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OXY-FUEL COMBUSTION OF SOLID PARTICLES IN THE DROP TUBE FURNACE

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OXY-FUEL COMBUSTION OF SOLID PARTICLES IN THE DROP TUBE FURNACE

Edward Chukwuemeka, BEng in Mechanical Engineering

Submitted in fulfillment of the requirements for the degree of Master of Science in Mechanical & Aerospace Engineering

School of Engineering and Digital Sciences

Department of Mechanical & Aerospace Engineering Nazarbayev University

53 Kabanbay Batyr Avenue, Astana, Kazakhstan, 010000

Supervisor: Assistant Professor Yerbol Sarbassov Co-supervisor: Assistant Professor Dhawal Shah

June 2023

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DECLARATION

“I hereby, declare that this manuscript, entitled “Oxy-Fuel Combustion of Solid fuel Particles in the Drop Tube Furnace”, is the result of my own work except for quotations and citations, which have been duly acknowledged”.

“I also declare that, to the best of my knowledge and belief, it has not been previously or concurrently submitted, in whole or in part, for any other degree or diploma at Nazarbayev University or any other national or intentional institution.”

Name: Edward Chukwuemeka

Date: 27.06.2023

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Abstract

Oxy-fuel combustion of solid fuel in a laboratory refers to the process of burning solid fuel in the presence of oxygen enriched gas to produce heat and combustion products, with the aim of studying combustion chemistry and/or emissions.

In this laboratory experiment, the combustion of pulverized high and low ash content coals and biomasses from Kazakhstan was studied using a drop tube furnace. The ultimate and proximate analysis was conducted beforehand to determine the composition of ash, moisture, and volatile matter in the solid fuel. The combustion tests were carried out in both air (O2/N2) and oxy-fuel (O2/CO2) environments. A 95cm long quartz tube was used as the Drop Tube and was kept at a temperature between 900 to 1000 °C. The particle size of the fuels was averaged at 400 microns. High-resolution images of the fuel conversion process in the Drop Tube were recorded to analyze the combustion process. To achieve complete burn-out, the remaining oxygen concentration in the flue gas was maintained at 5-7%. The temperature profile of each coal and biomass was taken during the heating zone and used for the thermogravimetric analysis. The results of the experiment are expected to show the flue gas emission at 900 to 1000°C for both air and oxy-fuel environments. These results will be compared to determine the temperature that equates to that of compressed air.

Generally, this experiment will provide valuable insights into the combustion of high and low ash content coals and biomasses gotten from Kazakhstan in different environments. The results will inform future studies on the development of cleaner and more efficient combustion technologies. The use of high-resolution images to study the fuel conversion process will also aid in the understanding of the complex processes involved in combustion. By comparing the results obtained in air and oxy- fuel environments, it will be possible to determine which environment provides the most efficient combustion for these fuels.

Keywords:

Combustion, oxy-fuel, thermogravimetric analysis, drop tube furnace, combustion efficiency.

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Acknowledgement

I extend my deepest gratitude to Assistant Professor Yerbol Sarbassov, my lead supervisor, for consistently demonstrating a passion for research. Under his guidance, I have gained a ton of knowledge, and I am immensely grateful for the opportunity to conduct research under your supervision.

I would also like to express my sincere appreciation to Assistant Professor Dhawal Shah, my co- supervisor, for his vital support and assistance throughout the entire project's duration. His unwavering commitment and profound interest in my thesis progress, as well as his timely academic advice and r approach to research, have significantly contributed to the successful completion of my thesis.

I also want to appreciate Professor Yerkin Abdildin, for his master's thesis lectures, all the rehearsals conducted in class in preparation for the final presentation, and his constructive criticisms. In addition, I cannot forget my ever supportive laboratory assistant, Sultan Ybray, who is ever ready and available to help solve some of my technical problems, I say thank you.

I would like to acknowledge Nazarbayev University, particularly the School of Engineering and Digital Sciences, and the staff Mechanical and Aerospace Engineering Department for their support and encouragement throughout my MSc program.

Lastly, I extend my heartfelt gratitude to my family, including my beloved mother and sisters, for their unwavering support throughout my MSc studies and their unshakable faith in me. I would also like to thank my friends and colleagues for their constant support during my research and thesis writing journey. Their support has been invaluable.

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Table of Contents

Abstract ... 3

List of Abbreviations ... 7

List of Tables ... 8

List of Figures ... 9

CHAPTER 1 ... 11

INTRODUCTION ... 11

1.1 Research Background ... 11

1.2 Motivation of the study ... 11

1.3 Research Objectives ... 12

CHAPTER 2 ... 14

LITERATURE REVIEW ... 14

2.1 Fundamentals of Oxy-Fuel Combustion ... 14

2.2 CCS Overview ... 14

2.2.2 Benefits and Limitations of Pre-Combustion Capture. ... 15

2.2.3 Post Combustion Capture ... 16

2.2.4 Benefits and Limitations of Post-Combustion Capture ... 17

2.3 Oxy -fuel Combustion Capture ... 18

2.3.1 Benefits of Oxy-Fuel Combustion ... 19

2.3.2 Advancements in the study of Oxy-Fuel combustion in furnaces and boilers ... 19

2.4 Proximate and Ultimate analysis of Coal Samples ... 21

2.5 Combustion ... Error! Bookmark not defined. CHAPTER 3 ... 32

METHODOLOGY ... 32

3.1 Elemental Analysis of Coal samples ... 32

3.2 Ash Content Determination ... 32

3.3 Moisture Content Determination ... 32

3.4 Volatile Matter and Fixed Carbon Determination ... 32

3.5 Sample Preparation... 33

3.6 Quality Control ... 33

3.7 Interpretation of results ... 35

3.8 Thermogravimetric Analysis ... 35

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Equipment: ... 36

3.9 Procedure ... 36

3.10 Sample loading ... 37

3.11 TGA measurement ... 37

3.14 Description of a Drop Tube Furnace ... 38

CHAPTER 4 ... 40

RESULTS AND DISCUSSIONS ... 40

CHAPTER 5 ... 53

CONCLUSION AND RECOMMENDATION... 53

REFERENCES ... 56

APPENDIX ... 59

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List of Abbreviations

ASU Air Separation Unit

CCS “Carbon Capture and Storage”

CCUS “Carbon Capture Utilization and Storage”

CO Carbon mono oxide CO2 Carbon di oxide

CFD Computational Fluid Dynamics DTF Drop Tube Furnace

DTG Differential Thermogravimetric

DTGA Differential Thermogravimetric Analysis EDS Energy-Dispersive Spectroscopy

FB Fluidized Bed

IEA International Energy Agency NOX Nitrogen Oxides

IGCC Integrated gasification combined cycle MSW Municipal Solid Waste

PC Pulverized Coal RT Residence Time RDF Refuse-Derived Fuel

NGCC Natural gas combined cycle SEM Scanning Electron Microscope TGA Thermogravimetric Analysis VDTF Vertical Drop Tube Furnace

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List of Tables

Table 1. Summary of Recent Research on Oxy-Fuel Combustion 21

Table 2. Modified “Proximate and Ultimate analysis” of different coals from different regions 22

Tablle 3 Summary of Proximate and Ultimate analysis of Shubarkol and Ekibastuz coal 33

Table 4 Oxygen and CO2 concentration in gas analyzer 43

Table 5 Oxy-fuel case 1 (21% O2, 79%CO2) 45

Table 6 Oxy-fuel case 2 (30% O2, 70%CO2) 46

Table 7 Oxy-fuel case 3 (40% O2, 60%CO2) 47

Table 8 Combustion efficiency in air environment 49

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List of Figures

Figure 1. “A flow chart of oxy-fuel combustion technology for power generation with CCS” 14

Figure 2. Technological flow chart for Pre-combustion Capture 15

Figure 3. Post-combustion capture technology in power plants 16

Figure 4. Oxy-fuel Combustion process. 17

Figure 5. Oxy-fuel combustion capture technology in power plants 18

Figure 6. “TG and DTG” curves for in-nature “samples and sawdust residues” following combustion using conventional fuel and oxy-fuel in DTF. 23

Figure 8. Basic flow diagram of combustion in a DTF 24

Figure 9. Schematic diagram of a drop tube furnace 26

Figure 10. Image of different oxy-fuel combustion 29

Figure 11. Samples of Shubarkol, Ekibastuz coals as well as wheat straw 32

Figure 12. Thermogravimetric Analyzer 35

Figure 13. Schematic diagram of a drop tube furnace 37

Figure 14. TGA and DTGA curves for Shubarkol coal 39

Figure 15. TGA and DTGA of Ekibastuz coal 41

Figure 16. TGA and DTGA of wheat straw 42

Figure 17a. Oxygen concentration of different coal and biomass at different temperature (air) 44

Figure 17b. CO2 concentration of different coal and biomass at different temperature (air) 45

Figure 18. Oxygen concentration of different coal and biomass at different temperature (oxy1) 46

Figure 19. Oxygen concentration of different coal and biomass at different temperature (oxy2) 47

Figure 20. Oxygen concentration of different coal and biomass at different temperature (oxy3) 48

Figure 21. Combustion efficiencies for fuel 49

Figure 22. Mass balance for combustion experiment 49

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Figure 23. Images showing Combustion of (a) Shubarkol coal in air environment (b) Ekibastuz in air environment (c) Shubarkol in oxy-fuel (21% O279%CO2) (d) Shubarkol in oxy-fuel(30%O2, 70%C O2) (e) Shubarkol in oxy-fuel(40% O2 and 60%C O2). 50

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CHAPTER 1 INTRODUCTION

1.1 Research Background

Recently there have been a significant increase in the CO2 emission from various sources such as coal-fired power plants, heavy industry and many other sectors of the economy[1]. This is thought to be the main driver of the climate change with global warming[2]. Coal is largely anticipated to continue to be one of the key energy sources for many years, especially in the emerging countries, due to its large reserves and inexpensive cost[1]. A prospective “renewable energy” source such as biomass waste materials can be utilized or co-fired in the existing power plants with minimal retrofitting to generate both heat and electricity, which is thought to be carbon neutral[3]. In addition to that, a potential technology such as carbon capture and storage(CCS) with clean fuel conversion processes becoming more popular as a result of the recent growth in environmental consciousness.[4].

The International Monetary Fund has predicted that as wages increased, coal will gradually phase out in favor of cleaner, more convenient, and more effective fuels like oil, natural gas, and, more lately, renewable energy[2]. According to some analysts, the recent rapid rise in the world's population, industry, and economy has been preceded by the growth in search for products and services without regard to quality of life. According to some forecasts, energy consumption will actually increase as a result of this growth in goods and services and will double by the year 2050[5].

1.2 Motivation of the study

Oxy-coal combustion is one of the CCS concept that proposes the recirculation of the flue gas and reuse it with oxygen for conversion of any sort of fuel[6]. As a result, the product gas mainly consists of CO2 and H2O, and minor pollutants such as NOx/SOx which typically can be removed from the process. Such alteration and the ensuing shift in the in-furnace gas constituents have an impact on the fuel combustion environment when compared to a typical air-firing mode. Particularly this might affect the parameter like fuel reactivity, burnout rate and overall combustion performance. The time it took for devolatilization to start to occur was unaffected by using CO2 instead of N2, but the time it took for coal particles to ignite was prolonged[7]. A promising methods for FB combustion is oxy- combustion sometimes referred to as O2/CO2 combustion. In oxy fuel environment, solid fuel is burned under controlled oxygen and recirculated flue gas. This is similar to the normal combustion

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that occurs place in O2/N2 environment. After oxy-combustion, the CO2 is produced with purity higher than 90% that can fulfil the underground storage requirements[8].

Biomass energy is a form of energy produced or generated by organisms, living or non-living[9]. One of the most popular biomass materials that is used for energy include but not limited to corn, wood, manure and some garbage. The energy from these organisms could be combusted to produce heat and thereafter converted into electricity. Biomass can be similar to coal because energy might not be available after the carbon is half burned.

1.3 Research Objectives

Oxy-fuel combustion is a process in which a fuel is burned in an oxygen-enriched environment. This mixture can either be pure oxygen or a blend of recirculated flue gas. For this experiment the main aim was to perform oxy-fuel combustion of low quality coal (high ash content) in the drop tube furnace. The Objectives for the experiments are as follows

• Perform thermogravimetric, TGA and thermal analysis of fuel samples along with calorimetric values using the bomb calorimeter;

• Setting up a drop tube furnace

• Design of experiment and experimental conditions

• Characterizing the combustion or ignition behaviors fuel samples(coal and biomass), during the tests in a DTF

• Data elaboration and analysis

1.4 Thesis Structure

This thesis is structured into five chapters. The first chapter introduces the topic and the background of what the topic entails, it emphasizes the motivation behind the topic and the research objectives.

The second chapter provides a detailed information on past research on the topic and related topics. It emphasizes on the conventional combustion technologies, their advantages and disadvantages. It also points out the best technology that is required for safe and efficient carbon capture. It explores previous studies related to oxy-fuel combustion of solid fuel.

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The methodology part described the experimental set-up, fuel selection and preparation, experimental conditions and data collection. Chapter 4 discusses the results and analysis of the data collected such as the combustion efficiency, image analysis, CO2 emission and the comparison of fuel conversions in DTF. Conclusion and recommendation is discussed in chapter 5. It recapitulates the findings from the experiment, it talks about the limitations and future work.

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CHAPTER 2

LITERATURE REVIEW

2.1 Fundamentals of Oxy-Fuel Combustion

A recently developed method for electricity production involves the combustion of fuels with high oxygen content. This approach uses air that has gone through a purification process to remove nitrogen and argon, resulting in an oxygen-rich mixture. This mixture is then combined with the fuel, typically coal or natural gas, in a combustor, producing a stream of carbon dioxide as a byproduct[1].

Oxy-fuel combustion technique reduces CO2 efficiently, as has been demonstrated by numerous researchers working in this field. The flowchart in Figure 1 depicts the process of generating electricity with CCS using oxy-fuel combustion. This technology uses pure oxygen instead of air to react with carbon in fuel during conversion. This makes sure that CO2 and water vapor are the predominant components of exit gas (H2O)[3]. Other emissions, such as NOx, SOx, have dramatically decreased in the interim.[10] Additionally, Oxy-fuel combustion significantly reduces CO2 emissions from the exhaust.

2.2 CCS Overview

The International Energy Agency (IEA) predicts that Carbon Capture and Storage (CCS) technology could reduce carbon emissions from coal combustion by over 90% and be responsible for the largest reduction in emissions by 2050, contributing to a 13% decrease in total emissions. The three main methods of CO2 capture in CCS are pre-combustion, oxygen-fuel combustion, and post-combustion.

This technology is seen as a crucial step towards limiting global temperature which was found to be 2°C per year.The goal of CCS technology is to drastically reduce carbon dioxide emissions. This technology is especially crucial for the ongoing shift from the economy dependent on fossil fuels to the innovative sustainable energy future[10]. The larger carbon capture, utilization, and storage (CCUS) technique, which consists of the following: CO2 capture at substantial stationary sources (such as coal-fired plants), application of the CO2 that was caught “such as gas injection for enhanced oil recovery”, petrochemicals' raw materials, transporting the CO2 captured in storage locations, injection-based long-term CO2 storing at the storage location (sequestration)[11]. The difference and

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the benefits that exist between this three type of carbon capture and storage will be emphasized in the following paragraph.

Figure 1. A flow diagram depicting the oxy-fuel technology used for power generation with carbon capture and storage (CCS) in a general sense[10]

2.2.1

Pre Combustion Capture

Pre-combustion capture is based on integrated gasification combined cycle (IGCC) technology. The aim of this technology is to generate syngas through partial oxidation, which is high in hydrogen (H2) and carbon monoxide (CO). The CO is then oxidized to carbon dioxide (CO2), increasing the concentration of CO2 in the syngas[12]. The generated H2 is used as fuel for combustion in the boiler, and the remaining CO2 is removed from the syngas through physical adsorption or chemical absorption. This process results in a higher concentration of CO2 and reduced emission of pollutants like C, S and others that are removed from coal before combustion. However, the complex nature of the system and high operating and investment costs are some of the challenges associated with this technology[13].

2.2.2 Benefits and Limitations of Pre-Combustion Capture.

High efficiency and extremely straightforward removal of carbon from fossil fuels are just two of the significant benefits of pre-combustion capture. The increased concentration of CO2 found in syngas enhances the effectiveness of adsorption, which can lead to the creation of a fuel that is potentially

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less harmful to the environment. Furthermore, this technology has been thoroughly examined by scientist in anticipation of wide implementation and commercialization. Additionally, it can be easily incorporated into existing facilities thereby reducing the cost of implementation[1].

However, the base gasification process has a higher overall capital cost than traditional pulverized coal power plants. Pre-combustion capture has several significant challenges, including the limited number of facilities that use integrated gasification combined cycle technology, challenges associated with using fuels that contain high levels of hydrogen, and difficulties with transferring heat effectively[12].

Figure 2. Technological process for Pre-combustion Capture[14]

2.2.3 Post Combustion Capture

The process of post-combustion capture entails the removal of harmful substances such as particulate matter, sulfur oxides, nitrogen oxides, and carbon dioxide from the exhaust gases generated by power plants that utilize coal or natural gas. To accomplish this, a separation unit is added to the existing firing system. CO2 can be sequestered using low-temperature distillation, chemical absorption, or gas membrane separation technologies. The technology is mature, making it relatively straightforward to implement in current coal-fired power plants. [14]. However, because of the relatively low CO2

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concentration in flue gas from coal-fire, a significant amount of flue gas must be treated by the capture container after combustion. Physical adsorption has a poor CO2 recovery rate and a small adsorption capacity, in contrast. Chemical adsorption requires significant amounts of energy for regeneration, thus it is expensive to operate. Large-scale industrial applications are challenging because the membrane separation technique is not yet developed.[1]

Figure 3. Post-combustion capture technology in power plants[14]

2.2.4 Benefits and Limitations of Post-Combustion Capture

The maturity of post-combustion carbon capture technology is a crucial advantage over other carbon capture systems [11]. Due to the fact that it was developed before “World War II”, this technique also serves as the most cutting-edge carbon capture technology. This implies that, should the need arise, there are established procedures for ensuring that the technology is effectively implemented into industrial applications for maintenance. Another benefit is how easily the technology can be used in both new and old plants[6]. The low carbon capture efficiency of this technique, in another sense, is a significant disadvantage as a result of the low CO2 content in the flue gas. Another drawback is that the method is often associated with a high amount of parasitic infestation and costly production of electricity.

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2.3 Oxy -fuel Combustion Capture

Oxy-fuel CCS research has expanded due to greenhouse gas emissions and climate change concerns.

Oxygen-fuel combustion (CCS) outperforms "pre and post-combustion capture" for CCS. Oxy-fuel combustion technology is a cost-effective and cutting-edge CO2 collection method for coal-fired plants[15]. Oxy-fuel combustion increases flue gas CO2 to facilitate sequestration and compression.

Instead of air, the combustion chamber receives recovered flue gas (primarily CO2) and pure oxygen.

This increases flue gas CO2 production, lowering capture costs. Oxy-fuel combustion has higher combustion efficiency, full fuel combustion, lower exhaust volume, and lower NOx emissions than air combustion[1]. The US's Argonne National Laboratory reported that oxygen-fuel combustion technology requires boiler modifications. Thus, the system requires a cheap initial cost and can run at scale provided the technology is developed. Oxy-fuel combustion reduces CO2 emissions[14].

Figure 4. Oxy-fuel Combustion process.

Adopted from http://hardwareparts.mfgmachined.com/why-oxyfuel.html

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Figure 5. Oxy-fuel combustion capture technology in plants[14]

2.3.1 Benefits of Oxy-Fuel Combustion

Burning fuel with oxygen rather than air is referred to as oxygen-fuel combustion, and it results in a greater concentration of carbon dioxide in the exhaust gases. This strategy contributes to a reduction in emissions of NOx and an increase in the quality of CO2 output. Producing oxygen in its purest form, however, calls for a considerable amount of energy and can cause temperatures to soar. A significant quantity of the flue gas must be reused in order to keep the temperature at a level that is acceptable.

In addition, the procedure necessitates the utilization of a device for the separation of air, which results in increased expenses as well as an increased need for energy[16].

2.3.2 Advancements in the study of Oxy-Fuel combustion in furnaces and boilers

In the year 1982, the concept of utilizing oxy-fuel combustion in coal-burning power plants in order to produce high-purity CO2 was first put forward[1]. This technique includes burning coal in a combination of CO2 and oxygen rather than in regular air, which has the potential to aid in CO2

recovery and minimize emissions of air pollution. Since that time, scientists have been investigating the possibility of using furnaces and boilers that use oxy-fuel combustion. Recent developments in the study of the drop tube furnace are outlined in the following table for your convenience. This particular research subfield is quite essential. In a nutshell, the primary focus of current research has been on analyzing the many advantages and disadvantages associated with oxy-fuel combustion in drop tube furnaces.

Table 1. Summary of Recent Research on Oxy-Fuel Combustion

Publication Year Type Summary of Focus Author(s)

2010 Review and

Experiment

Focuses on the fundamentals of combustion, such as temperatures of

flames and “heat transfer, ignition and burnout, emissions”, and the

characteristics of fly ash, when examining the information that has

[17]

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been published about the oxy-fuel process.

2017 Experiment/Modelling This study has demonstrated that pulverized coal, biomass, and their

blends may be characterized effectively and simply by using VDTF testing in conjunction with

image processing techniques.

[18]

2019 Experiment Using the TGA, DTR, and flat-

flame burner, the inquiry comprises trials with low and high heating rates (FFB).The information helped

to assist the creation of a thorough kinetic model for the conversion of

coal in air and oxy-fuel atmospheres.

[4]

2019 Experiment Physical and Chemical Behavior of Byproducts and Emissions Resulting from Biomass Oxy-fuel

Combustion in DTF

[19]

2020 Modelling This study uses CFD for modelling Oxy-fuel Combustion technique in

power plants

[14]

2020 Experiment,

Modelling and Simulation

Evaluation of a one-dimensional numerical model that was constructed to support experimental

research on coal and biomass combustion in a drop tube furnace.

The model was based on the literature.

[20]

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2021 Review This paper examines the most

innovative carbon capture method for coal-fired boilers using oxygen-

fuel combustion.

[13]

2021 Review Oxy-fuel burning in internal

combustion engines for carbon capture and storage

[10]

2021 Experiment This study aims to “examine the thermal and combustion characteristics of RDF samples" and

their component parts that were collected from MSW dumps in Nur-

Sultan.

[21]

2022 Review This review focused on changes to

power generating systems that use

“oxy-fuel combustion, including Several advanced oxy-fuel configurations, pressurized oxy-fuel

combustion, and flue gas enriched oxy-fuel combustion”.

[1]

2.4 Proximate and Ultimate analysis of Coal Samples

Coal is a combustible and carbonaceous solid materials that results from plant decomposition. By comparing the color of the various sorts of coal—brown to black, respectively, it may distinguish between high-rank and low-rank coal[13]. The source of vegetation includes substantial woody plant antecedents as well as low plant forms like moss. Although the carbon content of coal provides the heating value, other parameters, such as moisture content, ash content, and sulfur content play a significant influence in defining the rank for a particular source of coal[22]. In order to establish coal rank, demonstrate the “ratio of combustible to incombustible constituents”, or otherwise proxy

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analysis measures moisture, fixed carbon, volatile matter, and the ash contained in coals to establish the foundation for trading, evaluating and making other transactions related to coal for different objectives. Ultimate analysis is a convenient way to report the major organic elemental composition of coal. For this analysis, a coal sample is burned in an analyzer, which calculates the weight percentages of carbon, hydrogen, nitrogen, sulfur, and ash in the coal sample.

Table 2. Modified “Proximate and Ultimate analysis” of different coals from different regions[23],[13]

PROXIMATE ANALYSIS(wt.

% dry basis)

Australia n Coal

Columbia n Coal

Brazilian Coal(Bituinou s)

Pakistan US

Coal(Pittsbur ge)

Nigeria n Coal

Ash 10.4 26.5 32 34.83 22.2 20.02

Fixed Carbon 74.4 42.2 40.3 36.24 77.8 28.98

Volatile Matter 15.2 31.3 27.66 20.35 0 52.65

ULTIMATE ANALYSIS(wt.

% dry basis)

Carbon 88.1 76.7 77.4 61.9 66.2 53.27

Hydrogen 4.7 5.7 5.6 5.18 8.6 4.97

Nitrogen 1.9 1.4 1.7 1.16 2.66 2.67

Sulphur 0.7 1.4 0.7 0.69 4.9 1.82

Oxygen 4.6 14.9 14.6 11.01 22.1 12.43

A portion of the original mineral substance in coal that does not burn is represented by the ash content.

For steam coals and their application in industrial furnaces, ash output is a crucial factor. Lower heating (Calorific) value is correlated with greater ash yield. High ash content in coal decreases its thermal efficiency, hinders combustion, and lengthens the burning process[21].

The amount of coal that needs to be burned in a solid condition is represented by the fixed carbon.

Understanding fixed carbon is useful when choosing combustion equipment since its shape and hardness indicate a fuel's caking qualities.The fixed carbon content is used to measure the amount of char produced during thermochemical conversion. Once the volatile materials have been removed, there remains a solid residue that can be burned. The yield of char produced during the

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thermochemical conversion process increases as fixed carbon concentration increases[24]. The most prevalent volatile substances in coal are sulfur dioxide, carbon dioxide, and water. When the fuel is heated and easily ignites, Volatile matter is forced out, helping the ignition of the coal. The basic rule is that coal burns more slowly and gets harder to ignite when the Volatile Matter declines and the fuel ratio (fuel ratio = fixed carbon/Volatile Matter) rises. Low volatile coal requires less turbulence during burning and takes longer to finish than high volatile coal. The burners near one side of the furnace roof feed the primary air and coal vertically downward. The gas outlet runs along a predetermined path through a different side of the roof.

2.5 Experiment in the drop tube furnace

The combustion characteristics of solid fuels, such as coal and biomass, are commonly investigated using a Drop Tube Furnace (DTF), where a sample is burned in a high-temperature environment and the resulting reaction products are analyzed to determine important parameters such as ignition temperature and burnout time[25]. Another technique called Thermogravimetric Analysis (TGA) can evaluate the weight loss of the samples that can help to evaluate combustion behavior of fuels. The fuel had a high calorific value and could be used as a substitute energy source. The researchers also found that the fuel had high volatile matter and low ash content, which made it suitable for burning.[21].

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24 Figure 6. Schematic of a vertical drop tube furnace.[26]

In a study that focused on four different fuels, namely, beech wood, oak wood, wheat straw, and coal, and investigates their combustion characteristics under different conditions.

The results of the study show that the combustion behavior of the fuels varies significantly depending on the fuel type and combustion conditions. Beech and oak wood showed a relatively stable combustion behavior with a well-defined char burnout zone, while wheat straw showed a high rate of volatile release and a relatively low burnout efficiency[23]. Coal, on the other hand, exhibited a highly efficient combustion process with a low amount of unburned carbon.

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Figure 7. Profiles of the three coals' temperatures, gas species concentrations, and burnout along the DTF's axis (b)profiles of temperature, gas species concentration, and particle burnout along the drop tube furnace's axis.[23]

The study also highlights the importance of the experimental setup and conditions in determining the combustion behavior of solid fuels. The use of a drop tube furnace, which allows for controlled heating rates and residence times, was found to be an effective method for studying the combustion behavior of solid fuels.

The combustion of coal and biomass fuels has been extensively studied in recent years due to the increasing demand for renewable energy sources and the need to reduce greenhouse gas emissions.

TGA has been used to investigate the combustion properties of various coal and biomass fuels, including coal, wood, straw, and agricultural waste. The results of these studies have shown that coal and biomass fuels have different combustion characteristics, with biomass fuels generally having lower ignition temperatures and higher burnout times than coal. [17] Provides an overview of the oxy- fuel combustion technology for solid fuels. The authors describe the basic principles of oxy-fuel combustion, the advantages and challenges associated with the technology, and the current state of the art. The study found that the main challenge of oxy-fuel combustion is to maintain stable flame conditions while avoiding carbon dioxide recycling.

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The temperature of the char particle was gauged during the combustion tests using both pre-calibrated two-color pyrometer and a flexible thermocouple[27]. According to the findings, the pore structure of the char produced in an H2O environment was superior to that produced in a CO2 and N2 atmosphere.

The burnout time reduced and the particle temperature increased as expected as the oxygen content increased. Burnout times for the various ranks of coal char were as follows: anthracite > bituminous coal > lignite[27]. Intriguingly, compared to O2/CO2 and O2/N2 combustion, O2/H2O combustion may accomplish a shorter and a lower of char concurrently regardless of the environment or oxygen level.

The ignition and burning characteristics of individual particles from two types of biomass waste and three types of coal were evaluated in the hot combustion byproducts of a CH4-fueled Hencken burner [3]. The flue gas was injected with particles of lignite, bituminous coal, anthracite, and residues of corn and wheat straw, all of which were between 125 and 150 um in size. The study examined the temperature and oxygen content of flue gas, using a combination of nitrogen and oxygen, as well as carbon dioxide and oxygen. Images of individual burning particles were captured using an ICCD camera equipped with a filter that only allows light with a wavelength of 430 nm to pass through, and the CH* chemiluminescence was also captured in a time-resolved manner.[3],[17]. The findings demonstrate that whereas bituminous coal and anthracite particles lit heterogeneously in both cases, biomass and lignite particles ignited uniformly. For the biomass and lignite particles, the volatiles were gas-phase-combusted in an engulfing flame around the particle, and the char was then oxidized heterogeneously. The coal particles burned more quickly than the biomass particles. With an increase in their volatile content, the igniting delay time for the three coals dropped practically linearly. All solid fuels took longer to ignite when CO2 took the place of N2, and volatiles burned off more slowly[19]. In another study, concentrated was on the outcomes of burning pulverized coal and biomass fuels in a Visual Drop Tube Furnace, where a combustion flame created by continuous fuel input was viewed and captured using a high speed camera. The fuel igniting properties have been successfully translated by the automatic picture post processing method used to quantify the data.

According to the findings of the coal combustion experiments, the decrease in the fuel's volatile content is connected with an

The materials and residues from in-nature were assessed using TG/DTG (thermogravimetric/derivative thermogravimetric), SEM pictures, and EDS analyses (energy- dispersive spectroscopy). Some of the most significant morphological variations in the in natural materials were seen in the SEM pictures[21],[28]. The TG/DTG curves in naturally occurring pine sawdust and the residues produced by various thermochemical processes (conventional and oxy-fuel

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combustion) in DTF are shown in Figures (a) and (b) below. The natural sample's DTG curve (b) shows well-defined peaks at 328 and 460 degrees Centigrade, which correspond to maximal combustion rates and can be attributed to the thermal degradation of holocellulose and remaining lignin. Crystalline samples are often characterized by thin peaks and elongation.

Figure 8. Shows the TG and DTG curves for in-nature samples and pine sawdust residues following combustion using conventional fuel (80% N2) and oxy-fuel (80% CO2) in DTF.

Figure 9. TG for (a) and DTG for (b) curves of the in- natura samples and sugarcane bagasse residues

after conventional combustion (80% N2) and oxy-fuel combustion (80% CO2) in DTF.

Nitrogen does not participate in combustion[21]. It is a harmful component because it increases stack temperatures by absorbing heat from the combustion process. Reduced combustion efficiency are a

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result of both high CO levels and extra air. While combustion in oxy-fuel environment makes the combustion highly efficient even though the oxygen also absorbs heat from the combustion process.

Similar to this, the study contrasts in-nature samples of sugarcane bagasses burned in conventional combustion at 80% N2 with oxy-fuel combustion at 80% CO2 in a drop tube furnace using thermogravimetric analysis (TGA) and derivative thermogravimetric analysis (DTGA). The temperature in the experiment is 700°C, the heating rate is 10°C/min, the sample weight is 10MG, and the flow rate of the synthetic air is 100 liters per minute[28]. The graph above shows the results, which show a "Shoulder" about 310°C, which denotes a significant hemicellulose content as well as the simultaneous breakdown of hemicellulose and cellulose. The "Shoulder" for the oxy-fuel combustion of sugar cane bagasse was not found; instead, a peak was seen at 445° that was attributed to the remaining lignin breakdown. Other research comparing various biomasses and coals have been conducted by various authors, and most of the results of TGA analysis are comparable[21].

In a study of a combination of biomasses and coals, the ignition and combustion properties of individual particles of two types of biomass waste and three types of coal were studied by analyzing the hot combustion byproducts of a CH4-fueled Hencken burner. The flue gas was injected with particles of lignite, bituminous coal, anthracite, and residues of corn and wheat straw, all of which were between 125 and 150 m in size. The flue gas had an average temperature of 1550 K and a mean oxygen content of about 15 mol%. Environments of synthetic air and CO2/O2 were used for the studies. An ICCD camera with a 430 nm band-pass filter was used to take images of the single burning particles' CH* chemiluminescence that were temporally resolved[23]. The findings demonstrate that whereas “bituminous coal and anthracite particles ignited heterogeneously in both N2/O2 and CO2/O2

environments, biomass and lignite particles” ignited uniformly. For the biomass and lignite particles, the volatiles were gas-phase-combusted in an engulfing flame around the particle, and the char was then oxidized heterogeneously. The coal particles burned more quickly than the biomass particles[27].

With an increase in their volatile content, the igniting delay time for the three coals dropped practically linearly. All solid fuels took longer to ignite when CO2 took the place of N2, and volatiles burned off more slowly. All solid fuels burned with significantly less intensity in the CO2/O2 environment than it did in the N2/O2 environment[3].

There are very many published experimental work done on oxy-fuel combustion. Most of which are done with different kinds of biomass from different regions of the world, different forms of coal and a combination of coal and biomasses. The review of these literatures cannot be over emphasized as

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the aim of this work is to carry out oxy-fuel combustion on biomasses and coals available in Kazakhstan. Among the work that will be carried out include Pyrolysis, TGA, Burnout time of different coals, Modelling and Validation of results.

The combustion of solid fuels, such as coal and biomass, produces CO2 as a byproduct. The amount of CO2 produced can be influenced by the type of oxygen (or air) used in the combustion process.

When oxy-fuel is used, the concentration of O2 can be controlled, potentially leading to a higher percentage of CO2 production compared to when normal air (O2/N2) is used. Increasing the O2

percentage in the oxy-fuel mixture can increase the amount of CO2 produced.

2.6 Image Processing of Combustion capture

The complexity of flames and related phenomena can be better understood by oxy-fuel studies performed in drop tube furnaces. In order to evaluate combustion efficiency, emissions, and flame characteristics, accurate measurement and analysis of flame temperature is required. Researchers may investigate the combustion process in great depth with the help of photographs of the flames thanks to image processing tools, which are both non-invasive and inexpensive[18]. Taking good pictures of a flame is the first step in doing a temperature analysis. Images of flames have been captured using a wide range of imaging modalities, from high-speed cameras and infrared cameras to laser-induced fluorescence. For a reliable depiction of the flame structure and temperature distribution, these pictures are usually taken at varying exposure durations and in carefully regulated experimental circumstances.

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30 Figure 10. Image of different oxy-fuel combustion[29]

Preprocessing is critical for improving flame images by removing unwanted noise and artifacts that can interfere with analysis. Picture denoising, augmentation of contrast and brightness, picture registration, and background subtraction are all common preprocessing techniques. These methods enhance flame visibility and allow more precise temperature estimation[18]. Estimating the temperature of a flame is an important part of the image processing required for oxy-fuel research.

Gray-level-based methods, color-based methods, and spectrum analysis techniques are only few of the many that have been proposed in the literature for temperature estimation. The color-based approaches take advantage of the spectrum features of the flame, while the gray-level methods use the intensity information in the photos to estimate the temperature[30]. The temperature distribution within a flame can be accurately mapped using spectral analysis methods like flame emission spectroscopy. Accurate temperature estimation requires validating image-based observations against known temperature benchmarks through the process of calibration. Thermocouples, pyrometers, and reference flames of established temperatures are used in calibration procedures. In order to ensure the accuracy of the image processing methods, the estimated temperatures are checked against the

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calibrated readings. Recent developments in image processing techniques have greatly increased the accuracy and efficiency of flame temperature estimation, but this improvement has not come without its share of challenges. Among these is the use of convolutional neural networks and other machine learning methods for analyzing fire pictures. But there are still obstacles to overcome, such as distorted images from flame flickering, segmenting flames in complicated surroundings, and balancing precision and computing complexity.

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CHAPTER 3

METHODOLOGY

3.1 Elemental Analysis of Coal samples

In order to determine the key physical and chemical properties of the Ekibastuz coal and Shubarkol coal, a comprehensive fuel analysis was conducted. The fuel analysis included determination of ash content, moisture content, volatile matter, and fixed carbon.

3.2 Ash Content Determination

The ash content of the coal samples was determined using the standard ISO 18122:2015E method. In this method, a known weight of coal sample was combusted in a muffle furnace at a temperature of 525°C for 30minutes. The ash residue was collected, weighed and the ash content was calculated as the percentage of the original weight of the sample.

3.3 Moisture Content Determination

The moisture content of the coal samples was determined using the standard ISO 18134-3:2015E method. In this method, a known weight of coal sample was dried in an oven at a temperature of 110°C until a constant weight was obtained. The moisture content was calculated as the difference between the original weight of the sample and the weight after drying, expressed as a percentage of the original weight.

3.4 Volatile Matter and Fixed Carbon Determination

The volatile matter and fixed carbon content of the coal samples was determined using the standard ISO 18123:2015E method. In this method, a known weight of coal sample was combusted in a bomb calorimeter under controlled conditions. The volatile matter was calculated as the percentage of the original weight of the sample that was lost during combustion, while the fixed carbon was calculated as the difference between the original weight and the weight of the ash and volatile matter[31].

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3.5 Sample Preparation

A representative sample of Ekibastuz coal and Shurbakol coal was obtained from the mine site. The sample was crushed and sieved to obtain a particle size of 150-300um. The prepared sample was used for the fuel analysis.

Figure 11. Samples of Shubarkol, Ekibastuz coals as well as wheat straw

3.6 Quality Control

Quality control measures were taken to ensure the accuracy and reliability of the fuel analysis results.

Duplicate samples were analyzed for each coal type and the average of the duplicates was used for data analysis. The standard reference materials were also analyzed to verify the accuracy of the analysis method. The purpose of the fuel analysis was to determine the primary physical and chemical qualities of the Ekibastuz coal and the Shubarkol coal. These properties included the amount of ash, the amount of moisture, the amount of volatile matter, and the amount of fixed carbon. In order to evaluate the acceptability of the coals as potential sources of energy and to compare the coals' behavior when they are burned, the results of the fuel analysis will be employed.

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Table 3. Summary of Proximate and Ultimate analysis of Shubarkol and Ekibastuz coal Proximate analysis (wt. %) Shubarkol coal Ekibastuz coal

Moisture content 2.19 1.37

Fixed carbon 50.16 40.13

Volatile matter 46.5 22.38

Ash content 7.33 36.125

Ultimate Analysis (wt.%)

Ash 7.33 36.13

Carbon 70.93 50.22

Hydrogen 5.05 3.10

Nitrogen 1.81 1.40

Sulphur < 0.01 0.60

Oxygen 22.20 8.56

Wheat Straw

Proximate Analysis (wt. %)

Moisture 3.08

Fixed carbon 11.90

Volatile matter 77.69

Ash content 7.33

Ultimate Analysis (wt. %)

Ash 7.33

Carbon 49.5

Hydrogen 6.2

Nitrogen 0.6

Sulphur 0.2

Oxygen 36.17

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35 Ultimate analysis:

• The ultimate analysis involves determining the carbon, hydrogen, nitrogen, sulfur, and oxygen content of the substance. Here are the steps

• Carbon determination: Weigh 1g of the sample, heat it in a combustion tube, and pass it through a carbon dioxide absorbent. The increase in weight of the absorbent gives the carbon content.

• To determine the amount of hydrogen, take one gram of the sample, weigh it, then heat it in a combustion tube and run it through a water absorbent. The amount of hydrogen that has been absorbed can be calculated based on the rise in the absorbent's weight.

• Nitrogen determination: Weigh 1g of the sample, heat it in a combustion tube, and pass it through a nitrogen absorbent. The increase in weight of the absorbent gives the nitrogen content.

• To determine the amount of sulfur, take one gram of the sample, weigh it, then heat it in a combustion tube before putting it through a sulfur absorbent. The amount of sulfur present can be calculated using the increase in the absorbent's weight.

• Oxygen determination: Subtract the sum of the carbon, hydrogen, nitrogen, and sulfur content from 100 to get the oxygen content.

3.7 Interpretation of results

The results obtained from the proximate and ultimate analysis can be used to assess the fuel quality of the substance. The higher the fixed carbon content and the lower the moisture and ash content, the better the fuel quality. For the ultimate analysis, the carbon content is the most important factor, as it is the primary contributor to the energy content of the fuel.

Overall, the proximate and ultimate analysis can provide valuable information for industries that use these substances as fuel. By knowing the fuel quality of a substance, they can optimize their operations and reduce their environmental impact.

3.8 Thermogravimetric Analysis

Thermogravimetric analysis (TGA) is a technique used to investigate the thermal stability of a material by measuring the weight loss as a function of temperature or time under controlled conditions. In this

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methodology, we will discuss the TGA of Shurbakol coal, Ekibastuz coal, and wheat straw. The assumed operating parameters are as follows:

1. Temperature range: 30°C to 900°C 2. Heating rate: 10°C/min

3. Atmosphere: Nitrogen (purity 99.99%)

Equipment:

Thermogravimetric analyzer (TGA) equipped with a high-precision balance, a furnace, and a gas flow system, sample crucibles (alumina or platinum), Sample holder

Figure 12. Thermogravimetric Analyzer[32]

3.9 Procedure

Preparation of samples:

• Coal samples: Shurbakol coal and Ekibastuz coal are ground to a particle size of 500- 600 microns and stored in a desiccator to maintain the moisture content.

• Wheat straw samples: Wheat straw is ground to a particle size of 250-300 microns and stored in a desiccator to maintain the moisture content.

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3.10 Sample loading

• Coal samples: About 25 mg of coal samples are loaded into the alumina crucible and sealed with a lid.

• Wheat straw samples: About 5-10 mg of wheat straw samples are loaded into the platinum crucible and sealed with a lid.

3.11 TGA measurement

The sample crucibles are loaded onto the sample holder and placed inside the TGA furnace.

The TGA is purged with nitrogen gas (99.99%) at a flow rate of 20 ml/min to remove any atmospheric moisture. The TGA is programmed to heat the samples from 30°C to 900°C at a heating rate of 10°C/min under a constant flow of nitrogen gas. The weight loss of the samples is continuously recorded as a function of temperature.

3.12 Experimental Conditions

• Heating rate = 5°C/min

• Length of quartz tube = 95cm

• Heating zone = 65 cm

• Thickness of quartz tube = 3mm

• Pressure = 1.5bar

• Flowrate = 1l/min

• Particle size = 400microns

• Weight of sample = 3g

• Temperature = 900°C to 1000°C

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O2 N2 CO2

T

Temperature Controller

text

Mixer

Feeder with speed controller Injector

Camera Heating

Element

Gas Analyzer

Figure 13. Schematic diagram of a drop tube furnace

3.13 Description of a Drop Tube Furnace

The study of high-temperature phenomena including combustion, gasification, and pyrolysis can be carried out in a drop tube furnace as shown in figure 6, which is a specific kind of high-temperature furnace. The operation of this furnace is based on the free-fall of a sample material inside of a quartz tube while the temperature is maintained at a constant level. The drop tube furnace that was employed for the execution of this methodology has a quartz tube that is 60 centimeters in length and has an internal diameter of 36 centimeters and an external diameter of 38 centimeters. Temperatures ranging from 30 to 3000 degrees Celsius are possible within the furnace thanks to its adjustable heat settings.

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The needed temperature may be reached in the furnace thanks to a heating element that is constructed out of a high-temperature resistant material such as silicon carbide[20]. This element delivers the necessary heat to reach the desired temperature. After being placed in a sample container, the material to be tested is then loaded into the top of the furnace using a loading mechanism. The sample holder is constructed in such a way that it will keep the sample from moving around or being disturbed in any way while it is falling freely. As soon as the sample is put into the furnace, it is allowed to fall freely through the quartz tube while the temperature is being carefully maintained. The temperature is monitored and controlled using a thermocouple and a PID controller, which guarantees that the temperature will be accurately controlled and will remain steady throughout the experiment. When the sample reaches the bottom of the furnace, it is removed and placed in a collection receptacle so that it can be analyzed further [33]. The collection vessel is designed to capture the sample without any loss or contamination, allowing for accurate and precise analysis of the sample.

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CHAPTER 4

RESULTS AND DISCUSSIONS

The weight loss of the samples is plotted against temperature. The thermograms obtained are analyzed for the onset temperature, peak temperature, and weight loss of each stage of the thermal degradation.

The thermal degradation of the samples is characterized by different stages of weight loss, which correspond to different types of reactions occurring in the samples.

Shubarkol Coal

The graph of Shubarkol coal's weight decrease indicates two separate stages, as can be seen. The coal's moisture is lost during the first stage, which starts when the temperature is below 200 °C. The decomposition of organic materials in the coal causes the second stage, which happens between 200°C and 800°C. As a result of the relatively substantial weight loss during this stage, it can be concluded that the coal contains a sizable amount of volatile matter. The coal's leftover carbon is burned during the last step of weight loss, which takes place above 800°C.

Figure 14. TGA and DTGA curves for Shubarkol coal

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The graph illustrates that the DTGA curve for Shubarkol coal has two peaks. The degradation of hemicellulose and cellulose in the coal is linked to the first peak, which rises between 200°C and 380°C. The second peak, which happens between 400 and 800 degrees Celsius, is connected to the breakdown of lignin and other high molecular weight substances in coal. The TGA and DTGA analysis of Shubarkol coal in a nitrogen atmosphere are consistent with the high volatile matter concentration and good quality of this coal when compared to earlier investigations

Ekibastuz Coal

The weight loss curve of Ekibastuz coal exhibits three separate stages, as shown by the graph in figure 4.2. The coal's moisture is lost during the first stage, which starts when the temperature is below 100°C. The decomposition of volatile stuff in the coal causes the second stage, which happens between 100°C and 700°C. The comparatively small weight loss during this step shows that the coal contains just a small amount of volatile matter. The coal's leftover carbon is burned during the last step of weight loss, which takes place above 700°C.

The graph also demonstrates that the Ekibastuz coal's DTGA curve has three peaks. The coal's internal moisture decomposes at a temperature between 100°C and 200°C, which causes the first peak to appear. The degradation of hemicellulose and cellulose in the coal is responsible for the second peak, which appears between 200°C and 400°C. The third peak is connected to the breakdown of lignin and other high molecular weight chemicals in the coal, which takes place at a temperature between 500°C and 850°C.

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Figure 15. TGA and DTGA of Ekibastuz coal

Wheat Straw

Figure 16 depicts weight losses of wheat straw. The loss of moisture from the wheat straw happens in the first stage, which starts when the temperature is below 100°C. The degradation of hemicellulose and cellulose in the wheat straw causes the second step, which takes place between 100°C and 400°C.

As a result of the weight loss that occurs at this stage being so significant, there must be a lot of volatile stuff present in the wheat straw. The degradation of lignin and other high molecular weight substances in the wheat straw is linked to the last stage of weight loss, which takes place above 400°C.

In the analysis of wheat straw using DTGA in a nitrogen environment. The graph depicts peaks of the wheat straw DTGA curve. The decomposition of moisture in the wheat straw is linked to the first set of peaks, which happens between 100°C and 200°C. The second peak, which happens between 250

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and 400 degrees Celsius, is connected to the breakdown of hemicellulose and cellulose in wheat straw.

The third peak is connected to the breakdown of lignin and other high molecular weight substances in wheat straw, which takes place at a temperature between 400°C and 600°C.

Important details about wheat straw's thermal stability and breakdown characteristics can be learned from the TGA and DTGA analyses performed under a nitrogen atmosphere.

Figure 16. TGA and DTGA of wheat straw

Wheat straw could be used as a source of renewable energy through combustion or gasification due to the comparatively high amount of volatile stuff it contains. Wheat straw has a relatively low ash level, which might improve its ability to burn. To completely assess the potential of wheat straw as a solid fuel source, more research is necessary. Overall, the investigation of wheat straw using TGA and DTGA offers significant insights into the thermal behavior of this renewable resource.

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4.1 Combustion Data Visualization

After series of experiment in the DTF, data was collected and are appropriately represented in the following graphs.

Combustion in compressed air environment

The three different samples were burnt in the DTF in the presence of compressed air and the concentration O2 across three different temperatures.

Table 4a. Oxygen concentration seen in the gas analyzers

900°C 950°C 1000°C

Shubarkol 7% 6.5% 5%

Ekibastuz 7.5% 7% 6%

Wheat straw 5.5% 5.5% 5.5%

Table 4b. CO2 Concentration

900°C 950°C 1000°C

Shubarkol 17% 18% 20%

Ekibastuz 18% 19% 20.5%

Wheat straw 19% 19.5% 21%

The results of the CO2 concentrations at different temperatures for the three different forms of fuel (Shubarkol coal, Ekibastuz coal, and wheat straw) reveal that the combustion of these fuels leads to an increasing concentration of carbon dioxide in the gas analyzer as the temperature increases. Higher temperatures encourage more complete combustion, which in turn leads to the generation of carbon dioxide as a byproduct of the combustion process. This is a typical pattern that may be observed during the combustion process.These interpretations shed light on the behavior of CO2 concentrations throughout the burning of a variety of fuels at several different temperatures.

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Figure 17a. Oxygen concentration of different coal and biomass at different temperature (air) The results reveal that the oxygen contents in compressed air for both Shubarkol and Ekibastuz coals decrease with increasing temperature. Less oxygen in the gas analyzer means more efficient combustion at higher temperatures. While wheat straw's oxygen concentration remains stable, implying a constant combustion behavior across the studied temperature range, rice straw's oxygen concentration fluctuates.

0.00%

1.00%

2.00%

3.00%

4.00%

5.00%

6.00%

7.00%

8.00%

9 0 0 9 2 0 9 4 0 9 6 0 9 8 0 1 0 0 0 1 0 2 0

O2CONCENTRATION

TEMPERATURE

O

2

CONCENTRATION VS TEMPERATURE

shubarkol Ekibastuz wheat straw

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Figure 17b. CO2 concentration of different coal and biomass at different temperature (air)

Table 5. Oxy-fuel case 1(21%O2 and 79%CO2)

Oxy 1 900°C 950°C 1000°C

Shubarkol 7% 6.8% 6%

Ekibastuz 7.5% 7.5% 7%

Wheat straw 5.5% 5% 5%

0%

5%

10%

15%

20%

25%

9 0 0 9 2 0 9 4 0 9 6 0 9 8 0 1 0 0 0 1 0 2 0

%CO2

TEMPERATURE

CO

2

CONCENTRATION VS TEMPERATURE

shubarko l Ekibastuz

wheat straw

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Figure 18. Oxygen concentration of different coal and biomass at different temperature (oxy-fuel

case 1)

Results reveal that in oxy-fuel combustion settings, oxygen concentrations in the gas analyser change with fuel type and temperature. While the oxygen concentration in Ekibastuz coal remains constant regardless of temperature, it decreases somewhat in Shubarkol coal as the temperature rises. Like Shubarkol coal, the oxygen content of wheat straw decreases as the temperature rises.

Table 6. Oxy –fuel (case 2) (30%O2 and 70%CO2)

Oxy 2 900°C 950°C 1000°C

Shubarkol 7% 8% 9.5%

Ekibastuz 10% 11% 12%

Wheat straw 7% 9% 9%

0%

1%

2%

3%

4%

5%

6%

7%

8%

900 920 940 960 980 1000 1020

O2 Conc.

Temperature

O2 Conc. vs Temperature(Oxy1)

shubark ol Ekibastu z wheat straw

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Figure 19. Oxygen concentration of different coal and biomass at different temperature (oxy-fuel

case 2)

Gas analyzer results for oxy-fuel combustion with 30% O2 and 70% CO2 demonstrate that oxygen concentrations vary for different fuels and temperatures. The gas analyzer shows that the concentration of oxygen in Shubarkol coal, Ekibastuz coal, and wheat straw rises as the temperature rises.The rise in the concentration of oxygen depicts that there is excess oxygen available for combustion. These interpretations enable for a comparison of fuels to be made under situations where oxygen concentrations are held constant at 30% during oxy-fuel burning.

Table 7. Oxy-fuel case 3 (40%O2 and 60%CO2)

Oxy 3 900°C 950°C 1000°C

Shubarkol 10.5% 11% 12%

Ekibastuz 12% 13% 13%

Wheat straw 9% 10% 10%

0.00%

2.00%

4.00%

6.00%

8.00%

10.00%

12.00%

14.00%

900 920 940 960 980 1000 1020

%O2 CONC.

TEMP °C

O

2

CONC. VS TEMP.(OXY2)

Shubarkol

Ekibastuz

Wheat straw

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Figure 20. Oxygen concentration of different coal and biomass at different temperature (oxy-fuel

case 3)

Gas analyzer readings for oxy-fuel combustion with 40% O2 and 60% CO2 demonstrate that the oxygen concentration in both Shubarkol coal and Ekibastuz coal rises as the temperature rises. The oxygen concentration in wheat straw increases similarly, though to a lesser extent than in the coal samples. At nearly twice the quantity of oxygen found in air and oxy-fuel, this high oxygen content demonstrates that there is surplus oxygen available for combustion. At 21%, the oxygen content was nearly twice that of air or oxy-fuel. These interpretations shed light on the behavior of oxygen concentrations at various fuels and temperatures during oxy-fuel combustion using 40% O2 and 60%

CO2.

4.2 Combustion Efficiency

Combustion efficiency can be calculated using the following equation.

Combustion efficiency =1 − [஺௢

஺௜ × ܥ݅/ܥ݋] x 100%

Ao and Ai are ash content before and after combustion. Co and Ci represents the carbon content before and after combustion in the DTF.

0.00%

2.00%

4.00%

6.00%

8.00%

10.00%

12.00%

14.00%

9 0 0 9 2 0 9 4 0 9 6 0 9 8 0 1 0 0 0 1 0 2 0

%

Сурет

Figure 1. A flow diagram depicting the oxy-fuel technology used for power generation with carbon  capture and storage (CCS) in a general sense[10]
Figure 2. Technological process for Pre-combustion Capture[14]
Figure 3.  Post-combustion capture technology in power plants[14]
Figure 4 . Oxy-fuel Combustion process.
+7

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