Zhengbin He

Reducing wood drying time by application of ultrasound pretreatment

ABSTRACT Industrial wood is typically dried artificially after felling. The drying process is often very lengthy and consumes a large amount of energy, however, and inappropriate drying schedule can cause defects in the wood. Pretreatments such as ultrasound show the potential to reduce wood drying time without impacting quality. This study investigated the influence of ultrasound pretreatment on vacuum drying behavior, hydroxyl content, and microstructural properties of fast-growing wood samples. Pretreatments were performed at ultrasound intensity of 10 W cm−2 and frequencies of 28 and 40 kHz, respectively, for 30, 60, and 90 min, respectively, then pretreated samples were dried at 40°C temperature under absolute pressure of 0.08 MPa. Results showed that ultrasound pretreatment did shorten the wood vacuum drying time, increase effective water diffusivity, open water channels, decompose wood extractives, and decrease hydroxyl content. In effect, ultrasound pretreatment can be applied to successful reduce wood drying time.

Influence of a urea–formaldehyde resin adhesive on pyrolysis characteristics and volatiles emission of poplar particleboard

To investigate the influence of urea–formaldehyde resin (UF resin) adhesive on the thermal utilization of wood waste, the pyrolysis of particleboard and its main components (poplar and UF resin) are studied in this paper. Thermogravimetric analysis combined with Fourier transform infrared spectrometry (TG-FTIR), gas chromatography coupled with mass spectrometry (GC-MS) and ultimate analysis were used to investigate the pyrolysis process and product characteristics of poplar and UF resin and particleboard. The thermogravimetric curves show that, compared to poplar and UF resin, pyrolysis of particleboard produces more char and less volatile matter. A distributed activation energy method is used to retrieve kinetic parameters from the measurements. The activation energy of particleboard is lower than that of poplar during the main pyrolysis stage. The activation energies of poplar and particleboard are 140–200 kJ mol−1, while that of UF resin is 150–300 kJ mol−1. Evolved gaseous products during the pyrolysis of poplar, such as CH4, CO, CO2, are found. N-Compounds are the main volatile products of UF resin. Moreover, N-components of particleboard are mainly produced by UF resin. The influence of UF resin on the pyrolysis liquid of particleboard is mainly on the nitrogen compounds. More nitrogenous compounds are detected in the pyrolysis liquid of particleboard, and the relative amount of nitrogenous compounds is 23.40% more than that in poplar pyrolysis liquid.

Influence of ultrasound-assisted extraction on the pyrolysis characteristics and kinetic parameters of eucalyptus

In this study, the influence of ultrasound-assisted extraction on eucalyptus samples with special focus on pyrolysis characteristics and kinetic parameters was explored. Ultrasound and Soxhlet extraction were used to pretreat samples respectively, then samples were assayed by component analysis, TG-FTIR, and kinetic analysis. Ultrasound-assisted extraction did change the physiochemical characteristics of eucalyptus samples, particularly in regards to the quantity of extractives obtained. In TG and DTG curves, ultrasound-extracted samples reflected lower residual weight ratio (17.77%) and higher maximum weight loss rate (-22.92%/min), and were accompanied by a slight shift in the weight loss rate peak to lower temperature (366°C). The volatiles produced during pyrolysis and the discrepancies of product distribution between experimental and controlled groups were explored based on TG-FTIR spectra. According to kinetic analysis results, ultrasound-treated samples showed higher activation energy at the primary portion of thermal degradation with an average of 206.09kJ/mol.

Effects of Ultrasound Pretreatment on Eucalyptus Thermal Decomposition Characteristics As Determined by Thermogravimetric, Differential Scanning Calorimetry, and Fourier Transform Infrared Analysis

Samples were pretreated by ultrasound at 300 W and 28 kHz in three different solutions. The thermal degradation characteristics of the samples were then characterized via thermogravimetric, differential scanning calorimetry, and Fourier transform infrared analysis in a nitrogen environment. The characteristic of gas product release, the formation mechanisms of the main products, and the mechanistic basis for the effects of ultrasound on wood components were studied. The results showed that the gaseous products are the same with ultrasound pretreatment but the amounts are changed. The gaseous products mainly constitute of CO, H2O, CO2, CH4, and CH3COOH, and more gaseous products were produced at 361 °C than at 308 °C. The reaction rates for specimens pretreated in aqueous soda solution proceeded faster than specimens pretreated in aqueous acetic acid solution and distilled water. Moreover, the maximum FTIR spectra absorbance appeared around 341 °C for specimens pretreated in aqueous soda solution but appeared around 369 °C for the control sample and samples pretreated in distilled water or acetic acid solution. The heat flows for specimens pretreated in aqueous soda solution, compared to control group, was much lower. Additionally, hydroxyl and hydroperoxy radicals provided by ultrasound cavitation in alkaline conditions act to intensify the overall rates of reactions.

Heat Transfer Characteristics during Superheated Steam Vacuum Drying of Poplar

Abstract Superheated steam vacuum drying shows major advantages in terms of reducing the boiling point of water and speeding up the drying process, but to our knowledge, no researcher has addressed the effects of drying conditions on heat transfer characteristics during superheated steam vacuum drying of wood. In this study, we did so using fast-growing poplar. Temperatures inside the wood were measured and the convective heat transfer coefficients calculated under temperature conditions of 35°C, 55°C, and 70°C and absolute pressures of 0.03, 0.06, and 0.1 MPa. The results of our subsequent analysis showed that the ultimate temperatures inside wood increase alongside increasing absolute pressure at the set temperature conditions and are lower than that of the drying medium. In addition, we found that convective heat transfer coefficients increase as absolute pressure increases at the set temperatures and also increase as temperature increases at set absolute pressure conditions. We then established a conv...

Preliminary study on method of vacuum drying

Chinese fir was taken as specimen in this paper. Firstly, specimens were preheated to 80°C, and then the pressure in the drying box was vacuumized to the needed vacuum degree (absolute pressures were 0.06, 0.04 and 0.02MPa respectively), finally, pressure in the drying box was recovered to the atmospheric pressure by vapor from wood during drying period. The results indicated that the drying rates increased along with the decrease of the absolute pressure and the drying rates were 2.19, 2.39, 2.46 (%/h) when the absolute pressures were 0.06, 0.04, 0.02MPa respectively. Then, the drying rates equations under the conditions of temperature being 80°C and absolute pressures being 0.06, 0.04, 0.02MPa respectively were regressed and the results also showed that it was better to use low pressure when wood moisture content was high while better to use high pressure during drying wood with low moisture content.