Catalytic Tar Conversion in Two Different Hot Syngas Cleaning Systems

Tar in the product gas of biomass gasifiers reduces the efficiency of gasification processes and causes fouling of system components and pipework. Therefore, an efficient tar conversion in the product gas is a key step of effective and reliable syngas production. One of the most promising approaches is the catalytic decomposition of the tar species combined with hot syngas cleaning. The catalyst must be able to convert tar components in the synthesis gas at temperatures of around 700 °C downstream of the gasifier without preheating. A Ni-based doped catalyst with high activity in tar conversion was developed and characterized in detail. An appropriate composition of transition metals was applied to minimize catalyst coking. Precious metals (Pt, Pd, Rh, or a combination of two of them) were added to the catalyst in small quantities. Depending on the hot gas cleaning system used, both transition metals and precious metals were co-impregnated on pellets or on a ceramic filter material. In the case of a pelletized-type catalyst, the hot gas cleaning system revealed a conversion above 80% for 70 and 110 h. The catalyst composed of Ni, Fe, and Cr oxides, promoted with Pt and impregnated on a ceramic fiber filter composed of Al2O3(44%)/SiO2(56%), was the most active catalyst for a compact cleaning system. This catalyst was catalytically active with a naphthalene conversion of around 93% over 95 h without catalyst deactivation.

A Review of Hot Gas Cleaning Techniques for Hydrogen Chloride Removal from Biomass-Derived Syngas

Considering the pressing challenges of supply security and climate change, advanced processes to produce electricity and biofuels from biomass have to be developed. Biomass gasification is a very promising technology, but there is a lack of comprehensive reviews, specifically on the technologies for hydrogen chloride hot gas cleanup, which are necessary in order to work at the same temperature and respect the limits of advanced downstream components. In this review, the Cl content of the main biomasses in Europe is given, and data on syngas content and the tolerance of downstream equipment are highlighted. Hot gas cleaning technologies, which have the advantage of improved thermal efficiency are reviewed, analyzing the thermodynamic and primary and secondary methods. This review identifies NaAlO2 and Na2CO3 within 450–550 °C as the most effective sorbents, which are able to reduce the concentration of HCl below 1 ppm. Nevertheless, H2S cannot be simultaneously removed and has to be removed first, because it reduces the HCl adsorption sorbent capacity.

Impact of Char Properties and Reaction Parameters on Naphthalene Conversion in a Macro-TGA Fixed Char Bed Reactor

Catalytic tar removal is one of the main challenges restricting the successful commercialization of biomass gasification. Hot gas cleaning using a heterogeneous catalyst is one of the methods used to remove tar. In order to economically remove tar, an efficient low-cost catalyst should be applied. Biomass char has the potential to be such a catalyst. In this work, the reactor parameters that affect the conversion of a model tar component “naphthalene” were investigated employing an in situ thermogravimetric analysis of a fixed bed of biomass char. The following reactor and catalyst parameters were investigated: bed temperature (750 to 900 °C), gas residence time in the char bed (0.4 to 2.4 s), char particle size (500 to 1700 μm), feed naphthalene concentration, feed gas composition (CO, CO2, H2O, H2, CH4, naphthalene, and N2), char properties, and char precursor. It was found that the biomass char has a high activity for naphthalene conversion. However, the catalytic performance of the biomass char was affected by the gasification reactions that consumed its carbon, and the coke deposition that reduced its activity. Furthermore, high ash and iron contents enhanced char activity. The results of this work will be used in the design of a process that uses biomass char as an auto-generated catalyst in the gasification process.

New Energy Development and Energy Chemical Engineering (Topic Field) Released of Alkali Species under High Pressure Gasification of Pakistani Coal

Inorganic species are released during pressurized gasification, can cause severe problem of hot corrosion. The direct utilization of coal is harmful for power plants. The aim of work to obtained comprehensive knowledge of release alkali species Na-,K-,Cl and S-species prior to carry out experiment. Therefore thermodynamic equilibrium calculations were performed by Fact Sage 5.2 and simulated the gasification environment at elevated pressure.Three soft Pakistani coal such as Lakhra (Vad < 41.44%), Thar (Vad < 42.02%) and Sor-range ((Vad < 21.11%) belong to Lignite and sub-bituminous coal were selected and releasing order was calculated by plotting mole fraction of each species Vs pressure (5 to 15bar ) at 1000°C.On the basis of predicted releasing order the H2S can be predicted most stable species under gasification at elevated pressure. The high released amount of SO2, H2S, NaCl, KCl and HCl was predicted for LKH and SRC at 5 and 15 bar pressure and 1000°C temperature. Comparing with high pressure the predicted released of H2S was found higher than SO2, NaCl, KCl and HCl at 15 bar pressure while the released of SO2was observed lower than H2S, NaCl, KCl and HCl at 5 bar pressure during gasification process. The above available predicted information is valuable for hot gas cleaning technology.