Using Ilmenite To Reduce the Tar Yield in a Dual Fluidized Bed Gasification System

Abstract

Biomass gasification plays an important role in the emerging production of second-generation biofuels. One of the major challenges facing biomass gasification is to find simple and efficient ways to reform tar components. While the tar causes operational problems, it can be reformed to increase the chemical efficiency of the gasification process. With respect to tar reforming, catalytic materials are of special interest. Many of the materials that have been proposed as promising catalysts are metal oxide-based materials. However, metal oxides also have the ability to transport oxygen when subjected to alternating oxidizing and reducing atmospheres, similar to that which occurs in a dual fluidized bed gasification system. In this work, ilmenite was used as the catalytic material in the Chalmers 2–4 MWth dual fluidized bed gasifier to decrease the yield of tar. The ilmenite was mixed with the silica sand, which was used as the bed material, to investigate how the level of ilmenite affected chemical efficiency and tar yield. Furthermore, energy balance calculations were established to elucidate the general aspects of oxygen transport in dual fluidized bed gasification systems. The results presented in this paper reveal that adding low levels of ilmenite reduces the tar yield by ∼50%mass. However, the oxygen transport induced by ilmenite caused a reduction in the chemical efficiency of the gasifier and the heating value of the gas, compared to using 100% silica sand as the bed material. The impact of adding ilmenite was found to be dependent upon the operational conditions of the gasifier; a low fluidization velocity gave the highest reduction of the tar yield, whereas higher fluidization velocities led to increased levels of heavy components. Overall, the use of ilmenite as a catalyst for reduction of the yield of tar appears promising, provided that the level of oxygen transport can be restricted.

Characteristics of olivine as a bed material in an indirect biomass gasifier

“…Considering that silica sand is commonly used as the bed material in the Chalmers unit, the results obtained in the present study for the yields of tar in the produced gas can be compared to the reference case described by Larsson et al [38]. In Fig.…”

Bark as feedstock for dual fluidized bed gasifiers-Operability, efficiency, and economics

“…Silica sand can also cause agglomeration, which causes problems for both the activity and operation of the fluidized bed. 34,35 The dirt and sand contaminating the shredded bark explain why there is a relatively large difference in Si, K, and Ca in the ash between the three different measurement days.…”

“…Traces of silica in the bed should be avoided, as silica absorbs potassium very effectively, permanently reducing the overall bed material activity. Silica sand can also cause agglomeration, which causes problems for both the activity and operation of the fluidized bed . The dirt and sand contaminating the shredded bark explain why there is a relatively large difference in Si, K, and Ca in the ash between the three different measurement days.…”

Investigations into the effects of volatile biomass tar on the performance of Fe-based CLC oxygen carrier materials

“…A large proportion of biomass/CLC research has focused on the development of bio-syngas upgrading/ tar removal systems [24,30,31]. Larsson et al [32] studied ilmenite as a tar cracking catalyst to upgrade biosyngas from gasification of woody biomass in a 2-4 MW th interconnected fluidized bed system. Adding small (∼12 wt%) amounts of ilmenite to a solids inventory of sand reduced the tar yield by ∼50 wt%, but reduced the cold gas efficiency by 10%.…”