A new weighted‐sum‐of‐gray‐gases model for oxy‐combustion scenarios

A new weighted‐sum‐of‐gray gases (WSGG) model that is based on the statistical narrow band model (SNB) RADCAL is proposed for use in computational fluid dynamic (CFD) simulations of air and oxy‐combustion. When employed in conjunction with the discrete ordinates (DO) method, the model predictions compare well against line‐by‐line benchmark data that have been made available recently that are based on the latest spectroscopic databases. Furthermore, the model compares well against the EM2C SNB model calculations that have served as benchmark data in three‐dimensional geometries. Radiative transfer calculations in these prototypical problems therefore confirm recent experimental observations that SNB RADCAL and EM2C SNB serve as good model databases to develop approximate radiative property models. To achieve an optimum balance of speed and accuracy in computationally intensive CFD simulations, non‐gray formulations of the WSGG model are also employed with the P1 model and solutions are compared against those generated by the DO model. While the P1 model gave favorable comparisons when cold, black walls were present, the errors in the surface incident radiative flux predictions increased in the presence of hot, reflecting walls. Finally, in fully coupled simulations of natural gas combustion under air‐firing and oxy‐firing modes, the predicted incident radiative flux profiles were distinctly different between the gray and non‐gray calculations at regions of high temperature gradients, while the centerline temperature predictions were comparatively unaffected. The effects of turbulence radiation interactions were also accounted for through the temperature self‐correlation term. However, the magnitudes of the temperature fluctuations were small and localized within this furnace and did not significantly alter our predictions. Copyright © 2012 John Wiley & Sons, Ltd.     

New weighted‐sum‐of‐gray‐gases model for typical pressurized oxy‐fuel conditions

Pressurized oxy‐fuel combustion technology has received considerable attention due to its ability to improve the overall system efficiency and to control CO₂ emissions. The characteristics of radiation heat transfer are significant for pressurized oxy‐fuel gas mixture and different from those under atmospheric conditions. Therefore, to calculate the radiation characteristics of pressurized oxy‐fuel gas mixture quickly and accurately, new weighted‐sum‐of‐gray‐gases (WSGG) model for pressurized oxy‐fuel conditions was first presented in this paper, which was applied in 3 typical high pressure conditions: 5, 10, and 15 bar. The new WSGG model correlations were suitable for pressurized conditions with a molar ratio range of 0.125‐2, temperature range of 400‐2500 K, and path length range of 0.1‐20 m. Calculations for a variety of typical pressurized oxy‐fuel combustion cases showed that the new WSGG model can accurately predict the radiation characteristics and heat transfer characteristics of the gas mixtures compared with the SNB model benchmark. In addition, the application of the previous atmospheric WSGG models yielded non‐ideal results under pressurized conditions. Consequently, the new model can provide efficient and accurate radiation heat transfer results for pressurized oxy‐fuel conditions and can be used to design pressurized oxy‐fuel combustion furnaces or boilers.     

Effect of varying fuel types on oxy‐combustion performance

In search for clean energy solutions in a global warming era, oxy‐fuel combustion systems are promising. In the study, combustion products are calculated, and exergy analysis is done using the proposed multifeature equilibrium combustion model. And the results obtained for oxy‐combustion of different fuels at various oxygen fractions are given in comparison with conventional combustion. For validation, the model results are compared with popular combustion calculation tools, GASEQ and CEA. Effect of oxygen content on oxy‐combustion exergy analysis is calculated, also considering changes in equivalence ratio and combustion chamber inlet temperature. Moreover, indicating parameters for combustion performance, temperature ratio, chemical exergy, physical exergy, total specific exergy, and exergy destruction are utilized in the calculations elaborately. Changes in combustion product mole fractions are explained for rich and lean combustion regions. And also, specific exergy results are presented. In terms of exergy destruction, oxy‐combustion is more advantageous than conventional combustion. It has been shown that exergy destruction in combustion process with conventional air is approximately 1.5 times higher compared with 21% oxy‐combustion, both at different equivalence ratios and at different combustion chamber inlet temperatures. Nowadays, environment‐friendly, clean energy production systems are growing in numbers. In this concept, exergetic analyses of combustion for different fuels and greener natural gas, compared with diesel, gasoline, and methanol, are given in comparison. Considering four fuel types, advantageous and disadvantageous cases are presented for oxy‐combustion at different oxygen fractions and conventional combustion. As a result, diesel fuel is more advantageous than the other three fuel types, in terms of temperature ratio and exergy. Natural gas combustion appears to be disadvantageous in terms of specific exergy and temperature ratio, but it is the most advantageous in terms of exergy destruction. Consequently, distinctive comparison is done for oxy‐combustion and conventional combustion, determining positive and negative effects for different fuels.     

Fuel injection characteristics of diesel‐stimulated natural gas combustion

Although dual‐fuel (DF) engines using a low cetane number primary fuel such as natural gas (NG) ignited by a pilot diesel spray have been the subject of much investigation over years, there are still many unknown problems related to the fundamental combustion process of two fuels. In this work, a quiescent constant volume combustion bomb and a 3‐D numerical model have been used to study the effects of injection nozzle characteristics on the combustion of pre‐mixed NG/air with pilot distillate spray. Experimental tests were conducted on combustion process of pre‐mixed natural gas/air with pilot injection pressure of 30 and 20 MPa with a 4 hole injector, and also with injector nozzle of 8 and 4 holes. The global results obtained from computations compared well with the experimental results. Copyright © 1999 John Wiley & Sons, Ltd.     

Numerical study on steam‐added mild combustion

Numerical study on flame structure and NO emission is conducted covering a wide range of atmospheric temperature, high temperature, and mild combustion regimes in H₂‐Air laminar flames diluted with steam. Special concern is focused on the difference of flame structure and NO emission behaviour between high‐temperature combustion and mild combustion modes. The important role of chemical effects of added steam in flame structure and NO emission behaviour is also discussed. It is seen that there exists an oxidizer‐side temperature limit which the combustion mode changes from high temperature combustion to mild combustion. In high temperature combustion modes the OH production via the reaction step, (‐R23) is suppressed while in mild combustion modes is enhanced by the increase of oxidizer‐side temperature. It is also found that chemical effects of added steam are influenced by the competition between both the reaction steps, (R21) and (‐R23). NO emission index increases with increasing oxidizer‐side temperature and decreases with mole fraction of added steam. The remarkably produced OH due to chemical effects of added steam does not contribute to the increase of NO but plays a role of holdback on NO in thermal mechanism. It is also seen that in both the high temperature combustion and mild combustion modes NO emission indicates a consistently similar tendency, and is consequently recognized that in the whole ranges steam addition suppresses NO emission. Copyright © 2004 John Wiley & Sons, Ltd.     

Experimental and numerical analysis of oxy‐fuel combustion in a porous plate reactor

The present work focuses on studying experimentally and numerically the oxy‐fuel combustion characteristics inside a porous plate reactor towards the application of oxy‐combustion carbon capture technology. Initially, non‐reactive flow experiments are performed to analyze the permeation rate of oxygen in order to obtain the desired stoichiometric ratios. A numerical model is developed for non‐reactive and reactive flow cases. The model is validated against the presently recorded experimental data for the non‐reacting flow cases, and it is validated against the available literature data for oxy‐fuel combustion for the reacting flow cases. A modified two‐step oxy‐combustion reaction kinetics model for methane is implemented in the present model. Simulations are performed over wide range of operating oxidizer ratios (O₂/CO₂ ratio), from OR = 0.2 to OR = 0.4, and over wide range of equivalence ratios, from φ = 0.7 to φ = 1.0. The flame length was decreased as a result of the increase of the oxidizer ratio. Effects of CO₂ recirculation amount on the oxy‐combustion flame stability are examined. A reduction in combustion temperature and increase in flame fluctuations are encountered while increasing CO₂ concentration inside the reactor. At high equivalence ratio, the combustion temperature and flame stability are improved. At low equivalence ratio, the flame length is increased, and the flame was moved towards the reactor center line. Copyright © 2015 John Wiley & Sons, Ltd.     

A spherical cell model for multi‐component droplet combustion in a dilute spray

A model for sphericosymmetric thin‐flame combustion of a multi‐component fuel droplet in a dilute spray has been developed using a unit cell approach. The gas‐phase transport has been modelled as convective–diffusive while the liquid‐phase processes as transient–diffusive. Convective heat and mass transfer condition has been used at the cell surface. The results indicate that evaporation and combustion characteristics of the droplet are strongly affected by the variation of both ambient conditions and convective transfer coefficients. Using the model, the effects of droplet spacing in spray, ambient oxidizer concentration, ambient temperature and pressure have been considered. Droplet life increases with decrease in droplet spacing, ambient temperature and ambient oxidizer concentration. However, droplet life has a weak dependence on ambient pressure. Copyright © 2001 John Wiley & Sons, Ltd.     

Influence of inlet flow conditions on the performance of a swirl‐stabilized combustor burning liquid fuel spray

A numerical model of liquid fuel spray combustion is developed to study the effects of inlet flow conditions of primary and dilution air on the performance of a swirl‐stabilized axi‐symmetric combustor. The model is based on two‐phase stochastic separated flow approach. A standard k–ϵ model with logarithmic law of the wall for the near‐wall region is adopted for the solution of the gas phase turbulence. The chemical reaction is taken as a single step, irreversible, global one with the rate determined by the kinetically and diffusionally controlled rates. The liquid spray is divided into a finite number of droplet classes with the size distribution following a probability function. It has been observed that an improved pattern factor and better combustion efficiency can be obtained when both the primary and the dilution air streams enter the combustor with swirl, but in the counter‐rotating directions. However, the combustor pressure loss factor increases for the counter‐rotating flow entries of the primary and the dilution air compared to the co‐rotating air entries or to the swirled primary and non‐swirled dilution air entries. Copyright © 2000 John Wiley & Sons, Ltd.     

The black smoke control in a chain‐grate stoker‐fired boiler at the time of ignition and restart of the combustion

The black smoke is always emitted from the chimney in the chain‐grate stoker‐fired boiler at the time of ignition at ambient temperature and restart of the combustion after temporary flameout in China. The purpose of the work is to reduce the black smoke emission. A laboratory fixed‐grate model has been used to simulate the combustion of coal in chain‐grate stoker‐fired boiler. The CO and O₂ concentration in the flue gas have been measured with a flue gas analyser, and the black smoke emitted from the chimney has been screened with Charge Couple Device (CCD) video camera. Power 2^# coal, sized at 5–25 mm, has been fired in the fixed‐grate model. The secondary air has been used to enhance the turbulence in the furnace after the numerical simulation. The results of experiments show that the emission of the black smoke at the time of ignition of the coal at ambient temperature is more serious than that of restart of the combustion after the temporary flameout for the case of the temperature; the secondary air is helpful for reducing the black smoke emission for enhancing the intensity of the turbulence in the furnace; selection of coal particle size is necessary, the smaller the size of the coal is, the more serious the black smoke emission is, and the effect of reducing the black smoke emission with the secondary air is more evident with smaller‐size coal. The industrial test has been employed to study the effect of the air demand. It indicates that rational stoichiometric air/fuel ratio is helpful for reducing the black smoke emission in the restart of the combustion after the temporary flameout. Copyright © 2006 John Wiley & Sons, Ltd.     

Non‐gray modeling of radiative heat transfer in hydrogen combustion scenarios

New weighted‐sum‐of‐gray‐gases model (WSGGM) parameters for H₂O vapor are derived from emissivity correlations in the open literature and presented for use in hydrogen combustion simulations. Predictions employing the new WSGGM are seen to compare favorably against the spectral‐line‐based WSGGM on benchmark problems as well as in media conditions representative of turbulent hydrogen diffusion flames (Sandia Flame A and a model hydrogen gas‐turbine combustor). The Sandia Flame A calculations were performed in a decoupled manner employing experimental measurements of temperature and gas compositions as inputs. The measured temperature variance data were employed to model the turbulence–radiation interactions. A coupled computational fluid dynamic (CFD) calculation was performed to obtain the conditions within the gas‐turbine combustor geometry. The observed accuracies of the proposed set of WSGGM parameters in conditions encompassing a wide range of H₂O vapor concentrations and temperature non‐homogeneities encountered in combustion media make them amenable to implementation in CFD codes. Copyright © 2011 John Wiley & Sons, Ltd.     

Numerical study of hydrogen‐enriched methane–air combustion under ultra‐lean conditions

The demand for gas turbines that accept a variety of fuels has continuously increased over the last decade. Understanding the effects of varying fuel compositions on combustion characteristics and emissions is critical to designing fuel‐flexible combustors. In this study, the combustion characteristics and emissions of methane and hydrogen‐enriched methane were both experimentally and numerically investigated under ultra‐lean conditions (Ø ≤ 0.5). This study was performed using global mechanisms with a one‐step mechanism by Westbrook and Dryer and a two‐step mechanism with an irreversible and reversible CO/CO₂ step (2sCM1 and 2sCM2). Results show that the 2sCM2 mechanism under‐predicted the temperature, major species, and NO_x by more than 100% under ultra‐lean conditions; thus, we proposed a modified‐2sCM2 mechanism to better simulate the combustion characteristics. The mechanisms of Westbrook, 2sCM1, and modified 2sCM2 predicted the temperature and the CO₂ emission with an average deviation of about 5% from the experimental values. Westbrook and 2sCM1, however, over‐predicted the NO_x emission by approximately 81% and 152%, respectively, as compared with an average under‐prediction of 11% by the modified‐2sCM2 mechanism. The numerical results using the proposed modified‐2sCM2 mechanism shows that the presence of hydrogen in the fuel mixture inhibits the oxidation of methane that led to the formation of unburned hydrocarbons in the flame. We also showed that for any given fuel compositions of H₂/CH₄, there is an optimum equivalence ratio at which the pollutant emissions (CO and NO_x) from the combustor are minimal. Zero CO and 5 ppm NO_x emissions were observed at the optimal equivalence ratio of 0.45 for a fuel mixture containing 30% H₂. The present study provides a basis for ultra‐lean combustion toward achieving zero emissions from a fuel‐flexible combustor. Copyright © 2016 John Wiley & Sons, Ltd.     

Energy efficiency trade‐off with phasing of HCCI combustion

Homogeneous charge compression ignition (HCCI) combustion in diesel engines offers the potential of simultaneous low NOx and soot emissions. However, this is normally accompanied by high hydrocarbon (HC) levels in the exhaust and an early combustion phasing before the top‐dead‐center (TDC) that may drain out substantial amounts of fuel energy from the engine cycle. Exhaust gas recirculation is usually applied to delay the onset of combustion, thereby shifting the phasing of the heat release close to the TDC. Although the retarded phasing improves the engine energy efficiency, a significant increase in HC and carbon monoxide emissions will deteriorate the combustion efficiency. Therefore, an inherent trade‐off exists between the combustion phasing and the combustion efficiency that needs to be minimized for improved energy efficiency. In this work, both theoretical and experimental studies have been carried out to evaluate the combustion efficiency‐phasing (CEP) trade‐off. Engine tests have been conducted to analyze the losses in combustion (burning) and phasing efficiencies, and along with theoretical analyses, the CEP trade‐off has been evaluated in terms of a ‘coefficient of combustion inefficiency’ (CCI). The CCI quantitatively correlates the losses in combustion and phasing efficiencies and provides a reference for improving the combustion phasing of the HCCI operation vis‐à‐vis the combustibles in the exhaust. The focus of this research is to carry out a quantitative analysis of the energy efficiency of HCCI cycles. Copyright © 2011 John Wiley & Sons, Ltd.     

Oxy‐fuel combustion characteristics and kinetics of microalgae and its mixture with rice straw using thermogravimetric analysis

The thermal behavior of rice straw, microalgae, and their mixture was studied by thermogravimetric analysis (TGA). Co‐combustion of rice straw and microalgae broadened the temperature range of combustion, facilitated ignition, and promoted burnout. The blend ratio of microalgae should be less than or equal to 10% in a 20%O₂/80%N₂ atmosphere and 30% in a 20%O₂/80%CO₂ atmosphere to reach a higher comprehensive combustion index (CCI) value than the individual fuels. The co‐combustion with a small ratio of microalgae could remedy partial negative effects on combustion performance caused by the replacement of N₂ using CO₂. The interaction of blends depended on the atmosphere and temperature range. The prediction of the combustion performance of blends by a weighted sum of individual fuels worked better in an O₂/CO₂ atmosphere at low temperatures, while better in an O₂/N₂ atmosphere at high temperatures. The simulation using the model which contained 2 parallel multi‐order reactions matched with the thermogravimetric curves well, and blending reduced activation energies of the second stage.     

Numerical study on flash‐boiling spray of multicomponent fuel

Flash‐boiling occurs when a fuel is injected into a combustion chamber where the ambient pressure is lower than the saturation pressure of the fuel. It has been known that flashing is a favorable mechanism for atomizing liquid fuels. On the other hand, alternative fuels, such as gaseous fuels and oxygenated fuels, are used to achieve low exhaust emissions in recent years. In general, most of these alternative fuels have high volatility and flash‐boiling takes place easily in the fuel spray when injected into the combustion chamber of an internal combustion engine under high pressure. In addition the multicomponent mixture of high‐ and low‐volatility fuels has been proposed in the previous study in order to control the spray and combustion processes in an internal combustion engine. It was found that the multicomponent fuel produces flash‐boiling with an increase in the initial fuel temperature. Therefore, it is important to investigate these flash‐boiling processes in fuel spray. In the present study, the submodels of a flash‐boiling spray are constructed. These submodels consider the bubble nucleation, growth, and disruption in the nozzle orifice and injected fuel droplets. The model is implemented in KIVA3V and the spray characteristics of multicomponent fuel with and without flashing are numerically investigated. In addition, these numerical results are compared with experimental data obtained in the previous study using a constant volume vessel. The flashing spray characteristics from numerical simulation qualitatively show good agreement with the experimental results. In particular, it is confirmed from both the numerical and experimental data that flash‐boiling effectively accelerates the atomization and vaporization of fuel droplets. This means that a lean homogeneous mixture can be quickly formed using flash‐boiling in the combustion chamber. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(5): 369–385, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20117     

Experimental research of high‐temperature regenerative heat transfer

A small‐scale high‐temperature air combustion experimental system was set up. The effects of the switching period on the heat transfer characteristics of a regenerator were discussed, and an optimal switching period was suggested. The temperature distribution in the combustion chamber was analyzed and the emission of NO_X and CO with the operational parameters was summarized. The decomposability of CF₄ was primarily studied. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(5): 359–368, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20118     

A simplified fuel‐NOx model based on regression analysis

The mechanism of detailed chemical reactions in combustion is very complicated, especially when the formation of a pollutant such as NO_x is considered. Based on regression analysis, a simplified fuel–NO_x model is developed for premixed flame. The new model is available for a wider range of temeperature and fuel–air ratios compared with De Soete's (1975) fuel NO model. The reduction CHi species on NO is considered so that the model can be used in both fuel‐lean and fuel‐rich combustion systems. After a great simulation of a one‐dimensional premixed flame system using Miller and Bowman's (1989, Prog. Energy Combust. Sci., 15, 287) detailed elementary reaction model, the calculation of all the reaction rates is presented based on regression analysis. Copyright © 1999 John Wiley & Sons, Ltd.     

Thermal transport phenomena of turbulent jet diffusion flames by means of anisotropic k–ϵ–t2–ϵt model

A numerical study is performed on transport phenomena in a turbulent jet diffusion flame of hydrogen from a vertical circular nozzle. An anisotropic k–ϵ–t² –ϵ_t model and the eddy‐dissipation model are employed to simulate thermal fluid flow and combustion phenomena, respectively. The governing boundary‐layer equations are discretized by means of a control volume finite‐difference technique and are numerically solved. The model predicts the experimental data in the existing literature. It is found from the study that (i) the model employed here can be applied to combustion phenomenon, and (ii) the presence of flame enhances the anisotropy of turbulence and causes a substantial attenuation in the turbulent kinetic energy, that is, most turbulent kinetic energy in the flame in the downstream part is laden exclusively in the streamwise fluctuation. Copyright © 1999 John Wiley & Sons, Ltd.     

Thermo‐economic investigation: an insight tool to analyze NGCC with calcium‐looping process and with chemical‐looping combustion for CO2 capture

In this work, three kinds of natural gas‐based power generation processes for CO₂ capture and storage, that is, natural gas‐combined cycle with pre‐combustion decarburization (NGCC‐PRE), NGCC‐PRE with calcium‐looping process, and NGCC‐PRE with chemical‐looping combustion (NGCC‐CLC), are analyzed by Aspen Plus. The effects of two decisive variables (i.e., steam‐to‐natural gas (S/NG) ratio and oxygen‐to‐natural gas (O/NG) ratio) on the thermodynamic performances of individual process, such as energy and exergy efficiencies, are investigated systematically. Based on simulation outcomes, all the three processes are favored by operating at S/NG = 2.0 and O/NG = 0.65. Furthermore, comparisons of individual system efficiencies and exergy destruction contributor are herein involved. The results show that the highest system efficiencies and lowest exergy destruction are achieved in the NGCC‐CLC process. In addition, capital investment, dynamic payback period, net present value, and internal rate of return are used for deciding the economic feasibility and surely are involved in this work for comparison purpose. Copyright © 2016 John Wiley & Sons, Ltd.     

Evaluation of Mg‐MOF‐74 for post‐combustion carbon dioxide capture through pressure swing adsorption

This paper presents a computational study of an energy‐efficient technique for post‐combustion CO₂ capture using novel material, namely, Mg‐MOF‐74, using pressure swing adsorption (PSA) processes. A detailed one‐dimensional, transient mathematical model has been formulated to include the heat and mass transfer, the pressure drop and multicomponent mass diffusion. The PSA model has been further extended by incorporating a heat regenerating process to enhance CO₂ sequestration. The heat dissipated during adsorption is stored in packed sand bed and released during desorption step for heating purpose. The model has been implemented on a MATLAB program using second‐order discretization. Validation of the model was performed using a complete experimental data set for CO₂ sequestration using zeolite 13X. Simulation of the PSA experiment on fixed bed has been carried out to evaluate the capacity of Mg‐MOF‐74 for CO₂ capture with varying feed gas temperature of 28 and 100 °C, varying pressurization and purge times and heat regeneration. It was discovered that the PSA process with heat regeneration system might be advantageous because it achieves equivalent amount of CO₂ sequestration in fewer PSA cycles compared with PSA without heat regeneration system. Based on the simulated conditions, CO₂ recovery with Mg‐MOF‐74 gives high percentage purity (above 98%) for the captured CO₂. Copyright © 2015 John Wiley & Sons, Ltd.     

Lignite‐fired air‐blown IGCC systems with pre‐combustion CO2 capture

Detailed analyses based on mass and energy balances of lignite‐fired air‐blown gasification‐based combined cycles with CO₂ pre‐combustion capture are presented and discussed in this work. The thermodynamic assessment is carried out with a proprietary code integrated with Aspen Plus^® to carefully simulate the selective removal of both H₂S and CO₂ in the acid gas removal station. The work focuses on power plants with two combustion turbines, with lower and higher turbine inlet temperatures, respectively, as topping cycle. A high‐moisture lignite, partially dried before feeding the air‐blown gasification system, is used as fuel input. Because the raw lignite presents a very low amount of sulfur, a particular technique consisting of an acid gas recycle to the absorber, is adopted to fulfill the requirements related to the presence of H₂S in the stream to the Claus plant and in the CO₂‐rich stream to storage. Despite the operation of the H₂S removal section representing a significant issue, the impact on the performance of the power plant is limited. The calculations show that a significant lignite pre‐drying is necessary to achieve higher efficiency in case of CO₂ capture. In particular, considering a wide range (10–30 wt.%) of residual moisture in the dried lignite, higher heating value (HHV) efficiency presents a decreasing trend, with maximum values of 35.15% and 37.12% depending on the type of the combustion turbine, even though the higher the residual moisture in the dried coal, the lower the extraction of steam from the heat recovery steam cycle. On the other hand, introducing the specific primary energy consumption for CO₂ avoided (SPECCA) as a measure of the energy cost related to CO₂ capture, lower values were predicted when gasifying dried lignite with higher residual moisture content. In particular, a SPECCA value as low as 2.69 MJ/kg_CO2 was calculated when gasifying lignite with the highest (30 wt.%) residual moisture content in a power plant with the advanced combustion turbine. Ultimately, focusing on the power plants with the advanced combustion turbine, air‐blown gasification of lignite brings about a reduction in HHV efficiency equal to almost 1.5 to 2.8 percentage points, depending on the residual moisture in the dried lignite, if compared with similar cases where bituminous coal is used as fuel input. Copyright © 2016 John Wiley & Sons, Ltd.