1 Introduction
Microwave heating has the advantages of high heating rate, ease of
start-up and shut-down, and low thermal inertia. Therefore, it is widely
used in biomass treatment and conversion such as drying, roasting,
pyrolysis, gasification and carbonization [1-5]. However, few
studies on industrial scale microwave device for biomass conversion were
reported [6-8]. One main reason is the lack of knowledge about the
interaction between microwaves and various biomass materials [9].
Therefore, the improvement in microwave device is necessary.
In recent years, microwave-assisted biomass pyrolysis has attracted much
attention. The non-premixing, i.e., the feedstock is directly poured on
the heated microwave absorbent bed for pyrolysis reactions is one of
methods adopted for microwave pyrolysis [10]. Based on the
non-premixing method, our group designed a microwave-assisted reactor
coupled with atomization feeding and used it in the pyrolysis of methyl
ricinoleate [11-14]. We have achieved good results in a small-scale
microwave reactor and now focus on the device scale-up. In fact, this
reactor can work continuously and efficiently for the pyrolysis
reactions, which can be used in the pyrolysis of biomass and oils,
therefore it has the potential of industrial application, and the
scale-up process is of great significance.
The surface of SiC microwave absorbent bed is the main site of pyrolysis
reactions in non-premixing microwave pyrolysis reactor, in consequence,
the uniformity and stability of the temperature distribution for the bed
surface without feeding is important to the scale-up. Due to the limited
penetration depth of microwave and the existence of heat transfer, the
temperature distribution on the bed surface has particularly
significance to the pyrolysis process in a large-scale microwave device.
Some reports on temperature distribution under microwave heating through
the simulation method have been found [15-17]. However, the
temperature distribution of the entire bed surface was rarely studied
experimentally since the accurate temperature measurement in
microwave devices is complex
especially for large-scale devices. Infrared thermal imager can be used
to determine the surface temperature nondestructively based on
contactless temperature measurement technology. With the development of
infrared thermal imaging technology, the distribution of surface
temperature under microwave heating was monitored and studied by
infrared thermography [19-21]. The infrared thermal imager has
characteristics of spatial visualization of two-dimensional temperature
distribution and large temperature measurement area [18]. Therefore,
it can be used in the measurement of temperature distribution in
large-scale microwave devices.
For the scale-up of microwave pyrolysis reactor, a promising route is to
use multiple low-power magnetrons rather than single large-power
magnetron, which has the advantages of low equipment cost and ease of
maintenance [9]. Thus, it is necessary to investigate the effect of
multiple magnetrons position on the temperature distribution of the bed
surface in the microwave-assisted pyrolysis large-scale reactor.
However, the influence of magnetron position on microwave heating was
previously studied mostly by simulation [22].
In this work, a non-premixing microwave pyrolysis large-scale reactor
equipped with ten 1 kW magnetrons was developed. The influence of
magnetron position on the temperature distribution of the SiC microwave
absorbent bed without feeding was studied using the infrared
thermography.