Chuangzhi Wu

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.

A review on the energy production, consumption, and prospect of renewable energy in China

China is the second largest energy consumer in the world. This paper reviews the production and consumption of traditional and renewable energy in China over the past three decades. It also presents an overview on the research and development of renewable energy, such as solar, biomass, geothermal, ocean and wind energy in China. Study indicated that the usage of renewable energy in China shows a promising prospect in the near future, of which biomass is found to be one of the most promising renewable energy resources that have great potential for development in China.

Pyrolysis of waste tires in a circulating fluidized-bed reactor

Using a circulating fluidized bed (CFB) as the main reactor, an integrated process development unit was operated aiming at the pyrolysis of waste tires. The main chemical processes in the CFB can be divided into two zones corresponding to pyrolysis and secondary reactions. The pyrolysis of tire powder was carried out at various pyrolysis temperatures, particle sizes of tire powder and feed positions. The effects of temperature, residence time and heating rate on pyrolysis were analyzed based on the experimental data. The main trends are that (1) a long residence time contributes to secondary reactions and (2) lower temperature and heating rate favor carbonization, which reduces the oil yield. Analysis of the pyrolytic oil shows that the predominant components are aromatics, followed by alkanes, non-hydrocarbons and asphalt.

An economic analysis of biomass gasification and power generation in China

With vast territory and abundant biomass resources China appears to have suitable conditions to develop biomass utilization technologies. As an important decentralized power technology, biomass gasification and power generation (BGPG) has a potential market in making use of biomass wastes. In spite of the relatively high cost for controlling secondary pollution by wastewater, BGPG is economically feasible and can give a financial return owing to the low price of biomass wastes and insufficient power supply at present in some regions of China. In this work, experimental data from 1 MW-scale circulating fluidized bed (CFB) BGPG plants constructed recently in China were analyzed; and it was found that the unit capital cost of BGPG is only 60-70% of coal power station and its operation cost is much lower than that of conventional power plants. However, due to the relatively low efficiency of small-scale plant, the current BGPG technology will lose its economic attraction when its capacity is smaller than 160 kW or the price of biomass is higher than 200 Yuan RMB/ton. The development of medium-scale BGPG plants, with capacity ranging from 1000 to 5000 kW, is recommended; as is the demonstration of BGPG technology in suitable enterprises (e.g. rice mill and timber mill) in developing countries where large amounts of biomass wastes are available so that biomass collection and transportation can be avoided and the operation cost can be lowered.

Biomass Pyrolysis in an Argon/Hydrogen Plasma Reactor

This paper presents the experimental results of biomass pyrolysis in a laboratory argon/hydrogen plasma reactor. The samples tested were wood and rice husk. The gaseous product was found to contain mainly H2, CO, C2H2 and CH4. The conversion of carbon and oxygen from the biomass feed to gaseous product can reach up to 79 % and 72 %, respectively. The results indicate that plasma pyrolysis of biomass may be a useful way for gaseous fuel production.

Kinetic study of hydrolysis of xylan and agricultural wastes with hot liquid water.

We investigated the kinetics of hot liquid water (HLW) hydrolysis over a 60-min period using a self-designed setup. The reaction was performed within the range 160-220 degrees C, under reaction conditions of 4.0 MPa, a 1:20 solid:liquid ratio (g/mL), at 500 rpm stirring speed. Xylan was chosen as a model compound for hemicelluloses, and two kinds of agricultural wastes-rice straw and palm shell-were used as typical feedstocks representative of herbaceous and woody biomasses, respectively. The hydrolysis reactions for the three kinds of materials followed a first-order sequential kinetic model, and the hydrolysis activation energies were 65.58 kJ/mol for xylan, 68.76 kJ/mol for rice straw, and 95.19 kJ/mol for palm shell. The activation energies of sugar degradation were 147.21 kJ/mol for xylan, 47.08 kJ/mol for rice straw and 79.74 kJ/mol for palm shell. These differences may be due to differences in the composition and construction of the three kinds of materials. In order to reduce the decomposition of sugars, the hydrolysis time of biomasses such as rice straw and palm shell should be strictly controlled.

Exergy-based ecological optimization for a generalized irreversible Carnot refrigerator

AbstractThe optimal exergy-based ecological performance of an irreversible Carnot refrigerator with the losses of heat-resistance, heat leak and internal irreversibility, in which heat transfer between the working fluid and the heat reservoirs obeys a generalized heat transfer law QΔ(Tn), is derived by considering an ecological optimization criterion as the objective function, which consists of maximizing a function representing the best compromise between the exergy output rate and exergy loss rate (entropy production rate) of the refrigerator. Some special examples are discussed. Numerical examples are given to show the effects of heat transfer law, heat leakage and internal irreversibility on the optimal performance of the generalized irreversible refrigerator. The results can provide some theoretical guidance for the design of practical refrigerators.

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.

Performance of Diesel cycle with heat transfer, friction and variable specific heats of working fluid

AbstractThe performance of an air standard Diesel cycle with heat transfer loss, friction-like term loss and variable specific heats of working fluid is analysed by using finite time thermodynamics. The relationships between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relationship between the power output and the efficiency of the cycle are derived by detailed numerical examples. Moreover, the effects of temperature dependent specific heats of working fluid on the irreversible cycle performance are analysed. The results show that the effects of temperature dependent specific heats of working fluid on the irreversible cycle performance are obvious, and they should be considered in practice cycle analysis. The results obtained in the present paper may provide guidance for the design of practice Diesel engines.

The ecological optimization of a generalized irreversible Carnot heat pump for a generalized heat transfer law

AbstractThe optimal ecological performance of an irreversible Carnot heat pump with the losses of heat resistance, heat leak and internal irreversibility, in which heat transfer between the working fluid and the heat reservoirs obeys a generalized heat transfer law q∝(ΔT)n,is derived by considering an ecological optimization criterion as the objective function, which consists of maximizing a function representing the best compromise between the exergy output rate and exergy loss rate (entropy production rate) of the heat pump. Some special examples are discusses.A numerical example is given to show the effects of heat transfer law, heat leakage and internal irreversibility on the optimal performance of the generalized irreversible heat pump. The results can provide some theoretical guidance for the design of practical heat pumps.