Polynuclear aromatic hydrocarbons in fly ash from pressurized fluidized bed gasification of fuel blends. A discussion of the contribution of textile to PAHs

The identification and quantification of 20 different polynuclear aromatic hydrocarbons (PAHs) in the fly ash from a pressurized fluidized bed (PFB) air gasification system based:on hot gas filtering were determined by GC-MS analysis. A comparison was made on the basis of the results from two different sets of experiments with varied gasifier feedstock. The first set included four experiments with pure wood biomass as the gasifier fuel. In the second set a mixture of biomass and 10 wt % textile waste was used. The comparison showed that the distribution of the PAHs in the fly ash was strongly dependent on the gasifier feedstock but that the operational parameters, such as pressure and air/fuel ratio, showed minor effects. The relative content of the heavier compounds was larger for the pure biomass: experiments, while the lighter compounds became predominant in the case of the mixtures. The study showed that the decisive parameter influencing the formation was the structure of each PAH rather than its molecular weight. Thermal decomposition of the added textile resulted in the formation of phenylic radicals. The excessive occurrence of such intermediates/compounds favored the formation of the simple structured PAHs with relatively low molecular weights. The largest contribution of the textile was to PAHs consisting of two benzene rings with at least one C-C bond between, such as dibenzofurane, fluorene, and biphenyl. Formation of the PAHs consisting of two joined benzene rings, such as naphthalene and 1- and 2-methylnaphthalene, was also strongly affected by the textile addition. The smallest effect of the mixing was observed in the contents of the heavier compounds consisting of more than three benzene:rings. The differences in the relative concentrations of same compounds, such as phenanthrene and triphenylene, can be explained in the terms of their reactivity

Alkali metal emission from filter ash and fluidized bed material from PFB gasification of biomass

The alkali metal emission from materials collected in a PFB biomass gasification pilot plant has been characterized. Samples of SiC filter ash and fluidized bed particles from different operating conditions were subjected to a constant heating rate up to 1000 degrees C in a nitrogen atmosphere, and the alkali metal emission was monitored continuously by a surface ionization technique. For all samples, two characteristic emission intervals are identified. In the range 100-500 degrees C, a small fraction of the alkali metal content is emitted. Above 600 degrees C, the alkali metal release increases sharply and the rise is close to exponential up to 900 degrees C. For fluidized bed particles, the alkali metal emission is significantly lower for agglomerates compared to material used during 1 day, which is attributed to the formation of less volatile compounds. For the filter ash samples, the alkali metal emission is enhanced in samples collected after longer filter cleaning intervals, indicating that the formation of a filter deposit improves the alkali capture efficiency

Kinetics of ammonia decomposition in hot gas cleaning

Reduction in the amount of ammonia in fuel gas from biomass gasification was studied. Experiments were carried out in a fixed-bed reactor dt 200-1000 degrees C, 21 atm. A kinetic model for ammonia decomposition was developed. The partial pressure of hydrogen in the fuel gas was a key factor to model ammonia decomposition. Activation energies in the empty reactor, on carbon, and in a sand bed were similar, 130-140 kJ/mol. The frequency factors for carbon and sand were 10 times as large as for the empty reactor. The activation energy for a Ni-based catalyst was 111-113 kJ/mol. Carbon deposit deactivated the Ni-based catalyst. High temperature was found to be essential for avoiding carbon fouling and for achieving high ammonia removal efficiency. Estimation of the ammonia reduction for fuel gas showed that a moderate amount of ammonia could be removed by use of the Ni-based pellets at 800 degrees C

Tar formation in pressurized fluidized bed air gasification of woody biomass

The tars from an air-blown pressurized bubbling fluidized bed 90 kW (thermal) pilot biomass gasifier and also from an 18 MW IGCC demonstration plant were analyzed. The accuracy of the sampling method and its advantage/disadvantage was compared with other methods

Catalytic hot gas cleaning of fuel gas from an air-blown pressurized fluidized-bed gasifier

Catalytic ammonia decomposition and tar reduction by a Ni catalyst were studied using a feed gas from a pilot-scale pressurized fluidized-bed gasifier. Tests were conducted in a tubular fixed-bed reactor with a space time of about 3 s at 800-900 degreesC and 12 atm. Ammonia removals of 35-95% and light tar conversions of 90-95% were observed. The amount of the light hydrocarbons was found to have a negative effect on the ammonia decomposition. An ammonia concentration in the fuel gas, gas residence time, and catalytic bed temperature also had a significant influence on the ammonia removal efficiency. After the catalyst, CO2 and CO approached equilibrium values,but the content of H-2 and H2O was lower because of reactions with tar. The heating value of the fuel gas remained the same; The gasification efficiency increased by about 10%, mainly because of catalytic tar cracking. Deactivation of the catalyst was not observed in the fuel gas containing 50-150 ppm H2S and about 10 g/Nm(3) tar