Release of K, Cl, and S during Pyrolysis and Combustion of High-Chlorine Biomass

Abstract

The release of critical ash-forming elements during the pyrolysis and combustion of corn stover has been investigated through controlled lab-scale experiments supported by multicomponent and multiphase thermodynamic equilibrium calculations. Fuel samples were treated under isothermal conditions ranging from 500 to 1150 °C, under both pyrolysis and combustion atmospheres. The volatilized material was quantified by means of mass balances based on char and ash elemental analysis, compared to a corresponding feedstock fuel analysis. Close relations between the observed K and Cl release are found, suggesting that Cl is the main facilitator for K release through sublimation of KCl, determined to begin as the reaction temperature approaches 700À800 °C. K is present in abundance relative to Cl, and the K release is found to cease as the fuel reaches complete dechlorination. In addition, around 50 wt % of the Cl is released at temperatures below 500 °C, presumably as HCl formed through ion-exchange reactions with functional groups in the organic matrix. Complete dechlorination was achieved under combustion conditions as the temperature exceeded 800 °C. Approximately 50 wt % of the feedstock S is released at temperatures below 500 °C. This low-temperature release is related to the decomposition of the organic matrix, releasing the organically associated S. Under combustion conditions, the S release increases gradually at temperatures exceeding 800 °C, eventually reaching complete desulfurization at 1150 °C. The silicate/ alumina chemistry is found to play a significant role in the alkali retention. The Si-rich sample is capable of retaining all excess K not released as KCl.

High Temperature Corrosion under Laboratory Conditions Simulating Biomass-Firing: A Comprehensive Characterization of Corrosion Products

“…Although the Reaction 6 is thermodynamically favourable (∆G = -683 kJ(T = 500 o C) and -617 kJ(T = 600 o C)) [45], it is still unknown if the initiation process under straw-firing conditions proceeds according to the route in equation (1) and (2), which results in K2CrO4-formation, or through the additional stage according to equation (6). To substantiate this, pure K2CrO4 crystals were exposed in the present work to similar conditions simulating straw-firing.…”

“…Since biomass contains significant amounts of flame-volatile alkali metal salts [6][7][8][9], the ash deposit challenges from combustion of these fuels differ considerably from fossil fuels. Through diffusion, thermophoresis, condensation or inertial impaction, gaseous alkali species, alkali-rich aerosols and fly ash particles are able to form thick deposits on cooler parts of the heat exchangers, where heat is transferred from the hot flue gas into the steam cycle [10][11][12][13].…”

Effect of Charcoal and Kraft-Lignin Addition on Coke Compression Strength and Reactivity

“…However, with addition rates up to 10%, their total input increases only moderately (S, Na), or even decreases (K) due to the low ash amount. Furthermore, organically-associated sulfur in Kraft-lignin can be partially released in the carbonization stage [42], enhancing its metallurgical properties. In future studies, attention should be placed to the hot strength of the bio-cokes, as done in [24,25] for different coke grades.…”

Chemical Characterization and Source Apportionment of Household Fine Particulate Matter in Rural, Peri-urban, and Urban West Africa

“…Biomass smoke is primarily characterized by K, Cl, S, and BC. 25,26 Potassium in biomass smoke is emitted mostly as potassium salts such as KCl and K 2 SO 4 ; with aging, most KCl particles are converted to K 2 SO 4 . 24,37 Road dust and traffic emission are characterized by Al, Si, Ca, Fe, Zn, and BC.…”