- Email: [email protected]
combustion cycle: relationships between sulfur and calorific value distribution during coal pyrolysis
Conference
Abstracts
Fluorine in Asturian coals M. R. Mnrtinez-Turuzona, J. M. Cardin
G. P. Suurez-Fernandez
Institute National de1 Carbbn, 33080 Oviedo, Spain
La Corredoria,
and
Apartado
73,
Although fluorine is present in coals in very small amounts, the majority of this element is released to the environment as HF during combustion and it may be harmful to the environment under certain conditions. Even though a large body of data on fluorine in coals of diff‘erent origin has been published, it is still not possible to give a clear account of the mode of combination of this element in coal for two main reasons: one is the largely different characteristics of the coals examined and the second, the difficulty of conversion of the fluorine compounds present in coals into a form suitable for analysis. Moreover, despite the widespread use of Asturian coals for electricity generation, very little information is available on the concentration and mode of occurrence of fluorine in these coals. For these reasons, the aims of our work were: (i) to determine the concentration of fluorine present in a set of samples from the Asturian basin (North of Spain); (ii) to compare two different methods for fluorine determination; and (iii) to establish the likely presence of fluorine in these coals as fluorapatite Ca,(PO,), (OH, F, Cl). The 70 samples studied in this work range from bituminous coals to anthracites and they included run-of-mine samples with an ash content of 4&60wt% and washed products with an ash content lower than 40%. Fluorine content in these samples ranges between 10 and 600 ppm, and differences in concentration values determined by the calorimetric bomb method (ASTM standard D 3761-91) and the pyrohydrolitic method (Doolan, K. J. Anal. Chirn. Acta. 1987, 202, 61) can reach 200 ppm. A positive correlation between fluorine concentration and ash content has been observed. This positive correlation is more evident when it is inferred from the concentrations in the different densimetric fractions separated from a single coal. An association of fluorine in mineral species that can be easily eliminated by coal cleaning processes is indicated from these results. Moreover, analysis of phosphorus in the coals and also in the densimetric fractions separated from a single coal has proved that fluorapatite is a minor fluorine mineral in the Asturian coals.
Detection of polycyclic aromatic hydrocarbons from coal utilization A. M. Mastral, C. Pardos Instituto
B. Ruhio, M. 7: Izquierdo,
de Carboquimica,
Apdo
C. Mayoral
589, 50080
Zaragoza,
and
Spain
A method has been developed to measure the polycyclic aromatic hydrocarbons (PAH) emitted during different processes of coal conversion. The method is based on passing the gaseous emissions of different coal conversion processes through an atmospheric contamination sampler with Teflon filters. These filters arc later extracted with NJ-dimethylformamide and the extract is analysed through molecular fluorescence without any previous separation, detecting several PAH. The formation of the different PAH is related to the operating conditions.
Effects of high-temperature burnout on the oxidation kinetics of Dietz coal chars Kent M. McDonald, Walter Reade, Mark Richard F. Cope and William C. Hecker
R. Swensen,
Department of Chemical Engineering and Advanced Combustion Engineering Research Center (ACERC), Brigham Young University, 350 CB, Provo, UT 84602, USA In today’s era of environmental commercial coal users is obtaining
Fuel 1993
Volume
The fate of trace elements at coal-fired power plants R. Meij
Kema, Business Unit Kema Environmental Services, PO Box 9035, 6800 ET Arnhem, The Netherlands After the reintroduction of coal as a fuel for power plants, Kema has started a large research programme on the fate of (trace) elements at coal-fired power plants. In this research programme the element concentrations of coal, bottom ash, pulverized-fuel ash (PFA, ash collected in the electrostatic precipitators, ESPs), fly ash (as present in the flue gases downstream of the ESP) were studied. Also, ample attention was given to minor and trace elements present in the vapour phase in the flue gases downstream of the ESP (As, B, Br, Cl, F, Hg, I. Se). An important factor in this research programme is to establish the relationship of theelements in the different streams. For this purpose, mass balances were determined to obtain a good impression of the accuracy of the measurements. A total of 16 experiments was performed. The collection efficiency was established for a new generation of high-etficicncy ESP of-the total particulate matter and for each individual element. In an ESP, the gaseous inorganic trace elements are generally not removed. Nowadays all large coal-fired power plants in the Netherlands are equipped with wet flue gas desulphurization (FGD) plants. In one experiment, the fate of (trace) elements in such an installation were studied in detail. It appeared that in the FGD plant 90% of the total particulate matter is removed, but that the fly dust emitted consists of about 4O’/b fly ash and that gypsum is the major source. Half of the fly dust emitted originates in evaporated droplets. Hence, the demisters are of vital importance for the emissions. In a wet FGD plant the gaseous inorganic trace elements are also removed. The removal of these elements was measured at all FGDs in the Netherlands.
Combined pyrolysis/combustion cycle: relationships between sulfur and calorific value distribution during coal pyrolysis R. Molirler.
J. I/: Iharra
and M. J. Lcizaro
Institute de Carboquimica, 50080 Zaragoza, Spain
CSIC, PO Box 589,
awareness a primary concern of
a high level of carbon conversion (burnout). High burnout with a resulting low level of residual carbon in the fly ash is desirable both from an efficiency standpoint and to facilitate disposal. The current study has been undertaken to better understand the effects of burnout on char reactivity.
718
The effects of both extent and type of burnout on char oxidation rates and rate parameters (apparent activation energy and oxygen reaction order) have been investigated for chars prepared from Dietz (subbituminous B) coal. Starting chars were prepared in a flat flame methane burner under two flame conditions. the first beine 0% post-flame O,, and the second being 4% post-flame 0,. Two series of chars with a wide variety of high-temperature oxidation burnouts were obtained by taking the two starting flame-produced chars and oxidizing them to various conversion levels in a drop tube reactor at high temperature (1300 to 1500 K). Low-temperature intrinsic oxidation rates and kinetics of these partially burned-out char samples were then determined using isothermal TGA. Also, low-temperature oxidation burnout was studied by oxidizing the two starting chars to a continuum of burnout levels in the TGA at low temperature (550 to 750K) and measuring their instantaneous rates. High-temperature global rates were determined using optical velocity measurements and a Ti-tracer burnout measurement technique. N, BET surface areas were measured, as was hydrogen to carbon ratio (H/C). CaO surface area was measured for selected samples. Intrinsic rates (in units of g/g,,,id,,, s) of chars partially burned out at high temperatures were found to decrease with burnout level, while those of chars burned out at low temperatures were essentially constant with burnout level. The rate of oxidation per CaO surface area, however, was quite constant with high-temperature oxidation burnout as CaO dispersion was found to decrease with exposure to high temperature. Values of apparent activation energy increased by 20 to 30% with increasing burnout level. This was consistent for both high- and low-temperature burnout. Oxygen reaction orders ranged from 0.74 to 0.53 and generally showed a decrease with burnout level.
72 Number
5
The combined pyrolysis/combustion cycle is an advanced process for coal cleanmg combustion. In this process, the coal is pyrolysed prior to combustion in order to obtain a partially desulfurized char and a fuel gas. The char is burnt in a fluidized or a circulating bed combustor where sulfur is retained by an absorbent. The pyrolysis gas is mixed,
Conference gases and they are burnt in order after cleaning with the combustion to increase. the _ eas temperature before being fed into the turbine. The distribution of sulfur and calorific value from coal into the gas and char fractions during the pyrolysis step is very important because it affects the performance of the combustor, and the temperature in the gas turbine. Sulfur and calorific value evolutions are related to each other since sulfur release is matched to volatile matter release which influences the calorific value of char and gases. In this paper, the influence of pyrolysis conditions: temperature, pressure and time on sulfur and calorific value distribution is studied. Pyrolysis has been carried out in a laboratory-scale fluidized bed unit orovided with a flash feeding device in order to ensure a very high heating rate and so a practi&lly isothermal operation. A high&lfir, low-rank coal from Teruel (Spain) has been used. Pyrolysis runs have been selected according to a composite factorial design with three variables, P, 7; t, and two levels (T=823-1023 K; P=O.l-1.1 MPa; r= 10-30 min). The pyrolysis responses have been fitted to surface equations by using statistical fitting methods. Several surface-response correlation models have been obtained in order to predict the sulfur released from char combustion (Sr), the fraction of the coal sulfur retained in char (FSC), the fraction of the coal sulfur evolved into the gases (FSG), the calorific value of char (CVC), the calorific value of eases (CVG). the fraction of the coal calorific value retained in char (FCVC) and the fraction of the coal calorific value evolved into the gases (FCVG). Furthermore, some crossed responses such as the thermal desulfurization rate for char (TDR. AS x thermal vield), and the thermal sulfur rate for char (FSC/FCVC) and gas (FSG/FCVG) have been evaluated. Temnerature has been shown to have the most imDortant effect on all resdonses. Pressure has no effect on Sr, FSC, FSG’and TDR, while it has a crossed effect, depending on Tand t, on FCVC. FCVG has a maximum at P=O.6 MPa. Time has a moderate effect at low temperature. but it does not play an important role at temperatures higher than 923 K. From these distribution models, the pyrolysis conditions needed to obtain some desirable distributions are deduced. For instance, the highest TDR is obtained at a temperature of 913 K and a pyrolysis time of I5 min. At these conditions, FSC is 0.50 and FCVC is 0.76. If more severe pyrolysis conditions are used, the sulfur distributions do not vary significantly but FCVC decreases down to 0.66. On the contrarv. at lower temoeratures FSC increases UD to 0.67 and FCVC does not’increase signifi’cantly. This maximum foi TDR is due to the high release of sulfur and oxygen observed at temperatures up to 923 K. Oxygen removal from char increases CVC. At higher temperatures, release of sulfur is lower and CVC decreases as a consequence of CH, and H, removal, so, the combined effect is a decrease of TDR.
Use of Brazilian coal for coke production E. Osdrio and A. C. F. Vilela
Universidade Federal do Rio Grande do Sul, Departamento de Metalurgia, Osvaldo Aranha, 99, 6” andar, 90035-190 Porto Alegre, Brazil A study to verify the technical viability of the use of South Brazilian coal from the Chico-LomH coalfield has been made in order to increase the use of national coal in coke production. Samples were initially characterized according to their chemical, physical, plastic and Detrograuhic orooerties. The coking exneriments were carried out in a pilot Turnace.’ T
Production possibility of super-clean coal from Turkish bituminous coal G. Cizbayoglu and M. Mamurekli Middle
East
Department,
Technical
Ankara,
University,
Mining
Engineering
Turkey
Coal has some major impurities such as ash and sulfur. In order to produce a clean coal, the inorganic constituents of coal should be
Abstracts
removed as much as possible. The extent of reduction is closely related to the inherent ash content of the coal. In this research, the possibility of super-clean coal production from Zonguldak bituminous coal by heavy medium separation and flotation techniques was investigated. The coal sample used was the (- 50+ 18 mm) size jig concentrate of Central Washery of Zonguldak. It was composed of 12.1 I % ash and 0.41% total sulfur. The vitrain band of the same coal contained 3.28% ash and 0.22% total sulfur. By applying a two-step heavy medium separation, it was possible to reduce the ash content from 12.1 I % down to 4.00%. Final cleaning was carried out by flotation. In order to determine the optimum flotation conditions to produce a super-clean coal, the effects of different types of collector and frother were investigated. Kerosene, creosote, and fuel oil were used as collectors. Frothers tested were amyl alcohol. nonyl alcohol and MIBC (methyl isobutyl carbinol). The effect of pH, the consumptions of collector and frother, the grinding and flotation times were also studied. The optimum result was obtained using 170g/ton kerosene and 160g/ton MIBC. The investigation showed that it was possible to produce a coal product containing 2.16% ash and 0.42% total sulfur from Zonguldak bituminous coals.
Selective oxidation pretreatments for the enhanced desulfurization of coal S. R. Palmer,
E. J. Hippo and X. A. Dorai
Southern Illinois University at Carbondale, Department of Mechanical Engineering and Energy Processes, Carbondale. IL 62901, USA The primary objective of this study was to evaluate selective oxidation as a pretreatment for the enhanced desulfurization of Illinois Basin coals cusing a variety of mild thermal/chemical processes. Both an Illinois no. 6 and an Indiana no. 5 coal were selectively oxidized with peroxyacetic acid in the pretreatment step. The products were then treated with various hydroxide and carbonate bases, using either water, methanol or ethanol as the solvent system. Other reaction variables investigated included reaction temperature, reaction time, pyrolysis pressure, particle size of the coal and the level of oxidation in the pretreatment step. Throughout the study the selectively oxidized coals were compared to unoxidized control coals. The desulfurization of some selectively oxidized, sulfur-containing model compounds was also investigated. The results from these studies overwhelmingly show that selective oxidation with peroxyacetic acid significantly enhances the level of desulfurization that may be obtained with subsequent chemical/thermal treatments. Indeed, every process investigated, including simple ovrolvsis experiments. showed sulfur removal in the pretreatment step and tie sudsequent step to be substantially additive. In addition, the reactivity of the sulfur in the coal towards desulfurization was enhanced bv the selective oxidation pretreatment. Thus the severity of desulfurization conditions can be reduced by employing this oretreatment. Sulfur contents lower than 0.25% were obtained for selectively oxidized coals in which the original total sulfur content was 4.4% and the original organic sulfur content 3.1%. This represents a total sulfur reduction of abound 94% and a reduction in organic sulfur of at least 92%. This is beyond the level required for compliance with Clean Air Act legislation. No unoxidized coal, regardless of the desulfurization treatment, approached this level of sulfur removal. It should be noted that the sulfur removals obtained are superior to those of the molten caustic leaching process and are obtained under less severe conditions. In general, it was found that alcohol/carbonate base combinations were more effective desulfurizing agents than alcohol/hydroxide base systems for the desulfurization of the selectively oxidized coals. However, significant desulfurization was also obtained using aqueous Na,CO,. Possible synergistic interactions between the alcohol and the base are suspected. It was found that as the reaction temperature increased so did the level of desulfurization. Surprisinglv, the particle size of the feed coal (over the range studied) did n&t appear to i&uence reaction kinetics. However, it was determined that the level of selective oxidation in the pretreatment step was very important in determining the success of subsequent desulfurization treatments. In addition, it was found that lowering. the pressure in the reaction vessel gave improved desulfurization. Indeed, over 70% of the sulfur in the Illinois no. 6 coal could be removed by performing vacuum pyrolysis on the selectively oxidized coal.
Fuel 1993
Volume
72 Number
5
719
Abstracts
Fluorine in Asturian coals M. R. Mnrtinez-Turuzona, J. M. Cardin
G. P. Suurez-Fernandez
Institute National de1 Carbbn, 33080 Oviedo, Spain
La Corredoria,
and
Apartado
73,
Although fluorine is present in coals in very small amounts, the majority of this element is released to the environment as HF during combustion and it may be harmful to the environment under certain conditions. Even though a large body of data on fluorine in coals of diff‘erent origin has been published, it is still not possible to give a clear account of the mode of combination of this element in coal for two main reasons: one is the largely different characteristics of the coals examined and the second, the difficulty of conversion of the fluorine compounds present in coals into a form suitable for analysis. Moreover, despite the widespread use of Asturian coals for electricity generation, very little information is available on the concentration and mode of occurrence of fluorine in these coals. For these reasons, the aims of our work were: (i) to determine the concentration of fluorine present in a set of samples from the Asturian basin (North of Spain); (ii) to compare two different methods for fluorine determination; and (iii) to establish the likely presence of fluorine in these coals as fluorapatite Ca,(PO,), (OH, F, Cl). The 70 samples studied in this work range from bituminous coals to anthracites and they included run-of-mine samples with an ash content of 4&60wt% and washed products with an ash content lower than 40%. Fluorine content in these samples ranges between 10 and 600 ppm, and differences in concentration values determined by the calorimetric bomb method (ASTM standard D 3761-91) and the pyrohydrolitic method (Doolan, K. J. Anal. Chirn. Acta. 1987, 202, 61) can reach 200 ppm. A positive correlation between fluorine concentration and ash content has been observed. This positive correlation is more evident when it is inferred from the concentrations in the different densimetric fractions separated from a single coal. An association of fluorine in mineral species that can be easily eliminated by coal cleaning processes is indicated from these results. Moreover, analysis of phosphorus in the coals and also in the densimetric fractions separated from a single coal has proved that fluorapatite is a minor fluorine mineral in the Asturian coals.
Detection of polycyclic aromatic hydrocarbons from coal utilization A. M. Mastral, C. Pardos Instituto
B. Ruhio, M. 7: Izquierdo,
de Carboquimica,
Apdo
C. Mayoral
589, 50080
Zaragoza,
and
Spain
A method has been developed to measure the polycyclic aromatic hydrocarbons (PAH) emitted during different processes of coal conversion. The method is based on passing the gaseous emissions of different coal conversion processes through an atmospheric contamination sampler with Teflon filters. These filters arc later extracted with NJ-dimethylformamide and the extract is analysed through molecular fluorescence without any previous separation, detecting several PAH. The formation of the different PAH is related to the operating conditions.
Effects of high-temperature burnout on the oxidation kinetics of Dietz coal chars Kent M. McDonald, Walter Reade, Mark Richard F. Cope and William C. Hecker
R. Swensen,
Department of Chemical Engineering and Advanced Combustion Engineering Research Center (ACERC), Brigham Young University, 350 CB, Provo, UT 84602, USA In today’s era of environmental commercial coal users is obtaining
Fuel 1993
Volume
The fate of trace elements at coal-fired power plants R. Meij
Kema, Business Unit Kema Environmental Services, PO Box 9035, 6800 ET Arnhem, The Netherlands After the reintroduction of coal as a fuel for power plants, Kema has started a large research programme on the fate of (trace) elements at coal-fired power plants. In this research programme the element concentrations of coal, bottom ash, pulverized-fuel ash (PFA, ash collected in the electrostatic precipitators, ESPs), fly ash (as present in the flue gases downstream of the ESP) were studied. Also, ample attention was given to minor and trace elements present in the vapour phase in the flue gases downstream of the ESP (As, B, Br, Cl, F, Hg, I. Se). An important factor in this research programme is to establish the relationship of theelements in the different streams. For this purpose, mass balances were determined to obtain a good impression of the accuracy of the measurements. A total of 16 experiments was performed. The collection efficiency was established for a new generation of high-etficicncy ESP of-the total particulate matter and for each individual element. In an ESP, the gaseous inorganic trace elements are generally not removed. Nowadays all large coal-fired power plants in the Netherlands are equipped with wet flue gas desulphurization (FGD) plants. In one experiment, the fate of (trace) elements in such an installation were studied in detail. It appeared that in the FGD plant 90% of the total particulate matter is removed, but that the fly dust emitted consists of about 4O’/b fly ash and that gypsum is the major source. Half of the fly dust emitted originates in evaporated droplets. Hence, the demisters are of vital importance for the emissions. In a wet FGD plant the gaseous inorganic trace elements are also removed. The removal of these elements was measured at all FGDs in the Netherlands.
Combined pyrolysis/combustion cycle: relationships between sulfur and calorific value distribution during coal pyrolysis R. Molirler.
J. I/: Iharra
and M. J. Lcizaro
Institute de Carboquimica, 50080 Zaragoza, Spain
CSIC, PO Box 589,
awareness a primary concern of
a high level of carbon conversion (burnout). High burnout with a resulting low level of residual carbon in the fly ash is desirable both from an efficiency standpoint and to facilitate disposal. The current study has been undertaken to better understand the effects of burnout on char reactivity.
718
The effects of both extent and type of burnout on char oxidation rates and rate parameters (apparent activation energy and oxygen reaction order) have been investigated for chars prepared from Dietz (subbituminous B) coal. Starting chars were prepared in a flat flame methane burner under two flame conditions. the first beine 0% post-flame O,, and the second being 4% post-flame 0,. Two series of chars with a wide variety of high-temperature oxidation burnouts were obtained by taking the two starting flame-produced chars and oxidizing them to various conversion levels in a drop tube reactor at high temperature (1300 to 1500 K). Low-temperature intrinsic oxidation rates and kinetics of these partially burned-out char samples were then determined using isothermal TGA. Also, low-temperature oxidation burnout was studied by oxidizing the two starting chars to a continuum of burnout levels in the TGA at low temperature (550 to 750K) and measuring their instantaneous rates. High-temperature global rates were determined using optical velocity measurements and a Ti-tracer burnout measurement technique. N, BET surface areas were measured, as was hydrogen to carbon ratio (H/C). CaO surface area was measured for selected samples. Intrinsic rates (in units of g/g,,,id,,, s) of chars partially burned out at high temperatures were found to decrease with burnout level, while those of chars burned out at low temperatures were essentially constant with burnout level. The rate of oxidation per CaO surface area, however, was quite constant with high-temperature oxidation burnout as CaO dispersion was found to decrease with exposure to high temperature. Values of apparent activation energy increased by 20 to 30% with increasing burnout level. This was consistent for both high- and low-temperature burnout. Oxygen reaction orders ranged from 0.74 to 0.53 and generally showed a decrease with burnout level.
72 Number
5
The combined pyrolysis/combustion cycle is an advanced process for coal cleanmg combustion. In this process, the coal is pyrolysed prior to combustion in order to obtain a partially desulfurized char and a fuel gas. The char is burnt in a fluidized or a circulating bed combustor where sulfur is retained by an absorbent. The pyrolysis gas is mixed,
Conference gases and they are burnt in order after cleaning with the combustion to increase. the _ eas temperature before being fed into the turbine. The distribution of sulfur and calorific value from coal into the gas and char fractions during the pyrolysis step is very important because it affects the performance of the combustor, and the temperature in the gas turbine. Sulfur and calorific value evolutions are related to each other since sulfur release is matched to volatile matter release which influences the calorific value of char and gases. In this paper, the influence of pyrolysis conditions: temperature, pressure and time on sulfur and calorific value distribution is studied. Pyrolysis has been carried out in a laboratory-scale fluidized bed unit orovided with a flash feeding device in order to ensure a very high heating rate and so a practi&lly isothermal operation. A high&lfir, low-rank coal from Teruel (Spain) has been used. Pyrolysis runs have been selected according to a composite factorial design with three variables, P, 7; t, and two levels (T=823-1023 K; P=O.l-1.1 MPa; r= 10-30 min). The pyrolysis responses have been fitted to surface equations by using statistical fitting methods. Several surface-response correlation models have been obtained in order to predict the sulfur released from char combustion (Sr), the fraction of the coal sulfur retained in char (FSC), the fraction of the coal sulfur evolved into the gases (FSG), the calorific value of char (CVC), the calorific value of eases (CVG). the fraction of the coal calorific value retained in char (FCVC) and the fraction of the coal calorific value evolved into the gases (FCVG). Furthermore, some crossed responses such as the thermal desulfurization rate for char (TDR. AS x thermal vield), and the thermal sulfur rate for char (FSC/FCVC) and gas (FSG/FCVG) have been evaluated. Temnerature has been shown to have the most imDortant effect on all resdonses. Pressure has no effect on Sr, FSC, FSG’and TDR, while it has a crossed effect, depending on Tand t, on FCVC. FCVG has a maximum at P=O.6 MPa. Time has a moderate effect at low temperature. but it does not play an important role at temperatures higher than 923 K. From these distribution models, the pyrolysis conditions needed to obtain some desirable distributions are deduced. For instance, the highest TDR is obtained at a temperature of 913 K and a pyrolysis time of I5 min. At these conditions, FSC is 0.50 and FCVC is 0.76. If more severe pyrolysis conditions are used, the sulfur distributions do not vary significantly but FCVC decreases down to 0.66. On the contrarv. at lower temoeratures FSC increases UD to 0.67 and FCVC does not’increase signifi’cantly. This maximum foi TDR is due to the high release of sulfur and oxygen observed at temperatures up to 923 K. Oxygen removal from char increases CVC. At higher temperatures, release of sulfur is lower and CVC decreases as a consequence of CH, and H, removal, so, the combined effect is a decrease of TDR.
Use of Brazilian coal for coke production E. Osdrio and A. C. F. Vilela
Universidade Federal do Rio Grande do Sul, Departamento de Metalurgia, Osvaldo Aranha, 99, 6” andar, 90035-190 Porto Alegre, Brazil A study to verify the technical viability of the use of South Brazilian coal from the Chico-LomH coalfield has been made in order to increase the use of national coal in coke production. Samples were initially characterized according to their chemical, physical, plastic and Detrograuhic orooerties. The coking exneriments were carried out in a pilot Turnace.’ T
Production possibility of super-clean coal from Turkish bituminous coal G. Cizbayoglu and M. Mamurekli Middle
East
Department,
Technical
Ankara,
University,
Mining
Engineering
Turkey
Coal has some major impurities such as ash and sulfur. In order to produce a clean coal, the inorganic constituents of coal should be
Abstracts
removed as much as possible. The extent of reduction is closely related to the inherent ash content of the coal. In this research, the possibility of super-clean coal production from Zonguldak bituminous coal by heavy medium separation and flotation techniques was investigated. The coal sample used was the (- 50+ 18 mm) size jig concentrate of Central Washery of Zonguldak. It was composed of 12.1 I % ash and 0.41% total sulfur. The vitrain band of the same coal contained 3.28% ash and 0.22% total sulfur. By applying a two-step heavy medium separation, it was possible to reduce the ash content from 12.1 I % down to 4.00%. Final cleaning was carried out by flotation. In order to determine the optimum flotation conditions to produce a super-clean coal, the effects of different types of collector and frother were investigated. Kerosene, creosote, and fuel oil were used as collectors. Frothers tested were amyl alcohol. nonyl alcohol and MIBC (methyl isobutyl carbinol). The effect of pH, the consumptions of collector and frother, the grinding and flotation times were also studied. The optimum result was obtained using 170g/ton kerosene and 160g/ton MIBC. The investigation showed that it was possible to produce a coal product containing 2.16% ash and 0.42% total sulfur from Zonguldak bituminous coals.
Selective oxidation pretreatments for the enhanced desulfurization of coal S. R. Palmer,
E. J. Hippo and X. A. Dorai
Southern Illinois University at Carbondale, Department of Mechanical Engineering and Energy Processes, Carbondale. IL 62901, USA The primary objective of this study was to evaluate selective oxidation as a pretreatment for the enhanced desulfurization of Illinois Basin coals cusing a variety of mild thermal/chemical processes. Both an Illinois no. 6 and an Indiana no. 5 coal were selectively oxidized with peroxyacetic acid in the pretreatment step. The products were then treated with various hydroxide and carbonate bases, using either water, methanol or ethanol as the solvent system. Other reaction variables investigated included reaction temperature, reaction time, pyrolysis pressure, particle size of the coal and the level of oxidation in the pretreatment step. Throughout the study the selectively oxidized coals were compared to unoxidized control coals. The desulfurization of some selectively oxidized, sulfur-containing model compounds was also investigated. The results from these studies overwhelmingly show that selective oxidation with peroxyacetic acid significantly enhances the level of desulfurization that may be obtained with subsequent chemical/thermal treatments. Indeed, every process investigated, including simple ovrolvsis experiments. showed sulfur removal in the pretreatment step and tie sudsequent step to be substantially additive. In addition, the reactivity of the sulfur in the coal towards desulfurization was enhanced bv the selective oxidation pretreatment. Thus the severity of desulfurization conditions can be reduced by employing this oretreatment. Sulfur contents lower than 0.25% were obtained for selectively oxidized coals in which the original total sulfur content was 4.4% and the original organic sulfur content 3.1%. This represents a total sulfur reduction of abound 94% and a reduction in organic sulfur of at least 92%. This is beyond the level required for compliance with Clean Air Act legislation. No unoxidized coal, regardless of the desulfurization treatment, approached this level of sulfur removal. It should be noted that the sulfur removals obtained are superior to those of the molten caustic leaching process and are obtained under less severe conditions. In general, it was found that alcohol/carbonate base combinations were more effective desulfurizing agents than alcohol/hydroxide base systems for the desulfurization of the selectively oxidized coals. However, significant desulfurization was also obtained using aqueous Na,CO,. Possible synergistic interactions between the alcohol and the base are suspected. It was found that as the reaction temperature increased so did the level of desulfurization. Surprisinglv, the particle size of the feed coal (over the range studied) did n&t appear to i&uence reaction kinetics. However, it was determined that the level of selective oxidation in the pretreatment step was very important in determining the success of subsequent desulfurization treatments. In addition, it was found that lowering. the pressure in the reaction vessel gave improved desulfurization. Indeed, over 70% of the sulfur in the Illinois no. 6 coal could be removed by performing vacuum pyrolysis on the selectively oxidized coal.
Fuel 1993
Volume
72 Number
5
719