Weigang Lin

Gas-sensitive properties and structure of nanostructured ( - materials prepared by mechanical alloying

The gas-sensitive properties of nanostructured 94, 85, 71 and 7 mol% materials prepared by high-energy ball milling have been investigated in atmospheres containing alcohol, CO and gases. It has been found that the materials show a high sensitivity with a short response time to the alcohol gas and almost no sensitivity to the other two gases, CO and in the concentration ranges studied. Furthermore, the gas-sensitive behaviour of these materials in response to the alcohol gas has been discussed on the basis of the microstructure of the materials. It is found that the tin ion content in and tin ions on the surface of particles may play an important role in the enhancement of the gas sensitivity.

Wavelet analysis of dynamic behavior in fluidized beds

Wavelet analysis has been used for studying dynamic behavior of fluidized beds, which proved effective in resolution of time series into different scales of components with distinct structure and in identification of transition from the dense phase to the dilute phase. By examining wavelet spectrum functions of various dynamic signals measured from fluidized beds, it is indicated that the signals can be decomposed into three scales of components: micro-scale (particle size), meso-scale (cluster size) and macro-scale (unit size). The principal component method was employed for phase separation from concentration signals measured by the optical probe. In this method, the maximum scale parameter s(0) of the wavelet spectrum function was chosen as the optimum scale parameter. The principal component method can reduce the computation time significantly and remain the benefit offered by the direct method described in our previous publication (Ren & Li, in: L. S. Fan, T. M. Knowlton (Eds.), Fluidization, Vol. IX, Engineering Foundation, New York, 1998, p. 629.). The method was also extended to detect the boundaries of clusters in 2-D digital images acquired from fluidized beds

Emissions of SO2, NO and N2O in a circulating fluidized bed combustor during co-firing coal and biomass

This paper presents the experimental investigations of the emissions of SO2, NO and N20 in a bench scale circulating fluidized bed combustor for coal combustion and co-firing coal and biomass. The thermal capacity of the combustor is 30 kW. The setup is electrically heated during startup. The influence of the excess air, the degree of the air staging, the biomass share and the feeding position of the fuels on the emissions of SO2, NO and N2O were studied. The results showed that an increase in the biomass shares resulted in an increase of the CO concentration in the flue gas, probably due to the high volatile content of the biomass. In co-firing, the emission of SO2 increased with increasing biomass share slightly, however, non-linear increase relationship between SO2 emission and fuel sulfur content was observed. Air staging significantly decreased the NO emission without raising the SO2 level. Although the change of the fuel feeding position from riser to downer resulted in a decrease in the NO emission level, no obvious change was observed for the SO2 level. Taking the coal feeding position R as a reference, the relative NO emission could significantly decrease during co-firing coal and biomass when feeding fuel at position D and keeping the first stage stoichiometry greater than 0.95. The possible mechanisms of the sulfur and nitrogen chemistry at these conditions were discussed and the ways of simultaneous reduction of SO2, NO and N20 were proposed.

Hydrodynamics of a commercial scale CFB boiler-study with radioactive tracer particles

This paper presents the experimental results with radioactive tracer particles in an 80 MWth circulating fluidized-bed boiler. Batches of γ-ray emitting tracer particles were injected into the standpipe. The response curves of the impulse injection were measured by a set of successive scintillation detectors located at different parts of the boiler. The results show that there are significant differences of the response signals when boiler loading changes. A model has been developed to obtain information from the experimental data. The particle recirculating rate is obtained by fitting the model to the experimental data. In the same way, the average particle velocities in the furnace are estimated. The impact of loading on the particle recirculating rate and on the hydrodynamics of the boiler is discussed.

Combustion of Biomass in Fluidized Beds: Problems and Some Solutions Based on Danish Experiences

This paper summarizes the major problems in firing and co-firing the annual biomass, such as straw, in both lab-scale and full-scale fluidized bed combustors. Two types of problems were studied: operational problems, such as agglomeration, deposition and corrosion; and emission problems, e.g. emissions of NO and SO2 . Measurements of deposition and corrosion rate on the heat transfer surfaces, as well as gas phase alkali metal concentrations, were performed in full scale CFB boilers (an 80 MWth and a 20 MWth plant), which have been co-firing coal with straw and other biomass. Severe corrosion and deposition were observed in the superheater located in the loop-seal of the 80 MWth boiler. The boiler load variation has impact on the operation parameters. When the fraction of biomass with a high K-content (>1 wt. %) was higher than 60% on a thermal basis, the boiler suffered from severe agglomeration problems. Lab-scale experiments were carried out for the fundamental understanding of phenomena found in full-scale boilers and for testing possible solutions to the problems. The results showed a strong tendency of agglomeration in fluidized beds during combustion of straw, which normally have a high content of potassium and chlorine. The results indicate that the operational problems may be minimized by a combination of additives, improved boiler design, split of combustion air and detection of agglomeration at an early stage.Copyright

A Comparison of Monomeric Phenols Produced from Lignin by Fast Pyrolysis and Hydrothermal Conversions

Abstract Lignin, a by-product in biorefining industries such as lignocellulose-to-ethanol and paper-making processes, is a promising renewable source for value-added phenolic chemicals. Hydrothermal conversion and fast pyrolysis are two main thermo-chemical approaches for depolymerization of lignin. Hydrothermal conversion is a low temperature (250–500°C) and high pressure (5–30 MPa) process particularly suited for high moisture materials, whereas fast pyrolysis takes place at atmospheric pressure and moderate temperatures in the absence of oxygen and requires drying of the feedstock. In this paper, we present experimental results that provide a comparison of distributions of monomeric phenols produced by fast pyrolysis and hydrothermal conversion of lignin. Hydrothermal conversion experiments were performed in a 150 ml autoclave at 300°C for 30 minutes with different alkaline concentrations. Pyrolysis was carried out in a spouted bed reactor at 500°C. Hydrothermal conversion of lignin under 1 M alkaline solutions resulted in lower char yields (12.1%) compared to fast pyrolysis, which resulted in 54.5% solid yields. Monomer phenols obtained from hydrothermal conversion of lignin were found to have a narrower distribution dominated by catechol and its methyl derivative. In contrast, fast pyrolysis produced a wider distribution of monomeric phenols dominated by guaiacol and its derivatives with various chains substituted para to the hydroxyl group. Mechanisms of lignin fast pyrolysis and the methoxy group conversion under hydrothermal conditions were proposed respectively. In conclusion, hydrothermal technology is better suited for production of value added monomer phenols from lignin.

Modification performance of Hypercoal as an additive on co-carbonization of coal

Abstract Modification performance of Hypercoal (HPC) extracted from brown coal as an additive on the structure of carbonization products through co-carbonization with two different coals was examined. The dimension and texture changes of products were observed using polarization microscope and scanning electron microscope. The results show that the pore structure of carbonization products from caking coal is improved by adding additive with larger size, however smaller particles and more additive amount are favorable for weakly caking coal. As a good candidate of binding substance with high thermoplasticity, HPC particles were found to have a tendency to be well dispersed and further excellent adhesion between coal particles. Excessive expansion of product from caking coal can be inhibited in appropriate conditions. The number and diameter of pore are reduced and pore walls are thickened by adding HPC. Fluidity and fusibility of weakly caking coal are accelerated by the colloid in additive, which would lead to mechanical properties of products improved. Moreover, more factors affecting the product structure via single-carbonization and co-carbonization were taken into account, including moisture in coal and molding pressure of artifact. Special pore structure is formed in the products owing to moisture, and the influence of molding pressure on products is different with coal properties.

Pyrolysis of cellulose under catalysis of SAPO-34, ZSM-5, and Y zeolite via the Py-GC/MS method

ABSTRACT Bio-oil from pyrolysis of biomass is an important renewable source for liquid fuel and/or for chemicals. However, the application of bio-oil was severely restricted due to its high viscosity, acidity, and low heating value. Hence, it is necessary to upgrade the bio-oil for deoxygenation or for chemicals by catalytic reactions. In this paper, the catalytic behaviors of SAPO-34, ZSM-5, and Y zeolite on pyrolysis of cellulose were investigated via pyrolyzer combined with gas chromatography and mass spectrometer (Py-GC/MS) method in Py-mode. The results showed that ZSM-5 and Y zeolite could promote the conversions of oxygen-containing components to gases, water, aromatics, and phenols. Comparatively, more gas and water were generated under the catalysis of Y zeolite at lower temperatures, while at temperatures above 700°C, the effect of ZSM-5 became more distinct; aromatics were more generated under the catalysis of ZSM-5, while Y zeolite exerted a more distinct role in promoting the formation of phenols. The effect of SAPO-34 caused more water and furfural derivatives, less aromatics and phenols, and exerted a weak influence on gases.

Product Distribution From Flash Pyrolysis of Coal in a Fast Fluidized Bed

The flash pyrolysis of Huolinhe coal was carried out in a fast-entrained bed reactor. The investigation focuses on the effects of pyrolysis temperature and particle size on pyrolysis product distributions and gas and liquid compositions. Increasing temperature results in an increase of the gaseous product. There is an optimum temperature on the maximum liquid yield, which is around 650°C. An increase in particle size leads to a decrease of liquid products. Some amount of phenol group was found in the liquid products, which may produce the chemicals with high value. The results provide fundamental data and optimal conditions to maximize light oils yields for the coal topping process.Copyright

Conversion of furan derivatives for preparation of biofuels over Ni–Cu/C catalyst

ABSTRACT Conversions of furfural and 5-hydroxymethylfurfural as model components in bio-oil were investigated over Ni–Cu/C catalyst with formic acid as hydrogen donor in isopropanol solvent to produce biofuels. The effects of reaction temperature, feed ratio, and reaction time were studied. A high yield of 2-methylfuran up to 91 mol% was obtained from furfural in 8 h at 200°C, and under same conditions 80 mol% yield of 2,5-dimethylfuran could also be obtained from 5-hydroxymethylfurfural in 6 h. The results verified the catalyst performance and the availability of the reaction conditions for producing biofuels from furan derivatives.