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The Pennsylvania State University

The Graduate School

College of Energy and Mineral Engineering

AN INVESTIGATION OF SYNERGISTIC EFFECT DURING CO-PYROLYSIS

OF COAL AND PINE SAWDUST AT MODERATE TEMPERATURES

A Thesis in

Energy and Geo Environmental Engineering

Robert E. Snow III

Submitted in Partial Fulfillment

of the Requirements

for the Degree of

Master of Science

May 2012

The Thesis of Robert E Snow III was reviewed and approved* by the following:

Sarma V. Pisupati Associate Professor of Energy and Mineral Engineering Thesis Advisor

Dinesh K. Agrawal Professor of Engineering Science and Mechanics Director of Microwave Processing and Engineering at The Materials Research Institute

Yaw D. Yeboah Professor of Energy and Mineral Engineering Head of the Department of Energy and Mineral Engineering

Larry Grayson Professor of Energy and Mineral Engineering Graduate Program Office of Energy and Mineral Engineering

*Signatures are on file in the Graduate School

Abstract

An increasing population growth and the improvements made to the lifestyles of developing countries are leading to an ever increasing need for energy of all kinds. This increase in energy demand will also lead to an increase in the emissions generated by the current energy production methods. These facts combined with the depletion of the world’s available fossil fuels have led to a movement towards the increased use of renewable energy sources.

This work focuses on the conversion of both a renewable fuel, Silver Maple sawdust, and a fossil fuel, Dietz subbituminous coal, into gaseous fuel. It is important to utilize a locally available biomass sample. Silver maple is a common woody biomass readily available in the northeastern

United States. This study investigates the effects of co-utilization on the gaseous products of the pyrolysis process. Pyrolysis is the thermal decomposition of organic matter in an oxygen-free environment.

The objective of this study is to investigate the potential synergistic effect of adding biomass to coal during pyrolysis on the gaseous products. The objective was met by carrying out lab scale pyrolysis experiments in an electrical tube furnace. The feedstock consisted of 0%, 5%, 10%,

20% and 100% biomass. All feedstock blending combinations were heated to 700˚ C and 900˚ C in order to observe any effects of temperature on the synergistic effect of blending.

It was observed that higher biomass concentration increase the quantity of syngas produced. The addition of this biomass species to this coal did not have a synergistic effect on the gaseous production of this process. While promoting hydrogen producing reactions such as methane reforming all effects observed were linear. There was no synergistic effect observed for the co- pyrolyzing of silver maple sawdust and Dietz subbituminous coal. iii

Table of Contents

List of Figures ...... vii

List of Tables ...... ix

Acknowledgements ...... x

Chapter 1 Introduction ...... 1

Motivation ...... 1

1.2 Literature Review...... 4

1.2.1 Coal and Biomass Gasification and Pyrolysis ...... 4

1.2.2 Effect of Temperature ...... 6

1.2.2.1 Effect of Temperature on Gas Composition ...... 6

1.2.2.2 Effect of Temperature on Gas Yield/Heating Value...... 11

1.2.2.3 Effect of Temperature on Char/Tar Yield ...... 13

1.2.3 Effect of Feedstock ...... 13

1.2.3.1 Effect of Feedstock on Gas Composition ...... 15

1.2.3.2 Effect of Feedstock on Gas Yield ...... 18

1.2.3.3 Effect of Feedstock on Tar/Char Yield ...... 18

1.2.4 Effect of Moisture Content ...... 19

1.2.5 Effect of H/C Ratio ...... 20

1.3 Hypothesis and Problem Statement ...... 22

1.4 Research Objectives ...... 24

Chapter 2 Methodology ...... 25

2.1 Silver Maple Preparation ...... 25

2.2 Coal Preparation...... 26

2.3 Experimental Setup ...... 27

2.3.1 Pyrolysis Conditions ...... 29

2.3.2 Pyrolysis Temperatures ...... 30

2.4 Methods for Products ...... 33

2.4.1 Product Fractions ...... 33

2.4.2 Char Methods ...... 34

2.4.3 Gas Methods ...... 34

Chapter 3 Experimental Results and Discussion ...... 36

3.1 Product Fractions ...... 36

3.1.1 Effect of Feedstock ...... 36

3.1.2 Effect of Temperature ...... 38

3.1.3 Effect of Time ...... 40

3.2 Char Analysis ...... 42

3.2.1 Effect of Feedstock ...... 42

3.2.2 Effect of Temperature ...... 44

3.3 Gas Analysis ...... 46

3.3.1 Effect of Feedstock ...... 46

3.3.2 Effect of Temperature ...... 47

3.3.3 Effect of Time ...... 48

Chapter 4 Conclusions and Recommendations ...... 56

4.1 Conclusions ...... 56

4.2 Recommendations for Future Work...... 59

References ...... 61

List of Figures

Figure 1.1 Effect of Pyrolysis temperature on yields of (a) CO2 and (b) CO [48] ...... 7

Figure 1.2 Effect of Pyrolysis temperature on yields of (a) CH4 and (b) H2 [48] ...... 7

Figure 1.3 Variation of gas product compositions with reaction temperatures [34]...... 8

Figure 1.4 H2 yield from coal B pyrolysis at different temperatures. Bars represent average

measured value at each temperature [35] ...... 8

Figure 1.5 Plots for yield of hydrogen from pyrolysis and steam gasification of beech wood at

different temperatures. [18] ...... 8

Figure 1.6 Plots for yield of hydrogen from pyrolysis and steam gasification of wheat straw at different temperatures.[18] ...... 8

Figure 1.7 Yields of H2, CO and CO2 at different pyrolysis temperatures [11] ...... 8

Figure 1.8 Product yields (on the basis of dry weight of sample) of fast pyrolysis from

microalgae at different pyrolysis temperatures [19] ...... 12

Figure 1.9 The pyrolysis of rice straw and sawdust pyrolysis at different temperatures. [31] ..... 12

Figure 1.11 Gas yield vs. temperature [46]...... 12

Figure 1.10 Energy distributions (%) in each fraction from conventional (CP) and microwave

(MWP) pyrolysis. [1] ...... 12

Figure 1.12 Gas formation rates of (a) H2, (b) CH4, (c) H2O, (d) CO, and (e) CO2 from TG

pyrolysis of lignite and corncob [55]...... 17

Figure 2.1 Experimental Setup ...... 28

Figure 2.2 Temperature Modeling at 700º C ...... 32

vii

Figure 2.3 Temperature Modeling at 900º C ...... 32

Figure 3.1 Weight distributions of product fractions at 700 º C ...... 37

Figure 3.2 Weight distributions of product fractions at 900 º C ...... 37

Figure 3.3 Gas Fraction Trend with Different Biomass Content ...... 39

Figure 3.4 Gas Fraction Trend at Different Temperatures ...... 39

Figure 3.5 Volume of gas produced with respect to time at 700ºC ...... 41

Figure 3.6 Volume of gas produced with respect to time at 900ºC ...... 41

Figure 3.7 Char analyses for 700 º C...... 43

Figure 3.8 Char analyses for 900 º C...... 43

Figure 3.9 Temperature comparison of the proximate analysis of char ...... 45

Figure 3.10 Gas Species of Gas Product at 700 º C after 5 min...... 50

Figure 3.11 Gas Species of Gas Product at 700 º C after 10 min...... 50

Figure 3.12 Gas Species of Gas Product at 700 º C after 15 min...... 51

Figure 3.13 Gas Species of Gas Product at 700 º C after 20 min...... 51

Figure 3.14 Gas Species of Gas Product at 900 º C after 5 min...... 52

Figure 3.15 Gas Species of Gas Product at 900 º C after 10 min...... 52

Figure 3.16 Gas Species of Gas Product at 900 º C after 15 min...... 53

Figure 3.17 Gas Species of Gas Product at 900 º C after 20 min...... 53

viii

List of Tables

Table 1.1 Composition (vol%) and HHV of the gasses produced from the conventional(CP) and microwave pyrolysis (MWP) of coffee hulls at different temperatures [1]...... 9

Table 1.2 Properties of Coal for different ranks ...... 14

Table 2.1 As Received Properties of Silver Maple Samples ...... 25

Table 2.2 As Received Properties of Coal Samples ...... 26

Table 2.3 Values for temperature simulation ...... 31

Table 3.1 Gas Species Fraction for Coal (ml/g) ...... 54

Table 3.2 Gas Species Fraction for 5% Biomass (ml/g) ...... 54

Table 3.3 Gas Species Fraction for 10% Biomass (ml/g) ...... 54

Table 3.4 Gas Species Fraction for 20% Biomass (ml/g) ...... 55

Table 3.5 Gas Species Fraction for Biomass (ml/g) ...... 55

Table 3.6 Total Gas Volume of Individual Species for Given Concentration and Temperature .. 55

Acknowledgements

First and foremost I would like to thank Dr. Sarma Pisupati for providing continued guidance and support throughout my Master’s studies. I would like to thank my committee members, Dr.

Dinesh Agrawal and Dr. Yaw D Yeboah for their continued assistant and unique perspectives through my experimental trials.

With my initial Master’s project centering around microwave heating my advancements were driven by Doug Smith and Dr. Dinesh Agrawal continued assistance. My early work would not have been possible without the expertise of Doug Smith. His glass blowing skills and ability to produce intricate glass designs in a timely manner drove early productivity. Doug Smith was also a great man to get to know and be around. He will be greatly be missed and forever remember by all of those whom lives he touched.

The support staff of the Penn State Energy Institute and Material Research Institute was a great assistance throughout. I would like to individual thank Joe Kerns, Jeff Long, Dania Fonseca and

Ron Wasco for their countless hours of training on the instruments necessary to complete my work.

I need to thank Sarma Pisupati and Yaw Yeboah for providing me with financial opportunities to fun my studies and research thus far. Their continued support and guidance in the field of teaching has forever changed my life. They both have provided me with opportunities to expand my horizons and teach multiple classes. The experience I have gained from these opportunities has forever changed my life.

I would like to also thank each and every individual that has worked alongside myself in Dr.

Pisupati’s research group. Brad, Aime, Nari, Hari, Roshan, Ojobane, Prabhat, Latosha and x

Vasudev have all provided me with the assistance and guidance necessary. I would also like to thank my close friends and family for their continued support and positivity especially when things looked down.

Chapter 1 Introduction

Motivation

There are several methods for utilizing the energy stored within biomass. However, gasification processes appear to offer technological advantages for medium to large scale applications [2].

Gasification is a process that converts carbonaceous materials into syngas (a mixture of hydrogen and carbon monoxide) by reacting raw material at high temperatures with controlled amount of oxygen and steam. Gasification, as a thermochemical process is the thermal treatment which results in a high proportion of gaseous products and relatively small proportions of ash and char [3, 4].

Pyrolysis is the most basic process in the thermo chemical conversion of biomass and is the first step in both gasification and combustion [5-12]. This process is defined as the thermal degradation of the sample by heat in the absence of oxygen, which results in the production of char, liquid and gaseous products [13-18]. Thermochemical processes, such as pyrolysis, are available to convert biomass and other fuel sources into more useful energy [12, 16-18].

Biomass is the most commonly used form of renewable energy [19], and is defined as the organic material derived in the recent past from the reaction between CO2, water, sunlight and

other nutrients via photosynthesis [20]. Biomass energy currently represents approximately 3%

of the United States’ final energy consumption, much lower than Coal (21%), Natural Gas (25%)

and Petroleum (37%) [21]. Biomass energy consumption is larger on the global scale because of

large use in undeveloped nations. The utilization of biomass in industrialized nations is

becoming more attractive as it is a renewable resource and it is considered to be CO2 neutral [22-

29]. When biomass grows it “inhales” CO2 and converts it into the energy it needs to grow and

survive. It has been stated, very optimistically, that when the biomass is processed the maximum

amount of CO2 it can release is that of which it has already absorbed which makes biomass to

have net CO2 to be zero [1, 10, 30-32].

When biomass is processed efficiently it can provide the world with high energy outputs that can

help offset and eventually replace the need for fossil fuels [20]. Of these high energy end

products one of the most useful is syngas. Syngas is a mixture of CO and H2 in gaseous form.

Syngas can be utilized as a clean alternative to fossil fuels in power generation, production of derived liquid fuels such as methanol, dimethyl ether and synthetic diesel as well as an input into fuel cells for electricity production [33].

Coal is the oldest fossil fuel used by human beings, and has the potential to be the major energy resource in the future for the world [34]. Coal is, and will continue to be, an important energy source for the foreseeable future [35] due to its high availability and multitude of useful products it can be converted into. The co-firing of biomass and coal is presently being considered as an effective means of reducing greenhouse gasses [36, 37]. The co-utilization of coal and biomass for energy production results in pollutant reduction, most notably the effects on NOx, SOx, CO2

and volatile organic compounds (VOC) [23-26, 28, 36, 38-42]. Pisupati et al. [43] showed that

when bio-oils are combined with lime to form Bio-Lime their use in further thermochemical processing will reduce the emissions of NOx and SO2.

This work focuses on the production of bio-gas from pyrolysis and the possible synergistic

effects of co-pyrolyzing coal and biomass together at moderate temperatures of 700˚ C and 900˚

1.2 Literature Review

1.2.1 Coal and Biomass Gasification and Pyrolysis

Gasification is a thermochemical process that utilizes heat, pressure and steam to convert

carbonaceous materials into synthesis gas. This process occurs with a fraction of the

stoichiometric oxygen necessary for combustion. In general this equivalence ratio, the amount

of oxygen used over the stoichiometric oxygen (on a mass basis), is on the order of twenty

percent. Gasification can be considered incomplete combustion producing carbon monoxide and

hydrogen gas instead of the usual water and carbon monoxide that come from combustion.

Gasification allows us to be able to use fuels, such as biodegradable waste, which would

otherwise have been disposed of. Gasification is an endothermic reaction that requires the addition of heat in order to achieve equilibrium. Due to its flexibility, gasification has been proposed as the basis for “energy refineries” producing a variety of products both chemical and energetic. [44]. Gasification is also considered to be one of the most efficient methods to convert biomass to combustible gas [32].

The principal reactions that occur in gasification are oxygenolysis, hydrogenolysis and hydrolysis. Oxygenolysis is the reaction with oxygen to produce carbon monoxide and carbon dioxide. Hydrogenolysis is the reaction of carbon with hydrogen to produce methane.

Hydrolysis is the reaction of carbon with water to produce hydrogen gas, carbon monoxide and carbon dioxide. [44]

Occurring in the early stages of gasification is the process of pyrolysis. This process dates back to at least Egyptian times, when tar for caulking and certain embalming agents were made by pyrolysis [29]. Unlike gasification and combustion pyrolysis occurs with no extrinsic oxygen.

Pyrolysis converts the feedstock into char, tar and gasses such as hydrogen, methane and carbon monoxide. Like gasification, pyrolysis can utilize fuels that would have been waste. The pyrolysis of coal distills the hydrogen-rich volatile matter and a carbon-rich solid residue remains. The principle material property that determines the volatile yield of pyrolysis is the hydrogen to carbon ratio [44]. Pyrolysis processes have been improved and are now widely used with coke and charcoal production [29].

Thermal processing, in this case pyrolysis and gasification, of coal and biomass can differ greatly. The physical properties of coal and biomass are greatly different. While coal is hard and easy to grind biomass, in this study woody biomass, is soft and difficult to grind. Uniform particle size is relatively easy to attain for coal and very difficult for biomass. In this study sawdust was utilized which removed the need to grind the sample down. The chemical makeup of coal is also vastly different than biomass. Biomass samples will typically have a higher volatile matter (70-90% wt.) than coal samples (30-40% wt.) [44]. Biomass char is a highly reactive material in comparison to coal char. Samples of biomass will have much higher hydrogen content, which is useful in co-utilization as biomass will act as a hydrogen donor for the coal sample. Because of its weaker bonding, biomass samples break down faster and at lower temperatures than coal samples will. This poses a problem for the co-utilization as it is preferable for intermediate interactions to have the feedstock react at similar temperatures.

1.2.2 Effect of Temperature

Pyrolysis is a process consisting of many chemical reactions which take place simultaneously.

The reaction rates for each reaction are dependent on the gasification temperature of the system

being observed. Some reactions are exothermic while others are endothermic. Naturally when

the temperature increases the endothermic reactions will be favored, in their forward direction,

while the opposite trend will be seen in exothermic reactions.

1.2.2.1 Effect of Temperature on Gas Composition

An increase in temperature will alter which reactions are dominant and thus which products

would be favored. When the temperature is increased it will favor the water-gas shift reaction

which is:

(1) CO(g) + H2O(g) ==== CO2(g) + H2(g) -42.3 kJ/kmol

When the water gas shift is favored it should produce larger amounts of hydrogen gas when the temperature increases. Literature clearly shows trends that correspond to this increase in hydrogen at higher temperatures [1, 2, 30, 32, 45, 46]. Figures 1.2-1.7 show non-linear trends for the production of hydrogen gas with respect to an increasing temperature. The non-linearity in hydrogen gas shows that as there is an increase in temperature to 800ºC or greater we can obtain greater increases in hydrogen gas as we continue to increase temperature. Balat et al,

Dominguez et al, and Zhang et al have all noticed this increasing trend for the production of

hydrogen [1, 11, 47]. An interpretation of this data would conclude that reactions occurring in these samples at these temperatures are favoring the consumption of carbon monoxide and this then shifts towards the production of hydrogen. The higher the temperature the greater is the shift in these reactions. At higher temperatures it can be observed that the reactions shift to favor the destruction and break down of hydrocarbons into smaller hydrocarbons or hydrogen and carbon monoxide [1, 11]. If we would like to produce a hydrogen rich syngas then a higher pyrolysis temperature of around 900-1000˚C would be the optimal situation.

Figure 1.1 Effect of Pyrolysis temperature on yields of Figure 1.2 Effect of Pyrolysis temperature on yields of (a) CO2 and (b) CO [48] (a) CH4 and (b) H2 [48]

Figure 1.3 Variation of gas product compositions with Figure 1.4 H2 yield from coal B pyrolysis at different reaction temperatures [34]. temperatures. Bars represent average measured value at each temperature [35]

Figure 1.5 Plots for yield of hydrogen from pyrolysis Figure 1.6 Plots for yield of hydrogen from pyrolysis and steam gasification of beech wood at different and steam gasification of wheat straw at different temperatures. [18] temperatures.[18]

Figure 1.7 Yields of H2, CO and CO2 at different pyrolysis temperatures [11]

] .

32.75 32.75 1.22 1.22 40.06 40.06 2.15 2.15 72.81 3.84 3.84 17.73 17.73 6.74 6.74 0.56 0.56 1000 ˚C ˚C 1000 15.5

different temperatures [ 1 29.28 29.28 1.30 1.30 38.15 38.15 1.95 1.95 67.43 2.50 2.50 22.70 22.70

7.13 7.13 0.78 0.78 800 ˚C ˚C 800 14.0 14.0 hulls at

25.80 25.80 1.38 1.38 35.64 35.64 2.01 2.01 61.44 2.28 2.28 28.42 28.42 MWP 7.25 7.25 0.88 0.88 500 ˚C ˚C 500 12.5 12.5

24.01 24.01 1.12 1.12 27.00 27.00 1000 ˚C 1000 3.68 3.68 51.01 2.40 2.40 32.12 32.12 13.1 13.1

11.66 11.66

1.53

2.05 2.05 23.05 23.05 1.30 1.30 1000 ˚C ˚C 1000 29.85 29.85

12.7 12.7 2.93 2.93 1.43 52.90

32.08 32.08 10.66 10.66

.88 .88 10.5 10.5 800 ˚C ˚C 800 20.87 1.24

25.84 1.54 1.75 46.71 0 10.85 39.14

20.62 20.62 0.45 0.45 6.6 6.6 CP 9.28 9.28 0.60 1.65 29.90 0.36 0.36 56.58 56.58 11.28 11.28 Temperature

6 H 2

4 6 4

9 4 2 + CO (vol.%) /CO (vol.%) H H H Table 1.1 Composition (vol%) and HHV of the gasses produced from the conventional(CP) and microwave pyrolysis (MWP) of coffee of (MWP) pyrolysis microwave and conventional(CP) the from produced gasses the of HHV and (vol%) Composition 1.1 Table 2 2 2 2 2 2 CH CO C H CO C H C ˚C 500 H HHV (MJ/kg)

When observing CO and CO2 yields different literature sources have noticed and documented

different trends. Dominguez et al noticed trends of increasing CO with increased temperature

[1]. Dominguez et al mentioned that a higher content of potassium in the sample could have been acting as a catalyst for the reaction (6) and thus have a higher concentration of CO than other samples [1]. The data obtained by Mathieu and Dubuisson show a decrease in CO, they

both conclude that as the temperature increases the Boudouard reaction (6) accounts for an

increase of CO at the expense of C and CO2 [32]. Ballat et al [47] reported increases in the CO

concentration as the temperature increased. It can be seen from Table 1.1 that there is a small increase in CO from 500˚ C to 800˚ C and then a much larger increase up to 1000º C. Figure 1.3

shows an exponential growth of CO while Figure 1.7 shows a plateau of growth and then a

further expansion at a much higher temperature. Similar discrepancies occurred when looking at

the trends of CO2 with an increased temperature. Herguido et al and Franco et al [2, 46] noticed

increases in the water-gas shift reaction (4) resulting in an increased amount of CO2. It can be

observed that CO2 decreases due to an increase in rates of the dry reforming reactions of CH4

(3)(4), light hydrocarbons, tars, and biomass which all consume CO2 [45]. Zhang et al [11]

noticed an increase in CO2 up until about 1200˚ C and then a decrease. Balat et al [47] noticed a decrease of CO2 over the temperatures observed. Other discrepancies can be accounted for by

the use of different temperature ranges for the experiments. There was a general trend for a

maximum point for both CO and CO2 which would optimize the yields. Different trends would

be observed based on which temperature ranges are being studied and which biomass fuel is

being observed. An increase of CO and a decrease of CO2 at high temperature can be accounted

for by the favoring of the reverse Methane Dry Reforming Reaction (2).

(2) CH4(g) + CO2(g) ==== 2 CO(g) + 2 H2(g) +247 kJ/mol

1.2.2.2 Effect of Temperature on Gas Yield/Heating Value

When temperature is increased there is a global agreement that the overall gaseous yield for the gasification process will also increase. The increase of the gas yield with temperature increase is

due first to the greater production of gas in the initial pyrolysis (faster at higher temperatures).

An increase in gaseous products obtained from pyrolysis at higher temperatures is shown in the

data from [1, 19, 29, 31] and can be observed in Figures 1.8-1.11. Secondly, the endothermic

reactions of the char are:

(3) C(s) + H2O(g) ==== CO(g) + H2(g) +122.6 kJ/mol

(4) C(s) + 2 H2O(g) ==== CO2(g) + 2 H2(g) +90.1kJ/mol

(5) 2 C(s) + 2 H2O (g) ==== CH4(g) + CO2(g)

(6) C(s) + CO2(g) ==== 2 CO(g) +164.9 kJ/mol

These reactions reduce the amount of char and produce gaseous byproducts. Thirdly, the steam

cracking and reforming of the tars, which increase with temperature, result in an increased gas

yield. As should be observed, there is also an increase in carbon conversion efficiency with an

increase in temperature as more carbon is being converted to such gases as CO, CO2 and CH4.

[46]. The high concentrations of CO and CO2 in the pyrolysis gasses are mainly due to the high

degree of deoxygenation produced during the pyrolysis experiments [1].

It is understood that as the hydrogen content of the fuel is increasing along with a decrease in the hydrocarbon content, which should occur at higher temperatures as has been previously described, the heating value of the gas obtained should decrease. Herguido et al and Franco et al both agree with this observation [2, 46]. Narvaez et al explain that as temperature increases the

yield of H2, CO and C2H2 increase and thus the lower heating value increases. Both papers that show an increasing trend in heating value explain the increase to be due to increased carbon efficiency, however increased carbon efficiency would produce more CO, CO2 and H2 which have lower heating values than the hydrocarbons that were consumed to create these products.

Figure 1.8 Product yields (on the basis of dry weight of sample) of fast pyrolysis from microalgae at different Figure 1.9 The pyrolysis of rice straw and sawdust pyrolysis temperatures [19] pyrolysis at different temperatures. [31]

Figure 1.11 Gas yield vs. temperature [46]

Figure 1.10 Energy distributions (%) in each fraction from conventional (CP) and microwave (MWP) pyrolysis. [1]

1.2.2.3 Effect of Temperature on Char/Tar Yield

The effect of temperature on char was first observed within the pyrolysis process. A decrease in pyrolysis char yields when the temperature is increased is mainly attributed to an increase in the devolatilization of the organic material, although partial gasification of the char may also be occurring at the same time [1, 31, 49].

Similarly to the decomposition of char with rising temperatures decreasing trends were seen with the decomposition of tar during gasification. Tar cracking and steam reforming lead to a higher gaseous yield and larger consumption of the tar. The following reactions govern these two mechanisms:

(7) CnHx ==== n C + H2 푥 2

(8) CnHx + m H2O ==== n CO + + H2 푥 �푚 2 � An increase in temperature will increase the rates of equation (7) and (8) thus reducing tar

content [30, 46, 50, 51].

1.2.3 Effect of Feedstock

For a long time people will depend on the use of fossil fuels to provide energy. This is especially

the case for coal utilization for electricity, which is due to the large supplies of coal and the ease in which you can transport coal. There is currently over a 100 year reserve of coal in the world.

Since coal is easily ground it can be densely packed and stored for transportation via rail or freighter. With an increased emphasis on cleaning up the emissions and reducing the use of fossil fuels, blending of coal and biomass is a topic of emphasis.

Unfortunately not all coals are similar. Depending on the age and location of the coal being utilized the properties of the coal will differ. There are generally four major ranks of coal; lignite, subbituminous, bituminous and anthracite. The properties of these different coals are shown in Table 1.2. Different coals also have different sulfur and mineral contents which can make all the difference in processing byproducts.

Table 1.2 Properties of Coal for different ranks

Lignite Subbituminous Bituminous Anthracite

% C 65-72 72-76 76-90 90-96

% H 5% → → 2%

% O 30% → → 1%

% Moisture 70-30 30-10 10-5 5

BTU/lb. 7000 10,000 12,000-15,000 15,000

The different compositions of biomass feedstock namely lignin, cellulose and hemicellulose, along with the different decomposition behaviors of each individual component lead to the diversity that can be observed in pyrolysis and gasification of biomass feedstock. Cellulosic biomass materials quickly decompose in a temperature range of 320˚-400˚ C. With slower decomposition rates, woody materials tend to be the most difficult for pyrolysis and have the longest duration, while the pyrolysis of straw materials begins at much earlier times and lower temperatures than the other two while having a medium reaction rate [10]. 14

The effect of the utilization of different feedstock is important to look into because of the vast differences in what biomass feedstock is available for different regions at different times of year.

In order to produce a useful product, whether it is power or syngas, from pyrolysis of biomass there will more than likely be multiple forms of biomass utilized. These different biomasses range from different woody and plant products to municipal solid waste and sewage sludge, to algae and other carbon based organisms. These feeds should be utilized based on what is readily available for the location at which it will be utilized.

It is important to look at the behaviors of the different feedstock. Coal devolatilization starts around 300˚C and peak around 460˚C, while biomass will start around 200˚C and peak around

370˚C [48]. These temperatures will dictate how fast and at what point different decompositions will occur. An intriguing part of co-utilization of coal and biomass is to see if the lower temperature devolatilization of biomass can lower the activation energy of the coal and therefore induce processes such as pyrolysis and gasification at lower temperatures. If the activation energy is lowered enough to have both biomass and coal feedstock react simultaneously we expect some synergistic effects.

1.2.3.1 Effect of Feedstock on Gas Composition

Since biomass and coal have different properties and different behaviors, they will produce different end products. Figures 1.1 and 1.2 show a comparison of coal and biomass (sawdust) pyrolysis products at different temperatures. The sawdust will produce more carbon monoxide

and carbon dioxide than coal throughout the temperature ranges while only at higher

temperatures can the differences in methane and hydrogen be observed [48].

Each type of biomass has a different composition within itself and therefore, will produce a different end product from the other biomass types. These differences, as previously explained, can be accounted for by their individual content of cellulose, hemicellulose and lignin. A

biomass high in lignin content will have a tendency to form anhydrocellulose and levoglucosan

[29]. As compared to lignin, cellulose will produce more CO and CH4 [52]. Hemicellulose

produces more volatiles, less chars and less tars than cellulose [29]. Lignin produces more

residual char than cellulose while producing a liquid product that is approximately 15% tar and a

gaseous product containing methane, ethane and CO [29]. Lignin will also produce more CO2

and H2 than cellulosic biomass [52].

Pyrolysis products also differ from one rank of coal to another. Xiong et al. [34] showed that lignite pyrolysis produced more carbon monoxide and carbon dioxide but less methane and C2

and C3 components than the pyrolysis of bituminite. Luo et al. [53] looked into the differences

in pyrolysis products as a function of particle size and found that as the particle size decreased

the hydrogen and carbon monoxide content would increase while the carbon dioxide content

would decrease. Coals will also vary by the location where they formed and were subsequently

mined from.

Differences in the gas products obtained have been observed for coal and biomass samples.

Zhang et al. [54] looked at legume straw and Dayan lignite and noticed increases in CO, CO2,

CH4 and H2 for an increased blend of biomass. Sonobe et al. [55] looked into individual gasses

produced for different temperature ranges for both coal and corncob. Figure 1.12 shows that

corncob will produce greater amounts of H2, CH4, CO and CO2 at the lower temperatures but as the temperature increases the production out of coal will be greater [55].

Figure 1.12 Gas formation rates of (a) H2, (b) CH4, (c) H2O, (d) CO, and (e) CO2 from TG pyrolysis of lignite and corncob [55]. 17

1.2.3.2 Effect of Feedstock on Gas Yield

When pyrolyzing biomass the end products depend greatly on the makeup of the biomass utilized. As was previously discussed, the concentrations of cellulose, lignin and hemicellulose affect the outcome of the pyrolysis process. With a high concentration of cellulose in the biomass feedstock, the gaseous yield will be much higher than that of lignin [49]. This is preferable for the overall process of syngas production.

Previous studies have found that biomass produces a larger gas fraction than coal. While these studies agree they do not agree on the relationship of temperature to this change in gas fraction.

Sonobe et al. [55, 56]observed that the gas fraction for coal and corncob to be closer at high temperatures while Zhang et al. [54] found that increasing temperatures made the difference in coal and straw gas fractions more pronounced. These contradicting opinions could be accounted for by the differences in feedstock that was used for the biomass sample. Although we can conclude this is the reason for the differences this is an aspect of this experiment that will need to be further investigated.

1.2.3.3 Effect of Feedstock on Tar/Char Yield

Tar content of the biomass pyrolysis products is one of the most important factors affecting the superseding reactions and processes. Tar and char yields should react in a manner opposite of

the gas yield. A feedstock that yields a large portion of gas will yield a small portion of char.

Higher concentration of lignin in the biomass feedstock will produce more char than cellulosic biomass. The porosity of the char and tars created will affect the cracking process and determine the amount of char and tar produced. Particles with lower porosities will cause the tars to remain a longer time inside the particle and thus more of the tar would be cracked to form gas [49, 52].

The ash content within the feedstock will influence the amount of char produced. A feedstock with a high ash content like straw, will produce more char [46].

Comparisons of coal and biomass pyrolysis show that coal will produce more char than biomass samples [36, 54, 55, 57-59]. Sjöström et al. [57] observed that this trend is more pronounced at lower temperatures. Similarly it was found that coal and blends containing high amounts of coal produce less tar than biomass samples [38, 54, 57]. However, Zhang et al. [54] observed that while at lower temperatures their results are in agreement with this previous statement at higher temperatures there is very little difference in the tar yield and that coal will produce slightly more tar than char.

It can be concluded that the combination of coal and biomass in co-pyrolysis will reduce the amount of tar and char produced as compared to them being processed separately.

1.2.4 Effect of Moisture Content

By its nature, biomass will have some moisture content within it. The moisture content in the biomass pyrolysis can increase the H/C ratio of the resulting gas yield [30]. The benefits of the increase in H/C will be discussed later. Along with increasing this ratio, moisture in pyrolysis

also helps the water-gas shift reaction (2). This reaction, as previously stated, will increase the

H2 content of the resultant gas [2, 45]. Moisture also fuels the steam-char reaction producing H2

and CO. As a result of this reaction the steam introduced will increase the dry gas heating value

[50]. While some moisture is ok, the coal sample will be dried before being pyrolyzed.

1.2.5 Effect of H/C Ratio

The hydrogen to Carbon ratio can give a glimpse into the structure of the biomass. Cellulose is a

carbohydrate and can be represented by CH2O or H-C-OH with an H/C ratio of 2.0. Lignin has a complex benzoic structure; a rough formula for lignin can be C10H13O4 and H/C ratio of 1.3.

The hydrogen to carbon ratio can affect multiple aspects of the gasification of biomass. Different

ratios would support different outcomes and more so different end products. Higher values of

the H/C ratio would reduce the tar due to the following reaction:

(9) CnHx + m H2O ==== n CO + + H2 푥 �푚 2 � Increased H/C ratio would increase the H2 concentration in the resultant gas. A maximum H2

content would occur at an H/C ratio of about 2.3. With the increase in CO and H2 in the resultant

gas the lower heating value of the gas would increase [30].

It is also worth noting that because of its structure coal will have a much lower H/C ratio than biomass samples will. In accordance to previous statements this will produce less hydrogen gas from the pyrolysis of coal than for biomass. Therefore blending biomass and coal will help the

pyrolysis of coal to produce more hydrogen gas due to a higher overall H/C ratio with biomass acting as a hydrogen donor.

1.3 Hypothesis and Problem Statement

There are many factors regarding why researchers are looking into the co-processing of biomass

and coal, the highest importance being the economic factors and emissions reductions. To

increase the overall feasibility of co-processing it would be required that the two types of feedstock interact synergistically. This synergy would create a performance enhancement in energy generation and thus result into a more economically superior product.

When looking at the thermal co-processing of coal and biomass, synergy is when the two fuels

react at the same time and their intermediates react with one another producing a non-additive

product. In the case of coal and biomass co-processing the biomass will donate hydrogen to the coal to assist in the methane dry reforming reactions. This reaction is driven by hydrogen gas to

react with the carbon from the coal.

Different researchers have found different synergies in the co-processing of biomass. Haykiri-

Acma et al and Jones et al [39, 60] observed reductions in NOx, SOx, VOC, PAH and TOC when

biomass was present in the co-processing of coal. Zhang et al [54] noticed that there was

synergy in the product yields of the gas, liquid and char yields where the blended samples are not

in accordance with their parent fuels. Sonobe et al [55] observed synergistic effects by the low-

temperature thermal decomposition of lignite by the exothermic heat released from corncob

pyrolysis.

Woody biomass contains potassium and potassium salts, these components act as catalysts in the

pyrolysis of coal [59]. At larger biomass quantities the catalytic effect of potassium on coal may

lead to some observed synergy. Biomass tends to have an excess of hydrogen which reacts with

coal during pyrolysis causing such synergistic effects as the desulfurization of the coal [54, 61].

Sjöström et al [57] reported that the high thermochemical activity, high volatile content and the

active radicals from devolatilization of the biomass could lead to the synergy observed.

This study will look at the gasses produced from the co-pyrolysis of silver maple sawdust and

sub bituminous coal at 700˚C and 900˚C for biomass concentrations of 0%, 10%, 20% and

100%.

At biomass concentrations that are practical it is anticipated that co-pyrolyzing silver maple

sawdust and sub-bituminous coal at moderate temperatures will have minimal if any synergistic

effect. Many studies have looked into producing synergy with coal and biomass blends but have

ignored the practical limitations of these blends. The limitations placed on this study are

designed to determine where any synergy seen in the thermal processing is occurring. While the

blending of a woody biomass and coal should have a higher quality of gaseous products than

utilization of coal alone, it should not produce a synergistic effect. Blending of feedstock would

reduce the production of NOx, SOx, PAH and PM. This prediction is based on studies that have

shown linear data trends for the gas quantity produced. These studies have shown that the

feedstock will react individually at different times and thus their intermediates will have minimal

interaction [36, 38, 39, 55, 59, 60, 62].

1.4 Research Objectives

In order to get a grasp on what is the cause of any synergy observed in the gasification or combustion processes the pyrolysis of those products must first be investigated. Since pyrolysis

is the first process to occur for either of the previously mentioned thermochemical processes we

can narrow down where and why synergy either exists or does not exist in the co-processing of coal and biomass.

The overall goal of this research would be to find a synergistic scenario where the addition of biomass to coal will produce a large amount of hydrogen gas, generally in the form of syngas, to later be used as a hydrogen fuel source.

Chapter 2 Methodology

2.1 Silver Maple Preparation

The biomass utilized for this study is silver maple sawdust. This biomass stock was derived from the sawdust of a twelve year old silver maple tree that was being cut down for safety reasons. The tree was completely healthy before being cut down. Once the tree was cut the sawdust was gathered and ground down to a particle size less than 2mm. Due to the softness of wood it was deemed too difficult and unnecessary to grind the sample down any further.

The proximate and ultimate analyses of the biomass sample are shown in Table 2.1. A LECO

701 thermo-gravimetric analyzer was used for the proximate analysis, a LECO SC144DR determined the sulfur content, and a LECO TruSpec CHN analyzer was used for the elemental analysis.

Table 2.1 As Received Properties of Silver Maple Samples

Organic Fractiona Moisture VM Ash FC C H N S Ob H/c

7.96 80.12 0.41 11.51 47.60 6.38 0.18 0.00 45.72 1.61 a Dry, ash free basis b Calculated by difference

2.2 Coal Preparation

The coal sample used in this study was pulverized Deitz sub-bituminous coal. The sample was air dried to remove moisture and then ground in a ball mill so that 70% passed through 200 mesh screen. To get the coal ready for experimental studies, individual samples were heated to 107˚C and held there for an hour to remove any remaining moisture.

Table 2.2 As Received Properties of Coal Samples

Organic Fractiona Moisture VM Ash FC C H N S Ob H/c

22.01 34.58 3.75 39.66 56.82 3.95 0.77 0.34 12.36 0.0695 a Dry, ash free basis b Calculated by difference

2.3 Experimental Setup

Figure 2.1 shows the experimental schematic of the experimental studies. Since we are looking

at pyrolysis there must be an absence of oxygen in the reactor. To obtain an oxygen free

environment the reactor is purged with helium. Helium gas flow is monitored through an air

flow meter. The helium then flows into an alumina tube reactor (914mm in length x 45 mm i.d.).

On the other end of the tube there is an exhaust line that runs to an exhaust hood in the lab and

the exhaust line for the experiment that leads into the condensing units. Three consecutive

vacuum tubes filled up with dichloromethane submerged in ice baths were determined necessary

to condense all condensable products. Non-condensable gasses then run to the series of four 1

liter gas sampling bulbs. Four gas sampling bulbs were used so that any time dependent

synergistic effects could be observed. Each gas sampling bulb was filled with water so that

when the gasses flow into the bulb the gasses will displace the water so we can both collect the

gasses and record the volumes. Each experiment concluded with the collection of two 150µl gas samples from each bulb in gas sampling syringes (VIV series-A). Actual volumes of pyrolysis gases were calculated by the difference of the volume of gas in the sampling bulb from the flow rate of the helium multiplied by five minutes, as each bulb collected five minutes of gas accordingly.

Figure 2.1 Experimental Setup

2.3.1 Pyrolysis Conditions

Each of the samples underwent pyrolysis at both 700˚C and 900˚C. The pyrolysis experiments took place inside of the alumina tube as previously described. Helium gas was flowed at a rate

of 750ml/min for one hour to create an oxygen free environment. Brad Hartwell had previously

found that this purging method created an environment with 1.4 molar percentage of oxygen. An

alumina boat was filled with 0.2000g of the samples and placed inside of a 107˚C furnace for an

hour to remove all moisture from the sample [63]. This mass was chosen so that the particle

interactions were minimized so that all synergistic effects shown would be due to the interaction

of the coal and biomass intermediates during the pyrolysis process. Once the reactor was at

temperature and purged of oxygen the alumina boat containing the sample is placed inside the

end of the furnace tube. At this location the temperature was recorded to be approximately

200˚C and 275˚C for heating zone temperatures of 700˚ and 900˚C respectably. At this

temperature it is know that pyrolysis does not occur and that all that will occur is further drying,

there should be minimal to no moisture content at this point, and an insignificant amount of

lignin decomposition. At this point the tube was again closed off and purged for another 5

minutes. Once purged again the cap was removed to allow a rod to move the boat into the

heating zone of the reactor. The exhaust cap was immediately reconnected and the gas flow rate

was then reduced to 100 ml per minute. The first of the four gas sampling bulbs is opened up

and the collection of non-condensable gases begins. After five minutes the first sampling bulb is

closed off and the second bulb is opened up for collection. This process is repeated for a total

run time of 20 minutes. After 20 minutes the end cap is again removed and the sample is pulled

out of the heating zone and allowed to cool. Samples were allowed to cool for at least five minutes after the experiment was concluded.

Each individual trial was repeated three times for reproducibility. Once data was collected for each trial in triplicate the data points were averaged and then that averaged data was plotted.

Reproducibility is a very important aspect of all scientific research.

2.3.2 Pyrolysis Temperatures

Luo et. al. [53] stated that the material temperature is the most important parameter concerned, but it is very difficult to measure accurately because of the existence of large temperature gradients between particles, even in a single particle, owing to the low thermal conductivity of the test material. Gauging the hearth temperature is much easier that gauging the actual material temperature. The change of the hearth temperature can approximately reflect the material temperature change, so that the hearth temperature can be thought of as the pyrolysis temperature. The type K thermocouple was used to measure the temperature profile in the heating zone of the hearth [53].

The temperatures of 700˚C and 900˚C were chosen for this study. These temperatures were chosen so there could be a comparative analysis of low temperature pyrolysis and high temperature pyrolysis. The goal of using multiple temperature ranges is to observe if there are any synergistic effects due to the temperature the feedstock is processed at. Since the sample is inserted into a reactor at the pyrolysis temperature being observed the higher temperature should also have a higher heating rate.

To ensure that the samples are achieving the necessary pyrolysis temperatures the reaction temperature was modeled. To get an acceptable model the thermodynamics are simplified to have conduction on one side through the alumina tube and on the other five sides by helium. It

was further simplified by assuming that once the alumina crucible reached the required

temperature the feedstock would also be at that temperature. This was assumed because the

crucible is a much larger bulk than the feedstock. Figure 2.2 and Figure 2.3 show the modeled

temperatures for 700º C and 900º C respectably. It can be seen that in both cases it takes less

than 15 seconds for the sample to reach the same temperature as the furnace.

The equation used for the simulation is an energy balance for transient conditions as follows:

[ ( ) + ( )] = 4 4 푑푇 − ℎ 푇 − 푇∞ 휀휎 푇 − 푇푠푢푟 퐴푆 휌푉퐶 푑푡 Where = , , = 1800 / , , 푇푠 1−푇푠 2 푘 2 ℎ 푇푠 ∞−푇푠 2 �퐿� 푊 푚 ∙ 퐾 Table 2.3 Values for temperature simulation

Variable k L As ɛ σ Vc

Value 18 W/m∙K 0.01 m 0.0022 m2 0.8 5.67x10-8W/m2 K 880 J/kg K

Figure 2.2 Temperature Modeling at 700º C

Figure 2.3 Temperature Modeling at 900º C

2.4 Methods for Products

2.4.1 Product Fractions

To properly gauge the weight loss of the pyrolysis of the sample it is necessary to measure the

mass of the sample before and after each experiment run. After pyrolysis the char was collected

and placed inside an air tight container. These containers were then placed inside of a desiccator

until further analysis was done.

Due to the high conversion to gaseous products and the small mass of the initial sample there

was an immeasurable small amount of bio-oil collected. The collection method for bio-oil

started off by running the exhaust gas through three condensers of dichloromethane. To keep the

dichloromethane at a low temperature, so that condensing was maximized, the vacuum tubes

used for the condensing were submerged in ice baths. After the experiment was run all three vacuum tubes of dichloromethane were collected into a single beaker. This beaker was then heated and stirred at 40˚C to boil off the dichloromethane and leave only the bio-oil behind.

There was no condensation observed on the walls of the reactor. Upon removal of dichloromethane the beaker was weighed with the bio-oil, the bio-oil was then dissolved and removed with acetone and the beaker was then weighed again. For all experimental studies the difference in the weights, the mass of the bio-oil, was smaller than the margin of error for the scales we used (thousands of a gram) and thus determined to be negligible.

For the gas fraction both the mass and the volume were recorded. Since it is very difficult to measure the mass of the gas, the mass was calculated by subtracting the mass of the solid fraction from the initial mass of the sample. It was assumed that there was no liquid fraction and

that all moisture was converted to gas. The setup contained four 1-liter gas sampling bulbs to measure the gas volume. After each experiment the water displacement was recorded as the volume of the gas fraction.

2.4.2 Char Methods

After the char samples were collected, proximate analysis was performed. A Perkin Elmer TGA

7 Thermogravimetric Analyzer was used because of the extremely small mass of the char samples. Thermal gravimetric analysis (TGA) is an experimental technique recording continuous data of weight loss as a function of time as the sample is heated at a given rate to certain temperatures. When studying samples of approximately five milligrams, the thermal processes undergone by the material are controlled by chemical kinetics. TGA studies are useful for the comprehension of pulverized fuel thermal conversion and to acquire knowledge about the chemical structure of materials [64]. Since there was such a small amount of sample it was only possible to run proximate analysis on the char and not ultimate analysis.

2.4.3 Gas Methods

The product gases of these pyrolysis experiments were all characterized using a Shimadzu GC-

17a gas chromatograph. Two 150µl samples of gas were collected from each gas sampling bulb for each experiment. These syringe samples were then injected into the chromatograph. The

chromatograph consists of a Flame Ionization Detector (FID) and a Thermal Conductivity

Detector (TCD).

Operation of the chromatograph has a continuous flow of helium gas at 30ml/min. Once the system is warmed up the samples are injected into the two detectors. The system heats up to

35˚C and held there for 5 minutes. The temperature then is raised at a rate of 10˚C per minute until it reaches 200˚C. The system holds at 200˚C for two minutes at which point the analysis is concluded and system temperature is dropped back down to 35˚C for the next sample’s analysis.

In order to get an accurate analysis of the gasses, gas standards are run each day the tests were being run. Since conditions such as temperature and humidity can change day to day, running the standards daily gives us an accurate measure for each species every time.

Chapter 3 Experimental Results and Discussion

3.1 Product Fractions

3.1.1 Effect of Feedstock

Figure 3.1 and Figure 3.2 show the percent weight distribution on an ash free basis of the char (solid residue) and gas (incondensable volatiles) for the 700˚C and 900˚C experiments. No matter what fraction of biomass was used in this study there was no significant oil production.

This is due to the small sample size used as was previously explained. The largest amount of gas was produced from the 100% biomass sample and the least was from the 100% coal sample. The biomass samples should produce greater quantities of gaseous matter than coal because their constituents break down easily at low temperatures. It is observable from Figure 3.1 that a fraction greater than 10% of biomass in the sample will produce more gaseous products than char at 700˚C. At 900˚C, as can be seen in Figure 3.2 this parity does not exist as all mixtures produce more gaseous matter than char. These temperature effects will be discussed later.

The increase of gas yield and the subsequent char yield are linear with respect to the percent biomass in sample. A linear trend with respect to the percent biomass in the sample shows there is no synergistic effect on the gas fraction when pyrolyzing coal and biomass together. The linear trends observed in Figure 3.1 and Figure 3.2 are:

Gas Fraction700 = (0.5822)Biomass Fraction + 0.3398

Gas fraction900 = (0.4167)Biomass Fraction + 0.5534 36

1.0 0.9 700˚C Gas Fraction = (0.5822)Biomass Fraction + 0.3398 0.8 0.7

0.6 0.5 Char % 0.4 Gas % Mass Fraction 0.3 Linear (Gas %) 0.2 0.1 0.0 0% 20% 40% 60% 80% 100% Biomass

Figure 3.1 Weight distributions of product fractions at 700 º C

1.0 Gas fraction = (0.4167)Biomass Fraction + 0.5534 0.9 900˚C 0.8 0.7

0.6 0.5 Char % 0.4 Gas % Mass Fraction 0.3 Linear (Gas %) 0.2 0.1 0.0 0% 20% 40% 60% 80% 100% Biomass

Figure 3.2 Weight distributions of product fractions at 900 º C

3.1.2 Effect of Temperature

Figure 3.3 shows the gas fraction as a function of the biomass fraction in the sample at 700˚C and 900˚C. As was previously stated for both temperatures the gas yield increases linearly as you increase the percentage of silver maple in the sample. Again there is a linear trend in the data and thus suggests that there is no synergistic effect of co-pyrolysis. At 700˚C there is a greater change in gas yield from coal to biomass, increasing from ~33% to ~90%, than there is for 900˚C, which increases from ~55% to ~97%. This trend is due to the temperatures in which the different feedstock was pyrolyzed. Coal is known to pyrolyze at higher temperatures than biomass and thus at lower temperature the pyrolysis of coal is slower to react while the biomass is already undergoing pyrolysis. At higher temperatures both the coal and biomass samples are highly reactive and the change from one feedstock to the other is much more gradual. Figure 3.4 shows the trends of each specimen mixture at 700˚C and 900˚C. It is obvious that all mixtures produce more gas (mass %) at higher temperature. As shown before the increase is more noticeable for the samples with lower biomass content. This is due to coal having higher activation energy for pyrolysis than the biomass. Higher activation energy will cause the feed to begin breaking down and pyrolyzing at a later point in the pyrolysis process.

1.0 0.9 0.8 0.7 0.6 0.5 700 0.4 Gas Fraction 900 0.3 0.2 0.1 0.0 0% 20% 40% 60% 80% 100% Biomass

Figure 3.3 Gas Fraction Trend with Different Biomass Content

1.0 0.9 0.8 0.7

0.6 Coal 0.5 5% 0.4 10% Gas Fraction 0.3 20% 0.2 BM 0.1 0.0 600 700 800 900 1000 Temperature (˚C)

Figure 3.4 Gas Fraction Trend at Different Temperatures

3.1.3 Effect of Time

Another important aspect in the co-pyrolysis of coal and biomass is time, since we would like to

have the pyrolysis of the sample fully complete and thus utilize as much of the feedstock as

possible. In order to ensure complete pyrolysis the residence time, time that the sample is at the

proper temperature, should be long enough. If the residence time is too short the sample will not

fully pyrolyze and the char will contain useful energy. Therefore, optimization of the residence

time is very important for achieving the high overall process efficiency.

As can be observed from Figure 3.5 and 3.6 the total amount of gas produced increases from 5 minutes to 10 minutes and then drops off tremendously. As expected the most gas is produced by the 100% biomass sample and then it decreases down to lowest value in case of pure coal

sample. Since the gas production out of almost all specimens is minimal for times greater than

10 minutes it can be concluded that most of the gas generation takes place in the first 10 minutes of the experiment. Therefore, an optimum residence time is around 10 minutes. It is recommended to have any following experimental studies end at this time, thus allowing us to observe the trends at smaller time intervals.

600 700º C 500

400 Coal 300 5% 10% Volume (mL) Volume 200 20% BM 100

0 5 7 9 11 13 15 17 19 Time (min)

Figure 3.5 Volume of gas produced with respect to time at 700ºC

500 450 900º C 400 350

300 Coal 250 5% 200 10% Volume (mL) Volume 150 20% 100 BM 50 0 5 7 9 11 13 15 17 19 Time (min)

Figure 3.6 Volume of gas produced with respect to time at 900ºC

3.2 Char Analysis

3.2.1 Effect of Feedstock

Figure 3.7 and 3.8 show the Thermo Gravimetric Analysis of the chars obtained from the

pyrolysis experiments. As the biomass content in the sample is increased the volatile matter

(VM) and ash content in the char will also increase. This increase in biomass fraction in the sample will cause a decrease in the fixed carbon (FC) left in the char sample. These values are the percentage of the overall char sample mass. Since the overall mass of the biomass char is less than that of the coal sample the actual amount of ash for the coal will be larger than the biomass sample.

Observing the trends in Figure 3.7 and 3.8 it is noticeable that the data acts linearly. This linear relationship suggests that there is no synergistic effect on the char when combining silver maple sawdust with a sub-bituminous coal. The data for the ash fraction is not displayed as we do not

expect there to be any synergistic effect on the ash fraction.

70% 700º C 60%

50%

40%

Char 30% VM FC 20%

10%

0% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Biomass

Figure 3.7 Char analyses for 700 º C.

80% 900º C 70%

60%

50%

40% Char VM 30% FC

20%

10%

0% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Biomass

Figure 3.8 Char analyses for 900 º C.

3.2.2 Effect of Temperature

Figure 3.9 shows the temperature relationship for the volatile matter, ash and fixed carbon for the char samples over all blend ratios. Looking first at the volatile matter it is observable that the temperature does not play much of a factor in the amount produced. There is a more pronounced effect of temperature in the ash fraction of the char. As you increase temperature you will produce a smaller amount of ash as more radicals are released in the high temperature pyrolysis.

The trend for fixed carbon shows a difference for the 100% coal samples with 900˚C having a larger percentage of fixed carbon. The samples that are 100% biomass have similar fixed carbon for both temperatures. Again all of these trends are linear and show no signs of and synergistic effects.

Figure 3.9 Temperature comparison of the proximate analysis of char

3.3 Gas Analysis

3.3.1 Effect of Feedstock

Comparison of Table 2.1 and Table 2.2 shows that there is more hydrogen in biomass than there is in coal. This coupled with the low activation energy silver maple needs to pyrolyze compared to coal at moderate temperatures are responsible for higher biomass concentrations producing more hydrogen gas. This trend can be observed in Table 3.6. It is observable in Figure 3.7 –

Figure 3.14 that as you increase the percentages of biomass present in the feedstock the higher the quality of the gasses that will be produced from pyrolysis. This observation is more evident for times of 5 minutes and 10 minutes as compared to 15 minutes and 20 minutes because of the volatility of biomass and its affinity to complete its reactions at lower exposure time than coal samples would.

Different authors have suggested that synergy would occur with higher concentrations of biomass in the feedstock. The data collected for these experimental studies shows that this is not the case for the feedstock used. This may be because the samples utilized too small of a fraction of biomass to observe these synergistic effects.

3.3.2 Effect of Temperature

Figures 3.7 - 3.14 and Tables 3.1-3.5 show the volume per gram of ash free sample of the species

of the gas fraction. Up to and, in most cases, including 15 minutes the species increase in

magnitude as the temperature increases. Again this is generally due to the increasing reactivity

and pyrolysis of the specimen producing more gas. The time effects on the gas fraction will be

discussed later.

At higher temperatures the Boudard, Water-Gas Shift and Methane Dry Reforming reactions are

favored due to their endothermic nature. All three of these reactions also favor the production of

hydrogen. This trend can be observed in Table 3.6 for all of the feedstock. No matter the sample composition, as the temperature rises the hydrogen yield increases as these reactions predict.

With this increase in hydrogen gas yield it is also observable that methane and ethylene yields decrease with an increased temperature. The increased temperature breaks down these hydrocarbons to hydrogen and either carbon monoxide or carbon dioxide.

With coal pyrolysis beginning at higher temperatures than biomass the changes in species production at low temperature pyrolysis versus higher temperature pyrolysis will be more pronounced for the higher coal content samples. Hydrogen production is almost 100ml/g higher at 900˚C than 700˚C for 100% coal sample. As the amount of biomass in the sample is increased, the increases in hydrogen production from 700˚C to 900˚C decrease to 90 ml/g,

80ml/g and 70ml/g for biomass concentrations of 5%, 10% and 20% respectably. Thus the effect of temperature is greater on coal than biomass as expected.

High coal concentrations show that more carbon dioxide is produced at 700˚C while more carbon monoxide is produced at 900˚C. This suggests that at 700˚C, for coal samples, reactions (1), (4) and (5) are the driving reactions while at 900˚C reactions (2), (3) and (6) are the dominant driving reactions.

3.3.3 Effect of Time

One of the focuses of this study was to see if there was synergy at a certain point in the pyrolysis process. Figures 3.10 - 3.17 show the gas products for the pyrolysis at 700˚C and 900˚C at 5 minutes, 10 minutes, 15 minutes and 20 minutes. Collecting gas samples at different times allows for the analysis of what products are produced at different points in the processing and in what quantities. With this information it can be inferred what reactions are dominant at which point of the pyrolysis process. These data points are also shown in Tables 3.1-3.5. Looking first at sheer volume of gaseous products it can be observed that the majority of gas production occurs in the first 10 minutes of the pyrolysis process. The dramatic drop off of the gas volume after 10 minutes shows that the reactions have run low or out of free hydrogen and carbon, the driving forces of these reactions.

For both temperatures and at all proportions of biomass the hydrogen production peaks around

10 minutes and then decreases for all times after this point. The reactions previously discussed would have run with high proficiency in the first half of the time of the experimental studies and thus depleted the carbon and hydrogen sources allowing for minimal proficiency of these

reactions after 10 minutes. After 10 minutes it can be concluded that any promising reactions have ceased and production of a gaseous product is no longer beneficial.

70 700º 5 Min 60

methane 40 ethylene mg/g 30 hydrogen

20 carbon monoxide carbon dioxide 10

0 0% 20% 40% 60% 80% 100% Biomass

Figure 3.10 Gas Species of Gas Product at 700 º C after 5 min.

100 90 700º 10 Min 80 70 60 methane 50 ethylene mg/g 40 hydrogen 30 carbon monoxide 20 carbon dioxide 10 0 0% 20% 40% 60% 80% 100% Biomass

Figure 3.11 Gas Species of Gas Product at 700 º C after 10 min.

14 700º 15 Min 12

methane 8 ethylene mg/g 6 hydrogen

4 carbon monoxide carbon dioxide 2

0 0% 20% 40% 60% 80% 100% iomass

Figure 3.12 Gas Species of Gas Product at 700 º C after 15 min.

3.5 700º 20 Min 3

2.5

2 methane ethylene mg/g 1.5 hydrogen carbon monoxide 1 carbon dioxide 0.5

0 0% 20% 40% 60% 80% 100% Biomass

Figure 3.13 Gas Species of Gas Product at 700 º C after 20 min.

45 900º 5 Min 40

30 methane 25 ethylene

mg/g 20 hydrogen 15 carbon monoxide 10 carbon dioxide 5

0 0% 20% 40% 60% 80% 100% Biomass

Figure 3.14 Gas Species of Gas Product at 900 º C after 5 min.

60 900º 10 Min 50

40 methane 30 ethylene mg/g hydrogen 20 carbon monoxide carbon dioxide 10

0 0% 20% 40% 60% 80% 100% Biomass

Figure 3.15 Gas Species of Gas Product at 900 º C after 10 min.

25 900º 15 Min

15 methane ethylene mg/g 10 hydrogen carbon monoxide

5 carbon dioxide

0 0% 20% 40% 60% 80% 100% Biomass

Figure 3.16 Gas Species of Gas Product at 900 º C after 15 min.

20 900º 20 Min 18 16 14 12 methane 10 ethylene mg/g 8 hydrogen 6 carbon monoxide 4 carbon dioxide 2 0 0% 20% 40% 60% 80% 100% Biomass

Figure 3.17 Gas Species of Gas Product at 900 º C after 20 min.

Coal 700˚C 900˚C Time 5 10 15 20 5 10 15 20 methane 3.08 5.26 0.24 0.12 7.91 4.93 0.27 0.05 ethylene 27.54 24.00 1.40 0.72 5.38 2.66 0.62 0.15 hydrogen 0.02 0.96 0.52 0.19 1.34 1.42 0.68 0.43 carbon monoxide 14.02 14.50 1.86 1.52 22.80 9.70 3.70 3.48 carbon dioxide 10.78 48.19 5.64 2.88 19.13 5.13 2.36 12.85 Total 55.44 92.91 9.66 5.43 56.56 23.83 7.63 16.96

Table 3.1 Gas Species Fraction for Coal (ml/g)

0.05 700˚C 900˚C Time 5 10 15 20 5 10 15 20 methane 3.11 5.74 0.41 0.12 8.28 5.94 0.14 0.04 ethylene 28.45 29.88 2.01 0.73 8.96 2.92 0.33 0.14 hydrogen 0.10 1.07 0.55 0.11 1.35 1.57 0.67 0.41 carbon monoxide 15.64 20.47 2.41 1.57 24.90 10.03 3.72 3.22 carbon dioxide 13.89 51.98 6.10 2.87 19.68 6.58 2.53 13.17 Total 61.19 109.13 11.49 5.40 63.18 27.04 7.37 16.98

Table 3.2 Gas Species Fraction for 5% Biomass (ml/g)

0.10 700˚C 900˚C Time 5 10 15 20 5 10 15 20 methane 3.54 7.83 0.49 0.13 8.71 6.18 0.11 0.05 ethylene 29.66 30.81 2.59 0.74 9.77 3.17 0.27 0.14 hydrogen 0.16 1.18 0.59 0.00 1.38 1.57 0.63 0.39 carbon monoxide 17.19 22.33 3.05 1.58 25.77 10.87 3.73 2.52 carbon dioxide 15.78 52.91 6.23 2.95 20.35 9.56 2.85 13.68 Total 66.33 115.06 12.95 5.39 65.97 31.35 7.59 16.78

Table 3.3 Gas Species Fraction for 10% Biomass (ml/g)

0.20 700˚C 900˚C Time 5 10 1 20 5 10 15 20 methane 4.19 9.11 0.57 0.16 9.26 6.22 0.10 0.05

ethylene 31.39 35.88 3.47 0.82 13.08 3.63 0.25 0.13

hydrogen 0.27 1.27 0.64 0.00 1.39 1.68 0.61 0.34

carbon monoxide 18.65 27.30 3.55 1.59 26.52 13.08 4.11 1.91 carbon dioxide 19.44 55.99 6.73 2.88 21.03 11.34 3.80 14.73

Total 73.95 129.55 14.97 5.45 71.28 35.95 8.87 17.16

Table 3.4 Gas Species Fraction for 20% Biomass (ml/g)

BM 700˚C 900˚C Time 5 10 15 20 5 10 15 20 methane 11.74 15.97 0.67 0.17 14.33 15.20 0.09 0.03 ethylene 49.41 88.37 11.79 0.74 38.16 13.17 0.22 0.09

hydrogen 0.93 2.47 0.99 0.00 1.47 3.84 0.60 0.04 carbon monoxide 44.16 77.43 7.72 1.46 32.81 45.77 9.45 0.32 carbon dioxide 62.32 76.98 7.69 2.66 23.69 56.34 20.41 17.61

Total 168.56 261.22 28.87 5.03 110.45 134.31 30.78 18.09

Table 3.5 Gas Species Fraction for Biomass (ml/g)

Coal 5% 10% 20% Biomass

700 900 700 900 700 900 700 900 700 900 methane 31.15 60.55 33.59 66.28 42.91 69.29 50.24 71.92 102.21 136.47 ethylene 109.87 23.20 125.06 32.53 130.64 35.16 146.54 44.99 307.79 135.97 hydrogen 48.53 141.90 52.36 146.84 54.91 145.72 62.28 148.03 125.61 218.32 carbon monoxide 65.40 104.64 82.20 110.38 90.53 113.05 104.77 120.27 268.15 232.91 carbon dioxide 88.08 66.22 97.67 70.40 101.63 77.92 110.99 85.41 195.31 198.07

Table 3.6 Total Gas Volume of Individual Species for Given Concentration and Temperature

Chapter 4 Conclusions and Recommendations

4.1 Conclusions

During co-pyrolysis of coal and silver maple sawdust at moderate temperatures all variables

observed responded linearly for concentrations of sample going from pure coal to pure biomass.

Therefore, it can be concluded that no synergy occurred in production of the gaseous species

during pyrolysis in the temperature range examined. This suggests that at 700º C and 900º C in a

helium environment for the given biomass concentrations the pyrolysis of coal and the pyrolysis

of biomass occur separately or there is no stabilization of radicals as expected even though the

feedstock is mixed together. When the reactions occur separately there will be no synergy and

the results will be additive. If the reactions occurred simultaneously then most likely the

intermediates would interact and possibly produce a non-additive synergistic effect. With the

two feedstock having different reactivities for pyrolysis this is no surprise.

As could be predicted hydrogen and syngas production are more prevalent as the amount of biomass in the sample increases. Because the biomass species used has much higher hydrogen content than coal it should produce more hydrogen gas. Higher temperatures promoted the

endothermic reactions that produce hydrogen gas and therefore, an increase in hydrogen

production was observed at 900˚C as compared to 700˚C. These reactions are based on the

breaking down of hydrocarbons such as methane and ethylene to hydrogen gas and carbon monoxide or carbon dioxide as was demonstrated in these experimental studies.

Small sample sizes led to an inability to produce and subsequently collect the oil fraction of the byproducts. This study was designed to avoid interparticle interactions and in order to accomplish this feat the sample had to be dispersed in such a manner that it was as close to a monolayer as possible. This was done so that the feedstock individual particles spread out.

Early experimental studies demonstrated that this method required larger sample size so as to not lose any sample or resultant char in the process of moving the sample boat into or out of the furnace. Low densities and small particle size allowed for high potential of losses from sample blowing away.

These experiments included a time variable in the collection of gasses to assess the potential synergies at different points in the process reactions. It was concluded that there was no synergy at any point in the times observed because all data trends acted linearly and in an additive nature.

It is also worth noting that after about ten minutes very little useful product gasses were produced as the reactions slowed down and in some cases ceased to produce hydrogen. It was also concluded that a proper residence time for this size sample would be ten minutes and not the full twenty minutes that was used in this study.

This study showed that no synergy occurred between this coal sample and silver maple sawdust when co-pyrolyzed in the temperature range. This provides a stepping stone to look into further processes such as gasification to see if there is synergy there. If synergy is observed in these later processes this experiment provides evidence that the synergy existed in the reactions of those processes and not of pyrolysis.

The observations from this study can be extrapolated to temperatures outside the selected region.

Since the temperatures were selected based on the proficiency for synergistic interaction to occur

at moderate temperatures there would be no anticipated synergistic interaction at higher or lower temperatures. However, it is anticipated that at lower temperatures the gaseous production, primarily hydrogen gas, would decrease due to the exothermic nature of the driving reactions.

We can also expect to have more hydrocarbons in the gas sample for the same reason. At higher temperatures it can be expected that further char and tar cracking would occur and thus generate more gaseous products such as hydrogen gas. This will only be true for temperatures at which the feedstock would be sintered. Sintering would result in unprocessed sample being trapped inside of a sintered shell. This would result in both lower gaseous production and conversion efficiency as the mass of the unprocessed solid matter would be greater.

4.2 Recommendations for Future Work

The overall goal of this research was to find if there is synergy in the co-gasification of biomass and coal. In these experimental studies one coal sample and one biomass sample were blended

and co-pyrolyzed to observe the prospect of synergy. The next step in a series of experiments

would be looking into different types of biomass, not just woody, and to see how these different

biomass samples react with different ranks of coal. Due to the nature of low rank coals it

appeared that synergistic co-processing not only has the most likelihood for these samples but

would also provide the greatest benefits to society overall.

It was concluded that the feedstock would react individually at different temperature ranges. In

order to generate more or any synergistic effects we must look into catalysts that would lower the

activation energy of the coal pyrolysis so that the pyrolysis process would overlap at a similar temperature as the biomass feedstock. In order to produce the desired effects the feedstock must react at the same time so that their intermediate radicals will have the ability to react with one another producing more products.

Possible synergy has been mentioned in the liquid fraction of the products in some studies. If this synergy was a point of interest it would be wise to look into the use of algae as the biomass feedstock. Since these experimental studies produced too small of a fraction of liquid products it would also be wise to look into scaling the sample size up so as to produce more products.

To further the knowledge on synergy in co-processing it would be beneficial to process the samples in different atmospheres. Pyrolysis was observed in an inert atmosphere and no synergy was found for these samples. Moving forward, looking at different equivalence ratios for

gasification and different non-inert atmospheres such as carbon dioxide would be extremely

beneficial.

Looking at the time of experimental studies it is observable that after the ten minute mark in the

pyrolysis experiments the gas production decreases greatly and becomes minimal. Future work

in this area of study should take into consideration this time limitation and decrease the overall

exposure time so as to use less energy and increase the overall efficiency of the process.

Many species of biomass contain high quantities of potassium, a known catalyst for thermal

processing. This potassium content can potentially account for the synergy observed in high

biomass blend samples (<50%). In order to assess this theory any synergistic scenarios should have the potassium stripped from biomass to account for the exact cause of synergy.

An additional variable that can be introduced to observe the full potential of synergy in co-

processing is the utilization of microwave heating. Microwaves could aide not only in the

reduction in the energy input into the system but also in the full processing time of the process.

By its inherent nature, coal will couple better with microwaves better than biomass sample will.

Since it couples better with the microwaves the heating of the coal sample will drive the coupling

and therein heating of the biomass species. This dependency of the biomass on the coal sample

could lead to the breakdown of both species at similar times allowing for the interactions of their

intermediates which is the driving force behind synergy.

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