Dry Ash-free Basis Research Articles

Aerial Oxidation of Kangal/Sivas Lignite at 70°C and 90°C

The results of a study on the formation of alkali soluble humic acids and the increase of oxygen concentration during the oxidation of Kangal/Sivas lignite are reported. The oxidation reaction was conducted in an open circuit system at 70°C and then at 90°C for 12 h, respectively, in a day. The supply of oxygen in the sample by air was allowed to proceed for 2–12 days with 2 day intervals for the parallel samples, and oxygen concentration in the sample oxidized increased from 25.28% to 29.50%. Particular attention was directed to determining the optimum oxidation period, airflow rate, and energy balance in the reactions. Potassium humate (K-Humate) salt, a product of the reaction between the alkali soluble humic acids and potassium hydroxide solution, was obtained with 75.53% recovery in dry ash free (daf\\hr) basis from the sample oxidized in air for 96 h and sized to −0.246 + 0.104 mm.

Consideration of Spent Mushroom Compost as a Source of Energy

AbstractThe success of the Irish mushroom industry has led to its rapid expansion, particularly in the border counties. Mushrooms grow in a compost of poultry litter, straw and gypsum. After the mushrooms are gathered the spent mushroom compost (SMC) has traditionally been land spread as fertiliser. However, as more intensive practices are adopted, there is insufficient land available for the waste. The difficulties presented in disposing of SMC with environmental sensitivity are now a limiting factor on further growth of the industry.This paper investigates the potential of SMC combustion with energy recovery. The availability and composition of SMC has been considered with regard to its potential as an energy feedstock. Analyses showed that, on a dry ash free basis, SMC has a calorific value equivalent to sewage sludge. Compositional analysis confirmed the dry fuel as consistent in make‐up and showed the moisture content to remain within 60 to 77 percent, on an as received basis. SMC was found during combustion trials to be a suitable feedstock for combustion in a bubbling fluidised bed unit. Sensitivity studies determined a gate fee of £6.8/tonne for such a process which will compare favourably with landfill prices as they rise form the current £5/tonne.

Fractional conversion of char N to no in an entrained flow reactor

Char samples have been produced, under oxidative pyrolysis conditions, from Australian bituminousand subbituminous coals under high heating rate conditions in an entrained flow reactor. The samples were collected, characterized, and stored under iner gas. The chars were then combusted in the entrained flow reactor, using Ar/O2 mixtures (to eliminate thermal NOx formation and to enable determination of formed N2), and the amounts of NO and N2 produced were determined for a range of temperatures and residence times. The fractional conversion of NO to nitrogen-containing products was determined from the NO and N2 measurements. This is the first time this technique has been applied at this scale to determine the selectivity of char N conversion to NO. It is not possible to discern significant differences between the four chars studied. The results show that, under stoichiometric conditions (=1), char N will be released at a rate determined by the char burnout. An overall fractional conversion of char N to NO of 0.5±0.1 for =1 represents a reasonable summary of the data. Under fuel-lean conditions, fractional conversions as high as 0.7–0.8 are observed, while under fuel-rich conditions, fractional conversions as low as 0.3–0.4 are observed. These results include chars prepared from parent coals with N contents ranging from 1.07 to 2.20 wt. % (dry ash-free basis) and coal types including subbituminous and bituminous. The implications for predictive methods and modeling of NOx emissions are discussed.

Physical structure and combustion properties of super fine pulverized coal particle

Physical structures and combustion properties of super fine pulverized coal particles of eight Chinese coals, Heshan subbituminous coals and Jincheng lean coals from two areas of China, have been investigated using accelerated surface area and porosimetry, thermobalance (TGA), and Fourier transform infrared spectrometer. Results showed that the particle specific surface area and pore volume increased greatly when the coal particle size was reduced. The higher the carbon content on a dry ash-free basis is, the larger the particle specific surface area and pore volume are. When the coal particle size decreases, the combustion process can be largely improved, ignition temperature is reduced, and SO2 emission from coal combustion is also lower.

An initial assessment of spent mushroom compost as a potential energy feedstock

The Irish mushroom industry has expanded rapidly in the last decade, particularly in the border counties. Its success has generated concern, however, as the production of spent mushroom compost (SMC) has increased. Until recently, SMC as an agricultural waste has been disposed of without due consideration to the environment. As County Councils increasingly address river pollution, restrictions will prevent expansion of the mushroom industry without an SMC waste management solution. This paper looks at the availability and composition of SMC and considers its potential as an energy feedstock. Variability in SMC composition was investigated by sampling from various locations over several months. Analyses showed that, on a dry ash free basis, SMC has a calorific value equivalent to sewage sludge which has been successfully fired for many years. Compositional analysis confirmed the dry fuel as consistent in make-up and showed the moisture content to vary within 60–77%, on an as-received basis.

Characterization of Pore Structure of Turkish Coals

Pore structure of coal has a great influence on its behavior during mining, preparation, and utilization. Characterization of the pore structure of twelve Turkish coals from different geographic locations and with carbon contents varying between 61 and 84% (on dry ash-free basis) was carried out using different techniques. The volume and area of macropores were determined by mercury intrusion porosimetry. Mesopore volumes and areas were determined by N2 gas adsorption at 77 K using the Barrett−Joyner−Halenda (BJH) method. Brunauer−Emmet−Teller (BET) areas were calculated using the same data. Micropore volumes and areas were determined by the application of the Dubinin−Radushkevich (DR) equation to the CO2 adsorption data at 298 K. True and apparent densities of coals were measured by helium and mercury displacement. Pore size distributions were evaluated using data thus obtained. Small-angle X-ray scattering (SAXS) technique was also employed to determine the surface area of some samples. The highest BET ...

Activated carbons from bituminous coal: effect of mineral matter content

A bituminous coal from Puertollano Basin (Spain) was selected on the basis of previous study as the most suitable raw precursor to prepare activated carbons. In fact, this coal gave the best results among a total of 10 different Spanish coals that covered a wide range of coal rank. Its initial ash level (19 wt%) was decreased in the coal mine facilities by different intensive hydropneumatic washing, yielding fractions with 12 and 8 wt% ash. Another fraction was also obtained from the original coal with 5 wt% ash by an HCl/HF washing treatment. These four coals were carbonised at 850°C and activated at 850°C for different activation times in steam and carbon dioxide, to analyse the effect of ash level on the porosity development of the resulting carbons. Contrary to what might be expected (catalysis effect, pore blocking and impediment of suitable porosity development), the initial ash level does not affect the porosity development. Those samples with a lower ash (at the same burn-off degree) yield higher micropore volumes. But when the results are presented in terms of dry ash free basis, the same porosity development is attained regardless of the initial ash level. Comparing the behaviour of steam and carbon dioxide as activating agents, the pore structure and pore volumes attained are quite similar, though the pore sizes of steam samples are slightly wider than those of carbon dioxide samples. The Dubinin–Stoeckli equation applied to experimental adsorption isotherm was used to follow the porosity development during activation for each reactive gas.

Performance of a Burner with Coal and Coal-Bio-Solid Fuel Blends

Powerplants spend nearly 50 billion dollars a year on fuel cost, and coal accounts for over 55% of the fuel used in the utility industries. The fuel cost could be reduced by supplementing coal fuels with alternative renewable fuels such as the byproducts of industries located in the vicinity of the powerplants. One of the byproducts of feedlots is manure, a biosolid fuel that is cheaper than coal, on a tonnage and heat-value basis. Coal-manure or, more simply, blend technology is proposed as a beneficial use of manure for powerplants located near feedlots. Experiments were performed in a small-scale boiler burner facility with coal only, and then for 80:20 blends on a wet-weight (as-received basis). Data were taken during the warm up, gasification, and combustion. Three types of feedlot manure were examined for blending: raw feedlot, partially composted feedlot, and finished composted feedlot. A summary of the findings is as follows: 1) Manure contained up to 80% volatile matter (VM) on a dry ash-free basis, which was twice the VM of conventional coal. 2) Combustion efficiency was slightly higher with the coal-manure than with coal. 3) NO A emission increased from 420 ppm at 80% burned fraction (BF) to 550 ppm at 95% BF for coal, whereas corresponding numbers for the were 620-550 ppm. 4) SO* increased from 30 to 180 ppm for coal, whereas for the it was nearly 0 ppm up to 90 % BF, but increased to 10 ppm at 95% BF.

98/03101 Yields of oil products from thermochemical biomass conversion processes

This paper examines the use of organic co-solvent (n-heptane, toluene and anisole, up to 10 wt.%) in the hydrothermal liquefaction of macroalgal biomass as a means of achieving in situ fractionation of the biocrude product according to polarity. The filamentous freshwater macroalga Oedogonium was grown under nutrient-depleted conditions to achieve a low nitrogen content, 1.1 wt.% N. Its hydrothermal liquefaction in a continuous pilot plant reactor (300–350 °C, 3–5 min and 2–5 wt.% loadings) yielded up to 25 wt.% (dry ash-free basis, daf) extractable biocrude. More severe conditions led to biocrudes in higher yields, with reduced oxygen and slightly increased nitrogen contents, and with lower viscosity. The presence of co-solvents had little effect on the total biocrude yield but gave rise to in situ separation of the biocrude into distinct fractions associated with the organic phase (designated solvent oil) and the aqueous phase (designated DCM oil). The amount of solvent oil produced exceeded the amount that could be extracted at room temperature, by that solvent, from the product mixture obtained in the absence of co-solvent. The relative proportions and properties of the solvent and DCM fractions varied with the polarity of the co-solvent. Anisole co-solvent dissolved nearly all the biocrude and the resulting viscous oil was similar to that obtained without co-solvent. On the other hand, solvent oil produced with n-heptane (~ 7.4 wt.% daf yield, or ~ 37% of the total biocrude) had significantly reduced levels of nitrogen (1.1 wt.%) and oxygen (12.5 wt.%) and possessed relatively low viscosity. Toluene co-solvent HTL produced a solvent oil with intermediate yield and properties. Co-solvent HTL offers a simple and effective means of fractionating HTL biocrude on the basis of polarity. A non-polar co-solvent such as n-heptane produces an enhanced product fraction more suitable for hydrotreating than the mixed product obtained without co-solvent.

Gasification characteristics of coal in a moving bed pressure gasifier

Gasification of six Indian coals was carried out in a moving bed pressure gasification pilot plant in oxygen-blown mode. The effect of operating pressure on the gasification characteristics such as raw gas yield as well as methane yield from 1000 kg coal on dry ash free basis (d.a.f.), oxygen consumption for the gasification of 1000 kg coal (d.a.f.) and the requirement of coal (d.a.f.) for the production of 1000 Nm 3 COH 2 mixture were examined. Combining the present data for Indian coals with published data for lignite and coals from other countries, correlations between the rank of coal and its gasification characteristics are proposed. From a detailed error analysis, it has been possible to conclude that the gasification characteristics of coals of a wide ranging rank expressed as carbon ratio or coalification index can be predicted by these correlations with reasonable accuracy. It is further concluded that predictions based on carbon ratio are more accurate.

Behaviour of extractives in a bark steam dryer

The bark extractives from steam drying of bark residues at a pulp mill were studied in order to evaluate their role in the formation of deposits in the dryer. The lipid compositions of bark, condensate and deposit samples taken from a back-pressure steam dryer plant were analyzed by gas chromatography and mass spectrometry. The main lipid groups released from bark and found in the condensate were free fatty acids and resin acids, dominated by unsaturated C 18 acids and dehydroabietic acid respectively. The release of these acid groups was 0.3% of the dry bark feed, corresponding to 50 wt% of the free fatty acid and resin acid content of the bark feed. It was assumed that these acids contribute by their tackiness to the formation of deposits at various sites of the dryer. The deposit samples taken from the dryer contained the same lipid compound groups as the bark raw material. However, their extract and lipid contents varied considerably, 2.9–40% and 0.5–18% on a dry ash-free basis, respectively, depending on their site in the dryer. The lipid composition of the deposit on a recycling fan was close to that of the condensate containing large amounts of fatty acids and resin acids. The deposit on heat exchanger tubes consisted of bark dust containing degraded bark suberin, and of fatty acids and resin acids carried with the steam.

Formation and behaviour of organic compounds in biomass dryers

The organic compounds released in the thermal drying of biomass, and their behaviour in downstream sections, were studied to determine their effect on the formation of deposits in processes and on the environment. The releases were studied by using laboratory-scale fluidizedbed drying experiments carried out on peat, pine bark, and birch bark at different temperatures. In addition, bark, condensate, and deposit samples were taken from a pressurized steam dryer at a pulp mill. Aging experiments were carried out for deposit samples in a microautoclave. All the samples were analysed for lipophilic extractives by using capillary-gas chromatography and mass spectrometry. The hydrophilic compounds released were analysed by using various chromatographic methods. Different organic hydrophilic and lipophilic compounds were released in drying. The amount of identified compounds released from peat increased from 1 to 10 wt% of feed, calculated on a dry ash-free basis, as the temperature rose from 190 to 350°C. The amounts for pine bark and birch bark at 150–350°C were 0·1–11 wt% and 0·3–17 wt%, respectively. The main hydrophilic compounds released from raw materials were carboxylic acids, methanol, aldehydes, anhydroglucoses, and furanoic compounds. The hydrophilic compounds may cause an organic load on the recipient or emissions to the air. The major lipophilic-compound groups released from peat consisted of fatty acids, those from pine bark of fatty and resin acids, and those from birch bark of triterpenoid alcohols. The fatty and resin acids were found to be enriched in the deposit samples from the heat-exchanger tubes and the recycling fan of the bark dryer, when compared with the bark feed. The tacky lipids released, which consisted mainly of fatty and resin acids, were assumed to be potential precursors to deposits found on the surfaces of peat and bark dryers.

Functional forms of nitrogen in coals and the release of coal nitrogen as NO x precursors (HCN and NH 3)

The influence of coal nitrogen on the pyrolytic release of NOx precursors, (HCN and NH3), has been investigated for a range of Australian coals. Functional forms of nitrogen in the coals were determined by X-ray photoelectron spectroscopy. Pyrrolic-type nitrogen predominated (50–60% coal nitrogen), but pyridinic and quaternary forms were also detected. The proportion of pyridinic increased and that of quaternary decreased with increasing carbon contents of the coals. Four coals, ranging in rank from brown to bituminous and in nitrogen content from 0.6–2.0%, dry ash free basis, were pyrolyzed in a fluidized bed reactor at temperatures ranging from 500 to 1100°C, gas residence times of 0.3–0.5 s and particle heating rates of 104 K s−1. Formation of HCN and NH3 occurred at higher temperatures than that required for maximum tar yields; cracking reactions of the tars are a probable source of HCN and NH3. However, the results show that release of nitrogen from structures which are not volatilised as tar also occurs. The major nitrogen-containing components of the tars were identified and quantified by gas chromatography. Nitrogen contained in pyridinic groups was more stable than that in pyrrolic groups; thus, a higher pyrolysis temperature was necessary to release nitrogen as HCN and NH3 from the pyridinic groups. For the range of coals and pyrolysis conditions studied here, however, nitrogen release (as a proportion of total coal nitrogen), in the form of NOx precursors, did not depend on coal type or coal nitrogen content.

Organic compounds released in fluidized-bed drying of peat, bark and lignite

Organic compounds released in peat drying in a laboratory fluidized-bed reactor were analyzed by chromatographic methods in order to evaluate process operational and environmental aspects. For comparison, pine bark and lignite were also studied. Using steam as fluidizing gas, the release of condensable organic compounds comprised 2% and 25% of peat, calculated on a dry ash-free basis, when drying peat for 0.5 s at 190 and 350 °C, respectively. The corresponding release of noncondensable gaseous components was 1% and 6% at these temperatures, and carbon dioxide accounted for over 70% of the total non-condensable gases. The release of organic compounds at 250°C from peat was nearly four-fold and fifty-fold compared with that of bark and lignite, respectively. The organic materials released from peat were mainly aliphatic mono- and dicarboxylic acids (C 1−C 28), methanol, aliphatic aldehydes, anhydroglucoses and furanoic compounds.

Correlation of gasification rates of various coals measured by a rapid heating method in a steam atmosphere at relatively low temperatures

Twenty-five kinds of coals (carbon content on dry ash-free basis, C[%], ranges from 65.0 to 92.8%) were pyrolysed and gasified simultaneously by use of a rapid heating method (heating rate ≈ 1600 K min −1) in steam at temperatures between 750 and 850 °C to clarify the factors which control the gasification rates of various coals. The relationships were examined in detail between the reactivity of each coal, represented by the initial gasification rate − r cm0, and various properties such as pore surface area of char, ultimate and proximate analyses of coal, reflectance of coal, contents of metals in char, and the amount of oxygen trapped by char. For gasification at 800 °C, the relation between − r cm0 and the carbon content C[%] changed abruptly at C ≈ 75–80%. For higher rank coals ( C > 75–80%), − r cm0 was rather small and was well correlated by C[%]. On the other hand, the plot of − r cm0 versus C % scattered largely for the lower rank coals ( C < 75–80%). For these coals, the rate of CO 2 formation was much greater than that of CO formation, and was almost proportional to − r cm0. The CO 2 formation reaction is known to be catalysed by alkali or alkaline earth metals such as Na, K and Ca. Then the reactivities of lower rank coals were supposed to be controlled mainly by the catalytic effect of the minerals in the coal.

The self heating of commercial powdered activated carbons

AbstractThe self heating characteristics of a series of activated carbon samples have been studied in relation to their chemical/physical properties. It appears that ease of self heating is related to the oxygen content of the carbon on a dry ash free basis, and from this it can be shown that all carbons manufactured by the steam activation process can be considered non‐hazardous for shipping purposes.A simple test is described to differentiate between the potentially hazardous and non‐hazardous in chemically activated carbons and semi‐products.The results of this investigation are fully supported by the shipping records over the past 40 years of European carbon manufacturers who are responsible for over 50% of activated carbon shipped world wide.

Dispersibility of Coal in a Supersonic Field

IN the course of experiments on the solubility (or dispersibility) of coals in organic solvents, it was observed that the pyridine-insoluble (α) fraction of a Northumberland coal (82·6 per cent carbon and 5·1 per cent hydrogen on the dry ash-free basis) became partially dissolved (or dispersed) when suspended in pure dry pyridine and exposed to supersonic waves (c. 25 kc./sec.) for 15 min. When the extract thus formed was recovered by removal of the solvent under reduced pressure in an atmosphere of dry oxygen-free nitrogen, it formed a black, free-running solid that was only very slightly soluble in boiling pyridine. The elementary composition of this material was practically identical with that of the original α-fraction, both being reduced to the pure coal basis.

The devolatilization of coal seams in South Wales

In South Wales there is a pronounced regional devolatilization of the coals towards a major thrust—the Main Thrust—which is observable immediately beyond the north-western margin of the coalfield. There is also a subsidiary regional devolatilization towards the Gower zone of compression, but this is apparent only on the southern rim of the coalfield. In South Wales, as well as devolatilization in a horizontal plane, there is marked devolatilization of coal seams with depth. This devolatilization in a vertical plane is towards a plane of shear or of stress (inferred to be the underground extension of the Main Thrust) and is demonstrated by the trend and by the values of the coal-seam isovols. From the trend of the isovols it is deduced that at depth the plane dips gently, approximately towards the south-south-east. The proposition is propounded that the volatile content of a South Wales seam (dry ash-free basis) expressed as a percentage of the original volatile content of a true coal seam, varies with the square of the distance of the seam from the plane of shear or stress, and the following formula is deduced :— where V 1 represents the volatile content (expressed as a percentage as indicated above) of the upper seam; V 2 the volatile content of the lower seam; y the vertical distance in feet between the seams; θ the angle of inclination of an underlying plane of shear or stress. The formula is tested in 49 cases where the volatile contents of upper and lower seams in vertical sequence have been determined by chemical analyses. These cases cover the full range of coal types with vertical distances between the seams up to 2457 feet. The close degree of correspondence between the actual and calculated values constitutes a measure of the validity of the formula. A corollary to the formula is the recognition of a coal-type band for South Wales. With the aid of the formula, the South Wales anthracite field is delimited, and the net reserves are estimated at 4000 million tons.