Zhaoqiu Zhou

Effects of metal catalysts on CO2 gasification reactivity of biomass char

The effects of five metal catalysts (K, Na, Ca, Mg, and Fe) on CO(2) gasification reactivity of fir char were studied using thermal gravimetric analysis. The degree of carbonization, crystal structure and morphology of char samples was characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The CO(2) gasification reactivity of fir char was improved through the addition of metal catalysts, in the order K>Na>Ca>Fe>Mg. XRD analysis indicated that Na and Ca improved the formation of crystal structure, and that Mg enhanced the degree of carbon structure ordering. SEM analysis showed that spotted activation centers were distributed on the surface of char samples impregnated with catalysts. Moreover, a loose flake structure was observed on the surface of both K-char and Na-char. Finally, the kinetic parameters of CO(2) gasification of char samples were calculated mathematically.

Operational characteristics of a 1.2-MW biomass gasification and power generation plant

In this study, we analyzed the operational characteristics of a 1.2-MW rice husk gasification and power generation plant located in Changxing, Zhejiang province, China. The influences of gasification temperature, equivalence ratio (ER), feeding rate and rice husk water content on the gasification characteristics in a fluidized bed gasifier were investigated. The axial temperature profile in the dense phase of the gasifier showed that inadequate fluidization occurred inside the bed, and that the temperature was closely related to changes in ER and feeding rate. The bed temperature increased linearly with increasing ER when the feeding rate was kept constant, while a higher feeding rate corresponded to a lower bed temperature at fixed ER. The gas heating value decreased with increasing temperature, while the feeding rate had little effect. When the gasification temperature was 700-800 degrees C, the gas heating value ranged from 5450-6400 kJ/Nm(3). The water content of the rice husk had an obvious influence on the operation of the gasifier: increases in water content up to 15% resulted in increasing ER and gas yield, while water contents above 15% caused aberrant temperature fluctuations. The problems in this plant are discussed in the light of operational experience of MW-scale biomass gasification and power generation plants.

Study on biomass circulation and gasification performance in a clapboard-type internal circulating fluidized bed gasifier.

We investigated the solid particle flow characteristics and biomass gasification in a clapboard-type internal circulating fluidized bed reactor. The effect of fluidization velocity on particle circulation rate and pressure distribution in the bed showed that fluidization velocities in the high and low velocity zones were the main operational parameters controlling particle circulation. The maximum internal circulation rates in the low velocity zone came almost within the range of velocities in the high velocity zone, when u(H)/u(mf)=2.2-2.4 for rice husk and u(H)/u(mf)=3.5-4.5 for quartz sand. In the gasification experiment, the air equivalence ratio (ER) was the main controlling parameter. Rice husk gasification gas had a maximum heating value of around 5000 kJ/m(3) when ER=0.22-0.26, and sawdust gasification gas reached around 6000-6500 kJ/m(3) when ER=0.175-0.24. The gasification efficiency of rice husk reached a maximum of 77% at ER=0.28, while the gasification efficiency of sawdust reached a maximum of 81% at ER=0.25.

Effects of chemical form of sodium on the product characteristics of alkali lignin pyrolysis.

The effects of Na as organic bound form or as inorganic salts form on the pyrolysis products characteristics of alkali lignin were investigated by using thermogravimetric analyzer coupled with Fourier transform infrared spectrometry (TG-FTIR), tube furnace and thermo-gravimetric analyzer (TGA). Results of TG-FTIR and tube furnace indicated that the two chemical forms Na reduced the releasing peak temperature of CO and phenols leading to the peak temperature of the maximum mass loss rate shifted to low temperature zone. Furthermore, organic bound Na obviously improved the elimination of alkyl substituent leading to the yields of phenol and guaiacol increased, while inorganic Na increased the elimination of phenolic hydroxyl groups promoting the formation of ethers. It was also found the two chemical forms Na had different effects on the gasification reactivity of chars. For inorganic Na, the char conversion decreased with increasing the char forming temperature, while organic bound Na was opposite.

Research on the Gasification Characteristics of the Industrial Residues of Kenaf

As an useful biomass resource, the industrial residues of kenaf were tested on its gasification characteristics in an existing bubbling fluidized bed gasifier system. The gasification resoults showed that the gas produced under fine gasification operating conditions was combustible and the heating value of the gas could meet the demand of gas engines to generate electricity. But much fly ash produced and the carbon content in the fly ash was high, resulting in low gasification efficiency. Because of the low gasification efficiency, systematical power generating efficiency based on the facility is estimated as low as about 10%, but may be increased to about 12% at optimized condition.

Kinetic Studies on the Pyrolysis and Combustion of Bio-oil

Thermogravimetric analysis of the bio-oil produced from wood powder by self-heating biomass fast pyrolysis facility was carried out in O2 and N2 atmosphere under different heating rates (5°C/min-20°C/min) to a maximum temperature of 1000°C. The results indicate that bio-oil pyrolysis occurs in two steps. The first concerns the evaporation of low-boiling point compounds (formaldehyde, acetone, methanol, ethanol and so on) and the reactions among different compounds and then followed by the cracking of heavy fractions. Bio-oil combustion occurs in three steps. The first two are similar with the process of bio-oil pyrolysis, and then the char formed during the previous process of evaporating and cracking combusts rapidly. Both the DTG and DSC curves show a peak value corresponding to the combustion of the solid residue. On the basis of TG data, the kinetic fittings of each reaction period during pyrolysis and combustion were carried out.

Comparative Study on the 1MW and 5.5MW Biomass Gasification and Power Generation Systems

Small to middle-scale Biomass Gasification & Power Generation (BGPG) technology has sufficient flexibility and strong adaptability in line with loading conditions, and can be operated easily. It is suitable for the developing countries with dispersed biomass resource. A 1MW BGPG system has been developed by Guangzhou Institute of Energy Conversion, CAS since 1998. The system consists of a CFB gasifier, a gas purifying system, five parallel gas engines rated 200 kW each, and a wastewater treatment system. It can be used as the self-supply power plant by rice mills and timber mill factories with cheap biomass resources. To promote market competitiveness, a 5.5 MW BGPG system has been developing since 2005. It mainly consists of a CFB gasifier, a gas-purifying system, ten sets of 450kWe gas engines, a waste heat boiler, a 1.5MWe steam turbine, and waste water treatment system. Its overall efficiency has been improved from 18% of the 1MW system to 26-28%. The design and operation performances of the two systems and their characteristics are introduced.