**1. Introduction**

Due to environmental constraints and a lack of access to natural resources, the feedstocks of several industrial sectors are changing, which is one reason why many industrial applications use new fuel sources and blends of feedstocks, including biomass, lignin, coal, and petcoke. The intrinsic variability in feedstock makes it challenging to design, operate, and optimize a chemical process, where detailed information regarding hydrodynamics, transport phenomena, and reaction kinetics among other subjects, is essential.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The gasification of coal technology also faces many issues, including low efficiency, the presence of tar, high capital, and operating costs. Furthermore, power efficiency of gasification decreases by the presence of ash in coal, which is also a major constituent of air pollutants.

the undesirable secondary reactions. Based on the dielectric properties of the irradiated materials, MWH can dramatically diminish operating costs and the potential of a thermal hazard since it only interacts with particular types of materials. This aspect would lead to producing materials with a novel microstructure and/or initiate reactions that cannot be initiated when CH is applied. Also, it can perform the existing reactions under conditions that are entirely different from that of CH. The main reason behind these unique merits is the ability to concentrate the generated heat energy at a particular component among others, which might affect the reaction kinetics. The high precision and safety of the microwave heating technology offer a greater level of control that, consequently, presides over the target end in a delegated manner. As microwave irradiation is easily and rapidly initiated and terminated, such a mechanism would lead to reducing the undesirable intermediate thermal steps and, in turn, enhance the production rate. Indeed, these unique advantages and others help in the fundamental understanding of the energy conversion mechanism of MWH and how it impacts the chemical reaction engineering, especially when a non-conventional

Innovative Microreactors for Low-grade Feedstock Gasification

http://dx.doi.org/10.5772/intechopen.74602

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The main objective of this chapter is to demonstrate two of the up-to-date systems developed for a better understanding of the chemical reactions behind the processing of complex feedstocks. To do so, the abundance and characteristics of low-grade feedstocks are debated. The common problems associated with the processing of such non-conventional materials are presented. The novel microreactors that have recently been developed in academia, including the fluidized bed thermogravimetric analyzer and the microwave thermogravimetric analyzer that was developed in the PEARL group, are elucidated. PEARL stands for process engineer-

The materials that were used for the fluidized bed TGA are the Western Canadian lignite coal (WLC) and ash free coal. The ash free coal was produced by the Department of Chemical and Materials Engineering, University of Alberta, Canada. It was produced by solvent extraction [2, 3, 6, 7]. The proximate and the ultimate analyses are presented in **Table 1**. Furthermore, K<sup>2</sup>

was the commercial catalyst that was used for the catalytic ash free coal gasification experiments.

The virgin material processed in the developed MW-TGA was softwood kraft lignin that precipitated from a Canadian kraft mill using the LignoForce System™, a patent pending process. The CHNS of lignin are C=63.27%, H=5.79%, N=0.07%, and S=1.56%, and the approximate analyses are fixed: carbon=37%, volatiles=62%, and ash=1%. Further analysis of the pro-

*2.1.2. Materials for the experiments in the microwave thermogravimetric analyzer*

cessed material can be found in the references [8–12].

TiO<sup>3</sup>

feedstock is processed.

ing advanced research lab [5].

*2.1.1. Experiments in the fluidized bed TGA*

**2. Experiments**

**2.1. Material**

One of the main problems in a low-grade coal gasification process is the formation of deposits, which can prevent gas flow and heat transfer, thereby obstructing the operation of the process. High-process efficiency could be theoretically and thermodynamically obtained with low-rank coal by using better solid-gas contacting systems and catalysts.

The common problem of all gasification technologies is building an appropriate apparatus to develop reliable kinetics. Since the gasifier is at the heart of a coal gasification plant, the overall performance of the plant can be successfully analyzed based on the reliability of the reactor modeling. The design of a gasifier is based on the reliability of the kinetics used for this purpose.

During the last few decades, a limited effort has been made to investigate these topics when a complex feedstock is being processed. In addition, a few microreactors have been invented to overcome the issues and limitations associated with the conventional instruments used to investigate the abovementioned topics. Microreactors are used in the field of chemical engineering for their advantages over reactors of traditional sizes. The microreactors are more powerful due to their small size so the gravitational force can be neglected. The surface forces will therefore be greater and the mass and energy transfer to the reactor will be higher.

Different experimental techniques can be applied to help define some reactions, for instance, solid fuel pyrolysis, combustion, gasification and thermal decomposition of polymers. Thermogravimetric analysis, differential thermal analysis, and differential scanning calorimetry are three experimental techniques used to determine the kinetics and the mechanism of gas-solid reactions that are thermally activated. There are some limitations with the thermogravimetric technique due to non-uniform temperatures, non-homogeneity of the distribution of gas-solid and solid-solid materials, low heating rates, not enough solid samples to represent the homogeneity of it, and the bulk, interparticle, and intraparticle diffusion control. This led to the invention of the first fluidized bed thermogravimetric analyzer that has the potential to decrease and eliminate these limitations [1, 4].

One of the advantages of the FBTGA due to fluidization is good mixing for a better distribution of solid and gas particles. It is therefore possible using the fluidized bed reaction chamber to achieve uniformity in the sample temperature, eliminate bulk and interparticle diffusion controls, have an acceptable quantity of solid sample, and obtain a higher heating rate. The main benefit is the new FBTGA that can be used to test and define catalytic gas-solid reactions on a smaller scale to gain a better overall view on an industrial scale.

The second novel system presented in this work is a TGA powered by microwave heating (MWH). The dominant mechanism of MWH, which relies on the direct volumetric energy conversion within the irradiated material, has established MWH in a significant number of industrial applications. Superseding the superficial heat transfer of conventional heating (CH) with that of MWH avoids most of the problems associated with CH, the most paramount being the temperature gradient inside and outside the heated materials that prompt the undesirable secondary reactions. Based on the dielectric properties of the irradiated materials, MWH can dramatically diminish operating costs and the potential of a thermal hazard since it only interacts with particular types of materials. This aspect would lead to producing materials with a novel microstructure and/or initiate reactions that cannot be initiated when CH is applied. Also, it can perform the existing reactions under conditions that are entirely different from that of CH. The main reason behind these unique merits is the ability to concentrate the generated heat energy at a particular component among others, which might affect the reaction kinetics. The high precision and safety of the microwave heating technology offer a greater level of control that, consequently, presides over the target end in a delegated manner. As microwave irradiation is easily and rapidly initiated and terminated, such a mechanism would lead to reducing the undesirable intermediate thermal steps and, in turn, enhance the production rate. Indeed, these unique advantages and others help in the fundamental understanding of the energy conversion mechanism of MWH and how it impacts the chemical reaction engineering, especially when a non-conventional feedstock is processed.

The main objective of this chapter is to demonstrate two of the up-to-date systems developed for a better understanding of the chemical reactions behind the processing of complex feedstocks. To do so, the abundance and characteristics of low-grade feedstocks are debated. The common problems associated with the processing of such non-conventional materials are presented. The novel microreactors that have recently been developed in academia, including the fluidized bed thermogravimetric analyzer and the microwave thermogravimetric analyzer that was developed in the PEARL group, are elucidated. PEARL stands for process engineering advanced research lab [5].
