Interactions of Olivine and Silica Sand with Potassium- or Silicon-Rich Agricultural Residues under Combustion, Steam Gasification, and CO₂ Gasification

Abstract

Interactions between olivine or silica sand and potassium (K)-rich grape marc or silicon (Si)-rich wheat straw were studied in a fixed-bed reactor under combustion, steam, or a CO 2 gasification atmosphere. This study focused on the effects of atmosphere composition, feedstock, and bed material type on the thermochemical aspects of agglomeration. The agglomeration extent of grape marc with olivine as the bed material under air and steam atmospheres is significantly less than with silica sand. The presence of CO 2 , compared to that of O 2 or steam, was found to promote the reaction between K and olivine by facilitating the production of reactive silica from olivine carbonization. The use of olivine promotes the release of K by more than 10% compared with silica. No significant differences were observed in the agglomeration extent of wheat straw in its interaction with either olivine or silica sand. Nevertheless, olivine alters the agglomeration mechanism of wheat straw to become "melting-induced" from "coatinginduced" in a silica bed.

Agglomeration of Olivine with Potassium- or Silicon-Rich Agricultural Residues Under Conditions Relevant to Dual Fluidized Bed Gasification

“…The previous study of grape marc with olivine sand using a fixed-bed reactor showed that greater agglomeration is induced under the CO 2 gasification atmosphere compared to that under air and steam, which was associated with the carbonization of olivine. 60 However, the present investigation with the same feedstock and bed material indicated an inhabitation of the agglomeration process due to a restricted char conversion process under the CO 2 atmosphere compared with steam. Such difference revealed that CO 2 as the gasification agent can influence the reactivity of olivine sand as well as the extent of transformation of K contents in the char particles, both of which are required to drive the agglomeration process to occur.…”

“…Our previous study of similar feedstock showed that the wheat straw exhibits a higher degree of sintering than the grape marc under the same thermal conditions. 60 The presence of molten char particles with a large specific outer surface area can cause many bed particles to adhere rapidly and cause bed agglomeration, which can explain the rapid bed defluidization that occurred during the combustion of wheat straw. Figure 10b presents the magnified cross-sectional image of an agglomerate in the size range of 0.212−0.355 mm.…”

“…No pelletization was needed for the grape marc samples, as they exhibited no 1, which have been reported in the previous study. 60 Raw olivine sand was used as the bed material and was obtained from a mining site in Vienna, Austria. The olivine particles were sieved to a size range of 0.075−0.212 mm, whose properties are shown in Table 2, which have been reported in the previous study.…”

Review of Biomass Agglomeration for Fluidized-Bed Gasification or Combustion Processes with a Focus on the Effect of Alkali Salts

“…In addition, for the marine macroalage, the steam atmosphere leads to more low-melting-point alkali silicates when compared with the air/N 2 atmosphere. Li et al also concluded that, for grape marc, the steam atmosphere retains more K in the agglomerates when compared with a CO 2 /N 2 (50% (v/v) CO 2 ) or air/N 2 (5% (v/v) O 2 ) atmospheres. For olivine sand, agglomerates are formed under the CO 2 /N 2 (50% (v/v) CO 2 ) atmosphere due to the formation of amorphous silica by the reaction between forsterite with CO 2 .…”

Characterization of Ashes from Co-Firing Biochar with Coal under Pulverized-Fuel Conditions

“…Biomass can be a sustainable feedstock for future energy security and sustainable development depending on its production, for example, mallee biomass in rural and regional Australia. , Direct combustion of biomass is a mature technology for power generation. − Recycling nutrients in ashes from biomass combustion to the soil is important for the sustainable development of a biomass-based industry. This is possible for mallee biomass combustion because all the inorganic elements (nutrients and toxic trace elements, if any) are uptaken from the soil during tree growth.…”