Petroleum and Coal Article Open Access CHARACTERIZATION OF ASH CONTENT, COKING TENDENCIES AND EVALUA- TION OF PHYSICOCHEMICAL PROPERTIES OF OKOBO COALS (original) (raw)
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2017
The mineral content of coal affects the type of ash that will be produced on combustion. Despite the same volatile matter content, the Okobo 1 FSI is 3.7 with ash content of 16.7 while Okobo 2 FSI is 6.8 with an ash content of 8.2. Ash fusion is 1,400oC, various ash slagging index indices such as silica ratio (Sr), basic to acidic oxide (B/A), and sulphur index (Rs) for Okobo coal are: 85, 0.13, 0.23 respectively implying low slagging characteristics. The Gross Calorific Value GCV of Okobo 1 and Okobo 2 are 20.88 MJ/Kg (8796 Btu/lb) and 19.86MJ/Kg (8536 Btu/lb) respectively congruous with lowest grade of subbituminous coal termed the “sub-bituminous C grade” according to ASTM classification. The fixed carbon values are 59.5% (Okobo 1) and 59.7% (Okobo 2) while the moisture content of Okobo 1 is 12.8 and Okobo2 is 23.1, an indication of possible coking with beneficiation. The total alkali of the coal (0.63%) is less than 2%, Silica (SiO2) is 62.3%, potassium as K2O, % is 0.53 Fe2O3 i...
Comparative study of the quality of some coals from the Zibo coal field
Energy, 2003
The basic chemical composition of coal and ash is an important but insufficient characteristic for the reliable explanation of coal properties. The modes of occurrence of the elements, their origin and concentration in coal, as well as their behavior during the coalification process, are also very important parameters for coal quality. The characteristics noted above can be used as a
In this paper, characterization and ash chemistry of selected Nigeria coal samples were investigated to determine its suitability as a solid fuel. The three coal samples considered originated from Northern Benue trough, Central Benue trough and Anambra Basin of Nigeria where proven reserve deposits are found. The coal samples were analysed using various analytical methods such as thermosgravimetric analysis (TGA) and X-ray Fluorescence spectroscopy (XRF) analyses. The ash chemistry indices used in predicting the performance of the coal samples includes basic to acidic oxide (B/A), silica ratio, iron index and sulphur slagging index (Rs). The TGA profile suggests that Enugu coal showed high thermal stability than that of Okaba and Maiganga coals but had an ash content higher by a factor of 2.0 when compared with Okaba and Maiganga coals. Maiganga coal however has the highest heating value of 27.40 MJ/kg when compared to Okaba coal (25.74 MJ/kg) and Enugu coal (22.92 MJ/kg). The silic...
Characterization and Ash Chemistry of Selected Nigerian Coals for Solid Fuel Combustion
2017
In this paper, characterization and ash chemistry of selected Nigeria coal samples were investigated to determine its suitability as a solid fuel. The three coal samples considered originated from Northern Benue trough, Central Benue trough and Anambra Basin of Nigeria where proven reserve deposits are found. The coal samples were analysed using various analytical methods such as thermosgravimetric analysis (TGA) and X-ray Fluorescence spectroscopy (XRF) analyses. The ash chemistry indices used in predicting the performance of the coal samples includes basic to acidic oxide (B/A), silica ratio, iron index and sulphur slagging index (Rs). The TGA profile suggests that Enugu coal showed high thermal stability than that of Okaba and Maiganga coals but had an ash content higher by a factor of 2.0 when compared with Okaba and Maiganga coals. Maiganga coal however has the highest heating value of 27.40 MJ/kg when compared to Okaba coal (25.74 MJ/kg) and Enugu coal (22.92 MJ/kg). The silic...
Influence of coal quality on combustion behaviour and mineral phases transformations
Coal is still an important resource for power generation. The combustion behaviour of various types of coal is dependent on its ash properties. These are the most important fuel characteristics in the design and operation of commercial boilers. The present study aims to evaluate the whole coal seam quality, coal ash behaviour, fundamental mechanisms, which more closely simulate the conditions of a pulverised coal-fired boiler. The authors formed seven representative samples from overall 126 band-by-band samples of Prajapara coal block (PCB) borehole of Ib valley coal basin, Odisha, India. Authors have carried technological, elemental and petrographical analysis of coal samples. The major oxides and minerals present in coal ash samples were characterised by inductively coupled plasma optical emission spectrometer (ICP-OES) and X–ray diffraction (XRD). The volatile matter (VMdaf) and ash (Ad) yields vary from 42.05–44.49 and 30.82–32.12 wt% respectively. The mean vitrinite reflectance ranges from 0.46 to 0.64%. Moreover, FactSage thermodynamics Model (FactSage 6.3) was used for understanding of the coal ash fusion behaviour in boiler operation and to predict the phase transformations that occur during the process of coal combustion which is a chemical thermodynamic models of oxide systems. FactSage provides mineralogical characteristics of coal which are in agreement with XRD analysis of coal. SiO2, Al2O3, K2O appears to influence positively fusion characteristics where as Fe2O3 and MgO have negative effect on it. The datasets provide information about the contribution of major oxides towards the ash fusion temperatures (AFT). The linear regression analysis of high temperature ash (HTA) composition and AFT indicate trend, which may be used to determine the predictive indices for slagging, fouling, and abrasion propensities during combustion practices.
Free-swelling index (FSI) and dilation are useful indicators to predict the strength of coke that may be derived from a particular coal. FSI is a measure of a coal ability to swell and cake during heating. Both coal from Ovbiowun and Oloku are considered to have poor coking and swelling tendencies as inferred from the derived FSI values (2.04 and 1.48 respectively) as well as > 36% in volatiles. GCV/HHV is determined from both proximate and ultimate analyses values as input parameters using a generally proven formula. GCV of Ovbiowun coal is 28.7MJ/Kg which is within range of 26.7 – 30.2 MJ/Kg for " high volatile C bituminous ". Oloku coal has GCV of 25.3 MJ/Kg which is within the range of 24.4 – 26.7 MJ/Kg for " Sub bituminous A grade ". For Ovbiowun coals, the Ibs of CO2/ MMBtu (gross) = 167.44 Ibs/Btu, 4596 Ib/tonne and for Oloku coals, Ibs of CO2/ MMBtu (gross) = 164.21 Ibs/Btu, 4376 Ib/tonne. This strongly agrees with Oloku coals as sub-bituminous and Ovbiowun coals as bituminous, having higher carbon content and thus more CO2 production. The fuel ratio for both Ovbiowun and Oloku is 0.98 and 0.91 respectively which is a referral to bituminous grade. The vitrinite reflectance as determined for the studied samples was 0.48 for Ovbiowun coals and 0.43 for Oloku coals implying bituminous and sub-bituminous coals respectively. No coal bedded methane is produced from both coals. The Roga index as well as their dilation is inferred to be around 0-20. Ovbiowun coals have 65 HGI and Oloku coal is 87 HGI due to higher moisture content. The moisture content of Oloku coal (15.0) is higher than Ovbiowun (10.8) while the volatile matter (as received) for Oloku (40.7) is lower than Ovbiowun (41.7). From the > 10% moisture and ash content, coal in both study area is unsuitable for coke production. Also the derived Hydrogen % for Ovbiowun (63.3%) is greater than Oloku (57.43) implying more maturity in Ovbiowun coals.
Coal being an economic deposit can be used for various purposes depending on their properties and composition. Hence, the need to carry out detail investigation on Ankpa coals. Ankpa coals fall within the Mamu Formation of Anambra Basin in southeastern Nigeria. The coals were investigated to deduce the rank and the coal quality with respect to power generation, cokability, handling, fueling, combustion, agglomeration and slagging potential. Nine coal samples were collected from two boreholes (BH-2) and (BH-4) having depth of 16.5m and 27.4m respectively and were subjected to proximate, ultimate and elemental analyses. Moisture content ranges from 2.10 to 8.75 wt%, Ash content, 4.45 to 26.8 wt%, volatile matter, 40.10 to 56.9 wt% and the fixed carbon 20.45 to 39.24 wt%. The moderate moisture, low to high ash content and high volatiles matter in the coals suggest high volatile sub-bituminous, non coking coal. The carbon content range from 23.3 to 52.4%, hydrogen, 1.73 to 6.88%, oxygen, 9.57 to 18.9%, Nitrogen, 1.42 to 2.93% and sulphur, 0.73 to 4.15 %. The sulphur content (> 0.8%) and Nitrogen content (>1.5%) indicates non coking coal and would pollute the atmosphere during combustion by releasing flue gases. The agglomeration and slagging were deduced by the ratio of C/H, FC/V, SiO2/Al2O3, Fe2O3/CaO, Silica ratio (G), and Base/Acid ratio (B/A). The agglomeration level and tendency of the coals to slag varies from weak-strong. The coals are not suitable for coking but can be used for power generation, combustion applications and fuelling due to it high combustibility.