Influence of In-Bed Catalysis by Ash-Coated Olivine on Tar Formation in Steam Gasification of Biomass

Abstract

The use of catalytic bed materials represents a state-of-the-art solution for controlling the concentration of tars in fluidized bed biomass steam gasifiers. Ash-coated olivine is commonly applied as a bed material in gasifiers, owing to its relatively high catalytic activity towards tar species. However, the mechanisms and conversion pathways that are influenced by the ashcoated olivine used as an in-bed catalyst are not fully understood. The present work examines how ash-layered olivine prevents the formation of biomass-derived tar at an early stage of their formation. Tests involving olivine at different stages of activation and at different temperatures were carried out in the Chalmers 2-4-MWth DFB gasifier. A detailed characterization of the tar and light hydrocarbon fractions is presented and discussed in relation to the sources of the aromatic species. It is concluded that the ash-coated olivine prevents the formation of aromatic tar species by promoting steam reforming of early tar precursors. Gas-phase interactions of the early tar precursors and bed material contribute to the observed tar reduction. The results indicate that olivine interferes with the cyclization routes that involve C2H2 and C3 hydrocarbons.

Syngas for biorefineries from thermochemical gasification of lignocellulosic fuels and residues—5 years’ experience with an advanced dual fluidized bed gasifier design

“…However, an intermixture of limestone is favorable for the gasification process. The addition of 10-20% limestone to the main bed material olivine seems to have the same effect as the activation [59,60] or calcium/ash layer formation [8,61] on olivine particles during long-term gasification operation at industrial plants. Therefore, most of the presented test runs were conducted with pure limestone or bed material mixtures with the addition of limestone.…”

“…The advantage of olivine is its catalytic activity due to the formation of calcium-rich layers on the surface of the particles during long-term operation. These layers are formed due to the interaction of bed material particles with ash from the biomass and improve the catalytic activity, which is especially important in tar-destruction processes [60,61,73]. Since olivine is relatively expensive, and its availability is regionally limited, the focus of many investigations is on finding alternative bed materials that are inexpensive and available worldwide.…”

Dual Fluidized Bed Gasification Configurations for Carbon Recovery from Biomass

“…Measurement System. The measurement system of the Chalmers DFB gasifier has been extensively described by Berdugo Vilches et al 48 Only a brief summary is given here. A slipstream from the raw gas is extracted and filtered to remove the particulate matter.…”

“…The first substream is quenched with cold isopropanol to remove the tar and moisture and is then sent to a microgas chromatograph, where the composition of the dry gas is analyzed. The tar is sampled from that same substream, prior to its quenching, using the solid-phase adsorption method, which has been described by Israelsson et al The elution of the adsorption columns and the analysis of the eluate are described elsewhere. , The second raw gas substream is cracked in a high-temperature reactor (HTR) at 1700 °C to produce a syngas that consists exclusively of H 2 , CO, CO 2 , and H 2 O. This enables the quantification of the degree of gasification, as well as of the amount of carbon in the form of hydrocarbons with more than three carbon atoms, referred to as “TOC” in Table .…”

Layer formation on K-feldspar in fluidized bed combustion and gasification of bark and chicken manure

“…A kinetic rate expression was empirically derived for olivine after an ash-rich layer has formed [11]. Berdugo Vilches et al proposed a first overview of the main transformation reactions pathways of tar species when olivine, activated through interaction with ash components, is used as in-bed catalyst [12]. Optimization of the operation of an industrial-scale DFB steam gasification plant based on the activation of the bed material through interaction with feedstock ash was reported by Kuba et al [13].…”