The partitioning of a solid fuel into volatile matter and char during utilization is among the most fundamentally important fuel characteristics. The main reason is that during combustion and gasification, volatiles burn away in tens or hundreds of milliseconds, whereas char burnout requires a few seconds and char gasification requires tens of seconds. Beyond the total yield, the composition of volatiles is also important. Volatiles consist of noncondensable gases with high heating value, light oils suitable as fuels and feedstocks, and high-boiling tars for subsequent refining. There are also many precursors to noxious gases, including HCN, NH₃, H₂S, and COS. Volatiles also contain trace amounts of species that have been associated with fouling, slagging, and corrosion, including HCl, NaOH, Na(m), KOH, and K(m). Char burning rates affect process temperatures and heat recovery rates. Char burnout levels are especially important, because they directly determine combustion efficiencies. Char burnout also indirectly determines the suitability of flyash for premium flyash utilization methods. Gasification technology may ultimately supercede pulverized fuel boilers for power production, based on its higher operating efficiencies, more favorable emissions, and multifuel capability. Char gasification rates determine residence time requirements for complete conversion and indirectly affect flyash deposition and slagging behavior.

PC Coal Lab^® predicts the yields and compositions of the volatiles from any coal, biomass, and petroleum coke at virtually any operating conditions, along with complete combustion histories and complete gasification histories. This information is the cornerstone of reliable forecasts of fuel quality impacts on technological performance, emissions, and product quality for all the most important utilization schemes. Combustion engineers will use it to formulate more powerful regression variables for their correlations for fuel quality impacts on flame stability, near-burner heat release, and emissions. Gasifier developers will use it to estimate performance for a wide selection of solid fuels. Environmental specialists will use the information to assess the cumulative impact of fuel switches and co-firing with opportunity fuels across a regional utility operation. Computational analysts will use PC Coal Lab^® to specify the parameter values that they use in CFD simulations and process design applications involving solid fuel utilization technologies.

This website is full of briefs on past applications with PC Coal Lab^®, especially in the sections on Pulverized Fuel Boilers, Support for CFD, Gasification Systems, Opportunity Fuels, and Fluidized Beds. Feel free to request additional information on any of these applications. If you do not see anything like your application, contact NEA to discuss your interests.

In devolatilization modeling, FLASHCHAIN^® has always been based on the proximate and ultimate analyses as the only sample-specific input requirement, whereas other models firmly connected the accuracy of their predictions to monumental laboratory support with ¹³C NMR, FTIR, and other advanced diagnostics. This feature is an enormous advantage because it opened up virtually the entire literature database on laboratory testing for FLASHCHAIN^® validations. Even reports on tests conducted decades ago almost always contain proximate and ultimate analyses for the subject fuels, so the data could be used to validate FLASHCHAIN^® predictions. In contrast, only a miniscule fraction of this database includes the highly specialized analyses required by the other models. Consequently, the validation database for FLASHCHAIN^® is simply enormous compared to the competition.

NEA has published validations in tests with over 300 fuels, and performed consulting work with over 2000 coals from all geographical regions worldwide, diverse forms of biomass (woods, grasses, agricultural residues, paper), various black liquors, residual petroleum fractions, and numerous petroleum cokes. The first validations for near-atmospheric pressure were supplemented with additional data at elevated pressures for 100 coals at pressures to 16.7 MPa. Then, in 1995, NEA began to conduct blind evaluations, in which prospective clients gave us fuel properties and test conditions but not the measured product distributions for devolatilization. Time and time again, FLASHCHAIN^® consistently predicted total yields within the measurement uncertainties in nine of ten cases. Learn More.

By comparison, the accuracy of predicted char conversion histories is highly ambiguous. Combustion experts have compiled a few dozen physical, chemical, morphological, and structural factors that affect char conversion kinetics. But the literature does not describe a single testing program in which these factors were reported for different solid fuels along with time-resolved extents of conversion and detailed operating conditions. So it is simply impossible for NEA or anyone else to accurately predict intrinsic char conversion reactivities from even an extensive series of analytical tests on the fuel. Accordingly, NEA strongly recommends a one-point calibration with char conversion data whenever accurate predictions are needed for specific fuel samples. The calibration data can be obtained with an entrained-flow reactor or thermogravimetric analyzer (TGA), or lab- or pilot scale furnace or gasifier. Whatever the system, calibration conditions closer to the conditions in the application of interest will always improve the accuracy of the model predictions. Once the initial reactivities have been calibrated, CBK delivers accurate predictions for broad ranges of particle size, gas composition, and pressure. For char oxidation, this procedure has been validated with 235 independent tests that characterized 11 coals, 2 coal chars, and a graphite, heating rates approaching 10°C/s, furnace temperatures to 1527°C, pressures to 2.0 MPa, and O₂ levels to 100 %. For gasification, CBK/G was validated with 452 independent tests that characterized 26 coals, heating rates approaching 10⁵°C/s, furnace temperatures to 1500°C, pressures to 3.0 MPa, and broad ranges of CO₂, H₂O, CO, and H₂ levels. Learn More.

PC Coal Lab^® has already been licensed by companies and universities in the USA, Canada, Japan, China, Korea, Taiwan, India, the UK, France, Germany, Hungary, and South Africa, and utilized extensively by NEA’s licensees with numerous local and world-traded solid fuels. Also, NEA recently reported an evaluation involving about 100 Chinese coals. Since no systematic discrepancies have been reported by any of our licensees, it is difficult to conceive of fuels from anywhere that cannot be accurately described by NEA’s reaction mechanisms.

PC Coal Lab^® is assembled from eight independent modules, so you can select the capabilities that best meet your needs. As your needs change, simply add modules to expand the capabilities. Module 1 simulates total weight loss and the yields of gas, tar, and char from any coal at any operating conditions based on FLASHCHAIN^®. It is the entry level package. Module 2 simulates total weight loss plus the yields of tar, total noncondensible gases, CO, CO₂, H₂O, CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈, H₂, H₂S, COS, SO₂ and HCN, plus the elemental compositions (C/H/O/N/S) of char and tar, expressed in both the coal element fractions and weight percentages. Module 2 also describes the transformations of primary devolatilization products into soot, CO, H₂, CH₄, C₂H₂, H₂O, CO₂, H₂S, and HCN as occurs spontaneously at temperatures above 900 °C. Module 7 describes tar conversion under reducing conditions at any temperature. It predicts the yields of oils and additional noncondensables and the yields and compositions of PAH for any thermal history at moderate temperatures, and also the nucleation and growth of soot at hotter temperatures. The analysis is suitable for simulations of volatiles transformations in fixed- and fluidized bed reactors, and also in CFBCs, p. f. furnaces, and multi-stage systems, where volatiles are processed at conditions that are much different from those in the primary devolatilization stage. Module 8 describes how elevated H₂ pressures affect all stages of coal pyrolysis and tar conversion. It predicts the enhancement of tar yields and total weight loss, and also describes the hydrogenation of tar in the free stream, which is the only means to disrupt the conversion of tar into soot at moderately high temperatures.

Module 4 adds char reactivity based on the expanded version of Prof. Robert Hurt’s Carbon Burnout Kinetics (CBK/E) model. This model describes deactivation due to thermal annealing and the associated reductions in burning rate during the very latest stages of carbon oxidation. It has also been fully validated for applications at elevated pressure. Module 4 predicts complete burnout histories for both char and soot, including the dynamics of mass loss, particle temperature, and size changes as well as the ultimate values of loss-on-ignition (LOI) and extent of burnout based on either coal or char. Module 6 adds gasification reactivities for char and soot based on CBK/G. The original deactivation and ash encapsulation mechanisms in CBK are retained, but the kinetics have been expanded for simultaneous gasification by H₂O, CO₂, and H₂ with inhibition by H₂ and CO. Module 6 predicts complete gasification histories, including the dynamics of mass loss, particle temperature, and changes in size and density as well as the ultimate values of unburned carbon emissions and extent of gasification based on either coal or char. It has also been fully validated for applications at elevated pressure against an extensive database on gasification kinetics for diverse coals and biomass chars.

Module 5 expands all reaction mechanisms in a particular package for applications involving any kind of petroleum coke and biomass, including raw and torrefied woods, grasses, and agricultural residues. A version for black liquor at low temperatures is also available. Biomass is now analyzed as cylindrical particles to account for the strong impact of variations in aspect ratio. With Module 5, all the capabilities of the other seven modules are the same when they are applied to these opportunity fuels, except that additional oxygenated products appear in the product distributions from biomass. And the fuel’s proximate and ultimate analyses remain the only sample-specific input data requirement.

Module 3 assigns nominal reaction rates to any of the products of devolatilization, and to the predicted tar conversion histories, and to the oxidation and gasification histories of char and soot, provided that the primary modules on these stages are also installed. In other words, it automatically assigns parameter values for the simple global rate laws used in CFD simulations, given only the coal’s proximate and ultimate analyses and the test conditions. For example, with Modules 1 and 2, it specifies the parameters in a single first-order reaction (or two competing reactions or a distributed activation energy model) that match the transient weight loss from the FLASHCHAIN^® simulations, or specifies rates for tar release or volatile-N release, or any other species of particular interest. This module also specifies global rate expressions and parameter values that closely match the extents of tar conversion, including soot production during tar decomposition and oils production during tar hydroconversion. It also specifies global rate expressions and parameter values that closely match the extents of char conversion from the full char oxidation and char gasification mechanisms in Modules 4 and 6. It also directly supports CFD with a complete set of thermophysical properties (density and specific heat) and rate parameters (stoichiometric coefficients, rate constants, and reaction enthalpies) that can be entered directly as fuel property specifications into CFD simulations and process design applications.

The package is provided with full documentation and the four dozen previous installations of PC Coal Lab^® have gone smoothly. Purchases are based on a one-time payment; there are no annual maintenance fees. The package is distributed under a license that reserves all copyrights and trademarks with NEA. Licensees are free to use the output predictions without restrictions, but may not distribute the package outside of their institutions. NEA uses a USB hardware security key to prevent unauthorized distribution. The software is delivered with five keys to enable applications on five CPUs; networked installations are not supported. Additional keys can be purchased for NEA’s cost of the keys, plus shipping and handling. Packages based on all eight modules have already been shipped to utility OEMs and burner services companies in the U.S., Japan, Europe, Canada, India, Korea, Taiwan, China, and South Africa. For help in selecting modules for your application of interest, current prices, and purchase terms, contact NEA.

PC Coal Lab^®’s two test configurations imply strong connections to their physical counterparts in fuel laboratories. Such connections are important when the accuracy of the predictions is being evaluated in a direct quantitative comparison against lab test data. But usually this package will be used in design work, troubleshooting, and even more comprehensive simulations. In these applications, users should feel free to manipulate the input specifications that determine thermal histories in both the drop-tube and the wire-grid to simply generate the thermal histories of their greatest interest. Curious users will quickly notice that variations in heating rate of a factor of two are not all that significant whenever their focus is on ultimate yields and product distributions. And they will also find that the shape of a temperature history of exponential form can be manipulated by specifying different gas and wall temperatures or different particle sizes in the drop-tube simulations.

These features enable users to characterize the devolatilization behavior in more complex reaction systems. Of course, the range of thermal histories in a complex system must first be described with a suitable thermal analysis that will necessarily be more sophisticated than the one in PC Coal Lab^®. But given these thermal histories, it is almost always possible to find the operating conditions in the drop tube or wire grid configurations that will impart very similar heating rates, ultimate reaction temperatures, and reaction times. It does not matter if the simulated gas or furnace temperatures or the particle size are consistent with their counterparts in the complex physical system. Provided that the thermal history of the fuel and the pressure are the same, then the predicted devolatilization behavior will be relevant. In this broader sense, PC Coal Lab^® supports two thermal histories. One is of exponential form with decelerating heating rates throughout, and the other has uniform heating rates.

Only rarely have we confronted completely different kinds of thermal histories, even among applications involving the most complex coal utilization technology. For these rare cases, users can simply enter a completely arbitrary thermal history into an optional input file and bypass the internal thermal history calculation entirely. Similarly, the reactive gas concentrations of O₂ for oxidation and of H₂O, CO₂, CO, and H₂ for gasification can be entered in optional text files to represent profiles of gas composition across furnaces and gasifiers. Ambient temperature profiles can be entered in the same way. The fuel gasification module also supports an operating mode whereby the fuel suspension loading is specified, and the gas composition is continuously updated to be in chemical equilibrium while the fuel is consumed via gasification chemistry.

PC Coal Lab^® is not a user-friendly software package with a graphical user interface and modern storage capabilities; rather, it is an executable file that accepts input via two to six text files. Since the input data is strictly formatted, NEA urges users to automate the extraction of input data from their preferred storage files into the input text files for a PC Coal Lab^® execution. The results are presented in two formats. All calculated values are loaded into a MS Excel spreadsheet in comma-delimited format at the finest time resolution for post-processing. Alternatively, more than two dozen one-page reports are issued in text format on groups of results, such as noncondensable gases from devolatilization, the char burnout history, or the thermophysical properties and rate parameters for an associated CFD simulation. Each simulation handles up to five sets of fuel properties and up to five sets of operating conditions, and can conceivably generate more than 600 pages of reports. Accordingly, users can elect to issue only the reports of greatest interest.

The only sample-specific fuel properties are the proximate analysis, which are the mass percentages of moisture, ash, volatiles, and fixed carbon, and the ultimate analysis, which are the mass percentages of C, H, O, N, and S. Users without in-house facilities can obtain them through contract analytical labs at minimal cost. An aspect ratio for raw and torrefied biomass particles is highly recommended. For cases where devolatilization is the primary focus, the only additional inputs are the test conditions, which specify the thermal history of fuel temperature as a function of time, and the pressure and particle size. Thermal histories can be specified in terms of a uniform heating rate to an ultimate temperature for a prescribed period, or as the temperatures of the ambient gas and wall plus the total transit time and particle size. Ambient temperatures may be either isothermal or variable throughout the transit time.

The same information is required for cases that also involve char conversion via combustion or gasification. In addition, the concentrations of all reactive gases must be specified, either as uniform values or as transient profiles. However, it is currently impossible for NEA or anyone else to accurately predict intrinsic char conversion reactivities from even an extensive series of analytical tests on the fuel. Accordingly, NEA strongly recommends a one-point calibration with char conversion data whenever accurate predictions are needed for specific fuel samples. The calibration data can be obtained with an entrained-flow reactor or thermogravimetric analyzer (TGA), or lab- or pilot scale furnace or gasifier. Whatever the system, calibration conditions closer to the conditions in the application of interest will always improve the accuracy of model predictions. To summarize, devolatilization may be accurately simulated with only the proximate and ultimate analyses, but the accuracy of char conversion simulations is usually determined by calibrations for the initial char reactivity parameter.

The results are presented in two formats. All calculated values are loaded into a MS Excel spreadsheet in comma-delimited format at the finest time resolution for post-processing. Alternatively, more than two dozen one-page reports are issued in text format on groups of results, such as noncondensable gases from devolatilization, the char burnout history, or the thermophysical properties and rate parameters for an associated CFD simulation. Each simulation handles up to five sets of fuel properties and up to five sets of operating conditions, and can conceivably generate more than 600 pages of reports. Accordingly, users can elect to issue only the reports of greatest interest. Also, NEA can prepare output reports to satisfy user specifications upon request.

The primary limitation of PC Coal Lab^® – and the greatest potential source of confusion – is that the package contains no chemistry among noncondensable species in the gas phase. In other words, PC Coal Lab^® describes the chemical transformations in the condensed fuel phase and for tar, but omits all reactions among noncondensable species, including gaseous hydrocarbons, CO, H₂, CO₂, H₂O, HCN, NH₃, and H₂S. This is potentially confusing because this website and NEA’s publications are full of simulation applications involving pulverized fuel flames, furnaces, CFBCs, FBCs, and entrained flow and fluidized bed gasifiers, and all of them incorporate PC Coal Lab^®. But they also incorporate completely separate elementary reaction mechanisms for chemistry among noncondensable gases and on soot, and complex sequencing programs that account for chemical source terms from both the condensed and gas phases to accurately converge to the local gas compositions. In these simulations, PC Coal Lab^® only provides the source terms from the solid fuel phase and from tar decomposition. Consequently, PC Coal Lab^®, per se, cannot fully simulate any of these utilization systems, because it is a kinetics package rather than a device simulator. (Of course, NEA frequently develops device simulators according to client specifications on a consulting basis, and these invariably call PC Coal Lab^®.)

Will the chemistry among noncondensable gases affect test data even in simple, lab-scale tests ? Primary devolatilization products released into nonreactive gases from coal at 600°C or from biomass at 500°C or hotter are transformed by secondary volatiles pyrolysis. At high temperatures, the complex distribution of primary products is quickly reduced to soot, CO, CO₂, H₂O, H₂, CH₄, and C₂H₂, plus trace amounts of noxious gases. At moderate temperatures, the conversion is much slower, and PAH and oils persist along with the noncondensables. Version 4.2 of PC Coal Lab^® predicts the distributions of secondary pyrolysis products for both situations. However, without the tar decomposition mechanism, users will need to use good judgment when they compare predictions to measurements taken from high-temperature flow systems, because the extent of conversion of primary volatiles into secondary pyrolysis products is often incomplete and is usually not monitored directly. Notwithstanding this uncertainty, the total yields and char properties should always be directly comparable.

Other processes are affected by secondary volatiles pyrolysis in much less obvious ways. When coals are heated rapidly, volatiles escape on such short time scales that secondary volatiles pyrolysis within the particles can be neglected. But for processes that involve relatively slow heating rates, the primary product distributions will be transformed by secondary pyrolysis even when chemistry is inhibited in the gaseous atmosphere surrounding the coal. (Nitrogen-species distributions provide the most direct evidence for an important role for secondary pyrolysis under slow heating conditions.) For this reason, PC Coal Lab^® should not be used for applications involving heating rates slower than about 1°C/s.

Similar reasoning will guide the applicability of the predictions from PC Coal Lab^® for reactive gas environments, particularly combustion, gasification, and hydrogasification systems. Provided that the flux of volatiles is strong enough to prevent a reactive gas from counter-diffusing through the internal pore system of a devolatilizing coal particle to contact the condensed coal phase, the primary devolatilization mechanism cannot be affected by the reactive gas. Of course, the primary products will be converted into combustion or gasification products under less severe conditions than they would otherwise be transformed by secondary volatiles pyrolysis. Whereas these types of volatiles transformation are not included in V. 4.2, the total volatiles yields from PC Coal Lab^® should still be accurate under any conditions. Reactive gases also may release or consume energy, which indirectly affects primary devolatilization by changing the fuel’s thermal history. Such changes are included in V.4.2 for combustion around individual particles, but not for surface reactions involving reactants other than O₂ or for volatiles gasification or for suspensions at appreciable loadings.

Another group of restrictions comes from the omission of transport resistances in FLASHCHAIN^®’s formulation for PC Coal Lab^®. As particle size is increased, the resistance to volatiles escape increases, eventually reaching the point where the pressure within particles exceeds the ambient values. PC Coal Lab^® sets the internal pressure equal to the ambient pressure, and may therefore overpredict the yields from larger particles for some thermal histories. This situation is not simple enough to be characterized in terms of particle size alone, because volatiles escape rates increase in direct proportion to increases in the heating rate. Results in the literature suggest that the critical size is a few hundred microns for a heating rate of 10⁴°C/s, so PC Coal Lab^® applications with pulverized fuels are generally secure. Analogous limitations related to particle size may arise where intraparticle heat transfer resistances are large enough to cause significant temperature gradients across the particle radius.

People new to NEA’s reaction mechanisms should start with two survey articles, the first on FLASHCHAIN^® and CBK/E and the second on CBK/G:

S. Niksa, G. Liu, and R. H. Hurt, “Coal Conversion Submodels for Design Applications at Elevated Pressures. Part I. Devolatilization and Char Oxidation,” Prog. Energy Combust. Sci., 29(5):425-477 (2003).

G.-S. Liu and S. Niksa, “Coal conversion submodels for design applications at elevated pressures. Part II. Char Gasification,” Prog. Energy Combust. Sci., 30(6):697-717 (2004).

There are also the following other survey articles:

S. Niksa, “Process Chemistry of Coal Utilization: Impacts of Coal Quality and Operating Conditions,” Woodhead Publishing, Elsevier, London, ISBN 978-0-12-818713-5, Nov. 2019.

S. Niksa, “Predicting the Devolatilization Behavior of Any Coal From Its Ultimate Analysis,” Combustion and Flame, 100: 384-394 (1995a).

S. Niksa, “Predicting the Evolution of Fuel Nitrogen From Various Coals,” Twenty-Fifth Symposium (International) On Combustion, The Combustion Institute, Pittsburgh, 1994a, pp. 537-544.

S. Niksa and C.-W. Lau, “Global Rates of Devolatilization of Various Coal Types,” Combustion and Flame, 94: 293-307 (1993).

S. Niksa, “Rapid Coal Devolatilization as an Equilibrium Flash Distillation,” AIChE Journal, 34(5): 790-802 (1988a).

S. Niksa, “Modeling the Devolatilization Behavior of High Volatile Bituminous Coals,” Twenty-Second Symposium (International) On Combustion, The Combustion Institute, Pittsburgh, 1988b, p. 105.

S. Niksa, “Predicting the Rapid Devolatilization of Diverse Forms of Biomass with bio-FLASHCHAIN^®,” Proc. Combust. Inst., 24: 2727-2733 (2000).

T. Lang and R.H. Hurt, “Char Combustion Reactivities for a Suite of Diverse Solid Fuels and Char-Forming Organic Model Compounds.” Proc. Combust. Inst., 29:423-31 (2002).

Hurt, R. H. and J. M. Calo, “Semi-global intrinsic kinetics for char combustion modeling.” Combust. Flame 125:1138-1149 (2001).

Hurt, R. H., J.-K. Sun, and M. Lunden, “A Kinetic Model of Carbon Burnout in Pulverized Coal Combustion.” Combust. Flame 113(1/2): 181 (1997).