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The fate of trace elements at coal-fired power plants
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,
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,