- Email: [email protected]
Selective oxidation pretreatments for the enhanced desulfurization of coal
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
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