Indonesian Sub-bituminous Coal Research Articles

Study of surface charge and chemical properties of ex-gold mining soil ameliorated with Indonesian sub-bituminous coal

Contamination of mercury (Hg) in ex-gold mining soil is the impetus for the development of amelioration technology that utilizes Indonesian sub-bituminous coal to study the soil surface charge and the chemical properties of ex-gold mining soil. This research was aimed to study surface charge and chemical properties of ex-gold mining soil ameliorated with Indonesian sub-bituminous coal. The experimental design used in this study was a Completely Randomized Design with three replications. The treatment was implemented in a pot with the equivalent dose: A = 0 (0.0g); B = 10 (0.5g); C = 20 (1.0g); D = 30 (1.5g), and (E) 40 t ha−1 (2g 100g−1 soil). The results showed amelioration technology with Indonesian sub-bituminous coal, at the application of 40 t ha-1 on ex-gold mining soils, could increase the soil surface charge (ΔpH) by 0.60 through changes in chemical properties of the ex-gold mining soil, where there was an increase in pH (H2O) EC, CEC, and SOM, respectively of 0.37; 0.04 dS m−1; 2.14 cmol kg−1 and 7.83% compared to the control. Soil surface charge was supported by soil minerals [Quartz (SiO2)] and an increase in the chemical properties of the ex-mining soil ameliorated with Indonesian sub-bituminous coal which caused Hg to decrease by 2.50 mg kg−1 compared to the control.

Gasification of Indonesian Sub-bituminous Coal with Different Gasifying Agents Using Ca and K Catalysts

Syngas, liquid fuels, and chemicals could be obtained through coal gasification. The catalytic effect of K2CO3 and CaCO3 on gasification with H2O/CO2 mixtures was studied in this research. The syngas production and char reactivity were compared with different gasifying atmospheres by using two catalysts. The H2/CO mole ratio was between 0.5 and 3 by varying the H2O/CO2 ratios, which could be used for the chemical synthesis. Higher carbon conversion during char gasification was achieved with the mixed atmosphere (H2O/CO2 = 80/20) than with pure steam and CO2 atmospheres by using both catalysts. Further, the coal sample was investigated by Brunauer–Emmett–Teller measurements and emission scanning electron microscopy, and the higher surface area of coal particles and highly dispersed catalyst may be responsible for the observed higher reactivity with mixed gasifying agents.

감압건조, 희석침전, 분무건조 방식으로 제조된 무회분석탄의 특성

본 연구에서는 용매추출 공정 중 최종 건조 과정에서 회수방식을 달리하여 무회분석탄을 제조한 후 물리적 특성과 화학적 구조를 비교하였다. 무회분석탄 제조에는 아역청탄 등급의 Kideco coal과 극성용매인 N-methyl-2-pyrrolidone(NMP)를 사용하였으며, 회수방식으로는 감압건조, 희석침전, 분무건조 방식을 사용하였다. 제조된 무회분석탄의 물성변화를 확인하기 위해 공업분석, 원소분석, 발열량분석을 실시하였고, 화학적 구조를 알아보고자 FT-IR, NMR 분석을 하였다. 공업분석을 통해 무회분석탄의 회분함량이 원탄에 비해 줄어든 것을 확인하였다. FT-IR 분석 결과 감압건조로 회수한 샘플은 추출용매의 피크가 나타나는 반면 희석침전방식으로 제조한 무회분석탄에는 추출용매 피크가 사라지는 것을 확인하였다. 희석침전방식을 사용할 경우 다른 회수방식에 비해 저온공정이 가능하였고, 추출용매로부터 무회분석탄을 보다 확실하게 분리할 수 있었다. Solid ash-free coal (AFC) samples recovered from solvent-extracted solution by vacuum drying, dilution precipitation and spray drying methods were compared in terms of physical properties and chemical structure. AFC was prepared by using Kideco coal (Indonesian sub-bituminous coal) and polar N-methyl-2-pyrrolidone (NMP) solvent as raw materials. The physical properties of the AFCs were characterized with proximate, ultimate, and calorific value analysis. In analyzing the chemical structure, FTIR and NMR were used. the proximate analysis showed much reduced ash in the AFCs compared to parent raw coal. The FTIR result showed that the extraction solvent was not fully removed from the AFC prepared by vacuum drying. However, the solvent was not detected in the AFC recovered by using dilution precipitation. Dilution precipitation has advantages over the other two methods, since it can be done at relatively low temperature and separate ash-free coal from extraction solvent more effectively.

Experimental and kinetic study of catalytic steam gasification of low rank coal with an environmentally friendly, inexpensive composite K2CO3–eggshell derived CaO catalyst

The objective of this research was to study effects of composite catalysts (K2CO3 and eggshell derived CaO) on gasification of Indonesian sub-bituminous KPU coal, which was conducted in a fixed bed reactor at atmospheric pressure. The effects of composite catalysts were evaluated from two sections: syngas compositions and reactivity. At 800°C, the H2 yield of 1.34mol/mol-C was obtained and the H2 fraction was 62vol% when using the composite catalyst (15%K+5%ES). Compared with only utilization of pure K2CO3 and no catalyst, the composite catalyst (15%K+5%ES) could increase the yields of H2 by 6% and 123%. In addition, a CO yield of 0.32mol/mol-C was obtained by utilizing composite catalyst (15%K+5%ES), and the CO yield increased by 19% compared with utilization of K2CO3 and increased by 100% compared with no catalyst utilization. Through regression, kinetic parameters were determined from the random pore model (RPM), which provided a basis for design and operation of a realistic system. The RPM could adequately describe the conversion rate. Compared with results of non-catalytic steam gasification, the composite catalyst (15%K+5%ES) was active in increasing the carbon conversion rate constant by more than three times within 700–900°C due to its ability to reduce the activation energy of gasification by about 38%. It can be concluded that the composite catalyst not only enhances the catalytic effect, but also is environmentally friendly and inexpensive.

Synergistic effect of co-firing woody biomass with coal on NOx reduction and burnout during air-staged combustion

Hybrid technologies combining fuel blending and air-staging processes have been applied to a pulverized coal fired furnace to reduce NOx emissions. In this study, an Australian bituminous coal (Whitehaven), an Indonesian sub-bituminous coal (Adaro), and an Indonesian woody biomass were selected as fuel with blending ratio of 10%, 20%, and 30% of the low-rank fuels, and the air-staging levels were set to 235mm, 390mm, 585mm, and 760mm. The purpose of this study was to investigate the synergistic effect of woody biomass co-firing on the level of NOx emissions and the degree of carbon burnout under air-staged conditions. For single coals, sub-bituminous coal was more favorable than that for bituminous coal to reduce NOx emissions due to low fuel-N composition. This tendency was more dominant with increasing the air staging levels. In the co-firing of woody biomass with coal, as the biomass is highly volatile but has a low carbon content, it could be successfully applied to low-NOx combustion under air-staged conditions. In addition, the degree of carbon burnout and the flame temperature both increased. As a result of this research, we determined that hybrid NOx reduction technologies have the potential to reduce exhaust gas emissions and enhance combustion performance. A dominant synergistic effect on NOx reduction and carbon burnout was observed when woody biomass co-firing with coal was applied to air-staged combustion.

Thermogravimetric analysis of the behavior of sub-bituminous coal and cellulosic ethanol residue during co-combustion

The influence of the addition of cellulosic ethanol residue (CER) on the combustion of Indonesian sub-bituminous coal was analyzed by non isothermal thermo-gravimetric analysis (TGA). The effect of blends ratio (5%, 10%, 15% and 20%), interaction mechanism, and heating rate (5°C/min, 10°C/min, 15°C/min, 20°C/min) on the combustion process was studied. The results show that the increase of the blending ratio allows to achieve the increase of the combustibility index from 7.49E−08 to 5.26E−07 at the blending ratio of 20%. Two types of non-isothermal kinetic analysis methods (Ozawa–Flynn–Wall and Vyazovkin) were also applied. Results indicate that the activation energy of the blends decreases with increasing the conversion rate. In particular, the blending ratio of 20% confirms to have the better combustion performance, with the average value of the activation energy equal to 41.10kJ/mol obtained by Ozawa–Flynn–Wall model and 31.17kJ/mol obtained by Vyazovkin model.

Steam gasification of Indonesian subbituminous coal with calcium carbonate as a catalyst raw material

The effect of Ca catalysts prepared from CaCO3 on the steam gasification of Indonesian subbituminous coal at 700–800°C is examined. The char obtained by pyrolyzing the coal with 0.59wt.% of Ca (dry basis) showed conversions in steam gasification at 750 and 800°C of around 70 and 90wt.% (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 CaCO3 was initially present in the ion-exchanged form, and as a finely dispersed calcium species after pyrolysis. These results confirm that CaCO3 is effective as a catalyst raw material in the steam gasification of subbituminous coal, even at low catalyst loadings.

Effect of thermal decomposition products of coal on anodic reactions in direct carbon fuel cells

The effect of inherent volatile matter in fuels on anodic electrochemical reactions was investigated in a direct carbon fuel cell (DCFC). Through thermal decomposition, raw coals, which are used as power source in the DCFC system, release gases under an operating temperature of 700°C. These exhaust gases change the gas composition around the anode and affect the system’s electrochemical reaction. To investigate the effect of produced gases, a comparative study was conducted between Indonesian sub-bituminous coal and char obtained through thermal treatment. The open circuit voltage of raw coal increased to 0.23 V compared with that of char. The maximum power density of raw coal (52 mW/cm2) was also higher than that of char (37 mW/cm2) because of the enhanced electron transport caused by the additional reaction of hydrogen, methane, and carbon monoxide. The influence of volatile matter on the anodic electrolyte-electrode interface was analyzed with the use of the equivalent circuit induced from fitting the impedance data.

석탄 열분해 생성물이 직접탄소연료전지에서 애노드 반응에 미치는 영향에 대한 연구

Effect of inherent volatile matters in fuels on electrochemical reactions of anode was investigated for a single direct carbon fuel cell (DCFC). Raw coals used as power source in the DCFC release light gases into the atmosphere under the operating temperature of DCFC (700℃) by thermal decomposition and only char remained. These exhausted gases change the gas composition around anode and affect the electrochemical oxidation reaction of system. To investigate the effect of produced gases, comparative study was conducted between Indonesian sub-bituminous coal and its char obtained through thermal treatment, carbonizing. Maximum power density of raw coal (52mW/cm 2 ) was appeared higher than that of char (37mW/cm 2 ) because the gases produced from the raw coal during thermal decomposition gave additional positive results to electrochemical reaction of the system. The produced gases from coals were analyzed using TGA and FT-IR. The influence of volatile matters on anodic electrolyte- electrode interface was observed by the equivalent circuit induced from fitting of impedance spectroscopy data.

Chlorine Release during Fixed-Bed Gasification of Coal Chars with Carbon Dioxide

CO2 gasification of two kinds of coal chars has been carried out using a fixed-bed quartz reactor mainly at 0.1 MPa and 1000 °C to investigate the behavior of chlorine release during char gasification. For this purpose, an Indonesian sub-bituminous coal or an American bituminous coal is first pyrolyzed at 400 °C/min up to 1000 °C, and the resulting char is gasified in situ at 1000 °C with 50 vol % CO2. The Cl contents of the sub-bituminous and bituminous coal chars are 310 and 1300 μg/g-dry, respectively. Conversion of the Cl to gas species increases with increasing char conversion, and there is an almost 1:1 linear relationship between the two. Chlorine distribution depends strongly on char conversion: yield of water-soluble Cl species increases significantly with increasing conversion up to approximately 50 mass %-daf and then levels off, whereas that of water-insoluble Cl increases more remarkably at the latter stage of the gasification. No measurable amounts of Cl2 are detectable, irrespective of the extent of char conversion, but HCl can be detected significantly. The temperature-programmed desorption run of an activated carbon sorbent recovered after gasification also shows that most of the water-insoluble Cl is thermally stable even at a high temperature of 1000 °C. The formation of water-insoluble Cl-functional groups is discussed mainly on the basis of the results of some model experiments and subsequent Cl 2p XPS measurements.

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.

Gasification of a pulverized sub-bituminous coal in CO 2 at atmospheric pressure in an entrained flow reactor

Char gasification by CO 2 may play an important role in oxy-fuel applications and affect particle temperature histories and overall reaction rates during combustion. This paper presents the results of a complete set of experiments of char gasification in CO 2 performed with a pulverized Indonesian sub-bituminous coal in an entrained flow reactor under realistic conditions; series of burnout curves at different reactor temperatures (1040–1300 °C) and CO 2 concentrations (0.7–100%) reveal consistent trends in the gasification rates. The study included also devolatilization and oxidation tests with this coal in the same experimental facility. The data are used to derive apparent kinetics for the three processes, in a manner similar to that followed in a previous work for the oxidation of a pulverized coal. The gasification kinetic parameters and reaction rates measured are then compared with values taken or derived from previous works by others, obtained by thermogravimetric analysis or experiments in entrained flow reactors. Finally, the relevance of char gasification in the overall reaction rate under conditions representative of those in an industrial boiler is explored, in particular for the case of oxy-coal combustion.

Firing a sub-bituminous coal in pulverized coal boilers configured for bituminous coals

It is important to adapt utility boilers to sub-bituminous coals to take advantage of their environmental benefits while limiting operation risks. We discuss the performance impact that Adaro, an Indonesian sub-bituminous coal with high moisture content, has on opposite-wall and tangentially-fired utility boilers which were designed for bituminous coals. Numerical simulations were made with GLACIER, a computational-fluid-dynamic code, to depict combustion behavior. The predictions were verified with full-scale test results. For analysis of the operational parameters for firing Adaro coal in both boilers, we used EXPERT system, an on-line supervision system developed by Israel Electric Corporation. It was concluded that firing Adaro coal, compared to a typical bituminous coal, lowers NO x and SO 2 emissions, lowers LOI content and improves fouling behavior but can cause load limitation which impacts flexible operation.

Gasification of an Indonesian subbituminous coal in a pilot-scale coal gasification system

Indonesian Roto Middle subbituminous coal was gasified in a pilot-scale dry-feeding gasification system and the produced syngas was purified with hot gas filtering and by low temperature desulfurization to the quality that can be utilized as a feedstock for chemical conversion. Roto middle coal produced syngas that has a typical composition of 36–38% CO, 14–16% H2, and 5–8% CO2. Particulates in syngas were 99.8% removed by metal filters at the operating temperature condition of 200–250°C. Sulfur containing compounds of H2S and COS in syngas were also desulfurized in the Fe chelate system to yield less than 0.5 ppm level. The full stream gasification and syngas purifying system has been successfully operated and thus can provide clean syngas for the research on the conversion of syngas to chemicals like DME and on the future IGFC using fuel cells.

Investigation on Indonesian sub-bituminous coal after peroxyacetic acid treatments

Ni/Mo and Co/Mo are two of the most commonly used and effective catalysts used in coal liquefaction. Recent work has reported a ∼40 wt% difference in conversion between Ni/Mo and Co/Mo-treated Loy Yang brown coal hydrogenated at 400°C without added solvent or sulfur. However, this study shows that under the same reaction conditions the difference in conversion between Ni/Mo and Co/Mo-treated coal decreases with increasing carbon content (rank) of the coal (Wyoming, Wadge, Surat Basin). Furthermore, for a bituminous Surat Basin coal the pattern of catalytic activity of Ni, Co, Mo and their combinations differs from that for a brown (Loy Yang) coal as follows. In no-solvent, no-added-sulfur hydrogenations, the catalytic activity of the individual metals was much greater for the Surat Basin coal, but the increased activity of Ni and Co did not carry over to increased promotion of Mo catalysis by these metals. The effect of added sulfur on the activity of the individual metals was also different for the two coals. The distribution of the catalyst metals in the coal particles was different in the Loy Yang and Surat Basin coals, but this cannot explain all the observed differences in catalytic behaviour.

Optimization of Two-Stage Liquefaction of Tanito Harum Coal with FeNi Catalyst Supported on Carbon Black

Two-stage liquefaction of Tanito Harum coal (Indonesian sub-bituminous coal) was examined in an autoclave of 50 mL capacity at various temperatures for the first stage and various reaction times for the first and second stages under the hydrogen pressure of 15 MPa, using Fe(10 wt %)Ni(10 wt %) catalyst supported on carbon nanoparticles (Ketjen Black:KB). When the total reaction time in the first and second stages was fixed to 120 min, the best conditions of two-stage liquefaction were at 380 °C for 15 min in the first stage and then at 450 °C for 105 min in the second stage at a hydrogen pressure of 15 MPa, providing the maximum oil yields of 80 and 66 wt % (daf coal base) with or without H-donor solvent, respectively. The results also showed that these conditions produced fewer amounts of hydrocarbon gases and lower sulfur content in the oil. The conversion of H-donor solvent (tetralin) after the liquefaction was much lower (13%) than that of the single-stage liquefaction (21%). In addition, the residue yield was much lower (9%) than that of the single-stage (15%) in the solvent-free liquefaction. It is confirmed that prolonged reaction time in the second stage is more favorable than in the first stage. The effects of the first-stage (low temperature) liquefaction both with and without solvent are discussed to explain the optimum conditions of two-stage liquefaction.

Pressurized drop tube furnace tests of global coal gasification characteristics

Pressurized drop tube furnace (PDTF) tests were performed with an Indonesian sub-bituminous coal while temperature, oxygen/coal ratio, steam/coal ratio and pressure were systematically varied. The tests were designed to investigate the effects of these experimental parameters on the pulverized coal gasification characteristics at elevated pressure. The results showed that the gasification at elevated pressure is more productive than that at atmospheric pressure, considering the carbon conversion and cold gas efficiency. The oxygen/coal ratio at the maximum cold gas efficiency ranged between 0.5 and 0.7 g/g. Only when the temperature was sufficiently high, did the increase of steam/coal ratio result in the improvement of cold gas efficiency. As the pressure increased, the contribution of carbon conversion by heterogeneous reactions increased while the conversion by pyrolysis decreased. Copyright © 2000 John Wiley & Sons, Ltd.

Thermally induced chemical changes in the macromolecular structure of an Indonesian coal

A short time variable temperature heat treatment in moist air at 250°C has been applied to an Indonesian sub-bituminous coal to produce a thermally stabilised coal product and to effect an irreversible lowering of the Equilibrium Moisture Content. Elemental analyses show that the uptake of oxygen is less than expected for an oxidative fixed temperature heat treatment over the same time period and sulphur is significantly reduced in concentration. Pyrograms at 340 and 600°C show that the heat treatment raises the pyrolytic yield at 600°C whilst reducing it at 340°C. DRIFT and 13C SS MAS NMR spectroscopy have been used to follow chemical changes. Oxygen uptake appears to occur at bridging and other sp 2 carbons to yield substituted aromatics including phenols. These phenolic groups can react to form esters and ethers. In general, the functional groups observed are those conventionally described for coal oxidation but differ significantly in the thermally stabilised coal in that there is a reduced concentration of carbonyl groups; attack on aliphatic carbons is less; and oxygen substitution is emphasised.

Flash pyrolysis of coals. A new approach of classification

Hybrid technologies combining fuel blending and air-staging processes have been applied to a pulverized coal fired furnace to reduce NOx emissions. In this study, an Australian bituminous coal (Whitehaven), an Indonesian sub-bituminous coal (Adaro), and an Indonesian woody biomass were selected as fuel with blending ratio of 10%, 20%, and 30% of the low-rank fuels, and the air-staging levels were set to 235 mm, 390 mm, 585 mm, and 760 mm. The purpose of this study was to investigate the synergistic effect of woody biomass co-firing on the level of NOx emissions and the degree of carbon burnout under air-staged conditions. For single coals, sub-bituminous coal was more favorable than that for bituminous coal to reduce NOx emissions due to low fuel-N composition. This tendency was more dominant with increasing the air staging levels. In the co-firing of woody biomass with coal, as the biomass is highly volatile but has a low carbon content, it could be successfully applied to low-NOx combustion under air-staged conditions. In addition, the degree of carbon burnout and the flame temperature both increased. As a result of this research, we determined that hybrid NOx reduction technologies have the potential to reduce exhaust gas emissions and enhance combustion performance. A dominant synergistic effect on NOx reduction and carbon burnout was observed when woody biomass co-firing with coal was applied to air-staged combustion.

Investigation of effect of solvent quality on Indonesian subbituminous coal liquefaction under short contact time conditions

The role of the solvent upon Indonesian subbituminous coal during short contact time liquefaction in microreactors is examined by using various solvents such as non-polar hydroaromatics, non-polar aromatics, polar hydroaromatics and polar aromatics. The importance of solvents on the ability to convert coal to pyridine soluble (coal conversion) and pentane soluble (oil yield) products is evaluated. The hydrogen donor capability of the solvent is found to be the most important controlling factor. In the absence of hydroaromatics, such phenolic compounds as 1-naphthol can improve coal conversion, but a highly negative yield of oil is observed.