desulfurization in co-firing of sewage sludge and wooden biomass in a bubbling fluidized bed combustor under air and oxy-fuel conditions

This work presents results of an experimental investigation of a direct addition of Ca-based sorbent for SO2 capture in a bubbling fluidized bed combustion. The fuel of interest was secondary biomass represented by a dried sewage sludge, which was mixed with primary biomass represented by wooden pellets in a weight ratio of 30:70. The performance of this SO2 capture approach is compared in air and oxy-fuel combustion conditions, since the different gas environment in the bed significantly affects the SO2 capture process. The experiments were carried out in an experimental bubbling fluidized bed combustor with a power load of about 30 kW.Sewage sludge is typical for its high ash content and has sufficient dimensions and attrition resistance to create the fluidized bed without the support of external bed materials. However, it typically consists of S-containing organic substances, resulting in the presence of SOX in the off-gas. A reference case was initially conducted without any sorbent addition in order to investigate the effect of sulfur self-retention in the fuel ash. The sulfur retention in the ash reached almost 45 % in air- and up to 55 % under oxy-combustion.In the next phase, the performance of Ca-based sorbents in sulfur capture was evaluated. The sorbents were represented by two types of limestone with diverse CaCO3 content produced at different locations. The experiments were carried out with three Ca/S mole ratios (1.5, 3, and 4.5). The effect of the fluidized bed temperature was also investigated as the most important parameter.The SO2 capture ratio (used as a performance indicator) was calculated based on emission factors, due to the different specific volumes of flue gas in the air and oxy-fuel modes. The results show in general a significantly higher SO2 capture ratio under oxy-fuel conditions. The differences are more significant in lower Ca/S ratios, where the SO2 capture ratio increased from 46 % under air conditions to 75 % under oxy-fuel for Ca/S = 1.5. In the case of the highest Ca/S ratio examined (Ca/S = 4.5), the increase in SO2 capture was from 90 % to 95 %.

Dynamics of large-scale bubbling fluidized bed combustion plants for heat and power production

Bubbling fluidized bed combustion (BFBC) plants for combined heat and power (CHP) production have traditionally been dispatched under slow load changes. As the amount of variable renewable electricity increases in energy systems worldwide, knowledge regarding the transient capabilities of the gas and water-steam sides of BFBC plants is required. The aim of this work is to investigate the dynamic performance of large-scale BFBC plants when accounting for both the gas and water-steam sides. To do so, this paper presents a dynamic model of BFB-CHP plants that result from connecting a model of the gas side to a process model of the water-steam side. The plant model output is validated by comparisons with operational data measured in a 130-MWth BFBC plant that produces electricity, district heating (DH) water and steam for industrial clients. The validation shows that the model can satisfactorily describe both multi-load steady-state operation and load transients. The simulation results highlight the fact that the water-steam cycle achieves stabilization more rapidly after changes in the DH line and steam delivered to customers, as compared to changes in the combustor load. The timescales of the plant outputs for different changes have been calculated, with stabilization times ranging from 2 to 15 min for the power production versus 2–25 min characterizing the DH production. Compared to the stabilization times of the gas side, the water-steam side is an order of magnitude slower, thereby limiting the transient operation capabilities of BFB-CHP plants.

Coupling of spectral thermal radiation model with a comprehensive system model for co-combustion of biomass in bubbling fluidized bed

A previously developed 1-D comprehensive model for a bubbling fluidized bed combustor (BFBC) co-firing lignite with cotton residue and limestone is coupled with a 3-D spectral and gray radiation models utilizing method of lines (MOL) solution of discrete ordinates method (DOM). The performance of the coupled models is assessed by comparing their predictions of temperature profiles and gaseous emissions (i) with those of original FBC model without coupling and (ii) with the in-situ measurements from Middle East Technical University (METU) 0.3 MWt BFBC. Comparisons between fluidized bed combustion (FBC) system models with and without radiation reveal that the spectral model improves the predictions only slightly. This is considered to be due to the very small temperature difference between the freeboard medium and hot refractory side walls which results in lower rates of heat transfer from the freeboard to the walls. Furthermore, radiative heat transfer in the freeboard is dominated both by combustion gases and particles.

Experimental verification of the impact of the air staging on the NOx production and on the temperature profile in a BFB

The results of an experimental research on air staging in a bubbling fluidized bed (BFB) combustor are presented within this paper. Air staging is known as an effective primary measure to reduce NOX formation. However, in the case of a number of industrial BFB units, it does not have to be sufficient to meet the emission standards. Then selective non-catalytic reduction (SNCR) can be a cost-effective option for further reduction of the already formed NOX. The required temperature range at the place of the reducing agent injection for an effective application of the SNCR without excessive ammonia slip is above the temperatures normally attained in BFBs. The aim of this paper is to evaluate the impact of staged air injection on the formation of NOX in BFB combustors and to examine the possibility of increasing the freeboard temperature. Several experiments with various secondary/primary air ratios were performed with a constant oxygen concentration in the flue gas. The experiments were carried out using wooden biomass and lignite as fuel in a 30 kWth laboratory scale BFB combustor. Furthermore, the results were verified using a 500 kWth pilot scale BFB unit. The results confirmed that the air staging can effectively move the dominant combustion zone from the dense bed to the freeboard section, and thus the temperatures for an effective application of the SNCR can be obtained.

Performance and validation of a radiation model coupled with a transient bubbling fluidized bed combustion model

None of the transient bubbling fluidized bed combustor (BFBC) models couples the solution of radiative transfer equation with the solution of conservation equations of other transport processes although thermal radiation is of considerable importance in such systems, as such an objective requires both accurate and computationally efficient methods for not only the solution of radiative transfer but also the estimation of radiative properties of particle-laden combustion gases. Therefore, in this study, a 1-D transient comprehensive system model for combustion of lignite is coupled with a 3-D radiation model based on method of line solution of discrete ordinates method utilizing one gas spectral line-based weighted sum of gray gases for spectral gas properties, Mie theory for gray particle properties, and gray wall properties. Predictive accuracy of the model is validated against (i) predictions of a computationally inefficient spectral radiation model and (ii) measurements of transient temperature and concentrations of the species O2 and CO obtained from METU 0.3 MWt atmospheric bubbling fluidized bed combustion test rig firing lignite. The outcome of this study provides a comprehensive, accurate, and computationally efficient tool for simulation of transient BFBCs and highlights the significant impact of radiative heat transfer in modeling of industrial boilers.

Influence of soot on radiative heat transfer in bubbling fluidized bed combustors

The effect of soot particles and aggregates on radiative heat transfer in bubbling fluidized bed combustors is investigated. For this purpose, a soot radiative property model based on Rayleigh scattering theory is coupled with in-house developed 1-D gray and spectral radiation codes and a 3-D spectral radiation code based on method of lines solution of discrete ordinates method for the application of (i) a 1-D slab problem involving combustion gases and soot and (ii) freeboard of a 0.3 MWt atmospheric bubbling fluidized bed combustion test rig including combustion gases, fly ash particles and soot. The predictions of the 1-D radiation code reveal that (i) Planck-mean soot radiative properties provide reasonably accurate radiative heat transfer predictions (ii) soot particle diameter and number of soot particles in an aggregate do not considerably influence the net wall heat fluxes and source terms as absorption coefficient of soot is not significantly affected by those parameters and is orders of magnitude higher than scattering coefficient. Application of 3-D radiation model to the test rig shows that soot significantly contributes to radiative heat transfer in the freeboards of bubbling fluidized bed combustors. Soot has a noticeable impact on radiation even at very low volume fractions.

Influence of bag filter ash to spectral thermal radiation in fluidized bed combustors co-fired with biomass

Influence of fine particles collected in bag filter on spectral thermal radiation is investigated in the freeboard of a 0.3 MWt atmospheric bubbling fluidized bed combustion test rig where lignite, lignite/olive residue, and lignite/hazelnut shell blends are fired with limestone addition. For this purpose, a 3-D radiation code based on method of lines solution of discrete ordinates method coupled with banded one gas spectral line-based weighted sum of gray gases for spectral gas properties, Mie theory for spectral particle properties and spectral wall properties is utilized. The radiation code is implemented by considering first presence of combustion gases only, then combustion gases with bag filter particles (less than 14 μm) only, and then combustion gases with coarse cyclone and fine bag filter particles. The results of this study reveal that particle absorption and scattering are dominated by coarse cyclone particles during combustion of lignite only while they are dominated by bag filter particles during co-combustion of biomass and lignite owing to higher amount of fine particles originated from biomass combustion. During co-firing, contribution of cyclone particles to thermal radiation decreases while those of combustion gases and fine particles originated from biomass combustion increase.

Bubblig Fluidized Bed Combustor (Dept.M)

A Bubbling Fluidized Bed Combustor (BFBC) is designed and set-up to investigate the combustion processes of sub-bituminous Egyptian coal particles and wood. The effect of changing the coal particles size, with keeping the fluidized air velocity constant, on: gas temperatures, heat flux to the combustor wall, radiant-convective overall heat transfer coefficient and combustion level of coal particles is investigated. The highest combustion level is found at coal particles size of 17 mm. The heat transfer coefficient in the case of coal combustion is extremely greater by 500% than that of wood combustion.

Performance of banded SLW-1 in presence of non-gray walls and particles in fluidized bed combustors

In this study, banded one gas spectral line-based weighted sum of gray gases (banded SLW-1) model is coupled with a 3-D radiation code based on method of lines (MOL) solution of discrete ordinates method (DOM) for freeboard of METU 0.3 MWt atmospheric bubbling fluidized bed combustion (ABFBC) test rig containing non-gray gas, non-gray particle mixture bounded by non-gray walls. Spectral parameters of banded SLW-1 are estimated by the approach based on two emissivities calculated at two different path lengths L1 and L2. The predictive accuracy of banded SLW-1 model is tested by comparing its incident wall heat flux and source term predictions with measurements and predictions of banded SLW. The results indicate that band-wise selection of L1 and L2 based on spectrally averaged mean beam length provides the most accurate radiative heat transfer predictions. Furthermore, based on a sensitivity analysis on the test rig under consideration, utilization of path lengths L1 and L2 which are 0.10 and 1.10 times of the spectrally dependent mean beam length is found to yield the best radiative heat transfer predictions in terms of accuracy. Incident heat flux and source term predictions of banded SLW-1 are found to be in reasonable agreement with those of banded SLW under both air and oxy-fired conditions. Furthermore, CPU time requirement of banded SLW-1 is about 20–25 times lower than that of banded SLW. With the introduction of fly ash recycling, particle load increases an order of magnitude leading to further improvement in the accuracy of banded SLW-1. On the other hand, gray wall assumption leads to accurate radiative heat flux predictions whereas this assumption leads to considerable inaccuracies in the source term predictions in the upper region of freeboard. However, those inaccuracies become insignificant with the introduction of fly ash recycling. Application of the model to different wall conditions common in the industry indicates that discrepancies between the source term predictions of gray and non-gray cold water wall and those of gray and non-gray cold slag covered water wall are insignificant for the combustion test rig under consideration which is attributed to the combined effects of low wall temperatures and similar gray and non-gray wall emissivities.

Agglomeration and the effect of process conditions on fluidized bed combustion of biomasses with olivine and silica sand as bed materials: Pilot-scale investigation

Bubbling fluidized bed combustion of biomass has benefits of fuel flexibility, high combustion efficiency, and lower emissions. Bed agglomeration is where bed particles adhere together with alkali silicate melts and can lead to unscheduled plant shutdown. This pilot-scale study investigates performance and agglomeration when varying fuel (white wood, oat hull waste, miscanthus, wheat straw), bed height, bed material, and includes a novel spatial analysis of agglomerates from different bed locations. White wood was the best performing fuel and did not undergo bed defluidization due to its low ash content (0.5% mass as received), whereas wheat straw (6.67% mass as received ash) performed worst (defluidization times <25 min). Olivine was a superior bed material to silica sand, with 25%+ longer defluidization times with the worst performing fuel (wheat straw). Calcium-rich layers formed at olivine particle surfaces within wheat straw ash melts, and capillary action drew potassium silicate melt fractions into olivine particle fractures. An analysis of agglomerate samples from different bed spatial locations following tests with oat hull waste showed that ash layers on agglomerates retrieved further from the landing point of fuel onto the bed had reduced potassium and elevated calcium, likely due to reduced availability of fresh fuel ash for reaction with bed material.

Dry additive desulfurization in oxyfuel bubbling fluidized bed combustor

This work presents research results of direct sorbent addition for SO2 capture from a lignite coal combustion in a bubbling fluidized bed (BFB). SO2 capture ratio in air and in full oxyfuel combustion conditions is compared in real environment, using a 30 kW BFB combustor. The first part studies the sulfur self-retention in the fuel ash. It shows significantly more efficient SO2 capture increase from 15% in air conditions to 45% in oxyfuel conditions. The next part concerns evaluation of optimal temperature for the SO2 capture and a sorbent performance is evaluated in the last part. Two varieties of sorbents based on CaCO3 were used, differing significantly in purity, geological age and BET surface area. The optimal fluidized bed temperature for SO2 capture was for air combustion about 840 °C and for oxyfuel combustion about 880 °C. The sorbent performance was studied at three different Ca/S molar ratios (1.5, 3 and 5). The results show the fundamental differences between air and oxyfuel conditions in real combustion environment, and also reveal the differences between the sorbents. In general, significantly higher SO2 capture ratio was reached in oxyfuel conditions. At Ca/S equal to 5, it is possible to reach the SO2 capture as high as 98% in oxyfuel mode. The BET surface of the sorbent is important mainly at lower Ca/S molar ratios. The difference in SO2 capture between the sorbents is below 10% relative at Ca/S molar ratio 3 and it further decreases with increasing Ca/S ratio.

Modeling of Fluidized Bed Combustion of Lignite with High Nitrogen Content Cotton Residue

ABSTRACT A comprehensive system model, previously developed for prediction of combustion behaviors of Turkish lignites, lignite/hazelnut shell, and lignite/olive residue blends in a 0.3-MWt atmospheric bubbling fluidized bed combustor (ABFBC), is extended for modeling of co-combustion of Turkish lignite and cotton residue. Cotton residue has high nitrogen content (~4.1 wt% ar) unlike lignite (~0.9 wt% ar), olive residue (~1.6 wt% ar), and hazelnut shell (~0.5 wt% ar), which leads to relatively high emissions of nitric oxides (NO x ) and nitrous oxide (N2O). For accurate prediction of emissions of NO and N2O, a sufficiently detailed NO and N2O formation and reduction reaction scheme is incorporated into the existing model. The assessment of the accuracy of the model is tested by comparing its predictions with the experimental data obtained in a 0.3-MWt ABFBC where a typical Turkish lignite is co-fired with limestone and cotton residue. Reasonable agreement is obtained between the predicted and measured O2, CO, CO2, SO2, NO, and N2O concentrations and temperature profiles. The results obtained in this study show that the addition of cotton residue increases emission of total nitrogenous species due to its high nitrogen content, but the main effect is observed in the increase of N2O formation. Furthermore, determination of the fuel nitrogen partitioning into char and volatiles and distribution of volatile nitrogen species are found to be the most important parameters for modeling of NO and N2O emissions in bubbling fluidized bed combustors.

파일럿 규모의 기포 유동층 반응기를 이용한 석탄과 하수 슬러지 고형 연료의 혼소에 대한 실험적 연구

In this study, the co-combustion characteristics of coal and sewage sludge were investigated using 100 kWSUBth/SUB bubbling fluidized bed (BFB) combustion system. Sub-bituminous coal (Coal), dried sewage sludge solid fuel (DSS), and hydrothermal carbonization sewage sludge solid fuel (HTCSS) were considered as fuel blends. The higher heating value of HTCSS was about 1,500 kcal/kg higher than that of DSS since the fuel ratio, H/C and O/C ratio were improved by the hydrothermal carbonization. The hardgrove grindability index (HGI) was performed to understand the feasibility of industrial applications. In the pilot-scale BFB experiment, the heat input, as 72 kWSUBth/SUB, was fixed in all cases. The mixing ratios of HTCSS and DSS were 2, 5 and 10% respectively based on the higher heating value. Under the co-combustion conditions, the temperature in the reactor was increased in the freeboard zone due to the higher volatile matter of HTCSS and DSS than Coal. The trend of CO and NOSUBx/SUB emissions was similar in all cases as mixing ratio was increased. However, SO₂ emission was decreased in HTCSS co-combustion case due to the lower sulfur content compared to than that of DSS. Ash acquired after BFB combustion was analyzed by XRF to evaluate the slagging/fouling tendency. The variation of slagging/fouling tendency was minor in all cases.

Simulation of combustion of sesame and broad bean stalks in the freeboard zone inside a pilot-scale bubbling fluidized bed combustor using CFD modeling

A two-dimensional numerical model has been developed to simulate combustion of sesame and broad bean stalks in the freeboard zone of a pilot-scale Bubbling Fluidized Bed Combustor (BFBC). Eulerian–Lagrangian approach is used so, the gas phase is treated as a continuum by solving the time-averaged Navier-Stokes equations and a Discrete Phase Model (DPM) is used to model the solid phase. The combustion in the freeboard was simulated to be consistent with the experimental conditions and the real combustor work. Prediction of composition for gas and solid phases at the freeboard inlet was performed. A series of simulations have been performed to examine the effect of chemical kinetic parameters, solid phase parameters, gas phase parameters and heat flux through walls on the numerical results. The model results were validated by comparing with experimental results obtained from the BFBC. The maximum absolute deviations corresponding to the numerical results of the mole fraction of flue gas species at the exit were 3.07% for the sesame stalks and 10.89% for the broad bean stalks. The numerical results of the axial temperature distribution have maximum absolute deviations 14.77% and 14.69% for the sesame stalks and broad bean stalks, respectively. It was found that the model simulation results are in a good agreement with the experimental data obtained from the experiments. In the present model, the deviations of the flue gas species and axial temperature distribution along the freeboard height are found within the literature limits.

Defluidization Prediction and Prevention during Cocombustion of ReEngineered Feedstock with Coal in a Bubbling Fluidized Bed Combustor

Despite the increase in applications of renewable energy sources, coal combustion for electricity production remains important. The use of alkali and alkaline earth sorbents to address the emissions or their introduction during cocombustion of biomass can cause defluidization of fluidized bed combustors. This article presents the results obtained from an extensive experimental campaign aimed at exploring the performance of different defluidization inhibition measures and defluidization outcomes of a pilot-scale atmospheric bubbling fluidized bed combustor cofired with ReEngineered Feedstock (ReEF) and coal. ReEF is a solid fuel made from the nonrecyclable fraction of municipal solid waste to which alkaline air emission control reagents are physically bound. The cocombustion of coal and ReEF combines fuel- and sorbent-blending techniques for improved combustion and higher efficiency emission reduction. An earlier study of the group proved these favorable aspects during the cocombustion of a granular bitumi...

Experimental Investigation of Combustion Characteristics and Emissions for a Pilot-Scale Bubbling Fluidized Bed Combustor Fueled by Biomass Chips of Sesame and Broad Bean Stalks

ABSTRACTThe study work investigated the combustion characteristics and gaseous emissions during burning chips of sesame and broad bean stalks in a pilot-scale Bubbling Fluidized Bed Combustor (BFBC). The effects of the startup temperature, excess air percentage, moisture content, and injection location of secondary air on axial temperature profiles along the combustor and flue gas emissions were studied. The results indicated that biomass fuel characteristics have a significant role in the distribution of axial temperature along the reactor height. A great effect on the axial temperature profile was detected when the startup temperature was changed. The 30% and 100% excess air represent the near percentages for better combustion characteristics for burning the stalks of broad bean and sesame, respectively. Enhancement was observed in the combustion behavior when using the dried samples compared to the as-received samples. Higher values of axial temperature and lower concentrations of flue gas emissions are a result of rising injection location of the secondary air. The combustion efficiency reached to 92.4% for burning the sesame stalks and 96.6% for the broad bean stalks. Based on an energy balance performed on the BFBC, the thermal efficiency was ranged from 28.2% to 59.4% for SS and from 17.2% to 42.1% for broad bean stalks.

Sesame and Broad Bean Stalks: Mixing Characteristics of Chips as a Biomass Fuel for Bubbling Fluidized Bed Combustor

Abstract Mixing and segregation characteristics of biomass particles are of practical importance because the in-bed combustion efficiency of volatile matter affects the vertical location of biomass in bubbling fluidized bed combustor. Sesame and broad bean stalk biomass materials mixed with sand used in this study. The superficial gas velocity, biomass chip length, sand particle size and mass fraction of biomass varied as experimental variables. The mixing and segregation behavior of mixtures were analyzed in terms of mixing index. It was found that the variability in the chip-shape made the sesame chips is quantitatively and qualitatively higher homogeneity and mixedness than the broad bean chips. The optimum overall mixing index for the sesame and the broad bean is around 0.96 and 0.84 at dimensionless superficial gas velocity (U/Umf) of 2.0 (1.40 m/sec) and 2.1 (1.25 m/sec), respectively. It was found that as the mean diameter increased and the sphericity decreased, the mixing quality decreased. The average sand particle size of 371 µm can keep good mixing with biomass chips of both materials, compared with average particle sizes of sand 550 and 700 µm. Increasing the initial biomass mass fraction yields a poor mixing of the investigated biomass stalks.

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.

Assessment of gas radiative property models in the presence of nongray particles

ABSTRACTIn this study, a radiation code based on the method of lines solution of the discrete ordinates method for the prediction of radiative heat transfer in nongray gaseous media is developed by incorporation of two different spectral gas radiative property models, banded spectral line-based weighted sum of gray gases (banded SLW) and gray wide band (GWB) approximation in the presence of nongray absorbing–emitting–scattering particles. The aim is to introduce an accurate and CPU efficient spectral gas radiation model, which is compatible with spectral fuel/ash particle property models. Input data required for the radiation code and its validation are provided from two combustion tests previously performed in a 300 kWt atmospheric bubbling fluidized bed combustor test rig burning low calorific value Turkish lignite with high volatile matter/fixed carbon (VM/FC) ratio in its own ash. The agreement between wall heat fluxes and source term predictions obtained by global and banded SLW models reveal that global SLW model can be converted to an accurate wide band gas model (banded SLW) which can directly be coupled with spectral particle radiation. Furthermore, assessment of GWB approximation by benchmarking its predictions against banded SLW model shows that GWB gives reasonable agreement with a higher CPU efficiency when the particle absorption coefficient is at least in the same order of magnitude with the gas absorption coefficient.