FLASHCHAIN theory for rapid coal devolatilization kinetics. 1. Formulation

Niksa, Stephen; Kerstein, Alan R.

doi:10.1021/ef00029a006

Cited by 257 publications

(162 citation statements)

References 3 publications

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“…Comparison with some of the existing vapor pressure correlations are shown in Niksa-Kerstein [1991] correlations. These correlations were selected for comparison because they are widely used in coal pyrolysis models.…”

Section: E5 Results Of the Vapor Pressure Measurementsmentioning

confidence: 99%

Vapor pressures and heats of vaporization of primary coal tars

Suuberg¹

1992

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Executive SummaryThis project had as its main focus the determination of vapor pressures of coal pyrolysis tars. It involved performing measurements of these vapor pressures and from them, developing vapor pressure correlations suitable for use in advanced pyrolysis models (those models which explicitly account for mass transport limitations).This report is divided into five main chapters. Each chapter is a relatively "stand-alone" section. Chapter A reviews the general nature of coal tars and gives a summary of existing vapor pressure correlations for coal tars and model compounds. It is shown that the heterogeneous nature and the complexity of coal tars have made it unrealistic to apply detailed vapor pressure correlations which take into account the variation in the chemical structure of the tars. The significant product of this study is a much improved understanding of the volatility and thermal behavior of coal tars. The volatility was studied by vacuum sublimation and Knudsen effusion experiments. The volatility behavior is considerably more complicated than had been earlier believed.The tars evaporate in a "distillation-like" fashion. More volatile species are lost earlier in the process, leaving behind a progressively less volatile residue. The results suggest that there are three very different classes of compounds, and therefore, at least three different vapor pressure behaviors. The first corresponds to compounds of high molecular weight and significant alkyl character, the second to compounds with significant hydroxyl group content and medium molecular weight, and the third to medium molecular weight aromatic compounds without hydroxyl groups. Hydrogen bonding plays a major role in the determining the tar volatility. vi There has been concern in pyrolysis modeling about how closely Raoult's law is followed in coal tar. It appears from our results that the assumption of ideal mixture behavior could be acceptable for rough models of pyrolysis despite the possibility of strong specific interactions between certain functional groups.The results from the current work show that measuring the vapor pressures of complicated and thermally unstable mixtures is possible at low temperatures. There has also been some concern about condensation-type reactions influencing the results of vapor

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Section: E5 Results Of the Vapor Pressure Measurementsmentioning

confidence: 99%

Vapor pressures and heats of vaporization of primary coal tars

Suuberg¹

1992

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“…In contrast, during coal combustion the knowledge of the exact chemical species liberated during coal devolatilization and char oxidation is unclear. Several coal devolatilization studies propose species evolution rates; however, these models have not been coupled to a detailed chemical reaction mechanism (Niksa, 1994;Niksa, 1991;Solomon et al, 1991).…”

Section: No Formation Mechanism For Pulverized-coal Applicationsmentioning

confidence: 99%

Combustion 2000

Levasseur¹,

Goodstine²,

Ruby³

et al. 2001

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. The objective of this report is to emphasize the results and achievements of the program and not to archive every detail of the past six years of effort. These details are already available in the twenty-two quarterly reports previously submitted to DOE and in the final report from Phase I. The report is divided into three major foci, indicative of the three operational groupings of the program as it evolved, was restructured, or overtaken by events. In each of these areas, the results exceeded DOE goals and expectations.HIPPS Systems and Cycles (including thermodynamic cycles, power cycle alternatives, baseline plant costs and new opportunities) HITAF Components and Designs (including design of heat exchangers, materials, ash management and combustor design)Testing Program for Radiative and Convective Air Heaters (including the design and construction of the test furnace and the results of the tests)There are several topics that were part of the original program but whose importance was diminished when the contract was significantly modified. The elimination of the subsystem testing and the Phase III demonstration lessened the relevance of subtasks related to these efforts. For example, the cross flow mixing study, the CFD modeling of the convective air heater and the power island analysis are important to a commercial plant design but not to the R&D product contained in this report. These topics are of course, discussed in the quarterly reports under this contract.The DOE goal for the High Performance Power Plant System ( HIPPS ) is high thermodynamic efficiency and significantly reduced emissions. Specifically, the goal is a 300 MWe plant with > 47% (HHV) overall efficiency and ≤ 0.1 NSPS emissions. This plant must fire at least 65% coal with the balance being made up by a premium fuel such as natural gas.To achieve these objectives requires a change from complete reliance of coal-fired systems on steam turbines (Rankine cycles) and moving forward to a combined cycle utilizing gas turbines (Brayton cycles) which offer the possibility of significantly greater efficiency. This is because gas turbine cycles operate at temperatures well beyond current steam cycles, allowing the working fluid (air) temperature to more closely approach that of the major energy source, the combustion of coal. In fact, a good figure of merit for a HIPPS design is just how much of the enthalpy from coal combustion is used by the gas turbine.The efficiency of a power cycle varies directly with the temperature of the working fluid and for contemporary gas turbines the optimal turbine inlet temperature is in the range of 2300-2500 °F (1260-1371 °C). These temperatures are beyond the working range of currently available alloys and are also in the range of the ash fusion temperature of most coals. These two sets of physical properties combine to produce the major engineering challenges for a HIPPS design. ivThe UTRC team developed a design hierarchy to impose more rigor in our approach. Once the size of the plant had been determined by t...

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“…Therefore, mechanisms of the formation of volatile products in coal pyrolysis still remains inconsistent and elusive, even though new reaction models for coal pyrolysis have been proposed in recent years. (Solomon et al 1988;Grant and Pugmire 1989;Kerstein 1990, 1992;Solomon et al 1990a, b, c;Niksa 1991aNiksa , b, c, 1995Solomon 1994;Tian et al 2001).…”

Section: Introductionmentioning

confidence: 99%

Characteristics of gas evolution profiles during coal pyrolysis and its relation with the variation of functional groups

Zhang

Takeda

et al. 2017

Int J Coal Sci Technol

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Strict relation between the substituents or functional groups attached to the coal macromolecules and the generation of the volatile products, e.g., CH 4 , H 2 O, CO, CO 2 , etc., during the coal pyrolysis is an important but confusing subject. In this paper, quadrupole mass spectrometry, gas chromatography, and 13 C nuclear magnetic resonance are applied to real-time monitoring the formations of volatile products, off-line quantitative determination of the total products from the pyrolysis of a sub-bituminous coal (SC), and the changes of diverse substitents in the SC along with coke foamation, respectively. These measurements are also performed for the pyrolysis of a caking coal to contrast SC. The qualitative and quantitative data reveal that, during coal pyrolysis, the functional groups related with the formation of CO, i.e., ether, carbonyl, and anhydride, can directly generate CO via bond breaking, or take a detour of the formation of other intermediates via condensation and recombination firstly. Moreover, the formations of CO 2 and CH 4 are related to the direct removal of -COO-and -CH 3 , respectively.

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FLASHCHAIN theory for rapid coal devolatilization kinetics. 1. Formulation

Cited by 257 publications

References 3 publications

Vapor pressures and heats of vaporization of primary coal tars

Vapor pressures and heats of vaporization of primary coal tars

Combustion 2000

Characteristics of gas evolution profiles during coal pyrolysis and its relation with the variation of functional groups

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