Fluidized Bed Two-Stage Gasification Process for Clean Fuel Gas Production from Herb Residue: Fundamentals and Demonstration

Abstract

A new two-stage gasification process, decoupling complex biomass gasification from biomass pyrolysis and char gasification, has been proposed for the production of clean industrial fuel gas. In this work, Chinese herb residues will be used as raw material, and the fundamental studies and demonstration of this process were conducted on an externally heated laboratory two-stage gasification setup and an industrial demonstration plant, respectively. The fundamental studies found that the appropriate operation of the upstream fluidized bed (FB) pyrolyzer occurred at 700 °C and the suitable conditions for effective tar removal in the downstream gasifier were as follows: 850 °C, an equivalent ratio of air (ER) at 0.04, and a retention time of tar-containing fuel gas above 0.9 s. On the basis of these fundamental data, an autothermal demonstration plant treating 600 kg of herb residue per hour was built and successfully commissioned for its continuous running to verify the technology feasibility. The running data showed that the tar content in the gasified gas was as low as 400 mg/Nm3 at temperatures of 700 °C for the FB pyrolyzer and 850 °C for the transport fluidized bed gasifier. The produced fuel gas had a heating value of ∼5.0 MJ/Nm3. All of these displayed well the technical characteristics and demonstrated the process feasibility for this newly developed gasification technology.

Process analysis of a two‐stage fluidized bed gasification system with and without pre‐drying of high‐water content coal

“…After passing through the boiler, the fuel gas product is obtained by removing the fly ash further using a bag filter. [ 22 ] In cases without fuel pre‐drying, the coal with an original water content is directly fed into the pyrolyzer. The steam, that is used for fuel drying in the pre‐drying operations is outputted as a by‐product.…”

“…[5][6][7] For fuel gas production, fluidized bed gasifiers are more attractive and economical for applications in mid-and small-scale plants due to excellent heat/mass transfer, adaptability to low rank and wider particle size distribution of solid fuels. [8,9] Two-stage fluidized bed gasification (TSFBG) is an advanced gasification technology that consists of two subprocesses, namely, fuel pyrolysis and pyrolysis products gasification. By employing such a two-stage gasification technology, tars on the surfaces of chars produced in the pyrolysis process can be catalytically and/or thermally cracked in the high temperature gasification process; therefore, a fuel gas with a very low tar content can be produced, which is vital for industrial processes.…”

Green Waste/Wood Pellet Pyrolysis in a Pilot-Scale Rotary Kiln: Effect of Temperature on Product Distribution and Characteristics

“…Hence, tar removal and the increase of gaseous products yield from biomass are serious challenges. The two-stage combined pyrolysis-gasification appears to be effective for thermochemical biomass conversion producing an important gas yield, low tar contents and high biomass conversion rates 1,2 . In a combined pyrolysis-gasification process, biomass is pyrolyzed in the first stage and the pyrolysis gases (volatile products) are gasified or reformed in the second one 3,4 .…”

Analysis of gasification and tar reforming with in-situ generated char and steam

“…take place separately and sometimes unconventionally. Staged gasification has seen a growth in popularity because of the low tar yields (< 500 mg/Nm 3 ) and high carbon conversions (> 90%) obtained, and has been researched worldwide to different results (Leijenhorst et al, 2015;Henriksen et al, 2006;Zeng et al, 2016;Wang et al, 2007;Trippe et al, 2011). For example, the group led by Henriksen in the Technical University of Denmark (Henriksen et al, 2006;Gadsbøl et al, 2019) developed a pioneering staged gasifier system, where in contrast with conventional gasification, pyrolysis and char gasification occur in separate reactors.…”

“…For example, the Biomass Technology Group in the Netherlands (Leijenhorst et al, 2015) proposed the use of low temperature staged gasification using Ni and Pt-based catalysts, using an air-vapor mixing device with air entering the vapour steam through many small holes and three additional mixing devices to increase turbulence and found that increasing the turbulence during gasification resulted in changes in the hydrocarbons composing the tar mixture. Zeng et al (2016) proposed a design for an autothermal two-stage fluidised biomass gasification reactor; while the tar yields obtained from the experiments are still relatively high (around 400 mg/Nm 3 ), the proposed reactor has a relatively high capacity (600 kg/h) for a novel technology. Based on emerging approaches, the overall aim of this work is to numerically simulate and present a concept for the development of a novel staged-gasification system that uses a fluidised bed of char and steam generated in the gasifier itself.…”