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The present study investigates the impact of biomass origin on the properties of biochar and its interaction with different treatment conditions, CO2 adsorption, and regeneration ability. The bioch...

The coadsorption of Hg⁰ and SO₃ on pure and Cu/Mn doped CeO₂(110) surfaces were investigated using the Density Functional Theory (DFT) method. A p (2 × 2) supercell periodic slab model with seven atomic layers was constructed to represent the CeO₂(110) surface. The results indicated that Hg⁰ physically adsorbed on the CeO₂(110) surface, while Hg⁰ chemically adsorbed on the Cu/Mn doped CeO₂(110) surface, which agree well with the experimental results that Cu and Mn doped CeO₂ greatly improved the Hg⁰ adsorption capacity of the adsorbent. The calculated results suggested that SO₃ more easily adsorbs on the above three surfaces than Hg⁰ due to the higher adsorption energy. The adsorption configurations and electronic structures indicated SO₃ reacted with O atoms of the surface to form SO₄²– species. Hence, SO₃ inhibits Hg⁰ adsorption on the CeO₂(110) surface by competing with Hg⁰ for surface lattice oxygen. In addition, SO₃ decreased the activity of the surface O atoms, which directly caused the negative effect on Hg⁰ adsorption.

Biochar is a solid by-product of thermochemical conversion of biomass to bio-oil and syngas. It has a carbonaceous skeleton, a small amount of heteroatom functional groups, mineral matter, and water. Biochar’s unique physicochemical structures lead to many valuable properties of important technological applications, including its sorption capacity. Indeed, biochar’s wide range of applications include carbon sequestration, reduction in greenhouse gas emissions, waste management, renewable energy generation, soil amendment, and environmental remediation. Aside from these applications, new scientific insights and technological concepts have continued to emerge in the last decade. Consequently, a systematic update of current knowledge regarding the complex nature of biochar, the scientific and technological impacts, and operational costs of different activation strategies are highly desirable for transforming biochar applications into industrial scales. This communication presents a comprehensive review of physical activation/modification strategies and their effects on the physicochemical properties of biochar and its applications in environment-related fields. Physical activation applied to the activation of biochar is discussed under three different categories: I) gaseous modification by steam, carbon dioxide, air, or ozone; II) thermal modification by conventional heating and microwave irradiation; and III) recently developed modification methods using ultrasound waves, plasma, and electrochemical methods. The activation results are discussed in terms of different physicochemical properties of biochar, such as surface area; micropore, mesopore, and total pore volume; surface functionality; burn-off; ash content; organic compound content; polarity; and aromaticity index. Due to the rapid increase in the application of biochar as adsorbents, the synergistic and antagonistic effects of activation processes on the desired application are also covered.

The present study discusses a novel ultrasound promoted amination technique to functionalize graphene oxide (GO) for CO2 adsorption. Graphene oxide was synthesized following the modified Hummer’s method. The developed functionalization technique integrates the advantages of low-frequency ultrasonic physical activation with the chemical functionalization using tetraethylenepentamine (TEPA). Acoustic treatment exfoliates the clusters of graphene oxide and enhances the surface area for the subsequent amine functionalization and CO2 adsorption. Changes in textural properties, surface functionalities, thermal stability, and elemental compositions were examined before and after activation of graphene oxide. The characterization results revealed substantial increment of N content, from 0.08 in pristine to 4.84% in functionalized GO and the subsequent reduction in surface area from 289 to 198 m2/g in the functionalized GO, indicating attachment of TEPA to GO structure. CO2 adsorption experiments were conducted under diluted CO2 with the partial pressure of 0.10 atm. at 338 K and the results revealed that ultrasonic-TEPA activated GO possessed enhanced adsorption capacity of 1.2 mmol g−1 over pristine GO. While pristine GO could only achieve the maximum adsorption capacity of 0.3 mmol g−1 at 303 K. Besides, the sonochemically modified adsorbent showed stable cyclic adsorption-regeneration performance with only 1% reduction in adsorption capacity after 10 cycles. Finally, the effectiveness of the developed physicochemical activation technique was determined by comparing its adsorption capacity with the adsorbents found from literature.

The present study discusses a novel biochar activation technique consisting of physical modification using low frequency ultrasound and chemical functionalization with individual amines and their b...

The objectives of a series of our researches are to determine the feasibility of applying ultrasonic pretreatment prior to biochar gasification. As per the initial results, the heating value (HV) of biochar significantly increased after acoustic treatment in water with dissolved CO2 (AIChE Journal, 2014;60:1054–1065). Accordingly, emphasis of the current work is placed on the parameters governing the HV of biochar in the early stage of the treatment. Switchgrass and miscanthus biochars were treated under different conditions. The reactant ratio, biochar:water:CO2, exhibited profound impacts on the synergism. The highest (but not yet systematically optimized) ratio of HV increase (or HV Gain, HG) to ultrasound energy supplied (ES) takes place when biochar-to-water ratio, or BC:W, equals 0.06 g/ml. The observed HG/ES is about 10, suggesting that the energy consumption is only a fraction of the acoustic energy supplied. Miscanthus biochar’s HV increases by up to 4.6% after treatment at 5% amplitude for 135 s (HG = 33 cal/g). For the same run, miscanthus biochar's H content increased by 42.7%. Changes in HV can be mediated by mineral leaching, C or H fixation, or O content loss. Mineral leaching is influenced by pH and CO2 concentration. CO2 and water are the sole contributors to C and H gains, respectively. CO2 concentration in the solution during the treatment is also affected by mass transfer limitations, ultrasound power, and design of the three-phase reactor. Increasing the BC:W ratio initially enhances the cavitation nuclei on the fluid/solid surface, and therefore sonolysis. The subsequent decrease in HV with increasing BC:W may be due to the limitation in ultrasound penetration and H supply from water. Carbon and hydrogen fixation may be connected to the formation of H2, CO, formic acid, formaldehyde, and associated radicals during sonolysis of aqueous CO2.

A series of biochars were prepared from rice(RI), tobacco(TO), corn(CO), wheat(WH), millet(MI), and black bean straw(BB). These biochars were used to study the mechanism of elemental mercury(Hg0) adsorption by hydrochloric acid modified biochars. The biochars were modified by 1 M hydrochloric acid (HCl) and then used in a fixed-bed Hg0 adsorption experiment. As would be expected, the results indicated that HCl modification increased the Hg0 adsorption performance of the six biochars. After modification, the Hg0 adsorption efficiency of tobacco biochar increased from 8.2% to 100.0%, and the average Hg0 adsorption capacity of the biochars increased by 61 times. The acid modification dissolved the metal compounds in the biochar, reducing the metal content and increasing the average surface area of the biochar. The average surface area of the raw biochars increased from 29.9 to 110.1 m2/g after HCl modification. The extra surface area was mostly created in the micropores, leading to a significant increase in the amount of micropores. These micropores effectively adsorbed the Cl atoms, which acted as active sites for Hg0. In the adsorption process, Hg0 diffused into the interior of modified biochars via mesopores, and finally the adsorbed Cl in the micropores reacted with Hg0 to form HgCl2.

Biochar (BC) generated from thermal and hydrothermal cracking of biomass is a carbon-rich product with the microporous structure. The graphene-like structure of BC contains different chemical functional groups (e.g. phenolic, carboxylic, carbonylic, etc.), making it a very attractive tool for wastewater treatment, CO2 capture, toxic gas adsorption, soil amendment, supercapacitors, catalytic applications, etc. However, the carbonaceous and mineral structure of BC has a potential to accept more favorable functional groups and discard undesirable groups through different chemical processes. The current review aims at providing a comprehensive overview on different chemical modification mechanisms and exploring their effects on BC physicochemical properties, functionalities, and applications. To reach these objectives, the processes of oxidation (using either acidic or alkaline oxidizing agents), amination, sulfonation, metal oxide impregnation, and magnetization are investigated and compared. The nature of precursor materials, modification preparatory/conditions, and post-modification processes as the key factors which influence the final product properties are considered in detail; however, the focus is dedicated to the most common methods and those with technological importance.

This paper describes a two-stage biochar activation process for CO2 capture, which includes acoustic treatment and amination. Contrarily to traditional carbon activation at temperatures above 700 °C, both stages of the current process are conducted at or near room temperature. It is known that CO2 can be fixed on the edge carbons of polycyclic aromatics hydrocarbons (PAHs) through thermal and reductive photo-carboxylation. Our previous work on biochar suggested that carbon of CO2 could be chemically fixed on biochar through acoustic or photochemical treatment of biochar in water/CO2 systems under ambient conditions. Separately, the graphene oxide (GO) literature reveals that carboxylic acids, epoxy and hydroxyl groups on biochar surface often serve as the active sites for converting GO to a new family of chemicals; amines are commonly grafted on these groups in the functionalization. Biochar has graphite and graphitic oxide clusters that consist of the oxygen functional groups mentioned above. These oxygen functionalities can be utilized for CO2 adsorption when functionalized with amine. Thus, the present study focuses on maximizing the CO2 capture capacity by manipulating the physicochemical structure of a pinewood-derived biochar. In this two-stage process, 30 s sonication at ambient temperature was applied to physically activate biochar prior to functionalization. Low-frequency ultrasound irradiation exfoliates and breaks apart the irregular graphitic layers of biochar, and creates new/opens the blocked microspores, thus enhancing the biochar’s porosity and permeability that are the keys in functionalization and subsequent CO2 capture. The sono-modified biochar was then functionalized with tetraethylenepentamine (TEPA) in the presence of two activating agents. The changes in surface characteristics, functional groups, graphene-like structure, and functionalization using activating agents were examined in detail and the capacity of the final products in CO2 removal was tested. The experimental results revealed that CO2 capture capacity, from a flow containing 10 and 15 vol% CO2, was almost 7 and 9 times higher, respectively, for ultrasound-treated amine-activated biochar, compared to raw biochar. The optimum capacity was 2.79 mmol/g at 70 °C and 0.15 atm CO2 partial pressure. Cyclic adsorption and desorption tests revealed that the CO2 capture capacity decreased 44% after 15 cycles.

Biochar, known as a byproduct of biomass pyrolysis, was prepared from rice straw (R6), tobacco straw (T6), corn straw (C6), wheat straw (W6), millet straw (M6), and black bean straw (B6) in high purity nitrogen at 600 °C. Chlorine (Cl) non-thermal plasma was used to increase Cl active sites on biochar to promote the mercury removal efficiency. The physio-chemical properties of biochar were characterized by proximate analysis, ultimate analysis, BET, SEM, TGA, FTIR, and XPS. Modification by chlorine plasma increased the Hg0 removal efficiency of the biochar from around 8.0% to 80.0%. The Hg0 adsorption capacity of T6 was 36 times higher after Cl2 plasma modification. Plasma caused the biochar surface to become porous and promoted the thermal stability of the biochar. Sulfur (S) content remained in the range of 0.5–0.7%, elemental/organic sulfur and sulfide were converted to sulfate during plasma treatment. The relative intensity of the oxygen functional groups (C O, C O and C(O) O C) were enhanced, while the content of oxygen (O) in biochar decreased. The main reason for the improved mercury removal efficiency by modified biochars was attributed to the increased number of C Cl groups on the surface of the biochars induced by Cl2 plasma. The C Cl groups functioned as activated sites and promoted the Hg0 removal efficiency.

Primary particles emitted from fuel combustion mainly involve filterable particulate matter (FPM) and condensable particulate matter (CPM). Particularly, CPM has emerged as a subject for further emission control. This study investigated the effects of the sampling temperature and excess air coefficient (EAC) on the total mass, chemical speciation, and particle size distribution of CPM by integrating Electrical Low-Pressure Impactor+ (ELPI+) sampling devices with the EPA Method 202 (dry impinger method). The total mass of CPM increased with the sampling temperature and EAC. Specifically, the total concentration of CPM was 10.51–39.93 mg/m3, in which the mass fraction of organic species varied between 8.74 and 49.80%, and the organic components in CPM followed the ranking order of alkanes/alkenes (62.6–78.6%), oxygen-containing volatile organic compounds (OVOCs) (19.7–35.4%), and aromatics (5.6%). Compared with other inorganic species such as HCl and NOX, SO3 had a higher migration tendency from the flue gas to CPM. The particle size distribution suggested that heterogeneous condensation was responsible for the whole size range of particles in CPM, whereas the homogeneous condensation led to the increase of finer particles (smaller than 0.2 µm). Accordingly, adjusting the emission temperature and EAC could help to control the emission of CPM.

Biochar was subjected to N2-plasma treatment after adsorbing water or oxygen. The mercury removal efficiency of the obtained samples was tested. The results of H2O-thermogravimetric and O2-temperature programmed desorption show that biochar had adsorption capacity for both water and oxygen during storage. The adsorbed water exhibited an inhibitory effect on mercury removal. However, after plasma treatment, water decomposed into oxygen-containing active radicals and combined with biochar to form oxygen-containing functional groups. The generated functional groups compensated for the inhibition of mercury capture. After the biochar adsorbed oxygen, the biochar was easily sintered under plasma, thereby reducing the mercury removal performance. The oxygen-containing functional groups formed by plasma treatment of oxygen adsorbed biochar also improved the mercury removal efficiency. Hg-temperature programmed desorption revealed that Hg0 could be oxidised by the generated oxygen-containing functional group to form HgO. Correlation analysis showed that the oxygen adsorbed by the biochar from air during storage was the main source of oxygen-containing functional groups generated under a non-oxygen plasma environment. The correlation coefficient was up to 0.999. During normal storage, the oxygen adsorbed by the adsorbent from the air can be converted into oxygen-containing functional groups during the plasma modification process, thereby oxidising Hg0.

A critical literature review suggests that carbonaceous compounds react with (CO2 +H2O) mixture through thermal, photochemical, and sonochemical/sonophysical routes. A biochar was selected for studying these effects at 60°C and 1 atm for its potential benefits on power generation and CO2 capture. All treatments remove sizable minerals (K, Na, and Si) detrimental in power generation, and introduce carbon (up to 16% of original carbon in biochar) into the biochar matrix. Most treatments show increased hydrogen (up to 24%). Treatments lead to notable increased heating value of biochar (up to 50%). Treated biochars show increase (up to 19 fold) in internal surface area. The ultrasound energy output is a fraction of the increased heating value. Thus, pretreatment is potentially attractive for increasing the energy efficiency in combustion and gasification. Moreover, better understandings of the salient reactions of these processes will be advantageous for the development of advanced adsorbents for CO2 capture. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1054–1065, 2014

It is known that NO in the flue gas can be effectively converted to NO2 by O3. The objective of this work is to investigate the feasibility of simultaneously abating NO2 and SO2 from flue gas by liquid-phase conversion. A suite of cost-effective additives for enhancing NO2 absorption through enriching the concentration of sulfite ion, SIV, in the liquid phase has been evaluated under pH similar to traditional flue-gas desulfurization (FGD). Experiments were conducted in a lab-scale washing tower with CaSO3 slurry, including metal and non-metal additives: FeSO4, FeCl2, Fe2(SO4)3, MnSO4, MnCl2, MgSO4, MgCl2, (NH4)2SO4, and NH4Cl. All of these additives enhance the absorption efficiency of NO2. Ferrous sulfate, FeSO4, is the most effective additive, with absorption efficiency reaching 95%, but the loss of additive is high because of the oxidation of FeII into FeIII. Ammonium sulfate, (NH4)2SO4, has similar absorption efficiency but shows lower loss during absorption. Its absorption efficiency improves with a...

This work demonstrates that biomass fly ash, a carbon-containing by-product of a commercial pine-bark fired grate boilers, is a more viable and effective NO reducing agent than lignite char in a gasstream containing NO, O 2 and He in a tubular reactor at 300 to 600 °C that simulates the post-combustion zones. It requires no chemical or physical activation. It seems to follow the reburning mechanisms reported earlier. CO is a pivotal reaction intermediate. Alkali and alkaline earth metals catalyze both carbon oxidation leading to CO formation, and oxygen tranfer leading to CO scavenging of surfaceoxides formed after adsorption of NO. Empirical rate expressions for carbon oxidation and NO reduction are developed. The following rate model is used to recover the rate constants of carbon oxidation in the simulated flue gas. d X d t = k ( 1 − X ) ( P oxygen ) m A exp( − k c h a r d e a c t i v a t i o n t ) where X , t , k , P oxygen , m , A and k char deactivation denote carbon conversion, reaction time, rate constant based on per unit surface area, partial pressure of O 2 at the inlet, reaction order, N 2 BET surface area per unit weight of the sample, and rate of carbon deactivation, respectively. A first-order rate expression is adopted for recovering the rate constants of NO reduction.

Potential substitutes of natural gas and lignite fly ash as NO and HCN reducing agents, respectively, for heterogeneous reburning were examined in a bench-scale apparatus equipped with a simulated reburning and a burnout furnace. Selection of NO reducing agent is based on fuel volatility and nitrogen functionality. HCN reducing agent selection is based on literature data. A wide range of waste materials and industrial by-products show overall NO reduction efficiency up to 88% at reburning stoichiometric ratio 0.90 or 0.95. Mixed fuel containing scrap tire and Fe 2 O 3 is particularly effective. Though its cost is constrained by the energy-intensive operation of grinding the tire, the estimated raw-material cost is better than that of natural gas reburning and highly competitive against SCR. A first-level approximation study of the selectivities of nitrogen species to form NO in burnout zone reveals the importance of HCN and char nitrogen reaction mechanisms.

Polar solvents are known to swell coal, break hydrogen bonds in the macromolecular structure, and enhance coal liquefaction efficiencies. The effects of the pretreatment of coal using supercritical CO{sub 2} on its physical structure and combustion properties have been studied at the bench-scale level. Emphasis has been placed on NO reburning, NO emissions during air-fired and oxy-fired combustion, and loss on ignition (LOI). Pretreatment was found to increase porosity and to significantly alter the fuel nitrogen reaction pathways. Consequently, NO reduction during reburning using bituminous coal increased, and NO emissions during oxidation of lignite decreased. These two benefits were achieved without negative impacts on LOI.

It is known that polar solvents swell coal, break hydrogen-bonds in the macromolecular structure, and enhance coal liquefaction efficiencies. The effects of drying, interaction with supercritical CO2 and degassing on the physical structure of coal have been studied using gas sorption technique and a scanning electron microscope (SEM). Both drying and interaction with supercritical CO2 drastically change the micropore and mesopore surface area, absolute volume, and volume distribution in both bituminous coal and lignite. Degassing removes debris in the pore space which allows for better analysis of the changes in the morphology that were induced by drying and exposure to supercritical CO2. SEM reveals that interaction of bituminous coal with supercritical CO2 results in an abundance of carbon structures similar to the maceral collinite.

In a recent study, we discovered that oxygen from the gas phase, organic portions of the coal, and minerals in the coal have profound influence on the formation and desorption of stable surface oxides in the early stages of coal combustion. In an attempt to isolate the effects of minerals, demineralized coals (DMC) are oxidized in O{sub 2} with a contact time less than 1 s, and the amount and strength of stable surface oxides are characterized by temperature-programmed desorption (TPD) up to 1650{sup o}C. Young chars derived from both demineralized lignite and bituminous coals show low and flat TPD profiles over a wide temperature range, signifying the minerals' catalytic activities in forming stable surface oxides for both coals. Indeed, the oxidation rates of chars from both bituminous coals and lignite, estimated based on the O{sub 2} concentrations entering and exiting the Al{sub 2}O{sub 3} reactor, were higher than their DMC counterparts. Moreover, graphite, containing no minerals and organically bound oxygen, has an even lower oxidation rate. Similar to those for the raw coals, the combined oxygen balance and elemental analysis of chars from DMC suggests that the oxygen in the organic portion of the lignite activates oxygen turnover andmore » carbon oxidation during its combustion; neither chars from raw nor demineralized bituminous coals possess these properties. X-ray photoelectron spectroscopy (XPS) of raw and demineralized bituminous coals and their char show peaks at around 532.0 eV in the O(1s) difference spectrum, suggesting the possible existence of intercalated stable surface oxides. 35 refs., 7 figs., 4 tabs.« less

To obtain representative temperature-programmed desorption (TPD) profiles of young oxidized chars up to 1650 °C with minimal reactor wall interferences, the chemistry and physics of four ceramic materials has been critically reviewed. A two-staged experimental apparatus is then uniquely designed to produce chars in an Al2O3 flow reactor with 1−21% O2 followed by in situ TPD with a SiC tube. Comparison of TPD profiles of oxidized chars with those from pyrolyzed chars and ashes suggests early-stage char oxidation is profoundly influenced by oxygen from three sources: organics oxygen, mineral matters, and gas phase O2. Young chars oxidized at 1000 °C with less than 0.3 s residence time shows CO desorption peaks during TPD at three distinct temperatures: 730, 1280, and 1560 °C. The peaks at 730 °C are mainly caused by incomplete devolatilization. The peaks at 1280 °C mainly represent desorption of stable surface oxides and incomplete devolatilization. Increasing the gas phase oxidants notably increases the am...

This paper reports our first study on the deactivation of young chars in flame conditions. The quantity and strength of surface oxides on young chars are monitored in situ by temperature-programmed desorption (TPD) up to 1700 °C. Young chars contain more abundant surface oxides than old chars over a wide range of temperature. Lignite chars possess more oxides than chars derived from a bituminous coal. Chars oxidized at 629 °C show desoprtion products at three distinct temperatures: 725, 1430, and 1700 °C. The TPD peaks around 725 °C correspond to activation energies in the range of 107-170 kJ/mol and have been well-documented in the literature. CO desorbed at around 1430 °C corresponds to activation energies over 300 kJ/mol, signifying the possible roles of strongly bound oxides on the basal planes of carbon. Search of the oxygen source for the huge amount of CO production at 1700 °C reveals that commonly adopted alumina tubes and support materials decompose to Al 2 O (g) and emit a notable amount of O 2 at temperatures above 1300 °C. Moreover, alumina tube and support materials react with CO and form CO 2 ; they also react with carbon and form CO and aluminum oxycarbides. SiC tube, on the other hand, is oxidized by O 2 , CO 2 , and H 2 O and forms SiO (g) , SiO 2(s) , Si-(OH) 4(g) , and CO above 650 °C. Moreover, Si can also form through a secondary reaction of SiC and SiO 2 . Thus, alumina appears suitable for the oxidation part of the experiments, where up to 120 ppm of O 2 emission is acceptable at a temperature of 1700 °C. SiC appears acceptable for TPD, though a small amount of SiC may be oxidized by the TPD product, CO 2, at temperatures above 900 °C. Oxidation of SiC prior to TPD should be avoided.

Recent study of heterogeneous reburning suggests effective NO reduction requires an adequate carbon source and a pool of catalysts that reduces not only NO, but also the reaction intermediate HCN [Chen WY and Tang L. Variables, kinetics and mechanisms of heterogeneous reburning. AIChE J 2001;47:2781-2797]. The current work demonstrates that ashes from lignite-fired power plants contain these desirable catalytic ingredients. Their reactivity is slightly lower than that of ashes produced in laboratory at lower temperatures, probably due to the formation of crystalline structure. The current work also demonstrates that for the power plants remote from lignite resources, ashes from biomass-fired grate boilers are a remarkably effective and economical substitute. About 85% of NO reduction efficiency appears achievable at a stoichiometric ratio 0.945. The raw-material cost estimates of the mixed-fuel technology suggest that it could be competitive with selective catalytic reduction (SCR).

The variables, kinetics, and mechanisms of heterogeneous reburning were studied in a flow reactor with a simulated flue gas. The efficiency of heterogeneous reburning depends on the origin of the char, char preparation history and the presence of oxidants, CO2 and O2, and the reducing agent CO, in reburning. Estimated intrinsic rate constants for surface NO reduction in various gaseous environments were compared with those published. In addition to its large surface area, the effectiveness of lignite char appears to be due to its ability to promote two consecutive reactions: (1) the gasification of char by CO2 and O2 for production of CO; (2) the removal of surface oxygen complexes, including those formed after adsorption of NO, by gaseous CO, for the regeneration of reactive sites. Moreover, lignite ash also catalyzes the decomposition of HCN, a major intermediate of NO conversion during gas reburning. These observations suggest that reburning by a mixed fuel containing natural gas and lignite char can be a potentially attractive route for the in–furnance control of nitrogen oxide.

Pyrolysis occurs in the initial stage of coal combustion where the volatile tar is generated. An important property of this volatile tar is its molecular-weight distribution. Coal tar contains varying sizes of monomers which are connected by linkages of varying strengths, thereby necessitating a stochastic approach. The present work has adopted the stochastic population balance of the system to derive the master equation for predicting the statistics of this molecular weight distribution of tar as functions of time. The tar produced during pyrolysis is assumed to undergo decomposition to low molecular weight compounds. Moreover, the system containing all tar molecules is lumped into a limited number of states, each representing a particular molecular weight range. The equations for the means, variances, and covariances of the random variables, each representing the number of tar molecules in an individual state in the system, have been derived from the master equation. The model has been compared with the experimental data obtained with both a heated-grid reactor and an entrained-flow reactor to recover the major parameters of the model, i.e. the transition and exit intensity functions. The transition intensity functions exhibit the temperature dependence of the Arrhenius type.

Isotopically labeled N15O was used to study the interaction of fuel nitrogen from coal with NO in a simulated reburning environment. Experiments were conducted in an alumina flow reactor operated at 1100°C with a reaction time estimated at 0.2 s. A North Dakota lignite and a Pittsburgh #8 bituminous coal were burned with a simulated flue gas containing 1000 ppm of N15O. Stoichiometric ratios ranged from 0.7 to 1.0. Species and isotope separation were accomplished using GC/MS. The ratio of labeled to unlabeled isotopes of each major nitrogen-containing species varied with stoichiometry, but not with coal type. Delayed nitrogen evolution from both coals was evident from the data. Data analysis showed that significant N2 production (i.e., greater than 50%) probably occurred through non-NO pathways. Little N15O was observed, indicating low conversion rates of intermediates to NO after significant nitrogen evolved from the coal.

The breakage of coal particles into smaller fragments during the devolatilization stage mostly occurs randomly due to the heterogeneous structure of coal, thereby necessitating a stochastic approach for modeling. In the present work, the master equation approach has been proposed for predicting the statistics of the size distribution of the coal particles during their stepwise degradation. The particle-size distribution has been lumped into a limited number of states, each representing a particular volume range. The master equation and the equations for the means, variances, and covariances of the random variables, each representing the number of particles in the individual states in the system, have also been derived from the stochastic population balance. Simulation has been performed with a stiff differential equation solver to predict the dynamic particle number statistics at any time. By fitting the model to experimental data, the transition intensity function is found to be inversely proportional to the square of particle radius.

The effect of reburning fuel type on the partitioning of fixed-nitrogen species in the fuel-rich stage of reburning was studied in a bench scale flow reactor. Methane, hexane, benzene, bituminous coal, and lignite were used as reburning fuels. A simulated flue gas consisting of CO 2 (16.8%), 0 2 (1.95%), NO (1000ppm), and helium was used for experiments at 1100 o C and ca. 0.2s residence time. The total fixed nitrogen (TFN) speciation was found to depend strongly on fuel type ans stoichiometric ratio (SR). Rich stoichiometries promoted conversion of NO to HCN, whereas conversion of HCN to N 2 was promoted by lean stoichiometries. In this stimulated reburning stage, the optimum stoichiometry of TFN production for gaseous fuels was ca. SR=0.95

In this work, the dispersion of CO and CO 2 from temperature-programmed desorption of char before they reach the mass spectrometer is sequentially examined by a set of methods

The susceptibility of a group of US coals to the production of light gaseous and liquid hydrocarbons during flash hydrogenation is examined. Eight coals ranging from lignite to high-volatile A bituminous and representing five provinces, have been flash heated in 101.3 MPa of flowing hydrogen using a bench scale reactor. A 0.6 s gas phase residence time was provided to hydrocrack the vapour products. Temperatures ranged from 750 to 850°C, where maximum yields of ethane and BTX (benzene+toluene + xylene) are found. The carbon conversion decreased with increasing rank at fixed reaction conditions. Methane yields are highest for lignite. Peak ethane yields range from 6.4 to 9% carbon conversion. BTX yields have a shallow maximum at intermediate ranks, decreasing towards high and low rank coals. Total liquid yields range from 14 to 43%. Although a definite variation of yield with rank is evident, the trends, especially total liquid yields, are attended by considerable scatter. Rank is not the only, and indeed may not be the most significant variable in determining the yield of individual species in flash hydrogenation. To establish the significant variables a stepwise regression procedure was applied to the experimental data using information from the elemental, proximate and petrographic compositions of the coals as independent variables. Two variables are adequate in all cases to correlate species yield and coal properties. Exinite appears to be capable of increasing the amount of liquid obtained from other macerals.

An interesting correlation has been observed between the volatile yield for three coal conversion processes and the oxygen and aliphatic hydrogen (Hal) content of the coal. The three processes are: (1) rapid pyrolysis in vacuum, (2) hydropyrolysis at ≈10 MPa hydrogen, and (3) liquefaction with tetralin at 400 °C. The volatile yield for the first two processes and for low sulphur coals studied in the third process may be predicted with the equation: Yield≈0.8 OT+15 Hal where: OT, the organic oxygen concentration measured by ultimate analysis; and Hal is the aliphatic hydrogen concentration determined from Fourier Transform infrared (FTIR) measurements. The similarity of yields for these processes suggests that they are basically controlled by thermal decomposition. Justification for the above equation is offered by considering a recently developed model for thermal decomposition of coal. The correlation does not fit a group of high sulphur coals studied in the liquefaction programme. These coals have extremely high volatile yields which may be a result of catalytic activity.