Zhanlong Song

A microwave reactor for characterization of pyrolyzed biomass

A microwave reactor (MWR) was designed to investigate microwave-induced pyrolysis of biomass. Condensation of tars on the quartz reactor and the pipelines was prevented by an electric heating device, and a temperature control function allowed determination of product characteristics at constant temperatures. Temperature had an important influence on microwave pyrolysis; the yields of gas products increased from 17.69 wt.% to 22.27 wt.% and the ratio of combustible gas to total gas products increased from 67.21 vol.% to 77.14 vol.% as the temperature increased from 400 °C to 600 °C. A large number of volatiles was released as temperature increased, resulting in an increase in the number of pores of the coke and a uniform pore structure was obtained. The specific surface area of coke increased from 0.89 m(2)/g (400 °C) to 9.81m(2)/g (600 °C) and the pore volume increased from 0.006 cm(3)/g (400 °C) to 0.012 cm(3)/g (600 °C), but the average pore size decreased from 282.16 nm (400 °C) to 46.64 nm (600 °C).

Microwave pyrolysis of wheat straw: Product distribution and generation mechanism

Microwave pyrolysis of wheat straw is studied, combined with analysis of products, the distribution and generation pathway of products are investigated. Only a small amount of volatiles released when microwave pyrolysis of pure straw. Mixtures of adding CuO and Fe3O4 can pyrolyze, and the majority in pyrolysis products is in liquid-phase. Severe pyrolysis occur after adding carbon residue, the CO content in pyrolysis gas products is high, and the maximum volume content of H2 can exceed 35 vol.%. The high-temperature is helpful for increasing the yield of combustible gas in gaseous products, in particular the H2 production, but also helpful for improving the conversion of sample. Pyrolysis is carried out layer by layer from the inside to outside. As the internal material firstly pyrolyze and pyrolysis products released pass through the low temperature zone, the chance of occurrence of secondary reactions is reduced.

Drying behavior of lignite under microwave heating

ABSTRACT Because of lignite’s high moisture content, it must be dried before most applications. Microwave radiation may be suitable for efficient drying because of its special heating properties. This study investigated the drying behavior of lignite samples from eastern Inner Mongolia by microwave thermogravimetric analysis. Three stages of microwave drying were observed: preheating, fast weight loss, and falling rate drying periods. Samples’ surface temperatures increased dramatically during preheating, dropped slightly in the second period, and rose again in the final period. The measured surface temperature was <95°C during microwave heating. The overall moisture content decreased more rapidly under higher microwave power. Fine lignite particles (diameter <0.2 mm) and lump samples (particle size 10 mm) dried better than granular lignite (particle size 1–2 mm). The samples also underwent slight natural drying (1–2% point reduction in moisture content) after microwave treatment. The critical moisture content of lignite (11–15% under experimental conditions) was redefined. Energy consumption was analyzed to evaluate the feasibility of the proposed drying process.

Numerical simulation of hot-spot effects in microwave heating due to the existence of strong microwave-absorbing media

Hot spots can occur in microwave heating when the heated materials have different microwave absorbing properties, resulting in non-uniform temperature distribution. Understanding the features and extent of hot-spot effects can be essential in microwave-assisted processes, but little has been reported quantitatively due to the difficulty in direct determination. The issues are measured experimentally and numerically simulated using silicon carbide (SiC) particles dispersed in paraffin oil as a representative case here. Hot spots are definitively shown to exist and may trigger temperature gaps between surrounding substances at the magnitude of several hundred degrees Celsius or even higher in certain cases. The temperature gaps are enhanced for larger sized SiC particles, with a higher heat generation rate and increasing heating time. The extent of hot-spot effects substantially depends on how much and how quickly heat generated by the strong microwave absorbing media can be transferred to the weak ones. The findings have great practical value. By choosing materials with strong microwave absorption, or where discharges occur due to microwave–metal interactions, prominent hot spots can be intentionally forged and the temperature gradient may be tailored to enhance chemical reactions and catalytic processes for specific scientific and engineering applications.

Pyrolysis of tyre powder using microwave thermogravimetric analysis: Effect of microwave power.

The pyrolytic characteristics of tyre powder treated under different microwave powers (300, 500, and 700 W) were studied via microwave thermogravimetric analysis. The product yields at different power levels were studied, along with comparative analysis of microwave pyrolysis and conventional pyrolysis. The feedstock underwent preheating, intense pyrolysis, and final pyrolysis in sequence. The main and secondary weight loss peaks observed during the intense pyrolysis stage were attributed to the decomposition of natural rubbers and synthetic rubbers, respectively. The total mass loss rates, bulk temperatures, and maximum temperatures were distinctively higher at higher powers. However, the maximum mass loss rate (0.005 s-1), the highest yields of liquid product (53%), and the minimum yields of residual solid samples (43.83%) were obtained at 500 W. Compared with conventional pyrolysis, microwave pyrolysis exhibited significantly different behaviour with faster reaction rates, which can decrease the decomposition temperatures of both natural and synthetic rubber by approximately 110 °C–140 °C.

Kinetics of Pyrolysis of Straw Bales by Microwave Heating

The direct pyrolysis of large size biomass is a difficulty, and it seems to be that microwave pyrolysis is a novel process to overcome the problem. This paper presents the experimental results of microwave pyrolysis process for straw bales in a microwave thermogravimetric analyzer the first time. TG and DTG analysis techniques are adopted to study the pyrolysis behaviors of straw bales systematically. The experimental results show that the input power of microwave, heating time and temperature have important effects on pyrolysis process. Reaction kinetics for microwave pyrolysis of straw bale is analyzed theoretically. A one-step comprehensive model is used to describe the microwave pyrolytic reaction in this experiment. The activation energies for the corn and wheat straw under microwave power of 334 and 668 W/ (kg straw) are 24.4, 26.8 kJ/mol and 67.2, 70.3 kJ/mol, respectively, the pyrolytic reaction is first order. The activation energy and pre-exponential factor increase with the increasing of microwave power. The experiment of microwave pyrolysis provides a new method for the wide uses of straws.

Experimental Study of Microwave-Induced Discharge and Mechanism Analysis Based on Spectrum Acquisition

When conductor or semiconductor materials are exposed to microwave radiation in different atmospheres (Ar, He, N2, and O2+N2) intense discharge phenomena are observed. The discharge phenomena, generated when strips of the metals Fe, Al, and Zn or particles of the semiconductor SiC are irradiated with microwaves, are characterized experimentally using spectrum acquisition and analysis. Filamentary discharge is observed in an Ar atmosphere while spark discharge is observed in He, N2, and O2+N2 atmospheres. The spectral lines of the discharges are concentrated mainly in the visible region, but there are also peaks in the ultraviolet region. The nature of the discharge and the specific details of the spectra are influenced by: 1) the target metal or semiconductor used; 2) the atmosphere; and 3) the microwave field characteristics. The spectra always consist of two parts: one corresponding to the target metal or semiconductor irradiated by the microwaves and the other due to the formation of the high-energy excitation states of atoms, molecules, and ions induced in the gaseous atmosphere. The microwave-induced discharge and the corresponding luminous and plasma effects have potential uses as energy sources in many applications including chemical or photocatalytic enhancement of reactions and the destruction of volatile organic compounds for which preliminary results are encouraging.

Coal fly ash/CoFe2O4 composites: a magnetic adsorbent for the removal of malachite green from aqueous solution

A coal fly ash/CoFe2O4 (CFA/CFO) magnetic composite was synthesized by a facile hydrothermal synthesis method, and then used as an adsorbent for the removal of malachite green (MG) dye from water. The structure, morphology, and properties of the composite were characterized by XRF, SEM, XRD, FT-IR, BET and VSM techniques. A batch adsorption experiment on the removal of MG was performed with CFA/CFO, and the effect of various experimental parameters, such as the adsorbent dosage and contact time of MG at 25 °C, were investigated. Three isotherm models, namely the Langmuir, Freundlich, and Dubinin–Kaganer–Radushkevich (DKR) models, were applied to describe the adsorption process. The results indicated that the Freundlich and DKR models fit quite well with the experimental data. Thermal and microwave methods were used and compared in the regeneration experiment. All the results indicated that the as-prepared composite should be considered as a potential low-cost adsorbent for easy and efficient removal of MG from water.

Self-Heat Recuperative Microwave and Hot-Air-Combined Drying of Lignite

ABSTRACT In this study, experiments on hot-air drying of lignite were conducted with some important parameters. The moisture content of lignite decreased from 33.40% to 20.84% when dried by hot air (temperature: 80°C, velocity: 4 m/s) alone for 30 min; the thermal efficiency of the hot-air dryer was about 82%. Later on, a self-heat recuperative microwave and hot-air-combined drying system for lignite was designed. The system was divided into three stages: The first stage was the preheat stage, using waste heat of steam evaporated in the microwave dryer to preheat the lignite; the second was the microwave drying stage, using microwaves to dry the preheated lignite; the third was the cooling stage, where dried lignite was cooled by the drying medium of the preheater. Assuming the final moisture content of dried product was 10.00%, the moisture content of lignite would reduce from 33.00% to 26.50% at the preheater and continue to reduce from 26.50% to 10.00% at the second stage. If half of the energy needed by the preheater was provided by the flue gas introduced, the moisture content of lignite would reduce from 33.00% to 21.55% at the preheater and continued to reduce from 21.55% to 10.00% at the microwave dryer.

Technical and Economic Analysis on Syngas Production from Biomass Gasification

The processes and routes of syngas production from biomass gasification were first outlined, and the key processes of this technology were highlighted in the paper. Simultaneously, the cost of syngas production from biomass gasification was evaluated to be RMB 1.05/Nm 3 when the handling capacity of gasifier, material cost and system operating rate is separately fixed to be lton/h, RMB 250/ton and 0.8. On this basis, the influences of these three aspects (handling capacity of gasifier, material cost and system operating rate) on the syngas production cost were analyzed. It could be concluded that the reduction in the syngas production cost could be achieved by raising handling capacity of gasifier, reducing material cost and enhancing system operating rate. Finally, the prospect of this technology was put forward from technical and economic points of view.