An Improved Model of Sulfur Self-Retention by Coal Ash During Coal Combustion in FBC

2005 ◽  
Author(s):  
Vasilije Manovic ◽  
Borislav Grubor
Keyword(s):  
Thermal Decomposition ◽  
Fluidized Bed ◽  
Coal Ash ◽  
Sulfur Oxides ◽  
Mineral Matter ◽  
Fluidized Bed Combustion ◽  
Particle Volume ◽  
Reaction Rate Constants ◽  
Dependent Relation ◽  
Improved Model

During combustion of coal a significant amount of sulfur may be retained in ash due to the reactions between mineral matter in coal and sulfur oxides. This process is known as sulfur self-retention and its significance lies in the fact that a part of sulfur oxides, one of the main pollutants during combustion of coal, is not released in the atmosphere. Sulfur self-retention is influenced by parameters that depend on coal characteristics and combustion conditions. The interest for this process was enhanced with the introduction of fluidized bed combustion (FBC) technology since the temperatures and other conditions are favorable for sulfur self-retention. Investigation of this process, primarily modeling, is the subject of this work. The presented model is based on the previously developed model for the combustion of porous char particles under FBC conditions, along with a changing grain size model of sulfation of the CaO grains dispersed throughout the char particle volume. Incorporating the phenomena of sintering, reduction of the produced CaSO4 with CO, thermal decomposition of the produced CaSO4, as well as allowing for the different reactivity of various forms of calcium make major improvements of the model. A temperature dependent relation for the CaO grain radius takes sintering into account. Reductive and thermal decomposition were taken into account by the corresponding reaction rate constants of the Arrhenius type. The reactivity of the calcium forms in coal was considered by different initial radius of the CaO grains. The model was verified by the experimental results of sulfur self-retention of three Serbian coals during combustion in a fluidized bed combustion reactor. The comparison with the experimentally obtained results showed that the model can adequately predict the levels of the obtained values of sulfur self-retention efficiencies, as well as the influence of temperature, coal type and coal particle size.

scholarly journals Research in the fluidized bed combustion in the Laboratory for thermal engineering and energy - Part A: Achievements in targeted fundamental research

2019 ◽  
Vol 23 (Suppl. 5) ◽  
pp. 1637-1653
Author(s):  
Borislav Grubor ◽  
Dragoljub Dakic ◽  
Stevan Nemoda ◽  
Milica Mladenovic ◽  
Milijana Paprika ◽  
...  
Keyword(s):  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Coal Ash ◽  
Thermal Engineering ◽  
Fluidized Bed Combustion ◽  
Particle Combustion ◽  
Research Activities ◽  
Energy Part ◽  
Char Particle ◽  
Fundamental Research

The paper gives a review of the most important results of extensive targeted fundamental research program on fluidized bed combustion in the Laboratory for Thermal Engineering and Energy of the VINCA Institute of Nuclear Sciences. The paper presents a detailed overview of research activities from the beginning in the second half of the 1970'' up to present days. Starting with the motives for initiating the investigations in this field, the paper highlights various phases of research and points out the main results of all research activities, not only the ones that are focused in this paper. Targeted fundamental research topics that are overviewed in this paper are heat and mass transfer, coal particle fragmentation, char particle combustion, sulfur self-retention by coal ash itself, as well as circulating fluidized bed modeling.

Fluidized bed combustion of refuse-derived fuel in presence of protective coal ash

2005 ◽  
Vol 87 (1) ◽  
pp. 33-44 ◽  
Author(s):  
Eduardo Ferrer ◽  
Martti Aho ◽  
Jaani Silvennoinen ◽  
Riku-Ville Nurminen
Keyword(s):  
Fluidized Bed ◽  
Coal Ash ◽  
Fluidized Bed Combustion ◽  
Refuse Derived Fuel

Utilization of coal ash from fluidized-bed combustion boilers as road base material

1995 ◽  
Vol 14 (2) ◽  
pp. 69-77 ◽  
Author(s):  
T. Takada ◽  
I. Hashimoto ◽  
K. Tsutsumi ◽  
Y. Shibata ◽  
S. Yamamuro ◽  
...  
Keyword(s):  
Fluidized Bed ◽  
Base Material ◽  
Coal Ash ◽  
Fluidized Bed Combustion ◽  
Road Base

Attrition Behavior of Coal Ash Under Circulating Fluidized Bed Combustion Conditions

2003 ◽  
Author(s):  
Franz Winter ◽  
Xin Liu
Keyword(s):  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Coal Ash ◽  
Operating Conditions ◽  
Laboratory Scale ◽  
Silica Sand ◽  
Electrical Heating ◽  
Fluidized Bed Combustion ◽  
Bed Temperature ◽  
Wide Range

The attrition behavior of ash produced from two bituminous and one anthracite coal was studied under laboratory-scale circulating fluidized bed combustor (CFBC) conditions. After the ash was produced in the oven, the ash sample with a size range from 0.1 to 1 mm was fed into the hot CFBC, which was heated by electrical heating shells and fluidized by air. The laboratory-scale CFBC was operated with using fine silica sand (40 to 80 μm) as bed material. After a certain time the operation was stopped, all particles were collected and sieving analysis was performed to obtain the actual particle size distribution (PSD) of the coal ash. The operating conditions were changed in a wide range, i.e. the bed temperature from 600 to 850°C, the fluidizing velocity from 1.2 to 2 m/s, the residence time from 60 to 120 min and the design of the cyclone. The effects of operating conditions and coal type were studied and their relative importance is discussed. Elemental analysis of the coal ashes showed that Si and Ca may play an important role during attrition.

Mineral Matter Transformation of Coal Ash under Gasification Atmosphere: A Case of Huolinhe Lignite

2011 ◽  
Vol 347-353 ◽  
pp. 3732-3735 ◽  
Author(s):  
Feng Hai Li ◽  
Jie Jie Huang ◽  
Yi Tian Fang ◽  
Yang Wang
Keyword(s):  
Low Temperature ◽  
Alkali Metal ◽  
Fluidized Bed ◽  
Coal Ash ◽  
Volume Ratio ◽  
Phase Changes ◽  
Mineral Matter ◽  
Alkali Metal Oxide ◽  
Reducing Atmosphere ◽  
Initial Melting

Experiments have been conducted with Huolinhe lignite low temperature ashes (HLH-LTA) to investigate the mineral behaviors under gasification atmosphere (H2/CO2=1:1, volume ratio) with the temperature increase by SEM and XRD. The results show that the contents of SO3 and alkali metal oxide (e.g. K2O, Na2O) are higher in the HLH-LTA than that in laboratory HLH ashes. The formation of some low-melting ferrous eutectic compounds causes the initial melting temperature of HLH-LTA is lower about 300 °C than its deformation temperature. The formation of slag during HLH fluidized-bed gasification is the results of the interaction among minerals and phase changes with the temperature increases under reducing atmosphere.

Slag-Coal Interface Phenomena

1966 ◽  
Vol 88 (1) ◽  
pp. 40-44 ◽  
Author(s):  
E. Raask
Keyword(s):  
Carbon Monoxide ◽  
Molten Slag ◽  
Iron Carbide ◽  
Coal Ash ◽  
Sulfur Oxides ◽  
Mineral Matter ◽  
Slag Removal ◽  
Interface Phenomena ◽  
Coal Particles ◽  
Initial Melting

In a cyclone system of combustion or gasification with molten-slag removal a large proportion of the coal is thrown to the slag-coated cyclone walls before it has time to burn. The welting properties of coal-ash slag on devolatilized coal, the evolution of gases from molten slag when in contact with coal particles, and the effect of mineral matter on combustion of coal have been investigated briefly using a heating microscope. Coal-ash slag does not wet coal or coal residues, thus combustion of the coal particles on the surface of molten slag is not retarded. Evolution of gases lakes place from the slag (a) on its initial melting with release of sulfur oxides, and above 1400 C where carbon monoxide is given off when the slag is in contact with coal. The latter is explained in terms of the formation of iron carbide at the slug/carbon interface, the carbide then diffuses into the slag where it reads with silica.

Understanding the Behavior of Calcium Compounds in Petroleum Coke Fluidized Bed Combustion (FBC) Ash

2006 ◽  
Vol 128 (4) ◽  
pp. 290-299 ◽  
Author(s):  
E. J. Anthony ◽  
L. Jia ◽  
S. M. Burwell ◽  
J. Najman ◽  
E. M. Bulewicz
Keyword(s):  
Particle Size ◽  
Fluidized Bed ◽  
Petroleum Coke ◽  
Bound Water ◽  
Mineral Matter ◽  
Fluidized Bed Combustion ◽  
Free Lime ◽  
Size Fractions ◽  
Lime Content ◽  
Calcium Compounds

With growing understanding of the differences between solid residues from the fluidized bed combustion of petroleum coke and of coal, the significance of fuel-derived and sorbent-derived components of the ash has become clearer. It is well documented that hydration of the ashes is necessary prior to disposal or utilization or as a reactivation method. Initially, hydration of the lime was thought to involve water reacting only with CaO to form Ca(OH)2 but when the free lime content of the ashes is looked at before and after hydration, it is apparent that the process is more complex. Detailed analyses have shown that the free lime can decrease and vary within the same ash in different particle size ranges. The complexity of the reactions is reflected in problems with the assessment of the free lime content of the materials and the effect of hydration on different particle size fractions of the ash. The free lime content of the ash is significantly lower than expected based on the elemental analysis. Bed ash from the circulating fluidized bed combustion boilers owned and operated by the Nelson Industrial Steam Company Ltd. (NISCO) was examined in detail to elucidate the fate of calcium in the ash during hydration, using a range of techniques. The objective of the study is to determine the amount of CaO available for hydration/reactivation and to better understand interactions of Ca and other mineral components of the ash. Analysis results indicate that in NISCO ashes up to about 6% of the analytical CaO may be combined as acid soluble and insoluble OCCs (other calcium compounds). This implies up to about 10% less free lime than would be inferred from standard chemical analyses. About 1% of the missing CaO can be present as acid insoluble Ca and Mg vanadates, with up to 2% bound in soluble OCCs. The remaining 3-4% is still not accounted for. It is clear that even very minor quantities of mineral matter, other than CaO or CaSO4, associated mainly with the coarser size fractions, are important. The amount of bound water in the hydrated ash, other than that combined in portlandite or brucite, can be as large as 3-5%. This cannot be ignored when sample mass change on hydration or heating is used as a measure of the extent of CaO to Ca(OH)2 conversion.

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