Lignite char

Charcoal—sulfur processes need low ash hardwood charcoal, prepared at 400—500°C under controlled conditions. At the carbon disulfide plant site, the charcoal is calcined before use to expel water and residual hydrogen and oxygen compounds. This precalcination step minimises the undesirable formation of hydrogen sulfide and carbonyl sulfide. Although wood charcoal is preferred, other sources of carbon can be used including coal (30,31), lignite chars (32,33), and coke (34). Sulfur specifications are also important low ash content is necessary to minimise fouling of the process equipment. 

Material Lignite Char Gas Nitrogen Column Diameter 15 cm Velocity 0.46 m/s Bed Height 30 cm Particle Diameter ... 

Char nitrogen enrichment which occurs at low burnoff at 773 K, has been observed during the partial combustion of shale particles (4). The results at 798 and 823 K are in agreement with the results of Song 05) for the oxidation of a 1750 K lignite char at 1250 K. It appears that the rates of oxidation of char carbon and nitrogen are equal at the temperatures of interest in practical combustors. 

Pore structure can markedly affect char reactivity. Coals in general are highly porous with a polymodal pore size distribution. Pores normally are classified into macropores (>500 A in diameter), transitional pores (20-500 A in diameter), and micropores (<20 A in diameter). Upon pyrolysis, the pores in the coal open up, but the, char still contains microporosity. Coal chars in general, and lignitic chars in particular, retain coal s polymodal pore distribution. Surface areas of coal chars are in the range 100-800 m2/g. Most of this surface area and, therefore, most of the active surface reside inside the pores, so accessibility of reactive gases to active sites is very important. 

Catalysis of Lignite Char Gasification by Exchangeable Calcium and Magnesium... 

It is noted, however, that lignite char reactivity decreases rapidly as final heat treatment temperature increases (3,4) or as soak time at temperature increases ( ). Radovic and co-workers ( 5) have shown that the majority of this decrease can be correlated with a decrease in CaO dispersion in the case of Ca loaded demineralized (Dem) lignite chars. 

Exchangeable cations play an important role in the behavior of lignite coals in coal conversion processes. It is, therefore, important that a fundamental understanding be attained, first of the possible interaction of exchangeable cations in lignites with each other, and, second, of the possible effects on the subsequent catalytic activity of the cations for lignite char gasification. 

The addition of Mg to Ca does not have a significant effect on the subsequent activity of Ca for lignite char gasification under the slow heating conditions used in this study. Their catalytic effects were found to be additive, indicating that they did not interact in any significant way. This was supported by XRD results which showed that the sintering of CaO was not reduced by the presence of MgO. 

The adsorptive properties of carbon were well known long before the terms active and activated had been coined. In the early literature, data on the adsorptive properties appear under many varied names blood char, coconut char, bone char, lignite char, and others. More recently references appear under deco/orizing-carbon and also under various brand names (Table 1 2). 

An acceptor life study in the continuous unit was carried out as follows. An inventory of fresh acceptor, usually 16 X 28 mesh, was established in the regenerator while an inventory of 35 X 150 mesh devolatilized lignite char was established in the gasifier. The operating pressure was normally set at 300 p.s.i.a. The regenerator was heated to the desired temperature (usually 1910°-1940°F.) while fluidized with... 

Acceptor 16 X 28 mesh Tymochtee dolomite Char 35 X 150 mesh devolatilized lignite char System pressure, 20 atm. 

Huggins FE, Shah N, Huffman GP, Lytle FW, Greegor RB, Jenkins RG (1988b) In situ XAFS investigation of calcium and potassium catalytic species during pyrolysis and gasification of lignite chars. Fuel 67 1662-1667... 

Lee, J.K., et al.. Sulfur dioxide adsorption over activated lignite char prepared from fluidized bed pyrolysis, Chem. Eng. Sci., 49(24A), 4483-4490 (1994). 

A lignite char obtained by carbonisation in a stainless-steel, swept, fixed-bed reactor[9] was used to produce the activated carbons in the presence of CO2. This solid was produced in several batch reactions of 60 g of lignite particles (diameter 0.2 - 0.5 mm) with a heating rate of 8 C/min until 900+3 C and this temperature was held for 3 hours to ensure effective devolatilisation. A stream of 21/min of N2 was introduced to sweep the volatiles. 

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