South African Bituminous Coal Research Articles

Determination of mercury thermospecies in South African coals in the enhancement of mercury removal by pre-combustion technologies

Samples of South African bituminous coals were analysed for total mercury (Hg) and Hg thermospecies concentrations using an RA-915 + Zeeman Mercury Analyser. Total mercury concentrations in samples of coals (n = 57) ranged between 10 ng g−1 and 493 ng g−1 with a mean value of 150 ± 53 ng g−1. Thermospecies of Hg were determined by monitoring Hg response as a function of sample temperature, increasing at 0.8 °C/s from ambient to 720 °C. This approach provides important information on thermal release of Hg species, as indicated by their appearance over specific temperature intervals. This permits identification of the presence of Hg thermospecies in coal and their quantification in each time (temperature) interval. It was found that 76% of tested bituminous coal samples release Hg species within low temperature intervals (20–180 °C and180–360 °C). The information generated in this study will aid in the selection of suitable coals for pre-combustion treatment that can lead to significant reduction of atmospheric Hg emission during coal combustion at power stations. This analytical approach can also be used for the creation of a system of coal classification based on the temperature of release of various Hg thermospecies.

Co-pyrolysis of South African bituminous coal and Scenedesmus microalgae: Kinetics and synergistic effects study

In this work, the co-pyrolysis of coal and algae is explored with special emphasis on decomposition kinetics and the possibility of the existence of synergistic effects. Modelling and kinetics analysis based approaches were used for the investigation of the existence of synergistic effects. The co-pyrolysis kinetics was studied using the model-free, Coats–Redfern integral method. The kinetics were evaluated for 1st and 2nd order reaction models. Results reveal that Scenedesmus microalgae is characterised by a two stage decomposition process that occurs at temperature ranges of 200–400 °C and 500–700 °C with activation energy of 145.5 and 127.3 kJ/mol, respectively. Bituminous coal has a two stage, slow decomposition process that occurs at temperature ranges of 400–700 °C and above 750 °C with an activation energy of 81.8 and 649.3 kJ/mol, respectively. Furthermore, co-pyrolysis of coal and microalgae is characterised by three stages whose kinetics are dominated by the pyrolysis of the individual materials. For the studied range of coal/algae ratios, the three pyrolysis stages occur in the approximate temperature ranges of 200–400 °C, 430–650 °C and above 750 °C, with activation energies in the ranges of 131–138, 72–78 and 864.5–1235 kJ/mol, respectively. Modelling and kinetics study showed that there is strong evidence of interactions between coal and microalgae that manifest as synergistic effects especially in the second and third stages of decomposition.

The carbon dioxide, methane and nitrogen high-pressure sorption properties of South African bituminous coals

In this paper, we report the CO2, CH4 and N2 sorption isotherms of four dry South African bituminous coals at pressures up to 16 MPa at 55 °C. The sorption capacities of the samples with respect to the adsorbate gases decreased in the order: CO2 > CH4 ≈ N2 by weight, and CO2 > CH4 > N2 by volume. A new model, based on a hybrid Dubinin-Radushkevich and Henry law approach (DR-HH) provided substantially better fits to the sorption isotherm data than the previously used modified DR (M-DR) model. Obtained uncertainty metrics show that the DR-HH model generally returned lower error sum of squares (ESS) and root mean square (RMS) residuals, and higher quality of fit (QOF) compared to the M-DR model. The net heat of sorption, βEs, of the samples for the three adsorbate gases were generally low (8.5–12.8 kJ/mol), but comparable to previous determinations of other coals, indicating that physisorption was the dominating sorption mechanism. The sorption capacities of the samples were found to be rank-dependent as they decreased with increasing vitrinite reflectance and elemental carbon content. The micropore properties of the samples as measured by both CO2 low-pressure gas adsorption (LPGA) and small angle X-ray scattering (SAXS), impacted the sorption properties of the sample more than both the mesopore and macropore properties determined from N2 LPGA, SAXS, and mercury intrusion porosimetry. The sorption capacities of the samples were found to increase with increasing lithotypes abundance, suggesting that lithotype bandings enhances either the fluid transport processes or the micropore properties of the coal matrix. In addition, it has been demonstrated that critical properties of the adsorbate gases influenced their sorption properties.

Solvent Extraction of a South African Bituminous Coal using a Model Biomass-derived Phenolic Mixture

A model biomass-derived phenolic mixture was investigated for its solvent ability for extraction of a South African bituminous coal at temperatures of 300-360 °C. A previous study showed that phenol gave the highest extraction yield of 49.5 wt. % (daf) for bituminous coal at 360 °C, with an oil yield of 26.3 wt. % (daf). The phenolic products produced from sweet sorghum bagasse via an alkaline liquefaction process were identified and reported earlier and a model biomass-derived phenolic mixture was formulated, evaluated and results used in this study. The model mixture gave an extraction yield of 37.1 wt. % (daf) and oil yield of 16.9 wt. % (daf) at 360 °C. This solvent mixture was found to be less effective for high extraction yields when compared to phenol at mild temperatures. This could be due to phenol being a better hydrogen carrier than the solvent mixture during the internal redistribution of hydrogen in the coal. The infrared spectroscopy results of the coal and extraction products obtained using the model mixtures showed similar functional groups. These results demonstrate that the use of a model biomass-derived phenolic mixture has the potential to depolymerize coal and produce high-value chemicals from coal. Keywords: Coal extraction, bituminous coal, depolymerization, biomass-derived solvent.

Low-High Temperature Flue Gas Direct Injection in South African Bituminous and Anthracite Coals:Sorption Capacity Assessment

Low-High Temperature Flue Gas Direct Injection in South African Bituminous and Anthracite Coals:Sorption Capacity Assessment

Release of Nitrogenous Volatile Species from South African Bituminous Coals during Pyrolysis

The influence of typical South African coal attributes on the release of nitrogen into the volatile stream during pyrolysis was studied by utilizing three bituminous coals. The majority of South African coals are characterized by high mineral matter and are rich in inertinite maceral. Pyrolysis was conducted in a bench-scale fluidized bed (FB) at 740–980 °C, and also in a drop-tube furnace (DTF) at 1000–1400 °C. Levels of nitrogenous species in the volatile stream in the form of NH3, HCN, and tar-N were determined. Nitrogen functional forms of tars released at low temperatures were predominantly distinguished by high levels of pyrrolic nitrogen, followed by pyridinic and quaternary nitrogen, respectively. Tars liberated at 740 °C possessed similar nitrogen functional form attributes as those of parent coals. However, an increase in pyrolysis temperature caused a gradual increase in quaternary nitrogen as well as a concurrent decrease in pyrrolic nitrogen and a concomitant subtle decrease in pyridinic nitr...

Transformation of nitrogen functional forms and the accompanying chemical-structural properties emanating from pyrolysis of bituminous coals

Characterisation of simultaneous changes in nitrogen functionalities and condensed aromatic crystallites during pyrolysis of bituminous coals was conducted. X-ray photoelectron spectroscopy (XPS) was utilised to determine nitrogen functional forms in three South African bituminous coals and the subsequent transformation in respective chars. Corresponding structural properties of coal and char were deduced through X-ray diffraction (XRD) analysis. Carbon structural properties in parent coals were also determined by solid state 13C nuclear magnetic resonance (ss NMR). The chars were prepared by pyrolysis at 740–980 °C in a bench-scale fluidised-bed (FB) and at 1000–1400 °C in a drop-tube furnace (DTF). The changes in XPS N 1s spectra of the coals through the respective chars were used to determine the nitrogen functionality transformations. Deconvolution of the XPS N 1s spectra revealed that pyrrolic nitrogen decreased with increasing pyrolysis temperature while quaternary nitrogen increased appreciably. Simultaneously, information deduced from XRD spectra showed that aromaticity (fa) and average crystallite diameter (La) increased with severity of pyrolysis temperature in all the chars, while the fraction of amorphous carbon (XA) and degree of disorder index (DOI) decreased significantly. Chars derived from the vitrinite-rich (also high in total reactive macerals) coal were more susceptible to thermal treatment with regard to nitrogen functional forms and other carbon crystallite transformations; high temperature chars only contained pyridinic and quaternary nitrogen, and exhibited a significant increase in crystallite height (Lc) and the average number of aromatic carbons (Nave). Aromaticity of coals determined from ss 13C NMR and XRD corresponded. Comparison of structural changes brought by pyrolysis, as measured by XPS and XRD, showed that a good correlation existed between increasing quaternary nitrogen and fa. In a marked contrast, the diminishing of pyrrolic nitrogen displayed a good efficacy with DOI and XA. The reported concomitant transformations of nitrogen functional forms with char morphological changes are considered precursors to nitrogen release. This will inform future detailed studies on the conversion of coal nitrogen in solid fuel fired systems, such as in the applications of low-NOx burner technologies towards the release and reduction of nitrogen oxides in pulverised coal combustion.

Effectivity of Phenol during Solvent Extraction of a South African Bituminous Coal under Mild Conditions

Solvent extraction of a South African bituminous coal was carried out under mild conditions (<400 °C) with a holding time of 20 min and an initial nitrogen (N2) pressure of 6 MPa. Thermal degradation of coal with phenol results in the depolymerization of the coal, yielding coal-derived liquids and insoluble residues. The effectiveness of phenol for solvent extraction of coal within the temperature range of 300–360 °C was investigated, with a focus on the quality of the coal-derived liquids. It was found that an increase in temperature from 300 °C to 360 °C resulted in an increase in the conversion and yields of both oil and gas, and a reduction in the intermediate components (preasphaltenes + asphaltenes, PAAs). The conversion and extraction yields of hexane-soluble (HS) oils were 49.5% (daf) and 26.3% (daf), respectively (daf = dry ash-free), for thermal depolymerization reactions at 360 °C. It seems that the extraction process dissolves molecular fragments of the coal, because the infrared spectra of the coal and the extraction products are similar. The SimDis results of the coal-derived liquids (300–360 °C) indicated that the samples consisted of light vacuum gas oil (23–31 wt %), distillate fuel oil (16–30 wt %), heavy vacuum gas oil (18–34 wt %), and residual oil (3–16 wt %). These results show the potential of phenol as a solvent to extract South African bituminous coal at mild temperatures for value-added liquid fuels and add to the general knowledge of the potential utilization of the Permian-aged South African bituminous coals.

Coal pyrolysis: Comparative evaluation of the technical performance of two Southern Hemisphere demineralized bituminous coals

Differences in the physico-chemical properties of char can fundamentally affect the reactivity of the char during conversion processes and even the reaction pathway. Transformations from coal to char using a high heating rate have been thoroughly assessed; however, there is less information on the reactivity of this transition to chars. Two South African bituminous coals of ≤75μm were acid washed, and subjected to a slow heating rate of 25°C/min from 450 to 700°C at atmospheric atmosphere. The chars were characterized by physical, chemical and petrographic evaluations. The effect of the heat treatment conditions on the reactivity of the chars towards oxygen under chemical kinetic controlled regime was assessed. The oxygen content of the resultant chars was also measured directly by scanning electron microscope (SEM) attached with element detector sensor (EDS) technique. The coals are medium rank C bituminous (Rov=0.73 for high volatile and Rov=0.78 for low volatile). Char properties determined revealed correlations of the chemical structural changes during the coal to char transition. The findings of this study would suggest that the loss of carbon combustion reactivity cannot be assessed on the basis of its time-temperature history only, but the extent of carbon interaction with oxygen also come into play. The synergy of reactions induced by modifications of the carbon structure, oxygen uptake and the reaction between oxygen and the resultant chars is presented and discussed.

The effect of acid demineralising bituminous coals and de-ashing the respective chars on nitrogen functional forms

An opportunity presented itself to compare changes in nitrogen functional forms brought by the acid treatment of South African bituminous coals and their respective chars. X-ray photoelectron spectroscopy (XPS) was used to determine functional forms of the raw coals, acid-treated coals, respective chars prepared at 740 and 980°C in a bench-scale fluidised-bed (FB), and at 1000 and 1400°C in a drop-tube furnace (DTF), as well as their corresponding de-ashed remnants. The XPS N 1s spectra for the raw coals were typically similar to previous widely reported bituminous coals, of which pyrrolic nitrogen was the predominant form of organically bound nitrogen, followed by pyridinic and quaternary nitrogen. In pyrolysed chars, quaternary nitrogen was the dominant form followed by pyridinic, pyrrolic and protonated-/oxidised heterocyclic nitrogen forms respectively. Nonetheless, XPS N 1s analysis for DTF severely pyrolysed chars (1000 and 1400°C) prepared from high ash and vitrinite-rich coal, and also a char (1400°C) from a relatively low ash and inertinite-rich coal, gave a spectra with only two sub-peaks corresponding to quaternary and pyridinic nitrogen. It seems that the HCl/HF/HCl sequential demineralising/de-ashing process had no effect on the nitrogen functional forms of raw coals and the entire chars prepared from the FB. De-ashing of DTF severely pyrolysed chars emanating from high ash and inertinite-rich coal exhibited no marked change to the nitrogen functional forms. However, acid treatment of DTF chars derived from a high ash and vitrinite-rich coal, a char from relatively low ash and inertinite-rich coal, which initially contained pyridinic and quaternary nitrogen resulted in additional nitrogen moieties of pyrrolic and protonated/oxidised nitrogen.

Fluidized bed co-combustion of hydrothermally treated paper sludge with two coals of different rank

Fluidized bed co-combustion of raw paper sludge (Raw-PS) and hydrothermally treated paper sludge (HTT-PS) with either low (Lo-Coal) or high reactivity coal (Hi-Coal) was investigated. The paper sludge was treated in a pilot-scale hydrothermal reactor at 197°C and 1.9MPa for 30min. South African bituminous and Thai subbituminous coals were selected as representative of Lo-Coal and Hi-Coal, respectively. A 110-mm bubbling fluidized bed combustor was used in this study. During the steady combustion tests the nominal temperature was 858°C, the fluidization velocity was 0.5m/s, and the excess air was varied as 20%, 40%, and 60%. Both single fuel combustion and co-combustion were tested. Co-combustion tests were conducted by feeding the sludge at mixing ratios of 30% and 50% (mass basis) with coal. The main focus of this study was on NOx emissions and unburned carbon performance. Results showed that at 30% mixing ratio using HTT-PS instead of Raw-PS could reduce NOx emission by 3–6% and 9–17% in the case of Lo-Coal and Hi-Coal, respectively, and the loss of unburned carbon could be decreased by 15–18% and 36–53% for Lo-Coal and Hi-Coal, respectively. The particle size distribution of fly ash of all samples was similar regardless of the excess air variation. On the whole, the hydrothermally treated paper sludge showed better performance for co-combustion with coal and would be a better choice compared to the original raw paper sludge.

The effect of acid washing on the pyrolysis products derived from a vitrinite-rich bituminous coal

Extensive characterization of the pyrolysis products, derived from raw and acid washed samples of a vitrinite-rich South African bituminous coal is reported. Pyrolysis experiments were carried out with use of a modified Fischer Assay setup at 520, 750 and 900°C. Gaseous products were analyzed by gas chromatography (GC); tar yields by simulated distillation (SimDis), gas chromatography mass spectrometry and –flame ionization detection (GC–MS and –FID) and size exclusion chromatography (SEC-UC), and the char yields by proximate, ultimate and Brunauer–Emmett–Teller (BET) CO2 adsorption analyses. The water and tar yields of the acid washed coal fraction (AW TWD) was found to be lower, whilst the gas yields were found to be significantly higher than that of the raw coal fraction (TWD). The char yields were not significantly affected by acid washing. Some of the differences in pyrolysis product yields can be related to increased porosity of the acid washed coal fraction. GC analysis of the derived pyrolysis gases indicated that the AW TWD derived gas contained higher yields of H2, CH4, CO2, C2H4, C2H6, C3H4, C3H6 and C4s when compared to the gas derived from the TWD fraction, whilst the CO yield from the TWD fraction was greater at all final pyrolysis temperatures. Analyses of the tar fraction by means of SimDis, GC–MS and –FID and SEC-UV indicated that the acid washed coal derived tars where more aromatic in nature, containing more higher boiling point components, which increased with increasing final pyrolysis temperature. On the other hand, the tars derived from the TWD coal contained lighter boiling point components with increasing final pyrolysis temperature. The changes in the pyrolysis behavior of the bituminous coal are due to the removal of the mineral matter and also the influence of the acid washing process. This study confirmed that acid washing of coal changes the pyrolysis products composition of a bituminous coal.

Chemical–structural properties of South African bituminous coals: Insights from wide angle XRD–carbon fraction analysis, ATR–FTIR, solid state 13 C NMR, and HRTEM techniques

South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation of South Africa (Chair Grant No.: 86880, UID 85643, Grant No.: 85632)

Coal quality and uranium distribution in Springbok Flats Coalfield samples

'&8;0454 The presence of coal in the Springbok Flats Coalfield (SFC) has been known since the beginning of the 1900s. However, the SFC has not been mined to any degree of economic profit, mostly due to the presence of uranium in the coal. Five boreholes were drilled in the SFC (BH1 to BH5); BH5 intersected two coal zones, the other boreholes intersected one coal zone. Coal samples were collected, selected, and characterized using proximate, ultimate, and calorific value analyses. X-ray fluorescence, instrumental neutron activation analysis, and inductively coupled plasma mass spectrometry were used to determine uranium content. The BH1 intersection and the upper coal zone in BH5 had ash contents higher than 50% and were considered to be primarily carbonaceous shale. BH2 was observed to have better coal quality, resembling typical South African bituminous coal used in local electricity generation. The highest uranium content was found in BH3 (up to 199 mg kg -1, followed by BH2 and BH1. BH4, the upper coal zone in BH5, and the lower coal zone in BH5 all had uranium contents averaging less than 10 mg kg-1. Uranium in the SFC samples was found both in the coal and carbonaceous shale. For all boreholes except BH5, uranium is concentrated within the uppermost 1 m of the coal zone. X-ray fluorescence was the preferred analytical technique since the analysis gave consistent results that compared well with instrumental neutron activation analysis results.

Characterization of several kinds of coal and biomass for pyrolysis and gasification

Sotacarbo is currently developing several research projects to optimize a coal and biomass gasification process for small- and medium-scale power generation and hydrogen production. To achieve this goal, between 2007 and 2008, Sotacarbo built a flexible pilot platform in its Research Centre in the Serbariu former coal mine (Sardinia, Italy), which is still very much into operation. The platform includes a demonstration and a pilot air-blown fixed-bed gasifiers, the latter tested for more than 2200h and equipped with a flexible syngas treatment line for combined power generation and CO2-free hydrogen production.This paper reports the characterization of several kinds of fuels in terms of pyrolysis and gasification performance. In particular, a number of different coal and biomass samples have been tested, including South African bituminous coal, Sardinian high sulphur Sulcis sub-bituminous coal, lignites from Alaska and Hungary and stone pine wood chips.An improved understanding of coal and biomass pyrolysis may be useful to predict the reactor performance in a gasification process and also to optimize the experimental campaigns in the pilot plant. Therefore, before the tests in the pilot-scale gasification unit, fuels are typically characterized by a thermogravimetric analysis to evaluate the pyrolysis behavior.Among all the tested coals, Usibelli lignite from Alaska is the most reactive one. Its derivative thermogravimetric (DTG) profile presents a clear pyrolysis peak at 478°C. The pilot-scale experimental results show that the gasification of 24kg/h of Usibelli lignite allows the production of 79.67kg/h of raw syngas, characterized by a lower heating value of 5.14MJ/kg. An opposite behavior is shown by the South African bituminous coal, which does not present a peak in the DTG curve, as a consequence of the low volatile content in the fuel structure. This is confirmed by the gasification tests in the atmospheric fixed-bed plant, which show a low coal consumption and, as a consequence, a low syngas production (46.83kg/h). Wood chips presents a very significant peak in the DTG profile at the temperature of 318°C but, due to the low energy density, its gasification involves a low syngas production (23.31kg/h).

Hot treatment and upgrading of syngas obtained by co-gasification of coal and wastes

Nowadays there is a great interest in producing energy through co-gasification of low grade coals and waste blends to increase the use of alternative feedstocks with low prices. The experimental results showed that the viability of co-gasification to process such blends and that by the right manipulation of coal and biomass or waste blends, syngas treatment and upgrading may be simplified and the cost of the overall process may be reduced. Blends of three different coal grades (sub-bituminous coal from Puertollano mines, South African bituminous coal and German brown coal) with two different types of biomass (pine and olive oil bagasse) or polyethylene (PE) were co-gasified. Blend co-gasification showed to be beneficial to reduce the negative characteristics of some coals, such as the high ash and sulphur contents, especially of Puertollano coal. Syngas obtained by these blends was hot cleaned and undesirable syngas components (tar, NH3 and H2S) were measured along the hot treatment tested, which proved to be suitable to treat syngas produced by a wide range of feedstocks. Different routes for syngas cleaning were analysed to reduce unsuitable components to values required by most common end-uses. The results obtained showed that the type of feedstock to be gasified is a key outcome on initial syngas composition, affecting greatly syngas cleaning needs, its application and the economic viability of the overall process.

Behaviour of selected major elements during fixed-bed gasification of South African bituminous coal

The Sasol–Lurgi Fixed Bed Dry Bottom gasifier (S–L FBDB) treats a feed coal containing c.a. 30% ash forming minerals, which means that there are complex mineralogical processes occurring simultaneously with each other, and in the gasification reactions, within the reactor. To obtain an understanding of the mineral transformational behaviour, a quenched commercial-scale S–L FBDB gasifier was sampled and characterized mineralogically. Crystalline phases measured by XRD analyses show the ash exiting the reactor contains anorthite, quartz, mullite, cristobalite, diopsite, mayenite, anhydrite, muscovite, hematite, and magnetite, with the non-crystalline proportion in the ash bed c.a. 53%. While many of the reactions in gasification are kinetically controlled, the equilibrium analysis using the Fact-Sage 5.3 modelling program provided a computational approach useful in supporting some, though not all, of the experimentally observed chemical and physical behaviour of elements in gasification. Interpretation of hypothetical model output results was of limited utility, since interstitial/matrix aluminosilicate glasses, which are known to form in practise, cannot be modelled at present because no thermodynamic data is available for these species in the Fact-Sage databases.

CO2 Adsorption Inside the Pore Structure of Different Rank Coals during Low Temperature Oxidation of Open Air Coal Stockpiles

Steam coals are used in utilities worldwide for electrical power production. During monitoring of gases evolved via the weathering processes of large coal piles under open air storage and laboratory simulations, it has been observed that large amounts of carbon dioxide are adsorbed by the coal. Thus, one should take into account that appreciable amounts of CO2 formed by the low temperature oxidation (LTO) of the coal are trapped inside the pore structure of the coal as well as when studying LTO processes and performing kinetic evaluations of CO2 production, the amounts of CO2 released and adsorbed should be calculated. As the coals used for power production are often stored in large piles (>100 000 tons) for long periods, these piles are prone to undergo weathering which might result in self-heating of the coal piles and, in extreme cases, can spontaneously combust. Furthermore, the adsorption is also rank dependent and deviates from coal to coal. The effect of coal rank has been characterized with a South African bituminous coal and with Indonesian sub-bituminous coal which are currently in use in Israeli utilities as well as two German lignites which are consumed in German utilities. The results indicate that only the higher rank coals (bituminous and sub-bituminous) exhibit significant adsorption of CO2.

On the effects of firing semi-anthracite and bituminous coal under oxy-fuel firing conditions

Traditional wisdom has lead to the design of a boiler being dictated by its fuel. Typically, lignite requires a large boiler to accommodate the moisture content and ash behaviour and anthracite needs a design with a long residence time to allow for complete combustion. Thus the result is that different boiler designs are required for different fuel types. This work demonstrates that it is possible to fire under oxy-fuel firing conditions different fuels in potentially a single combustion environment. In the present work a short series of scoping tests firing Russian semi-anthracite under air and oxy-fuel firing conditions on the RWEnpower Combustion Test Facility (CTF) have been performed and result compared to firing a South African bituminous coal. An IFRF swirl burner was used. The purpose behind this work was to determine whether oxy-fuel firing offered the potential for firing a wider range of coal qualities on a swirl stabilised burner than is conventional showing that stable combustion can be achieved with semi-anthracite as with bituminous coal. In this short communication, it is shown that this is possible. Flame photographs of the Russian semi-anthracite coal fired on air and under oxy-fuel firing conditions at recycle ratios of 75%, 72% and 68% were taken. The air firing condition produced a non-luminous flame in the near burner region. For oxy-fuel firing at 75% recycle ratio, the flame is also non-luminous and more so that the air firing case. When the recycle ratio is reduced from 75% to 68% the flame becomes increasingly luminous and at 68% an intense flame was observed well anchored into the burner quarl. Radiative heat flux measurements were taken with the Russian semi-anthracite coal at 68% recycle ratio and compared to the South African bituminous coal at 68% recycle ratio and on air. In general the peak in radiative heat flux for the Russian semi-anthracite at 68% recycle ratio compared to the South African bituminous coal on air is slightly higher reflecting the effect of oxygen enrichment and the higher calorific value of the semi-anthracite. It can also be observed that the location of the peak in radiative heat flux with Russian semi-anthracite coal at 68% recycle is displaced downstream. In the near burner region, the radiation intensity is lower for the Russian semi-anthracite at 68% recycle ratio compare to South African bituminous coal at 68% recycle ratio and on air reflecting the lower (but not insignificant) intensity of combustion in this region for the Russian semi-anthracite coal.

Chemical Looping Combustion of Solid Fuels in a 10 kWthUnit

The present study is based on previous results from batch experiments which were conducted in a 10 kW<sub>th<sub/> chemical looping combustor for solid fuels using ilmenite, an iron titanium oxide, as the oxygen carrier with two solid fuels: a Mexican petroleum coke and a South African bituminous coal. These experiments involved testing at different fuel reactor temperatures, up to 1030°C, and different particle circulation rates between the air and fuel reactors. Previous results enabled modeling of the reactor system. In particular, it was possible to derive a correlation between measured operational data and actual circulation mass flow, as well as a model that describes the carbon capture efficiency as a function of the residence time and the char reactivity. Moreover, the kinetics of char conversion could be modeled and results showed good agreement with experimental values. The purpose of the present study was to complete these results by developing a model to predict the conversion of syngas with ilmenite in the fuel reactor. Here, kinetic data from investigations of ilmenite in TGA and batch fluidized bed reactors were used. Results were compared with the actual conversions during operation in this 10 kW<sub>th<sub/> unit.