Primary Release of Alkali and Alkaline Earth Metallic Species during the Pyrolysis of Pulverized Biomass

Abstract

Release of alkali and alkaline earth metallic (AAEM) species was examined during pyrolysis of pulverized pine and sugarcane bagasse. The use of a wire-mesh reactor enabled the investigation of the primary release of AAEM species from pyrolyzing particles suppressing secondary interaction between them. Upon heating the pine at 1000°C s -1 up to 800°C, 15-20% of each AAEM species was released during the tar evolution and afterward. Further isothermal heating caused nearly complete release of alkalis within 150 s, while the release of alkaline earths terminated at levels of 20-40%. Heating the pine at 1°C s -1 up to 800°C brought about the release of AAEM species mainly after the tar evolution. Chlorides of AAEM species were found to be very minor volatiles over the range of conditions. Variations in K release with operating variables were reasonably explained by considering that elemental K volatilized from the charbonded AAEM species was a major volatile K species. None of AAEM species were significantly released when a fixed bed of the pine was heated at 1°C s -1 up to 900°C without forced gas flow through the bed. It was suggested that repeated desorption from and adsorption onto the char surface within the fixed bed inhibited the release of AAEM species from the fixed bed and resultantly allowed them to transform into thermally stable char-bonded ones and/or nonvolatiles such as silicates.

Effects of Biomass Feedstocks and Gasification Conditions on the Physiochemical Properties of Char

“…A higher ER usually leads to a higher gasification temperature due to more heat generated from intensified oxidation. The increases in gasification temperature and amount of oxygen in turn increase volatilization of the minerals (K and Ca) [27] and reaction with the carbon during gasification. The intensified oxidation with increase in ER would also consume more biomass carbon, reducing the carbon content of char and thus increasing the mineral contents in the char.…”

Biomass derived tar decomposition over coal char bed

“…So it could be assumed that the increased K content in the spent char600 might be due to the formation of the phenolate group (K−O−C) that bonded between the released K from rice straw and carbon matrix of coal char [25][26][27] . The phenolate group has been reported to be a catalytic species for carbon-steam reaction [27][28][29][30] . At the same time, the volatilization of AAEM over the coal char surfaces was promoted by the H-radicals which released from the thermal cracking of rice straw derived volatiles, following the reaction:…”

Absorption of Microwaves in Low Intensity Eucalyptus Litter Fire

“…During vegetation combustion, volatile K and Na species diffuse and attach to oxygen containing carboxyl groups in charcoal matrix forming organo-alkali structures such as K-O-C [11]. The high combustion rates (up to 100 Ks −1 ) combined with forced gas convection of light gases such as hydrogen radical (H + ) through the organic structure facilitate rapid evolution of alkali atoms from the thermally decomposing charcoal into the flame.…”

“…The high combustion rates (up to 100 Ks −1 ) combined with forced gas convection of light gases such as hydrogen radical (H + ) through the organic structure facilitate rapid evolution of alkali atoms from the thermally decomposing charcoal into the flame. This occurs when H + and other light volatiles react with the alkali containing carboxyl groups to displace alkali atoms from charcoal attachment sites [11]. The released alkali atoms (e.g., Na(g)) are excited by heat and consequently collide with other excited flame particles.…”