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Dual fluidized bed gasification (DFBG) technology requires a combination of two fluidized beds. Fluidized bed (FB), on the other hand, has different types depending on, for example, the gas velocity inside the bed. The present article intends to clarify what types of FBs should be chosen for the FB combination of the DFBG in terms of improving gasification efficiency and enhancing tar-destruction capability. Gasification tests in a 5.0 kg/h pilot gasification plant demonstrated that under the same conditions the combination of a dense low-velocity FB (LVFB) fuel gasifier and a high-velocity pneumatic riser (HVPR) char combustor allowed higher gasification efficiency and lower tar production than the combination of an HVPR fuel gasifier and an LVFB char combustor did. Consequently, the article concludes that the superior technique choice for the DFBG is to deploy its fuel gasification into an LVFB and its char combustion into an HVPR. An HVPR char combustor is necessary because it maintains the steady circulation of particles between the two involved beds. The ProblemDual fluidized bed gasification (DFBG) technology for solid fuels such as coal and biomass is catching an increasingly greater interest of academic researchers and industrial engineers because the technology can provide N 2 -free feedstock for chemical synthetic processes 1 and produce CO 2 -captured H 2 -rich product gases. 2 This has resulted in various DFBG systems devised and put into technical development. Figure 1 displays a recently proposed conception based on the DFBG idea, which was disclosed in a NEDO-financed technical program. 3 The proposal intended to build a biomass DFBG technology with a compact configuration that integrates the involved two fluidized beds into one unit. The base of the unit, i.e., the first reactor of the system, is a fluidized bed (FB) operated in the dense bubbling/ turbulent fluidization regime. Seating on the base FB (usually at its vertical center), another reactor is a pneumatic riser upward prolonged and having its bottom section immersed in the particle bulk of the base FB. The base FB and the riser have independent cyclones. The solid particle circulation between both beds is via the cyclone of the riser and the interstice between the riser bottom and the distributor of the base FB.As illustrated in Figure 1a, the original design feeds biomass fuel into the pneumatic riser. Corresponding to this, steam is injected into the riser as the fluidizing gas and gasification reagent. Through contact with hot sand, the heat carrier particles (HCPs) from the base FB, the fuel is pyrolyzed and further its resulting char is gasified by reacting with steam reactant inside the riser. As shown in the figure, the produced gas is independently drawn out of the system as the product gas, while the unreacted char, captured in the cyclone of the riser, is returned to the base FB with the HCPs to bring about therein the exothermic char combustion and in turn to reheat the HCPs. Because the base FB has its independent exhaust, t...

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Calcium oxide has long been recognized as an effective in-bed catalyst for reforming or cracking tars generated in thermally decomposing hydrocarbon fuels such as biomass. Under pressures as high as 20 atm, the oxide was also widely tested as a good CO 2 acceptor to capture CO 2 on-site to produce high-caloric pipeline gas from gasifying coal and coal-coke. By using CaO as an additive of the fuel and bed material, the research detailed in this research note demonstrated that CaO could also be a substantially good CO 2 acceptor for the atmospheric gasification of biomass, provided the reaction temperature is appropriately low, such as not much over 973 K. At temperatures >1073 K, the additive exhibited basically the catalytic effect only, which led the H 2 content of the product gas to increase and the tar release with the gas to decrease.

Coffee grounds refer to a kind of high-moisture biomass refuses generated in drink works. With a national technical program, we recently worked on converting this biomass waste into middle-caloric product gas. The conversion proceeded in two consecutive steps, via first fuel drying/upgrading and in turn pyrolytic gasification of the dried fuel with the so-called dual fluidized bed gasification (DFBG) technology. The present paper investigated the gasification of dried coffee grounds in a 5.0 kg/h pilot DFBG facility, with the aim of demonstrating the adaptability of the technique to the tested fuel and clarifying its chemically possible efficiency. It was shown that gasifying dried coffee grounds with moisture of about 10 wt % through DFBG at about 1073 K is easy to convert more than 70% of fuel's C into product gas, and the gas can have a higher heating value (HHV) over 3500 kcal/m3 n . Nonetheless, the tar load in the product gas was sometimes up to 50 g/m3 n . Increasing the steam/fuel mass ratio and decreasing the fuel particle size reduced the tar yield, but the available reduction degree was limited. Inclusion of a small amount of air into steam (gasification reagent) appeared efficient to lower the tar content of the product gas, but only the O2/C molar ratios below 0.1 are applicable in the view of preventing the HHV of the product gas from becoming lower than 3000 kcal/m3 n . As a consequence, other tar elimination techniques were suggested to be necessary for the gasification of coffee grounds via DFBG. Furthermore, the paper demonstrated that for DFBG using steam as the gasification reagent its attainable C conversion likely determines the parameters, such as H conversion, cold gas efficiency, tar content in the product gas, and product gas molar composition.

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