Biomass is an important primary energy source as well as renewable energy source. As the most promising biomass utilization method, gasification/pyrolysis produces not only useful fuel gases, char and chemicals, but also some byproducts like fly ash, NOx, SO2 and tar. Tar in the product gases will condense at low temperature, and lead to clogged or blockage in fuel lines, filters and engines. Moreover, too much tar in product gases will reduce the utilization efficiency of biomass. Therefore, the reduction or decomposition of tar in biomass derived fuel gases is one of the biggest obstacles in its utilization for power generation. In this paper, we review the literatures pertaining to tar reduction or destruction methods during biomass gasification/pyrolysis. On the basis of their characteristics, the current tar reduction or destruction methods can be broadly divided into five main groups: mechanism methods, self-modification, thermal cracking, catalyst cracking and plasma methods.

The reduction and control technology of tar during biomass gasification/pyrolysis: An overview

Syngas from gasification of carbonaceous feedstocks is used for power production and synthesis of fuels and commodity chemicals. Impurities in gasification feedstocks, especially sulfur, nitrogen, chlorine, and ash, often find their way into syngas and can interfere with downstream applications. Incomplete gasification can also produce undesirable products in the raw syngas in the form of tar and particulate char. This paper reviews the technologies for removing contaminants from raw syngas. These technologies are classified according to the gas temperature exiting the cleanup device: hot (T > 300 °C), cold (T < ∼100 °C), and warm gas cleaning regimes. Cold gas cleanup uses relatively mature techniques that are highly effective although they often generate waste water streams and may suffer from energy inefficiencies. The majority of these techniques are based on using wet scrubbers. Hot gas cleaning technologies are attractive because they avoid cooling and reheating the gas stream. Many of these are still under development given the technical difficulties caused by extreme environments. Warm gas cleaning technologies include traditional particulate removal devices along with new approaches for removing tar and chlorine.

A review of cleaning technologies for biomass-derived syngas

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1076&context=biosysengfacpub

Switchgrass for Bioethanol and Other Value-Added Applications: A Review

Gasification of biomass is a promising source of fuels and other chemical products. However, the removal of tars, ammonia, hydrogen sulfide, and other byproducts from the raw gas is required. The gas clean‐up technology that offers more advantages is hot catalytic gas conditioning downstream of the gasifier reactor. Here, we review the applications of basic, acidic, metallic, and redox catalysts for the removal of such by-products and research strategies to prevent coke accumulation on the catalytic surface, to increase the resistance to sulfur poisoning, and to bring the by‐product removal reactions to temperatures below 600°C.

Hot Gas Removal of Tars, Ammonia, and Hydrogen Sulfide from Biomass Gasification Gas

Numerous reviews have been found related to individual studies on coal gasification (CG) and biomass gasification (BG). However, this review deals mainly with the CO-gasification (COG) of numerous types of coal and biomass and then compares their results with those obtained using coal and biomass gasification in detail. There are several process parameters which have a direct effect on the gasification process and among them temperature is the most significant one. In this paper, the production of H2, CO2, CO, CH4, and other hydrocarbons in CG, BG and COG with the variation of temperature is reviewed in detail. As it mainly influences the gaseous products and their characteristic behaviour, this review takes into account the effect of temperature on various other parameters such as carbon conversion, gas yield, calorific value, cold gas efficiency as well as tar and char contents in various kinds of coals, biomasses and their mixtures under catalytic or non-catalytic conditions.

The effect of temperature on various parameters in coal, biomass and CO-gasification: A review

We are investigating catalytic gasification of coal char using biomass-derived potassium salts. Alkali metal salts, especially those containing potassium, are excellent promoters of gasification reactions but are generally considered too expensive for commercial use. Fast-growing biomass, which contains large quantities of potassium, may prove to be an excellent source of inexpensive gasification catalyst. A series of CO2-char gasification tests were performed in a thermogravimetric analyzer (TGA) to evaluate the catalytic activity of alkali-rich biomass-derived materials. Both switchgrass char and switchgrass ash displayed catalytic activity in mixtures with coal char produced from Illinois No. 6 coal. The results obtained with switchgrass ash were especially impressive, with an almost eight-fold increase in coal char gasification rate at 895°C in a 10:90 mixture of coal char and switchgrass ash. These results give encouragement that biomass could be the source of inexpensive, coal gasification catalysts.

Qin Liu

Papers

Catalytic effects observed during the co-gasification of coal and switchgrass