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Thesis for the Degree of Doctor of Philosophy Investigating the Reaction Kinetics of Tropical Wood Biomass - A Prospect for Energy Recovery Kehinde Olubukola Oluoti

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Page 1: Investigating the Reaction Kinetics of Tropical …hb.diva-portal.org/smash/get/diva2:910296/INSIDE01.pdfThesis for the Degree of Doctor of Philosophy Investigating the Reaction Kinetics

Thesis for the Degree of Doctor of Philosophy

Investigating the Reaction Kinetics of Tropical Wood

Biomass - A Prospect for Energy Recovery

Kehinde Olubukola Oluoti

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1. Introduction

1.1 Aim of the study

The aim of this study was to extensively examine the availability and the candidacy of

tropical wood biomass towards energy recovery purposes. The set of kinetic

parameters necessary as a prelude towards a viable deployment of the fuel material

were evaluated. This was with a view to verifying the thermal properties of the

materials under varied pyrolysis and gasification reaction conditions, employing

several kinetic methods and models. The materials were subjected to pretreatment

reactions (such as energy densification and torrefaction) in order to determine

properties such as energy yield, hydrophobicity, etc. as compared to the non-tropical

samples which are already being deployed for energy recovery purposes in the

developed countries.

1.2 Justification

Biomass wood waste is regarded as a viable option for the development of clean and

renewable energy. Going by the status quo, energy conversion from fossil fuels

releases a lot of greenhouse gases (GHG) into the atmosphere at the detriment of the

humankind. Compared to fossil fuels, wood fuel conversion is “carbon neutral” and

would reduce the net CO2 atmospheric emission levels. Moreover, The Inter-

governmental Panel on Climate Change’s (IPCC) last assessment report, for example,

outlined the emissions reductions needed from countries the world over to stabilize

concentrations of (GHG) consistent with limiting warming to 2°C. Further research has

continued to examine the global GHG emissions reductions necessary to avert

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dangerous climate change, with the general decision to go renewable as regards

energy production. In essence, wood waste utilization for energy production is an

acceptable option and a research into thermal properties of the tropical wood waste is

highly important so as to enhance its use for energy conversion purposes in the

tropical countries.

1.3 Biomass

Biomass as a renewable source is made of organic materials readily available to

generate a number of energy resources such as electricity, gaseous or liquid fuels, and

heat. Biomass resources for fuel purposes include fuelwood, agricultural waste and

crop residue, sawdust and wood shavings. Over the years in Nigeria, fuelwood and

charcoal have constituted between 32 % and 40 % of total primary energy

consumption largely dominated by households (Oyedepo, 2012). In 2008, about 80 %

of Nigerian households were dependent on firewood as cooking fuel. In the developed

world however, bioenergy has not only been well established but extensively

researched. With the development of state-of-the-art products and services, modern

bioenergy has indeed been a tremendous success in satisfying humanity needs in

terms of provision of essential energy services (Silveira, 2005).

1.4 Wood waste and national need

In developing countries such as Nigeria, wood-processing companies and industries

generate a huge amount of waste in form of wood shavings, sawdust, etc. and are,

often openly burnt without control, thereby emitting particles and gases into the

atmosphere (Oguntoke et al., 2013). Pollutants from wood burning include

particulates, sulphur oxides, nitrous oxides, formaldehyde, carbon monoxide and

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organic matter. In addition, burning about I kg of wood releases close to 129 μg/m3 of

carbon monoxide, 700 μg/m3 of formaldehyde, 3300 μg/m3 of particulates, and 800

μg/m3 of benzene into the environment (Mohagheghzadeh et al., 2006). Dioxins and

plicatic acids are other constituents present in the wood smoke.

The world’s population has increased sharply from 1.65 billion to well over 6 billion

people in the 20th century (Akinola & Fapetu, 2015) . One of the direct consequences

of this is the overall increase in the world’s energy demand. Emodi and Boo (2015)

suggested strategies in sustainable energy development. These strategies, among

others, include the replacement of fossil fuels by various forms of renewable energy

(RE). Wood, being the most common form of biomass is considered relevant in this

direction. In essence, with the Government’s political will coupled with effective

application of public-private partnership (PPP), factors such as:

proper management; finance and adequate studies of the electricity

need/requirement of the host areas;

feasibility study of the proposed installation sites; and

the technical know-how concerning the deployment of mini-grid systems for

localities not connected to the national grid

Power provision as the national need could be effectively addressed and so made

available to the teeming populace not yet connected to the national grid.

1.5 Energy from biomass – alternative technologies

In poor countries of the world, biomass fuels (predominantly wood fuels) are common

source of bioenergy. With their technologies being majorly traditional, efforts are

being made to improve on the technologies by integrating biomass harvesting for

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energy purposes. According to Silveira (2005), about 1 percent of the world’s

electricity production comes from biomass. When used to generate energy, wood

waste is considered carbon-neutral because it releases no more carbon into the

atmosphere than it absorbs during its lifetime.

Table 1.1: Inter-relation and overview assessment of primary and integrated

conversion technologies

Primary conversion Form of

energy

recoverable

Integrated

conversion

technology

connection

Remarks

Heat Gas-fired boiler Commercial

(steam for

steam turbine)

Fixed and fluidized bed

gasification of wood

waste and other

forestry products

Power

Gas turbine Commercial

Micro turbine Commercial

Fuel cell Emerging

Stirling engine Emerging

Internal combustion

engine

Commercial and

highly deployed

Indirect fired gas

turbine

Commercial

Biomass pyrolysis Heat Oil-fired boiler Commercial

Power Indirect fired gas

turbine

Commercial

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Stirling engine Emerging

Direct conversion of

biomass in gasifiers

(fixed and fluidized

bed)

Heat Heat exchanger Commercial

Power Steam turbine Commercial

As a result, bioenergy can reduce the amount of carbon dioxide released into the

atmosphere if it replaces non-renewable sources of energy. However, with direct and

integrated conversion technologies, energy trapped within biomass structure can be

transformed into power/or heat. The transformation options include pyrolysis,

gasification, and anaerobic digestion. Examples of integrated technologies (Paper II)

include steam turbine, indirect fired gas turbine, gas-fired boiler, internal-combustion

engine (IC), micro turbine, oil-fired boiler, gas turbine, fuel cell, heat exchanger and

Stirling engine. Most prominently, integrated conversion technologies further

transform the combusted gas into heat and power. A description of the different

options is found in Table 1.1.

1.6 Gasification

Currently, combustion is a mature technology which is suitable for biomass conversion.

The combustion process converts chemical energy stored in biomass into heat,

mechanical power and electricity using equipment such as furnaces, boilers, steam

turbines and generators. However, the gasification process has synthetic gas (syngas)

as the key product which mostly consists of carbon monoxide (CO) and hydrogen (H2),

which can be converted into energy (steam and/or electricity), other gases, fuels,

and/or chemicals. According to Young (2010), converting syngas to different products

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can be categorized under different options. These are power option, Biochemistry

option, and chemistry option and each option has its special output (Chen et al., 2011).

These options are illustrated below:

1. Power option: Generates heat and/electricity.

2. Chemistry option: Converts syngas into fuels and chemicals by catalytic

chemistry.

3. BioChemistry option: Converts syngas into products such as methanol, ethanol,

Converts syngas into products such as methanol, ethanol,

etc. using biotechnology processes

The use of bioenergy not only could replace the use of fossil fuels but also keep

atmospheric concentrations of greenhouse gases at acceptable levels. It also helps to

achieve the objectives of the framework convention on climate change (FCCC). Studies

about bioenergy potential estimation give a thorough understanding of the sources,

types, amount and distribution of bioenergy potentials. All these aspects can help

assess how much bioenergy can substitute and supplement energy shortage, the

possible degree to which bioenergy could contribute to decrease greenhouse gas, and

how to arrange rational development and utilization of bioenergy.

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2. Background

2.1 Resource recovery in the developing world

Resource recovery is a well-researched phenomenon in the developed world, with

countries tending towards zero waste societies (Taherzadeh & Richards, 2016). In

Africa, its implementation is far from encouraging going by the site of heaps of wastes

around towns and cities in most countries in the continent. However, governments of

these countries are making frantic efforts to change the situation. For low income

countries, the average solid waste generated in markets, households, and from

horticultural and agricultural practices is about 0.4 - 0.6 kg/person/day (Cofie et al.,

2009). The organic waste fraction in the form of wood waste remains the largest

population which can be recovered for energy purposes (Demirbas, 2009). Figure 2.1

shows the organic matter in municipal solid waste for some African cities.

Figure 2.1: The percentages of organic matter in the municipal solid waste of some

major African cities (modified from Cofie et al. (2009))

0

20

40

60

80

100

Ibadan Kampala Accra Kigali Nairobi

Org

anic

mat

ter,

%

Some African cities

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2.2 Forests and sawmills in Nigeria

2.2.1 Forest resources

Across Local Government Areas (LGAs) in Nigeria, forest income plays an important

role in poverty alleviation (Fonta & Ayuk, 2013). The forest is not only important for

material goods but also a valuable ecological and cultural resource. The forestry

subsector has over the years contributed immensely to the socio-economic

development in the country. It ranks among one of the highest revenue and

employment generating sectors. It also serves as resource base for many forest

industries.

The major wood processing industries in Nigeria are typically large capacity facilities

industry such as large sawmills, plywood mills, pulp and paper plants and a large

numbers of small scale wood products manufacturing companies such as furniture

industries, cabinet makers and carpentry. Round-wood in Nigeria comes mostly from

natural high forest zone of the country, in particular from the Southern State of Cross

River, Edo, Delta, Ogun, Ondo, Ekiti, Osun and Oyo States of Nigeria (Bello and

Mijinyawa, 2010).

Forests are seen by most people, particularly planners and decision makers, as a

source of one product: wood. Yet they are the source of a host of non-wood products

of immense value to the communities within and around them. These products include

foods, fibres, wildlife, water, building and handicraft materials, gums, spices, dyes,

animal fodder and medicines.

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Figure 2.2: A map showing the forest region in eastern Nigeria (Culled from Okoji

(2001))

With reference to the latter, FAO (1994) estimates that the active ingredients in 25

percent of all prescription drugs come directly from medicinal plants, although not all

of the these grow in forest habitat, and that the global value of plant based drugs is

about US $43 billion a year. The implication is, therefore, that non-timber forest

resources multiply opportunities for entrepreneurship. In addition, forests constitute a

vital part of the environment. They conserve watersheds, soil and water. They protect

land from wind and water erosion, modulate climate and sequester carbon thereby

buffering the global warming attributed to increasing levels of CO2. Although forests

provide these resources, deforestation is taking place at an accelerating rate in south

eastern Nigeria. About 350,000 ha of forest and natural vegetation are lost annually

due to various factors. In the Cross River State, for example, Atte (1997) estimates that

as much as 14000 ha of the moist lowland tropical forest is lost each year as a result of

deforestation.

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2.2.2 Sawmills

A sawmill is an installation or facility in which cut logs are sawed into standard-sized

boards and timbers (Figure 2.3). The saws used in such an installation are generally

three types: the circular saw, which consists of a disk with teeth around its edge; the

band saw, which consists of a hoop of flexible metal that runs over pulleys and has

teeth along one edge; and the log gang saw, which consists of saw blades separated by

desired distances in a frame that oscillates as a log is fed into it. Logs are fed to gang

saws through pressure rollers that ensure straight cutting.

Figure 2.3: Lumbering activities in a Nigerian sawmill

With other saws the log rides on a conveyor or carriage. Provision is made for

placement of the log in a new position for each cut, by the worker who rides the

carriage or by one who operates the saw. Sawmills account for about 93% of the total

number of wood-based industries in Nigeria.

These mills are concentrated in the southwestern part of the country, with Ondo,

Ogun and Lagos States having the largest numbers. The main type of log conversion

machine used in these mills is the CD horizontal band saw. The Lumber recovery factor

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in most sawmills varies between 45 and 50%. This implies that about 50-55 % of log

input into sawmills are left as wood residues or wastes.

2.3 Wood waste management

With the generation of a lot of wastes- sawdust, wood off-cuts, wood backs, plain

shavings, wood rejects, etc. coupled with an absence of proper disposal methods,

these wastes are burnt in the open air along the bank of streams and rivers (Figure

2.4). As the demand for woods and its products increases, the volume of wastes being

generated cannot but increase. Hence, one of the greatest environmental problems

facing our cities and towns today is how to properly dispose of the waste being

generated daily by the ever-increasing activities of the sawmill industries. Odewunmi

(2001) observed that waste generation is a concomitant aspect of living; it cannot be

banished but can only be managed. The problems posed by these wastes are many:

they degrade the urban environment, reduce its aesthetic value, produce offensive

odors during the rains and pollute the air with smoke when burnt uncontrollably.

Figure 2.4: Poor wood waste management in Nigeria

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They also constitute health hazards in themselves if they are not timely disposed and

thus become breeding places for worms and insects. The sawdust is often spilled into

the lagoons, waterways, etc. and sometimes blocking the drainages and canals into the

lagoon.

The blockages of canals and drainages also cause flooding in the hinterland during

raining season. They also constitute bad working environment for those working in the

area, due to accumulation of wastes over a period of time, most especially during

raining season. Personal information from respondents on the waste disposal system

in the mills (Bello and Mijinyawa, 2010) is as obtained below:

Table 2.1: Mill waste disposal methods in the mill site

Waste Disposal Method Frequency

Response

Percentage

Response

Dump sites for wood waste to be disposed via burning

10 15.56

Heap wastes within the open spaces and burn on daily basis

31 48.45

Local food vendors and villagers pack for domestic use

12 18.77

Disposal for Agricultural uses and animal bedding

6 9.38

Other means of disposal apart from above

5 7.82

Total 64 100

Source: Bello and Mijinyawa (2010)

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2.4 Potentials for improving energy access through renewable energy

While at the same time combating the challenges of global warming, achieving

sustainable development through energy security is crucial. In this regard, the

utilisation of renewable energy resources, such as solar, wind, hydro, biomass and

geothermal energy, appears to be one of the most efficient and sustainable ways of

achieving this target. Globally, there has been upward trend in the utilisation of

renewable energy in the generation of modern energy (electricity). Table 2.2 presents

the developments and share of renewable energy in electricity generation in some

countries. Renewable, except hydro, have zero shares in power generation in Nigeria

despite its abundant existence in the country. Meanwhile, economically-feasible

renewable energy potential in Nigeria is projected to contribute with 2,036 MW, 6,905

MW and 68,345 MW to the electricity production in the country in the short, medium

and long-term respectively. This would then provide more than 37% of Nigeria’s total

energy consumption in the long-run. The national wood timber demand is projected to

increase to 91 million tonnes by 2030. This has great implications on sustainable

environment, food security and health of the low income households who depend

largely on wood fuels.

The strategic ways of controlling this problem is a dual approach of reducing

consumption rate through promotion of more efficient wood stoves and deployment

of alternatives to fuelwood through policy instrument and development of renewable

energy technology. Specifically, the government needs to address the problems posed

by deforestation by making use of these resources efficiently through improved

renewable energy technologies, thereby reducing the direct use of traditional biomass

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(fuelwood, crop residue, municipal wastes, sawdust, etc.) and improves modern

energy access.

Table 2.2: Share of electricity generation from renewable sources for selected

countries, 2000 –2006 (modified from Oseni (2012))

Year 2000 Year 2006

Country Including hydro Excluding

hydro

Including hydro Excluding

hydro

Austria 72.3 2.8 67.6 8.4

Germany 6.3 2.5 12.0 8.7

Italy 18.9 2.5 18.0 5.4

Portugal 30.3 4.2 34.0 10.4

Spain 16.3 3.0 18.7 9.6

UK 2.6 1.3 5.0 4.1

Turkey 24.9 0.2 26.3 0.2

Nigeria 40.3 0.0 34.7 0.0

With the envisaged deployment of wood waste for power production (Paper II), the

conversion technologies (pyrolysis and gasification) are extensively examined. It is

however worthy of note that there are similarities in the conversions of coal and

biomass. This informs the possibility of employing the services of the existing coal-

conversion facilities for the conversion of wood waste biomass (Oluoti et al., 2014).

While biomass can be described as a young coal with a known minimum gasification

temperature at 800 °C, coal has 900 °C as its minimum gasification temperature

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(Higman C., 2008). However, biomass (especially wood) in the lower gasification

temperature range produces a lot of tars (Devi et al., 2003; Swierczynski et al., 2008).

Preceding the gasification process is the devolatilization process, equally known as

pyrolysis. The raw wood waste is processed as fuel and fed into a gasifier. With the

help of an oxidant mostly (O2 or steam), the fuel in the gasifier is converted first into

char, tars, and gases during pyrolysis and then turned into ash, giving out the synthetic

gas (syngas). The syngas can be cleaned and sent into a gas engine or turbine to

produce electricity (Paper II). The schematic diagram of the process is seen in figure

2.5.

Figure 2.5: Flow diagram for power production from wood waste using gasification

(Paper II)

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2.4.1 Pyrolysis – overview, products and applications

During thermal conversion of biomass, the first step after drying is devolatilization,

which starts the release of the volatile matter from the solid fuels. This step is also

known as pyrolysis and it occurs in an inert atmosphere (Bulushev & Ross, 2011). In

general, thermochemical conversion of biomass falls into two main approaches which

are pyrolysis and gasification (Canabarro et al., 2013; Sharma et al., 2015). Biomass

conversion via pyrolysis and gasification is represented in figure 2.6.

Figure 2.6: Energy conversion of biomass (pyrolysis and gasification) to chemical fuels

and additives

For non-catalytic pyrolysis of biomass (as the case of wood), the mode of pyrolysis

employed determines the relative amount in which the biomass itself, char, liquid and

gas are formed as well as, the type of the pyrolysis system employed (Bulushev & Ross,

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2011). According to Bridgwater (2006), the different models employable for pyrolysis

reaction are fast, slow, and intermediate. The complete description is as shown in

Table 2.3. During pyrolysis, hemicellulose decomposes between 250–400 °C and about

20 wt. % of char is produced as the reaction temperature goes up to around 720 °C.

Compared with hemicellulose, cellulose decomposes at a temperature in the range of

310 –430 °C, leaving behind about 8 wt. % char. Lignin has a decomposition

temperature in the range of 300 – 530 °C.

Table 2.3: Modes of pyrolysis, reaction circumstances and product distribution

Reaction circumstances Products (100%)

Model Working

temp. (°C)

Exposure time Gas Liquid Char

Fast 500 Short (1s) 13 75 12

Slow 400 Very long 35 30 35

Intermediate 500 Moderate (about 10-20 s)

30 50 20

The char yield from lignin breakdown is about 55 wt.% (Williams & Besler, 1996). For

the carbohydrate content of the biomass, they depolymerise even at low temperature

to give smaller units. As dehydration takes place at about 300 °C, unsaturated

polymers and chars are produced. At temperatures higher than 300 °C, there is

massive rupture of C-C and C-H bonds and thus giving the products of pyrolysis in the

process (Brezinsky et al., 1988). The products include CO, CO2 and CH4. From pyrolysed

wood wastes, both the gases and the solid residues are useful in heat recovery

applications. The latter can further be used for agricultural purposes, especially in the

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production of fertilizer. Bio-oil as the liquid product has wider applications (Czernik &

Bridgwater, 2004), and can be upgraded to high-quality hydrocarbon fuels for further

use in boilers, engines and turbines. Applications of pyrolysis oil (bio-oil) include: heat

and power, transport fuel and biorefinery to other products.

Heat and power

Bio-oils are already being used in place of fossil fuels for medium or large-scale (co-)

combustion of natural gas, coal or heating oil-fired boilers, furnaces and turbines

(Czernik & Bridgwater, 2004). Aside its GHG savings of about 90 % compared to the

fossil fuel (FAO, 2008), it ensures some sustainability as the source (wood biomass) is

renewable.

Transport fuels

Second generation (advanced) biofuels can be obtained from bio-oils via direct

upgrading or through co-refining in existing refineries. It is also obtainable from

synthetic gas being processed and upgraded catalytically to produce fuels such as

DME, methanol and Fischer-Tropsch diesel. The two identified routes being envisaged

(Graça et al., 2013) for the production of biofuels from bio-oil include:

(1) Hydrodeoxygenation (HDO) of bio-oil to produce fuel or a feedstock

capable of being used in oil refinery.

(2) Processing of bio-oil to produce synthetic gas and then further processed to

transport fuel.

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2.4.2 Gasification – overview, products and applications

Gasification is a thermo-chemical process in which combustible gases are obtained

from the transformation of biomass undergoing thermal treatment (Zheng, 2013).

During the process, fuel biomass is exposed to a temperature range of about 850 -

1100 °C under an atmosphere of controlled oxygen (no combustion) or steam. The

product gases (syngas) from the process can be used to produce varieties of chemicals

and transport liquid fuels (Swanson et al., 2010). The type of gasifier employed for the

conversion and the way the fuel is fed in into the unit determine the name of the

gasification technology employed. The three generic fixed-bed gasification

technologies are updraft, downdraft and cross-draft. Other technologies are bubbling

bed, circulating fluidized, entrained bed, spouted bed and cyclone. The gasification

technology employed is usually optimized based on the feedstock as regards the

residence time and the operating temperature employed. According to Mullen et al.

(2010), about 35-45 % of energy contained in biomass feedstock is consumed during

the gasification process. For the purpose of power generation, integration of biomass

gasification with a gas engine is effective in small-scale (less than 10 MW power

output). For higher power output, steam turbines are employed. Syngas conversion to

transportation liquid fuels and other chemicals (bio-refinery) is made possible via for

example the Fischer-Tropsch process.

2.5 National need - wood waste to the rescue

For Nigeria as a country, the use of renewable materials such as wood waste to

address some national need is a possibility. The dwindling oil prices, the increasing

population and the pressing need to improve on the social amenities have made it

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necessary to go the way of renewable option for solutions. Inadequate power

provision is a national issue that could be addressed with the use of the abundant

renewable wood wastes. Nigeria could harness this huge dump of wood wastes to

augment the existing power supply and also provide electricity for those not

connected to the national grid (Paper II). Such conversion however, would require the

application of energy recovery processes such as pyrolysis and gasification (Paper I).

This also would involve the study of the reaction conditions and product analysis

(Paper III, IV, and V). The kinetic parameter results from these studies would assist in

the design of suitable reactor for the optimum conversion of these resources for

energy use. Considering the totality of biomass waste produced in Nigeria, it is

estimated that about 41 TWh of electricity may come from biomass waste resources

(Figure 2.8)

Figure 2.8: Biomass resources in Nigeria and their power generating potentials (Paper

II).

0

5

10

15

20

25

30

Fuel wood Agrowaste Sawdust Municipal solidwaste

TWh

Biomass resources in Nigeria

Electricity generationpotential

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3. Experimental and Methodologies

3.1 Biomass fuel samples

A total of six tropical biomass species were employed during the research. They were

obtained as sawmill wastes from Nigeria. Their local (Nigerian) and the botanical

names are as indicated in the Table 3.1. Also listed are their numerical values for

density (Air-dry).

Table 3.1: List of wood waste samples employed in this study

S/no Local name Botanical name

1 Teak Tectona grandis (Paper I)

2 Obobo Guarea thompsonii (Paper I)

3 Ayinre Albizia gummifera (Paper III)

4 Ahun Alstonia congensis (Paper IV)

5 Araba Ceiba pentandra (Paper IV)

6 Arere Triplochiton scleroxylon (Paper V)

All samples were collected as wood logs and further sun-dried (supervised) for an

average of about three weeks. This is done to ensure low moisture content. Prior to

being used for experimental runs, the sun-dried samples were size-reduced using

RETSCH SM 100 cutting mill to an average final size in the range of 0.20 to 2.00 (Paper

I, III, IV, and V).

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Tabl

e 3.

2: C

ombi

ned

com

posit

ion

in m

ass-

% o

f dry

fuel

s and

hig

her h

eatin

g va

lues

(HHV

) in

kJ/g

dry

fuel

for a

ll th

e w

ood

sam

ples

Loca

l

nam

e

Bota

nica

l nam

e M

oist

ure

%

(105

°C)

Ash

%ts

(550

°C)

C %

ts

(dry

)

H %

ts

(dry

)

N %

ts

(dry

)

S %

ts

(dry

)

HHV

kJ/g

Tea

k Te

cton

a gr

andi

s 7.

7 1.

0 51

.2

6.2

0.19

0.

012

19.0

3 ±

0.02

Obo

bo

Guar

ea th

omso

nii

6.6

5.3

48.3

5.

7 0.

34

0.03

5 18

.78

± 0.

16

Ayi

nre

Albi

zia g

umm

ifera

5.

3 1.

5 49

.4

6.1

0.36

0.

027

19.2

9 ±

0.08

Ahu

n Al

ston

ia c

onge

nsis

7.0

1.1

51.4

6.

0 0.

49

0.03

3 18

.08

± 0.

21

Ara

ba

Ceib

a pe

ntan

dra

6.6

1.5

49.7

6.

0 0.

45

0.02

9 18

.43

± 0.

11

Are

re

Trip

loch

iton

scle

roxy

lon

7.5

1.9

50.1

6.

0 0.

53

0.04

6 18

.44

± 0.

09

ts=t

otal

solid

, C=c

arbo

n, H

=hyd

roge

n, N

=nitr

ogen

, S=s

ulph

ur

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3.1.1 Proximate and ultimate analyses for all the wood samples

The respective energy content of the above-listed samples is a function of their

chemical compositions (Chen et al., 2014). It is important to note that the presence of

inorganics and moisture reduces the energy content of the samples (Wilson et al.,

2011). The proximate and ultimate analyses of the samples were made at BELAB AB

and the results as shown in Table 3.2. Except for Obobo with higher ash content

compared to others, all other results are similar for the samples considered in this

study.

Figure 3.1: Bomb calorimeter

3.1.2 Heating values

The calorific values (HHV) of the materials were evaluated using ASTM D240 and ASTM

D5865 standards. A bomb calorimeter (Fig. 3.1) manufactured by IKA was used (model

C 200). The analysis was initialized by weighing about 0.5 g of the materials in a

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crucible and placed inside the calorimeter. The runs were duplicated and the results as

shown in Table 3.2.

3.2 Thermogravimetric analysis

In solid-phase thermal degradation studies, thermogravimetric analysis is widely used.

It has widespread applications in biomass pyrolysis and gasification studies as

employed in Branca et al. (2007); Momoh et al. (1996); Stenseng et al. (2001); Teng

and Wei (1998). The thermogravimetric analyser (TGA) brand employed throughout

this research is a DynTherm HP by Rubotherm GmbH and shown in Fig. 3.2.

Figure 3.2: Thermogravimetric analyser (TGA)

It measures the loss in mass during thermal decomposition as a result of release of

volatiles as the reaction proceeds under preferred range of operating conditions such

as temperature, pressure, heating rates and gas flow rates. The main components are

the automated gas-dosing system and the suspension magnetic balance. It is an

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electromagnetic balance, which makes it specifically suitable for high pressure as there

is no physical connection between the test area and the balance. The complete unit is

controlled by a software called MessPro.

3.2.1 Mass loss

The property being investigated employing thermogravimetric analysis is mass (White

et al., 2011), and it is measured as the changes in sample mass as the reaction

proceeds. The data generated can be graphically represented in several ways. An

example of such is the mass loss curve in paper IV (Figure 3.3a). For the Teak sample

employed at different heating rates, the differences in pyrolysis zones are evident.

(a)

20

40

60

80

100

0 20 40 60 80 100

Wei

ght (

% w

t)

Time (min)

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(b)

Figure 3.3: (a) Weight loss for Teak at different heating rates (Paper I) (b) Derivative

plots for Araba at different heating rates (Paper IV).

3.2.2 Derivative thermogravimetry (DTG)

Taking the first derivative of the mass loss gives DTG curves (i.e., -dm/dt ) (Figure 3.3b)

provides the instantaneous reaction rate (Mészáros et al., 2004). It is also possible

from the DTG curves to obtain the peak temperature (where the maximum conversion

rate occurs) for the decomposition process (Vamvuka et al., 2003). Figure 3.3b

represents the DTG curves for Araba at different heating rates.

3.3 Torrefaction experiment and property change measurements

Alongside the TGA, torrefaction experiments were conducted (Paper IV) with the aid

of Nabertherm oven (model p330) under a controlled nitrogen atmosphere with a flow

rate of 0.833 Lmin-1 and a heating rate of 20 °C/min, the fuel samples were exposed to

different temperatures of either 150, 200, 250 or 300 °C. The samples were held in the

torrefaction reactor (the oven) for varied number of minutes (holding times). The

0

5

10

15

20

25

30

0 20 40 60 80 100

Deriv

. wei

ght (

% w

t/m

in)

Time (min)

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resulting masses (chars at high temperatures) obtained were subsequently used for

mass and energy yield estimations. Moisture uptake measurement (hydrophobicity)

was also carried out using a constant climate chamber HPP108 (manufactured by

Memmert) set at a relative humidity of 85 % and a temperature of 45 °C (typical

conditions in the tropics) for a total time of 24 hours.

3.4 Analysis of char morphology

Biomass gasification is preceded by devolatilization (pyrolysis) reaction. During the

process, the reaction temperature is maintained at a high temperature of 800 °C

leading to the release of steam and other volatiles. The remaining solid is referred to

as chars. Aside other factors, the pyrolysis conditions such as temperature, pressure,

heating rates, etc. employed during the reaction determines the microstructure of the

produced chars (Altun et al., 2003; Aouad et al., 2002; Demirbas, 2004; Mani et al.,

2010). The varied char morphology as regards pore and fibre orientations and

alignments are investigated using a Quanta FEG 200/400/600 scanning electron

microscope (SEM) with an operating voltage of 10 kV (Figure 3.4a). For further spot

analysis of SEM micrographs, an Astec SEM-EDX spot analyser (Figure 3.4b) was used.

The elemental percentage compositions of the selected areas are characterized by the

spot analyser, specifying the average, minimum, maximum and the sum.

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(a) (b) Figure 3.4: (a) Quanta FEG 200/400/600 scanning electron microscope (SEM), (b) Aztec SEM-EDX spot analyser.

3.5 Thermochemical processes and parameter determination

The thermogravimetric analyser (TGA) was employed to determine the kinetic

parameters during thermal conversion. In literature, several thermochemical processes

are available and these include combustion, pyrolysis, gasification and liquefaction.

The TGA offers the opportunity to either only pyrolyse the samples to form chars

(Paper I, II, and V) or continue through to gasification (Paper I, II, and V).

For the pyrolysis process, the pre-treated sample is first dried to a constant mass at a

temperature of 105 °C in the TGA. The pyrolysis is made by heating the sample in inert

atmosphere of nitrogen gas to the required pyrolysis temperature with a pre-

determined heating rate (Paper I, III, IV, and V). For the gasification process, the char

obtained from the pyrolysis process is isothermally gasified using a gasifying agent (Air,

O2, CO2, or steam). Meanwhile, kinetic parameters derived experimentally are affected

by reaction conditions such as temperature (Demirbas, 2004; Grønli et al., 2002),

heating rate (Cetin et al., 2004; Mermoud et al., 2006), residence time (Scott & Piskorz,

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1982), particle size (Demirbas, 2004), and pressure (Cetin et al., 2005). In terms of char

formation, the quantity of the char produced in cellulose pyrolysis varies with the

reaction pressure and the sample size (Yan et al., 2010). Yuan et al. (2011) discovered

that the residence time of the volatiles in the biomass matrix during the

devolatilization process determines the extent of the char produced. Mermoud et al.

(2006) also studied the influence of heating rate on the steam gasification of wood

char particles.

3.5.1 Pyrolysis kinetics

Generally, the kinetic expressions for biomass thermal decomposition can be

expressed under isothermal or non-isothermal conditions and formulated with respect

to a combination of solid-state reaction kinetic and Arrhenius equations. For

isothermal conditions, the form is

= exp . ( ) (1)

And for non-isothermal form with accompanying heating rate = written as

= . exp . ( ) (2)

The combination of , , and ( ) are designated as the kinetic triplet and often

employed to investigate biomass pyrolysis reactions. The models and methods used

throughout this study together with their governing equation are displayed in Table

3.3.

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Table 3.3: List of methods employed for kinetic parameter determination

Category Method Governing Equation

Flynn-Wall-Osawa

(FWO)(Paper I) log = log ( ) 2.315 0.4567

Kissinger-Akahira-

Sunose (KAS) (Paper

I)

ln = 1 ln ( )

Model-free

Methods

Friedman (Paper I,

V) ln = ln + ln(1 )

Li-Tang (Paper I) ln = + ( )

Kissinger (Paper I) ln = ln + ln (1 )

Model-

fitting

Method

Coats & Redfern

(Paper I and IV) ln ( ) = ln 1 2 –

Kennedy and Clark

(Paper I)

ln ( )( ) =

The term ( ) in Equation 1 denotes the changes in physical or chemical properties of

the samples as the gasification proceeds and it has different expressions when

considering each of the above-listed models (Zhang et al., 2014). For the model-fitting

methods, the recurrent term represents the integral function of the various

mechanisms (Khawam & Flanagan, 2006a; Maitra et al., 2007; White et al., 2011). The

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various solid-state reaction models employed throughout this research study included:

Reaction order (Paper I and IV); Avrami-Erofeev (Paper I); Diffusional 1D (Paper I); and

Contracting geometry (Paper I).

The full list of the used models (mechanisms) and that of others together with their

various expressions for and are well represented in the works of White et al.

(2011), Khawam and Flanagan (2006a) and Maitra et al. (2007). Cadenato et al. (2007)

and Budrugeac et al. (2007) established that a reaction mechanism can be declared

suitable based on the correlation coefficient (R2) and that the closer the R2 to unity,

the better the assumed mechanism represents the reaction. In the event of similar R2

values between different assumed mechanisms, Cadenato et al. (2007) and Budrugeac

et al. (2007) suggested comparing the calculated activation energies at different

models with the average activation energy from iso-conversional methods (Paper I).

3.5.2 Gasification kinetics

Biomass gasification follows a trend whereby the fuel is pyrolysed or devolatilized to

produce char. The solid carbonaceous fuel is being converted into combustible gas by

partial combustion (Sheth & Babu, 2010), and subsequently gasified using gasifying

agents such as air, CO2 or steam. However, the quality and nature of the chars

produced during pyrolysis depend on different factors such as biomass characteristics

and process conditions (Guizani et al., 2015). Compared with the initial process of char

formation (pyrolysis), the char conversion (gasification) process that follows is rate-

limiting meaning that this step is often slower than the initial pyrolysis. The kinetic

study of gasification is important to understand its reactivity in the process gasifier

(Ollero et al., 2003; Ollero et al., 2002). According to Zhang et al. (2014), different

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kinetic models are employed for the conversion analysis of chars formed under

different reaction conditions. For this reason, the interpretation of the conversion data

from the biomass gasification reaction throughout this study was made using four

selected gas-solid gasification models: Shrinking-core model (SCM) (Paper I and III);

volumetric reaction model (VRM)(Paper I and III); modified volume reaction model

(mVRM)(Paper III); and Random pore model (RPM)(Paper V). Table 3.4 gives a brief

description of the four kinetic models listed above.

The apparent kinetic reaction constant for each model is determined from the plot of

their respective linearized rate equations (Paper III). For a group of models employed

as above, the widely applied statistical methods to determine the relative ability of

each models to describe the experimental data include correlation coefficients (R2)

values and average error test (Paper V). The process starts with the pyrolysis of the

raw fuel samples into char and the gasification of the char follows producing ash as the

left-over in the presence of a single (or mixed) gasifying agent.

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Ta

ble

3.4:

Em

ploy

ed g

as-s

olid

reac

tion

mod

els a

nd th

eir a

ssum

ptio

ns

Mod

els

Assu

mpt

ions

Li

near

form

of r

ate

Equa

tion

Conv

ersio

n Eq

uatio

n SC

M

Reac

tion

star

ts a

t the

ext

erna

l sur

face

(Now

icki

et a

l., 2

011;

Zo

u et

al.,

200

7) a

nd m

oves

tow

ards

the

cent

re p

rodu

cing

an

unr

eact

ed in

ner m

ater

ial w

ith c

ontin

uous

ly sh

rinki

ng

core

(Bel

l et a

l., 2

010;

Kum

ar e

t al.,

200

8).

Part

icle

dia

met

er d

ecre

ases

whi

le th

e po

rosit

y is

cons

tant

(S

eo e

t al.,

201

0).

Grai

ns (w

ith a

ssum

ed sp

heric

al sh

ape)

und

ergo

es re

duce

d co

re d

iam

eter

as t

he re

actio

n pr

ocee

ds (F

erm

oso

et a

l.,

2008

).

3[1(1)

]=

=1(1

t/3)

VRM

The

char

par

ticle

s un

derg

o a

hom

ogen

ous

reac

tion

(Seo

et

al.,

2010

) with

a d

ecre

asin

g su

rfac

e ar

ea a

s th

e co

nver

sion

proc

eeds

(Kar

mak

ar &

Dat

ta, 2

011)

.

-ln( 1) =

=1(

) m

VRM

Th

e ap

pare

nt r

ate

cons

tant

cha

nges

with

the

sol

id r

eact

ion

(Yi,

1984

).

-ln( 1) =(

)

=1exp (

() ) RP

M

Pore

su

rfac

es

over

lap,

re

duci

ng

the

area

av

aila

ble

for

reac

tion

(Fer

mos

o et

al.,

200

9).

Char

s ar

e po

rous

mat

eria

ls fil

led

with

cyl

indr

ical

por

es

havi

ng u

nequ

al d

iam

eter

s (Irf

an e

t al.,

201

1).

Pore

size

s in

crea

se a

s ga

sific

atio

n re

actio

n pr

ocee

ds,

with

po

re w

alls

bein

g m

erge

d le

adin

g to

a r

educ

ed n

umbe

r of

po

res (

Bell

et a

l., 2

010)

.

( 2 )[(1

ln( 1) )

1]=

=1exp [(1

1+2

)/]

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4. Results and Discussions from the Appended Papers

4.1 National need- electricity

Nigeria’s electricity consumption per capita is one of the lowest in the world and it is

standing at 115 kWh per person. This is about 3 % of what is obtainable in South Africa

(Paper II). The effect of non-availability of stable and adequate supply of electricity has

made the Federal Government of Nigeria, companies and individuals to explore the

possibility of generating power from renewable sources. With the decreasing power

production level coupled with ever-increasing population in Nigeria, the problem of

power supply could get worse. At the moment, only about 50 % of the total population

has access to electricity (Ohiare, 2015). To improve on the power supply, the use of

wood waste for power production cannot be over-emphasized. Sambo (2009)

estimated that the total amount of wood waste produced by the lumber industry in

Nigeria is about 1.8 million tonne/yr and this could generate about 1.3 TWh of

electricity (Paper II). For Paper II, the emphasis was on the biomass and the

technicalities of the energy conversion/recovery towards the purpose of electricity

production. The technicalities of conversion include: Pyrolysis and its kinetics (Papers I

and V); Gasification and its kinetics (Papers I, III, and V); Torrefaction (a pretreatment

method) and its kinetics (Paper IV); and Reaction parameter variations (Papers I, III, IV,

and V) were all studied. As a representation of tropical wood samples, the species

employed were: Tectona grandis (Paper I); Albizia gummifera (Paper III); Alstonia

congensis (Paper III); Ceiba pentandra (Paper IV); and Triplochiton scleroxylon (Paper

V). Apart from taking care of waste wood material to prevent health and

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environmental hazards, its envisaged conversion to electricity addresses the power

shortage in the country.

4.1.1. Biomass power technologies

To address the national need (power problem), gasification of the abundant wood

waste could be of great importance as it involves the conversion of the fuel into

electrical power. Other products as highlighted earlier are heat and other biofuels for

other applications other than power. Studies in Paper II have shown that the

integration of biomass gasification technology for the production of fuel gas for use in

the different biomass power technologies employed (i.e. gas turbine, micro gas

turbine, steam turbine, internal combustion engine and Stirling engine) enhanced the

overall electrical performance (which exceeded 30 %).

4.1.2 Evaluation of biomass power technologies

For the purpose of mini-grid deployment towards the production of power (small-

scale) using biomass and waste as fuel, the power technologies listed above are

evaluated for electrical efficiency and economic feasibility. It is however good to note

that most of these technologies are yet to be commercially deployed. Therefore, the

proposed evaluations were made based on the parameters obtained from

demonstration plants and other information gathered from the operating conditions

(Reference conditions). Meanwhile, using an example of Ile-Ife city in the southwest of

Nigeria, the wood residue generated per day was estimated at 20 tonne/day. The

biomass power technologies evaluations were based on this figure. For economic

evaluation, the indicators considered include the fixed capital cost (or total capital

cost) (CFCC) and total capital investment cost (CTCI). The electrical efficiency of each

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power technology was evaluated from the reference plants based on the energy value

of the biomass fuel and process modifications in some of the technologies. The cost

and efficiencies for the processes are shown in Table 4.1.

It is estimated that the steam the turbine and gas turbine technologies require more

capital compared to others. The working capital cost (CWCC) (or running capital cost) is

assumed to be 20 % of the CFCC (Syed et al., 2012). It is also clear from the result array

(Table 4.1) that the costs for the Stirling engine and the internal combustion engine are

the lowest of all and therefore considered as good candidates for small-scale power

production. However, issues relating to the use of referenced pilot-scale conditions

could be observed here regarding the electrical efficiency results for the Biomass

Power Technologies. Although a better electrical efficiency for internal combustion

engine compared to micro gas turbine was displayed, literature review indicates the

opposite. Gimelli et al. (2012) indicated that a micro gas turbine operating at 6 bar

pressure could increase its electrical performance to 31 % below an electric output

range of 500 KW. The direct implication of this is that micro gas turbine compared to

internal combustion engine gives a better electric performance when used for mini-

grid micro power application is desired.

Table 4.1: Economic and electrical performance evaluation results for biomass power

technologies

Biomass power

technologies

Economic evaluation

Electrical performance

CFCC ($/kWel) CTCI ($/kWel) Electric efficiency (%)

Micro Gas Turbine 6100 7300 30

Gas Turbine 6200 7400 29

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Internal Combustion Engine 2800 2800 33

Stirling Engine 3300 3900 20

Steam Turbine 6200 7500 23

4.2 Biomass pyrolysis – the kinetics and reaction model mechanism

A fundamental and typical graphical representation of generated data from the

devolatilization runs of any of the samples listed in Table 3.1 is shown in Fig. 3.3 (a) &

(b). Employing different heating rates (°C/min) and temperatures as variables for the

devolatilization reaction, a compilation of the main pyrolysis temperature range (i.e.

temperature interval for the maximum material loss (Kumar et al., 2008)) and the peak

temperature for Ahun and Araba (Paper IV) is shown in Table 4.2. Kissinger (1956)

defined peak temperature as the temperature at which the maximum reaction rate

occurs. Peak temperatures increase with heating rate (Pantoleontos et al., 2009;

Vamvuka et al., 2003; Várhegyi, 2007) Várhegyi (2007) and Vamvuka et al. (2003).

Araba and Ahun (Paper IV) followed the trend as shown in Table 4.2.

Table 4.2: Active pyrolysis temperature range and peak for the devolatilization process

for Ahun and Araba (Paper IV)

Ahun Araba

Heating rate (°C/min)

Active pyrolysis range (°C)

Peak temperature (°C)

Active pyrolysis range

(°C)

Peak temperature

(°C) 5 202 - 277 253.76 165 - 273 257

10 213 - 280 252.46 184 - 275 259

15 222 - 287 260.94 195 - 286 272

20 238 - 283 272.56 205 - 288 276

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4.2.1 Iso-conversional (model-free) approach

From the model-free method mentioned earlier, and using Teak as an example,

evaluated results for Ea

clear from the figure that the activation energy changes with conversion, . A slight

jump is observed between conversions 0.1 to 0.3 and according to Yao et al. (2008),

the jump is attributed to the material experiencing accelerated decomposition. Also

from the figure, observations show that at conversions beyond 0.6, a distorted trend is

observed which indicates decomposition with multi-step reaction mechanism.

However, comparison of the Ea results from the model-free methods with those from

Tsamba et al. (2006), Slopiecka et al. (2012) and Yao et al. (2008) shows a good

agreement.

Conversion ( )

Figure 4.1: Profile plot of activation energy (Ea ) against conversion ( ) values from Iso-

conversional methods (Paper I)

E a (k

J/m

ol)

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4.2.2 Model-fitting approach

Khawam and Flanagan (2006a) listed the basis for the classification of models used in

the study of solid-state kinetics. These include geometrical contraction, reaction

order, diffusion and nucleation. The four mechanisms employed in this model-fitting

approach include Avrami-Erofeev, Reaction order, Diffusional and Contracting

geometry (Paper I). In the work of Khawam and Flanagan (2006b), it was claimed that

a suitable reaction mechanism can however be identified and also characterized based

on the values of correlation coefficient (R2), i.e. the closer the value to unity the better

the chance of being selected.

According to , the calculated activation energies from different

models could be compared with the average activation energy from model-free

methods. In evaluating the Ea results involving the sample conversion (Obobo), four

mechanisms were considered with third order as the average Ea values obtained at n=3

for all the mechanisms were in agreement with those from model-free methods.

Meanwhile, It is clear from the displayed results (Table 4.3) that only the Reaction

order and Diffusional models gave results in agreement with what was obtained from

the iso-conversional methods.

Table 4.3: Obobo and its reaction model mechanism results (Modified from Paper I)

Model Average activation

energy, Ea (KJ/mol)

Average pre-exponential

factor, A (min-1) R2

Reaction order 149.48 6.37E+16 0.9762 Avrami-Erofeev

22.69

12.00E+00

0.9579

Diffusional (1D)

149.99

7.82E+13

0.9682

Contracting geometry

79.77

1.60E+08

0.9779

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Considering the results for Obobo from the two methods (model-free and model-

fitting), the Ea values obtained are similar to those reported in the literature for non-

tropical species (Slopiecka et al., 2012; Tsamba et al., 2006; Yao et al., 2008). Since

these non-tropical samples are already deployed for energy recovery purposes, the

tropical counterparts are equally looking good as promising fuel stock for energy

recovery.

4.3 Gasification of wood biomass – kinetic model approach

Some of the gasifying agents commonly used include CO2 (Paper I and IV), steam

(Paper III), air (Cao et al., 2006; Gil et al., 1999), hydrogen (Cheng et al., 2012), air-

steam (Lv et al., 2004; Meng et al., 2011), and O2-enriched air (Mastellone et al., 2012).

According to Zhang et al. (2006), gasification reactivity of the product char from the

pyrolysis reaction are influenced by several factors. These factors may include the type

of gasifying agent, reaction conditions and the char properties (e.g. morphology). In

this work however, CO2 and steam are the two gasifying agents employed, while the

reaction conditions include the partial pressures of CO2 (Paper I), partial pressures of

steam (Paper III), gasification temperatures (Paper III). As listed in Table 3.4, the

models were employed due to the reason of their assumptions being in tune with the

nature of the tropical biomass employed in this study as requisites for their optimum

conversion.

With the biomass fuel particle in form of sawdust and turning to char after being

pyrolysed, the assumptions above are adaptable to the char properties. Therefore, the

model could be used to interpret the gasification reaction of the chars. In Paper I,

Tectona grandis was pyrolysed and the chars subsequently gasified. The char

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conversion was evaluated with gas-solid reaction models such as VRM and SCM and

the gasification rate estimated. Table 4.4 gives the char formation and conversion

history together with the evaluated gasification rate constants.

It is clear from the results that VRM gave a better description of the conversion

reaction and Obobo looks more reactive compared to Teak considering their

respective K for the two different models (VRM and SCM) considered.

Table 4.4: Pyrolysis-gasification conversion and model determination of apparent

gasification rate constant, K (min-1) of Teak and Obobo

Fuel

Pyrolysis conditions

Gasification conditions

Employed models

Apparent

gasification rate constant

(min-1)

Botanical name

Local name

Heating rate (°C min-1)

Temp. (°C)

Gasifying agent

Temp. (°C)

Tectona

grandis

Teak 2 - 20 900 CO2 1000 VRM

SCM

0.1784 ± 0.01

0.1333 ± 0.02

Guarea

thomsonii

Obobo 2 - 20 900 CO2 1000 VRM

SCM

0.2285 ± 0.02

0.1652 ± 0.03

Apart from the apparent gasification kinetic rate constant, K from the plots of different

models, other kinetic parameters are also evaluated. These parameters included the

activation energy, Ea and the Frequency factor, A evaluated via the Arrhenius plot

using concentrations, flow rates or partial pressures during gasification reaction at

different reaction temperatures. For example, a combined Arrhenius plot for both

linear (model-free) and calculated (model-fitting) data for Ayinre sample undergoing

steam gasification at a partial pressure of 3.0 bar (Paper III) is shown in Figure 4.2. The

kinetic constants (Ea & A) are shown in Table 4.6.

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Figure 4.2: Combined Arrhenius plot for linear and calculated (model-fitting) data for Ayinre at a partial pressure of 3.0 bar (Paper III)

Table 4.5: The evaluated kinetic parameters (Ea (kJ/mol) and A (h-1)) for steam gasification of wood char using experimental and calculated (model-fitting) data from different models (Paper III)

Data Type Ea (kJ/mol) A (h-1)

Experimental 48.13 5.09E + 02

SCM 49.29 3.45E + 02

VRM 49.89 1.55E + 03

mVRM 32.54 1.79E + 04

From the result array in Table 4.5 above, mVRM with the lowest activation energy

value at 32.54 kJ/mol and the corresponding Frequency factor 1.79E + 04 is best suited

to describe the experimental reaction having, when compared to other models, the

highest R2 value at 0.9959 (Paper III).

-1.0

1.0

3.0

5.0

7.0

0.75 0.80 0.85 0.90 0.95 1.00 1.05

lnK

(h-1

)

1000 K/T

Linear model

SCM

VRM

mVRM

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4.4 Reaction parameter variation and the effects

Variations in process variables affect the nature and the rates of lignocellulosic

decomposition reactions (Pinto et al., 2003). In this thesis, an example of the effects of

reaction variables on the reaction kinetics of the wood fuel under investigation was

demonstrated by the reaction behaviour Ayinre under steam gasification with varied

partial pressures and gasification (Paper III). Table 4.6 below represents the evaluated

char gasification rate constants as estimated with paired reaction variables of

gasification temperatures and steam partial pressures. The general trend indicates an

increase in gasification rate constant with increase in steam partial pressure and the

reaction temperature. Another means of showing the impact of operating condition is

demonstrated by Figure 4.3, indicating a typical trend involving the effect of varying

the temperatures of reaction on the char conversion reaction considering a particular

steam partial pressure (in this case 4.0 bar). The higher the reaction temperature, the

faster the reaction time.

Table 4.6: Char gasification rate constant results KVRM (min-1) from steam partial pressure and gasification temperature as paired reaction variables

2.0 bar 3.0 bar 4.0 bar 5.0 bar

700 °C 0.05 0.06 0.07 0.08

800 °C 0.11 0.09 0.20 0.19

900 °C 0.17 0.14 0.31 0.24

1000 °C 0.24 0.25 0.29 0.33

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Figure 4.3: Effect of varying reaction temperature on char conversion reaction (Paper III).

At chosen conditions of elevated temperatures and absence of oxygen, wood samples

are pyrolysed to produce chars (Park & Jang, 2012; Tripathi et al., 2016). The different

chars produced often have varied reaction rates during gasification. In other words,

the reactivity of chars is strongly dependent on its formation history (Chen et al., 1997;

Okumura et al., 2009). In the work of Chen et al. (1997), birch wood was pyrolysed

under varied reaction conditions. A rapid heating rate for the birch sample gives a char

with higher reactivity compared with those produced with a slow heating rate. From

paper V, the effect of varied pyrolysis conditions on the morphology and gasification

reactivity of Arere was studied.

Similar to the earlier results (Cetin et al., 2005; Okumura et al., 2009), It was found that

the reactivity of chars formed decreased with increasing pyrolysis pressure. With

increased pressure, the pores become larger with thinner walls and less surface area is

available for the reaction. The char conversion during gasification is faster with

increased pyrolysis heating rate. This is due to the fact that the pores collapse and then

0.1

0.3

0.5

0.7

0.9

0 20 40 60 80 100

Conv

ersio

n

Reaction time, min

700°C800°C900°C1000°C

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fragmentize, leading to an increased surface area available for reaction. An overall

representation of the phenomenon is as represented in Figure 4.4 indicating the effect

of pyrolysis conditions (heating rate and pressure) on the reactivity of the reacting

char.

A detailed representation of the effects of variations in the pyrolysis conditions relative

to the gasification reaction constant K is represented in Figure 4.4. An example of a

trend from the figure shows that at a pyrolysis pressure of 1.0 bar, increasing the

heating rate of the raw fuel conversion during pyrolysis from 5 to 20 °C/min gave

gasification reactivity increasing from 0.0369 to 0.0398 min-1. However, increasing the

pyrolysis pressure to 6.0 bar (for example) produces a decreasing range of K values for

the respective heating rate considered as compared to those from 1.0 bar.

Figure 4.4: The effect of pyrolysis conditions (pressure and heating rate) on the reactivity of Arere char undergoing gasification reaction (modified from Paper V).

0.034

0.035

0.036

0.037

0.038

0.039

0.040

0.041

0.0 2.0 4.0 6.0 8.0

Reac

tivity

, min

-1

Pyrolysis pressure, bar

5 °C/min

10 °C/min

20 °C/min

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4.4.1 Analysis of fuel char microstructures – SEM approach

Changes in pyrolysis conditions (heating rate and pressure) and their effects on the

morphology and gasification reactivities of Arere chars were investigated (Paper V).

The scanning electron microscope (SEM) probe was deployed to expose the

micrographic changes in orientations and populations of the pores as the gasification

reaction proceeds using the Back-scattered electron (BSE) imaging method. This leads

to different reactivities for different chars. Cetin et al. (2005) claimed that the

diameters of the pores increase with pyrolysis pressure, leading to a reduction in the

number of pores. With this, the available surface for reaction is reduced resulting in

the eventual reduction in gasification reactivities for the chars.

Considering heating rate during pyrolysis, it can be summed up that at high heating

rates; the pores are highly ruptured leading to an increase in total area available for

reaction with the gasifying agent. The varied reactivity was as a result of different

orientations and microstructures of the chars. An example of this is shown in Figure

4.5 representing the morphology of chars formed at a constant heating rate of 5

°C/min (noted as H5) and at increasing pressure (i.e., P1H5, P4H5, P6H5. Where P1, P4,

and P6 represent 1, 4, and 6 bar, respectively). From the micrograph denoted P1H5, the

near-natural microstructural orientation of micro fibres and mini pores. Micrograph

P4H5 shows a considerable growth in the number of visible pores with distinct

measurable diameters with the pyrolysis pressure being increased to 4.0 bar. From

micrograph P6H5, the pyrolysis pressure was increased to 6.0 bar and the pores are

now bigger with larger measurable diameters compared to those of lower pyrolysis

pressures.

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Figure 4.5: Pore structure and distribution of chars showing the effect of increased

pyrolysis pressure (paper V).

However, a different trend is observed with an increasing heating rate. The pores

rupture with increasing heating rate leading to increased surface area available for

reaction by the gasifying agent. The resultant effect is the increased gasification

reactivities obtained.

4.5 Metal crystals in biomass chars

Biomass components play an important role in the pyrolysis characteristics and

product distribution of biomass (Raveendran et al., 1996) with emphasis on distributed

Alkali and Alkaline Earth Metal (AAEM) species in biomass.

In the work of Lv et al. (2010), AAEM species present in the ash were investigated and

it was found out that the alkaline and the alkaline earth metals have strong influence

on the reactivity of biomass. Fahmi et al. (2007), found that during conversion,

biomass experiences strong catalytic effect from the AAEM species within the body of

the converting mass. However, the interaction between the AAEM species and the

converting char provides a platform for analysing the catalytic activity of the AAEM

species (Lv et al., 2010). Other authors such as Asadullah et al. (2010) and Gil et al.

P1H5 P4H5 P6H5

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(2015) also corroborated both the existence and the catalytic influence of AAEM. They

worked with chars from olive and coffee wastes and suspected high reactivity

responses most probably as a result of the catalytic effect of the AAEM species. In

paper V, chars produced under different pyrolysis conditions were examined with

respect to its microstructure. The micrographs obtained were further spot-analysed

with SEM-EDX. The results indicated presence of metal crystals predominantly

consisting of calcium. An example of such analysis is as shown in Figure 4.6a & b and

the percentage compositions of the crystals analysed are displayed in Tables 4.8 and

4.9, respectively.

Figure 4.6: BSE images of analysed regions for Arere chars produced at 10 °C/min

heating rate and 1.0 bar (a), and 20 °C/min and 6.0 bar (b)-modified from paper V.

Table 4.8: Results of the spot analyses of the BSE images of an Arere char produced at 10 °C/min at 1.0 bar. The regions analysed are 1, 2, 3 and 4, according to Fig. 4.6(a). All results are given in weight % (modified from Paper V). Spectrum C O Na Mg P S K Ca Total

1 46.1 32.9 0.2 - - 0.4 0.7 19.7 100.0

2 41.3 40.2 - - - 0.4 0.3 17.9 100.0

3 85.3 12.7 0.4 0.1 - - 1.0 0.5 100.0

a b

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4 86.2 12.1 0.2 - 0.2 - 0.7 0.6 100.0

Table 4.9: Results of the spot analyses of the BSE images of an Arere char produced at 20 °C/min at 6.0 bar. The regions analysed are 1, 2, 3, 4 and 5, according to Fig. 4.6(b). All results are given in weight % (modified from Paper V).

Spectrum C O Na Mg Al S K Ca Total 1 41.9 38.7 - - 0.1 - 0.3 19.0 100.0

2 89.9 7.6 0.1 0.1 0.1 0.2 0.9 1.2 100.0

3 90.0 8.0 0.1 - 0.2 - 0.8 0.8 100.0

4 89.7 6.6 0.1 0.2 0.2 0.2 1.3 1.8 100.0

5 45.7 35.3 - - - - 0.4 18.7 100.0

It can be concluded from the work of Di Blasi et al. (1999) and Gil et al. (2015) that the

predominant calcium present within the biomass body as shown above could be

responsible for the high reactivity of wood biomass chars as already reported in the

literatures.

4.6 Mechanisms and rate laws of CO2 and steam gasified chars.

According to Karlström et al. (2015), the reactivity towards CO2 of a biomass is similar

to that towards steam. It is observed that the latter has a slightly higher reactivity

compared to the former (most times by a factor of 2-5). During CO2 gasification of

biomass chars, the oxygen exchange mechanism (Di Blasi, 2009) is represented as

follows:

K1 Cf + CO2 C(O) + CO (1)

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K2 C(O)+ CO Cf + CO2 (2)

K3 C(O) CO (3)

Where Cf, C(O) represent an active sight and a carbon-oxygen complex, respectively.

K1, K2, and K3 are rate constants.

The steady state concentration of C(O) is lowered by the presence of CO as an inhibitor

(eqn. 2). Applying the steady state assumption for the C(O) complex, the CO2

gasification rate, r (which accounts for temperature and reactant partial pressure

effects) with respect to eqns. (1) – (3) is given as (Di Blasi, 2009):

= (4)

Where , are the partial pressures of CO and CO , respectively. However, in the

event of the inhibiting effect exerted by CO being negligible together with the fact that

the concentration of CO is small, a simple global model can be applied (Di Blasi, 2009)

as thus:

C + CO 2 CO, = ( / ) (5) Where A, E, and R are the frequency factor, the activation energy and the universal gas

constant, respectively. The symbol n is an empirical parameter that represents the

reaction order. Similar to CO2 gasification is the steam type. However, gasification with

steam is more complex due to the action of H2, CO2 and CO following the equilibrium

of the water gas shift reaction.

CO + H2O = CO2 + H2 (6)

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The reaction is often slow especially in the absence of catalysts or inorganic matter in

biomass. Two basic mechanisms are involved in the steam gasification of biomass and

they are the oxygen exchange mechanism and the hydrogen inhibition (Barrio et al.,

2008; Hüttinger & Merdes, 1992). Laurendeau (1978) established that oxygen

exchange mechanism (eqns. 7 – 9) is preferred due to its ability to be supported by

pieces of confirmatory evidence.

K1 Cf + H2O C(O) + H2 (7)

K2 C(O) + H2 Cf+ H2O (8)

K1 C(O) CO (9)

An elementary mechanism for the carbon-steam reaction is represented as

2Cf + H2O C(H) + C(OH) (10)

C(OH) + Cf C(O)+ C(H) (11)

2C(H) Cf + H2 (12)

C(O) CO (13)

C(H) and C(OH) are intermediates which are short-lived, leaving the steps in eqns. (10)

- (13) reduced to the oxygen exchange mechanism as represented by the eqns. (1) –

(3). Similar to CO2 gasification, most kinetic analysis of char gasification with steam

consider a global model:

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C + H2O 2 CO + H2, = ( / ) (14)

In paper III, Ayinre chars were steam gasified and the rate parameters for the char

activation reaction rate (similar to that of eqn. 14) was obtained. This result, together

with others from wood biomass materials from the literature are summarised in Table

4.10.

The kinetic result in Table 4.10 indicates that the exponent of the steam partial

pressure is in the range 0.4 – 1.0 for wood biomass (except for the Japanese Ceder

which gave 0.22). Ayinre gave the lowest apparent activation energy and one of the

highest exponential values (0.58). These two phenomena point to the fact that tropical

wood biomass samples are highly reactive during thermal treatment for energy

recovery. The presence of calcium (as part of AAEM) in Arere, as shown in the char

spot analysis, is an added factor supporting the enhanced reactivity.

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Tabl

e 4.

10:

Stea

m g

asifi

catio

n ra

te e

xpre

ssio

ns fo

r cha

rs w

ith th

e ac

com

pany

ing

pyro

lysis

and

gas

ifica

tion

cond

ition

s.

Fuel

Re

fere

nce

Pyro

lysis

Con

ditio

n T g

(K)

P H2O

(kPa

) St

eam

gas

ifica

tion

reac

tion

rate

,

Popl

ar

woo

d

Haw

ley

et

al. (

1983

)

Part

icle

size

rang

e 1

– 2

mm

at

973

K

1073

– 1

273

0.88

- 23

=6.57

×10exp (156 )

Birc

h Ba

rrio

et a

l.

(200

8)

Slow

pyr

olys

is at

873

; (0

.045

0.06

3) m

m c

har

1023

– 1

123

10 –

30

=2.62×10e

xp237. (() )

Ayin

re

Pape

r III

Sl

ow p

yrol

ysis

at 1

0 K/

min

, 117

3

K

973

– 12

73

20 –

50

=179×10e

xp (32.54 ). ( 1)

Saw

dust

part

icle

Kojim

a et

al. (

1993

)

In a

flui

dise

d be

d at

112

3 –

1123

K

1123

– 1

123

0 - 5

8 =1173

exp (179 ).

Woo

d

chip

Sun

et a

l.

(200

7)

Char

form

atio

n no

t spe

cifie

d 97

3 –

1123

30

- 91

=15.9

3×10exp (

171.4 ). ( 1)

Japa

nese

Cede

r

Mat

sum

oto

et a

l. (2

009)

Char

form

atio

n no

t spe

cifie

d 11

73 –

147

3 25

- 30

0 =9.99

×10exp136

. (() )

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5. Conclusions and Future Studies

5.1 Conclusions

Wood waste could be deployed to tackle part of the power production problem if

effectively put into use. With abundant wood waste, a country such as Nigeria could

benefit from proper management and eventual deployment for power-generating

purposes. Due to perceived differences in weather, soil properties, local temperature,

etc. the kinetic properties of these tropical samples are a key to achieving an optimum

energy recovery when deployed for energy use.

The kinetic results (most especially the parameters) are highly useful in the design, re-

design, configuration or reconfiguration of the existing or new gasifiers (or reactors)

for fuel conversion purposes.

Energy densification via torrefaction of the tropical biomass wood samples can

enhance the deployment of torrefied samples for mini-grid applications. Ahun and

Araba (tropical samples) behave in a similar manner as compared with Olive mill waste

and Willow biomass samples during torrefaction which indicates a possibility of using

these tropical wood biomasses for power-production via mini-grid system. In essence,

for places far away from production source, the raw wood materials can be energy-

densified and made transportable to be used for power need and conversions far from

the production source. Also, the kinetic results of torrefaction process (as a

pretreatment) can be optimised to get the optimum treatment mechanism for the raw

fuel materials for future energy recovery purposes.

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5.2 Future studies

Further studies are suggested be directed towards converting the tropical wood

samples using a pilot-scale fixed-bed reactor. This is important for determining the

behaviour of the samples close to what is obtainable on an industrial scale.

Furthermore, since only the stem parts were used in the present study, a focus on the

use of a mixture of several parts of the samples would be of great importance as wood

samples from the sawmills are not just stem parts but a mixture of several parts and

different shapes of the wood, such as bark, sawdust, coarse residues (off-cuts, edgings,

and stumps), planer shavings, etc. Finally, single gasifying agents were used in the

present study. Attempt should be made to make use of a mixture of different gasifying

agents and also at varied partial pressures and then compare the results in terms of

the energy and other product yields. This would expand the database as regards the

conversion of tropical biomass with a view to obtaining an optimum yield under

optimum conversion conditions.

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References

Akinola, A.O., Fapetu, O.P. 2015. Characteristics Study of Wood Wastes from Sawmills.

British Journal of Applied Science & Technology, 6(6), 606-612.

Altun, N.E., Hicyilmaz, C., Kök, M.V. 2003. Effect of particle size and heating rate on the

pyrolysis of Silopi asphaltite. Journal of Analytical and Applied Pyrolysis, 67(2),

369-379.

Aouad, A., Bilali, L., Benchanâa, M., Mokhlisse, A. 2002. Kinetic Aspect of Thermal

Decomposition of Natural Phosphate and its Kerogen. Influence of heating rate

and mineral matter. Journal of Thermal Analysis and Calorimetry, 67(3), 733-743.

Asadullah, M., Zhang, S., Min, Z., Yimsiri, P., Li, C.-Z. 2010. Effects of biomass char

structure on its gasification reactivity. Bioresource Technology, 101(20), 7935-

7943.

Barrio, M., Gøbel, B., Rimes, H., Henriksen, U., Hustad, J.E., Sørensen, L.H. 2008. Steam

Gasification of Wood Char and the Effect of Hydrogen Inhibition on the Chemical

Kinetics. in: Progress in Thermochemical Biomass Conversion, Blackwell Science

Ltd, pp. 32-46.

Bell, D.A., Towler, B.F., Fan, M. 2010. Coal gasification and its applications. William

Andrew.

Bello, S.R., Mijinyawa, Y. 2010. Assessment of injuries in small scale sawmill industry of

south western Nigeria. Agricultural Engineering International: CIGR Journal,

12(1).

Page 59: Investigating the Reaction Kinetics of Tropical …hb.diva-portal.org/smash/get/diva2:910296/INSIDE01.pdfThesis for the Degree of Doctor of Philosophy Investigating the Reaction Kinetics

58

Branca, C., Iannace, A., Di Blasi, C. 2007. Devolatilization and Combustion Kinetics of

Quercus cerris Bark. Energy & Fuels, 21(2), 1078-1084.

Brezinsky, K., Hura, H.S., Glassman, I. 1988. Oxidation/pyrolysis chemistry as related to

fuel sooting tendencies. Energy & Fuels, 2(4), 487-493.

Bridgwater, T. 2006. Biomass for energy. Journal of the Science of Food and

Agriculture, 86(12), 1755-1768.

-isothermal kinetic study on the

decomposition of Zn acetate-based sol-gel precursor. Journal of Thermal Analysis

and Calorimetry, 88(3), 699-702.

Bulushev, D.A., Ross, J.R.H. 2011. Catalysis for conversion of biomass to fuels via

pyrolysis and gasification: A review. Catalysis Today, 171(1), 1-13.

Cadenato, A., Morancho, J.M., Fernández-Francos, X., Salla, J.M., Ramis, X. 2007.

Comparative kinetic study of the non-isothermal thermal curing of bis-

GMA/TEGDMA systems. Journal of Thermal Analysis and Calorimetry, 89(1), 233-

244.

Canabarro, N., Soares, J.F., Anchieta, C.G., Kelling, C.S., Mazutti, M.A. 2013.

Thermochemical processes for biofuels production from biomass. Sustainable

Chemical Processes, 1(1), 22-22.

Cao, Y., Wang, Y., Riley, J.T., Pan, W.-P. 2006. A novel biomass air gasification process

for producing tar-free higher heating value fuel gas. Fuel Processing Technology,

87(4), 343-353.

Page 60: Investigating the Reaction Kinetics of Tropical …hb.diva-portal.org/smash/get/diva2:910296/INSIDE01.pdfThesis for the Degree of Doctor of Philosophy Investigating the Reaction Kinetics

59

Cetin, E., Gupta, R., Moghtaderi, B. 2005. Effect of pyrolysis pressure and heating rate

on radiata pine char structure and apparent gasification reactivity. Fuel, 84(10),

1328-1334.

Cetin, E., Moghtaderi, B., Gupta, R., Wall, T.F. 2004. Influence of pyrolysis conditions

on the structure and gasification reactivity of biomass chars. Fuel, 83(16), 2139-

2150.

Chen, C., Luo, J., Qin, W., Tong, Z. 2014. Elemental analysis, chemical composition,

cellulose crystallinity, and FT-IR spectra of Toona sinensis wood. Monatshefte für

Chemie - Chemical Monthly, 145(1), 175-185.

Chen, G., Yu, Q., Sjöström, K. 1997. Reactivity of char from pyrolysis of birch wood.

Journal of Analytical and Applied Pyrolysis, 40–41, 491-499.

Chen, W.-H., Cheng, W.-Y., Lu, K.-M., Huang, Y.-P. 2011. An evaluation on improvement

of pulverized biomass property for solid fuel through torrefaction. Applied

Energy, 88(11), 3636-3644.

Cheng, C.K., Foo, S.Y., Adesina, A.A. 2012. Thermodynamic analysis of glycerol-steam

reforming in the presence of CO2 or H-2 as carbon gasifying agent. International

Journal of Hydrogen Energy, 37(13), 10101-10110.

Cofie, O.O., Drechsel, P., Agbottah, S., Veenhuizen, R.v. 2009. Resource recovery from

urban waste: Options and challenges for community-based composting in sub-

Saharan Africa. Desalination, 248(1–3), 256-261.

Czernik, S., Bridgwater, A.V. 2004. Overview of Applications of Biomass Fast Pyrolysis

Oil. Energy & Fuels, 18(2), 590-598.

Page 61: Investigating the Reaction Kinetics of Tropical …hb.diva-portal.org/smash/get/diva2:910296/INSIDE01.pdfThesis for the Degree of Doctor of Philosophy Investigating the Reaction Kinetics

60

Demirbas, A. 2004. Effects of temperature and particle size on bio-char yield from

pyrolysis of agricultural residues. Journal of Analytical and Applied Pyrolysis,

72(2), 243-248.

Demirbas, A. 2009. Reuse of Wood Wastes for Energy Generation. Energy Sources, Part

A: Recovery, Utilization, and Environmental Effects, 31(19), 1687-1693.

Devi, L., Ptasinski, K.J., Janssen, F.J.J.G. 2003. A review of the primary measures for tar

elimination in biomass gasification processes. Biomass and Bioenergy, 24(2), 125-

140.

Di Blasi, C. 2009. Combustion and gasification rates of lignocellulosic chars. Progress in

Energy and Combustion Science, 35(2), 121-140.

Di Blasi, C., Buonanno, F., Branca, C. 1999. Reactivities of some biomass chars in air.

Carbon, 37(8), 1227-1238.

Emodi, N.V., Boo, K.-J. 2015. Sustainable Energy Development in Nigeria: Overcoming

Energy Poverty. International Journal of Energy Economics and Policy, 5(2).

Fahmi, R., Bridgwater, A.V., Darvell, L.I., Jones, J.M., Yates, N., Thain, S., Donnison, I.S.

2007. The effect of alkali metals on combustion and pyrolysis of Lolium and

Festuca grasses, switchgrass and willow. Fuel, 86(10), 1560-1569.

FAO. 1994. The Role of Forests in Food Security. Assessed on 18th Feb., 2016

(http://www.fao.org/docrep/x0262e/x0262e03.htm).

FAO. 2008. The State of Food and Agriculture, Part I: Biofuels: Prospects, Risks and

Opportunities, Chapter 5, Section Key messages, p.71. Assessed on 18th Feb.,

2016 (http://www.fao.org/docrep/011/i0100e/i0100e00.htm).

Page 62: Investigating the Reaction Kinetics of Tropical …hb.diva-portal.org/smash/get/diva2:910296/INSIDE01.pdfThesis for the Degree of Doctor of Philosophy Investigating the Reaction Kinetics

61

Fermoso, J., Arias, B., Pevida, C., Plaza, M.G., Rubiera, F., Pis, J.J. 2008. Kinetic models

comparison for steam gasification of different nature fuel chars. Journal of

Thermal Analysis and Calorimetry, 91(3), 779-786.

Fermoso, J., Stevanov, C., Moghtaderi, B., Arias, B., Pevida, C., Plaza, M.G., Rubiera, F.,

Pis, J.J. 2009. High-pressure gasification reactivity of biomass chars produced at

different temperatures. Journal of Analytical and Applied Pyrolysis, 85(1), 287-

293.

Fonta, W.M., Ayuk, E.T. 2013. Measuring the role of forest income in mitigating

poverty and inequality: evidence from south-eastern Nigeria. Forests, Trees and

Livelihoods, 22(2), 86-105.

Gil, J., Corella, J., Aznar, M.a.P., Caballero, M.A. 1999. Biomass gasification in

atmospheric and bubbling fluidized bed: effect of the type of gasifying agent on

the product distribution. Biomass and Bioenergy, 17(5), 389-403.

Gil, M.V., Riaza, J., Álvarez, L., Pevida, C., Rubiera, F. 2015. Biomass devolatilization at

high temperature under N2 and CO2: Char morphology and reactivity. Energy,

91, 655-662.

Gimelli, A., Luongo, A., Amoresano, A. 2012. Experimental data and thermodynamic

analysis of biomass steam power plant with two different configurations plant.

International Review of Mechanical Engineering, 6(6), 1109-1116.

Graça, I., Lopes, J.M., Cerqueira, H.S., Ribeiro, M.F. 2013. Bio-oils Upgrading for Second

Generation Biofuels. Industrial & Engineering Chemistry Research, 52(1), 275-

287.

Page 63: Investigating the Reaction Kinetics of Tropical …hb.diva-portal.org/smash/get/diva2:910296/INSIDE01.pdfThesis for the Degree of Doctor of Philosophy Investigating the Reaction Kinetics

62

Grønli, M.G., Várhegyi, G., Di Blasi, C. 2002. Thermogravimetric Analysis and

Devolatilization Kinetics of Wood. Industrial & Engineering Chemistry Research,

41(17), 4201-4208.

Guizani, C., Louisnard, O., Sanz, F.J.E., Salvador, S. 2015. Gasification of woody biomass

under high heating rate conditions in pure CO2: Experiments and modelling.

Biomass and Bioenergy, 83, 169-182.

Hawley, M.C., Boyd, M., Anderson, C., DeVera, A. 1983. Gasification of wood char and

effects of intraparticle transport. Fuel, 62(2), 213-216.

Higman C. 2008. Gasification. 2nd edition ed. Elsevier Inc., New York.

Hüttinger, K.J., Merdes, W.F. 1992. The carbon-steam reaction at elevated pressure:

Formations of product gases and hydrogen inhibitions. Carbon, 30(6), 883-894.

Irfan, M.F., Usman, M.R., Kusakabe, K. 2011. Coal gasification in CO 2 atmosphere and

its kinetics since 1948: a brief review. Energy, 36(1), 12-40.

Karlström, O., Costa, M., Brink, A., Hupa, M. 2015. CO2 gasification rates of char

particles from torrefied pine shell, olive stones and straw. Fuel, 158, 753-763.

Karmakar, M.K., Datta, A.B. 2011. Generation of hydrogen rich gas through fluidized

bed gasification of biomass. Bioresource technology, 102(2), 1907-1913.

Khawam, A., Flanagan, D.R. 2006a. Basics and applications of solid-state kinetics: A

pharmaceutical perspective. Journal of Pharmaceutical Sciences, 95(3), 472-498.

Khawam, A., Flanagan, D.R. 2006b. Solid-state kinetic models: Basics and mathematical

fundamentals. Journal of Physical Chemistry B, 110(35), 17315-17328.

Page 64: Investigating the Reaction Kinetics of Tropical …hb.diva-portal.org/smash/get/diva2:910296/INSIDE01.pdfThesis for the Degree of Doctor of Philosophy Investigating the Reaction Kinetics

63

Kissinger, H.E. 1956. Variation of peak temperature with heating rate in differential

thermal analysis. Journal of research of the National Bureau of Standards, 57(4),

217-221.

Kojima, T., Assavadakorn, P., Furusawa, T. 1993. Measurement and evaluation of

gasification kinetics of sawdust char with steam in an experimental fluidized bed.

Fuel Processing Technology, 36(1), 201-207.

Kumar, A., Wang, L., Dzenis, Y.A., Jones, D.D., Hanna, M.A. 2008. Thermogravimetric

characterization of corn stover as gasification and pyrolysis feedstock. Biomass

and Bioenergy, 32(5), 460-467.

Laurendeau, N.M. 1978. Heterogeneous kinetics of coal char gasification and

combustion. Progress in Energy and Combustion Science, 4(4), 221-270.

Lv, D., Xu, M., Liu, X., Zhan, Z., Li, Z., Yao, H. 2010. Effect of cellulose, lignin, alkali and

alkaline earth metallic species on biomass pyrolysis and gasification. Fuel

Processing Technology, 91(8), 903-909.

Lv, P.M., Xiong, Z.H., Chang, J., Wu, C.Z., Chen, Y., Zhu, J.X. 2004. An experimental

study on biomass air–steam gasification in a fluidized bed. Bioresource

Technology, 95(1), 95-101.

Maitra, S., Mukherjee, S., Saha, N., Pramanik, J. 2007. Non-isothermal decomposition

kinetics of magnesite. Cerâmica, 53, 284-287.

Mani, T., Murugan, P., Abedi, J., Mahinpey, N. 2010. Pyrolysis of wheat straw in a

thermogravimetric analyzer: Effect of particle size and heating rate on

devolatilization and estimation of global kinetics. Chemical Engineering Research

and Design, 88(8), 952-958.

Page 65: Investigating the Reaction Kinetics of Tropical …hb.diva-portal.org/smash/get/diva2:910296/INSIDE01.pdfThesis for the Degree of Doctor of Philosophy Investigating the Reaction Kinetics

64

Mastellone, M.L., Zaccariello, L., Santoro, D., Arena, U. 2012. The O.sub.2-enriched air

gasification of coal, plastics and wood in a fluidized bed reactor. Waste

Management, 32(4), 733.

Matsumoto, K., Takeno, K., Ichinose, T., Ogi, T., Nakanishi, M. 2009. Gasification

reaction kinetics on biomass char obtained as a by-product of gasification in an

entrained-flow gasifier with steam and oxygen at 900–1000 °C. Fuel, 88(3), 519-

527.

Meng, X., De Jong, W., Fu, N., Verkooijen, A.H.M. 2011. Biomass gasification in a 100

kWth steam-oxygen blown circulating fluidized bed gasifier: Effects of

operational conditions on product gas distribution and tar formation. Biomass

and Bioenergy, 35(7), 2910-2924.

Mermoud, F., Salvador, S., Van de Steene, L., Golfier, F. 2006. Influence of the pyrolysis

heating rate on the steam gasification rate of large wood char particles. Fuel,

85(10), 1473-1482.

Mészáros, E., Várhegyi, G., Jakab, E., Marosvölgyi, B. 2004. Thermogravimetric and

Reaction Kinetic Analysis of Biomass Samples from an Energy Plantation. Energy

& Fuels, 18(2), 497-507.

Mohagheghzadeh, A., Faridi, P., Shams-Ardakani, M., Ghasemi, Y. 2006. Medicinal

smokes. Journal of Ethnopharmacology, 108(2), 161-184.

Momoh, M., Eboatu, A.N., Kolawole, E.G., Horrocks, A.R. 1996. Thermogravimetric

Studies of the Pyrolytic Behaviour in Air of Selected Tropical Timbers. Fire and

Materials, 20(4), 173-181.

Page 66: Investigating the Reaction Kinetics of Tropical …hb.diva-portal.org/smash/get/diva2:910296/INSIDE01.pdfThesis for the Degree of Doctor of Philosophy Investigating the Reaction Kinetics

65

Mullen, C.A., Boateng, A.A., Goldberg, N.M., Lima, I.M., Laird, D.A., Hicks, K.B. 2010.

Bio-oil and bio-char production from corn cobs and stover by fast pyrolysis.

Biomass and Bioenergy, 34(1), 67-74.

-

isothermal kinetic study on the decomposition of Zn acetate-based Sol-gel

precursor: Part 1. Application of the isoconversional methods. Journal of Thermal

Analysis and Calorimetry, 89(2), 505-509.

Nowicki, L., Antecka, A., Bedyk, T., Stolarek, P., Ledakowicz, S. 2011. The kinetics of

gasification of char derived from sewage sludge. Journal of Thermal Analysis and

Calorimetry, 104(2), 693-700.

Oguntoke, O., Otusanya, O.K., Annegarn, H.J. 2013. Emission of pollutants from wood

waste incineration at sawmills in Abeokuta metropolis, Nigeria. International

Journal of Environmental Studies, 70(6), 964-975.

Ohiare, S. 2015. Expanding electricity access to all in Nigeria: a spatial planning and

cost analysis. Energy, Sustainability and Society, 5(1), 1-18.

Okoji, M. 2001. Depletion of forest resources in south eastern Nigeria: who loses?

Environmentalist, 21(3), 197-203.

Okumura, Y., Hanaoka, T., Sakanishi, K. 2009. Effect of pyrolysis conditions on

gasification reactivity of woody biomass-derived char. Proceedings of the

Combustion Institute, 32(2), 2013-2020.

Ollero, P., Serrera, A., Arjona, R., Alcantarilla, S. 2003. The CO2 gasification kinetics of

olive residue. Biomass and Bioenergy, 24(2), 151-161.

Page 67: Investigating the Reaction Kinetics of Tropical …hb.diva-portal.org/smash/get/diva2:910296/INSIDE01.pdfThesis for the Degree of Doctor of Philosophy Investigating the Reaction Kinetics

66

Ollero, P., Serrera, A., Arjona, R., Alcantarilla, S. 2002. Diffusional effects in TGA

gasification experiments for kinetic determination. Fuel, 81(15), 1989-2000.

Oluoti, K., Megwai, G., Pettersson, A., Richards, T. 2014. Nigerian Wood Waste: A

Dependable and Renewable Fuel Option for Power Production. World Journal of

Engineering and Technology, 2(0), 234-248.

Oseni, M.O. 2012. Improving households’ access to electricity and energy consumption

pattern in Nigeria: Renewable energy alternative. Renewable and Sustainable

Energy Reviews, 16(6), 3967-3974.

Oyedepo, S.O. 2012. On energy for sustainable development in Nigeria. Renewable and

Sustainable Energy Reviews, 16(5), 2583-2598.

Pantoleontos, G., Basinas, P., Skodras, G., Grammelis, P., Pintér, J.D., Topis, S.,

Sakellaropoulos, G.P. 2009. A global optimization study on the devolatilisation

kinetics of coal, biomass and waste fuels. Fuel Processing Technology, 90(6), 762-

769.

Park, S.-W., Jang, C.-H. 2012. Effects of pyrolysis temperature on changes in fuel

characteristics of biomass char. Energy, 39(1), 187-195.

Pinto, F., Franco, C., André, R.N., Tavares, C., Dias, M., Gulyurtlu, I., Cabrita, I. 2003.

Effect of experimental conditions on co-gasification of coal, biomass and plastics

wastes with air/steam mixtures in a fluidized bed system. Fuel, 82(15–17), 1967-

1976.

Raveendran, K., Ganesh, A., Khilar, K.C. 1996. Pyrolysis characteristics of biomass and

biomass components. Fuel, 75(8), 987-998.

Page 68: Investigating the Reaction Kinetics of Tropical …hb.diva-portal.org/smash/get/diva2:910296/INSIDE01.pdfThesis for the Degree of Doctor of Philosophy Investigating the Reaction Kinetics

67

Sambo, A.S. 2009. The Place of Renewable Energy in the Nigerian Energy Sector. World

Future Council Workshop on Renewable Energy Policies, 10 October 2009,(Addis

Ababa, ), Ethiopia.

Scott, D.S., Piskorz, J. 1982. The flash pyrolysis of aspen-poplar wood. The Canadian

Journal of Chemical Engineering, 60(5), 666-674.

Seo, D.K., Lee, S.K., Kang, M.W., Hwang, J., Yu, T.-U. 2010. Gasification reactivity of

biomass chars with CO2. Biomass and Bioenergy, 34(12), 1946-1953.

Sharma, R., Sheth, P.N., Birla Institute of, T., Science, P.I. 2015. Thermo-Chemical

Conversion of Jatropha Deoiled Cake: Pyrolysis vs. Gasification. International

Journal of Chemical Engineering and Applications, 6(5), 376-380.

Sheth, P.N., Babu, B.V. 2010. Production of hydrogen energy through biomass (waste

wood) gasification. International Journal of Hydrogen Energy, 35(19), 10803-

10810.

Silveira, S. 2005. Bioenergy - Realizing the Potential. Elsevier Science & Technology,

Jordan Hill, GBR.

Slopiecka, K., Bartocci, P., Fantozzi, F. 2012. Thermogravimetric analysis and kinetic

study of poplar wood pyrolysis. Applied Energy, 97, 491-497.

Stenseng, M., Jensen, A., Dam-Johansen, K. 2001. Investigation of biomass pyrolysis by

thermogravimetric analysis and differential scanning calorimetry. Journal of

Analytical and Applied Pyrolysis, 58–59, 765-780.

Sun, H., Song, B.-H., Jang, Y.-W., Kim, S.-D., Li, H., Chang, J. 2007. The characteristics of

steam gasification of biomass and waste filter carbon. Korean Journal of

Chemical Engineering, 24(2), 341-346.

Page 69: Investigating the Reaction Kinetics of Tropical …hb.diva-portal.org/smash/get/diva2:910296/INSIDE01.pdfThesis for the Degree of Doctor of Philosophy Investigating the Reaction Kinetics

68

Swanson, R.M., Platon, A., Satrio, J.A., Brown, R.C. 2010. Techno-economic analysis of

biomass-to-liquids production based on gasification. Fuel, 89, Supplement 1, S11-

S19.

Swierczynski, D., Courson, C., Kiennemann, A. 2008. Study of steam reforming of

toluene used as model compound of tar produced by biomass gasification.

Chemical Engineering and Processing: Process Intensification, 47(3), 508-513.

Syed, S., Janajreh, I., Ghenai, C. 2012. Thermodynamics equilibrium analysis within the

entrained flow gasifier environment. International Journal of Thermal and

Environmental Engineering, 4(1), 47-54.

Taherzadeh, M.J., Richards, T. 2016. Resource recovery to approach zero municipal

waste. CRC Press, Taylor & Francis Group, Boca Raton.

Teng, H., Wei, Y.-C. 1998. Thermogravimetric Studies on the Kinetics of Rice Hull

Pyrolysis and the Influence of Water Treatment. Industrial & Engineering

Chemistry Research, 37(10), 3806-3811.

Tripathi, M., Sahu, J.N., Ganesan, P. 2016. Effect of process parameters on production

of biochar from biomass waste through pyrolysis: A review. Renewable and

Sustainable Energy Reviews, 55, 467-481.

Tsamba, A.J., Yang, W., Blasiak, W., Energi- och, u., Materialvetenskap, Kth, Skolan för

industriell teknik och, m. 2006. Pyrolysis characteristics and global kinetics of

coconut and cashew nut shells. Fuel Processing Technology, 87(6), 523-530.

Vamvuka, D., Kakaras, E., Kastanaki, E., Grammelis, P. 2003. Pyrolysis characteristics

and kinetics of biomass residuals mixtures with lignite . Fuel, 82(15–17), 1949-

1960.

Page 70: Investigating the Reaction Kinetics of Tropical …hb.diva-portal.org/smash/get/diva2:910296/INSIDE01.pdfThesis for the Degree of Doctor of Philosophy Investigating the Reaction Kinetics

69

Várhegyi, G. 2007. Aims and methods in non-isothermal reaction kinetics. Journal of

Analytical and Applied Pyrolysis, 79(1), 278-288.

White, J.E., Catallo, W.J., Legendre, B.L. 2011. Biomass pyrolysis kinetics: A

comparative critical review with relevant agricultural residue case studies.

Journal of Analytical and Applied Pyrolysis, 91(1), 1-33.

Williams, P.T., Besler, S. 1996. The influence of temperature and heating rate on the

slow pyrolysis of biomass. Renewable Energy, 7(3), 233-250.

Wilson, L., Yang, W., Blasiak, W., John, G.R., Mhilu, C.F. 2011. Thermal characterization

of tropical biomass feedstocks. Energy Conversion and Management, 52(1), 191-

198.

Yan, F., Zhang, Y., Zhang, L., Hu, Z., Cheng, G., Jiang, C., Xu, T., He, P., Luo, S., Xiao, B.

2010. Hydrogen-rich gas production by steam gasification of char derived from

cyanobacterial blooms (CDCB) in a fixed-bed reactor: Influence of particle size

and residence time on gas yield and syngas composition. International Journal of

Hydrogen Energy, 35(19), 10212-10217.

Yao, F., Wu, Q., Lei, Y., Guo, W., Xu, Y. 2008. Thermal decomposition kinetics of natural

fibers: Activation energy with dynamic thermogravimetric analysis. Polymer

Degradation and Stability, 93(1), 90-98.

Yi, S.C. 1984. Application of the Modified Volume Reaction Model to Gas-solid Non-

catalytic Reactions with Structural Changes. University of Iowa.

Young. 2010. Municipal Solid Waste to Energy Conversion Processes: Economic,

Technical, and Renewable Comparisons. John Wiley & Sons, Inc, New Jersey.

Page 71: Investigating the Reaction Kinetics of Tropical …hb.diva-portal.org/smash/get/diva2:910296/INSIDE01.pdfThesis for the Degree of Doctor of Philosophy Investigating the Reaction Kinetics

70

Yuan, S., Chen, X.-l., Li, J., Wang, F.-c. 2011. CO2 gasification kinetics of biomass char

derived from high-temperature rapid pyrolysis. Energy & Fuels, 25(5), 2314-2321.

Zhang, J.L., Wang, G.W., Shao, J.G., Zuo, H.B. 2014. A Modified Random Pore Model for

the Kinetics of Char Gasification. Bioresources, 9(2), 3497-3507.

Zhang, L., Huang, J., Fang, Y., Wang, Y. 2006. Gasification Reactivity and Kinetics of

Typical Chinese Anthracite Chars with Steam and CO2. Energy & Fuels, 20(3),

1201-1210.

Zheng, H. 2013. Corn stover steam gasification, Vol. 3567496, University of Minnesota.

Ann Arbor, pp. 277.

Zou, J.H., Zhou, Z.J., Wang, F.C., Zhang, W., Dai, Z.H., Liu, H.F., Yu, Z.H. 2007. Modeling

reaction kinetics of petroleum coke gasification with CO2. Chemical Engineering

and Processing: Process Intensification, 46(7), 630-636.