Xinzhi Liu

Assessment of hydrothermal carbonization and coupling washing with torrefaction of bamboo sawdust for biofuels production

Two kinds of biofuels were produced and compared from hydrothermal carbonization (HTC) and coupling washing with torrefaction (CWT) processes of bamboo sawdust in this study. The mass and energy yields, mass energy density, fuel properties, structural characterizations, combustion behavior and ash behavior during combustion process were investigated. Significant increases in the carbon contents resulted in the improvement of mass energy density and fuel properties of biofuels obtained. Both HTC and CWT improved the safety of the biofuels during the process of handling, storing and transportation. The ash-related issues of the biofuels were significantly mitigated and combustion behavior was remarkably improved after HTC and CWT processes of bamboo sawdust. In general, both HTC and CWT processes are suitable to produce biofuels with high fuel quality from bamboo sawdust.

Effect of inorganic species on torrefaction process and product properties of rice husk

The objective of this study was to evaluate the effect of inorganic species on torrefaction process and product properties. Torrefaction process of raw and leached rice husk was performed at different temperatures between 210 and 270 °C. Inorganic species have significant effect on the torrefaction process and properties of torrefaction products. The results indicated that solid yield increased, gas yield decreased and liquid yield remained unchanged for leached rice husk when compared to raw rice husk. Gas products from torrefaction process mainly contained CO2 and CO, and leaching process slightly reduced the volume concentration of CO2. Removal of inorganic species slightly decreased water content and increased organic component content in liquid products. Acetic acid, furfural, 2,3-dihydrobenzofuran and levoglucosan were the dominant components in liquid product. Inorganic species enhanced the effect of deoxygenation and dehydrogenation during torrefaction process, resulting in the enrichment of C component in solid products.

Sewage Sludge Flow and Drying Characteristics in Paddle Dryers

Sewage sludge from wastewater treatment is being more and more produced in many countries. For sewage sludge disposal, drying operation is usually required and greatly energy-consuming. Paddle dryers, one kind of indirect dryers, are widely used in removing moisture of sewage sludge recently, but the design, to some extent, still depends on empirical and limited data. In this paper, we presented preliminary experimental results of sewage sludge drying based on a 3 m2 paddle dryer prototype. The effects of thermal oil inlet temperature on outlet moisture content and mass flowrate of initial sludge are recorded and analyzed. A simple monotonic relation between mass flowrate of initial sludge and thermal oil inlet temperature does not exist. Besides, we performed the drying experiment of adding low-value biomass (rice husk) into wet sewage sludge. The results show that the drying performance is improved significantly.

Drying Characteristics of Fine-Particle Lignite in Paddle Dryers

Drying is an important way to improve the quality of lignite with high moisture. In this paper, a single-shaft paddle dryer experimental system was built to investigate the drying characteristics of fine-particle lignite with diameter 0-5mm. The experimental results show that with the increasing in shaft rotation speed the flow rate of lignite increases linearly approximately and the residence time decreases correspondingly. Increasing the inclination angle of dryer frame helps increase the flow rate. Both shaft rotation speed and heating source (heat transfer oil) temperature have significant effects on outlet moisture content of lignite. Shaft rotation speed affects the average heat transfer coefficient greatly and heating source temperature affects it weakly for specified conditions. It is found that for 5-12mm coarse-particle lignite, flow is not smooth and the average heat transfer coefficient is much less than that of fine-particle lignite. This research shows that it is feasible technically to dry fine-particle lignite by using paddle dryers, but not suitable to dry coarse-particle lignite.

Experimental Investigation on Flame Propagation Speed of Rice Husk Ash in Fixed Beds

Rice husk ash (RHA) is the product of rice husk pyrolysis or combustion, which contains inherent ash in original rice husk and non-converted fixed carbon. Due to large amounts of inherent silicon dioxide in rice husk, the decarbonized residue of RHA has great value as industrial materials. One basic method to remove carbon from RHA is roasting. Because of low carbon content in RHA and low roasting reaction velocity, the roasting process takes a long time. In this case, fixed-bed roasting is suitable for removing carbon from RHA. In the present work, experimental study on RHA decarbonization is conducted based on a specially-designed multi-section fixed-bed roasting. The experimental results show that under the experimental conditions, the flame propagation spread of RHA in fixed beds is in the range 0.833 to 0.121mm/s. The results documented in this paper provide the basis for further developing large-scale engineering devices.

The modified model for pyrolysis of cylindrical wood

Pyrolysis is known as one of the promising thermochemical conversion techniques in producing solid (charcoal), liquid (tar) and gaseous products. In the present study, deposition coefficient, i.e. the fraction of volatile and gases deposited on the char due to the secondary reaction, is introduced to modify the chemical kinetics model and the heat transfer model. The fourth order Runge-Kutta method is used to solve the kinetic model and the tri-diagonal matrix algorithm is used to solve the heat transfer model for cylindrical wood with the radius in the range 0.003 m ~ 0.011 m and the final pyrolysis temperature in the range 623 K ~ 780 K. The numerical results provide the final pyrolysis time and the effects of secondary reaction. As the wood radius increases, the final pyrolysis time and the effect of secondary reaction increase. Finally, the model developed in the present study is validated by experimental data. It is shown that the simulating results based on the modified model agree well with experimental results and are better than that based on models in literatures which does not consider deposition coefficient.

The modified model for predicting the products distribution in pyrolysis of biomass

Pyrolysis is known as one of the promising thermochemical conversion routes in producing solid (charcoal), liquid (tar) and gaseous products. In the present study, deposition coefficient, defined as the fraction of volatile and gases deposited on the char due to the secondary reaction, is introduced to modify the kinetics model in literatures. The effects of heating rates, heating temperatures and deposition coefficients on pyrolysis products distribution under non-isothermal and isothermal conditions are discussed. The investigation based on the modified model shows that the deposition coefficient affects the secondary reaction products distribution significantly. When the deposition coefficient increases, the generation rate and the concentration of char increase and the volatile and gases in secondary reaction decrease. The results indicate that primary reaction plays a dominant role in volatile and gases generation and secondary reaction plays a dominant role in char generation. The work in this paper provides useful information for optimal design of biomass gasifiers and reactors.

Constructal Design of Refrigeration Devices

The objective of refrigeration is to achieve and maintain a temperature below that of the surroundings. The refrigeration industry is expanding worldwide to fulfill the increasing needs to ensure living conditioning of humans. For example, in China, 10,272 million domestic refrigerators and freezers were manufactured in 2009 [1]. The adverse aspect is that refrigeration devices consume a large amount of energy in the world, which invokes more efficient and economical design. The design of refrigeration devices involves many aspects, in which fluid flow is a key mechanism. Due to the complexity of flow process in refrigeration applications, to a large extent, trial-and-error method has been the mainstream technique for a long time. Since Bejan proposed the constructal law in 1996 [2], principle-based flow system optimization technique has been practiced by many engineers in diverse fields [3, 4]. Like in other flow engineering fields, constructal theory is playing a more and more important role in improving the design of refrigeration devices [3–12]. In this chapter, we present our recent advances in constructal optimization in refrigeration devices through two case studies, i.e., domestic freezers and heat pump water heaters.