Gasification Of Low-rank Coal Research Articles

Promoting effect of various biomass ashes on the steam gasification of low-rank coal

Application of biomass ash as a catalyst to improve gasification rate is a promising way for the effective utilization of waste ash as well as for the reduction of cost. Investigation on the catalytic activity of biomass ash to the gasification of low rank coal was performed in details in the present study. Ashes from 3 kinds of biomass, i.e. brown seaweed/BS, eel grass/EG, and rice straw/RS, were separately mixed with coal sample and gasified in a fixed bed downdraft reactor using steam as the gasifying agent. BS and EG ashes enhanced the gas production rate greater than RS ash. Higher catalytic activity of BS or EG ash was mainly attributed to the higher content of alkali and alkaline earth metal (AAEM) and lower content of silica in it. Higher content of silica in the RS ash was identified to have inhibiting effect for the steam gasification of coal. Stable catalytic activity was remained when the amount of AAEM in the regenerated ash was maintained as that of the original one.

Investigation of Low Rank Coal Gasification in a Two-Stage Downdraft Entrained-Flow Gasifier

Low-rank coal contains more inherent moisture, high alkali metals (Na, K, Ca), high oxygen content, and low sulfur than high-rank coal. Low-rank coal gasification usually has lower efficiency than high-rank coal, since more energy has been used to drive out the moisture and volatile matters and vaporize them. Nevertheless, Low-rank coal comprises about half of both the current utilization and the reserves in the United States and is the largest energy resource in the United States, so it is worthwhile and important to investigate the low-rank coal gasification process. In this study, the two-stage fuel feeding scheme is investigated in a downdraft, entrained-flow, and refractory-lined reactor. Both a high-rank coal (Illinois No.6 bituminous) and a low-rank coal (South Hallsville Texas Lignite) are used for comparison under the following operating conditions: 1) low-rank coal vs. high-rank coal, 2) one-stage injection vs. two-stage injection, 3) low-rank coal with pre-drying vs. without pre-drying, and 4) dry coal feeding without steam injection vs. with steam injection at the second stage. The results show that 1) With predrying to 12% moisture, syngas produced from lignite has 538 K lower exit temperature and 18% greater Higher Heating Value (HHV) than syngas produced from Illinois #6. 2) The two-stage fuel feeding scheme results in a lower wall temperature (around 100 K) in the lower half of the gasifier than the single-stage injection scheme. 3) Without pre-drying, the high inherent moisture content in the lignite causes the syngas HHV to decrease by 27% and the mole fractions of both H2 and CO to decrease by 33%, while the water vapor content increases by 121% (by volume). The low-rank coal, without pre-drying, will take longer to finish the demoisturization and devolatilization processes, resulting in delayed combustion and gasification processes.

Low rank coal – CO2 gasification: Experimental study, analysis of the kinetic parameters by Weibull distribution and compensation effect

Gasification is generally considered as the most effective for low rank coal exploitation and CO2 gasification offers the advantage of upgrading an environmentally detrimental gas. Isothermal CO2 gasification tests of Greek low rank coal were performed in a tubular fixed bed reactor, to study the effect of the various reaction conditions. Greek lignite was quite reactive with CO2, resulting in high conversions even at short reaction times, while the obtained chars remained reactive after devolatilisation, as the continuous increase of conversion indicated. Conversion was very sensitive to temperature due to both pyrolysis and C–CO2 reactions, and for the granulometries studied (up to 1000 μm) the gasification rate was independent of particle size. CO2 partial pressure affected the gasification rate at low CO2 partial pressures, since the reactivity of lignite remained high (conversion ∼85% w/w daf) even for 0.25 atm CO2 partial pressure. The presence of CO retarded the reaction and the gasification rate decreased rapidly as the concentration of CO increased. The first order Volume Reaction Model (VMR) adopted was proven quite effective in describing the experimental results. Experimental results showed that the activation energy (E) varied with time, passing through a wide maximum between 10 and 15 min. The pre-exponential factor (k0) follows the behaviour of the activation energy, however, it exhibits a more sharp maximum at the same time region. The variations of the kinetic parameters with time could be attributed to the different nature of carbon atoms gasified and the changes of the number of active collisions, as the gasification reaction proceeds. As the gasification reaction advanced the Arrhenius parameters (E and k0) increased or decreased simultaneously, exhibiting a compensation effect. The probability density function (pdf) of the Weibull distribution was employed successfully to depict the variations of the kinetic parameters, E and k0.

고함수 저등급 석탄의 초임계수 가스화 특성

Study on clean and efficient utilization technology for low rank coal with high moisture content is actively ongoing due to limited reserves of petroleum and of high grade coal and serious climate change caused by fossil fuel usage. In the present study, supercritical water gasification of low rank coal was performed. With increasing reaction temperature, content of combustible gases such as <TEX>$H_2$</TEX> and <TEX>$CH_4$</TEX> in the syngas increased while the <TEX>$CO_2$</TEX> content decreased. As the reaction pressure increased from 210 to 300 bar, the <TEX>$CO_2$</TEX> content in the syngas increased while the hydrocarbon gas content decreased. The <TEX>$H_2$</TEX> and <TEX>$CH_4$</TEX> content in the syngas increased slightly with pressure. With the addition of Pd, Pt, and Ru catalysts, it was possible to improve the production of <TEX>$H_2$</TEX>. Moreover, the increase of active metal content in the catalyst increased the <TEX>$H_2$</TEX> productivity. The Ru catalyst shows the best performance for increasing the <TEX>$H_2$</TEX> content in the syngas, while decreasing the <TEX>$CO_2$</TEX> content.

Co-pyrolysis of low rank coals and biomass: Product distributions

Pyrolysis and gasification of combined low rank coal and biomass feeds are the subject of much study in an effort to mitigate the production of green house gases from integrated gasification combined cycle (IGCC) systems. While co-feeding has the potential to reduce the net carbon footprint of commercial gasification operations, success of this strategy requires investigation of the effects of coal/biomass co-feeding on reaction kinetics and product distributions. Southern yellow pine was pyrolyzed in a semi-batch type drop tube reactor with either Powder River Basin sub-bituminous coal or Mississippi lignite at several temperatures and feed ratios. Product gas composition of expected primary constituents (CO, CO2, CH4, H2, H2O, and C2H4) was determined by in situ mass spectrometry while minor gaseous constituents were determined using a GC–MS. Product distributions are fit to linear functions of temperature, and quadratic functions of biomass fraction, for use in computational co-pyrolysis simulations.The results are shown to yield significant nonlinearities, particularly at higher temperatures and for lower ranked coals. The co-pyrolysis product distributions evolve more tar, and less char, CH4, and C2H4, than an additive pyrolysis process would suggest. For lignite co-pyrolysis, CO and H2 production are also reduced. The data suggests that rapid pyrolysis of biomass produces hydrogen that stabilizes large radical structures generated during the early stages of coal pyrolysis. Stabilization causes these structures to be released as tar, rather than crosslinking with one another to produce secondary char and light gases. Finally, it is shown that, for the two coal types tested, co-pyrolysis synergies are more significant as coal rank decreases, likely because the initial structure in these coals contains larger pores and smaller clusters of aromatic structures which are more readily retained as tar in rapid co-pyrolysis.

The kinetic study of catalytic low-rank coal gasification under CO2 atmosphere using MVRM

In this study, we carried out a kinetic investigation and analysis of the syngas produced by low-rank coal gasification. We conducted a proximate and ultimate analysis of six types of coals in order to measure the amount of sulfur and ash. The coal was then analyzed using a thermo gravimetric analyzer (TGA) to select a suitable sample. The selected Samhwa coal sample was mixed with catalysts. Samples mixed with catalysts were used to determine the activation energy under CO2 atmosphere using the modified volume reaction model (MVRM). An analysis of the resulting syngas was performed using gas chromatography (GC).

Performance of an IGCC Plant with Carbon Capture and Coal-CO2-Slurry Feed: Impact of Coal Rank, Slurry Loading, and Syngas Cooling Technology

The high heat capacity and latent enthalpy of vaporization of water lead to a low gasification efficiency in gasifiers fed with coal-water slurry. Liquid carbon dioxide, CO2(l), has been suggested as an alternative slurrying medium to improve the efficiency of low-rank coal gasification in integrated gasification combined cycle power plants with carbon capture. Steady-state process simulation is used in this work to confirm published findings and present a comprehensive assessment of the impact of the coal rank, gasifier cooling technology, and CO2 slurry loading uncertainty on the performance advantage of CO2 slurry-fed plants. A power generation efficiency improvement of up to 25% (5%-points) is predicted, which is shown to increase with decreasing coal rank and to be highest for full-quench gasifier cooling technology; the latter is a significant source of capital cost savings and is especially attractive when combined with CO2 slurry feed. Using CO2(l) instead of water slurry reduces the performance penalty of low-rank coal gasification by half, thus substantially improving the feedstock flexibility of the plant. With a single exception, the performance benefit of coal-CO2 slurry was found to be outside the uncertainty range of the slurry loading, which is still one of the key unknowns of this alternative feed system.

The production of separate streams of pure hydrogen and carbon dioxide from coal via an iron-oxide redox cycle

A chemical looping process using the redox reactions of iron oxide has been used to produce separate streams of pure H2 and CO2 from a solid fuel. An iron oxide carrier prepared using a mechanical mixing technique and comprised of 100wt.% Fe2O3 was used. It was demonstrated that hydrogen can be produced from three representative coals – a Russian bituminous, a German lignite and a UK sub-bituminous coal. Depending on the fuel, pure H2 with [CO] ≲50vol.ppm can be obtained from the proposed process. The cyclic stability of the iron oxide carrier was not adversely affected by contaminants found in syngas which are gaseous above 273K. Stable quantities of H2 were produced over five cycles for all three coals investigated. Independent of the fuel, SO2 was not formed during the oxidation with steam, i.e. the produced H2 was not contaminated with SO2. Since oxidation with air removes contaminants and generates useful heat and pure N2 for purging, it should be included in the operating cycle. Overall, it was demonstrated that the proposed process may be an attractive approach to upgrade crude syngas produced by the gasification of low-rank coals to pure H2, representing a substantial increase in calorific value, whilst simultaneous capturing CO2, a greenhouse gas.

No.35 イオン交換法で調製したナノCa/Na複合触媒を用いる低炭化度炭のガス化(ガス化・燃焼・液化(3))

No.35 イオン交換法で調製したナノCa/Na複合触媒を用いる低炭化度炭のガス化(ガス化・燃焼・液化(3))

Molecular modelling and experimental studies on steam gasification of low-rank coals catalysed by iron species

Pyrolysis and catalytic steam gasification of brown coal containing iron hydroxyl complexes have been investigated experimentally and with semi-empirical and density functional theory molecular modelling. Pyrolysis yielded mainly CO2, CO, and reduced iron species. Catalytic steam gasification at 900 °C after 15 min, consumed 20 wt.% additional char and a higher than expected yield of H2 due to post-gasification reactions; inorganic and organic oxygen in char increased compared to pyrolysis. Apparent turnover numbers for catalytic gasification were 12–22 mole of carbon per mole of iron. The distribution of iron species in brown coal indicated small iron clusters are likely to form on heating; pyrolysis was thus modelled using molecules of char with [Fe3], [Fe5] and [Fe3O], and the active site for gasification was shown to be [Fe–C]. The mechanism of catalytic gasification involved H2O chemi-adsorbed on [Fe–C], formation of the [Fe ← OH2] coordination bond, with H2 produced via iron hydride complexes. Formation of CO was via oxygen insertion into [Fe–C] to form [Fe–O–C] that decomposed into CO and another [Fe–C] site. Lower activation barriers were obtained for concerted chemistry involving iron-hydrides. Active sites in char were accessible to H2O as pores had developed around iron species; large sized iron species were not catalytically active but caused large pores to form in char.

Transformations of sodium during gasification of low-rank coal

Specially prepared forms of a high-sulphur South Australian lignite containing sodium in two forms; as a carboxylate, forming a part of the coal organic matter or as soluble salt (NaCl) were investigated. The influence of gasification environment (gas type, temperature and time) on the transformations of sodium and the extent of vaporisation were studied. Contrary to theoretical equilibrium calculations for the high levels of sulphur present in the coal, no sodium sulphide formation was found upon the transformation of carboxylate sodium. Experiments confirmed rather the formation of sodium carbonate during gasification or pyrolysis of the sulphur-rich coal. Sodium was found to evaporate, with sodium release higher during gasification in steam or carbon dioxide than for pyrolysis in nitrogen. The release of sodium and chlorine from coal containing sodium chloride was disproportionate. Almost all of the chlorine was measured to have been released during gasification and pyrolysis by 850 °C. The release of sodium was nearly half of that of chlorine and inferred to be in the form of sodium chloride vapour. Identification of sodium carbonate in the residual pyrolysed char confirms the reaction of sodium chloride with hydrogen from coal carboxylic acid groups. Neither sodium sulphide nor sodium hydroxide was identified in char for coal containing sodium chloride.

Influence of gas environment on reactions between sodium and silicon minerals during gasification of low-rank coal

Thermodynamic equilibrium calculations were performed to determine the possible compositions and conditions for formation of potential liquid phases responsible for fluidised bed agglomeration during gasification of a high-sulphur low-rank coal from South Australia. The coals from this region of Australia are typically characterised by containing high levels of sodium, silica and sulphur. The transformation behaviour of the form of sodium present in coal, as either a carboxylate forming part of the coal organic matter or as soluble salt (NaCl) and its reaction with silicon compounds (silica or kaolin) is presented. The influence of temperature and gas atmosphere on equilibrium composition was evaluated. Thermodynamic equilibrium calculations show that the distribution of sodium among the produced species will depend on the form of sodium in the coal, the gas atmosphere and the forms in which silicon is present in the coal. Steam was found to have the most significant effect causing a lowering of the sodium carbonate melting point temperature.

Role of Calcium Hydroxide in Supercritical Water Gasification of Low-Rank Coal

Gasification of low-rank coals in supercritical water was carried out in an autoclave by heating temperature to 690 °C and elevating autogenous pressure to 30 MPa. An attempt was made to investigate the catalytic effect of calcium hydroxide on the gasification. It was found that the presence of Ca(OH)2 facilitates the extraction of volatile matter from coal and the decomposition of the volatile matter to small molecule gases, with a decrease in the amount of residual char. The production of H2 is enhanced by the catalytic effect of Ca(OH)2 both on the water-added degradation of the volatile matter and on the gasification of the coal char, despite a slow procession of the char gasification. Moreover, Ca(OH)2 serves to capture CO2 as CaCO3. After the slurry of Ca(OH)2 and a Yallourn coal with the Ca/C molar ratio of 0.6 had been heated at 690 °C and 30 MPa, the yields of H2 and CH4 were, respectively, 0.35 and 0.18 NL/g of coal (daf), with little gaseous CO2 and liquid products.

Variation of sodium forms and char reactivity during gasification of a South Australian low-rank coal

Experiments were performed to determine the gasification rate of South Australian Lochiel coal in CO 2 at temperatures between 750 and 950 °C. Five samples were prepared, namely, raw coal, acid-washed coal, and acid-washed coal doped with 5 wt % Na 2 CO 3 , 5 wt % CaCO 3 , and 2.5 wt % Na 2 CO 3 +2.5 wt % CaCO 3 , and gasified in a TGA apparatus. While the acid-washed coal incurred a low but invariant reactivity, the raw and carbonate-doped samples experienced an increase in gasification rate with carbon conversion up to ca. 90% conversion, after which the gasification rate rapidly fell to zero at 100% conversion. It was speculated that transformation of the cations in samples during gasification might be responsible for the observed variation in the gasification rate. Further experiments using the 5 wt % Na 2 CO 3 —doped coal sample identified that the rising concentration of the active cations in the char was the primary reason for the increasing gasification rate before 90% conversion, but the lack of carbon availability was responsible for the rapid fall in gasification rate above 90% conversion. Before gasification, sodium in the 5 wt % Na 2 CO 3 —doped coal was about 30% water soluble and 70% water insoluble but acid soluble. Upon gasification, the water-insoluble sodium but acid-soluble sodium decreased to about 25% of the total sodium and remained invariant with time and temperature. The acid-insoluble sodium incurred an initial increase to 15% and then continuously reacted with silicates in the presence of coal. Heat treatment rapidly destroyed carboxylic functional groups and thus reduced the ion-exchange capacity of the acid-washed coal sample. The changes in sodium forms and quantity and the effect of heat treatment on the content of carboxylic functional groups and ion-exchange capacity explained the variation of gasification rate with carbon conversion. The change in the total surface area of the char during gasification was not the dominating factor influencing the char gasification rate.

Characterisation of spouting behaviour of coal ash with thermo-mechanical analysis

Bed material agglomeration and loss of fluidization present a major problem in fluidized bed combustion or gasification of low rank coals. Ash particles start to agglomerate and fluidization becomes unstable at temperatures well below the ash softening point measured by the ASTM methods. Attempts have been made to develop a method to determine this characteristic temperature. This paper presents results from an investigation into thermo-mechanical analysis (TMA) as a potential technique. It is shown that, when applied to the coating materials at a heating rate of less than 5°C/min under a force of 0.5 N, the technique can successfully detect the point at which the particles change its spouting or fluidization characteristics.

Gasification of a South Australian low-rank coal with carbon dioxide and steam: kinetics and reactivity studies

Experimental gasification studies are reported for a highly reactive South Australian low-rank coal, Bowmans coal, with steam and with carbon dioxide in a single-particle reactor operating at atmospheric pressure and at temperatures between 714 and 892°C. Gasification rate at a given temperature is found to be independent of particle size, suggesting that the gasification rate follows the homogeneous model. The observed gasification rate constants are as follows. For CO 2 gasification: k = 1327 exp( −10945 T ) [A = 1327 min −1, E a = 91 kJ mol −1] For H 2O gasification: k = 261276 exp( −15733 T ) [A = 261276 min −1, E a = 131 kJ mol −1] It is found that the reactivity of Bowmans coal is far higher than for other coals reported in the literature, because of to its high inherent content of inorganic matter. Acid-washed Bowmans coal has similar reactivity to other low-inorganic-content low-rank coals. Gasification reactivity follows the other Na > K > Ca > Ni with the same anions. The combined effect of different cations is found to be less than for the sum of the individual cations. Heat treatment of acid-washed coal prior to ion exchange results in greatly reduced reactivity due to loss of carboxylic functional groups. Reactivity can be varied by removing or adding active cations. A reasonably good correlation is found to exist between gasification reactivity and total Na + Ca cation content.

Catalytic gasification of coal for the production of fuel cell feedstock

Fuel cell technology is advancing rapidly. This creates a critical need for economical hydrogen production. Proper levels of H 2 and CH 2 for fuel cell feed could result from catalytic gasification of low-rank coal. Bench-scale steam gasification catalyst testing was carried out on Illinois No. 6 bituminous and Center North Dakota lignite coals with catalysts containing Fe, Ni, Ca, or K and some combinations of these. All of the catalysts tested showed a modest catalytic effect with both coals, ranging from negligible to nearly 30-fold increase in reaction rate. Nickel and iron enhanced the rate slightly, while increasing methane concentration.

Development of techniques for monitoring gas-phase sodium species formed during coal combustion and gasification

The development of techniques suitable for on-line analysis of gas-phase molecular sodium species, resulting from the combustion and gasification of low-rank coals is described. In particular two techniques have been demonstrated, these are: (a) laser-induced photofragment fluorescence and (b) microwave spectroscopy. The photofragment technique can be applied in situ and yields excellent detection limits (<0.1 ppb of NaCl and 1 ppb NaOH) with good discrimination between the two major gas-phase species — NaCl and NaOH. Limitations of this technique include absorption of the ultraviolet (UV) photolysis excitation by other chemical species and particulates. Microwave spectroscopy shows promise in determining the sodium species distribution in the gas-phase. A purpose built analytical instrument (known as MILLIJET HT) is being developed for application in high-temperature environments. Early results indicate detection limits of <100 ppb NaCl. Lack of sensitivity for NaOH is being attributed to the formation of NaOH dimers and larger clusters. Detailed calculations of the dimer structure and the dimer-monomer reaction have been undertaken in order to maximise the performance of the instrument.

Steam gasification of low-rank coals with a chlorine-free iron catalyst from ferric chloride

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSteam gasification of low-rank coals with a chlorine-free iron catalyst from ferric chlorideYasuo Ohtsuka and Kenji AsamiCite this: Ind. Eng. Chem. Res. 1991, 30, 8, 1921–1926Publication Date (Print):August 1, 1991Publication History Published online1 May 2002Published inissue 1 August 1991https://doi.org/10.1021/ie00056a038RIGHTS & PERMISSIONSArticle Views233Altmetric-Citations28LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (745 KB) Get e-Alerts Get e-Alerts

The characterization of organomineral components of low-rank coals

A methodology of characterizing organomineral components of As Pontes and Meirama Spanish brown coals is developed. Analytical electron microscopy provided indirect evidence for the association of alkaline-earth elements to the organic matter of coal. Fourier transform infrared spectroscopy yielded information on the nature of bonding of inorganic elements to carboxyl groups. Quantitative results were obtained by methods implying extraction or oxidative leaching followed by analysis of cations. The resulting set of procedures leads to a comprehensive characterization of this type of coal components, and deserves interest due to their role in combustion and gasification of low-rank coals.