Physicochemical Approach To Blend Biomass

Abstract

A physicochemical methodology for blending biomass to solve ash agglomeration in combustion processes has been used. The method is based on prediction of high melting point compounds by phase diagram and FactSage calculations coupled with experiments at laboratory and pilot scales. Experimental validation of the calculations was carried out by annealing at 1000 °C followed or not by air quenching at the laboratory scale, using either compressed ash or biomass pellets. Samples were characterized using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and powder X-ray diffraction. Two biomasses, oak bark, a sawmill residue, and wheat straw, an agricultural residue, were selected on the basis of their ash composition (rich in Ca, K, or Si). Several mixtures were selected with a minimum of the liquid phase calculated by thermodynamic equilibrium. The results show that the chemical reaction was obtained after annealing because new phases were obtained, whereas they were absent from the ashes of single biomasses. The mixture is not simply a dilution. A slightly smaller chemical reaction was observed in biomass pellets than in compressed ash. These results agree with the predictions, except for the K2Ca6Si4O15 ternary compound, absent from the thermodynamic databases but clearly identified in the ash of the 50:50 wheat straw/oak bark mixture. To our knowledge, it is the first time that this phase has been observed in biomass ashes. It has been recently observed in phase equilibria and crystallographic studies. This underlines the interest of the predictions but also the need to improve existing thermodynamic databases, especially on the CaO–K2O–SiO2 system.

K4CaSi6O15—Solving a 90‐year‐old riddle

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“…29,30 The physics of resin flow into a mold under pressure is similar to the seepage problem and so similar approaches have been used also to model the flow of resin into a mold containing fiber mats. 23,[31][32][33][34][35][36][37][38] The models are used in these cases to determine the resin flow front and mold filling times corresponding to different infiltration conditions.…”

“…On the Accepted Article other hand, the ternary system is also important for the interpretation of the properties and manufacturing of technical, as well as ancient glasses [17][18][19][20] . Furthermore, detailed knowledge concerning the solid-state characteristics of the existing crystalline compounds occurring in the system K 2 O-CaO-SiO 2 is of essence for the identification of these phases in technical products 16,[21][22][23] . Likewise, the results from experimental phase analytical studies represent an indispensable input for any kind of thermodynamic modelling including database development for slag relevant oxides [24][25][26][27] .…”

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“…[17][18][19][20] Furthermore, detailed knowledge concerning the solid-state characteristics of the existing crystalline compounds occurring in the system K 2 O-CaO-SiO 2 is of the essence for the identification of these phases in technical products. 16,[21][22][23] Likewise, the results from experimental phase analytical studies represent an indispensable input for any kind of thermodynamic modeling including database development for slag-relevant oxides. [24][25][26][27] In the course of our ongoing project to unravel the number of crystalline phases in the system K 2 O-CaO-SiO 2 , we found evidence that the so-called 2:1:6 phase (K 4 CaSi 6 O 15 ) reported by Morey et al 1 may, indeed, represent a valid and relevant composition for an existing potassium calcium silicate.…”