Abstract
Filtering-catalytic candles, filled with an annular packed-bed of commercial Ni-catalyst pellets (∼600 g), were successfully tested for in situ syngas cleaning in a fluidized-bed biomass steam gasifier [Fuel Process. Technol.2019, 191, 44−53, DOI: 10.1016/j.fuproc.2019.03.018]. Those tests enabled the macroscopic evaluation of gasification and gas cleaning as a whole, requiring a more specific assessment of the catalyst performance inside the filter candle. To this end, steam reforming tests of tar key compounds (naphthalene and toluene; thiophene in traces to observe sulfur deactivation) were performed with a laboratory-scale packed-bed reactor containing the same catalyst pellets (<7 g). A lumped kinetics was derived, referred to a pseudocomponent representing tars. This was then validated by simulation of the annular catalytic packed bed inside the filter candle, obtaining numerical results in fair agreement with gasifier outputs. As a result, the lab-scale investigation with a small amount of catalyst provides reliable predictions of tar catalytic reforming in industrial-scale filtering-catalytic candles.
Highlights
Biomass attracted the attention of researchers and industry for applications in energy and biofuels production.[1−4] This interest was driven by several governmental programs, promoting the use of renewable sources and biofuels:[1] The European Union (EU) set the goal of a 10% share of biofuels in the transport industry by 2020;5 in the USA, the production of biofuels is expected to reach 36 billion gallons by 2022.6 This kind of policy, which has continued in the EU by the passing of European green deal,[7] might represent in the near future a viable means for economic growth, as well as a necessary approach to face the issues related to climate change.[1,8]
This work aims to fill this gap by three complementary approaches: (i) investigating the activity of the same Ni-based catalyst pellets utilized by Savuto et al.,[24] by means of a laboratory-scale packed-bed reactor rig for the steam reforming of synthetic tar mixtures; (ii) inferring a lumped kinetic law for tar steam reforming, assuming a generic tar mixture to be represented by a carbonaceous pseudocomponent (Ctar), the carbon atoms of which are involved in the steam reforming process; and (iii) validating the kinetic model so developed, by simulations of the behavior of a full scale filtering-catalytic candle segment, placed in the gasifier freeboard
Weight hourly space velocities (WHSV, eq 12) and WHSV referred to Ctar (WHSVCtar, eq 13) were higher than those experienced by Ni-catalyst pellets in the filtering-catalytic candles during hot gas cleaning in the gasifier freeboard of Savuto et al.;[24] this allowed testing the catalyst in more severe conditions and getting data suitable for the kinetic characterization
Summary
Biomass attracted the attention of researchers and industry for applications in energy and biofuels production (e.g., methanol, ethanol, mixed alcohols, dimethyl ether, synthetic natural gas, and hydrogen).[1−4] This interest was driven by several governmental programs, promoting the use of renewable sources and biofuels:[1] The European Union (EU) set the goal of a 10% share of biofuels in the transport industry by 2020;5 in the USA, the production of biofuels is expected to reach 36 billion gallons by 2022.6 This kind of policy, which has continued in the EU by the passing of European green deal,[7] might represent in the near future a viable means for economic growth, as well as a necessary approach to face the issues related to climate change.[1,8]Steam gasification of biomass is a relevant route to produce syngas, and biofuels, with a reduced environmental footprint;[1] the cleaning of raw syngas, mainly consisting of removal of particulate and tar, is a key step of the biomass-to-fuel chain, which has not been fully developed yet.[9,10] This work deals with the issue of tar removal.A fluidized-bed gasifier, using biomass as a fuel, produces tars in the order of magnitude of a few g Nm−3,9 which leave the reactor in the form of vapors or aerosol, along with main gaseous products (H2, CO, CO2, CH4, and H2O).[11]. Steam gasification of biomass is a relevant route to produce syngas, and biofuels, with a reduced environmental footprint;[1] the cleaning of raw syngas, mainly consisting of removal of particulate and tar, is a key step of the biomass-to-fuel chain, which has not been fully developed yet.[9,10] This work deals with the issue of tar removal. Catalytic steam reforming seems to be the best way to eliminate tar compounds, converting them into additional syngas and recovering their energy content, while reducing the amount of pollutants in gasification products.[13,14]
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