Amir Abolhassani Ph.D. student; University of Saskatchewan

Energy from "Biomass"

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Biomass (wood) has been combusted to produce heat but after 17th century and with tangible shortage of wood and coal in populated industrial cities other methods of energy production were investigated. These procedures can be classified into two major groups: (1) thermochemical processes, which use heat and catalysts and (2) biochemical processes, which use microorganisms and enzymes.

The main objective of gasification is to produce syngas that is a mixture of carbon monoxide (CO) and hydrogen (H2). Syngas is used in Fischer-Tropsch synthesis to produce liquid fuels. Unconverted inorganic portion or ash, water (H2O), CO2, methane (CH4) and higher alkanes, tar or heavy hydrocarbons, N2, NOx and SOx are other compounds in the product, which will be omitted during the process development. Gasification has many benefits compared to other fuel production processes. The wide range of feedstock that can be utilized, variety of products, low flue gas production and low to zero emissions of CO2 and NOx are some of the advantages. It can produce high efficiency when combined in power cycles. The use of biomass in gasification process has the benefit of omitting the need to extract or import fossil fuels and it has no net CO2 contribution to the atmosphere. Gasification is a complex, multi-zone process and it is currently difficult to control the process. Purification cost of the products is a drawbacks and tar formation is current challenge in the feasibility of gasification plants.

Catalytic Biomass gasification

Tar formation is one of the main challenges in gasification. Heavy hydrocarbons condense on pipelines and block the flow. Many gasifiers operate at high temperatures to reduce the probability of tar formation or break the bonds of heavy hydrocarbons. High temperature necessitates special gasifier materials, lower efficiency and extra energy input. These outcomes threaten the economy of gasification especially if this extra energy cannot be recovered. A successful approach is to use catalysts to lower gasifier operating temperature and participate in tar cracking reactions. They can also facilitate or prevent the formation of certain components e.g. increasing the H2/CO ratio in the product or suppressing methane production. Added cost of catalyst, catalytic activity reduction over time and difficulty in recovering and recycling of the catalyst are some of the issues in catalytic gasification. Another impediment is fouling and poisoning of the catalyst during the process. Coke formation, which is a common phenomenon inside the gasifier can reduce the activity of the catalyst by blocking the pores or covering active sites.

A proper catalysts for biomass gasification besides being cheap and having no toxicity must be able to convert tars to gas products effectively but also provide acceptable syngas ratio. It should be active in presence of NOx and SOx and have participate in methane reforming reactions. Being resistant to attrition and deactivation due to sintering, poisoning or carbon fouling and ability of be regenerated easily are some of other properties of a good catalyst. web templates All catalysts used in catalytic gasification of biomass can be classified in five groups:

natural minerals, alkali metal catalysts, iron based catalysts, nickel based catalyst and novel tri-metallic catalysts
  • natural minerals
  • alkali metal catalysts
  • iron based catalysts
  • nickel based catalyst
  • novel catalysts such as tri-metallic catalysts

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