**2. Experiments**

#### **2.1. Material**

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.

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

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

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

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

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

low-rank coal by using better solid-gas contacting systems and catalysts.

the potential to decrease and eliminate these limitations [1, 4].

on a smaller scale to gain a better overall view on an industrial scale.

purpose.

238 Gasification for Low-grade Feedstock

#### *2.1.1. Experiments in the fluidized bed TGA*

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> TiO<sup>3</sup> was the commercial catalyst that was used for the catalytic ash free coal gasification experiments.

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

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


**Table 1.** Analysis of the Western Canadian lignite coal [2].

#### **2.2. Apparatus description**

#### *2.2.1. Fluidized bed TGA*

A schematic of the first microreactor presented in this book chapter is shown in **Figure 1**. This apparatus represents the first fluidized bed thermogravimetric analyzer (FB-TGA) in the world. It comprises a quartz reactor that can operate at temperatures from 25 to 1200o C, furnace and measuring instruments, such as thermocouples, two mass flow controllers, pressure transducers and load cell. The FBTGA is connected to a data acquisition system. The fluidization is set to the minimum rate for any temperature using specific software. The quartz operates at atmospheric pressure with a wide range of solid samples, with a maximum amount of 50 g.

**Figure 1.** Fluidized bed TGA. Reproduced from reference [1].

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241

**Figure 2.** Microwave thermogravimetric analyzer.

#### *2.2.2. Microwave thermogravimetric analyzer*

Two significant modifications were performed to make a traditional microwave oven work as a TGA. To accurately measure the weight loss of the payload during exposure to microwaves, the carrier reactor was directly connected to a scale fixed on the top of the oven through two opposing side-holes, as shown in **Figure 2**. To measure the transient mean temperature of the payload during the exposure to microwaves, an innovative thermometer called an "air-thermometer" was designed and made. That thermometer's theory is mainly based on the direct relationship between the pressure and temperature of a constant volume of gas. As soon as the temperature of the thermometer probe increases, the pressure of the gas that is inside the probe increases as well. The measured increase in the gas pressure is, then, translated to find the temperature of the payload. It is worth mentioning that the thermometer probe is made of

**Figure 1.** Fluidized bed TGA. Reproduced from reference [1].

**2.2. Apparatus description**

*2.2.2. Microwave thermogravimetric analyzer*

**Table 1.** Analysis of the Western Canadian lignite coal [2].

A schematic of the first microreactor presented in this book chapter is shown in **Figure 1**. This apparatus represents the first fluidized bed thermogravimetric analyzer (FB-TGA) in the

**Canadian lignite coal Ash free coal**

and measuring instruments, such as thermocouples, two mass flow controllers, pressure transducers and load cell. The FBTGA is connected to a data acquisition system. The fluidization is set to the minimum rate for any temperature using specific software. The quartz operates at atmospheric pressure with a wide range of solid samples, with a maximum amount of 50 g.

Two significant modifications were performed to make a traditional microwave oven work as a TGA. To accurately measure the weight loss of the payload during exposure to microwaves, the carrier reactor was directly connected to a scale fixed on the top of the oven through two opposing side-holes, as shown in **Figure 2**. To measure the transient mean temperature of the payload during the exposure to microwaves, an innovative thermometer called an "air-thermometer" was designed and made. That thermometer's theory is mainly based on the direct relationship between the pressure and temperature of a constant volume of gas. As soon as the temperature of the thermometer probe increases, the pressure of the gas that is inside the probe increases as well. The measured increase in the gas pressure is, then, translated to find the temperature of the payload. It is worth mentioning that the thermometer probe is made of

C, furnace

world. It comprises a quartz reactor that can operate at temperatures from 25 to 1200o

Fixed carbon 34.3 46.7 Volatile matter 39.3 53.2 Ash 15.4 Trace Moisture 11.1 Trace

C 57.2 88.9 H 4.3 5.1 N 1.20 1.5 O 21.1 24.9 S 0.1 0.0

*2.2.1. Fluidized bed TGA*

Proximate analysis (wt. % a.r.)

240 Gasification for Low-grade Feedstock

Ultimate analysis (wt. %)

a.r. as received

**Figure 2.** Microwave thermogravimetric analyzer.

quartz and the working gas is air. This means that almost no interactions between the applied electromagnetic waves and the materials mentioned above have taken place. This aspect ensures that the innovated thermometer does not suffer from the drawbacks of traditional thermometers. A manifold that consists of seven ports is connected at the outlet of the reactor to enable splitting the gas/vapor product at different times/temperatures for kinetics and other purposes. Farag and his co-authors have called the developed system the MW-TGA, which, at the time, was the first MW-TGA developed in the literature. For further details, kindly refer to [9, 10, 13, 14].

infrared spectroscopy (FT-IR). For the three steps, the condensed tar at the exit of the reactor

For this second application, about 5 g of lignite coal and ash free coals >500 μm and <600 μm in size were fluidized with 40 g of olivine sand, >180 μm and < 212 μm in size. The experiments of

those for ash free coal gasification were established in a gas mixture of 3% oxygen-balance nitrogen. The heating rate was 40 °C/min and the particle density for the olivine sand was 3290 kg·m−3. The gas flow rate was changed, based on the strategy developed for the fluidized bed TGA, depending on the temperature to maintain the bed at the minimum fluidization regime [1].

heated up to 800 °C under air atmosphere for 5 h. The results from the weight loss measurement and gas analysis demonstrated and confirmed that the commercial catalyst was stable. In all of the experiments, the K/C weight ratio was 10%, where K and C represent the amount

Strategic procedures were performed to enable investigating the product yield and composition obtained from the microwave thermal cracking of lignin. The freezing zone that was used to collect the liquid product was kept at −18°C and the entire tubing barrier to the condensation system was kept at 200°C to prevent any condensation before the freezing zone. Then, the reactor was filled with the raw material and connected as shown in **Figure 2**. Subsequently, the signal cables and the air thermometer were installed, and an inert environment was cre-

When the reaction started, all the valves of the product manifold were closed, except one that was used for collecting the product. Afterward, at a certain temperature/time, the opened port was switched off, and the closed one was switched on to start receiving the product during another interval temperature/time. Once the reaction was eventually completed, the obtained liquids and the solid product were cold to the ambient temperature. The liquid product was separated into the oil phase, which has the most organic chemicals, and the aqueous phase,

The proof of the concept of the fluidized bed TGA was carried out with the thermal decomposition of the calcium hydroxide. The results for the fluidized bed and conventional TGAs are shown in **Figure 3**. For the conventional TGA, three different amounts of calcium hydroxide (10, 25, and 140 mg) were tested, while 4 g of calcium hydroxide were used in the FB-TGA.

which is lower in density than the oil phase and mostly water and sent for analysis.

and coal respectively.

, 20 g of the commercial catalyst was fluidized and

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), whereas

243

coal gasification were carried out in a gas mixture of 5% oxygen-balance nitrogen (N2

TiO<sup>3</sup>

TiO<sup>3</sup>

.

*2.3.2. Catalytic ash free coal gasification in FB-TGA: the second application*

was burned off at 750°C.

To test the stability of the catalyst K2

of K and C that are contained in K2

ated by purging the system with N2

**3. Results and discussion**

**3.1. Proof of the concept of the fluidized bed TGA**

*2.3.3. Microwave thermogravimetric analyzer (MW-TGA)*

#### *2.2.3. Saddle reactor*

In the chemical reaction where a gas phase is one of the leading products, using a fluidized gas to overcome the heat and mass transfer limitations creates an issue. This issue is mainly related to the dilution of the produced gas. To overcome this problem, a novel reactor—called "saddle reactor"—has been designed and built in PEARL labs. As shown in **Figure 3**, the saddle reactor consists of two V-shaped pairs of arms connected at their bottoms by a small chamber. One of these two V-shaped is twisted by 90°; it is the optimum angle for the best mixing efficiency− which has been proofed in our previous publications. A set of heating elements is distributed in each arm to reach the needed temperature of performing the reaction. The power of those heaters was calculated and chosen to provide the heat energy required to achieve a particular end. Four built-in thermocouples are employed to control the input power to the heating elements and avoid reaching their melting points. A fifth thermocouple is fixed in the middle of the chamber that combines all the heating elements. This thermocouple controls the whole system based on the temperature of the payload. This means that the five measured temperatures are used to control the heating power of the system. The outlet of the saddle reactor is connected to two analytical techniques, GC and FTIR, to analyze the gas product.

#### **2.3. Experimental procedures**

#### *2.3.1. Coal pyrolysis and gasification in the FB-TGA: the first application*

The experiments for this first application of the FB-TGA were carried out in three steps: coal pyrolysis, partial oxidation of char, and coal gasification. The pyrolysis was performed in a nitrogen atmosphere. The heating rate was 40°C/min up to a maximum temperature of 700°C. The reactional system stabilized at 700°C for more than three hours. Novel kinetic parameters were developed for coal pyrolysis reactions from the collected data during the whole experiment time. During the second step, a specific gas mix of 5% oxygen-balance nitrogen was used to partially oxidize the produced char from the first step. The same heating rate and program were used. The experimental data were collected and used to derive kinetic parameters for the partial oxidation of the char. The third step in the FB-TGA was the coal gasification. During this third step, two different experiments were separately carried out under different conditions. The first one was at 650°C, while the second one was at 750°C. The two reactions were repeated three times. The method of collecting data was the same and the heating method was the same as the one that was used for the first two steps. The product gases, such as CO, CO2 , H2 , CH4 and H2 O, were measured by a system of gas chromatography (GC)/Fourier-transform infrared spectroscopy (FT-IR). For the three steps, the condensed tar at the exit of the reactor was burned off at 750°C.

#### *2.3.2. Catalytic ash free coal gasification in FB-TGA: the second application*

quartz and the working gas is air. This means that almost no interactions between the applied electromagnetic waves and the materials mentioned above have taken place. This aspect ensures that the innovated thermometer does not suffer from the drawbacks of traditional thermometers. A manifold that consists of seven ports is connected at the outlet of the reactor to enable splitting the gas/vapor product at different times/temperatures for kinetics and other purposes. Farag and his co-authors have called the developed system the MW-TGA, which, at the time, was the first MW-TGA developed in the literature. For further details,

In the chemical reaction where a gas phase is one of the leading products, using a fluidized gas to overcome the heat and mass transfer limitations creates an issue. This issue is mainly related to the dilution of the produced gas. To overcome this problem, a novel reactor—called "saddle reactor"—has been designed and built in PEARL labs. As shown in **Figure 3**, the saddle reactor consists of two V-shaped pairs of arms connected at their bottoms by a small chamber. One of these two V-shaped is twisted by 90°; it is the optimum angle for the best mixing efficiency− which has been proofed in our previous publications. A set of heating elements is distributed in each arm to reach the needed temperature of performing the reaction. The power of those heaters was calculated and chosen to provide the heat energy required to achieve a particular end. Four built-in thermocouples are employed to control the input power to the heating elements and avoid reaching their melting points. A fifth thermocouple is fixed in the middle of the chamber that combines all the heating elements. This thermocouple controls the whole system based on the temperature of the payload. This means that the five measured temperatures are used to control the heating power of the system. The outlet of the saddle reactor is

connected to two analytical techniques, GC and FTIR, to analyze the gas product.

The experiments for this first application of the FB-TGA were carried out in three steps: coal pyrolysis, partial oxidation of char, and coal gasification. The pyrolysis was performed in a nitrogen atmosphere. The heating rate was 40°C/min up to a maximum temperature of 700°C. The reactional system stabilized at 700°C for more than three hours. Novel kinetic parameters were developed for coal pyrolysis reactions from the collected data during the whole experiment time. During the second step, a specific gas mix of 5% oxygen-balance nitrogen was used to partially oxidize the produced char from the first step. The same heating rate and program were used. The experimental data were collected and used to derive kinetic parameters for the partial oxidation of the char. The third step in the FB-TGA was the coal gasification. During this third step, two different experiments were separately carried out under different conditions. The first one was at 650°C, while the second one was at 750°C. The two reactions were repeated three times. The method of collecting data was the same and the heating method was the same as the one that was used for the first two steps. The product gases, such as CO, CO2

O, were measured by a system of gas chromatography (GC)/Fourier-transform

*2.3.1. Coal pyrolysis and gasification in the FB-TGA: the first application*

kindly refer to [9, 10, 13, 14].

242 Gasification for Low-grade Feedstock

**2.3. Experimental procedures**

H2 , CH4

and H2

*2.2.3. Saddle reactor*

For this second application, about 5 g of lignite coal and ash free coals >500 μm and <600 μm in size were fluidized with 40 g of olivine sand, >180 μm and < 212 μm in size. The experiments of coal gasification were carried out in a gas mixture of 5% oxygen-balance nitrogen (N2 ), whereas those for ash free coal gasification were established in a gas mixture of 3% oxygen-balance nitrogen. The heating rate was 40 °C/min and the particle density for the olivine sand was 3290 kg·m−3. The gas flow rate was changed, based on the strategy developed for the fluidized bed TGA, depending on the temperature to maintain the bed at the minimum fluidization regime [1].

To test the stability of the catalyst K2 TiO<sup>3</sup> , 20 g of the commercial catalyst was fluidized and heated up to 800 °C under air atmosphere for 5 h. The results from the weight loss measurement and gas analysis demonstrated and confirmed that the commercial catalyst was stable. In all of the experiments, the K/C weight ratio was 10%, where K and C represent the amount of K and C that are contained in K2 TiO<sup>3</sup> and coal respectively.

#### *2.3.3. Microwave thermogravimetric analyzer (MW-TGA)*

Strategic procedures were performed to enable investigating the product yield and composition obtained from the microwave thermal cracking of lignin. The freezing zone that was used to collect the liquid product was kept at −18°C and the entire tubing barrier to the condensation system was kept at 200°C to prevent any condensation before the freezing zone. Then, the reactor was filled with the raw material and connected as shown in **Figure 2**. Subsequently, the signal cables and the air thermometer were installed, and an inert environment was created by purging the system with N2 .

When the reaction started, all the valves of the product manifold were closed, except one that was used for collecting the product. Afterward, at a certain temperature/time, the opened port was switched off, and the closed one was switched on to start receiving the product during another interval temperature/time. Once the reaction was eventually completed, the obtained liquids and the solid product were cold to the ambient temperature. The liquid product was separated into the oil phase, which has the most organic chemicals, and the aqueous phase, which is lower in density than the oil phase and mostly water and sent for analysis.
