Online Measurements of Alkali and Heavy Tar Components in Biomass Gasification

Abstract

Tar and alkali metal compounds are released during biomass gasification and have a major impact on the operation and performance of gasification processes. Herein we describe a novel method for characterization of alkali and heavy tar compounds in the hot product gas formed during gasification. Gas is continuously extracted, cooled and diluted, which results in condensation of tar and alkali into aerosol particles. The thermal stability of these particles is subsequently evaluated using a volatility tandem differential mobility analyzer (VTDMA) method. The technique is adopted from aerosol science where it is frequently used to characterize the thermal properties of aerosol particles. Laboratory studies show that pure and mixed alkali salts and organic compounds evaporate in well-defined temperature ranges, which can be used to determine the chemical composition of particles. The performance of the VTDMA is demonstrated at a 4 MW th dual fluidized bed gasifier using two different types of online sampling systems. Alkali metal compounds and a wide distribution of heavy tar components with boiling points above 400 °C are observed in the product gas. Implications and potential further improvements of the technique are discussed.

Mini-Review on Hot Gas Filtration in Biomass Gasification: Focusing on Ceramic Filter Candles

“…45 Currently, the literature concerning the soot mechanism from a biomass gasification is still very limited. 42 Gall et al 40 developed a volatility tandem differential mobility analyzer (VTDMA) method for the characterization of alkali and heavy tar compounds in the hot product gas formed from a 4-MWth dual fluidized-bed (DFB) gasifier. As shown in Figure 6, the volatile fractions consisting of different tar and alkali compounds evaporate, and the particle size decreases with the increasing temperature of the product gas.…”

“…Both online and offline instruments had been used to characterize the nanosized aerosol PMs in the hot product gas from biomass gasification, ,, and particle size distributions with two distinct modes were established . The fine mode (15–140 nm, 640 mg/m 3 , 2 × 10 10 PMs/cm 3 ) was supposed to contain mainly heavy tars formed through a homogeneous nucleation and condensation on alkali nuclei; another intermediate mode (140–670 nm, 38 mg/m 3 , 4.3 × 10 6 PMs/cm 3 ) was assumed to be a mixture consisting of original PMs formed by condensed alkali vapors and tars from the gasifier .…”

“…Remaining volume fraction of size-selected particles sampled from a DFB gasifier (points) as a function of oven temperature. Results from laboratory experiments (lines) are included for comparison . Reproduced with permission from ref .…”

“…Results from laboratory experiments (lines) are included for comparison . Reproduced with permission from ref . Copyright 2017 ACS.…”

Characterization and Reactivity Study of Coal Bottom Ash for Utilization in Biomass Gasification as an Adsorbent/Catalyst for Cleaner Fuel Production

“…8 Gasification is a promising method for fuel production but it still faces problems of product gas quality and the formation of unwanted products like higher hydrocarbons (tar) that not only affect the product yield but also cause operational problems like clogging, deposition, and sintering. 13 In the past two decades, catalytic gasification technology has gained attention due to its potential to improve the product gas quality and minimize the byproduct formation. The catalyst used for gasification must-have attributes, such as low cost, thermal and chemical stability, ability to improve the selectivity of products like syngas or methane, reduction in tar formation, and long life span.…”