Biomass gasification gas cleaning for downstream applications: A comparative critical review

Biomass is the only source on earth that can store solar energy in the chemical bond during its growth. This stored energy can be utilized by means of thermochemical conversion of biomass. Gasification is one of the promising thermochemical conversion technologies, which converts biomass to burnable gases, often termed as producer gas. Major components of this gas are hydrogen, carbon monoxide and methane. Depending on the purity, this gas can be used in the furnace for heat generation and in the internal combustion engine and fuel cell for power generation or it can be converted to liquid hydrocarbon fuels and chemicals via the Fischer-Tropsch synthesis method. Despite numerous applications of the biomass gasification gas, it is still under developing stage due to some severe technological challenges. Impurities such as tar, particulate matters and poisonous gases including ammonia, hydrochloric acid and sulfur gases, which are unavoidably produced during gasification, create severe problems in downstream applications. Therefore, the cleaning of producer gas is essential before being utilized. However, the conventional physical filtration is not a technically and environmentally viable process for gasification gas cleaning. The utilization of catalyst for hot gas cleaning is one of the most popular technologies for gas cleaning. The catalyst bed can reform tar molecules to gas on the one hand and destroy or adsorb poisonous gases and particulates on the other hand, so as to produce clean gas. However, numerous criteria need to be considered to select the suitable catalyst for commercial use. In this review, the advantages and disadvantages of different gas cleaning methods are critically discussed and concluded that the catalytic hot gas cleaning with highly efficient catalyst is the most viable options for large-scale production of clean producer gas.