Reduction in the amount of ammonia in fuel gas from biomass gasification was studied. Experiments were carried out in a fixed-bed reactor at 200-1000°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°C.

A series of tests were performed to investigate reforming of reagent-grade propane-1,2,3-triol, (C 3 H 8 O 3 ) commonly called glycerin, to produce a H 2 rich gas. Effects of the operating parameters, oxygen to carbon ratio, steam to carbon ratio, and temperature, were determined using a factorial experimental design. A mathematical model defining the effect of the three parameters was derived and used to improve the hydrogen yield. From the range of experimental conditions, it was concluded that the oxygen to carbon ratio, as well as the interaction between oxygen to carbon ratio and temperature had the most important effects on H 2 yield. A 4.5 mol quantity of hydrogen was produced per mole of glycerin at experimental conditions of oxygen to carbon ratio of 0, steam to carbon ratio of 2.2, and temperature of 804 °C. This is 65% of the maximum theoretical H 2 yield, and 90% of the H 2 yield predicted by thermochemical equilibrium. A 1.4 mol quantity of CO was also produced per mole of glycerin, presenting the potential for additional production of 1.4 mol H 2 /mol glycerin. A water gas shift reactor was added to the process and operated at 369 °C, producing a final yield of 5.3 mol H 2 /mol glycerin, 75% of the maximum stoichiometric hydrogen yield. Crude glycerin obtained from biodiesel production was finally tested (without the water gas shift reactor) as a feed and compared with reagent-grade glycerin results. The initial crude glycerin hydrogen yield, 4.4 mol H 2 /mol glycerin, was almost identical to that of reagent-grade glycerin, but carbon formation and coking increased the pressure drop through the catalyst bed causing the test to be terminated. Possible contaminants, chloride and sodium cations, present in crude glycerin as byproducts of biodiesel synthesis were added to reagent-grade glycerin and tested in the reformer, producing results similar to those observed for the crude glycerin reforming test.

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.Two fractions of tars were identified: (a) one GC-MS detectable tar fraction consisting of PAHs ranging from naphthalene to benzo(g,h,i)perylene, (b) an unknown fraction that, despite its solubility in dichloromethane, could not be identified by GC-MS, but instead was analyzed by TGA/DTA. A study of parameters such as gasification temperature, equivalence ratio (ER), and particle size showed relationships that could explain the behavior in the two different gasifiers. For large particles (>1.5 mm), the GC-MS detectable fraction was more than 90 wt % of the total tars. Increased temperature decreased the conversion of fuels to the tars. For small fuel particles (∼0.7 mm), the proportion of the GC-MS detectable tars was low but increased with an increase in temperature. The unknown tar fraction lost 46 wt % at 1 atm in an air atmosphere between the temperatures 220 and 480°C. The final weight was achieved at 620°C. Increased ER slightly decreased the tar formation. The most profound effect of the ER was on benzene formation, which increased drastically with an increase in ER. The proportion of the heavier polyaromatic hydrocarbons (PAHs) declined with an increase in ER. The mechanism of tar formation based on the fundamentals of the pyrolysis reaction is discussed.

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 fixedbed reactor with a space time of about 3 s at 800-900°C 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, CO 2 and CO approached equilibrium values, but the content of H 2 and H 2 O 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 H 2 S and about 10 g/Nm 3 tar.

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