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Calcium ion exchange was performed in Indonesian low-rank coal using saturated aqueous solutions of Ca(OH)2 at 30.0 ± 0.1 °C without pH adjustment. The Ca2+ concentration and pH were monitored during ion exchange. A coal product was obtained with 3.2 mass% Ca2+. Gasification of the ion-exchanged samples was conducted in a circulating dual bubbling fluidized bed (CDBFB) reactor at 700 °C, 800 °C, and 900 °C. Coal carbon conversion into carbonaceous gases (CO, CO2, CH4, and C2 hydrocarbons) using the Ca2+-exchanged coal achieved 78% at 900 °C in the CDBFB. The Ca catalyst led to the greatest rate enhancement at 800 °C, resulting in a twofold increase in the gas product yield compared to that without Ca. A comparison of carbon conversion between the CDBFB and fixed-bed reactors revealed that the conversion value using the CDBFB at 700 °C was very small. Regarding an examination of this influence in detail, it seems that the existing H2 adhered primarily to the active sites of the char, and the use of Ca2+-exchanged coal led to a reverse shift reaction.

Pyrolysis of 29 coals with carbon contents of 71–92 mass% on a dry, ash-free basis (daf) has been performed mainly in a temperature-programmed mode at 10°C/min up to 800°C with a flow-type fixed bed quartz reactor, and some factors controlling HCl formation have been examined. The rate profiles of HCl formation exhibit at least three distinct peaks at around 260–360, 470–510 and 580–630°C, and the lowest temperature peak is present for 8 coals alone, whereas the middle and highest temperature peaks are common with almost all of the coals. The HCl profile is also affected by the size of coal particles and the height of coal particles in the fixed bed. Yields of HCl and char-Cl at 800°C for 28 coals except an American bituminous coal are 44–95 and 4–54%, respectively, and tar-Cl is as low as ≤ 7% in all cases. The chlorine distribution is almost independent of the heating rate in the range of 2.5–400°C/min and has no distinct relationship with carbon or chlorine content in coal, but HCl tends to increase with increasing amount of (Na + 2Ca) in coal with a corresponding decrease in char-Cl. When an Indonesian sub-bituminous coal is injected into an O2-blown entrained bed gasifier under pressure, there is an almost 1:1 relationship between carbon and nitrogen conversions, whereas the sulfur and chlorine are enriched in the remaining char, and the degree of the enrichment is higher with chlorine. The method of evaluating coal-Cl forms quantitatively using model chlorine compounds is proposed.

Ca2+ and Na+ cations were separately or consecutively ion-exchanged with an Indonesian low-rank coal using saturated aqueous solutions of Ca(OH)2 and/or soda ash at 20–40 °C without pH adjustment. This was done by adding aqueous solutions of the soda ash and/or calcium hydroxide to a dispersion of coal particles in deionized water, while monitoring the Na+ and Ca2+ concentrations and pH of the resulting mixture. A 3.5 mass % Ca2+-exchanged coal, a 1.6 mass % Na+-exchanged coal and a 3.8 mass % Ca2+- and 1.0 mass % Na+-exchanged coal were obtained. The catalytic pyrolysis and subsequent gasification of these ion-exchanged specimens were performed in a fixed bed quartz reactor at 650, 700, or 750 °C. X-ray diffraction analyses of the samples pyrolyzed at 700 °C found no evidence of Na or Ca species, indicating that these were present as nanoscale particles. The Ca2+/Na+-exchanged coal underwent steam gasification more readily than the other samples, with complete char conversion of this material following 1...

Ion-exchange reactions of brown and sub-bituminous coals with natural soda ash, composed of >99% Na2CO3, have been studied at 20–40 °C without any pH-adjusting reagents, and the pyrolysis and subsequent steam gasification of the resulting Na+-exchanged coals have been conducted using a fixed-bed quartz reactor at 700 °C. When the Na+ concentration and pH of an aqueous mixture of coal and soda ash are monitored during the ion-exchange process, both values decrease at a greater rate with brown coal with a higher content of COOH groups, indicating that ion exchange of Na+ with H+ of the COOH group is the predominant process. About 65% of COOH can be exchanged with Na+ ions under optimal conditions, irrespective of the coal type. The reactivity of these raw coals in steam at 700 °C is similar, with char conversions of less than 20 mass %, even after 2 h of reaction. Exchanged Na promoted the gasification of both coals at this temperature, but the rate profiles were different: conversion of brown coal increase...

The effect of Ca catalysts prepared from CaCO 3 on the steam gasification of Indonesian subbituminous coal at 700–800 °C is examined. The char obtained by pyrolyzing the coal with 0.59 wt.% of Ca (dry basis) showed conversions in steam gasification at 750 and 800 °C of around 70 and 90 wt.% (dry ash and catalyst free basis), which were 2 and 1.5 times larger than those of the coal without the Ca catalyst, respectively. The activity of this Ca catalyst was as high as that prepared using an aqueous solution of Ca(OH) 2 . The TPD and XRD measurements demonstrated that the Ca catalyst from CaCO 3 was initially present in the ion-exchanged form, and as a finely dispersed calcium species after pyrolysis. These results confirm that CaCO 3 is effective as a catalyst raw material in the steam gasification of subbituminous coal, even at low catalyst loadings.

Cost of catalysts is a crucial factor in realizing coal catalytic gasification process. In this study, inexpensive raw materials, soda ash (Na 2 CO 3 ) and slaked lime (Ca(OH) 2 ), were selected as catalyst precursors, and Na-, Ca- and Ca/Na-loaded coals were prepared by an ion-exchange procedure using a sub-bituminous coal (Adaro coal, Indonesia). These coal samples were rapidly pyrolyzed and in-situ gasified in an atmospheric drop-tube reactor (DTR) at 850–1000 °C under a steam partial pressure of 0.05 MPa. The Na and Ca catalysts showed remarkable activity for gasification, and the Ca/Na-loaded coal exhibited the highest reactivity among the coal samples prepared. The char yield of the Ca/Na-loaded coal at 1000 °C was as low as 17.6 mol-C per 100 mol-C of coal, and more than 70% (on carbon basis) of its primary char was gasified within 3 s. At 900 °C, the coal with Ca-loading of 3.2 wt.% showed catalytic activity higher than the coal with Ca-loading of 0.52 wt.%. At 950 and 1000 °C, however, the coal with the lower Ca-loading showed higher activity. The XRD analysis suggested that the Ca catalyst with the lower loading was more resistant to coarsening along with the progress of char gasification.

In order to understand chlorine chemistry in coal pyrolysis, the dynamics of HCl evolution and changes in chlorine functional forms during temperature-programmed pyrolysis of eight Argonne premium coal samples have been examined with an online HCl-monitoring technique and by the Cl 2p X-ray photoelectron spectroscopy (XPS) method. The rate profiles of HCl evolved show at least three distinct peaks at 390, 520, and 600 °C, and the presence of these peaks depends strongly on the type of coal. The HCl peak at 390 °C appears with four coals alone and becomes considerably small by water washing, whereas the high-temperature peaks above 450 °C observed with almost all of the coals do not change significantly after washing. Yields of HCl up to 1000 °C are in the range of 50–90% in many cases, and the yield tends to decrease with increasing atomic Ca/Cl ratio in coal. The chlorine XPS analyses show that the chlorine in each coal is enriched at the surface and composed of inorganic and organic functional forms. Th...

The fate of coal-N in the fixed-bed pyrolysis of 25 coals with 62−81 wt % (daf) C has been studied with a quartz reactor at 1000 °C under ambient pressure to examine the effects of metal cations present naturally in these coals on the partitioning of coal-N into N2, NH3, HCN, tar-N, and char-N. Nitrogen mass balances for all runs fall within the reasonable range of 100 ± 5%, and N2 is the predominant product for all of the coals. As the N2 yield increases, the sum of NH3, HCN, and tar-N is unchanged significantly, whereas the char-N yield decreases almost linearly, showing that most of N2 originates from char-N. When eight kinds of inherent metals, such as Na, Mg, Al, Si, K, Ca, Fe, and Ti, are determined by the conventional method and related with the N2 yield, there exists a strong, direct correlation between the Fe content and N2 formation for low-rank coals with less than 75 wt % (daf) C. Transmission electron microscopy coupled with an energy-dispersive analysis of X-rays (TEM−EDAX) measurements afte...

The present review paper highlights on the recent progress in Japan on the hot gas cleanup of HCl, H2S and NH3 in raw fuel gas for coal-based, combined cycle power generation technologies. It has been shown that NaAlO2, prepared by mixing Na2CO3 solution with Al2O3 sol, can reduce HCl in an air-blown gasification gas from the initial 200 ppm to

The present review focuses on elucidating the chemistry of nitrogen release during coal pyrolysis, in particular, on making clear catalytic roles of inherent Ca and Fe ions in not only the partitioning of volatile-N to tar-N, HCN, NH 3 and N 2 but also the conversion of char-N to N 2 . In slow heating rate pyrolysis of low-rank coals at 1000 °C with a fixed bed reactor, the demineralization with acid washing increases tar-N and HCN, but it decreases NH 3 . On the other hand, the ion-exchange of Ca 2+ ions with the demineralized coals shows the nearly reverse effect on the distribution of these nitrogen species, though the physical mixing of Ca(OH) 2 is almost ineffective. Since the sum of tar-N, HCN and NH 3 is unchanged significantly in any cases, it is likely that Ca cations, which exist originally in the ion-exchanged forms, can control the partitioning of volatile-N to tar-N, HCN, and NH 3 . The Fe 3+ ions precipitated on the demineralized coals catalyze the decomposition of tar-N, HCN and NH 3 into N 2 . The evolution of N 2 from coal-N occurs even in the absence of any metal cations added. The extent is generally larger with a lower rank coal, at a slower heating rate and a higher temperature, and at a longer solid residence time when coal is rapidly pyrolyzed. N 2 yield at 1350 °C reaches about 70% at maximum. Since a strong reverse correlation exists between N 2 and char-N, N 2 originates predominantly from char-N (and/or precursors). Demineralization of low-rank coals decreases N 2 , whereas subsequently added Fe or Ca cations enhance N 2 mainly at ≤ 1000 °C or ≥ 1000 °C, respectively. As the sum of naturally present Fe and Ca cations increases, N 2 yield at 1350 °C tends to increase up to about 1 mass%. It can be proposed that fine particles of metallic Fe and CaO, which are formed from these inherent ion-exchanged cations, promote efficiently N 2 formation from char-N through solid–solid interactions with heterocyclic nitrogen forms in char matrix.

Catalytic decomposition of 2000 ppm NH 3 in different atmospheres with an Australian α-FeOOH-rich limonite ore at 750-950 °C under a high space velocity of 45000 h-1 has been studied with a cylindrical quartz reactor to develop a novel hot gas cleanup method of removing NH 3 from fuel gas produced in an air-blown coal gasification process for an integrated gasification combined cycle (IGCC) technology. The limonite shows very high catalytic activity for the decomposition of NH 3 diluted with inert gas at 750 °C, regardless of whether the catalyst material is subjected to H 2 reduction before the reaction or not. Conversion of NH 3 to N 2 over the reduced limonite reaches ≥99% at 750-950 °C, and the catalyst maintains the high performance for about 40 h at 750 °C. When the decomposition reaction is carried out in the presence of fuel gas components, the coexistence of syngas (20% CO/10% H 2 ) causes not only the serious deactivation of the limonite catalyst but also the appreciable formation of deposited carbon and CO 2 . On the other hand, the addition of 10% CO 2 or 3% H 2 O to the syngas improves the catalytic performance and concurrently suppresses the carbon deposition almost completely, and the NH 3 conversion in the 3% H 2 O-containing syngas reaches about 90% and almost 100% at 750 and 850 °C, respectively. Influential factors controlling the catalytic activity of the limonite ore in the coexistence of fuel gas components are discussed on the basis of the results of the powder X-ray diffraction measurements, thermodynamic calculations, and some model experiments.

Functional forms of the unburned carbon present in six kinds of coal fly ashes have been examined mainly by the temperature-programmed desorption (TPD)/temperature-programmed oxidation (TPO) and laser Raman spectroscopy (LRS) methods. The carbon contents of the ash samples range from 0.4 to 4.1 mass%. The LRS analysis shows that the C consists of both amorphous and crystallized forms, and the proportion of the former is as large as 50-65 C%. Further, the TPD measurement exhibits that the C contains several types of surface oxygen species, such as carboxyl and lactone/acid anhydride groups, which can readily be decomposed into CO2 up to 700 °C to provide active carbon sites. The results of the TPD also indicate that the ashes have surface CaCO3, and most of this species can be converted to CaO and CO2 around 600-700 °C. Interestingly, there is a significant correlation between organic fluorine concentrations and carboxyl/lactone/acid anhydride groups or surface CaCO3 contents in the ash samples. It might thus be possible that the formation of organic F forms proceeds through gas-solid-solid interactions among HF (and/or F2) in flue gas, active carbon sites and surface Ca species produced around 600-700 °C downstream of coal-fired boilers.

The fate of the chlorine and fluorine present in a sub-bituminous coal from Indonesia during pyrolysis and gasification has been studied with fixed and entrained bed reactors. The rate profile for HCl evolved in the temperature programmed pyrolysis exhibits the main and shoulder peaks at 480 and 600 °C, respectively. Model experiments and subsequent Cl 2p XPS measurements show that HCl reacts with metal impurities and carbon active sites at 500 °C to be retained as inorganic and organic chlorine forms, from which HCl evolves again at elevated temperatures. It is suggested that the HCl observed in the coal pyrolysis may originate from the above-mentioned chlorine functionalities formed by secondary reactions involving the nascent char. In the CO2 gasification of the 900 °C char at 1000 °C and 2.5 MPa, any measurable amounts of HCl and HF could not be detected even at a high conversion of 75 wt% (daf), suggesting the accumulation of these halogens in the residual char. When the coal is injected into an O2-blown, entrained bed gasifier at 1200–1400 °C under 2.6 MPa, the partial oxidation proceeds to a larger extent at a higher O2/coal ratio, whereas the chlorine and fluorine are enriched in the remaining char, and the extent of the enrichment at the latter stage of gasification is larger with the fluorine. The XPS measurements of the chars reveal the presence of the broad F 1 s peak, which can cover a wide range of binding energies attributable to inorganic and organic fluorine. The halogen enrichment during gasification is discussed in terms of secondary reactions of HCl and HF with char.

A novel hot gas cleanup method to decompose a low concentration of NH3 to N2 with metal cations present inherently in low rank coals has been studied with a quartz reactor under the conditions of 750–850 8C, 0.1 MPa and high space velocity of 45,000 h K1 . Each coal is pyrolyzed at 900 8C to prepare the char, which is subjected to the decomposition of 2000 ppm NH3 after pretreatment with H2. All of five chars examined promote NH3 decomposition in inert gas, but the promotion effect depends strongly on the kind of char and can correlate more closely with the Fe content than with the Ca content. This result may indicate that the Fe plays a crucial role in the reaction. A commercial activated carbon with a very low Fe content of !0.05 wt% exhibits lower conversion of NH3 to N2 than five chars. The TEM pictures reveal the formation of nanoscale particles of Fe and Ca components on a brown coal char that provides the largest catalytic performance. The char maintains the high conversion level of 80% during 25 h reaction at 750 8C and achieves the complete decomposition of NH3 at 850 8C. The co-feeding of a mixture of H2, CO, and CO2 does not change significantly the catalytic activity of the char at a steady state, whereas the coexistence of 2000 ppm H2S lowers it in the whole range of time on stream. It is proposed by combining the XRD and TPD observations with our previous results that the catalytic decomposition of NH3 in inert gas with the chars derived from low rank coals proceeds through two cycle mechanisms involving iron metal, iron nitrides, CaO and CaCN2. q 2005 Elsevier Ltd. All rights reserved.

The evolution of HCl during pyrolysis of 16 coals with different ranks at a heating rate of 10 °C/min has been studied with an online monitoring method. Approximately 50%−95% of total chlorine is converted to HCl up to 800 °C, and the remainder is mostly retained in the char, which leads to a strong reverse correlation between the two. As the sum of Na and Ca naturally present in coal increases, the amount of HCl tends to decrease. The temperature dependence of the rate of HCl evolved differs with each coal and shows at least four peaks at 280, 360, 480, and 580 °C. The former two peaks are present for two coals alone, whereas the higher temperature HCl formation at ≥450 °C is common for almost all of the coals. The HCl peaks at 280 and 360 °C are considerably small by water washing. When model chlorine compounds added to activated carbon, such as hydrated NaCl, hydrated CaCl2, and organic hydrochlorides, are pyrolyzed in the same manner as above, HCl formation occurs dominantly between 250 and 450 °C in ...

Decomposition of NH3 to N2 with Fe and Ca catalysts supported on brown coal chars has been studied with a cylindrical quartz reactor from a viewpoint of hot gas cleanup. The catalyst is prepared by pyrolyzing a brown coal with Fe or Ca ions added. In the decomposition of 2000 ppm NH3 diluted with He at 750 °C and at a space velocity of 45,000 l/h, 2–6 wt% Fe catalysts are more active than not only 6 wt% Ca catalyst but also 8 wt% Fe catalyst loaded on a commercial activated carbon. The transmission electron microscope observations show that fine iron particles with the sizes of 20–50 nm account for the higher catalytic performances. When reaction temperature is increased to 850 °C, all of Fe and Ca catalysts on the chars achieve complete decomposition of NH3. The co-feeding of H2 with 2000 ppm NH3 improves the performance of the 2% Fe catalyst at 750 °C, but contrarily the coexistence of syngas (CO/H2=2) deactivates it remarkably, whereas the addition of CO2 to syngas restores the catalytic activity of the Fe to the original state without syngas. The powder X-ray diffraction and temperature programmed desorption measurements strongly suggest that the Fe and Ca catalysts promote NH3 decomposition through cycle mechanisms involving the formation of N-containing intermediate species and the subsequent decomposition to N2.

Pyrolysis of five coals has been carried out at 1000−1350 °C and different heating rates with fixed-bed and free-fall reactors to examine carbon structures in devolatilized chars. The X-ray diffraction measurements show the formation of crystallized carbon with turbostratic structures, depending strongly on coal type and severity of pyrolysis. The proportion of the carbon with low rank coals decreases by demineralization with acid washing but contrarily increases by subsequent addition of Ca2+ ions, irrespective of heating rate, and a small amount of 0.5−1 wt % Ca works efficiently. It is thus likely that Ca2+ ions naturally present as ion-exchanged forms in low rank coals determine dominantly the extent of carbon crystallization at higher temperatures. The Ca added is transformed to fine particles of CaO upon pyrolysis, and a larger amount of CO is formed in the presence of the Ca. A mechanism for the Ca-enhanced carbon crystallization is discussed in terms of solid−solid interactions between CaO particl...

Nitrogen release from two low rank coals during rapid pyrolysis at 1300 °C has been studied with a graphite-made drop tube reactor, in which a graphite filter is installed for controlling a residence time of coal particles. Nitrogen distribution depends strongly on the time. At 0 s, 60−65% of coal-N is retained in the chars, and the rest is released as tar-N, HCN, NH3, and N2. When the time is prolonged to 120 s, N2 yield increases dramatically and reaches 40−55%, whereas char-N decreases mainly. There is the reverse time dependence between N2 and char-N. Demineralization with HCl washing decreases N2 but increases char-N, and the addition of 1 wt % Ca to the demineralized coal shows almost the reverse effect on N2 and char-N. The deconvolution results of C(002) XRD lines reveal that the proportion of crystallized carbon in every char increases with increasing time. The linear relationship between the proportion and N2 yield exists among all of the samples used, which strongly suggests that N2 formation f...

The effects of Ca catalysts on nitrogen release during heat treatment of polyacrylonitrile-derived carbon and pyrolysis of low rank coals have been studied with a fixed bed quartz reactor in a stream of high purity He. In the temperature-programmed treatment at 10 °C/min of the carbon with 3 wt % Ca, the Ca promotes N2 formation at 850−1000 °C and the catalytic effect is larger at a higher temperature. When a low rank coal, after demineralization and subsequent addition of 3 wt % Ca, is pyrolyzed in the same manner as above, the Ca enhances the rate of N2 formation at 850−1100 °C at largest by a factor of 15. In the fast heating pyrolysis at 400 °C/min of the demineralized samples, the Ca at loading of 1−3 wt % also increases N2 yields at 1200−1350 °C irrespective of type of coal. These observations and nitrogen distribution indicate that the N2 increased by Ca addition arises mainly from solid-phase reactions of heterocyclic nitrogen forms. The X-ray diffraction measurements after heat treatment and pyro...

Nitrogen release from several coals with different ranks during CO 2 gasification at 0.1 MPa and 1000°C has been studied with a fixed-bed quartz reactor. Among HCN, NH 3 , N 2 , and tar-N analyzed, N 2 is the main product for all the samples in the whole range of coal conversion. As the gasification of every char after devolatilization proceeds, N 2 increases with a corresponding decrease in the nitrogen in each residue. This shows that the N 2 formed originates mostly from solid–gas reactions. When N 2 yield is evaluated on the basis of char-N remaining just after devolatilization, it is almost independent of type of parent coal and demineralization with HCl washing. Only the extent of char gasification can determine the yield, which reaches about 65% after complete gasification. The rate of N 2 formation is always lower than that of CO production. It is thus suggested that accumulation of N-containing surface species is necessary for the start of N 2 formation.

Iron catalysts precipitated on brown and bituminous coals promote conversion reactions of coal nitrogen to N 2 during pyrolysis at 900 °C, and the N 2 evolved from the brown coal arises mainly from char nitrogen (char-N). The present study, thus, focuses on clarifying the effect of the iron on char-N functionality and elucidating interactions between the two mainly with X-ray photoelectron spectroscopy (XPS). The N 1s spectra of brown coal chars revealed that the catalyst lowered the ratio of pyrrolic-N/pyridinic-N irrespective of the depth of the char, indicating the preferential formation of N 2 from pyrrolic-N. In the Fe 2p and N 1s XPS spectra of the Fe-bearing chars, Ar sputtering removed surface iron oxides to expose the metallic phase and concurrently increased the proportion of pyridinic-N with the corresponding decrease in quaternary-N. It is suggested that there are strong interactions between the iron and char-N even in the process of N 2 formation. Iron particles were more finely dispersed on the brown coal char and in closer contact with it, which accounts for higher conversion of char-N to N 2 . A schematic mechanism for this conversion process is discussed in terms of solid-solid reactions of metallic iron and char-N.

The highlight of this review article is a novel method to remove fuel-bound nitrogen as N2 during coal pyrolysis in an inert atmosphere. When a Cl-free iron catalyst is precipitated on Australian brown coal from FeCl 3 solution using Ca(OH) 2 , N2 yield increases with increasing pyrolysis temperature and reaches 50% at 900°C, whereas it is < 5% without the iron. A low loading (1 wt% Fe) is sufficient for the remarkable formation of N2, and the use of H2 instead of inert He is unnecessary. The iron catalyst decreases the partitioning to not only volatile nitrogen (tar, HCN, and NH3) but also char nitrogen. A smaller catalytic effect of the precipitated iron is observed with bituminous coal. The iron catalyst after pyrolysis exists as fine particles with a smaller size of 20-30 nm for the brown coal char, Fe3C and graphitized carbon being also present. It is likely that N2 originates mainly from solid phase reactions involving the formation and subsequent decomposition of iron nitrides. In the pyrolysis of different coals at 1000°C, N2 yields for low-rank coals from China and Germany reach 50-60% despite the absence of catalyst. Demineralization with HCI washing removes mainly Fe and Ca elements from these coals and drastically decreases N2 yield with a corresponding increase in nitrogen retention in the chars. The Ca ion-exchanged with the demineralized coals is inactive for N2 formation. Iron nanoparticles, derived from Fe-containing minerals, catalyze predominantly solid phase reactions to extract N2 from char and/or precursors.

Sixteen coals from brown to bituminous coal have been pyrolyzed in high-purity He at 400 K/min up to 1000 °C with a fixed bed reactor, and the nitrogen distribution has been examined in detail. Nitrogen mass balances fall within 96−103%. Not only volatile nitrogen (HCN, NH3, and tar) but also N2 is formed, and among these N2 is the dominant product for almost all of the coals. Conversion of coal nitrogen to N2 depends strongly on coal type. A German brown coal gives the highest conversion of ≈60%, followed by ≈50% from a Chinese lignite. No relationship between N2 formation and coal rank is observed. As N2 increases, volatile nitrogen decreases slightly, but char nitrogen decreases remarkably, which means a strong, reverse correlation between N2 and char nitrogen. When the lignite char devolatilized at 600 °C is heated to 1000 °C, conversion of the nitrogen to N2 proceeds almost exclusively. These observations show that N2 originates mostly from char nitrogen and/or precursors. The mechanism of N2 formati...

Interactions between CaCO3 and low-rank coals were examined, and the steam gasification of the resulting Ca-loaded coals was carried out at 973 K with a thermobalance. Chemical analysis and FT-IR spectra show that CaCO3 can react readily with COOH groups to form ion-exchanged Ca and CO2 when mixed with brown coal in water at room temperature. The extent of the exchange is dependent on the crystalline form of CaCO3, and higher for aragonite naturally present in seashells and coral reef than for calcite from limestone. The FT-IR spectra reveal that ion-exchange reactions also proceed during kneading CaCO3 with low-rank coals. The exchanged Ca promotes gasification and achieves 40−60-fold rate enhancement for brown coal with a lower content of inherent minerals. Catalyst effectiveness of kneaded CaCO3 depends on the coal type, in other words, the extent of ion exchange.

To examine the influence of calcium on the mechanisms of brown coal pyrolysis and gasification, the morphology of chars from raw and calcium-exchanged Yallourn brown coal was analysed. The chars were obtained by slow pyrolysis in a thermo gravimetric analyser and rapid pyrolysis in fluidized bed reactors operating at atmospheric pressure and at 1.1 MPa. They were examined by optical microscopy to determine reflectance and the percentage of particles that had become plastic during pyrolysis. In addition to confirming calcium's inhibiting effect on tar yield, the results from the rapid pyrolysis experiments show that in the presence of calcium, char reflectivity decreases, char H/C ratio increases, and the proportion of particles going through a plastic stage decreases. Calcium's inhibition of plasticity development is augmented by high pressure in the fluidized bed reactor. The effects appear to be attributable to the action of carboxylate calcium as a cross-linking agent, leading to the formation of a tighter char structure which traps the organic material that would otherwise be liberated as tar. The presence of Ca also increases the H/C ratio of the chars produced by slow pyrolysis, but the mechanism of pyrolysis differs, since in slow pyrolysis none of the particles showed evidence of plasticity. In slow pyrolysis, calcium's influence on char reflectivity depends on the holding temperature, since temperature determines the extents of both coal devolatilization and catalytic transformations. The roles of calcium in these processes and their influence on optical anisotropy and reflectance are discussed.

The possibility of substituting the neural network for “the empirical sense of grading with worker’s eyes” is discussed in the color grading of apples. The whole image data collecting system is developed to overcome the unequal light intensity. The grades; Super excellent Excellent, Good, Poor colored and Injured are separated with neural networks.

A subbituminous coal was used to determine the distribution of N 2 , NH 3 , and HCN during slow rate heating pyrolysis in He and gasification in 10% CO 2 +He balance. During pyrolysis, the N 2 was the major product followed by NH 3 and HCN. During gasification, the N 2 yields were significantly enhanced and those of NH 3 and HCN decreased. Partial demineralization of coal resulted in a decrease in carbon and nitrogen conversion. This effect was also evident by comparing the nitrogen and carbon conversions of chars prepared at 500 o C from the fresh and demineralized coals. The addition of ultrafine Fe to coal increased conversion of carbon and nitrogen to N 2 during gasification but had little effect during pyrolysis. Thus, during the former more than 80% of the coal nitrogen was released ax N 2 . Also, in the presence of Fe the temperature of N 2 release was decreased by about 100 o C both during pyrolysis and gasification. During gasification of chars prepared at 1000 o C, the conversion of the coal nitrogen to N 2 was much lower than that of carbon

A novel method of removing coal nitrogen as N2 during pyrolysis has been studied with a fluidized bed reactor under atmospheric pressure. When Loy Yang brown coal with iron catalysts precipitated from FeCl3 solution is pyrolysed in He at 900 °C, 50–60% of the coal nitrogen is converted to N2, whereas the conversion to N2 is

A new method for preparing active iron catalysts for coal gasification at low temperatures has been studied by using FeCl[sub 3] as a raw material. Iron catalysts are precipitated onto brown coal probably in the form of FeOOH from an aqueous solution of FeCl[sub 3] by using three additives (urea, Ca(OH)[sub 2], and ammonia) and by hydrolysis. The use of Ca(OH)[sub 2] gives the highly dispersed, most active iron catalyst, which achieves complete gasification in steam within 60 min at 973 K and at 5 wt % Fe. The specific gasification rate with the most active catalyst is about 20 times that without catalyst, and it increases as the reaction proceeds. The X-ray diffraction measurements show that Fe[sub 3]O[sub 4] is the stable species throughout the gasification regardless of the catalyst preparation method. The sequence of catalyst effectiveness and the difference in the rate profiles among these catalysts can be elucidated on the basis of the degree of Fe[sub 3]O[sub 4] dispersion.

To make clear some factors controlling the formation of hexachlorobenzene (HCB) in the process of electric arc furnace (EAF) steelmaking, six dust samples recovered from different bag filters in commercial EAF steelmaking plants have been characterized with XRD, SEM-EPMA, XPS and temperature-programmed desorption (TPD) techniques. These dust samples contain 1.9–8.0 mass% of chlorine element, and the XPS and TPD measurements exhibit that the Cl is enriched at the dust surface and composed of the inorganic and organic functionalities, part of the Cl being evolved as HCl in the temperature region of flue gas treatment. All of the samples also include 2.1–6.4 mass% of carbon element, and some of the C can release CO 2 in the TPD up to 300 °C to form active carbon sites. The number is related closely to HCB concentration of each dust. Further, it is suggested that the Zn present in the samples consists of ZnFe 2 O 4 , ZnO and surface ZnCO 3 , and the dust with a larger content of the ZnCO 3 has a higher concentration of HCB. It is possible that HCB formation occurs via gas–solid–solid interactions among gaseous Cl-containing compounds in flue gas, active carbon sites and surface Zn-species produced in exhaust ducts and bag filters.

Sulfur removal during the fluidized bed combustion of coal has been carried out at temperatures of 960–1140 K. Coal impregnated with calcium magnesium acetate (CMA) is used as a sulfur sorbent. The amount of CMA actually loaded is larger for brown coal with a higher ion-exchange capacity. CMA shows no significant effect on the burn-off irrespective of the coal type and temperature. However, calcium impregnation is effective for in-bed sulfur removal. The efficiency depends on the coal type, probably the type of sulfur in the coal; a high sulfur retention is attained for Illinois No. 6 coal with a large proportion of pyritic sulfur in spite of low Ca/S ratios of around 0.5. In the coprocessing of bituminous coal with impregnated low-sulfur brown coal, the highly dispersed calcium in the brown coal captures effectively the sulfur evolved during the combustion of the bituminous coal.

Publisher Summary This chapter deals with coal gasification, which refers to the reactions of coal with air, oxygen, steam, carbon dioxide, hydrogen or a mixture of these gases to yield a gaseous product. These products can be used either as a source of energy or as a raw material for the synthesis of chemicals, liquid fuels or other gaseous fuels. The gasification converts solid coal into gaseous products. Since coal combustion is defined as the reactions of coal with air or oxygen, it can be regarded as a special case of coal gasification. When as-received Victorian brown coal is heated up under gasification conditions, it first undergoes dewatering and pyrolysis. Unlike bituminous coals and many other low rank coals, Victorian brown coals have large contents of moisture (60 - 65 %). The dewatering process is therefore particularly important from a practical point of view. In the pyrolysis step (sometimes referred to as devolatilisation), inorganic and hydrocarbon gases as well as tarry vapors evolve as volatile matters to leave a solid residue as char. Subsequently, a relatively slow reaction of the devolatilised char with a gasifying agent takes place predominantly.

Publisher Summary This chapter discusses the effect of the iron catalyst on the functionality of char nitrogen. X-ray photoelectron spectroscopy (XPS) is the most successful technique for studying the functionality of nitrogen in coal and char. The presence of the iron catalyst precipitated onto brown coal lowers the ratio of pyrrolic to pyridinic nitrogen in the char after pyrolysis at 900°C. The residual nitrogen in the char decreases with the formation of nitrogen (N 2 ) during the iron-catalyzed pyrolysis. The catalyst promotes the preferential nitrogen removal from pyrrolic nitrogen forms. Efficient conversion of coal nitrogen to N 2 in the pyrolysis process preceding combustion contributes to the reduction of the NO x emissions.

Publisher Summary This chapter discusses the influence of coal type, pyrolysis conditions, demineralization, and iron catalyst on the formation of nitrogen (N2) during the fix-bed pyrolysis of several coals with different ranks. The analyses of five coals with size fraction 150–250 μm, where the nitrogen contents are around 2 % are tabulated in the chapter. Two coals, ZN and NS coal are demineralized at elevated temperatures with hydrochloric acid and sodium hydroxide, respectively. The high-temperature ashes from the original and demineralized coals are characterized by X-ray diffraction (XRD) analysis. Nitrogen conversions to N2 and char nitrogen in the fixed-bed pyrolysis of coals at 1000° C are strongly dependent on the coal type, and at the highest, 50 % of coal nitrogen is converted to N2. Conversion to N2 increases linearly with increasing pyrolysis temperature in the range of 600–1000° C, but contrarily, nitrogen retention in the char decreases with temperature. When a low-rank coal containing large amounts of exchangeable metal cations is demineralized by acid washing, conversion to N2 decreases drastically. A nanophase iron catalyst promotes the formation of N2.

Three kinds of iron catalysts are precipitated onto an Australian brown coal from an aqueous solution of FeCl 3 by using urea, Ca(OH) 2 , or NH 3 , as an additive. All the iron species on coal are found to be finely dispersed FeOOH by the XRD and ESCA measurements, and they are reduced to metallic iron during pyrolysis. The use of urea gives the highest metal dispersion. All the catalysts show gasification activities in atmospheric H 2 at 873 K and the iron catalyst prepared with urea is most effective. These observations suggest that the metal dispersion is a key factor for controlling the catalytic activity and that the present hydrogasification may proceed through a hydrogen spillover mechanism.

Publisher Summary This chapter discusses a study to investigate the effects of Ca ion on the thermal behavior of brown coal. The Yallourn coal used in the slow heating experiments was a low ash brown coal from the Latrobe Valley, Australia, with elemental composition 67.4% C, 4.6% H, 0.6% N, 0.3% S, and 27.1% O on a dry ash-free basis. Coal particles of size 75–106 μm were paralyzed in nitrogen under slow heating conditions in a thermogravimetric analyzer. Char samples were mounted in epoxy resin, polished, and examined under oil immersion using an incident light microscope. The raw char samples are richer in plastic particles than the Ca char samples and in the raw and Ca chars, the percentage of the plastic particles increases as pyrolysis temperature becomes higher. If the heating rate and holding time are the same, the reflectance increases as the pyrolysis temperature increases. The reflectance of the chars increases as the holding time becomes longer.

Publisher Summary This chapter discusses a study to analyze the catalyst effectiveness of calcium carbonate in steam gasification of low rank coals. In the study, the analyses of four coals with low ranks from different countries were done. CaCO3 was added onto raw coal by different methods; mainly CaCO3 was kneaded with coal particles in deionized water by using a mortar grinder. The nominal Ca loading was 4.4 wt% as a metal in every case. Gasification runs were carried out with a thermobalance; CaCO3-loaded coals were rapidly heated in steam (80 kPa) and soaked for 2 h at 973 K. To make clear the change in chemical form of CaCO3 in the catalyst addition step, the Fourier transform infrared spectroscopy spectra of Ca-loaded coals were measured using the diffuse reflectance method, the X-ray diffraction measurements were carried out, and the amount of CO2 evolved during mixing CaCO3 and coal in water was determined. The results showed that the kneaded carbonate promoted the gasification of all the coals examined to a large extent. The effectiveness of CaCO3 catalyst was strongly dependent on the coal type.

The paper reports high conversion (about 50 %) of coal nitrogen to N 2 upon pyrolysis and clarifies the factors controlling N 2 formation. Fe and/or Ca containing minerals show the catalytic effect on N 2

Brown coal with iron catalyst precipitated from FeCl 3 solution has been pyrolyzed in He or H 2 at 600-900 °C with a fluidized bed reactor. The presence of the iron at loadings of 3-7 wt % changes dramatically the fate of coal nitrogen during pyrolysis at 900 °C; 50-60 % of coal nitrogen is readily converted to N 2 , resulting in a low residual nitrogen in the char. Changing the fluidizing gas from He to H 2 shows no significant effect on the conversion to N 2 . It is probable that ultrafine iron particles of around 50 nm in the reduced state are responsible for the present nitrogen removal

Steam gasification of 16 coals with different ranks and sulfur contents was carried out isothermally at 873-973 K in the presence of Ca(OH) 2 with a thermobalance. The catalyst at 5 wt % Ca promotes the gasification of all the coals. The calcium on low-rank coals giving moderate reactivities without catalyst shows large rate enhancement, which leads to complete gasification within 30 min at 973 K and lowers the gasification temperature by 110-150 K. The finely dispersed Ca species is formed on the chars after devolatilization of low-rank coals with Ca-(OH) 2 , and responsible for high catalytic activity. The calcium catalyst is less effective with high sulfur coals, and some of the sulfur evolved on coal devolatilization is captured by the calcium, but CaS loaded onto brown coal is still active in the gasification. Apparent activation energies are unchanged or slightly decreased by Ca(OH) 2 addition in most cases. The catalytic effect is discussed in terms of catalyst dispersion, sulfur poisoning, and inherent minerals.

In the previous study it was found that the nickel catalyst impregnated on brown coals shows excellent activity in the gasification reaction. In this study more cheap catalyst, Ca (OH) 2, was used as starting material. The chemical state during the steam gasification was determined and the reactivity was determined in the temperature range from 600 to 800°C. Ion-exchanged Ca was transformed to finely dispersed CaCO3 upon pyrolysis and the extensive crystal growth of CaCO3 was observed during the course of steam gasification. Near the end of gasification CaCO3 was converted to CaO owing to the decrease of CO2 content in the atmosphere. About 2 wt% of Ca content was enough to enhance the reactivity of coal by a factor of 10 at 650°C. In order to obtain the same reaction rate, 750°C is necessary without catalyst. This catalytic effect was more significant when compared with the data for the Ca-catalyzed gasification of American low-rank coals.

The removal of mineral matter from coal was attempted by caustic digestion followed by acid washing. A mild treatment at 460 K was found to be sufficient to remove most minerals and yet to avoid any substantial loss of heating value. The reaction products were identified by X-ray diffraction. Mass balance of each element was also clarified. The removal of major components, quartz and kaolinite, was rather easy, whereas the removal of Ca and Fe compounds strongly depended on the type of mineral matter.

Pyrolysis and steam gasification of Yallourn brown coal with Na, Ca and Ni catalysts were carried out in a fluidized bed reactor at 1.1MPa. The Na or Ca ion was loaded on the coal by the ion-exchange method using NaCl or Ca (OH) 2 solution, and Ni catalyst was impregnated from Ni (NH3) 6CO3 solution. When the coal was pyrolyzed in N2 stream at 1.1MPa, the weight loss was smaller in the presence of these catalysts because of a smaller evolution of tar. The tar was decom-posed to carbon and gaseous materials with the Ni, and it was converted into gas at higher temperatures with the Na and Ca.These catalysts promoted the steam gasification of brown coal under pressurized atmospheres. The addition of Ni, Na and Ca lowered the gasification temperature by 220, 70 and 150K, respectively. The reactivity of Ni-loaded coal levelled off at around 970K and the coal conversion of 80%, whereas the reactivity of Ca-loaded coal increased with temperature and the conversion reached 93% at 1080K. The conversion of coal carbon to gas and the total amount of product gas were considerably larger for the catalyst-loaded coals, because these catalysts promoted the reaction of tar with H2O as well as the gasification of char. The Ni catalyst was found to be more suitable for the direct produc-tion of methane by the reaction between brown coal and steam, and the Ca catalyst was suitable for the production of H2-rich gas. It was also found that the gasification catalyst could be used to control the H2/CO ratio in product gas.

Steam gasification of calcium-loaded Yallourn coal has been carried out with a thermobalance. Calcium catalyst showed a high activity at ≈950K. Calcium hydroxide, carbonate, acetate, nitrate and chloride exhibited similar catalyst effectiveness. The gasification rate increased with increasing the calcium loading, and at a loading of 5 wt%, complete gasification was attained within 25 min at 973 K. Comparison of the uncatalysed and catalysed rates showed that calcium catalyst can lower the reaction temperature by 150K. The impregnation of calcium salt on devolatilized char in place of raw coal resulted in the formation of rather large catalyst particles, and their activity was low. High temperature X-ray diffraction analysis revealed that the interconversion between calcium carbonate and oxide takes place readily in the gasification temperature region. Calcium carbonate was the predominant species during the gasification at 923 K. Catalysis of calcium was discussed in terms of a carbonate-oxide cycle mechanism.

In order to find a better method of catalyst addition for gasification of coals, some new or improved methods have been developed by our laboratory.As one of them, nickel and potassium carbonate were impregnated on the surfaces of four coals oxi-dized by nitric acid at 40t.The amount of nickel actually loaded on oxidized coals was much larger than on original coals.The better dispersion of nickel particles on the char surface of oxidized Leopold coal was observed by scanning electron microscope.An eight-fold increase in the concentration of carboxyl functional groups was obtained on the oxidized coal.Therefore the better dispersion is due mainly to the increased amount of nickel ion combined with these groups.The rates of steam gasification of the catalyst-impregnated coals were much higher with oxidized coals than with original coals.For example, when 2.0% of catalyst metal was impregnated on Shin-Yubari coal, the ratio of initial gasification rate with the oxidized coal to that with the original one at 750t was 2.0 for nickel and 3.8 for potassium carbonate.The finely dispersed catalyst on oxidized coals may lead to the higher gasification rate.An extraordinary high activity of nickel catalyst was observed when it was impregnated on coals which had a large amount of carboxyl groups.

Nickel catalyst exhibited an extremely high activity in the gasification of some low rank coals at a temperature as low as 750 K. Approximately 85% of Yallourn coal was converted within 30 min in steam at 773 K. A high nickel loading, > 4 wt% was necessary. It seems essential for coal high in oxygen and low in sulphur to be gasified in this manner. Oxygen-containing functional groups on the coal surface seemed to play an important role in keeping the nickel catalyst in a finely dispersed state. Hydrogen sulphide was strongly adsorbed on the nickel catalyst and retarded this reaction. Hydrogen and carbon dioxide were the main products of low-temperature steam gasification. Similar low-temperature gasification reactions were also observed in hydrogen and in carbon dioxide.