Experimental Study on Product Gas and Tar Removal in Air–Steam Gasification of Corn Straw in a Bench-Scale Internally Circulating Fluidized Bed

Abstract

Excessive consumption of fossil fuels and its negative global effects have resulted in increasing interest in biomass energy. This paper presents an experimental study on biomass gasification reactions in an internally circulating fluidized bed gasifier (ICFBG). This work uses compressed corn straw as the raw material and studies the influence of different factors (temperature, equivalent ratio (ER), catalyst, and S/B ratios) on gasification products, in which S/B ratios are defined as the ratios of the steam rate to the biomass feeding rate. The experimental results show that when the bed material is the coal ash residue and air is used as the gasification agent, an increase in temperature from 700 to 900 °C reduces the CO2 and CH4 contents, whereas the H2 and CO contents increase. When a gasification agent is air–steam and the temperature is maintained at 700 °C, with a gradual increase in the amount of steam supplied to the gasifier, the CO2 and H2 contents gradually increase. Besides, an increase in the temperature, S/B ratio, and mixing proportion of dolomite leads to a gradual decrease in the tar content as well as the proportion of light tar, while the proportion of heavy tar becomes relatively high. In addition, we obtained experimental data for an actual gasifier and conducted a brief comparative analysis with the ICFBG developed in this study. The results show that the data provided by the ICFBG developed in this study can serve as a reference and theoretical basis for the operation of actual gasifiers in power plants.

A comprehensive review of primary strategies for tar removal in biomass gasification

“…They observed that tar composition evolves with increasing temperature to more stable species in the range of secondary and tertiary tar (of higher molecular weight) due to the rearrangement reactions at the expense of the reduction or absence of tar containing branched or heteroatom compounds. Similar results have been reported in the literature [166,175,176].…”

“…Two bed materials were tested and a considerable tar reduction was attained when gasification runs were conducted at 900 • C (they reported tar values of 2.17 and 0.15 g Nm − 3 with silica sand and coal bottom ash, respectively). Guo et al [166] reported a tar reduction to one third (from 6.2 g Nm − 3 at 700 • C to 2.02 g Nm − 3 at 900 • C) in the corn straw gasification conducted in a bench-scale internal circulating fluidized bed at the ER of 0.21. Rapagnà et al [163] conducted the steam gasification of almond shells in a fluidized bed using olivine as bed material.…”

A Review on Biomass Gasification: Effect of Main Parameters on Char Generation and Reaction

“…Besides, these large gas bubbles in the dense phase will suppress the diffusion rate of oxidizing mediums and thus reduce the total efficiency of char gasification in the reactor. Sometimes, a circulating fluidized bed is needed to alleviate these limitations of low carbon conversion ratio in the bubbling fluidized bed, via using a solid with a smaller size and the circulating loop to increase the residence time …”

“…Sometimes, a circulating fluidized bed is needed to alleviate these limitations of low carbon conversion ratio in the bubbling fluidized bed, via using a solid with a smaller size and the circulating loop to increase the residence time. 53 Figure 5 shows the hydrodynamics of gas−solid flow and the time history of biomass particles in a bubbling fluidized bed gasifier. Solid particles with great back mixing and excellent gas−solid mixing could allow the inner bed to have a uniform temperature and enhance the mass and heat transfer.…”

Fluidised Bed Gasification of Diverse Biomass Feedstocks and Blends—An Overall Performance Study

“…The gas composition should also be adapted to reach the synthesis process specifications (target H 2 /CO ratio usually). This can be performed by adapting the gasification conditions and the type of bed material [2], or by using catalysts in fixed beds after the gasification step [3].…”