Oxygen-Blown Entrained Flow Gasification of Biomass: Impact of Fuel Parameters and Oxygen Stoichiometric Ratio

Abstract

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.

Studies on Syngas Fermentation With Clostridium carboxidivorans in Stirred-Tank Reactors With Defined Gas Impurities

“…Ammonia serves as a nitrogen source for C. carboxidivorans and thus boosts batch process performance if additionally supplied by the syngas. The typical amounts of NH 3 in real synthesis gas of 4,500 ppm NH 3 (Kremling et al, 2017;Kremling, 2018) would result in a maximum dissolved NH 3 concentration of 0.133 mol L −1 NH 3 in batch processes after 144 h, which corresponds to 7.1 g L −1 NH 4 Cl at the gas flow rate of 0.083 L L −1 min −1 applied in our fermentation studies assuming 100% absorption in the fermentation medium without microbial consumption. As a consequence, typical NH 3 concentrations in real syngas will have no negative effect but may improve syngas batch fermentation processes with C. carboxidivorans.…”

“…H 2 S serves as a possible sulfur source for C. carboxidivorans and acts as a reducing agent, and thus improves the process performance if additionally supplied by the syngas. 500 ppm H 2 S, a usual concentration in real syngas (Kremling et al, 2017;Kremling, 2018), corresponds to 0.33 g L −1 H 2 S at the maximum after 144 h in batch processes at a gas flow of 0.083 L L −1 min −1 , assuming full absorption of H 2 S in the fermentation medium without microbial consumption applying the Henry constant for H 2 S (3.1 bar mol −1 in pure water) at 310 K and 1 bar (Suleimenov and Krupp, 1994). Stripping of H 2 S was not observed within the lower detection limit of the µGC instrument applied for online gas analysis (50 ppm H 2 S).…”

“…At acidic pH, HNO 2 is unstable and decomposes into HNO 3 and NO (Chan et al, 1976;Joshi et al, 1985). A real syngas from gasification of biogenic residues typically contains around 200 ppm NO x (Kremling et al, 2017;Kremling, 2018). This would result in a maximum of 0.006 mol L −1 NO 2 − (0.41 g L −1 NaNO 2 ) after 144 h at a gas flow of 0.083 L L −1 min −1 , assuming 100% absorption and no consumption FIGURE 7 | Autotrophic batch processes in continuously gassed stirred-tank bioreactors with C. carboxidivorans (p CO = 800 mbar, p CO2 = 200 mbar, F gas = 0.083 L L −1 min −1 , T = 37 • C, P V −1 = 15.1 W L −1 , pH ini = 6.0, no pH control) with no addition of NaNO 2 (reference process, black diamond, black line), addition of 0.1 g L −1 NaNO 2 (gray square, gray solid line), and addition of 0.5 g L −1 NaNO 2 (gray triangle, gray dashed line) after C. carboxidivorans concentrations of at least 0.3 g L −1 CDW were observed, indicated by a process time of 0 h. Error bars indicate the standard deviation of four reference processes; other batch processes were performed once.…”

“…A real synthesis gas, for example, from the gasification of biogenic residues, often consists of a wide variety of other components besides the main components CO, CO 2 , and H 2 like ammonia, hydrogen cyanide, nitrogen oxide species, hydrogen sulfide, sulfoxides, COS, CS 2 , or short-chain hydrocarbons and tar (Briesemeister et al, 2017;Kremling et al, 2017). Especially the usage of synthesis gas from the gasification of biogenic residues is a promising approach for the application of a waste to value process.…”

“…Especially the usage of synthesis gas from the gasification of biogenic residues is a promising approach for the application of a waste to value process. Typical orders of magnitude for the trace components in syngases from entrained-flow gasification of biogenic residues are 0.1-6.0% CH 4 , 4,500 ppm NH 3 , 150 ppm HCN, 200 ppm H 2 S, and 200 ppm NO X (Briesemeister et al, 2017;Kremling et al, 2017;Kremling, 2018). Some of these species can have beneficial effects on the microbial growth and production, while others can have inhibiting or even toxic effects.…”