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Theses and Dissertations Theses and Dissertations

1-1-2018

Using Agricultural Wastes and Additives to Improve Properties Using Agricultural Wastes and Additives to Improve Properties

and Lower Manufacturing Costs Associated with Biomass Energy and Lower Manufacturing Costs Associated with Biomass Energy

Pellets Pellets

Cody Blake

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Using agricultural wastes and additives to improve properties and lower manufacturing

costs associated with biomass energy pellets

By

TITLE PAGE

Cody Blake

A Dissertation

Submitted to the Faculty of

Mississippi State University

in Partial Fulfillment of the Requirements

for the Degree of Doctor of Philosophy

in Forest Resources

in the Department of Sustainable Bioproducts

Mississippi State, Mississippi

December 2018

Copyright by

Cody Blake

2018

Using agricultural wastes and additives to improve properties and lower manufacturing

costs associated with biomass energy pellets

By

APPROVAL PAGE

Cody Blake

Approved:

____________________________________

Jason T. Street

(Major Professor)

____________________________________

R. Dan Seale

(Committee Member)

____________________________________

H. Michael Barnes

(Committee Member/Graduate Coordinator)

____________________________________

Hui Wan

(Committee Member)

____________________________________

George Hopper

Dean

College of Forest Resources

Name: Cody Blake

ABSTRACT

Date of Degree: December 14, 2018

Institution: Mississippi State University

Major Field: Forest Resources

Major Professor: Jason T. Street

Title of Study: Using agricultural wastes and additives to improve properties and lower

manufacturing costs associated with biomass energy pellets

Pages in Study: 63

Candidate for Degree of Doctor of Philosophy

The objectives of this dissertation’s studies were to determine the effects of

different additives on biomass wood pellets’ physical properties and the production

energy required to produce each treatment. Chapter II was completed using a pneumatic

pelletizer as a small scale test to determine effects of different additives. The pneumatic

pelletizer was a good indicator of which additives can be successfully pelletized. The

results of this chapter show that using bio-oil can significantly increase calorific value,

without significantly decreasing durability and significantly increasing production energy

required. Corn starch, in a 4% treatment, was shown to not hinder durability or calorific

value significantly, but significantly lower production energy. Biochar was shown to be

an additive insignificant in production due to such a low durability.

Chapter III is a scaled up pelleting study, which takes additives from Chapter II

as well as multiple new additives to determine each one’s effects on the physical

properties and production energy effects. The larger scale, Sprout Walden pelletizer gave

much different results than that of the pneumatic pelletizer. The results tend to prove

beneficial to durability, calorific value, and bulk density with multiple of the treatments.

Vegetable oil was a treatment shown to be less beneficial with each increase in additive

and would not be recommended in a production setting at such levels.

Chapter IV focused on the economic effect of the pellets produced in Chapter III.

Equations were made to determine the possible marginal revenue using each of the

treatments. The marginal revenue equations take into account the changes in durability

and calorific value. Biochar 4%, and vegetable oil at 1% and 2% show that an increase in

marginal revenue could be possible with these treatments.

ii

DEDICATION

This dissertation is dedicated to the friends and family, which have pushed and

encouraged me throughout my research program. To God Almighty for the blessings I

have received thus far in life, I owe all to him. To my parents, Steve and Diane, who have

been a continual support of my academic work all through my years in school and have

made sure I have not lost sight of the end goals. To my grandparents, Charles and

Elizabeth Blake and George and Mary Hazlewood, for teaching how to hold myself as

gentleman and productive man of society, while caring for those I come into contact with

through life. To my beautiful and amazing wife, Carrie, her patience, understanding and

willingness to help has proven to be a constant encouragement and positivity through all

of the small/large setbacks. To my friends I have made throughout graduate school and

before, all of whom have been a source of relief and great memories over the years. To

undergraduate advisor and professors, Dr. Sandy Mehlhorn and John Cole thank you for

the encouragement to pursue and higher degree and encouragement to finish. To the

University of Tennessee at Martin for providing a higher level of education to push me in

learning all that was possible and introducing me to numerous lifelong friends. To my

brother of Alpha Gamma Rho, Alpha Upsilon, for the friendships helping to encourage

me through graduate school and life. To Mississippi State University for the opportunity

and education to allow me to share my research to better those around me and those

finding my findings beneficial. To Sustainable Bioproducts for the lifelong friends,

iii

business acquaintances and professors who pushed me to better myself inside and out of

the classroom. To Dr. Jason Street for being an excellent mentor and professor with

answers to any and all questions that have arose though my degree. Thank you to all that

I have and have not mentioned, you all have made this dream possible and obtainable.

iv

ACKNOWLEDGEMENTS

This material is based upon work that is supported by the National Institute of Food and

Agriculture, U.S. Department of Agriculture, and McIntire Stennis under 1008126. The

authors wish to acknowledge the support of U.S. Department of Agriculture (USDA),

Research, Education, and Economics (REE), Agriculture Research Service (ARS),

Administrative and Financial Management (AFM), Financial Management and

Accounting Division (FMAD) Grants and Agreements Management Branch (GAMB),

under Agreement No. 5B-0202-4-001. Any opinions, findings, conclusion, or

recommendations expressed in this publication are those of the author(s) and do not

necessarily reflect the view of the U.S. Department of Agriculture.” The authors

acknowledge the support from USDA Forest Service Forest Products Laboratory (FPL)

in Madison, Wisconsin, as a major contributor of technical assistance, advice, and

guidance to this research. This research was conducted in cooperation with Mississippi

State University.

v

TABLE OF CONTENTS

DEDICATION .................................................................................................................... ii

ACKNOWLEDGEMENTS ............................................................................................... iv

LIST OF TABLES ............................................................................................................ vii

LIST OF FIGURES ......................................................................................................... viii

I. INTRODUCTION ................................................................................................1

II. USING A PNEUMATIC PELLETIZER TO TEST ADDITIVES IN

BIOMASS PELLETS FOR IMPROVEMENTS IN PHYSICAL

PROPERTIES ...........................................................................................4

Abstract ..................................................................................................................4 Keyword: Biomass pellet, pneumatic pelletizer, corn starch, biochar,

whole bio-oil, fractionated bio-oil, wood only ....................................4

Introduction ...........................................................................................................4 Materials ................................................................................................................6

Pneumatic Pelletizer ........................................................................................6 Feedstock and Additives ..................................................................................8

Methods .................................................................................................................9 Results and Discussion ........................................................................................12

Calorific Value ..............................................................................................12 Durability .......................................................................................................12 Energy Consumed during Production ...........................................................13 Discussion ......................................................................................................19

Summary and Conclusions ..................................................................................19

References ...........................................................................................................21

III. PILOT SCALE STUDY OF ADDITIVES IN BIOMASS PELLETS

FOR IMPROVEMENTS IN PHYSICAL PROPERTIES AND

PRODUCTION EFFECTS .....................................................................23

Abstract. ...............................................................................................................23 Keywords: biomass pellets, biochar, bio-oil, corn starch, vegetable

oil, microcrystalline cellulose, hardwood, sweet potato, and

micronized rubber powder .................................................................23 Introduction .........................................................................................................23 Materials ..............................................................................................................25

vi

Pelletizer ........................................................................................................25

Feedstock and Additives ................................................................................26 Methods ...............................................................................................................27

Results .................................................................................................................30 Durability .......................................................................................................32 Bulk Density ..................................................................................................35 Calorific Value ..............................................................................................38

Summary and Conclusions ..................................................................................41

References ...........................................................................................................44

IV. ECONOMICAL ANALYSIS OF WOOD BIOMASS PELLETING

WITH ADDITIVES WHEN ACCOUNTING FOR CHANGES

IN CALORIFIC VALUE AND DURABILITY.....................................46

Abstract. ...............................................................................................................46 Keywords: Pelleting Additive, Economics Assessment, Pellet

Production, Energy Cost ....................................................................47 Introduction .........................................................................................................47 Calculation Methods: ...........................................................................................48

Equations .............................................................................................................49 Results .................................................................................................................51

Summary and Conclusions ..................................................................................54 Disscussion ..........................................................................................................55 References ...........................................................................................................56

V. RESEARCH CONCLUSIONS AND FUTURE STUDY

SUGGESTIONS .....................................................................................58

Conclusions .........................................................................................................58 Future Studies ......................................................................................................61

VI. REFERENCES ...................................................................................................63

vii

LIST OF TABLES

2.1 Particle size distribution. ....................................................................................9

2.2 Standards for benchmarks and comparison. ....................................................10

2.3 Moisture content of samples. ...........................................................................18

2.4 Dimensions of pellet samples. .........................................................................18

3.1 Particle distribute for southern pine feedstock.................................................27

3.2 Production data during pelletization. ...............................................................31

3.3 Durability descriptive data. ..............................................................................34

3.4 Bulk density descriptive data. ..........................................................................37

3.5 Calorific value descriptive data. ......................................................................40

4.1 Production variables.........................................................................................50

4.2 Prices of additives and feedstocks. ..................................................................50

4.3 Marginal revenue difference compared to control. ..........................................51

viii

LIST OF FIGURES

2.1 Pneumatic pelletizer. ..........................................................................................7

2.2 LabVIEW user interface screen. ........................................................................8

2.3 Results and grouping of calorific value (MJ/kg) content (as created). ............14

2.4 Calorific value (MJ/kg) content on a dry basis. ...............................................15

2.5 Results and grouping of durability tests...........................................................16

2.6 Results and grouping of energy consumed. .....................................................17

3.1 Sprout Walden pelletizer..................................................................................26

3.2 Durability means. .............................................................................................33

3.3 Bulk density means graph. ...............................................................................36

3.4 Calorific value means. .....................................................................................39

1

CHAPTER I

INTRODUCTION

Wood pelleting has become an important field of study in recent years due to the

ever increasing needs for energy throughout the world. Most research has been carried

out in European countries, with relatively few published studies being performed in the

United States (especially on southern yellow pine). The supply of fossil fuel is finite, so

research involving the use of renewable biomass is being conducted around the world to

find alternate sources of energy (Shafiee and Topal, 2009). Over 400 million dry tons of

crop residues are available in the United States alone, and a significant amount of

renewable biomass energy from these residues can be used to replace fossil fuels (US

DOE, 2003). The European Union has an agreement to implement a 20% share of

renewable energy sources and a 20% reduction on greenhouse gases by the year 2020

(Barroso, 2008). With a push to reduce coal emissions, bituminous coal has a calorific

value higher that wood pellets at 22.2 MJ/kg (Goodarzi et al., 2008). Since coal is a non-

renewable resource, wood pellets have the opportunity to replace coal burning facilities

and reduce the emissions from coal.

The EU has recently pushed for improving biomass energy production, while

writing guidelines for companies importing biomass wood pellet additives that are

acceptable. The EU has a stipulation that wood pellet additives in production may not

exceed 1.8% and any additive used may not be chemically altered during the production

2

of the additive desired foe palletization enhancement (European Biomass Association

(AEBIOM), 2015).

Previous research has shown to improve pellet qualities by using different types

of starch and reduce energy input up to 14% (Ståhl et al., 2012). Potato flour, potato peel

residues, and lignosulphate were all used to test each’s effectiveness on compaction

properties and lignosulphate showed promise by increasing the production rate

(Kuokkanen et al., 2011). Corn starch is an additive that is more widely used in the wood

pellet industry, while sweet potatoes are generally a food type substance. Sweet potatoes

(Ipomoea batatas) were used as a new potential revenue stream for waste/unusable sweet

potatoes if positive results were found. Tarasov et al. (2013) discovered through multiple

additives that motor oil and vegetable oil decrease density and only slightly increase

calorific value. Pyrolysis oil, or bio-oil, is a viable option for use as an additive for

producing wood pellets due to its high calorific value compared to wood alone from

~18.5 MJ/kg of pine wood and ~22.5 MJ/kg of the bio-oil produced from pine wood

(Hassan et al., 2009). Since bio-oil is liquid, the application is similar to that of applying

additional water when adjusting moisture. Bio-oil seems to have a tacky consistently in

the lab during production, which could help bind smaller particles to each other and help

increase durability in production. Microcrystalline cellulose is considered a dry binder in

pharmaceutical tableting, acts as a lubricant and reduces friction when moisture in

present (Thoorens et al., 2014).

This dissertation is written as a series of papers following the format of the

American Society of Agricultural and Biological Engineers to which they will be

submitted.

3

While any additive is stipulated to not exceed 1.8% in production, the studies in

Chapter II and Chapter III exceed such condition for a better understanding of how an

increase of each additive could influence pelleting conditions and pellet properties.

Chapter III gives insight in to the pellets produced in Chapter II and the energy used to

produce each treatment and compares the amount of revenue to a control sample to

determine whether or not each treatment could prove to be economically beneficial when

adjusting the value based on the calorific value and durability of the final product.

Chapter II involves bench scale testing of a few additives using a pneumatic

piston pelletizer, which provided results that could potentially be used to determine if a

particular additive would have a chance to improve pellet production and pellet

characteristics when used in an industrial pellet production facility. The pneumatic

pelletizer was built using a LabVIEW program designed to control a heating rope around

a cylindrical die, the piston to actuate with a controlled timer, and a data logger to write

data to a Microsoft Excel Spreadsheet. Additives used in this chapter included biochar,

corn starch, fractionated bio-oil, whole bio-oil and a control. Additives were tested in 2

and 4 wt% increments to understand if adding a particular additive significantly improved

pellet properties.

Chapter III discusses a pilot scale study of how additives used in Chapter II affect

the pelletization process when pellets are produced on an industrial scale. Additional

additives were also investigated in Chapter III to test non-conventional additives that

could be thought of as waste.

4

CHAPTER II

USING A PNEUMATIC PELLETIZER TO TEST ADDITIVES IN BIOMASS

PELLETS FOR IMPROVEMENTS IN PHYSICAL PROPERTIES

Abstract

This study’s primary objective was to determine different additives impact the

properties of southern yellow pine biomass pellets. The specific variables studied include

the energy consumed in production, durability, and calorific value. A pneumatic pelleting

device was constructed to allow more precise production of each pellet, while mimicking

industry’s machinery. A specific moisture and temperature was selected to obtain an

optimum quality before additives were used. Statistical analysis showed that additives

had a significant effect on each of the three tested parameters. The energy consumption

results showed that corn starch at 4 wt% consumed the least mean amount of energy for

production, 3359 kJ/kg. Durability results revealed that corn starch at a 4 wt% had the

highest mean retained material at 90.53%. Calorific values found from the study revealed

that fractionated bio-oil at a 4 wt% had the highest mean content of 20.5 MJ/kg.

Keyword: Biomass pellet, pneumatic pelletizer, corn starch, biochar, whole bio-oil,

fractionated bio-oil, wood only

Introduction

The United States Department of Energy estimates that over 400 million dry tons

of crop residues are produced in the United States alone (US DOE, 2003). These crops

leave tons of residual material behind that is currently wasted, and more research is

5

necessary to determine new methods of using this type of residual biomass in

commercially made solid fuels to lower manufacturing costs and improve pellet qualities.

Energy products in the renewable energy sector can be improved by researching new

techniques and methods to insure waste can be used to more efficiently to create solid

fuels.

The supply of fossil fuels will be diminished within the next 40-100 years, so

finding new renewable fuel sources is important (Shafiee and Topal, 2009). Fossil fuels

take millions of years to form and are responsible for producing approximately 80% of

the world’s energy (31.3% oil, 28.6% coal, and 21.2% natural gas) (International Energy

Agency, 2016). Renewable biomass sources used for energy can be produced in a much

shorter period of time than these traditional energy sources.

Woody biomass is a renewable resource, which when pelletized can be an

alternative to fossils fuels, such as coal. By pelletizing biomass, the bulk density of the

material can be increased by a factor of 4 to 10 times, which reduces the cost of

transportation and storage (Cao et al., 2015). The demand for biomass pellets as a means

of energy has increased significantly worldwide, with a very high demand in Europe. In

Sweden alone, the use of biomass for energy has almost doubled from 68 TWh to about

130 TWh from 1993 to 2013 (Kjarstad and Johnsson, 2016).

The use of additives in pellets to improve properties has been practiced in

industry, and these additives can also reduce energy and maintenance costs associated

with pelletization. Some additives include residuals from the tree, which are normally

removed before the pelleting starts, and include pine cones and bark (Ahn et al., 2014).

Waste wrapping paper has also been used to help bridge the voids within a pellet, but

6

using wrapping paper with the temperatures used in normal pelleting procedures does not

allow for significant improvement in pellet properties (Kong et al., 2012). White sugar,

molasses and sulphite liquor were tested as a method to improve pellet quality with

results showing an increase in durability, 10-20%, a small increase of durability, 1-3%,

and molasses showed a benefit of reducing energy usage (M. Ståhl et al., 2016; Magnus

Ståhl et al., 2016). Some research has proven the use agricultural waste, such as corn

stover, switchgrass, wheat and barley straw can increase the density of an energy pellet

(Mani et al., 2006). Starch has been shown to add moisture resistance, increase hardness

and increase durability levels when added in the pelletization process (Jezerska et al.,

2014).

The objectives of this study were to assess the use of additives in biomass pellets

to (1) reduce the amount of energy required in production, (2) increase pellet durability,

and (3) increase the calorific value of the biomass pellets.

Materials

Pneumatic Pelletizer

A pneumatic pelletizer (Fig. 1) was created and designed to be able to control

small scale experiments on individual feedstocks to be pelleted. This machine was

designed to simulate the industry’s rolling die by filling one die with small amounts of

material, and compressing it to gradually produce a pellet. The pelletizer was built with

an inner die diameter of 7.83 mm (0.31 in) and a length of 66.04 mm (2.60 in)

(compression ratio of 8.4).

7

Figure 2.1 Pneumatic pelletizer.

This pelletizer was run using LabVIEW software (Fig. 2). The design of the

program allowed for a user interface in which the user had the ability to control the die

temperature, time between the piston engaging, starting and stopping the pelleting

process, while writing all data to an excel file. The pelletizer program counted the

number of strokes from the first stroke of new feed stock until all of the feedstock was no

longer visible and no more material was in the die. The number of strokes was used to

calculate the amount of energy consumed along with the collected data of the average

pressure of each test.

8

Figure 2.2 LabVIEW user interface screen.

Feedstock and Additives

Southern yellow pine with no additives was used as the baseline or control group

of all the pellets made, as well as the feedstock material for producing biochar and the

bio-oil used for this study. The particle size distribution used in this study can be seen on

Table 2.1. These particle sizes were used to ensure the consistency of particles in each

pellet (Payne, 1997). Pure corn starch (CS) was purchased at a local supermarket. Bio-oil

was created using a pyrolysis process with an auger reactor at 450 oC using the same

process described in previous studies (Luo, Guda, et al., 2016; Luo, Street, et al., 2016).

As the gases condensed, the liquid oil was collected and the entire liquid fraction was

designated as whole bio-oil (WBO). A bio-oil fraction collected at temperatures of 20-30

oC and mixed with the fraction collected at 110 oC – 400 oC was collected to bypass the

water phase fraction in the temperature range of 30 oC – 110 oC and designated

fractionated bio-oil (FBO). The biochar (BC), from which the oil was derived in

9

pyrolysis, was collected and used in this study. The additives in this study were used in

two increments of two and four percent.

Table 2.1 Particle size distribution.

Sieve Size (mm) Sieve Number Percentage of material

retained on the sieve (wt %)

3.36 6 1%

2.00 10 5%

1.00 18 20%

0.50 35 30%

0.25 60 24%

<0.25 Bottom/Collector 20%

Methods

Depending on the scale of the pelleting process, even a relatively minor decrease

in energy consumption or maintenance costs can have a significant effect on the amount

of money saved, which was a primary goal of this study. Although the study did not use

industrial equipment, the testing methods were completed in accordance with many

industry standards and as a benchmark to grade the pellet quality. The pellet quality

known as ‘Utility Grade’ was attempted to be exceeded in this study. The standards for

pellet quality benchmarks can be seen in Table 2.2.

10

Table 2.2 Standards for benchmarks and comparison.

Industrial Pellet Standards

Fuel

Property

Unit I1 I2 I3 Analysis

Method

Origin - Stemwood

- Chemically

untreated

wood

-Forest

plantation

and virgin

wood

-Chemically

untreated

used wood

-Forest

plantation

and virgin

wood

-By-

products and

residues

-Chemically

untreated

used wood

EN ISO

17225-1

Length mm 3.15< L <40 3.15 < L <

40

3.15 < L <

40

ISO 17829

Diameter mm 6 (±1)

8 (±1)

6 (±1)

8 (±1)

6 (±1)

8 (±1)

10 (±1)

12 (±1)

ISO 17829

Durability wt% w.b. 97.5<DU<99.0 97 < DU <

99.0

96.5 < DU <

99.0

ISO 1783-

1

Calorific

Value

MJ/kg

(BTU/lb)

> 16.5 (~7100) > 16.5

(~7100)

> 16.5

(~7100)

ISO 18125

Feedstock moisture content was found using a moisture analyzer (DSC 500, Delta

Support Company, Panorama City, CA) as well as the moisture content of the additives

on a solids (dry) basis, to determine the mass of the particle sizes required, the amount of

additive to add, and an amount of water to produce the required feedstock mixture. Each

pellet blend was created from a feedstock weight of 8.50 grams. After weighing out each

sample, the additive and wood were mixed to ensure the wood particles and additives

were evenly distributed.

Prior tests were performed on southern pine particles without any additives to obtain the

optimum temperature and moisture content to use for this specific pelletizer which would

produce pellets with the most advantageous properties. Temperatures levels of 120 oC,

11

140 oC, 160 oC, 180 oC, and 200 oC were tested against moisture levels of 10, 12, 14, 16,

18, and 20%. The pellets produced with the most advantageous properties were created at

200 °C with a 14% moisture content. The fast retention time and elevated moisture

content ensured that no charring was seen on the exterior of the pellet. Feedstock blends

were placed in the hopper and were stirred between piston engagements to ensure

particles were secured in the piston trough. Eleven pellet samples were created for each

treatment, in which the first used to create a clog in the die; the next 10 pellets were

analyzed.

Ten pellets were collected from each additive mixture treatment and were

weighed, dimensionally measured, and the moisture content was evaluated. After 1 week

the pellets from each treatment mixture were then again weighed, measured and

evaluated for their moisture content. Seven pellet samples of the 10 collected were used

to determine a durability using a modified version of the ASAE S269.5 standard (ASAE,

2012). The other 3 pellets samples were used in an adiabatic bomb calorimeter test to

determine their calorific value according to ASTM 5373 (ASTM, 2003). Energy

consumption, for all pellets, was calculated using equations 1-3:

𝐹 = 𝑝 ∗ 𝐴 (1)

where p is the gauge pressure (psi), A is the bore area (in2), and F is the force (lbf)

exerted by the pneumatic cylinder,

𝑊𝑠 = 𝐹 ∗ 𝑑 (2)

where d is the distance that the piston travels 92.20 mm (3.63 in) and Ws is the energy

content in one stroke of the piston (psi), is the number of strokes required to form a

pellet.

12

𝑊𝑇𝑜𝑡𝑎𝑙 = ∑ 𝑊𝑠𝑖𝑛𝑖=1 (3)

where WTotal is the total amount of work required to produce one pellet (kJ). By then

dividing WTotal by the feedstock weight, the amount of work per mass (kJ/kg) was

calculated to determine the amount of energy required to produce each pellet. These

equations allow for the determination of how a specific additive will act as a lubricant to

decrease the amount of energy required to produce a pellet.

Heating values (MJ/kg) were adjusted for calibration errors and moisture content

(MC) found in the pellets tested.

𝐴𝑑𝑗𝑢𝑠𝑡𝑒𝑑𝑀𝐽

𝑘𝑔= (

𝐹𝑜𝑢𝑛𝑑𝑀𝐽

𝑘𝑔−𝐵𝑒𝑛𝑧𝑜𝑛𝑖𝑐 𝑎𝑐𝑖𝑑 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒

1−𝑀𝐶) (4)

Results and Discussion

Calorific Value

The calorific value results (Figure 2.3) show that the FBO at the level of 4 wt%

had the highest MJ/kg. CS at a level of 2 wt% had the lowest mean MJ/kg. The groupings

of different additives show that WO and CS were significantly lower than FBO, WBO,

and BC at an alpha value of 0.05. The FBO increased the calorific value of the pellets the

most on average. Dry basis calorific contents (Figure 2.4).

Durability

Durability results (Figure 2.5) show that CS at a level of 4 wt% had the highest

durability average of 90.53 %. The BC at a level of 4 wt% had the most significant

negative effect on durability at 53.43%. The grouping for durability shows that when the

13

BC was used at both the 2 wt% and 4 wt% levels, it caused the durability to be

significantly lower than all the other additives.

Energy Consumed during Production

The results concerning the energy consumed during production (Figure 2.6)

shows that when BC at a level of 2 wt% was used, the most energy was required for

pellet creation, 4200 kJ/kg. The CS additive at a level of 4 wt% caused the least amount

of energy to be required with a result of 3358 kJ/kg.

14

Fig

ure

2.3

R

esult

s an

d g

roupin

g o

f ca

lori

fic

val

ue

(MJ/

kg)

conte

nt

(as

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B

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AA

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A

AA

B

18

.50

19

.00

19

.50

20

.00

20

.50

21

.00

21

.50

22

.00

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Trea

tmen

t

Cal

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15

Fig

ure

2.4

C

alori

fic

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ue

(MJ/

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nt

on a

dry

bas

is.

B

B

AA

A

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17

17

.518

18

.519

19

.520

20

.521

MJ/kg

Trea

tmen

t

Cal

ori

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Val

ue

(Dry

Bas

is)

16

Fig

ure

2.5

R

esult

s an

d g

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g o

f dura

bil

ity t

ests

.

A

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B

C

A

A

AA

A

0.0

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10

.00

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20

.00

%

30

.00

%

40

.00

%

50

.00

%

60

.00

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.00

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80

.00

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.00

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17

Fig

ure

2.6

R

esult

s an

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roupin

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f en

erg

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onsu

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.

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34

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38

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42

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46

00

.00

kJ/kg

Trea

tmen

ts

Ener

gy C

on

sum

ed

18

Moisture determinations (Table 2.3) were made as soon as the pellets were

produced to allow for a better understanding of how well each additive absorbed moisture

in the cooling or storage stages of the pelleting process. The pellets were stored in a

conditioned room at 65% relative humidity and 24 oC. The pellets were mostly

unchanged by the storage conditions over one weeks’ time with dimensional

measurements recorded (Table 2.4).

Table 2.3 Moisture content of samples.

Table 2.4 Dimensions of pellet samples.

Additive Southern

Pine (no

additive)

Corn

Starch 2%

Corn

Starch 4%

Bio-Char

2%

Bio-Char

4%

Whole

Bio-oil

2%

Whole

Bio-oil

4%

Frac Bio-

oil 2%

Frac Bio-

oil 4%

Day 1

Moisture

(%)

1.81±0.60 4.01±

1.48

4.76±0.71 4.52±0.70 4.42±0.31 3.33±0.45 3.26±0.40 3.84±0.32 3.57±0.44

Week 1

Moisture

(%)

2.62±0.44 4.83±1.05 4.85±0.72 4.56±0.54 5.32±0.75 4.29±0.68 4.09±0.70 4.34±1.20 4.10±0.68

Additive Southern

Pine (no

additive)

Corn

Starch 2%

Corn

Starch 4%

Bio-Char

2%

Bio-Char

4%

Whole Bio-

oil 2%

Whole Bio-

oil 4%

Frac Bio-

oil 2%

Frac Bio-

oil 4%

Day 1

Length

(cm)

14.03±0.77 18.04±1.10 15.52±0.82 18.47±1.54 18.26±0.41 15.17±0.61 15.38±1.55 15.07±0.62 15.65±0.62

Day 1

Diameter

(cm)

0.88±0.01 0.88±0.01 0.87±.01 0.87±0.02 0.88±0.01 0.88±0.02 0.88±0.02 0.88±0.01 0.88±0.01

Week 1

Length

(cm)

14.07±0.80 18.41±0.82 15.63±0.77 17.97±0.67 18.51±0.55 15.23±0.56 18.61±1.16 15.05±0.66 15.71±0.85

Week 1

Diameter

(cm)

0.88±0.01 0.88±0.01 0.87±0.01 0.87±0.02 0.87±0.01 0.88±0.01 0.88±0.01 0.88±0.01 0.88±0.01

19

Discussion

The only significant difference when comparing the net calorific value was found

between the CS and the WO pellets when a total comparison was made with the BC,

WBO, and FBO. The BC additive improved the calorific value, but the durability

characteristic decreased. CS at 4% showed the highest significant difference in durability.

The results from each area of this study give an insight for using a particular additive to

improve a certain aspect of southern pine pellets. More studies need to be completed to

better understand the effects of multiple additives on these pellets.

Summary and Conclusions

The results from this study indicate that it is possible to affect properties of

biomass pellets with small amounts of additives. Minor effects occurred most often, but it

is possible that larger sample sizes from a larger production process could yield results of

greater significance. The results from this study suggest that using small amounts of

additives in biomass pellets can substantially affect the pellet properties concerning the

energy content, the durability, and the energy required to produce the pellets. In both the

calorific value and energy consumption tests, increasing the amount of any additive from

2-4% did not have a statistically significant effect on the biomass pellets produced except

when using the CS. When the CS was increased to 4% in the energy consumption test,

the energy requirement was significantly reduced. The durability test proved that the bio-

oil additives (whole and fractionated) were relatively similar to one another, and an

increase in CS did lead to an increase in durability overall. Adding more BC significantly

decreased durability as the additive was increased from 2 wt% to 4 wt%. A significant

20

difference from the control pellet was found in the property concerning the calorific value

when compared BC, FBO and WBO.

Deciding to use an additive could prove to be more helpful than results from this

study fully showed. Bio-oil in either form, whole or fractionated, could add a slight

increase to durability, energy consumption, and a significant increase to MJ/kg content,

while also acting as a lubricant that could help aid in decreasing tool wear to lower

maintenance costs. It is possible to use more than one additive in the biomass pellets,

assuming the combination does not counteract the other additive. The use of more than

one additive would also lead to an increased cost for pellet production. Future economic

studies are warranted and will be performed dealing with the production of the additives

for use in the overall pellet production.

21

References

Ahn, B. J., Chang, H., Lee, S. M., Choi, D. H., Cho, S. T., Han, G. seong, Yang, I.

(2014). Effect of binders on the durability of wood pellets fabricated from Larix

kaemferi C. and Liriodendron tulipifera L. sawdust. Renewable Energy, 62(2014),

18–23. https://doi.org/10.1016/j.renene.2013.06.038

ASAE. (2012). ASAE S269.5 Densified Products for Bulk Handling — Definitions and

Method. St. Joseph, MI.

ASTM. (2003). D5865 - Standard Test Method for Gross Calorific Value of Coal and

Coke. West Conshohocken, PA: ASTM Int.

Cao, L., Yuan, X., Li, H., Li, C., Xiao, Z., Jiang, L., … Zeng, G. (2015). Complementary

effects of torrefaction and co-pelletization: Energy consumption and

characteristics of pellets. Bioresource Technology, 185, 254–262.

https://doi.org/10.1016/j.biortech.2015.02.045

International Energy Agency. (2016). Key world energy statistics. Statistics. Paris:

International Energy Agency. https://doi.org/10.1787/key_energ_stat-2016-en

Jezerska, L., Zajonc, O., Rozbroj, J., Vyletělek, J., Zegzulka, J. (2014). Research on

effect of spruce sawdust with addeed starch on flowability on pelletization on the

material. IERI Procedia, 8, 154-163. https://doi.org/10.1016/j.ieri.2014.09.026

Kjarstad, J., Johnsson, F. (2016). The role of biomass to replace fossil fuels in a regional

energy system: The case of west Sweden. Thermal Science, 20(4), 1023–1036.

https://doi.org/10.2298/TSCI151216113K

Kong, L., Tian, S., He, C., Du, C., Tu, Y., Xiong, Y. (2012). Effect of waste wrapping

paper fiber as a “solid bridge” on physical characteristics of biomass pellets made

from wood sawdust. Applied Energy, 98, 33–39.

https://doi.org/10.1016/j.apenergy.2012.02.068

Luo, Y., Guda, V. K., Hassan, E. B., Steele, P. H., Mitchell, B., Yu, F. (2016).

Hydrodeoxygenation of oxidized distilled bio-oil for the production of gasoline

fuel type. Energy Conversion and Management, 112, 319–327.

https://doi.org/10.1016/j.enconman.2015.12.047

Luo, Y., Street, J., Steele, P., Entsminger, E., Guda, V. (2016). Activated Carbon Derived

from Pyrolyzed Pinewood Char using Elevated Temperature, KOH, H3PO4, and

H2O2. BioResources, 11(4), 10433–10447.

https://doi.org/10.15376/biores.11.4.10433-10447

22

Mani, S., Sokhansanj, S., Bi, X., Turhollow, A. (2006). Economics of producing fuel

pellets from biomass. Applied Engineering in Agriculture, 22(3), 421–426.

https://doi.org/10.13031/2013.20447

Payne, J. D. (1997). Troubleshooting the pelleting process. American Soybean

Association.

Shafiee, S., Topal, E. (2009). When will fossil fuel reserves be diminished? Energy

Policy, 37(1), 181–189. https://doi.org/10.1016/j.enpol.2008.08.016

Ståhl, M., Berghel, J., Granström, K. (2016). Improvement of wood fuel pellet quality

using sustainable sugar additives. BioResources, 11(2), 3373–3383.

Ståhl, M., Berghel, J., Williams, H. (2016). Energy efficiency, greenhouse gas emissions

and durability when using additives in the wood fuel pellet chain. Fuel Processing

Technology, 152, 350-355. https://doi.org/10.1016/j.fuproc.2016.06.031

US DOE. (2003). Roadmap for Agricultural Biomass Feedstock Supply in the United

States. DOE/NE-ID-11129, November.

23

CHAPTER III

PILOT SCALE STUDY OF ADDITIVES IN BIOMASS PELLETS FOR

IMPROVEMENTS IN PHYSICAL PROPERTIES AND PRODUCTION EFFECTS

Abstract.

The goal of this study was to test multiple additives in the production of southern

pine biomass wood pellets to determine the possible benefits of using each additive for

improving pelleting properties. A control was compared to 20 different treatments and

their effect involving comparisons of pellet durability, bulk density, and calorific value.

Biochar, bio-oil, corn starch, vegetable oil, hardwood, micronized rubber powder,

microcrystalline cellulose and sweet potatoes were all added in different concentrations

to determine each effect the additive had on pellet properties. Vegetable oil at levels of

2% and 4% were found to have the significantly poorest performance concerning

durability and bulk density, while also producing the highest amount of fines. The vast

majority of the treatments prove to not be significantly different from the control, with

the exception of corn starch which could be considered beneficial in for pellet production

at the most advantageous concentrations.

Keywords: biomass pellets, biochar, bio-oil, corn starch, vegetable oil,

microcrystalline cellulose, hardwood, sweet potato, and micronized rubber powder

Introduction

Research from a pneumatic testing was scaled up in this chapter to determine the

effects that a larger industrial pelletizer had on several of the additives of interest. The

24

bench-scale pneumatic pelletizer was designed to be used only as a testing mechanism to

ensure innovative

additives could be pelletized successfully. Large-scale testing provides data for the

industrial process and allows the best representation of how each of the additives react to

the advanced heat and pressure of a roller die. Mixed hardwood (HW) was used to better

understand if improvements to pellet properties could be realized by co-pelleting

hardwoods with softwoods and whether or not HW can be beneficial as another feedstock

to use despite lower lignin content and needing a different compression ratio when solely

being pelleted as compared to softwoods (Holt et al., 2006; Stelte et al., 2011). Corn

starch (CS) is a renewable and mass produced additive that is used as a bonder and

stabilizing additive, which when compressed with temperatures above 140°C can help to

bond wood particles in the pelletizing process (Ståhl et al., 2012). Potato flour and peels

have been used to help with binding, but the findings from this research showed no

significant improvements of the pellet properties (Kuokkanen et al., 2011). Sweet

potatoes (Ipomea batatas) have been found to have a higher gelation point than that of

potatoes (Solanum tuberosum) which could extent the time before crystallization in the

high temperatures of a pellet mill (Collado et al., 1999; Kim et al., 1995).

Microcrystalline cellulose (MCC) is used as pharmaceutical binding substance, which

can theoretically could fill voids and help to bind small particles and fines (Sun, 2008).

Vegetable oil (VO) can improve the lubricity of the pelleting process, which can help

reduce the amount of energy needed to push pellets through the die, lower the frictional

force and therefore lower the temperature of the pellet die (Fasina and Colley, 2008).

25

While this study uses virgin VO, an unused mix of peanut and soybean oil, literature

suggests that waste, or used vegetable oil could also prove beneficial to calorific values

(Mišljenović et al., 2015). Sweet potatoes were dehydrated and powdered to act as a

binder due to slightly higher starch peak gelation temperature (Tetchi et al., 2007).

Biochar (BC) is a waste/byproduct of pyrolysis or gasification reactions and in small

scale pelleting has shown to improve the net calorific value (Hassan et al.; Yang et al.,

2014) and durability (Reza et al., 2012, 2014). Bio-oil (BO) is novel treatment thought to

improve wood pellet calorific value and improve durability due to the tackiness of the oil.

Micronized rubber powder (MRP) is a novel pellet additive thought to help with

hydrophobicity and durability due to the gelation, or malleability, at increased

temperatures to bind with the wood particles more tightly as the pellets cool and cure.

The main objective in this study involves the inclusion of additives in an

industrial pelleting process to determine if pellet properties and the pellet production

process can be improved.

Materials

Pelletizer

A 125 HP Sprout Waldron Pelletizer (Figure 3.1) was used for the production of

the biomass pellets with the additives. The pelletizer was fitted with a compression ratio

of 9 throughout all testing for comparable results. The inner die hole diameter measured

0.25 inches. The higher HP of the pelletizer was intended to give companies and other

researchers a better indication of how such additives effect power consumption during the

process.

26

Figure 3.1 Sprout Walden pelletizer.

Feedstock and Additives

Southern yellow pine (Pinus spp.) shavings (SYP) was the primary feed stock for

all pellet testing. The SYP was collected from SouthEastern Timber Products in

Ackerman, MS. The feedstock was found to have no bark being from shavings of lumber

production. A mix of hardwood (HW) shavings were collected from Marietta Wood

Supply in Marietta, MS. Bio-oil (BO) was produced in the pyrolysis lab at Mississippi

State University using SYP, and biochar (BC) was collected from the waste stream of

Weyerhaeuser’s gasifier which was the heat source for their continuous dry kiln in

Philadelphia, MS. Sweet Potatoes (SwP) were purchased from local grocery stores and

dehydrated and ground to a powder for a more homogenous mix. Microcrystalline

cellulose (MCC) was purchased from ChemCenter (La Jolla, CA, USA) with a lab scale

purity. Vegetable oil (VO), a mixture of peanut and soybean oil was purchased as an

additive to help lubricate and bind pellets together (LouAna Oils, Brea, CA, USA). Corn

starch (CS) was purchased in a bulk 50 lb bag (Argo, Oakbrook Terrace, IL, USA).

27

Micronized rubber powder (MRP) MicroDyne 180 was from Lehigh Technologies

(Tucker, GA, USA)

Methods

SYP was sieved with a Universal Vibrating Screen shaker table (Type S, Number

1354, Racine, Wisconsin, USA) to separate particles smaller than 3.25 mm from larger

particles, which were taken to a Bauer grinder (Model 248, Springfield, OH, USA) to

reduce particle size until passed through the sieve (Table 3.1). Bulk bags were filled with

SYP particles and taken to be pelletized at the Pace Seed Lab on the campus of

Mississippi State University.

A Davis mixer (HD-5, H.C. Davis Sons Manufacturing Co., Inc, Bonner Springs,

KS, USA) was filled with approximately 300 lbs of material, moisture samples were

analyzed with a (110v Dsh-50-10, Techtongda, Rancho Cucamonga, CA, USA) to use the

moisture

Table 3.1 Particle distribute for southern pine feedstock.

Sieve Size % Particles

2.00 mm + 1.4

1.00 mm 49.3

0.50 mm 29.4

0.25 mm 12.6

< 0.25 mm 7.3

concentrations found in the feedstock to calculate the amount of water to add to obtain a

moisture level between ~11-13%. Water was added using a pressurized canister with a

VEEJET model H-VV stainless steel 110o spray tip on a spray wand at 130 psi. Once the

concentration of moisture in the material reached the desired level, additive amounts

28

were calculated using an Excel solver by taking into account the moisture in the material,

moisture in the additive and desired percentage of additive needed for each test. Each

treatment was mixed for approximately 15 minutes and removed from the mixer and

placed back into 55 gal barrels until the start of each test.

Raw whole corn was used to heat up the die and clean each die hole for the

woody biomass to pass through. The pellets formed during the first 2 minutes and the last

2 minutes of the feedstock entering the pelletizer were not collected to ensure that ample

amount of material passed through the pelletizer to definitively rule out any cross-

contamination of the subsequent feedstock/additive to be pelletized. Plastic bins were

used to collect each additive tested as pellets were being produced. During each pelleting

run, a sample of feed entering into the pelletizer and a sample of pellets being produced

were collected to determine how the resultant moisture of pellets was affected.

The pelletizer outputs an amperage reading associated with the amount of

material entering the mill, and the amperage was increased to approximately 85 amps at

the beginning of the test. Once a consistent reading of the ~85 amps, the material feed

rate was not adjusted to provide a more consistent reading of effects of each additive and

how the feed rate was affected. A temperature gun was used to obtain a specific point of

which collection of the control pellets could be started, generally around 190°F.

Temperatures were also taken to better understand the effect of the additive as it heats the

die through output temperature of the material after it was pelletized.

Collected pellets were placed onto cooling rack with 0.25” mesh screens to allow

air to cool both top and bottom pellets. The pellets were pushed back and forth to allow

fines to be completely separated and fall through the screen to be collected on a tarp

29

below. Pellets were allowed to cool overnight and collected into bins and weighed. Fines

beneath each cooling screen were also collected and weighed to determine the ratio of

fines to pellets produced.

Data was collected during the pelleting process to generally understand how much

moisture was removed and how production from using each treatment differed.

Production rate measurements were found gravimetrically and samples were taken over a

1 minute interval to calculate the production rate on a ton/hr basis. Moisture IN and OUT

was the feed moisture content collected before falling into the rolling die and pellet

sample collected once the final pelletized material was pushed through the die. A final

moisture was taken after at least a week of curing time to allow pellets to adjust to

ambient moisture in the air in the storage facility.

Pellets were tested to determine the following characteristics: bulk density,

durability, higher calorific value (MJ/kg).

Bulk density was calculated using a modification of the ASAE S269.5 standard

by filling a 2450 mL cylinder with pellets (ASAE, 2012). Pellets were added in

increments and shaken three times to ensure pellets were not causing unnecessary voids.

Five replicates were completed on each additive. ASTM D1102 was not strictly followed

because the amount of pellets produced for each treatment did not allow for samples to be

duplicated properly.

Durability tests were carried out according to ASAE S269.5 (ASAE, 2012) with a

custom built rolling box designed to the specifications given in the standard. The standard

called for 500 gram samples and these samples were tested in the rolling box at 50 rpm

30

for 10 minutes. Each sample was sieved using a number 10 (2mm) sieve for 30 seconds,

before and after each test.

Higher heating values (MJ/kg) samples were taken using an isoperibol oxygen

bomb calorimeter (ASTM, 2003). A Parr 6200 Isoperibol Calorimeter (Moline, IL, USA)

was used for this test with ultra-high purity oxygen. Heating values were adjusted for

calibration errors and moisture content (MC) found in the pellets tested.

𝐴𝑑𝑗𝑢𝑠𝑡𝑒𝑑𝑀𝐽

𝑘𝑔= (

𝐹𝑜𝑢𝑛𝑑𝑀𝐽

𝑘𝑔−𝐵𝑒𝑛𝑧𝑜𝑛𝑖𝑐 𝑎𝑐𝑖𝑑 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒

1−𝑀𝐶) (1)

Statistical analysis of durability, bulk density, and MJ/kg content was performed

using IBM SPSS Statistics 25 (Armonk, New York, USA). An ANOVA was run for each

variable with a Levine’s test to determine whether or not a non-equal variance was found.

If a significance was found using the Levine’s test, the significance of the data was

determined using the Game-Howell method which does not assume equal variances and

sample sizes. In each case, a significance was found, a concluding Game-Howell analysis

was needed to determine significance in all cases.

Results

Each treatment had multiple production variables table during the pelleting

process (Table 3.2). VO had adverse effects concerning the pellet production rate and

amount of fines produced. The pellet production temperature decreased during pelleting

for each VO treatment as the percentage of VO increased; however, the amount of fines

also increased and a significant jump in fines is undesirable in production leading to the

conclusion that the temperature drop caused the die to be excessively cooled for pellets to

31

properly form. VO over lubricated the die and did not allowing for the proper

temperature or compression to occur to produce pellets. Most other treatments had

similar results as the control, except the MRP 1% and the HW 50% had slightly higher

fines percentages. The large amount of HW 50% fines could be explained by the higher

temperature seen in the output of the pellets. The compression ratio used in this case is

much higher than what is used in most hardwood pellet mills (a compression ratio of 7 or

8 is traditionally used) and the larger compression ratio caused a greater amount of

friction to occur which led to higher temperature measurements to be found with the

pellets produced. This also produced a significant amount of moisture loss.

Table 3.2 Production data during pelletization.

Treatment Production rate

(ton/hr)

Fines

(wt%)

Moisture

in (wt%)

Moisture

out (wt%)

Temperature

(oF) Cured

moisture

(wt%) In Out

Control 16.77 1.68 11.59 5.15 109 216 6.53

CS 1% 16.10 1.97 12.54 3.31 132 220 6.63

CS 2% 17.00 0.87 12.27 2.43 138 204 6.70

CS 4% 16.20 1.09 12.58 3.12 133 208 6.86

HW 10% 16.30 1.31 12.52 2.5 138 216 6.63

HW 25% 14.40 2.17 13.36 3.11 134 221 5.86

HW 50% 14.10 6.28 12.98 1.86 160 254 4.90

Veg Oil 1% 18.40 3.57 12.01 5.02 128 201 7.69

Veg Oil 2% 20.30 14.00 11.36 6.25 104 199 7.89

Veg Oil 4% 20.00 31.07 12.09 5.62 100 188 8.18

Biochar 0.5% 15.30 1.48 12.14 4.59 124 218 6.63

Biochar 1% 15.70 1.78 11.64 3.82 127 218 6.30

Biochar 2% 15.80 2.34 11.17 4.15 125 221 6.44

Biochar 4% 20.50 1.10 13.15 3.44 110 225 6.78

Sweet Potato 0.5% 15.90 0.98 11.72 5.4 119 215 7.40

Sweet Potato 1% 16.00 1.51 12.07 5.41 118 209 7.14

MCC 0.1% 16.80 0.99 10.98 4.98 118 218 6.47

MCC 0.5% 16.00 1.32 11.36 5.05 118 210 6.87

MCC 1% 15.30 1.50 12.13 5.34 114 213 7.26

MRP 1% 15.20 3.48 11.99 4.22 127 207 6.92

Bio-oil 0.5% 16.40 1.00 11.41 4.55 129 216 6.63

32

Durability

Durability data was collected with five replications of each treatment and the

control samples. Industry standards state a durability ≥97.5% is acceptable. Only two

treatments, vegetable oil at 2% and 4%, had a mean durability lower than the acceptable

industry standard requirements. Figure 3.2 was created from the results in Table 3.3.

The pellets produced with vegetable oil at 2% and 4% were found to have

significantly lower mean durability values when compared with the other samples. VO

4% had the lowest durability at 86.7%. The corn starch additive at 4% had the highest

average durability but it did not significantly differ from many of the other treatments.

The control was significantly lower than the corn starch additive at 4%, proving the CS

4% additive could be beneficial to improve pellet characteristics at the 4% level.

Corn starch at the 2% and 4% level yielded the highest pellet durability values,

but these values were not significant when compared with the biochar at all levels, the

MCC at the 0.1 and 1% levels, the sweet potato at all levels, the lower corn starch level

of 1%, the bio-oil at 0.5%, and the MRP at 1%. Selecting the treatment with the highest

significance could prove beneficial to help the produce a more durable pellet.

33

Fig

ure

3.2

D

ura

bil

ity m

eans.

CD

DE

EE

DE

DE

CD

C

B

A

DE

DE

DE

ED

ED

ED

EC

DD

EC

DE

CD

E

82

.00

%

84

.00

%

86

.00

%

88

.00

%

90

.00

%

92

.00

%

94

.00

%

96

.00

%

98

.00

%

10

0.0

0%

% Durability

Trea

tmen

t

Du

rab

ility

Mea

ns

34

Tab

le 3

.3

Dura

bil

ity d

escr

ipti

ve

dat

a.

Dura

bili

ty D

escri

ptive

Da

ta

N

M

ea

n

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. D

evia

tio

n

Std

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nce

In

terv

al fo

r M

ea

n

Min

imu

m

Ma

xim

um

L

ow

er

Bo

un

d

Upp

er

Bo

un

d

Con

tro

l 1

5

97

.87

0.5

4

0.1

4

97

.57

98

.17

96

.60

98

.72

HW

10

%

5

98

.12

0.2

7

0.1

2

97

.79

98

.45

97

.72

98

.38

HW

25

%

5

98

.10

0.1

2

0.0

5

97

.96

98

.25

97

.94

98

.22

HW

50

%

5

97

.65

0.1

0

0.0

4

97

.52

97

.77

97

.52

97

.74

CS

1%

5

9

8.1

8

0.1

2

0.0

5

98

.03

98

.32

98

.04

98

.36

CS

2%

5

9

8.7

0

0.2

0

0.0

9

98

.45

98

.96

98

.42

98

.90

CS

4%

5

9

8.9

4

0.0

5

0.0

2

98

.87

99

.00

98

.88

98

.98

BC

0.5

%

5

98

.20

0.4

0

0.1

8

97

.71

98

.69

97

.60

98

.58

BC

1%

5

9

8.5

5

0.4

1

0.1

8

98

.05

99

.06

97

.86

98

.94

BC

2%

5

9

8.4

2

0.1

0

0.0

4

98

.30

98

.55

98

.28

98

.54

BC

4%

5

9

8.6

6

0.0

9

0.0

4

98

.54

98

.77

98

.54

98

.76

VO

1%

5

9

7.6

0

0.1

5

0.0

7

97

.41

97

.78

97

.46

97

.84

VO

2%

5

9

4.9

0

0.4

0

0.1

8

94

.40

95

.40

94

.36

95

.40

VO

4%

5

8

9.6

6

0.7

6

0.3

4

88

.71

90

.60

88

.64

90

.74

MC

C 0

.1%

5

9

8.4

7

0.1

5

0.0

7

98

.28

98

.65

98

.32

98

.72

MC

C 0

.5%

5

9

8.0

1

0.2

3

0.1

0

97

.72

98

.30

97

.78

98

.26

MC

C 1

%

5

98

.28

0.4

9

0.2

2

97

.67

98

.88

97

.42

98

.62

Sw

P 0

.5%

5

9

8.3

7

0.3

5

0.1

6

97

.94

98

.80

97

.78

98

.68

Sw

P 1

%

5

98

.30

0.8

7

0.3

9

97

.23

99

.38

96

.80

99

.00

MR

P 1

%

5

98

.03

0.4

0

0.1

8

97

.53

98

.53

97

.42

98

.46

BO

0.5

%

5

98

.04

0.3

9

0.1

7

97

.55

98

.52

97

.48

98

.50

To

tal

11

5

97

.69

1.9

1

0.1

8

97

.33

98

.04

88

.64

99

.00

35

Bulk Density

Bulk density data was collected using a 2450 mL graduated cylinder. The cylinder

was tared on the scale and the weight of the pelleting in the cylinder was divided by 2.45

to obtain a kg/m3 data point with 5 replicates for each treatment. Figure 3.3 was created

from the Table 3.4 results.

The vegetable oil additive at the 2 and 4% levels had significantly the two lowest

bulk density values with the vegetable oil 4% additive being significantly the lowest. The

hardwood 25% was the treatment with the highest mean bulk density, but this value was

not significantly different from many other treatments including: Control, MCC 0.5%

HW 10%, MCC 0.1% BC 0.5%, 1%, 2%, and HW 50%.

While only looking at bulk density for a conclusion, it could be stated that with no

significant difference from the control, using any treatment would prove to be

insignificant for benefits to pelleting bulk densities during a production setting. A visual

trend was treatments producing longer pellets could have produced a negative effect on

the bulk density by creating larger voids and not filling air space between pellets as well.

Separate testing would be needed to prove this theory.

36

Fig

ure

3.3

B

ulk

den

sity

mea

ns

gra

ph.

GD

E

CD

CD

GG

EFG

DE

B

A

EFG

FGFG

DE

CD

CD

GG

EF

C

DEF

52

0

54

0

56

0

58

0

60

0

62

0

64

0

66

0

68

0

70

0

72

0

kg/m³

Trea

tmen

t

Bu

lk D

ensi

ty M

ean

s

37

Tab

le 3

.4

Bulk

den

sity

des

crip

tiv

e dat

a.

N

M

ea

n

Std

. D

evia

tio

n

Std

. E

rro

r 9

5%

Co

nfide

nce

In

terv

al fo

r M

ea

n

Min

imu

m

Ma

xim

um

L

ow

er

Bo

un

d

Upp

er

Bo

un

d

Con

tro

l 1

5

70

3.0

2

8.3

6

2.1

6

69

8.4

0

70

7.6

6

68

6.4

9

71

4.2

4

HW

10

%

5

70

0.8

2

9.1

0

4.0

7

68

9.5

2

71

2.1

3

69

1.7

1

71

4.3

7

HW

25

%

5

70

4.8

0

4.9

4

2.2

1

69

8.6

6

71

0.9

4

69

8.5

7

71

1.2

7

HW

50

%

5

69

2.2

2

4.6

4

2.0

8

68

6.4

6

69

7.9

8

68

7.3

9

69

9.3

1

CS

1%

5

6

81

.82

19

.49

8.7

2

65

7.6

3

70

6.0

3

65

5.3

9

70

8.6

5

CS

2%

5

6

64

.32

10

.00

4.4

7

65

1.9

1

67

6.7

4

65

1.5

1

67

6.3

7

CS

4%

5

6

66

.17

10

.32

4.6

2

65

3.3

6

67

9.0

0

65

6.4

9

68

2.8

2

BC

0.5

%

5

69

3.9

0

4.6

4

2.0

7

68

8.1

4

69

9.6

6

68

8.1

2

70

0.6

1

BC

1%

5

6

95

.63

2.8

7

1.2

8

69

2.0

7

69

9.1

9

69

2.6

1

69

8.7

3

BC

2%

5

6

95

.56

4.3

2

1.9

3

69

0.2

0

70

0.9

2

69

0.5

3

70

1.7

1

BC

4%

5

6

83

.18

2.4

5

1.1

0

68

0.1

3

68

6.2

2

68

0.7

8

68

6.6

1

VO

1%

5

6

78

.65

5.9

1

2.6

4

67

1.3

2

68

5.9

9

67

2.8

6

68

5.0

2

VO

2%

5

6

28

.04

4.2

5

1.9

0

62

2.7

7

63

3.3

1

62

0.5

7

63

1.0

6

VO

4%

5

5

96

.79

4.3

5

1.9

5

59

1.3

9

60

2.1

9

59

0.8

2

60

2.0

4

MC

C 0

.1%

5

7

00

.51

2.7

3

1.2

2

69

7.1

2

70

3.9

0

69

7.8

8

70

4.5

7

MC

C 0

.5%

5

7

01

.40

7.8

6

3.5

1

69

1.6

5

71

1.1

6

69

2.0

8

71

1.9

6

MC

C 1

%

5

69

1.8

0

4.9

2

2.2

0

68

5.6

9

69

7.9

0

68

4.6

9

69

6.6

5

Sw

P 0

.5%

5

6

65

.38

9.2

9

4.1

5

65

3.8

4

67

6.9

1

65

7.1

8

68

0.6

1

Sw

P 1

%

5

67

0.6

9

8.7

3

3.9

0

65

9.8

5

68

1.5

2

66

1.9

2

68

4.8

6

MR

P 1

%

5

65

8.7

8

5.1

0

2.2

8

65

2.4

4

66

5.1

1

65

3.3

9

66

6.7

8

BO

0.5

%

5

68

4.5

9

4.8

2

2.1

6

67

8.6

0

69

0.5

7

67

7.3

9

68

9.7

1

To

tal

11

5

68

1.0

5

26

.84

2.5

0

67

6.0

9

68

6.0

1

59

0.8

2

71

4.3

7

38

Calorific Value

Calorific values were collected with each sample having 3 replicates for each

treatment. Control had 9 total replicates to account for the 3 days needed to complete the

testing for all treatments in this study. A Parr bomb calorimeter was used to test each

sample to obtain the calorific value of each additive treatment. The calorific value was

adjusted to account for calibration errors and moisture found in each treatment. Benzoic

acid has a known calorific value, which allowed for calculating the adjustment required

in the calorimeter readings. Moisture was taken out to obtain a dry basis for all tests.

Figure 3.4 was created from the results in Table 3.5.

The calorific values of the samples showed that the control sample was again in

the lower significance levels; showing there is improvement that can be made with the

treatments in this study. Treatments contained within the highest significance level, BC

0.5%, 2%, 4%, VO 1%, 2%, 4%, CS 1%, 2%, 4%, and MRP 1%, would all significantly

improve the calorific value of the pellets in production. Although VO at all levels were in

the highest significance level, production using this treatment would not readily form

pellets and produce a higher amount of fines, making such additive ineffective when put

into practice. VO showed no benefit to durability and was below the industry standard for

2% and 4%, which causes concern in production.

39

Fig

ure

3.4

C

alori

fic

val

ue

mea

ns.

AB

C

CD

CD

CD

C

AB

A

C

CD

D

CD

BC

CD

CD

BC

AB

A

AA

CD

AB

C

18

.00

18

.50

19

.00

19

.50

20

.00

20

.50

MJ/kg

Trea

tmen

t

Cal

ori

fic

Val

ue

Mea

ns

40

Tab

le 3

.5

Cal

ori

fic

val

ue

des

crip

tiv

e dat

a.

N

M

ea

n

Std

. D

evia

tio

n

Std

. E

rro

r

95

% C

onfide

nce

In

terv

al fo

r M

ea

n

Min

imu

m

Ma

xim

um

L

ow

er

Bo

un

d

Upp

er

Bo

un

d

Con

tro

l 9

1

9.2

8

0.3

2

0.1

1

19

.04

19

.53

18

.89

19

.83

CS

1%

3

1

9.8

5

0.1

2

0.0

7

19

.55

20

.15

19

.76

19

.98

CS

2%

3

1

9.7

1

0.1

1

0.0

6

19

.45

19

.97

19

.59

19

.78

CS

4%

3

1

9.5

6

0.0

9

0.0

5

19

.33

19

.78

19

.46

19

.64

HW

10

%

3

19

.50

0.0

6

0.0

3

19

.36

19

.65

19

.44

19

.56

HW

25

%

3

19

.15

0.1

0

0.0

6

18

.91

19

.39

19

.04

19

.22

HW

50

%

3

18

.76

0.0

8

0.0

5

18

.56

18

.97

18

.71

18

.86

VO

1%

3

1

9.5

0

0.0

2

0.0

1

19

.46

19

.53

19

.48

19

.51

VO

2%

3

1

9.7

0

0.0

6

0.0

4

19

.55

19

.85

19

.63

19

.74

VO

4%

3

2

0.0

0

0.0

7

0.0

4

19

.84

20

.17

19

.94

20

.07

BC

0.5

%

3

19

.52

0.1

0

0.0

6

19

.27

19

.76

19

.41

19

.60

BC

1%

3

1

9.4

8

0.1

3

0.0

7

19

.17

19

.80

19

.35

19

.60

BC

2%

3

1

9.6

6

0.1

1

0.0

6

19

.40

19

.92

19

.58

19

.78

BC

4%

3

1

9.6

4

0.0

8

0.0

5

19

.44

19

.85

19

.55

19

.70

Sw

P 0

.5%

3

1

9.3

0

0.0

7

0.0

4

19

.14

19

.47

19

.23

19

.37

Sw

P 1

%

3

19

.18

0.0

8

0.0

5

18

.98

19

.38

19

.09

19

.24

MC

C 0

.1%

3

1

8.8

9

0.0

2

0.0

1

18

.83

18

.95

18

.86

18

.91

MC

C 0

.5%

3

1

9.0

5

0.0

8

0.0

4

18

.86

19

.25

18

.99

19

.14

MC

C 1

%

3

19

.09

0.0

2

0.0

1

19

.04

19

.14

19

.07

19

.11

MR

P 1

%

3

19

.72

0.1

6

0.0

9

19

.33

20

.10

19

.54

19

.81

BO

0.5

%

3

19

.30

0.1

5

0.0

9

18

.93

19

.67

19

.13

19

.40

To

tal

69

19

.41

0.3

3

0.0

4

19

.33

19

.49

18

.71

20

.07

41

Summary and Conclusions

Certain additives used for pellet production in this study showed a great potential

to improve on the overall properties of wood biomass pellets created on an industrial

scale. Control pellets were only in the highest significance group concerning bulk

density, which could be attributed to pellet length. Bulk density had the control in the

highest significance group which so the use of any treatment used in this study to

significantly improve the bulk density of SYP pellets would be ineffective. Durability

tests revealed that the control group was in the lower significance level meaning that

improvements could be made with the treatments including: Corn starch 1% 2%, 4%,

biochar 0.5%, 2%, 4%, MRP 1%, MCC 0.5%, 1%, SwP 0.5%, 1%, HW 10%, 25%, and

BO 0.5%. These additives can be used to significantly improve durability. The calorific

value of SYP pellets could be significantly improved by using the following treatments in

production: BC 0.5%, 2%, 4%, CS 1%, 2%, 4%, VO 2%, 4%, and MRP 1%.

While each test has importance, an overview of all the tests show that VO at all

levels was not an effective additive to improve pellet properties in 2 of the 3 tests. VO

also produced a massive amount of fines in the production stage and cooled the pelletizer

excessively so that pellets could not be formed properly. Smaller treatment sizes could be

tested to determine if a smaller additive concentration of VO could give significant

improvements.

MRP 1% was in a lower significance grouping in 2 of the 3 tests, bulk density and

durability. The MRP additive did cause the SYP pellets to have a higher net calorific

value, but it was not significantly different when compared with the Control pellets

produced. MRP at the 1% level itself can be assumed to not be effective to improve pellet

42

properties significantly in an industrial pelleting process. However, higher level of

inclusion may improve these properties and warrants future study.

The CS additive at an inclusion of 2%, and 4% was found to be significantly

higher than the control concerning pellet durability, while the CS 4% additive had a

higher mean. In the bulk density and calorific value categories, the CS additives at 2%

and 4% were found have no significant difference from the control. CS provided a

significant improvement of pellet durability, but there was no significant difference in

bulk density and the calorific value of the pellets produced.

BO at 0.5% was seen to have no significant difference in all 3 tests and it can be

concluded that it was ineffective in a production setting. Issues with applying the BO

could be the main issue for the data collected to be skewed. The BO was difficult to spray

applicate, and became extremely viscous when at atmospheric temperatures. BO could

potentially prove to be a beneficial additive if the application process is solved.

MCC additive levels at 0.1%, 0.5%, and 1% were found to not be significantly

different concerning the calorific value and durability categories when compared with the

control. MCC at 1% was significantly lower concerning bulk density, while MCC 0.1%

and 0.5% were similar.

The SwP additive at all levels was found to significantly lower both the durability

and calorific value of SYP wood pellets. Bulk density was significantly lower at all

levels. SwP can be assume to be a nonviable treatment to significantly improve pellet

properties.

HW was found to have no significant difference in all 3 tests. HW could be

assumed to hinder the pelleting production due to the high amount of fines produced.

43

BC 0.5%, 1%, and 2% were found to have no significant difference in all 3 tests

completed. BC 4% was found to have a significantly lower bulk density, significantly

higher durability, yet no significant difference in calorific value when compared to the

control in each case. BC could be assumed to not provide any significant difference

overall when applied to pelleting production based on the pellet properties alone.

Further testing need to be completed on all treatments to determine if multiple

treatments combined could provide any significant improvement from the control pellets.

A test comparing bulk density to average pellet length would help to initiate a model to

prove that longer pellets have a consistently lower bulk density. More testing of the

pellets produced, such as trace metals and off-gassing, need to be completed to better

understand if treatments comply with industry standards. Varying the compression ratios

of the die could also be carried out to determine if significantly different results could be

found with higher or lower compression ratios.

44

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Method. St. Joseph, MI.

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Mišljenović, N., Mosbye, J., Schüller, R. B., Lekang, O.-I., Salas-Bringas, C. (2015).

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Reza, M. T., Uddin, M. H., Lynam, J. G., Coronella, C. J. (2014). Engineered pellets

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Ståhl, M., Berghel, J., Frodeson, S., Granström, K., Renström, R. (2012). Effects on

pellet properties and energy use when starch is added in the wood-fuel pelletizing

process. Energy and Fuels, 26(3), 1937–1945. https://doi.org/10.1021/ef201968r

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(2011). Fuel pellets from biomass: The importance of the pelletizing pressure and

its dependency on the processing conditions. Fuel, 90(11), 3285–3290.

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46

CHAPTER IV

ECONOMICAL ANALYSIS OF WOOD BIOMASS PELLETING WITH ADDITIVES

WHEN ACCOUNTING FOR CHANGES IN CALORIFIC VALUE AND

DURABILITY

Abstract.

Woody biomass production has three important tests to determine the quality of

the production process: durability, calorific value, and bulk density. Using different

additives can improve one or more of these qualities, yet not be significantly different

from control pellet characteristics created with no additives. While these tests are

regulated by industry standards, businesses and corporations producing pellet at the set

standard have no need to use additives proving to have no significant difference in

quality, but will invest money into an additive that can be proven to save costs associated

with energy usage. The goal of this study is to prove that energy savings can be had when

using particular additives. The variables taken into account include the: input energy

requirement of the pelletizer, durability of the pellets, rate of production, and calorific

value of the pellets when compared to a baseline pelleting process.

47

Keywords: Pelleting Additive, Economics Assessment, Pellet Production, Energy

Cost

Introduction

Research in the production of biomass wood pellet is far and wide, from includes

various pelleting feedstocks, additives, pretreatments, and machinery configurations to

produce an energy source from relatively low-cost materials (Ahn et al., 2014; Cao et al.,

2015; M. Ståhl et al., 2016; Magnus Ståhl et al., 2016). Pelleting, or densifying, waste

materials with low bulk densities allows for more material to be transported and used in

larger quantities. Research exploring the inclusion of additives into wood biomass pellet

production is scarce, and companies using additives may not be willing to share such

information to the general public or other companies.

The European Pellet Council has certain requirement for additives in pellets,

stipulating that a maximum of 1.8% is able to be used in production, and the additive

should not be chemically altered during the production of the additive (European

Biomass Association (AEBIOM), 2015). Finding an additive to significantly improve

pellet qualities can be challenging and economic/production data is not readily available

in many cases. Ståhl et al. reported economic benefits involving energy consumption

with 3% oxidized corn starch by lowering the average energy consumption by 14% (

2012). Alakangas and Paju published a report stating the possibility of using additives,

but they are not used very often in manufacturing of wood pellets due to an increased

cost, combustion hampering, and off gassing issues (Alakangas and Paju, 2002).

Economics on other parts of the pelleting process have been studied, such as grinding,

screening, storage and cooling, to determine portions where waste can be adjusted

48

(Alakangas and Paju, 2002; Pirraglia et al., 2013). This study sheds light on the economic

value of using additives in industrial pellet manufacturing.

Pre-treatments of pellet feedstocks have been studied intently to determine the

optimum treatment to reduce the cost of producing biomass wood pellets. Sikkema et al.

studied numerous treatments, such as southern yellow pine pellets, multiple torrefaction

levels of southern pine, hardwoods, and other trash biomass, by co-firing materials with

coal to determine a viable option. However, they concluded that economically southern

pine pellets would prove most electrically cost effective (Sikkema et al., 2011). Nunes et

al. explains the benefits of co-firing torrefied materials, but determined that much more

research is needed on the process, and a better understanding of torrefaction is needed for

larger scale operations (Nunes et al., 2014).

The goal of this study is to show that may the costs associated with the energy

input for each treatment can have a large economic impact.

Calculation Methods:

Calculations to estimate possible revenue were completed to determine whether

electrical input could out weight the properties, even with non-significant increases in

pellet properties.

The treatments were tested to determine the effects that each additive had on the

pelletizer’s energy consumption during pelletization. An Extech PQ3450 3-phase power

analyzer/logger was attached at the electrical panel to the wires running current to power

the pelletizer. While the pelletizer was running the data logger collected a data point

every 2 seconds for a more accurate overview as the test was being carried out. The

49

average kW usage was used to help determine the potential electrical cost per ton of

pellets created using a particular additive each year.

Other pellet properties of the pellets created, such as durability and calorific

value, were taken into account for to determine the marginal revenue. The calorific value

was used to determine the overall revenue before durability and electrical costs could be

subtracted. A higher calorific value increased the revenue received for each treatment.

The durability percentage was used to determine the adjusted revenue. Equations 1-7

were used to compare the costs involved when using the various additives described in

this study. Equation 1 describes the base cost of the control pellets that were assumed to

be $250 per ton.

Equations

$

𝑀𝐽/𝑘𝑔=

(250

2000)

𝑀𝐽/𝑘𝑔 𝐶𝑜𝑛𝑡𝑟𝑜𝑙 (1)

𝑃𝑒𝑙𝑙𝑒𝑡 $

𝑇𝑜𝑛=

𝑀𝐽/𝑘𝑔

𝑙𝑏∗

$

𝑀𝐽/𝑘𝑔∗ 2000 (2)

𝑂𝑣𝑒𝑟𝑎𝑙𝑙 𝑅𝑒𝑣𝑒𝑛𝑢𝑒 =𝑡𝑜𝑛𝑠

ℎ𝑟∗

𝑃𝑒𝑙𝑙𝑒𝑡 $

𝑡𝑜𝑛 (3)

𝐴𝑑𝑗𝑢𝑠𝑡𝑒𝑑 𝑅𝑒𝑣𝑒𝑛𝑢𝑒 = 𝑂𝑣𝑒𝑟𝑎𝑙𝑙 𝑅𝑒𝑣𝑒𝑛𝑢𝑒 ∗ 𝐷𝑢𝑟𝑎𝑏𝑖𝑙𝑖𝑡𝑦 (4)

𝐸𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝐶𝑜𝑠𝑡 =$

𝑘𝑊ℎ𝑟∗

𝑘𝑊ℎ𝑟

𝑡𝑜𝑛∗

𝑡𝑜𝑛

𝑦𝑒𝑎𝑟 (5)

𝐴𝑑𝑑𝑖𝑡𝑖𝑣𝑒 𝐶𝑜𝑠𝑡 =𝑡𝑜𝑛

𝑦𝑒𝑎𝑟∗

𝐴𝑑𝑑𝑖𝑡𝑖𝑣𝑒 𝐶𝑜𝑠𝑡

𝑡𝑜𝑛∗ % 𝐴𝑑𝑑𝑖𝑡𝑖𝑣𝑒 (6)

𝑁𝑒𝑡 𝑅𝑒𝑣𝑒𝑛𝑢𝑒 = 𝐴𝑑𝑗𝑢𝑠𝑡𝑒𝑑 𝑅𝑒𝑣𝑒𝑛𝑢𝑒 − 𝐸𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝐶𝑜𝑠𝑡 − 𝐴𝑑𝑑𝑖𝑡𝑖𝑣𝑒 𝐶𝑜𝑠𝑡 (7)

The data from Table 4.1 was used in the calculations above to determine the

economic benefit of Marginal Revenue/year found in Table 4.2 when each treatment is

compared to the control.

50

Table 4.1 Production variables.

Table 4.2 Prices of additives and feedstocks.

% MJ/kg Durability ton/year kWh/ton

Control 0 19.28 97.87 4024.00 101.56

HW 10% 0.1 19.50 98.12 3912.00 99.15

HW 25% 0.25 19.15 98.10 3456.00 116.55

HW 50% 0.5 18.76 97.65 3384.00 132.32

CS 1% 0.01 19.85 98.18 3864.00 102.63

CS 2% 0.02 19.71 98.70 4080.00 95.09

CS 4% 0.04 19.56 98.94 3888.00 95.12

Biochar 0.5% 0.005 19.52 98.20 3672.00 105.59

Biochar 1% 0.01 19.48 98.55 3768.00 106.92

Biochar 2% 0.02 19.66 98.42 3792.00 108.14

Biochar 4% 0.04 19.64 98.66 4920.00 99.30

Veg Oil 1% 0.01 19.50 97.60 4416.00 84.65

Veg Oil 2% 0.02 19.70 94.90 4872.00 61.65

Veg Oil 4% 0.04 20.00 89.66 4800.00 53.45

MCC 0.1% 0.001 18.89 98.47 4032.00 98.15

MCC 0.5% 0.005 19.05 98.01 3840.00 99.90

MCC 1% 0.01 19.09 98.28 3672.00 101.64

Sweet Potato 0.5% 0.005 19.30 98.37 3816.00 99.42

Sweet Potato 1% 0.01 19.18 98.30 3840.00 96.47

MRP 1% 0.01 19.72 98.03 3648.00 98.39

Bio-oil 0.5% 0.005 19.30 98.04 3936.00 100.83

51

Feedstock/Additive Price/ton Comment Citation

Southern yellow

pine

$ 250 Assumed

Mixed Hardwood $ 20 Assumed

Biochar $ 20 Assumed

Bio-oil $ 220 Found (Environment Agency, 2009; Steele et

al., 2012)

Corn starch $ 1280 Found (“Cornstarch | Bulk Apothecary,” 2018)

Vegetable oil $ 1740 Found (“Soybean Oil | Bulk Apothecary,” 2018)

Sweet potato $ 20 Assumed

MRP $ 1000 Found (“MicroDyneTM | Lehigh Technologies |

Micronized Rubber Powder (MRP),”

2018)

MCC $ 1700 Found (“Mcc/Avicel/ Microcrystalline Cellulose

Powder Favorable Price – Buy

Microcrystalline Cellulose Powder,

Avicel Price Product on Alibaba.com,”

2018)

Results

Results from these calculations (Table 4.3) show that the benefits of using additives

in different treatment percentages can improve a revenue margin, while not necessarily

improving pellet properties significantly. This research was carried out to better

understand the possibilities of improving manufacturing costs and have a further insight

of the data outside of pellet property improvements or by simply stating a reduction in

energy input.

Table 4.3 Marginal revenue difference compared to control.

52

Hardwood was shown to have an incremental decrease in marginal revenue with

Treatment Marginal Revenue Difference

Biochar 4% $ 1,188,099.59 $ 240,288.43

Veg Oil 2% $ 984,191.82 $ 36,380.66

Veg Oil 1% $ 978,904.17 $ 31,093.02

Control $ 947,811.15 $ -

MCC 0.1% $ 929,771.59 $ (18,039.57)

HW 10% $ 927,875.24 $ (19,935.92)

Bio-oil 0.5% $ 925,388.48 $ (22,422.68)

Biochar 2% $ 912,909.49 $ (34,901.67)

Sweet Potato 0.5% $ 904,853.42 $ (42,957.74)

Sweet Potato 1% $ 904,622.26 $ (43,188.89)

Biochar 1% $ 900,938.74 $ (46,872.42)

CS 1% $ 890,958.48 $ (56,852.67)

CS 2% $ 889,738.69 $ (58,072.46)

Biochar 0.5% $ 877,267.79 $ (70,543.36)

MCC 0.5% $ 862,568.33 $ (85,242.82)

MRP 1% $ 845,294.16 $ (102,517.00)

MCC 1% $ 797,153.08 $ (150,658.07)

HW 25% $ 788,342.69 $ (159,468.46)

Veg Oil 4% $ 758,807.13 $ (189,004.02)

CS 4% $ 742,861.38 $ (204,949.77)

HW 50% $ 729,724.00 $ (218,087.15)

53

each increase in the treatment. A 10% HW treatment reduced revenue by almost $20,000,

while a treatment of 50% HW was shown to have much more drastic effects by losing

over $218,000 in marginal revenue. Hardwood is not a beneficial added in this study for

economic gain.

Corn starch was incrementally worse for marginal revenue with each increase in

treatment percentage. 1 and 2% show a loss just under $60,000 per year to marginal

revenue, while a jumping significantly to almost $205,000 with a 4% treatment of corn

starch. Corn starch would be considered an economically poor choice for marginal

revenue, despite any benefit seen to pellet properties.

Biochar had an increasing incremental relationship to marginal revenue. As a 0.5%

treatment was increased to a final 4% total treatment, a boost to over $240,000 could be

seen at the 4% treatment, being the only treatment with marginal revenue gained. Biochar

would be an economically beneficial choice, but issues could arise in the future if waste

streams of companies were turned to a marketable product.

Bio-oil with a treatment of 0.5% was seen to be economically worse for marginal

revenue by losing around $22,500. Most tests for Bio-oil should be completed to

determine better application procedures and higher treatment percentages to discover a

positive or negative trend to pellet properties and marginal revenue.

Sweet potato at both treatment levels was show to have similar loses to marginal

revenue, with around $43,000 lost. Although sweet potato was concerned a waste stream

for this study, a steady supply sweet potatoes could become an issue being the harvesting

season is short and is limited to only certain agricultural regions.

54

MRP lost over $100,000 in marginal revenue as compared to the control sample

group. MRP can be considered an economically poor choice for marginal revenue. Most

tests on pellet properties and toxicity reports need to be completed to also can a more

complete understanding in the use of MRP in production

MCC was increasingly negative for marginal revenue per year with each increase of

treatment percentage. 0.1% lost around $18,000 of marginal revenue per year, while an

increase up to 1% lost nearly $151,000 in marginal revenue per year. MCC is considered

bad for marginal revenue per year with increasing lose for higher treatment percentages.

MCC could have issues meeting the qualification of additive since chemicals are need to

produce such a product.

Vegetable oil was beneficial to marginal revenue at 1% treatment, adding nearly

$31,000, and by adding more 1%, increased marginal revenue per year to over $36,000 at

a 2% treatment. A 4% treatment a negative effects to marginal revenue per year with a

loss over $135,000. Vegetable oil at 1% met industry standard of durability, while 2%

fell short of that goal. Only a small percentage of vegetable is suggest to add marginal

revenue per year, yet more tests need to be run to determine long term effects of running

such an additive for extended amounts of time.

Summary and Conclusions

Results from this economics study show the difficultly to persuade industry to using

additives to improve pellet properties alone. Additives were soon in large part to be not

beneficial to marginal revenue per year. Biochar at 4%, vegetable oil 1% and 2% were

the only treatment to show marginal revenue gain from using each treatment in

production. While each of the three treatments show gain, skepticism can arise with

55

biochar being a waste stream with a possibility for char production companies to market

the char as a product and not as waste. Vegetable oil need to be tested for longer duration

to determine the effects of residue build up, increased die lubrication possibility over a

time period, and pellet properties associated with a longer test.

Disscussion

More tests need to be completed on the additives and treatments to determine more

trends and pellet properties associated with each additive. Bio-oil needs to be tested in

more treatments to determine the possibly of marginal revenue gain or loss with higher

percentages of treatment. Although Stahl et al found a 14% decrease in energy

consumption, this analysis shows concern for the economical benefit not out weighing

the use of corn starch (Stahl et al., 2012).

More studies on economic effects of additives in the wood biomass industry to

better understand the effect additives have on possible economic gain. This study is to

give a starting point for future studies to occur to investigate more in depth methods of

calculating industry budgets for additive use.

56

References

Ahn, B. J., Chang, H., Lee, S. M., Choi, D. H., Cho, S. T., Han, G. seong, Yang, I.

(2014). Effect of binders on the durability of wood pellets fabricated from Larix

kaemferi C. and Liriodendron tulipifera L. sawdust. Renewable Energy, 62(2014),

18–23. https://doi.org/10.1016/j.renene.2013.06.038

Alakangas, E., Paju, P. (2002). Wood pellets in Finland - technology , economy , and

market. OPET report 5, 64.

Cao, L., Yuan, X., Li, H., Li, C., Xiao, Z., Jiang, L., … Zeng, G. (2015). Complementary

effects of torrefaction and co-pelletization: Energy consumption and

characteristics of pellets. Bioresource Technology, 185, 254–262.

https://doi.org/10.1016/j.biortech.2015.02.045

Cornstarch | Bulk Apothecary. (n.d.). Retrieved September 24, 2018, from

https://www.bulkapothecary.com/cornstarch/

Environment Agency. (2009). Minimising greenhouse gas emissions from biomass

energy generation. Retrieved from

http://www.globalbioenergy.org/uploads/media/0904_Environment_Agency_-

_Minimising_greenhouse_gas_emissions_from_biomass_energy_generation.pdf

European Biomass Association (AEBIOM). (2015). EN plus For Wood Pellets EN plus

Handbook Part 3 : Pellet Quality Requirements, (August), 1–16.

https://doi.org/10.1017/CBO9781107415324.004

Mcc/ Avicel/ Microcrystalline Cellulose Powder Favorable Price - Buy Microcrystalline

Cellulose Powder,Avicel Price Product on Alibaba.com. (n.d.). Retrieved

September 24, 2018, from https://www.alibaba.com/product-detail/MCC-avicel-

microcrystalline-cellulose-powder-

favorable_60599949955.html?spm=a2700.galleryofferlist.normalList.60.4e784b9

7UQYgg9

MicroDyneTM | Lehigh Technologies | Micronized Rubber Powder (MRP). (2018).

Retrieved September 24, 2018, from

http://lehightechnologies.com/products_services/microdyne/

Nunes, L. J. R., Matias, J. C. O., Catalão, J. P. S. (2014). A review on torrefied biomass

pellets as a sustainable alternative to coal in power generation. Renewable and

Sustainable Energy Reviews, 40, 153–160.

https://doi.org/10.1016/j.rser.2014.07.181

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Pirraglia, A., Gonzalez, R., Saloni, D., Denig, J. (2013). Technical and economic

assessment for the production of torrefied ligno-cellulosic biomass pellets in the

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https://doi.org/10.1016/j.enconman.2012.09.024

Sikkema, R., Steiner, M., Junginger, M., Hiegl, W., Hansen, M. T., Faaij, A. (2011). The

European wood pellet markets: current status and prospects for 2020, 5, 250–278.

https://doi.org/10.1002/bbb.277

Soybean Oil | Bulk Apothecary. (n.d.). Retrieved September 24, 2018, from

https://www.bulkapothecary.com/raw-ingredients/bulk-natural-oils/soybean-oil/

Ståhl, M., Berghel, J., Frodeson, S., Granström, K., Renström, R. (2012). Effects on

pellet properties and energy use when starch is added in the wood-fuel pelletizing

process. Energy and Fuels, 26(3), 1937–1945. https://doi.org/10.1021/ef201968r

Ståhl, M., Berghel, J., Granström, K. (2016). Improvement of Wood Fuel Pellet Quality

Using Sustainable Sugar Additives. BioResources, 11(2), 3373–3383.

Ståhl, M., Berghel, J., Williams, H. (2016). Energy efficiency, greenhouse gas emissions

and durability when using additives in the wood fuel pellet chain. Fuel Processing

Technology, 152, 350-355. https://doi.org/10.1016/j.fuproc.2016.06.031

Steele, P., Puettmann Venkata, M. E., Penmetsa, K., Cooper, J. E. (2012). Life-Cycle

Assessment of Pyrolysis Bio-Oil Production*. Forest Products Journal, 62(4),

326–334. https://doi.org/10.13073/FPJ-D-12-00016.1

58

CHAPTER V

RESEARCH CONCLUSIONS AND FUTURE STUDY SUGGESTIONS

Conclusions

The overall research throughout this PhD program gives a great insight to the

possibilities to small scale testing methods, scaling production give different results and

the possibilities to see economically benefits with pellet properties not significantly

different from a control test. The result from this dissertation will hopefully increase the

awareness of using additives in pellet production to help manufacturing companies to

make a more informed decision to benefit each’s companies’ bottom line.

Scaling up from the pneumatic pelletizer to the Sprout Walden pelletizer did not

show the same effects for multiple reasons. The pneumatic pelletizer does not mimic

industry as closely as thought before the scale up testing was done in that the way

compression is not produced in the same manner. While the piston creates a straight line

of compression, the Sprout Walden compressed the feedstock in such a way that it

pushed small amounts in a rolling fashion from one side of the die hole to the opposite

side of the die hole. This difference in compression style also changes in the amount of

compression with the rolling die have a much greater compression pressure. Some of the

benefits of scaling up to the Sprout Walden are a better understanding of the additives

and treatments on a closer to industry pelletizer, the ability to see electrical/amperage

changes, and the amount of pellets that can be produced. The downfalls of scaling up

59

would be the amount of material needed for the production, equipment cost is much

greater, repair costs, and research universities/center may not have the space for such

equipment.

Additives used were seen have significant impact on the pellet properties and

energy consumption. With the pneumatic pelletizer obstacles were faced trying to

determine temperatures, moisture needed, pressure regulation, and particles distribution

to produce optimal pellets. Energy consumption was calculated using strokes, die length,

area and force used a data logger attached to power box was used. The pneumatic

pelletizer was seen as a way to mimic the rolling die used in industry and for the larger

scale tests. The conclusions of the pneumatic tests were that no significant results were

found for many of the additives used in different treatment percentages.

In a comparison of the pneumatic tests and the large scale study additives,

biochar, at both 2% and 4%, was seen to significantly decrease biochar, at all levels: 1, 2

and 4%, yielded significantly higher durability than that of the control test. This was

explained by the increase pressure of a much larger pelletizer and more consistent flow of

material into the die holes. Biochar has similar effects in energy in both chapters with

having a higher energy input usage, yet the economic study shows a potential gross

revenue increase with a small addition of biochar that decrease with increase percentages.

Corn starch, using a pneumatic pelletizer, was found to have no significant change in

MJ/kg or durability, but a larger scale pelletizer’s results suggests, corn starch to have a

significantly higher MJ/kg and durability when compared to the control tests. Corn starch

was found in both studies to have an increasing effect in energy usage as the percentage

of corn starch was increased. Bio-oil was used in a whole and fractionated form during

60

the pneumatic tests, which led to the determination for only using a whole bio-oil in the

testing for the large scale study. Bio-oil was found to have only a significant change in

MJ/kg using the pneumatic pelletizer, while the Sprout Walden study had no significant

change was found in any of the tests completed. The economic study showed a slight

reduction to yearly revenue when using a 0.5% of bio-oil. A concerning factor with using

bio-oil is the application and off gassing during a production setting. Finding a good

application method is difficult, but could allow for better results with a higher percentage

of bio-oil is used, assuming off gassing is not an issue.

Other additives, such as sweet potatoes, microcrystalline cellulose, vegetable oil,

micronized rubber powder and a mix of hardwoods, was used for a further look into the

possibilities of ways to improve properties and energy usage with the Sprout Walden

pelletizer. Sweet Potatoes were found to have no significantly improvement in either

durability or MJ/kg, but a lower bulk density significance was found. Sweet potatoes, in

both treatments, were found to have a decrease in yearly revenue by ~$43,000 if a bulk

purchase for the additive could be found as a waste stream and not a market value. MCC

was found to have no significant difference at all levels when considering MJ/kg and

durability, but 1% MCC was significantly lower in bulk density. From an economic stand

point, MCC was shown to be increasing worse on marginal revenue with each increase of

treatment percentage. Vegetable oil was found to have significantly differences in only

the 4% treatment, while being significantly the worst in bulk density and durability. The

usage for vegetable oil can be assumed to invalid due to such low durability, bulk density

and high fines production despite showing a great revenue margin for a 4% treatment.

Micronized rubber powder showed a lower significance in both bulk density and

61

durability, but having a slightly higher MJ/kg that was not significantly different from the

control. MRP is an explorative additive with a negative result in increasing marginal

revenue per year. Hardwood pellet are not a new concept, but in these studies serve as

another form of current production material. Hardwood is complicated material to

pelletize due to a lower amount of lignin than softwood (White, 1987). In these studies,

hardwood was found to have no significant benefit to all three tests with a Sprout Walden

pelletizer, while showing an incremental decrease as hardwood percentage increase in

marginal revenue.

Future Studies

While this dissertation give insight into multiple additive and each benefit

correlating with the treatment amount, many other studies need to completed to better

understand the full aspects of the additives used. Ash and volatile matter tests will be

completed after this study on the pellets produced to determine increases/decreases and

whether the treatments comply with industry standards. Elemental analysis and off

gassing tests need to be completed on such additives as MRP and bio-oil to determine

toxicity and harmful aspects in combustion are present. Vegetable oil has promise to

lower energy input, but more tests need to be completed at lower percentages could prove

beneficial. A longer scale study needs to be completed for a firmer understanding of how

the longer each additives is run, the effects had on the pellets, energy consumption, die

wear, and pelletizer cleaning. Additives could have more significant results if a longer die

life is found and roller patterns are not worn down. More tests to be completed could

include multiple additives. Finding a balance between two additives, such as biochar and

62

vegetable oil could prove beneficial in lowering production energy while improving

physical properties enough to promote marginal revenue.

63

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