Due to the high conversion rates and the low tar amounts in the product gas, entrained flow gasification of biomass can be an alternative process to state of the art gasification technologies, e.g., fluidized-bed gasifiers. Feedstock treatment is mandatory for entrained flow gasification (EFG). However, it has the potential of making residuals available for energetic use. In this study, the feasibility of EFG of solid biomass in an industrial-like test rig with a state of the art pneumatic dense-phase coal feeding system is shown. Four biomassestorrefied wood (TW), beech wood (B), hydrothermal carbonized green waste (HCG), and corn cobs (CoC)were used and compared to Rhenish lignite (RL). Especially, the gasification behavior of hydrothermal carbonized biomass is rarely known from the literature. The study includes a comparison of the fuels regarding feeding behavior, conversion rate, achievable gas composition, and cold gas efficiency (CGE) as well as tar formation. The oxygen stoichiometric ratio λ was varied from 0.35 to 0.55. Investigations have shown that B is not appropriate for the stable, long-term operation of a pneumatic dense-phase feeding system. B and CoC exhibited higher conversion rates at low λ values due to their higher volatile matter compared to the other fuels. The highest CGE of all trials was achieved with CoC (66.3%). B, CoC, and TW exhibited high amounts of CH 4 in the product gas, even at high temperatures. With regard to fuel conversion, HCG and TW generally behaved more like RL. Although EFG is often referred to be a tar-free technology, tar formationinvestigated by solidphase adsorptionwas observed for all fuels especially at low λ values. Due to the high temperatures, mainly tertiary tars (e.g., naphthalene) were detected. A significant higher amount of tar was observed only for B (3.5 g/m 3 ). For all of the other fuels, the total amount of tar was <1 g/m 3 in all of the trials. Regarding feeding behavior, conversion rates and gas composition TW and HCG seem to be suitable as substitutes in coal fed gasification plants.

Hydrothermal carbonization was used to convert green waste into a high-quality biocoal that was applied to an air-blown entrained-flow gasifier. Fuel-specific operating parameters are required to achieve complete fuel conversion and operate the gasifier at high efficiency. Therefore, different air-to-fuel equivalence ratios and steam addition were applied to investigate effects on gasifier performance. Fuel and carbon conversion were determined by char-particle analysis. The syngas composition and cold gas efficiencies were determined and the solidphase adsorption method was used for tar measurements. It was shown that owing to high conversion rates and comparably low tar loading, biocoal is very applicable for entrained-flow gasification. Higher gas preheating temperatures would improve the process.

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The formation of tars in gasifiers based on fluidized- or fixed-bed technology is a major problem in biomass gasification. By pretreating biomass using hydrothermal carbonization (HTC), entrained-flow gasification becomes applicable. Oxygen-blown entrained-flow gasifiers (EFGs) operate at very high process temperatures, leading to an almost tar-free syngas. However, in decentralized small-scale units, preferably air is used as the gasification agent, which, in turn, causes lower gasifier temperatures. The specific impacts of air-blown gasification conditions and fuel properties of biocoal from HTC on tar formation require particular attention. Therefore, in this work, tar formation under air-blown gasification conditions is investigated using solid-phase adsorption at an electrically heated EFG with temperatures of 900–1300 °C and different air/fuel equivalence ratios λ. Furthermore, tars are measured in the hot syngas of an industrial-like autothermal EFG. HTC biocoals of various feedstocks (beech, biogenic residuals, municipal waste, and green waste), raw biomass (corn cobs), and fossil fuel (Rhenish lignite) are used as fuels. The results show that the main influencing parameter on tar loading in the syngas is the temperature, whereas the residence time and λ have less impact. However, in autothermal operation, the choice of λ controls the gasifier temperature and, thus, effectively affects the resulting tar loading. Identified tar compounds are mainly light polycyclic aromatic hydrocarbons, of which naphthalene is the most frequently occurring. At 1300 °C, tar loading is reduced to less than 0.2 g/Nm3, which allows for direct syngas use in internal combustion engines.

Air-blown entrained flow gasification of biomass has the potential of overcoming tar-related problems that occur in fixed bed or fluidized bed gasifiers. For designing entrained flow reactors (EFR), specific information on the gasification behavior of the fuel is required. Therefore, experiments with biocoal from the hydrothermal carbonization of different feedstock (beech, biogenic residuals, municipal waste, and green waste) are performed under EFR conditions and compared to lignite. Pyrolysis chars from biocoals and lignite are obtained in EFR at 900−1300 °C for a reactivity analysis. Intrinsic reaction rates of the char reactions with CO 2 , H 2 O and O 2 are measured in a thermogravimetric analyzer. Compared to lignite, chars from biocoal are less reactive due to smaller surface areas and less catalytic ash constituents. Char samples from gasification with varying air-tofuel equivalence ratios, λ, and residence times are sampled from an autothermal gasifier and from a laboratory-scale EFR at 900− 1300 °C. Carbon and overall conversions are determined by means of the ash-tracer method. The evolution of particle size, surface area, and density of the chars with increasing conversion is measured, and simple model approaches are applied to describe the observed behavior. The results show that fuel properties and gasification conditions significantly influence the prevailing reaction regimes and require particular consideration.