Edward Furimsky

Characterization of trace element emissions from coal combustion by equilibrium calculations

Abstract A computer model based on equilibrium thermodynamics was used to characterize emissions of trace elements, such as arsenic (As), lead (Pb), cadmium (Cd), selenium (Se) and mercury (Hg), from pulverized coal combustion (PCC) and fluidized bed combustion (FBC). For PCC, most of the As, Pb and Cd entered fly ash, whereas most of the Se and Hg were in the vapor phase. For an air/coal ratio=1.1, all Cd was in the solid phase, whereas for 1.0 all Cd was in the vapor phase. The same change in the air/coal ratio had a much less pronounced effect on partitioning of other trace elements, however, it shifted the condensation of the trace elements compounds to lower temperatures. The air/coal ratio influenced the type of trace element-containing compounds in the vapor phase. Chlorine (Cl) in coal had a pronounced effect on the emissions of Hg and Pb. For FBC, more of the trace elements entered bottom ash rather than fly ash. Also, partitioning of the trace elements was influenced by the distribution of limestone and/or its products between fly ash and bottom ash. Limestone had a diluting effect on the content of trace elements in the ashes. The effect of the Ca/S ratio on partitioning of trace elements was less pronounced than that of the air/coal ratio. Thus, sulfides of calcium and iron were present in the ashes when the air/coal ratio was lower than 1.1. A low air/coal ratio had an adverse effect on gaseous emissions as well.

Assessment of coal combustion in O2+CO2 by equilibrium calculations

The facility for analysis of chemical thermodynamics (F*A*C*T) method based on the Gibbs energy minimization principle was used for the environmental assessment of coal combustion in O2+CO2 mixture compared with that in air. For the former case, the calculations predict higher emissions of CO and lower emissions of NOx. For both combustion media, SOx emissions are governed by O2 concentration, whereas distribution of trace metals was unaffected when O2 concentration in the O2+CO2 mixture approached that in air. The effect of O2+CO2 mixture on the distribution of chlorine- and alkali-containing compounds in the vapor phase was minor compared with that in air. In spite of the large excess of CO2 in combustion medium, sulfation was the predominant reaction occurring in ash.

Gasification of oil sand coke: Review

Abstract The production of synthetic crude from the tar sands in Western Canada has been steadily increasing. Most of the delayed coke produced by Suncor is combusted on site, whereas all fluid coke produced by Syncrude is stockpiled. The database on the chemical and physical properties of the oil sand coke, including the composition and fusion properties of the mineral matter, has been established. The reactivity of the coke was determined by oxygen chemisorption, fixed bed and fluid bed bench scale gasification and pilot plant gasification. The reactivity of the oil sand coke for gasification is rather low and comparable to high rank coals, such as anthracite. Slurrability tests revealed that a solid concentration in water, approaching 70 wt.%, can be achieved. Gasification is the front runner among clean technologies for the conversion of carbonaceous solids to useful products. Several commercial gasifiers are available to cover the wide range of severity. Because of the low reactivity of oil sands coke, high severity conditions are required to achieve high gasification conversion. Such conditions can be attained in entrained bed gasifiers. Gasifiers employing both dry and slurry feeding systems are suitable. A high efficiency, low SO x and NO x emissions, as well as a low solid waste production are among the key advantages of the gasification technology compared with the competing technologies. Commercial gasification of oil sands coke is delayed because of the availability of natural gas on the site of the upgrading plants. Potential for the transportation of the oil sand coke to USA for electricity generation using the integrated gasification combined-cycle (IGCC) technology was evaluated.

Effect of alkali and alkaline earth metals on nitrogen release during temperature programmed pyrolysis of coal

Abstract Formation of HCN, NH 3 , and N 2 during fixed-bed pyrolysis at 10K min −1 has been studied using coal samples after partial demineralization followed by addition of metal hydroxides from aqueous systems. Without additives, NH 3 is the predominant product at ≤ 700°C, showing the two peaks in the formation rate profile, whereas N 2 is the only product at ≥ 800°C. The presence of NaOH, KOH and Ca(OH) 2 promotes considerable NH 3 formation between 450 and 600°C, but in contrast suppresses HCN formation in this region. The Ca shows the largest effect on both the promotion and suppression. It is likely that the NH 3 increased by Ca addition arises partly from HCN, but mainly from secondary reactions of tar-N. These hydroxides affect N 2 formation in quite different manners: the Na decreases the rate between 700 and 950°C, and the K changes it less significantly than the Na, but the Ca remarkably increases the rate in a low temperature region of 550–700°C. These different features are discussed in terms of solid-phase reactions of alkali metal carbonates with char-N and secondary decomposition reactions of tar-N on CaO particles. As a result, total conversion of coal-N to HCN, NH 3 and N 2 up to 1000°C increases in the sequence of Na

Characterization of cokes from fluid/flexi-coking of heavy feeds

Abstract Several streams of coke particles which are generated during the fluid/flexi-coking operation vary in chemical and physical properties. At least six and eight coke streams can be identified in the fluid-coking and flexi-coking mode, respectively. The final coke residue disposed from the operation, particularly from the fluid-coking, is the most important because its storage and utilization require attention. Difference in chemical composition between the fluid-coke and flexi-coke confirm that the latter was exposed to more severe conditions. The layered structure of the coke particles was typical for both fluid-coke and flexi-coke. The surface area of the latter was greater and mean particle diameter smaller than that of the fluid-coke. With respect to a fuel type utilization, an uncertainty exists between the reactivity of the fluid-coke relative to that of the flexi-coke.

Gasification of brown coal and char with carbon dioxide in the presence of finely dispersed iron catalysts

Abstract Gasification of brown coal and char with CO 2 using iron catalysts precipitated from an aqueous solution of FeCl 3 has been studied. When the pyrolyzed char is gasified in the temperature-programmed mode, the presence of the iron can lower the temperature giving the maximal rate of CO formation by 130–160 K, a larger lowering being observed at a higher loading in the range of ≤ 3 wt.% Fe. The specific rates of the isothermal gasification of iron-bearing chars at 1173 and 1223 K increase with increasing char conversion, resulting in complete gasification within a short reaction time. Comparison of the initial rates of uncatalyzed and catalyzed gasification reveals that iron addition can lower the reaction temperature by 120 K. Mossbauer spectra show that the precipitated iron exists as fine FeOOH particles, which are reduced mainly to Fe 3 C on charring at 1123 K. Most of the Fe 3 C is transformed into α-Fe and γ-Fe at the initial stage of gasification, and subsequently these species are oxidized to FeO and Fe 3 O 4 . The changes during gasification are discussed in terms of solid-gas and solid-solid reactions.

Prediction of coal reactivity during combustion and gasification by using petrographic data

Abstract Petrographic data were correlated with calorific value, oxygen content, fuel ratio, ignition temperature, oxygen chemisorption and selected gasification reactivity data of twenty one Canadian coals (17 from Western and 4 from Eastern Canada). Both parameters are suitable for predicting other coal properties particularly in the absence of mineral matter effects. Using ignition temperature and oxygen chemisorption the series of coals can be divided into three groups. The first group, characterized by low ignition temperatures and low oxygen chemisorption, had mean vitrinite reflectance and/or petrofactor less than 0.6 and/or 7.0. The second group, characterized by the largest oxygen chemisorption and intermediate ignition temperatures had mean vitrinite reflectance and/or petrofactor in the range of 0.6 to 1.0 and/or 7.0 to 11.0. The third group, characterized by the highest ignition temperatures and the lowest oxygen chemisorption had mean vitrinite reflectance and/or petrofactor greater than about 1.0 and/or 11.0. Calorific value and ignition temperature are good correlating parameters for low rank coals, whereas fuel ratio is suitable for higher rank coals. The petrofactor as a correlating parameter offered little advantage compared with the mean vitrinite reflectance.

Characterization of Canadian coals by nuclear magnetic resonance spectroscopy

Abstract Apparent aromaticities of a series of Canadian coals of different rank were estimated by solid state nuclear magnetic resonance spectroscopy. The aromaticities varied from 0.57 for a lignite up to 0.86 for a semi-anthracite coal. The aromaticities correlated well with fixed carbon and oxygen content of the coals as well as with the mean reflectance of the coals. Correlations were also established between aromaticities and the H/C and H aru /C ar ratios of the coals. Uncertainties in calculation of the hypothetical H aru /C ar ratios, from experimental data were pointed out. Structural parameters of the chars derived from the coals by pyrolysis at 535°C were, also, estimated. The H/C and H aru /C ar ratios of the chars were markedly lower than those of coals. This was complemented by higher apparent aromaticities of the chars compared with the coals.

Relation between particle size and properties of some bituminous coals

Abstract Coal fractions of different size distributions exhibited different H C ratio, ash and sulphur contents, and surface structures. This was confirmed using two low-sulphur and two high-sulphur bituminous coals. The effect was much less pronounced for low-sulphur coals than for high-sulphur coals. A significant difference in properties was noted between the two high-sulphur coals in spite of similar basic compositional parameters. This was confirmed by the fractal dimensionality factor D of Illinois No. 6 coal, which exceeded the theoretical value.

Quantification of chlorine and alkali emissions from fluid bed combustion of coal by equilibrium calculations

Abstract A computer model based on the Gibbs energy minimization principle was used to identify and quantify chlorine (Cl)- and alkali-containing species formed in the temperature range from 1100 to 1200 K, air/coal ratio of 1.0 and 1.1 and Ca/S ratio varying from 0 to 2.5 using low and high Cl content coals. HCl, KCl and NaCl were the major Cl-containing volatile compounds. The amount of HCl in the vapor phase decreased and that of KCl and NaCl increased with increasing Ca/S ratio from 0 to 2.5, whereas the increase in the air/coal ratio from 1.0 to 1.1 had the opposite effect. KCl and NaCl were the major, and KOH, NaOH, K 2 SO 4 and Na 2 SO 4 the minor alkali-containing species in the vapor phase of all the cases analyzed. The amount of all alkali metal-containing compounds increased with increasing Ca/S ratio and decreased with increasing air/coal ratio from 1.0 to 1.1. For the low Cl coal, the relative contribution of KOH and NaOH to the overall alkali emissions was greater than that for the high Cl coal.