Version 4.2 describes char combustion from ignition throughout the latest stages of burnout based on the expanded version Prof. Robert Hurt’s Carbon Burnout Kinetics Model (CBK/E). Complete burnout histories are reported, along with the histories for the temperatures, sizes, and densities of individual particles. Version 4.2 also describes char gasification by H2O (with inhibition by H2), CO2 (with inhibition by CO), and H2 with NEA’s own expanded version of CBK called CBK/G.
The package also automatically analyzes any of the output to specify the kinetic parameters in simple rate expressions that give the same predictions as NEA’s comprehensive reaction mechanisms. In turn, these rates can be directly input into CFD simulations and process design applications to dramatically improve the depiction of fuel quality impacts.
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.
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.
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 char gasification reactivity 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 for both char and soot, 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.
Module 5 expands all reaction mechanisms in a particular package for applications involving any kind of petroleum coke and biomass, including papers, woods, grasses, and agricultural residues. A version for black liquor at low temperatures is also available. With Module 5, all the capabilities of the other six 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 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 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 three 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.
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.
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.
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.
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, “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).